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Ann. Geophys., 23, 2975-2982, 2005
www.ann-geophys.net/23/2975/2005/
© European Geosciences Union 2005
Fluxes of energetic protons and electrons measured on board the Oersted satellite
J. Cabrera1, M. Cyamukungu1, P. Stauning3, A. Leonov1,2, P. Leleux1, J. Lemaire1, and G. Grégoire1
1Center for Space Radiations (CSR), Chemin du cyclotron 2, 1348 Louvain-la-Neuve, Belgium
2Moscow Engineering and Physics Institute (MEPHI), Kashirskoe Shosse 31, 115 409 Moscow, Russia
3Danish Meteorological Institute (DMI), Lyngbyveij 100, DK-2100, Copenhagen, Denmark
Abstract. The Charged Particle Detector (CPD) on board the Oersted
satellite (649 km perigee, 865 km apogee and 96.48° inclination)
currently measures energetic protons and electrons. The measured peak fluxes
of E>1 MeV electrons are found to confirm the predictions of AE8-MAX,
though they occur at a geographical position relatively shifted in the SAA.
The fluxes of protons are one order of magnitude higher than the predictions
of AP8-MAX in the energy range 20-500 MeV. This huge discrepancy between
AP8 and recent measurements in LEO was already noticed and modelled in
SAMPEX/PSB97 and TPM-1 models. Nevertheless some other LEO measurements such
as PROBA and CORONA-F result in flux values in good agreement with AP8 within
a factor 2. The anisotropy of the low-altitude proton flux, combined with
measurement performed on board three-axis stabilised satellites, has been
suspected to be one possible source of the important discrepancies observed
by different missions. In this paper, we evaluate the effect of anisotropy on
flux measurements conducted using the CPD instruments. On the basis of the
available data, we confirm the inaccuracy of AP8 at LEO and suggest methods
to improve the analysis of data in future flux measurements of energetic
protons at low altitudes.
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