Solar Activity in the Green Corona Over Cycle 23

The intensity of the green coronal line (5303Å, Fe {\sc xiv), which is directly proportional to the electron density as well as the temperature of the corona, is a good and sensitive indicator of the reflection of the photospheric activity in the emission corona, mapping also the evolution of the magnetic fields in the active regions on the solar surface. In cycle 23 (1996 -2007), the average intensity of the green corona was of about 30% less when compared with that of the preceding cycle; this, however, does not necessarily imply a lower temperature of the corona, but rather a smaller number of active regions and/or smaller strength of local magnetic fields in the latter. The maximum of the intensity of the green corona was observed in August 2001, preceding for about one and a half year that of sunspot number. Moreover, the increased intensities were not observed continuously in time and heliographic latitude, but rather in particular latitudes, with a slight time-lag between the north and south hemispheres. It is well known that a time-latitudinal distribution of the intensity of the green corona features two kinds of large-scale motions. The first is the so-called polar branch, which separates from the "main flow" in the middle latitudes in the cycle minimum, lasts for about 3 -4 years and disappears at the time of the maxima of solar activity near the poles. The other is the equatorial (or principal) branch, which after separation in middle-latitudes moves first towards the poles, then roughly 2 years after the polar branch reached the poles makes a U-turn at upper heliographic latitudes of ±70 degrees, and migrates towards the equator where it disappears in the next minimum; the life-time of this branch is about 18 years. Given the time of the splitting of the two branches, we can guess the time of the maximum and minimum of the forthcoming cycle - cycle 24: the corresponding numbers are 2011 and 2012.5 for the time of the "double" maximum and 2019 for the time of minimum.