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Sample records for solar flare occurrence

  1. Active Longitude and Solar Flare Occurrences

    NASA Astrophysics Data System (ADS)

    Gyenge, N.; Ludmány, A.; Baranyi, T.

    2016-02-01

    The aim of the present work is to specify the spatio-temporal characteristics of flare activity observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Geostationary Operational Environmental Satellite (GOES) in connection with the behavior of the longitudinal domain of enhanced sunspot activity known as active longitude (AL). By using our method developed for this purpose, we identified the AL in every Carrington Rotation provided by the Debrecen Photoheliographic Data. The spatial probability of flare occurrence has been estimated depending on the longitudinal distance from AL in the northern and southern hemispheres separately. We have found that more than 60% of the RHESSI and GOES flares is located within +/- 36^\\circ from the AL. Hence, the most flare-productive active regions tend to be located in or close to the active longitudinal belt. This observed feature may allow for the prediction of the geo-effective position of the domain of enhanced flaring probability. Furthermore, we studied the temporal properties of flare occurrence near the AL and several significant fluctuations were found. More precisely, the results of the method are the following fluctuations: 0.8, 1.3, and 1.8 years. These temporal and spatial properties of the solar flare occurrence within the active longitudinal belts could provide us with an enhanced solar flare forecasting opportunity.

  2. On the Occurrence of Solar Flares Observed with the Burst and Transient Source Experiment

    NASA Astrophysics Data System (ADS)

    Biesecker, Douglas Alan

    This dissertation is an investigation of solar flare and microflare occurrence rates, times, and sizes in the context of solar flare occurrence models and periods, and coronal heating. Solar flares, explosive releases of energy with effects observed at earth, are not fully understood. Microflares, smaller versions of typical solar flares, were previously only observed during a short balloon experiment. They may provide clues to understanding solar flares by allowing us to test what we already know about large solar flares. The Compton Gamma-Ray Observatory's (GRO) Burst and Transient Source Experiment (BATSE) is used to search for solar flares. This study differs from others because it is the most sensitive with a long observing time. We have used an automated algorithm to search thirteen months of BATSE discriminator data. This algorithm enabled us to detect flares at the instrumental threshold. In this work we extend the flare size frequency distribution down to sizes smaller than previously observed in long-term experiments and find that the observed flares are not a significant heat source for the corona. We find that the power-law shape previously measured applies to flares as small as the instrumental threshold. We test the data for systematic variations in power-law index of the flare size frequency distribution. There is only evidence for variation of the power-law index with the phase of a 51-day period. Time series analyses are used to uncover periodic features in the daily flare occurrence rate. There is evidence for a flare size threshold effect in periodic activity. There are also characteristic activity time scales evident in the daily flare rate. We test for randomness of solar flare occurrence and find no apparent correlation between times of flare occurrence. We also find no correlation between flare size and the time interval between flares. These findings support the avalanche flare model of Lu and Hamilton (1991) but are inconsistent with the occurrence model of Rosner and Vaiana (1978).

  3. Solar flares

    NASA Technical Reports Server (NTRS)

    Zirin, H.

    1974-01-01

    A review of the knowledge about solar flares which has been obtained through observations from the earth and from space by various methods. High-resolution cinematography is best carried out at H-alpha wavelengths to reveal the structure, time history, and location of flares. The classification flares in H alpha according to either physical or morphological criteria is discussed. The study of flare morphology, which shows where, when, and how flares occur, is important for evaluating theories of flares. Consideration is given to studies of flares by optical spectroscopy, radio emissions, and at X-ray and XUV wavelengths. Research has shown where and possibly why flares occur, but the physics of the instability involved, of the particle acceleration, and of the heating are still not understood.

  4. Solar Flares

    NASA Technical Reports Server (NTRS)

    Savage, Sabrina

    2013-01-01

    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.

  5. Solar Flares

    NASA Technical Reports Server (NTRS)

    Shih, Albert

    2011-01-01

    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.

  6. Evolution of Self-organized criticality in the solar corona and its role in solar flare occurrence

    NASA Astrophysics Data System (ADS)

    Awasthi, Arun Kumar; Jain, Rajmal

    The statistical behavior of power-law distribution of solar flare frequency versus respective energy released is known to be scale invariant. However, as individual solar flare originates from a completely independent magnetic-field configuration from other flare, the aforesaid behavior is puzzling. This riddle was solved by proposing solar coronal magnetic field to be in a state of self-organized criticality (SOC). As the magnetic field parameters are found to be a good proxy for build-up and trigger of flare energy release, we explore the signatures of SOC occurrence and evolution in the corona by employing photospheric magnetic-field and coronal X-ray flux. Firstly, we explored long duration statistical photosphere-corona coupling through studying the full-disk magnetic-field parameters and co-temporal disk-integrated coronal X-ray flux for very high flare productive months viz. October 2003, August 2004 and September 2005. We estimated photospheric magnetic flux and coronal X-ray flux to be varying in the range of 5 10(28) - 3 10(29) Mx and 1 10(-7) - 2 10(-4) Watts/m(2) . This study revealed that photospheric magnetic flux and coronal X-ray flux have been co-varying non-linearly following a power-law relationship. Moreover, the relationship between flare-associated active regions magnetic flux and respective coronal X-ray flux has been investigated. In this study, we also employed the observations of pre-flare quiet time in addition to the flare duration. This investigation also consistently reveals power-law relationship between photospheric magnetic flux and coronal X-ray flux as also obtained for aforesaid long-term study. In addition, we have also noticed a photospheric magnetic flux over which the flare X-ray flux undergoes avalanche. We have termed this magnetic flux as critical magnetic flux and the same is estimated to be a flare-dependent quantity and varying in the range of 1.2 - 3.5 10(26) Mx for the flares considered in this study. We are investigating this term in statistical sense for large number of flares in view of its possible association to the SOC state of the corona.

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

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

    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.

  8. Solar flare observations and solar flare models

    NASA Technical Reports Server (NTRS)

    Hyder, C. L.

    1973-01-01

    The use of solar flare models based on specific and detailed observations of solar flares is discussed. A process for determining the validity of various solar models is analyzed. The process relegates the infall-impact model for flares to a secondary role in high energy solar events. The strictly thermal infall-impact model cannot lead to temperatures greater than five million degrees K. Another process is needed to explain the high energy aspects of solar flares which are related to temperatures equal to or greater than 10 to the 7th power degrees K, nonthermal X-ray and radio emissions, white light flares, high energy particles from the sun, and gamma ray producing particles in the sun.

  9. Parameterization of solar flare dose

    SciTech Connect

    Lamarche, A.H.; Poston, J.W.

    1996-12-31

    A critical aspect of missions to the moon or Mars will be the safety and health of the crew. Radiation in space is a hazard for astronauts, especially high-energy radiation following certain types of solar flares. A solar flare event can be very dangerous if astronauts are not adequately shielded because flares can deliver a very high dose in a short period of time. The goal of this research was to parameterize solar flare dose as a function of time to see if it was possible to predict solar flare occurrence, thus providing a warning time. This would allow astronauts to take corrective action and avoid receiving a dose greater than the recommended limit set by the National Council on Radiation Protection and Measurements (NCRP).

  10. Variability of the occurrence frequency of solar flares as a function of peak hard X-ray rate

    NASA Technical Reports Server (NTRS)

    Bai, T.

    1993-01-01

    We study the occurrence frequency of solar flares as a function of the hard X-ray peak count rate, using observations of the Solar Maximum Mission. The size distributions are well represented by power-law distributions with negative indices. As a better alternative to the conventional method, we devise a maximum likelihood method of determining the power-law index of the size distribution. We find that the power-law index of the size distribution changes with time and with the phase of the 154-day periodicity. The size distribution is steeper during the maximum years of solar cycle 21 (1980 and 1981) than during the declining phase (1982-1984). The size distribution, however, is flatter during the maximum phase of the 154-day periodicity than during the minimum phase. The implications of these findings are discussed.

  11. Understanding Solar Flare Statistics

    NASA Astrophysics Data System (ADS)

    Wheatland, M. S.

    2005-12-01

    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.

  12. Solar flares. [plasma physics

    NASA Technical Reports Server (NTRS)

    Rust, D. M.

    1979-01-01

    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.

  13. Flare models: Chapter 9 of solar flares

    NASA Technical Reports Server (NTRS)

    Sturrock, P. A. (Editor)

    1979-01-01

    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.

  14. Using subsurface helicity measurements to predict flare occurrence

    NASA Astrophysics Data System (ADS)

    Reinard, A. A.; Henthorn, J.; Komm, R.; Hill, F.

    2009-12-01

    Solar flares are responsible for a number of hazardous effects including disabling high-frequency radio communications, interfering with GPS measurements, and disrupting satellites. Forecasting flare occurrence is very difficult, giving little advanced notice of these events. One possible means for predicting flare occurrence lies in helioseismology, i.e. analysis of the region below the active region for signs of an impending flare. Time series helioseismic data collected by the Global Oscillation Network Group (GONG) have been analyzed for a subset of active regions that produce large flares and a subset with very high magnetic field strength that produce no flares. A predictive parameter has been developed and analyzed using discriminant analysis as well as traditional forecasting tools such as the Heidke skill score. Preliminary results indicate this parameter predicts flare occurrence with a high success rate.

  15. COMPTEL solar flare observations

    NASA Technical Reports Server (NTRS)

    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

    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.

  16. Understanding Solar Flares

    NASA Astrophysics Data System (ADS)

    Antiochos, Spiro K.; Karpen, J. T.; DeVore, C. R.

    2012-05-01

    Solar flares and their associated coronal mass ejections are the most energetic explosions in the solar system. The largest events pose the greatest space weather dangers to life and civilization, and are of extreme importance to human space exploration. They also provide the best opportunity to study the universal processes of magnetic reconnection and particle acceleration that underlie most solar activity. The two great mysteries of solar flares are: how can so much energy be released so quickly, and how can such a large fraction (50% or more) end up in energetic particles. We present results from recent numerical modeling that sheds new light on these mysteries. These calculations use the highest spatial resolution yet achieved in order to resolve the flare dynamics as clearly as possible. We conclude from this work that magnetic island formation is the defining property of magnetic reconnection in the solar corona, at least, in the large-scale current sheet required for a solar flare. Furthermore, we discuss the types of future observations and modeling that will be required to solve definitively the solar flare mysteries. This work was supported, in part, by the NASA TR&T and SR&T Programs.

  17. The physics of solar flares

    NASA Technical Reports Server (NTRS)

    Tandberg-Hanssen, Einar; Emslie, A. Gordon

    1988-01-01

    Solar flare phenomena are examined in an introduction for advanced undergraduate and graduate physics students. Chapters are devoted to the history of observations, flare spectroscopy, flare magnetohydrodynamics, flare plasma physics, radiative processes in the solar plasma, preflare conditions, the impulsive phase, the gradual phase, and coronal mass ejections. Diagrams, graphs, and photographs are provided.

  18. Electron beams in solar flares

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

    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.

  19. Theory of solar flares

    NASA Astrophysics Data System (ADS)

    Forbes, T.

    The calculation of solar flare emissions from first principles requires consideration of the coronal reconnection process which releases magnetic energy in the corona, the transport process which conveys this energy to the chromosphere, and the evaporation process which injects mass back into the corona to form the flare loops. Although numerous calculations of this kind have been carried out on the latter two processes, very few have been done on the first one, that is how reconnection heats and accelerates plasma over the course of the flare. The main reason so few calculations have been done is that the way the reconnection process converts magnetic energy into heat and flows depends critically on the mechanism which initiates the flare, and the nature of this mechanism is poorly understood at the present time. Here we present a theoretical light curve for a flare based on the assumption that the initiating mechanism is an ideal-MHD instability which drives reconnection at a current sheet that forms after flare onset.

  20. Solar Flare Physics

    NASA Technical Reports Server (NTRS)

    Schmahl, Edward J.; Kundu, Mukul R.

    2000-01-01

    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.

  1. Solar flare model atmospheres

    NASA Technical Reports Server (NTRS)

    Hawley, Suzanne L.; Fisher, George H.

    1994-01-01

    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.

  2. Solar flare model atmospheres

    NASA Technical Reports Server (NTRS)

    Hawley, Suzanne L.; Fisher, George H.

    1993-01-01

    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.

  3. Solar Flare Physics

    NASA Technical Reports Server (NTRS)

    Schmahl, Edward J.; Kundu, Mukul R.

    1998-01-01

    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.

  4. Avalanches and the distribution of solar flares

    NASA Technical Reports Server (NTRS)

    Lu, Edward T.; Hamilton, Russell J.

    1991-01-01

    The solar coronal magnetic field is proposed to be in a self-organized critical state, thus explaining the observed power-law dependence of solar-flare-occurrence rate on flare size which extends over more than five orders of magnitude in peak flux. The physical picture that arises is that solar flares are avalanches of many small reconnection events, analogous to avalanches of sand in the models published by Bak and colleagues in 1987 and 1988. Flares of all sizes are manifestations of the same physical processes, where the size of a given flare is determined by the number of elementary reconnection events. The relation between small-scale processes and the statistics of global-flare properties which follows from the self-organized magnetic-field configuration provides a way to learn about the physics of the unobservable small-scale reconnection processes. A simple lattice-reconnection model is presented which is consistent with the observed flare statistics. The implications for coronal heating are discussed and some observational tests of this picture are given.

  5. Solar Flares and Their Prediction

    NASA Technical Reports Server (NTRS)

    Adams, Mitzi L.

    1999-01-01

    Solar flares and coronal mass ejection's (CMES) can strongly affect the local environment at the Earth. A major challenge for solar physics is to understand the physical mechanisms responsible for the onset of solar flares. Flares, characterized by a sudden release of energy (approx. 10(exp 32) ergs for the largest events) within the solar atmosphere, result in the acceleration of electrons, protons, and heavier ions as well as the production of electromagnetic radiation from hard X-rays to km radio waves (wavelengths approx. = 10(exp -9) cm to 10(exp 6) cm). Observations suggest that solar flares and sunspots are strongly linked. For example, a study of data from 1956-1969, reveals that approx. 93 percent of major flares originate in active regions with spots. Furthermore, the global structure of the sunspot magnetic field can be correlated with flare activity. This talk will review what we know about flare causes and effects and will discuss techniques for quantifying parameters, which may lead to a prediction of solar flares.

  6. The COMPTEL solar flare catalog

    SciTech Connect

    Ryan, J.; Varendorff, M.; McConnell, M.; Forrest, D.; Schoenfelder, V.; Lichti, G.; Diehl, R.; Rank, G.; Bennett, K.; Hanlon, L.; Winkler, W.; Swanenburg, B.; Bloemen, H. Hermsen, W.

    1993-01-01

    COMPTEL, the Imaging Compton Telescope on the Compton Gamma Ray Observatory, has registered many solar gamma ray flares during its two years on orbit. It detects and measures gamma rays from flares by two methods: (1) utilizing two independent large NaI gamma ray spectrometers operating from 0.2 to 2 MeV and 0.6 to 10 MeV and (2) using the telescope and imaging capabilities to acquire spectra from 0.75 to 30 MeV. Solar neutrons can also be measured in the telescope mode. The authors report here the solar gamma ray flare list compiled from COMPTEL data in the two modes of operation. They also describe the methods of searching for flares in the COMPTEL data and the qualitative nature of the flares detected.

  7. Ion acceleration in impulsive solar flares

    NASA Technical Reports Server (NTRS)

    Steinacker, Jurgen; Jaekel, Uwe; Schlickeiser, Reinhard

    1993-01-01

    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.

  8. Solar Chromosphere Flare Spectrograph

    NASA Astrophysics Data System (ADS)

    Choudhary, Debi Prasad

    This paper describes develop of a two channel echelle spectrograph, Solar Chromospheric Flare Spectreograph (SCFC), to observe the optical spectra at the locations of ares and explosive events on the Sun. The SCFS is designed to record spectra in two channels in the wavelength range of 350-890 nm, which has several chromospheric spectral lines. The SCFS will have a multi-fiber based slit capable of observing at 100 locations of the active region magnetic field polarity inversion lines. The field of view of SCFS will be 80 x 80 arc sec with spatial resolution of 8 arc sec. The spectral resolution of 60,000 will be adequate for measuring Doppler velocities of about 5 km/s. The instrument is designed using off-the-shelves optical and mechanical parts with minimum fabrication at an in-house machine shop. We propose to integrate the SCFS with the full-disk Halpha telescope at the Big Bear Solar Observatory that is operating semi-automatically a round the year except for weather interruptions. The SCFS observations will also be mainly used to study the physics of ares, but part of the time will be devoted to classroom educational activities.

  9. Seismic Emission From Solar Flares

    NASA Astrophysics Data System (ADS)

    Lindsey, C. A.; Donea, A.

    2005-05-01

    Local helioseismic diagnostics applied to helioseismic observations from the Michelson Doppler Imager (MDI) on the Solar Heliospheric Observatory (SOHO) have shown the clear signature of seismic emission from three flares during the advent of SOHO. All three of these flares showed the signatures of ?-ray emission indicating the involvement of accelerated protons. Two of the acoustically active flares were recent, October 28 and 29 of 2003, and were observed by RHESSI. In both of these instances, the sources of the acoustic emission acoustic source, determined by computational seismic holography, coincided closely with compact ? -ray signatures of protons. Elementary considerations ofenergy and momentum transfer appear to make chromospheric and photospheric heating by protons favorable for seismic emission from flares. If this is actually the case, proton diagnostics of flares from RHESSI would be useful for identifying acoustically active flares for the Helioseismic Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO), and possibly for the SOHO/MDI. Given a clear understanding of the effects of flares on Doppler signatures in active regions, acoustic emission from flares can give us a powerful control utility for seismic diagnostics of active regions subphotospheres. This research has benefitted greatly from the keen insights of Valentina Zharkova, Gerald Share, Hugh Hudson, and Sam Krucker. It has been supported by grants from the Living with a Star and Supporting Research and Technology programs of the National Aeronautics and Space Administration and the Stellar Astronomy and Astrophysics branch of the National Science Foundation.

  10. Largest Solar Flare on Record

    NASA Technical Reports Server (NTRS)

    2001-01-01

    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)

  11. Solar Flare Models

    NASA Astrophysics Data System (ADS)

    Forbes, T.; Murdin, P.

    2000-11-01

    Even though FLARES have been observed on the Sun for nearly 150 years, their origin remains a mystery. At the present time there is no generally accepted model which explains why they occur, but there do exist models which successfully explain certain limited aspects such as the formation of flare loops and ribbons. Before discussing particular models, we review the constraints imposed on models ...

  12. Solar Flares and the Chromosphere

    NASA Astrophysics Data System (ADS)

    Fletcher, Lyndsay

    2015-08-01

    During a solar flare, the chromosphere emits across a large fraction of the electromagnetic spectrum, providing diagnostic information on heating, dynamics and flare energy transport by both thermal and non-thermal means. The evolution of chromospheric ribbons and footpoints also traces the progress of coronal reconnection, and links radiation output with magnetic evolution. Since the chromosphere emits the majority of a flare's radiation, the current emphasis on chromospheric observations by missions such as IRIS, and future large facilities such as the DKIST, is very beneficial to flare research. In this talk I will overview recent developments in observations and theory of flaring chromospheres and make some suggestions about profitable future avenues for research.

  13. Solar Flare Aimed at Earth

    NASA Technical Reports Server (NTRS)

    2002-01-01

    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

  14. Radiation hydrodynamics in solar flares

    SciTech Connect

    Fisher, G.H.

    1985-10-18

    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.

  15. SCATTERING POLARIZATION IN SOLAR FLARES

    SciTech Connect

    Štěpán, Jiří; Heinzel, Petr

    2013-11-20

    There is ongoing debate about the origin and even the very existence of a high degree of linear polarization of some chromospheric spectral lines observed in solar flares. The standard explanation of these measurements is in terms of the impact polarization caused by non-thermal proton and/or electron beams. In this work, we study the possible role of resonance line polarization due to radiation anisotropy in the inhomogeneous medium of the flare ribbons. We consider a simple two-dimensional model of the flaring chromosphere and we self-consistently solve the non-LTE problem taking into account the role of resonant scattering polarization and of the Hanle effect. Our calculations show that the horizontal plasma inhomogeneities at the boundary of the flare ribbons can lead to a significant radiation anisotropy in the line formation region and, consequently, to a fractional linear polarization of the emergent radiation of the order of several percent. Neglecting the effects of impact polarization, our model can provide a clue for resolving some of the common observational findings, namely: (1) why a high degree of polarization appears mainly at the edges of the flare ribbons; (2) why polarization can also be observed during the gradual phase of a flare; and (3) why polarization is mostly radial or tangential. We conclude that radiation transfer in realistic multi-dimensional models of solar flares needs to be considered as an essential ingredient for understanding the observed spectral line polarization.

  16. Impulsivity Parameter for Solar Flares

    NASA Astrophysics Data System (ADS)

    Fajardo-Mendieta, W. G.; Martínez-Oliveros, J. C.; Alvarado-Gómez, J. D.; Calvo-Mozo, B.

