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3-D nonlinear force-free field reconstruction of solar active region 11158 by direct boundary integral equation  

Yihua Yan   Submitted: 2013-06-05 18:21

A 3-D coronal magnetic field is reconstructed for the NOAA active region 11158 on February 14, 2011. A GPU-accelerated direct boundary integral equation (DBIE) method is implemented. This is approximately 1000 times faster than the original DBIE used on solar non-linear force-free field modeling. Using the SDO/HMI vector magnetogram as the bottom boundary condition, the reconstructed magnetic field lines are compared with the projected EUV loop structures as observed by SDO/AIA at front view and the STEREO A/B spacecraft at side views for the first time. They show very good agreement three-dimensionally so that the topology configurations of the magnetic fields can be analyzed, thus its role in the flare process of the active region can be better understood. A quantitative comparison with some stereoscopically reconstructed coronal loops shows that the present averaged misalignment angles are at the same order as the state-of-the-art results obtained with reconstructed coronal loops as prescribed conditions. It is found that the observed coronal loop structures can be grouped into a number of closed and open field structures with some central bright coronal loop features around the polarity inversion line. The reconstructed highly-shearing magnetic field lines agree very well with the low-lying sigmoidal filament along the polarity inversion line. They are in a pivot position to all other surrounding coronal structures, and a group of electric current lines co-aligned with the central bright EUV loops overlying the filament channel is also obtained. This central lower-lying magnetic field loop system must have played a key role in powering the flare. It should be noted that while a strand-like coronal feature along the polarity inversion line may be related to the filament, one cannot simply attribute all the coronal bright features along the polarity inversion line to manifestation of the filament without any stereoscopically information. The numerical procedure and the comparison against a benchmark test case are also presented to validate that the DBIE method is rigorous and effective.

Authors: Rui Wang, Yihua Yan, Baolin Tan
Projects: SDO-AIA,SDO-HMI,STEREO

Publication Status: Solar Physics, accepted
Last Modified: 2013-06-11 11:32
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Relaxation of magnetic field relative to plasma density revealed from microwave zebra patterns associated with solar flares  

Yihua Yan   Submitted: 2012-11-01 19:52

It is generally considered that the emission of microwave zebra pattern (ZP) structures requires high density and high temperatures, which is similar to the situation of the flaring region where primary energy releases. Therefore, the parameters analysis of ZPs may reveal the physical conditions of the flaring source region. This work investigates the variations of 74 microwave ZP structures observed by Chinese Solar Broadband Radio Spectrometer (SBRS/Huairou) at 2.6-3.8 GHz in 9 solar flares, and found that the ratio between the plasma density scale height LN and the magnetic field scale height LB in emission source displays a tendency of decrease during the flaring processes. The ratio LN/LB is about 3-5 before the maximum of flares. It decreases to about 2 after the maximum. The detailed analysis of three typical X-class flares implied that the variation of LN/LB during the flaring process is most likely due to the topological changes of the magnetic field in the flaring source region, and the step-wise decrease of LN/LB possibly reflects the magnetic field relaxation relative to the plasma density when the flaring energy released. This result may also constrain the solar flare modeling to some extent.

Authors: Sijie Yu, Yihua Yan, and Baolin Tan
Projects: ACE,GOES X-rays ,Hinode/XRT,Nobeyama Radioheliograph,TRACE

Publication Status: ApJ, accepted
Last Modified: 2012-11-04 15:13
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The Morphologic Properties of Magnetic networks over the Solar Cycle 23  

Yihua Yan   Submitted: 2012-10-17 19:41

The morphologic properties of the magnetic networks during Carrington Rotations (CR) 1955 to 2091 (from 1999 to 2010) have been analyzed by applying the watershed algorithm to magnetograms observed by the Michelson Doppler Interferometer (MDI) on board the Solar and Heliospheric Observatory (SOHO) spacecraft. We find that the average area of magnetic cells on the solar surface at lower latitudes (within ?50 deg) are smaller than those at higher latitudes (beyond ?50 deg). Statistical analysis of these data indicates that the magnetic networks are of fractal in nature, and the average fractal dimension is Df = 1.253?0.011. We also find that both the fractal dimension and the size of the magnetic networks are anti-correlated with the sunspot area. This is perhaps because a strong magnetic field can suppress spatially modulated oscillation, compress the boundaries of network cells, leading to smoother cell boundaries. The fractal dimension of the cell deviates that predicted from an isobar of Kolmogorov k-5/3 homogeneous turbulence.

