The investigators will use multi-point riometer measurements in conjunction with in-situ satellite data, to improve understanding of the precipitation of energetic electrons into the ionosphere from their magnetospheric origins. Energetic electrons in the 10's of kilo-electron volt (KeV) range precipitate to the upper D- and lower E region ionosphere, and are responsible for enhanced ionization. This same particle population is important in the inner magnetosphere, as it provides a source of waves, and acts as a seed population for relativistic electrons in the radiation belts. In situ observations of plasma populations and waves are usually limited to a single point, which complicates temporal and spatial analysis. Also, the lifespan of satellite missions is often limited to several years, which does not allow the inference of long-term climatology of magnetospheric conditions and solar cycle dependencies. Multi-point remote sensing of the ionospheric plasma conditions can provide a global view of the ionospheric and magnetospheric conditions, and the coupling between magnetospheric and ionospheric phenomena can be examined on time-scales that allow comprehensive statistical analysis. The investigators will inter-calibrate riometers with satellite measurements of precipitating fluxes and also compare to variations in the trapped electron population in the equatorial plane. Comparison with in-situ observations of precipitating fluxes will show which energy electrons can be measured by riometers and allow development of maps of latitudinal and magnetic local time (MLT) distributions of precipitation. The team will also study how precipitation depends on the solar wind conditions and geomagnetic indexes. Comparison with trapped population measurements from satellites will quantify the fraction of the loss to the atmosphere vs loss to the outer boundary of trapping and the outward transport. Long-term riometer measurements, which are correlated with fluxes of precipitating energetic electrons, can be used in the future as a proxy for magnetospheric wave activity. Electron precipitation can also modify ionospheric conductivity, which will influence magnetosphere-ionosphere coupling. This study supports the Van Allen Probe mission by demonstrating how remote sensing of ionospheric precipitation can help scientists understand processes in the magnetosphere and radiation belts. The results of the study will advance knowledge of magnetosphere-ionosphere coupling, which is important to provide better quality conductance estimates in the E-region ionosphere. Additionally, the energetic electrons in the 10's of keV range act as a seed population for relativistic electrons, which may damage satellite systems and hardware. In addition, the precipitation of energetic electrons directly influences the upper atmospheric chemistry, and represents a link between solar and magnetospheric activity, and climate.
