印度洋偶极子对中国南海夏季西南季风水汽输送的影响

利用NCEP/NCAR再分析资料和中科院大气物理研究所PIAP3大气环流模式,分析了印度洋偶极子对夏季中国南海西南季风水汽输送的影响。结果表明,印度洋偶极子正位相期间夏季中国南海西南水汽输送较强,负位相期间则较弱。原因可归结为以下:正位相期间,MJO（Madden-Julian Oscillation）多活动于热带西印度洋,其向东传播受到阻碍,但经向传播明显,通常可传播至孟加拉湾地区,同时PIAP3显示印度洋季风槽位置偏北,且印尼以西过赤道气流较强,从而使得这一地区气旋性环流得到建立与加强。孟加拉湾地区对应着较强的对流活动以及深厚积云对流加热,从而通过对流加热的二级热力响应使西太平洋副热带高压位置向北推进,进而使得南海地区西南季风水汽输送得到建立与加强。在此期间孟加拉湾、中南半岛至南海地区对流活动较强,而苏门答腊沿岸对流活动受到抑制,由此增强了Reverse-Hadley环流,使低层经向风较强,进而增强了南海西南季风的水汽输送,PIAP3大气环流模式证实了Reverse-Hadley环流的增强。负位相期间,MJO多活动于热带东印度洋,在东传过程中受到Walker环流配置影响,在140°E赤道附近形成东西向非对称积云对流加热热源,其东侧Kelvin波响应加强了东风异常并配合副热带高压南缘东风压制了中国南海的西南季风水汽输送。在此期间,MJO在南海地区的经向传播较强,但经向传播常止步于南海地区15°N附近,虽携带大量水汽,但深厚积云对流强烈地消耗水汽使大气中水汽含量降低,PIAP3大气环流模式证实负位相期间深厚积云对流对水汽消耗加大,从而使得负位相期间南海地区水汽含量与正位相期间大体相近,但由于经向风不足使水汽向北输送较弱。     

热带印度洋MJO活动对孟加拉湾西南夏季风季节内振荡的影响

通过对1979—2008年热带太平洋30—60 d振荡(Madden-Julian Oscillation,MJO)指数、美国国家环境预报中心再分析资料和日本气象厅降水资料的分析,发现热带东印度洋MJO强度和传播状况影响孟加拉湾西南夏季风季节内振荡及相关低频环流、对流和降水分布。当热带东印度洋MJO在春末夏初较活跃时,孟加拉湾西南季风季节内振荡活动在4—8月比其不活跃时提前约20 d(约1/2个周期),其对于孟加拉湾西南季风季节内振荡的影响可持续整个季风期,使西南季风的季节内振荡不仅酝酿期和活跃期提前发生,季风期有所延长,季节内振荡也更强。西南季风季节内振荡具有明显的北传和东传特征,北传沿孟加拉湾通道从赤道向副热带推进,而东传则沿10°—20°N从孟加拉湾向东传至南海地区。春末夏初时热带东印度洋MJO的异常状况,正是通过对西南季风季节内振荡东传和北传的影响,进而对孟加拉湾西南季风季节内振荡在季风期的酝酿、维持和活跃产生作用,这种作用同时体现在强度和时间上。孟加拉湾西南夏季风季节内振荡强度与热带东印度洋MJO在4月21日—5月5日的活动呈现显著负相关,当热带东印度洋MJO在春末夏初较活跃时,孟加拉湾西南夏季风季节内振荡的强度较大,在5—8月经历3次季节内振荡波动,低频对流场和环流场在1—3位相(孟加拉湾西南夏季风季节内振荡为正位相)和4—6位相(负位相)时呈反位相特征,这是由MJO低频对流的东传及在孟加拉湾和南海这两个通道上的北传引起的。从印度半岛到菲律宾群岛的降水在1—3位相和4—6位相上分别为正异常和负异常,其中,在第2位相(孟加拉湾西南季风季节内振荡波峰)和第5位相(孟加拉湾西南季风季节内振荡波谷)时分别为降水最大正异常和最大负异常。反之,在热带印度洋MJO在春末夏初不活跃年时,孟加拉湾西南夏季风季节内振荡活动较弱,强度偏弱且振荡也不规律。     

