georgoulis

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Author name code: georgoulis
ADS astronomy entries on 2022-09-14
author:"Georgoulis, Manolis K."

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Title: Towards coupling full-disk and active region-based flare
prediction for operational space weather forecasting
Authors: Pandey, Chetraj; Ji, Anli; Angryk, Rafal A.; Georgoulis,
Manolis K.; Aydin, Berkay
2022FrASS...9.7301P Altcode:
Solar flare prediction is a central problem in space weather forecasting
and has captivated the attention of a wide spectrum of researchers due
to recent advances in both remote sensing as well as machine learning
and deep learning approaches. The experimental findings based on
both machine and deep learning models reveal significant performance
improvements for task specific datasets. Along with building models,
the practice of deploying such models to production environments under
operational settings is a more complex and often time-consuming process
which is often not addressed directly in research settings. We present
a set of new heuristic approaches to train and deploy an operational
solar flare prediction system for ≥M1.0-class flares with two
prediction modes: full-disk and active region-based. In full-disk mode,
predictions are performed on full-disk line-of-sight magnetograms using
deep learning models whereas in active region-based models, predictions
are issued for each active region individually using multivariate
time series data instances. The outputs from individual active region
forecasts and full-disk predictors are combined to a final full-disk
prediction result with a meta-model. We utilized an equal weighted
average ensemble of two base learners' flare probabilities as our
baseline meta learner and improved the capabilities of our two base
learners by training a logistic regression model. The major findings
of this study are: 1) We successfully coupled two heterogeneous
flare prediction models trained with different datasets and model
architecture to predict a full-disk flare probability for next 24
h, 2) Our proposed ensembling model, i.e., logistic regression,
improves on the predictive performance of two base learners and the
baseline meta learner measured in terms of two widely used metrics
True Skill Statistic (TSS) and Heidke Skill Score (HSS), and 3) Our
result analysis suggests that the logistic regression-based ensemble
(Meta-FP) improves on the full-disk model (base learner) by ∼9% in
terms TSS and ∼10% in terms of HSS. Similarly, it improves on the
AR-based model (base learner) by ∼17% and ∼20% in terms of TSS and
HSS respectively. Finally, when compared to the baseline meta model,
it improves on TSS by ∼10% and HSS by ∼15%.

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Title: A physics-based prototype tool to forecast the probability
of SEP occurrence using modelled shock wave parameters
Authors: Kouloumvakos, Athanasios; Dalmasse, Kévin; Georgoulis,
Manolis K.; Rouillard, Alexis; Papaioannou, Athanasios; Anastasiadis,
Anastasios; Paouris, Evangelos; Vasalos, George; Indurain, Mikel
2022cosp...44.1180K Altcode:
Over the last decade, great efforts have been taken place focusing
on the development and the improvement of forecasting models of space
weather (SW) hazards. These models are essential in support of space
operations and for human space exploration. The most important drivers
of intense SW are the coronal mass ejections (CMEs) and their associated
shock waves. These can accelerate particles to relativistic energies
which are one of the main safety concerns for humans in space and
space-based technology. We present a physics-based multi-module scheme
that is developed to forecast the probability of SEP occurrence. The
developed prototype consists of three main modules, namely, (1) a
shock propagation model, (2) a magnetic field connectivity module that
provides the connectivity solutions for different input magnetograms and
various observers from the low corona to interplanetary (IP) space, (3)
a coronal plasma module that utilizes different density and solar wind
speed models (empirical or MHD). The two main inputs to the tool are
the identified active regions (ARs) at the visible solar disk and the
expected maximum CME speed, both provided by the Advanced Solar Particle
Events Casting System (ASPECS) forecasting system of the National
Observatory of Athens (NOA). The magnetic connectivity is provided
by the Institut de Recherche en Astrophysique et Planétologie's
magnetic connectivity tool (IRAP-MCT). The model calculates the wave
kinematics, and the connection times and shock parameters at the field
lines connected to the observers. These calculations are performed for
each identified AR. The evolution of the shock parameters can be used
to construct a binary prediction model of SEPs. We will present results
from the prototype and we will show how a binary classification of solar
events to SEP/non-SEP events is possible. We will discuss limitations
and further improvements of the model. Integration of the tool as a
part of the IRAP-MCT is currently underway. The development of this
prototype has received funding from the European Union's Horizon 2020
research and innovation programme under grant agreement No. 870405
(EUHFORIA 2.0).

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Title: The Importance of Method Redundancy in Studying Pre-Eruption
Evolution in Solar Active Regions
Authors: Georgoulis, Manolis K.; Pariat, Etienne; Liu, Yang; Thalmann,
Julia K.
2022cosp...44.1358G Altcode:
In a recent synergistic work stemming from a prior International
Space Science Institute (ISSI) Working Group, the evolution of
magnetic helicity in an intensely eruptive solar active region was
studied using several different helicity calculation methods. This
was the first time all these methods were tested on real solar data,
without the possibility of a ground truth. Focusing on the pre-eruption
evolution prior to an eruptive X-class flare (SOL2006-12-13T02:14X3.4)
in NOAA active region (AR) 10930, we reveal a more complex picture than
what any single method might convey. Through imperfect but overall
converging calculations from different methods, we find artifacts
that could mislead conclusions. More importantly, we find evidence of
competing physical tendencies in the active region whose omission could
lead to counterintuitive, hence misleading, again, conclusions. While
for the Sun we have the capability to use different data and methods
for related purposes, this is not the case for other eruptive stars,
which is a fact calling for robust modeling approaches, relying
on scarce and indirect observations of stellar magnetic fields and
CME properties. Confluence of any data available and modeling could
offer the redundancy needed to critically assess partial findings
and reconcile them into a physically consistent picture of stellar
eruptions, quite possibly with qualitative / quantitative similarities
and differences from the eruptions of our own Sun.

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Title: 4π Heliospheric Observing System - 4π-HeliOS: Exploring
the Heliosphere from the Solar Interior to the Solar Wind
Authors: Raouafi, Nour E.; Gibson, Sarah; Ho, George; Laming,
J. Martin; Georgoulis, Manolis K.; Szabo, Adam; Vourlidas, Angelos;
Mason, Glenn M.; Hoeksema, J. Todd; Velli, Marco; Berger, Thomas;
Hassler, Donald M.; Kinnison, James; Viall, Nicholeen; Case, Anthony;
Newmark, Jeffrey; Lepri, Susan; Krishna Jagarlamudi, Vamsee; Raouafi,
Nour; Bourouaine, Sofiane; Vievering, Juliana T.; Englander, Jacob A.;
Shannon, Jackson L.; Perez, Rafael M.; Chattopadhyay, Debarati; Mason,
James P.; Leary, Meagan L.; Santo, Andy; Casti, Marta; Upton, Lisa A.
2022cosp...44.1530R Altcode:
The 4$\pi$ Heliospheric Observing System (4$\pi$-HeliOS) is an
innovative mission concept study for the next Solar and Space
Physics Decadal Survey to fill long-standing knowledge gaps in
Heliophysics. A constellation of spacecraft will provide both remote
sensing and in situ observations of the Sun and heliosphere from a
full 4$\pi$-steradian field of view. The concept implements a holistic
observational philosophy that extends from the Sun's interior, to the
photosphere, through the corona, and into the solar wind simultaneously
with multiple spacecraft at multiple vantage points optimized for
continual global coverage over much of a solar cycle. The mission
constellation includes two spacecraft in the ecliptic and two flying as
high as $\sim$70$^\circ$ solar latitude. 4$\pi$-HeliOS will provide
new insights into the fundamental processes that shape the whole
heliosphere. The overarching goals of the 4$\pi$-HeliOS concept are
to understand the global structure and dynamics of the Sun's interior,
the generation of solar magnetic fields, the origin of the solar cycle,
the causes of solar activity, and the structure and dynamics of the
corona as it creates the heliosphere. The mission design study is
underway at the Johns Hopkins Applied Physics Laboratory Concurrent
Engineering Laboratory (ACE Lab), a premier mission design center,
fostering rapid and collaborative mission design evolutions.

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Title: The SAWS-ASPECS Solar Energetic Particle (SEP) Advanced
Warning System
Authors: Anastasiadis, Anastasios; Aran, Angels; Georgoulis, Manolis
K.; Jiggens, Piers; Balasis, Georgios; Vainio, Rami; Dierckxsens,
Mark; Giannakis, Omiros; Sandberg, Ingmar; Papaioannou, Athanasios;
Paassilta, Miikka; Paouris, Evangelos; Vasalos, George; Iqbal, Zafar;
Aminalragia-Giamini, Sigiava
2022cosp...44.1184A Altcode:
Solar particle events (SPEs) are radiation storms induced by
eruptive processes on the Sun, namely solar flares and, more
prominently, Coronal Mass Ejections (CMEs). These SPEs represent
a concern for spacecraft launch and early orbit phase, mission and
aircraft operators given the effects on electronics and the threat
for human physiology. The SAWS-ASPECS system is a web based tool
(http://phobos-srv.space.noa.gr/), that collates and combines outputs
from different modules providing forecasts of solar phenomena,
solar proton event occurrence and solar proton flux and duration
characteristics. The system incorporates two basic operational
modes: the forecasting (pre-event) and the nowcasting (post-event)
mode. Concerning the pre-event forecasting mode, the starting point is
the flare prediction. The outputs of the flare prediction are utilized
in the provision of a conditional likelihood of SPE occurrence and
an estimation of the expected characteristics (e.g. peak flux and
duration) of a forthcoming SPE, with errors for different energies
and as a function of different forecasting horizons. Concerning the
post-event mode, the predictions for the probability of SPE occurrence
and expected peak flux continuously evolve through updates based on
near-real time inputs (e.g. solar flare and coronal mass ejections
data/characteristics) received by the system. In addition, for
the first time the complete time profile of the SPE at respective
energies is provided in near real-time, utilizing both simulations
and observations. This presentation will give an overview of the
SAWS_ASPECS system. \underline{Acknowledgements:} The SAWS-ASPECS
system was developed, receiving funding through the ESA activity Solar
Energetic Particle (SEP) Advanced Warning System (SAWS) ESA Contract
No. 4000120480/NL/LF/hh.

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Title: Assessment of near sun axial CME magnetic field.
Authors: Koya, Shifana; Patsourakos, Spiros; Georgoulis, Manolis K.;
Nindos, Alexander
2022cosp...44.1405K Altcode:
The magnetic origin and the role of magnetic helicity in solar eruptions
are known for several years. Here we present a survey of near-Sun
axial coronal mass ejection (CME) magnetic fields that are obtained
by applying a semi-analytical method that calculates the magnetic
helicity of the source active region relying primarily on photospheric
vector magnetograms. The geometrical parameters of CMEs observed by
STEREO/SECCHI and SOHO/LASCO are obtained by fitting the GCS magnetic
flux rope model. We use the estimated near-Sun CME magnetic fields to
infer ICME magnetic fields and to validate them with existing in-situ
magnetometer observation at L1. We conclude that the proposed method,
including the proposed inferences from the survey, is useful for CME
magnetic field forecasting purposes, solar-stellar connection and
projecting towards potential properties of stellar CMEs.

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Title: Exploratory Analysis of Magnetic Polarity Inversion Line
Metadata and Eruptive Characteristics of Solar Active Regions
Authors: Aydin, Berkay; Georgoulis, Manolis K.; Martens, Petrus;
Angryk, Rafal A.; Ji, Anli; Khasayeva, Nigar
2022cosp...44.3223A Altcode:
Magnetic polarity inversion lines (PILs) detected in solar active
regions and features engineered from them have been recognized as
one of the essential features for predicting key characteristics of
explosive and eruptive instabilities, such as solar flares and coronal
mass ejections. We have built a systematic and comprehensive dataset
of polarity inversion lines from line-of-sight magnetograms in HMI
Active Region Patches (HARPs) data series. Our dataset covers the
series ranging from May 2010 to December 2021. The dataset includes
PIL-related binary masks of rasters (i.e., thinned PIL, the region
of polarity inversion (RoPI), and the convex hull of PIL) as well as
time series metadata extracted from these masks. We will introduce
this multi-modal solar dataset and present some key results of our
first exploratory analysis. We will further highlight relationships
between the time evolution characteristics of magnetic PILs and provide
an empirical analysis and predictive heuristics to demonstrate the
usefulness of multi-modal PIL data in forecasting solar flares, both
confined and eruptive. In particular, we will show the similarities and
differences between pre-flare series of eruptive and confined flares
and explore the relationships between PIL characteristics and the
cumulative flare index. While this line of work is just starting, we
emphasize the use of machine-learning-ready datasets for both physical
and operational purposes, from understanding the key ingredients
of the pre-instability phase in active regions to assigning fully
validated forecast probabilities for major solar events that largely
shape heliospheric space weather.

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Title: Automatic detection of small-scale EUV brightenings observed
by the Solar Orbiter/EUI
Authors: Alipour, N.; Safari, H.; Verbeeck, C.; Berghmans, D.;
Auchère, F.; Chitta, L. P.; Antolin, P.; Barczynski, K.; Buchlin,
É.; Aznar Cuadrado, R.; Dolla, L.; Georgoulis, M. K.; Gissot, S.;
Harra, L.; Katsiyannis, A. C.; Long, D. M.; Mandal, S.; Parenti,
S.; Podladchikova, O.; Petrova, E.; Soubrié, É.; Schühle, U.;
Schwanitz, C.; Teriaca, L.; West, M. J.; Zhukov, A. N.
2022A&A...663A.128A Altcode: 2022arXiv220404027A
Context. Accurate detections of frequent small-scale extreme ultraviolet
(EUV) brightenings are essential to the investigation of the physical
processes heating the corona. Aims: We detected small-scale
brightenings, termed campfires, using their morphological and
intensity structures as observed in coronal EUV imaging observations
for statistical analysis. Methods: We applied a method based
on Zernike moments and a support vector machine (SVM) classifier
to automatically identify and track campfires observed by Solar
Orbiter/Extreme Ultraviolet Imager (EUI) and Solar Dynamics Observatory
(SDO)/Atmospheric Imaging Assembly (AIA). Results: This method
detected 8678 campfires (with length scales between 400 km and 4000 km)
from a sequence of 50 High Resolution EUV telescope (HRIEUV)
174 Å images. From 21 near co-temporal AIA images covering the same
field of view as EUI, we found 1131 campfires, 58% of which were
also detected in HRIEUV images. In contrast, about 16%
of campfires recognized in HRIEUV were detected by AIA. We
obtain a campfire birthrate of 2 × 10−16 m−2
s−1. About 40% of campfires show a duration longer than 5
s, having been observed in at least two HRIEUV images. We
find that 27% of campfires were found in coronal bright points and
the remaining 73% have occurred out of coronal bright points. We
detected 23 EUI campfires with a duration greater than 245 s. We found
that about 80% of campfires are formed at supergranular boundaries,
and the features with the highest total intensities are generated at
network junctions and intense H I Lyman-α emission regions observed
by EUI/HRILya. The probability distribution functions for
the total intensity, peak intensity, and projected area of campfires
follow a power law behavior with absolute indices between 2 and 3. This
self-similar behavior is a possible signature of self-organization,
or even self-organized criticality, in the campfire formation
process. Supplementary material (S1-S3) is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202243257/olm">https://www.aanda.org</A>

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Title: All-Clear in Solar Energetic Particles (SEP) Event Forecasting:
Feasibility and Challenges
Authors: Georgoulis, Manolis K.
2022cosp...44.3220G Altcode:
Equally important to the prediction of a solar weather phenomenon
affecting space weather in the heliosphere is the prediction of no such
phenomenon occurring from the Sun within a certain forecast window. This
has been conventionally coined an "All-Clear" forecast. Predicting
All Clear is imperative for sensitive operations in space involving
vulnerable humans and equipment in orbit or in future deep space
expeditions on the surface of the Moon or even Mars. All Clear is
the antipode of an event forecasting, but I will argue that simply
taking the complementary of the full-Sun event probability is crudely
oversimplified, particularly for rare events, completely ignoring
False Negatives. Conversely, precluding an All Clear if a hint of
a possible event exists in a solar source is infeasible, completing
ignoring False Positives, particularly in solar maximum conditions. I
will attempt to specify All Clear for Solar Energetic Particle (SEP)
event forecasting and will aim to highlight the issues, ambiguity
and ambivalence surrounding it. Different event definitions and
potential refined estimates on the basis of an outlier analysis will
also be discussed. Particular emphasis will be further given to False
Negative (Misses) due to solar sources that have not yet rotated to
the earthward solar hemisphere. This is a discussion and debate in
progress but will shape the state-of-the-art if and when a consensus
within the community is reached.

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Title: Identifying the Terrestrial Exoplanets which Deserve More
Scrutiny for Atmosphere Viability: the mASC method
Authors: Samara, Evangelia; Patsourakos, Spiros; Georgoulis, Manolis K.
2022cosp...44.1395S Altcode:
We introduce a practical and physically intuitive method to assess
whether a given exoplanet is a viable candidate for the existence of
an atmosphere, thanks to an efficient magnetospheric shielding from
intense space weather activity from its host star. Our proposed mASC
(magnetic Atmosphere Sustainability Constraint) relies on a best-case
scenario for a dynamo-generated planetary magnetic field and subsequent
magnetic pressure, and a worst-case scenario for the magnetic pressure
of stellar CMEs. The method estimates a dimensionless ratio R whose
excursion from unity implies accordingly an "atmosphere likely" (R
&lt; 1) or an "atmosphere unlikely" (R &gt; 1) scenario. In this work,
we implement our mASC on six "famous" exoplanets whose discovery was
greeted with praise and hopes of habitability. These are Kepler-438b,
Proxima-Centauri b, and Trappist-1d, -1e, -1f, -1g. We conclude that
for none of them the existence of an atmosphere is likely while our
findings are robust for five out of six cases. We conclude that the
mASC ratio could help set observing priorities and suggest which
exoplanets deserve further scrutiny, possibly toward the ultimate
search of potential biosignatures, among other objectives.

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Title: Investigating possible EUV precursors of major solar flares
Authors: AndrÉ-Hoffmann, Augustin; Patsourakos, Spiros; Georgoulis,
Manolis K.; Nindos, Alexander
2022cosp...44.2481A Altcode:
Large-scale solar eruptions that produce major flares and fast coronal
mass ejections are often associated with precursor activity that
may start several hours before the main event. Such activity may be
observed from the photosphere all the way to the transition region
and corona but it is not clear whether it plays an essential role in
the eruption initiation. To investigate this question we search for
precursor activity in Extreme Ultra-violet (EUV) images obtained by the
Atmospheric Imaging Assembly (AIA) instrument on board Solar Dynamics
Observatory (SDO) within a 24-hour window prior to large eruptive
events and investigate whether they contribute to the restructuring and
overall evolution of the magnetic field that leads to eruptions. We
cross-check our findings by performing the same search in relatively
quiet active regions. By comparing the results from the eruptive and
quiet active regions we attempt to identify possible signatures that
could be useful in both the short-term prediction of major flare events
and an enhanced physical understanding of the preflare phase.

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Title: Exploring Heuristics in Full-Disk Aggregation from Individual
Active Region Prediction of Solar Flares
Authors: Pandey, Chetraj; Georgoulis, Manolis K.; Aydin, Berkay;
Angryk, Rafal A.; Ji, Anli
2022cosp...44.3457P Altcode:
Ensemble modeling can boost the predictive confidence of base
learners (weak learners) by producing a more optimal model suitable
for operational forecasting. In cases where the base learners have
uniformity in the problem formulation and datasets, it becomes a
relatively easier task to generate a new meta-model that enhances
prediction capabilities. In this work, we deal with coupling two
solar flare prediction models in which our base learners are trained
with two different paradigms: (i) a full-disk mode, where prediction
models are trained using full-disk line-of-sight magnetograms and deep
learning architectures to issue a full-disk flare probability, and (ii)
an active region-based mode, where models utilize multivariate time
series data and a multivariate Time Series Forest (TSF) classifier to
issue a prediction for each valid active region individually. So far
in the literature, individual active region forecasts are aggregated
by computing the probability of flare from at least one active region
assuming conditional independence and then these flare probabilities are
used to compute a full-disk flare occurrence probability by means of a
meta-model. However, our empirical analysis on active region aggregation
shows that the method of aggregation can be considered rather subjective
depending on the distribution of individual models' output. We
observe that exploring different heuristics while aggregation impacts
the predictive performance of the AR-based models and consequently
the meta-models. This shows a need for searching an AR-aggregation
heuristic that suits the overall probability distribution of our two
base learners. In this research, we present different AR-aggregation
heuristics in consideration to the flare probability distribution of
our base learners and introduce a more effective heuristic for active
region aggregation by verifying performance improvement using metrics
such as the True Skill Statistic and the Heidke Skill Score.

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Title: Influence of coronal hole morphology on the solar wind speed
at Earth
Authors: Samara, Evangelia; Magdalenić, Jasmina; Rodriguez, Luciano;
Heinemann, Stephan G.; Georgoulis, Manolis K.; Hofmeister, Stefan J.;
Poedts, Stefaan
2022A&A...662A..68S Altcode: 2022arXiv220400368S
Context. It has long been known that the high-speed stream (HSS) peak
velocity at Earth directly depends on the area of the coronal hole
(CH) on the Sun. Different degrees of association between the two
parameters have been shown by many authors. In this study, we revisit
this association in greater detail for a sample of 45 nonpolar CHs
during the minimum phase of solar cycle 24. The aim is to understand how
CHs of different properties influence the HSS peak speeds observed at
Earth and draw from this to improve solar wind modeling. Aims:
The CHs were extracted based on the Collection of Analysis Tools for
Coronal Holes which employs an intensity threshold technique applied to
extreme-ultraviolet filtergrams. We first examined all the correlations
between the geometric characteristics of the CHs and the HSS peak
speed at Earth for the entire sample. The CHs were then categorized
in two different groups based on morphological criteria, such as the
aspect ratio and the orientation angle. We also defined the geometric
complexity of the CHs, a parameter which is often neglected when the
formation of the fast solar wind at Earth is studied. The quantification
of complexity was done in two ways. First, we considered the ratio
of the maximum inscribed rectangle over the convex hull area of the
CH. The maximum inscribed rectangle provides an estimate of the area
from which the maximum speed of the stream originates. The convex hull
area is an estimate of how irregular the CH boundary is. The second
way of quantifying the CH complexity was carried out by calculating
the CH's fractal dimension which characterizes the raggedness of the
CH boundary and internal structure. Methods: When treating
the entire sample, the best correlations were achieved between the
HSS peak speed observed in situ, and the CH longitudinal extent. When
the data set was split into different subsets, based on the CH aspect
ratio and orientation angle, the correlations between the HSS maximum
velocity and the CH geometric characteristics significantly improved
in comparison to the ones estimated for the whole sample. By further
dividing CHs into subsets based on their fractal dimension, we found
that the Pearson's correlation coefficient in the HSS peak speed -
CH area plot decreases when going from the least complex toward
the most complex structures. Similar results were obtained when we
considered categories of CHs based on the ratio of the maximum inscribed
rectangle over the convex hull area of the CH. To verify the robustness
of these results, we applied the bootstrapping technique. The method
confirmed our findings for the entire CH sample. It also confirmed the
improved correlations, compared to the ones found for the whole sample,
between the HSS peak speed and the CH geometric characteristics when we
divided the CHs into groups based on their aspect ratio and orientation
angle. Bootstrapping results for the CH complexity categorizations are,
nonetheless, more ambiguous. Results: Our results show that the
morphological parameters of CHs such as the aspect ratio, orientation
angle, and complexity play a major role in determining the HSS peak
speed at 1 AU. Therefore, they need to be taken into consideration
for empirical models that aim to forecast the fast solar wind at Earth
based on the observed CH solar sources.

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Title: First Application of a Theoretically Derived Coupling
Function in Cosmic-Ray Intensity for the Case of the 10 September
2017 Ground-Level Enhancement (GLE 72)
Authors: Xaplanteris, L.; Gerontidou, M.; Mavromichalaki, H.;
Rodriguez, J. V.; Livada, M.; Georgoulis, M. K.; Sarris, T. E.;
Spanos, V.; Dorman, L.
2022SoPh..297...73X Altcode:
In this work we implement an analytically derived coupling function
between ground-level and primary proton particles for the case of
ground-level enhancement events (GLEs). The main motivation for this
work is to determine whether this coupling function is suitable for the
study of both major cases of cosmic-ray (CR) variation events, namely
GLEs and Forbush decreases. This version of the coupling function, which
relies on formalism used in quantum field theory (QFT) computations,
has already been applied to Forbush decreases yielding satisfactory
results. In this study, it is applied to a GLE event that occurred on 10
September 2017. For the analytical derivations, normalized ground-level
cosmic-ray data were used from seven neutron-monitor stations with
low cutoff rigidities. To assess and evaluate the results for the
normalized proton intensity, we benchmark them with the time series for
the proton flux, as recorded by the GOES 13 spacecraft during the same
time period. The theoretically calculated results for proton energy
≥1 GeV are in general agreement with the recorded data for protons
with energy &gt;700 MeV, presenting a least-squares linear best fit
with slope 0.75 ±0.17 and a Pearson correlation coefficient equal to
0.62. We conclude that the coupling function presented in this work
is the first coupling function that is well applicable to both cases
of cosmic-ray intensity events, namely GLEs and Forbush decreases.

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Title: Integrated Geostationary Solar Energetic Particle Events
Catalog: GSEP
Authors: Rotti, Sumanth; Aydin, Berkay; Georgoulis, Manolis K.;
Martens, Petrus C.
2022arXiv220412021R Altcode:
We present a catalog of solar energetic particle (SEP) events covering
solar cycles 22, 23 and 24. We correlate and integrate three existing
catalogs based on Geostationary Operational Environmental Satellite
(GOES) integral proton flux data. We visually verified and labeled
each event in the catalog to provide a homogenized data set. We have
identified a total of 341 SEP events of which 245 cross the space
weather prediction center (SWPC) threshold of a significant proton
event. The metadata consists of physical parameters and observables
concerning the possible source solar eruptions, namely flares and
coronal mass ejections for each event. The sliced time series data
of each event, along with intensity profiles of proton fluxes in
several energy bands, have been made publicly available. This data set
enables researchers in machine learning (ML) and statistical analysis
to understand the SEPs and the source eruption characteristics useful
for space weather prediction.

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Title: Revisiting the Solar Research Cyberinfrastructure Needs:
A White Paper of Findings and Recommendations
Authors: Nita, Gelu; Ahmadzadeh, Azim; Criscuoli, Serena;
Davey, Alisdair; Gary, Dale; Georgoulis, Manolis; Hurlburt, Neal;
Kitiashvili, Irina; Kempton, Dustin; Kosovichev, Alexander; Martens,
Piet; McGranaghan, Ryan; Oria, Vincent; Reardon, Kevin; Sadykov,
Viacheslav; Timmons, Ryan; Wang, Haimin; Wang, Jason T. L.
2022arXiv220309544N Altcode:
Solar and Heliosphere physics are areas of remarkable data-driven
discoveries. Recent advances in high-cadence, high-resolution
multiwavelength observations, growing amounts of data from realistic
modeling, and operational needs for uninterrupted science-quality data
coverage generate the demand for a solar metadata standardization and
overall healthy data infrastructure. This white paper is prepared as
an effort of the working group "Uniform Semantics and Syntax of Solar
Observations and Events" created within the "Towards Integration of
Heliophysics Data, Modeling, and Analysis Tools" EarthCube Research
Coordination Network (@HDMIEC RCN), with primary objectives to discuss
current advances and identify future needs for the solar research
cyberinfrastructure. The white paper summarizes presentations and
discussions held during the special working group session at the
EarthCube Annual Meeting on June 19th, 2020, as well as community
contribution gathered during a series of preceding workshops and
subsequent RCN working group sessions. The authors provide examples
of the current standing of the solar research cyberinfrastructure, and
describe the problems related to current data handling approaches. The
list of the top-level recommendations agreed by the authors of the
current white paper is presented at the beginning of the paper.

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Title: A Systematic Magnetic Polarity Inversion Line Detection
Dataset from SDO/HMI Magnetogram
Authors: Ji, Anli; Cai, Xumin; Aydin, Berkay; Georgoulis, Manolis;
Angryk, Rafal
2021AGUFMSH55A1818J Altcode:
Magnetic polarity inversion line (PIL) detected from solar active
regions and features engineered from them have been recognized as
one of the essential features for predicting key characteristics of
eruptive events such as flares and coronal mass ejections. However,
in most cases, PIL masks are generated as a byproduct and they are not
comprehensively available for public use. To fill the gap in this field,
we introduce a large-scale PIL dataset that can be used for various
space weather forecasting tasks. The dataset is created using the
geometries from the HMI Active Region Patches (HARPs) and involves 4,090
HARP series ranging from May 2010 to March 2019. This dataset includes
PIL-related binary masks as rasters (i.e., thinned PIL, the region of
polarity inversion (RoPI), and the convex hull of PIL) and time series
metadata extracted from these masks. The PIL detection procedure is
based on an edge detection technique along with magnetic field strength
and PIL size filter. First, we identify positive and negative polarity
regions with a magnetic field strength threshold. Then, we utilize
the Canny edge detector and morphological operations to both positive
and negative regions to identify coarse PILs. Finally, we generate
PILs by applying magnetic field strength and PIL size filter to the
coarse PILs as mentioned above. We envision that this comprehensive PIL
dataset will benefit space weather analytics research, specifically
in understanding the PIL structure and evolution, and complementing
the existing datasets used for space weather forecasting.

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Title: Which Terrestrial Exoplanets Deserve More Scrutiny for
Atmosphere Viability?
Authors: Samara, Evangelia; Patsourakos, Spiros; Georgoulis, Manolis
2021AGUFM.U44B..05S Altcode:
We introduce a practical and physically intuitive method to assess
whether a given exoplanet is a viable candidate for the existence of
an atmosphere thanks to an efficient magnetospheric shielding from
intense space weather activity originating from its host star. Our
proposed mASC (magnetic Atmosphere Sustainability Constraint) relies on
a best-case scenario for the dynamo-generated planetary magnetic field
and subsequent magnetic pressure, and a worst-case scenario for the
magnetic pressure of stellar CMEs. It provides a dimensionless ratio
R whose excursion from unity implies accordingly an atmosphere likely
(R &lt; 1) or an atmosphere unlikely (R &gt; 1) scenario. In this work,
we implement our mASC on six famous exoplanets whose discovery was
greeted with praise and hopes of habitability. These are Kepler-438b,
Proxima-Centauri b, and Trappist-1d, -1e, -1f, -1g. The results show
that for none of them the existence of an atmosphere is likely while
our findings are robust for five out of six cases. We conclude that
the mASC ratio could help set observing priorities and suggest which
exoplanets deserve further scrutiny, possibly toward the ultimate
search of potential biosignatures, among other objectives.

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Title: Magnetic Helicity Estimations in Models and Observations of
the Solar Magnetic Field. IV. Application to Solar Observations
Authors: Thalmann, J. K.; Georgoulis, M. K.; Liu, Y.; Pariat, E.;
Valori, G.; Anfinogentov, S.; Chen, F.; Guo, Y.; Moraitis, K.; Yang,
S.; Mastrano, Alpha; ISSI Team on Magnetic Helicity
2021ApJ...922...41T Altcode: 2021arXiv210808525T
In this ISSI-supported series of studies on magnetic helicity in the
Sun, we systematically implement different magnetic helicity calculation
methods on high-quality solar magnetogram observations. We apply
finite-volume, discrete flux tube (in particular, connectivity-based)
and flux-integration methods to data from Hinode's Solar Optical
Telescope. The target is NOAA Active Region 10930 during a 1.5-day
interval in 2006 December that included a major eruptive flare
(SOL2006-12-13T02:14X3.4). Finite-volume and connectivity-based methods
yield instantaneous budgets of the coronal magnetic helicity, while
the flux-integration methods allow an estimate of the accumulated
helicity injected through the photosphere. The objectives of our work
are twofold: a cross-validation of methods, as well as an interpretation
of the complex events leading to the eruption. To the first objective,
we find (i) strong agreement among the finite-volume methods, (ii)
a moderate agreement between the connectivity-based and finite-volume
methods, (iii) an excellent agreement between the flux-integration
methods, and (iv) an overall agreement between finite-volume- and
flux-integration-based estimates regarding the predominant sign and
magnitude of the helicity. To the second objective, we are confident
that the photospheric helicity flux significantly contributed to the
coronal helicity budget and that a right-handed structure erupted from
a predominantly left-handed corona during the X-class flare. Overall,
we find that the use of different methods to estimate the (accumulated)
coronal helicity may be necessary in order to draw a complete picture
of an active region corona, given the careful handling of identified
data (preparation) issues, which otherwise would mislead the event
analysis and interpretation.

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Title: Space Weather research in the Digital Age and across the full
data lifecycle: Introduction to the Topical Issue
Authors: McGranaghan, Ryan M.; Camporeale, Enrico; Georgoulis, Manolis;
Anastasiadis, Anastasios
2021JSWSC..11...50M Altcode:
The onset and rapid advance of the Digital Age have brought challenges
and opportunities for scientific research characterized by a
continuously evolving data landscape reflected in the four V's of big
data: volume, variety, veracity, and velocity. The big data landscape
supersedes traditional means of storage, processing, management, and
exploration, and requires adaptation and innovation across the full
data lifecycle (i.e., collection, storage and processing, analytics,
and representation). The Topical Issue, "Space Weather research in
the Digital Age and across the full data lifecycle", collects research
from across the full data lifecycle (collection, management, analysis,
and communication; collectively "Data Science") and offers a tractable
compendium that illustrates the latest computational and data science
trends, tools, and advances for Space Weather research. We introduce
the paradigm shift in Space Weather and the articles in the Topical
Issue. We create a network view of the research that highlights the
contribution to the change of paradigm and reveals the trends that
will guide it hereafter.

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Title: Improved Approach in the Coupling Function Between Primary
and Ground Level Cosmic Ray Particles Based on Neutron Monitor Data
Authors: Xaplanteris, L.; Livada, M.; Mavromichalaki, H.; Dorman,
L.; Georgoulis, M. K.; Sarris, T. E.
2021SoPh..296...91X Altcode:
In this work an improved approach of existing approximations on the
coupling function between primary and ground-level cosmic-ray particles
is presented. The proposed coupling function is analytically derived
based on a formalism used in Quantum Field Theory calculations. It
is upgraded compared to previous versions with the inclusion of a
wider energy spectrum that is extended to lower energies, as well
as an altitude correction factor, also derived analytically. The
improved approximations are applied to two cases of Forbush decreases
detected in March 2012 and September 2017. In the analytical procedure
for the derivation of the primary cosmic-ray spectrum during these
events, we also consider the energy spectrum exponent γ to be varied
with time. For the validation of the findings, we present a direct
comparison between the primary spectrum and the amplitude values
derived by the proposed method and the obtained time series of the
cosmic-ray intensity at the rigidity of 10 GV obtained from the Global
Survey Method. The two sets of results are found to be in very good
agreement for both events as denoted by the Pearson correlation factors
and slope values of their scatter plots. In such way we determine the
validity and applicability of our method to Forbush decreases as well
as to other cosmic-ray phenomena, thus introducing a new, alternative
way of inferring the primary cosmic-ray intensity.

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Title: Verification Of A Practical Magnetic Helicity Budget
Calculation And Its Contribution To Axial Field Estimates Of Solar
And Stellar CMEs
Authors: Georgoulis, M. K.
2021AAS...23821320G Altcode:
Initial work by Georgoulis, Tziotziou &amp; Raouafi (ApJ, 759:1,
2012) on the estimation of the coronal relative magnetic helicity
budget in solar active regions has been scrutinized in multiple
occasions by comparison to 'ground-truth' calculations of the volume
helicity using classical formulas, mainly in synthetic magnetic
configurations. The so-called connectivity-based helicity / energy
calculation method infers a coronal magnetic connectivity matrix without
three-dimensional extrapolation or magnetohydrodynamical modeling and
then calculates magnetic energy and relative helicity budgets on a
discretized flux tube ensemble as per the inferred connectivity. We
briefly report on the comparison of the method with classical 'finite
volume' methods applied to real solar active regions, in which the
coronal magnetic field has been inferred by nonlinear force-free
extrapolations. Then we describe a recent extension of this line on
work that relies on the fundamental conservation principle for the
magnetic helicity to infer a worst-case axial magnetic field (Bz) for
solar and stellar coronal mass ejections (CMEs) at various locations
in the helio-/astro-sphere. Besides connecting the flaring with the
CME manifestations in the eruptive active regions, this approach
can contribute to an improved understanding of stellar forcing on
exoplanetary systems and has, in fact, led to the recent derivation
of an atmosphere sustainability constraint for terrestrial exoplanets.

