南中國海對流雲簇研究

A Study of Cloud Clusters over the South China Sea

曾憲瑗(H. Y. Tseng) ； 童茂祥(M. S. Tung)

《大氣科學》 15卷1期 (1987/03) Pp. 103-112

摘要

南中國海地區全年中，在不同季風期間於不同之部分區域，皆有影響航空及航海安全之對流雲簇出現。經由不同季風期間之對流雲簇變化分析，得知在西南季風期前及西南季風期後內，對流雲簇出現之位置以間熱帶輻合區之相關最為密切。西南季風期間，則視季風環流是處於活躍期或不活躍期而定，且兩者又與季風槽線相位變化關係密切。當季風槽線出現在20°N附近屬季風活躍期，有利於本區大部分地點的對流雲發生，反之槽線在7°N以南則僅南端有對流雲，屬不活躍期。再者槽線相位變化與西藏高原500 hPa溫度變化亦息息相關，即高原增溫時為季風活躍期，降溫則為不活躍期。但本區內有颱風或熱帶氣旋接近時，活躍的季風環流反變為高原降溫期。冬季東北季風期內對流雲簇之生成，係以東北氣流是否能在赤道處形成低壓而定。此外，高層200 hPa氣流場形態，亦與赤道區對流雲簇的發生有直接相關。

並列摘要

All the year round there are convective cloud clusters in the South China Sea. More specifically, convective clusters are present in certain portions of the area in different monsoon periods. These clusters have important influences on the safely of both air and sea navigations.Seasonal changes of these cloud clusters are analyzed, and the results are as follows:1. Within the pre-monsoon and post-monsoon periods, convective cloud clusters are dominant in the ITCZ.2. Within the SW-monsoon period, the general circulation can further be divided into Active period and Inactive period depending upon the phase change of the monsoon trough.i. Active monsoon period-the monsoon trough is situated at 20°N, it is liable to have convective cloud clusters in most portions of the area.ii. Inactive monsoon period-the monsoon trough is situated to the south of 7°N, and only some clusters may be present at the edge of the areaThe phase change of the monsoon trough has close relation to the temperature change of 500 hPa over the Plateau of Tibet. In other words, when the plateau is heated it is in the Active monsoon period. When the plateau is cooled, it is in the Inactive monsoon period. Nevertheless, when a typhoon or tropical cyclone approaches the area, it is in the active monsoon period but the plateau is cooling.3. Within the NE-monsoon period of winter time, convective clusters are present only when there is a Low forming around the equator. In addition, whether there are convective cloud clusters near the equator has direct relation to the moisture at 200 hPa above the Plateau of Tibet.