164 research outputs found
Testing predictors of eruptivity using parametric flux emergence simulations
Solar flares and coronal mass ejections (CMEs) are among the most energetic
events in the solar system, impacting the near-Earth environment. Flare
productivity is empirically known to be correlated with the size and complexity
of active regions. Several indicators, based on magnetic-field data from active
regions, have been tested for flare forecasting in recent years. None of these
indicators, or combinations thereof, have yet demonstrated an unambiguous
eruption or flare criterion. Furthermore, numerical simulations have been only
barely used to test the predictability of these parameters. In this context, we
used the 3D parametric MHD numerical simulations of the self-consistent
formation of the flux emergence of a twisted flux tube, inducing the formation
of stable and unstable magnetic flux ropes of Leake (2013, 2014). We use these
numerical simulations to investigate the eruptive signatures observable in
various magnetic scalar parameters and provide highlights on data analysis
processing. Time series of 2D photospheric-like magnetograms are used from
parametric simulations of stable and unstable flux emergence, to compute a list
of about 100 different indicators. This list includes parameters previously
used for operational forecasting, physical parameters used for the first time,
as well as new quantities specifically developed for this purpose. Our results
indicate that only parameters measuring the total non-potentiality of active
regions associated with magnetic inversion line properties, such as the
Falconer parameters , , and , as well as the
new current integral and length parameters, present a
significant ability to distinguish the eruptive cases of the model from the
non-eruptive cases, possibly indicating that they are promising flare and
eruption predictors.Comment: 46 pages, 16 figures, accepted for publication in Space Weather and
Space Climate on June, 8t
X-ray and UV investigation into the magnetic connectivity of a solar flare
We investigate the X-ray and UV emission detected by RHESSI and TRACE in the
context of a solar flare on the 16th November 2002 with the goal of better
understanding the evolution of the flare. We analysed the characteristics of
the X-ray emission in the 12-25 and 25-50 keV energy range while we looked at
the UV emission at 1600 {\AA}. The flare appears to have two distinct phases of
emission separated by a 25-second time delay, with the first phase being
energetically more important. We found good temporal and spatial agreement
between the 25-50 keV X-rays and the most intense areas of the 1600 {\AA} UV
emission. We also observed an extended 100-arcsecond < 25 keV source that
appears coronal in nature and connects two separated UV ribbons later in the
flare. Using the observational properties in X-ray and UV wavelengths, we
propose two explanations for the flare evolution in relation to the spine/fan
magnetic field topology and the accelerated electrons. We find that a
combination of quasi separatrix layer reconnection and null-point reconnection
is required to account for the observed properties of the X-ray and UV
emission.Comment: 8 pages, 8 figures, published in Astronomy and Astrophysic
Temporal Evolution of the Magnetic Topology of the NOAA Active Region 11158
We studied the temporal evolution of the magnetic topology of the active
region (AR) 11158 based on the reconstructed three-dimensional magnetic fields
in the corona. The \nlfff\ extrapolation method was applied to the 12 minutes
cadence data obtained with the \hmi\ (HMI) onboard the \sdo\ (SDO) during five
days. By calculating the squashing degree factor Q in the volume, the derived
quasi-separatrix layers (QSLs) show that this AR has an overall topology,
resulting from a magnetic quadrupole, including an hyperbolic flux tube (HFT)
configuration which is relatively stable at the time scale of the flare ( hours). A strong QSL, which corresponds to some highly sheared arcades
that might be related to the formation of a flux rope, is prominent just before
the M6.6 and X2.2 flares, respectively. These facts indicate the close
relationship between the strong QSL and the high flare productivity of AR
11158. In addition, with a close inspection of the topology, we found a
small-scale HFT which has an inverse tear-drop structure above the
aforementioned QSL before the X2.2 flare. It indicates the existence of
magnetic flux rope at this place. Even though a global configuration (HFT) is
recognized in this AR, it turns out that the large-scale HFT only plays a
secondary role during the eruption. In final, we dismiss a trigger based on the
breakout model and highlight the central role of the flux rope in the related
eruption.Comment: Accepted by Ap
Hooked flare ribbons and flux-rope related QSL footprints
We studied the magnetic topology of active region 12158 on 2014 September 10
and compared it with the observations before and early in the flare which
