Turbulence in Three‐Dimensional Simulations of Magnetopause Reconnection

Abstract

We present detailed analysis of the turbulence observed in three‐dimensional particle‐in‐cell simulations of magnetic reconnection at the magnetopause. The parameters are representative of an electron diffusion region encounter of the Magnetospheric Multiscale (MMS) mission. The turbulence is found to develop around both the magnetic X line and separatrices, is electromagnetic in nature, is characterized by a wave vector k given by kρe∼(meTe/miTi)0.25 with ρe the electron Larmor radius, and appears to have the ion pressure gradient as its source of free energy. Taken together, these results suggest the instability is a variant of the lower hybrid drift instability. The turbulence produces electric field fluctuations in the out‐of‐plane direction (the direction of the reconnection electric field) with an amplitude of around ±10 mV/m, which is much greater than the reconnection electric field of around 0.1 mV/m. Such large values of the out‐of‐plane electric field have been identified in the MMS data. The turbulence in the simulations controls the scale lengths of the density profile and current layers in asymmetric reconnection, driving them closer to ρeρi than the ρe or de scalings seen in 2‐D reconnection simulations, and produces significant anomalous resistivity and viscosity in the electron diffusion region.

Determining L‐M‐N Current Sheet Coordinates at the Magnetopause From Magnetospheric Multiscale Data

“…The conclusion is that the magnetopause models do not very well represent the observed current sheet orientation. This is evidence for a large local deformation of the magnetopause, such as could result from a “lower‐hybrid drift‐like instability” (Ergun et al, ; Le et al, ; Price et al, ), the Kelvin‐Helmholtz instability or a plasma/field structure from the solar wind impinging on the magnetopause.…”

“…We conclude that there must have been a large, spatially and temporally localized, deformation of the magnetopause shape during the event, causing a large deviation of the predicted normal direction from the Shue and Lin models. The physical reason for this behavior remains unclear but is possibly related to localized reconnection activity in combination with a lower‐hybrid drift‐like instability (Ergun et al, ; Le et al, ; Price et al, ), large‐amplitude Kelvin‐Helmholtz waves, or a plasma/field structure from the solar wind impinging on the magnetopause.…”

MMS Observation of Asymmetric Reconnection Supported by 3‐D Electron Pressure Divergence

“…Due to the long duration of the magnetopause crossing (∼30 s), it is possible that the configuration of the magnetopause changed over the course of the event. It is also possible that kinetic‐scale instabilities cause the local current and boundary orientations to differ from the larger‐scale configuration (Ergun, Holmes, et al, ; Ergun et al, ; Price et al, , ). Four‐point timing analysis (Schwartz, ) of the B Z G S E reversal point (at approximately 07:36:55 UT) yields a normal vector of [0.98011, 0.192104, −0.049797], again in GSE, and a boundary velocity of −31 km/s .…”

“…This structured magnetopause was similar in character to the corrugated magnetopause of Ergun et al () and the lower hybrid drift turbulence of Roytershteyn et al (). Price et al, noted that the wrapping of the normal electric field E N into the direction of the current ( M ) resulted in greatly enhanced . Le et al (), which analyzed a 3‐d simulation of the same event studied by Price et al (, ), found that these oscillations in the current layer caused intense parallel electron heating as was observed by MMS (Burch et al, ).…”

“…Nakamura et al (), Price et al (, ), and Le et al () have all recently performed 3‐d PIC simulations of MMS EDR events. Nakamura et al () analyzed a large‐scale simulation of the very large guide field Kelvin‐Helmholtz vortex reconnection event of Eriksson et al ().…”