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1

Asymmetric Statistical Properties of the Solar Cycle 23 Deduced from Sunspots, Plages and Flare Occurrences  

NASA Astrophysics Data System (ADS)

The statistical properties of sunspot, active regions (plages) and filament distributions obtained from the automated Solar Feature Catalogues (SFC, http://solar.inf.brad.ac.uk) and their relation to flare distributions are presented for 1996-2005. We present distributions of sunspot numbers with given areas for different phases and the whole solar cycle 23. Statistical sunspot and plage area distributions revealed a strong North-South asymmetry of about 0.2-0.6 for sunspots, plages and flare occurrences with two basic periods of about 9 and 2.5 years. The distributions of sunspot and flare occurrences at different latitudes and longitudes in Northern and Southern hemispheres and their magnetic tilts are compared with their total and excess magnetic fields during the whole period of observations. The application of these results to the solar dynamo models is discussed.

Zharkova, Valentina; Zharkov, S.

2006-06-01

2

Solar Flares  

NSDL National Science Digital Library

This page details and resources that help support an understanding of solar flares on our sun. When we are drawing a sun on a piece of paper, they usually look like this: Cartoon Picture of a Sun The spiky lines have a name - Solar Flares. This is when the sun releases gas and heat into the atmosphere. Click on this picture to see what a solar flare looks like. Picture of a Solar Flare 2 In this video, you ...

Mrs. Verlengia

2011-12-10

3

Accepted by ApJ. Periodicities in Solar Flare Occurrence  

E-print Network

(Kile & Cliver 1991); production of solar energetic protons (Bai & Cliver 1990; Gabriel et al. 1990); production of energetic electrons in interplanetary space (Dr¨oge et al. 1990). Many researchers studied that the periodicity near 154 days operated during cycles 19­21 (Lean & Brueckner 1989; Lean 1990; Oliver et al. 1998

Bai, Taeil

4

Solar Flares  

NASA Technical Reports Server (NTRS)

Because the Earth resides in the atmosphere of our nearest stellar neighbor, events occurring on the Sun's surface directly affect us by interfering with satellite operations and communications, astronaut safety, and, in extreme circumstances, power grid stability. Solar flares, the most energetic events in our solar system, are a substantial source of hazardous space weather affecting our increasingly technology-dependent society. While flares have been observed using ground-based telescopes for over 150 years, modern space-bourne observatories have provided nearly continuous multi-wavelength flare coverage that cannot be obtained from the ground. We can now probe the origins and evolution of flares by tracking particle acceleration, changes in ionized plasma, and the reorganization of magnetic fields. I will walk through our current understanding of why flares occur and how they affect the Earth and also show several examples of these fantastic explosions.

Savage, Sabrina

2013-01-01

5

Latitudinal And Longitudinal Distributions Of S unspots And Solar Flare Occurrence In The Cycle 23 From T he Solar Feature Catalogues  

NASA Astrophysics Data System (ADS)

The statistical properties of sunspot and active regions (plages) distributions obtained from the automated Solar Feature Catalogues (SFC, http://solar.inf.brad.ac.uk) for 1996-2005 and their relation to H? flare occurrences are presented. The average monthly flare occurrences during the cycle 23 correlate rather closely with but do not follow exacly the sunspot area variations. The temporal distribution of solar flare occurrences at different latitudes in the Northern and Southern hemispheres reveal strong asymmetry reflected in periodic domination either one or another hemisphere that follows closely those of the plage and sunspot areas. The latitudinal distribution of flare occurences in the whole period reveal a well defined maximum at 20 in the Northern hemisphere that is likely to be associated with the domination of the Northern hemisphere in the sunspot formation during the solar amximum years. The longitudinal distributions of flare occurrences in the cycle 23 averaged in latitudes over a year reveal a persistend longitude of 200 with small fluctuations about 10 with the period of about 1-1.5 years. Possible implications on solar dynamo models of the detected latitudinal and logitudinal asymmetries in the sunspot, active region and flare occurrences are discussed.

Zahrkova, V. V.; Zharkov, S. I.

2007-01-01

6

A 154-day periodicity in the occurrence of hard solar flares?  

NASA Technical Reports Server (NTRS)

An analysis of the temporal distribution of 139 solar flares monitored by the Gamma Ray Spectrometer aboard the Solar Maximum Mission is reported. It is found that, instead of being randomly distributed in time, these events have a tendency to occur in groups with a mean spacing of about 154 days (75 nHz) over the observing interval. A larger sample of flares with an X-ray classification of M 2.5 or larger recorded by the GOES satellite showed a similar regularity.

Rieger, E.; Kanbach, G.; Reppin, C.; Share, G. H.; Forrest, D. J.; Chupp, E. L.

1984-01-01

7

Occurrence of solar flares viewed with GPS: Statistics and fractal nature  

NASA Astrophysics Data System (ADS)

In this paper we describe the statistical properties of the EUV solar flux sudden variation. The solar flux variation is modeled as a time series characterized by the subsolar Vertical Total Electron Content double difference in time, computed with dual-frequency GNSS (Global Navigation Satellite Systems) measurements in the daylight hemisphere (GNSS solar flare indicator rate parameter). We propose a model that explains its characteristics and the forecasting limitations. The sudden overionization pattern is assumed to be of solar origin, and the data used in this study was collected during the last solar cycle. The two defining characteristics of this time series are an extreme variability (i.e., in a solar cycle one can find events at 400? from the mean value) and a temporal correlation that is independent of the timescale. We give a characterization of a model that explains the empirical results and properties such as (a) the persistence and presence of bursts of solar flares and (b) their long tail peak values of the solar flux variation. We show that the solar flux variation time series can be characterized by a fractional Brownian model for the long-term dependence, and a power law distribution for the extreme values that appear in the time series.

Monte-Moreno, Enrique; Hernndez-Pajares, Manuel

2014-11-01

8

The relationship between solar flares and solar sector boundaries  

NASA Technical Reports Server (NTRS)

A superposed epoch analysis of 1964-1970 solar flares shows a marked increase in flare occurrence within a day of (-+) solar sector boundaries, as well as a local minimum in flare occurrence near (+-) sector boundaries. This perference for (-+) boundaries is more noticeable for Northern Hemisphere flares, where these polarities match the Hale polarity law, but is not reversed in the south. Plage regions do not show such a perference.

Dittmer, P. H.

1974-01-01

9

Understanding Solar Flare Statistics  

NASA Astrophysics Data System (ADS)

A review is presented of work aimed at understanding solar flare statistics, with emphasis on the well known flare power-law size distribution. Although avalanche models are perhaps the favoured model to describe flare statistics, their physical basis is unclear, and they are divorced from developing ideas in large-scale reconnection theory. An alternative model, aimed at reconciling large-scale reconnection models with solar flare statistics, is revisited. The solar flare waiting-time distribution has also attracted recent attention. Observed waiting-time distributions are described, together with what they might tell us about the flare phenomenon. Finally, a practical application of flare statistics to flare prediction is described in detail, including the results of a year of automated (web-based) predictions from the method.

Wheatland, M. S.

2005-12-01

10

The solar flare myth  

Microsoft Academic Search

Many years of research have demonstrated that large, nonrecurrent geomagnetic storms, shock wave disturbances in the solar wind, and energetic particle events in interplanetary space often occur in close association with large solar flares. This result has led to a paradigm of cause and effect - that large solar flares are the fundamental cause of these events in the near-Earth

J. T. Gosling

1993-01-01

11

Statistical properties of sunspot, active region distributions and flare occurrences in the cycle 23 as detected from the Solar Feature Catalogues  

NASA Astrophysics Data System (ADS)

The statistical properties of sunspot and active regions (plages) distributions and their relation to flare distributions are presented for 1996-2005 from the automated Solar Feature Catalogues from the SOHO and Meudon Observatories (SFC, http://solar.inf.brad.ac.uk). Cross-correlation analysis is carried out between flare sizes, locations, significance and active region/sunspot parameters including magnetic field extracted in SFC. Sunspot and plage area distributions reveals a strong North-South asymmetry of about 0.2 and the period of about 7-8 years for sunspots and of 0.5 and period of 9 years for plages with both asymmetries decreasing towards the next cycle minimum. The temporal distribution of solar flare occurrences in Northern and Southern hemispheres, at different latitudes and longitudes are compared with those of plage and sunspot areas and LOS magnetic fields. The application of these results to the solar activity forecast is discussed.

Zharkova, V. V.; Zharkov, S. I.

2006-08-01

12

Solar flares. [plasma physics  

NASA Technical Reports Server (NTRS)

The present paper deals with explosions in a magnetized solar plasma, known as flares, whose effects are seen throughout the electromagnetic spectrum, from gamma-rays through the visible and to the radio band. The diverse phenomena associated with flares are discussed, along with the physical mechanisms that have been advanced to explain them. The impact of solar flare research on the development of plasma physics and magnetohydrodynamics is noted. The rapid development of solar flare research during the past 20 years, owing to the availability of high-resolution images, detailed magnetic field measurements, and improved spectral data, is illustrated.

Rust, D. M.

1979-01-01

13

Flare models: Chapter 9 of solar flares  

NASA Technical Reports Server (NTRS)

By reviewing the properties of solar flares analyzed by each of the seven teams of the Skylab workshop, a set of primary and secondary requirements of flare models are derived. A number of flare models are described briefly and their properties compared with the primary requirements. It appears that, at this time, each flare model has some strong points and some weak points. It has not yet been demonstrated that any one flare model meets all the proposed requirements.

Sturrock, P. A. (editor)

1979-01-01

14

COMPTEL solar flare observations  

NASA Technical Reports Server (NTRS)

COMPTEL as part of a solar target of opportunity campaign observed the sun during the period of high solar activity from 7-15 Jun. 1991. Major flares were observed on 9 and 11 Jun. Although both flares were large GOES events (greater than or = X10), they were not extraordinary in terms of gamma-ray emission. Only the decay phase of the 15 Jun. flare was observed by COMPTEL. We report the preliminary analysis of data from these flares, including the first spectroscopic measurement of solar flare neutrons. The deuterium formation line at 2.223 MeV was present in both events and for at least the 9 Jun. event, was comparable to the flux in the nuclear line region of 4-8 MeV, consistent with Solar-Maximum Mission (SSM) Observations. A clear neutron signal was present in the flare of 9 Jun. with the spectrum extending up to 80 MeV and consistent in time with the emission of gamma-rays, confirming the utility of COMPTEL in measuring the solar neutron flux at low energies. The neutron flux below 100 MeV appears to be lower than that of the 3 Jun. 1982 flare by more than an order of magnitude. The neutron signal of the 11 Jun. event is under study. Severe dead time effects resulting from the intense thermal x-rays require significant corrections to the measured flux which increase the magnitude of the associated systematic uncertainties.

Ryan, J. M.; Aarts, H.; Bennett, K.; Debrunner, H.; Devries, C.; Denherder, J. W.; Eymann, G.; Forrest, D. J.; Diehl, R.; Hermsen, W.

1992-01-01

15

The solar flare myth  

NASA Technical Reports Server (NTRS)

Many years of research have demonstrated that large, nonrecurrent geomagnetic storms, shock wave disturbances in the solar wind, and energetic particle events in interplanetary space often occur in close association with large solar flares. This result has led to a pradigm of cause and effect - that large solar flares are the fundamental cause of these events in the near-Earth space environmemt. This paradigm, which I call 'the solar flare myth,' dominates the popular perception of the relationship between solar activity and interplanetary and geomagnetic events and has provided much of the pragmatic rationale for the study of the solar flare phenomenon. Yet there is good evidence that this paradigm is wrong and that flares do not generally play a central role in producing major transient disturbances in the near-Earth space environment. In this paper I outline a different paradigm of cause and effect that removes solar flares from their central position in the chain of events leading from the Sun to near-Earth space. Instead, this central role is given to events known as coronal mass ejections.

Gosling, J. T.

1993-01-01

16

BATSE Solar Flare Spectroscopy  

NASA Technical Reports Server (NTRS)

This final report describes the progress originally proposed: (1) the continued improvement of a software and database environment capable of supporting all users of BATSE solar data as well as providing scientific expertise and effort to the BATSE solar community; (2) the continued participation with the PI team and other guest investigators in the detailed analysis of the BATSE detectors' response at low energies; (3) using spectroscopic techniques to fully exploit the potential of electron time-of-flight studies; and, (4) a full search for flare gamma-ray line emission at 2.2 MeV from all GOES X-class flares observed with BATSE.

Schwartz, R. A.

1998-01-01

17

Electron beams in solar flares  

NASA Technical Reports Server (NTRS)

A list of publications resulting from this program includes 'The Timing of Electron Beam Signatures in Hard X-Ray and Radio: Solar Flare Observations by BATSE/Compton Gamma-Ray Observatory and PHOENIX'; 'Coherent-Phase or Random-Phase Acceleration of Electron Beams in Solar Flares'; 'Particle Acceleration in Flares'; 'Chromospheric Evaporation and Decimetric Radio Emission in Solar Flares'; 'Sequences of Correlated Hard X-Ray and Type 3 Bursts During Solar Flares'; and 'Solar Electron Beams Detected in Hard X-Rays and Radiowaves.' Abstracts and reprints of each are attached to this report.

Aschwanden, Markus J.; Dennis, Brian R.; Benz, Arnold O.

1994-01-01

18

Inter-occurrence Times in the Bak-Tang-Wiesenfeld Sandpile Model: A Comparison with the Turbulent Statistics of Solar Flares  

E-print Network

A sequence of bursts observed in an intermittent time series may be caused by a single avalanche, even though these bursts appear as distinct events when noise and/or instrument resolution impose a detection threshold. In the Bak-Tang-Wiesenfeld sandpile, the statistics of quiet times between bursts switches from Poissonian to scale invariant on raising the threshold for detecting instantaneous activity, since each zero-threshold avalanche breaks into a hierarchy of correlated bursts. Calibrating the model with the time resolution of GOES data, qualitative agreement with the inter-occurrence time statistics of solar flares at different intensity thresholds is found.

Maya Paczuski; Stefan Boettcher; Marco Baiesi

2005-06-20

19

Solar Flare Physics  

NASA Technical Reports Server (NTRS)

During the past year we have been working with the HESSI (High Energy Solar Spectroscopic Imager) team in preparation for launch in early 2001. HESSI has as its primary scientific goal photometric imaging and spectroscopy of solar flares in hard X-rays and gamma-rays with an approx. 2 sec angular resolution, approx. keV energy resolution and approx. 2 s time resolution over the 6 keV to 15 MeV energy range. We have performed tests of the imager using a specially designed experiment which exploits the second-harmonic response of HESSI's sub-collimators to an artificial X-ray source at a distance of 1550 cm from its front grids. Figures show the response to X-rays at energies in the range where HESSI is expected to image solar flares. To prepare the team and the solar user community for imaging flares with HESSI, we have written a description of the major imaging concepts. This paper will be submitted for publication in a referred journal.

Schmahl, Edward J.; Kundu, Mukul R.

2000-01-01

20

Solar flare model atmospheres  

NASA Astrophysics Data System (ADS)

Solar flare model atmospheres computed under the assumption of energetic equilibrium in the chromosphere are presented. The models use a static, one-dimensional plane-parallel geometry and are designed within a physically self-consistent coronal loop. Assumed flare heating mechanisms include collisions from a flux of nonthermal electrons and X-ray heating of the chromosphere by the corona. The heating by energetic electrons accounts explicitly for variations of the ionized fraction with depth in the atmosphere. X-ray heating of the chromosphere by the corona incorporates a flare loop geometry by approximating distant portions of the loop with a series of point sources, while treating the loop leg closest to the chromospheric footpoint in the plane-parallel approximation. Coronal flare heating leads to increased heat conduction, chromospheric evaporation and subsequent changes in coronal pressure; these effects are included self-consistently in the models. Cooling in the chromosphere is computed in detail for the important optically thick H I, Ca II and Mg II transitions using the non-local thermodynamic equilibrium (non-LTE) prescription in the program MULTI. Hydrogen ionization rates from X-ray photoionization and collisional ionization by nonthermal electrons are included explicitly in the rate equations. The models are computed in the 'impulsive' and 'equilibrium' limits, and in a set of intermediate 'evolving' states. The impulsive atmospheres have the density distribution frozen in the pre-flare configuration, while the equilibrium models assume the entire atmosphere is in hydrostatic and energetic equilibrium. The evolving atmospheres represent intermediate stages where hydrostatic equilibrium has been established in the chromosphere and corona, but the corona is not yet in energetic equilibrium with the flare heating source. Thus, for example, chromospheric evaporation is still in the process of occurring. We have computed the chromospheric radiation that results from a range of coronal heating rates, with particular emphasis on the widely observed diagnostic H(alpha). Our conclusion is that the H(alpha) fluxes and profiles actually observed in flares can only be produced under conditions of a low-pressure corona with strong beam heating. Therefore we suggest that H(alpha) in flares is produced primarily at the footprints of newly heated loops where significant evaporation has not yet occurred. As a single loop evolves in time, no matter how strong the heating rate may become, the H(alpha) flux will diminish as the corona becomes denser and hence more effective at stopping the beam. This prediction leads to several observable consequences regarding the spatial and temporal signatures of the X-ray and H(alpha) radiation during flares.

Hawley, Suzanne L.; Fisher, George H.

1994-05-01

21

Solar flare model atmospheres  

NASA Technical Reports Server (NTRS)

Solar flare model atmospheres computed under the assumption of energetic equilibrium in the chromosphere are presented. The models use a static, one-dimensional plane-parallel geometry and are designed within a physically self-consistent coronal loop. Assumed flare heating mechanisms include collisions from a flux of nonthermal electrons and X-ray heating of the chromosphere by the corona. The heating by energetic electrons accounts explicitly for variations of the ionized fraction with depth in the atmosphere. X-ray heating of the chromosphere by the corona incorporates a flare loop geometry by approximating distant portions of the loop with a series of point sources, while treating the loop leg closest to the chromospheric footpoint in the plane-parallel approximation. Coronal flare heating leads to increased heat conduction, chromospheric evaporation and subsequent changes in coronal pressure; these effects are included self-consistently in the models. Cooling in the chromosphere is computed in detail for the important optically thick H I, Ca II and Mg II transitions using the non-local thermodynamic equilibrium (non-LTE) prescription in the program MULTI. Hydrogen ionization rates from X-ray photoionization and collisional ionization by nonthermal electrons are included explicitly in the rate equations. The models are computed in the 'impulsive' and 'equilibrium' limits, and in a set of intermediate 'evolving' states. The impulsive atmospheres have the density distribution frozen in the pre-flare configuration, while the equilibrium models assume the entire atmosphere is in hydrostatic and energetic equilibrium. The evolving atmospheres represent intermediate stages where hydrostatic equilibrium has been established in the chromosphere and corona, but the corona is not yet in energetic equilibrium with the flare heating source. Thus, for example, chromospheric evaporation is still in the process of occurring. We have computed the chromospheric radiation that results from a range of coronal heating rates, with particular emphasis on the widely observed diagnostic H(alpha). Our conclusion is that the H(alpha) fluxes and profiles actually observed in flares can only be produced under conditions of a low-pressure corona with strong beam heating. Therefore we suggest that H(alpha) in flares is produced primarily at the footprints of newly heated loops where significant evaporation has not yet occurred. As a single loop evolves in time, no matter how strong the heating rate may become, the H(alpha) flux will diminish as the corona becomes denser and hence more effective at stopping the beam. This prediction leads to several observable consequences regarding the spatial and temporal signatures of the X-ray and H(alpha) radiation during flares.

Hawley, Suzanne L.; Fisher, George H.

1994-01-01

22

Automatic Solar Flare Tracking  

Microsoft Academic Search

\\u000a In October 2003 we began a four year project whose goal is to build a real-time space weather monitoring and forecasting system.\\u000a A major component of the project is the use of image processing and pattern recognition techniques to detect and characterize\\u000a three important solar activities in realtime: filament eruptions, flares, and emerging flux regions. In this paper we describe

Ming Qu; Frank Y. Shih; Ju Jing; Haimin Wang; David Rees

2004-01-01

23

Solar flare model atmospheres  

NASA Technical Reports Server (NTRS)

Solar flare model atmospheres computed under the assumption of energetic equilibrium in the chromosphere are presented. The models use a static, one-dimensional plane parallel geometry and are designed within a physically self-consistent coronal loop. Assumed flare heating mechanisms include collisions from a flux of non-thermal electrons and x-ray heating of the chromosphere by the corona. The heating by energetic electrons accounts explicitly for variations of the ionized fraction with depth in the atmosphere. X-ray heating of the chromosphere by the corona incorporates a flare loop geometry by approximating distant portions of the loop with a series of point sources, while treating the loop leg closest to the chromospheric footpoint in the plane-parallel approximation. Coronal flare heating leads to increased heat conduction, chromospheric evaporation and subsequent changes in coronal pressure; these effects are included self-consistently in the models. Cooling in the chromosphere is computed in detail for the important optically thick HI, CaII and MgII transitions using the non-LTE prescription in the program MULTI. Hydrogen ionization rates from x-ray photo-ionization and collisional ionization by non-thermal electrons are included explicitly in the rate equations. The models are computed in the 'impulsive' and 'equilibrium' limits, and in a set of intermediate 'evolving' states. The impulsive atmospheres have the density distribution frozen in pre-flare configuration, while the equilibrium models assume the entire atmosphere is in hydrostatic and energetic equilibrium. The evolving atmospheres represent intermediate stages where hydrostatic equilibrium has been established in the chromosphere and corona, but the corona is not yet in energetic equilibrium with the flare heating source. Thus, for example, chromospheric evaporation is still in the process of occurring.

Hawley, Suzanne L.; Fisher, George H.

1993-01-01

24

Solar flare model atmospheres  

NASA Astrophysics Data System (ADS)

Solar flare model atmospheres computed under the assumption of energetic equilibrium in the chromosphere are presented. The models use a static, one-dimensional plane parallel geometry and are designed within a physically self-consistent coronal loop. Assumed flare heating mechanisms include collisions from a flux of non-thermal electrons and x-ray heating of the chromosphere by the corona. The heating by energetic electrons accounts explicitly for variations of the ionized fraction with depth in the atmosphere. X-ray heating of the chromosphere by the corona incorporates a flare loop geometry by approximating distant portions of the loop with a series of point sources, while treating the loop leg closest to the chromospheric footpoint in the plane-parallel approximation. Coronal flare heating leads to increased heat conduction, chromospheric evaporation and subsequent changes in coronal pressure; these effects are included self-consistently in the models. Cooling in the chromosphere is computed in detail for the important optically thick HI, CaII and MgII transitions using the non-LTE prescription in the program MULTI. Hydrogen ionization rates from x-ray photo-ionization and collisional ionization by non-thermal electrons are included explicitly in the rate equations. The models are computed in the 'impulsive' and 'equilibrium' limits, and in a set of intermediate 'evolving' states. The impulsive atmospheres have the density distribution frozen in pre-flare configuration, while the equilibrium models assume the entire atmosphere is in hydrostatic and energetic equilibrium. The evolving atmospheres represent intermediate stages where hydrostatic equilibrium has been established in the chromosphere and corona, but the corona is not yet in energetic equilibrium with the flare heating source. Thus, for example, chromospheric evaporation is still in the process of occurring.

Hawley, Suzanne L.; Fisher, George H.

1993-12-01

25

Solar Flares and particle acceleration  

E-print Network

prominent in X-rays, UV/EUV and radio . but can be seen from radio to 100 MeV #12;Solar flares and accelerated particles #12;Solar flares and accelerated particles From Emslie et al., 2004, 2005 Free magnetic

26

Solar Flare Physics  

NASA Technical Reports Server (NTRS)

We have continued our previous efforts in studies of fourier imaging methods applied to hard X-ray flares. We have performed physical and theoretical analysis of rotating collimator grids submitted to GSFC(Goddard Space Flight Center) for the High Energy Solar Spectroscopic Imager (HESSI). We have produced simulation algorithms which are currently being used to test imaging software and hardware for HESSI. We have developed Maximum-Entropy, Maximum-Likelihood, and "CLEAN" methods for reconstructing HESSI images from count-rate profiles. This work is expected to continue through the launch of HESSI in July, 2000. Section 1 shows a poster presentation "Image Reconstruction from HESSI Photon Lists" at the Solar Physics Division Meeting, June 1998; Section 2 shows the text and viewgraphs prepared for "Imaging Simulations" at HESSI's Preliminary Design Review on July 30, 1998.

Schmahl, Edward J.; Kundu, Mukul R.

1998-01-01

27

Solar flare tracking using image processing techniques  

Microsoft Academic Search

Abstract. Automatic property measurement of solar flares through their complete cyclic development is valuable in the ,studies of solar flares. From the analysis of solar H? images, we are able to use the Support Vector Machine (SVM) to automatically detect flares, and apply image segmentation techniques to compute the properties of solar flares. Wealso,present our solution for automatically tracking the

Ming Qu; Frank Y. Shih; Ju Jing; Haimin Wang

2004-01-01

28

Solar flare interval distribution for probabilistic flare forecasting method  

NASA Astrophysics Data System (ADS)

Determining of more likely model for solar flare interval distribution is an essential step in probabilistic solar flare forecasting method in space weather research. In this presentation we discuss statistical models for solar flare interval distribution in individual active regions. We first discuss some problems with a conventional procedure to derive probability density functions from any data set and propose a new procedure, which uses the maximum likelihood method and Akaike Information Criterion (AIC) to objectively compare some competing probability density functions. Previous studies on solar flare interval distribution in individual active regions only dealt with constant or time-dependent Poisson process models, and no other models were discussed. We examine three models -exponential, lognormal, and inverse Gaussian- as competing models for probability density functions. We analyzed solar flare data in 55 active regions that are listed in the GOES soft X-ray flare catalog for the years from 1981 to 2005 by using the new procedure. We found that lognormal and inverse Gaussian models are more likely models than the exponential model for solar flare interval distribution in individual active regions. The results suggest that solar flares do not occur randomly in time; rather, solar flare intervals appear to be regulated by solar flare mechanisms. We briefly mention a probabilistic solar flare forecasting method as an application of a solar flare interval distribution analysis.

Kubo, Yuki

29

Ion acceleration in impulsive solar flares  

NASA Technical Reports Server (NTRS)

Nonrelativistic spectra of protons and ions accelerated in impulsive solar flares are derived using more realistic turbulence power spectra. The calculation is based on a particle transport equation extracted from a second step acceleration model containing stochastic acceleration. The turbulence model is generalized to waves with a small angle to the magnetic field vector and to turbulence power spectra with spectral indices s smaller than 2. Due to the occurrence of impulsive flares at low coronal heights, Coulomb losses at the dense coronal plasma and diffusive particle escape are taken into account. The ion spectra show deviations from long-duration spectra near the Coulomb barrier, where the losses become maximal. The Z-squared/A-dependence of the Coulomb losses leads to spectral variations for different ions. We present a method to estimate the turbulence parameters and injection conditions of the flare particles using ion ratios like Fe/O of impulsive flares.

Steinacker, Jurgen; Jaekel, Uwe; Schlickeiser, Reinhard

1993-01-01

30

Largest Solar Flare on Record  

NASA Technical Reports Server (NTRS)

The largest solar flare ever recorded occurred at 4:51 p.m. EDT, on Monday, April 2, 2001. as Observed by the Solar and Heliospheric Observatory (SOHO) satellite. Solar flares, among the solar systems mightiest eruptions, are tremendous explosions in the atmosphere of the Sun capable of releasing as much energy as a billion megatons of TNT. Caused by the sudden release of magnetic energy, in just a few seconds, solar flares can accelerate solar particles to very high velocities, almost to the speed of light, and heat solar material to tens of millions of degrees. The recent explosion from the active region near the sun's northwest limb hurled a coronal mass ejection into space at a whopping speed of roughly 7.2 million kilometers per hour. Luckily, the flare was not aimed directly towards Earth. Second to the most severe R5 classification of radio blackout, this flare produced an R4 blackout as rated by the NOAA SEC. This classification measures the disruption in radio communications. Launched December 2, 1995 atop an ATLAS-IIAS expendable launch vehicle, the SOHO is a cooperative effort involving NASA and the European Space Agency (ESA). (Image courtesy NASA Goddard SOHO Project office)

2001-01-01

31

Solar Flare Aimed at Earth  

NASA Technical Reports Server (NTRS)

At the height of the solar cycle, the Sun is finally displaying some fireworks. This image from the Solar and Heliospheric Observatory (SOHO) shows a large solar flare from June 6, 2000 at 1424 Universal Time (10:24 AM Eastern Daylight Savings Time). Associated with the flare was a coronal mass ejection that sent a wave of fast moving charged particles straight towards Earth. (The image was acquired by the Extreme ultaviolet Imaging Telescope (EIT), one of 12 instruments aboard SOHO) Solar activity affects the Earth in several ways. The particles generated by flares can disrupt satellite communications and interfere with power transmission on the Earth's surface. Earth's climate is tied to the total energy emitted by the sun, cooling when the sun radiates less energy and warming when solar output increases. Solar radiation also produces ozone in the stratosphere, so total ozone levels tend to increase during the solar maximum. For more information about these solar flares and the SOHO mission, see NASA Science News or the SOHO home page. For more about the links between the sun and climate change, see Sunspots and the Solar Max. Image courtesy SOHO Extreme ultaviolet Imaging Telescope, ESA/NASA

2002-01-01

32

Radiation hydrodynamics in solar flares  

SciTech Connect

Solar flares are rather violent and extremely complicated phenomena, and it should be made clear at the outset that a physically complete picture describing all aspects of flares does not exist. From the wealth of data which is available, it is apparent that many different types of physical processes are involved during flares: energetic particle acceleration, rapid magnetohydrodynamic motion of complex field structures, magnetic reconnection, violent mass motion along magnetic field lines, and the heating of plasma to tens of millions of degrees, to name a few. The goal of this paper is to explore just one aspect of solar flares, namely, the interaction of hydrodynamics and radiation processes in fluid being rapidly heated along closed magnetic field lines. The models discussed are therefore necessarily restrictive, and will address only a few of the observed or observable phenomena. 46 refs., 6 figs.

Fisher, G.H.

1985-10-18

33

Solar flare proton evaluation at geostationary orbits for engineering applications  

Microsoft Academic Search

Presents the results of novel analyses of spacecraft solar flare proton measurements for solar cycles 20, 21, and 22. Solar events and cycles were classified and ranked by fluence and frequency of occurrence, and events were characterized by the mean energy of the proton spectral distributions. Spacecraft observations permitted a detailed study of event characteristics, such as special consideration of

E. G. Stassinopoulos; G. J. Brucker; D. W. Nakamura; C. A. Stauffer; G. B. Gee; J. L. Barth

1996-01-01

34

Rapid fluctuations in solar flares  

NASA Technical Reports Server (NTRS)

Study of rapid fluctuations in the emission of radiation from solar flares provides a promising approach for probing the magneto-plasma structure and plasma processes that are responsible for a flare. It is proposed that elementary flare bursts in X-ray and microwave emission may be attributed to fine structure of the coronal magnetic field, related to the aggregation of photospheric magnetic field into magnetic knots. Fluctuations that occur on a subsecond time-scale may be due to magnetic islands that develop in current sheets during magnetic reconnection. The impulsive phase may sometimes represent the superposition of a large number of the elementary energy-release processes responsible for elementary flare bursts. If so, the challenge of trying to explain the properties of the impulsive phase in terms of the properties of the elementary processes must be faced. Magnetic field configurations that might produce solar flares are divided into a number of categories, depending on: whether or not there is a filament; whether there is no current sheet, a closed current sheet, or an open current sheet; and whether the filament erupts into the corona, or is ejected completely from the Sun's atmosphere. Analysis of the properties of these possible configurations is compared with different types of flares, and to Bai's subdivision of gamma-ray/proton events.

Sturrock, Peter A.

1986-01-01

35

Solar-Flare Shielding With Regolith at  

E-print Network

Solar-Flare Shielding With Regolith at a Lunar-Base Site _T jo_m E. Nealy, John W. Wilson are envisioned, environmental parameters such as high-energy, charged-particle radiation from solar flares and galactic cosmic rays become very impor- tant. Large solar flares can release great quantities of high-energy

Rathbun, Julie A.

36

Scaling Laws of Solar and Stellar Flares  

NASA Astrophysics Data System (ADS)

In this study we compile for the first time comprehensive data sets of solar and stellar flare parameters, including flare peak temperatures Tp, flare peak volume emission measures EMp, and flare durations ?f from both solar and stellar data, as well as flare length scales L from solar data. Key results are that both the solar and stellar data are consistent with a common scaling law of EMp~T4.7p, but the stellar flares exhibit ~250 times higher emission measures (at the same flare peak temperature). For solar flares we observe also systematic trends for the flare length scale L(Tp)~T0.9p and the flare duration ?F(Tp)~T0.9p as a function of the flare peak temperature. Using the theoretical RTV scaling law and the fractal volume scaling observed for solar flares, i.e., V(L)~L2.4, we predict a scaling law of EMp~T4.3p, which is consistent with observations, and a scaling law for electron densities in flare loops, np~T2p/L~T1.1p. The RTV-predicted electron densities were also found to be consistent with densities inferred from total emission measures, np=(EMp/qVV)1/2, using volume filling factors of qV=0.03-0.08 constrained by fractal dimensions measured in solar flares. Solar and stellar flares are expected to have similar electron densities for equal flare peak temperatures Tp, but the higher emission measures of detected stellar flares most likely represent a selection bias of larger flare volumes and higher volume filling factors, due to low detector sensitivity at higher temperatures. Our results affect also the determination of radiative and conductive cooling times, thermal energies, and frequency distributions of solar and stellar flare energies.

Aschwanden, Markus J.; Stern, Robert A.; Gdel, Manuel

2008-01-01

37

Biggest Solar Flare on Record  

NASA Technical Reports Server (NTRS)

View an animation from the Extreme ultraviolet Imaging Telescope (EIT). At 4:51 p.m. EDT, on Monday, April 2, 2001, the sun unleashed the biggest solar flare ever recorded, as observed by the Solar and Heliospheric Observatory (SOHO) satellite. The flare was definitely more powerful than the famous solar flare on March 6, 1989, which was related to the disruption of power grids in Canada. This recent explosion from the active region near the sun's northwest limb hurled a coronal mass ejection into space at a whopping speed of roughly 7.2 million kilometers per hour. Luckily, the flare was not aimed directly towards Earth. Solar flares, among the solar system's mightiest eruptions, are tremendous explosions in the atmosphere of the Sun capable of releasing as much energy as a billion megatons of TNT. Caused by the sudden release of magnetic energy, in just a few seconds flares can accelerate solar particles to very high velocities, almost to the speed of light, and heat solar material to tens of millions of degrees. Solar ejections are often associated with flares and sometimes occur shortly after the flare explosion. Coronal mass ejections are clouds of electrified, magnetic gas weighing billions of tons ejected from the Sun and hurled into space with speeds ranging from 12 to 1,250 miles per second. Depending on the orientation of the magnetic fields carried by the ejection cloud, Earth-directed coronal mass ejections cause magnetic storms by interacting with the Earth's magnetic field, distorting its shape, and accelerating electrically charged particles (electrons and atomic nuclei) trapped within. Severe solar weather is often heralded by dramatic auroral displays, northern and southern lights, and magnetic storms that occasionally affect satellites, radio communications and power systems. The flare and solar ejection has also generated a storm of high-velocity particles, and the number of particles with ten million electron-volts of energy in the space near Earth is now 10,000 times greater than normal. The increase of particles at this energy level still poses no appreciable hazard to air travelers, astronauts or satellites, and the NOAA SEC rates this radiation storm as a moderate S2 to S3, on a scale that goes to S5. Monday's solar flare produced an R4 radio blackout on the sunlit side of the Earth. An R4 blackout, rated by the NOAA SEC, is second to the most severe R5 classification. The classification measures the disruption in radio communications. X-ray and ultraviolet light from the flare changed the structure of the Earth's electrically charged upper atmosphere (ionosphere). This affected radio communication frequencies that either pass through the ionosphere to satellites or are reflected by it to traverse the globe. The SOHO mission is being conducted collaboratively between the European Space Agency and NASA. Images courtesy SOHO Project, NASA's Goddard Space Flight Center

2002-01-01

38

Evidence for magnetic reconnection in solar flares  

NASA Astrophysics Data System (ADS)

From a study of the magnetic field topology in an active region, evidence is derived that solar flares are produced by magnetic reconnection. We study a complex group with two active regions (AR 25 t 1 and AR 2512) for three consecutive days, June 13-15 1980. The observed longitudinal magnetic field is used to model the coronal magnetic field by the potential field created by a series of magnetic charges. This computed field matches satisfactorily the Ho fibrils and the observed transverse field direction. A set of flares occurs principally in the northern group (AR 2511). During these three days, two different magnetic configurations in succession are responsible for the occurrence of these flares: first the intrusion of a new opposite flux in the following polarity, secondly the emergence of new flux between the main polarities. In this last case flares occurred, although the emerging bipole is almost parallel to the main bipole. We show that even in this bipolar configuration a separator is present and that observed H flare ribbons are located near the intersection of the computed separatrices with the photosphere. This provides strong support to a model where reconnection releases the stored magnetic energy. The induced evolution of the magnetic field forces reconnection along others separators. They are connected by magnetic field lines to fainter kernels.

Demoulin, P.; van Driel-Gesztelyi, L.; Schmieder, B.; Hemoux, J. C.; Csepura, G.; Hagyard, M. J.

1993-04-01

39

Magnetic Flux Transients during Solar Flares  

NASA Astrophysics Data System (ADS)

Solar flares result from the sudden release of energy stored in the magnetic field of the solar atmosphere, attributed to magnetic reconnection. In this work, we use line-of-sight magnetograms to study the changes in photospheric magnetic field during large solar flares. The magnetograms are derived from observations using NASA's Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory, and have a cadence of 3 minutes at a 0.5 arcsecond spatial resolution. We studied the inferred magnetic flux changes in 11 X-class flares from (2011-2012) and 26 M-class flares (2011). Of the 37 flares, 32 exhibited short-lived (less than 30 minutes) magnetic flux transients (MFTs) during the progress of the flare, similar to those by Maurya et al. (2012). We note that MFTs were co-temporal with GOES X-ray peaks. Flares with rapid rises (impulsive flares) had stronger transients while those with slower rises (gradual flares) had weak or no MFTs. Finally, flares with stronger GOES X-ray peaks (flare class) showed stronger MFTs. We believe that these changes are non-physical because the changes in the magnetic field are transient (the magnetic field returns to the pre-flare state) and coincide with the impulsive phase of the flare. This work supported by the US Airforce Office of Scientific Research and the AFRL/RV Space Scholar Program.

Balasubramaniam, K. S.; Delgado, F.; Hock, R. A.

2013-12-01

40

Parameterization of solar flare dose  

E-print Network

. 8 Five minute averaged X-ray and proton fluxes for the 19 October 1989 through 13 November 1989, as measured at the NOAA GOES satellite. . . . . . . . 21 2. 9 Material shot off the Sun by a solar flare. Along with high-energy radiation, a solar.... Shielding thickness: 0. 0 g/cmz of aluminum. . 47 4. 3 Dose equivalent as a function of time for the event of August 1989. Shielding thickness: 0. 5 8/cmz of aluminum. . 48 4. 4 Dose equivalent as a function of time between 10/19/89 and 11...

Lamarche, Anne Helene

2012-06-07

41

Solar flares controlled by helicity conservation  

NASA Technical Reports Server (NTRS)

The energy release in a class of solar flares is studied on the assumption that during burst events in highly conducting plasma the magnetic helicity of plasma is approximately conserved. The available energy release under a solar flare controlled by the helicity conservation is shown to be defined by the magnetic structure of the associated prominence. The approach throws light on some solar flare enigmas: the role of the associated prominence. The approach throws light on some solar flare enigmas: the role of the associated prominences; the discontinuation of the reconnection of magnetic lines long before the complete reconnection of participated fields occurs; the existence of quiet prominences which, in spite of their usual optical appearance, do not initiate any flare events; the small energy release under a solar flare in comparison with the stockpile of magnetic energy in surrounding fields. The predicted scale of the energy release is in a fair agreement with observations.

Gliner, Erast B.; Osherovich, Vladimir A.

1995-01-01

42

Solar flares induced D-region ionospheric and geomagnetic perturbations  

NASA Astrophysics Data System (ADS)

The D-region ionospheric perturbations caused by solar flares which occurred during January 2010-February 2011, a low solar activity period of current solar cycle 24, have been examined on NWC transmitter signal (19.8 kHz) recorded at an Indian low latitude station, Allahabad (Geographic lat. 25.75N, long. 81.85E). A total of 41 solar flares, including 21 C-class, 19 M-class and 01 X-class, occurred during the daylight part of the NWC-Allahabad transmitter receiver great circle path. The local time dependence of solar flare effects on the change in the VLF amplitude, time delay between VLF peak amplitude and X-ray flux peak have been studied during morning, noon and evening periods of local daytime. Using the Long Wave Propagation Capability code V 2.1 the D-region reference height (H/) and sharpness factor (?) for each class of solar flare (C, M and X) have been estimated. It is found that D-region ionospheric parameters (H/, ?) strongly depend on the local time of flare's occurrence and their classes. The flare time electron density estimated by using H/ and ? shows maximum increase in the electron density of the order of ~80 times as compared to the normal day values. The electron density was found to increase exponentially with increase in the solar flux intensity. The solar flare effect on horizontal component (H) of the Earth's magnetic field over an equatorial station, Tirunelveli (Geographic lat., 8.7N, long., 77.8E, dip lat., 0.4N), shows a maximum increase in H of ~8.5% for M class solar flares. The increase in H is due to the additional magnetic field produced by the ionospheric electrojet over the equatorial station.

Selvakumaran, R.; Maurya, Ajeet K.; Gokani, Sneha A.; Veenadhari, B.; Kumar, Sushil; Venkatesham, K.; Phanikumar, D. V.; Singh, Abhay K.; Siingh, Devendraa; Singh, Rajesh

2015-02-01

43

Solar flare leaves sun quaking  

NASA Astrophysics Data System (ADS)

Dr. Alexander G. Kosovichev, a senior research scientist from Stanford University, and Dr. Valentina V. Zharkova from Glasgow (United Kingdom) University found the tell-tale seismic signature in data on the Sun's surface collected by the Michelson Doppler Imager onboard the Solar and Heliospheric Observatory (SOHO) spacecraft immediately following a moderate-sized flare on July 9, 1996. "Although the flare was a moderate one, it still released an immense amount of energy," said Dr. Craig Deforest, a researcher with the SOHO project. "The energy released is equal to completely covering the Earth's continents with a yard of dynamite and detonating it all at once." SOHO is a joint project of the European Space Agency and NASA. The finding is reported in the May 28 issue of the journal Nature, and is the subject of a press conference at the spring meeting of the American Geophysical Union in Boston, Mass., May 27. The solar quake that the science team recorded looks much like ripples spreading from a rock dropped into a pool of water. But over the course of an hour, the solar waves traveled for a distance equal to 10 Earth diameters before fading into the fiery background of the Sun's photosphere. Unlike water ripples that travel outward at a constant velocity, the solar waves accelerated from an initial speed of 22,000 miles per hour to a maximum of 250,000 miles per hour before disappearing. "People have looked for evidence of seismic waves from flares before, but they didn't have a theory so they didn't know where to look," says Kosovichev. Several years ago Kosovichev and Zharkova developed a theory that can explain how a flare, which explodes in space above the Sun's surface, can generate a major seismic wave in the Sun's interior. According to the currently accepted model of solar flares, the primary explosion creates high-energy electrons (electrically charged subatomic particles). These are funneled down into a magnetic flux tube, an invisible tube of magnetic energy, and produce X-rays, microwaves and a shock wave that heats the solar surface. Kosovichev and Zharkova developed a theory that predicts the nature and magnitude of the shock waves that this beam of energetic electrons should create when they slam down into the solar atmosphere. Although their theory directed them to the right area to search for the seismic waves, the waves that they found were 10 times stronger than they had predicted. "They were so strong that you can see them in the raw data," Kosovichev says. The solar seismic waves appear to be compression waves like the "P" waves generated by an earthquake. They travel throughout the Sun's interior. In fact, the waves should recombine on the opposite side of the Sun from the location of the flare to create a faint duplicate of the original ripple pattern, Kosovichev predicts. Now that they know how to find them, the SOHO scientists say that the seismic waves generated by solar flares should allow them to verify independently some of the conditions in the solar interior that they have inferred from studying the pattern of waves that are continually ruffling the Sun's surface. SOHO is part of the International Solar-Terrestrial Physics (ISTP) program, a global effort to observe and understand our star and its effects on our environment. The ISTP mission includes more than 20 satellites, coupled with with ground-based observatories and modeling centers, that allow scientists to study the Sun, the Earth, and the space between them in unprecedented detail. ISTP is a joint program of NASA, ESA, Japan's Institute for Astronautical Science, and Russia's Space Research Institute. Still images of the solar quake can be found at the following internet address: FTP://PAO.GSFC.NASA.GOV/newsmedia/QUAKE/ For further information, please contact : ESA Public Relations Division Tel:+33(0)1.53.69.71.55 Fax: +33(0)1.53.69.76.90 3

1998-05-01

44

Oscillatory processes in solar flares  

NASA Astrophysics Data System (ADS)

Electromagnetic (radio, visible-light, UV, EUV, x-ray and gamma-ray) emission generated by solar and stellar flares often contains pronounced quasi-periodic pulsations (QPPs). Physical mechanisms responsible for the generation of long-period QPP (with periods longer than 1 s) are likely to be associated with MHD processes. The observed modulation depths, periods and anharmonicity of QPP suggest that they can be linked with some kind of MHD auto-oscillations, e.g. an oscillatory regime of magnetic reconnection. Such regimes, of both spontaneous and induced nature, have been observed in resistive-MHD numerical simulations. The oscillations are essentially nonlinear and non-stationary. We demonstrate that a promising novel method for their analysis is the empirical mode decomposition technique.

Nakariakov, V. M.; Inglis, A. R.; Zimovets, I. V.; Foullon, C.; Verwichte, E.; Sych, R.; Myagkova, I. N.

2010-12-01

45

Oscillatory processes in solar flares  

E-print Network

Electromagnetic (radio, visible-light, UV, EUV, X-ray and gamma-ray) emission generated by solar and stellar flares often contains pronounced quasi-periodic pulsations (QPP). Physical mechanisms responsible for the generation of long-period QPP (with the periods longer than one second) are likely to be associated with MHD processes. The observed modulation depths, periods and anharmonicity of QPP suggest that they can be linked with some kind of MHD auto-oscillations, e.g. an oscillatory regime of magnetic reconnection. Such regimes, of both spontaneous and induced nature, have been observed in resistive-MHD numerical simulations. The oscillations are essentially nonlinear and non-stationary. We demonstrate that a promising novel method for their analysis is the Empirical Mode Decomposition technique.

Nakariakov, V M; Zimovets, I V; Foullon, C; Verwichte, E; Sych, R; Myagkova, I N

2010-01-01

46

Explosive evaporation in solar flares  

NASA Technical Reports Server (NTRS)

This paper develops a simple analytical model for the phenomenon of 'explosive evaporation' driven by nonthermal electron heating in solar flares. The model relates the electron energy flux and spectrum, plus details of the preflare atmosphere, to the time scale for explosive evaporation to occur, the maximum pressure and temperature to be reached, rough estimates for the UV pulse emission flux and duration, and the evolution of the blueshifted component of the soft X-ray lines. An expression is given for the time scale for buildup to maximum pressures and the onset of rapid motion of the explosively evaporating plasma. This evaporation can excite a rapid response of UV line and continuum emission. The emission lines formed in the plasma approach a given emissivity-weighted blueshift speed.

Fisher, George H.

1987-01-01

47

MAGNETIC FIELD STRUCTURES TRIGGERING SOLAR FLARES AND CORONAL MASS EJECTIONS  

SciTech Connect

Solar flares and coronal mass ejections, the most catastrophic eruptions in our solar system, have been known to affect terrestrial environments and infrastructure. However, because their triggering mechanism is still not sufficiently understood, our capacity to predict the occurrence of solar eruptions and to forecast space weather is substantially hindered. Even though various models have been proposed to determine the onset of solar eruptions, the types of magnetic structures capable of triggering these eruptions are still unclear. In this study, we solved this problem by systematically surveying the nonlinear dynamics caused by a wide variety of magnetic structures in terms of three-dimensional magnetohydrodynamic simulations. As a result, we determined that two different types of small magnetic structures favor the onset of solar eruptions. These structures, which should appear near the magnetic polarity inversion line (PIL), include magnetic fluxes reversed to the potential component or the nonpotential component of major field on the PIL. In addition, we analyzed two large flares, the X-class flare on 2006 December 13 and the M-class flare on 2011 February 13, using imaging data provided by the Hinode satellite, and we demonstrated that they conform to the simulation predictions. These results suggest that forecasting of solar eruptions is possible with sophisticated observation of a solar magnetic field, although the lead time must be limited by the timescale of changes in the small magnetic structures.

Kusano, K.; Bamba, Y.; Yamamoto, T. T. [Solar-Terrestrial Environment Laboratory, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601 (Japan); Iida, Y.; Toriumi, S. [Department of Earth and Planetary Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Asai, A., E-mail: kusano@nagoya-u.jp [Unit of Synergetic Studies for Space, Kyoto University, 17 Kitakazan Ohmine-cho, Yamashina-ku, Kyoto 607-8471 (Japan)

2012-11-20

48

Interplanetary shock waves generated by solar flares  

Microsoft Academic Search

Recent observational and theoretical studies of interplanetary shock waves associated with solar flares are reviewed. An attempt is made to outline the framework for the genesis, life and demise of these shocks. Thus, suggestions are made regarding their birth within the flare generation process, MHD wave propagation through the chromosphere and inner corona, and maturity to fully-developed coronal shock waves.

Murray Dryer

1974-01-01

49

Soliton and strong Langmuir turbulence in solar flare processes  

NASA Technical Reports Server (NTRS)

The occurrence of modulational instability in the current sheet of a solar flare is investigated. Special attention is given to the plasma microinstability in this sheet and its relation to the flare process. It is found that solitons or strong Langmuir turbulence are likely to occur in the diffusion region under solar flare conditions in which the electric resistivity could be enhanced by several orders of magnitude in the region, resulting in significant heating and stochastic acceleration of particles. A numerical example is used to demonstrate the transition of the magnetic field velocity and plasma density from the outer MHD region into the diffusive region and then back out again with the completion of the energy conversion process. This is all made possible by an increase in resistivity of four to five orders of magnitude over the classical value.

Song, M. T.; Wu, S. T.; Dryer, M.

1989-01-01

50

Composition of energetic particles from solar flares  

NASA Technical Reports Server (NTRS)

We present a model for composition of heavy ions in the Solar Energetic Particles (SEP). The SEP composition in a typical large solar particle event reflects the composition of the Sun, with adjustments due to fractionation effects which depend on the First Ionization Potential (FIP) of the ion and on the ratio of ionic charge to mass (Q/M). Flare-to flare variations in composition are represented by parameters describing these fractionation effects and the distributions of these parameters are presented.

Garrard, T. L.; Stone, E. C.

1994-01-01

51

Solar Eruptions: Coronal Mass Ejections and Flares  

NASA Technical Reports Server (NTRS)

This lecture introduces the topic of Coronal mass ejections (CMEs) and solar flares, collectively known as solar eruptions. During solar eruptions, the released energy flows out from the Sun in the form of magnetized plasma and electromagnetic radiation. The electromagnetic radiation suddenly increases the ionization content of the ionosphere, thus impacting communication and navigation systems. Flares can be eruptive or confined. Eruptive flares accompany CMEs, while confined flares hav only electromagnetic signature. CMEs can drive MHD shocks that accelerate charged particles to very high energies in the interplanetary space, which pose radiation hazard to astronauts and space systems. CMEs heading in the direction of Earth arrive in about two days and impact Earth's magnetosphere, producing geomagnetic storms. The magnetic storms result in a number of effects including induced currnts that can disrupt power grids, railroads, and underground pipelines

Gopalswamy, Nat

2012-01-01

52

Energy release in solar flares  

NASA Technical Reports Server (NTRS)

Team 2 of the Ottawa Flares 22 Workshop dealt with observational and theoretical aspects of the characteristics and processes of energy release in flares. Main results summarized in this article stress the global character of the flaring phenomenon in active regions, the importance of discontinuities in magnetic connectivity, the role of field-aligned currents in free energy storage, and the fragmentation of energy release in time and space.

Brown, John C.; Correia, Emilia; Farnik, Frantisek; Garcia, Howard; Henoux, Jean-Claude; La Rosa, Ted N.; Machado, Marcos E. (compiler); Nakajima, Hiroshi; Priest, Eric R.

1994-01-01

53

Dependence Of Solar Proton Events On Flare And Cme Parameters  

NASA Astrophysics Data System (ADS)

In this study we have examined the probability of solar proton events (SEPs) and their peak fluxes depending on flare (intensity, longitude and impulsive time) and CME parameters (linear speed and angular width). For this we used the NOAA SPE events and their associated flare data from 1976 to 2006 and CME data from 1997 to 2006. From this study, we found that about only 3.5% (1.9% for M-class and 21.3% for X-class) of the flares are associated with the proton events. It is also found that this fraction strongly depends on longitude; for example, the fraction for 30W < L < 90W is about three times larger than that for 30E < L < 90E. The occurrence probability of solar proton events for flares with long duration (? 0.3 hours) is about 2 (X-class flare) to 7 (M-class flare) times larger than that for flares with short duration (< 0.3 hours). In the case of halo CMEs with V ? 1500km/s, 36.1% are associated with SPEs but in the case of partial halo CME (120 ? AW < 359) with 400 km/s ? V < 1000 km/s, only 0.9% are associated with SPEs. The relationship between X-ray flare peak intensity and proton flux as well as its correlation coefficient strongly depends on longitude and impulsive time. It is also noted that the relationship between CME speed and proton flux depends on longitude as well as direction parameter.

Park, Jinhye; Moon, Y.

