Regional circulation patterns inducing coastal upwelling in the Baltic Sea

Abstract Atmospheric feedback involved in the occurrence of coastal upwelling a small semi-enclosed sea basin, i.e., Baltic Sea, was analysed, and regional circulation conditions triggering different sections were identified. Upwelling summer season (June–August, years 1982–2017) recognized on basis surface temperature patterns. Circulation defined using (1) established daily indices zonal meridional airflow (2) synoptic situation at level distinguished by applying rotated principal component analysis to pressure data. The 12 patterns differed substantially intensity location their centres. mean seasonal frequency generally higher along western shores than meridionally oriented eastern varied from less 10 over 30% more predestined sections, northwestern coast Gulf Bothnia, northern Finland southern Swedish coast. Due variable orientations coastlines, could occur under almost any prevailing wind direction, thus, each classified induce some sections. As deduced fields for pattern, mostly alongshore winds triggered upwelling, which is line with Ekman rule. With time, also be induced stress normal coastline seaward winds.