【作者】 孙晓娟；

【导师】 王盘兴； 汪学良；

【作者基本信息】 南京信息工程大学 ， 气象学， 2013， 博士

【摘要】 大气活动中心(ACA)是月平均海平面气压(SLP)场中全年或季节地出现在特定地理区域的巨大高压、低压系统,ACA的季节变化决定区域气候的季节变化,它们的异常及遥联与大气环流和区域气候异常关系密切,故它们也是大气环流异常与短期气候预测的重要研究对象。本文用Hadley研究中心160年(1850～2009年)月平均SLP场资料,确定了北半球ACA成员及性质。对冬季北半球的5个ACA,定义了物理意义清晰的环流指数(面积S、强度P、中心位置λc、φc),并完成了它们的计算,初步分析了它们的气候及异常特征。在此基础上,研究了ACA的气候效应,ACA的遥联,ACA异常及遥联与大气热机热源热汇异常的关系,取得了对冬季北半球ACA的较系统和较深入的认识。论文的主要结论是：1)用可靠资料论证了北半球存在6个ACA,它们是北大西洋上的冰岛低压(LI)、北大西洋高压(HA),北太平洋上的阿留申低压(LA)、北太平洋高压(HP)和亚洲大陆上的蒙古高亚(HM)、印度低压(LIN)。其中,冬半年位于高纬的LI.HM、LA和夏半年位于低纬的LIN是半永久性ACA；全年位于低纬大洋上的HA和HP是永久性ACA,或准永久性ACA(冬季弱)。2)按统一的定义和计算方法、用可靠的资料算出了1850-2009年冬季北半球5个ACA(LI、HA、HM、LA、HP)的季、月环流指数(S、P、λc、φc)160年序列。用它们中具有独立性的三个环流指数(P、λc、φc)定量地分析了ACA的气候及异常特征,论证了其自身的合理性,从而为大气环流异常及短期气候预测研究,提供了一套有应用价值的环流指数。3)冬季北半球ACA均对所在地及周边一定区域的气候及异常有显著的、符合天气动力学意义的影响。其中,海洋上ACA对气候的影响范围远大于陆上ACA,ACA强度异常对气候的影响大于位置异常的影响,ACA异常对气温的影响大于对降水的影响。北大西洋上的LI.HA对气候异常的影响在分布区域及影响性质两方面均十分相似,而北太平洋上的LA.HP对气候异常影响的性质则近于相反。影响中国冬季气候及异常的ACA主要是HM, HM强年,全国(除西南地区外)冬季气温偏低、四川和华北局部地区降水偏多；其次是位于上游的LI、HA的影响,LI、HA强年,我国‘三北’部分地区气温偏高；LA、HP对中国气候异常的影响相对弱。4)北半球冬季5个ACA间存在3对强显著遥联：LI～HA、LI～HM和LA～HP。LI～HA即北大西洋涛动(NAO), LI～HM和LA～HP则是相邻高压、低压强度负相关、气压正相关的新型遥联。冬季北太平洋上国际日更线附近的一对南北遥联,因其南方无高压环流实体支持,本质上是‘遥相关型’、而非‘涛动’,应当称为北太平洋遥相关型(NP)。冬季北半球ACA的遥联可区分为两个相对独立的遥联系统：北大西洋／欧亚大陆遥联系统由LI～HA、LI～HM共同构成,北太平洋遥联系统仅由LA～HP构成。我国位于北大西洋／欧亚大陆遥联系统东部,冬季大气环流及气候异常主要受它的影响。5)ACA异常及遥联与海洋外强迫的关系如下：高纬海冰异常主要影响北大西洋／欧亚大陆遥联系统,海冰偏多(极涡偏强)年,HM减弱、LI加强、位置偏南,北大西洋涛动加强；北太平洋上的LA、HP无明显异常。低纬海洋海表温度(SST)异常主要影响北太平洋遥联系统,热带中东太平洋SST异常偏高(El Nino事件发生)年,LA加强、HP主体所在区域Hadley环流下沉支偏弱,HP减弱。6) CCSM4模式大气、海洋中ACA遥联与同期实际大气遥联接近；但在海洋对冬季北半球ACA遥联及其外强迫模拟中,高纬海冰与同期PV、ACA的相关不显著,热带SST对北大西洋LI、HA的显著强迫与实际不符。更多还原

