Performance evaluation of regional climate model to simulate sub-seasonal variability of Indian Summer Monsoon

The study aims to evaluate the regional climate model (RegCM) over South Asian (SA) CORDEX domain to represent seasonal and sub-seasonal variability of Indian Summer Monsoon (ISM). The model’s ability is evaluated by conducting two sets of experiments using one-tier approach of coupling the RegCM with a simple mixed-layer slab ocean model (SOM) and the two-tier approach of prescribing sea surface temperature (SST) to RegCM. Two model experiments are initialized at 1st January 2000 for a period of 13 year continuous simulation at a spatial resolution of 50 km. It is found that, one-tier approach realistically represents the spatial distribution of precipitation with significant improvement noticed over central India (CI) and head Bay of Bengal (BoB) regions. In addition, it also fairly reproduced the observed mean meridional circulation response to the diabatic heating produced during ISM. Most importantly, in one-tier approach the model could able to represent the observed SST and precipitation (P) relationship with significant improvement in correlation and model response time. An important result is the representation of northwest-southeast tilt of precipitation anomalies during active/break phase of monsoon. Additionally, the lagged response of vertical profiles of specific humidity, omega, vorticity and divergence over CI with respect to peak rainfall anomaly (active phase) are relatively better represented in one-tier approach. In brief, coupling improves the performance of RegCM in simulating the space–time characteristics of monsoon ISO mode.