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Mini-filament Eruptions Triggering Confined Solar Flares Observed by ONSET and SDO  

Shuhong Yang   Submitted: 2018-06-07 02:22

Using the observations from the Optical and Near-infrared Solar Eruption Tracer and the Solar Dynamics Observatory, we study an M5.7 flare in AR 11476 on 2012 May 10 and a micro-flare in the quiet Sun on 2017 March 23. Before the onset of each flare, there is a reverse S-shaped filament above the polarity inversion line. Then the filaments become unstable and begin to rise. The rising filaments gain the upper hand over the tension force of the dome-like overlying loops and thus successfully erupt outward. The footpoints of the reconnecting overlying loops successively brighten and are observed as two flare ribbons, while the newly formed low-lying loops appear as the post-flare loops. These eruptions are similar to the classical model of successful filament eruptions associated with coronal mass ejections. However, the erupting filaments in this study move along large-scale lines and eventually reach the remote solar surface, i.e., no filament material is ejected into the interplanetary space. Thus both the flares are confined ones. These results reveal that some successful filament eruptions can trigger confined flares. Our observations also imply that this kind of filament eruptions may be ubiquitous on the Sun, from active regions with large flares to the quiet Sun with micro-flares.

Authors: Shuhong Yang, Jun Zhang
Projects: Other,SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in ApJL
Last Modified: 2018-06-07 12:35
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Block-induced complex structures building the flare-productive solar active region 12673  

Shuhong Yang   Submitted: 2017-10-18 18:26

Solar active region (AR) 12673 produced 4 X-class, 27 M-class, and numerous lower class flares during its passage across the visible solar disk in September 2017. Our study is to answer the questions why this AR was so flare-productive and how the X9.3 flare, the largest one of the last decade, took place. We find that there was a sunspot in the initial several days, and then two bipolar regions emerged nearby it successively. Due to the standing of the pre-existing sunspot, the movement of the bipoles was blocked, while the pre-existing sunspot maintained its quasi-circular shaped umbra only with the disappearance of a part of penumbra. Thus, the bipolar patches were significantly distorted, and the opposite polarities formed two semi-circular shaped structures. After that, two sequences of new bipolar regions emerged within the narrow semi-circular zone, and the bipolar patches separated along the curved channel. The new bipoles sheared and interacted with the previous ones, forming a complex topological system, during which numerous flares occurred. At the highly sheared region, a great deal of free energy was accumulated. On September 6, one negative patch near the polarity inversion line began to rapidly rotate and shear with the surrounding positive fields, and consequently the X9.3 flare erupted. Our results reveal that the block-induced complex structures built the flare-productive AR and the X9.3 flare was triggered by an erupting filament due to the kink instability. To better illustrate this process, a block-induced eruption model is proposed for the first time.

Authors: Shuhong Yang, Jun Zhang, Xiaoshuai Zhu, Qiao Song
Projects: GOES X-rays,SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in ApJL
Last Modified: 2017-10-18 20:42
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Sunspot Light Walls Suppressed by Nearby Brightenings  

Shuhong Yang   Submitted: 2017-06-22 19:01

Light walls, as ensembles of oscillating bright structures rooted in sunspot light bridges, have not been well studied, although they are important for understanding sunspot properties. Using the Interface Region Imaging Spectrograph and Solar Dynamics Observatory observations, here we study the evolution of two oscillating light walls each within its own active region (AR). The emission of each light wall decays greatly after the appearance of adjacent brightenings. For the first light wall, rooted within AR 12565, the average height, amplitude, and oscillation period significantly decrease from 3.5 Mm, 1.7 Mm, and 8.5 min to 1.6 Mm, 0.4 Mm, and 3.0 min, respectively. For the second light wall, rooted within AR 12597, the mean height, amplitude, and oscillation period of the light wall decrease from 2.1 Mm, 0.5 Mm, and 3.0 min to 1.5 Mm, 0.2 Mm, and 2.1 min, respectively. Particularly, a part of the second light wall becomes even invisible after the influence of nearby brightening. These results reveal that the light walls are suppressed by nearby brightenings. Considering the complex magnetic topology in light bridges, we conjecture that the fading of light walls may be caused by a drop in the magnetic pressure, where flux is cancelled by magnetic reconnection at the site of the nearby brightening. Another hypothesis is that the wall fading is due to the suppression of driver source (p-mode oscillation), resulting from the nearby avalanche of downward particles along reconnected brightening loops.

