Thermodynamics of Dipolarization Fronts of Magnetic Reconnection in Anisotropic Plasma: MMS Observations and Resistive Double-polytropic MHD Simulations

Abstract

Abstract Dipolarization fronts (DFs) of magnetic reconnection are a transient field structure accompanied with a sharp increase of magnetic field component normal to plasma sheet and a high-speed plasma flow. The thermodynamics of DFs in the anisotropic plasma, which have not been studied so far, are investigated in this paper using two-dimensional, resistive magnetohydrodynamic simulations with double-polytropic energy laws in which two polytropic exponents, γ ∥ and , are used as parameters to describe various thermodynamic conditions. The subscripts ∥ and denote, respectively, directions parallel and perpendicular to the local magnetic field. Four different types of DFs observed by the Magnetospheric Multiscale Mission (MMS) in the plasma sheet of the Earth's magnetotail are presented—namely, (1) both temperatures T ∥ and decrease; (2) both T ∥ and increase; (3) T ∥ decreases while increases; (4) T ∥ increases while decreases. By using four different pairs of γ ∥ and , these four types of DFs can be reproduced, where the thermodynamics of Type-4 DF may correspond to the double-adiabatic Chew–Goldberger–Low conditions. It is concluded that the thermodynamic condition is seen to resemble most closely an adiabatic process for Type-1, -2, and -4 DFs, but to an isothermal process for Type-3 DF.