High speed magnetized flows in the quiet Sun

Abstract

Context. We analyzed spectropolarimetric data recorded with Hinode/SP in quiet-Sun regions located at the disk center. We found single-lobed Stokes V profiles showing highly blue-and red-shifted signals. Oftentimes both types of events appear to be related to each other. Aims. We aim to set constraints on the nature and physical causes of these highly Doppler-shifted signals, as well as to study their spatial distribution, spectropolarimetric properties, size, and rate of occurrence. Also, we plan to retrieve the variation of the physical parameters with optical depth through the photosphere. Methods. We have examined the spatial and polarimetric properties of these events using a variety of data from the Hinode spacecraft. We have also inferred the atmospheric stratification of the physical parameters by means of the inversion of the observed Stokes profiles employing the Stokes Inversion based on Response functions (SIR) code. Finally, we analyzed their evolution using a time series from the same instrument. Results. Blue-shifted events tend to appear over bright regions at the edge of granules, while red-shifted events are seen predominantly over dark regions on intergranular lanes. Large linear polarization signals can be seen in the region that connects them. The magnetic structure inferred from the time series revealed that the structure corresponds to a Ω-loop, with one footpoint always over the edge of a granule and the other inside an intergranular lane. The physical parameters obtained from the inversions of the observed Stokes profiles in both events show an increase with respect to the Harvard-Smithonian reference atmosphere in the temperature at log τ 500 ∈ (−1, −3) and a strong magnetic field, B ≥ 1 kG, at the bottom of the atmosphere that quickly decreases upward until vanishing at log τ 500 ≈ −2. In the blue-shifted events, the LOS velocities change from upflows at the bottom to downflows at the top of the atmosphere. Redshifted events display the opposite velocity stratification. The change of sign in LOS velocity happens at the same optical depth in which the magnetic field becomes zero. Conclusions. The physical mechanism that best explains the inferred magnetic field configuration and flow motions is a siphon flow along an arched magnetic flux tube. Further investigation is required, however, as the expected features of a siphon flow cannot be unequivocally identified.

Analysis of horizontal flows in the solar granulation

“…Therefore, as pointed out by Bellot Rubio (2009), the physical mechanism behind the satellite lobes seems to be unrelated to any magnetic field configuration. This property indicates that they cannot be associated to the events studied in (Quintero Noda et al 2014a), discarding the possibility that these horizontal flows were the connection between the opposite footpoints analysed in the cited work. We estimate the density of events taking into account how many pixels of the observed map fulfils the threshold criteria imposed, see Section 2.2.…”

“…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.…”

Analysis of spatially deconvolved polar faculae

“…We take advantage of the knowledge acquired in Quintero Noda et al (2014a) andQuintero Noda et al (2015) to determine this maximum number of nodes. We allowed seven nodes for the temperature T(τ), five for the line of sight (LOS) component of the velocity v los (τ), five for the magnetic field strength B(τ), three for the inclination of the magnetic field γ(τ), and two for the azimuthal angle of the magnetic field φ (τ).…”

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

“…These events were explained in terms of magnetic reconnection, where freshly emerged flux tubes within granules interact with pre-existing fields in intergranular areas (Borrero et al 2013;Quintero Noda et al 2013). Quintero Noda et al (2014) found that the extremely blueshifted events, observed by Hinode/SP, are often accompanied by redshifted Stokes V signals. Together, they represent footpoints of magnetic Ωloops with flows along them.…”

“…Together, they represent footpoints of magnetic Ωloops with flows along them. Quintero Noda et al (2014) argued that the siphon flow mechanism (Montesinos & Thomas 1993) was the only explanation for those flow motions along the arched magnetic flux tubes.…”