Plasma observations in the distant magnetotail under Northward IMF

The structure and dynamics of the magnetosphere are significantly different during intervals of northward interplanetary magnetic field (IMF) compared to when the IMF is southward. Under northward IMF, reconnection occurs at higher latitudes tailward of the cusps. High latitude reconnection occurring simultaneously in both hemispheres can close significant amounts of open flux in the magnetospheric lobes resulting in an almost entirely closed magnetosphere and has been linked to characteristic auroral signatures, such as cusp-aligned arcs.

Under northward IMF the magnetosphere becomes dominated by closed magnetic flux with associated trapped particles populations which are thought to provide the source particle population for auroral cusp-aligned arcs (Milan et al., 2023; Mooney et al, 2024). However, the structure and properties of the distant magnetotail under northward IMF are poorly understood. We have performed a statistical analysis of ARTEMIS crossings of the distant magnetotail (X_GSE ~ -60 R_E) between 2011 - 2016 to investigate the magnetic field and plasma characteristics in the magnetotail under northward IMF conditions compared to southward IMF conditions. Under southward IMF, the magnetotail is dominated by magnetic pressure with no significant associated plasma population. However, under northward IMF we find that statistically the central distant magnetotail contains denser, hotter plasma and that the plasma pressure in the magnetotail is typically larger than the magnetic pressure. We suggest that the observed hotter, denser plasma population in the central magnetotail could indicate that the plasma sheet extends down to the distant magnetotail under northward IMF.