Farley-Buneman instabilities in the Auroral region: Continuous hybrid simulations and empirical modeling

Abstract:

The magnetosphere couples with the high-latitude ionosphere through the Earth’s magnetic field lines. This coupling occurs mainly through energetic particle precipitations and electromagnetic fields. In the auroral E region, these processes cause Hall currents that drive Farley-Buneman instabilities, generating a spectrum of field-aligned plasma density irregularities. Even though coherent backscatter radars provide precise Doppler information from these structures, simultaneous experiments are needed to assess empirical models relating Doppler spectra with plasma state parameters. This lack of data for direct comparisons motivates the need for new validation criteria. On the other hand, although fully kinetic particle-in-cell simulations of Farley-Buneman instabilities offer the most complete description of the underlying physics, its computational cost for studying non-local phenomena is tremendous. In order to capture non-local physics, new methods based on hybrid and continuous approaches have to be explored.

In this work, we propose a way to assess the mathematical and physical consistency of a convection model which relates coherent scatter spectra with electron convection. Given that the convection model doesn't contain any explicit assumption of incompressibility, we will argue that if the convection field satisfies this condition within experimental error, then the model estimates are accurate. Finally, we present a new continuous hybrid simulation of Farley-Buneman waves, where electrons and ions are modeled using a fluid and kinetic formalism, respectively. We investigate phase speed saturation and examine whether the phase speeds scale with the background electric field in the way observed by the coherent scatter radar. We also try to quantify wave turning effects, examine whether wave heating is commensurate with incoherent scatter radar observations, and determine the dominant wavelength of the waves.