The Season-dependent Characteristics Of Air-Sea System Of Indian And Pacific Ocean And Their Influence On Interannual Climate Variability Over China

The season-dependent characteristics of spatial distribution of time evolution of the Pacific and Indian Ocean Sea Surface Temperature Anomalies (SSTA) and their influence on interannual climate variability over China as well as the mechanism are investigated in this study. The data used include NCEP/NCAR reanalysis, SMIP2SST as well as the monthly mean precipitation and surface air temperature data of160meteorological stations in China during the period from1960to2002. The methods used include EOF analysis, SVD analysis, correlation analysis, synthesis analysis, wavelet Analysis. The results are summarized as follows:1) Spatial distribution of the leading EOF modes of SSTA in Pacific Ocean is an El Nino-like distribution. The corresponding period is primarily quasi-one year and3-5years. The leading two modes of SSTA in Indian Ocean include the uniformly signed Indian Basin-wide Mode (IOBM) and Indian Ocean Dipole Mode (IODM), respectively. The period of IOBM is primarily1-2years and the period of IODM is primarily4-8years. IODM is most pronounced in autumn and weakest in spring. IOBM is most pronounced in spring.2) The air-sea coupling characteristics of SSTA and the related atmospheric circulation in the Northern Hemisphere are obtained by an SVD analysis. The leading pattern (SVD1) is an El Nino-like distribution in the oceanic component. The corresponding atmospheric component is found to be seasonally dependent. The atmospheric component is a PNA-like pattern in winter of SVD1. The leading air-sea coupling is an IOBM in oceanic component and a PNA-like pattern in the atmosphere. The IOBM is mainly a response to ENSO signal in winter while is not obvious in other seasons. The second SVD (SVD2) mode is an IODM in oceanic components and the corresponding atmospheric components is also quite seasonally dependent. The IODM includes not only ENSO-related variability but also some ENSO-independent characteristics.3) Considering the bridge role played by the atmospheric circulation between the tropical SSTA forcing and mid-high latitudes climate response, the temporal correlations between the climate variability over China and oceanic components of SVD is examined. Results shows that, the Pacific Ocean components of SVD1are significantly positively correlated with the precipitation over Jiangnan region and South China in autumn and winter. Positive correlation between the Indian Ocean components of SVD1and precipitation over China in spring and winter. The SVD2are significantly positively correlated with precipitation in spring and autumn. The Pacific Ocean components of SVD1are significantly positively correlated with the surface air temperature (SAT) in summer and autumn. SVD2are significantly positively correlated with precipitation with SAT over eastern coastal areas in winter. The Indian Ocean components of SVD1are most significantly positive correlated with SAT in autumn. SVD2are significantly positively correlated with SAT in winter.4) The following results are obtained through lead-lag correlation analysis. The Pacific Ocean component of SVD1in summer is significantly positively correlated with the precipitation on Yangtze River basin and its southern regions in late autumn. The significant correlation can be traced to3-5months later. The Indian Ocean component of SVD1in winter is significantly positively correlated with precipitation in late spring over the middle and lower reaches of the Yangtze River of the North China region. The significant correlation time can be traced to2-3months later. The significant correlation time of Pacific Ocean SSTA with SAT can be traced to4-6months later. The significant correlation time of India Ocean SSTA with SAT can be traced to5-6months later.5) The impact of Indian SSTA of SVD1in wintertime on the interannual variability of the precipitation over China in spring is remarkable and this SSTA pattern can be used as a potential predictor of spring precipitation in China. Possible mechanisms behind the relationship between Indian Ocean SSTA and spring precipitation over China are investigated. When the Indian Ocean SSTA is on its positive phase of SVD1(IOBM), the Indian Ocean SST becomes warmer and the East Asian jet stream and the East Asian trough become weaker than normal. This leads to more transportation of water vapor to central eastern China from southeastern coast of East Asia. Therefore are favorable for more-than-normal precipitation in spring over the middle and lower reaches of the Yangtze River of the North China region.