Magnar Gullikstad Johnsen

In this study we examine how a deep-learning based forecast of local, ground-based geomagnetic field variations trained on solar wind parameters available in real time might be improved by including information contained in an accurate forecast of solar wind conditions. This is accomplished using a long short-term memory (LSTM) model together with magnetic field measurements made at the Rørvik magnetometer station in Mid-Norway. We use Advanced Composition Explorer (ACE) satellite measurements of solar wind and interplanetary magnetic field (IMF) conditions at the first Sun-Earth Lagrange point, and historical lists of coronal mass ejection (CME) impacts at Earth to train and validate the LSTM model. We find that accurate information about the IMF B _z component and solar wind speed are important for obtaining a reasonably accurate ( r ² ≥0.5) forecast of local geomagnetic activity over forecasting horizons beyond ∼3 h. Information about CME arrival time is only important when accompanied by accurate, relatively high-resolution information about IMF B _z . In the absence of the latter, CME arrival time information does not contribute to model performance. This empirical result amounts to a quantitative demonstration of the widely recognized impact of IMF orientation on CME geoeffectiveness. This result also highlights that new innovations, probably in the form of new prediction capabilities of conditions in interplanetary space, will be required to produce accurate forecasts of local geomagnetic disturbances beyond a forecast horizon of 1 h.

We present NORVIS (NORdlys Versatile Imaging Spectrograph), a portable broadband imaging spectrograph developed for ground-based auroral observations. Based on the Star'Ex optical concept, NORVIS is optimized for auroral emissions and covers approximately 380–860 nm in a single acquisition at a moderate spectral resolution of 1.2 nm FWHM. The instrument combines auroral spectroscopy, wide-field context imaging, field operation, automated spectral reduction, and centralized data archiving within a researcher-citizen science framework. First observations were obtained during a campaign at Skibotn Observatory, Norway, in February 2026, during which approximately 1200 spectra were acquired and reduced over three observing nights, with typical exposure times of 30 s. These observations demonstrate the simultaneous detection of key auroral emissions, including the N2+ 1NG bands at 391.4 and 427.8 nm and the [O I] emissions at 557.7 and 630.0/636.4 nm, while also providing access to the Hα region and to O I emissions at 777.4 and 844.6 nm. Representative observations illustrate the potential of NORVIS for emission-ratio diagnostics and geometry-aware interpretation of auroral structures. NORVIS is intended to form the basis of a distributed observing network, with coordinated deployments planned in Kiruna, Skibotn, Svalbard, and northern Finland, followed by permanent installations at Kiruna, Skibotn, the Kjell Henriksen Observatory in Svalbard, and Nyrölä.

We present first-light observations of auroral imaging polarimetry with the Polaribotn camera, a monochrome micropolarizer-based instrument equipped with narrowband filtering at the O(¹S) 557.7 nm green line. The instrument was operated simultaneously with the Corbel Cru polarimeter during a campaign in Skibotn, Norway, allowing a direct comparison with the existing narrow-field reference framework. The common field of view was identified empirically from the intensity time series, and the Polaribotn measurements show good agreement with Corbel Cru in both degree and angle of linear polarization. Extending the analysis to 63 regions of interest across the full image reveals that DoLP and AoLP do not respond in the same way to auroral structures: DoLP decreases in the brightest arc regions, whereas AoLP often remains coherent over a large fraction of the field of view. The corresponding (q,u) analysis points to a strong scene-wide polarization component with local intensity-dependent perturbations. Although the present dataset does not yet allow a definitive interpretation of the physical origin of the polarization, it demonstrates that auroral imaging polarimetry is feasible and provides spatial information not accessible to previous narrow-field instruments.

We statistically investigated the occurrence characteristics of internal modulation (IM), a rapid intensity modulation of a few hertz embedded in pulsating aurora (PsA), using high-speed ground-based optical data obtained with qCMOS cameras. For datasets acquired at Kiruna, Sweden, and Skibotn, Norway, we applied a two-step hierarchical machine-learning classification, first identifying the presence of PsA and then determining whether IM was present within the PsA. This enabled IM, which has previously been examined mainly through case studies, to be quantified for the first time in a systematic and statistically comparable manner. The results show that the fraction of PsA accompanied by IM increases toward the morning-sector magnetic local time (MLT) sector and tends to be higher at the lower-latitude site, Kiruna, than at the higher-latitude site, Skibotn. Representative examples from the classification results show that, on the midnight sector, IM commonly appears as a hierarchical structure superposed on clear main pulsations, whereas on the morning sector, the main pulsation tends to be relatively weak and the IM component often becomes dominant, suggesting that the morphology of IM itself also depends on MLT. These results suggest that IM is not merely an apparent subtype accompanying PsA, but rather a diagnostic feature that may provide insight into the wave–particle interaction underlying PsA.

We present first-light observations of auroral imaging polarimetry with the Polaribotn camera, a monochrome micropolarizer-based instrument equipped with narrowband filtering at the O(¹S) 557.7 nm green line. The instrument was operated simultaneously with the Corbel Cru polarimeter during a campaign in Skibotn, Norway, allowing a direct comparison with the existing narrow-field reference framework. The common field of view was identified empirically from the intensity time series, and the Polaribotn measurements show good agreement with Corbel Cru in both degree and angle of linear polarization. Extending the analysis to 63 regions of interest across the full image reveals that DoLP and AoLP do not respond in the same way to auroral structures: DoLP decreases in the brightest arc regions, whereas AoLP often remains coherent over a large fraction of the field of view. The corresponding (q,u) analysis points to a strong scene-wide polarization component with local intensity-dependent perturbations. Although the present dataset does not yet allow a definitive interpretation of the physical origin of the polarization, it demonstrates that auroral imaging polarimetry is feasible and provides spatial information not accessible to previous narrow-field instruments.

