On the spatial character of the ∼10 h electron spectrum modulation in the Jovian magnetosphere

Abstract

On its voyage in the south duskside Jovian magnetosphere, after leaving the plasma sheet, Ulysses entered a large scale high latitude layer of energetic ions and electrons, extending from ∼49RJ to ∼83RJ. Ulysses traveled within this region from the end of day 41 until the first magnetopause crossing, early on day 43, 1992 and during later expansions of the magnetosphere. Between the time interval ∼15UT, d41–12UT, d 43, Ulysses recorded: (a) ∼10h periodic variations of the azimuthal and longitudinal components of the magnetic field, (b) spectral index peaks, increased fluxes j⊥ of ∼90° pitch angle electrons and relatively higher fluxes j⊥ in higher energy channels in phase with (at times of) magnetopause crossings, (c) decreasing fluxes during magnetopause approaches, and (d) ∼10h periodic flux, spectral and anisotropy variations of ∼40–∼300keV electrons almost in phase (or with some phase shift) with the 10h magnetic field modulation. These observations strongly suggest that flux, spectral and anisotropy data are well organized in terms of the distance from the magnetopause. We infer that the ∼10h periodicities of electron flux, spectral and anisotropy data are produced by intensity gradients in the direction from the magnetopause toward the interior of the large scale of energetic electron layer and the ∼10h periodic motion of the magnetosphere/magnetopause.