Concurrent Variation Between The East Asian Polar-front Jet And Subtropical Jet In Winter And Its Association With The Temperature And Rainfall In China

By using NCEP/NCAR reanalysis dataset and observed daily temperature dataset at stations in China, the temperature and rainfall during the winter cold air activities are examined in terms of the concurrent intensity variation between the East Asian polar-front jet (EAPJ) and the subtropical jet (EASJ). The regional averages of300hPa wind over two domains (45°N-60°N,70°E-110°E) and (27.5°N-37.5°N,130°E-160°E), respectively, were used to measure the strength of the East Asian polar-front jet and subtropical jet. Based on the jet intensity changes, four situations were classified, in which strong EAPJ corresponds to strong EASJ, weak EAPJ to weak EASJ, strong EAPJ to weak EASJ, weak EAPJ to strong EASJ. Then, the features of winter cold air activities were analyzed from the aspects of cold air intensity, route, duration, origin and the strength and area of the rainfall in terms of the two jet intensity changes. The conclusions are as follows:(1) It is found that during SS situation, relatively weak cold air activities with short duration intrude into the inland and costal region of Northeast China from inner Mongolia. The genesis of the cold air could be traced back to the east of Novaya Zemlya. Rainfall area moves from south China to Southeast coast, with less rainfall to the south of the Yangtze river. During WW situation, strong cold air activities with long duration intrude into most part of China from Northern Xinjiang. The genesis of the cold air could be traced back to the west of Lake Balkhash. Rainfall area stabilized in the Yangtze River Basin, with significantly positive anomalies. During SW situation, relatively strong cold air activities with short duration intrude into north China from northeast. The temperature drop is not obvious in south China. The genesis of the cold air could be traced back to western Siberia. Rainfall area move north from the southeast China, but is mainly in the south of the Yangtze river, and less rainfall takes place in the north of the lower reaches of the Yangtze River and the south of the middle and upper reaches of it. During WS situation, relatively weak cold air activities intrude from Inner Mongolia, affecting almost the whole eastern China. The genesis of cold air could be traced back to the west of Lake Baikal. Rainfall area is located in the south of the Yangtze River, with less rainfall to the north and more rainfall to the south of the Yangtze River. In addition, we analyzed circulation features corresponding to the different jet intensity changes. During WW situation, the Siberian High is relatively strong, and the Aleutian low is weak, and the East Asian trough is relatively deep, and northerly wind in eastern China is strong, horizontal wind strengthen north of50°N. During WS situation, the Siberian High is relatively strong, and the Aleutian low is strong, and the East Asian trough is deep, but northerly wind in eastern China is weak. During another two situations (WS and SW), the Siberian High is relatively weak, and the East Asian trough is not deep, and northerly wind in eastern China is weak, horizontal wind weaken north of50°N.(2) At the monthly time scale, during SS situation, anomalous cooling appears in Northeast China, concurrent with a warming outside this region, and rainfall is reduced in Jianghuai region and South China. During WW situation, cold temperature anomalies are seen from northern Xinjiang all the way to South China, with the temperature in other regions being higher than normal. more rainfall appears to the north of Yangtze river and in South China and less rainfall takes place in the lower reach of Yangtze river. During SW situation, anomalous warming exits in most parts of China and rainfall pattern resembles that under the WW condition. During WS situation, cold anomalies in temperature overlie most parts of China, except for Northeast China and Southern Xinjiang. Rainfall is reinforced in South China and the southern part of Jianghuai area, while it is less to the north of Yangtze river. Lagged correlation analysis shows that during SS situation, the temperature significantly increases within the whole China and rainfall in enhanced to the south of Yangtze river. During WW situation, significant warm temperature anomalies are located in Northern Xinjiang, and meanwhile a cold anomaly is present in the Southeast China. For precipitation,it tends to be less to the south side area of the Yangtze river. During SW situation, negative temperature anomalies appears in Northern Xinjiang, whereas positive anomalies exist to the east of105°E. For precipitation, there are positive anomalies along the coast and negative anomalies in Guangxi, Hunan, and Guizhou provinces. During SW situation, significant negative (positive) temperature anomalies are seen in the coast region of South China (Southern Xinjiang and Northeast China). For precipitation, more rainfall tends to emerge under this situation.In addition, through an analysis of two events of cold air activity in the2012-2013winter, it was found that the conclusion is consistent with that of the climatological analysis.