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Relativistic solar cosmic rays can effectively be used for studying the processes of particle acceleration within the flare region and the corona, as well as their escape from the solar atmosphere and their propagation in the interplanetary space. The Sun occasionally emits cosmic rays of sufficiently high energy to cause increases of the intensity recorded by ground level detectors such as neutron monitors and muon telescopes, known as ground level enhancements (GLEs) (Shea and Smart, 1993; 2002; Storini and Laurenza, 2003). These enhancements characterize only one relativistic part of the entire solar cosmic ray spectrum. The detection threshold for neutron monitors of standard type (NM-64 or IGY) is significantly lower arising to primary proton kinetic energy ~435 MeV/nucleon (or magnetic rigidity ~1 GV/nucleon). If the energy of primary protons is less than 435 MeV neutron monitors do not practically respond them due to atmospheric absorption of neutrons. A historical beginning of ...
Relativistic solar cosmic rays can effectively be used for studying the processes of particle acceleration within the flare region and the corona, as well as their escape from the solar atmosphere and their propagation in the interplanetary space. The Sun occasionally emits cosmic rays of sufficiently high energy to cause increases of the intensity recorded by ground level detectors such as neutron monitors and muon telescopes, known as ground level enhancements (GLEs) (Shea and Smart, 1993; 2002; Storini and Laurenza, 2003). These enhancements characterize only one relativistic part of the entire solar cosmic ray spectrum. The detection threshold for neutron monitors of standard type (NM-64 or IGY) is significantly lower arising to primary proton kinetic energy ~435 MeV/nucleon (or magnetic rigidity ~1 GV/nucleon). If the energy of primary protons is less than 435 MeV neutron monitors do not practically respond them due to atmospheric absorption of neutrons. A historical beginning of solar cosmic observations was set by the occurrence of the GLEs on 28 February 1942, in July 1946 and November 1949 (Adams and Braddick, 1950). The greatest ground level enhancement of solar cosmic rays ever recorded by neutron monitors (until January 2005) available to detailed analysis was observed on 23 February 1956. The characteristics and the peculiarities of this event have been studied by many researchers (Meyer at al., 1956; Pfotzer, 1958; Miroshnichenko, 1970; Adams and Gelman, 1984; Smart and Shea, 1990; Belov et al., 2005a; b). Since that time hundreds of proton events and tens of GLEs were registered, but all of them rank below this one by one order of magnitude or more. However, on 20 January 2005, one of the largest ground level enhancements ever recorded, GLE-69, was registered in the neutron monitors of the worldwide network (Belov et al., 2005c; Plainaki et al., 2005b). In this thesis, a new technique for modeling the dynamical behavior of GLEs throughout their evolving, based on the method of coupling coefficients (Dorman, 1957; 2004) as well as on the determination of neutron monitor asymptotic directions, is proposed. The so called NM-BANGLE Model (Neutron Monitor Anisotropic GLE Model) couples primary solar cosmic rays at the top of the Earth's atmosphere with the secondary ones detected at ground level by neutron monitors, during GLE events. An efficient optimization method based on the Levenberg-Marquardt algorithm has been applied in order to calculate the various GLE parameters in the most reliable and precise way (Levenberg, 1944; Marquardt, 1963; More, 1977). As a result, the evolution of several GLE parameters such as the solar cosmic ray spectrum, the anisotropy and the particle flux distribution is calculated. Consequently crucial information on the propagation of solar energetic particles in the interplanetary magnetic field is revealed. In order to work effectively the NM-BANGLE Model has to take into account the influence of the Earth’s magnetospheric field on the solar energetic particle propagation in the near Earth interplanetary space. Moreover, neutron monitors located at different sites on the Earth’s surface record secondary particles originating from primaries that come in general from different directions in space. Due to the particle motion inside the geomagnetic field, each ground level detector is capable of recording particles produced by primaries originating from a limited set of directions in space, which is called asymptotic cone of viewing. Each neutron monitor of the worldwide network, therefore, comprises a unique tool for the cosmic ray study revealing information on the primary cosmic ray spectrum as well as on the arrival direction of the primary particles. Consequently, each neutron monitor is proved to be a magnetospheric window in the near Erath interplanetary space providing us with crucial information on the Earth’s “magnetospheric optics” for primary cosmic rays. In this thesis the asymptotic directions of viewing for a significant number of neutron monitors stations widely distributed around the globe covering a wide range of latitudes, longitudes and rigidities have been calculated using the Tsyganenko 1989 magnetospheric field model for the time period of the big solar cosmic ray event of January 2005. Moreover, peculiarities and differences between the intensities of secondary solar particles occurring between different neutron monitor stations related to their different asymptotic directions of viewing during the ground level enhancement of 20 January 2005 are discussed
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