The magnetic field of the equatorial magnetotail: AMPTE/CCE observations at R < 8.8 RE

The Active Magnetospheric Particle Tracer Explorers/Charge Composition Explorer (AMPTE/CCE) magnetic field experiment has provided extensive measurements of the vector field near the equatorial plane in the inner magnetotail. Taillike distortions from the dipole field direction may reach 80° near the AMPTE/CCE apogee of 8.8 RE. The Bz (north-south) field component in dipole coordinates was always positive within 0.5 RE of the equatorial current sheet, indicating that neutral lines were never seen inside of 8.8 RE. South of −0.5 RE, Bz values are sometimes southward due to extremely taillike fields and the southward tilt of the tail in dipole coordinates during northern hemisphere winter. Fields are most taillike near midnight and during times of high Kp. At 8.5 RE the equatorial field magnitude depressions are roughly half the dipole field strength of 51 nT. These depressions are larger at lesser distances reaching −40 nT at 3.4 RE for Kp ≤ 2- and −80 nT for Kp ≥ 3+. The equatorial crossing points of midnight field lines are computed using the observed field depressions. Mapping auroral boundaries along these distorted field lines indicates that most auroral arcs map to magnetospheric locations beyond 12 RE, but that low latitude arcs may well occur on closed field lines earthward of this distance. Evidence is found confirming that a cross-tail field component in the inner magnetotail is related to the interplanetary sector structure but, contrary to earlier results, the effect is found to be larger during geomagnetically disturbed times.

[1]  C. Russell,et al.  The warped neutral sheet and plasma sheet in the near‐Earth geomagnetic tail , 1986 .

[2]  D. Fairfield.  The magnetic field of the equatorial magnetotail from 10 to 40 RE , 1986 .

[3]  David G. Sibeck,et al.  An ISEE 3 study of average and substorm conditions in the distant magnetotail , 1985 .

[4]  Y. Feldstein,et al.  The auroral luminosity structure in the high-latitude upper atmosphere: Its dynamics and relationship to the large-scale structure of the Earth's magnetosphere , 1985 .

[5]  M. Acuna,et al.  The AMPTE CCE Magnetic Field Experiment , 1985, IEEE Transactions on Geoscience and Remote Sensing.

[6]  D. Evans.  An Association Between Discrete Aurora and Energetic Particle Boundaries L. R. LYONS Space Science Laboratory, NASA Marshall Space Flight Center , 1984 .

[7]  D. Baker.  Particle and field signatures of substorms in the near magnetotail , 2013 .

[8]  J. Sauvaud,et al.  A statistical study of the dynamics of the equatorward boundary of the diffuse aurora in the pre-midnight sector , 1983 .

[9]  W. Hughes,et al.  Observation of an IMF sector effect in the Y magnetic field component at geostationary orbit , 1983 .

[10]  David T. Young,et al.  Correlations of magnetospheric ion composition with geomagnetic and solar activity , 1982 .

[11]  W. J. Burke,et al.  DMSP/F2 electron observations of equatorward auroral boundaries and their relationship to magnetospheric electric fields , 1981 .

[12]  D. Fairfield.  A statistical determination of the shape and position of the geomagnetic neutral sheet , 1980 .

[13]  E. W. Hones,et al.  Magnetic fields in flowing magnetotail plasmas and their significance for magnetic reconnection , 1979 .

[14]  E. W. Hones.  Transient phenomena in the magnetotail and their relation to substorms , 1979 .

[15]  D. Fairfield.  On the average configuraton of the geomagnetic tail , 1979 .

[16]  C. Meng,et al.  Search for the magnetic neutral line in the near‐Earth plasma sheet, 1. Critical reexamination of earlier studies on magnetic field observations , 1976 .

[17]  B. Thomas,et al.  HEOS Observations of the Configuration of the Magnetosphere , 1975 .

[18]  M. Sugiura,et al.  A magnetospheric field model incorporating the OGO 3 and 5 magnetic field observations , 1973 .

[19]  A. Nishida,et al.  Synoptic survey for the neutral line in the magnetotail during the substorm expansion phase , 1973 .

[20]  M. Sugiura.  Equatorial current sheet in the magnetosphere , 1972 .

[21]  T. Skillman,et al.  Magnetospheric‐field distortions observed by Ogo 3 and 5 , 1971 .

[22]  D. Fairfield.  Average magnetic field configuration of the outer magnetosphere. , 1968 .

[23]  G. Starkov,et al.  CHANGE IN THE BOUNDARIES OF THE OVAL AURORAL ZONE. , 1967 .

[24]  E. W. Hones,et al.  Characteristics of the plasma sheet in the Earth's magnetotail , 1967 .