Authors: Chong Huang, Yihua Yan, Yin Zhang, Baolin Tan and Gang Li
Projects: SoHO-MDI

Publication Status: The Astrophysical Journal, Volume 759, Issue 2, 106 (2012)
Last Modified: 2012-11-02 11:14
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Subject will be restored when possible  

Yihua Yan   Submitted: 2007-10-08 04:16

On 2006 December 13 during the solar minimum, the superactive region NOAA 10930 at S05W33 disk location produced an X3.4/4B flare at 02:40 UT. Fine structures were observed in the radio spectra, which include spikes, reverse slope type III bursts, type U burst, V-shaped burst, pulsations, zebra patterns and firstly-discovered sub-second spiky zebra-like structures, superimposed in the 2.6 - 3.8 GHz type IV bursts. The radio fine structures during the impulsive phase of the flare may be closely associated with coronal structures during the magnetic reconnection process as revealed by {Hinode} soft X-ray images. Thus these microwave fine structure observations may provide very useful diagnostics in the primary energy release sites when they occur in the impulsive flare phase. For this flare event, the estimated coronal magnetic field is about 50 - 170 G in the rising phase of the flare with a source density of about 1 imes1011cm-3. The field strength and plasma density are about 90-200 G and 1.27 imes1011cm-3 around the flare maximum.

Authors: Yihua Yan, Jing Huang, Bin Chen, Takashi Sakurai
Projects: Hinode,RHESSI,SoHO-MDI

Publication Status: PASJ Vol.59, 2007 (Hinode issue)
Last Modified: 2007-10-08 07:11
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Subject will be restored when possible  

Yihua Yan   Submitted: 2007-10-08 04:16

On 2006 December 13 during the solar minimum, the superactive region NOAA 10930 at S05W33 disk location produced an X3.4/4B flare at 02:40 UT. Fine structures were observed in the radio spectra, which include spikes, reverse slope type III bursts, type U burst, V-shaped burst, pulsations, zebra patterns and firstly-discovered sub-second spiky zebra-like structures, superimposed in the 2.6 - 3.8 GHz type IV bursts. The radio fine structures during the impulsive phase of the flare may be closely associated with coronal structures during the magnetic reconnection process as revealed by {Hinode} soft X-ray images. Thus these microwave fine structure observations may provide very useful diagnostics in the primary energy release sites when they occur in the impulsive flare phase. For this flare event, the estimated coronal magnetic field is about 50 - 170 G in the rising phase of the flare with a source density of about 1 imes1011cm-3. The field strength and plasma density are about 90-200 G and 1.27 imes1011cm-3 around the flare maximum.

Authors: Yihua Yan, Jing Huang, Bin Chen, Takashi Sakurai
Projects: Hinode,RHESSI,SoHO-MDI

Publication Status: PASJ Vol.59, 2007 (Hinode special issue, in press)
Last Modified: 2007-10-08 17:14
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Subject will be restored when possible  

Yihua Yan   Submitted: 2007-10-08 04:16

On 2006 December 13 during the solar minimum, the superactive region NOAA 10930 at S05W33 disk location produced an X3.4/4B flare at 02:40 UT. Fine structures were observed in the radio spectra, which include spikes, reverse slope type III bursts, type U burst, V-shaped burst, pulsations, zebra patterns and firstly-discovered sub-second spiky zebra-like structures, superimposed in the 2.6 - 3.8 GHz type IV bursts. The radio fine structures during the impulsive phase of the flare may be closely associated with coronal structures during the magnetic reconnection process as revealed by {Hinode} soft X-ray images. Thus these microwave fine structure observations may provide very useful diagnostics in the primary energy release sites when they occur in the impulsive flare phase. For this flare event, the estimated coronal magnetic field is about 50 - 170 G in the rising phase of the flare with a source density of about 1 imes1011cm-3. The field strength and plasma density are about 90-200 G and 1.27 imes1011cm-3 around the flare maximum.