begins at 17:21 UT (SOL2014-09-10T17:45:00). Our results show that the
sigmoidal structure and flare ribbons of this active region observed by SDO/AIA
can be well reproduced from a Grad-Rubin non linear force free field
extrapolation method. Various inverse-S and -J shaped magnetic field lines,
that surround a coronal flux rope, coincide with the sigmoid as observed in
different extreme ultraviolet wavelengths, including its multi-threaded curved
ends. Also, the observed distribution of surface currents in the magnetic
polarity where it was not prescribed is well reproduced. This validates our
numerical implementation and set-up of the Grad-Rubin method. The modeled
double inverse-J shaped Quasi-Separatrix Layer (QSL) footprints match the
observed flare ribbons during the rising phase of the flare, including their
hooked parts. The spiral-like shape of the latter may be related to a complex
pre-eruptive flux rope with more than one turn of twist, as obtained in the
model. These ribbon-associated flux-rope QSL-footprints are consistent with the
new standard flare model in 3D, with the presence of a hyperbolic flux tube
located below an inverse tear drop shaped coronal QSL. This is a new step
forward forecasting the locations of reconnection and ribbons in solar flares,
and the geometrical properties of eruptive flux ropes.Comment: Accepted for publication in Ap
A Circular-ribbon Solar Flare Following an Asymmetric Filament Eruption
The dynamic properties of flare ribbons and the often associated filament
eruptions can provide crucial information on the flaring coronal magnetic
field. This Letter analyzes the GOES-class X1.0 flare on 2014 March 29
(SOL2014-03-29T17:48), in which we found an asymmetric eruption of a sigmoidal
filament and an ensuing circular flare ribbon. Initially both EUV images and a
preflare nonlinear force-free field model show that the filament is embedded in
magnetic fields with a fan-spine-like structure. In the first phase, which is
defined by a weak but still increasing X-ray emission, the western portion of
the sigmoidal filament arches upward and then remains quasi-static for about
five minutes. The western fan-like and the outer spine-like fields display an
ascending motion, and several associated ribbons begin to brighten. Also found
is a bright EUV flow that streams down along the eastern fan-like field. In the
second phase that includes the main peak of hard X-ray (HXR) emission, the
filament erupts, leaving behind two major HXR sources formed around its central
dip portion and a circular ribbon brightened sequentially. The expanding
western fan-like field interacts intensively with the outer spine-like field,
as clearly seen in running difference EUV images. We discuss these observations
in favor of a scenario where the asymmetric eruption of the sigmoidal filament
is initiated due to an MHD instability and further facilitated by reconnection
at a quasi-null in corona; the latter is in turn enhanced by the filament
eruption and subsequently produces the circular flare ribbon.Comment: 7 pages, 5 figures, accepted to ApJ Letter
Recommended from our members
The flare likelihood and region eruption forecasting (FLARECAST) project: flare forecasting in the big data & machine learning era
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
Propriétés magnétiques des structures éruptives solaires
Solar eruptions constitute the most energetic phenomena of the solar system. In a few tens of minutes, an energy comparable to hundred thousand times the annual world human energy consumption is released in the solar atmosphere. During these events, magnetized matter, as well as energetic particles and radiations, are ejected toward the interplanetary space and frequently interact with the Earth magnetic environment. For our society, which relies more and more on technologies, the impact of these eruptions is becoming an ever-increasing concern, requiring us to learn how to guard against their detrimental effects. Solar eruption prediction, within the scope of the emerging applied discipline of space weather, requires to understand the physical mechanisms that generates these eruptions. The work presented in this thesis corresponds to fundamental researches in physics of the Sun-Earth relations. The overall objective targets the development of new tools to forecast solar activity. The framework of study of these phenomena is magnetohydrodynamics, the physical paradigm adapted to the study of the hot magnetized plasma that constitutes the solar atmosphere. The present studies focus on analyzing the properties of the source regions of the eruptions, the solar active regions, which main visible counterpart are the solar sunspots. These active regions correspond to intense concentrations of magnetic fields, which constitutes the energy source that fuels the eruptions. Understanding the trigger of solar eruption thus relies on the determination of the magnetic properties of the active regions. The research methodology