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On open and closed field line regions in Tsyganenko's field model and their possible associations with horse collar aurorasThe boundary between open and closed field lines is investigated in the empirical Tsyganenko (1987) magnetic field model. All field lines extending to distances beyond -70 R(E), the tailward velocity limit of the Tsyganenko model are defined as open, while all other field lines, which cross the equatorial plane earthward of -70 R(E) and are connected with the earth at both ends, are assumed closed. It is found that this boundary at the surface of the earth, identified as the polar cap boundary, can exhibit the arrowhead shape, pointed toward the sun, which is found in horse collar auroras. For increasing activity levels, the polar cap increases in area and becomes rounder, so that the arrowhead shape is less pronounced. The presence of a net B(y) component can also lead to considerable rounding of the open flux region. The arrowhead shape is found to be closely associated with the increase of B(z) from the midnight region to the flanks of the tail, consistent with a similar increase of the plasma sheet thickness.
Document ID
19910043382
Document Type
Reprint (Version printed in journal)
Authors
Birn, J. (Los Alamos National Lab. NM, United States)
Hones, E. W., Jr. (Los Alamos National Laboratory NM, United States)
Craven, J. D. (Los Alamos National Lab. NM, United States)
Frank, L. A. (Iowa, University Iowa City, United States)
Elphinstone, R. D. (Calgary, University Canada)
Stern, D. P. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 14, 2013
Publication Date
March 1, 1991
Publication Information
Publication: Journal of Geophysical Research
Volume: 96
ISSN: 0148-0227
Subject Category
GEOPHYSICS
Funding Number(s)
CONTRACT_GRANT: NGL-16-001-002
CONTRACT_GRANT: NASA ORDER S-56312-D
CONTRACT_GRANT: NAG5-483
Distribution Limits
Public
Copyright
Other