The cosmic-ray flare effect: 2. The flare effects of May 4, November 12, and November 15, 1960

Abstract

The observations of the flare effects of May 4 and November 12 and 15, 1960, are analyzed, particular attention being given to obtaining an understanding of the anisotropies that existed in the cosmic-ray fluxes during the events. For each event it is found that the flux was greatest from a direction to the west of the sun. During the May 4 event the flux was greatest from, and symmetrical about, a direction 55° to the west of the sun, and 10° north of the ecliptic, for more than 9 hours after the commencement of the flare effect. The differential rigidity spectrum is investigated, the power-law exponent being calculated to be −5.0 at 1045 UT, and shown to be decreasing (that is, the spectrum steepening) with time. For the November 12 event, it is shown that an anisotropy persisted until about 1900 UT, when the radiation rapidly became isotropic. At this same time, the counting rates of all neutron detectors increased very suddenly and a Forbush decrease was observed by meson detectors. It is shown that at about 1600 UT an additional anisotropic flux of radiation arrived at the earth from within the hemisphere centered upon the sun, and between 1700 and 1800 UT an additional anisotropic flux arrived from the opposite direction. For the November 15 event, it is shown that the radiation became isotropic within about 90 minutes of the commencement of the flare effect. The anisotropies at early times are studied, the most important observation being that particles were arriving from some directions in space for approximately 30 minutes before any arriving from the opposite direction.