The statistical analysis of atmospheric blocking in the Northern Hemisphere
Based on the data of the.daily 500hPa in the Northern Hemisphere from 1,971 to 1988, the blocking.activities along 60°N is statistically analysed. The results show that the frequency of blocking activities in the latitu- dinal variation is characterized by four wave patterns and the position of the maximum wave peak is at the 20°W. The seasonal variation of blocking in the region of eastern Atlantic, central Pacific and from East-European to Urals is the most obvious. The blocking activities can be divided into three patterns, eastward and westward mobile, and stationary. The probability of the stationary blocking accounts for 55.1%. It is predominant in summer. On the cantrary, the blocking of the mobile pattern is predominant in autumn and winter. Its average living period is 11,5 days. The long-range variations of blocking in all regions show the period of quasi-biennial osciallation.