In-situ spacecraft observations are critical to our study and understanding of the various phenomena that couple mass, momentum, and energy throughout near-Earth space and beyond. However, on-orbit telemetry constraints can severely limit the capability of spacecraft to transmit high-cadence data, and missions are often only able to telemeter a small percentage of their captured data at full rate. This presents a programmatic need to prioritize intervals with the highest probability of enabling the mission’s science goals. Larger missions such as the Magnetospheric Multiscale mission (MMS) aim to solve this problem with a Scientist-In-The-Loop (SITL), where a domain expert flags intervals of time with potentially interesting data for high-cadence data downlink and subsequent study. Although suitable for some missions, the SITL solution is not always feasible, especially for low-cost missions such as CubeSats and NanoSats. This manuscript presents a generalizable method for the detection of anomalous data points in spacecraft observations, enabling rapid data prioritization without substantial computational overhead or the need for additional infrastructure on the ground. Specifically, Principal Components Analysis and One-Class Support Vector Machines are used to generate an alternative representation of the data and provide an indication, for each point, of the data’s potential for scientific utility. The technique’s performance and generalizability is demonstrated through application to intervals of observations, including magnetic field data and plasma moments, from the CASSIOPE e-POP/Swarm-Echo and MMS missions.

Widely employed to model collisionless plasma phenomena occurring naturally in Earth’s magnetic environment, throughout the heliosphere, and in laboratory fusion devices, the Vlasov equation self-consistently describes the fundamental kinetic dynamics of plasma particles as they are accelerated through phase space via electric and magnetic forces. The Fast Plasma Investigation (FPI) onboard NASA’s Magnetospheric Multiscale (MMS) four-spacecraft mission sufficiently resolves the seven spatial, temporal, and velocity-space dimensions of phase space needed to directly observe terms in the Vlasov equation, as recently demonstrated by Shuster et al. [2021] in the context of electron-scale current layers at the reconnecting magnetopause. These results motivate novel exploration of the types of distinct kinetic signatures in ∂fe/∂t, v⋅∇fe, and (F/me)⋅∇vfe which are associated with the magnetic reconnection process, where F = −e(E + v×B) represents the Lorentz force on an electron, and fe specifies the electron phase space density. We apply this approach to characterize the structure of the velocity-space gradient terms in the electron Vlasov equation measured by MMS. Discussion of the uncertainties which arise when computing the velocity-space gradients of the FPI phase space densities is presented, along with initial validation of the (F/me)⋅∇vfe measurements by comparison to the ∂fe/∂t and v⋅∇fe terms. Successful measurement of the force term (F/me)⋅∇vfe in the Vlasov equation suggests a new technique for inferring spatial gradients from single spacecraft measurements which may be applied to improve the spatial resolution of the electron pressure divergence ∇⋅Pe necessary to understand the microphysics of the electron diffusion region of magnetic reconnection. Reference: Shuster, J. R., et al. (2021), Structures in the terms of the Vlasov equation observed at Earth’s magnetosphere, Nature Physics, doi:10.1038/s41567-021-01280-6.

Magnetopause Kelvin-Helmholtz (KH) waves are believed to mediate solar wind plasma transport via small-scale mechanisms. Vortex-induced reconnection (VIR) was predicted in simulations and recently observed using NASA’s Magnetospheric Multiscale (MMS) mission data. Flux Transfer Events (FTEs) produced by VIR at multiple locations along the periphery of KH waves were also predicted in simulations but detailed observations were still lacking. Here we report MMS observations of an FTE-type structure in a KH wave trailing edge during KH activity on 5 May 2017 on the dawnside flank magnetopause. The structure is characterised by (1) bipolar magnetic BY variation with enhanced core field BZ and (2) enhanced total pressure with dominant magnetic pressure. The cross-section size of the FTE is found to be consistent with vortex-induced flux ropes predicted in the simulations. Unexpectedly, we observe an ion jet (VY), electron parallel heating, ion and electron density enhancements, and other signatures that can be interpreted as a reconnection exhaust at the FTE central current sheet. Moreover, pitch angle distributions of suprathermal electrons on either side of the current sheet show different properties, indicating different magnetic connectivities. This FTE-type structure may thus alternatively be interpreted as two interlaced flux tubes with reconnection at the interface as reported by Kacem et al. (2018) and Øieroset et al. (2019). The structure may be the result of interaction between two flux tubes, likely produced by multiple VIR at the KH wave trailing edge, and constitutes a new class of phenomenon induced by KH waves.

We use a newly developed global Hall MHD code to investigate how reconnection drives magnetotail asymmetries in small magnetospheres. Here, we consider a scaled-down, Earth-like magnetosphere where we have artificially inflated the ion inertial length ($\delta_i$) to one Earth radius (the real Earth’s $\delta_i\approx 1/15-1/20 R_E \approx 300-400\unit{km}$ in the magnetotail). This results in a magnetotail width on the order of $30 \delta_i$, slightly smaller than Mercury’s tail and much smaller than Earth’s. At this small size, we find that the Hall effect has significant impact on the global flow pattern, changing from a symmetric, Dungey-like convection under resistive MHD to an asymmetric pattern similar to that found in previous Hall MHD simulations of Ganymede’s subsonic magnetosphere as well as other simulations of Mercury’s using multi-fluid or embedded kinetic physics. We demonstrate that the Hall effect is sufficient to induce a dawnward asymmetry in observed dipolarization front locations and find quasi-periodic global scale dipolarizations under steady, southward solar wind conditions. On average, we find a thinner current sheet dawnward; however, the measured thickness oscillates with the dipolarization cycle. During the flux-pileup stage, the dawnward current sheet can be thicker than the duskward sheet. This could be an explanation for recent observations that suggest Mercury’s current sheet is actually thicker on the duskside: a sampling bias due to a longer-lasting “thick’ state in the sheet.