Satellite-based model constraint on cloud microphysical processes and its link to radiative forcing of aerosol-cloud interaction

This study seeks for a better use of multi-sensor satellite observations of cloud and precipitation for evaluating and constraining the cloud microphysical processes in global climate models and for investigating their link to global estimates of radiative forcing due to aerosol-cloud interaction. To this end, we first employ a methodology for diagnosing warm rain processes with a combined use of active and passive satellite measurements of the cloud-precipitation system. The multi-variate statistics of radar reflectivity, cloud optical depth, and effective particle radius constructed with the methodology are compared between satellite observations and a suite of sensitivity experiments conducted using a global climate model with alternate parameterizations of the auto-conversion process to evaluate the warm rain process representations of various parameterizations against satellite observations. The cloud responses to aerosol perturbations are then investigated for alternate auto-conversion parameterizations with two structurally different precipitation treatments, namely diagnostic and prognostic precipitation, to reveal their systematically different dependences on auto-conversion through differing interactions with wet-scavenging process. This also makes a significant difference in estimated magnitude of radiative forcing due to aerosol-cloud interaction and its sensitivity to auto-conversion parameterizations in the model. These results imply that additional satellite-based diagnostics on wet-scavenging process would be required for better constraining the model representation of the aerosol-cloud-precipitation interaction process and thus for narrowing down the uncertainty range of the radiative forcing. Furthermore, the satellite-based diagnostics of warm rain process is also extended into mixed-phase precipitation with the aid of cloud thermodynamic phase information from lidar and imager to observationally probe how “phase transition” of precipitation occurs on the global scale. Its potential use for model evaluations of ice-containing clouds and their interaction with aerosol perturbations will also be discussed in the presentation.