与长江流域旱涝相联系的全球低频环流场

THE CHARACTERS OF LOW FREQUENCY CIRCULATION AROUND THE GLOBE AND ITS RELATIONSHIP WITH THE FLOOD/DROUGH IN THE CHANGJIANG RIVER VALLEY

通过对梅雨前后低频风场和速度势场的分析，发现全球低频风场不仅在长江流域的旱年（１９８１、１９８５、１９８８）及涝年（１９８０、１９８３）表现出显著的不同，而且在同一年的夏季降水变化的不同位相中也表现出明显相反的环流分布。着眼于１９８０、１９８８两年，我们发现这种不同与低频速度势场的波动有关。１９８０年降水与东亚季风区内低频振荡的北传以及南半球高纬的涡旋列不断东移相联系。而１９８８年降水变化则是与源于热带太平洋中部的小低频涡旋北进发展有密切的关系。对于影响降水变化的机制，我们认为１９８０年的情况可能与全球冷热源分布以及沃克环流的低频变化有关。

In this paper, a concret analysis was made on the characters of the low frequency wind and velocity potential fields around the time of Meiyu. It is found that remarkable distinct circulation patterns in the low frequency wind fields around the globe not only exist in the drought (1981,1985,1988) and flood (1980,1983) years,but also exist in the stages of the drought (or flood) years when precipitation is increasing or decreasing. Concentrating on the years of 1980 and 1988,we find that it is caused by the wave in the low frequency velocity potential fields which connect the precipitation in the Changjiang River valley with the low frequency wind fields around the globe.In the year of 1980,precipitation responds quite well to the northward propagation of LFO in the East Asia monsoon region and the vortex train propagating eastward in the high latitudes of Southern Hemisphere. In the year of 1988,variation of precipitation was closely rela ted with the movement of the low frequency vortex which originates from the small low frequency vortex in the east of the tropical Pacific. It is thought that heat/cold source pattern and Wal ker circulation can be the mechanism which affects the precipitation, while the mechanism in 1988 remains to be discussed.