 |
| Titel |
ESR and EISCAT observations of the response of the cusp and cleft to IMF orientation changes |
| VerfasserIn |
I. W. McCrea, M. Lockwood, J. Moen, F. Pitout, P. Eglitis, A. D. Aylward, J.-C. Cerisier, A. Thorolfssen, S. E. Milan |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
0992-7689
|
| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 18, no. 9 ; Nr. 18, no. 9, S.1009-1026 |
| Datensatznummer |
250014053
|
| Publikation (Nr.) |
 copernicus.org/angeo-18-1009-2000.pdf |
|
|
|
|
|
| Zusammenfassung |
We report observations of the cusp/cleft
ionosphere made on December 16th 1998 by the EISCAT (European incoherent
scatter) VHF radar at Tromsø and the EISCAT Svalbard radar (ESR). We compare
them with observations of the dayside auroral luminosity, as seen by meridian
scanning photometers at Ny Ålesund and of HF radar backscatter, as observed by
the CUTLASS radar. We study the response to an interval of about one hour when
the interplanetary magnetic field (IMF), monitored by the WIND and ACE
spacecraft, was southward. The cusp/cleft aurora is shown to correspond to a
spatially extended region of elevated electron temperatures in the VHF radar
data. Initial conditions were characterised by a northward-directed IMF and
cusp/cleft aurora poleward of the ESR. A strong southward turning then occurred,
causing an equatorward motion of the cusp/cleft aurora. Within the equatorward
expanding, southward-IMF cusp/cleft, the ESR observed structured and elevated
plasma densities and ion and electron temperatures. Cleft ion fountain upflows
were seen in association with elevated ion temperatures and rapid eastward
convection, consistent with the magnetic curvature force on newly opened field
lines for the observed negative IMF By. Subsequently, the ESR
beam remained immediately poleward of the main cusp/cleft and a sequence of
poleward-moving auroral transients passed over it. After the last of these, the
ESR was in the polar cap and the radar observations were characterised by
extremely low ionospheric densities and downward field-aligned flows. The IMF
then turned northward again and the auroral oval contracted such that the ESR
moved back into the cusp/cleft region. For the poleward-retreating, northward-IMF
cusp/cleft, the convection flows were slower, upflows were weaker and the
electron density and temperature enhancements were less structured. Following
the northward turning, the bands of high electron temperature and cusp/cleft
aurora bifurcated, consistent with both subsolar and lobe reconnection taking
place simultaneously. The present paper describes the large-scale behaviour of
the ionosphere during this interval, as observed by a powerful combination of
instruments. Two companion papers, by Lockwood et al. (2000) and
Thorolfsson et al. (2000), both in this issue, describe the detailed
behaviour of the poleward-moving transients observed during the interval of
southward Bz, and explain their morphology in the context of
previous theoretical work.
Key words: Ionosphere (ionosphere - magnetosphere
interactions; auroral ionosphere; plasma temperature and density) |
| |
|
| Teil von |
|
|
|
|
|
|
|
|