2011-05-01

54

An Observational Overview of Solar Flares  

NASA Technical Reports Server (NTRS)

We present an overview of solar flares and associated phenomena, drawing upon a wide range of observational data primarily from the RHESSI era. Following an introductory discussion and overview of the status of observational capabilities, the article is split into topical sections which deal with different areas of flare phenomena (footpoints and ribbons, coronal sources, relationship to coronal mass ejections) and their interconnections. We also discuss flare soft X-ray spectroscopy and the energetics of the process. The emphasis is to describe the observations from multiple points of view, while bearing in mind the models that link them to each other and to theory. The present theoretical and observational understanding of solar flares is far from complete, so we conclude with a brief discussion of models, and a list of missing but important observations.

Fletcher, Lyndsay; Battaglia, M.; Dennis, Brian R.; Liu, W.; Milligan, R. O.; Hudson, H. S.; Krucker, S.; Phillips, K.; Bone, L.; Veronig, A.; Caspi, A.; Temmer, M.

2011-01-01

55

CONTINUUM ELECTROMAGNETIC RADIATION FROM SOLAR FLARES  

Microsoft Academic Search

Continuum electromagnetic radiation from solar flares is discussed in ; terms of the energy loss processes of electrons in the solar atmosphere. It is ; shown that it is possible to attribute the continuum radiation both at radio ; frequencies and at visible frequencies to synchrotron radiation by exponential ; rigidity distributions of electrons. (auth);

W. A. Stein; E. P. Ney

1963-01-01

56

RADIO EMISSION OF SOLAR FLARE PARTICLE ACCELERATION  

E-print Network

RADIO EMISSION OF SOLAR FLARE PARTICLE ACCELERATION A. O. Benz Abstract The solar corona is a very be considered as a particle accelerator. The free mobility of charged particles in a dilute plasma to accelerate particles in resonance. From a plasma physics point of view, acceleration is not surprising

57

2 Solar flare signatures of the ionospheric GPS total electron content 3 J. Y. Liu,1,2  

E-print Network

2 Solar flare signatures of the ionospheric GPS total electron content 3 J. Y. Liu,1,2 C. H. Lin,1, ionospheric solar flare effects on the total electron content (TEC) and 7 associated time rate of change (r. The occurrence times and 9 locations of 11 solar flares are isolated from the 1­8 A° X-ray radiations of the 10

Chen, Yuh-Ing

58

Modelling the impulsive phase of solar flares  

NASA Astrophysics Data System (ADS)

Solar flares are the most energetic events in the solar system. In order to study this sudden release of energy and evaluate the response of the solar chromosphere to the deposition of thermal energy, we simulate the conditions of the solar atmosphere by creating a 1D plane-parallel atmospheric model and analyze the energy transport of a beam of non-thermal electrons that is injected at the top of the coronal loop. This is done using a numerical model which combines the radiative hydrodynamic equations (RADYN code - Carlsson & Stein, 1992) with the calculation of particle acceleration and transport (Flare code - Petrosian & Liu, 2004). With this model, it is for example possible to compare the emission of solar flares in several lines with available observations. The assemblage of high resolution chromospheric flare observations from the IRIS imaging spectrograph makes it an excellent time for this work. We discuss how accelerated particle heating and energy deposition rate are affected by the variation of cut-off energy and flux of non-thermal electrons as well as spectral index and investigate the response of the atmosphere to the acceleration of particles. Our flare simulation treats each atom in non-LTE condition and calculates in detail the transitions between its energy levels. It also assumes an optically thick atmosphere, which is crucial for understanding how energy is transported from the chromosphere deep into the photosphere.

Rubio da Costa, F.; Petrosian, V.; Liu, W.; Carlsson, M.

2013-12-01

59

Dependence of solar proton events on their associated activities: Flare parameters  

NASA Astrophysics Data System (ADS)

In this study we have examined the occurrence probability of solar proton events and their peak fluxes depending on three flare parameters (X-ray peak flux, longitude, and impulsive time). For this we used NOAA solar energetic particle events from 1976 to 2006 and their associated X-ray flare data. As a result, we selected 166 proton events that were associated with major flares: 85 events associated with X-class flares and 81 events associated with M-class flares. The occurrence probability especially strongly depends on three parameters as follows. (1) We found that about only 3.5% (1.9% for M-class and 21.3% for X-class) of the flares are associated with the proton events. (2) It is also found that this fraction strongly depends on longitude; for example, the fraction for 30W < L ? 90W is about three times larger than that for 30E < L ? 90E. (3) We also note that the occurrence probability of solar proton events associated with long-duration (?0.3 h) flares is about 2 (X-class flare) to 7 (M-class flare) times larger than that with short-duration (<0.3 h) flares. (4) The largest difference is found between the eastern short-duration M-class flare group (0.3%) and the western long-duration X-class flare group (46.5%). In addition, the relationship between X-ray flare peak flux and proton peak flux as well as its correlation coefficient are strongly dependent on longitude and impulsive time.

Park, Jinhye; Moon, Y.-J.; Lee, D. H.; Youn, Saepoom

2010-10-01

60

REMOTE OSCILLATORY RESPONSES TO A SOLAR FLARE  

SciTech Connect

The processes governing energy storage and release in the Sun are both related to the solar magnetic field. We demonstrate the existence of a magnetic connection between the energy released by a flare and increased oscillatory power in the lower solar atmosphere. The oscillatory power in active regions tends to increase in response to explosive events at other locations, but not in the active region itself. We carry out timing studies and show that this effect is probably caused by a large-scale magnetic connection between the regions, instead of a globally-propagating wave. We show that oscillations tend to exist in longer-lived wave trains with short periods (P < 200 s) at the time of a flare. These wave trains may be mechanisms by which flare energy can be redistributed throughout the solar atmosphere.

Andic, A.; McAteer, R. T. J. [Astronomy Department, NMSU, MSC 4500, P.O. Box 30001, Las Cruces, NM 88003 (United States)

2013-07-20

61

Solar flare proton evaluation at geostationary orbits for engineering applications  

SciTech Connect

This work presents the results of novel analyses of spacecraft solar flare proton measurements for solar cycles 20, 21, and 22. Solar events and cycles were classified and ranked by fluence and frequency of occurrence, and events were characterized by the mean energy of the proton spectral distributions. Spacecraft observations permitted a detailed study of event characteristics, such as special consideration of solar minimum flares and cycle variability. Tables and curves are presented to allow evaluations of potential threats to spacecraft survivability at GEO, particularly for types of flare environments that emulate solar cycle 22. Upsets for major events are calculated for several Bendel A parameter values and shield thicknesses, and effective energy thresholds of events are determined as a function of these variables. Critical fluence levels, required to cause errors, versus A are presented. SEU`s (single event upsets) of 93L422 devices on TDRS-1 are evaluated for various shielding conditions. Finally, upset dependencies on A and shield thickness are correlated with event fluences for threshold energies of >30, >50, and >60 MeV.

Stassinopoulos, E.G.; Barth, J.L. [National Aeronautics and Space Administration, Greenbelt, MD (United States). Goddard Space Flight Center] [National Aeronautics and Space Administration, Greenbelt, MD (United States). Goddard Space Flight Center; Brucker, G.J. [Radiation Effects Consultants, West Long Branch, NJ (United States)] [Radiation Effects Consultants, West Long Branch, NJ (United States); Nakamura, D.W.; Stauffer, C.A.; Gee, G.B. [SES, Inc., Greenbelt, MD (United States)] [SES, Inc., Greenbelt, MD (United States)

1996-04-01

62

Positron annihilation radiation from solar flares  

NASA Technical Reports Server (NTRS)

Positron-annihilation radiation has been observed from the June 21, 1980 and June 3, 1982 flares by the gamma-ray spectrometer on the Solar Maximum Mission satellite. The observed 0.511-MeV line fluences from the flares were 14.6 + or - 3.3 gamma/sq cm and 103 + or - 8 gamma/sq cm, respectively. Measurement of the line width establishes an upper limit to the temperature in the annihilation region of 3 x 10 to the 6th K. The time dependence of the 0.511-MeV line during the 1980 flare is consistent with the calculations of Ramaty et al. (1983) for positrons created in the decay of radioactive nuclei. The time dependence of the 0.511-MeV line for the 1982 flare is more complex and requires more detailed study.

Share, G. H.; Chupp, E. L.; Forrest, D. J.; Rieger, E.

1983-01-01

63

Deterministically Driven Avalanche Models of Solar Flares  

NASA Astrophysics Data System (ADS)

We develop and discuss the properties of a new class of lattice-based avalanche models of solar flares. These models are readily amenable to a relatively unambiguous physical interpretation in terms of slow twisting of a coronal loop. They share similarities with other avalanche models, such as the classical stick-slip self-organized critical model of earthquakes, in that they are driven globally by a fully deterministic energy-loading process. The model design leads to a systematic deficit of small-scale avalanches. In some portions of model space, mid-size and large avalanching behavior is scale-free, being characterized by event size distributions that have the form of power-laws with index values, which, in some parameter regimes, compare favorably to those inferred from solar EUV and X-ray flare data. For models using conservative or near-conservative redistribution rules, a population of large, quasiperiodic avalanches can also appear. Although without direct counterparts in the observational global statistics of flare energy release, this latter behavior may be relevant to recurrent flaring in individual coronal loops. This class of models could provide a basis for the prediction of large solar flares.

Strugarek, Antoine; Charbonneau, Paul; Joseph, Richard; Pirot, Dorian

2014-08-01

64

A solar tornado caused by flares  

NASA Astrophysics Data System (ADS)

An enormous solar tornado was observed by SDO/AIA on 25 September 2011. It was mainly associated with a quiescent prominence with an overlying coronal cavity. We investigate the triggering mechanism of the solar tornado by using the data from two instruments: SDO/AIA and STEREO-A/EUVI, covering the Sun from two directions. The tornado appeared near to the active region NOAA 11303 that produced three flares. The flares directly influenced the prominence-cavity system. The release of free magnetic energy from the active region by flares resulted in the contraction of the active region field. The cavity, owing to its superior magnetic pressure, expanded to fill this vacated space in the corona. We propose that the tornado developed on the top of the prominence due to the expansion of the prominence-cavity system.

Panesar, N. K.; Innes, D. E.; Tiwari, S. K.; Low, B. C.

2014-01-01

65

Solar flare X-ray polarimetry  

NASA Technical Reports Server (NTRS)

The motivation for high quality solar flare X-ray polarization measurements are discussed in general. The design of the proposed instrument is described and then the sensitivity and energy response are discussed. The laboratory work which demonstrates that the earlier lithium contamination problem was solved, is described.

Chanan, G. A.; Novick, R.

1986-01-01

66

Absolute Abundance Measurements in Solar Flares  

NASA Astrophysics Data System (ADS)

We present measurements of elemental abundances in solar flares with EVE/SDO and EIS/Hinode. EVE observes both high temperature Fe emission lines Fe XV-XXIV and continuum emission from thermal bremsstrahlung that is proportional to the abundance of H. By comparing the relative intensities of line and continuum emission it is possible to determine the enrichment of the flare plasma relative to the composition of the photosphere. This is the first ionization potential or FIP bias (F). Since thermal bremsstrahlung at EUV wavelengths is relatively insensitive to the electron temperature it is important to account for the distribution of electron temperatures in the emitting plasma. We accomplish this by using the observed spectra to infer the differential emission measure distribution and FIP bias simultaneously. In each of the 21 flares that we analyze we find that the observed composition is close to photospheric. The mean FIP bias in our sample is F=1.17+-0.22. Furthermore, we have compared the EVE measurements with corresponding flare observations of intermediate temperature S, Ar, Ca, and Fe emission lines taken with EIS. Our initial calculations also indicate a photospheric composition for these observations. This analysis suggests that the bulk of the plasma evaporated during a flare comes from deep in the chromosphere, below the region where elemental fractionation in the non-flaring corona occurs.

Warren, Harry

2014-06-01

67

SORCE Monitors Solar Variability during Record Solar Flares - Video version  

NSDL National Science Digital Library

The SORCE mission monitors solar variability to determine its impact on the Earths climate. The X-ray photometer aboard SORCE observes the record-breaking solar flares in the Fall of 2003. The line graph shows the photometers measured solar radiation flux in the 1-7 nanometer wavelength band (x-ray) measured in milliwatts per square meter. The ultraviolet (195 Angstrom) imagery from SOHO-EIT (green) illustrates where the flares (the bright white spots) are located on the solar disk. This version has the contents slightly smaller for use in video.

Bridgman, Tom; Newcombe, Marte; Rottman, Gary; Woods, Tom

2004-02-20

68

SORCE Monitors Solar Variability during Record Solar Flares  

NSDL National Science Digital Library

The SORCE mission monitors solar variability to determine its impact on the Earths climate. The X-ray photometer aboard SORCE observes the record-breaking solar flares in the Fall of 2003. The line graph shows the photometers measured solar radiation flux in the 1-7 nanometer wavelength band (x-ray) measured in milliwatts per square meter. The ultraviolet (195 Angstrom) imagery from SOHO-EIT (green) illustrates where the flares (the bright white spots) are located on the solar disk.

Bridgman, Tom; Newcombe, Marte; Rottman, Gary; Woods, Tom

2004-02-20

69

Periodicities of solar flare and its relations  

NASA Technical Reports Server (NTRS)

Daily flare index during period between March 1975 and May 1978, were studied by using power spectral analysis method. There are periodicities between 4.5 days to 21.7 days. Our results confirm the periodicity around 12.5 days found by several authors. This periodicity was attributed to the rotation of solar core. Long term periodicities were given where 88 and 320 days periodicities were confirmed. The relation between these periodicities and other solar activities periodicity were given.

Hady, Ahmed A.

1995-01-01

70

Solar Flare Impacts on Ionospheric Electrodynamics  

NASA Technical Reports Server (NTRS)

The sudden increase of X-ray and extreme ultra-violet irradiance during flares increases the density of the ionosphere through enhanced photoionization. In this paper, we use model simulations to investigate possible additional contributions from electrodynamics, finding that the vertical E X B drift in the magnetic equatorial region plays a significant role in the ionosphere response to solar flares. During the initial stage of flares, upward E X B drifts weaken in the magnetic equatorial region, causing a weakened equatorial fountain effect, which in turn causes lowering of the peak height of the F2 region and depletion of the peak electron density of the F2 region. In this initial stage, total electron content (TEC) enhancement is predominantly determined by solar zenith angle control of photoionization. As flares decay, upward E X B drifts are enhanced in the magnetic equatorial region, causing increases of the peak height and density of the F2 region. This process lasts for several hours, causing a prolonged F2-region disturbance and TEC enhancement in the magnetic equator region in the aftermath of flares. During this stage, the global morphology of the TEC enhancement becomes predominantly determined by these perturbations to the electrodynamics of the ionosphere.

Qian, Liying; Burns, Alan G.; Solomon, Stanley C.; Chamberlin, Phillip C.

2012-01-01

71

Global aspects of solar flares  

NASA Astrophysics Data System (ADS)

Existing global models for flares do not include an essential ingredient in the electrodynamics: the inductive electric field due to the time-varying magnetic field. How the large (? 1010 V) electromotive force and the current it drives can be included in a model is discussed. Alfvn waves play an important role in transporting energy and potential, and in redistributing current on a global scale.

Melrose, Don

2013-06-01

72

Observations of particle acceleration in solar flares  

NASA Technical Reports Server (NTRS)

Solar flares provide several examples of nonthermal particle acceleration. The paper reviews the information gained about these processes via X-ray and gamma-ray astronomy, which can presently distinguish among three separate particle-acceleration processes at the sun: an impulsive accelerator of more than 20 keV electrons, a gradual accelerator of more than 20 keV electrons, and a gradual accelerator of more than 10 MeV ions. The acceleration energy efficiency (total particle energy divided by total flare energy) of any of these mechanisms cannot be less than about 0.1%, although the gradual acceleration does not occur in every flare. The observational material suggests that both the impulsive and gradual accelerations take place preferentially in closed magnetic-field structures, but that the electrons decay in these traps before they can escape. The ions escape very efficiently.

Hudson, H. S.

1979-01-01

73

A solar tornado triggered by flares?  

E-print Network

Solar tornados are dynamical, conspicuously helical magnetic structures mainly observed as a prominence activity. We investigate and propose a triggering mechanism for the solar tornado observed in a prominence cavity by SDO/AIA on September 25, 2011. High-cadence EUV images from the SDO/AIA and the Ahead spacecraft of STEREO/EUVI are used to correlate three flares in the neighbouring active-region (NOAA 11303), and their EUV waves, with the dynamical developments of the tornado. The timings of the flares and EUV waves observed on-disk in 195\\AA\\ are analyzed in relation to the tornado activities observed at the limb in 171\\AA. Each of the three flares and its related EUV wave occurred within 10 hours of the onset of the tornado. They have an observed causal relationship with the commencement of activity in the prominence where the tornado develops. Tornado-like rotations along the side of the prominence start after the second flare. The prominence cavity expands with acceleration of tornado motion after the ...

Panesar, N K; Tiwari, S K; Low, B C

2012-01-01

74

Measurements of Absolute Abundances in Solar Flares  

NASA Astrophysics Data System (ADS)

We present measurements of elemental abundances in solar flares with the EUV Variability Experiment (EVE) on the Solar Dynamics Observatory. EVE observes both high temperature Fe emission lines (Fe XV-Fe XXIV) and continuum emission from thermal bremsstrahlung that is proportional to the abundance of H. By comparing the relative intensities of line and continuum emission it is possible to determine the enrichment of the flare plasma relative to the composition of the photosphere. This is the first ionization potential or FIP bias (f). Since thermal bremsstrahlung at EUV wavelengths is relatively insensitive to the electron temperature, it is important to account for the distribution of electron temperatures in the emitting plasma. We accomplish this by using the observed spectra to infer the differential emission measure distribution and FIP bias simultaneously. In each of the 21 flares that we analyze we find that the observed composition is close to photospheric. The mean FIP bias in our sample is f = 1.17 0.22. This analysis suggests that the bulk of the plasma evaporated during a flare comes from deep in the chromosphere, below the region where elemental fractionation occurs.

Warren, Harry P.

2014-05-01

75

TESTING AUTOMATED SOLAR FLARE FORECASTING WITH 13 YEARS OF MICHELSON DOPPLER IMAGER MAGNETOGRAMS  

SciTech Connect

Flare occurrence is statistically associated with changes in several characteristics of the line-of-sight magnetic field in solar active regions (ARs). We calculated magnetic measures throughout the disk passage of 1075 ARs spanning solar cycle 23 to find a statistical relationship between the solar magnetic field and flares. This expansive study of over 71,000 magnetograms and 6000 flares uses superposed epoch (SPE) analysis to investigate changes in several magnetic measures surrounding flares and ARs completely lacking associated flares. The results were used to seek any flare associated signatures with the capability to recover weak systematic signals with SPE analysis. SPE analysis is a method of combining large sets of data series in a manner that yields concise information. This is achieved by aligning the temporal location of a specified flare in each time series, then calculating the statistical moments of the 'overlapping' data. The best-calculated parameter, the gradient-weighted inversion-line length (GWILL), combines the primary polarity inversion line (PIL) length and the gradient across it. Therefore, GWILL is sensitive to complex field structures via the length of the PIL and shearing via the gradient. GWILL shows an average 35% increase during the 40 hr prior to X-class flares, a 16% increase before M-class flares, and 17% increase prior to B-C-class flares. ARs not associated with flares tend to decrease in GWILL during their disk passage. Gilbert and Heidke skill scores are also calculated and show that even GWILL is not a reliable parameter for predicting solar flares in real time.

Mason, J. P.; Hoeksema, J. T., E-mail: JMason86@sun.stanford.ed, E-mail: JTHoeksema@sun.stanford.ed [W. W. Hansen Experimental Physics Laboratory, Stanford University, 450 Serra Mall, Stanford, CA 94305-4085 (United States)

2010-11-01

76

Carbon-poor solar flare events  

NASA Technical Reports Server (NTRS)

A survey of energetic particle flux enhancements over the period from October 1973 to December 1977 has been performed by using the University of Maryland/Max-Planck-Institut ULET sensor on the IMP 8 spacecraft. During the four-year period of the study, it is found that the most extreme periods of Fe enrichment compared with oxygen were during solar flare events in February 1974 and May 1974. In these same events, the carbon abundance with respect to oxygen was significantly depleted when compared with a value C:O of about 0.45:1 for typical solar flares. These observations, taken together with previously reported He-3 enrichment in these events, give strong evidence for the importance of a wave-particle interaction in the preinjection heating of the ambient matter.

Mason, G. M.; Gloeckler, G.; Hovestadt, D.

1979-01-01

77

Impulsive phase explosive dynamics. [of solar flares  

NASA Technical Reports Server (NTRS)

Observational evidence and theoretical models for explosive mass motion in the impulsive phase of solar flares are reviewed. Data showing X-ray blueshifts and H-alpha redshifts are presented in graphs and diagrams and interpreted in terms of upward-moving material at 10 million K and downward-moving material at 10,000 K. This motion is found to be most simply explained in terms of explosive chromospheric evaporation.

Canfield, Richard C.

1986-01-01

78

Explosive plasma flows in a solar flare  

NASA Technical Reports Server (NTRS)

Solar Maximum Mission soft X-ray data and Sacramento Peak Observatory H-alpha observations are combined in a study of the impulsive phase of a solar flare. A blue asymmetry, indicative of upflows, was observed in the coronal Ca XIX line during the soft X-ray rise phase. A red asymmetry, indicative of downflows, was observed simultaneously in chromospheric H-alpha emitted from bright flare kernels during the period of hard X-ray emission. Combining the velocity data with a measurement of coronal electron density, it is shown that the impulsive phase momentum of upflowing soft X-ray-emitting plasma equalled that of the downflowing H-alpha-emitting plasma to within one order of magnitude. In particular, the momentum of the upflowing plasma was 2 x 10 to the 21st g cm/s while that of the downflowing plasma was 7 x 10 to the 21st g cm/s, with a factor of 2 uncertainty on each value. This equality supports the explosive chromospheric evaporation model of solar flares, in which a sudden pressure increase at the footprint of a coronal loop produces oppositely directed flows in the heated plasma.

Zarro, Dominic M.; Canfield, Richard C.; Metcalf, Thomas R.; Strong, Keith T.

1988-01-01

79

Ion Acceleration and Transport in Solar Flares  

NASA Technical Reports Server (NTRS)

The purpose of the work proposed for this grant was to develop a promising model for ion acceleration in impulsive solar flares. Solar flares are among the most energetic and interesting phenomena in the solar system, releasing up to 10(exp 32) ergs of energy over timescales ranging from a few tens of seconds to a few tens of minutes. Much of this energy appears as energetic electrons and ions, which produce a wide range of observable radiations. These radiations, in turn, are valuable diagnostics of the acceleration mechanism, the identification of which is the fundamental goal of solar flare research. The specific mechanism we proposed to investigate was based on cascading Alfven waves, the essence of which was as follows: During the primary flare energy release, it is widely believed that magnetic free energy is made available through the large-scale restructuring of the flare magnetic field. Any perturbation of a magnetic field will lead to the formation of MagnetoHydroDynamic (MHD) waves of wavelength comparable to the initial scale of the perturbation. Since the scalesize of a flare energy release region will likely be 10(exp 8)-10(exp 9) cm, the MHD waves will be of very long wavelength. However, it is well known that wave steepening will lead to a cascade of wave energy to smaller wavelengths. Now, MHD waves consist of two specific modes-the Alfven wave and the fast mode wave, and it is the Alfven wave which can interact with the ambient ions and accelerate them via cyclotron resonance. As the Alfven waves cascade to smaller wavenumbers, they can resonate with ions of progressively lower energy, until they eventually (actually, this is less than approx. 1 s) can resonate with ions in the thermal distribution. These ions are then energized out of the thermal background and, since lower-frequency waves are already present as a result of the cascading, to relativistic energies. Hence, cascading Alfven waves naturally accelerate ions from thermal to relativistic energies in one step with one basic mechanism.

Miller, James A.

1995-01-01

80

Size Distributions of Solar Flares and Solar Energetic Particle Events  

NASA Technical Reports Server (NTRS)

We suggest that the flatter size distribution of solar energetic proton (SEP) events relative to that of flare soft X-ray (SXR) events is primarily due to the fact that SEP flares are an energetic subset of all flares. Flares associated with gradual SEP events are characteristically accompanied by fast (much > 1000 km/s) coronal mass ejections (CMEs) that drive coronal/interplanetary shock waves. For the 1996-2005 interval, the slopes (alpha values) of power-law size distributions of the peak 1-8 Angs fluxes of SXR flares associated with (a) >10 MeV SEP events (with peak fluxes much > 1 pr/sq cm/s/sr) and (b) fast CMEs were approx 1.3-1.4 compared to approx 1.2 for the peak proton fluxes of >10 MeV SEP events and approx 2 for the peak 1-8 Angs fluxes of all SXR flares. The difference of approx 0.15 between the slopes of the distributions of SEP events and SEP SXR flares is consistent with the observed variation of SEP event peak flux with SXR peak flux.

Cliver, E. W.; Ling, A. G.; Belov, A.; Yashiro, S.

2012-01-01

81

Automatic Solar Flare Tracking Using Image-Processing Techniques  

Microsoft Academic Search

Measurement of the evolution properties of solar flares through their complete cyclic development is crucial in the studies of Solar Physics. From the analysis of solar Ha images, we used Support Vector Machines (SVMs) to automatically detect flares and applied image segmentation techniques to compute their properties. We also present a solution for automatically tracking the apparent separation motion of

Ming Qu; Frank Shih; Ju Jing; Haimin Wang

2004-01-01

82

Stochastic Acceleration of Electrons in Solar Flares  

NASA Astrophysics Data System (ADS)

Stochastic particle acceleration (SPA) is a process in which turbulent fluctuations or randomly phased waves energize particles. We develop an SPA model for electron acceleration in solar flares based on turbulent fast magnetosonic waves and transit-time damping. Our model is two dimensional in both velocity space and wavenumber space, so that it takes into account anisotropy in the wave power spectrum P and electron distribution function f. We use quasilinear theory to obtain a set of equations that describes the coupled evolution of P and f. We solve these equations numerically, and find that the electron distribution function develops a power-law-like non-thermal tail between energies Emin and Emax. We obtain approximate analytic expressions for Emin and Emax that describe how these minimum and maximum energies depend upon plasma parameters such as the electron temperature and number density. We compare our results to previous studies that assume that P and f are isotropic and use our analysis to explain the observed hard x-ray spectrum seen in the June 27, 1980 flare. In our numerical simulations, the power-law indices of the electron energy spectra range from -2.3 to -4.4. The absolute values of these indices are larger than the corresponding values in studies with isotropic P and f and closer to the observed values in solar flares.

Pongkitiwanichakul, P.; Chandran, B. D.

2012-12-01

83

A slingshot model for solar flares  

NASA Technical Reports Server (NTRS)

Recent observations of intense, impulsive gamma-ray and X-ray-emitting solar flares underline the suddenness of these events. The simultaneous emission of X-rays greater than 40 keV from electron bremsstrahlung and gamma-rays requiring several MeV protons shows that all particles must be accelerated in less than 5 s. This paper proposes a simple model to explain such events, using the energy stored in the stretched field lines of a coronal arch. When reconnection occurs at the top of the arch, field lines retract like stretched rubber bands, sweeping up plasma and acting like a piston or slingshot. When the slug of plasma caught in the magnetic fields strikes the photosphere, it deposits its considerable kinetic energy, heating and compressing the intruding slug. Ten slugs of 100 km radius striking the photosphere may account for the 10 to the 29th ergs radiation from loop flares.

Benford, Gregory

1991-01-01

84

The impulsive flux transfer solar flare model  

NASA Astrophysics Data System (ADS)

A revised impulsive-flux-transfer solar-flare model is proposed in which magnetic reconnection and an electric double layer are combined and interact. The model requires a single stage of acceleration and several stages of deceleration and thermalization. The time development of flare parameters is calculated using a circuit analog that treats the double layer as an effective resistance, which is computed from the ultrarelativistic Child-Langmuir law. The model indicates that: (1) accelerated particles are quasi-thermalized at the ends of the double layer; (2) the electrons generate thermal X-rays, and the protons produce neutrons by spallation reactions with heavy nuclei; and (3) the neutrons travel to the photosphere, capturing protons to produce nuclear gamma-ray emission.

Baum, P. J.; Bratenahl, A.

85

Relationship between Solar Energetic Particles and Properties of Flares and CMEs: Statistical Analysis of Solar Cycle 23 Events  

NASA Astrophysics Data System (ADS)

A statistical analysis of the relationship between solar energetic particles (SEPs) and properties of solar flares and coronal mass ejections (CMEs) is presented. SEP events during solar cycle 23 are selected which are associated with solar flares originating on the visible hemisphere of the Sun and at least of magnitude M1. Taking into account all flares and CMEs that occurred during this period, the probability for the occurrence of an SEP event near Earth is determined. A strong rise of this probability is observed for increasing flare intensities, more western locations, larger CME speeds and halo CMEs. The correlations between the proton peak flux and these solar parameters are derived for a low (>10 MeV) and high (>60 MeV) energy range excluding any flux enhancement due to the passage of fast interplanetary shocks. The obtained correlation coefficients are: 0.55+-0.07 (0.63+-0.06) with flare intensity and 0.56+-0.08 (0.40+-0.09) with the CME speed for E>10 MeV (E>60 MeV). For both energy ranges, the correlations with flare longitude and CME width are very small or non-existent. Furthermore, the occurrence probabilities, correlation coefficients and mean peak fluxes are derived in multi-dimensional bins combining the aforementioned solar parameters. The correlation coefficients are also determined in different proton energy channels ranging from 5 to 200 MeV. The results show that the correlation between the proton peak flux and the CME speed decreases with energy, while the correlation with the flare intensity shows the opposite behavior. Furthermore, the correlation with the CME speed is stronger than the correlation with the flare intensity below 15 MeV and becomes weaker above 20 MeV. Excluding the flux enhancements due to interplanetary shocks, only a small but not very significant change is observed in the correlation between the peak flux below 7 MeV and the CME speed.

Dierckxsens, M.; Tziotziou, K.; Dalla, S.; Patsou, I.; Marsh, M. S.; Crosby, N. B.; Malandraki, O.; Tsiropoula, G.

2015-01-01

86

The solar flare heavy ion environment for single-event upsets - A summary of observations over the last solar cycle, 1973-1983  

Microsoft Academic Search

A summary of observations of the flux of 25 to 400 MeV\\/nucleon heavy ions from solar flares is presented covering the period from late 1973 to early 1984. Distributions of flare occurrence frequency versus fluence, energy spectra, and composition are presented for the 30 events observed during this period, to quantify the variability of the heavy ion environment. A comparison

D. L. Chenette; W. F. Dietrich

1984-01-01

87

Behavior of the F2 region ionospheric electron and ion temperatures during the solar flare  

NASA Astrophysics Data System (ADS)

The ionospheric electron and ion temperatures data recorded by RPA payload aboard SROSS- C2 satellite have been used to study the effect of solar flares on ionospheric F region heating. The data on solar flare have been obtained from National Geophysical Data Center (NGDC) Boulder, Colorado (USA). A carefully quantitative analysis of electron and ion temperatures data recorded during the occurrence of solar flares shows the consistent enhancement in both the temperatures on the dayside earth's ionosphere. The estimated enhancement for the average electron temperature is from 1.3 to 1.9 times whereas for ion temperature it is from 1.2 to 1.4 times to the normal day's average temperature. The enhancement in ionospheric temperatures is mainly due to high energy X-rays and ultraviolet radiations produced during the solar flares. These high-energy radiations reach to the earth's ionosphere and heat the plasma. The solar flare does not have any significant effect on the nightside ionospheric region. A comparison with the temperature obtained from IRI-95 model also shows similar enhancement. Key words: Ionospheric temperatures, F2 region, Solar Flares, RPA data

Sharma, Dinesh Kumar

88

Comment on 'The solar flare myth' by J. T. Gosling  

NASA Technical Reports Server (NTRS)

In a recent paper Gosling (1993) claims that solar flares are relatively unimportant for understanding the terrestrial consequences of solar activity, and argues that coronal mass ejections (CMEs) produce the most powerful terrestrial disturbances. This opinion conflicts with observation, as it is well known that CMEs and flares are closely associated, and we disagree with Gosling's insistence on a simplistic cause-and-effect description of the interrelated phenomena of a solar flare. In this brief response we present new Yohkoh data and review older results that demonstrate the close relationships among CMEs, flares, filament eruptions, and other forms of energy release such as particle acceleration.

Hudson, Hugh; Haisch, Bernhard; Strong, Keith T.

1995-01-01

89

Energetic-particle abundances in impulsive solar flare events  

NASA Technical Reports Server (NTRS)

We report on the abundances of energetic particles from impulsive solar flares, including those from a survey of 228 He-3 rich events, with He-3/He-4 is greater than 0.1, observed by the International Sun Earth Explorer (ISEE) 3 spacecraft from 1978 August through 1991 April. The rate of occurrence of these events corresponds to approximately 1000 events/yr on the solar disk at solar maximum. Thus the resonant plasma processes that enhance He-3 and heavy elements are a common occurrence in impulsive solar flares. To supply the observed fluence of He-3 in large events, the acceleration must be highly efficient and the source region must be relatively deep in the atmosphere at a density of more than 10(exp 10) atoms/cu cm. He-3/He-4 may decrease in very large impulsive events because of depletion of He-3 in the source region. The event-to-event variations in He-3/He-4, H/He-4, e/p, and Fe/C are uncorrelated in our event sample. Abundances of the elements show a pattern in which, relative to coronal composition, He-4, C, N, and O have normal abundance ratios, while Ne, Mg, and Si are enhanced by a factor approximately 2.5 and Fe by a factor approximately 7. This pattern suggests that elements are accelerated from a region of the corona with an electron temperature of approximately 3-5 MK, where elements in the first group are fully ionized (Q/A = 0.5), those in the second group have two orbital electrons (Q/A approximately 0.43), and Fe has Q/A approximately 0.28. Ions with the same gyrofrequency absorb waves of that frequency and are similarly accelerated and enhanced. Further stripping may occur after acceleration as the ions begin to interact with the streaming electrons that generated the plasma waves.

Reames, D. V.; Meyer, J. P.; Von Rosenvinge, T. T.

1994-01-01

90

Development of Empirical Forecast Models of Geomagnetic Storms, Solar Proton Events, and Solar Flares based on Solar Information  

NASA Astrophysics Data System (ADS)

We are developing empirical space weather (solar flares, solar proton events, and geomagnetic storms) forecast models based on solar information. These models have been set up with the concept of probabilistic forecast using historical events. Major findings can be summarized as follows. First, we presented a concept of storm probability map depending on CME parameters as well as contingency tables between prediction and observation with their statistical parameters. Second, we suggested a new geoeffective CME parameter, earthward direction parameter, and demonstrated its importance in terms of the forecast of geomagnetic storms. Third, the importance of solar magnetic field orientation for storm occurrence was examined. Fourth, the relationship among coronal hole-CIR-storm relationship has been investigated, Fifth, the CIR forecast based on coronal hole information is possible but the storm forecast is challenging. Sixth, a new proton event forecast method depending on flare parameters (flare strength, duration, and longitude) as well as CME parameter (speed and angular width) has been suggested. Seventh, we are examining the probability of solar flares depending on sunspot McIntosh classification and its area change (as a proxy of flux change).

Moon, Y.; Kim, R.; Park, J.

2010-12-01

91

A Statistical Solar Flare Forecast Method  

E-print Network

A Bayesian approach to solar flare prediction has been developed, which uses only the event statistics of flares already observed. The method is simple, objective, and makes few ad hoc assumptions. It is argued that this approach should be used to provide a baseline prediction for certain space weather purposes, upon which other methods, incorporating additional information, can improve. A practical implementation of the method for whole-Sun prediction of Geostationary Observational Environment Satellite (GOES) events is described in detail, and is demonstrated for 4 November 2003, the day of the largest recorded GOES flare. A test of the method is described based on the historical record of GOES events (1975-2003), and a detailed comparison is made with US National Oceanic and Atmospheric Administration (NOAA) predictions for 1987-2003. Although the NOAA forecasts incorporate a variety of other information, the present method out-performs the NOAA method in predicting mean numbers of event days, for both M-X and X events. Skill scores and other measures show that the present method is slightly less accurate at predicting M-X events than the NOAA method, but substantially more accurate at predicting X events, which are important contributors to space weather.

M. S. Wheatland

2005-05-14

92

PRODUCTIVITY OF SOLAR FLARES AND MAGNETIC HELICITY INJECTION IN ACTIVE REGIONS  

SciTech Connect

The main objective of this study is to better understand how magnetic helicity injection in an active region (AR) is related to the occurrence and intensity of solar flares. We therefore investigate the magnetic helicity injection rate and unsigned magnetic flux, as a reference. In total, 378 ARs are analyzed using SOHO/MDI magnetograms. The 24 hr averaged helicity injection rate and unsigned magnetic flux are compared with the flare index and the flare-productive probability in the next 24 hr following a measurement. In addition, we study the variation of helicity over a span of several days around the times of the 19 flares above M5.0 which occurred in selected strong flare-productive ARs. The major findings of this study are as follows: (1) for a sub-sample of 91 large ARs with unsigned magnetic fluxes in the range from (3-5) x 10{sup 22} Mx, there is a difference in the magnetic helicity injection rate between flaring ARs and non-flaring ARs by a factor of 2; (2) the GOES C-flare-productive probability as a function of helicity injection displays a sharp boundary between flare-productive ARs and flare-quiet ones; (3) the history of helicity injection before all the 19 major flares displayed a common characteristic: a significant helicity accumulation of (3-45) x 10{sup 42} Mx{sup 2} during a phase of monotonically increasing helicity over 0.5-2 days. Our results support the notion that helicity injection is important in flares, but it is not effective to use it alone for the purpose of flare forecast. It is necessary to find a way to better characterize the time history of helicity injection as well as its spatial distribution inside ARs.

Park, Sung-hong; Wang Haimin [Space Weather Research Laboratory, New Jersey Institute of Technology, 323 Martin Luther King Boulevard, 101 Tiernan Hall, Newark, NJ 07102 (United States); Chae, Jongchul, E-mail: sp295@njit.ed [Astronomy Program and FPRD, Department of Physics and Astronomy, Seoul National University, Seoul 151-742 (Korea, Republic of)

2010-07-20

93

Prediction of Solar Proton Events Depending on X-ray Flare Peak Flux, Longitude, and Impulsive Time  

NASA Astrophysics Data System (ADS)

In this study, we have examined the longitudinal dependence of solar proton events and their relationships with x-ray flares. For this we used NOAA solar energetic particle (SEP) events from 1976 to 2006 and their associated X-ray flare data. As a result, we found that about only 3.5% (1.9% for M-class and 21.3% for X-class) of the flares are associated with the proton events. It is also found that this fraction strongly depends on longitude; for example, the fraction for 30W < L ? 90W is about three times larger than that for 30E < L ? 90E. The occurrence probability of solar proton events for flares with long duration (? 0.3 hours) is about 2 (X-class flare) to 7 (M-class flare) times larger than that for flares with short duration (< 0.3 hours). The relationship between X-ray flare peak flux and proton peak flux as well as its correlation coefficient are strongly dependent on longitude. Using these results, we suggest a new proton event forecast method with two-steps: (1) solar proton occurrence probability prediction according to the contingency tables depending on its associated flare strength, longitude, and impulsive time, (2) solar proton peak flux prediction using the result of a multiple linear regression method. In addition, we examined the characteristics of five proton events without flares but with CMEs. By considering solar rotation rate and the history of flares in backside active regions using SOHO LASCO and SOHO MDI data, we could identify that they are all back side events ranging from 90W and 120W. This interpretation is supported by that the dependence of their rise times on longitude is consistent with the previous empirical formula.

Park, Jinhye; Moon, Y.; Lee, D.

2009-05-01

94

The Role of Solar Flares in the Variability of the Extreme Ultraviolet Solar Spectral Irradiance  

NASA Astrophysics Data System (ADS)

X-ray and extreme ultraviolet (EUV, 0--121.6 nm) emission from the solar corona has long been used to provide insight into the dynamics and evolution of solar flares. The EUV Variability Experiment (EVE) onboard NASA's Solar Dynamics Observatory (SDO) measures the solar spectral irradiance in the EUV at a wide range of temperatures (7,000 K to 10 MK), capturing the complete evolution of the transition region and corona during solar flares. The goal of this thesis is to use the new observations obtained by EVE to quantify how the EUV spectral irradiance varies in response to solar flares. Most observation-based research on solar flares is done by studying individual, usually large, solar flares. My work takes a different approach. From 1 May 2010 to 31 August 2011, SDO observed over 750 solar flares. I created the EVE flare catalog to examine all of these events to produce a complete picture of the EUV variability of flares. In the process, I discovered that flares can be placed into one of five EUV flare categories. The EUV irradiance signature of these categories is unique and closely related to the magnetic structure of the flare region. Confined flares are the most ubiquitous type of flare. They are non-eruptive flares and appear as the sudden brightening of a coherent bundle of coronal loops. Localized eruptive flares are small point-like flares associated with EUV surges or jets. Arcade flares are the classic CSHKP-type flare and are identified observationally by an eruption followed by arcade of flare loops in the corona and two bright ribbons of footpoint emission in the chromosphere and transition region. EUV late phase flares are characterized by two spatially and temporally separate but related reconnection events. Finally, flares that do not fit into any of the four other flare categories are called "strange" flares. I also used the Enthaply-Based Thermal Evolution of Loops (EBTEL) code to model the heating rate of the corona during flares. By fitting the input parameters of the model to the EVE data, I determined that the rate of energy release during reconnection strongly influences the EUV irradiance signature. Each of these EUV flare categories has a different heating rate profile, which is related to the underlying magnetic structure of the flare region.

Hock, Rachel Allison

95

Prediction of solar proton events based on flare and CME parameters  

NASA Astrophysics Data System (ADS)

In this study we have examined the probability of solar proton events (SPEs) and their peak fluxes depending on flare (flux, longitude and impulsive time) and CME parameters (linear speed and angular width). For this we used the NOAA SPE list and their associated flare data from 1976 to 2006 and CME data from 1997 to 2006. We found that about 3.5% (1.9% for M-class and 21.3% for X-class) of the flares are associated with SPEs. It is also found that this fraction strongly depends on longitude; for example, the fraction for 30W < L < 90W is about three times larger than that for 30E < L < 90E. The occurrence probability of SPEs for flares with long duration (? 0.3 hours) is about 2 (X-class flare) to 7 (M-class flare) times larger than that for flares with short duration (< 0.3 hours). In the case of halo CMEs with V ? 1500km/s, 36.1% are associated with SPEs but in the case of partial halo CME (120 ? AW < 359) with 400 km/s ? V < 1000 km/s, only 0.9% are associated with SPEs. The relationships between X-ray flare peak flux and SPE peak flux are strongly dependent on longitude and impulsive time. The relationships between CME speed and SPE peak flux depend on longitude as well as direction parameter. From this study, we suggest a new SPE forecast method with three-steps: (1) SPE occurrence probability prediction according to the contingency tables depending on flare and CME parameters, (2) SPE flux prediction depending on flare and CME parameters, and (3) SPE peak time.

Park, J.; Moon, Y.

2011-12-01

96

Automated recognition of solar flares in real-time data  

Microsoft Academic Search

Summary form only given. The focus of the automatic solar flare detection is on the development of efficient feature-based classifiers. The three principal techniques used in this work are multi-layer perceptron (MLP), radial basis function (RBF), and support vector machine (SVM) classifiers. We have experimented and compared these three methods for solar flare detection on the solar H? (hydrogen-alpha) images

Ming Qu; F. Y. Shih; Ju Jing; Haimin Wang

2005-01-01

97

Observation of H ? line impact polarization in solar flares  

NASA Astrophysics Data System (ADS)

We present the results of studying the impact linear polarization of 32 solar flares of X-ray classes C, M, and X (two flares) observed with the Large Solar Vacuum Telescope. It has turned out that there is evidence for impact polarization only in 13 of them. The newly obtained data have confirmed that the linear Stokes parameters are predominantly 2-7%, while the spatial sizes of flaring points with nonzero Stokes parameters are small (1?-2?). Two features of the manifestation of impact polarization in flares revealed by these studies are of greatest interest: (1) at the two foot points of a single flare loop or an arcade of loops, both the H ? intensity profiles and the Stokes profiles differ in behavior; (2) based on the H ? line, we have found for the first time that the sign of the Stokes parameters changes not only across the flare ribbon but also with depth of the chromosphere.

Firstova, N. M.; Polyakov, V. I.; Firstova, A. V.

2014-07-01

98

THE 22-YEAR SOLAR MAGNETIC CYCLE. II. FLARE ACTIVITY  

E-print Network

THE 22-YEAR SOLAR MAGNETIC CYCLE. II. FLARE ACTIVITY G. MARI, M. D. POPESCU, A. C. DONEA, M. MIERLA The manifestation of the 22-year solar periodicity, referred to as the solar magnetic cycle or Hale cycle (HC), can be observed in the solar magnetic field character at large scale as well as in its smaller scale character

99

Testing Solar Flare Models with BATSE  

NASA Technical Reports Server (NTRS)

We propose to use high-sensitivity Burst and Transient Source Experiment (BATSE) hard X-ray observations to test the thick-target and electric field acceleration models of solar flares. We will compare the predictions made by these models with hard X-ray spectral observations obtained with BATSE and simultaneous soft X-ray Ca XIX emission observed with the Yohkoh Bragg Crystal Spectrometer (BCS). The increased sensitivities of the BATSE and BCS (relative to previous detectors) permits a renewed study of the relationship between heating and dynamical motions during the crucial rise phase of flares. With these observations, we will: (1) investigate the ability of the thick-target model to explain the temporal evolution of hard X-ray emission relative to the soft X-ray blueshift during the earliest stages of the impulsive phase; and (2) search for evidence of electric-field acceleration as implied by temporal correlations between hard X-ray spectral breaks and the Ca XIX blueshift. The proposed study will utilize hard X-ray lightcurve and spectral measurements in the 10-100 keV energy range obtained with the BATSE Large Area Detectors (LAD). The DISCLA and CONT data will be the primary data products used in this analysis.

Zarro, Dominic M.

1995-01-01

100

Stochastic acceleration of solar flare protons  

NASA Technical Reports Server (NTRS)

The acceleration of solar flare protons is considered by cyclotron damping of intense Alfven wave turbulence in a magnetic trap. The energy diffusion coefficient is computed for a near-isotropic distribution of super-Alfvenic protons and a steady-state solution for the particle spectrum is found for both transit-time and diffusive losses out of the ends of the trap. The acceleration time to a characteristic energy approximately 20 Mev/nucl can be as short as 10 sec. On the basis of phenomenological arguments an omega/2 frequency dependence for the Alfven wave spectrum is inferred. The correlation time of the turbulence lies in the range .0005 less than tau/corr less than .05s.

Barbosa, D. D.

1978-01-01

101

Electron precipitation in solar flares - Collisionless effects  

NASA Astrophysics Data System (ADS)

A large fraction of the electrons which are accelerated during the impulsive phase of solar flares stream towards the chromosphere and are unstable to the growth of plasma waves. The linear and non-linear evolution of plasma waves as a function of time is analyzed with the use of a set of rate equations that follow in time the nonlinearly coupled system of plasma waves - ion fluctuations. As an outcome of the fast transfer of wave energy from the beam to the ambient plasma, non-thermal electron tails are formed which can stabilize the anomalous Doppler resonance instability that is responsible for the pitch angle scattering of the beam electrons. The authors estimate the non-collisional losses of the precipitating electrons and discuss the observational implications of their results.

Vlahos, L.; Rowland, H. L.

1984-10-01

102

Capabilities of GRO/OSSE for observing solar flares  

NASA Technical Reports Server (NTRS)

The launch of the Gamma Ray Observatory (GRO) near solar maximum makes solar flare studies early in the mission particularly advantageous. The Oriented Scintillation Spectrometer Experiment (OSSE) on GRO, covering the energy range 0.05 to 150 MeV, has some significant advantages over the previous generation of satellite-borne gamma-ray detectors for solar observations. The OSSE detectors will have about 10 times the effective area of the Gamma-Ray Spectrometer (GRS) on Solar Maximum Mission (SMM) for both photons and high-energy neutrons. The OSSE also has the added capability of distinguishing between high-energy neutrons and photons directly. The OSSE spectral accumulation time (approx. 4s) is four times faster than that of the SMM/GRS; much better time resolution is available in selected energy ranges. These characteristics will allow the investigation of particle acceleration in flares based on the evolution of the continuum and nuclear line components of flare spectra, nuclear emission in small flares, the anisotropy of continuum emission in small flares, and the relative intensities of different nuclear lines. The OSSE observational program will be devoted primarily to non-solar sources. Therefore, solar observations require planning and special configurations. The instrumental and operational characteristics of OSSE are discussed in the context of undertaking solar observations. The opportunities for guest investigators to participate in solar flare studies with OSSE is also presented.

Kurfess, J. D.; Johnson, W. N.; Share, G. H.; Hulburt, E. O.; Matz, S. M.; Murphy, R. J.

1989-01-01

103

Stochastic Particle Acceleration in Impulsive Solar Flares  

NASA Technical Reports Server (NTRS)

The acceleration of a huge number of electrons and ions to relativistic energies over timescales ranging from several seconds to several tens of seconds is the fundamental problem in high-energy solar physics. The cascading turbulence model we have developed has been shown previously (e.g., Miller 2000; Miller & Roberts 1995; Miner, LaRosa, & Moore 1996) to account for all the bulk features (such as acceleration timescales, fluxes, total number of energetic particles, and maximum energies) of electron and proton acceleration in impulsive solar flares. While the simulation of this acceleration process is involved, the essential idea of the model is quite simple, and consists of just a few parts: 1. During the primary flare energy release phase, we assume that low-amplitude MHD Alfven and fast mode waves are excited at long wavelengths, say comparable to the size of the event (although the results are actually insensitive to this initial wavelength). While an assumption, this appears reasonable in light of the likely highly turbulent nature of the flare. 2. These waves then cascade in a Kolmogorov-like fashion to smaller wavelengths (e.g., Verma et al. 1996), forming a power-law spectral density in wavenumber space through the inertial range. 3. When the mean wavenumber of the fast mode waves has increased sufficiently, the transit-time acceleration rate (Miller 1997) for superAlfvenic electrons can overcome Coulomb energy losses, and these electrons are accelerated out of the thermal distribution and to relativistic energies (Miller et al. 1996). As the Alfven waves cascade to higher wavenumbers, they can cyclotron resonate with progressively lower energy protons. Eventually, they will resonate with protons in the tail of the thermal distribution, which will then be accelerated to relativistic energies as well (Miller & Roberts 1995). Hence, both ions and electrons are stochastically accelerated, albeit by different mechanisms and different waves. 4. When the protons become superAlfvenic (above about 1 MeV/nucleon), they too can suffer transit-time acceleration by the fast mode waves and will receive an extra acceleration "kick." The basic overall objective of this 1 year effort was to construct a spatially-dependent version of this acceleration model and this has been realized.

Miller, James A.

2001-01-01

104

Collisionless Three-dimensional Reconnection in Impulsive Solar Flares  

Microsoft Academic Search

Two subclasses of impulsive solar flares, observed with the Hard X-Ray Telescope (HXT) onboard Yohkoh, have been discovered by Sakao et al. The two subclasses can be characterized as more impulsive (MI) and less impulsive (LI) flares, the former having a shorter total duration of the impulsive phase in the hard X-ray emission than the latter. We assume that in

Boris V. Somov; Takeo Kosugi; Taro Sakao

1998-01-01

105

Impulsive Magnetic Reconnection in Phenomena of Solar Flares and CMEs  

Microsoft Academic Search

It has been demonstrated that the solar flare impulsive non-thermal hard X-ray emission during the flare rise phase correlates temporarily with acceleration of CME upward motion via an impulsive magnetic reconnection process. The observed dynamical evolution of CME motion was fitted with MHD simulations of arcade field reconnection and flux rope evolution using different anomalous resistivity models to identify the

C. Z. Cheng; Y. H. Yang; G. S. Choe

2008-01-01

106

Constraining Solar Flare Differential Emission Measures with EVE and RHESSI  

NASA Astrophysics Data System (ADS)

Deriving a well-constrained differential emission measure (DEM) distribution for solar flares has historically been difficult, primarily because no single instrument is sensitive to the full range of coronal temperatures observed in flares, from lsim2 to gsim50 MK. We present a new technique, combining extreme ultraviolet (EUV) spectra from the EUV Variability Experiment (EVE) onboard the Solar Dynamics Observatory with X-ray spectra from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), to derive, for the first time, a self-consistent, well-constrained DEM for jointly observed solar flares. EVE is sensitive to ~2-25 MK thermal plasma emission, and RHESSI to gsim10 MK together, the two instruments cover the full range of flare coronal plasma temperatures. We have validated the new technique on artificial test data, and apply it to two X-class flares from solar cycle 24 to determine the flare DEM and its temporal evolution; the constraints on the thermal emission derived from the EVE data also constrain the low energy cutoff of the non-thermal electrons, a crucial parameter for flare energetics. The DEM analysis can also be used to predict the soft X-ray flux in the poorly observed ~0.4-5 nm range, with important applications for geospace science.

Caspi, Amir; McTiernan, James M.; Warren, Harry P.

2014-06-01

107

C3-class Solar Flare Eruption - Duration: 0:13.  

NASA Video Gallery

Just as sunspot 1105 was turning away from Earth on Sept. 8, the active region erupted, producing a C3-class solar flare (peak @ 2330 UT) and a fantastic prominence. This is a three color closeup o...

108

Predictive Capabilities of Avalanche Models for Solar Flares  

NASA Astrophysics Data System (ADS)

We assess the predictive capabilities of various classes of avalanche models for solar flares. We demonstrate that avalanche models cannot generally be used to predict specific events because of their high sensitivity to the embedded stochastic process. We show that deterministically driven models can nevertheless alleviate this caveat and be efficiently used for predictions of large events. Our results suggest a new approach for predictions of large (typically X-class) solar flares based on simple and computationally inexpensive avalanche models.

