An investigation of the structure of rotational discontinuities

The structure of rotational discontinuities (RDs) has been studied through hybrid simulations for a range of propagation angle Θbn between the discontinuity normal and the upstream magnetic field and plasma β. For sufficiently narrow initial states, the simulations produce quasi‐steady “reverse rotation” magnetic field structures for 30° ≤ Θbn ≤ 60° and 0 < β ≤ 1 on a time scale of roughly 200 Ωi−1. This structure is characterized by a right handed field rotation upstream joined smoothly to a left handed field rotation downstream; its width decreases from 60–70 c/ωpi at Θbn = 30° to less than 25 c/ωpi at Θbn = 60°. The magnetic field hodograms of our RD results have a distinctive S‐shape which is most pronounced in simulations with small Θbn and initially right handed rotations. The reverse rotation structure is the net result of the expansion of the initial current layer via the fast and intermediate wave modes.