Study of the Electron Velocity Inside Sub‐Ion‐Scale Magnetic Holes in the Solar Wind by MMS Observations

Electron vortices are a key element in the sub‐ion magnetic hole. Here, we investigate the electron velocity inside two sub‐ion magnetic holes in the solar wind based on the Magnetospheric Multiscale (MMS) mission. We find that the observational electron velocities inside the magnetic holes are contributed by the combination of the electron diamagnetic (Ve,dia), E × B (Ve,E), magnetic gradient (Ve,▽B) and curvature (Ve,R) drifts. Ve,dia, Ve,▽B, and Ve,R are comparable, while Ve,E is very small inside the hole. The weak Ve,E could result from the electric field approximately perpendicular to the magnetic field inside the structure. The value of Ve,▽B + Ve,R is near 0; thus, Ve,dia is approximately equal to the observational electron velocity. The current density contributed by the electron diamagnetic, magnetic gradient and curvature drift motions is self‐consistent with the magnetic depression inside the hole, suggesting that these three electron drift motions play a crucial role in stabilizing the magnetic hole in the mirror‐stable astrophysical plasma environment. Key Points Electron vortices exist in the sub‐ion‐scale magnetic holes in the solar wind The electron vortex is mainly contributed by the combination of the electron diamagnetic, magnetic gradient, and curvature drifts The magnetic gradient and curvature drifts almost cancel each other out; thus, the electron vortex can be explained by the diamagnetic drift