【作者】 邹燕；

【导师】 赵平；

【作者基本信息】 中国气象科学研究院 ， 气象学， 2009， 博士

【摘要】 本文基于既有的关于夏季中纬度亚洲大陆和太平洋对流层中上层温度纬偏年际变化存在的大尺度东西向反位相现象,即亚洲—太平洋涛动(Asian—Pacific Oscillation,简称APO)的研究成果,以夏季APO强度指数来定量表征东亚副热带夏季风强度。然后,本文系统分析了秋冬季也存在的APO现象及其与东亚副热带冬季风环流和温压场特征的关系,得出秋冬季APO强弱也能较好地表征东亚副热带冬季风强度的年际变化。在对比了分别基于美国关岛联合台风警报中心、东京区域专业气象中心以及上海台风研究所三组台风数据集的热带气旋(tropical cyclone,以下简称TC)频数等统计差异性的基础上,选择1976—2005年联合台风警报中心台风最佳路径资料和NCEP/NCAR再分析月平均资料,采用相关分析与合成分析等统计方法,分别分析了夏季和秋冬季APO强弱与同期东亚—西北太平洋海—气环境的关系,并进一步探讨APO强弱与我国近海TC活跃度的关系及其联系机制。鉴于秋冬季APO强弱与El Nio(La Nia)现象的显著相关,本文利用CAM3.0全球大气模式对北太平洋海温的强廹作用进行了模拟试验。全文主要结论如下: (1)无论是夏季还是秋冬季,我国近海TC的活跃度与同期APO强弱均存在密切关系。夏季APO强(弱)年西北太平洋TC活动密集区偏西(东)偏北(南),我国东部近海TC明显增多(减少)。初秋(9—10月)和深秋初冬(11—12月)APO强(弱)年西北太平洋TC活动密集区偏西(东),我国南部近海TC增多(减少)。(2)夏季APO强度变化可通过改变我国近海对流层纬向风垂直切变、低层辐合与对流等局地环境场从而影响我国近海TC活跃度。APO强(弱)年,东亚副热带夏季风加强(减弱),我国东部近海低层存在气旋(反气旋)性环流异常和对流加强(减弱),对流层纬向风垂直切变减小(加强),近海环境有利(不利)于TC的维持和发展。(3)夏季APO强弱也与南海—热带西太平洋季风槽强度、位置和以及对流层中层引导气流等关系紧密,即通过改变西北太平洋TC活动密集区分布和移动路径从而也影响着进入我国近海TC的多少: APO强(弱)年南海—热带西太平洋季风槽偏北偏西(偏南偏东),热带西太平洋TC活动密集带偏北偏西(偏南偏东),有利于进入我国东部近海TC的增多(减少)。与此同时,APO强(弱)年西北太平洋副热带高压(以下简称副高)偏北偏东(偏南偏西),副高南侧偏东气流减弱(加强),有利于TC的西北行或偏北(南)西行,进入我国东部近海的TC将增多(减少)。(4)秋冬季,APO强度变化与东亚副热带冬季风环流和温压场存在着密切关联。9—10月APO偏强年东亚副热带冬季风偏弱,在大气环流上表现为东亚中高纬环流呈纬向,东亚沿海大槽减弱,副高偏北偏东,中纬度东亚大陆与低纬热带海域间的Hadley经向环流减弱,北半球中低纬存在的纬向垂直环流也减弱。11—12月APO偏强年东亚副热带冬季风偏强,在大气环流上表现为东亚沿海大槽加强南伸,副高偏弱偏东,东亚大陆与近赤道热带西太平洋海域间的Hadley环流和热带东、西太平洋间的Walker环流均显著加强。(5)初秋APO强度影响我国近海TC活跃度的可能机制是通过改变我国近海纬向风垂直切变、低层辐合和对流场等局地环境以及影响副高强度和位置、引导气流等大尺度环流形势来实现的:APO强(弱)年,东亚副热带冬季风减弱(加强),副高加强西伸(减弱东移),中低纬对流层西太平洋为偏东(西)风异常,有(不)利于TC的西行或近海转向点偏西(东),进入我国近海的TC将增加(减少)。同时,APO强(弱)年我国近海对流层高低层纬向风垂直切变减小(增大)、对流加强(减弱)以及南海气旋(反气旋)环流异常的存在也使得我国近海环境有(不)利于TC的维持和发展。(6)深秋初冬APO影响我国南部近海TC活跃度的可能机制包括改变冷空气强度、纬向风垂直切变、低层辐合场以及引导气流来实现的。APO强(弱)时东亚副热带冬季风加强(减弱),副高东移南退(西伸北抬),热带西太平洋对流层中高层出现偏东(西)风异常,使得我国南部近海西风纬向风垂直切变减小(增大),而华南沿海低层东北风(西南风)异常又使得南海出现气旋(反气旋)性环流异常,且南海至热带西太平洋西区冷空气强度偏弱,因此我国南部近海环境有(不)利于TC的维持和发展;同时,APO强(弱)年热带西太平洋对流层中层引导气流为偏东(西)风异常,有(不)利于TC的西行或转向点偏西(东),进入我国东南近海TC将增多(减少)。(7)尽管秋冬季APO强弱与El Ni o(La Ni a)现象关系紧密,而数值试验结果显示,无论是初秋还是深秋初冬,强El Ni o(La Ni a)发生时的热带太平洋海温强廹并不能激发出APO。更多还原

【Abstract】 In the context of scientific findings regarding a large-scale E–W negative correlation of the interannual variation of summer instantaneous temperature fields in the middle– upper troposphere over the Asia and the northern hemisphere Pacific region, referred to as Asian– Pacific Oscillation (APO) hereinafter, the paper is devoted to summer APO characterized quantitatively intensity of summer monsoons at Eastern Asian subtropics (EAS). A systematic analysis is also performed about the autumn and winter APO, as well as their relationships with the atmospheric circulation and temperature/pressure fields of the winter monsoons at Eastern Asian subtropics, respectively. Results show that the strength of autumn/winter APO can quantitatively represent the interannual variation of winter Eastern Asian Subtropical Monsoon intensity.From the statistical differences between annual frequencies of tropical cyclones (TC) given by the best track datasets of Joint Typhoon Warning Center (JTWC), Japan Meteorological Agency (JMA) and Shanghai Typhoon Institute (STI), the 1976-2005 JTWC TC optimal tracks and related NCEP/NCAR reanalysis monthly mean data are utilized for study by means of both correlation and composite analysis, by