A Statistical and Multiscale study of Kelvin-Helmholtz events under different IMF orientations

The Kelvin-Helmholtz instability (KHI) is a shear-driven phenomenon frequently observed at the Earth's low-latitude magnetopause when the velocity shear is super Alfvénic. KHI represents a way for plasmas to give rise to a turbulent scenario and to convert the energy due to the large-scale motion of the shear flow into heat. Indeed, the evolution of the KHI is characterized by the nonlinear coupling of different modes, which tends to generate smaller and smaller vortices along the shear layer. Both kinetic simulations and in situ measurements, focusing on the kinetic effects during the nonlinear phase of the instability, have shown the generation of strong current sheets between well-developed vortices, and temperature anisotropy and agyrotropy at both ion and electron scales, in accordance with the multi-scale nature of the phenomenon.

Moreover, KHI is thought to play a crucial role in the transport of solar wind plasma into the magnetosphere and to efficiently contribute to the formation of the low latitude boundary layer. Although the instability threshold is equally satisfied during both northward and southward interplanetary magnetic field (IMF) conditions, in-situ measurements show that KHI privileges the northward orientation. We investigate this different behavior by analyzing the kinetic features at both boundaries and inside the KH structures. Thus, we statistically investigate several KHI crossings observed by the Magnetospheric Multiscale mission for different IMF orientations. Our statistical study can provide a better understanding about the global dynamics of the near Earth's environment and gives an important contribution to the solar wind-magnetosphere coupling mechanism.