Author name code: park-sung-hong
ADS astronomy entries on 2022-09-14
=author:"Park, Sung-Hong"
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Title: Solar Flares and Magnetic Helicity
Authors: Toriumi, Shin; Park, Sung-Hong
Bibcode: 2022arXiv220406010T
Altcode:
Solar flares and coronal mass ejections are the largest energy release
phenomena in the current solar system. They cause drastic enhancements
of electromagnetic waves of various wavelengths and sometimes eject
coronal material into the interplanetary space, disturbing the magnetic
surroundings of orbiting planets including the Earth. It is generally
accepted that solar flares are a phenomenon in which magnetic energy
stored in the solar atmosphere above an active region is suddenly
released through magnetic reconnection. Therefore, to elucidate the
nature of solar flares, it is critical to estimate the complexity
of the magnetic field and track its evolution. Magnetic helicity,
a measure of the twist of coronal magnetic structures, is thus used
to quantify and characterize the complexity of flare-productive active
regions. This chapter provides an overview of solar flares and discusses
how the different concepts of magnetic helicity are used to understand
and predict solar flares.
Title: Using Machine Learning Tools To Estimate Photospheric Velocity
Fields Prior To The Formation Of Active Regions.
Authors: Lennard, Matthew; Tremblay, Benoit; Asensio Ramos, Andres;
Hotta, Hideyuki; Iijima, Haruhisa; Park, Sung-Hong; Silva, Suzana;
Verth, Gary; Fedun, Viktor
Bibcode: 2021AGUFMSH45B2371L
Altcode:
In recent years a number of major advances have been made using
numerical modelling to better our understanding of magnetic structures
and the evolution of active regions (AR, see e.g. Hotta &
Iijima, 2020; Chen et al, 2021). In particular, these high resolution
simulations provide us with the means to study the photospheric flows
associated with the aforementioned magnetic structures. In practice,
plasma flows at the solar surface cannot be directly recovered;
the component transverse to the line-of-sight must be inferred from
observational data. Inferences depend on the method, the observational
data used as input, the spatial resolution of the data and its
cadence. Tracking methods such as local correlation tracking (LCT)
are promising, but the flows they measure are optical and cannot be
used to estimate the flow patterns of an AR until shortly before the
emergence of flux. Another issue with applying LCT to estimate AR
flows is that the recovered velocity field is usually not smooth,
which precludes advanced flow analysis. Besides, depending on the
data, there is a considerable chance of having 'holes' in the velocity
field. Therefore, although LCT methodology can help give a hint on
general flow properties, a more sophisticated technique is necessary
to perform proper analysis on the flow topology. There are also
limitations in the region of the Sun in which we can accurately track
flows as well as problems with accurately extracting longitudinal and
latitudinal velocities. Recently, deep learning has shown promise in
capturing subtleties in Quiet Sun flows at spatial and temporal scales
that typically cannot be recovered by tracking methods (Asensio Ramos
et al, 2017). The DeepVel neural network is trained to infer plasma
flows from surface data using examples from detailed numerical models
(i.e., supervised learning). Using a version of DeepVel that was
trained using a high-resolution numerical simulation of the evolution
of an AR (e.g. Hotta & Iijima, 2020) we developed the algorithm
for predicting flow trajectories from high resolution observational
data. This method was directly compared with previous contenders for
tracking flows and shows more realistic plasma flow field estimation
as well as an increase of reconstruction efficiency.
Title: The flare likelihood and region eruption forecasting
(FLARECAST) project: flare forecasting in the big data & machine
learning era
Authors: Georgoulis, Manolis K.; Bloomfield, D. Shaun; Piana,
Michele; Massone, Anna Maria; Soldati, Marco; Gallagher, Peter T.;
Pariat, Etienne; Vilmer, Nicole; Buchlin, Eric; Baudin, Frederic;
Csillaghy, Andre; Sathiapal, Hanna; Jackson, David R.; Alingery,
Pablo; Benvenuto, Federico; Campi, Cristina; Florios, Konstantinos;
Gontikakis, Constantinos; Guennou, Chloe; Guerra, Jordan A.;
Kontogiannis, Ioannis; Latorre, Vittorio; Murray, Sophie A.; Park,
Sung-Hong; von Stachelski, Samuelvon; Torbica, Aleksandar; Vischi,
Dario; Worsfold, Mark
Bibcode: 2021JSWSC..11...39G
Altcode: 2021arXiv210505993G
The European Union funded the FLARECAST project, that ran from January
2015 until February 2018. FLARECAST had a research-to-operations
(R2O) focus, and accordingly introduced several innovations into the
discipline of solar flare forecasting. FLARECAST innovations were:
first, the treatment of hundreds of physical properties viewed as
promising flare predictors on equal footing, extending multiple
previous works; second, the use of fourteen (14) different machine
learning techniques, also on equal footing, to optimize the immense
Big Data parameter space created by these many predictors; third,
the establishment of a robust, three-pronged communication effort
oriented toward policy makers, space-weather stakeholders and the wider
public. FLARECAST pledged to make all its data, codes and infrastructure
openly available worldwide. The combined use of 170+ properties (a
total of 209 predictors are now available) in multiple machine-learning
algorithms, some of which were designed exclusively for the project,
gave rise to changing sets of best-performing predictors for the
forecasting of different flaring levels, at least for major flares. At
the same time, FLARECAST reaffirmed the importance of rigorous training
and testing practices to avoid overly optimistic pre-operational
prediction performance. In addition, the project has (a) tested new
and revisited physically intuitive flare predictors and (b) provided
meaningful clues toward the transition from flares to eruptive flares,
namely, events associated with coronal mass ejections (CMEs). These
leads, along with the FLARECAST data, algorithms and infrastructure,
could help facilitate integrated space-weather forecasting efforts
that take steps to avoid effort duplication. In spite of being
one of the most intensive and systematic flare forecasting efforts
to-date, FLARECAST has not managed to convincingly lift the barrier of
stochasticity in solar flare occurrence and forecasting: solar flare
prediction thus remains inherently probabilistic.
Title: Magnetic Helicity Flux across Solar Active Region
Photospheres. II. Association of Hemispheric Sign Preference with
Flaring Activity during Solar Cycle 24
Authors: Park, Sung-Hong; Leka, K. D.; Kusano, Kanya
Bibcode: 2021ApJ...911...79P
Altcode: 2021arXiv210213331P
In our earlier study (Paper I) of this series, we examined the
hemispheric sign preference (HSP) of magnetic helicity flux dH/dt
across photospheric surfaces of 4802 samples of 1105 unique active
regions (ARs) observed during solar cycle 24. Here, we investigate
any association of the HSP, expressed as a degree of compliance,
with flaring activity, analyzing the same set of dH/dt estimates as
used in Paper I. The AR samples under investigation are assigned to
heliographic regions (HRs) defined in the Carrington longitude-latitude
plane with a grid spacing of 45° in longitude and 15° in latitude. For
AR samples in each of the defined HRs, we calculate the degree of HSP
compliance and the average soft X-ray flare index. The strongest flaring
activity is found to be in one distinctive HR with an extremely low-HSP
compliance of 41% as compared to the mean and standard deviation of
62% and 7%, respectively, over all HRs. This sole HR shows an anti-HSP
(i.e., <50%) and includes the highly flare-productive AR NOAA 12673,
however this AR is not uniquely responsible for the HR's low HSP. We
also find that all HRs with the highest flaring activity are located
in the southern hemisphere, and they tend to have lower degrees of HSP
compliance. These findings point to the presence of localized regions
of the convection zone with enhanced turbulence, imparting a greater
magnetic complexity and a higher flaring rate to some rising magnetic
flux tubes.
Title: Data-driven MHD Simulation of Successive Solar Plasma Eruptions
Authors: Kaneko, Takafumi; Park, Sung-Hong; Kusano, Kanya
Bibcode: 2021ApJ...909..155K
Altcode: 2021arXiv210112395K
Solar flares and plasma eruptions are sudden releases of magnetic
energy stored in the plasma atmosphere. To understand the physical
mechanisms governing their occurrences, three-dimensional magnetic
fields from the photosphere up to the corona must be studied. The
solar photospheric magnetic fields are observable, whereas the coronal
magnetic fields cannot be measured. One method for inferring coronal
magnetic fields is performing data-driven simulations, which involves
time-series observational data of the photospheric magnetic fields with
the bottom boundary of magnetohydrodynamic simulations. We developed
a data-driven method in which temporal evolutions of the observational
vector magnetic field can be reproduced at the bottom boundary in the
simulation by introducing an inverted velocity field. This velocity
field is obtained by inversely solving the induction equation and
applying an appropriate gauge transformation. Using this method,
we performed a data-driven simulation of successive small eruptions
observed by the Solar Dynamics Observatory and the Solar Magnetic
Activity Telescope in 2017 November. The simulation well reproduced
the converging motion between opposite-polarity magnetic patches,
demonstrating successive formation and eruptions of helical flux ropes.
Title: Lagrangian chaotic saddles and objective vortices in solar
plasmas
Authors: Chian, Abraham C. -L.; Silva, Suzana S. A.; Rempel, Erico L.;
Bellot Rubio, Luis R.; Gošić, Milan; Kusano, Kanya; Park, Sung-Hong
Bibcode: 2020PhRvE.102f0201C
Altcode:
We report observational evidence of Lagrangian chaotic saddles
in plasmas, given by the intersections of finite-time unstable and
stable manifolds, using an ≈22 h sequence of spacecraft images of the
horizontal velocity field of solar photosphere. A set of 29 persistent
objective vortices with lifetimes varying from 28.5 to 298.3 min are
detected by computing the Lagrangian averaged vorticity deviation. The
unstable manifold of the Lagrangian chaotic saddles computed for ≈11
h exhibits twisted folding motions indicative of recurring vortices in
a magnetic mixed-polarity region. We show that the persistent objective
vortices are formed in the gap regions of Lagrangian chaotic saddles
at supergranular junctions.
Title: Magnetic Helicity Flux across Solar Active Region
Photospheres. I. Hemispheric Sign Preference in Solar Cycle 24
Authors: Park, Sung-Hong; Leka, K. D.; Kusano, Kanya
Bibcode: 2020ApJ...904....6P
Altcode: 2020arXiv201006134P
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
that 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 4802 samples
of 1105 unique active regions (ARs) that appeared over an 8 yr period
from 2010 to 2017 during solar cycle 24, using photospheric vector
magnetic field observations by the Helioseismic and Magnetic Imager
(HMI) on board 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 and (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 a flux-transport dynamo may reinforce the
HSP for ARs at higher latitudes.