北半球夏季30～60天季节内振荡年代际变化及其对中国东部降水和气温的影响

本文利用1979～2020年基于中国台站观测的高分辨格点化逐日降水和气温资料以及NCEPⅡ大气再分析资料,探讨了亚洲季风区夏季30～60 d大气季节内振荡（BSISO1）的年代际变化及其对中国东部降水和气温的影响。在1997～2008年（P1阶段）,BSISO1年代际偏强,而在2009～2018年（P2阶段）,BSISO1年代际偏弱。在P1阶段,BSISO1仅对江淮流域的降水和气温具有显著的调控作用,对华南地区的影响较弱;而在P2阶段,BSISO1对江淮流域的降水和气温的调控作用减弱,但对华南地区的降水和温度具有显著的调控作用。在P1阶段,BSISO1有关的异常抑制（活跃）对流可从赤道西太平洋北传至南海—西北太平洋,激发出一个连接南海和江淮流域的经向垂直次级环流圈,引起江淮流域强烈的异常上升（下沉）运动和低层水汽辐合（辐散）,造成局地降水的持续性偏多（偏少）,气温的持续性偏低（偏高）。相比P1阶段,在P2阶段江淮流域的季节平均水汽显著减少,BSISO1有关的水汽垂直输送减弱,削弱了江淮流域季节内降水变化。但在P2阶段,BSISO1相关的异常抑制（活跃）对流可进一步北传到达相对偏北的华南...     

不同PDO背景下华南前汛期锋面和季风降水的水汽输送差异

基于华南地区60个站点的逐日降水资料及NCEP再分析资料,采用拉格朗日后向气流轨迹模式(HYSPLIT_4.9),分析了1960—2012年PDO (Pacific Decadal Oscillation,太平洋年代际振荡)不同相位期间,华南前汛期锋面和季风降水的水汽输送轨迹、主要源地及不同源地水汽的降水贡献率的差异。结果表明:1)锋面降水阶段,在PDO正相位期间,西太平洋-中国南海-孟加拉湾水汽较多;夏季风降水阶段,在PDO正位相期间,北印度洋-孟加拉湾-中国南海的整层水汽含量较多。2)锋面降水阶段,水汽主要来自西北太平洋与中国南海,在PDO正相位期间,副热带高压位置偏北,使得西太平洋水汽输送路径偏北,有更多水汽向华南输送,有利于华南季风降水形成,降水与PDO呈显著的正相关关系。3)季风降水阶段,在PDO正位相期间,尽管北印度洋-孟加拉湾-中国南海的整层水汽含量大,但并未都输送至华南,故形成的有效季风降水偏少,降水与PDO呈显著的负相关关系。     

