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. Six typical cases are displ...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. Six 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 in a cluster of mixed polarities is detected at the position of a granule as soon as the granule breaks up. （4） A dipole emerges accompanied by the development of a granule, and the two elements of the dipole are rooted 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 the 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 in a granular cell, the granule shrinks and then disappears. （7） Horizontal magnetic fields are enhanced at the places where dipoles emerge and where opposite polarities cancel each other, but only the horizontal fields between the dipolar elements point in an orderly way from the positive elements to the negative ones. Our results reveal that granules and small-scale magnetic fluxes 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 canceling magnetic element. This phenomenon may be caused by the upward flow produced by magnetic reconnection below the photosphere.展开更多
From the observed vector magnetic fields by the Solar Optical Telescope/ Spectro-Polarimeter aboard the satellite Hinode, we have examined whether or not the quiet Sun magnetic fields are non-potential, and how the G-...From the observed vector magnetic fields by the Solar Optical Telescope/ Spectro-Polarimeter aboard the satellite Hinode, we have examined whether or not the quiet Sun magnetic fields are non-potential, and how the G-band filigrees and Ca II network bright points （NBPs） are associated with the magnetic non-potentiality. A sizable quiet region in the disk center is selected for this study. The new findings by the study are as follows. （1） The magnetic fields of the quiet region are obviously non-potential. The region-average shear angle is 40°, the average vertical current is 0.016A m^-2, and the average free magnetic energy density, 2.7× 10^2erg cm^-3. The magnitude of these non-potential quantities is comparable to that in solar active regions. （2） There are overall correlations among current helicity, free magnetic energy and longitudinal fields. The magnetic non-potentiality is mostly concentrated in the close vicinity of network elements which have stronger longitudinal fields. （3） The filigrees and NBPs are magnetically characterized by strong longitudinal fields, large electric helicity, and high free energy density. Because the selected region is away from any enhanced network, these new results can generally be applied to the quiet Sun. The findings imply that stronger network elements play a role in high magnetic non-potentiality in heating the solar atmosphere and in conducting the solar wind.展开更多
We present properties of intensity oscillations of a sunspot in the photo- sphere and chromosphere using G band and Ca u H filtergrams from Hinode. Intensity power maps as function of magnetic field strength and frequ...We present properties of intensity oscillations of a sunspot in the photo- sphere and chromosphere using G band and Ca u H filtergrams from Hinode. Intensity power maps as function of magnetic field strength and frequency reveal reduction of power in the G band with an increase in photospheric magnetic field strength at all frequencies. In Ca II H, however, stronger fields exhibit more power at high frequen- cies, particularly in the 4.5-8.0 mHz band. Power distributions in different locations of the active region show that the oscillations in Ca II H exhibit more power compared to that of the G band. We also relate the power in intensity oscillations with differ- ent components of the photospheric vector magnetic field using near simultaneous spectro-polarimetric observations of the sunspot from the Hinode spectropolarime- ter. The photospheric umbral power is strongly anti-correlated with the magnetic field strength and its line-of-sight component but there is a good correlation with the trans- verse component. A reversal of this trend is observed in the chromosphere except at low frequencies （V≤ 1.5 mHz）. The power in sunspot penumbrae is anti-correlated with the magnetic field parameters at all frequencies （1.0 ≤ v ≤ 8.0 mHz） in both the photosphere and chromosphere, except that the chromospheric power shows a strong correlation in the frequency range 3-3.5 mHz.展开更多
Magnetic non-potentiality is important for understanding flares and other solar activities in active regions （ARs）. Five non-potential parameters, i.e. electric current, current helicity, source field, photospheric ...Magnetic non-potentiality is important for understanding flares and other solar activities in active regions （ARs）. Five non-potential parameters, i.e. electric current, current helicity, source field, photospheric free energy, and angular shear, are calculated to quantify the non-potentiality of NOAA AR 11158. Benefitting from the high spatial resolution, high cadence and continuous temporal coverage of vector mag- netograms from the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory, both the long-term evolution of the AR and the rapid change during flares are studied. We confirm that, compared with the magnetic flux, the magnetic non-potentiality has a closer connection with the flare, and the emerging flux regions are important for understanding the magnetic non-potentiality and flares. The main re- suits are as follows. （1） The vortex in the source field directly displays the deflection of the horizontal magnetic field. The deflection corresponds to the fast rotating sunspot with a time delay, which suggests that the sunspot rotation leads to an increase in the non-potentiality. （2） Two areas that have evident changes in the azimuth of the vector magnetic field are found near the magnetic polarity inversion line. The change rates of the azimuth are about 1.3° h-1 and 3.6° h-1, respectively. （3） Rapid and prominent increases are found in the variation of helicity during four flares in the regions where their initial brightening occurs. The recovery of the increases takes 3-4 h for the two biggest flares （X2.2 and M6.6）, but only takes about 2 h for the two other smaller flares （M2.2 and M1.6）.展开更多
The solar active region NOAA 11719 produced a large two-ribbon flare on 2013 April 11. We have investigated sudden variations in the photospheric magnetic fields in this active region during the flare by employing mag...The solar active region NOAA 11719 produced a large two-ribbon flare on 2013 April 11. We have investigated sudden variations in the photospheric magnetic fields in this active region during the flare by employing magnetograms obtained in the spectral line Fe I 6173 A acquired by the Helioseismic and Magnetic Imager （HMI） onboard the Solar Dynamics Observatory （SDO） spacecraft. The analysis of the line-of-sight magnetograms from HMI show sudden and persistent magnetic field changes at different locations of the active region before the onset of the flare and during the flare. The vector magnetic field observations available from HMI also show coincident variations in the total magnetic field strength and its inclination angle at these locations. Using the simultaneous Dopplergrams obtained from HMI, we observe perturbations in the photospheric Doppler signals following the sudden changes in the magnetic fields in the aforementioned locations. The power spectrum analysis of these velocity signals shows enhanced acoustic power in these affected locations during the flare as compared to the pre-flare condition. Accompanying these observations, we have also used nearly simultaneous chromospheric observations obtained in the spectral line Ha 6562.8 A by the Global Oscillation Network Group （GONG） to study the evolution of flare- ribbons and intensity oscillations in this active region. The Ha intensity oscillations also show enhanced oscillatory power during the flare in the aforementioned locations. These results indicate that the transient Lorentz force associated with sudden changes in the magnetic fields could drive localized photospheric and chromospheric oscillations, like the flare-induced oscillations in the solar atmosphere.展开更多
