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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
The Swedish Infrasound Network
The Lidstrom-microphone
The Lidstrom-microphone: the frequency
              response
Wind noise reduction: wind barriers
     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)
Infrasonic chirps
Time scale and dilation no.
Infrasonic chirps
Possible association with sprites
Cross-wind propagation
Case study on May 13, 2003: Jamton
Case study on May 13, 2003: Lycksele
Positions of events (x)
   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.
Satellite image May 13, 2003 0914UT
  Occurrence of chirps 1994-2004

Station     Number of observed chirps
Kiruna      None
Jamton      114
Lycksele    5
Uppsala     2
Azimuth distribution of chirps observed
              in Jamton
Temporal distribution of chirps during
             1994-2004
Solar activity (sunspot numbers)
           1994-2004
Infrasonic signatures from thunderstorms
Thunderstorm cells on July 8, 2005 at
             1424UT
High resolution analysis: angle-of-arrival
           and trace velocity
Geometry of the signal from a cloud-to-
          cloud discharge
High resolution analysis of a lightning
         signature: azimuth
High resolution analysis of a lightning
       signature: trace velocity
Wavelet spectrum of the signature
High resolution analysis of a lightning
 signature: trace velocity vs azimuth
 Trace velocity and the temperature

Elevation:
         E=cos-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
Thermistor masts
Temperature layers
Temperature waves
Temperature bursts
Horizontal extent: 75m
      separation
Dynamical properties
Dynamical properties
   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/abstract
  s/256abs.php
An unidentified ”sawtooth” signature
  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
An unidentified ”sawtooth” signature
                Conclusion
• An efficient tool to monitor processes
  resulting in a pressure transient/transients

				
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posted:5/14/2011
language:English
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