Analysis of the ground level enhancements on 14 July 2000 and on 13 December 2006 using neutron monitor data

Abstract: On the basis of neutron monitor data we estimate the energy spectrum, anisotropy axis direction and pitch-angle distribution of solar energetic particles during two major ground level enhancements (GLE 59 on 14 July 2000 and GLE 70 on 13 December 2006). For the analysis we use a newly computed neutron monitor yield function. The method consists of several consecutive steps: definition of the asymptotic viewing cones of neutron monitor stations considered for the data analysis by computations of cosmic ray particles propagation in a model magnetosphere with the MAGNETOCOSMICS code; computation of the neutron monitor model responses and derivation of the solar energetic particle characteristics on the basis of inverse problem solution. The pitch-angle distribution and rigidity spectrum of high-energy protons are obtained as function of time in the course of ground level enhancements. A comparison with previously reported results is performed and reasonable agreement is achieved. A discussion of the obtained results is included as well their possible application is included.