PNNL

Abstract

Marine boundary-layer clouds play a critical role in the Earth’s energy balance. Their microphysical and radiative properties are highly impacted by ambient aerosols and dynamical forcings. In this study, we evaluate the representation of these clouds and related aerosol-cloud interactions processes in the E3SM climate model in the single-column model (SCM) framework, against field measurements collected during the NASA ACTIVATE campaign, as well as intercompare with high-resolution process-level models. Results show that E3SM-SCM, driven by the ERA5 reanalysis, reproduces the cloud properties as good as the high-resolution WRF simulations. For stronger surface forcings combined with a weaker subsidence taken from a regional WRF simulation, E3SM-SCM and WRF-LES produce thicker clouds. This indicates that a proper match of large-scale dynamics, sub-grid scale parameterizations, and model configurations is needed to obtain optimal performance of cloud simulations. In the E3SM-SCM sensitivity test with given dynamics but perturbations in aerosol properties, higher aerosol number concentration leads to more numerous but smaller cloud droplets, resulting in stronger shortwave cloud forcing. This apparent Twomey effect is consistent with prior climate model studies. Cloud liquid water path shows a weakly positive relation with cloud droplet number concentration associated with precipitation suppression, which does not reveal the nonlinear relation approximated from prior observations and E3SM studies, warranting future investigation. Our findings indicate that the SCM framework is a key tool to bridge the gap between climate models, high-resolution models, and field observations to facilitate process-level understanding