Authors: Shuhong Yang, Jun Zhang, Robertus Erdélyi, Yijun Hou, Xiaohong Li, Limei Yan
Projects: IRIS,SDO-AIA,SDO-HMI

Publication Status: accepted for publication in ApJL
Last Modified: 2017-06-28 08:42
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Enhancement of a sunspot light wall with external disturbances  

Shuhong Yang   Submitted: 2016-11-30 21:39

Based on the Interface Region Imaging Spectrograph observations, we study the response of a solar sunspot light wall to external disturbances. A flare occurrence near the light wall caused material to erupt from the lower solar atmosphere into the corona. Some material falls back to the solar surface, and hits the light bridge (i.e., the base of the light wall), then sudden brightenings appear at the wall base followed by the rise of wall top, leading to an increase of the wall height. Once the brightness of the wall base fades, the height of the light wall begins to decrease. Five hours later, another nearby flare takes place, a bright channel is formed that extends from the flare towards the light bridge. Although no obvious material flow along the bright channel is found, some ejected material is conjectured to reach the light bridge. Subsequently, the wall base brightens and the wall height begins to increase again. Once more, when the brightness of the wall base decays, the wall top fluctuates to lower heights. We suggest, based on the observed cases, that the interaction of falling material and ejected flare material with the light wall results in the brightenings of wall base and causes the height of the light wall to increase. Our results reveal that the light wall can be not only powered by the linkage of p-mode from below the photosphere, but may also be enhanced by external disturbances, such as falling material.

Authors: Shuhong Yang, Jun Zhang, Robert Erdélyi
Projects: IRIS,SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in ApJL
Last Modified: 2016-12-14 13:55
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Oscillation of newly formed loops after magnetic reconnection in the solar chromosphere  

Shuhong Yang   Submitted: 2016-02-23 06:21

With the high spatial and temporal resolution Hα images from the New Vacuum Solar Telescope, we focus on two groups of loops with a X-shaped configuration in the dynamic chromosphere. We find that the anti-directed loops approach each other and reconnect continually. The connectivity of the loops is changed and new loops are formed and stack together. The stacked loops are sharply bent, implying that they are greatly impacted by the magnetic tension force. When another more reconnection process takes place, one new loop is formed and stacks with the previously formed ones. Meanwhile, the stacked loops retract suddenly and move toward the balance position, performing an overshoot movement, which led to an oscillation with an average period of about 45 s. The oscillation of newly formed loops after magnetic reconnection in the chromosphere is observed for the first time. We suggest that the stability of the stacked loops is destroyed due to the join of the last new loop and then suddenly retract under the effect of magnetic tension. Because of the retraction, another lower loop is pushed outward and performs an oscillation with the period of about 25 s. The different oscillation periods may be due to their difference in three parameters, i.e., loop length, plasma density, and magnetic field strength.

Authors: Shuhong Yang, Yongyuan Xiang
Projects: New Vacuum Solar Telescope (NVST),SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in ApJL
Last Modified: 2016-02-24 12:02
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Trigger of a blowout jet in a solar coronal mass ejection associated with a flare  

Shuhong Yang   Submitted: 2015-11-05 19:44

Using the multi-wavelength images and the photospheric magnetograms from the Solar Dynamics Observatory, we study the flare which was associated by the only one coronal mass ejection (CME) in active region (AR) 12192. The eruption of a filament caused a blowout jet, and then an M4.0 class flare occurred. This flare was located at the edge of AR instead of in the core region. The flare was close to the apparently "open" fields, appearing as extreme-ultraviolet structures that fan out rapidly. Due to the interaction between flare materials and "open" fields, the flare became an eruptive flare, leading to the CME. Then at the same site of the first eruption, another small filament erupted. With the high spatial and temporal resolution Hα data from the New Vacuum Solar Telescope at the Fuxian Solar Observatory, we investigate the interaction between the second filament and the nearby "open" lines. The filament reconnected with the "open" lines, forming a new system. To our knowledge, the detailed process of this kind of interaction is reported for the first time. Then the new system rotated due to the untwisting motion of the filament, implying that the twist was transferred from the closed filament system to the "open" system. In addition, the twist seemed to propagate from the lower atmosphere to the upper layers, and was eventually spread by the CME to the interplanetary space.