---------------------------------------------------------
Title: How to Train Your Flare Prediction Model: Revisiting Robust
Sampling of Rare Events
Authors: Ahmadzadeh, Azim; Aydin, Berkay; Georgoulis, Manolis K.;
Kempton, Dustin J.; Mahajan, Sushant S.; Angryk, Rafal A.
2021ApJS..254...23A Altcode: 2021arXiv210307542A
We present a case study of solar flare forecasting by means of metadata
feature time series, by treating it as a prominent class-imbalance
and temporally coherent problem. Taking full advantage of pre-flare
time series in solar active regions is made possible via the Space
Weather Analytics for Solar Flares (SWAN-SF) benchmark data set, a
partitioned collection of multivariate time series of active region
properties comprising 4075 regions and spanning over 9 yr of the Solar
Dynamics Observatory period of operations. We showcase the general
concept of temporal coherence triggered by the demand of continuity
in time series forecasting and show that lack of proper understanding
of this effect may spuriously enhance models' performance. We further
address another well-known challenge in rare-event prediction, namely,
the class-imbalance issue. The SWAN-SF is an appropriate data set
for this, with a 60:1 imbalance ratio for GOES M- and X-class flares
and an 800:1 imbalance ratio for X-class flares against flare-quiet
instances. We revisit the main remedies for these challenges and
present several experiments to illustrate the exact impact that each
of these remedies may have on performance. Moreover, we acknowledge
that some basic data manipulation tasks such as data normalization
and cross validation may also impact the performance; we discuss
these problems as well. In this framework we also review the primary
advantages and disadvantages of using true skill statistic and Heidke
skill score, two widely used performance verification metrics for the
flare-forecasting task. In conclusion, we show and advocate for the
benefits of time series versus point-in-time forecasting, provided
that the above challenges are measurably and quantitatively addressed.

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Title: The flare likelihood and region eruption forecasting
(FLARECAST) project: flare forecasting in the big data &amp; 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
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.

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Title: A Readily Implemented Atmosphere Sustainability Constraint
for Terrestrial Exoplanets Orbiting Magnetically Active Stars
Authors: Samara, Evangelia; Patsourakos, Spiros; Georgoulis, Manolis K.
2021ApJ...909L..12S Altcode: 2021arXiv210207837S
With more than 4300 confirmed exoplanets and counting, the next
milestone in exoplanet research is to determine which of these
newly found worlds could harbor life. Coronal mass ejections (CMEs),
spawned by magnetically active, superflare-triggering dwarf stars,
pose a direct threat to the habitability of terrestrial exoplanets, as
they can deprive them of their atmospheres. Here we develop a readily
implementable atmosphere sustainability constraint for terrestrial
exoplanets orbiting active dwarfs, relying on the magnetospheric
compression caused by CME impacts. Our constraint focuses on an
understanding of CMEs propagation in our own Sun-heliosphere system
that, applied to a given exoplanet requires as key input the observed
bolometric energy of flares emitted by its host star. Application of our
constraint to six famous exoplanets, Kepler-438b, Proxima Centauri b,
and Trappist-1d, -1e, -1f, and -1g, within or in the immediate proximity
of their stellar host's habitable zones showed that only for Kepler-438b
might atmospheric sustainability against stellar CMEs be likely. This
seems to align with some recent studies that, however, may require far
more demanding computational resources and observational inputs. Our
physically intuitive constraint can be readily and en masse applied, as
is or generalized, to large-scale exoplanet surveys to detect planets
that warrant further scrutiny for atmospheres and, perhaps, possible
biosignatures at higher priority by current and future instrumentation.

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Title: Data Benchmarking for Solar Flare, CME and SEP Event
Forecasting: Different Prediction and Verification Needs, Unified
Authors: Georgoulis, Manolis K.; Martens, Petrus; Aydin, Berkay;
Ahmadzadeh, Azim; Kempton, Dustin J.; Angryk, Rafal A.
2021cosp...43E2357G Altcode:
In this synergistic, interdisciplinary work we convey two principles
that we consider central to improving space weather forecast
capabilities of current and future modeling efforts: first, that
data, model and performance verification tasks are equally important
and should be treated on equal footing. Second, that the solar end
of adverse space weather, comprising flares, coronal mass ejections
(CMEs) and Solar Energetic Particle (SEP) events should be viewed and
treated as a single, albeit multi-faceted, physical problem, rather
than as a set of standalone problems corresponding to each facet. We
present paradigms for both of these principles: first, we discuss a
solar flare benchmark dataset in which the data are fully verified
and we have taken steps to verify different forecast models and their
performance. We show that unverified models lead to much degraded
performance. Second, we outline the main aspects of a methodology to
forecast SEP events in terms of temporal profile and peak proton flux
starting from forecasting their source eruptions in the Sun. Performance
needs dictate the introduction of two modeling tiers, one for eruption
forecasting and projected SEP properties and another for updated,
forecast SEP properties in case of SEP-eligible eruptions. This practice
enables a dual validation of the performance for both tiers, at the
same time constraining applicable uncertainties that could otherwise
render the overall task untenable. Benefits of this approach in terms
of both operations-to-research and research-to-operations are profound
and can lead to both an improved physical understanding of vast swaths
of the heliosphere, along with future prediction services combining
computational efficiency with proven, quantifiable value.

---------------------------------------------------------
Title: Properties Determining Eruption Initiation and
Planeto-Effectiveness of Eruptive Transients in Magnetically Active
Stars
Authors: Georgoulis, Manolis K.; Patsourakos, Spiros; Zhang, Hongqi;
Nindos, Alexander; Samara, Evangelia; Sadykov, Viacheslav M.
2021cosp...43E.993G Altcode:
We present a combined theoretical and data analysis approach to,
first, understand why magnetic eruptions and corresponding ejecta are
triggered in strong-field regions of the Sun and magnetically active
stars and, second, assess the key physical parameters responsible for
the planeto-effectiveness of these eruptions, both on Earth and in
other (exo-)planets. This approach converges on one physical parameter
besides magnetic energy, at least for stellar coronae of high magnetic
Reynolds numbers allowing this parameter to be conserved even under
confined energy release: magnetic helicity. Helicity, via the magnetic
energy-helicity diagram, should be treated equally with magnetic
energy. Due to magnetic helicity accumulation in solar active regions
and its inverse cascading, solar - and stellar, correspondingly -
eruptions may become inevitable after a certain 'point-of-no-return'
is reached. We identify this critical instant as the time when
magnetic polarity inversion lines in active-region photospheres
accumulate fluxes that generate fields stronger than local equipartition
values. Furthermore, using the conserved helicity budgets we abstractly
model post-eruption flux ropes and their transit through astrospheres,
reaching exoplanets and compressing their magnetospheres via magnetic
pressure effects. A rudimentary validation between the near-Sun and
L1 axial magnetic field values of these data-constrained flux ropes is
encouraging and allows us to further constrain scaling laws appropriate
for the astrospheric transit of these ropes. Importantly, we also find
that exoplanets orbiting magnetically active dwarf stars at orbital
radii that are fractions of an astronomical unit seem to be strong
contenders for eruption-driven atmospheric erosion that may gradually
even deprive them from their atmospheres. Some famous exoplanet cases
are examined under this prism. Future improvements are expected by
widely anticipated space- (Parker Solar Probe and Solar Orbiter)
and ground-based (Daniel K. Inouye Solar Telescope) observations.

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Title: ESA's SEP Advanced Warning System: The ASPECS Project
Authors: Jiggens, Piers; Aran, Angels; Georgoulis, Manolis K.;
Balasis, Georgios; Vainio, Rami; Dierckxsens, Mark; Giannakis,
Omiros; Sandberg, Ingmar; Papaioannou, Athanasios; Paassilta, Miikka;
Anastasiadis, Anastasios; Paouris, Evangelos; Vasalos, George; Iqbal,
Zafar; Aminalragia-Giamini, Sigiava; Tsigkanos, Antonis
2021cosp...43E1041J Altcode:
Solar particle events (SPEs) are radiation storms induced by eruptive
processes on the Sun, namely solar flares and, more prominently,
Coronal Mass Ejections (CMEs). These SPEs represent a concern for the
spacecraft, launch, human spaceflight and aircraft operators given the
effects on electronics and human physiology. The outcome of the ASPECS
(Advanced Solar Particle Event Casting System) project represents
the first tool for forecasting Solar Energetic Particles (SEPs) from
several days before the commencement of the radiation storm up to
nowcasting of the evolution of the storm. This is achieved by a 3-tier
system combining the forecasting of flares, the statistical forecast
of events based on flare and CME characteristics and physical and
analytical modelling for predicting particle flux profiles. The module
in the process is the prediction of flares. The flare forecast used as
a proxy of SPEs due to the relative maturity of this element of space
weather forecasting relative to CME forecasting. The present model for
forecasting flares is based on the B-effective parameter of Georgoulis
et al. that captures complexity in addition to magnetic field strength
of active region. This model has been extended to make predictions for
periods from 6 hours to 3 days and fits made to extend forecasts to the
highest intensity flares. The central plank of the system forecasts the
likelihood of SPEs from input flare and CME characteristics of location
and magnitude, and velocity and width respectively by use of a method
based on Bayesian statistics. When both sets of inputs are available,
the system combines the forecasts and adapts them when neutron monitors
trigger a GLE (from the fastest particles arriving first indicating
an SPE is commencing) and electron fluxes (whose absence after a given
time indicates no event). This module outputs peak fluxes forecasts for
events for protons at four energies (&gt;10, &gt;30, &gt;100 and &gt;300
MeV). Before a solar event, this module uses a separate sub-module
for data-driven forecasting of SPE likelihood across the different
energies based on a historical SPE occurrence as a function of active
region location and flare size (taken from the first module). The final
module forecasts the flux profile of the SPE for each energy based
on a set of physically-reconstructed profiles using the SOLPENCO(-2)
tool given input parameters of solar source longitude and the peak
flux prediction. This profile is adjusted with observed fluxes as and
when the particles are detected in space. If the initially profile is
found to not be well fit to the observed data then the system chooses
another physicallyreconstructed profile from the database. If the
event progresses in a way that no profile can fit the observations
then an analytical profile, based on the work of Kahler and Ling,
replaces the SOLPENCO(-2) output. This is especially important in the
downstream region which is not modelled by SOLEPNCO(-2). The result
is the pre-operational version of ESA's SEP Advanced Warning System
(SAWS) spanning energies of interest for different end users. The
software is developed in a modular way to take advantage of new
modelling developments and data as it becomes available. An extensive
verification and validation process is underway to arrive at a stable
system to be used by a range of operators. This work has been carried
out by the Institute for Astronomy, Astrophysics, Space Applications
and Remote Sensing (IAASARS) at the National Observatory of Athens and
the Space Applications and Research Consultancy (SPARC) in Greece,
the University of Turku in Finland, the University of Barcelona in
Spain and the Belgian Institute for Space Aeronomy under ESA contract
No. 4000120480/17/NL/LF/hh.

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Title: Coronal Sigmoids and Chromospheric Filaments - A relation?
Authors: Venkataramanasastry, Aparna; Georgoulis, Manolis K.;
Martens, Petrus
2021cosp...43E1765V Altcode:
Sigmoids are forward (S-shaped) or inverse (Z-shaped) features
on the Sun that are seen at coronal heights in X-ray or high
temperature extreme ultraviolet (EUV) wavelengths. The sharpest
and brightest of them are highly eruptive. They usually deform or
disappear via coronal mass ejections. This makes it important to
understand X-ray sigmoids because of their relevance for space-weather
forecasting purposes. Chromospheric filaments are generally observed
as absorption features in H$\alpha$ wavelengths. In this work, we
observe chromospheric filaments lying under the sigmoids in order to
correlate the chiralities of the two features. We expect that if the
formation mechanisms of filaments and sigmoids are similar then they
should have same chirality. We have conducted a joint survey of the
sigmoids and the underlying filaments between 2007 and 2017. We use
Hinode soft and hard X-ray data for sigmoid images and GONG H$\alpha$
data for the filaments. We find a total of 84 sigmoids with filaments
within the said time period. Among these we have 41 forward and
43 inverse sigmoids. In the 41 forward sigmoids, 8 (20%) filaments
are dextral, 21 (50%) are sinistral and 12 (30%) ambiguous. In the
inverse sigmoids, 16 filaments (37%) are dextral, 13 (30%) sinistral
and 14 (33%) ambiguous. It is evident from this analysis that there
is no clear correspondence between filament chirality and the sigmoid
handedness. This result warrants further investigation. We therefore
perform calculations of magnetic helicity in the photospheric regions
that encloses the footprints of sigmoids and filaments to primarily
obtain the sign of their helicities. For many of the cases mentioned
above, we use SHARP (Space-weather HMI Active Region Patch) vector
magnetograms to serve as the photospheric boundary condition to which we
apply the linear force-free magnetic helicity and energy formulations
of Georgoulis \&amp; LaBonte (2007). We will report on the findings
of this study during the 43rd COSPAR General Assembly. References
Georgoulis, M. K. \&amp; LaBonte, B. J., ApJ, 2007, 671, 1034

---------------------------------------------------------
Title: Differential Emission Measure Evolution as a Precursor of
Solar Flares
Authors: Gontikakis, C.; Kontogiannis, I.; Georgoulis, M. K.; Guennou,
C.; Syntelis, P.; Park, S. H.; Buchlin, E.
2020arXiv201106433G Altcode:
We analyse the temporal evolution of the Differential Emission Measure
(DEM) of solar active regions and explore its usage in solar flare
prediction. The DEM maps are provided by the Gaussian Atmospheric
Imaging Assembly (GAIA-DEM) archive, calculated assuming a Gaussian
dependence of the DEM on the logarithmic temperature. We analyse
time-series of sixteen solar active regions and a statistically
significant sample of 9454 point-in-time observations corresponding to
hundreds of regions observed during solar cycle 24. The time-series
analysis shows that the temporal derivatives of the Emission Measure
dEM/dt and the maximum DEM temperature dTmax/dt frequently exhibit
high positive values a few hours before M- and X-class flares,
indicating that flaring regions become brighter and hotter as the flare
onset approaches. From the point-in-time observations we compute the
conditional probabilities of flare occurrences using the distributions
of positive values of the dEM/dt, and dTmax/dt and compare them with
corresponding flaring probabilities of the total unsigned magnetic flux,
a conventionally used, standard flare predictor. For C-class flares,
conditional probabilities have lower or similar values with the ones
derived for the unsigned magnetic flux, for 24 and 12 hours forecast
windows. For M- and X-class flares, these probabilities are higher
than those of the unsigned flux for higher parameter values. Shorter
forecast windows improve the conditional probabilities of dEM/dt,
and dTmax/dt in comparison to those of the unsigned magnetic flux. We
conclude that flare forerunner events such as preflare heating or small
flare activity prior to major flares reflect on the temporal evolution
of EM and Tmax. Of these two, the temporal derivative of the EM could
conceivably be used as a credible precursor, or short-term predictor,
of an imminent flare.

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Title: Decoding the Pre-Eruptive Magnetic Field Configurations of
Coronal Mass Ejections
Authors: Patsourakos, S.; Vourlidas, A.; Török, T.; Kliem, B.;
Antiochos, S. K.; Archontis, V.; Aulanier, G.; Cheng, X.; Chintzoglou,
G.; Georgoulis, M. K.; Green, L. M.; Leake, J. E.; Moore, R.; Nindos,
A.; Syntelis, P.; Yardley, S. L.; Yurchyshyn, V.; Zhang, J.
2020SSRv..216..131P Altcode: 2020arXiv201010186P
A clear understanding of the nature of the pre-eruptive magnetic
field configurations of Coronal Mass Ejections (CMEs) is required
for understanding and eventually predicting solar eruptions. Only
two, but seemingly disparate, magnetic configurations are considered
viable; namely, sheared magnetic arcades (SMA) and magnetic flux ropes
(MFR). They can form via three physical mechanisms (flux emergence,
flux cancellation, helicity condensation). Whether the CME culprit
is an SMA or an MFR, however, has been strongly debated for thirty
years. We formed an International Space Science Institute (ISSI) team to
address and resolve this issue and report the outcome here. We review
the status of the field across modeling and observations, identify
the open and closed issues, compile lists of SMA and MFR observables
to be tested against observations and outline research activities
to close the gaps in our current understanding. We propose that the
combination of multi-viewpoint multi-thermal coronal observations
and multi-height vector magnetic field measurements is the optimal
approach for resolving the issue conclusively. We demonstrate the
approach using MHD simulations and synthetic coronal images.

---------------------------------------------------------
Title: Models and data analysis tools for the Solar Orbiter mission
Authors: Rouillard, A. P.; Pinto, R. F.; Vourlidas, A.; De Groof, A.;
Thompson, W. T.; Bemporad, A.; Dolei, S.; Indurain, M.; Buchlin, E.;
Sasso, C.; Spadaro, D.; Dalmasse, K.; Hirzberger, J.; Zouganelis, I.;
Strugarek, A.; Brun, A. S.; Alexandre, M.; Berghmans, D.; Raouafi,
N. E.; Wiegelmann, T.; Pagano, P.; Arge, C. N.; Nieves-Chinchilla,
T.; Lavarra, M.; Poirier, N.; Amari, T.; Aran, A.; Andretta, V.;
Antonucci, E.; Anastasiadis, A.; Auchère, F.; Bellot Rubio, L.;
Nicula, B.; Bonnin, X.; Bouchemit, M.; Budnik, E.; Caminade, S.;
Cecconi, B.; Carlyle, J.; Cernuda, I.; Davila, J. M.; Etesi, L.;
Espinosa Lara, F.; Fedorov, A.; Fineschi, S.; Fludra, A.; Génot,
V.; Georgoulis, M. K.; Gilbert, H. R.; Giunta, A.; Gomez-Herrero, R.;
Guest, S.; Haberreiter, M.; Hassler, D.; Henney, C. J.; Howard, R. A.;
Horbury, T. S.; Janvier, M.; Jones, S. I.; Kozarev, K.; Kraaikamp,
E.; Kouloumvakos, A.; Krucker, S.; Lagg, A.; Linker, J.; Lavraud,
B.; Louarn, P.; Maksimovic, M.; Maloney, S.; Mann, G.; Masson, A.;
Müller, D.; Önel, H.; Osuna, P.; Orozco Suarez, D.; Owen, C. J.;
Papaioannou, A.; Pérez-Suárez, D.; Rodriguez-Pacheco, J.; Parenti,
S.; Pariat, E.; Peter, H.; Plunkett, S.; Pomoell, J.; Raines, J. M.;
Riethmüller, T. L.; Rich, N.; Rodriguez, L.; Romoli, M.; Sanchez,
L.; Solanki, S. K.; St Cyr, O. C.; Straus, T.; Susino, R.; Teriaca,
L.; del Toro Iniesta, J. C.; Ventura, R.; Verbeeck, C.; Vilmer, N.;
Warmuth, A.; Walsh, A. P.; Watson, C.; Williams, D.; Wu, Y.; Zhukov,
A. N.
2020A&A...642A...2R Altcode:
Context. The Solar Orbiter spacecraft will be equipped with a wide
range of remote-sensing (RS) and in situ (IS) instruments to record
novel and unprecedented measurements of the solar atmosphere and
the inner heliosphere. To take full advantage of these new datasets,
tools and techniques must be developed to ease multi-instrument and
multi-spacecraft studies. In particular the currently inaccessible
low solar corona below two solar radii can only be observed
remotely. Furthermore techniques must be used to retrieve coronal
plasma properties in time and in three dimensional (3D) space. Solar
Orbiter will run complex observation campaigns that provide interesting
opportunities to maximise the likelihood of linking IS data to their
source region near the Sun. Several RS instruments can be directed
to specific targets situated on the solar disk just days before
data acquisition. To compare IS and RS, data we must improve our
understanding of how heliospheric probes magnetically connect to the
solar disk. Aims: The aim of the present paper is to briefly
review how the current modelling of the Sun and its atmosphere
can support Solar Orbiter science. We describe the results of a
community-led effort by European Space Agency's Modelling and Data
Analysis Working Group (MADAWG) to develop different models, tools,
and techniques deemed necessary to test different theories for the
physical processes that may occur in the solar plasma. The focus here
is on the large scales and little is described with regards to kinetic
processes. To exploit future IS and RS data fully, many techniques have
been adapted to model the evolving 3D solar magneto-plasma from the
solar interior to the solar wind. A particular focus in the paper is
placed on techniques that can estimate how Solar Orbiter will connect
magnetically through the complex coronal magnetic fields to various
photospheric and coronal features in support of spacecraft operations
and future scientific studies. Methods: Recent missions such as
STEREO, provided great opportunities for RS, IS, and multi-spacecraft
studies. We summarise the achievements and highlight the challenges
faced during these investigations, many of which motivated the Solar
Orbiter mission. We present the new tools and techniques developed
by the MADAWG to support the science operations and the analysis of
the data from the many instruments on Solar Orbiter. Results:
This article reviews current modelling and tool developments that ease
the comparison of model results with RS and IS data made available
by current and upcoming missions. It also describes the modelling
strategy to support the science operations and subsequent exploitation
of Solar Orbiter data in order to maximise the scientific output
of the mission. Conclusions: The on-going community effort
presented in this paper has provided new models and tools necessary
to support mission operations as well as the science exploitation of
the Solar Orbiter data. The tools and techniques will no doubt evolve
significantly as we refine our procedure and methodology during the
first year of operations of this highly promising mission.

---------------------------------------------------------
Title: The Solar Orbiter Science Activity Plan. Translating solar
and heliospheric physics questions into action
Authors: Zouganelis, I.; De Groof, A.; Walsh, A. P.; Williams, D. R.;
Müller, D.; St Cyr, O. C.; Auchère, F.; Berghmans, D.; Fludra,
A.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic, M.;
Owen, C. J.; Rodríguez-Pacheco, J.; Romoli, M.; Solanki, S. K.;
Watson, C.; Sanchez, L.; Lefort, J.; Osuna, P.; Gilbert, H. R.;
Nieves-Chinchilla, T.; Abbo, L.; Alexandrova, O.; Anastasiadis, A.;
Andretta, V.; Antonucci, E.; Appourchaux, T.; Aran, A.; Arge, C. N.;
Aulanier, G.; Baker, D.; Bale, S. D.; Battaglia, M.; Bellot Rubio,
L.; Bemporad, A.; Berthomier, M.; Bocchialini, K.; Bonnin, X.; Brun,
A. S.; Bruno, R.; Buchlin, E.; Büchner, J.; Bucik, R.; Carcaboso,
F.; Carr, R.; Carrasco-Blázquez, I.; Cecconi, B.; Cernuda Cangas, I.;
Chen, C. H. K.; Chitta, L. P.; Chust, T.; Dalmasse, K.; D'Amicis, R.;
Da Deppo, V.; De Marco, R.; Dolei, S.; Dolla, L.; Dudok de Wit, T.;
van Driel-Gesztelyi, L.; Eastwood, J. P.; Espinosa Lara, F.; Etesi,
L.; Fedorov, A.; Félix-Redondo, F.; Fineschi, S.; Fleck, B.; Fontaine,
D.; Fox, N. J.; Gandorfer, A.; Génot, V.; Georgoulis, M. K.; Gissot,
S.; Giunta, A.; Gizon, L.; Gómez-Herrero, R.; Gontikakis, C.; Graham,
G.; Green, L.; Grundy, T.; Haberreiter, M.; Harra, L. K.; Hassler,
D. M.; Hirzberger, J.; Ho, G. C.; Hurford, G.; Innes, D.; Issautier,
K.; James, A. W.; Janitzek, N.; Janvier, M.; Jeffrey, N.; Jenkins,
J.; Khotyaintsev, Y.; Klein, K. -L.; Kontar, E. P.; Kontogiannis,
I.; Krafft, C.; Krasnoselskikh, V.; Kretzschmar, M.; Labrosse, N.;
Lagg, A.; Landini, F.; Lavraud, B.; Leon, I.; Lepri, S. T.; Lewis,
G. R.; Liewer, P.; Linker, J.; Livi, S.; Long, D. M.; Louarn, P.;
Malandraki, O.; Maloney, S.; Martinez-Pillet, V.; Martinovic, M.;
Masson, A.; Matthews, S.; Matteini, L.; Meyer-Vernet, N.; Moraitis,
K.; Morton, R. J.; Musset, S.; Nicolaou, G.; Nindos, A.; O'Brien,
H.; Orozco Suarez, D.; Owens, M.; Pancrazzi, M.; Papaioannou, A.;
Parenti, S.; Pariat, E.; Patsourakos, S.; Perrone, D.; Peter, H.;
Pinto, R. F.; Plainaki, C.; Plettemeier, D.; Plunkett, S. P.; Raines,
J. M.; Raouafi, N.; Reid, H.; Retino, A.; Rezeau, L.; Rochus, P.;
Rodriguez, L.; Rodriguez-Garcia, L.; Roth, M.; Rouillard, A. P.;
Sahraoui, F.; Sasso, C.; Schou, J.; Schühle, U.; Sorriso-Valvo, L.;
Soucek, J.; Spadaro, D.; Stangalini, M.; Stansby, D.; Steller, M.;
Strugarek, A.; Štverák, Š.; Susino, R.; Telloni, D.; Terasa, C.;
Teriaca, L.; Toledo-Redondo, S.; del Toro Iniesta, J. C.; Tsiropoula,
G.; Tsounis, A.; Tziotziou, K.; Valentini, F.; Vaivads, A.; Vecchio,
A.; Velli, M.; Verbeeck, C.; Verdini, A.; Verscharen, D.; Vilmer, N.;
Vourlidas, A.; Wicks, R.; Wimmer-Schweingruber, R. F.; Wiegelmann,
T.; Young, P. R.; Zhukov, A. N.
2020A&A...642A...3Z Altcode: 2020arXiv200910772Z
Solar Orbiter is the first space mission observing the solar plasma
both in situ and remotely, from a close distance, in and out of the
ecliptic. The ultimate goal is to understand how the Sun produces
and controls the heliosphere, filling the Solar System and driving
the planetary environments. With six remote-sensing and four in-situ
instrument suites, the coordination and planning of the operations are
essential to address the following four top-level science questions:
(1) What drives the solar wind and where does the coronal magnetic field
originate?; (2) How do solar transients drive heliospheric variability?;
(3) How do solar eruptions produce energetic particle radiation that
fills the heliosphere?; (4) How does the solar dynamo work and drive
connections between the Sun and the heliosphere? Maximising the
mission's science return requires considering the characteristics
of each orbit, including the relative position of the spacecraft
to Earth (affecting downlink rates), trajectory events (such
as gravitational assist manoeuvres), and the phase of the solar
activity cycle. Furthermore, since each orbit's science telemetry
will be downloaded over the course of the following orbit, science
operations must be planned at mission level, rather than at the level
of individual orbits. It is important to explore the way in which those
science questions are translated into an actual plan of observations
that fits into the mission, thus ensuring that no opportunities are
missed. First, the overarching goals are broken down into specific,
answerable questions along with the required observations and the
so-called Science Activity Plan (SAP) is developed to achieve this. The
SAP groups objectives that require similar observations into Solar
Orbiter Observing Plans, resulting in a strategic, top-level view of
the optimal opportunities for science observations during the mission
lifetime. This allows for all four mission goals to be addressed. In
this paper, we introduce Solar Orbiter's SAP through a series of
examples and the strategy being followed.

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Title: Solar Flare Prediction Using Magnetic Field Diagnostics above
the Photosphere
Authors: Korsós, M. B.; Georgoulis, M. K.; Gyenge, N.; Bisoi, S. K.;
Yu, S.; Poedts, S.; Nelson, C. J.; Liu, J.; Yan, Y.; Erdélyi, R.
2020ApJ...896..119K Altcode: 2020arXiv200512180K
In this article, we present the application of the weighted horizontal
gradient of magnetic field (WGM) flare prediction method
to three-dimensional (3D) extrapolated magnetic configurations of
13 flaring solar active regions (ARs). The main aim is to identify
an optimal height range, if any, in the interface region between the
photosphere and lower corona, where the flare onset time prediction
capability of WGM is best exploited. The optimal height
is where flare prediction, by means of the WGM method, is
achieved earlier than at the photospheric level. 3D magnetic structures,
based on potential and nonlinear force-free field extrapolations, are
constructed to study a vertical range from the photosphere up to the
low corona with a 45 km step size. The WGM method is applied
as a function of height to all 13 flaring AR cases that are subject to
certain selection criteria. We found that applying the WGM
method between 1000 and 1800 km above the solar surface would improve
the prediction of the flare onset time by around 2-8 hr. Certain caveats
and an outlook for future work along these lines are also discussed.

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Title: Machine Learning in Heliophysics and Space Weather Forecasting:
A White Paper of Findings and Recommendations
Authors: Nita, Gelu; Georgoulis, Manolis; Kitiashvili, Irina; Sadykov,
Viacheslav; Camporeale, Enrico; Kosovichev, Alexander; Wang, Haimin;
Oria, Vincent; Wang, Jason; Angryk, Rafal; Aydin, Berkay; Ahmadzadeh,
Azim; Bai, Xiaoli; Bastian, Timothy; Filali Boubrahimi, Soukaina; Chen,
Bin; Davey, Alisdair; Fereira, Sheldon; Fleishman, Gregory; Gary, Dale;
Gerrard, Andrew; Hellbourg, Gregory; Herbert, Katherine; Ireland,
Jack; Illarionov, Egor; Kuroda, Natsuha; Li, Qin; Liu, Chang; Liu,
Yuexin; Kim, Hyomin; Kempton, Dustin; Ma, Ruizhe; Martens, Petrus;
McGranaghan, Ryan; Semones, Edward; Stefan, John; Stejko, Andrey;
Collado-Vega, Yaireska; Wang, Meiqi; Xu, Yan; Yu, Sijie
2020arXiv200612224N Altcode:
The authors of this white paper met on 16-17 January 2020 at the New
Jersey Institute of Technology, Newark, NJ, for a 2-day workshop that
brought together a group of heliophysicists, data providers, expert
modelers, and computer/data scientists. Their objective was to discuss
critical developments and prospects of the application of machine and/or
deep learning techniques for data analysis, modeling and forecasting
in Heliophysics, and to shape a strategy for further developments in
the field. The workshop combined a set of plenary sessions featuring
invited introductory talks interleaved with a set of open discussion
sessions. The outcome of the discussion is encapsulated in this white
paper that also features a top-level list of recommendations agreed
by participants.

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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
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: Multivariate time series dataset for space weather data
analytics
Authors: Angryk, Rafal A.; Martens, Petrus C.; Aydin, Berkay; Kempton,
Dustin; Mahajan, Sushant S.; Basodi, Sunitha; Ahmadzadeh, Azim; Cai,
Xumin; Filali Boubrahimi, Soukaina; Hamdi, Shah Muhammad; Schuh,
Michael A.; Georgoulis, Manolis K.
2020NatSD...7..227A Altcode:
We introduce and make openly accessible a comprehensive, multivariate
time series (MVTS) dataset extracted from solar photospheric vector
magnetograms in Spaceweather HMI Active Region Patch (SHARP) series. Our
dataset also includes a cross-checked NOAA solar flare catalog that
immediately facilitates solar flare prediction efforts. We discuss
methods used for data collection, cleaning and pre-processing of the
solar active region and flare data, and we further describe a novel
data integration and sampling methodology. Our dataset covers 4,098
MVTS data collections from active regions occurring between May 2010 and
December 2018, includes 51 flare-predictive parameters, and integrates
over 10,000 flare reports. Potential directions toward expansion of the
time series, either "horizontally" - by adding more prediction-specific
parameters, or "vertically" - by generalizing flare into integrated
solar eruption prediction, are also explained. The immediate tasks
enabled by the disseminated dataset include: optimization of solar flare
prediction and detailed investigation for elusive flare predictors or
precursors, with both operational (research-to-operations), and basic
research (operations-to-research) benefits potentially following in
the future.

---------------------------------------------------------
Title: Which Machine- or Deep-Learning Methods are Most Appropriate
for Solar Flare Prediction? Possibly, a Misleading Question
Authors: He, H.; Georgoulis, M. K.
2019AGUFMSH34A..01H Altcode:
Over the past decade, machine-learning methods for solar flare
prediction have been established as a necessity in order to browse
through the immense parameter space of promising flare-predictive
properties in solar active regions. This obvious big data problem
requires advanced computer science methods to be tackled, in an
endeavor that has demonstrably reached out to communities beyond
heliophysics. However, as in any new research avenue, the landscape
of techniques and methodologies is constantly changing in an unplanned
and unpredictable way, with groundbreaking results yet to be produced
and shown conclusively. Recent collaborative works compare very
different methods that, however, deliver very similar, far from
perfect, results. We aim to provide a preliminary interpretation of
this situation by asserting that the specific machine- (and deep-,
very recently) learning methods employed for solar flare forecasting
may not be the most important element here: their training and testing
practices, however, are. Training and testing over active-region
property metadata can significantly change the results of any method,
in a way that if very different methods share the same testing /
testing pattern, they tend to give similar, invariably imperfect,
results. To this one must add the relative deficiency of timeseries
analysis methods for flare forecasting, along with the unmitigated
severe class imbalance problem, stemming from the intrinsic rarity of
major flares: machine-learning methods require class-balanced event /
no-event data sets (this remains to be seen for deep-learning ones)
so their performance is consistently below expectations. We identify
some early attempts toward this second level of efforts, in hopes of
instigating further discussion and, hopefully, progress.

---------------------------------------------------------
Title: Magnetic Impact of Propagating Interplanetary Coronal Mass
Ejections in the Solar and Stellar Habitability Zones
Authors: Georgoulis, M. K.; Samara, E.; Patsourakos, S.
2019AGUFMSH43A..05G Altcode:
We recount recent results of a statistical method that assigns an
axial magnetic field to CME flux ropes, inferred via the fundamental
conservation principle of magnetic helicity in solar active region
sources. We then extrapolate the near-Sun CME magnetic field to
1 AU, juxtaposing the extrapolation with tens of magnetic-cloud
observations. Uncertainties given, we manage to statistically
reproduce observations, thereby proposing a simple method that
alleviates unnecessary complexity, while featuring applicability on
a case-by-case basis. At a second level, we generalize CME magnetic
configurations and stellar activity, expanding to flaring M-dwarf
and Sun-like stars. We correlate the magnetic energy of stellar,
assumed eruptive, flares with their helicity and extrapolate again to
stellar habitable zones. From assumed planetary equatorial magnetic
fields we predict atmospheric erosion by CME activity for a number of
recently discovered exoplanets (Keppler 438b; Proxima b; the TRAPPIST
system), thought promising for harboring life. Preliminary results
show that knowledge of the planetary equatorial magnetic field can
impose a valuable constraint for exoplanet habitability. Meanwhile, (1)
terrestrial atmospheric erosion seems unlikely even for unrealistically
intense solar eruptions and (2) the likelihood of absence of atmosphere
due to CME-induced erosion in many of the studied exoplanets seems high.

---------------------------------------------------------
Title: Challenges with Extreme Class-Imbalance and Temporal Coherence:
A Study on Solar Flare Data
Authors: Ahmadzadeh, Azim; Hostetter, Maxwell; Aydin, Berkay;
Georgoulis, Manolis K.; Kempton, Dustin J.; Mahajan, Sushant S.;
Angryk, Rafal A.
2019arXiv191109061A Altcode:
In analyses of rare-events, regardless of the domain of application,
class-imbalance issue is intrinsic. Although the challenges are known to
data experts, their explicit impact on the analytic and the decisions
made based on the findings are often overlooked. This is in particular
prevalent in interdisciplinary research where the theoretical aspects
are sometimes overshadowed by the challenges of the application. To
show-case these undesirable impacts, we conduct a series of experiments
on a recently created benchmark data, named Space Weather ANalytics for
Solar Flares (SWAN-SF). This is a multivariate time series dataset of
magnetic parameters of active regions. As a remedy for the imbalance
issue, we study the impact of data manipulation (undersampling and
oversampling) and model manipulation (using class weights). Furthermore,
we bring to focus the auto-correlation of time series that is inherited
from the use of sliding window for monitoring flares' history. Temporal
coherence, as we call this phenomenon, invalidates the randomness
assumption, thus impacting all sampling practices including different
cross-validation techniques. We illustrate how failing to notice this
concept could give an artificial boost in the forecast performance
and result in misleading findings. Throughout this study we utilized
Support Vector Machine as a classifier, and True Skill Statistics as
a verification metric for comparison of experiments. We conclude our
work by specifying the correct practice in each case, and we hope that
this study could benefit researchers in other domains where time series
of rare events are of interest.

