On open and closed field line regions in Tsyganenko's field model and their possible associations with horse collar auroras

Journal Article · Fri Mar 01 00:00:00 EST 1991 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/90JA02124· OSTI ID:5268173

Birn, J; Hones, Jr, E W ^[1]; Craven, J D; Frank, L A ^[2]; Elphinstone, R D ^[3]; Stern, D P ^[4]

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1. Los Alamos National Lab., NM (USA)
2. Univ. of Iowa, Iowa City (USA)
3. Univ. of Calgary, Alberta (Canada)
4. NASA Goddard Space Flight Center, Greenbelt, MD (USA)

Using the empirical Tsyganenko (1987) long model as a prime example of a megnetospheric field model, the authors have attempted to identify the boundary between open and closed field lines. They define as closed all field lines that are connested with the Earth at both ends and cross the equatorial plane earthward of x = {minus}70 R{sub E}, the tailward validity limit of the Tsyganenko model. They find that the form of the open/closed boundary at the Earth's surface, identified with the polar cap boundary, can exhibit the arrowhead shape, pointed toward the Sun, observed in horse collar auroras (Hones et al., 1989). The polar cap size in the Tsyganenko model increases with increasing K{sub p} values, and it becomes rounder and less pointed. The superposition of a net B{sub y} field, which is the expected consequence of an IMF B{sub y}, rotates the polar cap pattern and, for larger values, degrades the arrowhead shape, resulting in polar cap configurations consistent with known asymmetries in the aurora. The pointedness of the polar cap shape also diminishes or even completely disappears if the low-latitude magnetopause is assumed open and located considerably inside of the outermost magnetic flux surface in the Tsyganenko model. The arrowhead shape of the polar cap is found to be associated with a strong increase of B{sub z} from midnight toward the tail flanks, which is observed independently, and is possibly related to the NBZ field-aligned current system, observed during quiet times and strongly northward IMF B{sub z}. The larger B{sub z} values near the flanks of the tail cause more magnetic flux to close through these regions than through the midnight equatorial region.

• OSTI ID: 5268173
• Journal Information: Journal of Geophysical Research; (United States), Vol. 96:A3; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
AURORAE
EARTH MAGNETOSPHERE
MATHEMATICAL MODELS
POLAR REGIONS
MAGNETIC FIELD CONFIGURATIONS
AURORAL OVAL
BOUNDARY LAYERS
COMPARATIVE EVALUATIONS
INTERPLANETARY MAGNETIC FIELDS
MAGNETIC FLUX
MAGNETIC SURFACES
MAGNETOPAUSE
MAGNETOTAIL
EARTH ATMOSPHERE
EVALUATION
LAYERS
MAGNETIC FIELDS
640201* - Atmospheric Physics- Auroral
Ionospheric
& Magetospheric Phenomena