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Photospheric Shear Flows in Solar Active Regions and Their Relation to Flare Occurrence  

Sung-Hong Park   Submitted: 2018-07-22 19:31

Solar active regions (ARs) that produce major flares typically exhibit strong plasma shear flows around photospheric magnetic polarity inversion lines (MPILs). It is therefore important to quantitatively measure such photospheric shear flows in ARs for a better understanding of their relation to flare occurrence. Photospheric flow fields were determined by applying the Differential Affine Velocity Estimator for Vector Magnetograms (DAVE4VM) method to a large data set of 2,548 co-aligned pairs of AR vector magnetograms with 12-min separation over the period 2012-2016. From each AR flow-field map, three shear-flow parameters were derived corresponding to the mean (Smean), maximum (Smax) and integral (Ssum) shear-flow speeds along strong-gradient, strong-field MPIL segments. We calculated flaring rates within 24 hr as a function of each shear-flow parameter, and also investigated the relation between the parameters and the waiting time (τ) until the next major flare (class M1.0 or above) after the parameter observation. In general, it is found that the larger Ssum an AR has, the more likely it is for the AR to produce flares within 24 hr. It is also found that among ARs which produce major flares, if one has a larger value of Ssum then τ generally gets shorter. These results suggest that large ARs with widespread and/or strong shear flows along MPILs tend to not only be more flare productive, but also produce major flares within 24 hr or less.

Authors: S.-H. Park, J. A. Guerra, P. T. Gallagher, M. K. Georgoulis, D. S. Bloomfield
Projects: None

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2018-07-23 10:01
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Study of Magnetic Helicity Injection in the Active Regions NOAA 9236 Producing Multiple Flare-associated CME Events  

Sung-Hong Park   Submitted: 2013-08-27 18:14

To better understand a preferred magnetic field configuration and its evolution during Coronal Mass Ejection events, we investigated the spatial and temporal evolution of photospheric magnetic fields in the active region NOAA 9236 that produced eight flare-associated CMEs during the time period of 2000 November 23-26. The time variations of the total magnetic helicity injection rate and the total unsigned magnetic flux are determined and examined not only in the entire active region but also in some local regions such as the main sunspots and the CME-associated flaring regions using SOHO/MDI magnetogram data. As a result, we found that: (1) in the sunspots, a large amount of postive (right-handed) magnetic helicity was injected during most of the examined time period, (2) in the flare region, there was a continuous injection of negative (left-handed) magnetic helicity during the entire period, accompanied by a large increase of the unsigned magnetic flux, and (3) the flaring regions were mainly composed of emerging bipoles of magnetic fragments in which magnetic field lines have substantially favorable conditions for making reconnection with large-scale, overlying, and oppositely directed magnetic field lines connecting the main sunspots. These observational findings can also be well explained by some MHD numerical simulations for CME initiation (e.g., reconnection-favored emerging flux models). We therefore conclude that reconnection-favored magnetic fields in the flaring emerging flux regions play a crucial role in producing the multiple flare-associated CMEs in NOAA 9236.

Authors: Sung-Hong Park, Kanya Kusano, Kyung-Suk Cho, Jongchul Chae, Su-Chan Bong, Pankaj Kumar, So-Young Park, Yeon-Han Kim, Young-Deuk Park
Projects: None

Publication Status: 22 pages, 7 figures, accepted for publication in ApJ
Last Modified: 2013-08-28 14:58
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The Occurrence and Speed of CMEs Related to Two Characteristic Evolution Patterns of Helicity Injection in Their Solar Source Regions  

Sung-Hong Park   Submitted: 2012-03-08 19:46

Long-term (a few days) variation of magnetic helicity injection was calculated for 28 solar active regions which produced 47 CMEs to find its relationships with the CME occurrence and speed using SOHO/MDI line-of-sight magnetograms. As a result, we found that the 47 CMEs can be categorized into two different groups by two characteristic evolution patterns of helicity injection in their source active regions which appeared for about 0.5-4.5 days before their occurrence: (1) a monotonically increasing pattern with one sign of helicity (Group A; 30 CMEs in 23 active regions) and (2) a pattern of significant helicity injection followed by its sign reversal (Group B; 17 CMEs in 5 active regions). We also found that CME speed has a correlation with average helicity injection rate with linear correlation coefficients of 0.85 and 0.63 for Group A and Group B, respectively. In addition, these two CME groups show different characteristics as follows: (1) the average CME speed of Group B (1330km s-1) is much faster than that of Group A (870km s-1), (2) the CMEs in Group A tend to be single events, whereas those in Group B mainly consist of successive events, and (3) flares related to the CMEs in Group B are relatively more energetic and impulsive than those in Group A. Our findings therefore suggest that the two CME groups have different pre-CME conditions in their source active regions and different CME characteristics.

