The 18 November 2015 Magnetopause Crossing: The GEM Dayside Kinetic Challenge Event Observed by MMS/HPCA

Abstract

At Earth's dayside magnetopause, the fundamental process known as magnetic reconnection is responsible for connecting geomagnetic field lines to interplanetary magnetic field lines and converting magnetic energy into particle energy and heat. As part of a coordinated analysis effort by the Geospace Environment Modeling (GEM) community to determine the reconnection location and other aspects of reconnection, a magnetopause crossing by the Magnetospheric Multiscale (MMS) mission on 18 November 2015 was selected. The crossing occurred during stable solar wind and dominantly southward interplanetary magnetic field conditions. The MMS satellites were located close to the subsolar region and observed southward accelerated ion jets during encounters with the magnetopause boundary layers, indicating the presence of an active X‐line north of the satellites. Using proton distributions from the Hot Plasma Composition Analyzer (HPCA) instruments, the distance from the spacecraft to the reconnection site was initially determined to be between 5 to 7 RE. A slight rotation of the interplanetary magnetic field caused a change of the magnetic topology at the magnetopause. This topology change produced conditions which are known to change the location of the X‐line. After the change, the location of the component reconnection line was estimated to be less than 4 RE, but most likely was much closer to the observing satellites.

Magnetosheath Microstructure: Mirror Mode Waves and Jets during Southward IP Magnetic Field

“…It is important to mention that the B z discontinuity detected by MMS was also observed upstream of the bow shock by Wind spacecraft as Kitamura et al (2016) and Trattner et al (2020) showed. As seen in Figure 2 of Kitamura et al (2016), the change from negative B z to positive values occurred through two discontinuities, and not in a smooth way as was observed by MMS in the magnetosheath.…”

“…Thus, it is possible that MMS could go through the separatrix, where particles beams are expected to show higher parallel velocities as in the J1 and J2 cases. In a recent study, Trattner et al (2020) identified J1 and J2 jets as signatures of the magnetopause boundary layer and mentioned that the southward accelerated ion Journal of Geophysical Research: Space Physics 10.1029/2020JA027940 jets are evidence of an active X-line north of the MMS satellites. This would explain why we observe two ion populations: the more dense, unaccelerated population has its origin in the magnetosheath, while the accelerated, less dense population comes from the magnetosphere.…”

“…The transition from negative to positive B z in the SW was accompanied by a small increment in the density that lasted around ∼8 min. As we discuss below, it is highly probable (see Figure 3 in Trattner et al, 2020) that this small enhancement in plasma density is modified as the material crosses the shock and travels through the magnetosheath, leading to the large enhancement in density within J3 at the time of the smooth B z rotation observed by MMS. Figure 1 also shows the existence of anticorrelated plasma density and B field fluctuations, which we identify as mirror mode waves.…”

Characteristics of Minor Ions and Electrons in Flux Transfer Events Observed by the Magnetospheric Multiscale Mission

“…Also similar to the 11 October 2015 interval discussed here, the reconnection line was far from MMS during the GEM 18 November 2015 crossing (~5-7 R E ), based on HPCA ion distributions (the reconnection line during the GEM interval then approached the MMS spacecraft as the IMF slightly rotated). A more comprehensive description of the relative distance between MMS and the magnetopause reconnection site during the GEM interval is provided in the companion paper of this special issue by Trattner et al (2020). Figure 15 is in the same format as Figure 2 and shows a 20-min interval centered upon the MMS burst mode segment within which this magnetosheath FTE was observed.…”

Long and Active Magnetopause Reconnection X‐Lines During Changing IMF Conditions

“…The correct solar wind convection times to the magnetopause were determined by individually lining up IMF rotations observed at the Wind satellite with magnetic field rotations in the magnetosheath observed by MMS/FGM (e.g., Trattner et al, 2018). A detailed description of the methodology to convect the solar wind data to the magnetopause is discussed below in the description of Figure 2 and can also be found in Trattner et al (2020).…”