Excursion-set structure factor of the auroral electric field
Abstract
A spacecraft crossing the aurora cannot tell whether structures in the field-aligned currents are short-lived or merely small. However, by tracking clusters of coherent radar echoes from aurorae and Fourier-transforming motion-shifted echo pairs across radar snapshots, we can calculate the dynamic structure factor of the point-clouds, thereby quantifying the auroral electric field's spatial power and its persistence from 5 to 40 km, in regions where the radar look-direction is perpendicular to the geomagnetic field. This follows from the fact that coherent E-region radar echoes appear only where the ionospheric electric field exceeds the Farley-Buneman instability threshold, and so a point-target imaging radar naturally samples the field's excursion set; the field's spatiotemporal correlations are discernible from that point process. We find that the echo pattern moves with its cluster: large-scale structures persist for tens of seconds, but scales under 10 km renew within seconds, and conjunctions with Swarm satellite pairs replicate the same scale dependence in field-aligned currents. Coherent radar can thus quantify multi-scale variability in the auroral electric field on Alfvénic timescales.
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BibTeX
@misc{ivarsen2026excursionset,
title = {{Excursion-set structure factor of the auroral electric field}},
author = {Magnus F Ivarsen and Kaili Song and Jean-Pierre St-Maurice and Glenn C Hussey},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2606.26854},
eprint = {2606.26854},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.26854},
note = {CC BY-SA 4.0},
}
RIS
TY - UNPB
TI - Excursion-set structure factor of the auroral electric field
AU - Magnus F Ivarsen
AU - Kaili Song
AU - Jean-Pierre St-Maurice
AU - Glenn C Hussey
PY - 2026
DA - 2026/10/27
PB - arXiv
DO - 10.48550/arxiv.2606.26854
UR - https://arxiv.org/abs/2606.26854
AB - A spacecraft crossing the aurora cannot tell whether structures in the field-aligned currents are short-lived or merely small. However, by tracking clusters of coherent radar echoes from aurorae and Fourier-transforming motion-shifted echo pairs across radar snapshots, we can calculate the dynamic structure factor of the point-clouds, thereby quantifying the auroral electric field's spatial power and its persistence from 5 to 40 km, in regions where the radar look-direction is perpendicular to the geomagnetic field. This follows from the fact that coherent E-region radar echoes appear only where the ionospheric electric field exceeds the Farley-Buneman instability threshold, and so a point-target imaging radar naturally samples the field's excursion set; the field's spatiotemporal correlations are discernible from that point process. We find that the echo pattern moves with its cluster: large-scale structures persist for tens of seconds, but scales under 10 km renew within seconds, and conjunctions with Swarm satellite pairs replicate the same scale dependence in field-aligned currents. Coherent radar can thus quantify multi-scale variability in the auroral electric field on Alfvénic timescales.
ER -