Evolution of symmetric reconnection layer in the presence of parallel shear flow

Abstract

The development of the structure of symmetric reconnection layer in the presence of a shear flow parallel to the antiparallel magnetic field component is studied by using a set of one-dimensional (1D) magnetohydrodynamic (MHD) equations. The Riemann problem is simulated through a second-order conservative TVD (total variation diminishing) scheme, in conjunction with Roe's averages for the Riemann problem. The simulation results indicate that besides the MHD shocks and expansion waves, there exist some new small-scale structures in the reconnection layer. For the case of zero initial guide magnetic field (i.e., B y0 ¼ 0), a pair of intermediate shock and slow shock (SS) is formed in the presence of the parallel shear flow. The critical velocity of initial shear flow V zc is just the Alfven velocity in the inflow region. As V z1 increases to the value larger than V zc , a new slow expansion wave appears in the position of SS in the case V z1 < V zc , and one of the current densities drops to zero. As plasma b increases, the out-flow region is widened. For B y0 = 0, a pair of SSs and an additional pair of time-dependent intermediate shocks (TDISs) are found to be present. Similar to the case of B y0 ¼ 0, there exists a critical velocity of initial shear flow V zc . The value of V zc is, however, smaller than the Alfven velocity of the inflow region. As plasma b increases, the velocities of SS and TDIS increase, and the out-flow region is widened. However, the velocity of downstream SS increases even faster, making the distance between SS and TDIS smaller. Consequently, the interaction between SS and TDIS in the case of high plasma b influences the property of direction rotation of magnetic field across TDIS. Thereby, a wedge in the hodogram of tangential magnetic field comes into being. When b ! 1, TDISs disappear and the guide magnetic field becomes constant.

Electric structure of dipolarization fronts associated with interchange instability in the magnetotail

“…We solve equation by using the second‐order total variation diminishing scheme proposed by Harten [], which has been used to study the evolution of reconnection layer in the presence of parallel shear flow in one‐dimensional framework [ Lu and Cao , ].…”

Polytropic index of central plasma sheet ions based on MHD Bernoulli integral

“…Many important large‐scale and mesoscale magnetospheric physical processes occur in the plasma sheet, such as energy and mass transports, plasma convection, magnetic field reconnection, and MHD waves. The polytropic index is a key parameter in the MHD descriptions of these physical processes [ Birn et al ., ; Borovsky et al ., ; Cao et al ., ; Chen and Wolf , ; Lu and Cao , ; Lu et al ., , ; Ma and Bhattacharjee , ]. For example, when the polytropic index α = 5/3 in the plasma sheet (i.e., adiabatic convection), the pressure in the near‐Earth plasma sheet predicted from adiabatic theory in the near‐Earth tail is extremely high (exceeding the observed pressure by a considerable factor).…”

“…Polytropic index also indicates the characteristics of a system energy change; e. g., α < 5/3 represents that the system energy is loss or the system is cooling, α > 5/3 represents that the system energy increases or the system is heating. Chen and Wolf, 1999;Lu and Cao, 2011;Lu et al, 2013Lu et al, , 2002Ma and Bhattacharjee, 2001]. For example, when the polytropic index α = 5/3 in the plasma sheet (i.e., adiabatic convection), the pressure in the near-Earth plasma sheet predicted from adiabatic theory in the near-Earth tail is extremely high (exceeding the observed pressure by a considerable factor).…”