Based on Dulk and Marsh＇s approximate theory about nonthermal gyrosyn- chrotron radiation, one simple impulsive microwave burst with a loop-like structure is selected for radio diagnostics of the coronal magnetic fie...Based on Dulk and Marsh＇s approximate theory about nonthermal gyrosyn- chrotron radiation, one simple impulsive microwave burst with a loop-like structure is selected for radio diagnostics of the coronal magnetic field and column density of non- thermal electrons, which are calculated from the brightness temperature, polarization degree, and spectral index, as well as the turnover frequency, observed by using the Nobeyama Radioheliograph and the Nobeyama Radio Polarimeters, respectively. Very strong variations （up to one or two orders of magnitude） of the calculated transverse and longitudinal magnetic fields with respect to the line-of-sight, as well as the cal- culated electron column density, appear in the looptop and footpoint sources during the burst. The absolute magnitude and varied range of the transverse magnetic field are evidently larger than those of the longitudinal magnetic field. The time evolution of the transverse magnetic field is always anti-correlated with that of the longitudi- nal magnetic field, but positively correlated with that of the electron column density. These results strongly support the idea that quantifying the energy released in a flare depends on a reconstruction of the coronal magnetic field, especially for the trans- verse magnetic field, and they are basically consistent with the recent theoretical and observational studies on the photospheric magnetic field in solar flares.展开更多
We present a rare observation of direct magnetic interaction between an activating filament and a coronal hole （CH）. The filament was a quiescent one located at the northwest of the CH. It underwent a nonradial acti...We present a rare observation of direct magnetic interaction between an activating filament and a coronal hole （CH）. The filament was a quiescent one located at the northwest of the CH. It underwent a nonradial activation, during which filament material constantly fell and intruded into the CH. As a result, the CH was clearly destroyed by the intrusion. Brightenings appeared at the boundaries and in the interior of the CH, meanwhile, its west boundaries began to retreat and the area gradually shrank. It is noted that the CH went on shrinking after the end of the intrusion and finally disappeared entirely. Following the filament activation, three coronal dimmings （D1-D3） were formed, among which D1 and D2 persisted throughout the complete disappearance of the CH. The derived coronal magnetic configuration shows that the filament was located below an extended loop system, which obviously linked D1 to D2. By extrapolating this result, our observations imply that the interaction between the filament and the CH involved direct intrusion of the filament material to the CH and the disappearance of the CH might be due to interchange reconnection between the expanding loop system and the CH＇s open field.展开更多
Magnetic topology has been a key to the understanding of magnetic energy release mechanism. Based on observed vector magnetograms, we have determined the threedimensional （3D） topology skeleton of the magnetic field...Magnetic topology has been a key to the understanding of magnetic energy release mechanism. Based on observed vector magnetograms, we have determined the threedimensional （3D） topology skeleton of the magnetic fields in the active region NOAA 10720. The skeleton consists of six 3D magnetic nulls and a network of corresponding spines, fans, and null-null lines. For the first time, we have identified a spiral magnetic null in Sun＇s corona. The magnetic lines of force twisted around the spine of the null, forming a ＇magnetic wreath＇ with excess of free magnetic energy and resembling observed brightening structures at extraultraviolet （EUV） wavebands. We found clear evidence of topology eruptions which are referred to as catastrophic changes of topology skeleton associated with a coronal mass ejection （CME） and an explosive X-ray flare. These results shed new lights on the structural complexity and its role in explosive magnetic activity. The concept of flux rope has been widely used in modelling explosive magnetic activity, although their observational identity is rather obscure or, at least, lacking of necessary details up to date. We suggest that the magnetic wreath associated with the 3D spiral null is likely an important class of the physical entity of flux ropes.展开更多
Using the multi-wavelength data from the Atmospheric Imaging Assembly （AIA） onboard the Solar Dynamics Observatory （SDO） spacecraft, we study a jet occurring in a coronal hole near the northern pole of the Sun. Th...Using the multi-wavelength data from the Atmospheric Imaging Assembly （AIA） onboard the Solar Dynamics Observatory （SDO） spacecraft, we study a jet occurring in a coronal hole near the northern pole of the Sun. The jet presented distinct upward helical motion during ejection. By tracking six identified moving features （MFs） in the jet, we found that the plasma moved at an approximately constant speed along the jet＇s axis. Meanwhile, the MFs made a circular motion in the plane transverse to the axis. Inferred from linear and trigonometric fittings to the axial and transverse heights of the six tracks, the mean values of the axial velocities, transverse velocities, angular speeds, rotation periods, and rotation radii of the jet are 114 km s-1, 136 km s-1, 0.81° s-1, 452 s and 9.8 × 10^3 km respectively. As the MFs rose, the jet width at the corresponding height increased. For the first time, we derived the height variation of the longitudinal magnetic field strength in the jet from the assumption of magnetic flux conservation. Our results indicate that at heights of 1 × 10^4 -7 × 10^4 km from the base of the jet, the flux density in the jet decreases from about 15 to 3 G as a function of B = 0.5（R/R） - 1）-0.84 （G）. A comparison was made with other results in previous studies.展开更多
Solar flares strongly influence space weather and human activities, and their prediction is highly complex. The existing solutions such as data based approaches and model based approaches have a common shortcoming whi...Solar flares strongly influence space weather and human activities, and their prediction is highly complex. The existing solutions such as data based approaches and model based approaches have a common shortcoming which is the lack of human engagement in the forecasting process. An image-case-based reasoning method is introduced to achieve this goal. The image case library is com- posed of SOHO/MDI longitudinal magnetograms, the images from which exhibit the maximum hori- zontal gradient, the length of the neutral line and the number of singular points that are extracted for retrieving similar image cases. Genetic optimization algorithms are employed for optimizing the weight assignment for image features and the number of similar image cases retrieved. Similar image cases and prediction results derived by majority voting for these similar image cases are output and shown to the forecaster in order to integrate his/her experience with the final prediction results. Experimental results demonstrate that the case-based reasoning approach has slightly better performance than other methods, and is more efficient with forecasts improved by humans.展开更多
