Abstract:

Based on the meteorological observation network data of the Winter Olympics Games, the high-resolution reanalysis data of ERA5 (ECMWF Reanalysis v5) (0.25°×0.25°), the conventional sounding data, and the laser radar and wind profile radar data, a rain-to-snow weather process in Zhangjiakou area of the Winter Olympics Games from November 17-19, 2020 was analyzed.The variables analyzed include the circulation situation, temperature and relative humidity, microphysical and radar characteristics, and other new data.The results show that the warm and wet southwest airflow in the early stage of the low layer provides water vapor and energy conditions for precipitation, and the strong dry and cold advection in the later stage provides favorable conditions for phase transition.When rain turns to snow in the competition area, the temperature at 700 hPa is below -2℃, while the temperature at 850 hPa is below 2℃.The rapid decline of the height of zero-temperature level is an important temperature criterion for phase transition.When the 0℃ line drops to about 400 m above the ground, the phase of precipitation in the competition area has turned into pure snow, and the shift of the wind direction at a low level has certain indicative significance for the phase transition of rain and snow in the competition area.As the content of cloud ice and snow water increases gradually, the phase of rain and snow begins to change after the cloud ice and snow water reach the maximum.The maximum detection height of lidar during snowfall is significantly lower than that during rainfall.The change of low-level wind field of wind profiler radar is closely related to the phase state of rain and snow, and the change of vertical velocity detected by wind profiler radar can also reflect the transformation of rain and snow phase state.

Key words: Winter Olympic Games, Rain and snow phase, Temperature and relative humidity, Wind profile radar