AIR TEMPERATURE VARIABILITY OVER THE WESTERN AREAS OF RUSSIA AND ADJACENT COUNTRIES IN THE 20TH CENTURY

M. Yu. Bardin

The structure of large-scale air temperature variability over the western part of the former USSR (20–80°E) in winter and summer periods has been investigated. The main trends in interdecadal temperature variability have been analyzed, and similarities and dissimilarities with Northern Hemisphere temperature in the late 19th–early 20th century have been found: a pronounced interdecadal variability, a general warming trend, especially noticeable after 1970, and lack of temperature maximums in the 1940s for most of the territory under consideration. Variance and trend estimates have been obtained (for the periods from 1886 and from 1970) for nine large areas. The first two EOFs of temperature have been analyzed: the first EOF both in summer and in winter represents oscillations of mean temperature for the region considered, the second EOF in winter describes the “north–south” oscillation and in summer the “west–east” oscillation. The first two EOFs account for 82.3% of total variance in winter and 74.5% in summer. Spectral properties of temperature series have been studied using ordinary fast Fourier transformation, wavelet transform, and singular spectrum analysis. A quasi-biennial temperature oscillation component (a period of about 2.5 years) is shown to be typical of both seasons. The first principal component (PC) of mean temperature in the region exhibits a pronounced oscillation in winter with a period of about 10 years, while the second PC in winter has a 20-year period. It is shown that in analyzing trend in mean temperature of the region, the inclusion of a natural 10-year oscillation considerably increases its statistical significance; in particular, the trend formally insignificant against the background of natural variability for the period from 1970 becomes significant at the 2.5% level.