scholarly journals When hot meets cold: post-flare coronal rain

2021 ◽  
Author(s):  
Wenzhi Ruan ◽  
Yuhao Zhou ◽  
Rony Keppens
Keyword(s):  
Extreme Ultraviolet ◽  
Impulsive Phase ◽  
Flare Loop ◽  
Gradual Phase ◽  
Stellar Flares ◽  
Flare Loops ◽  
Long Duration ◽  
Energy Cycle ◽  
Coronal Density ◽  
Coronal Rain

Abstract All solar flares demonstrate a prolonged, hourlong post-flare (or gradual) phase, characterized by arcade-like, post-flare loops (PFLs) visible in many extreme ultraviolet (EUV) passbands. These coronal loops are filled with hot – ~30MK – and dense plasma, evaporated from the chromosphere during the impulsive phase of the flare, and they very gradually recover to normal coronal density and temperature conditions. During this gradual cooling down to ~1MK regimes, much cooler – ~0.01MK – and denser coronal rain is frequently observed inside PFLs. Understanding PFL dynamics in this long-duration, gradual phase is crucial to the entire corona-chromosphere mass and energy cycle. Here we report the first simulation in which a solar flare evolves from pre-flare, over impulsive phase all the way into its gradual phase, which successfully reproduces post-flare coronal rain. This rain results from catastrophic cooling caused by thermal instability, and we analyse the entire mass and energy budget evolution driving this sudden condensation phenomenon. We find that the runaway cooling and rain formation also induces the appearance of dark post-flare loop systems, as observed in EUV channels. We confirm and augment earlier observational findings, suggesting that thermal conduction and radiative losses alternately dominate the cooling of PFLs. Since reconnection-driven flares occur in many astrophysical settings (stellar flares, accretion disks, galactic winds and jets), our study suggests a new and natural pathway to introduce multi-thermal structuring.

scholarly journals Solar extreme ultraviolet (EUV) flare observations and findings from the Solar Dynamics Observatory (SDO) EUV Variability Experiment (EVE)

2015 ◽  
Vol 11 (S320) ◽  
pp. 27-40
Author(s):  
Thomas N. Woods ◽  
Francis G. Eparvier ◽  
James P. Mason
Keyword(s):  
Extreme Ultraviolet ◽  
Late Phase ◽  
Impulsive Phase ◽  
The Sun ◽  
Solar Dynamics Observatory ◽  
X Ray ◽  
Gradual Phase ◽  
Stellar Flares ◽  
Solar Dynamics ◽  
Coronal Dimming

AbstractNew solar soft X-ray (SXR) and extreme ultraviolet (EUV) irradiance observations from NASA Solar Dynamics Observatory (SDO) EUV Variability Experiment (EVE) provide full coverage from 0.1 to 106 nm and continuously at a cadence of 10 seconds for spectra at 0.1 nm resolution. These observations during flares can usually be decomposed into four distinct characteristics: impulsive phase, gradual phase, coronal dimming, and EUV late phase. Over 6000 flares have been observed during the SDO mission; some flares show all four phases, and some only show the gradual phase. The focus is on the newer results about the EUV late phase and coronal dimming and its relationship to coronal mass ejections (CMEs). These EVE flare measurements are based on observing the sun-as-a-star, so these results could exemplify stellar flares. Of particular interest is that new coronal dimming measurements of stars could be used to estimate mass and velocity of stellar CMEs.

scholarly journals Stellar flare diagnostics from multi–wavelength observations

2009 ◽  
Vol 5 (S264) ◽  
pp. 288-291 ◽  
Author(s):  
Alexander V. Stepanov ◽  
Yuri T. Tsap ◽  
Yulia G. Kopylova
Keyword(s):  
Scaling Law ◽  
Electric Circuit ◽  
Plasma Parameters ◽  
Stellar Flare ◽  
Flare Loop ◽  
X Ray ◽  
Stellar Flares ◽  
Flare Loops ◽  
Red Dwarfs ◽  
Multi Wavelength

AbstractQuasi–periodic pulsations in various wavebands are natural manifestations of emission of stellar flares. We suggest a diagnostic tool of stellar flares based on the coronal seismology and the solar–stellar analogy. Two approaches are used: (I) flare loop as a resonator for MHD oscillations and (II) flare loop as an equivalent electric circuit. Using optical, X–ray, and radio data we obtained flare plasma parameters for the red dwarfs EQ Peg, AT Mic, and AD Leo. The characteristic length of stellar flare loops l ~ R* and their electric currents turned out to be one–two orders of magnitude lager than the solar ones. Advantages of proposed diagnostics in comparison to the scaling law methods are given.

