The velocity components driving the feature and its visibility. Panel (a) shows the direction of the tangent (T), normal (N) and binormal (B) along the field line for this snapshot. Panel (b) shows the feature on the field line viewed in the proxy. Panel (c) shows the line-of-sight (vertical) velocity and outlines the feature with the magenta contour. Panels (d)-(f) show the flow components along a bunch of field lines traced through the feature.