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Periodic auroral events at the midday polar cap boundary: Implications for solar wind‐magnetosphere coupling
Author(s) -
Sandholt P. E.,
Moen J.,
Opsvik D.
Publication year - 1992
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 - 10.1029/92gl01275
Subject(s) - geophysics , magnetopause , noon , interplanetary magnetic field , magnetosheath , magnetosphere , solar wind , physics , polar , ionosphere , geology , substorm , atmospheric sciences , magnetic field , astronomy , quantum mechanics
An interesting observed phenomenon of day‐side auroral activity is the periodic sequence of moving bright forms observed at the polar cap boundary during southward‐directed interplanetary magnetic field (IMF) conditions. The optical events reported here are elliptical‐shaped bright 630.0 nm forms of ∼ 200 km (N‐S) × 300–500 km (E‐W) spatial extent. They move eastward near the noon meridian with velocities of ∼ 1.5 km s −1 and repeat at intervals of 5–10 min. Coordinated ground and satellite observations show that these auroral forms slow down and fade out after ∼ 10 min., within the region of mantle precipitation. The present ground observations support the earlier indication that the direction of east‐west motion along the polar cap boundary at/near magnetic noon is determined by the IMF B y polarity, consistent with models of field tension on magnetic flux tubes connected with the solar wind. The optical characteristics of the events documented here may have important implications for the nature of magnetic merging at the magnetopause and the associated transfer of energy and momentum to the ionosphere in the cusp/mantle region.