Hu Tiantian, Yi Xiaoyuan, Wu Di, et al. Simulation of mesoscale convection process into sea based on downscaling method. J Appl Meteor Sci, 2022, 33(6): 711-723. DOI:  10.11898/1001-7313.20220606.
Citation: Hu Tiantian, Yi Xiaoyuan, Wu Di, et al. Simulation of mesoscale convection process into sea based on downscaling method. J Appl Meteor Sci, 2022, 33(6): 711-723. DOI:  10.11898/1001-7313.20220606.

Simulation of Mesoscale Convection Process into Sea Based on Downscaling Method

DOI: 10.11898/1001-7313.20220606
  • Received Date: 2022-06-26
  • Rev Recd Date: 2022-08-04
  • Available Online: 2022-11-21
  • Publish Date: 2022-11-17
  • 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.
  • Fig. 1  Simulation domain

    Fig. 2  Composite reflectivity factor of Tanggu and Cangzhou radars on 12 May and 13 Jul in 2018

    Fig. 3  500 hPa height(the blue isoline, unit: dagpm), temperature(the red isoline, unit: ℃) and wind(the barb); 925 hPa water vapor flux(the shaded), height(the blue isoline, unit: dagpm), temperature(the red isoline, unit: ℃) and wind(the barb); surface sea level pressure(the grey isoline, unit: hPa), 2 m temperature(the shaded) and 10 m wind(the barb) on 12 May and 13 Jul in 2018

    Fig. 4  Max reflectivity factor from RMAPS-Ocean and after two times downscaling on 12 May and 13 Jul in 2018

    Fig. 5  The same as in Fig. 4, but for the sensitivity experiment

    Fig. 6  Convective available potential energy(the shaded, unit: J), 0-6 km vertical wind shear(the red isoline, unit: m·s-1) and 850 hPa wind(the barb) on 12 May and 13 Jul in 2018

    Fig. 7  Vertical cross-section of buoyancy B(the shaded) and the combination(the arrow) of zonal wind(unit: m·s-1) and vertical movement(unit: 10-1m·s-1) on 12 May and 13 Jul in 2018(the vertical cross-sections are made along the black line in Fig.4, blue solid lines in the bottom of the figures denote the sea surface)

    Fig. 8  Vertical profile of apparent heat source Q1, apparent moist sink Q2, as well as effects of local change Q1_lc and Q2_lc, horizontal advection Q1_adv and Q2_adv, vertical transfer Q1_vt and Q2_vt effects on 12 May and 13 Jul in 2018(the selected region is shown in red box in Fig. 4)

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