Strugarek, A.; Charbonneau, P.

2014-11-01

109

Models of the Solar Atmospheric Response to Flare Heating  

NASA Technical Reports Server (NTRS)

I will present models of the solar atmospheric response to flare heating. The models solve the equations of non-LTE radiation hydrodynamics with an electron beam added as a flare energy source term. Radiative transfer is solved in detail for many important optically thick hydrogen and helium transitions and numerous optically thin EUV lines making the models ideally suited to study the emission that is produced during flares. I will pay special attention to understanding key EUV lines as well the mechanism for white light production. I will also present preliminary results of how the model solar atmosphere responds to Fletcher & Hudson type flare heating. I will compare this with the results from flare simulations using the standard thick target model.

Allred, Joel

2011-01-01

110

EVIDENCE FOR HOT FAST FLOW ABOVE A SOLAR FLARE ARCADE  

SciTech Connect

Solar flares are one of the main forces behind space weather events. However, the mechanism that drives such energetic phenomena is not fully understood. The standard eruptive flare model predicts that magnetic reconnection occurs high in the corona where hot fast flows are created. Some imaging or spectroscopic observations have indicated the presence of these hot fast flows, but there have been no spectroscopic scanning observations to date to measure the two-dimensional structure quantitatively. We analyzed a flare that occurred on the west solar limb on 2012 January 27 observed by the Hinode EUV Imaging Spectrometer (EIS) and found that the hot (?30MK) fast (>500 km s{sup 1}) component was located above the flare loop. This is consistent with magnetic reconnection taking place above the flare loop.

Imada, S. [Solar-Terrestrial Environment Laboratory (STEL), Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601 (Japan)] [Solar-Terrestrial Environment Laboratory (STEL), Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601 (Japan); Aoki, K.; Hara, H.; Watanabe, T. [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka-shi, Tokyo 181-8588 (Japan)] [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka-shi, Tokyo 181-8588 (Japan); Harra, L. K. [UCL-Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Surrey RH5 6NT (United Kingdom)] [UCL-Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Surrey RH5 6NT (United Kingdom); Shimizu, T. [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara-shi, Kanagawa 229-8510 (Japan)] [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara-shi, Kanagawa 229-8510 (Japan)

2013-10-10

111

Upper limits on the total radiant energy of solar flares  

Microsoft Academic Search

We establish limits on the total radiant energy of solar flares during the period 1980 February November, using the solar-constant monitor (ACRIM) on board the Solar Maximum Mission. Typical limits amount to 6 1029 erg\\/s for a 32-second integration time, with 5s statistical significance, for an impulsive emission; for a gradual component, about 4 1032 ergs total

H. S. Hudson; R. C. Willson

1983-01-01

112

High-energy particles associated with solar flares  

NASA Technical Reports Server (NTRS)

High-energy particles, the so-called solar cosmic rays, are often generated in association with solar flares, and then emitted into interplanetary space. These particles, consisting of electrons, protons, and other heavier nuclei, including the iron-group, are accelerated in the vicinity of the flare. By studying the temporal and spatial varation of these particles near the earth's orbit, their storage and release mechanisms in the solar corona and their propagation mechanism can be understood. The details of the nuclear composition and the rigidity spectrum for each nuclear component of the solar cosmic rays are important for investigating the acceleration mechanism in solar flares. The timing and efficiency of the acceleration process can also be investigated by using this information. These problems are described in some detail by using observational results on solar cosmic rays and associated phenomena.

Sakurai, K.; Klimas, A. J.

1974-01-01

113

The Carrington Solar Flares of 1859: Consequences on Life.  

PubMed

The beginning of September 1859 was the occasion of the first and unique observation of a giant solar white light flare, auroral displays were observed at low latitudes and geomagnetic observatories recorded exceptional storms. This paper reviews the impact of the event on the earth system with a special emphasis on living processes using the historical record and current scientific analysis. The data used includes reports from the telegraph operators, mortality and morbidity records, proxies as agricultural production. Comparisons with later solar flare events will be attempted on the basis of the record and the consequences of an event of comparable magnitude to the 1859 set of flares will be discussed. PMID:25351684

Muller, C

2014-10-30

114

Electron Trapping and Precipitation in Asymmetric Solar Flare Loops  

NASA Astrophysics Data System (ADS)

Acceleration, propagation, and energy loss of particles energized in solar flares cannot be studied separately because their radiative signatures observed in the form of hard X-ray bremsstrahlung or radio gyrosynchrotron emission represent a convolution of all these processes. We analyze hard X-ray emission from solar flares using a kinematic model that includes free-streaming electrons (having an energy-dependent time-of-flight delay) as well as temporarily trapped electrons (which are pitch-angle scattered by Coulomb collisional scattering) to determine various physical parameters (trapping times, flux asymmetry, loss-cone angles, magnetic mirror ratios) in flare loops with asymmetric magnetic fields.

Aschwanden, M. J.; Fletcher, L.; Sakao, T.; Kosugi, T.; Hudson, H.

2000-05-01

115

Studying the thermal/non-thermal crossover in solar flares  

NASA Technical Reports Server (NTRS)

This report describes work performed under contract NAS5-32584 for Phase 3 of the Compton Gamma Ray Observatory (CGRO) from 1 November 1993 through 1 November 1994. We have made spectral observations of the hard x-ray and gamma-ray bremsstrahlung emissions from solar flares using the Burst and Transit Source Experiment (BASTE) on CGRO. These measurements of their spectrum and time profile provided valuable information on the fundamental flare processes of energy release, particle acceleration, and energy transport. Our scientific objective was to study both the thermal and non-thermal sources of solar flare hard x-ray and gamma-ray emission.

Schwartz, R. A.

1994-01-01

116

MAGNETIC NONPOTENTIALITY IN PHOTOSPHERIC ACTIVE REGIONS AS A PREDICTOR OF SOLAR FLARES  

SciTech Connect

Based on several magnetic nonpotentiality parameters obtained from the vector photospheric active region magnetograms obtained with the Solar Magnetic Field Telescope at the Huairou Solar Observing Station over two solar cycles, a machine learning model has been constructed to predict the occurrence of flares in the corresponding active region within a certain time window. The Support Vector Classifier, a widely used general classifier, is applied to build and test the prediction models. Several classical verification measures are adopted to assess the quality of the predictions. We investigate different flare levels within various time windows, and thus it is possible to estimate the rough classes and erupting times of flares for particular active regions. Several combinations of predictors have been tested in the experiments. The True Skill Statistics are higher than 0.36 in 97% of cases and the Heidke Skill Scores range from 0.23 to 0.48. The predictors derived from longitudinal magnetic fields do perform well, however, they are less sensitive in predicting large flares. Employing the nonpotentiality predictors from vector fields improves the performance of predicting large flares of magnitude {>=}M5.0 and {>=}X1.0.

Yang Xiao; Lin Ganghua; Zhang Hongqi; Mao Xinjie, E-mail: yangx@nao.cas.cn [Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Beijing 100012 (China)

2013-09-10

117

Ionospheric Currents Flowing along the Terminator during Solar Flares  

NASA Astrophysics Data System (ADS)

Solar flares occasionally produce geomagnetic disturbances known as solar flare effects (sfe). Flare electromagnetic radiation causes the ionization enhancement mainly in the sunlit hemisphere, resulting in the enhancement of ionospheric currents. The amplitude of sfe at the dip equator sometimes reaches 100 nT from an large solar flare. Such large sfe events from 2000 to 2005 (three events) were examined using these extended magnetometer networks: (1) the Circum-pan Pacific Magnetometer Network (CPMN) [http://www.serc.kyushu-u.ac.jp/index_e.html], (2) the International Real-time Magnetic Observatory Network (INTERMAGNET) [http://www.intermagnet.org] and (3) the World Data Center for Geomagnetism, Kyoto (WDC) [http://wdc.kugi.kyoto-u.ac.jp/index.html]. Geomagnetic data obtained from more than 100 stations all over the world were analyzed and ionospheric currents due to each solar flare were estimated. We discovered ionospheric currents flowing along the dusk and dawn terminators. These currents are considered as Hall currents arising from charge accumulation along terminators during solar flares.

Yamazaki, Y.; Yumoto, K.; Uozumi, T.; Abe, S.; Cpmn Group

2010-12-01

118

Magnetic Energy Dissipation in 200 Solar Flares Measured with SDO  

NASA Astrophysics Data System (ADS)

We present the first statistical study of magnetic energetics in solar flares. The amount of dissipated magnetic energy during solar flares provides the fundamental limit on the flare energy budget that is partitioned into the kinetic and potential energy of CMEs, acceleration of nonthermal particles, and radiation in soft X-rays, EUV, UV, and bolometric luminosity. The determination of the dissipated magnetic energy requires the calculation of nonlinear force-free field (NLFFF) solutions during flares,which can quantify the nonpotential E_N(t), the potential E_P(t), and the free magnetic energy E_{free}(t)=E_N(t)-E_P(t), which itself represents an upper limit on the magnetic energy dE_diss that can be dissipated during a flare. Here we developed a NLFFF forward-fitting code that fits a nonpotential field in terms of vertical currents with helically twisted field lines to automatically traced coronal loops from 7 AIA wavelength filters and apply it to 200 M- and X-class flares that havebeen observed during the first 4 years of the Solar Dynamics Observatory (SDO) mission. We cacluate the free energy with a cadence of 6 minutes during all 200 flares, and find significantmagnetic energy decreases dE_diss in almost all flares, in the order of E_diss ~ 10(31)-10(32) erg, which amounts to a fraction of dE_diss/E_P ~ 0.01-0.3 of the potential magnetic energy E_P. We find that the dissipated energy dE_diss cannot simply be determined by an energy difference before and after the flare, because the hydrodynamic evolution causes brightenings and dimmings of helically twisted loops (sigmoids) in the flare core region, which acts as a time-dependent illumination effect of nonpotential loop structures.

Aschwanden, Markus J.

2014-06-01

119

Prediction of solar flares for the Space Exploration Initiative  

NASA Technical Reports Server (NTRS)

The 21st century is likely to see the start of the manned exploration and settlement of the inner solar system. NASA's plans for this endeavor are focused upon the Space Exploration Initiative which calls for a return to the Moon, to stay, followed by manned missions to Mars. To execute these missions safely provides solar physics with both a challenge and an opportunity. As the past solar maximum has clearly demonstrated, the Sun, through the solar flare process, is capable of generating and accelerating to high energies large fluxes of protons whose cumulative dose to unprotected astronauts can be fatal. It will be the responsibility of solar physicists to develop an accurate physical description of the mechanisms of flare energy storage and release, and of particle acceleration and propagation through interplanetary space upon which to base a sound method of flare and energetic particle prediction.

Davis, John M.

1994-01-01

120

Implications of RHESSI Observations for Solar Flare Models and Energetics  

NASA Technical Reports Server (NTRS)

Observations of solar flares in X-rays and gamma-rays provide the most direct information about the hottest plasma and energetic electrons and ions accelerated in flares. The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) has observed over 18000 solar flares in X-rays and gamma-rays since its launch in February of 2002. RHESSI observes the full Sun at photon energies from as low as 3 keV to as high as 17 MeV with a spectral resolution on the order of 1 keV. It also provides images in arbitrary bands within this energy range with spatial resolution as good as 3 seconds of arc. Full images are typically produced every 4 seconds, although higher time resolution is possible. This unprecedented combination of spatial, spectral, and temporal resolution, spectral range and flexibility has led to fundamental advances in our understanding of flares. I will show RHESSI and coordinated observations that confirm coronal magnetic reconnection models for eruptive flares and coronal mass ejections, but also present new puzzles for these models. I will demonstrate how the analysis of RHESSI spectra has led to a better determination of the energy flux and total energy in accelerated electrons, and of the energy in the hot, thermal flare plasma. I will discuss how these energies compare with each other and with the energy contained in other flare-related phenomena such as interplanetary particles and coronal mass ejections.

Holman, Gordon D.

2006-01-01

121

Magnetic Shear in Two-ribbon Solar Flares  

NASA Astrophysics Data System (ADS)

Solar flares, filament eruptions and coronal mass ejections (CMEs) are energetic events that have great influences on the space weather that we live in. Storage of the energy released in these eruptions requires non-potential magnetic fields, i.e., sheared or twisted fields. In this thesis, we carry out a detailed and systematic study on the sheared magnetic field configuration as well as its important role in solar eruptions. This is an important part of our effort to understand and predict our space weather. This work primarily focuses on the analysis of multi-wavelength observations, while the nonlinear force-free field (NLFFF) modeling of one active region is also explored. The main results of this study are: (1) For the X17 flare on Oct. 28th 2003, we find that the cessation of the strong-to-weak shear change of the footpoints occurs in the middle of the impulsive phase. The phenomenon is interpreted in terms of the splitting of the sheared envelope field of the greatly sheared core rope during the early phase of the flare. (2) This shear motion of the footpoints has been found to be common, i.e., 43 out of 50 of the well-observed (by TRACE) two-ribbon flares we studied show this shear motion, we call these flares type I flares. We also find that in 10 Type I flares having both measured shear angles and corresponding hard X-ray observations, the cessation of shear change is 0~2 min earlier than the end of the impulsive phase, which may suggest that the change from the impulsive to gradual phase is related to magnetic shear change. (3) For a sample of 18 Type I flares associated with CMEs, we find that the magnetic flux and the change of shear angle of the footpoints are significantly correlated with the intensity of flare/CME events, while the initial shear angle of the footpoints is not. This observations indicate that the intensity of flare/CME events may depend on the released magnetic free energy rather than the total free energy stored prior to the flare. We also find that a linear combination of the aforementioned parameters shows a much stronger correlation with the intensity of flare/CME events than each parameter itself. (4) Hinode/XRT observations of two X-class flares which occurred in December 2006 show that one part of the sheared core field erupted, while the other stayed behind during the flares. This may explain why a large part of the filament is still seen in TRACE after the flare. We also find that the post-flare core field is clearly less sheared than the pre-flare core field, which is consistent with the idea that the energy released during the flares is stored in the highly sheared fields prior to the flare. (5) Using the flux rope insertion method, we explore the NLFFF modeling of active region 10953, which produced several small flares and filament activations. We find good NLFFF models that fit the observations before a C8.5 flare, but not for the case after the flare. The flux rope contains strongly sheared but weakly twisted magnetic fields. Before the C8.5 flare, this active region is close to an eruptive state: the axial flux in the flux rope is close to the threshold value for eruption.

Su, Y. N.

2010-04-01

122

Solar flare nuclear gamma rays and interplanetary proton events  

NASA Technical Reports Server (NTRS)

We compared flare gamma ray line (GRL) events and solar energetic proton (SEP) events for the period from Feb. 1980 - Jan. 1985 and substantiated earlier results showing a lack of correlation between gamma-ray-producing ions and interplanetary protons. This poor correlation results primarily from several large SEP events that originated in flares without detectable gamma ray emission. The converse case of GRL events unassociated with SEP events is rare. We present evidence which suggests that the ratio of trapped to escaping protons in GRL/SEP flares depends on the spatial scale size of the flare. We affirm the result of Bai and Dennis (1985) that GRL flares are generally accompanied (75 percent) by metric Type 2 bursts.

Cliver, E. W.; Forrest, D. J.; Mcguire, R. E.; Vonrosenvinge, T. T.; Reames, D. V.; Cane, H. V.; Kane, S. R.

1987-01-01

123

Energetic solar flare particles and interplanetary shock waves  

NASA Technical Reports Server (NTRS)

Estimates from hard X-ray measurements show that for many flares the bulk of the flare energy is released in the form of approximately 10-100-keV energy electrons. The interaction of these electrons with the solar atmosphere can produce the optical, UV, EUV, and radio emissions observed during the flare impulsive phase. In addition, explosive heating and evaporation of the chromosphere by these electrons can produce the roughly 10 million K soft X-ray plasma. For the large solar flares which produce interplanetary shock waves, the accelerated approximately 10-100-keV electron population may produce the heating and mass motion required for mass ejection and the formation of the shock wave. The shock wave can in turn accelerate ions and electrons to higher energy as it travels through the corona and interplanetary medium.

Lin, R. P.

1977-01-01

124

Critical Issues For Understanding Particle Acceleration in Impulsive Solar Flares  

Microsoft Academic Search

This paper, a review of the present status of existing models for particle acceleration during impulsive solar flares, was inspired by a week-long workshop held in the Fall of 1993 at NASA Goddard Space Flight Center. Recent observations from Yohkoh and the Compton Gamma Ray Observatory, and a reanalysis of older observations from the Solar Maximum Mission, have led to

James A. Miller; Peter J. Cargill; A. Gordon Emslie; Gordon D. Holman; Brian R. Dennis; Ted N. La Rosa; Robert M. Winglee; Stephen G. Benka; S. Tsuneta

1997-01-01

125

A Computational Model for Solar Flare Particle Propagation  

Microsoft Academic Search

A realistic inclusivemodel for the post-acceleration propagation of solar flare particles is presented that is suitable for numerical solution. The model assumes diffusion and energy loss in the solar atmosphere, gradual escape into the interplanetary medium, anisotropic energy-dependent diffusion in a stochastic interplanetary magnetic field whose average con- figuration is the Archimedian spiral pattern, convection and adiabatic deceleration produced by

Ronald C. Englade; Enrico Fermi

1971-01-01

126

Sign singularity and flares in solar active region NOAA 11158  

E-print Network

Solar Active Region NOAA 11158 has hosted a number of strong flares, including one X2.2 event. The complexity of current density and current helicity are studied through cancellation analysis of their sign-singular measure, which features power-law scaling. Spectral analysis is also performed, revealing the presence of two separate scaling ranges with different spectral index. The time evolution of parameters is discussed. Sudden changes of the cancellation exponents at the time of large flares, and the presence of correlation with EUV and X-ray flux, suggest that eruption of large flares can be linked to the small scale properties of the current structures.

Sorriso-Valvo, Luca; Kazachenko, Maria D; Krucker, Sam; Primavera, Leonardo; Servidio, Sergio; Vecchio, Antonio; Welsch, Brian T; Fisher, George H; Lepreti, Fabio; Carbone, Vincenzo

2015-01-01

127

Solar He-3: Information from nuclear reactions in flares  

NASA Technical Reports Server (NTRS)

Information on solar He-3 from nuclear reactions in flares was considered. Consideration was also given to the development of models for these reactions as well as the abundance of He-3 in the photosphere. Data show that abundances may be explained by nuclear reactions of flare acceleration protons and alpha particles with the ambient atmosphere, provided that various assumptions are made on the directionality of the interacting beams and acceleration of the particles after production.

Ramaty, R.; Kozlovsky, B.

1974-01-01

128

X-ray spectra of solar flares obtained with a high-resolution bent crystal spectrometer  

NASA Technical Reports Server (NTRS)

Preliminary results obtained for three solar flares with the bent crystal spectrometer on the SMM are presented. Resonance and satellite lines of Ca XIX and XVIII and Fe XXV and XXIV are observed together with the Fe XXVI Lyman-alpha line. Plasma properties are deduced from line ratios and evidence is presented for changes of line widths coincident with the occurrence of a hard X-ray impulsive burst. Fe K-alpha spectra from a disk center and a limb flare agree with the predictions of a fluorescence excitation model. However, a transient Fe K-alpha burst observed in a third flare may be explained by the collisional ionization of cool iron by energetic electrons.

Culhane, J. L.; Rapley, C. G.; Bentley, R. D.; Gabriel, A. H.; Phillips, K. J.; Acton, L. W.; Wolfson, C. J.; Catura, R. C.; Jordan, C.; Antonucci, E.

1981-01-01

129

Non-Relativistic Electron Beam Stability in Solar Flares  

NASA Astrophysics Data System (ADS)

The thick-target electron beam model has been used for decades as a viable description for the production of solar flare hard X-ray emission. The required very rapid transport of energy to the footpoints during solar flares is achieved in this model by fast electrons traversing the loop to deposit their energy in the dense chromosphere. For some of the largest flares the currents (up to 1017 Amps or 1036 electrons/sec) inferred can significantly exceed the Alfven-Lawson limit suggesting that the assumed electron beam is inherently unstable. In this paper, we use the spectral and spatial resolution of RHESSI to explore whether the conditions for a stable non-thermal electron beam exist in large solar flares. The incident electron spectra at flaring footpoints are derived from the RHESSI photon spectra while an upper limit to the footpoint area is detremined form the hard X-ray images. We determine the electron beam density needed to produce the hard X-ray emission for two large flares, July 17, 2002 (M8.5) and October 28, 2003 (X17.2) and determine whether such beams are viable in these cases. We gratefully acknowledge support from NASA (NAS5-02048).

Daou, A. G.; Alexander, D.; Metcalf, T. R.

2004-05-01

130

Can we explain atypical solar flares?  

NASA Astrophysics Data System (ADS)

Context. We used multiwavelength high-resolution data from ARIES, THEMIS, and SDO instruments to analyze a non-standard, C3.3 class flare produced within the active region NOAA 11589 on 2012 October 16. Magnetic flux emergence and cancellation were continuously detected within the active region, the latter leading to the formation of two filaments. Aims: Our aim is to identify the origins of the flare taking the complex dynamics of its close surroundings into account. Methods: We analyzed the magnetic topology of the active region using a linear force-free field extrapolation to derive its 3D magnetic configuration and the location of quasi-separatrix layers (QSLs), which are preferred sites for flaring activity. Because the active region's magnetic field was nonlinear force-free, we completed a parametric study using different linear force-free field extrapolations to demonstrate the robustness of the derived QSLs. Results: The topological analysis shows that the active region presented a complex magnetic configuration comprising several QSLs. The considered data set suggests that an emerging flux episode played a key role in triggering the flare. The emerging flux probably activated the complex system of QSLs, leading to multiple coronal magnetic reconnections within the QSLs. This scenario accounts for the observed signatures: the two extended flare ribbons developed at locations matched by the photospheric footprints of the QSLs and were accompanied with flare loops that formed above the two filaments, which played no important role in the flare dynamics. Conclusions: This is a typical example of a complex flare that can a priori show standard flare signatures that are nevertheless impossible to interpret with any standard model of eruptive or confined flare. We find that a topological analysis, however, permitted us to unveil the development of such complex sets of flare signatures. Movies associated to Figs. 1, 3, and 9 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/574/A37

Dalmasse, K.; Chandra, R.; Schmieder, B.; Aulanier, G.

2015-02-01

131

X1.6 Class Solar Flare on Sept. 10, 2014 - Duration: 0:37.  

NASA Video Gallery

An X1.6 class solar flare flashes in the middle of the sun on Sept. 10, 2014. These images were captured by NASA's Solar Dynamics Observatory. It first shows the flare in the 171 Angstrom wavelengt...

132

Wavelet Analysis of Solar Flare Hard X-Rays  

NASA Astrophysics Data System (ADS)

We apply a multiresolution analysis to hard X-ray (HXR) time profiles f(t) of solar flares. This method is based on a wavelet transform (with triangle-shaped wavelets), which yields a dynamic decomposition of the power at different timescales T, the scalogram P(T, t). For stationary processes, time-averaged power coefficients, the scalegram S(T), can be calculated. We develop an algorithm to transform these (multiresolution) scalegrams S(T) into a standard distribution function of physical timescales, N(T). We analyze 647 solar flares observed with the Compton Gamma Ray Observatory (CGRO), recorded at energies >=25 keV with a time resolution of 64 ms over 4 minutes in each flare. The main findings of our wavelet analysis are: 1. In strong flares, the shortest detected timescales are found in the range Tmin ~ 0.1-0.7 s. These minimum timescales are found to correlate with the flare loop size r (measured from Yohkoh images in 46 flares), according to the relation Tmin(r) ~ 0.5(r/109 cm) s. Moreover, these minimum timescales are subject to a cutoff, Tmin(ne) >~ TDefl(ne), which corresponds to the electron collisional deflection time at the loss-cone site of the flare loops (inferred from energy-dependent time delays in CGRO data). 2. In smoothly varying flares, the shortest detected timescales are found in the range Tmin ~ 0.5-5 s. Because these smoothly varying flares exhibit also large trap delays, the lack of detected fine structure is likely to be caused by the convolution with trapping times. 3. In weak flares, the shortest detected timescales cover a large range, Tmin ~ 0.5-50 s, mostly affected by Poisson noise. 4. The scalegrams S(T) show a power-law behavior with slopes of ?max ~ 1.5-3.2 (for strong flares) over the timescale range of [Tmin, Tpeak]. Dominant peaks in the timescale distribution N(T) are found in the range Tpeak ~ 0.5-102 s, often coinciding with the upper cutoff of N(T). These observational results indicate that the fastest significant HXR time structures detected with wavelets (in strong flares) are related to physical parameters of propagation and collision processes. If the minimum timescale Tmin is associated with an Alfvnic crossing time through elementary acceleration cells, we obtain sizes of racc ~ 75-750 km, which have a scale-invariant ratio racc/r ~ 0.03 to flare loops and are consistent with cell sizes inferred from the frequency bandwidth of decimetric millisecond spikes.

Aschwanden, Markus J.; Kliem, Bernhard; Schwarz, Udo; Kurths, Jrgen; Dennis, Brian R.; Schwartz, Richard A.

1998-10-01

133

Lunar surface cosmic ray experiment. [including solar flare studies  

NASA Technical Reports Server (NTRS)

The galactic cosmic ray and solar flare experiment on Apollo 16 is reported. The published papers presented describe the experiment, equipment, data processing techniques, and operational history. The principle findings include: (1) The composition of heavy ions in interplanetary space at energies between approximately 30 and 130 MeV/nucleon is the same, within experimental errors. (2) The ability of a Lexan stack to determine simultaneously the energy spectra of major elements from He up to Fe in the energy interval 0.2 to 30 MeV/nucleon revealed systematic changes in the composition of solar flare particles as a function of energy. (3) Heavy ions emitted in a solar flare appear to be completely stripped of electrons, and are not in charge equilibrium at the time of acceleration and releases from the sun.

Price, P. B.

1974-01-01

134

Conduction-driven chromospheric evaporation in a solar flare  

NASA Technical Reports Server (NTRS)

Observations of gentle chromospheric evaporation during the cooling phase of a solar flare are presented. Line profiles of the low-temperature (T of about 6 x 10 to the 6th K) coronal Mg XI line, observed with the X-Ray Polychromator on the Solar Maximum Mission, show a blueshift that persisted for several minutes after the impulsive heating phase. This result represents the first detection of an evaporation signature in a soft X-ray line formed at this low temperature. By combining the Mg XI blueshift velocity data with simultaneous measurements of the flare temperature derived from Ca XIX observations, it is demonstrated that the upward flux of enthalpy transported by this gently evaporating plasma varies linearly with the downward flux of thermal energy conducted from the corona. This relationship is consistent with models of solar flares in which thermal conduction drives chromospheric evaporation during the early part of the cooling phase.

Zarro, Dominic M.; Lemen, James R.

1988-01-01

135

Common SphinX and RHESSI observations of solar flares  

NASA Astrophysics Data System (ADS)

The Polish X-ray spectrofotometer SphinX has observed a great number of solar flares in the year 2009 - during the most quiet solar minimum almost over the last 100 years. Hundreds of flares have been recorded due to excellent sensitivity of SphinX's detectors. The Si-PIN diodes are about 100 times more sensitive to X-rays than GOES X-ray Monitors. SphinX detectors were absolutely calibrated on Earth with a use of the BESSY synchrotron. In space observations were made in the range 1.2-15~keV with 480~eV energy resolution. SphinX data overlap with the low-energy end of the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) data. RHESSI detectors are quite old (7 years in 2009), but still sensitive enough to provide us with observations of extremely weak solar flares such as those which occurred in 2009. We have selected a group of flares simultaneously observed by RHESSI and SphinX and performed a spectroscopic analysis of the data. Moreover, we compared the physical parameters of these flares plasma. Preliminary results of the comparison show very good agreement between both instruments.

Mrozek, T.; Gburek, S.; Siarkowski, M.; Sylwester, B.; Sylwester, J.; Gryciuk, M.

136

Automatic Solar Flare Tracking Using Image Processing Qu Ming and Shih Frank (shih@njit.edu)  

E-print Network

Automatic Solar Flare Tracking Using Image Processing Techniques Qu Ming and Shih Frank (shih the properties of solar flares. We also present our solution for automatically tracking the apparent separation demonstrate automatic motion tracking of solar flares. In Section 5, experimental results are shown. Finally

137

Solar Flare Tracking Using Image Processing Techniques , Frank Y. Shih1  

E-print Network

Solar Flare Tracking Using Image Processing Techniques Ming Qu1 , Frank Y. Shih1 , Ju Jing2 is presented. In Section 4, we demonstrate automatic solar flare motion tracking. In Section 5 grants IIS-0324816, ATM 0233931 and ATM 0313591. Abstract. Automatic property measurement of solar flares

138

Solar Flare Intermittency and the Earth's Temperature Anomalies Nicola Scafetta1,2  

E-print Network

Solar Flare Intermittency and the Earth's Temperature Anomalies Nicola Scafetta1,2 and Bruce J; published 17 June 2003) We argue that Earth's short-term temperature anomalies and the solar flare data sets that corresponds to the one that would be induced by the solar flare intermittency. The mean

Scafetta, Nicola

139

PPPL-3450 PPPL-3450 Solar Flare Mechanism Based on Magnetic Arcade  

E-print Network

PPPL-3450 PPPL-3450 UC-70 Solar Flare Mechanism Based on Magnetic Arcade Reconnection and Island, 00, 000­000, 2000 Solar Flare Mechanism Based on Magnetic Arcade Reconnection and Island Merging C. Z-0451 (Received ; Revised ; Accepted ) We propose a model describing physical processes of solar flares based

140

Modelling the effects of a solar flare on INTEGRAL  

NASA Astrophysics Data System (ADS)

The delayed effects of a large solar flare proton flux on the ?-ray instruments on-board INTEGRAL have been modelled. We simulated exposing INTEGRAL to a varying flux over a period of five days. The total integrated input proton flux for the flare chosen was 1.51014 protons. The induced count rates due to this proton flux over an energy range of 30 MeV - 2 GeV one minute after the end of the flare are 345.9+/-0.5 c/s for IBIS (the imager) and 10.03+/-0.06 c/s for SPI (the spectrometer). Spectra one minute after the end of the flare are shown for each instrument. The most significant spectral lines have been identified and the isotopic half-lives compared to the half-lives of the total count rates.

Perfect, C. L.; Bird, A. J.; Dean, A. J.; Diallo, N.; Ferguson, C.; Lei, F.; Lockley, J. J.

2001-09-01

141

Solar cosmic ray, solar wind, solar flare, and neutron albedo measurements, part C  

NASA Technical Reports Server (NTRS)

All mineral detectors exposed on Apollo 16 had high surface track densities probably produced by a solar flare that occurred during the mission. The heavy ions followed a power law spectrum with exponent approximately 3 down to approximately 200 KeV/nucleon. The abundance of low-energy particle tracks observed in this flare may explain the high track densities observed in lunar dust grains. Pristine heavy-particle tracks in feldspar give long tracks. Shallow pits similar to those expected from extremely heavy solar wind ions were observed in about the expected number. Initial results give a low apparent value of neutron albedo relative to theory.

Burnett, D.; Hohenberg, C.; Maurette, M.; Monnin, M.; Walker, R.; Wollum, D.

1972-01-01

142

A thermal/nonthermal approach to solar flares  

NASA Technical Reports Server (NTRS)

An approach for modeling solar flare high-energy emissions is developed in which both thermal and nonthermal particles coexist and contribute to the radiation. The thermal/nonthermal distribution function is interpreted physically by postulating the existence of DC sheets in the flare region. The currents then provide both primary plasma heating through Joule dissipation, and runaway electron acceleration. The physics of runaway acceleration is discussed. Several methods are presented for obtaining approximations to the thermal/nonthermal distribution function, both within the current sheets and outside of them. Theoretical hard x ray spectra are calculated, allowing for thermal bremsstrahlung from the heated plasma electrons impinging on the chromosphere. A simple model for hard x ray images of two-ribbon flares is presented. Theoretical microwave gyrosynchrotron spectra are calculated and analyzed, uncovering important new effects caused by the interplay of thermal and nonthermal particles. The theoretical spectra are compared with observed high resolution spectra of solar flares, and excellent agreement is found, in both hard x rays and microwaves. The future detailed application of this approach to solar flares is discussed, as are possible refinements to this theory.

Benka, Stephen G.

1991-01-01

143

Energetic Correlation Between Solar Flares and Coronal Mass Ejections  

NASA Technical Reports Server (NTRS)

We find a strong correlation between the kinetic energies (KEs) of the coronal mass ejections (CMEs) and the radiated energies of the associated solar flares for the events that occurred during the period of intense solar activity between 18 October and 08 November 2003. CME start times, speeds, mass and KEs were taken from Gopalswamy et al. (2005), who used SOHO/LASCO observations. The GOES observations of the associated flares were analyzed to find the peak soft X-ray (SXR) flux, the radiated energy in SXRs (L(sub sxR)), and the radiated energy from the emitting plasma across all wavelengths (L(sub hot)). RHESSI observations were also used to find the energy in non-thermal electrons, ions, and the plasma thermal energy for some events. For two events, SORCE/TIM observations of the total solar irradiance during a flare were also available to give the total radiated flare energy (L(sub total)).W e find that the total flare energies of the larger events are of the same order of magnitude as the CME KE with a stronger correlation than has been found in the past for other time intervals.

Dennis, Brian R.; Medlin, Drew A.; Haga, Leah; Schwartz, Richard a.; Tolbert, A. Kimberly

2007-01-01

144

MULTIWAVELENGTH ANALYSIS OF A SOLAR FLARE ON 2002 APRIL 15  

NASA Technical Reports Server (NTRS)

We carried out a multiwavelength analysis of the solar limb flare on 2002 April 15. The observations all indicate that the flare occurred in an active region with an asymmetric dipole magnetic configuration. The earlier conclusion that magnetic reconnection is occurring in a large-scale current sheet in this flare is M e r supported by these observations: (1) Several bloblike sources, seen in RHESSI 12-25 keV X-ray images later in the flare, appeared along a line above the flare loops. These indicate the continued presence of the current sheet and are likely to be magnetic islands in the stretched sheet produced by the tearing-mode instability. (2) A cusplike structure is seen in Nobeyama Radioheliogiaph (NoRH) 34 GHz microwave images around the time of the peak flare emission. We quantitatively demonstrate that the X-ray-emitting thermal plasma seen with RHESSI had a higher temperature than the microwave-emitting plasma seen with NoRH. Since the radio data preferentially see cooler thermal plasma, this result is consistent with the picture in which energy release occurs at progressively greater heights and the hard X-rays see hot new loops while the radio sees older cooling loops. The kinetic energy of the coronal mass ejection (CME) associated with this flare was found to be about 1 order of magnitude less than both the thermal energy in the hot plasma and the nonthermal energy carried by the accelerated electrons in the flare, as deduced from the RHESSI observations. This contrasts with the higher CME kinetic energies typically deduced for large flares.

Sui, Linhui; Holman, Gordon D.; White, Stephen M.; Zhang, Jie

2005-01-01

145

Variability of Thermosphere and Ionosphere Responses to Solar Flares  

NASA Technical Reports Server (NTRS)

We investigated how the rise rate and decay rate of solar flares affect the thermosphere and ionosphere responses to them. Model simulations and data analysis were conducted for two flares of similar magnitude (X6.2 and X5.4) that had the same location on the solar limb, but the X6.2 flare had longer rise and decay times. Simulated total electron content (TEC) enhancements from the X6.2 and X5.4 flares were 6 total electron content units (TECU) and approximately 2 TECU, and the simulated neutral density enhancements were approximately 15% -20% and approximately 5%, respectively, in reasonable agreement with observations. Additional model simulations showed that for idealized flares with the same magnitude and location, the thermosphere and ionosphere responses changed significantly as a function of rise and decay rates. The Neupert Effect, which predicts that a faster flare rise rate leads to a larger EUV enhancement during the impulsive phase, caused a larger maximum ion production enhancement. In addition, model simulations showed that increased E x B plasma transport due to conductivity increases during the flares caused a significant equatorial anomaly feature in the electron density enhancement in the F region but a relatively weaker equatorial anomaly feature in TEC enhancement, owing to dominant contributions by photochemical production and loss processes. The latitude dependence of the thermosphere response correlated well with the solar zenith angle effect, whereas the latitude dependence of the ionosphere response was more complex, owing to plasma transport and the winter anomaly.

Qian, Liying; Burns, Alan G.; Chamberlin, Philip C.; Solomon, Stanley C.

2011-01-01

146

SOLAR CYCLE VARIATIONS OF THE OCCURRENCE OF CORONAL TYPE III RADIO BURSTS AND A NEW SOLAR ACTIVITY INDEX  

SciTech Connect

This Letter presents the results of studies of solar cycle variations of the occurrence rate of coronal type III radio bursts. The radio spectra are provided by the Learmonth Solar Radio Observatory (Western Australia), part of the USAF Radio Solar Telescope Network (RSTN). It is found that the occurrence rate of type III bursts strongly correlates with solar activity. However, the profiles for the smoothed type III burst occurrence rate differ considerably from those for the sunspot number, 10.7 cm solar radio flux, and solar flare index. The type III burst occurrence rate (T3BOR) is proposed as a new index of solar activity. T3BOR provides complementary information about solar activity and should be useful in different studies including solar cycle predictions and searches for different periodicities in solar activity. This index can be estimated from daily results of the Automated Radio Burst Identification System. Access to data from other RSTN sites will allow processing 24 hr radio spectra in near-real time and estimating true daily values of this index. It is also shown that coronal type III bursts can even occur when there are no visible sunspots on the Sun. However, no evidence is found that the bursts are not associated with active regions. It is also concluded that the type III burst productivity of active regions exhibits solar cycle variations.

Lobzin, Vasili; Cairns, Iver H.; Robinson, Peter A. [School of Physics, University of Sydney, New South Wales (Australia)

2011-07-20

147

The Solar Flare Dynamics Imager: A Low-Cost Mission for This Solar Maximum  

Microsoft Academic Search

The Solar Flare Dynamics Imager (SolFDI) is a very low-cost flare mission proposed for this upcoming solar maximum. It is based on a small solar EUV telescope\\/spectrograph for Spartan Lite, NASA's new ejectable hitchhiker spacecraft. The experiment's main scientific objective is to investigate the spatial, temporal, and velocity structure of the upflowing hot plasma frequently observed in soft X-ray lines

J.-P. Wulser; M. E. Bruner; K. T. Strong; R. C. Canfield; J. L. Culhane; J. T. Mariska; R. Polidan

1997-01-01

148

A RECONNECTING CURRENT SHEET IMAGED IN A SOLAR FLARE  

SciTech Connect

Magnetic reconnection changes the magnetic field topology and powers explosive events in astrophysical, space, and laboratory plasmas. For flares and coronal mass ejections (CMEs) in the solar atmosphere, the standard model predicts the presence of a reconnecting current sheet, which has been the subject of considerable theoretical and numerical modeling over the last 50 years, yet direct, unambiguous observational verification has been absent. In this Letter, we show a bright sheet structure of global length (>0.25 R {sub sun}) and macroscopic width ((5-10)x10{sup 3} km) distinctly above the cusp-shaped flaring loop, imaged during the flare rising phase in EUV. The sheet formed due to the stretch of a transequatorial loop system and was accompanied by various reconnection signatures. This unique event provides a comprehensive view of the reconnection geometry and dynamics in the solar corona.

Liu Rui; Liu Chang; Wang Haimin [Space Weather Research Laboratory, Center for Solar-Terrestrial Research, NJIT, Newark, NJ 07102 (United States); Lee, Jeongwoo [Department of Physics, NJIT, Newark, NJ 07102 (United States); Wang, Tongjiang [Catholic University of America and NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Stenborg, Guillermo, E-mail: rui.liu@njit.ed [Interferometrics, Inc. Herndon, VA 20171 (United States)

2010-11-01

149

High Energy Gamma Ray Lines from Solar Flares  

NASA Technical Reports Server (NTRS)

A number of nuclear states have been identified as possible candidates for producing high-energy gamma-ray line emission in solar flares. For one high-energy line, resulting from the decay of C-12 (15.11 MeV), the excitation cross sections and branching radios have been studied extensively. In a solar flare, the ratio of the flux of 15. 11 -MeV gamma rays to the flux of 4.44-MeV gamma rays depends critically on the spectral index of the flare-accelerated protons. Prospects for being able to determine that spectral index using results from HESSI observations together with the analytic results of Crannell, Crannell, and Ramaty (1979) will be presented.

Crannell, Carol Jo

2000-01-01

150

The Solar Flare: A Strongly Turbulent Particle Accelerator  

E-print Network

Chapter 5 The Solar Flare: A Strongly Turbulent Particle Accelerator L. Vlahos, S. Krucker, and P) and particle acceleration during such an event are rarely discussed together in the same article. Many the topic of particle acceleration is often presented as an addi- tional complication to be addressed

California at Berkeley, University of

151

Particle acceleration in solar flares: observations versus numerical simulations  

E-print Network

Particle acceleration in solar flares: observations versus numerical simulations A O Benz, P C processes such as isotropization and magnetic trapping are made. Keywords: Particle acceleration, hard X. As the electric field of reconnection with possible parallel component capable of particle acceleration is limited

152

The energetic importance of accelerated electrons in solar flares  

Microsoft Academic Search

It has been claimed that a large fraction of the total energy released in a solar flare goes initially into accelerated electrons. These electrons generate the observed hard X-ray bremsstrahlung emission as they lose most of their energy by coulomb collisions in the lower corona and chromosphere to heat the plasma seen in soft X- rays. From several recent studies

B. Dennis; A. Veronig

2002-01-01

153

A laboratory solar flare simulation using colinear bipolar flux pairs  

Microsoft Academic Search

The plasma physics process of magnetic field line reconnection is experimentally studied in a Double Solenoid Device (DSD). The DSD incorporates the magnetic topology postulated as necessary for a process where the magnetic fields of two bipolar sun spot group merge and through reconnection produce a solar flare. Magnetic probing and Kerr Cell photography were used to diagnose the plasma

G. A. Crockett

1980-01-01

154

Diagnosis of accelerated electrons in solar flare with radio observation  

Microsoft Academic Search

Many problems still remain in particle acceleration in solar flare; energy release site, particle acceleration mechanism, ratio of nonthermal energy to whole released energy, maximum energy of particles, energy spectrum of accelerated particles, spatial and temporal scale of acceleration, difference of accelerated condition between ions and electrons, etc. In this study, we discuss the characteristics of accelerated electrons using statistical

Tomoko Kawate; Ayumi Asai; Kiyoshi Ichimoto

2010-01-01

155

Daily Solar Flare Forecasts Based on SDO Observations of Solar Magnetic Complexity  

NASA Astrophysics Data System (ADS)

We herewith present a new empirical model of strong solar flares. Neural networks have been trained to recognise the relationship between the magnetic field complexity of active regions and strong solar flares. SHARP (Space weather HMI Active Region Patches) parameters have been used as indicators of the magnetic complexity. GOES 1-8 X-ray fluxes described intensities of solar flares. The model's operational space weather forecast capabilities was tested against SHARP near real-time data. An operational version of the model will be available on the website of the Swedish Space Weather Center (SRC) of International Space Environment Service (ISES).

Lundstedt, Henrik; Andersson, Viktor

2014-05-01

156

Max '91: Flare research at the next solar maximum  

NASA Technical Reports Server (NTRS)

To address the central scientific questions surrounding solar flares, coordinated observations of electromagnetic radiation and energetic particles must be made from spacecraft, balloons, rockets, and ground-based observatories. A program to enhance capabilities in these areas in preparation for the next solar maximum in 1991 is recommended. The major scientific issues are described, and required observations and coordination of observations and analyses are detailed. A program plan and conceptual budgets are provided.

Dennis, Brian; Canfield, Richard; Bruner, Marilyn; Emslie, Gordon; Hildner, Ernest; Hudson, Hugh; Hurford, Gordon; Lin, Robert; Novick, Robert; Tarbell, Ted

1988-01-01

157

Theoretical studies on rapid fluctuations in solar flares  

NASA Technical Reports Server (NTRS)

Rapid fluctuations in the emission of solar bursts may have many different origins e.g., the acceleration process can have a pulsating structure, the propagation of energetic electrons and ions can be interrupted from plasma instabilities and finally the electromagnetic radiation produced by the interaction of electrostatic and electromagnetic waves may have a pulsating behavior in time. In two separate studies the conditions for rapid fluctuations in solar flare driven emission were analyzed.

Vlahos, Loukas

1986-01-01

158

Automatic Tracking of Active Regions and Detection of Solar Flares in Solar EUV Images  

NASA Astrophysics Data System (ADS)

Solar catalogs are frequently handmade by experts using a manual approach or semi-automated approach. The appearance of new tools is very useful because the work is automated. Nowadays it is impossible to produce solar catalogs using these methods, because of the emergence of new spacecraft that provide a huge amount of information. In this article an automated system for detecting and tracking active regions and solar flares throughout their evolution using the Extreme UV Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO) spacecraft is presented. The system is quite complex and consists of different phases: i) acquisition and preprocessing; ii) segmentation of regions of interest; iii) clustering of these regions to form candidate active regions which can become active regions; iv) tracking of active regions; v) detection of solar flares. This article describes all phases, but focuses on the phases of tracking and detection of active regions and solar flares. The system relies on consecutive solar images using a rotation law to track the active regions. Also, graphs of the evolution of a region and solar evolution are presented to detect solar flares. The procedure developed has been tested on 3500 full-disk solar images (corresponding to 35 days) taken from the spacecraft. More than 75 % of the active regions are tracked and more than 85 % of the solar flares are detected.

Caballero, C.; Aranda, M. C.

2014-05-01

159

NEW SOLAR EXTREME-ULTRAVIOLET IRRADIANCE OBSERVATIONS DURING FLARES  

SciTech Connect

New solar extreme-ultraviolet (EUV) irradiance observations from the NASA Solar Dynamics Observatory (SDO) EUV Variability Experiment provide full coverage in the EUV range from 0.1 to 106 nm and continuously at a cadence of 10 s for spectra at 0.1 nm resolution and even faster, 0.25 s, for six EUV bands. These observations can be decomposed into four distinct characteristics during flares. First, the emissions that dominate during the flare's impulsive phase are the transition region emissions, such as the He II 30.4 nm. Second, the hot coronal emissions above 5 MK dominate during the gradual phase and are highly correlated with the GOES X-ray. A third flare characteristic in the EUV is coronal dimming, seen best in the cool corona, such as the Fe IX 17.1 nm. As the post-flare loops reconnect and cool, many of the EUV coronal emissions peak a few minutes after the GOES X-ray peak. One interesting variation of the post-eruptive loop reconnection is that warm coronal emissions (e.g., Fe XVI 33.5 nm) sometimes exhibit a second large peak separated from the primary flare event by many minutes to hours, with EUV emission originating not from the original flare site and its immediate vicinity, but rather from a volume of higher loops. We refer to this second peak as the EUV late phase. The characterization of many flares during the SDO mission is provided, including quantification of the spectral irradiance from the EUV late phase that cannot be inferred from GOES X-ray diagnostics.

Woods, Thomas N.; Hock, Rachel; Eparvier, Frank; Jones, Andrew R. [Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303 (United States); Chamberlin, Phillip C.; Klimchuk, James A. [NASA Goddard Space Flight Center, Solar Physics Laboratory, Greenbelt, MD 20771 (United States); Didkovsky, Leonid; Judge, Darrell [Space Sciences Center, University of Southern California, Los Angeles, CA 90089 (United States); Mariska, John; Warren, Harry [Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States); Schrijver, Carolus J. [Lockheed Martin Solar and Astrophysics Laboratory, Palo Alto, CA 94304 (United States); Webb, David F. [Institute for Scientific Research, Boston College, Chestnut Hill, MA 02467 (United States); Bailey, Scott [Electrical and Computer Engineering Department, Virginia Tech, Blacksburg, VA 24061 (United States); Tobiska, W. Kent, E-mail: tom.woods@lasp.colorado.edu [Space Environment Technologies, Pacific Palisades, CA 90272 (United States)

2011-10-01

160

Solar Flare Impulsive Phase Observations from SDO and Other Observatories  

NASA Technical Reports Server (NTRS)

With the start of normal operations of the Solar Dynamics Observatory in May 2010, the Extreme ultraviolet Variability Experiment (EVE) and the Atmospheric Imaging Assembly (AIA) have been returning the most accurate solar XUV and EUV measurements every 10 and 12 seconds, respectively, at almost 100% duty cycle. The focus of the presentation will be the solar flare impulsive phase observations provided by EVE and AIA and what these observations can tell us about the evolution of the initial phase of solar flares. Also emphasized throughout is how simultaneous observations with other instruments, such as RHESSI, SOHO-CDS, and HINODE-EIS, will help provide a more complete characterization of the solar flares and the evolution and energetics during the impulsive phase. These co-temporal observations from the other solar instruments can provide information such as extending the high temperature range spectra and images beyond that provided by the EUV and XUV wavelengths, provide electron density input into the lower atmosphere at the footpoints, and provide plasma flows of chromospheric evaporation, among other characteristics.

Chamberlin, Phillip C.; Woods, Thomas N.; Schrijver, Karel; Warren, Harry; Milligan, Ryan; Christe, Steven; Brosius, Jeffrey W.

2010-01-01

161

EGRET High Energy Capability and Multiwavelength Flare Studies and Solar Flare Proton Spectra  

NASA Technical Reports Server (NTRS)

The accomplishments of the participation in the Compton Gamma Ray Observatory Guest investigator program is summarized in this report. The work involved the study of Energetic Gamma Ray Experiment Telescope (EGRET)/Total Absorption Shower Counter(TASC) flare data. The specific accomplishments were the use of the accelerator neutron measurements obtained at the University of New Hampshire to verify the TASC response function and to modify the TASC fitting program to include a high energy neutron contribution, and to determine a high energy neutron contribution to the emissions from the 1991 June 11, solar flare. The next step in the analysis of this event was doing fits to the TASC energy-loss spectra as a function of time. A significant hardening of the solar proton spectrum over time was found for the flare. Further data was obtained from the Yohkoh HXT time histories and images for the 1991 October 27 flare. The results to date demonstrate that the TASC spectral analysis contributes crucial information on the particle spectrum interacting at the Sun. The report includes a paper accepted for publication, a draft of a paper to be delivered at the 26th International Cosmic Ray Conference and an abstract of a paper to be presented at the Meeting of the American Physical Society.

Chupp, Edward L.

1998-01-01

162

Bulk Acceleration of Electrons in Solar Flares?  

NASA Astrophysics Data System (ADS)

In two recent papers it has been argued that RHESSI observations of two coronal above-the-loop-top hard X-ray sources, together with EUV observations, show that ALL the electrons in the source volumes must have been accelerated. I will briefly review these papers and show that the interpretation most consistent with the combined flare observations is multi-thermal, with hot, thermal plasma in the above-the-loop-top sources and only a fraction, albeit a substantial fraction, of the electrons accelerated. Thus, there is no credible scientific evidence for bulk acceleration of electrons in flares. Differential emission measure (DEM) models deduced from SDO/AIA and RHESSI data, including the inversion of the AIA data to determine DEM, will be discussed as part of this analysis.

Holman, Gordon D.

2014-06-01

163

Energetic electrons as an energy transport mechanism in solar flares  

NASA Technical Reports Server (NTRS)

A review is conducted of the observations and theory relating to the role of energetic electrons in the solar flare, with particular emphasis on discriminating between 'thermal' and 'nonthermal' origins of these electrons. Diagnostics in hard X-rays, especially those relating to the recent observations of the SMM and Hinotori satellites are discussed. Attention is briefly given to the response of the atmosphere to energy input in the form of high energy electrons, in particular through the diagnostics of both the Fe K-alpha feature and optically thin transition region lines such as OV. Finally, the relative roles of electron and proton heating in gamma-ray flare events are discussed.

Emslie, A. G.

1983-01-01

164

Effects of solar flares on the ionosphere of Mars.  

PubMed

All planetary atmospheres respond to the enhanced x-rays and ultraviolet (UV) light emitted from the Sun during a flare. Yet only on Earth are observations so continuous that the consequences of these essentially unpredictable events can be measured reliably. Here, we report observations of solar flares, causing up to 200% enhancements to the ionosphere of Mars, as recorded by the Mars Global Surveyor in April 2001. Modeling the altitude dependence of these effects requires that relative enhancements in the soft x-ray fluxes far exceed those in the UV. PMID:16497929

Mendillo, Michael; Withers, Paul; Hinson, David; Rishbeth, Henry; Reinisch, Bodo

2006-02-24

165

Acceleration of runaway electrons and Joule heating in solar flares  

NASA Technical Reports Server (NTRS)

The electric field acceleration of electrons out of a thermal plasma and the simultaneous Joule heating of the plasma are studied. Acceleration and heating timescales are derived and compared, and upper limits are obtained on the acceleration volume and the rate at which electrons can be accelerated. These upper limits, determined by the maximum magnetic field strength observed in flaring regions, place stringent restrictions upon the acceleration process. The role of the plasma resistivity in these processes is examined, and possible sources of anomalous resistivity are summarized. The implications of these results for the microwave and hard X-ray emission from solar flares are examined.

Holman, G. D.

1984-01-01

166

Earth Planets Space, 00, 000--000, 2000 Solar Flare Mechanism Based on Magnetic Arcade  

E-print Network

Earth Planets Space, 00, 000--000, 2000 Solar Flare Mechanism Based on Magnetic Arcade Reconnection of solar flares based on re­ sistive reconnection of magnetic field subject to continuous increase of magnetic shear in the arcade. The individual flaring process consists of magnetic reconnec­ tion of arcade

167

Measurements and Modeling of Total Solar Irradiance in X-class Solar Flares  

NASA Astrophysics Data System (ADS)

The Total Irradiance Monitor (TIM) from NASA's SOlar Radiation and Climate Experiment can detect changes in the total solar irradiance (TSI) to a precision of 2 ppm, allowing observations of variations due to the largest X-class solar flares for the first time. Presented here is a robust algorithm for determining the radiative output in the TIM TSI measurements, in both the impulsive and gradual phases, for the four solar flares presented in Woods et al., as well as an additional flare measured on 2006 December 6. The radiative outputs for both phases of these five flares are then compared to the vacuum ultraviolet (VUV) irradiance output from the Flare Irradiance Spectral Model (FISM) in order to derive an empirical relationship between the FISM VUV model and the TIM TSI data output to estimate the TSI radiative output for eight other X-class flares. This model provides the basis for the bolometric energy estimates for the solar flares analyzed in the Emslie et al. study.

