Role of Local Air-Sea Interaction in Tropical Atlantic Variability

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

xZ20

SST dipole

Y_ITCZ

Servain ’99, GRL

Nobre and Shukla 1996, JC

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

SST’

Eq 30N30S

Cloud-SST Feedback

Okumura et al. ’01, GRLXie & Saito ’01, JC

Seager et al. 2001, JC

Carton et al. 1996, JPO

(Hakkinen and Mo 2001, JC)

x

h

SST

’=0

Xie et al. 1999, GRL

Chang et al. 2000, JC Sutton et al. 2000, JC

Okumura et al. (2001), GRL

SST and surface wind (JFM)

Chiang et al. 2001, JAS

Obs

LinearModel

Corr(NCEP, Model) 79-98

U

V

Also Chung et al. 2001, JGR

Chang et al. 2001, JC

Xie and Tanimoto ’98, GRL

Zonal-mean model simulation

Chang et al. ‘01, J. Climate

Cross-equatorial interaction

Obs

H. Okajima 2001

Processes that weaken inter-hemispheric interaction

Correlation

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