南海至西太平洋一带夏季低空越赤道气流和季风的初步研究

本文对南海至西太平洋一带夏季低空越赤道气流的情况和西南季风的来源,进行了初步研究。发现:(1)就气候平均而言,东非低空急流的影响范围,包括印度南部、孟加拉湾南部直到中南半岛南部和南海南部。在这一范围内,夏季月平均西南季风强度的年际变化十分一致;(2)夏季在中南半岛南部、南海南部,西南季风的主要来源是上游印度、孟加拉湾地区,直接来自南半球的气流比重不大。而热带西北太平洋的西南季风,则主要来自南半球;(3)在110-140°E 的赤道地区,并不存在一支主要的越赤道气流;(4)在150°E 附近的新几内亚东岸,有一条越赤道气流的通道。热带西北太平洋的西南季风,主要就是这支越赤道气流转向而成(但似乎要求这支气流的南风分量强度超过某一下限,即存在一阈值,才能对西北太平洋的西南季风变化有影响)。新几内亚岛上的山脉,对南半球东南信风的阻挡,是形成这支越赤道气流的重要原因之一;(5)大致在15°N 以南的南亚至西北太平洋地区,其西南季风主要由二支气流构成:一支在非洲东岸附近越过赤道,成为东非低空急流,经印度南部,往下游一直影响到南海南部;另一支在新几内亚东岸附近越过赤道,转向成西南气流影响西北太平洋。

A PRELIMINARY STUDY ON THE LOW-LEVEL CROSS-EQUATORIAL AIR FLOW AND THE SUMMER MONSOON FROM SOUTH CHINA SEA TO THE WEST PACIFIC

Based on data of July and August for years 1974-1977,the general circulation in the equatorial regions from south China Sea to the West Pacific is studied. It is found that, so far as the climatological average is concerned, the East African low-level jet can influence the south parts of India, Bay of Bengal, Indo-China, and South China Sea. In this regions, the interannual changes of monthly mean intensity of southwest monsoon are consistent with each other. There is a channel of cross-equatorial flow located at about 15°E near the east coast of New Guinea, while in the area of 110-140°E equator there is no strong and consistent southerly cross-equatorial flow. To the east of New Guinea, the air from Southern Hemisphere crosses the equator and turns to southwesterly flow blowing in the Nerthwestern Pacific. The topographical influence of the high mountains in New Guinea is the important cause of the excistence of this cross-equatorial flow. Tt is found that the southwest monsoon in the southern parts of Indo-China and South China Sea mainly comes from southern India and Bay of Bengal, it does not directly comes from the Southern Hemisphere.But the southwest monsoon in tropical Nerthwestern Pacific comes directly from Southern Hemisphere. The intensity of the southerly component of cross-equatorial flow near the east coast of New Guinea closely relates to the intensity of the southwest monsoon in the tropical Nerthwestern Pacific. Hence, the southwest monsoon to the south about 15°N from Southern Asia to Nerthwestern Pacific consists of two branches of air flow, one is the East African low-level jet, which flows from southern India to South China Sea, and the other comes from the Southern Hemisphere crossing equator near 150°E.