1988年8月广东省罕见异常天气的分析

本文分析讨论了1988年8月广东省出现异常天气的主要原因,并在此基础上提出一些可能成为此种反常天气预报线索的相关因子或前期征兆。结论认为,该月没有灾害性热带气旋影响广东,但同时却又出现较长的连阴雨天气,其主要原因是由于东亚大气环流出现异常——中纬西风带和西太平洋副热带高压脊均比常年偏南近十个纬度所造成。在这种类似于春末夏初的大尺度环流形势控制下,热带西北太平洋(包括南海)的局地条件不利于灾害性热带气旋形成,而更东面的海区生成的灾害性热带气旋则全部偏北行或转向;另一方面,季风雨带的位置比常年偏南得多,落在华南。 上述环流系统和天气的异常,与赤道东太平洋海温异常有一定关系,且海温变化超前。该年4—7月东亚西风环流指数的变化也提供了若干前兆。综合考察这些因素,有可能预先对这种环流和天气的异常作出定性的估计。

ANALYSIS ON THE UNCOMMON ABNORMAL WEATHER EVENTS OVER GUANGDONG IN AUGUST 1988

In this paper, the main factors responsible for the occurrence of abnormal weather events over Guangdong province in August 1988 was analysed and discussed, and several correlation factors or precursors which might be considered as the predictors of such abnormality were suggested. The conclusions are as follows.The main cause for no damage-producing tropical cyclone ravaging Guangdong but a long period of rainy days and excess rainfall stil happened there was due to the anomalous atmospheric circulation over East Asia, i. e. , the position of both the mid-latitude westerlies and the western Pacific subtropical high pressure situated far southward (near 10 degrees latitude) from their normal. Under the influence of such a large-scale atmospheric circulation which resembled to the situation of deep spring or early summer, the local conditions around the western North Pacific and the Sorth China Sea were unfavorable for any development of tropical disturbance, whereas all those damage-producing tropical cyclones developed over eastern waters tended to take northward or recurving paths. On the other hand, the position of the monsoon rain band appeared on South China, much southward from its average.It was found that above-mentioned unusual atmospheric circulation systems and weather events were closely related to the anomalous SST of the equatorial eastern Pacific (SSTA), and the SSTA varied in precession. Furthermore, the variation of westerly circulation index over East Asia from April to July provided some precursors as well.. By investigating into these factors it is believed possible to make a qualitative pre-diagnosis on such kinds of atmospheric circulation and weather events.