The monsoon-ENSO teleconnection and different ENSO regimes in a flux corrected future climate Andrew Turner, Pete Inness, Julia Slingo IPSL/CGAM workshop on Tropical Climate May 2005

Why flux adjust? Coupled GCMs generating mean climatologies more in line with observations are more likely to simulate the correct interannual variability of tropical precipitation (Sperber and Palmer, 1996). State of equatorial Pacific SSTs long regarded as an important predictor of the Asian summer monsoon (Charney and Shukla, 1981; many others). For a GCM to be used for seasonal prediction it should be able to simulate both these SSTs and the teleconnection between them and the monsoon. This depends on the Walker circulation being correctly represented.

The Model HadCM3: Atmosphere: 3.75 x2.5 at L30 (better representation of intraseasonal tropical convection then L19 – Inness et al., 2001). Ocean: 1.25 x1.25, 20 levels. 100 year integration.

Why flux adjust?

HadCM3 mean summer climate 3.75lon x 2.5lat, L30 configuration (Inness et al., 2001)

HadCM3 mean summer climate

Heat flux adjustments Flux adjustments devised by Inness et al. (2003) to give better representation of MJO. Annual cycle of FA applied to a 100 year coupled integration. Tropical Pacific and Indian Oceans only. Annual mean Standard deviation

Improvements to the mean state

ENSO properties in the current climate Shallower and more intense thermocline in HadCM3FA, coupled with warmer SSTs on the equator (higher coupling strength) allows for stronger ENSO. Biennial increase related to coupling strength. all are Nino-3 regions

ENSO properties in the current climate DJF Nino-3 SST lag-correlated with equatorial Pacific SST (after Ashrit et al., 2003) El Nino periodicity has greater spread. Better warm pool behaviour; pre-El Nino extension more WWEs, which help trigger El Nino (Vecchi and Harrison, 2000; Lengaigne et al., 2004) ERA-40HadCM3HadCM3FA

The monsoon-ENSO teleconnection Stronger and better timed teleconnection with flux adjustments. Monsoons feed back on Pacific system to further intensify ENSO. Warmest waters further east, repositioning the convection and Walker circulation. See Turner et al for more information! HadCM3HadCM3FA

The effect of climate change

ENSO properties in future climate

The teleconnection

Summary and the future… Current climate: Flux adjustments, whilst having some drawbacks, can help correct mean state and have beneficial effect on monsoon predictability. Stronger teleconnection (and greater coupling); more realistic Walker circulation & El Nino development. Flux adjustments highlight the danger in assuming a linear system, anomaly forecasting etc. Future climate: Combining increased greenhouse gases with flux correction may be pushing HadCM3 closer to some bifurcation point. An extreme monsoon may be sending ENSO into the limiting cycle, due to increased air-sea interaction in the west Pacific.

Summary and the future… Need to determine: Why is 2xCO 2 FA able to flip between different regimes? What causes the regime change? anomalous monsoon (increased air-sea coupling), period of intense WWEs? A further HadCM3FA 2xCO2 integration will see if biennial regime returns.

References Ashrit et al. (2003) J. Meteorol. Soc. Jpn., 81. Charney and Shukla (1981) Monsoon Dynamics: predictability of monsoons, CUP Inness et al. (2001) Clim. Dyn., 17. Inness et al. (2003) J. Clim., 16. Lengaigne et al. (2004) Clim. Dyn., 23. Turner et al. (2005) Q. J. R. Meteorol. Soc., 131.(607) Vecchi and Harrison (2000) J. Clim., 31.