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Sound Waves from the Northern Lights. Jada Maxwell. Photo courtesy of Bjorn Jorgensen, 18 January 2005, near Tromsø, Norway http://www.spaceweather.com/aurora/images2005/17jan05/Jorgensen1.jpg. Coronal Mass Ejection (CME).

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Sound waves from the northern lights l.jpg
Sound Waves from the Northern Lights

Jada Maxwell

Photo courtesy of Bjorn Jorgensen, 18 January 2005, near Tromsø, Norway

http://www.spaceweather.com/aurora/images2005/17jan05/Jorgensen1.jpg


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Coronal Mass Ejection (CME)

Illustration by Steele Hill, courtesy of NASAhttp://sohowww.nascom.nasa.gov/localinfo/steele.html


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Particles Spiral Down Field Lines

Image: Fundamentals of Physics, 2005


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Particles Spiral Down Field Lines

Particles 2

  • Collide with atomic and molecular oxygen and nitrogen

  • Emit energy as light


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This Creates the Aurorae

  • Northern Lights = Aurora Borealis

  • Southern Lights = Aurora Australis

Image courtesy of Shawn Malonehttp://www.lakesuperiorphoto.com


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Can we hear the aurorae?

  • Anecdotal evidence of auroral sounds

  • hissing, popping, crackling, swooshing

  • corresponds with motions of light


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6 minutes

  • Sound would take at least 6 minutes to travel from the aurora to the ground

  • No recordings of audible aurorae


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Evidence of Infrasoundfrom Aurorae

  • Humans can hear between 20 and 20,000 Hertz (Hz)

  • Infrasound is below 20 Hz

  • Currently being investigated






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Types of Magnetic Waves

  • Alfvén waves (s-mode)

  • Magnetosonic waves (p-mode)

S-mode image courtesy of Georgia State Universityhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/tralon.html

BBC animations




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Beta is a Clue

Gas Pressure

Beta = β =

Magnetic Field Pressure


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Plasma is like…

β = 1 is important


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Mechanism for Transformation

y (B0, k)

y (B0)

x (v1, B1)

x (v1, B1, k)

z (E1)

z (E1)

Alfvén waves

Magnetosonic waves


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Mechanism for Transformation

y (B0, k)

y (B0)

v1 p

v1 p

x (v1, B1)

x (v1, B1, k)

E1 p

E1 p

z (E1)

z (E1)

Alfvén waves to

Acoustic waves

Magnetosonic waves to

Acoustic waves


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β= 1 in Earth’s atmosphere?

When Beta = 1


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What have we learned?

MHD Waves

?

observed

CMEs

Infrasound

observed

observed

Aurorae


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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


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Image Sources:

  • NASAhttp://sohowww.nascom.nasa.gov/localinfo/steele.html

  • Shawn Malonehttp://www.lakesuperiorphoto.com

  • Halliday/Resnick/Walker. Fundamentals of Physics, John Wiley & Sons, 2005, p 746

Website:

http://academic.evergreen.edu/m/maxjad02


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