HIGH-FREQUENCY INTERNAL WAVES IN THE STRONGLY SHEARED CURRENTS OF THE UPPER EQUATORIAL PACIFIC - OBSERVATIONS AND A SIMPLE SPECTRAL MODEL

Statistics of high-frequency (0.24.5 cph) fluctuations are derived from moored upper ocean measurements of currents and temperatures at four latitudes spanning the equator along 140-degrees-W. Some of the more unusual statistics include (1) nonunity ratios of kinetic energy to potential energy; (2) nonunity ratios of zonal to meridional kinetic energy; (3) nonzero current-temperature coherence amplitudes, with depth-dependent phases; and (4) high vertical coherence amplitudes, with approximately 180-degrees phases, between current measurements spanning the thermocline. A simple model of shear-modified internal waves is employed to gain insight into the causes of the latitudinal variability of the statistics. Much of this variability can be attributed to the vertical advection of significantly different mean vertical shears by a spectrum of internal waves. The statistics also suggest that the spectrum of high-frequency internal waves in the upper equatorial Pacific differs in important ways from canonical spectral models. The statistics are consistent with a model based on vertical modes which neglect advection by the mean flow, provided the energy in the first mode is much less than (about 0.3 times) that in the spectrum described by Garrett and Munk (1972, 1975, 1979) and Munk (1981) and two to four times as much energy propagates eastward as westward. Some of the statistics are inconsistent with the simple internal wave model examined, possibly indicating contamination by mooring motion.