1. Improved hindcasts of Indian monsoon rainfall using a Tier 1.5 approach Fred Kucharski, Annalisa Bracco 1, Jürgen Kröger, Franco Molteni 2, Jin Ho Yoo Earth System Physics, the Abdus Salam International Centre for Theoretical Physics, Trieste, Italy – jkroeger@ictp.it 1 now at Georgia Tech, Atlanta, GA, USA 2 now at ECMWF, Reading, England

2. ENSO – Asian Summer Monsoon teleconnection Regression of precipitation onto NINO3.4 (190-240E, 5S-5N) in JJAS Kucharski et al. (2007) IMR index

3. Lead-lag correlations between Indian rain and ENSO NINO3 (150-90W, 5S-5N) and JJAS-IMR (70-95E, 10-30N) indices Kucharski et al. (2007)

4. The ICTP coupled global climate model Tier1.5: global atmosphere and local ocean ICTP atmospheric GCM “SPEEDY” Spectral dynamical core (Held and Suarez 1994) Resolution: T30L8 (~ 3.75 deg x 3.75 deg) Simplified physical parameterizations (Molteni, 2003) MIAMI ocean GCM “MICOM” (v2.9; Bleck et al., 1992) Indian Ocean configuration (30E - 135E, 30S – 30N) 1 deg x 1 deg, 20 isopycnal layers Sponge layer and initialization data from Levitus (1994) Prescribed SST outside ocean GCM domain!

5. The ICTP coupled global climate model Experimental set-up: from Tier1 & Tier2 to Tier1.5 1 Only the ECMWF, Meteofrance (METF), UK-Metoffice (UKMO) hindcasts (1959-1999) are considered SST forcingIndian OceanEns. #Purpose OBS-TIER1.5HadISSTcoupled10Potential predictability DEM-TIER1.5DEMETER 1 coupled27Actual predictability OBS-TIER2HadISST 25Tier2 vs. Tier1.5

6. DEMETER seasonal hindcasts predicted (ECMWF) vs. observed SST

7. Indian summer monsoon rainfall (JJAS) IMR & NINO3.4 indices La Nina (> 1 stdv) El Nino (> 1 stdv)

8. Indian summer monsoon rainfall hindcasted IMR & NINO3.4 indices La Nina (> 1 stdv) El Nino (> 1 stdv)

9. IMR correlations Correlation skill (indiv. membrs.) and coefficient (CRU observ.) Correlation skillCorrelation coefficient OBS-TIER1.50.680.62 DEMETER multi model0.570.43 ECMWF only0.540.24 METF only0.460.39 UKMO only0.710.39 DEM-TIER1.5 multi model0.700.51 SSTs from ECMWF0.660.43 SSTs from METF0.660.44 SSTs from UKMO0.780.49 DEMETER+DEM-TIER1.50.54 OBS-TIER20.680.31

10. ENSO – Asian Monsoon teleconnection Regression of precipitation onto NINO3.4 in JJAS

11. DEMETER seasonal hindcasts predicted vs. observed SST

12. The Tier1.5 approach considerably improves the DEMETER hindcasts has great potential to aim as a tool for seasonal predictions of IMR confirms the importance of coupled air-sea feedbacks in the Indian Ocean

13. JJAS mean SST bias in the DEMETER models

14. ICTP AGCM stand-alone model: GCM of intermediate complexity  Spectral dynamical core (Held and Suarez 1994)  Truncation currently at T30 (~3.75x3.75 degrees)  5, 7 or (recently) 8 vertical levels  Variables: Vor, Div, T, log(ps) and Q  Physical parameterizations of Convection (mass flux) Large-scale condensation (RH criterion) Clouds (diagnosed) Short-wave radiation (two spectral bands) Long-wave radiation (four spectral bands) Surface fluxes of momentum and energy (bulk formulas) Vertical diffusion  Land-temperature calculated in simple model of 1-m soil layer  Mixed-layer option

15. Ingredients:  SST from HadISST or DEMETER 1 as “pacemaker” Suite of experiments:  OBS-TIER1.5: coupled GCM (Indic) + HadISST elsewhere  DEM-TIER1.5: coupled GCM (Indic) + DEMETER elsewhere  OBS-TIER2: atmospheric GCM + HadISST everywhere The ICTP coupled global climate model Experimental set-up: from Tier1 & Tier2 to Tier1.5 1 Only the ECMWF, Meteofrance, UK-Metoffice Tier1 hindcasts are considered