Geometry of Magnetic Fluctuations near the Sun from PSP

Abstract

Solar wind magnetic fluctuations exhibit anisotropy due to the presence of a mean magnetic field in the form of the Parker spiral. Close to the Sun, direct measurements were not available until the recently launched Parker Solar Probe (PSP) mission. The nature of anisotropy and geometry of the magnetic fluctuations play a fundamental role in dissipation processes and in the transport of energetic particles in space. Using PSP data, we present measurements of geometry and anisotropy of the inner heliosphere magnetic fluctuations, from fluid to kinetic scales. The results are surprising and different from 1 au observations. We find that fluctuations evolve characteristically with size scale. However, unlike 1 au solar wind, at the outer scale, the fluctuations are dominated by wavevectors quasi-parallel to the local magnetic field. In the inertial range, average wave vectors become less field-aligned, but still remain more field aligned than near-Earth solar wind. In the dissipation range, the wavevectors become almost perpendicular to the local magnetic field in the dissipation range, to a much higher degree than those indicated by 1 au observations. We propose that this reduced degree of anisotropy in the outer scale and inertial range is due to the nature of large-scale forcing outside the solar corona.

Accepted for publication in the Astrophysical Journal

References in corpus (12)

• The Solar Probe Cup on Parker Solar Probe
• Acceleration and propagation of Solar Energetic Particles
• Shear-Driven Transition to Isotropically Turbulent Solar Wind Outside the Alfven Critical Zone
• Fading Coronal Structure and the Onset of Turbulence in the Young Solar Wind
• Enhanced Energy Transfer Rate in Solar Wind Turbulence Observed near the Sun from Parker Solar Probe
• Turbulence Transport Modeling and First Orbit Parker Solar Probe (PSP) Observations
• Anisotropy of Solar-Wind Turbulence in the Inner Heliosphere at Kinetic Scales: PSP Observations
• Characterization of the Turbulent Magnetic Integral Length in the Solar Wind: From 0.3 to 5 Astronomical Units
• The Near-Sun Streamer Belt Solar Wind: Turbulence and Solar Wind Acceleration
• The Ion Transition Range of Solar Wind Turbulence in the Inner Heliosphere: Parker Solar Probe Observations
• Observations of Energetic-Particle Population Enhancements along Intermittent Structures near the Sun from Parker Solar Probe
• The Solar Cycle Variations of the Anisotropy of Taylor Scale and Correlation Scale in the Solar Wind Turbulence

Cited by in corpus (8)

• Inertial range magnetic fluctuation anisotropy observed from PSP first seven orbits
• The incompressible energy cascade rate in anisotropic solar wind turbulence
• On the evolution of the Anisotropic Scaling of Magnetohydrodynamic Turbulence in the Inner Heliosphere
• Anisotropic Magnetic Turbulence in the Inner Heliosphere -- Radial Evolution of Distributions observed by Parker Solar Probe
• Taylor microscale and effective Reynolds number near the Sun from PSP
• Solar Energetic Particle event onsets at different heliolongitudes: The effect of turbulence in Parker Spiral Geometry
• Cosmic ray transport near the Sun
• Isotropization and Evolution of Energy-Containing Eddies in Solar Wind Turbulence: Parker Solar Probe, Helios 1, ACE, WIND, and Voyager 1