The morphology of average solar flare time profiles from observations of the Sun’s lower atmosphere

ABSTRACT We study the decay phase of solar flares in several spectral bands using a method based on that successfully applied to white light flares observed on an M4 dwarf. We selected and processed 102 events detected in the Sun-as-a-star flux obtained with SDO/AIA images in the 1600 and 304 Å channels and 54 events detected in the 1700 Å channel. The main criterion for the selection of time profiles was a slow, continuous flux decay without significant new bursts. The obtained averaged time profiles were fitted with analytical templates, using different time intervals, that consisted of a combination of two independent exponents or a broken power law. The average flare profile observed in the 1700 Å channel decayed more slowly than the average flare profile observed on the M4 dwarf. As the 1700 Å emission is associated with a similar temperature to that usually ascribed to M dwarf flares, this implies that the M dwarf flare emission comes from a more dense layer than solar flare emission in the 1700 Å band. The cooling processes in solar flares were best described by the two exponents model, fitted over the intervals t1 = [0, 0.5]t1/2 and t2 = [3, 10]t1/2, where t1/2 is time taken for the profile to decay to half the maximum value. The broken power-law model provided a good fit to the first decay phase, as it was able to account for the impact of chromospheric plasma evaporation, but it did not successfully fit the second decay phase.

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The Environment of the Young Earth in the Perspective of An Young Sun

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317004288 ◽

2016 ◽

Vol 12 (S328) ◽

pp. 315-328

Author(s):

Vladimir S. Airapetian

Keyword(s):

Space Weather ◽

Solar Flares ◽

Geomagnetic Storms ◽

Lower Atmosphere ◽

Early Earth ◽

Uv Emission ◽

Weather Events ◽

Active Stars ◽

Magnetohydrodynamic Models ◽

The Impact

AbstractOur Sun, a magnetically mild star, exhibits space weather in the form of magnetically driven solar explosive events (SEE) including solar flares, coronal mass ejections and energetic particle events. We use Kepler data and reconstruction of X-ray and UV emission from young solar-like stars to recover the frequency and energy fluxes from extreme events from active stars including the young Sun. Extreme SEEs from a magnetically active young Sun could significantly perturb the young Earth's magnetosphere, cause strong geomagnetic storms, initiate escape and introduce chemical changes in its lower atmosphere. I present our recent simulations results based on multi-dimensional multi-fluid hydrodynamic and magnetohydrodynamic models of interactions of extreme CME and SEP events with magnetospheres and lower atmospheres of early Earth and exoplanets around active stars. We also discuss the implications of the impact of these effects on evolving habitability conditions of the early Earth and prebiotic chemistry introduced by space weather events at the early phase of evolution of our Sun.

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Electrons and X-Ray Emission of Solar Flares

Symposium - International Astronomical Union ◽

10.1017/s007418090008832x ◽

1990 ◽

Vol 142 ◽

pp. 409-413

Author(s):

V. G. Kurt

Keyword(s):

Solar Activity ◽

Statistical Analysis ◽

Solar Flare ◽

Frequency Dependence ◽

Power Law ◽

Solar Flares ◽

X Rays ◽

Fast Electrons ◽

X Ray ◽

Flare Frequency

A statistical analysis of solar flare X-rays and interplanetary particle fluxes, measured onboard VENERA-13, 14 Spacecraft, was performed. The correlation of fluences for different manifestations of solar flares is strong, especially for fast electrons and hard and soft X-ray emissions. Frequency dependence on fluence value ϵi for practically all Kinds of solar flare emission can be described by power law ν (ϵ > ϵO) ∼ ϵ−0.45±0.15 which does not change significantly with solar activity. For different Hα flare importances the values of ϵi were obtained. It is proposed that appearance of certain energy flare frequency is strongly dependent on some scale factor.

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Evaluating the Impact of Pre-clustering and Class Imbalance on Solar Flare Forecasting

10.5753/eniac.2018.4441 ◽

2018 ◽

Author(s):

Mirelle C. Bueno ◽

Guilherme P. Coelho ◽

Ana Estela A. Da Silva ◽

André L. S. Gradvohl

Keyword(s):

Machine Learning ◽

Solar Flare ◽

Transmission Lines ◽

Solar Flares ◽

Power Transmission ◽

Class Imbalance ◽

The Sun ◽

Power Transmission Lines ◽

Short Circuits ◽

The Impact

Among the phenomena that occur on the surface of the Sun, solar flares may cause several damages, from short circuits in power transmission lines to complete interruptions in telecommunications systems. In order to mitigate these effects, many works have been dedicated to the proposal of mechanisms capable of predicting the occurrence of solar flares. In this context, the present work sought to evaluate two aspects related to machine learning-based solar flare forecasting: (i) the impact of class imbalance in training datasets on the performance of the predictors; and (ii) whether the incorporation of a pre-clustering step prior to the classifiers training contributes to a better prediction.

