Local time dependence of non-störmer cutoff for 1.5-Mev protons in quiet geomagnetic field

Abstract

Two solid‐state detector telescopes, vertically and horizontally oriented, were launched into a polar orbit during a time of low geomagnetic activity. A small flux of 1.5‐Mev protons, interacting with the geomagnetic field as individual particles, was observed at all latitudes above a characteristic cutoff latitude. The observed vertical cutoff was 65° (equivalent dipole latitude) on the night side and 67° on the day side, as compared with a theoretical Störmer cutoff of 76°. The local time dependence was also apparent in the cutoff transition width characterized by the difference in the latitude at which the flux is first detectable and the latitude at which the maximum (plateau) flux is first observed. On the night side, the transition width was about 1°; on the day side it was about 3° and variable. The horizontal cutoff latitudes were similar. Essentially identical results were obtained over north and south poles. These results are not adequately predicted by currently postulated cutoff theories and should be considered in the calculation of proton fluxes associated with polar‐cap absorption.

Nonadiabatic particle motion in the magnetosphere

“…That there is good agreement between theory and observations suggests that nonadiabatic particle motion in a static field is responsible for the polar cap structure during the time of Flindt's observations. Other measurements of low-altitude pitch angle distributions [Stone, 1964;McDiarmid and Burrows, 1969] give results that are in reasonable This discussion is based on a static field model that provides only a basis to which wave particle effects may be added. The boundaries described earlier are no longer applicable when the geomagnetic field is disturbed, since then Xt --•(3B/Ot) must also be considered.…”

Penetration of solar protons to synchronous altitude

“…Direel measurements of solar protons aboard spacecraft [Pieper et al, 1962;Stone, 1964; Paulikas et al, 1968; Blake et al, 1968a, b; Fillius, 1968] as well as riometer measurements [Leinbach, 1967] have provided convincing evidence that these protons can penetrate deeper into the magnetosphere than predicted by the StSrmer theory.…”

Flux of Cosmic-Ray Electrons Between 17 and 63 MeV

“…16 " 18 It is also supported by diurnal variations in the geomagnetic cutoff inferred from measurements of low-energy protons. 19 ' 20 Direct evidence that particles of rigidity near 40 MV have direct access to at least some parts of the polar-cap region comes from simultaneous observations of comparable intensities of solar protons on Mariner 4, far outside the magnetosphere, and on Injun 4 in a low polar orbit. 21 Thus we consider our measured nighttime flux to be representative of the interplanetary flux and unaffected by geomagnetic cutoffs.…”