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| Titel |
Polar cap convection/precipitation states during Earth passage of two ICMEs at solar minimum |
| VerfasserIn |
P. E. Sandholt, Y. Andalsvik, C. J. Farrugia |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 28, no. 4 ; Nr. 28, no. 4 (2010-04-30), S.1023-1042 |
| Datensatznummer |
250016824
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| Publikation (Nr.) |
 copernicus.org/angeo-28-1023-2010.pdf |
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| Zusammenfassung |
| We report important new aspects of
polar cap convection and precipitation
(dawn-dusk and inter-hemisphere asymmetries)
associated with the different levels of forcing of the magnetosphere
by two interplanetary (IP) magnetic clouds
on 20 November 2007 and 17 December 2008
during solar minimum.
Focus is placed on two intervals of
southward magnetic cloud field with large negative By
components (Bx=−5 versus 0 nT) and with
high and low plasma densities, respectively, as
detected by
spacecraft Wind.
The convection/precipitation states are
documented by DMSP spacecraft (Southern Hemisphere)
and SuperDARN radars (Northern Hemisphere).
The (negative) By component of the cloud field is accompanied by a
newly-discovered flow channel (called here FC 2)
threaded by old open field lines
(in polar rain precipitation)
at the dusk and dawn
sides of the polar cap in the Northern and
Southern Hemispheres, respectively,
and a corresponding
Svalgaard-Mansurov (S-M) effect in ground
magnetic deflections. On 20 November 2007 the
latter S-M effect in the Northern winter
Hemisphere appears in the form of
a sequence
of six 5–10 min long magnetic deflection events in the
71–74° MLAT/14:30–16:00 MLT sector.
The X-deflections are consistent with
the flow direction in FC 2 (i.e. caused by Hall currents)
in both IP cloud cases.
The presence of a lobe cell and associated polar arcs
in the Southern (summer) Hemisphere in the low density
(1–2 cm−3) and Bx=0 ICME case
is accompanied by the dropout
of polar rain precipitation in the dusk-side regime of
sunward polar cap convection and inward-directed Birkeland current.
The low-altitude observations are discussed in
terms of momentum transfer via dynamo processes in the high- and low-latitude
boundary layers
and Birkeland currents located poleward of the traditional
R1-R2 system. |
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