A Comparison of GLobal airglOW (GLOW) and MCNP-based Models Applied to the Coupled Photon-Electron Transport and Photo-Electron Heating of Ambient Electrons at Swarm Altitudes.
Abstract
Absorption of EUV radiation from the sun by the neutral atmosphere and its ionization causes ambient electron gas heating, which causes heating of ambient ions. Our investigation of this complicated process is based on new knowledge of the photon, electron, and atomic structure data relevant to photoelectron transport in the latest version of the ENDF/B VI.8 cross-section library. We will apply obtained results to ionospheric electron and ion temperature measurements from Langmuir probes onboard the European Space Agency's Swarm satellite mission.
In this research, we compare GLOW (Solomon at al., 1978) model of the photoelectron production and transport with MCNP6 (Werner, 2017) coupled single-event electron transport. We apply measured EUV photon flux from the Heroux at al., 1974 paper, in the range 56 to 1025.72 (O2 ionization energy cutoff) Angstroms as an input to both approaches. We validate ionization rate altitude profiles of molecular nitrogen and oxygen and atomic oxygen obtained from MCNP6 run, with those from Heroux at al., (1974), and GLOW, using the same neutral atmosphere composition derived from the NRLMSISE-00 (Picone, 2002) model. We show that at Swarm altitudes (above ~350 km), ambient electron gas does not significantly affect photoelectron transport, which is not the case at lower altitudes. To validate the GLOW chemistry model, we compare calculations of the GLOW electron density below 200 km with SAMI2 (Huba at al., 2000) electron density altitude profiles. Getting GLOW and MCNP6 photoelectron spectra and SAMI2 ambient electron densities, we calculate photoelectron heating rates. We use Mott electron-electron cross -sections because the limit of classical mechanics occurs for low electron velocity only (Ve << e2/ Ћ = 2.2 ·106 m/s), which is about the speed of electrons with energies close to the oxygen ionization threshold (2.1 ·106 m/s). The classical Rutherford cross-sections underestimate the electron-electron cross-section significantly. Finally, we compare the obtained MCNP-derived photoelectron heating rates with those from GLOW calculations. We find that applying realistic EUV source and contemporary coupled photon-electron transport of photoelectrons can improve electron heating rate calculations. Substituting an analytical expression for the energy transfer rate from photoelectrons to thermal electrons implemented in GLOW (Swartz and Nisbet, 1971) on an approach based on Mott cross-sections applied to the electron scattering on free electron affects the precision of the electron heating rate calculations- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMSA0040002K
- Keywords:
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- 2431 Ionosphere/magnetosphere interactions;
- IONOSPHERE;
- 7924 Forecasting;
- SPACE WEATHER;
- 7954 Magnetic storms;
- SPACE WEATHER;
- 7959 Models;
- SPACE WEATHER