A large portion of the Ar^ ions are precipitated in the ionosphere where they may stimulate airglow emission. The resulting emissions may be comparable with the airglow due to natural processes (Ref. 1). This is not usually considered serious, but it has recently been pointed out that even minor increases in the sky illumination at mid and low latitudes can interfere severely with the conduct of ground-based astronomy (Ref. 2). The natural airglow is the dominant source of interference with observation of faint celestial objects. (The contribution due to all the stars in the sky is not well known, but appears to be slightly less.) The airglow due to Ar+ precipitation must be carefully evaluated, which entails estimation (poorly known) of the cross sections for excitation by direct impact. The Ar'1' ions that remain in the plasmasphere would profoundly affect wave and particle processes there. The lifetimes of low energy Ar ions are measured in days (Ref. 1); the effects would be expected to persist through the entire period of SPS construction activity. There is no doubt that the high energy electron content of the trapped radiation belts is strongly influenced by the cold plasma density (Ref. 3). The precise mechanism for removal of relativistic electrons is not, however, fully understood. The most popular candidate is an interaction with electromagnetic ion cyclotron waves near the plasmapause (Ref. 4). There are difficulties with that mechanism — it has not been thoroughly tested and confirmed. The difficulties have mostly to do with how waves generated by trapped ions can resonate with trapped electrons (Ref. 5).; the cold plasma approximation breaks down and only very energetic electrons can be affected by the waves. It appears that other processes must be involved in both dayside relativistic precipitation events and quiet time diffusion. After major geomagnetic storms there seem to be processes that remove 1-3 MeV electrons, both inside the plasmasphere and far outside, with lifetimes of the order of 10 days (Ref. 6). Assuming removal of relativistic electron by interactions with ion cyclotron waves probably gives the largest possible enhancement of relativistic electron fluxes. A pressing need remains for more research on loss mechanisms for energetic electrons. REFERENCES 1. Chiu, Y.T., J.M. Cornwall, J.G. Luhman, and M. Schulz, The Aerospace Corporation, SSL-79 (7824)-l. 2. Sky and Telescope, 57, 444, May 1979 letters by P.E. Glaser, G.T. Davidson, A.T. Young. 3. Cornwall, J.M., M. Schulz, J. Geophys. Res., 76, 7791 (1971); correction, J. Geophys. Res., 78, 6830 (1973). 4. Thorne, R.M., and C.F. Kennel, J. Geophys. Res., 76, 4446, 1971. 5. Davidson, G.T., J. Atm. Terr. Phys., 40, 1087 (1978). 6. West, H.I., Jr., and G.T. Davidson; to be published.
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