东亚地区水汽输送与重庆夏季旱涝的联系

利用NCEP/NCAR(1960—2006年)的全球再分析格点资料,研究了东亚地区水汽输送异常与重庆夏季旱涝的关系。结果表明:当重庆夏季(7~8月)降水偏多(涝)时,欧亚地区中高纬维持"两脊一槽"的"双阻"型:乌拉尔山和鄂霍茨克海地区分别存在阻高,贝加尔湖地区为一槽区。冷空气沿着贝加尔湖槽后偏北风和乌拉尔山阻塞高压的南支西风南下进入中国。热带太平洋地区为显著的高度距平正异常区。副热带地区是高度距平负异常区,西太平洋副热带高压脊线位置偏南、强度偏强。来自热带海洋地区的暖湿气流分别沿西太平洋副热带高压西南侧和经印度、孟加拉湾两条主要路径进入中国。当来自高、低纬地区的冷、暖空气在长江流域中上游相遇,就会造成重庆等长江中上游地区降水异常偏多,发生洪涝。反之,降水偏少(旱)年,在欧亚中高纬地区存在"一槽一脊"的环流形势:乌拉尔山附近为一深厚的槽区;鄂霍茨克海阻塞高压异常发展,一直延伸到贝加尔湖附近;西欧地区维持着深厚的高压脊。西太平洋副热带高压位置偏北、偏东,主体基本退出中国大陆地区。整个热带为高度距平负异常区。这样环流形势致使东亚地区中高纬地区受乌拉尔山大槽影响盛行偏南风,不利于冷空气南下。低纬地区的暖湿气流沿着西太平洋副热带高压南面的东南气流从华南进入中国。这样的环流配置易造成南下的冷空气偏弱,同时使来自热带地区的暖空气向北推进到中国华北和东北地区,致使冷、暖空气无法在长江中上游地区交汇,该区域降水显著减少,形成干旱。     

欧亚中高纬春季地表感热异常与长江中下游夏季降水的可能联系

利用国家气候中心提供的中国区域753站降水观测资料、ECMWF逐月地表感热通量再分析资料和NECP/NCAR再分析资料,讨论了欧亚大陆中高纬春季地表感热异常与长江中下游夏季降水之间的联系及其相关的物理机制。分析发现欧亚大陆中高纬春季地表感热异常与长江中下游地区夏季降水存在显著的正相关:感热偏强期,长江中下游夏季降水偏多;感热偏弱期,长江中下游夏季降水偏少。春季感热异常偏强时,夏季东亚副热带西风急流主体位置偏东、强度偏强、范围偏大,长江中下游地区主要受辐合上升气流控制,水汽输送条件好,降水异常偏多。而春季感热偏弱时,情况大致相反,则夏季降水异常偏少。研究表明欧亚大陆中高纬春季地表感热通量异常变化对我国长江中下游夏季降水预测具有一定的指示意义。     

东亚副热带西风急流位置异常对长江中下游夏季降水的影响

利用NCEP/NCAR 200 hPa月平均风场再分析资料,定义东亚大陆对流层上层不同经度上最大西风所在位置的平均纬度为东亚副热带西风急流轴线指数,该指数能准确反映东亚副热带西风急流位置的南北变化及其对长江中下游降水的影响,并能较好地体现东亚夏季风盛行期间对流层低层与高层的纬向风场变化特征。分析表明,该指数的时间变化具有与长江中下游夏季降水较一致的年代际变化及年际振荡特征。对东亚副热带西风急流位置异常年的大气环流差异分析表明,急流异常偏北时,南亚高压偏弱,位置偏北偏西,呈伊朗高压型;西太平洋副热带高压(下称西太副高)偏弱、位置偏东偏北;气流的辐合上升区北移至华北一带,而长江流域低层风场为辐散异常,上升气流较常年偏弱,降水偏少。急流异常偏南时,南亚高压偏强,位置偏南偏东,呈青藏高压型;西太副高偏强、位置偏西偏南;长江流域地区上空低层有较强辐合上升气流,高层有较强的气流辐散,对流旺盛,雨带在此维持,容易引发洪涝。     