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The escape of trapped electrons in the decay phase of solar flare

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313002408 ◽

2012 ◽

Vol 8 (S294) ◽

pp. 153-154

Author(s):

Jing Huang

Keyword(s):

Solar Flare ◽

Solar Flares ◽

Pitch Angle ◽

Escape Rate ◽

Decay Phase ◽

Coulomb Collision ◽

Energetic Electrons ◽

Trapped Electrons ◽

Flare Loops ◽

Angle Scattering

AbstractFrom the observations of radio and HXR bursts, the escape rate of energetic electrons trapped in the flare loops is studied based on the trap-plus-precipitation model for the kinematics of energetic electrons in solar flares. Coulomb collision is regarded as the main pitch angle scattering of trapped electrons in the decay phase of the event on 2004 December 1. The escape rate of trapped electrons decreases firstly and then increases, which indicates the evolution of the plasma density in the flare loops during the decay phase.

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Understanding solar flares from optical observations: How do particle beams affect the lower atmosphere?

Advances in Space Research ◽

10.1016/s0273-1177(03)90409-1 ◽

2003 ◽

Vol 32 (12) ◽

pp. 2393-2402 ◽

Cited By ~ 1

Author(s):

P HEINZEL

Keyword(s):

Solar Flares ◽

Lower Atmosphere ◽

Optical Observations ◽

Particle Beams

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Searching for energy-resolved quasi-periodic oscillations in AGN

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa4024 ◽

2021 ◽

Author(s):

Dominic I Ashton ◽

Matthew J Middleton

Keyword(s):

Power Law ◽

Spectral Component ◽

Broad Band ◽

Initial Study ◽

Periodic Oscillations ◽

Single Observation ◽

Curved Space ◽

Multiple Observations ◽

Band Noise ◽

The Impact

Abstract X-ray quasi-periodic oscillations (QPOs) in AGN allow us to probe and understand the nature of accretion in highly curved space-time, yet the most robust form of detection (i.e. repeat detections over multiple observations) has been limited to a single source to-date, with only tentative claims of single observation detections in several others. The association of those established AGN QPOs with a specific spectral component has motivated us to search the XMM-Newton archive and analyse the energy-resolved lightcurves of 38 bright AGN. We apply a conservative false alarm testing routine folding in the uncertainty and covariance of the underlying broad-band noise. We also explore the impact of red-noise leak and the assumption of various different forms (power-law, broken power-law and lorentzians) for the underlying broad-band noise. In this initial study, we report QPO candidates in 6 AGN (7 including one tentative detection in MRK 766) from our sample of 38, which tend to be found at characteristic energies and, in four cases, at the same frequency across at least two observations, indicating they are highly unlikely to be spurious in nature.

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Superhydrophobicity in perfection: the outstanding properties of the lotus leaf

Beilstein Journal of Nanotechnology ◽

10.3762/bjnano.2.19 ◽

2011 ◽

Vol 2 ◽

pp. 152-161 ◽

Cited By ~ 285

Author(s):

Hans J Ensikat ◽

Petra Ditsche-Kuru ◽

Christoph Neinhuis ◽

Wilhelm Barthlott

Keyword(s):

Chemical Composition ◽

Water Repellency ◽

Contact Angles ◽

Dense Layer ◽

Lotus Effect ◽

Nano Structure ◽

Lotus Leaf ◽

Water Drops ◽

The Impact ◽

Unique Chemical

Lotus leaves have become an icon for superhydrophobicity and self-cleaning surfaces, and have led to the concept of the ‘Lotus effect’. Although many other plants have superhydrophobic surfaces with almost similar contact angles, the lotus shows better stability and perfection of its water repellency. Here, we compare the relevant properties such as the micro- and nano-structure, the chemical composition of the waxes and the mechanical properties of lotus with its competitors. It soon becomes obvious that the upper epidermis of the lotus leaf has developed some unrivaled optimizations. The extraordinary shape and the density of the papillae are the basis for the extremely reduced contact area between surface and water drops. The exceptional dense layer of very small epicuticular wax tubules is a result of their unique chemical composition. The mechanical robustness of the papillae and the wax tubules reduce damage and are the basis for the perfection and durability of the water repellency. A reason for the optimization, particularly of the upper side of the lotus leaf, can be deduced from the fact that the stomata are located in the upper epidermis. Here, the impact of rain and contamination is higher than on the lower epidermis. The lotus plant has successfully developed an excellent protection for this delicate epistomatic surface of its leaves.

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