Determine the magnetic topology of the ambiguous eVDF lacking anti-parallel strahl

Determine whether the electron velocity distribution function observed by MMS at 14:23:25.230 UT on April 24, 2023—characterized by magnetic-cloud-like magnetic field and ion signatures, magnetic-cloud-like parallel electron energy flux, and an absence of anti-parallel strahl—corresponds to (i) magnetic cloud plasma on a field line no longer connected to the solar corona or (ii) a dusk-wing flux tube for which reconnection north of MMS has ceased, thereby producing no energetic anti-parallel electrons.

Background

During the April 24, 2023 CME magnetic cloud with sub-Alfvénic solar wind, MMS encountered multiple magnetic topologies including Alfvén wing filaments and newly closed field lines formed by dual-wing reconnection. Electron velocity distribution functions (eVDFs) were used as tracers to diagnose these topologies, with strahl-bearing magnetic cloud (MC) electrons distinguishing solar-wind-connected field lines and keV field-aligned electrons indicating reconnection-driven populations.

At 14:23:25.230 UT, MMS observed an eVDF with MC-like magnetic field, ions, and parallel energy flux but lacking the anti-parallel strahl. The authors identify two plausible interpretations: an MC field line that has lost solar coronal connection or a dusk-wing field line where reconnection north of MMS has turned off, resulting in no energetic anti-parallel electrons. Discriminating between these possibilities is necessary to unambiguously identify the field-line topology in this interval.

References

Based on the established characterizations, this topology cannot be determined conclusively and remains an open question.

— Earth's Alfvén Wings: Unveiling Dynamic Variations of Field-line Topologies with Electron Distributions  (2409.00247 - Gurram et al., 2024) in Section 'Characterizing electrons distributions at different topologies', discussion of Fig. \ref{fig:strahlmiss}h2 (14:23:25.230 UT)