scholarly journals Drifting of the line-tied footpoints of CME flux-ropes

2019 ◽  
Vol 621 ◽  
pp. A72 ◽  
Author(s):  
Guillaume Aulanier ◽  
Jaroslav Dudík
Keyword(s):  
Standard Model ◽  
Extreme Ultraviolet ◽  
Current Model ◽  
Three Dimensional ◽  
Flux Rope ◽  
Outer Edge ◽  
Flare Loop ◽  
Flare Loops ◽  
Field Lines ◽  
Line Tying

Context. Bridging the gap between heliospheric and solar observations of eruptions requires the mapping of interplanetary coronal mass ejection (CME) footpoints down to the Sun’s surface. But this not straightforward. Improving the understanding of the spatio-temporal evolutions of eruptive flares requires a comprehensive standard model. But the current model is only two-dimensional and cannot address the question of interplanetary CME footpoints. Aims. Existing 3D extensions to the standard model show that flux-rope footpoints are surrounded by curved-shaped quasi-separatrix layer (QSL) footprints that can be related with hook-shaped flare-ribbons. We build upon this finding and further address the joint questions of their time-evolution, and of the formation of flare loops at the ends of the flaring polarity inversion line (PIL) of the erupting bipole, which are both relevant for flare understanding in general and for interplanetary CME studies in particular. Methods. We calculated QSLs and relevant field lines in an MHD simulation of a torus-unstable flux-rope. The evolving QSL footprints are used to define the outer edge of the flux rope at different times, and to identify and characterize new 3D reconnection geometries and sequences that occur above the ends of the flaring PIL. We also analyzed flare-ribbons as observed in the extreme ultraviolet by SDO/AIA and IRIS during two X-class flares. Results. The flux-rope footpoints are drifting during the eruption, which is unexpected due to line-tying. This drifting is due to a series of coronal reconnections that erode the flux rope on one side and enlarge it on the other side. Other changes in the flux-rope footpoint-area are due to multiple reconnections of individual field lines whose topology can evolve sequentially from arcade to flux rope and finally to flare loop. These are associated with deformations and displacements of QSL footprints, which resemble those of the studied flare ribbons. Conclusions. Our model predicts continuous deformations and a drifting of interplanetary CME flux-rope footpoints whose areas are surrounded by equally evolving hooked-shaped flare-ribbons, as well as the formation of flare loops at the ends of flaring PILs which originate from the flux-rope itself, both of which being due to purely three-dimensional reconnection geometries. The observed evolution of flare-ribbons in two events supports the model, but more observations are required to test all its predictions.

scholarly journals Solar Flares: The Gradual Phase

1989 ◽  
Vol 104 (1) ◽  
pp. 399-417
Author(s):  
Zdeněk Švestka
Keyword(s):  
Energy Release ◽  
Cosmic Ray ◽  
Impulsive Phase ◽  
Wide Energy Range ◽  
X Rays ◽  
Radio Waves ◽  
Gradual Phase ◽  
Flare Loops ◽  
Magnetic Modelling ◽  
Wide Energy

AbstractOne has to distinguish between two kinds of the gradual phase of flares: (1) a gradual phase during which no energy is released so that we see only cooling after the impulsive phase (a confined flare), and (2) a gradual phase during which energy release continues (a dynamic flare).The simplest case of (1) is a single-loop flare which might provide an excellent opportunity for the study of cooling processes in coronal loops. But most confined flares are far more complicated: they may consist of sets of unresolved elementary loops, of conglomerates of loops, or they form arcades the components of which may be excited sequentially. Accelerated particles as well as hot and cold plasma can be ejected from the flare site (coronal ‘tongues', flaring arches, sprays, bright and dark surges) and these éjecta may cool more slowly than the source flare itself.However, the most important flares on the Sun are flares of type (2) in which a magnetic field opening is followed by subsequent reconnection of fieldlines that may continue for many hours after the impulsive phase. Therefore, the main attention in this review is paid to the gradual phase of this category oflong-decay flares. The following items are discussed in particular: The wide energy range of dynamic flares: from eruptions of quiescent filaments to most powerful cosmic-ray flares. Energy release at the reconnection site and modelling of the reconnection process. The ‘post-flare’ loops: evidence for reconnection; observations at different wavelengths; energy deposit in the chromosphere, chromospheric ablation, and velocity fields; loops in emission; shrinking loops; magnetic modelling. The gradual phase in X-rays and on radio waves. Post-flare X-ray arches: observations, interpretation, and modelling; relation to metric radio events and mass ejections, multiple-ribbon flares and anomalous events, hybrid events, possible relations between confined and dynamic flares.

