Magnetic and velocity fields of a solar pore

Abstract

Context. Solar pores are intermediate-size magnetic flux features that emerge at the surface of the Sun. The absence of a filamentary penumbra indicates that there is a relatively simple magnetic structure with a prevailing vertical magnetic field. Aims. Relations between the magnetic field components, line-of-sight velocities, and horizontal motions in and around a large pore (D eff = 8. 5) are analysed to provide observational constraints on theoretical models and numerical simulations. Methods. Spectropolarimetric observations in Fe I 617.3 nm of the pore NOAA 11005 with the IBIS spectrometer attached to the Dunn Solar Telescope are inverted into series of maps of thermal, magnetic, and velocity parameters using the SIR code. Horizontal velocities are obtained from series of white-light images by means of local correlation tracking. Results. The magnetic field B extends from the visible pore border of more than 3. 5 and has a radial structure in a form of spines that are co-spatial with dark intergranular lanes. The horizontal component B hor is more extended than the vertical component B z . The temperature linearly decreases with increasing B z , by about −300 K kG −1 in the photosphere and −800 K kG −1 in the umbra. The temperature contrast of granulation increases with increasing magnetic field strength and is then suppressed for B z > 1200 G. Granular upflows dominate in regions with B z < 600-700 G. Line-of-sight velocities are lower in stronger fields, except for fast isolated downflows at the pore's border. The velocity signature of granulation is suppressed completely for B hor > 1000 G. Horizontal motions of granules start to be damped for B z > 500 G and recurrently exploding granules appear only in magnetic fields comparable to or weaker than the equipartition field strength 400 G.

Dynamics of the solar atmosphere above a pore with a light bridge

“…Concentric running waves propagate through the filamentary structure with the speed of sound and the observed characteristics of acoustic oscillations correspond to those in a superpenumbra. Although a strong horizontal magnetic field responsible for the formation of a penumbra is missing in the pore, the magnetic field of B 1500 G at the pore's border inclined by 40 • (Sobotka et al 2012) manifests itself in the middle photosphere by short bright filaments seen A84, page 12 of 14 in the Ca II line wings (Fig. 1b) and its field lines, which return to opposite-polarity patches dispersed in the photosphere around the pore, very probably form the filamentary structure with superpenumbral characteristics in the chromosphere.…”

“…Short bright filaments surround the pore's edge. These filaments are a manifestation of an inclined magnetic field that extends beyond the pore's visible boundary in the form of spines (Sobotka et al 2012).…”

“…This is caused by the more inclined magnetic field in the large eastern umbral core, which expands faster above the LB than the almost vertical magnetic field from the smaller core. In Sobotka et al (2012) we determined the magnetic-field inclination and azimuth in the LB from inversions of Stokes profiles of Fe I 617.33 nm, observed simultaneously with the Ca II line. The azimuth direction is perpendicular to the LB axis.…”

The magnetic field in the solar atmosphere

“…Much of the flux in ARs that is not in the form of sunspots is organized in magnetic concentrations (much) smaller than spots, either in the form of pores or, most commonly, magnetic elements. Magnetic pores, sunspot-like features that are characterized by the absence of a penumbra, carry fluxes of some 10 20 to 10 21 Mx (Thomas and Weiss 2004;Sobotka et al 2012). Magnetic elements within ARs carry fluxes of 10 18 to 10 20 Mx (Abramenko and Longcope 2005).…”

“…The flux in ARs that is not in the form of sunspots is concentrated in either pores or magnetic elements. The properties of pores include diameters of some Mm and field strengths of 1 to 2 kG (Thomas and Weiss 2004;Sobotka et al 2012). Magnetic elements have diameters smaller than ≈350 km and exhibit field strengths of 1 to 2 kG (Stenflo 1973;Rabin 1992;Rüedi et al 1992).…”