We study the magnetic structure of five well-known active regions that produced great flares （X5 or larger）. The six flares under investigation are the X12 flare on 1991 June 9 in AR 6659, the X5.7 flare on 2000 Jul...We study the magnetic structure of five well-known active regions that produced great flares （X5 or larger）. The six flares under investigation are the X12 flare on 1991 June 9 in AR 6659, the X5.7 flare on 2000 July 14 in AR 9077, the X5.6 flare on 2001 April 6 in AR 9415, the X5.3 flare on 2001 August 25 in AR 9591, the X17 flare on 2003 October 28 and the X10 flare on 2003 October 29, both in AR 10486. The last five events had corresponding LASCO observations and were all associated with Halo CMEs. We analyzed vector magnetograms from Big Bear Solar Observatory, Huairou Solar Observing Station, Marshall Space Flight Center and Mees Solar Observatory. In particular, we studied the magnetic gradient derived from line-of-sight magnetograms and magnetic shear derived from vector magnetograms, and found an apparent correlation between these two parameters at a level of about 90%. We found that the magnetic gradient could be a better proxy than the shear for predicting where a major flare might occur： all six flares occurred in neutral lines with maximum gradient. The mean gradient of the flaring neutral lines ranges from 0.14 to 0.50 G km^-1, 2.3 to 8 times the average value for all the neutral lines in the active regions. If we use magnetic shear as the proxy, the flaring neutral line in at least one, possibly two, of the six events would be mis-identified.展开更多
Three new longitudinal magnetic field parameters are extracted from SOHO/MDI magnetograms to characterize properties of the stressed magnetic field in active regions, and their flare productivities are calculated for ...Three new longitudinal magnetic field parameters are extracted from SOHO/MDI magnetograms to characterize properties of the stressed magnetic field in active regions, and their flare productivities are calculated for 1055 active regions. We find that the proposed parameters can be used to distinguish flaring samples from non-flaring samples. Using the long-term accumulated MDI data, we build the solar flare prediction model by using a data mining method. Furthermore, the decision boundary, which is used to divide flaring from non-flaring samples, is determined by the decision tree algorithm. Finally, the performance of the prediction model is evaluated by 10-fold cross validation technology. We conclude that an efficient solar flare prediction model can be built by the proposed longitudinal magnetic field parameters with the data mining method.展开更多
Solar active region （AR） 11283 is a very magnetically complex region and it has produced many eruptions. However, there exists a non-eruptive filament in the plage region just next to an eruptive one in the AR, whic...Solar active region （AR） 11283 is a very magnetically complex region and it has produced many eruptions. However, there exists a non-eruptive filament in the plage region just next to an eruptive one in the AR, which gives us an opportunity to perform a comparison analysis of these two filaments. The coronal magnetic field extrapolated using our CESE-MHD-NLFFF code reveals that two magnetic flux ropes （MFRs） exist in the same extrapolation box supporting these two filaments, respectively. Analysis of the magnetic field shows that the eruptive MFR contains a bald-patch separatrix surface （BPSS） co- spatial very well with a pre-eruptive EUV sigmoid, which is consistent with the BPSS model for coronal sigmoids. The magnetic dips of the non-eruptive MFRs match Hα observation of the non-eruptive filament strikingly well, which strongly supports the MFR-dip model for filaments. Compared with the non-eruptive MFR/filament （with a length of about 200 Mm）, the eruptive MFR/filament is much smaller （with a length of about 20 Mm）, but it contains most of the magnetic free energy in the extrapolation box and holds a much higher free energy density than the non-eruptive one. Both the MFRs are weakly twisted and cannot trigger kink instability. The AR eruptive MFR is unstable because its axis reaches above a critical height for torus instability, at which the overlying closed arcades can no longer confine the MFR stably. On the contrary, the quiescent MFR is very firmly held by its overlying field, as its axis apex is far below the torus-instability threshold height. Overall, this comparison investigation supports that an MFR can exist prior to eruption and the ideal MHD instability can trigger an MFR eruption.展开更多
We analyzed the data on co-rotating interaction regions （CIRs） measured by the Advanced Composition Explorer （ACE） and Solar TErrestrial RElations Observatory （STEREO） from 2007 to 2010. The CIRs were observed b...We analyzed the data on co-rotating interaction regions （CIRs） measured by the Advanced Composition Explorer （ACE） and Solar TErrestrial RElations Observatory （STEREO） from 2007 to 2010. The CIRs were observed by STEREO B （STB）, ACE and STEREOA （STA） one after another, and a total of 28 CIRs were identified in this work. Since the same characteristics of CIRs were detected by these three spacecraft at three different locations and times, these data can help us to study the evolutions of CIRs. For a single event, the properties of CIRs observed by the three spacecraft were quite different and could be explained by spatial or temporal variations. For all these 28 CIRs, STA and STB observed similar mean parameters, such as peak magnetic field strength （offset 11%）, peak and change in solar wind speed （offset 3% and 10% respectively）, peak proton temperature （offset 14%） and peak perpendicular pressure （offset 15%）. Surprisingly, STA detected much higher （41%） peak density of protons than STB.展开更多
We report and analyze observational evidence of global kink oscillations in a solar filament as observed in Ha by instruments administered by National Solar Observatory （NSO）/Global Oscillation Network Group （GONG...We report and analyze observational evidence of global kink oscillations in a solar filament as observed in Ha by instruments administered by National Solar Observatory （NSO）/Global Oscillation Network Group （GONG）. An M1.1-class flare in active region （AR） 11692 occurred on 2013 March 15 and induced a global kink mode in the filament lying towards the southwest of AR 11692. We find periods of about 61-67 minutes and damping times of 92-117 minutes at positions of three ver- tical slices chosen in and around the filament apex. We find that the waves are damped. From the observed period of the global kink mode and damping timescale using the theory of resonant absorption, we perform prominence seismology. We estimate a lower cut-off value for the inhomogeneity length scale to be around 0.34-0.44 times the radius of the filament cross-section.展开更多
