Drift turbulence, particle transport, and anomalous dissipation at the reconnecting magnetopause

Abstract

Using fully kinetic 3D simulations, the reconnection dynamics of asymmetric current sheets are examined at the Earth's magnetopause. The plasma parameters are selected to model MMS magnetopause diffusion region crossings with guide fields of 0.1, 0.4, and 1 of the reconnecting magnetosheath field. In each case, strong drift-wave fluctuations are observed in the lower-hybrid frequency range at the steep density gradient across the magnetospheric separatrix. These fluctuations give rise to cross-field electron particle transport. In addition, this turbulent mixing leads to significantly enhanced electron parallel heating in comparison to 2D simulations. We study three different methods of quantifying the anomalous dissipation produced by the drift fluctuations, based on spatial averaging, temporal averaging, and temporal averaging followed by integrating along magnetic field lines. Comparison of the different methods reveals complications in identifying and measuring the anomalous dissipation. Nevertheless, the anomalous dissipation from short wavelength drift fluctuations appears weak for each case, and the reconnection rates observed in 3D are nearly the same as in 2D models. The 3D simulations feature a number of interesting new features that are consistent with recent MMS observations, including cold beams of magnetosheath electrons that penetrate into the hotter magnetospheric inflow, the related observation of decreasing temperature in regions of increasing total density, and an effective turbulent diffusion coefficient that agrees with predictions from quasi-linear theory.

Turbulence and Transport During Guide Field Reconnection at the Magnetopause

“…The MMS observations also reveal that electrons are often frozen‐in to the fluctuations (Graham et al, ). Previous simulations based on this event and two others (Le et al, ) revealed the development of drift wave fluctuations as well as noting the accompanying enhancement of cross‐field electron transport and parallel heating. These results complemented discussions of transport by lower‐hybrid turbulence across magnetopause boundary layers in the context of hybrid simulations (Gary & Sgro, ) as well as Cluster (Vaivads et al, ) and MMS observations (Graham et al, ).…”

“…However, whether the strong turbulence measured at the magnetopause actually drives transport or produces the necessary dissipation remain open questions as previous three‐dimensional simulations of reconnection‐driven turbulence did not adequately address the impact of frozen‐in electrons on transport (Le et al, , ; Price et al, , ). The turbulence that develops in the strong density gradient across the magnetopause has characteristic time scales that are intermediate between the electron and ion gyrofrequencies.…”

Kinetic Dissipation Around a Dipolarization Front

“…In contrast, the main contribution to the electron dissipation parameter comes from the off-diagonal components of the pressure tensor and traceless strain rate tensor D (e) 5 = −2Π (e) xz D (e) xz (blue frames in Figure 2) suggesting the energy transfer between the perpendicular and parallel to the magnetic field components of the electron velocity distribution. At the same time, the spatial distribution of the electron dissipation Pi-D (e) shown in Figure 1d suggests that it is provided by the LHDI, which is indeed known to heat electrons (Daughton et al, 2004;Huba et al, 1977;Le et al, 2018). Strong LHDI activity was found in 3-D PIC simulations of reconnection (Roytershteyn et al, 2012) and DFs (Divin et al, 2015;Lapenta et al, 2014;Sitnov et al, 2014) as well as in their space yz .…”

Magnetic Reconnection in Three Dimensions: Modeling and Analysis of Electromagnetic Drift Waves in the Adjacent Current Sheet

“…Observations of magnetic reconnection at the Earth's magnetopause regularly indicate nearby strong wave activity and/or turbulence (e.g., Eastwood et al, 2009), particularly at the magnetopause current sheet adjacent to the electron diffusion region (EDR) on the magnetosphere side Chen et al, 2017;Ergun et al, 2017). This turbulence or activity appears as strong fluctuations in the magnetic field (B) and particle density (n) and may be a result from the unstable current sheet adjacent to the magnetic reconnection region (e.g., Daughton, 2003;Daughton et al, 2004;Daughton et al, 2011;Ergun et al, 2017;Ji et al, 2004Ji et al, , 2005Karimabadi et al, 2007;Lapenta et al, 2006;Le et al, 2018;Nakamura et al, 2016;Price et al, 2016Price et al, , 2017Roytershteyn et al, 2012Roytershteyn et al, , 2013. These instabilities are of importance as they may influence the magnetic reconnection evolution and influence the three-dimensional (3-D) structure of magnetic reconnection.…”