Understanding how low energy electrons control the variability of the Earth's electron radiation belts
The electron radiation belts are regions of geomagnetically trapped electrons, surrounding the Earth, presenting hazards to operational satellites. On the timeframe of hours, both the energy and particle flux of the radiation belts can change by orders of magnitude. Variations in the high energy rel...
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| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
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Darwin
2019
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| Online Access: | https://doi.org/10.17863/CAM.41530 https://www.repository.cam.ac.uk/handle/1810/294431 |
| Summary: | The electron radiation belts are regions of geomagnetically trapped electrons, surrounding the Earth, presenting hazards to operational satellites. On the timeframe of hours, both the energy and particle flux of the radiation belts can change by orders of magnitude. Variations in the high energy relativistic electron flux depend on transport, acceleration, loss processes, and importantly, on the lower energy seed (10s – 100s keV) population. Seed population electrons are supplied to the radiation belt region during geomagnetically active periods and can be accelerated to higher energies via a range of processes. Unlike the higher energy, $>$1 MeV electrons, the azimuthal drift of the seed population is strongly affected by the convection electric field. Using fourteen years of electron flux data from low Earth orbit (LEO) satellites, a statistical study was performed on the magnetic local time distribution of three seed population energies, across a range of activity levels, defined by the geomagnetic indices AE, AE*, Kp, the solar wind velocity, and V$_sw$B$_z$. During periods of high activity, dawn-dusk flux asymmetries of over an order of magnitude were observed for $>$30 and $>$100 keV electrons, due to increased flux in the dawn sector. For $>$300 keV electrons, magnetic local time asymmetries were also present, but arose primarily due to a decrease in the average dusk-side flux beyond L* $\sim$4.5. A novel method was developed that utilizes measurements from low altitude, polar orbiting POES and MetOp satellites to retrieve the seed population at a pitch angle of 90$^o$. The resulting dataset offers a high time resolution, across multiple magnetic local time planes, and was used to formulate event-specific low energy boundary conditions for the British Antarctic Survey Radiation Belt Model (BAS-RBM). This new low energy boundary condition from LEO data has a higher spatial and temporal resolution, and a broader L* coverage, than previous work. The impact of variations in the seed population on ... |
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