¹British Antarctic Survey (NERC), Cambridge, U.K.,
²Department of Physics, University of Otago, Dunedin, New Zealand,
³Sodankylä Geophysical Observatory, University of Oulu, Sodankylä, Finland,
⁴Space Weather Prediction Center, NOAA, Boulder, Colorado,
⁵Centre d'Etude Spatiale des Rayonnements, Toulouse, France,
⁶Laboratoire de Physique et Chimie de l'Environnement, Orleans, France

Abstract

AARDDVARK data from a radiowave receiver in Sodankyla, Finland have been used to monitor transmissions from the very low frequency communications transmitter, NAA, (24.0 kHz, 44^o N, 67^o W, L=2.9) in USA since 2004. The transmissions are influenced by outer radiation belt (L=3-7) energetic electron precipitation. In this study we have been able to show that the observed transmission amplitude variations can be used to routinely determine the flux of energetic electrons entering the atmosphere. Our analysis of the NAA observations shows that electron precipitation fluxes can vary by three orders of magnitude during geomagnetic storms. Comparison of the ground-based estimates of precipitation flux with satellite observations from DEMETER and POES indicates a broad agreement during geomagnetic storms, but some differences in the quiet-time levels, with the satellites observing higher fluxes than those observed from the ground. Typically when averaging over L=3-7 we find that the >100 keV POES "trapped" fluxes peak at about 10⁶ el.cm^-2s^-1str^-1 during geomagnetic storms, with the DEMETER >100 keV drift loss cone showing peak fluxes of 10⁵ el.cm^-2s^-1str^-1, and both the POES >100 keV "loss" fluxes and the NAA ground-based >100 keV precipitation fluxes showing peaks of ~10⁴ el.cm^-2s^-1str^-1. The analysis of NAA amplitude variability has the potential of providing a detailed, near real-time, picture of energetic electron precipitation fluxes from the outer radiation belts.