Characteristic of bioclimatic conditions in Poland based on Physiologically Equivalent Temperature.

The aim of the study was to characterise bioclimatic conditions in Poland in the times of progressing warming. This type of research permits the verification whether the progressing climate warming also translates into a change in bioclimatic conditions. This study was based on data obtained for the period 1966-2021 from 37 synoptic stations located in Poland. All the data series were uniform and obtained from the data base of the Institute of Meteorology and Water Management-National Research Institute (IMGW-PIB). The study revealed high variability of bioclimatic conditions in Poland both in spatial and in temporal terms. The lowest mean annual PET values were recorded in the north and north-east of the country and the highest in the south-west of Poland. The study revealed changes in the frequency of occurrence of days with cold and heat stress, as well as days with no thermal stress. The most intensive changes were determined for days with cold stress. A decrease in the number of days in this category translated into an increase in the number of days with no thermal stress and days with heat stress.

Biometeorological conditions during cold spells in south-east Poland and west Ukraine.

The aim of this research is to analyze the biometeorological conditions, based on the Physiologically Equivalent Temperature (PET) thermal index, during cold spells (CSs) in south-east Poland and west Ukraine during the years 1966-2021. The research shows a high variability of the occurrence of CSs in the study period and a clear increase in the frequency and total duration of CSs in the east of the study area. The number of CSs in the analyzed years varies from 6 cases in the west (in Katowice) to 34 in the east of the study area (in Shepetivka). The total duration of CSs varied from 26 days (in Raciborz and Katowice) to 166 days (in Rivne). At the majority of stations, CSs occurred most frequently in the first two decades (1966/1967-1975/1976, 1976/1977-1985/986) and in the last full decade (2006/2007-2015/2016). The average PET values at 12:00 UTC during CSs decreased eastwards throughout the study domain and were generally lower than -20.0 °C in the west of Ukraine, while in south-east Poland varied between -18.1 and -20.0 °C. At 40% of stations across the study domain, the lowest average PET values were recorded during a cold spell in January 1987, with PET values varying from -28.0 °C in Chernivtsi to -12.7 °C in Yaremche. The longest or one of the longest spells in most stations (in 77% of stations across the study domain) was the cold spell of 2012 and characterized by mean PET values ranging from -25.4 °C in Rivne to -19.5 °C in Zakopane.

Occurrence and synoptic background of strong and very strong frost in spring and autumn in Central Europe.

The objective of the paper was the determination of the circulation conditions of occurrence of strong and very strong frost in Central Europe. A frost day was defined as a day with the minimum temperature lower than 0 °C and maximum temperature higher than 0 °C. Moreover, a division of frost was performed in terms of value of minimum temperature, resulting in the designation of mild frost (up to - 2.0 °C), moderate frost (from - 2.1 to - 4 °C), strong frost (from - 4.1 to - 6 °C) and very strong frost (< - 6 °C). The study was based on data from the years 1966-2015 from the Institute of Meteorology and Water Management-National Research Institute, Deutscher Wetterdienst and National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR). The analysis of baric conditions employed values of pressure at sea level, height of isobaric surface of 500 hPa and air temperature at a level of 850 hPa, as well as their anomalies. The spatial analysis showed that the number of frost days in spring and autumn increased from the west to the east of Central Europe. A decrease in the number of frost days, however, is observed over the prevailing area. Average conditions favouring the occurrence of strong and very strong frost both in spring and autumn were related to higher than average pressure at sea level over the prevailing area of the Euro-Atlantic sector. Such baric conditions caused advections of cool air masses from the northern sector.