CORDEX South Asia Model

IITM RegCM4

CCCR-IITM is participating in the CORDEX-South Asia by using the REGional Climate Model version 4 (RegCM4) for dynamical downscaling of regional climate over West and South Asia. The RegCM4 system is a community model coordinated by the International Centre for Theoretical Physics (ICTP). The dynamical core of the RegCM4 is similar to that of the hydrostatic version of the National Center for Atmospheric Research (NCAR)-Pennsylvania State University (PSU) Mesoscale Model version 5 (MM5) (Grell et al., 1994) and is thus a hydrostatic, compressible, sigma-p vertical coordinate model run on an Arakawa B-grid. RegCM4 has multiple choices for the parameterization of the sub-grid scale physical processes. A detailed description of RegCM4 is given by Giorgi et al. (2012).

The RegCM4 domain set up for CORDEX-South Asia integrations cover West and South Asia and the adjoining Indian Ocean. The number of grid points in Mercator map projection is 254 (west-east) by 168 (north-south), with a horizontal resolution of 50 km. A 23-sigma (50 hPa) vertical grid is used. The selected physics schemes include a mixed cumulus convection scheme with the Grell (Grell, 1993) over land and the Emanuel (Emanuel, 1991; Emanuel and Zivkovic-Rothman, 1999) over the ocean grid boxes. The radiative transfer package is based on NCAR Community Climate Model version 3 (CCM3; Kiehl et al. 1996), which includes the effects of greenhouse gases (H2O, O3, O2, CO2, NO2, CH4, and CFCs), clouds, atmospheric aerosols, and cloud ice. The planetary boundary layer is parametrized by the Holtslag et al. (1990) scheme and the NCAR Community Land Model version 3.5 (CLM3.5) is used for the land surface processes (Olseson et al., 2008).

The experiments are conducted for 76 years; 20-year simulation for evaluating the present (1989-2008) climate and 56-year simulation of the historical (1950-2005) climate. The present climate simulation is driven with the global European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric interim reanalysis (Dee et al. 2011). The historical climate simulation is driven with the historical run of the IITM-LMDz model.

Please see below for a quick view of the RegCM4 simulated monthly surface air temperature and precipitation:

Evaluation run: IITM-RegCM4(ERAint)

Historical run: IITM-RegCM4(LMhist)

IITM LMDz

A new and emerging scientific activity that has been initiated in CCCR is very high-resolution simulations of the present-day monsoon climate and future projections using Ultra-High Resolution Global Climate Models. The ultra-high resolution monsoon simulations are being conducted at the High Performance Computer (HPC) facility at IITM as part of research collaboration between CCCR and LMD to generate high-resolution simulations of monsoon for present-day and future projections. The climate model is based on a version of an atmospheric GCM from LMDZ, France. The model has a zooming capability in a 35 km x 35 km resolution over Indian monsoon region and 1 x 1 degree lat - lon resolution elsewhere. Presently, the CCCR is among the top few groups in the world engaged in monsoon simulations using such ultra-high resolution models. The model integration is already started with following runs.