Abstract:
Near-inertial motions were observed at all current meters in an array of five moorings spanning the
continental margin off central Oregon during October 1977 to January 1978. All moorings were between
10 and 130 km from shore, in water depths between 100 m and 2500 m. Largest near-inertial amplitudes
(> 30 cm/s) were observed at the uppermost current meters of the offshore moorings, although these were
below the surface mixed layer. The near-inertial energy generally decreased with increasing depth, and
there was less near-inertial energy over the continental shelf than at similar depths offshore. The energy
levels observed over the shelf were about the same as observed there during summer 1973, and the energy
levels observed offshore were comparable with those observed in the open North Atlantic. Horizontal
coherence scales were large, exceeding 115km during the first half of the observational period and about 60
km during the second half; estimates of the horizontal wavelength (50 km during the first half and 20 km
during the second half suggest that the coherence scale is of the order of three wavelengths. Although we
did not have current data in the surface mixed layer nor wind measurements over each mooring, the
available meteorological data (synoptic pressure charts and hourly wind and pressure at Newport) suggest
that most of the near-inertial energy was forced by the local wind.
