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Title: Isolating the Temperature Feedback Loop and Its Effects on Surface Temperature.
Creator: Sejas, Sergio A., Cai, Ming
Abstract/Description: Climate feedback processes are known to substantially amplify the surface warming response to an increase of greenhouse gases. When the forcing and feedbacks modify the temperature response they trigger temperature feedback loops that amplify the direct temperature changes due to the forcing and nontemperature feedbacks through the thermal-radiative coupling between the atmosphere and surface. This study introduces a new feedback-response analysis method that can isolate and quantify the...
Show moreClimate feedback processes are known to substantially amplify the surface warming response to an increase of greenhouse gases. When the forcing and feedbacks modify the temperature response they trigger temperature feedback loops that amplify the direct temperature changes due to the forcing and nontemperature feedbacks through the thermal-radiative coupling between the atmosphere and surface. This study introduces a new feedback-response analysis method that can isolate and quantify the effects of the temperature feedback loops of individual processes on surface temperature from their corresponding direct surface temperature responses. The authors analyze a 1% yr 21 increase of CO2 simulation of the NCAR CCSM4 at the time of CO2 doubling to illustrate the new method. The Planck sensitivity parameter, which indicates colder regions experience stronger surface temperature responses given the same change in surface energy flux, is the inherent factor that leads to polar warming amplification (PWA). This effect explains the PWA in the Antarctic, while the direct temperature response to the albedo and cloud feedbacks further explains the greater PWA of the Arctic. Temperature feedback loops, particularly the one associated with the albedo feedback, further amplify the Arctic surface warming relative to the tropics. In the tropics, temperature feedback loops associated with the CO2 forcing and water vapor feedback cause most of the surface warming. Overall, the temperature feedback is responsible for most of the surface warming globally, accounting for nearly 76% of the global-mean surface warming. This is 3 times larger than the next largest warming contribution, indicating that the temperature feedback loop is the preeminent contributor to the surface warming.
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Date Issued: 2016-08
Identifier: FSU_libsubv1_wos_000380764400018, 10.1175/JAS-D-15-0287.1
Format: Citation

Title: Gutzwiller renormalization group.
Creator: Lanata, Nicola, Yao, Yong-Xin, Deng, Xiaoyu, Wang, Cai-Zhuang, Ho, Kai-Ming, Kotliar, Gabriel
Abstract/Description: We develop a variational scheme called the "Gutzwiller renormalization group" (GRG), which enables us to calculate the ground state of Anderson impurity models (AIM) with arbitrary numerical precision. Our method exploits the low-entanglement property of the ground state of local Hamiltonians in combination with the framework of the Gutzwiller wave function and indicates that the ground state of the AIM has a very simple structure, which can be represented very accurately in terms of a...
Show moreWe develop a variational scheme called the "Gutzwiller renormalization group" (GRG), which enables us to calculate the ground state of Anderson impurity models (AIM) with arbitrary numerical precision. Our method exploits the low-entanglement property of the ground state of local Hamiltonians in combination with the framework of the Gutzwiller wave function and indicates that the ground state of the AIM has a very simple structure, which can be represented very accurately in terms of a surprisingly small number of variational parameters. We perform benchmark calculations of the single-band AIM that validate our theory and suggest that the GRG might enable us to study complex systems beyond the reach of the other methods presently available and pave the way to interesting generalizations, e.g., to nonequilibrium transport in nanostructures.
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Date Issued: 2016-01-06
Identifier: FSU_libsubv1_wos_000367665400002, 10.1103/PhysRevB.93.045103
Format: Citation

Title: North Atlantic Decadal Variability of Ocean Surface Fluxes.
Creator: Hughes, Paul J., Bourassa, Mark A., Kim, Kwang-Yul, Cai, Ming, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The spatial and temporal variability of the surface turbulent heat fluxes over the North Atlantic is examined using the new objectively produced FSU3 monthly mean 1°x1° gridded wind and surface flux product for 1978-2003. The FSU3 product is constructed from in situ ship and buoy observations via a variational technique. A cost function based on weighted constraints is minimized in the process of determining the surface fluxes. The analysis focuses on a low frequency (basin wide) mode of...
Show moreThe spatial and temporal variability of the surface turbulent heat fluxes over the North Atlantic is examined using the new objectively produced FSU3 monthly mean 1°x1° gridded wind and surface flux product for 1978-2003. The FSU3 product is constructed from in situ ship and buoy observations via a variational technique. A cost function based on weighted constraints is minimized in the process of determining the surface fluxes. The analysis focuses on a low frequency (basin wide) mode of variability where the latent and sensible heat flux anomalies transition from mainly positive to negative values around 1998. It is hypothesized that the longer time scale variability is linked to changes in the large scale circulation patterns possibly associated with the Atlantic Multidecadal Oscillation (AMO; Schlesinger and Ramankutty 1994, Kerr 2000). The changes in the surface heat fluxes are forced by fluctuations in the mean wind speed. Zonal averages show a clear dissimilarity between the turbulent heat fluxes and wind speed for 1982-1997 and 1998-2003 over the region extending from the equator to roughly 40°N. Larger values are associated with the earlier time period, coinciding with a cool phase of the AMO. The separation between the two time periods is much less evident for the humidity and air/sea temperature differences. The largest differences in the latent heat fluxes, between the two time periods, occur over the tropical, Gulf Stream, and higher latitude regions of the North Atlantic, with magnitudes exceeding 15 Wm-2. The largest sensible heat flux differences are limited to areas along the New England coast and poleward of 40°N.
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Date Issued: 2006
Identifier: FSU_migr_etd-3672
Format: Thesis

Title: Modified JMA ENSO Index and Its Improvements to ENSO Classification.
Creator: Keeling, Travis B., O’Brien, James J., Cunningham, Philip, Cai, Ming, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: El Nino-Southern Oscillation (ENSO) is a widely known phenomenon that affects many areas including the southeast United States. Over the southeast U.S. the Japan Meteorological Agency (JMA) ENSO index was modified to establish better classifications. In order to properly understand the effects of ENSO on this location a new approach was needed. Spatial resolution was improved by utilization of the PRISM dataset. PRISM provided monthly precipitation and temperature data over the contiguous US...
Show moreEl Nino-Southern Oscillation (ENSO) is a widely known phenomenon that affects many areas including the southeast United States. Over the southeast U.S. the Japan Meteorological Agency (JMA) ENSO index was modified to establish better classifications. In order to properly understand the effects of ENSO on this location a new approach was needed. Spatial resolution was improved by utilization of the PRISM dataset. PRISM provided monthly precipitation and temperature data over the contiguous US at 4 km resolution. Temporal resolution was improved by disregarding the traditional JMA definition of an ENSO year. The new definition requires six consecutive months of 0.5°C anomalies or larger to be listed as an ENSO event. By utilization of this definition, the ENSO index was modified to a monthly index from a yearly index. Many ENSO events begin in the summer months and end before the preceding September, therefore, an adoption of a monthly index is justified. Although several of the effects vary widely over the domain, there are a few prevalent patterns of ENSO effects. During warm phase, from November-April, wet conditions are seen in the coastal areas. July and August are both dry. From fall to spring, Florida and the Atlantic Coast are basically dry, however; the Mississippi River Valley doesn't appear wet as previous studies have indicted. Patterns of temperatures across the southeast are less variable than the precipitation. Differences between the ModJMA and JMA can be seen in several months, especially during late spring and early autumn. This result is not surprising based on the rigid definition of the JMA index. An interesting result presented itself throughout the study. Individual tropical storms can be identified with the increased resolution PRISM data provides. A state by state breakdown of the ModJMA conclusions provides regional summaries. The ModJMA better classifies ENSO periods and leads to a more precise impact of ENSO over the southeast United States.
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Date Issued: 2009
Identifier: FSU_migr_etd-3246
Format: Thesis

Title: Global Ice Cloud Properties and Their Radiative Effects: Satellite Observations and Radiative Transfer Modeling.
Creator: Hong, Yulan, Liu, Guosheng, Ellingson, Robert R., Cai, Ming, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Ice clouds play an important role in earth radiation balance by reflecting solar and absorbing thermal radiation, the so-called albedo versus greenhouse eects, which cause signicant dierential atmospheric heating and cooling in horizontal as well as vertical directions. Two active sensors onboard A-train satellites, CloudSat radar and CALIPSO lidar, for the rst time provide global proles of atmospheric ice clouds. A combination of radar and lidar becomes the state-of-the-art technique...
Show moreIce clouds play an important role in earth radiation balance by reflecting solar and absorbing thermal radiation, the so-called albedo versus greenhouse eects, which cause signicant dierential atmospheric heating and cooling in horizontal as well as vertical directions. Two active sensors onboard A-train satellites, CloudSat radar and CALIPSO lidar, for the rst time provide global proles of atmospheric ice clouds. A combination of radar and lidar becomes the state-of-the-art technique examining clouds of varying optical depth, as the former excels in probing thick clouds while the later is better suited to the thin ones. In this study, ice cloud properties derived by a combination of CloudSat and CALIPSO observations are adopted to character atmospheric ice clouds. Ice cloud climatological studies show that the global mean optical depth and eective radius are around 4 and 48 &mu m, respectively. Mean ice water path is approximately 110 g/m2 for all measurements and approximately 190 g/m2 for cloudy situations (conditional mean). Their occurrence frequencies and ice mass amount distributions do not just depend on their optical depth values, but also rely on seasons and day-night cycle. Meanwhile, ice water content and eective radius show dierent temperature dependent relationships among the tropics, mid- and high-latitudes. Ice cloud radiative eects are obtained by radiative transfer modelling. Simulations show global ice clouds net eects at the top of atmosphere (TOA) may slightly heat or cool the atmosphere-earth system depending on model parameterizations and allowing for uncertainties. Additionally, a cloud forcing spectrum over optical depth at the TOA shows that ice clouds with optical depth <5 display a positive net forcing on a global scale, inducing a warming eect, whereas ice clouds otherwise tend to be cooling. Regionally, ice clouds have a negative net forcing in the mid-latitude warm seasons due to a stronger solar albedo eect but a positive net forcing during cold seasons due to a stronger greenhouse eect. Moreover, ice cloud internal heating rate proles in the atmosphere indicate shortwave heating above but cooling below, whereas the longwave heating pattern is oppositive. This heating structure is regionally and seasonally dependent, and it is associated with optical depth values as well.
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Date Issued: 2014
Identifier: FSU_migr_etd-8807
Format: Thesis

Title: Estimate of Tropical Cyclone Parameters Based on Microwave Humidity Sounders.
Creator: Shi, Qi, Zou, Xiaolei, Cai, Ming, Wu, Zhaohua, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: TC structures consisting of eye, eyewall and rainband can be clearly resolved by Microwave Humidity Sounder (MHS) window channels. High brightness temperatures are found in cloud-free hurricane eye and cloud streaks, and low brightness temperatures are found in cloud rainbands. In this study, MHS is used to estimate TC center and radius of maximum wind. The TC center location is determined by the warmest brightness temperature of MHS channel 2 within TC eyewall region. The radius of maximum...
Show moreTC structures consisting of eye, eyewall and rainband can be clearly resolved by Microwave Humidity Sounder (MHS) window channels. High brightness temperatures are found in cloud-free hurricane eye and cloud streaks, and low brightness temperatures are found in cloud rainbands. In this study, MHS is used to estimate TC center and radius of maximum wind. The TC center location is determined by the warmest brightness temperature of MHS channel 2 within TC eyewall region. The radius of maximum wind is estimated based on the radial profiles brightness temperatures calculating at six-degree azimuthal angles. The shortest distance between the hurricane center and the minimum point of brightness temperature with some minimum points on its neighboring radial profiles is taken as the estimate of the radius of maximum wind. This method for estimating the TC center location and the radius of maximum wind was applied to twelve arbitrarily selected TCs that occurred in 2010, 2011 or 2012 over Atlantic basin. More than 78% of cases have the differences of TC center location and radius of maximum wind between MHS and NHC being less than 15 km and 10 km, respectively. The infrared observations from Advanced Very High Resolution Radiometer (AVHRR) on board the same satellite as MHS are also used for further comparison. It was found that the large differences between MHS estimate and Best Track analysis seem to occur for TCs with asymmetric structure or high-latitude locations.
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Date Issued: 2014
Identifier: FSU_migr_etd-8887
Format: Thesis

Title: Relationship Between Meridional Mass Circulation and Extreme Temperature Events in the Southern Hemisphere.
Creator: Yan, Ruikai, Cai, Ming, Chagnon, Jeffrey M., Liu, Guosheng, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Abstract/Description: This study explores extreme surface temperature events in Southern Hemisphere winter (June – August) from 1979 to 2011 and their relation with meridional mass circulation by using daily ERA-interim Re-Analysis data from European Center for Medium-Range Weather Forecasts (ECMWF). Meridional mass circulation indices are developed to quantitatively represent the warm air mass being transported into the polar region in the upper atmosphere and the cold air mass being transported out of the polar...
Show moreThis study explores extreme surface temperature events in Southern Hemisphere winter (June – August) from 1979 to 2011 and their relation with meridional mass circulation by using daily ERA-interim Re-Analysis data from European Center for Medium-Range Weather Forecasts (ECMWF). Meridional mass circulation indices are developed to quantitatively represent the warm air mass being transported into the polar region in the upper atmosphere and the cold air mass being transported out of the polar region in the lower atmosphere. Our results show that weaker poleward warm air mass transport aloft is associated with weaker cold air transport toward equator in the lower troposphere, resulting in cold air being confined in the polar regions. Similarly, stronger poleward warm air mass transport in the upper atmosphere is related to stronger cold air transport out of the polar regions, causing enormous cold air outbreaks in the mid-latitude regions. We find that regions to the south of 45S exhibit a robust relationship between surface air temperature anomalies and meridional mass circulation. Weaker circulation is associated with abnormally cold in Antarctica and abnormally warm in regions from 45S to 60S. Conversely, stronger circulation is related to anomalously warm in Antarctica and anomalously cold in the surrounding continental shelf, particularly over Weddell-Scotia Sea and north Ross Sea where are the two preferred routes for cold air coming out of Antarctica. On the other hand, temperature anomalies over the regions north of 45S are not sensitive to the meridional circulation variability. The fact that surface air temperature anomalies over the Southern Ocean rarely exceed 4C suggests that cold air coming out of Antarctic has limited impacts on the Southern Ocean due to its large thermal inertia. In summary, the meridional mass circulation indices provide a robust diagnostics for extreme cold events in 45S - 90S domain very well, but may not be adequate to describe all cold events over the vast mid-latitude regions in the Southern Hemisphere.
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Date Issued: 2016
Identifier: FSU_2016SP_Yan_fsu_0071N_13259
Format: Thesis

Title: Attributing Contributions to the Seasonal Cycle of Anthropogenic Warming in a Simple Radiative- Convective Global Energy Balance Model.
Creator: Sejas, Sergio A., Cai, Ming, Ellingson, Robert G., Wu, Zhaohua, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: A simple one-dimensional seasonal atmosphere-ocean energy balance model is used to study the seasonal and latitudinal response of the model climate to a doubling of the CO2 concentration. A new climate feedback analysis method, formulated in Lu and Cai (2009a), is used to isolate contributions (partial temperature changes) of the external forcing alone and subsequent feedbacks to the total temperature change experienced by the model climate. In this study, the relative importance of the...
Show moreA simple one-dimensional seasonal atmosphere-ocean energy balance model is used to study the seasonal and latitudinal response of the model climate to a doubling of the CO2 concentration. A new climate feedback analysis method, formulated in Lu and Cai (2009a), is used to isolate contributions (partial temperature changes) of the external forcing alone and subsequent feedbacks to the total temperature change experienced by the model climate. In this study, the relative importance of the external forcing alone (the CO2 doubling), surface ice-albedo feedback, water vapor feedback, changes in poleward heat transport, changes in vertical sensible heat flux, and changes in heat storage are analyzed. The partial temperature change due to the water vapor feedback is substantially the largest contributor to the globally averaged surface warming. The ice-albedo feedback plays a smaller role, but also significantly contributes to the overall warming of the surface. The most important negative feedback, counteracting the surface warming, is the change in the vertical sensible heat flux. However, though the water vapor feedback is most responsible for the overall surface warming, it is not the feedback most responsible for the seasonal and spatial pattern of the surface warming. The climate of this model indicates that there is a surface polar warming amplification, with a maximum occurring in late summer/early fall. The feedback most responsible for this polar warming amplification and seasonal pattern in this model is the surface ice-albedo feedback, which is largest at high latitudes in summer.
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Date Issued: 2011
Identifier: FSU_migr_etd-0278
Format: Thesis