Title: Time Series Analysis of Photospheric Magnetic Parameters
of Flare-Quiet Versus Flaring Active Regions: Scaling Properties
of Fluctuations
Authors: Lee, Eo-Jin; Park, Sung-Hong; Moon, Yong-Jae
Bibcode: 2020SoPh..295..123L
Altcode: 2020arXiv200813085L
Time series of photospheric magnetic parameters of solar active regions
(ARs) are used to answer the question whether scaling properties of
fluctuations embedded in such time series help to distinguish between
flare-quiet and flaring ARs. We examine a total of 118 flare-quiet and
118 flaring AR patches, Helioseismic and Magnetic Imager Active Region
Patches (called HARPs), which were observed from 2010 to 2016 by the
Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics
Observatory (SDO). Specifically, the scaling exponent of fluctuations
is derived applying the Detrended Fluctuation Analysis (DFA) method
to a dataset of 8-day time series of 18 photospheric magnetic
parameters at 12-min cadence for all HARPs under investigation. We
first find a statistically significant difference in the distribution
of the scaling exponent between the flare-quiet and flaring HARPs,
in particular for some space-averaged, signed parameters associated
with magnetic field line twist, electric current density, and current
helicity. The flaring HARPs tend to show higher values of the scaling
exponent compared to those of the flare-quiet ones, even though there is
considerable overlap between their distributions. In addition, for both
the flare-quiet and the flaring HARPs the DFA analysis indicates that i)
time series of most of various magnetic parameters under consideration
are non-stationary, and ii) time series of the total unsigned magnetic
flux and the mean photospheric magnetic free energy density in general
present a non-stationary, persistent property, while the total unsigned
flux near magnetic polarity inversion lines and parameters related to
current density show a non-stationary, anti-persistent trend in their
time series.
Title: An Observational Test of Solar Plasma Heating by Magnetic
Flux Cancellation
Authors: Park, Sung-Hong
Bibcode: 2020ApJ...897...49P
Altcode: 2020arXiv200507953P
Recent observations suggest that magnetic flux cancellation may play
a crucial role in heating 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 canceling magnetic flux sources of opposite
polarities. For this test, we analyzed photospheric magnetic field
and multiwavelength ultraviolet/extreme ultraviolet (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 redshifted 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-1. Several impulsive EUV brightenings, with differential
emission measure 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-1 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.
Title: A Comparison of Flare Forecasting Methods. IV. Evaluating
Consecutive-day Forecasting Patterns
Authors: Park, Sung-Hong; Leka, K. D.; Kusano, Kanya; Andries, Jesse;
Barnes, Graham; Bingham, Suzy; Bloomfield, D. Shaun; McCloskey,
Aoife E.; Delouille, Veronique; Falconer, David; Gallagher, Peter T.;
Georgoulis, Manolis K.; Kubo, Yuki; Lee, Kangjin; Lee, Sangwoo; Lobzin,
Vasily; Mun, JunChul; Murray, Sophie A.; Hamad Nageem, Tarek A. M.;
Qahwaji, Rami; Sharpe, Michael; Steenburgh, R. A.; Steward, Graham;
Terkildsen, Michael
Bibcode: 2020ApJ...890..124P
Altcode: 2020arXiv200102808P
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 in which we
describe the methodology, details, and results of flare forecasting
comparison efforts, we focus here on patterns of forecast outcomes
(success and failure) over multiday periods. A novel analysis is
developed to evaluate forecasting success in the context of catching
the first event of flare-active periods and, conversely, 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.
Title: Onset Mechanism of M6.5 Solar Flare Observed in Active
Region 12371
Authors: Kang, Jihye; Inoue, Satoshi; Kusano, Kanya; Park, Sung-Hong;
Moon, Yong-Jae
Bibcode: 2019ApJ...887..263K
Altcode: 2019arXiv191105337K
We studied a flare onset process in terms of stability of a
three-dimensional (3D) magnetic field in active region 12371 producing
an eruptive M6.5 flare in 2015 June 22. In order to reveal the 3D
magnetic structure, we first extrapolated the 3D coronal magnetic
fields based on time series of the photospheric vector magnetic fields
under a nonlinear force-free field (NLFFF) approximation. The NLFFFs
nicely reproduced the observed sigmoidal structure which is widely
considered to be preeruptive magnetic configuration. In particular,
we found that the sigmoid is composed of two branches of sheared arcade
loops. On the basis of the NLFFFs, we investigated the sheared arcade
loops to explore the onset process of the eruptive flare using three
representative magnetohydrodynamic instabilities: the kink, torus,
and double arc instabilities (DAI). The DAI, recently proposed by
Ishiguro & Kusano, is a double arc loop that can be more easily
destabilized than a torus loop. Consequently, the NLFFFs are found to
be quite stable against the kink and torus instabilities. However,
the sheared arcade loops formed prior to the flare possibly become
unstable against the DAI. As a possible scenario for the onset
process of the M6.5 flare, we suggest a three-step process: (1)
double arc loops are formed by the sheared arcade loops through the
tether-cutting reconnection during an early phase of the flare, (2)
the DAI contributes to the expansion of destabilized double arc loops,
and (3) finally, the torus instability makes the full eruption.
Title: Which Photospheric Characteristics Are Most Relevant to
Active-Region Coronal Mass Ejections?
Authors: Kontogiannis, Ioannis; Georgoulis, Manolis K.; Guerra,
Jordan A.; Park, Sung-Hong; Bloomfield, D. Shaun
Bibcode: 2019SoPh..294..130K
Altcode: 2019arXiv190906088K
We investigate the relation between characteristics of coronal mass
ejections and parameterizations of the eruptive capability of solar
active regions widely used in solar flare-prediction schemes. These
parameters, some of which are explored for the first time, are
properties related to topological features, namely, magnetic
polarity-inversion lines (MPILs) that indicate large amounts of
stored non-potential (i.e. free) magnetic energy. We utilize the
Space Weather Database of Notifications, Knowledge, Information
(DONKI) and the Large Angle and Spectrometric Coronograph (LASCO)
databases to find flare-associated coronal mass ejections and
their kinematic characteristics, while properties of MPILs are
extracted from Helioseismic and Magnetic Imager (HMI) vector
magnetic-field observations of active regions to extract the
properties of source-region MPILs. The correlation between all
properties and the characteristics of CMEs ranges from moderate to
very strong. More significant correlations hold particularly for
fast CMEs, which are most important in terms of adverse space-weather
manifestations. Non-neutralized currents and the length of the main
MPIL exhibit significantly stronger correlations than the rest of the
properties. This finding supports a causal relationship between coronal
mass ejections and non-neutralized electric currents in highly sheared,
conspicuous MPILs. In addition, non-neutralized currents and MPIL length
carry distinct, independent information as to the eruptive potential of
active regions. The combined total amount of non-neutralized electric
currents and the length of the main polarity-inversion line, therefore,
reflect more efficiently than other parameters the eruptive capacity
of solar active regions and the CME kinematic characteristics stemming
from these regions.
Title: A Comparison of Flare Forecasting Methods. III. Systematic
Behaviors of Operational Solar Flare Forecasting Systems
Authors: Leka, K. D.; Park, Sung-Hong; Kusano, Kanya; Andries, Jesse;
Barnes, Graham; Bingham, Suzy; Bloomfield, D. Shaun; McCloskey,
Aoife E.; Delouille, Veronique; Falconer, David; Gallagher, Peter
T.; Georgoulis, Manolis K.; Kubo, Yuki; Lee, Kangjin; Lee, Sangwoo;
Lobzin, Vasily; Mun, JunChul; Murray, Sophie A.; Hamad Nageem, Tarek
A. M.; Qahwaji, Rami; Sharpe, Michael; Steenburgh, Robert A.; Steward,
Graham; Terkildsen, Michael
Bibcode: 2019ApJ...881..101L
Altcode: 2019arXiv190702909L
A workshop was recently held at Nagoya University (2017 October
31-November 2), sponsored by the Center for International Collaborative
Research, at the Institute for Space-Earth Environmental Research,
Nagoya University, Japan, to quantitatively compare the performance
of today’s operational solar flare forecasting facilities. Building
upon Paper I of this series, in Paper II we described the participating
methods for this latest comparison effort, the evaluation methodology,
and presented quantitative comparisons. In this paper, we focus on
the behavior and performance of the methods when evaluated in the
context of broad implementation differences. Acknowledging the short
testing interval available and the small number of methods available,
we do find that forecast performance: (1) appears to improve by
including persistence or prior flare activity, region evolution,
and a human “forecaster in the loop” (2) is hurt by restricting
data to disk-center observations; (3) may benefit from long-term
statistics but mostly when then combined with modern data sources
and statistical approaches. These trends are arguably weak and must
be viewed with numerous caveats, as discussed both here and in Paper
II. Following this present work, in Paper IV (Park et al. 2019) we
will present a novel analysis method to evaluate temporal patterns of
forecasting errors of both types (i.e., misses and false alarms). Hence,
most importantly, with this series of papers, we demonstrate the
techniques for facilitating comparisons in the interest of establishing
performance-positive methodologies.