Authors: Sung-Hong Park, Kyung-Suk Cho, Su-Chan Bong, Pankaj Kumar, Jongchul Chae, Rui Liu, Haimin Wang
Projects: None

Publication Status: accepted for publication in ApJ
Last Modified: 2012-03-09 21:05
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Time Evolution of Coronal Magnetic Helicity in the Flaring Active Region NOAA 10930  

Sung-Hong Park   Submitted: 2010-08-09 11:50

To study the three-dimensional (3D) magnetic field topology and its long-term evolution associated with the X3.4 flare of 2006 December 13, we investigate the coronal relative magnetic helicity in the flaring active region (AR) NOAA 10930 during the time period of December 8-14. The coronal helicity is calculated based on the 3D nonlinear force-free magnetic fields reconstructed by the weighted optimization method of Wiegelmann, and is compared with the amount of helicity injected through the photospheric surface of the AR. The helicity injection is determined from the magnetic helicity flux density proposed by Pariat et al. using Solar and Heliospheric Observatory/Michelson Doppler Imager magnetograms. The major findings of this study are the following. (1) The time profile of the coronal helicity shows a good correlation with that of the helicity accumulation by injection through the surface. (2) The coronal helicity of the AR is estimated to be -4.3times1043 Mx2 just before the X3.4 flare. (3) This flare is preceded not only by a large increase of negative helicity, -3.2times1043 Mx2, in the corona over ~1.5 days but also by noticeable injections of positive helicity though the photospheric surface around the flaring magnetic polarity inversion line during the time period of the channel structure development. We conjecture that the occurrence of the X3.4 flare is involved with the positive helicity injection into an existing system of negative helicity.

Authors: Sung-Hong Park, Jongchul Chae, Ju Jing, Changyi Tan, Haimin Wang
Projects: None

Publication Status: ApJ, 2010, 720, 1102-1107
Last Modified: 2010-08-18 08:20
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Productivity of Solar Flares and Magnetic Helicity Injection in Active Regions  

Sung-Hong Park   Submitted: 2010-05-19 20:08

The main objective of this study is to better understand how magnetic helicity injection in an active region is related to the occurrence and intensity of solar flares. We therefore investigate magnetic helicity injection rate and unsigned magnetic flux, as a reference. In total, 378 active regions are analyzed using SOHO/MDI magnetograms. The 24-hour averaged helicity injection rate and unsigned magnetic flux are compared with the flare index and the flare-productive probability in next 24 hours following an measurement. In addition, we study the variation of helicity over a span of several days around the times of the 19 flares above M5.0 which occurred in selected strong flare-productive active regions. The major findings of this study are: (1) for a sub-sample of 91 large active regions with unsigned magnetic fluxes in the range from 3 to 5 imes1022 Mx, there is a difference in magnetic helicity injection rate between flaring active regions and non-flaring active regions by a factor of 2; (2) the GOES C-flare-productive probability as a function of helicity injection displays a sharp boundary between flare-productive active regions and flare-quiet ones; (3) the history of helicity injection before all the 19 major flares displayed a common characteristic: a significant helicity accumulation of (3-45) imes1042 Mx2 during a phase of monotonically increasing helicity over 0.5 to 2 days. Our results support the notion that helicity injection is important in flares, but it is not effective to use it alone for the purpose of flare forecast. It is necessary to find a way to better characterize the time history of helicity injection as well as its spatial distribution inside active regions.

Authors: Park, S.-H., Chae, J., and Wang, H.
Projects: SoHO-MDI

Publication Status: ApJ (in press)
Last Modified: 2010-05-20 15:17
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Abstracts by Author
Photospheric Shear Flows in Solar Active Regions and Their Relation to Flare Occurrence
Study of Magnetic Helicity Injection in the Active Regions NOAA 9236 Producing Multiple Flare-associated CME Events
The Occurrence and Speed of CMEs Related to Two Characteristic Evolution Patterns of Helicity Injection in Their Solar Source Regions
Time Evolution of Coronal Magnetic Helicity in the Flaring Active Region NOAA 10930
Productivity of Solar Flares and Magnetic Helicity Injection in Active Regions

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