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| Titel |
Coordinated Cluster and ground-based instrument observations of transient changes in the magnetopause boundary layer during an interval of predominantly northward IMF: relation to reconnection pulses and FTE signatures |
| VerfasserIn |
M. Lockwood, A. Fazakerley, H. Opgenoorth, J. Moen, A. P. Eyken, M. Dunlop, J.-M. Bosqued, G. Lu, C. Cully, P. Eglitis, I. W. McCrea, M. A. Hapgood, M. N. Wild, R. Stamper, W. Denig, M. Taylor, J. A. Wild, G. Provan, O. Amm, K. Kauristie, T. Pulkkinen, A. Strømme, P. Prikryl, F. Pitout, A. Balogh, H. Rème, R. Behlke, T. Hansen, R. Greenwald, H. Frey, S. K. Morley, D. Alcaydé, P.-L. Blelly, E. Donovan, M. Engebretson, Mark Lester, J. Watermann, M. F. Marcucci |
| 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 ; 19, no. 10/12 ; Nr. 19, no. 10/12, S.1613-1640 |
| Datensatznummer |
250014138
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| Publikation (Nr.) |
 copernicus.org/angeo-19-1613-2001.pdf |
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| Zusammenfassung |
We study a series of
transient entries into the low-latitude boundary layer (LLBL) of all four
Cluster spacecraft during an outbound pass through the mid-afternoon
magnetopause ( [ XGSM, YGSM, ZGSM ] ≈ [ 2, 7, 9 ] RE).
The events take place during an interval of northward IMF, as seen in the data
from the ACE satellite and lagged by a propagation delay of 75 min that is
welldefined by two separate studies: (1) the magnetospheric variations prior to
the northward turning (Lockwood et al., 2001, this issue) and (2) the field
clock angle seen by Cluster after it had emerged into the magnetosheath (Opgenoorth
et al., 2001, this issue). With an additional lag of 16.5 min, the transient
LLBL events correlate well with swings of the IMF clock angle (in GSM) to near
90°. Most of this additional lag is explained by ground-based observations,
which reveal signatures of transient reconnection in the pre-noon sector that
then take 10–15 min to propagate eastward to 15 MLT, where they are observed
by Cluster. The eastward phase speed of these signatures agrees very well with
the motion deduced by the cross-correlation of the signatures seen on the four
Cluster spacecraft. The evidence that these events are reconnection pulses
includes: transient erosion of the noon 630 nm (cusp/cleft) aurora to lower
latitudes; transient and travelling enhancements of the flow into the polar
cap, imaged by the AMIE technique; and poleward-moving events moving into the
polar cap, seen by the EISCAT Svalbard Radar (ESR). A pass of the DMSP-F15
satellite reveals that the open field lines near noon have been opened for some
time: the more recently opened field lines were found closer to dusk where the
flow transient and the poleward-moving event intersected the satellite pass.
The events at Cluster have ion and electron characteristics predicted and
observed by Lockwood and Hapgood (1998) for a Flux Transfer Event (FTE), with
allowance for magnetospheric ion reflection at Alfvénic disturbances in the
magnetopause reconnection layer. Like FTEs, the events are about 1 RE
in their direction of motion and show a rise in the magnetic field
strength, but unlike FTEs, in general, they show no pressure excess in their
core and hence, no characteristic bipolar signature in the boundary-normal
component. However, most of the events were observed when the magnetic field
was southward, i.e. on the edge of the interior magnetic cusp, or when the
field was parallel to the magnetic equatorial plane. Only when the satellite
begins to emerge from the exterior boundary (when the field was northward), do
the events start to show a pressure excess in their core and the consequent
bipolar signature. We identify the events as the first observations of FTEs at
middle altitudes.
Key words. Magnetospheric physics
(magnetopause, cusp and boundary layers; magnetosphere-ionosphere interactions;
solar wind-magnetosphere interactions) |
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