IMPROVED M(2) OCEAN TIDE FROM TOPEX POSEIDON AND GEOSAT ALTIMETRY/

TOPEX/POSEIDON (T/P) collinear differences have been used to extract e rrors in the M(2) tide model of Cartwright and Ray (1991). The fluctua tion of the power of these differences clearly shows the need for corr ections at a period of about 60 days, close to the aliased periods of the M(2) and S-2 tides. The level of the necessary changes at this per iod is about 4 cm (rms). Further detailed analysis of collinear differ ences in 4 degrees x4 degrees bins, allowing for determination of up t o 6 luni-solar and ''ocean weather'' tides (annual and semiannual), sh ows that the M(2) corrections are well discriminated from the others a nd have a global power of 3.5 cm (rms). Both in-phase and out-of-phase components of the corrections have similar broad scale characteristic s dominated by a few meridionally oriented bands. The T/P-derived M(2) model shows rms deviations of 3.1 cm with data at 80 selected ocean i sland and bottom gauges compared with 3.9 cm for the Cartwright and Ra y (1991) model. A weighted combination of Geosat and T/P-derived model s achieves residuals of 2.8 cm (rms) with this global tide gauge data.