亚洲夏季风季节内振荡对云南主汛期降水的影响Ⅱ:云南主汛期季节内振荡活动过程及其对MJO活动的响应

利用NCEP OLR、风场再分析资料和日本APHRO_MA_V1003R1降水资料,针对云南主汛期季节内振荡(ISO)活跃年分析了对应低频对流场、环流场和降水的异常特征,以及热带印度洋大尺度振荡MJO分别激发孟加拉湾西南季风ISO和南海热带季风ISO,从而对云南主汛期ISO和降水产生的影响.在云南主汛期ISO活跃年,低频对流场和环流场在云南ISO波动的1～3位相和4～6位相呈反位相特征,这主要由热带印度洋低频对流东传、北传和副热带西太平洋低频对流西传造成的.热带印度洋的低频对流在发展过程中,一方面沿孟加拉湾西岸向西南-东北方向传播,激发了孟加拉湾西南季风ISO活跃并继续向云南传播;另一方面沿孟加拉湾以南继续东传到南海,激发了南海热带季风ISO活跃并北传到副热带中国东部地区,再沿副热带西传至云南,越过云南后与沿孟加拉湾西岸从东北方向传来的低频对流在孟加拉湾以北地区交汇,完成了一个经纬向接力传播的周期.云南主汛期降水在1～3位相由于副热带低频对流西传和孟加拉湾低频对流东北向传播而处于正距平(第2位相降水最多);在4～6位相,由于副热带低频对流抑制区西传和孟加拉湾低频对流抑制区东北向传播而降水减少(第5位相降水最少),云南主汛期降水与当地低频对流有较好的对应关系.当热带印度洋MJO较强时,4-7月以两条路径向云南的三次传播增强和提前,使得云南主汛期ISO活动也加强,对应产生三次低频对流活跃期,这种MJO由热带印度洋向云南的传播需要30～40天的时间.因此,正是热带印度洋MJO分别对孟加拉湾西南季风ISO和南海热带季风ISO的激发,使得东亚夏季风和南亚夏季风这两个亚洲夏季风系统共同作用于云南主汛期ISO,影响当地降水.     

MJO活动对云南5月降水的影响

本文分析了1979～2008年5月MJO(Madden and Julian Oscillation)不同位相上大尺度环流对流和水汽输送的异常情况及其对云南5月降水的影响。按MJO活动中心位置从西向东分为8个位相, 在不同位相上, 云南5月降水呈现出明显的差异:第4～6位相(MJO对流中心位于赤道印度洋中部至西太平洋)降水偏多, 而第7～8位相(赤道太平洋中部以东)和第1～3位相(赤道印度洋中西部)降水偏少, 其中以第6位相的降水正异常和第2位相的负异常最为显著。在MJO 1～8位相中, 对流主体从热带印度洋东移。在第1～3位相, 孟加拉湾还未形成西南向水汽输送, 而云南又处于水汽辐散区, 降水较少;第4位相时对流主体到达90°N附近, 部分对流云系向孟加拉湾北传, 并在孟加拉湾生成气旋性环流, 向云南输送水汽, 云南降水增多;第5位相时对流主体传到南海, 部分对流云系在南海北传, 同时在南海形成北传的气旋性环流;第6位相时赤道MJO对流主体虽然东移出孟加拉湾, 但孟加拉湾和南海的两个气旋性环流依然继续北传, 孟加拉湾气旋东部的西南风和南海气旋西部的东北风在云南交汇, 云南被强烈的水汽辐合区控制, 降水最充沛。第7～8位相时, 对流主体减弱, 东移到南海和西太平洋一带, 孟加拉湾转向为偏北风, 停止向云南输送水汽, 且云南处于水汽辐散区控制, 降水偏少。因此, MJO主体在东传过程中, 激发了热带对流在孟加拉湾和南海两条通道上的北传, 强盛的水汽输送和两个海区气旋环流的有利配置是造成云南5月降水的重要原因。     

热带印度洋夏季水汽输送特征及对南亚季风区降水的影响

利用NCEP/NCAR再分析环流资料、CMAP降水量和NOAA海温资料研究了热带印度洋夏季水汽输送的时空变化特征,并考察其对南亚季风区夏季降水的影响.热带印度洋夏季异常水汽输送第一模态表现为异常水汽从南海向西到达孟加拉湾后分成两支,其中一支继续往西到达印度次大陆和阿拉伯海,对应印度半岛南端和中南半岛的西风水汽输送减弱,导致这些区域降水减少;第二模态表现为异常水汽从赤道东印度洋沿赤道西印度洋、阿拉伯海、印度半岛、中南半岛的反气旋输送,印度和孟加拉湾南部为反气旋异常水汽输送,水汽辐散、降水减少,而印度东北部为气旋性水汽输送,水汽辐合、降水增多.就水汽输送与局地海温的关系而言,水汽输送第一模态与热带印度洋海温整体增暖关系密切,而第二模态与同期印度洋偶极子关系密切.     

