T. Oba

Chromospheric polarimetry through multiline observations of the 850-nm spectral region

Future solar missions and ground-based telescopes aim to understand the magnetism of the solar chromosphere. We performed a supporting study in Quintero Noda et al. focused on the infrared Ca (II) ...

Height-dependent Velocity Structure of Photospheric Convection in Granules and Intergranular Lanes with Hinode/SOT

The solar photosphere is the visible surface of the Sun, where many bright granules, surrounded by narrow dark intergranular lanes, are observed everywhere. The granular pattern is a manifestation of convective motion at the photospheric level, but its velocity structure in the height direction is poorly understood observationally. Applying bisector analysis to a photospheric spectral line recorded by the Hinode Solar Optical Telescope, we derived the velocity structure of the convective motion in granular regions and intergranular lanes separately. The amplitude of motion of the convective material decreases from 0.65 to 0.40 km s−1 as the material rises in granules, whereas the amplitude of motion increases from 0.30 to 0.50 km s−1 as it descends in intergranular lanes. These values are significantly larger than those obtained in previous studies using bisector analysis. The acceleration of descending materials with depth is not predicted from the convectively stable condition in a stratified atmosphere. Such convective instability can be developed more efficiently by radiative cooling and/or a gas pressure gradient, which can control the dynamical behavior of convective material in intergranular lanes. Our analysis demonstrated that bisector analysis is a useful method for investigating the long-term dynamic behavior of convective material when a large number of pixels is available. In addition, one example is the temporal evolution of granular fragmentation, in which downflowing material develops gradually from a higher layer downward.

Solar polarimetry through the K i lines at 770 nm

We characterize the K I D1 & D2 lines in order to determine whether they could complement the 850 nm window, containing the Ca II infrared triplet lines and several Zeeman sensitive photospheric lines, that was studied previously. We investigate the effect of partial redistribution on the intensity profiles, their sensitivity to changes in different atmospheric parameters, and the spatial distribution of Zeeman polarization signals employing a realistic magnetohydrodynamic simulation. The results show that these lines form in the upper photosphere at around 500 km and that they are sensitive to the line of sight velocity and magnetic field strength at heights where neither the photospheric lines nor the Ca II infrared lines are. However, at the same time, we found that their sensitivity to the temperature essentially comes from the photosphere. Then, we conclude that the K I lines provide a complement to the lines in the 850 nm window for the determination of atmospheric parameters in the upper photosphere, especially for the line of sight velocity and the magnetic field.

Chromospheric polarimetry through multiline observations of the 850-nm spectral region – II. A magnetic flux tube scenario

In this publication, we continue the work started in Quintero Noda et al., examining this time a numerical simulation of a magnetic flux tube concentration. Our goal is to study if the physical phe ...

Study of the polarization produced by the Zeeman effect in the solar Mg i b lines

We appreciate the help of the anonymous referee that, during the revision process, provided us comments and suggestions that allowed improving the manuscript. CQN acknowledges the support of the ISAS/JAXA International Top Young Fellowship and the JSPS KAKENHI grant number 18K13596. The SUNRISE-3 project is supported in Japan by the funding from ISAS/JAXA for the smallscale program for novel solar observations and the JSPS KAKENHI grant numbers 18H03723 and 18H05234. This research was supported by the Research Council of Norway through its Centres of Excellence scheme, project number 262622. This work has also been supported by Spanish Ministry of Economy and Competitiveness through the project ESP-2016-77548-C5-1-R. DOS also acknowledges financial support through the Ramon y Cajal fellowships.

Solar polarimetry in the K I D2 line : A novel possibility for a stratospheric balloon

C. Quintero Noda acknowledges the support of the ISAS/JAXA International Top Young Fellowship (ITYF). This work was supported by the funding for the international collaboration mission (SUNRISE-3) of ISAS/JAXA. This project has received funding from the European Research Council (ERC) under the European Unions Horizon 2020 research and innovation programme (grant agreement No. 695075) and has been supported by the BK21 plus programme through the National Research Foundation (NRF) funded by the Ministry of Education of Korea. This work has also been supported by Spanish Ministry of Economy and Competitiveness through the project ESP-2016-77548-C5-1-R.

The Small-scale Structure of Photospheric Convection Retrieved by a Deconvolution Technique Applied to Hinode/SP Data

Solar granules are bright patterns surrounded by dark channels called intergranular lanes in the solar photosphere and are a manifestation of overshooting convection. Observational studies generally find stronger upflows in granules and weaker downflows in intergranular lanes. This trend is, however, inconsistent with the results of numerical simulations in which downflows are stronger than upflows through the joint action of gravitational acceleration/deceleration and pressure gradients. One cause of this discrepancy is the image degradation caused by optical distortion and light diffraction and scattering that takes place in an imaging instrument. We apply a deconvolution technique to Hinode/SP data in an attempt to recover the original solar scene. Our results show a significant enhancement in both, the convective upflows and downflows, but particularly for the latter. After deconvolution, the up- and downflows reach maximum amplitudes of -3.0 km/s and +3.0 km/s at an average geometrical height of roughly 50 km, respectively. We found that the velocity distributions after deconvolution match those derived from numerical simulations. After deconvolution the net LOS velocity averaged over the whole FOV lies close to zero as expected in a rough sense from mass balance.