Engineering topics
Publications and source records attributed to Farnik, Frantisek.
Team 2 of the Ottawa Flares 22 Workshop dealt with observational and theoretical aspects of the characteristics and processes of energy release in flares. Main results summarized in this article stress the global character of the flaring phenomenon in active regions, the importance of discontinuities in magnetic connectivity, the role of field-aligned currents in free energy storage, and the fragmentation of energy release in time and space.
We have followed the transit of two active regions across the western solar limb during June 29 through July 2, 1980, as imaged in 3.5-16 keV X-rays by HXIS aboard the SMM. During frequent brightenings of large-scale coronal structures, hard X-ray emission in the 11-16 keV energy band was recorded up to altitudes of 76,000 km. Soft X-rays could be seen in excess of 250,000 km altitude above the photospheric active region. Many X-ray brightenings low in the corona in the active regions were followed by enhancements high in the corona in the large-scale coronal structures. Although subsequent enhancements rarely appeared in the same position, similar portions of the corona brightened intermittently, indicating that the general configuration of the coronal structures above the active regions did not change much, in spite of the frequent energy inputs. These inputs were of two kinds: nonthermal, with very fast response at high coronal altitudes within seconds or tens of seconds, and thermal, with a delay of several minutes. The nonthermal response is short-lived, reflecting the time profile of the primary source; the thermal response is more gradual and longer lasting than the primary source. In some enhancements of large-scale coronal structures both these kinds of response occur and can be clearly recognized. There are also active-region brightenings without any response in the high corona and, vice versa, high-corona brightenings without any obvious primary source; in the latter case, it is likely that the source was hidden behind the limb.
Detailed H-alpha, UV-line, and X-ray observations are presented of an extended arch that developed as a consequence of a compact subflare to a length of 300,000 km, in an 'included' magnetic polarity of low magnetic field strength. This great arch was preceded by one an order of magnitude smaller, which masked the polarity inversion line filament in the subflare's early phase. The fact that both arches were simultaneously observed in all spectral domains, as well as their fine structure in H-alpha, is explainable only in terms of an arch composition that encompassed several unresolved portions of material having widely different temperatures.
A characterization is developed for the 57,000-km long arch-shaped coronal structure of November 6, 1980, which became the site, first, of 13 quasi-periodic X-ray brightenings, and then of a series of 17 flaring arches. A comparison of H-alpha, O V, and X-ray data for the SB arch has qualitatively confirmed that a hot conduction front producing X-rays in the least dense plasma is first present, and is followed by a decelerating, denser plasma bulk in O V, with an eventual, still-further-decelerating very dense plasma becoming visible in H-alpha emission.