Relativistic electron enhancements observed over a range of L shells trapped at high altitudes and precipitating at low altitudes into the atmosphere

Abstract

The fluxes of relativistic electrons at high altitudes were measured at the SCATHA satellite over the L shell range of 5.3–8.7 during both enhancements and depletions. Simultaneous observations of the precipitating fluxes of electrons (>1 MeV) were performed at low altitudes from the P78‐1 satellite. On a given pass of this satellite the fluxes of directly precipitating electrons in the bounce loss cone displayed bursts of enhancement, generally with observing times of less than 10 s. On the average these fluxes had a maximum value at L = 4.5–5.0. In the drift loss cone the quasi‐trapped electrons, all of which were about to precipitate into the atmosphere within a few minutes, were less intermittent and generally more intense, thereby providing a greater sensitivity for detecting precipitation. The ratio of the average fluxes of the directly precipitating electrons to the quasi‐trapped electrons increased with increasing L value. The coordinated data presented here have permitted for the first time a comparison to be made as a function of L shell between the precipitating and the high‐altitude trapped electron fluxes during relativistic electron enhancement events, some of which included electrons with energies extending to at least 5 MeV. The low‐ and high‐altitude fluxes of >1‐MeV electrons were found to track each other during the period studied (April–June 1979), with respect to both time and L shell variations. The average precipitating electron fluxes measured at low altitudes in the drift loss cone were lower than those at high altitude by a factor of about 3×10². For L = 5.3–7 the average fluxes in the bounce loss cone at low altitudes were estimated to be lower than the trapped fluxes at high altitude by a factor of about 3×104.