Sources of Ultra Low Frequency Total Electron Content Perturbations: Statistical Study

Perturbations in ionospheric Total Electron Content (TEC) with timescales of ~10 -1000 seconds can be driven from above by processes in the magnetosphere – including magnetospheric Ultra Low Frequency (ULF) waves – and below by processes such as acoustic-gravity waves in the atmosphere. Characterizing the subset of TEC perturbations related to ULF waves is of high priority as several studies have shown these perturbations impact ionospheric space weather, including large variations in ionospheric conductance. However, it is currently unknown whether ULF waves routinely drive TEC perturbations of significance for space weather; for example, whether they can routinely drive TEC perturbations associated with conductance variations large enough to affect magnetosphere-ionosphere current systems and ionospheric heating. Our goals in this work are to (1) better quantify TEC perturbation amplitudes caused by ULF waves and (2) develop methods for remote sensing ULF waves using TEC and, more generally, separate ULF TEC perturbations associated with magnetospheric waves from ULF TEC perturbations associated with driving from below. We present statistical analysis of ULF TEC perturbations during magnetic conjunction events observed during different driving conditions. We use Global Navigation Satellite System (GNSS)-derived TEC data, ground magnetometer data, THEMIS satellite data, and other datasets to determine whether the TEC perturbations are associated with magnetospheric ULF waves. We place these results in context with past studies of ULF TEC perturbations, discussing possible explanations for the wide range of TEC perturbation amplitudes found in past work. We finally discuss how we’re using observations and modeling to determine (1) whether ULF waves are routinely a source of TEC perturbations of significance for ionospheric space weather and (2) how to discriminate between ULF TEC perturbations driven from above and below.