Kinetic Scale Slow Solar Wind Turbulence in the Inner Heliosphere: Co-existence of Kinetic Alfvén Waves and Alfvén Ion Cyclotron Waves

Abstract

The nature of the plasma wave modes around the ion kinetic scales in highly Alfvénic slow solar wind turbulence is investigated using data from the NASA's Parker Solar Probe taken in the inner heliosphere, at 0.18 Astronomical Unit (AU) from the sun. The joint distribution of the normalized reduced magnetic helicity ${\sigma }_m({\theta }_{RB},\tau )$ is obtained, where ${\theta }_{RB}$ is the angle between the local mean magnetic field and the radial direction and $\tau$ is the temporal scale. Two populations around ion scales are identified: the first population has ${\sigma }_m({\theta }_{RB},\tau )<0$ for frequencies (in the spacecraft frame) ranging from 2.1 to 26 Hz for $60^{\circ }<{\theta }_{RB}<130^{\circ }$, corresponding to kinetic Alfvén waves (KAWs), and the second population has ${\sigma }_m({\theta }_{RB},\tau )>0$ in the frequency range [1.4, 4.9] Hz for ${\theta }_{RB}>150^{\circ }$, corresponding to Alfvén ion Cyclotron Waves (ACWs). This demonstrates for the first time the co-existence of KAWs and ACWs in the slow solar wind in the inner heliosphere, which contrasts with previous observations in the slow solar wind at 1 AU. This discrepancy between 0.18 and 1 AU could be explained, either by i) a dissipation of ACWs via cyclotron resonance during their outward journey, or by ii) the high Alfvénicity of the slow solar wind at 0.18 AU that may be favorable for the excitation of ACWs.

References in corpus (11)

• Anisotropic scaling of magnetohydrodynamic turbulence
• Switchbacks in the near-Sun magnetic field: long memory and impact on the turbulence cascade
• The Solar Probe Cup on Parker Solar Probe
• Ion Scale Electromagnetic Waves in the Inner Heliosphere
• On the Existence of the Kolmogorov Inertial Range in the Terrestrial Magnetosheath Turbulence
• Density Fluctuation Spectrum of Solar Wind Turbulence between Ion and Electron Scales
• Spectral Slope Variation at Proton Scales from Fast to Slow Solar Wind
• Cross Helicity Reversals In Magnetic Switchbacks
• Energy cascade rate measured in a collisionless space plasma with MMS data and compressible Hall magnetohydrodynamic turbulence theory
• Physical Interpretation of the Angle Dependent Magnetic Helicity Spectrum in the Solar Wind: The Nature of Turbulent Fluctuations near the Proton Gyroradius Scale
• Occurrence Rates and Heating Effects of Tangential and Rotational Discontinuities as Obtained from Three-dimensional Simulation of Magnetohydrodynamic Turbulence

Cited by in corpus (13)

• Parker Solar Probe: Four Years of Discoveries at Solar Cycle Minimum
• The Ion Transition Range of Solar Wind Turbulence in the Inner Heliosphere: Parker Solar Probe Observations
• The evolution of compressible solar wind turbulence in the inner heliosphere: PSP, THEMIS and MAVEN observations
• Characteristics of Magnetic Holes in the Solar Wind Revealed by Parker Solar Probe
• The Radial Distribution of Ion-scale Waves in the Inner Heliosphere
• The incompressible energy cascade rate in anisotropic solar wind turbulence
• Proton and electron temperatures in the solar wind and their correlations with the solar wind speed
• Anisotropy of Magnetic Field Spectra at Kinetic Scales of Solar Wind Turbulence as Revealed by Parker Solar Probe in the Inner Heliosphere
• A Statistical Study of the Compressible Energy Cascade Rate in Solar Wind Turbulence: Parker Solar Probe Observations
• Growth of Outward Propagating Fast-Magnetosonic/Whistler Waves in the Inner Heliosphere Observed by Parker Solar Probe
• The effects of finite electron inertia on helicity-barrier-mediated turbulence
• Turbulent heating in collisionless low-beta plasmas: imbalance, Landau damping, and electron-ion energy partition
• The role of the thermal properties of electrons on the dispersion properties of Alfvén waves in space plasmas