Access of solar electrons to closed field lines

Observations of solar electron fluxes, spectra, pitch-angle distributions, and temporal and spatial behavior are used in investigating the quasi-trapping region of the geomagnetosphere. Several features of this region are demonstrated using data from magnetic electron spectrometers on the polar-elliptical orbiting satellite OV1-19 (1969-25C) during the period April 12 to April 17, 1969. The results indicate that, although solar electrons have ready access to closed field lines, they do not become stably trapped in significant quantities. Sharp persistent gradients between the quasi-trapped zone and the polar plateau (a region of uniform isotropic fluxes) are regarded as indicating an abrupt transition between a region of the geomagnetic field that consists entirely of closed field lines (i.e., permit conjugate-point mirroring) and a second region in which the field lines either connect directly to the interplanetary field or extend into a tail that is very turbulent on the scale of the gyroradius of 0.1- to 2-Mev electrons.