夏季风活动与长江流域的旱涝

本文指出夏季风活动与我国主要雨区位置有对应的配合。中国大部分降水集中在夏季风时期对某一年来讲,虽然年或季的雨量可以接近正常,但这并不意味着全国降水都接近正常,有些地方多雨,有些地方少雨,甚至还有些地方遭受旱涝灾害。其次,作者对长江流域旱涝的高低空环流特征作了概括,发现夏季风活动与西太平洋副高及其脊的东、西移动有密切联系。特别是副热带环流及青藏高压和西太平洋副高之间的相互作用对长江流域旱涝起到重要作用。最后探讨季风形成的基本因子及其对夏季风活动的可能影响。

SUMMER MONSOON ACTIVITY AND THE DROUGHT OR FLOOD OF THE CHANG-JIANG RIVER

In this paper,an analysis is made firstly that the summer monsoon activity corresponds with the distribution of the main rain field in China, Rainfall here largely concentrates in the spell of summer monsoon. The total amount of annaul or seasonal rainfall may be close to normal for a particular year. But it does not mean that the rain fall in all parts of China will be approximate to normal, some parts may get more or less rain, whereas other places may suffer from drought or flood disasters.Secondly, the author summarized the characteristics of the upper and lower tro-pospheric circulation over the droughts and floods of the Chang-Jiang River, and found that there are close relationships between the summer monsoon activity and the position of the western pacific subtropical high, with its ridge stretching either westward or eastward.Particularly, the subtropical circulation and the interactions between the Tibetan high and the western Pacific high play an important role in drought or flood of the Chang-Jiang River.Finally, some fundamental factors in the formation of monsoou and its possible effects on the activity of summer monsoon are discussed. We have analyzed the climatic conditions in a period before the drought or flood, and found there are some fundamental factors influencing summer monsoon activity and the drought or flood in the Chang-Jiang River. For example the winter or spring monsoon circulations, the sea surface temperture in equatorial east Pacific ocean, the differential heating of the continent and ocean surface over Eastern Asia, the temperature variation of the Tibetan Plateau, the time of upper troposphere wind variation from westerlies to easterlies and so forth, do have a substantial influence on the onset of summer monsoon. These results.may be helpful for long-range forecasting of rainfall and the activity of summer monsoon.