    2016-02-01

    Three phases are typically observed during solar flares: the preflare, impulsive, and decay phases. During the impulsive phase, it is believed that the electrons and other particles are accelerated after the stored energy in the magnetic field is released by reconnection. The impulsivity of a solar flare is a quantifiable property that shows how quickly this initial energy release occurs. It is measured via the impulsivity parameter, which we define as the inverse of the overall duration of the impulsive phase. We take the latter as the raw width of the most prominent nonthermal emission of the flare. We computed this observable over a work sample of 48 M-class events that occurred during the current Solar Cycle 24 by using three different methods. The first method takes into account all of the nonthermal flare emission and gives very accurate results, while the other two just cover fixed energy intervals (30–40 keV and 25–50 keV) and are useful for fast calculations. We propose an alternative way to classify solar flares according to their impulsivity parameter values, defining three different types of impulsivity, namely, high, medium, and low. This system of classification is independent of the manner used to calculated the impulsivity parameter. Lastly, we show the relevance of this tool as a discriminator of different HXR generation processes.

  17. Rapid fluctuations in solar flares

    NASA Technical Reports Server (NTRS)

    Sturrock, Peter A.

    1986-01-01

    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.

  18. Mass ejections. [during solar flares

    NASA Technical Reports Server (NTRS)

    Rust, D. M.; Hildner, E.; Hansen, R. T.; Dryer, M.; Mcclymont, A. N.; Mckenna-Lawlor, S. M. P.; Mclean, D. J.; Schmahl, E. J.; Steinolfson, R. S.; Tandberg-Hanssen, E.

    1980-01-01

    Observations and model simulations of solar mass ejection phenomena are examined in an investigation of flare processes. Consideration is given to Skylab and other observations of flare-associated sprays, eruptive prominences, surges and coronal transients, and to MHD, gas dynamic and magnetic loop models developed to account for them. Magnetic forces are found to confine spray material, which originates in preexisting active-region filaments, within steadily expanding loops, while surges follow unmoving, preexisting magnetic field lines. Simulations of effects of a sudden pressure pulse at the bottom of the corona are found to exhibit many characteristics of coronal transients associated with flares, and impulsive heating low in the chromosphere is found to be able to account for surges. The importance of the magnetic field as the ultimate source of energy which drives eruptive phenomena as well as flares is pointed out.

  19. Solar flare emissions and geophysical disturbances

    NASA Technical Reports Server (NTRS)

    Sakurai, K.

    1973-01-01

    Various geophysical phenomena are produced by both wave and particle emissions from solar flares. Using the observed data for these emissions, a review is given on the nature of solar flares and their development. Geophysical phenomena are discussed by referring to the results for solar flare phenomena.

  20. Biggest Solar Flare on Record

    NASA Technical Reports Server (NTRS)

    2002-01-01

    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

  1. Turbulence, complexity, and solar flares

    NASA Astrophysics Data System (ADS)

    McAteer, R. T. James; Gallagher, Peter T.; Conlon, Paul A.

    2010-05-01

    The issue of predicting solar flares is one of the most fundamental in physics, addressing issues of plasma physics, high-energy physics, and modelling of complex systems. It also poses societal consequences, with our ever-increasing need for accurate space weather forecasts. Solar flares arise naturally as a competition between an input (flux emergence and rearrangement) in the photosphere and an output (electrical current build up and resistive dissipation) in the corona. Although initially localised, this redistribution affects neighbouring regions and an avalanche occurs resulting in large scale eruptions of plasma, particles, and magnetic field. As flares are powered from the stressed field rooted in the photosphere, a study of the photospheric magnetic complexity can be used to both predict activity and understand the physics of the magnetic field. The magnetic energy spectrum and multifractal spectrum are highlighted as two possible approaches to this.

  2. Magnetic reconnection in solar flares

    NASA Technical Reports Server (NTRS)

    Forbes, T. G.

    1991-01-01

    The magnetic energy stored in the corona is the only plausible source for the energy released during large solar flares. During the last 20 years most theoretical work has concentrated on models which store magnetic energy in the corona in the form of electrical currents, and a major goal of present day research is to understand how these currents are created, and then later dissipated during a flare. Another important goal is to find a flare model which can eject magnetic flux into interplanetary space. Although many flares do not eject magnetic flux, those which do are of special importance for solar-terrestrial relations since the ejected flux can have dramatic effects if it hits the Earth's magnetosphere. Three flare models which have been extensively investigated are the emerging-flux model, the sheared-arcade model, and the magnetic-flux-rope model. All of these models can store and release magnetic energy efficiently provided that rapid magnetic reconnection occurs. However, only the magnetic-flux-rope model appears to provide a plausible mechanism for ejecting magnetic flux into interplanetary space.

  3. Interplanetary shock waves associated with solar flares

    NASA Technical Reports Server (NTRS)

    Chao, J. K.; Sakurai, K.

    1974-01-01

    The interaction of the earth's magnetic field with the solar wind is discussed with emphasis on the influence of solar flares. The geomagnetic storms are considerered to be the result of the arrival of shock wave generated by solar flares in interplanetary space. Basic processes in the solar atmosphere and interplanetary space, and hydromagnetic disturbances associated with the solar flares are discussed along with observational and theoretical problems of interplanetary shock waves. The origin of interplanetary shock waves is also discussed.

  4. Solar flares and energetic particles.

    PubMed

    Vilmer, Nicole

    2012-07-13

    Solar flares are now observed at all wavelengths from ?-rays to decametre radio waves. They are commonly associated with efficient production of energetic particles at all energies. These particles play a major role in the active Sun because they contain a large amount of the energy released during flares. Energetic electrons and ions interact with the solar atmosphere and produce high-energy X-rays and ?-rays. Energetic particles can also escape to the corona and interplanetary medium, produce radio emissions (electrons) and may eventually reach the Earth's orbit. I shall review here the available information on energetic particles provided by X-ray/?-ray observations, with particular emphasis on the results obtained recently by the mission Reuven Ramaty High-Energy Solar Spectroscopic Imager. I shall also illustrate how radio observations contribute to our understanding of the electron acceleration sites and to our knowledge on the origin and propagation of energetic particles in the interplanetary medium. I shall finally briefly review some recent progress in the theories of particle acceleration in solar flares and comment on the still challenging issue of connecting particle acceleration processes to the topology of the complex magnetic structures present in the corona. PMID:22665901

  5. Ion Acceleration in Solar Flares

    NASA Technical Reports Server (NTRS)

    Miller, James A.; Weir, Sue B.

    1996-01-01

    Solar flares are among the most energetic and interesting phenomena in the Solar system, releasing up to 1032 ergs of energy on timescales of several tens of seconds to several tens of minutes. Much of this energy is in the form of suprathermal electrons and ions, which remain trapped at the Sun and produce a wide variety of radiations, as well as escape into interplanetary space, where they can be directly observed. The radiation from trapped particles consists in general of (1) continuum emission; (2) narrow gamma-ray nuclear deexcitation lines; and (3) high-energy neutrons observed in space or by ground-based neutron monitors. The particles that escape into space consist of both electrons and ions, which often have compositions quite different than that of the ambient solar atmosphere. Flares thus present many diagnostics of the particle acceleration mechanism(s), the identification of which is the ultimate goal of flare research. Moreover, flares in fact offer the only opportunity in astrophysics to study the simultaneous energization of both electrons and ions. Hopefully, an understanding of flares with their wealth of diagnostic data will lead to a better understanding of particle acceleration at other sites in the Universe. It is now generally accepted that flares are roughly divided into two classes: impulsive and gradual. Gradual events are large, occur high in the corona, have long-duration soft and hard X-rays and gamma rays, are electron poor, are associated with Type II radio emission and coronal mass ejections (CMEs), and produce energetic ions with coronal abundance ratios. Impulsive events are more compact, occur lower in the corona, produce short-duration radiation, and exhibit dramatic abundance enhancements in the energetic ions. Their He-3/He-4 ratio is - 1, which is a huge increase over the coronal value of about 5 x 10(exp -4), and they also posses smaller but still significant enhancements of Ne, Mg, Si, and Fe relative to He-4, C, N, and O. Specifically, above about 1 MeV nucleon(exp -1), the ratio of Fe to O is about 8 times larger than in the corona or in gradual flares, while the ratio of Ne, Mg, and Si to O is about 3 times higher; He-4, C, N, and 0 are not enchanced with respect to each other. In addition to these elemental enhancements, Ne and Mg have isotopic enhancements as well. The general scenario that has emerged from these (and other) observations is that energetic particles in gradual events are accelerated by a CME-driven shock, while those particles in impulsive events are accelerated by another mechanism(s).

  6. High Resolution Spectra of Solar Flares

    NASA Astrophysics Data System (ADS)

    Doschek, G. A.

    I discuss high-resolution solar flare spectra from the soft X-ray region through the extreme ultraviolet (EUV) wavelength regions. Spectra of solar flares at these wavelengths have been recorded since the late 1960s, beginning primarily with the NASA Orbiting Solar Observatory (OSO) series of spacecraft. Knowledge of EUV flare spectra took a quantum leap with the NASA Skylab Apollo Telescope Mount spectrographs in the early 1970s. Knowledge of the X-ray spectrum took a similar leap in the 1980s with the US Department of Defense P78-1 spacecraft, the NASA Solar Maximum Mission spacecraft (SMM), and the Japanese Hinotori spacecraft. Investigations of flare X-ray spectra continued with the BCS X-ray spectrometer experiment on the Japanese Yohkoh mission. Recently, EUV solar flare spectroscopy has been extended with the SUMER spectrometer on the ESA SOHO spacecraft. In addition to the above missions, significant contributions were made with instrumentation on a number of other spacecraft, e.g., the Soviet Intercosmos X-ray spectrometers. Our knowledge of the physical conditions in solar flares has been greatly expanded from analyses of X-ray and EUV flare spectra. I will discuss the general characteristics of the flare emission line and continuum spectra, and the physical processes that produce them. I will discuss what we have learned about solar flares from the spectra, and discuss solar flare spectra in terms of spectra expected from other astrophysical sources.

  7. FNAS/solar flare energetics

    NASA Technical Reports Server (NTRS)

    Machado, M. E.

    1992-01-01

    We have performed an extensive study of solar flare energy buildup and release, concentrating in two aspects: (1) relationship with 3D field topology and measured electric currents; and (2) flare onset characteristics as determined from combined x ray and ultraviolet observations. We extended our previous studies on the characteristic topology of flaring regions, by following the evolution of an active region over three consecutive days. From comparison with flare observations in x rays and h alpha, we found further support for the hypothesis that flares were triggered by taking place at the separators (3D generalization of and x-type neutral point). Furthermore, we found that emerging in flux at a site within the active regions where no (or little) activity was previously observed, caused the appearance of a secondary separator and thereon continuous triggering of activity at such site. Our topology arguments were then applied to a study of sympathetic activity between two regions within an active complex. Here again we found that interacting field structures along separators and separatrices, which act as pathways for recurrent flaring to spread between the regions, could be used to understand how activity spread to potentially explosive sites with the complex. We also finished our study of flare onset characteristics as determined from combined x ray and ultraviolet observations. Using a quasi-static modeling approach, we find that this phase is characterized by a relatively low level of energy release, 10 exp 26-27 erg/s, which is sufficient to produce 'gentle' evaporation, a shift in the location of the transition zone as compared to pre-flare conditions, and an increase in the temperature and density of coronal loops. All these changes have profound implications on the observed signatures of impulsive phase phenomena, which had been neglected in the past. As a follow-up of this investigation, we now plan to apply our results to the interpretation of high-sensitivity spectroscopic and hard x-ray data currently being gathered by the Yohkoh and Compton Gamma Ray Observatory satellites.

  8. Solar flares controlled by helicity conservation

    NASA Technical Reports Server (NTRS)

    Gliner, Erast B.; Osherovich, Vladimir A.

    1995-01-01

    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.

  9. Helium (3) Rich Solar Flares

    DOE R&D Accomplishments Database

    Colgate, S. A.; Audouze, J.; Fowler, W. A.

    1977-05-03

    The extreme enrichment of {sup 3} He {sup 4} He greater than or equal to 1 in some solar flares as due to spallation and the subsequent confinement of the products in a high temperature, kT approx. = 200 keV, high density, n{sub e} approx. = 3 x 10{sup 15} cm {sup -3} plasma associated with the magnetic instability producing the flare is interpreted. The pinch or filament is a current of high energy protons that creates the spallation and maintains the temperature that produces the high energy x-ray spectrum and depletes other isotopes D, Li, Be, and B as observed. Finally the high temperature plasma is a uniquely efficient spallation target that is powered by the interaction of stellar convection and self generated magnetic field.

  10. A Phase Diagram for Solar Flares

    NASA Astrophysics Data System (ADS)

    Balasubramaniam, K. S.; Winter, Lisa; Pernak, Rick

    2015-04-01

    Using the data from the NOAA/GOES X-ray observations of ~50,000 flares, we develop a Phase Diagram for solar flares. Such a Solar Flare Phase Diagram helps to trace the underlying energy structure of solar flares, and provides a prediction framework. The temperature (maximum ratio of short (0.5 - 4 A) to long band (1-8 A) band) and background solar x-ray radiation (at 1-8 A band) forms the basis of the phase diagram. Using the phase diagram and relevant statistical analysis, we derive insights into the eruptive nature of flares during the solar-cycle ramp (ramp up to and ramp down from solar maximum) phases and peak phase of the solar cycle.

  11. Solar flares induced D-region ionospheric and geomagnetic perturbations

    NASA Astrophysics Data System (ADS)

    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

    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.

  12. A statistic study of ionospheric solar flare activity indicator

    NASA Astrophysics Data System (ADS)

    Xiong, Bo; Ding, Feng; Ning, Baiqi; Wan, Weixing; Yu, You; Hu, Lianhuan

    According to the Chapman ionization theory, an ionospheric solar flare activity indicator (ISFAI) is given by the solar zenith angle and the variation rate of ionospheric vertical total electron content, which is measured from a global network of dual-frequency GPS receivers. The ISFAI is utilized to statistically analyze the ionospheric responses to 1439 M-class and 126 X-class solar flares during solar cycle 23 (1996-2008). The statistical results show that the occurrence of ISFAI peak increases obviously at 3.2 total electron content unit (TECU)/h (1 TECU = 1016 elm-2) and reaches the maximum at 10 TECU/h during M-class flares and 10 TECU/h and 40 TECU/h for X-class flares. ISFAI is closely correlated with the 26-34 nm extreme ultraviolet flux but poorly related to the 0.1-0.8 nm X-ray flux. The central meridian distance (CMD) of flare location is an important reason for depressing relationship between ISFAI and X-ray Flux. Through the CMD effect modification, the ISFAI has a significant dependence on the X-ray flux with a correlation coefficient of 0.76. The ISFAI sensitivity enables to detect the extreme X-class flares, as well as the variations of one order of magnitude or even smaller (such as for C-class flares). Meanwhile, ISFAI is helpful to the calibration of the X-ray flux at 0.1-0.8 nm observed by GOES during some flares. In addition, statistical results demonstrate that ISFAI can detect 80% of all M-class flares and 92% for all X-class ones during 1996-2008. Owing to the high sensitivity and temporal resolution, ISFAI can be utilized as a solar flare detection parameter to monitor space weather.

  13. Geomagnetic Solar Flare Effect Associated with the Most Powerful X-Class Solar Flares

    NASA Astrophysics Data System (ADS)

    Chukwudi Okpala, Kingsley

    2015-08-01

    The variation in the Earth’s magnetic field associated with X class solar flares have been studied. Thirty (30) most powerful X-class solar flares that occurred between 1976 and the end of the last solar cycle have been investigated with a view to understanding the effect of this class of flares on the geomagnetic field. The geomagnetic solar flare effect (sfe) associated with these solar flares, as observed in fifteen geomagnetic station with data resolution of minutes have been computed. We obtained a good correlation (r >0.73) between the normalized H component amplitude of the solar flare effect (Hsfe) and the intensity of the solar flare especially for the solar flares that occurred within 45o of the central meridian of the solar disk at. Stations within the mid latitude generally showed better correlation than those at higher latitudes. The Z component amplitude of the solar flare effect (Zsfe) generally showed weaker correlation (r>4.6) with the solar flare intensity, and this correlation was better for high latitude stations. The results from this study have important implications for our present understanding of the nature of- and complexities in- the ionizations that lead to the geomagnetic solar flare effect.

  14. Thermal Fronts in Solar Flares

    NASA Astrophysics Data System (ADS)

    Karlický, Marian

    2015-12-01

    We studied the formation of a thermal front during the expansion of hot plasma into colder plasma. We used a three-dimensional electromagnetic particle-in-cell model that includes inductive effects. In early phases, in the area of the expanding hot plasma, we found several thermal fronts, which are defined as a sudden decrease of the local electron kinetic energy. The fronts formed a cascade. Thermal fronts with higher temperature contrast were located near plasma density depressions, generated during the hot plasma expansion. The formation of the main thermal front was associated with the return-current process induced by hot electron expansion and electrons backscattered at the front. A part of the hot plasma was trapped by the thermal front while another part, mainly with the most energetic electrons, escaped and generated Langmuir and electromagnetic waves in front of the thermal front, as shown by the dispersion diagrams. Considering all of these processes and those described in the literature, we show that anomalous electric resistivity is produced at the location of the thermal front. Thus, the thermal front can contribute to energy dissipation in the current-carrying loops of solar flares. We estimated the values of such anomalous resistivity in the solar atmosphere together with collisional resistivity and electric fields. We propose that the slowly drifting reverse drift bursts, observed at the beginning of some solar flares, could be signatures of the thermal front.

  15. Electron acceleration in solar flares

    NASA Technical Reports Server (NTRS)

    Droge, Wolfgang; Meyer, Peter; Evenson, Paul; Moses, Dan

    1989-01-01

    For the period Spetember 1978 to December 1982, 55 solar flare particle events for which the instruments on board the ISEE-3 spacecraft detected electrons above 10 MeV. Combining data with those from the ULEWAT spectrometer electron spectra in the range from 0.1 to 100 MeV were obtained. The observed spectral shapes can be divided into two classes. The spectra of the one class can be fit by a single power law in rigidity over the entire observed range. The spectra of the other class deviate from a power law, instead exhibiting a steepening at low rigidities and a flattening at high rigidities. Events with power-law spectra are associated with impulsive (less than 1 hr duration) soft X-ray emission, whereas events with hardening spectra are associated with long-duration (more than 1 hr) soft X-ray emission. The characteristics of long-duration events are consistent with diffusive shock acceleration taking place high in the corona. Electron spectra of short-duration flares are well reproduced by the distribution functions derived from a model assuming simultaneous second-order Fermi acceleration and Coulomb losses operating in closed flare loops.

  16. Solar and Stellar Flares and Their Effects on Planets

    NASA Astrophysics Data System (ADS)

    Shibata, Kazunari

    2015-08-01

    Recent space observations of the Sun revealed that the solar atmosphere is full of explosions, such as flares and flare-like phenomena. These flares generate not only strong electromagnetic emissions but also nonthermal particles and bulk plasma ejections, which sometimes lead to geomagnetic storms and affect terrestrial environment and our civilization, damaging satellite, power-grids, radio communication etc. Solar flares are prototype of various explosions in our universe, and hence are important not only for geophysics and environmental science but also for astrophysics. The energy source of solar flares is now established to be magnetic energy stored near sunspots. There is now increasing observational evidence that solar flares are caused by magnetic reconnection, merging of anti-parallel magnetic field lines and associated magneto-plasma dynamics (Shibata and Magara 2011, Living Review). It has also been known that many stars show flares similar to solar flares, and often such stellar flares are much more energetic than solar flares. The total energy of a solar flare is typically 10^29 - 10^32 erg. On the other hand, there are much more energetic flares (10^33 - 10^38 erg) in stars, especially in young stars. These are called superflares. We argue that these superflares on stars can also be understood in a unified way based on the reconnection mechanism. Finally we show evidence of occurrence of superflares on Sun-like stars according to recent stellar observations (Maehara et al. 2012, Nature, Shibayama et al. 2013), which revealed that superflares with energy of 10^34 - 10^35 erg (100 - 1000 times of the largest solar flares) occur with frequency of once in 800 - 5000 years on Sun-like stars which are very similar to our Sun. Against the previous belief, these new observations as well as theory (Shibata et al. 2013) suggest that we cannot deny the possibility of superflares on the present Sun. Finally, we shall discuss possible impacts of these superflares on the Earth as well as exoplanets around these superflare stars.

