Publication Date:
2015-05-10
Description:
We investigate the characteristics of shear–generated turbulence in the natural environment by considering data from a number of cruises in the western equatorial Pacific. In this region the vertical shear of the flow is dominated by flow structures that have a relatively small vertical scale of O(10m). Combining data from all cruises we find a strong relationship between the turbulent dissipation rate, ϵ , vertical shear, S , and buoyancy frequency, N . Examination of ϵ at a fixed value of Richardson number, Ri = N 2 ∕ S 2 , shows that for a wide range of values of N , where u t is an appropriate velocity scale which we assume to be the horizontal velocity scale of the turbulence. The implied vertical length scale, ℓ v = u t ∕ N , is consistent with theoretical and numerical studies of stratified turbulence. Such behavior is found for Ri 〈 0.4. The vertical diffusion coefficient then scales as at a fixed value of Richardson number. The amplitude of ϵ is found to increase with decreasing Ri , but only modestly, and certainly less dramatically than suggested by some parameterization schemes. Provided the shear generating the turbulence is resolved our results point to a way to parameterize the unresolved turbulence. This article is protected by copyright. All rights reserved.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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