Very-Low-Frequency and Particle Rocket Experiment at Kerguelen Islands: 2. Particle measurements

Abstract

The mean particle distribution functions observed between 100 and 400 km at L∼3.7 are in agreement with other measurements made in the same energy range and at the same L value; our measurements extend the results toward lower energies and lower altitudes. The proton energy distribution is fitted by two experimental curves with e-folding energies E0∼50 kev up to energies of the order of 400 kev and E0∼1 Mev above. The same is generally true for the electron distribution, although the break in the spectrum is less marked, the e-folding energies being E0∼20 kev up to 100 kev and E0∼100 kev above. The ratio J⊥/J∥ is usually smaller for protons than for electrons, especially for one flight during which it was smaller than 1. Some characteristics of the particle fluxes have been observed in relation to VLF emissions: a flux increase of the newly injected electrons, both trapped and precipitated, is observed during dawn chorus events. A highly characteristic fluctuation (T∼80 sec) of the trapped electron intensities has been detected in coincidence with a VLF periodic hiss emission and a hydromagnetic wave of the same periodicity. This phenomenon is interpreted in the frame of reference of the quasi-linear theory as a pitch-angle scattering associated with VLF emission.