Termiczne pory roku w Poznaniu w drugiej połowie xx wieku

Thermal seasons in Poznań in the second half of the 20th century

Summary: Amongst studies devoted to the seasonal structure of the climate, works concerned with the issue of seasons distinguished on the basis of thermal criteria prevail. The authors of existing studies devoted to this issue have identified from 6 to 10 thermal seasons occurring in the territory of Poland. The first division of the annual thermal cycle into 6 periods was proposed by E. Romer (1904, 1949). The present study has also adopted the aforementioned division of the year into 6 thermal seasons. The author has carried out an analysis of the start and end dates of individual thermal seasons and their durations for individual years of the period 1951-2000. According to the adopted thermal "threshold" values, winter is a period in which the average daily air temperature is below 00C, early spring - a period when this temperature ranges from 0 to 50C, spring - a period when the average daily temperature ranges from 5 to 150C, summer - when it exceeds 150C, autumn - when this temperature ranges from 15 to 50C, and forewinter - a period when the average daily temperature ranges from 5 to 00C. Average monthly temperatures, which are commonly used to determine the beginning and end dates of thermal seasons, may be analysed using the graphical or computational method. The first of these methods consists in the reading of dates of attainment of a given thermal threshold from a histogram, while the computational method usually utilises R. Gumiński's formula (Gumiński 1950; Piotrowicz 2000). In the present study, the author used histograms plotted separately for each year to determine the beginning and end dates of the aforementioned thermal seasons in Poznań. Average decade temperatures were taken into consideration. Due to the relative by short research period, a review of the values of selected parameters describing the thermal seasons in Poznań in the second half of the 20th century permits us only to indicate shorter or longer series of years in which the duration of specific seasons or the commencement dates thereof differed considerably from average values typical of the entire half century. These deviations are, in the opinion of the author, a normal phenomenon and can hardly be considered an indication of a change in climatic relations. The very short series of data constituting the basis of the present study does not provide us with material premises for the formulation of other conclusions. Thus, the author has limited the analysis of thermal seasons solely to a numerical and graphical presentation of certain facts relating to the issue of the commencement dates and duration thereof, treating these parameters as one of the features describing contemporary climatic relations occurring in the Poznań region.

Trepińska J., Olecki Z. (red.), 2006, Klimatyczne aspekty środowiska geograficznego, IGiGP UJ, Kraków, s. 117-126.

Instytut Geografii i Gospodarki Przestrzennej UJ

ISBN 83-88424-16-5

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