DYNAMICS OF THE LOW-ALTITUDE ENERGETIC PROTON FLUXES BENEATH THE MAINTERRESTRIAL-RADIATION BELTS

At the interface between the upper atmosphere and the radiation belt r egion there exists a secondary radiation belt consisting mainly of ene rgetic ions that have become neutralized in the ring current and in th e main radiation belt and then re-ionized by collisions in the inner e xosphere. The time history of the proton fluxes in the 0.64-35 MeV ene rgy range was traced in the equatorial region beneath the main radiati on belts during the 3-year period from February 21, 1984, to March 26, 1987, using data obtained with the High-Energy Particle experiment on board the Japanese OHZORA satellite. During most of this period a fai rly small proton flux of similar to 1.2 cm(-2) s(-1) sr was detected o n geomagnetic field lines in the range 1.05 < L < 1.15. We report a fe w surprisingly deep and rapid flux decreases (flux reduction by typica lly 2 orders of magnitude). These flux decreases were also long in dur ation (lasting up to 3 months). We also registered abrupt flux increas es, such that magnitude of the proton flux enhancements could reach 3 orders of magnitude and with an enhancement duration of 1-3 days. Poss ible reasons for these unexpected phenomena are discussed.