Space-and ground-based measurements of radiation belt precipitation : extending the capabilities of cubesats and radars
Keywords: Aeronautics and Astronautics.

The overall dynamics of the Earth's radiation belts is governed by the constant competition between source and sink mechanisms. The purpose of this work is to advance our understanding of sink or loss processes due to energetic particle precipitation from the radiation belts into the atmosphere. We seek to assess and compare in situ space measurements of precipitating particles to ground-based remote sensing of their signature in the atmosphere. We use data collected by the Focused Investigations of Relativistic Electron Burst Intensity, Range and Dynamics II (FIREBIRD-II) CubeSats during conjunction times with Poker Flat Incoherent Scatter Radar (PFISR), as well as data collected by PFISR itself. In the ionosphere's D-region, the ionization rate cannot be directly measured, therefore it must be estimated from other measurements. From space-based measurements, we use precipitating particle flux to find ionization rate in the atmosphere through the Electron Precipitation Monte Carlo (EPMC) transport method. This ionization rate is used to calculate the expected electron density in the D-region through chemistry simulations using the Glukhov-Pasko-Inan five species (GPI5) atmospheric chemistry model. From ground-based measurements, we extract the ionization rate using inverse theory, particularly using a Bayesian perspective we obtain the ionization rate, with uncertainties in all associated parameters, from measurements of electron density of sub-relativistic and relativistic electron precipitation taking into consideration the time dependent nature of the detection signatures. The benefit of a time-dependent inversion method is critical when precipitation changes on timescales faster then relaxation. The method was tested on synthetic data and applied to specific data sets measured by PFISR with the goal to extend data capability from single-point to multi-point scales. The method is able to retrieve the ionization curves that return the expected electron densities when forward modeled, which validates our results. The modeled electron density captures the small scale structure of the precipitation with values 1-2 orders of magnitude lower than the electron density observed by the radar. Therefore, the need for inversion techniques that could take us from radar observed quantities to spacecraft observables arises. For one of the cases, assuming an exponential energy distribution led to a mean absolute percent error of approximately 22 % when comparing the ionization rate altitude profile fit to the curve inferred by inverting PFISR electron density. However, an arbitrary energy distribution improved the fit to the ionization rate as it produced an error of approximately 11.11 %, about half than the that of the previously assumed exponential distribution. For the other case, the error was approximately 10.82 with an arbitrary energy distribution. For both of these cases, the arbitrary energy distribution inversion results are comparable in magnitude and shape to those presented in Turunen et al. 2016 for the inversion of a single event of pulsating aurora observed by EISCAT. The methods established in this thesis provide a back and forth path between space and ground measurements of energetic electron precipitation, that can be extended beyond the D-region. The ionization rate inversion technique is applicable to any atmospheric chemistry model, it provides time dependent remote estimation of ionization rate in the D-region that can be used to infer the energy distribution of precipitation without assuming any particular spectral shape. This is accomplished with good temporal coverage and can be used to carry continuous diagnostics of high energy precipitating phenomena