The color of each point indicates the ratio between the spot width and spot height (w/h), i.e., the circularity of the ellipse. Yellow spots mark near-perfect circles where both ellipse axes have a similar length. The violet spots represent ellipses where one axis is significantly longer than the other. For better visibility, spots with high (w/h > 0.7) and low (w/h < 0.7) circularities are shown separately in Fig. in the SI. In the central region, the ellipses do not have a preferred angle, and the discharge spots are mostly circular. In contrast, the spots at the edges appear mostly as ellipses (violet color), which are predominantly oriented parallel to the wire surface (γ = 0°, green region in the Figure ). Less frequent but still dominant are ellipses with an angle γ = ±90°at the upper and lower part of the Figure (blue regions), hence, oriented perpendicular to the surface. From this analysis, we separate all discharges into two groups: i) discharges in the center of the wire, which appear mostly circu- lar and ii) discharges at the edge of the wire, appearing as ellipses. Different information can be obtained from the discharges within each of these groups.