Moore, Christopher Samuel; Chamberlin, Phillip Clyde; Hock, Rachel

2014-05-01

168

Upper limits on the total radiant energy of solar flares  

NASA Technical Reports Server (NTRS)

Limits on the total radiant energy of solar flares during the period February-November 1980 are established using data collected by the solar-constant monitor (ACRIM) on the Solar Maximum Mission satellite. Results show typical limits of 6 x 10 to the 29th erg/sec for a 32-second integration time, with 5-sigma statistical significance, for an impulsive emission. For a gradual component, about 4 x 10 to the 32nd ergs total radiant energy is found. The limits are determined to lie about an order of magnitude higher than the total radiant energy estimated from the various known emission components, which indicates the presence of a heretofore unknown dominant component of flare radiation.

Hudson, H. S.; Willson, R. C.

1983-01-01

169

Automated Feature Detection and Solar Flare Prediction Using SDO Data  

NASA Astrophysics Data System (ADS)

The importance of real-time processing of solar data especially for space weather applica-tions is increasing continuously, especially with the launch of SDO which will provide sev-eral times more data compared to previous solar satellites. In this paper, we will show the initial results of applying our Automated Solar Activity Prediction (ASAP) system for the short-term prediction of significant solar flares to SDO data. This automated system is cur-rently working in real-time mode with SOHO/MDI images and its results are available online (http://spaceweather.inf.brad.ac.uk/) whenever a new solar image available. This system inte-grates image processing and machine learning to deliver these predictions. A machine learning-based system is designed to analyse years of sunspots and flares data to extract knowledge and to create associations that can be represented using computer-based learning rules. An imaging-based real time system that provides automated detection, grouping and then clas-sification of recent sunspots based on the McIntosh classification and integrated within this system. The results of current feature detections and flare predictions of ASAP using SOHO data will be compared to those results of ASAP using SDO data and will also be presented in this paper.

Qahwaji, Rami; Ahmed, Omar; Colak, Tufan

170

X-Class: A Guide to Solar Flares - Duration: 3:02.  

NASA Video Gallery

Solar flares are classified according to their strength. The smallest ones are B-class, followed by C, M and X, the largest. A powerful X-class flare can create long lasting radiation storms, which...

171

Nonthermal Electrons in Solar Flares Derived from Microwave Jeongwoo Lee1  

E-print Network

Nonthermal Electrons in Solar Flares Derived from Microwave Spectra Jeongwoo Lee1 , Gelu M. Nita1 of particles -- radiation mechanisms: nonthermal -- Sun: corona -- Sun: flares -- Sun: radio radiation -- Sun

172

Extreme Ultra-Violet Spectroscopy of the Flaring Solar Chromosphere  

E-print Network

The extreme ultraviolet portion of the solar spectrum contains a wealth of diagnostic tools for probing the lower solar atmosphere in response to an injection of energy, particularly during the impulsive phase of solar flares. These include temperature and density sensitive line ratios, Doppler shifted emission lines and nonthermal broadening, abundance measurements, differential emission measure profiles, and continuum temperatures and energetics, among others. In this paper I shall review some of the advances made in recent years using these techniques, focusing primarily on studies that have utilized data from Hinode/EIS and SDO/EVE, while also providing some historical background and a summary of future spectroscopic instrumentation.

Milligan, Ryan O

2015-01-01

173

Thermal and non-thermal energies in solar flares  

E-print Network

The energy of the thermal flare plasma and the kinetic energy of the non-thermal electrons in 14 hard X-ray peaks from 9 medium-sized solar flares have been determined from RHESSI observations. The emissions have been carefully separated in the spectrum. The turnover or cutoff in the low-energy distribution of electrons has been studied by simulation and fitting, yielding a reliable lower limit to the non-thermal energy. It remains the largest contribution to the error budget. Other effects, such as albedo, non-uniform target ionization, hot target, and cross-sections on the spectrum have been studied. The errors of the thermal energy are about equally as large. They are due to the estimate of the flare volume, the assumption of the filling factor, and energy losses. Within a flare, the non-thermal/thermal ratio increases with accumulation time, as expected from loss of thermal energy due to radiative cooling or heat conduction. Our analysis suggests that the thermal and non-thermal energies are of the same magnitude. This surprising result may be interpreted by an efficient conversion of non-thermal energy to hot flare plasma.

Pascal Saint-Hilaire; Arnold O. Benz

2005-03-03

174

Temporal Variability of Ion Acceleration and Abundances in Solar Flares  

NASA Technical Reports Server (NTRS)

Solar flares accelerate both ions and electrons to high energies, and their X-ray and gamma-ray signatures not only probe the relationship between their respective acceleration, but also allow for the measurement of accelerated and ambient abundances. RHESSI observations have shown a striking close linear correlation of gamma-ray line fluence from accelerated ions greater than approximately 20 MeV and bremsstrahlung emission from relativistic accelerated electrons greater than 300 keV, when integrated over complete flares, suggesting a common acceleration mechanism. SMM/GRS observations, however, show a weaker correlation, and this discrepancy might be associated with previously observed electron-rich episodes within flares and/or temporal variability of gamma-ray line fluxes over the course of flares. We use the latest RHESSI gamma-ray analysis techniques to study the temporal behavior of the RHESSI flares, and determine what changes can be attributed to an evolving acceleration mechanism or to evolving abundances. We also discuss possible explanations for changing abundances.

Shih, Albert

2011-01-01

175

Temporal Variability of Ion Acceleration and Abundances in Solar Flares  

NASA Technical Reports Server (NTRS)

solar flares accelerate both ions and electrons to high energies, and their x-ray and gamma-ray signatures not only probe the relationship between their respective acceleration, but also allow for the measurement of accelerated and ambient abundances. RHESSI observations have shown a striking close linear correlation of gamma-ray line fluence from accelerated ions > approx 20 MeV and bremsstrahlung emission from relativistic accelerated electrons >300 kev, when integrated over complete flares, suggesting a common acceleration mechanism. SMM/GRS observations, however, show a weaker correlation, and this discrepancy might be associated with previously observed electron-rich episodes within flares and/or temporal variability of gamma-ray line fluxes over the course of flares. We use the latest RHESSI gamma-ray analysis techniques to study the temporal behavior of the RHESSI flares, and determine what changes can be attributed to an evolving acceleration mechanism or to evolving abundances. We also discuss possible explanations for changing abundances.

Shih, Albert Y.

2012-01-01

176

EGRET High Energy Capability and Multiwavelength Flare Studies and Solar Flare Proton Spectra  

NASA Technical Reports Server (NTRS)

UNH was assigned the responsibility to use their accelerator neutron measurements to verify the TASC response function and to modify the TASC fitting program to include a high energy neutron contribution. Direct accelerator-based measurements by UNH of the energy-dependent efficiencies for detecting neutrons with energies from 36 to 720 MeV in NaI were compared with Monte Carlo TASC calculations. The calculated TASC efficiencies are somewhat lower (by about 20%) than the accelerator results in the energy range 70-300 MeV. The measured energy-loss spectrum for 207 MeV neutron interactions in NaI were compared with the Monte Carlo response for 200 MeV neutrons in the TASC indicating good agreement. Based on this agreement, the simulation was considered to be sufficiently accurate to generate a neutron response library to be used by UNH in modifying the TASC fitting program to include a neutron component in the flare spectrum modeling. TASC energy-loss data on the 1991 June 11 flare was transferred to UNH. Also included appendix: Gamma-rays and neutrons as a probe of flare proton spectra: the solar flare of 11 June 1991.

Chupp, Edward L.

1997-01-01

177

Modelling the influence of photospheric turbulence on solar flare statistics.  

PubMed

Solar flares stem from the reconnection of twisted magnetic field lines in the solar photosphere. The energy and waiting time distributions of these events follow complex patterns that have been carefully considered in the past and that bear some resemblance with earthquakes and stockmarkets. Here we explore in detail the tangling motion of interacting flux tubes anchored in the plasma and the energy ejections resulting when they recombine. The mechanism for energy accumulation and release in the flow is reminiscent of self-organized criticality. From this model, we suggest the origin for two important and widely studied properties of solar flare statistics, including the time-energy correlations. We first propose that the scale-free energy distribution of solar flares is largely due to the twist exerted by the vorticity of the turbulent photosphere. Second, the long-range temporal and time-energy correlations appear to arise from the tube-tube interactions. The agreement with satellite measurements is encouraging. PMID:25247788

Mendoza, M; Kaydul, A; de Arcangelis, L; Andrade, J S; Herrmann, H J

2014-01-01

178

A laboratory solar flare simulation using colinear bipolar flux pairs  

NASA Astrophysics Data System (ADS)

The plasma physics process of magnetic field line reconnection is experimentally studied in a Double Solenoid Device (DSD). The DSD incorporates the magnetic topology postulated as necessary for a process where the magnetic fields of two bipolar sun spot group merge and through reconnection produce a solar flare. Magnetic probing and Kerr Cell photography were used to diagnose the plasma conditions to infer whether or not a solar flare could be simulated, and to test Sweet's flare hypothesis. The field topology is cylindrically symmetric and contains a semi-circular X-type neutral line and four distinct topological flux cells. Magnetic fields of up to 4 K gauss are generated by a ringing discharge from a 300 microfrequency high voltage capacitor bank through fourlinear solenoids embedded in an aluminum base plate. The solenoids are arranged in a colinear N-S-N-S array. The plasma is created by an intense induced electrical discharge through a low pressure Argon gas filling the bell jar above the solenoids. No substantial energy was stored in the induced plasma current systems, and no rapid energy release or flaring event was observed.

Crockett, G. A.

1980-08-01

179

Particle Acceleration by Fast Modes in Solar Flares  

E-print Network

We address the problem of particle acceleration in solar flares by fast modes which may be excited during the reconnection and undergo cascade and are subjected to damping. We extend the calculations beyond quasilinear approximation and compare the acceleration and scattering by transit time damping and gyroresonance interactions. We find that the acceleration is dominated by the so called transit time damping mechanism. We estimate the total energy transferred into particles, and show that our approach provides sufficiently accurate results We compare this rate with energy loss rate. Scattering by fast modes appears to be sufficient to prevent the protons from escaping the system during the acceleration. Confinement of electrons, on the other hand, requires the existence of plasma waves. Electrons can be accelerated to GeV energies through the process described here for solar flare conditions.

Huirong Yan; A. Lazarian; V. Petrosian

2008-05-08

180

RADIO EMISSION FROM ACCELERATION SITES OF SOLAR FLARES  

SciTech Connect

This Letter takes up the question of what radio emission is produced by electrons at the very acceleration site of a solar flare. Specifically, we calculate incoherent radio emission produced within two competing acceleration models-stochastic acceleration by cascading MHD turbulence and regular acceleration in collapsing magnetic traps. Our analysis clearly demonstrates that radio emission from acceleration sites (1) has sufficiently strong intensity to be observed by currently available radio instruments, and (2) has spectra and light curves that are distinctly different in these two competing models, which makes them observationally distinguishable. In particular, we suggest that some of the narrowband microwave and decimeter continuum bursts may be a signature of the stochastic acceleration in solar flares.

Li Yixuan; Fleishman, Gregory D. [Center for Solar-Terrestrial Research, New Jersey Institute of Technology, Newark, NJ 07102 (United States)], E-mail: yl89@njit.edu, E-mail: gfleishm@njit.edu

2009-08-10

181

Thermal Evolution and Radiative Output of Solar Flares Observed by the EUV Variability Experiment (EVE)  

NASA Astrophysics Data System (ADS)

This paper describes the methods used to obtain the thermal evolution and radiative output during solar flares as observed by the Extreme ultraviolet Variability Experiment (EVE) onboard the Solar Dynamics Observatory (SDO). How EVE measurements, due to the temporal cadence, spectral resolution and spectral range, can be used to determine how the thermal plasma radiates at various temperatures throughout the impulsive and gradual phase of flares is presented and discussed in detail. EVE can very accurately determine the radiative output of flares due to pre- and in-flight calibrations. Events are presented that show that the total radiated output of flares depends more on the flare duration than the typical GOES X-ray peak magnitude classification. With SDO observing every flare throughout its entire duration and over a large temperature range, new insights into flare heating and cooling as well as the radiative energy release in EUV wavelengths support existing research into understanding the evolution of solar flares.

Chamberlin, P. C.; Milligan, R. O.; Woods, T. N.

2012-07-01

182

A Statistical Analysis of Loop-Top Motion in Solar Limb Flares  

NASA Technical Reports Server (NTRS)

Previous studies of hot, thermal solar flare loops imaged with the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) have identified several flares for which the loop top shrinks downward early in the impulsive phase and then expands upward later in the impulsive phase (Sui & Holman 2003; Sui, Holman & Dennis 2004; Veronig et al. 2005). This early downward motion is not predicted by flare models. We study a statistical sample of RHESSI flares to assess how common this evolution is and to better characterize it. In a sample of 88 flares near the solar lin$ that show identifiable loop structure in RHESSI images, 66% (58 flares) showed downward loop-top motion followed by upward motion. We therefore conclude that the early downward motion is a frequent characteristic of flare loops. We obtain the distribution of the timing of the change from downward to upward motion relative to flare start and peak times. We also obtain the distributions of downward and upward speeds.

Holman, Gordon D.; Sui, Linhui; Brosius, D. G.; Dennis, Brian R.

2005-01-01

183

Ionospheric response to the solar flare of 14 July 2000  

Microsoft Academic Search

We present our observations of the global ionospheric response to the X-class solar flare that started the Bastille Day storm on 14 June 2000. The observations were made using the Low-Resolution Airglow and Aurora Spectrograph (LORAAS) instrument on the Advanced Research and Global Observation Satellite (ARGOS). The ARGOS is in a Sun-synchronous orbit at 0230\\/1430 LT at approximately 840 km

K. F. Dymond; S. A. Budzien; A. C. Nicholas; S. E. Thonnard; R. P. McCoy; R. J. Thomas; J. D. Huba; G. Joyce

2004-01-01

184

Statistical study of the reconnection rate in solar flares  

Microsoft Academic Search

Reconnection rate defined by (inflow velocity)\\/(Alfvn velocity) is one of the key parameters for understanding the physics of magnetic reconnection. In this paper we utilize the method for determining the reconnection rate from observational data suggested by Isobe et al. (2002) for 7 solar flares and 2 giant arcades. We have found that the reconnection rate is 0.0010.2, which is

H. Isobe; T. Morimoto; S. Eto; N. Narukage; K. Shibata

2002-01-01

185

Solar Flares, Type III Radio Bursts, CMEs, and Energetic Particles  

NASA Technical Reports Server (NTRS)

Despite the fact that it has been well known since the earliest observations that solar energetic particle events are well associated with solar flares it is often considered that the association is not physically significant. Instead, in large events, the particles are considered to be only accelerated at a shock driven by the coronal mass ejection (CME) that is also always present. If particles are accelerated in the associated flare, it is claimed that such particles do not find access to open field lines and therefore do not escape from the low corona. However recent work has established that long lasting type III radio bursts extending to low frequencies are associated with all prompt solar particle events. Such bursts establish the presence of open field lines. Furthermore, tracing the radio bursts to the lowest frequencies, generated near the observer, shows that the radio producing electrons gain access to a region of large angular extent. It is likely that the electrons undergo cross field transport and it seems reasonable that ions do also. Such observations indicate that particle propagation in the inner heliosphere is not yet fully understood. They also imply that the contribution of flare particles in major particle events needs to be properly addressed.

Cane, H. V.

2004-01-01

186

The Energetic Importance of Accelerated Electrons in Solar Flares  

NASA Technical Reports Server (NTRS)

It has been claimed that a large fraction of the total energy released in a solar flare goes initially into accelerated electrons. These electrons generate the observed hard X-ray bremsstrahlung emission as they lose most of their energy by coulomb collisions in the lower corona and chromosphere to heat the plasma seen in soft X-rays. From several recent studies of the Neupert Effect - the empirical result that for many flares the time integral of the hard X-ray emission closely matches the temporal variation of the soft X-ray emission - it appears that the fraction of the released energy going into accelerated electrons is lower, on average, for smaller flares. Also, from relative timing differences, about 25% of all flares are inconsistent with the Neupert Effect. The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is uniquely capable of investigating the Neupert Effect since it covers soft X-rays down to 3 keV (when both attenuators are out of the field of view) and hard X-rays with keV energy resolution. It has arcsecond-class angular resolution and sub-second time resolution. Several M-class flares have already been detected by RHESSI and I will present their detailed time histories for different energy ranges. I will also present hard and soft X-ray images that reveal the spatial relation between the hot plasma and the accelerated electrons. The results are in general agreement with the Neupert Effect, but they also suggest that there must be other heating mechanisms besides the thermalization of accelerated electrons, even during the impulsive phase.

Dennis, Brian R.; Oegerle, William (Technical Monitor)

2002-01-01

187

Spectral Diagnostics and Radiative Hydrodynamics of Solar Flares  

NASA Astrophysics Data System (ADS)

Solar flares are one of the most significant active phenomena in the solar atmosphere. It is involved in very complicated physical processes, including energy release, plasma instability, acceleration and propagation of energetic particles, radiation and dynamics of the flaring atmosphere, mass motions and ejections, and so on. Enhanced radiation during flares spans virtually the entire electromagnetic spectrum originating from different layers of the solar atmosphere. High energetic particles and strong radiations that are produced during the flare eruptions play a major role in space weather. Therefore, it is very important and necessary to study the mechanisms of solar flares. In this thesis, combined with ground and space observations, the theoretical calculations are used to study the spectral features and radiation mechanisms of solar flares. In particular, our research is concentrated on the diagnostics of non-thermal processes and origin of the white-light flares. The main contents are described as follows: (1) Different chromospheric lines are used to diagnose the heating mechanisms in flares. We calculate the H? and Ca II 8542 line profiles based on four different atmospheric models, including the effects of non-thermal electron beams with various energy fluxes. These two lines have different responses to the thermal and non-thermal effects, and can be used to diagnose the thermal and non-thermal heating processes. We apply our method to an X-class flare occurred on 2001 October 19 and find that the non-thermal effects at the outer edge of the flare ribbon are more notable than that at the inner edge, while the temperature at the inner edge seems higher. On the other hand, the results show that non-thermal effects increase rapidly in the rise phase and decrease quickly in the decay phase, but the atmospheric temperature can still keep relatively high for some time after getting to its maximum. For the two kernels that we analyze, the maximum energy fluxes of the electron beams are approximately 1010 erg cm-2 s-1 and 1011 erg cm-2 s-1, respectively. However, the atmospheric temperatures are not so high, i.e., lower than or slightly higher than that of the weak flare model F1 at the two kernels. We discuss the implications of the results for the two-ribbon flare models. (2) The white-light emission in solar flares is studied by radiative hydrodynamic simulations. It is believed that solar white-light flares (WLFs) originate from the lower chromosphere and upper photosphere. In particular, some recently observed WLFs show a very large continuum enhancement at 1.56 ?m where the opacity reaches its minimum. Therefore, it is important to make clear how the energy is transferred to the lower layers responsible for the production of WLFs. Based on radiative hydrodynamic simulations, we study the role of non-thermal electron beams in increasing the continuum emission. We vary the parameters of the electron beams and disk positions and compare the results with observations. The electron beam heated model can explain most of the observational white-light enhancements. (3) The effect of periodic non-thermal electron beam on chromospheric lines is studied. Heated by the periodic non-thermal electrons, the H? line center and wings show the same periodicity as the injected electrons. The line center and wings have different time delays compared to the bombarded electron beam. The line center has a relatively small phase difference. The red and blue wings also show different time delays. The blue wing shows a smaller phase difference compared to the red wing. The phase differences between the line center and wings can be explained by their different formation layers. However, the phase difference between the red and blue wings can not be fully explained in this manner. A possible explanation is that the macroscopic velocity field changes the emission and absorption features at the red and blue wings. The above results provide useful information for diagnosing the heating processes by using the fine time structures observ

Cheng, J. X.

2011-03-01

188

Detection of the Acceleration Site in a Solar Flare  

NASA Astrophysics Data System (ADS)

We report the observation of an unusual cold, tenuous solar flare (ApJL, v. 731, p. L19, 2011), which reveals itself via numerous and prominent non-thermal manifestations, while lacking any noticeable thermal emission signature. RHESSI hard X-rays and 0.1-18 GHz radio data from OVSA and Phoenix-2 show copious electron acceleration (1035 electrons per second above 10 keV) typical for GOES M-class flares with electrons energies up to 100 keV, but GOES temperatures not exceeding 6.1 MK. The HXR footpoints and coronal radio sources belong, supposedly, to a single magnetic loop, which departs strongly from the corresponding potential loop (obtained from a photospheric extrapolation) in agreement with the apparent need of a non-potential magnetic field structure to produce a flare. The imaging, temporal, and spectral characteristics of the flare have led us to a firm conclusion that the bulk of the microwave continuum emission from this flare was produced directly in the acceleration region. We found that the electron acceleration efficiency is very high in the flare, so almost all available thermal electrons are eventually accelerated. However, given a relatively small flaring volume and rather low thermal density at the flaring loop, the total energy release turned out to be insufficient for a significant heating of the coronal plasma or for a prominent chromospheric response giving rise to chromospheric evaporation. Some sort of stochastic acceleration process is needed to account for an approximately energy-independent lifetime of about 3 s for the electrons in the acceleration region. This work was supported in part by NSF grants AGS-0961867, AST-0908344, and NASA grants NNX10AF27G and NNX11AB49G to New Jersey Institute of Technology. This work was supported by a UK STFC rolling grant, STFC/PPARC Advanced Fellowship, and the Leverhulme Trust, UK. Financial support by the European Commission through the SOLAIRE and HESPE Networks is gratefully acknowledged.

Fleishman, Gregory D.; Kontar, E. P.; Nita, G. M.; Gary, D. E.

2011-05-01

189

ANALYSIS OF THE IMPULSIVE PHASE OF A SOLAR FLARE AT SUBMILLIMETER WAVELENGTHS  

E-print Network

of the energy released during solar events is transferred to ambient electrons, which gain energy up to few tens in the main flare site, as in Kundu et al. (2001). Solar high-frequency (mm and submm) radio observationsANALYSIS OF THE IMPULSIVE PHASE OF A SOLAR FLARE AT SUBMILLIMETER WAVELENGTHS JEAN PIERRE RAULIN1

California at Berkeley, University of

190

Solar Flare Impulsive Phase Emission Observed with SDO/EVE  

NASA Astrophysics Data System (ADS)

Differential emission measures (DEMs) during the impulsive phase of solar flares were constructed using observations from the EUV Variability Experiment (EVE) and the Markov-Chain Monte Carlo method. Emission lines from ions formed over the temperature range log Te = 5.8-7.2 allow the evolution of the DEM to be studied over a wide temperature range at 10 s cadence. The technique was applied to several M- and X-class flares, where impulsive phase EUV emission is observable in the disk-integrated EVE spectra from emission lines formed up to 3-4 MK and we use spatially unresolved EVE observations to infer the thermal structure of the emitting region. For the nine events studied, the DEMs exhibited a two-component distribution during the impulsive phase, a low-temperature component with peak temperature of 1-2 MK, and a broad high-temperature component from 7 to 30 MK. A bimodal high-temperature component is also found for several events, with peaks at 8 and 25 MK during the impulsive phase. The origin of the emission was verified using Atmospheric Imaging Assembly images to be the flare ribbons and footpoints, indicating that the constructed DEMs represent the spatially average thermal structure of the chromospheric flare emission during the impulsive phase.

Kennedy, Michael B.; Milligan, Ryan O.; Mathioudakis, Mihalis; Keenan, Francis P.

2013-12-01

191

Detection and Analysis of Neutron Emissions from Solar Flares  

NASA Astrophysics Data System (ADS)

The Sun provides unique opportunities to study particle acceleration at flares using data from detectors placed on the surface of the Earth and on board spacecrafts. Particles may gain high energies by several physical mechanisms. Differentiating between these possibilities is a fundamental problem of cosmic ray physics. In some of the most energetic events, neutrons produced in solar flares provide information that keeps the signatures of the acceleration site. A summary of some representative solar neutron events observed on the surface of the Earth, including associated X and gamma-ray observations from spacecrafts will be presented. The solar neutron event that occurred on September 7th 2005 and detected by several observatories at Earth is analyzed closely, since it produced evidence of acceleration of particles by the Sun to energies up to tens of GeV according to comparisons of data with detailed numerical simulations of a Solar Neutron Telescope. In addition, the progress in the plans to install a new Scintillator Solar Cosmic Ray Super Telescope (SciCRST) on the top of Mount Sierra Negra (4600m asl) in the east of Mexico will be discussed. Results obtained with a prototype of the SciCRST that operated in the mountain during 2010 and 2011 will be presented together with preliminary data of the SciCRST tests done in Puebla, Mexico (2200m asl).

Valdes-Galicia, J. F.

2013-05-01

192

Solar Flare Observations E N CYC LO PE D IA O F AS T R O N O MY AN D AS T R O PHYS I C S Solar Flare Observations  

E-print Network

have been a major, unexplained problem of astrophysics for more than a hundred years. History of solar flare observations The history of flare observations is a fascinating unfolding of a persisting enigma associated with major solar flares. These discov- eries could only mean that the flare phenomenon

193

Preliminary Results of Optical Solar Flare Spectra Studies Using a 40Channel Densitometer  

Microsoft Academic Search

Multi-channel CCD receivers are available for solar spectral research in the Astronomical Observatory of Shevchenko University of Kiev. The observational material considered here are 24 echelle spectrograms of the flare of July 15, 1981 and certain other disk and limb flares. Some temporal aspects of flare development are discussed, as well as properties of metal lines and the structure of

V. A. Ostapenko

1997-01-01

194

Microwave subsecond pulses in solar flares - source localization, emission mechanism  

NASA Astrophysics Data System (ADS)

The observations of bursts with fine temporal structures is one of few ways to study the primary energy release sites in solar flares. The localization of their sources in a flare region using the Siberian Solar Radio Telescope data (5.7 GHz) provide us with the unique possibility to determine plasma parameters, and to verify emission mechanisms. The simultaneous spectral observations (5.2 - 7.7 GHz) were provided by National Astronomical Observatories/Beijing spectropolarimeters. An analysis is made of the subsecond pulses of different types: short duration wide band pulses, U-type cm-bursts, the bursts with the "zebra" pattern. The suggestion is justified that in many cases the frequency drifts are response to the plasma density dynamics in the local sites in flare loops. It is argued that the conditions of emission escaping from the source strongly influent the apparent source sizes and the polarization degree of the subsecond sources. This research was supported by Grants 02-02-39030 and 03-02-16229 of RFBR, and E02-3.2-489 of Education department of Russia.

Altyntsev, A. T.; Kardapolova, N. N.; Kuznetsov, A. A.; Lesovoi, S. V.; Meshalkina, N. S.; Yan, Y.

195

Magnetic and Dynamical Photospheric Disturbances Observed During an M3.2 Solar Flare  

NASA Astrophysics Data System (ADS)

This Letter reports on a set of full-Stokes spectropolarimetric observations in the near-infrared He i 10830 spectral region covering the pre-flare, flare, and post-flare phases of an M3.2 class solar flare. The flare originated on 2013 May 17 and belonged to active region NOAA 11748. We detected strong He i 10830 emission in the flare. The red component of the He i triplet peaks at an intensity ratio to the continuum of about 1.86. During the flare, He i Stokes V is substantially larger and appears reversed compared to the usually larger Si i Stokes V profile. The photospheric Si i inversions of the four Stokes profiles reveal the following: (1) the magnetic field strength in the photosphere decreases or is even absent during the flare phase, as compared to the pre-flare phase. However, this decrease is not permanent. After the flare, the magnetic field recovers its pre-flare configuration in a short time (i.e., 30 minutes after the flare). (2) In the photosphere, the line of sight velocities show a regular granular up- and downflow pattern before the flare erupts. During the flare, upflows (blueshifts) dominate the area where the flare is produced. Evaporation rates of ? {{10}-3} and ? {{10}-4} g cm?2 s?1 have been derived in the deep and high photosphere, respectively, capable of increasing the chromospheric density by a factor of two in about 400 s.

Kuckein, C.; Collados, M.; Manso Sainz, R.

2015-02-01

196

Complex Dynamic Flows in Solar Flare Sheet Structures  

NASA Technical Reports Server (NTRS)

Observations of high-energy emission from solar flares often reveal the presence of large sheet-like structures, sometimes extending over a space comparable to the Sun's radius. Given that these structures are found between a departing coronal mass ejection and the post-eruption flare arcade, it is natural to associate the structure with a current sheet; though the relationship is unclear. Moreover, recent high-resolution observations have begun to reveal that the motions in this region are highly complex, including reconnection outflows, oscillations, and apparent wakes and eddies. We present a detailed first look at the complicated dynamics within this supra-arcade plasma, and consider implications for the interrelationship between the plasma and its embedded magnetic field.

McKenzie, David E.; Reeves, Katharine K.; Savage, Sabrina

2012-01-01

197

Measurements on a shock wave generated by a solar flare  

NASA Technical Reports Server (NTRS)

Shock waves generated by intense solar flares may be driven by a large amount of ejected mass, about 5 x 10 to the 16th g, and the total energy involved may be of the order of 10 to the 32nd erg. The shocks may have initial velocities of the order of 2,000 km/s and, in their exodus through the corona, may be accompanied by fast-moving optical transients, the emission of highly characteristic radio signatures and the acceleration of particles to quasi-relativistic velocities. Here, a review is presented of data on a high-velocity shock generated by a flare on 18 August 1979, 1400 UT, and comments are provided on some previously deduced velocities for the shock. Attention is given to a model, based on current computer programs to account for the overall characteristics of the shock as it propagated through the corona and the interplanetary plasma.

Maxwell, A.; Dryer, M.

1982-01-01

198

Measurements on a shock wave generated by a solar flare  

NASA Astrophysics Data System (ADS)

Shock waves generated by intense solar flares may be driven by a large amount of ejected mass, about 5 x 10 to the 16th g, and the total energy involved may be of the order of 10 to the 32nd erg. The shocks may have initial velocities of the order of 2,000 km/s and, in their exodus through the corona, may be accompanied by fast-moving optical transients, the emission of highly characteristic radio signatures and the acceleration of particles to quasi-relativistic velocities. Here, a review is presented of data on a high-velocity shock generated by a flare on 18 August 1979, 1400 UT, and comments are provided on some previously deduced velocities for the shock. Attention is given to a model, based on current computer programs to account for the overall characteristics of the shock as it propagated through the corona and the interplanetary plasma.

Maxwell, A.; Dryer, M.

1982-11-01

199

Singly charged energetic helium emitted in solar flares  

NASA Technical Reports Server (NTRS)

First direct charge state measurements of 0.41-1.05 MeV per nucleon helium accelerated at the sun reveal surprisingly large abundances of singly ionized helium, with typical He(+)/He(++) ratios between 0.04 and 0.21. This unexpected overabundance of He(+) was observed in each of the three large solar-flare particle events which occurred between 1978 August and 1979 October. The data were obtained with the Max-Planck-Institut/University of Maryland Experiment on board the ISEE-3 spacecraft. The observations suggest either strong coronal temperature inhomogeneities including cool regions of approximately 100,000 K or injection of 'cold' chromospheric/photospheric material into the flare acceleration region.

Hovestadt, D.; Hoefner, H.; Klecker, B.; Scholer, M.; Gloeckler, G.; Ipavich, F. M.; Fan, C. Y.; Fisk, L. A.; Ogallagher, J. J.

1981-01-01

200

Max 1991: Flare Research at the Next Solar Maximum. Workshop 1: Scientific Objectives  

NASA Technical Reports Server (NTRS)

The purpose of the Max 1991 program is to gather coordinated sets of solar flare and active region data and to perform interpretive and theoretical research aimed at understanding flare energy storage and release, particle acceleration, flare energy transport, and the propagation of flare effects to Earth. The workshop was divided into four areas of concern: energy storage, energy release, particle acceleration, and energy transport.

Canfield, Richard C.; Dennis, Brian R.

1988-01-01

201

The Soft X-Ray/Microwave Ratio of Solar and Stellar Flares and Coronae  

NASA Technical Reports Server (NTRS)

We have carried out plasma diagnostics of solar flares using soft X-ray (SXR) and simultaneous microwave observations and have compared the ratio of X-ray to microwave luminosities of solar flares with various active late-type stars available in the published literature. Both the SXR low-level ('quiescent') emission from stellar coronae and the flaring emission from the Sun and stars are generally interpreted as thermal radiations of coronal plasmas. On the other hand, the microwave emission of stars and solar flares is generally attributed to an extremely hot or nonthermal population of electrons. Solar flare SXR are conventionally measured in a narrower and harder passband than the stellar sources. Observations of the GOES-2 satellite in two energy channels have been used to estimate the luminosity of solar flares as it would appear in the ROSAT satellite passband. The solar and stellar flare luminosities fit well at the lower end of the active stellar coronae. The flare SXR/microwave ratio is similar to the ratio for stellar coronae. The average ratio follows a power-law relation L(sub X) varies as L(sub R)(sup 0.73 +/- 0.03) over 10 orders of magnitude from solar microflares to RS CVn and FK Com-type coronae. Dwarf Me and Ke stars, and RS CVn stars are also compatible with a linear SXR/microwave relation, but the ratio is slightly different for each type of star. Considering the differences between solar flares, stellar flares and the various active stellar coronae, the similarity of the SXR/microwave ratios is surprising. It suggests that the energetic electrons in low-level stellar coronae observed in microwaves are related in a similar way to the coronal thermal plasma as flare electrons to the flare thermal plasma, and, consequently, that the heating mechanism of active stellar coronae is a flare-like process.

Benz, A. O.; Guedel, M.

1994-01-01

202

Relationship of Ground Level Enhancement with Solar Flare, Coronal Mass Ejection and Solar Energetic Particle  

NASA Astrophysics Data System (ADS)

Ground level enhancement (GLE) is the sudden increase in the cosmic ray intensity (CRI) which is thought to be caused by solar eruption. In this study we have analyzed the CRI data from 1968 through 2008 registered by several Neutron Monitors and deduced increase rate (%) of GLE events using the 5-minute data mainly from Oulu Neutron Monitor (ONM) and Calgary Neutron Monitor (CNM). To investigate the relations of GLEs with solar X-ray flares, coronal mass ejections (CMEs) and solar energetic particles (SEPs), we have inspected the peak time and peak intensity differences of GLE events. As results, we have found that the peak time (UT) differences vary mostly within 20 minutes when the peak intensities vary mostly within 50% at CNM and ONM. It has been observed that GLE events are associated with strong flares as well as fast /halo CMEs. Almost 62% of the flares associated with strong GLE were originated from south-west active region while 38% of the flares were originated from north-west active region. On an exception, an apparently weaker flare associated with GLE is not actually a weaker flare, rather a large flare existing behind the limb. The average of GLE associated CMEs is (1916.60 km/s) much faster than the average (458.53 km/s) of all CMEs. The fluences of the high energy proton flux (PF > 100MeV) associated with the GLE are stronger than those associated with non-GLE events. We will introduce our results briefly and discuss on the relationship of GLE with flare, CME and SEP.

Firoz, K. M.; Cho, K.; Lee, J.; Kumar, P.; Hwang, J.; Oh, S. Y.

2009-12-01

203

On the Importance of the Flare's Late Phase for the Solar Extreme Ultraviolet Irradiance  

NASA Technical Reports Server (NTRS)

The new solar extreme ultraviolet (EUV) irradiance observations from NASA Solar Dynamics Observatory (SDO) have revealed a new class of solar flares that are referred to as late phase flares. These flares are characterized by the hot 2-5 MK coronal emissions (e.g., Fe XVI 33.5 nm) showing large secondary peaks that appear many minutes to hours after an eruptive flare event. In contrast, the cool 0.7-1.5 MK coronal emissions (e.g., Fe IX 17.1 nm) usually dim immediately after the flare onset and do not recover until after the delayed second peak of the hot coronal emissions. We refer to this period of 1-5 hours after the fl amrea sin phase as the late phase, and this late phase is uniquely different than long duration flares associated with 2-ribbon flares or large filament eruptions. Our analysis of the late phase flare events indicates that the late phase involves hot coronal loops near the flaring region, not directly related to the original flaring loop system but rather with the higher post-eruption fields. Another finding is that space weather applications concerning Earth s ionosphere and thermosphere need to consider these late phase flares because they can enhance the total EUV irradiance flare variation by a factor of 2 when the late phase contribution is included.

Woods, Thomas N.; Eparvier, Frank; Jones, Andrew R.; Hock, Rachel; Chamberlin, Phillip C.; Klimchuk, James A.; Didkovsky, Leonid; Judge, Darrell; Mariska, John; Bailey, Scott; Tobiska, W. Kent; Schrijver, Carolus J.; Webb, David F.; Warren, Harry

2011-01-01

204

The isotopic composition of solar flare accelerated magnesium  

NASA Technical Reports Server (NTRS)

Measurements of the abundances of three isotopes of magnesium in solar energetic particles are reported. Data were obtained from the Heavy Isotope Spectrometer Telescope on board the ISEE 3 spacecraft during a large solar particle event following the 2B solar flare of September 23, 1978. A two-dimensional maximum likelihood analysis of the mass determinations for each event, which were taken with a resolution of 0.23 amu, indicates a Mg-25/Mg-24 ratio of 0.14 (+0.05, -0.02) and a Mg-26/Mg-24 ratio of 0.15 (+0.04, -0.03) in the energy interval 12-36 MeV/n. The results are consistent with terrestrial magnesium isotope abundances.

Mewaldt, R. A.; Spalding, J. D.; Stone, E. C.; Vogt, R. E.

1981-01-01

205

Preliminary analyses of solar flare effects on geomagnetic H component at equatorial and low latitudes  

NASA Astrophysics Data System (ADS)

The study of solar flare effect (SFE) on geomagnetic H component at mid latitudes was carried out using data from INTERMAGNET website. M and X solar flare effects on three stations, Addis Ababa (AAE), Bangui (BNG), and Tamanrasset (TAM) were investigated. It was found that the ratio is greater than zero for all the three stations used, hence SFE enhances geomagnetic field in the equatorial and low latitudes. It was equally noted that the SFE on geomagnetic field is not just a simple augmentation at the pre-flare ionospheric currents over these stations. It is concluded that both pre-flare and solar flare amplitude variations of H are high in low and equatorial stations. Keywords: Solar flare, geomagnetic component, latitudes.

Ugonabo, Obiageli Josephine; Ugwu, Ernest Benjamin Ikechukwu; Nneka Okeke, Francisca

206

Relaxation of magnetic field relative to plasma density during solar flares  

NASA Astrophysics Data System (ADS)

We investigated the variations of 74 microwave ZP structures observed by Chinese Solar Broadband Radio Spectrometer at 2.6-3.8 GHz in 9 solar flares, found that the ratio between the plasma density scale height LN and the magnetic field scale height LB in emission source displays a tendency of decrease during the flaring process, indicates that LB increases faster than the LN during solar flares. The detailed analysis of the step-wise decrease of LN/LB in three typical X-class flares reveals the magnetic field relaxation relative to the plasma density.

Yu, Sijie; Yan, Yihua; Tan, Baolin

2013-07-01

207

Reconnection in substorms and solar flares: analogies and differences  

SciTech Connect

Magnetic reconnection is the crucial process in the release of magnetic energy associated with magnetospheric substorms and with solar flares. On the basis of three-dimensional resistive MHD simulations we investigate similarities and differences between the two scenarios. We address in particular mechanisms that lead to the onset of reconnection and on energy release, transport, and conversion mechanisms. Analogous processes might exist in the motion of field line footpoints on the sun and in magnetic flux addition to the magnetotail. In both cases such processes might lead to a loss of neighboring equilibrium, characterized by the formation of very thin embedded current sheet, which acts as trigger for reconnection. We find that Joule (or ohmic) dissipation plays only a minor role in the overall energy transfer associated with reconnection. The dominant transfer of released magnetic energy occurs to electromagnetic energy (Poynting) flux and to thermal energy transport as enthalpy flux. The former dominates in low-beta, specifically initially force-free current sheets expected for the solar corona, while the latter dominates in high-beta current sheets, such as the magnetotail. In both cases the outflow from the reconnection site becomes bursty, i.e. spatially and temporally localized, yet carrying most of the outflow energy. Hence an analogy might exist between bursty bulk flows (BBFs) in the magnetotail and pulses of Poynting flux in solar flares.

Birn, Joachim [Los Alamos National Laboratory

2008-01-01

208

Relating magnetic field strengths to hard X-ray emission in solar flares  

Microsoft Academic Search

The observation of hard X-ray (HXR) emission in solar flares provides important diagnostic information about the acceleration and subsequent transport of energetic electrons in the flare process. However, while hard X-rays are thought to be emitted from the flare footpoints through thick-target bremsstrahlung interactions, the details of the transport of accelerated electrons through the solar atmosphere still remains unclear. Trapping

C. P. Goff; S. A. Matthews; L. van Driel-Gesztelyi; L. K. Harra

2004-01-01

209

The directivity of high-energy emission from solar flares - Solar Maximum Mission observations  

NASA Technical Reports Server (NTRS)

The data base consisting of flares detected by the gamma-ray spectrometer (GRS) on board the Solar Maximum Mission (SMM) satellite is used to study the directivity of high-energy radiation. A number of observations are presented that, strongly indicate that the high-energy emission from flares is anisotropic. They are the following: (1) the fraction of events detected at energies above 300 keV near the limb is higher than is expected for isotropically emitting flares; (2) there is a statistically significant center-to-limb variation in the 300 keV to 1 MeV spectra of flares detected by the SMM GRS; (3) the 25-200 keV hard X-ray spectra measured during the impulsive phase by the SMM GRS show a center-to-limb variation; and (4) nearly all of the events detected at above 10 MeV are located near the limb.

Vestrand, W. Thomas; Forrest, D. J.; Chupp, E. L.; Rieger, E.; Share, G. H.

1987-01-01

210

The reason for magnetospheric substorms and solar flares  

NASA Technical Reports Server (NTRS)

It has been proposed that magnetospheric substorms and solar flares are a result of the same mechanism. It is suggested that this mechanism is connected with the escape, or attempted escape, of energized plasma from a region of closed magnetic field lines bounded by a magnetic bottle. In the case of the earth, it must be plasma that is able to maintain a discrete auroral arc, and it is proposed that the cross-tail current connected to the arc is filamentary in nature to provide the field-aligned current sheet above the arc.

Heikkila, W. J.

1983-01-01

211

Impulsive phase solar flare X-ray polarimetry  

NASA Technical Reports Server (NTRS)

The pioneering observational work in solar flare X-ray polarimetry was done in a series of satellite experiments by Tindo and his collaborators in the Soviet Union; initial results showed high levels of polarization in X-ray flares (up to 40%), although of rather low statistical significance, and these were generally interpreted as evidence for strong beaming of suprathermal electrons in the flare energy release process. However, the results of the polarimeter flown by the Columbia Astrophysics Laboratory as part of the STS-3 payload on the Space Shuttle by contrast showed very low levels of polarization. The largest value (observed during the impulsive phase of a single event) was 3.4% + or - 2.2%. At the same time but independent of the observational work, Leach and Petrosian (1983) showed that the high levels of polarization in the Tindo results were difficult to understand theoretically, since the electron beam is isotropized on an energy loss timescale. A subsequent comparison by Leach, Emslie, and Petrosian (1985) of the impulsive phase STS-3 result and the above theoretical treatment shows that the former is consistent with several current models and that a factor of approximately 3 improvement in sensitivity is needed to distinguish properly among the possibilities.

Chanan, Gary; Emslie, A. Gordon; Novick, Robert

1986-01-01

212

Space radiation dose analysis for solar flare of August 1989  

NASA Technical Reports Server (NTRS)

Potential dose and dose rate levels to astronauts in deep space are predicted for the solar flare event which occurred during the week of August 13, 1989. The Geostationary Operational Environmental Satellite (GOES-7) monitored the temporal development and energy characteristics of the protons emitted during this event. From these data, differential fluence as a function of energy was obtained in order to analyze the flare using the Langley baryon transport code, BRYNTRN, which describes the interactions of incident protons in matter. Dose equivalent estimates for the skin, ocular lens, and vital organs for 0.5 to 20 g/sq cm of aluminum shielding were predicted. For relatively light shielding (less than 2 g/sq cm), the skin and ocular lens 30-day exposure limits are exceeded within several hours of flare onset. The vital organ (5 cm depth) dose equivalent is exceeded only for the thinnest shield (0.5 g/sq cm). Dose rates (rem/hr) for the skin, ocular lens, and vital organs are also computed.

Nealy, John E.; Simonsen, Lisa C.; Sauer, Herbert H.; Wilson, John W.; Townsend, Lawrence W.

1990-01-01

213

SDO's View of May 5, 2010 Solar Flare - With Timeline - Duration: 0:11.  

NASA Video Gallery

This video shows a composite view of the solar flare on May 5, 2010, taken by the Solar Dynamics Observatory's (SDO) Atmospheric Imaging Assembly (AIA) cameras in multiple wavelengths (211, 193, 17...

214

SOHO Captures CME From X5.4 Solar Flare - Duration: 0:05.  

NASA Video Gallery

The Solar Heliospheric Observatory (SOHO) captured this movie of the sun's coronal mass ejection (CME) associated with an X5.4 solar flare on the evening of March 6, 2012. The extremely fast and en...

215

Exploring Magnetism in Solar Flares: A Teachers' Magnetism Activity Guide for Grades 8-12  

NSDL National Science Digital Library

Exploring Magnetism in Solar Flares is part of a series of guides highlighting the importance of magnetism in Earth and space sciences. It contains four activities exploring solar flares while addressing science, math, and literacy standards. The material is appropriate for grades 8-12. Lessons are available for download in PDF format.

2011-04-20

216

A SOLAR FLARE MODEL IN BETWEEN MHD AND CELLULAR AUTOMATON* Heinz Isliker1  

E-print Network

A SOLAR FLARE MODEL IN BETWEEN MHD AND CELLULAR AUTOMATON* Heinz Isliker1 , Anastasios Anastasiadis ­ MHD ABSTRACT The last decade several cellular automata (CA) models have been developed in order) and the reproduction of the observed solar flare statistics. On the other hand the energy release process has been

Anastasiadis, Anastasios

217

Dynamic Magnetography of Solar Flaring Loops Gregory D. Fleishman1,2  

E-print Network

with shaking, which allows the derivation of the magnetic field and other parameters along a solar flaring loop). However, the release of free magnetic energy in solar flares implies that the coronal magnetic field magnetic field strength and orientation relative to the line of sight. Recently Qiu et al. (2009

218

Global Energetics of Solar Flares. I. Magnetic Energies  

NASA Astrophysics Data System (ADS)

We present the first part of a project on the global energetics of solar flares and coronal mass ejections that includes about 400 M- and X-class flares observed with Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). We calculate the potential (Ep ), the nonpotential (E np) or free energies (E free = E np - Ep ), and the flare-dissipated magnetic energies (E diss). We calculate these magnetic parameters using two different NLFFF codes: the COR-NLFFF code uses the line-of-sight magnetic field component Bz from HMI to define the potential field, and the two-dimensional (2D) coordinates of automatically detected coronal loops in six coronal wavelengths from AIA to measure the helical twist of coronal loops caused by vertical currents, while the PHOT-NLFFF code extrapolates the photospheric three-dimensional (3D) vector fields. We find agreement between the two codes in the measurement of free energies and dissipated energies within a factor of <~ 3. The size distributions of magnetic parameters exhibit powerlaw slopes that are approximately consistent with the fractal-diffusive self-organized criticality model. The magnetic parameters exhibit scaling laws for the nonpotential energy, Enp \\propto E_p1.02, for the free energy, Efree \\propto E_p1.7 and Efree \\propto B\\varphi 1.0 L1.5, for the dissipated energy, Ediss \\propto E_p1.6 and Ediss \\propto Efree0.9, and the energy dissipation volume, V \\propto Ediss1.2. The potential energies vary in the range of Ep = 1 1031-4 1033 erg, while the free energy has a ratio of E free/Ep ? 1%-25%. The Poynting flux amounts to F flare ? 5 108-1010 erg cm-2 s-1 during flares, which averages to F AR ? 6 106 erg cm-2 s-1 during the entire observation period and is comparable with the coronal heating rate requirement in active regions.

Aschwanden, Markus J.; Xu, Yan; Jing, Ju

2014-12-01

219

The Observed Spectral Evolution of Solar Flare Hard X-Ray Emission  

NASA Technical Reports Server (NTRS)

The spectral evolution of flare emission may be characterized using color-color diagrams (CCDs), a technique which has been widely employed by the astrophysics community, but not yet by the solar flare community. CCDs are constructed for a sample of flares observed simultaneously by CGRO/BATSE and Yohkoh/HXT. It is found that flare spectral evolution follows one of only a few patterns, which generally evolve differently than the soft-hard-soft pattern put forth as the norm in previous work. The implications for the nature of flare energy release and acceleration/propagation models are discussed

Newton, Elizabeth; Giblin, Timothy

1999-01-01

220

Energy spectra of ions from impulsive solar flares  

NASA Technical Reports Server (NTRS)

A study of the energy spectra of ions from impulsive solar flares in the 0.1 to 100 MeV region is reported with data from the combined observations of experiments on the ISEE 3 and IMP 8 spacecraft. Most of the events studied are dominated by He, and these He spectra show a persistent steepening or break above about 10 MeV resulting in an increase in the power-law spectral indices from about 2 to about 3.5 or more. One event, dominated by protons, shows a clear maximum in the spectrum near 1 MeV. If the rollover in the spectrum below 1 MeV is interpreted as a consequence of matter traversal in the solar atmosphere, then the source of the acceleration would lie only about 800 km above the photosphere, well below the corona. An alternative interpretation is that trapping in the acceleration region directly causes a peak in the spectrum.

Reames, D. V.; Richardson, I. G.; Wenzel, K.-P.

1991-01-01

221

Energy spectra of ions from impulsive solar flares  

NASA Technical Reports Server (NTRS)

A study of the energy spectra of ions from impulsive solar flares in the 0.1-100 MeV region is reported. Most of the events studied are dominated by He and these He spectra show a persistent steepening or break above about 10 MeV resulting in an increase in the power-law spectral indices from about 2 to about 3.5 or more. Spectra of H, He-3, O, and Fe have spectral indices that are consistent with a value of about 3.5 above about 2 MeV/amu. One event, dominated by protons, shows a clear maximum in the spectrum near 1 MeV. If the rollover in the spectrum below 1 MeV is interpreted as a consequence of matter traversal in the solar atmosphere, then the source of the acceleration would lie only about 800 km above the photosphere, well below the corona. Alternative interpretations are that trapping in the acceleration region directly causes a peak in the resulting ion spectrum or that low-energy particles encounter significant additional scattering during transport from the flare.

Reames, D. V.; Richardson, I. G.; Wenzel, K.-P.

1992-01-01

222

Multispacecraft Observations of Solar Flare Particles in the Inner Heliosphere  

NASA Technical Reports Server (NTRS)

For a number of impulsive solar particle events we examine variations of maximum intensities and times to maximum intensity as a function of longitude, using observations from the two Helios spacecraft and near the Earth. We find that electrons in the MeV range can be detected more than 80 deg. from the flare longitude, corresponding to a considerably wider "well connected" region than that (approx. 20 deg. half width) reported for He-3-rich impulsive solar events. This wide range and the decrease of peak intensities with increasing connection angle revive the concept of some propagation process in the low corona that has a diffusive nature. Delays to the intensity maximum are not systematically correlated with connection angles. We argue that interplanetary scattering parallel to the average interplanetary magnetic field, that varies with position in space, plays an important role in flare particle events. In a specific case variations of the time profiles with radial distance and with particle rigidity are used to quantitatively confirm spatial diffusion. For a few cases near the edges of the well connected region the very long times to maximum intensity might result from interplanetary lateral transport.

Wibberenz, G.; Cane, H. V.

2007-01-01

223

Statistics and Classification of the Microwave Zebra Patterns Associated with Solar Flares  

NASA Astrophysics Data System (ADS)

The microwave zebra pattern (ZP) is the most interesting, intriguing, and complex spectral structure frequently observed in solar flares. A comprehensive statistical study will certainly help us to understand the formation mechanism, which is not exactly clear now. This work presents a comprehensive statistical analysis of a big sample with 202 ZP events collected from observations at the Chinese Solar Broadband Radio Spectrometer at Huairou and the Ond?ejov Radiospectrograph in the Czech Republic at frequencies of 1.00-7.60 GHz from 2000 to 2013. After investigating the parameter properties of ZPs, such as the occurrence in flare phase, frequency range, polarization degree, duration, etc., we find that the variation of zebra stripe frequency separation with respect to frequency is the best indicator for a physical classification of ZPs. Microwave ZPs can be classified into three types: equidistant ZPs, variable-distant ZPs, and growing-distant ZPs, possibly corresponding to mechanisms of the Bernstein wave model, whistler wave model, and double plasma resonance model, respectively. This statistical classification may help us to clarify the controversies between the existing various theoretical models and understand the physical processes in the source regions.

Tan, Baolin; Tan, Chengming; Zhang, Yin; Mszrosov, H.; Karlick, M.

