Multiphysics simulations of E3 EMP using Topanga*

We simulate the E3 electromagnetic pulse (EMP) from a high-altitude nuclear explosion (HANE) over the Ozarks, using the code Topanga. Topanga is a multiphysics hybrid particle in cell code that models plasma dynamics, ionospheric chemistry, X-ray ionization, and electromagnetic field evolution for a HANE on timescales of up to 100 seconds. The HANE scenario we model is based on the Starfish Prime nuclear test. We use experimentally measured magnetotelluric impedance tensors to calculate E3 electric fields in the ground.

The E3 electric field amplitude in our simulations for low ground conductivity values of approximately 1E-4 S/m is in the range of 10-15 V/km. This is a factor of 2-3 lower than the electric field amplitudes reported by Love et al. (2021), using the same magnetotelluric impedance tensors. Our analysis reveals that this discrepancy is due to differences in the E3 magnetic field signal used in the two studies. Whereas Love et al. (2021) used a generic E3 magnetic field signal based on an IEC report (1996), Topanga calculates electromagnetic fields ab-initio for a specific HANE scenario.

Our results show that accurate E3 electromagnetic waveforms in addition to realistic impedance tensors are required to model E3 EMP and quantitatively predict the hazard it poses to the power grid.