东亚夏季200hPa西风急流时空分布特征与我国夏季降水关系的初步分析

利用1961-2000年NCEP/NCAR再分析资料和全国各测站逐日夏季降水资料,分析了200 hPa西风急流的时空分布特征及其与我国夏季降水之间的关系.分析结果表明:①EOF展开的第一个模态所揭示的时空分布特征反映了北半球副热带西风急流围绕着夏季平均急流轴的南北变动,其对应的时间系数主要表现出西风急流围绕着夏季平均急流轴的南北变动存在着年际变化;在EOF分析的第二模态的空间分布图中,在60-150°E范围内西北-东南向呈现出Rossby波列分布,且有明显的线性增加趋势;在EOF分析的第三模态的空间分布图中,主要反映的是大气长波波状传播的特性.②东亚夏季西风急流位置的南北变动对我国夏季旱涝具有重要影响:夏季西风急流异常偏北时,我国长江中下游夏季降水异常偏少,河套、华北地区夏季降水异常偏多;夏季西风急流异常偏南时,我国长江中下游夏季降水异常偏多,河套、华北地区夏季降水异常偏少.     

夏季长江中下游和华南两类雨型的环流特征及预测信号

利用中国南方66站降水观测资料和NCEP/NCAR再分析资料,采用经验正交函数分解（EOF）、合成分析和相关分析等方法,对夏季长江中下游和华南两类雨型进行了划分,对比分析了两类雨型同期大气环流和前期海温及环流的差异,以探讨两类雨型的形成机制及前期预测信号。结果表明:20世纪80年代之前华南型出现的频次较高,之后长江中下游型出现频次增多;长江中下游型年西太平洋副热带高压（副高）偏强偏西偏南,东亚夏季风（EASM）偏弱,副热带西风急流位置偏南,乌拉尔山阻塞高压（乌阻）和鄂霍次克海阻塞高压（鄂阻）较强,欧亚中高纬以经向环流为主,冷暖空气在长江中下游辐合,导致长江中下游降水偏多;华南型年大气环流与长江中下游型年大体相反,登陆华南的台风偏多,冷暖空气在华南地区辐合,导致华南地区降水偏多;其中副高的脊线位置和中高纬阻塞强弱是长江中下游型和华南型形成的关键因素。两类雨型前期海温分析表明,长江中下游型年,前冬赤道中东太平洋和印度洋偏暖,为典型的东部型El Ni?o,副热带南印度洋偶极子（SIOD）呈负位相,春季El Ni?o衰减,SIOD负位相也减弱,但印度洋持续增暖;华南型年,前冬和春季的海洋演变与长江中下游型年大体相反;关键区域海温与长江中下游夏季降水（YRR）和华南夏季降水（SCR）的年际关系存在年代际变化,YRR和SCR与前冬Ni?o3.4指数、SIOD指数和春季热带印度洋全区一致海温模态（IOBW）指数的相关关系在80年代之后逐步减弱,这主要是由于这三个关键海温指数与EASM及副高脊线的相关关系在80年代之后逐步减弱;两类雨型前期大气环流差异分析表明,春季大气环流的差异性要比前冬显著,长江中下游型年,春季副高、南海副高、马斯克林高压（马高）、澳大利亚高压（澳高）均偏强,大西洋欧洲区极涡强度偏弱,北太平洋涛动（NPO）呈正位相;华南型年春季的关键环流系统异常不明显,仅大西洋欧洲区极涡强度偏强,NPO呈负位相。前期海温演变及春季大气环流关键系统的异常可以作为两类雨型年的一些预测信号。     

内蒙古夏季降水与亚洲纬向环流的联系

利用1980—2015年内蒙古地区116站逐月降水数据、NCEP/NCAR再分析资料及亚洲经、纬向环流指数资料等,分析内蒙古夏季降水与中高纬环流因子的关系。结果表明:近36 a内蒙古夏季降水呈显著减少趋势,且具有显著的年代际变化特征,在1999年发生显著突变。内蒙古夏季降水与亚洲纬向环流存在负相关关系,尤其是内蒙古东部显著相关。通过环流场合成分析发现,在亚洲纬向环流指数高(低)值年,500 hPa位势高度距平场上,欧亚上空呈现出"+、-、+"("-、+、-")的环流形势,使得乌拉尔山高压脊减弱(增强),贝加尔湖高空槽变浅(加深),南北冷暖空气交换减弱(增强);850 hPa风场上,亚洲纬向环流指数高(低)值年,中国北方地区上空受反气旋(气旋)性环流控制,对流活动较弱(强),而西太平洋上空为异常气旋(反气旋)性环流,同时副热带高压强度偏弱(强),位置偏南(北)、偏东(西),使得输送到内蒙古地区的水汽较少(多),造成内蒙古东部夏季降水偏少(多)。进一步分析发现,亚洲纬向环流指数高、低值年,200 h Pa纬向风距平场呈现相反的分布形势,在高(低)值年,西风急流轴位置偏西(东),强度偏弱(强),不利于(利于)内蒙古东部夏季降水偏多。     

