Amending the algorithm of aerosol-radiation interaction in WRF-Chem (v4.4)

Abstract. WRF-Chem is widely used to assess regional aerosol radiative feedback. However, in current version, aerosol optical properties are only calculated in four shortwave bands, and only two of them are used to “interpolate” optical properties towards 14 shortwave bands used in the Rapid Radiative Transfer Model (RRTMG) scheme. In this study, we use a “Resolved” algorithm to estimate aerosol radiative feedback in WRF-Chem, in which aerosol optical properties are calculated in all 14 shortwave bands. The impacts of changing this calculation algorithm are then evaluated. The simulation results of aerosol optical properties are quite different using the new “Resolved” algorithm, especially for dust aerosols. The alteration of aerosol optical properties result in considerably different aerosol radiative effects: the dust radiative forcing in the atmosphere simulated by the “Resovled” algorithm is about two times larger than the original “Interpolated” algorithm; The dust radiative forcing at top of the atmosphere (TOA) simulated by the “Interpolated” algorithm is negative in all Sahara region, while the “Resolved” algorithm simulates positive forcing at TOA and can exceed 10 W/m² in the Sahara desert, which is more consistent with previous studies. The modification also leads to changes in meteorological fields due to alterations in radiative feedback effects of aerosols. The surface temperature is changed due to the difference in radiation budget at the bottom of the atmosphere (BOT) and the heating effects by aerosols at the surface. Furthermore, the amendment of algorithm partially corrects the wind field and temperature simulation bias compared to the reanalysis data. The difference in planet boundary layer height can reach up to ~100 m in China and ~200 m in Sahara, further resulting in a greater surface haze considerably. The results show that correcting the estimation algorithm of aerosol radiative effects is necessary in WRF-Chem model.