Climatology, Seasonality, and Trends of Spatially Coherent Ocean Eddies

Ocean eddies influence regional and global climate by mixing and transporting heat, carbon, nutrients, and other properties. One of the most recognizable and ubiquitous features of oceanic variability are mesoscale eddies (vortices and meanders/jets) with spatial scales of tens to hundreds of kilometers. Vortices resemble Gaussian-like features in sea surface height which locally affect near-surface wind, cloud properties, and rainfall patterns; we refer to these Gaussian-like eddies as spatially coherent eddies. Although spatially coherent eddies are ubiquitous, their climatology, seasonality, and long-term temporal evolution is yet to be explored. Here, we examine the kinetic energy (KE) contained in spatially coherent eddies and present their temporal variability using satellite observations between 1993 and 2020. Around half of the transient KE contained by eddies corresponds to spatially coherent eddies. A strong seasonal cycle is observed in the spatially coherent eddy field, and correlates with the wind forcing at time-lags of 3-6 months. The seasonal correlation between wind forcing and spatially coherent eddies with diameters smaller than 120 km is faster (similar to 3 months), than that of coherent eddies with larger diameters (similar to 6 months). These lags between different spatially coherent eddy scales are consistent with the transfer of energy from small to large scales (inverse energy cascade). Our analysis highlights the relative importance of the spatially coherent eddy field in the KE budget, revealing a lagged response between the spatially coherent eddy and forcing at different time-scales, and showcases the seasonality, and multidecadal trends of coherent eddy properties over the global ocean.