Multiproxy Analysis of 1204 Solar Storm

What this research found

What would the medieval geomagnetic storm of around 1204 CE do to infrastructure that did not exist at the time? The event was scaled to 10 to 30 percent of the 1859 Carrington storm, the auroral oval was reconstructed around the modern north geomagnetic pole at three storm strengths, and the result was overlaid on extra-high-voltage power substations and polar flight routes across the Northern Hemisphere. At the central estimate the equatorward auroral edge reaches about 39.1 degrees north, and trans-polar flight corridors pick up waypoints flagged for complete high-frequency radio blackout.

• The c. 1204 CE event is treated as sub-extreme rather than Carrington-class, bracketed at 10 to 30 percent of the 1859 storm. That maps to a planetary K index of 6.5 at the low end, 7.5 as the central estimate, and 8.0 at the upper end.
• At the central Kp of 7.5 the equatorward edge of the auroral oval reaches roughly 39.1 degrees north geographic, with the oval itself drawn as a band 8 degrees of magnetic latitude wide.
• High-frequency radio disruption is graded per flight waypoint, with severe conditions set at more than 5 decibels of attenuation at 10 MHz and complete blackout at 10 decibels or more. Routes crossing the polar cap between Western Europe and East Asia, and those over northern Canada, accumulate the most complete-blackout waypoints.
• Transformer stress from geomagnetically induced current is scored on a normalised 0-to-1 index, and in the central bracket the mapped substations reach only about 0.40 of that scale. The largest values fall on high-latitude Canadian and Nordic nodes rather than on mid-latitude ones.

How it was done

Storm strength was bracketed at 10 to 30 percent of the Carrington event, yielding low, central, and upper planetary K index values. For each level the equatorward auroral boundary was drawn as small circles around the modern north geomagnetic pole taken from the International Geomagnetic Reference Field, at 80.65 degrees north and 72.68 degrees west, using a Feldstein-Starkov-style relation that sets the boundary in magnetic latitude as 67.5 minus 2.5 times Kp. A simulated Northern Hemisphere network of extra-high-voltage substations and polar flight routes was then overlaid on a north polar stereographic projection covering 25 to 90 degrees north, scoring each substation for transformer stress and each flight waypoint for high-frequency radio attenuation.

Data sources

• International Geomagnetic Reference Field — modern north geomagnetic pole at 80.65 degrees north, 72.68 degrees west
• Feldstein-Starkov-style auroral equatorward boundary parameterisation
• Simulated extra-high-voltage substation and polar flight-route networks for the Northern Hemisphere
• The 1859 Carrington event as the reference storm for scaling