Recent findings on angular distributions of dayside ring current energetic ions

Journal Article · Sat Dec 01 00:00:00 EST 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JA095iA12p20839· OSTI ID:5311737

Lui, A T.Y.; McEntire, R W; Sibeck, D G; Krimigis, S M ^[1]

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1. Johns Hopkins Univ., Laurel, MD (USA)

Angular distributions of dayside ring current energetic ions are studied with the Medium Energy Particle Analyzer (MEPA) on the Active Magnetospheric Particle Tracer Explorers/Charge Composition Explorer spacecraft. The anisotropy index n for pancake distribution during 10 geomagnetically quiet days is examined for the first time in the intermediate energies (50-1,000 keV) for which compositional information is now available. It is shown that n for protons and helium ions increases with L whereas n for CNO ions appears to be independent of L. The empirical formula n(E)=n{sub o} + k log{sub 10} (E(MeV)), for the energy dependence given by Fritz and Spjeldvik (1982), is extended to these energies and ion species. The parameter n{sub o} is found to increase generally with ion mass and L, except for CNO ions which show no noticeable L dependence. The parameter k appears to be independent of L and ion mass. The authors have also surveyed the varieties of pitch angle distributions. Two unusual distributions were detected during the September 4-7, 1984, geomagnetic storm. The first is a net field-aligned transport of ring current energetic ions at 6 {approx lt} L {approx lt} 9 and 1,030-1,300 MLT. Such a signature is shown most prominently by the heavy ions (mostly oxygen; E > 137 keV), to a lesser extent by helium ions (E > 72 keV), and only slightly by protons (E > 56 keV) which are the dominant ionic species. The second new feature is a sharp intensity enhancement over a pitch angle range centered at 90{degree} which occurs in all ionic species and energy passbands monitored by MEPA at 3 {approx lt} L {approx lt} 4 and 1,700-1,800 MLT. Its characteristics suggest that it represents the addition of a freshly injected ring current population in the main phase development of the storm, and not due to L shell splitting or wave-particle interaction.

• OSTI ID: 5311737
• Journal Information: Journal of Geophysical Research; (United States), Vol. 95:A12; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
EARTH MAGNETOSPHERE
IONIC COMPOSITION
IONS
ANGULAR DISTRIBUTION
ANISOTROPY
CHARGED-PARTICLE TRANSPORT
CNO CYCLE
ELECTRIC CURRENTS
HELIUM IONS
MAGNETIC STORMS
PROTONS
RADIATION BELTS
BARYONS
CHARGED PARTICLES
CURRENTS
DISTRIBUTION
EARTH ATMOSPHERE
ELEMENTARY PARTICLES
FERMIONS
HADRONS
NUCLEONS
RADIATION TRANSPORT
STAR BURNING
640201* - Atmospheric Physics- Auroral
Ionospheric
& Magetospheric Phenomena