Simulation of Mesoscale Convection Process into Sea Based on Downscaling Method

Abstract

Two processes of mesoscale convection moving eastward into the Bohai Bay on 12 May and 13 Jul in 2018, which are weakened process and enhanced process respectively, are simulated and analyzed by using the ocean-atmosphere-wave coupling model and dynamic downscaling method. Both processes occur under the control of strong southwesterly at low level and warm tongue near surface, which bring abundant water vapor and heat. The results show that the coupling model can simulate the right trend of the weakened process, but the wrong trend of the enhanced process, and the simulated intensity is overall weak. The simulation effects are improved obviously after the spatial resolution of the model increasing by using dynamic downscaling method twice. Through the comparison of sensitivity experiments, it is indicated that the coupling model has certain advantages in providing better initial and boundary conditions for the dynamic downscaling, which is suitable for the simulation, compared with the general atmospheric WRF model. Through the diagnosis and analysis of the simulation results, it's concluded that before the convection systems entering the sea, the convective available potential energy (CAPE) is large in the Bohai Bay and coastal areas. As the convection systems moving eastward into the sea, the CAPE is gradually consumed, but the supplement of CAPE in the enhanced process is stronger than that in the weakened process. The 0-6 km vertical wind shear condition of the enhanced process is also stronger than that of the weakened process in the Bohai Bay before the convection systems entering the sea, which is another favorable factor for the development of the convection. In the weakened process, the cold pool effect is increasingly stronger with an obvious rear inflow, and there is an obvious wind velocity convergence in the front of the cold pool during the convection systems moving. In the enhanced process, however, the strength of the cold pool is weaker, but the range is larger compared with the weakened process, and there is an obvious wind direction convergence in the front of the cold pool. In the weakened process, the underlying surface of the ocean provide less water vapor and heat energy for the convection region, making the convection difficult to maintain or further develop, while in the enhanced process the sea surface provides mass water vapor and heat energy transfer to the convective region when the convection system moving over the sea.

Keywords

• ocean-atmosphere-wave coupling model
• dynamic downscaling
• mesoscale convection system into the sea
• cold pool