Acceleration of particles in different parts of erupting Coronal Mass Electrons

2020 ◽  
Author(s):  
Valentina Zharkova ◽  
Qian Xia ◽  
Joel Dahlin ◽  
Spiro Antiochos
Keyword(s):  
Magnetic Field ◽  
Interplanetary Space ◽  
Flux Rope ◽  
Impulsive Phase ◽  
Particle Energy ◽  
Force Balance ◽  
Magnetic Islands ◽  
Flare Loop ◽  
Flare Loops ◽  
Energy Gains

<p>We examine particle energisation in CMEs generated via the breakout mechanism and explore both 2D and 3D MHD configurations. In the breakout scenario, reconnection at a breakout current sheet (CS) initiates the flux rope eruption by destabilizing the quasi-static force balance. Reconnection at the flare CS triggers the fast acceleration of the CME, which forms flare loops below and triggers particle acceleration in flares. We present test-particle studies that focus on two selected times during the impulsive and decay phases of the eruption and obtain particle energy gains and spatial distributions. We find that particles accelerated more efficiently in the flare CS than in the breakout CS even in the presence of large magnetic islands. The maximum particle energy gain is estimated from the energization terms based on the guiding-center approximation. Particles are first accelerated in the CSs (with or without magnetic islands) where Fermi-type acceleration dominates. Accelerated particles escape to the interplanetary space along open field lines rather than trapped in flux ropes, precipitate into the chromosphere along the flare loops, or become trapped in the flare loop top due to the magnetic mirror structure. Some trapped particles are re-accelerated, either via re-injection to the flare CS or through a local betatron-type acceleration associated with compression of the magnetic field. The energy gains of particles result in relatively hard energy spectra during the impulsive phase. During the gradual phase, the relaxation of the shear in magnetic field reduces the guiding magnetic field in the flare CS, which leads to a decrease in particle energization efficiency.</p>

Space and Time Distribution of Hard X-Ray Emission in a Loop at the Beginning of a Flare

1994 ◽  
Vol 144 ◽  
pp. 275-277
Author(s):  
M. Karlický ◽  
J. C. Hénoux
Keyword(s):  
Time Distribution ◽  
Electron Bombardment ◽  
Spatial Evolution ◽  
Superthermal Electrons ◽  
Flare Loop ◽  
X Ray ◽  
Superthermal Electron ◽  
Flare Loops ◽  
Chromospheric Evaporation ◽  
Temporal And Spatial

AbstractUsing a new ID hybrid model of the electron bombardment in flare loops, we study not only the evolution of densities, plasma velocities and temperatures in the loop, but also the temporal and spatial evolution of hard X-ray emission. In the present paper a continuous bombardment by electrons isotropically accelerated at the top of flare loop with a power-law injection distribution function is considered. The computations include the effects of the return-current that reduces significantly the depth of the chromospheric layer which is evaporated. The present modelling is made with superthermal electron parameters corresponding to the classical resistivity regime for an input energy flux of superthermal electrons of 109erg cm−2s−1. It was found that due to the electron bombardment the two chromospheric evaporation waves are generated at both feet of the loop and they propagate up to the top, where they collide and cause temporary density and hard X-ray enhancements.

scholarly journals Hydrodynamic Models of Solar and Stellar Flares

1989 ◽  
Vol 104 (1) ◽  
pp. 289-298
Author(s):  
Giovanni Peres
Keyword(s):  
High Resolution ◽  
Light Curve ◽  
Solar Flares ◽  
Impulsive Phase ◽  
Light Curves ◽  
Physical Parameters ◽  
The Sun ◽  
Hydrodynamic Models ◽  
X Ray ◽  
Stellar Flares

AbstractThis paper discusses the hydrodynamic modeling of flaring plasma confined in magnetic loops and its objectives within the broader scope of flare physics. In particular, the Palermo-Harvard model is discussed along with its applications to the detailed fitting of X-ray light curves of solar flares and to the simulation of high-resolution Caxix spectra in the impulsive phase. These two approaches provide complementary constraints on the relevant features of solar flares. The extension to the stellar case, with the fitting of the light curve of an X-ray flare which occurred on Proxima Centauri, demonstrates the feasibility of using this kind of model for stars too. Although the stellar observations do not provide the wealth of details available for the Sun, and, therefore, constrain the model more loosely, there are strong motivations to pursue this line of research: the wider range of physical parameters in stellar flares and the possibility of studying further the solar-stellar connection.

