Observational evidence supporting cross-field diffusion of neutral material in solar filaments

We investigate the temporal and spatial variation of the relative abundance of He to H in a sample of solar filaments by comparing cotemporal observations of Hα and He I λ10830 obtained at MLSO. Motivated by indications that cross-field diffusion of neutral filament material is an important mechanism in mass loss, the present study offers results that provide a convincing test of the mechanisms proposed in Gilbert and coworkers. Specifically, when observed across an entire disk passage, we find a majority of stable, quiescent filaments show a relative helium deficit in the upper portions of their structure coupled with a relative helium surplus in the lower regions, a consequence of the large loss timescale for neutral helium compared to neutral hydrogen. Moreover, we find that the variation of the relative He/H ratio is uniform across filament barbs and footpoints on both short and long timescales.