Enhancement of near-annual variability in the equatorial Pacific in 2000-2008

Abstract

Like the El Niño Southern Oscillation (ENSO), the near-annual mode is an air-sea coupled mode of the tropical Pacific that can emerge within a relatively cool mean state. It is documented here from satellite observations over the 2000-2008 period based on a covariance analysis between wind stress and zonal current anomalies. It is shown that near-annual variability is enhanced over the last decade. The signature of this mode consists of a zonal seesaw pattern for zonal current with westward (eastward) anomalous currents in the western (eastern) equatorial Pacific. A composite analysis allows identifying the peak and transition phases of this mode, particularly active over 2000-2004. It is suggested that the reduction of the interannual variability in the eastern Pacific over the last decade may be related to the enhancement of the near-annual mode.