We attempt to propose a method for automatically detecting the solar filament chirality and barb beating. We first introduce the concept of an unweighted undirected graph and adopt the Dijkstra shortest path algorithm...We attempt to propose a method for automatically detecting the solar filament chirality and barb beating. We first introduce the concept of an unweighted undirected graph and adopt the Dijkstra shortest path algorithm to recognize the filament spine. Then, we use the polarity inversion line （PIL） shift method for measuring the polarities on both sides of the filament, and employ the connected components labeling method to identify the barbs and calculate the angle between each barb and the spine to determine the bearing of the barbs, i.e., left or right. We test the automatic detection method with Ha filtergrams from the Big Bear Solar Observatory （BBSO） Ha archive and magnetograms observed with the Helioseismic and Magnetic Imager （HMI） on board the Solar Dynamics Observatory （SDO）. Four filaments are automatically detected and illustrated to show the results. The barbs in different parts of a filament may have opposite bearings. The filaments in the southern hemisphere （northern hemisphere） mainly have left-bearing （fight- bearing） barbs and positive （negative） magnetic helicity, respectively. The tested results demonstrate that our method is efficient and effective in detecting the bearing of filament barbs. It is demonstrated that the conventionally believed one-to-one correspondence between filament chirality and barb bearing is not valid. The correct detection of the filament axis chirality should be done by combining both imaging morphology and magnetic field observations.展开更多
Starting from a dipole field ment of field lines on the photosphere, and a given distribution of footpoint displacewe find axisymmetric, force-free field solutions in spherical coordinates that have the same distribut...Starting from a dipole field ment of field lines on the photosphere, and a given distribution of footpoint displacewe find axisymmetric, force-free field solutions in spherical coordinates that have the same distribution of normal field on the photosphere and magnetic topology as the dipole field. A photospheric shear is introduced in the azimuthal direction in a region that strides across the equator and ends at latitude λs. The footpoint displacement has a sine distribution in latitude and a peak amplitude of φm. The magnetic energy E, azimuthal flux Fφ, and magnetic helicity lit in the solar corona are then calculated for each force-free field solution. It is found that for a given shear region range λs, all of the three quantities increase monotonically with increasing φm. In particular, both Fφ and HT have a linear dependence on φm. When φm reaches a certain critical value φmc, the force-free field loses equilibrium, leading to a partial opening of the field and the appearance of a current sheet in the equatorial plane. At this point, E, Fφ and HT reach their maximum values, Ec, Fφc and HTo Ec increases, and Fφc and HTc decrease with decreasing λs. It is found that Ec is always smaller than the open field energy, in agreement with the Aly conjecture. Of the three critical parameters, Ec has the weakest dependence on λs. Therefore, if one is interested in the transition of a magnetic configuration from a stable state to a dynamic one, the magnetic energy is probably the most appropriate marker of the transition.展开更多
EUV cyclones are rotating structures in the solar corona, and they are usually rooted in the underlying rotating network magnetic fields in the photosphere. However, their connection with the surrounding magnetic fiel...EUV cyclones are rotating structures in the solar corona, and they are usually rooted in the underlying rotating network magnetic fields in the photosphere. However, their connection with the surrounding magnetic fields remains unknown. Here we report an observational study of four typical cyclones which are rooted in different kinds of magnetic fields. We use Solar Dynamics Observatory^Atmospheric Imaging Assembly data to investigate the rotation of EUV features in cyclones and Helioseismic and Magnetic Imager data to study the associated magnetic fields. The results show that, （1） an EUV cyclone rooted in a sunspot rotates with the photo- spheric magnetic field; （2） two EUV cyclones in two faculae of an active region are connected to the same sunspot of the active region but rotate oppositely; （3） an EUV cyclone is rooted in a coronal hole with weak open magnetic fields; （4） a pair of con- jugated cyclones is rooted in magnetic fields that have opposite polarity with opposite directions of rotation. The differences in the spatial extent of a cyclone, characteristics of its rotation and underlying fields indicate that cyclones are ubiquitous over the solar atmosphere and that the magnetic structures relevant to the cyclones are more complicated than expected.展开更多
With data from the Atmospheric Imaging Assembly and the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory, we present a mag- netic interaction between an isolated coronal hole （CH） and an emerg...With data from the Atmospheric Imaging Assembly and the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory, we present a mag- netic interaction between an isolated coronal hole （CH） and an emerging active re- gion （AR）. The AR emerged nearby the CH and interacted with it. Bright loops con- stantly formed between them, which led to a continuous retreat of the CH boundaries （CHBs）. Meanwhile, two coronal dimmings respectively appeared at the negative po- laxity of the AR and the east boundary of the bright loops, and the AR was partly disturbed. Loop eruptions followed by a flare occurred in the AR. The interaction was also accompanied by many jets and an arc-shaped brightening that appeared to be observational signatures of magnetic reconnection at the CHBs. By comparing the observations with the derived coronal magnetic configuration, it is suggested that the interaction between the CH and the AR excellently agreed with the model of inter- change reconnection. It appears that our observations provide obvious evidence for interchange reconnection.展开更多
基金supported by the National Natural Science Foundations of China (Nos. 10573025,40674081 and 40890161)the CAS Project KJCX2-YW-T04the National Basic Research Program of China under grant G2006CB806303
文摘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. Six 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 in a cluster of mixed polarities is detected at the position of a granule as soon as the granule breaks up. （4） A dipole emerges accompanied by the development of a granule, and the two elements of the dipole are rooted 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 the 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 in a granular cell, the granule shrinks and then disappears. （7） Horizontal magnetic fields are enhanced at the places where dipoles emerge and where opposite polarities cancel each other, but only the horizontal fields between the dipolar elements point in an orderly way from the positive elements to the negative ones. Our results reveal that granules and small-scale magnetic fluxes 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 canceling magnetic element. This phenomenon may be caused by the upward flow produced by magnetic reconnection below the photosphere.
