M. Zhou

Magnetospheric Multiscale observations of large-amplitude, parallel, electrostatic waves associated with magnetic reconnection at the magnetopause

We report observations from the Magnetospheric Multiscale satellites of large-amplitude, parallel, electrostatic waves associated with magnetic reconnection at the Earths magnetopause. The observe ...

MMS Observations of Ion-scale Magnetic Island in the Magnetosheath Turbulent Plasma

In this letter, first observations of ion-scale magnetic island from the Magnetospheric Multiscale mission in the magnetosheath turbulent plasma are presented. The magnetic island is characterized ...

Force Balance at the Magnetopause Determined with MMS: Application to Flux Transfer Events

The Magnetospheric Multiscale mission (MMS) consists of four identical spacecraft forming a closely separated (≤10 km) and nearly regular tetrahedron. This configuration enables the decoupling of spatial and temporal variations and allows the calculation of the spatial gradients of plasma and electromagnetic field quantities. We make full use of the well cross-calibrated MMS magnetometer and fast plasma instruments measurements to calculate both the magnetic and plasma forces in flux transfer events (FTEs), and evaluate the relative contributions of different forces to the magnetopause momentum variation. This analysis demonstrates that some but not all FTEs, consistent with previous studies, are indeed force-free structures in which the magnetic pressure force balances the magnetic curvature force. Furthermore, we contrast these events with FTE events that have non-force-free signatures.

On the origin of the crescent‐shaped distributions observed by MMS at the magnetopause

MMS observations recently confirmed that crescent-shaped electron velocity distributions in the plane perpendicular to the magnetic field occur in the electron diffusion region near reconnection sites at Earths magnetopause. In this paper, we reexamine the origin of the crescent-shaped distributions in the light of our new finding that ions and electrons are drifting in opposite directions when displayed in magnetopause boundary-normal coordinates. Therefore, E × B drifts cannot cause the crescent shapes. We performed a high-resolution multi-scale simulation capturing sub-electron skin depth scales. The results suggest that the crescent-shaped distributions are caused by meandering orbits without necessarily requiring any additional processes found at the magnetopause such as the highly asymmetric magnetopause ambipolar electric field. We use an adiabatic Hamiltonian model of particle motion to confirm that conservation of canonical momentum in the presence of magnetic field gradients causes the formation of crescent shapes without invoking asymmetries or the presence of an E × B drift. An important consequence of this finding is that we expect crescent-shaped distributions also to be observed in the magnetotail, a prediction that MMS will soon be able to test.

Identifying the electron diffusion region in a realistic simulation of Earth's magnetotail

A historic challenge to understanding geomagnetic activity is determining where in Earths magnetotail magnetic energy is converted into particle energy and heat by magnetic reconnection. Key to unravel this fundamental process is in determining the location and extent of the electron diffusion region (EDR) where the energy conversion is initiated. We have located the EDR during a substorm on 15 February 2008 by using a combination of global magnetohydrodynamic (MHD) and particle-in-cell (PIC) simulations. Solar wind data were used as input into the MHD simulation, which provided the initial and boundary conditions for the PIC calculation. The simulated reconnection rate was episodic with magnetic reconnection occurring every few seconds. The reconnection site moved several Earth radii in a few minutes. A parameter that measures the breakdown of electron gyrotropy about the magnetic field provided the clearest location of the EDR where changes in magnetic topology and particle acceleration are initiated.

Observation of high-frequency electrostatic waves in the vicinity of the reconnection ion diffusion region by the spacecraft of the Magnetospheric Multiscale (MMS) mission

We report Magnetospheric Multiscale observations of high-frequency electrostatic waves in the vicinity of the reconnection ion diffusion region on the dayside magnetopause. The ion diffusion region is identified during two magnetopause crossings by the Hall electromagnetic fields, the slippage of ions with respect to the magnetic field, and magnetic energy dissipation. In addition to electron beam modes that have been previously detected at the separatrix on the magnetospheric side of the magnetopause, we report, for the first time, the existence of electron cyclotron harmonic waves at the magnetosheath separatrix. Broadband waves between the electron cyclotron and electron plasma frequencies, which were probably generated by electron beams, were found within the magnetopause current sheet. Contributions by these high-frequency waves to the magnetic energy dissipation were negligible in the diffusion regions as compared to those of lower-frequency waves.

A statistical study of kinetic‐size magnetic holes in turbulent magnetosheath: MMS observations

Kinetic-size magnetic holes (KSMHs) in the turbulent magnetosheath are statistically investigated using high time resolution data from the MMS mission. The KSMHs with short duration (i.e., < 0.5 s) have their cross section smaller than the ion gyro-radius. Superposed epoch analysis of all events reveals that an increase in the electron density and total temperature, significantly increase (resp. decrease) the electron perpendicular (resp. parallel) temperature, and an electron vortex inside KSMHs. Electron fluxes at ~ 90° pitch angles with selective energies increase in the KSMHs, are trapped inside KSMHs and form the electron vortex due to their collective motion. All these features are consistent with the electron vortex magnetic holes obtained in 2D and 3D particle-in-cell simulations, indicating that the observed KSMHs seem to be best explained as electron vortex magnetic holes. It is furthermore shown that KSMHs are likely to heat and accelerate the electrons.

Observation of Three-dimensional Magnetic Reconnection in the Terrestrial Magnetotail

Study of magnetic reconnection has been focused on two-dimensional geometry in the past decades, whereas three-dimensional structures and dynamics of reconnection X-line are poorly understood. In this paper, we report Cluster multi-spacecraft observations of a three-dimensional magnetic reconnection X-line with a weak guide field (~25% of the upstream magnetic field) in the Earths magnetotail. We find that the X-line not only retreated tailward but also expanded across the tail following the electron flow direction with a maximum average speed of (0.04 - 0.15) VA,up, where VA,up is the upstream Alfven speed, or (0.14 - 0.57) Vde, where Vde is the electron flow speed in the out-of-plane direction. An ion diffusion region was observed by two spacecraft that were separated about 10 ion inertial lengths along the out-of-plane direction; however, these two spacecraft observed distinct magnetic structures associated with reconnection: one spacecraft observed dipolarization fronts while the other one observed flux ropes. This indicates that reconnection proceeds in drastically different ways in different segments along the X-line only a few ion inertial lengths apart.

Coordinated observations of two types of diffuse auroras near magnetic local noon by Magnetospheric Multiscale mission and ground all-sky camera

Structured diffuse auroras are often observed near magnetic local noon (MLN), but their generation mechanisms are poorly understood. We have found that two types of structured diffuse auroras with ...