Title: A Comparison of Flare Forecasting Methods. II. Benchmarks,
Metrics, and Performance Results for Operational Solar Flare
Forecasting Systems
Authors: Leka, K. D.; Park, Sung-Hong; Kusano, Kanya; Andries, Jesse;
Barnes, Graham; Bingham, Suzy; Bloomfield, D. Shaun; McCloskey,
Aoife E.; Delouille, Veronique; Falconer, David; Gallagher, Peter
T.; Georgoulis, Manolis K.; Kubo, Yuki; Lee, Kangjin; Lee, Sangwoo;
Lobzin, Vasily; Mun, JunChul; Murray, Sophie A.; Hamad Nageem, Tarek
A. M.; Qahwaji, Rami; Sharpe, Michael; Steenburgh, Robert A.; Steward,
Graham; Terkildsen, Michael
Bibcode: 2019ApJS..243...36L
Altcode: 2019arXiv190702905L
Solar flares are extremely energetic phenomena in our solar
system. Their impulsive and often drastic radiative increases,
particularly at short wavelengths, bring immediate impacts that motivate
solar physics and space weather research to understand solar flares
to the point of being able to forecast them. As data and algorithms
improve dramatically, questions must be asked concerning how well the
forecasting performs; crucially, we must ask how to rigorously measure
performance in order to critically gauge any improvements. Building
upon earlier-developed methodology of Paper I (Barnes et al. 2016),
international representatives of regional warning centers and
research facilities assembled in 2017 at the Institute for Space-Earth
Environmental Research, Nagoya University, Japan to, for the first time,
directly compare the performance of operational solar flare forecasting
methods. Multiple quantitative evaluation metrics are employed, with the
focus and discussion on evaluation methodologies given the restrictions
of operational forecasting. Numerous methods performed consistently
above the “no-skill” level, although which method scored top marks
is decisively a function of flare event definition and the metric
used; there was no single winner. Following in this paper series, we
ask why the performances differ by examining implementation details
(Leka et al. 2019), and then we present a novel analysis method to
evaluate temporal patterns of forecasting errors in Paper IV (Park
et al. 2019). With these works, this team presents a well-defined and
robust methodology for evaluating solar flare forecasting methods in
both research and operational frameworks and today’s performance
benchmarks against which improvements and new methods may be compared.
Title: Flare Productivity of Major Flaring Solar Active Regions:
A Time-Series Study of Photospheric Magnetic Properties
Authors: Lee, Eo-Jin; Park, Sung-Hong; Moon, Yong-Jae
Bibcode: 2018SoPh..293..159L
Altcode: 2018arXiv181012505L
A solar active region (AR) that produces at least one M- or X-class
major flare tends to produce multiple flares during its passage across
the solar disk. It will be interesting to see if we can estimate how
flare-productive a given major flaring AR is for a time interval of
several days through investigating time series of its photospheric
magnetic field properties. For this, we studied 93 major flaring ARs
that were observed from 2010 to 2016 by the Helioseismic and Magnetic
Imager (HMI) on board the Solar Dynamics Observatory (SDO). More
specifically, for each AR under study, the mean and fluctuation
were calculated from an 8-day time series of each of 18 photospheric
magnetic parameters extracted from the Space-weather HMI Active Region
Patch (SHARP) vector magnetogram products at 12 min cadence. We then
compared these with the AR 8-day flare index, which is defined as the
sum of soft X-ray peak fluxes of flares produced in the AR during the
same interval as the 8-day SHARP parameter time series. As a result,
we found that the 8-day flare index is well correlated with the mean
and/or fluctuation values of some magnetic parameters (with correlation
coefficients of 0.6 - 0.7 in log-log space). Interestingly, the 8-day
flare index shows a slightly better correlation with the fluctuation
than the mean for the SHARP parameters associated with the surface
integral of photospheric magnetic free energy density. We also discuss
how the correlation varies if the 8-day flare index is compared with
the mean or fluctuation calculated from an initial portion of the
SHARP parameter time series.
Title: A new analysis of stability of active regions for understanding
and predicting the onset of solar eruptions
Authors: Kusano, Kanya; Park, Sung-Hong; Iju, Tomoya; Muhamad, Johan;
Ishiguro, Naoyuki; Inoue, Satoshi; Bamba, Yumi
Bibcode: 2018csc..confE..25K
Altcode:
Solar flares and coronal mass ejections (CMEs) are believed to be the
explosive liberation of magnetic energy in the solar corona and may
cause space weather disturbances. However, the critical condition for
their onset is not yet well understood, and thus our predictability
of when, where, and how large events will occur is not sufficiently
reliable yet. Which kind of instability determines the critical
condition for the onset of solar eruptions is a key question of this
problem, because magnetohydrodynamic (MHD) instabilities must play an
important role in driving solar eruptions. The torus instability and
the kink-mode instability have been investigated as candidates of the
key driver of solar eruptions. Recently, Ishiguro and Kusano (2017)
proposed that a new instability called double-arc instability (DAI)
may work as the initial driver of solar flares and it can trigger the
onset of solar eruptions. Though the DAI is one of the hoop-force
driven instabilities like the torus instability (TI), the critical
condition of the DAI, given by a new parameter kappa, is different
from the TI. Based on the theory of the DAI, we have developed a
numerical model which can evaluate the stability and the stored free
energy within each solar active region using the nonlinear force-free
field extrapolation. We analyzed the various solar active regions by
applying this model onto the Space-weather HMI Active Region Patches
(SHARP). In this paper, we report the results of the analyses for
how the stability of the DAI evolved in several flare-active regions
and how that of 200 sampled active regions correlates with the flare
activities. The results are consistent with the theoretical scenario
of the DAI as the initial driver of solar eruptions and they suggest
that the kappa parameter could improve the prediction not only for
the capability of solar eruptions but also for the location where
large flares are most likely to be triggered within each active
region. Finally, we discuss the applicability of nonlinear force-free
field extrapolation for the operational forecast of solar flares.
Title: Magnetohydrodynamic Modeling of a Solar Eruption Associated
with an X9.3 Flare Observed in the Active Region 12673
Authors: Inoue, Satoshi; Shiota, Daikou; Bamba, Yumi; Park, Sung-Hong
Bibcode: 2018ApJ...867...83I
Altcode: 2018arXiv180902309I
On 2017 September 6, the solar active region 12673 produced an
X9.3 flare, regarded to be the largest to have occurred in solar
cycle 24. In this work we have performed a magnetohydrodynamic (MHD)
simulation in order to reveal the three-dimensional (3D) dynamics of
the magnetic fields associated with the X9.3 solar flare. We first
performed an extrapolation of the 3D magnetic field based on the
observed photospheric magnetic field prior to the flare and then used
this as the initial condition for the MHD simulation, which revealed a
dramatic eruption. In particular, we found that a large coherent flux
rope composed of highly twisted magnetic field lines formed during
the eruption. A series of small flux ropes were found to lie along
a magnetic polarity inversion line prior to the flare. Reconnection
occurring between each flux rope during the early stages of the eruption
formed the large, highly twisted flux rope. Furthermore, we observed a
writhing motion of the erupting flux rope. Understanding these dynamics
is important in the drive to increase the accuracy of space weather
forecasting. We report on the detailed dynamics of the 3D eruptive
flux rope and discuss the possible mechanisms of the writhing motion.
Title: Photospheric Shear Flows in Solar Active Regions and Their
Relation to Flare Occurrence
Authors: Park, Sung-Hong; Guerra, Jordan A.; Gallagher, Peter T.;
Georgoulis, Manolis K.; Bloomfield, D. Shaun
Bibcode: 2018SoPh..293..114P
Altcode: 2018arXiv180707714P
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 2548
coaligned 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 («S »), maximum
(Smax) and integral (Ssum) shear-flow speeds along
strong-gradient, strong-field MPIL segments. We calculated flaring
rates within 24 h as a function of each shear-flow parameter and we
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 h. 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 h or less.
Title: Operational Flare Forecasting Benchmarks and Initial
Performance Comparisons
Authors: Leka, K. D.; Park, Sung-Hong
Bibcode: 2018cosp...42E1978L
Altcode:
We present here select preliminary results from a recent workshop,
"Benchmarks for Operational Solar Flare Forecasts" held at the
Institute for Sun-Earth Environmental Research (ISEE) in Nagoya,
Japan, in late 2017. Numerous methods were tested in a head-to-head
operational forecasting performance exercise. Results are quantified
using standard validation metrics, with a preference for metrics based
on the probabilistic forecasts (rather than categorical results which
are impacted by probability thresholds). We present here a preliminary
analysis of the performance impacts of general method attributes,
addressing questions centered on ``which approaches demonstrate
improvement in operational performance, and which approaches do not?''
Title: The critical conditions for the onset of solar flares and
coronal mass ejections
Authors: Kusano, Kanya; Iju, Tomoya; Muhamad, Johan; Ishiguro, Naoyuki;
Inoue, Satoshi; Bamba, Yumi; Shiota, Daikou; Park, Sung-Hong; Asahi,
Yuki; Mizuno, Yuta
Bibcode: 2018cosp...42E1887K
Altcode:
Solar flares and coronal mass ejections (CMEs) are believed to be the
explosive liberation of magnetic energy in the solar corona. However,
the critical condition for their onset is not yet well understood, and
thus the accurate prediction of their onset is still difficult. Which
kind of instability determines the critical condition is a key question
of this problem, because magnetohydrodynamic (MHD) instabilities, e.g.,
the kink and torus modes of instabilities, may cause the explosive
energy liberation in the solar corona. Recently, Ishiguro and Kusano
(2017) proposed that a new instability called double-arc instability
(DAI) may work as the initial driver of solar flares and it can
trigger the onset of the solar eruption by destabilizing the torus
instability. In this paper, we analyze the spatiotemporal evolution
of three-dimensional magnetic field structure which is reconstructed
by the nonlinear force-free field (NLFFF) extrapolation technique for
the solar active regions NOAA 11158 and 12673. The result suggests
that the critical condition for the DAI well explains the onset of the
major flares occurred in these active regions. Finally, we discuss the
applicability of the critical condition to the prediction of flares and
CMEs based on the statistical analysis of three hundred active regions.
Title: Testing and Improving a Set of Morphological Predictors of
Flaring Activity
Authors: Kontogiannis, Ioannis; Georgoulis, Manolis K.; Park,
Sung-Hong; Guerra, Jordan A.
Bibcode: 2018SoPh..293...96K
Altcode: 2018arXiv180706371K
Efficient prediction of solar flares relies on parameters that
quantify the eruptive capability of solar active regions. Several
such quantitative predictors have been proposed in the literature,
inferred mostly from photospheric magnetograms and/or white-light
observations. Two of them are the Ising energy and the sum of the total
horizontal magnetic field gradient. The former has been developed from
line-of-sight magnetograms, while the latter uses sunspot detections
and characteristics, based on continuum images. Aiming to include
these parameters in an automated prediction scheme, we test their
applicability on regular photospheric magnetic field observations
provided by the Helioseismic and Magnetic Imager (HMI) instrument
onboard the Solar Dynamics Observatory (SDO). We test their efficiency
as predictors of flaring activity on a representative sample of active
regions and investigate possible modifications of these quantities. The
Ising energy appears to be an efficient predictor, and the efficiency
is even improved if it is modified to describe interacting magnetic
partitions or sunspot umbrae. The sum of the horizontal magnetic
field gradient appears to be slightly more promising than the three
variations of the Ising energy we implement in this article. The new
predictors are also compared with two very promising predictors: the
effective connected magnetic field strength and the total unsigned
non-neutralized current. Our analysis shows that the efficiency of
morphological predictors depends on projection effects in a nontrivial
way. All four new predictors are found useful for inclusion in an
automated flare forecasting facility, such as the Flare Likelihood
and Region Eruption Forecasting (FLARECAST), but their utility, among
others, will ultimately be determined by the validation effort underway
in the framework of the FLARECAST project.
