Creation of Theta-Auroras: The Isolation of Plasma Sheet Fragments in the Polar Cap

Science  24 Nov 1995:
Vol. 270, Issue 5240, pp. 1338-1341
DOI: 10.1126/science.270.5240.1338


The auroral oval is a ring of luminosity enclosing geomagnetic field lines connected to the solar wind. Occasionally the ring has a bar across it, which seems to imply a bifurcation of the open region. Here results confirm that this “θ-aurora” actually does represent this odd bifurcated configuration, and they demonstrate how it happens. It has hitherto been assumed that θ-auroras occur when the interplanetary magnetic field is directed northward, because that is true of most very-high-latitude arcs. In fact, θ-auroras occur exclusively during the dynamic reconfiguration that follows when the interplanetary magnetic field turns southward after a prolonged northward interval.