Title: An Analysis of Climate Feedback Contributions to the Land/Sea Warming Contrast.
Creator: Albert, Oriene S., Cai, Ming, Sura, Phillip, Liu, Guosheng, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The land/sea warming contrast being greater than unity is a well-known phenomenon in response to anthropogenic radiative forcing. The land/sea surface warming asymmetry is essentially a result of the differing surface and boundary layer properties over the land and ocean as well as the differing cloud feedbacks. In this study, we analyze the surface temperature response over the land and ocean, using the NCAR CCSM4, to a transient 1% yr-1 CO2 increase at the time of the doubling. The...
Show moreThe land/sea warming contrast being greater than unity is a well-known phenomenon in response to anthropogenic radiative forcing. The land/sea surface warming asymmetry is essentially a result of the differing surface and boundary layer properties over the land and ocean as well as the differing cloud feedbacks. In this study, we analyze the surface temperature response over the land and ocean, using the NCAR CCSM4, to a transient 1% yr-1 CO2 increase at the time of the doubling. The contributions of the external forcing (CO2) alone and various feedbacks are diagnosed using the Climate Feedback Response Analysis Method (CFRAM). This study found that the external forcing warms the land and ocean surfaces approximately the same, which suggests that the feedbacks are responsible for the warming contrast. Furthermore, this analysis confirms that the principal contributor to the above-unity land-to-sea warming ratio is the evaporation feedback; however, the results also indicate that the sensible heat flux feedback, which favors a greater warming for the ocean, has the largest land/sea warming difference. Consequently, the findings uniquely highlight the importance of other feedbacks in establishing the above-unity land-to-sea warming ratio. Specifically, the cloud and ocean dynamics/heat storage feedbacks are key contributors to the maintenance of the land/sea warming asymmetry. The results of this study provide a more holistic understanding of the climate feedbacks and their significance to the land and ocean temperature responses, when the climate is forced.
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Date Issued: 2014
Identifier: FSU_migr_etd-8929
Format: Thesis

Title: Spatiotemporal Variability and Prediction of Rainfall over the Eastern Caribbean.
Creator: Pologne, Lawrence, Cai, Ming, Krishnamurti, T. N., Hart, Robert, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Recent, recurrent, and extreme weather events have been a cause for concern over the Eastern Caribbean (EC). Given the dependence on rainfall of agriculture, the main stay of the fragile economies throughout the region, accurate and timely forecasts of seasonal rainfall need to be issued to facilitate decision making in Water Resource Management. Understanding the causes of climate variability can lead to the development of more robust models for climate prediction. So as a diagnostic...
Show moreRecent, recurrent, and extreme weather events have been a cause for concern over the Eastern Caribbean (EC). Given the dependence on rainfall of agriculture, the main stay of the fragile economies throughout the region, accurate and timely forecasts of seasonal rainfall need to be issued to facilitate decision making in Water Resource Management. Understanding the causes of climate variability can lead to the development of more robust models for climate prediction. So as a diagnostic approach, different techniques are employed. Empirical Orthogonal Function (EOF) analysis is performed in order to isolate the different modes of rainfall variability as well as investigating their amplitudinal modulations. The evolution of external forcing mechanisms that impact on precipitation extremes is also investigated with the use of composites. Based on the strength of the relationship between Sea Surface Temperature Anomalies (SSTA) and EC rainfall, a statistical model is subsequently developed using multivariate Canonical Correlation Analysis (CCA) to predict rainfall over the region on seasonal time scales. The CCA model demonstrated useful skill in predicting seasonal rainfall over the EC up to six months lead. The highest average predictive skill is realized for the June-July-August (JJA) season at one-month lead, while the lowest average skill is realized for the March-April-May (MAM) season at five months lead. The December-January-February (DJF) season maintained steady skill throughout six months lead. Below normal conditions are forecasted by the CCA model for the 2004/2005 dry season (DJF/2004-05, MAM/2005). This outlook is in part, verified from seasonal rainfall totals at two stations within the EC. The outlook for the coming rainy season is for above normal conditions.
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Date Issued: 2005
Identifier: FSU_migr_etd-0510
Format: Thesis

Title: Quasi-Biennial Variation in Kinematic Properties of Equatorial Waves.
Creator: Barton, Cory, Cai, Ming, Clarke, Allan, Sura, Philip, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Here we present a new method of identifying wave activity in the tropical stratosphere. NCEP reanalysis II data from January 1, 1979, to December 31, 2010, was used to diagnose properties of vertically-propagating equatorial waves, including wave speed, wave length, wave tilting, and pressure torque. We band-pass ltered time series of these properties to isolate frequencies corresponding to that of the QBO, of which mean zonal wind anomaly is used as a proxy. Every property was found to...
Show moreHere we present a new method of identifying wave activity in the tropical stratosphere. NCEP reanalysis II data from January 1, 1979, to December 31, 2010, was used to diagnose properties of vertically-propagating equatorial waves, including wave speed, wave length, wave tilting, and pressure torque. We band-pass ltered time series of these properties to isolate frequencies corresponding to that of the QBO, of which mean zonal wind anomaly is used as a proxy. Every property was found to display a strong quasi-biennial oscillation, indicating the activity of waves which translate these properties is linked to the QBO. The oscillation of properties which are dependent on wave type (Kelvin or Rossby-gravity wave), such as wave speed and wave length, are in phase with transitional periods from easterly mean zonal flow to westerly. Other properties which relate to the momentum carried by the waves prove to be in phase or of opposing phase as the QBO. This shows that the deposition of momentum by vertically-propagating waves peaks as the mean zonal flow peaks, providing evidence for the critical level absorption and regime descent theories of the QBO.
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Date Issued: 2012
Identifier: FSU_migr_etd-5318
Format: Thesis

Title: Third Intercomparison of Radiation Codes in Climate Models: Longwave Cloudy Sky Benchmarks and Comparisons with Approximate Methods.
Creator: Kablick, George P., Ellingson, Robert G., Cai, Ming, Liu, Guosheng, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: As a continuation to the shortwave phase of the third Intercomparison of Radiation Codes in Climate Models (ICRCCM III) by Barker et al. (2003), this study establishes longwave benchmarks for inhomogeneous cloud fields and compares the performance of three approximate, one-dimensional (1D) radiation models. The benchmarks are calculated using a correlated-k three-dimensional Monte Carlo (3DMC) algorithm that is validated via comparisons to line-by-line calculations for simple atmospheres. The...
Show moreAs a continuation to the shortwave phase of the third Intercomparison of Radiation Codes in Climate Models (ICRCCM III) by Barker et al. (2003), this study establishes longwave benchmarks for inhomogeneous cloud fields and compares the performance of three approximate, one-dimensional (1D) radiation models. The benchmarks are calculated using a correlated-k three-dimensional Monte Carlo (3DMC) algorithm that is validated via comparisons to line-by-line calculations for simple atmospheres. The approximate methods include an independent pixel approximation (IPA) and two cloud-overlap schemes: maximum/random (MRO) and random (RO). The test cases are the same as those used in the shortwave ICRCCM III, and were generated from various cloud resolving models (CRMs). These cases represent a variety of inhomogeneous cloud types that are important radiative forcing mechanisms of general circulation models (GCMs). Domain-averaged fluxes and heating rates from these six "real cloud" atmospheres show that the IPA is consistently more accurate than the cloud-overlap models with respect to the benchmarks. For example, comparisons of model results for the ATEX case yield a maximum cloud layer heating rate error of -20 K/day from using cloud-overlap models, whereas the IPA error is only -2.5 K/day. These differences can be attributed to the 3D effects of cloud radiation, and indicate the need to refine longwave 1D climate radiation codes so that they compensate for unresolved clouds.
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Date Issued: 2008
Identifier: FSU_migr_etd-3405
Format: Thesis

Title: A Quality Control Procedure for Assimilating Airs Radiance Data into a Mesoscale Model.
Creator: O‘Connor, Janna E., Zou, Xiaolei, Ellingson, Robert, Cai, Ming, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The steps involved in establishing and implementing a quality control procedure for AIRS radiance data prior to its use in a mesoscale model are discussed. The Limited Cloud-Clearing Data Removal (LCCDR) Algorithm utilizes AIRS channel maximum weighting function (WF) height, vertical structure of WF, and cloud height at each pixel to remove cloud-contaminated data points. Biweight statistics, which include a weighted average and weighted standard deviation, are implemented to remove remaining...
Show moreThe steps involved in establishing and implementing a quality control procedure for AIRS radiance data prior to its use in a mesoscale model are discussed. The Limited Cloud-Clearing Data Removal (LCCDR) Algorithm utilizes AIRS channel maximum weighting function (WF) height, vertical structure of WF, and cloud height at each pixel to remove cloud-contaminated data points. Biweight statistics, which include a weighted average and weighted standard deviation, are implemented to remove remaining data with large model deviations from observations. Two test cases are examined: a non-precipitation case and a case involving Hurricane Charley. The LCCDR algorithm effectively removes outliers due to cloud-contamination, producing a reduction in the mean difference between simulated and observed brightness temperatures. Biweight statistics further exclude points where simulated values disagree with AIRS data. For both cases, large discrepancies are found between AIRS observations and simulated surface brightness temperatures in terms of the range of brightness temperature change and intensity. Overall, AIRS radiances compared more favorably with simulated data shown by the reduction in root mean square error values after quality control and the increase in correlation coefficient values. Future work includes improving model ability to predict dry versus moist air boundaries and cyclone intensity through assimilation of AIRS radiance observations.
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Date Issued: 2006
Identifier: FSU_migr_etd-2469
Format: Thesis

Title: Diagnosis of Middle-Atmosphere Climate Sensitivity by the Climate Feedback-Response Analysis Method.
Creator: Zhu, Xun, Yee, Jeng-Hwa, Cai, Ming, Swartz, William H., Coy, Lawrence, Aquila, Valentina, Garcia, Rolando, Talaat, Elsayed R.
Abstract/Description: The authors present a new method to diagnose the middle-atmosphere climate sensitivity by extending the climate feedback-response analysis method (CFRAM) for the coupled atmosphere-surface system to the middle atmosphere. The middle-atmosphere CFRAM (MCFRAM) is built on the atmospheric energy equation per unit mass with radiative heating and cooling rates as its major thermal energy sources. MCFRAM preserves CFRAM's unique feature of additivity, such that partial temperature changes due to...
Show moreThe authors present a new method to diagnose the middle-atmosphere climate sensitivity by extending the climate feedback-response analysis method (CFRAM) for the coupled atmosphere-surface system to the middle atmosphere. The middle-atmosphere CFRAM (MCFRAM) is built on the atmospheric energy equation per unit mass with radiative heating and cooling rates as its major thermal energy sources. MCFRAM preserves CFRAM's unique feature of additivity, such that partial temperature changes due to variations in external forcing and feedback processes can be added to give a total temperature change for direct comparison with the observed temperature change. In addition, MCFRAM establishes a physical relationship of radiative damping between the energy perturbations associated with various feedback processes and temperature perturbations associated with thermal responses. In this study, MCFRAM is applied to both observations and model output fields to diagnose the middle-atmosphere climate sensitivity. The authors found that the largest component of the middle-atmosphere temperature response to the 11-yr solar cycle (solar maximum vs solar minimum) is the partial temperature change due to the variation of the solar flux. Increasing CO2 cools the middle atmosphere, whereas the partial temperature change due to changes in O-3 can be either positive or negative. The application of MCFRAM to model dynamical fields reconfirms the advantage of introducing the residual circulation to characterize middle-atmosphere dynamics in terms of the partial temperature changes. The radiatively driven globally averaged partial temperature change is approximately equal to the observed temperature change, ranging from -0.5 K near 25 km to -1.0 K near 70 km between solar maximum and solar minimum.
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Date Issued: 2016-01
Identifier: FSU_libsubv1_wos_000367396700001, 10.1175/JAS-D-15-0013.1
Format: Citation

Title: FEELING THE PULSE OF THE STRATOSPHERE An Emerging Opportunity for Predicting Continental-Scale Cold-Air Outbreaks I Month in Advance.
Creator: Cai, Ming, Yu, Yueyue, Deng, Yi, van den Cool, Huug M., Ren, Rongcai, Saha, Suru, Wu, Xingren, Huang, Jin
Abstract/Description: Extreme weather events such as cold-air outbreaks (CAOs) pose great threats to human life and the socioeconomic well-being of modern society. In the past, our capability to predict their occurrences has been constrained by the 2-week predictability limit for weather. We demonstrate here for the first time that a rapid increase of air mass transported into the polar stratosphere, referred to as the pulse of the stratosphere (PULSE), can often be predicted with a useful degree of skill 4-6...
Show moreExtreme weather events such as cold-air outbreaks (CAOs) pose great threats to human life and the socioeconomic well-being of modern society. In the past, our capability to predict their occurrences has been constrained by the 2-week predictability limit for weather. We demonstrate here for the first time that a rapid increase of air mass transported into the polar stratosphere, referred to as the pulse of the stratosphere (PULSE), can often be predicted with a useful degree of skill 4-6 weeks in advance by operational forecast models. We further show that the probability of the occurrence of continental-scale CAOs in midlatitudes increases substantially above normal conditions within a short time period from 1 week before to 1-2 weeks after the peak day of a PULSE event. In particular, we reveal that the three massive CAOs over North America in January and February of 2014 were preceded by three episodes of extreme mass transport into the polar stratosphere with peak intensities reaching a trillion tons per day, twice that on an average winter day. Therefore, our capability to predict the PULSEs with operational forecast models, in conjunction with its linkage to continental-scale CAOs, opens up a new opportunity for 30-day forecasts of continental scale CAOs, such as those occurring over North America during the 2013/14 winter. A real-time forecast experiment inaugurated in the winter of 2014/15 has given support to the idea that it is feasible to forecast CAOs 1 month in advance.
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Date Issued: 2016-08
Identifier: FSU_libsubv1_wos_000382430700016, 10.1175/BAMS-D-14-00287.1
Format: Citation

Title: Forecast Skill of the NCEP GFS Model in the Southern Hemisphere Stratosphere in 2006.
Creator: Brodowski, Christopher, Cai, Ming, Cunningham, Philip, Ahlquist, Jon, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: This study diagnoses the anomaly fields of the Southern Hemispheric stratosphere in the period from 1 January 2006 to 28 February 2007 and examines the forecasting skill of the NCEP GFS model for the Southern Hemisphere (SH) during this period. Observational and model forecast data were converted into anomaly field data in a semi-Lagrangian θ-PVLAT coordinate. The first two EOF modes of the potential vorticity (PV) anomaly in the θ-PVLAT coordinate constitute over 80% of the total variance....
Show moreThis study diagnoses the anomaly fields of the Southern Hemispheric stratosphere in the period from 1 January 2006 to 28 February 2007 and examines the forecasting skill of the NCEP GFS model for the Southern Hemisphere (SH) during this period. Observational and model forecast data were converted into anomaly field data in a semi-Lagrangian θ-PVLAT coordinate. The first two EOF modes of the potential vorticity (PV) anomaly in the θ-PVLAT coordinate constitute over 80% of the total variance. It was found that the SH stratospheric polar vortex is quite stable (with a period twice as long as its NH counterpart) and persistent, and that the NCEP GFS model forecasts exclusively dynamical processes such as the equatorial quasi-biennial oscillation (QBO) with extremely high success but possesses a cold bias in the troposphere and a warm bias in the stratosphere due to a lack of updated greenhouse gas information. Forecasting skill in the stratosphere was far higher than in the troposphere, and the second EOF modes possess higher forecast skill than the first. The good forecast skill in the stratosphere is due to the GFS's ability of capturing the slow poleward propagation of stratospheric thermal anomalies associated with the polar vortex oscillation. Overall forecast skill scores were high enough to indicate that the NCEP GFS model has great potential in stratospheric climate prediction, but the model needs timely evolving greenhouse gas information to improve further.
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Date Issued: 2008
Identifier: FSU_migr_etd-3008
Format: Thesis

