Comparative study of parameterization schemes for aerosol indirect effects in East Asia based on RegCM4

Cloud droplet nucleation, effective radius and cloud–water autoconversion rate (P) parameterization schemes are included in the fourth version of the Regional Climate Model (RegCM4). For cloud droplet nucleation, an empirical scheme (GI99), a semiempirical scheme (GH93), and a scheme based on aerosol activation theory (AG00) are involved. For P, a scheme dependent only on the cloud water mixing rate (Default), a scheme involving the droplet growth rate (BR67), a scheme highly correlated with aerosol components (BH94), a scheme weakly dependent on the components (TC80), a scheme involving the droplet size (LB95) and a scheme that derives a formula mathematically (IBS2) are adopted and tested. Dispersion (ε) is important when calculating the effective radius. Effective radius schemes with/without ε effects are further compared. An optimal combination of schemes is proposed. For cloud droplet nucleation, GH93 and AG00 are better. For P, LB95, BH94, and Default schemes could better simulate precipitation. Considering the ε effect would improve simulation accuracy. Overall, the AG00, BH94 and two-parameter-ε schemes are recommended for improving model simulations of precipitation in East Asia. The P schemes are compared when the aerosol 2nd indirect effects are investigated in East Asia. The change of net radiative flux at the top of the atmosphere from the schemes is −3.63 ± 4.05 W m⁻² in central to eastern China. The aerosol 2nd indirect effect is the most significant in the BH94 scheme, with average changes in cloud optical depth, net radiative flux, and precipitation of 1.63, −10.58 W m⁻², and -0.01 mm d⁻¹, respectively.