Beyond the L1 Horizon: Extending Geomagnetic Storm Forecast Lead Time

Geomagnetic storm forecasting is a central challenge in space weather research because severe events can disrupt power transmission, satellite operations, navigation, aviation, and low-Earth-orbit systems. Operational predictions based on in-situ solar wind measurements at the Sun-Earth L1 Lagrange point generally provide only tens of minutes of warning, often 30 minutes or less for fast, geoeffective solar wind. Comparable constraints apply across the wider space weather chain: solar flare and SEP forecasts likewise offer only minutes to a few hours of lead time for the most severe events, rarely enough for operators to act. Achieving warnings hours or days in advance requires better characterization of dynamic phenomena such as coronal mass ejections (CMEs), and their evolution through the heliosphere before reaching L1, improved modeling of the ambient solar wind and high-speed streams that condition CME propagation, and more accurate representation of solar-wind coupling across the magnetopause, magnetosphere, and ionosphere-thermosphere system. Advances in remote sensing, heliospheric imaging, multi-spacecraft observations, data assimilation, and Physics-informed neural network and machine-learning modeling offer opportunities for improved forecasting. However, uncertainties in CME and sheath structure, upstream propagation, dayside reconnection, magnetosheath transport, and the limited number of well-observed severe storms remain significant gaps.This Research Topic treats lead time, forecast skill, and physical interpretation as a coupled solar–heliosphere–geospace problem, spanning the chain from flares and CMEs through interplanetary propagation to their effects on geomagnetic activity, the radiation belts, and the ionosphere-thermosphere system. It seeks to determine how solar and heliospheric observations, upstream measurements (including from vantage points beyond L1, such as Sub-L1), and global magnetospheric monitoring can be integrated to extend warning times beyond the L1 constraint; to identify the physical processes controlling the transfer of solar-wind energy into geospace; and to evaluate assimilative, ensemble, hybrid, and machine-learning models against transparent baselines. Contributions should quantify forecast skill, state the evaluated lead time, and address uncertainty and reproducibility. Negative results, method limitations, and comparative benchmarks are encouraged, as are studies linking forecast performance with power-grid, satellite, orbital-drag, and navigation decisions.We welcome Original Research, Review, Mini-review, and Perspective articles addressing, but not limited to, the following themes:• Physical and observational limits on forecast lead time and conditions under which the L1 constraint can be exceeded, including long-lead CME arrival-time and geoeffectiveness prediction.• CME and ICME propagation, arrival-time prediction, geoeffectiveness, and sheath structure, including planarity, turbulence, Alfvénic structures, and reconnection-related features.• Solar flare and SEP forecasting and their relationship to CME initiation and interplanetary evolution.• Solar wind and high-speed stream modeling as a modulator of CME propagation and a driver of recurrent geomagnetic activity. • Heliospheric imaging and upstream spacecraft constellations, including Sub-L1 and other multi-point vantage points, as inputs beyond single-point L1 monitoring.• Geomagnetic activity indices, radiation belt flux prediction, and geomagnetically induced currents (GICs) as downstream forecast targets.• Ionosphere-thermosphere response to geomagnetic driving and implications for navigation, communications, and orbital drag.Studies on uncertainty quantification, ensemble forecasting, and assimilation of observations from vantage points like Sub-L1 are encouraged.We hope this Research Topic helps to connect the heliophysics and forecasting communities and moves the field toward genuinely actionable long-lead forecasts. Topic editors: Steven Petrinec, Ankush Bhaskar Source: https://www.frontiersin.org/research-topics/83615/beyond-the-l1-horizon-extending-geomagnetic-storm-forecast-lead-time