Tracking down the ENSO delayed oscillator with an adjointOGCMGeert
نویسنده
چکیده
The adjoint of an ocean general circulation model is used as a tool for investigating the causes of changes in ENSO SST indices. We identify adjoint Kelvin and Rossby waves in the sensitivities to sea level and wind stress at earlier times, which can be traced back for more than a year through western and weak eastern boundary reeections. Depending on the thermocline depth the rst and second baroclinic modes are excited. The sensitivities to the heat ux and SST are local and decay in about a month. The sensitivities to the uxes are converted into the innuence of SST using the adjoint of a statistical atmosphere model. Focusing on SST perturbations in the index region itself, we recover, up to a scale factor, the delayed oscillator concept.
منابع مشابه
On the ENSO Mechanisms
The El Niño-Southern Oscillation (ENSO) is an interannual phenomenon involved the tropical Pacific Ocean-atmosphere interactions. The oscillatory nature of ENSO requires both positive and negative ocean-atmosphere feedbacks. The positive feedback is dated back to Bjerknes' hypothesis in the 1960s, and different negative feedbacks have been proposed since the 1980s associated with the delayed os...
متن کاملLocking of El Niño’s Peak Time to the End of the Calendar Year in the Delayed Oscillator Picture of ENSO
El Niño events owe their name to their tendency to be locked to the seasonal cycle. A simple explanation is proposed here for the locking of the peak of ENSO’s basin-scale warming to the end of the calendar year. The explanation is based on incorporating a seasonally varying coupled ocean–atmosphere instability strength into the delayed oscillator mechanism for the ENSO cycle. It is shown that ...
متن کاملNOTES AND CORRESPONDENCE A Simple Model Study of ENSO Suppression by External Periodic Forcing*
The study of a forced delayed oscillator ENSO model suggests that the intensity of ENSO can be suppressed significantly by an external periodic forcing due to the nonlinear mechanism of frequency entrainment. This suppression of ENSO is most effective for ENSOs in the regime of unstable self-exciting oscillation and for forcing of frequencies close to that of ENSO. In particular, an annual cycl...
متن کاملReassessing Conceptual Models of ENSO
The complex nature of the El Niño–Southern Oscillation (ENSO) is often simplified through the use of conceptual models, each of which offers a different perspective on the ocean–atmosphere feedbacks underpinning the ENSO cycle. One theory, the unified oscillator, combines a variety of conceptual frameworks in the form of a coupled system of delay differential equations. The system produces a se...
متن کاملMechanisms of Seasonal – ENSO Interaction
The mechanisms by which the seasonal cycle in the equatorial Pacific affects ENSO are investigated using the Zebiak and Cane ENSO prediction model. The most dominant seasonal effect is found to be due to the wind divergence field, as determined by the seasonal motion of the ITCZ, through its effect on the atmospheric heating. The next-order seasonal effects are due to the seasonality of the bac...
متن کامل