The SST Anomalies Dipole in the Extratropical Pacific and Its Relationships with the ENSO Cycle

A sea surface temperature (SST) anomalies dipole was observed in the extratropical Pacific during the 1997-98 warm El Nino-Southern Oscillation (ENSO) event. This dipole is characterized by an anomalous warming along the coast of California and an anomalous cooling further west in the central Pacific. A similar pattern of SST anomalies has been found in a multi-decadal integration of the UCLA coupled atmosphere-ocean general circulation model (CGCM).

The CGCM simulation shows that the extratropical SST dipole has three dominant timescales: intraseasonal, interannual, and decadal. On the interannual timescale, the SST dipole is closely related to the ENSO cycle in the tropical Pacific. The development of the dipole is almost in phase with that of ENSO. Our analyses show that the in-phase variation of SST at these two latitudes is established mainly through the atmospheric circulation. Atmospheric thermal forcing, including suppressed/enhanced sensible and latent heat fluxes, is responsible for the generation of warm/cold SST centers of the dipole.

Results obtained from oceanic GCM simulations with observed atmospheric forcing will also be presented to address the relative importance of oceanic advection and atmospheric forcing for the development of the SST dipole on intraseasonal and decadal timescales.