Open AccessElectron temperature in the solar wind: Generic radial variation from kinetic collisionless models
Author(s) -
MeyerVernet Nicole,
Issautier Karine
Publication year - 1998
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/98ja02853
Subject(s) - physics , electron , adiabatic process , solar wind , electron temperature , kinetic energy , computational physics , electron density , mean kinetic temperature , range (aeronautics) , distribution function , atomic physics , plasma , classical mechanics , materials science , thermodynamics , quantum mechanics , composite material
We calculate analytically the radial profile of the average electron temperature in the solar wind with a kinetic collisionless model. The electron temperature profile at large distances r is the sum of a term oc r −4/3 plus a constant, with both terms of the same order of magnitude near r ∼ 1AU. This result is generic as it is weakly dependent on the particle velocity distributions in the corona. It provides a natural explanation for the observed electron temperature profile near 1 AU, which is in the low or middle part of the range between isothermal and adiabatic behaviors. The r −4/3 term comes from the isotropically distributed electrons confined by the heliospheric electric potential, which is found to have a similar radial variation. The constant term comes from the parallel temperature of the electrons energetic enough to escape. The calculated profile flattens as r increases and tends to be flatter in the high‐speed wind. We also give simple explicit expressions for the electron temperature and density at large distances and for the terminal wind velocity as a function of coronal parameters when the electron velocity distribution is a Kappa function, which is close to a Maxwellian with a suprathermal tail.