印度洋海温年际异常与热带夏季季节内振荡的关系及其数值模拟研究

利用观测分析资料和SINTEX-F海气耦合长时间(70年)数值模拟结果,分析了印度洋海温年际异常与热带夏季季节内振荡(BSISO)各种传播模态之间关系及其物理过程。结果表明,印度洋海温年际异常与热带BSISO关系密切,当印度洋为正(负)偶极子情况,中东印度洋北传BSISO减弱(加强);当印度洋为正(负)海盆异常(BWA)情况,印度洋西太平洋赤道地区(40°E -180°)东传BSISO加强(减弱)。印度洋海温年际变化通过大气环流背景场和BSISO结构影响热带BSISO不同传播模态强度的年际变化。在负(正)偶极子年夏季,由于对流层大气垂直东风切变加强(减弱),对流扰动北侧的正压涡度、边界层水汽辐合加强更明显(不明显),导致形成BSISO较强(弱)的经向不对称结构,因此北传BSISO偏强(减弱)。印度洋BWA模态通过影响赤道西风背景以及海气界面热力交换,导致赤道东传BSISO强度产生变化。在正BWA年夏季,赤道地区西风较明显,当季节内振荡叠加在这种西风背景下,扰动中心的东侧(西侧)风速减弱(加强)更明显,海面蒸发及蒸发潜热减弱(加强)更明显,导致扰动中心的东侧(西侧)海温升高(降低)幅度更大,从而使边界层产生辐合(辐散)更强、水汽更多(少),因此赤道东传BSISO偏强;而在负BWA年,赤道地区西风背景减弱,以上物理过程受削弱使赤道东传BSISO偏弱。     

1998年长江流域特大洪涝期水汽输送过程的诊断分析

利用基于拉格朗日方法的气流轨迹模式（HYSPLIT_V4.9）,结合轨迹聚类法和气块追踪法,探讨1998年6月12日—8月27日期间长江流域强降雨的水汽输送轨迹、主要水汽源地及其水汽贡献,发现此次强降水过程的水汽源地主要为印度洋、孟加拉湾—南海和太平洋;不同降水阶段水汽输送轨迹、水汽源地存在差异。降水第一阶段水汽主要来自孟加拉湾—南海,水汽输送贡献为35%。降水第二阶段水汽主要由印度洋、孟加拉湾—南海和太平洋三个区域共同提供,水汽输送贡献分别为32%、28%和31%。降水第三阶段则是来自印度洋和孟加拉湾—南海的水汽输送占主导地位,它们对降水的水汽输送贡献分别为33%和41%。降水第四阶段水汽主要来源于孟加拉湾—南海,贡献为40%。强降水过程中大气环流的调整,导致了不同阶段水汽源地的变化及各源地水汽贡献的差异。     

孟加拉湾西南季风与南海热带季风季节内振荡特征的比较

采用美国国家环境预报中心的向外长波辐射和风场资料及日本气象厅的降水资料,用30-60d滤波后的夏季风指数在孟加拉湾和南海的区域平均值分别代表孟加拉湾西南季风和南海热带季风季节内振荡,对两支季风的季节内振荡特征进行比较分析,发现孟加拉湾西南季风的季节内振荡和南海热带季风的季节内振荡在夏季风期间(5-10月)都有约3次半的波动.夏季风期间,在阿拉伯海-西太平洋纬带上,夏季风的季节内振荡有4次从阿拉伯海的东传和3次从西太平洋的西传,其中7月后东传可直达西太平洋.孟加拉湾和南海在夏季风期间都有4次季节内振荡的经向传播,但孟加拉湾在约15°N以南为季节内振荡从热带东印度洋的北传,在约15°N以北则为副热带季风季节内振荡的南传;而在南海则是4次季节内振荡从热带的北传.在以孟加拉湾西南季风季节内振荡和南海热带季风季节内振荡分别划分的6个位相中,都存在1-3位相和4-6位相中低频对流、环流形势相反的特征,这是由热带东印度洋季节内振荡的东传和北传所致.热带印度洋季节内振荡沿西南-东北向经过约14d传到孟加拉湾,激发了孟加拉湾西南季风季节内振荡的东传,经过约6d到达南海,激发了南海热带季风季节内振荡的北传,经过约25d到达华南,形成热带印度洋季节内振荡向华南的经纬向接力传播(45d).孟加拉湾西南季风季节内振荡所影响的降水主要是在20°N以南的热带雨带随低频对流的东移而东移;而南海热带季风季节内振荡所影响的降水除了这种热带雨带随低频对流的东移外,还有在20°N以北的东亚副热带地区存在雨带随南海低频对流的北移而北移.     

