Structure of the dissipation region in fluid simulations of asymmetric magnetic reconnection^a)

The structure of the dissipation region during asymmetric magnetic reconnection is studied assuming antiparallel magnetic fields in two dimensions. A physics-based prediction for the scaling of the thickness of the dissipation region in (collisionless) Hall reconnection is presented and confirmed with two-fluid simulations. However, the substructure of the dissipation region in these and additional single-fluid (magnetohydrodynamics) simulations disagrees with a recent model [Cassak and Shay, Phys. Plasmas 14, 102114 (2007)]. We attribute the disagreement to the lack of plasma mixing along newly reconnected field lines in fluid models, rendering the use of a fluid description of questionable validity for determining the dissipation region substructure. Applications to the dayside magnetopause are discussed.