SST Anomalies of ENSO and the Madden–Julian Oscillation in the Equatorial Pacific*

This study explores whether anomalies of sea surface temperature (SST) in the equatorial Pacific during warm events of El Niño–Southern Oscillation (ENSO) are related to the Madden–Julian oscillation (MJO). An index is derived from surface wind data of a global model reanalysis to measure forcing of oceanic Kelvin waves by wind stress associated with the MJO. This Kelvin wave forcing index of the MJO is used to relate interannual anomalies in seasonal activity of the MJO to interannual anomalies in equatorial SST for the 1980–99 time period. Evidence is found showing that during ENSO warm events, stronger Kelvin wave forcing in the western Pacific precedes greater SST anomalies in the eastern Pacific by 6–12 months. No such evidence, however, can be found for the period of 1950–79. The result suggests that during ENSO warm events, amplitudes of SST anomalies in the eastern Pacific can be affected by the MJO, at least for the 1980–99 period, through its seasonal activity of Kelvin wave forcing. A possible mechanism for such an MJO–ENSO relationship is described. How ENSO prediction can be benefited from the precursory signals of the MJO is discussed.