1. 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

2. Asian Monsoon Australian Monsoon Pacific North American Monsoon South
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)
11/18/03 IPRC Lunch Seminar

3. 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)
11/18/03 IPRC Lunch Seminar

4. Results from an intermediate air-sea
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)
11/18/03 IPRC Lunch Seminar

5. 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
SAM
tropical South American continent
* 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.
11/18/03 IPRC Lunch Seminar

6. 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
11/18/03 IPRC Lunch Seminar

7. 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)
11/18/03 IPRC Lunch Seminar

8. Monsoonal impacts on Pacific climate
Both North and South
American monsoons
North American monsoon
South American monsoon
Rainfall and surface-wind differences (May –March)
11/18/03 IPRC Lunch Seminar

9. SST Zonal Wind Meridional Wind Monsoonal impacts on Pacific climate
11/18/03 IPRC Lunch Seminar

10. Summary Asian-Australian monsoons can rectify the climatological
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)
11/18/03 IPRC Lunch Seminar

11. (Davey et al. 2002, Clim. Dyn. ) Cold bias and monsoon errors
11/18/03 IPRC Lunch Seminar

12. Possible causes for the cold bias in CGCMs:
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)
11/18/03 IPRC Lunch Seminar

13. (Kang et al. 2002) Cold bias and monsoon errors
11/18/03 IPRC Lunch Seminar

14. Cold bias and monsoon errors
Observed interannual variations
Monsoon errors of 10 AGCMs
11/18/03 IPRC Lunch Seminar

15. Regressed rainfall errors and 850-hPa wind biases
Cold bias and monsoon errors
Regressed rainfall errors and 850-hPa wind biases
11/18/03 IPRC Lunch Seminar

16. Cold bias and monsoon errors
Asian Summer Monsoon(ASM)
.vs.
Trades
Eastern North Pacific Summer
Monsoon (ENPSM)
.vs.
Trades
ENPSM-ASM
.vs.
Trades
11/18/03 IPRC Lunch Seminar

17. Cold bias and monsoon errors
Gill-type model
responses to the
regressed monsoon
rainfall errors
11/18/03 IPRC Lunch Seminar

18. Cold bias and monsoon errors
Responses of a
conceptual air-sea
coupled model
(Jin 1997)
to the changes
of external-forced
zonal winds.
11/18/03 IPRC Lunch Seminar

19. SST Bias Zonal-wind Bias Cold bias and monsoon errors
Oscillatory Regime
SST Bias
Zonal-wind Bias
11/18/03 IPRC Lunch Seminar

20. 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.
11/18/03 IPRC Lunch Seminar

21. Updated hybrid CGCM
100yr-mean
33yr-mean
ECHAM4 T30 AGCM +
An intermediate ocean
model (0.5ox0.5o)
Without heat flux correction
11/18/03 IPRC Lunch Seminar

22. Updated hybrid CGCM
11/18/03 IPRC Lunch Seminar

23. Updated hybrid CGCM
11/18/03 IPRC Lunch Seminar

24. ENSO annual phase locking Updated hybrid CGCM
11/18/03 IPRC Lunch Seminar

25. (Guilyardi et al. 2003, submitted to J. Climate)
Updated hybrid CGCM
SINTEX
CGCMs
(Guilyardi et al. 2003, submitted to J. Climate)
11/18/03 IPRC Lunch Seminar

26. Updated hybrid CGCM
11/18/03 IPRC Lunch Seminar

27. Thank You!

28. Cold bias and monsoon errors
Gill-type model
responses to the
regressed monsoon
rainfall errors
11/18/03 IPRC Lunch Seminar

29. OBS in winter OBS in summer TISO in boreal winter and summer
Updated hybrid CGCM
OBS in winter
TISO in boreal
winter and
summer
OBS in summer
11/18/03 IPRC Lunch Seminar

30. Wavenumber-frequency spectra of MJO in boreal winter
Updated Hybrid CGCM
Wavenumber-frequency spectra of MJO in boreal winter
(NDJFMA) averaged from 10oS to 5oN

31. Updated hybrid CGCM
11/18/03 IPRC Lunch Seminar

32. Updated hybrid CGCM
11/18/03 IPRC Lunch Seminar