arXiv subjects

Yuanyong Deng

Publications and source records attributed to Yuanyong Deng.

43 records · Page 3Linked to original sources

arXiv2018

Signatures of magnetic reconnection at the footpoints of fan shape jets on a light bridge driven by photospheric convective motions

Dynamical jets are generally found on Light bridges (LBs), which are key to studying sunspots decays. So far, their formation mechanism is not fully understood. In this paper, we used state-of-the-art observations from the Goode Solar Telescope, the Interface Region Imaging Spectrograph, the Spectro-Polarimeter on board Hinode and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory to analyze the fan shape jets on LBs in detail. Continuous upward motion of the jets in ascending phase is found from the H$α$ velocity, which lasts for 12 minutes and is associated with the H$α$ line wing enhancements. Two mini jets appear upon the bright fronts of the fan shape jets visible in the AIA 171 Å and 193 Å channels, with a time interval as short as 1 minute. Two kinds of small scale convective motions are identified in the photospheric images, along with the H$α$ line wing enhancements. One seems to be associated with the formation of a new convection cell and the other manifests as the motion of a dark lane passing through the convection cell. The finding of three lobes Stokes V profiles and their inversion with NICOLE code indicates that there is magnetic field lines with opposite polarities in LBs. From the H$α$ -0.8 Å images, we found ribbon like brightenings propagating along the LBs, possibly indicating slipping reconnection. Our observation supports that the fan shape jets under study are caused by the magnetic reconnection and photospheric convective motions play an important role in triggering the magnetic reconnection.

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arXiv2018

Observing Kelvin-Helmholtz instability in solar blowout jet

Kelvin-Helmholtz instability (KHI) is a basic physical process in fluids and magnetized plasmas, with applications successfully modelling e.g. exponentially growing instabilities observed at magnetospheric and heliospheric boundaries, in the solar or Earth's atmosphere and within astrophysical jets. Here, we report the discovery of the KHI in solar blowout jets and analyse the detailed evolution by employing high-resolution data from the Interface Region Imaging Spectrograph (IRIS) satellite launched in 2013. The particular jet we focus on is rooted in the surrounding penumbra of the main negative polarity sunspot of Active Region 12365, where the main body of the jet is a super-penumbral structure. At its maximum, the jet has a length of 90 Mm, a width of 19.7 Mm, and its density is about 40 times higher than its surroundings. During the evolution of the jet, a cavity appears near the base of the jet, and bi-directional flows originated from the top and bottom of the cavity start to develop, indicating that magnetic reconnection takes place around the cavity. Two upward flows pass along the left boundary of the jet successively. Next, KHI develops due to a strong velocity shear (~ 204 km s$^{-1}$) between these two flows, and subsequently the smooth left boundary exhibits a sawtooth pattern, evidencing the onset of the instability.

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arXiv2017

Observations of Running Penumbral Waves emerging in a Sunspot

We present results from the investigation of 5-min umbral oscillations in a single-polarity sunspot of active region NOAA 12132. The spectra of TiO, H$α$, and 304 Å are used for corresponding atmospheric heights from the photosphere to lower corona. Power spectrum analysis at the formation height of H$α$ - 0.6 Å to H$α$ center resulted in the detection of 5-min oscillation signals in intensity interpreted as running waves outside the umbral center, mostly with vertical magnetic field inclination $>15°$. A phase-speed filter is used to extract the running wave signals with speed $v_{ph}> 4$ km s$^{-1}$, from the time series of H$α$ - 0.4 Å images, and found twenty-four 3-min umbral oscillatory events in a duration of one hour. Interestingly, the initial emergence of the 3-min umbral oscillatory events are noticed closer to or at umbral boundaries. These 3-min umbral oscillatory events are observed for the first time as propagating from a fraction of preceding Running Penumbral Waves (RPWs). These fractional wavefronts rapidly separates from RPWs and move towards umbral center, wherein they expand radially outwards suggesting the beginning of a new umbral oscillatory event. We found that most of these umbral oscillatory events develop further into RPWs. We speculate that the waveguides of running waves are twisted in spiral structures and hence the wavefronts are first seen at high latitudes of umbral boundaries and later at lower latitudes of the umbral center.

