Climate Model Simulations of Indian summer monsoon M.Rajeevan National Atmospheric Research Laboratory, Tirupati And Ravi Nanjundiah Indian Institute of Science, Bangalore
Overview of the presentation • Dynamical Prediction of Indian monsoon • AMIP results • Coupled Model results • IPCC AR4 coupled model simulations of twentieth century climate of Indian summer monsoon
Atmospheric Modeling efforts • TOGA MONEG simulations • 1987 and 1988 • A large fraction of the variability of the simulated Indian monsoon was forced by the SST variations over the Pacific (Palmer et al. 1992) • AMIP simulations • January 1979- December 1988 • SST and Sea ice from observations as boundary conditions • Sperber and Palmer (1996) • Gadgil and Sajini (1998) • Wang et al (2004)
General Inferences from AMIP results • Two classes of models (GS 1998) • Models well simulated the seasonal migration of rain-belt over the Indian region (class-1) • Models not well simulated (class-2) • mean monsoon rainfall and the inter-annual variability of Indian summer monsoon interrelated. • AGCMs, when forced by observed sea surface temperature (SST), had problems in predicting inter-annual variation of Indian monsoon
OBSERVED RAINFALL (GPCP) AMIP-1 MODELS, Gadgil and Sajini (1998)
Wang et al. 2004 J Climate • Ensemble simulations of Asian-Australian monsoon anomalies using 11 AGCMs • Models’ simulations of anomalies of Asian monsoon are very poor compared to the El- Nino region. CLIVAR/international monsoon panel AGCM intercomparison
1979-1999 Wang et al. 2005, Geophys. Res. Letters
Obs. SST-Rainfall Correlation MME SST-Rainfall correlation Wang et al. 2005, Geophys. Res. Letters
EU-Ensembles project • 9 member ensembles • May initial conditions, ERA-40 atmosphere and soil initial conditions • Realistic boundary forcings: GHGs, aerosols, solar forcing etc • Hindcast production period for : 1991-2001 • 4 coupled models considered: • ARPEGE /OPA- CNRM • ECHAM/OM- MPI • GloSea- UKMO • IFS/HOPE - ECMWF
Scatter plots METEOFRANCE ECHAM 1994 1994 1997 1997 UK Met Office ECMWF 1994 1994 1997 1997
Wang et al 2008, Climate Dynamics • Coupled one-tier approach can enhance the predictability of the summer monsoon precipitation. • Future reanalysis should be carried out with coupled atmosphere and ocean models • While the MME in general better than individual models, the CFS ensemble hindcast outperforms the MME in terms of the biennial tendency and the amplitude.
OBSERVED RAINFALL Rainfall Maximum over Bay of Bengal/NE India, West Coast. Rainfall minimum over NW India/ SE India Another rainfall maximum over SE Equatorial Indian Ocean Northward migration of rainbelt (ITCZ) during the monsoon season Rainfall throughout the year over the equatorial Indian Ocean
Spatial Distribution of Bias in JJA Rainfall • There are large biases over the Indian region • More precipitation over the equatorial Indian Ocean and less precipitation over the CTCZ region
Annual Cycle of Rainfall averaged over the Indian Region Models simulate reasonable well the annual cycle of rainfall averaged over the Indian region (5-27.5 N, 65.0-87.5 E).
Northward migration of the rain-belt over the Indian Region Models show problems in predicting the northward migration of rainbelt. Model precipitation over the equatorial Indian Ocean is much more than observed.
Atmospheric GCM (AMIP) Coupled GCM (IPCC AR4)
OBSERVED SST CLIMATOLOGY MODEL SST- Observed SST
Conclusions • Coupled models with multi-model ensemble approach have shown promising results for seasonal prediction of monsoon rainfall, especially the NCEP GFS model. • The latest coupled models (IPCC AR4) have shown problems in simulating observed mean monsoon rainfall patterns, including the northward migration of primary rain-belt over the Indian region. • Problems in capturing the ISOs? • Problems in land surface processes in the models? • Problems in other Physics of the models? • IPCC models have • excess precipitation bias over the equatorial Indian Ocean • systematic cold SST bias in the tropics.