WHITE-LIGHT POLARIZATION AND LARGE-SCALE CORONAL STRUCTURES

The results of the white-light polarization measurements performed dur ing three solar eclipses (1973, 1980, 1991) are presented. The eclipse images were processed and analysed by the same technique and method a nd, consequently, the distributions of the polarization and coronal in tensity around the Sun were obtained in unified form for all three sol ar eclipses. The mutual comparisons of our results, and their comparis on with the distributions found by other authors, allowed the real acc uracy of the current measurements of the white-light corona polarizati on, which is not worse than +/-5%, to be estimated. We have investigat ed the behaviour of the polarization in dependence on heliocentric dis tance in helmet streamers and coronal holes. Simultaneous interpretati on of the data on polarization and intensity in white-light helmet str eamers is only possible if a considerable concentration of coronal mat ter (plasma) towards the plane of the sky is assumed. The values obtai ned for the coronal hole regions can be understood within the framewor k of a spherically symmetrical model of the low density solar atmosphe re. A tendency towards increasing polarization in coronal holes, conne cted with the decrease of the hole's size and with the transition from the minimum to the maximum of the solar cycle, was noticed. The probl em of how the peculiarities of the large-scale coronal structures are related to the orientation of the global (dipole) solar magnetic field and to the degree of the goffer character of the coronal and interpla netary current sheet is discussed briefly.