stituent in the model. As mentioned above, the ionospheric (500 km) concentration of argon ions was set equal to either the local concentration of hydrogen ions or of oxygen ions as nominal lower and upper limits. It must be recognized that these limits are at present arbitrary; eventually, these limits should be set by a detailed study of the fate of Ar+ in the magnetosphere. Several different fractional temperature increases were assumed. The results of the calculations are a bit tedious to be shown here in detail but the salient features are summarized by the right hand panel of Figure 15, in which T0 is set at 5 eV and T1 = 0. Our results show that the addition of the argon ions will not upset the normal distribution of the plasmaspheric hydrogen and oxygen; however, as shown by the right-hand panel, the addition of heat by the argon-ion interaction with the ambient medium or by Joule heating can drastically alter the plasmasphere. At high altitudes, hydrogen can be replaced by the heavier constituents (oxygen or a combination of oxygen and argon). These results are easily understood, because the increased heating drives O+ and H+ up the field line but the supply of ionospheric O+ is orders of magnitude higher than H+, thus increasing the proportion of 0 in the higher altitude region. This situation is further accentuated by the gravitational sinking of Ar+ relative to the accompanying electron, driving up more O+ to maintain charge neutrality. It must be recognized also that the assumed boundary conditions are simplifications of the actual situation, which is very far from steady state. The argon ions will be introduced onto different L shells at different times; plasma convection processes and radial diffusion can modify the spatial distribution of the argon which, because of the nature of its source, is already quite different from that of a normal plasmasphere constituent. In addition, interhemispheric flows, (Vickrey et al., 1979) which may affect the 46
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