THE DOUBLE-LAYER STRUCTURE OF THE HADLEY CIRCULATION AND ITS INTERDECADAL EVOLUTION CHARACTERISTICS

Based on the three-pattern decomposition of global atmospheric circulation(TPDGAC), this study investigates the double-layer structure of the Hadley circulation(HC) and its interdecadal evolution characteristics by using monthly horizontal wind field from NCEP/NCAR reanalysis data from 1948—2011. The following major conclusions are drawn: First, the double-layer structure of the HC is an objective fact, and it constantly exists in April,May, June, October and November in the Southern Hemisphere. Second, the double-layer structure is more obvious in the Southern than in the Northern Hemisphere. Since the double-layer structure is sloped in the vertical direction, it should be taken into consideration when analyzing the variations of the strength and location of the center of the HC.Third, the strength of the double-layer structure of the HC in the Southern Hemisphere consistently exhibits decadal variations with a strong, weak and strong pattern in all five months(April, May, June, October, and November), with cycles of 20-30 a and 40-60 a. Fourth, the center of the HC(mean position of the double-layer structure) in the Southern Hemisphere consistently and remarkably shifts southward in all the five months. The net poleward shifts over the 64 years are 5.18°, 2.11°, 2.50°, 1.79° and 5.76° for the five respective months, with a mean shift of 3.47°.     

局域Hadley环流及其与太平洋SST异常的联系

使用1979—2001年ERA-40月平均经向风计算了季风区(60～140°E)及Nio区(160°E～120°W)的质量流函数,并分析了两区Hadley环流的气候特征和强度变化,研究了Hadley环流强度与太平洋海表温度的联系。结果表明:(1)季风区气候态Hadley环流强于Nio区,环流位置偏北,夏半年尤为明显,造成差异的主要原因是海陆分布不均和赤道东太平洋冷水区的存在;(2)局域Hadley环流强度有明显的年际变化,23年来两区强度大致呈反相变化;(3)局域Hadley环流强度与太平洋海表温度关系密切,1月季风区(Nio区)环流强度与赤道中、东太平洋的Nio综合区海表温度负(正)相关,而与围绕着Nio综合区的c型区域海表温度正(负)相关,7月与1月的相关型基本一致,负相关比1月弱,特别是季风区;(4)ENSO事件对两区Hadley环流强度有不同影响,El Nio事件时季风区Hadley环流减弱、Nio区Hadley环流增强;La Nia时刚好相反,且Nio区的异常更明显。     

东亚低纬地区局地Hadley环流特征及其与大气臭氧的关系

利用1975—2008年NCEP/NCAR的逐月平均风场资料及1975—2001年ECMWF的逐月多层臭氧质量混合比资料,用大气环流三维分解方法研究了东亚低纬度地区之局地Hadley环流的结构及年代际演变特征,分析了该区域局地Hadley环流异常时对应大气臭氧的空间距平分布。研究结果表明:(1)东亚低纬度地区局地Hadley环流既与纬圈平均Hadley环流具有明显的季节变化,但又具有明显区别于纬圈平均Hadley环流的自身结构特征:除冬季存在明显向南、向北输送的两闭合环流圈外,局地Hadley环流在其余季节均以向南输送为主;(2)该局地Hadley环流具有不同于纬圈平均Hadley环流的年代际演变特征,在整个研究时段上以振荡变化为主,并没有表现出象纬圈平均值那样明显的增强趋势;(3)区域赤道上空平流层20～50 hPa大气臭氧的正负距平异常中包含有局地Hadley环流的异常信息:当局地Hadley环流异常强时,区域赤道上空20～50 hPa大气臭氧有一显著负距平异常中心,反之亦然。     

太平洋区域海温跃变及其与东亚夏季风的关系

本文利用英国气象局提供的全球SST月平均资料和NCAR／NCEP提供的500百帕高度场资料，分析了全球SSTA的年际和年代际变化，发现夏季全球SST在70年代发生了一次跃变，尤其北太平洋区域SST在1976年前后，由正距平变为负跨燕，并且跃变前后东亚夏季风也发了显著变化，我国汛期降水异常形势成相反分布，海温对东亚夏季风的影响途径和机制也发生了改变，1976年以前北太平洋区域海温起主要作用，跃变后，北太平洋区域海温异常与东亚夏季风关系变得不明显，而赤道中东太平洋海温的作用变得异常重要。     

