The jets in question are known as bursty bulk flows, or BBFs. They form when magnetic reconnection snaps stretched, energy-laden field lines in the magnetotail, the long nightside extension of Earth’s magnetic field. The newly reconnected flux tubes contract earthward under magnetic tension, accelerating plasma toward the inner magnetosphere at hundreds of kilometers per second. Each jet typically carries a dipolarization front, a boundary where the magnetic field abruptly snaps back toward a more dipolar, compressed geometry. Together, BBFs and their dipolarization fronts are thought to transport a large fraction of the energy and momentum that ultimately powers auroras and disturbs ground-based technology.

Between 18:00 and 22:00 UT on that December evening, the three inner THEMIS probes, positioned in the near-Earth plasma sheet, detected six distinct BBF intervals, with clear dipolarization signatures in the last four. Crucially, the magnetic footpoints of these flows, traced down the field lines to an altitude of 110 kilometers, mapped into the pre-midnight sector directly over northern Fennoscandia, an exceptionally well-instrumented patch of the auroral zone. There, the IMAGE magnetometer network, all-sky cameras at Skibotn and Kilpisjärvi, and the low-altitude Swarm A and C satellites stood ready to record whatever the tail threw at the ionosphere.

At the start of the interval, the team found the ionospheric current system in a stable configuration known as the Harang discontinuity, a boundary region where eastward and westward currents meet and turn northward. With each successive BBF arrival, this configuration became progressively distorted. The mapped footpoint of each flow landed in a region of counterclockwise vorticity in the horizontal equivalent current, the signature expected above an upward field-aligned current. Current magnitudes shifted within seconds to minutes, an auroral arc brightened in step with the flow detection, and the familiar Harang pattern gradually gave way to a clear, intensifying westward electrojet, the strong westward current channel that characterizes substorm expansion.

The escalation followed a striking progression. The first two dipolarizing intervals produced only auroral pseudo-breakups, modest brightenings of pre-existing arcs that shared some morphology with substorms but never developed the poleward expansion and global current reconfiguration of the real thing. The final two intervals, by contrast, displayed textbook auroral breakups with poleward expansion, classified as genuine substorms by the SOPHIE technique applied to SuperMAG ground data. In the last event, THEMIS measured a flow peaking at 605.5 kilometers per second, the westward electrojet surged and expanded, and the aurora bifurcated, brightened and raced poleward in near-perfect synchrony with the magnetotail signatures.

The scientific centerpiece of the study came during the fourth BBF, when the Swarm A and C satellites, flying side by side at roughly 480 kilometers altitude, crossed the mapped footpoint of the flow within minutes of its detection in the tail. Both spacecraft recorded a sharply localized pair of upward and downward field-aligned currents spanning only 35 to 50 kilometers in latitude, with current densities exceeding 1 microampere per square meter and peaks reaching 6.2 microamperes per square meter. The upward current sat directly beneath a discrete auroral arc, and the arc intensified at the very moment the current was measured. Notably, the dual-satellite method, which resolves only structures larger than about 150 kilometers, smoothed this narrow pair away entirely, showing that the finest structure of the BBF current system can only be captured by single-spacecraft measurements.

A multiscale minimum variance analysis of the Swarm magnetic data added further texture. The downward current proved planar and east-west aligned, while the upward current was distinctly non-planar and inclined away from the east-west direction, exactly the geometry predicted for the field-aligned currents flanking an earthward-moving plasma bubble. The team also tracked enhancements of 9 to 20 kiloelectronvolt electron fluxes in the tail that coincided with each arc brightening, suggesting these electrons, channeled along field lines, were sufficient to produce the auroral light without requiring additional acceleration closer to Earth.

The study also quantified the space weather consequences. Rapid variations of the horizontal ground magnetic field, the quantity that drives geomagnetically induced currents in power grids, spiked simultaneously with each of the last four dipolarizations, with peak amplitudes growing as the sequence progressed. The largest perturbation reached 213 nanotesla per minute at Tromsø, a value comparable to peaks reported in a recent catalog of events associated with actual power-grid disturbances, though the geophysical conditions in this case were milder. Maps of the Rate-Of-TEC-Index, a measure of ionospheric electron-density irregularities that degrade GPS signals, intensified in step with each dipolarization, peaking near 67 to 69 degrees north, right at the BBF footprints.

