| In this paper, The activity characters of the East Asian summer monsoon which have significant effects to weather and climate in China and the different time scales change of West Pacific subtropical high which is the one of main members consist of the East Asian summer monsoon system were researched using the NCEP/NCAR Reanalysis data, the daily precipitation data in 743 meteorological stations over China since the station established and atmospheric circulation data,The objective was to further reveal and understand the activity rhythm of the key factors influenced the retreat of rain belt in flood season and precipitation anomalies. These rhythms can be used to provide the scientific ideas and methods and improve the climate prediction level in flood season in China. In addition, the research of the regional climate change and its impact and assessment in Jiangsu area not only will help to enrich and improve the content of national climate change assessment but also provide scientific reference to government and public about how to deal with climate change. The main results obtained are as follows:1) The pentad-averaged west ridge point of West Pacific subtropical high which is considered an index describing the activities of subtropical high which position is very consistent with the climate rain belt of East Asian summer monsoon. The West Pacific subtropical high shows slowly northward advancing and obvious contraction in the period of northward advancing and eastward shrink (May.1-Sep.5) and the characteristics of stage is distinct,which have 3 relatively stable stages include the stage from the mid-May to the mid-Jun,the stage from the mid-Jun to the early Jul and the stage from mid-Jul to the early Sep; the period of southward retreat and westward movement shows the character of fast southward retreat and have 2 westward period:the period from Sep.11 to Seq.25 and the period from Oct.6 to Oct 20.2) The three stable stages of West Pacific subtropical high northward advancing are correspond to the three stages of East Asian summer monsoon northward.On average, when the west ridge point of West Pacific subtropical high sharp shrink to the Philippines northeast offshore and maintain relative stability, the five provinces include Guangdong, Guangxi, Fujian and Taiwan and Hainan in south China enter the pre-flooding season; when the west ridge point maintain in the Taiwan Strait, the Yangtze River and Huaihe River valleys and southeastern part of the northwest China enter rainy season, when the west ridge point again sharp shrink and stabilize to the southern island offshore in Japan, the north, northeast and northwest China into north rainy period; the two obvious west stretch time in the period of subtropical high southward retreat(from Seq,l to Seq,15 and Oct,6 to Oct,20) respectively led to the autumn rainy season in southeastern part of northwest and west China3) The monsoonal rainy seasons are divided according to criterion of the pentad-average precipitation relative coefficient greater than 1.5 and the precipitation duration and so on, the eastern rainy seasons consist of several adjacent monsoon rains period and local rain which length, rainfall intensity, the causes and relative importance are different. The eastern part of Northwest China's rainy season usually include Meiyu rainy season, northern rainy season and autumn rainy season, but these three sections of the composition of precipitation intensity is weak, with the drought period in summer in the rainy seasons. The rainy rainfall give priority to the total rainfall in the central and south of Shanxi and the rainfall bases on the northern rainy rainfall in Lanzhou and Yinchuan,while all these there rainy periods have equally important contribution in Tianshui, while the other three sections of Tianshui rain period is equally important. The rainfall is more relatively in spring and summer but which does not come to the monsoon standard in north piedmont of Tianshan Mountain in Xingjiang and west region in southern Xingjiang.4) The interdecadal variation of the intensity index of West Pacific subtropical high at 500hPa is very consistent with that of the west ridge point position of West Pacific subtropical high. The subtropical high has an obvious trend of strengthening and moving westward in recent 30 years. Before 1978, the intensity index of subtropical high was weaker and its position of west ridge point located east to the normal with small anormaly value, but the situation was contrary after 1978. Both of the period intensity index of subtropical high exhibits oscillation periods of 6-8 years and 18-20 years. The distribution of dry in Northern China while wet in Southern China and autumn rainfall in Northwest China decreased in recent 30 years are related to the interdecadal variation which the intensity of West Pacific subtropical high is strenthened and its position is westerly advancement together with the weakening East Asian summer monsoon.5) The average temperature of Jiangsu shows the increasing tendency in recent 50 years, and the southern average increasing rate of warming is higher than the jianghuai region and southern Huai River, where the whole province's temperature shows significant warming in spring and winter in whole province.The changes of average annual precipitation is relatively stable in which the amplitude of variation in jianghuai basin and southern Jiangsu is relatively large in 90's but steady in recent years, while the amplitude of variation in huaibei region is relatively large from beginning to end especially in recent decades, the precipitation shows the trend of increasing.6) In recent years, the disastrous weather days such as extreme heavy precipitation, strong convection, heat wave and cold wave, fog, freezing rain become more and stronger, The history records have been repeatedly broken, the incidence of extreme weather events arise increasingly, the meteorological disasters and its derivative disasters triggered by extreme weather shows the features of out-burst, multiple, intensity and disastrous influence.7) The future (2010-2039 year) climate changes in Jiangsu for three emission scenarios (SRES A2, A1B, B1) are projected by RegCM3 nested within the NCAR_CCSM3 AGCM. The results show that, the annual averaged temperature will rise mostly in the whole area for all three emission scenarios, in which temperature rising will be most distinct for B1 scenario, then less for A1B, and the least for A2. But for precipitation appear obviously different changes among three emission scenarios, in which precipitation will have an increasing tendency in northern area while a decreasing tendency in southern area for A1B, a decreasing tendency in most part of area for B1 scenario and an increasing tendency in most part of area for A2 scenario. Furthermore, the precipitation displays conspicuous variations in spring and summer for all three emission scenarios, but the changes are not evident in autumn and winter. |
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