[1] Dipolarization fronts (DFs) are frequently detected in the Earth's magnetotail from X GSM = À30 R E to X GSM = À7 R E . How these DFs are formed is still poorly understood. Three possible mechanisms have been suggested in previous simulations: (1) jet braking, (2) transient reconnection, and (3) spontaneous formation. Among these three mechanisms, the first has been verified by using spacecraft observation, while the second and third have not. In this study, we show Cluster observation of DFs inside reconnection diffusion region. This observation provides in situ evidence of the second mechanism: Transient reconnection can produce DFs. We suggest that the DFs detected in the near-Earth region (X GSM > À10 R E ) are primarily attributed to jet braking, while the DFs detected in the mid-or far-tail region (X GSM < À15 R E ) are primarily attributed to transient reconnection or spontaneous formation. In the jetbraking mechanism, the high-speed flow "pushes" the preexisting plasmas to produce the DF so that there is causality between high-speed flow and DF. In the transientreconnection mechanism, there is no causality between highspeed flow and DF, because the frozen-in condition is violated. Citation: Fu, H. S., et al. (2013), Dipolarization fronts as a consequence of transient reconnection: In situ evidence, Geophys. Res. Lett., 40,[6023][6024][6025][6026][6027]

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.

Photoelectrochemical (PEC) artificial leaves hold the potential to lower the costs of sustainable solar fuel production by integrating light harvesting and catalysis within one compact device. However, current deposition techniques limit their scalability, 1 while fragile and heavy bulk materials can affect their transport and deployment. Here, we demonstrate the fabrication of lightweight artificial leaves by employing thin, flexible substrates and carbonaceous protection layers. Lead halide perovskite photocathodes deposited onto indium tin oxide coated polyethylene terephthalate achieve an activity of 4266 µmol H2 g -1 h -1 using a platinum catalyst, whereas photocathodes with a molecular Co catalyst for CO2 reduction attain a high CO:H2 selectivity of 7.2 under a lower 0.1 sun irradiation. The corresponding lightweight perovskite-BiVO4 PEC devices display unassisted solar-to-fuel efficiencies of 0.58% (H2) and 0.053% (CO), respectively. Their potential for scalability is demonstrated by 100 cm 2 standalone artificial leaves, which sustain a comparable performance and stability of ≈24 h to their 1.7 cm 2 counterparts. Bubbles formed under operation further enable the 30-100 mg cm -2 devices to float, while lightweight reactors facilitate gas collection during outdoor testing on a river. The leaf-like PEC device bridges the gulf in weight between traditional solar fuel approaches, showcasing activities per gram comparable to photocatalytic suspensions and plant leaves. The presented lightweight, floating systems may enable open water applications, while avoiding competition with land use.

, the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites observed a significant intensification of chorus in response to the interplanetary shock in the Earth's dayside plasma trough. We analyze the wave-particle interaction and reveal that the chorus intensification can be caused by the gyroresonance between the chorus and the energetic electrons. When the electrons are scattered from resonance points to low-density regions along the diffusion curves, a part of their energy can be lost and then transferred to amplify the chorus. During the compression of the magnetosphere, the temperature anisotropy of electrons is enhanced. This makes the electron diffusion and chorus intensification very effective. The maximum growth rate after the shock is about 50% greater than that before the shock. The lower-energy (15-25 keV) electrons contribute more to the growth of chorus due to the larger density gradient along the diffusion curve. The <10 keV electrons are almost isotropic, so they contribute little to the amplification of chorus. We investigate the free energy for the chorus intensification and find that it can be generated through the local betatron acceleration and radial diffusion processes. The local betatron acceleration results from the shock-induced compression of the magnetosphere. The linear and nonlinear growth rates are also compared. We find that the linear diffusion process works well for the present case.

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.

