Numerical Simulation of a Torrential Rain Event in Beijing

With the parallel computing technique, numerical simulation with a 9-km resolution horizontal resolution grid nested inside a 27-km domain with the advanced regional prediction system (ARPS) model is conducted to study the mechanism of an orographic torrential rain event in Beijing. Results show that a cold and moist southeasterly airflow with strong wind speed convergence in the boundary from the Bohai sea pushing the warm convective unstable air in land climbs along the east slope of the Taihang mountain and triggers the convection. The southeasterly airflow mainly acts as the trigger mechanism together with the orography. The convective unstable air on the slope, at the top of the Taihang mountain and in land near Beijing is necessary for the occurring of the torrential rainfall. After the outbreak the convective system moves eastward. As a result, torrential rain occurs at the foot of the mountain at Mentougou.