A solar flare is a sudden, explosive release of energy on the Sun. The largest solar flares can reach temperatures exceeding 20 million degrees and can release energies exceeding that of a million hydrogen bombs; enough energy to power the United States for 100,000 years.
The solar flare process is not fully understood, but involves the release of vast energy stored in the magnetic fields threading the solar corona above active regions and sunspots.
The Yohkoh movie segments below show a few of the many solar flares observed during the Yohkoh mission. Although flares share many characteristics, notice how different each flare appears. The differences stem both from the shape of the magnetic field for each flare and the different viewing angle from the Earth.
The white box on each of the images shows the location of the flare on the Sun. Click on the image to see a movie of the flare. The colors on the images below and in the movies are reversed so that faint features can be seen.
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This flare was compact but very intense. Most flares occur in the "solar atmosphere" above the visible surface of the Sun and have little impact on the visible surface. However, some particularly intense flares, known as "white light flares", are seen on the visible surface. The 1991 November 15 flare was such an event. In the movie, the upper panel shows the flare in X-rays and the lower panel shows the flare in white light. If you look closely you can see the flare in the lower panel, indicating that this was a very energetic white light flare. |
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This flare occurred on the limb of the sun allowing us to see it as a side view. The loop-shaped structure of the flare results from the magnetic field in which the flare occurs. In the movie the upper panel shows the the SXT white light data and the lower panel shows the X-ray data. The flare is not seen in the white light data in this case. |
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The 1992 July 11 was a fairly typical small flare. It had a simple one-loop geometry. In the movie the upper panel shows the SXT white light data and the lower panel shows the X-ray data. The flare is not seen in the white light data in this case. |
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This example shows a ``large-scale eruptive event''. An enormous volume of
the solar atmosphere took part in this dramatic eruption; a region of the Sun
spanning 150 degrees of longitude and 40 degrees of latitude was heated to
temperatures in excess of 2-3 million degrees Celsius in a little over 17
hours. The subsequent disruption of the solar atmosphere resulted in a cloud
of solar material weighing 1 billion tons moving towards the Earth at a speed
of over
1 million miles per hour. Indeed, this event, first observed at the Sun on
14 April 1994, resulted in a strong geomagnetic storm at the Earth some 68
hours later. At present, there is a heated debate between solar physicists about whether these ``large-scale eruptive events'' can be truly classified as solar flares or not. Despite the obvious differences in spatial scale, events like that of April 14 1994 exhibit many similarities to the more compact flares highlighted on this page. The typical energies involved in these events are comparable to those in flares, the dynamical development is similar and the eruption in both cases is accompanied by a re-organization of the magnetic field in the solar corona. |
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In this complex event, you can see material ejected from the flare. The two panels show the flare in X-rays through two different X-ray filters on the SXT instrument. |
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The movie shows a small flare, that nonetheless resulted in the restructuring and expansion of the X-ray loops seen in the Sun's corona. There are a couple of gaps in the movie when Yohkoh's view of the Sun was blocked by the Earth. The single frame in the movie shows the X-rays observed by Yohkoh. |
[ GIF Movie | Java Script Movie | MPEG Movie ]