4th VERSIM Workshop, Prague, Czech Republic, 13-17 September 2010

Ground-based Estimates of Outer Radiation Belt Energetic Electron Precipitation Fluxes into the Atmosphere

M.A. Clilverd1, C.J. Rodger2, R.J. Gamble2, Th. Ulich3, T. Raita3, A. Seppala1, J.C. Green4, N.R. Thomson2, J.-A. Sauvaud5, M. Parrot6

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


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, 44o N, 67o 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.

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