【作者】 董丽娜；

【导师】 郭品文；

【作者基本信息】 南京信息工程大学 ， 气象学， 2009， 博士

【摘要】 东亚副热带西风急流由初夏至盛夏存在显著的变化,不仅存在急流北跳现象,急流中心还存在显著的西移现象。本文通过统计分析和动力诊断,利用NCEP/NCAR再分析资料、海温资料和中国降水资料对初夏至盛夏急流变化及其发生早晚对东亚气候的影响和成因进行了分析。主要结论如下:1.初夏至盛夏(7月初)我国东部地区急流北跳至37.5°N以北,急流中心由西太平洋地区西移至青藏高原地区,且急流北跳和急流中心西移不同时发生偏多。瞬变波在初夏至盛夏急流北跳和急流中心西移过程中作用有所不同,瞬变波的动力强迫作用有利于急流北跳的发生,却不利于急流中心西移的发生;热力强迫则对急流北跳和急流中心西移均有推动作用。2.初夏至盛夏急流北跳和急流中心西移对我国雨带北移影响不同。急流北跳与我国长江中下游梅雨结束密切相关,而急流中心西移与梅雨结束关系不大。但急流中心西移相对于急流北跳发生的早晚对雨带北移过程有重要影响,在急流中心西移早于急流北跳和二者同时发生年份,雨带从长江中下游地区直接推进至黄淮地区:在急流中心西移晚于急流北跳发生年份,雨带北移过程为长江中下游地区—淮河流域—黄淮地区。这是因为急流中心西移相对于急流北跳发生早晚不同,引起大气环流调整过程不同,从而雨带北推进程也不同。3.初夏至盛夏急流北跳时间和急流中心西移时间的年际变化具有比较好的一致性,急流中心西移偏晚和急流北跳偏晚常同时发生,急流中心西移偏早时急流北跳常偏早。初夏至盛夏急流北跳时间和急流中心西移时间与7月我国东部降水异常相关显著,急流北跳时间与7月长江中下游地区降水异常正相关,急流中心西移时间则与7月淮河流域降水异常正相关,与华北和河套地区降水异常负相关。当二者均发生偏早(晚)时,长江中下游地区至淮河地区降水异常偏少(多),华北和河套地区降水异常偏多(少);在急流北跳早而急流中心西移不偏早年份,长江中下游地区降水偏少,而淮河流域降水偏多,华北和河套地区降水偏少。而急流北跳时间与7月东亚急流纬度位置负相关,急流中心西移时间与7月青藏高原急流中心强度负相关,与经度位置正相关。可见,7月我国东部降水异常不仅与急流南北位置密切相关,与急流中心强度和经度位置也密切相关。4.急流北跳和急流中心西移发生早晚与大气内部瞬变扰动异常和下垫面热力异常密切相关。瞬变波异常的动力强迫作用对于急流北跳早晚异常的发生具有正反馈作用,对于急流中心西移早晚异常的发生具有负反馈作用;急流北跳时间与六月末至七月初青藏高原东部及其东侧地区地表温度的异常负相关,急流中心西移时间与青藏高原和东北亚地表温度的异常负相关,六月末至七月初地表温度异常引起上空对流层平均温度异常,大尺度运动风场向气压场适应,引起高空纬向风异常,从而影响急流突变的早晚。5.急流北跳发生时间年际变化的前期强影响信号为前期冬季西北太平洋海温,与急流北跳时间正相关;急流中心西移发生时间年际变化的前期强影响信号为前期冬季与急流中心西移时间正相关的东北太平洋海温和与急流中心西移时间负相关的赤道中东太平洋Nino3区海温,当前期冬季北太平洋海温和Nino3区海温中有一个发生异常,急流中心西移发生时间发生异常的概率很大。更多还原

【Abstract】 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.更多还原