Lower solar chromosphere-corona transition region. III - Implications of the observed quiet-sun emission measure including wave pressure effects

1990 ◽  
Vol 355 ◽  
pp. 309 ◽  
Author(s):  
D. Tod Woods ◽  
Thomas E. Holzer ◽  
Keith B. MacGregor
Keyword(s):  
Transition Region ◽  
Emission Measure ◽  
Pressure Effects ◽  
Solar Chromosphere ◽  
Wave Pressure ◽  
Quiet Sun

scholarly journals Models of Active Regions in the Transition Zone from UV Observations

1972 ◽  
Vol 14 ◽  
pp. 638-638
Author(s):  
A. M. Cantú ◽  
G. Poletto ◽  
G. L. Tagliaferri
Keyword(s):  
Transition Region ◽  
Transition Zone ◽  
Active Regions ◽  
Solar Chromosphere ◽  
Harvard College ◽  
Quiet Sun ◽  
Harvard College Observatory

The Harvard College Observatory UV spectroheliometer aboard the OSO-4 spacecraft has obtained the enhancement of active regions, i.e. the ratio of their intensity to that of the quiet Sun Ia and Iq, for several lines formed in the transition region between the solar chromosphere and the corona (The subscripts a an q indicate active and quiet regions, respectively.)

SUMER Observations of the Quiet‐Sun Transition Region

1999 ◽  
Vol 512 (2) ◽  
pp. 992-1005 ◽  
Author(s):  
N. W. Griffiths ◽  
G. H. Fisher ◽  
D. T. Woods ◽  
O. H. W. Siegmund
Keyword(s):  
Transition Region ◽  
Quiet Sun

The solar chromosphere and corona: Quiet Sun

1977 ◽  
Vol 25 (9) ◽  
pp. 893-894
Author(s):  
Carole Jordan
Keyword(s):  
Solar Chromosphere ◽  
Quiet Sun

scholarly journals Modeling the quiet Sun cell and network emission with ALMA

2020 ◽  
Vol 640 ◽  
pp. A57 ◽  
Author(s):  
C. E. Alissandrakis ◽  
A. Nindos ◽  
T. S. Bastian ◽  
S. Patsourakos
Keyword(s):  
Electron Temperature ◽  
Brightness Temperature ◽  
Absolute Calibration ◽  
Solar Chromosphere ◽  
Temperature Structure ◽  
Cell Interior ◽  
Network Cell ◽  
Quiet Sun ◽  
Millimeter Wavelengths ◽  
Cell Segregation

Observations of the Sun at millimeter wavelengths with the Atacama Large Millimeter/submillimeter Array (ALMA) offer a unique opportunity to investigate the temperature structure of the solar chromosphere. In this article we expand our previous work on modeling the chromospheric temperature of the quiet Sun, by including measurements of the brightness temperature in the network and cell interiors, from high-resolution ALMA images at 3 mm (Band 3) and 1.26 mm (Band 6). We also examine the absolute calibration of ALMA full-disk images. We suggest that the brightness temperature at the center of the solar disk in Band 6 is ∼440 K above the value recommended by White et al. (2017, Sol. Phys., 292, 88). In addition, we give improved results for the electron temperature variation of the average quiet Sun with optical depth and the derived spectrum at the center of the disk. We found that the electron temperature in the network is considerably lower than predicted by model F of Fontenla et al. (1993, ApJ, 406, 319) and that of the cell interior considerably higher than predicted by model A. Depending on the network/cell segregation scheme, the electron temperature difference between network and cell at τ = 1 (100 GHz) ranges from ∼660 K to ∼1550 K, compared to ∼3280 K predicted by the models; similarly, the electron temperature, Te ratio ranges from ∼1.10 to 1.24, compared to ∼1.55 of the model prediction. We also found that the network/cell Te(τ) curves diverge as τ decreases, indicating an increase of contrast with height and possibly a steeper temperature rise in the network than in the cell interior.

scholarly journals Transient brightenings in the quiet Sun detected by ALMA at 3 mm

2020 ◽  
Vol 638 ◽  
pp. A62 ◽  
Author(s):  
A. Nindos ◽  
C. E. Alissandrakis ◽  
S. Patsourakos ◽  
T. S. Bastian
Keyword(s):  
Solar Atmosphere ◽  
Power Law ◽  
Small Scale ◽  
Solar Chromosphere ◽  
Average Intensity ◽  
Quiet Sun ◽  
Brightness Temperatures ◽  
Weak Preference ◽  
Thermal Origin ◽  
First Time

