We report in situ observations of an electron jet generated by secondary reconnection within the outflow region of primary reconnection in the terrestrial magnetotail by the Magnetospheric Multiscale (MMS) mission. The MMS spacecraft first passed through the primary X-line and then crossed the electron jet in the outflow of primary reconnection. There are a series of small-scale flux ropes in the secondary reconnection region. Decoupling from the magnetic field for both ions and electrons, an intense out-of-plane current, unambiguous Hall currents, and a Hall electromagnetic field appear in the electron jet. Strong electron dissipation ( ), a nonzero electric field in the electron frame ( ), and electron crescent-like shaped distributions are detected in the center of the electron jet, implying that MMS spacecraft were likely passing through the electron diffusion region. The significant electron dissipation indicates that the electrons can be accelerated in the electron jet and the electron jet may be another important electron acceleration channel along with the electron diffusion region.

An ion‐scale flux rope (FR), embedded in a high‐speed electron flow (possibly an electron vortex), is investigated in the magnetotail using observations from the Magnetospheric Multiscale (MMS) spacecraft. Intense electric field and current and abundant waves are observed in the exterior and interior regions of the FR. Comparable parallel and perpendicular currents in the interior region imply that the FR has a non‐force‐free configuration. Electron demagnetization occurs in some subregions of the FR. It is surprising that strong dissipation (J × E' up to 2,000 pW/m3) occurs in the center of the FR without signatures of secondary reconnection or coalescence of two FRs, implying that FR may provide another important channel for energy dissipation in space plasmas. These features indicate that the observed FR is still highly dynamical, and hosts multiscale coupling processes, even though the FR has a very large scale and is far away from the reconnection site.

Kinetic-size magnetic holes (KSMHs) in the terrestrial magnetotail plasma sheet are statistically investigated using the observations from the Magnetospheric Multiscale mission. The scales of KSMHs are found to be smaller than one ion gyroradius or tens of electron gyroradii. The occurrence distributions of KSMHs have dawn–dusk asymmetry (duskside preference) in the magnetotail, which may be caused by the Hall effect. Most events of KSMHs (71.7%) are accompanied by a substorm, implying that substorms may provide favorable conditions for the excitation of KSMHs. However, there is a weak correlation between KSMHs and magnetic reconnection. The statistical results reveal that for most of the events, the electron total temperature and perpendicular temperature increase while the electron parallel temperature decreases inside the KSMHs. The electron temperature anisotropy (T e⊥/ ) is observed in 72% of KSMHs. Whistler-mode waves are frequently observed inside the KSMHs, and most (92%) KSMHs associated with whistler waves have enhancements of electron perpendicular distributions and satisfy the unstable condition of whistler instability. This suggests that the observed electron-scale whistler waves, locally generated by the electron temperature anisotropy, could couple with the electron-scale KSMHs. The observed features of KSMHs and their coupling to electron-scale whistlers are similar to the ones in the turbulent magnetosheath, implying that they are ubiquitous in the space plasmas. The generation of KSMHs in the plasma sheet could be explained by an electron vortex magnetic hole, magnetosonic solitons, and/or ballooning/interchange instabilities.

Abstract. The Double Star Project is a collaboration between Chinese and European space agencies, in which twoChinese magnetospheric research spacecraft, carrying Chinese and European instruments, have been launched into equatorial (on 29 December 2003) and polar (on 25 July 2004) orbits designed to enable complementary studies with the Cluster spacecraft. The two Double Star spacecraft TC-1 and TC-2 each carry a Double Star Plasma Electron and Current Experiment (PEACE) instrument. These two instruments were based on Cluster Flight Spare equipment, but differ from Cluster instruments in two important respects. Firstly, a Double Star PEACE instrument has only a single sensor, which must be operated in a manner not originally envisaged in the Cluster context in order to sample the full range of energies. Secondly, the DPU hardware was modified and major changes of onboard software were implemented, most notably a completely different approach to data compression has been adopted for Double Star, which allows high resolution 3-dimensional distributions to be transmitted almost every spin, a significant improvement over Cluster. This paper describes these instruments, and includes examples of data collected in various magnetospheric regions encountered by the spacecraft which have been chosen to illustrate the power of combined Double Star and Cluster measurements.