Flare-associated magnetic activity in the sun.

Abstract

Observations of the longitudinal Zeeman effects in a solar active center show the variations of magnetic field streng~h during a period of 144 minutes on 30 April 1958, which included the development and decay of a flare of importance I ~. The measurements show that the flare crossed the neutral line of zero longitudinal field, and, although the extremities lay in regions of steep field gradients, most of the flare area was a region of low gradient. A small but pronounced S pole within the flare area developed and faded away in exact synchronism with the flare intensity. However, the large magnetic changes affected the whole field of the active center. The integrated magnetic energy of the region underwent a sharp decrease of about 16 per cent during the 14 minute rising phase of flare intensity, and an even sharper recoverN to its initial value immediately after flare maximum. This behavior was shared by the large sunspot fields and the area outside the sunspots. On the assumption that the field was 5000 km deep, the energy change of the active center amounted to 4 X I0~' ergs. The Ha radiation of the flare during its life was about 1028 ergs. Thus the changes in magnetic energy prob~bly exceed the total radiation of the flare in the Balmer and Lyman series by a considerable factor. Sacramento Peak Observatory Sunspot, New Mexico