Amplitudes of Magnetopause Surface Waves: Comparison of THEMIS Observations with MHD Theory

The Earth’s magnetopause is the boundary separating the terrestrial and the interplanetary magnetic fields. Variations in solar wind pressure and structures originating from the solar wind or foreshock regions induce constant dynamic motion of this boundary. Furthermore, a high velocity shear between the magnetosheath and magnetospheric plasmas can trigger the Kelvin-Helmholtz instability. All these interactions can lead to the generation of waves on the magnetopause, which can either propagate along the magnetopause towards the nightside or form standing surface waves. These surface waves subsequently excite fluctuations within the ambient plasma on either side of the magnetopause, allowing them to propagate away perpendicular to the magnetopause. According to magnetohydrodynamic (MHD) theory, the amplitude of these waves is expected to decrease exponentially with distance from the boundary.

Utilizing the multi-spacecraft mission Time History of Events and Macroscale Interactions during Substorms (THEMIS), we are able to simultaneously observe surface waves at different distances perpendicular to the magnetopause. Here we present preliminary findings that compare these spacecraft observations with predictions from MHD theory.