Authors: Xiaohong Li, Shuhong Yang, Huadong Chen, Ting Li, Jun Zhang
Projects: Other,SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in ApJL
Last Modified: 2015-11-06 10:53
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Oscillating light wall above a sunspot light bridge  

Shuhong Yang   Submitted: 2015-04-14 18:43

With the high tempo-spatial Interface Region Imaging Spectrograph 1330 Å images, we find that many bright structures are rooted in the light bridge of NOAA 12192, forming a light wall. The light wall is brighter than the surrounding areas, and the wall top is much brighter than the wall body. The New Vacuum Solar Telescope Hα and the Solar Dynamics Observatory 171 Å and 131 Å images are also used to study the light wall properties. In 1330 Å, 171 Å, and 131 Å, the top of the wall has a higher emission, while in the Hα line, the wall top emission is very low. The wall body corresponds to bright areas in 1330 Å and dark areas in the other lines. The top of the light wall moves upward and downward successively, performing oscillations in height. The deprojected mean height, amplitude, oscillation velocity, and the dominant period are determined to be 3.6 Mm, 0.9 Mm, 15.4 km s-1, and 3.9 min, respectively. We interpret the oscillations of the light wall as the leakage of p-modes from below the photosphere. The constant brightness enhancement of the wall top implies the existence of some kind of atmospheric heating, e.g., via the persistent small-scale reconnection or the magneto-acoustic waves. In another series of 1330 Å images, we find that the wall top in the upward motion phase is significantly brighter than in the downward phase. This kind of oscillations may be powered by the energy released due to intermittent impulsive magnetic reconnection.

Authors: Shuhong Yang, Jun Zhang, Fayu Jiang, Yongyuan Xiang
Projects: IRIS,Other,SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in ApJL
Last Modified: 2015-04-15 11:25
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Magnetic reconnection between small-scale loops observed with the New Vacuum Solar Telescope  

Shuhong Yang   Submitted: 2014-12-03 18:35

Using the high tempo-spatial resolution Hα images observed with the New Vacuum Solar Telescope, we report the solid observational evidence of magnetic reconnection between two sets of small-scale anti-parallel loops with an X-shaped topology. The reconnection process contains two steps: a slow step with the duration of more than several tens of minutes, and a rapid step lasting for only about three minutes. During the slow reconnection, two sets of anti-parallel loops reconnect gradually, and new loops are formed and stacked together. During the rapid reconnection, the anti-parallel loops approach each other quickly, and then the rapid reconnection takes place, resulting in the disappearance of former loops. In the meantime, new loops are formed and separate. The region between the approaching loops is brightened, and the thickness and length of this region are determined to be about 420 km and 1.4 Mm, respectively. During the rapid reconnection process, obvious brightenings at the reconnection site and apparent material ejections outward along reconnected loops are observed. These observed signatures are consistent with predictions by reconnection models. We suggest that the successive slow reconnection changes the conditions around the reconnection site and triggers instabilities, thus leading to the rapid approach of the anti-parallel loops and resulting in the rapid reconnection.

Authors: Shuhong Yang, Jun Zhang, and Yongyuan Xiang
Projects: Other,SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in ApJL. Animations: http://ourstar.bao.ac.cn/~shuhongyang/files/apjl_reconnection/
Last Modified: 2014-12-04 10:54
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Fine Structures and Overlying Loops of Confined Solar Flares  

Shuhong Yang   Submitted: 2014-09-01 18:38

Using the Hα observations from the New Vacuum Solar Telescope at Fuxian Solar Observatory, we focus on the fine structures of three confined flares and the issue why all the three flares are confined instead of eruptive. All the three confined flares take place successively at the same location and have similar morphologies, so can be termed homologous confined flares. In the simultaneous images obtained by the Solar Dynamics Observatory, many large-scale coronal loops above the confined flares are clearly observed in multi-wavelengths. At the pre-flare stage, two dipoles emerge near the negative sunspot, and the dipolar patches are connected by small loops appearing as arch-shaped Hα fibrils. There exists a reconnection between the small loops, and thus the Hα fibrils change their configuration. The reconnection also occurs between a set of emerging Hα fibrils and a set of pre-existing large loops, which are rooted in the negative sunspot, a nearby positive patch, and some remote positive faculae, forming a typical three-legged structure. During the flare processes, the overlying loops, some of which are tracked by activated dark materials, do not break out. These direct observations may illustrate the physical mechanism of confined flares, i.e., magnetic reconnection between the emerging loops and the pre-existing loops triggers flares and the overlying loops prevent the flares from being eruptive.

