skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

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}
}
  • The author discusses the prediction of the arrival of coronal mass ejection events (CMEs) at earth by means of monitoring the arrival of energetic neutral atoms (ENAs) which proceed the CMEs arrival by 3 to 4 hours. Large CME have been identified as triggers for large geomagnetic storms, and advance warning of such events has practical value for health as well as electronic communications. ENAs are formed by recombination in the CME, and slowing of the CME in its traverse to the earth allows the ENAs to arrive in advance. The author discusses the magnitude of such arrivals, the energymore » characteristics of the atoms, and progress on systems to detect such events.« less
  • The interaction between the neutral solar-wind component and the ionized component of the interstellar gas may significantly influence the gas parameters. Proper allowance for this effect may alter our ideas about processes in the solar-wind deceleration zone, and measurements of the L..cap alpha.. brightness of the interstellar gas may have to be interpreted.
  • The solar wind flow around Venus is modeled numerically, with loading of the flux by heavy ions formed by photoionization of the neutral oxygen corona of Venus taken into account. It is shown that this effect can explain a whole series of features of the interaction of the solar wind with the planet, which had yet to be explained unambiguously, viz., the position of the shock wave, the characteristics of the solar wind flux, and the magnetic field behind the front.
  • We investigate the two-dimensional, steady state distributions of solar wind speed and 5-GeV cosmic ray flux with respect to the heliospheric current sheet and their variation with the solar cycle from late 1964 through mid-1982. Synoptic K coronameter data are used to locate the current sheet, taken as the center of the ''band of coronal streamers,'' during years of low and intermediate solar activity. We confirm the conclusion that the profile of the solar wind at 1 AU during these years consists of (1) a minimum in mean speed of
  • The coefficient of magnetohydrodynamic (MHD) eddy viscosity of the turbulent solar wind is calculated to be {nu}{sub eddy}{approx_equal}1.3x10{sup 17} cm{sup 2}/s: this coefficient is appropriate for velocity shears with scale thicknesses larger than the {approx}10{sup 6} km correlation length of the solar-wind turbulence. The coefficient of MHD eddy viscosity is calculated again accounting for the action of smaller-scale turbulent eddies on smaller scale velocity shears in the solar wind. This eddy viscosity is quantitatively tested with spacecraft observations of shear flows in co-rotating interaction regions (CIRs) and in coronal-mass-ejection (CME) sheaths and ejecta. It is found that the large-scale ({approx}10{supmore » 7} km) shear of the CIR fractures into intense narrow ({approx}10{sup 5} km) slip zones between slabs of differently magnetized plasma. Similarly, it is found that the large-scale shear of CME sheaths also fracture into intense narrow slip zones between parcels of differently magnetized plasma. Using the solar-wind eddy-viscosity coefficient to calculate vorticity-diffusion time scales and comparing those time scales with the {approx}100-h age of the solar-wind plasma at 1 AU, it is found that the slip zones are much narrower than eddy-viscosity theory says they should be. Thus, our concept of MHD eddy viscosity fails testing. For the freestream turbulence effect in solar-wind magnetosphere coupling, the eddy-viscous force of the solar wind on the Earth's magnetosphere is rederived accounting for the action of turbulent eddies smaller than the correlation length, along with other corrections. The improved derivation of the solar-wind driver function for the turbulence effect fails to yield higher correlation coefficients between measurements of the solar-wind driver and measurements of the response of the Earth's magnetosphere.« less