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Geomagnetically Induced Currents are unwanted currents that flow in large ground‐based conductive infrastructure and are a significant threat to bulk power grids. This susceptibility is increased at high latitudes due to the larger amplitude geomagnetic disturbances caused by the strong and dynamic auroral electrojet currents. In Sweden, there has been a record of disturbances connected to geomagnetically induced currents; the most documented was a blackout in Malmö, a city in southern Sweden, on 30 October 2003. However, on 24 April 2023, there was a transformer trip in the Bandsjö substation (near Sundsvall) around the time of enhanced space weather. In this paper, we investigate this event by studying the solar wind properties as well as geomagnetic disturbances. The study shows evidence that the transformer trip was caused by a strong geomagnetic disturbance in the morning sector. This was triggered by a high‐pressure sub‐structure within the interplanetary coronal mass ejection cloud, preceded by 2 hr of strong southward interplanetary magnetic field. Additionally, analysis of multiple ground magnetometers shows that the geomagnetic impact was highly spatially structured. Plain Language Summary: Space weather is a field of research that connects the changing conditions on the Sun and around near‐Earth space to effects on human technology and health. Occasionally, eruptions on the Sun will release large blobs of plasma known as interplanetary coronal mass ejections that travel outward into interplanetary space. When an interplanetary coronal mass ejection reaches Earth, it will interact with the Earth's near‐space environment, for example, by distorting and compressing the Earth's magnetic field. The focus of this study is a space weather phenomenon known as geomagnetically induced currents, which are unwanted currents that flow in large ground‐based conductors. Geomagnetically induced currents are caused by the changing Earth's magnetic field during the Earth's interaction with an interplanetary coronal mass ejection. Here, we study a trip of a Swedish power transformer to determine if it was caused by space weather. After our analysis, we show strong evidence that it was related to GICs, and we can also trace the effect to a clear feature inside the interplanetary coronal mass ejection. Key Points: An interplanetary coronal mass ejection cloud sub‐structure preceded by 2 hr of southward interplanetary magnetic field resulted in strong geoelectric fields in SwedenPower line voltage calculations show strong evidence that the large geoelectric fields caused a transformer to trip in SwedenThe geomagnetic disturbance was spatially structured, where the largest amplitude perturbation was recorded in Norway [ABSTRACT FROM AUTHOR]

This study focuses on the poorly known effect of polar cap patches (PCPs) on the ion‐neutral coupling in the F‐region. The PCPs were identified by total electron content measurements from the Global Navigation Satellite System (GNSS) and the ionospheric parameters from the Defense Meteorological Satellite Program spacecraft. The EISCAT incoherent scatter radars on Svalbard and at Tromsø, Norway observed that PCPs entered the nightside auroral oval from the polar cap and became plasma blobs. The ionospheric convection further transported the plasma blobs to the duskside. Simultaneously, long‐lasting strong upper thermospheric winds were detected in the duskside auroral oval by a Fabry‐Perot Interferometer (FPI) at Tromsø and in the polar cap by the Gravity Recovery and Climate Experiment satellite. Using EISCAT ion velocities and plasma parameters as well as FPI winds, the ion drag acting on neutrals and the time constant for the ion drag could be estimated. Due to the arrival of PCPs/blobs and the accompanied increase in the F‐region electron densities, the ion drag is enhanced between about 220 and 500 km altitudes. At the F peak altitudes near 300 km, the median ion drag acceleration affecting neutrals more than doubled and the associated median e‐folding time decreased from 4.4 to 2 hr. The strong neutral wind was found to be driven primarily by the ion drag force due to large‐scale ionospheric convection. Our results provide a new insight into ionosphere‐thermosphere coupling in the presence of PCPs/blobs. Plain Language Summary: This study investigates how the evolution of the polar cap patches (PCPs) affects the upper layer of the Earth's atmosphere, termed the thermosphere. PCPs are dense patches of charged particles that move from the dayside to the nightside of the high‐latitude ionosphere through the polar cap region. Using the measurements by multiple ground‐based instruments and satellites, this study found that PCPs can enhance the formation of strong upper thermospheric winds. The winds are primarily driven by the ion drag force due to the interactions between charged particles and neutral gases. The results show that because of the arrival of PCPs, which increase the F‐region electron densities in the auroral oval, the ion drag acceleration acting on the neutrals can more than double and the related time constant of the ion drag can be halved. Key Points: Transportation of polar cap patches (PCPs) and their development in the nightside auroral oval was observed by multiple instrumentsVery strong, long‐lasting westward upper thermospheric wind in the duskside oval was associated with large‐scale ionospheric convectionHigh electron density produced by PCPs increases the ion drag force that drives the upper thermospheric wind [ABSTRACT FROM AUTHOR]

