Comparative analysis of two major widespread freezing rain events in China in February 2024

Two large-scale snow and rain weather processes occurred in china from February 1-4, 2024 (Process 1, hereinafter), and February 19-24, 2024 (Process 2, hereinafter). During these two weather processes, the impact of freezing rain was extensive, the intensity of the disaster was severe, and the duration was long, which was rare in history. This study utilized multi-source observational data and ERA5 reanalysis data to focus on analyzing the environmental conditions and temperature layer characteristics of these two freezing rain events. The results indicate: (1) During both weather events, the 500 hPa weather patterns and influencing systems were quite similar, which were stably sustained, providing favorable conditions for widespread snow, rain, and freezing weather. However, there were differences in the low-level temperature configuration and the speed of movement. In Process 1, due to the slower movement of the cold air, the distribution of freezing rain was more concentrated. The initial southwest jet stream in Process 2 was stronger and positioned further north compared to Process 1, leading to the occurrence of freezing rain further northward. However, in the later stages, the rapid southward movement of strong cold air caused a fast-moving rain, snow, and ice, and thus a larger impacting range of the freezing rain. (2) In both processes, the mid-level warm layer was mainly located between 700 hPa and 850 hPa, while the low-level cold layer was mainly located below 900 hPa. The positions were lower than the classic conceptual model of a warm layer at 700 hPa and a cold layer at 850 hPa, which could easily lead to misjudgment of the weather situations and types. (3) Using the area method, the strength of the mid-level warm layer and the low-level cold layer was calculated separately for both processes. The results show that the strength of the warm and cold layers in Process 1 was weaker than in Process 2. In addition, the freezing rain in both processes mainly occurred in areas where the strength of the mid-level warm layer and the low-level cold layer were close.