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This study analyzes velocity distribution functions of ions in the solar wind measured by Parker Solar Probe at different distances from the Sun (11 and 28 solar radii). Using Hermite mathematical decomposition, researchers found evidence of turbulent cascades occurring in velocity space, with qualitative agreement between energization proxies and the Hermite analysis, suggesting a dual cascade process in both real space and velocity space. The analysis included different flow regimes (superalfvénic and subalfvénic) and examined connections between turbulent energy dissipation and distribution function fluctuations.
Why it matters
Understanding how energy cascades and dissipates in space plasmas is fundamental for predicting space weather effects that can impact satellite operations, communications systems, and power grids on Earth. These insights from the closest-ever solar wind measurements advance our theoretical understanding of collisionless plasma physics, which applies broadly to astrophysical environments.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
Abstract: In space plasmas, the rarity of collisions leads to complex structures in the velocity space where a turbulent cascade of the velocity distribution function fluctuations is thought to occur. Previous studies have explored this phenomenon using the Hermite decomposition of the ion velocity distribution function (VDF) in both magnetosheath data and numerical simulations. In this work, we investigate the Hermite spectrum of the ion VDFs measured by Parker Solar Probe in the inner heliosphere. We analyze a superalfv’enic stream at a radial distances of $R approx 28 R_{sun}$ and a subalfv’enic at $R approx 11 R_{sun}$, the former characterized by a prevalence of VDFs with suprathermal beams (also known as hammerhead). The Hermite analysis is also compared with various proxies of energization and dissipation, in order to establish a connection between turbulent cascades in real space and those in the velocity space. A qualitative agreement between the energization proxies and the Hermite analysis is observed. The results are suggestive of the presence of a dual cascade in real and velocity space.