The behavior of trapped electrons and protons at the lower edge of the inner radiation belt

Abstract

Fluxes and energy distributions of trapped electrons and fluxes of trapped protons have been measured at the lower edge of the inner radiation belt following two different energy selective redistributions of electrons at 1.34 Me v and at 0.74 Mev. Each of the two groups of electrons decayed at a rate that was in agreement with atmospheric scattering calculations. Thus it is concluded that at the time of the observations in October–November 1963, scattering by atmospheric collisions was the dominant over‐all loss mechanism for electrons trapped on magnetic shells with 1.145 ≲ L ≲ 1.160. All electrons on a given L shell with 0 ≲ hmin ≲ 350 km decayed at approximately the same rate, consistent with theoretical calculation. The unexpectedly large fluxes of electrons for 0 ≲ hmin ≲ 150 km and for 1.145 ≲ L ≲ 1.160 indicate a rather steady injection of electrons at high B values by processes in addition to small‐angle atmospheric scattering. The time behavior and the energy spectrum variations suggest that these electrons originated from a pitch‐angle redistribution of some of the electrons trapped at higher altitudes on the same or nearby magnetic field lines. The integral fluxes of protons above ∼70 Mev trapped on magnetic field lines with 1.145 ≲ L ≲ 1.160 were steady during this same time period. For 200 km ≲ hmin ≲ 350 km, the measured proton spatial distribution is consistent with that calculated using a source that is uniform in time and space (in this region) and a loss mechanism consisting of atmospheric ionization and excitation. For hmin ≲ 200 km the fluxes of trapped protons did not fall off with decreasing hmin as rapidly as predicted.

Precipitation of particles at low and middle latitudes

“…It is interesting to examine the possibility that the observations of precipitation of ring current protons by Moritz, It seems reasonably certain that Mozer and Crifo's observations are qualitatively and quantitatively different from the fluxes ascribed to the precipitation (through charge exchange) of ring current protons. Their findings may be, more likely, a local redistribution of low-energy trapped protons, more analogous to the redistributions observed by Imhofand Smith [1965b] for the case of electrons and postulated by Sood et al [1970] as the explanation of their results.…”

“…The recent measurements of quasi-trapped electron spectra [Imhof et al, 1973[Imhof et al, , 1974 show complexity in the energy spectrum that was not at all evident in the earlier work, although complex spectral structure was observed for trapped particles by Imhofand Smith [1965bSmith [ , 1966. Imhofet al [1973] measured the electron spectra in the lower fringes of the radiation belt with excellent energy resolution in the energy interval between 130 keV and 1 MeV.…”

“…The initial measurements of quasi-trapped electrons (see, e.g., Paulikas and Freden [1964]) were essentially devoid of spectral information, and only fluxes above various energy thresholds were usually reported. Later measurements [Imhof, 1968;Imhof and Smith, 1966] established that the electron spectrum, now free of fission product electrons, was in general quite steep, relatively few particles being at energies above • 1 M eV. Differences in spectral shape were found to arise as the electrons drifted through the anomaly (Figure 12 that the particle spectrum depends somewhat on magnetic activity.…”

“…Near the outer fringes of the inner belt, at L values between 1.7 and 1.8, peaks were frequently observed in the energy spectrum, the most pronounced peak occurring for quasi-trapped particles, i.e., particles drifting in paths with small hmm. A sample of the results obtained by Imhof et al [1973] is presented in Figure 13. As can be seen qualitatively from this figure, the energy of the discrete peak decreases very rapidly with increasing L value.…”

Saturn's Inner Magnetospheric Convection in the View of Zebra Stripe Patterns in Energetic Electron Spectra

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In the terrestrial inner radiation belt, the energy spectrogram of energetic electrons (10-100s keV) sometimes contains one or multiple peaks (Datlowe et al, 1985;Imhof & Smith, 1966;Imhof et al, 1981aImhof et al, , 1981b. These peaks form regular patterns that map on constant bounce-averaged drift frequencies across the entire inner radiation belt (Sauvaud et al, 2013).

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