The solar cycle 23 provided several strong ground level enhancements (GLEs). The first strong
GLE event of the cycle was observed on 14 July 2000 (the Bastille day event), while the last
was observed on 13 December 2006. In addition, the period of late October - early November
2003 was characterized by strong cosmic ray variability and sequence of three GLEs. Cycle 23
produced also the second largest event in the observational history - 20 January 2005 event. Here
we perform a precise analysis of spectral and angular characteristics of solar energetic particle
(SEP) events on the basis of neutron monitor (NM) data. We model particle propagation in the
Earth’s magnetosphere and atmosphere using a newly computed NM yield function at several altitudes
above the sea level. The method includes several consecutive steps: detailed computation
of asymptotic cones and rigidity cut-off of each NMstation used in the analysis, making an initial
guess of the inverse problem by assuming the apparent source position location in a convenient
way, application of the NM yield function for detector response modelling and subsequent optimization
procedure in order to derive spectral and angular characteristics of SEPs. Here, we
present results from analysis of several GLEs. The SEP spectra and pitch angle distributions were
obtained in their dynamical development throughout the events. We briefly demonstrate the capability
of the method to assess SEP features of sub-GLE events, the details reported in this volum.
Several case examples are discussed.