| Using regular meteorological observation data, NCEP 1°×1°reanalysis data, we analyze the short-term torrential rain process occurred in Gansu Province on August 7th. The results show that the subtropical high integrates with mainland high, and maintains at mid-latitude after it moved northward. The clockwise air around it bring warm-wet moisture from the Pacific Ocean to southern of Shanxi and middle part of Gansu, along Sichuan, Chongqing, Guizhou Province. Before the rainfall happens, the subtropical high broke from mainland high, so Gansu Province locates between these two high circulations. The dominant air form is southern air stream. On 100hPa,South Asian High last for many days in the west of 90°E, and on 700hPa, the main impact system are low shear line, easterly wave, tropical low and west wind trough, which cause this heavy rain together.Combining the satellite information and radar data, we further diagnose sever physical quantity. We find that the moisture condition in the Huanghe River valley is benefit to precipitation genesis. The lower layer upon rain-area is maintaining instability. The condition of high energy, saturation, potential instability benefit for the formation and maintenance of this rainfall. By analyzing moist enthalpy advection, we can make a 12-hour early forecast on energy accumulation and rain-area. Strong moist enthalpy advection area is where instability energy accumulates. Also we shouldn't overlook the role of upper jet stream. Heavy precipitation often occurs at southern of jet export, where it is also convergence air. The descend wind in the northern of upper jet stream bring cold-dry air downward, while the rising wind in the southern of upper jet stream bring warm-wet air upward. Thus, there produce the secondary circulation, which is benefit for heat exchange between lower and upper lever. Qinghai-Tibet Plateau mesoscale terrain has important effect on this rainstorm event.Using the mesoscale model (WRF), the numerical simulation is carried out. The results show that the WRF model can successfully simulate the process of heavy rain and the mesoscale system related to the process.With the high resolution database, we research ageostrophic-and-wet-QV, MPV and Z-helicity have good indications to synchronous rainfall. By analyzing ageostrophic-and-wet-QV,we find the descend wind alterates with rising wind, forming a latitudinal secondary circulation. The rain happens below rising wind area. By analyzing MPV, we find MPV2 plays an important role in rainstorm. Before the rain, there exists both convective and symmetry instabilities, which provide sufficient instable energy. But MPV2<0 trigger rainfall happening.By using the output database from WRF, we mainly investigate the relative humidity and PV.The results show that dry intrusion not only consists but also plays an important role in the development of the heavy rain process. During the Period of the heavy rain process, dry intrusion descends southward along the intense constant potential temperature lines, which promotes the lower cyclone. In the northern of rainfall area, there is a channel of ((?)θe)/((?)p)<0, leaning northwards with height, while the synchronous MPV2 is also negative. So, according the Theory of Baroclinc Vorticity Development, we consider that dry intrusion process make the low-level vorticity growing. Besides, the dry intrusion process has remarkable features on V-wind and temperature field.
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