Evolution in space and time of the quasi-static acceleration potential of inverted-V aurora and its interaction with Alfvenic boundary processes
2011 (English)In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 116, A00K13- p.Article in journal (Refereed) Published
Results are presented from Cluster crossings of the acceleration region of two inverted-V auroras located in the poleward part of an extensive substorm bulge. The particle and field data are used to infer the acceleration potentials of the arcs and their distribution in altitude and latitude. The C1 data are consistent with a symmetric potential pattern, composed of two negative U potentials and one positive U potential in between, and the C3 and C4 data are consistent with an asymmetric pattern, where the dominating potential structure extends deep into the polar cap boundary (PCB) region. The two patterns may either correspond to different stages of evolution of the same double arc system or represent two longitudinally separated double arc systems. For all spacecraft, the potential well of the poleward arc extends into the PCB region, whereas the density cavity does not but remains confined to R1. This suggests that the Alfvenic activity observed within the PCB region prevents the cavity formation, consistent with the associated FACs being roughly balanced over this region. The results show that Alfvenic and quasi-static acceleration operates jointly in the PCB region, varying from being about equally important (on C1) to being predominantly quasi-static (on C3/C4). The presence (absence) of an upward electron beam, associated with a positive potential structure and a downward current, observed by C1 (C4/C3) is expected from its short life time, shorter than the time lag between the Cluster spacecraft. The evolution involves both a broadening and a density reduction of the associated downward current sheet to below the critical current density above which parallel electric fields will form. The deepest potential well of 13 kV observed by C4 was located in Region 1, adjacent to the PCB region and coinciding with the deepest density cavity, with a minimum density of 0.1 cm(-3). The interface between Region 1 and the PCB region, coinciding with the steep density gradient, appears to be the leading edge of the cavity.
Place, publisher, year, edition, pages
2011. Vol. 116, A00K13- p.
PARALLEL ELECTRIC-FIELDS, PARTICLE-ACCELERATION, CURRENT REGION, DOUBLE-LAYERS, BLACK AURORA, MAGNETOSPHERE, IONOSPHERE, PLASMA
Astronomy, Astrophysics and Cosmology
IdentifiersURN: urn:nbn:se:kth:diva-41293DOI: 10.1029/2011JA016537ISI: 000294622600001ScopusID: 2-s2.0-80052537367OAI: oai:DiVA.org:kth-41293DiVA: diva2:444327
QC 201109282011-09-282011-09-262012-11-05Bibliographically approved