Magnetic Upflow Events in the Quiet-Sun Photosphere. I. Observations

Abstract

Rapid magnetic upflows in the quiet-Sun photosphere were recently uncovered from both SUNRISE/IMaX and Hinode/SOT observations. Here, we study magnetic upflow events (MUEs) from high-quality, high-(spatial, temporal, and spectral) resolution, and full Stokes observations in four photospheric magnetically sensitive Fe I lines centered at 5250.21, 6173.34, 6301.51, and 6302.50 Å acquired with the Swedish Solar Telescope (SST)/ CRISP. We detect MUEs by subtracting in-line Stokes V signals from those in the far blue wing whose signal-tonoise ratio (S/N) 7 . We find a larger number of MUEs at any given time (2.0 10 2 arcsec −2), larger by one to two orders of magnitude, than previously reported. The MUEs appear to fall into four classes presenting different shapes of Stokes V profiles with (I) asymmetric double lobes, (II) single lobes, (III) double-humped (two samepolarity lobes), and (IV) three lobes (an extra blueshifted bump in addition to double lobes), of which less than half are single-lobed. We also find that MUEs are almost equally distributed in network and internetwork areas and they appear in the interior or at the edge of granules in both regions. Distributions of physical properties, except for horizontal velocity, of the MUEs (namely, Stokes V signal, size, line-of-sight velocity, and lifetime) are almost identical for the different spectral lines in our data. A bisector analysis of our spectrally resolved observations shows that these events host modest upflows and do not show a direct indication of the presence of supersonic upflows reported earlier. Our findings reveal that the numbers, types (classes), and properties determined for MUEs can strongly depend on the detection techniques used and the properties of the employed data, namely, S/Ns, resolutions, and wavelengths.

Linear Polarization Features in the Quiet-Sun Photosphere: Structure and Dynamics

“…To detect LPFs in the differently treated LP maps, we employ an algorithm developed by Jafarzadeh, Rouppe van der Voort, and de la Cruz Rodríguez ( 2015 ). In detection procedure, the LP signal in a given LP map is cut at a certain signal threshold, which is defined as a factor of noise level (see Figure 2 ).…”

Analysis of horizontal flows in the solar granulation

“…These high speed velocities are usually translated into characteristic spectral features. From highly dopplershifted circular polarization signals with complex profile shapes as single-lobed (Borrero et al 2010;Quintero Noda et al 2014a;Jafarzadeh et al 2015) or multi-lobed profiles (Shimizu et al 2008a;Quintero Noda et al 2014b) to secondary satellite lobes in the intensity profiles (Bellot Rubio 2009). The reason behind this high speed plasma is still under debate and it seems that there is not a single answer.…”

On the effect of oscillatory phenomena on Stokes inversion results

“…To that end, we took the simulations of Vigeesh et al [49] and we used the NICOLE [23] code to synthesize the emergent Stokes profiles for both the moderate field and strong field simulations for the Fe ɪ 6301 Å and 6302 Å line pair. We chose these lines as they are commonly used lines in spectropolarimetric observations of small-scale magnetic fields [30,32,37,62,63]. Also, it has been noted that inverting multiple lines in tandem, may improve the resulting outputs [4,64], therefore, we wished to match as close as possible expected observation regimes for these facilities.…”