Submesoscale eddies in Lake Ladoga based on Sentinel-1 radar images from January to December 2016–2022

This study presents the results of the analysis of a long-term dataset of observations on the spatial-temporal variability of submesoscale eddy characteristics in Lake Ladoga using radar imagery. The initial data consisted of more than 3500 high-resolution Sentinel-1A/B satellite images for the period from January 2016 to December 2022. Generalized maps of the occurrence of submesoscale structures on the lake’s waters for the year and by seasons are presented. Average annual and seasonal estimates of the variability of the mean diameters of eddies with different type of rotation were obtained. It was shown that submesoscale structures are a common phenomenon throughout the lake during the period of direct thermal stratification and the presence of a near-surface pycnocline. Cyclonic structures with sizes up to 3 km were most frequently registered, which does not exceed the estimates of the average Rossby deformation radius for Lake Ladoga. Eddies were most often observed north of Valaam Island. No significant interannual variability in their characteristics was found; they were close to the average multi-year values. A pronounced intrayear variability in the characteristics of submesoscale structures was revealed, both in frequency and locations, and to a lesser extent in their sizes. It was established that eddies were most frequently observed in areas with depths of 50–100 meters, near frontal zones of different genesis. In specific cases, the instability in frontal zones in Lake Ladoga appears to be a dominant factor in the formation of small eddy groups, especially in the absence of significant topographic effects or wind influence.