|Tracing Acoustic-Gravity Waves from the Ocean into the Ionosphere: ONR BRC Project|
|2013 - 2016|
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Terence W. Bullett
Theory predicts strong coupling between waves in the atmosphere and the ocean at low frequencies where mechanical waves in both fluids should be treated as acoustic gravity waves (AGWs). It has been shown recently that for an underwater source, the power transmitted into the atmosphere through air-water interface can exceed the total power emitted by the same source in unbounded water by an order of magnitude or more, depending on wave frequency. Under somewhat idealized conditions, particularly strong transmission of AGWs from a compact underwater source into atmosphere has been predicted to occur in two narrow frequency bands with central frequencies of several mHz. Exact values of the central frequencies depend on the ocean depth and atmospheric conditions. These frequency bands can be called Transparency Windows. At a similar frequency, a transition in behavior of oceanic infragravity waves occurs; at higher frequencies the infragravity waves penetrate into the atmosphere only up to heights of the order of their wavelength, but below the transition frequency, the energy and momentum of infragravity waves are radiated into the atmosphere and are expected to reach the upper atmosphere, including thermosphere and ionosphere. This second effect may be called Wideband Transparency of the air-sea interface.
The project aims to confirm the two effects of transparency and will investigate their global consequences with theoretical and experimental means. Innovative passive techniques of noise interferometry will be applied to an unprecedented combination of ocean and ionosphere sensors. Data obtained with Deep-ocean Assessment and Reporting of Tsunami probes and with the Comprehensive Nuclear-Test-Ban Treaty Organization’s International Monitoring System’s hydroacoustic probes will be analyzed together with the data of precision ionospheric radio sounding performed with Dynasonde systems. Spectra of infragravity wave motions in the ocean will be compared with the spectra of AGWs measured over coastal regions at ionospheric altitudes to reveal peculiarities caused by the two effects of transparency mentioned above. Correlation and coherence calculations will be performed with the data of marine-based instruments and nearby Dynasondes. This will allow one to trace waves of oceanic origin and to quantify related transport of energy and momentum to thermospheric altitudes.
Web site of the program.
Godin O. A. Sound transmission through water-air interfaces: New insights into an old problem, Contemporary Physics, 49, p. 105–123 (2008). DOI: 10.1080/00107510802090415.
This link leads to a web interface to data storage and data analysis tools for Dynasondes participating in the project.
Oleg A. Godin, Nonlinear progressive acoustic-gravity waves: Exact solutions, Geophysical Research Abstracts, Vol. 15, EGU2013-1820, 2013, (EGU General Assembly, Vienna, Austria, 8-12 April 2013).