OLR与长江中游夏季降水的关联

用SVD方法分析了1、4、7月全球OLR与夏季(6—8月)中国华中区域降水场的关系,结果表明:若1月南非东部沿岸至西印度洋、北美北部OLR(Outgoing Longwave Radiation)偏低(偏高),或北非、美国西南沿岸及近海OLR偏高(偏低),则夏季长江中游降水将偏多(偏少)。若4月澳大利亚至东印度洋、日界线以东热带太平洋OLR偏低(偏高),或西北太平洋偏高(偏低),则夏季长江中游降水将偏多(偏少)。若7月东印度洋—澳大利亚大陆、东亚OLR偏低(偏高),则夏季华中区域长江及其以北降水将偏多(偏少),湖南和江西南部降水将偏少(偏多)。夏季长江中游旱、涝年前期OLR明显的区别在于热带太平洋:涝年1月东、西太平洋为明显负、正异常,4月这种异常进一步加剧;旱年1月正好相反,东、西太平洋为微弱的正、负异常,4月转为东、西太平洋为微弱的负、正异常。太平洋暖池OLR低值区(强对流区)4、7月持续偏南,是夏季长江中游降水偏多的另一重要信号。冬、春季OLR与夏季长江中游降水大尺度关联的可能机制为:若1月热带东、西太平洋OLR为明显负、正异常,4月这种异常进一步加剧,也即冬、春季热带太平洋Walker环流持续减弱,从而使夏季暖池对流活动减弱,热带辐合带偏南,Hadley环流偏弱,使夏季西太平洋副热带高压主体位置偏南,导致中国夏季主雨带不能北推至黄河流域,而长期滞留长江中下游,最后造成长江中游降水异常。     

热带印度洋偶极子与中国夏季年际气候异常关系的年代际变化

利用中国站点观测逐月降水和月平均气温资料以及NCEP/NCAR再分析资料,揭示了热带印度洋偶极子(IOD)与中国夏季气候异常关系的年代际变化.结果表明:IOD与中国夏季年际气候异常的关系既有稳定的一面,又存在着年代际变化.较为稳定的关系表现为:IOD与同年夏季长江黄河之间的降水变化存在显著负相关,与四川气温变化存在显著正相关;IOD与次年夏季四川降水存在显著正相关.伴随发生在20世纪70年代末的大尺度环流年代际转型,IOD与中国气候年际异常的联系亦发生变化:IOD正位相年的同年夏季降水异常型,由中国大部分地区偏少变为长江以南(北)偏多(少),气温由西南地区东部偏暖变为长江以南(北)偏冷(暖);次年夏季降水由全国大部分地区偏多变为长江以南(北)偏少(多),气温由全国大部分地区相关不显著变为黄河以南大部分地区显著偏暖.在IOD负位相年,中国夏季气候异常的特征与IOD正位相年相反.在20世纪70年代末的大尺度年代际气候转犁前后,与IOD相关的东亚大气环流异常特征明显不同.在IOD发展阶段,在70年代末以前,印度夏季风和南海季风偏强,副热带高压势力偏弱,导致中国华南大部分地区降水偏少,华北西部以及内蒙古中部等地降水偏多;70年代末以后,东亚大陆中纬度为弱的东风距平,导致新疆北部降水偏少,气温偏高,华南降水偏多.在IOD次年夏季,70年代末以前,华南、河套以及四川等地盛行偏南气流,降水偏多;70年代末以后,南亚高压和西太平洋副高偏西偏强,华南、江南降水偏少.     

