Figure 3

Proton flux profiles of several SEP events observed by the ACE and IMP-8 spacecraft as a function of the longitude of the parent solar event. These proton flux profiles are consistent with the presence of a traveling CME-driven shock which continuously injects energetic particles as it propagates away from the Sun. The concept of "cobpoint", defined by Heras et al. [1995] as the point of the shock front which magnetically connects to the observer, is very useful to describe the different types of SEP flux profiles. Solar events from the western hemisphere have rapid rises to maxima because, initially, the cobpoint is close to the nose of the shock near the Sun. These rapid rises are followed by gradual decreasing intensities because the cobpoint is at the eastern flank of the shock just where and when the shock is weaker. The observation of the shock at 1 AU in these western events depends on the width and strength of the shock. Near central meridian the cobpoint is initially located on the western flank of the shock and progressively moves toward the nose of the shock. Low-energy proton fluxes usually peak at the arrival of the shock, being part of what are known as energetic storm particle (ESP) events. For events originating from eastern longitudes, connection with the shock is established just a few hours before the arrival of the shock and the cobpoint moves from the weak western flank to the central parts of the shock; connection with the shock nose is only established when the shock is beyond the spacecraft and, usually, it is at this time when the peak particle flux is observed. The evolution of the low-energy ion flow anisotropy profiles throughout the SEP events reflects also the cobpoint motion along the shock front [Domingo et al., 1989]. This figure is derived from Figure~15 of Cane [1988].