Turbulence properties and kinetic signatures of electrons in Kelvin-Helmholtz waves during a geomagnetic storm

The Kelvin–Helmholtz instability (KHI), in its nonlinear phase, plays a significant role in transporting solar-wind plasma into Earth’s magnetosphere. This study investigates the turbulence properties and reconnection signatures observed at the edges of Kelvin–Helmholtz vortices during a geomagnetic storm. Temporal spectra of the magnetic field, electric field, and bulk ion velocity exhibit power-law behavior with slope changes near the ion gyrofrequency, as well as a distinct spectral knee near 0.14 Hz in the inertial range. The nonlinear KH vortices exhibit an alignment between the magnetic field and plasma velocity at large scales, which progressively weakens toward kinetic scales, consistent with trend in the magnetosheath. These inertial-scale properties indicate that KH vortices host strong turbulence and coherent structures even during their early nonlinear phase. In addition, MMS observes a reconnecting current sheet characterized by intense electron jets and signatures consistent with strong guide-field asymmetric reconnection at the magnetopause. Significant agyrotropy in the electron velocity distribution functions is detected both within the reconnecting current sheet and along the edges of the KH vortices. Together, these observations provide a multi-scale view of KH-driven turbulence and reconnection under strongly driven storm-time conditions.