2024年2月我国两次大范围雨雪冰冻天气对比

Comparison of Two Ice and Snow Storm Processes in China in February 2024

2024年1月31日—2月7日(过程Ⅰ)和2月19—25日(过程Ⅱ)我国中东部地区先后出现两次大范围、持续性的雨雪冰冻天气过程,利用地面观测、再分析资料、双偏振雷达、雨滴谱等分析两次过程的雨雪冰冻实况、微物理特征、环流形势和层结特征,并对比二者异同。结果表明:两次过程的影响区域、持续时间和总降水量接近,但过程Ⅰ积冰更厚、积雪更深,过程Ⅱ影响范围更广、降雪量更大。过程Ⅰ降水粒子从上到下呈3层结构特征,即冰晶层-融化层-液态层,过程Ⅱ呈4层结构特征,即冰晶层-融化层-液态层-再冻结层,导致过程Ⅰ冻雨更明显、积冰更厚,过程Ⅱ冰粒更多、积雪深度较浅、积冰厚度较薄。环流形势和层结特征显示两次过程均为西伯利亚高压和南支系统的协同作用,但过程Ⅱ低层急流强度和地面西伯利亚高压更强,导致过程Ⅱ中层暖层和低层冷层的强度均强于过程Ⅰ,而冷层更强是过程Ⅱ冰粒更明显的直接原因。

Two ice and snow storm processes hit middle and eastern China during 31 January to 7 February(ProcessⅠ)and 19 February to 25 February(ProcessⅡ)in 2024,which are the most extreme ice and snow events since 2009.After the long-lasting cryogenic freezing rain and snow weather in the beginning of 2008,studies about freezing rain and snow storm have effectively improved the ability of subjective forecast and objective forecast skills of these kinds of weather.However,the accuracy of forecasting ice,freezing rain,and snow storm cannot meet demands of society.Recently,the capability of new types of observations has significantly advanced,and the surface observation system is more complete.Utilizing these more comprehensive observations to analyze and compare characteristics of these two processes will be beneficial for precious,objective and quantitative forecast of ice and snow storm,ice-accretion for example.The ice and snow surface observations,reanalysis dataset,and new types of observations,including dual polarization radar and raindrop spectrum,are used to analyze the precipitation,snowfall,ice-accretion and so on.In addition,microphysical characteristics,atmospheric circulations,and stratification features of these two processes are summarized and compared,and causes for differences is researched.Results show that the affected areas,duration,and total amount of precipitation in these two processes are similar.ProcessⅠis characterized by deeper ice-accretion and snow depth,while ProcessⅡis characterized by a larger affected area and increased snowfall.The observation of dual polarization radar shows that there are three layers of precipitation drops for ProcessⅠ:An ice crystal layer,melting layer,and liquid layer from top to the bottom.However,there are four layers for ProcessⅡwhich are ice crystal layer,melting layer,liquid layer and refrozen layer from top to the bottom.So,for ProcessⅠ,there is no significant refreezing,and the precipitation droplets are mainly supercooled liquid falling through the cold layer near the surface.ProcessⅠis mainly characterized by freezing rain and deeper ice accretion.During ProcessⅡ,significant refrozen to mixed or solid precipitation near the surface happens which results in more ice pellets which is not good to ice-accretion.On the other hand,the density of ice pellets is larger than that of snow,resulting in thinner snow depth and less ice-acceration for ProcessⅡ.The atmospheric circulation and stratification features indicate that both processes are characterized by cooperation of Siberia high and southern branch trough.However,the lower-level jet and Siberia high of ProcessⅡare stronger than that of ProcessⅠ,leading to stronger warm layer and cold layer in ProcessⅡand the colder low level cold layer is the main reason for the significant ice pellet in ProcessⅡ.