Title: Footprint of the Dynamical Amplifier of Global Warming and Attribution of Models' Uncertainties.
Creator: Castet, Christelle Clémence, Cai, Ming, Kim, Kwang-Yul, Ruscher, Paul H., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The largest warming over the last several decades has been observed in high latitudes. Cai (2005) proposed that part of the large amplitude climate warming in high latitudes could be explained by the "dynamical amplifier" feedback. This study will first provide observational and modeling evidences to validate the dynamical amplifier theory. The second part will address the question whether part of the differences in the CGCM's global warming projections can be explained by the dynamical...
Show moreThe largest warming over the last several decades has been observed in high latitudes. Cai (2005) proposed that part of the large amplitude climate warming in high latitudes could be explained by the "dynamical amplifier" feedback. This study will first provide observational and modeling evidences to validate the dynamical amplifier theory. The second part will address the question whether part of the differences in the CGCM's global warming projections can be explained by the dynamical amplifier theory. The theory predicts an upward trend of the net radiation surplus (deficit) in low (high) latitudes forced by anthropogenic greenhouse gases. The radiation budget at the top of the atmosphere (TOA) using the ERA40 reanalysis and climate model simulations forced by anthropogenic radiative forcings made at 14 climate centers were analyzed. The results indicate that both the radiation energy surplus in low latitudes and deficit in high latitudes at the TOA have been strengthened over the last several decades. Such an intensification of the radiation energy imbalance at the TOA is also confirmed by most of the climate model simulations. Furthermore, the analysis of the net radiation budget between the surface and the TOA confirms that the change in the TOA energy imbalance is indeed due to the upward trend in the poleward heat transport, in accordance with the dynamical amplifier theory. There is a large model-to-model variability of the intensification of the poleward heat transport among the 14 climate model simulations. It is found that about 59% of the global warming projection uncertainties, which varies from 1.5K to 4K, forced by the 2×CO2 forcing can be explained by the variation of the intensification of the poleward heat transport among models. The inter-model variability of the change in the poleward heat transport explains about 66% of the warming projection uncertainties for the Northern Hemisphere (NH) and 54% for the Southern Hemisphere (SH). The differences in the poleward heat transport intensification also explain about 71% and 49% of the warming uncertainties in the NH and SH high latitudes. Therefore, it can be concluded that a large part of the uncertainties in the CGCM's global warming projections can be explained by the dynamical amplifier theory.
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Date Issued: 2005
Identifier: FSU_migr_etd-4053
Format: Thesis

Title: Climate Feedback Analysis of the GFDL IPCC AR4 Global Warming Simulation.
Creator: Castet, Christelle, Cai, Ming, Dewar, William, Zou, Xiaolei, Ruscher, Paul, Bourassa, Mark, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Both observed and modeled global warming pattern shows a large surface polar warming and a large upper atmospheric warming in the tropics. This pattern leads to an amplification (reduction) of the temperature gradient at upper levels (surface). Physical processes behind this temperature change are the external radiative forcing, and subsequent feedback processes that may amplify or dampen the climate response. This unique warming pattern suggests that high latitudes are very sensitive to...
Show moreBoth observed and modeled global warming pattern shows a large surface polar warming and a large upper atmospheric warming in the tropics. This pattern leads to an amplification (reduction) of the temperature gradient at upper levels (surface). Physical processes behind this temperature change are the external radiative forcing, and subsequent feedback processes that may amplify or dampen the climate response. This unique warming pattern suggests that high latitudes are very sensitive to climate change and also the area where the largest warming projection uncertainties occur. The objective of this study is to apply a new coupled atmosphere-surface climate feedback-response analysis method to quantify the contributions of the external forcing alone (doubling of carbon dioxide), and subsequent feedback processes to the 3-D global warming pattern in the GFDL_CM2.0 model. The feedbacks under consideration include the water vapor feedback, surface albedo feedback, surface turbulent heat flux feedback, and the sum of the change in cloud radiative forcing (CRF), vertical convective, and large-scale scale dynamical feedback. The partial temperature changes due to the external forcing and due to individual feedbacks are additive and their sum converges toward the temperature change produced by the original GFDL_CM2.0 global warming simulations. Therefore, our attributions of the global warming patter to individual thermodynamic and dynamical processes are mathematically robust and physically meaningful. The partial temperature change due to the water vapor feedback is found to be the largest contributor to the globally averaged surface warming. It is twice as large as the warming due to the external radiative forcing alone. The surface albedo feedback and change in surface cloud radiative forcing increase the surface temperature by a smaller amount. In addition, the changes in atmospheric cloud forcing and large-scale dynamics, as well as the surface turbulent heat flux feedback, contribute to an overall damping the surface warming. In terms of spatial pattern of global warming, the external forcing alone would cause a large surface warming in the extratropics. The water vapor feedback strengthens the tropical warming substantially and the ice/snow albedo feedback contributes to polar warming amplification. The atmospheric dynamical feedbacks associated with the enhancement of vertical convection in the tropics acts to amplify the warming in the upper troposphere at the expense of reducing the warming in the lower troposphere and at the surface in the tropics. The dynamical feedbacks due to the strengthening of the poleward energy transport contribute to a warming in the entire troposphere and the surface in high latitudes. At the surface and in the lower troposphere, the additional warming brought by the change in circulations strengthens the warming due to thermodynamical forcings (e.g., external forcing, water vapor feedback, and ice albedo feedback). In the upper troposphere, the warming brought by the change in circulations dominates the cooling due to thermodynamical forcings. As a result, the entire troposphere becomes warmer. The stratospheric cooling is entirely due to the external radiative forcing.
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Date Issued: 2009
Identifier: FSU_migr_etd-4050
Format: Thesis

Title: Climatological Characteristics of the Jet Streams over West Africa.
Creator: Suk, Jonathan David, Nicholson, Sharon E., Fuelberg, Henry E., Cai, Ming, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: This paper examines the climatology of the major jet steams over West Africa. Three prominent jets occur at varying heights in the atmosphere, and while each jet is zonal in its flow, their sizes, magnitudes, and directions vary greatly. The Tropical Easterly Jet is shown to be the strongest and most consistent in its location at approximately 200 to 150 hPa. As its name implies, this jet stream consists of easterly flow and has been the topic of many studies over the Tibetan Plateau and...
Show moreThis paper examines the climatology of the major jet steams over West Africa. Three prominent jets occur at varying heights in the atmosphere, and while each jet is zonal in its flow, their sizes, magnitudes, and directions vary greatly. The Tropical Easterly Jet is shown to be the strongest and most consistent in its location at approximately 200 to 150 hPa. As its name implies, this jet stream consists of easterly flow and has been the topic of many studies over the Tibetan Plateau and Indian Ocean due to its relationship with the Indian Monsoon. On a smaller scale, the African Easterly Jet is prominent over West Africa at approximately 700 to 600 hPa. Although it is associated with the African Monsoon, its strength is related to the temperature contrast between the dry desert to its north, and the cool, moist south-westerlies to the south. The third jet stream is the only one that is westerly in direction. It is the least studied of the three jets. The Low Level Westerlies are located between 1000 and 850 hPa. Although they exhibit a smaller velocity, they are believed to exert a significant influence on the precipitation pattern over West Africa. The goal of this project is to determine the climatological characteristics of the three jet streams, especially during the summer months of June, July, August, and September. Along with building a database to analyze the climatological trends of the jets, their interrelationships are also studied. The speed of the Low Level Westerlies is shown to have a significant correlation with the speed of the Tropical Easterly Jet. And, although the African Easterly Jet occurs in the center of the atmospheric column between the other two jets, it does not have a significant relationship to either of the jets located above and below. The conclusions of this paper naturally lend themselves to further research to help explain not only the reason why the Tropical Easterly Jet and the Low Level Westerlies are related, but also the influence that these systems have on the local environment. In addition, future research should determine the larger scale implications of each jet's location in relation to the other jet streams
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Date Issued: 2007
Identifier: FSU_migr_etd-0400
Format: Thesis

Title: Diagnosis and Analyis of Climate Feedbacks in the NCAR CCSM3.0.
Creator: Taylor, Patrick Charles, Ellingson, Robert G., Krishnamurti, Ruby, Cai, Ming, Clayson, Carol Anne, Liu, Guosheng, Department of Earth, Ocean and Atmospheric Sciences, Florida...
Show moreTaylor, Patrick Charles, Ellingson, Robert G., Krishnamurti, Ruby, Cai, Ming, Clayson, Carol Anne, Liu, Guosheng, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
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Abstract/Description: Climate feedbacks represent mechanisms that alter the sensitivity of the earth climate system. It has been suggested that the current spread in climate model sensitivity to a CO2 forcing is a result of different treatments of climate feedbacks. The determination of the climate system sensitivity is critical to understanding how the system will respond to a CO2 radiative forcing. The strength of a climate feedback is defined in terms of annual, global mean top of atmosphere (TOA) radiative...
Show moreClimate feedbacks represent mechanisms that alter the sensitivity of the earth climate system. It has been suggested that the current spread in climate model sensitivity to a CO2 forcing is a result of different treatments of climate feedbacks. The determination of the climate system sensitivity is critical to understanding how the system will respond to a CO2 radiative forcing. The strength of a climate feedback is defined in terms of annual, global mean top of atmosphere (TOA) radiative perturbation. However, contributions to the global, annual mean feedbacks can originate from different geographical regions and vertical layers within the atmosphere. In addition, the contributions to the annual mean TOA radiative perturbation can be disproportionately distributed throughout the annual cycle. This study performs offline, partial radiative perturbation-style, radiative calculations to determine the geographical, vertical, and seasonal distributions of the major climate feedbacks contributing to the TOA radiative energy budget: clouds, water vapor, temperature, and surface albedo. These feedback strengths are diagnosed from NCAR CCSM3.0 model output for the SRESA1B emission scenario simulated for the IPCC AR4. It is found that the tropics and sub-tropical climate responses drive the sign and strength of the water vapor and cloud feedbacks. In addition, a significant annual cycle of the SW cloud and surface albedo feedbacks is found. The inter-seasonal variations of the SW cloud and surface albedo feedbacks found here show a different pattern than previously published results. The radiative perturbations are then used as input into the newly developed Coupled Feedback Response Analysis Method (CFRAM), which uses a total energy based method to isolate partial temperature changes due to individual feedbacks in the atmosphere and at the surface. Many authors have calculated climate feedback radiative perturbations in different manners using seasonal mean, monthly mean, daily mean, and every time step model output. Monthly mean model output is used in this study. A comparison of the global mean clear sky TOA net flux calculation using monthly mean model output with the monthly mean model output TOA net flux reveals a global mean bias in the offline radiation calculations compared to the model simulated TOA net flux of +3.95 Wm-2 with a standard deviation of 3.78 Wm-2. In order to handle complexities associated with cloud overlap, the Monte Carlo Independent Column Approximation (MCICA) technique is uniquely adapted for use in the context of this study. This technique relies on a stochastic cloud generator using a maximum-random overlap rule to sample the monthly mean cloud frequency profile. It is shown that the global mean bias in the calculation of the TOA net flux compared to NCAR CCSM3.0 model output is +1.74 Wm-2 and a standard deviation of 6.71 Wm-2 using this technique. However, the results suggest that the technique provides a very good estimate of all feedback sensitivity parameters despite bias associated with using monthly mean model output.
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Date Issued: 2009
Identifier: FSU_migr_etd-1645
Format: Thesis

Title: A New Over-Land Rainfall Retrieval Algorithm Using Satellite Microwave Observations.
Creator: You, Yalei, Liu, Guosheng, Chicken, Eric, Cai, Ming, Ellingson, Robert, Misra, Vasu, Turk, Joseph, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: During the past two decades, the accuracy of rainfall retrieval based on passive microwave observations has been greatly improved, particularly over ocean. However, rainfall retrieval over land remains to be problematic. The objective of this study is to develop a new rainfall retrieval algorithm that provides better rainfall estimates over land. Toward that end, in the first part of this study, we focus on better understanding three key physical aspects which significantly influence the...
Show moreDuring the past two decades, the accuracy of rainfall retrieval based on passive microwave observations has been greatly improved, particularly over ocean. However, rainfall retrieval over land remains to be problematic. The objective of this study is to develop a new rainfall retrieval algorithm that provides better rainfall estimates over land. Toward that end, in the first part of this study, we focus on better understanding three key physical aspects which significantly influence the algorithm development, including signature from both high and low frequencies, the surface emissivity effect and rainfall profile structure. Although it has been long believed that the dominant signature of over land rainfall is the brightness temperature depression caused by ice scattering at high microwave frequencies (e.g., 85 GHz), our results in chapter 3 showed that the brightness temperature combinations from 19 and 37 GHz, i.e., V19-V37 (the letter V denotes vertical polarization, and the numbers denote frequency in GHz. Similar notations are used hereafter) or V21-V37 can explain ~10% more variance of near surface rainfall rate than the V85 brightness temperature. A plausible explanation to this result is that in addition to ice scattering signature, the V19-V37 channel contains liquid water information as well, which is more directly related to surface rain than ice water aloft. In addition, to better utilized the information from low frequency, we analyzed the instantaneous microwave land surface emissivity (MLSE) and its response to the previous rainfall (Chapter 4). Current rainfall retrieval algorithm over land has not yet taken the MLSE effect into consideration. Results showed that over grass, closed shrub and cropland, previous rainfall can cause the horizontally-polarized 10 GHz brightness temperature (TB) to drop by as much as 20 K with a corresponding emissivity drop of approximately 0.06, whereby previous rain exhibited little influence on the emissivity over forest due to the dense vegetation. We developed a technique to estimate the emissivity underneath precipitating radiometric scenes. Further, in chapter 5 the relationship between water paths and the surface rain is evaluated. Results showed that corresponding to a similar surface rainrate ice water path has large spatial variability, and the most prominent characteristic for the ice water path spatial distribution is the contrast between land and ocean. On average, the correlation (R2) between ice water path and surface rainrate is also larger over land than over ocean. Over the majority of land areas, R2 is ~0.36, with the exception of arid regions and the Indian subcontinent (~0.25). In the second part of this study (chapter 6 and chapter 7), a new Principal Component Analysis (PCA) based Bayesian algorithm is proposed to take full advantage all the brightness temperature observations. Results from this algorithm was compared with that from the TRMM facility algorithm. The unique features of the new retrieval algorithm are (1) physical parameters, including surface temperature, land cover type, elevation, freezing level height and storm height, are used to categorize the land surface conditions and rainfall profile structures. (2) the covariance matrix in the Bayesian framework is calculated based on real observations and is perfectly diagonal through the Principal Component Analysis transformation. It is demonstrated that the retrieved surface rain rate agrees much better with observations from TRMM precipitation Radar, compared to the results from TRMM facility algorithm over land. Particularly, no obvious over-estimations are observed when rainrate is less than 10 mm/hr. Validation using one year data show that the correlation between retrieved rainrate and observations is 0.73, while it is 0.65 between retrieved rainrate by TRMM facility algorithm and observations. The root mean square error (RMSE) is lowered by about 35%. In terms of the computational time, this algorithm is several order faster than other published Bayesian based algorithms. In addition, this algorithm can be conveniently adapted to other satellite platforms (e.g., SSM/I) due to its location and season independent characteristics.
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Date Issued: 2013
Identifier: FSU_migr_etd-8666
Format: Thesis

