Coastal upwelling involves an upward movement of deeper, usually colder, water to the surface. Satellite sea surface temperature (SST) observations and simulations with a hydrodynamic model show, however, that the coastal upwelling in the Baltic Sea in winter can bring warmer water to the surface. In this study, the satellite SST data collected by the advanced very high resolution radiometer (AVHRR) and the moderate-resolution imaging spectroradiometer (MODIS), as well as simulations with the Parallel Model 3D (PM3D) were used to identify upwelling events in the southern Baltic Sea during the 2010–2017 winter seasons. The PM3D is a three-dimensional hydrodynamic model of the Baltic Sea developed at the Institute of Oceanography, University of Gdańsk, Poland, in which parallel calculations enable high-resolution modelling. A validation of the model results with in situ observations and satellite-derived SST data showed the PM3D to adequately represent thermal conditions in upwelling areas in winter (91.5% agreement). Analysis of the frequency of warm upwellings in 12 areas of the southern Baltic Sea showed a high variability in January and February. In those months, the upwelling was most frequent, both in satellite imagery and in model results, off the Hel Peninsula (38% and 43% frequency, respectively). Upwelling was also frequent off the Vistula Spit, west of the Island of Rügen, and off the eastern coast of Skåne, where the upwelling frequency estimated from satellite images exceeded 26%. As determined by the PM3D, the upwelling frequency off VS and R was at least 25%, while off the eastern coast of Skåne, it reached 17%. The faithful simulation of SST variability in the winters of 2010–2017 by the high-resolution model used was shown to be a reliable tool with which to identify warm upwellings in the southern Baltic Sea.

The Odra River mouth area is a region of the Southern Baltic coastal zone especially prone to the influence of storm surges. In the present study, the height and extent of the Baltic storm surges, and temporal offsets of the respective maximum water level occurrences in the Odra River mouth area were explored using cross-correlation, cluster analysis and principal component analysis. The analyses were based on hourly water level readings retrieved from water gauging stations located along the lower Odra reaches and at the coasts of the Szczecin Lagoon and the Pomeranian Bay during storm surge years 2008/2009–2019/2020. The analysis of mutual relationships between water levels during storm surges indicated that the extent of marine influence on the lower Odra River and within the Szczecin Lagoon was variable during the studied surge events, and dependent on meteorological conditions (the strongest during the sustained occurrence of wind blowing from the northern sector), discharge from the Odra River catchment (the strongest at low discharge), ice conditions on the lower Odra (suppressing the storm surge propagation upstream), and general sea level in the Pomeranian Bay (stronger at high sea levels). The strongest correlation between sea levels at Świnoujście and water levels in the Szczecin Lagoon and the lower Odra was found at a 6–7 h offset. The extent of storm surges usually reached 100 km up the lower Odra channels, less frequently reaching 130 km away from the sea.

A 3D operational hydrodynamic model, developed at the Institute of Oceanography, University of Gdansk, was used to forecast extreme hydrographic events in the Oder Estuary. The model was based on the coastal ocean circulation model known as the Princeton Ocean Model (POM); it was adapted to Baltic conditions and to a 48-h numerical meteorological forecast. Wind-driven water backup in the Oder mouth necessitated working out a simplified operational model of river discharge, based on water budget in a stream channel. The model generates 60-h forecasts of water levels, currents, water temperature and salinity in the estuary. As the model adequately approximates hydrographic variability in the estuary, it can be regarded as a reliable tool for storm surges forecasting and for the assessment of Oder water spread in the Baltic. The forecast is rapidly accessed on its designated website, thereby providing assistance in decision-making by emergency situation centres and bodies that are responsible for navigation safety, port operation and environmental and flood protection of coastal areas. It is intended to fine-tune the model so that a better fit between the observed and computed data is obtained.

W pracy oszacowano częstość występowania i intensywność wezbrań sztormowych w ujściowym rejonie Odry w sezonach 1993/94–2016/17. Analizę przeprowadzono w oparciu o serie pomiarowe stanów wody, odczytanych na stacjach położonych wzdłuż dolnego biegu Odry oraz u wybrzeży Zatoki Pomorskiej i Zalewu Szczecińskiego. Rozpoznanie czasowej i przestrzennej zmienności stanów wody w rejonie badań wykazało znaczną nieregularność występowania wezbrań sztormowych. Po długich okresach o znikomej częstotliwości wezbrań rejestrowano okresy o nasilonym ich występowaniu. W przebiegu rocznym wezbrania najczęściej notowano od listopada do stycznia. Najrozleglejsze wezbranie sztormowe w ujściowym rejonie Odry zaobserwowano w październiku 2009 r. Bardzo wysokimi wezbraniami okazały się wezbrania z listopada 1995 r., stycznia 2012 r. oraz stycznia 2017 r. Wysokim i długotrwałym wezbraniom, o dalekim zasięgu oddziaływania w górę dolnej Odry, sprzyjał stopniowy i długotrwały wzrost poziomu morza u wybrzeży Zatoki Pomorskiej. Intensyfikacji wezbrań w ujściowym rejonie Odry sprzyjało ponadto wystąpienie wezbrań sztormowych podczas zwiększonego zasilania ze zlewni Odry, w okresie występowania zjawisk lodowych na dolnej Odrze oraz przy podwyższonym poziomie Morza Bałtyckiego.