Occurrence of winter atmospheric circulation regimes in Euro-Atlantic region and associated extreme weather anomalies in the Northern Hemisphere
B.A. Babanov1, V.A. Semenov1,2, M.G. Akperov1, I.I. Mokhov1,3, N.S. Keenlyside4
1A.M. Obukhov Institute of Atmospheric Physics Russian Academy of Sciences, Moscow, Russia
2Institute of Geography RAS, Moscow, Russia
3Lomonosov Moscow State University, Moscow, Russia
4Geophysical Institute, University of Bergen, Bergen, Norway
Keywords: atmospheric circulation, weather regimes, cluster analysis, weather anomalies, North-Atlantic Oscillation, Euro-Atlantics
Abstract
Quantitative estimates of regional features of the frequency distribution of extreme temperature, precipitation, and wind anomalies in the winter months in the extratropical zone of the Northern Hemisphere associated with atmospheric circulation regimes in the Euro-Atlantic sector are obtained. Using the k-means cluster analysis for the daily geopotential height fields from the ERA5 reanalysis for 1979-2021 four winter atmospheric circulation regimes are identified in the Euro-Atlantic sector corresponding to the North Atlantic Oscillation (NAO) in the positive (NAO+) and negative (NAO-) phases, Scandinavian blocking (SCAND), and regime with anomalously high pressure over the North Atlantic and low pressure over Europe (ATL). Characteristic fields and frequencies of occurrence of the regimes are analyzed. The NAO+ and NAO- regimes turned out to be asymmetric in the spatial structure with significantly different frequencies of occurrence (33% and 19%, respectively). Spatial distributions of the frequencies of occurrence of extreme weather anomalies associated with the regimes are also asymmetric. For all regimes, an asymmetric frequency of occurrence of positive and negative temperature anomalies is noted. During the period under study, no statistically significant trends in the seasonal frequency of the regimes and no large areas with statistically significant trends in the average seasonal fields of the regimes near the areas of geopotential height anomalies maxima are found, which can indicate the stability of these regimes under recent climate changes.
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