Moisture sources of extreme summer precipitation events in North Xinjiang and their relationship with atmospheric circulation

In this study, the daily observational precipitation data and NCEP reanalysis data during 1951-2014, Euler and Lagrangian method were used to investigate the moisture sources of summer extreme precipitation events in North Xinjiang. The results show that water vapor at low and upper levels of most summer heavy rain (more than 50 mm d−1 and less than 100 mm d−1) in North Xinjiang are mainly transported by westerly circulation from the North Atlantic Ocean and the Eurasian continent. However, rainstorms of more than 100 mm d−1, which are rarely observed, are dominated by vertically integrated moisture from the North Atlantic, Arctic Oceans, and the Eurasian continent, in addition to low-level moisture from the Indian Ocean. Among these sources, the anomalous low-level moisture from the Indian Ocean, which is closely associated with stronger meridional circulation, is considered to be more important with respect to rainstorms. On the days prior to rainstorm days, stronger meridional circulation leads to an anomalous pressure gradient force, which can transport low-level moisture from the Indian Ocean along the eastern periphery of the Tibetan Plateau to North Xinjiang. Furthermore, moisture from the North Atlantic, Arctic Oceans, the Eurasian continent, and the Indian Ocean converge together to influence rainstorm development in this region.