5 . the heavy-hard rainfall in transitional season is brought by mixed cloud systems whose movements are slow and less, and the echo depth are about 5 km and horizontal distance of strong echo are within 10km 5、過渡季節(jié)產(chǎn)生的大到暴雨過程大都為混合云系造成,混合云系移速慢,位置少動,強回波頂高度skm左右,強回波的水平距離在10km以內(nèi)。