Improved hindcasts of Indian monsoon rainfall using a Tier 1.5 approach Fred Kucharski, Annalisa...

Improved hindcasts of Indian monsoon rainfall using a Tier 1.5 approach

Fred Kucharski, Annalisa Bracco1, Jürgen Kröger,Franco Molteni2, Jin Ho Yoo

Earth System Physics, the Abdus Salam International Centre for Theoretical Physics,

Trieste, Italy – jkroeger@ictp.it

1now at Georgia Tech, Atlanta, GA, USA2now at ECMWF, Reading, England

ENSO – Asian Summer Monsoon teleconnectionRegression of precipitation onto NINO3.4 (190-240E, 5S-5N) in JJAS

Kucharski et al. (2007)

IMR index

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)

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!

The ICTP coupled global climate model

Experimental set-up: from Tier1 & Tier2 to Tier1.5

1Only the ECMWF, Meteofrance (METF), UK-Metoffice (UKMO) hindcasts (1959-1999) are considered

SST forcing Indian Ocean Ens. # Purpose

OBS-TIER1.5 HadISST coupled 10 Potential predictability

DEM-TIER1.5 DEMETER1 coupled 27 Actual predictability

OBS-TIER2 HadISST HadISST 25 Tier2 vs. Tier1.5

DEMETER seasonal hindcastspredicted (ECMWF) vs. observed SST

Indian summer monsoon rainfall (JJAS)IMR & NINO3.4 indices

La Nina (> 1 stdv)

El Nino (> 1 stdv)

Indian summer monsoon rainfallhindcasted IMR & NINO3.4 indices

La Nina (> 1 stdv)

El Nino (> 1 stdv)

IMR correlationsCorrelation skill (indiv. membrs.) and coefficient (CRU observ.)

Correlation skill Correlation coefficient

OBS-TIER1.5 0.68 0.62

DEMETER multi model 0.57 0.43

ECMWF only 0.54 0.24

METF only 0.46 0.39

UKMO only 0.71 0.39

DEM-TIER1.5 multi model 0.70 0.51

SSTs from ECMWF 0.66 0.43

SSTs from METF 0.66 0.44

SSTs from UKMO 0.78 0.49

DEMETER+DEM-TIER1.5 0.54

OBS-TIER2 0.68 0.31

ENSO – Asian Monsoon teleconnectionRegression of precipitation onto NINO3.4 in JJAS

DEMETER seasonal hindcastspredicted vs. observed SST

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

JJAS mean SST bias in the DEMETER models

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

Ingredients: SST from HadISST or DEMETER1 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

1Only the ECMWF, Meteofrance, UK-Metoffice Tier1 hindcasts are considered