"海棠"(Haitang)台风降水非对称分布成因初步研究

2005年第5号台风"海棠"登陆福建省前后所引发的降水呈明显的南北非对称分布特征。逐时MT1R静止气象卫星IR1云图分析揭示,陆地上台风环流云系呈南北非对称分布。浓白色的降水云区主要位于台风北侧,而在此期间,台风南侧云系则相对较暗。在WRF模式成功模拟的基础上,分析模拟的700 hPa高度上相对湿度和垂直上升运动场表明,垂直上升运动场呈现出与降水场相似的南北非对称分布特征,而台风南北两侧空气相对湿度呈均匀分布。进一步改进的湿Q矢量(Q*)以及地形抬升和地表摩擦作用(简称地形因子)分析表明,Q*矢量散度辐合区、地形因子强迫产生的垂直上升速度区都呈南北非对称分布特征。综合考虑指出,"海棠"台风降水分布的南北非对称性,主要由动力因子(Q*矢量(相当于上升运动)、地形抬升与地表摩擦以及垂直上升运动场)引起的,而热力条件(包括相对湿度)是不重要的。

Preliminary Study on Asymmetric Cause of Formation of Precipitation Associated with Typhoon Haitang

During the landfalling Fujian province of typhoon Haitang(No.5 in 2005) i.e.,at 08:00 on 19~20 July 2005(Beijing time),the precipitation associated with the typhoon had significantly south-north asymmetricfeature.The analysis of hourly MT1R GMS IR1 cloud image showed that typhoon circulation nephsystem appeared south-north asymmetricdistributions.The white cloud area bearing a close relation to precipitation lay primarily in the north of typhoon,however,the nephsystem in the south of typhoon was relatively weak with almost no white cloud area occurrence.Based on the successful simulation from WRF model,the analysisof the simulated relative humidityand vertical ascending motion at 700 hPa indicated that the asymmetric feature of the vertical upward motion was identical to the counterpart of precipitation in such a manner thatrelative humidityin the south and north of typhoon was almost equal.The further diagnostic results based on the revised wet Qvector(Q*),orographic lifting and surface friction(termed as orographic factors) depicted that both the convergence field of Q*vector divergence and the area of vertical ascending motion forced by orographic factors employed south-north asymmetricfeatures.Synthetic consideration indicated that Q*vector(equal to vertical ascending motion),orographic factors and vertical ascending motion are all the primary dynamical factors contributed to genesis of south-north asymmetriccharacteristic of precipitation associate with typhoon,however,thermodynamic factor(such as relative humidity) is not important(uniform).