Spectropolarimetry of an active region at the photosphere and chromosphere

Abstract

Initial results on the simultaneous spectropolarimetric observations of an active region at the photosphere and chromosphere are presented. For this purpose, the Fe I line at λ6569 and the H I at λ6563 (Hα) are used. Stratification of the line-of-sight (LOS) velocity and magnetic fields above an active region are discussed. The LOS magnetic field strengths are derived using the center-of-gravity (COG) method and the LOS velocity gradients are derived using the bisector technique. From this analysis it is found that both the velocity and magnetic gradients are larger in the umbral region above the sunspot compared to the penumbral region. And the magnetic field strength decreases much faster with height in the umbral region compared to the penumbral region. Upflows with larger LOS velocity gradients are located in the regions where stronger photospheric fields are observed.