| Popis: |
Precipitation patterns and variations over the Tibetan Plateau (TP) are mainly dominated by the Asian summer monsoon, the westerlies and their interactions. The precise scope of the Asian summer monsoon's influence, however, remains unclear. Referring to the climatological northern boundary index of the East Asian summer monsoon, this paper demonstrates that the 300 mm precipitation from May to September can be used as an index of the northern boundary of the Asian summer monsoon over the TP, and explores the spatial characteristics of the climatological and interannual northern boundary. The results show that the climatological northern boundary of Asian summer monsoon over the TP is located along the eastern Qilian Mountains-Tanggula Mountains-Qiangtang Plateau-Gangdise Mountains-Western Himalayas. It describes the boundary of the dryland during the rainy season and depicts the location of the convergence of westerly wind (westerlies) and southerly wind (monsoon) at lower troposphere over the TP. Precipitation variations in the north (south) area to the climatological northern boundary are considerably positively associated with changes in the latitudinal (longitudinal) water vapour budget. The interannual fluctuation range of northern boundary and the distribution of the TP's vegetation are related. The climatological northern boundary can more accurately reflect the region that is continuously under the influence of the monsoon and has a clearer understanding of the boundaries in the westerlies-monsoon circulation, ecology, and climate than the meteorological northern boundary (the pentad precipitation more than 4 mm/day). The westerlies influence zone, monsoon influence zone, and westerlies-monsoon transition zone are identified based on the interannual fluctuation range of northern boundary. This study can serve as a foundation for further investigation into the linkages between the westerlies-monsoon and the TP's hydrological and ecological systems. |
