Mapping vortex structures in the Caspian Sea

Abstract

We present results of observations of vortex structures in the Caspian Sea based on satellite images of the visible range obtained by Sentinel-2 (MSI), Landsat-5 (ТМ), Landsat-7 (ETM+) and Landsat – 8 (OLI). The initial goal of this work was to identify vortex structures and their main localization areas in the Caspian Sea. In this paper we used Ocean Color Data for two periods: 1999-2006 and 2007-2013, plus 2 recent years (2019 and 2020). Results of these periods were comparing between each other. About 50% of the scenes from the obtained data are covered by clouds due to difficult weather conditions over the Caspian Sea - a frequent changes of air masses in all seasons of the year. Among cloudless scenes, on average, vortex structures occur on 20-30% of scenes. According to the results of the analysis of the data obtained, a predominance of submesoscale cyclones and anticyclones is noted. It was noted that vortex structures were mainly found in the shelf zone of the Caspian Sea. More intense vortex formation is observed in the South Caspian. The main reasons for their formation: the flow of river runoff, complex bottom and coastal topography, the vorticity of the wind field, shear instability at the periphery of the main circulation elements. The mapping of the main circulation elements in Caspian Sea was carried out. For each part of the Caspian Sea, the six main areas of vortex formation were identified.