Rapid-changing ocean circulation seen thanks to the 1-day orbit
Swot sea level anomalies for April 2023 over the Gulf Stream, mapped from 250-m data. The satellite was on its 1-day calval orbit, thus showing rapid-changing ocean circulation patterns. (Credits Cnes/CLS/JPL)
Ocean circulation was once thought to be a collection of rather stable ocean currents. The first altimeters showed the ubiquitous variability of the ocean at the 200-300 km scale, with all its meanders and eddies, and allowed a new era to begin, including the prediction of this variability. Swot (Nasa/Cnes) sees more and faster-changing details. During the first six months of the mission, Swot was placed in an orbit that passed over the same point every day. Over a point where two tracks crossed, that meant twice a day. The goal was to validate the measurements, but it had the added benefit of observing rapidly changing features of the oceans. Above is an example in an energetic area, the Gulf Stream (east of the US East Coast) with a map every 12 hours over a full month (April 2023) with a resolution of 250 m (full resolution).
The animation shows the topography as observed by the KaRIn instrument. We can see a large eddy that stays long (the cold one in the upper left at the beginning of the animation, which stays almost all the time), eddies traveling and crossing both tracks, and very fast changes in the circulation with small eddies splitting and merging.
The successive maps are extremely consistent without post-processing. However, some days show artifacts from rain, noise from high waves, etc. The data used for this animation is not yet calibrated, so some tracks show a bias.
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