Imaging and Spectroscopic Observations of a Filament Channel and the Implications for the Nature of Counter-streamings

The dynamics of a filament channel are observed with imaging and spectroscopic telescopes before and during the filament eruption on 2011 January 29. The extreme ultraviolet (EUV) spectral observations reveal that there is no EUV counterparts of the H$\alpha$ counter-streamings in the filament channel, implying that the ubiquitous H$\alpha$ counter-streamings found by previous research are mainly due to longitudinal oscillations of filament threads, which are not in phase between each other. However, there exist larger-scale patchy counter-streamings in EUV along the filament channel from one polarity to the other, implying that there is another component of uni-directional flow (in the range of $\pm$10 km s$^{-1}$) inside each filament thread in addition to the implied longitudinal oscillation. Our results suggest that the flow direction of the larger-scale patchy counter-streaming plasma in the EUV is related to the intensity of the plage or active network, with the upflows being located at brighter areas of the plage and downflows at the weaker areas. Besides, we propose a new method to determine the chirality of an erupting filament based on the skewness of the conjugate filament drainage sites. It suggests that the right-skewed drainage corresponds to sinistral chirality, whereas the left-skewed drainage corresponds to dextral chirality.
Comment: 17 pages, 10 figures, published in ApJ, title changed slightly from previous version