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Asian monsoon forecasting is one of the most difficult aspects of the global weather prediction problem. This study focuses on the relationship between large-scale snow cover, the Asian summer rainfall, and sea surface temperature with upper level atmospheric circulation. The main data used in this thesis are satellite-derived snow cover over Eurasia, precipitation data for eight Asian regions, sea surface temperature in the Nino4 region and 850hPa geopotential height, during the period from 1971 to 1995. The satellite-derived snow cover data used is a longer period than that used in other studies. The main results of this thesis are as follows:
- Correlation between satellite-derived snow cover and ground-observed snow data on the Tibetan Plateau is poor and statistically significant at the 5% level only in January. Satellite-derived snow cover over the Tibetan Plateau cannot be relied on for studying linkages between snow cover and Indian summer rainfall. This may be because of inaccuracies in the data when used at the scale of the Tibetan Plateau.
- Eight sub-regions of Asian summer rainfall were defined (by using rotated principal component analysis of rainfall) to find the snow-rainfall relationship for the monsoonal regions in Asia. The Indian region contributes most to the total variance of rainfall in Asia, for both summer and annual totals, during the period from 1901 to 1996. The summer rainfall amount over the Indian region is a useful summer monsoon index, although it should not be regarded as being of general applicability since summer rainfall in other sub-regions of the Asia monsoon area does not all behave similarly.
- An inverse relationship between previous Eurasian snow cover and Indian summer rainfall, reported in previous studies, is generally confirmed by this study using extended satellite-derived snow cover data. However, the relationship is weak. Therefore, the possible robust linkage factor on the snow-rainfall relationship was calculated from 850hPa geopotential height. The 850hPa geopotential height index over the Bering Sea and the North Pacific Ocean areas captures the link between Eurasian winter snow cover and rainfall of all-India and mid-east China in the following summer, exhibiting significant correlations between snow cover, rainfall and geopotential height.
- The 200hPa (850hPa) velocity potential patterns for lighter Eurasian winter snow cover conditions are similar to the 200hPa (850hPa) velocity potential patterns for greater all-India summer rainfall, in terms of the divergence (convergence) centre near the Philippines. The divergence (convergence) centre at the 200hPa (850hPa) level is located near to the Philippines for the cases of greater all-India summer rainfall and lighter Eurasian winter snow cover conditions, while it shifts to eastwards for the cases of lower all-India summer rainfall and heavier Eurasian winter snow cover conditions.
- Higher Eurasian winter snow cover causes a weaker North Pacific High in the following summer. The decreased North Pacific High may weaken the easterlies over the equatorial Pacific Ocean, causing an increase in the SST of the eastern Pacific Ocean. Therefore, the previous Eurasian winter snow cover may play a role in helping to trigger a following winter El Nino event.
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