Cosmic Ray Flares Associated with the 1961 July Event

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Abstract
Four major flares are considered in relation to their acceleration of high-energy (> 1 BeV) protons towards the Earth: all were associated with the complex spot group of C.M.P. July 14. The flares of July 12 and 18, recorded with the Lyot heliograph at the Cape, are compared and their light-curves in H α are given. These two flares were comparable in importance and similar in other respects; yet the second generated a shower of high-energy protons, recorded by their secondary effects at ground level, while the first did not. The reasons for this difference are considered in terms of the magnetic field situation in the Sun–Earth space during the passage of the spot group across the solar disk. The flare of July 12 occurred at a time when the terrestrial environment was relatively free from magnetized plasmas: by July 18 the Earth had become enveloped by a radial magnetic field (magnetic bottle) reaching from the solar active region to beyond the Earth's orbit. The flares of July 18 and 20 thus found ready-made trajectories for the transport of their high-energy protons to the Earth. Heliographic co-ordinates are given for the 12 flares which have produced cosmic ray effects at ground level. The asymmetry of their positions on the solar disk is such as to suggest the existence at these times of radial magnetic fields: these connect Sun to Earth and have their lines of force bent convex to the west by solar rotation.

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