The Relation of Polar Arcs to Magnetotail Twisting and IMF Direction

Details The Relation of Polar Arcs to Magnetotail Twisting and IMF Direction The Relation of Polar Arcs to Magnetotail Twisting and IMF Direction

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsm12a0490k&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #SM12A-0490

Physics

2704 Auroral Phenomena (2407), 2736 Magnetosphere/Ionosphere Interactions, 2753 Numerical Modeling, 2776 Polar Cap Phenomena, 2784 Solar Wind/Magnetosphere Interactions

Scientific paper

A large statistical study of polar arcs utilizing the Polar UV imager reveals a strong solar wind control of large-scale polar arcs. They occur preferably for a high solar wind energy flux during northward IMF. Different types of polar arcs are triggered by different IMF clock angle changes. Oval-aligned arcs appear often during constant IMF, moving transpolar arcs usually develop after an IMF By sign change. The relation of these two polar arc types to changes in the magnetotail topology are investigated with help of the GUMICS-4 MHD code by Janhunen. The simulations show that for northward IMF with a nonzero IMF By component the magnetotail becomes long and highly twisted at its tailward end. The closed field line region reaches in this case high into the near-Earth tail lobes and poleward of the average polar cap boundary. The poleward displaced part of the polar cap boundary is a probable location for polar arcs to occur. In the case of an IMF By sign change the tail twist rotates such that in an intermediate state near-Earth and far-tail regions are oppositely twisted. This causes a bifurcation of the closed field line region in the tail and a bridge of closed field lines in the polar cap. The over the entire polar cap moving closed bridge indicates a moving transpolar arc.

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