【摘要】 利用常规地面观测资料、探空资料、ERA5再分析资料，对2021年11月6日北京地区快速雨转雪天气过程的降水相态特征及转换机制进行分析研究，结果表明：此次过程受高空槽和西南低空急流共同影响，地面受高压前部偏北风控制，降水开始阶段，导致雨向雪相态快速转换的主要机制是雨滴蒸发降温，当空气相对湿度较小时，蒸发效应显著，导致边界层温度迅速下降，降温幅度超过2℃/h,降水粒子相态由雨转雪；随着降水持续，边界层大气趋于饱和，降水粒子蒸发降温作用弱，冷平流成为雨向雪相态转换的主要机制。数值模式通常在降雨初始阶段，低空大气饱和度低时，对雨滴蒸发所造成的气温快速下降估计不足，导致数值模式预报雨雪相态转换时间偏晚。并通过对2023年1月12日一次雨转雪再转雨降水相态转换过程的对比分析，进一步验证了雨滴蒸发降温和冷平流在相态转换不同阶段的作用。更多还原

【Abstract】 Using conventional ground, sounding observation data and ERA5 reanalysis data, the phase characteristics of precipitation during the rainy and snowy weather process in the Beijing area on 6 November 2021, are analysed. We draw the following conclusions compared with the event on 12 January, 2023: In the starting stage of precipitation, cooling resulting from rainfall evaporation led to rapid transformation of rain and snow phases. Evaporative cooling caused by the rainfall stage played a decisive role in near-surface cooling, while the contribution of temperature advection to rain-snow phase transition was more important as the humidity increased. At the beginning of rainfall, the relative humidity was low, evaporation was significant during the rainfall stage, and relative humidity rapidly increased, leading to a sudden drop in temperature of more than 2 ℃/h. This caused the boundary layer temperature to drop rapidly, thus enabling the rapid conversion of rain and snow phases. Model prediction of the situation field was accurate; however, the ability to predict the cooling effect caused by evaporation at the initial stage of rainfall was poor. The predicted temperature decreased more slowly than observed, resulting in a delayed transition time of the rain and snow phase.更多还原