We present a study on the evolution of the small scale velocity field in a solar filament as it approaches to the eruption .
The observation was carried out by the Solar Dynamics Doppler Imager ( SDDI ) that was newly installed on the Solar Magnetic Activity Research Telescope ( SMART ) at Hida Observatory .
The SDDI obtains a narrow-band full disk image of the sun at 73 channels from H \alpha - 9.0 Å to H \alpha + 9.0 Å , allowing us to study the line-of-sight ( LOS ) velocity of the filament before and during the eruption .
The observed filament is a quiescent filament that erupted on 2016 November 5 .
We derived the LOS velocity at each pixel in the filament using the Becker ’ s cloud model , and made the histograms of the LOS velocity at each time .
The standard deviation of the LOS velocity distribution can be regarded as a measure for the amplitude of the small scale motion in the filament .
We found that the standard deviation on the previous day of the eruption was mostly constant around 2–3 km s ^ { -1 } , and it slightly increased to 3–4 km s ^ { -1 } on the day of the eruption .
It shows further increase with a rate of 1.1 m s ^ { -2 } about three hours before eruption and again with a rate of 2.8 m s ^ { -2 } about an hour before eruption .
From this result we suggest the increase in the amplitude of the small scale motions in a filament can be regarded as a precursor of the eruption .