Effect of Electron Precipitation on E-Region Instabilities in Auroral Regions and Magnetosphere-Ionosphere Coupling

Abstract:

During periods of intense geomagnetic activity, strong DC electric fields perpendicular to the geomagnetic field penetrate from the Earth's magnetosphere into the high-latitude E-region ionosphere where they dissipate energy, form electrojets, and drive plasma instabilities. In this weakly ionized and highly collisional region most of the field-aligned magnetospheric currents close. Also, in this region plasma instabilities give rise to small-scale plasma turbulence that modifies the large-scale ionospheric conductance. This affects the evolution of the entire Magnestoshere-Ionosphere-Thermosphere environment. The strongest of the E-region instabilities, the Farley-Buneman instability (FBI), is excited when the relative velocity between the magnetized electrons and unmagnetized ion exceeds the local ion-acoustic speed. At high latitudes, this usually occurs when the DC field exceeds the threshold value of ~20 mV/m. These and much stronger fields are not uncommon in the subauroral, auroral, and polar cap areas, especially during magnetospheric storms and substorms. At the same time, strongly perturbed high-latitude regions are often characterized by intense electron precipitation that can easily penetrate down to the E-region. Focusing on auroral regions where intense electron precipitation may overlap with strong driving DC fields and using a physics-based model of electron precipitation (STET), we have studied the distribution function modifications caused by precipitating electrons and the effect of these modifications on the instability onset and development. Our simulations have demonstrated that under realistic conditions of strong electron precipitation the plasma pressure of superthermal electrons may be comparable to, or even significantly exceed, the regular plasma pressure of the cold ionospheric plasma. The resultant total pressure increases the effective electron temperature and hence the FBI threshold field. This modifies the driving conditions for the instability onset and may have a significant feedback on the magnetosphere.
Work is supported by NASA LWS Grant #80NSSC19K0080.