Title: Assessing Sun Glint and Nonlocal Thermal Equilibrium Effects on CrIS Data Bias.
Creator: Yin, Mengtao, Cai, Ming, Ray, Peter S., Wu, Zhaohua, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Abstract/Description: The hyper-spectral Cross-track Infrared Sounder (CrIS) on board Suomi National Polar-orbiting Partnership (NPP) supports a continuing advance in numerical weather prediction (NWP) for improved short- to medium-range weather forecast skills. The assimilation of CrIS brightness temperature observations in NWP modeling systems requires the data biases be properly estimated and removed from data. Both the solar radiation reflected by sea surface into the satellite viewing direction and the solar...
Show moreThe hyper-spectral Cross-track Infrared Sounder (CrIS) on board Suomi National Polar-orbiting Partnership (NPP) supports a continuing advance in numerical weather prediction (NWP) for improved short- to medium-range weather forecast skills. The assimilation of CrIS brightness temperature observations in NWP modeling systems requires the data biases be properly estimated and removed from data. Both the solar radiation reflected by sea surface into the satellite viewing direction and the solar pumping that deviates the stratosphere from the local thermal equilibrium (LTE) introduce the significant biases in CrIS infrared shortwave observations. In this study, the effects of sun glint and nonlocal thermal equilibrium (NLTE) on CrIS data biases are assessed quantitatively. It is found that the newly-developed sun glint and NLTE models can dramatically reduce the CrIS data biases at infrared shortwave band during daytime. However, the biases still remain relatively large for CrIS infrared shortwave stratospheric channels after the NLTE correction. A further study confirms that the bias residuals after the NLTE correction mainly come from the input temperature profiles to the Radiative Transfer Model (RTM) not the RTM itself. It is found that the temperature profiles from the National Center for Environmental Prediction (NCEP) Global Forecast System (GFS), which serve as input to the Community Radiative Transfer Model (CRTM), have large cold biases in the upper stratosphere, leading to the large bias remnants of stratospheric channels. Compared with the temperature profiles from ERA Interim reanalysis, the cold biases of GFS temperature profiles increase with altitude and reach about 10 K near 1 hPa.
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Date Issued: 2015
Identifier: FSU_migr_etd-9498
Format: Thesis

Title: A One-Year Geostationary Satellite-Derived Fog Climatology for Florida.
Creator: Lefran, Daphne, Ray, Peter S., Cai, Ming, Wu, Zhaohua, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Abstract/Description: As reported by the University of Central Florida (UCF), Florida nearly leads the nation in fatal vehicle crashes due to fog and smoke conditions. Between 2002 and 2009, 299 deaths were due to vehicle crashes related to fog and smoke conditions. This is more than the amount of deaths by hurricanes and lightning strikes combined. It may be possible to reduce the number of fatalities and crashes by implementing an effective early warning system. A warning of impending fog conditions would allow...
Show moreAs reported by the University of Central Florida (UCF), Florida nearly leads the nation in fatal vehicle crashes due to fog and smoke conditions. Between 2002 and 2009, 299 deaths were due to vehicle crashes related to fog and smoke conditions. This is more than the amount of deaths by hurricanes and lightning strikes combined. It may be possible to reduce the number of fatalities and crashes by implementing an effective early warning system. A warning of impending fog conditions would allow DOT and other agencies the ability to monitor specific locations. However, fog is both spatially and temporally variable and surface observation equipment is widely dispersed. The challenge lies in the ability to forecast and detect the occurrence of fog from surface observations far removed from the location of fog occurrence. The spatial variability of fog frequency over the state of Florida is explored based on an evaluation of GOES Imager satellite data. A nighttime fog detection algorithm employing a bispectral thresholding technique involving brightness temperature differences (BTD) between two channels: 4 (10.7-μm) and 2 (3.9-μm) is presented. The performance of the fog product is validated using one year of AWOS/ASOS station observations in the period right before daybreak, showing moderate skill. The frequency of fog in Florida for 2012 is analyzed through application of this technique and is compared to interpolated fog frequencies based on ground observations. Seasonal and annual bias corrections are implemented to calibrate the satellite fog product observations and provide spatially continuous data of fog occurrence in Florida. While the satellite-derived fog product generally overestimated fog frequency, the pattern of fog occurrences agreed with the general spatial patterns found in station-derived climatologies, providing encouraging results. This analysis sets a basis for a satellite-based fog climatology that provides spatially continuous information of underlying fog dynamics. Future work involving assessments of satellite fog products over a multi-year period, as well as improved spatial resolution in the forthcoming GOES-R, will assist in furthering knowledge regarding regional fog risks and potentials.
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Date Issued: 2015
Identifier: FSU_migr_etd-9378
Format: Thesis

Title: Improved Vegetation Characterization and Freeze Statistics in a Regional Spectral Model for the Florida Citrus Farming Region.
Creator: Goto, Yoshie, O’Brien, James J., Krishnamurti, Ruby, Bourassa, Mark A., Cai, Ming, Ruscher, Paul, LaRow, Timothy, Department of Earth, Ocean and Atmospheric Sciences, Florida...
Show moreGoto, Yoshie, O’Brien, James J., Krishnamurti, Ruby, Bourassa, Mark A., Cai, Ming, Ruscher, Paul, LaRow, Timothy, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
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Abstract/Description: This study focused on the effective use of a numerical climate model for agriculture in Florida, especially in the citrus farming region of the Florida peninsula, because of the impact of agriculture to Florida's economy. For the analyses of the ensemble, the climate models used in this study were the FSU/COAPS Global Spectral Model and FSU/COAPS Regional Spectral Model (FSU/COAPS RSM) coupled with a land-surface model. The multi-convective scheme method and variable initial conditions were...
Show moreThis study focused on the effective use of a numerical climate model for agriculture in Florida, especially in the citrus farming region of the Florida peninsula, because of the impact of agriculture to Florida's economy. For the analyses of the ensemble, the climate models used in this study were the FSU/COAPS Global Spectral Model and FSU/COAPS Regional Spectral Model (FSU/COAPS RSM) coupled with a land-surface model. The multi-convective scheme method and variable initial conditions were used for the ensembles. Severe freezes impacting agriculture in Florida were associated with some major climate patterns, such as El Niño and Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO). In the first part of this study, seasonal ensemble integrations of the regional model were examined for the tendencies of freezes in the Florida peninsula during each ENSO or NAO phase is examined. Mean excess values of minimum temperatures from thresholds on the basis of the Generalized Pareto Distribution (GPD), which represents the extreme data in a dataset, were used to analyze the freezes in the regional model. According to some previous studies, El Niño winters obtain fewer freezes than the other ENSO phases. Although the ensemble comprised only 19 winters, the ensemble found variability patterns in minimum temperatures in each climate phase similar to the findings in the previous studies which were based on the observed data. The FSU/COAPS RSM was coupled with Community Land Model 2.0 (CLM2), to represent the land-surface conditions. Although the coupling improved the temperature forecast of the RSM, it still has a cold bias and simulates smaller diurnal temperature changes than actually occur in southern Florida. Among the prescribed surface data, Leaf Area Index (LAI) for southern Florida in the CLM2 is lower than those observed by MODIS (Moderate Resolution Imaging Spectroradiometer). In the first experiment of this part, the sensitivity of the temperature forecast to the LAI in the climate models was investigated, by modifying the LAI data in the CLM2 based on the monthly MODIS observations. In the second experiment, newly created prescribed datasets of LAI and plant functional types for the CLM2 based on the MODIS observations were applied to the RSM. The substitution increased the diurnal temperature change in southern Florida slightly but almost consistently.
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Date Issued: 2008
Identifier: FSU_migr_etd-4102
Format: Thesis

Title: Ensemble-Mean Dynamics of Low-Frequency Variability and Cloud Temperature Profile Retrieval Using GPS RO Data.
Creator: Lin, Lin, Zou, Xiaolei, Navon, I. Michael, Cai, Ming, Ellingson, Robert G., Krishnamurti, T. N., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The second-order closure for the ensemble-mean dynamics is validated using the approach of direct numerical ensemble simulations of a linear barotropic model with stochastic basic flows in extratropics. For various configurations of the stochastic basic flow and external forcing, the deterministic solutions under the second-order closure capture, with remarkable accuracy, the ensemble means and the associated eddy covariance fields of forced responses simulated by a 500-member numerical...
Show moreThe second-order closure for the ensemble-mean dynamics is validated using the approach of direct numerical ensemble simulations of a linear barotropic model with stochastic basic flows in extratropics. For various configurations of the stochastic basic flow and external forcing, the deterministic solutions under the second-order closure capture, with remarkable accuracy, the ensemble means and the associated eddy covariance fields of forced responses simulated by a 500-member numerical ensemble. Thus, the second-order closure is found to be adequate for describing the ensemble-mean linear dynamics with stochastic basic flows. Example of ensemble-mean solution shows the important role played by the stochastic synoptic eddy component of the basic flow in determining the ensemble-mean responses to external forcing. This study supports the notion that linear frameworks of ensemble-mean dynamics under second-order closure are useful tools for describing and understanding the dynamics of the synoptic eddy and the low-frequency flow (SELF) feedback and extratropical atmospheric low-frequency variability. Following a similar concept, the conceptual recharge oscillator model for the El Niño-Southern Oscillation phenomenon (ENSO) is utilized to study the influence of fast variability such as that associated with westerly wind bursts (WWB) on dynamics of ENSO and predictability. The ENSO-WWB interaction is simply represented by stochastic forcing modulated by ENSO-related sea surface temperature (SST) anomalies. An analytical framework is developed to describe the ensemble-mean dynamics of ENSO under stochastic forcing. Numerical ensemble simulations verify the main results derived from the analytical ensemble-mean theory: the state-dependent stochastic forcing enhances the instability of ENSO and its ensemble spread, generates asymmetry in the predictability of the onsets of cold and warm phases of ENSO, and leads to an ensemble-mean bias that may eventually contribute to a climate mean state bias. Clouds contribute greatly to the atmospheric variability within weather systems. Measurements of thermodynamic properties in cloudy airs are required to improve numerical weather forecasting models and for the study of the global radiation and hydrology budget. The Global Positioning System (GPS) radio occultation (RO) technique is not affected by clouds and has a high vertical resolution, making it ideally suited for cloud study. Temperatures retrieved from Constellation Observing System for Meteorology Ionosphere & Climate (COSMIC) RO measurements are compared with two operational weather assimilation models including the Prediction and National Center for Atmospheric Research (NCEP/NCAR) reanalysis and European Centre for Medium-Range Weather Forecasts (ECMWF) analysis. The cloudy GPS ROs during June 2007 and June to September 2006 are identified based on the collocated CloudSat data. Systematic bias of opposite sign between large-scale global analyses and observed RO profiles are found for cloudy and clear-sky conditions. It is also found that GPS wet retrieval lapse rate is nearly constant (~6oC/km) in the vertical while that from ECMWF increases with height from cloud middle to cloud top. A new GPS RO cloudy profile retrieval algorithm is proposed. A relative humidity parameter is introduced through an empirical relationship between CloudSat ice-water content and ECMWF relative humidity. The new cloudy temperature retrieval tends to be warmer than the GPS wet retrieval within the cloud and slightly colder near the cloud top, resulting in a cloudy lapse rate that agrees more closely with that of the ECMWF in the lower part of the cloud and increases with height (but faster than that of the ECMWF), and reaches a value of about 7.6oC/km near the cloud top. When the ice-water content measurements are absent, an empirical value of 0.85 is shown to be a good approximation for the relative humidity parameter.
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Date Issued: 2009
Identifier: FSU_migr_etd-1328
Format: Thesis

Title: Sea-Ice, Clouds and Atmospheric Conditions in the Arctic and Their Interactions as Derived from a Merged C3M Data Product.
Creator: Nag, Bappaditya, Cai, Ming, Tam, Christopher K. W., Clarke, Allan J., Liu, Guosheng, Speer, Kevin G. (Kevin George), Florida State University, College of Arts and Sciences,...
Show moreNag, Bappaditya, Cai, Ming, Tam, Christopher K. W., Clarke, Allan J., Liu, Guosheng, Speer, Kevin G. (Kevin George), Florida State University, College of Arts and Sciences, Program in Geophysical Fluid Dynamics
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Abstract/Description: The polar regions of the world constitute an important sector in the global energy balance. Among other effects responsible for the change in the sea-ice cover like ocean circulation and ice-albedo feedback, the cloud-radiation feedback also plays a vital role in modulation of the Arctic environment. However the annual cycle of the clouds is very poorly represented in current global circulation models. This study aimed to explore the atmospheric conditions in the Arctic on an unprecedented...
Show moreThe polar regions of the world constitute an important sector in the global energy balance. Among other effects responsible for the change in the sea-ice cover like ocean circulation and ice-albedo feedback, the cloud-radiation feedback also plays a vital role in modulation of the Arctic environment. However the annual cycle of the clouds is very poorly represented in current global circulation models. This study aimed to explore the atmospheric conditions in the Arctic on an unprecedented spatial coverage spanning 70°N to 80°N through the use of a merged data product, C3MData (derived from NASA's A-Train Series). The following three topics provide outline on how this dataset can be used to accomplish a detailed analysis of the Arctic environment and provide the modelling community with first information to update their models aimed at better forecasts. (1)The three properties of the Arctic climate system to be studied using the C3MData are sea-ice, clouds, and the atmospheric conditions. The first topic is to document the present states of the three properties and also their time evolutions or their seasonal cycles. (2)The second topic is aimed at the interactions or the feedbacks processes among the three properties. For example, the immediate alteration in the fluxes and the feedbacks arising from the change in the sea-ice cover is investigated. Seasonal and regional variations are also studied. (3)The third topics is aimed at the processes in native spatial resolution that drive or accompany with sea ice melting and sea ice growth. Using a composite approach based on a classification due to surface type, it is found that limitation of the water vapour influx from the surface due to change in phase at the surface featuring open oceans or marginal sea-ice cover to complete sea-ice cover is a major determinant in the modulation of the atmospheric moisture. The impact of the cloud-radiative effects in the Arctic is found to vary with sea-ice cover and seasonally. The effect of the marginal sea-ice cover becomes more and more pronounced in the winter. The seasonal variation of the dependence of the atmospheric moisture on the surface and the subsequent feedback effects is controlled by the atmospheric stability measured as a difference between the potential temperature at the surface and the 700hPa level. A regional analysis of the same suggests that most of the depiction of the variations observed is contributed from the North Atlantic region.
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Date Issued: 2016
Identifier: FSU_2016SU_Nag_fsu_0071E_13367
Format: Thesis

Title: Using Radar-Derived Parameters to Forecast Lightning Cessation for Nonisolated Storms.
Creator: Davey, Matthew John, Fuelberg, Henry E., Cai, Ming, Chagnon, Jeffrey M., Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Abstract/Description: Lightning inhibits normal operating conditions at the Kennedy Space Center (KSC) and other locations, leading to inconvenience and detrimental economic impacts. Lightning cessation guidance must safely protect lives and infrastructure. This research focuses on "nonisolated" lightning cases which we defined as one cell whose flashes had ceased while embedded in weak composite reflectivity (Z ≥ 15 dBZ) with another cell still producing flashes. The dataset consisted of 50 warm season (May...
Show moreLightning inhibits normal operating conditions at the Kennedy Space Center (KSC) and other locations, leading to inconvenience and detrimental economic impacts. Lightning cessation guidance must safely protect lives and infrastructure. This research focuses on "nonisolated" lightning cases which we defined as one cell whose flashes had ceased while embedded in weak composite reflectivity (Z ≥ 15 dBZ) with another cell still producing flashes. The dataset consisted of 50 warm season (May-September) nonisolated storms near KSC during 2013. The research utilized the National Lightning Detection Network (NLDN), the second generation Lightning Detection and Ranging (LDAR-II), and dual polarimetric radar data. These data were merged and analyzed using the Warning Decision Support System-Integrated Information (WDSS-II) at 1 min intervals. The parameters, such as horizontal reflectivity (ZH), that decreased greatest during the cessation period were ZH > 40 dBZ at -5°C, ZH > 35 dBZ at -10°C, graupel presence at -10°C, and graupel presence at -15°C. We tested 60 cessation schemes utilizing a wait time approach. Our safest scheme required that the distance from our decaying storm's 30 dBZ core to the closest signature of graupel associated with the active storm (30G) be greater than 10 nm (~19 km) and the horizontal reflectivity be less than 40 dBZ at -5°C for 10 min. In the independent (dependent dataset), this scheme produced one (zero) false alarm. More research is needed to analyze nonisolated cessation, since no algorithm produced perfect skill when applied to the independent dataset.
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Date Issued: 2016
Identifier: FSU_2016SP_Davey_fsu_0071N_13070
Format: Thesis

