The solar M-region problem - An old problem now facing its solution?

The solar M-region problem is briefly reviewed. The Mustel and the Allen-Saemundsson M-region schools are discussed in the light of (a) recent results on coronal structures and solar wind variations, and (b) statistical analyses of coronal-geomagnetic correlations. From this discussion it is suggested that the M-regions should be identified with the central portion of magnetically open solar regions, or coronal holes. With reference to the papers by Gulbrandsen (1973b, 1974), it is concluded that such an identification is in fact favoured by the great majority of analyses published on the M-region problem during the last 40 yr. It is assumed that historically, the M-region conflict has evolved from the scientific pecularity that geomagnetic phenomena which are actually related to magnetically open structures, were generally not studied in relation to such structures, but to closed magnetic configurations.