Association between energetic particle bursts and Birkeland currents in the geomagnetic tail

Journal Article · Wed Dec 01 04:00:00 EST 1948 · J. Geophys. Res.; (United States)

OSTI ID:5924041

Lui, A T.Y.; Krimigis, S M

IMP 8 observations in the geomagnetic tail of energetic particles at hundreds of keV and of the magnetic field are examined for a substorm period from 1700 to 1800 UT on March 3, 1976. For this interval, it is found that bursts of energetic protons detected at a downstream distance of approx.37 R/sub E/ in the midnight tail region are accompanied by east-west magnetic field perturbations indicative of Birkeland current sheets. The magnitude of the magnetic field perturbations ranges from approx.1 to 12 nT, corresponding to current densities of 1 to 9 mA/m when integrated over the current sheet thickness. These values are comparable to previous observations of Birkeland currents in the near-earth tail (X>-20 R/sub E/) and with the auroal-arc-assocciated Birkeland current densities at low altitudes scaled out to the tail region. The favorable comparison suggests that the closure of small-scale Birkeland current system systems, at least in these instances, lies tailward of approx.40 R/sub E/. The observed Birkeland current system and the magnitude of current densities are found to be consistent with ion tearing instability in the tail. The inferred wavelength of the tearing mode along the tail axis is approx.2 to 17 R/sub E/. In the context of the tearing model, the presence of Birkeland currents and the occasional isotropic distribution of energetic electrons (E/sub e/>0.22 MeV)= suggest that the energetic particle events in this study occur on closed magnetic field lines, even though strong tailward streaming dominates the particle anisotropy in these events.

• Research Organization: The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland
• OSTI ID: 5924041
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 89:A12; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

640203* -- Atmospheric Physics-- Magnetospheric Phenomena-- (-1987)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CURRENT DENSITY
EARTH ATMOSPHERE
ELECTRON DENSITY
ENERGY RANGE
IMP SATELLITES
ION DENSITY
ION DRIFT
KEV RANGE
KEV RANGE 100-1000
MAGNETIC BAYS
MAGNETOSPHERE
MAGNETOTAIL
SATELLITES