Configuration of the magnetotail near midnight during quiet and weakly disturbed periods: State of the magnetosphere

Journal Article · Tue Aug 01 04:00:00 EDT 1978 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JA083iA08p03805· OSTI ID:6798734

West, Jr, H I; Buck, R M; Kivelson, M G

Energetic-electron pitch angle data and magnetic field data obtained on inbound passes of Ogo 5 in 1968 near midnight during quiet periods have been studied. From observation of the vector field components along the orbit and knowledge of the satellite position when the pitch angle distributions changed from approximate isotropy (indicating non-guiding center particle motion) to the butterfly distribution (corresponding to adiabatic bounce orbits) the configuration of the near-earth tail fied for individual orbits has been inferred. The details of the modeling are presented in a companion paper. We find that quasi-steady field configurations near midnight can occur that are markedly different (ranging from taillike to fairly dipolelike) in different cases, even though the usual magnetic activity indicators (Kp,AE, auroral zone and mid-latitude magnetograms, and B/sub zgsm/ of the interplanetary magnetic field) differ but slightly from one case to another and indicate a quiet magnetosphere. The major differences in the data are that more intense lobe fields occur at the same distance down the tail for the more taillike field configurations (approx.30..gamma.. at 15 R/sub e/ for taillike configurations and approx.15..gamma.. at 15 R/sub e/ for more dipolelike configurations). There appears to be evidence that the more taillike configuration is associated with an enhanced dynamic pressure from the solar wind. The data, viewed in the light of previously published data obtained by the present experimenters and others, argue strongly that during quiet times the plasma sheet, in its azimuthal variation, is at its thinnest in the region near midnight. These results affect current ideas of the substorm growth phase and the evolution of energetic-electron pitch angle distributions in the postmidnight magnetosphere.

• Research Organization: Lawrence Livermore Laboratory, University of California, Livermore, California 94550
• OSTI ID: 6798734
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 83:A8; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

640203* -- Atmospheric Physics-- Magnetospheric Phenomena-- (-1987)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CHARGED-PARTICLE PRECIPITATION
ELECTRON PRECIPITATION
INCLINATION
MAGNETIC BAYS
MAGNETIC FIELD CONFIGURATIONS
MAGNETOTAIL
OGO SATELLITES
PLASMA SHEET
SATELLITES
SOLAR ACTIVITY
SOLAR WIND