  17. Solar flare leaves sun quaking

    NASA Astrophysics Data System (ADS)

    1998-05-01

    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

  18. Solar gamma rays. [in solar flares

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

    The theory of gamma ray production in solar flares is treated in detail. Both lines and continuum are produced. Results show that the strongest line predicted at 2.225 MeV with a width of less than 100 eV and detected at 2.24 + or - 2.02 MeV, is due to neutron capture by protons in the photosphere. Its intensity is dependent on the photospheric He-3 abundance. The neutrons are produced in nuclear reactions of flare accelerated particles which also produce positrons and prompt nuclear deexcitation lines. The strongest prompt lines are at 4.43 MeV from c-12 and at approximately 6.2 from 0-16 and N-15. The gamma ray continuum, produced by electron bremsstrahlung, allows the determination of the spectrum and number of accelerated electrons in the MeV region. From the comparison of the line and continuum intensities a proton-to-electron ratio of about 10 to 100 at the same energy for the 1972, August 4 flare. For the same flare the protons above 2.5 MeV which are responsible for the gamma ray emission produce a few percent of the heat generated by the electrons which make the hard X rays above 20 keV.

  19. Solar flares: A monograph from Skylab Solar Workshop II

    SciTech Connect

    Sturrock, P.A.

    1980-01-01

    Papers are presented on the current understanding of the physics of solar flares based on Skylab and other observations and theoretical considerations. Specific aspects of the solar flare problem considered include the preflare state, primary energy release, energetic particles, the impulsive phase, the chromosphere and transition region, mass ejections and the thermal X-ray flare plasma. Attention is also given to the various flare models, and the total radiative and mechanical energy outputs of the solar flare of Sept. 5, 1973, are estimated.

  20. A statistic study of ionospheric solar flare activity indicator

    NASA Astrophysics Data System (ADS)

    Xiong, Bo; Wan, Weixing; Ning, Baiqi; Ding, Feng; Hu, Lianhuan; Yu, You

    2014-01-01

    According to the Chapman ionization theory, an ionospheric solar flare activity indicator (ISFAI) is given by the solar zenith angle and the variation rate of ionospheric vertical total electron content, which is measured from a global network of dual-frequency GPS receivers. The ISFAI is utilized to statistically analyze the ionospheric responses to 1439 M-class and 126 X-class solar flares during solar cycle 23 (1996-2008). The statistical results show that the occurrence of ISFAI peak increases obviously at 3.2 total electron content unit (TECU)/h (1 TECU = 1016 el m-2) and reaches the maximum at 10 TECU/h during M-class flares and 10 TECU/h and 40 TECU/h for X-class flares. ISFAI is closely correlated with the 26-34 nm extreme ultraviolet flux but poorly related to the 0.1-0.8 nm X-ray flux. The central meridian distance (CMD) of flare location is an important reason for depressing relationship between ISFAI and X-ray Flux. Through the CMD effect modification, the ISFAI has a significant dependence on the X-ray flux with a correlation coefficient of 0.76. The ISFAI sensitivity enables to detect the extreme X-class flares, as well as the variations of one order of magnitude or even smaller (such as for C-class flares). Meanwhile, ISFAI is helpful to the calibration of the X-ray flux at 0.1-0.8 nm observed by GOES during some flares. In addition, the statistical results demonstrate that ISFAI can detect 80% of all M-class flares and 92% for all X-class ones during 1996-2008.

  1. X-ray spectroscopy of solar flares

    NASA Technical Reports Server (NTRS)

    Culhane, J. L.

    1981-01-01

    After a brief review of the nature of the solar corona, the X-ray output of solar flares is discussed in some detail with particular reference to emission line excitation mechanisms and to the information that can be obtained about the flare plasma from studies of the intensities, profiles and wavelengths of these lines. The X-ray crystal spectrometers on the NASA Solar Maximum Mission spacecraft are described and the interpretation of the spectra obtained with these instruments is discussed.

  2. The Two Complexes of Activity Observed in the Northern Hemisphere during 1982 and the 24-Day Periodicity of Flare Occurrence

    NASA Astrophysics Data System (ADS)

    Ruždjak, V.; Ruždjak, D.; Brajša, R.; Temmer, M.; Hanslmeier, A.

    Daily numbers of solarflares of importance classes ≥ 1 for the northern solar hemisphere in 1982 are studied applying wavelet power spectra (WPS). Special attention is paid to the occurrence of a 24-day period in the WPS. The wavelet power spectra method is combined with synoptic maps of the magnetic fields. Separately, flare indices of two activity complexes mainly contributing to flare occrrence in this period are examined. It is found that the detected 24-day signal in the WPS is mainly a consequence of the presence of the two flare activity complexes separated by about 45° in longitude during several succesive Carrington rotations.

  3. Explosive evaporation in solar flares

    NASA Technical Reports Server (NTRS)

    Fisher, George H.

    1987-01-01

    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.

  4. Far Infrared Observations of Solar Flares

    NASA Astrophysics Data System (ADS)

    Klein, K.; Trottet, G.; Molodij, G.; Smery, A.

    The infrared spectrum of solar flares is unknown over a wavelength range of three orders of magnitude. Yet, key processes related to the energy conversion during flares are expected to be seen there : the synchrotron emission of relativistic electrons and positrons would reveal the most energetic particles in the solar atmosphere. The thermal free-free emission of the upper photosphere and lower chromosphere shows the response of these low atmospheric layers to energy release in the flaring corona, and the analysis of this continuum would largely improve the quantitative knowledge of energy transport and deposition in flares. We outline these issues and describe a first attempt to open this wavelength range to flare observations, which is presently in preparation for a french-chinese microsatellite project (SMESE) at the next solar maximum.

  5. Transient particle acceleration associated with solar flares

    NASA Technical Reports Server (NTRS)

    Chupp, E. L.

    1990-01-01

    Mechanisms that apply to solar flares are discussed, and their applicability to other astrophysical sites, where transient X-ray and gamma-ray bursts occur, is tested. Two different approaches are used to determine the characteristics of the charged particles, accelerated in association with solar flares: (1) measurement of the energy spectra and composition of charged particles observed in space and believed to be associated with a specific solar flare; and (2) recording of electromagnetic emissions in the visible, ultraviolet, soft X-ray, hard X-ray, and gamma-ray spectral regions, and also high-energy neutrons produced in the solar atmosphere by the particles accelerated in association with the solar flare. It is suggested that, at the present level of knowledge, regions where particle acceleration and interactions occur are unlikely to be specified.

  6. Sunquakes and Two Types of Solar Flares

    NASA Astrophysics Data System (ADS)

    Kosovichev, Alexander

    2015-08-01

    Uninterrupted observations from Solar Dynamics Observatory provide unique opportunity for investigation of "sunquakes", helioseismic waves caused by strong localized impacts in the low atmosphere during impulsive phase of solar flares. The SDO observations show that these events are more frequent than previously thought. They are observed in solar flares from C- to X-classes. However, not all X-class flares produce sunquakes, and it is puzzling why some relatively weak flares produce sunquakes, while significantly more powerful flares do not. Using data from the Helioseismic and Magnetic Imager (HMI) and Atmospheric Imaging Assembly (AIA) I investigate properties of sunquakes by detecting and analyzing the seismic wave fronts and the sources of the flare impact, and discuss physical mechanisms of the impact. By comparing energetic and morphological characteristics of the flares with and without sunquakes, I present arguments that this phenomenon reflects a division between two classes of solar flares: confined and eruptive, which may be fundamentally different in terms of the energy release mechanism.

  7. Distant Suns: Solar Flares as Proxies for Stellar Flares

    NASA Astrophysics Data System (ADS)

    Kashyap, Vinay; Reeves, Kathy; Wargelin, Brad

    2009-09-01

    The solar corona has been a Rosetta stone directing our knowledge and understanding of stellar coronae. Because of its proximity, the Sun can be observed in great detail, and detailed physical models derived from such observations are often used to explain stellar phenomena. Large stellar flares are traditionally modeled as a single coronal loop evolving hydrodynamically. However, such a picture has no counterpart on the Sun, where flares are observed to be complex events, generally affecting large areas of an active region and resulting in post-flare loop arcades that have a different magnetic topology compared to the pre-flare region. Here we discuss a large flare on a dM3.5Ve dwarf, Ross 154, that was observed with Chandra. The flare shows a pronounced dual-decay structure. We model the event as a set of cascading loops in an arcade that are sequentially energized, leading to predicted light curves that also exhibit similar behavior. This work was supported by CXC NASA contract NAS8-39073 (VLK, BW) and XRT NASA contract NNM07AB07C (KR).

  8. MAGNETIC FIELD STRUCTURES TRIGGERING SOLAR FLARES AND CORONAL MASS EJECTIONS

    SciTech Connect

    Kusano, K.; Bamba, Y.; Yamamoto, T. T.; Iida, Y.; Toriumi, S.; Asai, A.

    2012-11-20

    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.

  9. Solar Flares and their Effects on Planets

    NASA Astrophysics Data System (ADS)

    Guinan, Edward Francis; Engle, Scott G.

    2015-08-01

    The effects of flares from the Sun on Earth and other solar-system planets are discussed. The strong X-ray - UV radiation and high plasma fluxes from flares can strongly effect solar system planets even as far out as the Jovian planets and their moons. Data from our "Sun in Time" program are used to study the flare properties of the Sun and solar-type stars from youth to old age. These data imply that the young Sun had numerous, very powerful flares that may have played major roles in the development and evolution of the early atmospheres of Earth and other terrestiral planets. These strong X-UV fluxes from flares can greatly effect the photochemistry of planetary atmospheres as well as ionizing and possibly eroding their atmospheres. Some examples are given. Also briefly discussed are effects of large flares from the present Sun on the Earth. Even though strong solar flares are rarer and less powerful than from the youthful Sun, they can cause significant damage to our communication and satellite systems, electrical networks, and threaten the lives of astronauts in space.This research is supported by grants from NASA (HST and Chandra) and NSF. We gratefully acknowledge this support

  10. Soliton and strong Langmuir turbulence in solar flare processes

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

    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.

  11. Energy release in solar flares

    NASA Technical Reports Server (NTRS)

    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

    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.

  12. Solar Eruptions: Coronal Mass Ejections and Flares

    NASA Technical Reports Server (NTRS)

    Gopalswamy, Nat

    2012-01-01

    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

  13. Solar Flares: Avalanche Models and Data Assimilation

    NASA Astrophysics Data System (ADS)

    Blanger, Eric; Charbonneau, Paul; Vincent, Alain

    2005-08-01

    Solar flares play an important part in space meteorology because they can eject charged particles that are the source of the geomagnetic storms on Earth. These storms can interfere with communication satellites and overload electric transformers. We need first to understand the physical mechanisms at the origin of flares and to be able to predict them sufficiently in advance. Several models to explain the mechanism of solar flares were suggested. We have investigated the self-organized criticality (or avalanche) model where an instability related to the reconnection of the magnetic field lines is propagated. The techniques of data assimilation were applied to a 2-D avalanche model. Data assimilation generates better forecasts by taking advantage of both the theoretical/numerical models and the observations. With the increase in computational power and the numerous satellites (SOHO, TRACE) observing the Sun with an improved spatial and temporal resolution, these methods will surely give us a better understanding of solar flares.

  14. Patchy Reconnection in Solar Flare

    NASA Astrophysics Data System (ADS)

    Linton, Mark

    2010-05-01

    Observations of downflows in flares and of the filamentary nature of flare loops suggest that some flare reconnection occurs in bursts and patches rather than in continuous, steady sheets. This presentation will discuss simulations of such patchy reconnection in Harris and Y-type current sheets. The role that various anomalous resistivity models can play in spontaneously creating such patches of reconnection will be studied. The formation of three dimensional transient shocks in the resulting reconnected fields will be explored. Finally, the propagation and extension of these reconnection patches will be studied and compared against observations of the propagation and extension of observed flare ribbons.

  15. Reverse Current in Solar Flares

    NASA Technical Reports Server (NTRS)

    Knight, J. W., III

    1978-01-01

    An idealized steady state model of a stream of energetic electrons neutralized by a reverse current in the pre-flare solar plasma was developed. These calculations indicate that, in some cases, a significant fraction of the beam energy may be dissipated by the reverse current. Joule heating by the reverse current is a more effective mechanism for heating the plasma than collisional losses from the energetic electrons because the Ohmic losses are caused by thermal electrons in the reverse current which have much shorter mean free paths than the energetic electrons. The heating due to reverse currents is calculated for two injected energetic electron fluxes. For the smaller injected flux, the temperature of the coronal plasma is raised by about a factor of two. The larger flux causes the reverse current drift velocity to exceed the critical velocity for the onset of ion cyclotron turbulence, producing anomalous resistivity and an order of magnitude increase in the temperature. The heating is so rapid that the lack of ionization equilibrium may produce a soft X-ray and EUV pulse from the corona.

  16. Solar Flares and the High Energy Solar Spectroscopic Imager (HESSI)

    NASA Technical Reports Server (NTRS)

    Holman, Gordon D.; Fisher, Richard R. (Technical Monitor)

    2001-01-01

    Solar flares are the biggest explosions in the solar system. They are important both for understanding explosive events in the Universe and for their impact on human technology and communications. The satellite-based HESSI is designed to study the explosive release of energy and the acceleration of electrons, protons, and other charged particles to high energies in solar flares. HESSI produces "color" movies of the Sun in high-energy X rays and gamma rays radiated by these energetic particles. HESSI's X-ray and gamma-ray images of flares are obtained using techniques similar to those used in radio interferometry. Ground-based radio observations of the Sun provide an important complement to the HESSI observations of solar flares. I will describe the HESSI Project and the high-energy aspects of solar flares, and how these relate to radio astronomy techniques and observations.

  17. An Observational Overview of Solar Flares

    NASA Technical Reports Server (NTRS)

    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

    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.

  18. Energetic electrons generated during solar flares

    NASA Astrophysics Data System (ADS)

    Mann, Gottfried

    2015-12-01

    > electrons are accelerated up to energies beyond 30 keV is one of the open questions in solar physics. A flare is considered as the manifestation of magnetic reconnection in the solar corona. Which mechanisms lead to the production of energetic electrons in the magnetic reconnection region is discussed in this paper. Two of them are described in more detail.

  19. Velocity structure of solar flare plasmas

    NASA Astrophysics Data System (ADS)

    Watanabe, Tetsuya; Watanabe, Kyoko; Hara, Hirohisa; Imada, Shinsuke

    Thanks to its increased sensitivity and spectral resolution, EIS enabled emission line profile analysis for the first time in solar EUV spectroscopy, and it found detailed structures in velocity and temperature in solar flares. A widely accepted model for solar flares incorporates magnetic reconnection in the corona which results in local heating as well as acceleration of nonthermal particle beams. The standard model of solar flares is called the CSHKP model, arranging the initials of model proposers. We find loop-top hot source, fast outflows nearby, inflow structure flowing to the hot source that appeared in the impulsive phase of long-duration eruptive flares. From the geometrical relationships of these phenomena, we conclude that they provide evidence for magnetic reconnection that occurs near the loop-top region. The reconnection rate is estimated to 0.05 - 0.1, which supports the Petschek-type magnetic reconnection. The nonthermal particle beams will travel unimpeded until they reach the cold, dense chromosphere, where the energy of the beam is predominantly used to heat the chromosphere at the foot points of flaring loops. Explosive chromospheric evaporation happens when the beam energy is high enough that the chromosphere cannot radiate away energy fast enough and hence expands at high velocities into the corona. Spatially resolved observations of chromopheric evaporation during the initial phases of impulsive flares, a few bright points of Fexxiii and Fexxiv emission lines at the footpoints of flaring loops present dominated blue-shifted components of 300 - 400 kms (-1) , while Fexv/xvi lines are nearly stationary, and Feviii and Sivii lines present +50 kms (-1) red shifts. We will review these new views on dynamical structure in flares.

  20. Modelling the impulsive phase of solar flares

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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.

  1. The Solar Flare Myth in solar-terrestrial physics

    SciTech Connect

    Gosling, J.T.

    1993-07-01

    Early observations of associations between solar flares and large non- recurrent geomagnetic storms, large {open_quote}solar{close_quote} energetic particle events, and transient shock wave disturbances in the solar wind led to a paradigm of cause and effect that gave flares a central position in the chain of events leading from solar activity to major transient disturbances in the near-earth space environment. However, research in the last two decades shows that this emphasis on flares is misplaced. In this paper the author outlines briefly the rationale for a different paradigm of cause and effect in solar- terrestrial physics that removes solar flares from their central position as the {open_quote}cause{close_quote} of major disturbances in the near-earth space environment. Instead, this central role of {open_quote}cause{close_quote} is played by events now known as coronal mass ejections, or CMEs.

  2. High Resolution Observations of Solar Flares [Invited

    NASA Astrophysics Data System (ADS)

    Sylwester, B.

    2002-01-01

    The most suitable data set available for investigation of flares has been accumulated by the Yohkoh instruments. The SXT collected a wealth of solar X-ray images including thousands of flare sequences. Over several past years, our team in Space Research Center (SRC) of Polish Academy of Sciences in Wroclaw has been interested in developing the numerical image enhancement techniques with the aim of increasing the resolution on SXT flare images. The algorithm has been worked out which allows for the image deblurring with oversampling. The code (ANDRIL) is available in the public domain (SolarSoft). The application of this algorithm allows to increase the resolution on the SXT images to the level of 1 arc sec. We performed the deconvolution of large number of flare sequences using ANDRIL algorithm. The analysis of these data allowed to study the morphology of million degree flaring plasma with the resolution comparable to TRACE. The main results will be presented in the review. In order to infer the thermodynamic parameters of the plasma from the analysis of deconvolved images their precise coalignment is required. Techniques which have been developed at SRC to achieve high accuracy of image coalignment will be presented. The application of filter ratio (Al12/Be119) technique to the deconvolved and coaligned images allows to study temperature and emission measure distributions in great details. These maps better resolve flare kernels located both at the summits and foot points of flaring loop structures. We have studied the thermodynamic properties of kernels and related them with the corresponding characteristics derived from the analysis of BCS and HXT data. Performed analysis improved considerably our understanding of solar flares. Many of the results and theoretical ideas presented in this review have been obtained in cooperation with the team from the Astronomical Institute of Wroclaw University.

  3. Remote Oscillatory Responses to a Solar Flare

    NASA Astrophysics Data System (ADS)

    Andi?, A.; McAteer, R. T. J.

    2013-07-01

    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.

  4. Carbon-poor solar flare events

    NASA Technical Reports Server (NTRS)

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

    1979-01-01

    Energetic particle flux enhancements over the period October 1973 - December 1977 were surveyed using ULET sensor on the IMP-8 spacecraft. During the four year period the most extreme periods of Fe enrichment compared to 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:0 is approximately 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 pre-injection heating of the ambient matter.

  5. Composition of energetic particles from solar flares.

    PubMed

    Garrard, T L; Stone, E C

    1994-10-01

    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. PMID:11539996

  6. Neutral pion production in solar flares

    NASA Technical Reports Server (NTRS)

    Forrest, D. J.; Vestrand, W. T.; Chupp, E. L.; Rieger, E.; Cooper, J. F.; Share, G. H.

    1985-01-01

    The Gamma-Ray Spectrometer (GRS) on SMM has detected more than 130 flares with emission approx 300 keV. More than 10 of these flares were detected at photon energies 10 MeV. Although the majority of the emission at 10 MeV must be from electron bremsstrahlung, at least two of the flares have spectral properties 40 MeV that require gamma rays from the decay of neutral pions. It is found that pion production can occur early in the impulsive phase as defined by hard X-rays near 100 keV. It is also found in one of these flares that a significant portion of this high-energy emission is produced well after the impulsive phase. This extended production phase, most clearly observed at high energies, may be a signature of the acceleration process which produces solar energetic particles (SEP's) in space.

  7. When and where to look to observe major solar flares

    NASA Technical Reports Server (NTRS)

    Bai, T.

    1989-01-01

    When and where to look is an important issue to observers planning to observe major solar flares. Prediction of major flares is also important because they influence the Earth's environment. Techniques for utilizing recently discovered solar hot spots and a solar activity periodicity of about 154 days in determining when and where to look to catch major flares are discussed.

  8. Deterministically Driven Avalanche Models of Solar Flares

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    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.

  9. A solar tornado triggered by flares?

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

    Context. Solar tornados are dynamical, conspicuously helical magnetic structures that are mainly observed as a prominence activity. Aims: We investigate and propose a triggering mechanism for the solar tornado observed in a prominence cavity by SDO/AIA on September 25, 2011. Methods: 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 are analysed in relation to the tornado activities observed at the limb in 171 . Results: Each of the three flares and its related EUV wave occurred within ten 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 the accelerating tornado motion after the third flare. Conclusions: Flares in the neighbouring active region may have affected the cavity prominence system and triggered the solar tornado. A plausible mechanism is that the active-region coronal field contracted by the "Hudson effect" through the loss of magnetic energy as flares. Subsequently, the cavity expanded by its magnetic pressure to fill the surrounding low corona. We suggest that the tornado is the dynamical response of the helical prominence field to the cavity expansion. Movies are available in electronic form at http://www.aanda.org

  10. Flare Hybrids

    NASA Astrophysics Data System (ADS)

    Tomczak, M.; Dubieniecki, P.

