||Comparison of Scattering Polarization Signals Observed by CLASP: Possible Indication of the
||526, Solar Polarization Workshop 8
||Ishikawa, R.; Trujillo Bueno, J.; Uitenbroek, H.; Kubo, M.; Tsuneta, S.; Goto, M.; Kano, R.; Narukage, N.; Bando, T.; Katsukawa, Y.; Ishikawa, S.; Giono, G.; Suematsu, Y.; Hara, H.; Winebarger, A.; Kobayashi, K.; Cirtain, J.; Champey, P.; Auchère, F.; Štěpán, J.; Belluzzi, L.; Asensio Ramos, A.; Manso Sainz, R.; De Pontieu, B.; Ichimoto, K.; Carlsson, M.; Casini, R.
||The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP; Kano et al. 2012; Kobayashi et al. 2012; Kubo et al. 2014)
observed, for the first time, the linear polarization produced by
scattering processes in the hydrogen Lyman-α (121.57 nm) and
Si III (120.56 nm) lines of the solar disk radiation.
The complexity of the observed scattering polarization
(i.e., conspicuous spatial variations in Q/I and U/I at
spatial scales of 10″–20″ and the absence of center-to-
limb variation at the Lyman-α center; see Kano et al. 2017)
motivated us to search for possible hints of the operation of the Hanle
effect by comparing: (a) the Lyman-α line center signal, for which
the critical field strength (BH) for the onset of the Hanle effect is
53 G, (b) the Lyman-α wing, which is insensitive to the Hanle
effect, and (c) the Si III line, whose BH = 290 G.
We focus on four regions with different total unsigned
photospheric magnetic fluxes (estimated from SDO/HMI observations),
and compare the corresponding U/I spatial variations in the
Lyman-α wing, Lyman-α center, and Si III line.
The U/I signal in the Lyman-α wing shows an antisymmetric spatial
distribution, which is caused by the presence of a bright structure in
all the selected regions, regardless of the total unsigned photospheric
In an internetwork region, the Lyman-α center shows an antisymmetric
spatial variation across the selected bright structure, but it does not
show it in other more magnetized regions.
In the Si III line, the spatial variation of U/I deviates from the
above-mentioned antisymmetric shape as the total unsigned photospheric
magnetic flux increases.
We argue that a plausible explanation of this differential behavior is
the operation of the Hanle effect.
This work, presented in an oral contribution at this Workshop, has been
published on The Astrophysical Journal (Ishikawa et al. 2017).