A technique for the study of short term cosmic ray variations : I) The origin-of-scatter technique

This paper introduces the "Origin-of-Scatter. technique, a theoretical method of calculating the countrate variation of an Earth-based cosmic ray detector (P>lGV), given the number density distribution of cosmic rays in interplanetary space. The flux at Earth which was last-scattered within a given volume element, when the relative cosmic ray number density is U=1.0, is determined for a set of volume elements in interplanetary space. Because this flux is proportional to U, these quantities can be used as coefficients to yield the flux for any arbitrary U. By summing over all volume elements the time dependent flux at Earth for any number density distribution can be obtained. An expression for these "origin-of-scatter. coefficients is derived, and the required parameters were obtained from cosmic ray trajectories calculated in a spiral interplanetary magnetic field model. The effects of superposed magnetic field irregularities are effectively included in terms of a scattering mean free path. Results for 4 representative stations are given. The dependence of the remote sensing ability of a detector on time of day and scattering mean free path is clearly seen. The effects on these results of departures from the idealized spiraI field model are discussed.