The Kinetic Expansion of Solar-wind Electrons: Transport Theory and Predictions for the Very Inner Heliosphere

Jeong, Seong-Yeop, Verscharen, Daniel, Vocks, Christian, Abraham, Joel B., Owen, Christopher J., Wicks, Robert, Fazakerley, Andrew N., Stansby, David, Berčič, Laura, Nicolaou, Georgios, Agudelo Rueda, Jeffersson A. and Bakrania, Mayur (2022) The Kinetic Expansion of Solar-wind Electrons: Transport Theory and Predictions for the Very Inner Heliosphere. The Astrophysical Journal, 927 (2). p. 162. ISSN 0004-637X

Jeong_2022_ApJ_927_162.pdf - Published Version
Available under License Creative Commons Attribution 4.0.

Download (1MB) | Preview
Official URL:


We propose a transport theory for the kinetic evolution of solar-wind electrons in the heliosphere. We derive a gyro-averaged kinetic transport equation that accounts for the spherical expansion of the solar wind and the geometry of the Parker spiral magnetic field. To solve our three-dimensional kinetic equation, we develop a mathematical approach that combines the Crank–Nicolson scheme in velocity space and a finite-difference Euler scheme in configuration space. We initialize our model with isotropic electron distribution functions and calculate the kinetic expansion at heliocentric distances from 5 to 20 solar radii. In our kinetic model, the electrons evolve mainly through the combination of ballistic particle streaming, the magnetic mirror force, and the electric field. By applying fits to our numerical results, we quantify the parameters of the electron strahl and the core part of the electron velocity distributions. The strahl fit parameters show that the density of the electron strahl is around 7% of the total electron density at a distance of 20 solar radii, the strahl bulk velocity and strahl temperature parallel to the background magnetic field stay approximately constant beyond a distance of 15 solar radii, and β∥s (i.e., the ratio of the strahl parallel thermal pressure to the magnetic pressure) is approximately constant with heliocentric distance at a value of about 0.02. We compare our results with data measured by the Parker Solar Probe. Furthermore, we provide theoretical evidence that the electron strahl is not scattered by the oblique fast-magnetosonic/whistler instability in the near-Sun environment.

Item Type: Article
Additional Information: Funding information: D.V. is supported by STFC Ernest Rutherford Fellowship ST/P003826/1. C. V. is supported by the Deutsche Forschungsgemeinschaft (DFG; German Research Foundation)—VO 2123/1-1. J. B. A. is supported by STFC grant ST/T506485/1. D.V., C.J.O., A.N.F., D.S., and L.B. are supported by STFC Consolidated Grant ST/S000240/1. R. T. W. is funded by STFC Consolidated Grant ST/V006320/1. J.A.A.R. is supported by the ESA Networking/Partnering Initiative (NPI) contract 4000127929/19/NL/MH/mg and the Colombian program Pasaporte a la Ciencia, Foco Sociedad—Reto 3, ICETEX grant 3933061. M. B. is supported by a UCL Impact Studentship, joint funded by the ESA NPI contract 4000125082/18/NL/MH/ic. We appreciate helpful discussions with Christopher Chen. This work was discussed at the "Joint Electron Project" at MSSL.
Subjects: F300 Physics
F500 Astronomy
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: Elena Carlaw
Date Deposited: 15 Mar 2022 11:33
Last Modified: 15 Mar 2022 11:45

Actions (login required)

View Item View Item


Downloads per month over past year

View more statistics