【作者】 杨建玲；

【导师】 刘秦玉；

【作者基本信息】 中国海洋大学 ， 气象学， 2007， 博士

【摘要】 本文采用NCEP/NCAR大气资料和HadISST资料集的SST资料,使用最大协方差分析(MCA)、回归等统计方法和海-气耦合模式数值试验,系统深入地研究了热带印度洋海表面温度年际变化(SSTA)主要模态对亚洲季风区大气环流变化的影响。确定了热带印度洋SSTA和亚洲季风区大气环流之间在年际尺度上的主要耦合模态;揭示了热带印度洋SSTA影响亚洲季风区大气环流“耦合主模态”所对应的海温及不同层次大气环流的异常变化;探讨了热带印度洋SSTA对亚洲季风区大气环流和降水、夏季南亚高压、夏季北半球中纬度绕球遥相关的主要影响及其机制,揭示了热带印度洋海盆模的“电容器”效应。得到的主要创新性成果如下:1.首次将“最大协方差分析”用于研究热带印度洋SSTA与亚洲季风区大气环流异常之间的耦合关系中,确定了当扣除ENSO对大气的直接影响后,热带印度洋SSTA和亚洲季风区大气环流异常之间的两个主要耦合模态:第一耦合模态对应的热带印度洋SSTA模态为海盆模,该模态在春季达峰值位相,而且相应的海温异常可以从春季持续到夏季;第二耦合模态对应的热带印度洋SSTA模态为偶极子模态,该模态在秋季达峰值位相。第一耦合模态最大协方差的方差贡献高达95%,而第二耦合模态最大协方差的方差贡献只有25%左右,故将第一耦合模态称为热带印度洋SSTA影响亚洲季风区大气环流的“耦合主模态”。2.给出了“耦合主模态”对应的热带印度洋海盆模对亚洲季风区大气环流的影响。春季,作为热源的热带印度洋暖海盆模态,会引起大气的“Matsuno-Gill pattern”响应,从而在高层青藏高原西侧形成高压异常,在低层引起孟加拉湾南部到赤道西太平洋地区较强的东风异常,西北太平洋地区的异常反气旋性环流以及东亚的南风异常。同时,热带印度洋暖海盆模可以导致热带印度洋海区低层气流辐合形成上升运动,引起海面降水异常偏多,大值区位于西南印度洋。东亚地区异常偏南气流可以输送更多水汽,在中国东部到日本南部降水异常偏多。菲律宾东部降水异常偏少。到了夏季,对应继续维持的热带印度洋暖海盆模态,大气的响应与春季有明显不同。夏季平均西南季风可以将由印度洋暖海盆模引起的异常偏多的水汽向青藏高原南侧地区输送,造成阿拉伯海东部-印度西部降水异常偏多,在该地区形成一新的热源,正是该热源在其西北侧引起的Rossby波响应使得青藏高压西侧异常高压与春季相比向西北方向有所偏移;同时新热源在低层引起辐合,使得印度西南季风、索马里急流加强,从而在整个热带印度洋地区形成异常顺时针环流,该异常环流又会加强水汽的向北输送,从而更加强该新热源,而该新热源又进一步加强这样的环流异常,两者互相促进,形成一个“正反馈过程”。同时夏季中纬度亚洲急流将青藏高原西侧异常高压信号沿急流波导向下游传播,引起日本海上空的高度场异常。西北太平洋异常反气旋性环流与春季相似,中国东部夏季风依然偏强,水汽输送和降水也偏多。对于冷位相的海盆模态,上述异常变化相反。总之,揭示了热带印度洋海盆模的“电容器”效应:ENSO首先对印度洋进行“充电”,形成热带印度洋海盆模,海盆模在ENSO峰值位相后的春季达峰值位相,并可以从春季持续到夏季;该模态又可以“放电”,首先影响青藏高原西侧异常高压,并通过中纬度急流波导的传播而影响更远地区的大气环流。印度夏季风通过水汽输送的途径放大了热带印度洋SSTA对大气环流的影响。3.通过比较热带太平洋ENSO和印度洋海盆模对夏季南亚高压的影响,进一步证实了印度洋海盆模的“电容器”作用,当SST升高(降低)会使南亚高压偏强(偏弱)。而ENSO对夏季南亚高压的直接影响并不显著,夏季南亚高压和前期Ni?o3指数之间显著正相关只是个表象,并不是ENSO的直接影响结果。4.发现了热带印度洋SST年际变化主模态可能引起北半球夏季中纬度绕球遥相关波列。本文证实了尽管热带印度洋与热带太平洋相比SSTA的振幅要小得多,但是通过夏季风对水汽的异常输送,形成新的异常热源,放大了热带印度洋SSTA对亚洲夏季风环流的影响,突出了热带印度洋SSTA在大气环流变异中的重要性。更多还原

