The boundary between the solar wind and Earth’s magnetic field, known as the magnetopause, is not a simple surface—it consists of multiple layers, including the outer and inner low-latitude boundary layers and a central current sheet. One key process that enables solar wind plasma to enter the magnetosphere is the Kelvin-Helmholtz Instability (KHI), which generates wave-like disturbances along this boundary.

Using data from 43 KHI events observed by the MMS mission, we find that these waves often begin to grow at the interface between the inner low-latitude boundary layer and the magnetosphere. As they evolve, the KH waves can increase in size and eventually roll up into vortices that are comparable in scale to the entire boundary layer. This growth facilitates the entry of solar wind particles into the magnetosphere.

To complement these observations, we use MHD simulations that incorporate the full structure of the boundary, including both inner and outer layers. These simulations allow us to explore different pathways for KH wave growth and better understand how multilayer boundaries influence the development of the instability. Together, our observational and simulation results offer a clearer picture of how KHI contributes to solar wind–magnetosphere coupling.