Authors: Shuhong Yang, Jun Zhang, and Yongyuan Xiang
Projects: GOES X-rays ,Other,SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in ApJL.
Last Modified: 2014-09-03 13:12
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New Vacuum Solar Telescope observations of a flux rope tracked by a filament activation  

Shuhong Yang   Submitted: 2014-03-04 20:07

One main goal of the New Vacuum Solar Telescope (NVST) which is located at the Fuxian Solar Observatory is to image the Sun at high resolution. Based on the high spatial and temporal resolution NVST Hα data and combined with the simultaneous observations from the Solar Dynamics Observatory for the first time, we investigate a flux rope tracked by a filament activation. The filament material is initially located at one end of the flux rope and fills in a section of the rope, and then the filament is activated due to magnetic field cancellation. The activated filament rises and flows along helical threads, tracking out the twisted flux rope structure. The length of the flux rope is about 75 Mm, the average width of its individual threads is 1.11 Mm, and the estimated twist is 1 pi. The flux rope appears as a dark structure in Hα images, a partial dark and partial bright structure in 304 Å, while as bright structures in 171 Å and 131 Å images. During this process, the overlying coronal loops are quite steady since the filament is confined within the flux rope and does not erupt successfully. It seems that, for the event in this study, the filament is located and confined within the flux rope threads, instead of being suspended in the dips of twisted magnetic flux.

Authors: Shuhong Yang, Jun Zhang, Zhong Liu, Yongyuan Xiang
Projects: Other,SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in ApJL
Last Modified: 2014-03-05 12:24
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Properties of Solar Ephemeral Regions at the Emergence Stage  

Shuhong Yang   Submitted: 2013-12-02 18:46

For the first time, we statistically study the properties of ephemeral regions (ERs) and quantitatively determine their parameters at the emergence stage based on a sample of 2988 ERs observed by the Solar Dynamics Observatory. During the emergence process, there are three kinds of kinematic performances, i.e., separation of dipolar patches, shift of ER's magnetic centroid, and rotation of ER's axis. The average emergence duration, flux emergence rate, separation velocity, shift velocity, and angular speed are 49.3 min, 2.6 ? 1015 Mx s^-1, 1.1 km s-1, 0.9 km s-1, and 0degr.6 min^-1, respectively. At the end of emergence, the mean magnetic flux, separation distance, shift distance, and rotation angle are 9.3 ? 1018 Mx, 4.7 Mm, 1.1 Mm, and 12degr.9, respectively. We also find that the higher the ER magnetic flux is, (1) the longer the emergence lasts, (2) the higher the flux emergence rate is, (3) the further the two polarities separate, (4) the lower the separation velocity is, (5) the larger the shift distance is, (6) the slower the ER shifts, and (7) the lower the rotation speed is. However, the rotation angle seems not to depend on the magnetic flux. Not only at the start time, but also at the end time, the ERs are randomly oriented in both the northern and the southern hemispheres. Besides, neither the anticlockwise rotated ERs, nor the clockwise rotated ones dominate the northern or the southern hemisphere.

Authors: Shuhong Yang, Jun Zhang
Projects: SDO-AIA,SDO-HMI

Publication Status: accepted for publication in ApJ
Last Modified: 2013-12-03 10:15
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Emerging dimmings of active regions observed by SDO  

