Exceptional thermal anomalies in the Atlantic-European area of the sub-polar zone

Bibliogr. s. 104-105. Józef Twardosz podpisany: Robert Twardosz

Opracowanie oparto na wartościach średnich miesięcznych temperatury powietrza z 17 stacji meteorologicznych od Wybrzeży Grenlandii do Nowej Ziemi z 60-lecia 1951-2010. Do badań przyjęto stacje, w których temperatura średnia wieloletnia w najcieplejszym miesiącu, tj. w lipcu, nie przekracza 12°C. Za anomalne uznano te miesiące, w których temperatura różniła się od średniej wieloletniej przynajmniej o 2 odchylenia standardowe. Zbadano przebieg roczny występowania miesięcy o anomalii ujemnej (niezwykle zimnych) i dodatniej (nie-zwykle ciepłych) oraz tendencji zmian ich częstości w 60-leciu, a także rozkład przestrzenny najbardziej rozległych anomalii. Stwierdzono, że w ciągu 60 lat były 132 miesiące niezwykle zimne i 127 miesięcy niezwykle ciepłych. Najwięcej miesięcy niezwykle zimnych (41) i najmniej niezwykle ciepłych (11) było w 10-leciu 1961-1970; najmniej miesięcy niezwykle zimnych (3) i najwięcej niezwykle ciepłych (57) było w 10-leciu 2001-2010. Wzrost częstości miesięcy ciepłych zaznaczył się głównie w zachodniej części badanego obszaru

The study is based on average monthly temperature data from 17 weather stations located along a belt between the Greenland coast and the island of Novaya Zemlya and recorded during the period 1951-2010. The stations were selected to meet the criterion of a maximum long-term average temperature of 12°C for the warmest month, i.e. July. The anomalous month was defined as having an average temperature different from the long-term average by at least 2 standard deviations. Both positive (exceptionally warm) and negative (exceptionally cold) anomalies were analysed, as well as their trends of frequency change during the study period and the spatial distribution of the cases with the largest geographical spread. However, a majority of the anomalous months of each type were only recorded at single stations or at two neighbouring stations (of those included in the study), which would suggest spatially limited or even strictly local factors effecting such an exceptional temperature increase or drop. Exceptionally cold months (ECM) were more frequent than their warm counterparts (EWM), had a greater spatial extent and the scale of their anomaly tended to be larger (i.e. down to -12°C compared to maximum +10°C for EWMs). ECMs were more often linked in two-month or three-month series (31 such series), while multiple EWM series were fewer (18), but longer, lasting up to 6 months. The highest numbers of anomalous months were recorded during the decade 1961-1970 (41 ECM and 11 EWM) and the lowest numbers in the decade 2001-2010 (3 ECM and 57 EWM). The increase in the warm month activity was largely limited to the western end of the study area. The annual pattern of anomalous months was far more defined in the eastern section of the area, along the coast of a vast continent, than in the maritime west. This clear definition of the eastern pattern was mainly down to the frequency of ECMs and their large spatial extent. In the western section of the area the distribution of ECMs and EWMs is more balanced with a recent maximum of EWM frequency located in Iceland. ECMs coincide with the advection of cold air masses from the north and northeast, while EWMs tend to occur in association with southern warm advections.