Infrasonic Observations of Some Atmospheric Phenomena

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Infrasonic Observations of Some Atmospheric
Phenomena

• Ludwik Liszka
• Swedish Institute of Space Physics, SE-901 87,
  Umeå, Sweden

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The Swedish Infrasound Network
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The Lidstrom-microphone
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The Lidstrom-microphone the frequency response
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Wind noise reduction wind barriers
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Selection of the frequency window

• The choice of frequency range for the network was
  based on the discovery of the optimum detection
  window around 2 Hz by Procunier Sharp (1970)

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Infrasonic chirps
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Time scale and dilation no.
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Infrasonic chirps
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Possible association with sprites
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Cross-wind propagation
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Case study on May 13, 2003 Jamton
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Case study on May 13, 2003 Lycksele
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Positions of events (x)
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Background noise during the events

• Lycksele shows on that particular date the lowest
  amplitude of the uncorrelated background of all
  SIN stations, only 0.014 Pa (peak value). At
  Jämtön the corresponding amplitude is 0.045 Pa.

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Satellite image May 13, 2003 0914UT
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Occurrence of chirps 1994-2004

• Station Number of observed chirps
• Kiruna None
• Jamton 114
• Lycksele 5
• Uppsala 2

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Azimuth distribution of chirps observed in Jamton
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Temporal distribution of chirps during 1994-2004
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Solar activity (sunspot numbers) 1994-2004
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Infrasonic signatures from thunderstorms
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Thunderstorm cells on July 8, 2005 at 1424UT
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High resolution analysis angle-of-arrival and
trace velocity
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Geometry of the signal from a cloud-to-cloud
discharge
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High resolution analysis of a lightning
signature azimuth
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High resolution analysis of a lightning
signature trace velocity
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Wavelet spectrum of the signature
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High resolution analysis of a lightning
signature trace velocity vs azimuth
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Trace velocity and the temperature

• Elevation
• Ecos-1(C/ Vp).
• where C is the speed of sound and Vp is the
  trace velocity.
• C 20.75?T
• where T is the temperature in degrees Kelvin

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Thermistor masts
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Temperature layers
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Temperature waves
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Temperature bursts
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Horizontal extent 75m separation
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Dynamical properties
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Dynamical properties
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Summer atmosphere thunderstorm related
temperature waves

• Thermistor Measurements of Temperature
  Oscillations During the Arctic Summer Potential
  Coupling Between Severe Convective Thunderstorms
  and the Surface Prandtl Layer
• A report by Ludwik Liszka and Douglas ReVelle at
• http//www.umea.irf.se/ume/publications/abstracts/
  256abs.php

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An unidentified sawtooth signature
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An unidentified sawtooth signature

• Characterized by very high trace velocities
• Most likely not connected with human activities
  (a natural phenomenon)
• Indications of correlation across considerable
  distances

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An unidentified sawtooth signature
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Conclusion

• An efficient tool to monitor processes resulting
  in a pressure transient/transients