SOLAR-FLARE-INDUCED FORBUSH DECREASES - DEPENDENCE ON SHOCK-WAVE GEOMETRY

An analysis is presented of the effect of flare-induced shock waves on the intensity of relativistic cosmic rays at 1 AU. It was found that the intensity of cosmic ray protons falls abruptly as the shock wave passes the earth and recovers as the compression region moves into the outer heliosphere. The principal mechanism if sound to be simply prolonged containment of the cosmic ray particles in the region between the flare shock wave and the sun. This leads to additional adiabatic cooling of the particles and a corresponding decrease in particle intensity. Acceleration mechanisms at the shocks are found to play little role at relativistic energies. The dependence of both the maximum intensity decrease and recovery time on such parameters as particle diffusion coefficient, particle rigidity, and flare geometry is investigated. It is found that flares located to the east of the earth-sun line produce larger effects than those located to the west. The magnitude of the intensity reduction decreases as a function of increasing diffusion coefficient and increasing particle rigidity.