Photospheric flows around a quiescent filament

¹ Laboratoire d'Astrophysique de l'Observatoire Midi-Pyrénées, Université Paul Sabatier Toulouse III, CNRS, 57 Avenue d'Azeirex, BP 826, 65008 Tarbes Cedex, France e-mail: roudier@ast.obs-mip.fr
² LESIA, Observatoire de Paris, Section de Meudon, 92195 Meudon, France
³ LERMA, Observatoire de Paris, Section de Meudon, 92195 Meudon, France
⁴ National Solar Observatory, Sacramento Peak, Sunspot, NM 88349, USA
⁵ Sterrekundig Instituut Utrecht, Postbus 80 000, 3508 TA Utrecht, The Netherlands

Received: 27 October 2006
Accepted: 1 March 2007

Abstract

Context.The horizontal photospheric flows below and around a filament are one of the components in the formation and evolution of filaments. Few studies exist because they require multiwalength time sequences at high spatial resolution.

Aims.Our objective is to measure the horizontal photospheric flows associated with the evolution and eruption of a filament.

Methods.We present observations obtained in 2004 during the international JOP 178 campaign which involved eleven instruments both in space and at ground based observatories. We use TRACE WL, DOT and DST observation to derive flow maps which are then coaligned with intensity images and with the vector magnetic field map obtained with THEMIS/MTR.

Results.Several supergranulation cells cross the Polarity Inversion Line (PIL) and can transport magnetic flux through the PIL, in particular parasitic polarities. We present a detailed example of the formation of a secondary magnetic dip at the location of a filament footpoint. Large-scale converging flows, which could exist along the filament channel and contribute to its formation, are not observed. Before the filament's eruptive phase, we observe both parasitic and normal polarities being swept by a continuously diverging horizontal flow located in the filament gap. The disappearance of the filament initiates in this gap. Such purely horizontal motions could lead to destabilization of the filament and could trigger the sudden filament disappearance.