Title: Operational Flare Forecasting Benchmarks and Initial
Performance Comparisons
Authors: Leka, K. D.; Park, Sung-Hong; Barnes, Graham
Bibcode: 2018tess.conf41407L
Altcode:
It is the end of a magnetic cycle, and we recently asked two questions:
(1) "How well do operational flare forecasting methods presently
work?" and (2) "What is needed to quantitatively answer that question to
begin with?" We present here select preliminary results from a recent
workshop, "Benchmarks for Operational Solar Flare Forecasts" held at
the Institute for Sun-Earth Environmental Research (ISEE) in Nagoya,
Japan, in late 2017. Numerous methods were tested in a head-to-head
operational forecasting performance exercise. Results are quantified
using standard validation metrics, with a preference for metrics based
on the probabilistic forecasts (rather than categorical results which
are impacted by probability thresholds). We discuss how to best assess
the relative performance of different methods, and present an initial
analysis of general method attributes, addressing questions centered
on "which approaches lead to improvement in operational performance,
and which approaches do not?'' Support for the workshop and this
analysis is acknowledged from the Nagoya University/Institute for
Space-Earth Environmental Research (ISEE) Center for International
Collaborative Research (CICR).
Title: Connecting Coronal Mass Ejections to Their Solar Active Region
Sources: Combining Results from the HELCATS and FLARECAST Projects
Authors: Murray, Sophie A.; Guerra, Jordan A.; Zucca, Pietro; Park,
Sung-Hong; Carley, Eoin P.; Gallagher, Peter T.; Vilmer, Nicole;
Bothmer, Volker
Bibcode: 2018SoPh..293...60M
Altcode: 2018arXiv180306529M
Coronal mass ejections (CMEs) and other solar eruptive phenomena can be
physically linked by combining data from a multitude of ground-based
and space-based instruments alongside models; however, this can be
challenging for automated operational systems. The EU Framework Package
7 HELCATS project provides catalogues of CME observations and properties
from the Heliospheric Imagers on board the two NASA/STEREO spacecraft
in order to track the evolution of CMEs in the inner heliosphere. From
the main HICAT catalogue of over 2,000 CME detections, an automated
algorithm has been developed to connect the CMEs observed by STEREO
to any corresponding solar flares and active-region (AR) sources
on the solar surface. CME kinematic properties, such as speed and
angular width, are compared with AR magnetic field properties, such as
magnetic flux, area, and neutral line characteristics. The resulting
LOWCAT catalogue is also compared to the extensive AR property
database created by the EU Horizon 2020 FLARECAST project, which
provides more complex magnetic field parameters derived from vector
magnetograms. Initial statistical analysis has been undertaken on the
new data to provide insight into the link between flare and CME events,
and characteristics of eruptive ARs. Warning thresholds determined
from analysis of the evolution of these parameters is shown to be a
useful output for operational space weather purposes. Parameters of
particular interest for further analysis include total unsigned flux,
vertical current, and current helicity. The automated method developed
to create the LOWCAT catalogue may also be useful for future efforts
to develop operational CME forecasting.
Title: Forecasting Solar Flares Using Magnetogram-based Predictors
and Machine Learning
Authors: Florios, Kostas; Kontogiannis, Ioannis; Park, Sung-Hong;
Guerra, Jordan A.; Benvenuto, Federico; Bloomfield, D. Shaun;
Georgoulis, Manolis K.
Bibcode: 2018SoPh..293...28F
Altcode: 2018arXiv180105744F
We propose a forecasting approach for solar flares based on data from
Solar Cycle 24, taken by the Helioseismic and Magnetic Imager (HMI)
on board the Solar Dynamics Observatory (SDO) mission. In particular,
we use the Space-weather HMI Active Region Patches (SHARP) product that
facilitates cut-out magnetograms of solar active regions (AR) in the
Sun in near-realtime (NRT), taken over a five-year interval (2012 -
2016). Our approach utilizes a set of thirteen predictors, which are
not included in the SHARP metadata, extracted from line-of-sight and
vector photospheric magnetograms. We exploit several machine learning
(ML) and conventional statistics techniques to predict flares of
peak magnitude >M1 and >C1 within a 24 h forecast window. The
ML methods used are multi-layer perceptrons (MLP), support vector
machines (SVM), and random forests (RF). We conclude that random
forests could be the prediction technique of choice for our sample,
with the second-best method being multi-layer perceptrons, subject to
an entropy objective function. A Monte Carlo simulation showed that
the best-performing method gives accuracy ACC =0.93 (0.00 ), true
skill statistic TSS =0.74 (0.02 ), and Heidke skill score HSS =0.49
(0.01 ) for >M1 flare prediction with probability threshold 15%
and ACC =0.84 (0.00 ), TSS =0.60 (0.01 ), and HSS =0.59 (0.01 ) for
>C1 flare prediction with probability threshold 35%.
Title: Non-neutralized Electric Currents in Solar Active Regions
and Flare Productivity
Authors: Kontogiannis, Ioannis; Georgoulis, Manolis K.; Park,
Sung-Hong; Guerra, Jordan A.
Bibcode: 2017SoPh..292..159K
Altcode: 2017arXiv170807087K
We explore the association of non-neutralized currents with solar
flare occurrence in a sizable sample of observations, aiming to show
the potential of such currents in solar flare prediction. We used
the high-quality vector magnetograms that are regularly produced by
the Helioseismic Magnetic Imager, and more specifically, the Space
weather HMI Active Region Patches (SHARP). Through a newly established
method that incorporates detailed error analysis, we calculated
the non-neutralized currents contained in active regions (AR). Two
predictors were produced, namely the total and the maximum unsigned
non-neutralized current. Both were tested in AR time-series and a
representative sample of point-in-time observations during the interval
2012 - 2016. The average values of non-neutralized currents in flaring
active regions are higher by more than an order of magnitude than in
non-flaring regions and correlate very well with the corresponding
flare index. The temporal evolution of these parameters appears to
be connected to physical processes, such as flux emergence and/or
magnetic polarity inversion line formation, that are associated with
increased solar flare activity. Using Bayesian inference of flaring
probabilities, we show that the total unsigned non-neutralized current
significantly outperforms the total unsigned magnetic flux and other
well-established current-related predictors. It therefore shows good
prospects for inclusion in an operational flare-forecasting service. We
plan to use the new predictor in the framework of the FLARECAST project
along with other highly performing predictors.
Title: The 17 March 2015 storm: the associated magnetic flux rope
structure and the storm development
Authors: Marubashi, Katsuhide; Cho, Kyung-Suk; Kim, Rok-Soon; Kim,
Sujin; Park, Sung-Hong; Ishibashi, Hiromitsu
Bibcode: 2016EP&S...68..173M
Altcode:
The objective of this study is (1) to determine the magnetic cloud
(MC) structure associated with the 17 March 2015 storm and (2) to
gain an insight into how the storm developed responding to the solar
wind conditions. First, we search MC geometries which can explain the
observed solar wind magnetic fields by fitting to both cylindrical
and toroidal flux rope models. Then, we examine how the resultant
MC geometries can be connected to the solar source region to find
out the most plausible model for the observed MC. We conclude that
the observations are most consistently explained by a toroidal flux
rope with the torus plane nearly parallel to the ecliptic plane. It
is emphasized that the observations are characterized by the peculiar
spacecraft crossing through the MC, in that the magnetic fields to be
observed are southward throughout the passage. For understanding of
the storm development, we first estimate the injection rate of the
storm ring current from the observed Dst variation. Then, we derive
an expression to calculate the estimated injection rate from the
observed solar wind variations. The point of the method is to evaluate
the injection rate by the convolution of the dawn-to-dusk electric
field in the solar wind and a response function. By using the optimum
response function thus determined, we obtain a modeled Dst variation
from the solar wind data, which is in good agreement with the observed
Dst variation. The agreement supports the validity of our method to
derive an expression for the ring current injection rate as a function
of the solar wind variation.[Figure not available: see fulltext.]
Title: Enabling Solar Flare Forecasting at an Unprecedented Level:
the FLARECAST Project
Authors: Georgoulis, Manolis K.; Pariat, Etienne; Massone, Anna
Maria; Vilmer, Nicole; Jackson, David; Buchlin, Eric; Csillaghy,
Andre; Bommier, Veronique; Kontogiannis, Ioannis; Gallagher, Peter;
Gontikakis, Costis; Guennou, Chloé; Murray, Sophie; Bloomfield,
D. Shaun; Alingery, Pablo; Baudin, Frederic; Benvenuto, Federico;
Bruggisser, Florian; Florios, Konstantinos; Guerra, Jordan; Park,
Sung-Hong; Perasso, Annalisa; Piana, Michele; Sathiapal, Hanna;
Soldati, Marco; Von Stachelski, Samuel; Argoudelis, Vangelis;
Caminade, Stephane
Bibcode: 2016cosp...41E.657G
Altcode:
We attempt a brief but informative description of the Flare
Likelihood And Region Eruption Forecasting (FLARECAST) project,
European Commission's first large-scale investment to explore the
limits of reliability and accuracy for the forecasting of major solar
flares. The consortium, objectives, and first results of the project
- featuring an openly accessible, interactive flare forecasting
facility by the end of 2017 - will be outlined. In addition, we will
refer to the so-called "explorative research" element of project,
aiming to connect solar flares with coronal mass ejections (CMEs)
and possibly pave the way for CME, or eruptive flare, prediction. We
will also emphasize the FLARECAST modus operandi, namely the diversity
of expertise within the consortium that independently aims to science,
infrastructure development and dissemination, both to stakeholders and
to the general public. Concluding, we will underline that the FLARECAST
project responds squarely to the joint COSPAR - ILWS Global Roadmap
to shield society from the adversities of space weather, addressing
its primary goal and, in particular, its Research Recommendations
1, 2 and 4, Teaming Recommendations II and III, and Collaboration
Recommendations A, B, and D. The FLARECAST project has received funding
from the European Union's Horizon 2020 research and innovation programme
under grant agreement No. 640216.
