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The discrete and localized nature of the variable emission from active regionsUsing data from the Extreme Ultraviolet (EUV) Spectroheliometer on Skylab, we study the empirical characteristics of the variable emission in active regions. These simultaneous multi-wavelength observations clearly confirm that active regions consist of a complex of loops at different temperatures. The variable emission from this complex has very well-defined properties that can be quantitatively summarized as follows: (1) It is localized predominantly around the footpoints where it occurs at discrete locations. (2) The strongest variability does not necessarily coincide with the most intense emission. (3) The fraction of the area of the footpoints, (delta n)/N, that exhibits variable emission, varies by +/- 15% as a function of time, at any of the wavelengths measured. It also varies very little from footpoint to footpoint. (4) This fractional variation is temperature dependent with a maximum around 10(exp 5) K. (5) The ratio of the intensity of the variable to the average background emission, (delta I)/(bar-I), also changes with temperature. In addition, we find that these distinctive characteristics persist even when flares occur within the active region.
Document ID
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Arndt, Martina Belz
(Harvard-Smithsonian Center for Astrophysics, Cambridge, MA United States)
Habbal, Shadia Rifai
(Harvard-Smithsonian Center for Astrophysics, Cambridge, MA United States)
Karovska, Margarita
(Harvard-Smithsonian Center for Astrophysics, Cambridge, MA United States)
Date Acquired
August 16, 2013
Publication Date
March 1, 1994
Publication Information
Publication: Solar Physics
Volume: 150
Issue: 2-Jan
ISSN: 0038-0938
Subject Category
Solar Physics
Accession Number
Funding Number(s)
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