Ion Scale Electromagnetic Waves in the Inner Heliosphere

Abstract

Understanding the physical processes in the solar wind and corona which actively contribute to heating, acceleration, and dissipation is a primary objective of NASA's Parker Solar Probe (PSP) mission. Observations of coherent electromagnetic waves at ion scales suggests that linear cyclotron resonance and non-linear processes are dynamically relevant in the inner heliosphere. A wavelet-based statistical study of coherent waves in the first perihelion encounter of PSP demonstrates the presence of transverse electromagnetic waves at ion resonant scales which are observed in 30-50\% of radial field intervals. Average wave amplitudes of approximately 4 nT are measured, while the mean duration of wave events is of order 20 seconds; however long duration wave events can exist without interruption on hour-long timescales. Though ion scale waves are preferentially observed during intervals with a radial mean magnetic field, we show that measurement constraints, associated with single spacecraft sampling of quasi-parallel waves superposed with anisotropic turbulence, render the measured quasi-parallel ion-wave spectrum unobservable when the mean magnetic field is oblique to the solar wind flow; these results imply that the occurrence of coherent ion-scale waves is not limited to a radial field configuration. The lack of strong radial scaling of characteristic wave amplitudes and duration suggests that the waves are generated {\em{in-situ}} through plasma instabilities. Additionally, observations of proton distribution functions indicate that temperature anisotropy may drive the observed ion-scale waves.

References in corpus (9)

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• Switchbacks in the near-Sun magnetic field: long memory and impact on the turbulence cascade
• The Solar Probe Cup on Parker Solar Probe
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Cited by in corpus (16)

• The Evolution and Role of Solar Wind Turbulence in the Inner Heliosphere
• Switchbacks in the near-Sun magnetic field: long memory and impact on the turbulence cascade
• Parker Solar Probe observations of proton beams simultaneous with ion-scale waves
• Inferred Linear Stability of Parker Solar Probe Observations using One- and Two-Component Proton Distributions
• Kinetic Scale Slow Solar Wind Turbulence in the Inner Heliosphere: Co-existence of Kinetic Alfvén Waves and Alfvén Ion Cyclotron Waves
• The Enhancement of Proton Stochastic Heating in the near-Sun Solar Wind
• The Radial Dependence of Proton-scale Magnetic Spectral Break in Slow Solar Wind during PSP Encounter 2
• Turbulence in the outer heliosphere
• The Electromagnetic Signature of Outward Propagating Ion-Scale Waves
• The Ion Transition Range of Solar Wind Turbulence in the Inner Heliosphere: Parker Solar Probe Observations
• Kinetic-scale current sheets in near-Sun solar wind: properties, scale-dependent features and reconnection onset
• On quasi-parallel whistler waves in the solar wind
• Estimation of turbulent proton and electron heating rates via Landau damping constrained by Parker Solar Probe observations
• Electromagnetic Proton Beam Instabilities in the Inner Heliosphere: Energy Transfer Rate, Radial Distribution, and Effective Excitation
• Observational evidence for solar wind proton heating by ion-scale turbulence
• Coherence of ion cyclotron resonance for damping ion cyclotron waves in space plasmas