春季赤道东太平洋海温异常对东亚大气环流春夏季节演变的影响

利用NCEP高度场、风场及OLR资料，分析了春季赤道东太平洋海温异常对东亚大气环流春夏季节演变的影响，结果表明春季赤道东太平洋海温偏暖年，南海－菲律附近出现异常反气旋，西太平洋副高偏强偏西（副高5月占据南海），南海季风爆发迟；而春季海温偏冷年，南海－菲律宾近出现异常气旋，西太平洋副高偏弱偏东（副高5月东移出南海），南海行风爆发早。数值试验腠季赤道东太平洋海温异常不仅对东亚大气环流春季季节变化有明显影响，而且此影响可持续到夏季。     

RELATION BETWEEN SUMMER TYPHOON FREQUENCY ANOMALIES IN WEST PACIFIC AND ENSO EVENTS AND THE ANOMALOUS ATMOSPHERIC CIRCULATION CHARACTERISTICS

By using data of serially numbered typhoons in northwestern Pacific and NOAA OLR data and NCEP/NCAR reanalysis data of wind field, based on the statistics and study of the relationship between the calendar years with more (or fewer) summer typhoons and ENSO events, we compared the composites of OLR eigenvectors and tropical summer wind fields during El Nino and La Nina events with more or fewer than normal summer typhoons, respectively. The results show that, in summer, without remarkable systematic anomalies of Mascarene High and Australia High in South Hemisphere, the anomaly of Walker circulation will dominate and follow the rule of ENSO impacts to atmospheric circulation and typhoon frequency. Otherwise, when systematic anomalies of Australia High appear during the El Nino events, circulation anomalies in the South Hemisphere will dominate, and many more typhoons will occur. In 1999, which is a special year of La Nina events, northward and eastward monsoon was induced by the stronger Mascarene High, and fewer typhoons arose. The typhoon source are regions where weak vertical wind shear, warm pool in western Pacific and the area with monsoon troughs are overlapping with each other. Finally, this paper analyzes and compares the source locations and ranges of more (fewer) typhoons in the events of El Nino and La Nina, respectively.     

夏季西太平洋台风频数异常与ENSO事件的关系及大气环流异常特征

根据西太平洋编号台风资料、NOAA卫星观测OLR资料和NCEP／NCAR风场再分析资料,在统计和探讨夏季西太平洋台风多（少）发年与ENSO事件的关系的基础上,分别对夏季台风异常偏多或偏少的E1Nifio、LaNifia年的OLR特征量和热带夏季风环流进行合成对比分析。分析表明：夏季当南半球马斯可林高压和澳大利亚高压无明显的系统性异常时,Walker环流异常的影响占主导作用,并遵循ENSO事件对大气环流及台风频数影响的基本规律。若E1Nifio期间澳大利亚高压环流出现系统性异常时,南半球环流异常的影响则占主导地位,台风反而异常偏多。对于1999年LaNifia特殊年份,马斯可林高压异常偏强引发的季风西风偏北偏东,台风反而异常偏少。弱风速垂直切变区、西太平洋暖池和季风槽的重叠部分是台风频发源地,本文分别对E1Nifio、LaNifia台风异常偏多（少）年台风频发源地的位詈和范围作了比较分析．     

春夏季节转换中西太平洋副热带高压东移与大尺度环流和温度场变化关系

分析了由春向夏的季节转换过程中西太平洋副热带高压与大尺度环流和温度场之间的变化关系.结果表明:4月份,西太平洋副热带高压开始表现出向东移动特征,6月份它与向西移动的北美副高在东太平洋120～160 (W区域合并.这一期间,沿15～20 (N之间的纬圈环流同时表现出向东移动特征,该纬圈环流的上升支位于南海-西太平洋暖池一带,下沉支主要位于东太平洋180 (～120 (W区域.伴随上述变化,位于北半球太平洋的局地Hadley环流在纬向随时间表现出东强西弱变化特点.西太平洋副高向东移动与15～20 (N之间的纬圈环流和130 (W东太平洋局地Hadley环流在15～25 (N上空交汇、下沉密切相关.在由春向夏季节转换中,大气和海表温度关于赤道季节转换速率沿纬向表现出东慢西快差异,上述变化为西太平洋副热带高压的向东移动提供了有利的气候背景.     

INFLUENCE OF SPRING EQUATORIAL EASTERN PACIFIC SSTA ON THE SEASONAL CHANGE FROM SPRING TO SUMMER OF EASTERN ASIAN CIRCULATION

Based on the analysis of NCEP height, wind and OLR data, the influence of spring equatorial eastern Pacific SSTA on the seasonal change from spring to summer of eastern Asian circulation has been investigated. Results show that related to the warm (cold) spring SSTA in the equatorial eastern Pacific, the anomalous anticyclone (cyclone) circulation emerges around the South China Sea and the Philippines, the strong (weak) west Pacific subtropical high locates to the west (east) of its normal position, which induces to the late (early) onset of the South China Sea monsoon. The numerical simulations have also shown that the remarkable influence of spring SSTA in the equatorial eastern Pacific on the spring seasonal change of eastern Asian circulation will last till summer.     

