Electrons in the Young Solar Wind
Abstract
We present electron observations made by the Solar Wind Electrons Alphas and Protons experiment on the first two orbits of the Parker Solar Probe mission, which reached heliocentric distances as small as ~0.17 AU. The SWEAP instrument suite contains two electron sensors - the Solar Probe Analyzers (SPAN-A-E and SPAN-B-E on the ahead and behind faces of the spacecraft) - which together measure the majority of the electron distribution function. We derive the parameters of the electron core, halo, and strahl populations by utilizing a combination of fitting to model distributions and numerical integration of the measurements from the two SPAN sensors.
As expected, the electron core density and temperature increase with decreasing heliocentric distance, while the ratio of electron thermal pressure to magnetic pressure (beta) decreases. The density in the strahl also increases; however, the density of the halo plateaus and even decreases at perihelion, leading to a large strahl/halo ratio at closest approach. The core is anisotropic, and has a sunward drift relative to the proton flow velocity. This core drift is approximately balanced by the strahl, satisfying the zero-current condition necessary to maintain quasi-neutrality globally. The characteristics of the electron distributions near perihelion are clearly organized by solar wind flow speed, electron beta, and collisional age, including some trends which are no longer apparent at 1 AU. These trends help us understand the mechanisms that shape the solar wind electron distributions at an early stage of their evolution.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMSH12A..03H
- Keywords:
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- 7509 Corona;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY;
- 7513 Coronal mass ejections;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY;
- 7845 Particle acceleration;
- SPACE PLASMA PHYSICS;
- 7867 Wave/particle interactions;
- SPACE PLASMA PHYSICS