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Register a new userALMA and IRIS Observations of the Solar Chromosphere I: an On-Disk Type II Spicule
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Added by
Georgios Chintzoglou
Publication date
2020
fields
Physics
and research's language is
English
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We present observations of the solar chromosphere obtained simultaneously with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Interface Region Imaging Spectrograph (IRIS). The observatories targeted a chromospheric plage region of which the spatial distribution (split between strongly and weakly magnetized regions) allowed the study of linear-like structures in isolation, free of contamination from background emission. Using these observations in conjunction with a radiative magnetohydrodynamic 2.5D model covering the upper convection zone all the way to the corona that considers non-equilibrium ionization effects, we report the detection of an on-disk chromospheric spicule with ALMA and confirm its multithermal nature.
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We propose and employ a novel empirical method for determining chromospheric plage regions, which seems to better isolate plage from its surrounding regions compared to other methods commonly used. We caution that isolating plage from its immediate surroundings must be done with care in order to successfully mitigate statistical biases that, for instance, can impact quantitative comparisons between different chromospheric observables. Using this methodology, our analysis suggests that 1.25 mm wavelength free-free emission in plage regions observed with ALMA/Band6 may not form in the low chromosphere as previously thought, but rather in the upper chromospheric parts of dynamic plage features (such as spicules and other bright structures), i.e., near geometric heights of transition region temperatures. We investigate the high degree of similarity between chromospheric plage features observed in ALMA/Band6 (at 1.25 mm wavelength) and IRIS/Si IV at 1393r{A}. We also show that IRIS/Mg II h and k is not as well correlated with ALMA/Band6 as was previously thought, and we discuss the discrepancies with previous works. Lastly, we report indications for chromospheric heating due to propagating shocks supported by the ALMA/Band6 observations.
We analyze observations from the Interface Region Imaging Spectrograph of the Mg II k line, the Mg II UV subordinate lines, and the O I 135.6 nm line to better understand the solar plage chromosphere. We also make comparisons with observations from the Swedish 1 m Solar Telescope of the H{alpha} line, the Ca II 8542 line, and Solar Dynamics Observatory/Atmospheric Imaging Assembly observations of the coronal 19.3 nm line. To understand the observed Mg II profiles, we compare these observations to the results of numerical experiments. The single-peaked or flat-topped Mg II k profiles found in plage imply a transition region at a high column mass and a hot and dense chromosphere of about 6500 K. This scenario is supported by the observed large-scale correlation between moss brightness and filled-in profiles with very little or absent self-reversal. The large wing width found in plage also implies a hot and dense chromosphere with a steep chromospheric temperature rise. The absence of emission in the Mg II subordinate lines constrain the chromospheric temperature and the height of the temperature rise while the width of the O I 135.6 nm line sets a limit to the non-thermal velocities to around 7 km/s.
We present the first high-resolution Atacama Large Millimeter/Submillimeter Array (ALMA) observations of a sunspot at wavelengths of 1.3 mm and 3 mm, obtained during the solar ALMA Science Verification campaign in 2015, and compare them with the predictions of semi-empirical sunspot umbral/penumbral atmosphere models. For the first time millimeter observations of sunspots have resolved umbral/penumbral brightness structure at the chromospheric heights, where the emission at these wavelengths is formed. We find that the sunspot umbra exhibits a radically different appearance at 1.3 mm and 3 mm, whereas the penumbral brightness structure is similar at the two wavelengths. The inner part of the umbra is ~600 K brighter than the surrounding quiet Sun (QS) at 3 mm and is ~700 K cooler than the QS at 1.3 mm, being the coolest part of sunspot at this wavelength. On average, the brightness of the penumbra at 3 mm is comparable to the QS brightness, while at 1.3 mm it is ~1000 K brighter than the QS. Penumbral brightness increases towards the outer boundary in both ALMA bands. Among the tested umbral models, that of Severino et al. (1994) provides the best fit to the observational data, including both the ALMA data analyzed in this study and data from earlier works. No penumbral model amongst those considered here gives a satisfactory fit to the currently available measurements. ALMA observations at multiple mm wavelengths can be used for testing existing sunspot models, and serve as an important input to constrain new empirical models.
In this work we use solar observations with the ALMA radio telescope at the wavelength of 1.21 mm. The aim of the analysis is to improve understanding of the solar chromosphere, a dynamic layer in the solar atmosphere between the photosphere and corona. The study has an observational and a modeling part. In the observational part full-disc solar images are analyzed. Based on a modified FAL atmospheric model, radiation models for various observed solar structures are developed. Finally, the observational and modeling results are compared and discussed.
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