Taken together, the observations provide the first direct, multi-instrument picture of a coherent, time-aligned chain of coupling signatures linking recurrent magnetotail flows to the high-latitude ionosphere: localized vorticity in ionospheric currents, discrete arc brightenings, field-aligned current pairs on arc scales, and cumulative escalation toward substorm onset. The results lend strong support to the wedgelet picture of the substorm current wedge, in which many small current elements generated by individual flow bursts superpose to build the large-scale current system traditionally attributed to a single monolithic structure. For space weather forecasting, the message is sobering: even in the absence of a full substorm, BBFs with strong dipolarization fronts can generate localized, sharp perturbations capable of stressing technological systems, which means the small, fast events in the tail deserve attention in their own right.

Subject of Research: Magnetotail bursty bulk flows, dipolarization fronts, and their coupling to ionospheric currents and auroras during a substorm sequence

Article Title: Ionospheric currents and auroral signatures during successive earthward bursty bulk flows and dipolarization: a 7 December 2023 case study

Article References: Lanabere, V., Buchert, S., Blagau, A., George, H., Nanjo, S., Juusola, L., Dimmock, A. P., Wharton, S., Vanhamäki, H., Marghitu, O., Richard, L., Cai, L., Wallner, A. V. L., Kotova, D., Jin, Y., Hoppe, T., Carter, J. A., & Aikio, A. (2026). Ionospheric currents and auroral signatures during successive earthward bursty bulk flows and dipolarization: a 7 December 2023 case study. Annales Geophysicae, 44(2), 977-1001. https://doi.org/10.5194/angeo-44-977-2026

Image Credits: AI Generated

DOI: 10.5194/angeo-44-977-2026

Keywords: bursty bulk flows, dipolarization, magnetotail, ionosphere, field-aligned currents, aurora, substorm, THEMIS, Swarm, space weather, geomagnetically induced currents, Fennoscandia

The golden eagle occupies a precarious position in the Fennoscandian landscape. As an apex predator, it is long-lived, slow to reproduce, and needs enormous territories, characteristics that make it acutely vulnerable to human pressures. The species typically lays only one or two eggs, and young birds may not settle in a territory of their own until roughly five years of age. Survival during the early years is low, climbing steeply only as birds approach adulthood. This life history means that even modest increases in adult mortality can push a population into decline. Today the main breeding strongholds lie in the north, with smaller populations in southernmost Sweden and Denmark and a notable concentration of pairs on the Swedish island of Gotland.

The region’s eagles have already survived one brush with disaster. Persecution, habitat destruction, and the accumulation of environmental toxins drove the population down sharply in the early twentieth century, with local extinctions in several areas. Legal protections introduced from the 1970s onward allowed numbers to recover steadily, and the population is now considered stable, although breeding attempts and nesting success still swing widely from year to year depending on prey availability and weather. Recovery, however, does not erase history. Populations that pass through a bottleneck can lose genetic diversity, which in turn makes them more sensitive to future environmental shocks. Whether the Fennoscandian eagles carry such scars has been debated, with some microsatellite-based studies finding no bottleneck signature and others, drawing on museum specimens, documenting a loss of haplotypes and comparatively low variation relative to central Asia and the Caucasus.

Part of the uncertainty stems from the limitations of the genetic markers traditionally used. Microsatellites, the workhorses of wildlife genetics for decades, are individually informative but demand long, intact stretches of DNA, exactly what degraded non-invasive samples often lack. Shorter-read SNP markers, by contrast, tolerate fragmented DNA far better, and results from SNP panels are easier to compare across laboratories, a considerable advantage when a population ranges across three countries with separate monitoring programs. The trade-off is that each SNP carries less information than a microsatellite, so more markers are needed to achieve comparable power. The new panel meets that requirement by packing 96 markers onto a nanofluidic genotyping platform that can process large sample sets quickly and cheaply.

To build the panel, the team sequenced DNA from 96 golden eagles sampled across Sweden, Norway, Denmark, and Finland, working with the NGO Golden Eagle Sweden, the Swedish Veterinary Agency, and the Norwegian Institute for Nature Research. Most samples came from chicks ringed at nests or adults captured for other research projects, supplemented by tissue from birds found dead. RAD-sequencing initially surfaced nearly 30,000 candidate SNPs, which the researchers whittled down through filtering for biallelic markers, allele frequencies, Hardy-Weinberg equilibrium, and coverage. Validation on 81 independent samples, including 40 pulled-feather samples from Finnish nestlings and 41 Norwegian samples representing blood, bone, claw, eggshell, footpad, feather, and muscle tissue, left 95 final SNPs plus one marker from a previous study that determines sex.

The validation results were striking. Blood, footpad, and tissue samples achieved 100 percent amplification success, and the crucial non-invasive sources performed almost as well: shed, molted feathers reached 98 percent amplification, and plucked feathers 96.2 percent, a difference so small it was statistically indistinguishable. Because molted feathers actually edged out plucked ones on average, the authors argue that field workers can rely entirely on feathers gathered from the environment rather than plucking them from live birds, sparing both eagles and handlers the stress and injury risk of direct contact. Less useful were eggshells, bones, and claws, which each came from a single sample and showed amplification success ranging from roughly 62 to 89 percent.

