Abstract
In this study, the ion composition of flux transfer events (FTEs) observed within the magnetosheath proper is examined. These FTEs were observed just upstream of the Earth's postnoon magnetopause by the National Aeronautics and Space Administration (NASA) Magnetospheric Multiscale (MMS) spacecraft constellation. The minor ion characteristics are described using energy spectrograms, flux distributions, and ion moments as the constellation encountered each FTE. In conjunction with electron data and magnetic field observations, such observations provide important contextual information on the formation, topologies, and evolution of FTEs. In particular, minor ions, when combined with the field‐aligned streaming of electrons, are reliable indicators of FTE topology. The observations are also placed (i) in context of the solar wind magnetic field configuration, (ii) the connection of the sampled flux tube to the ionosphere, and (iii) the location relative to the modeled reconnection line at the magnetopause. While protons and alpha particles were often depleted within the FTEs relative to the surrounding magnetosheath plasma, the He+ and O+ populations showed clear enhancements either near the center or near the edges of the FTE, and the bulk plasma flow directions are consistent with magnetic reconnection northward of the spacecraft and convection from the dayside toward the flank magnetopause.
Highlights
Flux transfer events (FTEs) at the magnetopause are considered to be manifestations of transient magnetic reconnection between the interplanetary and magnetospheric magnetic fields
The enhancement of higher‐energy bidirectional electron flux beginning at 12:49:24 UT suggests that magnetic field lines comprising the core of the flux transfer events (FTEs) were closed at the time of the Magnetospheric Multiscale (MMS) encounter, with both ends connected to the ionosphere
Three of the four cases were sampled during nominal Parker spiral conditions; while the fourth case was sampled during a time minimal interplanetary magnetic field (IMF) |Bx|
Summary
Flux transfer events (FTEs) at the magnetopause are considered to be manifestations of transient magnetic reconnection between the interplanetary and magnetospheric magnetic fields. The time to sample a full 3‐D flux distribution using AMPTE‐ CCE/HPCE was 2 min (longer than the typical FTE duration; cf., Kawano & Russell, 1996), composite plasma distributions were painstakingly created by carefully considering the orientation of the changing magnetic field at each sampling energy and angular bin (38‐ms sample resolution) It was generally concluded from this investigation that the ion composition within the FTE was unlike the magnetosheath, magnetosphere, or the boundary layers. This is important for providing a more comprehensive understanding of particle flux transport of ion species between the solar wind, the magnetosphere, and the ionosphere resulting from transient magnetopause reconnection For this initial effort, we limit ourselves to a case study approach. The remainder of this paper compares and contrasts in detail the characteristics of these cases, with focus on the minor ion composition
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