Title: Coexistence of Leading Equatorial Coupled Modes for ENSO.
Creator: Bejarano-Avendano, Luis Fernando, Jin, Fei-Fei, Liu, Guosheng, Zou, Xiaolei, Cai, Ming, Clarke, Allan, O'Brien, James J., Program in Geophysical Fluid Dynamics, Florida State...
Show moreBejarano-Avendano, Luis Fernando, Jin, Fei-Fei, Liu, Guosheng, Zou, Xiaolei, Cai, Ming, Clarke, Allan, O'Brien, James J., Program in Geophysical Fluid Dynamics, Florida State University
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Abstract/Description: A comprehensive eigen-mode analysis of an intermediate coupled model linearized with respect to arrays of basic states is performed to study the regimes of leading ocean-atmosphere coupled modes of relevance to the El Niño Southern Oscillation phenomenon. Different kinds of leading modes are found to coexist and to become unstable under wide ranges of basic states and parameter conditions. In particular, two main kinds of modes have periods around 4 years and 2 years. They are thus referred...
Show moreA comprehensive eigen-mode analysis of an intermediate coupled model linearized with respect to arrays of basic states is performed to study the regimes of leading ocean-atmosphere coupled modes of relevance to the El Niño Southern Oscillation phenomenon. Different kinds of leading modes are found to coexist and to become unstable under wide ranges of basic states and parameter conditions. In particular, two main kinds of modes have periods around 4 years and 2 years. They are thus referred as to quasi-quadrennial (QQ), quasi-biennial (QB) modes, respectively. The positive coupled feedback destabilizes and quantizes the near-continuous spectrum for the low-frequency modes of the upper ocean dynamics giving rise to these leading modes with distinct periodicities. The QQ mode can be understood to a large extent by the mechanisms elucidated in the simple conceptual recharge oscillator which relays on slow oceanic dynamic adjustment of equatorial heat content, whereas anomalous advection of sea surface temperature by equatorial zonal current anomalies plays an important role in the QB mode. One of the findings of this study is that the QQ and QB mode may coalesce under realistic conditions through a codimension-2 degeneracy in the parameter space. The coexistence or multiplicity of ENSO-related coupled modes under present climate conditions may provide a plausible explanation for the observed dominating QQ and QB variability of rich ENSO behaviors.
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Date Issued: 2006
Identifier: FSU_migr_etd-1210
Format: Thesis

Title: Biases in Satellite-Derived Temperature Trends Due to Orbital Drift, Orbital Differences and Their Corrections.
Creator: Chen, Hong, Cai, Ming, Ray, Peter S., Wu, Zhaohua, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Abstract/Description: The measurements from Microwave Sounding Unit (MSU) and Advanced Microwave Sounding Unit-A (AMSU-A) have been extensively used for atmospheric temperature trend study during last several decades. The existences of inter-sensor biases and orbital drift, orbital differences among different satellites are two major challenges for climate study using long-term time series of satellite measurements. In this study, the impacts of orbital drift and orbital differences of satellites on AMSU-A derived...
Show moreThe measurements from Microwave Sounding Unit (MSU) and Advanced Microwave Sounding Unit-A (AMSU-A) have been extensively used for atmospheric temperature trend study during last several decades. The existences of inter-sensor biases and orbital drift, orbital differences among different satellites are two major challenges for climate study using long-term time series of satellite measurements. In this study, the impacts of orbital drift and orbital differences of satellites on AMSU-A derived temperature trends over Amazon rainforest are investigated. The AMSU-A near-nadir observations from NOAA-15, NOAA-18, NOAA-19, and MetOp-A during 1998 - 2014 are employed. The double difference method is firstly applied to obtain the estimates of inter-sensor biases for each paired AMSU-A instruments, in which NOAA-18 is used as a reference satellite. The inter-calibrated observations from the four satellites mentioned above are used to calculate monthly mean diurnal cycles of brightness temperature for each of the 15 AMSU-A channels. The diurnal correction method is then applied to all AMSU-A data using the estimated diurnal-cycle variations in order to obtain corrected data valid at the same local time. Finally, it is shown that the inter-sensor bias correction and diurnal correction have significant impacts on the AMSU-A derived long-term atmospheric temperature trends.
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Date Issued: 2015
Identifier: FSU_migr_etd-9303
Format: Thesis

Title: Diabatic Processes Modifying the Structure and Evolution of Idealized Baroclinic Life Cycle Simulations.
Creator: Glasser, Daisy, Chagnon, Jeffrey M., Cai, Ming, Liu, Guosheng, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Abstract/Description: Diabatic processes including latent heating and radiation are parameterized in numerical weather prediction (NWP) models and constitute a major source of error. Isolating the extent of diabatic modification in an extratropical cyclone in observational atmospheric data is difficult. This study analyzes four idealized Advanced Weather Research and Forecasting (WRF-ARW) model sensitivity experiments in which radiation or moisture are either included or withheld. The experiments consist of the...
Show moreDiabatic processes including latent heating and radiation are parameterized in numerical weather prediction (NWP) models and constitute a major source of error. Isolating the extent of diabatic modification in an extratropical cyclone in observational atmospheric data is difficult. This study analyzes four idealized Advanced Weather Research and Forecasting (WRF-ARW) model sensitivity experiments in which radiation or moisture are either included or withheld. The experiments consist of the following: no radiation and no moisture (NRNM), radiation and no moisture (RNM), moisture and no radiation (NRM), and radiation and moisture (RM). Simulations are of an idealized baroclinic wave in the midlatitudes. Because baroclinic waves are associated with synoptic scale weather events, these WRF-ARW simulations are the ideal platform to better understand the interactions of diabatic and dynamic processes. Inclusion of moisture and radiation has a significant impact on baroclinic wave structure and evolution. On the synoptic scale, the RM experiment demonstrates greatest amplification/depth, earliest growth, and was the only experiment with cyclonic breaking in the troposphere and high amplitude anticyclonic breaking in the lower stratosphere. On the sub-synoptic scale, vertical dipoles in isentropic potential vorticity (IPV) and cloud-scale anomalies developed in the middle to upper troposphere as the wave matured. While radiation alone yields no anomaly, and moisture alone yields a small anomaly, the inclusion of radiation and moisture together yields a significantly larger IPV anomaly. Anomalies may be due to constructive interference or nonlinear feedbacks between radiative cooling and latent heating. Results of this study have important implications for NWP, especially in the representation of physical processes via parameterization schemes. Knowledge gained about physical processes and their feedbacks on resolved flow might help to better understand error and bias in NWP models.
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Date Issued: 2016
Identifier: FSU_2016SU_Glasser_fsu_0071N_13462
Format: Thesis

Title: An Analysis of the Impacts of Western North Pacific Tropical Cyclones on Their Local and Large Scale Environment.
Creator: Schenkel, Benjamin A. (Benjamin Alan), Hart, Robert E., Dewar, William, Ellingson, Robert G., Cai, Ming, Clarke, Allan J., Department of Earth, Ocean and Atmospheric Sciences,...
Show moreSchenkel, Benjamin A. (Benjamin Alan), Hart, Robert E., Dewar, William, Ellingson, Robert G., Cai, Ming, Clarke, Allan J., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
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Abstract/Description: The following study examines the spatiotemporal response of the local scale and large scale environment to tropical cyclone (TC) passage. The research presented here is broken up into three chapters that can be separated into two parts. Given that the analysis of the environmental response to TC passage heavily relies upon the use of atmospheric reanalysis datasets, the first half of this dissertation (Chapter 2) will examine the fidelity of TC intensity, position, and intensity life cycle...
Show moreThe following study examines the spatiotemporal response of the local scale and large scale environment to tropical cyclone (TC) passage. The research presented here is broken up into three chapters that can be separated into two parts. Given that the analysis of the environmental response to TC passage heavily relies upon the use of atmospheric reanalysis datasets, the first half of this dissertation (Chapter 2) will examine the fidelity of TC intensity, position, and intensity life cycle within five reanalyses to determine what reanalyses can be used for when studying TCs. The results of this analysis show an underestimation of reanalysis TC intensity beyond what can be attributed to the coarse grid resolution of reanalyses. Moreover, the mean life cycle of normalized TC intensity within reanalyses exhibits an underestimation of pre-peak intensification rates as well as a delay in the timing of peak TC intensity relative to the Best Track. Significant discrepancies between reanalysis and Best-Track TC position are noted to exist particularly in regions that are observation deficient. Of the five reanalyses examined, the NCEP Climate Forecast System Reanalysis (CFSR) and JMA 25-yr Japanese Reanalysis (JRA-25) have the most robust representation of TCs particularly within the North Atlantic (NATL) and Western North Pacific (WPAC). The second half of this study examines the local scale (Chapter 3) and large scale (Chapter 4) impacts of WPAC TCs upon their environment using storm-relative composites. On local scales, TCs are found to cool sea surface temperatures (SSTs) for at least a month following TC passage. The feedbacks from the SST cold wake combined with an initial net flux divergence of energy from the column yields a significant cooling and drying of the atmosphere that is strongest in the lower troposphere. Restoration of the environment is eventually achieved through a return of SSTs to climatology and a net flux convergence of potential energy aloft. The large scale response of the environment is primarily associated with an anomalous drying of the lower and middle tropospheric atmospheric environment to the west and southwest of the TC. The drying appears to be caused by upper level convergence resulting from the interaction of the TC outflow with its environment. On the western side of the TC, both the upper level flow from the anticyclone of the Asian monsoon and the increasing inertial stability with latitude due to the meridional gradient of planetary vorticity limit the ventilation to the west of the TC yielding upper level convergence and subsidence. The area of anomalous drying to the southwest is associated with the convergent upper level flow from the right exit region of the anticyclonically curved equatorward outflow jet of the TC. Lastly, the meridional transport of total energy by TCs results in a substantial cross hemispheric export of dry static energy nearly 4000 km southwards as result of the upper level outflow jet of the TC. The meridional dry static energy transports by TCs appear to comprise a substantial portion of the total atmospheric dry static energy transports at the equator during late summer and early fall. In their totality, these results suggest that TCs may significantly impact their environment both on long temporal scales and large spatial scales with potentially significant aggregate climate impacts in the WPAC given the high frequency of TC occurrence.
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Date Issued: 2012
Identifier: FSU_migr_etd-5430
Format: Thesis

Title: Tropical Cyclone Inner-Core Dynamics: A Latent Heat Retrieval and Its Effects on Intensity and Structure Change; and the Impacts of Effective Diffusion on the Axisymmetrization Process.
Creator: Guimond, Stephen, Bourassa, Mark, Navon, Michael, Hart, Robert, Cai, Ming, Zou, Xiaolei, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Despite the fact that latent heating in cloud systems drives many atmospheric circulations, including tropical cyclones, little is known of its magnitude and structure due in large part to inadequate observations. In this work, a reasonably high-resolution (2 km), four-dimensional airborne Doppler radar retrieval of the latent heat of condensation is presented for rapidly intensifying Hurricane Guillermo (1997). Several advancements in the retrieval algorithm are shown including: (1)...
Show moreDespite the fact that latent heating in cloud systems drives many atmospheric circulations, including tropical cyclones, little is known of its magnitude and structure due in large part to inadequate observations. In this work, a reasonably high-resolution (2 km), four-dimensional airborne Doppler radar retrieval of the latent heat of condensation is presented for rapidly intensifying Hurricane Guillermo (1997). Several advancements in the retrieval algorithm are shown including: (1) analyzing the scheme within the dynamically consistent framework of a numerical model, (2) identifying algorithm sensitivities through the use of ancillary data sources and (3) developing a precipitation budget storage term parameterization. The determination of the saturation state is shown to be an important part of the algorithm for updrafts of ~ 5 m s-1 or less. The uncertainties in the magnitude of the retrieved heating are dominated by errors in the vertical velocity. Using a combination of error propagation and Monte Carlo uncertainty techniques, biases were found to be small, and randomly distributed errors in the heating magnitude were ~16 % for updrafts greater than 5 m s-1 and ~156 % for updrafts of 1 m s- 1. The impact of the retrievals is assessed by inserting the heating into realistic numerical simulations at 2 km resolution and comparing the generated wind structure to the Doppler radar observations of Guillermo. Results show that using the latent heat retrievals outperforms a simulation that relies on a state-of-the-art microphysics scheme (Reisner and Jeffery 2009), in terms of wind speed root-mean-square errors, explained variance and eye/eyewall structure. The incorrect transport of water vapor (a function of the sub-grid model and the numerical approximations to advection) and the restrictions on the magnitude of heat release that ensure the present model's stability are suggested as sources of error in the simulation without the retrievals. Motivated by the latent heat retrievals, the dynamics of vortex axisymmetrization from the perspective of thermal anomalies is investigated using an idealized, non-linear atmospheric model (HIGRAD). Attempts at reproducing the results of previous work (Nolan and Grasso 2003; NG03) revealed a discrepancy with the impacts of purely asymmetric forcing. While NG03 found that purely asymmetric heating led to a negligible, largely negative impact on the vortex intensification, in the present study the impacts of asymmetries are found to have an important, largely positive role. Absolute angular momentum budgets revealed that the essential difference between the present work and that of NG03 was the existence of a significant, axisymmetric secondary circulation in the basic-state vortex used in the HIGRAD simulations. This secondary circulation was larger than that present in NG03's simulations. The spin-up of the vortex caused by the asymmetric thermal anomalies was dominated by the axisymmetric fluxes of angular momentum at all times, indicating fundamentally different evolution of asymmetries in the presence of radial flow. Radial momentum budgets were performed to elucidate the mechanisms responsible for the formation of the physically significant secondary circulation. Results show that explicit (sub-grid) diffusion in the model was producing a gradient wind imbalance, which drives a radial inflow and associated secondary circulation in an attempt to re-gain balance. In addition, the production of vorticity anomalies from the asymmetric heating was found to be sensitive to the eddy diffusivity, with large differences between HIGRAD and the widely used WRF model for the exact same value of this uncertain parameter.
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Date Issued: 2010
Identifier: FSU_migr_etd-3920
Format: Thesis

