Evolutionary regimes of the green-line corona brightness during cycles 20–21

Abstract

Abstract A non-standard approach to the interpretation of patrol green-line corona observations is presented. The brightness distributions in the years 1964–1986 (cycles 20–21) combined into half-year intervals and three latitudinal zones, were analysed using the statistical method of principal components. It has been determined that the variation of brightness distribution with cycle phase and latitude zone may be described by the so-called model of evolving distribution. Along the evolution trajectory four straight-lined parts are detected that are characterized by their own evolutionary regimes. The transitions from one regime to another take place at the specific (turning) points found from the cyclic curves of other activity indices (actually, the relative Wolf numbers). A ‘latitude-time’ diagram was constructed to show the time development of these regimes. Similar features of cycles 20–21 in this diagram, as well as the differences between the even and odd cycles are described. The physical meaning of these phenomena is briefly discussed.