Identification of Kelvin-Helmholtz vortices at the Earth’s magnetosphere

Kelvin-Helmholtz instability is a widespread phenomenon in space plasmas, such as at the planetary magnetospheres. During its nonlinear phase, the generation of Kelvin-Helmholtz vortices takes place. The identification of such coherent structures is not straightforward in observational data contrary to numerical simulations where both temporal evolution and spatial behavior can be observed. Recently, a comparison between a hybrid Vlasov-Maxwell simulation and Magnetospheric Multi-Scale satellites observation of a Kelvin-Helmholtz event has shown the presence of kinetic features that can uniquely characterize the boundaries of Kelvin-Helmholtz vortices.  Indeed, a strong total current density has been observed in correspondence of the edges of each vortex associated with a weakly distorted distribution function from the equilibrium distribution; while the opposite occurs inside the vortex region. Moreover, a new tool has been proposed to distinguish the different phases of the Kelvin-Helmholtz instability and to identify the trajectory of the spacecraft across the vortex itself. Such a tool takes into consideration the mixing degree between the magnetospheric-like and magnetosheath-like particles population in the Earth environment. The clear identification of a vortex in in situ data is an important achievement since it can provide a better understanding of the role that Kelvin-Helmholtz instability plays in weakly collisional space plasmas in the contest of energy dissipation.

This work has received funding from the European Unions Horizon 2020 research and innovation programme under grant agreement no. 776262 (AIDA,).