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Paper: Shape and Structure of the White-Light Corona over Solar Cycles (Invited review)
Volume: 205, The Last Total Solar Eclipse of the Millennium in Turkey
Page: 17
Authors: Rusin, V.
Abstract: This paper puts together what we have observed and learned about shape and coronal structures in the white-light. Three different parameters have been used: ellipticity (flattening index), structures and the total brightness. All these parameters map the solar activity cycle and provide a continuity in eclipse observations over many decades. The white-light corona is nearly round at solar maximum (ellipticity is around zero). Distribution of helmet streamers is nearly uniformly distributed around the Sun. There are only a few helmet streamers above the equator at the minimum. The ellipticity reaches its maximum values 0.27-0.30 approximately 2 years prior to the minimum. Structure of the white-light corona shows a complex of its individual features, the most remarkable, helmet streamers, located above the inversion magnetic line detected in the photosphere. The other ones are: coronal holes, polar plumes, thread-like streamers, loops, arcades, coronal cavities, blades or sheets, and coronal spikes. Their size and lifetime has a great variability. The total brightness derived from the white-light in the height range between 1.03-6.00 solar radii varies between 0.48 times 10-6 (minimum) and 1.42 times 10-6 (maximum). There is a good relation between the ellipticity and total brightness. It is proposed that helmet streamers shift together with prominence belts from mid-latitudes at cycle minimum to the poles where they decay, at cycle maximum, similarly like prominence belts. Then, new streamers should arise in high-latitudes, like the green corona, and slowly move to the equator. The corona reflects a global development of solar magnetic fields (global and local) over solar cycle, including a reverse of the global dipole magnetic field at cycle maximum.
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