DETERMINATION OF OCEAN TIDES FROM THE FIRST YEAR OF TOPEX POSEIDON ALTIMETER MEASUREMENTS/

An improved geocentric global ocean tide model has been determined usi ng I year of TOPEX/POSEIDON altimeter measurements to provide correcti ons to the Cartwright and Ray (1991) model (CR91). The corrections wer e determined on a 3 degrees x 3 degrees grid using both the harmonic a nalysis method and the response method. The two approaches produce sim ilar solutions. The effect on the tide solution of simultaneously adju sting radial orbit correction parameters using altimeter measurements was examined. Four semidiurnal (N-2, M(2), S-2, and K-2), four diurnal (Q(1), O-1, P-1, and K-1), and three long-period (S-sa, M(m), and M(f )) constituents, along with the variation at the annual frequency, wer e included in the harmonic analysis solution. The observed annual vari ation represents the first global measurement describing accurate seas onal changes of the ocean during an El Nino year. The corrections to t he M(2) constituent 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 RM S, 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 gaug es gives RMS differences of 2.7 cm for M(2) and 1.7 cm for K-1. Compar able values when the CR91 model is used are 3.9 cm and 2.0 cm, respect ively. Examination of TOPEX/POSEIDON sea level anomaly variations usin g the new tide model further confirms that the tide model has been imp roved.