A.B. Polonsky, P.A. Sukhonos
Institute of Natural and Technical Systems, Russian Federation, Sevastopol, Lenin St., 28
This article clarifies the manifestations of the main large-scale atmospheric processes, typical for the Atlantic–European sector, in winter air temperature anomalies in the Black Sea–Caspian region. The results are based on decomposition of NCEP 20CR V2c atmospheric reanalysis data for the period 1851–2014 by empirical orthogonal functions (EOF) and composite analysis.
The linear trend of air temperature in the studied region in December–January for the specified period is positive, but insignificant. The contribution of the linear trend dispersion to the total air temperature dispersion in the region as a whole does not exceed 3%.
Analysis of the main modes of air temperature variability after removing the linear trend showed the following. The first three leading EOFs describe ~96% of the total air temperature variability in December–January. Moreover, the first EOF mode accounts for more than 69% of the total variance. This EOF is a manifestation of the «East Atlantic – Western Russia» mode, which strongly correlates with the «North Sea – North Caspian» mode. The positive phase of this mode describes the development of anticyclonic blocking and is accompanied by a statistically significant cooling of the surface layer over most of the Black Sea region. The absolute value of the surface layer temperature anomalies over this region exceeds 1.5–2.0 °С. The second EOF for air temperature fluctuations in December–January is characterized by a spatial structure with opposite signs to the north and south of 45 °N. The contribution of this EOF to the total air temperature variability is about a quarter of the contribution of the first EOF. This EOF is due to the North Atlantic Oscillation. The temperature anomalies induced by it over most of the region do not exceed 1.0 °C. The third EOF for air temperature fluctuations in December–January corresponds to the Scandinavian pattern. However, its contribution to the overall variability of air temperature is small.
Keywords: surface air temperature, atmospheric indices, Black Sea–Caspian region.
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