ИСТИНА

Every winter there is a water opening in the ice field (polynya) near the navigable Strait of Baltiysk in the Vistula Lagoon. The Vistula Lagoon is the second largest shallow estuarine lagoon of the Baltic Sea. The Lagoon is separated from the sea by a narrow sand spit. The main characteristic features of ice processes in the Vistula Lagoon are periodical ice breakdown and the polynya occurrence. We analysed 158 synthetic aperture radar (SAR) satellite images for the period from 26 December 2010 to 6 March 2017. The polynya was observed on 73 of them. The size of the polynya ranges from 1 to 22 square km with an average length of 3 km, and width of 4 km. It can have various shapes, either round or stretched along one of the axes (often into the Vistula Lagoon) with smooth or saw-edged borders. To examine the primary factors of polynya formation and its variability over time we correlated its characteristics with oceanic and atmospheric variables such as air temperature, wind speed and direction, and intrusions of sea water. It is assumed that there may be an additional factor (possibly surface waves) that may significantly influence the dynamics of the polynya. Research was supported by the theme N 0149-2014-0017 of State Assignment of the Institute of Oceanology of the Russian Academy of Sciences (2017-2019).