In this study we investigate the performance of the University of Michigan’s Space Weather Modeling Framework (SWMF) in prediction of ground magnetic perturbations (∆B) and their rate of change with time (dB/dt), which is directly connected to geomagnetically induced currents (GICs). We use the SWMF set-up where the global magnetosphere provided by the Block Adaptive Tree Solar-wind Roe-type Upwind Scheme (BATS-R-US) MHD code, is coupled to the inner magnetosphere and the ionospheric electrodynamics. The validation is done for ∆B and dB/dt separately. The performance is evaluated via data-model comparison through a metrics-based approach. For ∆B, the normalized root mean square error (nRMS) and the correlation coefficient are used. For dB/dt, the probability of detection, the probability of false detection, the Heidke skill score, and the frequency bias are used for different dB/dt thresholds. The performance is evaluated for eleven ground magnetometer stations located between 59 o and 85 o magnetic latitude and spanning about five magnetic local times. Eight geomagnetic storms are studied. Our results show that the SWMF predicts the northward component of the perturbations better at lower latitudes (59 o − 67 o ) than at higher latitudes (> 67 o ), whereas for the eastward component, the model performs better at high latitudes. Generally, the SWMF performs well in the prediction of dB/dt for a 0.3 nT/s threshold, with a high probability of detection ≈ 0.8, low probability of false detection (< 0.4), and Heidke skill score above zero. To a large extent the model tends to predict events as often as they are actually occurring in nature (frequency bias 1). With respect to the metrics measures, the dB/dt prediction performance generally decreases as the threshold is raised, except for the probability of false detection, which improves.

Direct impact excitation by precipitating electrons is believed to be the main source of 630.0 nm emissions in the cusp ionosphere. However, this paper investigates a different source, 630.0 emissions caused by thermally excited atomic oxygen O(1D) when high electron temperature prevail in the cusp. On 22 January 2012 and 14 January 2013, the European Incoherent Scatter Scientific Association (EISCAT) radar on Svalbard measured electron temperature enhancements exceeding 3000 K near magnetic noon in the cusp ionosphere over Svalbard. The electron temperature enhancements corresponded to electron density enhancements exceeding 1011 m−3 accompanied by intense 630.0 nm emissions in a field of view common to both the EISCAT Svalbard radar and a meridian scanning photometer. This offered an excellent opportunity to investigate the role of thermally excited O(1D) 630.0 nm emissions in the cusp ionosphere. The thermal component was derived from the EISCAT Radar measurements and compared with optical data. For both events the calculated thermal component had a correlation coefficient greater than 0.8 to the total observed 630.0 nm intensity which contains both thermal and particle impact components. Despite fairly constant solar wind, the calculated thermal component intensity fluctuated possibly due to dayside transients in the aurora.

Ground‐based technological systems, such as power grids, can be affected by geomagnetically induced currents (GIC) during geomagnetic storms and magnetospheric substorms. This motivates the necessity to numerically simulate and, ultimately, forecast GIC. The prerequisite for the GIC modeling in the region of interest is the simulation of the ground geoelectric field (GEF) in the same region. The modeling of the GEF in its turn requires spatiotemporal specification of the source which generates the GEF, as well as an adequate regional model of the Earth’s electrical conductivity. In this paper, we compare results of the GEF (and ground magnetic field) simulations using three different source models. Two models represent the source as a laterally varying sheet current flowing above the Earth. The first model is constructed using the results of a physics‐based 3‐D magnetohydrodynamic (MHD) simulation of near‐Earth space, the second one uses ground‐based magnetometers’ data and the Spherical Elementary Current Systems (SECS) method. The third model is based on a “plane wave” approximation which assumes that the source is locally laterally uniform. Fennoscandia is chosen as a study region and the simulations are performed for the September 7–8, 2017 geomagnetic storm. We conclude that ground magnetic field perturbations are reproduced more accurately using the source constructed via the SECS method compared to the source obtained on the basis of MHD simulation outputs. We also show that the difference between the GEF modeled using laterally nonuniform source and plane wave approximation is substantial in Fennoscandia.

Combined with the magnetic field, the distribution of charged particles in the inflow region is expected to control the rate of magnetic reconnection. This paper investigates how the reconnection process is altered by a cold, asymmetrically distributed, oxygen population, which is initially located away from the current layer in the inflow regions. A particle‐in‐cell simulation is used to gain further insight into the dynamics of the system. The time evolution of the reconnection process proceeds rapidly compared to the cyclotron period of O +. Therefore, the oxygen remains, to a good approximation, demagnetized. Thus, Alfvén scaling is not an adequate description of the reconnection rate. A scaling relation for the reconnection rate for an asymmetrically distributed, demagnetized species has been developed. Additionally, we find that an asymmetric density configuration leads to a distinct motion of the reconnection site and generates an asymmetry of the diffusion region and the Hall electric field.