Large-scale horizontal flows in the solar photosphere

LERMA, Observatoire de Paris, Section de Meudon, 92195 Meudon, FranceReceived February 2, 2008/ SubmittedABSTRACTAims. We study the influence of large-scale photospheric motions on the destabilization of an eruptive filament, observed on Oc tober6, 7, and 8, 2004, as part of an international observing campaign (JOP 178).Methods.Large-scale horizontal flows were invetigated from a series of MDI full-disc Dopplergrams and magnetograms. From theDopplergrams, we tracked supergranular flow patterns using the local correlation tracking (LCT) technique. We used both LCT andmanual tracking of isolated magnetic elements to obtain horizontal velocities from magnetograms.Results. We find that the measured flow fields obtained by the di fferent methods are well-correlated on large scales. The topology ofthe flow field changed significantly during the filament erupti ve phase, suggesting a possible coupling between the surface flow fieldand the coronal magnetic field. We measured an increase in the shear below the point where the eruption starts and a decrease in shearafter the eruption. We find a pattern in the large-scale horizontal flows at the solar surface that interact with di fferential rotation.Conclusions. We conclude that there is probably a link between changes in surface flow and the disappearance of the eruptivefilament.Key words. The Sun: Atmosphere – The Sun: Filaments – The Sun: Magnetic fi elds