【Abstract】 Based on NCEP/NCAR atmospheric data and SST data of HadISST dataset, some statistical methods, such as Maximum Covariance Analysis (MCA) and regression methods, and Ocean-atmosphere coupled model have been used to systematic and comprehensively study the impacts of the SST interannual anomaly (SSTA) in the Tropical Indian Ocean (TIO) on the atmospheric circulation in the Asian Monsoon Region (AMR) in this paper. It is found the dominating coupled modes between the SSTA in TIO and the atmospheric circulation anomaly in ARM at the interannual time scale. The variabilities of the SSTA in TIO and atmospheric circulation anomaly at different levels of the troposphere in AMR associated to the“dominating coupled modes”are revealed. The impacts of the SSTA in TIO on the atmospheric circulation and precipitation, the South Asian High (SAH) and Circumglobal teleconnection (CGT) in the boreal summer and their mechanisms are investigated. Then the“capacitor”role of the dominating mode of the SSTA in TIO has been revealed:1. It is the first time to using the MCA method for investigating the coupled relationship between the SSTA in TIO and atmospheric circulation in AMR and getting two mainly coupled modes between them after the ENSO direct impact signal is removed from the atmosphere. The SSTA mode associated to the first coupled modes, i.e. Indian Ocean Basin mode (IOBM), peaks in the spring and can persist to the ensuring summer. The SSTA associated to the second coupled modes, i.e. Indian Ocean Dipole (IOD) mode, peaks in the autumn. The covariance contribution of the maximum covariance of the first coupled modes is up to 95%, while for the second coupled modes is only about 25%. So the first coupled modes are called as a“dominating coupled modes”of the SSTA in TIO impacts on the atmospheric circulation in AMR in this study.2. The impacts of the IOBM associated to the“dominating coupled modes”on atmospheric circulation have been revealed.In spring, the warm IOBM, being a heat source, can induce the“Matsuno-Gill pattern”atmosphere response and make positive height anomaly over west to the Tibetan Plateau at upper level, easterly wind over areas from the south of the Bay of Bengal to the equatorial west Pacific, anticyclone over the northwest Pacific, and south wind over the East Asian at lower level. At the same time the IOBM can induce convergence at lower level around the TIO rim and ascending motion of the atmosphere, which can induce more precipitation anomalies with large values over the southwest Indian Ocean. The south wind anomalies over the East Asian can transport more water vapor to this region and make precipitation more over areas from the east China to the south Japan. The precipitation over the east of the Philippine is less.While in summer associated to the warm IOBM persisting from spring to summer, there are some obvious different responses of atmosphere comparing to that in spring. The southwesterly of the India summer monsoon is able to transport anomalous more moisture associated with the warm IOBM towards the south Asian, and induce more precipitation over east Arab Sea-west India and forming an additional heating source. It is this new heat source is responsible for the northwestward shift of the positive height anomaly west to the Tibetan Plateau at upper level. At the same time it can induce convergence at lower level and make the Somali jet stream and southwesterly of the Indian summer monsoon are stronger, and then form a clockwise circulation in the TIO. This clockwise circulation can transport more water vapor to northward and strength this new heat source. And this new heat source can further contribute to this circulation. Both promote to each other and form“a positive feedback”. On the other hand, the Asian jet stream over the mid-latitude can propagate signal of the anomalous high over west to the Tibetan Plateau downstream along the waveguide and induce the positive height anomaly over the Sea of Japan. The anticyclone in the northwest Pacific at low level is similar with that in spring. Also companied with this anticyclone, there are anomalous southerly over east of China, i.e. stronger East Asian summer monsoon, with more water vapor transporting and more precipitations. For the cool IOBM, above anomalies are opposite.In general, above investigation reveals the“capacitor”role of the IOBM: first the ENSO“charges”the TIO and induce IOBM, which peaks in the spring after the mature phase of the ENSO and can persist from spring to summer; then the IOBM can“discharge”and affect the anomaly high west to the Tibetan Plateau and remote atmospheric circulation by mid-latitude Asian jet stream propagation along wave guide. It is the India Summer monsoon that enlarges the impacts of the SSTA in TIO on the atmospheric circulation through water vapor transportation.3. By comparing the impacts of the IOBM and the ENSO on the SAH in the boreal summer, the“capacitor”role of the IOBM is revealed in further. The warm (cool) IOBM can make the SAH stronger (weaker). While the direct influence of the ENSO on SAH in boreal summer is insignificant. And it is pointed out that the positive significant correlation between the SAH in summer and the leading several months Ni?o3 index is only a superficies, and not the result from the direct influence of the ENSO.4. It is found that there is a possibility of the SSTA in TIO inducing the Circumglobal Teleconnection in the summertime mid-latitude circulation of the Northern Hemisphere.Although magnitude of the SSTA in TIO is much less than those of the tropical Pacific, the results of this study prove that the SSTA in TIO is of importance in affecting the atmospheric circulation through inducing atmospheric anomaly heating in the south Asian area by the Asian summer monsoon transportation of anomalous water vapor, which enlarges the impacts of the SSTA in TIO on the Asian summer monsoon circulation.更多还原