Distribution of energetic positive ion species above a diffuse midnight aurora
Observational approaches to the problem of magnetospheric plasma origin usually depend upon mass-discriminating measurements of ion distribution functions. A new instrument for this purpose has been developed and flown via sounding rockets above a diffuse midnight aurora during geomagnetically quiet conditions. The instrument combines wide mass and energy ranges (2.5< or =ME< or =160amu-keV), high mass resolution with good sensitivity, and superior rejection of undesired particles. Only ions identified as H/sup +/ and He/sup + +/ were detected, and the He/sup + +/ was not clearly above background, having an upper limit of 2--4% of the H/sup +/ intensity. All other ions, including the ionospheric species He/sup +/ and O/sup +/, had upper limits at a similar or smaller level. This situation contrasts sharply with a number of recently reported observations of large intensities of O/sup +/ during magnetic storms and may be characteristic of undisturbed periods. Though these results suggest a solar wind source for the ions, an admixture including an appreciable fraction of polar wind material (predominantly H/sup +/) is not precluded. The measured proton distribution was nearly isotropic over downcoming pitch angles at all energies and showed a depleted atmospheric source cone. The proton energy distribution had a best fit temperature of 4.5 keV and a number density of 0.17 cm/sup -3/, corresponding to a peak intensity just over 10/sup 5/ cm/sup -2/ s/sup -1/ keV/sup -1/. Altitudinal variations observed during the flight are consistent with the theory of charge exchange of a time steady incident proton population. These ion observations, taken together with electron observations reported in a companion paper, appear to be consistent with the model of diffuse auroras in which trapped plasma precipitates owing to strong pitch angle diffusion on auroral field lines linking the near-earth plasma sheet.
- Research Organization:
- Space Environment Labortory, NOAA Environmental Research Laboratories, Boulder, Colorado 80303
- OSTI ID:
- 5485463
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 84:A11
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
AURORAE
IONIC COMPOSITION
ANGULAR DISTRIBUTION
CHARGED-PARTICLE PRECIPITATION
DISTRIBUTION FUNCTIONS
ELECTRON TEMPERATURE
INCLINATION
ION TEMPERATURE
IONOSPHERE
DISTRIBUTION
EARTH ATMOSPHERE
PLANETARY IONOSPHERES
640201* - Atmospheric Physics- Auroral
Ionospheric
& Magetospheric Phenomena