This distrail within the outer regions of a stratocumulus cloud was caused by the jet wake of a low-flying aeroplane. Seen from Aplerbeck, Dortmund, June 2019. The contrail, which is the primary turbulence zone caused by the jet engine, is discernable as a narrow, contorted white vortex just above the lower edge of the transparent wake approximately halfway from centre to top right.
<a href="//commons.wikimedia.org/wiki/User:Franz_van_Duns" title="User:Franz van Duns">Franz van Duns</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>