which to investigate, separately, the relationships between the APO intensity and Eastern Asian-western North Pacific air-sea environment in summer and autumn/winter, with the linkage explored of APO vigor with TC activities over Chinese coastal waters and TC distribution over western North Pacific. In view of the close association between autumn/winter APO strength and El Ni?o ( or La Ni?a ) events, CAM3.0-modeling is performed mainly forced by sea surface temperature over tropical Pacific, with dominant conclusions given below.1) There is an intimate relation of the TC activities over the coastal waters to APO intensity either in summer or autumn/winter on a synchronous basis. In summer when APO is strong (weak), the western North Pacific TC activities are largely west- (east-) and north- (south-)ward of mean, so that the offshore TC increases (decreases) greatly in frequency over eastern Chinese coastal waters. In September– October and November– December when intense (feeble) APO is occurring, western North Pacific TC activities are mostly west- (east-) ward of average, resulting in the Chinese offshore TC increasing (decreasing) in number.2) Summertime APO impacts the offshore TC activities and distributions by altering the vertical shear of zonal winds, low-level convergence and convection over coastal waters of China. For intense (weak) APO years, the EAS summer monsoon is strengthened (reduced), and there emerge anomalous cyclonic (anticyclonic) circulations and reinforced (diminished) convections in the lower troposphere over the coastal waters of East China, as well as declining (intensifying) vertical shear of troposphere zonal winds, thereby providing favorable (unfavorable) condition for the maintenance and development of the offshore TC activities.3) Summertime APO intensity bears a close relation to the vigor and position of monsoon trough over the South-China Sea (SCS)– tropical western Pacific (TWP) and to the direction of steering airflows, i.e., they determine the TC annual frequency in Chines offshore waters by affecting the location of the TC concentration area and their tracks. When APO is strong (weak), the SCS-TWP monsoon trough is positioned north-(south-) and west-(east-)ward of mean, and the concentration belt of TWP TC activities is west- (east-) and north- (south-)ward of mean, thus responsible for an increased (decreased) frequency of TC in eastern coastal waters of China. Also, in the years of higher (lower) APO strength, the TWP subtropical high is north-(south-) and east-(west-)ward of mean, with the easterlies on its south side diminished (enhanced), consequently favorable for TC moving in the northwest or west by north (south) to cause more (fewer) TC to come into the coastal waters of East China.4) In autumn and winter, there is a close association of the APO intensity with the atmospheric circulation and temperature/pressure fields of the EAS winter monsoons. In September– October when APO is strong, the EAS winter monsoons are weakened, indicated by the circulation as zonal straight flows over middle-high latitudes of East Asia, declined East Asia deep trough, subtropical high north- and eastward of mean, as well as decreased Hadley cell (Walker circulation) over East Asia continent and