Michael A.H. Hedlin

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Studies in Atmospheric Acoustics at UCSD

• Michael A.H. Hedlin
• Laboratory for Atmospheric Acoustics
• Scripps Institution of Oceanography
• University of California, San Diego

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Overview of presentation

• Sources
• Clear-air turbulence
• Solid Earth/Atmosphere interaction
• Large-scale storms
• Bolides
• Atmosphere structure
• Use an encoded acoustic signal?
• Sensor technology
• OFIS
• Sensor grids

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Morning Glory

• Long, narrow, white
• Travel at 40-60 km/hr
• 150 -300 m above Earths surface
• Common in the Gulf of Carpenteria
• Seen elsewhere - e.g. Sable Island, Canada
• Seen in spring near dawn
• Formed by a solitary wave in lower
• atmosphere
• Thought to occur in the presence of a
• temperature inversion -gt a wave guide
• Perhaps due to collision of opposing ocean
• breeze fronts or during thunderstorm activity
• If they occur in a dry area (e.g. over land),
• generally there is no visible cloud

Leading edge
Trailing edge
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NOAA satellite image
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Study of the Solid Earth/ Atmosphere Interaction
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Solid Earth/Atmosphere Interaction
Modified from Calais and Minster, 1995
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Ionospheric perturbations

• Due to
• Coupling between gravity waves and ionosphere
• Caused by (partial list)
• Mining blasts
• Large earthquakes
• Rocket launches
• Can be investigated using dual-frequency GPS
• Radio frequencies broadcast at 1.58 GHz and 1.23
  GHz are dispersively delayed by interaction with
  electrons in ionosphere
• Delay proportional to electron content along
  line-of-sight between receiver and satellite
• Give us measure of ionospheric electron density

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From Calais, Minster, Hofton and Hedlin, 1998
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SCIGN
Continuously recording Operated by SCEC with
NASA/JPL, USGS, UCSD Funded by WM Keck
foundation, NSF, USGS, NASA
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From Calais et al, 2003
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Study of Storms

• Using the soon to-be-built IMS infrasound station
  in Cape Verde
• Can we use sound waves to learn about the
  embryonic stage of hurricanes?

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North Atlantic Hurricanes, 1931-1980
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IMS Infrasound Network
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Bolides

• Can we pin down the power law using larger
  bolides?
• Small numerous but not readily recorded
• Largest can be studied using ground- or
  space-based observing systems.
• Do the large bolides hold the key to the
  distribution of the largest and smallest
  earth-crossing asteroids?

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The structure of the atmosphere

• Possible to characterize atmosphere using an
  ATOC-style encoded acoustic signal?
• Any advantage over simple explosions?
• Might improve SNR from peak-power limited sources
  such as loudspeakers

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Sensor technology
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Daniels Filter
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OFIS
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Sensor grid
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L2As Portable Instrumentation
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L2As Portable Instrumentation

• IMS stations not necessarily tuned for natural
  events
• Have portable instrumentation we can use to
  supplement existing facilities if necessary
• Can be used to instrument new locations

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HPWRENHigh Performance Wireless Research and
Education Network
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HPWren
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