A comparison between computed and measured oceanic winds near the British Columbia coast

Abstract

Winds measured over the continental shelf off Vancouver Island during the summers of 1979 and 1980 are compared with winds computed by the National Marine Fisheries Service (Monterey, California), using synoptic surface atmospheric pressures. Although there is considerable qualitative similarity between the two sets of data, the computed 6‐hourly winds fail accurately to resolve short‐period fluctuations associated with transient wind systems and tend to underestimate the percentages of time of low and high wind speeds. In the frequency domain, the computed winds are representative of the oceanic winds for periods exceeding roughly 2 days but only marginally representative for periods of 1½–2 days. At periods less than about 1½ days, computed winds are not reliable indicators of oceanic wind variability. Moreover, the computed winds possess a large‐amplitude sea breeze (diurnal) component that is present in the inner shelf wind data but not in the outer shelf wind data. This sea breeze component in the computed winds originates through use of land‐based atmospheric pressure values and is not indicative of the offshore wind field. Spectra of the observed winds suggest a k−5/3law behavior (k is the horizontal wave number) consistent with the existence of a mesoscale, two‐dimensional, reverse cascading energy inertial range. Spectra for computed winds, on the other hand, are more consistent with a k−3 law appropriate to geostrophic turbulence and the existence of a macroscale, two‐dimensional, cascading enstrophy inertial range.