Some issues in diagnostics of solar chromospheric magnetic fields with the Mg b_2 line

Up to now, exact measurements of chromospheric magnetic fields have not been as successful as those done in the photosphere. We are currently engaging in diagnostics of chromospheric magnetic fields with the Mg b2 line by employing the Multi-Channel Solar Telescope at Huairou Solar Observing Station. Therefore, how to improve accuracy in the measurement is the main issue of our present study. To this end, we first study linear calibration coefficients for longitudinal and transverse components of chromospheric fields, which vary with wavelength, in the case of a weak field assumption. Then the polarization crosstalk introduced by instruments is analyzed in detail with two numerical simulation methods. Comparisons of the po- larization signals between cases with and without correction are presented. The result indicates that polarization accuracy is greatly improved after crosstalk correction.

Advanced Space-based Solar Observatory(ASO-S):an overview

The Advanced Space-based Solar Observatory(ASO-S)is a mission proposed for the 25 th solar maximum by the Chinese solar community.The scientific objectives are to study the relationships between the solar magnetic field,solar flares and coronal mass ejections(CMEs).Three payloads are deployed:the Full-disk vector Magneto Graph(FMG),the Lyman-αSolar Telescope(LST)and the Hard X-ray Imager(HXI).ASO-S will perform the first simultaneous observations of the photospheric vector magnetic field,non-thermal imaging of solar flares,and the initiation and early propagation of CMEs on a single platform.ASO-S is scheduled to be launched into a 720 km Sun-synchronous orbit in 2022.This paper presents an overview of the mission till the end of Phase-B and the beginning of Phase-C.

Data reduction and calibration of the FMG onboard ASO-S

The Full-disk vector Magneto Graph(FMG)instrument will carry out polarization observations at one wavelength position of the Fe I 5324.179?spectral line.This paper describes how to choose this single wavelength position,the relevant data-processing and the magnetic field calibrations based on the measured polarization signals at one single wavelength position.It is found that solar radial Doppler velocity,which can cause the spectral line to shift,is a disadvantageous factor for the linear calibration at one wavelength position.Observations at two symmetric wavelength positions may significantly reduce the wavelength shift effect(~75%),but simulations show that such polarization signals located at the solar limbs(e.g.,beyond the longitude range of±30°)are not free from the effect completely.In future work,we plan to apply machine learning techniques to calibrate vector magnetic fields,or employ full Stokes parameter profile inversion techniques to obtain accurate vector magnetic fields,in order to complement the linear calibration at the single wavelength position.

The Science Operations and Data Center (SODC) of the ASO-S mission

A ground data analysis center is very important to the success of a mission.We introduce the Science Operations and Data Center(SODC)for the ASO-S mission,which consists of a scientific operation subcenter,a data management subcenter,a data analysis subcenter and a user service subcenter.The mission planning process,instrument observation modes and the data volume are presented.We describe the data flow and processing procedures from spacecraft telemetry to high-level science data,and the long-term archival as well.The data policy and distributions are also briefly introduced.

Solar Magnetism and the Activity Telescope at HSOS

A new solar telescope system is described, which has been operating at Huairou Solar Observing Station （HSOS）, National Astronomical Observatories, Chinese Academy of Sciences （CAS）, since the end of 2005. This instrument, the Solar Magnetism and Activity Telescope （SMAT）, comprises two telescopes which respectively make measurements of full solar disk vector magnetic field and Ha observation. The core of the full solar disk video vector magnetograph is a birefringent filter with 0.1A bandpass, installed in the tele-centric optical system of the telescope. We present some preliminary observational results of the full solar disk vector magnetograms and Ha filtergrams obtained with this telescope system.

Magneto-acoustic waves in magnetic twisted flux tubes

At present,many works about MHD wave diagnostics in magnetic flux tubes are based on some pioneering works not considering the contributions of magnetic twist.Other works considered the effect on MHD waves,but the dispersion relationship they presented only gave the wave modes of m=0,1,2...The kink mode of m=−1 was absent.Therefore,in this work we present a complete dispersion relationship that includes both magnetic twist and the wave mode of m=−1.Analogous to the m=+1 wave mode,the mode of m=−1 also exhibits the mode change at finite kr0,from body to surface mode.The phase speeds of this mode are usually less than those of m=+1 mode.The harmonic curves of m=±1 modes in dispersion relationship diagrams are approximately symmetric in respect to a characteristic velocity,e.g.the tube velocity in flux tubes.Based on the present dispersion relationship,we revisit the issue of spiral wave patterns in sunspots and find that the magnetic twist has no great influence on their morphology in the frame of linear perturbation analysis.

Automatic detection and correction algorithms for magnetic saturation in the SMFT/HSOS longitudinal magnetograms

A longitudinal magnetic field often suffers the saturation effect in a strong magnetic field region when the measurement is performed at a single-wavelength point and linear calibration is adopted.In this study,we develop a method that can judge the threshold of saturation in Stokes V/I observed by the Solar Magnetic Field Telescope(SMFT)and correct it automatically.The procedure is to first perform the second-order polynomial fit to the Stokes V/I vs.I/I_(m)(I_(m) is the maximum value of Stokes I)curve to estimate the threshold of saturation,then reconstruct Stokes V/I in a strong field region to correct for saturation.The algorithm is demonstrated to be effective by comparing with the magnetograms obtained by the Helioseismic and Magnetic Imager(HMI).The accuracy rate of detection and correction for saturation is~99.4%and~88%respectively among 175 active regions.The advantages and disadvantages of the algorithm are discussed.

Statistical analysis of dynamic fibrils observed from NST/BBSO observations

We present the results obtained from the analysis of dynamic fibrils in NOAA active region （AR） 12132, using high resolution Ha observations from the New Solar Telescope operating at Big Bear Solar Observatory. The dynamic fibrils are seen to be moving up and down, and most of these dynamic fibrils are periodic and have a jet-like appearance. We found from our observations that the fibrils follow almost perfect parabolic paths in many cases. A statistical analysis on the properties of the parabolic paths showing an analysis on deceleration, maximum velocity, duration and kinetic energy of these fibrils is presented here. We found the average maximum velocity to be around 15 km s-1 and mean deceleration to be around 100 m s-2. The observed deceleration appears to be a fraction of gravity of the Sun and is not compatible with the path of ballistic motion due to gravity of the Sun. We found a positive correlation between deceleration and maximum velocity. This correlation is consistent with simulations done earlier on magnetoacoustic shock waves propagating upward.