Changing impact of large-scale atmospheric circulation variability on the water mass exchange and circulation of the Baltic Sea for the period 1950-2022

Different North Atlantic winter climate regimes force different circulation patterns in the Baltic Sea. Furthermore, as the atmospheric circulation, to a large extent, controls patterns of water circulation and biophysical aspects relevant for biological production, such as the vertical distribution of temperature, salinity and oxygen, alterations in weather regimes may severely impact the trophic structure and functioning of marine food webs (Hinrichsen et al. 2007). To understand the processes linking changes in the marine environment and climate variability of the Baltic Sea, it is essential to investigate all components of the climate system which of course include also the large-scale atmospheric circulation variability. Here we focus on the link between changes/shifts in the large-scale atmospheric conditions and their impact on the regional scale variability over the Baltic Sea area for the period 1950-2022. This work is mostly an extension of previous studies which focused on the response of the Baltic Sea circulation to climate variability for the period 1958-2008 (Lehmann et al. 2011, Lehmann et al. 2014). Now extended time series ECMWF ERA 5 reanalysis for 7 decades are available, highlighting recent changes in atmospheric conditions over the Baltic Sea area. The main focus of this work is to identify predominant large scale atmospheric circulation patterns (North Atlantic winter climate regimes) on a monthly/seasonal time scale controlling the development of regional atmospheric weather types over the Baltic Sea area, which in turn can be associated with different Baltic Sea circulation patterns and water mass exchange with the North Sea.