Dynamical Prediction of Indian Dynamical Prediction of Indian Monsoon Rainfall and the Role ofMonsoon Rainfall and the Role of

Indian OceanIndian Ocean

K. Krishna KumarK. Krishna KumarCIRES Visiting Fellow, University of Colorado, BoulderCIRES Visiting Fellow, University of Colorado, Boulder

kkrishna@colorado.edu

Martin P. HoerlingClimate Diagnostics Center, Boulder

andBalaji Rajagopalan

University of Colorado, Boulder

Current Practices of Dynamical Current Practices of Dynamical Monsoon Rainfall PredictionMonsoon Rainfall Prediction

2-tiered approach wherein SSTs are 2-tiered approach wherein SSTs are predicted first using a coupled model and predicted first using a coupled model and then the AGCMs are forced using these SST then the AGCMs are forced using these SST fieldsfields

Use persistent SSTs to run AGCMsUse persistent SSTs to run AGCMs Dynamical Downscaling using Regional Dynamical Downscaling using Regional

Climate Models taking lateral boundary Climate Models taking lateral boundary values from AGCM Simulationsvalues from AGCM Simulations

Skills of the Present Generation of AGCMsSkills of the Present Generation of AGCMs(Reproduced from the IRI Website)(Reproduced from the IRI Website)

We set out to examine the skills of monsoon rainfall in detail by involving long simulations made using observed SSTs with a suite of multi-model, multi-member ensemble runs.

Research Questions..?Research Questions..?

How skillful are the AGCMs in simulating Monsoon How skillful are the AGCMs in simulating Monsoon Rainfall over the Indian region?Rainfall over the Indian region?

Is specifying SSTs a constraint on realistic monsoon Is specifying SSTs a constraint on realistic monsoon simulations?simulations?

How sensitive are monsoon simulations to initial How sensitive are monsoon simulations to initial conditions?conditions?

What is the impact of coupling on Monsoon-ENSO What is the impact of coupling on Monsoon-ENSO relationships?relationships?

Are the ENSO related western Indian Ocean SSTs Are the ENSO related western Indian Ocean SSTs acting as negative feed-back on Monsoon-ENSO acting as negative feed-back on Monsoon-ENSO relations?relations?

Details of AGCMs UsedDetails of AGCMs Used

S.No.S.No. ModelModel ResolutionResolution Ens. SizeEns. Size Run LengthRun Length

1 ECHAM4 2.8x2.8 24 1950-2002

2 ECHAM3 2.8x2.8 10 1950-1999

3 GFDL 2.5x2.0 10 1951-2002

4 NASA 2.8x2.8 9 1950-2002

5 ECPC 1.8x1.8 7 1950-2001

6 MRF (NCEP) 2.8x2.8 13 1951-1994

7 ARPEGE 2.8x2.8 8 1948-1997

8 CCM3 2.8x2.8 12 1950-1999

9 CAM2 2.8x2.8 15 1950-2001

Climatology of Monsoon RainfallClimatology of Monsoon Rainfall

Monsoon-ENSO Relation in AGCM SimulationsMonsoon-ENSO Relation in AGCM Simulations

PDFs of CorrelationsPDFs of Correlations(1) Obs. Vs. Model ENS (2) PERPROG(1) Obs. Vs. Model ENS (2) PERPROG

Impact of Initial Conditions on Monsoon SimulationsImpact of Initial Conditions on Monsoon Simulations

Monsoon-ENSO Teleconnections: Coupled vs. Monsoon-ENSO Teleconnections: Coupled vs. Uncoupled ModelsUncoupled Models

GOGA: Obs SSTs globallyGOGA: Obs SSTs globally

DTEPOGA: Obs SSTs in DTEPOGA: Obs SSTs in Deep Tropical East Pacific Deep Tropical East Pacific and Climatological SSTs and Climatological SSTs elsewhereelsewhere

DTEPOGA_MLM: Same as DTEPOGA_MLM: Same as DTEPOGA but a Mixed DTEPOGA but a Mixed Layer Model used in the Layer Model used in the Indian OceanIndian Ocean

Progressive Improvement Progressive Improvement in Monsoon Rainfall in Monsoon Rainfall Simulation Skills:Simulation Skills: 1. Un-coupled AMIP

2. Un-coupled AMIP only in eastern tropical Pacific and Climatological SSTs elsewhere

3. AMIP in the Pacific and Mixed Layer Model in the Indian

Ocean

SummarySummary The skills of current generation AGCMs in simulating monsoon rainfall in India even

when forced with observed SSTs are very low.

However, there appears to be much higher predictive potential as evidenced by the large PERPROG skills.

No clear hint of higher skills either for models with better monsoon climatology or when multi-model-super ensembles are involved.

Specification of SSTs in the Indian Ocean appears to be the main reason for the low-skills.

An interactive ocean-atmosphere in the Indian Ocean (using even a simple mixed layer ocean model) produces more realistic monsoon simulations compared to specifying actual or climatological SSTs.

General belief that the ENSO related SSTs in the Indian Ocean (particularly the western Indian Ocean and the Arabian Sea) might act as a negative feedback on Monsoon-ENSO teleconnections appears to be wrong based on the above observations.

In general the monsoon-ENSO links are much stronger in fully coupled models compared to the AGCMs forced with observed/predicted SSTs.

The 2-tiered approach currently being pursued in seasonal forecasting needs immediate revision to achieve higher forecast skills for the Indian region. We also believe, this might be true for some other countries located in the warm pool region in the west Pacific and the Indian Ocean.