On the Significance of Ageostrophic Meridional Eddy-Induced Heat Flux in the Surface Ocean of the Antarctic Circumpolar Current

Ruiyi Chen aKey Laboratory of Physical Oceanography and Frontiers Science Center for Deep Ocean Multispheres and Earth System, College of Oceanic and Atmospheric Sciences, Ocean University of China, Qingdao, Shandong, China

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Yiyong Luo aKey Laboratory of Physical Oceanography and Frontiers Science Center for Deep Ocean Multispheres and Earth System, College of Oceanic and Atmospheric Sciences, Ocean University of China, Qingdao, Shandong, China

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Zhiwei Zhang aKey Laboratory of Physical Oceanography and Frontiers Science Center for Deep Ocean Multispheres and Earth System, College of Oceanic and Atmospheric Sciences, Ocean University of China, Qingdao, Shandong, China
bSanya Oceanographic Institution and Key Laboratory of Ocean Observation and Information of Hainan Province, Ocean University of China, Sanya, Hainan, China

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Fukai Liu aKey Laboratory of Physical Oceanography and Frontiers Science Center for Deep Ocean Multispheres and Earth System, College of Oceanic and Atmospheric Sciences, Ocean University of China, Qingdao, Shandong, China

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Abstract

Eddy-induced heat flux (EHF) convergence plays an important role in balancing the cooling of mean flows in the heat budget of Southern Ocean. This study investigates the EHF in the Southern Ocean and the surface ocean heat budget over the Antarctic Circumpolar Current (ACC) estimated through a high-resolution ocean assimilation product. In contrast to previous studies in which the estimation of the EHF in the Southern Ocean was based on the assumption that mesoscale eddies are quasi-geostrophic turbulence, we find that more than one third of the total meridional EHF in the surface layer is attributed to ageostrophic currents of eddies, and that the ageostrophic component of the EHF convergence is as important as its geostrophic component for the surface ocean heat budget over the ACC. In particular, the ageostrophic meridional EHF convergence accounts for 22% of the warming needed to balance the cooling from the mean flows during winter, equivalent to warming the surface ocean of the ACC by 0.14° C. The ageostrophic meridional EHF is likely caused by the stirring effect of ageostrophic secondary circulations in mesoscale eddies, which are induced by the turbulent thermal wind balance to restore the vertical shear of the upper layer in mesoscale eddies destructed by intense winter winds.

© 2024 American Meteorological Society. This is an Author Accepted Manuscript distributed under the terms of the default AMS reuse license. For information regarding reuse and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Yiyong Luo, yiyongluo@ouc.edu.cn

Abstract

Eddy-induced heat flux (EHF) convergence plays an important role in balancing the cooling of mean flows in the heat budget of Southern Ocean. This study investigates the EHF in the Southern Ocean and the surface ocean heat budget over the Antarctic Circumpolar Current (ACC) estimated through a high-resolution ocean assimilation product. In contrast to previous studies in which the estimation of the EHF in the Southern Ocean was based on the assumption that mesoscale eddies are quasi-geostrophic turbulence, we find that more than one third of the total meridional EHF in the surface layer is attributed to ageostrophic currents of eddies, and that the ageostrophic component of the EHF convergence is as important as its geostrophic component for the surface ocean heat budget over the ACC. In particular, the ageostrophic meridional EHF convergence accounts for 22% of the warming needed to balance the cooling from the mean flows during winter, equivalent to warming the surface ocean of the ACC by 0.14° C. The ageostrophic meridional EHF is likely caused by the stirring effect of ageostrophic secondary circulations in mesoscale eddies, which are induced by the turbulent thermal wind balance to restore the vertical shear of the upper layer in mesoscale eddies destructed by intense winter winds.

© 2024 American Meteorological Society. This is an Author Accepted Manuscript distributed under the terms of the default AMS reuse license. For information regarding reuse and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Yiyong Luo, yiyongluo@ouc.edu.cn
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