National Center for Physical Acoustics 1986 The University of Mississippi Hurricane Studies Using Infrasound Claus Hetzer 1, Roger Waxler 1, Carrick Talmadge 1, Milton Garces 2, Ken Gilbert 1, Henry Bass 1 1 National Center for Physical Acoustics The University of Mississippi 2 Infrasound Laboratory The University of Hawaii, Manoa Distribution A – Approved for public release; distribution unlimited.

National Center for Physical Acoustics 1986 The University of Mississippi Hurricane Readiness Hurricanes pose great danger to coastal communities Hurricane warnings often are not trusted and thus ignored Forecast of storm intensity at landfall particularly difficult Great interest in accurate remote sensing of hurricanes to improve short-term forecasting

National Center for Physical Acoustics 1986 The University of Mississippi Hurricane Infrasound: Microbaroms Hurricanes known to produce infrasound in microbarom band Microbaroms generated by nonlinear interaction of oppositely-directed ocean surface waves Infrasonic observations include Kirogi, Carlotta (2000), Daniel (2001), Adeline-Juliet, Katrina, Ophelia (2005), Usagi (2007) On gross scale, signal azimuths point at storm

National Center for Physical Acoustics 1986 The University of Mississippi Typhoon Usagi (2007) Palau: Lat 7.5N

National Center for Physical Acoustics 1986 The University of Mississippi Typhoon Usagi (2007) Detections consistently behind storm Atmospheric modeling predicts < 5° deviation

National Center for Physical Acoustics 1986 The University of Mississippi Cyclone Adeline-Juliet (2005)

National Center for Physical Acoustics 1986 The University of Mississippi Cyclone Adeline-Juliet (2005) Detections track storm roughly, but rarely point at eye

National Center for Physical Acoustics 1986 The University of Mississippi Hurricane Fabian (2003) Highest-intensity microseisms happen after storm passes the station!

National Center for Physical Acoustics 1986 The University of Mississippi Microbarom Source Region Some questions exist regarding the location of the infrasound source region All models require a mechanism for producing opposing wavetrains Proposed models generally take into account only waves generated by storm winds, i.e. Tabulevich (right)

National Center for Physical Acoustics 1986 The University of Mississippi More Inclusive Model Microbaroms may be generated by the interaction between storm waves and the ambient wave field This interaction can produce opposing swells hundreds of kilometers from the storm eye In agreement with previous and current work (Garces, Willis, Chevrot)

National Center for Physical Acoustics 1986 The University of Mississippi More Inclusive Model Fine detail from wave models may not be reliable, but general trends of opposition are evident Implication: acoustic modeling/monitoring of hurricanes requires knowledge of ambient wave field This may be nontrivial in near-landfall situations

National Center for Physical Acoustics 1986 The University of Mississippi Usagi: Pristine Case

National Center for Physical Acoustics 1986 The University of Mississippi Adeline-Juliet: More Complicated

National Center for Physical Acoustics 1986 The University of Mississippi Conclusions Microbarom bearing data for two observed hurricanes is seen to deviate from point of highest winds This appears to be a result of interactions with the ambient surface wave field, in agreement with microbarom theory and previous/current work Acoustic studies and models of hurricanes must take the ambient wave field into account This analysis should be expanded to as many known infrasound recordings of hurricanes as possible, particular from island stations

National Center for Physical Acoustics 1986 The University of Mississippi Next Steps More storms, more stations! Start running WaveWatch III model – higher resolution? Separate out source, propagation, array components of azimuth scatter Relationship: Δ az (W storm,W ambient )