Diagnostic Analysis Of Dry Intrusion In "03.10" Around Bohai Rainstorm Process

Based on observational datasets from micaps systerm, a severe heavy rain occurred in Bohai area during 10-12 October 2003 is studied. The primary diagnostic analyses show that the low interest inlevel 500hpa , mesoscale convergence on shear line and the strong conflict of warm and cold mass on front is the characteristics of the macroscale circulation in this rainfall process. And stably maintaining of high and low jets make for the rainfall. The condition of energy is lower than in summer, it is stability on rainfall area, the form and maintenance of this rainfall benefits for the dynamical power offered by jet.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. 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. In addition, based on the model output it is found that the level is symmetry instability.