Geoelectric Fields Driven by Ultra Low Frequency Waves: A Missing Link in our Understanding of Geomagnetically Induced Currents

Geomagnetic perturbations (B_GEO) related to magnetospheric Ultra Low Frequency (ULF) waves induce electric fields within the conductive Earth - geoelectric fields (E_GEO) - that in turn drive geomagnetically induced currents. Though numerous past studies have examined ULF wave B_GEO from a space weather perspective, few studies have linked ULF waves with E_GEO. Using recently available magnetotelluric impedance and E_GEO measurements in the contiguous United States, we explore the relationship between ULF waves and E_GEO. We use satellite, ground-based radar, B_GEO, and E_GEO measurements in a case study of a plasmaspheric virtual resonance (PVR), demonstrating that the PVR E_GEO has significant spatial variation in contrast to a relatively uniform B_GEO, consistent with spatially varying Earth conductivity. We further show ULF wave E_GEO measurements during two storms are comparable to once-per-century geoelectric hazard maps. We use both results to highlight the need for more research characterizing ULF wave E_GEO.