Title: Observations of a Series of Flares and Associated Jet-like
Eruptions Driven by the Emergence of Twisted Magnetic Fields
Authors: Lim, Eun-Kyung; Yurchyshyn, Vasyl; Park, Sung-Hong; Kim,
Sujin; Cho, Kyung-Suk; Kumar, Pankaj; Chae, Jongchul; Yang, Heesu;
Cho, Kyuhyoun; Song, Donguk; Kim, Yeon-Han
Bibcode: 2016ApJ...817...39L
Altcode: 2015arXiv151201330L
We studied temporal changes of morphological and magnetic properties
of a succession of four confined flares followed by an eruptive flare
using the high-resolution New Solar Telescope (NST) operating at the Big
Bear Solar Observatory (BBSO) and Helioseismic and Magnetic Imager (HMI)
magnetograms and Atmospheric Image Assembly (AIA) EUV images provided by
the Solar Dynamics Observatory (SDO). From the NST/Hα and the SDO/AIA
304 Å observations we found that each flare developed a jet structure
that evolved in a manner similar to evolution of the blowout jet: (1)
an inverted-Y-shaped jet appeared and drifted away from its initial
position; (2) jets formed a curtain-like structure that consisted
of many fine threads accompanied by subsequent brightenings near
the footpoints of the fine threads; and finally, (3) the jet showed
a twisted structure visible near the flare maximum. Analysis of the
HMI data showed that both the negative magnetic flux and the magnetic
helicity have been gradually increasing in the positive-polarity region,
indicating the continuous injection of magnetic twist before and during
the series of flares. Based on these results, we suggest that the
continuous emergence of twisted magnetic flux played an important role
in producing successive flares and developing a series of blowout jets.
Title: Comparison between the eruptive X2.2 flare on 2011 February
15 and confined X3.1 flare on 2014 October 24
Authors: Jing, Ju; Xu, Yan; Lee, Jeongwoo; Nitta, Nariaki V.; Liu,
Chang; Park, Sung-Hong; Wiegelmann, Thomas; Wang, Haimin
Bibcode: 2015RAA....15.1537J
Altcode:
We compare two contrasting X-class flares in terms of magnetic free
energy, relative magnetic helicity and decay index of the active regions
(ARs) in which they occurred. The events in question are the eruptive
X2.2 flare from AR 11158 accompanied by a halo coronal mass ejection
(CME) and the confined X3.1 flare from AR 12192 with no associated
CME. These two flares exhibit similar behavior of free magnetic energy
and helicity buildup for a few days preceding them. A major difference
between the two flares is found to lie in the time-dependent change
of magnetic helicity of the ARs that hosted them. AR 11158 shows a
significant decrease in magnetic helicity starting ∼4 hours prior
to the flare, but no apparent decrease in helicity is observed in AR
12192. By examining the magnetic helicity injection rates in terms
of sign, we confirmed that the drastic decrease in magnetic helicity
before the eruptive X2.2 flare was not caused by the injection of
reversed helicity through the photosphere but rather the CME-related
change in the coronal magnetic field. Another major difference we find
is that AR 11158 had a significantly larger decay index and therefore
weaker overlying field than AR 12192. These results suggest that the
coronal magnetic helicity and the decay index of the overlying field
can provide a clue about the occurrence of CMEs.
Title: Causes of the Sep. 12-13, 2014 geomagnetic storms
Authors: Cho, Kyung-Suk; Kim, Rooksoon; Park, Sung-Hong; Kim, Sujin
Bibcode: 2015IAUGA..2249582C
Altcode:
Solar cycle 24 is very modest compared to previous solar cycles. The
solar maximum phase may have been reached in the middle of 2014 and
the sunspot number has decreased since the beginning of 2015. During
this period, it has been reported that only few events produced strong
X-class flares, solar proton events, and geomagnetic storms. In this
study we have investigated causes of the multiple geomagnetic storms
occurred on September 12-13, 2014. The geomagnetic storm forecast
model based on the CME observations was used for identification of
the causes of the geomagnetic storms. Details of the solar source
region were investigated to give an answer why the geomagnetic
storms were not so strong even though they were related to fast
coronal mass ejections with large earth-ward direction. As a result,
we found that the first weak storm was driven by the CME related to
M4.6 flare and the second minor storm was driven by one of the fast
CMEs related to strong X1.6 flare. Our result shows that the reason
why the second storm was not strong is that it was caused by the CME
with northward magnetic field. Therefore we suggest that one of the
essential ingredients for geomagnetic storm forecasting is to find
out the magnetic field direction of earth-ward CMEs, which can be
accomplished by investigating magnetic fields of their solar source
regions a few days before their arrival to the earth.
Title: Development of technique to detect and classify small-scale
magnetic flux cancellation and rapid blue-shifted excursions
Authors: Chen, Xin; Deng, Na; Lamb, Derek A.; Jing, Ju; Liu, Chang;
Liu, Rui; Park, Sung-Hong; Wang, Haimin
Bibcode: 2015RAA....15.1012C
Altcode: 2015arXiv150101226C
We present a set of tools for detecting small-scale solar magnetic
cancellations and the disk counterpart of type II spicules (the
so-called Rapid Blueshifted Excursions (RBEs)), using line-of-sight
photospheric magnetograms and chromospheric spectroscopic observations,
respectively. For tracking magnetic cancellation, we improve the
Southwest Automatic Magnetic Identification Suite (SWAMIS) so that
it is able to detect certain obscure cancellations that can be easily
missed. For detecting RBEs, we use a normalized reference profile to
reduce false-positive detections caused by the non-uniform background
and seeing condition. Similar to the magnetic feature tracking in
SWAMIS, we apply a dual-threshold method to enhance the accuracy of
RBE detection. These tools are employed to analyze our coordinated
observations using the Interferometric BIdimensional Spectrometer at the
Dunn Solar Telescope of the National Solar Observatory and Hinode. We
present the statistical properties of magnetic cancellations and RBEs,
and explore their correlation using this data set.
Title: Burst Locating Capability of the Korean Solar Radio Burst
Locator (KSRBL)
Authors: Hwangbo, Jung-Eun; Bong, Su-Chan; Park, Sung-Hong; Lee,
Dae-Young; Cho, Kyung-Suk; Lee, Jaejin; Park, Young-Deuk
Bibcode: 2015JASS...32...91H
Altcode:
The Korean Solar Radio Burst Locator (KSRBL) is a solar radio
spectrograph observing the broad frequency range from 0.245 to 18 GHz
with the capability of locating wideband gyrosynchrotron bursts. Due to
the characteristics of a spiral feed, the beam center varies in a spiral
pattern with frequency, making a modulation pattern over the wideband
spectrum. After a calibration process, we obtained dynamic spectra
consistent with the Nobeyama Radio Polarimeter (NoRP). We compared and
analyzed the locations of bursts observed by KSRBL with results from
the Nobeyama Radioheliograph (NoRH) and Atmospheric Imaging Assembly
(AIA). As a result, we found that the KSRBL provides the ability to
locate flaring sources on the Sun within around 2'.
Title: A Trio of Confined Flares in AR 11087
Authors: Joshi, Anand D.; Forbes, Terry G.; Park, Sung-Hong; Cho,
Kyung-Suk
Bibcode: 2015ApJ...798...97J
Altcode:
We investigate three flares that occurred in active region, AR 11087,
observed by the Dutch Open Telescope (DOT) on 2010 July 13, in a
span of three hours. The first two flares have soft X-ray class B3,
whereas the third flare has class C3. The third flare not only was the
largest in terms of area and brightness but also showed a very faint
coronal mass ejection (CME) associated with it, while the earlier two
flares had no associated CME. The active region, located at 27° N,
26° E, has a small U-shaped active region filament to the south of
the sunspot, and a quiescent filament is located to its west. Hα
observations from DOT, as well as extreme-ultraviolet images and
magnetograms from the STEREO spacecraft and Solar Dynamics Observatory,
are used to study the dynamics of the active region during the three
flares. Our observations imply that the first two flares are confined
and that some filament material drains to the surface during these
flares. At the onset of the third flare downflows are again observed
within the active region, but a strong upflow is also observed at the
northern end of the adjacent quiescent filament to the west. It is at
the latter location that the CME originates. The temporal evolution of
the flare ribbons and the dynamics of the filaments are both consistent
with the idea that reconnection in a pre-existing current sheet leads
to a loss of equilibrium.
Title: Magnetic Structure and Nonthermal Electrons in the X6.9 Flare
on 2011 August 9
Authors: Hwangbo, Jung-Eun; Lee, Jeongwoo; Park, Sung-Hong; Kim,
Sujin; Lee, Dae-Young; Bong, Su-Chan; Kim, Yeon-Han; Cho, Kyung-Suk;
Park, Young-Deuk
Bibcode: 2014ApJ...796...80H
Altcode:
The 2011 August 9 flare is one of the largest X-ray flares of sunspot
cycle 24, but spatial information is rather limited due to its position
close to the western limb. This paper presents information about
the location of high-energy electrons derived from hard X-ray and
microwave spectra obtained with the Reuven Ramaty High-Energy Solar
Spectroscopic Imager (RHESSI) and the Korean Solar Radio Burst Locator
(KSRBL), respectively. The KSRBL microwave spectrum shows significant
fluxes at low frequencies, implying that the high-energy electrons
reside in a coronal volume highly concentrated at strong magnetic
fields, and rapidly expanding with decreasing magnetic fields. After a
simple modeling of the microwave spectrum, we found that the microwave
source should be located above the inner pair of magnetic poles in a
large quadrupolar configuration. The time-dependent evolution of the
magnetic field distribution and total nonthermal energy derived from
the microwave spectra is also consistent with the standard picture
of multiple magnetic reconnections recurring at a magnetic null point
that forms above the magnetic quadrupoles and moves up with time.
