scholarly journals Model Calculations of Solar Wind Expansion Including an Enhanced Fraction of Ionizing Electrons

1980 ◽  
Vol 91 ◽  
pp. 159-162
Author(s):  
E. F. Petelski ◽  
H. J. Fahr ◽  
H. W. Ripken
Keyword(s):  
Solar Wind ◽  
Impact Ionization ◽  
Hydrogen Atoms ◽  
Interstellar Gas ◽  
Model Calculations ◽  
Neutral Gas ◽  
Continuity Equations ◽  
Velocity Effect ◽  
Collective Interactions ◽  
Ionization Velocity

Collective interactions of the solar wind and newly ionized interstellar gas cause turbulent electron heating to ionizing energies analogous to laboratory experiments on the critical ionization velocity effect. Implications for solar wind and interstellar gas dynamics are calculated by simultaneously solving continuity equations for solar wind protons, interstellar hydrogen atoms, and energetic electrons. Electron impact ionization is shown to be practically as important as photoionization, giving rise to a stronger deceleration and heating of the distant solar wind, a weaker terminating shock, a smaller stand-off distance of the helio pause, and implying higher densities of the outer solar wind and the interstellar neutral gas.

Remarks on the diffuse interstellar lines

1967 ◽  
Vol 31 ◽  
pp. 91-93 ◽  
Author(s):  
G. Herzberg
Keyword(s):  
Hydrogen Atoms ◽  
Interstellar Gas

It is suggested that the diffuse interstellar lines are produced in the interstellar gas by molecules consisting of a few hydrogen atoms and one other atom, such as CH4+ or NH4. Diffuseness of the lines is assumed to result from predissociation of these molecules.

The heating of the solar wind by the interstellar neutral gas

1985 ◽  
Vol 90 (A12) ◽  
pp. 12040 ◽  
Author(s):  
P. A. Isenberg ◽  
P. P. Chih ◽  
L. A. Fisk
Keyword(s):  
Solar Wind ◽  
Neutral Gas

scholarly journals Commission 49: Interplanetary Plasma and Heliosphere: (Plasma Interplanetaire et Heliosphere)

2000 ◽  
Vol 24 (1) ◽  
pp. 77-84
Author(s):  
F. Verheest ◽  
M. Vandas ◽  
B. Buti ◽  
N.F. Cramer ◽  
M. Dryer ◽  
...  
Keyword(s):  
Solar Wind ◽  
Gas Flow ◽  
Recent Literature ◽  
Interplanetary Space ◽  
Charged Dust ◽  
Interstellar Gas ◽  
Interplanetary Plasma ◽  
Flow Through ◽  
Transient Events ◽  
Solar Wind Composition

In the last decade the triennial reports from Commission 49 have covered various topics like (nonlinear) plasma processes, magnetohydrodynamic phenomena and flows in the heliosphere, solar wind composition, transient events in, and latitudinal dependencies of, the heliosphere, interstellar gas flow through the interface region, kinetic versus magnetohydrodynamic theory in heliospheric plasmas and charged dust in space plasmas. Continuing the tradition of summarizing specific aspects to give astronomers outside our own specialty a flavour of our field, we now address recent advances in understanding coronal mass ejections in interplanetary space and the inner heliospheric solar wind under quiet and perturbed conditions. We owe a great debt of gratitude to the eminent contributors for their valiant efforts in writing these succinct but clear reports and guiding us through the recent literature.

scholarly journals Effect of the non-uniform solar chromospheric Lyα radiation on determining the coronal H I outflow velocity

2019 ◽  
Vol 627 ◽  
pp. A18 ◽  
Author(s):  
S. Dolei ◽  
D. Spadaro ◽  
R. Ventura ◽  
A. Bemporad ◽  
V. Andretta ◽  
...  
Keyword(s):  
Solar Wind ◽  
Neutral Hydrogen ◽  
Radiation Condition ◽  
Brightness Distribution ◽  
Computational Time ◽  
Hydrogen Atoms ◽  
Line Intensities ◽  
Outflow Velocity ◽  
Chromospheric Emission ◽  
Outer Corona

