Comparison of Van Allen Probes Energetic Electron Data with Corresponding GOES-15 Measurements: 2012 - 2018

Measurements of energetic electron fluxes (especially at energies E > 0.8 and >2 MeV) have been made for many years by sensor systems on board the Geostationary Operational Environmental Satellite (GOES) series of geostationary orbit spacecraft. These long-term data have become a mainstay for monitoring the state of the Earth’s radiation environment and the state of space weather. We have carried out a study directly comparing the comprehensive radiation belt particle measurements from the NASA dual-spacecraft Van Allen Probes (Radiation Belt Storm Probes) sensor systems with selected GOES operational data. The Van Allen Probes have measured the fluxes, energy spectra, and pitch angle properties of radiation belt electrons virtually continuously from September 2012 through 2018. In this study, we make statistical comparisons of Van Allen Probes electron data near L=6 with concurrent daily averages of equivalent GOES-15 flux values. We also are able to compare Van Allen Probes data at various other L-values and at a much broader range of particle energies with the more limited baseline GOES-15 values. These comparisons inform us about the relative calibrations between the scientific and operational systems, and also allow us to assess how well GOES data correlate with radiation belt behavior well away from the geostationary orbit location. We find that simple GOES daily-average fluxes often are less than corresponding Van Allen Probes daily-averaged fluxes at L~6 by as much as two orders of magnitude (or more). Our analysis shows that this is largely due to strong radial flux gradients near geostationary orbit altitudes, but other factors also are at play. These results indicate that considerable care must be exercised when employing GOES measurements as indicators of overall radiation belt electron properties.