A Western Pacific Oscillator Paradigm for the El Niño‐Southern Oscillation

Abstract

Abstract. A data-based hypothesis is presented on the mechanism of the E1 Nifio-Southern Oscillation (ENSO), a major determinant of interannual global climate variability. The hypothesis emphasizes the importance of off-equator sea surface temperature and sea level pressure variations west of the dateline for initiating equatorial easterly winds over the far western Pacific. These winds compete with westerly winds over the equatorial central Pacific enabling the coupled oceanatmosphere system to oscillate. Consistent with this hypothesis, an analogical oscillator model is constructed that produces ENSO-like oscillations. The proposed mechanism differs from the delayed oscillator paradigm in that wave reflection at the western boundary is not a necessary condition for the coupled ocean-atmosphere system to oscillate.

Role of subsurface entrainment temperature (Te) in the onset of El Niño events, as represented in an intermediate coupled model

“…The mechanism for the roles of reflected signals at the western boundary and off-equatorial anomalies seen in this modeling work is consistent in some extent with the so-called western Pacific Oscillator theory (Weisberg and Wang 1997). In the atmosphere, condensation heating in the western and central Pacific was induced by twin offequatorial cyclones and westerly wind anomalies at the equator.…”

The influence of boreal winter extratropical North Pacific Oscillation on Australian spring rainfall

“…In turn, these force a pattern of atmospheric circulation anomalies, including westerly wind stress anomalies, along the equatorial western Pacific. These subsequently lead to SST warming anomalies in austral spring over the tropical central-eastern Pacific by triggering an eastward propagating and downwelling Kelvin wave (Barnett et al 1989; Weisberg and Wang 1997;Vimont et al 2003a, b;Alexander et al 2010). Warming of SST in austral spring over the tropical central-eastern Pacific induces an anomalous Walker circulation, with its western subsiding branch over Australia, suppressing convection and reducing rainfall in northern and eastern Australia.…”

The initial errors that induce a significant “spring predictability barrier” for El Niño events and their implications for target observation: results from an earth system model

“…One is the local "upwelling pathway" in which the SSTA is directly related to thermocline depth anomalies over the eastern equatorial Pacific, and the other "wind coupling pathway" provides a remote coupling through wave dynamics. Moreover, most theoretical ENSO oscillator models emphasize the importance of oceanic wave propagation processes associated with the upperocean heat content (OHC) anomalies (Suarez and Schopf 1988;Battisti and Hirst 1989;Weisberg and Wang 1997;Picaut et al 1997). In particular, Jin (1997a, b) proposed that it is the phase lag between the zonal mean thermocline depth over the entire equatorial Pacific and the SST anomaly in the eastern Pacific that leads to an oscillation of ENSO.…”