Colloquium on Nov. 6, 2025

Polarization in Spectral lines

Speaker: Hao Li (National Space Science Center)

Venue: SWIFAR Building 2111

Time: 16:00 PM, Thursday, Nov. 6, 2025

Abstract:

polarization of the electromagnetic radiation emerging from the solar atmosphere carries information on the physical properties of the emitting plasma, including the magnetic field. Therefore, the study of the polarized solar spectrum is key to uncovering the properties of the magnetic field, which in turn allows us to better understand the physical processes taking place in the solar atmosphere. Among the spectral lines formed in the Chromosphere, the Mg II h and k lines holds significant diagnostic potential. The Chromospheric Layer Spectropolarimeter was launched twice in 2019 and 2021, successfully acquiring spectropolarimetric observations across the Mg II h and k lines. The interpretation of these data has demonstrated the capability for inferring the magnetic field in the upper chromosphere through spectropolarimetry in these lines. In this talk, we briefly introduce the physical mechanisms behind the polarization of the Mg II h and k lines, including the joint action of the Zeeman and Hanle effects, the magneto-optical effect, partial frequency redistribution, and atomic level polarization, all of which are essential for modeling the polarization of these lines. We also provide an overview of recent progress in the interpretation of the Stokes profiles of the Mg II h and k lines.