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- Title
Effects of Electron Precipitation on E‐Region Instabilities: Theoretical Analysis.
- Authors
Dimant, Y. S.; Khazanov, G. V.; Oppenheim, M. M.
- Abstract
During periods of strong geomagnetic activity, intense currents and electric fields originating in the magnetosphere inundate the high‐latitude E‐region ionosphere. These strong electric fields drive plasma instabilities, including the Farley‐Buneman instability (FBI). These instabilities give rise to small‐scale plasma turbulence that modifies the large‐scale ionospheric conductance that, in turn, affects the evolution of the magnetosphere‐ionosphere‐thermosphere system. Also, during geomagnetic storms, high‐energy precipitating electrons, ≳5 keV, frequently penetrate down to the same regions where the intense currents and electric fields exist. This research examines the effects of precipitating electrons on the generation of the FBI and shows that, under many common conditions, it can easily suppress the FBI in a predictable manner. We demonstrate that the plasma pressure of superthermal electrons may significantly exceed the regular plasma pressure of the cold ionospheric plasma. This effect will increase the FBI threshold and suppress the instability in auroral regions. However, our detailed theoretical analysis shows that the effect of the superthermal precipitating electrons on the FBI threshold is much stronger than the pressure effect. The energy dependence of the electron‐N2 collision frequency can greatly enhance the effect of this additional pressure, further suppressing the FBI, even at a moderate precipitation level. Therefore, we expect that precipitation will exert an additional significant feedback on the magnetosphere by preventing the elevated conductivity caused by FBI driven turbulence. Both the turbulence‐enhanced conductivities and this suppression should be taken into account in global modeling of the magnetosphere‐ionosphere coupling. Plain Language Summary: From time to time, elevated solar activity disturbs the near‐Earth environment, creating within the Earth's magnetosphere tangible geomagnetic storms. During these events, strong electric fields often penetrate down to the lower high‐latitude Earth's ionosphere where intense electric currents close. These currents provide strong magnetosphere‐ionosphere coupling. At altitudes between 100 and 120 km, the penetrated electric fields are often intense enough to generate plasma instability which, in turn, causes turbulence, heats electrons, and affects the large‐scale ionospheric conductance. This conductance is an important element of a global electric circle surrounding our planet. During the storm time, it is always possible that highly energetic electrons from the distant magnetospheric regions precipitate into the Earth's atmosphere, leading to the spectacular effect of Aurora Borealis. This theoretical research predicts that if these energetic electrons penetrate down to the lower‐ionosphere regions at the time of strong electric field able to generate plasma instability then these electrons will suppress this instability within the auroral regions, thus affecting the global ionospheric conductance. Proper understanding of these effects is important for accurate predictive modeling of the near‐Earth space plasmas, especially for the timely predictions of potentially devastating effects of solar activity on the human life and technology. Key Points: During geomagnetic storms, strong electric fields and intense electron precipitation frequently overlap in the E‐region ionosphereWithout precipitation, strong electric fields drive E‐region instabilities, leading to plasma turbulence and increased conductanceStrong electron precipitation dramatically raises the instability threshold, largely suppressing the instability inside the auroral regions
- Subjects
ATMOSPHERIC electron precipitation; GEOMAGNETISM; ATMOSPHERIC electricity; ELECTRIC fields; MAGNETIC storms
- Publication
Journal of Geophysical Research. Space Physics, 2021, Vol 126, Issue 12, p1
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1029/2021JA029884