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Title: Kinetic Properties of the Neutral Solar Wind

Abstract

Charge-exchange collisions between the solar wind protons and interstellar hydrogen produce a distinctive population of neutral hydrogen streaming radially at nearly the solar-wind speed. This tenuous population, known as the neutral solar wind (NSW) is thought to play a key role in the appearance of the Interplanetary Boundary EXplorer ribbon, a bright circular band in the sky that is the source of neutral hydrogen with energies near 1 keV. According to the leading model of the ribbon, the velocity distribution of NSW hydrogen is imparted on the pickup ions (PUIs) generated via charge exchange with the interstellar protons beyond the heliopause, and in this way controls the stability of the resulting ring distribution of PUIs against hydromagnetic wave generation. In this paper, we examine the velocity distributions of the NSW atoms in the heliosphere and the outer heliosheath regions by following the phase-space trajectories of the Boltzmann equation. It is demonstrated that these distributions are highly anisotropic, with the parallel (radial) temperature greatly exceeding the perpendicular temperature. Ions picked up near 90° from the anisotropic NSW would form a stable ring distribution capable of generating the ribbon flux. We also discuss a second population of neutrals born in charge transfermore » collisions with interstellar PUIs, the so-called neutralized pickup ion (NPI) component. Their high thermal velocities translate into large parallel velocity spread of the daughter ribbon PUIs, which would adversely affect plasma stability in local interstellar space.« less

Authors:
;  [1]
  1. Department of Space Science and Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL 35899 (United States)
Publication Date:
OSTI Identifier:
22661243
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 838; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ANISOTROPY; ATOMS; BOLTZMANN EQUATION; CHARGE EXCHANGE; DISTRIBUTION; HELIOSPHERE; HYDROGEN; HYDROMAGNETIC WAVES; INTERSTELLAR SPACE; ION TEMPERATURE; IONS; PHASE SPACE; PLASMA; PROTONS; SOLAR WIND; STABILITY; VELOCITY

Citation Formats

Florinski, V., and Heerikhuisen, J., E-mail: vaf0001@uah.edu, E-mail: jh0004@uah.edu. Kinetic Properties of the Neutral Solar Wind. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA6441.
Florinski, V., & Heerikhuisen, J., E-mail: vaf0001@uah.edu, E-mail: jh0004@uah.edu. Kinetic Properties of the Neutral Solar Wind. United States. doi:10.3847/1538-4357/AA6441.
Florinski, V., and Heerikhuisen, J., E-mail: vaf0001@uah.edu, E-mail: jh0004@uah.edu. Mon . "Kinetic Properties of the Neutral Solar Wind". United States. doi:10.3847/1538-4357/AA6441.
@article{osti_22661243,
title = {Kinetic Properties of the Neutral Solar Wind},
author = {Florinski, V. and Heerikhuisen, J., E-mail: vaf0001@uah.edu, E-mail: jh0004@uah.edu},
abstractNote = {Charge-exchange collisions between the solar wind protons and interstellar hydrogen produce a distinctive population of neutral hydrogen streaming radially at nearly the solar-wind speed. This tenuous population, known as the neutral solar wind (NSW) is thought to play a key role in the appearance of the Interplanetary Boundary EXplorer ribbon, a bright circular band in the sky that is the source of neutral hydrogen with energies near 1 keV. According to the leading model of the ribbon, the velocity distribution of NSW hydrogen is imparted on the pickup ions (PUIs) generated via charge exchange with the interstellar protons beyond the heliopause, and in this way controls the stability of the resulting ring distribution of PUIs against hydromagnetic wave generation. In this paper, we examine the velocity distributions of the NSW atoms in the heliosphere and the outer heliosheath regions by following the phase-space trajectories of the Boltzmann equation. It is demonstrated that these distributions are highly anisotropic, with the parallel (radial) temperature greatly exceeding the perpendicular temperature. Ions picked up near 90° from the anisotropic NSW would form a stable ring distribution capable of generating the ribbon flux. We also discuss a second population of neutrals born in charge transfer collisions with interstellar PUIs, the so-called neutralized pickup ion (NPI) component. Their high thermal velocities translate into large parallel velocity spread of the daughter ribbon PUIs, which would adversely affect plasma stability in local interstellar space.},
doi = {10.3847/1538-4357/AA6441},
journal = {Astrophysical Journal},
number = 1,
volume = 838,
place = {United States},
year = {Mon Mar 20 00:00:00 EDT 2017},
month = {Mon Mar 20 00:00:00 EDT 2017}
}