Title: 우주환경 지상관측기 자료통합시스템 개발
Title: 우주환경 지상관측기 자료통합시스템 개발
Title: Development of Data Integration System for Ground-Based Space
Weather Observational Facilities
Authors: Baek, Ji-Hye; Choi, Seonghwan; Lee, Jae-Jin; Kim, Yeon-Han;
Bong, Su-Chan; Park, Young-Deuk; Kwak, Young-Sil; Cho, Kyung-Suk;
Hwang, Junga; Jang, Bi-Ho; Yang, Tae-Yong; Hwang, Eunmi; Park,
Sung-Hong; Park, Jongyeob
Bibcode: 2013PKAS...28...65B
Altcode:
No abstract at ADS
Title: Study of Magnetic Helicity Injection in the Active Region NOAA
9236 Producing Multiple Flare-associated Coronal Mass Ejection Events
Authors: Park, Sung-Hong; Kusano, Kanya; Cho, Kyung-Suk; Chae,
Jongchul; Bong, Su-Chan; Kumar, Pankaj; Park, So-Young; Kim, Yeon-Han;
Park, Young-Deuk
Bibcode: 2013ApJ...778...13P
Altcode: 2013arXiv1308.5774P
To better understand a preferred magnetic field configuration and its
evolution during coronal mass ejection (CME) 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 positive (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.
Title: Multiwavelength Study of a Solar Eruption from AR NOAA 11112
I. Flux Emergence, Sunspot Rotation and Triggering of a Solar Flare
Authors: Kumar, Pankaj; Park, Sung-Hong; Cho, K. -S.; Bong, S. -C.
Bibcode: 2013SoPh..282..503K
Altcode: 2012arXiv1210.3413K
We analyze the multiwavelength observations of an M2.9/1N flare
that occurred in the active region (AR) NOAA 11112 in the vicinity
of a huge filament system on 16 October 2010. SDO/HMI magnetograms
reveal the emergence of a bipole (within the existing AR) 50 hours
prior to the flare event. During the emergence, both the positive and
negative sunspots in the bipole show translational as well as rotational
motion. The positive-polarity sunspot shows significant motion/rotation
in the south-westward/clockwise direction, and we see continuously
pushing/sliding of the surrounding opposite-polarity field region. On
the other hand, the negative-polarity sunspot moves/rotates in the
westward/anticlockwise direction. The positive-polarity sunspot rotates
≈ 70∘ within 30 hours, whereas the one with negative
polarity rotates ≈ 20∘ within 10 hours. SDO/AIA 94 Å
EUV images show the emergence of a flux tube in the corona, consistent
with the emergence of the bipole in HMI. The footpoints of the flux
tube were anchored in the emerging bipole. The initial brightening
starts at one of the footpoints (western) of the emerging loop system,
where the positive-polarity sunspot pushes/slides towards a nearby
negative-polarity field region. A high speed plasmoid ejection (speed
≈ 1197 km s−1) was observed during the impulsive phase
of the flare, which suggests magnetic reconnection of the emerging
positive-polarity sunspot with the surrounding opposite-polarity
field region. The entire AR shows positive-helicity injection before
the flare event. Moreover, the newly emerging bipole reveals the
signature of a negative (left-handed) helicity. These observations
provide unique evidence of the emergence of twisted flux tubes from
below the photosphere to coronal heights, triggering a flare mainly
due to the interaction between the emerging positive-polarity sunspot
and a nearby negative-polarity sunspot by the shearing motion of the
emerging positive sunspot towards the negative one. Our observations
also strongly support the idea that the rotation can most likely be
attributed to the emergence of twisted magnetic fields, as proposed
by recent models.
Title: Multiwavelength Study of a Solar Eruption from AR NOAA 11112:
II. Large-Scale Coronal Wave and Loop Oscillation
Authors: Kumar, Pankaj; Cho, K. -S.; Chen, P. F.; Bong, S. -C.;
Park, Sung-Hong
Bibcode: 2013SoPh..282..523K
Altcode: 2012arXiv1210.3417K
We analyze multiwavelength observations of an M2.9/1N flare that
occurred in AR NOAA 11112 on 16 October 2010. AIA 211 Å EUV images
reveal the presence of a faster coronal wave (decelerating from ≈
1390 to ≈ 830 km s−1) propagating ahead of a slower wave
(decelerating from ≈ 416 to ≈ 166 km s−1) towards
the western limb. The dynamic radio spectrum from Sagamore Hill
radio telescope shows the presence of a metric type II radio burst,
which reveals the presence of a coronal shock wave (speed ≈ 800 km
s−1). The speed of the faster coronal wave, derived from
AIA 211 Å images, is found to be comparable to the coronal shock
speed. AIA 171 Å high-cadence observations showed that a coronal
loop, which was located at a distance of ≈ 0.32R⊙ to
the west of the flaring region, started to oscillate by the end of
the impulsive phase of the flare. The results indicate that the faster
coronal wave may be the first driver of the transversal oscillations
of coronal loop. As the slower wave passed through the coronal loop,
the oscillations became even stronger. There was a plasmoid eruption
observed in EUV and a white-light CME was recorded, having velocity of
≈ 340 - 350 km s−1. STEREO 195 Å images show an EIT
wave, propagating in the same direction as the lower-speed coronal
wave observed in AIA, but decelerating from ≈ 320 to ≈ 254 km
s−1. These observations reveal the co-existence of both
waves (i.e. coronal Moreton and EIT waves), and the type II radio
burst seems to be associated with the coronal Moreton wave.
Title: Evolution of Relative Magnetic Helicity and Current Helicity
in NOAA Active Region 11158
Authors: Jing, Ju; Park, Sung-Hong; Liu, Chang; Lee, Jeongwoo;
Wiegelmann, Thomas; Xu, Yan; Deng, Na; Wang, Haimin
Bibcode: 2012ApJ...752L...9J
Altcode:
Both magnetic and current helicities are crucial ingredients for
describing the complexity of active-region magnetic structure. In this
Letter, we present the temporal evolution of these helicities contained
in NOAA active region 11158 during five days from 2011 February 12
to 16. The photospheric vector magnetograms of the Helioseismic and
Magnetic Imager on board the Solar Dynamic Observatory were used as
the boundary conditions for the coronal field extrapolation under the
assumption of nonlinear force-free field, from which we calculated
both relative magnetic helicity and current helicity. We construct a
time-altitude diagram in which altitude distribution of the magnitude
of current helicity density is displayed as a function of time. This
diagram clearly shows a pattern of upwardly propagating current
helicity density over two days prior to the X2.2 flare on February
15 with an average propagation speed of ~36 m s-1. The
propagation is synchronous with the emergence of magnetic flux into
the photosphere, and indicative of a gradual energy buildup for the
X2.2 flare. The time profile of the relative magnetic helicity shows
a monotonically increasing trend most of the time, but a pattern
of increasing and decreasing magnetic helicity above the monotonic
variation appears prior to each of two major flares, M6.6 and X2.2,
respectively. The physics underlying this bump pattern is not fully
understood. However, the fact that this pattern is apparent in the
magnetic helicity evolution but not in the magnetic flux evolution
makes it a useful indicator in forecasting major flares.
Title: The Occurrence and Speed of CMEs Related to Two Characteristic
Evolution Patterns of Helicity Injection in Their Solar Source Regions
Authors: Park, Sung-Hong; Cho, Kyung-Suk; Bong, Su-Chan; Kumar,
Pankaj; Chae, Jongchul; Liu, Rui; Wang, Haimin
Bibcode: 2012ApJ...750...48P
Altcode: 2012arXiv1203.1690P
Long-term (a few days) variation of magnetic helicity injection
was calculated for 28 solar active regions that produced 47 coronal
mass ejections (CMEs) to find its relationship to 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 ~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
(1330 km s-1) is much faster than that of Group A (870
km 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.
Title: Initiation of Coronal Mass Ejection and Associated Flare
Caused by Helical Kink Instability Observed by SDO/AIA
Authors: Kumar, Pankaj; Cho, K. -S.; Bong, S. -C.; Park, Sung-Hong;
Kim, Y. H.
Bibcode: 2012ApJ...746...67K
Altcode: 2011arXiv1111.4360K
In this paper, we present multiwavelength observations of helical
kink instability as a trigger of a coronal mass ejection (CME) which
occurred in active region NOAA 11163 on 2011 February 24. The CME
was associated with an M3.5 limb flare. High-resolution observations
from the Solar Dynamics Observatory/Atmospheric Imaging Assembly
suggest the development of helical kink instability in the erupting
prominence, which implies a flux rope structure of the magnetic
field. A brightening starts below the apex of the prominence with
its slow rising motion (~100 km s-1) during the activation
phase. A bright structure, indicative of a helix with ~3-4 turns, was
transiently formed at this position. The corresponding twist of ~6π-8π
is sufficient to generate the helical kink instability in a flux rope
according to recently developed models. A slowly rising blob structure
was subsequently formed at the apex of the prominence, and a flaring
loop was observed near the footpoints. Within 2 minutes, a second blob
was formed in the northern prominence leg. The second blob erupts (like
a plasmoid ejection) with the detachment of the northern prominence
leg, and flare intensity maximizes. The first blob at the prominence
apex shows rotational motion in the counterclockwise direction in the
plane of sky, interpreted as the unwinding motion of a helix, and it
also erupts to give the CME. RHESSI hard X-ray (HXR) sources show the
two footpoint sources and a loop-top source during the flare. We found
RHESSI HXR flux, soft X-ray flux derivative, and CME acceleration in
the low corona correlate well, which is in agreement with the standard
flare model (CSHKP). We also discuss the possible role of ballooning
as well as torus instabilities in driving the CME. We conclude that
the CME and flare were triggered by the helical kink instability in
a flux rope and accelerated mainly by the torus instability.
