Sea ice in the Baltic Sea during 1993/94–2020/21 ice seasons from satellite observations and model reanalysis

Abstract. This study investigates the sea ice characteristics of the Baltic Sea using Copernicus satellite and model reanalysis data products from 1993 onward. Our primary focus is on assessing the performance of the latest Copernicus model reanalysis product in estimating the ice season evolution compared to the satellite dataset. The model estimates an earlier start to the ice season; it generally matches satellite data regarding the season's end. In addition, the model ice thickness is compared with the ice chart-based data. Across the Baltic Sea, declining trends for sea ice are observed. The sea ice characteristics during the recent period (2007/08–2020/21) show decreased sea ice fraction and thickness compared to the preceding period (1993/94–2006/07) of the study. The decrease in sea ice thickness is greater than 50 % in some areas during the spring season. The trend analysis in the study reveals a uniform pattern toward shorter ice seasons (the most prominent being in Bothnian Bay with a range of approximately 1–3 d yr−1 of decline in ice season), reduced sea ice extent (SIE) and reduced mean ice thickness (reaching up to −0.7 cm yr−1).