Representation of moist convective processes in Coupled Model Intercomparison Project Phase 5 and Phase 6 models for the simulation of Indian summer monsoon intraseasonal variability

Abstract

AbstractThis study assesses the simulation of the Boreal Summer Intraseasonal Oscillation (BSISO), particularly the moist convective processes associated with the BSISO in 10 models from phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6). Most of the models show a slower northward propagation of the BSISO and cannot simulate the origin of positive rainfall anomalies over the equatorial Indian Ocean. The generation of barotropic vorticity to the north of the convection centre leads to the northward shift of moisture convergence resulting in the northward propagation of convection. This mechanism is also insufficient in the models. The models show a lack of consistent evolution of moisture with increasing rain rates. Some of the CMIP6 models such as MPI‐ESM1‐2‐LR, FGOALS‐f3‐L, and NorESM2‐MM exhibit better northward propagation and the associated moist processes. A random relationship between vertical velocity, specific humidity, and precipitation is seen in the observation. On the other hand, the models show a deterministic relationship among these parameters with a much higher fraction of convective rain than large‐scale rain. Only FGOALS‐f3‐L (from the CMIP6 family), which uses convection resolving precipitation parameterization, where the convective and stratiform precipitation is calculated explicitly, produces the variability seen in the observation to a large extent.