Evolution of Field-Aligned Currents by Alfvén Wave Propagation

Abstract:

Changes in field-aligned currents are mediated by the propagation of shear Alfvén waves along geomagnetic field lines. These waves are largely generated by magnetospheric convection on both large and small spatial scales. The interaction of Alfvén waves with the ionosphere results in the reflection and/or absorption of these waves, depending on the ionospheric conductance. Shear Alfvén waves can also be excited by mode conversion from compressional waves, both due to inhomogeneity of the Alfvén speed in the magnetosphere and to the Hall conductivity in the ionosphere. Such mode conversion can lead to the development of field line resonances, which can lead to the formation of small-scale field-aligned currents. Multi-satellite observations from missions such as Cluster and Swarm can lead to a better understanding of the fine-scale structure of these field-aligned currents. These interactions will be illustrated by means of a three-dimensional model for the propagation of MHD waves in the dipolar regions of the magnetosphere that includes conductivity differences between day and night sides.