E-Print Archive

There are 4291 abstracts currently viewable.


Search:

Advanced Search
Options
Main Page Add New E-Print Submitter
Information
Feedback
News Help/FAQ About Preferences
Manage Key Phrase
Notification
* News 04/04/20 * The archive is using a new backend database. This has thrown up a few SQL errors in the last few days. If you have any issues please email adavey@nso.edu with either the number of eprint you are trying to edit or a link to your preprint.

Magnetic Helicity Flux across Solar Active Region Photospheres: I. Hemispheric Sign Preference in Solar Cycle 24  

Sung-Hong Park   Submitted: 2020-10-13 18:55

A hemispheric preference in the dominant sign of magnetic helicity has been observed in numerous features in the solar atmosphere: i.e., left-handed/right-handed helicity in the northern/southern hemisphere. The relative importance of different physical processes which may contribute to the observed hemispheric sign preference (HSP) of magnetic helicity is still under debate. Here, we estimate magnetic helicity flux (dH/dt) across the photospheric surface for 4,802 samples of 1,105 unique active regions (ARs) that appeared over an 8-year period from 2010 to 2017 during solar cycle 24, using photospheric vector magnetic field observations by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). The estimates of dH/dt show that 63% and 65% of the investigated AR samples in the northern and southern hemispheres, respectively, follow the HSP. We also find a trend that the HSP of dH/dt increases from ~50-60% up to ~70-80% as ARs (1) appear at the earlier inclining phase of the solar cycle or higher latitudes; (2) have larger values of |dH/dt|, the total unsigned magnetic flux, and the average plasma flow speed. These observational findings support the enhancement of the HSP mainly by the Coriolis force acting on a buoyantly rising and expanding flux tube through the turbulent convection zone. In addition, the differential rotation on the solar surface as well as the tachocline α-effect of flux-transport dynamo may reinforce the HSP for ARs at higher latitudes.

Authors: Sung-Hong Park, K. D. Leka, Kanya Kusano
Projects: None

Publication Status: Accepted for publication in ApJ
Last Modified: 2020-10-14 13:11
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

An Observational Test of Solar Plasma Heating by Magnetic Flux Cancellation  

Sung-Hong Park   Submitted: 2020-05-19 01:38

Recent observations suggest that magnetic flux cancellation may play a crucial role to heat the Sun's upper atmosphere (chromosphere, transition region, corona). Here, we intended to validate an analytic model for magnetic reconnection and consequent coronal heating, driven by a pair of converging and cancelling magnetic flux sources of opposite polarities. For this test, we analyzed photospheric magnetic field and multi-wavelength UV/EUV observations of a small-scale flux cancellation event in a quiet-Sun internetwork region over a target interval of 5.2 hr. The observed cancellation event exhibits a converging motion of two opposite-polarity magnetic patches on the photosphere and red-shifted Doppler velocities (downflows) therein consistently over the target interval, with a decrease in magnetic flux of both polarities at a rate of 1015 Mx/s. Several impulsive EUV brightenings, with DEM values peaked at 1.6-2.0 MK, are also observed in the shape of arcades with their two footpoints anchored in the two patches. The rate of magnetic energy released as heat at the flux cancellation region is estimated to be in the range of (0.2-1)1024 erg/s over the target interval, which can satisfy the requirement of previously reported heating rates for the quiet-Sun corona. Finally, both short-term (a few to several tens of minutes) variations and long-term (a few hours) trends in the magnetic energy release rate are clearly shown in the estimated rate of radiative energy loss of electrons at temperatures above 2.0 MK. All these observational findings support the validity of the investigated reconnection model for plasma heating in the upper solar atmosphere by flux cancellation.

Authors: Sung-Hong Park
Projects:

Publication Status: Accepted for publication in ApJ
Last Modified: 2020-06-08 17:00
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

A Comparison of Flare Forecasting Methods. IV. Evaluating Consecutive-Day Forecasting Patterns  

Sung-Hong Park   Submitted: 2020-01-09 21:46

A crucial challenge to successful flare prediction is forecasting periods that transition between "flare-quiet" and "flare-active". Building on earlier studies in this series (Barnes et al. 2016; Leka et al. 2019a,b) in which we describe methodology, details, and results of flare forecasting comparison efforts, we focus here on patterns of forecast outcomes (success and failure) over multi-day periods. A novel analysis is developed to evaluate forecasting success in the context of catching the first event of flare-active periods, and conversely, of correctly predicting declining flare activity. We demonstrate these evaluation methods graphically and quantitatively as they provide both quick comparative evaluations and options for detailed analysis. For the testing interval 2016-2017, we determine the relative frequency distribution of two-day dichotomous forecast outcomes for three different event histories (i.e., event/event, no-event/event and event/no-event), and use it to highlight performance differences between forecasting methods. A trend is identified across all forecasting methods that a high/low forecast probability on day-1 remains high/low on day-2 even though flaring activity is transitioning. For M-class and larger flares, we find that explicitly including persistence or prior flare history in computing forecasts helps to improve overall forecast performance. It is also found that using magnetic/modern data leads to improvement in catching the first-event/first-no-event transitions. Finally, 15% of major (i.e., M-class or above) flare days over the testing interval were effectively missed due to a lack of observations from instruments away from the Earth-Sun line.

Authors: S.-H. Park, K. D. Leka, K. Kusano, J. Andries, G. Barnes, S. Bingham, D. S. Bloomfield, A. E. McCloskey, V. Delouille, D. Falconer, P. T. Gallagher, M. K. Georgoulis, Y. Kubo, K. Lee, S. Lee, V. Lobzin, J.-C. Mun, S. A. Murray, T. A. M. H. Nageem, R. Qahwaji, M. Sharpe, R. A. Steenburgh, G. Steward, M. Terkildsen
Projects: None

Publication Status: Accepted for publication in ApJ (December 26, 2019)
Last Modified: 2020-01-10 12:08
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

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
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

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
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

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
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

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
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 

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
Go to main E-Print page  Edit Entry  Download Preprint  Delete Entry 


Key
Go to main E-Print pageGo to main E-Print page.
Download PreprintDownload Preprint.
Submitter's HomepageSubmitters Homepage.
Edit EntryEdit Entry.
Delete AbstractDelete abstract.

Abstracts by Author
Magnetic Helicity Flux across Solar Active Region Photospheres: I. Hemispheric Sign Preference in Solar Cycle 24
An Observational Test of Solar Plasma Heating by Magnetic Flux Cancellation
A Comparison of Flare Forecasting Methods. IV. Evaluating Consecutive-Day Forecasting Patterns
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

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

Archive Maintainer
Alisdair Davey



© 2000-2020 Solar Physics Group - Montana State University