Spatial structuring of prominence spicules. Top left panel: same as the bottom left panel in Fig. 1b. The black dotted line crosses a few structures at that instance. Top right panel: we plot the AIA 171 Å intensity along the dotted line from the top left panel. Bottom panel: AIA 171 Å RMS intensity along the dotted line that is displayed in the top panel of Fig. 1d. See Appendix C for discussion.