Antti Pulkkinen

The May 2024 geomagnetic storm was one of the most severe in the past 20 years. Understanding how large geomagnetic disturbances (GMDs) impact geomagnetically induced currents (GICs) within electrical power grid networks is key to ensuring their resilience. We have assembled and synthesized a large and unique set of GMD‐related data, compared model predictions with measurements, and identified empirical relationships for GICs in the contiguous United States for this storm. Measurement data include GIC data from 47 sites and magnetometer data from 17 sites. Model data include GIC computed by the Tennessee Valley Authority (TVA) power system operators at 4 sites, GIC computed using a reference model at 47 sites, and the difference in the surface magnetic field from a baseline computed at 12 magnetometer sites from three global magnetospheric models—the Multiscale Atmosphere‐Geospace Environment Model (MAGE), Space Weather Modeling Framework (SWMF), and Open Geospace General Circulation Model (OpenGGCM). GIC measured and computed by TVA had a correlation coefficient and a prediction efficiency between 0.4 and 0.7. The horizontal magnetic field perturbation from a baseline, , computed by MAGE, SWMF, and OpenGGCM had a correlation r from 0.21 to 0.65. Two empirical relationships were considered: (a) how the correlation between measured GIC site pairs depended on differences in site separation distance, scaling factor (related to ground conductivity), and geomagnetic latitude; and (b) a regression model for the maximum magnitude at each site given the product of (related to magnetic latitude) and .

The May 2024 geomagnetic storm was one of the most severe in the past 20 years. Understanding how large geomagnetic disturbances (GMDs) impact geomagnetically induced currents (GICs) within electrical power grid networks is key to ensuring their resilience. We have assembled and synthesized a large and unique set of GMD-related data, compared model predictions with measurements, and identified empirical relationships for GICs in the contiguous United States for this storm. Measurement data include GIC data from 47 sites and magnetometer data from 17 sites. Model data include GIC computed by the Tennessee Valley Authority (TVA) power system operators at four sites, GIC computed using a reference model at 47 sites, and the difference in the surface magnetic field from a baseline (∆B) computed at 12 magnetometer sites from three global magnetospheric models — the Multiscale Atmosphere-Geospace Environment Model (MAGE), Space Weather Modeling Framework (SWMF), and Open Geospace General Circulation Model (OpenGGCM). GIC measured and modeled by TVA had a correlation coefficient >0.8 and a prediction efficiency between 0.4 and 0.7. The horizontal magnetic field perturbation from a baseline, ∆BH , computed by MAGE, SWMF, and OpenGGCM had a correlation r from 0.21 to 0.65. Two empirical relationships were considered: (1) how the correlation between measured GIC site pairs depended on differences in site separation distance, β scaling factor (related to ground conductivity), and geomagnetic latitude; and (2) a regression model for the maximum GIC magnitude at each site give the product of α (related to magnetic latitude) and β.

In this work, we describe an approach to characterize the ground response to geomagnetic storm drivers and recalculate the scaling factors that are used in the North American Reliability Corporation (NERC) TPL‐007 geomagnetic disturbance (GMD) standard based on magnetotelluric (MT) survey measurements. The new ground response scaling factors indicate a significantly wider range of ground responses from the one‐dimensional model responses used in the original NERC GMD standards framework. Further, the region Mid‐West area west of the great lakes and North‐East around New England and areas along the Appalachian Mountains appear to be particularly exposed to the geoelectric field hazard under extreme space weather conditions. A more complete validation of MT data in geomagnetically induced currents applications is warranted before usage of the presented results as a basis for possible updates to the NERC GMD standard.

Natural hazards, such as weather in space and the terrestrial environment, have the potential to disrupt critical technologies and infrastructures that contribute to national security and economic advancement. Enhancing our understanding of natural hazards is a central part to developing mitigation strategies to avert their impact on technological assets and/or infrastructure. With the support of the broader scientific community, the International Space Weather Initiative (ISWI) and the African Geophysical Society (AGS) successfully organized two international events in September–October 2023, namely, the ISWI space weather school and the AGS Annual Conference. Both events were locally hosted by the Physics Society of Zambia in Lusaka, Zambia. This paper is a summary report of the two events, highlighting efforts focused on advancing scientific research in Africa. The report also outlines some of the major challenges faced and discusses key considerations for organizing future meetings.

