dot
Detailansicht
Katalogkarte GBA
Katalogkarte ISBD
Suche präzisieren
Drucken
Download RIS
Hier klicken, um den Treffer aus der Auswahl zu entfernen
Titel Separating spatial and temporal variations in auroral electric and magnetic fields by Cluster multipoint measurements
VerfasserIn T. Karlsson, G. T. Marklund, S. Figueiredo, T. Johansson, S. Buchert
Medientyp Artikel
Sprache Englisch
ISSN 0992-7689
Digitales Dokument URL
Erschienen In: Annales Geophysicae ; 22, no. 7 ; Nr. 22, no. 7 (2004-07-14), S.2463-2472
Datensatznummer 250014935
Publikation (Nr.) Volltext-Dokument vorhandencopernicus.org/angeo-22-2463-2004.pdf
 
Zusammenfassung
Cluster multipoint measurements of the electric and magnetic fields from a crossing of auroral field lines at an altitude of 4RE are used to show that it is possible to resolve the ambiguity of temporal versus spatial variations in the fields. We show that the largest electric fields (of the order of 300mV/m when mapped down to the ionosphere) are of a quasi-static nature, unipolar, associated with upward electron beams, stable on a time scale of at least half a minute, and located in two regions of downward current. We conclude that they are the high-altitude analogues of the intense return current/black auroral electric field structures observed at lower altitudes by Freja and FAST. In between these structures there are temporal fluctuations, which are shown to likely be downward travelling Alfvén waves. The periods of these waves are 20-40s, which is not consistent with periods associated with either the Alfvénic ionospheric resonator, typical field line resonances or substorm onset related Pi2 oscillations. The multipoint measurements enable us to estimate a lower limit to the perpendicular wavelength of the Alfvén waves to be of the order of 120km, which suggests that the perpendicular wavelength is similar to the dimension of the region between the two quasi-static structures. This might indicate that the Alfvén waves are ducted within a wave guide, where the quasi-static structures are associated with the gradients making up this waveguide.
 
Teil von