Solar flares

spaceweb@oulu.fi - last update: 20 November 1998, 1600 UT (RR)

Solar flares are huge explosions on the surface of the Sun. They were first observed by Carrington (1860) and Hodgson (1860) in connection with the great aurora of 1859. Flares are very fast processes, with time scales of only a few minutes, and they are thought to be formed as the sunspot related magnetic field structures get twisted and sheared and release energy via magnetic reconnection. That they usually occur along the dividing or neutral line between oppositely directed magnetic fields supports this theory.

Flares are characterized and monitored by their brightness in X-rays, but they radiate energy from radio frequencies up to Gamma-rays. Also energetic particles are released: the solar energetic particles (SEP) form a subset of cosmic rays. As a consequence, phenomena like

Sudden ionospheric disturbances (SID; due to X-rays)
Polar cap absorption events (PCA)

occur in the Earth's ionosphere. For more information, see space weather.

References

Carrington, R. C., Description of a singular appearance seen on the Sun on September 1, 1859, Mon. Not. R. Astron. Soc., 20, 13, 1860.
Hodgson, R., On a curious appearance seen in the Sun, Mon. Not. R. Astron. Soc., 20, 16, 1860.