Graduate Thesis Or Dissertation
 

Sea surface height and geostrophic velocity variability in the California current system as observed from the TOPEX altimeter

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  • Eight years (1994-2000) of data from the TOPEX/Poseidon satellite altimeter are used to investigate the variability of the sea surface height and geostrophic velocity of the California Current system. The TOPEX/Posiedon satellite measures SSH along an exact-repeat set of groundtracks with a 10-day repeat cycle. In the domain studied here (140° - 110°W, 24° - 50°N) the groundtrack separation ranges from 200-300 km, decreasing with increased latitude. Along-track resolution is 5.75 km. Variances of SSH and across-track geostrophic velocities are presented. The annual SSH and velocity variances show the envelope of high variance associated with the California Current as a C shaped region from the coast at 45°N south to an offshore limit of ~135°W between 35° - 40°N and then back toward shore south of the California Bight at 30°N. High values of velocity variance are O(400) cm²s⁻² at 38°N and 126°W. Seasonal variances describe the development of the California Current system. In spring (defined here as March-May) as the system begins to develop, higher velocity variance is seen near the coast. By summer the variance has increased and moved farther offshore, before peaking in fall. Winter shows the energy moving farther offshore as it weakens. The velocity variance is partitioned into within season and seasonal mean variances to understand the contribution of inter-annual differences to the variance. The within season variance dominates in summer and fall, while the seasonal mean variance contributes significantly in winter. The offshore transport of SSH and energy is investigated by constructing Hovmöller diagrams (time versus longitude) at different latitudes. The offshore propagation speeds are shown to compare well with theoretical Rossby wave speeds south of 35°N but to be larger by a up to factor of 1.5 north of 35°N. The seasonal development is also described by showing seasonal wavenumber spectra on four descending and four ascending groundtracks in the domain. As the CC system develops, wavenumber energy increases at 200-300 km wavelengths on groundtracks closest to the coast. This energy propagates offshore and weakens. At the offshore tracks the wavenumbers show weaker energies and shorter wavelengths (150-200 km).
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