Numerical Simulation and Diagnosis of a Nocturnal Warming Process in the Hebei Winter Olympic Games Area

Nocturnal warming is a frequent weather phenomenon in the Hebei Winter Olympic Games area, and its accurate simulation and forecast are very important for the construction of the competition area and guarantee of the competition. By introducing the higher resolution terrain data, the mesoscale regional numerical model WRFv4.1.5 was used to reproduce the nocturnal warming process, and the meteorological characteristics and causes of the process were explored. Results show that: (1) the process is affected by the northeast cold vortex, (2) the cold advection is significant at the middle and upper levels, (3) the wind shear is strong at the high and low levels, and (4) there are obvious advection differences. At the same time, the variation characteristics of meteorological elements near the surface are obvious, including the decrease in relative humidity, increase in wind speed, decrease in sea level pressure, and enhancement of surface heat flux and long-wave radiation. In addition, the strong wind shear and advection difference between the upper and lower levels easily produces vertical mixing. The isentropic surface fluctuation is obvious and the turbulence is strengthened, which further strengthens the turbulent vertical mixing movement, enhances the moving heat flux transport, and produces the abnormal increase of night temperature.