大兴机场近4年降雪统计及相态转换机制讨论

Snowfall Statistics and Phase Transition Mechanism at Daxing Airport in Recent 4 years

摘要: 利用北京大兴国际机场2019.10月~2023.3月的自动观测系统地面气象观测数据、欧洲中心ERA5再分析资料、大兴机场微波辐射计和毫米波测云天气雷达资料，对大兴机场自开航以来冬半年降雪过程进行归类与分析，探讨在多相态降水过程中地面温度的作用。再选取具有相似气候特征的两次多相态降水过程进行对比分析，揭示形成降水相态转换的原因。最后，通过对大兴机场所有多相态降水过程的统计，提取降水相态的判别机制。结果表明：1) 自开航以来，大兴机场总共发生降雪过程29次，其中共10次多相态降水过程。2) 降水相态形成并不单受地面温度制约，与机场的气候特征、天气特征、温度层结的分布等因素均有关。3) 在降雨向降雪转换的过程中，冰雪层厚度占总云层的比例随低层温度的下降而上升，并且云中固态凝结物下落路径变短，降低了固态凝结物在下落过程中融化的概率，出现相态转换现象。4) 地面温度0℃及以下，850 hPa −4℃及以下时，降水相态多为降雪；地面温度2℃及以上，850 hpa温度−4℃及以上时，降水相态多为降雨；地面温度为0~2℃，850 hpa温度−4~0℃之间时，降水相态多为雨雪混合状态。5) 在多相态降水过程中，温度变化不明显时，冰雪层的厚度、冰雪层下边界距地面的距离，亦可作为降水相态转换的判别机制。

Abstract: Based on the ground meteorological observation data of automatic observation system of Bei-jing Daxing International Airport from October 2019 to March 2023.3, ERA5 reanalysis data of European center, microwave radiometer and millimeter-wave weather radar data of Daxing International Airport, the snowfall process of Daxing International Airport in winter and half a year since its opening was classified and analyzed. The effect of ground temperature in the process of multi-phase precipitation was discussed. Then two multi-phase precipitation processes with similar climatic characteristics were selected for comparative analysis to reveal the reasons for the formation of precipitation phase transition. Finally, through the statistics of all the multi-phase precipitation processes in Daxing Airport, the identification mechanism of precipi-tation phase is extracted. The results show that: 1) there have been 29 snowfall processes at Daxing Airport since the beginning of the voyage, including 10 multiphase precipitation pro-cesses. 2) The formation of precipitation phase state is not only restricted by surface temperature, but also related to the climatic characteristics, weather characteristics and distribution of temperature stratification of the airport. 3) During the transition from rainfall to snowfall, the ratio of ice and snow thickness to the total cloud layer increases with the decrease of low temperature, and the falling path of solid condensation in the cloud becomes shorter, which reduces the probability of the solid condensation melting in the falling process, and the phase transition phenomenon occurs. 4) When the ground temperature is 0˚C or below and 850 hPa −4˚C or below, the precipitation phase is mostly snow. When the ground temperature is 2˚C or above, and the temperature of 850 hpa is −4˚C or above, the precipitation phase is mostly rainfall. When the ground temperature is 0~2˚C and the temperature of 850 hpa is −4~0˚C, the precipitation phase is mostly mixed with rain and snow. 5) In the process of multi-phase precipitation, when the temperature change is not obvious, the thickness of ice and snow layer and the distance between the boundary of ice and snow layer and the ground can also be used as the identification mechanism of precipitation phase transition.