Context. Broad-band images of the solar chromosphere in the Ca ii H&K line cores around active regions are covered with fine bright elongated structures called bright fibrils. The mechanisms that form these structures and cause them to appear bright are still unknown. Aims. We aim to investigate the physical properties, such as temperature, line-of-sight velocity, and microturbulence, in the atmosphere that produces bright fibrils and to compare those to the properties of their surrounding atmosphere. Methods. We used simultaneous observations of a plage region in Fe i 6301-2 Å, Ca ii 8542 Å, Ca ii K, and Hα acquired by the CRISP and CHROMIS instruments on the Swedish 1-m Solar Telescope. We manually selected a sample of 282 Ca ii K bright fibrils. We compared the appearance of the fibrils in our sample to the Ca ii 8542 Å and Hα data. We performed non-local thermodynamic equilibrium (non-LTE) inversions using the inversion code STiC on the Fe i 6301-2 Å, Ca ii 8542 Å, and Ca ii K lines to infer the physical properties of the atmosphere. Results. The line profiles in bright fibrils have a higher intensity in their K 2 peaks compared to profiles formed in the surrounding atmosphere. The inversion results show that the atmosphere in fibrils is on average 100−200 K hotter at an optical depth log(τ 500 nm ) = −4.3 compared to their surroundings. The line-of-sight velocity at chromospheric heights in the fibrils does not show any preference towards upflows or downflows. The microturbulence in the fibrils is on average 0.5 km s −1 higher compared to their surroundings. Our results suggest that the fibrils have a limited extent in height, and they should be viewed as hot threads pervading the chromosphere.

We present detailed characteristics of linear polarization features (LPFs) in the quiet-Sun photosphere from high-resolution observations obtained with Sunrise/IMaX. We explore differently treated data with various noise levels in linear polarization signals, from which structure and dynamics of the LPFs are studied. Physical properties of the detected LPFs are also obtained from the results of Stokes inversions. The number of LPFs and their sizes and polarization signals are found to be strongly dependent on the noise level and on the spatial resolution. While the linear polarization with a signal-to-noise ratio covers about 26% of the entire area in the least noisy data in our study (with a noise level of in the unit of Stokes continuum), the detected (spatially resolved) LPFs cover about 10% of the area at any given time, with an occurrence rate on the order of  arcsec−2. The LPFs were found to be short lived (in the range of 30 – 300 s), relatively small structures (radii of  – 1.5 arcsec), highly inclined, posing hG fields, and they move with an average horizontal speed of 1.2 km s−1. The LPFs were observed (almost) equally on both upflow and downflow regions, with an intensity contrast always larger than that of the average quiet Sun.