Thermodynamical properties associated with the Indian summer monsoon rainfall using a regional climate model

The regional climate model version 4.5 (RegCM4.5) is used to investigate thermal and dynamical processes associated with the Indian summer monsoon rainfall. The RegCM4.5 is run over the South Asia COordinated Regional Climate Downscaling Experiment (CORDEX) domain during 1990 to 2014 (25 years). The model realistically simulates the Indian summer monsoon rainfall (ISMR), tropospheric temperature and its gradient, and circulation patterns over the Indian region. The effect of Arabian Sea moisture transport on the ISMR is studied. It is argued that the weaker inward zonal transport and stronger outward meridional moisture transport from the Arabian Sea to the Indian subcontinent lead to reduced precipitation (dry bias) over India. The soil moisture over the Indian land points is significantly positively correlated to the precipitation over the region. The water budget analysis reveals that the moisture flux convergence values are slightly underestimated as compared to the precipitation minus evapotranspiration values over India. It is shown that the RegCM captures the eddy heat flux (EHF) and eddy momentum flux (EMF) variability over the Indian monsoon region. The model exhibits a distinct EHF dipole pattern between central India (20° N–30°N) and northern India (> 35° N) during the JJAS in the lower atmosphere. The monthly variability of the EMF over the Indian region suggests that EMF propagates northwards and upwards and becomes weaker from March onwards up to May. The EMF remains lowest during the monsoon season. The EMF again becomes stronger from Oct onwards with propagation of eddies in the opposite direction.