Climatic changes in Estonia during the second half of the 20th century in relationship with changes in large-scale atmospheric circulation |
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| Authors: | J Jaagus |
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| Institution: | (1) Department of Geography, University of Tartu, Estonia |
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| Abstract: | Summary Trends in the time series of air temperature, precipitation, snow cover duration and onset of climatic seasons at ten stations
in Estonia during 1951–2000 are analysed. Using the conditional Mann-Kendall test, these trends are compared with trends in
the characteristics of large-scale atmospheric circulation: the NAO and AO indices, frequency of circulation forms according
to the Vangengeim-Girs’ classification, and the northern hemisphere teleconnection indices. The objective of the study is
to estimate the influence of trends in circulation on climate changes in Estonia. Statistically significant increasing trends
in air temperature are detected in January, February, March, April and May, in winter (DJF), spring (MAM) and in the cold
period (NDJFM). The trends in precipitation, as a rule, differ from station to station. Increasing trends are present during
the cold half-year – from October until March – and also in June. Snow cover duration has decreased in Estonia by 17–20 days
inland and by 21–36 days on the coast. The onsets of early spring and spring have shifted to an earlier date. Some important
changes have occurred in the parameters of atmospheric circulation during 1951–2000. Intensity of zonal circulation, i.e.
westerlies, has increased during the cold period, especially in February and March. Results of the conditional Mann-Kendall
test indicate that the intensification of westerlies in winter is significantly related to climate changes in winter and also
in spring. A negative trend in the East Atlantic Jet (EJ) index, i.e. the weakening of the westerlies in May has caused warming
during that month. Decrease in northerly circulation, i.e. in frequency of circulation form C and in East Atlantic/West Russia
teleconnection index (EW) is related to an increase in precipitation in October. |
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