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Register a new userStereoscopic Analysis of the 19 May 2007 Erupting Filament
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A filament eruption, accompanied by a B9.5 flare, coronal dimming and an EUV wave, was observed by the Solar TERrestrial Relations Observatory (STEREO) on 19 May 2007, beginning at about 13:00 UT. Here, we use observations from the SECCHI/EUVI telescopes and other solar observations to analyze the behavior and geometry of the filament before and during the eruption. At this time, STEREO A and B were separated by about 8.5 degrees, sufficient to determine the three-dimensional structure of the filament using stereoscopy. The filament could be followed in SECCHI/EUVI 304 A stereoscopic data from about 12 hours before to about 2 hours after the eruption, allowing us to determine the 3D trajectory of the erupting filament. From the 3D reconstructions of the filament and the chromospheric ribbons in the early stage of the eruption, simultaneous heating of both the rising filamentary material and the chromosphere directly below is observed, consistent with an eruption resulting from magnetic reconnection below the filament. Comparisons of the filament during eruption in 304 A and Halpha show that when it becomes emissive in He II, it tends to disappear in Halpha, indicating that the disappearance probably results from heating or motion, not loss, of filamentary material.
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The full 3-D vector magnetic field of a solar filament prior to eruption is presented. The filament was observed with the Facility Infrared Spectropolarimeter at the Dunn Solar Telescope in the chromospheric He i line at 10830 {AA} on May 29 and 30, 2017. We inverted the spectropolarimetric observations with the HAnle and ZEeman Light (HAZEL) code to obtain the chromospheric magnetic field. A bimodal distribution of field strength was found in or near the filament. The average field strength was 24 Gauss, but prior to the eruption we find the 90th percentile of field strength was 435 Gauss for the observations on May 29. The field inclination was about 67 degree from the solar vertical. The field azimuth made an angle of about 47 to 65 degree to the spine axis. The results suggest an inverse configuration indicative of a flux rope topology. He i intensity threads were found to be co-aligned with the magnetic field direction. The filament had a sinistral configuration as expected for the southern hemisphere. The filament was stable on May 29, 2017 and started to rise during two observations on May 30, before erupting and causing a minor coronal mass ejection. There was no obvious change of the magnetic topology during the eruption process. Such information on the magnetic topology of erupting filaments could improve the prediction of the geoeffectiveness of solar storms.
We studied the dynamics of the solar atmosphere in the region of a large quiet-Sun filament, which erupted on 21 October 2010. The filament eruption started at its northern end and disappeared from the H$alpha$ line-core filtergrams line within a few hours. The very fast motions of the northern leg were recorded in ultraviolet light by AIA. We aim to study a wide range of available datasets describing the dynamics of the solar atmosphere for five days around the filament eruption. This interval covers three days of the filament evolution, one day before the filament growth and one day after the eruption. We search for possible triggers that lead to the eruption of the filament. The surface velocity field in the region of the filament were measured by means of time-distance helioseismology and coherent structure tracking. The apparent velocities in the higher atmosphere were estimated by tracking the features in the 30.4 nm AIA observations. To capture the evolution of the magnetic field, we extrapolated the photospheric line-of-sight magnetograms and also computed the decay index of the magnetic field. We found that photospheric velocity fields showed some peculiarities. Before the filament activation, we observed a temporal increase of the converging flows towards the filaments spine. In addition, the mean squared velocity increased temporarily before the activation and peaked just before it, followed by a steep decrease. We further see an increase in the average shear of the zonal flow component in the filaments region, followed by a steep decrease. The photospheric l.o.s. magnetic field shows a persistent increase of induction eastward from the filament spine. The decay index of the magnetic field at heights around 10 Mm shows a value larger than critical at the connecting point of the northern filament end.
Using high spatial and temporal data from the New Vacuum Solar Telescope (NVST) and the Solar Dynamics Observatory (SDO), we present unambiguous observations of recurrent two-sided loop jets caused by magnetic reconnection between erupting minifilaments and nearby large filament. The observations demonstrate that three two-sided loop jets, which ejected along the large filament in opposite directions, had similar appearance and originated from the same region. We find that a minifilament erupted and drove the first jet. It reformed at the same neutral line later, and then underwent partial and total eruptions, drove the second and third jets, respectively. In the course of the jets, cool plasma was injected into the large filament. Furthermore, persistent magnetic flux cancelation occurred at the neutral line under the minifilament before its eruption and continued until the end of the observation. We infer that magnetic flux cancellation may account for building and then triggering the minifilament to erupt to produce the two-sided loop jets. This observation not only indicates that two-sided loop jets can be driven by minifilament eruptions, but also sheds new light on our understanding of the recurrent mechanism of two-sided loop jets.
Multivariate methods have been recently introduced and successfully applied for the discrimination of signal from background in the selection of genuine very-high energy gamma-ray events with the H.E.S.S. Imaging Atmospheric Cerenkov Telescope. The complementary performance of three independent reconstruction methods developed for the H.E.S.S. data analysis, namely Hillas, model and 3D-model suggests the optimization of their combination through the application of a resulting efficient multivariate estimator. In this work the boosted decision tree method is proposed leading to a significant increase in the signal over background ratio compared to the standard approaches. The improved sensitivity is also demonstrated through a comparative analysis of a set of benchmark astrophysical sources.
We present a comprehensive study of a series of recurrent jets that occurred at the periphery of the NOAA active region 12114 on 2014 July 7. These jets were found to share the same source region and exhibited rotational motions as they propagated outward. The multi-wavelength imaging observations made by the AIA and {it IRIS} telescopes reveal that some of the jets contain cool plasma only, while some others contain not only cool but also hot plasma. The Doppler velocities calculated from the {it IRIS} spectra show a continuous evolution from blue to red shifts as the jet motions change from upward to downward. Additionally, some jets exhibit opposite Doppler shifts on their both sides, indicative of rotating motions along their axes. The inclination angle and three-dimensional velocity of the largest jet were inferred from the imaging and spectroscopic observations, which show a high consistence with those derived from the stereoscopic analysis using dual-perspective observations by {it SDO}/AIA and {it STEREO}-B/EUVI. By relating the jets to the local UV/EUV and full-disk {it GOES} X-ray emission enhancements, we found that the previous five small-scale jets were triggered by five bright points while the last/largest one was triggered by a C1.6 solar flare. Together with a number of type III radio bursts generated during the jet eruptions as well as a weak CME that was observed in association with the last jet, our observations provide evidences in support of multi-scale magnetic reconnection processes being responsible for the production of jet events.
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