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| Titel |
Magnetic Flux Transport and Pressure Variations at Magnetotail Plasma Flow Bursts during Geomagnetically Quiet Times |
| VerfasserIn |
M. Nowada, S.-Y. Fu, G. K. Parks, Z.-Y. Pu, V. Angelopoulos, C. W. Carlson, H.-U. Auster |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250060018
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| Zusammenfassung |
| The fast plasma flows in the geomagnetotail are observed during both geomagnetically active
and quiet times. However, it has been unclear about the fundamental difference in the plasma
fast flows between at two different geomagnetic conditions, that is, the generation mechanism
of, and pictures of the energy transport and balance at the fast plasma flows. Magnetic
reconnection in the magnetotail has been believed as one of the most possible mechanisms to
generate the fast plasma flows regardless of the geomagnetic conditions. Recently,
Nowada et al. [2012], however, demonstrated that the magnetotail magnetic reconnection
does not always contribute to the generation of the fast plasma flows at geomagnetically
quiet times based on the THEMIS measurements. It is very important to reveal
how the energy transport and balance in the magnetotail in association with these
plasma fast flows are on obtaining a clue to elucidate an essential difference in
the plasma fast flows between during active and quiet geomagnetic conditions.
Based on three events of the magnetotail plasma flow bursts, which are transient fast
plasma flows with the durations between 1 and 2 minutes, during geomagnetically
quiet times, observed by THEMIS, we examined detailed variations of the electric
field as a proxy of the flux transport aspect, and associated pressure. The main
characteristics of these events are shown as follows; 1) the GSM-X component of the
plasma velocity (Vx) was higher than 300 km/s 2) associated parallel (V--) and
perpendicular (V-¥) velocities to the local magnetic field line were higher than 200 km/s
3) the flow bursts were observed during which AL and AU indices were lower
than 40 nT, and simultaneous Kp index range was between -1 and 1. For almost
events, the parallel (E--) and perpendicular (E-¥) components of the electric field to
the local magnetic field line were much stronger than the dawn-dusk electric field
component (Ey). This result implies that a larger amount of the magnetic flux was
transported into the parallel and perpendicular directions to the local magnetic field line
than the dawn-dusk direction at the flow bursts. However, in the Ey component,
the contribution from the dawn-to-dusk electric field (VxBz) was much greater
than that from the dusk-to-dawn component (VzBx). Furthermore, for two events,
significant reduction of the plasma pressure, and enhancement of the north-south
magnetic field component (Bz) were observed at/near the flow bursts. Simultaneous
total pressure was well-balanced, indicating that the magnetotail during the plasma
flow bursts was in the state of equilibrium. Based on these results, “bubble” might
play a crucial role for generating the plasma flow bursts at geomagnetically quiet
times.
Reference:
Nowada, M., S. -Y. Fu, G. K. Parks, Z. -Y. Pu, V. Angelopoulos, C. W. Carlson, H. -U.
Auster (2012), Plasma flow bursts in the magnetotail during geomagnetically quiet
times 2: Relation to the magnetic reconnection and substorm process, to be submitted
to Journal of Geophysical Research -Space Physics-.
Corresponding Author : Motoharu Nowada (nowada@pku.edu.cn) |
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