During geomagnetically active times, Joule (or frictional) heating in the Lower Thermosphere‐Ionosphere is a significant source of thermal energy, greatly affecting density, temperature, composition and circulation. At the same time, Joule heating and the associated Pedersen conductivity are amongst the least known parameters in the upper atmosphere in terms of their quantification and spatial distribution, and their parameterization by geomagnetic parameters shows large discrepancies between estimation methodologies, primarily due to a lack of comprehensive measurements in the region where they maximize. In this work we perform a long‐term statistical comparison of Joule heating as calculated by the NCAR Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM) and as obtained through radar measurements by the European Incoherent Scatter Scientific Association (EISCAT). Statistical estimates of Joule heating and Pedersen conductivity are obtained from a simulation run over the 11 year period spanning from 2009 until 2019 and from radar measurements over the same period, during times of radar measurements. The results are statistically compared in different Magnetic Local Time sectors and Kp level ranges in terms of median values and percentiles of altitude profiles. It is found that Joule heating and Pedersen conductivity are higher on average in TIE‐GCM than in EISCAT for low Kp and are lower than EISCAT for high Kp. It is also found that neutral winds cannot account for the discrepancies between TIE‐GCM and EISCAT. Comparisons point toward the need for a Kp‐dependent parameterization of Joule heating in TIE‐GCM to account for the contribution of small scale effects. Plain Language Summary: During times of high solar activity, Joule (or frictional) heating in the Lower Thermosphere‐Ionosphere is a significant source of thermal energy, greatly affecting density, temperature, composition and circulation. Joule heating is largely unknown, due to a lack of measurements in the altitude ranges where it maximizes. In this work we compare Joule heating estimates from the NCAR Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM) and as obtained through radar measurements by the European Incoherent Scatter Scientific Association (EISCAT), from a simulation run over the 11 year period spanning from 2009 until 2019 and from radar measurements over the same period. The results are compared in different Magnetic Local Time sectors and Kp level ranges in terms of median values and percentiles of altitude profiles. It is found that Joule heating and Pedersen conductivity are higher on average in TIE‐GCM than in EISCAT for low activity levels and are lower than EISCAT for high activity levels. It is also found that neutral winds cannot account for the discrepancies between TIE‐GCM and EISCAT. Comparisons point toward the need for a new parameterization of Joule heating in TIE‐GCM to account for the contribution of small scale effects. Key Points: Joule heating and Pedersen conductivity are calculated in Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM) and European Incoherent Scatter Scientific Association (EISCAT) during solar cycle 24, as a function of Kp, Magnetic Local Time and altitudeJoule heating and Pedersen conductivity in TIE‐GCM are under‐estimated for high Kp compared to EISCAT measurementsComparisons point toward the need for parameterization of small scale effects in TIE‐GCM [ABSTRACT FROM AUTHOR]

