Summary of Abstract Submission

Abstract Submission No. IO50-06-0014PresentationPoster

EVALUATION OF CORDEX RCMS IN SIMULATION OF NORTHWARD AND EASTWARD PROPAGATION OF THE INDIAN SUMMER MONSOON

Swati Singh*1, Subimal Ghosh1

1 Indian Institute of Technology Bombay, India

ABSTRACT :

Indian summer monsoon contributes around 70-80% of total rainfall, is associated with fluctuation in the convective activities due to northward (30-60 days) and eastward propagating (10-20 days) boreal summer intra-seasonal oscillation (BSISO) leading to intra-seasonal variability (active and break spells) in the monsoon. In present analysis evaluation of 9 CORDEX RCMs is done in simulating propagation characteristics (northward and eastward) of the BSISO for the period of 1970-2005 with respect to their host CMIP5 GCMs and JRA-55 reanalysis data set as observation. JRA-55 is selected as observation data based on its availability for desired period and good correlation with other two reanalysis data sets (ERA-INTERIM and MERRA). Eastward (northward) propagations as illustrated by lag-longitude (lag-latitude) diagram of regressed 20-100 days band pass filtered precipitation anomalies averaged between 5˚S-5˚N (70˚E-95˚E) for eastward (northward) propagation. The 20-100 day band pass filtered precipitation anomalies averaged over 10˚S-5˚N and 75˚E-100˚E (12˚N-22˚N and 70˚E-90˚E) is used as reference time series for regression, for the estimation of eastward (northward) propagation. In present analysis, it is found that RCMs do not show skills in capturing the propagation characteristics of BSISO and also perform poorly than host GCMs. Though RCMs are not designed for large scale circulation, but their poor performances in simulating two important monsoon mechanisms, as compared to their host GCMs, do not make the outputs fully reliable. We emphasize on careful selection on nudging option, coupling with ocean models rather than SST forcing and selection of nested domain for better simulation of regional monsoon system.