Magnetic and velocity fields of a solar pore

¹ Astronomical Institute, Academy of Sciences of the Czech Republic (v.v.i.), Fričova 298, 25165 Ondřejov, Czech Republic
e-mail: msobotka@asu.cas.cz
² Department of Physics, University of Roma Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma, Italy

Received: 8 August 2011
Accepted: 18 November 2011

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.