Characteristics and Causes of a Continuous Heavy Rainfall Process in Hengduan Mountains,Northwest Yunnan Province
The characteristics and causes of the continuous severe precipitation process that occurred in the Hengduan Mountains of northwest Yunnan Province from May 24 to 27,2020 are analyzed based on the ERA5 reanalysis data and precipitation data from Nujiang Meteorological Station as well as the HYSPLIT model and synoptic diagnostic analysis method.The results suggest that:(1)During this continuous severe precipitation process,the south branch trough stabilized in the south of Qinghai-Tibet Plateau due to the adjustment of atmospheric circulation in the middle to high latitudes.The increased wind speed from the upwind area caused westerly jet to come into being in the upper atmosphere and southwest airflow to converge in the lower atmosphere.The 93～98°E,26～28°E area maintains latitudinal winds greater than 20 m·s-and expanding eastwards.(2)The accumulated precipitation in the process at the Gongshan Meteorological Station ranked the second in records,and the maximum number of continuous torrential rain days was extreme.The maximum hourly rainfall reached 9.9 mm,and the long duration was an important feature in this severe precipitation process.(3)During the severe precipitation process,it was noticeable that there was strong convergence in the lower atmosphere and strong divergence in the middle and upper atmosphere,so the effect of air suction was obvious.Before the period of heavy precipitation,the center of strong low-level convergence and strong mid-level dispersion in the 97～99° E region corresponds to the area of heavy precipitation,and the period of intensification of mid-and upper-level updrafts corresponds well to the period of concentrated precipitation.Moreover,the variation of physical parameter indicated the changing trend of precipitation.(4)On account of the moisture transport from the lower to the upper atmosphere,the relative humidity higher than 90％extended to the upper atmosphere.The moisture mainly originated from the Bay of Bengal and the Arabian Sea,with some moisture from the trumpet topography and synoptic systems.The finding of this research can deepen the understanding of such process and provide references in the forecasting and warning services.
continuous heavy precipitationsouth branch troughwesterly jetsource of moisture
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