Improved precipitation extremes and climatology in a regional coupled model simulation over CORDEX south Asia domain

Abstract:

The South Asian continents are densely populated and their economy is largely dependent on agriculture which primarily depends on the summer monsoon (June-September). The region is highly vulnerable to climate variability and change. It has been well established that the SST anomalies in the Indian and the Pacific Ocean attributes to the monsoon interannual as well as intraseasonal variability. Most of the CMIP3 and CMIP5 climate models have difficulty in simulating the mean climate over South Asia. Regional Climate Models (RCMs) however simulate orographic induced precipitation better, but show limited ability to simulate mean precipitation over land and an overestimation over ocean more generally. These systematic differences between climate models and observation's may be related to poorly represented ocean dynamics and SST.

For the first time a regional coupled atmosphere–ocean model is developed to study the monsoon climatology over the CORDEX South Asia domain. The REgional atmosphere MOdel REMO with 50km horizontal resolution is coupled via Oasis coupler to the Max Planck Institute for Meteorology global ocean – sea ice model MPIOM with increased resolution over the Indian Ocean (up to 20 km). Hereafter this coupled system will be called as ROM. For this study, four simulations for the period 1958-2001 are performed (i) REMO forced with ECMWF ERA40 reanalysis (ii) ROM forced with ECMWF ERA40 reanalysis (iii) REMO forced with MPI-ESM-LR CMIP5 historical simulation (iv) ROM forced with MPI-ESM-LR CMIP5 historical simulation. Differences in coupled and un-coupled RCM simulations are analyzed to investigate the effect of coupling on simulated climate, especially precipitation daily annual cycles and monthly spatial patterns. It has been observed that simulated feedback of ocean SST has positive influence on precipitation simulation of ROM both over land and ocean. The intensity of tropical cyclone is well simulated by the model ROM which improves the monsoon intraseasonal variability. Detail possible mechanisms responsible for such an improvement will be presented at conference.