The Electromagnetic Signature of Outward Propagating Ion-Scale Waves

Abstract

First results from the Parker Solar Probe (PSP) mission have revealed ubiquitous coherent ion-scale waves in the inner heliosphere, which are signatures of kinetic wave-particle interactions and fluid-scale instabilities. However, initial studies of the circularly polarized ion-scale waves observed by PSP have only thoroughly analyzed magnetic field signatures, precluding a determination of solar-wind frame propagation direction and intrinsic wave-polarization. A comprehensive determination of wave-properties requires measurements of both electric and magnetic fields. Here, we use full capabilities of the PSP/FIELDS instrument suite to measure both the electric and magnetic components of circularly polarized waves. Comparing spacecraft frame magnetic field measurements with the Doppler-shifted cold-plasma dispersion relation for parallel transverse waves constrains allowable plasma frame polarizations and wave-vectors. We demonstrate that the Doppler-shifted cold-plasma dispersion has a maximum spacecraft frequency $f_{sc}^{\ast }$ for which intrinsically right-handed fast-magnetosonic waves (FMWs) propagating sunwards can appear left-handed in the spacecraft frame. Observations of left-handed waves with $|f|>f_{sc}^{\ast }$ are uniquely explained by intrinsically left-handed, ion-cyclotron, waves (ICWs). We demonstrate that electric field measurements for waves with $|f|>f_{sc}^{\ast }$ are consistent with ICWs propagating away from the sun, verifying the measured electric field. Applying the verified electric field measurements to the full distribution of waves suggests that, in the solar wind frame, the vast majority of waves propagate away from the sun, indicating that the observed population of coherent ion-scale waves contains both intrinsically left and right hand polarized modes.

References in corpus (12)

• Switchbacks in the near-Sun magnetic field: long memory and impact on the turbulence cascade
• The Solar Probe Cup on Parker Solar Probe
• Magnetic connectivity of the ecliptic plane within 0.5 AU : PFSS modeling of the first PSP encounter
• Ion Scale Electromagnetic Waves in the Inner Heliosphere
• Parker Solar Probe observations of proton beams simultaneous with ion-scale waves
• Statistical Study of Whistler Waves in the Solar Wind at 1 AU
• Cross Helicity Reversals In Magnetic Switchbacks
• Experimental determination of whistler wave dispersion relation in the solar wind
• Whistler wave generation by halo electrons in the solar wind
• Physical Interpretation of the Angle Dependent Magnetic Helicity Spectrum in the Solar Wind: The Nature of Turbulent Fluctuations near the Proton Gyroradius Scale
• The Violation of the Taylor Hypothesis in Measurements of Solar Wind Turbulence
• Linear Stability in the Inner Heliosphere: Helios Reëvaluated

Cited by in corpus (10)

• Parker Solar Probe: Four Years of Discoveries at Solar Cycle Minimum
• The In Situ Signature of Cyclotron Resonant Heating
• Strong perpendicular velocity-space in proton beams observed by Parker Solar Probe
• Statistical analysis of orientation, shape, and size of solar wind switchbacks
• Density Fluctuations Associated with Turbulence and Waves: First Observations by Solar Orbiter
• Kinetic-scale current sheets in near-Sun solar wind: properties, scale-dependent features and reconnection onset
• The Radial Distribution of Ion-scale Waves in the Inner Heliosphere
• Modeling ion beams, kinetic instabilities, and waves observed by the Parker Solar Probe near perihelia
• Wave-particle energy transfer directly observed in an ion cyclotron wave
• Growth of Outward Propagating Fast-Magnetosonic/Whistler Waves in the Inner Heliosphere Observed by Parker Solar Probe