Inertial torques on curved atmospheric fibres*

Atmospheric fibres accelerate the air as they move. This results in fluid-inertia torques that rotate the fibres, influencing their transport through the air. Little is known about this effect, beyond the general consensus that it is significant, because most theory of inertial torques is for axisymmetric particles. However, atmospheric fibres tend to lack this symmetry. Here we determine theoretically how breaking of axisymmetry changes the dynamics of rigid curved fibres in air. We find that planar fibres still align in quiescent air, but settle at an oblique angle with gravity. Our results make it clear that inertial alignment is a general and thus important factor for the transport of atmospheric particles.