Tuesday, 24 January 2017: 8:30 AM
4C-2 (Washington State Convention Center )
Maps covering about half of the continental United States are presented of geoelectric amplitude that is exceeded, on average, once per century in response to extreme-intensity geomagnetic activity. These maps are constructed using an empirical parameterization of induction: local estimates of Earth-surface impedance, obtained at discrete geographic sites from magnetotelluric survey data, are convolved with latitude-dependent statistical maps of extreme-value geomagnetic activity, obtained from decades of 1-minute resolution magnetic observatory data. Geoelectric amplitudes are estimated for geomagnetic waveforms having 240-s sinusoidal period and amplitudes over 10 minutes that exceed a once-per-century threshold. As a result of the combination of geographic differences in geomagnetic activity and Earth-surface impedance, once-per-century geoelectric amplitudes span more than two orders of magnitude and are an intricate function of location. Specifically: for north-south induction, geoelectric amplitudes across large parts of the United States have a median value of 0.26 V/km; for east-west geomagnetic variation the median value is 0.23 V/km. However, at some sites, such as in northern Minnesota, once-per-century amplitudes exceed 14.00 V/km for north-south geomagnetic variation (23.34 V/km for east-west variation), while just over 100 km away, amplitudes are only 0.08 V/km (0.02 V/km). At some sites in the continental United States, once-per-century geoelectric amplitudes exceed the 1.7 V/km realized in Quebec during the March 1989 storm.
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