On the Role of the Solar Corona and Transition Region in the Excitation of the Spectrum of Neutral Helium

1997 ◽  
Vol 489 (1) ◽  
pp. 375-394 ◽  
Author(s):  
Vincenzo Andretta ◽  
Harrison P. Jones
Keyword(s):  
Solar Corona ◽  
Transition Region

Generation of Short-scale Electrostatic Fields in the Solar Atmosphere and the Role of Helium Ions

2021 ◽  
Vol 922 (1) ◽  
pp. 48
Author(s):  
H. Saleem ◽  
Shaukat Ali Shan ◽  
A. Rehman
Keyword(s):  
Shear Flow ◽  
Transition Region ◽  
Electric Fields ◽  
Hydrogen Plasma ◽  
Theoretical Models ◽  
Inhomogeneous Field ◽  
Helium Ions ◽  
Low Frequencies ◽  
Short Scale

Abstract Theoretical models are presented to show that expansion of plasma in the radial direction from a denser solar surface to a rarefied upper atmosphere with short-scale inhomogeneous field-aligned flows and currents in the form of thin threads itself is an important source of electrostatic instabilities. Multifluid theory shows that the shear flow–driven purely growing electric fields appear in the transition region. On the other hand, plasma kinetic theory predicts that the short-scale current sheets (or filaments) produce current-driven electrostatic ion acoustic (CDEIA) waves in the hydrogen plasma of the transition region that damp out in the system through wave–particle interactions and increase the temperature. Similar processes take place in the solar corona and act positively for increasing the temperature further and maintaining it. The shear flow–driven instabilities and CDEIA waves have short perpendicular wavelengths of the order of 1 m and low frequencies of the order of 1 or several Hz when the ions’ shear flow scale length is considered to be of the order of 1 km. It is pointed out that the purely growing fluid instabilities turn into oscillatory instabilities and the growth rates of kinetic CDEIA wave instabilities are reduced when the dynamics of 10% helium ions is taken into account along with 90% hydrogen ions. Therefore, the role of helium ions should not be ignored in the study of wave dynamics in solar plasma.

The role of the flagellar transition region: inferences from the analysis of a Chlamydomonas mutant with defective transition region structures

1991 ◽  
Vol 99 (4) ◽  
pp. 731-740
Author(s):  
JONATHAN W. JARVIK ◽  
JOSEPH P. SUHAN
Keyword(s):  
Transition Region ◽  
Basal Body ◽  
Wild Type ◽  
Central Pair ◽  
Normal Transition ◽  
Thin Section Electron Microscopy ◽  
Concomitant Reduction ◽  
Section Electron ◽  
Type Variable

Thin-section electron microscopy of the Chlamydomonas reinhardtii mutant vfl-2 revealed striking defects in the transition region between basal body and flagellum. In place of the highly organized transition cylinders and stellate fibers characteristic of wild type, variable quantities of poorly organized electron-dense material were present. In many cases the transition region was penetrated by central pair microtubules that passed from the axoneme into the basal body. On the basis of these observations we propose that an important function of the structures present in the normal transition region is to physically exclude the central pair microtubules from the basal body. The transition region is the site of flagellar autotomy – the process by which doublet microtubules are severed and flagella are released from the cell. It has been claimed that autotomy is caused by contraction of the centrin-containing stellate fibers, resulting in the mechanical severing of the doublet microtubules and a concomitant reduction of the diameter of the axoneme adjacent to the abscission point. Our observations do not support this claim in that vfl-2 cells, which lack organized stellate fibers, display effective autotomy unaccompanied by detectable narrowing of the axoneme.

scholarly journals Magnetohydrodynamic calculation of the temperature and wind velocity profile of the solar transition region. Preliminary results.

2018 ◽  
Vol 145 ◽  
pp. 03009 ◽  
Author(s):  
Todor M. Mishonov ◽  
Albert M. Varonov ◽  
Nedeltcho I. Zahariev ◽  
Rositsa V. Topchiyska ◽  
Boian V. Lazov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Spectral Density ◽  
Solar Corona ◽  
Temperature Profile ◽  
Transition Region ◽  
Wind Velocity ◽  
Spectral Lines ◽  
Mhd Waves ◽  
Dimensional Approximation ◽  
Height Dependence

The sharp almost step like increase the temperature in the transition region (TR) between chromosphere and solar corona is well-known from decades; for first time we are giving a detailed magnetohydrodynamic (MHD) calculation of the height dependence of the temperature. The width of the transition region is evaluated by maximal value of the logarithmic derivative of the temperature. At fixed heating, only MHD can give such a narrow width and in such sense, even the qualitative agreement with the observational data, gives the final verdict what the heating mechanism of the solar corona is. Static profiles of the temperature and wind velocity are calculated for static frequency dependent spectral density of the incoming MHD waves; no time dependent computer simulations. At fixed spectral density of MHD waves, the MHD calculation predicts height dependence of the non-thermal broadening of spectral lines and its angular dependence. For illustration is used one dimensional approximation of completely ionized hydrogen plasma in weak magnetic field, but it is considered that the width of the TR is weakly dependent with respect of further elaboration. The analyzed MHD calculation is a numerical confirmation of the qualitative concept of self-induced opacity of the plasma with respect to MHD waves. The plasma viscosity strongly increases with the temperature. Heated by MHD waves, plasma increases the wave absorption and this positive feedback leads to further heating. The static temperature profile is a result of a self-consistent calculation of propagation of MHD wave through the static background of wind and temperature profile. The numerical method allows consideration of incoming MHD waves with an arbitrary spectral density. Further elaboration of the method are briefly discussed: influence of second viscosity in the chromospheric part of the TR, influence of the magnetic field on the coronal side of the TR and investigation of such type effects on the width of the TR.

Role of radio wave reflection during radio occultation by the solar corona

1985 ◽  
Vol 28 (7) ◽  
pp. 549-556 ◽  
Author(s):  
A. I. Kucheryavenkov ◽  
A. G. Pavel'ev ◽  
S. N. Rubtsov ◽  
O. I. Yakovlev
Keyword(s):  
Solar Corona ◽  
Radio Wave ◽  
Radio Occultation ◽  
Wave Reflection

scholarly journals Nonequilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind (Invited Review)

Solar Physics ◽  
2017 ◽  
Vol 292 (8) ◽  
Author(s):  
Jaroslav Dudík ◽  
Elena Dzifčáková ◽  
Nicole Meyer-Vernet ◽  
Giulio Del Zanna ◽  
Peter R. Young ◽  
...  
Keyword(s):  
Solar Wind ◽  
Solar Corona ◽  
Transition Region ◽  
Nonequilibrium Processes
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