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Wind Sea behind a Cold Front and Deep Ocean Acoustics

Wind Sea behind a Cold Front and Deep Ocean Acoustics A rapid and broadband (1 h, 1 < f < 400 Hz) increase in pressure and vertical velocity on the deep ocean floor was observed on seven instruments comprising a 20-km array in the northeastern subtropical Pacific. The authors associate the jump with the passage of a cold front and focus on the 4- and 400-Hz spectra. At every station, the time of the jump is consistent with the front coming from the northwest. The apparent rate of progress, 10–20 km h −1 (2.8–5.6 m s −1 ), agrees with meteorological observations. The acoustic radiation below the front is modeled as arising from a moving half-plane of uncorrelated acoustic dipoles. The half-plane is preceded by a 10-km transition zone, over which the radiator strength increases linearly from zero. With this model, the time derivative of the jump at a station yields a second and independent estimate of the front’s speed, 8.5 km h −1 (2.4 m s −1 ). For the 4-Hz spectra, the source physics is taken to be Longuet-Higgins radiation. Its strength depends on the quantity , where F ζ is the wave amplitude power spectrum and I the overlap integral. Thus, the 1-h time constant observed in the bottom data implies a similar time constant for the growth of the wave field quantity behind the front. The spectra at 400 Hz have a similar time constant, but the jump occurs 25 min later. The implications of this difference for the source physics are uncertain. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Physical Oceanography American Meteorological Society

Wind Sea behind a Cold Front and Deep Ocean Acoustics


AMERICAN METEOROLOGICAL SOCIETY Journal of Physical Oceanography EARLY ONLINE RELEASE This is a preliminary PDF of the author-produced manuscript that has been peer-reviewed and accepted for publication. Since it is being posted so soon after acceptance, it has not yet been copyedited, formatted, or processed by AMS Publications. This preliminary version of the manuscript may be downloaded, distributed, and cited, but please be aware that there will be visual differences and possibly some content differences between this version and the final published version. The DOI for this manuscript is doi: 10.1175/JPO-D-15-0221.1 The final published version of this manuscript will replace the preliminary version at the above DOI once it is available. If you would like to cite this EOR in a separate work, please use the following full citation: Farrell, W., J. Berger, J. Bidlot, M. Dzieciuch, W. Munk, R. Stephen, and P. Worcester, 2016: Windsea behind a cold front and deep ocean acoustics. J. Phys. Oceanogr. doi:10.1175/JPO-D-15-0221.1, in press. © 2016 American Meteorological Society LaTeX File (.tex, .sty, .cls, .bst, .bib) Click here to download LaTeX File (.tex, .sty, .cls, .bst, .bib) Windsea.tex W. E. Farrell J. Berger Scripps Institution of Oceanography J-R. Bidlot European Center for Medium-Range Weather Forecasting M. Dzieciuch Scripps Institution of Oceanography W. Munk Scripps Institution of Oceanography R. A. Stephen Woods Hole Oceanographic Institution P. F. Worcester Scripps Institution of Oceanography Corresponding author address: Del Mar, CA E-mail: wef@farrell-family.org A Generated using v4.3.2 of the AMS L TEX template ABSTRACT A rapid and broad-band (1 hr, 1 < f < 400 Hz) increase in pressure and vertical velocity on the deep ocean floor was observed on seven instruments comprising a 20 km array in the Northeastern sub-tropical Pacific. We associate the jump with the passage of a cold front and focus on the 4 and 400 Hz spectra. At every...
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Publisher
American Meteorological Society
Copyright
Copyright © 2015 American Meteorological Society
ISSN
0022-3670
eISSN
1520-0485
DOI
10.1175/JPO-D-15-0221.1
Publisher site
See Article on Publisher Site

Abstract

A rapid and broadband (1 h, 1 < f < 400 Hz) increase in pressure and vertical velocity on the deep ocean floor was observed on seven instruments comprising a 20-km array in the northeastern subtropical Pacific. The authors associate the jump with the passage of a cold front and focus on the 4- and 400-Hz spectra. At every station, the time of the jump is consistent with the front coming from the northwest. The apparent rate of progress, 10–20 km h −1 (2.8–5.6 m s −1 ), agrees with meteorological observations. The acoustic radiation below the front is modeled as arising from a moving half-plane of uncorrelated acoustic dipoles. The half-plane is preceded by a 10-km transition zone, over which the radiator strength increases linearly from zero. With this model, the time derivative of the jump at a station yields a second and independent estimate of the front’s speed, 8.5 km h −1 (2.4 m s −1 ). For the 4-Hz spectra, the source physics is taken to be Longuet-Higgins radiation. Its strength depends on the quantity , where F ζ is the wave amplitude power spectrum and I the overlap integral. Thus, the 1-h time constant observed in the bottom data implies a similar time constant for the growth of the wave field quantity behind the front. The spectra at 400 Hz have a similar time constant, but the jump occurs 25 min later. The implications of this difference for the source physics are uncertain.

Journal

Journal of Physical OceanographyAmerican Meteorological Society

Published: Nov 16, 2015

References