Questions: 1. What is the frequency of occurrence and magnitude of electron precipitation as a function of geomagnetic latitude? 2. What is the influence on the D-region? 3. What is the influence of ionization caused by electrons and accompanying bremsstrahlung on atmospheric ozone? 4.4.3 Depletion versus Enhancement of the Radiation Belts (Curtis) The question of whether the radiation belt fluxes are depleted or enhanced depends strongly on the deposition mechanism for the Ar beam in the plasmasphere. Three mechanisms of beam stopping have been suggested, namely, stopping of the ion cloud, loss of the beam sheath, and plasma instabilities. If the beam is stopped by an ion-cloudlike mechanism (Chiu, et al. 1979) the deposited Ar+ will have energies much lower than the beam energy. Thus the deposited Ar+ will be essentially cold, i.e., it will have energies of the order of plasma energies in the plasmasphere. The cold Ar can suppress the ion cyclotron instability and hence enhance the flux of radiation belt electrons. If, however, the ion beam sheath loss mechanism of Curtis and Grebowsky (1979) is the dominant effect, the Ar+ deposited in the magnetosphere has energies of the order of the beam energy, and hence the deposited Ar is hot and anisotropic. The hot Ar+ will give rise to plasma wave turbulence and hence pitch angle scattering of both the hot Ar and radiation belt protons will occur. In this case the radiation belt protons could perhaps be depleted if the resonance relations have the appropriate numerical values. Plasma instabilities could give rise to either hot or cold Ar+, depending on whether pitch angle scattering or energy degradation is the dominant result of the plasma instability. Although the hot Ar+ cools off during its residence in the plasmasphere via electron Coulomb scattering and driving plasma instability turbulence, it is not clear that the hot Ar+ has sufficient time to become cold Ar before it is removed from the plasmasphere via precipitation and charge exhange. Thus, it may well be the case that the initial beam dissipation mechanisms outlined here will strongly determine the character of the modifications to the radiation belt. Since the greatest radiation belt fluxes +occur near the magnetic equator, plasmasphere heating which can increase 0 in the plasmasphere and hence suppress ion cyclotron turbulence will be limited to the lower levels of the plasmasphere, and most likely would not be as important as cold Ar in ion cyclotron suppression.
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