Coronal Electron Temperature inferred from the Strahl Electrons in the Inner Heliosphere: Parker Solar Probe and Helios observations

Abstract

The shape of the electron velocity distribution function plays an important role in the dynamics of the solar wind acceleration. Electrons are normally modelled with three components, the core, the halo, and the strahl. We investigate how well the fast strahl electrons in the inner heliosphere preserve the information about the coronal electron temperature at their origin. We analysed the data obtained by two missions, Helios spanning the distances between 65 and 215 R${}_S$, and Parker Solar Probe (PSP) reaching down to 35 R${}_S$ during its first two orbits around the Sun. The electron strahl was characterised with two parameters, pitch-angle width (PAW), and the strahl parallel temperature (T${}_{s\parallel }$). PSP observations confirm the already reported dependence of strahl PAW on core parallel plasma beta (${\beta }_{ec\parallel }$)\citep{Bercic2019}. Most of the strahl measured by PSP appear narrow with PAW reaching down to 30${}^o$. The portion of the strahl velocity distribution function aligned with the magnetic field is for the measured energy range well described by a Maxwellian distribution function. T${}_{s\parallel }$ was found to be anti-correlated with the solar wind velocity, and independent of radial distance. These observations imply that T${}_{s\parallel }$ carries the information about the coronal electron temperature. The obtained values are in agreement with coronal temperatures measured using spectroscopy (David et al. 2998), and the inferred solar wind source regions during the first orbit of PSP agree with the predictions using a PFSS model (Bale et al. 2019, Badman et al. 2019).

References in corpus (12)

• Solar Orbiter: Exploring the Sun-heliosphere connection
• 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
• Electrons in the Young Solar Wind: First Results from the Parker Solar Probe
• A transonic collisionless model of the solar wind
• Scattering of Strahl Electrons in the Solar Wind between 0.3 and 1 au: Helios Observations
• Electron energy partition across interplanetary shocks: I. Methodology and Data Product
• Electron energy partition across interplanetary shocks: II. Statistics
• Kinetic Theory and Fast Wind Observations of the Electron Strahl
• Electron Strahl and Halo Formation in the Solar Wind
• Suprathermal electron strahl widths in the presence of narrow-band whistler waves in the solar wind
• Tests for coronal electron temperature signatures in suprathermal electron populations at 1 AU

Cited by in corpus (23)

• Parker Solar Probe: Four Years of Discoveries at Solar Cycle Minimum
• Enhanced proton parallel temperature inside patches of switchbacks in the inner heliosphere
• Electron heat flux in the near-Sun environment
• Particle-In-Cell simulation of whistler heat flux instabilities in the solar wind: heat flux regulation and electron halo formation
• The Radial Evolution of the Solar Wind as Organized by Electron Distribution Parameters
• Whistler wave occurrence and the interaction with strahl electrons during the first encounter of Parker Solar Probe
• Precision Electron Measurements in the Solar Wind at 1 au from NASA's Wind Spacecraft
• On the role of solar wind expansion as a source of whistler waves: scattering of suprathermal electrons and heat flux regulation in the inner heliosphere
• Directly comparing coronal and solar wind elemental fractionation
• Total Electron Temperature Derived from Quasi-Thermal Noise Spectroscopy In the Pristine Solar Wind: Parker Solar Probe Observations
• Source-dependent properties of two slow solar wind states
• Parker Solar Probe Observations of Suprathermal Electron Flux Enhancements Originating from Coronal Hole Boundaries
• Sensitivity of solar wind mass flux to coronal temperature
• Quantifying the diffusion of suprathermal electrons by whistler waves between 0.2 and 1 AU with Solar Orbiter and Parker Solar Probe
• Stochastic diffusion of electrons interacting with whistler-mode waves in the solar wind
• Temperature inversion in a confined plasma atmosphere: coarse-grained effect of temperature fluctuations at its base
• A Kinetic Model of Solar Wind Acceleration Driven by Ambipolar Electric Potential and Velocity-Space Diffusion
• Formation of Magnetic Switchbacks via expanding Alfvén Waves
• Quasi-parallel anti-sunward propagating whistler waves associated to the electron-deficit in the near-Sun solar wind: Particle-in-Cell simulation
• Ambipolar electric field and potential in the solar wind estimated from electron velocity distribution functions
• Investigating the Relationship Between Physical Properties and Spatial Irregularities at Coronal Hole Boundaries
• Formation of Suprathermal Electron Populations in the Expanding, Turbulent Solar Wind
• Radial evolution of thermal and suprathermal electron populations in the slow solar wind from 0.13 to 0.5 au : Parker Solar Probe Observations