A numerical model of torsional Alfven eigenmodes in the Earth's core

We investigate torsional Alfvén eigenmodes in the Earth's outer core. These eigenmodes exhibit energy equally distributed between magnetic and kinetic components, with their motion predominantly columnar. This columnar nature has previously enabled the development of approximate inviscid one-dimensional models. In contrast, our study employs a three-dimensional numerical model that incorporates viscosity, an electrically conductive inner core, and a thin, conductive layer at the bottom of the mantle. This configuration allows angular momentum exchange between the outer core, the solid inner core, and the mantle. Using this model, we systematically examine the key properties of these modes, particularly their columnarity, torques, and decay rates. We study how these properties vary with the magnetic diffusivity and viscosity of the outer core, as well as with the electrical conductance of the mantle's bottommost layer.