In this paper, dayside magnetopause energy transport (energy transport across the separatrix surface to the magnetopause boundary layer and energy transport inside the magnetopause boundary layer) and its dependence on the magnetopause dynamic evolution under purely southward interplanetary magnetic field (IMF) conditions are studied via a 3-D global hybrid simulation. By investigating the energy transport across the separatrix surface, current layer surface, and magnetopause surface, we find that the energy transport from the magnetosheath to the magnetopause boundary layer is mainly in the form of electromagnetic energy, while the energy transport directly across the magnetopause surface to the magnetosphere is mainly in the form of plasma energy. The energy transport across the magnetopause surface exhibits temporal variability, driven by the dynamic evolution of reconnection and flux rope. During the development of multiple X-lines reconnection and flux rope, a substantial portion of solar wind energy does not directly penetrate the dayside magnetopause to the magnetosphere. Instead, it is transported with the reconnection outflow and flux rope from low latitude to high latitude, and with the drifting flow from the subsolar region to the tail magnetopause within the magnetopause current layer. These results significantly improve our understanding of solar wind-magnetosphere coupling at the dayside magnetopause.

Magnetic reconnection is a fundamental process known to play a crucial role in electron acceleration and heating, however, the mechanism of electron energization during reconnection is still not fully understood. This study introduces a novel electron acceleration mechanism in which electrons can be accelerated by secondary reconnection in the separatrix region. The secondary reconnection occurs in a thin current sheet resulted from the shear of the out-of-plane Hall magnetic fields of the primary magnetopause reconnection. It results in intense electron energy fluxes towards the primary X-line. This result will likely be an important piece in the puzzle of particle acceleration by reconnection.

We study the dynamic evolution of dayside magnetopause reconnection locations and their dependence on the interplanetary magnetic field (IMF) cone angle via 3-D global-scale hybrid simulations. Cases with finite IMF Bx and Bz but By=0 are investigated. It is shown that the dayside magnetopause reconnection is unsteady under quasi-steady solar wind conditions. The reconnection lines during the dynamic evolution are not always parallel to the equatorial plane even under purely southward IMF conditions. Magnetopause reconnection locations can be affected by the generation, coalescence, and transport of flux ropes (FRs), reconnection inside the FRs, and the magnetosheath flow. In the presence of an IMF component Bx, the magnetopause reconnection initially occurs in high-latitude regions downstream of the quasi-perpendicular bow shock, followed by the generation of multiple reconnection regions. In the later stages of the simulation, a dominant reconnection region is present in low-latitude regions, which can also affect reconnection in other regions. The global distribution of reconnection lines under a finite IMF Bx is found to not be limited to the region with maximum magnetic shear angle.

A document by Liangjin Song. Click on the document to view its contents.

How are particles being energized by turbulent electromagnetic fields is an outstanding question in plasma physics and astrophysics. This paper investigates the electron acceleration mechanism in strong turbulence (δB/B0 ~ 1) in the Earth’s magnetosheath based on the novel observations of the Magnetospheric Multiscale (MMS) mission. We find that electrons are magnetized in turbulent fields for the majority of the time. By directly calculating the electron acceleration rate from Fermi, betatron mechanism, and parallel electric field, it is found that electrons are primarily accelerated by the parallel electric field within coherent structures. Moreover, the acceleration rate by parallel electric fields increases as the spatial scale reduces, with the most intense acceleration occurring over about one ion inertial length. This study is an important step towards fully understanding the turbulent energy dissipation in weakly collisional plasmas.

This paper presents a comprehensive study of the intense current structure (ICS) at the dayside magnetopause, by using the high-resolution data from the Magnetospheric Multiscale (MMS) mission. About 3,600 ICSs with current density exceeding 1.2 μA/m2 have been detected during phase 1a and 1b within the magnetopause boundary layer (MBL). We find that most ICSs have a temporal duration of less than 1 second and thickness of less than one ion inertial length. The number of ICSs decreases with the thickness increasing from the electron-scale to the ion-scale. The occurrence rate of the ICS is relatively higher close to Earth and in the dusk sector near the meridian, probably caused by the large solar wind dynamic pressure. In a local boundary normal coordinate system, the occurrence rate is higher on the magnetosheath side. For most ICSs, the current is carried by electrons. The perpendicular current is larger than the parallel current for more ICSs. The energy conversion J·E is primarily through the perpendicular current and electric field, while the non-ideal energy conversion J·E’ is mainly dominated by the parallel component. ICSs provide much stronger energy conversion and dissipation compared to the ambient plasma in the MBL. This study improves our understanding of the characteristics of the ICS and its role in solar wind-magnetosphere coupling.

We investigate whistler-mode waves and broadband electrostatic waves (EWs) within an ion diffusion region (IDR) at the magnetopause. The quasi-parallel whistlers are observed in the separatrix regions associated with the electron anisotropy or loss-cone, while the oblique whistlers, the Buneman-type waves, and the oblique EWs are observed in the center of the current sheet associated with the accelerated electron or ion beams. The whistlers are linked with Buneman-type waves by the electron Pacman distribution rather than the wave-wave process. The accelerated cold electron beams excite the Buneman-type instabilities and make the anisotropy or loss-cone of hot electrons less apparent, which led to the conversion of the whistlers from quasi-parallel to oblique. Additionally, the oblique EWs are associated with the ion beams produced by the multiple X-line reconnection. These results provide a further understanding of the relation between plasma waves and plasma kinetics in the IDR.