A model of the solar chromosphere-corona transition region based on classical thermal conduction

1990 ◽  
Vol 362 ◽  
pp. 364 ◽  
Author(s):  
R. Grant Athay
Keyword(s):  
Transition Region ◽  
Thermal Conduction ◽  
Solar Chromosphere

scholarly journals Experiment to Determine the Temperature Structure in the Solar Chromosphere and Corona

1972 ◽  
Vol 14 ◽  
pp. 668-669
Author(s):  
C. R. Negus
Keyword(s):  
Transition Region ◽  
Extreme Ultraviolet ◽  
Normal Incidence ◽  
Research Unit ◽  
Emission Lines ◽  
Solar Chromosphere ◽  
Temperature Structure ◽  
Ultraviolet Emission ◽  
Ionization Temperature ◽  
Intensity Ratios

An experiment is in course of preparation at the Astrophysics Research Unit at Culham for flight on a Sun-pointing rocket. It is designed to determine the ionization temperature and electron density as a function of height in the temperature range of about 8 × 104 K to 3 × 106 K by measuring limb to disk intensity ratios of extreme ultraviolet emission lines in the 170 to 850 Å region. The work is an extension of current experiments in which normal-incidence spectrographs are used to determine the structure lower in the chromosphere-corona transition region.

scholarly journals Radiation Hydrodynamics in Solar Flares

1986 ◽  
Vol 89 ◽  
pp. 53-74
Author(s):  
George H. Fisher
Keyword(s):  
Heating Rate ◽  
Transition Region ◽  
Solar Flares ◽  
Thermal Model ◽  
Thermal Conduction ◽  
Thick Target ◽  
Pressure Increase ◽  
Electromagnetic Spectrum ◽  
X Ray ◽  
Upper Limit

AbstractSolar flares are currently understood as the explosive release of energy stored in the form of stressed magnetic fields. In many cases, the released energy seems to take the form of large numbers of electrons accelerated to high energies (the nonthermal electron “thick target” model), or alternatively plasma heated to very high temperatures behind a rapidly moving conduction front (the “thermal” model). The transport of this energy into the remaining portion of the atmosphere results in violent mass motion and strong emission across the electromagnetic spectrum. Radiation processes play a crucial role in determining the ensuing plasma motion.One important phenomenon observed during flares is the appearance in coronal magnetic loops of large amounts of upflowing, soft X-ray emitting plasma at temperatures of 1−2×107 [K]. It is believed that this is due to chromospheric evaporation, the process of heating cool (T - 104[K]) chromospheric material beyond its ability to radiate. Detailed calculations of thick target heating show that if nonthermal electrons heat the chromosphere directly, then the evaporation process can result in explosive upward motion of X-ray emitting plasma if the heating rate exceeds a threshold value. In such a case, upflow velocities approach an upper limit of roughly 2.35 cs as the heating rate is increased beyond the threshold, where cs is the sound speed in the evaporated plasma. This is known as explosive evaporation. If the flare heating rate is less than the threshold, evaporation takes place indirectly through thermal conduction of heat deposited in the corona by the energetic electrons. Upflows in this case are roughly 10 to 20% of the upper limit. Evaporation by thermal model heating always takes place through thermal conduction, and the computed upflow speeds seem to be about 10% to 20% of the upper limit, independent of the energy flux.The pressure increase in the evaporated plasma for either the thick target or thermal model leads to a number of interesting phenomena in the flare chromosphere. The sudden pressure increase initiates a downward moving “chromospheric condensation”, an overdense region which gradually decelerates as it accretes material and propagates into the gravitationally stratified chromosphere. Solutions to an equation of motion for this condensation shows that its motion decays after about one minute of propagation into the chromosphere. When the front of this downflowing region is supersonic relative to the atmosphere ahead of it, a radiating shock will form. If the downflow is rapid enough, the shock strength should be sufficient to excite UV radiation normally associated with the transition region, and furthermore, the radiating shock will be brighter than the transition region. These results lead to a number of observationally testable relationships between the optical and ultraviolet spectra from the condensation and radiating shock.

Plasma flows in the quiet solar chromosphere-corona transition region

2015 ◽  
Vol 70 (2) ◽  
pp. 153-159 ◽  
Author(s):  
O. V. Dunin-Barkovskaya ◽  
B. V. Somov
Keyword(s):  
Transition Region ◽  
Solar Chromosphere ◽  
Plasma Flows
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