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Title: Feature Ranking of Active Region Source Properties in Solar
Flare Forecasting and the Uncompromised Stochasticity of Flare
Occurrence
Authors: Campi, Cristina; Benvenuto, Federico; Massone, Anna Maria;
Bloomfield, D. Shaun; Georgoulis, Manolis K.; Piana, Michele
2019ApJ...883..150C Altcode: 2019arXiv190612094C
Solar flares originate from magnetically active regions (ARs) but
not all solar ARs give rise to a flare. Therefore, the challenge of
solar flare prediction benefits from an intelligent computational
analysis of physics-based properties extracted from AR observables,
most commonly line-of-sight or vector magnetograms of the active
region photosphere. For the purpose of flare forecasting, this
study utilizes an unprecedented 171 flare-predictive AR properties,
mainly inferred by the Helioseismic and Magnetic Imager on board the
Solar Dynamics Observatory (SDO/HMI) in the course of the European
Union Horizon 2020 FLARECAST project. Using two different supervised
machine-learning methods that allow feature ranking as a function
of predictive capability, we show that (i) an objective training and
testing process is paramount for the performance of every supervised
machine-learning method; (ii) most properties include overlapping
information and are therefore highly redundant for flare prediction;
(iii) solar flare prediction is still—and will likely remain—a
predominantly probabilistic challenge.

---------------------------------------------------------
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
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
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
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: The source and engine of coronal mass ejections
Authors: Georgoulis, Manolis K.; Nindos, Alexander; Zhang, Hongqi
2019RSPTA.37780094G Altcode:
Coronal mass ejections (CMEs) are large-scale expulsions of coronal
plasma and magnetic field propagating through the heliosphere. Because
CMEs are observed by white-light coronagraphs which, by design, occult
the solar disc, supporting disc observations (e.g. in EUV, soft X-rays,
Halpha and radio) must be employed for the study of their source
regions and early development phases. We review the key properties of
CME sources and highlight a certain causal sequence of effects that may
occur whenever a strong (flux-massive and sheared) magnetic polarity
inversion line develops in the coronal base of eruptive active regions
(ARs). Storing non-potential magnetic energy and helicity in a much
more efficient way than ARs lacking strong polarity inversion lines,
eruptive regions engage in an irreversible course, making eruptions
inevitable and triggered when certain thresholds of free energy
and helicity are crossed. This evolution favours the formation of
pre-eruption magnetic flux ropes. We describe the steps of this
plausible path to sketch a picture of the pre-eruptive phase of CMEs
that may apply to most events, particularly the ones populating the
high end of the energy/helicity distribution, that also tend to have
the strongest space-weather implications. This article is part
of the theme issue 'Solar eruptions and their space weather impact'.

---------------------------------------------------------
Title: Sheared Magnetic Arcades and the Pre-eruptive Magnetic
Configuration of Coronal Mass Ejections: Diagnostics, Challenges
and Future Observables
Authors: Patsourakos, Spiros; Vourlidas, A.; Anthiochos, S. K.;
Archontis, V.; Aulanier, G.; Cheng, X.; Chintzoglou, G.; Georgoulis,
M. K.; Green, L. M.; Kliem, B.; Leake, J.; Moore, R. L.; Nindos, A.;
Syntelis, P.; Torok, T.; Yardley, S. L.; Yurchyshyn, V.; Zhang, J.
2019shin.confE.194P Altcode:
Our thinking about the pre-eruptive magnetic configuration of Coronal
Mass Ejections has been effectively dichotomized into two opposing
and often fiercely contested views: namely, sheared magnetic arcades
and magnetic flux ropes. Finding a solution to this issue will have
important implications for our understanding of CME initiation. We
first discuss the very value of embarking into the arcade vs. flux rope
dilemma and illustrate the corresponding challenges and difficulties to
address it. Next, we are compiling several observational diagnostics of
pre-eruptive sheared magnetic arcades stemming from theory/modeling,
discuss their merits, and highlight potential ambiguities that could
arise in their interpretation. We finally conclude with a discussion
of possible new observables, in the frame of upcoming or proposed
instrumentation, that could help to circumvent the issues we are
currently facing.

---------------------------------------------------------
Title: Deriving the Near-Sun Magnetic Field of Coronal Mass Ejections
from Magnetic Helicity Conservation
Authors: Patsourakos, Spiros; Georgoulis, M. K.; Petroulea, G.;
Vourlidas, A.; Nieves-Chinchilla, T.
2019shin.confE.222P Altcode:
The near-Sun magnetic field of Coronal Mass Ejections represents
a key parameter for assessing their energetics and structuring, and
additionally, it is a major element of methods/applications/simulations
aiming to predict the magnetic field of Earth-directed CMEs upon
impact at geospace. Diagnostics of CME magnetic fields in the corona
can be achieved via observations in the radio domain, which however,
are currently not available on a regular basis. Therefore, several
methods to infer the CME magnetic field in the corona have recently
emerged. We developed one such method which is based on the magnetic
helicity conservation principle applied to flux rope CMEs. Its
input parameters could be readily retrieved from the analysis of
HMI magnetograms and SOHO/STEREO WL coronagraph images. We present
parametric and case-study applications of this method, and discuss how
it be could be used to predict the CME magnetic field magnitude at 1 AU.

---------------------------------------------------------
Title: Machine Learning in Solar Eruption Forecasting: a Scene-Setting
Attempt
Authors: Georgoulis, Manolis K.; Martens, P. C.; Angryk, R. A.; Aydin,
B.; Ahmadzadeh, A.
2019shin.confE..89G Altcode:
Over the nearly three decades of space weather forecasting efforts,
increased awareness suggests that conventional solar physics may
not suffice to fully understand, and ultimately predict, eruptive
solar activity, particularly the rarest trio of major flare, coronal
mass ejection and solar energetic particle events. Both statistical
and computer science techniques and approaches, such as machine and
deep learning, seem apt to break ground in both pursuits, namely, in
enhancing physical understanding and in enabling forecasts reliable
enough to become practical. Like any promising new trend, however,
machine and deep learning methods entail major challenges. In this
brief account, we discuss a subset of these challenges whose efficient
tackling can spur further progress. These major issues became evident in
the framework of the European Union Flare Likelihood and Region Eruption
Forecasting (FLARECAST) project on solar flare forecasting. The most
substantial of them, that can easily mislead results, comparisons
and interpretation, include climatology and uncertainties thereof,
the construction of the training and test samples in machine learning
methods and the class imbalance problem that becomes conspicuous when
forecasting increasingly rare events. The above underline the need
for benchmarking standards against which new methods are to be tested,
verified and validated. We discuss a such benchmark, namely the Space
Weather data ANalytics (SWAN) benchmark dataset for flare prediction,
established at the Georgia State University Astroinformatics Cluster,
that aims to tackle climatology and the construction of training and
test samples. In addition, we show indicative, preliminary results
of efforts tackling the class imbalance problem on the GSU SWAN flare
prediction data.

---------------------------------------------------------
Title: Coronal Mass Ejection Initiation: a Likely Irreversible
Evolutionary Process
Authors: Georgoulis, Manolis K.
2019shin.confE..92G Altcode:
Combining original results and review assessments, we shed new light
to the asserted necessity of the Sun to relieve itself from the excess
magnetic helicity it produces via coronal mass ejections (CMEs). In
particular, we argue that fast, active-region CME initiation is an
irreversible consequence of the formation of intense magnetic polarity
inversion lines (PILs) in the low solar atmosphere. By “intense”
we mean PILs on which the magnetic field strength is well above the
equipartition value, even at photospheric altitudes. The formation of
intense PILs is exclusively related to the action of non-neutralized
(net) electric currents along the PILs that give rise to a Lorentz
tension force able to move the plasma and cause the observed velocity
shear along PILs. Shear gives rise to quasi-steady, confined magnetic
reconnection along the PIL that efficiently converts the substantial
mutual magnetic helicity of the sheared magnetic arcade (SMA) into
self helicity (twist and writhe), enabling a pre-eruption magnetic
flux rope (MFR) that will eventually destabilize if the SMA does not
erupt already via breakout. Invariably, either SMAs or MFRs shed a
significant fraction of the source active region helicity into the
heliosphere. This progression, leading to at least one major eruption,
lasts for as long as there is flux emergence to sustain the strong PIL
and during a significant part of the active region decay phase, until
Lorentz tension weakens and helicity expulsion is significant enough
to allow the dissolution of the active region. This mechanism is yet to
be validated conclusively, but its validation path is clear. If proven,
it will show that the dichotomy between SMA and MFR in the pre-eruption
evolution of eruptive active regions is of little practical meaning:
with the same end result, namely the expulsion of magnetic helicity,
pre-eruption MFRs will form if the coronal magnetic topology is not
sufficient to enable a direct SMA eruption.

---------------------------------------------------------
Title: Preface: Solar physics advances from the interior to the
heliosphere
Authors: Georgoulis, Manolis K.; Kontar, Eduard P.
2019AdSpR..63.1387G Altcode:
Solar Physics has been experiencing a golden era of unprecedented
observations and voluminous data for nearly three decades. While
much of the progress in the 1990s and 2000s was spurred by flagship
space missions, the latest decade has also seen the culmination
of game-changing ground-based facilities, long sought after by the
community. Observing the Sun from space has indisputable benefits;
however, space missions have a relatively limited lifespan, mainly
because of the unforgiving deep space or orbital conditions and our
limited ability to maintain them after launch. This is not the case
for ground-based facilities that can, in principle, serve and train
entire generations of researchers.

---------------------------------------------------------
Title: Analysis and interpretation of inner-heliospheric SEP events
with the ESA Standard Radiation Environment Monitor (SREM) onboard
the INTEGRAL and Rosetta Missions
Authors: Georgoulis, Manolis K.; Papaioannou, Athanasios;
Sandberg, Ingmar; Anastasiadis, Anastasios; Daglis, Ioannis A.;
Rodríguez-Gasén, Rosa; Aran, Angels; Sanahuja, Blai; Nieminen,
Petteri
2018JSWSC...8A..40G Altcode:
Using two heliospheric vantage points, we study 22 solar energetic
particle (SEP) events, 14 of which were detected at both locations. SEP
proton events were detected during the declining phase of solar cycle
23 (November 2003-December 2006) by means of two nearly identical
Standard Radiation Environment Monitor (SREM) units in energies
ranging between 12.6 MeV and 166.3 MeV. In this work we combine SREM
data with diverse solar and interplanetary measurements, aiming
to backtrace solar eruptions from their impact in geospace (i.e.,
from L1 Lagrangian point to Earth's magnetosphere) to their parent
eruptions at the Sun's low atmosphere. Our SREM SEP data support
and complement a consistent inner-heliospheric description of solar
eruptions (solar flares and coronal mass ejections [CMEs]) and their
magnetospheric impact. In addition, they provide useful information
on the understanding of the origin, acceleration, and propagation of
SEP events at multi-spacecraft settings. All SEP events in our sample
originate from major eruptions consisting of major (&gt;M-class) solar
flares and fast (&gt;1800 km/s, on average), overwhelmingly (&gt;78%)
halo, CMEs. All but one SEP event studied are unambiguously associated
with shock-fronted CMEs, suggesting a CME-driven shock acceleration
mechanism. Moreover, a significant correlation is found between
the SEP event peak and the onset of the storm sudden commencement,
that might help improve prediction of magnetospheric disturbances. In
general, SEP events correlate better with interplanetary (i.e., in-situ;
L1-based) than with solar eruption features. Our findings support (a)
the routine use of cost-effective SREM units, or future improvements
thereof, for the detection of SEP events and (b) their implementation
in multi-spacecraft settings as a means to improve both the physical
understanding of SEP events and their forecasting.

---------------------------------------------------------
Title: On the Evolution of Pre-Flare Patterns of a 3-Dimensional
Model of AR 11429
Authors: Korsós, M. B.; Poedts, S.; Gyenge, N.; Georgoulis, M. K.;
Yu, S.; Bisoi, S. K.; Yan, Y.; Ruderman, M. S.; Erdélyi, R.
2018IAUS..335..294K Altcode: 2018arXiv180100433K
We apply a novel pre-flare tracking of sunspot groups towards improving
the estimation of flare onset time by focusing on the evolution of the
3D magnetic field construction of AR 11429. The 3D magnetic structure
is based on potential field extrapolation encompassing a vertical
range from the photosphere through the chromosphere and transition
region into the low corona. The basis of our proxy measure of activity
prediction is the so-called weighted horizontal gradient of magnetic
field (WGM) defined between spots of opposite polarities
close to the polarity inversion line of an active region. The temporal
variation of the distance of the barycenter of the opposite polarities
is also found to possess potentially important diagnostic information
about the flare onset time estimation as function of height similar
to its counterpart introduced initially in an application at the
photosphere only in Korsós et al. (2015). We apply the photospheric
pre-flare behavioural patterns of sunspot groups to the evolution of
their associated 3D-constructed AR 11429 as function of height. We found
that at a certain height in the lower solar atmosphere the onset time
may be estimated much earlier than at the photosphere or at any other
heights. Therefore, we present a tool and recipe that may potentially
identify the optimum height for flare prognostic in the solar atmosphere
allowing to improve our flare prediction capability and capacity.

---------------------------------------------------------
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
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: Eruptive Flare Initiation and the CME Magnetic Field
Authors: Georgoulis, Manolis K.; Patsourakos, Spiros; Kontogiannis,
Ioannis
2018cosp...42E1180G Altcode:
We recount very recent results on the correlation between photospheric
characteristics of eruptive solar active regions and coronal mass
ejection (CME) occurrence / characteristics. In particular, we
argue that one of the most relevant parameters for CME occurrence
is the non-neutralized electric currents appearing exclusively along
intense, shear-ridden magnetic polarity-inversion lines (PILs) in the
photosphere of eruptive active regions. These currents are simply
lacking in the absence of strong PILs and shear. While the physics
underlying non-neutralized currents is rich and shows far-reaching
ramifications, we will focus on the injection of magnetic helicity
due to non-neutralized currents in the pre-eruption phase, that will
then be bodily transported via the CME. For a conductive plasma of
high magnetic Reynolds number, such as that of the solar corona,
we show how the fundamental helicity conservation principle can lead
to estimates of, first, the CME's axial magnetic field strength and,
second, the anticipated magnetic field strength of the interplanetary
CME (ICME) on the verge of geospace. We discuss how this analysis
can be viewed as a meaningful initial or boundary condition for more
elaborate inner-heliospheric propagation models that further consider
the orientation of the ICME magnetic field, thus leading to an improved
understanding and prediction of ICME geoeffectiveness. Part of this
work has been supported by the EU Horizon-2020 FLARECAST project
(grant agreement no. 640216).

---------------------------------------------------------
Title: Towards common validation and verification procedures in the
ongoing SSA Space Weather Service Network
Authors: Borries, Claudia; Glover, Alexi; Georgoulis, Manolis K.;
Perry, Chris; Dierckxsens, Mark; Tsagouri, Ioanna
2018cosp...42E.400B Altcode:
In the framework of the Space Situational Awareness Programme (SSA) of
the European Space Agency (ESA), the Space WEather (SWE) segment aims to
help end-users in a wide range of SWE affected sectors to mitigate the
effects on their systems, reducing costs and improving reliability. In
the SWE segment, five Expert Service Centres (ESCs), the SSA Space
Weather Coordination Centre (SSCC) and the SSA Space Weather Data
Centre (SWE-DC) form the SSA SWE network. This network is providing
SWE services to users dependent on space weather conditions. The SWE
services are composed of an extensive number of products provided
by numerous contributing expert groups. Each product is delivered
to the SSA SWE network with a full package of documentation and
user guidance. This includes results of validation and verification
procedures helping the end-user to identify the appropriate products
for each application. The currently diverse procedures for product
validation and verification hamper the comparison and evaluation of
different products. Therefore, the SWE network aims to harmonize these
procedures. Here, an overview of the ESCs product validation assessment
and planning for the current activity will be given, including examples
of best practice and approaches for common validation and verification
procedures.

---------------------------------------------------------
Title: A method to assess planetary habitability based on the effects
of CME magnetic fields on planetary magnetospheres
Authors: Samara, Evangelia; Georgoulis, Manolis K.
2018shin.confE.216S Altcode:
In this work, we propose a methodology to assess planetary surface
habitability for any newly discovered exoplanet lying in the habitable
zone of a low mass, superflare, main-sequence star. While habitability
is usually a function of multiple parameters (i.e. the size of the
planet, the composition of its atmosphere, the existence of liquid
water, orbital or rotational dynamics), the presented method primarily
focuses on stellar activity and its effects on potentially existing
planetary magnetospheres stemming from dynamo-generated magnetic
fields. The area our method applies to, is split in two regimes
depending on whether the exoplanet of interest is tidally locked or
tidally unlocked to its mother star. In the former case, a ratio
between a conditional (Beq) and a best-case equatorial planetary
magnetic field (Bstev), is calculated. A smaller-than-unity value
of that ratio favors the formation of a stable atmosphere adequate
to host surface, atmosphere-dependent habitability. In the latter
case (tidally unlocked regime), a ratio between a conditional (Beq)
and the terrestrial magnetic field (Bearth) is estimated, which
indirectly implies how easy or hard it is for an exoplanet to sustain
an atmosphere. For a ratio's value lower than unity, there is hope
for surface habitability since its magnetic field is assumed equal to,
or larger than, the terrestrial one. On the other hand, a value higher
than one casts doubts on surface habitability, because even a strong,
terrestrial magnetic field is not sufficient to secure an atmosphere
for the exoplanet. Both ratios concerning the two different spatial
regimes of our method's application are based on the observed mother
star's activity and are calculated on the critical magnetopause distance
of two planetary radii, below which atmospheric erosion phenomena are
assumed to start taking place.

---------------------------------------------------------
Title: Forecast Verification in the Framework of the EU FLARECAST
Project
Authors: Georgoulis, Manolis K.; Massone, Anna Maria; Jackson, David;
Benvenuto, Federico; Piana, Michele; Bloomfield, Shaun; Florios,
Konstantinos; Campi, Cristina; Worsfold, Mark
2018cosp...42E1181G Altcode:
We describe the main practices and results of the comprehensive
forecast verification effort undertaken in the framework of the
EU FLARECAST project for solar flare prediction. In discussing
FLARECAST, we compare between previous verification efforts of solar
flare forecasting products or services and the potential advances
brought by the FLARECAST project, that served as a uniform platform
for testing numerous and diverse flare forecasting methods. Results
shown include major skill score values and extensive ranking of
flare-predictive parameters. We further advocate for a robust error
assessment of the scores and parameters involved in the verification
process, that would provide the basis of a much-needed, continuous
assessment of solar flare forecasting capabilities. In concluding, we
list the discussion areas and recommendations addressed by the COSPAR
- ILWS Roadmap, indicating the locations where the FLARECAST project
has been contributing and providing feedback, potentially enabling
further advances in the verification of forecasting activities of
solar and heliospheric weather. This work has received support by the
EU Horizon-2020 FLARECAST project (grant agreement no. 640216).

---------------------------------------------------------
Title: Testing and Improving a Set of Morphological Predictors of
Flaring Activity
Authors: Kontogiannis, Ioannis; Georgoulis, Manolis K.; Park,
Sung-Hong; Guerra, Jordan A.
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: The Ambivalent Role of Field-Aligned Electric Currents in
the Solar Atmosphere
Authors: Georgoulis, Manolis K.
2018GMS...235..371G Altcode:
No abstract at ADS

---------------------------------------------------------
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.
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 &gt;M1 and &gt;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 &gt;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
&gt;C1 flare prediction with probability threshold 35%.

---------------------------------------------------------
Title: Active Region Photospheric Magnetic Properties Derived from
Line-of-Sight and Radial Fields
Authors: Guerra, J. A.; Park, S. -H.; Gallagher, P. T.; Kontogiannis,
I.; Georgoulis, M. K.; Bloomfield, D. S.
2018SoPh..293....9G Altcode: 2017arXiv171206902G
The effect of using two representations of the normal-to-surface
magnetic field to calculate photospheric measures that are related
to the active region (AR) potential for flaring is presented. Several
AR properties were computed using line-of-sight (Blos) and
spherical-radial (Br) magnetograms from the Space-weather HMI
Active Region Patch (SHARP) products of the Solar Dynamics Observatory,
characterizing the presence and features of magnetic polarity inversion
lines, fractality, and magnetic connectivity of the AR photospheric
field. The data analyzed correspond to ≈4 ,000 AR observations,
achieved by randomly selecting 25% of days between September 2012 and
May 2016 for analysis at 6-hr cadence. Results from this statistical
study include: i) the Br component results in a slight
upwards shift of property values in a manner consistent with a
field-strength underestimation by the Blos component;
ii) using the Br component results in significantly lower
inter-property correlation in one-third of the cases, implying more
independent information as regards the state of the AR photospheric
magnetic field; iii) flaring rates for each property vary between
the field components in a manner consistent with the differences
in property-value ranges resulting from the components; iv) flaring
rates generally increase for higher values of properties, except the
Fourier spectral power index that has flare rates peaking around a
value of 5 /3 . These findings indicate that there may be advantages
in using Br rather than Blos in calculating
flare-related AR magnetic properties, especially for regions located
far from central meridian.

---------------------------------------------------------
Title: The Next Level in Automated Solar Flare Forecasting: the EU
FLARECAST Project
Authors: Georgoulis, M. K.; Bloomfield, D.; Piana, M.; Massone,
A. M.; Gallagher, P.; Vilmer, N.; Pariat, E.; Buchlin, E.; Baudin,
F.; Csillaghy, A.; Soldati, M.; Sathiapal, H.; Jackson, D.; Alingery,
P.; Argoudelis, V.; Benvenuto, F.; Campi, C.; Florios, K.; Gontikakis,
C.; Guennou, C.; Guerra, J. A.; Kontogiannis, I.; Latorre, V.; Murray,
S.; Park, S. H.; Perasso, A.; Sciacchitano, F.; von Stachelski, S.;
Torbica, A.; Vischi, D.
2017AGUFMSA21C..07G Altcode:
We attempt an 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 achieved for the forecasting of major solar flares. We
outline the consortium, top-level objectives and first results of
the project, highlighting the diversity and fusion of expertise
needed to deliver what was promised. The project's final product,
featuring an openly accessible, fully modular and free to download
flare forecasting facility will be delivered in early 2018. The
project's three objectives, namely, science, research-to-operations and
dissemination / communication, are also discussed: in terms of science,
we encapsulate our close-to-final assessment on how close (or far)
are we from a practically exploitable solar flare forecasting. In
terms of R2O, we briefly describe the architecture of the FLARECAST
infrastructure that includes rigorous validation for each forecasting
step. From the three different communication levers of the project we
finally focus on lessons learned from the two-way interaction with the
community of stakeholders and governmental organizations. The FLARECAST
project has received funding from the European Union's Horizon 2020
research and innovation programme under grant agreement No. 640216.

---------------------------------------------------------
Title: A New Spin to Exoplanet Habitability Criteria
Authors: Georgoulis, M. K.; Patsourakos, S.
2017AGUFM.P53E2676G Altcode:
We describe a physically- and statistically-based method to infer
the near-Sun magnetic field of coronal mass ejections (CMEs) and then
extrapolate it to the inner heliosphere and beyond. Besides a ballpark
agreement with in-situ observations of interplanetary CMEs (ICMEs) at
L1, we use our estimates to show that Earth does not seem to be at risk
of an extinction-level atmospheric erosion or stripping by the magnetic
pressure of extreme solar eruptions, even way above a Carrington-type
event. This does not seem to be the case with exoplanets, however,
at least those orbiting in the classically defined habitability
zones of magnetically active dwarf stars at orbital radii of a small
fraction of 1 AU. We show that the combination of stellar ICMEs and
the tidally locking zone of mother stars, that quite likely does not
allow these exoplanets to attain Earth-like magnetic fields to shield
themselves, probably render the existence of a proper atmosphere
in them untenable. We propose, therefore, a critical revision of
habitability criteria in these cases that would limit the number of
target exoplanets considered as potential biosphere hosts.

---------------------------------------------------------
Title: Non-neutralized Electric Currents in Solar Active Regions
and Flare Productivity
Authors: Kontogiannis, Ioannis; Georgoulis, Manolis K.; Park,
Sung-Hong; Guerra, Jordan A.
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: Predicting Flares and Solar Energetic Particle Events: The
FORSPEF Tool
Authors: Anastasiadis, A.; Papaioannou, A.; Sandberg, I.; Georgoulis,
M.; Tziotziou, K.; Kouloumvakos, A.; Jiggens, P.
2017SoPh..292..134A Altcode:
A novel integrated prediction system for solar flares (SFs) and solar
energetic particle (SEP) events is presented here. The tool called
forecasting solar particle events and flares (FORSPEF) provides
forecasts of solar eruptive events, such as SFs with a projection
to occurrence and velocity of coronal mass ejections (CMEs), and
the likelihood of occurrence of an SEP event. In addition, the
tool provides nowcasting of SEP events based on actual SF and CME
near real-time data, as well as the SEP characteristics (e.g. peak
flux, fluence, rise time, and duration) per parent solar event. The
prediction of SFs relies on the effective connected magnetic field
strength (Beff) metric, which is based on an assessment
of potentially flaring active-region (AR) magnetic configurations,
and it uses a sophisticated statistical analysis of a large number
of AR magnetograms. For the prediction of SEP events, new statistical
methods have been developed for the likelihood of the SEP occurrence
and the expected SEP characteristics. The prediction window in the
forecasting scheme is 24 hours with a refresh rate of 3 hours, while
the respective prediction time for the nowcasting scheme depends on
the availability of the near real-time data and ranges between 15 - 20
minutes for solar flares and 6 hours for CMEs. We present the modules
of the FORSPEF system, their interconnection, and the operational
setup. Finally, we demonstrate the validation of the modules of the
FORSPEF tool using categorical scores constructed on archived data,
and we also discuss independent case studies.

---------------------------------------------------------
Title: A Helicity-Based Method to Infer the CME Magnetic Field
Magnitude in Sun and Geospace: Generalization and Extension to
Sun-Like and M-Dwarf Stars and Implications for Exoplanet Habitability
Authors: Patsourakos, S.; Georgoulis, M. K.
2017SoPh..292...89P Altcode: 2017arXiv170703579P
Patsourakos et al. (Astrophys. J.817, 14, 2016) and Patsourakos and
Georgoulis (Astron. Astrophys.595, A121, 2016) introduced a method to
infer the axial magnetic field in flux-rope coronal mass ejections
(CMEs) in the solar corona and farther away in the interplanetary
medium. The method, based on the conservation principle of magnetic
helicity, uses the relative magnetic helicity of the solar source
region as input estimates, along with the radius and length of the
corresponding CME flux rope. The method was initially applied to
cylindrical force-free flux ropes, with encouraging results. We hereby
extend our framework along two distinct lines. First, we generalize
our formalism to several possible flux-rope configurations (linear
and nonlinear force-free, non-force-free, spheromak, and torus) to
investigate the dependence of the resulting CME axial magnetic field
on input parameters and the employed flux-rope configuration. Second,
we generalize our framework to both Sun-like and active M-dwarf stars
hosting superflares. In a qualitative sense, we find that Earth may
not experience severe atmosphere-eroding magnetospheric compression
even for eruptive solar superflares with energies ≈104
times higher than those of the largest Geostationary Operational
Environmental Satellite (GOES) X-class flares currently observed. In
addition, the two recently discovered exoplanets with the highest
Earth-similarity index, Kepler 438b and Proxima b, seem to lie in the
prohibitive zone of atmospheric erosion due to interplanetary CMEs
(ICMEs), except when they possess planetary magnetic fields that are
much higher than that of Earth.

---------------------------------------------------------
Title: Magnetic Helicity Estimations in Models and Observations of
the Solar Magnetic Field. III. Twist Number Method
Authors: Guo, Y.; Pariat, E.; Valori, G.; Anfinogentov, S.; Chen,
F.; Georgoulis, M. K.; Liu, Y.; Moraitis, K.; Thalmann, J. K.; Yang, S.
2017ApJ...840...40G Altcode: 2017arXiv170402096G
We study the writhe, twist, and magnetic helicity of different
magnetic flux ropes, based on models of the solar coronal magnetic
field structure. These include an analytical force-free Titov-Démoulin
equilibrium solution, non-force-free magnetohydrodynamic simulations,
and nonlinear force-free magnetic field models. The geometrical
boundary of the magnetic flux rope is determined by the quasi-separatrix
layer and the bottom surface, and the axis curve of the flux rope is
determined by its overall orientation. The twist is computed by the
Berger-Prior formula, which is suitable for arbitrary geometry and
both force-free and non-force-free models. The magnetic helicity is
estimated by the twist multiplied by the square of the axial magnetic
flux. We compare the obtained values with those derived by a finite
volume helicity estimation method. We find that the magnetic helicity
obtained with the twist method agrees with the helicity carried by the
purely current-carrying part of the field within uncertainties for
most test cases. It is also found that the current-carrying part of
the model field is relatively significant at the very location of the
magnetic flux rope. This qualitatively explains the agreement between
the magnetic helicity computed by the twist method and the helicity
contributed purely by the current-carrying magnetic field.

---------------------------------------------------------
Title: Magnetic helicity estimations in models and observations of
the solar magnetic field
Authors: Valori, Gherardo; Pariat, Etienne; Anfinogentov, Sergey;
Chen, Feng; Georgoulis, Manolis; Guo, Yang; Liu, Yang; Moraitis,
Kostas; Thalmann, Julia K.; Yang, Shangbin
2017EGUGA..19.3692V Altcode:
Magnetic helicity, as one of the few conserved quantities
in magneto-hydrodynamics, is often invoked as the principle
driving the generation and structuring of magnetic fields in a
variety of environments, from dynamo models in stars and planets,
to post-disruption reconfigurations of tokamak's plasmas. Most
particularly magnetic helicity has raised the interest of solar
physicists, since helicity is suspected to represent a key quantity for
the understanding of solar flares and the generation of coronal mass
ejections. In recent years, several methods of estimation of magnetic
helicity have been proposed and already applied to observations and
numerical simulations. However, no systematic comparison of accuracy,
mutual consistency, and reliability of such methods has ever been
performed. We present the results of the first benchmark of several
finite-volume methods in estimating magnetic helicity in 3D test
models. In addition to finite volume methods, two additional methods
are also included that estimate magnetic helicity based either on the
field line's twist, or on the field's values on one boundary and an
inferred minimal volume connectivity. The employed model tests range
from solutions of the force-free equations to 3D magneto-hydrodynamical
numerical simulations. Almost all methods are found to produce the same
value of magnetic helicity within few percent in all tests. However,
methods show differences in the sensitivity to numerical resolution and
to errors in the solenoidal property of input fields. Our benchmark of
finite volume methods allows to determine the reliability and precision
of estimations of magnetic helicity in practical cases. As a next step,
finite volume methods are used to test estimation methods that are
based on the flux of helicity through one boundary, in particular
for applications to observation-based models of coronal magnetic
fields. The ultimate goal is to assess if and how can helicity be
meaningfully used as a diagnostic of the evolution of magnetic fields
in the solar atmosphere.

---------------------------------------------------------
Title: Solar Magnetic Data Analysis for the FLARECAST Project
Authors: Guerra, J. A.; Park, S. H.; Kontogiannis, I.; Bloomfield,
D.; Gallagher, P.; Georgoulis, M. K.
2016AGUFMSH11C2234G Altcode:
The Flare Likelihood And Region Eruption foreCASTing (FLARECAST) project
is an EU H2020-funded consortium project aiming to develop an advanced
solar flare forecasting system by implementing state-of-the-art
solar data analysis and flare prediction algorithms. The Solar
Physics Group at Trinity College Dublin is in charge of the analysis
of observational data to extract solar active region properties
that serve as input for the prediction algorithms. The calculated
active region properties correspond to a non-exhaustive list of
parameters that have demonstrated a strong flare association, such as
Schrijver's R-value, the Fourier power spectrum exponent, the effective
connected magnetic field (Beff), the horizontal field decay index,
and the weighted length of strong-gradient polarity inversion lines
(WLSG). Parameters were calculated from Spaceweather HMI Active Region
Patch (SHARP) magnetograms, a data product of the Helioseismic and
Magnetic Imager (HMI) magnetograph on the Solar Dynamics Observatory
(SDO). SHARPs provide photospheric vector-magnetic field (B) images
in near-realtime. For this study, results from a statistical study
performed on a robust subsample of the entire SHARP dataset will be
presented. In the framework of the FLARECAST predictor component,
this study focuses, for the first time, on differences between
parameter values found when the radial magnetic field component, Br,
is used instead of the line-of-sight component, Blos. The effect of
active region longitudinal position is discussed, as well as the flare
association of the properties.

---------------------------------------------------------
Title: Solar flares, coronal mass ejections and solar energetic
particle event characteristics
Authors: Papaioannou, Athanasios; Sandberg, Ingmar; Anastasiadis,
Anastasios; Kouloumvakos, Athanasios; Georgoulis, Manolis K.;
Tziotziou, Kostas; Tsiropoula, Georgia; Jiggens, Piers; Hilgers, Alain
2016JSWSC...6A..42P Altcode:
A new catalogue of 314 solar energetic particle (SEP) events extending
over a large time span from 1984 to 2013 has been compiled. The
properties as well as the associations of these SEP events with their
parent solar sources have been thoroughly examined. The properties of
the events include the proton peak integral flux and the fluence for
energies above 10, 30, 60 and 100 MeV. The associated solar events
were parametrized by solar flare (SF) and coronal mass ejection (CME)
characteristics, as well as related radio emissions. In particular,
for SFs: the soft X-ray (SXR) peak flux, the SXR fluence, the
heliographic location, the rise time and the duration were exploited;
for CMEs the plane-of-sky velocity as well as the angular width were
utilized. For radio emissions, type III, II and IV radio bursts were
identified. Furthermore, we utilized element abundances of Fe and
O. We found evidence that most of the SEP events in our catalogue
do not conform to a simple two-class paradigm, with the 73% of them
exhibiting both type III and type II radio bursts, and that a continuum
of event properties is present. Although, the so-called hybrid or mixed
events are found to be present in our catalogue, it was not possible
to attribute each SEP event to a mixed/hybrid sub-category. Moreover,
it appears that the start of the type III burst most often precedes
the maximum of the SF and thus falls within the impulsive phase of the
associated SF. At the same time, type III bursts take place within
≈5.22 min, on average, in advance from the time of maximum of the
derivative of the SXR flux (Neupert effect). We further performed
a statistical analysis and a mapping of the logarithm of the proton
peak flux at E &gt; 10 MeV, on different pairs of the parent solar
source characteristics. This revealed correlations in 3-D space and
demonstrated that the gradual SEP events that stem from the central part
of the visible solar disk constitute a significant radiation risk. The
velocity of the associated CMEs, as well as the SXR peak flux and
fluence, are all fairly significantly correlated to both the proton peak
flux and the fluence of the SEP events in our catalogue. The strongest
correlation to SEP characteristics is manifested by the CME velocity.

---------------------------------------------------------
Title: An observationally-driven kinetic approach to coronal heating
Authors: Moraitis, K.; Toutountzi, A.; Isliker, H.; Georgoulis, M.;
Vlahos, L.; Chintzoglou, G.
2016A&A...596A..56M Altcode: 2016arXiv160307129M; 2016arXiv160307129T
 Aims: Coronal heating through the explosive release of magnetic
energy remains an open problem in solar physics. Recent hydrodynamical
models attempt an investigation by placing swarms of "nanoflares" at
random sites and times in modeled one-dimensional coronal loops. We
investigate the problem in three dimensions, using extrapolated coronal
magnetic fields of observed solar active regions. Methods: We
applied a nonlinear force-free field extrapolation above an observed
photospheric magnetogram of NOAA active region (AR) 11 158. We then
determined the locations, energy contents, and volumes of "unstable"
areas, namely areas prone to releasing magnetic energy due to locally
accumulated electric current density. Statistical distributions of
these volumes and their fractal dimension are inferred, investigating
also their dependence on spatial resolution. Further adopting a
simple resistivity model, we inferred the properties of the fractally
distributed electric fields in these volumes. Next, we monitored the
evolution of 105 particles (electrons and ions) obeying
an initial Maxwellian distribution with a temperature of 10 eV,
by following their trajectories and energization when subjected
to the resulting electric fields. For computational convenience,
the length element of the magnetic-field extrapolation is 1 arcsec,
or 725 km, much coarser than the particles' collisional mean free
path in the low corona (0.1-1 km). Results: The presence of
collisions traps the bulk of the plasma around the unstable volumes,
or current sheets (UCS), with only a tail of the distribution gaining
substantial energy. Assuming that the distance between UCS is similar
to the collisional mean free path we find that the low active-region
corona is heated to 100-200 eV, corresponding to temperatures exceeding
2 MK, within tens of seconds for electrons and thousands of seconds for
ions. Conclusions: Fractally distributed, nanoflare-triggening
fragmented UCS in the active-region corona can heat electrons and ions
with minor enhancements of the local resistivity. This statistical
result is independent from the nature of the extrapolation and the
spatial resolution of the modeled active-region corona. This finding
should be coupled with a complete plasma treatment to determine whether
a quasi-steady temperature similar to that of the ambient corona can be
maintained, either via a kinetic or via a hybrid, kinetic and fluid,
plasma treatment. The finding can also be extended to the quiet solar
corona, provided that the currently undetected nanoflares are frequent
enough to account for the lower (compared to active regions) energy
losses in this case.