Decadal change in the boreal summer intraseasonal oscillation

A decadal change in activity of the boreal summer intraseasonal oscillation (BSISO) was identified at a broad scale. The change was more prominent during August–October in the boreal summer. The BSISO activity during 1999–2008 (P2) was significantly greater than that during 1984–1998 (P1). Compared to P1, convection in the BSISO was enhanced and the phase speed of northward-propagating convection was reduced in P2. Under background conditions, warm sea surface temperature (SST) anomalies in P2 were apparent over the tropical Indian Ocean and the western tropical Pacific. The former supplied favorable conditions for the active convection of the BSISO, whereas the latter led to a strengthened Walker circulation through enhanced convection. This induced descending anomalies over the tropical Indian Ocean. Thermal convection tends to be suppressed by descending anomalies, whereas once an active BSISO signal enters the Indian Ocean, convection is enhanced through convective instability by positive SST anomalies. After P2, the BSISO activity was weakened during 2009–2014 (P3). Compared to P2, convective activity in the BSISO tended to be inactive over the southern tropical Indian Ocean in P3. The phase speed of the northward-propagating convection was accelerated. Under background conditions during P3, warmer SST anomalies over the maritime continent enhance convection, which strengthened the local Hadley circulation between the western tropical Pacific and the southern tropical Indian Ocean. Hence, the convection in the BSISO over the southern tropical Indian Ocean was suppressed. The decadal change in BSISO activity correlates with the variability in seasonal mean SST over the tropical Asian monsoon region, which suggests that it is possible to predict the decadal change.

     

Intraseasonal Oscillation of Tropospheric Ozone over the Indian Summer Monsoon Region

Boreal summer intraseasonal oscillation(BSISO) of lower tropospheric ozone is observed in the Indian summer monsoon(ISM) region on the basis of ERA-Interim reanalysis data and ozonesonde data from the World Ozone and Ultraviolet Radiation Data Centre. The 30–60-day intraseasonal variation of lower-tropospheric ozone shows a northwest–southeast pattern with northeastward propagation in the ISM region. The most significant ozone variations are observed in the Maritime Continent and western North Pacific. In the tropics, ozone anomalies extend from the surface to 300 hPa; however, in extratropical areas, it is mainly observed under 500 hPa. Precipitation caused by BSISO plays a dominant role in modulating the BSISO of lower-tropospheric ozone in the tropics, causing negative/positive ozone anomalies in phases 1–3/5–6. As the BSISO propagates northeastward to the western North Pacific, horizontal transport becomes relatively more important, increasing/reducing tropospheric ozone via anticyclonic/cyclonic anomalies over the western North Pacific in phases 3–4/7–8.As two extreme conditions of the ISM, most of its active/break events occur in BSISO phases 4–7/1–8 when suppressed/enhanced convection appears over the equatorial eastern Indian Ocean and enhanced/suppressed convection appears over India, the Bay of Bengal, and the South China Sea. As a result, the BSISO of tropospheric ozone shows significant positive/negative anomalies over the Maritime Continent, as well as negative/positive anomalies over India, the Bay of Bengal,and the South China Sea in active/break spells of the ISM. This BSISO of tropospheric ozone is more remarkable in break spells than in active spells of the ISM, due to the stronger amplitude of BSISO in the former.     

