S. Y. Huang

Electron acceleration in the reconnection diffusion region: Cluster observations

We present one case study of magnetic islands and energetic electrons in the reconnection diffusion region observed by the Cluster spacecraft. The cores of the islands are characterized by strong c ...

Whistler‐mode waves inside flux pileup region: Structured or unstructured?

During reconnection, a flux pileup region (FPR) is formed behind a dipolarization front in an outflow jet. Inside the FPR, the magnetic field magnitude and Bz component increase and the whistler-mode waves are observed frequently. As the FPR convects toward the Earth during substorms, it is obstructed by the dipolar geomagnetic field to form a near-Earth FPR. Unlike the structureless emissions inside the tail FPR, we find that the whistler-mode waves inside the near-Earth FPR can exhibit a discrete structure similar to chorus. Both upper band and lower band chorus are observed, with the upper band having a larger propagation angle (and smaller wave amplitude) than the lower band. Most chorus elements we observed are “rising-tone” type, but some are “falling-tone” type. We notice that the rising-tone chorus can evolve into falling-tone chorus within <3 s. One of the factors that may explain why the waves are unstructured inside the tail FPR but become discrete inside the near-Earth FPR is the spatial inhomogeneity of magnetic field: we find that such inhomogeneity is small inside the near-Earth FPR but large inside the tail FPR.

Electromagnetic energy conversion at dipolarization fronts: Multispacecraft results

Dipolarization fronts (DFs) are believed to play important roles in transferring plasmas, magnetic fluxes, and energies in the magnetotail. Using the Cluster observations in 2003, electromagnetic energy conversion at the DFs is investigated by case and statistical studies. The case study indicates strongest energy conversion at the DF. The statistical study shows the similar features that the energy of the fields can be significantly transferred to the plasmas (load, J · E > 0) at the DFs. These results are consistent with some recent simulations. Examining the electromagnetic fluctuations at the DFs, we suggest that the wave activities around the lower hybrid frequency may play an important role in the energy dissipation.

Identifying magnetic reconnection events using the FOTE method

A magnetic reconnection event detected by Cluster is analyzed using three methods: Single-spacecraft Inference based on Flow-reversal Sequence (SIFS), Multispacecraft Inference based on Timing a Structure (MITS), and the First-Order Taylor Expansion (FOTE). Using the SIFS method, we find that the reconnection structure is an X line; while using the MITS and FOTE methods, we find it is a magnetic island (O line). We compare the efficiency and accuracy of these three methods and find that the most efficient and accurate approach to identify a reconnection event is FOTE. In both the guide and nonguide field reconnection regimes, the FOTE method is equally applicable. This study for the first time demonstrates the capability of FOTE in identifying magnetic reconnection events; it would be useful to the forthcoming Magnetospheric Multiscale (MMS) mission.

Quadrupolar pattern of the asymmetric guide-field reconnection

With high-resolution data of the recently launched Magnetospheric Multiscale (MMS) mission, we report a magnetic reconnection event at the dayside magnetopause. This reconnection event, having a density asymmetry Nhigh/Nlow≈2 on the two sides of the reconnecting current sheet and a guide field Bg≈0.4B0 in the ‘out-of-plane’ direction, exhibit all the two-fluid features: Alfvenic plasma jets in the outflow region, bipolar Hall electric fields toward the current sheet center, quadrupolar Hall magnetic fields in the ‘out-of-plane’ direction, and the corresponding Hall currents. Obviously, the density asymmetry Nhigh/Nlow≈2 and the guide field Bg≈0.4B0 are not sufficient to dismiss the quadrupolar pattern of Hall reconnection. This is different from previous simulations, where the bipolar pattern of Hall reconnection was suggested.

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.

Electron jet detected by MMS at dipolarization front: Electron jet detected by MMS at dipolarization front

Using MMS high-resolution measurements, we present the first observation of fast electron jet (V-e similar to 2,000 km/s) at a dipolarization front (DF) in the magnetotail plasma sheet. This jet, w ...