Authors: Yihua Yan, Jing Huang, Bin Chen, Takashi Sakurai
Projects: Hinode,RHESSI,SoHO-MDI

Publication Status: PASJ Vol.59, 2007 (Hinode special issue, in press)
Last Modified: 2007-10-08 17:18
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Subject will be restored when possible  

Yihua Yan   Submitted: 2007-10-08 04:16

On 2006 December 13 during the solar minimum, the superactive region NOAA 10930 at S05W33 disk location produced an X3.4/4B flare at 02:40 UT. Fine structures were observed in the radio spectra, which include spikes, reverse slope type III bursts, type U burst, V-shaped burst, pulsations, zebra patterns and firstly-discovered sub-second spiky zebra-like structures, superimposed in the 2.6 - 3.8 GHz type IV bursts. The radio fine structures during the impulsive phase of the flare may be closely associated with coronal structures during the magnetic reconnection process as revealed by {Hinode} soft X-ray images. Thus these microwave fine structure observations may provide very useful diagnostics in the primary energy release sites when they occur in the impulsive flare phase. For this flare event, the estimated coronal magnetic field is about 50 - 170 G in the rising phase of the flare with a source density of about 1 imes1011cm-3. The field strength and plasma density are about 90-200 G and 1.27 imes1011cm-3 around the flare maximum.

Authors: Yihua Yan, Jing Huang, Bin Chen, Takashi Sakurai
Projects: Hinode,RHESSI,SoHO-MDI

Publication Status: PASJ Vol.59, 2007 (Hinode special issue, in press)
Last Modified: 2007-10-08 17:20
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A radio burst and its associated CME on 17 March 2002  

Yihua Yan   Submitted: 2006-09-17 23:35

In this study we present a detailed analysis, based on multi-wavelength observations and magnetic field extrapolation, of a radio and X-ray event observed on March 17, 2002. This event was accompanied by a Coronal Mass Ejection (CME) observed by the Large-Angle Spectrometric Coronagraph (LASCO) aboard SOHO. During the main event, the RHESSI mission observed a hard X-ray emission correlated in time with the development of a type III burst group. The CME development, the hard X-ray emission, and the type III burst group appear to be closely associated. The multi-frequency Nanc cay Radioheliograph (NRH) shows that the type III bursts are produced at a distance from the active region which progressively increases with time. Their emitting sources are distributed along the western edge of the CME. We conclude the type III electron beams propagate in the interface region between the ascending CME and the neighboring open field lines. Due to the development of the CME, this region becomes progressively highly compressed. By measuring, at each frequency, the shift versus time of the type III positions, we estimate that the electron density, in this compression region, increased roughly by a factor 10 over a few minutes. Another signature of this compression region is a narrow white light feature interpreted as a coronal shock driven by the CME lateral expansion.

Authors: Y. Yan, M. Pick, M. Wang, S. Krucker, A. Vourlidas
Projects: RHESSI,SoHO-MDI,SoHO-LASCO

Publication Status: Solar Physics, accepted
Last Modified: 2006-09-17 23:35
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On the Coronal Magnetic Field Configuration and Solar Flare/CME Process  

Yihua Yan   Submitted: 2006-01-08 23:44

The coronal magnetic field configuration is important for understanding the energy storage and release processes that account for flares and/or CMEs. Here we present a model which is based on the work for potential magnetic field problems that only applies the condition at infinity with the boundary condition on the solar surface specified. We also discuss some recent progress on general force-free field models. For some event analyses, we have employed MDI/SOHO longitudinal magnetogram insected into the synoptic magnetogram to obtain whole boundary condition over the solar surface. Globally, the extrapolated global magnetic field structures effectively demonstrate the case for the disk signature of the radio CMEs and the evolution of the radio sources during the CME/flare processes.

