Ermolli, I; Solanki, S. K; Tlatov, A. G; Krivova, N. A; Ulrich, R. K; Singh, J
(Institute of Physics, 2009-06)
Various observatories around the globe started regular full-disk imaging of the solar atmosphere in the Ca II K line in the early decades of the 20th century. The archives made by these observations have the potential of ...