2021/02/28 by Die Duan, Jiansen He, Trevor A. Bowen +5 · 1 citation
Physics and Astronomy · #physics.space-ph #astro-ph.SR
paper · pdf · doi:10.3847/2041-8213/ac07ac
4 figures; submitted to apjl
arxiv created 2021/05/15 · arxiv updated 2021/07/14
The anisotropy of solar wind turbulence is a critical issue in understanding the physics of energy transfer between scales and energy conversion between fields and particles in the heliosphere. Using the measurement of Parker Solar Probe (PSP), we present an observation of the anisotropy at kinetic scales in the slow, Alfvénic, solar wind in the inner heliosphere. The magnetic compressibility behaves as expected for kinetic Alfvénic turbulence below the ion scale. A steepened transition range is found between the inertial and kinetic ranges in all directions with respect to the local background magnetic field direction. The anisotropy of k_⊥ ≫ k_∥ is found evident in both transition and kinetic ranges, with the power anisotropy P_⊥/P_∥ > 10 in the kinetic range leading over that in the transition range and being stronger than that at 1 au. The spectral index varies from αt∥=-5.7± 1.0 to αt⊥=-3.7± 0.3 in the transition range and αk∥=-3.12± 0.22 to αk⊥=-2.57± 0.09 in the kinetic range. The corresponding wavevector anisotropy has the scaling of k_∥ ∼ k_⊥0.71± 0.17 in the transition range, and changes to k_∥ ∼ k_⊥0.38± 0.09 in the kinetic range, consistent with the kinetic Alfvénic turbulence at sub-ion scales.