Journal article
The Sunward Electron Deficit: A Telltale Sign of the Sun's Electric Potential
The Astrophysical journal, Vol.916(1), p.16
07/01/2021
DOI: 10.3847/1538-4357/ac096e
Abstract
As the Parker Solar Probe explores new regions of the inner heliosphere, it travels ever deeper into the electric potential of the Sun. In the near-Sun environment, a new feature of the electron distribution emerges, in the form of a deficit in the sunward suprathermal population. The lower boundary of this deficit forms a cutoff in phase space, at an energy determined by the electric potential drop between the observation point and the outer heliosphere. We explore the characteristics of the sunward deficit and the associated cutoff, as well as the properties of the plasma in which we observe them. The deficit occurs in similar to 60%-80% of electron observations within similar to 0.2 au, and even more frequently in plasma with low beta, low collisional age, and a more anisotropic electron core population. At greater distances, the deficit rapidly disappears, as the suprathermal halo grows, with these two trends likely related. The cutoff energy varies linearly with the local electron core temperature, confirming a direct relationship to the ambipolar electric potential. Meanwhile, the cutoff width varies with beta and collisional age, suggesting that energy diffusion plays a role in erasing the deficit. The nearly ubiquitous occurrence of the sunward deficit in the inner heliosphere suggests that we may need to reconsider the functional forms commonly used to represent electron distributions in this environment.
Details
- Title: Subtitle
- The Sunward Electron Deficit: A Telltale Sign of the Sun's Electric Potential
- Creators
- J. S. Halekas - University of IowaL. Bercic - University College LondonP. Whittlesey - University of California, BerkeleyD. E. Larson - University of California, BerkeleyR. Livi - University of California, BerkeleyM. Berthomier - Laboratoire de Physique des PlasmasJ. C. Kasper - Smithsonian Astrophysical ObservatoryA. W. Case - Smithsonian Astrophysical ObservatoryM. L. Stevens - Smithsonian Astrophysical ObservatoryS. D. Bale - University of California, BerkeleyR. J. MacDowall - Goddard Space Flight CenterM. P. Pulupa - University of California, Berkeley
- Resource Type
- Journal article
- Publication Details
- The Astrophysical journal, Vol.916(1), p.16
- Publisher
- Iop Publishing Ltd
- DOI
- 10.3847/1538-4357/ac096e
- ISSN
- 0004-637X
- eISSN
- 1538-4357
- Number of pages
- 9
- Grant note
- DOI: 10.13039/100000104, name: National Aeronautics and Space Administration, award: NNN06AA01C
- Language
- English
- Date published
- 07/01/2021
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984429013402771
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