摘要
本文根据1951—1955年五年高空和地面的资料,对夏季过程进行了分析,得到下面几点结果:1.在东亚地区的四个主要经度带上以65°,120°和140°经度带的500毫巴强西风中心的位置和强度变化,对东亚自然天气季节的划分是最良好的指标。东经65°经度带上南边低纬度强西风的消失是梅雨期开始前的征兆。东经140°经度带上强西风在北纬40°以南消失时是夏季开始的征兆。和它相关联的过程是东亚高空大槽的消失和太平洋副热带高压带北移至30°—40°纬度带间,这个期间平均是在7月13日左右,也是江南梅雨结束的时候。故梅雨是夏季以前的盛行过程,它和500毫巴强西风区或锋区是有密切的联系的。2.东经140°经度带上500毫巴强西风在北纬30°—40°重现时,是夏季结束秋季开始的征兆,和它相关连的天气过程是在该经度带上高空大槽重新建立,地面大陆冷高压从新地岛东部向东南下达华北地区。这个时间平均是在9月5日左右。故东亚夏季的长度平均仅55日。3.从500毫巴强西风在各经度带上出现的情况来看,一般是西部比东部消失得早,出现得迟,不如冬季那样先在上游首先建立,在春夏之交这种相反的演变,似非地形的分支可以解释的。4.在夏季自然天气季节所出现的盛行天气过程主要是表现在太平洋副热带高压随上游气压场的不同,及其和同纬度上的西藏高原的相对位置的不同至少有四种不同的情况。
The synoptic process on 500mb over Asiatic natural synoptic region have been analized for 5 summers.The results are given below:1.The variation of the position and strength of the maximum westerly wind belt at 500mb surface along four meridians 65°E,105°E,120°E,140°E gives a good index in determing the natural synoptic seasons over Eastern Asiatic synoptic natural region.The disappearence of the low latitude westerly wind maximum along 65°E is the first indication of the beginning of Bai-U period.When the westerlies wind maximum belt to the south of 40°N completely disappears along 140°E summer begins.This is accompanied with the filling of the Asiatic main trough over Japan and the Northward shiff of the Pacific subtropical high pressure belt from low latitudes to 30°-40°N.The mean date on which summer begins is nearly on 13th,July.It is also the end of Bai-U over middle Yangtze river.Thence the synoptic process in Bai-U period is the prevailing process before summer season.The precipitation in this period is closely related to the strength of the maximum wind belt i.e.socalled frontal zone.2.When the 600mb maximum westerly wind belt appears again at 30°-40°N along 140°E,begins author.The synoptic process,which associates with it,is the reestablishment of the Asiatic main trough over Japan.And the surface cold continental high comes down to North China from the east of Novaya Zemlya Island.The average time of the arrival of Autumn is nearly on 5th,September.Hence the duration of summer is on the average only 55 days.8.According to the analysis of the time variation of maximum westerlies on 30°-40°N along each of the four meridians,the westerly maximum generally disappears earlier in west than in east but establishes later in west than in east during autumn.The phenomeanon that the maximum westerly first generates in the east during autumn can hardly be explained by the splitting of the jet stream.4.From the analysis,the prevailing process of the natural summer season largely depends upon the variations in the upper westerlies over Ural region and the west-east relative position of the Pacific subtropical high with respect to the Tibet plateau.
作者
刘匡南
邬鸿勋
LIU KWANG-NAN;WU HUNG-SHUN(Institute of Meteorology and Geophysics)
出处
《气象学报》
1956年第3期219-242,共24页
Acta Meteorologica Sinica
