Temporal evolution of the electric field accelerating electrons away from the auroral ionosphere

Citation
Gt. Marklund et al., Temporal evolution of the electric field accelerating electrons away from the auroral ionosphere, NATURE, 414(6865), 2001, pp. 724-727
Citations number
24
Categorie Soggetti
Multidisciplinary,Multidisciplinary,Multidisciplinary
Journal title
NATURE
ISSN journal
00280836 → ACNP
Volume
414
Issue
6865
Year of publication
2001
Pages
724 - 727
Database
ISI
SICI code
0028-0836(200112)414:6865<724:TEOTEF>2.0.ZU;2-3
Abstract
The bright night-time aurorae that are visible to the unaided eye are cause d by electrons accelerated towards Earth by an upward-pointing electric fie ld(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 beha viour of the electric fields-a knowledge of which is crucial to an understa nding of their nature-cannot be resolved uniquely by single satellite measu rements. Here we report on the first observations by a formation of identic ally instrumented satellites crossing a beam of upward-accelerated electron s. The structure of the electric potential accelerating the beam grew in ma gnitude and width for about 200 s, accompanied by a widening of the downwar d-current sheet, with the total current remaining constant. The 200-s times cale suggests that the evacuation of the electrons from the ionosphere cont ributes to the formation of the downward-pointing magnetic-field-aligned el ectric fields. This evolution implies a growing load in the downward leg of the current circuit, which may affect the visible discrete aurorae.