Characteristics of energy conversion and energy flux densities at the Kelvin–Helmholtz vortex

The Kelvin–Helmholtz (KH) instability serves as an important process for transporting the solar wind mass and energy into the Earth’s magnetosphere. However, energy conversion and energy transport at the vortices driven by the KH instability have not been investigated in detail thus far. Here, using high-resolution data from the Magnetospheric Multiscale (MMS) spacecraft, we compare characteristics of energy conversion and energy flux densities between a linear and a nonlinear KH vortex. We find that the linear KH vortex is acting as a generator region (∫J·E < 0, where J is the current density and E is the electric field) whereas the nonlinear KH vortex is a load region (∫J·E > 0). The energy flux densities increase significantly at the trailing edge of KH vortices. At the linear KH vortex, energy transfer is equally contributed by enthalpy, ion kinetic, and Poynting fluxes, whereas in the nonlinear case, the energy is mainly transported in the form of the Poynting flux and electron kinetic energy and heat fluxes are negligible. These results help us better understand the role of KH vortices in energy conversion and transport at the Earth’s magnetopause.