When it comes to telling individual eagles apart, the panel is exceptionally precise. The probability that two unrelated individuals would share the same genotype across all 95 markers is about 5.11 times 10 to the minus 30, and even full siblings can be discriminated with a probability of identity of roughly 4.06 times 10 to the minus 20. Exclusion probabilities for parentage analysis exceeded 0.99997 whether or not one parent was already known. Genotyping accuracy was similarly strong: across ten feather samples run twice, the average error rate was just 1.979 percent, and seven of the ten samples showed zero mismatches and 100 percent amplification. The one problematic sample, with an error rate above 10 percent, also had the lowest amplification success, reinforcing a well-established principle of non-invasive genetics that genotyping quality tracks sample quality and that strict amplification thresholds are essential.

Sex determination proved equally dependable. The CHD1ZW marker correctly assigned the sex of 40 of 41 previously sexed samples, with the single failure attributable to missing data rather than a mismatch, and it worked consistently in replicate runs. Assessing family relationships revealed both the panel’s strengths and its limits. Simulations of 10,000 pairs per relationship class showed that the panel correctly classifies close relatives, meaning parent-offspring pairs or full siblings, about 90 percent of the time, and unrelated pairs about 88.6 percent of the time. Half-siblings, however, were correctly identified in only 77.1 percent of simulated cases, blurring into both the unrelated and first-order categories. The overall classification accuracy of 86.5 percent means the panel can credibly distinguish unrelated birds from close relatives, which is what matters most for estimating territory turnover and dispersal, but researchers should treat half-sibling assignments with caution, echoing earlier findings that roughly 100 SNPs separate close kin from strangers but not degrees in between.

The panel also delivered a first broad genetic picture of the Fennoscandian population using its own markers. Observed and expected heterozygosity were closely matched across most regions, inbreeding coefficients hovered near zero, and genetic differentiation among populations was low, at FST around 0.04, consistent with earlier evidence of gene flow both within Fennoscandia and between Fennoscandia and the Alps. Even Gotland, despite its island geography, showed no elevated inbreeding or depressed diversity, though the authors caution that only seven Gotland samples were available and that the number of markers may be too small to detect subtle inbreeding. A Finnish outlier with a heterozygote deficit almost certainly reflects a sample size of just two birds rather than a genuine biological signal, since a larger Finnish microsatellite study found no such deficit. Notably, the panel doubled as a species check: white-tailed eagle feathers, which can be mistaken for golden eagle feathers in the field, produced genotypes with very low heterozygosity and abundant missing data, fingerprints that let researchers filter out misidentified samples before they contaminate an analysis.

The broader significance extends well beyond eagles. Norway and Sweden already monitor wolverines, brown bears, and wolves through non-invasive genetic sampling, and a comparable system for golden eagles promises data on reproductive success, territory turnover, and gene flow that nest visits alone cannot provide. Because SNP results travel cleanly between laboratories, the panel opens the door to coordinated monitoring across Norway, Sweden, and Finland, and to building shared databases for a population that ignores national borders. In Japan, where microsatellite studies of the local golden eagle emphasized the value of continuous genetic monitoring for catching early signs of bottlenecks and declining connectivity, the same logic applies. For a species still shadowed by forestry, infrastructure expansion, and climate change, a tool that converts a molted feather on the forest floor into a named, sexed, and relatedness-mapped individual could become the difference between spotting a population’s decline early and reading about it in the statistics afterward.

Subject of Research: Development and validation of a 96-SNP genetic panel for non-invasive monitoring of the Fennoscandian golden eagle population

Article Title: A Genetic Tool for Non‐Invasive Monitoring of Fennoscandian Golden Eagles (Aquila chrysaetos)

Article References: Lindberg, B., Kleven, O., Kvist, L., Norman, A., Köningsson, H., Jacobsen, K.-O., Nilsson, P.-O., Singh, N. J., & Spong, G. (2026). A Genetic Tool for Non‐Invasive Monitoring of Fennoscandian Golden Eagles ( Aquila chrysaetos ). Ecology and Evolution, 16(9), Article e74386. https://doi.org/10.1002/ece3.74386

Image Credits: AI Generated

DOI: 10.1002/ece3.74386

Keywords: golden eagle, Aquila chrysaetos, SNP panel, non-invasive genetic sampling, Fennoscandia, genetic monitoring, wildlife forensics, feather DNA, relatedness, conservation genetics, raptor ecology, nanofluidic genotyping