Opposite polarity field with convective downflow and its relation to magnetic spines in a sunspot penumbra

¹ Institute for Solar Physics, Royal Swedish Academy of Sciences, AlbaNova University Center, 10691 Stockholm, Sweden
e-mail: scharmer@astro.su.se
² Stockholm Observatory, Dept. of Astronomy, Stockholm University, AlbaNova University Center, 10691 Stockholm, Sweden
³ Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden

Received: 13 December 2012
Accepted: 6 March 2013

Abstract

We discuss NICOLE inversions of Fe i 630.15 nm and 630.25 nm Stokes spectra from a sunspot penumbra recorded with the CRISP imaging spectropolarimeter on the Swedish 1-m Solar Telescope at a spatial resolution close to 0$\stackrel{\mathrm{″}}{.}$15. We report on narrow, radially extended lanes of opposite polarity field, located at the boundaries between areas of relatively horizontal magnetic field (the intra-spines) and much more vertical field (the spines). These lanes harbor convective downflows of about 1 km s^-1. The locations of these downflows close to the spines agree with predictions from the convective gap model (the “gappy penumbra”) proposed six years ago, and more recent three-dimensional magnetohydrodynamic simulations. We also confirm the existence of strong convective flows throughout the entire penumbra, showing the expected correlation between temperature and vertical velocity, and having vertical root mean square velocities of about 1.2 km s^-1.