---------------------------------------------------------
Title: Near-Sun and 1 AU magnetic field of coronal mass ejections:
a parametric study
Authors: Patsourakos, S.; Georgoulis, M. K.
2016A&A...595A.121P Altcode: 2016arXiv160900134P
 Aims: The magnetic field of coronal mass ejections (CMEs)
determines their structure, evolution, and energetics, as well as their
geoeffectiveness. However, we currently lack routine diagnostics of
the near-Sun CME magnetic field, which is crucial for determining the
subsequent evolution of CMEs. Methods: We recently presented
a method to infer the near-Sun magnetic field magnitude of CMEs and
then extrapolate it to 1 AU. This method uses relatively easy to deduce
observational estimates of the magnetic helicity in CME-source regions
along with geometrical CME fits enabled by coronagraph observations. We
hereby perform a parametric study of this method aiming to assess its
robustness. We use statistics of active region (AR) helicities and CME
geometrical parameters to determine a matrix of plausible near-Sun CME
magnetic field magnitudes. In addition, we extrapolate this matrix
to 1 AU and determine the anticipated range of CME magnetic fields
at 1 AU representing the radial falloff of the magnetic field in
the CME out to interplanetary (IP) space by a power law with index
αB. Results: The resulting distribution of the
near-Sun (at 10 R⊙) CME magnetic fields varies in the
range [0.004, 0.02] G, comparable to, or higher than, a few existing
observational inferences of the magnetic field in the quiescent
corona at the same distance. We also find that a theoretically and
observationally motivated range exists around αB = -1.6
± 0.2, thereby leading to a ballpark agreement between our estimates
and observationally inferred field magnitudes of magnetic clouds (MCs)
at L1. Conclusions: In a statistical sense, our method provides
results that are consistent with observations.

---------------------------------------------------------
Title: Magnetic Helicity Estimations in Models and Observations of
the Solar Magnetic Field. Part I: Finite Volume Methods
Authors: Valori, Gherardo; Pariat, Etienne; Anfinogentov, Sergey;
Chen, Feng; Georgoulis, Manolis K.; Guo, Yang; Liu, Yang; Moraitis,
Kostas; Thalmann, Julia K.; Yang, Shangbin
2016SSRv..201..147V Altcode: 2016SSRv..tmp...68V; 2016arXiv161002193V
Magnetic helicity is a conserved quantity of ideal magneto-hydrodynamics
characterized by an inverse turbulent cascade. Accordingly, it
is often invoked as one of the basic physical quantities driving
the generation and structuring of magnetic fields in a variety of
astrophysical and laboratory plasmas. We provide here the first
systematic comparison of six existing methods for the estimation of
the helicity of magnetic fields known in a finite volume. All such
methods are reviewed, benchmarked, and compared with each other,
and specifically tested for accuracy and sensitivity to errors. To
that purpose, we consider four groups of numerical tests, ranging
from solutions of the three-dimensional, force-free equilibrium, to
magneto-hydrodynamical numerical simulations. Almost all methods are
found to produce the same value of magnetic helicity within few percent
in all tests. In the more solar-relevant and realistic of the tests
employed here, the simulation of an eruptive flux rope, the spread
in the computed values obtained by all but one method is only 3 %,
indicating the reliability and mutual consistency of such methods in
appropriate parameter ranges. However, methods show differences in the
sensitivity to numerical resolution and to errors in the solenoidal
property of the input fields. In addition to finite volume methods,
we also briefly discuss a method that estimates helicity from the
field lines' twist, and one that exploits the field's value at one
boundary and a coronal minimal connectivity instead of a pre-defined
three-dimensional magnetic-field solution.

---------------------------------------------------------
Title: A Comparison of Flare Forecasting Methods. I. Results from
the “All-Clear” Workshop
Authors: Barnes, G.; Leka, K. D.; Schrijver, C. J.; Colak, T.;
Qahwaji, R.; Ashamari, O. W.; Yuan, Y.; Zhang, J.; McAteer, R. T. J.;
Bloomfield, D. S.; Higgins, P. A.; Gallagher, P. T.; Falconer, D. A.;
Georgoulis, M. K.; Wheatland, M. S.; Balch, C.; Dunn, T.; Wagner, E. L.
2016ApJ...829...89B Altcode: 2016arXiv160806319B
Solar flares produce radiation that can have an almost immediate effect
on the near-Earth environment, making it crucial to forecast flares
in order to mitigate their negative effects. The number of published
approaches to flare forecasting using photospheric magnetic field
observations has proliferated, with varying claims about how well
each works. Because of the different analysis techniques and data
sets used, it is essentially impossible to compare the results from
the literature. This problem is exacerbated by the low event rates of
large solar flares. The challenges of forecasting rare events have long
been recognized in the meteorology community, but have yet to be fully
acknowledged by the space weather community. During the interagency
workshop on “all clear” forecasts held in Boulder, CO in 2009,
the performance of a number of existing algorithms was compared
on common data sets, specifically line-of-sight magnetic field and
continuum intensity images from the Michelson Doppler Imager, with
consistent definitions of what constitutes an event. We demonstrate
the importance of making such systematic comparisons, and of using
standard verification statistics to determine what constitutes a good
prediction scheme. When a comparison was made in this fashion, no one
method clearly outperformed all others, which may in part be due to the
strong correlations among the parameters used by different methods to
characterize an active region. For M-class flares and above, the set
of methods tends toward a weakly positive skill score (as measured
with several distinct metrics), with no participating method proving
substantially better than climatological forecasts.

---------------------------------------------------------
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
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: A Robust Method to Predict the Near-Sun and Interplanetary
Magnetic Field Strength of Coronal Mass Ejections: Parametric and
Case Studies
Authors: Patsourakos, Spiros; Georgoulis, Manolis K.
2016cosp...41E1531P Altcode:
Predicting the near-Sun, and particularly the Interplanetary (IP),
magnetic field structure of Coronal Mass Ejections (CMEs) and
interplanetary counterparts (ICMEs) is a topic of intense research
activity. This is because Earth-directed CMEs with strong southward
magnetic fields are responsible for the most powerful geomagnetic
storms. We have recently developed a simple two-tier method to
predict the magnetic field strength of CMEs in the outer corona
and in the IP medium, using as input the magnetic-helicity budget
of the source solar active region and stereoscopic coronagraphic
observations. Near-Sun CME magnetic fields are obtained by utilizing
the principle of magnetic helicity conservation of flux-rope CMEs
for coronagraphic observations. Interplanetary propagation of the
inferred values is achieved by employing power-law prescriptions of the
radial evolution of the CME-ICME magnetic fields. We hereby present a
parametric study of our method, based on the observed statistics of
input parameters, to infer the anticipated range of values for the
near-Sun and interplanetary CME-ICME magnetic fields. This analysis
is complemented by application of our method to several well-observed
major CME-ICME events.

---------------------------------------------------------
Title: Solar Flare Prediction Science-to-Operations: the ESA/SSA
SWE A-EFFort Service
Authors: Georgoulis, Manolis K.; Tziotziou, Konstantinos; Themelis,
Konstantinos; Magiati, Margarita; Angelopoulou, Georgia
2016cosp...41E.656G Altcode:
We attempt a synoptical overview of the scientific origins of the
Athens Effective Solar Flare Forecasting (A-EFFort) utility and
the actions taken toward transitioning it into a pre-operational
service of ESA's Space Situational Awareness (SSA) Programme. The
preferred method for solar flare prediction, as well as key efforts
to make it function in a fully automated environment by coupling
calculations with near-realtime data-downloading protocols (from the
Solar Dynamics Observatory [SDO] mission), pattern recognition (solar
active-region identification) and optimization (magnetic connectivity
by simulated annealing) will be highlighted. In addition, the entire
validation process of the service will be described, with its results
presented. We will conclude by stressing the need for across-the-board
efforts and synergistic work in order to bring science of potentially
limited/restricted interest into realizing a much broader impact
and serving the best public interests. The above presentation was
partially supported by the ESA/SSA SWE A-EFFort project, ESA Contract
No. 4000111994/14/D/MRP. Special thanks go to the ESA Project Officers
R. Keil, A. Glover, and J.-P. Luntama (ESOC), M. Bobra and C. Balmer
of the SDO/HMI team at Stanford University, and M. Zoulias at the
RCAAM of the Academy of Athens for valuable technical help.

---------------------------------------------------------
Title: Predicting the near-Sun and Interplanetary Magnetic Field of
CMEs using photospheric magnetograms and coronagraph images
Authors: Patsourakos, Spiros; Georgoulis, Manolis
2016EGUGA..18.4784P Altcode:
Earth-directed Coronal Mass Ejections (CMEs) containing a strong
southward magnetic-field component upon arrival at 1 AU statistically
account for the most powerful geomagnetic storms. Unfortunately, though,
we currently lack routine diagnostics of the magnetic field of CMEs
and its evolution in the inner heliosphere and the interplanetary (IP)
medium. We hereby present a simple, yet powerful and easy-to-implement,
method to deduce the near-Sun and IP magnetic field entrained in CMEs,
by using photospheric magnetograms of the solar source regions and
multi-viewpoint coronagraph images of the corresponding CMEs. The
method relies on the principle of magnetic-helicity conservation
in low plasma-beta, flux-rope CMEs and a power-law prescription of
the radial evolution of the CME magnetic field in the IP medium. We
outline a parametric study based on the observed statistics of input
parameters to calculate a matrix of magnetic-field solutions for 10000
synthetic CMEs. The robustness and possible limitations / ramifications
of the method are deduced by a comparison with the distributions of
the predicted CME-ICME magnetic fields at 0.3 and 1 AU using actual
Messenger and ACE published observations.

---------------------------------------------------------
Title: 25 Years of Self-organized Criticality: Numerical Detection
Methods
Authors: McAteer, R. T. James; Aschwanden, Markus J.; Dimitropoulou,
Michaila; Georgoulis, Manolis K.; Pruessner, Gunnar; Morales, Laura;
Ireland, Jack; Abramenko, Valentyna
2016SSRv..198..217M Altcode: 2015SSRv..tmp...31M; 2015arXiv150608142M
The detection and characterization of self-organized criticality
(SOC), in both real and simulated data, has undergone many
significant revisions over the past 25 years. The explosive
advances in the many numerical methods available for detecting,
discriminating, and ultimately testing, SOC have played a critical
role in developing our understanding of how systems experience and
exhibit SOC. In this article, methods of detecting SOC are reviewed;
from correlations to complexity to critical quantities. A description
of the basic autocorrelation method leads into a detailed analysis
of application-oriented methods developed in the last 25 years. In
the second half of this manuscript space-based, time-based and
spatial-temporal methods are reviewed and the prevalence of power
laws in nature is described, with an emphasis on event detection and
characterization. The search for numerical methods to clearly and
unambiguously detect SOC in data often leads us outside the comfort
zone of our own disciplines—the answers to these questions are often
obtained by studying the advances made in other fields of study. In
addition, numerical detection methods often provide the optimum link
between simulations and experiments in scientific research. We seek
to explore this boundary where the rubber meets the road, to review
this expanding field of research of numerical detection of SOC systems
over the past 25 years, and to iterate forwards so as to provide some
foresight and guidance into developing breakthroughs in this subject
over the next quarter of a century.

---------------------------------------------------------
Title: The Major Geoeffective Solar Eruptions of 2012 March 7:
Comprehensive Sun-to-Earth Analysis
Authors: Patsourakos, S.; Georgoulis, M. K.; Vourlidas, A.; Nindos,
A.; Sarris, T.; Anagnostopoulos, G.; Anastasiadis, A.; Chintzoglou,
G.; Daglis, I. A.; Gontikakis, C.; Hatzigeorgiu, N.; Iliopoulos, A. C.;
Katsavrias, C.; Kouloumvakos, A.; Moraitis, K.; Nieves-Chinchilla, T.;
Pavlos, G.; Sarafopoulos, D.; Syntelis, P.; Tsironis, C.; Tziotziou,
K.; Vogiatzis, I. I.; Balasis, G.; Georgiou, M.; Karakatsanis, L. P.;
Malandraki, O. E.; Papadimitriou, C.; Odstrčil, D.; Pavlos, E. G.;
Podlachikova, O.; Sandberg, I.; Turner, D. L.; Xenakis, M. N.; Sarris,
E.; Tsinganos, K.; Vlahos, L.
2016ApJ...817...14P Altcode:
During the interval 2012 March 7-11 the geospace experienced a
barrage of intense space weather phenomena including the second
largest geomagnetic storm of solar cycle 24 so far. Significant
ultra-low-frequency wave enhancements and relativistic-electron dropouts
in the radiation belts, as well as strong energetic-electron injection
events in the magnetosphere were observed. These phenomena were
ultimately associated with two ultra-fast (&gt;2000 km s-1)
coronal mass ejections (CMEs), linked to two X-class flares launched
on early 2012 March 7. Given that both powerful events originated from
solar active region NOAA 11429 and their onsets were separated by less
than an hour, the analysis of the two events and the determination
of solar causes and geospace effects are rather challenging. Using
satellite data from a flotilla of solar, heliospheric and magnetospheric
missions a synergistic Sun-to-Earth study of diverse observational
solar, interplanetary and magnetospheric data sets was performed. It was
found that only the second CME was Earth-directed. Using a novel method,
we estimated its near-Sun magnetic field at 13 R⊙ to be
in the range [0.01, 0.16] G. Steep radial fall-offs of the near-Sun
CME magnetic field are required to match the magnetic fields of the
corresponding interplanetary CME (ICME) at 1 AU. Perturbed upstream
solar-wind conditions, as resulting from the shock associated with the
Earth-directed CME, offer a decent description of its kinematics. The
magnetospheric compression caused by the arrival at 1 AU of the shock
associated with the ICME was a key factor for radiation-belt dynamics.

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Title: 25 Years of Self-Organized Criticality: Solar and Astrophysics
Authors: Aschwanden, Markus J.; Crosby, Norma B.; Dimitropoulou,
Michaila; Georgoulis, Manolis K.; Hergarten, Stefan; McAteer, James;
Milovanov, Alexander V.; Mineshige, Shin; Morales, Laura; Nishizuka,
Naoto; Pruessner, Gunnar; Sanchez, Raul; Sharma, A. Surja; Strugarek,
Antoine; Uritsky, Vadim
2016SSRv..198...47A Altcode: 2014arXiv1403.6528A; 2014SSRv..tmp...29A
Shortly after the seminal paper "Self-Organized Criticality: An
explanation of 1/ f noise" by Bak et al. (1987), the idea has been
applied to solar physics, in "Avalanches and the Distribution of Solar
Flares" by Lu and Hamilton (1991). In the following years, an inspiring
cross-fertilization from complexity theory to solar and astrophysics
took place, where the SOC concept was initially applied to solar flares,
stellar flares, and magnetospheric substorms, and later extended to
the radiation belt, the heliosphere, lunar craters, the asteroid belt,
the Saturn ring, pulsar glitches, soft X-ray repeaters, blazars,
black-hole objects, cosmic rays, and boson clouds. The application
of SOC concepts has been performed by numerical cellular automaton
simulations, by analytical calculations of statistical (powerlaw-like)
distributions based on physical scaling laws, and by observational
tests of theoretically predicted size distributions and waiting
time distributions. Attempts have been undertaken to import physical
models into the numerical SOC toy models, such as the discretization
of magneto-hydrodynamics (MHD) processes. The novel applications
stimulated also vigorous debates about the discrimination between SOC
models, SOC-like, and non-SOC processes, such as phase transitions,
turbulence, random-walk diffusion, percolation, branching processes,
network theory, chaos theory, fractality, multi-scale, and other
complexity phenomena. We review SOC studies from the last 25 years
and highlight new trends, open questions, and future challenges,
as discussed during two recent ISSI workshops on this theme.

---------------------------------------------------------
Title: Preface: Advances in solar physics
Authors: Georgoulis, Manolis K.; Nakariakov, Valery M.
2015AdSpR..56.2677G Altcode:
The idea for this special issue of Advances in Space Research (ASR)
was formulated during the 14th European Solar Physics Meeting (ESPM-14)
that took place in Dublin, Ireland in September 2014. Since ASR does not
publish conference proceedings, it was decided to extend a general call
to the international solar-physics community for manuscripts pertinent
to the following thematic areas: New and upcoming heliospheric
observational and data assimilation facilities.

---------------------------------------------------------
Title: Analysing the Effects of Apodizing Windows on Local Correlation
Tracking Using Nirvana Simulations of Convection
Authors: Louis, Rohan E.; Ravindra, B.; Georgoulis, Manolis K.;
Küker, Manfred
2015SoPh..290.1135L Altcode: 2015arXiv150202530L; 2015SoPh..tmp...25L
We employ different shapes of apodizing windows in the local
correlation tracking (LCT) routine to retrieve horizontal velocities
using numerical simulations of convection. LCT was applied on a time
sequence of temperature maps generated by the Nirvana code with four
different apodizing windows, Gaussian, Lorentzian, trapezoidal, and
triangular, with varying widths. In terms of correlations (between
the LCT-retrieved and simulated flow field), the triangular and the
trapezoidal perform the best and worst, respectively. By segregating
the intrinsic velocities in the simulations on the basis of their
magnitudes, we find that for all windows a significantly higher
correlation is obtained for the intermediate and high-velocity bins and
only modest or weak values in the low-velocity bins. The differences
between the LCT-retrieved and simulated flow fields were determined
spatially. They show large residuals at or close to the boundary of
granules. The extent to which the horizontal flow vectors retrieved by
LCT are similar to the simulated values entirely depends on the width
of the central peak of the apodizing window for a given σ. Even though
LCT suffers from a lack of spatial content, as seen in simulations,
its simplicity and speed could serve as a viable first-order tool to
probe horizontal flows. This would be an ideal tool for large data sets.

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Title: Validation and Benchmarking of a Practical Free Magnetic
Energy and Relative Magnetic Helicity Budget Calculation in Solar
Magnetic Structures
Authors: Moraitis, K.; Tziotziou, K.; Georgoulis, M. K.; Archontis, V.
2014SoPh..289.4453M Altcode: 2014arXiv1406.5381M; 2014SoPh..tmp..122M
In earlier works we introduced and tested a nonlinear force-free
(NLFF) method designed to self-consistently calculate the coronal
free magnetic energy and the relative magnetic helicity budgets of
observed solar magnetic structures. In principle, the method requires
only a single, photospheric or low-chromospheric, vector magnetogram
of a quiet-Sun patch or an active region and performs calculations
without three-dimensional magnetic and velocity-field information. In
this work we strictly validate this method using three-dimensional
coronal magnetic fields. Benchmarking employs both synthetic,
three-dimensional magnetohydrodynamic simulations and nonlinear
force-free field extrapolations of the active-region solar corona. Our
time-efficient NLFF method provides budgets that differ from those of
more demanding semi-analytical methods by a factor of approximately
three, at most. This difference is expected to come from the physical
concept and the construction of the method. Temporal correlations show
more discrepancies that are, however, soundly improved for more complex,
massive active regions, reaching correlation coefficients on the order
of, or exceeding, 0.9. In conclusion, we argue that our NLFF method
can be reliably used for a routine and fast calculation of the free
magnetic energy and relative magnetic helicity budgets in targeted
parts of the solar magnetized corona. As explained in this article and
in previous works, this is an asset that can lead to valuable insight
into the physics and triggering of solar eruptions.

---------------------------------------------------------
Title: Validation of the magnetic energy vs. helicity scaling in
solar magnetic structures
Authors: Tziotziou, K.; Moraitis, K.; Georgoulis, M. K.; Archontis, V.
2014A&A...570L...1T Altcode: 2014arXiv1409.8117T
 Aims: We assess the validity of the free magnetic energy -
relative magnetic helicity diagram for solar magnetic structures. 
Methods: We used two different methods of calculating the free magnetic
energy and the relative magnetic helicity budgets: a classical,
volume-calculation nonlinear force-free (NLFF) method applied to
finite coronal magnetic structures and a surface-calculation NLFF
derivation that relies on a single photospheric or chromospheric vector
magnetogram. Both methods were applied to two different data sets,
namely synthetic active-region cases obtained by three-dimensional
magneto-hydrodynamic (MHD) simulations and observed active-region cases,
which include both eruptive and noneruptive magnetic structures. Results: The derived energy-helicity diagram shows a consistent
monotonic scaling between relative helicity and free energy with
a scaling index 0.84 ± 0.05 for both data sets and calculation
methods. It also confirms the segregation between noneruptive and
eruptive active regions and the existence of thresholds in both free
energy and relative helicity for active regions to enter eruptive
territory. Conclusions: We consider the previously reported
energy-helicity diagram of solar magnetic structures as adequately
validated and envision a significant role of the uncovered scaling in
future studies of solar magnetism.

---------------------------------------------------------
Title: Energy and helicity budgets of solar quiet regions
Authors: Tziotziou, K.; Tsiropoula, G.; Georgoulis, M. K.;
Kontogiannis, I.
2014A&A...564A..86T Altcode: 2014arXiv1403.0730T
 Aims: We investigate the free magnetic energy and relative
magnetic helicity budgets of solar quiet regions. Methods:
Using a novel nonlinear force-free method that requires single solar
vector magnetograms we calculated the instantaneous free magnetic
energy and relative magnetic helicity budgets in 55 quiet-Sun vector
magnetograms. Results: As in a previous work on active regions,
we constructed here for the first time the (free) energy-(relative)
helicity diagram of quiet-Sun regions. We find that quiet-Sun regions
have no dominant sense of helicity and show monotonic correlations
a) between free magnetic energy/relative helicity and magnetic
network area and, consequently, b) between free magnetic energy and
helicity. Free magnetic energy budgets of quiet-Sun regions represent
a rather continuous extension of respective active-region budgets
towards lower values, but the corresponding helicity transition is
discontinuous because of the incoherence of the helicity sense in
contrast to active regions. We furthermore estimated the instantaneous
free magnetic-energy and relative magnetic-helicity budgets of the
entire quiet Sun, as well as the respective budgets over an entire solar
cycle. Conclusions: Derived instantaneous free magnetic energy
budgets and, to a lesser extent, relative magnetic helicity budgets
over the entire quiet Sun are similar to the respective budgets of a
sizeable active region, while total budgets within a solar cycle are
found to be higher than previously reported. Free-energy budgets are
similar to the energy needed to power fine-scale structures residing
at the network, such as mottles and spicules.

---------------------------------------------------------
Title: Free magnetic energy and relative magnetic helicity diagnostics
for the quality of NLFF field extrapolations
Authors: Moraitis, Kostas; Archontis, Vasilis; Tziotziou, Konstantinos;
Georgoulis, Manolis K.
2014cosp...40E2169M Altcode:
We calculate the instantaneous free magnetic energy and relative
magnetic helicity of solar active regions using two independent
approaches: a) a non-linear force-free (NLFF) method that requires
only a single photospheric vector magnetogram, and b) well known
semi-analytical formulas that require the full three-dimensional (3D)
magnetic field structure. The 3D field is obtained either from MHD
simulations, or from observed magnetograms via respective NLFF field
extrapolations. We find qualitative agreement between the two methods
and, quantitatively, a discrepancy not exceeding a factor of 4. The
comparison of the two methods reveals, as a byproduct, two independent
tests for the quality of a given force-free field extrapolation. We find
that not all extrapolations manage to achieve the force-free condition
in a valid, divergence-free, magnetic configuration. This research has
been co-financed by the European Union (European Social Fund - ESF)
and Greek national funds through the Operational Program "Education
and Lifelong Learning" of the National Strategic Reference Framework
(NSRF) - Research Funding Program: Thales. Investing in knowledge
society through the European Social Fund.

---------------------------------------------------------
Title: Irreversibility and the Point of No Return in the Evolution
of Eruptive Active Regions
Authors: Georgoulis, Manolis K.
2014cosp...40E.966G Altcode:
We combine multiple methods and findings to demonstrate that those
eruptive solar active regions that form intense photospheric magnetic
polarity inversion lines (PILs) enter a domain of irreversible
evolution that will unavoidably force them to erupt at least once,
giving rise to a major flare and an associated fast CME. Electric
currents, Lorentz forces, free magnetic energy storage, and magnetic
helicity, all play major roles in bringing the magnetic configuration
on the verge of instability. The inferred irreversibility stems from
the conservative properties of magnetic helicity in high magnetic
Reynolds-number plasmas. In addition, the long-standing and fiercely
debated classification of eruptive magnetic structures into sheared
arcades and flux ropes is found to be of relatively little meaning:
by means of the evolution above, the simplest possible sheared-arcade
structure may gradually evolve into a flux rope susceptible to the
helical-kink and the torus instabilities, among other destabilization
mechanisms. Research partially supported by the EU Seventh Framework
Programme under grant agreement No. PIRG07-GA-2010-268245 and by the
European Union Social Fund (ESF) and Greek national funds through the
Operational Program "Education and Lifelong Learning" of the National
Strategic Reference Framework (NSRF) - Research Funding Program:
Thales. Investing in knowledge society through the European Social Fund.

---------------------------------------------------------
Title: Using Magnetic Helicity Diagnostics to Determine the Nature
of Solar Active-Region Formation
Authors: Georgoulis, Manolis K.
2014cosp...40E.967G Altcode:
Employing a novel nonlinear force-free (NLFF) method that
self-consistently infers instantaneous free magnetic-energy and
relative magnetic-helicity budgets from single photospheric vector
magnetograms, we recently constructed the magnetic energy-helicity
(EH) diagram of solar active regions. The EH diagram implies dominant
relative helicities of left-handed or right-handed chiralities for
the great majority of active regions. The amplitude (budget) of these
helicities scales monotonically with the free magnetic energy. This
constructive, strongly preferential accumulation of a certain sense
of magnetic helicity seems to disqualify recently proposed mechanisms
relying on a largely random near-surface convection for the formation
of the great majority of active regions. The existing qualitative
formation mechanism for these regions remains the conventional
Omega-loop emergence following a buoyant ascension from the bottom
of the convection zone. However, exceptions to this rule include
even eruptive active regions: NOAA AR 11283 is an obvious outlier
to the EH diagram, involving significant free magnetic energy with a
small relative magnetic helicity. Relying on a timeseries of vector
magnetograms of this region, our methodology shows nearly canceling
amounts of both senses of helicity and an overall course from a weakly
left-handed to a weakly right-handed structure, in the course of which
a major eruption occurs. For this and similarly behaving active regions
the latest near-surface formation scenario might conceivably be employed
successfully. Research partially supported by the EU Seventh Framework
Programme under grant agreement No. PIRG07-GA-2010-268245 and by the
European Union Social Fund (ESF) and Greek national funds through the
Operational Program "Education and Lifelong Learning" of the National
Strategic Reference Framework (NSRF) - Research Funding Program:
Thales. Investing in knowledge society through the European Social Fund.

---------------------------------------------------------
Title: Higher topological invariants of magnetic field lines:
observational aspects
Authors: Illarionov, Egor; Smirnov, Alexander; Georgoulis, Manolis K.;
Sokoloff, Dmitry; Akhmet'ev, Peter
2014cosp...40E1270I Altcode:
Topology of magnetic field lines is directly involved in
magnetohydrodynamic (MHD) theorems and equations. Being an invariant of
motion in ideal MHD conditions, the magnetic field-line topology is a
natural obstacle to the relaxation of magnetic field into a current-free
(potential) field and contrariwise limits a dynamo generation. Usage
of these conservational laws and writing of numerical relations require
a quantification of topology. One of the simplest existing measures of
magnetic topology is the mutual magnetic helicity, that expresses the
combined action of interaction and linkage between different magnetic
field lines. For practical purposes there exists the revised concept
of relative magnetic helicity, that allows to estimate the complexity
of field-line topology in case of open volume, i.e. when magnetic
lines cross the boundaries of given 3D region. At the same time this
concept remains a simple interpretation of linkage number in terms
of individual lines. Our point however is that magnetic helicity is
far from being unique or comprehensive quantification of magnetic
field-line topology. To improve the situation we introduce a set of
higher invariants which extends the idea of relative helicity and
provides a new means to describe the magnetic field-line topology. To
practically study the possibility of implementation of higher
topological invariants we reconstruct several moments of mutual helicity
from observed solar vector magnetograms with extrapolated magnetic field
above the photosphere and discuss to what extent such knowledge could
be instructive for understanding of the solar magnetic field evolution.

---------------------------------------------------------
Title: Free magnetic energy and relative magnetic helicity in active
and quiet solar regions and their role in solar dynamics
Authors: Tziotziou, Konstantinos; Archontis, Vasilis; Tsiropoula,
Georgia; Georgoulis, Manolis K.; Moraitis, Kostas; Kontogiannis,
Ioannis
2014cosp...40E3428T Altcode:
We present a novel non-linear force-free method for the calculation of
the instantaneous free magnetic energy and relative magnetic helicity
budgets of a solar region from a single photospheric/chromospheric
vector magnetogram. Our objective is to study the role of these
quantities both in solar eruptions and in quiet-Sun dynamics. The
validity of the method is tested using both observations and synthetic
magnetohydrodynamical (MHD) models. The method is applied for the
derivation of the energy-helicity (EH) diagram of solar active regions
(ARs) from a sample of 162 vector magnetograms corresponding to 42
different ARs, suggesting the existence of 4×10(31) erg and 2×10(42)
Mx(2) thresholds in free energy and relative helicity, respectively, for
ARs to enter eruptive territory. Furthermore, the dynamical evolution
of both quantities in eruptive NOAA AR 11158, using a high-cadence
5-day time series of vector magnetograms, suggests the formation of
increasingly helical pre-eruption structures and a causal relation
between flares and Coronal Mass Ejections (CMEs). The method is
also used to derive helicity and energy budgets in quiet Sun regions
and construct the respective EH diagram. Our results highlight the
importance of both energy and helicity in AR evolution and quiet-Sun
dynamics and instigate further research on the underlying physics with
three-dimensional MHD models. This work is supported by EU's Seventh
Framework Programme via a Marie Curie Fellowship.

---------------------------------------------------------
Title: Toward an Efficient Prediction of Solar Flares: Which
Parameters, and How?
Authors: Georgoulis, M. K.
2013Entrp..15.5022G Altcode:
Solar flare prediction has become a forefront topic in contemporary
solar physics, with numerous published methods relying on numerous
predictive parameters, that can even be divided into parameter
classes. Attempting further insight, we focus on two popular classes
of flare-predictive parameters, namely multiscale (i.e., fractal
and multifractal) and proxy (i.e., morphological) parameters, and we
complement our analysis with a study of the predictive capability of
fundamental physical parameters (i.e., magnetic free energy and relative
magnetic helicity). Rather than applying the studied parameters to
a comprehensive statistical sample of flaring and non-flaring active
regions, that was the subject of our previous studies, the novelty of
this work is their application to an exceptionally long and high-cadence
time series of the intensely eruptive National Oceanic and Atmospheric
Administration (NOAA) active region (AR) 11158, observed by the
Helioseismic and Magnetic Ima! ger on board the Solar Dynamics
Observatory. Aiming for a detailed study of the temporal evolution of
each parameter, we seek distinctive patterns that could be associated
with the four largest flares in the AR in the course of its five-day
observing interval. We find that proxy parameters only tend to show
preflare impulses that are practical enough to warrant subsequent
investigation with sufficient statistics. Combining these findings
with previous results, we conclude that: (i) carefully constructed,
physically intuitive proxy parameters may be our best asset toward
an efficient future flare-forecasting; and (ii) the time series
of promising parameters may be as important as their instantaneous
values. Value-based prediction is the only approach followed so far. Our
results call for novel signal and/or image processing techniques to
efficiently utilize combined amplitude and temporal-profile information
to optimize the inferred solar-flare probabilities.

---------------------------------------------------------
Title: Magnetic helicity and free energy in solar active regions
Authors: Moraitis, K.; Georgoulis, M.; Tziotziou, K.; Archontis, V.
2013hell.confS..21M Altcode:
We study the evolution of the non-potential free magnetic energy
and relative magnetic helicity budgets in solar active regions
(ARs). For this we use a time-series of a three-dimensional, synthetic
AR produced by magnetohydrodynamical (MHD) simulations. As a first
step, we calculate the potential magnetic field that has the same
normal components with the MHD field along all boundaries of the AR,
by solving Laplace's equation. The free magnetic energy of the AR is
then easily derived. From the two fields, MHD and potential one, we
calculate the corresponding vector potentials with a recently proposed
integration method. The knowledge of both fields and their respective
vector potentials throughout the AR, allows us to estimate the relative
magnetic helicity budget of the AR. Following this procedure for each
snapshot of the AR, we reconstruct the evolution of free energy and
helicity in the AR. Our method reproduces, for a synthetic AR, the
energy/helicity relations known to hold in real active regions.

---------------------------------------------------------
Title: A statistical study of current-sheet formation above solar
active regions based on selforganized criticality
Authors: Dimitropoulou, M.; Isliker, H.; Vlahos, L.; Georgoulis, M.;
Anastasiadis, A.; Toutountzi, A.
2013hell.conf...16D Altcode:
We treat flaring solar active regions as physical systems having
reached the self-organized critical state. Their evolving magnetic
configurations in the low corona may satisfy an instability criterion,
related to the excession of a specific threshold in the curl of the
magnetic field. This imposed instability criterion implies an almost
zero resistivity everywhere in the solar corona, except in regions where
magnetic-field discontinuities and. hence, local currents, reach the
critical value. In these areas, current-driven instabilities enhance
the resistivity by many orders of magnitude forming structures which
efficiently accelerate charged particles. Simulating the formation
of such structures (thought of as current sheets) via a refined SOC
cellular-automaton model provides interesting information regarding
their statistical properties. It is shown that the current density in
such unstable regions follows power-law scaling. Furthermore, the size
distribution of the produced current sheets is best fitted by power
laws, whereas their formation probability is investigated against
the photospheric magnetic configuration (e.g. Polarity Inversion
Lines, Plage). The average fractal dimension of the produced current
sheets is deduced depending on the selected critical threshold. The
above-mentioned statistical description of intermittent electric
field structures can be used by collisional relativistic test particle
simulations, aiming to interpret particle acceleration in flaring active
regions and in strongly turbulent media in astrophysical plasmas. The
above work is supported by the Hellenic National Space Weather Research
Network (HNSWRN) via the THALIS Programme.

---------------------------------------------------------
Title: Free Magnetic Energy and Helicity in Active and Quiet Solar
Regions and their role in Solar
Authors: Tziotziou, K.; Georgoulis, M. K.; Tsiropoula, G.; Moraitis,
K.; Kontogiannis, I.
2013hell.conf....6T Altcode:
We present a novel nonlinear force-free method designed to calculate
the instantaneous free magnetic energy and relative magnetic helicity
budgets of a solar region from a single photospheric/chromospheric
vector magnetogram of the region. Our objective is to study the role of
these quantities in solar eruptions and quiet-Sun dynamics. We apply the
method to (1) derive the energy/helicity diagram of solar active regions
from a sample of 162 vector magnetograms corresponding to 42 different
active regions (ARs), suggesting that there exist 4 1031 erg and 2 1042
Mx2 thresholds in free energy and relative helicity, respectively, for
ARs to enter eruptive territory, (2) study the dynamics of eruptive NOAA
AR 11158 using a high-cadence 5-day time series of vector magnetograms,
suggesting the formation of increasingly helical pre-eruption structures
and a causal relation between flares and Coronal Mass Ejections (CMEs)
and, (3) derive helicity and energy budgets in quiet Sun regions and
construct the respective energy/helicity diagram. Our results highlight
the importance of these two parameters in AR evolution and quiet-Sun
dynamics and instigate further research including detailed analysis
with synthetic, magnetohydrodynamical models. This work is supported by
EU's Seventh Framework Programme via a Marie Curie Fellowship and by
the Hellenic National Space Weather Research Network (HNSWRN) via the
THALIS Programme.

---------------------------------------------------------
Title: Genesis of Free Magnetic Energy and Helicity in Solar Active
Regions and their Role in Solar Eruptions
Authors: Georgoulis, M.
2013hell.confQ..17G Altcode:
Eruptive solar magnetic configurations are revisited in view of their
magnetic energy and (relative) magnetic helicity budgets. We calculate
these budgets via a novel self-consistent technique that requires
neither photospheric flow velocity fields nor three-dimensional
coronal magnetic field extrapolations of the observed photospheric
structure. A single vector magnetogram of the structure is sufficient
for the calculation of the instantaneous electric-current-induced
(free) magnetic energy and helicity budgets. We apply the method to
the intensely eruptive NOAA active region (AR) 11158 and report on
the following findings: (1) significant budgets of free magnetic
energy and helicity are developed in the AR, sufficient to power
more than the observed eruptions; (2) eruption-related decreases of
both budgets are noted, allowing estimation of the energy/helicity
budgets of the eruptions themselves; (3) the AR complies with our
previously and independently introduced energy/helicity diagram of
solar active regions; and (4) a non-ideal transformation of mutual
free energy and helicity terms into respective self terms results
in increasingly helical pre-eruption structures. These findings
suggest a new causal view of solar eruptions and the pre-eruption
evolution of solar active regions. Parallel analysis with synthetic,
magnetohydrodynamical models of active regions is underway, aiming to
scrutinize our data analysis and subsequent interpretation. This work
is supported by EU's Seventh Framework Programme via a Marie Curie
Fellowship and by the Hellenic National Space Weather Research Network
(HNSWRN) via the THALIS Programme.