In this work, we describe an approach to characterize the ground response to geomagnetic storm drivers and recalculate the scaling factors that are used in the NERC TPL-007 geomagnetic disturbance (GMD) standard based on magnetotelluric (MT) survey measurements. The new ground response scaling factors indicate a significantly wider range of ground responses from the one-dimensional model responses used in the original NERC geomagnetic disturbance standards framework. Futher, the region Mid-West west of the great lakes and north-East around New England and areas along the Appalachian mountains appear to be particularly exposed to the geoelectric field hazard under extreme space weather conditions. A more complete validation of MT data in GIC applications is warranted before usage of the presented results as a basis for possible updates to the NERC GMD standard.

On 20 December 2015, three THEMIS spacecrafts detected a nightside magnetotail reconnection event at about 04:36 UT. The spacecrafts (P5, P4, and P3) had their footprints located over North America in the near vicinity of the Gillam ground magnetometer station in Canada. Multipoint observations, both in space and from the ground, allow for an examination of the spatiotemporal characteristics of the disturbance on the ground and the associated physical drivers in the magnetosphere and ionosphere. This study shows that the geomagnetic field dB/dt localization observed at Gillam ground magnetometer site was caused by an isolated substorm onset near that location driven by a nightside magnetotail reconnection event detected by three THEMIS spacecrafts that were located near the central plasma sheet. This event represents the first observation of ground dB/dt localization that is directly linked to nightside magnetotail fast flow bursts and reconnection event.

An announcement of the passing of Editor of Space Weather, Jennifer Gannon.

The 1859 Carrington event is the most intense geomagnetic storm in recorded history, and the literature provides numerous explanations for what drove the negative H perturbation on the Earth. There is debate on what dominated the event. Our analysis shows a combination of causes of similar orders of magnitude. Previous analyses generally rely upon the observed H perturbation at Colaba, India; historic newspaper reports; and empirical models. We expand the analysis using two Space Weather Modeling Framework simulations to examine what drove the event. We compute contributions from currents and geospace regions to the northward B field on Earth's surface, B_N. We examine magnetospheric currents parallel and perpendicular to the local B field, ionospheric currents, and gap region field–aligned currents (FACs). We also evaluate contributions from the magnetosheath, near–Earth, and neutral sheet regions. A combination of currents and geospace regions significantly contribute to B_N on the Earth's surface, changing as the storm evolves. At storm onset, magnetospheric currents and gap–region FACs dominate in the equatorial region. At auroral latitudes, gap–region FACs and ionospheric currents are the largest contributors. At storm peak, azimuthal magnetospheric currents and gap–region FACs dominate at equatorial latitudes. Gap–region FACs and ionospheric currents dominate in the auroral zone, down to mid‐latitudes. Both the magnetosheath and FACs contribute at storm peak, but are less significant than that from the near–Earth ring current. During recovery, the near–Earth ring current is the largest contributor at equatorial latitudes. Ionospheric currents and gap–region FACs dominate in the auroral zone.

A characteristic feature of the main phase of geomagnetic storms is the dawn‐dusk asymmetric depression of low‐ and mid‐latitude ground magnetic fields, with largest depression in the dusk sector. Recent work has shown, using data taken from hundreds of storms, that this dawn‐dusk asymmetry is strongly correlated with enhancements of the dawnside westward electrojet and this has been interpreted as a “dawnside current wedge” (DCW). Its ubiquity suggests it is an important aspect of stormtime magnetosphere‐ionosphere (MI) coupling. In this work we simulate a moderate geomagnetic storm to investigate the mechanisms that give rise to the formation of the DCW. Using synthetic SuperMAG indices we show that the model reproduces the observed phenomenology of the DCW, namely the correlation between asymmetry in the low‐latitude ground perturbation and the dawnside high‐latitude ground perturbation. We further show that these periods are characterized by the penetration of mesoscale bursty bulk flows (BBFs) into the dawnside inner magnetosphere. In the context of this event we find that the development of the asymmetric ring current, which inflates the dusk‐side magnetotail, leads to asymmetric reconnection and dawnward‐biased flow bursts. This results in an eastward expansion and multiscale enhancement of the dawnside electrojet. The electrojet enhancement extends across the dawn quadrant with localized enhancements associated with the wedgelet current systems of the penetrating BBFs. Finally, we connect this work with recent studies that have shown rapid, localized ground variability on the dawnside which can lead to hazardous geomagnetically induced currents.