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An Electromagnetic Vorticity and Velocity Sensor for Observing Finescale Kinetic Fluctuations in the Ocean

An Electromagnetic Vorticity and Velocity Sensor for Observing Finescale Kinetic Fluctuations in... An instrument has been developed that measures finescale velocity and vorticity in seawater based on the principles of motional induction. This instrument, the electromagnetic vorticity meter (EMVM), measures components of the gradient and Laplacian of the electrostatic potential field induced by the motion of seawater through an applied magnetic field. The principal innovation described here is the development of a sensor for measuring small-scale vorticity. The sensor head consists of a strong NdFeB magnet, a five-electrode array, low-noise preamplifiers, and 20-Hz digitizers. The main electronics includes attitude sensors, batteries, a microprocessor, and a hard disk. The vorticity sensors are usually carried on a heavy towed vehicle capable of vertically profiling to 200 m and at tow speeds of several knots. The theoretical response functions of the EMVM are evaluated for velocity and vorticity. Extensive measurements were obtained in Pickering Passage, Washington, as the sensor vertically profiled in an unstratified tidal channel. During periods of strong flow, the vertical structure of all properties confirmed expectations for a fully developed turbulent bottom boundary layer. EMVM observations of velocity and vorticity are shown to be in agreement with the theoretical response function for isotropic turbulence. A principal result is that the vertical flux of spanwise vorticity (i.e., w ′′ ωω ′′ y ) is positive (i.e., flux is away from seabed) and vertically uniform. The vertical eddy diffusivity for vorticity is about 5 ×× 10 −−2 m 2 s −−1 , which is about the same value as for momentum. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Atmospheric and Oceanic Technology American Meteorological Society

An Electromagnetic Vorticity and Velocity Sensor for Observing Finescale Kinetic Fluctuations in the Ocean

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Publisher
American Meteorological Society
Copyright
Copyright © 1997 American Meteorological Society
ISSN
1520-0426
DOI
10.1175/1520-0426(1999)016<1647:AEVAVS>2.0.CO;2
Publisher site
See Article on Publisher Site

Abstract

An instrument has been developed that measures finescale velocity and vorticity in seawater based on the principles of motional induction. This instrument, the electromagnetic vorticity meter (EMVM), measures components of the gradient and Laplacian of the electrostatic potential field induced by the motion of seawater through an applied magnetic field. The principal innovation described here is the development of a sensor for measuring small-scale vorticity. The sensor head consists of a strong NdFeB magnet, a five-electrode array, low-noise preamplifiers, and 20-Hz digitizers. The main electronics includes attitude sensors, batteries, a microprocessor, and a hard disk. The vorticity sensors are usually carried on a heavy towed vehicle capable of vertically profiling to 200 m and at tow speeds of several knots. The theoretical response functions of the EMVM are evaluated for velocity and vorticity. Extensive measurements were obtained in Pickering Passage, Washington, as the sensor vertically profiled in an unstratified tidal channel. During periods of strong flow, the vertical structure of all properties confirmed expectations for a fully developed turbulent bottom boundary layer. EMVM observations of velocity and vorticity are shown to be in agreement with the theoretical response function for isotropic turbulence. A principal result is that the vertical flux of spanwise vorticity (i.e., w ′′ ωω ′′ y ) is positive (i.e., flux is away from seabed) and vertically uniform. The vertical eddy diffusivity for vorticity is about 5 ×× 10 −−2 m 2 s −−1 , which is about the same value as for momentum.

Journal

Journal of Atmospheric and Oceanic TechnologyAmerican Meteorological Society

Published: Aug 4, 1997

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