河南北中部一次雨雪冰冻过程的相态特征分析

Characteristics of the precipitation phase during a rainfall/snowfall and freezing event in northern and central Henan

2023年末河南北中部出现一次大范围雨雪冰冻过程,降水相态复杂多变,并伴有区域性雷暴,较为罕见。利用常规观测、ERA5再分析以及风廓线雷达和双偏振雷达资料等对此次过程的相态特征及成因进行分析。结果表明:(1)500 hPa横槽转竖、南支槽东移,700 hPa西南急流发展,地面先后受东路及西路冷空气影响,导致河南北中部出现持续性大范围雨雪冰冻天气。(2)冷垫以上的条件不稳定性、锋区附近的条件对称不稳定以及强锋生环流上升支为对流天气发生发展提供有利条件,是强雨雪、雷暴及冰雹产生的主要原因。(3)过程中冻雨对应“厚暖层(100-200 hPa)-冷层”层结结构,冰粒对应“冰晶层-薄暖层(50-100 hPa)-冷层”结构,纯雪对应整层冷层,雨夹雪对应近地面出现浅薄暖层。(4)风廓线雷达水平风场产品可定性反映低层西南急流和近地面冷空气强度的变化,不同相态降水的垂直速度产品差异明显,可为相态转变短临的监测和预报提供参考。(5)双偏振产品显示,冻雨和纯雪对应相关系数最大(≥0.99),雨夹雪相关系数最小(0.85~0.9);冰粒中层融化层显著,其高度处差分反射率因子最大,相关系数最小。

At the end of 2023,a large-scale rainfal/snowfall and freezing event occurred in northern and central Henan,featuring variable precipitation phases and accompanied by regional thunderstorms,which was relatively rare.This paper analyzed this process by using the data from conventional observations,ERA5 reanalysis,wind profile radar,and dual-polarization radar with a focus on the characteristics of precipitation phases and cause.The results are as follows.(1)At 500 hPa,the horizontal trough turned vertical,and the south branch trough moved eastward,while at 700 hPa,the southwest jet developed.Meanwhile,the ground was affected by the cold air from the east and the west successively,which led to the persistent large-scale freezing rain and snow weather in northern and central Henan.(2)The conditional instability above the cold cushion,the conditional symmetry instability near the frontal zone,and the upward branch of strong frontogenesis circulation provided a favorable condition for the occurrence and development of convective weather,which were the main causes of heavy rain and snow,thunderstorm,and hail.(3)During the process,the freezing rain corresponded to a"thick warm layer(100-200 hPa)-cold layer"stratification,with the ice pellets linking to a"layer of ice crystals-thin warm layer(50-100 hPa)-cold layer"stratification.While the pure snow and sleet corresponded to an entirely cold layer stratification and a shallow warm layer near the ground,respectively.(4)The horizontal wind field products of wind profile radar can qualitatively reflect the changes in the low-level southwest jet stream and the intensity of cold air near the ground.The differences in the vertical velocity products of different precipitation phases are significant,providing a reference for the monitoring and forecasting of short-term phase transitions.(5)The dual-polarization products revealed that the freezing rain and pure snow had the highest correlation coefficients(≥0.99),while the sleet had the lowest(0.85-0.9).The ice pellets showed a significant middle-layer melting,with a maximum differential reflectivity and a minimum correlation coefficient at that level.