A Composite Spectrum of Vertical Shear in the Upper Ocean

Abstract

Results from three separate velocity profilers operated nearly simultaneously in the northwest Atlantic in 1975 are used to form a composite shear spectrum over vertical wavelengths from 100 m down to a few centimeters. This exercise constitutes an intercomparison of the three different measurement techniques and reveals a shear spectrum which is approximately fiat at a WKB-scaled level from k = 0.01 cpm through k0 ≈ 0.1 cpm, then falls as k−1 to a buoyancy wavenumber k0 = (N3/ϵ)1/2 determined by the local average Väisälä frequency N and the volume-averaged dissipation rate ϵ. Various consequences of the observed shear spectral shape are explored. Abstract Results from three separate velocity profilers operated nearly simultaneously in the northwest Atlantic in 1975 are used to form a composite shear spectrum over vertical wavelengths from 100 m down to a few centimeters. This exercise constitutes an intercomparison of the three different measurement techniques and reveals a shear spectrum which is approximately fiat at a WKB-scaled level from k = 0.01 cpm through k0 ≈ 0.1 cpm, then falls as k−1 to a buoyancy wavenumber k0 = (N3/ϵ)1/2 determined by the local average Väisälä frequency N and the volume-averaged dissipation rate ϵ. Various consequences of the observed shear spectral shape are explored.