2014-01-01

224

A Helioseismic Survey to Investigate Relationships between Subsurface Flows beneath Large Active Regions and Solar Flares  

NASA Astrophysics Data System (ADS)

A survey of the subsurface flow properties of about 120 of the largest active regions, determined from the application of helioseismic holography to Dopplergrams obtained with the HMI instrument onboard the Solar Dynamics Observatory, is being carried out. The overriding goal is to characterize differences in the subsurface flows between active regions associated with eruptive flares and the flows observed in relatively quiescent regions. Applications to flare forecasting comprise only one part of this investigation, since the potential response of the subsurface environment to eruptive events during and after their occurrence is also of scientific interest. Other priorities include understanding the limitations of the helioseismic methods, identifying and correcting systematic effects, and validating the reliability of the measurements using artificial data. While inversions to determine the variation with depth of subsurface flows are planned, preliminary results will be discussed which make use of proxies for near-surface depth-integrated properties, including the horizontal component of the flow divergence and the vertical component of the flow vorticity.This work is supported by the Solar Terrestrial Program of the National Science Foundation, through grant AGS-1127327, and by the National Oceanic and Atmospheric Administration SBIR program.

Braun, Douglas; Leka, K D.; Barnes, Graham

2014-06-01

225

Universality in solar flares, magnetic storms, earthquakes and pre-seismic electromagnetic emissions by means of nonextensivity  

NASA Astrophysics Data System (ADS)

The field of study of complex systems holds that the dynamics of complex systems are founded on universal principles that may used to describe disparate problems ranging from particle physics to economies of societies. A corollary is that transferring ideas and results from investigators in hitherto disparate areas will cross-fertilize and lead to important new results. In this contribution we investigate a universal behavior, if any, in solar flares, magnetic storms, earthquakes and pre-seismic electromagnetic (EM) emissions. A common characteristic in the dynamics of the above-mentioned four phenomena is that the energy release is basically fragmentary, the events being composed of elementary building blocks. By analogy with earthquakes, magnitude of the magnetic storms, solar flares and pre-seismic electromagnetic emissions can be appropriately defined. The key-question we can ask in the frame of complexity is whether the magnitude distribution of earthquakes, magnetic storms, solar flares and pre-fracture EM emissions obeys to the same law. A central property of the magnetic storm, solar flare, and earthquake preparation process is the possible occurrence of coherent large-scale collective with a very rich structure resulting from the repeated nonlinear interactions among its constituents. Consequently, the non-extensive statistical mechanics is an appropriate arena to investigate universality, if any, in magnetic storm, solar flare, earthquake and pre-failure electromagnetic emission occurrence. A model for earthquake dynamics consisting of two rough profiles interacting via fragments filling the gap has been recently introduced by Solotongo-Costa and Posadas [2004]. An energy distribution function, which gives the Gutenberg-Richter law as a particular case, is analytically deduced. Therefore, the primary question we can ask in the frame of complexity is whether the aforementioned equation not only successfully describes the magnitude distribution of earthquakes in various seismic regions but magnetic storms, solar flares and pre-seismic EM emissions rooted in activation of a single fault, as well. A subsequent question is whether this equation successfully describes the magnitude distribution in all the cases under study with similar nonextensive entropic parameter q. We show that both two key-questions accept positive answer. It is worth mentioning that the estimated for the q-nonextensive parameters is in full agreement with the upper limit q < 2 obtained from several independent studies involving the Tsallis nonextensive framework.

Eftaxias, K. A.; Balasis, G.; Papadimitriou, C.; Mandea, M.

2009-12-01

226

Wavelength Dependence of Solar Flare Irradiation and its Influence on the Thermosphere  

NASA Technical Reports Server (NTRS)

The wavelength dependence of solar flare enhancement is one of the important factors determining how the Thermosphere-Ionosphere (T-I) system response to flares. To investigate the wavelength dependence of solar flare, the Flare Irradiance Spectral Model (FISM) has been run for 34 X-class flares. The results show that the percentage increases of solar irradiance at flare peak comparing to pre-flare condition have a clear wavelength dependence. In the wavelength range between 0 - 195 nm, it can vary from 1% to 10000%. The solar irradiance enhancement is largest ( 1000%) in the XUV range (0 - 25 nm), and is about 100% in EUV range (25 - 120 nm). The influence of different wavebands on the T-I system during the October 28th, 2003 flare (X17.2-class) has also been examined using the latest version of National Center for Atmospheric Research (NCAR) Thermosphere- Ionosphere-Electrodynamics General Circulation Model (TIE-GCM). While the globally integrated solar energy deposition is largest in the 0 - 14 nm waveband, the impact of solar irradiance enhancement on the thermosphere at 400 km is largest for 25 - 105 nm waveband. The effect of 122 - 195 nm is small in magnitude, but it decays slowly.

Huang, Yanshi; Richmond, Arthur D.; Deng, Yue; Qian, L.; Solomon, S.; Chamberlin, P.

2012-01-01

227

Predictions of reconnected flux, energy and helicity in eruptive solar flares  

NASA Astrophysics Data System (ADS)

In order to better understand the solar genesis of interplanetary magnetic clouds, I model the magnetic and topological properties of several large eruptive solar flares and relate them to observations. My main hypothesis is that the flux ropes ejected during eruptive solar flares are the result of a sequence of magnetic reconnections. To test this hypothesis, I use the three-dimensional Minimum Current Corona model of flare energy storage (Longcope, 1996) together with pre-flare photospheric magnetic field and flare ribbon observations to predict the basic flare properties: reconnected magnetic flux, free energy, and flux rope helicity. Initially, the MCC model was able to quantify the properties of the flares that occur in active regions with only photospheric shearing motions. Since rotating motions may also play a key role in the flare energetics, I develop a method for including both shearing and rotating motions into the MCC model. I use this modified method to predict the model flare properties and then compare them to the observed quantities. Firstly, for two flares in active regions with fast rotating sunspots, I find that the relative importance of shearing and rotation to those flares depends critically on their location within the parent active region topology. Secondly, for four flares analyzed with the MCC model (three flares described here and one flare described in Longcope et al. (2007)), I find that the modeled flare properties agree with the observed properties within the uncertainties of the methods used. This agreement compels me to believe that the magnetic clouds associated with these four solar flares are formed by low-corona magnetic reconnection during the eruption as modeled by the MCC model, rather than eruption of pre-existing structures in the corona or formation in the upper corona with participation of the global magnetic field. I note that since all four flares occurred in active regions without significant pre-flare flux emergence and/or cancellation, the energy and helicity values I find are due primarily to shearing and rotating motions, which are sufficient to account for the observed flare energy and MC helicity.

Kazachenko, Maria Dmitiyevna

2010-12-01

228

Solar wind heavy ions from flare-heated coronal plasma  

NASA Technical Reports Server (NTRS)

Information concerning the coronal expansion is carried by solar-wind heavy ions. Distinctly different energy-per-charge ion spectra are found in two classes of solar wind having the low kinetic temperatures necessary for E/q resolution of the ion species. Heavy-ion spectra which can be resolved are most frequently observed in the low-speed interstream (IS) plasma found between high speed streams; the streams are thought to originate from coronal holes. Although the sources of the IS plasma are uncertain, the heavy-ion spectra found there contain identifiable peaks of O, Si, and Fe ions. Such spectra indicate that the IS ionization state of O is established in coronal gas at a temperature of approximately 1.6 million K, while that of Fe is frozen in farther out at about 1.5 million K. On occasion anomalous spectra are found outside IS flows in solar wind with abnormally depressed local kinetic temperatures. The anomalous spectra contain Fe(16+) ions, not usually found in IS flows, and the derived coronal freezing-in temperatures are significantly higher. The coronal sources of some of these ionizationally hot flows are identified as solar flares.

Bame, S. J.; Asbridge, J. R.; Feldman, W. C.; Fenimore, E. E.; Gosling, J. T.

1979-01-01

229

Terahertz photometers to observe solar flares from space (SOLAR-T project)  

NASA Astrophysics Data System (ADS)

The space experiment SOLAR-T designed to observe solar flares at THz frequencies was completed. We present the concept, fabrication and performance of a double THz photometers system. An innovative optical setup allows observations of the full solar disk and the detection of small burst transients at the same time. It is the first detecting system conceived to observe solar flare THz emissions on board of stratospheric balloons. The system has been integrated to data acquisition and telemetry modules for this application. SOLAR-T uses two Golay cell detectors preceded by low-pass filters made of rough surface primary mirrors and membranes, 3 and 7 THz band-pass filters, and choppers. Its photometers can detect small solar bursts (tens of solar flux units) with sub second time resolution. One artificial Sun setup was developed to simulate actual observations. Tests comprised the whole system performance, on ambient and low pressure and temperature conditions. It is intended to provide data on the still unrevealed spectral shape of the mysterious THz solar flares emissions. The experiment is planned to be on board of two long-duration stratospheric balloon flights over Antarctica and Russia in 2014-2016. The SOLAR-T development, fabrication and tests has been accomplished by engineering and research teams from Mackenzie, Unicamp and Bernard Lyot Solar Observatory; Propertech Ltda.; Neuron Ltda.; and Samsung, Brazil; Tydex LCC, Russia; CONICET, Argentina; the stratospheric balloon missions will be carried in cooperation with teams from University of California, Berkeley, USA (flight over Antarctica), and Lebedev Physical Institute, Moscow, Russia (flight over Russia).

Kaufmann, Pierre; Raulin, Jean-Pierre

230

Spatial structure of high energy photon sources in solar flares  

NASA Technical Reports Server (NTRS)

Stereoscopic observations of high energy (greater than about 100 keV) photon emission from five solar flares have been made with the X-ray spectrometers aboard the ISEE-3 and Pioneer Venus Orbiter spacecraft. The observed altitude structure of the photon source and its dependence on the photon energy and time during a flare are compared with the predictions of thermal and non-thermal models of the hard X-ray source. In the case of the impulsive source, it is found that (1) the thermal model with adiabatic compression and expansion of a magnetically confined plasma and the thin target (non-thermal) model are not consistent with the observations; (2) the thick target (non-thermal) model and the dissipative thermal model are partially in agreement with the observations; (3) the emission probably originates in many individual non-thermal sources distributed in altitude, the lower altitude sources being brighter than those at higher altitude. In the case of the gradual source, it is found that (1) models with purely coronal sources are not consistent with the observations; (2) a partial precipitation model with trapped as well as precipitating electrons is consistent with the observations.

Kane, S. R.

1983-01-01

231

MHD discontinuities in solar flares: continuous transitions and plasma heating  

NASA Astrophysics Data System (ADS)

The conservation laws on a surface of discontinuity in the ideal magnetohydrodynamics (MHD) allow changing a discontinuity type with gradual (continuous) changes in conditions of plasma. Then there are the so-called transition solutions that satisfy simultaneously two types of discontinuities. We obtain all transition solutions on the basis of a complete system of boundary conditions for the MHD equations. We also found an expression describing a jump of internal energy of the plasma flowing through the discontinuity. It allows, firstly, to construct a generalized scheme of possible transitions between MHD discontinuities, and secondly, to examine the dependence of plasma heating by plasma density and configuration of the magnetic field near the surface of the discontinuity (i.e., by the type of the MHD discontinuity). The problem of the heating of "superhot" plasma (with the electron temperature is greater than 10 keV) in solar flares are discussed. It is shown that the best conditions for heating are carried out in the vicinity of the reconnecting current layer near the areas of reverse currents. Bibl.: B.V.Somov. Plasma Astrophysics, Part II: Reconnection and Flares, Second Edition. (New York: Springer SBM, 2013).

Ledentsov, Leonid; Somov, Boris

232

Solar Flare Probability depending on Sunspot Classification, Its Area, and Its Area Change  

NASA Astrophysics Data System (ADS)

We have investigated solar flare probability depending on sunspot classification, its area, and its area change using only solar white light data. For this we used the McIntosh sunspot group classification and then selected most flare-productive six sunspot groups : DKI, DKC, EKI, EKC, FKI and FKC. For each group, we classified it into three sub-groups according to sunspot area change : increase, steady, and decrease. For sunspot data, we used the NOAA active region information for 19 years (from January 1992 to December 2010): daily sunspot class and its area corrected for the projection effect. As a result, we find that the mean flare rates and the flare probabilities for the "increase" sub-groups are noticeably higher than those for other sub-groups. In the case of the (M+X)-class flares of `kc groups, the mean flare rates of the "increase"sub-groups are more than two times than those of the "steady"sub-groups. In the case of DKC sunspot group, the (M+X)-class flare probability of the "increase" sub-group is 53% while the "decrease" and "steady" sub-groups are 27% and 24%, respectively. This is statistical evidence that magnetic flux emergence is an very important mechanism for triggering solar flares since sunspot area can be a good proxy of magnetic flux. In addition, we are examining the relationship between sunspot area and solar flare probability. For this, we classified each sunspot group into two sub-groups: large and small. In the case of compact group, the solar flare probabilities noticeably increase with its area. We are going to develop a flare probability model depending on sunspot class, its area, and its area change.

Lee, Kang-Jin; Moon, Y.

2011-05-01

233

Coronal mass ejections and major solar flares: The great active center of March 1989  

NASA Technical Reports Server (NTRS)

The solar flare and coronal mass ejection (CME) events associated with the large and complex March 1989 active region are discussed. This active region gave us a chance to study the relation of CME with truly major solar flares. The work concentrates on questions of the relation of CMEs and flares to one another and to other types of activity on the Sun. As expected, some major (X-3B class) flares had associated CMEs. However, an unexpected finding is that others did not. In fact, there is strong evidence that the X4-4B flare of March 9th had no CME. This lack of a CME for such an outstanding flare event has important implications to theories of CME causation.Apparently, not all major flares cause CMEs or are caused by CMEs. The relations between CMEs and other types of solar activity are also discussed. No filament disappearances are reported for major CMEs studied here. Comparing these results with other studies, CMEs occur in association with flares and with erupting prominences, but neither are required for a CME. The relation between solar structures showing flaring without filament eruptions and structures showing filament eruptions without flares becomes important. The evolutionary relation between an active flaring sunspot region and extensive filaments without sunspots is reviewed, and the concept of an 'evolving magnetic structure' (EMS) is introduced. It is suggested that all CMEs arise in EMSs and that CMEs provide a major path through which azimuthal magnetic fields escape form the Sun during the solar cycle.

Feynman, Joan; Hundhausen, Arthur J.

1994-01-01

234

Regularized energy-dependent solar flare hard x-ray spectral index  

E-print Network

The deduction from solar flare X-ray photon spectroscopic data of the energy dependent model-independent spectral index is considered as an inverse problem. Using the well developed regularization approach we analyze the energy dependency of spectral index for a high resolution energy spectrum provided by Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The regularization technique produces much smoother derivatives while avoiding additional errors typical of finite differences. It is shown that observations imply a spectral index varying significantly with energy, in a way that also varies with time as the flare progresses. The implications of these findings are discussed in the solar flare context.

Eduard P. Kontar; Alexander L. MacKinnon

2005-06-05

235

Influence of Solar X-ray Flares on the Earth-Ionosphere Waveguide  

NASA Astrophysics Data System (ADS)

A simultaneous analysis of solar flare X-ray irradiance and VLF signal amplitude on the GQD/22.1 kHz trace was carried out. Solar flare data were taken from GOES 12 satellite listings. The VLF amplitude data were recorded by means of the AbsPAL (Absolute Phase and Amplitude Logger) at the Institute of Physics, Belgrade, Serbia. It was found that solar flare events from class C to class X affect the VLF signal amplitude in various ways and can be classified according to the type of effect produced in the Earth-ionosphere waveguide on the VLF propagation.

Grubor, D.; Sulic D.; Zigman, V.

2005-12-01

236

Numerical modeling of the energy storage and release in solar flares  

NASA Technical Reports Server (NTRS)

This paper reports on investigation of the photospheric magnetic field-line footpoint motion (usually referred to as shear motion) and magnetic flux emerging from below the surface in relation to energy storage in a solar flare. These causality relationships are demonstrated by using numerical magnetohydrodynamic simulations. From these results, one may conclude that the energy stored in solar flares is in the form of currents. The dynamic process through which these currents reach a critical value is discussed as well as how these currents lead to energy release, such as the explosive events of solar flares.

Wu, S. T.; Weng, F. S.

1993-01-01

237

Neutrino Solar Flare detection for a saving alert system of satellites and astronauts  

E-print Network

Largest Solar Neutrino Flare may be soon detectable by Deep Core neutrino detector immediately and comunicate to satellites or astronauts. Its detection is the fastest manifestation of a later (tens minutes,hours) dangerous cosmic shower. The precursor trigger maybe saving satellites and even long flight astronauts lives. We shall suggest how. Moreover their detection may probe the inner solar flare acceleration place as well as the neutrino flavor mixing in a new different parameter windows. We show the updated expected rate and signature of neutrinos and antineutrinos in largest solar flare for present tens Megaton Deep Core telescope at tens Gev range. Speculation for additional Icecube gigaton array signals are also considered.

Daniele Fargion

2011-06-19

238

Far-IR and radio thermal continua in solar flares  

E-print Network

With the invention of new far-infrared (FIR) and radio mm and sub-mm instruments (DESIR on SMESE satellite, ESO-ALMA), there is a growing interest in observations and analysis of solar flares in this so far unexplored wavelength region. Two principal radiation mechanisms play a role: the synchrotron emission due to accelerated particle beams moving in the magnetic field and the thermal emission due to the energy deposit in the lower atmospheric layers. In this contribution we explore the time-dependent effects of beams on thermal FIR and radio continua. We show how and where these continua are formed in the presence of time dependent beam heating and non-thermal excitation/ionisation of the chromospheric hydrogen plasma.

Kaparov, J; Karlick, M; Moravec, Z; Varady, M

2009-01-01

239

Konus- Wind and Helicon- Coronas-F observations of solar flares  

NASA Astrophysics Data System (ADS)

Results of solar flare observations obtained in the Konus- Wind experiment from November, 1994 to December, 2013 and in the Helicon Coronas-F experiment during its operation from 2001 to 2005, are presented. For the periods indicated Konus- Wind detected in the trigger mode 834 solar flares, and Helicon- Coronas-F detected more than 300 solar flares. A description of the instruments and data processing techniques are given. As an example, the analysis of the spectral evolution of the flares SOL2012-11-08T02:19 (M 1.7) and SOL2002-03-10T01:34 (C5.1) is made with the Konus- Wind data and the flare SOL2003-10-26T06:11 (X1.2) is analyzed in the 2.223 MeV deuterium line with the Helicon- Coronas-F data.

Pal'shin, V. D.; Charikov, Yu. E.; Aptekar, R. L.; Golenetskii, S. V.; Kokomov, A. A.; Svinkin, D. S.; Sokolova, Z. Ya.; Ulanov, M. V.; Frederiks, D. D.; Tsvetkova, A. E.

2014-12-01

240

Konus-Wind and Helicon-Coronas-F Observations of Solar Flares  

E-print Network

Results of solar flare observations obtained in the Konus-Wind experiment from November, 1994 to December, 2013 and in the Helicon Coronas-F experiment during its operation from 2001 to 2005, are presented. For the periods indicated Konus-Wind detected in the trigger mode 834 solar flares, and Helicon-Coronas-F detected more than 300 solar flares. A description of the instruments and data processing techniques are given. As an example, the analysis of the spectral evolution of the flares SOL2012-11-08T02:19 (M 1.7) and SOL2002-03-10T01:34 (C5.1) is made with the Konus-Wind data and the flare SOL2003-10-26T06:11 (X1.2) is analyzed in the 2.223 MeV deuterium line with the Helicon-Coronas-F data.

Pal'shin, V D; Aptekar, R L; Golenetskii, S V; Kokomov, A A; Svinkin, D S; Sokolova, Z Ya; Ulanov, M V; Frederiks, D D; Tsvetkova, A E

2014-01-01

241

DETERMINATION OF STOCHASTIC ACCELERATION MODEL CHARACTERISTICS IN SOLAR FLARES  

SciTech Connect

Following our recent paper, we have developed an inversion method to determine the basic characteristics of the particle acceleration mechanism directly and non-parametrically from observations under the leaky box framework. Earlier, we demonstrated this method for obtaining the energy dependences of the escape time and pitch angle scattering time. Here, by converting the Fokker-Planck equation to its integral form, we derive the energy dependences of the energy diffusion coefficient and direct acceleration rate for stochastic acceleration in terms of the accelerated and escaping particle spectra. Combining the regularized inversion method of Piana et al. and our procedure, we relate the acceleration characteristics in solar flares directly to the count visibility data from RHESSI. We determine the timescales for electron escape, pitch angle scattering, energy diffusion, and direct acceleration at the loop top acceleration region for two intense solar flares based on the regularized electron flux spectral images. The X3.9 class event shows dramatically different energy dependences for the acceleration and scattering timescales, while the M2.1 class event shows a milder difference. The discrepancy between the M2.1 class event and the stochastic acceleration model could be alleviated by a turbulence spectrum that is much steeper than the Kolmogorov-type spectrum. A likely explanation of the X3.9 class event could be that the escape of electrons from the acceleration region is not governed by a random walk process, but instead is affected by magnetic mirroring, in which the scattering time is proportional to the escape time and has an energy dependence similar to the energy diffusion time.

Chen, Qingrong; Petrosian, Vah [Department of Physics, Stanford University, Stanford, CA 94305 (United States)

2013-11-01

242

Magnetic and dynamical photospheric disturbances observed during an M3.2 solar flare  

E-print Network

This letter reports on a set of full-Stokes spectropolarimetric observations in the near infrared He I 10830 A spectral region covering the pre-, flare, and post-flare phases of an M3.2 class solar flare. The flare originated on 2013 May 17 and belonged to active region NOAA 11748. We detected strong He I 10830 A emission in the flare. The red component of the He I triplet peaks at an intensity ratio to the continuum of about 1.86. During the flare, He I Stokes V is substantially larger and appears reversed compared to the usually larger Si I Stokes V profile. The photospheric Si I inversions of the four Stokes profiles reveal the following: (1) the magnetic field strength in the photosphere decreases or is even absent during the flare phase, as compared to the pre-flare phase. However, this decrease is not permanent. After the flare the magnetic field recovers its pre-flare configuration in a short time (i.e., in 30 minutes after the flare). (2) In the photosphere, the line-of-sight velocities show a regular...

Kuckein, C; Sainz, R Manso

2015-01-01

243

Multi-wavelength analysis of high energy electrons in solar flares: a case study of August 20, 2002 flare  

E-print Network

A multi-wavelength spatial and temporal analysis of solar high energy electrons is conducted using the August 20, 2002 flare of an unusually flat (gamma=1.8) hard X-ray spectrum. The flare is studied using RHESSI, Halpha, radio, TRACE, and MDI observations with advanced methods and techniques never previously applied in the solar flare context. A new method to account for X-ray Compton backscattering in the photosphere (photospheric albedo) has been used to deduce the primary X-ray flare spectra. The mean electron flux distribution has been analysed using both forward fitting and model independent inversion methods of spectral analysis. We show that the contribution of the photospheric albedo to the photon spectrum modifies the calculated mean electron flux distribution, mainly at energies below 100 keV. The positions of the Halpha emission and hard X-ray sources with respect to the current-free extrapolation of the MDI photospheric magnetic field and the characteristics of the radio emission provide evidence of the closed geometry of the magnetic field structure and the flare process in low altitude magnetic loops. In agreement with the predictions of some solar flare models, the hard X-ray sources are located on the external edges of the Halpha emission and show chromospheric plasma heated by the non-thermal electrons. The fast changes of Halpha intensities are located not only inside the hard X-ray sources, as expected if they are the signatures of the chromospheric response to the electron bombardment, but also away from them.

J. Kasparova; M. Karlicky; E. P. Kontar; R. A. Schwartz; B. R. Dennis

2005-08-30

244

Electron Acceleration in Solar Flares: Observations versus Numerical S imulations  

NASA Astrophysics Data System (ADS)

We use RHESSI hard X-ray observations to constrict electron acceleration in solar flares, generally considered as a primary recipient of the released energy. X-ray sources in the corona have been previously discovered and tentatively associated with bremsstrahlung emission of the acceleration site. RHESSI imaging spectroscopy can temporally resolve the non-thermal spectrum of the coronal source for the first time. We compare the time behaviour with the predictions of stochastic acceleration, as described by transit-time damping of MHD turbulence excited by reconnection. The results in 5 limb events indicate soft-hard-soft (shs) behaviour of the coronal source emission in the course of an X-ray peak (the more intense, the harder the spectrum). The shs behaviour thus constitutes a conspicuous property of the acceleration process. The temporal behaviour of the spectrum can be quantitatively described a pivot point near a photon energy of 20 keV at which the spectrum remains constant in time. We solve a diffusion equation for the interaction of waves and particles including trapping, escape and particle replenishment. The solution yields a spectrum that is approximately a power-law in the observed range of energies, having a spectral index in the observed range. However, the theoretically derived pivot point is generally at energy lower than observed. For this reason we include transport effects, such as produced by an electric potential, or scattering in the coronal source (trapping) to bring the pivot energy up to the observed value. Escaping particles propagate to the base of the loop in the dense chromosphere. These precipitating particles are identified as origin of the observed hard X-ray footpoints. Observations and simulations show that solar flare electron acceleration is a process that involves interactions with the connecting loop. The observations are consistent with stochastic acceleration in a relatively dense medium (up to 10^11 cm^-3) and high wave energy densities (up to 0.001 magnetic). The comparison also constrains the global flare geo-metry, requiring coupling between the coronal source and the footpoints.

Benz, A. O.; Grigis, P. C.; Battaglia, M.

2006-08-01

245

Early Abnormal Temperature Structure of X-ray Looptop Source of Solar Flares  

E-print Network

. In classical flare models, an energy releasing site (or the site of magnetic reconnection) is located aboveEarly Abnormal Temperature Structure of X-ray Looptop Source of Solar Flares Jinhua Shen1-ray looptop source at higher energy bands will be higher in altitude, for which we can define as normal

246

Reply. [to comment on 'The solar flare myth' by J. T. Gosling  

NASA Technical Reports Server (NTRS)

In replying to a comment by Hudson et. al. (1995) in regards to Gosling (1993), Gosling (1995) holds that solar flares do not play a major role in geomagnetic storms. According to Gosling, Hudson et. al. has done nothing to demonstrate that flares either produce coronal mass ejections (CMEs) or cause major disturbances in the near-Earth space environment.

Gosling, J. T.

1995-01-01

247

SAR arc occurrence frequency during cycle 23 of solar activity  

Microsoft Academic Search

The occurrence frequency of SAR arcs during 1997 2006 has been analyzed based on the photometric observations at the Yakutsk meridian (Maimaga station, corrected geomagnetic coordinates: 57 N, 200 E). SAR arcs appeared in 114 cases (500 h) during 370 nights of observations (3170 h). The occurrence frequency of SAR arcs increases to 27% during the growth phase of solar

V. N. Alekseev; I. B. Ievenko

2008-01-01

248

Solar Energy-An Everyday Occurrence  

ERIC Educational Resources Information Center

Describes a solar energy research project sponsored by the Energy Research and Development Administration and conducted at Timonium School in Maryland. Elementary student involvement in solar energy studies resulting from the project is noted. (MDR)

Keister, Carole; Cornell, Lu Beth

1978-01-01

249

Observations of interplanetary energetic charged particles from gamma-ray line solar flares  

NASA Technical Reports Server (NTRS)

Observations of interplanetary energetic ions from the 7 June, 21 June and 1 July 1980 gamma ray line solar flares are presented. The observations are from the Max-Planck-Institut/University of Maryland Ultra Low Energy Wide Angle Telescope aboard the ISEE-3 spacecraft. Both June flares produced relatively low intensity proton events at earth with peak intensities at 10-20 MeV approximately 5 x .01 protons square cm sec sr MeV)-1. Neither flare showed evidence of being enriched in either 3He or Fe at approximately 1 MeV/nucleon. The 1 July flare produced no observable ion or electron enhancements.

Pesses, M. E.; Klecker, B.; Gloeckler, G.; Hovestadt, D.

1981-01-01

250

Response of the equatorial and low-latitude ionosphere to an intense X-class solar flare (X7/2B) as observed on 09 August 2011  

NASA Astrophysics Data System (ADS)

In this paper, we present response of equatorial and low-latitude ionosphere to an intense solar flare of class X7/2B that peaked at 08:05 UT on 09 August 2011 in the solar cycle 24. Global positioning system total electron content (TEC) observations in the sunlit hemisphere show enhancement of ~3 TEC units, while geomagnetic H component observations indicate sudden decrease and increase in their strength at equatorial and low-latitude stations, respectively, at several stations in the sunlit hemisphere. In addition, equatorial electrojet strength over Indian region reveals commencement of counter electrojet. Simultaneous Canadian Advanced Digital Ionosonde observations at Tirunelveli, an equatorial station in India, show the disappearance of ionogram echoes during the flare event indicating absorption of radio signals in the D region. Strong equatorial blanketing type Es layer was observed in the ionogram records at Tirunelveli prior to the occurrence of the solar flare that continued for several hours though it became weak/absent during the flare event. Ionogram records on the control day show regular F layer movement without any blanketing type Es layer. Very low frequency (VLF) observations at Allahabad, an Indian low-latitude station, show enhanced VLF amplitude signal during the same time revealing the sudden enhancement of D region ionization. Using the observations presented here, an attempt has been made to study the impact of the solar flares on the electrodynamics of the equatorial and low-latitude ionosphere.

Sripathi, S.; Balachandran, N.; Veenadhari, B.; Singh, R.; Emperumal, K.

2013-05-01

251

SDO Captures Release of X1.2 Class Solar Flare - Duration: 0:15.  

NASA Video Gallery

This movie shows imagery from NASA's Solar Dynamics Observatory as the sun emitted an X-class flare on Jan. 7, 2014. The movie shows light in the 1600 Angstrom wavelength showing both sunspots visi...

252

Solar flare X-ray polarimeter utilizing a large area thin beryllium scattering disk  

NASA Technical Reports Server (NTRS)

A model of a solar flare X-ray polarimeter utilizing a large-area thin beryllium scattering disk was developed using Monte Carlo techniques for several classes of solar flares. The solar-flare polarimeter consists of a 30-cm-diam Be disk of about 1/3 of a scattering length thickness, which is surrounded by a cylindrical detector composed of six segmented panels of NaI scintillators, each coupled to 15 photomultiplier tubes. The instrument is sensitive to X-rays from 10 to 100 keV. For a class-M-2 solar flare observed for 10 sec from a balloon at an altitude of 150,000 ft, the minimum detectable polarization at the 99 percent statistical confidence level was found to be 1-6 percent over the energy range 20-100 keV.

Gotthelf, E.; Hamilton, T.; Novick, R.; Chanan, G.; Emslie, A.; Weisskopf, M.

1989-01-01

253

SDO Sees Late Phase in Solar Flares - Duration: 0:20.  

NASA Video Gallery

On May 5, 2010, shortly after the Solar Dynamics Observatory (SDO) began normal operation, the sun erupted with numerous coronal loops and flares. Many of these showed a previously unseen "late pha...

254

Variation in Nuclear Decay Rates as a Possible Predictor of Solar Flares  

NASA Astrophysics Data System (ADS)

Jenkins and Fischbach (Astroparticle Physics, 31, 407, 2009) have recently found evidence for fluctuations in the decay rates of radioactive isotopes in association with solar flares. Jenkins et al. (Astroparticle Physics, 32, 42, 2010) have also found strong evidence for annual variations in measurements of decay rates acquired at the Brookhaven National Laboratory (BNL) and at the Physikalisch-Technische Bundesanstalt (PTB) in Germany. If these claims are confirmed, they pose important questions in particle physics and in solar physics, with the intriguing possibility that such measurements may lead to procedures for predicting the occurrence of some solar flares. The purpose of this presentation is to discuss these questions. The strongest feature of the variability of isotopic decay rates is an annual variation in both BNL and PTB data. The phases of these variations rule out the possibility that they are due either to the annual variation in temperature or to the annual variation in Sun-Earth distance. However, we found some time ago that the solar neutrino flux, as measured at Earth, is influenced not only by the varying Sun-Earth distance, but also by the variation in the heliospheric latitude of the Sun-Earth vector (Sturrock,Walther, and Wheatland, Astrophys. J., 507, 978, 1998). The phases of the annual variation in the BNL and PTB data are consistent with the combined effect of varying Sun-Earth distance and varying heliospheric latitude. This result suggests that the decay rates may be influenced by solar neutrinos. This interpretation would require a revision of neutrino physics. In order to check this hypothesis, it would clearly be desirable to be able to compare decay data with neutrino data. The difficulty is that the decay-rate variations amount to only a few parts in 10,000. This is far too small a fraction to be detectable in neutrino data. However, we have recently found that there is a close association between variations in the solar neutrino flux and variations in solar irradiance. Hence we may, with caution, use irradiance data as a proxy for neutrino data. This has the advantage that irradiance data has been measured several times a day with very high accuracy for over thirty years. We shall present recent results on the comparison of decay data and irradiance data, and comment on possible processes that might explain these associations. This work was supported by the National Science Foundation through grant AST-0607572.

Sturrock, P. A.; Buncher, J.; Fischbach, E.; Gruenwald, J.; Javorsek, D.; Jenkins, J.; Krause, D.; Mattes, J.

2009-12-01

255

A mechanism for the abundance enhancements of heavy nuclei in solar flare particle events  

NASA Technical Reports Server (NTRS)

A mechanism is proposed to account for the recently reported abundance enhancements of heavy nuclei in solar flares. The mechanism requires two acceleration stages for its operation: First, fully stripped ions are accelerated to suprathermal energies, and subsequently, a fraction of these ions are Fermi accelerated to higher energies. It is shown that because injection into Fermi acceleration is rigidity dependent and the ions may pick up electrons during transport to the Fermi acceleration region, an enhancement of the abundances of heavy nuclei can occur. The degree of the enhancement depends on a number of factors particular to each flare, so that the degree of enhancement may be variable from flare to flare, or may be a function of time within a given flare. In some flares, conditions may be such that no enhancement would be expected.

Cartwright, B. G.; Mogro-Campero, A.

1973-01-01

256

Directivity and its energy dependence in solar flare energetic emission  

NASA Technical Reports Server (NTRS)

We have studied 72 solar flares simultaneously observed by the Gamma-Ray Spectrometer (GRS, 0.3-1 MeV) and the Hard X-Ray Burst Spectrometer (HXRBS, 30-500 keV) on the Solar Maximum Mission (SMM). Using the spectral analysis results, we studied spectal and size distribution center-to-limb variations for both instruments. The GRS observations show significant center-to-limb variations in both spectral and size distributions, while HXRBS observations show insignificant variations. In general, the GRS spectra are harder than the HXRBS spectra, and their difference increases from center to limb, suggesting that a flattening of the spectrum above 300 keV is inevitable for the gamma-ray emissions. We corrected for the effect of spacecraft pointing and combined HXRBS and GRS data to obtain spectra over the energy range of 0.03-1 MeV. The fluences at various energies were calculated and normalized to the total fluence of the burst to measure the directivity. It is found that the directivity increases with increasing energy, from 1.1 at 50 keV to 6.5 at 1 MeV. These results are consistent with anisotropic electron beams and the physics of Coulomb collision and bremsstrahlung.

Li, Peng

1995-01-01

257

The Solar Flare Sulfur Abundance from RESIK Observations  

NASA Astrophysics Data System (ADS)

The RESIK instrument on CORONAS-F spacecraft observed several sulfur X-ray lines in three of its four channels covering the wavelength range 3.8-6.1 during solar flares. The fluxes are analyzed to give the sulfur abundance. Data are chosen for when the instrument parameters were optimized. The measured fluxes of the S XV 1s 2-1s4p (w4) line at 4.089 gives A(S) = 7.16 0.17 (abundances on a logarithmic scale with A(H) = 12) which we consider to be the most reliable. Estimates from other lines range from 7.13 to 7.24. The preferred S abundance estimate is very close to recent photospheric abundance estimates and to quiet-Sun solar wind and meteoritic abundances. This implies no fractionation of sulfur by processes tending to enhance the coronal abundance from the photospheric that depend on the first ionization potential (FIP), or that sulfur, though its FIP has an intermediate value of 10.36 eV, acts like a "high-FIP" element.

Sylwester, J.; Sylwester, B.; Phillips, K. J. H.; Kuznetsov, V. D.

2012-06-01

258

THE SOLAR FLARE SULFUR ABUNDANCE FROM RESIK OBSERVATIONS  

SciTech Connect

The RESIK instrument on CORONAS-F spacecraft observed several sulfur X-ray lines in three of its four channels covering the wavelength range 3.8-6.1 A during solar flares. The fluxes are analyzed to give the sulfur abundance. Data are chosen for when the instrument parameters were optimized. The measured fluxes of the S XV 1s{sup 2}-1s4p (w4) line at 4.089 A gives A(S) = 7.16 {+-} 0.17 (abundances on a logarithmic scale with A(H) = 12) which we consider to be the most reliable. Estimates from other lines range from 7.13 to 7.24. The preferred S abundance estimate is very close to recent photospheric abundance estimates and to quiet-Sun solar wind and meteoritic abundances. This implies no fractionation of sulfur by processes tending to enhance the coronal abundance from the photospheric that depend on the first ionization potential (FIP), or that sulfur, though its FIP has an intermediate value of 10.36 eV, acts like a 'high-FIP' element.

Sylwester, J.; Sylwester, B. [Space Research Centre, Polish Academy of Sciences, 51-622, Kopernika 11, Wroclaw (Poland); Phillips, K. J. H. [Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT (United Kingdom); Kuznetsov, V. D., E-mail: js@cbk.pan.wroc.pl, E-mail: bs@cbk.pan.wroc.pl, E-mail: kjhp@mssl.ucl.ac.uk, E-mail: kvd@izmiran.ru [Institute of Terrestrial Magnetism and Radiowave Propagation (IZMIRAN), Troitsk, Moscow (Russian Federation)

2012-06-01

259

Flares and Antiflares on Young Solar Analog EK Draconis  

NASA Astrophysics Data System (ADS)

EK Draconis (HD129333: G1.5 V) is a well-known young (50 Myr) solar analog. In 2012, Hubble Space Telescope returned to EK Dra to follow up a far-UV SNAPshot visit by HST's Cosmic Origins Spectrograph two years earlier. The brief SNAP pointing had found surprisingly redshifted subcoronal Si IV (T~ 8x104 K), which also displayed impulsive variability, curiously uncorrelated with species at lower temperatures (C II: 2x104K) or higher (Fe XXI: 1x107K). Serendipitously, the follow-on program witnessed one of the largest FUV flares ever recorded on a sun-like star, which nevertheless displayed even stronger redshifts (downflows) than had been seen earlier, contrary to the violent blueshifts expected from such explosive events. At the same time, a velocity cross-calibration by Space Telescope Imaging Spectrograph (STIS) uncovered systematic deviations in the wavelength scales of COS, that were partly, but not entirely, responsible for the previously reported SNAP redshifts. However, the (now smaller, but still about 10 km s-1) Si IV redshifts did not vary with rotational phase, so are not likely caused by "Doppler imaging' effects. Instead, the downflows might be signatures of catastrophic coronal cooling events (`"antiflares'). All in all, the new COS/STIS program documents a complex, energetic, dynamic outer atmosphere of the young solar analog.

Ayres, Thomas R.

2015-01-01

260

High-resolution X-ray spectra of solar flares. IV - General spectral properties of M type flares  

NASA Technical Reports Server (NTRS)

The spectral characteristics in selected narrow regions of the X-ray spectrum of class M solar flares are analyzed. High-resolution spectra in the ranges 1.82-1.97, 2.98-3.07, 3.14-3.24 and 8.26-8.53 A, which contain lines important for the determination of electron temperature and departure from ionization equilibrium, were recorded by spaceborne Bragg crystal spectrometers. Temperatures of up to 20,000,000 K are obtained from line ratios during flare rise phases in M as well as X flares, while in the decay phase the calcium temperature can be as low as 8,000,000 K, which is significantly lower than in X flares. Large nonthermal motions (on the order of 130 km/sec at most) are also observed in M as well as X flares, which are largest during the soft X-ray rise phase. Finally, it is shown that the method proposed by Gabriel and Phillips (1979) for detecting departures of electrons from Maxwellian velocity distributions is not sufficiently sensitive to give reliable results for the present data.

Feldman, U.; Doschek, G. A.; Kreplin, R. W.; Mariska, J. T.

1980-01-01

261

Effect of an X-Class solar flare on the OI 630 nm dayglow emissions  

NASA Astrophysics Data System (ADS)

We present a striking event that shows a prompt effect of an X-class solar flare (X6.2/3B) in the neutral optical dayglow emissions. This flare occurred on 13 December 2001 at 1424 UT and peaked at 1430 UT. The peak- to pre-flare X-ray intensity ratio as observed by GOES-10 was greater than 300 and the EUV flux observed by SEM/SOHO was greater by around 60%. As a response to this flare, the daytime redline (OI 630 nm) column integrated emission intensity measured from Carmen Alto (23.16S, 70.66W), in Chile, showed a prompt increase of around 50%. Our results show that this prompt enhancement in the thermospheric dayglow seems to be caused mainly due to an increase in photoelectrons due to a sudden increase in the solar EUV flux associated with this flare.

Das, Uma; Pallamraju, Duggirala; Chakrabarti, Supriya

2010-08-01

262

Effect of an X-Class Solar Flare on the OI 630 nm Dayglow Emissions  

NASA Technical Reports Server (NTRS)

We present a striking event that shows a prompt effect of an X-class solar flare (X6.2/3B) in the neutral optical dayglow emissions. This flare occurred on 13 December 2001 at 1424 UT and peaked at 1430 UT. The peak-to pre-flare X-ray intensity ratio as observed by GOES-10 was greater than 300 and the EUV flux observed by SEM/SOHO was greater by around 60%. As a response to this flare, the daytime redline (OI 630 nm) column integrated emission intensity measured from Carmen Alto (23.16degS, 70.66degW), in Chile, showed a prompt increase of around 50%. Our results show that this prompt enhancement in the thermospheric dayglow seems to be caused mainly due to an increase in photoelectrons due to a sudden increase in the solar EUV flux associated with this flare.

Das, Uma; Pallamraju, Duggirala; Chakrabarti, Supriya

2010-01-01

263

Particle acceleration and radiation by direct electric fields in flaring complex solar active regions  

E-print Network

Particle acceleration and radiation by direct electric fields in flaring complex solar active-Meudon, 92195 Meudon Cedex, FRANCE Abstract The acceleration and radiation of solar energetic particles with the existing observations. 1 Introduction The approach used for particle acceleration models proposed for solar

Anastasiadis, Anastasios

264

Effective recombination coefficient and solar zenith angle effects on low-latitude D-region ionosphere evaluated from VLF signal amplitude and its time delay during X-ray solar flares  

NASA Astrophysics Data System (ADS)

Excess solar X-ray radiation during solar flares causes an enhancement of ionization in the ionospheric D-region and hence affects sub-ionospherically propagating VLF signal amplitude and phase. VLF signal amplitude perturbation (DeltaA) and amplitude time delay (Deltat) (vis- a-vis corresponding X-ray light curve as measured by GOES-15) of NWC/19.8 kHz signal have been computed for solar flares which is detected by us during Jan-Sep 2011. The signal is recorded by SoftPAL facility of IERC/ICSP, Sitapur (22() 27'N, 87() 45'E), West Bengal, India. In first part of the work, using the well known LWPC technique, we simulated the flare induced excess lower ionospheric electron density by amplitude perturbation method. Unperturbed D-region electron density is also obtained from simulation and compared with IRI-model results. Using these simulation results and time delay as key parameters, we calculate the effective electron recombination coefficient (alpha_{eff}) at solar flare peak region. Our results match with the same obtained by other established models. In the second part, we dealt with the solar zenith angle effect on D-region during flares. We relate this VLF data with the solar X-ray data. We find that the peak of the VLF amplitude occurs later than the time of the X-ray peak for each flare. We investigate this so-called time delay (Deltat). For the C-class flares we find that there is a direct correspondence between Deltat of a solar flare and the average solar zenith angle Z over the signal propagation path at flare occurrence time. Now for deeper analysis, we compute the Deltat for different local diurnal time slots DT. We find that while the time delay is anti-correlated with the flare peak energy flux phi_{max} independent of these time slots, the goodness of fit, as measured by reduced-chi(2) , actually worsens as the day progresses. The variation of the Z dependence of reduced-chi(2) seems to follow the variation of standard deviation of Z along the T_x-R_x propagation path. In other words, for the flares having almost constant Z over the path a tighter anti-correlation between Deltat and phi_{max} was observed.

Basak, Tamal; Chakrabarti, Sandip Kumar

265

Effective recombination coefficient and solar zenith angle effects on low-latitude D-region ionosphere evaluated from VLF signal amplitude and its time delay during X-ray solar flares  

NASA Astrophysics Data System (ADS)

Excess solar X-ray radiation during solar flares causes an enhancement of ionization in the ionospheric D-region and hence affects sub-ionospherically propagating VLF signal amplitude and phase. VLF signal amplitude perturbation (? A) and amplitude time delay (? t) (vis--vis corresponding X-ray light curve as measured by GOES-15) of NWC/19.8 kHz signal have been computed for solar flares which is detected by us during Jan-Sep 2011. The signal is recorded by SoftPAL facility of IERC/ICSP, Sitapur (22? 27'N, 87? 45'E), West Bengal, India. In first part of the work, using the well known LWPC technique, we simulated the flare induced excess lower ionospheric electron density by amplitude perturbation method. Unperturbed D-region electron density is also obtained from simulation and compared with IRI-model results. Using these simulation results and time delay as key parameters, we calculate the effective electron recombination coefficient ( ? eff ) at solar flare peak region. Our results match with the same obtained by other established models. In the second part, we dealt with the solar zenith angle effect on D-region during flares. We relate this VLF data with the solar X-ray data. We find that the peak of the VLF amplitude occurs later than the time of the X-ray peak for each flare. We investigate this so-called time delay (? t). For the C-class flares we find that there is a direct correspondence between ? t of a solar flare and the average solar zenith angle Z over the signal propagation path at flare occurrence time. Now for deeper analysis, we compute the ? t for different local diurnal time slots DT. We find that while the time delay is anti-correlated with the flare peak energy flux ? max independent of these time slots, the goodness of fit, as measured by reduced- ? 2, actually worsens as the day progresses. The variation of the Z dependence of reduced- ? 2 seems to follow the variation of standard deviation of Z along the T x - R x propagation path. In other words, for the flares having almost constant Z over the path a tighter anti-correlation between ? t and ? max was observed.

Basak, Tamal; Chakrabarti, Sandip K.

2013-12-01

266

Coordinated soft X-ray and H-alpha observation of solar flares  

NASA Technical Reports Server (NTRS)

Soft X-ray, Ca XIX, and H-alpha observations obtained for a set of four solar flares in the impulsive phase are analyzed. A blue asymmetry was observed in the coronal Ca XIX line during the soft-Xray rise phase in all of the events. A red asymmetry was observed simultaneously in chromospheric H-alpha at spatial locations associated with enhanced flare heating. It is shown that the impulsive phase momentum of upflowing soft X-ray plasma equalled that of the downflowing H-alpha plasma to within an order of magnitude. This supports the explosive chromospheric evaporation model of solar flares.

Zarro, D. M.; Canfield, R. C.; Metcalf, T. R.; Lemen, J. R.

1988-01-01

267

Propagation of solar flare-associated interplanetary shock waves in the heliospheric meridional plane  

NASA Technical Reports Server (NTRS)

An analysis is conducted for 149 flare-associated shock wave events based on interplanetary scintillation observational data. All of the flare-associated shock waves tend to propagate toward the low latitude region near the solar equator for flares that are located in both the solar Northern and Southern Hemispheres. Also, the fastest propagation directions tend toward the heliospheric current sheet near 1 AU. This tendency is caused by the dynamic action of near-sun magnetic forces on the ejected coronal plasma that traverses the helmet-like magnetic topologies near the sun outward to the classical topology that is essentially parallel to the heliospheric current sheet.

Wei, Fengsi; Dryer, Murray

1991-01-01

268

Predictions of Energy and Helicity in Four Major Eruptive Solar Flares  

NASA Astrophysics Data System (ADS)

In order to better understand the solar genesis of interplanetary magnetic clouds (MCs), we model the magnetic and topological properties of four large eruptive solar flares and relate them to observations. We use the three-dimensional Minimum Current Corona model (Longcope, 1996, Solar Phys. 169, 91) and observations of pre-flare photospheric magnetic field and flare ribbons to derive values of reconnected magnetic flux, flare energy, flux rope helicity, and orientation of the flux-rope poloidal field. We compare model predictions of those quantities to flare and MC observations, and within the estimated uncertainties of the methods used find the following: The predicted model reconnection fluxes are equal to or lower than the reconnection fluxes inferred from the observed ribbon motions. Both observed and model reconnection fluxes match the MC poloidal fluxes. The predicted flux-rope helicities match the MC helicities. The predicted free energies lie between the observed energies and the estimated total flare luminosities. The direction of the leading edge of the MC's poloidal field is aligned with the poloidal field of the flux rope in the AR rather than the global dipole field. These findings compel us to believe that magnetic clouds associated with these four solar flares are formed by low-corona magnetic reconnection during the eruption, rather than eruption of pre-existing structures in the corona or formation in the upper corona with participation of the global magnetic field. We also note that since all four flares occurred in active regions without significant pre-flare flux emergence and cancelation, the energy and helicity that we find are stored by shearing and rotating motions, which are sufficient to account for the observed radiative flare energy and MC helicity.

Kazachenko, Maria D.; Canfield, Richard C.; Longcope, Dana W.; Qiu, Jiong

2012-03-01

269

Short-Term Solar Flare Prediction Using a Sequential Supervised Learning Method  

NASA Astrophysics Data System (ADS)

Solar flares are powered by the energy stored in magnetic fields, so evolutionary information of the magnetic field is important for short-term prediction of solar flares. However, the existing solar flare prediction models only use the current information of the active region. A sequential supervised learning method is introduced to add the evolutionary information of the active region into a prediction model. The maximum horizontal gradient, the length of the neutral line, and the number of singular points extracted from SOHO/MDI longitudinal magnetograms are used in the model to describe the nonpotentiality and complexity of the photospheric magnetic field. The evolutionary characteristics of the predictors are analyzed by using autocorrelation functions and mutual information functions. The analysis results indicate that a flare is influenced by the 3-day photospheric magnetic field information before flare eruption. A sliding-window method is used to add evolutionary information of the predictors into machine learning algorithms, then C4.5 decision tree and learning vector quantization are employed to predict the flare level within 48 hours. Experimental results indicate that the performance of the short-term solar flare prediction model within the sequential supervised learning framework is significantly improved.

Yu, Daren; Huang, Xin; Wang, Huaning; Cui, Yanmei

2009-03-01

270

Solar Radio Bursts at Meter Wavelengths Temporally Associated with Solar Flares and CMEs  

NASA Astrophysics Data System (ADS)

The present work consists in an investigation into 4 solar type II radio bursts temporally associated with solar flares and CMEs recorded by Compound Astronomical Low-frequency Low-cost Instrument (CALLISTO-BR), operating in the frequency range of 45 - 870 MHz, between October 2010 and February 2011. Although the solar type II radio bursts are Known as signatures of magnetohydrodynamic (MHD) shocks moving outward across the solar corona, there are long-standing controversies about how these shocks are brought out. While some works come up with the hint that the solar flares are their origins, others indicate the coronal mass ejections (CMEs) as their most likely driver. For all 4 analyzed type II events, comprised of a typical one and 3 split-band variants, the outcomes were: emitting source speeds of 440 - 1131 km s-1; electron number densities of (0.62 - 3.85) 108 cm-3; magnetic field strengths of 1.06 - 4.26 G; density jumps at the shock front of 1.22 - 2.37; Mach numbers of 1.15 - 2 .15; Alfvn speeds of 295 - 474 km s-1; Alfvn Mach numbers of 1.06 - 3.41; beta parameters of 0.07 - 6.66; and temperatures of (0.23 - 22.0) 106 K. Notwithstanding all 4 analyzed type II events were associated with the impulsive phases of the flares and, very likely, with the acceleration phases of the CMEs, the evolution of the CMEs and the interpretation of their physical parameters provided strong clues that all 4 analyzed type II events were brought out by CME-driven shocks.

Cunha-Silva, R. D.; Fernandes, F. C.; Selhorst, C. L.

2012-12-01

271

Models and Comparisons of Long Duration and Impulsive Solar Flare Events from SDO  

NASA Astrophysics Data System (ADS)

We compare observational signatures of two GOES C8-class solar flares through instrumentation on Solar Dynamics Observatory (SDO). Data from the Atmospheric Imaging Assembly (AIA) and the Extreme Ultraviolet Variability Experiment (EVE) provide a unique look at the sun through global scale, fast cadence, high-resolution photometric and spectral measurements; this data is ideal for analyzing the temporal evolution of flare properties. The two flares studied differ in both time scale and morphology, one may be classified as a long duration event (LDE), while the other is highly impulsive. Differences are noted in behavior in the AIA EUV bands as well as several spectral lines. Furthermore, we apply both zero and one dimensional multi-threaded hydrodynamic loop models to synthesize light curves and spectra for each flare. Funding provided by NSF REU solar physics program at CfA, grant number ATM-0851866 and Marlboro College.

Bowen, Trevor; Testa, P.; Reeves, K.

2012-01-01

272

Predictions Of Energy And Helicity In Four Major Eruptive Solar Flares  

NASA Astrophysics Data System (ADS)

In order to better understand the solar genesis of interplanetary magnetic clouds (MCs) we model the magnetic and topological properties of four large eruptive solar flares and relate them to observations. We use the three-dimensional Minimum Current Corona model and observations of pre-flare photospheric magnetic field and flare ribbons to derive values of reconnected magnetic flux, flare energy, flux rope helicity and orientation of the flux rope poloidal field. We compare model predictions of those quantities to flare and MC observations and within the estimated uncertainties of the methods used find the following. The predicted model reconnection fluxes are equal to or lower than the observed reconnection fluxes from the ribbon motions. Both observed and model reconnection fluxes match the MC poloidal fluxes. The predicted flux rope helicities match the MC helicities. The predicted free energies lie between the observed energies and the estimated total flare luminosities. The direction of the leading edge of the MC's poloidal field is aligned with the poloidal field of the flux rope in the AR rather than the global dipole field. These findings compel us to believe that magnetic clouds associated with these four solar flares are formed by low-corona magnetic reconnection during the eruption, rather than eruption of pre-existing structures in the corona or formation in the upper corona with participation of the global magnetic field. We also note that since all four flares occurred in active regions without significant pre-flare flux emergence and cancellation, the energy and helicity we find are stored by shearing and rotating motions, which are sufficient to account for the observed radiative flare energy and MC helicity.

