Abstract
Investigation of extreme thermal conditions is important from the perspective of global warming. Therefore, this study has been undertaken in order to determine the frequency, timing and spatial extent of extremely cold months in winter time at 60 weather stations across Europe over a sixty-year period from 1951 to 2010. Extremely cold months (ECMs) are defined as months in which the average air temperature is lower than the corresponding multi-annual average by at least 2 standard deviations. Half of all the ECMs occurred in the years 1951–1970 (33 out of 67). The lowest number of ECMs was recorded in the decade 1991–2000, but since the beginning of the 21st century, their density and territorial extent has started to increase again. The extremely cold months with ECMs of the greatest spatial extent, covering at least one third of the stations (over 20 stations), included: February 1954 (22), February 1956 (36), January 1963 (25), and January 1987 (23 stations).
Highlights
Winter weather conditions, including air temperature, over the European land mass are determined by the North Atlantic Oscillation
The study is based on average monthly values of air temperature in the years 1951-2010 recorded at 60 weather stations on the European continent and the British Isles (Table 1)
In the years 1951-2010, 387 cases of extremely cold months (ECMs) were recorded across the 60 stations in Europe, which occurred during 67 months of the 60-year period
Summary
Winter weather conditions, including air temperature, over the European land mass are determined by the North Atlantic Oscillation. The positive phase of the NAO, relatively warm air from over the Atlantic flows in over Europe, whereas during its negative phase there is advection of cold, often freezing, Arctic air from the north or continental polar air from the east (Hirschi and Sinha 2007, Cattiaux et al 2010, Wang et al 2010, Ouzeau et al 2011, Buchan et al 2014) Longer spells of such advection, which are usually caused by the build-up of high-pressure blocking systems, lead to periods with anomalously low air temperatures in various parts of the continent (e.g., Kossowska-Cezak 1997, Jaagus 2006, Bardin 2007, Isayev and Sherstyukov 2008, Sidorenkov and Orlov 2008, Ugryumov and Khar’kova 2008, Van den Besselaar et al 2010). Literature includes other studies on the topic, e.g., Baur (1954), Graham et al (2006), Hirschi and Sinha (2007), Hirschi (2008), Cattiaux et al (2010), Wang et al (2010), Ouzeau et al (2011), and Buchan et al (2014), yet they concern different areas of Europe and different periods
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