Fine-scale spatial structure in the pitch angle distributions of energetic particles near the midnight trapping boundary
Article first published online: 20 SEP 2012
Copyright © 1977 by the American Geophysical Union.
Journal of Geophysical Research
Volume 82, Issue 32, pages 5215–5221, 1 November 1977
How to Cite
1977), Fine-scale spatial structure in the pitch angle distributions of energetic particles near the midnight trapping boundary, J. Geophys. Res., 82(32), 5215–5221, doi:10.1029/JA082i032p05215., , and (
- Issue published online: 20 SEP 2012
- Article first published online: 20 SEP 2012
- Manuscript Accepted: 22 JUL 1977
- Manuscript Received: 19 MAY 1977
Near the trapping boundary at local midnight the ratio of precipitating to trapped fluxes of electrons (0.16–2.4 MeV) and of protons (0.04–0.95 MeV) observed at low satellite altitudes (∼750 km) is a strong function of both particle energy and L value. On a particular L shell, isotropy is often observed for particles above a given energy, whereas below that energy the precipitating fluxes are much lower than the trapped fluxes. The onset of isotropy typically occurs at a sharply defined energy threshold which decreases rapidly with increasing L value. The occurrences of isotropy for electrons and protons together show a consistent variation with L when they are considered in terms of magnetic rigidity. For the onset of isotropy the equivalent gyroradius at the equator of particles with the same energy and a 90° pitch angle spans the range ∼5 km to ∼500 km and varies approximately as (L — L0 — 0.1)1.8, where L0 is the L shell at which isotropy occurs for electrons with an equatorial gyroradius of 10 km. The observed magnetic rigidity thresholds for isotropy may provide a measure of the effective scale length of the inhomogeneities of the geomagnetic field.