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Wind-Generated Equatorial Kelvin Waves Observed Across the Pacific Ocean

C. C. EriksenDepartment of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, 02139

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M. B. BlumenthalMassachusetts Institute of Technology-Woods Hole Oceanographic Institution Joint Program in Oceanography, Cambridge and Woods Hole, MA 02543

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S. P. HayesPacific Marine Environmental Laboratory/NOAA, Seattle, WA 98105

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P. RipaCentro de Investigatión Científica y Eseñanza Superior de Ensenada (CICESE), Ensenada, Baja California, Mexico

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Abstract

Sea-level fluctuations during 1978–80 at equatorial Pacific islands separated by as much as one-quarter of the earth's circumference are coherent at periods of 1–6 weeks with phases implying eastward propagation. Eastward speeds are 16 ± 7.5% higher than expected for a linear, first-baroclinic-mode Kelvin wave (based upon hydrography). Zonal winds in the western Pacific exhibit variation on meridional scales comparable to those of equatorial-ocean baroclinic motions. Roughly one-quarter of sea-level variance in the 1–6 week period range can be explained by local zonal wind alone. The observed admittance magnitude, O[0.1 cm sea level per (m s−1)2 zonal wind pseudo-stress], and phase lag (a few days, sea level lagging wind) can be accounted for in a linear model of baroclinic equatorial Kelvin waves generated by a crudely idealized wind patch of 1000 km zonal scale. Zonal winds at the equator excite, among other things, low-mode Kelvin waves which are recognizable O(10000 km) to the east of the forcing.

Abstract

Sea-level fluctuations during 1978–80 at equatorial Pacific islands separated by as much as one-quarter of the earth's circumference are coherent at periods of 1–6 weeks with phases implying eastward propagation. Eastward speeds are 16 ± 7.5% higher than expected for a linear, first-baroclinic-mode Kelvin wave (based upon hydrography). Zonal winds in the western Pacific exhibit variation on meridional scales comparable to those of equatorial-ocean baroclinic motions. Roughly one-quarter of sea-level variance in the 1–6 week period range can be explained by local zonal wind alone. The observed admittance magnitude, O[0.1 cm sea level per (m s−1)2 zonal wind pseudo-stress], and phase lag (a few days, sea level lagging wind) can be accounted for in a linear model of baroclinic equatorial Kelvin waves generated by a crudely idealized wind patch of 1000 km zonal scale. Zonal winds at the equator excite, among other things, low-mode Kelvin waves which are recognizable O(10000 km) to the east of the forcing.

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