Wind sea behind a cold front and deep ocean acoustics
Farrell, W. E.
Stephen, Ralph A.
Worcester, Peter F.
MetadataShow full item record
KeywordAtm/Ocean Structure/ Phenomena; Atmosphere-ocean interaction; Cold fronts; Marine boundary layer; Sea state
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 Fζ 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.
Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 1705-1716, doi:10.1175/JPO-D-15-0221.1.
Showing items related by title, author, creator and subject.
Stern, Melvin E.; Mellor, Florence K. (Woods Hole Oceanographic Institution, 1983-11)"Baroclinic instability as the largest scale of motion participating in the cross frontal oceanic transport process" was the theme of the 25th summer program at G.F.D. Killworth (Cambridge University) reviewed ...
Lin, Ying-Tsong; Lynch, James F. (Acoustical Society of America, 2011-12-13)The horizontal ducting of sound by an oceanic temperature front over a sloping bottom is studied with an idealized wedge model consisting of a lateral interface across the slope. The water outside the frontal interface has ...
Spall, Michael A. (American Meteorological Society, 2007-08-01)The influences of strong gradients in sea surface temperature on near-surface cross-front winds are explored in a series of idealized numerical modeling experiments. The atmospheric model is the Naval Research Laboratory ...