基金supported by the National Natural Science Foundation of China (10873020, 10703007, G10573025, 40674081, 10603008, 10733020 and 40890161)the Chinese Academy of Sciences Project KJCX2-YW-T04the National Basic Research Program of China(G2006CB806303)
文摘From the observed vector magnetic fields by the Solar Optical Telescope/ Spectro-Polarimeter aboard the satellite Hinode, we have examined whether or not the quiet Sun magnetic fields are non-potential, and how the G-band filigrees and Ca II network bright points （NBPs） are associated with the magnetic non-potentiality. A sizable quiet region in the disk center is selected for this study. The new findings by the study are as follows. （1） The magnetic fields of the quiet region are obviously non-potential. The region-average shear angle is 40°, the average vertical current is 0.016A m^-2, and the average free magnetic energy density, 2.7× 10^2erg cm^-3. The magnitude of these non-potential quantities is comparable to that in solar active regions. （2） There are overall correlations among current helicity, free magnetic energy and longitudinal fields. The magnetic non-potentiality is mostly concentrated in the close vicinity of network elements which have stronger longitudinal fields. （3） The filigrees and NBPs are magnetically characterized by strong longitudinal fields, large electric helicity, and high free energy density. Because the selected region is away from any enhanced network, these new results can generally be applied to the quiet Sun. The findings imply that stronger network elements play a role in high magnetic non-potentiality in heating the solar atmosphere and in conducting the solar wind.
基金Support for the post-launch operation is provided by JAXA and NAOJ (Japan), STFC (UK), NASA (USA), ESA and NSC (Norway)financial the German Science Foundation (DFG) under grant DE 787/3-1
文摘We present properties of intensity oscillations of a sunspot in the photo- sphere and chromosphere using G band and Ca u H filtergrams from Hinode. Intensity power maps as function of magnetic field strength and frequency reveal reduction of power in the G band with an increase in photospheric magnetic field strength at all frequencies. In Ca II H, however, stronger fields exhibit more power at high frequen- cies, particularly in the 4.5-8.0 mHz band. Power distributions in different locations of the active region show that the oscillations in Ca II H exhibit more power compared to that of the G band. We also relate the power in intensity oscillations with differ- ent components of the photospheric vector magnetic field using near simultaneous spectro-polarimetric observations of the sunspot from the Hinode spectropolarime- ter. The photospheric umbral power is strongly anti-correlated with the magnetic field strength and its line-of-sight component but there is a good correlation with the trans- verse component. A reversal of this trend is observed in the chromosphere except at low frequencies （V≤ 1.5 mHz）. The power in sunspot penumbrae is anti-correlated with the magnetic field parameters at all frequencies （1.0 ≤ v ≤ 8.0 mHz） in both the photosphere and chromosphere, except that the chromospheric power shows a strong correlation in the frequency range 3-3.5 mHz.
基金supported by the National Basic Research Program of China(973 program,Grant No. 2011CB811403)the National Natural Science Foundation of China (Grant Nos. 11025315,10921303,10973019,11003024,40890161,11203037 and 41074123)the CAS Project KJCX2-EW-T07
文摘Magnetic non-potentiality is important for understanding flares and other solar activities in active regions （ARs）. Five non-potential parameters, i.e. electric current, current helicity, source field, photospheric free energy, and angular shear, are calculated to quantify the non-potentiality of NOAA AR 11158. Benefitting from the high spatial resolution, high cadence and continuous temporal coverage of vector mag- netograms from the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory, both the long-term evolution of the AR and the rapid change during flares are studied. We confirm that, compared with the magnetic flux, the magnetic non-potentiality has a closer connection with the flare, and the emerging flux regions are important for understanding the magnetic non-potentiality and flares. The main re- suits are as follows. （1） The vortex in the source field directly displays the deflection of the horizontal magnetic field. The deflection corresponds to the fast rotating sunspot with a time delay, which suggests that the sunspot rotation leads to an increase in the non-potentiality. （2） Two areas that have evident changes in the azimuth of the vector magnetic field are found near the magnetic polarity inversion line. The change rates of the azimuth are about 1.3° h-1 and 3.6° h-1, respectively. （3） Rapid and prominent increases are found in the variation of helicity during four flares in the regions where their initial brightening occurs. The recovery of the increases takes 3-4 h for the two biggest flares （X2.2 and M6.6）, but only takes about 2 h for the two other smaller flares （M2.2 and M1.6）.
