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This paper presents results on modelling the ground level response of thehigher energy protons for the 2005 January 20 ground level enhancement (GLE).This event, known as GLE 69, produced the highest intensity of relativisticsolar particles since the famous event on 1956 February 23. The location ofrecent X-ray and gamma-ray emission (N14 W61) was near to Sun-Earth connectingmagnetic field lines, thus providing the opportunity to directly observe theacceleration source from Earth. We restrict our analysis to protons of energygreater than 450 MeV to avoid complications arising from transport processesthat can affect the propagation of low energy protons. In light of this revisedapproach we have reinvestigated two previous GLEs: those of 2000 July 14 (GLE59) and 2001 April 15 (GLE 60). Within the limitations of the spectral formsemployed, we find that from the peak (06:55 UT) to the decline (07:30 UT)phases of GLE 69, neutron monitor observations from 450 MeV to 10 GeV are bestfitted by the Gallegos-Cruz & Perez-Peraza stochastic acceleration model. Incontrast, the Ellison & Ramaty spectra did not fit the neutron monitorobservations as well. This result suggests that for GLE 69, a stochasticprocess cannot be discounted as a mechanism for relativistic particleacceleration, particularly during the initial stages of this solar event. ForGLE 59 we find evidence that more than one acceleration mechanism was present,consistent with both shock and stochastic acceleration processes dominating atdifferent times of the event. For GLE 60 we find that Ellison & Ramaty spectrabetter represent the neutron monitor observations compared to stochasticacceleration spectra. The results for GLEs 59 and 60 are in agreement with ourprevious work.

An Improved Model for Relativistic Solar Proton Acceleration applied to the 2005 January 20 and Earlier Events