Shuhong Yang   Submitted: 2012-10-18 21:50

With the observations from the Atmospheric Imaging Assembly and the Helioseismic and Magnetic Imager aboard the emph{Solar Dynamics Observatory}, we statistically investigate the emerging dimmings (EDs) of 24 isolated active regions (IARs) from June 2010 to May 2011. All the IARs present EDs in lower temperature lines (e.g., 171 {AA}) at their early emerging stages, meanwhile in higher temperature lines (e.g., 211 {AA}), the ED regions brighten continuously. There are two type of EDs: fan-shaped and halo-shaped. There are 19 fan-shaped EDs and 5 halo-shaped ones. The EDs appear several to more than ten hours delay to the first emergence of the IARs. The shortest delay is 3.6 hr and the longest 19.0 hr. The EDs last from 3.3 hr to 14.2 hr, with a mean duration of 8.3 hr. Before the appearance of the EDs, the emergence rate of the magnetic flux of the IARs is from 1.2 imes 1019 Mx hr-1 to 1.4 imes 1020 Mx hr-1. The larger the emergence rate is, the shorter the delay time is. While the dimmings appear, the magnetic flux of the IARs ranges from 8.8 imes 1019 Mx to 1.3 imes 1021 Mx. These observations imply that the reconfiguration of the coronal magnetic fields due to reconnection between the newly-emerging flux and the surrounding existing fields results in a new thermal distribution which leads to a dimming for the cooler channel (171 {AA}) and brightnening in the warmer channels.

Authors: Jun Zhang, Shuhong Yang, Yang Liu, Xudong Sun
Projects: SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in ApJL
Last Modified: 2012-10-19 09:56
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Self-cancellation of ephemeral regions in the quiet Sun  

Shuhong Yang   Submitted: 2012-05-16 09:06

With the observations from the Helioseismic and Magnetic Imager aboard the Solar Dynamics Observatory, we statistically investigate the ephemeral regions (ERs) in the quiet Sun. We find that there are two types of ERs: normal ERs (NERs) and self-cancelled ERs (SERs). Each NER emerges and grows with separation of its opposite polarity patches which will cancel or coalesce with other surrounding magnetic flux. Each SER also emerges and grows and its dipolar patches separate at first, but a part of magnetic flux of the SER will move together and cancel gradually, which is described with the term ''self-cancellation'' by us. We identify 2988 ERs among which there are 190 SERs, about 6.4% of the ERs. The mean value of self-cancellation fraction of SERs is 62.5%, and the total self-cancelled flux of SERs is 9.8% of the total ER flux. Our results also reveal that the higher the ER magnetic flux is, (i) the easier the performance of ER self-cancellation is, (ii) the smaller the self-cancellation fraction is, and (iii) the more the self-cancelled flux is. We think that the self-cancellation of SERs is caused by the submergence of magnetic loops connecting the dipolar patches, without magnetic energy release.

Authors: Shuhong Yang, Jun Zhang, Ting Li, Yang Liu
Projects: SDO-HMI

Publication Status: Accepted for publication in ApJL
Last Modified: 2012-05-16 12:33
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Ubiquitous rotating network magnetic fields and EUV cyclones in the quiet Sun  

Shuhong Yang   Submitted: 2011-09-22 22:47

This abstract was corrupted following database problems and is being recovered. It will be restored as quickly as possible. Any questions, please send them to Alisdair. Sorry for any incovenience.


Authors: Jun Zhang and Yang Liu
Projects: SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in ApJL
Last Modified: 2011-09-25 05:08
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SDO Observations of Magnetic Reconnection at Coronal Hole Boundaries  

Shuhong Yang   Submitted: 2011-03-18 17:12

With the observations from the Atmospheric Imaging Assembly (AIA) andthe Helioseismic andMagnetic Imager (HMI) aboard the Solar Dynamics Observatory, weinvestigate the coronal holeboundaries (CHBs) of an equatorial extension of polar coronal hole. Atthe CHBs, lots of extreme-ultraviolet (EUV) jets, which appear to be the signatures of magneticreconnection, are observed in the193Å images, and some jets occur repetitively at the same sites. Theevolution of the jets is associatedwith the emergence and cancelation of magnetic fields. We notice thatboth the east and the westCHBs shift westward, and the shift velocities are close to thevelocities of rigid rotation compared withthose of the photospheric differential rotation. This indicates thatmagnetic reconnection at CHBsresults in the evolution of CHBs and maintains the rigid rotation ofcoronal holes.

