The Analysis Of The Variations Of The East Asian Subtropical Westerly Jet From Early Summer To Midsummer And Its Anomalies

The variations of the East Asian subtropical westerly jet from early summer to midsummer are significant,which includes not only the northward jump phenomenon of jet but also the westward jump phenomenon of jet center.Using NCEP/NCAR reanalysis datasets,sea surface temperature datasets and precipitation datasets of China,the variations of the East Asian subtropical westerly jet from early summer to midsummer,the effect and reasons of the early or late occurrences of the East Asian Subtropical Westerly Jet variations on the circulation anomaly over East Asia are studied through statistical analysis and dynamic diagnosis.The main results are as followed:1.The jet over East China jump northward to the north area of 37.5°N and jet center move westward from the West Pacific to the Qinghai-Tibet Plateau from early summer to midsummer(at early July).The northward jump of the jet over East China and the westward jump of jet center from the West Pacific to the Qinghai-Tibet Plateau don't mostly take place simultaneously.The roles of the transient waves isn't same which is that dynamic forcing of the transient waves is favorable to the occurrences of the northward jump of jet and isn't favorable to the occurrences of the western movement of jet center and the heat forcing play promoting role in the occurrences of the northward jump of jet and in the occurrences of the western movement of jet center.2.The impacts of the northward jump of jets and the westward movement of East Asian westerly jet center on the rain belt moving northward are different which is that the northward jump of jets cause the rain belt north move from the Middle and Lower Reaches of the Yangtze River Area and the withdraw of Mei-yu season,whereas the westward movement of jet center have no corresponding relation of the withdraw of Mei-yu season.The earlier or later occurrence of the westward movement of jet center than the northward jump of jets effects the process of the rain belt moving northward which is that the rain belt move northward from middle-lower yangtze area to Huaihe River and then to area between yellow-river and Huaihe-river for the years that the dates of the westward movement of jet center is later than one of the northward jump of jets and from middle-lower yangtze area to area between yellow-river and Huaihe-river in other years because the earlier or later occurrence of the westward movement of jet center than the northward jump of jets cause the process of circulation variations which make the different process of the rain belt moving northward.3.The dates of the northward jump of jets and the westward movement of East Asian westerly jet center from early summer to midsummer exhibit preferable consistent annual variation,which is that the northward jump of jets and the westward movement of East Asian westerly jet center mostly both take place later and the northward jump of jets often take places early when the westward movement of East Asian westerly jet center take places early.There are closely positive correlation between the dates of the northward jump of jet and the precipitation in Middle-Lower Yangtze Area,positive correlation between the dates of the westward jump of jet center and the precipitation in the Huaihe River basin and negative correlation between the dates of the westward jump of jet center and the precipitation in North China and Ordos Region.When the northward jump of jets and the westward movement of East Asian westerly jet center from early summer to midsummer both take place early(later) the precipitation in Middle-Lower Yangtze Area and the Huaihe River basin is abnormal less(more) and in North China and Ordos Region is abnormal more(less),whereas when the northward jump of jets take place early and the westward movement of East Asian westerly jet center from early summer to midsummer don't take place early the precipitation in Middle-Lower Yangtze Area is abnormal less,in the Huaihe River basin is abnormal more and in North China and Ordos Region is abnormal less.There are closely negative correlation between the dates of the northward jump of jet and the latitude of jet in July,negative correlation between the dates of the westward jump of jet center and the strength of jet center over Qinghai-Tibet Plateau and positive correlation between the dates of the westward jump of jet center and the longitude of jet center over Qinghai-Tibet Plateau.So the precipitation of East China in July is not only closely related to the latitude of jet and but also the strength and longitude of jet center over Qinghai-Tibet Plateau in July.4.The anomaly dynamic forcing of the transient waves and anomaly heat forcing of earth surface have important influence on earlier or later occurrences of the East Asian Subtropical Westerly Jet from Early Summer to Midsummer.The dynamic forcing of the transient anomalies has a positive feedback to earlier or later occurrences of the jet northward jump and has a negative feedback to earlier or later occurrences of the western movement of jet center.There are closely negative correlation between the dates of the northward jump of jet and the surface temperature on Qinghai-Tibet Plateau and its east side,negative correlation between the dates of the westward jump of jet center and the surface temperature on Qinghai-Tibet Plateau and Northeast Asia.The anomalies of surface temperature cause anomalies of mean tropospheric temperature and then anomalies of upper zonal wind because wind field adapt to pressure field in large-scale atmospheric motion with the result of the early or late occurrence of jet variations.5.The previous strong influence signal of the dates of the northward jump of jets is northwest Pacific SST in the previous winter with positive correlation.The previous strong influence signals of the dates of the westward jump of jet center is northeast Pacific SST in the previous winter with closely positive correlation,another is the equatorial central and eastern Pacific SST(Nino3 area) in the previous winter with closely negative correlation.The probability of anomalous date of the westward jump of jet center is higher when SST of northern Pacific or Nino3 area in the previous winter is anomalous.