Evidence of quiet-Sun chromospheric activity related to an emerging small-scale magnetic loop

Gömöry P.¹, Balthasar H.², Puschmann K.G.²

¹ Astronomical Institute of the Slovak Academy of Sciences, 05960 Tatranská Lomnica, Slovakia
² Leibniz-Institut fur Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany

Abstract:
Aims. We investigate the temporal evolution of magnetic flux emergence in the quiet-Sun atmosphere close to disk center.
Methods. We combined high-resolution SoHO/MDI magnetograms with TRACE observations taken in the 1216 A channel to analyze the temporal evolution of an emerging small-scale magnetic loop and its traces in the chromosphere.
Results. We find signatures of flux emergence very close to the edge of a supergranular network boundary located at disk center. The new emerging flux appeared first in the MDI magnetograms in form of an asymmetric bipolar element, i.e., the patch with negative polarity is roughly twice as weak as the corresponding patch with opposite polarity. The average values of magnetic flux and magnetic flux densities reached 1.6x10^18 Mx, -8.5x10^17 Mx, and 55 Mx/cm^2, -30 Mx/cm^2, respectively. The spatial distance between the opposite polarity patches of the emerged feature increased from about 2.5 arcsec to 5.0 arcsec during the lifetime of the loop, which was 36 min. A more precise lifetime-estimate of the feature was not possible because of a gap in the temporal sequence of the MDI magnetograms. The chromospheric response to the emerged magnetic dipole occurred ~9 min later than in the photospheric magnetograms. It consisted of a quasi-periodic sequence of time-localized brightenings visible in the 1216 A TRACE channel for ~14 min that were co-spatial with the axis connecting the two patches of opposite magnetic polarity.
Conclusions. We identify the observed event as a small-scale magnetic loop emerging at photospheric layers that subsequently rose to the chromosphere. We discuss the possibility that the fluctuations detected in the chromospheric emission probably reflect magneticfield oscillations which propagate to the chromosphere in the form of waves.