13.4 Mean state and SST variability of the South-Eastern Pacific: a model study (2009

13.4

Mean state and SST variability of the South-Eastern Pacific: a model study

Thomas Toniazzo, NCAS-Climate, University of Reading, Reading, United Kingdom

We show that about a third of the ENSO-like variability in

the HadCM3 OAGCM is associated with variability in the

South-East Pacific (SEP) area which is independent of ENSO

and which is at least partly forced by extratropical

variability in the Southern Hemisphere.

Equatorward propagation of SST anomalies preceding

equatorial warming in the east Pacific is seen in HadCM3 as

well as in observational datasets and in several AR4 models.

In the SEP area, SST tendencies are controlled mainly by surface latent heat fluxes. Via the coupling with the

low-level winds, they propagate equatorward in a

wind-evaporation-SST (WES) mode.

However, this mode is damped and requires external forcing.

This appears to be provided by surface SW cloud forcing, in

turn linked with extratropical circulation anomalies in the

Southern Ocean storm-track.

Anomalies in oceanic advection and coastal upwelling only

account for a small fraction of anomalous SST tendencies in

the SEP.

The simulated climate in this area is affected by large

errors such as lack in stratocumulus clouds, reduced

southerly wind stress, and warm SSTs.

Investigation of the possible sources of such errors

indicates that the near-field orographic forcing of the

meridional wind component is the dominant factor for the

mean SST error in this model.

The model's variability in the SEP does not appear to depend

strongly on its mean bias.