Transcript ENSO changes due to heat flux adjustment in current and

IPSL/CGAM workshop on Tropical Climate
26-27 May 2005
The monsoon-ENSO
teleconnection and different
ENSO regimes in a flux corrected
future climate
Andrew Turner, Pete Inness, Julia Slingo
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
Annual mean
Standard deviation
• 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.
Improvements to the mean state
Improvements to the mean state
ENSO properties in the current climate
all are Nino-3 regions
• 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.
ENSO properties in the current climate
ERA-40
HadCM3
HadCM3FA
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)
The monsoon-ENSO teleconnection
See Turner et al. 2005 for more information!
• Stronger and better timed teleconnection
with flux adjustments.
• Monsoons feed back on Pacific system
to further intensify ENSO.
HadCM3
HadCM3FA
• Warmest waters further east,
repositioning the convection
and Walker circulation.
The effect of climate change
The effect of climate change
ENSO properties in future climate
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 2xCO2 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.