Quiescent prominences I Prominence Feet


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SOLAR PROMINENCES

Of the many fascinating phenomena associated with the Sun, solar prominences surely rate amongst the most incredible and bewildering of the observed features there. Situated in the Sun's extremely hot and tenuous upper atmosphere, the solar corona, these structures are basically comprised of cool, dense plasma confined in the form of thin, vertical sheets. Typically they possess a temperature in the range of 5-10,000 K and a particle density of about 10^1^7m^-^3 these quantities being approximately 100 times cooler and more dense than the corresponding values in the surrounding environment.

Prominences may be broadly categorised into two classes: 'active' prominences and 'quiescent' prominences. The former class contains highly dynamic and eruptive events which last for only minutes or hours. These are generally associated with solar flares and are often fairly violent occurences. Sometimes they are observed as material that is rapidly ejected into the corona (surges) with velocities of several hundred kilometres per second. On other occasions they are seen as well organised loop-like structures. This occurs when they are trapped in closed magnetic loops and so the dense plasma is channelled along the magnetic field thus highlighting the loop. The plasma drains continuously down the legs of such loops towards the solar surface, the photosphere.


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AWH/JOC Sep 95