Numerical Simulation of the Formation and Dissipation of a Cold Air Pool in the Chongli Winter Olympic Games Area

Based on the mesoscale regional numerical model (WRF) and a spectral nudging method, this study simulates a cold air pool (CAP) process during the 2021 Winter Olympics test competition. The vertical change in the wind and temperature fields during this process has been analyzed, and the specific reasons for the formation and dissipation of the CAP have been demonstrated. The results show that the stationary synoptic situation formed the general background for the maintenance and development of the CAP. During the development of the CAP, a temperature inversion layer was rapidly established from top to bottom, and a southeast cold air flow appeared at the bottom of the valley. Affected by the downward gravitational wind, the cold air accumulated at the bottom of the valley, and the CAP deepened. After sunrise, the mesoscale winds over the mountain were reestablished. The temperature inversion layer was eroded from the bottom, and the structure of the CAP was destroyed. Strong nocturnal radiation cooling was the main reason for the formation of the CAP. Differences in the intensity of radiation cooling cause differences in the cooling range of the CAP. Sudden enhancement of radiational cooling after midnight created favorable conditions for the maintenance and development of the CAP in the middle and later periods. Through analysis of the evolution of the potential temperature profile, friction velocity, and boundary layer height during the process, it can be confirmed that the development of turbulent activity is an important factor in influencing the dissipation of the temperature inversion and the destruction of the CAP structure.