Magnetospheric Multiscale Observation of Kinetic Signatures in the Alfven Vortex

• Alfven vortex is a multiscale nonlinear structure that contributes to the intermittency of turbulence. Despite previous explorations mostly on the spatial properties of the Alfven vortex (i.e., scale, orientation, and motion), the plasma characteristics within the Alfven vortex are unknown. Moreover, the connection between the plasma energization and the Alfven vortex still remains unclear. Based on high-resolution in situ measurements from the Magnetospheric Multiscale mission, we report for the first time distinctive plasma features within an Alfven vortex. This Alfven vortex is identified as being a 2D (k(perpendicular to) >> k(parallel to) ) quasi-monopole with a radius of 10 proton gyroscales. Its magnetic fluctuations delta B-perpendicular to are anti-correlated with velocity fluctuations delta V-perpendicular to, thus the parallel current density j(parallel to) and flow vorticity omega(parallel to) 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(parallel to), while the electron temperature variations are correlated with omega(parallel to). Furthermore, the temperature anisotropies, together with the non-Maxwellian kinetic effects, exhibit strong enhancement at peaks of vertical bar omega(parallel to)vertical bar(vertical bar j(parallel to)vertical bar) within the vortex. Comparison between observations and numerical/theoretical results are made. In addition, the energy-conversion channels and the compressibility associated with the Alfven vortex are discussed. These results may help to understand the link between coherent vortex structures and the kinetic processes, which determines how turbulence energy dissipates in the weakly collisional space plasmas.

Ämnesord

NATURVETENSKAP  -- Fysik -- Fusion, plasma och rymdfysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Fusion, Plasma and Space Physics (hsv//eng)

NATURVETENSKAP  -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)

Nyckelord

plasmas

turbulence

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