副高外围对流雨带中的对流—对称不稳定及锋生的诊断分析

对2009年8月25日西太平洋副热带高压（简称副高）西北外围对流雨带的云图特征进行了分析，利用WRF3.3中尺度模式对对流雨带的发生发展进行了数值模拟，在模拟较成功的基础上，利用模式输出结果分析了对流雨带发生时的对称不稳定、对流不稳定、惯性不稳定以及锋生等。结果表明：副高外围对流雨带由若干具有一定间隔的对流单体构成，单体在随对流层中层气流的移动中逐渐发展直至消亡。对流雨带的西北侧为宽广的带状斜压云系，东南侧为副高控制的晴空区。对流雨带发生于对流层低层（700 hPa以下）的对称不稳定区，700～500 hPa存在对流不稳定和弱的惯性不稳定。随着对流的发展，700～500 hPa的对流不稳定度明显减弱，而惯性不稳定明显加强。对流层低层为倾斜上升区，中高层为垂直上升区，左侧对应下沉气流，呈现明显的倾斜对流和垂直对流的混和特征，体现了对流—对称不稳定的作用。对流层低层（750 hPa以下）锋生的存在提供了对流—对称不稳定能量释放的有利条件。对流雨带与500～800 hPa等厚度线基本平行，而与500 hPa等高线存在明显的交角，雨带中的对流单体随环境气流移动，雨带符合与对称不稳定相联系的带状降水特征。上述结论对实际预报副高外围对流雨带的位置和走向具有指示意义。

Analysis of Convective-Symmetric Instabilities and Frontogenesis in a Convective Rain Band on the Northwest Edge of WPSH

The cloud characteristics of a convective rain band that occurred on the northwest edge of the western Pacific subtropical high (WPSH) on August 25, 2009 are analyzed using infrared cloud images. Using the ARW-WRF V3.3 model, the occurrence and development of the convective rain band are simulated. Based on the success of the simulation, the symmetric, convective, inertial instabilities, and frontogenesis of the convective rain band are studied using the model output. The results show that the convective rain band on the northwest edge of the WPSH consists of a number of mesoscale convective cells, which develop and die out when moving with the middle troposphere environmental flow and often bring heavy rain in their passing-by region. There is a broad baroclinic cloud band on the northwest side of the band and a cloudless sky controlled by WPSH on the southeast side. The convective band occurs in the symmetric unstable area below 700 hPa and there are convective and weak inertial instabilities between 700 and 500 hPa. With the development of the convection, the convective instability becomes weak, but the inertial instability becomes intensified between 700 and 500 hPa. The convective body is an obvious mixture of slanted convection and vertical convection, with slanted upward flow in the low troposphere, vertical upward flow in the mid-high troposphere, and downward flow on the left side of the body, reflecting the energy release of convective-symmetric instabilities. The frontogenesis below 750 hPa provides an advantage for energy release of convective-symmetric instabilities. The band is nearly parallel to 800-500 hPa constant thickness lines, which deviates from 500 hPa contour lines. The convective body in the rain band moves with environmental flow, showing that the rain band is in accordance with banded precipitation characteristics, which is associated with symmetric instability. The above conclusions can be used for operational forecast on the location and orientation of the convective rain band on the northwest edge of WPSH.