中国夏季降水与太平洋SSTA年代际变化关系的初步研究

利用1951-2001年逐月NCEP再分析高度场、风场资料，COADS海表温度资料及中国147个台站逐月降水资料，运用SVD分析、SVD与回归分析相结合等方法，研究了太平洋SSTA与中国夏季降水年代际变化的相互关系，发现热带西太平洋是影响中国华南降水年代际变化的关键区，1950年代-1970年代后期，该海域SSTA为正，对应中国长江以南地区的夏季降水偏多，而长江以北则偏少；1970年代以后反之；影响中国长江中下游地区及其两侧降水年代际变化的关键区在中纬中部北太平洋，1970年代后期-1990年代前期，该海域SSTA为负，对应长江中下游夏季降水偏多，其两侧降水偏少；影响中国东北降水年代际变化的关键区是低纬中太平洋，1970年代-1980年代前期，低纬中太平洋SSTA为负，与之对应，中国东北夏季降水偏少；1950年代～1960年代中期、1990年代前、中期则反之。进一步对太平洋SSTA年代际变化影响中国夏季降水年代际变化的可能机制作了初步的研究。     

中国东部夏季降水特征及其与西太平洋副高的关系

利用中国东部160个气象观测站1951年-2012年夏季（6-8月）的月平均降水资料,运用EOF分析方法,分析中国东部夏季降水的时空分布特征及其与西太平洋副热带高压的关系。结果表明:（1)夏季,中国东部降水大值区域从华南移到江淮流域,然后到达华北和东北地区。（2) 中国东部夏季降水EOF第一模态空间分布为长江以北与黄河以南地区之间存在一个降水大值雨带, EOF第二模态显示出整个东部沿海地区的降水量以长江为界,长江以南降水偏少,长江以北降水偏多,且江南与江北的降水呈反位相。（3)在西太平洋副热带高压较强的年份,江淮流域降水偏少,华北地区降水偏多;西太平洋副热带高压较弱的年份,江淮流域降水偏多,华南地区降水偏少。     

Potential Connection between the Australian Summer Monsoon Circulation and Summer Precipitation over Central China

This study investigated the connection between the Australian summer monsoon(ASM) and summer precipitation over central China. It was found that,following a weaker-than-normal ASM, the East Asian summer monsoon and western North Pacific subtropical high tend to be stronger, yielding anomalous northward moisture to be transported from the western Pacific to central China. Besides, anomalous upwelling motion emerges over 30–37.5°N, along 110°E. Consequently,significant positive summer precipitation anomalies are located over central China. Further analysis indicated that the boreal winter sea surface temperature(SST) in the Indian Ocean and South China Sea shows positive anomalies in association with a weaker-than-normal ASM. The Indian Ocean warming in boreal winter could persist into the following summer because of its own long memory, emanating a baroclinic Kelvin wave into the Pacific that triggers suppressed convection and an anomalous anticyclone. Besides, the abnormal SST signal in the South China Sea develops eastward with time because of local air-sea interaction, causing summer SST warming in the western Pacific. The SST warming can further affect East Asian atmospheric circulation and precipitation through its impact on convection.     

影响南海夏季风爆发因子的诊断研究

通过南海夏季风爆发偏早年和偏晚年前期冬春季东亚地区的环流、积雪及海温等要素特征的诊断分析,揭示了南海夏季风爆发时间早晚与前期冬季东亚大气环流、热带对流、热源及热带太平洋海温的异常分布有密切联系,南海夏季风爆发偏早年的前期有冬季风偏强,高原积雪偏少,海洋大陆地区的对流活跃、热源增强及LaNina型海温分布等主要特征;南海夏季风爆发偏晚年的前期特征则基本相反。根据1997～1998年冬春环流、积雪及海温等的特征作了1998年南海夏季风爆发时间的预测,其结果与1998年的实况基本一致。     

东亚季风区夏季风强度和降水的配置关系

1979～2000年东亚地区夏季风强度和夏季总降水之间的关系被分为四种类型:A:强季风、强降水;B:强季风、弱降水;C:弱季风、强降水;D:弱季风、弱降水.通过研究不同关系对应的大气环流特征和SST异常,并分析不同要素在季风和降水关系变化中的作用,发现在季尺度上东亚季风区夏季风强度和地区同期降雨总量的关系具有多面性特征,此关系取决于环流场的整体配置,其中西太平洋副高﹑南亚高压和中高纬阻塞形式为三个起主导作用的因素.另外,海温变化对东亚季风和总降水的关系有明显的影响,尤其是北太平洋﹑印度洋和南海区域海温.合成分析结果表明500 hPa东亚异常波列和东亚夏季风强度密切相关,但波形与东亚季风区夏季总降水强弱没有明显联系.     

