江淮气旋暖锋上小对流带的非地转湿Q矢量诊断分析

Diagnostic Analysis of Ageostrophic Wet-Q-Vector in Small Convective Zone on Warm Front of Jiang-Huai Cyclone

利用WRF模式对2014年7月4日20时-5日14时发生在安徽中南部由江淮气旋引起的强降水过程进行模拟,得到暖锋上一类中-β尺度小对流带的雷达回波与实况有较好的一致性,运用非地转湿Q矢量对此对流带内部次级环流、降水落区和锋生锋消进行诊断。结果表明,湿Q矢量分量的正负和湿Q矢量散度可以指示经向或纬向垂直环流,小对流带始终与湿Q矢量散度带相伴随,小对流带内部存在方向相反的次级环流,在湿Q矢量辐合区域上升,在湿Q矢量辐散区域下沉。根据湿Q矢量与温度梯度矢量乘积的正负指示的锋生,无法完全诊断江淮气旋暖锋上中-β尺度小对流带导致的降水落区。降水最终落在700 hPa高度层湿Q矢量辐合区附近,这与水汽通量辐合区受小雨带内部次级环流中下沉气流的拖曳作用有关。

A heavy rainfall case caused by Jiang-Huai cyclone that occurred in southern Anhui province from12:00 BT July 4 to 06:00 BT July 5 2014 was simulated using WRF model.The results showed that the simulated meso-β-scale small convective on warm front were consistent with the observation,and the secondary circulation,frontogenesis and precipitation of little rain belts were diagnosed by using ageostrophic wet-Q-vector.It is found that the positive and negative wet-Q-vector component and the wet-Q-vector divergence could indicate the radial or latitudinal vertical circulation.The small convective belt was accompanied by wet-Q-vector divergence belt.Two secondary circulations appeared in the small convective belt with opposite direction,rising in the wet-Q-vector convergence area and sinking in the wet-Q-vector divergence area.The precipitation area of meso-β-scale small convection zone could not be diagnosed using the positive and negative frontogenesis indicated by the product of wet-Q-vector and temperature gradient vector.The rainfall finally fell near the wet-Q-vector convergence region on the left at 700 hPa height layer,which was related to the drag of the downdraft in the secondary circulation of the light rain belt.