Interannual variability and dynamics of intraseasonal wind rectification in the equatorial Pacific Ocean

Abstract

The rectification of intraseasonal wind forcing on interannual sea surface temperature anomalies (SSTA) and sea level anomalies (SLA) associated with El Nino–Southern Oscillation (ENSO) during 1993–2016 are investigated using the LICOM ocean general circulation model forced with daily winds. The comparisons of the experiments with and without the intraseasonal wind forcing have shown that the rectified interannual SSTA and SLA by the intraseasonal winds are much weaker than the total interannual SSTA and SLA in the cold tongue, due to the much weaker rectified than the total interannual Kelvin and Rossby waves in the equatorial Pacific Ocean. The dynamics of the rectification are through the nonlinear zonal and vertical advection by the background currents, which produces downwelling equatorial Kelvin waves during El Nino. The meridional advection is much smaller than the zonal and vertical advection, suggesting that the rectification is not induced by the Ekman dynamics or the thermocline rectification. The rectified interannual Kelvin waves are found to be much smaller than reflected at the Pacific western boundary and those forced by the interannual winds, suggesting that the latter two play a much more important role in ENSO dynamics than the intraseasonal winds. The results of this study suggest an unlikely significant role of oceanic nonlinear rectification by intraseasonal winds during the onset and cycling of El Nino.