The Geomagnetic Storm Ceiling: A Bound on Geoelectric Field and Line Current from the Fastest Field Changes Earth Delivers

Uniform-Earth magnetotelluric bound on geoelectric field and geomagnetically induced current. At an extrapolated ceiling of 5,000 nT/min the largest surface field is 23 V/km on 10,000 ohm-m ground (0.73 V/km on 10 ohm-m ground), about 23,000 V across a 1,000 km corridor and about 353 A per phase under stated circuit assumptions. The model reproduces the March 1989 Quebec regional field of about 1.5 V/km at an implied resistivity of about 4,600 ohm-m. Fields of thousands of V/km would require a resistivity of about 1.9e7 ohm-m and fail by a factor of about 43.