    2015-12-01

    On the basis of the Solar Maximum Mission observations, Švestka ( Solar Phys. 121, 399, 1989) introduced a new class of flares, the so-called flare hybrids. When they start, they look like typical compact flares (phase 1), but later on, they look like flares with arcades of magnetic loops (phase 2). We summarize the characteristic features of flare hybrids in soft and hard X-rays as well as in the extreme ultraviolet; these features allow us to distinguish flare hybrids from other flares. In this article, additional energy release or long plasma cooling timescales are suggested as possible causes of phase 2. We estimate the frequency of flare hybrids, and study the magnetic configurations favorable for flare hybrid occurrence. Flare hybrids appear to be quite frequent, and the difference between the lengths of magnetic loops in the two interacting loop systems seem to be a crucial parameter for determining their characteristics.

  11. A solar tornado caused by flares

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    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.

  12. Predicting large solar flares with data assimilation

    NASA Astrophysics Data System (ADS)

    Strugarek, Antoine; Charbonneau, Paul

    2015-08-01

    Solar and stellar flares are magnetically-driven, scale-invariant energy release events spanning over 8 orders of magnitude in energy. The prediction of the largest solar flares, of class X, is a particularly hard task due the scarcity of such events. The detailed 3D modelling of flaring active regions still requires today too much numerical resources to be routinely used for near real-time predictions. Alternative, empirical models hence have to be designed to perform such predictions. Among the models that adequately reproduce the power-law distribution in flare sizes, avalanche models have the advantage of being numerically cheap to operate. However, they usually rely on a stochastic driver, which can be expected to degrade their predictive capabilities. Building on the pioneering work of Lu and Hamilton, we develop a class of avalanche models which succeed in minimizing the built-in stochastic ingredients while retaining the solar flares power-law distribution. We show that the largest avalanches occurring in these models are robust with respect to the stochastic realization, which opens new perspectives for the prediction of the largest (and most dangerous) solar flares.We further combine data assimilation of the GOES X-ray flux with our avalanche models to carry out actual predictions. The GOES X-ray flux is transformed into a series of peaks that is fed to the model, which automatically finds an initial condition that is compatible with the observed series of events. We then test our prediction model against past GOES large events and discuss the possibility to use our data assimilation package in near real-time applications.

  13. Discuss on Energy Release in Solar Flare

    NASA Astrophysics Data System (ADS)

    Lu, Runbao

    In this paper I give a shortly discuss on current theory and give a new mechanism of energy release in solar flare "electron-ions bound state and its introducing nuclear reaction " model. Main opinions of this model are following : There are two independent process in solar flare, soft x-ray emission ( 12.5keV) and hard x-ray emission (?25keV). There are three kinds of line emission: 12.5keV(p-e-p 12.5keV), 25keV(p-e-A+ 25keV), 25keV(d+-e-d+ 25keV), There is (d,d) fusion in solar flare. The analysis about these phenomena is given. Producing mechanism of x-ray emission and energetic particle production is very different between current theory and new one "electron-ions bound state and its introducing nuclear reaction " model. I think that solar flare is process of glow discharge with hydrogen or deuterium gas in the sun. Observations of RHESSI proved evidence.

  14. The energy spectra of solar flare electrons

    NASA Technical Reports Server (NTRS)

    Evenson, P. A.; Hovestadt, D.; Meyer, P.; Moses, D.

    1985-01-01

    A survey of 50 electron energy spectra from .1 to 100 MeV originating from solar flares was made by the combination of data from two spectrometers onboard the International Sun Earth Explorer-3 spacecraft. The observed spectral shapes of flare events can be divided into two classes through the criteria of fit to an acceleration model. This standard two step acceleration model, which fits the spectral shape of the first class of flares, involves an impulsive step that accelerates particles up to 100 keV and a second step that further accelerates these particles up to 100 MeV by a single shock. This fit fails for the second class of flares that can be characterized as having excessively hard spectra above 1 MeV relative to the predictions of the model. Correlations with soft X-ray and meter radio observations imply that the acceleration of the high energy particles in the second class of flares is dominated by the impulsive phase of the flares.

  15. Solar Flare Impacts on Ionospheric Electrodynamics

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

    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.

  16. High energy component of solar flares

    NASA Astrophysics Data System (ADS)

    Makhmutov, Vladimir; Kurt, Victoria; Bazilevskaya, Galina; Kaufmann, Pierre; Raulin, Jean-Pierre; Stozhkov, Yuri; Yushkov, Boris; Grechnev, Victor

    We have analysed experimental data from the satellites CORONAS-F, YOHKOH, TRACE, GOES and data recorded by the ground based Solar Submillimeter Telescope (SST) during the solar flares on August 25, 2001 and November 4, 2003. Almost simultaneous changes in the > 10-50 MeV gamma-ray spectra and in the > 200 GHz radio flux time profile were found at the very beginning of the impulsive phase of these events. We discuss possible reasons for these observed effects.

  17. Observations of particle acceleration in solar flares

    NASA Technical Reports Server (NTRS)

    Hudson, H. S.

    1979-01-01

    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.

  18. Spatial Scaling Law in Solar Flares

    NASA Astrophysics Data System (ADS)

    Aschwanden, Markus

    How do the observed macroscopic scales observed in solar flares relate to the theoretically implied microscopic scales of energy release and particle acceleration processes. We approach this question by investigating the fast milli-second time scales observed during the impulsive flare phase in hard X-ray and radio wavelengths and their relation to the spatial scales observed in hard and soft X-ray images. Previous studies with Yohkoh and CGRO data established a scaling law between the temporal and spatial scales. We investigate also the fractal spatial patterns of flares observed at arc-second spatial resolution with TRACE and deduce the fractal dimension in 2D and filling factors in 3D. We discuss the implications of these observational results for the spatial scaling of the underlying magnetic reconnection processes.

  19. Characteristics of energetic solar flare electron spectra

    NASA Technical Reports Server (NTRS)

    Moses, Dan; Droege, Wolfgang; Meyer, Peter; Evenson, Paul

    1989-01-01

    A 55 event survey of energy spectra of 0.1-100 MeV interplanetary electrons originating from solar flares as measured by two spectrometers onboard the ISEE 3 (ICE) spacecraft for the years 1978-1982 has been completed. Spectra generated using the maximum flux of a given event in each energy channel were restricted to events with a well-defined flux rise time. Two broad groups of electron spectra are considered. In one group, the spectra are well represented by a single power law in rigidity with spectral index in the range 3-4.5. The spectra in the other group deviate from a power law in rigidity systematically in that they harden with increasing rigidity. Events with near power-law spectra are found to be correlated with long-duration soft X-ray events, whereas those with hardening spectra are correlated with short-duration events. The possible variation of acceleration and propagation processes with the properties of the flare site is discussed, using the duration of the soft X-ray flare emission as an indicator of the physical parameters of the flare site (flare volume, density, coronal height, and magnetic field geometry).

  20. A search for auroral type motions in solar flares

    NASA Technical Reports Server (NTRS)

    Beckers, J. M.; Gilliam, L. B.; Stern, D. P.

    1977-01-01

    Because of analogies between auroras and solar flares, and because of well-established motion along auroras (the so-called westward travelling surge), one might expect systematic motion of brightness to occur along flare ribbons. The Sacramento Peak Observatory flare records of 37 double-ribbon solar flares observed from 1968 to 1972 were examined for evidence of such systematic motion, but results of the investigation were negative.

  1. MEASUREMENTS OF ABSOLUTE ABUNDANCES IN SOLAR FLARES

    SciTech Connect

    Warren, Harry P.

    2014-05-01

    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.

  2. Prediction of Solar Flare Size and Time-to-Flare Using Support Vector Machine Regression

    NASA Astrophysics Data System (ADS)

    Boucheron, Laura E.; Al-Ghraibah, Amani; McAteer, R. T. James

    2015-10-01

    We study the prediction of solar flare size and time-to-flare using 38 features describing magnetic complexity of the photospheric magnetic field. This work uses support vector regression to formulate a mapping from the 38-dimensional feature space to a continuous-valued label vector representing flare size or time-to-flare. When we consider flaring regions only, we find an average error in estimating flare size of approximately half a geostationary operational environmental satellite (GOES) class. When we additionally consider non-flaring regions, we find an increased average error of approximately three-fourths a GOES class. We also consider thresholding the regressed flare size for the experiment containing both flaring and non-flaring regions and find a true positive rate of 0.69 and a true negative rate of 0.86 for flare prediction. The results for both of these size regression experiments are consistent across a wide range of predictive time windows, indicating that the magnetic complexity features may be persistent in appearance long before flare activity. This is supported by our larger error rates of some 40 hr in the time-to-flare regression problem. The 38 magnetic complexity features considered here appear to have discriminative potential for flare size, but their persistence in time makes them less discriminative for the time-to-flare problem.

  3. A phenomenological model of solar flares

    NASA Technical Reports Server (NTRS)

    Colgate, S. A.

    1978-01-01

    The energy of solar flares is derived from the magnetic energy of fields convected to the sun's surface and subsequently converted to heat and energetic particles within the chromosphere. The circumstances of this conversion in most current models is magnetic flux annihilation at a neutral sheet. An analysis is conducted of the constraints of flux annihilation. It is shown that the present evidence of solar cosmic rays, X-rays, gamma-rays, and total energy suggests a choice of annihilation not at a neutral point, but by an enhanced dissipation of a field-aligned current. The field configuration is related both to its origin and to the extensive theory and laboratory experiments concerned with this configuration in magnetic fusion. The magnetic field model is applied to the August 4 flare. It is shown how the plasma heating in the annihilation region balanced by thermal conduction leads to a plasma temperature of about 20 million deg K.

  4. The coalescence instability in solar flares

    NASA Astrophysics Data System (ADS)

    Tajima, T.; Brunel, F.; Sakai, J.-I.; Vlahos, L.; Kundu, M. R.

    The nonlinear coalescence instability of current carrying solar loops can explain many of the characteristics of the solar flares such as their impulsive nature, heating and high energy particle acceleration, amplitude oscillations of electromagnetic and emission as well as the characteristics of two-dimensional microwave images obtained during a flare. The plasma compressibility leads to the explosive phase of loop coalescence and its overshoot results in amplitude oscillations in temperatures by adiabatic compression and decompression. It is noted that the presence of strong electric fields and super-Alfvenic flows during the course of the instability play an important role in the production of nonthermal particles. A qualitative explanation on the physical processes taking place during the nonlinear stages of the instability is given.

  5. Carbon-poor solar flare events

    NASA Technical Reports Server (NTRS)

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

    1979-01-01

    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.

  6. Ca XV line ratios in solar flares

    SciTech Connect

    Keenan, F.P.; Berrington, K.A.; Aggarwal, K.M.; Widing, K.G.

    1988-04-01

    Recent R-matrix calculations of electron impact excitation rates for Ca XV have been used to obtain theoretical density-sensitive emission line ratios which are applicable to solar flares. Results for electron densities derived from the I(208.71 A)/I(200.95 A), I(181.90 A)/I(200.95 A), and I(215.37 A)/I(200.95 A) values for solar flares obtained by the Skylab NRL S082A slitless spectrograph are in excellant agreement. Ca XV electron densities are found to compare favorably with those determined from the line ratios of ions formed at similar electron temperatures. The results provide support for the accuracy of the adopted atomic data and for the line ratio calculation method. 27 references.

  7. Soft X-Ray Pulsations in Solar Flares

    NASA Astrophysics Data System (ADS)

    Simões, P. J. A.; Hudson, H. S.; Fletcher, L.

    2015-12-01

    The soft X-ray emissions ( hν>1.5 keV) of solar flares mainly come from the bright coronal loops at the highest temperatures normally achieved in the flare process. Their ubiquity has led to their use as a standard measure of flare occurrence and energy, although the overwhelming bulk of the total flare energy goes elsewhere. Recently Dolla et al. ( Astrophys. J. Lett. 749, L16, 2012) noted quasi-periodic pulsations (QPP) in the soft X-ray signature of the X-class flare SOL2011-02-15, as observed by the standard photometric data from the GOES ( Geostationary Operational Environmental Satellite) spacecraft. In this article we analyse the suitability of the GOES data for this type of analysis and find them to be generally valuable after September, 2010 (GOES-15). We then extend the result of Dolla et al. to a complete list of X-class flares from Cycle 24 and show that most of them (80 %) display QPPs in the impulsive phase. The pulsations show up cleanly in both channels of the GOES data, making use of time-series of irradiance differences (the digital time derivative on the 2-s sampling). We deploy different techniques to characterise the periodicity of GOES pulsations, considering the red-noise properties of the flare signals, finding a range of characteristic time scales of the QPPs for each event, but usually with no strong signature of a single period dominating in the power spectrum. The QPP may also appear on somewhat longer time scales during the later gradual phase, possibly with a greater tendency towards coherence, but the sampling noise in GOES difference data for high irradiance values (X-class flares) makes these more uncertain. We show that there is minimal phase difference between the differenced GOES energy channels, or between them and the hard X-ray variations on short time scales. During the impulsive phase, the footpoints of the newly forming flare loops may also contribute to the observed soft X-ray variations.

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

    SciTech Connect

    Mason, J. P.; Hoeksema, J. T. E-mail: JTHoeksema@sun.stanford.ed

    2010-11-01

    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.

  9. Solar flare effects on the zodiacal light

    NASA Technical Reports Server (NTRS)

    Misconi, N. Y.

    1976-01-01

    Results are reported for an observational and theoretical study of possible solar-flare effects on the zodiacal light. A seven-year search for flare-induced brightness variations in the light is described which discovered no significant changes in either the level of brightness from night to night or the shape of the main zodiacal-light cone at elongations greater than 25 deg from the sun. Several possible dynamical effects of solar flares on the zodiacal dust cloud are investigated theoretically, including increased ion drag from a passing shock wave, possible rotational bursting of dust particles as a result of ion impacts, and fluorescence of the dust particles. It is found that the kinetic energy carried by shock-front ions is not sufficient to cause the dust to fluoresce, that increased ion drag may be significant only at heliocentric distances less than 0.1 AU, and that particles larger than 10 microns cannot attain bursting speeds at the appropriate distances. The question is considered of whether changes in the brightness of the polarized component as a result of variations in electron number density can be observed from earth or the Helios solar probe.

  10. Explosive plasma flows in a solar flare

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

    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.

  11. Size Distributions of Solar Flares and Solar Energetic Particle Events

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

    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.

  12. SIZE DISTRIBUTIONS OF SOLAR FLARES AND SOLAR ENERGETIC PARTICLE EVENTS

    SciTech Connect

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

    2012-09-10

    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 ({>=}1000 km s{sup -1}) 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 A fluxes of SXR flares associated with (a) >10 MeV SEP events (with peak fluxes {>=}1 pr cm{sup -2} s{sup -1} sr{sup -1}) 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 A 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.

  13. Solar flares, proton showers, and the space shuttle

    SciTech Connect

    Rust, D.M.

    1982-05-28

    The chief unpredictable hazard for astronauts is energetic proton radiation from solar flares. In some orbits, there is no reasonable level of shielding material that will protect shuttle occupants from potentially lethal doses of radiation. The effects of a solar flare that occurred during the first flight of the Columbia are discussed and current flare research reviewed. The emphasis is on progress made during the recent international Solar Maximum Year toward understanding the origins of proton showers. 46 references, 9 figures.

  14. Acceleration of electrons during the flash phase of solar flares

    NASA Technical Reports Server (NTRS)

    Kane, S. R.

    1974-01-01

    The characteristics of the electron acceleration process operating during the flash phase of solar flares are deduced from the high time resolution observations of impulsive solar X rays greater than or equal to 10 keV and other flash phase emissions from small solar flares, and the implications of these findings are discussed.

  15. Acceleration of runaway electrons in solar flares

    NASA Astrophysics Data System (ADS)

    Moghaddam-Taaheri, E.; Goertz, C. K.

    1990-03-01

    The dc electric field acceleration of electrons out of a thermal plasma and the evolution of the runaway tail are studied numerically, using a relativistic quasi-linear code based on the Ritz-Galerkin method and finite elements. A small field-aligned electric field is turned on at a certain time. The resulting distribution function from the runaway process is used to calculate the synchrotron emission during the evolution of the runaway tail. It is found that, during the runaway tail formation, which lasts a few tens of seconds for typical solar flare conditions, the synchrotron emission level is low, almost ot the same order as the emission from the thermal plasma, at the high-frequency end of the spectrum. However, the emission is enhanced explosively in a few microseconds by several orders of magnitude at the time the runaway tail stops growing along the magnetic field and tends toward isotropy due to the pitch-angle scattering of the fast particles. Results indicate that, in order to account for the observed synchrotron emission spectrum of a typical solar flare, the electric field acceleration phase must be accompanied or preceded by a heating phase which yields an enhanced electron temperature of about 2-15 keV in the flare region if the electric field is 0.1-0.2 times the Dreicer field and cyclotron-to-plasma frequency ratios are of order 1-2.

  16. BATSE flare observations in Solar Cycle 22

    NASA Technical Reports Server (NTRS)

    Schwartz, R. A.; Dennis, B. R.; Fishman, G. J.; Meegan, C. A.; Wilson, R. B.; Paciesas, W. S.

    1992-01-01

    The Hard X-Ray Burst Spectrometer (HXRBS) group at GSFC has developed and is maintaining a quick-look analysis system for solar flare hard x-ray data from the Burst and Transient Source Experiment (BATSE) on the recently launched Compton Gamma-Ray Observatory (GRO). The instrument consists, in part, of 8 large planar detectors, each 2025 sq cm, placed on the corners of the GRO spacecraft with the orientation of the faces being those of a regular octahedron. Although optimized for the detection of gamma-ray bursts, these detectors are far more sensitive than any previous spacecraft-borne hard x-ray flare instrumentation both for the detection of small microflares and the resolution of fine temporal structures. The data in this BATSE solar data base are from the discriminator large area (DISCLA) rates. From each of eight detectors there are hard x-ray data in four energy channels, 25-50, 50-100, 100-300, and greater than 300 keV with a time resolution of 1.024 seconds. These data are suitable for temporal correlation with data at other wavelengths, and they provide a first look into the BATSE and other GRO instrument flare data sets. The BATSE and other GRO principle investigator groups should be contacted for the availability of data sets at higher time or spectral resolution or at higher energies.

  17. A slingshot model for solar flares

    NASA Technical Reports Server (NTRS)

    Benford, Gregory

    1991-01-01

    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.

  18. Influence of solar flares on the X-ray corona

    NASA Technical Reports Server (NTRS)

    Rust, D. M.; Batchelor, D. A.

    1986-01-01

    Sequences of X-ray images of solar flares, obtained with the Hard X-ray Imaging Spectrometer on the SMM spacecraft, reveal many dynamical phenomena. Movies of 20 flares recorded with 6-sec time resolution were examined. A preliminary analysis of the events as a group are presented, and some new aspects of the well-studied May 21, 1980 flare and a November 6, 1980 flare are discussed.

  19. Isotopic overabundances and the energetic particle model of solar flares

    NASA Technical Reports Server (NTRS)

    Perez-Enriquez, R.; Bravo, S.

    1985-01-01

    According to the energetic particle model of solar flares particles are efficiently accelerated in the magnetic field loop of an active region (AR) by hydromagnetic turbulence. It is demonstrated that the isotopic overabundances observed in some flares are not a consequence of the flare itself but are characteristic of the plasma in the AR. Only when a flare releases the plasma into the interplanetary space it is possible to observe this anomalous composition at spacecraft locations.

  20. Large scale solar magnetic fields at the site of flares, the greatness of flares, and solar-terrestrial disturbances

    NASA Technical Reports Server (NTRS)

    Dodson, H. W.; Hedeman, E. R.; Roelof, E. C.

    1982-01-01

    Evidence is presented for an intrinsically solar effect which may dominate such solar-terrestrial correlations as that reported by Chertkov (1976), where large H-alpha flares during 1967-1972 in solar active regions with overlying fields on a 100,000 km scale and predominantly north-to-south orientation were more efficient in the production of geomagnetic disturbances than comparable flares in regions whose fields at the flare sites were directed south-to-north. In addition to being responsible for geomagnetic disturbance enhancements, this purely solar effect may cause solar wind velocity and solar flare proton flux enhancements. If the effect can be generalized to other portions of the solar cycle, it could improve present understanding of the flare mechanism and therefore prove useful in the prediction of solar-terrestrial disturbances.

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

    NASA Astrophysics Data System (ADS)

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

    1995-03-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

    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.

  3. The flares of August 1972. [solar flare characteristics and spectra

    NASA Technical Reports Server (NTRS)

    Zirin, H.; Tanaka, K.

