Spatial distribution and statistical properties of small-scale convective vortex-like motions in a quiet-Sun region

Abstract

High-resolution observations of a quiet-Sun internetwork region taken with the Solar 1-m Swedish Telescope in La Palma are analysed. We determine the location of small-scale vortex motions in the solar photospheric region by computing the horizontal proper motions of smallscale structures on time-series of images. These plasma convectively driven swirl motions are associated to (1) downdrafts (that have been commonly explained as corresponding to sites where the plasma is cooled down and hence returned to the interior below the visible photospheric level) and (2) horizontal velocity vectors converging on a central point. The sink cores are proved to be the final destination of passive floats tracing plasma flows towards the centre of each vortex. We establish the occurrence of these events to be 1.4 × 10 −3 and 1.6 × 10 −3 vortices Mm −2 min −1 , respectively, for the two time-series analysed here.

DeepVel: Deep learning for the estimation of horizontal velocities at the solar surface

“…The same behavior is seen in the vorticity, with values that also reach −0.03 s −1 at τ 500 = 1, where negative means clockwise rotation. This value of vorticity is an order of magnitude larger than that detected with LCT (Bonet et al 2010;Vargas Domínguez et al 2011;Requerey et al 2017), but comparable to that found in simulations (e.g., Kitiashvili et al 2011).…”

“…Such a cellular pattern is commonly found in both observations and hydrodynamical simulations when the LCT technique is applied to intensity images Muller et al 1992;Roudier et al 1998;Matloch et al 2010;Yelles Chaouche et al 2011;Requerey et al 2017). At the junction of mesogranular cells, smaller structures such as converging flows (Bonet et al 2010;Vargas Domínguez et al 2011;Requerey et al 2017) are also observed. The locations of the convergence centers are indicated by red circles in Figs.…”

“…Small-scale vortex flows have been first detected as swirling motions of bright points (Bonet et al 2008), and later through LCT (Bonet et al 2010;Vargas Domínguez et al 2011;Requerey et al 2017). They have a diameter of ∼1 Mm (Bonet et al 2008(Bonet et al , 2010Vargas Domínguez et al 2011), their lifetime varies from 5 to 20 min (Bonet et al 2008(Bonet et al , 2010, and they appear to be located at mesogranular junctions (Requerey et al 2017). The spatial distribution and size of such vortices is shown by red circles in Fig.…”

“…Current three-dimensional magnetohydrodynamical simulations are able to very well reproduce convection in a magnetized plasma, so one expects that the simulated velocities are a good representation of the real velocities in the Sun. These studies have revealed that granules are good tracers for large-scale persistent horizontal flows such as meso-and supergranular flows (e.g., Simon et al 1988;Muller et al 1992;De Rosa & Toomre 2004;Yelles Chaouche et al 2011;Langfellner et al 2015) or photospheric vortex flows (Brandt et al 1988;Bonet et al 2010;Vargas Domínguez et al 2011;Requerey et al 2017). The instantaneous velocity fields, which have been obtained by correlating two consecutive frames, also recover the overall morphological features of the flow, but they lack the fine structure observed in the simulated velocities (Louis et al 2015;Yelles Chaouche et al 2014).…”

Converging photospheric vortex flows close to the polarity inversion line of a fully emerged active region

“…On larger scales, rotational motions were observed in sunspots, and they are usually associated with energy and helicity buildup and later release by flare and/or coronal mass ejection (Brown et al, 2003;Hiremath and Suryanarayana, 2003;Hiremath et al, 2005;Yan and Qu, 2007;Yan et al, 2008Yan et al, , 2009Yan et al, , 2012Min and Chae, 2009;Kazachenko et al, 2010;Zhu et al, 2012;Jiang et al, 2012;Vemareddy et al, 2012Vemareddy et al, , 2016Hardersen et al, 2013;Wang et al, 2014Wang et al, , 2016Ruan et al, 2014;Gopasyuk, 2015;Li and Liu, 2015;Suryanarayana et al, 2015). The rotation of sunspots is usually very slow; this means that the evolution of the magnetic field in the corona associated with it would be slow as well.…”