Radial distributions of equatorial phase space density for outer radiation belt electrons

We present the first direct observations of equatorial electron phase space density (PSD) as a function of the three adiabatic invariants throughout the outer radiation belt using data from the Solid State Telescopes on THEMIS-D. We estimate errors in PSD that result from data fitting and uncertainty in the calculation of the second and third invariants based on performance-weighted results from seven different magnetic field models. The PSD gradients beyond geosynchronous orbit (GEO) are energy dependent, revealing different source regions for the relativistic and non-relativistic populations. Specifically, the PSD distribution of outer belt relativistic electrons is peaked near L* approximate to 5.5. These features are typical for the outer belt, based on a survey of a two-month period from 01 Feb.-31 Mar. 2010. The results are consistent with previous studies, which were based on off-equatorial observations, but remove the high uncertainties introduced from mapping by using truly equatorial measurements (i.e., within only a few degrees of the magnetic equator) and quantifying the error in PSD. The newly calibrated THEMIS-SST dataset forms a powerful tool for exploration of the near-Earth magnetosphere, especially when combined with the upcoming RBSP mission. Citation: Turner, D. L., V. Angelopoulos, Y. Shprits, A. Kellerman, P. Cruce, and D. Larson (2012), Radial distributions of equatorial phase space density for outer radiation belt electrons, Geophys. Res. Lett., 39, L09101, doi:10.1029/2012GL051722.