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 = 20.75T

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/abstracts/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