اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدSmall-scale motions in solar filaments as the precursors of eruptions
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Filaments, the dense cooler plasma floating in the solar corona supported by magnetic fields, generally exhibit certain activations before they erupt. In our previous study (Seki et al. 2017 ), we observed that the standard deviation of the line-of-sight (LOS) velocities of the small-scale motions in a filament increased prior to its eruption. However, because that study only analyzed one event, it is unclear whether such an increase in the standard deviation of LOS velocities is common in filament eruptions. In this study, 12 filaments that vanished in H{alpha} line center images were analyzed in a manner similar to the one in our previous work; these included two quiescent filaments, four active region filaments, and six intermediate filaments. We verified that in all the 12 events, the standard deviation of the LOS velocities increased before the filaments vanished. Moreover, we observed that the quiescent filaments had approximately 10 times longer duration of an increase in the standard deviation than the other types of filaments. We concluded that the standard deviation of the LOS velocities of the small-scale motions in a filament can potentially be used as the precursor of a filament eruption.
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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 Act
ivity 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 AA to H$alpha$ + 9.0 AA, 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 Beckers 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.
A filament, a dense cool plasma supported by the magnetic fields in the solar corona, often becomes unstable and erupts. It is empirically known that the filament often demonstrates some activations such as a turbulent motion prior to eruption. In ou
r previous study (Seki et al. 2017), we analysed the Doppler velocity of an H{alpha} filament and found that the standard deviation of the line-of-sight-velocity (LOSV) distribution in a filament, which indicates the increasing amplitude of the small-scale motions, increased prior to the onset of the eruption. Here, we present a further analysis on this filament eruption, which initiated approximately at 03:40UT on 2016 November 5 in the vicinity of NOAA AR 12605. It includes a coronal line observation and the extrapolation of the surrounding magnetic fields. We found that both the spatially averaged micro-turbulence inside the filament and the nearby coronal line emission increased 6 and 10 hours prior to eruption, respectively. In this event, we did not find any significant changes in the global potential-field configuration preceding the eruption for the past 2 days, which indicates that there is a case in which it is difficult to predict the eruption only by tracking the extrapolated global magnetic fields. In terms of space weather prediction, our result on the turbulent motions in a filament could be used as the useful precursor of a filament eruption.
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