Abstract
Abstract. Mesoscale ocean processes are prevalent in many parts of the global oceans and may contribute substantially to the meridional movement of heat. Yet earlier global surveys of meridional temperature fluxes and heat transport (HT) have not formally distinguished between mesoscale and large-scale contributions, or they have defined eddy contributions based on temporal rather than spatial characteristics. This work uses spatial filtering methods to separate large-scale (gyre and planetary wave) contributions from mesoscale (eddy, recirculation, and tropical instability wave) contributions to meridional HT. Overall, the mesoscale temperature flux (MTF) produces a net poleward meridional HT at midlatitudes and equatorward meridional HT in the tropics, thereby resulting in a net divergence of heat from the subtropics. In addition to MTF generated by propagating eddies and tropical instability waves, MTF is also produced by stationary recirculations near energetic western boundary currents, where the temperature difference between the boundary current and its recirculation produces the MTF. The mesoscale contribution to meridional HT yields substantially different results from temporally based “eddy” contributions to meridional HT, with the latter including large-scale gyre and planetary wave motions at low latitudes. Mesoscale temperature fluxes contribute the most to interannual and decadal variability of meridional HT in the Southern Ocean, the tropical Indo-Pacific, and the North Atlantic. Surface eddy kinetic energy (EKE) is not a good proxy for MTF variability in regions with the highest time-mean EKE, though it does explain much of the temperature flux variability in regions of modest time-mean EKE. This approach to quantifying mesoscale fluxes can be used to improve parameterizations of mesoscale effects in coarse-resolution models and assess regional impacts of mesoscale eddies and recirculations on tracer fluxes.
Highlights
In regions of the ocean where waters of different temperatures and densities converge, instabilities form that transport heat across latitude lines
This study extends the methodology that Delman and Lee (2020) used in the North Atlantic in order to better understand the specific contribution of mesoscale processes to meridional temperature fluxes and meridional heat transport (HT)
The analysis demonstrates that the locations and eddy kinetic energy (EKE) levels of the most energetic regions of the ocean are well represented in the Parallel Ocean Program (POP) simulation (Fig. 1)
Summary
In regions of the ocean where waters of different temperatures and densities converge, instabilities form that transport heat across latitude lines. Not all mesoscale flow features take the form of coherent vortices, and the actual movement of coherent eddies likely accounts for a relatively small portion of the fluxes associated with the mesoscale (e.g., Hausmann and Czaja, 2012; Abernathey and Haller, 2018; Sun et al, 2019) Another commonly used approach is to quantify the “eddy” contribution to meridional HT based on the deviation of v and T from the temporal (rather than zonal) mean (e.g., Cox, 1985; Jayne and Marotzke, 2002; Aoki et al, 2013; Griffies et al, 2015; Ushakov and Ibrayev, 2018).
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