MMS Observations of Storm‐Time Magnetopause Boundary Layers in the Vicinity of the Southern Cusp

Abstract

For southward interplanetary magnetic field (IMF), day-side reconnection produces a low-latitude magnetopause BL composed of newly reconnected magnetic flux. On the magnetosheath side, the magnetosheath boundary layer (MSBL) contains both magnetosphere and magnetosheath plasma (Cowley, 1982;Eastman & Hones, 1979;Mitchell et al., 1987). At the low-shear magnetopause, electrons above 50 eV can be used as an indicator of the transition from magnetosheath to MSBL, due to the changing topological connection (Fuselier et al., 1997). The low-latitude boundary layer (LLBL; Nakamura, 2021), composed of magnetospheric reconnected field lines, is where the solar wind plasma penetrates Earth's magnetosphere. The purpose of this study is to illuminate the physics of these boundaries layers during geomagnetic storms.Typically, geomagnetically disturbed periods are characterized by enhanced entry of plasma, stronger convection, and more magnetospheric transport. Although, less is known about the magnetopause BLs during strong disturbances, since the number of useful observations is limited by the frequency of storms, occurring at about 20/year (Reyes et al., 2021). For a moderate storm, Sonnerup (1971) reported an Explorer-12 crossing of both the MSBL and LLBL, providing early evidence for the open magnetosphere model. Maynard et al. (1991) studied BL dynamics during a storm based on multi-spacecraft observations and concluded that the x-line extended over a significant range of local time, allowing the magnetosheath plasma access into the magnetosphere over this range.

Hemispheric symmetry and asymmetry of poleward moving radar auroral forms (PMRAFs) and associated polar cap patches during a geomagnetic storm

“…Despite the small IMF By component, PMRAFs still show interesting asymmetry, indicating an important role played by local ionospheric conditions. During the event, MMS crossed the magnetopause in proximity to the southern cusp and detected multiple boundary layers as well as kinetic signature of reconnection [33]. The current paper complements [33] by reporting the macroscopic impact of magnetopause reconnection in the ionosphere and its symmetry and asymmetry between hemispheres.…”

“…FIGURE 1Field-of-Views (FOVs) of the SuperDARN radars analyzed in the current study at 2245 UT. This is also the time when MMS entered the magnetopause boundary layer from the magnetosheath[33]. Panel (A) is for the Southern Hemisphere, and Panel (B) is for the Northern Hemisphere.…”

Statistical analysis of overlapping double ion energy dispersion events in the northern cusp

“…We also drop those which correspond to energies we do not associate with the magnetosheath (threshold of 10 3.5 eV). We note that this excludes magnetosheath particles which may be accelerated to super-magnetosheath energies (Burkholder et al, 2022).…”