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Researchers developed an automated tracking method for small-scale plasma irregularities in Earth's auroral ionosphere using VHF radar data, revealing how these structures move with electric fields from the magnetosphere. Analysis of 74,517 tracked clusters over four years shows speeds ranging from 300 to 4,000 m/s that follow a power-law distribution, with validation from satellite measurements showing agreement within a factor of two. During the May 2024 geomagnetic super-storm, the team detected an extreme cluster moving at 11,240 m/s, implying an electric field of approximately 560 mV/m.
Why it matters
This work provides a new parameterization for predicting energy dissipation in the ionosphere during geomagnetic storms, which is critical for improving space weather models. The method can help quantify sub-grid-scale heating processes that current models miss, potentially improving forecasts of ionospheric disturbances that affect satellite operations and communications.
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⚠️ Preprint – Noch nicht peer-reviewed
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Abstract: Three-metre Farley-Buneman irregularities observed by the textsc{icebear} VHF radar organize into clusters whose apparent motion follows the electric field mapped from the magnetosphere. We track these clusters automatically: each is bounded by an $alpha$-shape at every time step, consecutive frames are associated by an optimal assignment combining shape overlap with a predicted displacement. Births, deaths, splits, and mergers are monitored, and each trajectory is reduced to per-segment velocities by piecewise linear regression. Tracked speeds are validated against in-situ ion drifts measured by DMSP F16 during two conjunctions in May 2021. Across four years of disturbed conditions, the speed distribution of 74,517 tracked clusters agrees with Swarm A cross-track ion drifts to within a factor of two in probability density for all speeds between 300 and 4000 m/s, and the radar-tracked speed distribution continues as a power law well beyond the noise limit imposed on Swarm by spacecraft attitude jitter. Binning by geomagnetic activity yields a parameterization of the field dispersion conditional on threshold exceedance, $sigma^2 = 3.68 times 10^5$ (SME/100 nT)$^{0.353}$~m$^2$ s$^{-2}$, equivalent to 30 to 60 mV/m across the observed activity range, which supplies the amplitude statistics entering the variance term of height-integrated Joule dissipation. During the 10 May 2024 super-storm, on closed field lines equatorward of the dayside cusp, we retrieved an upper-tail sample of this distribution, finding a cluster moving at $11,240pm660$ m/s and implying a field of approximately 560 mV/m. Together with the unstable fraction of a space weather model’s grid volume, our parameterization can in future close the sub-grid contribution to the storm-time heating budget in the auroral ionosphere.
Source: Extreme, transient bursts of energy in the auroral ionosphere. I. Predictive radar tracking