The Source of Discrepancies in Cloud and Precipitation Susceptibilities between GCMs and A-Train Retrievals

This study identifies a fundamental flaw of a general circulation model (GCM) in representation of the aerosol-cloud-precipitation interaction. A systematic difference is found in the response of liquid water path (LWP) to aerosol perturbations between the model and A-Train satellite observations; the model shows a globally uniform increase of LWP with increasing aerosol turbidity, while the response of LWP from the A-Train varies in sign from region to region. The satellite-observed response of LWP is also found to closely relate to meteorological/macrophysical factors in addition to the microphysics. The model does not reproduce this variability of the cloud susceptibility since the parameterization of autoconversion process assumes only a suppression of rain formation in response to increased cloud droplet number with a lack of buffering mechanisms, which has been recognized as a critical aspect of the climate system. This causes a fundamental bias in prediction of the future climate change. We currently plan to apply a 2-moment prognostic precipitation framework in the MIROC-SPRINTARS to overcome this issue. The details of single-column tests will be also shown in the presentation. This study was supported by Grant-in-Aid for JSPS Research Fellows (15J05544), for Scientific Research (15K12190), and the Environment Research and Technology Development Fund (S-12-3) of the Ministry of the Environment, Japan.