一次雨雪天气过程的风廓线雷达特征

Analysis of Wind Profile Radar Characteristics During a Rain and Snow Weather Process

利用3部风廓线雷达资料对2016年2月12—13日鲁中地区出现的一次雨雪天气过程进行分析。结果表明:(1)此次雨雪天气是由低涡和地面气旋共同作用造成的一次回流降水过程,强降水出现在气旋中心的北侧冷区中,925 h Pa和近地面气温下降到0℃以下是雨转雪的重要标志。(2) 1 km以下超低空风场变化是降水开始的信号,低层冷垫强度的变化决定降水相态的转变,降雪时雷达最大探测高度比降雨时有明显下降;低空切变指数在降水开始和结束时会出现较大幅度增大,降雨持续阶段低空切变指数的小幅增加与雨强增强相对应。(3)风廓线雷达垂直速度不仅能体现降水强度的变化,同时也能反映降水相态的变化,降雨转雨夹雪转降雪过程中近地面的垂直速度逐渐变小。(4)大气折射率结构常数和信噪比随高度均呈现逐渐减小趋势,两者的变化能够反映降水强度的变化,均具有零度层亮带特征,亮带的消失对应降雪的开始。

Based on the data from three wind profile radars,the rain and snow weather process in the central part of Shandong Province from February 12 to 13,2016 was analyzed.The results are as follows:(1)This rain and snow weather was the return-flow precipitation mainly caused by the combination of low-altitude vortex and surface cyclone.Heavy precipitation occurred in the cold and north side of the cyclone center.The temperature on 925 hPa and near-surface dropping below 0℃was the important indicator of the conversion from rainfall to snowfall.(2)The change of wind field below 1 km was the signal of precipitation start.The change of strength of low-layer cold pad determined the transition of precipitation phase.The maximum detection height of the radar during snowfall was significantly lower than that during rainfall.The low-altitude wind-shear index would increase significantly at the beginning and end of precipitation.The small increase of the low-altitude wind-shear index during the continuous rainfall period corresponded to the increase of rainfall intensity.(3)The vertical velocity of the wind profile radar could not only reflect the change of precipitation intensity,but also reflect the change of precipitation phase.The vertical velocity near ground gradually decreased during phase transition.(4)Both structure constant of atmospheric reflective index and signal-to-noise ratio showed a decreasing trend with height,and the changes of them could reflect the change of precipitation intensity.They all had zero-level bright band characteristics,and the disappearance of bright band corresponded to the beginning of snowfall.