Mechanistic Impacts of a Scale-Aware Convection Scheme on Typhoon Intensity

This study investigates the impact of a scale-aware convective parameterization scheme (CPS) on the simulation of typhoon track and intensity through a series of experiments using the Global-to-Regional Integrated forecast SysTem (GRIST) model. Through a series of experiments using the GRIST model, we investigate the impact of scale-aware CPS on the simulation of typhoon track and intensity. The results of four typhoon cases show that scale-aware CPS helps to reduce the track error by about 15 km and the intensity error by about 10%, demonstrating the benefits of scale-aware CPS on typhoon modeling. The Lekima case is then used as an example to illustrate the reasons behind the improved typhoon intensity with scale-aware CPS. By analyzing the budget equation of surface pressure tendency contributed by different physical processes, we found the pressure depression due to CPS heating is about 0.6 hPa h^-1 weaker when scale-aware CPS is applied. However, the microphysics process takes up the convective instability left over by CPS and outweighs the reduction in parameterized convection, yielding a net pressure depression of about 1 hPa h^-1. This suggests the suppression of sub-grid convection favors the stimulation of stronger microphysics heating due to stronger grid-scale ascending. Further examination of the inner-core precipitation validates the assertion. Indeed, when the scale-aware CPS is applied, the microphysics precipitation and corresponding diabatic heating in the inner-core region increase by about 9.5% and 13.8% respectively, which more than offsets the decrease in precipitation and diabatic heating of the CPS component. This is accompanied by stronger grid-scale ascending and accelerated radial winds, with the low-level inflow and upper-level outflow increased by about 2 m s^-1. In summary, by suppressing sub-grid convection and enhancing microphysics process, the scale-aware CPS intensifies the secondary circulation, producing stronger diabatic heating and thus enhanced typhoon intensity.