Low-latitude waters (subtropical areas of the northern hemisphere). On the other hand, in November– December when APO is weak, the EAS winter monsoons are strengthened, demonstrated by the circulation as intensified East Asia deep trough expanding to the south, decreased subtropical high eastward of mean, and significantly strengthened Hadley cell (Walker circulation) over East Asia continent and equatorial waters (tropical Pacific).5)In early autumn (September– October) the APO intensity affects offshore TC activities through a possible mechanism to alter the zonal wind vertical shear, low-level convergence and convective fields as the local environment over coastal waters of China , as well as west Pacific subtropical high’s position, intensity and steering flow’s direction as the large-scale circulation pattern. For strong (weak) APO the subtropical winter monsoon is decreased(increased) while the subtropical high is enhanced (weakened), with the high’s ridge line extending (retreating) more westward (eastward), and the troposphere of middle-lower latitude western Pacific is under the control of anomalous easterly (westerly) wind, all these are favorable (unfavorable) for TC traveling westward or the TC turning point toward the shore over coastal waters being east- (west-)ward of average, making the yearly TC frequency increase (decrease). Besides, in the year of stronger (weaker) APO the offshore zonal wind vertical shear in the higher and lower troposphere becomes decreased (increased), convection is enhanced (enfeebled) and the SCS cyclonic (anticyclonic) circulation undergoes anomaly, all these favor (do not favor) the maintenance and intensification of the offshore TC activities.6) In late autumn and early winter (November– December), the possible mechanism for APO vigor impinging on the southern coastal TC activities acts to alter cold air strength, vertical shear of zonal winds, the low-level convergence intensity and steering airflow’s direction. For strong (weaker) APO, the subtropical winter monsoon enhances (enfeebles), the subtropical high moves south- (north) and east-(west-) ward, the middle and upper troposphere of tropical western Pacific is under the control of anomalous easterly (westerly) winds, decreasing (increasing) the vertical shear of zonal westerlies over coastal waters of south China, while anomalies happen to SCS cyclonic (anticyclonic) circulation because of the lower anomalous northeast (southwest) winds over south coasts of China, plus declined(enriched) cold air in the SCS and western TWP, all these are favorable for intensifying (weakening) the TC maintenance and development in southern China coastal waters. Meanwhile, in years of intense (weak) APO, the steering airflow in the TWP middle troposphere is under the control of anomalous easterly (westerly) winds, a condition favorable (unfavorable) for TC traveling westward or the TC turning point towards the shore being west-(east-)ward of mean, causing a larger (smaller) number of TC in the coastal waters of southeast China.7) Despite the fact that the APO vigor in autumn and winter bears an intimate relation to El Ni?o or La Ni?a events , modelings show that these vigorous episodes excite no APO both in September– October and November– December.更多还原