【Abstract】 An atmospheric center of action(ACA) is defined as a spatially extensive high-pressure or low-pressure system in the monthly mean sea level pressure (SLP) field, stagnating over a specific geographic area throughout the year and/or season. Seasonal variations of ACA determine the seasonality of the regional climate. The anomaly and teleconnection of ACA are closely related with atmospheric circulation and regional climate anomalies. Therefore, ACA is an important research subject of the atmospheric circulation anomalies and short-term climate prediction. The members and characteristics of ACA over the Northern Hemisphere are identified using Hadley monthly mean SLP dataset (from1850to2009). The circulation indices (area S, the intensity P, the center position) with clear physical meaning of5ACAs are defined and calculated for winter season over the Northern Hemisphere, and their climatic and abnormal features of ACA are preliminarily analyzed. On this basis, the climatic effects of the ACA, teleconnection between ACAs and the relationship between the abnormal teleconnection of ACA and abnormal heat source-sink of atmospheric heat engine are researched, through which more systematic and more in-depth understanding of the ACA for winter over the Northern Hemisphere are obtained. The main conclusions are as follows:1)There are6ACAs over the Northern Hemisphere demonstrated by reliable data, including Icelandic low(LI) and North Atlantic subtropical high (HA) over the North Atlantic, Aleutian Low (LA) and North Pacific subtropical high (HP) over the North Pacific, together with Mongolian high (HM) and India low(LIN) over the Asian continent. Among them, LI, HM, LA at the high latitudes throughout the winter season and LIN at the low latitudes throughout the summer season are semi-permanent ACAs. HA and HP in low-latitude ocean throughout the year are permanent ACAs, or quasi-permanent ACAs (Winter weak).2) The seasonal and monthly Circulation Indices (S、P、λc、φc) of five ACAs (LI, HA, HM, LA, HP) from1850to2009are calculated by uniform definitions and calculation methods, based on reliable data. The climatic and abnormal characteristics of the ACA are quantitatively analyzed and the reasonableness is demonstrated by the three independent Circulation Indices (P、λc、φc). Thus, a set of application value circulation indices are provided for atmospheric circulation anomaly and short-term climate prediction research.3) It is demonstrated that the ACA significantly affects the climate and anomaly at the location and the surrounding area, according with the synoptic dynamics significance. The impact area of ACA on climate is much larger on the ocean than on the continent. The impact on climate from ACA intensity anomalies is greater than from its position anomalies. The impact on temperatures is greater than on precipitation from ACA anomalies. The impacts of LI and HA over the North Atlantic on climate anomalies in both the properties and the distribution areas are very similar, while the impact on properties of climate anomalies is nearly opposite. HM is the main ACA that affects China’s winter climate and anomalies. In winter, the temperature is lower on China (except Southwest Region) and precipitation over Sichuan and some areas of North China is more on the positive phase of HM. LI and HA, which located on the upstream of China, are the secondary ACAs that affects on China’s winter climate and anomalies. When LI and HA are stronger, the temperature is higher over China’s’Three North’parts. The impacts of LA and HP on China climate anomalies are relatively weak.4) It is revealed that there are three significant teleconnections among five ACAs in winter over the Northern Hemisphere, which are LI-HA, LI-HM and LA-HP. LI-HA is the North Atlantic Oscillation (NAO). LI-HM and LA-HP are newly defined teleconnections. The intensity of LI’s (LA’s) and HM’s (HP’s) is negatively correlated. The teleconnections among ACAs in winter over the Northern Hemisphere are divided into two relatively independent systems:(1) the North Atlantic/Eurasia teleconnection system consists of LI-HA and LI-HM, and (2) North Pacific teleconnection system includes only LA-HP. Winter season atmospheric circulation and climate anomalies in China are mainly influenced by the North Atlantic/Eurasia teleconnection system.5) The relationships among climate anomalies, teleconnections of ACAs, and Ocean external forcing can be summarized as follows:(1) Sea ice anomalies at high-latitude mainly affect the North Atlantic/Eurasia teleconnection system. When sea ice is above normal, polar vortex is stronger, HM is weaker, LI is stronger and shifts southward, and NAO is stronger. LA and HP over the North Pacific have no obvious anomalies.(2) SST anomalies over tropical central East Pacific mainly affect teleconnection system over the North Pacific. Positive SST anomalies over tropical central East Pacific cause LA strengthening and HP weakening, and the sinking branch of Hadley circulation associated with HP move southward and become weaker.6) CCSM4can qualitatively simulate the teleconnections of ACA in comparison to observations. However, role of the tropical ocean as external forcing is overemphasized in the simulations for controlling ACA anomoalies and teleconnection. Forcing mechanism due to sea ice at high-latitude and polar vortex is under estimated in model simulations, as compared with observed data.更多还原