The Use of ACE Electron, Proton, and Alpha Monitor (EPAM) Data in Severe Geomagnetic Storm Forecasting

Recent research, in both the science and engineering communities, indicates that an extreme geomagnetic disturbance (GMD) could result in a profound impact on national critical infrastructure, especially the electric power grid. In response, the Federal Energy Regulatory Commission (FERC) made a ruling in May 2013 which mandates development of reliability standards that address the impact of GMDs on the electric power grid. In part, the ruling requires owners and operators of the Bulk-Power System to develop and implement operational procedures to mitigate GMD effects. Early warning of severe GMDs is paramount in these operational procedures.

NOAA's space weather forecasters are responsible for GMD warnings to support the continuous and reliable operation of the nation's Bulk-Power System. NOAA forecasters rely on L1 libration point solar wind observations for CME detection and short-term, high-confidence, warnings of a GMD. This provides typically 15-45 minutes of lead-time to the onset of the storm. However, enhancements in the energetic ion measurements on the Electron, Proton, and Alpha Monitor (EPAM) instrument on the NASA ACE spacecraft have proven to be a valuable indicator of geomagnetic storm intensity, minutes and sometimes hours before the shock arrives at L1.

This relationship between energetic ion enhancements (EIEs) and large geomagnetic storms was established by Smith et al. [Smith, Z., Murtagh, W., Smithtro, C. Relationship between solar wind low-energy energetic ion enhancements and large geomagnetic storms. J. Geophys. Res. 109, A01110, 2004. doi:10.1029/ 2003JA010044]. They found an excellent correlation between storms with Kp7 and the peak flux of large energetic ion enhancements. Their research was confined to the rise and maximum of Solar Cycle 23 (1998–2001) and a forecasting technique was developed and tested on that time period. We extend this research to cover the remaining years of Solar Cycle 23 (2002-2008) and the rise phase of Cycle 24 (2008-2013) to assess performance of the technique over a full solar cycle. We also explore the relationship of EIEs measured on the EPAM 47–65 keV channel and GMDs as measured by other storm geomagnetic storm indices, e.g., Ap.