应用气象学报 (Jul 2024)
Comparison of Two Ice and Snow Storm Processes in China in February 2024
Abstract
Two ice and snow storm processes hit middle and eastern China during 31 January to 7 February (Process Ⅰ) and 19 February to 25 February (Process Ⅱ) 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. Process Ⅰ is characterized by deeper ice-accretion and snow depth, while Process Ⅱ is 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 Process Ⅰ: An ice crystal layer, melting layer, and liquid layer from top to the bottom. However, there are four layers for Process Ⅱ which are ice crystal layer, melting layer, liquid layer and refrozen layer from top to the bottom. So, for Process Ⅰ, there is no significant refreezing, and the precipitation droplets are mainly supercooled liquid falling through the cold layer near the surface. Process Ⅰ is mainly characterized by freezing rain and deeper ice accretion. During Process Ⅱ, 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 Process Ⅱ. 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 Process Ⅱ are stronger than that of Process Ⅰ, leading to stronger warm layer and cold layer in Process Ⅱ and the colder low level cold layer is the main reason for the significant ice pellet in Process Ⅱ.
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