Eastward Transients in the Dayside Ionosphere II: A Parallel-plate Capacitor-Like Effect

TL;DR

This paper reports on eastward-moving electric field structures in the dayside ionosphere during geomagnetic storms, proposing a new capacitor-like effect driven by wave-particle interactions and turbulence, challenging traditional cusp-region explanations.

Contribution

It introduces the concept of a parallel-plate capacitor-like effect caused by turbulent Hall currents during storms, offering a new perspective on dayside ionospheric electrodynamics.

Findings

Eastward electric field structures observed during storms.

Association with turbulent Hall currents and wave-particle interactions.

Proposed a new capacitor-like mechanism in the ionosphere.

Abstract

During the 23 April 2023 geospace storm, we observed chorus wave-driven, energetic particle precipitation on closed magnetic field lines in the dayside magnetosphere. Simultaneously and in the ionosphere's bottom-side, we observed signatures of impact ionization and strong enhancements in the ionospheric electric field, via radar-detection of meter-scale turbulence, and with matching temporal characteristics as that of the magnetospheric observations. We detailed this in a companion paper. In the present article, we place those observations into context with the dayside ionosphere, and describe a remarkably similar event that took place during the May 2024 geospace superstorm. In both cases, fast, eastward-moving electric field structures were excited equatorward of the ionospheric cusp, on closed magnetic field-lines -- observations that challenge existing modes of explanation for electrodynamics in the cusp-region, where most such observations are interpreted in the context of poleward-moving auroral forms. Instead, primarily eastward-moving electric field structures were associated with turbulent Hall currents that are perhaps characteristically excited during geospace storms by wave-particle interactions near magnetospheric equator or by proton precipitation characteristics in the cusp, forming a `parallel-plate capacitor-like effect'. We propose that transient eastward electrodynamic bursts in the dayside ionosphere might be a common, albeit previously unresolved, feature of geomagnetic storms.