Positional evolution of magnetic foci in the polar regions of the Sun with the phase of the solar activity cycle

摘要

The behavior of magnetic foci-intersection points of tangents to ray structures in the polar corona of the Sun-is studied. This behavior reflects the evolution of the large-scale magnetic field near the poles, and is one of only a few sources of information on the polar magnetic field of the Sun. For the first time, the positions of the magnetic foci are plotted as a function of the solar-cycle phase for a full cycle, based not only on total-eclipse images but also on daily coronal observations in the FeIX and FeX (171 angstrom) lines carried out with the EIT telescope on the SOHO satellite. The temporal behavior of the foci over a cycle differs appreciably from that inferred from isolated observations during eclipses. The curve agrees fairly well with the model of the global-field evolution suggested by us previously.