Observations of the Mf ocean tide from Geosat altimetry

Zonal averages of the 13.66‐day Mf tide are derived from one year of Geosat altimetry records. The orbit errors are reduced by 1/revolution corrections taken over long (several day) arcs. The short‐period tides are removed using a model previously derived by us from the same data. The Mf zonal averages indicate definite nonequilibrium character at nearly all latitudes. The imaginary admittances indicate a Q of at least 8; such a value is consistent with a simplified theory of coupled gravitational and vorticity modes and suggests a value for Proudman's ‘friction period’ about 123 days.