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

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 Charles University in Prague, Faculty of Mathematics and Physics, Astronomical Institute, V Holešovičkách 2, 18000 Praha 8, Czech Republic
³ Department of Physics, University of Roma Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma, Italy

Received: 26 June 2013
Accepted: 30 September 2013

Abstract

Context. Solar pores are small sunspots lacking a penumbra that have a prevailing vertical magnetic-field component. They can include light bridges at places with locally reduced magnetic field. Like sunspots, they exhibit a wide range of oscillatory phenomena.

Aims. A large isolated pore with a light bridge (NOAA 11005) is studied to obtain characteristics of a chromospheric filamentary structure around the pore, to analyse oscillations and waves in and around the pore, and to understand the structure and brightness of the light bridge.

Methods. Spectral imaging observations in the line Ca II 854.2 nm and complementary spectropolarimetry in Fe I lines, obtained with the DST/IBIS spectrometer and HINODE/SOT spectropolarimeter, were used to measure photospheric and chromospheric velocity fields, oscillations, waves, the magnetic field in the photosphere, and acoustic energy flux and radiative losses in the chromosphere.

Results. The chromospheric filamentary structure around the pore has all important characteristics of a superpenumbra: it shows an inverse Evershed effect and running waves, and has a similar morphology and oscillation character. The granular structure of the light bridge in the upper photosphere can be explained by radiative heating. Acoustic waves leaking up from the photosphere along the inclined magnetic field in the light bridge transfer enough energy flux to balance the entire radiative losses of the light-bridge chromosphere.

Conclusions. A penumbra is not a necessary condition for the formation of a superpenumbra. The light bridge is heated by radiation in the photosphere and by acoustic waves in the chromosphere.