Title: Geometry of the 20 November 2003 magnetic cloud
Authors: Marubashi, Katsuhide; Cho, Kyung-Suk; Kim, Yeon-Han; Park,
Yong-Deuk; Park, Sung-Hong
Bibcode: 2012JGRA..117.1101M
Altcode: 2012JGRA..11701101M
This study is an attempt to find a coherent interpretation of the
link between the 20 November 2003 magnetic cloud (MC) and its solar
source. Most previous studies agree on the orientation of the MC, but
the orientation is nearly perpendicular to the axis of the post-eruption
arcade (PEA) or the orientation of the neutral line in the solar source
region. We first determine the geometry of this MC by fitting methods
with both torus and cylinder models. Three possible geometries are
obtained, which can reproduce the observed magnetic field variations
associated with the MC, one from the cylinder fit and two from the torus
fit. The cylinder fit gives the MC orientation with a tilt of a large
angle (∼60°) from the ecliptic plane and nearly perpendicular to the
PEA axis, being similar to those from previous studies. In contrast,
two torus fit results give the MC axis with tilt angles less than
20° from the ecliptic plane. The two torus results correspond to
the spacecraft encounter with the eastern flank of the flux rope loop
(model A) and the western flank of the loop (model B), respectively. In
either case, the orientation of the loop around the apex is nearly
parallel to the PEA as observed by the SOHO/extreme ultraviolet imaging
telescope instrument in the most plausible solar source region of a
halo coronal mass ejection (CME), which appeared in the field of view
of Large Angle and Spectrometric Coronagraph (LASCO) C2 at 08:50 UT,
18 November 2003. The magnetic helicity of the PEA region is positive
in agreement with the helicity of the MC. The 3-D reconstruction from
the Solar Mass Ejection Imager data shows that the main part of the
ejected plasma expands mainly to the west of the Sun-Earth line. Thus,
we reach the most straightforward interpretation of the link between the
MC and its solar source as follows. The MC was created in association
with the launch of the CME that was first observed by the LASCO C2 at
08:50 UT, 18 November 2003, and propagated through interplanetary space
with its orientation almost unchanged. The spacecraft encountered the
eastern flank of the loop as described by model A.
Title: Observing the reconnection region in a transequatorial
loop system
Authors: Liu, Rui; Wang, Tong-Jiang; Lee, Jeongwoo; Stenborg,
Guillermo; Liu, Chang; Park, Sung-Hong; Wang, Hai-Min
Bibcode: 2011RAA....11.1209L
Altcode:
A vertical current sheet is a crucial element in many flare/coronal
mass ejection (CME) models. For the first time, Liu et al. reported
a vertical current sheet directly imaged during the flare rising
phase with the EUV Imaging Telescope (EIT) onboard the Solar and
Heliospheric Observatory (SOHO). As a follow-up study, here we present
the comprehensive analysis and detailed physical interpretation of
the observation. The current sheet formed due to the gradual rise
of a transequatorial loop system. As the loop legs approached each
other, plasma flew at ~ 6 km s-1 into a local area where a
cusp-shaped flare loop subsequently formed and the current sheet was
seen as a bright, collimated structure of global length (>= 0.25
Rodot) and macroscopic width ((5-10)×103km),
extending from 50 Mm above the flaring loop to the border of the EIT
field of view (FOV). The reconnection rate in terms of the Alfvén
Mach number is estimated to be only 0.005-0.009, albeit a halo CME was
accelerated from ~ 400 km s-1 to ~ 1300 km s-1
within the coronagraph FOV. Drifting pulsating structures at metric
frequencies were recorded during the impulsive phase, implying tearing
of the current sheet in the high corona. A radio Type III burst
occurred when the current sheet was clearly seen in EUV, indicative of
accelerated electrons beaming upward from the upper tip of the current
sheet. A cusp-shaped dimming region was observed to be located above the
post-flare arcade during the decay phase in EIT; both the arcade and the
dimming expanded with time. With the Coronal Diagnostic Spectrometer
(CDS) aboard SOHO, a clear signature of chromospheric evaporation was
seen during the decay phase, i.e., the cusp-shaped dimming region was
associated with plasma upflows detected with EUV hot emission lines,
while the post-flare loop was associated with downflows detected with
cold lines. This event provides a comprehensive view of the reconnection
geometry and dynamics in the solar corona.
Title: Study of Magnetic Helicity Injection in the Active Region
NOAA 11158 Associated with the X-class Flare of 2011 February 15
Authors: Park, Sung-Hong; Cho, K.; Kim, Y.; Bong, S.; Gary, D. E.;
Park, Y.
Bibcode: 2011SPD....42.2227P
Altcode: 2011BAAS..43S.2227P
The main objective of this study is to examine a long-term (a few
days) precondition and a trigger mechanism for an X2.2 flare peaking
at 01:56 UT on 2011 February 15 in GOES soft X-ray flux. For this,
we investigated the variation of magnetic helicity injection through
the photospheric surface of the flare-productive active region NOAA
11158 during (1) the long-term period of February 11 to 15 with a
1-hour cadence and (2) the short-term period of 01:26 to 02:10 UT
on February 15 with a 45-second cadence. The helicity injection was
determined using line-of-sight magnetograms with high spatial and
temporal resolution taken by the Helioseismic and Magnetic Imager
(HMI) onboard the Solar Dynamics Observatory (SDO). As a result, we
found two characteristic phases of helicity injection related to the
X2.2 flare. A large amount of positive helicity was first injected
over 2 days with a phase of monotonically increasing helicity. And
then the flare started simultaneously with a significant injection of
the opposite (negative) sign of helicity around the flaring magnetic
polarity inversion line. This observational finding clearly supports
the previous studies that there is a continuous injection of helicity
a few days before flares and a rapid injection of the helicity in the
opposite sign into an existing helicity system triggers flares.
Title: Gradual Inflation of Active-region Coronal Arcades Building
up to Coronal Mass Ejections
Authors: Liu, Rui; Liu, Chang; Park, Sung-Hong; Wang, Haimin
Bibcode: 2010ApJ...723..229L
Altcode: 2010arXiv1008.4863L
The pre-coronal mass ejection (pre-CME) structure is of great
importance to understanding the origin of CMEs, which, however, has
been largely unknown for CMEs originating from active regions. In
this paper, we investigate this issue using the wavelet-enhanced EUV
Imaging Telescope (EIT) observations combined with the Large Angle and
Spectrometric Coronagraph, Michelson Doppler Imager, and GOES soft X-ray
observations. Selected for studying are 16 active-region coronal arcades
whose gradual inflation lead up to CMEs. Twelve of them clearly build
upon post-eruptive arcades resulting from a preceding eruption; the
remaining four are located high in the corona in the first place and/or
have existed for days. The observed inflation lasts for 8.7 ± 4.1 hr,
with the arcade rising from 1.15 ± 0.06 R sun to 1.36 ±
0.07 R sun within the EIT field of view (FOV). The rising
speed is less than 5 km s-1 most of the time. Only at the
end of this quasi-static stage does it increase to tens of kilometers
per second over tens of minutes. The arcade then erupts out of the
EIT FOV as a CME with similar morphology. This pre-CME structure is
apparently unaffected by the flares occurring during its quasi-static
inflation phase, but is closely coupled with the flare occurring during
its acceleration phase. For four events that are observed on the disk,
it is found that the gradual inflation of the arcade is accompanied by
significant helicity injection from the photosphere. In particular,
a swirling structure, which is reminiscent of a magnetic flux rope,
was observed in one of the arcades over 4 hr prior to the subsequent
CME, and the growth of the arcade is associated with the injection of
helicity of opposite sign into the active region via flux emergence. We
propose a four-phase evolution paradigm for the observed CMEs, i.e.,
a quasi-static inflation phase which corresponds to the buildup of
magnetic free energy in the corona, followed by the frequently observed
three-phase paradigm, including an initial phase, an acceleration phase,
and a gradual phase.
Title: Time Evolution of Coronal Magnetic Helicity in the Flaring
Active Region NOAA 10930
Authors: Park, Sung-Hong; Chae, Jongchul; Jing, Ju; Tan, Changyi;
Wang, Haimin
Bibcode: 2010ApJ...720.1102P
Altcode: 2010arXiv1008.1558P
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 -4.3
× 1043 Mx2 just before the X3.4 flare. (3) This
flare is preceded not only by a large increase of negative helicity,
-3.2 × 1043 Mx2, in the corona over ~1.5 days
but also by noticeable injections of positive helicity through 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.
Title: Productivity of Solar Flares and Magnetic Helicity Injection
in Active Regions
Authors: Park, Sung-hong; Chae, Jongchul; Wang, Haimin
Bibcode: 2010ApJ...718...43P
Altcode: 2010arXiv1005.3416P
The main objective of this study is to better understand how magnetic
helicity injection in an active region (AR) is related to the occurrence
and intensity of solar flares. We therefore investigate the magnetic
helicity injection rate and unsigned magnetic flux, as a reference. In
total, 378 ARs are analyzed using SOHO/MDI magnetograms. The 24 hr
averaged helicity injection rate and unsigned magnetic flux are compared
with the flare index and the flare-productive probability in the next
24 hr following a 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 ARs. The
major findings of this study are as follows: (1) for a sub-sample of
91 large ARs with unsigned magnetic fluxes in the range from (3-5)
× 1022 Mx, there is a difference in the magnetic helicity
injection rate between flaring ARs and non-flaring ARs 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
ARs 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) × 1042
Mx2 during a phase of monotonically increasing helicity over
0.5-2 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 ARs.
Title: Time Evolution of Coronal Magnetic Helicity in the Flaring
Active Region NOAA 10930
Authors: Park, Sung-Hong; Jing, J.; Wang, H.
Bibcode: 2010AAS...21640508P
Altcode: 2010BAAS...41..890P
To study the three-dimensional (3D) magnetic field topology and its
long-term (a few days) evolution associated with the X3.4 flare of
2006 December 13, we investigate the temporal evolution of the relative
coronal magnetic helicity in NOAA active region (AR) 10930 during the
time period of December 8, 21:20 UT through December 14, 5:00 UT. The
coronal helicity is calculated based on the 3D nonlinear force-free
(NLFF) magnetic fields reconstructed by the optimization method
(Wheatland et al. 2000) as implemented by Wiegelmann (2004). As the
boundary conditions for the force-free reconstruction, we use the
preprocessed Hinode Spectropolarimeter (SP) vector magnetograms in
which the net Lorentz force and the torque in the photosphere are
minimized (see Wiegelmann et al. 2006 for the details). The major
findings of this study are: (1) a negative (left-handed) helicity
of -5×1043 Mx2 in the AR corona is estimated
right before the X3.4 flare; (2) the major flare is preceded by
a significantly and consistently large amount of negative helicity
injection (-2×1043 Mx2) into the corona over 2
days; (3) the temporal variation of helicity is comparable to that of
the rotational speed in the southern sunspot with positive polarity;
(4) in general, the time profile of the coronal helicity is well-matched
with that of the helicity accumulation by the time integration of the
simplified helicity injection rate (Chae 2001) determined by using
SOHO MDI magnetograms; (5) at the time period of the channel structure
development (December 11, 4:00-8:00 UT) with newly emerging flux and
just right before the C5.7 class flare, the time variation of the
coronal helicity shows a rapid and huge increase of negative helicity,
but that of the helicity accumulation by MDI magnetograms indicates
a monotonous increase of negative helicity.
