Cosmic Ray Flares Associated with the 1961 July Event

Abstract

Four major flares are considered in relation to their acceleration of high-energy (>1 Bev) protons toward the earth. All are associated with the complex spot group that crossed the certral meridian on July 14, 1981. The flares of July 12 and 18, recorded with a heliograph, are compared and their light-curves in H alpha are given. These flares are comparable in importance and similar in other respects; yet the second generates a shower of high-energy protons, recorded by their secondary effects at ground level, while the first does not. The reasons for this difference are considered in terms of the magnetic fteld situation in the sun-earth space during the passage of the spot group across the solar disk. The flare of July 12 occurs at a time when the terrestrial environment is relatively free from magnetized plasmas; but by July 18 the earth is enveloped by a radial magnetic field (magnetic bottle) reaching from the solar active region beyond the earth's orbit. The flares of July 18 and 20 thus find ready-made trajectories for the transport of their high-energy protons to the eanth. Heliographic co-ordinates are given for the 12 flares known to have produced cosmic ray effects at groundmore » level. The asymmetry of their positions on the solar disk is such as to suggest the existence at these times of radial magnetic fields, which connect sun to earth and have their lines of force bern convex to the west by solar rotation. (auth)« less