We derived maps of the solar wind outflow velocity of coronal neutral hydrogen atoms at solar minimum in the altitude range 1.5–4.0 R⊙. We applied the Doppler dimming technique to coronagraphic observations in the UV H I Lyα line at 121.6 nm. The technique exploits the intensity reduction in the coronal line with increasing velocities of the outflowing plasma to determine the solar wind velocity by iterative modelling. The Lyα line intensity is sensitive to the wind outflow velocity and also depends on the physical properties of coronal particles and underlying chromospheric emission. Measurements of irradiance by the chromospheric Lyα radiation in the corona are required for a rigorous application of the Doppler dimming technique, but they are not provided by past and current instrumentations. A correlation function between the H I 121.6 nm and He II 30.4 nm line intensities was used to construct Carrington rotation maps of the non-uniform solar chromospheric Lyα radiation and thus to compute the Lyα line irradiance throughout the outer corona. Approximations concerning the temperature of the scattering H I atoms and exciting solar disc radiation were also adopted to significantly reduce the computational time and obtain a faster procedure for a quick-look data analysis of future coronagraphic observations. The effect of the chromospheric Lyα brightness distribution on the resulting H I outflow velocities was quantified. In particular, we found that the usual uniform-disc approximation systematically leads to an overestimated velocity in the polar and mid-latitude coronal regions up to a maximum of about 50−60 km s−1 closer to the Sun. This difference decreases at higher altitudes, where an increasingly larger chromospheric portion, including both brighter and darker disc features, contributes to illuminate the solar corona, and the non-uniform radiation condition progressively approaches the uniform-disc approximation.

scholarly journals Turbulence in the diffuse magneto-ionized medium: observational aspects

2015 ◽  
Vol 11 (A29B) ◽  
pp. 720-722
Author(s):  
Marijke Haverkorn
Keyword(s):  
Magnetic Fields ◽  
Milky Way ◽  
Turbulent Energy ◽  
Spectral Lines ◽  
Observational Methods ◽  
Interstellar Gas ◽  
Ionized Gas ◽  
Neutral Gas ◽  
Velocity Information ◽  
Gas Component

AbstractTurbulence in the interstellar medium is ubiquitous. The turbulent energy density in the gas is significant, and comparable to energy densities of magnetic fields and cosmic rays. Studies of the turbulent interstellar gas in the Milky Way have mostly focused on the neutral gas component, since various spectral lines can give velocity information. Probing turbulent properties in the ionized gas, let alone in magnetic fields, is observationally more difficult. A number of observational methods are discussed below which provide estimates of the maximum scale of fluctuations, the Mach number and other turbulence characteristics.

scholarly journals On the physical conditions in interstellar H I gas

1970 ◽  
Vol 38 ◽  
pp. 182-185
Author(s):  
M. Grewing ◽  
U. Mebold ◽  
K. Rohlfs
Keyword(s):  
High Latitude ◽  
Weighted Average ◽  
Interstellar Gas ◽  
Low Latitude ◽  
Physical Conditions ◽  
Neutral Gas ◽  
Ionization Ratio

Weighted average values of the ionization ratio ne/nH for the interstellar gas can be obtained from a comparison of pulsar data and 21-cm emission measurements. For high latitude pulsars this procedure is straight forward and reasonably free from assumptions. The resulting ionization ratios are high (ne/nH = 0.39). If this is compared with values as given by the theory of ionization and heating of interstellar gas by subcosmic rays, temperatures for the ‘neutral’ gas above 104 K are obtained. For low latitude pulsars this procedure depends to a much larger extend on the assumed distance of the objects and on the ionization theory. Here the values found are ne/nH = 0.07 and Te = 2000 K.

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