Extratropical subduction and decadal modulation of El Niño

Abstract

An extension of the Battisti/Hirst delayed oscillator model is developed in an attempt to understand the potential effects of extratropical subduction on El Niño. In particular, a meridional delay term is included to parameterise the effects of extratropical subduction on eastern equatorial Pacific pycnocline anomalies. The magnitude of the eastern equatorial pycnocline displacement, and the time delay for its response to an extratropical sea surface temperature anomaly, are inferred from both ocean and coupled atmosphere-ocean GCM experiments. The inclusion of the delayed subduction term causes El Niño to modulate on decadal-interdecadal timescales, consistent with observations and the expectations of Gu and Philander.