Global properties of magnetotail current sheet flapping: THEMIS perspectives
A sequence of magnetic field oscillations with an amplitude of up to 30 nT and a time scale of 30 min was detected by four of the five THEMIS spacecraft in the magnetotail plasma sheet. The probes P1 and P2 were at <I>X</I>=−15.2 and −12.7 <I>R<sub>E<...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2009-01-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/27/319/2009/angeo-27-319-2009.pdf |
| Summary: | A sequence of magnetic field oscillations with an amplitude of up to 30 nT
and a time scale of 30 min was detected by four of the five THEMIS spacecraft
in the magnetotail plasma sheet. The probes P1 and P2 were at <I>X</I>=−15.2 and
−12.7 <I>R<sub>E</sub></I> and P3 and P4 were at <I>X</I>=−7.9 <I>R<sub>E</sub></I>. All four probes were at
−6.5><I>Y</I>>−7.5 <I>R<sub>E</sub></I> (major conjunction). Multi-point timing analysis of the
magnetic field variations shows that fronts of the oscillations propagated
flankward (dawnward and Earthward) nearly perpendicular to the direction of
the magnetic maximum variation (<I>B</I><sub>1</sub>) at velocities of 20–30 km/s. These
are typical characteristics of current sheet flapping motion. The observed
anti-correlation between ∂<I>B</I><sub>1</sub>/∂<I>t</I> and the Z-component of
the bulk velocity make it possible to estimate a flapping amplitude of 1 to
3 <I>R<sub>E</sub></I>. The cross-tail scale wave-length was found to be about 5 <I>R<sub>E</sub></I>.
Thus the flapping waves are steep tail-aligned structures with a lengthwise
scale of >10 <I>R<sub>E</sub></I>. The intermittent plasma motion with the cross-tail
velocity component changing its sign, observed during flapping, indicates
that the flapping waves were propagating through the ambient plasma.
Simultaneous observations of the magnetic field variations by THEMIS
ground-based magnetometers show that the flapping oscillations were observed
during the growth phase of a substorm. |
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| ISSN: | 0992-7689 1432-0576 |