Moreton waves

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/second, in conjunction with a big coronal mass ejection in February 2009.[6][7]

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/second 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

  • 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.
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