On the Characteristics of the FLR in Non-uniform Magnetosphere

Abstract:

Solar wind impinges on the dayside magnetopause, and it is one of the main energy sources that generate ultra-low frequency (ULF) waves in the Earth’s magnetosphere. Field line resonance (FLR) can occur through the coupling between the compressional wave and shear Alfven wave. The wave mode is converted from the compressional mode, that is excited from the solar wind impact, to shear Alfven mode, or FLR. There have been numerical studies on non-axisymmetric effects using a 3-D box model with straight magnetic field lines assumed; thus the inhomogeneity lies in a two-dimensional plane. However, it is essential to incorporate the curved geometry that gives non-uniform Alfven speed distribution along the field line to fully understand the properties of FLR such as polarization, higher harmonic features, and arrival time. We have conducted three-dimensional MHD simulations to investigate how non-uniformity in all three directions affects the temporal characteristics of FLR. Our results show that the FLR persists in such non-uniform condition and the polarization rotates with respect to the constant eigenfrequency surface. It suggests that the FLR signals can be a mixture of the toroidal and poloidal components in a non-axisymmetric environment.