1. 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). 100 year integration. (atmosphere: Pope et al., 2000, ocean: Gordon et al., 2000). L30 used in this configuration which produces more realistic representation of intraseasonal tropical convection – MJO – than L19 (Inness et al., 2001). ERA-40 Reanalysis (1958-1997). CMAP for tropical precipitation 1979-1997; Xie and Arkin, 1997. All –India Rainfall (AIR) gauge-based 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 Seasonally varying flux adjustments 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 saved to generate a mean annual cycle, then applied to a new 100 year integration (HadCM3FA).

9. Heat flux adjustments 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. Annual Mean 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 differences with HadCM3 HadCM3FA mean summer (JJAS) 850hPa winds 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 Stronger and better timed teleconnection with flux adjustments. Lag-correlation of summer (JJAS) DMI with Nino-3 SSTs High summer Nino- 3 anomalies associated with weak Asian summer monsoon (dynamically). HadCM3 fails to reproduce timing of the teleconnection.

14. The monsoon-ENSO teleconnection Monsoons feed back on Pacific system to further intensify ENSO. 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.

15. The monsoon-ENSO teleconnection 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) HadCM3HadCM3FA

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

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

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

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 (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: 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.