We performed two tests to check the constancy of proton pressure along the field lines crossing the tail equator at r similar to 8...20 RE We use the isotropic boundaries as the reference field lines when comparing the pressure measured at low altitude with the plasma sheet pressure computed from either the magnetic field models or empiric formulas. The tests show that both pressure values are close to each other indicating a high degree of isotropy of the proton distributions.

Based on these results we analysed the pressure values at low altitudes near the equatorward auroral arcs on the nightside. These pressure values in five cases ranged between 0.1 and 0.4 nPa indicating that the equatorward arcs originate in the current sheet portion of the plasma sheet (at distances >10-12 Re). This is also consistent with are location near (or poleward of) the electron isotropic boundary, whose interpretation as the boundary of nonadiabatic scattering in the weak (