地球環境変化とヒマラヤ・チベット山塊の役割 タクラマカン砂漠週辺の降水と水蒸気輸送場の経年変動

Abstract

Interannual variations of summertime precipitation over arid and semi-arid regions in China and Mongolia are investigated. The correlation between variations in summer precipitation in these regions and all-India monthly rainfall, and atmospheric circulation are then examined. The interannual variation of summer precipitation of Taklimakan Desert is mainly related to the windward mid-latitude circulation. A clear negative correlation between the interannual variation of precipitation of this region and all-India monsoon rainfall is seen in June and July. This relationship is caused by a rather local atmospheric circulation change seen over Central Asia.Water vapor transport around the arid region of the Interior of the Eurasian Continent was then investigated using the re-analysis objective analysis data provided by the European Centre for Medium range Weather Forecast (ECMWF). Mongolia and northern China receive water vapor from the northwest through the vertically integrated water vapor transporting fields of the mean summer. One water source for these regions is located in Western Siberia. In the lower troposphere, most of the water vapor is transported to the Taklimakan Desert from the northwest along the eastern periphery of Tianshan Mountains in the mean summer state.By compositing the water vapor transport pattern of heavy precipitation, we found that the southerly water vapor routes pass over the Tibetan Plateau and along the eastern periphery of the Plateau in the lower troposphere. This water vapor flux pattern is related with the southwestward extending trough located to the north of this region and the ridge located in Central Asia. Because of this pattern, more water vapor comes from the south in a wet year (e.g., 1981) than normal years.