We investigate a fifteen-day period in October 2011. Auroral observations by the SSUSI instrument onboard the DMSP F16, F17, and F18 spacecraft indicate that the polar regions were covered by weak cusp-aligned arc emissions whenever the IMF clock angle was small, |θ|<45°, which amounted to 30% of the time. Simultaneous observations of ions and electrons in the tail by the Cluster C4 and Geotail spacecraft showed that during these intervals dense (1 cm-3) plasma was observed, even as far from the equatorial plane of the tail as |ZGSE| = 13 RE. The ions had a pitch angle distribution peaking parallel and antiparallel to the magnetic field and the electrons had pitch angles that peaked perpendicular to the field. We interpret the counter-streaming ions and double loss-cone electrons as evidence that the plasma was trapped on closed field lines, and acted as a source for the cusp-aligned arc emission across the polar regions. This suggests that the magnetosphere was almost entirely closed during these periods. We further argue that the closure occured as a consequence of dual-lobe reconnection at the dayside magnetopause. Our finding forces a significant re-evaluation of the magnetic topology of the magnetosphere during periods of northwards IMF.

During periods of northward interplanetary magnetic field (IMF), the magnetospheric structure and dynamics are dramatically different compared to the southward IMF case. Previous studies using both observations and simulations have shown that the magnetotail becomes dominated by closed magnetic flux and associated trapped particle populations. In this study, we analyse three intervals of plasma observed in the high latitude magnetotail during a period of prolonged northward IMF, coinciding with observations of cusp-aligned arcs in the polar region. We observe that the plasma is typically continuous with some substructure observed on length scales of 0.5 - 1.5 R$_E$ which may be linked to the substructure observed in cusp-aligned arcs. The plasma characteristics in each of the three intervals studied are similar. The ion and electron densities are on the order of 0.2 - 1 cm$^{-3}$. The electron energies typically vary between 10$^2$ - 10$^3$ eV. The ion energies are higher compared to the electron energies and range between 10$^2$ - 10$^4$ eV. The ion temperatures are on the order of 5 - 18 MK. The speed of the plasma crossing the Cluster spacecraft is between 4 - 21 km/s which is on the order of magnitude of convection speeds in the magnetotail plasma sheet. We tentatively suggest that this may provide supporting evidence for dual lobe reconnection acting to trap plasma within the magneotsphere and resulting cusp-aligned arc formation.