Improved theoretical estimates of the zonal propagation of global nonlinear mesoscale eddies

Liu, Ran, Wang, Yan, Zhai, Xiaoming, Balwada, Dhruv and Mak, Julian (2025) Improved theoretical estimates of the zonal propagation of global nonlinear mesoscale eddies. Journal of Geophysical Research - Oceans, 130 (6). ISSN 2169-9275

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Abstract

Mesoscale eddies are essential for transport and mixing processes in the global ocean, with their characteristic westward propagation being a significant finding from the satellite altimetry era. Traditional predictions of their zonal propagation rely on the theoretical phase speed of long baroclinic Rossby waves; however, this approach is known to overestimate eddy speeds equatorward of approximately ~35 latitudes. To address this issue, we incorporate local eddy wavelengths inferred from satellite-based eddy radii into the estimation of global eddy speeds, thereby significantly reducing the overestimation biases in mid- to low-latitude regions. This improvement is consistent with the observation that mesoscale eddies in these latitudes have length scales comparable to the local deformation scales and thus refrain from satisfying the long-wave approximation, whereas the long baroclinic Rossby wave phase speed remains useful for capturing the most energetic but less abundant eddies. The remaining discrepancies between the revised theoretical speeds and observations primarily stem from uncertainties in the background zonal flow, spatial variability of vertical modal structures (and the associated deformation radii), and estimation of local eddy length scales. These findings have important implications for understanding long-range mesoscale eddy propagation and eddy-driven mixing in the global ocean, which are anticipated to benefit future ocean model developments and enhance predictions of mesoscale eddy dynamics.

Item Type:	Article
Additional Information:	Open Research information: All calculation and figure generation codes used in this study are available from Liu (2025). Observational eddy propagation speeds derived from the Radon transform are provided by C. W. Hughes and can also be accessed from Liu (2025). The surface mode deformation radius data, provided by Lacasce and Groeskamp, can be retrieved from Liu (2025). The altimetric Mesoscale Eddy Trajectories Atlas (META3.2 DT) was produced by SSALTO/DUACS and distributed by AVISO+ (https://aviso.altimetry.fr) with support from CNES, in collaboration with IMEDEA (DOI: 10.24400/527896/a01-2022.005.YYMMDD for the used META3.2 DT allsat version. The EN.4.2.2.c14 data (Good et al., 2013; Cheng et al., 2014) were obtained from https://www.metoffice.gov.uk/hadobs/en4/ and are © British Crown Copyright, Met Office, provided under a Non-Commercial Gov563 ernment Licence (http://www.nationalarchives.gov.uk/doc/non-commercial-government564 licence/version/2/). Funding information: This work is supported by the Research Grants Council (RGC) of Hong Kong under the award General Research Fund 16305321, and by the Center for Ocean Research (CORE), a joint research center between Laoshan Laboratory and HKUST. XZ and JM acknowledge financial support from the Royal Society Kan Tong Po International Fellowship KTP/R1/231008.
Faculty \ School:	Faculty of Science > School of Environmental Sciences
UEA Research Groups:	Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences
Depositing User:	LivePure Connector
Date Deposited:	12 Jun 2025 09:30
Last Modified:	24 Jun 2025 14:30
URI:	https://ueaeprints.uea.ac.uk/id/eprint/99492
DOI:	10.1029/2025JC022518

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