Ronan, R. | Engineering Papers

NASA NTRS1985

Spatial and temporal variations of solar coronal loops

Skylab EUV observations of an active region near the solar limb with both hot and cool loops present were analyzed. The observed intensity variations for hot loops were small, typically a few percent over a period of 30 min. The cool loops exhibited stronger variations, sometimes appearing and disappearing in 5 to 10 min. Most of the cool material observed in the loops appeared to be caused by the downward flow of coronal rain and by the upward ejection of chromospheric material in surges. The frequent EUV brightenings observed near the loop footpoints appear to have been produced by both in situ transient energy releases and the infall/impact of coronal rain. The mean energy input required to balance the radiative and conductive cooling of the hot loops is approximately 0.003 erg/cu cm/s.

Habbal, S. R.↗

NASA NTRS1985

Impulsive phenomena in a small active region

The temporal and spatial variations of EUV emission from a small growing active region were investigated. Frequent localized short-term (about a few minutes) fluctuations in EUV emission were observed throughout the 7.2 hr interval when the most continuous observations were acquired. Approximately 20 percent of the 5-arcsec x 5-arcsec pixels had intensity variations exceeding a factor of 1.3 for the chromospheric L-alpha line, a factor of 1.5 for lines formed in the chromospheric-coronal transition region and a factor of 1.4 for the coronal Mg X line. A subflare in the region produced the largest intensity enhancements, ranging from a factor of about 2.3 for the chromospheric L-alpha line to about 8 for the transition region and coronal lines. The EUV fluctuations in this small active region are similar to those observed in coronal bright points, suggesting that impulsive heating is an important, perhaps dominant form of heating the upper chromospheric and lower coronal plasmas in small magnetic bipolar regions. The responsible mechanism most likely involves the rapid release of magnetic energy, possibly associated with the emergence of magnetic flux from lower levels into the chromosphere and corona.

Withbroe, G. L.↗