资源环境科技发展态势分析平台

This paper presents the results of an investigation of the variability in macro-circulation forms at the mid-tropospheric level distinguished in the Vangengeim-Girs (V-G) classification. The number of days and of uninterrupted periods of at least 2days (so-called episodes) with V-G forms were analysed based on the daily atmospheric circulation catalogue for the period 1949-2010. The average number of circulation episodes per year (51) and their average persistence (6-9 days) were determined. When analysing the short-term variability, the frequency of transitions between macroforms: W <-> E, E <-> C and W <-> C was calculated. It was found that these sequences were random in character. Changes in average frequencies of V-G macroforms in an annual cycle were evaluated and the seasons of dominant zonal (W) and meridional (E, C) circulation patterns distinguished. In the years 1949-2010, four circulation epochs were separated, differing in the macroform frequency quotients-fW/fE, fW/fC and fE/fC. Three epochs were meridional (until 1988) and the last one is zonal. A growing trend was observed in the number of circulation episodes, indicating an increase in the frequency of changes of circulation forms. This rise was attributed to the growing frequency of the W episodes and the decreasing number and persistence of E episodes in the last two decades of the analysed period.