Aims. We investigate transient brightenings, that is, weak, small-scale episodes of energy release, in the quiet solar chromosphere; these episodes can provide insights into the heating mechanism of the outer layers of the solar atmosphere. Methods. Using Atacama Large Millimeter/submillimeter Array (ALMA) observations, we performed the first systematic survey for quiet Sun transient brightenings at 3 mm. Our dataset included images of six 87″ × 87″ fields of view of the quiet Sun obtained with angular resolution of a few arcsec at a cadence of 2 s. The transient brightenings were detected as weak enhancements above the average intensity after we removed the effect of the p-mode oscillations. A similar analysis, over the same fields of view, was performed for simultaneous 304 and 1600 Å data obtained with the Atmospheric Imaging Assembly. Results. We detected 184 3 mm transient brightening events with brightness temperatures from 70 K to more than 500 K above backgrounds of ∼7200 − 7450 K. All events showed light curves with a gradual rise and fall, strongly suggesting a thermal origin. Their mean duration and maximum area were 51.1 s and 12.3 Mm2, respectively, with a weak preference of appearing at network boundaries rather than in cell interiors. Both parameters exhibited power-law behavior with indices of 2.35 and 2.71, respectively. Only a small fraction of ALMA events had either 304 or 1600 Å counterparts but the properties of these events were not significantly different from those of the general population except that they lacked their low-end energy values. The total thermal energies of the ALMA transient brightenings were between 1.5 × 1024 and 9.9 × 1025 erg and their frequency distribution versus energy was a power law with an index of 1.67 ± 0.05. We found that the power per unit area provided by the ALMA events could account for only 1% of the chromospheric radiative losses (10% of the coronal ones). Conclusions. We were able to detect, for the first time, a significant number of weak 3 mm quiet Sun transient brightenings. However, their energy budget falls short of meeting the requirements for the heating of the upper layers of the solar atmosphere and this conclusion does not change even if we use the least restrictive criteria possible for the detection of transient brightenings.

scholarly journals Observations of the Quiet Sun with 6″ Resolution

1980 ◽  
Vol 86 ◽  
pp. 53-55
Author(s):  
M. R. Kundu ◽  
A. P. Rao ◽  
F. T. Erskine ◽  
J. D. Bregman
Keyword(s):  
High Resolution ◽  
Radio Emission ◽  
Transition Region ◽  
Spatial Resolution ◽  
Radio Telescope ◽  
Solar Radio ◽  
High Spatial Resolution ◽  
Solar Radio Emission ◽  
Quiet Sun ◽  
Millimeter Wavelengths

Solar radio emission at centimeter and millimeter wavelengths originates in the chromosphere and transition region and is a useful probe for the temperature and density in these regions. High spatial resolution observations of the quiet sun provide valuable information on the structure of the solar atmosphere. We have performed high resolution (~ 6″ (E-W) x 15″ (N-S)) observations at 6 cm with the Westerbork Synthesis Radio Telescope (WSRT) in June 1976 in order to search for the radio analog of the supergranulation network and to study the extent and symmetry of limb brightening. The use of the WSRT for high spatial resolution solar mapping has been described by Bregman and Felli (1976), Kundu et al. (1977), and others.

scholarly journals The multi-thermal chromosphere

2020 ◽  
Vol 634 ◽  
pp. A56 ◽  
Author(s):  
J. M. da Silva Santos ◽  
J. de la Cruz Rodríguez ◽  
J. Leenaarts ◽  
G. Chintzoglou ◽  
B. De Pontieu ◽  
...  
Keyword(s):  
Thermal Structure ◽  
Low Frequency ◽  
Solar Chromosphere ◽  
Quiet Sun ◽  
Average Brightness ◽  
Near Ultraviolet ◽  
Plage Region ◽  
Hydrogen Ionization ◽  
Two Parameters ◽  
Average Brightness Temperature

Context. Numerical simulations of the solar chromosphere predict a diverse thermal structure with both hot and cool regions. Observations of plage regions in particular typically feature broader and brighter chromospheric lines, which suggests that they are formed in hotter and denser conditions than in the quiet Sun, but also implies a nonthermal component whose source is unclear. Aims. We revisit the problem of the stratification of temperature and microturbulence in plage and the quiet Sun, now adding millimeter (mm) continuum observations provided by the Atacama Large Millimiter Array (ALMA) to inversions of near-ultraviolet Interface Region Imaging Spectrograph (IRIS) spectra as a powerful new diagnostic to disentangle the two parameters. We fit cool chromospheric holes and track the fast evolution of compact mm brightenings in the plage region. Methods. We use the STiC nonlocal thermodynamic equilibrium (NLTE) inversion code to simultaneously fit real ultraviolet and mm spectra in order to infer the thermodynamic parameters of the plasma. Results. We confirm the anticipated constraining potential of ALMA in NLTE inversions of the solar chromosphere. We find significant differences between the inversion results of IRIS data alone compared to the results of a combination with the mm data: the IRIS+ALMA inversions have increased contrast and temperature range, and tend to favor lower values of microturbulence (∼3−6 km s−1 in plage compared to ∼4−7 km s−1 from IRIS alone) in the chromosphere. The average brightness temperature of the plage region at 1.25 mm is 8500 K, but the ALMA maps also show much cooler (∼3000 K) and hotter (∼11 000 K) evolving features partially seen in other diagnostics. To explain the former, the inversions require the existence of localized low-temperature regions in the chromosphere where molecules such as CO could form. The hot features could sustain such high temperatures due to non-equilibrium hydrogen ionization effects in a shocked chromosphere – a scenario that is supported by low-frequency shock wave patterns found in the Mg II lines probed by IRIS.

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