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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Updated hybrid CGCM 11/18/03 IPRC Lunch Seminar

Updated hybrid CGCM 11/18/03 IPRC Lunch Seminar

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

(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

Updated hybrid CGCM 11/18/03 IPRC Lunch Seminar

Thank You!

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

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

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

Updated hybrid CGCM 11/18/03 IPRC Lunch Seminar

Updated hybrid CGCM 11/18/03 IPRC Lunch Seminar