Solar flare high energy alpha particles and their storage in interplanetary space

Abstract

A scintillation counter telescope and a Cerenkov counter flown by high altitude balloon measured the relativistic α-particle flux in the late stages of the November 12–13, 1960, solar flare event. The integral solar α-particle flux was found to be 55 part/sec m2 ster for kinetic energies greater than 560 Mev/nucleon (R>2.3 bv). Combined with the results of Biswas, Fichtel, and Guss (31<E<112 Mev/nucleon) obtained at the same time, the data are consistent with a differential kinetic energy spectrum ∝E−4 or a differential magnetic rigidity spectrum ∝R−7 and do not agree with an exponential magnetic rigidity spectrum. The two Forbush decreases of cosmic ray intensity beginning at 1930 UT, November 12, 1960, and 1030 UT, November 13, 1960, provided a unique opportunity to study the storage and propagation of solar particles in interplanetary space. Steljes, Carmichael, and McCracken have suggested that relativistic solar particles, though trapped to some extent behind the ‘front’ associated with the first Forbush decrease, ‘leaked’ out continuously to the galaxy. The time variation of the relativistic solar α particles observed here indicates that early in the event the particles initially trapped in the region between the two ‘fronts’ associated with the Forbush decreases also leaked backward into the region between the second front and the sun. At the time of measurement, the fluxes in the two regions were approximately equal and the net flux across this second front was insignificant.