Dust aerosols affect Earth’s climate through direct and indirect perturbations of global energy balance, and interactions with atmospheric chemistry and biosphere. Therefore, it is important to quantify representation of dust aerosols in global climate models. Recent developments of high-resolution climate models have two-fold effects on simulating dust and “climate state-dependent” natural aerosols through changes of their emissions and meteorological fields on aerosol removal. Here we examine dust simulations in the DOE Earth System Model (ACME) with observations, and quantify the impact of increasing model resolution from low res (1 deg) to high-res (0.25 degree) on direct radiative forcing by dust.
Compare to the low-res model, increase of model resolution by 4 times leads to 29% higher dust emissions, due to improved surface heterogeneity and subgrid wind speeds. Dust aerosol optical depth (AOD) increases from 0.026 to 0.037 by 42%. On the other hand, wet removal of all the aerosols is more efficient in the high-res due to enhanced cloud and precipitation processes. The enhancement of aerosol removal compensates for the increase of dust emissions and AOD, resulting in a global mean AOD (0.145) similar to the low-res model (0.143).This suggests that higher model resolution leads to a larger contribution of dust to total aerosol direct radiative effect. Constrained by observationally derived dust AOD, emissions of dust (and sea salt) aerosols are downscaled, thus the predicted global AOD decreases by 16%, with larger changes on the regional scale. Since dust AOD is dominated by contribution of fine-mode dust, coarse-mode dust masses are less constrained by AOD observations. We will further use surface observations of dust deposition to optimize the dust emissions in the ACME model. Sensitivity studies of different dust size distributions at emission will also be examined. Direct radiative forcing by dust will be estimated and the resulting changes because of increasing model resolution will be discussed.