Moreton wave

Moreton wave

Animation of a Moreton wave which occurred on December 6, 2006

A Moreton wave is the chromospheric signature of a large-scale solar coronal shock wave. Described as a kind of solar "tsunami",[1] they are generated by solar flares. They are named for American astronomer Gail Moreton, an observer at the Lockheed Solar Observatory in Burbank who spotted them in 1959.[2][3][4] He discovered them in time-lapse photography of the chromosphere in the light of the Balmer alpha transition.

There were few follow-up studies for decades. Then the 1995 launch of the Solar and Heliospheric Observatory led to observation of coronal waves, which cause Moreton waves. Moreton waves were a research topic again. (SOHO's EIT instrument discovered another, different wave type called "EIT waves".) [5] The reality of Moreton waves (aka fast-mode MHD waves) has also been confirmed by the two STEREO spacecraft. They observed a 100,000-km-high wave of hot plasma and magnetism, moving at 250 km/s, in conjunction with a big coronal mass ejection in February 2009.[6][7]

Solar Tsunami

Moreton waves propagate at a speed of 500–1500 km/s (this range does not agree with the just-quoted STEREO observation of a 250 km/s speed). Yutaka Uchida interpreted Moreton waves as MHD fast mode shock waves propagating in the corona.[8] He links them to type II radio bursts, which are radio-wave discharges created when coronal mass ejections accelerate shocks.[9]

Moreton waves can be observed primarily in the band.[10]

See also

References

  1. ^ Phillips, Tony (November 24, 2009). "Monster Waves on the Sun are Real". NASA. Retrieved 16 July 2010. 
  2. ^ Moreton, G. E. (1960). "Hα Observations of Flare-Initiated Disturbances with Velocities ~1000 km/sec". Astronomical Journal 65: 494.  
  3. ^ Moreton, G. E. & Ramsey, H. E. (1960). "Recent Observations of Dynamical Phenomena Associated with Solar Flares". Publications of the Astronomical Society of the Pacific 72 (428): 357.  
  4. ^ Athay, R. Grant; Moreton, Gail E. (1961). "Impulsive Phenomena of the Solar Atmosphere. I. Some Optical Events Associated with Flares Showing Explosive Phase". Astrophysical Journal 133: 935.  
  5. ^ Thompson, B.; Plunkett, S. P.; Gurman, J. B.; Newmark, J.S.; St. Cyr, O.C.; Michels, D.J. (1998). "SOHO/EIT observations of an Earth-directed coronal mass ejection on May 12, 1997". Geophysical Research Letters 25: 2465–2468.  
  6. ^ Atkins, William (26 November 2009). "STEREO spacecraft finds gigantic tsunami on Sun". iTWire. Retrieved 16 July 2010. 
  7. ^ JPL/NASA (November 19, 2009). "Mystery of the Solar Tsunami -- Solved". PhysOrg.com. Retrieved 16 July 2010. 
  8. ^ Sakurai, Takashi (3 September 2002). "SolarNews Newsletter". Solar Physics Division, American Astronomical Society. Retrieved 15 June 2011. 
  9. ^ Layton, Laura (May 15, 2009). "STEREO Spies First Major Activity of Solar Cycle 24". NASA. Retrieved 15 June 2011. 
  10. ^ Narukage, N.; et al., Shigeru; Kadota, Miwako; Kitai, Reizaburo; Kurokawa, Hiroki; Shibata, Kazunari (2004). "Moreton waves observed at Hida Observatory" (PDF). Proceedings IAU Symposium 2004 (223): 367–370.  
  • More of Moreton's papers can be found here (SAO/NASA System).

External links

  • "Have you ever heard the Sun?" - many recordings (MP3 format) of solar radio emissions including a solar flare shockfront.