Characteristics of the precipitation phase during a rainfall/snowfall and freezing event in northern and central Henan

At the end of 2023, a large-scale rainfall/snowfall and freezing event occurred in northern and central Henan, featuring variable precipitation phases and accompanied by regional thunderstorms, which was relatively rare. This paper analyzed this process by using the data from conventional observations, ERA5 reanalysis, wind profile radar, and dual-polarization radar with a focus on the characteristics of precipitation phases and cause. The results are as follows. (1) At 500 hPa, the horizontal trough turned vertical, and the south branch trough moved eastward, while at 700 hPa, the southwest jet developed. Meanwhile, the ground was affected by the cold air from the east and the west successively, which led to the persistent large-scale freezing rain and snow weather in northern and central Henan. (2) The conditional instability above the cold cushion, the conditional symmetry instability near the frontal zone, and the upward branch of strong frontogenesis circulation provided a favorable condition for the occurrence and development of convective weather, which were the main causes of heavy rain and snow, thunderstorm, and hail. (3) During the process, the freezing rain corresponded to a "thick warm layer (100-200 hPa)-cold layer" stratification, with the ice pellets linking to a "layer of ice crystals - thin warm layer (50-100 hPa) - cold layer" stratification. While the pure snow and sleet corresponded to an entirely cold layer stratification and a shallow warm layer near the ground, respectively. (4) The horizontal wind field products of wind profile radar can qualitatively reflect the changes in the low-level southwest jet stream and the intensity of cold air near the ground. The differences in the vertical velocity products of different precipitation phases are significant, providing a reference for the monitoring and forecasting of short-term phase transitions. (5) The dual-polarization products revealed that the freezing rain and pure snow had the highest correlation coefficients (≥0.99), while the sleet had the lowest (0.85~0.9). The ice pellets showed a significant middle-layer melting, with a maximum differential reflectivity and a minimum correlation coefficient at that level.