北太平洋海表持续加热对夏季中国降水及大气环流的影响

用海温距平累积和讨论了北太平洋海温异常持续加热对夏季中国降水和大气环流的影响。结果表明：ＳＴＰＮＡ（海温的太平洋北美遥相关型）指数距平累积和与江淮流域夏季降水有密切的相关,与全国雨带的类型也有较好的联系。进而讨论了ＳＴＰＮＡ指数距平累积和对大气环流的影响。     

INTERDECADAL VARIATIONS OF INTERACTION BETWEEN NORTH PACIFIC SSTA AND EAST ASIAN SUMMER MONSOON

Identification of key SST zones is essential in predicting the weather / climate systems in East Asia. With the SST data by the U.K. Meteorological Office and 40-year geopotential height and wind fields by NCAR / NCEP, the relationship between the East Asian summer monsoon and north Pacific SSTA is studied, which reveals their interactions are of interdecadal variation. Before mid-1970's, the north Pacific SSTA acts upon the summer monsoon in East Asia through a great circle wavetrain and results in more rainfall in the summer of the northern part of China. After 1976, the SSTA weakens the wavetrain and no longer influences the precipitation in North China due to loosened links with the East Asian summer monsoon. It can be drawn that the key SST zones having potential effects on the weather / climate systems in East Asia do not stay in one particular area of the ocean but rather shift elsewhere as governed by the interdecadal variations of the air-sea interactions. It is hoped that the study would help shed light on the prediction of drought / flood spans in China.     

AIR-SEA COUPLING MODES OF TROPICAL PACIFIC SSTA AND WIND STRESS FIELDS

The EOF thechnique is employed to investigate the characteristic modes of spatial distribution and features of temporal variation in the context of 1970-1989 wind stress and SSTA datasets over the tropical Pacific. Results show similar variation in the time coefficients of the first eigenvectors for the wind stress and SSTA fields, revealing air-sea interaction and coupling at the multiple space/time scales,which are in fairly good correspondence to the E1 Nino cycle.     

东亚季风指数及其与大尺度热力环流年际变化关系

将东西向海平面气压差与低纬度高、低层纬向风切变相结合 ,定义了东亚季风指数 ,该季风指数较好地反映了东亚冬、夏季风变化。其中 ,夏季风指数年际异常对西太平洋副热带高压南北位置变化和长江中下游旱涝具有较强的反映能力。分析表明 :东亚夏季风年际变化与印度洋 -西太平洋上空反 Walker环流及夏季越赤道南北半球间的季风环流呈显著正相关关系。在强、弱异常东亚夏季风年份 ,异常的 Walker环流在西太平洋上的辐合 (辐散 )中心在垂直方向不重合 ,高层 ( 2 0 0 h Pa)速度势与东亚夏季风显著相关区域位于西北太平洋上 ,该异常环流的高层的辐合 (辐散 )通过改变低层空气质量而影响夏季 50 0 h Pa西北太平洋副热带高压。采用 SVD分析进一步发现 :与海温耦合的异常 Walker环流在西太平洋上空的上升支表现出南北半球关于赤道非对称结构 ,亚澳季风区受该异常 Walker环流控制。因而 ,东亚季风与热带海气相互作用可直接通过这种纬向非对称的 Walker环流发生联系。     

PRINCIPAL MODES OF THE SOUTH PACIFIC SSTA IN JUNE, JULY AND AUGUST AND THEIR RELATIONS TO ENSO AND SAM

The relationships of variations of sea surface temperature anomalies (SSTA) in the South Pacific with ENSO and Southern Hemisphere Annular Mode (SAM) are examined in the present article by employing the NCEP-NCAR reanalysis from 1951 to 2006. Two principal modes of South Pacific SSTA are obtained using the EOF (Empirical Orthogonal Function) analysis for austral winter (June, July and August). Our results suggest that EOF1 is closely related with ENSO and EOF2 links to SAM. The EOF1 varies largely on an interannual and EOF2 on a decadal scale. The time series of coefficients of EOF1 is highly correlated simultaneously with Nino3 index. However, the time series of coefficients of EOF2 is significantly correlated with the March-April-May mean SAM index. Both the EOF1 and EOF2 are found in significant correlation to summer precipitation over China. With higher-than-normal SSTs in the eastern South Pacific and simultaneously lower SSTs in the western South Pacific in June-July-August, the summertime rainfall is found to be less than normal in northern China. As displayed in EOF2 of SSTA, in years with lower-than-normal SSTs in mid-latitude southern and equatorial eastern Pacific and higher-than-normal SSTs in the equatorial middle Pacific in March-April-May, the summer precipitation in August tends to be more than normal in regions south of Yangtze River.     