中国近海海表温度对气候变暖及暂缓的显著响应

基于多套全球海温再分析数据和2种线性趋势分析方法,评估了1958-2014年中国近海海表温度（SST）的变化及其对全球气候变化的响应特征,并与全球平均地表温度特别是与若干重要海区的SST做了比较。研究表明：在全球变暖的显著加速期（1980年代和1990年代）,中国近海区域年平均SST表现出更快速的升温特征,其速率达0.60℃/10a,是同期全球平均升温速率的5倍以上;在变暖暂缓期（1998-2014年）,中国近海SST出现显著的下降趋势。研究还表明,中国近海区域SST的年代际变化与太平洋年代际涛动（PDO）的位相转换一致,前者SST的快速上升（下降）期与PDO正（负）位相最大值的时期相对应,PDO可能是通过东亚季风和黑潮影响中国近海SST的年代际变化。     

Asian summer monsoon onset in simulations and CMIP5 projections using four Chinese climate models

The reproducibility and future changes of the onset of the Asian summer monsoon were analyzed based on the simulations and projections under the Representative Concentration Pathways(RCP) scenario in which anthropogenic emissions continue to rise throughout the 21 st century(i.e. RCP8.5) by all realizations from four Chinese models that participated in the Coupled Model Intercomparison Project Phase 5(CMIP5). Delayed onset of the monsoon over the Arabian Sea was evident in all simulations for present-day climate, which was associated with a too weak simulation of the low-level Somali jet in May.A consistent advanced onset of the monsoon was found only over the Arabian Sea in the projections, where the advanced onset of the monsoon was accompanied by an increase of rainfall and an anomalous anticyclone over the northern Indian Ocean. In all the models except FGOALS-g2, the enhanced low-level Somali jet transported more water vapor to the Arabian Sea, whereas in FGOALS-g2 the enhanced rainfall was determined more by the increased wind convergence. Furthermore,and again in all models except FGOALS-g2, the equatorial SST warming, with maximum increase over the eastern Pacific,enhanced convection in the central West Pacific and reduced convection over the eastern Indian Ocean and Maritime Continent region, which drove the anomalous anticyclonic circulation over the western Indian Ocean. In contrast, in FGOALS-g2, there was minimal(near-zero) warming of projected SST in the central equatorial Pacific, with decreased convection in the central West Pacific and enhanced convection over the Maritime Continent. The broader-scale differences among the models across the Pacific were related to both the differences in the projected SST pattern and in the present-day simulations.     

夏季季节内振荡对西北太平洋台风活动的影响

利用夏季季节内振荡(Boreal Summer Intraseasonal Oscillation, BSISO)指数和台风密集度分析了夏季季节内振荡和西北太平洋台风活动的关系。台风密集度定义为一天内500 km范围内台风出现的概率,与台风经纬度位置相比,台风密集度可更灵活地表达台风生成及移动特征。结果表明夏季季节内振荡对台风活动有明显的调制作用。当夏季季节内振荡指数1(BSISO1)处于第1、5、6、7、8位相时,南海及菲律宾以东海域台风活动明显增强;当夏季季节内振荡指数2(BSISO2)处于第2、3、4位相时,西北太平洋台风活动也明显增强。当夏季季节内振荡处于这些位相时,台风活动增强与南海及菲律宾以东海域环流气旋式异常、对流活动正异常相一致。      

热带夏季风场与对流场季节内振荡传播模比较

利用1979-2007年卫星观测日平均OLR资料以及NCEP/DOE第2套再分析资料中的风场资料,采用有限区域波一频分析、合成分析等方法,分析对比对流层高、低层风场与对流场所表征的热带北半球夏季季节内振荡(BSISO)各种传播模态谱分布气候特征及其年际异常。结果表明:各要素反映的BSISO各种模态的气候特征及其年际变化存在一定差异,总体而言对流层低层风(850hPa纬向风或经向风)与对流比较一致。850hPa经向风(纬向风)所反映的纬向(经向)传播BSISO谱分布气候特征与对流情况最相似。在ENSO发展年,850hPa经向风反映的赤道东传波加强趋势与对流较为一致;850hPa纬向风、经向风反映的北传波变化趋势都与对流相似。在ENSO衰减年,850hPa纬向风(经向风)反映的赤道东传波(赤道外西传波)减弱趋势与对流较为一致;对流以及850hPa经向风、200hPa纬向风和200hPa经向风4种要素都能体现南海及周边地区北传波明显减弱这一特征。对流和850hPa纬向风所反映的北传波与印度洋偶极子模态之间关系一致。     