Little is currently known about the optical phenomenon known as Steve. The first scientific publication on the subject suggests that Steve is associated with an intense subauroral ion drift (SAID). However, additional inquiry is warranted as this suggested relationship as it is based on a single case study. Here we present eight occurrences of Steve with coincident or near‐coincident measurements from the European Space Agency's Swarm satellites and show that Steve is consistently associated with SAID. When satellite observations coincident with Steve are compared to that of typical SAID, we find the SAID associated with Steve to have above average peak ion velocities and electron temperatures, as well as extremely low plasma densities. Key Points: Eight Steve events were identified in all‐sky imager measurements with coincident or near‐coincident measurements from the Swarm satellitesIn all cases, evidence of subauroral ion drifts are observed in Swarm measurementsAll measurements of SAID overlapping with Steve have very fast ion flows, high electron temperatures, and extremely low plasma densities [ABSTRACT FROM AUTHOR]

Knowledge of Mars's ionosphere has been significantly advanced in recent years by observations from Mars Express and lately Mars Atmosphere and Volatile EvolutioN. A topic of particular interest are the interactions between the planet's ionospheric plasma and its highly structured crustal magnetic fields and how these lead to the redistribution of plasma and affect the propagation of radio waves in the system. In this paper, we elucidate a possible relationship between two anomalous radar signatures previously reported in observations from the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument on Mars Express. Relatively uncommon observations of localized, extreme increases in the ionospheric peak density in regions of radial (cusp‐like) magnetic fields and spread echo radar signatures are shown to be coincident with ducting of the same radar pulses at higher altitudes on the same field lines. We suggest that these two observations are both caused by a high electric field (perpendicular to B) having distinctly different effects in two altitude regimes. At lower altitudes, where ions are demagnetized and electrons magnetized, and recombination dominantes, a high electric field causes irregularities, plasma turbulence, electron heating, slower recombination, and ultimately enhanced plasma densities. However, at higher altitudes, where both ions and electrons are magnetized and atomic oxygen ions cannot recombine directly, the high electric field instead causes frictional heating, a faster production of molecular ions by charge exchange, and so a density decrease. The latter enables ducting of radar pulses on closed field lines, in an analogous fashion to interhemispheric ducting in the Earth's ionosphere. Key Points: MARSIS on MEX observed both echoes from distant ionospheric irregularities as well as locally ducted echoes in close successionBoth effects are consistent with the presence of extended, small‐scale field‐aligned density irregularitiesWe suggest that these may be the direct result of strong electric fields present at ionospheric altitudes [ABSTRACT FROM AUTHOR]

We present Swarm satellite and EISCAT radar observations of electrodynamical parameters in the midnight sector at high latitudes. The most striking feature is a plasma flow channel located equatorward of the polar cap boundary within the dawn convection cell. The flow channel is 1.5° wide in latitude and contains southward electric field of 150 mV/m, corresponding to eastward plasma velocities of 3,300 m/s in the F‐region ionosphere. The theoretically computed ion temperature enhancement produced by the observed ion velocity is in accordance with the measured one by the EISCAT radar. The total width of the auroral oval is about 10° in latitude. While the poleward part is electric field dominant with low conductivity and the flow channel, the equatorward part is conductivity dominant with at least five auroral arcs. The main part of the westward electrojet flows in the conductivity dominant part, but it extends to the electric field dominant part. According to Kamide and Kokubun (1996), the whole midnight sector westward electrojet is expected to be conductivity dominant, so the studied event challenges the traditional view. The flow channel is observed after substorm onset. We suggest that the observed flow channel, which is associated with a 13‐kV horizontal potential difference, accommodates increased nightside plasma flows during the substorm expansion phase as a result of reconnection in the near‐Earth magnetotail. Key Points: Plasma flow channel with velocity of 3,300 m/s in the ionospheric F region is formed on the poleward part of the auroral ovalFlow channel accommodates increased plasma flows likely caused by magnetotail reconnection after substorm onsetMidnight auroral oval is electric field dominant on the poleward part and conductivity dominant on the equatorward part [ABSTRACT FROM AUTHOR]