Simultaneous closed magnetic field line polar arcs and substorms

Details Simultaneous closed magnetic field line polar arcs and substorms Simultaneous closed magnetic field line polar arcs and substorms

May 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001jastp..63..643w&link_type=abstract

Journal of Atmospheric and Solar-Terrestrial Physics, Volume 63, Issue 7, p. 643-655.

Physics

1

Scientific paper

Viking UV images of the northern hemisphere auroral region were examined during simultaneous substorms and polar arcs. Of 120 substorm events, 43 recorded polar arcs. In all events the substorm and polar arc were identified with the images, and a strict definition of the term polar arc has been applied to rigorously eliminate any ambiguous cases from this study. In addition, simultaneous events of substorms and polar arcs were separated into four cases: dawnside polar arcs before substorm onset, dawnside polar arcs after onset, duskside polar arcs before onset, and duskside polar arcs after onset. Superposition epoch plots of the average polar arc intensity over time with respect to substorm onset were created. Overall, these plots suggest a weak coupling between the polar arc and the substorm mechanisms. In most of the simultaneous cases, little or no motion of the polar arc was measured. This observation, combined with the various intensity minimum determined in the superposition epoch plots, suggests little or no change occurs in the thickness of the plasma sheet as many substorm models predict. Furthermore, magnetic field line mapping frequently indicates magnetic field lines of polar arcs stretch far down the magnetotail (i.e., greater than 50 Earth Radii), while substorms appear to be located within 20 Re. This concept, combined with the theory that the interaction between the polar arcs and substorms is weak, suggests that substorms cannot be a distant magnetotail event, otherwise there would be a stronger interaction between the two.

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