Off-equatorial westward propagating Rossby waves in the tropical Pacific during the 1982-83 and 1986-87 ENSO events

Analysis of anomalous vertically averaged temperatures (TAV) in the tropical Pacific Ocean for the eight-year period 1979-86, finds the development during the onset phase, one to two years before the mature phase of the two ENSO events of the period, having dynamically significant similarities both north and south of the equator. The analysis shows that there were positive anomalies on the maritime western boundary in both hemispheres during autumn/winter of the onset phase, not in one hemisphere or the other. During both ENSO events, the dynamical off-equatorial influence was found only to have initiated the ENSO event; off-equatorial influence dominated the first half of the ENSO year, diminishing during the peak phase of the event (i.e., northern summer of both ENSO years), and replaced during the second half of the ENSO year by strictly equatorial influences related to the development of anomalous westerly winds on the equator in the western equatorial Pacific.