一次西南涡特大暴雨的中尺度诊断分析

采用LAPS中尺度分析模式大气资料，对2008年7月一次西南涡暴雨过程进行天气学降水运动的中尺度诊断计算与分析。诊断计算包括：可降水量、层结不稳定能量、对流可降水量、水汽权重平均风速、水汽通量散度、云水、云冰总量及其通量散度和垂直速度与凝结函数降水率等。结果表明：“西南涡-切变线”系统的暴雨发生在暖湿气团与变性冷气团之间的中尺度风场辐合上升运动区，中尺度雨团发生在层结不稳定的暖湿气团一侧。计算的中尺度垂直运动与凝结函数降水率场，降水率为暴雨到特大暴雨。计算的水汽通量辐合降水率与凝结函数降水率不会完全重合，且水汽通量辐合既可致中尺度“雨”，又可成大尺度“云”，并且云水、云冰通量辐合/辐散，可解释为它们的“正”/“负”碰并增长，而碰并增长产生水凝物增量（降水率）也促成大暴雨。因此，在凝结函数降水率场中产生的中、小尺度对流雨团，加上水汽与云水、云冰通量辐合及其碰并增长，并且借助层结不稳定能量释放和可能产生的强迫“次级环流”及水汽与云水、云冰输送，是这次“西南涡-切变线”系统造成襄樊特大暴雨的天气学成因。

A meso-scale diagnostic analysis of torrential rain caused by a southwest vortex in China

Based on the atmospheric data from LAPS(local analysis and prediction system),a torrential rain process caused by a southwest vortex in July 2008 in China was analyzed.The probable precipitation,instable energy of stratification,convective precipitable precipitation,mean wind speed of water vapor weight,water vapor flux divergence,the total cloud water and cloud ice and its flux divergence,vertical velocity and condensation function precipitation rates and so on were calculated and diagnosed.The results indicate that the torrential rain from"a southwest vortex shear line system"occurs in the ascending areas due to meso-scale wind field convergence between the warm-wet air mass and cold air mass and is located on the side of warm-wet air mass of unstable stratification.The calculation of the meso-scale vertical motion and the field of the condensation function precipitation rate show that the grade of precipitation rate reaches the heavy rain to rainstorm.The calculated precipitation rate of water vapor flux convergence is not entirely consistent with that of the condensation function.The water vapor flux convergence not only produces meso-scale"rain",but also large-scale"cloud",and cloud moisture and cloud ice flux convergence or divergence is their positive or negative"collection growth"and then forms incremental hydrometeors(precipitation rate),which helps to produce a heavy rain.Thus,the synoptic reasons for the heavy rain in Xiangfan include the meso-scale and small-scale convective rain mass produced by the field of the condensation function precipitation rate,the water vapor,the flux convergence of cloud moisture and cloud ice,the cloud particle"collection growth",the energy release from unstable stratification,the possible"secondary circulation"stimulated by forcing,and the transportation of water vapor,cloud moisture and cloud ice.