Evaluation of Autoconversion Schemes and Microphysical Processes in the MIROC-SPRINTARS with Satellite Observations

Abstract:

This study examines autoconversion schemes in warm rain, which are commonly used in general circulation models. The model used in this study is an aerosol climate model, MIROC-SPRINTARS, which is employed for sensitivity experiments in a single-model framework to preclude biases from different treatments of the aerosol-cloud-precipitation interaction. The results show that both micro- and macrophysical parameters (e.g., cloud effective radius, and liquid water path (LWP)) are highly sensitive to the schemes. The ratio of accretion to autoconversion (Acc/Aut ratio), also shows a high sensitivity depending on the schemes. The Acc/Aut ratio monotonically increases with increasing LWP, however, Kessler-type schemes with autoconversion threshold tend to predict the ratio significantly lower than model-based schemes without autoconversion threshold. The potential uncertainty in the warm rain process is still large, but a significant improvement of cloud radiative effect cannot be expected by changing just the auto-conversion scheme. This means that more fundamental errors are still left in other processes of the model. We currently plan to apply the prognostic precipitation including drizzle in the MIROC-SPRINTARS to overcome this issue.

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.