Mesoscale Analysis of a Heavy Rainstorm in Yulin City of Northern Shaanxi

[Objective] The study aims at analyzing a regional rainstorm in Yulin City of northern Shaanxi.[Method] Based on conventional meteorological data,from the aspects of circulation pattern,mesoscale system,water vapor and dynamical conditions,a regional rainstorm occuring during July 1-3,2011 in Yulin City of northern Shaanxi was discussed.[Result] There was a small closed subtropical high near Fujian,around which southwest air flow existed constantly,providing water vapor for rainstorm areas for a long time;plateau trough moved eastwards,which provided dynamical field for rainstorm areas;the convergence between northeast cold air and low-level jet flow triggered this rainstorm;rainstorm areas were closely related to mesoscale low-pressure,and the storm appeared in the low-level jet flow in front of mesoscale low pressure;cloud systems in upper trough and low-level jet flow combined,increased and generated rainstorm cloud cluster,while brightness temperature on the top of clouds was below-90 ℃.[Conclusion] The research could provide theoretical foundation for forecast of rainstorms in future.