Effects of air�Csea coupling on the boreal summer intraseasonal oscillations over the tropical Indian Ocean

The effects of air?Csea coupling over the tropical Indian Ocean (TIO) on the eastward- and northward-propagating boreal summer intraseasonal oscillation (BSISO) are investigated by comparing a fully coupled (CTL) and a partially decoupled Indian Ocean (pdIO) experiment using SINTEX-F coupled GCM. Air?Csea coupling over the TIO significantly enhances the intensity of both the eastward and northward propagations of the BSISO. The maximum spectrum differences of the northward- (eastward-) propagating BSISO between the CTL and pdIO reach 30% (25%) of their respective climatological values. The enhanced eastward (northward) propagation is related to the zonal (meridional) asymmetry of sea surface temperature anomaly (SSTA). A positive SSTA appears to the east (north) of the BSISO convection, which may positively feed back to the BSISO convection. In addition, air?Csea coupling may enhance the northward propagation through the changes of the mean vertical wind shear and low-level specific humidity. The interannual variations of the TIO regulate the air?Csea interaction effect. Air?Csea coupling enhances (reduces) the eastward-propagating spectrum during the negative Indian Ocean dipole (IOD) mode, positive Indian Ocean basin (IOB) mode and normal years (during positive IOD and negative IOB years). Such phase dependence is attributed to the role of the background mean westerly in affecting the wind-evaporation-SST feedback. A climatological weak westerly in the equatorial Indian Ocean can be readily reversed by anomalous zonal SST gradients during the positive IOD and negative IOB events. Although the SSTA is always positive to the northeast of the BSISO convection for all interannual modes, air?Csea coupling reduces the zonal asymmetry of the low-level specific humidity and thus the eastward propagation spectrum during the positive IOD and negative IOB modes, while strengthening them during the other modes. Air?Csea coupling enhances the northward propagation under all interannual modes due to the persistent westerly monsoon flow over the northern Indian Ocean.     

THE RELATIONSHIP BETWEEN SCS SUMMER MONSOON INTENSITY AND OCEANIC THERMODYNAMIC VARIABLES AT DIFFERENT TIME SCALE

The oscillation characteristics of 1948 - 2003 South China Sea (SCS) summer monsoon intensity (SCSSMI) is analyzed by wavelet transform and the relationship between SCSSMI filtered by Lanczos filter at different time scale and oceanic thermal conditions is studied. The results show that SCSSMI exhibits dominant interannual (about 4 a), decadal (about 9 a) and interdecadal (about 38 a) oscillation periods. The interannual variation is the strongest and the interdecadal variation the weakest. The region of significant correlation between SCS summer monsoon intensity and oceanic thermodynamic variables at different time scale is greatly different. Significant correlation area of interannual variation of SCSSMI is concentrated in near equatorial region. Corresponding correlation displays quasi-biannual variability. If positive anomalies of SST and the depth of thermocline happen in eastern equatorial Indian Ocean and western equatorial Pacific, and negative anomalies of SST and the depth of thermocline happen in western equatorial Indian Ocean and eastern equatorial Pacific in previous autumn and winter, the interannual variation of SCSSMI will enhance. If the condition is contrary, interannual variation of SCSSMI will weaken. The interannual variation of SCSSMI will influence SST. The region surrounding SCS and east of Australia shows significantly negative correlation in autumn, and significantly positive correlation exhibits in west equatorial Indian Ocean, eastern equatorial Pacific and equatorial Atlantic in winter. The decadal variation of SCSSMI is modulated by PDO. Interdecadal variation of SCSSMI is relevant to the global warming and PDO.