Pulsations of precipitating energetic electrons: ACTIVE satellite data

We present the patterns of high frequency energetic electron (similar to 20 to similar to 300 keV) pulsations in middle latitudes, in subauroral and auroral regions, based on low altitude nearly polar orbiting satellite (Intercosmos-24, project ACTIVE) measurements. Two detectors with different orientations allowed the fluxes within and outside the loss cone to be compared. The trapped electrons do not exhibit the strong pulsations observed within the bounce loss cone. The pitch angle diffusion coefficient changes significantly on time scales comparable to or even shorter than the bounce period of electrons. The same is valid for changes of precipitating electron energy spectra. There are indications that both pitch angle and energy diffusion are in operation. VLF emissions at f < 3.5 kHz with a complicated structure are observed simultaneously with the electron pulsations, but there is no clear correlation between waves and particles. If the characteristics of the electron pulsations and VLF emissions are of a temporal character, they are qualitatively consistent with the models of nonlinear wave particle interactions, or with the concept of a flowing cyclotron maser. However, the pulsations may originate from fine spatial structure. Variability of the precipitation flux implies short time and/or small scale changes of ionization at altitudes down to 70 km. (C) 1998 Elsevier Science Ltd. All rights reserved.