Analysis of sub-mesoscale eddies in the Baltic Sea based on SAR imagery and model wind data

Abstract

We discuss the spatio-temporal distribution of sub-mesoscale eddies seen in synthetic aperture radar (SAR) imagery of the Baltic Sea. Analyzing about 1250 Envisat Advanced SAR (ASAR) images acquired between 2009 and 2011 almost 7000 sub-mesoscale eddies were discovered. Since the visibility of vortical structures in SAR imagery significantly depends on the near-surface wind speed, wind data from a numerical model of the Baltic Sea were additionally used to improve our eddy statistics. Within the method proposed herein only those parts of SAR images are considered for the calculation of eddy statistics, which were acquired when the wind speed conditions were favorable for eddy manifestations. As a result, and despite the fact that eddies were generally observed all over the Baltic Sea, we show that the south-western part of the Baltic Sea seems to have especially high sub-mesoscale eddy activity.