Asymmetric Responses of the Western Tropical Pacific Sea Level to El
Niño and La Niña
Abstract
The western tropical Pacific (WTP) exhibits large interannual sea level
anomalies (SLAs), and the sea level falling in El Niño is evidently
stronger than the rising in La Niña. The asymmetry is most prominent
near 160°E with the response to El Niño larger by three times and
becomes less obvious near the western boundary. Sensitivity experiments
of a simplified ocean model suggest that the asymmetry in surface wind
forcing structure between El Niño and La Niña is critical. The El Niño’s
westerly wind anomaly patch locates more east than the La Niña’s
easterly wind patch during the mature stage, and its upwelling effects
are accumulated over a wider longitude range and cause stronger negative
SLAs in the WTP. Near the western boundary, however, upwelling effects
are attenuated by easterly wind anomalies during El Niño conditions. The
asymmetric ocean responses to ENSO winds may participate in the
asymmetry of ENSO cycle.