Transient, Turbulent Hall Currents in the Sunlit Terrestrial Ionosphere

At night in Earth's polar regions, energetic aurorae frequently penetrate into the atmosphere, driving turbulent electrojet currents in the bottomside ionosphere. During the day, however, Earth's plasma environment become highly conductive, caused by the constant extreme ultraviolet radiation emitted from the Sun. The high-conductivityplasma in the dayside ionosphere can effectively short out plasma turbulence around aurorae, and so electrojet turbulence is rare in the dayside high-latitude ionosphere. In this report, we show observations to the contrary. During the onset of the 23 April 2023 geomagnetic storm, we observe prolific small-scale plasma turbulence in the dayside E-region on closed magnetic field-lines just equatorward of the cusp. Using data from two orbiting satellites, we infer the location of the cusp and the widespread presence of diffuse aurorae, through observations of particle precipitation and wave-particle interactions near the magnetospheric equator. The diffuse aurorae pass electric fields and produce unstable gradients in the plasma density. The number and intensity of the falling charges overwhelm the capacity of the lower ionosphere to neutralize the charges, spurring the growth of turbulent electrojets. We thereby establish correlation and causality between observations of chorus wave activity near the magnetospheric equator and observations of turbulent electrojets in the ionosphere on closed magnetic field-lines. We discuss the implications that this discovery bears for the electrodynamics of the dayside ionosphere.