On the ionospheric coupling of auroral electric fields
2009 (English)In: Nonlinear processes in geophysics, ISSN 1023-5809, E-ISSN 1607-7946, Vol. 16, no 2, 365-372 p.Article in journal (Refereed) Published
The quasi-static coupling of high-altitude potential structures and electric fields to the ionosphere is discussed with particular focus on the downward field-aligned current (FAC) region. Results are presented from a preliminary analysis of a selection of electric field events observed by Cluster above the acceleration region. The degree of coupling is here estimated as the ratio between the magnetic field-aligned potential drop,Delta Phi(II), as inferred from the characteristic energy of upward ion (electron) beams for the upward (downward) current region and the high-altitude perpendicular (to B) potential, Delta Phi(perpendicular to), as calculated by integrating the perpendicular electric field across the structure. For upward currents, the coupling can be expressed analytically, using the linear current-voltage relation, as outlined by Weimer et al. (1985). This gives a scale size dependent coupling where structures are coupled (decoupled) above (below) a critical scale size. For downward currents, the current-voltage relation is highly non-linear which complicates the understanding of how the coupling works. Results from this experimental study indicate that small-scale structures are decoupled, similar to small-scale structures in the upward current region. There are, however, exceptions to this rule as illustrated by Cluster results of small-scale intense electric fields, correlated with downward currents, indicating a perfect coupling between the ionosphere and Cluster altitude.
Place, publisher, year, edition, pages
2009. Vol. 16, no 2, 365-372 p.
return current region, temporal evolution, black aurora, cluster, satellite, acceleration, zone
IdentifiersURN: urn:nbn:se:kth:diva-18381ISI: 000265743500019ScopusID: 2-s2.0-77949445383OAI: oai:DiVA.org:kth-18381DiVA: diva2:336427
QC 201005252010-08-052010-08-05Bibliographically approved