Inertial-Range Reconnection in Magnetohydrodynamic Turbulence and in the Solar Wind

In situ spacecraft data on the solar wind show events identified as magnetic reconnection with wide outflows and extended “$X$ lines,” ${10}^3–{10}^4$ times ion scales. To understand the role of turbulence at these scales, we make a case study of an inertial-range reconnection event in a magnetohydrodynamic simulation. We observe stochastic wandering of field lines in space, breakdown of standard magnetic flux freezing due to Richardson dispersion, and a broadened reconnection zone containing many current sheets. The coarse-grain magnetic geometry is like large-scale reconnection in the solar wind, however, with a hyperbolic flux tube or apparent $X$ line extending over integral length scales.

Figure 1

Top: Event from the MHD simulation, at point (2.964,0.908,5.841) along a cut in the $y$ direction. Magnetic fields (left) normalized by $B_{\text{rms}}=0.24$, and velocity fields (right) by local upstream Alfven velocity $V_A=0.7$. Bottom: Event from Wind spacecraft data, on January 14, 2008, 13:50 h, normalized by $B_{\text{rms}}=2.5\mathrm{nT}$, $V_A=75\mathrm{km}/\mathrm{s}$. Distance $x$ is normalized by $L$. MVF components are identified as $L$ (red solid line), $M$ (green dotted line), $N$ (blue dashed line).

Figure 2

$B$ isosurface at half maximum value 1.11 in yellow. $\mathbf{B}$ lines sampled along $N$ direction in green and $L$ direction in red. The original 1D spatial cut is the thick black line.

Figure 3

Same as Fig. 2, except for $\overline{\mathbf{B}}$ rather than $\mathbf{B}$. The isosurface is for the half maximum value $|\overline{\mathbf{B}}|=0.301$. The blue vectors on the field lines are $\overline{\mathbf{u}}$ (in the local plasma frame).

Figure 4

The quasiseparatrix layer $Q_{\perp }=32$ in cyan, and its cross section in a plane normal to the $M$ direction in magenta.

Figure 5

Top: Current isosurfaces at the half maximum value $j=69.1$ in green. In red, origin points at time $t=0$ of magnetic field at final point $({\mathbf{x}}_f,t_f)=(3.31,0.083,6.07,2.00)$. Bottom: Backward mean-square dispersion $⟨r_{\perp }^2(\tau )⟩$ orthogonal to $L$ direction as blue line. Reference curve $⟨r_{\perp }^2⟩=8\lambda \tau$ in green and $⟨r_{\perp }^2⟩=0.02{\tau }^{8/3}$ in red.