Authors: Yihua Yan
Projects: None

Publication Status: Space Science Reviews, 2006, in press
Last Modified: 2006-01-08 23:44
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Direct Boundary Integral Formulation for Solar Force-Free Magnetic Fields  

Yihua Yan   Submitted: 2005-11-14 20:49

A direct boundary integral formulation for a force-free magnetic field with finite energy content in the semi space above the Sun is presented. This is a new formulation for a 3-D non-linear force-free field in which the boundary data can easily be incorporated. We have proposed an optimal method to numerically find the non-constant- α force-free field solution at any position in semi-space. Therefore the present computational procedure for the new representation is actually a point-wise method so that no volume integration is needed. A test case study has been carried out to demonstrate the convergence, accuracy and efficiency of the numerical procedures. The computational procedure is quite robust. The agreement between numerical and exact results validate the correctness and merits of the new formulation and computational procedure proposed. The application of the new direct boundary integral formulation to practical solar magnetic field problems is straightforward and prospective.

Authors: Yihua Yan, Zhuheng Li
Projects: None

Publication Status: ApJ, 20 February 2006, v638 2 issue (in press)
Last Modified: 2005-11-14 20:49
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The Magnetic Topological Structure and Energy of the 2B/X2 Flare in NOAA 8100  

Yihua Yan   Submitted: 2001-09-24 03:07

In this paper, we reconstruct the finite energy force-free magnetic field of the active region NOAA 8100 on 4 November 1997 above the photosphere. In particular, the 3-D magnetic field structures before and after a 2B/X2 flare at 05:58 UT in this region are analyzed. The magnetic field lines were extrapolated in close coincidence with the Yohkoh soft X-ray (SXR) loops accordingly. It is found that the active region is composed of an emerging flux loop, a complex loop system with differential magnetic field shear, and large-scale, or open field lines. Similar magnetic connectivity has been obtained for both instants but apparent changes of the twisting situations of the calculated magnetic field lines can be observed that properly align with the corresponding SXR coronal loops. We conclude that this flare was triggered by the interaction of an emerging flux loop and a large loop system with differential magnetic field shear, as well as large-scale, or open field lines. The onset of the flare was at the common footpoints of several interacting magnetic loops and confined near the footpoints of the emerging flux loop. The sheared configuration remained even after the energetic flare, as demonstrated by calculated values of the twist for the loop system, which means that the active region was relaxed to a lower energy state but not completely to the minimum energy state (two days later another X-class flare occurred in this region).

Authors: Yihua Yan, Yang Liu, Maki Akioka, Fengsi Wei
Projects:

Publication Status: Solar Physics, 201 (2):337-355, July 2001.
Last Modified: 2001-09-24 03:07
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Group of type III bursts and its associated spikes  

Yihua Yan   Submitted: 2001-07-24 03:15

A group of type III bursts in solar radio bursts, observed with the 2.6-3.8 GHz spectrometer of the Beijing Astronomical Observatory on April 15 1998, is selected and analyzed. The type III bursts are associated with a large number of spikes, which have been recorded by the spectrometer at high temporal resolution (8 ms). We report the observational characteristics of the type III bursts and the corresponding spikes including duration, frequency bandwidth, drift rate and quasi-periodicity. Afterwards we discuss the space scale, the brightness temperature and the magnetic field strength at the emission source region. Finally we investigate the mechanism which would cause the quasi-periodicity of the type III bursts and the short time scale of the spikes theoretically. It is suggested that the type III bursts and the spikes differ clearly between their source regions in the space scale, the brightness temperature, the magnetic field strength and the magnetic structure.

Authors: Shujuan Wang, Yihua Yan, Qijun Fu
Projects:

Publication Status: Astronomy and Astrophysics, v.373, p.1083-1088 (2001)
Last Modified: 2001-08-24 00:54
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Drifting radio bursts and fine structures in the 0.8-7.6 GHz frequency range observed in the NOAA 9077 AR (July 10-14, 2000) solar flares  

Yihua Yan   Submitted: 2001-04-15 21:12

The 0.8-7.6 GHz global and detailed radio spectra of the four most intense flares observed in the NOAA 9077 active region (July 10-14, 2000) are presented. The radio bursts of these flares and their sequence reveal features indicative of topological similarities among the flares under study. The drifting pulsation structures were found to be the typical signatures of these flares. Furthermore, many other fine structures such as narrowband drifting lines, drifting harmonic structure with zebra patterns, drifting branches of narrowband dm-spikes, and structures with fast positively and negatively drifting bursts are shown in the context of the whole radio flares. Some of them were observed for the first time. The relationships among them and the resulting interpretations are summarized. The characteristic periods of the drifting pulsation structures and the magnetic field in the zebra radio source are determined.

