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Sound Waves from the Northern
Lights
Photo courtesy of Bjorn Jorgensen, 18 January 2005, near Tromsø, Norway
http://www.spaceweather.com/aurora/images2005/17jan05/Jorgensen1.jpg
Jada Maxwell
• How are aurorae created?
• Sound waves from the aurorae
• Wave transformation in the Sun’s atmosphere
• Wave transformation in Earth’s atmosphere
Can magnetic waves in the aurorae transform into sound
waves?
Chain of EventsThe aurora is created by a chain of
events, beginning with energy from the sun.
Image courtesy of Tom Michalikhttp://faculty.rmwc.edu/tmichalik/solarwind.htm
The Magnetosphere
Image courtesy of Minnesota Technologhttp://technolog.it.umn.edu/technolog/novdec97/cover.htm
Coronal Mass Ejection (CME)
Illustration by Steele Hill, courtesy of NASAhttp://sohowww.nascom.nasa.gov/localinfo/steele.html
Particles 2
• Collide with atomic and molecular oxygen and nitrogen
• Emit energy as light
Particles Spiral Down Field Lines
This Creates the
Aurorae
Image courtesy of Shawn Malonehttp://www.lakesuperiorphoto.com
• Northern Lights = Aurora Borealis
• Southern Lights = Aurora Australis
Nearly Mirror Images
Aurora Borealis
Aurora Australis
Images courtesy of NOAAhttp://sec.noaa.gov/pmap/
Can we hear the aurorae?
Anecdotal evidence of auroral sounds
• hissing, popping, crackling, swooshing
• corresponds with motions of light
6 minutes• Sound would take at least 6 minutes to travel from the aurora to the ground
• No recordings of audible aurorae
• Humans can hear between 20 and 20,000 Hertz (Hz)
• Infrasound is below 20 Hz
• Currently being investigated
• Gas expansion
Evidence of Infrasound from Aurorae
• Alfvén waves (s-mode)
• Magnetosonic waves (p-mode)
Types of Magnetic Waves
S-mode image courtesy of Georgia State Universityhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/tralon.html
BBC animations
Resonance
• All material has a frequency that it vibrates at
• Matching the frequency allows the material to absorb energy
• Singing wine glass
Resonance in the Ionosphere
When β = 1,
• Energy from magnetic waves can be absorbed by the atmosphere
Mechanism for Transformation
y (B0, k)
z (E1)
x (v1, B1)
y (B0)
x (v1, B1, k)
z (E1)
Alfvén waves Magnetosonic waves
Mechanism for Transformation
y (B0, k)
z (E1)
x (v1, B1)
y (B0)
x (v1, B1, k)
z (E1)
Alfvén waves toAcoustic waves
Magnetosonic waves to Acoustic waves
E1 p E1 p
Mechanism for Transformation
y (B0, k)
z (E1)
x (v1, B1)
y (B0)
x (v1, B1, k)
z (E1)
Alfvén waves toAcoustic waves
Magnetosonic waves to Acoustic waves
v1 p v1 p
E1 p E1 p
Future Plans
• Gather data from satellite observations of resonant acoustic and Alfvén waves in a single CME induced geomagnetic event
• Evaluate how wave velocities, frequencies and wavelengths change as altitude and β changes
• Use data of auroral infrasound observed at Earth’s surface to extrapolate speeds in the ionosphere and compare to magnetic wave speeds
Thanks to:
• Dr. E.J. Zita for her guidance, input and helpful discussions
• Paul Lessard for helpful discussions
Image Sources:▪ NOAA (National Oceanic & Atmospheric Administration)http://sec.noaa.gov/pmap/
▪ NASAhttp://sohowww.nascom.nasa.gov/localinfo/steele.html
▪ SpaceWeather.com http://www.spaceweather.com/aurora/images2005.htm
▪ Shawn Malonehttp://www.lakesuperiorphoto.com
▪ Tom Michalikhttp://faculty.rmwc.edu/tmichalik/solarwind.htm
▪ Minnesota Technologhttp://technolog.it.umn.edu/technolog/novdec97/cover.htm
▪ Halliday/Resnick/Walker. Fundamentals of Physics, John Wiley & Sons, 2005, p 746
▪ Freedman, R.A. and W.J. Kaufman. Universe, 6th ed. W.H. Freeman & Co., 2002, p 404
▪ Wolf, R. Magnetosphere of Earth: Ring Current. Encyclopedia of Aston. & Astrophys. 2005