Determination of ocean tides from the first year of TOPEX/POSEIDON altimeter measurements

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Abstract
An improved geocentric global ocean tide model has been determined using 1 year of TOPEX/POSEIDON altimeter measurements to provide corrections to the Cartwright and Ray (1991) model (CR91). The corrections were determined on a 3°×3° grid using both the harmonic analysis method and the response method. The two approaches produce similar solutions. The effect on the tide solution of simultaneously adjusting radial orbit correction parameters using altimeter measurements was examined. Four semidiurnal (N2, M2, S2, and K2), four diurnal (Q1, O1, P1, and K1), and three long‐period (Ssa, Mm, and Mƒ) constituents, along with the variation at the annual frequency, were included in the harmonic analysis solution. The observed annual variation represents the first global measurement describing accurate seasonal changes of the ocean during an El Niño year. The corrections to the M2constituent have an RMS of 3.6 cm and display a clear banding pattern with regional highs and lows reaching 8 cm. The improved tide model reduces the weighted altimeter crossover residual from 9.8 cm RMS, when the CR91 tide model is used, to 8.2 cm RMS. Comparison of the improved model to pelagic tidal constants determined from 80 tide gauges gives RMS differences of 2.7 cm for M2and 1.7 cm for K1. Comparable values when the CR91 model is used are 3.9 cm and 2.0 cm, respectively. Examination of TOPEX/POSEIDON sea level anomaly variations using the new tide model further confirms that the tide model has been improved.

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