Comparison of the 0. 1--17 keV/e ion composition in the near equatorial magnetosphere between quiet and disturbed conditions
Data from the plasma composition experiment on ISEE 1 were used to investigate the relative number densities and energy characteristics of H/sup +/, He/sup + +/, He/sup +/, and O/sup +/ in the near-equatorial magnetosphere at L< or =12 during magnetically quiet and disturbed conditions. The ''quiet'' data were selected on the basis of both Dst and Kp over approx.5 day periods preceeding the data accumulations, and the ''active'' data were from periods of Dst< or approx. =-100..gamma... The ions included in this study had energies in the range of 0.1< or =E/Q< or approx. =17 keV/e. The data naturally subdivide into two largely different sets in terms of a dipole L parameter. (1) At L< or approx. =5 the ion density is dominated by three species, H/sup +/, O/sup +/, and He/sup +/, appearing in variable ratios. The He/sup + +/ is a small component and is generally obscured by background counts caused by penetrating MeV electrons. The O/sup +/ is the most abundant species in well over half of the plasma samples, whereas the H/sup +/ is more abundant in the remaining samples. No sample with statistically significant counts shows He/sup +/ to be the most abundant ion, although the He/sup +/ exceeds the H/sup +/ in density in several cases. The O/sup +//H/sup +/ and He/sup +//H/sup +/ ratios increase toward the inner edge of the ring current population and are, on the average, highest during quiet conditions.(2) At L>5 all four spicies 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+ ratios decrease with increasing L, whereas the He++/H+ ratio slowly increases. 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 similar mean energy in this region (approx. 4--6 keV), whereas the He++ is 2--3 times more energetic.
- Research Organization:
- Space Sciences Laboratory, Lockheed Palo Alto Research Laboratory, Palo Alto, California 94304
- OSTI ID:
- 6716663
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 87:A8
- Country of Publication:
- United States
- Language:
- English
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