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Sound Waves from the Northern Lights

Sound Waves from the Northern Lights

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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