Monsoonal impacts on the Pacific climate and its

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Monsoonal impacts on the Pacific climate and its
implication for the cold bias in CGCMs
Xiouhua Fu
1, In what degree can the adjacent monsoons
impact the climatology and variability of the
equatorial Pacific? 2, Could be the cold bias in
many CGCMs a projection of systematic errors in
representing the monsoons? 3, a tool for further
study the updated version of our hybrid CGCM.

Collaborators Bin Wang, Fei-fei Jin, Julian P.
McCreary, and Tim Li
11/18/03 IPRC Lunch Seminar
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Asian Monsoon
North American Monsoon
South American Monsoon
Australian Monsoon
Pacific
Important roles of air-sea coupling on Pacific
climate and variability ENSO Bjerknes (1969),
Zebiak and Cane (1987), Suarez and Schopf
(1988), Jin (1997), Wang et al.
(2001), An and Jin (2001) Annual Cycle Chang and
Philander (1994), Xie (1994), Li and Philander
(1996), Wang and Fu (2001), Fu and
Wang (2001) Annual Mean Neelin and Dijkstra
(1995), Philander et al. (1996), Jin (1998),
Xie (1998), Wang and Wang (1999), Xie and
Saito (2001)
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Influences of adjacent continental heatings on
the surface winds of Tropical Pacific
a), Control
b), No Zonal SST Gradient in Pacific
(b)-(a)
(Stone and Chervin 1984)
(Fu and Wang 2003)
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Monsoonal impacts on Pacific climate
Results from an intermediate air-sea coupled
model with specified clouds (Fu and Wang 2001).
(Equatorial Annual Cycle)
(Equatorial Annual Mean)
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Monsoonal impacts on Pacific climate
Five experiments with intermediate coupled model
Labels Monthly-mean forces Annual-mean forces
CTL Global tropics No
PAC Tropical Pacific Outside the tropical Pacific
ASM Tropical Pacific Asian-Australian sector Other tropical region
NAM The above region tropical North American continent Other tropical region
SAM The above region tropical South American continent Other tropical region
Forces include surface temperature and clouds.
Surface temperature outside the tropical Pacific
is the 1000-hPa air temperature (ECMWF) over land
and the observed SST (Reynolds 1988) over
oceans the clouds are from the ISCCP data set.
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Monsoonal impacts on Pacific climate
Rectification on the mean
(CTL-PAC) (ASM-PAC)
Mean SST changes due to Asian-Australian monsoons
Mean surface-wind changes due to
Asian- Australian monsoons
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Monsoonal impacts on Pacific climate
(SST)
Impacts of North American monsoons on the annul
cycles of the equatorial SST and zonal winds.
(Us)
(SST)
Impacts of South American monsoons on the annul
cycles of the equatorial SST and zonal winds.
(Us)
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Monsoonal impacts on Pacific climate
Both North and South American monsoons
North American monsoon
South American monsoon
Rainfall and surface-wind differences (May March)
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Monsoonal impacts on Pacific climate
SST
Zonal Wind
Meridional Wind
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Monsoonal impacts on Pacific climate
Summary Asian-Australian monsoons can rectify
the climatological mean of the equatorial
Pacific SST through enhancing the mean strength
of trades. American continental monsoons affect
primarily the eastern Pacific SST annual cycle.
The Central and North American monsoons have
little influence on the annual cycle of SST in
the cold tongue. However, the South American
monsoon exerts profound impact on the annual
variations of the southeast trades in the
eastern Pacific, thus is an important external
forcing of the SST annual cycle in the eastern
Pacific. (Fu and Wang, 2003, J. Climate)
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Cold bias and monsoon errors
(Davey et al. 2002, Clim. Dyn. )
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Cold bias and monsoon errors
North American Monsoon
Asian Monsoon
South American Monsoon
Australian Monsoon
Pacific
Possible causes for the cold bias in CGCMs 1)
Inappropriate radiative/dynamic/air-sea feedbacks
in the equatorial Pacific (Sun et al. 2003)
2) Oceanic mixing (Richards et al. 2003) 3)
Surface wind bias projected from adjacent
monsoon errors (Fu, Jin and Wang 2003)
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Cold bias and monsoon errors
(Kang et al. 2002)
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Cold bias and monsoon errors
Observed interannual variations
Monsoon errors of 10 AGCMs
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Cold bias and monsoon errors
Regressed rainfall errors and 850-hPa wind biases
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Cold bias and monsoon errors

• Asian Summer Monsoon(ASM)
• .vs.
• Trades

Eastern North Pacific Summer Monsoon
(ENPSM) .vs. Trades
ENPSM-ASM .vs. Trades
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Cold bias and monsoon errors
Gill-type model responses to the regressed
monsoon rainfall errors
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Cold bias and monsoon errors
Responses of a conceptual air-sea coupled
model (Jin 1997) to the changes of
external-forced zonal winds.
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Cold bias and monsoon errors
Oscillatory Regime
SST Bias
Zonal-wind Bias
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Cold bias and monsoon errors
Summary The equatorial easterly is
systematically exaggerated in 10 AGCMs from
CLIVAR/monsoon inter-comparison project. It is
largely due to the enhanced monsoon in the west
of Pacific basin and reduced monsoon in the east
of the basin. The monsoon-bias-induced wind
errors can result in a significant cold bias
through invoking the Bjerknes positive air-sea
feedback in the equatorial Pacific, which is
demonstrated with a highly idealized coupled
model. Our finding suggests that the problem of
Pacific cold bias in CGCMs may not only be rooted
in the representation of the atmosphere-ocean
feedback within the basin but also in the
systematic errors in the adjacent monsoon
systems.
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Updated hybrid CGCM
100yr-mean
33yr-mean
ECHAM4 T30 AGCM An
intermediate ocean model (0.5ox0.5o) Without
heat flux correction
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Updated hybrid CGCM
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Updated hybrid CGCM
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Updated hybrid CGCM
ENSO annual phase locking
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Updated hybrid CGCM
SINTEX CGCMs
(Guilyardi et al. 2003, submitted to J. Climate)
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Updated hybrid CGCM
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Thank You!
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Cold bias and monsoon errors
Gill-type model responses to the regressed
monsoon rainfall errors
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Updated hybrid CGCM
OBS in winter
TISO in boreal winter and summer
OBS in summer
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Updated Hybrid CGCM
Wavenumber-frequency spectra of MJO in boreal
winter (NDJFMA) averaged from 10oS
to 5oN
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Updated hybrid CGCM
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Updated hybrid CGCM
11/18/03 IPRC Lunch Seminar