Investigating the impact of subgrid-scale aerosol-cloud interaction on mesoscale meteorology prediction

Abstract. Aerosol-cloud interaction (ACI) significantly influences global and regional weather systems and is a critical focus in numerical weather prediction (NWP), but subgrid-scale ACI effects are often overlooked. Here, subgrid-scale ACI mechanism is implemented by explicitly treating cloud microphysics in KFeta convective scheme, which realizes real-time subgrid-scale size-resolved hygroscopic aerosol activation and cloud radiative feedback, in a mesoscale atmospheric chemistry model CMA_Meso5.1/CUACE to investigate its impacts on meteorology prediction in summer over central and eastern China. Results show that incorporating subgrid-scale ACI refines cloud representation even in some grid-scale unsaturated areas and subsequently leads to attenuated surface downward shortwave radiation with regional mean bias (MB) decreasing by 23.1 %. The increased cloud radiative forcing results in lower temperature and higher relative humidity (RH) at 2 m, helping to reduce regional MB by 40 % and 18.1 %. Temperature vertical structure and RH below ~900 hPa are improved accordingly due to cooling and humidifying. Subgrid-scale ACI further significantly enhances precipitation, especially at grid-scale, thus reducing regional MB by 34.4 %. The differences in subgrid-scale ACI effects between various subregions are related to convective conditions and model local errors. Additionally, compared to simulations with anthropogenic emissions turned off, subgrid-scale actual aerosol inhibits cumulative precipitation during a typical heavy rainfall event by 5.6 %, aligning it with observations, associated with lower autoconversion at subgrid-scale and less available water vapor for grid-scale condensation, suggesting competitions between subgrid- and grid-scale cloud. This study demonstrates the importance of real-time subgrid-scale ACI in NWP models and the necessity of multiscale ACI studies.