scholarly journals Distinguishing between coronal cloud prominences and channel prominences and their associations with solar and stellar flares

2015 ◽  
Vol 11 (S320) ◽  
pp. 278-287
Author(s):  
Sara F. Martin ◽  
Oddbjorn Engvold ◽  
Yong Lin ◽  
Jacqueline Alves da Silva
Keyword(s):  
Magnetic Fields ◽  
Sunspot Number ◽  
Maximum Height ◽  
Stellar Flares ◽  
Curved Trajectories ◽  
Coronal Magnetic Fields ◽  
Coronal Rain

AbstractTo better understand the differences between coronal cloud prominences and channel prominences, we systematically identified and analyzed coronal cloud prominences recorded in SDO/AIA images at 304 Å from 2010 May 20 through 2012 April 28. For the 225 cases identified, their numbers vary directly with the sunspot number. Their durations are typically less than 3 days. Their most frequent maximum height is 90,000 + and - 10,000 km. We offer our hypothesis that many coronal cloud prominences originate from some of the mass of previously erupted filaments ejected high out of their filament channels; subsequently part of this mass falls and collects in leaky magnetic troughs among coronal magnetic fields which constrain the leaked mass to slowly drain downward along curved trajectories where it appears as coronal rain. Currently there is inadequate evidence for a convincing correspondence between either coronal cloud prominences or channel prominences with stellar prominences detected to date.

scholarly journals Stellar flares versus luminosity: XUV-induced atmospheric escape and planetary habitability

2020 ◽  
Vol 500 (1) ◽  
pp. L1-L5
Author(s):  
Dimitra Atri ◽  
Shane R Carberry Mogan
Keyword(s):  
Extreme Ultraviolet ◽  
Wide Energy Range ◽  
X Rays ◽  
Loss Mechanism ◽  
Atmospheric Escape ◽  
Stellar Flares ◽  
Wide Energy ◽  
A Minor ◽  
Atmospheric Loss ◽  
Planetary Habitability

ABSTRACT Space weather plays an important role in the evolution of planetary atmospheres. Observations have shown that stellar flares emit energy in a wide energy range (1030–1038 erg), a fraction of which lies in X-rays and extreme ultraviolet (XUV). These flares heat the upper atmosphere of a planet, leading to increased escape rates, and can result in atmospheric erosion over a period of time. Observations also suggest that primordial terrestrial planets can accrete voluminous H/He envelopes. Stellar radiation can erode these protoatmospheres over time, and the extent of this erosion has implications for the planet’s habitability. We use the energy-limited equation to calculate hydrodynamic escape rates from these protoatmospheres irradiated by XUV stellar flares and luminosity. We use the flare frequency distribution of 492 FGKM stars observed with TESS to estimate atmospheric loss in habitable zone planets. We find that for most stars, luminosity-induced escape is the main loss mechanism, with a minor contribution from flares. However, flares dominate the loss mechanism of ∼20 per cent M4–M10 stars. M0–M4 stars are most likely to completely erode both their proto- and secondary atmospheres, and M4–M10 are least likely to erode secondary atmospheres. We discuss the implications of these results on planetary habitability.

scholarly journals Long-Duration Solar and Stellar Flares

1989 ◽  
Vol 104 (1) ◽  
pp. 313-322
Author(s):  
Giannina Poletto
Keyword(s):  
Solar Flares ◽  
Classification Scheme ◽  
High Spatial Resolution ◽  
Physical Parameters ◽  
Additional Information ◽  
Stellar Flares ◽  
Long Duration ◽  
Model Predictions ◽  
Flare Region ◽  
Reconnection Model

AbstractAccording to one of the most popular classifications, solar flares may be assigned either to the category of small short-lived events, or to the category of large, long-duration two-ribbon (2-R) flares. Even if such a broad division oversimplifies the flare phenomenon, our knowledge of the characteristics of stellar flares is so poor, that it is worthwhile to investigate the possibility of adopting this classification scheme for stellar flares as well. In particular we will analyze Einstein observations of a long duration flare on EQ Peg to establish whether it might be considered as a stellar analogy of 2-R solar events. To this end we apply to EQ Peg data a reconnection model, developed originally for solar 2-R flares, and conclude that stellar observations are consistent with model predictions, although additional information is required to identify uniquely the physical parameters of the flare region. Application of the model to integrated observations of a 2-R solar flare, for which high spatial resolution data are also available, shows, however, that future integrated observations may allow us to solve the ambiguities of the model and use it as a diagnostic tool for a better understanding of stellar flares.

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