Curvature-Induced Subduction in a Cyclonic Eddy
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phoc-JPO-D-25-0063.1.pdf
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Published version
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24.01 MB
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Author(s)
Wu, Weiguang
Middleton, Leo
Tarry, Daniel R
D’Asaro, Eric A
Mahadevan, Amala
Date Issued
December 1, 2025
Journal
Journal of Physical Oceanography
Publisher
American Meteorological Society
Citation
Wu, W., L. Middleton, D. R. Tarry, E. A. D’Asaro, and A. Mahadevan, 2025: Curvature-Induced Subduction in a Cyclonic Eddy. J. Phys. Oceanogr., 55, 2313–2334.
Version
Final published version
Abstract
In situ observations of a 10-km-scale elliptical cyclonic eddy reveal vertical subduction of chlorophyll-rich surface waters around the edges of the eddy where the flow curvature changes abruptly. The process is explained by relating flow curvature to horizontal divergence and vortex stretching using a theoretical framework that we develop in a local flow-following reference frame. The observed signatures of subduction, which extend from the surface to depths O(100) m, coincide with estimates from the variations of curvature number around the eddy, defined as Cu ≡ V/(fR), where V is the speed, R is the radius of curvature, and f is the Coriolis parameter. An idealized model successfully simulates the observed subduction process, uncovering a three-dimensional pathway where surface waters within the cyclone subduct along the domed isopycnal surfaces and ultimately detach from the eddy as filaments. By decomposing the frontogenetic Q vector in the omega equation for vertical velocity, we identify the role of curvature-induced frontogenesis in driving subduction. Submesoscale flows exhibit highly curved flow paths, and curvature-induced frontogenesis, which differs from the traditionally emphasized confluence-induced frontogenesis, can play a significant role in modifying vertical transport.
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DOI of Published Version
https://doi.org/10.1175/JPO-D-25-0063.1
