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The horizontal coherence of inertial oscillations was investigated using the records from six current meters moored on the Oregon continental shelf and whose separation distance varied from approximately 9 to 35 km. The rotary component method for analyzing vector time series was used to form the cross spectra and coherencies for 15 pairs of records, the length of which varied from 10 to 27 days. The velocity field was found to be highly coherent for periods greater than about 10 days. The coherencies at the inertial frequency, which were generally quite low, could be accounted for (with some exceptions) by a consideration of both the separation distance and a simple representation of the effects of stratification.

A common observation in major coastal upwelling regions is a reversal of the mean longshore current with depth during active upwelling. A numerical model and a simple analytical model applied to a two-layer ocean on a beta-plane indicate that this undercurrent cannot exist for upwelling off an east-west (zonal) coastline. The models are applied to the coastal upwelling occurring on the Campeche Bank during the period from March to September. The beta-plane solutions for upwelling along an east-west coastline resemble f-plane solutions for a meridional (N–S) coastline. In particular, the hypothesis explaining the undercurrent of Hurlburt and Thompson cannot hold for upwelling along a zonal coastline. The results in this paper form a new hypothesis which could be tested by measuring currents on the Campeche Bank during active upwelling.