We present first-light observations of auroral imaging polarimetry with the Polaribotn camera, a monochrome micropolarizer-based instrument equipped with narrowband filtering at the O(¹S) 557.7 nm green line. The instrument was operated simultaneously with the Corbel Cru polarimeter during a campaign in Skibotn, Norway, allowing a direct comparison with the existing narrow-field reference framework. The common field of view was identified empirically from the intensity time series, and the Polaribotn measurements show good agreement with Corbel Cru in both degree and angle of linear polarization. Extending the analysis to 63 regions of interest across the full image reveals that DoLP and AoLP do not respond in the same way to auroral structures: DoLP decreases in the brightest arc regions, whereas AoLP often remains coherent over a large fraction of the field of view. The corresponding (q,u) analysis points to a strong scene-wide polarization component with local intensity-dependent perturbations. Although the present dataset does not yet allow a definitive interpretation of the physical origin of the polarization, it demonstrates that auroral imaging polarimetry is feasible and provides spatial information not accessible to previous narrow-field instruments.

We examine the geoelectric field and geomagnetically induced current (GIC) in Northern Europe during the May 2024 superstorm using a recently developed method: The divergence-free part of the geoelectric field (E_DF), associated with rapid magnetic field variations, is estimated from ground-based magnetic field observations using spherical elementary current systems. The curl-free part of the geoelectric field (E_CF), associated with charge accumulation, is estimated from E_DF using coefficients that depend on ground conductivity and linearly relate E_CF to E_DF in the time domain. We apply the method to both regional 10 s International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer observations and global 1 min SuperMAG observations by adopting a global triangular grid adapted to local magnetometer density. We compare the resulting GIC in the Finnish benchmark power grid and conclude that, in the absence of ground conductivity information and higher cadence data, E_DF estimated from 1 min magnetic field observations alone can provide a reasonable proxy for GIC activity in a power grid compared to 10 s geoelectric field. However, polarization of the geoelectric field due to lateral variations in ground conductivity can produce intense GIC at substations connected to transmission lines traversing regions of enhanced geoelectric field. GIC at such substations may be poorly described by E_DF alone.

We examine the geoelectric field and geomagnetically induced current (GIC) in Northern Europe during the May 2024 superstorm using a recently developed method: The divergence-free part of the geoelectric field (E_DF), associated with rapid magnetic field variations, is estimated from ground-based magnetic field observations using spherical elementary current systems. The curl-free part of the geoelectric field (E_CF), associated with charge accumulation, is estimated from E_DF using coefficients that depend on ground conductivity and linearly relate E_CF to E_DF in the time domain. We apply the method to both regional 10 s International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer observations and global 1 min SuperMAG observations by adopting a global triangular grid adapted to local magnetometer density. We compare the resulting GIC in the Finnish benchmark power grid and conclude that, in the absence of ground conductivity information and higher cadence data, E_DF estimated from 1 min magnetic field observations alone can provide a reasonable proxy for GIC activity in a power grid compared to 10 s geoelectric field. However, polarization of the geoelectric field due to lateral variations in ground conductivity can produce intense GIC at substations connected to transmission lines traversing regions of enhanced geoelectric field. GIC at such substations may be poorly described by E_DF alone.

We identify a previously unrecognized population of rapid geomagnetic variations associated with cusp dynamics. These variations produce distinct summertime signatures in the high–latitude ground magnetometer observations near the cusp. In this study, we apply four years of data from the high time resolution West Greenland magnetometer chain and perform a statistical analysis of rapid geomagnetic variations in the ultra low frequency (ULF) regime as a function of season, magnetic latitude, magnetic local time, and interplanetary magnetic field parameters. The magnetic perturbations are characterised using a broadband metric that integrates variability in the 10–600 s period range. This metric captures geomagnetic responses to transient, impulsive, and wave-like magnetospheric phenomena as well as ULF wave activity. We find that rapid geomagnetic variability at the highest latitudes, in the cusp and beyond, is sensitive to seasonal change, indicating that the ionospheric currents generating the observed ground magnetic signatures depend on solar illumination to obtain sufficient conductivities. This effect, in concert with dipole tilt, was investigated, and a clear cusp-related population during summer was found. In winter, this population weakens owing to a lack of sunlight and merges with other signals such as ULF waves associated with Alfvénic interhemispheric bouncing further south, and, thus, becomes indiscernible. Furthermore, we discuss other aspects of our statistical analysis and briefly address relationships between our detected signals and other known cusp phenomena.

We statistically investigated the occurrence characteristics of internal modulation (IM), a rapid intensity modulation of a few hertz embedded in pulsating aurora (PsA), using high-speed ground-based optical data obtained with qCMOS cameras. For datasets acquired at Kiruna, Sweden, and Skibotn, Norway, we applied a two-step hierarchical machine-learning classification, first identifying the presence of PsA and then determining whether IM was present within the PsA. This enabled IM, which has previously been examined mainly through case studies, to be quantified for the first time in a systematic and statistically comparable manner. The results show that the fraction of PsA accompanied by IM increases toward the morning-sector magnetic local time (MLT) sector and tends to be higher at the lower-latitude site, Kiruna, than at the higher-latitude site, Skibotn. Representative examples from the classification results show that, on the midnight sector, IM commonly appears as a hierarchical structure superposed on clear main pulsations, whereas on the morning sector, the main pulsation tends to be relatively weak and the IM component often becomes dominant, suggesting that the morphology of IM itself also depends on MLT. These results suggest that IM is not merely an apparent subtype accompanying PsA, but rather a diagnostic feature that may provide insight into the wave--particle interaction underlying PsA.