Ambient noise and surface wave dissipation in the ocean
Felizardo, Francis C.
MetadataShow full item record
There is a growing consensus that the sound generated by breaking waves is responsible for much of the ambient noise level in the ocean. While numerous field measurements have shown a strong correlation between the ambient noise spectrum level (N) in the range 100Hz to 25kHz and wind speed in the ocean, very little has been done to establish a comparable correlation between the ambient noise spectrum level and surface wave field parameters. The difficulty in establishing this relationship is remarkable given that the frequency and intensity of wave breaking are dependent on the characteristics of the wave field. In Fall 1991, an experiment was conducted from the research platform Flip 130 kilometers off the coast of Oregon, where the ambient noise between 2.5 and 25 kHz, the wind speed, and the sea surface elevation using wire wave gauges were measured. The correlation between N and the root mean square wave amplitude a was found to be poor but could be improved if the swell was filtered out from the wave elevation time series. The influence of swell on the value of a was disproportionate to the level of ambient noise since its characteristics were not directly due to the local wind-wave conditions. Observations of the dependence of the high frequency wind waves and the directional wave spectrum under turning winds suggested that the high frequency wave components responded more quickly to changes in the wind speed and wind direction than the energy-containing frequencies. The ambient noise level also correlated well with the root mean square wave slopes. This is consistent with previous laboratory measurements which showed that the steepness of a packet of waves correlates with the strength of wave breaking and with characteristics of breaking waves such as loss of momentum flux, dissipation, initial volume of air entrained, mixing, and sound generation. Comparisons of surface wave dissipation estimates using field measurements and models developed by Phillips (1985) and Hasselmann (1974) show that although the two models have very different forms, they give values that are comparable in magnitude. The relationship between the ambient noise level and log of dissipation give correlation coefficients (0.93-0.95) that are comparable to those between ambient noise and wind speed. The mean square acoustic pressure was shown to vary with the dissipation, with p2 ∝ D0.6-0.8. The results suggest that measurements of ambient sound may prove to be useful in inferring surface wave dissipation.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1993
Showing items related by title, author, creator and subject.
Understanding the ocean carbon and sulfur cycles in the context of a variable ocean : a study of anthropogenic carbon storage and dimethylsulfide production in the Atlantic Ocean Levine, Naomi M. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2010-02)Anthropogenic activity is rapidly changing the global climate through the emission of carbon dioxide. Ocean carbon and sulfur cycles have the potential to impact global climate directly and through feedback loops. Numerical ...
Silverthorne, Katherine E. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2010-06)Observational and modeling techniques are employed to investigate the thermal and inertial upper ocean response to wind and buoyancy forcing in the North Atlantic Ocean. First, the seasonal kinetic energy variability of ...
Advanced geophysical studies of accretion of oceanic lithosphere in Mid-Ocean Ridges characterized by contrasting tectono-magmatic settings Xu, Min (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2012-02)The structure of the oceanic lithosphere results from magmatic and extensional processes taking place at mid-ocean ridges (MORs). The temporal and spatial scales of the variability of these two processes control the ...