Earth's Alfv\'en wings driven by the April 2023 Coronal Mass Ejection

TL;DR

This paper describes a rare interaction regime where Earth's magnetosphere forms Alfvén wings during a 2023 CME, revealing new plasma and magnetic connection features with implications for planetary space weather.

Contribution

It reports the first observations of Earth's Alfvén wings driven by a CME, highlighting new plasma channels and magnetic reconnection processes in sub-Alfvénic conditions.

Findings

Detection of unshocked, accelerated CME plasma impacting Earth's magnetosphere

Observation of magnetic connection channels via wing filaments

Evidence of magnetic reconnection between CME and Earth's magnetic field

Abstract

We report a rare regime of Earth's magnetosphere interaction with sub-Alfv\'enic solar wind in which the windsock-like magnetosphere transforms into one with Alfv\'en wings. In the magnetic cloud of a Coronal Mass Ejection (CME) on April 24, 2023, NASA's Magnetospheric Multiscale mission distinguishes the following features: (1) unshocked and accelerated cold CME plasma coming directly against Earth's dayside magnetosphere; (2) dynamical wing filaments representing new channels of magnetic connection between the magnetosphere and foot points of the Sun's erupted flux rope; (3) cold CME ions observed with energized counter-streaming electrons, evidence of CME plasma captured due to reconnection between magnetic-cloud and Alfv\'en-wing field lines. The reported measurements advance our knowledge of CME interaction with planetary magnetospheres, and open new opportunities to understand how sub-Alfv\'enic plasma flows impact astrophysical bodies such as Mercury, moons of Jupiter, and exoplanets close to their host stars.