文摘The solar active region NOAA 11719 produced a large two-ribbon flare on 2013 April 11. We have investigated sudden variations in the photospheric magnetic fields in this active region during the flare by employing magnetograms obtained in the spectral line Fe I 6173 A acquired by the Helioseismic and Magnetic Imager （HMI） onboard the Solar Dynamics Observatory （SDO） spacecraft. The analysis of the line-of-sight magnetograms from HMI show sudden and persistent magnetic field changes at different locations of the active region before the onset of the flare and during the flare. The vector magnetic field observations available from HMI also show coincident variations in the total magnetic field strength and its inclination angle at these locations. Using the simultaneous Dopplergrams obtained from HMI, we observe perturbations in the photospheric Doppler signals following the sudden changes in the magnetic fields in the aforementioned locations. The power spectrum analysis of these velocity signals shows enhanced acoustic power in these affected locations during the flare as compared to the pre-flare condition. Accompanying these observations, we have also used nearly simultaneous chromospheric observations obtained in the spectral line Ha 6562.8 A by the Global Oscillation Network Group （GONG） to study the evolution of flare- ribbons and intensity oscillations in this active region. The Ha intensity oscillations also show enhanced oscillatory power during the flare in the aforementioned locations. These results indicate that the transient Lorentz force associated with sudden changes in the magnetic fields could drive localized photospheric and chromospheric oscillations, like the flare-induced oscillations in the solar atmosphere.
基金Supported by the National Natural Science Foundation of China(Grant Nos. 10773032,11073058 and 10833007)the National Basic Research Program of China (973 program,No. 2011CB811402)
文摘Based on Dulk and Marsh＇s approximate theory about nonthermal gyrosyn- chrotron radiation, one simple impulsive microwave burst with a loop-like structure is selected for radio diagnostics of the coronal magnetic field and column density of non- thermal electrons, which are calculated from the brightness temperature, polarization degree, and spectral index, as well as the turnover frequency, observed by using the Nobeyama Radioheliograph and the Nobeyama Radio Polarimeters, respectively. Very strong variations （up to one or two orders of magnitude） of the calculated transverse and longitudinal magnetic fields with respect to the line-of-sight, as well as the cal- culated electron column density, appear in the looptop and footpoint sources during the burst. The absolute magnitude and varied range of the transverse magnetic field are evidently larger than those of the longitudinal magnetic field. The time evolution of the transverse magnetic field is always anti-correlated with that of the longitudi- nal magnetic field, but positively correlated with that of the electron column density. These results strongly support the idea that quantifying the energy released in a flare depends on a reconstruction of the coronal magnetic field, especially for the trans- verse magnetic field, and they are basically consistent with the recent theoretical and observational studies on the photospheric magnetic field in solar flares.
基金Supported by the National Natural Science Foundation of China
文摘We present a rare observation of direct magnetic interaction between an activating filament and a coronal hole （CH）. The filament was a quiescent one located at the northwest of the CH. It underwent a nonradial activation, during which filament material constantly fell and intruded into the CH. As a result, the CH was clearly destroyed by the intrusion. Brightenings appeared at the boundaries and in the interior of the CH, meanwhile, its west boundaries began to retreat and the area gradually shrank. It is noted that the CH went on shrinking after the end of the intrusion and finally disappeared entirely. Following the filament activation, three coronal dimmings （D1-D3） were formed, among which D1 and D2 persisted throughout the complete disappearance of the CH. The derived coronal magnetic configuration shows that the filament was located below an extended loop system, which obviously linked D1 to D2. By extrapolating this result, our observations imply that the interaction between the filament and the CH involved direct intrusion of the filament material to the CH and the disappearance of the CH might be due to interchange reconnection between the expanding loop system and the CH＇s open field.
基金the National Natural Science Foundation of China
文摘Magnetic topology has been a key to the understanding of magnetic energy release mechanism. Based on observed vector magnetograms, we have determined the threedimensional （3D） topology skeleton of the magnetic fields in the active region NOAA 10720. The skeleton consists of six 3D magnetic nulls and a network of corresponding spines, fans, and null-null lines. For the first time, we have identified a spiral magnetic null in Sun＇s corona. The magnetic lines of force twisted around the spine of the null, forming a ＇magnetic wreath＇ with excess of free magnetic energy and resembling observed brightening structures at extraultraviolet （EUV） wavebands. We found clear evidence of topology eruptions which are referred to as catastrophic changes of topology skeleton associated with a coronal mass ejection （CME） and an explosive X-ray flare. These results shed new lights on the structural complexity and its role in explosive magnetic activity. The concept of flux rope has been widely used in modelling explosive magnetic activity, although their observational identity is rather obscure or, at least, lacking of necessary details up to date. We suggest that the magnetic wreath associated with the 3D spiral null is likely an important class of the physical entity of flux ropes.
基金supported by the National Natural Science Foundation of China(Grant Nos.11103090,11025315,40890161,10921303,40825014, and 40890162)the CAS project KJCX2-YW-T04,the National Basic Research Program of China (973 Program,No.2011CB811403)the Shandong Provincial Natural Science Foundation, China(ZR 2011AQ009)
文摘Using the multi-wavelength data from the Atmospheric Imaging Assembly （AIA） onboard the Solar Dynamics Observatory （SDO） spacecraft, we study a jet occurring in a coronal hole near the northern pole of the Sun. The jet presented distinct upward helical motion during ejection. By tracking six identified moving features （MFs） in the jet, we found that the plasma moved at an approximately constant speed along the jet＇s axis. Meanwhile, the MFs made a circular motion in the plane transverse to the axis. Inferred from linear and trigonometric fittings to the axial and transverse heights of the six tracks, the mean values of the axial velocities, transverse velocities, angular speeds, rotation periods, and rotation radii of the jet are 114 km s-1, 136 km s-1, 0.81° s-1, 452 s and 9.8 × 10^3 km respectively. As the MFs rose, the jet width at the corresponding height increased. For the first time, we derived the height variation of the longitudinal magnetic field strength in the jet from the assumption of magnetic flux conservation. Our results indicate that at heights of 1 × 10^4 -7 × 10^4 km from the base of the jet, the flux density in the jet decreases from about 15 to 3 G as a function of B = 0.5（R/R） - 1）-0.84 （G）. A comparison was made with other results in previous studies.
