关键词: 甘肃, 大暴雨, 特征, 分析

Abstract: The prediction for heavy rainfall in northeastern Tibetan Plateau is of vital importance in the work for disastrous weather forecast around northwest Region of China. There are many regional heavy rainfall and local severe convection in Gansu province which result in geological disasters in high frequency in early and middle August in 2010. The heaviest rainfall in flood season in 2010 was the one happened in 11～13 Aug in the east of the Yellow River in Gansu，which is famous for its intensity，coverage and duration. Several characteristics from different aspects of this heavy rainfall event were comprehensively analyzed based on the observed station data and NCEP reanalysis data，such as precipitation condition，circulation background，moisture conditions，dynamic condition and convective instability factor. Besides，the characteristics of the mesoscale cloud cluster and the radar echoes were summarized. The results show that:（1）Even though the event lasted for a long time，the heaviest section just occurred in a short time with a strong intensity and destructive damages. The main circulation background，which includes strong subtropical high，southward action of northern cold air and active Tibetan Plateau shear lines，is favorable for the formation of the rainfall. （2）The direct influence systems are the front at 500hPa and the low vortex with shear line at 700hPa. （3）The properly configuration of many factors provides a good condition for developing a rainfall in dynamic，thermodynamic and energetic environmental conditions，these factors include low level vortex maximum，water vapor convergence，ascending motion，positive helicity center and instable energy of stratification. （4）The trigger mechanism of the rainfall is the development of the mesoscale shear line on the low level，the quick strengthened warm-moist air from the southwest and the suction action of the atmosphere. During 02～08 on August 12，The shear line in the middle-southern Gansu developed and then led to the heavy rainfall event. （5）It is indicated that there was a obvious mesoscale system when several meso-β-scale convective cloud cluster moved to the east and enhanced along the south shear line at 700 hPa. The typical patterns which have convergence in the bottom layer and divergence in upper layer in the meso-β-scale convective cloud cluster caused the rainfall developed to a serious level. Therefore，several mesoscale cloud clusters emerged continuously and then the precipitation reached the maximum one by one. （6）Radar echo characteristics show that cyclonic convergence flow field is one of the important elements for strengthening the rainfall. The main innovation point of this paper is to improve the forecast technique for heavy rainfall by using the conventional meteorological data and the short-term monitoring data.

Key words: Gansu, heavy rainfall, characteristics, analysis