暖干背景下的河南春季极端雨雪天气成因分析

Analysis on Weather Causes of a spring extreme rain-snow event under warm-dry backgroud condition over Henan

中文关键词:  暖干背景，极端雨雪，条件对称不稳定，降水相态，相变降温

英文关键词:warm-dry backgroud condition  extreme rain-snow event  conditional symmetric instability  precipitation phase  phase-change Cooling

中文摘要:

      处于过渡季节的春季极端雨雪天气预报,一直以来都是预报中的难点。文章利用常规地面观测、探空观测资料、雷达和ERA5再分析数据,对2023年3月16日发生在河南的一次极端雨雪天气成因进行了分析,重点关注了其极端降水及复杂雨雪相态转换成因,主要结论如下：此次过程是一次发生在暖干背景下由高空槽东移配合低涡切变北抬造成的极端雨雪天气,过程前后天气转折性强,过程期间降雪强度大、强降雪时段长,降雪时段地面气温始终维持在0℃附近,雨雪相态转换复杂；异常偏强的极端动力强迫特征,是此次过程小时降水强度较大的重要因素,对流层低层异常偏强的低空急流所伴随的热动力强迫,是造成其极端异常动力强迫的重要原因,条件对称不稳定,则在一定程度上加剧了其垂直上升运动的发展,低涡移动缓慢、回波系统走向与移向夹角较小,是其降水持续较长时间的关键；过程前期气温异常偏高,15日的冷空气降温,为其实现雨雪相态的转换提供了可能,过程开始阶段对流层低层存在明显干层,与此相伴随的由降水粒子蒸发等相变过程造成的降温,是其雨转雪天气发生的重要降温机制,干层的存在及降水的持续发展,成为其温度能否降到0℃附近的关键,大气趋于饱和之后,冰晶粒子的融化降温在其降雪相态维持中也起到了十分重要的作用。

英文摘要:

      Extreme rain and snow events during the transitional season have always been difficult to forcast. In this paper, a spring extreme rain-snow event over Henan on 16 March 2023 was studied by using conventional surface observations, radiosonde observations, radar and ERA5 reanalysis data,focusing on the causes of its extreme precipitation and complex phase transition of rain and snow. The main conclusions are as follows: this process is an extreme rain and snow event caused by an upper trough moving easterly combined with a low vortex shear moving northly under warm-dry backgroud condition. The big turning changes of weather before and after the event, combined with the strong snowfall intensity, the longer duration of high snowfall rate,and the complax phase transition process occuring near 0℃, makes it very difficult to forcast. During the process, the abnormally strong extreme dynamic forcing, resulting from the thermodynamic forcing accompanied by the abnormally strong low-level jet in the lower troposphere and the conditional symmetric instability, is an important factor for the high hourly precipitation rate, and the slow movement of the low vortex and the small angle between the trend and direction of the echo system are the key to the long-term precipitation .The temperature at the early stage of the process was abnormally high, and the cooling process occurring on the 15th , makes it possible for the transition from rain to snow.At the beginning of the process, there is an obvious dry layer in the lower troposphere .During the process, the cooling effect caused by phase transition processes such as precipitation particle evaporation, is an important cooling mechanism for the occurrence of rain-to-snow weather,and the existence of the dry layer and the continuous development of precipitation are the key to whether the temperature can drop to around 0°C. After the atmosphere becomes saturated, the melting of ice crystal particles cooling mechanism also plays a very important role in the maintenance of its snowfall phase.