The motion of low-rigidity cosmic rays in the Earth's magnetic field and the effects of external fields

Abstract

A general approach is made to the discussion of motion of low-rigidity cosmic rays in a dipole field; it rests on the characteristics of the motion of these particles in the Alfven regime and a family of trajectories passing near the origin of the dipole itself, called nullbahnen, first calculated by Stormer. The general rigidity range of applicability of the method is discussed. It is found that within this range of applicability the asymptotic directions of the particles outside the earth field may be determined for a wide range of arrival latitudes and arrival directions with respect to the vertical without resorting to the numerical integration of trajectories. The presentation is extended to the earth's real field; asymptotic directions applicable to certain locations are presented and discussed for solar-flare particles and galactic variations detected by neutron monitors as well as lower-rigidity particles detectable only at balloon and satellite altitudes. Finally, the effects of external fields on the asymptotic directions are discussed, and the asymptotic directions appropriate to the arrival of solar-flare particles as detected by neutron monitors at sea level in the presence of ring currents are presented.