基金supported by the National Natural Science Foundation of China (Grant No. 11078010)
文摘Solar flares strongly influence space weather and human activities, and their prediction is highly complex. The existing solutions such as data based approaches and model based approaches have a common shortcoming which is the lack of human engagement in the forecasting process. An image-case-based reasoning method is introduced to achieve this goal. The image case library is com- posed of SOHO/MDI longitudinal magnetograms, the images from which exhibit the maximum hori- zontal gradient, the length of the neutral line and the number of singular points that are extracted for retrieving similar image cases. Genetic optimization algorithms are employed for optimizing the weight assignment for image features and the number of similar image cases retrieved. Similar image cases and prediction results derived by majority voting for these similar image cases are output and shown to the forecaster in order to integrate his/her experience with the final prediction results. Experimental results demonstrate that the case-based reasoning approach has slightly better performance than other methods, and is more efficient with forecasts improved by humans.
基金Supported by the National Natural Science Foundation of China.
文摘We study the magnetic structure of five well-known active regions that produced great flares （X5 or larger）. The six flares under investigation are the X12 flare on 1991 June 9 in AR 6659, the X5.7 flare on 2000 July 14 in AR 9077, the X5.6 flare on 2001 April 6 in AR 9415, the X5.3 flare on 2001 August 25 in AR 9591, the X17 flare on 2003 October 28 and the X10 flare on 2003 October 29, both in AR 10486. The last five events had corresponding LASCO observations and were all associated with Halo CMEs. We analyzed vector magnetograms from Big Bear Solar Observatory, Huairou Solar Observing Station, Marshall Space Flight Center and Mees Solar Observatory. In particular, we studied the magnetic gradient derived from line-of-sight magnetograms and magnetic shear derived from vector magnetograms, and found an apparent correlation between these two parameters at a level of about 90%. We found that the magnetic gradient could be a better proxy than the shear for predicting where a major flare might occur： all six flares occurred in neutral lines with maximum gradient. The mean gradient of the flaring neutral lines ranges from 0.14 to 0.50 G km^-1, 2.3 to 8 times the average value for all the neutral lines in the active regions. If we use magnetic shear as the proxy, the flaring neutral line in at least one, possibly two, of the six events would be mis-identified.
基金supported by the National Basic Research Program of China (973 Program, Grant No. 2011CB811406)the National Natural Science Foundation of China(Grant Nos.11273031,10733020,10921303 and 11078010)the China Meteorological Administration grant (No. GYHY201106011)
文摘Three new longitudinal magnetic field parameters are extracted from SOHO/MDI magnetograms to characterize properties of the stressed magnetic field in active regions, and their flare productivities are calculated for 1055 active regions. We find that the proposed parameters can be used to distinguish flaring samples from non-flaring samples. Using the long-term accumulated MDI data, we build the solar flare prediction model by using a data mining method. Furthermore, the decision boundary, which is used to divide flaring from non-flaring samples, is determined by the decision tree algorithm. Finally, the performance of the prediction model is evaluated by 10-fold cross validation technology. We conclude that an efficient solar flare prediction model can be built by the proposed longitudinal magnetic field parameters with the data mining method.
基金supported by the 973 program under grant 2012CB825601the Chinese Academy of Sciences (KZZD-EW-01-4)+3 种基金the National Natural Science Foundation of China (Nos.41204126,41231068,41274192,41031066 and 41374176)the Specialized Research Fund for State Key Laboratoriessupported by NSFAGS1153323 and AGS1062050support by the Youth Innovation Promotion Association of CAS (2015122)
文摘Solar active region （AR） 11283 is a very magnetically complex region and it has produced many eruptions. However, there exists a non-eruptive filament in the plage region just next to an eruptive one in the AR, which gives us an opportunity to perform a comparison analysis of these two filaments. The coronal magnetic field extrapolated using our CESE-MHD-NLFFF code reveals that two magnetic flux ropes （MFRs） exist in the same extrapolation box supporting these two filaments, respectively. Analysis of the magnetic field shows that the eruptive MFR contains a bald-patch separatrix surface （BPSS） co- spatial very well with a pre-eruptive EUV sigmoid, which is consistent with the BPSS model for coronal sigmoids. The magnetic dips of the non-eruptive MFRs match Hα observation of the non-eruptive filament strikingly well, which strongly supports the MFR-dip model for filaments. Compared with the non-eruptive MFR/filament （with a length of about 200 Mm）, the eruptive MFR/filament is much smaller （with a length of about 20 Mm）, but it contains most of the magnetic free energy in the extrapolation box and holds a much higher free energy density than the non-eruptive one. Both the MFRs are weakly twisted and cannot trigger kink instability. The AR eruptive MFR is unstable because its axis reaches above a critical height for torus instability, at which the overlying closed arcades can no longer confine the MFR stably. On the contrary, the quiescent MFR is very firmly held by its overlying field, as its axis apex is far below the torus-instability threshold height. Overall, this comparison investigation supports that an MFR can exist prior to eruption and the ideal MHD instability can trigger an MFR eruption.
基金supported by a National Natural Science Foundation of China (No. 11203083)
文摘We analyzed the data on co-rotating interaction regions （CIRs） measured by the Advanced Composition Explorer （ACE） and Solar TErrestrial RElations Observatory （STEREO） from 2007 to 2010. The CIRs were observed by STEREO B （STB）, ACE and STEREOA （STA） one after another, and a total of 28 CIRs were identified in this work. Since the same characteristics of CIRs were detected by these three spacecraft at three different locations and times, these data can help us to study the evolutions of CIRs. For a single event, the properties of CIRs observed by the three spacecraft were quite different and could be explained by spatial or temporal variations. For all these 28 CIRs, STA and STB observed similar mean parameters, such as peak magnetic field strength （offset 11%）, peak and change in solar wind speed （offset 3% and 10% respectively）, peak proton temperature （offset 14%） and peak perpendicular pressure （offset 15%）. Surprisingly, STA detected much higher （41%） peak density of protons than STB.
