TROPICAL INSTABILITY WAVE KINEMATICS - OBSERVATIONS FROM THE TROPICALINSTABILITY WAVE EXPERIMENT

The kinematics of planetary waves originating from instability of the nearsurface equatorial currents are reported on using velocity measure ments from an array of acoustic Doppler current profilers deployed in the equatorial Pacific during the Tropical Instability Wave Experiment . A distinctive wave season was observed from August to December 1990, with wave energy confined primarily above the core of the Equatorial Undercurrent. Particle motions in the horizontal plane are described b y eccentric ellipses oriented toward the north, but tilting into the c yclonic shear of the South Equatorial Current. The tilt is maximum nea r the surface just north of the equator and decreases to the south and with depth. The distribution of wave variance is narrowband in both f requency and zonal wavenumber, with central period, zonal wavelength, and westward directed phase propagation estimated to be 500 hours, 106 0 km, and 59 cm s(-1), respectively. Neither the meridional nor the ve rtical wavenumber component is statistically different from zero. Thes e results generally agree with previous findings on tropical instabili ty waves from the Atlantic and Pacific Oceans, and, in the undersample d arena of geophysical measurements, they provide an example where sta tistical inference is supported by an ensemble of independent measurem ents.