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Sound Waves from the Northern Lights

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. Can magnetic waves in the aurorae transform into sound waves?. How are aurorae created?

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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. Can magnetic waves in the aurorae transform into sound waves? • How are aurorae created? • Sound waves from the aurorae • Wave transformation in the Sun’s atmosphere • Wave transformation in Earth’s atmosphere

  3. How are aurorae created?

  4. The aurora is created by a chain of events, beginning with energy from the sun. Chain of Events Image courtesy of Tom Michalikhttp://faculty.rmwc.edu/tmichalik/solarwind.htm

  5. The Magnetosphere Image courtesy of Minnesota Technologhttp://technolog.it.umn.edu/technolog/novdec97/cover.htm

  6. The Ring Current 2.5 to 7 RE Image: M of E: Ring Current, 2005

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

  8. South-North Magnetic Orientation of CME

  9. North-South Magnetic Orientation of CME

  10. Magnetic Reconnection on Dayside of Earth

  11. Magnetic Field Lines are Drawn Back to Magnetotail

  12. Magnetotail is Compressed

  13. Magnetic Reconnection in Magnetotail

  14. Substorm Current Wedge & Field-aligned Currents Ring current

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

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

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

  18. Nearly Mirror Images Aurora Borealis Aurora Australis Images courtesy of NOAAhttp://sec.noaa.gov/pmap/

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

  20. 6 minutes • Sound would take at least 6 minutes to travel from the aurora to the ground • No recordings of audible aurorae

  21. Explanations of Audible Sounds • Psychological • Freezing Breath • “Brush discharge”

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

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

  24. Sound Waves on the Sun Created by Convection

  25. Sound Waves Propagate through Sun’s Atmosphere Sun

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

  27. 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

  28. My Question Can magnetic waves in the aurorae transform into sound waves?

  29. Magnetic Waves Earth

  30. Transform into Sound Waves Earth

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

  32. Plasma is like… β = 1 is important

  33. Resonance • All material has a frequency that it vibrates at • Matching the frequency allows the material to absorb energy • Singing wine glass

  34. Resonance in the Ionosphere When β = 1, • Energy from magnetic waves can be absorbed by the atmosphere

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

  36. Mechanism for Transformation y (B0, k) y (B0) 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

  37. 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

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

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

  40. 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

  41. Thanks to: • Dr. E.J. Zita for her guidance, input and helpful discussions • Paul Lessard for helpful discussions

  42. 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

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

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