| Summary: | We report on the characteristics of the diurnally varying electron flux observed near the polar cap. The discussion is based on balloon observations, made near Fort Churchill, Manitoba, in 1967, of both the electron flux vertically incident on the atmosphere and the electron splash albedo. We measured an electron splash albedo flux below 100 Mev equal to the flux of electrons below 100 Mev incident on the atmosphere during daytime. The observed diurnal variations of the flux of electrons with energies ≲100 Mev is consistent with geomagnetic cutoff variations calculated for models of the magnetosphere. We deduce a geomagnetic ctuoff rigidity of ≲17 Mv for the nighttime interval and between 70 and 110 Mv for the daytime interval at an invariant latitude near 68° in 1967. © 1969 American Geophysical Union. Received December 18, 1968; revised June 5, 1969. We profited from stimulating discussions with Professor E. C. Stone. This work was supported by the National Aeronautics and Space Administration under grant NGL-05-002-007. Published - jgr7697.pdf
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