Title: Understanding Climate Feedback Contributions to the Surface Temperature Response.
Creator: Sejas, Sergio A., Cai, Ming, Wang, Xiaoming, Ellingson, R. G., Sura, Philip, Wu, Zhaohua, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and...
Show moreSejas, Sergio A., Cai, Ming, Wang, Xiaoming, Ellingson, R. G., Sura, Philip, Wu, Zhaohua, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: Climate feedback mechanisms are known to substantially affect the surface temperature response to an external forcing. This study aims to advance our physical and quantitative understanding of forcing and feedback contributions to the surface temperature response to an external forcing. The dissertation begins with a comprehensive overview of the climate feedback concept and the frameworks used to interpret the effects of forcing and feedbacks on surface temperature. The climate feedback...
Show moreClimate feedback mechanisms are known to substantially affect the surface temperature response to an external forcing. This study aims to advance our physical and quantitative understanding of forcing and feedback contributions to the surface temperature response to an external forcing. The dissertation begins with a comprehensive overview of the climate feedback concept and the frameworks used to interpret the effects of forcing and feedbacks on surface temperature. The climate feedback-response analysis method (CFRAM), a relatively new climate feedback framework whose advantages over the traditional climate feedback analysis framework are delineated, is then used to study the seasonal surface temperature response to a doubling of CO2 in a global warming simulation of the NCAR CCSM4. This allows us for the first time to explain the major features of the seasonal warming structure quantitatively. Polar regions, for example, experience the largest warming and the greatest seasonal variation, with maximum warming in fall/winter and minimum warming in summer. In summer, the large cancelations between the shortwave and longwave cloud feedbacks and between the surface albedo feedback warming and the cooling from the ocean heat storage/dynamics feedback lead to a warming minimum. In polar winter, surface albedo and shortwave cloud feedbacks are nearly absent due to a lack of insolation. However, the ocean heat storage feedback relays the polar warming due to the surface albedo feedback from summer to winter, and the longwave cloud feedback warms the polar surface. Therefore, the seasonal variations in the cloud feedback, surface albedo feedback, and ocean heat storage/dynamics feedback, directly caused by the strong annual cycle of insolation, contribute primarily to the large seasonal variation of polar warming. Furthermore, the CO2 forcing, and water vapor and atmospheric dynamics feedbacks add to the maximum polar warming in fall/winter. The CFRAM allows for a process-based decomposition of the temperature response into individual contributions by the forcing and non-temperature feedbacks, which implicitly include the thermal-radiative coupling (i.e., temperature feedback) effects between the surface and atmosphere. To uncover this hidden effect in the CFRAM, this study develops and introduces a method known as the surface feedback-response analysis method (SFRAM) to isolate the temperature feedback effects on surface temperature, allowing for a physical and quantitative understanding of the temperature feedback effects. The temperature feedback effect is found to be the most important contributor to the surface temperature change, accounting for nearly 76% of the global mean surface warming. From the CFRAM perspective, the temperature feedback effect is just the indirect effects of the forcing and non-temperature feedbacks. The SFRAM analysis, in conjunction with the CFRAM results, indicates that in general the indirect effects of the forcing and non-temperature feedbacks on the surface temperature change are larger than the direct effects; thus demonstrating the influence and strength of the temperature feedback effect in the CFRAM results. By isolating the temperature feedback loop, an understanding of why the indirect effects are generally larger than direct effects is achieved. The SFRAM also serves as a bridge to the traditional TOA feedback analysis. A comparison of the SFRAM results with those of the traditional TOA feedback analysis indicates the largest disparity in interpretation is given for the lapse-rate feedback, which is shown to just stem from a misinterpretation of the temperature feedback effects on surface temperature. A better and more intuitive explanation is achieved through the surface perspective of the SFRAM than the TOA perspective of the traditional feedback analysis. A reconciliation of the surface and TOA perspectives is achieved once the temperature feedback effects are included with the effects of the forcing and non-temperature feedbacks, as in the CFRAM analysis.
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Date Issued: 2014
Identifier: FSU_migr_etd-9244
Format: Thesis

Title: TAG: A Timing Adaptive Grouping Protocol for Smart Grid Communications.
Creator: Cai, Ziyuan, Yu, Ming, Li, Hui, Meyer-Baese, Anke, Steurer, Michael Morten, Andrei, Petru, Florida State University, College of Engineering, Department of Electrical and...
Show moreCai, Ziyuan, Yu, Ming, Li, Hui, Meyer-Baese, Anke, Steurer, Michael Morten, Andrei, Petru, Florida State University, College of Engineering, Department of Electrical and Computer Engineering
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Abstract/Description: The prospect of SG is green, power efficient, and economical to its customers. Many emerging innovations have reached a consensus that the traditional power grids need to be combined with modern data networks, in order to establish a new platform that supports distributed renewable energy devices, electrical measuring sensors, and intelligent energy management and control systems, etc. For example, an energy management system is proposed to connect data aggregators with renewable energy...
Show moreThe prospect of SG is green, power efficient, and economical to its customers. Many emerging innovations have reached a consensus that the traditional power grids need to be combined with modern data networks, in order to establish a new platform that supports distributed renewable energy devices, electrical measuring sensors, and intelligent energy management and control systems, etc. For example, an energy management system is proposed to connect data aggregators with renewable energy devices in the network area. A wireless sensor network is used to provide the communications between SG data centers and consumers, and manage residential energy with an optimization-based scheme. In SG, the stability of an energy management scheme becomes heavily dependent on accurate real-time communications among intelligent energy management agencies in residential homes, micro-grids, and main grids. Within a large-scale distributed (or centralized) smart grid (SG), the communication network is designed to connect multiple power management systems and collect data from hundreds or thousands of power sensors over a wide geographical area. One dominant feature of innovated SG communication network is that one power device is coupled with a single Ethernet or non-Ethernet communication agent to exchange control state or management information with others. Generally speaking, an intelligent agent helps its corresponding power device negotiating with other peers to dynamically form an ad-hoc group through the data network infrastructures. Then, many meaningful power management algorithms are operated in the logical group. The grouping topology recognized by a specific agent needs to reform when the participating group members can not satisfy the demand from operating power management algorithms. Upon our ad-hoc ideas, the main problem arises: in a changed group, the networking size, traffic load, queueing effect and security requirement are varied, so an agent experiences different communication cost over group reforming. We define such inevitable difference as communication inconsistency of SG ad-hoc grouping. If the timeout parameters of communication control are set statically in grouping procedures, the inconsistency definitely triggers the timeout, crashes the group and aborts the running cycle of power management algorithms very often. Thus in this work, an adaptive timing solution is developed for connecting distributed intelligent agents in ad-hoc manner to greatly enhance the flexibility and performance of grouping algorithms in SG communication network. A timing adaptive grouping (TAG) protocol is proposed to make every distributed agent capable of adjusting its operational timing configurations (OTCs) in pace with the changing of ad-hoc groups, so that prevents the harmfulness of communication inconsistency to the stability of grouping procedures. More specifically, we first develop a set of queueing model to describe the network traffic of various power management applications among distributed agents in connection with different scale of ad-hoc grouping topologies. Second, the security cost of SG communications is modeled, estimated and validated with various grouping agents' characteristics. Third, based on the network grouping model including both queueing and security cost, we analyze the ad-hoc delay performance and illustrate that the model can be used to predict the average operating delays of networking agents. Fourth, based on the delay parameters derived from previous modeling, the TAG protocol is developed with our Smart Timing Adaptive (STA) algorithm to facilitate each distributed agent dynamically judging variant ad-hoc grouping conditions. Finally, we have implemented a validation testbed with the capabilities of integrated real-time communication and power exchange to demonstrate the ad-hoc grouping operation of SG power management applications. Due to the ripple effect of inconsistent communication delays among the ad-hoc SG groups with dynamic changing topology, the network performance becomes a major concern to support power management applications. To deal with that, in a large NSF project of Future Renewable Electric Energy Delivery and Management (FREEDM), we implement a SG prototype, called the FREEDM Hardware-in-the-loop (HIL) testbed. The so-called Distributed Grid Intelligences (DGIs) act as the distributed intelligent agents in the SG prototype which can group specific peers to exchange power load among power demands and supplies. There are also many other existing works contributing a variety of platforms to integrate power and communication systems. But, in our FREEDM project, we build a SG testbed, which is a new platform that combines an HIL power system and a real-time communication system. The power system devices are managed by the DGIs that are connected into the communication networks. The DGIs act as intelligent energy management agencies for the power system, while information nodes for the communication networks. The DGI instances are coded on embedded computer boards with processing and communication capabilities. A DGI represents its power device to communicate with other DGI instances or DGI nodes. DGIs being connected in LAN and WAN may be grouped together to meet the power demand and supply requirement. A DGI group may cover a LAN, or a LAN and WAN simultaneously, depending on the location of DGI nodes. When electrical faults isolate a section from the power system, in communicational sense, the section is still connected to and can exchange the information of grid states with other sections in the power system. The real-time and HIL features of the testbed are reflected in the design of both power and communication systems. To implement the concept of HIL in the power system, some power devices are implemented by real-world electrical hardware, while other devices are simulated in the Real Time Digital Simulator (RTDS) platform. To implement the concept of HIL in the communication system for the DGIs, the DGI LANs are implemented by Ethernet switches, while the DGI WAN is simulated in real-time by OPNET, a network simulator program. Within OPNET, there is a system-in-the-loop (SITL) interface that interprets DGI traffic between real packet formats and simulated formats.
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Date Issued: 2015
Identifier: FSU_migr_etd-9562
Format: Thesis

Title: Radial-Vertical Profiles of Tropical Cyclone Derived from Dropsondes.
Creator: Ren, Wei, Cai, Ming, Misra, Vasubandhu, Sura, Philip, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Abstract/Description: The scopes of this thesis research are two folds: the first one is to the construct the intensity-based composite radial-vertical profiles of tropical cyclones (TC) using GPS-based dropsonde observations and the second one is to identify the major deficiencies of Mathur vortices against the dropsonde composites of TCs. The intensity-based dropsonde composites of TCs advances our understanding of the dynamic and thermal structure of TCs of different intensity along the radial direction in and...
Show moreThe scopes of this thesis research are two folds: the first one is to the construct the intensity-based composite radial-vertical profiles of tropical cyclones (TC) using GPS-based dropsonde observations and the second one is to identify the major deficiencies of Mathur vortices against the dropsonde composites of TCs. The intensity-based dropsonde composites of TCs advances our understanding of the dynamic and thermal structure of TCs of different intensity along the radial direction in and above the boundary layer where lies the devastating high wind that causes property damages and storm surges. The identification of the major deficiencies of Mathur vortices in representing the radial-vertical profiles of TC of different intensity helps to improve numerical predictions of TCs since most operational TC forecast models need to utilize bogus vortices, such as Mathur vortices, to initialize TC forecasts and simulations. We first screen all available GPS dropsonde data within and round 35 named TCs over the tropical Atlantic basin from 1996 to 2010 and pair them with TC parameters derived from the best-track data provided by the National Hurricane Center (NHC) and select 1149 dropsondes that have continuous coverage in the lower troposphere. The composite radial-vertical profiles of tangential wind speed, temperature, mixing ratio and humidity are based for each TC category ranging from "Tropical Storm" (TS) to "Hurricane Category 1" (H1) through "Hurricane Category 5" (H5). The key findings of the dropsonde composites are: (i) all TCs have the maximum tangential wind within 1 km above the ground and a distance of 1-2 times of the radius of maximum wind (RMW) at the surface; (ii) all TCs have a cold ring surrounding the warm core near the boundary layer at a distance of 1-3 times of the RMW and the cold ring structure gradually diminishes at a higher elevation where the warm core structure prevails along the radial direction; (iii) the existence of such shallow cold ring outside the RMW explains why the maximum tangential wind is within 1 km above the ground and is outside the RMW, as required by the hydrostatic and gradient wind balance relations; (iv) one of the main differences among TCs of different intensity, besides the speed of the maximum tangential wind, is the vertical extent of near-saturated moisture air layer inside the core. A weaker TC tends to have a deep layer of the near-saturated moisture air layer whereas a stronger TC has a shallow one; (v) another main difference in the thermal structure among TCs of different intensity is the intensity and vertical extent of the warm core extending from the upper layer to the lower layer. In general, a stronger TC has a stronger warm core extending downward further into lower layer and vice versa. The features (iv) and (v) are consistent with the fact that a stronger TC tends to have stronger descending motion inside the core. The main deficiencies of Mathur vortices in representing the radial-vertical profiles of TC of different intensity are (i) Mathur vortices of all categories have the maximum wind at the surface; (ii) none of Mathur vortices have a cold ring outside the warm core near the boundary layer; (iii) Mathur vortices tend to overestimate warm core structure in reference to the horizontal mean temperature profile; (iv) Mathur vortices tend to overestimate the vertical depth of the near-saturated air layer near the boundary layer.
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Date Issued: 2014
Identifier: FSU_migr_etd-9235
Format: Thesis

Title: Spatio-Temporal Evolutions of Non-Orthogonal Equatorial Wave Modes Derived from Observations.
Creator: Barton, Cory, Cai, Ming, Niu, Xufeng, Clarke, Allan J., Speer, Kevin G. (Kevin George), Sura, Philip, Florida State University, College of Arts and Sciences, Program in...
Show moreBarton, Cory, Cai, Ming, Niu, Xufeng, Clarke, Allan J., Speer, Kevin G. (Kevin George), Sura, Philip, Florida State University, College of Arts and Sciences, Program in Geophysical Fluid Dynamics
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Abstract/Description: Equatorial waves have been studied extensively due to their importance to the tropical climate and weather systems. Historically, their activity is diagnosed mainly in the wavenumber-frequency domain. Recently, many studies have projected observational data onto parabolic cylinder functions (PCFs), which represent the meridional structure of individual wave modes, to attain time-dependent spatial wave structures. The non-orthogonality of wave modes has yet posed a problem when attempting to...
Show moreEquatorial waves have been studied extensively due to their importance to the tropical climate and weather systems. Historically, their activity is diagnosed mainly in the wavenumber-frequency domain. Recently, many studies have projected observational data onto parabolic cylinder functions (PCFs), which represent the meridional structure of individual wave modes, to attain time-dependent spatial wave structures. The non-orthogonality of wave modes has yet posed a problem when attempting to separate data into wave fields where the waves project onto the same structure functions. We propose the development and application of a new methodology for equatorial wave expansion of instantaneous flows using the full equatorial wave spectrum. By creating a mapping from the meridional structure function amplitudes to the equatorial wave class amplitudes, we are able to diagnose instantaneous wave fields and determine their evolution. Because all meridional modes are shared by some subset of the wave classes, we require constraints on the wave class amplitudes to yield a closed system with a unique solution for all waves' spatial structures, including IG waves. A synthetic field is analyzed using this method to determine its accuracy for data of a single vertical mode. The wave class spectra diagnosed using this method successfully match the correct dispersion curves even if the incorrect depth is chosen for the spatial decomposition. In the case of more than one depth scale, waves with varying equivalent depth may be similarly identified using the dispersion curves. The primary vertical mode is the 200 m equivalent depth mode, which is that of the peak projection response. A distinct spectral power peak along the Kelvin wave dispersion curve for this value validates our choice of equivalent depth, although the possibility of depth varying with time and height is explored. The wave class spectra diagnosed assuming this depth scale mostly match their expected dispersion curves, showing that this method successfully partitions the wave spectra by calculating wave amplitudes in physical space. This is particularly striking because the time evolution, and therefore the frequency characteristics, is determined simply by a timeseries of independently-diagnosed instantaneous horizontal fields. We use the wave fields diagnosed by this method to study wave evolution in the context of the stratospheric QBO of zonal wind, confirming the continuous evolution of the selection mechanism for equatorial waves in the middle atmosphere. The amplitude cycle synchronized with the background zonal wind as predicted by QBO theory is present in the wave class fields even though the dynamics are not forced by the method itself. We have additionally identified a time-evolution of the zonal wavenumber spectrum responsible for the amplitude variability in physical space. Similar to the temporal characteristics, the vertical structures are also the result of a simple height cross-section through multiple independently-diagnosed levels.
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Date Issued: 2016
Identifier: FSU_2016SP_Barton_fsu_0071E_13099
Format: Thesis

