Production Of Energetic Electrons Research Articles

Jupiter's radiation belts

A model for the production and loss of energetic electrons in Jupiter's radiation belt is presented. It is postulated that the electrons originate in the solar wind and are diffused in toward the planet by perturbations which violate the particles' third adiabatic invariant. At large distances, magnetic perturbations, electric fields associated with magnotospheric convection, or interchange instabilities driven by thermal plasma gradients may drive the diffusion. Inside about 10 R J the diffusion is probably driven by electric fields associated with the upper atmosphere dynamo which is driven by neutral winds in the ionosphere. The diurnal component of the dynamo wind fields produces a dawn-dusk asymmetry in the decimetric radiation from the electrons in the belts, and the lack of obvious measured asymmetries in the decimetric radiation measurements provides estimates of upper limits for these Jovian ionospheric neutral winds. The average diurnal winds are less than or comparable to those on earth, but only modest fluctuating winds are required to drive the energetic electron diffusion referred to above. The winds required to diffuse the energetic particles across the orbit of the satellite lo in a time equal to their drift period are also estimated. If Io is non-conducting, modest winds are required, but if Io is conducting, only small winds are needed. It is concluded that both protons and electrons are diffused in from the solar wind to small distances without serious losses occurring due to the particles being swept up by the satellites. Consideration of proton and electron diffusion in energy shows that once the electrons become relativistic, the ratio of proton to electron energy increases. Thus, if protons and electrons have the same energy in the solar wind, when the electrons reach nMeV, the protons will be nMeV if n ⪡ 1 or n 2 MeV if n ⪢ 1. If the proton-to-electron energy ratio is initially, e.g., 5, then these figures are 5 n and 5 n 2, respectively.

Some observations of energetic electrons in the outer radiation zone during magnetic bays

Changes in the cutoff boundary latitude and flux of electrons Ee > 40 kev in the midnight sector of the outer radiation belt during periods when magnetic bays are in progress are studied in this paper from the data obtained by the University of Iowa satellite Injun 4. From this study, it is observed that (1) the outer-zone flux in the midnight sector increases without any change in the boundary latitude during the expansion phase of a magnetic bay and (2) in addition to the increase in flux, there is also an extension of the boundary to higher latitudes during the recovery phase of a magnetic bay. From these observations, it is suggested that magnetic field line merging may not play a primary role in the production of energetic auroral electrons and that acceleration of particles takes place in the outer zone itself and not far out in the magnetotail.

Evidence suggesting dumping of semitrapped electrons on the night side of the Earth

Processes leading to the production of energetic electrons and their precipitation into the auroral atmosphere are believed to take place in the earth's magnetosphere. Details as to how these electrons appear on and are removed from the magnetic lines linking the distant field and the auroral atmosphere are currently unknown, although all processes presumably result from interactions with the solar wind. The older interpretation of particle precipitation as simply dumping of the statically trapped radiation from the outer zone has largely given way to the concept of local acceleration for a number of compelling reasons [O'Brien, 1962; Winckler, 1962]. Nevertheless, the character of the precipitation may, in some instances, still be related to the local quasi-trapped reservoir of particles.