![]() ![]() 1994) and (ii) the seasonal modulation of ENSO’s coupled instabilities ( Philander et al. Two possible mechanisms have been proposed to explain the phase locking of ENSO variance: (i) the frequency locking of ENSO to period forcing due to nonlinear interaction of the seasonal forcing and the inherent ENSO cycle ( Jin et al. Although several negative feedbacks could explain how the coupled ocean–atmosphere system oscillates, for example, via a recharge–discharge oscillator ( Jin 1996, 1997a, b) or delayed oscillators ( Suarez and Schopf 1988), the underlying physical mechanisms for phase locking of ENSO peak to the boreal winter season still remain elusive. The onset of ENSO events generally occurs during boreal spring and summer, while most events peak in boreal winter, with the amplitudes decaying in the next spring. The asymmetry of the sharpness of ENSO phase locking is induced by the asymmetric effect of state-dependent noise forcing in El Niño and La Niña events.Įl Niño–Southern Oscillation (ENSO) is the dominant climate mode of variability in the tropical Pacific on interannual time scales, having a significant impact on global weather and climate. Furthermore, the strength of phase locking is mainly controlled by the linear growth/decay rate, the amplitude of seasonal modulation of growth/decay rate, the amplitude of noise, the SST-dependent factor of multiplicative noise, and the linear frequency. The preferred month of ENSO peak time depends critically on the phase and strength of the seasonal modulation of the ENSO growth/decay rate. Further, the impact on ENSO phase locking from annual cycle modulation of the growth/decay rate, stochastic forcing, nonlinearity, and linear frequency are examined in the RO model. ![]() The difference between the nonlinear phase-locking mechanism and linear phase-preference mechanism is largely smoothed out in the presence of noise forcing. ![]() In addition, the linear/nonlinear mechanism of ENSO phase preference/phase locking is investigated using RO model. The RO model reproduces the main phase-locking characteristics found in observations, and the results show that the phase locking of ENSO is mainly dominated by the seasonal modulation of ENSO growth/decay rate. The conceptual ENSO recharge oscillator (RO) model is adopted to examine the ENSO phase-locking behavior in terms of its peak time, strength of phase locking, and asymmetry between El Niño and La Niña events. This phase locking is a fundamental ENSO property that is determined by its basic dynamics. El Niño–Southern Oscillation (ENSO) events tend to peak at the end of the calendar year, a phenomenon called ENSO phase locking. ![]()
0 Comments
Leave a Reply. |