Processes Regulating Low-Cloud Response to Aerosol and Temperature Perturbations in a Global Climate Model

Monday, December 10, 2018 - 09:45
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Cloud responses to temperature and aerosol perturbations are considered major uncertainty sources in climate projections. In this study, we perform the one-at-a-time type of perturbed physics ensemble to quantify the parametric sensitivity of cloud (Cess) feedback and anthropogenic aerosol indirect effects associated with the process representations in the cloud macrophysics (e.g., cloud phase, subgrid cloud variability), microphysics (e.g., droplet sedimentation, autoconversion, accretion), and convection (e.g., turbulence, subgrid vertical velocity, entrainment) parameterizations in the Energy Exascale Earth System Model (E3SM) Atmosphere Model version 1 (EAMv1). We find that processes that affect cloud response to temperature perturbations often also affect cloud response to aerosol perturbations. Changes in the cloud responses can be explained by the changes in precipitation efficiency, cloud-top entrainment, and vertical mixing. We quantify the contribution of these mechanisms to the low cloud responses in different cloud regimes, aerosol regimes, and large-scale dynamical regimes. We also assess the utility of satellite observations as constraints for models, and identify conditions where satellite measurements can serve as strong constraints. This study provides insights into the connections between process representations and the system response, guiding future model development and calibration while reducing the uncertainty in the cloud responses to external forcings.

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