Superposed Epoch Analysis of GPS Total Electron Content Variations Driven by Geomagnetic Storms

Increasingly dense networks of ground-based Global Positioning System (GPS) receivers allow for imaging of large-scale ionospheric electron density structures at high spatial and temporal resolution. Strong gradients associated with the edges of these density structures have been related to smaller-scale irregularity formation and outages of aircraft navigation services. In this study, we present a superposed epoch analysis of GPS total electron content (TEC) variations driven by geomagnetic storms during the current solar cycle (2008 - present). The analysis is focused on the northern hemisphere where greater GPS receiver coverage is available in the North American, European, and Japanese sectors. Globally distributed measurements of vertically-integrated GPS TEC are first binned into 1° × 1° cells at 5 min cadence and then organized by storm phase to calculate the deviation from 27-day TEC averages for large-scale ionospheric structures such as storm enhanced density, tongue of ionization, and midlatitude trough. The resulting maps of TEC variations are then compared with similar distributions of ionospheric irregularities and airglow as seen by ground-based networks of HF radars and all-sky imagers. By improving our understanding of these multi-scale ionospheric storm phenomena we are able to produce better global models and forecasting techniques.