Magnetospheric Multiscale Observation of Kinetic Signatures in the Alfv��n Vortex

Alfv��n vortex is a multi-scale nonlinear structure which contributes to intermittency of turbulence. Despite previous explorations mostly on the spatial properties of the Alfv��n vortex (i.e., scale, orientation, and motion), the plasma characteristics within the Alfv��n vortex are unknown. Moreover, the connection between the plasma energization and the Alfv��n vortex still remains unclear. Based on high resolution in-situ measurement from the Magnetospheric Multiscale (MMS) mission, we report for the first time, distinctive plasma features within an Alfv��n vortex. This Alfv��n vortex is identified to be two-dimensional ($k_{\bot} \gg k_{\|}$) quasi-monopole with a radius of ~10 proton gyroscales. Its magnetic fluctuations $��B_{\bot}$ are anti correlated with velocity fluctuations $��V_{\bot}$, thus the parallel current density $j_{\|}$ and flow vorticity $��_{\|}$ are anti-aligned. In different part of the vortex (i.e., edge, middle, center), the ion and electron temperatures are found to be quite different and they behave in the reverse trend: the ion temperature variations are correlated with $j_{\|}$, while the electron temperature variations are correlated with $��_{\|}$. Furthermore, the temperature anisotropies, together with the non-Maxwellian kinetic effects, exhibit strong enhancement at peaks of $|��_{\|}| (|j_{\|}|)$ within the vortex. Comparison between observations and numerical/theoretical results are made. In addition, the energy-conversion channels and the compressibility associated with the Alfv��n vortex are discussed. These results may help to understand the link between coherent vortex structures and the kinetic processes, which determines how turbulence energy dissipate in the weakly-collisional space plasmas.