Interchange motions near the prominence lower boundary. A constant-radius slice at r = 1.02 R_⊙ shows the relation between the filamentary density structure and radial motion. Panel (A) enlarges the boxed barb-bearing region in panel (B). Both panels show logarithmic number density, with positive v_r contours in panel (A) tracing narrow upflow lanes. Panel (C) shows the radial velocity.