Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997arep...41..836b&link_type=abstract
Astronomy Reports, Volume 41, Issue 6, November 1997, pp.836-844
Astronomy and Astrophysics
Astronomy
2
Scientific paper
Results of high-angular-resolution observations of the quiet Sun at 3-32 cm during the 22nd activity cycle are presented. Weak variations of the radio intensity of quiet regions are detected, which are visible at wavelengths of 8-32 cm and disappear toward 3 cm. The excess emission during the decay phase has a nearly flat spectrum, suggesting it is thermal emission from optically thin layers of the corona. Taking these coronal layers into account increases the brightness temperature during the decay phase by 40% compared to its value at the cycle minimum; this corresponds to a modest variation of the mean electron density of the quiet corona. X-ray data make it possible to distinguish two coronal components outside active regions that are associated with the cyclic variation detected: (1) loop arcades above quiescent filaments (prominences) and rarified high arches joining active regions with distant knots of opposite magnetic polarity; (2) the diffuse corona, recorded during various dynamic processes. Coronal holes become visible against the background of the quiet Sun at centimeter wavelengths only when the background level is minimal.
Borovik Valeria N.
Livshitz M. A.
Medar' V. G.
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