Climate Variability and Change in High Asia Mountains: the interplay between the Indian Monsoon and the Westerly disturbances

The regional climate in the Himalaya is dominated by two major climatic systems that control water supply: the Indian summer monsoon (ISM) that extends approximately from June to September and winter western disturbances (WD) from November to February. The interplay between these systems results in two climatic regimes that play distinct roles for the water cycle in High Asia Mountains with implications for billions of people. Understanding the spatiotemporal variability of these major regional climatic systems is therefore essential to realistically predict the impacts of climate change on glacier mass balance and in the water supply in the region in future scenarios of climate change. Here we examine the intraseasonal-to-interannual variability of the ISM and the WD with distinct approaches. An ISM index is obtained by performing combined EOF analysis (CEOF) of some of the most important variables that characterize the seasonal cycle of the ISM: integrated moisture flux, 200hPa zonal wind (U200) and temperature at 2m (T2m). The Climate Forecast System Reanalysis (CFSR) is used to derive the index (1979-2012). Projections of the CEOF onto the tropical rainfall measurement mission (TRMM) precipitation indicate that the first CEOF (CEOF-1) captures the large-scale features of the East Asia Monsoon. The second CEOF (CEOF-2) is associated with the ISM and its time coefficient is then used as an index for the monsoon (hereafter ISMI). We show that the ISMI can be used to define the onset and demise of ISM, and its amplitude is associated with total seasonal precipitation. Moreover, the spectral analysis of the ISMI indicates peaks on intraseasonal time-scales that are related to active and break phases of the monsoon. Moreover, during the winter variations in CEOF-2 are associated with the WD. We use these proxies to investigate variations and changes in the ISM and the WD and the mechanisms whereby these dominant climatic systems have affected temperature and precipitation over High Asia in the last 3 decades. Moreover, we use this approach to examine teleconnections with El Nino/Southern Oscillation and the Antarctic Oscillation (on interannual time-scale) and the Madden-Julian Oscillation (on intraseasonal time scales). This research has been supported by the National Science Foundation (NSF- 1116105).