Three low-energy particle events: Modeling the influence of the parent interplanetary shock

Abstract

We have reproduced the 35-1600 keV fluxes and anisotropies of two large particle events associated with interplanetary shocks triggered by solar activity (a flare or a filament disappearance). These events, 1979 February 18 (E59 deg) and 1981 December 8 (W45 deg), together with the 1979 April 24 event (E10 deg) already modeled by Heras et al. (1992), constitute a set that allows a comparative study of the influence, upstream of the shock, of the large-scale shock structure on the associated low-energy particle event. Using a compound model for shock and particle propagation in the interplanetary medium (up to 1 AU), we have derived the injection rate of shock-accelerated particles released into the interplanetary medium as a function of time, and the mean free path for their propagation along the interplanetary magnetic field. We stress the relevance of the initial time of connection between the shock and the spacecraft, which is associated with the heliolongitude of the solar source, to explain the observed flux and anisotropy profiles. We have quantified the variations of the efficiency of shock particle acceleration as the shock approaches the spacecraft, relating them to the magnetic field and plasma conditions at the shock region magnetically connected to the observer. We find that for the east and central meridian events this efficiency increases as the shock approaches the observer's position, while it decreases for the west event, trends which are also followed by the representative velocity and magnetic field jumps across the shocks. The absence of solar particles and the existence of a wide turbulent foreshock region also appear to be relevant factors to explain the derived values of the injection rates.