There are two dominant sources of low-energy electrons and positrons (20MeV - 1GeV) observed
at the top of the atmosphere: cosmic rays, and atmospheric secondaries. The latter are produced by
the interaction of Cosmic Ray nuclei in the atmosphere either directly above the detector or near the
magnetic conjugate point. Upwards-moving secondaries at the conjugate point that have a rigidity
lower than the local geomagnetic cutoff can become trapped along the geomagnetic field lines and
re-enter the atmosphere by the detector. These are referred to as re-entrant splash albedo. These
particles escape the geomagnetic field if their rigidity exceeds the local geomagnetic cutoff. At high
latitude, the geomagnetic cutoff depends on location and time. The cutoff is effectively zero during
nighttime when the albedo particles of any rigidity can escape via the magnetotail. Thus, the re-
entrant albedo enhances the observed flux only during the daytime when the geomagnetic cutoff
is non-zero. The balloon-borne spectrometer AESOP-Lite (Anti-Electron Sub-Orbital Payload
Low Energy) observed these diurnal transitions at energies between 20MeV and 300MeV during
its May 2018 flight from Kiruna, Sweden to Ellesmere Island, Canada. These observations show
a time difference in the diurnal geomagnetic cutoff transitions between electrons and positrons.
We simulate the trajectory of these particles observed during the 2018 flight to investigate the
charge-sign and rigidity dependence of the particle’s path through the magnetosphere during the
day-night transitions.