Between 7 and 8 September 2017, Earth experienced extreme space weather events. We have combined measurements made by the IMAGE magnetometer array, ionospheric equivalent currents, geomagnetically induced current (GIC) recordings in the Finnish natural gas pipeline, and multiple ground conductivity models to study the Fennoscandia ground effects. This unique analysis has revealed multiple interesting physical and technical insights. We show that although the 7–8 September event was significant by global indices (Dst∼150 nT), it produced an unexpectedly large peak GIC. It is intriguing that our peak GIC did not occur during the intervals of largest geomagnetic depressions, nor was there any clear upstream trigger. Another important insight into this event is that unusually large and rare GIC amplitudes (>10 A) occurred in multiple Magnetic Local Time (MLT) sectors and could be associated with westward and eastward electrojets. We were also successfully able to model the geoelectric field and GIC using multiple models, thus providing a further important validation of these models for an extreme event. A key result from our multiple conductivity model comparison was the good agreement between the temporal features of 1‐D and 3‐D model results. This provides an important justification for past and future uses of 1‐D models at Mäntsälä which is highly relevant to additional uses of this data set. Although the temporal agreement (after scaling) was good, we found a large (factor of 4) difference in the amplitudes between local and global ground models due to the difference in model conductivities. Thus, going forward, obtaining accurate ground conductivity values are key for GIC modeling.

International audienceA Doppler-type shift in the kinetic energy of atomic Auger electrons emitted after fast dissociation of O3 molecules is observed. The resonant Auger spectrum from the decay of repulsive core-excited states reflects both the early molecular ozone decay and that from excited dissociation fragments. The kinetic energy of the fragment is manifested as an energy shift of the atomic Auger lines when the measurement is made under certain conditions. We report measurements of the energy-split atomic fragment emission lines arising from dissociation on a time scale comparable to the core-hole lifetime. For the O 1s–* states the kinetic energy release amounts to several electron volts. We report measurements for excitation of both the terminal and central oxygen 1s electrons. A simple kinematic model for extracting a lower limit for the kinetic-energy release is presented and is compared with the result of a Born–Haber cycle, which may be seen as an estimate of the maximum energy releas

Faraday's law of induction is responsible for setting up a geoelectric field due to the variations in the geomagnetic field caused by ionospheric currents. This drives geomagnetically induced currents (GICs) which flow in large ground‐based technological infrastructure such as high‐voltage power lines. The geoelectric field is often a localized phenomenon exhibiting significant variations over spatial scales of only hundreds of kilometers. This is due to the complex spatiotemporal behavior of electrical currents flowing in the ionosphere and/or large gradients in the ground conductivity due to highly structured local geological properties. Over some regions, and during large storms, both of these effects become significant. In this study, we quantify the regional variability of dB/dt using closely placed IMAGE stations in northern Fennoscandia. The dependency between regional variability, solar wind conditions, and geomagnetic indices are also investigated. Finally, we assess the significance of spatial geomagnetic variations to modeling GICs across a transmission line. Key results from this study are as follows: (1) Regional geomagnetic disturbances are important in modeling GIC during strong storms; (2) dB/dt can vary by several times up to a factor of three compared to the spatial average; (3) dB/dt and its regional variation is coupled to the energy deposited into the magnetosphere; and (4) regional variability can be more accurately captured and predicted from a local index as opposed to a global one. These results demonstrate the need for denser magnetometer networks at high latitudes where transmission lines extending hundreds of kilometers are present.

One of the most prominent (and potentially dangerous) features of space weather are geomagnetically induced currents, commonly known as GICs. The understanding of GICs is a major concern in order to preserve the power and communication systems and other technology on the ground. GICs are currents induced by rapid fluctuations in the Earth's magnetic field in any extended conducting technological infrastructure and can lead to malfunction or black outs of high-voltage power transmission systems (