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| Titel |
Dayside aurora and the role of IMF ∣By∣/∣Bz∣: detailed morphology and response to magnetopause reconnection |
| VerfasserIn |
P. E. Sandholt, C. J. Farrugia, W. F. Denig |
| 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 ; 22, no. 2 ; Nr. 22, no. 2 (2004-01-01), S.613-628 |
| Datensatznummer |
250014786
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| Publikation (Nr.) |
 copernicus.org/angeo-22-613-2004.pdf |
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| Zusammenfassung |
We document the detailed spatio-temporal structure of the dayside aurora
during intervals of ongoing dayside magnetopause
reconnection, primarily during interplanetary magnetic field
(IMF) Bz≤0 conditions.
The present study is based on ground
auroral observations in combination with particle precipitation data from
a DMSP spacecraft. We describe auroral forms corresponding to
the following particle precipitation
regimes identified by Newell and Meng (1994):
(i) central plasma sheet (CPS), (ii) precipitation void, (iii) dayside
boundary plasma sheet (BPS), and (iv) cusp (LLBL/cusp/mantle).
Two distinctly different auroral configurations
are observed, corresponding to different regimes of the IMF clock
angle (θ) and the ∣By∣/∣Bz∣ ratio.
Two regimes are defined. In regime (I) θ lies within
∼ 90–135° and ∣By∣/∣Bz∣>1 (By-dominated), while in regime (II)
θ is in the range
135°–180° and ∣By∣/∣Bz∣<1 (Bz-dominated).
Within regime (I)
the auroral response to reconnection events typically
progresses from lower to higher latitudes in stages as indicated below:
(A) equatorward boundary intensifications (EBIs):
sequential brightenings of closely spaced, fragmented,
rayed bands (BPS aurora) within the ∼08:00–15:00 MLT sector,
each of which are moving
noonward/sunward, (B) poleward
moving auroral forms (PMAFs): forms expanding westward
from the postnoon side (By>0) and later appearing as a poleward
expanding form in the convection throat in the ∼09:00–12:00 MLT
sector, with a fading phase in the regime of
mantle precipitation.
During strongly southward IMF conditions (regime II),
the intense PMAF activity is
replaced by a more latitudinally restricted,
but longitudinally wide aurora of moderate intensity.
The latter auroral state is accompanied by a
2-cell convection pattern which is rather symmetrical about noon.
This state is very different from the convection/FAC configuration present
during IMF regime (I), with its strong
zonal flows (convection current), more intense FAC sheets and
PMAF activity in the midday sector.
The strong IMF regulation of the dayside BPS aurora, consisting of
keV electrons,
and its location with respect to the green line auroral
gap (precipitation void), indicate
that it is an important signature of the reconnection
process, located on open boundary layer field lines.
The observed longitudinal bifurcation of the auroral brightenings (EBIs)
preceding PMAFs is consistent with
antiparallel magnetopause reconnection.
Key words. Magnetospheric physics (auroral phenomena
magnetopause, cusp, and boundary layers: solar windmagnetosphere
interactions) – Ionosphere (particle precipitation) |
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