Authors: Shuhong Yang, Jun Zhang, Ting Li, Yang Liu
Projects: SDO-AIA,SDO-HMI

Publication Status: accepted for publication in ApJL
Last Modified: 2011-03-18 18:20
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Vector Magnetic Fields and Current Helicities in Coronal Holes and Quiet Regions  

Shuhong Yang   Submitted: 2010-11-01 21:50

In the solar photosphere, many properties of coronal holes (CHs) are not known, especially vector magnetic fields. Using observations from Hinode, we investigate vector magnetic fields, current densities and current helicities in two CHs and compare them with two normal quiet regions (QRs) for the first time. We find that, in the CHs and QRs, the areas where large current helicities are located are mainly co-spatial with strong vertical and horizontal field elements both in shape and location. In the CHs, horizontal magnetic fields, inclination angles, current densities and current helicities are larger than those in the QRs. The mean vertical current density and current helicity, averaged over all the observed areas including the CHs and QRs, are approximately 0.008 A m-2 and 0.005 G^2 m-1, respectively. The mean current density in magnetic flux concentrations where the vertical fields are stronger than 100 G is as large as 0.012 ? 0.001 A m-2, consistent with that in the flare productive active regions. Our results imply that the magnetic fields, especially the strong fields, both in the CHs and QRs are nonpotential.

Authors: Shuhong Yang, Jun Zhang, Ting Li, Mingde Ding
Projects: Hinode/SOT

Publication Status: ApJ (accepted)
Last Modified: 2010-11-02 09:28
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Dipolar Evolution in a Coronal Hole Region  

Shuhong Yang   Submitted: 2009-08-04 21:01

Using observations from the SOHO, STEREO and Hinode, we investigate magnetic field evolution in an equatorial coronal hole region. Two dipoles emerge one by one. The negative element of the first dipole disappears due to the interaction with the positive element of the second dipole. During this process, a jet and a plasma eruption are observed. The opposite polarities of the second dipole separate at first, and then cancel with each other, which is first reported in a coronal hole. With the reduction of unsigned magnetic flux of the second dipole from 9.8x1020 Mx to 3.0x1020 Mx in two days, 171 Å brightness decreases by 75% and coronal loops shrink obviously. At the cancellation sites, the transverse fields are strong and point directly from the positive elements to the negative ones, meanwhile Doppler red-shifts with an average velocity of 0.9 km s-1 are observed, comparable to the horizontal velocity (1.0 km s-1) derived from the cancelling island motion. Several days later, the northeastern part of the coronal hole, where the dipoles are located, appears as a quiet region. These observations support the idea that the interaction between the two dipoles is caused by flux reconnection, while the cancellation between the opposite polarities of the second dipole is due to the submergence of original loops. These results will help us to understand coronal hole evolution.

Authors: Shuhong Yang, Jun Zhang, and Juan Manuel Borrero
Projects: Hinode/SOT,SoHO-EIT,SoHO-MDI,STEREO

Publication Status: accepted by ApJ
Last Modified: 2009-08-05 14:22
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Interaction between Granulation and Small-Scale Magnetic Flux Observed by Hinode  

Shuhong Yang   Submitted: 2009-05-11 00:05

With the polarimetric observations obtained by the Spectro-Polarimeter on board Hinode, we study the relationship between granular development and magnetic field evolution in the quiet Sun. 6 typical cases are displayed to exhibit interaction between granules and magnetic elements, and we have obtained the following results. (1) A granule develops centrosymmetrically when no magnetic flux emerges within the granular cell. (2) A granule develops and splits noncentrosymmetrically while flux emerges at an outer part of the granular cell. (3) Magnetic flux emergence as a cluster of mixed polarities is detected at the position of a granule as soon as the granule breaks up. (4) A dipole emerges accompanying with the development of a granule, and the two elements of the dipole root in the adjacent intergranular lanes and face each other across the granule. Advected by the horizontal granular motion, the positive element of the dipole then cancels with pre-existing negative flux. (5) Flux cancellation also takes place between a positive element, which is advected by granular flow, and its surrounding negative flux. (6) While magnetic flux cancellation takes place at a granular cell, the granule shrinks and then disappears. (7) Horizontal magnetic fields enhance at the places where dipoles emerge and where opposite polarities cancel with each other, but only the horizontal fields between the dipolar elements point orderly from the positive element to the negative one. Our results reveal that granules and small-scale magnetic flux influence each other. Granular flow advects magnetic flux, and magnetic flux evolution suppresses granular development. There exist extremely large Doppler blue-shifts at the site of one cancelling magnetic element. This phenomenon may be caused by the upward flow produced by magnetic reconnection below the photosphere.

