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| Titel |
Experimental study of nonlinear interaction of plasma flow with charged thin current sheets: 2. Hall dynamics, mass and momentum transfer |
| VerfasserIn |
S. Savin, E. Amata, M. André, M. Dunlop, Y. Khotyaintsev, P. M. E. Décréau, J. L. Rauch, J. G. Trotignon, J. Buechner, B. Nikutowski, J. Blecki, A. Skalsky, S. Romanov, L. Zelenyi, A. M. Buckley, T. D. Carozzi, M. P. Gough, P. Song, H. Rème, A. Volosevich, H. Alleyne, E. Panov |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 13, no. 4 ; Nr. 13, no. 4 (2006-08-10), S.377-392 |
| Datensatznummer |
250011807
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| Publikation (Nr.) |
 copernicus.org/npg-13-377-2006.pdf |
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| Zusammenfassung |
| Proceeding with the analysis of Amata et al. (2005), we suggest that the
general feature for the local transport at a thin magnetopause (MP) consists
of the penetration of ions from the magnetosheath with gyroradius larger
than the MP width, and that, in crossing it, the transverse potential
difference at the thin current sheet (TCS) is acquired by these ions,
providing a field-particle energy exchange without parallel electric fields.
It is suggested that a part of the surface charge is self-consistently
produced by deflection of ions in the course of inertial drift in the
non-uniform electric field at MP.
Consideration of the partial moments of ions with different energies
demonstrates that the protons having gyroradii of roughly the same size or
larger than the MP width carry fluxes normal to MP that are about 20% of
the total flow in the plasma jet under MP. This is close to the excess of
the ion transverse velocity over the cross-field drift speed in the plasma
flow just inside MP (Amata et al., 2005), which conforms to the contribution
of the finite-gyroradius inflow across MP. A linkage through the TCS between
different plasmas results from the momentum conservation of the
higher-energy ions. If the finite-gyroradius penetration occurs along the MP
over ~1.5 RE from the observation site, then it can completely
account for the formation of the jet under the MP. To provide the downstream
acceleration of the flow near the MP via the cross-field drift, the weak
magnetic field is suggested to rotate from its nearly parallel direction to
the unperturbed flow toward being almost perpendicular to the accelerated
flow near the MP.
We discuss a deceleration of the higher-energy ions in the MP normal
direction due to the interaction with finite-scale electric field bursts in
the magnetosheath flow frame, equivalent to collisions, providing a charge
separation. These effective collisions, with a nonlinear frequency proxy of
the order of the proton cyclotron one, in extended turbulent zones are a
promising alternative in place of the usual parallel electric fields invoked
in the macro-reconnection scenarios. Further cascading towards electron
scales is supposed to be due to unstable parallel electron currents, which
neutralize the potential differences, either resulted from the ion- burst
interactions or from the inertial drift.
The complicated MP shape suggests its systematic velocity departure from the
local normal towards the average one, inferring domination for the MP
movement of the non-local processes over the small-scale local ones.
The measured Poynting vector indicates energy transmission from the MP into
the upstream region with the waves triggering impulsive downstream flows,
providing an input into the local flow balance and the outward movement of
the MP.
Equating the transverse electric field inside the MP TCS by the Hall term in
the Ohm's law implies a separation of the different plasmas primarily by the
Hall current, driven by the respective part of the TCS surface charge. The
Hall dynamics of TCS can operate either without or as a part of a
macro-reconnection with the magnetic field annihilation. |
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