Role of autoconversion process in assessing the low-level clouds over the southern Indian Ocean in Climate Forecast System (CFS) version 2

The sensitivity of a modified realistic critical droplet radius concerning the rain autoconversion process on the simulation of low-level clouds over the southern Indian Ocean (SIO) has been investigated. Two simulations are performed with the National Centers for Environmental Prediction (NCEP) Climate Forecast System version 2 (CFSv2) model, one (CFSCR) with default physically based cloud scheme (WRF single-moment 6-class microphysics scheme (WSM6)) and the other with modified CFSCR (CFSCR-Mod). In CFSCR-Mod, the critical droplet radius as a function of the rain autoconversion process is revised. Keeping in mind the variability of cloud condensation nuclei (CCN) over the land and ocean, the critical droplet radius is put differently over land and ocean. The fidelity of both the models in simulating SIO low-level clouds is evaluated concerning different observational and re-analysis products. Observations exhibit the prominent occurrence of low-level clouds over the SIO in the 30–10°S latitudinal and 80–100°E longitudinal belt. The analysis reveals that CFSCR-Mod has a better fidelity to capturing low-level clouds due to its more realistic autoconversion process and realistic cloud microphysics.