Structure of the dissipation region in fluid simulations of asymmetric magnetic reconnection

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.