that is employed is based on close and synergistic combination of different means of investigation; analytical theory, conceptual modeling, numerical experimentation, and multi-wavelength multi-instrument observational analysis. Thanks to these methods, several fundamental quantities and physical properties are being studied: the very magnetic field, its topology and its structuration in potential and non-potential fields, the associated energies, the induced electric currents, and finally magnetic helicity, an underrated quantity up to now. Through the synthesis of about sixty scientific studies, this thesis intends to demonstrate that, while each quantity provides distinct information, these are complementary and enables a global description of eruptive magnetic fields, allowing the creation of an actual 3D standard model for solar eruptions. Regarding solar eruptions prediction, the studies on the theory of the measurement of magnetic helicity, now allow to truly and correctly estimate this quantity and determine its link with eruptivity. Preliminary studies of numerical experiments show that magnetic helicity could be the ground base of efficient diagnostics of the eruptive state of solar active regions.Les éruptions solaires constituent les phénomènes les plus énergétiques du système solaire. En quelques dizaines de minutes, une énergie comparable à cent mille fois la consommation annuelle humaine d'énergie est libérée dans l'atmosphère solaire. Lors de ces évènements, de la matière magnétisée, ainsi que des rayonnements et des particules énergétiques, sont éjectés vers l'espace interplanétaire et peuvent interagir avec l'environnement magnétique de la Terre. Pour notre société toujours plus technologique, l'impact de ces éruptions devient ainsi un enjeu de plus en plus important nécessitant d'apprendre à nous prémunir de leurs effets nocifs. La prévision des éruptions solaires, dans le cadre de la discipline émergente de la météorologie de l'espace, requiert la compréhension des mécanismes physiques générant ces éruptions.Le travail présenté dans ce mémoire, porte sur des recherches fondamentales en physique des relations Soleil-Terre. L'objectif global vise au développement de nouveaux outils de prédiction de l'activité solaire. Le cadre physique dans lequel sont étudiés ces phénomènes est celui de la magnétohydrodynamique (MHD), paradigme adapté aux plasmas chauds magnétisés qui constituent l'atmosphère solaire. L'objet du travail porte sur l'analyse des propriétés des régions sources de ces éruptions solaires, les régions actives, dont les tâches solaires sont la principale signature visible. Ces régions actives correspondent à des concentrations de champs magnétiques intenses, constituant la source d'énergie des éruptions. La compréhension du déclenchement des éruptions solaires repose ainsi sur la détermination des propriétés magnétiques des régions actives.La méthodologie de recherche utilisée se base sur une combinaison étroite et synergique entre différents axes d'investigation, des travaux théoriques de modélisations conceptuelles et analytiques, des expérimentations numériques et de l'analyse observationnelle multi-instruments et multi-longueurs d'ondes d'évènements actifs. A l'aide de ces méthodes, plusieurs grandeurs et propriétés physiques fondamentales sont étudiées : le champ magnétique lui-même, sa topologie et sa structuration en champs potentiel et non-potentiel, les énergies associées, les courants électriques induits et finalement l'hélicité magnétique, quantité dont l'importance a été relativement sous-estimée jusqu'à présent.A travers la synthèse d'une soixantaine de travaux scientifiques, ce mémoire tente de montrer que, bien que chacune de ces quantités apporte un éclairage distinct, elles fournissent des informations complémentaires qui permettent d'aboutir à une description globale des champs magnétiques éruptifs, ce qui se traduit par la mise en place d'un véritable modèle 3D standard des éruptions solaires. Concernant la prédiction des éruptions solaires, les travaux sur la théorie de la mesure de l'hélicité magnétique permettent désormais de véritablement mesurer correctement cette quantité et d'établir son lien avec l'éruptivité. Les études préliminaires d'expériences numériques montrent que l'hélicité magnétique pourrait être à la base de diagnostics efficaces de l'état éruptif des régions actives solaires
How numerical simulations allow us to interpret the dynamics of UV and X-ray emissions during a solar flare
International audienc
Récentes avancées en modélisation magnétohydrodynamique des évènements éruptifs solaires
National audienc
Magnetohydrodynamics
Hydromagnetics; Magneto-fluid dynamics Acronyms MHD Magnetohydrodynamics Definition Magnetohydrodynamics (MHD) is a physical paradigm pertinent to describe the dynamics of electrically conducting fluids, such as plasmas, electrolytes, and liquid metals. MHD couples fluids dynamics with electromagnetism
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