Coronal rotation dependence on the solar cycle phase

A study of the green corona rotation rate, during the period 1970-1974, confirms that the differential rotation degree varies systematically through a solar cycle and that the corona rotates in an almost rigid manner before sunspot minimum. During the first two years, 1970-1971, the differential rotation degree, characteristic of high solar activity periods is detected. While during the years of declining activity, 1972-1974, a drastic decrease of the differential rotation degree occurs and the green corona rotates almost rigidly, as the coronal holes observed in the same period. These conclusions are valid only for the rotation of coronal features with lifetime of at least one solar rotation. (Auth.)