ANNUAL VARIATION OF SEA-SURFACE SLOPES OVER THE SCOTIAN SHELF AND GRAND-BANKS FROM GEOSAT ALTIMETRY

The Geosat radar altimeter data from approximately 60 repeat cycles of the Exact Repeat Mission (ERM) over the period November 1986 to Septe mber 1989 have been analysed to show the annual variations of the sea- surface slopes, corrected for ocean tides, over the Scotian Shelf and the Grand Banks. A coastal tidal model developed at the Bedford Instit ute of Oceanography, combined with the global tidal model of Schwiders ki, is employed to remove the tidal signals from the sea-surface heigh ts over those regions. Linear regression is used to estimate the sea-s urface slopes over the inner shelf region, the outer shelf region, or a combination of the two along the Geosat ground tracks. Harmonic anal ysis is applied to the time series of sea-surface slopes to derive the annual signals, showing that amplitudes are of order of 5 x 10(-7) (5 Cm/100 km) with onshore slopes positive in winter and negative in sum mer. The largest annual cycles occur over the outer portion of the Lau rentian Channel and the southern Grand Banks. The annual cycles differ between the eastern and western portions of the Scotian Shelf. in the east, the signal is synchronized with that of the Laurentian Channel, whereas in the west, the phase of the signal is advanced by 2-3 month s. The annual signals over the eastern Scotian Shelf are comparable an d consistent with historical hydrographic data along the Halifax Hydro graphic Section. The amplitude and phase over the western Scotian Shel f are consistent with the adjusted sea level at the Halifax Station. T he annual variability of the sea-sur ace slopes over the Scotian Shelf and the Grand Banks is thought to be induced by the seasonal outflow from the Gulf of St Lawrence through Cabot Strait, and possibly by an annual cycle in the Slope Water current.