The three-dimensional structure of the solar corona

The surface where the radial component of the solar magnetic field changes sign is computed for a minimum corona. It is shown that ( I) the projection of the folds of this surface onto the plane of the sky is consistent with the helmet structures observed during the eclipse of June 30, 1954, (2) the re are type I and type 2 helmets, according to the well-known classificatio n of coronal structures; (3) some elements of this sign-change surface of t he radial field can be classified as so-called envelopes. The results obtai ned suggest that more complex coronal structures can be described in a simi lar way. An MHD model of polar plumes is considered, (C) 2001 MAIK "Nauka/I nterperiodica".