---------------------------------------------------------
Title: A Data-Driven, Integrated Flare Model Based on Self-Organized
Criticality
Authors: Dimitropoulou, M.; Isliker, H.; Vlahos, L.; Georgoulis, M.
2013hell.conf....7D Altcode:
We interpret solar flares as events originating in solar active regions
having reached the self-organized critical state, by alternatively
using two versions of an "integrated flare model" - one static and
one dynamic. In both versions the initial conditions are derived
from observations aiming to investigate whether well-known scaling
laws observed in the distribution functions of characteristic flare
parameters are reproduced after the self-organized critical state
has been reached. In the static model, we first apply a nonlinear
force-free extrapolation that reconstructs the three-dimensional
magnetic fields from two-dimensional vector magnetograms. We then locate
magnetic discontinuities exceeding a threshold in the Laplacian of the
magnetic field. These discontinuities are relaxed in local diffusion
events, implemented in the form of cellular-automaton evolution
rules. Subsequent loading and relaxation steps lead the system to
self-organized criticality, after which the statistical properties of
the simulated events are examined. In the dynamic version we deploy an
enhanced driving mechanism, which utilizes the observed evolution of
active regions, making use of sequential vector magnetograms. We first
apply the static cellular automaton model to consecutive solar vector
magnetograms until the self-organized critical state is reached. We
then evolve the magnetic field inbetween these processed snapshots
through spline interpolation, acting as a natural driver in the dynamic
model. The identification of magnetically unstable sites as well as
their relaxation follow the same rules as in the static model after each
interpolation step. Subsequent interpolation/driving and relaxation
steps cover all transitions until the end of the sequence. Physical
requirements, such as the divergence-free condition for the magnetic
field vector, are approximately satisfied in both versions of the
model. We obtain robust power laws in the distribution functions of
the modelled flaring events with scaling indices in good agreement
with observations. We therefore conclude that well-known statistical
properties of flares are reproduced after active regions reach
self-organized criticality. The significant enhancement in both the
static and the dynamic integrated flare models is that they initiate
the simulation from observations, thus facilitating energy calculation
in physical units. Especially in the dynamic version of the model,
the driving of the system is based on observed, evolving vector
magnetograms, allowing for the separation between MHD and kinetic
timescales through the assignment of distinct MHD timestamps to each
interpolation step.

---------------------------------------------------------
Title: Acceleration and solar origin of solar energetic particles
observed by SREM units
Authors: Anastasiadis, A.; Georgoulis, M.; Daglis, I.; Sandberg, I.;
Nieminen, P.
2013hell.confQ..14A Altcode:
Within the previous solar cycle 23, SREM units onboard ESA's INTEGRAL
and Rosetta spacecraft detected several tens of Solar Energetic Particle
Events (SEPEs) and accurately pinpointed their onset, rise, and decay
times. We have undertaken a detailed study to determine the solar
sources and the subsequent interplanetary coronal mass ejections (ICMEs)
that gave rise to these events, as well as the timing of SEPEs with
regard to the onset of possible geomagnetic activity triggered by these
ICMEs. We find that virtually all SREM SEPEs can be associated with
CME-driven shocks. Moreover, for a number of wellstudied INTEGRAL/SREM
SEPEs we see an association between the SEPE peak and the shock passage
at L1, subject to the heliographic location of the source solar active
region. Shortly after the SEPE peak (typically within a few hours), the
ICMEdriven modulation of the magnetosphere kicks in, often associated
with a dip of the Dst index, indicating storm conditions in geospace. In
essence we find that SREM SEPEs can be seamlessly fit into a coherent
and consistent heliophysical interpretation of solar eruptions all the
way from Sun to Earth. Their contribution to space-weather forecasting
may be significant and warrants additional investigation.

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Title: Particle acceleration and nanoflare heating in coronal loops
Authors: Gontikakis, C.; Patsourakos, S.; Efthymiopoulos, C.;
Anastasiadis, A.; Georgoulis, M.
2013hell.conf...18G Altcode:
We model nanoflare heating of extrapolated active-region coronal loops
via the acceleration of electrons and protons in Harris-type current
sheets. The kinetic energy of the accelerated particles is estimated
using semi-analytical and test-particle-tracing approaches. Vector
magnetograms and photospheric Doppler velocity maps of NOAA active
region 09114, recorded by the Imaging Vector Magnetograph (IVM),
were used for this analysis in order to compute a current-free field
extrapolation of the active-region corona. The corresponding Poynting
fluxes at the footpoints of 5000 extrapolated coronal loops were then
calculated. Assuming that reconnecting current sheets develop along
these loops, we utilized previous results to estimate the kinetic-energy
gain of the accelerated particles and we related this energy to
nanoflare heating and macroscopic loop characteristics. Kinetic
energies of 0.1 to 8~keV (for electrons) and 0.3 to 470~keV (for
protons) were found to cause heating rates ranging from 10^-6 to 1
erg s^-1 cm^-3. Hydrodynamic simulations show that such heating rates
can sustain plasma in coronal conditions inside the loops and generate
plasma thermal distributions which are consistent with active region
observations. We concluded the analysis by computing the form of Xray
spectra generated by the accelerated electrons using the thick target
approach that were found to be in agreement with observed X-ray spectra,
thus supporting the plausibility of our nanoflare-heating scenario. This
work is supported by EU's Seventh Framework Programme via a Marie Curie
Fellowship and by the Hellenic National Space Weather Research Network
(HNSWRN) via the THALIS Programme.

---------------------------------------------------------
Title: Particle Acceleration in a Statistically Modeled Solar
Active-Region Corona
Authors: Toutounzi, A.; Vlahos, L.; Isliker, H.; Dimitropoulou, M.;
Anastasiadis, A.; Georgoulis, M.
2013hell.conf....8T Altcode:
Elaborating a statistical approach to describe the spatiotemporally
intermittent electric field structures formed inside a flaring solar
active region, we investigate the efficiency of such structures
in accelerating charged particles (electrons). The large-scale
magnetic configuration in the solar atmosphere responds to the strong
turbulent flows that convey perturbations across the active region by
initiating avalanche-type processes. The resulting unstable structures
correspond to small-scale dissipation regions hosting strong electric
fields. Previous research on particle acceleration in strongly turbulent
plasmas provides a general framework for addressing such a problem. This
framework combines various electromagnetic field configurations obtained
by magnetohydrodynamical (MHD) or cellular automata (CA) simulations,
or by employing a statistical description of the field's strength
and configuration with test particle simulations. Our objective is to
complement previous work done on the subject. As in previous efforts,
a set of three probability distribution functions describes our
ad-hoc electromagnetic field configurations. In addition, we work on
data-driven 3D magnetic field extrapolations. A collisional relativistic
test-particle simulation traces each particle's guiding center
within these configurations. We also find that an interplay between
different electron populations (thermal/non-thermal, ambient/injected)
in our simulations may also address, via a re-acceleration mechanism,
the so called `number problem'. Using the simulated particle-energy
distributions at different heights of the cylinder we test our results
against observations, in the framework of the collisional thick target
model (CTTM) of solar hard X-ray (HXR) emission. The above work is
supported by the Hellenic National Space Weather Research Network
(HNSWRN) via the THALIS Programme.

---------------------------------------------------------
Title: Sun-to-Earth Analysis of a Major Geoeffective Solar Eruption
within the Framework of the
Authors: Patsourakos, S.; Vlahos, L.; Georgoulis, M.; Tziotziou,
K.; Nindos, A.; Podladchikova, O.; Vourlidas, A.; Anastasiadis, A.;
Sandberg, I.; Tsinganos, K.; Daglis, I.; Hillaris, A.; Preka-Papadema,
P.; Sarris, M.; Sarris, T.
2013hell.conf...10P Altcode:
Transient expulsions of gigantic clouds of solar coronal plasma into
the interplanetary space in the form of Coronal Mass Ejections (CMEs)
and sudden, intense flashes of electromagnetic radiation, solar flares,
are well-established drivers of the variable Space Weather. Given the
innate, intricate links and connections between the solar drivers and
their geomagnetic effects, synergistic efforts assembling all pieces
of the puzzle along the Sun-Earth line are required to advance our
understanding of the physics of Space Weather. This is precisely the
focal point of the Hellenic National Space Weather Research Network
(HNSWRN) under the THALIS Programme. Within the HNSWRN framework,
we present here the first results from a coordinated multi-instrument
case study of a major solar eruption (X5.4 and X1.3 flares associated
with two ultra-fast (&gt;2000 km/s) CMEs) which were launched early
on 7 March 2012 and triggered an intense geomagnetic storm (min Dst
=-147 nT) approximately two days afterwards. Several elements of
the associated phenomena, such as the flare and CME, EUV wave, WL
shock, proton and electron event, interplanetary type II radio burst,
ICME and magnetic cloud and their spatiotemporal relationships and
connections are studied all way from Sun to Earth. To this end, we
make use of satellite data from a flotilla of solar, heliospheric and
magnetospheric missions and monitors (e.g., SDO, STEREO, WIND, ACE,
Herschel, Planck and INTEGRAL). We also present our first steps toward
formulating a cohesive physical scenario to explain the string of the
observables and to assess the various physical mechanisms than enabled
and gave rise to the significant geoeffectiveness of the eruption.

---------------------------------------------------------
Title: Interpreting Eruptive Behavior in NOAA AR 11158 via the
Region's Magnetic Energy and Relative-helicity Budgets
Authors: Tziotziou, Kostas; Georgoulis, Manolis K.; Liu, Yang
2013ApJ...772..115T Altcode: 2013arXiv1306.2135T
In previous works, we introduced a nonlinear force-free method
that self-consistently calculates the instantaneous budgets of free
magnetic energy and relative magnetic helicity in solar active regions
(ARs). Calculation is expedient and practical, using only a single
vector magnetogram per computation. We apply this method to a time
series of 600 high-cadence vector magnetograms of the eruptive NOAA
AR 11158 acquired by the Helioseismic and Magnetic Imager on board the
Solar Dynamics Observatory over a five-day observing interval. Besides
testing our method extensively, we use it to interpret the dynamical
evolution in the AR, including eruptions. We find that the AR builds
large budgets of both free magnetic energy and relative magnetic
helicity, sufficient to power many more eruptions than the ones it gave
within the interval of interest. For each of these major eruptions,
we find eruption-related decreases and subsequent free-energy and
helicity budgets that are consistent with the observed eruption (flare
and coronal mass ejection (CME)) sizes. In addition, we find that (1)
evolution in the AR is consistent with the recently proposed (free)
energy-(relative) helicity diagram of solar ARs, (2) eruption-related
decreases occur before the flare and the projected CME-launch times,
suggesting that CME progenitors precede flares, and (3) self terms of
free energy and relative helicity most likely originate from respective
mutual terms, following a progressive mutual-to-self conversion pattern
that most likely stems from magnetic reconnection. This results in the
non-ideal formation of increasingly helical pre-eruption structures
and instigates further research on the triggering of solar eruptions
with magnetic helicity firmly placed in the eruption cadre.

---------------------------------------------------------
Title: Combining Particle Acceleration and Coronal Heating via
Data-constrained Calculations of Nanoflares in Coronal Loops
Authors: Gontikakis, C.; Patsourakos, S.; Efthymiopoulos, C.;
Anastasiadis, A.; Georgoulis, M. K.
2013ApJ...771..126G Altcode: 2013arXiv1305.5195G
We model nanoflare heating of extrapolated active-region coronal loops
via the acceleration of electrons and protons in Harris-type current
sheets. The kinetic energy of the accelerated particles is estimated
using semi-analytical and test-particle-tracing approaches. Vector
magnetograms and photospheric Doppler velocity maps of NOAA active
region 09114, recorded by the Imaging Vector Magnetograph, were
used for this analysis. A current-free field extrapolation of the
active-region corona was first constructed. The corresponding Poynting
fluxes at the footpoints of 5000 extrapolated coronal loops were then
calculated. Assuming that reconnecting current sheets develop along
these loops, we utilized previous results to estimate the kinetic
energy gain of the accelerated particles. We related this energy
to nanoflare heating and macroscopic loop characteristics. Kinetic
energies of 0.1-8 keV (for electrons) and 0.3-470 keV (for protons)
were found to cause heating rates ranging from 10-6 to 1
erg s-1 cm-3. Hydrodynamic simulations show
that such heating rates can sustain plasma in coronal conditions
inside the loops and generate plasma thermal distributions that are
consistent with active-region observations. We concluded the analysis
by computing the form of X-ray spectra generated by the accelerated
electrons using the thick-target approach. These spectra were found
to be in agreement with observed X-ray spectra, thus supporting the
plausibility of our nanoflare-heating scenario.

---------------------------------------------------------
Title: Dynamic data-driven integrated flare model based on
self-organized criticality
Authors: Dimitropoulou, M.; Isliker, H.; Vlahos, L.; Georgoulis, M. K.
2013A&A...553A..65D Altcode:
Context. We interpret solar flares as events originating in active
regions that have reached the self-organized critical state. We describe
them with a dynamic integrated flare model whose initial conditions
and driving mechanism are derived from observations. Aims: We
investigate whether well-known scaling laws observed in the distribution
functions of characteristic flare parameters are reproduced after
the self-organized critical state has been reached. Methods:
To investigate whether the distribution functions of total energy,
peak energy, and event duration follow the expected scaling laws,
we first applied the previously reported static cellular automaton
model to a time series of seven solar vector magnetograms of the NOAA
active region 8210 recorded by the Imaging Vector Magnetograph on May
1 1998 between 18:59 UT and 23:16 UT until the self-organized critical
state was reached. We then evolved the magnetic field between these
processed snapshots through spline interpolation, mimicking a natural
driver in our dynamic model. We identified magnetic discontinuities
that exceeded a threshold in the Laplacian of the magnetic field after
each interpolation step. These discontinuities were relaxed in local
diffusion events, implemented in the form of cellular automaton
evolution rules. Subsequent interpolation and relaxation steps
covered all transitions until the end of the processed magnetograms'
sequence. We additionally advanced each magnetic configuration that
has reached the self-organized critical state (SOC configuration)
by the static model until 50 more flares were triggered, applied
the dynamic model again to the new sequence, and repeated the same
process sufficiently often to generate adequate statistics. Physical
requirements, such as the divergence-free condition for the magnetic
field, were approximately imposed. Results: We obtain robust
power laws in the distribution functions of the modeled flaring events
with scaling indices that agree well with observations. Peak and total
flare energy obey single power laws with indices -1.65 ± 0.11 and
-1.47 ± 0.13, while the flare duration is best fitted with a double
power law (-2.15 ± 0.15 and -3.60 ± 0.09 for the flatter and steeper
parts, respectively). Conclusions: We conclude that well-known
statistical properties of flares are reproduced after active regions
reach the state of self-organized criticality. A significant enhancement
of our refined cellular automaton model is that it initiates and further
drives the simulation from observed evolving vector magnetograms, thus
facilitating energy calculation in physical units, while a separation
between MHD and kinetic timescales is possible by assigning distinct
MHD timestamps to each interpolation step.

---------------------------------------------------------
Title: The relation between Magnetic Energy and Helicity and their
accumulation in Eruptive Solar Active Regions
Authors: Tziotziou, K.; Georgoulis, M. K.; Raouafi, N. -E.
2013ASPC..470...59T Altcode:
Magnetic free energy and relative magnetic helicity are two important
quantities characterizing solar active regions (ARs). Although the
importance of free magnetic energy storage for solar eruptions is
widely accepted, the role of magnetic helicity, that quantifies the
stress and distortion of the magnetic field compared to its lowest
(potential) energy state, is still under debate. A new nonlinear
force-free method designed to calculate the instantaneous free magnetic
energy and relative magnetic helicity budgets of a solar active region
from a single vector magnetogram is presented. A sample of 40 vector
magnetograms corresponding to different eruptive and non-eruptive ARs
is used to calculate their free magnetic energy and relative magnetic
helicity budgets, aiming to find a statistically robust correlation
between them. The derived correlation implies that magnetic helicity,
besides free magnetic energy, is a crucial ingredient for active
regions hosting major (M-class and higher) solar eruptions. Eruptive
active regions appear well segregated from non-eruptive ones in both
free energy and relative helicity with eruptive major flares occurring
in ARs with free energy and helicity exceeding 4×1031
erg and 2×1042 Mx2, respectively. Helicity is
expelled from ARs mainly in the form of coronal mass ejections (CMEs)
and the above helicity threshold agrees well with estimates of typical
helicity contents of CMEs.

---------------------------------------------------------
Title: Non-neutralized Electric Current Patterns in Solar Active
Regions: Origin of the Shear-generating Lorentz Force
Authors: Georgoulis, Manolis K.; Titov, Viacheslav S.; Mikić, Zoran
2012ApJ...761...61G Altcode: 2012arXiv1210.2919G
Using solar vector magnetograms of the highest available spatial
resolution and signal-to-noise ratio, we perform a detailed study
of electric current patterns in two solar active regions (ARs): a
flaring/eruptive and a flare-quiet one. We aim to determine whether
ARs inject non-neutralized (net) electric currents in the solar
atmosphere, responding to a debate initiated nearly two decades ago
that remains inconclusive. We find that well-formed, intense magnetic
polarity inversion lines (PILs) within ARs are the only photospheric
magnetic structures that support significant net current. More intense
PILs seem to imply stronger non-neutralized current patterns per
polarity. This finding revises previous works that claim frequent
injections of intense non-neutralized currents by most ARs appearing
in the solar disk but also works that altogether rule out injection of
non-neutralized currents. In agreement with previous studies, we also
find that magnetically isolated ARs remain globally current-balanced. In
addition, we confirm and quantify the preference of a given magnetic
polarity to follow a given sense of electric currents, indicating a
dominant sense of twist in ARs. This coherence effect is more pronounced
in more compact ARs with stronger PILs and must be of sub-photospheric
origin. Our results yield a natural explanation of the Lorentz force,
invariably generating velocity and magnetic shear along strong PILs,
thus setting a physical context for the observed pre-eruption evolution
in solar ARs.

---------------------------------------------------------
Title: Magnetic Energy and Helicity Properties of Eruptive Solar
Active Regions
Authors: Georgoulis, M. K.; Tziotziou, K.; Raouafi, N.
2012AGUFMSH53B..02G Altcode:
We outline a new nonlinear force-free method designed to
self-consistently calculate the magnetic energy and the relative
magnetic helicity budgets of solar active regions using only
a single vector magnetogram at the lower atmospheric boundary
of these regions. The method is fast and has been successfully
validated with well-known magnetic-energy and relative-helicity
formulas that, however, are model-dependent and more computationally
demanding. Application of the method to a sizable sample of vector
magnetograms reveals that eruptive active regions exceed well-defined,
physically meaningful thresholds in both their magnetic free-energy
and relative magnetic-helicity budgets. Moreover, application to
a high-cadence vector-magnetogram timeseries of an eruptive region
observed by the Helioseismic and Magnetic Imager onboard the Solar
Dynamics Observatory leads to a physical interpretation of the region's
dynamical evolution and reveals eruption-related energy and helicity
changes. Several intriguing possibilities suggesting promising research
avenues emerge from this analysis and are briefly discussed.

---------------------------------------------------------
Title: Magnetic Energy and Helicity Budgets in the Active-region
Solar Corona. II. Nonlinear Force-free Approximation
Authors: Georgoulis, Manolis K.; Tziotziou, Kostas; Raouafi,
Nour-Eddine
2012ApJ...759....1G Altcode: 2012arXiv1209.5606G
Expanding on an earlier work that relied on linear force-free (LFF)
magnetic fields, we self-consistently derive the instantaneous
free magnetic energy and relative magnetic helicity budgets of
an unknown three-dimensional nonlinear force-free (NLFF) magnetic
structure extending above a single known lower-boundary magnetic field
vector. The proposed method does not rely on the detailed knowledge
of the three-dimensional field configuration but is general enough to
employ only a magnetic connectivity matrix on the lower boundary. The
calculation yields a minimum free magnetic energy and a relative
magnetic helicity consistent with this free magnetic energy. The
method is directly applicable to photospheric or chromospheric vector
magnetograms of solar active regions. Upon validation, it basically
reproduces magnetic energies and helicities obtained by well known,
but computationally more intensive and non-unique, methods relying on
the extrapolated three-dimensional magnetic field vector. We apply
the method to three active regions, calculating the photospheric
connectivity matrices by means of simulated annealing, rather than a
model-dependent NLFF extrapolation. For two of these regions we correct
for the inherent LFF overestimation in free energy and relative helicity
that is larger for larger, more eruptive, active regions. In the third
region studied, our calculation can lead to a physical interpretation of
observed eruptive manifestations. We conclude that the proposed method,
including the proposed inference of the magnetic connectivity matrix,
is practical enough to contribute to a physical interpretation of the
dynamical evolution of solar active regions.

---------------------------------------------------------
Title: The Magnetic Energy-Helicity Diagram of Solar Active Regions
Authors: Tziotziou, Kostas; Georgoulis, Manolis K.; Raouafi,
Nour-Eddine
2012ApJ...759L...4T Altcode: 2012arXiv1209.5612T
Using a recently proposed nonlinear force-free method designed for
single-vector magnetograms of solar active regions, we calculate
the instantaneous free magnetic energy and relative magnetic helicity
budgets in 162 vector magnetograms corresponding to 42 different active
regions. We find a statistically robust, monotonic correlation between
the free magnetic energy and the relative magnetic helicity in the
studied regions. This correlation implies that magnetic helicity, in
addition to free magnetic energy, may be an essential ingredient for
major solar eruptions. Eruptive active regions appear well segregated
from non-eruptive ones in both free energy and relative helicity with
major (at least M-class) flares occurring in active regions with free
energy and relative helicity exceeding 4 × 1031 erg and 2
× 1042 Mx2, respectively. The helicity threshold
agrees well with estimates of the helicity contents of typical coronal
mass ejections.

---------------------------------------------------------
Title: Study of the Three-Dimensional Shape and Dynamics of Coronal
Loops Observed by Hinode/EIS
Authors: Syntelis, P.; Gontikakis, C.; Georgoulis, M. K.;
Alissandrakis, C. E.; Tsinganos, K.
2012SoPh..280..475S Altcode: 2012SoPh..tmp..119S; 2012arXiv1206.0126S
We study plasma flows along selected coronal loops in NOAA Active
Region 10926, observed on 3 December 2006 with Hinode'sEUVImaging
Spectrograph (EIS). From the shape of the loops traced on intensity
images and the Doppler shifts measured along their length we compute
their three-dimensional (3D) shape and plasma flow velocity using a
simple geometrical model. This calculation was performed for loops
visible in the Fe VIII 185 Å, Fe X 184 Å, Fe XII 195 Å, Fe XIII
202 Å, and Fe XV 284 Å spectral lines. In most cases the flow is
unidirectional from one footpoint to the other but there are also cases
of draining motions from the top of the loops to their footpoints. Our
results indicate that the same loop may show different flow patterns
when observed in different spectral lines, suggesting a dynamically
complex rather than a monolithic structure. We have also carried out
magnetic extrapolations in the linear force-free field approximation
using SOHO/MDI magnetograms, aiming toward a first-order identification
of extrapolated magnetic field lines corresponding to the reconstructed
loops. In all cases, the best-fit extrapolated lines exhibit left-handed
twist (α&lt;0), in agreement with the dominant twist of the region.

---------------------------------------------------------
Title: Preface
Authors: Nakariakov, V. M.; Georgoulis, M. K.; Poedts, S.; van
Driel-Gesztelyi, L.; Mandrini, C. H.; Leibacher, J.
2012SoPh..280..295N Altcode: 2012SoPh..tmp..226N
No abstract at ADS

---------------------------------------------------------
Title: Micro-Sigmoids as Progenitors of Polar Coronal Jets
Authors: Raouafi, N. -E.; Bernasconi, P. N.; Rust, D. M.; Georgoulis,
M. K.
2012ASPC..454..299R Altcode:
Observations from the Hinode X-ray telescope (XRT) are used to study
the structure of X-ray bright points (XBPs), sources of coronal
jets. Several jet events are found to erupt from S-shaped bright
points, suggesting that coronal micro-sigmoids are progenitors of the
jets. The observations may help to explain numerous characteristics
of coronal jets, such as helical structures and shapes. They also
suggest that solar activity may be self-similar within a wide range
of scales in terms of both properties and evolution of the observed
coronal structures.

---------------------------------------------------------
Title: Pre-Eruption Magnetic Configurations in the Low Atmosphere
of Solar Active Regions
Authors: Georgoulis, Manolis K.
2012cosp...39..604G Altcode: 2012cosp.meet..604G
Major solar eruptions, namely flares and coronal mass ejections, rely
on significant local accumulations of non-potential (free; stored in
electric currents) magnetic energy and, quite likely, magnetic helicity
in the solar atmosphere. Without [both of] them, eruptions cannot
be powered. Simple tests can show that most free energy and helicity
reside close to the lower atmospheric boundary in solar active regions,
i.e. their photospheric or low chromospheric interface. Therefore,
the pre-eruption configuration in this boundary should reflect these
high free-energy and helicity conditions that jointly determine the
degree of non-potentiality in active regions. We review the two main
active-region photospheric/low-chromospheric configurations leading
to major eruptions: instances of intense magnetic flux emergence in
the absence of intense magnetic polarity inversion lines (PILs),
and instances of strong PILs. In these configurations we discuss
multiple measures that can be thought of as proxies of free magnetic
energy and helicity and we outline a method to actually calculate these
budgets. Combining information from different, but concerted, analyses
and approaches, a new picture of eruption initiation emerges. We
highlight this new insight and project on its physical plausibility
and the advances that it may bring.

---------------------------------------------------------
Title: Automated Detection of Eruptive Structures for Solar Eruption
Prediction
Authors: Georgoulis, Manolis K.
2012cosp...39..605G Altcode: 2012cosp.meet..605G
The problem of data processing and assimilation for solar eruption
prediction is, for contemporary solar physics, more pressing than
the problem of data acquisition. Although critical solar data, such
as the coronal magnetic field, are still not routinely available,
space-based observatories deliver diverse, high-quality information
at such a high rate that a manual or semi-manual processing becomes
meaningless. We discuss automated data analysis methods and explain,
using basic physics, why some of them are unlikely to advance eruption
prediction. From this finding we also understand why solar eruption
prediction is likely to remain inherently probabilistic. We discuss
some promising eruption prediction measures and report on efforts to
adapt them for use with high-resolution, high-cadence photospheric and
coronal data delivered by the Solar Dynamics Observatory. Concluding,
we touch on the problem of physical understanding and synthesis of
different results: combining different measures inferred by different
data sets is a yet-to-be-done exercise that, however, presents our
best opportunity of realizing benefits in solar eruption prediction
via a meaningful, targeted assimilation of solar data.

---------------------------------------------------------
Title: Plasma Blobs in the Solar Polar Regions: Outflows or Waves?
Authors: Raouafi, Nour-Eddine; Bernasconi, P. N.; Georgoulis, M. K.
2012AAS...22020104R Altcode:
We analyze EUV images from the Solar Dynamic Observatory
(SDO). Anti-sunward propagating blob are found almost everywhere within
the solar polar regions with velocities ranging from a few 10 km s-1
to more than 100 km s-1. These structures are either flows or waves. In
the former case they may reflect the structure of the nascent fast solar
wind. The case is also important for the heating of the coronal plasma.

---------------------------------------------------------
Title: Comment on “Resolving the 180° Ambiguity in Solar Vector
Magnetic Field Data: Evaluating the Effects of Noise, Spatial
Resolution, and Method Assumptions”
Authors: Georgoulis, Manolis K.
2012SoPh..276..423G Altcode: 2011arXiv1106.4682G
In a recent paper, Leka et al. (Solar Phys. 260, 83, 2009) constructed
a synthetic vector magnetogram representing a three-dimensional
magnetic structure defined only within a fraction of an arcsec
in height. They rebinned the magnetogram to simulate conditions of
limited spatial resolution and then compared the results of various
azimuth disambiguation methods on the resampled data. Methods relying
on the physical calculation of potential and/or non-potential magnetic
fields failed in nearly the same, extended parts of the field of view
and Leka et al. (Solar Phys. 260, 83, 2009) attributed these failures
to the limited spatial resolution. This study shows that the failure
of these methods is not due to the limited spatial resolution but due
to the narrowly defined test data. Such narrow magnetic structures
are not realistic in the real Sun. Physics-based disambiguation
methods, adapted for solar magnetic fields extending to infinity,
are not designed to handle such data; hence, they could only fail this
test. I demonstrate how an appropriate limited-resolution disambiguation
test can be performed by constructing a synthetic vector magnetogram
very similar to that of Leka et al. (Solar Phys. 260, 83, 2009) but
representing a structure defined in the semi-infinite space above
the solar photosphere. For this magnetogram I find that even a simple
potential-field disambiguation method manages to resolve the ambiguity
very successfully, regardless of limited spatial resolution. Therefore,
despite the conclusions of Leka et al. (Solar Phys. 260, 83, 2009),
a proper limited-spatial-resolution test of azimuth disambiguation
methods is yet to be performed in order to identify the best ideas
and algorithms.

---------------------------------------------------------
Title: Are Solar Active Regions with Major Flares More Fractal,
Multifractal, or Turbulent Than Others?
Authors: Georgoulis, Manolis K.
2012SoPh..276..161G Altcode: 2011SoPh..tmp...15G; 2011SoPh..tmp..411G; 2011SoPh..tmp..146G;
2011SoPh..tmp..215G; 2011arXiv1101.0547G
Multiple recent investigations of solar magnetic-field measurements have
raised claims that the scale-free (fractal) or multiscale (multifractal)
parameters inferred from the studied magnetograms may help assess the
eruptive potential of solar active regions, or may even help predict
major flaring activity stemming from these regions. We investigate these
claims here, by testing three widely used scale-free and multiscale
parameters, namely, the fractal dimension, the multifractal structure
function and its inertial-range exponent, and the turbulent power
spectrum and its power-law index, on a comprehensive data set of
370 timeseries of active-region magnetograms (17 733 magnetograms
in total) observed by SOHO's Michelson Doppler Imager (MDI) over
the entire Solar Cycle 23. We find that both flaring and non-flaring
active regions exhibit significant fractality, multifractality, and
non-Kolmogorov turbulence but none of the three tested parameters
manages to distinguish active regions with major flares from
flare-quiet ones. We also find that the multiscale parameters,
but not the scale-free fractal dimension, depend sensitively on the
spatial resolution and perhaps the observational characteristics of
the studied magnetograms. Extending previous works, we attribute the
flare-forecasting inability of fractal and multifractal parameters to
i) a widespread multiscale complexity caused by a possible underlying
self-organization in turbulent solar magnetic structures, flaring and
non-flaring alike, and ii) a lack of correlation between the fractal
properties of the photosphere and overlying layers, where solar
eruptions occur. However useful for understanding solar magnetism,
therefore, scale-free and multiscale measures may not be optimal tools
for active-region characterization in terms of eruptive ability or,
ultimately, for major solar-flare prediction.

---------------------------------------------------------
Title: Nanoflare heating of coronal loops in an active region
triggered by reconnecting current sheets
Authors: Gontikakis, C.; Patsourakos, S.; Efthymiopoulos, C.;
Anastasiadis, A.; Georgoulis, M.
2012hell.conf....7G Altcode:
The purpose of this work is to study the heating of coronal loops,
produced by the acceleration of particles inside reconnecting current
sheets (RCS) which represent nanoflares. We also study the hydrodynamic
response of the loops atmosphere to such a heating event. The RCS are
formed as discontinuities of the loop magnetic field caused by the
photospheric shuffling motions. The coronal loops are represented
by the closed magnetic lines of force calculated by the magnetic
field extrapolation of the active region NOAA 9114 magnetogram. The
photospheric motions at the loops footpoints are measured using local
correlation tracking. The magnetic and electric fields accelerating
particles at the RCS are computed using the loop magnetic fields and
the photospheric motions. We further discuss the question of energy
conservation inside the current sheet, and we present the statistical
distributions of quantities relevant for particles acceleration and
coronal heating for a number of the active region's coronal loops.

---------------------------------------------------------
Title: Computer Vision for the Solar Dynamics Observatory (SDO)
Authors: Martens, P. C. H.; Attrill, G. D. R.; Davey, A. R.; Engell,
A.; Farid, S.; Grigis, P. C.; Kasper, J.; Korreck, K.; Saar, S. H.;
Savcheva, A.; Su, Y.; Testa, P.; Wills-Davey, M.; Bernasconi, P. N.;
Raouafi, N. -E.; Delouille, V. A.; Hochedez, J. F.; Cirtain, J. W.;
DeForest, C. E.; Angryk, R. A.; De Moortel, I.; Wiegelmann, T.;
Georgoulis, M. K.; McAteer, R. T. J.; Timmons, R. P.
2012SoPh..275...79M Altcode: 2011SoPh..tmp..144M; 2011SoPh..tmp..213M; 2011SoPh..tmp....8M
In Fall 2008 NASA selected a large international consortium to produce
a comprehensive automated feature-recognition system for the Solar
Dynamics Observatory (SDO). The SDO data that we consider are all of the
Atmospheric Imaging Assembly (AIA) images plus surface magnetic-field
images from the Helioseismic and Magnetic Imager (HMI). We produce
robust, very efficient, professionally coded software modules that
can keep up with the SDO data stream and detect, trace, and analyze
numerous phenomena, including flares, sigmoids, filaments, coronal
dimmings, polarity inversion lines, sunspots, X-ray bright points,
active regions, coronal holes, EIT waves, coronal mass ejections
(CMEs), coronal oscillations, and jets. We also track the emergence and
evolution of magnetic elements down to the smallest detectable features
and will provide at least four full-disk, nonlinear, force-free magnetic
field extrapolations per day. The detection of CMEs and filaments is
accomplished with Solar and Heliospheric Observatory (SOHO)/Large
Angle and Spectrometric Coronagraph (LASCO) and ground-based Hα
data, respectively. A completely new software element is a trainable
feature-detection module based on a generalized image-classification
algorithm. Such a trainable module can be used to find features that
have not yet been discovered (as, for example, sigmoids were in the
pre-Yohkoh era). Our codes will produce entries in the Heliophysics
Events Knowledgebase (HEK) as well as produce complete catalogs for
results that are too numerous for inclusion in the HEK, such as the
X-ray bright-point metadata. This will permit users to locate data on
individual events as well as carry out statistical studies on large
numbers of events, using the interface provided by the Virtual Solar
Observatory. The operations concept for our computer vision system is
that the data will be analyzed in near real time as soon as they arrive
at the SDO Joint Science Operations Center and have undergone basic
processing. This will allow the system to produce timely space-weather
alerts and to guide the selection and production of quicklook images and
movies, in addition to its prime mission of enabling solar science. We
briefly describe the complex and unique data-processing pipeline,
consisting of the hardware and control software required to handle
the SDO data stream and accommodate the computer-vision modules, which
has been set up at the Lockheed-Martin Space Astrophysics Laboratory
(LMSAL), with an identical copy at the Smithsonian Astrophysical
Observatory (SAO).

---------------------------------------------------------
Title: On the shape of active region coronal loops observed by
Hinode/EIS.
Authors: Syntelis, P.; Gontikakis, C.; Alissandrakis, C.; Georgoulis,
M.; Tsinganos, K.
2012hell.confQ..14S Altcode:
We study plasma flows in NOAA Active Region (AR) 10926, observed on
December 3, 2006 with Hinode's EUV Imaging Spectrograph (EIS). We
measured the line-of-sight velocity along coronal loops in the Fe
VIII 185A, Fe X 184A , Fe XII 195A, Fe XIII 202A, and Fe XV 284A
spectral lines and reconstructed the three dimensional (3D) shape
and velocity of plasma flow using a simple geometrical model. In
most cases the flow is unidirectional from one footpoint to the other,
resembling siphon flow. However there are also cases of draining motions
from the top of the loops to their footpoints. The multi-wavelength
observations of the AR indicate that similar loops may show different
flow patterns if observed in different spectral lines. We have also
carried out magnetic field extrapolations using an SOHO/MDI and an
SOT/Spectropolarimeter (SP) magnetogram, in order to identify magnetic
field lines corresponding to the reconstructed 3D loops.

