The GIC and Geomagnetic Response Over Fennoscandia to the 7–8 September 2017 Geomagnetic Storm

Abstract

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.

Identification of potential precursors for the occurrence of Large-Scale Traveling Ionospheric Disturbances in a case study during September 2017

“…This is not obvious from the Dst and IE indices, but it is indicated by the peaks in ROTI and AATR. Strong electrodynamic processes are also evident considering the results of Dimmock et al (2019), who reported significant geomagnetically induced currents (GIC) at 18 UT in Fennoscandia. Since neither the solar wind and IMF, nor the geomagnetic indices show significant perturbations at that time, magnetosphereionosphere electrodynamics must be the source of the LSTID and the GIC.…”

“…Thus, the IEC are horizontal equivalent ionospheric currents which correspond to the observed ground magnetic field. It is important to point out that, in reality, the true ionospheric currents correspond to a combination of horizontal and field-aligned currents, and it is not possible to distinguish those by using ground magnetometer data only (Pulkkinen et al, 2003;Dimmock et al, 2019). The IEC provide valuable information about the ionospheric electrodynamics and magnetosphere-ionosphere coupling and it is derived by the Finnish Meteorological Institute (FMI) using the spherical elementary current system method (Amm, 1997;Amm & Viljanen, 1999;Pulkkinen et al, 2003).…”

Exploring the Influence of Lateral Conductivity Contrasts on the Storm Time Behavior of the Ground Electric Field in the Eastern United States

“…Computations of the GEF within the second, most populated, group of papers (Beggan et al, ; Bailey et al, , ; Divett et al, ; Dimmock et al, ; Liu et al, ; Marshall et al, ; Nakamura et al, ; Püthe & Kuvshinov, ; Püthe et al, ; Pokhrel et al, ; Rosenqvist & Hall, ; Wang et al, , among others) rely on a numerical modeling of the GEF, either with a thin sheet or fully 3‐D conductivity models of the Earth. 3‐D conductivity models can be compiled using, for instance, results of regional MT surveys or/and exploiting global and regional maps of bathymetry, sediment thickness, etc.…”

Nighttime Magnetic Perturbation Events Observed in Arctic Canada: 2. Multiple‐Instrument Observations

“…These events can induce large geoelectric fields and geomagnetically-induced currents that can have harmful effects on electrical power grids. Nighttime perturbation events have often been associated with magnetic storms and auroral substorm onsets, but several studies have suggested that other, more localized magnetospheric and/or ionospheric processes, including poleward auroral expansions and small-scale ionospheric current vortices, also may drive these events [Viljanen, 1997;Pulkkinen et al, 2003;Huttunen et al, 2002;Ngwira et al, 2015Ngwira et al, , 2018Belakhovsky et al, 2018;Kozyreva et al, 2018, andDimmock et al, 2019].…”