近几十年青藏高原夏季风变化趋势及其对中国东部降水的影响

根据NCEP/NCAR、NCEP/DOE和ERA40再分析资料以及中国596个台站逐月降水观测资料,利用相关分析、小波分析和交叉谱分析等统计方法,分析了近几十年青藏高原夏季风变化趋势及其对中国东部降水的影响,探讨了影响高原夏季风长期变化的可能原因.结果表明:高原夏季风具有年际和年代际的多时间尺度变化特征,在1958～2...     

南亚高压的南北偏移与我国夏季降水的关系

该文定义了一个能较好反映南亚高压南北偏移的指数,并发现该指数与我国夏季降水,尤其是华北和长江流域的降水,无论在年际变化上还是长期趋势上都具有十分显著的相关关系。南亚高压位置偏北时,在我国东部至日本上空存在一个显著的异常反气旋,其中心自上而下向南倾斜,在高层给华北地区带来辐散,在低层使得气流在长江流域辐散,在华北地区辐合,造成华北地区降水偏多,长江流域降水偏少。同时,南亚高压偏北对应着高层西风急流以及中层西太平洋副热带高压偏北,使得我国整个雨带偏北。此外,通过与海温的相关分析发现,南亚高压的长期偏南趋势可能受到印度洋增暖的直接影响。南北偏移指数可作为预测我国夏季区域降水的重要指标,在气候预测业务中有一定的应用价值。     

Moisture Transport in the Asian Summer Monsoon Region and Its Relationship with Summer Precipitation in China

The characteristics of moisture transport over the Asian summer monsoon region and its relationship with summer precipitation in China are examined by a variety of statistical methods using the NCEP/NC AR reanalysis data for 1948-2005.The results show that:1) The zonal-mean moisture transport in the Asian monsoon region is unique because of monsoon activities.The Asian summer monsoon region is a dominant moisture sink during summer.Both the Indian and East Asian monsoon areas have their convergence cente...     

Predictability of South China Sea Summer Monsoon Onset

Predicting monsoon onset is crucial for agriculture and socioeconomic planning in countries where millions rely on the timely arrival of monsoon rains for their livelihoods. In this study we demonstrate useful skill in predicting year-to-year variations in South China Sea summer monsoon onset at up to a three-month lead time using the GloSea5 seasonal forecasting system. The main source of predictability comes from skillful prediction of Pacific sea surface temperatures associated with El NiÑo and La NiÑa. The South China Sea summer monsoon onset is a known indicator of the broadscale seasonal transition that represents the first stage of the onset of the Asian summer monsoon as a whole. Subsequent development of rainfall across East Asia is influenced by subseasonal variability and synoptic events that reduce predictability, but interannual variability in the broadscale monsoon onset for East Asian summer monsoon still provides potentially useful information for users about possible delays or early occurrence of the onset of rainfall over East Asia.     

