Thermal conditions in the summer season on the Polish coast of the Baltic Sea in 1966-2015

Abstract

The Baltic Sea coast is characterized by a large frequency of days with biometeorologically adverse effects. In many Polish and foreign studies there are issues related to the increase in the frequency of warm days, hot days, and heat waves. The present study introduces the characteristics of thermal conditions on the Polish coast in the 1966-2015 multiyear period, as well as the identification of circulation conditions favoring the occurrence of extremely warm periods. The analysis included the maximum temperature data (obtained from five measurement stations), on the basis of which the characteristics such as: average maximum air temperature, sum of maximum air temperatures occurring in summer, warm days (T max >25 °C), hot days and heat waves (T max >30 °C) were determined. The existing thermal classification proposed by Lorenc (2000) was also used in relation to the maximum daily temperature. In addition, there appeared a topic of atmospheric circulation regarding the determination of conditions for the occurrence of exceptionally warm months (mean T max >T s +1.5σ). The research results indicate an increase in the average maximum temperature (T max) in the summer season in 1966-2015. The changes are particularly visible in the western part of the research area (0.43 °C/10 years). Furthermore, the observed warming was translated into a higher occurrence of warm and hot days, which was discussed by other authors in the context of the whole of Poland. The occurrence of exceptionally warm months has reached the maximum frequency in the last 15 years, which is associated with positive anomalies of the sea level pressure and the 500 hPa isobaric surface. Periods of occurrence of the above mentioned anomalies were related to the presence of high pressure systems and the advection of air masses from the eastern sector (according to the presented T850 maps).

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“…The observed warming was also confirmed by the increased frequency of warm extremes (Unkašević and Tošić, 2013). The changes taking place were also documented for the whole of Europe (Klein Tank and Können, 2003;Della-Marta et al, 2007;Shevchenko et al, 2014;Tomczyk et al, 2019) and globally (e.g., Alexander et al, 2006).…”