30TH INTERNATIONAL COSMIC RAY CONFERENCE Relativistic solar cosmic ray events (1956-2006) from GLE modeling studies E.V. V ASHENYUK 1 , YU.V. BALABIN 1 , L.I. MIROSHNICHENKO 2, 4 , J. PEREZ-PERAZA 2 , A. GALLEGOS-CRUZ 3 1 PGI, Apatity, Murmansk Region, 184209, Russia 2 Instituto de Geofisica, UNAM, C.U., Coyoacan, 04510, Mexico D.F., Mexico 3 UPIICSA, IPN, Iztacalco, 08400, Mexico D.F., Mexico 4 IZMIRAN, Troitsk, Moscow Region, 142190, Russia vashenyuk@pgi.kolasc.net.ru Abstract: The modeling analysis of 14 large GLEs occurred in the period 1956-2006 on the data of the worldwide neutron monitors has been performed. In all studied cases two distinct RSP populations (components) were revealed: the early impulse-like intensity increase with exponential energy spec- trum (prompt component), and the late gradual increase with a softer energy spectrum of the power law form (delayed component). The exponential spectrum may be an evidence of the acceleration by electric fields arising in the reconnecting current sheets in the corona. The possible source of delayed component particles can be stochastic acceleration at the MHD turbulence in expanding flare plasma. Introduction In this paper, based on the data of neutron moni- tors we consider regularities of relativistic solar protons (RSP) generation and release from the Sun in the 14 large Ground Level Enhancements (GLE) events occurring in the period 1956-2006. The worldwide NM network may be considered as a united multidirectional solar proton spec- trometer in the relativistic energy domain. With the modeling of the NM responses to an anisot- ropic solar proton flux and comparing them with observations the parameters of primary solar protons outside the magnetosphere can be ob- tained [1, 2]. In this study we have carried out the analysis of 14 SCR events at ground level. One of the basic results of this study was the detection of two distinct populations (components) of relativ- istic solar cosmic rays: prompt (PC) and delayed (DC) ones. The PC and DC have various spectra and anisotropy characteristics and, probably vari- ous sources on the Sun. Modeling technique of the GLE Using the data of ground based neutron monitor network the parameters of primary solar protons outside magnetosphere can be obtained by a modeling [1, 2]. Our recent modeling technique, in general, is similar to that of [2], as it takes into account the contribution in the neutron monitor response not only vertical, but also oblique inci- dent particles. This kind of analysis requires the data of no less than 20-25 ground-based cosmic ray stations, and consists of a few steps: 1. Definition of asymptotic viewing cones of the NM stations under study by the particle trajectory computations in a model magnetosphere. 2. Calculation of the NM responses at variable primary solar proton flux parameters. 3. Deriving with a least square procedure solar proton parameters (namely, energy spectrum, anisotropy axis direction, pitch-angle distribution) outside the magnetosphere by comparison of computed ground based detector responses with observations. Determination of asymptotic viewing cones of NM stations under study was carried out by com- putations of the particle trajectories in the magne- tosphere model Tsyganenko2001 [3] with a step in rigidity of 0.001 GV. For each given value of rigidity we calculated nine trajectories of particles that were “launched” in vertical, as well as in inclined directions under the angle of 20o in eight equally spaced azimuths. The response function of a given neutron monitor to anisotropic flux of Proceedings of the 30th International Cosmic Ray Conference Rogelio Caballero, Juan Carlos D’Olivo, Gustavo Medina-Tanco, Lukas Nellen, Federico A. Sánchez, José F. Valdés-Galicia (eds.) Universidad Nacional Autónoma de México, Mexico City, Mexico, 2008 Vol. 1 (SH), pages 253–256 ID 658 253