Authors: Karlický, M.; Yan, Y.; Fu, Q.; Wang, S.; Jiricka, K.; Meszarosova, H.; Liu, Y.
Projects:

Publication Status: Astronomy and Astrophysics, v.369, p.1104-1111 (2001)
Last Modified: 2001-04-15 21:12
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Extended radio emission after the soft X-ray maximum of the NOAA 9077 AR solar flare on July 10, 2000  

Yihua Yan   Submitted: 2001-04-02 00:01

An extended radio emission after a soft X-ray (SXR) maximum was detected in the active region NOAA 9077 by several observatories for the solar flare after 21:42 UT on July 10, 2000. Also some radio fine structures before the enduring radio emission were observed with the 1.0-2.0 GHz spectrometer of Beijing Astronomical Observatory (BAO) in the same time. We apply a shear-driven quadrupolar reconnection model (SQR) to analyze the fine structures and the related radio emission. We find that the footpoint shear motion of the flux loop is accompanied with the emerging up of the loop during the reconnection process. We tentatively interpret the extended radio emission as the nonthermal radiation caused by a new reconnection process between emerging flux loop and pre-existing overarching loop after the soft X-ray maximum.

Authors: Shujuan Wang, Yihua Yan, and Qijun Fu
Projects:

Publication Status: A&A letters, 2001, in press
Last Modified: 2001-04-02 00:01
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The magnetic rope structure and associated energetic processes in the 2000 July 14 solar flare  

Yihua Yan   Submitted: 2001-03-26 20:23

In the reconstructed non-linear force-free magnetic field of NOAA active region 9077 before the X5.7/3B (10:24 UT) flare on 14 July 2000, we reveal for the first time the presence of a magnetic rope from the extrapolation of the 3-D magnetic field structure. This magnetic rope is located in a space above the magnetic neutral lines of the filament. The calculated field lines of the rope rotate around its axis for more than 3 turns. Overlying the rope are multi-layer magnetic arcades with different orientations. These arcades are in agreement with TRACE observations. The estimated free magnetic energy in this rope system is about 1.6 imes1032 erg. Such magnetic field structure provides a favorable model for the interpretation of the energetic flare processes as revealed by Hα , EUV and radio observations. In particular, the intermittent co-spatial brightening of the rope in EUV 1600 AA~ leading to the onset of the flare suggests that the rope instability may have triggered the flare event, and the drifting pulsation structure in the decimetric frequency range is considered to manifest the initial phase of the coronal mass ejection.

Authors: Yihua Yan, Yuanyong Deng, Marian Karlický, Qijun Fu, Shujuan Wang, Yuying Liu
Projects:

Publication Status: ApJL, v551, April 2001, in press
Last Modified: 2001-03-26 20:32
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Abstracts by Author
3-D nonlinear force-free field reconstruction of solar active region 11158 by direct boundary integral equation
Relaxation of magnetic field relative to plasma density revealed from microwave zebra patterns associated with solar flares
The Morphologic Properties of Magnetic networks over the Solar Cycle 23
Subject will be restored when possible
Subject will be restored when possible
Subject will be restored when possible
Subject will be restored when possible
A radio burst and its associated CME on 17 March 2002
On the Coronal Magnetic Field Configuration and Solar Flare/CME Process
Direct Boundary Integral Formulation for Solar Force-Free Magnetic Fields
The Magnetic Topological Structure and Energy of the 2B/X2 Flare in NOAA 8100
Group of type III bursts and its associated spikes
Drifting radio bursts and fine structures in the 0.8-7.6 GHz frequency range observed in the NOAA 9077 AR (July 10-14, 2000) solar flares
Extended radio emission after the soft X-ray maximum of the NOAA 9077 AR solar flare on July 10, 2000
The magnetic rope structure and associated energetic processes in the 2000 July 14 solar flare

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