Authors: Jun Zhang, Shuhong Yang and Chunlan Jin
Projects: Hinode/SOT

Publication Status: Accepted by RAA
Last Modified: 2009-05-11 07:49
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Response of the solar atmosphere to magnetic field evolution in a coronal hole region  

Shuhong Yang   Submitted: 2009-04-16 20:22

Context. Coronal holes (CHs) are deemed to be the sources of the fast solar wind streams that lead to recurrent geomagnetic storms and have been intensively investigated, but not all the properties of them are known well. Aims. We mainly research the response of the solar atmosphere to the magnetic field evolution in a CH region, such as magnetic flux emergence and cancellation for both network (NT) and intranetwork (IN). Methods. We study an equatorial CH observed simultaneously by HINODE and STEREO on July 27, 2007. The HINODE/SP maps are adopted to derive the physical parameters of the photosphere and to research the magnetic field evolution and distribution. The G band and Ca ii H images with high tempo-spatial resolution from HINODE/BFI and the multi-wavelength data from STEREO/EUVI are utilized to study the corresponding atmospheric response of different overlying layers. Results. We explore an emerging dipole locating at the CH boundary. Mini-scale arch filaments (AFs) accompanying the emerging dipole were observed with the Ca II H line. During the separation of the dipolar footpoints, three AFs appeared and expanded in turn. The first AF divided into two segments in its late stage, while the second and third AFs erupted in their late stages. The lifetimes of these three AFs are 4, 6, 10 minutes, and the two intervals between the three divisions or eruptions are 18 and 12 minutes, respectively. We display an example of mixed-polarity flux emergence of IN fields within the CH and present the corresponding chromospheric response. With the increase of the integrated magnetic flux, the brightness of the Ca II H images exhibits an increasing trend. We also study magnetic flux cancellations of NT fields locating at the CH boundary and present the obvious chromospheric and coronal response.We notice that the brighter regions seen in the 171 Å images are relevant to the interacting magnetic elements. By examining the magnetic NT and IN elements and the response of different atmospheric layers, we obtain good positive linear correlations between the NT magnetic flux densities and the brightness of both G band (correlation coeffcient 0.85) and Ca II H (correlation coefficient 0.58).

Authors: S. H. Yang, J. Zhang, C. L. Jin, L. P. Li, and H. Y. Duan
Projects: Hinode/SOT,SoHO-EIT,SoHO-MDI,STEREO

Publication Status: Accepted by A&A
Last Modified: 2009-04-17 08:19
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Abstracts by Author
Mini-filament Eruptions Triggering Confined Solar Flares Observed by ONSET and SDO
Block-induced complex structures building the flare-productive solar active region 12673
Sunspot Light Walls Suppressed by Nearby Brightenings
Enhancement of a sunspot light wall with external disturbances
Oscillation of newly formed loops after magnetic reconnection in the solar chromosphere
Trigger of a blowout jet in a solar coronal mass ejection associated with a flare
Oscillating light wall above a sunspot light bridge
Magnetic reconnection between small-scale loops observed with the New Vacuum Solar Telescope
Fine Structures and Overlying Loops of Confined Solar Flares
New Vacuum Solar Telescope observations of a flux rope tracked by a filament activation
Properties of Solar Ephemeral Regions at the Emergence Stage
Emerging dimmings of active regions observed by SDO
Self-cancellation of ephemeral regions in the quiet Sun
Ubiquitous rotating network magnetic fields and EUV cyclones in the quiet Sun
SDO Observations of Magnetic Reconnection at Coronal Hole Boundaries
Vector Magnetic Fields and Current Helicities in Coronal Holes and Quiet Regions
Dipolar Evolution in a Coronal Hole Region
Interaction between Granulation and Small-Scale Magnetic Flux Observed by Hinode
Response of the solar atmosphere to magnetic field evolution in a coronal hole region

Related Pages
MSU Solar Physics.
Max Millennium Science Mail Archive.
Max Millennium Message of the Day Mail Archive.
Max Millennium Flare Catalog

Archive Maintainer
Alisdair Davey



© 2003 Solar Physics Group - Montana State University