    1973-01-01

    Observations of the August, 1972 flares at Big Bear and Tel Aviv, involving monochromatic movies, magnetograms, and spectra, are analyzed. The region (McMath 11976) showed inverted polarity from its inception on July 11; the great activity was due to extremely high shear and gradients in the magnetic field, as well as a constant invasion of one polarity into the opposite; observations in lambda 3835 show remarkable fast flashes in the impulsive flare of 18:38 UT on Aug. 2 with lifetimes of 5 sec, which may be due to dumping of particles in the lower chromosphere. Flare loops show evolutionary increases of their tilts to the neutral line in the flares of Aug. 4 and 7. Spectroscopic observations show red asymmetry and red shift of the H alpha emission in the flash phase of the Aug. 7 flare, as well as substantial velocity shear in the photosphere during the flare, somewhat like earthquake movement along a fault. Finally the total H alpha emission of the Aug. 7 flare could be measured accurately as about 2.5 x 10 to the 30th power erg, considerably less than coarser previous estimates for great flares.

  4. Adiabatic heating in impulsive solar flares

    NASA Technical Reports Server (NTRS)

    Maetzler, C.; Bai, T.; Crannell, C. J.; Frost, K. J.

    1977-01-01

    The dynamic X-ray spectra of two simple, impulsive solar flares are examined together with H alpha, microwave and meter wave radio observations. X-ray spectra of both events were characteristic of thermal bremsstrahlung from single temperature plasmas. The symmetry between rise and fall was found to hold for the temperature and emission measure. The relationship between temperature and emission measure was that of an adiabatic compression followed by adiabatic expansion; the adiabatic index of 5/3 indicated that the electron distribution remained isotropic. Observations in H alpha provided further evidence for compressive energy transfer.

  5. Spectral Hardening in Solar Flares and Evolution of Proton Events resulting CME acceleration

    NASA Astrophysics Data System (ADS)

    Tripathi, Sharad Chandra; Gwal, Ashok Kumar; Jain, Rajmal; Awasthi, Arun Kumar; Khan, Parvaiz A.; Purohit, Pramod K.

    2012-07-01

    We probe the spectral hardening of solar flares emission in view of associated solar proton events (SEPs) at earth and coronal mass ejection (CME) acceleration as a consequence. In this investigation we undertake 60 SEPs of the Solar Cycle 23-24 alongwith associated Solar Flares and CMEs. We employ the X-ray emission in Solar flares observed by Reuven Ramaty Higly Energy Solar Spectroscopic Imager (RHESSI) and Solar X-Ray Spectrometer (SOXS) in order to estimate flare plasma parameters. Further, we employ the observations from Geostationary Operational Environmental Satellites (GOES) and Large Angle and Spectrometric Coronagraph (LASCO), for SEPs and CMEs parameter estimation respectively. We report a good association of soft-hard-harder (SHH) spectral behavior with occurrence of Solar Proton Events. In addition, we have found a good correlation (R=0.71) in SEPs spectral hardening and CME velocity. We conclude that the Protons as well as CMEs gets accelerated at the Flare site and travel all the way in interplanetary space and then by re-acceleration in interplanetary space CMEs produce Geomagnetic Storms in geospace. This seems to be a statistically significant mechanism of the SEPs and initial CME acceleration in addition to the standard scenario of SEP acceleration at the shock front of CMEs.

  6. Ionic charge distributions of energetic particles from solar flares

    NASA Technical Reports Server (NTRS)

    Mullan, D. J.; Waldron, W. L.

    1986-01-01

    The effects which solar flare X-rays have on the charge states of solar cosmic rays is determined quantitatively. Rather than to characterize the charge distribution by temperature alone, it is proposed that the X-ray flux at the acceleration site also is used. The effects of flare X-rays are modeled mathematically.

  7. SECONDARY FLARE RIBBONS OBSERVED BY THE SOLAR DYNAMICS OBSERVATORY

    SciTech Connect

    Zhang, Jun; Li, Ting; Yang, Shuhong E-mail: liting@nao.cas.cn

    2014-02-20

    Using the observations from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, we statistically investigate the flare ribbons (FRs) of 19 X-class flares of the 24th solar cycle from 2010 June to 2013 August. Of these 19 flares, the source regions of 16 can be observed by AIA and the FRs of each flare are well detected, and 11 of the 16 display multiple ribbons. Based on the ribbon brightness and the relationship between the ribbons and post-flare loops, we divide the multiple ribbons into two types: normal FRs, which are connected by post-flare loops and have been extensively investigated, and secondary flare ribbons (SFRs), which are weaker than the FRs, not connected by post-flare loops, and always have a short lifetime. Of the 11 SFRs, 10 appear simultaneously with the FRs, and none of them have post-flare loops. The last one, on the other hand, appears 80 minutes later than the FR, lasts almost two hours, and also has no post-flare loops detected. We suggest that the magnetic reconnection associated with this SFR is triggered by the blast wave that results from the main flare. These observations imply that in some flare processes, more than two sets of magnetic loops or more than twice the number of magnetic reconnections are involved.

  8. PRODUCTIVITY OF SOLAR FLARES AND MAGNETIC HELICITY INJECTION IN ACTIVE REGIONS

    SciTech Connect

    Park, Sung-hong; Wang Haimin; Chae, Jongchul

    2010-07-20

    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.

  9. Ultrarelativistic electrons and solar flare gamma-radiation

    NASA Technical Reports Server (NTRS)

    Semukhin, P. E.; Kovaltsov, G. A.

    1985-01-01

    Ten solar flares with gamma radiation in excess of 10 MeV were observed. Almost all took place within a heliolatitude greater than 60 deg, close to the solar limb, an indication of the essential anisotropy of high-energy gamma radiation. This high-energy solar flare gamma radiation can be explained by the specific features of the bremsstrahlung of ultrarelativistic electrons trapped within the magnetic arc of the solar atmosphere, even if the acceleration of the electrons is anisotropic.

  10. High-resolution X-ray spectra of solar flares

    NASA Astrophysics Data System (ADS)

    Doschek, G. A.

    2006-01-01

    I discuss high-resolution solar flare soft X-ray spectra and also comment on some recent results from extreme ultraviolet (EUV) spectroscopy. Spectra of solar flares at these wavelengths have been recorded since the late 1960s, beginning primarily with the NASA Orbiting Solar Observatory (OSO) series of spacecraft. Knowledge of EUV flare spectra took a quantum leap with the NASA Skylab Apollo Telescope Mount spectrographs in the early 1970s. Knowledge of the X-ray spectrum took a similar leap in the 1980s with the US Department of Defense P78-1 spacecraft, the NASA Solar Maximum Mission spacecraft (SMM), and the Japanese ISAS Hinotori spacecraft. Investigations of flare X-ray spectra continued with the Bragg Crystal Spectrometer (BCS) experiment on the Japanese Yohkoh mission. EUV solar flare spectroscopy has been extended with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer and the Coronal Diagnostics Spectrometer (CDS) on the ESA Solar and Heliospheric Observatory (SOHO) spacecraft. Recently, more Bragg crystal spectra have become available from experiments such as the RESIK spectrometers on the Russian Coronas-F spacecraft. In addition to the above missions, significant earlier contributions were made with instrumentation on a number of other spacecraft, e.g., the Soviet Intercosmos X-ray spectrometers. Our knowledge of the physical conditions in solar flares has been greatly expanded from analyses of X-ray and EUV flare spectra. I discuss the general characteristics of the flare emission line and continuum spectra, and the physical processes that produce them. I summarize what we have learned about solar flares from the spectra, and highlight a few problems and prospects for future solar flare research.

  11. Solar Flare Super-Events: When they Can Occur and the Energy Limits of their Realization

    NASA Astrophysics Data System (ADS)

    Ishkov, Vitaly N.

    2015-03-01

    For the successful development of terrestrial civilization it is necessary to estimate the space factors, including phenomena on Sun, which can ruin it or cause such catastrophic loss, that the restoration to the initial level can take unacceptably long time. Super-powerful solar flares are the only such phenomena. Therefore an attempt is undertaken to estimate the possibility of such super-event occurrence at this stage of our star evolution. Since solar flare events are the consequence of the newly emerging magnetic fluxes interacting with the already existing magnetic fields of active regions, are investigated the observed cases which lead to the realization of such super-events. From the observations of the maximal magnetic fluxes during the period of reliable solar observations, the conclusion is made that the super- extreme solar flares cannot significantly exceed the most powerful solar flares which have already been observed. On the statistics of the reliable solar cycles the sunspot groups, in which occurred the most powerful solar super-events (August- September 1859 - solar cycle 10; June 1991 - SC 22; October-November 2003 - SC 23) appeared in the periods of the solar magnetic field reorganization between the epochs of "increased" and "lowered" solar activity.

  12. FINE STRUCTURES AND OVERLYING LOOPS OF CONFINED SOLAR FLARES

    SciTech Connect

    Yang, Shuhong; Zhang, Jun; Xiang, Yongyuan

    2014-10-01

    Using the Hα observations from the New Vacuum Solar Telescope at the Fuxian Solar Observatory, we focus on the fine structures of three confined flares and the issue why all the three flares are confined instead of eruptive. All the three confined flares take place successively at the same location and have similar morphologies, so can be termed homologous confined flares. In the simultaneous images obtained by the Solar Dynamics Observatory, many large-scale coronal loops above the confined flares are clearly observed in multi-wavelengths. At the pre-flare stage, two dipoles emerge near the negative sunspot, and the dipolar patches are connected by small loops appearing as arch-shaped Hα fibrils. There exists a reconnection between the small loops, and thus the Hα fibrils change their configuration. The reconnection also occurs between a set of emerging Hα fibrils and a set of pre-existing large loops, which are rooted in the negative sunspot, a nearby positive patch, and some remote positive faculae, forming a typical three-legged structure. During the flare processes, the overlying loops, some of which are tracked by activated dark materials, do not break out. These direct observations may illustrate the physical mechanism of confined flares, i.e., magnetic reconnection between the emerging loops and the pre-existing loops triggers flares and the overlying loops prevent the flares from being eruptive.

  13. The Conundrum of the Solar Pre-Flare Photospheric State.

    NASA Astrophysics Data System (ADS)

    Leka, KD; Barnes, Graham; Wagner, Eric

    2015-08-01

    Knowledge of the state of the solar photospheric magnetic field at a single instant in time does not appear sufficient to predict the size and timing of impending solar flares. Such knowledge may provide necessary conditions, such as the free magnetic energy needed for a flare to occur. Given the necessary conditions, it is often assumed that the evolution of the field, possibly by only a small amount, may trigger the onset of a flare. We present the results of a study using time series of photospheric vector field data from the Helioseismic and Magnetic Imager (HMI) on NASA's Solar Dynamics Observatory (SDO) to quantitatively parameterize both the state and evolution of solar active regions - their complexity, magnetic topology and energy - as related to solar flare events. We examine both extensive and intensive parameters and their temporal behavior, in the context of both large and small flaring episodes. Statistical tests based on nonparametric Discriminant Analysis are used to compare pre-flare epochs to a control group of flare-quiet epochs and active regions. Results regarding the type of photospheric signature examined and the efficacy of using the present state vs. temporal evolution to predict solar flares is quantified by standard skill scores.This work is made possible by contracts NASA NNH12CG10C and NOAA/SBIR WC-133R-13-CN-0079.

  14. Flare heating and ionization of the low solar chromosphere. II - Observations of five solar flares

    NASA Technical Reports Server (NTRS)

    Metcalf, Thomas R.; Canfield, Richard C.; Saba, Julia L. R.

    1990-01-01

    Two neutral Mg spectral lines formed in the temperature-minimum region and the low chromosphere, at 4571 and 5173 A, are used to quantify the changes in the atmospheric structure as a function of time during five solar flares. Eight proposed flare heating and ionization mechanisms and predictions of the effects of each on the temperature minimum region are discussed. Two Mg spectral observations made at the National Solar Observatory (Sacramento Peak), along with observations of hard and soft X-rays from the SMM and GOES satellites, are compared to the predictions of the eight proposed mechanisms. The initial effects in all five flares are consistent with backwarming by enhanced Balmer- and Paschen-continuum radiation originating in the upper chromosphere. Extended heating observed in two of the flares is most likely due to UV irradiation. In all cases heating by the dissipation of nonreversed electric currents, collisions with an electron or proton beam, irradiation by soft X-rays, and dissipation of Alfven waves are eliminated.

  15. Energetics of Three Solar Flares Observed by RHESSI

    NASA Technical Reports Server (NTRS)

    Holman, G. D.; Dennis, B. R.; Sui, Linhui

    2004-01-01

    We compare the energy content of the thermal plasma and suprathermal electrons in three solar flares observed by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). Fits of computed isothermal and thick-target bremsstrahlung spectra to RHESSI X-ray spectra are used to deduce the instantaneous energy content of the X-ray-emitting plasma and the accumulated energy in suprathermal electrons throughout the three flares. We minimize the energy in the suprathermal electrons by assuming that the electron distributions have a low-energy cutoff that is no lower than the highest cutoff energy that provides a good fit to the X-ray spectra. The energetics of the 2002 April 15 M1 flare and the 2002 April 21 X2 flare are computed and compared with results for the 2002 July 23 X5 flare. We find that for all three. flares the energy in nonthermal electrons is comparable to the energy contained in the thermal plasma.

  16. Adiabatic heating in impulsive solar flares

    NASA Technical Reports Server (NTRS)

    Maetzler, C.; Bai, T.; Crannell, C. J.; Frost, K. J.

    1978-01-01

    A study is made of adiabatic heating in two impulsive solar flares on the basis of dynamic X-ray spectra in the 28-254 keV range, H-alpha, microwave, and meter-wave radio observations. It is found that the X-ray spectra of the events are like those of thermal bremsstrahlung from single-temperature plasmas in the 10-60 keV range if photospheric albedo is taken into account. The temperature-emission correlation indicates adiabatic compression followed by adiabatic expansion and that the electron distribution remains isotropic. H-alpha data suggest compressive energy transfer. The projected areas and volumes of the flares are estimated assuming that X-ray and microwave emissions are produced in a single thermal plasma. Electron densities of about 10 to the 9th/cu cm are found for homogeneous, spherically symmetric sources. It is noted that the strong self-absorption of hot-plasma gyrosynchrotron radiation reveals low magnetic field strengths.

  17. Testing Solar Flare Models with BATSE

    NASA Technical Reports Server (NTRS)

    Zarro, Dominic M.

    1995-01-01

    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.

  18. Development of Daily Solar Maximum Flare Flux Forecast Models for Strong Flares

    NASA Astrophysics Data System (ADS)

    Shin, Seulki; Chu, Hyoungseok

    2015-08-01

    We have developed a set of daily solar maximum flare flux forecast models for strong flares using Multiple Linear Regression (MLR) and Artificial Neural Network (ANN) methods. We consider input parameters as solar activity data from January 1996 to December 2013 such as sunspot area, X-ray maximum flare flux and weighted total flux of the previous day, and mean flare rates of McIntosh sunspot group (Zpc) and Mount Wilson magnetic classification. For a training data set, we use the same number of 61 events for each C-, M-, and X-class from Jan. 1996 to Dec. 2004, while other previous models use all flares. For a testing data set, we use all flares from Jan. 2005 to Nov. 2013. The statistical parameters from contingency tables show that the ANN models are better for maximum flare flux forecasting than the MLR models. A comparison between our maximum flare flux models and the previous ones based on Heidke Skill Score (HSS) shows that our all models for X-class flare are much better than the other models. According to the Hitting Fraction (HF), which is defined as a fraction of events satisfying that the absolute differences of predicted and observed flare flux in logarithm scale are less than equal to 0.5, our models successfully forecast the maximum flare flux of about two-third events for strong flares. Since all input parameters for our models are easily available, the models can be operated steadily and automatically on daily basis for space weather service.

  19. Ultraheavy element enrichment in impulsive solar flares

    SciTech Connect

    Eichler, David

    2014-10-10

    Particle acceleration by cascading Alfvén wave turbulence was suggested as being responsible for energetic particle populations in {sup 3}He-rich solar flares. In particular, it was noted that the damping of the turbulence by the tail of the particle distribution in rigidity naturally leads to the dramatic enhancement of a pre-accelerated species—as {sup 3}He is posited to be—and superheavy elements. The subsequent detection of large enrichment of ultraheavies, relative to iron, has apparently confirmed this prediction, lending support to the original idea. It is shown here that this picture could be somewhat sharpened by progress in understanding the three-dimensional geometrical details of cascading Alfvén turbulence. The mechanism may be relevant in other astrophysical environments where the source of turbulence is nonmagnetic, such as clusters of galaxies.

  20. Millimeter radio evidence for containment mechanisms in solar flares

    NASA Technical Reports Server (NTRS)

    Mayfield, E. B.; White, K. P., III; Shimabukuro, F. I.

    1974-01-01

    Recent theories of solar flares are reviewed with emphasis on the aspects of pre-flare heating. The heating evident at 3.3-mm wavelength is analyzed in the form of daily maps of the solar disk and synoptic maps compiled from the daily maps. It is found that isotherms defining antenna temperature enhancements of 340 K correspond in shape and location to facular areas reported by Waldmeier. Maximum enhancements occur over sunspots or near neutral lines of the longitudinal magnetic fields which indicates heating associated with chromospheric currents. These enhancements are correlated with flare importance number and are observed to increase during several days preceding flaring. This evidence for a containment mechanism in the chromosphere is collated with current theories of solar flares.

  1. IRIS Observations of the Solar Atmospheric Response to Flares

    NASA Astrophysics Data System (ADS)

    Wuelser, Jean-Pierre

    2014-06-01

    The Interface Region Imaging Spectrograph (IRIS) is a NASA Small EXplorer mission to observe the sun. It observes high resolution images and spectra in the chromospheric C II and Mg II lines, the transition region Si IV and O IV lines, and the coronal XXI line.Since its launch on June 27 2013, IRIS has observed several solar flares. The high spatial resolution of IRIS, and its range of spectral lines allow a detailed analysis of the flare energy deposition and flare dynamics in the lower solar atmosphere, especially in conjunction with complementary observations from SDO, Hinode, and RHESSI. We present initial IRIS observations of the solar flare response in a broader observational context and discuss how IRIS can provide new insight into the flare process.

  2. White-light continuum in solar and stellar flares

    NASA Astrophysics Data System (ADS)

    Kowalski, Adam Francis

    2015-08-01

    During solar and stellar flares, the majority of the radiated energy from the lower atmosphere escapes as white-light continuum emission in the near-ultraviolet and optical wavelength regimes. The time-dependent spectral energy distribution of white-light emission is important for assessing biomarkers in planetary atmospheres around M dwarfs and for constraining models of heating at the highest densities in flares. I will discuss the observational characteristics of white-light emission from recent spectroscopic observations of M dwarf flares, and I will describe a new interpretation of these spectra as revealed in a radiative-hydrodynamic model of an extreme chromospheric condensation. I will give an overview of the properties of white-light emission in solar flares and the new information obtained for the brightest solar flare kernels observed with IRIS.

  3. Particle acceleration by a solar flare termination shock.

    PubMed

    Chen, Bin; Bastian, Timothy S; Shen, Chengcai; Gary, Dale E; Krucker, Säm; Glesener, Lindsay

    2015-12-01

    Solar flares--the most powerful explosions in the solar system--are also efficient particle accelerators, capable of energizing a large number of charged particles to relativistic speeds. A termination shock is often invoked in the standard model of solar flares as a possible driver for particle acceleration, yet its existence and role have remained controversial. We present observations of a solar flare termination shock and trace its morphology and dynamics using high-cadence radio imaging spectroscopy. We show that a disruption of the shock coincides with an abrupt reduction of the energetic electron population. The observed properties of the shock are well reproduced by simulations. These results strongly suggest that a termination shock is responsible, at least in part, for accelerating energetic electrons in solar flares. PMID:26785486

  4. Solar Flare Superevents: When they Occur and the Energy Limits of their Realization

    NASA Astrophysics Data System (ADS)

    Ishkov, V. N.

    2014-10-01

    Statistics reliable series of relative sunspot numbers (timeline in 164 - 14 solar cycles - SC) to give a consistent picture of the solar cyclicity. This pattern provides for regular changes of magnetic field generation in the solar convection zone in the transition from the epoch of the "higher" solar activity (SC 7-11 and 18-22) to the epoch of the "lower" solar activity (SC 12-16) and vice versa - from the epoch of the "lower" to "higher" solar activity. Before each such epoch occurs a change of the magnetic field generation regime in the solar convective zone, which occurs during approximate one physical 22-year cycle of solar activity. The reconstruction of the sunspot-forming regime, apparently, could be observed in the SC 10-11 and SC 22-23, when the magnetic field of the solar convection zone having been converted to the "lower" solar activity. In SC 17-18 was a similar restructuring of magnetic fields to the era of the "higher" solar activity. On this statistics the most powerful solar flare super events (1859, VIII-IX - SC 10; 1991, VI - SC 22; 2003, X - XI - SC 23) were observed precisely in these periods of magnetic field reconstruction. They all were occurrence in the anomalously large solar sunspot groups with the areas of ? 2300 mvh. Since solar flare events are the consequence of interaction of new magnetic flux with the already existing magnetic field of active region, are examined the cases of the observations, which lead to the solar flare superevents. The attempt to estimate maximally possible amounts of intensity and power of solar flare super-events is made.

