Solar cycle variation of Coronal green line index
During 1966-2008 (cycles 20-23), the evolutions of sunspots Rz and solar flare index SF show similar evolution, a rising phase, a broad maximum and a declining phase in each cycle. On the other hand, coronal holes are more frequent in the declining phase of each cycle. Hence, the coronal green line index CG, which represents coronal heating, is expected to be similar to sunspots and solar flare index during the rising and maximum phases of solar cycle but dissimilar in the declining phase. Observations show that this was true, but the excess of CG in the declining phase was small compared to the CG intensities at solar maximum. Thus, the coronal hole contribution could not be unique, or even major one, for the large coronal heating.
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