长江下游酷暑与冷夏的分析

ANALYSIS OF THE SWELTERING AND COLD SUMMER AT THE LOWER REACHES OF THE CHANGJIANG RIVER

长江下游的酷暑与冷夏是旱涝以外的另一种重要灾害性天气,本文以南京为代表,确定了长江下游酷暑年和冷夏年的三条标准。盛夏(7—8月)温度主要决定于7月平均温度T,并与副热带高压和中高纬度的冷空气活动以及印度季风低压—ITCZ有关。在酷暑年,印度低压更为频繁而强烈,位置略偏南;副热带高压较强,且直接控制江淮流域。100hPa青藏高压明显偏强,位置偏北偏东;青藏高原上常有500hPa暖中心东移。冷夏年三种成因:一是冷空气较强,梅雨明显而持久;二是ITCZ和热带系统强而活跃,盛夏频繁影响长江流域;三是以上两种天气系统的影响,形成混合型冷夏。

Sweltering and cold summer at the lower reaches of the Changjiang River is another im-portant disastrous weather phenamenon in addition to drought-waterlogging. In this paper, Nanjing is taken as a representative station to define three criteria of sweltering year and cold summer year at the lower reaches of the Changjiang River. Temperature in mid-summer (July桝ugust) mainly depends on temperature in July. It closely relates to the subtropical high, cold air activity at middle-higher latitude and Indian monsoon depression ITCZ. In sweltering year, the Indian depression is more frequent and stronger with rather south position; the subtropical high is stronger and directly predominates on the Changjiang-Huaihe Rivers; the Tibetan anticyclone at lOOhPa is obviously stronger with a position rather north and east; and usually some SOOhPa warm centers move eastward from Tibefan Plateau. The amospheric circulation feature in cold summer year is just opposite to it. There are three kinds of forma-tion causes for cold summer year. Firstly, cold air is rather strong with a significant and sust-ained Mei-yu. Secondly, ITCZ and tropical weather systems are strong and active, they frequ-ently give impact on the Changjiang River. The third is the mixed type. There is only one cause of sweltering summer which is the direct predomination of subtropical high.