Assessment of climate models in relation to the low‐level clouds over the southern Indian Ocean

Abstract

AbstractAgainst the backdrop of limited fidelity of climate models in capturing low‐level cloud variability, the representation of the southern Indian Ocean (SIO) marine boundary layer (MBL) clouds and their transition from low to deep cloud have been investigated in this study. A historical run of 26 models, that featured in the Coupled Model Intercomparison Project Phase 5 (CMIP5), and the National Centers for Environmental Prediction (NCEP)'s Climate Forecast System version 2.0 (CFSv2) models have been analysed along with different observational and reanalysis products. Observations clearly show the prominent occurrence of MBL low‐level clouds over the SIO in a 30–10°S latitudinal and 80–100°E longitudinal belt. Furthermore, there is a gradual transition from low to deep cloud towards the north of the Equator. The results reveal that the CMIP5 models were hardly able to capture the MBL low‐level clouds due to inaccurate temperature inversion and lower‐tropospheric stability (LTS) simulations. As compared to observations, the CMIP5 models show limited fidelity in capturing the transition from low to deep cloud at the north of the Equator. In this study, evaluation of one version of the CFS in which the convective parameterization is changed to the revised simplified Arakawa–Schubert (RSAS) scheme is carried out. In another CFS version (CFSR) with a more physically based cloud scheme (WRF Single‐Moment 6‐Class microphysics scheme; WSM6), comparisons are made with the default CFSv2 (CTRL) and RSAS. Only very few models, such as the MPI‐ESM‐LR, MRI, HadGEM, and NorESM models from among the 26 CMIP5 suites, and CFSCR from among the CFS suites, showed some fidelity in capturing the low‐level clouds over the SIO. This highlights that significant improvement is needed in climate models to improve the representation of the MBL over the SIO.