極東における夏季のブロッキングの特性と形成,消滅過程に関する統計的研究

抄録

The purpose of this study is to clarify the characteristics of blockings appeared in summer over East Asia and the developement or the dissipation processes of the blockings from the view point of stationary Rossby wave propagation.
The latitudinal structure of zcnal mean flow at the 500 mb level in summer over Fast Asia during 1946-1985 are classified by means of principal component analysis to result in six types of circulation regimes (1A, 1B, 2A, 2B, 3A, 3B). Among these circulation regimes, two types of regimes, Type 1A and Type 3B, are obtained as blocking patterns. The former appears mainly in June and the first ten days of July and the latter in the middle and the last ten days of July and August (Fig. 2). The former has more strong persistency than the latter (Fig. 4), During the occurrence periods of both blockings, the anticyclone at surface lies over the Sea of Okhotsk and the temperature anomalies are markedly negative all around Japan (Fig. 5 and Fig. 6).
The transition probabilities between six types of circulation regimes are calculated. Those which have high transition probabilities are selected, and composite maps for the 500mb level isobaric heights are prepared taking by the circulation regime to appear at next pentad -into consideration. Differences between the composite maps are investigated and the character istic feature about the developement and the dissipation processes for Type IA and Type 3B blocking are found as follows.
Type 1A: In the developement stage of blocking, two Rossby wave trains begin to be seen remarkably. One is that which appears high (H) over Atlantic south-western Europe-low (L) over north-eastern Europe→H over the west of Tibet. Another is that which appears L over the east of Tibet→H over the east of Siberia. In the dissipation stage of blocking, the Rossby wave trains having a opposite mark to ones appeared in the developement stage begin to appear. It seems that such stationary Rossby wave propagation contributes largely to the blocking (Fig. 9 and Fig. 10).
Type 3B: In the developement stage, Rossby wave train which has its origin in the neighbourhood of Japan, is extended to North America (L near to Japan→H over Aleutian→L over Alaska). On the other hand, the appearance of Rossby wave train occurred from the neighbourhood of Oasipean Sea to Pacific Ocean seems to contribute to dissipation of the blocking (Fig. 11 and Fig.12)