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The Impacts Of The Dominating Modes Of The SST Interannual Variation In The Tropical Indian Ocean On The Atmospheric Circulation In The Asian Monsoon Region

Posted on:2008-01-08Degree:DoctorType:Dissertation
Country:ChinaCandidate:J L YangFull Text:PDF
GTID:1100360242455512Subject:Science of meteorology
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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.
Keywords/Search Tags:Indian Ocean Basin mode, summer monsoon, atmospheric circulation, South Asian High, Vapor transportation
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