---------------------------------------------------------
Title: Monitoring solar energetic particles with an armada of
European spacecraft and the new automated SEPF (Solar Energetic
Proton Fluxes) Tool
Authors: Sandberg, I.; Daglis, I. A.; Anastasiadis, A.; Balasis, G.;
Georgoulis, M.; Nieminen, P.; Evans, H.; Daly, E.
2012hell.conf....8S Altcode:
Solar energetic particles (SEPs) observed in interplanetary medium
consist of electrons, protons, alpha particles and heavier ions (up
to Fe), with energies from dozens of keVs to a few GeVs. SEP events,
or SEPEs, are particle flux enhancements from background level (&lt;
1 pfu, particle flux unit = particle cm-2sr-1s-1) to several orders
of magnitude in the MeV range, and lasting from several hours to a
few days. Intense SEPEs can reach fluence values as high as 1010
protons cm-2 for E &gt; 30 MeV. The main part of SEPEs results
from the acceleration of particles either by solar flares and/or by
interplanetary shocks driven by Coronal Mass Ejections (CMEs); these
accelerated particles propagate through the heliosphere, traveling
along the interplanetary magnetic field (IMF). SEPEs show significant
variability from one event to another and are an important part of space
weather, because they pose a serious health risk to humans in space and
a serious radiation hazard for the spacecraft hardware which may lead
to severe damages. As a consequence, engineering models, observations
and theoretical investigations related to the high energy particle
environment is a priority issue for both robotic and manned space
missions. The European Space Agency operates the Standard Radiation
Environment Monitor (SREM) on-board six spacecraft: Proba-1, INTEGRAL,
Rosetta, Giove-B, Herschel and Planck, which measures high-energy
protons and electrons with a fair angular and spectral resolution. The
fact that several SREM units operate in different orbits provides a
unique chance for comparative studies of the radiation environment
based on multiple data gathered by identical detectors. Furthermore,
the radiation environment monitoring by the SREM unit onboard Rosetta
may reveal unknown characteristics of SEPEs properties given the fact
that the majority of the available radiation data and models only
refer to 1AU solar distances. The Institute for Space Applications and
Remote Sensing of the National Observatory of Athens (ISARS/NOA) has
developed and validated a novel method to obtain flux spectra from SREM
count rates. Using this method and by conducting detailed scientific
studies we have showed in previous presentations and papers that the
exploration and analysis of SREM data may contribute significantly to
investigations and modeling efforts of SPE generation and propagation in
the heliosphere and in the Earth's magnetosphere. ISARS/NOA recently
released an automated software tool for the monitoring of Solar
Energetic Proton Fluxes (SEPF) using measurements of SREM. The SEPF tool
is based on the automated implementation of the inverse method developed
by ISARS/NOA, permitting the calculation of high-energy proton fluxes
from SREM data. Results of the method have been validated for selected
number of past solar energetic particle events using measurements from
other space-born proton monitors. The SEPF tool unfolds downlinked
SREM count-rates, calculates the omnidirectional differential proton
fluxes and provides results to the space weather community acting as
a multi-point proton flux monitor on a daily-basis. The SEPF tool is a
significant European space weather asset and will support the efforts
towards an efficient European Space Situational Awareness programme.

---------------------------------------------------------
Title: Solar Energetic Particle Events detected by the Standard
Radiation Environment Monitor (SREM) onboard INTEGRAL
Authors: Georgoulis, M.; Daglis, I. A.; Anastasiadis, A.; Sandberg,
I.; Balasis, G.; Nieminen, P.
2012hell.conf...10G Altcode:
The SREM is a cost-effective instrument mounted onboard multiple ESA
missions. The SREM objective is the in-situ measurement of high-energy
solar particles at the spacecraft location. Within the previous solar
cycle 23, SREM units onboard ESA's INTEGRAL and Rosetta missions
detected several tens of SEPEs and accurately pinpointed their onset,
rise, and decay times. We have undertaken a detailed study to determine
the solar sources and subsequent interplanetary coronal mass ejections
(ICMEs) that gave rise to these events, as well as the timing of SEPEs
with the onset of possible geomagnetic activity triggered by these
ICMEs. We find that virtually all SREM SEPEs may be associated with
CME-driven shocks. For a number of well-studied INTEGRAL/SREM SEPEs,
moreover, we see an association between the SEPE peak and the shock
passage at L1. Shortly (typically within a few hours) after the
SEPE peak, the ICME-driven modulation of the magnetosphere kicks
in, with either an increase or a dip of the Dst index, indicating
stormy conditions in geospace. We conclude that, pending additional
investigation, SREM units may prove useful for a short-term prediction
of inclement space-weather conditions in Geospace, especially if
mounted onboard dayside missions ahead of the magnetospheric bow shock.

---------------------------------------------------------
Title: On Our Ability to Predict Major Solar Flares
Authors: Georgoulis, Manolis K.
2012ASSP...30...93G Altcode: 2012snc..book...93G
We discuss the outstanding problem of solar flare prediction
and briefly overview the various methods that have been developed
to address it. A class of these methods, relying on the fractal
and multifractal nature of solar magnetic fields, are shown to be
inadequate for flare prediction. More promise seems delivered by
morphological methods applying mostly to the photospheric magnetic
configuration of solar active regions but a definitive assessment
of their veracity is subject to a number of caveats. Statistical and
artificial-intelligence methods are also briefly discussed, together
with their possible shortcomings. The central importance of proper
validation procedures for any viable method is also highlighted,
together with the need for future studies that will finally judge
whether practically meaningful flare prediction will ever become
possible, if only purely probabilistic.

---------------------------------------------------------
Title: Pre-Eruption Magnetic Configurations in the Active-Region
Solar Photosphere
Authors: Georgoulis, Manolis K.
2011IAUS..273..495G Altcode:
Most solar eruptions occur above strong photospheric magnetic polarity
inversion lines (PILs). What overlays a PIL is unknown, however, and
this has led to a debate over the existence of sheared magnetic arcades
vs. helical magnetic flux ropes. We argue that this debate may be of
little meaning: numerous small-scale magnetic reconnections, constantly
triggered in the PIL area, can lead to effective transformation
of mutual to self magnetic helicity (i.e. twist and writhe) that,
ultimately, may force the magnetic structure above PILs to erupt to
be relieved from its excess helicity. This is preliminary report of
work currently in progress.

---------------------------------------------------------
Title: Simulating flaring events in complex active regions driven
by observed magnetograms
Authors: Dimitropoulou, M.; Isliker, H.; Vlahos, L.; Georgoulis, M. K.
2011A&A...529A.101D Altcode: 2011arXiv1102.2352D
Context. We interpret solar flares as events originating in active
regions that have reached the self organized critical state, by using
a refined cellular automaton model with initial conditions derived
from observations. Aims: We investigate whether the system,
with its imposed physical elements, reaches a self organized critical
state and whether well-known statistical properties of flares,
such as scaling laws observed in the distribution functions of
characteristic parameters, are reproduced after this state has been
reached. Methods: To investigate whether the distribution
functions of total energy, peak energy and event duration follow
the expected scaling laws, we first applied a nonlinear force-free
extrapolation that reconstructs the three-dimensional magnetic
fields from two-dimensional vector magnetograms. We then locate
magnetic discontinuities exceeding a threshold in the Laplacian of the
magnetic field. These discontinuities are relaxed in local diffusion
events, implemented in the form of cellular automaton evolution
rules. Subsequent loading and relaxation steps lead the system to
self organized criticality, after which the statistical properties
of the simulated events are examined. Physical requirements, such
as the divergence-free condition for the magnetic field vector, are
approximately imposed on all elements of the model. Results:
Our results show that self organized criticality is indeed reached
when applying specific loading and relaxation rules. Power-law indices
obtained from the distribution functions of the modeled flaring events
are in good agreement with observations. Single power laws (peak and
total flare energy) are obtained, as are power laws with exponential
cutoff and double power laws (flare duration). The results are also
compared with observational X-ray data from the GOES satellite for our
active-region sample. Conclusions: We conclude that well-known
statistical properties of flares are reproduced after the system
has reached self organized criticality. A significant enhancement
of our refined cellular automaton model is that it commences the
simulation from observed vector magnetograms, thus facilitating
energy calculation in physical units. The model described in this
study remains consistent with fundamental physical requirements,
and imposes physically meaningful driving and redistribution rules.

---------------------------------------------------------
Title: Nonlinear Force-Free Reconstruction of the Global Solar
Magnetic Field: Methodology
Authors: Contopoulos, I.; Kalapotharakos, C.; Georgoulis, M. K.
2011SoPh..269..351C Altcode: 2010arXiv1011.5356C; 2011SoPh..tmp...23C
We present a novel numerical method that allows the calculation of
nonlinear force-free magnetostatic solutions above a boundary surface on
which only the distribution of the normal magnetic field component is
given. The method relies on the theory of force-free electrodynamics
and applies directly to the reconstruction of the solar coronal
magnetic field for a given distribution of the photospheric radial
field component. The method works as follows: we start with any initial
magnetostatic global field configuration (e.g. zero, dipole), and along
the boundary surface we create an evolving distribution of tangential
(horizontal) electric fields that, via Faraday's equation, give rise to
a respective normal-field distribution approaching asymptotically the
target distribution. At the same time, these electric fields are used as
boundary condition to numerically evolve the resulting electromagnetic
field above the boundary surface, modeled as a thin ideal plasma with
non-reflecting, perfectly absorbing outer boundaries. The simulation
relaxes to a nonlinear force-free configuration that satisfies the
given normal-field distribution on the boundary. This is different from
existing methods relying on a fixed boundary condition - the boundary
evolves toward the a priori given one, at the same time evolving the
three-dimensional field solution above it. Moreover, this is the first
time that a nonlinear force-free solution is reached by using only the
normal field component on the boundary. This solution is not unique,
but it depends on the initial magnetic field configuration and on the
evolutionary course along the boundary surface. To our knowledge, this
is the first time that the formalism of force-free electrodynamics,
used very successfully in other astrophysical contexts, is applied to
the global solar magnetic field.

---------------------------------------------------------
Title: Three-dimensional Structure of a Solar Active Region from
Spatially and Spectrally Resolved Microwave Observations
Authors: Tun, Samuel D.; Gary, Dale E.; Georgoulis, Manolis K.
2011ApJ...728....1T Altcode:
We report on the structure of the solar atmosphere above active
region (AR) 10923, observed on 2006 November 10, as deduced from
multi-wavelength studies including combined microwave observations
from the Very Large Array (VLA) and the Owens Valley Solar Array
(OVSA). The VLA observations provide excellent image quality
at a few widely spaced frequencies, while the OVSA data provide
information at many intermediate frequencies to fill in the spectral
coverage. Images at 25 distinct frequencies are used to provide
spatially resolved spectra along many lines of sight in the AR,
from which microwave spectral diagnostics are obtained for deducing
maps of temperature, magnetic field, and column density. The derived
quantities are compared with multiwavelength observations from the
Solar and Heliospheric Observatory and Hinode spacecraft, and with a
current-free magnetic field extrapolation. We find that a two-component
temperature model is required to fit the data, in which a hot (&gt;2
MK) lower corona above the strong-field plage and sunspot regions
(emitting via the gyroresonance process) is overlaid with somewhat
cooler (~1 MK) coronal loops that partially absorb the gyroresonance
emission through the free-free (Bremsstrahlung) process. We also find
that the extrapolated potential magnetic fields can quantitatively
account for the observed gyroresonance emission over most of the AR,
but in a few areas a higher field strength is required. The results
are used to explore the coronal configuration needed to explain the
observations. These results show that the bulk of free-free emission
in both radio and X-rays emanates from two loop systems, distinguished
by the location of their loop footpoints. We discuss the implications
of such comparisons for studies of AR structure when better microwave
spectral imaging becomes available in the future.

---------------------------------------------------------
Title: Oscillations in a network region observed in the Hα line
and their relation to the magnetic field
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.; Georgoulis,
M. K.
2010A&A...524A..12K Altcode:
 Aims: Our aim is to gain a better understanding of the
interaction between acoustic oscillations and the small-scale magnetic
fields of the Sun. To this end, we examine the oscillatory properties
of a network region and their relation to the magnetic configuration of
the chromosphere. We link the oscillatory properties of a network region
and their spatial variation with the variation of the parameters of the
magnetic field. We investigate the effect of the magnetic canopy and the
diverging flux tubes of the chromospheric network on the distribution
of oscillatory power over the network and internetwork. Methods:
We use a time series of high resolution filtergrams at five wavelengths
along the Hα profile observed with the Dutch Open Telescope, as
well as high resolution magnetograms taken by the SOT/SP onboard
HINODE. Using wavelet analysis, we construct power maps of the 3,
5 and 7 min oscillations of the Doppler signals calculated at ±0.35
Å and ±0.7 Å from the Hα line center. These represent velocities
at chromospheric and photospheric levels respectively. Through
a current-free (potential) field extrapolation we calculate the
chromospheric magnetic field and compare its morphology with the
Hα filtergrams. We calculate the plasma β and the magnetic field
inclination angle and compare their distribution with the oscillatory
power at the 3, 5 and 7 min period bands. Results: Chromospheric
mottles seem to outline the magnetic field lines. The Hα ± 0.35
Å Doppler signals are formed above the canopy, while the Hα ± 0.7
Å corresponding ones below it. The 3 min power is suppressed at the
chromosphere around the network, where the canopy height is lower than
1600 km, while at the photosphere it is enhanced due to reflection. 3,
5 and 7 min oscillatory power is increased around the network at the
photosphere due to reflection of waves on the overlying canopy, while
increased 5 and 7 min power at the chromosphere is attributed mainly
to wave refraction on the canopy. At these high periods, power is also
increased due to p-mode leakage because of the high inclinations of the
magnetic field. Conclusions: Our high resolution Hα observations
and photospheric magnetograms provide the opportunity to highlight
the details of the interaction between acoustic oscillations and the
magnetic field of a network region. We conclude that several mechanisms
that have been proposed such as p-mode leakage, mode conversion,
reflection and refraction of waves on the magnetic canopy may act
together and result to the observed properties of network oscillations.

---------------------------------------------------------
Title: Micro-Sigmoids as Progenitors of Polar Coronal Jets
Authors: Raouafi, N. -E.; Bernasconi, P. N.; Rust, D. M.; Georgoulis,
M. K.
2010arXiv1009.2951R Altcode:
Observations from the Hinode X-ray telescope (XRT) are used to study
the structure of X-ray bright points (XBPs), sources of coronal
jets. Several jet events are found to erupt from S-shaped bright
points, suggesting that coronal micro-sigmoids are progenitors of the
jets. The observations may help to explain numerous characteristics
of coronal jets, such as helical structures and shapes. They also
suggest that solar activity may be self-similar within a wide range
of scales in terms of both properties and evolution of the observed
coronal structures.

---------------------------------------------------------
Title: Micro-sigmoids as Progenitors of Coronal Jets: Is Eruptive
Activity Self-similarly Multi-scaled?
Authors: Raouafi, N. -E.; Georgoulis, M. K.; Rust, D. M.; Bernasconi,
P. N.
2010ApJ...718..981R Altcode: 2010arXiv1005.4042R
Observations from the X-ray telescope (XRT) on Hinode are used to study
the nature of X-ray-bright points, sources of coronal jets. Several
jet events in the coronal holes are found to erupt from small-scale,
S-shaped bright regions. This finding suggests that coronal
micro-sigmoids may well be progenitors of coronal jets. Moreover,
the presence of these structures may explain numerous observed
characteristics of jets such as helical structures, apparent transverse
motions, and shapes. Analogous to large-scale sigmoids giving rise to
coronal mass ejections (CMEs), a promising future task would perhaps
be to investigate whether solar eruptive activity, from coronal jets to
CMEs, is self-similar in terms of properties and instability mechanisms.

---------------------------------------------------------
Title: Heating Distribution Along Coronal Loops in two Active Regions
Using a Simple Electrodynamic Calculation
Authors: Gontikakis, C.; Georgoulis, M.; Contopoulos, I.; Dara, H. C.
2010ASPC..424...25G Altcode:
The heating along hundreds of coronal loops of non flaring active
regions is computed using a simple electrodynamic model. Photospheric
motions generate electric fields inducing, electric potential
differences at the footpoints of loops. These potential differences
generate electric currents that lead to Ohmic heating. We computed
the magnetic field extrapolation from the magnetograms of two
active regions, namely NOAA AR 9366 (SOHO/MDI) and NOAA AR 10963,
(HINODE/SOT). Closed magnetic field lines model the coronal loops. For
each loop we computed the heating function and obtained the hydrostatic
distribution of temperature and pressure. We found that the coronal
heating is stronger near the footpoints of the loops and asymmetric
along them. We obtained scaling laws that correlate the mean volumetric
heating with the loop length, and the heating flux, through the loop
footpoints with the magnetic field strength at the footpoints. Our
results are in qualitative agreement with observations (see Gontikakis
et al. 2008 for more details).

---------------------------------------------------------
Title: Simulating Flaring Events via an Intelligent Cellular Automata
Mechanism
Authors: Dimitropoulou, M.; Vlahos, L.; Isliker, H.; Georgoulis, M.
2010ASPC..424...28D Altcode:
We simulate flaring events through a Cellular Automaton (CA) model,
in which, for the first time, we use observed vector magnetograms as
initial conditions. After non-linear force free extrapolation of the
magnetic field from the vector magnetograms, we identify magnetic
discontinuities, using two alternative criteria: (1) the average
magnetic field gradient, or (2) the normalized magnetic field curl
(i.e. the current). Magnetic discontinuities are identified at the
grid-sites where the magnetic field gradient or curl exceeds a specified
threshold. We then relax the magnetic discontinuities according to
the rules of Lu and Hamilton (1991) or Lu et al. (1993), i.e. we
redistribute the magnetic field locally so that the discontinuities
disappear. In order to simulate the flaring events, we consider
several alternative scenarios with regard to: (1) The threshold
above which magnetic discontinuities are identified (applying low,
high, and height-dependent threshold values); (2) The driving process
that occasionally causes new discontinuities (at randomly chosen grid
sites, magnetic field increments are added that are perpendicular (or
may-be also parallel) to the existing magnetic field). We address the
question whether the coronal active region magnetic fields can indeed
be considered to be in the state of self-organized criticality (SOC).

---------------------------------------------------------
Title: The "Sigmoid Sniffer” and the "Advanced Automated Solar
Filament Detection and Characterization Code” Modules
Authors: Raouafi, Noureddine; Bernasconi, P. N.; Georgoulis, M. K.
2010AAS...21640232R Altcode:
We present two pattern recognition algorithms, the "Sigmoid
Sniffer” and the "Advanced Automated Solar Filament Detection and
Characterization Code,” that are among the Feature Finding modules
of the Solar Dynamic Observatory: 1) Coronal sigmoids visible
in X-rays and the EUV are the result of highly twisted magnetic
fields. They can occur anywhere on the solar disk and are closely
related to solar eruptive activity (e.g., flares, CMEs). Their
appearance is typically synonym of imminent solar eruptions, so
they can serve as a tool to forecast solar activity. Automatic
X-ray sigmoid identification offers an unbiased way of detecting
short-to-mid term CME precursors. The "Sigmoid Sniffer” module is
capable of automatically detecting sigmoids in full-disk X-ray images
and determining their chirality, as well as other characteristics. It
uses multiple thresholds to identify persistent bright structures on
a full-disk X-ray image of the Sun. We plan to apply the code to X-ray
images from Hinode/XRT, as well as on SDO/AIA images. When implemented
in a near real-time environment, the Sigmoid Sniffer could allow 3-7
day forecasts of CMEs and their potential to cause major geomagnetic
storms. 2)The "Advanced Automated Solar Filament Detection and
Characterization Code” aims to identify, classify, and track solar
filaments in full-disk Hα images. The code can reliably identify
filaments; determine their chirality and other relevant parameters
like filament area, length, and average orientation with respect to
the equator. It is also capable of tracking the day-by-day evolution
of filaments as they traverse the visible disk. The code was tested by
analyzing daily Hα images taken at the Big Bear Solar Observatory from
mid-2000 to early-2005. It identified and established the chirality
of thousands of filaments without human intervention.

---------------------------------------------------------
Title: Computer Vision for SDO: First Results from the SDO Feature
Finding Algorithms
Authors: Martens, Petrus C.; Attrill, G.; Davey, A.; Engell, A.;
Farid, S.; Grigis, P.; Kasper, J.; Korreck, K.; Saar, S.; Su, Y.;
Testa, P.; Wills-Davey, M.; Bernasconi, P.; Raouafi, N.; Georgoulis,
M.; Deforest, C.; Peterson, J.; Berghoff, T.; Delouille, V.; Hochedez,
J.; Mampaey, B.; Verbeek, C.; Cirtain, J.; Green, S.; Timmons, R.;
Savcheva, A.; Angryk, R.; Wiegelmann, T.; McAteer, R.
2010AAS...21630804M Altcode:
The SDO Feature Finding Team produces robust and very efficient
software modules that can keep up with the relentless SDO data stream,
and detect, trace, and analyze a large number of phenomena including:
flares, sigmoids, filaments, coronal dimmings, polarity inversion
lines, sunspots, X-ray bright points, active regions, coronal holes,
EIT waves, CME's, coronal oscillations, and jets. In addition we track
the emergence and evolution of magnetic elements down to the smallest
features that are detectable, and we will also provide at least four
full disk nonlinear force-free magnetic field extrapolations per day. During SDO commissioning we will install in the near-real time data
pipeline the modules that provide alerts for flares, coronal dimmings,
and emerging flux, as well as those that trace filaments, sigmoids,
polarity inversion lines, and active regions. We will demonstrate
the performance of these modules and illustrate their use for science
investigations.

---------------------------------------------------------
Title: Solar Magnetic Helicity Injected into the Heliosphere:
Magnitude, Balance, and Periodicities Over Solar Cycle 23
Authors: Georgoulis, M. K.; Rust, D. M.; Pevtsov, A. A.; Bernasconi,
P. N.; Kuzanyan, K. M.
2009ApJ...705L..48G Altcode:
Relying purely on solar photospheric magnetic field measurements that
cover most of solar cycle 23 (1996-2005), we calculate the total
relative magnetic helicity injected into the solar atmosphere, and
eventually shed into the heliosphere, over the latest cycle. Large
active regions dominate the helicity injection process with ~5.7
× 1045 Mx2 of total injected helicity. The
net helicity injected is lsim1% of the above output. Peculiar
active-region plasma flows account for ~80% of this helicity; the
remaining ~20% is due to solar differential rotation. The typical
helicity per active-region CME ranges between (1.8-7) × 1042
Mx2 depending on the CME velocity. Accounting for various
minor underestimation factors, we estimate a maximum helicity injection
of ~6.6 × 1045 Mx2 for solar cycle 23. Although
no significant net helicity exists over both solar hemispheres,
we recover the well-known hemispheric helicity preference, which is
significantly enhanced by the solar differential rotation. We also
find that helicity injection in the solar atmosphere is an inherently
disorganized, impulsive, and aperiodic process.

---------------------------------------------------------
Title: The correlation of fractal structures in the photospheric
and the coronal magnetic field
Authors: Dimitropoulou, M.; Georgoulis, M.; Isliker, H.; Vlahos, L.;
Anastasiadis, A.; Strintzi, D.; Moussas, X.
2009A&A...505.1245D Altcode: 2009arXiv0908.3950D
Context: This work examines the relation between the fractal properties
of the photospheric magnetic patterns and those of the coronal
magnetic fields in solar active regions. Aims: We investigate
whether there is any correlation between the fractal dimensions of
the photospheric structures and the magnetic discontinuities formed in
the corona. Methods: To investigate the connection between the
photospheric and coronal complexity, we used a nonlinear force-free
extrapolation method that reconstructs the 3d magnetic fields using 2d
observed vector magnetograms as boundary conditions. We then located
the magnetic discontinuities, which are considered as spatial proxies
of reconnection-related instabilities. These discontinuities form
well-defined volumes, called here unstable volumes. We calculated
the fractal dimensions of these unstable volumes and compared them
to the fractal dimensions of the boundary vector magnetograms. Results: Our results show no correlation between the fractal
dimensions of the observed 2d photospheric structures and the
extrapolated unstable volumes in the corona, when nonlinear force-free
extrapolation is used. This result is independent of efforts to
(1) bring the photospheric magnetic fields closer to a nonlinear
force-free equilibrium and (2) omit the lower part of the modeled
magnetic field volume that is almost completely filled by unstable
volumes. A significant correlation between the fractal dimensions of
the photospheric and coronal magnetic features is only observed at the
zero level (lower limit) of approximation of a current-free (potential)
magnetic field extrapolation. Conclusions: We conclude that
the complicated transition from photospheric non-force-free fields
to coronal force-free ones hampers any direct correlation between
the fractal dimensions of the 2d photospheric patterns and their
3d counterparts in the corona at the nonlinear force-free limit,
which can be considered as a second level of approximation in this
study. Correspondingly, in the zero and first levels of approximation,
namely, the potential and linear force-free extrapolation, respectively,
we reveal a significant correlation between the fractal dimensions of
the photospheric and coronal structures, which can be attributed to the
lack of electric currents or to their purely field-aligned orientation.

---------------------------------------------------------
Title: SOLIS Vector Spectromagnetograph: Status and Science
Authors: Henney, C. J.; Keller, C. U.; Harvey, J. W.; Georgoulis,
M. K.; Hadder, N. L.; Norton, A. A.; Raouafi, N. -E.; Toussaint, R. M.
2009ASPC..405...47H Altcode: 2008arXiv0801.0013H
The Vector Spectromagnetograph (VSM) instrument has recorded
photospheric and chromospheric magnetograms daily since August
2003. Full-disk photospheric vector magnetograms are observed
at least weekly and, since November 2006, area-scans of active
regions daily. Quick-look vector magnetic images, plus X3D and FITS
formated files, are now publicly available daily. In the near future,
Milne-Eddington inversion parameter data will also be available and
a typical observing day will include three full-disk photospheric
vector magnetograms. Besides full-disk observations, the VSM is
capable of high temporal cadence area-scans of both the photosphere
and chromosphere. Carrington rotation and daily synoptic maps are
also available from the photospheric magnetograms and coronal hole
estimate images.

---------------------------------------------------------
Title: Computer Vision for The Solar Dynamics Observatory
Authors: Martens, Petrus C.; Angryk, R. A.; Bernasconi, P. N.; Cirtain,
J. W.; Davey, A. R.; DeForest, C. E.; Delouille, V. A.; De Moortel,
I.; Georgoulis, M. K.; Grigis, P. C.; Hochedez, J. E.; Kasper, J.;
Korreck, K. E.; Reeves, K. K.; Saar, S. H.; Savcheva, A.; Su, Y.;
Testa, P.; Wiegelmann, T.; Wills-Davey, M.
2009SPD....40.1711M Altcode:
NASA funded a large international consortium last year to produce
a comprehensive system for automated feature recognition in SDO
images. The data we consider are all AIA and EVE data plus surface
magnetic field images from HMI. Helioseismology is addressed by another
group. We will produce robust and very efficient software modules
that can keep up with the relentless SDO data stream and detect, trace,
and analyze a large number of phenomena, including: flares, sigmoids,
filaments, coronal dimmings, polarity inversion lines, sunspots,
X-ray bright points, active regions, coronal holes, EIT waves, CME's,
coronal oscillations, and jets. In addition we will track the emergence
and evolution of magnetic elements down to the smallest features
that are detectable, and we will also provide at least four full
disk nonlinear force-free magnetic field extrapolations per day. A completely new software element that rounds out this suite is a
trainable feature detection module, which employs a generalized image
classification algorithm to produce the texture features of the images
analyzed. A user can introduce a number of examples of the phenomenon
looked and the software will return images with similar features. We
have tested a proto-type on TRACE data, and were able to "train" the
algorithm to detect sunspots, active regions, and loops. Such a module
can be used to find features that have not even been discovered yet,
as, for example, sigmoids were in the pre-Yohkoh era. Our codes
will produce entries in the Helio Events Knowledge base, and that will
permit users to locate data on individual events as well as carry out
statistical studies on large numbers of events, using the interface
provided by the Virtual Solar Observatory.

---------------------------------------------------------
Title: Just how much Helicity did the Sun Shed in Solar Cycle
23? Magnitude, Balance, Periodicities, and Further Implications
Authors: Georgoulis, Manolis K.; Rust, D. M.; Pevtsov, A. A.;
Bernasconi, P. N.; Kuzanyan, K. M.
2009SPD....40.0606G Altcode:
Using solar magnetic field measurements, we calculate the total
relative magnetic helicity injected in the solar atmosphere and
eventually transported to the heliosphere in the course of the
latest solar cycle. We report on (i) the magnitude of the heliospheric
helicity over cycle 23, (ii) the net helicity and its significance,
and (iii) the possible periodicities of helicity injection in
the solar atmosphere. Our simple calculations raise several questions
regarding the fundamental nature of solar magnetism. The lack of
significant net helicity may place the solar dynamo in the category
of astrophysical dynamos without a net helicity effect over an
average time scale. The strong enhancement of the hemispheric helicity
preference by solar differential rotation - although the latter has a
much weaker effect than intrinsic active-region plasma flows - warrants
further investigation. Finally, the absence of any credible periodicity
of helicity injection, in spite of numerous reported periodicities in
solar activity, perhaps prompts the re-evaluation of the notion that the
Sun works through a sequence of internal cycles: active-region emergence
and evolution appears as an inherently disorganized, aperiodic process.

---------------------------------------------------------
Title: On the Helical Fields Guiding Near-Relativistic Electron
Beams in the Heliosphere
Authors: Rust, David M.; Haggerty, D. K.; Georgoulis, M. K.;
Stenborg, G.
2009SPD....40.3202R Altcode:
Wavelet processing of the LASCO images of the solar corona brings
out many subtle details that are easily missed in the intensity
images. Specifically, wavelet processing can enhance the edges on
large and small scales making it easier to detect and define helical
features. We used the processed LASCO images obtained during the
period 1997 -2001 to study the structure and motions of nearly radial
streamers extending from coronal holes adjacent to flaring active
regions. Some of the streamers show outward-propagating twist. These
helical fields extend into the heliosphere where they would reach 1
AU with a path length generally greater than the 1.2 AU of idealized
fields following the Parker spiral. We focused on the regions from our
earlier work (Rust et al., ApJ 687, 635, 2008) on flares associated
with beams of near-relativistic electrons detected at 1 AU with the ACE
spacecraft. Our study shows that the electron beam's typical delay of
about 10 min in arriving at 1 AU may be due to their following a helical
path from Sun to Earth. According to the reconnection jet model, the
helical component may be introduced to open fields by earlier events
involving reconnections with emerging, twisted flux ropes. Our study
implies that the escaping electrons may be accelerated at the same
time as the trapped electrons that produce X-ray flare emissions. NASA supported this work with grant NNG 05GM69G.

---------------------------------------------------------
Title: On the Solar Origins of Open Magnetic Fields in the Heliosphere
Authors: Rust, David M.; Haggerty, Dennis K.; Georgoulis, Manolis K.;
Sheeley, Neil R.; Wang, Yi-Ming; DeRosa, Marc L.; Schrijver, Carolus J.
2008ApJ...687..635R Altcode:
A combination of heliospheric and solar data was used to identify open
magnetic fields stretching from the lower corona to Earth orbit. 35
near-relativistic electron beams detected at the ACE spacecraft
"labeled" the heliospheric segments of the open fields. An X-ray
flare occurred &lt;20 minutes before injection of the electrons
in 25 events. These flares labeled the solar segment of the open
fields. The flares occurred in western-hemisphere active regions (ARs)
with coronal holes whose polarity agreed with the polarity of the
beam-carrying interplanetary fields in 23 of the 25 events. We conclude
that electron beams reach 1 AU from open AR fields adjacent to flare
sites. The Wang &amp; Sheeley implementation of the potential-field
source-surface model successfully identified the open fields in
36% of cases. Success meant that the open fields reached the source
surface within 3 heliographic deg of the interplanetary magnetic field
connected to ACE at 1 AU. Inclusion of five near misses improves
the success rate to 56%. The success rate for the Schrijver &amp;
DeRosa PFSS implementation was 50%. Our results suggest that, even
if the input magnetic data are updated frequently, the PFSS models
succeed in only ~50% of cases to identify the coronal segment of open
fields. Development of other techniques is in its infancy.

---------------------------------------------------------
Title: Erratum: "Tests and Comparisons of Velocity-Inversion
Techniques" (ApJ, 670, 1434 [2007])
Authors: Welsch, B. T.; Abbett, W. P.; DeRosa, M. L.; Fisher, G. H.;
Georgoulis, M. K.; Kusano, K.; Longcope, D. W.; Ravindra, B.; Schuck,
P. W.
2008ApJ...680..827W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Probing Open Magnetic Fields at the Sun with near-relativistic
electron beams
Authors: Haggerty, D. K.; Rust, D. M.; Georgoulis, M. K.
2008AGUSMSH43B..06H Altcode:
Processes associated with solar flares accelerate and inject
near-relativistic electrons onto open coronal field lines. Some of
these electron events propagate nearly scatter-free to 1 AU, where their
spectra and angular distributions can be measured. We used a carefully
selected list of electron events for which both the solar and near-Earth
positions are well known. Soft X-ray images from Yohkoh determined the
positions of coronal holes near active regions as well as the flares
associated with the electron events. We chose relatively small events
that exhibit nearly Gaussian shaped time-intensity profiles. These
events should incur minimal coronal and heliospheric transport effects,
which can affect the Sun-to-Earth path length. Twenty-five events
met our criteria for inclusion in the study. We use three different
methods to estimate the path-length of the electrons and two different
potential-field source-surface calculations to trace the open fields
from their intersection with the heliospheric field at 2.5 solar radii
down to the base of the corona. We report on the successes and failures
of these PFSS models to identify open fields in/near active regions
and to indicate correctly which open coronal fields are connected to
the interplanetary magnetic field at Earth.

---------------------------------------------------------
Title: The Fundamental Instability of Solar Magnetic Eruptions
Authors: Georgoulis, M. K.
2008AGUSMSP23B..06G Altcode:
We present a simple metric that can adequately quantify the eruptive
potential of solar active regions while in their pre-eruption
phases. Regions with intense magnetic polarity inversion lines exhibit
larger values of this metric, dubbed the effective connected magnetic
field strength, Beff. Calculating the pre-flare values of Beff in 93
flaring active regions and the peak Beff-values in 205 non-flaring ones
we find a clear segregation between the two populations that helps draw
a quantitative distinction between eruptive and non-eruptive active
regions. Larger Beff-values statistically correlate with stronger
flares and faster, more impulsively accelerated, coronal mass ejections
(CMEs). Besides the obvious implications for space weather forecasting,
this study underlines the fundamental insight that the Beff metric can
bring toward a physical understanding of solar eruptions. A possible new
eruption concept may eventually unify previous eruption models, relax
excessive requirements posed by some of these models, and naturally
explain confined vs. eruptive flares or fast (active-region) vs. slow
(quiet-Sun) CMEs.

---------------------------------------------------------
Title: Automatic Active-Region Identification and Azimuth
Disambiguation of the SOLIS/VSM Full-Disk Vector Magnetograms
Authors: Georgoulis, M. K.; Raouafi, N. -E.; Henney, C. J.
2008ASPC..383..107G Altcode: 2007arXiv0706.4444G
The Vector Spectromagnetograph (VSM) of the NSO's Synoptic Optical
Long-Term Investigations of the Sun (SOLIS) facility is now operational
and obtains the first-ever vector magnetic field measurements of the
entire visible solar hemisphere. To fully exploit the unprecedented
SOLIS/VSM data, however, one must first address two critical problems:
first, the study of solar active regions requires an automatic,
physically intuitive, technique for active-region identification
in the solar disk. Second, use of active-region vector magnetograms
requires removal of the azimuthal 180° ambiguity in the orientation
of the transverse magnetic field component. Here we report on an
effort to address both problems simultaneously and efficiently. To
identify solar active regions we apply an algorithm designed to locate
complex, flux-balanced, magnetic structures with a dominant East--West
orientation on the disk. Each of the disk portions corresponding
to active regions is thereafter extracted and subjected to the
Nonpotential Magnetic Field Calculation (NPFC) method that provides a
physically-intuitive solution of the 180° ambiguity. Both algorithms
have been integrated into the VSM data pipeline and operate in real
time, without human intervention. We conclude that this combined
approach can contribute meaningfully to our emerging capability for
full-disk vector magnetography as pioneered by SOLIS today and will be
carried out by ground-based and space-borne magnetographs in the future.

