the role of the basic state in the enso-monsoon relationship and implications for predictability...
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The role of the basic state in the ENSO-monsoon relationship and
implications for predictabilityAndrew Turner, Pete Inness, Julia Slingo
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).
The model & datasets• HadCM3 3.75lon x 2.5lat (~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.
What’s wrong with the model?Summer DMI lag-correlated with Nino-3 SSTs
Mean summer surface temperature
HadCM3 mean summer (JJAS)
differences with ERA-40
Mean summer (JJAS) 850mb winds
HadCM3
differences with ERA-40
Mean summer (JJAS) precipitation
HadCM3
differences with CMAP
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 10S-10N relaxed back to climatology.
• Anomalous heat fluxes saved to generate a mean annual cycle, then applied to a new 100 year integration (HadCM3FA).
Heat flux adjustments
• Large fluxes (up to 186Wm-2 at 120W) into the cold tongue.
• Much smaller (~30W.m-2) over Maritime Continent and Indian Ocean.
Annual Mean
Standard deviation of cycle
• Small annual cycle apart from upwelling region off African coast.
Improvements to the mean stateHadCM3FA mean summer (JJAS) surface temperature
differences with HadCM3
HadCM3 differences with ERA-40
Improvements to the mean state
differences with HadCM3
HadCM3FA mean summer (JJAS) 850hPa winds
HadCM3 differences with ERA-40
Improvements to the mean stateHadCM3FA mean summer (JJAS) precipitation
differences with HadCM3
HadCM3 differences with CMAP
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.
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.
The monsoon-ENSO teleconnectionComposite 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)
HadCM3 HadCM3FA
The effect of climate changesummer (JJAS) 850hPa wind differences: 2xCO2-1xCO2
HadCM3
HadCM3FA
The effect of climate changesummer (JJAS) precipitation differences: 2xCO2-1xCO2
HadCM3
HadCM3FA
The effect of climate change
HadCM3FA
HadCM3
summer (JJAS) surface temperature differences: 2xCO2-1xCO2
The teleconnectionLag-correlation of summer (JJAS) Indian rainfall with Nino-3 SSTs
Future ENSO?irregular period
biennial period
SummaryCurrent 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.
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