The configuration change and Train effect mechanism of multi-cell storm

Abstract: Using low-level thermal and dynamical retrieval system of 4Dvar based on Variational Doppler Radar Analysis System(VDRAS), some multi-cell storm systems occurring in Beijing area have been investigated, and this paper uncovers the physical mechanism of configuration processes, intensity change and train effect phenomena during the linear multi-cell storm transmitting. The resolute shows that: (1) to the multi-cell storm system that the transmission direction of the cells is in keeping with convective band such as squall line, the configuration change , for example, the linear reflectivity become arched one, and intensity changes of the cells are connected with interaction of cells' transmitting process and environmental low level air. If the frontal inflow is a warm and moist air stream, and there is stronger vapor convergence, the cell flourishes more and transmits faster; otherwise the cell weakens and transmits slowly, therefore, to the squall line system nowcasting, the cross area of the multi-cell transmitting direction and the environmental vapor convergent line should be close followed with interest, where the cell will “move” faster and the most violent convection will take place. (2) To the multi-cell system which shows character of train effect, the cell's transmitting feature and developing environment are almost completely different with the multi-cell above mentioned. Generally, the train effect phenomena occur in low level warm and moist air stream or neighboring low level jet , and ambient atmosphere is conditional unstable. The transmitting mechanism of storm cell is able to be connected with the propagation and stimulation of inertial gravity wave. The warm and moist air stream or low level jet is a warm and vapor advection transmitting band, When inertial gravity wave propagates from high to low èse, the wave receives energy from ambient atmosphere and develops constantly, therefore, during the storm cells transmitting , gradually enhancing cells, which arrange in a row, will produce torrential rain center in leading end of the wave train.