TPXO.3 is a global model of ocean tides, which best-fits, in a least-squares sense, the Laplace Tidal Equations and cross-over data from the first 116 TOPEX/Poseidon orbit cycles. The methods used to compute the model are described in detail by Egbert, Bennett, and Foreman [1994; EBF]. TPXO.3, described by Egbert [1997], is an improved version of TPXO.1 (TPXO.2), the model originally presented in EBF. The tides are provided as complex amplitudes of earth-relative sea-surface elevation for eight primary harmonic constituents (K1, O1, P1, Q1, M2, S2, N2, K2), on a 512x256 grid between latitudes of 79.71 degrees S and 69.71 degrees N.
A tidal synthesis program ("tide"), which computes tidal corrections for a given time and location, is provided with the model file. This program applies bilinear interpolation to the gridded model file of complex harmonic constants, at the desired location. The tidal synthesis program uses interpolation of the tidal admittances in the diurnal and semi-diurnal bands to include 9 additional minor constituents (J1, NO1, OO1, RHO1, 2N2, MU2, NU2, L2, T2). The synthesis program also adds the long period constituents MF, MM, and SSA using the standard equilibrium forms. All of the usual nodal corrections have been applied. Note that the tides output by "tide" are geocentric, or altimetric tides and are suitable for direct use as corrections for TOPEX/Poseidon or other altimetric data.
TPXO.3 reduced the RMS T/P cross-over difference from 0.4524 m (no tidal correction), to 0.0937 m. For comparison, the RMS cross-over difference for the other tidal corrections on the T/P GDR were 0.1199 m for SCH80, and 0.1120 for CR91. TPXO.3 thus resulted in variance reductions of 39% and 30% relative to SCH80 and CR91, respectively. Note that all models were compared at the same set of cross-overs, and that the quoted RMS values are unweighted. Smaller RMS values are obtained for all models when the comparison is restricted to open ocean (e.g., greater than 1000 m depth) cross-overs. For the 78 pelagic validation gauges proposed by Cartwright and Ray, the RMS misfits of TPXO.3 for the four constituents were 0.0275 m (M2); 0.0165 m (S2); 0.0125 m (O1); 0.0161 m (K1).
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