---------------------------------------------------------
Title: Magnetic complexity in eruptive solar active regions and
associated eruption parameters
Authors: Georgoulis, Manolis K.
2008GeoRL..35.6S02G Altcode: 2007arXiv0712.0143G
Using an efficient magnetic complexity index in the active-region solar
photosphere, we quantify the preflare strength of the photospheric
magnetic polarity inversion lines in 23 eruptive active regions with
flare/CME/ICME events tracked all the way from the Sun to the Earth. We
find that active regions with more intense polarity inversion lines
host statistically stronger flares and faster, more impulsively
accelerated, CMEs. No significant correlation is found between the
strength of the inversion lines and the flare soft X-ray rise times,
the ICME transit times, and the peak D st indices of the
induced geomagnetic storms. Corroborating these and previous results,
we speculate on a possible interpretation for the connection between
source active regions, flares, and CMEs. Further work is needed to
validate this concept and uncover its physical details.

---------------------------------------------------------
Title: Tests and Comparisons of Velocity-Inversion Techniques
Authors: Welsch, B. T.; Abbett, W. P.; De Rosa, M. L.; Fisher, G. H.;
Georgoulis, M. K.; Kusano, K.; Longcope, D. W.; Ravindra, B.; Schuck,
P. W.
2007ApJ...670.1434W Altcode:
Recently, several methods that measure the velocity of magnetized
plasma from time series of photospheric vector magnetograms have been
developed. Velocity fields derived using such techniques can be used
both to determine the fluxes of magnetic energy and helicity into the
corona, which have important consequences for understanding solar
flares, coronal mass ejections, and the solar dynamo, and to drive
time-dependent numerical models of coronal magnetic fields. To date,
these methods have not been rigorously tested against realistic,
simulated data sets, in which the magnetic field evolution and
velocities are known. Here we present the results of such tests
using several velocity-inversion techniques applied to synthetic
magnetogram data sets, generated from anelastic MHD simulations of
the upper convection zone with the ANMHD code, in which the velocity
field is fully known. Broadly speaking, the MEF, DAVE, FLCT, IM, and
ILCT algorithms performed comparably in many categories. While DAVE
estimated the magnitude and direction of velocities slightly more
accurately than the other methods, MEF's estimates of the fluxes of
magnetic energy and helicity were far more accurate than any other
method's. Overall, therefore, the MEF algorithm performed best in
tests using the ANMHD data set. We note that ANMHD data simulate
fully relaxed convection in a high-β plasma, and therefore do not
realistically model photospheric evolution.

---------------------------------------------------------
Title: Survey of Magnetic Helicity Injection in Regions Producing
X-Class Flares
Authors: LaBonte, B. J.; Georgoulis, M. K.; Rust, D. M.
2007ApJ...671..955L Altcode:
Virtually all X-class flares produce a coronal mass ejection (CME),
and each CME carries magnetic helicity into the heliosphere. Using
magnetograms from the Michelson Doppler Imager on the Solar
and Heliospheric Observatory, we surveyed magnetic helicity
injection into 48 X-flare-producing active regions recorded by
the MDI between 1996 July and 2005 July. Magnetic helicity flux
was calculated according to the method of Chae for the 48 X-flaring
regions and for 345 non-X-flaring regions. Our survey revealed that a
necessary condition for the occurrence of an X-flare is that the peak
helicity flux has a magnitude &gt;6×1036 Mx2
s-1. X-flaring regions also consistently had a higher net
helicity change during the ~6 day measurement intervals than nonflaring
regions. We find that the weak hemispherical preference of helicity
injection, positive in the south and negative in the north, is caused
by the solar differential rotation, but it tends to be obscured by the
intrinsic helicity injection, which is more disorganized and tends to be
of opposite sign. An empirical fit to the data shows that the injected
helicity over the range 1039-10 43 Mx2
s-1 is proportional to magnetic flux squared. Similarly,
over a range of 0.3-3000 days, the time required to generate the
helicity in a CME is inversely proportional to the magnetic flux
squared. Most of the X-flare regions generated the helicity needed
for a CME in a few days to a few hours.

---------------------------------------------------------
Title: Magnetic Energy and Helicity Budgets in the Active Region
Solar Corona. I. Linear Force-Free Approximation
Authors: Georgoulis, Manolis K.; LaBonte, Barry J.
2007ApJ...671.1034G Altcode: 2007arXiv0706.4122G
We self-consistently derive the magnetic energy and relative magnetic
helicity budgets of a three-dimensional linear force-free magnetic
structure rooted in a lower boundary plane. For the potential magnetic
energy we derive a general expression that gives results practically
equivalent to those of the magnetic virial theorem. All magnetic energy
and helicity budgets are formulated in terms of surface integrals
applied to the lower boundary, thus avoiding computationally intensive
three-dimensional magnetic field extrapolations. We analytically and
numerically connect our derivations with classical expressions for the
magnetic energy and helicity, thus presenting a unified treatment of
the energy/helicity budgets in the constant-alpha approximation that
is lacking so far. Applying our derivations to photospheric vector
magnetograms of an eruptive and a noneruptive solar active region,
we find that the most profound quantitative difference between these
regions lies in the estimated free magnetic energy and relative magnetic
helicity budgets. If this result is verified with a large number of
active regions, it will advance our understanding of solar eruptive
phenomena. We also find that the constant-alpha approximation gives
rise to large uncertainties in the calculation of the free magnetic
energy and the relative magnetic helicity. Therefore, care must be
exercised when this approximation is applied to photospheric magnetic
field observations. Despite its shortcomings, the constant-alpha
approximation is adopted here because this study will form the basis
of a comprehensive nonlinear force-free description of the energetics
and helicity in the active region solar corona, which is our ultimate
objective.

---------------------------------------------------------
Title: Quantifying turbulence in solar magnetic fields: can this
help predict solar eruptions?
Authors: Georgoulis, M. K.
2007AGUFMSH14B..01G Altcode:
Magnetic fields in solar active regions present us with a beautiful,
although inextricable, complexity, and undergo dynamical evolution that
is often far from predictable. This behavior is commonly attributed
to the inherently turbulent, filamentary nature of magnetic fields
in the solar atmosphere. We ask whether this turbulence and its
manifestations can help us predict solar eruptions. To this purpose,
we briefly outline the physical relationship between turbulence and
(critical) self-organization, as well as their phenomenology, such as
spatiotemporal intermittency, self-similar fragmentation, fractality,
and multifractality of solar active-region magnetic fields. We also
review the array of techniques that have been recently implemented
to quantify these turbulent features and we apply them to numerous
flaring and nonflaring active regions aiming toward quantitative
flare prediction. Results and conclusions are presented in hopes
to intrigue and stimulate further discussion on this fascinating,
clearly outstanding, problem.

---------------------------------------------------------
Title: Quantitative Forecasting of Major Solar Flares
Authors: Georgoulis, Manolis K.; Rust, David M.
2007ApJ...661L.109G Altcode:
We define the effective connected magnetic field, Beff,
a single metric of the flaring potential in solar active regions. We
calculated Beff for 298 active regions (93 X- and M-flaring,
205 nonflaring) as recorded by SOHO/MDI during a 10 yr period covering
much of solar cycle 23. We find that Beff is a robust
criterion for distinguishing flaring from nonflaring regions. A
well-defined 12 hr conditional probability for major flares depends
solely on Beff. This probability exceeds 0.95 for M-class and
X-class flares if Beff&gt;1600 G and Beff&gt;2100
G, respectively, while the maximum calculated Beff-values
are near 4000 G. Active regions do not give M-class and X-class
flares if Beff&lt;200 G and Beff&lt;750 G,
respectively. We conclude that Beff is an efficient
flare-forecasting criterion that can be computed on a timely basis
from readily available data.

---------------------------------------------------------
Title: Assessment Of The Eruptive Potential In Solar Active Regions
Authors: Georgoulis, Manolis K.; Rust, D. M.
2007AAS...210.9325G Altcode: 2007BAAS...39Q.215G
Solar active regions involving massive amounts of magnetic flux and
conspicuous polarity inversion lines have always been considered likely
sources of major flares and fast active-region CMEs. We quantify the
magnetic complexity in the photospheric boundary of active regions
and thereafter infer a well-defined 12-24-hour likelihood of major
eruptions. Vector magnetograms are not required for our analysis,
which is validated by application to about 300 active regions observed
by SoHO/MDI over a period of a few to several days each. The proposed
single metric favors a well-defined physical mechanism for major flares
and CMEs and may lead to a detailed, quantitative, understanding of
the flare/CME phenomenon. This work has received partial support by
NASA Grant NNG05-GM47G.

---------------------------------------------------------
Title: The Fundamental Role Of Magnetic Helicity In Major Solar
Eruptions
Authors: Rust, David M.; Georgoulis, M. K.
2007AAS...210.2913R Altcode: 2007BAAS...39R.139R
What is the role magnetic helicity plays in solar eruptions? To find
out, we calculate the magnetic helicity flux for 48 X-class flaring
solar active regions and for 345 M-class flaring regions. Each region
was observed over a period of a few, to several, days by SoHO/MDI. We
find consistently higher helicity buildup rates for the X-flaring
regions. X-class flares do not occur if the peak helicity flux is
smaller than 6 x 1036 Mx2/s, with most nonflaring
regions showing much smaller peaks. The weak hemispheric preference of
magnetic helicity is caused by the solar differential rotation,
but it is blurred by the intrinsic helicity injection which is more
disorganized and of opposite sign. Notably, X-flaring regions can
generate the helicity for a typical CME within a few hours to a few
days, contrary to most flare-quiescent regions that require from several
tens to hundreds of days. We conclude that accumulation of magnetic
helicity is a precondition for major flare/CME events. This work has
received partial support by NASA Grants NAG5-13504 and NNG05-GM47G.

---------------------------------------------------------
Title: LWS TR&amp;T Project on the CME - ICME Connection: A Progress
Report
Authors: Georgoulis, M. K.
2006AGUFMSH21B..07G Altcode:
During the second year of the above LWS TR&amp;T Grant, we report on
our efforts and progress. The Project highlights and will continue
to uncover the wealth of eruptive diagnostics that can be obtained by
studying vector (but also line-of-sight) magnetograms of solar active
regions. Here we focus on one particular aspect of active-region
physics: the elusive relation between the free magnetic energy and
the magnetic helicity budget of eruptive and non-eruptive active
regions. Besides shedding light into the eruption process itself,
this analysis can uncover the true relation between the magnetic
structures of the propagating ICMEs and that of the progenitor CMEs
and the source active regions. This, as the title suggests, is the
ultimate objective of the Project.

---------------------------------------------------------
Title: Goals and Progress of the LWS Focused Science Topic on the
CME--ICME Connection
Authors: Mikic, Z.; Deforest, C.; Devore, R.; Georgoulis, M.; Jackson,
B.; Nitta, N.; Pizzo, V.; Odstrcil, D.
2006AGUFMSH21B..05M Altcode:
Our team addresses the NASA Living With a Star (LWS) Focused Science
Topic "to determine the solar origins of the plasma and magnetic flux
observed in an interplanetary Coronal Mass Ejection (ICME)." In short,
this team is examining the CME--ICME connection. Our team was formed
as a result of awards from the LWS Targeted Research &amp;Technology
competition in the fall of 2004. Our team is investigating the detailed
relationship between the plasma and magnetic fields in active regions,
the source regions of CMEs, and subsequent in situ measurements in
interplanetary magnetic clouds. We plan to study this connection through
detailed numerical simulations of CME initiation and propagation,
theoretical investigations, and studies of the properties of active
regions, CMEs, and magnetic clouds. We will discuss the goals of
our team, how it fits into NASA's missions, and our progress so
far. Research supported by NASA's Living With a Star Program.

---------------------------------------------------------
Title: An Overview of Existing Algorithms for Resolving the
180° Ambiguity in Vector Magnetic Fields: Quantitative
Tests with Synthetic Data
Authors: Metcalf, Thomas R.; Leka, K. D.; Barnes, Graham; Lites,
Bruce W.; Georgoulis, Manolis K.; Pevtsov, A. A.; Balasubramaniam,
K. S.; Gary, G. Allen; Jing, Ju; Li, Jing; Liu, Y.; Wang, H. N.;
Abramenko, Valentyna; Yurchyshyn, Vasyl; Moon, Y. -J.
2006SoPh..237..267M Altcode: 2006SoPh..tmp...14M
We report here on the present state-of-the-art in algorithms used
for resolving the 180° ambiguity in solar vector magnetic field
measurements. With present observations and techniques, some assumption
must be made about the solar magnetic field in order to resolve
this ambiguity. Our focus is the application of numerous existing
algorithms to test data for which the correct answer is known. In
this context, we compare the algorithms quantitatively and seek to
understand where each succeeds, where it fails, and why. We have
considered five basic approaches: comparing the observed field to a
reference field or direction, minimizing the vertical gradient of the
magnetic pressure, minimizing the vertical current density, minimizing
some approximation to the total current density, and minimizing some
approximation to the field's divergence. Of the automated methods
requiring no human intervention, those which minimize the square of
the vertical current density in conjunction with an approximation for
the vanishing divergence of the magnetic field show the most promise.

---------------------------------------------------------
Title: Distinguishing Eruptive From Non-eruptive Solar Active Regions
Authors: Georgoulis, Manolis K.
2006SPD....37.2003G Altcode: 2006BAAS...38..248G
Every intense magnetic flux accumulation in the Sun, known
as activeregion (AR), engages into small-scale energy release
activitiesmanifesting themselves as sub-flares. Of the several
thousands of ARsthat emerge, evolve, and disappear within a typical
solar cycle,however, only a tiny percentage will ever trigger one
or more majorflares (X- or M-class). These flares are most commonly
related tofurther eruptive activity, such as coronal mass ejections
(CMEs).Identifying eruptive ARs while in their pre-eruption phases
will bethe subject of this presentation. With little doubt existing
over themagnetic origin of solar eruptions, I will highlight possible
areas offuture research in AR magnetic fields. The timing of magnetic
fieldstudies is excellent in view of the anticipated wealth of
vectormagnetogram data from SOLIS, Solar-B, and the SDO. While our goal
ispractical, namely the quantitative assessment of the eruptivepotential
of ARs, the recommended tactic entails fundamental physicalproperties
of AR magnetic fields such as their three-dimensionalstructure, energy
budgets, and complexity, reflected on theirhelical properties. The
elusive role of magnetic helicity in solareruptions and our limitations
in assessing it will be particularlyemphasized.

---------------------------------------------------------
Title: Reconstruction of an Inductive Velocity Field Vector from
Doppler Motions and a Pair of Solar Vector Magnetograms
Authors: Georgoulis, Manolis K.; LaBonte, Barry J.
2006ApJ...636..475G Altcode: 2005astro.ph.11447G
We outline a general methodology to infer the inductive velocity
field vector in solar active regions. For the first time, both
the field-aligned and the cross-field velocity components are
reconstructed. The cross-field velocity solution accounts for the
changes of the vertical magnetic field seen between a pair of successive
active region vector magnetograms via the ideal induction equation. The
field-aligned velocity is obtained using the Doppler velocity and the
calculated cross-field velocity. Solving the ideal induction equation
in vector magnetograms measured at a given altitude in the solar
atmosphere is an underdetermined problem. In response, our general
formalism allows the use of any additional constraint for the inductive
cross-field velocity to enforce a unique solution in the induction
equation. As a result, our methodology can give rise to new velocity
solutions besides the one presented here. To constrain the induction
equation, we use a special case of the minimum structure approximation
that was introduced in previous studies and is already employed here
to resolve the 180° ambiguity in the input vector magnetograms. We
reconstruct the inductive velocity for three active regions, including
NOAA AR 8210, for which previous results exist. Our solution believably
reproduces the horizontal flow patterns in the studied active regions
but breaks down in cases of localized rapid magnetic flux emergence or
submergence. Alternative approximations and constraints are possible
and can be accommodated into our general formalism.

---------------------------------------------------------
Title: Emergence of undulatory magnetic flux tubes by small scale
reconnections
Authors: Pariat, E.; Aulanier, G.; Schmieder, B.; Georgoulis, M. K.;
Rust, D. M.; Bernasconi, P. N.
2006AdSpR..38..902P Altcode:
With Flare Genesis Experiment (FGE), a balloon borne observatory
launched in Antarctica on January 2000, series of high spatial
resolution vector magnetograms, Dopplergrams, and Hα filtergrams
have been obtained in an emerging active region (AR 8844). Previous
analyses of this data revealed the occurence of many short-lived
and small-scale H α brightenings called 'Ellerman bombs'
(EBs) within the AR. We performed an extrapolation of the field above
the photosphere using the linear force-free field approximation. The
analysis of the magnetic topology reveals a close connexion between
the loci of EBs and the existence of "Bald patches" (BP) regions
(BPs are regions where the vector magnetic field is tangential to
the photosphere). Some of these EBs/BPs are magnetically connected
by low-lying field lines, presenting a serpentine shape. This results
leads us to conjecture that arch filament systems and active regions
coronal loops do not result from the smooth emergence of large scale
Ω-loops, but rather from the rise of flat undulatory flux tubes which
get released from their photospheric anchorage by reconnection at BPs,
which observational signature is Ellerman bombs.

---------------------------------------------------------
Title: Observation of Small Scale Reconnection Role in Undulated
Flux Tube Emergence
Authors: Pariat, E.; Aulanier, G.; Schmieder, B.; Georgoulis, M. K.;
Rust, D. M.; Bernasconi, P. N.
2005ESASP.596E..34P Altcode: 2005ccmf.confE..34P
No abstract at ADS

---------------------------------------------------------
Title: A New Technique for a Routine Azimuth Disambiguation of Solar
Vector Magnetograms
Authors: Georgoulis, Manolis K.
2005ApJ...629L..69G Altcode:
We introduce a nonpotential magnetic field calculation (NPFC) technique
to perform azimuth disambiguation in solar vector magnetograms. It is
shown that resolving the 180° ambiguity would be a numerically fully
determined problem if the vertical electric current density was known
a priori. Since this is not the case, we enforce a minimum-magnitude
current density solution. The NPFC disambiguation is otherwise
assumption-free, with the quality of the results depending on
the quality of the measurements. The NPFC method first infers the
nonpotential magnetic field component responsible for the assumed
vertical currents and then determines the vertical magnetic field
whose potential extrapolation, added to the nonpotential field,
best reproduces the observationally inferred horizontal magnetic
field. The technique is fast, effective, and physically sound, so it
may be instrumental in a routine, real-time, disambiguation of future
space-borne solar vector magnetograms.

---------------------------------------------------------
Title: Distinguishing Between Eruptive and Quiescent Solar Active
Regions
Authors: Georgoulis, M. K.; Labonte, B. J.
2005AGUSMSH53B..05G Altcode:
We present a method to fully evaluate the energy-helicity formula in
solar active regions by using only photospheric vector magnetograms of
these active regions. At the moment, the method relies on the linear
force-free approximation and provides the total magnetic energy,
the magnetic energy of the vacuum (potential) magnetic field, and the
non-potential (free) magnetic energy relating to the total magnetic
helicity in an active region. The formulation of the technique allows
an upgrade to a nonlinear force-free evaluation of the energy-helicity
formula, which will be a more realistic approach especially when
chromospheric vector magnetograms of solar active regions become
available. Even with the linear force-free approximation, however,
we find that the magnitudes of the total helicity, as well as the
ratios of the free magnetic energy to the total magnetic energy are
distinctly higher for eruptive active regions as compared to quiescent
active regions. Eruptive active regions produce flares and might trigger
CMEs, so the method presents a viable way to discriminate between these
two types of active regions even in case a single vector magnetogram
of these active regions is available.

---------------------------------------------------------
Title: Boundary Flows in Solar Active Regions
Authors: Georgoulis, M. K.; Labonte, B. J.
2005AGUSMSH51C..10G Altcode:
We present a general technique to calculate the flow field at the
altitude where vector magnetic field measurements of solar active
regions have been obtained. The velocity field vector is reconstructed
fully by solving the ideal induction equation of magnetohydrodynamics
for the cross-field velocity component and by utilizing the
Doppler velocity information to calculate the field-aligned velocity
component. Because solving the induction equation is an under-determined
problem, we have formulated our technique in such a way as to provide a
unique solution of the induction equation when the vertical (normal to
the boundary) component of the cross-field velocity is prescribed. We
provide examples of various possible choices for the cross-field
vertical velocity and we discuss the respective results. Moreover, we
showcase the validity of our technique by predicting the particular area
of NOAA active region 8210 from which a flare and a CME were triggered,
using the reconstructed velocity field vector.

---------------------------------------------------------
Title: Turbulence In The Solar Atmosphere: Manifestations And
Diagnostics Via Solar Image Processing
Authors: Georgoulis, Manolis K.
2005SoPh..228....5G Altcode: 2005astro.ph.11449G
Intermittent magnetohydrodynamical turbulence is most likely at work
in the magnetized solar atmosphere. As a result, an array of scaling
and multi-scaling image-processing techniques can be used to measure
the expected self-organization of solar magnetic fields. While these
techniques advance our understanding of the physical system at work,
it is unclear whether they can be used to predict solar eruptions,
thus obtaining a practical significance for space weather. We
address part of this problem by focusing on solar active regions
and by investigating the usefulness of scaling and multi-scaling
image-processing techniques in solar flare prediction. Since solar
flares exhibit spatial and temporal intermittency, we suggest that
they are the products of instabilities subject to a critical threshold
in a turbulent magnetic configuration. The identification of this
threshold in scaling and multi-scaling spectra would then contribute
meaningfully to the prediction of solar flares. We find that the fractal
dimension of solar magnetic fields and their multi-fractal spectrum of
generalized correlation dimensions do not have significant predictive
ability. The respective multi-fractal structure functions and their
inertial-range scaling exponents, however, probably provide some
statistical distinguishing features between flaring and non-flaring
active regions. More importantly, the temporal evolution of the above
scaling exponents in flaring active regions probably shows a distinct
behavior starting a few hours prior to a flare and therefore this
temporal behavior may be practically useful in flare prediction. The
results of this study need to be validated by more comprehensive works
over a large number of solar active regions. Sufficient statistics may
also establish critical thresholds in the values of the multi-fractal
structure functions and/or their scaling exponents above which a flare
may be predicted with a high level of confidence.

---------------------------------------------------------
Title: Transport of Magnetic Helicity and Dynamics of Solar Active
Regions
Authors: Georgoulis, M. K.; Labonte, B. J.; Rust, D. M.
2005HiA....13..117G Altcode:
We outline a simple method to monitor variations of the magnetic
helicity the current helicity and the non-potential (free) magnetic
energy on the photospheric boundary of solar active regions. Explicit
manifestations of dynamical activity in the solar atmosphere such as
flares coronal mass ejections and filament eruptions may be related to
these variations. While similar methods require knowledge of the vector
potential and the velocity field vector on the photosphere our method
requires only the photospheric potential magnetic field corresponding
to the observed magnetograms. The calculation of the potential field
for any given magnetogram is straightforward. Moreover our method
relies on the constant-alpha force-free approximation assumed to hold
in the active region. Whether the above is a realistic assumption
can be tested using an array of well-documented methods. Therefore
our technique may prove quite useful to at least a subset of active
regions in which the linear force-free approximation is justifiable.

---------------------------------------------------------
Title: Forecasting and Real-Time Diagnostics of Solar Coronal Mass
Ejections
Authors: Georgoulis, M. K.; Labonte, B. J.
2004AGUFMSA43B..02G Altcode:
We discuss an operational, fully automated, algorithm to follow
the dynamical evolution and the buildup of magnetic instabilities
that give rise to coronal mass ejections (CMEs) in solar active
regions. The tool relies on vector magnetic field measurements
of the active region photosphere / chromosphere and performs the
following tasks: (1) resolution of the 180-degree ambiguity in
the magnetic field measurements and preparation for further use,
(2) calculation of the magnetic forces and electric currents in
the active region photosphere/chromosphere, (3) reconstruction of
a magnetohydrodynamic velocity field corresponding to the measured
magnetic field to calculate the buildup rate of the magnetic helicity
in the active region atmosphere, and (4) estimation of the total
magnetic helicity in the active region corona. We present examples
showing that (I) flare- and CME-prolific active regions have much
higher magnetic helicity, stronger magnetic forces and more intense
cross-field electric currents than quiescent active regions, and
(II) the magnetic helicity, chirality, magnetic flux, and magnetic
energy of a CME can be calculated in real time from the results of the
algorithm before and after the CME. As a result, we can both identify
potentially eruptive areas on the visible solar disk and provide
detailed quantitative diagnostics of the resulting CMEs. Additional
work is required to predict the geoeffectiveness of these CMEs. For
the algorithm to be useful we need full-disk, ideally uninterrupted,
coverage of the solar magnetic field vector. This information will
be available in a few years with the Helioseismic and Magnetic Imager
(HMI) on board the Solar Dynamics Observatory (SDO; launch 2008). At
the moment, full-disk vector magnetograms will be provided by the
ground-based Vector Spectro-Magnetograph (VSM) of the Synoptic Optical
Long-Term Investigation of the Sun (SOLIS) telescope. We will utilize
the SOLIS vector magnetograms as soon as they become available.

---------------------------------------------------------
Title: An Integrated Program to Forecast Geostorms
Authors: Labonte, B. J.; Rust, D.; Bernasconi, P.; Georgoulis, M.
2004AGUFMSA51B0243L Altcode:
We have developed several operational products and automated tools for
assessing the helicity content of solar regions and their probability of
launching a geoeffective coronal mass ejection. These include detection
of active region sigmoids, measurement of magnetic helicity injection
in active regions, measurement of the sense of helicity in solar
filaments, and the estimate of magnetic helicity content of active
regions from vector magnetogram observations. In this presentation
we discuss a new program to integrate the separate products and tools
into a single product that provides a quantitative mid-term forecast
of solar activity that results in geomagnetic storms.

---------------------------------------------------------
Title: Vertical Lorentz Force and Cross-Field Currents in the
Photospheric Magnetic Fields of Solar Active Regions
Authors: Georgoulis, Manolis K.; LaBonte, Barry J.
2004ApJ...615.1029G Altcode:
We demonstrate that the vertical Lorentz force and a corresponding lower
limit of the cross-field electric current density can be calculated
from vector magnetograms of solar active regions obtained at a single
height in the solar atmosphere, provided that the vertical gradient
of the magnetic field strength is known at this height. We use a
predicted vertical magnetic field gradient derived from a previous
analysis. By testing various force-free solutions, we find that the
numerical accuracy of our method is satisfactory. Applying the method
to active region photospheric vector magnetograms, we find vertical
Lorentz forces ranging from several hundredths to a few tenths of
the typical photospheric gravitational force, and typical cross-field
current densities up to several times 10 mA m-2. The typical
vertical current density is found to be 2-3 times smaller, on the order
of 10-15 mA m-2. These differences are above the associated
uncertainties. The values of the cross-field currents decrease in an
averaged vector magnetogram, but the ratio of the cross-field to the
vertical current density increases, also above the uncertainties. We
conclude that the photospheric active region magnetic fields are not
force-free, contrary to the conjectures of some recent studies.

---------------------------------------------------------
Title: Resistive Emergence of Undulatory Flux Tubes
Authors: Pariat, E.; Aulanier, G.; Schmieder, B.; Georgoulis, M. K.;
Rust, D. M.; Bernasconi, P. N.
2004ApJ...614.1099P Altcode:
During its 2000 January flight, the Flare Genesis Experiment observed
the gradual emergence of a bipolar active region, by recording a series
of high-resolution photospheric vector magnetograms and images in the
blue wing of the Hα line. Previous analyses of these data revealed the
occurrence of many small-scale, transient Hα brightenings identified
as Ellerman bombs (EBs). They occur during the flux emergence,
and many of them are located near moving magnetic dipoles in which
the vector magnetic field is nearly tangential to the photosphere. A
linear force-free field extrapolation of one of the magnetograms was
performed to study the magnetic topology of small-scale EBs and their
possible role in the flux emergence process. We found that 23 out of 47
EBs are cospatial with bald patches (BPs), while 15 are located at the
footpoints of very flat separatrix field lines passing through distant
BPs. We conclude that EBs can be due to magnetic reconnection, not only
at BP locations, but also along their separatrices, occurring in the
low chromosphere. The topological analysis reveals, for the first time,
that many EBs and BPs are linked by a hierarchy of elongated flux tubes
showing aperiodic spatial undulations, whose wavelengths are typically
above the threshold of the Parker instability. These findings suggest
that arch filament systems and coronal loops do not result from the
smooth emergence of large-scale Ω-loops from below the photosphere,
but rather from the rise of undulatory flux tubes whose upper parts
emerge because of the Parker instability and whose dipped lower parts
emerge because of magnetic reconnection. EBs are then the signature
of this resistive emergence of undulatory flux tubes.

---------------------------------------------------------
Title: On the Self-Similarity of Unstable Magnetic Discontinuities
in Solar Active Regions
Authors: Vlahos, Loukas; Georgoulis, Manolis K.
2004ApJ...603L..61V Altcode:
We investigate the statistical properties of possible magnetic
discontinuities in two solar active regions over the course
of several hours. We use linear force-free extrapolations to
calculate the three-dimensional magnetic structure in the active
regions. Magnetic discontinuities are identified using various selection
criteria. Independently of the selection criterion, we identify large
numbers of magnetic discontinuities whose free magnetic energies
and volumes obey well-formed power-law distribution functions. The
power-law indices for the free energies are in the range [-1.6,
-1.35], in remarkable agreement with the power-law indices found in the
occurrence frequencies of solar flare energies. This agreement and the
strong self-similarity of the volumes that are likely to host flares
suggest that the observed statistics of flares may be the natural
outcome of a preexisting spatial self-organization accompanying the
energy fragmentation in solar active regions. We propose a dynamical
picture of flare triggering consistent with recent observations by
reconciling our results with the concepts of percolation theory and
self-organized criticality. These concepts rely on self-organization,
which is expected from the fully turbulent state of the magnetic fields
in the solar atmosphere.

---------------------------------------------------------
Title: On the Resolution of the Azimuthal Ambiguity in Vector
Magnetograms of Solar Active Regions
Authors: Georgoulis, Manolis K.; LaBonte, Barry J.; Metcalf, Thomas R.
2004ApJ...602..446G Altcode:
We introduce a “structure minimization” technique to resolve the
azimuthal ambiguity of 180°, intrinsic in solar vector magnetic
field measurements. We resolve the 180° ambiguity by minimizing the
inhomogeneities of the magnetic field strength perpendicular to the
magnetic field vector. This relates to a minimization of the sheath
currents that envelope the solar magnetic flux tubes, thus allowing
for more space-filling and less complex magnetic fields. Structure
minimization proceeds in two steps: First, it derives a local solution
analytically, by means of a structure minimization function. Second,
it reaches a global solution numerically, assuming smoothness of the
magnetic field vector. Structure minimization (i) is disentangled from
any use of potential or linear force-free extrapolations and (ii)
eliminates pixel-to-pixel dependencies, thus reducing exponentially
the required computations. We apply structure minimization to four
active regions, located at various distances from disk center. The
minimum structure solution for each case is compared with the
“minimum energy” solution obtained by the slower simulated
annealing algorithm. We find correlation coefficients ranging from
significant to excellent. Moreover, structure minimization provides
an ambiguity-free vertical gradient of the magnetic field strength
that reveals the variation of the magnetic field with height. The
simplicity and speed of the method allow a near real-time processing
of solar vector magnetograms. This task was not possible in the past
and may be of interest to both existing and future solar missions and
ground-based magnetographs.

---------------------------------------------------------
Title: Emerging Flux and the Heating of Coronal Loops
Authors: Schmieder, B.; Rust, D. M.; Georgoulis, M. K.; Démoulin,
P.; Bernasconi, P. N.
2004ApJ...601..530S Altcode:
We use data collected by a multiwavelength campaign of observations
to describe how the fragmented, asymmetric emergence of magnetic flux
in NOAA active region 8844 triggers the dynamics in the active-region
atmosphere. Observations of various instruments on board Yohkoh, SOHO,
and TRACE complement high-resolution observations of the balloon-borne
Flare Genesis Experiment obtained on 2000 January 25. We find that
coronal loops appeared and evolved rapidly ~6+/-2 hr after the first
detection of emerging magnetic flux. In the low chromosphere, flux
emergence resulted in intense Ellerman bomb activity. Besides the
chromosphere, we find that Ellerman bombs may also heat the transition
region, which showed “moss” ~100% brighter in areas with Ellerman
bombs as compared to areas without Ellerman bombs. In the corona,
we find a spatiotemporal anticorrelation between the soft X-ray (SXT)
and the extreme ultraviolet (TRACE) loops. First, SXT loops preceded
the appearance of the TRACE loops by 30-40 minutes. Second, the TRACE
and SXT loops had different shapes and different footpoints. Third,
the SXT loops were longer and higher than the TRACE loops. We conclude
that the TRACE and the SXT loops were formed independently. TRACE loops
were mainly heated at their footpoints, while SXT loops brightened in
response to coronal magnetic reconnection. In summary, we observed a
variety of coupled activity, from the photosphere to the active-region
corona. Links between different aspects of this activity lead to
a unified picture of the evolution and the energy release in the
active region.

---------------------------------------------------------
Title: Emerging Flux and the Heating of Coronal Loops
Authors: Schmieder, B.; Démoulin, P.; Rust, D. M.; Georgoulis, M. K.;
Bernasconi, P. N.
2004IAUS..219..483S Altcode: 2003IAUS..219E..18S
We suggest that coronal loop heating is caused by dissipation of
magnetic energy as new magnetic flux emerges from the photosphere. Based
on data from a multi wavelength campaign of observations during the
flight of the Flare Genesis Experiment we describe how emergence
of flux from the photosphere appears directly to heat the corona
to 2-3 MK. Following intense heating the loops cool and become
visible through the filters of the TRACE (Transition Region and
Coronal Explorer)instrument at one million degrees. We determine the
relaxation time of the cooling and compare it withtheoretical heating
functions. The proposed mechanism is well accepted in flare loops but
we suggest that the mechanism is generally valid and helps to explain
the visibility of active region loops in transition region lines.

---------------------------------------------------------
Title: Emergence of undulatory magnetic flux tubes by small scale
reconnections
Authors: Pariat, E.; Aulanier, G.; Schmieder, B.; Georgoulis, M. K.;
Rust, D. M.; Bernasconi, P. N.
2004cosp...35.1482P Altcode: 2004cosp.meet.1482P
With Flare Genesis Experiment (FGE), a balloon borne observatory
launched in Antarctica on January 2000, series of high spatial
resolution vector magnetograms, Dopplergrams, and Hα filtergrams
have been obtained in an emerging active region (AR 8844). Previous
analyses of this data revealed the occurence of many short-lived and
small-scale Hα brightenings called 'Ellerman bombs' (EBs) within the
AR. We performed an extrapolation of the field above the photosphere
using the linear force-free field approximation. The analysis of the
magnetic topology reveals a close connexion between the loci of EBs
and the existence of “Bald patches” regions (BPs are regions where
the vector magnetic field is tangential to the photosphere). Among
47 identified EBs, we found that 23 are co-spatial with a BP, while
19 are located at the footpoint of very flat separatrix field lines
passing throught a distant BP. We reveal for the first time that
some of these EBs/BPs are magneticaly connected by low-lying lines,
presenting a 'sea-serpent' shape. This results leads us to conjecture
that arch filament systems and active regions coronal loops do not
result from the smooth emergence of large scale Ω loops, but rather
from the rise of flat undulatory flux tubes which get released from
their photospheric anchorage by reconnection at BPs, whose observational
signature is Ellerman bombs.

---------------------------------------------------------
Title: Statistical Properties of Flaring and Sub-Flaring Activity
in the Solar Atmosphere
Authors: Georgoulis, Manolis K.
2004hell.conf...15G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Lorentz Forces and Helicity Diagnostics in Solar Active
Regions Based on a Fast Resolution of the Azimuthal Ambiguity in
Solar Vector Magnetograms
Authors: Georgoulis, Manolis K.; Labonte, Barry J.; Rust, David M.
2004hell.conf...82G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Calculation of a Minimum Total Magnetic Helicity in Solar
Active Regions
Authors: Georgoulis, M. K.; Labonte, B. J.
2003AGUFMSH51A..03G Altcode:
Despite its extreme importance, the calculation of the total magnetic
helicity in solar active regions remains an unresolved problem in
solar physics. On the other hand, the helicity variations in an active
region can be calculated partially, for longitudinal magnetograms,
or in full, for vector magnetograms, but only by using coarse,
uncertain velocity field maps, calculated by means of correlation
tracking techniques. Whether one should apply correlation tracking
to magnetograms or white-light continuum images is also unclear,
as the two inputs do not yield identical outputs. We present a
technique that provides a lower limit of the total magnetic helicity
in active regions, without using any velocity fields. The temporal
variation of the total helicity can also be calculated in full if
a series of vector magnetograms is available. The method relies on
a comparison between the best linear force-free approximation and
the potential approximation for a given photospheric boundary and
begins by demonstrating that a commonly used formula for the magnetic
helicity density in the linear force-free approximation is, in fact,
erroneous. We have tested our method on vector magnetograms acquired by
the Imaging Vector Magnetograph (IVM) of the University of Hawaii. We
discuss the pros and cons of our approach and we compare our results for
the magnetic helicity variations with results obtained when classical
methods are employed.

