The January 20, 2005 event provided a wake-up call to space weather forecasters when the >100 MeV proton intensities reached their highest levels in more than 15 years. This event was also the 2nd largest ground-level event of all time, reaching peak intensity only 18 minutes after the onset of the associated X-ray flare. If this event was accelerated by a CME-driven shock, the shock must have formed very low in the corona and accelerated particles to GeV energies within ~10 minutes or less (Mewaldt et al. 2005a; Saiz et al. 2005), presenting a significant challenge to shock acceleration models. On the other hand, Simnett (2006) and others have suggested that the January 20 SEPs were accelerated by the X7 flare.
Shock geometry may be a key parameter for understanding how particles can be rapidly accelerated to very high energies. According to simulations by Giacalone (2005), particles can be accelerated much more rapidly at quasi- perpendicular shocks than they can at quasi-parallel shocks. Although it has also been claimed that quasi-perpendicular shocks have a higher injection threshold than quasi-parallel shocks and therefore favor the acceleration of pre-existing suprathermal ions over thermal seed particles (Tylka et al. 2005), this is a subject of controversy (Giacalone 2005). These controversies are best tested close to the Sun, where particles are accelerated to higher energies than at 1 AU.
We, therefore, have to test whether:
- there is a correlation between shock geometry and the composition and energy spectra of particles when the shock is still close to the Sun (Giacalone 2005; Mewaldt et al., 2005; Saiz et al. 2005),
- anomalous diffusion mechanisms can give shorter acceleration times (Zimbardo and Perri, 2013).