LOCKING OF EL NINOS PEAK TIME TO THE END OF THE CALENDAR YEAR IN THE DELAYED OSCILLATOR PICTURE OF ENSO

El Nino events owe their name to their tendency to be locked to the se asonal cycle. A simple explanation is proposed here for the lacking of the peak of ENSO's basin-scale warming to the end of the calendar yea r. The explanation is based on incorporating a seasonally varying coup led ocean-atmosphere instability strength into the delayed oscillator mechanism for the ENSO cycle. It is shown that the seasonally varying amplification of the Rossby and Kelvin ocean waves by the coupled inst ability forces the events to peak when this amplification is at its mi nimum strength, at the end of the calendar year. The mechanism is demo nstrated using a simple delayed oscillator model and is further analyz ed using the Cane-Zebiak model. Being based on the oversimplified dela yed oscillator paradigm of ENSO, the proposed mechanism cannot be expe cted to fully explain the locking of observed events to the end of the year. However, the wave dynamics perspective it offers to approaching the ENSO phase-lacking problem may serve as a first step toward a ful ler explanation based on more realistic models and additional data ana lysis.