Geographia Polonica (2013) vol. 86, iss. 4

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The occurrence of atmospheric thaw in Poland over the last 50 years

Małgorzata Czarnecka, Jadwiga Nidzgorska-Lencewicz

Geographia Polonica (2013) vol. 86, iss. 4, pp. 327-361
doi: https://doi.org/10.7163/GPol.2013.27

Abstract

The study is concerned with the temporal and spatial characterisation of atmospheric thaw variability in Poland. The phenomenon was described on the basis of mean daily values of air temperature for the winter months October-March over the period 1960/61-2009/10 obtained from 34 meteorological stations of the Institute of Meteorology and Water Management (IMGW). It has been shown that atmospheric thaws occur on average as soon as 10 days after the firstinstance of a decrease in temperature below 0ºC lasting at least 3 days. Atmospheric thaws are a constant element ofthe climate in Poland and occur with a frequency of 30-45% of the calendar winter (December-February) and 30% toalmost 50% of the period of the thermic winter, that is the period between the date of the first decrease of mean daily airtemperature below 0ºC with a duration of at least three days and the date of its permanent increase above 0ºC. Thaws are most common in the western part of Poland, particularly in the north-west, which, despite having the latest on set of the first thaws, is characterised by a high proportion of winter thaws of a length of 30 days and more. The spatial distribution of thaw is strongly dependent on longitude and less on height above sea level. Multiyear variability of thawdays is determined by atmospheric circulation. In the whole country (apart from the mountains) the correlation betweenthe frequency of thaw occurrence in January, February, and March and the Jones NAO index is statistically significantat a significance level of α=0.01, and coefficients of determination fluctuate in general from 40 to 50% in January andFebruary, and from 20 to 25% in March. The role of circulation expressed by NAO index in the explanation of the variability of thaw occurrence was statistically insignificant

Keywords: atmospheric thaws, thaw periods ≥ 10, 20, 30 days, thaw-start and thaw-end date, temporal variability, spatial distribution, NAO index

Małgorzata Czarnecka, West Pomeranian University of Technology Department of Meteorology and Climatology Papieża Pawła VI 3A, 71-459 Szczecin: Poland
Jadwiga Nidzgorska-Lencewicz, West Pomeranian University of Technology Department of Meteorology and Climatology Papieża Pawła VI 3A, 71-459 Szczecin: Poland