Title: Study of magnetic helicity in solar active regions and its
relationship with solar eruptions
Authors: Park, Sung-Hong
Bibcode: 2010PhDT.......286P
Altcode:
No abstract at ADS
Title: Temporal Evolution of Free Magnetic Energy Associated with
Four X-Class Flares
Authors: Jing, Ju; Chen, P. F.; Wiegelmann, Thomas; Xu, Yan; Park,
Sung-Hong; Wang, Haimin
Bibcode: 2009ApJ...696...84J
Altcode:
We study the temporal variation of free magnetic energy
E free around the time of four X-class flares. The
high-cadence photospheric vector magnetograms obtained by the digital
vector magnegograph system at the Big Bear Solar Observatory are
used as the boundary conditions to reconstruct the three-dimensional
nonlinear force-free (NLFF) coronal field. In order to remove the
effect of the net Lorentz force and torque acting in the photosphere,
the vector magnetograms are preprocessed using the method devised by
Wiegelmann et al.. Then a well-tested multigrid-like optimization
code by Wiegelmann is applied to the preprocessed boundary data to
extrapolate the NLFF coronal field with which we are able to estimate
the free energy E free. In all the four events, we find
a significant drop of E free starting ~15 minutes before
the peak time of the associated nonthermal flare emission, although
long-term trend varies from event to event. We discuss the physical
implication of the result, i.e., the magnetic relaxation is already
going on in the corona well before the flare reconnection.
Title: Three-Dimensional Structure Analysis of Electric Current
Helicity in AR NOAA 10930 Associated with the X3.4 Flare of 2006
December 13
Authors: Park, Sung-Hong; Jing, J.; Wang, H.
Bibcode: 2009SPD....40.2012P
Altcode:
We investigate the three-dimensional (3D) electric current helicity
in active region NOAA 10930 before and after the 4B/X3.4 flare of
2006 December 13. By using the optimization method (Wheatland et
al. 2000) as implemented by Wiegelmann (2004), we extrapolate the 3D
nonlinear force-free magnetic fields. The Hinode vector magnetograms
preprocessed by the method devised by Wiegelmann et al (2006) are
used as the boundary conditions for the extrapolation. The averaged
unsigned current helicity is calculated in local areas of the central
darkening region around the flaring magnetic polarity inversion line and
a peripheral brightening region at progressively higher altitude. We
also examine the spatial relationship between the unsigned current
helicity and soft X-ray emission from Hinode XRT.
Title: The Variation of Relative Magnetic Helicity around Major Flares
Authors: Park, Sung-Hong; Lee, Jeongwoo; Choe, G. S.; Chae, Jongchul;
Jeong, Hyewon; Yang, Guo; Jing, Ju; Wang, Haimin
Bibcode: 2008ApJ...686.1397P
Altcode: 2010arXiv1004.2856P
We have investigated the variation of magnetic helicity over a span
of several days around the times of 11 X-class flares which occurred
in seven active regions (NOAA 9672, 10030, 10314, 10486, 10564, 10696,
and 10720) using the magnetograms taken by the Michelson Doppler Imager
(MDI) on board the Solar and Heliospheric Observatory (SOHO). As a
major result we found that each of these major flares was preceded
by a significant helicity accumulation, (1.8-16) × 1042
Mx2 over a long period (0.5 to a few days). Another finding
is that the helicity accumulates at a nearly constant rate, (4.5-48)
× 1040 Mx2 hr-1, and then becomes
nearly constant before the flares. This led us to distinguish the
helicity variation into two phases: a phase of monotonically increasing
helicity and the following phase of relatively constant helicity. As
expected, the amount of helicity accumulated shows a modest correlation
with time-integrated soft X-ray flux during flares. However, the
average helicity change rate in the first phase shows even stronger
correlation with the time-integrated soft X-ray flux. We discuss the
physical implications of this result and the possibility that this
characteristic helicity variation pattern can be used as an early
warning sign for solar eruptions.
Title: Statistical Correlations between Parameters of Photospheric
Magnetic Fields and Coronal Soft X-Ray Brightness
Authors: Tan, Changyi; Jing, Ju; Abramenko, V. I.; Pevtsov, A. A.;
Song, Hui; Park, Sung-Hong; Wang, Haimin
Bibcode: 2007ApJ...665.1460T
Altcode:
Using observations of more than 160 active regions, we investigate
the relationship between the coronal X-ray brightness, LB,
and five parameters derived from the photospheric magnetic fields. The
coronal X-ray brightness and the magnetic measures were obtained
from co-aligned SFD composite images from the Yohkoh SXT and
full-disk magnetograms from the SOHO MDI, respectively. The
magnetic parameters are (1) the length of strong-gradient
magnetic neutral lines, LGNL, (2) the magnetic energy
dissipation, ɛ, (3) the unsigned line-of-sight magnetic flux, Φ,
(4) the horizontal velocities, Vh, of random footpoint
motions in the photosphere, and (5) a proxy for the Poynting flux,
E=(1/4π)VhBz2, which characterizes
the energy flux from the photosphere into the corona due to random
footpoint motions. All measures except Vh were analyzed
in both the extensive (total) and intensive (average over an area)
forms. In addition, we used the area-averaged strong gradient
(>50 G) of the magnetic field, ∇Bz, as an intensive
form of LGNL. We found that the Pearson correlation
coefficient between the total X-ray brightness and the total magnetic
measures decreases as 0.97, 0.88, 0.86, and 0.47 for Φ, E, ɛ, and
LGNL, respectively. The correlation coefficient between
the averaged X-ray brightness and the averaged magnetic measures
varied as 0.67, 0.71, 0.57, and 0.49 for <Φ>, , <ɛ>,
and <∇Bz>, respectively. We also found that the
velocities of the footpoint motions have no dependencies with Φ and
LB. We concluded that the observed high correlation between
LB and E is mainly due to the magnetic field. The energy
of the Poynting flux is in the range 106.7-107.6
ergs cm-2 s-1 for the majority of active regions,
which is sufficient to heat the corona due to footpoint random motions
of magnetic flux tubes.
Title: Two Phases of Helicity Variation Around Major Flares
Authors: Park, Sung-Hong; Chae, J.; Jeong, H.; Choe, G.; Lee, J.;
Yang, G.; Jing, J.; Wang, H.
Bibcode: 2006SPD....37.2201P
Altcode: 2006BAAS...38..249P
We have investigated the magnetic helicity injection rates in three
active regions (NOAA 10484, 10486 and 10696) around the times of four
X-class flares using the MDI/SOHO magnetograms. In all cases, the
total magnetic flux of the individual active region changed little
with time, and the helicity variation is directly related to the
variation of field line winding. This also justifies our measurement of
magnetic helicity injection rates using a local correlation tracking
method. Our analysis reveals that there were two distinct phases of
helicity variation around those flares. In the first phase that starts
a few days before the flare onset, the helicity accumulates at a nearly
constant rate. The second phase usually starts 3-12 hours before the
flare onset and lasts until 3-20 hours after the flare. During this
phase, the helicity injection rate is negligible and the magnitude
of helicity remains almost constant or increases only slightly. This
characteristic pattern in the helicity evolution may imply a physical
link between magnetic winding and flare occurrence, and could be used
as an early warning sign of impending flares.
Title: The Effect of Bright Lenses on the Astrometric Observations
of Gravitational Microlensing Events
Authors: Jeong, Youngjin; Han, Cheongho; Park, Sung-Hong
Bibcode: 1999ApJ...511..569J
Altcode:
In current microlensing experiments, information about the physical
parameters of individual lenses is obtained from the Einstein
timescales. However, the nature of MACHOs is still very uncertain,
despite the large number of detected events. This uncertainty is mainly
due to the degeneracy of the lens parameters in the measured Einstein
timescales. The degeneracy can be improved in a general fashion if
the angular Einstein ring radius θE, and thus the MACHO
proper motion, can be measured by conducting accurate astrometric
measurements of centroid displacement in the source-star image. In this
paper, we analyze the influence of bright lenses on the astrometric
measurements of the centroid displacement and investigate the effect on
the determination of θE. We find that if an event is caused
by a bright lens, the centroid displacement is distorted by the flux
of the lens, and the resulting astrometric ellipse becomes rounder
and smaller with increasing lens brightness, causing an incorrect
determination of the angular Einstein ring radius. A lens-blended
event cannot be distinguished from a dark-lens event just from the
trajectory of the measured centroid displacements because both events
have elliptical trajectories; this is the degeneracy between dark and
bright-lens events. For the resolution of the bright-lens degeneracy,
additional information from high-precision photometric and spectroscopic
follow-up observations of the event are required.
Title: The Effect of Bright Lenses in the Astrometric Measurements
of MACHO Proper Motion
Authors: Jeong, Youngjin; Han, Cheongho; Park, Sung-Hong
Bibcode: 1998astro.ph..7165J
Altcode:
In current microlensing experiments, the information about the physical
parameters of individual lenses are obtained from the Einstein
timescales. However, the nature of MACHOs is still very uncertain
despite the large number of detected events. This uncertainty is mainly
due to the degeneracy of the lens parameters in the measured Einstein
timescales. The degeneracy can be lifted in a general fashion if the
angular Einstein ring radius $\theta_{\rm E}$, and thus the MACHO
proper motion, can be measured by conducting accurate astrometric
measurements of centroid displacement in the source star image. In this
paper, we analyze the influence of bright lenses on the astrometric
measurements of the centroid displacement and investigate this effect
on the determination of $\theta_{\rm E}$. We find that if an event is
caused by a bright lens, the centroid displacement is distorted by the
flux of the lens and resulting astrometric ellipse becomes rounder
and smaller with increasing lens brightness, causing an incorrect
determination of the angular Einstein ring radius. A lens-blended event
cannot be distinguished from a dark lens event from the trajectory
of the measured centroid displacements alone because both events have
elliptical trajectories: the degeneracy between dark and bright lens
events. We also find that even with information from the analysis of
the light curve of the event it will still be difficult to resolve
the degeneracy caused by the bright lens because the light curve is
also affected by lens blending.