Statistical survey of pitch angle distributions in core (0-50 eV) ions from dynamics explorer 1: Outflow in the auroral zone, polar cap, and cusp

Journal Article · Thu Sep 01 04:00:00 EDT 1994 · Journal of Geophysical Research

DOI:https://doi.org/10.1029/94JA00864· OSTI ID:166273

Giles, B L; Moore, T E; Chappell, C R ^[1]

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1. NASA Marshall Space Flight Center, Huntsville, AL (United States); and others

Core (0-50 eV) ion pitch angle measurements from the retarding ion mass spectrometer on Dynamics Explorer 1 are examined with respect to magnetic disturbance, invariant latitude, magnetic local time, and altitude for ions H{sup +}, He{sup +}, O{sup +}, M/Z=2 (D{sup +} or He{sup ++}), and O{sup ++}. Included are outflow events in the auroral zone, polar cap, and cusp, separated into altitude regions below and above 3 R{sub E}. In addition to the customary division into beam, conic, and upwelling distributions, the high-latitude observations fall into three categories corresponding to ion bulk speeds that are (1) less than, (2) comparable to, or (3) faster than that of the spacecraft. This separation, along with the altitude partition, serves to identify conditions under which ionospheric source ions are gravitationally bound and when they are more energetic and able to escape to the outer magnetosphere. Features of the cleft ion fountain inferred from single event studies are clearly identifiable in the statistical results. In addition, it is found that the dayside pre-noon cleft is a consistent source of escape velocity low-energy ions regardless of species or activity level and the dayside afternoon cleft, or auroral zone, becomes an additional source for increased activity. The auroral oval as a whole appears to be a steady source of escape velocity H{sup +}, a steady source of escape velocity He{sup +} ions for the dusk sector, and a source of escape velocity heavy ions for dusk local times primarily during increased activity. The polar cap above the auroral zone is a consistent source of low-energy ions, although only the lighter mass particles appear to have sufficient velocity, on average, to escape to higher altitudes. 57 refs., 11 figs., 1 tab.

• OSTI ID: 166273
• Journal Information: Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: A9 Vol. 99; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
ALTITUDE
AURORAL ZONES
DEUTERIUM IONS
EARTH MAGNETOSPHERE
EV RANGE 01-10
EV RANGE 10-100
FLUX DENSITY
HELIUM IONS
HYDROGEN IONS
INCLINATION
IONOSPHERE
OXYGEN IONS
POLAR CUSP
POLAR REGIONS