Magnetic helicity transport in corona and filament eruptions

Abstract

Using a 28-hour time series of line-of-sight magnetograms taken by the Michelson Doppler Imager (MDI), we determined the magnetic flux variations and the rate of magnetic helicity transport at the footpoints of a filament in active region NOAA 8375. The filament was characterized by a positive helicity change due to shearing motions in both footpoints and showed several partial eruptions during the observing time. In particular, we considered 4 events registered in the Hα daily reports of Solar Geophysical Data. We found a strong temporal correlation between filament eruptions and helicity transport from the photospheric magnetic structures at the filament footpoints into the corona: in at least one footpoint, all of the events were preceded by an evident increase and followed by a small decrease of the emerging magnetic flux and of the magnetic helicity change due to shearing motions. We compared these two mechanisms of helicity transport and found that the predominant role to drive filament instability is played by emergence of new magnetic flux from the convection zone.