Kazachenko, Maria; Canfield, R. C.; Longcope, D. W.; Qiu, J.

2011-05-01

273

Thermal Evolution and Radiative Output of Solar Flares Observed by the EUV Variability Experiment (EVE)  

NASA Technical Reports Server (NTRS)

This paper describes the methods used to obtain the thermal evolution and radiative output during solar flares as observed by the Extreme u ltraviolet Variability Experiment (EVE) onboard the Solar Dynamics Ob servatory (SDO). Presented and discussed in detail are how EVE measur ements, due to its temporal cadence, spectral resolution and spectral range, can be used to determine how the thermal plasma radiates at v arious temperatures throughout the impulsive and gradual phase of fla res. EVE can very accurately determine the radiative output of flares due to pre- and in-flight calibrations. Events are presented that sh ow the total radiated output of flares depends more on the flare duration than the typical GOES X-ray peak magnitude classification. With S DO observing every flare throughout its entire duration and over a la rge temperature range, new insights into flare heating and cooling as well as the radiative energy release in EUV wavelengths support exis ting research into understanding the evolution of solar flares.

Chamberlin, P. C.; Milligan, R. O.; Woods, T. N.

2012-01-01

274

A CLASSIFICATION SCHEME FOR TURBULENT ACCELERATION PROCESSES IN SOLAR FLARES  

SciTech Connect

We establish a classification scheme for stochastic acceleration models involving low-frequency plasma turbulence in a strongly magnetized plasma. This classification takes into account both the properties of the accelerating electromagnetic field, and the nature of the transport of charged particles in the acceleration region. We group the acceleration processes as either resonant, non-resonant, or resonant-broadened, depending on whether the particle motion is free-streaming along the magnetic field, diffusive, or a combination of the two. Stochastic acceleration by moving magnetic mirrors and adiabatic compressions are addressed as illustrative examples. We obtain expressions for the momentum-dependent diffusion coefficient D(p), both for general forms of the accelerating force and for the situation when the electromagnetic force is wave-like, with a specified dispersion relation {omega} = {omega}(k). Finally, for models considered, we calculate the energy-dependent acceleration time, a quantity that can be directly compared with observations of the time profile of the radiation field produced by the accelerated particles, such as those occuring during solar flares.

Bian, Nicolas; Kontar, Eduard P. [School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Emslie, A. Gordon, E-mail: n.bian@physics.gla.ac.uk, E-mail: eduard@astro.gla.ac.uk, E-mail: emslieg@wku.edu [Department of Physics and Astronomy, Western Kentucky University, Bowling Green, KY 42101 (United States)

2012-08-01

275

Magnetic shielding of interplanetary spacecraft against solar flare radiation  

NASA Technical Reports Server (NTRS)

The ultimate objective of this work is to design, build, and fly a dual-purpose, piggyback payload whose function is to produce a large volume, low intensity magnetic field and to test the concept of using such a magnetic field (1) to protect spacecraft against solar flare protons, (2) to produce a thrust of sufficient magnitude to stabilize low satellite orbits against orbital decay from atmospheric drag, and (3) to test the magsail concept. These all appear to be capable of being tested using the same deployed high temperature superconducting coil. In certain orbits, high temperature superconducting wire, which has now been developed to the point where silver-sheathed high T sub c wires one mm in diameter are commercially available, can be used to produce the magnetic moments required for shielding without requiring any mechanical cooling system. The potential benefits of this concept apply directly to both earth-orbital and interplanetary missions. The usefulness of a protective shield for manned missions needs scarcely to be emphasized. Similarly, the usefulness of increasing orbit perigee without expenditure of propellant is obvious. This payload would be a first step in assessing the true potential of large volume magnetic fields in the US space program. The objective of this design research is to develop an innovative, prototype deployed high temperature superconducting coil (DHTSC) system.

Cocks, Franklin H.; Watkins, Seth

1993-01-01

276

SAR arc occurrence frequency during cycle 23 of solar activity  

Microsoft Academic Search

The occurrence frequency of SAR arcs during 19972006 has been analyzed based on the photometric observations at the Yakutsk\\u000a meridian (Maimaga station, corrected geomagnetic coordinates: 57 N, 200 E). SAR arcs appeared in 114 cases (?500 h) during\\u000a ?370 nights of observations (?3170 h). The occurrence frequency of SAR arcs increases to 27% during the growth phase of solar\\u000a activity

V. N. Alekseev; I. B. Ievenko

2008-01-01

277

Constraining Models Of The Solar Chromosphere Using An X2 Flare Observed By SDO/EVE  

NASA Astrophysics Data System (ADS)

The GOES X2 solar flare of Feb 15, 2011 is analyzed to draw observational constraints in constructing a model of the chromosphere of the Sun during a solar flare, using the Pandora computer program [1]. Spectra from the MEGS-A&B component of EVE [2] on board the Solar Dynamics Observatory are used to analyze the lines and continuum [3]. The irradiances before and after the flare are used for modeling the time-evolution of the impulsive and decay phases of the flare. Significant increase in the intensities of multiple coronal and chromospheric emission lines (H, He, C, N, O, Si etc.) is seen. The observed increase in intensities will serve as constraints to the model program. Pandora performs iterative calculations for non-LTE radiative transfer with multiple ions and atoms. It includes the effects of particle diffusion and flow velocities in the equations of radiative transfer and ionization equilibrium. The fraction of the area on the Sun contributing to the chromospheric flare emission is presented. The upper limit for the intensity in the Lyman continuum due to the flare is accounted to be approximately 7% of that due to the entire surface area. The Lyman, He II and He I continua provide strong constraints for characterizing the chromosphere. The emission lines from the CHIANTI atomic database in these wavelength ranges are considered in order to avoid using optically thin emission lines from the corona. The behavior of changes in line features with time is analyzed. The light curves of different lines that contribute substantially to the flare spectra are studied. The temperatures at the peak of the flare with respect to that at the quiet Sun is estimated at different continuum wavelengths. The pre-flare and post-flare values from these light-curves are adapted to construct the model during the rise and decay phases. The effective intensity due to the lines and the relative times at which these lines peak are presented. The observed irradiance values for pre-flare and at the peak of the flare are compared with those obtained by the model at the different temperatures and ion densities. The differences are adopted to match the model to the realistic flare atmosphere. References [1] Avrett, E. H., & Loeser, R., 1992, in Modeling of Stellar Atmospheres, IAU Symp. 210. [2] Wood, T. N., Eparvier, F. G. Hock, R., et al., 2009, Solar Phys. 275, 115-143 [3] Milligan, R. O., Chamberlin, P. C., Hudson, S. H., et al., 2012, ApJL, 748, L14

Venkataramanasastry, A.; Murphy, N. A.; Avrett, E.

2013-12-01

278

SAR arc occurrence frequency during cycle 23 of solar activity  

NASA Astrophysics Data System (ADS)

The occurrence frequency of SAR arcs during 1997 2006 has been analyzed based on the photometric observations at the Yakutsk meridian (Maimaga station, corrected geomagnetic coordinates: 57 N, 200 E). SAR arcs appeared in 114 cases (500 h) during 370 nights of observations (3170 h). The occurrence frequency of SAR arcs increases to 27% during the growth phase of solar activity and has a clearly defined maximum 36% at a decline of cycle 23. The SAR arc registration frequency corresponds to the variations in geomagnetic activity in this solar cycle. The dates, UT, and geomagnetic latitudes of photometric observations are presented for 1997 2006.

Alekseev, V. N.; Ievenko, I. B.

2008-08-01

279

Plasma Heating in the Very Early and Decay Phases of Solar Flares  

NASA Astrophysics Data System (ADS)

In this paper, we analyze the energy budgets of two single-loop solar flares under the assumption that non-thermal electrons (NTEs) are the only source of plasma heating during all phases of both events. The flares were observed by RHESSI and GOES on 2002 September 20 and 2002 March 17, respectively. For both investigated flares we derived the energy fluxes contained in NTE beams from the RHESSI observational data constrained by observed GOES light curves. We showed that energy delivered by NTEs was fully sufficient to fulfill the energy budgets of the plasma during the pre-heating and impulsive phases of both flares as well as during the decay phase of one of them. We concluded that in the case of the investigated flares there was no need to use any additional ad hoc heating mechanisms other than heating by NTEs.

Falewicz, R.; Siarkowski, M.; Rudawy, P.

2011-05-01

280

The relative timing of microwaves and hard X-rays in solar flares  

NASA Technical Reports Server (NTRS)

The timing of impulsive microwave and hard X-ray emission in solar flares with sub-second precision was compared. In flares demonstrating time structure on a scale less than approximately 1 s, 10.6 GHz microwaves were delayed with respect to hard X-rays by about 0.2 s. The delay varied from flare to flare and also within flares. No significant correlation was shown between the observed time delays and the peak X-ray or microwave flux or their ratio. Discussion included the electron propagation time from the top to the bottom of the loop, differential light travel time caused by the possible varying locations of the X-ray and microwave sources and the possible contamination of the microwave spikes with approximately 2 x 10 to the 7th K thermal emission.

Cornell, M. E.; Hurford, G. J.; Kiplinger, A. L.; Dennis, B. R.

1984-01-01

281

Skylab ATM/S-056 X-ray event analyzer observations versus solar flare activity: An event compilation. [tables (data)  

NASA Technical Reports Server (NTRS)

An event compilation is presented which correlates ATM/S-056 X-ray event analyzer solar observations with solar flare activity. Approximately 1,070 h of pulse height analyzed X-ray proportional counter data were obtained with the X-ray event analyzer during Skylab. During its operation, 449 flares (including 343 flare peaks) were observed. Seventy events of peak X-ray emission or = Cl were simultaneously observed by ground based telescopes, SOLRAD 9 and/or Vela, and the X-ray event analyzer. These events were observed from preflare through flare rise to peak and through flare decline.

Wilson, R. M.

1977-01-01

282

Evidence for a spatially extended component of gamma rays from solar flares  

NASA Technical Reports Server (NTRS)

We present gamma-ray measurements of a large solar flare that occurred beyond the western solar limb on September 29, 1989. The gamma-ray spectrum shows a neutron capture line which is much stronger than predicted by limb-darkening curves that fit the measurements for flares on the visible hemisphere. We show that this strong neutron capture line can be explained if, in addition to the compact impulsive phase component that normally dominates the total fluence, there is a spatially extended component. For the September 29, 1989 flare we find that such a spatially extended region must subtend more than about 30 deg on the solar surface. We suggest that the extended component could be powered by particles that diffuse from a compact impulsive region or by particles that diffuse into the lower solar atmosphere from a large-scale acceleration site.

Vestrand, W. T.; Forrest, David J.

1993-01-01

283

Inferring the Energy Distribution of Accelerated Electrons in Solar Flares from X-ray Observations  

NASA Technical Reports Server (NTRS)

Knowledge of the energy distribution of electrons accelerated in solar flares is important for constraining possible acceleration mechanisms and for understanding the relationships between flare X-ray sources, radio sources, and particles observed in space. Solar flare hard X-rays are primarily emitted from dense, thick-target regions in the lower atmosphere, but the electrons are understood to be accelerated higher in the corona. Various processes can distort the X-ray spectrum or the energy distribution of electrons before they reach the thick-target region. After briefly reviewing the processes that affect the X-ray spectrum and the electron distribution, I will describe recent results from a study of flare spectra from RHESSI to determine the importance of these processes in inferring the energy distribution of accelerated electrons.

Holman, Gordon D.; Sui, Linhui; Su, Yang

2008-01-01

284

Nonplanar mhd model for solar flare-generated disturbances in the heliospheric equatorial plane  

Microsoft Academic Search

An analysis, with a representative (canonical) example of solar-flare-generated equatorial disturbances, is presented for the temporal and spatial changes in the solar wind plasma and magnetic field environment between the Sun and one astronomical unit (AU). Our objective is to search for first order global consequences rather than to make a parametric study. The analysis - an extension of earlier

S. T. Wu; M. Dryer; S. M. Han

1983-01-01

285

Ionospheric electron density response to solar flares as viewed by Digisondes  

NASA Astrophysics Data System (ADS)

Solar flares are explosive events on the Sun that release energetic particles, X-rays, EUV, and radio emissions that have an almost immediate impact on Earth's ionosphere-thermosphere (IT) system and/or on operational systems that are affected by IT conditions. To assess such impacts, it is a key that we know how the ionosphere is modified. An objective of this paper is to evaluate how digisondes might serve in this role. Toward this end we utilize data from the Millstone Hill digisonde to reveal the height versus time bottomside F region responses to three X-class flares (X28, X8.3, and X1.7) at a middle latitude site. In terms of percent increase with respect to a preflare hourly mean, the long-lived (> 15-30 min) responses to these flares maximize between about 150 and 250 km and measurably last ~0.75-1.5 h after flare maximum. The relative magnitudes of these responses are complicated by flare position on the solar disk, which determines how much of the EUV solar emissions are attenuated by the solar atmosphere. At Millstone Hill there was little measurable response to these flares near the F2 layer peak; however, at the magnetic equator location of Jicamarca, the F2 peak electron density increased by ~15-40%. Herein, all of these flare response characteristics are interpreted in terms of available modeling results. We propose that such digisonde data, in combination with first-principles models and high-resolution measurements of solar EUV flux emissions (e.g., from Solar Dynamics Observatory/EUV Variability Experiment), can lead us to a deeper understanding of the ionospheric photochemistry and dynamics that underlies a predictive capability.

Handzo, R.; Forbes, J. M.; Reinisch, Bodo

2014-04-01

286

Extreme Ultraviolet Variability of the Large Solar Flare on April 21, 2002 and the Terrestrial Photoelectron Response  

Microsoft Academic Search

The near-simultaneous observations of the solar extreme ultraviolet (EUV) irradiance and terrestrial photoelectron distribution during and after the large solar flare on April 21, 2002 provide for a distinctive study of the effects that a solar flare can have on Earth's upper atmosphere. The solar EUV irradiance from 0.1-195 nm was measured by the Solar EUV Experiment (SEE) aboard the

F. G. Eparvier; T. N. Woods; S. M. Bailey; W. K. Peterson; S. C. Solomon; H. Garcia; J. L. Lean; H. P. Warren; C. W. Carlson; J. P. McFadden

2002-01-01

287

Forecast of daily solar flare peak flux using regressive and neural network methods  

NASA Astrophysics Data System (ADS)

We have developed a set of daily solar flare peak flux forecast models using the multiple linear regression, auto regression, and artificial neural network methods. We consider input parameters as solar activity data from January 1996 to December 2013 such as sunspot area, X-ray flare peak flux, weighted total flux Tf=1*Fc+10*Fm+100*Fx of previous day, mean flare rates of a given McIntosh sunspot group (Zpc), and a Mount Wilson magnetic classification. The hitting rate is defined as the fraction of events whose absolute differences between the observed and predicted fluxes in a logarithm scale are ? 0.5. The best three input parameters related to the observed flare peak flux are weighted total flare flux of previous day, Mount Wilson magnetic classification, and sunspot area. The hitting rates of flares stronger than M5 class, which is regarded to be significant for space weather forecast, are as follows: 0% for the multiple linear regression method, 30% for the auto regression method, and 69% for the neural network method. Especially, we note that for the forecast of strong flares, the neural network method is much more effective than the other methods.

Shin, Seulki; Lee, Jin-Yi; Moon, Yong-Jae

2014-06-01

288

Soft X-ray heating of the solar chromosphere during the gradual phase of two solar flares  

NASA Astrophysics Data System (ADS)

In this paper we perform an analysis of the energetics of the solar flaring chromosphere irradiated by soft X-rays (SXR) emitted from overlying hot flare loops. To study an expected SXR heating we used the observations of two solar flares obtained with the Multichannel Subtractive Double Pass (MSDP) spectrograph attached to the Large Coronagraph of the Wroc?aw University. SXR observations of these flares come from the Yohkoh SXR telescope (SXT). From MSDP spectral images we derived mean H? line profiles which were then used to construct semi-empirical non-LTE models of the chromosphere in the analyzed areas of flares. On the basis of SXR observations we calculated the mean emission measure EM and the temperature in flaring coronal structures located above the H? kernels under study and these two quantities were used to compute the SXR irradiation of the chromosphere between 1-300 . For each flare model we then evaluated the energy deposit due to such irradiation and compared it with the net radiative cooling rates at all depths in the chromosphere. By means of such modelling we were able to demonstrate that the enhanced emission of selected H? kernels observed during the gradual phase of these two solar flares cannot be explained in terms of the SXR heating of the chromosphere. We found that radiative losses in all layers of the chromosphere exceeded the amount of the energy deposited by the SXR radiation. However, for stronger flares with much enhanced EM a certain contribution of SXR to the heating cannot be ruled out.

Berlicki, A.; Heinzel, P.

2004-06-01

289

Comparing Solar-Flare Acceleration of >-20 MeV Protons and Electrons Above Various Energies  

NASA Technical Reports Server (NTRS)

A large fraction (up to tens of percent) of the energy released in solar flares goes into accelerated ions and electrons, and studies indicate that these two populations have comparable energy content. RHESSI observations have shown a striking close linear correlation between the 2.223 MeV neutron-capture gamma-ray line and electron bremsstrahlung emission >300 keV, indicating that the flare acceleration of >^20 MeV protons and >300 keV electrons is roughly proportional over >3 orders of magnitude in fluence. We show that the correlations of neutron-capture line fluence with GOES class or with bremsstrahlung emission at lower energies show deviations from proportionality, primarily for flares with lower fluences. From analyzing thirteen flares, we demonstrate that there appear to be two classes of flares with high-energy acceleration: flares that exhibit only proportional acceleration of ions and electrons down to 50 keV and flares that have an additional soft, low-energy bremsstrahlung component, suggesting two separate populations of accelerated electrons. We use RHESSI spectroscopy and imaging to investigate a number of these flares in detail.

Shih, Albert Y.

2010-01-01

290

Observation and Interpretation of Energetic Neutral Hydrogen Atoms from the December 5, 2006 Solar Flare  

NASA Technical Reports Server (NTRS)

We discuss observations of energetic neutral hydrogen atoms (ENAs) from a solar flare/coronal mass ejection event reported by Mewaldt et al. (2009). The observations were made during the 5 December 2006 X9 solar flare, located at E79, by the Low Energy Telescopes (LETs) on STEREO A and B. Prior to the arrival of the main solar energetic particle (SEP) event at Earth, both LETs observed a sudden burst of 1.6 to 15 MeV particles arriving from the Sun. The derived solar emission profile, arrival directions, and energy spectrum all show that the <5 MeV particles were due to energetic neutral hydrogen atoms produced by either flare or shock-accelerated protons. RHESSI measurements of the 2.2-MeV gamma-ray line provide an estimate of the number of interacting flare-accelerated protons in this event, which leads to an improved estimate of ENA production by flare-accelerated protons. CME-driven shock acceleration is also considered. Taking into account ENA losses, we conclude that the observed ENAs must have been produced in the high corona at heliocentric distances .2 solar radii.

Barghouty, A. F.; Mewaldt, R. A.; Leske, R. A.; Shih, A. Y.; Stone, E. C.; Cohen, C. M. S.; Cummings, A. C.; Labrador, A. W.; vonRosenvinge, T. T.; Wiedenbeck, M. E.

2009-01-01

291

A Very Small and Super Strong Zebra Pattern Burst at the Beginning of a Solar Flare  

NASA Astrophysics Data System (ADS)

Microwave emission with spectral zebra pattern structures (ZPs) is frequently observed in solar flares and the Crab pulsar. The previous observations show that ZP is a structure only overlapped on the underlying broadband continuum with slight increments and decrements. This work reports an unusually strong ZP burst occurring at the beginning of a solar flare observed simultaneously by two radio telescopes located in China and the Czech Republic and by the EUV telescope on board NASA's satellite Solar Dynamics Observatory on 2013 April 11. It is a very short and super strong explosion whose intensity exceeds several times that of the underlying flaring broadband continuum emission, lasting for just 18 s. EUV images show that the flare starts from several small flare bursting points (FBPs). There is a sudden EUV flash with extra enhancement in one of these FBPs during the ZP burst. Analysis indicates that the ZP burst accompanying an EUV flash is an unusual explosion revealing a strong coherent process with rapid particle acceleration, violent energy release, and fast plasma heating simultaneously in a small region with a short duration just at the beginning of the flare.

Tan, Baolin; Tan, Chengming; Zhang, Yin; Huang, Jing; Mszrosov, Hana; Karlick, Marian; Yan, Yihua

2014-08-01

292

Gamma-ray lines and neutrons from solar flares  

NASA Technical Reports Server (NTRS)

The energy spectrum of accelerated protons and nuclei at the site of a limb flare was derived by a technique, using observations of the time dependent flux of high energy neutrons at the Earth. This energy spectrum is very similar to the energy spectra of 7 disk flares for which the accelerated particle spectra was previously derived using observations of 4 to 7 MeV to 2.223 MeV fluence ratios. The implied spectra for all of these flares are too steep to produce any significant amount of radiation from pi meson decay. It is suggested that the observed 10 MeV gamma rays from the flare are bremsstrahlung of relativistic electrons.

Ramaty, R.; Murphy, R. J.; Kozlovsky, B.; Lingenfelter, R. E.

1983-01-01

293

Gamma-ray lines and neutrons from solar flares  

NASA Technical Reports Server (NTRS)

The energy spectrum of accelerated protons and nuclei at the site of a limb flare was derived by a technique, using observations of the time dependent flux of high energy neutrons at the earth. This energy spectrum is very similar to the energy spectra of 7 disk flares for which the accelerated particle spectra was previously derived using observations of 4 to 7 MeV to 2.223 MeV fluence ratios. The implied spectra for all of these flares are too steep to produce any significant amount of radiation from pi meson decay. It is suggested that the observed 10 MeV gamma rays from the flare are bremsstrahlung of relativistic electrons. Previously announced in STAR as N83-19695

Ramaty, R.; Murphy, R. J.; Kozlovsky, B.; Lingenfelter, R. E.

1983-01-01

294

Mass Motions and Plasma Properties in the 107 K Flare Solar Corona  

NASA Astrophysics Data System (ADS)

In the present work, we analyze Solar Ultraviolet Measurement of Emitted Radiation (SUMER) observations of a solar limb flare that occurred on 1999 May 9. The analyzed data cover a time span of around 6.4 hr, during which an M-7.6 flare erupted and decayed in the field of view. Two selected regions along the SUMER slit have been considered for quantitative analysis. The main purpose of the present analysis is to measure the mass motions and the nonthermal velocities of the postflare plasmas and their temporal evolution. To achieve this we use lines having formation temperatures in the 2.5106 to 2107 K range from which we derive net mass motions and nonthermal velocities and compare them with the properties of the surrounding plasma not affected by the flare activity. To understand the physical conditions of the flaring plasma and of the surrounding material, we derive electron temperature, electron density, and emission measures of the emitting plasma. We find that bulk motions, initially of the order of several hundreds of kilometers per second in both directions, decay within 10 minutes from the flare onset; nonthermal velocities decay to preflare values of around 30 km s-1 in less than 2 hr from the maximum value of around 100 km s-1 at flare onset. The measured electron density does not seem to change during activity, while the flare plasma temperature steadily decays to preflare values. The temperature evolution is consistent with a radiatively cooling plasma, although the uncertainties associated to the measurement of the variation of thermal energy of the flare plasma prevent a definitive conclusion on possible continuous heating of the flaring plasma.

Landi, E.; Feldman, U.; Innes, D. E.; Curdt, W.

2003-01-01

295

The interpretation of hard X-ray polarization measurements in solar flares  

NASA Technical Reports Server (NTRS)

Observations of polarization of moderately hard X-rays in solar flares are reviewed and compared with the predictions of recent detailed modeling of hard X-ray bremsstrahlung production by non-thermal electrons. The recent advances in the complexity of the modeling lead to substantially lower predicted polarizations than in earlier models and more fully highlight how various parameters play a role in determining the polarization of the radiation field. The new predicted polarizations are comparable to those predicted by thermal modeling of solar flare hard X-ray production, and both are in agreement with the observations. In the light of these results, new polarization observations with current generation instruments are proposed which could be used to discriminate between non-thermal and thermal models of hard X-ray production in solar flares.

Leach, J.; Emslie, A. G.; Petrosian, V.

1983-01-01

296

Directivity of 100-500 keV solar flare hard X-ray emission  

NASA Technical Reports Server (NTRS)

We have identified 28 solar flares simultaneously observed by a SIGNE detector aboard the Venera 13 and Venera 14 spacecraft and the Hard X-Ray Burst Spectrometer (HXRBS) aboard the Solar Maximum Mission (SMM), over a wide range of observing angles. Fourteen of them were also observed by the Gamma Ray Spectrometer (GRS) on SMM and were included in a study of the directivity of solar X-radiation. The SIGNE and HXRBS energy coverages overlap in the 50-500 keV range, allowing a detailed comparison of energy spectra. Using this database, we have conducted stereoscopic studies of flare hard X-ray anisotropy. It is found that the 100-500 keV directivity is less than 3, both for the entire set of 28 flares and for the 14 flares which gave evidence for directivity in the SMM GRS study. We conclude that solar flare X-ray directivity can only be marginally present in our energy/observing angle range.

Li, P.; Hurley, K.; Barat, C.; Niel, M.; Talon, R.; Kurt, V.

1994-01-01

297

The mechanism of temperature and pressure changes in the Earth's atmosphere during solar flares  

NASA Technical Reports Server (NTRS)

The effect of solar flares on the weather on Earth is examined. It is concluded that the processes which arise in the atmosphere are so intricate that a single calculation of solar activity is insufficient for long-range forecasting. However, combined consideration of processes dependent upon the dynamic instability of the atmosphere and the effect of solar activity will contribute to the improvement of long-range forecasts.

Reshetov, V. D.

1979-01-01

298

Sensing the Earths low ionosphere during solar flares using VLF signals and goes solar X-ray data  

NASA Astrophysics Data System (ADS)

An analysis of D-region electron density height profile variations, induced by four isolated solar X-ray flares during period from September 2005 to December 2006, based on the amplitude and the phase delay perturbation of 22.1 kHz signal trace from Skelton (54.72 N, 2.88 W) to Belgrade (44.85 N, 20.38 E), coded GQD, was carried out. Solar flare data were taken from NOAA GOES12 satellite one-minute listings. For VLF data acquisition and recordings at the Institute of Physics, Belgrade, Serbia, the AbsPAL system was used. Starting from LWPCv21 code (Ferguson, 1998), the variations of the Earth-ionosphere waveguide characteristic parameters, sharpness and reflection height, were estimated during the flare conditions. It was found that solar flare events affected the VLF wave propagation in the Earth-ionosphere waveguide by changing the lower ionosphere electron density height profile, in a different way, for different solar flare events.

Kolarski, Aleksandra; Grubor, Davorka

2014-06-01

299

Solar Demon: near real-time Flare, Dimming and EUV wave monitoring  

NASA Astrophysics Data System (ADS)

Dimmings and EUV waves have been observed routinely in EUV images since 1996. They are closely associated with coronal mass ejections (CMEs), and therefore provide useful information for early space weather alerts. On the one hand, automatic detection and characterization of dimmings and EUV waves can be used to gain better understanding of the underlying physical mechanisms. On the other hand, every dimming and EUV wave provides extra information on the associated front side CME, and can improve estimates of the geo-effectiveness and arrival time of the CME. Solar Demon has been designed to detect and characterize dimmings, EUV waves, as well as solar flares in near real-time on Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) data. The detection modules are running continuously at the Royal Observatory of Belgium on both quick-look data, as well as synoptic science data. The output of Solar Demon can be accessed in near real-time on the Solar Demon website, and includes images, movies, light curves, and the numerical evolution of several parameters. Solar Demon is the result of collaboration between the FP7 projects AFFECTS and COMESEP. Flare detections of Solar Demon are integrated into the COMESEP alert system. Here we present the Solar Demon detection algorithms and their output. We will show several interesting flare, dimming and EUV wave events, and present general statistics of the detections made so far during solar cycle 24.

Kraaikamp, Emil; Verbeeck, Cis

300

Solar extreme ultraviolet variability of the X-class flare on 21 April 2002 and the terrestrial photoelectron response  

Microsoft Academic Search

The near-simultaneous observations of the solar extreme ultraviolet (EUV) irradiance and terrestrial photoelectron distribution during and after the X-class flare on 21 April 2002 provide for a distinctive study of the effects that a solar flare can have on Earth's upper atmosphere. The solar EUV irradiance from 0.1 to 195 nm was measured by the Solar EUV Experiment (SEE) aboard

Thomas N. Woods; Scott M. Bailey; W. K. Peterson; Stanley C. Solomon; Harry P. Warren; Francis G. Eparvier; Howard Garcia; Charles W. Carlson; James P. McFadden

2003-01-01

301

Transition Region Emission and the Energy Input to Thermal Plasma in Solar Flares  

NASA Technical Reports Server (NTRS)

Understanding the energetics of solar flares depends on obtaining reliable determinations of the energy input to flare plasma. X-ray observations of the thermal bremsstrahlung from hot flare plasma provide temperatures and emission measures which, along with estimates of the plasma volume, allow the energy content of this hot plasma to be computed. However, if thermal energy losses are significant or if significant energy goes directly into cooler plasma, this is only a lower limit on the total energy injected into thermal plasma during the flare. We use SOHO UVCS observations of O VI flare emission scattered by coronal O VI ions to deduce the flare emission at transition region temperatures between 100,000 K and 1 MK for the 2002 July 23 and other flares. We find that the radiated energy at these temperatures significantly increases the deduced energy input to the thermal plasma, but by an amount that is less than the uncertainty in the computed energies. Comparisons of computed thermal and nonthermal electron energies deduced from RHESSI, GOES, and UVCS are shown.

Holman, Gordon D.; Holman, Gordon D.; Dennis, Brian R.; Haga, Leah; Raymond, John C.; Panasyuk, Alexander

2005-01-01

302

The Solar Flare 4: 10 keV X-ray Spectrum  

NASA Technical Reports Server (NTRS)

The 4-10 keV solar flare spectrum includes highly excited lines of stripped Ca, Fe, and Ni ions as well as a continuum steeply falling with energy. Groups of lines at approximately 7 keV and approximately 8 keV, observed during flares by the broad-band RHESSI spectrometer and called here the Fe-line and Fe/Ni-line features, are formed mostly of Fe lines but with Ni lines contributing to the approximately 8 keV feature. Possible temperature indicators of these line features are discussed - the peak or centroid energies of the Fe-line feature, the line ratio of the Fe-line to the Fe/Ni-line features, and the equivalent width of the Fe-line feature. The equivalent width is by far the most sensitive to temperature. However, results will be confused if, as is commonly believed, the abundance of Fe varies from flare to flare, even during the course of a single flare. With temperature determined from the thermal continuum, the Fe-line feature becomes a diagnostic of the Fe abundance in flare plasmas. These results are of interest for other hot plasmas in coronal ionization equilibrium such as stellar flare plasmas, hot gas in galaxies, and older supernova remnants.

Phillips, K. J. H.

2004-01-01

303

Abrupt Longitudinal Magnetic Field Changes and Ultraviolet Emissions Accompanying Solar Flares  

NASA Astrophysics Data System (ADS)

We have used Transition Region and Coronal Explorer 1600 images and Global Oscillation Network Group (GONG) magnetograms to compare ultraviolet (UV) emissions from the chromosphere to longitudinal magnetic field changes in the photosphere during four X-class solar flares. An abrupt, significant, and persistent change in the magnetic field occurred across more than 10 pixels in the GONG magnetograms for each flare. These magnetic changes lagged the GOES flare start times in all cases, showing that they were consequences and not causes of the flares. Ultraviolet emissions were spatially coincident with the field changes. The UV emissions tended to lag the GOES start times for the flares and led the changes in the magnetic field in all pixels except one. The UV emissions led the photospheric field changes by 4 minutes on average with the longest lead being 9 minutes; however, the UV emissions continued for tens of minutes, and more than an hour in some cases, after the field changes were complete. The observations are consistent with the picture in which an Alfvn wave from the field reconnection site in the corona propagates field changes outward in all directions near the onset of the impulsive phase, including downward through the chromosphere and into the photosphere, causing the photospheric field changes, whereas the chromosphere emits in the UV in the form of flare kernels, ribbons, and sequential chromospheric brightenings during all phases of the flare.

Johnstone, B. M.; Petrie, G. J. D.; Sudol, J. J.

2012-11-01

304

Understanding X-Ray Source Motions in a Solar Flare Loop  

NASA Technical Reports Server (NTRS)

RHESSI images of a solar flare on 2002 November 28 showed a 3-6 keV hard X-ray source that was initially located at the flare loop top, split and propagated to the foot points of the loop during the flare rise phase, and then propagated back up to the loop top during the declining phase of the flare (Sai, Holman, & Dennis 2006). Higher energy X-ray sources were located lower in the legs of the loop during this period of source evolution, with X-rays above 25 keV seen only at the foot points. Sui, Holman, & Dennis suggested that this spatial evolution reflected the evolution of the spectral index and low-energy cutoff to the distribution of accelerated electrons in the flare. We construct a model flare loop and electron distribution injected at the top of this loop to reproduce the source evolution of the November 28 flare. We determine the constraints on the loop model and the evolution of the accelerated electron distribution. We also study the implications of the model for energy deposition into the loop plasma, and the integrated and imaged X-ray spectra. This work is supported in part by the RHESSI Project and the NASA Guest Investigator Program.

Holman, Gordon D.; Sui, L.; Dennis, B. R.

2006-01-01

305

ABRUPT LONGITUDINAL MAGNETIC FIELD CHANGES AND ULTRAVIOLET EMISSIONS ACCOMPANYING SOLAR FLARES  

SciTech Connect

We have used Transition Region and Coronal Explorer 1600 A images and Global Oscillation Network Group (GONG) magnetograms to compare ultraviolet (UV) emissions from the chromosphere to longitudinal magnetic field changes in the photosphere during four X-class solar flares. An abrupt, significant, and persistent change in the magnetic field occurred across more than 10 pixels in the GONG magnetograms for each flare. These magnetic changes lagged the GOES flare start times in all cases, showing that they were consequences and not causes of the flares. Ultraviolet emissions were spatially coincident with the field changes. The UV emissions tended to lag the GOES start times for the flares and led the changes in the magnetic field in all pixels except one. The UV emissions led the photospheric field changes by 4 minutes on average with the longest lead being 9 minutes; however, the UV emissions continued for tens of minutes, and more than an hour in some cases, after the field changes were complete. The observations are consistent with the picture in which an Alfven wave from the field reconnection site in the corona propagates field changes outward in all directions near the onset of the impulsive phase, including downward through the chromosphere and into the photosphere, causing the photospheric field changes, whereas the chromosphere emits in the UV in the form of flare kernels, ribbons, and sequential chromospheric brightenings during all phases of the flare.

Johnstone, B. M.; Petrie, G. J. D.; Sudol, J. J. [Department of Physics, West Chester University, West Chester, PA 19383 (United States)

2012-11-20

306

Fluorescent excitation of photospheric Fe K-alpha emission during solar flares  

NASA Technical Reports Server (NTRS)

The Bent Crystal Spectrometer on the NASA Solar Maximum Mission satellite provides high spectral and temporal resolution observations of the Fe K-alpha lines. Analyses have been conducted of spectra from almost 50 solar flares that occurred during 1980. These data strongly support fluorescent excitation of photospheric iron by photons of E greater than 7.11 keV emitted by the hot coronal plasma produced during the flare. After comparison of the data with a model, the observed K-alpha line widths are discussed along with estimates of the size of the emitting region, the height of the coronal source and the photospheric iron abundance.

Parmar, A. N.; Culhane, J. L.; Rapley, C. G.; Phillips, K. J. H.; Wolfson, C. J.; Acton, L. W.; Dennis, B. R.

1982-01-01

307

On the possibility of detecting solar flare effects in the zodiacal light  

NASA Technical Reports Server (NTRS)

To evaluate possible effects of solar flares on the brightness of the inner zodiacal light, it is necessary to consider the brightness contribution along the line of sight and as a function of sun-particle distance. For this purpose, models of the brightness contribution along the line of sight are presented for both dielectric and metallic particles with a spatial distribution of the form 1, 1/r, and 1/r-squared. These models are discussed in terms of the geometry of shock front interaction. A reported zodiacal light enhancement following a solar flare (Blackwell and Ingham, 1961) is analyzed on the basis of the shock front geometry.

Misconi, N. Y.; Hanner, M. S.

1975-01-01

308

Search for correlations between solar flares and decay rate of radioactive nuclei  

NASA Astrophysics Data System (ADS)

The decay rate of three different radioactive sources (40K, 137Cs and natTh) has been measured with NaI and Ge detectors. Data have been analyzed to search for possible variations in coincidence with the two strongest solar flares of the years 2011 and 2012. No significant deviations from standard expectation have been observed, with a few 10-4 sensitivity. As a consequence, we could not find any effect like that recently reported by Jenkins and Fischbach: a few per mil decrease in the decay rate of 54Mn during solar flares in December 2006.

Bellotti, E.; Broggini, C.; Di Carlo, G.; Laubenstein, M.; Menegazzo, R.

2013-03-01

309

High-energy particle production in solar flares (SEP, gamma-ray and neutron emissions). [solar energetic particles  

NASA Technical Reports Server (NTRS)

Electrons and ions, over a wide range of energies, are produced in association with solar flares. Solar energetic particles (SEPs), observed in space and near earth, consist of electrons and ions that range in energy from 10 keV to about 100 MeV and from 1 MeV to 20 GeV, respectively. SEPs are directly recorded by charged particle detectors, while X-ray, gamma-ray, and neutron detectors indicate the properties of the accelerated particles (electrons and ions) which have interacted in the solar atmosphere. A major problem of solar physics is to understand the relationship between these two groups of charged particles; in particular whether they are accelerated by the same mechanism. The paper reviews the physics of gamma-rays and neutron production in the solar atmosphere and the method by which properties of the primary charged particles produced in the solar flare can be deduced. Recent observations of energetic photons and neutrons in space and at the earth are used to present a current picture of the properties of impulsively flare accelerated electrons and ions. Some important properties discussed are time scale of production, composition, energy spectra, accelerator geometry. Particular attention is given to energetic particle production in the large flare on June 3, 1982.

Chupp, E. L.

1987-01-01

310

Solar Flare Impulsive Phase Footpoint Emission Observed with SDO/EVE  

NASA Astrophysics Data System (ADS)

The differential emission measure of solar flare plasmas was constructed using observations from the EUV Variability Experiment (EVE) and the Markov-Chain Monte Carlo method. Emission lines from ions formed over the temperature range Log T = 5.8 - 7.4 allow for the evolution of the DEM to be studied over a wide temperature range at 10s cadence. The DEM construction technique is applied to several M and X-class flares where impulsive phase EUV emission is observable in the disk-integrated EVE spectra. The emission is verified using AIA images to be originating from the flare ribbons and footpoints and EVE observations are used to infer the thermal structure of the EUV emitting flare chromosphere. For the nine events studied the constructed differential emission measures have a two component distribution during the impulsive phase. The low temperature component has peak temperatures of 1 - 2 MK, and a high temperature component peaking at 10 MK.

Kennedy, Michael; Milligan, R. O.; Mathioudakis, M.

2013-07-01

311

Multi-Wavelength Analysis of the March 26, 1991: Solar Flare  

NASA Technical Reports Server (NTRS)

We have engaged in detailed multi-wavelength analysis of the March 26, 1991, solar flare in order to develop a method of diagnostics of the physical processes responsible for the efficient acceleration of charged particles to high energies and also for diagnostics of the photospheric response to the injection of the accelerated particles. Consideration of this particular flare is of special interest because to date it is the only flare in which the gamma-ray emission with energies of 20-1000 MeV was registered throughout the entire development of the event in the optical, radio and soft x-ray bands. individual registration by the GAMMA-1 telescope of the energy and precise time for each registered gamma-ray photon allowed the maximum detailed investigation of the energy spectrum and flux evolution during the flare.

Kurt, V. G.; Akimov, V. V.; Hagyard, Mona J.; Hathaway, D. H.

1999-01-01

312

Observations of Unresolved Photospheric Magnetic Fields in Solar Flares Using Fe i and Cr i Lines  

NASA Astrophysics Data System (ADS)

The structure of the photospheric magnetic field during solar flares is examined using echelle spectropolarimetric observations. The study is based on several Fe i and Cr i lines observed at locations corresponding to brightest H? emission during thermal phase of flares. The analysis is performed by comparing magnetic-field values deduced from lines with different magnetic sensitivities, as well as by examining the fine structure of I V Stokes-profiles' splitting. It is shown that the field has at least two components, with stronger unresolved flux tubes embedded in weaker ambient field. Based on a two-component magnetic-field model, we compare observed and synthetic line profiles and show that the field strength in small-scale flux tubes is about 2 - 3 kG. Furthermore, we find that the small-scale flux tubes are associated with flare emission, which may have implications for flare phenomenology.

Gordovskyy, M.; Lozitsky, V. G.

2014-10-01

313

The solar minimum X2.6/1B flare and CME of 9 July 1996. Pt. 1; Solar data  

NASA Technical Reports Server (NTRS)

The solar observations from GOES-8, the Solar and Heliospheric Observatory (SOHO), and the Yohkoh satellite concerning the events of the X-class flare are discussed. The Michelson Doppler imager (MDI) magnetometer shows a new region of magnetic activity in AR 7978. The rapid development and evolution of this region is shown by the MDI and the extreme-ultraviolet Doppler telescope (EDT) data. The coronal mass ejections (CMEs) observed using coronagraphs are presented. The possible association between the CME and the X-flare is considered.

Andrews, M. D.; Dryer, M.; Aurass, H.; DeForest, C.; Kiplinger, A. L.; Meisner, R.; Paswaters, S. E.; Smith, Z.; Tappin, S. J.; Thompson, B. J.; Watari, S.-I.; Lamy, P.; Mann, G.; Schwenn, R.; Michels, D. J.; Brueckner, G. E.; Howard, R. A.; Koomen, M.

1997-01-01

314

Observational Evidence for Gentle Chromospheric Evaporation During the Impulsive Phase of a Solar Flare  

E-print Network

Observational evidence for gentle chromospheric evaporation during the impulsive phase of a C9.1 solar flare is presented using data from the Reuven Ramaty High-Energy Solar Spectroscopic Imager and the Coronal Diagnostic Spectrometer on board the Solar and Heliospheric Observatory. Until now, evidence for gentle evaporation has often been reported during the decay phase of solar flares, where thermal conduction is thought to be the driving mechanism. Here we show that the chromospheric response to a low flux of nonthermal electrons (>=5x10^9 ergs cm^-2 s^-1) results in plasma upflows of 13+/-16, 16+/-18, and 110+/-58 km s^-1 in the cool He I and O V emission lines and the 8 MK Fe XIX line. These findings, in conjunction with other recently reported work, now confirm that the dynamic response of the solar atmosphere is sensitively dependent on the flux of incident electrons.

Ryan O. Milligan; Peter T. Gallagher; Mihalis Mathioudakis; Francis P. Keenan

2006-03-24

315

New RHESSI Results on Particle Acceleration and Energy Release in Solar Flares  

NASA Technical Reports Server (NTRS)

The primary scientific objective of NASA RHESSI mission (launched February 2002) is to investigate the physics of particle acceleration and energy release in solar flares, through imaging and spectroscopy of X-ray gamma-ray continuum and gamma-ray lines emitted by accelerated electrons and ions, respectively. Here I summarize the new solar observations, including the first hard X-ray imaging spectroscopy, the first high resolution spectroscopy of solar gamma ray lines, the first imaging of solar gamma ray lines and continuum, and the highest sensitivity hard X-ray observations of microflares and type III solar radio bursts.

Lin, R. P.

2003-01-01

316

Energy Partitions and Evolution in a Purely Thermal Solar Flare  

E-print Network

This paper presents a solely thermal flare, which we detected in the microwave range from the thermal gyro- and free-free emission it produced. An advantage of analyzing thermal gyro emission is its unique ability to precisely yield the magnetic field in the radiating volume. When combined with observationally-deduced plasma density and temperature, these magnetic field measurements offer a straightforward way of tracking evolution of the magnetic and thermal energies in the flare. For the event described here, the magnetic energy density in the radio-emitting volume declines over the flare rise phase, then stays roughly constant during the extended peak phase, but recovers to the original level over the decay phase. At the stage where the magnetic energy density decreases, the thermal energy density increases; however, this increase is insufficient, by roughly an order of magnitude, to compensate for the magnetic energy decrease. When the magnetic energy release is over, the source parameters come back to ne...

Fleishman, Gregory D; Gary, Dale E

2015-01-01

317

The allowed lines of O IV near 1340 A in high electron density solar flares  

NASA Technical Reports Server (NTRS)

Intersystem lines of O IV near 1400 A have long been used as electron density diagnostics for solar plasmas at temperatures of around 160,000 K. In addition, however, several allowed lines of O IV near 1340 A should become visible in conditions of high plasma electron number density (greater than 10(exp 12)/cu cm), such as during a solar flare. We present observations of the 1340 A and 1400 A regions of the solar spectrum for two solar flares, obtained by the SO82B spectrograph on board Skylab. We examine three candidate lines for allowed O IV in the flare spectra which occur at the correct wavelengths, but show that two of these are actually blends dominated by resonantly excited molecular lines of H2. The third candidate line, at 1343.51 A, we identify as the O IV allowd line. We present the density and temperature sensitivity of the ratio of allowed and intersystem O IV lines R = I(1343.51 A)/I(1407.39 A). The 1343.51 A line is clearly present in the first solar flare spectrum, and the ratio value implies an electron density of log N(sub e) = 12.6. The second flare has a much weaker 1343.51 A profile, but again the ratio value implies a high electron density. Both these electron density values are in good agreement with estimates for each flare from independent diagnostic ratios. The simple presence alone of a clearly observed O IV 1343.51 A emission line implies an electron density greater than 10(exp 12)/cu cm.

Cook, J. W.; Keenan, F. P.; Bhatia, A. K.

1994-01-01

318

IMPLOSION OF CORONAL LOOPS DURING THE IMPULSIVE PHASE OF A SOLAR FLARE  

SciTech Connect

We study the relationship between implosive motions in a solar flare, and the energy redistribution in the form of oscillatory structures and particle acceleration. The flare SOL2012-03-09T03:53 (M6.4) shows clear evidence for an irreversible (stepwise) coronal implosion. Extreme-ultraviolet (EUV) images show at least four groups of coronal loops at different heights overlying the flaring core undergoing fast contraction during the impulsive phase of the flare. These contractions start around a minute after the flare onset, and the rate of contraction is closely associated with the intensity of the hard X-ray and microwave emissions. They also seem to have a close relationship with the dimming associated with the formation of the coronal mass ejection and a global EUV wave. Several studies now have detected contracting motions in the corona during solar flares that can be interpreted as the implosion necessary to release energy. Our results confirm this, and tighten the association with the flare impulsive phase. We add to the phenomenology by noting the presence of oscillatory variations revealed by Geostationary Operational Environmental Satellite soft X-rays (SXR) and spatially integrated EUV emission at 94 and 335 . We identify pulsations of ?60 s in SXR and EUV data, which we interpret as persistent, semi-regular compressions of the flaring core region which modulate the plasma temperature and emission measure. The loop oscillations, observed over a large region, also allow us to provide rough estimates of the energy temporarily stored in the eigenmodes of the active-region structure as it approaches its new equilibrium.

Simes, P. J. A.; Fletcher, L.; Hudson, H. S.; Russell, A. J. B., E-mail: paulo.simoes@glasgow.ac.uk, E-mail: lyndsay.fletcher@glasgow.ac.uk, E-mail: arussell@maths.dundee.ac.uk, E-mail: hhudson@ssl.berkeley.edu [SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ (United Kingdom)

2013-11-10

319

Implosion of Coronal Loops during the Impulsive Phase of a Solar Flare  

NASA Astrophysics Data System (ADS)

We study the relationship between implosive motions in a solar flare, and the energy redistribution in the form of oscillatory structures and particle acceleration. The flare SOL2012-03-09T03:53 (M6.4) shows clear evidence for an irreversible (stepwise) coronal implosion. Extreme-ultraviolet (EUV) images show at least four groups of coronal loops at different heights overlying the flaring core undergoing fast contraction during the impulsive phase of the flare. These contractions start around a minute after the flare onset, and the rate of contraction is closely associated with the intensity of the hard X-ray and microwave emissions. They also seem to have a close relationship with the dimming associated with the formation of the coronal mass ejection and a global EUV wave. Several studies now have detected contracting motions in the corona during solar flares that can be interpreted as the implosion necessary to release energy. Our results confirm this, and tighten the association with the flare impulsive phase. We add to the phenomenology by noting the presence of oscillatory variations revealed by Geostationary Operational Environmental Satellite soft X-rays (SXR) and spatially integrated EUV emission at 94 and 335 . We identify pulsations of ?60 s in SXR and EUV data, which we interpret as persistent, semi-regular compressions of the flaring core region which modulate the plasma temperature and emission measure. The loop oscillations, observed over a large region, also allow us to provide rough estimates of the energy temporarily stored in the eigenmodes of the active-region structure as it approaches its new equilibrium.

Simes, P. J. A.; Fletcher, L.; Hudson, H. S.; Russell, A. J. B.

2013-11-01

320

WHAT IS THE RELATIONSHIP BETWEEN PHOTOSPHERIC FLOW FIELDS AND SOLAR FLARES?  

SciTech Connect

We estimated photospheric velocities by separately applying the Fourier Local Correlation Tracking and Differential Affine Velocity Estimator methods to 2708 co-registered pairs of SOHO/MDI magnetograms, with nominal 96 minute cadence and approx2'' pixels, from 46 active regions (ARs) from 1996 to 1998 over the time interval tau{sub 45} when each AR was within 45{sup 0} of disk center. For each magnetogram pair, we computed the reprojected, average estimated radial magnetic field, B-tilde{sub R}; and each tracking method produced an independently estimated flow field, u. We then quantitatively characterized these magnetic and flow fields by computing several extensive and intensive properties of each; extensive properties scale with AR size, while intensive properties do not depend directly on AR size. Intensive flow properties included moments of speeds, horizontal divergences, and radial curls; extensive flow properties included sums of these properties over each AR, and a crude proxy for the ideal Poynting flux, S{sub R}=SIGMA|u|B-tilde{sub R}{sup 2}. Several quantities derived from B-tilde{sub R} were also computed, including: PHI, the total unsigned flux; R, a measure of the unsigned flux near strong-field polarity inversion lines; and SIGMAB-tilde{sub R}{sup 2}. Next, using correlation and discriminant analysis, we investigated the associations between these properties and flares from the GOES flare catalog, when averaged over both tau{sub 45} and shorter time windows of 6 and 24 hr. Our AR sample included both flaring and flare-quiet ARs; the latter did not flare above GOES C1.0 level during tau{sub 45}. Among magnetic properties, we found R to be most strongly associated with flare flux. Among extensive flow properties, the proxy Poynting flux, S{sub R} , was most strongly associated with flare flux, at a level comparable to that of R. All intensive flow properties studied were more poorly associated with flare flux than these extensive properties. Past flare activity was also associated with future flare occurrence. The largest coefficients of determination from correlations with flare flux that we performed are approx0.25, implying no single variable that we considered can explain the majority of variability in average flare flux.

Welsch, Brian T.; Li Yan; Fisher, George H. [Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450 (United States); Schuck, Peter W., E-mail: welsch@ssl.berkeley.ed [Heliophysics Science Division, Space Weather Laboratory, Code 674, NASA Goddard Space Flight Center, 8801 Greenbelt Road, Greenbelt, MD 20771 (United States)

2009-11-01

321

Energetic Electrons in Solar Flares - As Viewed in X-Rays  

NASA Technical Reports Server (NTRS)

Hard X-ray observations provide the most direct diagnostic we have of the suprathermal electrons and the hottest thermal plasma present in solar flares. The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is obtaining the most comprehensive observations of individual solar flares ever available in hard X-rays. For the first time, high-resolution spectra are available for a large number of flares that accurately display the spectral shape and its evolution and, in many cases, allow us to identify the transition from the bremsstrahlung X-rays produced by suprathermal electrons to the bremsstrahlung at lower energies emitted by thermal plasma. Also, for the first time, images can be produced in arbitrary energy bands above 3 keV, and spectra of distinct imaged components can be obtained. I will review what we have learned from RHESSI observations about flare suprathermal electron distributions and their evolution Next, I will present computations of the energy deposited by these suprathermal electrons in individual flares and compare this with the energy contained in the hot thermal plasma. I will point out unsolved problems in deducing both suprathermal electron distributions and the energy content of the thermal plasma, and discuss possible solutions. Finally, I will present evidence that electron acceleration is associated with magnetic reconnection in the corona.

Holman, Gordon D.

2004-01-01

322

OBSERVATIONAL EVIDENCE OF CHANGING PHOTOSPHERIC VECTOR MAGNETIC FIELDS ASSOCIATED WITH SOLAR FLARES  

SciTech Connect

Recent observations have provided evidence that the solar photospheric magnetic fields could have rapid and permanent changes in both longitudinal and transverse components associated with major flares. As a result, the Lorentz force (LF) acting on the solar photosphere and solar interior could be perturbed, and the change of LF is always nearly in the downward direction. However, these rapid and permanent changes have not been systematically investigated, yet, using vector magnetograms. In this paper, we analyze photospheric vector magnetograms covering five flares to study the evolution of photospheric magnetic fields. In particular, we investigate two-dimensional spatial distributions of the changing LF. Around the major flaring polarity inversion line, the net change of the LF is directed downward in an area of {approx}10{sup 19} cm{sup 2} for X-class flares. For all events, the white-light observations show that sunspots darken in this location after flares, and magnetic fields become more inclined, which is consistent with the ideas put forward by Hudson et al. and Fisher et al., and observations.

