AMOS Sydney Centre Seminar

July 2, 2008

7:30pm, Macquarie University - Room 143, Building E5A
Venue Information

Shayne Mcgregor
Department of Physical Geography, Macquarie University

"The interdecadal response of a stochastically forced Coupled Model of ENSO to observed off-equatorial region wind stress forcing"

Abstract

In this study we have investigated how extra-tropical to tropical oceanic transfers can affect the modelled equatorial Pacific variability of 1950 -2006 to determine whether these exchanges can be used to help explain the marked shift in ENSO behavior that occurred in the late 1970's. We also sought to identify the importance of Rossby waves incident on the western boundary in the remotely forced response and the implications for predictability. Stochastic forcing (SF) is estimated from NCEP-NCAR reanalysis surface winds for the period 1950 - 2006 using singular value decomposition analysis. The SF was then used to force the stable intermediate complexity coupled ENSO model a series of experiments which investigated the role of changes in the equatorial Pacific background state due to off-equatorial surface wind forcing. We conclude from this study that changes in the equatorial Pacific background state thermocline depth induced by off-equatorial surface wind forcing have a significant affect on the amplitude of the modeled ENSO events and they could be used to help explain the marked shift in ENSO behavior that occurred in the late 1970's. Further, we find that the addition of off-equatorial surface winds leads to an increase in the amplitudes of 1982/83 and 1997/98 ENSO events of almost 1ºC which gives the SF results more realistic amplitudes. Thus, the relatively small, potentially predictable, off-equatorial contribution to equatorial region variability appears critical for thresholds of ENSO. As such, we believe that a comprehensive understanding and more accurate seasonal-to-interannual prediction

Biography

Shayne Mcgregor is a PhD student in the Department of Physical Geography and also Risk Frontiers, at Macquarie University. He obtained a Masters (Hons) at Macquarie University in 2006. He drives a Kingswood and is a keen surfer.