Burkholder, BrandonChen, Li-JenSorathia, KareemLin, DongVines, SarahBowers, Charles F.2025-04-012025-04-012025-03-11https://doi.org/10.48550/arXiv.2502.16309http://hdl.handle.net/11603/37906When sub-Alfv´enic (Alfv´en Mach number MA < 1) plasmas impact Earth, the magnetosphere develops Alfv´en wings. A Multiscale Atmosphere Geospace Environment (MAGE) global simulation of the April 2023 geomagnetic storm, validated against Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE), reveals the mechanism of field-aligned current (FAC) generation and auroral precipitation for the terrestrial Alfv´en wings. Simulation and observations show northern hemisphere planetward flowing auroral electrons (negative FAC) are predominantly at magnetic local times (MLTs) 8-12. Just before the wings formed, solar wind conditions were similar and MA ∼ 1.4, yet the same FAC system extended from 9-18 MLT. Flow vorticity drives FACs at the boundary of the Alfv´en wings and unshocked solar wind. The Alfv´en wing shape presents a different obstacle to the solar wind compared to typical lobe fluxes, producing the unique FAC and auroral patterns. New insights about Alfv´en wing FACs will help to understand auroral features for exoplanets inside their host star’s Alfv´en zone14 pagesen-USThis work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.Public Domainhttps://creativecommons.org/publicdomain/mark/1.0/Physics - Space PhysicsText