Atmospheric circulation conditions during winter warm spells in Central Europe

The objective of the paper was to characterise the temporal and spatial variability of winter warm spells in Central Europe in the years 1966/1967-2015/2016 and to determine the circulation conditions of their occurrence. The applied data were obtained from the Polish Institute of Meteorology and Water Management, Deutscher Wetterdienst and the National Centre for Environmental Prediction/National Centre for Atmospheric Research. A warm spell was defined as a sequence of at least three warm days, i.e. when the maximum air temperature is higher than the 95th percentile of the probability density function designated from observation. The research has proven that over the study period the air temperature increased in the winter season in Central Europe and this translated into an increase in the number of warm days. An average of 3-5 warm spells was recorded per 10 years. The most numerous warm spells occurred during three winter seasons, i.e. 1989/1990, 2006/2007 and 2015/2016. The occurrence of warm spells was related to positive anomalies of geopotential heights over the study area in the cross section of the entire troposphere. Maximum anomalies appeared at 250 hPa geopotential height, and they developed on average 9 days before the commencement of warm spells over the study area

Patterns in the multiannual course of growing season in Central Europe since the end of the 19th century

The research identified patterns in the multiannual course of start and end dates, and length of growing sea son (GS) in Central Europe since the end of the 19th century in selected cities of Central Europe in the period 1893-2020. GS start in the analysed stations was characterised by high year-to-year variability, particularly in those located more southwards, i.e. in Prague and Vienna. A smaller variability occurred in GS end dates. The GS was subject to prolon gation, although these changes in particular cities were uneven and had different causes. In Toruń and Potsdam, its increase was caused by a greater shift of the end date, and in the remaining stations, it was determined by its earlier start date. Two subperiods were distinguished that differ in terms of intensity of changes of the start and end dates, as well as the length of the GS. The intensification was observed recently

Warm winter and cold summer spells in Spitsbergen and their circulation conditions

The objective of the study was to determine multi-annual changes and variability of occurrence of cold spells in summer and warm spells in winter on Spitsbergen in the period 1976–2016, and circulation conditions of their occurrence. Cold days in summer were defined as days with mean daily air temperature lower than temperature corresponding to the 10th percentile from daily temperature, and warm days in winter as days with mean daily air temperature exceeding the 90th percentile from daily air temperature. The research showed a statistically significant increase in mean air temperature, the rate of which in winter was more than four times higher than in summer. The observed warming translated into a decrease in the number of cold days in summer (-2.5 days/10 years in Svalbard Lufthavn and -1.3 days/10 years in Ny-Ålesund) and an increase in the number of warm days in winter (2.7 days/10 years in Svalbard Lufthavn and 2.4 days/10 years in Ny-Ålesund), and warm and cold spells related to the frequency of such days. The rate of the changes was higher in Svalbard Lufthavn than in Ny-Ålesund. The occurrence of cold days and cold spells was particularly related to the advection of air masses from the north-western sector. The occurrence of warm days and warm spells was related to the advection of air masses from the south-west

Thermal conditions relative to atmospheric circulation in the Christmas period in Poland

The main objective of this article was to determine thermal conditions in the Christmas period and the impact of atmospheric circulation on their formation. The article is based on data on the mean daily air temperature for 16 stations in Poland for the 1966–2014 multiannual period. In this period, no statistically signifcant changes of air tem- perature were observed, neither in December, nor the Christmas period. The occurrence of averagely warmer holidays was associated with the infow of maritime polar air masses from the western sector, while colder holidays occurred with the infow of continental polar air masses from the eastern sector

Cold Waves in Poznań (Poland) and Thermal Conditions in the City during Selected Cold Waves

The objective of the paper was to characterize the occurrence of cold days and cold waves in Poznań in the years 1966/67–2015/16, as well as to characterize thermal conditions in the city during selected cold waves in the years 2008/09–2015/16. The study was based on daily data on maximum and minimum air temperature for station Poznań-Ławica from the years 1966/67–2015/16 and daily air temperature values from eight measurement points located in the territory of the city in different types of land use from the years 2008/08–2015/16. In addition, to characterize thermal conditions during selected days forming cold waves, satellite images were used, on the basis of which the land surface temperature (LST) was calculated. A cold day was defined as a day with daily maximum temperature (Tmax) below the value of 5th annual percentile of Tmax, and a cold wave was defined as at least five consecutive cold days. The study showed an increase in Tmax in winter, which translated to a decrease in the number of cold days over the last 50 years, although the changes were not statistically significant. Thermal conditions in the city showed high variability in the winter season and during the analyzed cold waves

