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The response of a stochastically forced ENSO model to observed off-equatorial wind stress forcing

journal contribution
posted on 2023-05-16, 23:47 authored by McGregor, S, Neil HolbrookNeil Holbrook, Power, SB
This study investigates the response of a stochastically forced coupled atmosphere–ocean model of the equatorial Pacific to off-equatorial wind stress anomaly forcing. The intermediate-complexity coupled ENSO model comprises a linear, first baroclinic mode, ocean shallow water model with a steady-state, two–pressure level (250 and 750 mb) atmospheric component that has been linearized about a state of rest on the b plane. Estimates of observed equatorial region stochastic forcing are calculated from NCEP–NCAR reanalysis surface winds for the period 1950–2006 using singular value decomposition. The stochastic forcing is applied to the model both with and without off-equatorial region wind stress anomalies (i.e., poleward of 12.58 latitude). It is found that the multiyear changes in the equatorial Pacific thermocline depth ‘‘background state’’ induced by off-equatorial forcing can affect the amplitude of modeled sea surface temperature anomalies by up to 18C. Moreover, off-equatorial wind stress anomalies increased the modeled amplitude of the two biggest El Nin˜ o events in the twentieth century (1982/83 and 1997/98) by more than 0.58C, resulting in a more realistic modeled response. These equatorial changes driven by off-equatorial region wind stress anomalies are highly predictable to two years in advance and may be useful as a physical basis to enhance multiyear probabilistic predictions of ENSO indices.


Publication title

Journal of Climate










School of Geography, Planning and Spatial Sciences


American Meteorological Society

Place of publication


Rights statement

© 2009 American Meteorological Society

Repository Status

  • Restricted

Socio-economic Objectives

Climate variability (excl. social impacts)

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