Empirical ocean tide models estimated from TOPEX/POSEIDON altimetry

Abstract

Three empirical ocean tide models are determined from repeat cycles 10 to 78 of the TOPEX/POSEIDON (T/P) altimeter mission. The three models investigate the effects of the satellite orbit ephemeris on the ocean tides determined from T/P altimetry and the effect of extracting the free core nutation resonance in the definition of the diurnal ocean tide admittance. The altimetric data series use the Joint Gravity Model JGM‐2 geopotential orbit ephemeris and the preliminary JGM‐3 orbit ephemeris computed at the University of Texas, Center for Space Research. The altimetric data from the T/P mission are shown to have the precision necessary to estimate the monthly and fortnightly ocean tides in each bin. Inclusion of existing models of the ocean tides in the polar latitudes not sampled by the altimeter demonstrates the importance of these latitudes on spherical harmonic representations of the ocean tides. The ocean tides are first estimated in bins of size 2.834° in longitude by 1° in latitude and then smoothed to 1° by 1° grids within ±66° latitude. The orthotide response formalism of Groves and Reynolds (1975) is used to represent the diurnal and semidiurnal ocean tides, while a constant admittance is assumed across narrow bandwidths around each of the monthly (Mm), fortnightly (Mf), and termensual (Mt) tidal components. Comparisons of the T/P ocean tide models to tide gauge observations indicate their accuracies to be of the order of 2–3 cm. The T/P‐derived ocean tide models remove approximately 20 cm2 more of the T/P measured sea surface variance than the Cartwright and Ray (1991) tide model and show a 19 cm2 and 15 cm2 improvement over the Schwiderski (1980a, b) and Cartwright and Ray (1991) tide models, respectively, when compared to tide gauge estimates of the ocean tides.