Density Fluctuations Associated with Turbulence and Waves: First Observations by Solar Orbiter

Abstract

We use the plasma density based on measurements of the probe-to-spacecraft potential in combination with magnetic field measurements by MAG to study fields and density fluctuations in the solar wind observed by Solar Orbiter during the first perihelion encounter ($\sim$0.5~AU away from the Sun). In particular we use the polarization of the wave magnetic field, the phase between the compressible magnetic field and density fluctuations and the compressibility ratio (the ratio of the normalized density fluctuations to the normalized compressible fluctuations of B) to characterize the observed waves and turbulence. We find that the density fluctuations are out-of-phase with the compressible component of magnetic fluctuations for intervals of turbulence, while they are in phase for the circular-polarized waves around the proton cyclotron frequency. We analyze in detail two specific events with simultaneous presence of left- and right-handed waves at different frequencies. We compare observed wave properties to a prediction of the three-fluid (electrons, protons and alphas) model. We find a limit on the observed wavenumbers, $10^{-6}<k<7\times 10^{-6}$~m${}^{-1}$, which corresponds to wavelength $7\times 10^6>\lambda >10^6$~m. We conclude that most likely both the left- and right-handed waves correspond to the low-wavenumber part (close to the cut-off at ${\Omega }_{c\mathrm{He}++}$) proton-band electromagnetic ion cyclotron (left-handed wave in the plasma frame confined to the frequency range ${\Omega }_{c\mathrm{He}++}<\omega <{\Omega }_{c\mathrm{H}+}$) waves propagating in the outwards and inwards directions respectively. The fact that both wave polarizations are observed at the same time and the identified wave mode has a low group velocity suggests that the double-banded events occur in the source regions of the waves.

13 pages, 9 figures

References in corpus (10)

• The Solar Orbiter mission -- Science overview
• Density Fluctuation Spectrum of Solar Wind Turbulence between Ion and Electron Scales
• Energy Cascade Rate In Compressible Fast And Slow Solar Wind Turbulence
• Intermittency of Solar Wind Density Fluctuations From Ion to Electron Scales
• Correlations between the proton temperature anisotropy and transverse high-frequency waves in the solar wind
• The Electromagnetic Signature of Outward Propagating Ion-Scale Waves
• Whistler waves observed by Solar Orbiter / RPW between 0.5 AU and 1 AU
• Radial evolution of intermittency of density fluctuations in the fast solar wind
• Kinetic Electrostatic Waves and their Association with Current Structures in the Solar Wind
• Solar wind current sheets and deHoffmann-Teller analysis: First results of DC electric field measurements by Solar Orbiter

Cited by in corpus (13)

• The 17 April 2021 widespread solar energetic particle event
• Whistler waves observed by Solar Orbiter / RPW between 0.5 AU and 1 AU
• Kinetic Electrostatic Waves and their Association with Current Structures in the Solar Wind
• Backstreaming ions at a high Mach number interplanetary shock: Solar Orbiter measurements during the nominal mission phase
• Quantifying the diffusion of suprathermal electrons by whistler waves between 0.2 and 1 AU with Solar Orbiter and Parker Solar Probe
• Mirror mode storms observed by Solar Orbiter
• Parker Solar Probe observations of near-$f_{\mathrm{ce}}$ harmonics emissions in the near-Sun solar wind and their dependence on the magnetic field direction
• The effect of heavy ions on the dispersion properties of kinetic Alfvén waves in astrophysical plasmas
• The solar-wind angular-momentum flux observed during Solar Orbiter's first orbit
• Extent of the Magnetotail of Venus From the Solar Orbiter, Parker Solar Probe and BepiColombo Flybys
• Ion-Scale Solitary Structures in the Solar Wind Observed by Solar Orbiter and Parker Solar Probe
• Solar Electron Beam -- Langmuir Wave Interactions and How They Modify Solar Electron Beam Spectra: Solar Orbiter Observations of a Match Made in the Heliosphere
• Modelling spacecraft-emitted electrons measured by SWA-EAS experiment on board Solar Orbiter mission