Intraseasonal variability of Indian Summer Monsoon Rainfall in CMIP6 models simulation

Abstract

The reliability of the projection of Indian Summer Monsoon Rainfall (ISMR) and associated wind circulation in the simulation of the Coupled Climate Models (CCMs) is based on their ability to reproduce themselves in the control experiment. The performances of CCMs, namely BCC-CSM2-MR and BCC-ESM1 of the Beijing Climate Center, China, and MPI-ESM1-2-HR and MPI-ESM1-2-LR of Max Planck Institute (MPI) Germany, are evaluated under control experiment of CMIP6, since they had better performed in Coupled Model Intercomparison Project phase 5 (CMIP5). Under the historical experiment (control experiment) in the period from 1979 to 2014, the simulated wind circulation, relative humidity, and rainfall are evaluated on the seasonal and sub-seasonal scales during the Indian summer monsoon season (i.e. June-July-August-September). The simulated wind at pressure levels of 1000, 850, 700 and 200 hPa and relative humidity at similar pressure levels are considered for the evaluation. The India Meteorological Department (IMD) observed rainfall (0.25° x 0.25°) is taken to validate the model’s simulated rainfall. Further, to validate the zonal wind (u component), meridional wind (v component) and relative humidity, the reanalysed data (0.25° × 0.25°) at the pressure levels of 1000, 850, 700 and 200 hPa are taken from ERA5 of the European Centre for Medium-Range Weather Forecasting (ECMWF). The seasonal and monthly mean wind and relative humidity are vertically averaged from the levels of 1000 to 700 hPa, while monthly mean wind at the level of 200 hPa is considered for upper-level analysis. The models BCC-CSM2-MR, BCC-ESM1, MPI-ESM1-2-HR and MPI-ESM1-2-LR simulated wind, humidity and rainfall on the monthly and seasonal scales are validated against the respective observed/reanalysed data. The evaluations show that the CMIP6 model BCC-CSM2-MR performs well in reproducing relative humidity over the Arabian Sea and the Bay of Bengal. The model BCC-CSM2-MR and BCC-ESM1 perform well in simulating JJAS rainfall in comparison to observed rainfall of IMD.