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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


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    1. 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

    2. Coronal Mass Ejection (CME) Illustration by Steele Hill, courtesy of NASAhttp://sohowww.nascom.nasa.gov/localinfo/steele.html

    3. Particles Spiral Down Field Lines Image: Fundamentals of Physics, 2005

    4. Particles Spiral Down Field Lines Particles 2 • Collide with atomic and molecular oxygen and nitrogen • Emit energy as light

    5. This Creates the Aurorae • Northern Lights = Aurora Borealis • Southern Lights = Aurora Australis Image courtesy of Shawn Malonehttp://www.lakesuperiorphoto.com

    6. Can we hear the aurorae? • Anecdotal evidence of auroral sounds • hissing, popping, crackling, swooshing • corresponds with motions of light

    7. 6 minutes • Sound would take at least 6 minutes to travel from the aurora to the ground • No recordings of audible aurorae

    8. Evidence of Infrasoundfrom Aurorae • Humans can hear between 20 and 20,000 Hertz (Hz) • Infrasound is below 20 Hz • Currently being investigated

    9. The corona of the Sun is hotter than the surface! Image: Universe, 6th ed., 2002

    10. Sound Waves on the Sun Created by Convection

    11. Sound Waves Propagate through Sun’s Atmosphere Sun

    12. Energy of Sound Waves is Transformed into Magnetic Waves Sun

    13. 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

    14. Magnetic Waves Earth

    15. Transform into Sound Waves Earth

    16. Beta is a Clue Gas Pressure Beta = β = Magnetic Field Pressure

    17. Plasma is like… β = 1 is important

    18. Mechanism for Transformation y (B0, k) y (B0) x (v1, B1) x (v1, B1, k) z (E1) z (E1) Alfvén waves Magnetosonic waves

    19. 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

    20. β= 1 in Earth’s atmosphere? When Beta = 1

    21. What have we learned? MHD Waves ? observed CMEs Infrasound observed observed Aurorae

    22. 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

    23. 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