First Summer Rainstorm Observation, Diagnosis And Simulation In YunGui Plateau

The east of Yunnan-Guizhou Plateau which is located at the southeast slope ofQinghai-Tibet Plateau, has the special geographical position, the terrain and underlying surfacecondition, therefore the rainstorm weather has its special mechanism. In this paper a model lowtrough cold front class cloudburst weather was analyzed in detail by means of backgroundanalysis, observation analysis, diagnosis and numerical simulations, some significant conclusionscan be drawn.Based on the general survey of rainstorm examples among 21 years, the causes of plateaurainstorm in early summer were divided into three kinds of types: low trough cold front(stationary cold front), south trough thermal low, and mesolow shear.By analyzing the weather process and the environmental condition of a model low troughcold front heavy rainfall using the observed data, it was suggested that this process had theactivity of 4 strong rain groups, included two different rainfall weather types, and a series ofMcs.(mesoscale convective system).The important reason of this rainstorm was the interaction between the high-level jet andlow-level jet. The strengthening of high-and-low-level jet brought by a big adjustment ofWesterlies system, led to the joint of the cold and warm air of low-level at the plateau, and causedthis rainstorm. In lower flow field, this rainstorm was the result of three flows at differentlatitudes. The activity of north front and south front was essential to the rainstorm. In the verticalstructure, favorable configuration between the coupling of positive vortex and negativedivergence in mid-to-low level and the coupling of negative vorticity and strong divergence inmid-to-high level were formed by convection.There were two vorticity "conveyor belt" in this rainstorm process: PV decline disturbanceof upper troposphere in the mid-to-high-latitude was an important factor in the development ofthe mesoscale vortex in the lower level. The southwest airflow at the height of 700hPa straddlingHengduan mountain range, due to the friction and the decline along terrain, also caused thecarrier of vortex.Analysis of the MPV indicated that the cold air declining along the tilt had alsoled to the development of SVD. The rainstorm was enhanced by the release of the energytriggered by baroclinic instability, which was caused by the effect of cold and hot air on the wetisentropic surface.WRF model was used to successfully simulate this early summer cloudburst process in theplateau. The result showed that the deep non-adiabatic heating caused by latent heat led to thenon-geostrophic wind and the variation of high-and-low-level jet, and also led to the process ofcoordinatiom of non-geostrophic vorticity and divergence. The mutual coupling of vortex,divergence, and low pressure caused the development ofβ-mesoscale convective systems.Finally, the conceptual model of one kind of early summer rainstorm in this region wasproposed, which reflected the relationship of the interaction between factors that impacted the rainstorm; the viewpoint of discontinuous transmission of the south moves of the frontal systemwas also proposed. It was pointed out that in the early summer, discontinuous transmissionexisted in the process of the northern front which affected southwest moving southward, and thefrontogenesis at the low level of north plateau was the important factor in early summerrainstorm at the plateau. In this paper, the concept of Wumeng vortex was also proposed, which isaβ-mesoscale vortex originating near the north side of Wumeng Shan Mountain.It is a kind ofregional vortex that distinct from the southwest vortex, and one of the main factors affecting thesystem of rainstorm and strong convection weather at low level in the Eastern Yunnan-GuizhouPlateau.