Premium
Relation of substorm pre‐onset arc to large‐scale field‐aligned current distribution
Author(s) -
Nishimura Y.,
Lyons L. R.,
Kikuchi T.,
Angelopoulos V.,
Donovan E. F.,
Mende S. B.,
Lühr H.
Publication year - 2012
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2012gl053761
Subject(s) - substorm , arc (geometry) , geology , geophysics , physics , magnetic field , magnetosphere , geometry , mathematics , quantum mechanics
Substorm auroral onset often occurs along a pre‐existing arc that is associated with an enhanced upward field‐aligned current (FAC). To determine the location of the upward FAC of the pre‐onset arc relative to the large‐scale region 1 (R1) and 2 (R2) FACs, we present coordinated observations of the THEMIS all‐sky imagers and CHAMP satellite, where CHAMP passed over relatively stable, pre‐onset arcs within the 30 min period before substorm auroral onset. We found that the upward FAC corresponding to the pre‐onset arc is latitudinally separated from the upward R1 FAC within the onset MLT range. In contrast, the arc is located near the R1‐R2 boundary to the west and east of the onset MLT range. This MLT dependence suggests that an east‐west oriented upward FAC sheet forms within the downward R2 FAC as a precursor FAC signature for substorm auroral onset.