RELATIONSHIP BETWEEN INTERANNUAL VARIATION OF MERIDIONAL WIND ANOMALIES IN TROPICAL PACIFIC AND SSTA

The Singular Spectrum Analysis (SSA) method is used to conduct studies of periodicity of the SST and meridional winds in tropical Pacific Ocean. The results show that the air-sea system for the Pacific varies on quasi-4-year, quasi-2-year and interannual scales, with the quasi-4-year scale having the highest variability. Depending on the scale, the wind field has a varying degree of association with the SST anomalies. Difference is also found in the evolution of phase. In addition, the work discusses the difference in SSTA resulted from wind fields for quasi-4-year and quasi-2-year components.     

北太平洋海温异常与东亚夏季风相互作用的年代际变化

主要利用英国气象局提供的海温资料和ＮＣＡＲ／ＮＣＥＰ提供的４０年高度场及风场资料分析了东亚夏季风与北太平洋ＳＳＴＡ的关系，指出两者之间相互作用存在着年代际变化特征，７０年代中期以前，北太平海异常通过一大；圆波列作用于东亚夏季风，造成我国华北地区夏季降水偏多，７６年以后，北太平洋海温异常使大圆波列减弱，与东亚夏季风关系淡漠，不再影响华北降水。由此指出：影响东亚天气气候的海温关键区，并不总固定在某一海     

Hadley环流上升支演变特征及其与低纬大气臭氧变化的关系

利用最新的NCEP/NCAR的逐月平均风场资料及ECMWF的逐月多层臭氧质量混合资料,通过定义Hadley环流上升支强度指数(HAI),用质量流函数的方法研究了纬圈平均Hadley环流上升支的演变特征及其与低纬地区不同层次大气臭氧变化的关系。结果表明,①冬季和夏季HAI较大,最大值出现在2月和8月,春、秋季HAI较小,最小值出现在5月和11月;Hadley环流上升支的位置随季节和强度变化;冬季Hadley环流上升支所跨纬度最宽,夏季最窄。②各季节代表月份的HAI具有一定的年代际特征,即1月、4月具有负距平-相持-正距平的年代际特征,线性增强趋势明显;7月、10月则表现为距平的正-负-正变化,但7月HAI在2012年以后有明显减弱趋势。总体上各季节HAI从1990年代中后期开始逐渐增强。③除春季外,Hadley环流上升支对低纬对流层臭氧的动力输送作用显著,Hadley环流上升运动越强,上升支所对应纬度带对流层臭氧浓度越低,南北两个下沉区对流层臭氧浓度越高。④ HAI表现为强指数年时,低纬对流层臭氧整体表现为增加,平流层中下部臭氧减少,体现出彼此的长期综合影响。      

中纬度北太平洋SST异常与大气环流的关系

在分析北太平洋（６０°Ｎ～２０°Ｓ）ＳＳＴ距平分布特征的基础上，确定出北太平洋海流区为中纬度北太平洋ＳＳＴ变化最活跃的海区。讨论了该海区ＳＳＴ异常与大气环流的相互关系，并与赤道中、东太平洋ＳＳＴ异常和大气环流的相互影响进行了对比分析，发现北太平洋海流区ＳＳＴ异常时，大气环流存在显著的ＰＮＡ型环流。本文还指出在中纬度北太平洋ＳＳＴ异常与北半球大气环流的相互作用中，大气环流是首先启动的方面。     

北太平洋夏季大气环流的持续性异常及其对中国天气的影响

对太平洋北部持续性异常的研究表明，正、负异常的形热从发生、发展到消亡的演变过程十分相似，它们都始于东亚及西太平洋区域距平形势的变化，并在北太平洋及东亚地区出现一规则排列的距平异常区域，东亚及整个北半球的大气环流也相应地发生变化。太平洋北部环流的持续性异常对东亚特别是中国夏季的天气异常有重要影响。诊断分析和数值试验表明，夏季太平洋北部大气环流发生持续性异常与太平洋中低纬的海温异常关系密切。