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Measuring Turbulent Dissipation Using a Tethered ADCP

Lucas, N.S. and Simpson, J.H. and Rippeth, T.P. (2014) Measuring Turbulent Dissipation Using a Tethered ADCP. Journal of Atmospheric and Oceanic Technology, 31 (8). pp. 1826-1837. DOI: 10.1175/JTECH-D-13-00198.1

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Abstract

The structure function method for estimating the dissipation rate of turbulent kinetic energy, previously validated for measurements from seabed fixed mounts, is applied to data from 1.2-MHz acoustic Doppler current profiler (ADCP) instruments operating in pulse�pulse coherent mode and mounted in midwater below a tethered buoy. Movements of the buoy introduce additional relative velocity components, but it is hypothesized that these flow components should not seriously interfere with the turbulence information because (i) horizontal or vertical translation induces the same flow component in all cells of an ADCP beam and (ii) any rotation of the instrument about its center induces flow components that are normal to the beam direction, and thus neither affect the structure function. This hypothesis is tested by comparing a series of dissipation measurements from a moored ADCP with those from a free-falling Vertical Microstructure Profiler (VMP) shear probe deployed from a nearby research vessel. The results indicate generally good conformity in both mean and variability over almost two decades of dissipation rates. The noise level of the structure function estimates with the pulse�pulse coherent ADCP is close to that of the VMP at ~3 � 10�10 W kg�1. This approach offers the prospect of long time series measurements of dissipation rate from moorings, albeit with restricted vertical range of a few meters.

Item Type: Article
Subjects: Research Publications
Departments: College of Natural Sciences > School of Ocean Sciences
Date Deposited: 09 Dec 2014 16:27
Last Modified: 23 Sep 2015 02:59
ISSN: 0739-0572
URI: http://e.bangor.ac.uk/id/eprint/201
Identification Number: DOI: 10.1175/JTECH-D-13-00198.1
Publisher: American Meteorological Society
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