Electric current and magnetic field geometry in flapping magnetotail current sheets
Using four-point magnetic field measurements by the Cluster spacecraft, we statistically analyze the magnetic field and electric current configurations during rapid crossings of the current sheet observed in July-October 2001 at geocentric distances of 19 <i>R<sub>E</sub></i...
| Main Authors: | , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2005-06-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/23/1391/2005/angeo-23-1391-2005.pdf |
| Summary: | Using four-point magnetic field measurements by the Cluster
spacecraft, we statistically analyze the magnetic field and
electric current configurations during rapid crossings of the
current sheet observed in July-October 2001 at geocentric
distances of 19 <i>R<sub>E</sub></i>.
The database includes 78 crossings, specially selected to
apply multi-point data analysis techniques to calculate
vector derivatives.
Observed bipolar variations of <i>j<sub>z</sub></i>, often with | <i>j<sub>z</sub></i> |><i>j<sub>y</sub></i>,
indicate that the
electric currents follow kinks of the current sheet. The current
density varies between 5-25nA/m<sup>2</sup>. The half-thickness
of the current sheet during flapping varies over a wide range,
from 1 to 20 ion thermal gyroradii (<i>L<sub>cp</sub></i>), calculated
from average temperature and lobe magnetic field for each
crossing). We found no relationship between the tilt angle of the
current sheet normal and the half-thickness. In 68 cases the
magnetic field curvature vector has a positive (earthward)
<i>X</i>-component. Ten cases with a negative (tailward) curvature,
associated with reconnection, were detected within
0<<i>Y<sub>GSM</sub></i><7 <i>R<sub>E</sub></i>.
The minimum curvature radii vary mainly between 1 and
10 <i>L<sub>cp</sub></i>, and the adiabaticity parameter κ≤1 for 73% of the
events. The electric current density
during flapping is often off-central, i.e. the main current
density is shifted from the neutral sheet (| <i>B<sub>x</sub></i> |<5nT) to
the Northern or Southern Hemisphere. This is most likely a
temporal effect related to the flapping.
The analysis shows that the flapping motion of the current
sheet is associated with kink-like waves on the sheet
surface. The kink fronts, tilted in the <i>Y-Z</i>
plane, moved toward dawn in the morning half and toward dusk
in the evening half of the magnetotail. |
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| ISSN: | 0992-7689 1432-0576 |