On rotational discontinuities in both two‐fluid and hybrid models

Rotational discontinuities are studied in a two‐fluid model that includes finite ion inertia dispersion and in a hybrid model in which the full ion dynamics is retained while the electrons are treated as a massless fluid. We show that as in previous dissipative MHD studies, a rotational discontinuity is unstable in both models and evolves to a 2 → 3 intermediate shock, a slow rarefaction wave, and other waves. (However, due to the limitation in computational resources, the hybrid calculations are limited to low‐to‐medium ion beta.) In addition, we show that the so‐called Walén relation, which holds exactly for rotational discontinuities, can also be well satisfied by tran‐Alfvénic intermediate shocks. Thus intermediate shocks can be candidates for those observed structures that satisfy the Walén relation.