Fall streaks: Parabolic trajectories with a twist

Abstract

Fall streaks are arcs in the sky composed of ice crystals falling from high-altitude cirrus clouds. With the crystals falling at their vertical terminal velocity and their horizontal velocity that of the local wind, the streaks are parabolas if the wind increases linearly with height. The dynamics of fall streaks is formally identical with that of drag-free projectiles−but with a twist: the roles of horizontal and vertical coordinates are reversed.