1. Andrew Turner, Pete Inness, Julia Slingo
The role of the basic state in the ENSO-monsoon relationship and implications for predictability
Andrew Turner,
Pete Inness, Julia Slingo

2. Motivation
Asian summer monsoon affects more than 2 billion people in India, China and the rest of Southeast Asia.
Regional agriculture reliant on the timing, duration and intensity of the ASM – GCMs increasingly used to predict these details.
State of equatorial Pacific SSTs long regarded as an important predictor of the monsoon (e.g. Charney and Shukla, 1981).
Coupled GCMs generating mean climate closer to observations are more likely to correctly simulate the interannual variability of tropical precipitation (Sperber and Palmer, 1996).

3. The model & datasets
HadCM3 3.75lon x 2.5lat (~T42) year integration.
L30 used rather than L19 - more realistic intraseasonal tropical convection (MJO) and precip response to high SSTs (Inness et al., 2001; Spencer & Slingo, 2003).
ERA-40 Reanalysis ( ).
CMAP for tropical precipitation ; Xie and Arkin, 1997.
All –India Rainfall (AIR) gauge dataset; Parthasarathy et al., 1994.

4. What’s wrong with the model?
Summer DMI lag-correlated with Nino-3 SSTs

5. Mean summer surface temperature
HadCM3 mean summer (JJAS)
differences with ERA-40

6. Mean summer (JJAS) 850mb winds
HadCM3
differences with ERA-40

7. Mean summer (JJAS) precipitation
HadCM3
differences with CMAP

8. Heat flux adjustments
Traditionally used in older models (eg HadCM2) to prevent climate drift; HadCM3 does not have this problem.
Heat flux adjustments used here to study the effect of mean state error on the monsoon-ENSO system.
Devised by Inness et al. (2003) to investigate the role of systematic low-level zonal wind and SST errors on the MJO.
Coupled model run for 20 years, Indian and Pacific SSTs within 10S-10N relaxed back to climatology.
Anomalous heat fluxes generate a mean annual cycle which is applied to a new 100 year integration (HadCM3FA).

9. Heat flux adjustments
Annual Mean
Large fluxes (up to 186Wm-2 at 120W) into the cold tongue.
Much smaller (~30W.m-2) over Maritime Continent and Indian Ocean.
Standard deviation of cycle
Small annual cycle apart from upwelling region off African coast.

10. Improvements to the mean state
HadCM3FA mean summer (JJAS) surface temperature
differences with HadCM3
HadCM3 differences with ERA-40

11. Improvements to the mean state
HadCM3FA mean summer (JJAS) 850hPa winds
differences with HadCM3
HadCM3 differences with ERA-40

12. Improvements to the mean state
HadCM3FA mean summer (JJAS) precipitation
differences with HadCM3
HadCM3 differences with CMAP

13. The monsoon-ENSO teleconnection
Lag-correlation of summer (JJAS) DMI with Nino-3 SSTs
Stronger and better timed teleconnection with flux adjustments.

14. The monsoon-ENSO teleconnection
Lag-correlation of summer (JJAS) Indian rainfall with Nino-3 SSTs
Indian rainfall shares similar teleconnection pattern.
ERA-40 has poor representation when compared to gauge dataset.
Stronger and better timed teleconnection with flux adjustments.
Monsoons feed back on Pacific system to further intensify ENSO.

15. The monsoon-ENSO teleconnection
HadCM3
HadCM3FA
Composite evolution of equatorial Pacific total SSTs during El Nino
10 warm events composited from each model integration.
Warmest waters (absolute SSTs) are further east, past the dateline.
Convection and hence the rising branch of the Walker circulation is repositioned.
Warmer mean state means that even weak El Ninos in HadCM3FA may drive the teleconnection.
See Turner et al. (2005)

16. The effect of climate change
summer (JJAS) 850hPa wind differences: 2xCO2-1xCO2
HadCM3
HadCM3FA

17. The effect of climate change
summer (JJAS) precipitation differences: 2xCO2-1xCO2
HadCM3
HadCM3FA

18. The effect of climate change
summer (JJAS) surface temperature differences: 2xCO2-1xCO2
HadCM3
HadCM3FA

19. The teleconnection
Lag-correlation of summer (JJAS) Indian rainfall with Nino-3 SSTs

20. Future ENSO?
irregular period
biennial period

21. Summary Current climate:
Flux adjustments, whilst having some drawbacks, can help correct mean state and have beneficial effect on monsoon predictability.
Stronger teleconnection; more realistic Walker circulation & El Nino development.
Flux adjustments highlight the danger in assuming a linear system, anomaly forecasting etc.
Future climate:
Tendency to stronger monsoons in future climate scenario, irrespective of flux correction.
The sign and timing of the monsoon-ENSO teleconnection may not be robust.
Flux adjustment raises questions relating to the nature of ENSO in future climate.