Localized aurora beyond the auroral oval

Harald U. Frey


Aurora generally occurs within ovals around the geomagnetic poles. Each oval is
the result of continuously flowing currents into and out of the ionosphere.
Viewed from space these ovals appear as continuous and diffuse bands of light.
In recent years space-based and ground-based auroral imaging have revealed the
existence of localized regions of aurora.  They appear as arcs, spots, or
patches and are unrelated to the auroral oval as they display different
morphological, spatial, and temporal properties.  Some of these localized
aurorae are detached from the oval poleward or equatorward of it.  Others are
located on top of the oval and are brighter than the surrounding. Many of them
occur only during preferred solar wind conditions and orientations of the
interplanetary magnetic field (IMF).  This review describes the different
localized aurorae, their particle sources, and their favorable solar wind
conditions.  Physical processes that drive their appearance will be discussed.

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Submitted to Reviews in Geophysics, 2005