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Little eddy in a big ocean, seen by Swot

Image of the Month - April 2025

Swot SSH (superimposed on multimission gridded SSH (Duacs)), showing a submesoscale eddy off South Africa in the Atlantic Ocean, with a radius of about 15 km but an amplitude of 15 cm on August 2, 2023 (black boxes; gray/white contours denote Swot SSH). The eddy is also visible in sea surface temperature (b), and chlorophyll-A (c) satellite measurements. (d), a zoom in on the left Swot swath, showing SSH and velocity vectors computed by assuming geostrophy (from which the eddy seems to deviate, in fact). (from [Archer et al., 2024], Credit JPL)
Swot SSH (superimposed on multimission gridded SSH (Duacs)), showing a submesoscale eddy off South Africa in the Atlantic Ocean, with a radius of about 15 km but an amplitude of 15 cm on August 2, 2023 (black boxes; gray/white contours denote Swot SSH). The eddy is also visible in sea surface temperature (b), and chlorophyll-A (c) satellite measurements. (d), a zoom in on the left Swot swath, showing SSH and velocity vectors computed by assuming geostrophy (from which the eddy seems to deviate, in fact). (from [Archer et al., 2024], Credit JPL)

 
While classical altimetry enables to detect mesoscale features of 100-300 km (even when merging data from seven or more satellites), Swot can observe much smaller ones over all the oceans. Before Swot, the dynamics and energy associated with submesoscale ocean processes had never been observed from a global and systematic perspective, only glimpsed in imaging techniques. And, while we know that they play an important role in the large-scale ocean circulation and climate system in part through vertical mixing, the details - where they are located, how much do they contribute to both circulation and climate, etc - were missing.

Swot instantaneous 2D sea surface height mapping over its swaths enables to detect more Sea Level Anomaly variability than previous multimission maps, additional variability of which at least 30% corresponds to features smaller than 50 km. This will lead to the knowledge of velocity (kinetic energy) and pressure (potential energy) fields.

Such new knowledge and monitoring will help to better understand, and better model the ocean. The predictive and diagnostic capabilities of ocean models for the ocean, atmosphere, and climate system will thus be improved.

See also:

Reference:

  • Matthew Archer, Jinbo Wang, Patrice Klein et al. Global Submesoscale Ocean Dynamics Unveiled by Wide-Swath Satellite Altimetry, 07 October 2024, Preprint (Version 1) available at Research Square [https://doi.org/10.21203/rs.3.rs-5177358/v1] ; under review at Nature Portfolio
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