IMP 8 magnetic observations of the high-latitude tail boundary: Locations and force balance

Journal Article · Sat Dec 01 04:00:00 EST 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JA095iA12p20759· OSTI ID:5378364

Ohtani, S; Kokubun, S ^[1]

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1. Univ. of Tokyo (Japan)

IMP 8 (IMP J) magnetic field observations are used to determine the properties of the high-latitude tail boundary, which separates the tail lobe and the magnetosheath. Boundary crossings are marked by transitions from quiet lobe to disturbed magnetosheath fields. From five years (1978-1982) of IMP 8 observations, a data set of 244 boundary crossings has been identified in the X{sub GSM} range of {minus}15 to {minus}40 R{sub E} and {vert bar}Z{prime}{sub GSM}{vert bar}>15 R{sub E}, when Z{prime}{sub GSM} is the distance from the neutral sheet. The results suggest the following: (1) the tail cross section is slightly flattened in the north-south direction, (2) the high-latitude magnetotail field and boundary continue to flare antisunward out to 40 R{sub E} downstream of the Earth, and (3) interplanetary magnetic field (IMF) B{sub Z} and the solar wind dynamic pressure (but not, evidently, the solar wind magnetic pressure) control the boundary location. The dependence on IMF B{sub Z} is consistent with the buildup of magnetic fluxes in the magnetotail during periods of southward IMF B{sub Z}. Examination of the magnetic fields on each side of the boundary indicates the following: (1) the solar wind dynamic pressure determines the lobe-side field strength. (2) The flaring angle is estimated on the basis of the classical model of the Chapman-Ferraro problem. The result is consistent with the X dependence of the tail size and with the orientation of the lobe-side field (all have flaring angles of 7{degree}-8{degree}). (3) The IMF strength controls the sheath-side field strength, with a lesser contribution from the solar wind dynamic pressure. (4) The current flowing at the boundary primarily depends on the solar wind dynamic pressure. In summary, the present results indicate that the solar wind dynamic pressure is the most important factor determining the nature of the near-Earth magnetotail magnetopause.

• OSTI ID: 5378364
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 95:A12; ISSN 0148-0227; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

640201* -- Atmospheric Physics-- Auroral
Ionospheric
& Magetospheric Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BOUNDARY LAYERS
COORDINATES
EARTH ATMOSPHERE
EARTH MAGNETOSPHERE
INTERPLANETARY MAGNETIC FIELDS
LAYERS
MAGNETIC FIELDS
MAGNETIC FLUX
MAGNETOPAUSE
MAGNETOSHEATH
MAGNETOTAIL
MORPHOLOGY
PLASMA PRESSURE
PRESSURE EFFECTS
SATELLITES
SOLAR ACTIVITY
SOLAR WIND