Solar cosmic rays during the extremely high ground level enhancement on 23 February 1956

摘要

The 23 February 1956 ground level enhancement of the solar cosmic rayintensity (GLE05) is the most famous among the proton events observed since1942. But we do not have a great deal of information on this event due tothe absence of solar wind and interplanetary magnetic field measurements atthat time. Furthermore, there were no X-Ray or gamma observations and theinformation on the associated flare is limited. Cosmic ray data was obtainedexclusively by ground level detectors of small size and in some cases ofa non-standard design. In the present work all available data from neutronmonitors operating in 1956 were analyzed, in order to develop a model of thesolar cosmic ray behavior during the event. The time-dependentcharacteristics of the cosmic ray energy spectrum, cosmic ray anisotropy,and differential and integral fluxes have been evaluated utilizing differentisotropic and anisotropic models. It is shown that the most outstandingfeatures of this proton enhancement were a narrow and extremely intense beamof ultra-relativistic particles arriving at Earth just after the onset andthe unusually high maximum solar particle energy. However, the contributionof this beam to the overall solar particle density and fluency was notsignificant because of its very short duration and small width. Our estimateof the integral flux for particles with energies over 100 MeV places thisevent above all subsequent. Perhaps the number of accelerated low energyparticles was closer to a record value, but these particles passed mainly tothe west of Earth. style="line-height: 20px;">Many features of this GLE are apparently explained by the peculiarity of theparticle interplanetary propagation from a remote (near the limb) source.The quality of the available neutron monitor data does not allow us to becertain of some details; these may be cleared up by the incorporation into theanalysis of data from muonic telescopes and ionization chambers operating atthat time.Keywords. Interplanatary physics (Cosmic rays; Energeticparticles) – Solar physics, astrophysics and astronomy(Flares and mass injections)