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S.F. Martin (Helio Research)
In their most stable state, prominences are characterized by continuous mass flows at speeds of 5-20 km/sec along every part of their structure. In images having high spatial resolution, prominences always consist of very fine threads. Recent H\alpha Doppler observations show finely interleaved motions in opposite directions and over long distances along these threads, a phenomenon known as counterstreaming. This fine-scale bi-directional streaming is evidence that the local magnetic field within prominences is everywhere parallel with the prominence threads. At the sides of intermediate and quiescent prominences, are groups of threads along which mass flows to and from the chromosphere. These are known as barbs; prominence threads and barbs reveal whether a prominence is right-handed (dextral) or left-handed (sinistral). Counterstreaming along the barbs leads to the conclusion that the mass of prominence is continuously supplied from the low chromosphere or at the temperature minimum very near the photosphere. To understand the dynamics of these continuous mass flows, we must look to the sea of continuously interacting, small-scale bipolar magnetic fields beneath prominences.
In He II 304A images from the EIT experiment on the SOHO satellite, the speeds along the high axis of prominences are reported to be faster than in H\alpha with common speeds in the range of 10-30 km/sec. Prominences are also a few thousand kilometers taller and often tens of thousands of kilometers longer in He II 304A.
Prominences seen against the solar disk are often called filaments. Many filaments exhibit activated intervals when their flows are accelerated; at these times, they reveal additional varieties of motion. Activations can be caused by small flares near one end of a filament, by impact from flare waves, or by emerging magnetic regions near the filament but they also occur for no obvious reason. Only some activated intervals lead to eruption. NASA grants NAG5-9517 and NAG5-10852 are gratefully acknowledged.
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.