Alejandro SáizDavid RuffoloManit RujiwarodomJohn W. BieberJohn ClemPaul EvensonRoger PyleMarc L. DuldigJohn E. HumbleMahidol UniversityChulalongkorn UniversityBartol Research InstituteAustralian Antarctic DivisionUniversity of Tasmania2018-06-212018-06-212005-01-0129th International Cosmic Ray Conference, ICRC 2005. Vol.1, (2005), 229-2322-s2.0-84898992415https://repository.li.mahidol.ac.th/handle/20.500.14594/17190Besides producing the largest ground level enhancement (GLE) in half a century, the relativistic solar particles detected during the event of January 20, 2005 showed some interesting temporal and directional features, including extreme anisotropy. In this paper we analyze the time evolution of cosmic ray density and anisotropy as characterized by data from the "Spaceship Earth" network of neutron monitors by using numerical solutions of the Fokker-Planck equation for particle transport. We find that a sudden change in the transport conditions during the event is needed to explain the data, and we propose that this change was caused by the solar particles themselves.Mahidol UniversityPhysics and AstronomyConference PaperSCOPUS