Observations of polar rain at low and high altitudes
Observations in the distant magnetotail lobes (rapprox. >100 R/sub E/)= reveal that electrons in the approx.50- to 1000-eV energy range often exhibit strong, field-aligned bidirectional anisotropies. Because of large tail motions in the variable flow of the solar wind, ISEE 3 data provide extensive sampling of most tail plasma regions in rapid succession. It is found that bidirectional electron fluxes occur predominantly in the lobe connected directly to the sunward interplanetary magnetic field in the open magnetosphere model (north lobe for away sectors and south lobe for toward sectors). Using data from the low-altitude DMSP spacecraft, we compare polar rain electron intensities, energy spectra, and time variations at low altitudes with concurrent bidirectional electron properties measured by ISEE 3. The field-aligned lobe electron phase space densities above approx.200 eV agree well (i.e., to within a factor of approx.2--3) with DMSP-measured polar rain phase space densities near the polar cap. Furthermore, the spectral slopes above 200 eV also are similar at low and high altitudes. Below 100--200 eV there is a thermal electron population in the distant tail, probably arising from local entry of plasma through the distant magnetopause, which is not present at DMSP altitudes. These data suggest that the suprathermal tail lobe electrons are essentially a test particle population which can move freely along field lines to form polar rain; in contrast, the thermal electrons are bound to the tailward flowing lobe ion population far down the tail and thus cannot reach the polar cap regions. copyright American Geophysical Union 1987
- Research Organization:
- Los Alamos National Laboratory, Los Alamos, New Mexico
- OSTI ID:
- 5514271
- Journal Information:
- J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 92:A12; ISSN JGREA
- Country of Publication:
- United States
- Language:
- English
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Strong electron bidirectional anisotropies in the distant tail: ISEE 3 observations of polar rain
Bidirectional electron anisotropies in the distant tail: ISEE-3 observations of polar rain
Related Subjects
Ionospheric
& Magetospheric Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ANGULAR DISTRIBUTION
ANISOTROPY
ASYMMETRY
CHARGED-PARTICLE PRECIPITATION
DAILY VARIATIONS
DISTRIBUTION
EARTH ATMOSPHERE
EARTH MAGNETOSPHERE
ELECTRON PRECIPITATION
ENERGY RANGE
ENERGY SPECTRA
EV RANGE
EV RANGE 10-100
EV RANGE 100-1000
INTERPLANETARY MAGNETIC FIELDS
MAGNETIC FIELDS
MAGNETOTAIL
NOCTURNAL VARIATIONS
NORTH-SOUTH ASYMMETRY
PLASMA DRIFT
SOLAR ACTIVITY
SOLAR WIND
SPECTRA
VARIATIONS