Magnetic Flux Ropes in the Solar Photosphere: The Vector Magnetic Field under Active Region Filaments

Abstract

This study is an observational search for evidence of prominence-associated magnetic flux ropes at the photospheric level in plage regions away from sunspots. Although there are a few cases of supposed flux rope geometry in the photosphere of complex sunspot regions (notably δ sunspots), such cases appear to be fairly rare and therefore do not contribute significantly to the suspected emergence of magnetic helicity in active regions leading to the common eruption of coronal mass ejections. In the present study, the Advanced Stokes Polarimeter (ASP) at the Dunn Solar Telescope of the National Solar Observatory was used to measure simultaneously the evolution of the photospheric vector magnetic field and the structure of the chromosphere as seen in the Hα line. The high angular resolution of these vector field measurements coupled with the high polarimetric precision of the ASP has allowed the possible identification of flux rope (concave up) geometry in the photosphere below some narrow (and supposedly low-lying) active region filaments. Two cases of such occurrence are presented in detail. These results indicate that flux ropes may be rather common in normal (i.e., non-δ sunspot) active regions. Further observations should shed some light on origin of these flux ropes as either emerging from the solar interior or generated in the solar atmosphere as a consequence of driven magnetic footpoint motion and reconnection.