This project will investigate the theory of kinetic Alfven waves and wave packets along auroral field lines in the Earth's magnetosphere. Such waves play a major role in carrying energy from the outer magnetosphere to lower altitudes where the waves accelerate the precipitating electrons and ions that cause the aurora. Alfven waves also play an important role in generating the out-flowing plasma that populates the outer magnetosphere. While the theory of magnetohydrodynamics (MHD) is adequate to describe a wide variety of space plasma phenomena, the plasma processes that dominate the physics in the lower regions of auroral field lines are inherently kinetic and so are not well described by MHD theory. In addition, the auroral acceleration region is a strongly dynamic and inhomogeneous region, implying that standard local plasma kinetic theory is also limited in its ability to describe these phenomena. In particular, the auroral acceleration region is coupled to the collisional ionosphere, and in fact can change the conductivity of the ionosphere due to the precipitation of charged particles. Thus, a detailed study of the kinetic processes that accelerate auroral particles and the electrodynamic coupling of this region to the ionosphere is necessary to understand the basic plasma processes that power the aurora.
In particular, the project will investigate Alfvenic interactions in the ionospheric Alfven resonator. This is the resonant cavity formed in the topside auroral ionosphere by the large increase of the Alfven speed along auroral field lines. The research will focus on three processes that affect the coupling of the magnetosphere and ionosphere: (1) Non-local theory of kinetic Alfven waves that lead to the acceleration of auroral electrons, (2) nonlinear interactions between Alfven waves and wave packets trapped in the ionospheric Alfven resonator that can lead to structuring of the auroral current system and the formation of density cavities by the ejection of plasma into the outer magnetosphere, and (3) Ionospheric feedback interactions due to modifications of the ionospheric conductivity by electron precipitation. These processes will be studied by appropriate theoretical and numerical models based on existing numerical codes. Nonlinear modeling will enable the investigation of density and current structuring on auroral field lines. A three-dimensional model of the propagation of Alfven waves and their interaction with the ionosphere will be used to study the feedback interaction in great detail. This work will also serve the educational purpose of training graduate students in methods of developing and utilizing numerical plasma models. It will contribute to the understanding of the geospace system, which will assist society in its understanding of space weather processes that can impact communication and power systems.
