Magnetopause surface waves: A comparison of wave vector determination techniques using THEMIS observations

The Earth’s magnetopause is the boundary separating the terrestrial and the interplanetary magnetic field. Variations in solar wind pressure, as well as structures originating in the solar wind and foreshock regions, induce continuous motion of this boundary. In addition, strong velocity shear between magnetosheath and magnetospheric plasmas can trigger the Kelvin–Helmholtz instability. These processes can generate waves on the magnetopause that play a key role in governing mass transport and energy transfer between the solar wind and the magnetosphere.

Accurate estimation of the magnetopause wave vector is important for understanding interactions at the boundary. In this study, we compare different techniques for wave vector estimation. (1) Single-spacecraft methods require the determination of the boundary normal direction using approaches such as minimum variance analysis of the magnetic field (MVAB) or minimization of the Faraday residue (MFR), combined with estimates of the magnetopause phase velocity derived from ion measurements. (2) Cross-correlation analysis of magnetic field, density, and temperature measurements between different spacecraft allows estimation of wave vectors. In this context, modelling is used to explore potential systematic errors, for example arising from asymmetric waves, and to assess uncertainties in time-lag determination. (3) The wave telescope represents an alternative multi-spacecraft method to determine the wave vector.

Using observations from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission, we apply these methods to several magnetopause wave events. We present preliminary results of this comparison, providing insight into the respective limitations and uncertainties.