Study On The Variation And Mechanism Of Precipitation In Summer In Anhui

As one of China's major grain-producing areas,Anhui Province located in the juncture of the temperate zone with a semi-humid monsoon and subtropical monsoon,with frequent warm and cold air masses,variable weather and precipitation which often resulting in drought,flood and other natural disasters.For the large mountainous area and the sudden and centralized precipitation,Anhui Province suffers serious mountain torrents and soil and water loss.Consequently,it has a significantly guide to reasonably program on agricultural production,disaster prevention and reduction and addressing climate change by studying on the inter-decadal variation,spatial distribution characteristics and forming mechanism of summer precipitation in Anhui under the background of climate warming.In this paper,meteorological data(including precipitation data of 23 meteorological stations in Anhui Province,74 global atmospheric circulation indices collected by National Climate Center and NCEP/NCAR(National Centers for Environmental Prediction/National Center for Atmospheric Research)reanalysis data from 1972-2012)was adopted to study the forming mechanism of summer precipitation anomaly by means of liner trend,binomial moving average,Morlet wavelet analysis,EOF(Empirical Orthogonal Function),REOF(Rotated Empirical Orthogonal Function),correlation analysis and SVD(Singular Value Decomposition)from the perspective of the West Pacific subtropical high and the atmospheric circulation.The results showed:(1)The summer precipitation in Anhui distinctly showed the annual and decade variations exists.In the past 42 years,the summer precipitation generally represented an increasing trend,about 19.1mm per decade.But this increasing trend is not significant.In the late70's,the mid 80's,the mid 90's,the first 5 years of the 21 st century and in the early80's,the late 80's,after the mid 90's,from2005 to 2012 correspond to the less precipitation years and the more precipitation years,respectively.The interannual variation periods of the summer precipitation in Anhui showed 2~4 year and inter-decadal variation peridos showed 11~12 year and 22~25 year.(2)In addition,the summer precipitation in Anhui also showed the critical regionalism.The distribution of the summer precipitation in the whole area represented a gradual decreasing from the south to the north.As the climate getting warm,an increasing trend of precipitation was showed in the places of Huaibei,including Lixin,Fuyang,Dangshan,the south of Huangshan Mountain,Tunxi and Wuhu while the precipitation in the Jianghuai area including Changfeng and Tongcheng showed a decreasing trend.The(3)three main types of the summer the summer precipitation in Anhui are the characteristics of spatial consistency,adverse variation trend in north and south and variation trend in Huaibei,Huainan and Jianghuai.And the characteristics of spatial consistency showed the summer precipitation of Anhui increases in positive abnormal years and vice verse.The characteristics of adverse variation trend in north and south showed the summer precipitation in the south of Anhui increases while that in the north of Anhui decreases in positive abnormal years and vice verse.The last one is the characteristics of variation trend in Huaibei,Jianghuai and Huainan showed that the summer precipitation in the area of Huaibei and Huainan increases while that in Jianghuai decreases in negative abnormal years.(4)The latitudinal displacement of the West Pacific subtropical high in summer is an important factor that influences the summer precipitation in Anhui.In June,the position of subtropical high ride is partial to south,the western ridge point is partial to east,the subtropical high area is relative smaller and the subtropical high strength is relative weakened.When the 500 hpa height field rising from Taiwan Island to the East China Sea Area,near the area of 30°N,115°-145°E,the summer precipitation in Anhui is getting less in the same time and vice verse.In July,the position of subtropical high ride is partial to north,the western ridge point is partial to west,the subtropical high area is relative larger and the subtropical high strength is relative stronger.When the height field rising in the key area to the south of 30°N,the height field falling in the areas including from Yellow River basin to Korean Peninsula,Yellow Sea and Bohai Bay basin,from Japan Sea to eastern ocean of Japan Island,the summer precipitation in Anhui Province except Dangshan is getting more and vice verse.In August,the position of subtropical high ride is partial to north,the western ridge point is partial to east.When the 500 hpa height field in the areas of the West Pacific subtropical high rising,the 500 hpa height field falling in the areas including eastern ocean of Philippines,from Mongolia to the south of Siberia and from the eastern Siberia to Okhotsk Sea,the summer precipitation is decreasing and vice verse.In terms of the entire summer,the position of subtropical high ridge is located at 25°N?It's partial to north and south when compared to June and August respectively.The West ridge point position is located at 135°E.Compared to July,it's partial to east.When the 500 hpa height field rising in the areas from South China Sea to Philippines and its eastern ocean,the summer precipitation in the most areas of Anhui,excerpt for Dangshan,is increasing and vice verse.(5)The situation of atmospheric circulation in the abundant precipitation years and lacking precipitation years varied greatly.In the abundant precipitation years,high pressure appeared in the areas near Okhotsk Sea and Ural Mountain and the height field represented negative-positive-negative abnormal distribution from high to low latitudes that helped warm and cold air masses intersection.The position of subtropical high ride is partial to south,the western ridge point is partial to west,the subtropical high area is relative larger and the subtropical high strength is relative stronger.The Summer Monsoon Circulation in the tropical of East Asia is weakened,Meiyu Forntal Zone Circulation in Janghuai is enhanced which caused warm and humid air converging and ascending in lower troposphere and stimulated heavy summer precipitation in Anhui.But in the lacking precipitation years,the height field fall in the middle and high latitudes that is not conducive the north cold masses to south down.The position of subtropical high ride is partial to north,the western ridge point is partial to east,the subtropical high area is relative smaller and the subtropical high strength is relative enhanced.The Summer Monsoon Circulation in the tropical of East Asia is weaken,Meiyu Forntal Zone Circulation in Janghuai is weakened which caused cold air divergence and sinking down.Furthermore,the 's center intensity of the westerly jet stream over the Eurasian Continent and the West Pacific Ocean increases which results in the precipitation decreasing.