Splash Albedo Protons Between 4 and 315 MeV at High and Low Geomagnetic Latitudes

The differential energy spectrum of splash albedo protons has been measured at high geomagnetic latitude near Fort Churchill, Manitoba, at three periods of the solar cycle in 1966, 1967, and 1969 and at low latitude near Palestine, Texas, in 1967 by using a balloon-borne solid state detector telescope. We observed splash albedo proton fluxes between 4 and 315 MeV of 81 + 11, 70 + 11, and 48 + 8 protons/(m 2 s sr) at high latitude in 1966, 1967, and 1969 and of 37 + 9 protons/(m 2 s sr) at low latitude in 1967. The decreases from 1966 to 1969 are due to solar modulation of the cosmic ray parent nuclei. The albedo spectrum shows a similar shape for both latitudes. The difference in intensity can be explained by different local geomagnetic cutoffs; i.e., a significant contribution to the splash albedo flux arises from primary particles with rigidity below 4.5 GV. The splash albedo flux near Fort Churchill is consistent with corresponding fluxes previously reported near 53ø-55øN. The flux below 100 MeV near Palestine is significantly lower than that reported by Verma (1967).