Title: How Do Cloud Properties Contribute to Climate Change?.
Creator: Hussein, Ahmed A., Cai, Ming, Liu, Guosheng, Wu, Zhaohua, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Abstract/Description: Clouds play an important role in the earth's energy budget, and changes in their properties can remarkably impact the amount of warming in response to greenhouse gas increases. In this study, we applied the Coupled Feedback Response Analysis Method (CFRAM) to estimate the contributions of cloud property changes to the magnitude of the annual mean-surface temperature response in a transient simulation where CO2 increases at rate 1% yr-1 , using the NCAR Community Climate System Model, version...
Show moreClouds play an important role in the earth's energy budget, and changes in their properties can remarkably impact the amount of warming in response to greenhouse gas increases. In this study, we applied the Coupled Feedback Response Analysis Method (CFRAM) to estimate the contributions of cloud property changes to the magnitude of the annual mean-surface temperature response in a transient simulation where CO2 increases at rate 1% yr-1 , using the NCAR Community Climate System Model, version 4 (CCSM4). To examine closely the contributions of changes in cloud properties to the annual mean-surface temperature, the full-cloud level is divided into three levels in terms of the cloud-top pressure (CTP). This study found that the annual and global mean-surface temperature response is a warming of (+0.175 oK) due to the net cloud feedback that comes mainly from the positive SW cloud feedback. The medium (400 < CTP < 700 mb) clouds changes are the dominant contributors (+0.175 oK) to the surface warming due to their magnificent positive SW cloud feedback (+0.33 oK). High (CTP < 400 mb) clouds changes cause a weak negative contribution (-0.0218 oK) to the surface warming because of the close cancellation between their large negative SW and large positive LW high-cloud feedbacks. Low (CTP > 700 mb) cloud changes are the least contributors to SW and LW cloud feedbacks (positive SW and negative LW); however, they still contribute positively (+0.0217 oK) to the net cloud feedback with an absolute magnitude that is almost equal to the contribution of the high-cloud changes. Furthermore, this study found that the annual mean-surface temperature increases in the Polar Regions (60o-90o in both hemispheres) are due to the positive LW cloud feedback from the changes in the three cloud levels, mostly due to positive LW medium-cloud feedback. However, the annual mean surface warming for the region covered between (60o S-60o N) is due to the positive SW low- and medium-cloud feedbacks.
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Date Issued: 2014
Identifier: FSU_migr_etd-9190
Format: Thesis

Title: A Hybrid Lagrangian/Eulerian View of the Global Atmospheric Mass Circulation: Seasonal Cycle.
Creator: Shin, Chul-Su, Cai, Ming, Dewar, William K., Ellingson, Robert G., Liu, Guosheng, Sura, Philip, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: In this study, we have diagnosed diabatic heating, meridional adiabatic mass and angular momentum transport, and downward transfer of westerly angular momentum by the pressure torque in isentropic coordinates using daily NCEP-NCAR reanalysis II dataset for 32 years from January 1, 1979 to December 31, 2010. Mass and its associated angular momentum fluxes of instantaneous flow depict a snapshot of mass and angular momentum circulations at that time in the Lagrangian perspective, although they...
Show moreIn this study, we have diagnosed diabatic heating, meridional adiabatic mass and angular momentum transport, and downward transfer of westerly angular momentum by the pressure torque in isentropic coordinates using daily NCEP-NCAR reanalysis II dataset for 32 years from January 1, 1979 to December 31, 2010. Mass and its associated angular momentum fluxes of instantaneous flow depict a snapshot of mass and angular momentum circulations at that time in the Lagrangian perspective, although they are calculated on the Eulerian latitude-longitude coordinates. The hybrid Lagrangian/Eulerain view of instantaneous flow enables us to delineate how the diabatic heating and the pressure torque drive the local change of air mass and its angular momentum via the meridional mass circulation. One broad hemispheric cell of the meridional mass circulation exists in each hemisphere, which links the tropics to the extratropics and the troposphere to the stratosphere. Warm air mass heated by the diabatic heating in the tropics flows poleward to the extratropics where it sinks by the diabatic cooling. Cold air mass moves back to the tropics by adiabatic equatorward returning flow and diabatic heating near the ground. The air in the poleward branch moves in a down-gradient direction of earth angular momentum whereas the equatorward cold air branch is in an up-gradient direction of earth angular momentum. Embedded in the hemispheric mass circulation are three distinct but connected cells: the tropical Hadley cell, the stratospheric cell (part of Brewer-Dobson circulation in the winter hemisphere), and the extratropical Hadley cell. In the warm air branch of the tropical Hadley cell, poleward angular momentum transport associated with poleward mass fluxes is responsible for intensification of the subtropical jet. The excessive westerly angular momentum of the subtropical jet slows down significantly the poleward advancement of warm air mass as air mass mostly moves towards the east instead of the pole. As the air mass circulates around the subtropical latitudes, air experiences radiative cooling, resulting in downward cross-isentropic mass and angular momentum fluxes. Part of downward mass transport in the subtropics then joins the poleward warm air branch of the extratropical Hadley cell, connecting two tropospheric circulation cells. The remaining part continues to downward crossing isentropic surfaces and merges with the returning cold air branch of the extratropical Hadley cell. The merged air mass together moves equatorward diabatically (and with small portion adiabatically) as the returning flow of the tropical Hadley cell. In the cold air branch of the tropical Hadley cell, the surface frictional torque and mountain torque play a major role in adding the westerly angular momentum to the equatorward returning flow. In the extratropics, the meridional mass circulation is carried out mainly by the baroclinically amplifying (or westward tilted) waves. The westward tilted waves in the extratropical stratosphere account for a net poleward transport of air mass and its angular momentum aloft and a net equatorward transport of air mass and its angular momentum below, as well as a net downward transfer of westerly angular momentum by the pressure torque. As the warm air branch of the tropical Hadley cell, poleward transport of angular momentum aloft gives rise to the intensification of the stratospheric polar jet that in turn slows down the poleward mass transport into the polar region. More intense westward tilted wave activities near the polar jet act to remove the excessive westerly angular momentum aloft by the pressure torque. It helps to pave the way for further poleward mass transport in the warm air branch of the stratospheric circulation to overcome the increment of westerly angular momentum during the poleward air mass advancement. The westward tilted waves in the extratropical upper troposphere do the same thing, and are responsible for the extratropical Hadley cell. Strong downward mass transport from the stratosphere to the troposphere in the extratropics results in 1) much weaker equatorward returning flow in the lower stratosphere than poleward warm air flow in the upper stratosphere and 2) stronger equatorward returning flow of the extratropical Hadley cell than poleward warm air branch of the extratropical Hadley cell. In the cold air branch of the extratropical Hadley cell, the gain of angular momentum transferred from the layers above by the pressure torque helps to pave the way for further equatorward mass transport to overcome the lack of westerly angular momentum on the way to the lower latitudes. The equatorward returning flow of the extratropical Hadley cell is connected to that of the tropical Hadley cell in the subtropics by the diabatic heating near the ground.
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Date Issued: 2012
Identifier: FSU_migr_etd-5180
Format: Thesis

Title: Diagnosing Errors in the Structure of Rossby Waves on the Extratropical Tropopause in Medium-Range Operational Weather Forecasts.
Creator: Wilkerson, Justin, Chagnon, Jeffrey M., Hart, Robert E. (Robert Edward), Cai, Ming, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and...
Show moreWilkerson, Justin, Chagnon, Jeffrey M., Hart, Robert E. (Robert Edward), Cai, Ming, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: Rossby waves propagating along the extratropical tropopause have a dominant impact on weather at the surface in midlatitudes via baroclinic instability. While forecasts of waves by numerical weather prediction systems are limited by intrinsic unpredictability due to initial condition sensitivity, the statistical properties of these features should not contain biases if the models are optimally designed. In this study, statistical properties of upper level waves in forecasts are evaluated for...
Show moreRossby waves propagating along the extratropical tropopause have a dominant impact on weather at the surface in midlatitudes via baroclinic instability. While forecasts of waves by numerical weather prediction systems are limited by intrinsic unpredictability due to initial condition sensitivity, the statistical properties of these features should not contain biases if the models are optimally designed. In this study, statistical properties of upper level waves in forecasts are evaluated for the seasons 2008-2012. Wavelet transforms are used to analyze Rossby wave amplitude as a function of both wavelength and longitude. The wavelet transforms are applied to both analysis and forecast potential vorticity. The difference between the two reveals model error. This process is done for three operational centers: ECMWF, UKMET, and NCEP, over 5 winter seasons. A comparison is made of 5 dependencies: forecast center, interseasonal variation, longitude, lead time, and wavelength. Additionally, a wave breaking diagnostic is developed as a supplemental tool for determining wave structure errors in operational models. Breaking frequency determines how many points of longitude in the wave pattern on average per day were breaking. The analysis reveals: 1) On average, Rossby wave amplitude is under forecast in all 5 dependencies, statistically significant at the 95% confidence level, 2) The largest errors are found in regions of climatologically higher wave activity, 3) errors in ECMWF are smaller and accumulate more steadily than UKMET and NCEP, which demonstrate large error very early in forecasts, 4) The errors represent biases in the model, not a regression to the mean, and 5) There are large errors in the wave breaking frequency for all forecast centers. The results imply an inherent issue in operational models with forecasting wave amplitude. How the errors vary across the 5 dependencies and how the work may be expanded for further study are discussed.
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Date Issued: 2015
Identifier: FSU_migr_etd-9487
Format: Thesis

Title: Effects of ENSO, NAO (PVO), and PDO on Monthly Extreme Temperatures and Precipitation.
Creator: Brolley, Justin Michael, O'Brien, James J., Berg, Bernd, Ahlquist, Jon, Cai, Ming, Ruscher, Paul, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The El Nino-Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), the Pacific Decadal Oscillation (PDO), and the Polar Vortex Oscillation (PVO) produce conditions favorable for monthly extreme temperatures and precipitation. These climate modes produce upper-level teleconnection patterns that favor regional droughts, floods, heat waves, and cold spells, and these extremes impact agriculture, energy, forestry, and transportation. The above sectors prefer the knowledge of the worst...
Show moreThe El Nino-Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), the Pacific Decadal Oscillation (PDO), and the Polar Vortex Oscillation (PVO) produce conditions favorable for monthly extreme temperatures and precipitation. These climate modes produce upper-level teleconnection patterns that favor regional droughts, floods, heat waves, and cold spells, and these extremes impact agriculture, energy, forestry, and transportation. The above sectors prefer the knowledge of the worst (and sometimes the best) case scenarios. This study examines the extreme scenarios for each phase and the combination of phases that produce the greatest monthly extremes. Data from Canada, Mexico, and the United States are gathered from the Historical Climatology Network (HCN). Monthly data are simulated by the utilization of a Monte Carlo model. This Monte Carlo method simulates monthly data by the stochastic selection of daily data with identical ENSO, PDO, and PVO (NAO) characteristics. In order to test the quality of the Monte Carlo simulation, the simulations are compared with the observations using only PDO and PVO. It has been found that temperatures and precipitation in the simulation are similar to the model. Statistics tests have favored similarities between simulations and observations in most cases. Daily data are selected in blocks of four to eight days in order to conserve temporal correlation. Because the polar vortex occurs only during the cold season, the PVO is used during January, and the NAO is used during other months. The simulated data are arranged, and the tenth and ninetieth percentiles are analyzed. The magnitudes of temperature and precipitation anomalies are the greatest in the western Canada and the southeastern United States during winter, and these anomalies are located near the Pacific North American (PNA) extrema. Western Canada has its coldest (warmest) Januaries when the PDO and PVO are low (high). The southeastern United States has its coldest Januaries with high PDO and low PVO and warmest Januaries with low PDO and high PVO. Although extremes occur during El Nino or La Nina, many stations have the highest or lowest temperatures during neutral ENSO. In California and the Gulf Coast, the driest (wettest) Januaries tend to occur during low (high) PDO, and the reverse occurs in Tennessee, Kentucky, Ohio, and Indiana. Summertime anomalies, on the other hand, are weak because temperature variance is low. Phase combinations that form the wettest (driest) Julies form spatially incoherent patterns. The magnitudes of the temperature and precipitation anomalies and the corresponding phase combinations vary regionally and seasonally. Composite maps of geopotential heights across North America are plot for low, median, and high temperatures at six selected sites and for low, median, and high precipitation at the same sites. The greatest fluctuations occur near the six sites and over some of the loci of the PNA pattern. Geopotential heights tend to decrease (increase) over the target stations during the cold (warm) cases, and the results for precipitation are variable.
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Date Issued: 2007
Identifier: FSU_migr_etd-2999
Format: Thesis

Title: Diagnosis of the Marine Stratocumulus Cloud Variablity in the Annual Cycle over the Eastern Tropical Pacific and Atlantic Oceans.
Creator: Shin, Jinho, Cai, Ming, Song, Kaisheng, Ruscher, Paul H., Nicholson, Sharon E., Liu, Guosheng, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: This research identifies dominant modes of annual variability of the marine stratocumulus (MSc) cloud in the eastern tropical Pacific and Atlantic obtained from the International Satellite Cloud Climatology Project (ISCCP) dataset from January 1984 throughout December 2004, and describes the evolution of the macroscopic and radiative properties related with these physical modes. These modes are extracted from observational data using the cyclostationary empirical orthogonal function (CSEOF)...
Show moreThis research identifies dominant modes of annual variability of the marine stratocumulus (MSc) cloud in the eastern tropical Pacific and Atlantic obtained from the International Satellite Cloud Climatology Project (ISCCP) dataset from January 1984 throughout December 2004, and describes the evolution of the macroscopic and radiative properties related with these physical modes. These modes are extracted from observational data using the cyclostationary empirical orthogonal function (CSEOF) technique, which retrieves the evolution of each mode together with its amplitude time series. This, in combination with comprehensive analysis of the many key physical variables (e.g., SST, surface wind, stability, horizontal temperatures advection) associated with the mode enhances us to depict the understanding the dynamic and thermodynamic processes for the formation and dissipation of these low level clouds. Finally, the development of diagnostic and prognostic models for the low cloud amount (CA) is an additional feature of this research, and helps to improve low cloud parameterization by SST in global climate models in the long term. The main scientific objective of this study is to investigate the timing, location, strength, and moving direction of the SST and the cloud throughout the year and gain some insights for parameterization of cloud properties using the evolution of SST and the interaction relationship between SST and cloud over these eastern tropical oceans. The most pronounced features of the evolution of the SST and cloud property anomalies are equatorward expansion along the coastal regions of the eastern tropical Pacific and Atlantic, and westward propagation along the equator. A positive (negative) CA and the accompanying cold (warm) SST anomalies stretch equatorward along the coastal regions during Summer and early Fall (Winter and early Spring) seasons. With the negative correlation between SST and CA anomalies, CA leads SST about one month at latitude 15°-5°S of the coastal regions of the eastern tropical Pacific. In the view of large-scale environment at the surface, the "trough-like" discontinuity of distorted SLP anomaly due to the land-sea distribution causes the persistently strong southerly surface wind anomaly blowing outward from the contour of SLP anomaly. This southerly surface wind anomaly pumps up the coastal upwelling that drags the cold water from the lower depths of the ocean. This describes schematically the surface wind-SST process occurring over the coastal region of the eastern tropical Pacific (equatorward of 20°S). Considering the cloud effect in this region, the southerly wind off the coasts of the coastal region pumps up cold water from the ocean subsurface. The onset of cooling in the region is conducive to more clouds and less surface insolation, which further promotes southerly wind anomalies. This southerly induces locally stronger, more extensive dynamical and evaporative cooling. This cooling expands to northwest via southerly wind. This is a schematic description of the wind-SST-MSc relationship. The lag/lead pattern between variables supports this relationship. The meridional wind component (V) leads SST about one month in the region. The increasing (decreasing) shielding effect of shortwave radiation at the cloud top drives the cold (warm) SST anomaly. CA also leads SST about one month. After equatorward expansions of the SST and CA anomalies reach maximum, westward propagation of the positive (negative) CA and the cold (warm) SST anomalies starts to occur simultaneously along the equator. These propagations advance further east to the dateline in November (May) along the equator, where the SST gradient is maximum. Easterly surface wind plays an important role of westward propagation of cold SST anomaly and zonal gradient SST anomaly. Easterly surface wind starts to blow where zonal gradient of SST anomaly is negative along the western edge of the nearcoastal zone in the eastern tropical Pacific. At this point, it leads the negative zonal gradient of SST anomaly. As the easterly wind strengthens due to redistribution of SLP pattern by the zonal gradient of SST anomaly, it generates the equatorial upwelling, enhancing cold phase of SST anomaly. The cooling in the region generates more cloudiness and more reflection, which further enhances the gradient of SST anomaly and in turns, the resulting easterly wind anomaly becomes strong. This easterly causes locally stronger, more extensive dynamical and evaporative cooling as well. The schematic wind-SST-MSc relationship is described by the interesting lead/lag relationship between physical variables provides. The easterly wind in tropical equatorial Pacific leads the cold SST anomaly about one month due to equatorial upwelling from the ocean subsurface. However, there is no lag/lead relationship between SST (or stability) and CA, that is, their interaction happens simultaneously in this region. This lead/lag relationship is important in understanding any interactions between them (e.g., cloud-SST feedback, wind-SST feedback). Results of this analysis may lead to improvement of diagnostic model/parameterization for the MSc cloud properties in GCMs. Stability is defined as the difference of potential temperature between 700 hPa and the surface. It is reflected in the atmosphere and ocean field. Therefore, it can be better key physical variable to express the MSc CA variability than SST. Two major atmospheric factors to control stability over the eastern tropical Pacific and Atlantic: the vertical structure of the horizontal temperature advection at the surface and lower level, and subsidence at lower and upper levels. They play significant roles during the positive (negative) phase of CA anomaly. The horizontal temperature advection from warm air aloft (brought on by warm advection) coupled with cold air at the surface (caused by nighttime radiative cooling, cold advection, or a cold surface). Subsidence in the subtropics occurs over the MSc clouds and generates the temperature inversion at low troposphere because dry air aloft is compressed and warmed. Mixing between upper and lower level affects instability. Mixing increases warming below and cooling higher up in the atmosphere. This inversion plays to prevent mixing with drier air above the top of the marine atmospheric boundary layer (MABL) and maintain the moisture in the MABL. In this study, we also evaluate a new parameterization that generates the mean LWP, based on the Gaussian distribution of cloud depths, and assumption that internal homogeneity is due to variation of cloud depths. Based on our comparison of the parameterized results to observations, we discuss the possibility of applying the predicted distribution of mean LWP to a GCM.
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Date Issued: 2007
Identifier: FSU_migr_etd-1752
Format: Thesis

