Magnetospheric Multiscale Observations of the Source Region of Energetic Electron Microinjections Along the Duskside, High‐Latitude Magnetopause Boundary Layer

Abstract

The present paper demonstrates the first observations by the Magnetospheric Multiscale (MMS) mission of the counter‐streaming energetic electrons and trapped energetic protons, localized in the magnetic field depressions between the mirror mode peaks, in the Earth's dusk sector high‐latitude magnetosphere. This region is characterized by high plasma beta, strong ion temperature anisotropy, and intermediate plasma density between magnetospheric and magnetosheath plasma. We show that these plasma conditions are unstable for the drift mirror instability. The counter‐streaming electron feature resembles those of the previously reported energetic electron microinjections, but without the energy‐time dispersion signature. This suggests that MMS is passing through one of the potential microinjection source regions. The energetic ion data in the present study is mainly used to estimate the scale size of the mirror mode structures.

Identifying the Structure and Propagation of Dawnside Pc5 ULF Waves Using Space‐Ground Conjunctions

“…B z and the plasma pressure were anti‐phase with β . β had a large value (∼3) when observing intense discrete arcs in keogram, and the drift mirror instability parameter was much larger than 1 after 15:50 UT (Nykyri et al., 2021). Similar to the previous event, the high β value, high drift mirror instability parameter and anti‐correlation between the thermal and magnetic pressures suggest slow or drift mirror mode waves.…”

“…B x and B y were much smaller than B z . β (P i /P b , Figures 1Af and 1Bf) was above ∼1, and the drift mirror instability parameter (β ⊥ (P ⊥ /P ‖ − 1), Figures 1Ah and 1Bh) (Nykyri et al, 2021) was much larger than 1, indicating that the satellites were in the central plasma sheet and the drift mirror mode waves were unstable. THEMIS D had slightly smaller β (∼1.2 after 13:38 UT) compared with THEMIS E (∼1.5 after 13:38 UT), suggesting that THEMIS E was slightly closer to the neutral sheet than THEMIS D. The vertical lines mark individual peaks of β oscillations after 13:38 UT.…”

Energetic Electron Microinjections Observed by MMS in the Dusk Plasma Sheet and Drift Resonance Interpretation

“…Kavosi et al (2018) suggested that the bi-directional electrons are associated with KHW and FTEs at the dusk magnetopause. Nykyri et al (2021) considered that the source regions of these electrons are the diamagnetic cavities caused by magnetic reconnection in the duskside magnetospheric boundary. Nevertheless, our observations show that electrons of all pitch angles simultaneously get acceleration/deceleration in microinjections.…”

“…Recently, Nykyri et al. (2021) observed high fluxes of non‐dispersive counter‐streaming energetic electrons in the high‐latitude duskside magnetopause boundary layer from MMS data. They suggested that this could be a potential source region for the previously reported dispersive microinjection events, and the enhancements of electron fluxes were due to the Fermi mechanism in cavities of the mirror mode wave caused by low‐latitude reconnection for southward and duskward interplanetary magnetic field (IMF).…”

The Structure of the Cusp Diamagnetic Cavity and Test Particle Energization in the GAMERA Global MHD Simulation

“…Furthermore, the ultimate fate of these particles is another important aspect. It is possible that they provide some of the seed population to the radiation belts (Boyd et al., 2016; Nykyri et al., 2021; Tang et al., 2017) or escape to the magnetosheath (Cohen et al., 2017).…”