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Lennartsson & Sharp 1982
Lennartsson, W. and Sharp, R.D. (1982). A comparison of the 0.1–17 keV/e ion composition in the near equatorial magnetosphere between quiet and disturbed conditions. Journal of Geophysical Research 87: doi: 10.1029/JA087iA08p06109. issn: 0148-0227.

Data from the plasma composition experiment on ISEE 1 were used to investigate the relative number densities and energy characteristics of H+, He++, He+, and O+ in the near-equatorial magnetosphere at L≤12 during magnetically quiet and disturbed conditions. The ''quiet'' data were selected on the basis of both Dst and Kp over ~5 day periods preceeding the data accumulations, and the ''active'' data were from periods of Dst≲-100&ggr;. The ions included in this study had energies in the range of 0.1≤E/Q≲17 keV/e. The data naturally subdivide into two largely different sets in terms of a dipole L parameter. (1) At L≲5 the ion density is dominated by three species, H+, O+, and He+, appearing in variable ratios. The He++ is a small component and is generally obscured by background counts caused by penetrating MeV electrons. The O+ is the most abundant species in well over half of the plasma samples, whereas the H+ is more abundant in the remaining samples. No sample with statistically significant counts shows He+ to be the most abundant ion, although the He+ exceeds the H+ in density in several cases. The O+/H+ and He+/H+ ratios increase toward the inner edge of the ring current population and are, on the average, highest during quiet conditions. Both of these features are qualitatively consistent with a decay process dominated by charge exchange, but a comparison with published charge exchange rates seems to imply that other processes are also involved. All three ion species have a similar mean energy (~2--7 keV) within the energy window of the experiment, and all three have a low-energy component (0.1≤E/Q≲1 keV/e) that usually dominates the number density at the inner edge, at about L~3--4 during quiet conditions and L~2--3 during disturbed conditions. (2) At L>5 all four species may be present simultaneously in highly variable ratios, but the H+ is usually the most abundant, particularly during quiet conditions. As a rule, the O+/H+ and He+/H+ ratios decrease with increasing L, whereas the He++/H+ ratio slowly increases. Typical values in the outer magnetosphere (L~10--12) are 1-3% for the He++/H+ and He+/H+ ratios during both quiet and disturbed conditions, where the O+/H+ ratio may range from below 1% to over 200%, depending on the magnetic activity level. The highest O+/H+ ratios are found here during the early main phase of magnetic storms, which is contrary to the conditions at L<5. The H+,O+, and He+ all have a similar mean energy in this region (~4--6 keV), whereas the He++ is 2--3 times more energetic.

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Journal of Geophysical Research
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