Fine Analysis on the Rainfall Distribution of Meridional Shear Line Heavy Rain
Based on the conventional observational data and NCEP 1°×1° reanalysis data, two types of heavy rains in relation to the surrounding longitudinal shear lines with or without concomitant stationary front are investigated. The surface, high and low level synoptic configuration and interaction between cold and warm airs are carefully analyzed to supply the general conceptual model for the torrential rains in the southeast quadrant of the low vortex and to meet the requirement for refined forecasting. The results indicate that these types of shear lines with or without concomitant front are obviously different in the spatial structure. Because of the existing frontal structure in the shear line system that is accompanied by stationary front, the effect of front lifting is significant. And then, one of the favorable heavy rainfall zones is located in the surface inverted trough or the northerly airflow behind the surface low; another one is in the warm zone of the stationary front, resulting from the dry incursion above the warm conveyor belt during the phase of the interaction between cold and warm air, especially during the mature phase of the extratropical cyclone. On the other hand, during the meridional shear line heavy rain process without the accompanying of the stationary front, there is not the frontal system jointly affected by south winds and north winds so the extremly heavy rainfall appears in the southeast quadrant of the low level vortex. Another likely zone of so heavy rainfall is the overlap zone of the high θe tongue at 850 hPa, high specific humidity tongue and weak water vapor convergence that produce potential convective instability, without the infulence of the low level jet.