Su, J. T.; Jing, J.; Wang, H. M. [Space Weather Research Laboratory, New Jersey Institute of Technology, University Heights, Newark, NJ 07102-1982 (United States); Mao, X. J.; Wang, X. F.; Zhang, H. Q.; Deng, Y. Y.; Guo, J.; Wang, G. P., E-mail: sjt@bao.ac.cn [Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

2011-06-01

323

Microwave Zebra Pattern Structures in the X2.2 Solar Flare on 2011 February 15  

NASA Astrophysics Data System (ADS)

A zebra pattern (ZP) structure is the most intriguing fine structure on the dynamic spectrograph of a solar microwave burst. On 2011 February 15, an X2.2 flare event erupted on the solar disk, which is the first X-class flare since the solar Schwabe cycle 24. It is interesting that there are several microwave ZPs observed by the Chinese Solar Broadband Radio Spectrometer (SBRS/Huairou) at a frequency of 6.40-7.00 GHz (ZP1) and at a frequency of 2.60-2.75 GHz (ZP2) and by the Yunnan Solar Broadband Radio Spectrometer (SBRS/Yunnan) at a frequency of 1.04-1.13 GHz (ZP3). The most important phenomenon is the unusual high-frequency ZP structure (ZP1, up to 7.00 GHz) that occurred in the early rising phase of the flare and the two ZP structures (ZP2, ZP3) with relatively low frequencies that occurred in the decay phase of the flare. By scrutinizing the current prevalent theoretical models of ZP structure generations and comparing their estimated magnetic field strengths in the corresponding source regions, we suggest that the double plasma resonance model is the most probable one for explaining the formation of microwave ZPs, which may derive the magnetic field strengths at about 230-345 G, 126-147 G, and 23-26 G in the source regions of ZP1, ZP2, and ZP3, respectively.

Tan, Baolin; Yan, Yihua; Tan, Chengming; Sych, Robert; Gao, Guannan

2012-01-01

324

Fields and Flares: Understanding the Complex Magnetic Topologies of Solar Active Regions  

NASA Astrophysics Data System (ADS)

Sunspots are regions of decreased brightness on the visible surface of the Sun (photosphere) that are associated with strong magnetic fields. They have been found to be locations associated with solar flares, which occur when energy stored in sunspot magnetic fields is suddenly released. The processes involved in flaring and the link between sunspot magnetic fields and flares is still not fully understood, and this thesis aims to gain a better understanding of these topics. The magnetic field evolution of a number of sunspot regions is examined using high spatial resolution data from the Hinode spacecraft. The research presented in this thesis gives insight into both photospheric and coronal magnetic field evolution of flaring regions. Significant increases in vertical field strength, current density, and field inclination angle towards the vertical are observed in the photosphere just hours before a flare occurs, which is on much shorter timescales than previously studied. First observations of spatial changes in field inclination across a magnetic neutral line (generally believed to be a typical source region of flares) are also discovered. 3D magnetic field extrapolation methods are used to study the coronal magnetic field, using the photospheric magnetic field data as a boundary condition. Magnetic energy and free magnetic energy are observed to increase significantly a few hours before a flare, and decrease afterwards, which is a similar trend to the photospheric field parameter changes observed. Evidence of partial Taylor relaxation is also detected after a flare, as predicted by several previous studies. The results outlined in this thesis show that this particular field of research is vital in furthering our understanding of the magnetic nature of sunspots and its link to flare processes.

Murray, Sophie A.

2013-01-01

325

Study of Two Successive Three-ribbon Solar Flares on 2012 July 6  

NASA Astrophysics Data System (ADS)

This Letter reports two rarely observed three-ribbon flares (M1.9 and C9.2) on 2012 July 6 in NOAA AR 11515, which we found using H? observations of 0.''1 resolution from the New Solar Telescope and Ca II H images from Hinode. The flaring site is characterized by an intriguing "fish-bone-like" morphology evidenced by both H? images and a nonlinear force-free field (NLFFF) extrapolation, where two semi-parallel rows of low-lying, sheared loops connect an elongated, parasitic negative field with the sandwiching positive fields. The NLFFF model also shows that the two rows of loops are asymmetric in height and have opposite twists, and are enveloped by large-scale field lines including open fields. The two flares occurred in succession within half an hour and are located at the two ends of the flaring region. The three ribbons of each flare run parallel to the magnetic polarity inversion line, with the outer two lying in the positive field and the central one in the negative field. Both flares show surge-like flows in H? apparently toward the remote region, while the C9.2 flare is also accompanied by EUV jets possibly along the open field lines. Interestingly, the 12-25 keV hard X-ray sources of the C9.2 flare first line up with the central ribbon then shift to concentrate on the top of the higher branch of loops. These results are discussed in favor of reconnection along the coronal null line, producing the three flare ribbons and the associated ejections.

Wang, Haimin; Liu, Chang; Deng, Na; Zeng, Zhicheng; Xu, Yan; Jing, Ju; Cao, Wenda

2014-01-01

326

Study of Two Successive Three-ribbon Solar Flares Using BBSO/NST Observations  

NASA Astrophysics Data System (ADS)

We studied two rarely observed three-ribbon flares (M1.9 and C9.2) on 2012 July 6 in NOAA AR 11515, which we found using H? observations of 0.1 arcsec resolution from the New Solar Telescope and Ca II H images from Hinode. The flaring site is characterized by an intriguing "fish-bone-like" morphology evidenced by both Halpha images and a nonlinear force-free field (NLFFF) extrapolation, where two semi-parallel rows of low-lying, sheared loops connect an elongated, parasitic negative field with the sandwiching positive fields. The NLFFF model also shows that the two rows of loops are asymmetric in height and have opposite twists, and are enveloped by large-scale field lines including open fields. The two flares occurred in succession within half an hour and are located at the two ends of the flaring region. The three ribbons of each flare run parallel to the magnetic polarity inversion line, with the outer two lying in the positive field and the central one in the negative field. Both flares show surge-like flows in Halpha apparently toward the remote region, while the C9.2 flare is also accompanied by EUV jets possibly along the open field lines. Interestingly, the 12-25 keV hard X-ray sources of the C9.2 flare first line up with the central ribbon then shift to concentrate on the top of the higher branch of loops. These results are discussed in favor of reconnection along the coronal null line, producing the three flare ribbons and the associated ejections.

Wang, Haimin; Liu, Chang; Deng, Na; Zeng, Zhicheng; Xu, Yan; Jing, Ju; Cao, Wenda

2014-06-01

327

Quasi-periodic Pulsations in Solar and Stellar Flares: Re-evaluating their Nature in the Context of Power-law Flare Fourier Spectra  

NASA Astrophysics Data System (ADS)

The nature of quasi-periodic pulsations (QPPs) in solar and stellar flares remains debated. Recent work has shown that power-law-like Fourier power spectra are an intrinsic property of solar and stellar flare signals, a property that many previous studies of this phenomenon have not accounted for. Hence a re-evaluation of the existing interpretations and assumptions regarding QPPs is needed. We adopt a Bayesian method for investigating this phenomenon, fully considering the Fourier power-law properties of flare signals. Using data from the PROBA2/Large Yield Radiometer, Fermi/Gamma-ray Burst Monitor, Nobeyama Radioheliograph, and Yohkoh/HXT instruments, we study a selection of flares from the literature identified as QPP events. Additionally, we examine optical data from a recent stellar flare that appears to exhibit oscillatory properties. We find that, for all but one event tested, an explicit oscillation is not required to explain the observations. Instead, the flare signals are adequately described as a manifestation of a power law in the Fourier power spectrum. However, for the flare of 1998 May 8, strong evidence for an explicit oscillation with P ? 14-16 s is found in the 17 GHz radio data and the 13-23 keV Yohkoh/HXT data. We conclude that, most likely, many previously analyzed events in the literature may be similarly described by power laws in the flare Fourier power spectrum, without invoking a narrowband, oscillatory component. Hence the prevalence of oscillatory signatures in solar and stellar flares may be less than previously believed. The physical mechanism behind the appearance of the observed power laws is discussed.

Inglis, A. R.; Ireland, J.; Dominique, M.

2015-01-01

328

Time-dependent Density Diagnostics of Solar Flare Plasmas Using SDO/EVE  

NASA Astrophysics Data System (ADS)

Temporally resolved electron density measurements of solar flare plasmas are presented using data from the EUV Variability Experiment (EVE) on board the Solar Dynamics Observatory. The EVE spectral range contains emission lines formed between 104 and 107 K, including transitions from highly ionized iron (gsim10 MK). Using three density-sensitive Fe XXI ratios, peak electron densities of 1011.2-1012.1 cm-3 were found during four X-class flares. While previous measurements of densities at such high temperatures were made at only one point during a flaring event, EVE now allows the temporal evolution of these high-temperature densities to be determined at 10 s cadence. A comparison with GOES data revealed that the peak of the density time profiles for each line ratio correlated well with that of the emission measure time profile for each of the events studied.

Milligan, Ryan O.; Kennedy, Michael B.; Mathioudakis, Mihalis; Keenan, Francis P.

2012-08-01

329

Observations with the SMM gamma-ray spectrometer - The impulsive solar flares of 1980 March 29  

NASA Technical Reports Server (NTRS)

Gamma-ray continuum emission from 0.3 to 1 MeV was observed with the gamma-ray spectrometer on the Solar Maximum Mission satellite during two impulsive solar flares on 1980 March 29, from active region 2363 at 0918 UT and from active region 2357 at 0955 UT. Evidence is presented for a hardening of the spectrum during the impulsive phase of the flares. The photon intensity greater than 100 keV appears to decay at a slower rate than that at lower energies. Time-integrated photon spectra for both flares are incompatible with a single-temperature thermal-bremsstrahlung model. Upper limits for prompt and delayed gamma-ray lines are presented.

Ryan, J. M.; Forrest, D. J.; Chupp, E. L.; Cherry, M. L.; Reppin, C.; Rieger, E.; Pinkau, K.; Kanbach, G.; Share, G. H.; Kinzer, R. L.

1981-01-01

330

Comparison between Hinode/SOT and SDO/HMI, AIA data for the study of the solar flare trigger process  

NASA Astrophysics Data System (ADS)

Understanding the mechanism that produces solar flares is important not only from the scientific point of view but also for improving space weather predictability. There are numerous observational and computational studies that have attempted to reveal the onset mechanism of solar flares. However, the underlying mechanism of flare onset remains elusive. To elucidate the flare trigger mechanism, we analyzed several flare events which were observed by Hinode/Solar Optical Telescope (SOT) in our previous study. Because of the limitation of the SOT field of view, however, only four events in the Hinode data sets have been usable. Therefore, increasing the number of events is required for evaluating the flare trigger models. We investigated the applicability of data obtained by the Solar Dynamics Observatory (SDO) to increase the data sample for a statistical analysis of the flare trigger process. SDO regularly observes the full disk of the sun and all flares, although its spatial resolution is lower than that of Hinode. We investigated the M6.6 flare which occurred on 2011 February 13, and compared the analyzed data of SDO with the results of our previous study using Hinode/SOT data. Filter and vector magnetograms obtained by the Helioseismic and Magnetic Imager and filtergrams from the Atmospheric Imaging Assembly (AIA) 1600 were employed. From the comparison of small-scale magnetic configurations and chromospheric emission prior to the flare onset, we confirmed that the trigger region is detectable with the SDO data. We also measured the magnetic shear angles of the active region and the azimuth and strength of the flare trigger field. The results were consistent with our previous study. We concluded that statistical studies of the flare trigger process are feasible with SDO as well as Hinode data. We also investigated the temporal evolution of the magnetic field before the flare onset with SDO.

Bamba, Yumi; Kusano, Kanya; Imada, Shinsuke; Iida, Yusuke

2014-12-01

331

Relaxation of Magnetic Field Relative to Plasma Density Revealed from Microwave Zebra Patterns Associated with Solar Flares  

NASA Astrophysics Data System (ADS)

It is generally considered that the emission of microwave zebra pattern (ZP) structures requires high density and high temperature, which is similar to the situation of the flaring region where primary energy is released. Therefore, a parameter analysis of ZPs may reveal the physical conditions of the flaring source region. This work investigates the variations of 74 microwave ZP structures observed by the Chinese Solar Broadband Radio Spectrometer (SBRS/Huairou) at 2.6-3.8 GHz in nine solar flares, and we find that the ratio between the plasma density scale height LN and the magnetic field scale height LB in emission sources displays a tendency to decrease during the flaring processes. The ratio LN /LB is about 3-5 before the maximum of flares. It decreases to about 2 after the maximum. The detailed analysis of three typical X-class flares implies that the variation of LN /LB during the flaring process is most likely due to topological changes of the magnetic field in the flaring source region, and the stepwise decrease of LN /LB possibly reflects the magnetic field relaxation relative to the plasma density when the flaring energy is released. This result may also constrain solar flare modeling to some extent.

Yu, Sijie; Yan, Yihua; Tan, Baolin

2012-12-01

332

Ionization effects due to solar flare on terrestrial ionosphere  

NASA Technical Reports Server (NTRS)

Sudden frequency deviation ionospheric disturbances related to the flares of May 18 and 19, 1973 were observed from the NASA/MSFC high frequency Doppler sounder array system in Huntsville, Alabama. The results are compared with those observed at Table Mountain near Boulder, Colorado and at the University of Hawaii.

Wu, S. T.; Tan, A.

1976-01-01

333

Stochastic Particle Acceleration by Helical Turbulence in Solar Flares  

NASA Astrophysics Data System (ADS)

Modern X-ray and radio observations favor a stochastic (Fermi) acceleration mechanism of fast particles produced in flares, which implies that an accelerating turbulence must somehow be generated by the primary flare energy release. The very release of free magnetic energy is only possible if the magnetic field deviates from a potential one. We show that this magnetic field nonpotentiality, via its corresponding current helicity, necessarily results in a noticeable kinetic helicity of the turbulence generated at the flare site by the primary energy release. We study the role of the turbulence helicity on the particle acceleration and find that a nonzero turbulence helicity has a remarkably strong effect on the particle acceleration. The main reason for this strong helicity effect is that the helical component of the turbulence induces, through a well-known alpha-effect, a regular large-scale electric field capable of directly accelerating charged particles (like in the models with DC field acceleration). We estimate the turbulence kinetic helicity based on measured photospheric and extrapolated values of the current helicity and take into consideration the helical turbulence effect on stochastic particle acceleration. We find that this induced large-scale electric field can be comparable with the electron and estimated effective ion Dreicer fields, which has an immediate effect on charged particle extraction from the thermal pool and their injection into stochastic acceleration process. We have discovered that this, so far missing but highly important, ingredient of the particle stochastic acceleration by turbulence at the flare site is naturally consistent with such puzzling flare manifestations as spatial separation of electron and proton emission sites, electron beam formation, and enrichment of the accelerated particle population by 3He and other tiny ions. This work was supported in part by NSF grant AGS-0961867 and NASA grant NNX10AF27G to New Jersey Institute of Technology.

Fleishman, Gregory D.; Toptygin, I. N.

2012-05-01

334

Extreme Ultraviolet Late-Phase Flares: Before and During the Solar Dynamics Observatory Mission  

NASA Astrophysics Data System (ADS)

The solar extreme-ultraviolet (EUV) observations from the Solar Dynamics Observatory (SDO) have revealed interesting characteristics of warm coronal emissions, such as Fe xvi 335 emission, which peak soon after the hot coronal X-ray emissions peak during a flare and then sometimes peak for a second time hours after the X-ray flare peak. This flare type, with two warm coronal emission peaks but only one X-ray peak, has been named the EUV late phase (Woods et al., Astrophys. J. 739, 59, 2011). These flares have the distinct properties of i) having a complex magnetic-field structure with two initial sets of coronal loops, with one upper set overlaying a lower set, ii) having an eruptive flare initiated in the lower set and disturbing both loop sets, iii) having the hot coronal emissions emitted only from the lower set in conjunction with the X-ray peak, and iv) having the first peak of the warm coronal emissions associated with the lower set and its second peak emitted from the upper set many minutes to hours after the first peak and without a second X-ray enhancement. The disturbance of the coronal loops by the eruption is at about the same time, but the relaxation and cooling down of the heated coronal loops during the post-flare reconnections have different time scales with the longer, upper loops being significantly delayed from the lower loops. The difference in these cooling time scales is related to the difference between the two peak times of the warm coronal emission and is also apparent in the decay profile of the X-ray emissions having two distinct decays, with the first decay slope being steeper (faster) and the delayed decay slope being smaller (slower) during the time of the warm-coronal-emission second peak. The frequency and relationship of the EUV late-phase decay times between the Fe xvi 335 two flare peaks and X-ray decay slopes are examined using three years of SDO/ EUV Variability Experiment (EVE) data, and the X-ray dual-decay character is then exploited to estimate the frequency of EUV late-phase flares during the past four solar cycles. This study indicates that the frequency of EUV late-phase flares peaks before and after each solar-cycle minimum.

Woods, Thomas N.

2014-09-01

335

The contribution of microbunching instability to solar flare emission in the GHz to THz range of frequencies  

SciTech Connect

Recent solar flare observations in the sub-terahertz range have provided evidence of a new spectral component with fluxes increasing for larger frequencies, separated from the well-known microwave emission that maximizes in the gigahertz range. Suggested interpretations explain the terahertz spectral component but do not account for the simultaneous microwave component. We present a mechanism for producing the observed "double spectra." Based on coherent enhancement of synchrotron emission at long wavelengths in laboratory accelerators, we consider how similar processes may occur within a solar flare. The instability known as microbunching arises from perturbations that produce electron beam density modulations, giving rise to broadband coherent synchrotron emission at wavelengths comparable to the characteristic size of the microbunch structure. The spectral intensity of this coherent synchrotron radiation (CSR) can far exceed that of the incoherent synchrotron radiation (ISR), which peaks at a higher frequency, thus producing a double-peaked spectrum. Successful CSR simulations are shown to fit actual burst spectral observations, using typical flaring physical parameters and power-law energy distributions for the accelerated electrons. The simulations consider an energy threshold below which microbunching is not possible because of Coulomb repulsion. Only a small fraction of the radiating charges accelerated to energies above the threshold is required to produce the microwave component observed for several events. The ISR/CSR mechanism can occur together with other emission processes producing the microwave component. It may bring an important contribution to microwaves, at least for certain events where physical conditions for the occurrence of the ISR/CSR microbunching mechanism are possible.

Klopf, J. Michael [William and Mary College; Kaufmann, Pierre; Raulin, Jean-Pierre; Szpigel, Sergio

2014-07-01

336

Effect of radioactivity decrease. Is there a link with solar flares?  

E-print Network

Results obtained with multichannel installation created for long-term studies of various processes, are collated with the data published by J.H. Jenkins and E.Fischbach, who found a decrease of 54Mn radioactivity near the time of series of solar flares between 5 and 17 December 2006. Analysis of the data from our installation in December 2006 has not revealed any deviations from the usual behaviour of the count rates for 90Sr-90Y, 60Co and 239Pu sources. The same can be said of the data collected during the period of highly powerful solar flares between 19 October and 4 November 2003. Apparent drops in the count rate were detected between 10 and 12 May 2002 while registering the activity of 60Co and on 19 and 20 June 2004 for 90Sr-90Y source. Around the time of these events, no observations of large solar flares were reported. Thus, proposed link between the drop in the rates of radioactive decay and appearance of solar flares could not be confirmed. From obtained outcomes follows, that the radioactivity drop effect, if it really exists, is rather rare, and that the reason calling this effect unequally influences various radioactive sources.

A. G. Parkhomov

2010-05-15

337

Low-Energy Cosmic-Ray Events Associated with Solar Flares  

Microsoft Academic Search

As a result of the IGY riometer program, it has been found that the measure- ment of ionospheric absorption in arctic regions is a sensitive method of detecting low-energy cosmic rays associated with solar flares. The normal morphology of these events is described, and details are given of the 24 such events that have been detected in the period from

George C. Reid; Harold Leinbach

1959-01-01

338

Conductive flux in flaring solar chromospheres deduced from the linear polarization observations  

Microsoft Academic Search

The linear polarization of Halpha and S I 1437 lines produced in impact excitation by energetic electrons with an anisotropic velocity distribution function during solar flares is calculated. Selecting a function which represents the velocity distribution of electrons carrying heat flux, the relationship between conductive heat flux and linear line polarization has been computed. The application of the relationship

J. C. Henoux; D. Heristchi; G. Chambe; B. Woodgate; R. Shine; J. Beckers; M. Machado

1983-01-01

339

Relationship between Hard X-ray Emissions and Magnetic Field Strengths in Solar Flares  

Microsoft Academic Search

An asymmetric hard X-ray (HXR) characteristic in conjugate footpoints of newly reconnected magnetic fields, i.e. stronger HXR emissions with weaker magnetic fields and vice versa, is commonly observed in solar flares. It can be explained by the asymmetric magnetic mirroring that weaker magnetic fields would result in higher precipitation rate of energetic electrons from corona to chromosphere and thus stronger

M. Hsieh; Y. Yang; C. Z. Cheng

2009-01-01

340

Investigation of the energy-height relation for solar flare footpoints observed by RHESSI  

E-print Network

Investigation of the energy-height relation for solar flare footpoints observed by RHESSI T E0: Relation between a height and an energy of the source should be observed. Observed relation calculation) Energy: 15-50 keV Heights: 4000-700 km Aschwanden, M.J., Brown, J.C. & Kontar, E.P., 2002, Sol

Mrozek, Tomasz

341

Statistical properties of H-alpha and HXR flares in the cycle 23 in relation to sunspots and active regions detected from the Solar Feature Catalogues  

NASA Astrophysics Data System (ADS)

The statistical properties of H-alpha and hard X-ray solar flares are investigated in relation to the cycle variations in 1996-2006 of sunspots and active regions (plages) obtained from the automated Soar Feature Catalogues (SFC, http://solar.inf.brad.ac.uk). Cross-correlation analysis is carried out between flare sizes, locations, significance and active region/sunspot parameters including magnetic field extracted in SFC. Sunspot and plage area distributions reveals a strong North-South asymmetry of about 0.2 and the period of about 7-8 years for sunspots and of 0.5 and period of 9 years for plages with both asymmetries decreasing towards the next cycle minimum. The temporal distribution of solar flare occurrences in Northern and Southern hemispheres, at different latitudes and longitudes are compared with those of plage and sunspot areas and LOS magnetic fields. The spectral indices of HXR and gamma-ray emission wer used to estimate magnetic field components and their variations with the cycle. The application of these results to the solar activity forecast is discussed.

Zharkova, V.; Zharkov, S.

2006-12-01

342

Transition Region Emission and Energy Input to Thermal Plasma During the Impulsive Phase of Solar Flares  

E-print Network

The energy released in a solar flare is partitioned between thermal and non-thermal particle energy and lost to thermal conduction and radiation over a broad range of wavelengths. It is difficult to determine the conductive losses and the energy radiated at transition region temperatures during the impulsive phases of flares. We use UVCS measurements of O VI photons produced by 5 flares and subsequently scattered by O VI ions in the corona to determine the 5.0 thermal energy and the conductive losses deduced from RHESSI and GOES X-ray data using areas from RHESSI images to estimate the loop volumes, cross-sectional areas and scale lengths. The transition region luminosities during the impulsive phase exceed the X-ray luminosities for the first few minutes, but they are smaller than the rates of increase of thermal energy unless the filling factor of the X-ray emitting gas is ~ 0.01. The estimated conductive losses from the hot gas are too large to be balanced by radiative losses or heating of evaporated plasma, and we conclude that the area of the flare magnetic flux tubes is much smaller than the effective area measured by RHESSI during this phase of the flares. For the 2002 July 23 flare, the energy deposited by non-thermal particles exceeds the X-ray and UV energy losses and the rate of increase of the thermal energy.

J. C. Raymond; G. Holman; A. Ciaravella; A. Panasyuk; Y. -K. Ko; J. Kohl

2007-01-12

343

Temporal and spectral characteristics of solar flare hard X-ray emission  

NASA Technical Reports Server (NTRS)

Solar Maximum Mission observations of three flares that impose stringent constraints on physical models of the hard X-ray production during the impulsive phase are presented. Hard X-ray imaging observations of the flares on 1980 November 5 at 22:33 UT show two patches in the 16 to 30 keV images that are separated by 70,000 km and that brighten simultaneously to within 5 s. Observations to O V from one of the footprints show simultaneity of the brightening in this transition zone line and in the total hard X-ray flux to within a second or two. These results suggest but do not require the existence of electron beams in this flare. The rapid fluctuations of the hard X-ray flux within some flares on the time scales of 1 s also provide evidence for electron beams and limits on the time scale of the energy release mechanism. Observations of a flare on 1980 June 6 at 22:34 UT show variations in the 28 keV X-ray counting rate from one 20 ms interval to the next over a period of 10 s. The hard X-ray spectral variations measured with 128 ms time resolution for one 0.5 s spike during this flare are consistent with the predictions of thick-target non-thermal beam model.

Dennis, B. R.; Kiplinger, A. L.; Orwig, L. E.; Frost, K. J.

1985-01-01

344

Are solar flare emissions and CME acceleration related via magnetic reconnection?  

NASA Astrophysics Data System (ADS)

Recent solar observations have shown that both the impulsive flare non-thermal emissions and the maximum rate of increase in the flare soft X-ray emission occur at the time of maximum CME acceleration. By employing a non-uniform anomalous resistivity, our MHD simulation results relate the CME's accelerated rising motion with an impulsive magnetic reconnection rate and thus an enhanced reconnection electric field in the current sheet during the flare rise phase. For X-class flares the peak reconnection electric field is 1 kV/m, enough to accelerate electrons to over 100 keV in a field-aligned distance of 0.1 km and produce impulsive non-thermal emissions observed during the flare rise phase. Moreover, the temporal evolution and magnitude of the reconnection electric field are confirmed by the magnetic reconnection rate obtained from the observed magnetogram data and horizontally expanding motion of two-ribbon flare emissions. The simulated CME motion is also in good agreement with the observed CME motion.

Cheng, C. Z.; Choe, G. S.; Qiu, J.; Ren, Y.; Moon, Y. J.

2004-11-01

345

Semiempirical photospheric models of a solar flare on May 28, 2012  

NASA Astrophysics Data System (ADS)

The variation of the photosphere physical state during the decay phase of SF/B6.8-class solar flare on May 28, 2012 in active region NOAA 11490 is studied. We used the data of the spectropolarimetric observations with the French-Italian solar telescope THEMIS (Tenerife, Spain). Semi-empirical model atmospheres are derived from the inversion with SIR (Stokes Inversion based on Response functions) code. The inversion was based on Stokes profiles of six photospheric lines. Each model atmosphere has a two-component structure: a magnetic flux tube and non-magnetic surroundings. The Harvard Smithsonian Reference Atmosphere (HSRA) has been adopted for the surroundings. The macroturbulent velocity and the filling factor were assumed to be constant with the depth. The optical depth dependences of the temperature, magnetic field strength, and line-of-sight velocity are obtained from inversion. According to the received model atmospheres, the parameters of the magnetic field and the thermodynamical parameters changed during the decay phase of the flare. The model atmospheres showed that the photosphere remained in a disturbed state during observations after the maximum of the flare. There are temporal changes in the temperature and the magnetic field strength optical depth dependences. The temperature enhancement in the upper photospheric layers is found in the flaring atmospheres relative to the quiet-Sun model. The downflows are found in the low and upper photosphere at the decay phase of the flare.

Andriets, E. S.; Kondrashova, N. N.

2015-02-01

346

The evolution of energetic particles and the emitted radiation in solar flares. Ph.D. Thesis  

NASA Technical Reports Server (NTRS)

The evolution of accelerated particle distributions in a magnetized plasma and the resulting radiation are calculated, and the results are applied to solar flares. To study the radiation on timescales of order the particle lifetimes, the evolution of the particle distribution is determined by the use of the Fokker-Planck equation including Coulomb collisions and magnetic mirroring. Analytic solution to the equations are obtained for limiting cases such as homogeneous injection in a homogeneous plasma, and for small pitch angle. These analytic solutions are then used to place constraints on flare parameters such as density, loop length, and the injection timescale for very short implusive solar flares. For general particle distributions in arbitrary magnetic field and background density, the equation is solved numerically. The relative timing of microwaves and X-rays during individual flares is investigated. A number of possible sources for excessive microwave flux are discussed including a flattening in the electron spectrum above hard X-ray energies, thermal synchrotron emission, and trapping of electron by converging magnetic fields. Over shorter timescales, the Fokker-Planck equation is solved numerically to calculate the temporal evolution of microwaves and X-rays from nonthermal thick target models. It is shown that magnetic trapping will not account for the observed correlation of microwaves of approximately 0.15 seconds behind X-rays in flares with rapid time variation, and thus higher energy electrons must be accelerated later than lower energy electrons.

Lu, Edward Tsang

1989-01-01

347

ON THE ORIGIN OF THE EXTREME-ULTRAVIOLET LATE PHASE OF SOLAR FLARES  

SciTech Connect

Solar flares typically have an impulsive phase that is followed by a gradual phase as best seen in soft X-ray emissions. A recent discovery based on the EUV Variability Experiment observations on board the Solar Dynamics Observatory (SDO) reveals that some flares exhibit a second large peak separated from the first main phase peak by tens of minutes to hours, which is coined as the flare's EUV late phase. In this paper, we address the origin of the EUV late phase by analyzing in detail two late phase flares, an M2.9 flare on 2010 October 16 and an M1.4 flare on 2011 February 18, using multi-passband imaging observations from the Atmospheric Imaging Assembly on board SDO. We find that (1) the late phase emission originates from a different magnetic loop system, which is much larger and higher than the main phase loop system. (2) The two loop systems have different thermal evolution. While the late phase loop arcade reaches its peak brightness progressively at a later time spanning for more than one hour from high to low temperatures, the main phase loop arcade reaches its peak brightness at almost the same time (within several minutes) in all temperatures. (3) Nevertheless, the two loop systems seem to be connected magnetically, forming an asymmetric magnetic quadruple configuration. (4) Further, the footpoint brightenings in UV wavelengths show a systematic delay of about one minute from the main flare region to the remote footpoint of the late phase arcade system. We argue that the EUV late phase is the result of a long-lasting cooling process in the larger magnetic arcade system.

Liu Kai; Wang Yuming [School of Earth and Space Science, University of Technology and Science of China, Hefei 230026 (China); Zhang Jie; Cheng Xin, E-mail: kailiu@mail.ustc.edu.cn [School of Physics, Astronomy and Computational Sciences, George Mason University, 4400 University Drive, MSN 6A2, Fairfax, VA 22030 (United States)

2013-05-10

348

CONTINUUM CONTRIBUTIONS TO THE SDO/AIA PASSBANDS DURING SOLAR FLARES  

SciTech Connect

Data from the Multiple EUV Grating Spectrograph component of the Extreme-ultraviolet Variability Experiment (EVE) on board the Solar Dynamics Observatory (SDO) were used to quantify the contribution of continuum emission to each of the extreme ultraviolet (EUV) channels of the Atmospheric Imaging Assembly (AIA), also on SDO, during an X-class solar flare that occurred on 2011 February 15. Both the pre-flare-subtracted EVE spectra and fits to the associated free-free continuum were convolved with the AIA response functions of the seven EUV passbands at 10 s cadence throughout the course of the flare. It was found that 10%-25% of the total emission in the 94 , 131 , 193 , and 335 passbands throughout the main phase of the flare was due to free-free emission. Reliable measurements could not be made for the 171 channel, while the continuum contribution to the 304 channel was negligible due to the presence of the strong He II emission line. Up to 50% of the emission in the 211 channel was found to be due to free-free emission around the peak of the flare, while an additional 20% was due to the recombination continuum of He II. The analysis was extended to a number of M- and X-class flares and it was found that the level of free-free emission contributing to both the 171 and 211 passbands increased with increasing GOES class. These results suggest that the amount of continuum emission that contributes to AIA observations during flares is more significant than stated in previous studies which used synthetic, rather than observed, spectra. These findings highlight the importance of spectroscopic observations carried out in conjunction with those from imaging instruments so that the data are interpreted correctly.

Milligan, Ryan O.; McElroy, Sarah A., E-mail: r.milligan@qub.ac.uk [Astrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, University Road, Belfast BT7 1NN (United Kingdom)

2013-11-01

349

The wall of reconnection-driven magnetohydrodynamic turbulence in a large solar flare  

NASA Technical Reports Server (NTRS)

LaRosa and Moore (1993) recently proposed that the bulk dissipation of magnetic field that is required for the electron energization in the explosive phase of solar flares occurs in a 'fat current sheet', a wall of cascading magnetohydrodynamic (MHD) turbulence sustained by highly disordered driven reconnection of opposing magnetic fields impacting at a turbulent boundary layer. Here, we use the well-observed great two-ribbon eruptive flare of 1984 April 24/25 to assess the feasibility of both (1) the standard model for the overall three-dimensional form and action of the magnetic field and (2) the turbulent reconnection wall within it. We find (1) that the morphology of this flare closely matched that of the standard model; (2) the preflare sheared core field had enough nonpotential magnetic energy to power the flare; (3) the model turbulent wall required to achieve the flare's peak dissipative power easily fit within the overall span of the flaring magnetic field; (4) this wall was thick enough to have turbulent eddies large enough (diameters approximately 10(exp 8 cm) to produce the approximately ergs energy release fragments typically observed in the explosive phase of flares; (5) the aspect ratio (thickness/vertical extent) of the turbulent reconnection wall was in the 0.1-1 range expected by (Parker 1973). We therefore conclude that the viability of our version of the standard model (i.e., having the magnetic field dissipation occur in our turbulent reconnection wall) is well confirmed by this typical great two-ribbon eruptive flare.

Moore, R. L.; Larosa, T. N.; Orwig, L. E.

1995-01-01

350

A Comprehensive View of the Temperature Distribution in Solar Flares from EVE and RHESSI  

NASA Astrophysics Data System (ADS)

Solar flares accelerate electrons up to hundreds of MeV and heat plasma up to tens of MK, but the physical processes behind these phenomena remain poorly understood. While the ubiquitous 10-25 MK plasma is commonly accepted to result from chromospheric evaporation, evidence suggests that in intense (GOES M- and X-class) flares, the hottest, 20-50 MK plasma is directly heated in the corona, although the heating mechanism and its connection to the flare-accelerated non-thermal electrons is not yet understood. While observations of hard X-ray bremmstrahlung directly probe the non-thermal electron population, the spectra below 20-30 keV are typically dominated by strong thermal emission. The low-energy extent of the non-thermal spectrum can thus be only loosely quantified, which has significant implications for calculating flare energy budgets and for constraining possible acceleration mechanisms. Hence, a precise characterization of the thermal electron population is imperative. New extreme ultraviolet observations from the EUV Variability Experiment (EVE) on-board the Solar Dynamics Observatory (SDO), combined with X-ray data from the Reuven Ramaty High Energy Spectroscopic Imager (RHESSI), offer the most comprehensive view into the flare temperature distribution to date. EVE observes a wealth of EUV emission lines with peak formation temperatures of 2-20 MK, while RHESSI observes the X-ray bremsstrahlung of hot, 10-50 MK plasmas; combined, the two instruments have excellent temperature sampling and coverage over the full range of flare plasma temperatures. We have calculated differential emission measures (DEMs) using EVE and RHESSI independently, for separately observed events. We present a novel method of combining simultaneous EVE and RHESSI observations to determine the flare DEM, and its evolution, over the full 1-100 MK range during intense M/X flares. We present preliminary results from the 2011-Feb-15 X2.2 flare, and compare with the RHESSI non-thermal emission to discuss the implications for flare plasma heating.

Caspi, Amir; McTiernan, J. M.; Warren, H. P.

2012-05-01

351

Hard x-ray and Metric\\/Decimetric Radio Observations of the 20 February 2002 Solar Flare  

Microsoft Academic Search

The GOES C7.5 flare on 20 February 2002 at 11:07UT is one of the first solar flares observed by RHESSI at X-ray wavelengths.\\u000a It was simultaneously observed at metric\\/decimetric wavelengths by the Nanay radioheliograph (NRH) which provided images\\u000a of the flare between 450 and 150MHz. We present a first comparison of the hard X-ray images observed with RHESSI and of

N. Vilmer; S. Krucker; R. P. Lin

2002-01-01

352

Spectroscopic Observations of a Solar Flare and the Associated Coronal Mass Ejection  

NASA Astrophysics Data System (ADS)

We used data from the EUV Imaging Spectrometer (EIS) on board Hinode to examine a coronal mass ejection and a preceding flare observed on 21 November 2012 between 15:00 and 17:00 UT. Images from the Atmospheric Imaging Assembly on the Solar Dynamics Observatory were used to align the data from EIS with specific events occurring. We analyzed spectra of a few emission lines at three locations on the flare site and one location in the erupting prominence. On the flare site, we found line profiles showing typical characteristics of chromospheric evaporation: downflows at cooler lines and upflows at hotter lines. At one particular location on the flare site, we clearly identified dominant downflows on the order of 100 km/s in lines through Fe VIII to Fe XVI. To the best of our knowledge, this is the first time that such strong high-speed downflows have been spectroscopically observed in the impulsive phase of solar flares. The profile of the Fe VIII 184.54 line reveals two peaks and we were able to use the double Gaussian fit to separate the rapid downflows of dense material from the nearly stationary coronal background emission. For the erupting prominence, we were able to analyze multiple lines, cooler and warmer, of interest using this double Gaussian fit to separate the background emission from the emission of the ejected material. Our results show that the LOS velocities of the ejected material are about 100 km/s in the lower corona. Additionally, in each region of interest, we used the ratio of the density-sensitive line pair FeXII 195/186 to determine the electron density. Our results clearly show that the coronal densities were greatly enhanced during the flare. The density of the ejected material is also much larger than the typical coronal density. This research was supported by the NSF grant for the Solar Physics REU Program at the Smithsonian Astrophysical Observatory (AGS-1263241).

Murray, S.; Tian, H.; McKillop, S.

2013-12-01

353

Magnetohydrodynamic Simulation of the X2.2 Solar Flare on 2011 February 15: II. A Dynamics Connecting the Solar Flare and the Coronal Mass Ejection  

E-print Network

We clarify a relationship of the dynamics of a solar flare and a growing Coronal Mass Ejection (CME) by investigating the dynamics of magnetic fields during the X2.2-class flare taking place in the solar active region 11158 on 2011 February 15, based on simulation results obtained from Inoue et al. 2014. We found that the strongly twisted lines formed through the tether-cutting reconnection in the twisted lines of a nonlinear force-free field (NLFFF) can break the force balance within the magnetic field, resulting in their launch from the solar surface. We further discover that a large-scale flux tube is formed during the eruption as a result of the tether-cutting reconnection between the eruptive strongly twisted lines and these ambient weakly twisted lines. Then the newly formed large flux tube exceeds the critical height of the torus instability. The tether-cutting reconnection thus plays an important role in the triggering a CME. Furthermore, we found that the tangential fields at the solar surface illust...

Inoue, S; Magara, T; Choe, G S; Park, Y D

2015-01-01

354

Estimating upper limits of solar flare hard X-ray fluences for space missions near the Sun  

NASA Astrophysics Data System (ADS)

We present a method to estimate an upper limit of the mission integrated fluence of hard X-rays (HXRs) produced by solar flares for a probe traveling at heliocentric distances R<1 AU. By using (1) the number and peak of both soft X-ray (SXR) flares and microwave (MW) solar bursts observed during the last three solar cycles, (2) either frequency distributions of HXR flare parameters, or correlations between the HXR fluence and the SXR flare class or the MW burst flux intensity, and (3) virtual launches of the probe at different times throughout the last three solar cycles, we accumulate statistics of the mission-integrated HXR fluences and provide values at the 95% confidence level. We apply this method to the Solar Probe Plus mission.

Lario, D.; Decker, R. B.

2012-11-01

355

Form and energy of the shock waves from the solar flares of August 2, 4, and 7, 1972  

Microsoft Academic Search

The shape of the shock waves associated with the August 1972 solar flares was determined by comparing the plasma measurement data from the Prognoz, Prognoz 2, Pioneer 9, and Pioneer 10 space probes with observations of radio source scintillations and comet brightness. A nearly spherical shock wave form was obtained for two flares on August 2, and essentially nonspherical shock

G. N. Zastenker; V. V. Temny; C. dUston; J. M. Bosqued

1978-01-01

356

Quasi-periodic pulsations in solar and stellar flares: re-evaluating their nature in the context of power-law flare Fourier spectra  

E-print Network

The nature of quasi-periodic pulsations in solar and stellar flares remains debated. Recent work has shown that power-law-like Fourier power spectra, also referred to as 'red' noise processes, are an intrinsic property of solar and stellar flare signals, a property that many previous studies of this phenomenon have not accounted for. Hence a re-evaluation of the existing interpretations and assumptions regarding QPP is needed. Here we adopt a Bayesian method for investigating this phenomenon, fully considering the Fourier power law properties of flare signals. Using data from the PROBA2/LYRA, Fermi/GBM, Nobeyama Radioheliograph and Yohkoh/HXT instruments, we study a selection of flares from the literature identified as QPP events. Additionally we examine optical data from a recent stellar flare that appears to exhibit oscillatory properties. We find that, for all but one event tested, an explicit oscillation is not required in order to explain the observations. Instead, the flare signals are adequately descri...

Inglis, A R; Dominique, M

2014-01-01

357

The correlation of solar flare hard X-ray bursts with Doppler blueshifted soft X-ray flare emission  

NASA Technical Reports Server (NTRS)

We have investigated the temporal correlation between hard X-ray bursts and the intensity of Doppler blueshifted soft X-ray spectral line emission. We find a strong correlation for many events that have intense blueshifted spectral signatures and some correlation in events with modest blueshifts. The onset of hard X-rays frequently coincides to within a few seconds with the onset of blueshifted emission. The peak intensity of blueshifted emission is frequently close in time to the peak of the hard X-ray emission. Decay rates of the blueshifted and hard X-ray emission are similar, with the decay of the blueshifted emission tending to lag behind the hard X-ray emission in some cases. There are, however, exceptions to these conclusions, and, therefore, the results should not be generalized to all flares. Most of the data for this work were obtained from instruments flown on the Japanese Yohkoh solar spacecraft.

Bentley, R. D.; Doschek, G. A.; Simnett, G. M.; Rilee, M. L.; Mariska, J. T.; Culhane, J. L.; Kosugi, T.; Watanabe, T.

1994-01-01

358

Statistical Evidence for Contributions of Flares and Coronal Mass Ejections to Major Solar Energetic Particle Events  

NASA Astrophysics Data System (ADS)

Solar energetic particle (SEP) events are related to flares and coronal mass ejections (CMEs). This work is a new investigation of statistical relationships between SEP peak intensities - deka-MeV protons and near-relativistic electrons - and characteristic quantities of the associated solar activity. We consider the speed of the CME and quantities describing the flare-related energy release: peak flux and fluence of soft X-ray (SXR) emission, fluence of microwave emission. The sample comprises 38 SEP events associated with strong SXR bursts (classes M and X) in the western solar hemisphere between 1997 and 2006, and where the flare-related particle acceleration is accompanied by radio bursts indicating electron escape to the interplanetary space. The main distinction of the present statistical analysis from earlier work is that besides the classical Pearson correlation coefficient the partial correlation coefficients are calculated in order to disentangle the effects of correlations between the solar parameters themselves. The classical correlation analysis shows the usual picture of correlations with broad scatter between SEP peak intensities and the different parameters of solar activity, and strong correlations between the solar activity parameters themselves. The partial correlation analysis shows that the only parameters that affect significantly the SEP intensity are the CME speed and the SXR fluence. The SXR peak flux and the microwave fluence have no additional contribution. We conclude that these findings bring statistical evidence that both flare acceleration and CME shock acceleration contribute to the deka-MeV proton and near-relativistic electron populations in large SEP events.

Trottet, G.; Samwel, S.; Klein, K.-L.; Dudok de Wit, T.; Miteva, R.

2014-12-01

359

Radio diagnostics of the solar flaring loop parameters by the forward fitting method  

NASA Astrophysics Data System (ADS)

Numerical methods for solving the inverse problem of determining solar flaring loop physical parameters are sought and developed. This problem can be solved by fitting theoretically calculated radio emission characteristics (the flux or the degree of circular polarization) to the observed characteristics. Such a fitting is reduced to the solution of a system of equations with the observed and theoretically calculated radio emission characteristics on the right- and left-hand sides, respectively. The genetic algorithm method, which demonstrated good accuracy and calculation time when five parameters of a model flaring loop were recovered, has been used in fitting. After testing this method on the model sources, an algorithm was used to recover four parameters of the real flaring loop using the Nobeyama Radioheliograph data.

Morgachev, A. S.; Kuznetsov, S. A.; Melnikov, V. F.

2014-12-01

360

Physical State of the Photosphere at the Onset Phase of a Two-Ribbon Solar Flare  

NASA Astrophysics Data System (ADS)

We study the physical state of the photosphere at about 30 minutes before and at the onset of a 2N/M2 two-ribbon solar flare. Semiempirical photospheric models are obtained for two H?-kernels with the help of the SIR inversion code described by Ruiz Cobo and del Toro Iniesta ( Astrophys. J. 398, 375, 1992). The models derived from the inversion reproduce spectral observations in seven Fraunhofer lines. The inferred models show variations in all photospheric parameters both before and at the onset of the flare relative to the quiet-Sun model. The temperature enhancement in the upper photospheric layers is found in the atmospheres in both kernels. The dynamical structure in the models reveals the variations at the onset of the flare relative to the preflaring ones. The inferred atmospheres show some difference in the thermodynamical parameters of two kernels.

Chornogor, S. N.; Kondrashova, N. N.

2008-08-01

361

On the occurrence and the motion of fast impulsive coronal mass ejections associated with powerful flares and unassociated with eruptive filaments  

NASA Astrophysics Data System (ADS)

The formation and initial stage of the motion of several rapid, impulsive coronal mass ejections of the "halo" type (HCME) associated with flares of M and X class, but unassociated with the eruption of solar filaments, was studied using GOES-12/SXI, SOHO/EIT, and SDO/AIA data. The HCMEs considered can be divided into three groups according to the features of their formation: ( i) some HCMEs arise due to an imbalance of single emission looped structures observed in the 195 channel of an EIT instrument for several hours before the first recording of mass ejection in the field of view of an SXI X-ray telescope, and after the eruption, these loops become structural elements of HCMEs; ( ii) HCMEs can be formed as a result of an imbalance of several loops in the process of combining these loops into a single structure; and ( iii) HCME formation begins with the upward motion of the group of coronal loops observed using the AIA data first in the "hot" 131 channel, a few minutes later in the "cold" 211 channel, later in the 193 channel, and, finally, in the 171 channel. The action of moving looped structures on the overlying regions of the corona leads to the formation and the motion of the frontal structure of HCMEs with increased brightness. In this case, these eruptive loops do not become structural elements of HCMEs. All investigated HCMEs began their translational motion before the occurrence of the associated flares. According to the results of studying the kinematics of the considered HCMEs we concluded that there are two types of coronal mass ejections differing according to the time profile of the velocity, which is determined by the area and the magnetic configuration of the active region where the mass ejection was formed. It is shown that HCMEs occurring at different times in the same active region have the same type of velocity profile.

Fainshtein, V. G.; Zagainova, Yu. S.

2015-01-01

362

Analysis of Gamma-Ray Data from Solar Flares in Cycles 21 and 22  

NASA Technical Reports Server (NTRS)

One of our primary accomplishments under grant NAGW-35381 was the systematic derivation and compilation, for the first time, of physical parameters for all gamma-ray flares detected by the SMM GRS during its ten year lifetime. The flare parameters derived from the gamma-ray spectra include: bremsstrahlung fluence and best-fit power-law parameters, narrow nuclear line fluence, positron annihilation line fluence, neutron capture line fluence, and an indication of whether or not greater than 10 MeV emissions were present. We combined this compilation of flare parameters with our plots of counting rate time histories and flare spectra to construct an atlas of gamma-ray flare characteristics. The atlas time histories display four energy bands: 56-199 kev, 298526 keV, 4-8 MeV, and 10-25 MeV. These energy bands respectively measure nonrelativistic bremsstrahlung, trans-relativistic bremsstrahlung, nuclear de-excitation, and ultra-relativistic bremsstrahlung. The atlas spectra show the integrated high-energy spectra measured for all GRS flares and dissects them into electron bremsstrahlung, positron annihilation and nuclear emission components. The atlas has been accepted for publication in the Astrophysical Journal Supplements and is currently in press. The atlas materials were also supplied to the Solar Data Analysis Center at Goddard Space Flight Center and were made available through a web site at the University of New Hampshire. Since a uniform methodology was adopted for deriving the flare parameters, this atlas will be very useful for future statistical and correlative studies of solar flares-three independent groups are presently using it to correlate interplanetary energetic particle measurements with our gamma-ray measurements. A better model for the response of the GRS instrument to high energy radiation was also developed. A refined response model was needed because the old model was not adequate for predicting the first and second escape peaks associated with strong nuclear lines nor could it accurately describe the Compton continuum shape. The new response was developed using a GEANT based simulation code and tested against preflight calibration data. The refinement of the response model and the removal of systematic errors now allow more detailed spectral studies of the GRS gamma-ray measurements. This refined response function was supplied to the Solar DAC at Goddard and was also made available via a web site at the University of New Hampshire.

Vestrand, W. Thomas

1998-01-01

363

Electron Densities in Solar Flare Loops, Chromospheric Evaporation Upflows, and Acceleration Sites  

NASA Technical Reports Server (NTRS)

We compare electron densities measured at three different locations in solar flares: (1) in Soft X-Ray (SXR) loops, determined from SXR emission measures and loop diameters from Yohkoh Soft X-Ray Telescope maps (n(sub e, sup SXR) = (0.2-2.5) x 10(exp 11)/ cu cm); (2) in chromospheric evaporation upflows, inferred from plasma frequency cutoffs of decimetric radio bursts detected with the 0.1-3 GHz spectrometer Phoenix of ETH Zuerich (n(sub e, sup upflow) = (0.3-11) x 10(exp 10)/cu cm; and (3) in acceleration sites, inferred from the plasma frequency at the separatrix between upward-accelerated (type III bursts) and downward-accelerated (reverse-drift bursts) electron beams [n(sub e, sup acc) = (0.6-10) x 10(exp 9)/cu cm]. The comparison of these density measurements, obtained from 44 flare episodes (during 14 different flares), demonstrates the compatibility of flare plasma density diagnostics with SXR and radio methods. The density in the upflowing plasma is found to be somewhat lower than in the filled loops, having ratios in a range n(sub e, sup upflow)/n(sub e, sup SXR) = 0.02-1.3, and a factor of 3.6 higher behind the upflow front. The acceleration sites are found to have a much lower density than the SXR-bright flare loops, i.e., n(sub e, sup acc)/n(sub e, sup SXR) = 0.005- 0.13, and thus must be physically displaced from the SXR-bright flare loops. The scaling law between electron time-of-flight distances l' and loop half-lengths s, l'/s = 1.4 +/- 0.3, recently established by Aschwanden et al. suggests that the centroid of the acceleration region is located above the SXR-bright flare loop, as envisioned in cusp geometries (e.g., in magnetic reconnection models).

Aschwanden, Markus J.; Benz, Arnold O.

1996-01-01

364

Thermal and Nonthermal Contributions to the Solar Flare X-Ray Flux  

NASA Technical Reports Server (NTRS)

The relative thermal and nonthermal contributions to the total energy budget of a solar flare are being determined through analysis of RHESSI X-ray imaging and spectral observations in the energy range from approx. 5 to approx. 50 keV. The classic ways of differentiating between the thermal and nonthermal components - exponential vs. sources - can now be combined for individual flares. In addition, RHESSI's sensitivity down to approx. 4 keV and energy resolution of approx. 1 keV FWHM allow the intensities and equivalent widths of the complex of highly ionized iron lines at approx. 6.7 keV and the complex of highly ionized iron and nickel lines at approx. 8 keV to be measured as a function of time. Using the spectral line and continuum intensities from the Chianti (version 4.2) atomic code, the thermal component of the total flare emission can be more reliably separated from the nonthermal component in the measured X-ray spectrum. The abundance of iron can also be determined from RHESSI line-to-continuum measurements as a function of time during larger flares. Results will be shown of the intensity and equivalent widths of these line complexes for several flares and the temperatures, emission measures, and iron abundances derived from them. Comparisons will be made with 6.7-keV Fe-line fluxes measured with the RESIK bent crystal spectrometer on the Coronas-F spacecraft operating in third order during the peak times of three flares (2002 May 31 at 00:12 UT, 2002 December 2 at 19:26 UT, and 2003 April 26 at 03:OO UT). During the rise and decay of these flares, RESIK was operating in first order allowing the continuum flux to be measured between 2.9 and 3.7 keV for comparison with RHESSI fluxes at its low-energy end.

Dennis, Brian R.; Phillips, K. J. H.; Sylwester, Janusz; Sylwester, Barbara; Schwartz, Richard A.; Tolbert, A. Kimberley

2004-01-01

365

Optical Spectral Observations of a Flickering White-light Kernel in a C1 Solar Flare  

NASA Astrophysics Data System (ADS)

We analyze optical spectra of a two-ribbon, long-duration C1.1 flare that occurred on 2011 August 18 within AR 11271 (SOL2011-08-18T15:15). The impulsive phase of the flare was observed with a comprehensive set of space-borne and ground-based instruments, which provide a range of unique diagnostics of the lower flaring atmosphere. Here we report the detection of enhanced continuum emission, observed in low-resolution spectra from 3600 to 4550 acquired with the Horizontal Spectrograph at the Dunn Solar Telescope. A small, <=0.''5 (1015 cm2) penumbral/umbral kernel brightens repeatedly in the optical continuum and chromospheric emission lines, similar to the temporal characteristics of the hard X-ray variation as detected by the Gamma-ray Burst Monitor on the Fermi spacecraft. Radiative-hydrodynamic flare models that employ a nonthermal electron beam energy flux high enough to produce the optical contrast in our flare spectra would predict a large Balmer jump in emission, indicative of hydrogen recombination radiation from the upper flare chromosphere. However, we find no evidence of such a Balmer jump in the bluemost spectral region of the continuum excess. Just redward of the expected Balmer jump, we find evidence of a "blue continuum bump" in the excess emission which may be indicative of the merging of the higher order Balmer lines. The large number of observational constraints provides a springboard for modeling the blue/optical emission for this particular flare with radiative-hydrodynamic codes, which are necessary to understand the opacity effects for the continuum and emission line radiation at these wavelengths.

