Dayside reconnection under IMF By-dominated conditions: the formation and movement of bending arcs

J. A. Carter (1), S. E. Milan (1), R. C. Fear (1,2), A. Kullen (3), and M. R. Hairston (4)

(1) Department of Physics and Astronomy, University of Leicester, Leicester, U.K.
(2) Now at: School of Physics and Astronomy, University of Southampton, Southampton, U.K.
(3) Department of space and Plasma Physics, KTH Royal Institute of Technology, Stockholm, Sweden
(4) William B. Hanson Center for Space Sciences, The University of Texas at Dallas, Texas, U.S.A.

J. Geophys. Res. Space Physics, 120, doi:10.1002/2014JA020809, 2015

Abstract

Based upon a survey of global auroral images collected by the Polar Ultraviolet Imager, Kullen et al. (2002) subdivided polar cap auroral arcs into a number of categories, including that of “bending” arcs. We are concerned with those bending arcs that appear as a bifurcation of the dayside auroral oval and which subsequently form a spur intruding into the polar cap. Once formed, the spur moves poleward and antisunward over the lifetime of the arc. We propose that dayside bending arcs are ionospheric signatures of pulses of dayside reconnection and are therefore part of a group of transient phenomena associated with ?ux transfer events. We observe the formation and subsequent motion of a bending arc across the polar cap during a 30 min interval on 8 January 1999, and we show that this example is consistent with the proposed model. We quantify the motion of the arc and ?nd it to be commensurate with the convection ?ows observed by both ground-based radar observations and space-based particle ?ow measurements. In addition, precipitating particles coincident with the arc appear to occur along open ?eld lines, lending further support to the model.