Numerical Simulation And Diagnostic Analysis Of Dry Intrusion In "03.7" Changjiang-Huaihe Basins Rainstorm Process

Based on T213 and other observational datasets, a severe heavy rain occurred in Changjiang-Huaihe basins during 4-5 July 2003 is studied. The primary diagnostic analyses show that double or single block is the characteristics of the macroscale circulation in this rainfall process. The strong conflict of warm and cold mass, mesoscale convergence on Meiyu front, shear line, and stably maintaining of high and low jets make for the rainfall. The condition of high energy, saturation, potential instability benefits for the form and maintenance of this rainfall.The mesoscale numerical model MM5(V3) is used to simulate the heavy rain process. Using the model output with high spatial and temporal resolution, we study the characteristic and mechanism of the rainfall in more detail. The results show that dry intrusion not only consists but also plays an important role in the development of the heavy rain process. A transverse secondary circulation is produced by the coupling of high and low jets, while the sinking branch of the secondary circulation providing the dynamic conditions for the dry intrusion air. 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 addition, the pouring of upper-level dry air not only decreases ground temperature behind the front but also increases surface pressure and velocity. So lower-level convergence in front of the front is enhanced, and ascending velocity is boosted up, which reinforces the new convections and the rainfall.