HR: 0830h
AN: OS41B-0802    [PDF]
TI: An Uneven ENSO Oscillator From Changes in Climatology
AU: * Hsieh, W W
EM: whsieh@eos.ubc.ca
AF: Dept. of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4 Canada
AU: Ye, Z
EM: zye@eos.ubc.ca
AF: Dept. of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4 Canada
AU: Wu, A
EM: awu@eos.ubc.ca
AF: Dept. of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4 Canada
AB: A new `uneven ENSO oscillator' concept is introduced to describe the uneven changes in the ENSO warm phase and cool phase due to changes in the climatology, e.g. the Pacific climate regime shift around 1976. Using a neural network model for nonlinear canonical correlation analysis of the tropical Pacific wind stress anomalies and sea surface temperature anomalies, we compared the 1981-99 period to the 1961-75 period. During 1981-99, the location of the equatorial easterly anomalies during the ENSO cool phase was unchanged from the earlier period, but westerly anomalies during the warm phase were shifted eastward by up to 25$^\circ$. Based on the delay oscillator theory, such an eastward shift would lengthen the duration of the warm episodes by up to 45%, but leave the duration of the cool episodes unchanged, hence an uneven ENSO oscillator. The Lamont coupled model of the tropical Pacific was then used to study how changes in the model climatology would produce an uneven oscillator. The eastward shift in the westerly anomalies during the warm episodes and the lengthening of the warm episode duration were indeed found in the coupled model when the 1981-99 climatologies were used instead of the 1961-75 climatology. In particular, it was mainly the change in the wind stress climatology rather than the change in the upper ocean climatology which caused the eastward shift in the westerly anomalies. The uneven ENSO oscillator theory has implications not only for how ENSO changed under decadal/interdecadal variations in the climatology, but also under longer term climate change.
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 4231 Equatorial oceanography
DE: 4522 El Ni¤o
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting