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 onwards. Our primary focus is on assessing the performance of the latest Copernicus model reanalysis product in estimating ice season evolution compared to the satellite dataset. Firstly, the model reanalysis dataset is bias-corrected for further analysis. While the model estimates an earlier start to the ice season, it generally matches satellite data regarding the season’s end. Additionally, we find that the model tends to overestimate ice thickness compared to ice chart-based data. Across the Baltic Sea, declining trends for the sea ice are observed. The sea ice statistics during the recent period (2007–2021) show decreased sea ice fraction and thickness. The decrease in the sea ice thickness is over 50 % in some areas during the melting phase. Trend analysis in the study reveals a uniform pattern towards shorter ice seasons (most prominent being in Bothnian Bay with a range of approximately 1–3 days/year of decline in ice season), reduced sea ice extent (SIE) and reduced mean ice thickness (reaching up to -0.4 cm/year).