Extreme Birkeland Currents Are More Likely During Geomagnetic Storms on the Dayside of the Earth

Abstract

We examine the statistical distribution of large‐scale Birkeland currents measured by the Active Magnetosphere and Planetary Electrodynamics Response Experiment in four unique categories of geomagnetic activity for the first time: quiet times, storm times, quiet‐time substorms, and storm‐time substorms. A novel method is employed to sort data into one of these four categories, and the categorizations are provided for future research. The mean current density is largest during substorms and its standard deviation is largest during geomagnetic storms. Current densities which are above a low threshold are more likely during substorms, but extreme currents are far more likely during geomagnetic storms, consistent with a paradigm in which geomagnetic storms represent periods of enhanced variability over quiet times. We demonstrate that extreme currents are most likely to flow within the Region 2 current during geomagnetic storms. This is unexpected in a paradigm of the current systems in which Region 1 current is generally larger.

The Spatial Variation of Large‐ and Meso‐Scale Plasma Flow Vorticity Statistics in the High‐Latitude Ionosphere and Implications for Ionospheric Plasma Flow Models

“…The spatial variation of the PDF shape and scale was shown to be ordered by the large-scale flow vorticity and the magnetic field-aligned current (FAC) systems that couple the magnetosphere to the high-latitude ionosphere (FAC is proportional to vorticity in the limit of uniform ionospheric conductance). Coxon et al (2022Coxon et al ( , 2023 have shown that PDFs of FACs measured in the ionosphere are similarly leptokurtic, with a similar spatial variation in distribution shape and scale to the flow vorticity.…”