Plasma and energetic particle behaviors during asymmetric magnetic reconnection at the magnetopause

Abstract

The factors controlling asymmetric reconnection and the role of the cold plasma population in the reconnection process are two outstanding questions. We present a case study of multipoint Cluster observations demonstrating that the separatrix and flow boundary angles are greater on the magnetosheath than on the magnetospheric side of the magnetopause, probably due to the stronger density than magnetic field asymmetry at this boundary. The motion of cold plasmaspheric ions entering the reconnection region differs from that of warmer magnetosheath and magnetospheric ions. In contrast to the warmer ions, which are probably accelerated by reconnection in the diffusion region near the subsolar magnetopause, the colder ions are simply entrained by × drifts at high latitudes on the recently reconnected magnetic field lines. This indicates that plasmaspheric ions can sometimes play only a very limited role in asymmetric reconnection, in contrast to previous simulation studies. Three cold ion populations (probably H + , He + , and O + ) appear in the energy spectrum, consistent with ion acceleration to a common velocity.

Electron scale structures and magnetic reconnection signatures in the turbulent magnetosheath

“…The appearance of the two distinct cold and hot populations of ions leading to a non‐Maxwellian distribution suggests that these observations have taken place where ions were demagnetized [e.g., Dai et al , ; Zhou et al , ]. This idea is supported by the nongyrotropic shape of the ion distributions in VDF plots (Figures g and h), where an asymmetric reconnection [e.g., Lee et al , ] can lead to mixing up distinct sources of plasma with different energies. The separation of two populations in – plane along (Figure h) is also consistent with previous observations of ion diffusion region by Dai et al [] using Time History of Events and Macroscale Interactions during Substorms spacecraft.…”

Electrostatic solitary waves with distinct speeds associated with asymmetric reconnection

“…Figure shows an overview of the crossing observed by Cluster 2 (C2), which crosses the magnetopause approximately 5 R E north of the subsolar point. Both C1 and C3 observe northward ion outflows associated with reconnection, indicating that the spacecraft cross the magnetopause north of the reconnection X line (this reconnection event was analyzed by Lee et al [] using C3). C2 begins in the magnetosphere, identified by northward B , low plasma density n , and high electron temperature T e , then crosses the magnetopause into the ion outflow, then into the magnetosheath separatrix.…”

Observations of energetic particle escape at the magnetopause: Early results from the MMS Energetic Ion Spectrometer (EIS)

“…The magnetic topology at the magnetopause as reflected in distributions of lower energy particles (eV to several keV) and magnetic fields is well documented [e.g., Fuselier et al, 1995Fuselier et al, , 1997Lee et al, 2014] and is understood in terms of the characteristics of the low-latitude boundary layer (LLBL) [e.g., Eastman et al, 1976] and the particles flowing on reconnected magnetic field lines just outside the magnetopause that constitute the magnetosheath boundary layer (MSBL) [e.g., Cowley, 1982]. For energetic particles, the most common signature attributed to the presence of finite B n is monohemispheric streaming of energetic protons [West and Buck, 1976;Eccles and Fritz, 2002], sometimes associated with boundary-trapped energetic electrons [Williams et al, 1979;Scholer et al, 1982;Daly, 1982].…”