Conjugate Observations of the Evolution of Polar Cap Arcs in Both Hemispheres

We report results from the analysis of a case of conjugate polar cap arcs (PCAs) observed on 5 February 2006 in the Northern Hemisphere by the ground-based Yellow River Station all-sky imager (Svalbard) and in both hemispheres by the space-based DMSP/SSUSI and TIMED/GUVI instruments. The PCA\textquoterights motion in dawn-dusk direction shows a clear dependence on the interplanetary magnetic field (IMF) By component and presents a clear asymmetry between Southern and Northern Hemispheres, that is, formed on the duskside and moving from dusk to dawn in the Northern Hemisphere and vice versa in the other hemisphere. The already existing PCAs\textquoteright motion is influenced by the changes in the IMF By with a time delay of ~70\ min. We also observed strong flow shears/reversals around the PCAs in both hemispheres. The precipitating particles observed in the ionosphere associated with PCAs showed properties of boundary layer plasma. Based on these observations, we might reasonably expect that the topological changes in the magnetotail can produce a strip of closed field lines and local processes would set up conditions for the formation and evolution of PCAs.