The Earliest Onset Areas and Mechanism of the Tropical Asian Summer Monsoon

The multi-yearly averaged pentad meteorological fields at 850 hPa of the NCEP/NCAR reanalysis dada and the TBB fields of the Japan Meteorological Agency during 1980-1994 are analyzed. It is found that if the pentad is taken as the time unit of the monsoon onset, then the tropical Asian summer monsoon (TASM) onsets earliest, simultaneously and abruptly over the whole area in the Bay of Bengal (BOB), the Indo-China Peninsula (ICP), and the South China Sea (SCS), east of 90°E, in the 27th to 28th pentads of a year (Pentads 3 to 4 in May), while it onsets later in the India Peninsula (IP) and the Arabian Sea (AS), west of 90°E. The TASM bursts first at the south end of the IP in the 30th to 31st pentads near 10°N, and advances gradually northward to the whole area, by the end of June. Analysis of the possible mechanism depicts that the rapid changes of the surface sensible heat flux, air temperature, and pressure in spring and early summer in the middle to high latitudes of the East Asian continent between 100°E and 120癊are crucially responsible for the earliest onset of the TASM in the BOB to the SCS areas. It is their rapid changes that induce a continental depression to form and break through the high system of pressure originally located in the above continental areas. The low depression in turn introduces the southwesterly to come into the BOB to the SCS areas, east of 90°E, and thus makes the SCS summer monsoon (SCSSM) burst out earliest in Asia. In the IP to the AS areas, west of 90°E, the surface sensible heat flux almost does not experience obvious change during April and May, which makes the tropical Indian summer monsoon (TISM) onset later than the SCSSM by about a month. Therefore, it is concluded that the meridian of 90°E is the demarcation line between the South Asian summer monsoon (SASM, i.e., the TISM) and the East Asian summer monsoon (EASM, including the SCSSM). Besides, the temporal relations between the TASM onset and the seasonal variation of the South Asian high (SAH) are discussed, too, and it is found that there are good relations between the monsoon onset time and the SAH center positions. When the SAH center advances to north of 20°N, the SCSSM onsets, and to north of 25°N, the TISM onsets at its south end. Comparison between the onset time such determined and that with other methodologies shows fair consistency in the SCS area and some differences in the IP area.     

Analysis of Basic Features of the Onset of the Asian Summer Monsoon

In this paper,a relatively systematic climatological research on the onset of the Asian tropical summer monsoon(ATSM)was carried out.Based on a unified index of the ATSM onset,the advance of the whole ATSM was newly made and then the view that the ATSM firstly breaks out over the tropical eastern Indian Ocean and the middle and southern Indo-China Peninsula was further documented,which was in the 26th pentad(about May 10),then over the South China Sea(SCS)in the 28th pentad.It seems that the ATSM onset over the two regions belongs to the different stages of the same monsoon system.Then,the onset mechanism of ATSM was further investigated by the comprehensive analysis on the land-sea thermodynamic contrast,intraseasonal oscillation,and so on,and the several key factors which influence the ATSM onset were put forward.Based on these results,a possible climatological schematic map that the ATSM firstly breaks out over the tropical eastern Indian Ocean,the Indo-China Peninsula,and the SCS was also presented, namely seasonal evolution of the atmospheric circulation was the background of the monsoon onset;the enhancement and northward advance of the convections,the sensible heating and latent heating over the Indo-China Peninsula and its neighboring areas,the dramatic deepening of the India-Burma trough,and the westerly warm advection over the eastern Tibetan Plateau were the major driving forces of the summer monsoon onset,which made the meridional gradient of the temperature firstly reverse over this region and ascending motion develop.Then the tropical monsoon and precipitation rapidly developed and enhanced. The phase-lock of the 30-60-day and 10-20-day low frequency oscillations originated from different sources was another triggering factor for the summer monsoon onset.It was just the common effect of these factors that induced the ATSM earliest onset over this region.     

Assessment of the Summer South Asian High in Eighteen CMIP5 Models

The South Asian High(SAH) is one of the most important components of the Asian summer monsoon system. To understand the ability of state-of-the-art general circulation models(GCMs) to capture the major characteristics of the SAH, the authors evaluate 18 atmospheric models that participated in the Coupled Model Intercomparison Project Phase 5/Atmospheric Model Intercomparison Project(CMIP5/AMIP). Results show that the multi-model ensemble(MME) mean is able to capture the climatological pattern of the SAH, although its intensity is slightly underestimated. For the interannual variability of the SAH, the MME exhibits good correlation with the reanalysis for the area and intensity index, but poor skill in capturing the east-west oscillation of the SAH. For the interdecadal trend, the MME shows pronounced increasing trends from 1985 to 2008 for the area and intensity indexes, which is consistent with the reanalysis, but fails to capture the westward shift of the SAH center. The individual models show different capacities for capturing climatological patterns, interannual variability, and interdecadal trends of the SAH. Several models fail to capture the climatological pattern, while one model overestimates the intensity of the SAH. Most of the models show good correlations for interannual variability, but nearly half exhibit high root-mean-square difference(RMSD) values. Six models successfully capture the westward shift of the SAH center in the interdecadal trends, while other models fail. The possible causes of the systematic biases involved in several models are also discussed.