[1] During the period 19-22 November 2007, the near-equatorial satellites THEMIS D (ThD) and E (ThE) traversed the Earth's morningside magnetosphere once per day and for nearly 2 h the orbits tracked close to each other, providing an excellent opportunity to investigate the evolution of energetic electrons fluxes (EEFs) on two time scales. By analyzing the electrons in the energy range 100-300 keV, we have found that the EEFs undergo different evolutions in the different subregions of Earth's morningside magnetosphere during a moderate storm. The evolutions at three specific locations, showing, respectively, the features of electron loss, acceleration, and conservation, have been analyzed in detail. Our observations reveal that, during storm time, the evolution of EEFs involves five processes: (1) the resonant interaction between chorus and energetic electrons, which can contribute to both loss and acceleration of electrons depending on the distribution of phase space density, (2) the radial diffusion, which is indicated by the good coherence between ULF waves and EEFs and dominates in the region where the chorus is relatively weak; (3) the adiabatic transport, which affects the EEFs at L > 6 during the recovery phase and prefers to work on large time scale (>1 d); (4) the magnetopause shadowing, which can evacuate electrons at L > 7 during the storm main phase but play minor roles during the recovery phase, when the magnetopause was moving outward; (5) the magnetospheric convection, which can significantly affect the dynamics of the <100 keV but not the >100 keV electrons. All these five processes couple to each other and determine the EEFs together.Citation: Fu, H. S., J. B. Cao, B. Yang, and H. Y. Lu (2011), Electron loss and acceleration during storm time: The contribution of wave-particle interaction, radial diffusion, and transport processes,

Using a global magnetospheric MHD model coupled with a kinetic ring current model, we investigate the effects of magnetotail dynamics, particularly the earthward bursty bulk flows (BBFs) produced by the tail reconnection, on the global‐scale current systems. The simulation results indicate that after BBFs brake around X = −10 RE due to the dipolar “magnetic wall,” vortices are generated on the edge of the braking region and inside the inner magnetosphere. Each pair of vortex in the inner magnetosphere disturbs the westward ring current to arc radially inward as well as toward high latitudes. The resultant pressure gradient on the azimuthal direction induces region‐1 sense field‐aligned component from the ring current, which eventually is diverted into the ionosphere at high latitudes, giving rise to a pair of field‐aligned current (FAC) eddies in the ionosphere. On the edge of the flow braking region where vortices also emerge, a pair of region‐1 sense FACs arises, diverted from the cross‐tail duskward current, generating a substorm current wedge. This is again attributed to the increase of thermal pressure ahead of the bursty flows turning azimuthally. It is further found that when multiple BBFs, despite their localization, continually and rapidly impinge on the “wall,” carrying sufficient tail plasma sheet population toward the Earth, they can lead to the formation of a new ring current. These results indicate the important role that BBFs play in bridging the tail and the inner magnetosphere ring current and bring new insight into the storm‐substorm relation.

[1] The electric structure of dipolarization fronts (DFs) is very important to both DF dynamics and particle acceleration. We performed two-dimensional Hall MHD simulation to study the electric structure of DF produced by interchange instability on the scale of ion inertial length in the flow braking region of near-Earth tail. The results indicate that the Hall effect makes the structures of plasma density and magnetic field deformed in the dawn-dusk direction. This deformation is caused by the induced Lorentz force along the tangent plane of DF, which is associated with the outward moving of demagnetized ions driven by the ion-scale Earthward electric field on DF. In addition, the x component of electric field contributed jointly by Hall and electron pressure gradient terms along with Bz can produce a dawnward E × B drift to the whole "mushroom" structure. Inside the DF, the electric field is mainly produced by Hall term, and the contributions from the convectional and electron pressure gradient electric fields are very small. This indicates that the ion frozen-in condition of magnetic field is violated inside the DF. Therefore, it is the electric field contributed by Hall term inside the DF that changes the overall MHD "mushroom" pattern. The comparison between the simulation results and the observations of THEMIS satellites demonstrates that the model of Hall MHD simulation can reproduce the plasma and electric field observed at DF.