Disturbance of the Front Region of Magnetic Reconnection Outflow Jets due to the Lower-Hybrid Drift Instability

A 3D fully kinetic simulation shows that the lower-hybrid drift instability disturbs the front of magnetic reconnection outflow jets and additionally causes energy dissipation. The result is very consistent with a disturbance observed at the dipolarization front (DF) in Earth’s magnetotail by the Magnetospheric Multiscale (MMS) mission. A fully kinetic dispersion relation solver, validated by the MMS observations, further predicts that the disturbance of the reconnection jet front could occur over different parameter regimes in space plasmas including Earth’s DF and solar flares.

Figure 1

(a) A 3D view of magnetic field lines at $t=29{\omega }_{ci}^{-1}$ near the reconnection jet fronts with the 2D contours in the $x\text{−}z$ plane at $y=0$ and in the $x\text{−}y$ plane at $z=0$ of electron density $n_e$. ${\omega }_{ci}$ is the ion gyro frequency based on $B_b$. (b) Integrated amplitudes at each ($x$, $z$) grid point of $k_y$ modes for $E_y/(V_A{B}_b)$ in the range $m_y=1–11$ at $t=29{\omega }_{ci}^{-1}$. $V_A$ is the Alfvén speed based on $n_0$ and $B_b$. (c) Time evolutions of integrated amplitudes of $k_y$ modes for $E_y$ at $x=5.6–17.6$ and $z=0$.

Figure 2

Enlarged views near the reconnection jet fronts with the 2D contours of (a) the electron density $n_e$, (b) energy dissipation term $\mathit{J}·{\mathit{E}}^{\prime }$, and (c)–(f) parallel and perpendicular components of the current density ($J_{\parallel }$, $J_{\perp }$) and the electric field ($E_{\parallel }$, $E_{\perp }$). The dashed lines indicate the edge of the high-density region.

Figure 3

Values along the $x$ direction at $z=0$ averaged in the $y$ direction near the reconnection jet fronts (left panels) and the in situ observations by the MMS1 spacecraft for 7 s from 13∶04:52 UT on July 18, 2017 (right panels), of (a),(e) the $z$ ($l$) component of the magnetic field $B_z$ ($B_l$), (b),(f) electron density $n_e$, (c),(g) $y$ ($m$) component of the electric field $E_y(-E_m)$, and (d),(h) dissipation term. The blue curves in (a)–(d) show the standard deviations. The green curve in (h) shows the averaged value for four MMS spacecraft. Here $l$ and $m$ components in (e) and (g) are the parallel and perpendicular components to the ambient magnetic field used by Liu et al. [15], which corresponds to $z$ and $y$ in the simulation. The dashed lines indicate the edges of the high-density intervals.

Figure 4

Linear dispersion relations at the jet fronts derived by Umeda and Nakamura [19]. Panels show wave modes with wave normal angles quasiperpendicular to the ambient magnetic field ($\varphi =85°–89°$) for parameters (a) obtained from the simulation, (b) similar to (a) but for the real ion-to-electron mass ratio, (c) the same as (b) but for $T_i/T_e=0.5$, and (d) obtained from the MMS observations on July 18, 2017 [15].