Statistical evidence on the impact of foreshock effects on the Kelvin-Helmholtz waves at the Earth's magnetopause

An important mechanism for the transfer of energy across the boundary between the Earth's magnetic field and the solar wind involves the formation of waves and vortices at the magnetopause. These waves and vortices arise from the Kelvin–Helmholtz instability, which is caused by the difference in velocity between the magnetospheric plasma and the shocked solar wind plasma. From spacecraft observations and simulations, we know that Kelvin-Helmholtz waves can evolve and grow differently depending on their formation conditions and locations. Specifically, evidence from simulations indicates an impact from the foreshock on the development of the waves. However, this has not yet been fully confirmed by observations. Using the extensive in-situ data from the last solar cycle, we can compare the parameters of 3,335 KHI observations under different conditions. By applying different methods to determine the necessary plasma conditions at the boundary in wave parameter calculations, we are able to accumulate statistical evidence indicating whether the wave parameters of Kelvin–Helmholtz-induced waves are altered in the presence of a foreshock region upstream of the magnetopause. Our results suggest that, under certain solar wind conditions, the presence of the foreshock indeed alters the typical wave parameters of Kelvin-Helmholtz waves. This further reaffirms that the presence of the foreshock must be considered when understanding solar-terrestrial interactions.