ISSN 1006-9895

CN 11-1768/O4

Relationship between vertical convection structure and precipitation simulation bias in the tropical atmosphere: An analysis based on GAMIL3

The Institute of Atmospheric Physics, Chinese Academy of Sciences

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    Based on the LASG/IAP developed general circulation model GAMIL2 (G2) and GAMIL3 (G3), the simulation ability of tropical precipitation and convective vertical structure was evaluated, and the reasons for the improvement of precipitation simulation and the relationship between the vertical structure of tropical convection and precipitation simulation deviations were explored. Both versions of GAMIL precisely capture the main characteristics of tropical precipitation, while G3’s simulation are globally accurate than G2. The main improvement of the new version is to significantly reduce the positive precipitation bias in the tropical northwest Pacific Ocean. The water vapor budget diagnosis shows that the precipitation deviation mainly come from the evaporation term and the vertical advection dynamic term, and the latter comes from the combined effect of intensity of vertical motion and the vertical motion profiles. The vertical structure deviation of convection mainly exists in equatorial Indian Ocean and equatorial Atlantic Ocean areas, which mainly corresponds to weaker convergence component in lower atmosphere and higher altitude of detrainment. In the tropical northwest Pacific and equatorial Eastern Pacific, the typical “top-heavy” and “bottom-heavy” characteristic of the vertical motion profile are well represented, but the deeper convection than reanalysis data is still eminent. The wet static energy (MSE) budget shows that the excess net energy flux over the tropical Northwest Pacific is the main source of the modeled vertical motion deviation. However, the deeper vertical convective structure results in a larger gross moist stability (GMS), which offset the net energy flux deviation and inhibited the simulated convective intensity. the significant improvement of precipitation simulation in the tropical northwest Pacific in G3 Is mainly due to the reduction of positive deviation of convective intensity. The down-regulation of convective threshold and stratus threshold in G3 increase the frequency of convection and inhibits excessive intensity of vertical motion. The vertical structure of tropical convection has various and close relationships with precipitation deviation, which should be paid more attention to in future model development.

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  • Received:June 10,2021
  • Revised:September 15,2021
  • Adopted:October 08,2021
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