Multiscale studies of the three-dimensional dayside X-line

AbstractWe review recent experience from the Cluster, Double Star, and THEMIS missions for lessons that apply to the upcoming Magnetospheric Multiscale Mission (MMS) being developed for launch in 2014. On global scales, simulation and statistical studies lead to mean configurations of dayside reconnection, implying specific relative alignments of the inflow magnetic fields and X-line, with implications for MMS operations designed to maximize the number of close encounters with the diffusion region. At intermediate MHD-to-ion scales, reconstruction of features created by one or two X-lines have developed to the point where data from a cluster of spacecraft can determine their temporal trends and the approximate three-dimensional X-line structure. Recent petascale particle-in-cell (PIC) simulations of reconnection encompass three spatial dimensions with excellent resolution, and make striking predictions of electron scale physics that creates complex interacting flux ropes under component reconnection. High time resolution measurements from MMS will determine the detailed electron scale kinetics embedded within the global and MHD–ion scale contexts. These developments will lead to the refinement of our three-dimensional multiscale picture of reconnection, yielding improved understanding of the global, MHD, and local physics controlling the onset or quenching, variability, and mean rate of reconnection. This in turn will enable improved predictability of the structural features created by transient reconnection, and their space weather consequences

Neutral atom imaging of the magnetospheric cusps

The magnetospheric cusps separate closed dayside magnetospheric field lines from open field lines of the magnetotail mantle and lobes. All magnetospheric field lines that map to the magnetopause also pass through the cusp regions. Thus whenever magnetic reconnection occurs at the magnetopause, magnetosheath plasma can enter one or both of the cusp regions and charge exchange with the geocorona. The resulting energetic neutral atoms (ENAs) resulting from this charge exchange process propagate away from the cusps and are observed remotely by the Interstellar Boundary Explorer (IBEX). The asymmetry of the ENA intensities between the northern and southern cusps are strongly dependent upon the Earth's dipole tilt angle and are consistent with in situ cusp observations. These asymmetric fluxes in the cusp regions are suggested to be explained by the regions at the magnetopause where magnetic reconnection is expected

TRICE 2 Observations of Low-Energy Magnetospheric Ions Within the Cusp

On December 08, 2018 the Twin Rocket Investigation of Cusp Electrodynamics 2 (TRICE 2) mission was successfully launched. The mission consisted of two sounding rockets, each carrying a payload capable of measuring electron and ion distributions, electric and magnetic fields, and plasma waves occurring in the northern magnetospheric cusp. This study highlights the ion and wave observations obtained by TRICE 2 in the cusp and observations from the magnetospheric multiscale (MMS) spacecraft at the low-latitude magnetopause two hours prior to the TRICE 2 traversal of the cusp. Within the cusp, typical ion cusp features were observed, that is, energy-latitude dispersion of injected magnetosheath plasma. However, a lower energy population was also measured near the equatorward edge of the cusp on open field lines. Pitch-angle distributions of the low-energy ions suggest that this population was magnetospheric in origin, and not from ionospheric upflows. Data from MMS show that counterstreaming ions were present in the outer magnetosphere and low-latitude boundary layer at similar energies to those observed by TRICE 2 in the cusp. Correlations between the low-energy ions within the cusp and broadband extremely low frequency waves suggest that the low-energy magnetospheric ions that filled the flux tube may have undergone wave-particle interactions. These interactions may cause pitch-angle scattering of low-energy magnetospheric ions closer to the loss cone, thereby allowing them to precipitate into the cusp and be measured by the TRICE 2 sounding rockets

Sequential Observations of Flux Transfer Events, Poleward-Moving Auroral Forms, and Polar Cap Patches

We report the observation of solar wind‐magnetosphere‐ionosphere interactions using a series of flux transfer events (FTEs) observed by Magnetospheric MultiScale (MMS) mission located near the dayside magnetopause on 18 December 2017. The FTEs were observed to propagate duskward and either southward or slightly northward, as predicted under duskward and southward interplanetary magnetic field (IMF). The Cooling model also predicted a significant dawnward propagation of northward‐moving FTEs. Near the MMS footprint, a series of poleward‐moving auroral forms (PMAFs) occurred almost simultaneously with those FTEs. They propagated poleward and westward, consistent with the modeled FTE propagation. The intervals between FTEs, relatively consistent with those between PMAFs, strongly suggest a one‐to‐one correspondence between the dayside transients and ionospheric responses. The FTEs embedded in continuous reconnection observed by MMS and corresponding PMAFs individually occurred during persistent auroral activity recorded by an all‐sky imager strongly indicate that those FTEs/PMAFs resulted from the temporal modulation of the reconnection rate during continuous reconnection. With the decay of the PMAFs associated with the FTEs, patch‐like plasma density enhancements were detected to form and propagate poleward and then dawnward. Propagation to the dawn was also suggested by the Super Dual Auroral Radar Network (SuperDARN) convection and Global Positioning System (GPS) total electron content data. We relate the temporal variation of the driving solar‐wind and magnetospheric mechanism to that of the high‐latitude and polar ionospheric responses and estimate the response time