M. Dikpati1, M. B. Korsós2,3,4, A. A. Norton5, B. Raphaldini1,6, K. Jain7, S. W. McIntosh8, P. A. Gilman1, A. S. W. Teruya6, & N. E. Raouafi9
1 High Altitude Observatory, NSF-NCAR, 3080 Center Green Drive, Boulder, CO 80301, USA
2 School of Electrical and Electronic Engineering, University of Sheffield, Sheffield, S1 3JD, UK
3 Department of Astronomy, Eötvös Loránd University, H-1112 Budapest, Hungary
4 Hungarian Solar Physics Foundation, Petőfi tér 3, H-5700 Gyula, Hungary
5 Hansen Experimental Physics Laboratory, Stanford, CA 94305-4085, USA
6 Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, São Paulo, Brazil
7 National Solar Observatory, Boulder, CO 80303, USA
8 Lynker Space, Boulder, CO 80301, USA
9 Johns Hopkins Applied Physics Laboratory, Space Exploration Sector, Laurel, MD 20723-6099, USA
During the week of Mother’s Day 2024, the Sun unleashed a sequence of powerful events reminiscent of the historic 1859 “Carrington” storms. Active region (AR) 13664 became extremely active when another region, AR 13668, emerged nearby. Together, they produced multiple X-class flares and coronal mass ejections (CMEs), leading to geomagnetic disturbances on Earth comparable in intensity to some of the largest events on record. These eruptions disrupted critical systems, including GPS-based precision agriculture and satellite communications, underlining the urgent need for improved forecasting of major solar storms.
Traditionally, solar flare and CME forecasts rely on short-term, local indicators within individual active regions. Parameters such as active region morphology, helicity imbalance, and free magnetic energy density are monitored closely. Rapid changes in these quantities can offer forecasts with lead times of several hours. By exploring the global evolution of active region distributions on the Sun, this analysis shows that the large-scale organization of ARs across the solar surface holds valuable clues about major eruptions—not just hours, but potentially weeks before they occur.
Global Toroid Patterns and Eruption-Prone Longitudes
Over the past few years, several studies have revealed that active regions do not appear randomly across the Sun but instead emerge in organized spatial structures, namely aligning along tight, warped toroidal bands—“toroids”—that likely originate in a less turbulent region compared to the bulk of the convection zone, i.e. at/near the tachocline, where the subadiabatic stratification helps global organization.
A major finding is that eruptions preferentially occur in longitudes where the northern and southern toroids tip away from each other in latitude. In contrast, longitudes where the toroids overlap—tipping toward each other—are less likely to produce eruptive regions, possibly because magnetic flux from opposite hemispheres reconnects at depth, weakening the active regions.
Figure 1. Top: All flare-producing active regions are identified with NOAA numbers for May 14 global toroid patterns, derived from SDO/HMI data; yellow-circled ARs produced X-class flares, magenta-circled ARs M-class flares and cyan-circled ARs C-class flares. Non-flaring ARs are not circled, but they have been identified in white text with NOAA numbers. Bottom: May 14 toroid patterns derived from GONG data.
Figure 1 illustrates the longitudinal phases of these patterns during the Mother’s Day 2024 events. Multiple longitude intervals showed north–south toroids tipped apart, creating “eruption-prone” zones. By contrast, intervals with overlapping toroids were comparatively quiet. The situation was further complicated by a decaying active region in the southern hemisphere near 350° longitude, which interacted with new emergences to create additional magnetic complexity.
Importantly, our confidence in these toroidal patterns is strengthened by independent analyses from two data sources: high-resolution SDO/HMI magnetograms and coarser GONG data. While GONG-derived toroids appear slightly broader in latitude due to its lower resolution, both datasets reveal remarkably similar large-scale structures.
Magnetic Complexity and the Mother’s Day Superstorms
While global toroid patterns reveal where active regions are likely to emerge, the intensity of resulting eruptions depends on local magnetic complexity. The Mother’s Day superstorms were triggered by intricate interactions among multiple ARs emerging in close proximity (Figure 2). Such regions accumulate enormous magnetic free energy as their magnetic fields deviate strongly from potential configurations. Other processes also contribute to this energy buildup, namely helicity injection from beneath the surface creates imbalances, driving dynamic restructuring, multiple emergences in the same longitude intervals increase magnetic interactions, forming so-called “activity nests.”
Figure 2. Small-scale evolution of AR13664/8 is shown with three snapshots from HMI continuum (left) and radial magnetic field(right). (see also https://aasnova.org/2025/07/28/featured-image-mothers-day-superstorms/ ).
When these conditions coincide—eruption-prone toroid patterns combined with magnetically complex AR clusters—the likelihood of major flares and CMEs rises dramatically. The Mother’s Day 2024 events were such an example, where global-scale precursors and local-scale complexity aligned to produce one of the most significant solar storms in recent cycle 25.
Implications for Space Weather Forecasting
Methods based on local, small-scale AR dynamics offer only hours of warning, limiting operators’ ability to safeguard satellites, communication networks, and power infrastructure. Monitoring global toroid patterns, especially longitude intervals where northern and southern bands tip apart, can identify regions at risk well before eruptions occur. Once such regions are flagged, local magnetic parameters—morphology, helicity, magnetic energy—can be tracked to determine when these regions are approaching critical states likely to produce major eruptions. This two-tiered approach—global precursors followed by local diagnostics—could extend solar eruption forecasts from hours to potentially weeks, offering far more time for mitigation measures.
A major open question remains: how are the location and timing of active region emergences physically connected? Do global toroid patterns merely indicate where regions will emerge, or can they also predict when and how intensely they will erupt?
Understanding the recurrence of emergences in the same longitude intervals—so-called activity nests—is critical. These nests, where multiple ARs emerge sequentially or simultaneously, appear to be the progenitors of the largest solar eruptions. In the future, physics-based models need to be built by linking deep-seated processes, such as toroid evolution, flux emergence, and magnetic complexity.
More details can be found in the paper: Dikpati, M., Korsós, M. B., Norton, A. A., et al. 2025, ApJ, 988, 108, doi: 10.3847/1538-4357/addd09