一次中尺度带状暴雨机制分析

Analysis of a Process of Mesoscale Zonal Rainstorm

利用地面加密观测资料、常规探测资料和NCEP 1°×1°再分析资料等,从环流形势入手,通过对水汽通量、假相当位温、24 h变温、地面风场、湿焓和压能场等的诊断分析,研究此次暴雨过程的形成机制。结果表明,此次暴雨是在高层槽前和中低层切变南侧的西南气流中产生的;低空西南急流和低层西南风辐合为暴雨提供了充足的水汽,低层涡旋的辐合提供了垂直上升的动力,低层海上回流的冷空气是暴雨产生最直接的促发机制。高压能舌与等湿焓密集带呈带状,且走向一致,强湿焓平流出现时间比实际出现强降水的时间早。冷空气激发带状θse锋区能量释放,东北—西南向的强湿焓平流促使带状强对流的发生,闽东南部900~700 h Pa水汽通道畅通,但低层水汽不足,故仅在700 h Pa水汽通量高值中心形成暴雨,闽西北水汽匮乏,直接导致其未出现强降水。

By using the ground observation data,ground station data and NCEP 1° × 1°reanalysis data,we analyzed the water-vapor flux,potential pseudo-equivalent temperature,temperature variable within 24 h,surface wind field,moist enthalpy and pressure energy field based on circulation pattern. The formation mechanism this rainstorm process was researched. Results showed that this rainstorm occurred in the southwest air flow in the south low-level shear and before top slot. Low-level southwest jet and low-level southwest convergence provided plenty of water vapor for rainstorm. The low-level vortex convergence offered vertical rising power. Cold air in low-level sea back was the most direct trigger mechanism for the occurrence of rainstorm. Intensive belt of equal-humidity enthalpy and high pressure energy tongue were belt-like and had the same direction. Strong wet enthalpy advection appeared earlier than the strong precipitation. Cold air stimulated the energy release of zonal θse frontal. Strong moist enthalpy advection in the direction of northeast-southwest promoted the occurrence of zonal strong convection.Southeast Fujian had unblocked water vapor path at 900-700 h Pa,but the lower water vapor was insufficient. Thus,rainstorm appeared in the high value center of 700 h Pa water vapor flux. The lack of water vapor in northwest Fujian directly led to no heavy rain.