Quantifying the Role of Different Magnetospheric Plasma Waves in Diffuse Auroral Precipitation

Abstract:

Diffuse auroral pecipitation provides a major source of ionization for the high latitude upper atmosphere, and as such controls the spatial distribution of ionospheric conductivity and its variability during geomagnetic activity. The physical mechanisms responsible for diffuse auroral precipitation have been debated for several decades. But recent detailed modeling of the rates of electron scattering by plasma waves, together with new and improved observations of the wave and particle environment in space, have allowed us to identify the dominant mechanisms responsible for the precipitation of plasma sheet electrons into the atmosphere. At lower invariant latitude (L< 8) a combination of lower and upper band chorus emissions provides the dominant scattering mechanism and can also account for the unique anisotropic pitch angle distribution left in space, which can continue to provide the source for chorus excitation over the dawn side of the magnetosphere. However, at higher L shells the electron anisotropy is insufficient to cause chorus excitation, but the residual loss cone distribution can excite electrostatic cyclotron harmonic (ECH) waves, which are the dominant scattering agent at higher invariant latitude. Both chorus and ECH waves are capable of causing electron scattering at the strong diffusion rate during more intense geomagnetic activity, and this can lead to a significant reduction of plasma sheet electron flux able to reach the dayside, which acconts fore the strong day-night asymmetry of diffuse auroral precipitation.