On the generation of enhanced sunward convection and transpolar aurora in the high-latitude ionosphere by magnetic merging S. Eriksson, J.B.H. Baker, S.M. Petrinec, H. Wang, F.J. Rich, M. Kuznetsova, M.W. Dunlop, H. Reme, R.A. Greenwald, H.U. Frey, H.L Luhr, R.E. Ergun, A. Balogh, and C.W. Carlson The global appearance of quasi-stationary and oval-aligned transpolar auroral arcs (TPA) across the entire polar region is yet to be fully explained observationally during steady interplanetary magnetic field (IMF) By and northward IMF conditions. We here present an extensive set of observations from a single duskside event on 16 December 2001 suggesting that the dayside part of such TPAs form due to quasi-continuous merging between the IMF and the lobe magnetic field tailward of the cusp while the nightside part is associated with the upward field-aligned current (FAC) region of the Harang discontinuity. The IMAGE WIC instrument observes the duskside development of an oval-aligned TPA in the Northern Hemisphere (NH) during strong IMF |B| ~ 18 nT with generally steady positive IMF By and IMF Bz at an average ~56 deg. clock angle. The low-altitude CHAMP and FAST satellites confirm that the dayside TPA coincides with an upward northward IMF Bz (NBZ) FAC poleward of the region 1 FAC system. The region of diminished IMAGE WIC emissions in between the duskside auroral oval and the TPA is associated with a downward NBZ current. DMSP F14 suggests that the extreme dayside region of the downward NBZ current coincides with precipitating magnetosheath-like ions with reversed energy-latitude dispersion consistent with high-latitude reconnection. SuperDARN observes the presence of an ionospheric channel of enhanced sunward flows generally centered between the oppositely directed NBZ currents as expected for lobe reconnection. We associate the sunward flows with a clockwise high-latitude lobe convection vortex and the dayside part of the TPA. The nightside part of the TPA, however, is aligned with antisunward flow or the stagnation region of the Harang discontinuity and coincides with an upward FAC as observed by DMSP F14. Plasma and magnetic field observations by Cluster on the duskside NH flank confirm the presence of rotational discontinuities across the magnetopause at these times with changes in the magnetosheath plasma velocity that indicate an active merging region poleward of Cluster. A global MHD simulation generates an opposite pair of FACs on either side of a localized magnetopause merging region near (X, Y, Z)GSM = (-4.7, 5.4, 10.2) RE. This location conforms with the Cluster observations and the sense of the oppositely directed FACs agrees with the low-altitude NBZ observations. Sunward directed flows driven by j X B are also generated in between the simulated opposite FACs. _______________ Journal of Geophysical Research, in press, 2005