Relationships Between Summer South Asia High And Both Atmospheric Circulation In Northern Hemisphere And Precipitation Over China

Based on NCEP/NCAR reanalysis monthly height and wind data, using statistical and composite analysis, the relationships between summer South Asia High (SAH) in June, July and August and both atmospheric circulation in the Northern Hemisphere and precipitation over China are studied in this paper.(1) Summer South Asia High is a strong circulation system in northern hemisphere, which covers northern Arabia Peninsula, Iran Plateau, Tibetan Plateau, eastern China and western Pacific Ocean. In addition, South Asia High has a significant effect on the deepening and weakening of troughs and ridges on the westerly on the high latitude in northern hemisphere.(2) According to the number and position of SAH center, summer SAH in June, July and August is parted to different types respectively. In June, SAH is divided into three types, which are single center type, double center and multiple center type. Center of single center type mainly locates in the northern Indo China Peninsula and eastern Qinghai-Tibet Plateau, and SAH is weaker and its position is westward, besides, East Asian trough and North America trough deepened considerably, while position of south subtropical high locates southerly and intensity is weaker; Centers of double center type is located in the south of Iran Plateau and Qinghai-Tibet Plateau respectively, when SAH develops stronger, and North American trough deepens obviously, but troughs in western Europe and east Asia weaken; Centers of multiple center type distribute widely, when SAH develops the strongest and its position tends slightly eastward, and North America and Western Europe troughs deepen, while East Asia trough become weaker, and subtropical high moves westward and develops stronger. SAH in July and August are all divided into four types of single center type, double center type I, double center type II and multiple center type. In July, center of single type is located in the southern Iranian Plateau and Qinghai-Tibet Plateau, and its intensity is the weakest and its position stays westward, when East Asia trough, Western Europe trough and North America trough all deepen, and subtropical high is weaker; Centers of Double center type I are located in southern Iran plateau and Qinghai-Tibet Plateau, and SAH develops stronger and its position moves slightly eastward, when East Asia trough and Lake Baikal trough all abate, at the same time, troughs in Western Europe and North America weaken, and the subtropical high develops stronger; Centers of Double center type Ⅱ locate in Qinghai-Tibet Plateau and the western Pacific, and SAH develops the strongest, and polar vortex splits into two centers to North America, and East Asian trough significantly weakens, but western Europe and North America troughs deepen significantly, and the subtropical high develops stronger; SAH of multiple center type is weaker, when East Asia trough moves northward, and North America trough abates, troughs of central Europe and near Lake Baikal deepen. In August, center of single type locates over the Tibetan Plateau, and its intensity is the weakest, four troughs in the mid-latitude westerlies deepen significantly; Centers of double center type I are located in the southern Iranian plateau and Tibetan Plateau respectively, and SAH develops stronger than single center type, and polar vortex extends to North America, so North America trough deepens, and Western Europe and East Asian trough weaken significantly, and subtropical high develops stronger; Centers of double center type Ⅱ are located in Tibetan Plateau and its west and the western Pacific, and SAH crosses throughout the South Asia, besides, Western Europe and North America big troughs deepen considerably, and the East Asian trough is significantly weakened; Centers of multiple center type locate more on the western Pacific, and SAH and subtropical high develop stronger, East Asian trough and North America trough weaken significantly.(3) The intraseasonal variation of longitude location of Summer South Asia High has significant relationship with precipitation over China. According to the longitude position of centers of different types of SAH, the relationships between SAH in June, July and August and precipitation over China are studied respectively. In June, when SAH shows the western type, Yunnan-Guizhou plateau, south China and north region of northeast China are in wet, and west China, north of the Yangtze river and most region of southern northeast China are in dry; When SAH shows the east type, north of the Yangtze river basin and its north, south of the Yellow River, north of Xinjiang province and most region of northeast China are in wet, while most region of south China, southwest and west basin are in dry. In July, when SAH shows the west type, southern China, the Yellow River basin and its north are in wet, while west China, south of Yellow River and north of the Yangtze river are in dry; When it shows intermediate type, Yangtze river area, the Yellow River area, qaidam basin and northeast China are in wet, while most region of the north of the Yellow River, Hetao area, Xinjiang and southwest China are in dry; When it shows the east Type, north and northeast China and in most region of northwest China are in wet, while the Yangtze river basin and its south area are in dry significantly. In August, when SAH shows the west type, north of the Yellow River area, south of the Yangtze river and northeast China are in wet, while the west basin and north of the Yellow River region are in dry; When SAH shows the east type, the south of the Yangtze river region, north of the Yellow River and northwest China are in wet, while south of the Yangtze river, north of the Yellow River, north of the Tibetan Plateau and northeast China are in dry.