基金support from KU Leuven via GOA/2009-009support from the Interuniversity Attraction Poles Programme initiated by the Belgian Science Policy Office(IAP P7/08 Charm)+1 种基金supported by the Chinese foundations2011CB811402the National Natural Science Foundation of China(Grant Nos.11025314,10933003 and 10673004)
文摘We report and analyze observational evidence of global kink oscillations in a solar filament as observed in Ha by instruments administered by National Solar Observatory （NSO）/Global Oscillation Network Group （GONG）. An M1.1-class flare in active region （AR） 11692 occurred on 2013 March 15 and induced a global kink mode in the filament lying towards the southwest of AR 11692. We find periods of about 61-67 minutes and damping times of 92-117 minutes at positions of three ver- tical slices chosen in and around the filament apex. We find that the waves are damped. From the observed period of the global kink mode and damping timescale using the theory of resonant absorption, we perform prominence seismology. We estimate a lower cut-off value for the inhomogeneity length scale to be around 0.34-0.44 times the radius of the filament cross-section.
基金supported by NKBRSF (Grant Nos.2011CB811402 and 2014CB744203)the National Natural Science Foundation of China (Grant Nos.11203014,11533005 and 11025314)the grants from CSC201306190046 and CXZZ130041
文摘We attempt to propose a method for automatically detecting the solar filament chirality and barb beating. We first introduce the concept of an unweighted undirected graph and adopt the Dijkstra shortest path algorithm to recognize the filament spine. Then, we use the polarity inversion line （PIL） shift method for measuring the polarities on both sides of the filament, and employ the connected components labeling method to identify the barbs and calculate the angle between each barb and the spine to determine the bearing of the barbs, i.e., left or right. We test the automatic detection method with Ha filtergrams from the Big Bear Solar Observatory （BBSO） Ha archive and magnetograms observed with the Helioseismic and Magnetic Imager （HMI） on board the Solar Dynamics Observatory （SDO）. Four filaments are automatically detected and illustrated to show the results. The barbs in different parts of a filament may have opposite bearings. The filaments in the southern hemisphere （northern hemisphere） mainly have left-bearing （fight- bearing） barbs and positive （negative） magnetic helicity, respectively. The tested results demonstrate that our method is efficient and effective in detecting the bearing of filament barbs. It is demonstrated that the conventionally believed one-to-one correspondence between filament chirality and barb bearing is not valid. The correct detection of the filament axis chirality should be done by combining both imaging morphology and magnetic field observations.
基金Supported by the National Natural Science Foundation of China
文摘Starting from a dipole field ment of field lines on the photosphere, and a given distribution of footpoint displacewe find axisymmetric, force-free field solutions in spherical coordinates that have the same distribution of normal field on the photosphere and magnetic topology as the dipole field. A photospheric shear is introduced in the azimuthal direction in a region that strides across the equator and ends at latitude λs. The footpoint displacement has a sine distribution in latitude and a peak amplitude of φm. The magnetic energy E, azimuthal flux Fφ, and magnetic helicity lit in the solar corona are then calculated for each force-free field solution. It is found that for a given shear region range λs, all of the three quantities increase monotonically with increasing φm. In particular, both Fφ and HT have a linear dependence on φm. When φm reaches a certain critical value φmc, the force-free field loses equilibrium, leading to a partial opening of the field and the appearance of a current sheet in the equatorial plane. At this point, E, Fφ and HT reach their maximum values, Ec, Fφc and HTo Ec increases, and Fφc and HTc decrease with decreasing λs. It is found that Ec is always smaller than the open field energy, in agreement with the Aly conjecture. Of the three critical parameters, Ec has the weakest dependence on λs. Therefore, if one is interested in the transition of a magnetic configuration from a stable state to a dynamic one, the magnetic energy is probably the most appropriate marker of the transition.
基金supported by the National Basic Research Program of China under grant 2011CB811403the National Natural Science Foundation of China (11221063, 11303050, 11303049 and 11203037)+1 种基金the CAS Project KJCX2-EW-T07the Strategic Priority Research Program-The Emergence of Cosmological Structures of the Chinese Academy of Sciences, Grant No. XDB09000000
文摘EUV cyclones are rotating structures in the solar corona, and they are usually rooted in the underlying rotating network magnetic fields in the photosphere. However, their connection with the surrounding magnetic fields remains unknown. Here we report an observational study of four typical cyclones which are rooted in different kinds of magnetic fields. We use Solar Dynamics Observatory^Atmospheric Imaging Assembly data to investigate the rotation of EUV features in cyclones and Helioseismic and Magnetic Imager data to study the associated magnetic fields. The results show that, （1） an EUV cyclone rooted in a sunspot rotates with the photo- spheric magnetic field; （2） two EUV cyclones in two faculae of an active region are connected to the same sunspot of the active region but rotate oppositely; （3） an EUV cyclone is rooted in a coronal hole with weak open magnetic fields; （4） a pair of con- jugated cyclones is rooted in magnetic fields that have opposite polarity with opposite directions of rotation. The differences in the spatial extent of a cyclone, characteristics of its rotation and underlying fields indicate that cyclones are ubiquitous over the solar atmosphere and that the magnetic structures relevant to the cyclones are more complicated than expected.
基金Supported by the National Natural Science Foundation of China
文摘With data from the Atmospheric Imaging Assembly and the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory, we present a mag- netic interaction between an isolated coronal hole （CH） and an emerging active re- gion （AR）. The AR emerged nearby the CH and interacted with it. Bright loops con- stantly formed between them, which led to a continuous retreat of the CH boundaries （CHBs）. Meanwhile, two coronal dimmings respectively appeared at the negative po- laxity of the AR and the east boundary of the bright loops, and the AR was partly disturbed. Loop eruptions followed by a flare occurred in the AR. The interaction was also accompanied by many jets and an arc-shaped brightening that appeared to be observational signatures of magnetic reconnection at the CHBs. By comparing the observations with the derived coronal magnetic configuration, it is suggested that the interaction between the CH and the AR excellently agreed with the model of inter- change reconnection. It appears that our observations provide obvious evidence for interchange reconnection.