Atmospheric circulation during heat waves in Eastern Europe

This article aims to describe heat waves in Eastern Europe and to determine the synoptic situations which cause them. In this article, a hot day is defined as the one with a maximum temperature above the 95th percentile of all the values in the analysed period, and a heat wave is considered as a sequence of at least 5 such days. In the analysed period and within the investigated area, from 24 (Kaliningrad) to 55 (Kharkiv) heat waves were observed. The longest heat wave was recorded in Moscow in 2010, lasting as many as 45 days. In the analysed period, an increase in frequency and length of heat waves was observed within the analysed area. The occurrence of heat waves was connected with a high pressure system located over the eastern part of the continent, during which positive anomalies of sea level pressure and the 500 hPa geopotential height as well as positive T850 anomalies were recorded.12114

Impact of atmospheric circulation on the occurrence of very strong and extreme cold stress in Poland

The primary objective of the study was the determination of the spatial and multiannual variability of occurrence of days with very strong and extreme cold stress in Poland according to the Universal Thermal Climate Index (UTCI), as well as determination of baric conditions favouring their occurrence. The study was based on data from the years 1966/67 to 2018/19 from the Institute of Meteorology and Water Management – National Research Institute and National Centre for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR). The research showed a statistically significant decrease in the number of days with very strong and extreme cold stress on half of the analysed stations, and a slight tendency or no changes on the remaining stations. The occurrence of days with extreme cold stress in Poland, as revealed by the analysis was primarily related to the presence of high-pressure systems blocking zonal circulation. The study resulted in the designation of three circulation types, i.e. two types related to anticyclonic systems and one cyclonic type

Anomalies in the length of the growing season in Poland in the period 1966–2015

The purpose of the study was to determine the anomalous length of growing seasons, the frequency of their occurrence, and to determine the temporal and spatial changes of their frequency in Poland in the period 1966–2015. The analyses used daily average air temperature values for 30 stations located in Poland from years 1966–2015 (Fig. 1). The data was provided by the Institute of Meteorology and Water Management - National Research Institute. The growing season was defined as the period with average daily air temperature ≥5 °C. The start and end dates of the growing season were determined using the mathematical formulas proposed by R. Gumiński (1948). In the period 1966–2015 in Poland, anomalously short growing seasons occurred sporadically and covered the largest area of Poland in 1997. Short growing seasons were more frequent in the first three decades of the analyzed multi-year period, and long growing seasons were characterized by higher frequency in the second half of the surveyed period. Anomalously long growing seasons before 1990 occurred sporadically and only in individual stations. Anomalously short growing seasons occurred only in the middle eastern part of Poland, while anomalously long ones covered most of the country

PERIOD OF INTENSE VEGETATION IN POLAND IN THE YEARS 1966–2015

The purpose of this paper was to determine long-range and spatial variability of the start and end dates of a period of intense vegetation in Poland in 1966–2015. The article is based on average monthly air temperature values acquired for 20 Polish stations for 1966–2015, made available by the Institute of Meteorology and Water Management – the National Research Institute. Based on the obtained data, the dates of the beginning and end of the intense vegetation period were determined. In this study, the intense vegetation period was defined as one with an average daily air temperature ≥10°C. The mathematical formulas proposed by Gumiński (1948) were used to determine the dates of the beginning and end of the period. A period of intense vegetation in Poland in the years 1966–2015 has extended. The dates of the beginning of the period of intense vegetation changed in the latitudinal system from the south to the north while the intensity of changes in the date of the beginning in the studied area was characterized by longitudinal distribution – the most prominent in the west of Poland. The end of the intense vegetation period occurs earliest in the north-east of Poland, and latest in the west and the south. The end date changes were less significant than the start date changes. The length of the intense vegetation period ranges from the north-east to the south-west of Poland, and the most dramatic changes occurred in the west and the south-east of Poland