Refraction of the cyclonic microbarom signal by the cyclonic winds
Non-linear interaction of the ocean surface and atmosphere is known to produce narrow-band, low frequency, continuous acoustic and seismic radiation termed microbaroms and microseisms, respectively. The microbarom signal typically has an amplitude of a few microbars and a peak at 0.2 Hz. The microbaroms are generated by counter-propagating surface waves of equal period. The microbarom source location associated with a hurricane is believed to be due to the interaction of the waves produced by the cyclonic winds with the background ocean wave field and is generally located many kilometers from the eye of the storm, along a perpendicular to the direction of the ambient winds. Following up on a suggestion of Bedard and coworkers, propagation of the microbarom signal through the storm wind structure has been investigated using geometric acoustics in an inhomogeneous moving medium. Strong refraction of the signal is predicted. To observe this refraction we have deployed infrasound arrays along the US eastern seaboard. Predicted and measured back azimuths for propagation through the wind structure have been compared to the data recorded during the 2010 and 2011 Atlantic hurricane seasons.