  5. Stochastic Particle Acceleration in Impulsive Solar Flares

    NASA Technical Reports Server (NTRS)

    Miller, James A.

    2001-01-01

    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.

  6. Sun Releases X-class Solar Flare - Duration: 22 seconds.

    NASA Video Gallery

    This movie shows the July 6, 2012 X1.1 flare in the 171 Angstrom wavelength as captured by NASA’s Solar Dynamics Observatory (SDO). AR1515 was the source for this flare. AR1515 has been active ...

  7. A common stochastic process in solar and stellar flares

    NASA Astrophysics Data System (ADS)

    Li, Chuan; Fang, Cheng

    2015-08-01

    Solar flares, with energies of 1027 - 1032 ergs, are believed to be powered by sudden release of magnetic energy stored in the corona. Stellar flares, observationally 102 - 106 more intense than solar flares, are generally assumed to release energy through the same underlying mechanism: magnetic reconnection. It is thus expected similar statistical properties between two groups of flares. The selected candidates are 23400 solar flares observed over one solar cycle by GOES spacecraft and 3140 stellar flares from Kepler data adapted from the catalog of Balona (MNRAS, 447, 2714, 2015). We examine the flare frequency as a function of duration, energy, and waiting time. The distributions of flare duration and energy can be well understood in the context of the avalanche model of a self-organized criticality (SOC) system (Aschwanden, A&A, 539, 2, 2012). The waiting time distribution of the SOC system can be explained by a non-stationary Poisson process (Li et al. ApJ Letters, 792, 26, 2014).

  8. Capabilities of GRO/OSSE for observing solar flares

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

    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.

  9. Solar Flare Probability depending on Sunspot Characteristics and Their Changes

    NASA Astrophysics Data System (ADS)

    Lee, J.; Hong, S.; Kim, J.; Kim, Y.; Lee, J.; Moon, Y.; Lee, D.

    2012-12-01

    Solar flare prediction has been at the core of space weather research and a number of different approaches have been developed since THEO (McIntosh, 1990) system was introduced. However, many of space weather operation centers, i.e. International Space Environment Service's Regional Warning Centers, still rely on traditional flare prediction methods like THEO. THEO uses the McIntosh classification as the knowledge base for flare prediction and also, rules of thumb are incorporated by a human forecaster, including spot growth, magnetic topology inferred from sunspot structure and previous flare activity. The method is apparently somewhat subjective, because the forecast decision depends on the expertise of an operator and it has not been evaluated statistically. In this study, we have investigated solar flare probability depending on several sunspot characteristics (McIntosh classification, Mt. Wilson magnetic classification, sunspot area and previous flare activity) and their changes for the past three days. For this, we used NOAA sunspot and flare catalog from August 1996 to February 2011. A new index, WFP(Weighted Flare Probability), which includes solar flare strength and its historical probability, is introduced to quantify the effective contribution of flare activity. We found several interesting results as follows. First, WFP index increases not only when the sunspot magnetic complexity increases but also when the magnetic complexity decreases with almost the same proportion. Second, the index also increases for both cases of sunspot area increase and decrease. This result might be the evidence that the change (flux emergence or flux cancelation) of magnetic flux may trigger a flare since sunspot area can be a good proxy of magnetic flux. Third, active regions having significant flare activity history are much more active than those without. We are applying the multi-dimensional regression method to these data and automating the process of THEO. We have a plan to show how this new method works in practice by deploying at the Korean Space Weather Center.

  10. Development of Daily Maximum Flare-Flux Forecast Models for Strong Solar Flares

    NASA Astrophysics Data System (ADS)

    Shin, Seulki; Lee, Jin-Yi; Moon, Yong-Jae; Chu, Hyoungseok; Park, Jongyeob

    2016-03-01

    We have developed a set of daily maximum flare-flux forecast models for strong flares (M- and X-class) using multiple linear regression (MLR) and artificial neural network (ANN) methods. Our input parameters are solar-activity data from January 1996 to December 2013 such as sunspot area, X-ray maximum, and weighted total flare flux of the previous day, as well as mean flare rates of McIntosh sunspot group (Zpc) and Mount Wilson magnetic classifications. For a training dataset, we used 61 events each of C-, M-, and X-class from January 1996 to December 2004. For a testing dataset, we used all events from January 2005 to November 2013. A comparison between our maximum flare-flux models and NOAA model based on true skill statistics (TSS) shows that the MLR model for X-class and the average of all flares ( M{+}X-class) are much better than the NOAA model. According to the hitting fraction (HF), which is defined as a fraction of events satisfying the condition that the absolute differences of predicted and observed flare flux on a logarithm scale are smaller than or equal to 0.5, our models successfully forecast the maximum flare flux of about two-thirds of the events for strong flares. Since all input parameters for our models are easily available, the models can be operated steadily and automatically on a daily basis for space-weather services.

  11. Nuclear processes and neutrino production in solar flares

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

    The determination of flare neutrino flux is approached from the standpoint of recent observations and theoretical results on the nuclear processes in solar flares. Attention is given to the energy spectra and total numbers of accelerated particles in flares, as well as their resulting production of beta(+)-emitting radionuclei and pions; these should be the primary sources of neutrinos. The observed 0.511 MeV line flux for the June 21, 1980 flare is compared with the expected from the number and spectrum of accelerated particles.

  12. Solar flare count periodicities in different X-ray flare classes

    NASA Astrophysics Data System (ADS)

    Gao, Peng-Xin; Xu, Jing-Chen

    2016-04-01

    Using the Morlet wavelet transform and the Hilbert-Huang transform (HHT), we investigate the periodic behaviours of C, M and X-class flare counts, respectively, recorded by the Geostationary Operational Environmental Satellites (GOES) from 1983 May to 2014 December, which cover the two complete solar cycles (SCs) 22 and 23 as well as the part of declining phase of SC 21 and rise and maximum phases of SC 24. Analyses show that the periodic behaviours of various class flare counts are different. (1) Not all periods of various class flare counts appear dominant during the cycle maxima. For C-class flares, during SC 23, periods appear dominant during the maximum phase, however, compared to those during SC 23, there are more periods during the declining phase of SC 22; for M-class flares, during SCs 22 and 23, periods appear dominant during the cycle maxima; for X-class flares, during SC 22, almost all periods appear during the maximum phase; however, during SC 23, there are more periods during the declining phase compared to those during SC 22. (2) For C-class flares, the appearance of periods do not follow the amplitude of C-class flare cycles; while, for M and X-class flares, the appearance of periods follows the amplitude of the investigated corresponding class flare cycles. (3) From the overall trends, the 10 yr and longer time-scale trends of the monthly numbers of M and X-class flares, we can infer that the maximum values of the monthly M and X-class flare numbers would increase during SC 25.

  13. Constraining Solar Flare Differential Emission Measures with EVE and RHESSI

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    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.

  14. CONSTRAINING SOLAR FLARE DIFFERENTIAL EMISSION MEASURES WITH EVE AND RHESSI

    SciTech Connect

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

    2014-06-20

    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 ≲2 to ≳50 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 ≳10 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.

  15. TOWARD RELIABLE BENCHMARKING OF SOLAR FLARE FORECASTING METHODS

    SciTech Connect

    Bloomfield, D. Shaun; Higgins, Paul A.; Gallagher, Peter T.; McAteer, R. T. James

    2012-03-10

    Solar flares occur in complex sunspot groups, but it remains unclear how the probability of producing a flare of a given magnitude relates to the characteristics of the sunspot group. Here, we use Geostationary Operational Environmental Satellite X-ray flares and McIntosh group classifications from solar cycles 21 and 22 to calculate average flare rates for each McIntosh class and use these to determine Poisson probabilities for different flare magnitudes. Forecast verification measures are studied to find optimum thresholds to convert Poisson flare probabilities into yes/no predictions of cycle 23 flares. A case is presented to adopt the true skill statistic (TSS) as a standard for forecast comparison over the commonly used Heidke skill score (HSS). In predicting flares over 24 hr, the maximum values of TSS achieved are 0.44 (C-class), 0.53 (M-class), 0.74 (X-class), 0.54 ({>=}M1.0), and 0.46 ({>=}C1.0). The maximum values of HSS are 0.38 (C-class), 0.27 (M-class), 0.14 (X-class), 0.28 ({>=}M1.0), and 0.41 ({>=}C1.0). These show that Poisson probabilities perform comparably to some more complex prediction systems, but the overall inaccuracy highlights the problem with using average values to represent flaring rate distributions.

  16. Relation between the active region magnetic field and solar flares

    NASA Astrophysics Data System (ADS)

    Podgorny, A. I.; Podgorny, I. M.; Meshalkina, N. S.

    2013-11-01

    A weak active region (NOAA 11158) appeared on the solar disk near the eastern limb. This region increased rapidly and, having reached the magnetic flux higher than 1022 Mx, produced an X-class flare. Only weak field variations at individual points were observed during the flare. An analysis of data with a resolution of 45 s did not indicate any characteristic features in the photospheric field dynamics during the flare. When the flux became higher than 3 1022 Mx, active region NOAA 10720 produced six X-class flares. The field remained quiet during these flares. An increase in the magnetic flux above 1022 Mx is a necessary, but not sufficient, condition for the appearance of powerful flares. Simple active regions do not produce flares. A flare originates only when the field distribution in an active region is complex and lines of polarity inversion have a complex shape. Singular lines of the magnetic field can exist only above such active regions. The current sheets, in the magnetic field of which the solar flare energy is accumulated, originate in the vicinity of these lines.

  17. C3-class Solar Flare Eruption - Duration: 13 seconds.

    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...

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

    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...

  19. Energetic electrons in impulsive solar flares

    NASA Technical Reports Server (NTRS)

    Batchelor, D. A.

    1984-01-01

    A new analysis was made of a thermal flare model proposed by Brown, Melrose, and Spicer (1979) and Smith and Lilliequist (1979). They assumed the source of impulsive hard X-rays to be a plasma at a temperature of order 10 to the 8th power K, initially located at the apex of a coronal arch, and confined by ion-acoustic turbulence in a collisionless conduction front. Such a source would expand at approximately the ion-sound speed, C sub S = square root of (k T sub e/m sub i), until it filled the arch. Brown, Melrose, and Spicer and Smith and Brown (1980) argued that the source assumed in this model would not explain the simultaneous impulsive microwave emission. In contrast, the new results presented herein suggest that this model leads to the development of a quasi-Maxwellian distribution of electrons that explains both the hard X-ray and microwave emissions. This implies that the source sizes can be determined from observations of the optically-thick portions of microwave spectra and the temperatures obtained from associated hard X-ray observations. In this model, the burst emission would rise to a maximum in a time, t sub r, approximately equal to L/c sub s, where L is the half-length of the arch. New observations of these impulsive flare emissions were analyzed herein to test this prediction of the model. Observations made with the Solar Maximum Mission spacecraft and the Bern Radio Observatory are in good agreement with the model.

  20. Solar flare gamma-ray spectroscopy with CGRO-COMPTEL

    NASA Astrophysics Data System (ADS)

    Young, Christopher Alex

    2001-08-01

    The X-ray and ?-ray emission from solar flares provides important information about high-energy particles in solar flares. Energetic protons and ions interact with the solar atmosphere, giving rise to nuclear line emission at MeV energies and higher energy photons from the decay of neutral and charged pions. Electrons interact with the solar atmosphere producing a bremsstrahlung continuum. The solar flare spectrum is generally a superposition of these spectra with nuclear line emission dominating from ~1-8 MeV and the bremsstrahlung at lower and higher energies. The main goal of this thesis has been to explain a small part of a ?-ray flare observed by COMPTEL in June 1991. A difficult interval to explain in the 11 June 1991 solar flare is the Intermediate (Rank 1997) or Interphase (Murphy and Share 1999; Dunphy et al. 1999) immediately following the peak of the impulsive phase. All three analyses of this flare using COMPTEL, OSSE and EGRET data yielded a hard proton spectrum with a power law index around 2 using the 2.2 to 4.44 MeV fluence ratio. This hard of a spectrum would indicate the presence of a high- energy component above eight MeV and emission due to spallation products. However, none of the three instruments observed such a component. We discuss the standard techniques used in solar flare spectral deconvolution and introduce a new technique we use with the COMPTEL observations. This work presented the explanation that the proton spectrum is soft during this interval of the 11 June 1991 solar flare based on this new analysis of the COMPTEL observations. This means that the region of 2.223/4-7 MeV fluence space is largely unexplored for soft proton spectra. The use of this ratio must be reexamined for proton spectra with indices greater than 5 or 6. We then applied a model we developed for the transport of neutrons created from a soft proton spectrum to determine the photospheric 3He abundance during this flare. We calculated a 3He/H ratio of 8.7e-05 with a 1 a range of 1.96e-04 to 1.75e-05 for this flare using this new model. This is larger than all previous values reported. In addition, we presented an additional flare observation from COMPTEL. In response to a BACODINE cosmic gamma-ray burst alert, COMPTEL on the CGRO recorded gamma rays above 1 MeV from the C4 flare at 0221 UT 20 January 2000. This event, though at the limits of COMPTEL's sensitivity, clearly shows a nuclear line excess above the continuum. Using new spectroscopy techniques we were able to resolve individual lines. This allowed us to make a basic comparison of this event with the GRL (gamma ray line) flare distribution from SMM and also compare this flare with a well-observed large GRL flare seen by OSSE. We showed this flare is normal, i.e., it is a natural extension of the SMM distribution of flares. The analysis of this flare means there is no evidence for a lower flare size for proton acceleration. Protons even in small flares contain a large part of the accelerated particle energy.

  1. EVIDENCE FOR HOT FAST FLOW ABOVE A SOLAR FLARE ARCADE

    SciTech Connect

    Imada, S.; Aoki, K.; Hara, H.; Watanabe, T.; Harra, L. K.; Shimizu, T.

    2013-10-10

    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.

  2. Models of the Solar Atmospheric Response to Flare Heating

    NASA Technical Reports Server (NTRS)

    Allred, Joel

    2011-01-01

    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.

  3. The Carrington solar flares of 1859: consequences on life.

    PubMed

    Muller, C

    2014-09-01

    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

  4. Studying the thermal/non-thermal crossover in solar flares

    NASA Technical Reports Server (NTRS)

    Schwartz, R. A.

    1994-01-01

    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.

  5. The GPS measured SITEC caused by very intensive solar flares

    NASA Astrophysics Data System (ADS)

    Wan, W.; Yuan, H.; Liu, L.; Ning, B.

    The present work studies the sudden increment of total electron content (SITEC) on the ionosphere caused by several solar flares during the maximum solar activity years. According to the well-known Chapman theory of ionization, we first derived the relationship between the temporal variation rate of the total electron content (TEC) and the flare parameters. It is shown that the variation rate is proportional to the effective flare radiation flux, and inverse proportional to the Chapman function of the zenith angle. TEC data observed by the GPS networks located in China, Southeast Asia and Australia during several flare are used to statistically investigate relation among the observed TEC variation rate, the Chapman function of the zenith angle and the satellite observed flare radiation flux. The analyzed results show that the quantities are proportional or inverse proportional each other, as the theory predicted. The present work shows that GPS observation is a powerful tool in the investigation of solar flare effects on the ionosphere, i.e., the sudden ionospheric disturbances (SIDs). Because of its advantages on high precision, large geographical distribution good temporal resolution, GPS TEC observation may reveal quantitatively the process of ionospheric disturbances caused by solar flares. Therefore, our results are of significance in the space weather research.

  6. High-energy particles associated with solar flares

    NASA Technical Reports Server (NTRS)

    Sakurai, K.; Klimas, A. J.

    1974-01-01

    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.

  7. On reflecting boundary behind the Earth's orbit at propagation of fast particles from solar flares

    NASA Technical Reports Server (NTRS)

    Nishkovskikh, A. S.; Filippov, A. T.

    1985-01-01

    The flares of solar cosmic rays (SCR) associated with the presence of shocks in interplanetary magnetic field and with their propagation at significant heliocentric distances were always of great interest. Some events and problems concerning the peculiarities of propagation of flare CR in the interplanetary medium are considered. The distinguishing feature of such events is the presence of shock front behind the Earth's orbit having formed either directly in the process of shock generation on the Sun or at large heliocentric distances as a result of the interaction of fast and slow quasistationary recurrent solar wind (SW) streams. Based on the experimental material it is shown that the significant nonlinear disturbances in IMF behind the Earth's orbit can yield the occurrence of the additional SCR flux from shock front region as a result of the interaction of flare flux with shock and a partial reflection from it.

  8. The dark side of the Solar Flare Myth

    NASA Astrophysics Data System (ADS)

    Reames, D. V.

    Gosling [1993, 1994] reviewed the growing observational evidence that traveling interplanetary shocks, large solar energetic particle (SEP) events, and large nonrecurrent geomagnetic storms are produced by coronal mass ejections (CMEs), not by solar flares. The growing evidence for CMEs as the cause of these phenomena constituted a declaration of independence from the flare community, and certainly squelched the attitude of benign neglect that had beset interplanetary phenomena and observations. In one case it produced hostile dismay that [Jack Gosling and a few other revisionists] would [wage an assault on the last 30 years of solar-flare research] based on the [low-grade optical data that the CME people use] [Zirin, 1994]. Calmer objections were raised by Hudson, Haisch, and Strong [1995], who accept the interplanetary consequences of CMEs but suggest that [it is shortsighted to distinguish CMEs and flares.

  9. Imaging X-Ray Polarimeter for Solar Flares (IXPS)

    NASA Technical Reports Server (NTRS)

    Hosack, Michael; Black, J. Kevin; Deines-Jones, Philip; Dennis, Brian R.; Hill, Joanne E.; Jahoda, Keith; Shih, Albert Y.; Urba, Christian E.; Emslie, A. Gordon

    2011-01-01

    We describe the design of a balloon-borne Imaging X-ray Polarimeter for Solar flares (IX PS). This novel instrument, a Time Projection Chamber (TPC) for photoelectric polarimetry, will be capable of measuring polarization at the few percent level in the 20-50 keV energy range during an M- or X class flare, and will provide imaging information at the approx.10 arcsec level. The primary objective of such observations is to determine the directivity of nonthermal high-energy electrons producing solar hard X-rays, and hence to learn about the particle acceleration and energy release processes in solar flares. Secondary objectives include the separation of the thermal and nonthermal components of the flare X-ray emissions and the separation of photospheric albedo fluxes from direct emissions.

  10. Small Solar Flares: A C4 gamma-ray line flare observed by the COMPTEL CGRO

    NASA Astrophysics Data System (ADS)

    Young, C.; de Nolfo, G. A.; Ryan, J. M.

    2011-12-01

    Small flares have been identified mainly through X-ray data and have been shown to be prodigious during solar maximum periods (~1000/year during solar maximum). Current instruments capable of high-energy gamma-ray observations operate above the sensitivity threshold for observing gamma-ray emission from small flares (C-class and smaller). COMPtonTELescope (COMPTEL) on the Compton Gamma-Ray Observatory (CGRO) is not only sensitive to small C-class flares (well below that of Solar Maximum Mission (SMM)) but also registered unambiguous 2.2 MeV nuclear-line emission, suggesting the presence of an accelerated ion population. In response to a BACODINE cosmic gamma-ray burst alert, COMPTEL on the CGRO recorded gamma rays above 1 MeV from the C4 flare at 0221 UT 20 January 2000. This event, though at the limits of COMPTEL's sensitivity, clearly shows a nuclear line excess above the continuum. Using new spectroscopy techniques we were able to resolve individual lines. We compare this C-class event with the gamma-ray line (GRL) flare distribution SMM and from Ramaty High Energy Spectroscopic Imager (RHESSI) as well as with the well-observed large "standard" GRL flare observed by Oriented Scintillation Spectrometer Experiment (OSSE) aboard CGRO.

  11. Statistical characterization of Strong and Mid Solar Flares and Sun EUV rate monitoring with GNSS

    NASA Astrophysics Data System (ADS)

    Monte-Moreno, Enric; Hernandez-Pajares, Manuel; Garcia-Rigo, Alberto; Beniguel, Yannick; Orus-Perez, Raul; Prieto-Cerdeira, Roberto; Schlueter, Stefan

    2015-04-01

    The global network of permanent Global Navigation Satellite Systems (GNSS) receivers has become an useful and affordable way of monitoring the Solar EUV flux rate, especially -for the time being- in the context of Major and Mid geoeffective intensity Solar Flares (M. Hernandez-Pajares et al., Space Weather, doi:10.1029/2012SW000826, 2012). In fact the maturity of this technique (GNSS Solar FLAre Indicator, GSFLAI) has allowed to incorporate it in operational real-time (RT) conditions, thanks to the availability of global GNSS datastreams from the RT International GNSS Network (M. Caissy et al, GPS World, June 1, 2012), and performed in the context of the MONITOR and MONITOR2 ESA-funded projects (Y. Beniguel et al., NAVITEC Proc., 978-1-4673-2011-5 IEEE, 2012). The main goal of this presentation is to summarize a detailed recent study of the statistical properties of Solar Flares (E. Monte and M. Hernandez-Pajares, J. Geophys. Res., doi:10.1002/2014JA020206, 2014) by considering the GNSS proxy of EUV rate (GSFLAI parameter) computed independently each 30 seconds during the whole last solar cycle. An statistical model has been characterized that explains the empirical results such as (a) the persistence and presence of bursts of solar flares and (b) their long tail peak values of the solar flux variation, which can be characterized by: (1) A fractional Brownian model for the long-term dependence, and (2), a power law distribution for the time series extreme values. Finally, an update of the Solar Flares' occurrence during the recent months of Solar Activity, gathered in RT within MONITOR2 project, will close the paper.

