Earth's Alfvén Wings: Unveiling Dynamic Variations of Field-Line Topologies With Electron Distributions

Abstract

The magnetic cloud (MC) of the Coronal Mass Ejection on 24 April 2023, contains sub-Alfvénic solar wind, transforming Earth's magnetosphere from conventional bow-shock magnetotail configuration to Alfvén wings. Utilizing measurements from the Magnetosphere Multiscale (MMS) mission, we present for the first time electron distribution signatures as the spacecraft traverses through various magnetic topologies during this transformation. Specifically, we characterize electrons inside the sub-Alfvénic MC, on the dawn-dusk wing field lines and on the closed field lines. The signatures include strahl electrons in MC regions and energetic keV electrons streaming along the dawn and dusk wing field lines. We demonstrate the distribution signatures of dual wing reconnection, defined as reconnection between dawn-dusk Alfvén wing field lines and the interplanetary magnetic field (IMF). These signatures include four electron populations comprised of partially depleted MC electrons and bi-directional energetic electrons with variations in energy and pitch-angle. The distributions reveal evidence of bursty magnetic reconnection under northward IMF.