magnetic crochet

noun1

1. •
   A portion of a magnetograph recording showing electric currents in the Earth's ionosphere caused by a solar flare, identified by its characteristic shape, likened to a crochet hook.

   • Figure 3 illustrates the short wave fade-out and the magnetic crochet, both of which endure only so long as the burst of x-rays from the flare continues. — 1966