Abstract
This work presents the influence of atmospheric circulation on the occurrence of dry and wet periods in the central Polish region of Kujawy. The material on which the authors relied encompassed monthly totals of precipitation obtained from 10 weather stations in the period 1954–2018. Both dry and wet periods have been identified on the basis of monthly values of the Standardised Precipitation Index (SPI). Additionally, the calendar of circulation types over Central Poland was used to determine the atmospheric circulation indices: western (W), southern (S) and cyclonicity (C). The analyses have indicated that the region concerned experiences low precipitation totals in comparison with the rest of Poland. According to the circulation indices W, S and C, for Central Poland, the air mass advection from the West prevails over that from the East. Moreover, a slightly more frequent inflow of air from the South than from the North has been observed. The frequency of anticyclonic situations is higher than that of the cyclonic types in this part of Europe. Drought spells occurred in the study area at a clear dominance of anticyclonic circulation, with the inflow of air mostly from the North and with increased westerly circulation. On the other hand, the occurrence of wet periods was mainly influenced by cyclonic circulation during the advection of the masses from the South and West. Dry and wet periods accounted for 28% and 27% of the study period, respectively.
Highlights
The observed changeability in the occurrence of dry and wet periods results from atmospheric circulation which tends to favour either continental or oceanic influences, shaping the climate both globally and locally (Twardosz et al 2011)
Polish researchers often rely on the calendar of circulation types for southern Poland (Niedźwiedź 1981, 2017), which has been repeatedly applied to assess the influence of atmospheric circulation on precipitation in this part of the country (e.g. Niedźwiedź et al 2009; Twardosz 2009, 2010; Twardosz and Niedźwiedź 2001; Twardosz et al 2011)
The annual precipitation averaged in Kujawy was 524 mm in the years 1954–2018
Summary
The observed changeability in the occurrence of dry and wet periods results from atmospheric circulation which tends to favour either continental or oceanic influences, shaping the climate both globally and locally (Twardosz et al 2011). For the area of Poland, one can distinguish indices put forward by, e.g., Lityński (1969), Ustrnul (1997) and Niedźwiedź (2000) Those by Niedźwiedź (2000) are a modified version of the method suggested by Murray and Lewis (1966). They were used to study the long-term variability of atmospheric circulation and to assess its impact on the temporal and spatial changeability of selected meteorological elements in Poland (e.g. Niedźwiedź 2000; Falarz 2007; Niedźwiedź et al 2009) and in the Arctic (e.g. Araźny 2008; Niedźwiedź 2013b; Niedźwiedź and Łupikasza 2015)
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