---------------------------------------------------------
Title: Resolution of the Azimuthal Ambiguity in Photospheric Vector
Magnetograms of Solar Active Regions
Authors: Georgoulis, M. K.; LaBonte, B. J.
2003SPD....34.1103G Altcode: 2003BAAS...35Q.827G
We describe a simple technique to resolve the inherent azimuthal
ambiguity of 180o in vector magnetic field measurements of
solar active regions. The desired azimuth solution is the one that
minimizes an introduced function. This function includes a weighted
combination of the height derivative of the magnetic field strength,
calculated under conditions of minimum electric current density, and
the vertical component of a current density vector purely perpendicular
to the magnetic field lines. The above function reduces the number of
ambiguity states to two for each location on the heliographic plane. The
process is initially local, i.e., independent for each location on the
heliographic plane. Then, the initial azimuth solution is subjected
to a numerical analysis which yields the global azimuth solution
and ensures maximum continuity of the photospheric magnetic field
vector. This tactic reduces dramatically the required computing time to
only a small fraction of the time required by existing techniques. The
construction of the above-mentioned function is such that the method
works equally well for active regions located either near or far
from the center of the solar disk. The speed and simplicity of this
novel technique may lead to a near real-time processing of acquired
photospheric vector magnetograms. A reliable azimuth solution is a
prerequisite for further analysis of solar magnetic fields. Reaching
such a solution fast, is paramount for challenging modern problems,
such as space weather forecasting, for example.

---------------------------------------------------------
Title: Near-infrared chromospheric observatory
Authors: Labonte, Barry; Rust, David M.; Bernasconi, Pietro N.;
Georgoulis, Manolis K.; Fox, Nicola J.; Kalkofen, Wolfgang; Lin,
Haosheng
2003SPIE.4853..140L Altcode:
NICO, the Near Infrared Chromosphere Observatory, is a platform for
determining the magnetic structure and fources of heating for the
solar chromosphere. NICO, a balloon-borne observatory, will use the
largest solar telescope flying to map the magnetic fields, velocities,
and heating events of the chromosphere and photosphere in detail. NICO
will introduce new technologies to solar flight missions, such as
wavefront sensing for monitoring telescope alignment, real-time
correlation tracking and high-speed image motion compensation, and
wide aperture Fabry-Perot etalons for extended spectral scanning.

---------------------------------------------------------
Title: Transport of Helicity and Dynamics of Solar Active Regions
Authors: Georgoulis, Manolis K.; Rust, David M.; Labonte, Barry J.
2003IAUJD...3E..29G Altcode:
We outline a simple method to monitor variations of the magnetic
helicity the current helicity and the non-potential (free) magnetic
energy on the photospheric boundary of solar active regions. Explicit
manifestations of dynamical activity in the solar atmosphere such as
flares coronal mass ejections and filament eruptions may be related to
these variations. While similar methods require knowledge of the vector
potential and the velocity field vector on the photosphere our method
requires only the photospheric potential magnetic field corresponding
to the observed magnetograms. The calculation of the potential field
for any given magnetogram is straightforward. Moreover our method
relies on the constant-alpha force-free approximation assumed to hold
in the active region. Whether the above is a realistic assumption
can be tested using an array of well-documented methods. Therefore
our technique may prove quite useful to at least a subset of active
regions in which the linear force-free approximation is justifiable.

---------------------------------------------------------
Title: Flare Genesis Experiment: magnetic topology of Ellerman bombs
Authors: Schmieder, B.; Pariat, E.; Aulanier, G.; Georgoulis, M. K.;
Rust, D. M.; Bernasconi, P. N.
2002ESASP.506..911S Altcode: 2002svco.conf..911S; 2002ESPM...10..911S
Flare Genesis Experiment (FGE), a balloon borne Observatory was launched
in Antarctica on January 10, 2000 and flew during 17 days. FGE consists
of an 80 cm Cassegrain telescope with an F/1.5 ultra-low-expansion
glass primary mirror and a crystalline silicon secondary mirror. A
helium-filled balloon carried the FGE to an altitude of 37 km
(Bernasconi et al. 2000, 2001). We select among all the observations a
set of high spatial and temporal resolution observations of an emerging
active region with numerous Ellerman bombs (EBs). Statistical and
morphology analysis have been performed. We demonstrate that Ellerman
bombs are the result of magnetic reconnection in the low chromosphere
by a magnetic topology analysis. The loci of EBs coincide with "bald
patches" (BPs). BPs are regions where the vector field is tangential to
the boundary (photosphere) along an inversion line. We conclude that
emerging flux through the photosphere is achieved through resistive
emergence of U loops connecting small Ω loops before rising in the
chromosphere and forming Arch Filament System (AFS).

---------------------------------------------------------
Title: Statistics, morphology, and energetics of Ellerman bombs
Authors: Georgoulis, Manolis K.; Rust, David M.; Bernasconi, Pietro
N.; Schmieder, Brigitte
2002ESASP.505..125G Altcode: 2002IAUCo.188..125G; 2002solm.conf..125G
We have performed a detailed analysis of several hundreds Hα Ellerman
bombs in the low chromosphere, above an emerging flux region. We
find that Ellerman bombs may be small-scale, low-altitude, magnetic
reconnection events that heat the low chromosphere in the active
region. Their energy content varies between 1027 erg and
1028 erg, typical of sub-flaring activity.

---------------------------------------------------------
Title: The Near-Infrared Chromosphere Observatory
Authors: Rust, David M.; Bernasconi, Pietro N.; Labonte, Barry J.;
Georgoulis, Manolis K.; Fox, Nicola J.; Kalkofen, Wolfgang; Lin,
Haoseng
2002ESASP.505..561R Altcode: 2002IAUCo.188..561R; 2002solm.conf..561R
The Near-Infrared Chromosphere Observatory (NICO) is a proposed
balloon-borne observatory aiming to investigate the magnetic structure
and the sources of heating in the solar chromosphere. NICO will be based
on the successful Flare Genesis Experiment (FGE), a pioneer in applying
novel technologies for the study of the Sun. NICO will map magnetic
fields, velocity fields, and heating events in the chromosphere with
unprecedented quality.

---------------------------------------------------------
Title: Vector magnetic field observations of flux tube emergence
Authors: Schmieder, B.; Aulanier, G.; Pariat, E.; Georgoulis, M. K.;
Rust, D. M.; Bernasconi, P. N.
2002ESASP.505..575S Altcode: 2002IAUCo.188..575S; 2002solm.conf..575S
With Flare Genesis Experiment (FGE), a balloon borne Observatory high
spatial and temporal resolution vector magnetograms have been obtained
in an emerging active region. The comparison of the observations
(FGE and TRACE) with a linear force-free field analysis of the region
shows where the region is non-force-free. An analysis of the magnetic
topology furnishes insights into the existence of "bald patches"
regions (BPs are regions where the vector field is tangential to the
boundary (photosphere) along an inversion line). Magnetic reconnection
is possible and local heating of the chromopshere is predicted near the
BPs. Ellerman bombs (EBs) were found to coincide with few BPs computed
from a linear force-free extrapolation of the observed longitudinal
field. But when the actual observations of transverse fields were used
to identify BPs, then the correspondence with EB positions improved
significantly. We conclude that linear force-free extrapolations must
be done with the true observed vertical fields, which require the
measurement of the three components of the magnetic field.

---------------------------------------------------------
Title: Moving Dipolar Features in an Emerging Flux Region
Authors: Bernasconi, P. N.; Rust, D. M.; Georgoulis, M. K.; Labonte,
B. J.
2002SoPh..209..119B Altcode:
On 25 January, 2000, we observed active region NOAA 8844 with the
Flare Genesis Experiment (FGE), a balloon-borne observatory with an
80-cm solar telescope. FGE was equipped with a vector polarimeter and
a tunable Fabry-Pérot narrow-band filter. It recorded time series of
filtergrams, vector magnetograms and Dopplergrams at the Ca i 6122.2 Å
line, and Hα filtergrams with a cadence between 2.5 and 7.5 min. At
the time of the observations, NOAA 8844 was located at approximately
5° N 30° W. The region was growing rapidly; new magnetic flux was
constantly emerging in three supergranules near its center. We report on
the structure and behavior of peculiar moving dipolar features (MDFs)
in the emerging flux, and we describe in detail how the FGE data were
analyzed. In longitudinal magnetograms, the MDFs appeared to be small
dipoles flowing into sunspots and supergranule boundaries. Previously,
dipolar moving magnetic features (MMFs) have only been observed
flowing out from sunspots. The FGE vector magnetograms show that the
MDFs occurred in a region with nearly horizontal fields, the MDFs
being distinguished as undulations in these fields. We identify the
MDFs as stitches where the emerging flux ropes were still tied to the
photosphere by trapped mass. We present a U-loop model that accounts for
their unusual structure and behavior, as well as showing how emerging
flux sheds entrained mass.

---------------------------------------------------------
Title: Statistical Properties of the Energy Release in Emerging and
Evolving Active Regions
Authors: Vlahos, Loukas; Fragos, Tassos; Isliker, Heinz; Georgoulis,
Manolis
2002ApJ...575L..87V Altcode: 2002astro.ph..7340V
The formation and evolution of active regions are inherently complex
phenomena. Magnetic fields generated at the base of the convection zone
follow a chaotic evolution before reaching the solar surface. In this
article, we use a two-dimensional probabilistic cellular automaton
to model the statistical properties of the magnetic patterns formed
on the solar surface and to estimate the magnetic energy released in
the interaction of opposite polarities. We assume that newly emerged
magnetic flux tubes stimulate the emergence of new magnetic flux in
their neighborhood. The flux tubes move randomly on the surface of the
Sun, and they cancel and release their magnetic energy when they collide
with magnetic flux of opposite polarity, or diffuse into the “empty”
photosphere. We assume that cancellation of magnetic flux in collisions
causes “flares” and determine the released energy as the difference in
the square of the magnetic field flux (E~B2). The statistics
of the simulated flares follow a power-law distribution in energy,
f(E)~E-a, where a=2.2+/-0.1. The size distribution function
of the simulated active regions exhibits a power-law behavior with index
k~1.93+/-0.08, and the fractal dimension of the magnetized areas on
the simulated solar surface is close to DF~1.42+/-0.12. Both
quantities, DF and k, are inside the range of the observed
values.

---------------------------------------------------------
Title: Statistics, Morphology, and Energetics of Ellerman Bombs
Authors: Georgoulis, Manolis K.; Rust, David M.; Bernasconi, Pietro
N.; Schmieder, Brigitte
2002ApJ...575..506G Altcode:
We investigate the statistical properties of Ellerman bombs in the
dynamic emerging flux region NOAA Active Region 8844, underneath
an expanding arch filament system. High-resolution chromospheric
Hα filtergrams (spatial resolution 0.8"), as well as photospheric
vector magnetograms (spatial resolution 0.5") and Dopplergrams, have
been acquired by the balloon-borne Flare Genesis Experiment. Hα
observations reveal the first “seeing-free” data set on Ellerman
bombs and one of the largest samples of these events. We find that
Ellerman bombs occur and recur in preferential locations in the low
chromosphere, either above or in the absence of photospheric neutral
magnetic lines. Ellerman bombs are associated with photospheric
downflows, and their loci follow the transverse mass flows on the
photosphere. They are small-scale events, with typical size 1.8"×1.1"
, but this size depends on the instrumental resolution. A large number
of Ellerman bombs are probably undetected, owing to limited spatial
resolution. Ellerman bombs occur in clusters that exhibit fractal
properties. The fractal dimension, with an average value ~1.4, does
not change significantly in the course of time. Typical parameters
of Ellerman bombs are interrelated and obey power-law distribution
functions, as in the case of flaring and subflaring activity. We find
that Ellerman bombs may occur on separatrix, or quasi-separatrix,
layers, in the low chromosphere. A plausible triggering mechanism
of Ellerman bombs is stochastic magnetic reconnection caused by the
turbulent evolution of the low-lying magnetic fields and the continuous
reshaping of separatrix layers. The total energies of Ellerman bombs
are estimated in the range (1027, 1028) ergs, the
temperature enhancement in the radiating volume is ~2×103
K, and the timescale of radiative cooling is short, of the order of
a few seconds. The distribution function of the energies of Ellerman
bombs exhibits a power-law shape with an index ~-2.1. This suggests
that Ellerman bombs may contribute significantly to the heating of
the low chromosphere in emerging flux regions.

---------------------------------------------------------
Title: The Near-Infrared Chromosphere Observatory (NICO)
Authors: Rust, D. M.; Bernasconi, P. N.; LaBonte, B. J.; Georgoulis,
M. K.; Kalkofen, W.; Fox, N. J.; Lin, H.
2002AAS...200.3902R Altcode: 2002BAAS...34..701R
NICO is a proposed cost-effective platform for determining the magnetic
structure and sources of heating for the solar chromosphere. It is a
balloon-borne observatory that will use the largest solar telescope
flying and very high data rates to map the magnetic fields, velocities,
and heating events of the chromosphere and photosphere in unprecedented
detail. NICO is based on the Flare Genesis Experiment (FGE), which
has pioneered in the application of technologies important to NASA's
flight program. NICO will also introduce new technologies, such
as wavefront sensing for monitoring telescope alignment; real-time
correlation tracking and high-speed image motion compensation for
smear-free imaging; and wide aperture Fabry-Perot filters for extended
spectral scanning. The telescope is a classic Cassegrain design with
an 80-cm diameter F/1.5 primary mirror made of Ultra-Low-Expansion
glass. The telescope structure is graphite-epoxy for lightweight,
temperature-insensitive support. The primary and secondary mirror
surfaces are coated with silver to reflect more than 97% of the incident
solar energy. The secondary is made of single-crystal silicon, which
provides excellent thermal conduction from the mirror surface to its
mount, with negligible thermal distortion. A third mirror acts as a
heat dump. It passes the light from a 15-mm diameter aperture in its
center, corresponding to a 322"-diameter circle on the solar surface,
while the rest of the solar radiation is reflected back out of the
front of the telescope. The telescope supplies the selected segment
of the solar image to a polarization and spectral analysis package
that operates with an image cadence 1 filtergram/sec. On-board data
storage is 3.2 Terabytes. Quick-look images will be sent in near real
time to the ground via the TDRSS communications link.

---------------------------------------------------------
Title: Photospheric Vertical Current Density and Overlying Atmospheric
Activity in an Emerging Flux Region
Authors: Georgoulis, M. K.; Rust, D. M.; Bernasconi, P. N.;
Schmieder, B.
2002AAS...200.2004G Altcode: 2002BAAS...34..673G
Using high-resolution vector magnetograms obtained by the balloon-borne
Flare Genesis Experiment (FGE), we construct maps of the vertical
current density in the emerging flux region NOAA 8844. The vertical
current density has been decomposed into components that are
field-aligned and perpendicular to the magnetic field, thus allowing
a straightforward identification of force-free areas, as well as of
areas where the force-free approximation breaks down. Small-scale
chromospheric activity, such as H α Ellerman bombs and Ultraviolet
bright points in 1600 Åshow a remarkable correlation with areas of
strong current density. Simultaneous data of overlying coronal loops,
observed by TRACE in the Extreme Ultraviolet (171 Åand 195 Å), have
been carefully co-aligned with the FGE photospheric maps. We find
that the footpoints of the TRACE loops always coincide with strong
vertical currents and enhancements of the current helicity density. We
also investigate whether the force-free approximation is valid on the
photosphere during various evolutionary stages of the active region.

---------------------------------------------------------
Title: Sunspot Formation from Emerging Flux Ropes - Observations
from Flare Genesis
Authors: Rust, D. M.; Bernasconi, P. N.; Georgoulis, M. K.; LaBonte,
B. J.; Schmieder, B.
2001AGUSM..SP42A09R Altcode:
From January 10 to 27, 2000, the Flare Genesis payload observed
the Sun while suspended from a balloon in the stratosphere above
Antarctica. The goal of the mission was to acquire a long time series of
high-resolution images and vector magnetograms of the solar photosphere
and chromosphere. We obtained images, magnetograms and Dopplergrams
in the magnetically sensitive Ca I line at 6122 Angstroms. Additional
simultaneous images were obtained in the wing of H-alpha. On January
25, 2000, we observed in NOAA region 8844 at N05 W30. The rapid
development of a sunspot group that apparently included a delta spot
(two polarities within one umbra). We considered a variety of models
for interpreting these observations, including a twisted flux tube,
a bipole that annihilates, a bipole that submerges, and a field
distorted by mass loading. From the vector magnetograms and Doppler
measurements, we conclude that nearly horizontal flux ropes are swept
into the developing spot where they tilt upward to contribute to the
familiar nearly vertical sunspot fields. The largest flux rope exhibited
a twisted structure, and its angle with respect to the vertical was so
great that it could be mistaken for a positive magnetic field merging
into a negative sunspot. Flare Genesis was supported by NASA grant
NAG5-8331 and by NSF grant OPP-9909167.

---------------------------------------------------------
Title: Ellerman Bombs in a Solar Active Region: Statistical Properties
and Implications
Authors: Georgoulis, M. K.; Rust, D. M.; Bernasconi, P. N.
2001AGUSM..SP52B05G Altcode:
We have embedded the concept of Self-Organized Criticality (SOC) in
deterministic Cellular Automata (CA) models in an attempt to simulate
the emergence of flaring and sub-flaring activity in solar active
regions. SOC CA models reproduce reasonably well several aspects of the
statistical properties of flares and, moreover, they allow predictions
regarding the respective properties of the unresolved nanoflares. We
compare the above-mentioned predictions with observed arcsecond and
sub-arcsecond activity on the low-chromosphere, in a newly formed active
region. The source of the observations is the Flare Genesis Experiment
(FGE) which has provided us with high-resolution maps of the magnetic
field and the velocity field vectors on the photospheric boundary, as
well as Hα filtergrams on the low-chromosphere. Moreover, UV and EUV
data from TRACE are used for determining the activity on the overlying
atmospheric layers. We present preliminary results on the statistical
properties of transient Hα brightenings (Ellerman Bombs) which
correlate well with significant overlying UV emission. Implications
of these results, as well as potential directions for modeling the
low-lying activity in the solar atmosphere are discussed. This work
was sponsored by NASA grant NAG5-8331 and NSF grant OPP-9909162

---------------------------------------------------------
Title: Peculiar Moving Magnetic Features Observed With the Flare
Genesis Experiment
Authors: Bernasconi, P. N.; Rust, D. M.; Georgoulis, M. K.; LaBonte,
B. J.; Schmieder, B.
2001AGUSM..SP51A02B Altcode:
With the Flare Genesis Experiment (FGE), a balloon-borne 80-cm solar
telescope, we observed the active region NOAA 8844 on January 25,
2000 for several hours. FGE was equipped with a vector polarimeter
and a lithium-niobate Fabry-Perot narrow-band filter. It recorded
time series of filtergrams, vector magnetograms, and dopplergrams
at the CaI 6122.2 Angstroms line, as well as Hα filtergrams, with a
cadence between 2.5 and 7.5 minutes. At the time of the observations
NOAA 8844 was located at approximately 5 deg N, 30 deg W. It was a new
flux emergence that first appeared on the solar disk two days before
and was still showing a very dynamic behavior. Its two main polarity
parts were rapidly moving away from each other and new magnetic flux
was constantly emerging from its center. Here we describe the structure
and behavior of peculiar small moving magnetic dipoles (called moving
magnetic features MMF's) that we observed near the trailing negative
polarity sunspot of NOAA 8844. Presentations by D. M. Rust, and by
M. K. Georgoulis at this meeting will focus on other aspects of the
same active region. The MMF's took the form of small dipoles that first
emerged into the photosphere near the center of a supergranular cell
located next to the main trailing flux concentration. They rapidly
migrated towards the spot, following the supergranular flow. The two
polarities of the little dipoles did not separate; they moved together
with same speed and in the same direction. The dipoles were oriented
parallel to their motion toward the negative spot, with the positive
polarity always leading. MMF's usually move away from sunspots, and
their orientation is the reverse of what we see here. In addition,
we noted that the dipole structure was not symmetric. The field lines
of the trailing part of the MMF's (negative polarity) were always
much more perpendicular to the local horizontal than the ones of the
leading part. The trailing part looked more compact and circular, while
the leading part was more elongated in the direction of the motion. We
conclude that we observed a new type of MMF's with a totally different
magnetic structure than previously seen. We present a possible model
that could explain their unusual structure and behavior. This work
was supported by NASA grant NAG5-8331 and NSF grant OPP-9909167.

---------------------------------------------------------
Title: A comparison between statistical properties of solar X-ray
flares and avalanche predictions in cellular automata statistical
flare models
Authors: Georgoulis, M. K.; Vilmer, N.; Crosby, N. B.
2001A&A...367..326G Altcode:
We perform a tentative comparison between the statistical properties of
cellular automata statistical flare models including a highly variable
non-linear external driver and the respective properties of the WATCH
flare data base, constructed during the maximum of solar cycle 21. The
model is based on the concept of Self-Organized Criticality (SOC). The
frequency distributions built on the measured X-ray flare parameters
show the following characteristics: (1) The measured parameters (total
counts, peak count-rates and, to a lesser extent, total duration) are
found to be correlated to each other. Overall distribution functions of
the first two parameters are robust power laws extending over several
decades. The total duration distribution function is represented by
either two power laws or a power law with an exponential roll-over. (2)
By sub-grouping the peak count-rate and the total counts as functions of
duration and constructing frequency distributions on these sub-groups,
it is found that the slope systematically decreases with increasing
duration. (3) No correlation is found between the elapsed time interval
between successive bursts arising from the same active region and the
peak intensity of the flare. Despite the inherent weaknesses of the
SOC models to simulate realistically a number of physical processes
thought to be at work in solar active regions and in flares' energy
release, we show that the model is able to reproduce the bulk of the
above statistical properties. We thus underline two main conclusions:
(i) A global, statistical approach for the study of rapid energy
dissipation and magnetic field line annihilation in complex, magnetized
plasmas may be of equal importance with the localized, small-scale
Magnetohydrodynamic (MHD) simulations, and (ii) refined SOC models are
needed to establish a more physical connection between the cellular
automata evolution rules and the observations.

---------------------------------------------------------
Title: Microscale Structures on the Quiet Sun and Coronal Heating
Authors: Aletti, V.; Velli, M.; Bocchialini, K.; Einaudi, G.;
Georgoulis, M.; Vial, J. -C.
2000ApJ...544..550A Altcode:
We present some results concerning transient brightenings on the quiet
Sun, based on data from the Extreme-Ultraviolet Imaging Telescope on
board the Solar and Heliospheric Observatory. Histograms of intensity
are found to be well fitted by χ2 distributions for
small values of the intensity, while at high intensities power-law
distributions are always observed. Also, the emission presents the
same statistical properties when the resolution is downgraded by local
averaging; i.e., it appears to be self-similar down to the resolution
scale of the instruments. These properties are characteristic of
the emission from a forced turbulent system whose dissipation scale
is much smaller than the pixel dimension. On the basis of the data
presented as well as other published results and our present theoretical
understanding of MHD turbulence, we discuss the realism of the nanoflare
scenario of coronal heating.

---------------------------------------------------------
Title: Χωροχρονική εξέλιξη σύνθετων
κέντρων δράσης - μηχανισμοί έκλυσης
ενέργειας στο ηλιακό στέμμα Title:
Χωροχρονική εξέλιξη σύνθετων κέντρων
δράσης - μηχανισμοί έκλυσης ενέργειας
στο ηλιακό στέμμα

---------------------------------------------------------
Title: Spatiotemporal evolution
of complex active regions - mechanisms of energy release in the
solar corona;
Authors: Georgoulis, Manolis K.
2000PhDT.......275G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A Comparison between the WATCH Flare Data Statistical
Properties and Predictions of the Statistical Flare Model
Authors: Crosby, N.; Georgoulis, M.; Vilmer, N.
1999ESASP.446..247C Altcode: 1999soho....8..247C
Solar burst observations in the deka-keV energy range originating from
the WATCH experiment aboard the GRANAT spacecraft were used to perform
frequency distributions built on measured X-ray flare parameters
(Crosby et al., 1998). The results of the study show that: 1- the
overall distribution functions are robust power laws extending over
a number of decades. The typical parameters of events (total counts,
peak count rates, duration) are all correlated to each other. 2- the
overall distribution functions are the convolution of significantly
different distribution functions built on parts of the whole data set
filtered by the event duration. These "partial" frequency distributions
are still power law distributions over several decades, with a slope
systematically decreasing with increasing duration. 3- No correlation
is found between the elapsed time interval between successive bursts
arising from the same active region and the peak intensity of the
flare. In this paper, we attempt a tentative comparison between the
statistical properties of the self-organized critical (SOC) cellular
automaton statistical flare models (see e.g. Lu and Hamilton (1991),
Georgoulis and Vlahos (1996, 1998)) and the respective properties
of the WATCH flare data. Despite the inherent weaknesses of the
SOC models to simulate a number of physical processes in the active
region, it is found that most of the observed statistical properties
can be reproduced using the SOC models, including the various frequency
distributions and scatter plots. We finally conclude that, even if SOC
models must be refined to improve the physical links to MHD approaches,
they nevertheless represent a good approach to describe the properties
of rapid energy dissipation and magnetic field annihilation in complex
and magnetized plasmas. Crosby N., Vilmer N., Lund N. and Sunyaev R.,
A&amp;A; 334; 299-313; 1998 Crosby N., Lund N., Vilmer N. and Sunyaev
R.; A&amp;A Supplement Series; 130, 233, 1998 Georgoulis M. and Vlahos
L., 1996, Astrophy. J. Letters, 469, L135 Georgoulis M. and Vlahos L.,
1998, in preparation Lu E.T. and Hamilton R.J., 1991, Astroph. J.,
380, L89

---------------------------------------------------------
Title: Derivation of Solar Flare Cellular Automata Models from a
Subset of the Magnetohydrodynamic Equations
Authors: Vassiliadis, D.; Anastasiadis, A.; Georgoulis, M.; Vlahos, L.
1998ApJ...509L..53V Altcode:
Cellular automata (CA) models account for the power-law distributions
found for solar flare hard X-ray observations, but their physics
has been unclear. We examine four of these models and show that
their criteria and magnetic field distribution rules can be derived
by discretizing the MHD diffusion equation as obtained from a
simplified Ohm's law. Identifying the discrete MHD with the CA
models leads to an expression for the resistivity as a function
of the current on the flux tube boundary, as may be expected from
current-driven instabilities. Anisotropic CA models correspond to a
nonlinear resistivity η(J), while isotropic ones are associated with
hyperresistivity η(▽2J). The discrete equations satisfy
the necessary conditions for self-organized criticality (Lu): there
is local conservation of a field (magnetic flux), while the nonlinear
resistivity provides a rapid dissipation and relaxation mechanism. The
approach justifies many features of the CA models that were originally
based on intuition.

---------------------------------------------------------
Title: Variability of the occurrence frequency of solar flares and
the statistical flare
Authors: Georgoulis, Manolis K.; Vlahos, Loukas
1998A&A...336..721G Altcode:
Self-Organised Criticality (SOC), embedded in cellular automata
models, has been so far viewed as an attractive phenomenological
approach for studying the statistical behaviour of flaring activity
in solar active regions. Well-known statistical properties of flares,
like the robust scaling laws seen in the distribution functions of
characteristic parameters of the events, as well as correlations linking
those parameters, are successfully reproduced by SOC models. Recent
observations, however, challenge the flexibility of SOC, as they
reveal a variation of the flaring power-law indices over short-time
activity periods. The initial SOC models, based on a small-amplitude,
constant external driver and isotropic instability criteria, appear
inefficient to predict variable power-law indices. In this paper we
introduce a SOC-type numerical model, with a number of modifications of
the original SOC concept. We show that scaling laws and correlations
between the events' characteristic parameters survive under the
action of a highly variable driver. A variable driver initiates
a variability in the resulting power-law indices. We reproduce
qualitatively and quantitatively the statistics of flaring activity
during the 154-day periodicity. Moreover, small-scale, anisotropic
instability criteria imply the existence of a soft population of
events, with statistical properties analogous to those attributed to
the hypothetical nanoflares. We show that numerous small-scale events
could be the dominant energy release mechanism in cases of quiescent
coronal activity.

---------------------------------------------------------
Title: Statistical Properties of Magnetic Activity in the Solar Corona
Authors: Georgoulis, Manolis K.; Velli, Marco; Einaudi, Giorgio
1998ApJ...497..957G Altcode:
The long-time statistical behavior of a two-dimensional section of
a coronal loop subject to random magnetic forcing is presented. The
highly intermittent nature of dissipation is revealed by means of
magnetohydrodynamic (MHD) turbulence numerical simulations. Even with a
moderate magnetic Reynolds number, intermittency is clearly present in
both space and time. The response of the loop to the random forcing,
as described either by the time series of the average and maximum
energy dissipation or by its spatial distribution at a given time,
displays a Gaussian noise component that may be subtracted to define
discrete dissipative events. Distribution functions of both maximum
and average current dissipation, for the total energy content, the
peak activity, and the duration of such events are all shown to display
robust scaling laws, with scaling indices δ that vary from δ ~= -1.3
to δ ~= -2.8 for the temporal distribution functions, while δ ~=
-2.6 for the overall spatial distribution of dissipative events.

---------------------------------------------------------
Title: Microflare and nanoflare heating of active region loops.
Authors: Walsh, R. W.; Georgoulis, M.
1998joso.proc..105W Altcode:
In this work, the authors investigate the response of solar plasma
contained within a coronal loop structure to the random deposition
of many localised heating events on the scale of microflares and
nanoflares. A statistical flaring approach based on self-organised
criticality is used to generate the energy release which varies in
both space and time. It is shown that for a 20 Mm active region loop
although the average temperature over the duration of the simulation
remains at typical coronal temperatures, the plasma can flare to over
6×106K at certain stages in its evolution.

---------------------------------------------------------
Title: Electron Acceleration by Random DC Electric Fields
Authors: Anastasiadis, Anastasios; Vlahos, Loukas; Georgoulis,
Manolis K.
1997ApJ...489..367A Altcode:
We present a global model for the acceleration of electrons in the
framework of the statistical flare model of Vlahos et al. In this model,
solar flares are the result of an internal self-organized critical
(SOC) process in a complex, evolving, and highly inhomogeneous active
region. The acceleration of electrons is due to localized DC electric
fields closely related to the energy-release process in the active
region. Our numerical results for the kinetic energy distribution of
accelerated electrons show a power-law or an exponential-law behavior,
depending on the maximum trapping time of the energetic particles
inside the acceleration volume.

---------------------------------------------------------
Title: MHD Turbulence and Statistics of Energy Release in the
Solar Corona
Authors: Georgoulis, M.; Velli, M.; Einaudi, G.
1997ESASP.404..401G Altcode: 1997cswn.conf..401G
No abstract at ADS

---------------------------------------------------------
Title: Variability of the Occurrence Frequency of Solar Flares and
the Statistical Flare
Authors: Georgoulis, M. K.; Vlahos, L.
1997jena.confE..39G Altcode:
Self-Organized Criticality (SOC) embedded in cellular automata
models has been so far acknowledged as an adequate qualitative way
of studying the statistical behaviour of flaring activity in solar
active regions. These models are able of producing robust power
laws featuring the frequency distributions of the events obtained,
which are closely consistent with observations of flares, as well
as much steeper power-law cut-offs, which may indicate the existence
of the presently unobserved nanoflares. SOC models are based on the
substantial concept that active regions are driven dissipative nonlinear
dynamical systems. The role of the external driver is attributed to the
feedback of magnetic flux that is injected to the system through the
photospheric boundary and to the random shuffling of the footpoints
of coronal loops taking place on the upper photosphere. In previous
numerical studies, the driver used was an infinitesimal perturbation
acting on localized magnetic topologies due to which avalanche-type
instabilities were triggered. Furthermore, the resulting power-law
indices were unique. Recent observations, however, have shown that
the scaling indices of flares' frequency distributions are not kept
constant during certain phases of the solar activity, such as the
154-day periodicity. To tackle this problem we investigate the role of
the driver used, by introducing a highly variable driving mechanism. We
show that the variability of the driver induces a respective variability
in the resulting power-law indices. The variability of the indices
can be well represented by a linear dependence between them and
the driver's scaling index for both "nanoflaring" and "flaring"
activity. Furthermore, a first attempt of connecting the driver with
certain statistical properties of active regions is introduced. The
results stand closely in favor of the observations of flaring activity
during the 154-day periodicity.

---------------------------------------------------------
Title: Statistical Properties of Magnetic Activity in the Solar Corona
Authors: Georgoulis, M. K.; Einaudi, G.; Velli, M.
1997jena.confE..38G Altcode:
A long-time statistical analysis of a two-dimensional section of a
coronal loop has been carried out. The highly intermittent nature of
the spatiotemporal evolution of the system has been revealed by means of
Magnetohydrodynamic (MHD) Turbulence numerical simulations. Albeit the
moderate magnetic Reynolds number, intermittency is strikingly present
both in space and in time. This type of behaviour might physically
motivate statistical theories to describe the long-term evolution of
a turbulent corona, provided that such an environment is a driven
dissipative nonlinear dynamical system. The coronal loop is driven
by a random spatiotemporal magnetic forcing, which induces a noise
component in the resulting timeseries. If this component is properly
subtracted, the obtained spatiotemporal evolution can be statistically
described in terms of robust scaling laws, occurring in the distribution
functions of both maximum and average current dissipation for the
total energy content, the peak activity and the duration of the events
obtained. Adopting low-beta and large-aspect-ratio conditions for
the coronal loop, we emphasize that, higher spatial resolution could
well give rise both to localized equipartition, and to the emergence
of super-Dreicer electric fields built-up in the vicinity of strong,
intense current sheets.

---------------------------------------------------------
Title: Coronal Heating by Nanoflares and the Variability of the
Occurence Frequency in Solar Flares
Authors: Georgoulis, Manolis K.; Vlahos, Loukas
1996ApJ...469L.135G Altcode:
It has been proposed that flares in the solar corona may well be
a result of an internal self-organized critical (SOC) process in
active regions. We have developed a cellular automaton SOC model
that simulates flaring activity extending over an active sub-flaring
background. In the resulting frequency distributions we obtain two
distinct power laws. That of the weaker events is shorter and much
steeper (power law with index ~=-3.26) than that of the intermediate
and large events (power law with index ~=-1.73). The flatter power law
is in close agreement with observations of flares. Weaker events are
responsible for ~=90% of the total magnetic energy released, indicating
a possible connection of nanoflares with coronal heating. Moreover,
certain mechanisms cause the variability of the resulting indices
and may provide answers to the problem of the variability of flares'
occurrence frequency during the solar cycle.

---------------------------------------------------------
Title: Are Flares the Result of a self-organisation Process in
active Regions?
Authors: Georgoulis, M. K.; Vlahos, L.; Kluiving, R.
1996hell.conf...52G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The statistical flare.
Authors: Vlahos, L.; Georgoulis, M.; Kluiving, R.; Paschos, P.
1995A&A...299..897V Altcode:
Solar and stellar flares are interpreted so far as an instability
of a large scale magnetic neutral sheet. In this article, however,
we assume that the active region is highly inhomogeneous: a large
number of magnetic loops are simultaneously present interacting
and randomly forming discontinuities in many independent points in
space. These magnetic discontinuities release energy and force weaker
discontinuities in their neighbourhood to release energy as well. This
complex dynamical system releases constantly energy in the form of small
and large scale explosions. Clustering of many discontinuities in the
same area has the effect of larger scale explosions (flares). This
type of flare with spatiotemporal fragmentation and clustering in
small and large scale structures will be called here the statistical
flare. The statistical flare is simulated using avalanche models
originally introduced by Bak et al. (1988). Avalanche models applied
so far to solar flares (Lu &amp; Hamilton 1991) were isotropic (the
field was distributed equally to the closest neighbours of an unstable
point). These models simulate relatively large events (microflares and
flares). Here we introduce a more refined isotropic avalanche model
as well as an anisotropic avalanche model (energy is distributed only
among the unstable point and those neighbours that develop gradients
higher than a critical value). The anisotropic model simulates
better the smaller events (nanoflares): in contrast to the well-known
results of the isotropic model (a power law with index ~-1.8 in the
peak-luminosity distribution), the anisotropic model produces a much
steeper power law with index ~-3.5. Finally, we introduce a mixed model
(a combination of isotropic and anisotropic models) which gives rise
to two distinct power-law regions in the peak-luminosity distribution,
one with index ~-3.5 accounting for the small events, and one with index
~-1.8 accounting for large events. This last model therefore explains
coronal heating as well as flaring. The three models introduced in this
paper show length-scale invariant behaviour. Model-dependent memory
effects are detected in the peak-luminosity time series produced by
these models.