Abstract
In this paper, we investigate how photospheric material moves below a dark filament, and we study chromospheric gas motions inside the filament. In the photosphere we trace granular motions by means of a local correlation tracking (LCT) technique to derive horizontal velocity field, while inside the filament we obtain the line-of-sight velocity field by subtracting a blueshifted Hα image from a redshifted Hα image. We find that a typical value of horizontal photospheric velocity is 1 km s-1, and its divergence map maintains a large-scale pattern during several hours. We also find that photospheric motions around a filament channel are random in space and changeable in time. As for the motion inside the filament, our results show that there is an area of upward motions at one side of the filament axis and an area of downward motions at the other side, which means that filament material has a helical motion inside the filament. We think that these results provide new important information on theories of filament formation.
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