对流单体在杭州湾入海时的强度变化分析

Analysis on the Intensity Changes of Convective Cells in the Hangzhou Bay When Entering the Sea

为了研究对流单体在杭州湾入海时的强度变化情况,更好地预报对流单体的变化趋势,统计了2007年1月到2010年6月舟山雷达观测到的148个对流单体,以组合反射率因子、顶高、垂直液态含水量、径向速度、冰雹指数等条件来判断对流单体是加强还是维持或减弱。发现对流单体在海岸线附近加强或维持的几率比较大,在北岸入海后加强以及在南岸入海后减弱的几率较大,在傍晚到凌晨加强或维持的几率较大。对三个加强的典型个例,分别分析了海岸线附近的温湿特性、地面风的辐合、大气的层结稳定性等情况。对148个单体所处时刻的气温和相对湿度资料用GRADS进行插值,绘出等值线,然后统计整个杭州湾海域的最大气温差和相对湿度差以及水平风切变情况。统计结果:加强的单体,其环境温度、湿度梯度、风切变明显比减弱的大。最后得出结论,判断一个对流单体在杭州湾入海时是加强还是减弱,应从海岸线附近的温湿特性、地面风的辐合情况、大气的层结稳定性三方面的条件综合考虑。

Intensity changes of convective cells in the Hangzhou Bay observed by Zhoushan radar from January 2007 to June 2010 when entering the sea are studied,and they depend on the combined reflectivity factor,ET,VIL,radial velocity,hail index and so on.The results show that the possibility of convective cell strengthening or its maintenance nearby the coastline is quite big.Meantime,the possibility of convective cell strengthening nearby the north coastline is big,while the possibility of convective cell weakening nearby the south coastline is also big.The possibility of convective cell strengthening or maintaining from evening to dawn is still big.The temperature and humidity characteristics in the coastline,the surface wind convergence,and atmospheric stability are analyzed from three typical cases.And the mean values of the temperature,relative humidity gradients and horizontal wind shears in the Hangzhou Bay concerning various cell changes are calculated.The result shows that the three factors above of the strengthening cells are bigger than the weakening cells.In conclusion,the above three conditions should be considered when judging a convective cell in the Hangzhou Bay is strengthening or weakening.