Role of Local Air-Sea Interaction in Tropical Atlantic Variability
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Role of Local Air-Sea Interaction in Tropical Atlantic Variability
Shang-Ping XieInternational Pacific Research Center
University of Hawaii
• Atlantic El Nino • SST Dipole?• Ocean GCM• Coupled Feedback• Atmospheric GCM• Processes that weaken cross-eq.
feedback
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xZ20
SST dipole
Y_ITCZ
Servain ’99, GRL
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Nobre and Shukla 1996, JC
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NE Brazil rainfall
SST dipole
Quasi-decadal oscillation?
Mehta ’98, JC
Tourre et al. ’99, JC
Enfield et al. ’99, JGR
Black et al. ’99, Science
835-year sediment core
11.4 yr
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SST’
Eq 30N30S
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Cloud-SST Feedback
Okumura et al. ’01, GRLXie & Saito ’01, JC
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Seager et al. 2001, JC
Carton et al. 1996, JPO
(Hakkinen and Mo 2001, JC)
x
h
SST
’=0
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Xie et al. 1999, GRL
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Chang et al. 2000, JC Sutton et al. 2000, JC
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Okumura et al. (2001), GRL
SST and surface wind (JFM)
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Chiang et al. 2001, JAS
Obs
LinearModel
Corr(NCEP, Model) 79-98
U
V
Also Chung et al. 2001, JGR
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Chang et al. 2001, JC
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Xie and Tanimoto ’98, GRL
Zonal-mean model simulation
Chang et al. ‘01, J. Climate
Cross-equatorial interaction
Obs
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H. Okajima 2001
Processes that weaken inter-hemispheric interaction
Correlation
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Equatorial mode with Bjerknes feedback
Meridional/dipole mode
Statistical evidence
Surface heat flux (wind & cloud) dominates off-eq. SST variability
Near-eq. baroclinic response and barotropic teleconnection into the subtropics
Two-way coupling among cross-eq. SST gradient, ITCZ, and near-eq. wind
Processes that weaken this interaction: Asymmetric ITCZ and external forcing (NAO & ENSO)
Conclusions