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arXiv2017

A Complex Solar Coronal Jet with Two Phases

Jets often occur repeatedly from almost the same location. In this paper, a complex solar jet was observed with two phases to the west of NOAA AR 11513 on July 2nd, 2012. If it had been observed at only moderate resolution, the two phases and their points of origin would have been regarded as identical. However, at high resolution we find the two phases merge into one another and the accompanying footpoint brightenings occur at different locations. The phases originate from different magnetic patches rather than being one phase originating from the same patch. Photospheric line of sight (LOS) magnetograms show that the bases of the two phases lie in two different patches of magnetic flux which decrease in size during the occurrence of the two phases. Based on these observations, we suggest the driving mechanism of the two successive phases is magnetic cancellation of two separate magnetic fragments with an opposite polarity fragment between them.

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arXiv2014

Improved magnetogram calibration of SMFT and its comparison with the HMI

In this paper, we try to improve the magnetogram calibration method of the Solar Magnetic Field Telescope (SMFT). The improved calibration process fits the observed full Stokes information, using six points on the profile of Fe ı 5324.18 Å line, and the analytical Stokes profiles under the Milne-Eddington atmosphere model, adopting the Levenberg-Marquardt least-square fitting algorithm. In Comparison with the linear calibration methods, which employs one point, there is large difference in the strength of longitudinal field $B_l$ and tranverse field $B_t$, caused by the non-linear relationship, but the discrepancy is little in the case of inclination and azimuth. We conclude that it is better to deal with the non-linear effects in the calibration of $B_l$ and $B_t$ using six points. Moreover, in comparison with SDO/HMI, SMFT has larger stray light and acquires less magnetic field strength. For vector magnetic fields in two sunspot regions, the magnetic field strength, inclination and azimuth angles between SMFT and HMI are roughly in agrement, with the linear fitted slope of 0.73/0.7, 0.95/1.04 and 0.99/1.1. In the case of pores and quiet regions ($B_l$ $<$ 600 G), the fitted slopes of the longitudinal magnetic field strength are 0.78 and 0.87 respectively.

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arXiv2013

The Induced Electric Field Distribution in Solar Atmosphere

A method of calculating induced electric field is presented in this paper. Induced electric field in solar atmosphere is derived by the time variation of magnetic field when the charged particle accumulation is neglected. In order to get the spatial distribution of magnetic field, several extrapolation methods are introduced. With observational data from Helioseismic and Magnetic Imager (HMI) aboard the NASA's Solar Dynamics Observatory (SDO) on May 20th, 2010, we extrapolate the magnetic field to the upper atmosphere from the photosphere. By calculating the time variation of magnetic field, we can get the induced electric field. The derived induced electric field can reach a value of 100 V/cm and the average electric field has a maximum point at the layer of 360 km above the photosphere. The Monte Carlo statistics method is used to compute the triple integration of induced electric field.

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arXiv2012

On a Coronal Blowout Jet: The First Observation of a Simultaneously Produced Bubble-like CME and a Jet-like CME in a Solar Event

The coronal blowout jet is a peculiar category among various jet phenomena, of which the sheared base arch, often carrying a small filament, experiences a miniature version of blowout eruption that produces large-scale coronal mass ejection (CME). In this paper, we report such a coronal blowout jet with high-resolution multi-wavelength and multi-angle observations taken from Solar Dynamics Observatory, Solar Terrestrial Relations Observatory, and Big Bear Solar Observatory. For the first time, we find that a simultaneous bubble-like and a jet-like CMEs were dynamically related to the blowout jet that showed cool and hot components next to each other. Our observational results indicate that: (1) the cool component was resulted from the eruption of the filament contained within the jet's base arch, and it further caused the bubble-like CME; (2) the jet-like CME was associated with the hot component, which was the outward moving heated plasmas generated by the reconnection of the base arch and its ambient open field lines. On the other hand, bifurcation of the jet's cool component was also observed, which was resulted from the uncoupling of the erupting filament's two legs that were highly twisted at the very beginning. Based on these results, we propose a model to interpret the coronal blowout jet, of which the external reconnection not only produces the jet-like CME but also leads to the rising of the filament. Subsequently, internal reconnection starts underneath the rising filament and thereby causes the bubble-like CME.

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