Chromospheric Magnetic Field Measurements in a Flare and an Active Region Filament.

Intensity ( I) and circular polarization ( V) spectra using the 854.2 nm line of Ca ii with 3.65 pm spectral and 1 arcsecond spatial sampling were obtained with the SOLIS vector spectromagnetograph on 8 November 2011. An active region filament showing Doppler shifts as large as 50 km s and an unrelated C1.8 flare were observed. Line-of-sight flux density estimates of the magnetic field (B) were mapped as a function of wavelength in both of these features using the weak-field Zeeman-splitting approximation that V∝d I/d λ. The filament had a large amount of structure in intensity and velocity but remarkably little B structure, which varied smoothly from 35 to 55 G (gauss). Two flare emission kernels showed average B values of 415 and − 215 G, about 84 % of the underlying photospheric fields. Counter to this modest strength decrease with increasing height, in nearly all parts of the brighter flare kernel there appears to be a substantial gradient of B over the heights corresponding to the core of the 854.2 nm line. This variation, if verified, may be related to compression of the chromosphere associated with flare-induced evaporation. Alternatively, it might be a spurious result if the profile of the line core is narrowed in the magnetic part of the flare kernel. The results presented here are generally similar to previous, rather sparse observations. Observations of the type reported here are made daily and could be used to greatly increase knowledge about the chromospheric magnetic field in active solar features. [ABSTRACT FROM AUTHOR]