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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, A10210, doi:10.1029/2004JA010895, 2005

Multisatellite determination of the relativistic electron phase space density at geosynchronous orbit: Methodology and results during geomagnetically quiet times

Y. Chen

Los Alamos National Laboratory, Los Alamos, New Mexico, USA


R. H. W. Friedel

Los Alamos National Laboratory, Los Alamos, New Mexico, USA


G. D. Reeves

Los Alamos National Laboratory, Los Alamos, New Mexico, USA


T. G. Onsager

NOAA, Boulder, Colorado, USA


M. F. Thomsen

Los Alamos National Laboratory, Los Alamos, New Mexico, USA


Abstract

We develop and test a methodology to determine the relativistic electron phase space density distribution in the vicinity of geostationary orbit by making use of the pitch-angle resolved energetic electron data from three Los Alamos National Laboratory geosynchronous Synchronous Orbit Particle Analyzer instruments and magnetic field measurements from two GOES satellites. Owing to the Earth's dipole tilt and drift shell splitting for different pitch angles, each satellite samples a different range of Roederer L* throughout its orbit. We use existing empirical magnetic field models and the measured pitch-angle resolved electron spectra to determine the phase space density as a function of the three adiabatic invariants at each spacecraft. Comparing all satellite measurements provides a determination of the global phase space density gradient over the range L* ∼ 6–7. We investigate the sensitivity of this method to the choice of the magnetic field model and the fidelity of the instrument intercalibration in order to both understand and mitigate possible error sources. Results for magnetically quiet periods show that the radial slopes of the density distribution at low energy are positive, while at high energy the slopes are negative, which confirms the results from some earlier studies of this type. We further show that the observed gradients near geosynchronous are generally small, making them very sensitive to both calibration and magnetic field model choice. This paper lays the foundation for this method for future applications to disturbed periods and for future inclusion of additional satellite data.

Received 10 November 2004; accepted 8 July 2005; published 20 October 2005.

Keywords: radiation belts; relativistic electrons; phase space density; geosynchronous orbit.

Index Terms: 2774 Magnetospheric Physics: Radiation belts; 2720 Magnetospheric Physics: Energetic particles: trapped; 2730 Magnetospheric Physics: Magnetosphere: inner; 2794 Magnetospheric Physics: Instruments and techniques.

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Citation: Chen, Y., R. H. W. Friedel, G. D. Reeves, T. G. Onsager, and M. F. Thomsen (2005), Multisatellite determination of the relativistic electron phase space density at geosynchronous orbit: Methodology and results during geomagnetically quiet times, J. Geophys. Res., 110, A10210, doi:10.1029/2004JA010895.