  12. Solar flares and avalanches in driven dissipative systems

    NASA Technical Reports Server (NTRS)

    Lu, Edward T.; Hamilton, Russell J.; Mctiernan, J. M.; Bromund, Kenneth R.

    1993-01-01

    The contention of Lu and Hamilton (1991) that the energy release process in solar flares can be understood as avalanches of many small reconnection events is further developed. The dynamics of the complex magnetized plasma of solar active regions is modeled with a simple driven dissipative system, consisting of a vector field with local instabilities that cause rapid diffusion of the field. It is argued that the avalanches in this model are analogous to solar flares. The distributions of avalanches in this model are compared with the solar flare frequency distributions obtained from ISEE 3/ICE satellite observations. Quantitative agreement is found with the energy, peak luminosity, and duration distributions over four orders of magnitude in flare energy, from the largest flares down to the completeness limit of the observations. It is predicted that the power-law solar flare frequency distributions will be found to continue downward with the same logarithmic slopes to an energy of about 3 x 10 exp 25 ergs and duration of about 0.3 s, with deviations from power-law behavior below these values.

  13. Hinode magnetic-field observations of solar flares for exploring the energy storage and trigger mechanisms

    NASA Astrophysics Data System (ADS)

    Shimizu, Toshifumi; Inoue, Satoshi; Kawabata, Yusuke

    2015-08-01

    Solar flares abruptly release the free energy stored as a non-potential magnetic field in the corona and may be accompanied by eruptions of the coronal plasma. Magnetic reconnection is considered as a physical process in which the magnetic energy is converted to kinetic energy, thermal energy, and particle acceleration, but the location of magnetic reconnection is difficult to identify directly because of low emission measure at the reconnection region. We are still lack of observational knowledge on the 3D magnetic configuration and physical conditions for leading to flare trigger. Accurate measurements of vector magnetic fields at the solar photosphere, provided by the Solar Optical Telescope onboard Hinode, help us in exploring how the free energy is stored in the solar atmosphere and how the release of the energy is triggered. This presentation will review the magnetic field configuration and possible candidates for flare trigger primarily based on Hinode observations of some large flare events, which may include X5.4/X1.3 flares on 7 March 2012, X1.2 flare on 7 January 2014 and two M-class flares on 2 February 2014. The 7 March 2012 events were observed in an active region with delta-type sunspots, showing a strong shear in the entire magnetic system. For the sheared magnetic structure, the inclusion of a small-scale trigger field was identified near the polarity inversion line with excitation of a high-speed material flow in the horizontally oriented magnetic field formed nearly in parallel to the polarity inversion line. The observations suggest that gas dynamics at the solar surface play a vital role of leading to the onset of flares. The 7 January 2014 event is an exceptional event which most scientists would not be able to predict its occurrence. The flare unexpectedly happened apart from the sheared magnetic field region. The M-class flares on 2 February 2014 were observed in the magnetic field configuration, in which four magnetic domains were distributed on the solar surface and a null point might be formed in the coronal magnetic field originating from the four magnetic domains.

  14. Implications of RHESSI Observations for Solar Flare Models and Energetics

    NASA Technical Reports Server (NTRS)

    Holman, Gordon D.

    2006-01-01

    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.

  15. Particle acceleration by a solar flare termination shock

    NASA Astrophysics Data System (ADS)

    Chen, Bin; Bastian, Timothy S.; Shen, Chengcai; Gary, Dale E.; Krucker, Säm; Glesener, Lindsay

    2015-12-01

    Solar flares—the most powerful explosions in the solar system—are also efficient particle accelerators, capable of energizing a large number of charged particles to relativistic speeds. A termination shock is often invoked in the standard model of solar flares as a possible driver for particle acceleration, yet its existence and role have remained controversial. We present observations of a solar flare termination shock and trace its morphology and dynamics using high-cadence radio imaging spectroscopy. We show that a disruption of the shock coincides with an abrupt reduction of the energetic electron population. The observed properties of the shock are well reproduced by simulations. These results strongly suggest that a termination shock is responsible, at least in part, for accelerating energetic electrons in solar flares.

  16. Prediction of solar flares for the Space Exploration Initiative

    NASA Astrophysics Data System (ADS)

    Davis, John M.

    1994-06-01

    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.

  17. The probability of SWF occurrence in relation to solar activity

    NASA Astrophysics Data System (ADS)

    Morozova, L. P.

    1989-09-01

    Solar terrestrial researches have revealed substantial meaning of nonsteady events on the Sun, mainly solar flares, for the processes taking place in ionosphere. Solar flares result in the numerous consequences, account and prediction of which become necessary in our days. It is well known, that ionospheric disturbances following solar flares cause strong disturbances in the ionosphere, which severely violate radio systems (communication, navigation, etc.). Possibilities of sudden short wave fadeouts (SWF) prediction are considered.

  18. The probability of SWF occurrence in relation to solar activity

    NASA Technical Reports Server (NTRS)

    Morozova, L. P.

    1989-01-01

    Solar terrestrial researches have revealed substantial meaning of nonsteady events on the Sun, mainly solar flares, for the processes taking place in ionosphere. Solar flares result in the numerous consequences, account and prediction of which become necessary in our days. It is well known, that ionospheric disturbances following solar flares cause strong disturbances in the ionosphere, which severely violate radio systems (communication, navigation, etc.). Possibilities of sudden short wave fadeouts (SWF) prediction are considered.

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

    SciTech Connect

    Yang Xiao; Lin Ganghua; Zhang Hongqi; Mao Xinjie

    2013-09-10

    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.

  20. A COLD, TENUOUS SOLAR FLARE: ACCELERATION WITHOUT HEATING

    SciTech Connect

    Fleishman, Gregory D.; Nita, Gelu M.; Gary, Dale E.; Kontar, Eduard P.

    2011-04-10

    We report the observation of an unusual cold, tenuous solar flare, 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 (10{sup 35} electrons s{sup -1} 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 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. The implications of this finding for the flaring energy release and particle acceleration are discussed.

  1. An operational integrated short-term warning solution for solar radiation storms: introducing the Forecasting Solar Particle Events and Flares (FORSPEF) system

    NASA Astrophysics Data System (ADS)

    Anastasiadis, Anastasios; Sandberg, Ingmar; Papaioannou, Athanasios; Georgoulis, Manolis; Tziotziou, Kostas; Jiggens, Piers; Hilgers, Alain

    2015-04-01

    We present a novel integrated prediction system, of both solar flares and solar energetic particle (SEP) events, which is in place to provide short-term warnings for hazardous solar radiation storms. FORSPEF system provides forecasting of solar eruptive events, such as solar flares with a projection to coronal mass ejections (CMEs) (occurrence and velocity) and the likelihood of occurrence of a SEP event. It also provides nowcasting of SEP events based on actual solar flare and CME near real-time alerts, as well as SEP characteristics (peak flux, fluence, rise time, duration) per parent solar event. The prediction of solar flares relies on a morphological method which is based on the sophisticated derivation of the effective connected magnetic field strength (Beff) of potentially flaring active-region (AR) magnetic configurations and it utilizes analysis of a large number of AR magnetograms. For the prediction of SEP events a new reductive statistical method has been implemented based on a newly constructed database of solar flares, CMEs and SEP events that covers a large time span from 1984-2013. The method is based on flare location (longitude), flare size (maximum soft X-ray intensity), and the occurrence (or not) of a CME. Warnings are issued for all > C1.0 soft X-ray flares. The warning time in the forecasting scheme extends to 24 hours with a refresh rate of 3 hours while the respective warning time for the nowcasting scheme depends on the availability of the near real-time data and falls between 15-20 minutes. We discuss the modules of the FORSPEF system, their interconnection and the operational set up. The dual approach in the development of FORPSEF (i.e. forecasting and nowcasting scheme) permits the refinement of predictions upon the availability of new data that characterize changes on the Sun and the interplanetary space, while the combined usage of solar flare and SEP forecasting methods upgrades FORSPEF to an integrated forecasting solution. This work has been funded through the "FORSPEF: FORecasting Solar Particle Events and Flares", ESA Contract No. 4000109641/13/NL/AK

  2. On the Origin of Solar Flare's EUV Late Phase

    NASA Astrophysics Data System (ADS)

    Liu, Kai; Zhang, J.; Wang, Y.; Cheng, X.

    2012-05-01

    It has been well known that a solar flare typically has an impulsive phase, or the main energy release phase, immediately followed by a gradual phase or decay phase as best seen in soft X-ray emissions. A recent discovery based on EUV Variability Experiment (EVE) observations onboard Solar Dynamics Observatory (SDO) reveals that many flares exhibit a second large peak separated from the primary flare event by many minutes to hours; this second peak is coined as the flares EUV late phase (Woods et al. 2011). The EUV late phase is most evident in warm coronal emissions (e.g., Fe XVI 33.5 nm). In this Letter, we explore the origin of the EUV late phase through analyzing in detail two late phase flares, M2.9 flare on 2010 October 16 and M1.4 flare on 2011 February 18, using multi-passband imaging observations from Atmospheric Imaing Assembly (AIA) onboard SDO. We find that: (1) the late phase emissions originate from a different magnetic flux system from the main phase flare loop arcade. (2) The two flux systems are magnetically connected in topology, i.e., they share one common polarity magnetic region for one of their two footpoints. (3) The late phase loop arcade appears progressively in time from high to low temperatures, while the main phase arcade reaches the peak at almost the same time for all coronal temperatures. (4) The brightening of the isolated footpoint ribbon of late phase arcade is always tens of seconds later than the main phase ribbons. These results suggest that the late phase EUV emission, while originates from a different magnetic flux system, is possibly triggered by the eruption of the main phase flare through the interconnection of the two magnetic flux systems.

  3. Signatures of Accelerated Electrons in Solar and Stellar Flares

    NASA Astrophysics Data System (ADS)

    Benz, Arnold O.

    2015-08-01

    Flares energize electrons (and ions) to supra-thermal energies. In most cases the final distribution in momentum or energy space is non-Maxwellian. The non-thermal part of the energy can be the source for various emissions, including hard X-rays, synchrotron radiation and coherent radio emission. Such non-thermal emissions may contain information on the acceleration process. Several acceleration scenarios have been proposed: electric DC field, stochastic, and shock acceleration. There is observational evidence for all three scenarios. The new data come from SDO, X-ray (RHESSI), radio observations (Nobeyama, VLA and e-Callisto). Solar energetic particles are an additional channel of information.Tiny solar microflares and huge stellar flares in binary systems (RS CVns) and dMe dwarfs differ by more than 10 orders of magnitude in released energy. Yet the relation between peak luminosity in thermal (soft) X-ray and non-thermal synchrotron (radio) emission is surprisingly constant. This observational fact indicates that flare acceleration scales with energy release over a large range. Electron acceleration in flares seems to be a universal process. The constraint on simultaneous thermal X-rays and non-thermal (radio) synchrotron emission seems to select on particular kind of flare. In this subset, there seems to be only one type of acceleration.Yet, small deviations are noted: Small solar flares are softer in hard X-rays. Solar nanoflares are relatively weak in synchrotron emission. The recently noted case of radio-poor preflares will also be presented. The deviations suggest that the acceleration is less efficient in small flares and in the early phase of flares. Larger deviations are reported occasionally for solar flares and more often from stellar flares, where either thermal or non-thermal emission seems to be missing completely.The location of the acceleration in solar flares remains disputed. Observations suggesting acceleration in the soft X-ray top-tops, above top-tops and near the loop footpoints are presented. Whereas reconnection is well understood in MHD, acceleration of electrons (and ions) is not.

  4. Solar flares, proton showers, and the Space Shuttle

    NASA Technical Reports Server (NTRS)

    Rust, D. M.

    1982-01-01

    Attention is given the hazards posed to Space Shuttle crews by energetic proton radiation from inherently unpredictable solar flares, such as that of April 10-13, 1981, which was experienced by the Space Shuttle Columbia. The most energetic protons from this flare reached the earth's atmosphere an hour after flare onset, and would have posed a potentially lethal threat to astronauts engaged in extravehicular activity in a polar or geosynchronous orbit rather than the low-latitude, low-altitude orbit of this mission. It is shown that proton-producing flares are associated with energization in shocks, many of which are driven by coronal mass ejections. Insights gained from the Solar Maximum Year programs allow reconsideration of proton shower forecasting, which will be essential in the prediction of the weather that Space Shuttle astronauts will encounter during extravehicular activities.

  5. Energetic solar flare particles and interplanetary shock waves

    NASA Technical Reports Server (NTRS)

    Lin, R. P.

    1977-01-01

    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.

  6. Observations of solar flare gamma-rays and protons

    NASA Technical Reports Server (NTRS)

    Yoshimori, M.; Watanabe, H.

    1985-01-01

    Solar flare gamma-rays (4 to 7 MeV) and protons (8 to 500 MeV) were simultaneously observed from six flares on 1 Apr., 4 Apr., 27, Apr. 13, May 1981, 1 Feb. and 6 June 1982 by the Hinotori and GMS satellites. The relationship between 4 to 7 MeV gamma-ray fluences and peak 16 to 34 MeV proton fluxes for these flares are analyzed. It does not reveal an apparent correlation between these two parameters. The present result implies that the protons producing gamma-rays and the protons observed near the Earth do not always belong to the same population.

  7. Abundances from solar-flare gamma-ray line spectroscopy

    NASA Technical Reports Server (NTRS)

    Murphy, R. J.; Ramaty, R.; Forrest, D. J.; Kozlovsky, B.

    1985-01-01

    Elemental abundances of the ambient gas at the site of gamma ray line production inthe solar atmosphere are deduced using gamma ray line observations from a solar flare. The resultant abundances are different from local galactic abundances which are thought to be similar to photospheric abundances.

  8. Solar He-3: Information from nuclear reactions in flares

    NASA Technical Reports Server (NTRS)

    Ramaty, R.; Kozlovsky, B.

    1974-01-01

    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.

  9. TRANSITION REGION EMISSION FROM SOLAR FLARES DURING THE IMPULSIVE PHASE

    SciTech Connect

    Johnson, H.; Raymond, J. C.; Murphy, N. A.; Suleiman, R.; Giordano, S.; Ko, Y.-K.; Ciaravella, A.

    2011-07-10

    There are relatively few observations of UV emission during the impulsive phases of solar flares, so the nature of that emission is poorly known. Photons produced by solar flares can resonantly scatter off atoms and ions in the corona. Based on off-limb measurements by the Solar and Heliospheric Observatory/Ultraviolet Coronagraph Spectrometer, we derive the O VI {lambda}1032 luminosities for 29 flares during the impulsive phase and the Ly{alpha} luminosities of 5 flares, and we compare them with X-ray luminosities from GOES measurements. The upper transition region and lower transition region luminosities of the events observed are comparable. They are also comparable to the luminosity of the X-ray emitting gas at the beginning of the flare, but after 10-15 minutes the X-ray luminosity usually dominates. In some cases, we can use Doppler dimming to estimate flow speeds of the O VI emitting gas, and five events show speeds in the 40-80 km s{sup -1} range. The O VI emission could originate in gas evaporating to fill the X-ray flare loops, in heated chromospheric gas at the footpoints, or in heated prominence material in the coronal mass ejection. All three sources may contribute in different events or even in a single event, and the relative timing of UV and X-ray brightness peaks, the flow speeds, and the total O VI luminosity favor each source in one or more events.

  10. Can we explain atypical solar flares?

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    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

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

    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...

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

    NASA Technical Reports Server (NTRS)

    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

    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.

  13. Lunar surface cosmic ray experiment. [including solar flare studies

    NASA Technical Reports Server (NTRS)

    Price, P. B.

    1974-01-01

    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.

  14. Conduction-driven chromospheric evaporation in a solar flare

    NASA Technical Reports Server (NTRS)

    Zarro, Dominic M.; Lemen, James R.

    1988-01-01

    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.

  15. Common SphinX and RHESSI observations of solar flares

    NASA Astrophysics Data System (ADS)

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

    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.

  16. Microwave Type III Pair Bursts in Solar Flares

    NASA Astrophysics Data System (ADS)

    Tan, Baolin; Mészárosová, Hana; Karlický, Marian; Huang, Guangli; Tan, Chengming

    2016-03-01

    A solar microwave type III pair burst is composed of normal and reverse-sloped (RS) burst branches with oppositely fast frequency drifts. It is the most sensitive signature of the primary energy release and electron accelerations in flares. This work reports 11 microwave type III pair events in 9 flares observed by radio spectrometers in China and the Czech Republic at a frequency of 0.80–7.60 GHz during 1994–2014. These type III pairs occurred in flare impulsive and postflare phases with separate frequencies in the range of 1.08–3.42 GHz and a frequency gap of 10–1700 MHz. The frequency drift increases with the separate frequency (fx), the lifetime of each burst is anti-correlated to fx, while the frequency gap is independent of fx. In most events, the normal branches are drifting obviously faster than the RS branches. The type III pairs occurring in flare impulsive phase have lower separate frequencies, longer lifetimes, wider frequency gaps, and slower frequency drifts than that occurring in postflare phase. Also, the latter always has strong circular polarization. Further analysis indicates that near the flare energy release sites the plasma density is about {10}10{--}{10}11 cm‑3 and the temperature is higher than 107 K. These results provide new constraints to the acceleration mechanism in solar flares.

  17. Solar flare nuclear gamma-rays and interplanetary proton events

    NASA Technical Reports Server (NTRS)

    Cliver, E. W.; Forrest, D. J.; Cane, H. V.; Reames, D. V.; Mcguire, R. E.; Von Rosenvinge, T. T.

    1989-01-01

    Gamma-ray line (GRL) and solar energetic proton (SEP) events observed from February 1980 through January 1985 are compared in order to substantiate and better characterize the lack of correlation between GRL fluences and SEP event peak fluxes. The scatter plot of SEP event peak flux vs. GRL fluence is presented, and the ratio of 'solar' to 'interplanetary', about 10 MeV protons, is presented. It is shown that, while even large SEP events can originate in flares lacking detectable GRL emission, the converse case of flares with a significant GRL line fluence by lacking protons in space is rare. The ratio R of the number of about 10 MeV protons that produce GRL emission at the flare site to the number of about 10 MeV protons detected in space can vary from event to event by four orders of magnitude. There is a clear tendency for impulsive flares to have larger values of R than long-duration flares, where the flare time scale is given by the e-folding decay time of the associated soft X-ray emission.

  18. The acceleration and propagation of solar flare energetic particles

    NASA Technical Reports Server (NTRS)

    Forman, M. A.; Ramaty, R.; Zweibel, E. G.; Holzer, T. E. (Editor); Mihalas, D. (Editor); Sturrock, P. A. (Editor); Ulrich, R. K. (Editor)

    1982-01-01

    Observations and theories of particle acceleration in solar flares are reviewed. The most direct signatures of particle acceleration in flares are gamma rays, X-rays and radio emissions produced by the energetic particles in the solar atmosphere and energetic particles detected in interplanetary space and in the Earth's atmosphere. The implication of these observations are discussed. Stochastic and shock acceleration as well as acceleration in direct electric fields are considered. Interplanetary particle propagation is discussed and an overview of the highlights of both current and promising future research is presented.

  19. Protons from the decay of solar flare neutrons

    NASA Technical Reports Server (NTRS)

    Evenson, P.; Meyer, P.; Pyle, K. R.

    1983-01-01

    Fluxes of energetic protons in interplanetary space are observed which are interpreted as the decay products of neutrons generated in a solar flare on 1982 June 3 at 11:42 UT. Because of the particular geometry of this event the spectrum of neutrons escaping from the sun can be constructed with great accuracy in the kinetic energy range 10-100 MeV. The resulting spectrum places stringent constraints on the free parameters used in previously published calculations of neutron production in solar flares. An estimate is made of the diffusion mean free path of charged particles in the interplanetary medium in a new way.

  20. Modelling the effects of a solar flare on INTEGRAL

    NASA Astrophysics Data System (ADS)

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

    2001-09-01

    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.

  1. Excitation of helium resonance lines in solar flares

    SciTech Connect

    Porter, J.G.; Gebbie, K.B.; November, L.J.

