Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsm23b1692r&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SM23B-1692
Physics
2700 Magnetospheric Physics (6939), 2740 Magnetospheric Configuration And Dynamics, 2744 Magnetotail, 2760 Plasma Convection (2463), 2764 Plasma Sheet
Scientific paper
Magnetic field variations with amplitudes of 15 - 30 nT and a time scales of one to several tens of minutes frequently observed in the magnetotail plasma sheet are historically referred to as "flapping" motion of the magnetotail current sheet. Flapping can be either a response to variations of solar wind/IMF parameters or due to internal dynamics of the magnetotail plasma sheet. Relations of flapping to modes of the magnetospheric activity, such as substorms and BBFs, are discussed. THEMIS gives a possibility to track flapping waves on wide range of the geocentric distances in the equatorial magnetosphere with simultaneous monitoring of magnetic and auroral activities by GBOs. We study a sequence of magnetic field oscillations with amplitudes up to 30 nT and a time scales of 10-30 min, detected by four of the five THEMIS spacecraft. The probes P1 and P2 were at X=-15.2 and -12.7 RE, P3 and P4 were at X=-7.9 RE. All four probes were at -6.5>Y>-7.5 RE (major conjunction). Multi-point timing analysis of the magnetic field variations shows that fronts of the oscillations propagated flankward, quasi-perpendicular to the direction of the magnetic maximum variation at velocities of 20 - 30 km/s. The observed anti-correlation between ∂ Bx/∂ t and the Z-component of the bulk velocity make possible to estimate flapping amplitude to be of 1 to 3 RE. A cross-tail wave-length was found to be of about 5 RE Thus the flapping waves are narrow, steep, tail-aligned structures with the lengthwise scale >10 RE, i.e., flapping is a global mode of the energy transfer in the magnetotail. The vortex-like plasma motion, observed during flapping, indicates that the flapping waves were propagating through the ambient plasma. An IMF disturbance was detected by ACE, WIND and Geotail just prior to flapping. Observations of the magnetic field variations by ground-based magnetometers show that the flapping oscillations were observed during the growth phase of a substorm.
Angelopoulos Vassilis
Auster Uli
Glassmeier K.-
Larson David
Mann Ian
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