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| Titel |
Dynamical behavior of U-shaped double layers: cavity formation and filamentary structures |
| VerfasserIn |
N. Singh, C. Deverapalli, A. Rajagiri, I. Khazanov |
| 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 ; 12, no. 6 ; Nr. 12, no. 6 (2005-08-09), S.783-798 |
| Datensatznummer |
250010886
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| Publikation (Nr.) |
 copernicus.org/npg-12-783-2005.pdf |
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| Zusammenfassung |
Observations from the Polar and FAST satellites have revealed a host of
intriguing features of the auroral accelerations processes in the upward current region (UCR). These features include: (i)
large-amplitude parallel (
 ) and perpendicular ( )
fluctuating as well as quasi-static electric fields in density cavities,
(ii) fairly large-amplitude unipolar parallel electric fields like in a
strong double layer (DL), (iii) variety of wave modes,
(iv) counter-streaming of upward going ion beams and downward accelerated
electrons, (v) horizontally corrugated bottom region of the potential
structures (PS), in which electron and ion accelerations occur,
(vi) filamentary ion beams in the corrugated PS, and (vii) both upward and
downward moving narrow regions of parallel electric fields, inferred from
the frequency drifts of the auroral kilometric radiations. Numerical
simulations of U-shaped potential structures reveal that such observed
features of the UCR are integral parts of dynamically evolving auroral
U-shaped potential structures. Using a 2.5-D particle-in-cell (PIC) code we
simulate a U-shaped broad potentialstructure (USBPS). The dynamical behavior revealed by
the simulation includes: (i) recurring redistribution of the parallel
potential drop (PPD) in the PS, (ii) its up and downward
motion, (iii) formation of filaments in the potential and density
structures, and (iv) creation of filamentary as well as broad extended
density cavities. The formation of the filamentary structures is initiated
by an ion-beam driven instability of an oblique ion mode trapped inside a
broad cavity, when it becomes sufficiently thin in height. The filaments of
the PS create filamentary electron beams, which generate waves at
frequencies above the lower hybrid frequency, affecting plasma heating. This
results in plasma evacuation and formation of a cavity extended in height.
The waves associated with filamentary electron beams also evolve into
electron holes. The transverse and parallel scale lengths of the regions
with large
and as well as their magnitudes
are compared with satellite data. |
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