Fig. 5: Model of the auroral zone.

a Plot of the Earth’s dipole magnetic field lines (blue) and the segment (red) along the field line through the auroral acceleration region for L = 8.5 (or invariant latitude Λ = 70^∘). Profiles of (b) the Alfvén speed v_A (red) and electron thermal velocity v_te (blue) as well as (c) their ratio v_A/v_te (black) as a function of distance along the field line s. The dashed line shows the ratio v_A/v_te ≃ 3 relevant to the LAPD experiments reported here. The highlighted red region shows the experimental v_A/v_te corresponds to v_A/v_te in the auroral zone near a distance s of 3 \({\rm{{R}}_{E}}\).