渤海西岸降雪过程中偏东风在250 m塔层内的特征分析

利用天津铁塔观测资料、加密自动站和常规观测资料，针对4次渤海西岸典型降雪过程，分析了偏东风在降雪发生前后的演变特征。结果表明：4次降雪过程均属于回流降雪，其水汽来源与西南气流的水汽输送和近地面层的东风水汽输送有关；地面东风出现在降雪开始之前8 h以上，风速一般在2 m·s^-1左右，220 m高度可达12 m·s^-1左右。从造成东风的系统看，由南部北上的低压系统造成的东风或东南风湿度比较大，而由东北南下的冷高压造成的东风或东北风都比较干。出现最大降雪的时段，塔层的东风显著加大，而地面的风速变化不明显。

Analysis of easterly wind during snow within the 250 m tower layer in western coast of the Bohai Sea

Based on the observational data collected from the tower in Tianjin,intensive automatic weather stations and the conventionally meteorological data,the characteristics of the easterly wind were analyzed before and after four snow events.The results show that the four events are all backflow-type snow.The water vapor source is provided by southwest air flow and low level easterly wind.Surface easterly wind is ahead of 8 hours before snowfall whose wind speed is about 2 m·s-1 and is up to 12 m·s-1 at the 220 m height level.Easterly or southeasterly wind caused by northward low-pressure system from the south is relatively wet,while easterly or northeasterly wind caused by southward cold high pressure from the northeast is relatively dry.During the maximum snowfall period,the easterly wind at the tower layer increases significantly,while the ground wind speed changes insignificantly.