Lower solar chromosphere-corona transition region. I - Theoretical models with small temperature gradients

1990 ◽  
Vol 355 ◽  
pp. 295 ◽  
Author(s):  
D. Tod Woods ◽  
Thomas E. Holzer ◽  
Keith B. MacGregor
Keyword(s):  
Transition Region ◽  
Theoretical Models ◽  
Temperature Gradients ◽  
Solar Chromosphere ◽  
Small Temperature ◽  
Region I

scholarly journals Chromospheric counterparts of solar transition region unresolved fine structure loops

2018 ◽  
Vol 611 ◽  
pp. L6 ◽  
Author(s):  
Tiago M. D. Pereira ◽  
Luc Rouppe van der Voort ◽  
Viggo H. Hansteen ◽  
Bart De Pontieu
Keyword(s):  
Transition Region ◽  
Current Knowledge ◽  
Solar Limb ◽  
Theoretical Models ◽  
Solar Chromosphere ◽  
Solar Transition Region ◽  
Solar Transition ◽  
Heating And Cooling ◽  
Doppler Shifts ◽  
New Information

Low-lying loops have been discovered at the solar limb in transition region temperatures by the Interface Region Imaging Spectrograph (IRIS). They do not appear to reach coronal temperatures, and it has been suggested that they are the long-predicted unresolved fine structures (UFS). These loops are dynamic and believed to be visible during both heating and cooling phases. Making use of coordinated observations between IRIS and the Swedish 1-m Solar Telescope, we study how these loops impact the solar chromosphere. We show for the first time that there is indeed a chromospheric signal of these loops, seen mostly in the form of strong Doppler shifts and a conspicuous lack of chromospheric heating. In addition, we find that several instances have a inverse Y-shaped jet just above the loop, suggesting that magnetic reconnection is driving these events. Our observations add several puzzling details to the current knowledge of these newly discovered structures; this new information must be considered in theoretical models.

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.

Clustering of the resonant triads induced by vertical-shear instability in astrophysical discs

2020 ◽  
Vol 499 (3) ◽  
pp. 3222-3232
Author(s):  
Yuri Shtemler ◽  
Michael Mond
Keyword(s):  
Characteristic Frequency ◽  
Characteristic Time ◽  
Temperature Gradients ◽  
Shear Instability ◽  
Vertical Shear ◽  
Higher Dimension ◽  
Small Temperature ◽  
Common Mode ◽  
Vertical Speed ◽  
Resonant Triads

ABSTRACT Clustering of resonant triads that are induced by vertical-shear instability (VSI), driven by the combined effect of the vertical speed shear and small temperature gradients, is studied for vertically isothermal thin unmagnetized Keplerian discs. The authors’ recent study of isolated VSI resonant triads is extended to illustrate their clustering. The coupling conditions for two VSI resonant triads with one common mode are derived and generalized to higher dimension clustering. The clustering of two, three, and four triads connected via one common mode is numerically simulated. The numerical simulations demonstrate the chaotization of non-linear oscillations about the prototypes of the linearly stable modes with a growing cluster’s dimension that is accompanied by a decrease of the characteristic time of chaotization and an increase of the characteristic frequency of perturbations. The chaos associated with the VSI resonant clustering is believed to precede transition to sustainable turbulence in astrophysical discs.

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.

Elastoviscous Properties of Amorphous Polymers in the Transition Region. I

1952 ◽  
Vol 74 (13) ◽  
pp. 3378-3381 ◽  
Author(s):  
J. Bischoff ◽  
E. Catsiff ◽  
A. V. Tobolsky
Keyword(s):  
Transition Region ◽  
Amorphous Polymers ◽  
Region I

The phosphorus-31 and metal nuclear magnetic resonance spectra of complexes of tin(II) and lead(II) with tricyclohexylphosphine oxide, sulfide, and selenide

1982 ◽  
Vol 60 (23) ◽  
pp. 2921-2926 ◽  
Author(s):  
Philip A. W. Dean
Keyword(s):  
High Field ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Temperature Gradients ◽  
Large Temperature ◽  
Linear Variation ◽  
Small Temperature ◽  
Nuclear Magnetic Resonance Spectra ◽  
Small Temperature Variation ◽  
Reduced Temperature

The new stannous and plumbous complexes M(OP(C6H11)3)n2+ (n = 2 or 3, M = Sn or Pb) and [M(SP(C6H11)3)x(SeP-(C6H11)3)3−x]2+ (M = Sn or Pb) have been prepared in SO2 solution and characterized by their reduced temperature slow-exchange 31P and metal (119Sn or 207Pb) nmr spectra. No evidence could be found for complexes in which both OP(C6H11)3 and EP(C6H11)3 (E = S or Se) are coordinated to tin(II) or lead(II). The same pattern of chemical shifts is found in the 119Sn and 207Pb nmr spectra: δM(M(OP(C6H11)3)22+) < δM(M(OP(C6H11)3)32+ < δM(M(SP(C6H11)3)32+) < δM(M(SeP(C6H11)3)32+) and a monotonic but non-linear variation of δM with x for [M(SP(C6H11)3)x(SeP(C6H11)3)3−x]2+. From M(AsF6)2 in SO2 as reference, the range of the metal chemical shifts is 999–2079 ppm and 2407–7707 ppm in the 119Sn and 207Pb nmr spectra respectively. In the 31P nmr spectra, all of the appropriate two-bond M—P couplings are observed, but the fine structure expected from coupling to 31P could not always be observed in those metal nmr spectra which were measured at high field; it is suggested that these metal nmr spectra are "smeared out" by a combination of large temperature sensitivity of the metal chemical shifts and the small temperature variation allowed by the nmr spectrometer temperature controller and/or diffusion along any temperature gradients present along the length of the nmr sample.

A Discussion on solar studies with special reference to space observations - The structure of the chromosphere-corona transition region from limb and disk intensities

1971 ◽  
Vol 270 (1202) ◽  
pp. 81-98 ◽  
Keyword(s):  
Low Temperature ◽  
Special Reference ◽  
Transition Region ◽  
Solar Disk ◽  
Solar Limb ◽  
Hydrostatic Equilibrium ◽  
Temperature Gradients ◽  
Emission Lines ◽  
Atomic Data ◽  
Absolute Intensities

During a racket flight in April 1969, spectra were obtained of a region of the solar disk and at the solar limb. The absolute disk intensities derived from these data have been used to compute models of the transition region, making the assumptions that the relative abundances of different elements remain constant throughout the atmosphere, and that the electron pressure varies according to the equation of hydrostatic equilibrium. The models obtained are characterized by very steep temperature gradients. The relative intensities of emission lines in the disk and limb spectra have enabled the height of the emitting regions to be determined independently of the above assumptions, and independently of atomic data and absolute intensities. A comparison is made of the structure found by the two methods, and within the accuracy of the present data these are consistent. Emission from low temperature ( ~ 10 4 K) material is observed from heights up to 10 4 km above the transition region, and this probably originates in spicules.

Sign in / Sign up

Export Citation Format

Share Document