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We analyze Cluster data to explore the statistical properties of the magnetosheath electron boundary layer, observed outside the high‐latitude dayside magnetopause, under northward interplanetary magnetic field (IMF). We investigate the dependence of the presence and directionality of heated magnetosheath electrons in this layer on the geomagnetic dipole tilt and IMF tilt angles. The statistical results illustrate that the dipole tilt angle primarily controls the directionality of heated electrons in the magnetosheath boundary layer outside of the magnetopause. By contrast, the effect of the IMF tilt angle appears marginal. If the presence of such heated electrons is taken to be the signature of magnetosheath field lines that have reconnected with the high‐latitude magnetic field of the Earth, tailward of the cusp, these results indicate that the dipole tilt determines in which hemisphere high‐latitude reconnection of a given magnetosheath field line occurs first. The marginal impact of the IMF tilt angle may indicate that its potential effect is partially removed by the IMF passage through the bow shock and subsequent magnetic field draping at the dayside magnetopause. The frequent detection of bidirectional heated electrons outside the magnetopause additionally suggests that magnetosheath field lines may frequently reconnect in both hemispheres. Such a finding would support double high‐latitude reconnection as a potential mechanism for low‐latitude boundary layer formation under northward IMF.
Lavraud et al. (Wed,) studied this question.