Earth's outer electron radiation belt:sources, losses and predictions

摘要

The outer electron radiation belt is highly dynamic in space and time. Understanding the mechanisms that drive these variations is of high interest to the scientific community because of the negative effects that the radiation belt can have on satellite instrumentation. Evidence in support of a wide range of processes has been uncovered, yet a complete understanding of the relative contribution of each processes, and how these contributions vary over time, is yet to be fully determined. The first body of research (Chapter 4) follows the evolution of the electron radiation belt at geosynchronous orbit through three high-speed solar wind stream induced dropouts. Electron flux, magnetic field, and phase space density results from GOES-13 indicate that outwards adiabatic transport plays a key role in causing radiation belt flux dropouts at GEO. This leads to enhanced magnetopause losses and subsequent outwards radial diffusion. Other loss processes may also play a role. In the second body of research (Chapter 5), the partial moments (electron number density, temperature and energy density) from GOES-13 are compared to different solar wind parameters, both instantaneous and time delayed, in order to develop a coarse predictive capability. Using these partial moments allows for changes in the number of electrons and the temperature of the electrons to be distinguished, which is not possible with the particle flux output from individual instrument channels. It is found that using solely the solar wind velocity as a driver results in predicted values that accurately follow the general trend of the observed moments. Given that electron number density and temperature are the fundamental physical parameters of a plasma, the result is a testable model that addresses elementary plasma properties. Hence, for a Maxwellian plasma, it is possible to infer the flux at any energy, not just energy channels tied to a particular instrument. In the final research study (Chapter 6), the validity of using the cold plasma dispersion relation to infer the magnetic field wave power from the measured wave electric field is tested using Van Allen Probes EMFISIS observations in the chorus wave band (0.1-0.9 fce). Results from this study indicate that for observed wave intensities > 10-3 nT2, using the cold plasma dispersion relation results in an underestimate of the wave intensity by a factor of 2 or greater, 56% of the time over the full chorus wave band, 60% of the time for lower band chorus, and 59% of the time for upper band chorus. Hence during active periods, empirical wave models that are reliant on the cold plasma dispersion relation will underestimate chorus wave intensities to a significant degree, thus causing questionable calculation of wave-particle resonance effects on MeV electrons.