 |
| Titel |
Storm-time related mass density anomalies in the polar cap as observed by CHAMP |
| VerfasserIn |
R. Liu, H. Lühr, S.-Y. Ma |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
0992-7689
|
| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 28, no. 1 ; Nr. 28, no. 1 (2010-01-19), S.165-180 |
| Datensatznummer |
250016752
|
| Publikation (Nr.) |
 copernicus.org/angeo-28-165-2010.pdf |
|
|
|
|
|
| Zusammenfassung |
| Strong and localized thermospheric mass density events are observed in the
polar cap region by the CHAMP satellites at about 400 km altitude during
geomagnetic storms. During the 4 years considered (2002–2005) 29 storms with
Dst<−100 nT occurred, in 90% of them polar cap density anomalies were
detected. Based on the altogether 56 anomaly events a statistical analysis
was performed. The anomalies are of medium scale (500–1500 km) and seem to
have a short dwell-time (<1.5 h) in the polar cap. The relative density
enhancement is found to range around 2 in both hemispheres. The peak density
is in the Northern Hemisphere by a factor of 1.4 larger than in the southern.
Also the number of detected events in the north is twice as large as that in
the south (37 vs. 19). Mass density anomalies in the polar cap occur under
all interplanetary magnetic field (IMF) directions. Numerous strong anomalies
have been detected in positive and negative IMF Bz conditions when the
magnetic field strength is above 5 nT. Rather few events occurred for small
|Bz| (<5 nT) or for positive Bz combined with vanishing By. Some
of the density anomalies are accompanied by intensive small-scale
field-aligned currents (FACs). But about as many show no relation to FACs. If
FACs are present there, the current density is believed to be correlated with
the strength of the IMF Bz. Although this paper concentrates on the
presentation of the observations, we show for one event that the ion outflow
mechanism could be responsible for the mass density anomalies in the polar
cap. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|