Temporal evolution of the electric field accelerating electrons away from the auroral ionosphere
2001 (English)In: Nature, ISSN 0028-0836, Vol. 414, no 6865, 724-727 p.Article in journal (Refereed) Published
The bright night-time aurorae that are visible to the unaided eye are caused by electrons accelerated towards Earth by an upward-pointing electric field(1-3). On adjacent geomagnetic field lines the reverse process occurs: a downward-pointing electric field accelerates electrons away from Earth(4-11). Such magnetic-field-aligned electric fields in the collisionless plasma above the auroral ionosphere have been predicted(12), but how they could be maintained is still a matter for debate(13). The spatial and temporal behaviour of the electric fields-a knowledge of which is crucial to an understanding of their nature-cannot be resolved uniquely by single satellite measurements. Here we report on the first observations by a formation of identically instrumented satellites crossing a beam of upward-accelerated electrons. The structure of the electric potential accelerating the beam grew in magnitude and width for about 200 s, accompanied by a widening of the downward-current sheet, with the total current remaining constant. The 200-s timescale suggests that the evacuation of the electrons from the ionosphere contributes to the formation of the downward-pointing magnetic-field-aligned electric fields. This evolution implies a growing load in the downward leg of the current circuit, which may affect the visible discrete aurorae.
Place, publisher, year, edition, pages
2001. Vol. 414, no 6865, 724-727 p.
electrostatic potentials, current region, black aurora, altitude
IdentifiersURN: urn:nbn:se:kth:diva-21169DOI: 10.1038/414724aISI: 000172676200040OAI: oai:DiVA.org:kth-21169DiVA: diva2:339866
QC 201005252010-08-102010-08-10Bibliographically approved