Magnetic and Electric Phenomena in the Sun's Atmosphere associated with Sunspots

Abstract

The magnetic field in the Sun's atmosphere near a sunspot, and the electric field resulting from changes in the magnetic field, are computed for an isolated sunspot growing in a non-conducting, and also in a uniformly conducting, medium. For a conductivity of 10 −8 e.m.u., which applies in the absence of a magnetic field, it is shown that the velocity of propagation of the magnetic field is very slow; the conductivity must be less than 10 −13 e.m.u. if the field is to penetrate to distances of the order of 3 × 10 9 cm. in the time of growth of the sunspot. It is shown, however, that a rapid propagation can be brought about in the atmosphere by the decrease in conductivity perpendicular to the magnetic field. The discussion is extended to include fields resulting from the growth of bipolar groups.