Joanna Wibig

Abstract

The daily minimum and maximum temperatures at seven Polish stations were used in ananalysis of the occurrence of heatwaves in the years 1951-2006. Heatwaves were defi ned as days withtemperatures exceeding selected thresholds (tmax ≥25°C, tmax ≥30°C, tmin ≥18°C). The mean length ofa wave of very warm days lasts from 2-4 days, the longest no fewer than 23 days. Waves comprising hotdays and nights are shorter. The frequencies of very warm and hot days and hot nights increased in theanalyzed period, especially its second half (1979-2006). The occurrence of heatwaves characteristicallylinks up with high-pressure systems over Central Europe, along with associated blocking episodes.

Keywords: extreme temperatures, Sen’s slope, Lund classifi cation, composite method, Poland

Joanna Wibig, Department of Meteorology and Climatology, Faculty of Biology and Earth Science, University of Lodz Lipowa 81, 90-568 Łódź, Poland
Agnieszka Podstawczyńska, Department of Meteorology and Climatology, University of Łódź Narutowicza 88, 90-139 Łódź, Poland
Marcin Rzepa, Department of Meteorology and Climatology, University of Łódź Narutowicza 88, 90-139 Łódź, Poland
Piotr Piotrowski, Department of Meteorology and Climatology, University of Łódź Narutowicza 88, 90-139 Łódź, Poland

Abstract

The daily minimum and maximum temperatures at nine stations in Poland were used in ananalysis of the occurrence of coldwaves, where these are defi ned as days with temperatures exceedingselected thresholds (tmin ≤ -20°C, tmin ≤ -15°C and tmax ≤ -10°C) in the period 1951-2006. Cold nightsoccurred more often than very cold days and nights but the mean lengths of waves of cold nights weresimilar – lasting a little more than 2 days on average. The frequencies of extremely cold days revealeda slight, but statistically non-signifi cant downward trend. The occurrence of coldwaves was associatedwith high-pressure systems over Central Europe and with blocking episodes, but it was always linkedwith a thick layer of cold air.

Keywords: extremely low temperature, trend, Sen’s slope, least squares method, Poland

Joanna Wibig, Department of Meteorology and Climatology, Faculty of Biology and Earth Science, University of Lodz Lipowa 81, 90-568 Łódź, Poland
Agnieszka Podstawczyńska, Department of Meteorology and Climatology, University of Łódź Narutowicza 88, 90-139 Łódź, Poland
Marcin Rzepa, Department of Meteorology and Climatology, University of Łódź Narutowicza 88, 90-139 Łódź, Poland
Piotr Piotrowski, Department of Meteorology and Climatology, University of Łódź Narutowicza 88, 90-139 Łódź, Poland

Krzysztof Kożuchowski [kkozuchowski1@wp.pl], Department of Environment Dynamics and Bioclimatology, University of Łódź, Lipowa 81, 90-568 Łódź, Poland
Joanna Wibig, Department of Meteorology and Climatology, Faculty of Biology and Earth Science, University of Lodz Lipowa 81, 90-568 Łódź, Poland

Abstract

The study details the results of a search for changes in the annual rhythms for atmospheric pressure, air temperature and precipitation in Poland in the 19th and 20th cen-turies. In regard to atmospheric pressure, a reduction in the component amplitude of the annual cycle was noted. Values for annual amplitude of temperature exhibited a downward trend, as did data for the lengths of the seasons with temperatures below zero or in excess of 19°C. In turn, there was an upward trend for the duration of periods with temperatures several degrees above freezing or in the range 14-19°C. The most marked long-term upward trend to temperature was that noted for the five days 11-15 January, which have seen temperatures rise by as much as 4°C in the last decade. Annual courses for precipitation have demonstrated development of the half-year cyclical component responsible for relatively high winter pre-cipitation. Analysis of several time series has allowed for the deducing of decreasing con-tinentality of climate in Poland, a marked warming in the winter-spring period and a general weakening of seasonal contrasts regarding the climate.

Keywords: changes in air temperature and precipitation

Krzysztof Kożuchowski [kkozuchowski1@wp.pl], Department of Environment Dynamics and Bioclimatology, University of Łódź, Lipowa 81, 90-568 Łódź, Poland
Jan Degirmendżić, Department of Environmental Dynamics and Bioclimatology, Faculty of Biology and Earth Science, University of Lodz Lipowa 81, 90-568 Łódź, Poland
Krzysztof Fortuniak [krzysztof.fortuniak@geo.uni.lodz.pl], Zakład Meteorologii i Klimatologii, Uniwersytet Łódzki, Lipowa 81, 90-568 Łódź, Poland
Joanna Wibig, Department of Meteorology and Climatology, Faculty of Biology and Earth Science, University of Lodz Lipowa 81, 90-568 Łódź, Poland