Abstract
We have studied the early stages of development of two adjacent active regions observed at the center and the wings of Hα for six days. From the growth of spots and arch structures we found that periods of slow flux emergence were followed by periods of vigorous flux emergence. We observed arch filaments covering an appreciable range of sizes (from a length of about 27 000 km and a height of 2000–3000 km to a length of 45 000 km and a height of about 15 000 km). Individual arch filaments within the same arcade sometimes have different inclinations of their planes with respect to the vertical. We observed isolated cases of arches crossing each other at an angle of ∼45°. During their early stages arch filament systems are short and they expand at a rate of about 0.8 km s−1. The rate of growth of arch filament systems is faster when the orientation of the flux tubes is nearly parallel to the equator. Our observations suggest that the early part of the evolution of individual arch filaments in a grown system is not visible; however, in a few cases we observed arch filaments appearing as dark features near one footpoint and expanding towards the other, with a mean velocity of about 30 km s−1.
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Georgakilas, A.A., Zachariadis, T.G. & Alissandrakis, C.E. Evolution of an active region and associated Hα arch structures. Sol Phys 146, 241–258 (1993). https://doi.org/10.1007/BF00662012
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DOI: https://doi.org/10.1007/BF00662012