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Global Observations Of Horizontal Mixing From Argo Float And Surface Drifter Trajectories
Title
Global Observations Of Horizontal Mixing From Argo Float And Surface Drifter Trajectories.
Creator
Roach, Christopher J., Balwada, Dhruv, Speer, Kevin
Abstract/Description
Mixing by mesoscale eddies in the ocean plays a major role in setting the distribution of oceanic tracers, with important implications for physical and biochemical systems at local to global scales. Roach et al. (2016; https://doi.org/10.1002/2015JC011440) demonstrated that a two-particle analysis of Argo trajectories produces robust estimates of horizontal mixing in the Southern Ocean. Here we extend this analysis to produce global 1 degrees x1 degrees maps of eddy diffusivity at the nominal...
Show moreMixing by mesoscale eddies in the ocean plays a major role in setting the distribution of oceanic tracers, with important implications for physical and biochemical systems at local to global scales. Roach et al. (2016; https://doi.org/10.1002/2015JC011440) demonstrated that a two-particle analysis of Argo trajectories produces robust estimates of horizontal mixing in the Southern Ocean. Here we extend this analysis to produce global 1 degrees x1 degrees maps of eddy diffusivity at the nominal Argo parking depth of 1,000 m. We also applied this methodology to estimate surface eddy diffusivities from Global Drifter Program (GDP) surface drifters. The global mean eddy diffusivity was 543 +/- 155 m(2)/s at 1,000m and 2637 +/- 311 m(2)/s at the surface, with elevated diffusivities in regions of enhanced eddy kinetic energy, such as western boundary currents and along the Antarctic Circumpolar Current. The eddy kinetic energy at the equator is high at both the surface and depth, but the eddy diffusivity is only enhanced near the surface. At depth the eddy diffusivity is strongly suppressed due to the presence of mean flow. We used our observational estimates to test the validity of an eddy diffusivity parameterization that accounts for mixing suppression in the presence of zonal mean flows. Our results indicated that this parameterization generally agrees with the directly observed eddy diffusivities in the midlatitude and high-latitude oceans.
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Date Issued
2018-07-01
Identifier
FSU_libsubv1_wos_000441888200008, 10.1029/2018JC013750
Format
Citation
Metrics For The Evaluation Of The Southern Ocean In Coupled Climate Models And Earth System Models
Title
Metrics For The Evaluation Of The Southern Ocean In Coupled Climate Models And Earth System Models.
Creator
Russell, Joellen L., Kamenkovich, Igor, Bitz, Cecilia, Ferrari, Raffaele, Gille, Sarah T., Goodman, Paul J., Hallberg, Robert, Johnson, Kenneth, Khazmutdinova, Karina, Marinov,...
Show moreRussell, Joellen L., Kamenkovich, Igor, Bitz, Cecilia, Ferrari, Raffaele, Gille, Sarah T., Goodman, Paul J., Hallberg, Robert, Johnson, Kenneth, Khazmutdinova, Karina, Marinov, Irina, Mazloff, Matthew, Riser, Stephen, Sarmiento, Jorge L., Speer, Kevin, Talley, Lynne D., Wanninkhof, Rik
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Abstract/Description
The Southern Ocean is central to the global climate and the global carbon cycle, and to the climate's response to increasing levels of atmospheric greenhouse gases, as it ventilates a large fraction of the global ocean volume. Global coupled climate models and earth system models, however, vary widely in their simulations of the Southern Ocean and its role in, and response to, the ongoing anthropogenic trend. Due to the region's complex water-mass structure and dynamics, Southern Ocean carbon...
Show moreThe Southern Ocean is central to the global climate and the global carbon cycle, and to the climate's response to increasing levels of atmospheric greenhouse gases, as it ventilates a large fraction of the global ocean volume. Global coupled climate models and earth system models, however, vary widely in their simulations of the Southern Ocean and its role in, and response to, the ongoing anthropogenic trend. Due to the region's complex water-mass structure and dynamics, Southern Ocean carbon and heat uptake depend on a combination of winds, eddies, mixing, buoyancy fluxes, and topography. Observationally based metrics are critical for discerning processes and mechanisms, and for validating and comparing climate and earth system models. New observations and understanding have allowed for progress in the creation of observationally based data/model metrics for the Southern Ocean. Metrics presented here provide a means to assess multiple simulations relative to the best available observations and observational products. Climate models that perform better according to these metrics also better simulate the uptake of heat and carbon by the Southern Ocean. This report is not strictly an intercomparison, but rather a distillation of key metrics that can reliably quantify the "accuracy" of a simulation against observed, or at least observable, quantities. One overall goal is to recommend standardization of observationally based benchmarks that the modeling community should aspire to meet in order to reduce uncertainties in climate projections, and especially uncertainties related to oceanic heat and carbon uptake. Plain Language Summary Observationally based metrics are essential for the standardized evaluation of climate and earth system models, and for reducing the uncertainty associated with future projections by those models.
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Date Issued
2018-05-01
Identifier
FSU_libsubv1_wos_000436111400001, 10.1002/2017JC013461
Format
Thesis