Abstract:
We explore the extent to which stochastic atmospheric variability was
fundamental to development of extreme sea surface temperature anomalies
(SSTAs) during the 1997-8 El Niņo. The observed western equatorial Pacific
westerly zonal stress anomalies (τxa), which appeared between November
1996 and May 1997 as a series of episodic bursts, were largely reproducible by
an atmospheric general circulation model (AGCM) ensemble forced with observed
SST. Retrospective forecasts using a hybrid coupled model (HCM) indicate
that coupling only the part of τxa linearly related to large-scale
tropical Pacific SSTA is insufficient to capture the observed 1997 warming;
but, accounting in the HCM for all the τxa that was connected to
SST, recovers most of the strong SSTA warming. The AGCM-estimated range of
stochastic τxa forcing induces substantial dispersion in the forecasts,
but does not obscure the large-scale warming in most HCM ensemble members.
Slides from the 12-minute talk (PDF, 0.4 MB)