Temporal and Spatial Development of TEC Enhancements during Substorms

Total electron count (TEC) enhancements due to space weather are a threat to communications and global positioning systems. It is known that TEC enhancements occur during magnetic storms and can cover large areas for many hours, but it is also not uncommon for TEC enhancements on the order of a few TEC units to occur during substorms. Although much is known about storm‐associated TECs, the temporal and spatial characteristics of substorm‐associated TECs are not well established. By combining two‐dimensional maps of TECs over North America and Greenland and with maps of ionospheric currents derived with the spherical elementary current method [Weygand et al., 2011], we investigate the temporal and spatial changes of TEC enhancement events for both a single substorm and for multiple substorms combined using a two‐dimensional superposed‐epoch analysis. Both the single event analysis and the statistical analysis show an increase of TECs during the expansion phase. Substorm values of the TEC enhancements peak within 10 min after auroral onset and recover to nominal levels after about 40 min. TEC enhancements occur mainly within the nightside region 1 current system and cover millions of square kilometers. Furthermore, these enhancements appear to be associated with enhanced precipitating electron fluxes. These results address one of goals of the Space Weather Action Plan, which are to establish benchmarks for space weather events and improve modeling and prediction of their impacts on infrastructure. TEC enhancements occur in about 81% of 259 substorms examined TEC enhancements appear to be the result of either monoenergetic and/or broadband electron precipitation TEC enhancements occur mainly within the region 1 and Harang current system