Theory of Kinetic Alfven Waves on Auroral Field Lines

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This project will investigate the theory of kinetic Alfven waves 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 it accelerates the precipitating electrons and ions that cause the aurora. 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 magnetohydrodynamic (MHD) theory. The auroral acceleration region is coupled to the collisional ionosphere and can change the conductivity of the ionosphere. 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. This research will focus on three main processes that affect the coupling of the magnetosphere and ionosphere: (1) cross-scale coupling by nonlinear interactions of Alfven waves and wave packets, (2) evolution of the plasma density in the auroral zone, and (3) electron kinetic effects and ionospheric feedback in the three-dimensional ionosphere. These processes will be studied by analytical theoretical methods and numerical models based on existing numerical codes. A reduced MHD description based on the Strauss equations will be used to investigate nonlinear interactions across perpendicular spatial scales in the auroral zone. This nonlinear model will be extended to include two-fluid parallel dynamics which will enable the investigation of density evolution on auroral field lines and the formation of auroral density cavities. This work will 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. An understanding of the plasma physics of the Earth's auroral zone may serve as a model for particle acceleration processes in the solar corona as well as other cosmic plasmas.