Wind-forced equatorial wave dynamics of the Pacific Ocean during 2014/2015 and 2015/2016 El Niño events

Abstract

The equatorial wave dynamics of interannual sea level variations between 2014/2015 and 2015/2016 El Nino events are compared using the Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics Climate Ocean Model (LICOM) forced by the National Centers for Environmental Prediction (NCEP) reanalysis Ⅰ wind stress and heat flux during 2000-2015. In addition, the LICOM can reproduce the interannual variability of sea surface temperature anomalies (SSTA) and sea level anomalies (SLA) along the equator over the Pacific Ocean in comparison with the Hadley center and altimetric data well. We extracted the equatorial wave coefficients of LICOM simulation to get the contribution to SLA by multiplying the meridional wave structure. During 2014/2015 El Nino event, upwelling equatorial Kelvin waves from the western boundary in April 2014 reach the eastern Pacific Ocean, which weakened SLA in the eastern Pacific Ocean. However, no upwelling equatorial Kelvin waves from the western boundary of the Pacific Ocean could reach the eastern boundary during the 2015/2016 El Nino event. Linear wave model results also demonstrate that upwelling equatorial Kelvin waves in both 2014/2015 and 2015/2016 from the western boundary can reach the eastern boundary. However, the contribution from stronger westerly anomalies forced downwelling equatorial Kelvin waves overwhelmed that from the upwelling equatorial Kelvin waves from the western boundary in 2015. Therefore, the western boundary reflection and weak westerly wind burst inhibited the growth of the 2014/2015 El Nino event. The disclosed equatorial wave dynamics are important to the simulation and prediction of ENSO events in future studies.