Characterization and formation of on-disk spicules in the Ca II K and Mg II k spectral lines

We characterize, for the first time, type-II spicules in Ca II K 3934 Å using the CHROMIS instrument at the Swedish 1 m Solar Telescope. We find that their line formation is dominated by opacity shifts with the K3 minimum best representing the velocity of the spicules. The K2 features are either suppressed by the Doppler-shifted K3 or enhanced via increased contribution from the lower layers, leading to strongly enhanced but unshifted K2 peaks, with widening towards the line core as consistent with upper-layer opacity removal via Doppler-shift. We identify spicule spectra in concurrent IRIS Mg II k 2796Å observations with very similar properties. Using our interpretation of spicule chromospheric line formation, we produce synthetic profiles that match observations.

Chromospheric condensations and magnetic field in a C3.6-class flare studied via He I D3 spectro-polarimetry

Context. Magnetic reconnection during flares takes place in the corona, but a substantial part of flare energy is deposited in the chromosphere. However, high-resolution spectro-polarimetric chromospheric observations of flares are very rare. The most used observables are Ca II 8542 Å and He I 10830 Å. Aims. We aim to study the chromosphere during a C3.6 class flare via spectro-polarimetric observations of the He I D3 line. Methods. We present the first SST/CRISP spectro-polarimetric observations of He I D3. We analyzed the data using the inversion code HAZEL, and estimate the line-of-sight velocity and the magnetic field vector. Results. Strong He I D3 emission at the flare footpoints, as well as strong He I D3 absorption profiles tracing the flaring loops are observed during the flare. The He I D3 traveling emission kernels at the flare footpoints exhibit strong chromospheric condensations of up to ∼60 km s−1 at their leading edge. Our observations suggest that such condensations result in shocking the deep chromosphere, causing broad and modestly blueshifted He I D3 profiles indicating subsequent upflows. A strong and rather vertical magnetic field of up to ∼2500 G is measured in the flare footpoints, confirming that the He I D3 line is likely formed in the deep chromosphere at those locations. We provide chromospheric line-of-sight velocity and magnetic field maps obtained via He I D3 inversions. We propose a fan-spine configuration as the flare magnetic field topology. Conclusions. The He I D3 line is an excellent diagnostic to study the chromosphere during flares. The impact of strong condensations on the deep chromosphere has been observed. Detailed maps of the flare dynamics and the magnetic field are obtained.

Comparing the main oscillation characteristics in the solar chromosphere and magnetosphere based on studies made in ISTP SB RAS

The aim of this paper is to structure and extend the knowledge of solar chromospheric sources of oscillations in the solar wind and their relationships with pulsations registered in the magnetosphere. We compare the oscillation spectra that we observe using instruments of the Institute of Solar-Terrestrial Physics in different chromospheric structures with those observed in the solar wind and magnetosphere. We explore the possibility that the observed periodic variations of the chromospheric line widths can be interpreted as torsional Alfvén wave manifestation—this mode can propagate long distances without dissipating in the interplanetary space; it can penetrate into Earth’s magnetosphere directly or due to processes occurring at the plasmapause. We emphasize the similarities in the oscillation characteristics observed in different media, the similarities in the parameters of the media themselves and the processes developing in them. We believe that similar approaches can be applied to studying these media.

Comparing the main oscillation characteristics in the solar chromosphere and magnetosphere based on studies made in ISTP SB RAS

The aim of this paper is to structure and extend the knowledge of solar chromospheric sources of oscillations in the solar wind and their relationships with pulsations registered in the magnetosphere. We compare the oscillation spectra that we observe using instruments of the Institute of Solar-Terrestrial Physics in different chromospheric structures with those observed in the solar wind and magnetosphere. We explore the possibility that the observed periodic variations of the chromospheric line widths can be interpreted as torsional Alfvén wave manifestation—this mode can propagate long distances without dissipating in the interplanetary space; it can penetrate into Earth’s magnetosphere directly or due to processes occurring at the plasmapause. We emphasize the similarities in the oscillation characteristics observed in different media, the similarities in the parameters of the media themselves and the processes developing in them. We believe that similar approaches can be applied to studying these media.

Modeling the center-to-limb variation of the Ca i 4227 Å line using FCHHT models

The Ca i 4227 Å is a chromospheric line exhibiting the largest degree of linear polarization near the limb, in the visible spectrum of the Sun. Modeling the observations of the center-to-limb variations (CLV) of different lines in the Second Solar Spectrum helps to sample the height dependence of the magnetic field, as the observations made at different lines of sight sample different heights in the solar atmosphere. Supriya et al. (2014) attempted to simultaneously model the CLV of the (I, Q/I) spectra of the Ca i 4227 Å line using the standard 1-D FAL model atmospheres. They found that the standard FAL model atmospheres and also any appropriate combination of them, fail to simultaneously fit the observed Stokes (I, Q/I) profiles at all the limb distances (μ) satisfying at the same time all the observational constraints. This failure of 1-D modeling approach can probably be overcome by using multi-dimensional modeling which is computationally expensive. To eliminate an even wider choice of 1-D models, we attempt here to simultaneously model the CLV of the (I, Q/I) spectra using the FCHHT solar model atmospheres which are updated and recent versions of the FAL models. The details of our modeling efforts and the results are presented.

Isolated Sunspot with a Dark Patch in the Coronal Emission

On the base of the 17 GHz radio maps of the Sun taken with the Nobeyama Radio Heliograph we estimate plasma parameters in the specific region of the sunspot atmosphere in the active region AR 11312. This region of the sunspot atmosphere is characterized by the depletion in coronal emission (soft X-ray and EUV lines) and the reduced absorption in the a chromospheric line (He I 1.083 μm). In the ordinary normal mode of 17 GHz emission the corresponding dark patch has the largest visibility near the central solar meridian. We infer that the reduced coronal plasma density of about ~ 5 × 10