Kowalski, Adam F.; Cauzzi, Gianna; Fletcher, Lyndsay

2015-01-01

366

Evolution of the Loop-Top Source of Solar Flares--Heating and Cooling Processes  

E-print Network

We present a study of the spatial and spectral evolution of the loop-top (LT) sources in a sample of 6 flares near the solar limb observed by {\\it RHESSI}. A distinct coronal source, which we identify as the LT source, was seen in each of these flares from the early ``pre-heating'' phase through the late decay phase. Spectral analyses reveal an evident steep power-law component in the pre-heating and impulsive phases, suggesting that the particle acceleration starts upon the onset of the flares. In the late decay phase the LT source has a thermal spectrum and appears to be confined within a small region near the top of the flare loop, and does not spread throughout the loop, as is observed at lower energies. The total energy of this source decreases usually faster than expected from the radiative cooling but much slower than that due to the classical Spitzer conductive cooling along the flare loop. These results indicate the presence of a distinct LT region, where the thermal conductivity is suppressed significantly and/or there is a continuous energy input. We suggest that plasma wave turbulence could play important roles in both heating the plasma and suppressing the conduction during the decay phase of solar flares. With a simple quasi-steady loop model we show that the energy input in the gradual phase can be comparable to that in the impulsive phase and demonstrate how the observed cooling and confinement of the LT source can be used to constrain the wave-particle interaction.

Yan Wei Jiang; Siming Liu; Wei Liu; Vahe Petrosian

2005-08-24

367

A new approach to model particle acceleration and energy transfer in solar flares  

NASA Astrophysics Data System (ADS)

Motivated by available observations of two different flares in Ly? and H?, we model the conditions of the solar atmosphere using a radiation hydrodynamics code (RADYN, Carlsson & Stein, 1992) and analyze the energy transport carried by a beam of non-thermal electrons injected at the top of a 1D coronal loop. The numerical Ly? and H? intensities match with the observations. The electron energy distribution is assumed to follow a power law of the form (E/Ec )-? for energies greater than a cutoff value of Ec. Abbett & Hawley (1999) and Allred et al. (2005) assumed that the non-thermal electrons flux injected at the top of a flaring loop, the cut-off energy and the power law index are constant over time. An improvement was achieved by Allred & Hawley (2006), who modified the RADYN code in such a way that the input parameters were time dependent. Their inputs were based on observations of a flare obtained with RHESSI. By combining RADYN with the flare code from Stanford University which models the acceleration and transport of particles and radiation of solar flares in non-LTE regime, we can calculate the non-thermal electrons flux, the cut-off energy and the power law index at every simulated time step. The atmospheric parameters calculated by RADYN could in turn be used as updated inputs for "flare", providing several advantages over the results from Liu et al. (2009), who combined the particle acceleration code with a 1-D hydrodynamic code, improving the atmospheric conditions.

Rubio Da Costa, Fatima; Zuccarello, F.; Fletcher, L.; Labrosse, N.; Kasparova, J.; Proseck, T.; Carlsson, M.; Petrosian, V.; Liu, W.

2013-07-01

368

Small-scale Microwave Bursts in Long-duration Solar Flares  

NASA Astrophysics Data System (ADS)

Solar small-scale microwave bursts (SMBs), including microwave dot, spike, and narrow-band type III bursts, are characterized by very short timescales, narrow frequency bandwidth, and very high brightness temperatures. Based on observations of the Chinese Solar Broadband Radio Spectrometer at Huairou with superhigh cadence and frequency resolution, this work presents an intensive investigation of SMBs in several flares that occurred in active region NOAA 10720 during 2005 January 14-21. Especially for long-duration flares, the SMBs occurred not only in the early rising and impulsive phase, but also in the flare decay phase and even after the end of the flare. These SMBs are strong bursts with inferred brightness temperatures of at least 8.18 1011-1.92 1013 K, very short lifetimes of 5-18 ms, relative frequency bandwidths of 0.7%-3.5%, and superhigh frequency drifting rates. Together with their obviously different polarizations from background emission (the quiet Sun, and the underlying flaring broadband continuum), such SMBs should be individual, independent strong coherent bursts related to some non-thermal energy release and the production of energetic particles in a small-scale source region. These facts show the existence of small-scale strong non-thermal energy releasing activities after the flare maxima, which is meaningful for predicting space weather. Physical analysis indicates that a plasma mechanism may be the most favorable candidate for the formation of SMBs. From the plasma mechanism, the velocities and kinetic energy of fast electrons can be deduced and the region of electron acceleration can also be tracked.

Tan, Baolin

2013-08-01

369

Disturbances of both cometary and Earth's magnetospheres excited by single solar flares  

NASA Astrophysics Data System (ADS)

In the solar wind a comet plays the role of a windvane that moves three-dimensionally in the heliomagnetosphere. Among the solar systems bodies, only comets have a wide range of inclination angles of their orbital planes to the ecliptic plane ranging from 0 to 90 deg. Therefore, observations of cometary plasma tails are useful in probing the heliomagnetospheric conditions in the high heliolatitudinal region. A comet can be compared to a polar-orbiting probe encircling the Sun. We will introduce two rare cases in which the magnetospheres of both the comet and the Earth are disturbed by a single solar flare.

Konno, I.; Saito, T.; Kozuka, Y.; Nishioka, K.; Saito, M.; Takahashi, T.

1992-12-01

370

Quasi-periodic pulsations in solar hard X-ray and microwave flares  

NASA Technical Reports Server (NTRS)

For more than a decade, various studies have pointed out that hard X-ray and microwave time profiles of some solar flares show quasi-periodic fluctuations or pulsations. Nevertheless, it was not until recently that a flare displaying large amplitude quasi-periodic pulsations in X-rays and microwaves was observed with good spectral coverage and with a sufficient time resolution. The event occurred on June 7, 1980, at approximately 0312 UT, and exhibits seven intense pulses with a quasi-periodicity of approximately 8 seconds in microwaves, hard X-rays, and gamma-ray lines. On May 12, 1983, at approximately 0253 UT, another good example of this type of flare was observed both in hard X-rays and in microwaves. Temporal and spectral characteristics of this flare are compared with the event of June 7, 1980. In order to further explore these observational results and theoretical scenarios, a study of nine additional quasi-periodic events were incorporated with the results from the two flares described. Analysis of these events are briefly summarized.

Kosugi, Takeo; Kiplinger, Alan L.

1986-01-01

371

A Statistical Study of Gamma-Ray Emitting Solar Flares Observed with Yohkoh  

E-print Network

Gamma-ray emitting solar flares observed with Yohkoh were analyzed from a statistical viewpoint. The four-band hard X-ray (15--95 keV) photometric data, taken with the Hard X-ray Telescope onboard Yohkoh, were utilized in combination with the spectro-photometric gamma-ray (0.2--30 MeV) data obtained with the Gamma-Ray Spectrometer. The GOES class was also incorporated. Out of 2788 X-ray flares observed from 1991 October to 2001 December, 178 events with strong hard X-ray emission were selected. Among them, 40 flares were further found to show significant gamma-ray emission. A fractal dimension analysis and multi-band color--color plots of the 40 flares suggest that their soft X-ray to MeV gamma-ray spectral energy distributions involve at least four independent parameters. These are: (1) the overall flare size; (2) the relative intensities of the thermal vs. non-thermal signals; (3) the gamma-ray to hard X-ray intensity ratio; and (4) the hard X-ray spectral slope. These results are examined for possible selection effects. Also, the meanings of the third parameter are briefly considered.

Yukari Matsumoto; Kazuo Makishima; Jun'ichi Kotoku; Masato Yoshimori; Kazuharu Suga; Takeo Kosugi; Satoshi Masuda; Kouji Morimoto

2005-01-24

372

Magnetic Reconnection in Solar Flares and CMEs and in Laboratory Plasma Merging Experiments  

NASA Astrophysics Data System (ADS)

Impulsive magnetic reconnection has been shown to be the major mechanism responsible for explosive flare non-thermal energy release and acceleration of VME motion. It has been observed that for most large solar flares non-thermal emissions in hard X-rays (HXR) and millimeter/submillimeter waves impulsively rise and decade during the soft X-ray (SXR) emission rise phase. Moreover, the filament/CME upward motion is accelerated temporally in correlation with the impulsive enhancement of flare non-thermal emission and reconnection electric field in the current sheet in both simulations and observations. The peak reconnection electric field during flare impulsive phase is on the order of a few kV/m for X-class flares. Here, we demonstrated for the first time in laboratory plasma merging experiments the correlation of the magnetic reconnection rate with the acceleration of plasmoid ejected from the current sheet using the TS-4 device of the Tokyo University. Moreover, we also have found that the electron heating occurs in the current sheet and the ion heating occurs in the down-stream outflow region. Thus, we conclude that the plasmoid/CME acceleration is a key mechanism for the impulsive enhancement of magnetic reconnection rate (electric field).

Ono, Y.; Cheng, C.; Yang, Y.; Choe, G.

2011-12-01

373

Multiple Views of X1.4 Solar Flare on July 12, 2012 - Duration: 1:00.  

NASA Video Gallery

This video shows the July 12, 2012 X1.4 class solar flare in a variety of wavelength; 131- Teal colored, 335 - blue colored, 171 - yellow colored and finally a combined wavelength view. All video w...

374

Earth FUV Dayglow Response to the 20 January 2005 Solar Flare: TIMED and IMAGE Observations  

NASA Astrophysics Data System (ADS)

An X-class solar flare occurred on 20 January 2005 when the TIMED and IMAGE spacecraft were both well positioned to observe the response of Earth's dayglow emission intensity. Brightness enhancements during the flare relative to just before were determined at tangent altitudes of peak emission viewed toward the limb with TIMED. The TIMED observations were made at low solar zenith angles and show flare enhancements of roughly 15%, 30%, 30%, and 60%, respectively, for OI 130.4 nm, OI 135.6 nm, N2 LBH Short, and N2 LBH Long modes of the TIMED/GUVI instrument. However, GUVI observations of HI Lyman-alpha emission brightness do not show a significant brightness change. This lack of change in HI Lyman-alpha dayglow brightness is consistent with no significant change (<2%) in the solar Lyman-alpha flux observed with TIMED/SEE. Enhancements of emissions produced by photodissociation and photoelectron impact excitation sources are studied with IMAGE observations following Immel et al., JGR, 2003. Simulations of dayglow limb profiles to compare with the observations are produced using the NRLMSIS atmosphere model, the IRI90 ionosphere model, the GLOW photoelectron model, and the REDISTER radiative transfer model. The combined datasets enable a better study of the airglow sources most affected by the EUV and x-ray components of solar irradiance variability. We report our preliminary analysis of the response of FUV dayglow emissions to this event.

Retherford, K. D.; Gladstone, R.; Solomon, S. C.; Immel, T. J.

2005-05-01

375

The solar flare of the 14th of July 2000 (L3+C detector results)  

NASA Astrophysics Data System (ADS)

Aims.Several experiments have reported observations on possible correlations between the flux of high energy muons and intense solar flares. If confirmed, these observations would have significant implications for acceleration processes in the heliosphere able to accelerate protons and other ions to energies of at least tens of GeV. Methods: The solar flare of the 14 of July 2000 offered a unique opportunity for the L3+C experiment to search for a correlated enhancement in the flux of muons using the L3 precision muon spectrometer. Its capabilities for observing a directional excess in the flux of muons above 15 GeV (corresponding to primary proton energies above 40 GeV) are presented along with observations made on the 14th of July 2000. Results: We report an excess which appeared at a time coincident with the peak increase of solar protons observed at lower energies. The probability that the excess is a background fluctuation is estimated to be 1%. No similar excess of the muon flux was observed up to 1.5 h after the solar flare time.

Achard, P.; Adrian, O.; Aguilar-Benitez, M.; van den Akker, M.; Alcaraz, J.; Alemanni, G.; Allaby, J.; Aloisio, A.; Alviggi, M. G.; Anderhub, H.; Andreev, V. P.; Anselmo, F.; Arefiev, A.; Azemoon, T.; Aziz, T.; Bagnaia, P.; Bajo, A.; Baksay, G.; Baksay, L.; Bhr, J.; Baldew, S. V.; Banerjee, S.; Banerjee, Sw.; Barczyk, A.; Barillre, R.; Bartalini, P.; Basile, M.; Batalova, N.; Battiston, R.; Bay, A.; Becattini, F.; Becker, U.; Behner, F.; Bellucci, L.; Berbeco, R.; Berdugo, J.; Berges, P.; Bertucci, B.; Betev, B. L.; Biasini, M.; Biglietti, M.; Biland, A.; Blaising, J. J.; Blyth, S. C.; Bobbink, G. J.; Bhm, A.; Boldizsar, L.; Borgia, B.; Bottai, S.; Bourilkov, D.; Bourquin, M.; Braccini, S.; Branson, J. G.; Brochu, F.; Burger, J. D.; Burger, W. J.; Cai, X. D.; Capell, M.; Cara Romeo, G.; Carlino, G.; Cartacci, A.; Casaus, J.; Cavallari, F.; Cavallo, N.; Cecchi, C.; Cerrada, M.; Chamizo, M.; Chiarusi, T.; Chang, Y. H.; Chemarin, M.; Chen, A.; Chen, G.; Chen, G. M.; Chen, H. F.; Chen, H. S.; Chiefari, G.; Cifarelli, L.; Cindolo, F.; Clare, I.; Clare, R.; Coignet, G.; Colino, N.; Costantini, S.; de la Cruz, B.; Cucciarelli, S.; de Asmundis, R.; Dglon, P.; Debreczeni, J.; Degr, A.; Dehmelt, K.; Deiters, K.; della Volpe, D.; Delmeire, E.; Denes, P.; DeNotaristefani, F.; De Salvo, A.; Diemoz, M.; Dierckxsens, M.; Ding, L. K.; Dionisi, C.; Dittmar, M.; Doria, A.; Dova, M. T.; Duchesneau, D.; Duda, M.; Duran, I.; Echenard, B.; Eline, A.; El Hage, A.; El Mamouni, H.; Engler, A.; Eppling, F. J.; Extermann, P.; Faber, G.; Falagan, M. A.; Falciano, S.; Favara, A.; Fay, J.; Fedin, O.; Felcini, M.; Ferguson, T.; Fesefeldt, H; Fiandrini, E.; Field, J. H.; Filthaut, F.; Fisher, W.; Forconi, G.; Freudenreich, K.; Furetta, C.; Galaktionov, Yu.; Ganguli, S. N.; Garcia-Abia, P.; Gataullin, M.; Gentile, S.; Giagu, S.; Gong, Z. F.; Grabosch, H. J.; Grenier, G.; Grimm, O.; Groenstege, H.; Gruenewald, M. W.; Guida, M.; Guo, Y. N.; Gupta, S. K.; Gupta, V. K.; Gurtu, A.; Gutay, L. J.; Haas, D.; Haller, Ch.; Hatzifotiadou, D.; Hayashi, Y.; He, Z. X.; Hebbeker, T.; Herv, A.; Hirschfelder, J.; Hofer, H.; Hofer, H.; Hohlmann, M.; Holzner, A.; Hou, S. R.; Huo, A. X.; Ito, N.; Jin, B. N.; Jindal, P.; Jing, C. L.; Jones, L. W.; de Jong, P.; Josa-Mutuberra, I.; Kantserov, V.; Kaur, M.; Kawakami, S.; Kienzle-Focacci, M. N.; Kim, J. K.; Kirkby, J.; Kittel, W.; Klimentov, A.; Knig, A. C.; Kok, E.; Korn, A.; Kopal, M.; Koutsenko, V.; Krber, M.; Kuang, H. H.; Kraemer, R. W.; Krger, A.; Kuijpers, J.; Kunin, A.; Ladron de Guevara, P.; Laktineh, I.; Landi, G.; Lebeau, M.; Lebedev, A.; Lebrun, P.; Lecomte, P.; Lecoq, P.; Le Coultre, P.; Le Goff, J. M.; Lei, Y.; Leich, H.; Leiste, R.; Levtchenko, M.; Levtchenko, P.; Li, C.; Li, L.; Li, Z. C.; Likhoded, S.; Lin, C. H.; Lin, W. T.; Linde, F. L.; Lista, L.; Liu, Z. A.; Lohmann, W.; Longo, E.; Lu, Y. S.; Luci, C.; Luminari, L.; Lustermann, W.; Ma, W. G.; Ma, X. H.; Ma, Y. Q.; Malgeri, L.; Malinin, A.; Maa, C.; Mans, J.; Martin, J. P.; Marzano, F.; Mazumdar, K.; McNeil, R. R.; Meng, X. W.; Merola, L.; Meschini, M.; Metzger, W. J.; Mihul, A.; van Mil, A.; Milcent, H.; Mirabelli, G.; Mnich, J.; Mohanty, G. B.; Monteleoni, B.; Muanza, G. S.; Muijs, A. J. M.; Musy, M.; Nagy, S.; Nahnhauer, R.; Naumov, V. A.; Natale, S.; Napolitano, M.; Nessi-Tedaldi, F.; Newman, H.; Nisati, A.; Novak, T.; Nowak, H.; Ofierzynski, R.; Organtini, G.; Pal, I.; Palomares, C.; Paolucci, P.; Paramatti, R.; Parriaud, J.-F.; Passaleva, G.; Patricelli, S.; Paul, T.; Pauluzzi, M.; Paus, C.; Pauss, F.; Pedace, M.; Pensotti, S.; Perret-Gallix, D.; Petersen, B.; Piccolo, D.; Pierella, F.; Pieri, M.; Pioppi, M.; Pirou, P. A.; Pistolesi, E.; Plyaskin, V.; Pohl, M.; Pojidaev, V.; Pothier, J.; Prokofiev, D.; Qing, C. R.; Rahal-Callot, G.; Rahaman, M. A.; Raics, P.; Raja, N.; Ramelli, R.; Rancoita, P. G.; Ranieri, R.; Raspereza, A.; Ravindran, K. C.; Razis, P.; Rembeczki, S.; Ren, D.; Rescigno, M.; Reucroft, S.; Rewiersma, P.; Riemann, S.; Rojkov, A.; Romero, L.; Rosca, A.; Rosemann, C.; Rosenbleck, C.; Rosier-Lees, S.; Roth, S.; Rubio, J. A.; Ruggiero, G.; Rykaczewski, H.; Sakharov, A.; Saremi, S.; Sarkar, S.; Salicio, J.; Sanchez, E.; Schfer, C.; Schegelsky, V.; Schoeneich, B.; Schotanus, D. J.; Sciacca, C.; Servoli, L.; Shen, C. Q.; Shevchenko, S.; Shivarov, N.; Shoutko, V.; Shumilov, E.; Shvorob, A.; Son, D.; Souga, C.; Spillantini, P.; Steuer, M.; Stickland, D. P.; Stoyanov, B.; Straessner, A.; Sudhakar, K.; Sultanov, G.; Sun, L. Z.; Sushkov, S.; Suter, H.; Swain, J. D.; Szillasi, Z.; Tang, X. W.; Tarjan, P.; Tauscher, L.; Taylor, L.; Tellili, B.; Teyssier, D.; Timmermans, C.; Ting, Samuel C. C.; Ting, S. M.; Tonwar, S. C.; Tth, J.; Trowitzsch, G.; Tully, C.; Tung, K. L.; Ulbricht, J.; Unger, M.; Valente, E.

2006-09-01

376

The Gamma-Ray Imager/Polarimeter for Solar Flares (GRIPS)  

NASA Technical Reports Server (NTRS)

The balloon-borne Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS) instrument will provide a near-optimal combination of high-resolution imaging, spectroscopy, and polarimetry of solar-flare gamma-ray/hard X-ray emissions from approximately 20 keV to greater than approximately 10 MeV. GRIPS will address questions raised by recent solar flare observations regarding particle acceleration and energy release, such as: What causes the spatial separation between energetic electrons producing hard X-rays and energetic ions producing gamma-ray lines? How anisotropic are the relativistic electrons, and why can they dominate in the corona? How do the compositions of accelerated and ambient material vary with space and time, and why? The spectrometer/polarimeter consists of sixteen 3D position-sensitive germanium detectors (3D-GeDs), where each energy deposition is individually recorded with an energy resolution of a few keV FWHM and a spatial resolution of less than 0.1 cubic millimeter. Imaging is accomplished by a single multi-pitch rotating modulator (MPRM), a 2.5-centimeter thick tungsten alloy slit/slat grid with pitches that range quasi-continuously from 1 to 13 millimeters. The MPRM is situated 8 meters from the spectrometer to provide excellent image quality and unparalleled angular resolution at gamma-ray energies (12.5 arcsec FWHM), sufficient to separate 2.2 MeV footpoint sources for almost all flares. Polarimetry is accomplished by analyzing the anisotropy of reconstructed Compton scattering in the 3D-GeDs (i.e., as an active scatterer), with an estimated minimum detectable polarization of a few percent at 150-650 keV in an X-class flare. GRIPS is scheduled for a continental-US engineering test flight in fall 2013, followed by long or ultra-long duration balloon flights in Antarctica.

Shih, Albert Y.; Lin, Robert P.; Hurford, Gordon J.; Duncan, Nicole A.; Saint-Hilaire, Pascal; Bain, Hazel M.; Boggs, Steven E.; Zoglauer, Andreas C.; Smith, David M.; Tajima, Hiroyasu; Amman, Mark S.; Takahashi, Tadayuki

2012-01-01

377

Study of latitudinal response of solar x-ray flares associated with strong radio bursts using multi-technique observations  

NASA Astrophysics Data System (ADS)

The ionospheric effects due to solar flares (SF) have been intensively studied for several decades. It is now known that the SF effects can be observed from pre-dawn to post-dusk regions, with most pronounced signatures in the noon region (solar zenith angle is close to zero). It is generally demonstrated that enhancements in X-ray or EUV during solar flares cause an abrupt increase of the ionospheric electron density throughout the whole sunlit hemisphere. However, investigations of the ionospheric response to solar flares suggest that their impact on the ionosphere varies from event to event. The solar radio bursts (SRBs), a source of radio frequency interference are also generally associated with x-ray solar flare and acts as a threat to the trans-ionospheric signals. Considering this, we examined the SRBs using Nobeyama observations and found 34 radio burst events (>1000 sfu at 1GHz) to be closely associated with x-ray flares and CMEs during 2000-2012. We found 2 C-, 18 M- and 14 X-class solar flares are associated with these events. The 8 events out of these are very strong radio events (>10,000 sfu) and occurred with X-class of solar flares. The response of these flares on the ionosphere is investigated by using the data of vertical total electron content (TEC) measured by satellite altimeters TOPEX, Jason-1 and Jason-2. The preliminary results of observations from satellite altimeters show that the sudden enhancement in TEC is not simultaneous at the same time at all regions when the flare occurs and this also varies with the strength of the flare. In most of M and C- class flare events, we found an increase in TEC at most of the latitudes and time during the flare. We found that some of the X-class solar events weaken the equatorial ionization anomaly (EIA) moving equator ward and then disappears with the decrease in TEC. Other X-class events, on the contrary, showed a tendency to increase the EIA. To understand and support our results, multi-technique observations using ground-based GPS-receivers located world-wide and TEC data from the GPS-receiver onboard CHAMP satellite will be investigated which may provide more information about the peculiarities of the longitudinal and latitudinal response of the ionosphere

Aggarwal, M.; Astafyeva, E.

2013-12-01

378

Modeling subsolar thermospheric waves during a solar flare and penetration electric fields  

NASA Astrophysics Data System (ADS)

Thermospheric waves occurring around the time of the 14 July 2000 solar flare were investigated using the Global Ionosphere and Thermosphere Model. The simulation results showed that extensive acoustic and gravity waves were excited by the solar flare in the subsolar region. The subsolar buoyancy period at 400 km altitude was approximately 16 min. Gravity waves with frequencies lower than the buoyancy frequency traveled from the dayside to the nightside and converged in the longitudinal region that was the antisubsolar region when the flare occurred. Acoustic waves with frequencies well above the buoyancy frequency propagated upward from approximately 130 km altitude with increasing amplitudes. The power spectra of the vertical neutral winds in the acoustic branch peaked at a period of approximately 13 min, just below the buoyancy period. The gradient in pressure was the driver of the two waves, while the ion drag caused a phase delay between the variations in the pressure gradient and the vertical velocity in the acoustic waves. An anticorrelation in the high-frequency component of the vertical neutral wind exists between the subsolar and antisubsolar points at times away from the flare, which was driven by the rapid variations of the ion flows due to the penetration electric field. It is suggested that the penetration of the high-latitude interplanetary magnetic field electric field to low latitudes can drive neutral waves in the equatorial region through momentum coupling with rapidly changing ion flows.

Zhu, Jie; Ridley, Aaron J.

2014-12-01

379

CHARGE-EXCHANGE LIMITS ON LOW-ENERGY {alpha}-PARTICLE FLUXES IN SOLAR FLARES  

SciTech Connect

This paper reports on a search for flare emission via charge-exchange radiation in the wings of the Ly{alpha} line of He II at 304 A, as originally suggested for hydrogen by Orrall and Zirker. Via this mechanism a primary {alpha} particle that penetrates into the neutral chromosphere can pick up an atomic electron and emit in the He II bound-bound spectrum before it stops. The Extreme-ultraviolet Variability Experiment on board the Solar Dynamics Observatory gives us our first chance to search for this effect systematically. The Orrall-Zirker mechanism has great importance for flare physics because of the essential roles that particle acceleration plays; this mechanism is one of the few proposed that would allow remote sensing of primary accelerated particles below a few MeV nucleon{sup -1}. We study 10 events in total, including the {gamma}-ray events SOL2010-06-12 (M2.0) and SOL2011-02-24 (M3.5) (the latter a limb flare), seven X-class flares, and one prominent M-class event that produced solar energetic particles. The absence of charge-exchange line wings may point to a need for more complete theoretical work. Some of the events do have broadband signatures, which could correspond to continua from other origins, but these do not have the spectral signatures expected from the Orrall-Zirker mechanism.

Hudson, H. S. [SSL, UC Berkeley, CA 94720 (United States); Fletcher, L.; MacKinnon, A. L. [School of Physics and Astronomy, SUPA, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Woods, T. N., E-mail: hhudson@ssl.berkeley.edu [Laboratory for Atmospheric and Space Physics, University of Colorado, 1234 Innovation Dr., Boulder, CO 80303 (United States)

2012-06-20

380

Correlative analysis of hard and soft x ray observations of solar flares  

NASA Technical Reports Server (NTRS)

We have developed a promising new technique for jointly analyzing BATSE hard X-ray observations of solar flares with simultaneous soft X-ray observations. The technique is based upon a model in which electric currents and associated electric fields are responsible for the respective heating and particle acceleration that occur in solar flares. A useful by-product of this technique is the strength and evolution of the coronal electric field. The latter permits one to derive important flare parameters such as the current density, the number of current filaments composing the loop, and ultimately the hard X-ray spectrum produced by the runaway electrons. We are continuing to explore the technique by applying it to additional flares for which we have joint BATSE/Yohkoh observations. A central assumption of our analysis is the constant of proportionality alpha relating the hard X-ray flux above 50 keV and the rate of electron acceleration. For a thick-target model of hard X-ray production, it can be shown that cv is in fact related to the spectral index and low-energy cutoff of precipitating electrons. The next step in our analysis is to place observational constraints on the latter parameters using the joint BATSE/Yohkoh data.

Zarro, Dominic M.

1994-01-01

381

A STATISTICAL STUDY OF THE SPECTRAL HARDENING OF CONTINUUM EMISSION IN SOLAR FLARES  

SciTech Connect

The observed hard X-ray and {gamma}-ray continuum in solar flares is interpreted as Bremsstrahlung emission of accelerated non-thermal electrons. It has been noted for a long time that in many flares the energy spectra show hardening at energies around or above 300 keV. In this paper, we first conduct a survey of spectral hardening events that were previously studied in the literature. We then perform a systematic examination of 185 flares from the Solar Maximum Mission. We identify 23 electron-dominated events whose energy spectra show clear double power laws. A statistical study of these events shows that the spectral index below the break ({gamma}{sub 1}) anti-correlates with the break energy ({epsilon}{sub b}). Furthermore, {gamma}{sub 1} also anti-correlates with Fr, the fraction of photons above the break compared to the total photons. A hardening spectrum, as well as the correlations between ({gamma}{sub 1}, {epsilon}{sub b}) and ({gamma}{sub 1}, Fr), provide stringent constraints on the underlying electron acceleration mechanism. Our results support a recent proposal that electrons are being accelerated diffusively at a flare termination shock with a width of the order of an ion inertial length scale.

Kong, X.; Chen, Y. [Institute of Space Sciences and School of Space Science and Physics, Shandong University, Weihai 264209 (China); Li, G., E-mail: xl_kong@hotmail.com, E-mail: gang.li@uah.edu [Department of Physics and CSPAR, University of Alabama in Huntsville, Huntsville, AL 35899 (United States)

2013-09-10

382

COMBINED STEREO/RHESSI STUDY OF CORONAL MASS EJECTION ACCELERATION AND PARTICLE ACCELERATION IN SOLAR FLARES  

SciTech Connect

Using the potential of two unprecedented missions, Solar Terrestrial Relations Observatory (STEREO) and Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI), we study three well-observed fast coronal mass ejections (CMEs) that occurred close to the limb together with their associated high-energy flare emissions in terms of RHESSI hard X-ray (HXR) spectra and flux evolution. From STEREO/EUVI and STEREO/COR1 data, the full CME kinematics of the impulsive acceleration phase up to {approx}4 R{sub sun} is measured with a high time cadence of <=2.5 minutes. For deriving CME velocity and acceleration, we apply and test a new algorithm based on regularization methods. The CME maximum acceleration is achieved at heights h <= 0.4 R{sub sun}, and the peak velocity at h <= 2.1 R{sub sun} (in one case, as small as 0.5 R{sub sun}). We find that the CME acceleration profile and the flare energy release as evidenced in the RHESSI HXR flux evolve in a synchronized manner. These results support the 'standard' flare/CME model which is characterized by a feedback relationship between the large-scale CME acceleration process and the energy release in the associated flare.

Temmer, M.; Veronig, A. M. [IGAM/Kanzelhoehe Observatory, Institute of Physics, Universitaet Graz, Universitaetsplatz 5, A-8010 Graz (Austria); Kontar, E. P. [Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Krucker, S. [Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450 (United States); Vrsnak, B., E-mail: mat@igam.uni-graz.a, E-mail: asv@igam.uni-graz.a, E-mail: eduard@astro.gla.ac.u, E-mail: krucker@ssl.berkeley.ed, E-mail: bvrsnak@gmail.co [Hvar Observatory, Faculty of Geodesy, University of Zagreb, Kaciceva 26, HR-10000 Zagreb (Croatia)

2010-04-01

383

Searching for narrow-band oscillations in solar flares in the presence of frequency-dependent noise  

NASA Astrophysics Data System (ADS)

A common feature of solar flare emission is the appearance of short timescale fluctuations, often interpreted in terms of oscillatory signatures, and often referred to as quasi-periodic pulsations (QPPs) or quasi-periodic oscilations (QPOs). These fluctuations are an important diagnostic of solar plasma, as they are linked to the flare reconnection and particle acceleration sites. However, it has recently become clear that solar flare time series, like many astrophysical objects, are often dominated by frequency-dependent 'red' noise, rather than white noise. This frequency-dependent red-noise is commonly not taken into account when analyzing flare time-series for narrow-band oscillations. We demonstrate the application of a Bayesian method of searching for narrow-band oscillations in flares (based on Vaughan 2010) that fully accounts for frequency-dependent noise. We apply this method to the recent flares of 2011 February 15 and 2011 June 7, utilizing high-cadence EUV and X-ray data from the Proba-2/LYRA and Fermi/GBM instruments. While emphasizing that the observed fluctuations are a very real effect, we show that the emission from the selected events can be well described by a frequency-dependent noise model, without the need to invoke an explicit oscillatory mechanism. This presents a challenge to our current understanding of flare fluctuations, and suggests that narrow-band oscillations in flare emission may be much less prevalent than previously believed.

Inglis, Andrew; Ireland, Jack

2014-06-01

384

Chromospheric Evaporation and Decimetric Radio Emission in Solar Flares  

NASA Technical Reports Server (NTRS)

We have discovered decimetric signatures of the chromospheric evaporation process. Evidence for the radio detection of chromospheric evaporation is based on the radio-inferred values of (1) the electron density, (2) the propagation speed, and (3) the timing, which are found to be in good agreement with statistical values inferred from the blueshifted Ca xix soft X-ray line. The physical basis of our model is that free-free absorption of plasma emission is strongly modified by the steep density gradient and the large temperature increase in the upflowing flare plasma. The steplike density increase at the chromospheric evaporation front causes a local discontinuity in the plasma frequency, manifested as almost infinite drift rate in decimetric type III bursts. The large temperature increase of the upflowing plasma considerably reduces the local free-free opacity (due to the T-(exp -3/2) dependence) and thus enhances the brightness of radio bursts emitted at the local plasma frequency near the chromospheric evaporation front, while a high-frequency cutoff is expected in the high-density regions behind the front, which can be used to infer the velocity of the upflowing plasma. From model calculations we find strong evidence that decimetric bursts with a slowly drifting high-frequency cutoff are produced by fundamental plasma emission, contrary to the widespread belief that decimetric bursts are preferentially emitted at the harmonic plasma level. We analyzed 21 flare episodes from 1991-1993 for which broadband (100-3000 MHz) radio dynamic spectra from Phoenix, hard X-ray data from BATSE/CGRO, and soft X-ray data from GOES were available. We detected slowly drifting high-frequency cutoffs between 1.1 and 3.0 GHz, with drift rates of -41 +/- 32 MHz/s, extending over time intervals of 24 +/- 23 s. Developing a density model for type III-emitting flare loops based on the statistically observed drift rate of type III bursts by Alvarez & Haddock, we infer velocities of up to 360 km/s for the upflowing plasma, with an average of v(sub CE) = 236 +/- 130 km /s for episodes with 5-15 s duration. The mean electron density of the upflowing plasma is n(sub e) = 5.2(+/-3.1) x 10(exp 10) /cu cm when it is first detected in radio, at coronal altitudes of h(sub 0) = 9.2 +/- 2.3 Mm.

Aschwanden, Markus J.; Benz, Arnold O.

1995-01-01

385

Acoustic Oscillations in Solar and Stellar Flaring Loops  

E-print Network

Evolution of a coronal loop in response to an impulsive energy release is numerically modelled. It is shown that the loop density evolution curves exhibit quasi-periodic perturbations with the periods given approximately by the ratio of the loop length to the average sound speed, associated with the second standing harmonics of an acoustic wave. The density perturbations have a maximum near the loop apex. The corresponding field-aligned flows have a node near the apex. We suggest that the quasi-periodic pulsations with periods in the range 10-300 s, frequently observed in flaring coronal loops in the radio, visible light and X-ray bands, may be produced by the second standing harmonic of the acoustic mode.

V. M. Nakariakov; D. Tsiklauri; A. Kelly; T. D. Arber; M. J. Aschwanden

2004-02-10

386

Quasi-periodic Wiggles of Microwave Zebra Structures in a Solar Flare  

NASA Astrophysics Data System (ADS)

Quasi-periodic wiggles of microwave zebra pattern (ZP) structures with periods ranging from about 0.5 s to 1.5 s are found in an X-class solar flare on 2006 December 13 at the 2.6-3.8 GHz with the Chinese Solar Broadband Radio Spectrometer (SBRS/Huairou). Periodogram and correlation analysis show that the wiggles have two to three significant periodicities and are almost in phase between stripes at different frequencies. The Alfvn speed estimated from the ZP structures is about 700 km s-1. We find the spatial size of the wave-guiding plasma structure to be about 1 Mm with a detected period of about 1 s. This suggests that the ZP wiggles can be associated with the fast magnetoacoustic oscillations in the flaring active region. The lack of a significant phase shift between wiggles of different stripes suggests that the ZP wiggles are caused by a standing sausage oscillation.

Yu, Sijie; Nakariakov, V. M.; Selzer, L. A.; Tan, Baolin; Yan, Yihua

2013-11-01

387

Modulation of solar flare particles and track density profiles in gas-rich meteorite grains  

NASA Technical Reports Server (NTRS)

A solution is presented to the problem concerning the time-averaged solar flare particle flux as a function of kinetic energy and distance from the sun for a given particle injection spectrum at the sun within the framework of standard diffusion-convection-adiabatic deceleration theory with the diffusion coefficient independent of distance from the sun. Results of the calculations which give best agreement with observations at 1 AU are presented and discussed, with particular reference to their implications for gas-rich meteorites. Normalization at the orbit of earth is achieved via observed track density versus depth profiles in lunar vug crystals. It is shown that if gas-rich meteorite grains were irradiated in the asteroid belt and if source and modulation parameters have changed little since irradiation, the track density should be 'harder' than the lunar vug profile by about 0.2-0.3 in the index. Quantitative estimation of solar flare particle exposure ages is discussed.

Lee, M. A.

1976-01-01

388

Ion acceleration and abundance enhancements by electron beam instabilities in impulsive solar flares  

NASA Technical Reports Server (NTRS)

We show that a nonrelativistic electron beam in a hydrogen-helium solar flare plasma will excite H(+) electromagnetic ion cyclotron, shear Alfven, and R-X waves, in addition to waves resulting from the two-stream instability. The H(+) electromagnetic ion cyclotron and shear Alfven waves are able to selectively accelerate ambient He-3 and Fe, respectively, to MeV energies through first harmonic gyroresonance, and thereby account for the large (He-3)/(He-4) and Fe/C ratios seen in the energetic particles from impulsive solar flares. In this model, separate heating and acceleration mechanisms for either He-3 or Fe are not required, and Fe acceleration is quite efficient since it does not need to occur by second harmonic gyroresonance. The combination of the other two unstable modes is able to accelerate ions to hundreds of MeV if the particles become trapped in an electrostatic potential well of a two-stream wave.

Miller, James A.; Vinas, Adolfo F.

1993-01-01

389

Small-scale magnetic field diagnostics in solar flares using bisectors of I V profiles  

NASA Astrophysics Data System (ADS)

In the present study, spatially unresolved magnetic fields in solar flares are investigated by analyzing the fine structure of Zeeman splitting in two FeI lines. Namely, we consider bisector splitting of I V Stokes profiles in 5123.7 and 5233 ? lines. The analysis of bisector splitting functions (BSF) of the 5233 ? line averaged over 12 solar flares of different classes, from C5 to X1.4, reveals two distinct peaks, around ?? = 80-110 m? and 170-200 m?. Such peculiarities indicate the unacceptability of weak field approximation for FeI 5233 line and need interpretation in the framework of inhomogeneous models with strong magnetic field components. Consequently, we argue that the named two peaks can reflect the existence of two discrete modes of subtelescopic magnetic fields with strengths about 6 and 12 kG in photospheric layers.

Lozitsky, V. G.

2015-02-01

390

The Calculation and Observation of Gamma-Rays from Solar Flares  

NASA Astrophysics Data System (ADS)

Nuclear reactions, due to the interactions of the flare-accelerated particles with the ambient solar atmosphere, produce a wealth of gamma-ray line, neutron, positron, and ?-meson emissions. Such emissions have been observed in many solar flares. The principal mechanisms for the production of solar gamma-ray lines are nuclear deexcitation, neutron capture by proton, and positron-electron annihilation. The nuclear deexcitation spectrum consists of narrow lines resulting from the accelerated light-weight ions (protons and ?-particles) interacting with the ambient heavy nuclei, broad lines resulting from the accelerated heavy nuclei interacting with ambient H and He atoms, and nuclear continuum which includes a series of unresolved weak lines, compound continuum, and pre-equilibrium continuum. The solar gamma-rays are the most direct diagnostic tool for studying the acceleration and transportation of energetic particles in solar flares, especially for protons and heavy ions. They provide a wealth of information about the nature of accelerated particles, as well as the physical properties of ambient medium. TALYS is an efficient code for simulating nuclear reactions, and it can provide detailed calculations for all the information, including cross sections. Based on TALYS, we develop a new program of gamma-ray production, which improves the completeness and accuracy of the previous calculations. The theoretical frame of gamma-ray production in solar flares is treated in detail in the first half of the thesis. In addition, we take the 4.438 MeV line as an example to calculate the shapes of strong gamma-ray lines under different conditions. By comparison, we find that the shapes of gamma-ray lines (including Doppler width and shift) are closely related to the energy spectrum and angular distribution of accelerated ions, the solar atmospheric element abundance, and flare location, etc. As a result, the observation and analysis of spectral line shape will help us to obtain these physical parameters. In the latter part of the thesis, we employ a Monte Carlo simulation toolkit named GEANT4 to simulate the transport of neutron capture line in the solar atmosphere, and study the effect of Compton scattering on the gamma-ray spectrum by combing the theoretical calculation with observational data. By analyzing the flare which occurred on 2005 January 20 (X7.1/2B), we find that the vertical depth for neutron capture on hydrogen is about 8 g\\cdot cm^{-2} on average and higher than 15 g\\cdot cm^{-2} during the early phase of the flare. It is suggested that Compton scattering has a significant effect on the propagation of the neutron capture lines, especially during the early phase of the flare. Furthermore, by using the Compton-scattered continuum to correct the neutron capture line flux, we also find that the time evolution, not only the intensity but also the peak time of the flux, can be changed considerably compared with the values before the correction. This result demonstrates that the Compton effect of 2.223 MeV photons plays a significant role in a gamma-ray spectrum.

Chen, W.

2013-09-01

391

Solar flare ionization in the mesosphere observed by coherent-scatter radar  

NASA Technical Reports Server (NTRS)

The coherent-scatter technique, as used with the Urbana radar, is able to measure relative changes in electron density at one altitude during the progress of a solar flare when that altitude contains a statistically steady turbulent layer. This work describes the analysis of Urbana coherent-scatter data from the times of 13 solar flares in the period from 1978 to 1983. Previous methods of measuring electron density changes in the D-region are summarized. Models of X-ray spectra, photoionization rates, and ion-recombination reaction schemes are reviewed. The coherent-scatter technique is briefly described, and a model is developed which relates changes in scattered power to changes in electron density. An analysis technique is developed using X-ray flux data from geostationary satellites and coherent scatter data from the Urbana radar which empirically distinguishes between proposed D-region ion-chemical schemes, and estimates the nonflare ion-pair production rate.

Parker, J. W.; Bowhill, S. A.

1986-01-01

392

The Statistical Study of GOES Flux and Energy Distribution of Solar Flares  

NASA Astrophysics Data System (ADS)

In the first part of the talk, instead of taking into account the peak flux of solar flares in previously statistical study, we use all the data of GOES in the present work. The frequency distributions of 0.5-4 A and 1-8 A are presented. We propose a so-called pile up model to explain the observed distribution. With our model we can also explain the distribution difference at peak and valley years of solar activity. In the second part, using data from ESP/SDO, GOES, and RHESSI, we calculated the radiative energy loss in the channel of 0.1-7 nm, 0.1-0.8 nm, soft X-rays emitted by the thermal plasma, and the thermal energy at the flare peak time. The amount of these energies are compared and their distributions are presented.

Gan, Weiqun; Li, Youping

393

Satellite observed thermospheric impact of solar flares and possible implications for the early Earth  

NASA Astrophysics Data System (ADS)

The evolution of planetary atmospheres depends sensitively on the radiation and particle environment of the planet's hoststar. Atmospheric escape rates are strongly related especially to the soft X-ray (SXR) and extreme and far ultraviolett (EUV and FUV) parts of the solar spectrum. By means of observational data from low Earth orbiting (LEO) satellites it is possible to study the response of the earths thermosphere on enhanced EUV radiation events caused by solar flares. This enables one to estimate exobase temperatures and thermospheric particle densities under different radiation environments. So the flare events can be used as proxies for early Earth studies and for Earth-like atmospheres of potential exoplanets which are exposed to higher stellar EUV fluxes.

Pfleger, M.; Krauss, S.; Hausleitner, W.; Lammer, H.; Fichtinger, B.; Lichtenegger, H. I. M.

2013-09-01

394

Enrichment of 3He and Heavy Ions in Impulsive Solar Flares  

Microsoft Academic Search

The acceleration of 3He and heavy ions by electromagnetic hydrogen cyclotron waves in a direct single-stage process in impulsive solar flares is investigated analytically and with the help of test particle simulations. We illustrate in detail the mechanism by which a single monochromatic wave can accelerate such ions to MeV and even GeV energies. While somewhat idealized, a monochromatic wave

Ilan Roth; Michael Temerin

1997-01-01

395

Time and energy dependence of heavy ion abundances in solar flare energetic particle events  

NASA Technical Reports Server (NTRS)

Examples are presented of the time and energy dependence of the abundances and spectra of the major heavy ions He, C, O and Fe during solar flare events, taken from a survey using the UMD/MPI ULET telescope on IMP-8 during 1973-1977. In some cases, time variations were found in the O/He, O/C and Fe/O ratios which appear to be inconsistent with models based solely on rigidity dependent propagation in the interplanetary medium.

Mason, G. M.; Weiss, H.; Gloeckler, G.; Hovestadt, D.

1981-01-01

396

Gamma-Ray Line Versus Continuum Emission of Electron-Dominated Episodes During Solar Flares  

Microsoft Academic Search

Electron-dominated episodes or events during solar flares are characterized by a flattening of the electron bremsstrahlung continuum above about 1MeV. This flattening leads to a dominance of the continuum at MeV energies over nuclear emissions. We analyzed events recorded by the gamma-ray spectrometer on SMM with the aim to determine the nuclear contribution in the energy range between 4 and

E. Rieger; W. Q. Gan; H. Marschhuser

1998-01-01

397

Modeling the Response of the Martian Upper Atmosphere to Solar Flares  

NASA Astrophysics Data System (ADS)

Over the past decade, observations and models of Mars' atmosphere have enabled scientists to begin to focus not only on the climatology and global behavior of the atmosphere, but also on time-dependent behavior that extends over multiple spatial scales. The ability to study the effects of transient phenomena is not only important from a scientific perspective, but also from an operational one, since spacecraft are often asked to sample the atmosphere well below the exobase. Previous works have already begun to study the effects of solar flares on the ionosphere using observations (e.g. Mendillo et al., 2006; Mahajan et al, 2009). In this study, we utilize the recently developed and initially validated 3-D Mars Global Ionosphere-Thermopshere Model (M-GITM) to examine the effects of a large solar flare on the martian thermosphere and ionosphere. M-GITM simulates the atmosphere from the ground to exobase in spherical coordinates while relaxing the hydrostatic assumption and utilizing a terrain-following coordinate system. The model makes use of required physical processes, formulations, and subroutines that have been taken from existing lower and upper atmosphere Mars GCMs. In this study, we focus on the perturbation of the mass and electron densities caused by solar flares and examine the role that preconditioning plays in the response of the atmosphere.

Pawlowski, D. J.; Bougher, S. W.; Chamberlin, P. C.

2011-12-01

398

Time-dependent coronal shock acceleration of energetic solar flare particles  

NASA Technical Reports Server (NTRS)

A global time-dependent model is presented for the coronal and interplanetary shock acceleration and propagation of energetic solar flare particles. The calculations are carried out to help prove that coronal shock acceleration of solar flare particles is responsible for energetic solar flare event data gathered in interplanetary space. The model is based on the theory of diffusive shock acceleration, and requires particle speeds to be much greater than bulk velocities. Also, sufficient scattering must occur upstream and downstream of the shock for the particle scattering mean free path to be smaller than the characteristic scale lengths, which causes the same particles to encounter the shock repeatedly. A spherically symmetric shock wave is assumed, which leads to the same emission configuration for impulsively and monoenergetically emitted particles. Consideration is given to acceleration by compression at the shock front, adiabatic deceleration in the divergent downstream flow, the temporal evolution of the shock and the three-dimensional geometry of the corona. The model is used to generate normalized proton omnidirectional distributions at 1 AU and at the shock front. The spectral exhibit trends similar to those in observational data, especially proton acceleration times and the proton distribution profiles at 1 AU.

Lee, M. A.; Ryan, J. M.

1986-01-01

399

Collisionless shock formation and the prompt acceleration of solar flare ions  

NASA Technical Reports Server (NTRS)

The formation mechanisms of collisionless shocks in solar flare plasmas are investigated. The priamry flare energy release is assumed to arise in the coronal portion of a flare loop as many small regions or 'hot spots' where the plasma beta locally exceeds unity. One dimensional hybrid numerical simulations show that the expansion of these 'hot spots' in a direction either perpendicular or oblique to the ambient magnetic field gives rise to collisionless shocks in a few Omega(i), where Omega(i) is the local ion cyclotron frequency. For solar parameters, this is less than 1 second. The local shocks are then subsequently able to accelerate particles to 10 MeV in less than 1 second by a combined drift-diffusive process. The formation mechanism may also give rise to energetic ions of 100 keV in the shock vicinity. The presence of these energetic ions is due either to ion heating or ion beam instabilities and they may act as a seed population for further acceleration. The prompt acceleration of ions inferred from the Gamma Ray Spectrometer on the Solar Maximum Mission can thus be explained by this mechanism.

Cargill, P. J.; Goodrich, C. C.; Vlahos, L.

1988-01-01

400

Micrometeorites and solar flare particles in and out of the ecliptic. [lunar rocks track observation  

NASA Technical Reports Server (NTRS)

Using crystals grown into vugs from oriented lunar rocks as directional detectors of cosmic dust particles and solar flare nuclei, I have measured the angular distribution of the flux of micrometeoroids of mass 30 attograms to 80 femtograms. Hypervelocity impact craters of diameter 500 A to 10 microns and tracks from solar flare nuclei of energy 100 keV/amu to 20 MeV/amu were observed in crystals from rock 71055 facing lunar south and in crystals from rock 74255 facing lunar east. I have found that dust grains both in ecliptic orbits and in orbits inclined to the ecliptic have virtually identical mass-frequency distributions and similar shapes. I have evaluated the micrometeoroid fluxes after determining the exposure ages of the individual vug crystals by measuring the solar flare track density gradients in each crystal. The flux of particles of mass greater than 4 femtograms confined to the ecliptic is in good agreement with satellite measurements, suggesting that the micrometeoroid flux has been relatively constant over the past 35,000 yr. The flux of particles producing microcraters on a lunar surface facing south is lower than the ecliptic flux by a factor of about 7.

Hutcheon, I. D.

1975-01-01

401

The Spectral Evolution of Solar Flare Hard X-Ray Emission Observed with BATSE  

NASA Technical Reports Server (NTRS)

We present a more detailed characterization of spectral evolution in solar flare hard X-ray emission than has been previously described. Our characterization is consistent with some earlier results but utilizes higher time resolution data and reveals nuances in spectral evolution that have never been reported. We employ an underutilized data set, the Burst and Transient Source Experiment (BATSE) solar flare catalog, for our investigation and different methodology than previous studies. Our findings support the conclusion that properties of the particle Abstract: acceleration mechanism in flares, such as the acceleration rate or efficiency, are indeed important to understanding spectral evolution. On the other hand, time-of-flight models, which assume accelerator properties to be negligible, cannot explain the observed detailed spectral evolution, and correlations that we would expect to exist between spectral evolution patterns and parameters derived from time-of-flight model inversions are not supported by the data. In this fashion, we establish an observational context in which to interpret future High Energy Solar Spectroscopic Imager (HESSI) observations and delineate some constraints for theoretical models of particle acceleration.

Newton, Elizabeth K.; Giblin, Timothy

2000-01-01

402

The effect of solar-flare X-rays on radio-wave propagation  

NASA Astrophysics Data System (ADS)

Model calculations of variations of ionospheric electron density profiles in relation to variations of the solar X-ray spectrum are analyzed. It is shown that the season, the time of day, the geographic latitude, and the solar-flare spectrum all have an effect on the type of field-strength variations of long-wave radio signals, determined by variations of electron density profile. The strength of each of these factors is determined by the magnitude of the difference between the actual vertical profile of electron density and the summer midday level.

Turkeeva, B. A.

403

A Multi-Mission View of the AR9906 Solar Flare with Alternate Instrument Labels  

NSDL National Science Digital Library

Heres a view of the Sun, from the point of view of a fleet of Sun-observing spacecraft - SOHO, TRACE, and RHESSI. The time scales of the data samples in this visualization range from 6 hours to as short as 12 seconds and the display rate varies throughout the movie. The region and event of interest is the solar flare over solar active region AR9906 on April 21, 2002. In this visualization, black corresponds to no (current) instrument coverage (there used to be a LASCO C1 camera inside the ring of LASCO C2, but that instrument didnt recover after SOHO was temporarily lost in 1998).

Tom Bridgman

2003-01-31

404

A Multi-Mission View of the AR9906 Solar Flare without Instrument Labels  

NSDL National Science Digital Library

Heres a view of the Sun, from the point of view of a fleet of Sun-observing spacecraft - SOHO, TRACE, and RHESSI. The time scales of the data samples in this visualization range from 6 hours to as short as 12 seconds and the display rate varies throughout the movie. The region and event of interest is the solar flare over solar active region AR9906 on April 21, 2002. In this visualization, black corresponds to no (current) instrument coverage (there used to be a LASCO C1 camera inside the ring of LASCO C2, but that instrument didnt recover after SOHO was temporarily lost in 1998).

Tom Bridgman

2003-01-31

405

A Multi-Mission View of the AR9906 Solar Flare with Instrument Labels  

NSDL National Science Digital Library

Heres a view of the Sun, from the point of view of a fleet of Sun-observing spacecraft - SOHO, TRACE, and RHESSI. The time scales of the data samples in this visualization range from 6 hours to as short as 12 seconds and the display rate varies throughout the movie. The region and event of interest is the <