| Over a century ago, Blanford suggested a negative correlation between western Himalayan snow cover and the Northwest Indian summer monsoon rainfall, an observation that formed the basis of the hypothesis of a snow-monsoon feedback mechanism and resulted in the first forecast of the intensity of the summer monsoon in India. Recently, an opposite relationship between Tibetan snow cover and Indian summer monsoon has been proposed. However, the relatively short length of the instrumental observations restricts the further study of the relationship between these two components of the climate system. In this thesis a 196-year record of snow accumulation extracted from southern Himalayan ice cores is shown to contain a decreasing trend that began in the 1840s. In contrast, the Indian summer monsoon rainfall shows no evidence of such a trend. It is argued that the negative trend in the snow accumulation is associated with the weakening of trade winds over the Pacific Ocean. Evidence has shown that this negative trend in the snow accumulation is associated with the long-term changes in regional Hadley and Walker circulations during the latter half of the 20th century. The lack of a correlation between the Himalayan snow accumulation and Indian summer monsoon could be attributed to the extreme height of the ice core site that effectively decouples the two due to the highly stratified nature of the atmosphere.; The NAO and the AO have been identified as important modes of climate variability in the boreal winter. However, which one is most fundamental in describing this variability and the relationship between them are still important open questions. A key uncertainty is our lack of overall knowledge of the linkages between the North Atlantic and North Pacific Oceans. Using multiple techniques, the non-linear linkages between these basins are explored. In particular, a non-linear expression of the NAO in the North Pacific and an inter-decadal variability in the Pacific center of action in the AO mode have been identified. These findings can contribute to further understanding the boreal winter climate variability. Finally, a possible linkage between the tropics and the extratropics is discussed. |
