Cosmic Rays In The Magnetosphere At A Solar Activity Minimum (1996-1997): 2. Apparent Cutoff Rigidities

Apparent cutoff rigidities have been determined based on the trajectory computations performed for obliquely incident particles at geographic points along the route of the Italian Antarctic Expedition. The computations were made for eight azimuth (at an interval of 45degrees) and five zenith (at an interval of 15degrees) angles. Data on the dependence of the integral multiplicity of secondary neutrons (recorded by a neutron monitor) on the zenith angle of arrival of primary particles were also used to compute apparent cutoff rigidities. These data on integral multiplicity were obtained from theoretical computations of meson-nucleon cascades of primary protons of different rigidity coming into the Earth's atmosphere at zenith angles of 0degrees, 15degrees, 30degrees, 45degrees, 60degrees, and 75degrees [Dorman and Pakhomov, 1979]. Results of [Dorman and Pakhomov, 1979] have been verified and normalized using coupling coefficients obtained in [Dorman et al., 2000]. The computed apparent cutoff rigidities have been compared with apparent cutoff rigidities obtained in [Clem et al., 1997] and with rigidities computed in [Dorman et al., 2000], partially using a dipole approximation of the geomagnetic field.