Drift waves, intense parallel electric fields, and turbulence associated with asymmetric magnetic reconnection at the magnetopause

Abstract

Observations of magnetic reconnection at Earth's magnetopause often display asymmetric structures that are accompanied by strong magnetic field (B) fluctuations and large‐amplitude parallel electric fields (E||). The B turbulence is most intense at frequencies above the ion cyclotron frequency and below the lower hybrid frequency. The B fluctuations are consistent with a thin, oscillating current sheet that is corrugated along the electron flow direction (along the X line), which is a type of electromagnetic drift wave. Near the X line, electron flow is primarily due to a Hall electric field, which diverts ion flow in asymmetric reconnection and accompanies the instability. Importantly, the drift waves appear to drive strong parallel currents which, in turn, generate large‐amplitude (~100 mV/m) E|| in the form of nonlinear waves and structures. These observations suggest that turbulence may be common in asymmetric reconnection, penetrate into the electron diffusion region, and possibly influence the magnetic reconnection process.

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

“…Price et al () found that small‐scale turbulence developed in their simulation, causing large‐amplitude parallel electric fields and structure to form in the M − N plane of the current layer (see section 2 for L M N coordinate definition). 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 .…”

“…Ergun, Holmes, et al () and Ergun et al () reported observations of large‐amplitude parallel electrostatic waves, which they associated with drift‐instability‐driven “corrugations” of the magnetopause near the separatrix and X‐point. Cassak et al () and Genestreti et al () reported , the local per‐volume rate of work done on the plasma by the nonideal electric field, in central EDRs that were several orders of magnitude larger than what was predicted by 2.5‐d particle‐in‐cell (PIC) simulations.…”

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.…”

Evidence of Magnetic Nulls in Electron Diffusion Region

“…This means that most of the reconnection events (10 events) can be described using the two-dimensional model, although they are essentially three-dimensional. Such back-and-forth motion could be caused by time-varying solar wind conditions, large-amplitude magnetic waves, outflow obstructions, etc., but not caused by lower-hybrid waves (Ergun et al, 2017;Khotyaintsev et al, 2016), which exhibit fluctuations only in the electric field components. Here ξ < 40% is an empirical threshold given by Fu et al (2015) for quantifying the accuracy of FOTE.…”