An estimate of equatorial wave energy flux at 9‐ to 90‐day periods in the central Pacific

Abstract

Deep fluctuations in current along the equator in the Central Pacific are dominated by coherent structures which correspond closely to narrow‐band (in wave number) propagating equatorial waves. Currents were measured roughly at 1500 and 3000 m depths at 5 moorings between 144 and 148°W from January 1981 to March 1983 as part of the Pacific Equatorial Ocean Dynamics (PEQUOD) program. In each frequency band resolved, a single complex empirical orthogonal function accounts for half to three quarters of the observed variance in either zonal or meridional current. Dispersion for equatorial first meridional Rossby and Rossby gravity waves is consistent with the observed vertical‐zonal coherence structure. The observations indicate that energy flux is westward and downward in long first meridional mode Rossby waves at periods 45 days and longer and eastward and downward in short first meridional mode Rossby waves and Rossby‐gravity waves at periods 30 days and shorter. A local minimum in energy flux occurs at periods corresponding to a maximum in upper ocean meridional current energy contributed by tropical instability waves. Total vertical flux (energy transport per unit zonal distance) across the 9‐ to 90‐day period range is 2.5 kW/m.