Tom Elsden

Earth's curved magnetic field lines can oscillate (like waves on a string), at a range of frequencies with the lowest being termed ultra-low frequency (ULF) waves. In this poster we consider a specific subset of these waves known as high-m poloidal Alfvén waves, which have the characteristic that the wavelength in the radial direction is much larger than that in the azimuthal (angular) direction. Such waves are of geophysical importance as they can interact with energetic particles that are trapped and drifting in Earth's magnetic field. This has implications for space weather effects with spacecraft operations being negatively affected by such interactions. We perform computer simulations of how these waves evolve in a curved magnetic field like that of the Earth. We show that the structure of these waves changes in time, in a way that is unique to the geometry of the magnetic field, with the development of complex spatial structure.
The first slide gives an overview of the main features of Earth's magnetosphere, with a figure demonstrating the structure of the magnetic field and interaction with the solar wind. The second slide introduces Ultra-low frequency waves, and the effects that they can have on the aurora and energetic particles in Earth's radiation belts. The third slide goes into more detail on the specific wave type studied in this research, which is a magnetic field guided wave with a radial displacement to the field line known as a poloidal Alfven wave. The fourth and final slide presents the key research results, demonstrating through numerical simulations that an initially poloidal Alfven wave will develop a complex spatial structure in time. This happens due to the curvature of the dipole magnetic field. The results have implications for the interaction of these waves with radiation belt particles.