Title: Development of the "Optimal Filters" for Mitigation of Striping Noise in Satellite Microwave Temperature and Humidity Sounding Data.
Creator: Ma, Yuan, Cai, Ming, Yuan, Xin, Liu, Guosheng, Ray, Peter S., Chagnon, Jeffrey M., Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and...
Show moreMa, Yuan, Cai, Ming, Yuan, Xin, Liu, Guosheng, Ray, Peter S., Chagnon, Jeffrey M., Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: Advanced Technology Microwave Sounder (ATMS) has been flying on the Suomi National Polar-orbiting Partnership (NPP) satellite since October 28, 2011. A striping phenomenon contained in the global distribution of O (observations) minus B (model simulations) difference was detected in different ATMS channels. In this dissertation, optimal filters are designed for smoothing out the striping noise in warm counts, cold counts, warm load temperatures and scene counts. The optimal filters are...
Show moreAdvanced Technology Microwave Sounder (ATMS) has been flying on the Suomi National Polar-orbiting Partnership (NPP) satellite since October 28, 2011. A striping phenomenon contained in the global distribution of O (observations) minus B (model simulations) difference was detected in different ATMS channels. In this dissertation, optimal filters are designed for smoothing out the striping noise in warm counts, cold counts, warm load temperatures and scene counts. The optimal filters are developed based on the striping noise free results obtained by a combined method of the principal component analysis (PCA) and the Ensemble Empirical Mode Decomposition (EEMD). Using the two-point algorithm, antenna temperatures are then calculated with warm counts, cold counts, warm load temperatures and scene counts before and after applying the optimal filters. The patterns and magnitudes of the striping noise removed are very close to that from the PCA/EEMD method. It is further demonstrated that the striping noise is present in the scene counts and must be smoothed out in order to eliminate the striping noise in antenna temperatures. It is also shown that the optimal filters are superior to the conventional boxcar filters in terms of being able to effectively remove the striping noise in the high frequency range but not to alter the lower frequency weather signals. A set of 22 optimal filters on brightness temperature is also designed to remove the striping noise in different channels. Impacts of striping noise mitigation on small-scale weather features are investigated by comparing ATMS cloud liquid water path (LWP) retrieved before and after striping noise mitigation. It is shown that the optimal filters do not affect small-scale cloud features while smoothing out striping noise in brightness temperatures. It is also shown that the striping noise is present in the LWP retrievals if the striping noise in brightness temperatures of ATMS channels 1 and 2 is not removed. The amplitude of the striping noise in LWP is found to be linearly related to the magnitude of striping noise in ATMS brightness temperature observations. Striping noise is a general problem for microwave sensors, and is also identified within observations of a recent FY-3C MWTS. Striping noise within MWTS observation is with a magnitude of 1K, which is much larger than in ATMS. A transfer function is employed to explain the root cause of the striping noise. This transfer function is controlled by instrument parameters such as scan cycle, calibration integration time and scene integration time. Instrument noise is simulated by a white noise series with and without adding flicker noise. Power spectral analysis of this instrument noise is then forced by transfer function to produce the power spectral density of output noise. It is shown that flicker signal is the source of striping noise, and transfer function can modify the striping noise in terms of magnitude and peak frequency.
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Date Issued: 2015
Identifier: FSU_migr_etd-9642
Format: Thesis

Title: On the Obscured Relationship between Size and Intensity of Tropical Cyclones: A Preliminary Study.
Creator: Hathaway, Nikki Marie, Cai, Ming, Hart, Robert E. (Robert Edward), Liu, Guosheng (Professor of Earth, Ocean and Atmospheric Science), Florida State University, College of Arts...
Show moreHathaway, Nikki Marie, Cai, Ming, Hart, Robert E. (Robert Edward), Liu, Guosheng (Professor of Earth, Ocean and Atmospheric Science), Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: Both intuition and previous statistical analysis suggests that in general, hurricane size tends to increase with intensity. However, such statistical correlation, including the statistical significance and even the sign of the correlation, between hurricane size and intensity strongly depends on the sample hurricanes in the data pool for the correlation analysis. For example, there are ample instances when a hurricane at different times can have a similar size but differ in terms of intensity...
Show moreBoth intuition and previous statistical analysis suggests that in general, hurricane size tends to increase with intensity. However, such statistical correlation, including the statistical significance and even the sign of the correlation, between hurricane size and intensity strongly depends on the sample hurricanes in the data pool for the correlation analysis. For example, there are ample instances when a hurricane at different times can have a similar size but differ in terms of intensity and vice versa. Therefore, predictions based on intuition or statistics often fail when considering an individual hurricane. In this thesis research, we attempt to apply a theoretical model in conjunction with observational case studies to gain insight on the main factors that make the relationship between both hurricane size and intensity, obscured. This theoretical model will apply an analytical analysis of the inertial instability neutral radial profile of an isolated gradient-wind balanced circular vortex in an f-plane shallow water equation model, which shows that the relationship between the size and the maximum tangential wind speed is not unique, because the size also depends on the radius of maximum wind. The radial profile of wind under neutral conditions of inertial instability reveals that hurricane size and intensity can have either a positive, near-zero, or negative correlation depending on the sample of hurricanes in the dataset from which such correlation is obtained. The main conclusion derived from the theoretical model is that the relationship between hurricane size and intensity can be obscured due to only one specific factor (i.e., the radius of maximum wind) that also influences the size. The theoretical model also predicts that the latitudinal position only weakly obscures the relationship, as long as the hurricane is not too close to the equator. We have examined whether the size inferred from the radial profile of inertially neutral wind would be able to capture its observational counterparts. Specifically, we examined five selected hurricanes derived from the Extended Best Track (EBT) Data, namely Katrina (2005), Ike (2008), Gustav (2008), Sandy (2012), and Joaquin (2015). We have performed a correlation analysis on the observed size and the size predicted by the simple theoretical model by using the information of maximum wind speed and its radius of each of the five hurricanes throughout the phases of each tropical cyclone’s (TC) life cycle. We found that the size obtained from the barotropic inertially neutral radial profile underestimates the size of observed hurricane by a factor of 2-2.5. This suggests that the observed hurricane wind’s radial profile does not follow angular momentum conservation or an air parcel would lose angular momentum as it converges towards the eyewall, mainly due to surface drag and eddy-mixing processes. This finding also implies that there are other parameters besides these three factors (intensity, radius of maximum wind, and latitude) that influence an individual hurricane size. This implies that the relationship between size and intensity is more complex than that predicted by the simple theoretical model. Our analysis suggests that about 1/3 (48 out of 174) of the observed cases show that other factors may strongly affect hurricane size. By removing these 48 data points that are indicative of possible strong impacts from the external factors, the R-squared value of the linear regression line between the observed size and the size predicted by the theoretical model increases substantially (from R2 = 46.3% to 71.5% on average). The inspection of the timing and location of these “external” data points indicate that they often occur in situations when (i) encountering big islands or land mass (e.g., Cuba for Ike) and (ii) undergo a very rapid weakening/intensifying transition (Joaquin). Therefore, the size information predicted by the simple theoretical model does capture the size record for most the track records (126 out of 174), suggesting that the most important factors that influence hurricane size are both maximum wind speed and the radius of maximum wind speed.
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Date Issued: 2017
Identifier: FSU_SUMMER2017_Hathaway_fsu_0071N_13990
Format: Thesis

Title: Ice Cloud Properties and Their Radiative Effects: Global Observations and Modeling.
Creator: Hong, Yulan, Liu, Guosheng (Professor of Earth, Ocean and Atmospheric Science), Chicken, Eric, Ellingson, R. G., Cai, Ming, Wu, Zhaohua, Florida State University, College of...
Show moreHong, Yulan, Liu, Guosheng (Professor of Earth, Ocean and Atmospheric Science), Chicken, Eric, Ellingson, R. G., Cai, Ming, Wu, Zhaohua, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: Ice clouds are crucial to the Earth's radiation balance. They cool the Earth-atmosphere system by reflecting solar radiation back to space and warm it by blocking outgoing thermal radiation. However, there is a lack of an observation-based climatology of ice cloud properties and their radiative effects. Two active sensors, the CloudSat radar and the CALIPSO lidar, for the first time provide vertically resolved ice cloud data on a global scale. Using synergistic signals of these two sensors,...
Show moreIce clouds are crucial to the Earth's radiation balance. They cool the Earth-atmosphere system by reflecting solar radiation back to space and warm it by blocking outgoing thermal radiation. However, there is a lack of an observation-based climatology of ice cloud properties and their radiative effects. Two active sensors, the CloudSat radar and the CALIPSO lidar, for the first time provide vertically resolved ice cloud data on a global scale. Using synergistic signals of these two sensors, it is possible to obtain both optically thin and thick ice clouds as the radar excels in probing thick clouds while the lidar is better to detect the thin ones. First, based on the CloudSat radar and CALIPSO lidar measurements, we have derived a climatology of ice cloud properties. Ice clouds cover around 50% of the Earth surface, and their global-mean optical depth, ice water path, and effective radius are approximately 2 (unitless), 109 g m⁻² and 48 μm, respectively. Ice cloud occurrence frequency not only depends on regions and seasons, but also on the types of ice clouds as defined by optical depth (τ) values. Optically thin ice clouds (τ < 3) are most frequently observed in the tropics around 15 km and in the midlatitudes below 5 km, while the thicker clouds (τ > 3) occur frequently in the tropical convective areas and along the midlatitude storm tracks. Using ice retrievals derived from combined radar-lidar measurements, we conducted radiative transfer modeling to study ice cloud radiative effects. The combined effects of ice clouds warm the earth-atmosphere system by approximately 5 W m⁻², contributed by a longwave warming effect of about 21.8 W m⁻² and a shortwave cooling effect of approximately -16.7 W m⁻². Seasonal variations of ice cloud radiative effects are evident in the midlatitudes where the net effect changes from warming during winter to cooling during summer, and the net warming effect occurs year-round in the tropics (∼ 10 W m⁻² ). Ice cloud optical depth is shown to be an important factor in determining the sign and magnitude of the net radiative effect. On a global average, ice clouds with τ < 4.6 display a warming effect with the largest contributions from those with τ ~ 1.0. Optically thin and high ice clouds cause strong heating in the tropical upper troposphere, while outside the tropics, mixed-phase clouds cause strong cooling at lower altitudes (> 5 km). In addition, ice clouds occurring with liquid clouds in the same profile account for about 30% of all observations. These liquid clouds reduce longwave heating rates in ice cloud layers by 0-1 K/day depending on the values of ice cloud optical depth and regions. This research for the first time provides a clear picture on the global distribution of ice clouds with a wide range of optical depth. Through radiative transfer modeling, we have gained better knowledge on ice cloud radiative effects and their dependence on ice cloud properties. These results not only improve our understanding of the interaction between clouds and climate, but also provide observational basis to evaluate climate models.
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Date Issued: 2017
Identifier: FSU_SUMMER2017_Hong_fsu_0071E_13993
Format: Thesis

Title: Improving Satellite-Based Snowfall Estimation: A New Method for Classifying Precipitation Phase and Estimating Snowfall Rate.
Creator: Sims, Elizabeth M., Liu, Guosheng, Meyer-Baese, Anke, Bourassa, Mark Allan, Cai, Ming, Sura, Philip, Florida State University, College of Arts and Sciences, Department of Earth,...
Show moreSims, Elizabeth M., Liu, Guosheng, Meyer-Baese, Anke, Bourassa, Mark Allan, Cai, Ming, Sura, Philip, Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric Science
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Abstract/Description: In order to study the impact of climate change on the Earth's hydrologic cycle, global information about snowfall is needed. To achieve global measurements of snowfall over both land and ocean, satellites are necessary. While satellites provide the best option for making measurements on a global scale, the task of estimating snowfall rate from these measurements is a complex problem. Satellite-based radar, for example, measures effective radar reflectivity, Ze, which can be converted to...
Show moreIn order to study the impact of climate change on the Earth's hydrologic cycle, global information about snowfall is needed. To achieve global measurements of snowfall over both land and ocean, satellites are necessary. While satellites provide the best option for making measurements on a global scale, the task of estimating snowfall rate from these measurements is a complex problem. Satellite-based radar, for example, measures effective radar reflectivity, Ze, which can be converted to snowfall rate, S, via a Ze-S relation. Choosing the appropriate Ze-S relation to apply is a complicated problem, however, because quantities such as particle shape, size distribution, and terminal velocity are often unknown, and these quantities directly affect the Ze-S relation. Additionally, it is important to correctly classify the phase of precipitation. A misclassification can result in order-of-magnitude errors in the estimated precipitation rate. Using global ground-based observations over multiple years, the influence of different geophysical parameters on precipitation phase is investigated, with the goal of obtaining an improved method for determining precipitation phase. The parameters studied are near-surface air temperature, atmospheric moisture, low-level vertical temperature lapse rate, surface skin temperature, surface pressure, and land cover type. To combine the effects of temperature and moisture, wet-bulb temperature, instead of air temperature, is used as a key parameter for separating solid and liquid precipitation. Results show that in addition to wet-bulb temperature, vertical temperature lapse rate also affects the precipitation phase. For example, at a near-surface wet-bulb temperature of 0°C, a lapse rate of 6°C km-1 results in an 86 percent conditional probability of solid precipitation, while a lapse rate of -2°C km-1 results in a 45 percent probability. For near-surface wet-bulb temperatures less than 0°C, skin temperature affects precipitation phase, although the effect appears to be minor. Results also show that surface pressure appears to influence precipitation phase in some cases, however, this dependence is not clear on a global scale. Land cover type does not appear to affect precipitation phase. Based on these findings, a parameterization scheme has been developed that accepts available meteorological data as input, and returns the conditional probability of solid precipitation. Ze-S relations for various particle shapes, size distributions, and terminal velocities have been developed as part of this research. These Ze-S relations have been applied to radar reflectivity data from the CloudSat Cloud Profiling Radar to calculate the annual mean snowfall rate. The calculated snowfall rates are then compared to surface observations of snowfall. An effort to determine which particle shape best represents the type of snow falling in various locations across the United States has been made. An optimized Ze-S relation has been developed, which combines multiple Ze-S relations in order to minimize error when compared to the surface snowfall observations. Additionally, the resulting surface snowfall rate is compared with the CloudSat standard product for snowfall rate.
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Date Issued: 2017
Identifier: FSU_2017SP_Sims_fsu_0071E_13720
Format: Thesis

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