Quantifying the Role of Non-Adiabatic Processes in the Creation of the Outer Radiation Belt

We have reported (Fox et al., 2006) strong evidence that non-adiabatic (first invariant breaking) energization is required to explain the generation of Earth's outer electron radiation belt during intense storm events and also during more typical outer belt conditions. This evidence relies on the most conservative of assumptions that maximize the phase space densities of particle distributions adiabatically displaced in our models from the measured source population within the near-Earth magnetotail to the inner magnetospheric regions using initially only first adiabatic invariant transport, and subsequently first and second adiabatic invariant transport. Importantly, the phase space densities measured within the outer belt electron populations exceed the phase space densities of these adiabatically maximized source population distributions at energies > 1 MeV. By including the 2nd adiabatic invariant, we show that the angular distributions are strongly scattered during the transport and energization process. The scattering was so strong that we found it advisable to find another invariant in place of the combination of the 1st and 2nd. In this paper, we consider the isotropic invariant (Schulz, 1998). We compare the results of adiabatic transport followed by scattering against isotropic invariant transport. We find that this new approach demonstrates an even greater need for non- adiabatic processes with energies > 0.5 MeV profoundly affected. Below ~0.5 MeV the observed intensities are substantially below the adiabatic transport expectations. We test here the hypothesis that the lower-energy spectral intensities are constrained by Kennel-Petschek-type limits (Kennel and Petschek, 1966). The energization that electrons can acquire via non-adiabatic radial transport under these new constraints is determined using data from ISEE, and CRRES. Fox, N. J., B. H. Mauk, and J. B. Blake (2006), Role of non-adiabatic processes in the creation of the outer radiation belts, Geophys. Res. Lett., 33, L18108, doi:10.1029/2006GL026598. Kennel C. F. and Petschek H. E. Limit of stably trapped particle fluxes, J. Geophys. Res., 71, 1, 1-28, 1966. Schulz, M. (1998), Particle drift and loss rates under strong pitch angle diffusion in Dungey's model magnetosphere, J. Geophys. Res., 103, A1, 61-68