    1986-02-01

    The authors calculated helium resonance-line intensities for a set of six flare models corresponding to two rates of heating and three widely varying incident fluxes of soft x rays. They examine the differing ionization and excitation equilibria produced by these models, the processes that dominate the various cases, and the predicted helium line spectra. The line intensities and their ratios are compared with values derived from Skylab NRL spectroheliograms for a class M flare, thus determining (1) which of these models most nearly represents the density vs. temperature structure and soft x-ray flux in the flaring solar transition regions, and (2) the temperature and dominant mechanism of formation of the helium line spectrum during a flare.

  2. Study of the Effect of Solar Flares and the Solar Position on the NRK - Algiers VLF Signal Path

    NASA Astrophysics Data System (ADS)

    Bouderba, Yasmina; Tribeche, Mouloud; Amor Samir, Nait

    X-ray and UV radiations emitted from the sun during solar flares, may cause enhancement of the ionization in the lower ionosphere. To study the effect of solar flares and their occurrence in the daytime on the D layer of the ionosphere (60-90 Km), we used Very Low Frequency (VLF) data of the NRK-ALG GCP (NRK: 63.85 N, 22.45 W, 37.5 KHz; Algiers: 36.16 N, 3.13 E; Distance: 3495 Km). Since any ionospheric electron density change, VLF signal perturbations in both of amplitude (?A) and phase (??) are measured. However, from the measured ?A and ??, the ionospheric parameters: H (the reflecting height in Km) and ? (the increasing conductivity in Km-1) are then deduced using the Long wave probability code (LWPC). The results show that the signal perturbations parameters (?A and ??) increased with the X-ray flux. Thus, as a function of the solar flux, H decreases to lower altitudes, but B increases up to a saturation value. From the H and ? parameters, the electron density enhancement is then deduced. In addition to the experimental results, a numerical simulation of the D region disturbances due to solar flares was developed. Therefore, a comparison between the experimentally measured electron density and numerically determined is done as function of the solar flux and the solar zenith angle.

  3. White-light continuum emission from solar flare and plages: observations and modeling

    NASA Astrophysics Data System (ADS)

    Berlicki, Arkadiusz; Awasthi, Arun Kumar; Heinzel, Petr

    2015-08-01

    Observations of flares in optical continuum emission are very rare. Therefore, the analysis of such observations is very useful and may contribute to our understanding of the flaring chromosphere. We study the white-light continuum emission observed during the X6.9 flare observed on August 09, 2011. This emission comes not only from the flare ribbons but also form the nearby plage area observed within the active region. The main aim of this work is to disentangle the flare and plage emission and to understand the physical mechanisms responsible for the production of white-light continuum.There are two main mechanisms which can be responsible for the optical continuum emission of the solar atmosphere: enhanced photospheric H- continuum due to the temperature increase below the temperature minimum region, or hydrogen recombination continua (Balmer, Paschen) formed in solar chromosphere. In our work we analyse the physical conditions in solar active atmosphere in order to obtain the contribution from these two mechanisms to the whole continuum emission of the flare and plage.We analyzed the spatial, spectral and temporal evolution study of the flare and plage parameters by analyzing multi-wavelength observations obtained from ground and space based solar observatories. We study the morphological correlation of the white-light continuum emission observed with different instruments. Moreover, we also explore the non-thermal electron beam properties by forward fitting the observed X-ray spectra.The unique opportunity of an intense X6.9 flare occurrence close to the limb enabled us to explore the origin of white-light continuum with better visibility. The analysis of multi-wavelength data revealed the origin of this emission from the foot-points of the loops. Spatial association of HXR foot-points synthesized from RHESSI observations confirmed this finding. In addition, we found a good temporal correlation of hard (>30 keV) X-ray with the white-light emission. However, some active region areas which produce the continuum emission correspond rather to plages than to the flare kernels.

  4. A thermal/nonthermal approach to solar flares

    NASA Technical Reports Server (NTRS)

    Benka, Stephen G.

    1991-01-01

    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.

  5. Variability of Thermosphere and Ionosphere Responses to Solar Flares

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

    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.

  6. Ionization equilibrium in soft X-ray-emitting solar flares

    NASA Technical Reports Server (NTRS)

    Phillips, K. J. H.; Neupert, W. M.; Thomas, R. J.

    1974-01-01

    Studies of the 1.9-A line produced by highly ionized iron during a solar flare indicate that this emission occurs under conditions approaching a steady-state ionization equilibrium. Time-dependent and steady-state ionization equilibrium values are used for calculation of 1.9 A line fluxes per unit flare emission. The results are compared with those obtained by observations of some four solar flares, showing that the calculations from time-dependent equilibrium values approximate the observed line flux values with the same accuracy as the calculations from steady-state equilibrium values only when the electron densities are equal to or greater than 10 billion per cu cm.

  7. A RECONNECTING CURRENT SHEET IMAGED IN A SOLAR FLARE

    SciTech Connect

    Liu Rui; Liu Chang; Wang Haimin; Lee, Jeongwoo; Wang, Tongjiang; Stenborg, Guillermo

    2010-11-01

    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.

  8. Solar and Stellar Flares over Time: Effects on Hosted Planets

    NASA Astrophysics Data System (ADS)

    Guinan, Edward F.; DeWarf, Laurence E.; Engle, Scott G.; Gropp, Jeffrey

    2016-01-01

    The effects of flares from the Sun on Earth and other solar-system planets are presented. Also discussed are the flare properties of cooler, commonplace main-sequence K-M stars. Data from our "Sun in Time" program are used to study the flare properties of the Sun and solar-type stars from youth to old age. These studies are based on ground-based observations, UV and X-ray space missions (IUE & HST, ROSAT & Chandra) as well as a wealth of data from the Kepler Mission. The ultra-high precision photometry available from the Kepler Mission (and K2) has made it possible to study starspots, flare properties, and rotations of thousands of G, K, M stars. Superflares (defined as E > 10+33 ergs ~X-100 flares) on hundreds of mostly G and K stars have been found. (See e.g. Shibayama et al. 2013; Maehara et al. 2015; Notsu et al. 2013/15; Saar et al. 2015; Guinan et al. 2015). Using our Age-Rotation relations, we determine correlations of flares properties of the Sun and solar-type over a wide range of ages. We also compare these flare histories with the cooler, more common K- and M-type stars. The analysis of these datasets imply that the young Sun had numerous, very powerful flares that may have played major roles the evolution of the early atmospheres of Earth and other terrestrial planets. The strong X-UV fluxes and proton fluences from flares and associated plasmas from coronal mass ejection events can greatly affect the photochemistry of planetary atmospheres as well as ionizing and possibly eroding their atmospheres. Some examples are given. Also discussed are the effects of superflares from the present Sun on the Earth. Even though solar superflares are rarer (~1 per 300-500 yrs) than from the young Sun (> 1-2 per year), they could cause significant damage to our communication and satellite systems, electrical networks, and threaten the lives of astronauts in space..This research is supported by grants from NSF/RUI and NASA: NSF, AST 1009903; Chandra GO2-13020X, HST GO-13020.01. We are very grateful for this support

  9. Low energy particle composition. [energy spectra, particle emission - solar flares

    NASA Technical Reports Server (NTRS)

    Gloeckler, G.

    1975-01-01

    The energy spectra and composition of the steady or 'quiet-time' particle flux, whose origin is unknown was studied. Particles and photons which are associated with solar flares or active regions on the sun were also studied. Various detection techniques used to measure the composition and energy spectra of low energy particles are discussed. Graphs of elemental abundance and energy spectra are given.

  10. Filament eruptions and the impulsive phase of solar flares

    NASA Technical Reports Server (NTRS)

    Kahler, S. W.; Moore, R. L.; Kane, S. R.; Zirin, H.

    1988-01-01

    Filament motion during the onset of the solar flare impulsive phase is examined. The impulsive phase onset is established from profiles of about 30 keV X-ray fluxes and the rapid flare brightenings characteristic of the H-alpha flash phase. The filament motion begins several minutes before the impulsive or flash phase of the flare. No new accleration is observed in the motion of the filament during the onset of the impulsive phase for at least two of the four flares. The most common H-alpha brightenings associated with the impulsive phase lie near the magnetic inversion line roughly centered under the erupting filament. Filament speeds at the onset of the impulsive or flash phase lie in the range 30-180 km/s. These characteristics indicate that the filament eruption is not driven by the flare plasma pressure, but instead marks an eruption of magnetic field driven by a global MHD instability of the field configuration in the region of the flare.

  11. Statistical Study of the Reconnection Rate in Solar Flares

    NASA Astrophysics Data System (ADS)

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

    2002-01-01

    The soft X-ray telescope (SXT) aboard Yohkoh has established that the driving mechanism of solar flares is magnetic reconnection. However, the physics of reconnection has not been clarified. One of the current puzzles is: what determines the reconnection rateNULL The reconnection rate is defined as reconnected magnetic flux per unit time or equivalently the ratio of inflow speed into reconnection point to Alfven velocity in non-dimension, and is one of the most important physical quantities in reconnection physics. However, observations have not yet succeeded to statistically determine the reconnection rate because direct observation of reconnection inflow and coronal magnetic field is difficult. In this poster we present a method to determine the reconnection rate from observational data, which use the following relations: H = frac B2 4pi vinL2 vinB = vfootBfoot. Here H, L, vfoot and Bfoot are respectively the flare heating rate, size of the flare arcade, separation velocity of the two ribbon, and magnetic field strength of the foot points. Since these four quantities can be obtained from observational data, the relations above give the inflow velocity vin and coronal magnetic field B, and thus the reconnection rate can be determined. Appling this method to many flare observations, we will determine the reconnection rate in solar flares statistically. A preliminary result is presented.

  12. Statistical properties of super-hot solar flares

    SciTech Connect

    Caspi, Amir; Krucker, Säm; Lin, R. P.

    2014-01-20

    We use Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) high-resolution imaging and spectroscopy observations from ∼6 to 100 keV to determine the statistical relationships between measured parameters (temperature, emission measure, etc.) of hot, thermal plasma in 37 intense (GOES M- and X-class) solar flares. The RHESSI data, most sensitive to the hottest flare plasmas, reveal a strong correlation between the maximum achieved temperature and the flare GOES class, such that 'super-hot' temperatures >30 MK are achieved almost exclusively by X-class events; the observed correlation differs significantly from that of GOES-derived temperatures, and from previous studies. A nearly ubiquitous association with high emission measures, electron densities, and instantaneous thermal energies suggests that super-hot plasmas are physically distinct from cooler, ∼10-20 MK GOES plasmas, and that they require substantially greater energy input during the flare. High thermal energy densities suggest that super-hot flares require strong coronal magnetic fields, exceeding ∼100 G, and that both the plasma β and volume filling factor f cannot be much less than unity in the super-hot region.

  13. Impulsive Heating of Solar Flare Ribbons Above 10 MK

    NASA Astrophysics Data System (ADS)

    Simes, P. J. A.; Graham, D. R.; Fletcher, L.

    2015-06-01

    The chromospheric response to the input of flare energy is marked by extended extreme ultraviolet (EUV) ribbons and hard X-ray (HXR) footpoints. These are usually explained as the result of heating and bremsstrahlung emission from accelerated electrons colliding in the dense chromospheric plasma. We present evidence of impulsive heating of flare ribbons above 10 MK in a two-ribbon flare. We analyse the impulsive phase of SOL2013-11-09T06:38, a C2.6 class event using data from Atmospheric Imaging Assembly (AIA) on board of the Solar Dynamics Observatory (SDO) and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) to derive the temperature, emission measure and differential emission measure of the flaring regions and investigate the evolution of the plasma in the flaring ribbons. The ribbons were visible at all SDO/AIA EUV/UV wavelengths, in particular, at 94 and 131 filters, sensitive to temperatures of 8 MK and 12 MK. The time evolution of the emission measure of the plasma above 10 MK at the ribbons has a peak near the HXR peak time. The presence of hot plasma in the lower atmosphere is further confirmed by a RHESSI imaging spectroscopy analysis, which shows resolved sources at 11 - 13 MK that are associated with at least one ribbon. We found that collisional beam-heating can only marginally explain the power necessary to heat the 10 MK plasma at the ribbons.

  14. Impulsive Heating of Solar Flare Ribbons Above 10 MK

    NASA Astrophysics Data System (ADS)

    Simões, P. J. A.; Graham, D. R.; Fletcher, L.

    2015-12-01

    The chromospheric response to the input of flare energy is marked by extended extreme ultraviolet (EUV) ribbons and hard X-ray (HXR) footpoints. These are usually explained as the result of heating and bremsstrahlung emission from accelerated electrons colliding in the dense chromospheric plasma. We present evidence of impulsive heating of flare ribbons above 10 MK in a two-ribbon flare. We analyse the impulsive phase of SOL2013-11-09T06:38, a C2.6 class event using data from Atmospheric Imaging Assembly (AIA) on board of the Solar Dynamics Observatory (SDO) and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) to derive the temperature, emission measure and differential emission measure of the flaring regions and investigate the evolution of the plasma in the flaring ribbons. The ribbons were visible at all SDO/AIA EUV/UV wavelengths, in particular, at 94 and 131 Å filters, sensitive to temperatures of 8 MK and 12 MK. The time evolution of the emission measure of the plasma above 10 MK at the ribbons has a peak near the HXR peak time. The presence of hot plasma in the lower atmosphere is further confirmed by a RHESSI imaging spectroscopy analysis, which shows resolved sources at 11 - 13 MK that are associated with at least one ribbon. We found that collisional beam-heating can only marginally explain the power necessary to heat the 10 MK plasma at the ribbons.

  15. NEW SOLAR EXTREME-ULTRAVIOLET IRRADIANCE OBSERVATIONS DURING FLARES

    SciTech Connect

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

    2011-10-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Chupp, Edward L.

    1998-01-01

    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.

  17. Theoretical studies on rapid fluctuations in solar flares

    NASA Technical Reports Server (NTRS)

    Vlahos, Loukas

    1986-01-01

    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.

  18. Max '91: Flare research at the next solar maximum

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

    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.

  19. Solar neutrinos, solar flares, solar activity cycle and the proton decay

    NASA Technical Reports Server (NTRS)

    Raychaudhuri, P.

    1985-01-01

    It is shown that there may be a correlation between the galactic cosmic rays and the solar neutrino data, but it appears that the neutrino flux which may be generated during the large solar cosmic ray events cannot in any way effect the solar neutrino data in Davis experiment. Only initial stage of mixing between the solar core and solar outer layers after the sunspot maximum in the solar activity cycle can explain the higher (run number 27 and 71) of solar neutrino data in Davis experiment. But solar flare induced atmospheric neutrino flux may have effect in the nucleon decay detector on the underground. The neutrino flux from solar cosmic rays may be a useful guide to understand the background of nucleon decay, magnetic monopole search, and the detection of neutrino flux in sea water experiment.

  20. Solar Flare Impulsive Phase Observations from SDO and Other Observatories

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Caballero, C.; Aranda, M. C.

    2014-05-01

    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.

  2. Effects of solar flares on the ionosphere of Mars.

    PubMed

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

    2006-02-24

    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

  3. The development and cooling of a solar limb-flare

    NASA Technical Reports Server (NTRS)

    Veck, N. J.; Strong, K. T.; Jordan, C.; Simnett, G. M.; Cargill, P. J.; Priest, E. R.

    1984-01-01

    Observations of a flare that began in soft X-rays at 20:37 UT on April 12, 1980 at the west limb of the sun are discussed. The observations of the flare and postflare loops are first described, and the Solar Maximum Mission data are interpreted in terms of the temperature, density, and geometry of the emitting regions. The observed postflare cooling time is compared with that expected from radiation, conduction, and enthalpy flux. The loop model is discussed, and the observed events are compared with other proposed models.

  4. Acceleration of runaway electrons and Joule heating in solar flares

    NASA Technical Reports Server (NTRS)

    Holman, G. D.

    1984-01-01

    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.

  5. Large Solar Flares and Sheared Magnetic Field Configuration

    NASA Technical Reports Server (NTRS)

    Choudhary, Debi Prasad

    2001-01-01

    This Comment gives additional information about the nature of flaring locations on the Sun described in the article "Sun unleashes Halloween storm", by R. E. Lopez, et al. What causes the large explosions from solar active regions that unleash huge magnetic storms and adverse space weather? It is now beyond doubt that the magnetic field in solar active regions harbors free energy that is released during these events. Direct measurements of the longitudinal and transverse components of active region magnetic fields with the vector magnetograph at NASA Marshall Space Flight Center (MSFC), taken on a regular basis for the last 30 years, have found key signatures of the locations of powerful flares. A vector magnetograph detects and measures the magnetic shear, which is the deviation of the observed transverse magnetic field direction from the potential field. The sheared locations possess abundant free magnetic energy for solar flares. In addition to active region NOAA 10486, the one that produced the largest flares last October, the NASA/MSFC vector magnetograph has observed several other such complex super active regions, including NOAA 6555 and 6659.

  6. Low-latitude Ionospheric Heating during Solar Flares

    NASA Astrophysics Data System (ADS)

    Klenzing, J.; Chamberlin, P. C.; Qian, L.; Haaser, R. A.; Burrell, A. G.; Earle, G. D.; Heelis, R. A.; Simoes, F. A.

    2013-12-01

    The advent of the Solar Dynamics Observatory (SDO) represents a leap forward in our capability to measure rapidly changing transient events on the sun. SDO measurements are paired with the comprehensive low latitude measurements of the ionosphere and thermosphere provided by the Communication/Navigation Outage Forecast System (C/NOFS) satellite and state-of-the-art general circulation models to discuss the coupling between the terrestrial upper atmosphere and solar radiation. Here we discuss ionospheric heating as detected by the Coupled Ion-Neutral Dynamics Investigation (CINDI) instrument suite on the C/NOFS satellite during solar flares. Also discusses is the necessity of decoupling the heating due to increased EUV irradiance and that due to geomagnetic storms, which sometimes occur with flares. Increases in both the ion temperature and ion density in the subsolar topside ionosphere are detected within 77 minutes of the 23 Jan 2012 M-class flare, and the observed results are compared with the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM) using the Flare Irradiance Spectral Model (FISM) as an input.

  7. Observations and Modeling of Solar Flare Atmospheric Dynamics

    NASA Astrophysics Data System (ADS)

    Li, Y.

    2015-09-01

    Solar flares are one of the most energetic events in solar atmosphere, which last minutes to tens of minutes. The eruption of a solar flare involves energy release, plasma heating, particle acceleration, mass flows, waves, etc. A solar flare releases a large amount of energy, and its emission spans a wide wavelength range. Solar flares are usually accompanied by coronal mass ejections (CMEs); therefore they could significantly affect the space environments between the Earth and the Sun. At present, we do not fully understand the whole flare process. There are still many important questions to be resolved, such as when and where is the energy released? How long does the energy release last? What are the main ways of energy release? And how does the solar atmosphere respond to the energy release? To address these questions, we study in detail the flare heating and dynamic evolution. We first give a brief review of previous flare studies (Chapter 1), and introduce the observing instruments (Chapter 2) and the modeling method (Chapter 3) related to this thesis work. Then we use spectral data to investigate the chromospheric evaporation (Chapter 4). Based on the results, we further explore the flare heating problem. With observationally inferred heating functions, we model two flare loops, and compare the results with observations (Chapter 5). A consistency is achieved between modeling and observations. In addition, we model two different sets of flare loop systems with quite different heating profiles and dynamic evolutions (Chapter 6). The details are described as below. Firstly, we investigate the chromospheric evaporation in the flare on 2007 January 16 using line profiles observed by the Extreme-ultraviolet (EUV) Imaging Spectrometer (EIS) on board Hinode. Three points with different magnetic polarities at flare ribbons are analyzed in detail. We find that the three points show different patterns of upflows and downflows in the impulsive phase of the flare. The spectral lines at the first point are mostly blueshifted, with the hotter lines showing a dominant blueshifted component over the stationary one. At the second point, however, only weak upflows are detected; instead, notable downflows appear at high temperatures (up to 2.5-5.0 MK). The third point is similar to the second one except that it shows evidence of multi-component downflows. While the evaporated plasma falling back down as warm rain is a possible cause of the redshifts at the second and third points, the different patterns of chromospheric evaporation at the three points imply the existence of different heating mechanisms in the flaring region. Then, we study the flare heating and dynamics using the ``enthalpy-based thermal evolution of loops'' (EBTEL) model. We analyze an M1.0 flare on 2011 February 16. This flare is composed of two distinctive loop systems observed in EUV images. The UV 1600 Å emission at the feet of these loops exhibits a rapid rise, followed by enhanced emission in different EUV channels observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). Such a behavior is indicative of impulsive energy deposit, and the subsequent response of overlying coronal loops. Using the method recently developed, we infer empirical heating functions from the rapid rise of the UV light curves for the two loop systems, respectively, treated as two big loops with cross-sectional area of 5'' by 5'', and compute the plasma evolution in the loops using the EBTEL model. We further compute the synthetic EUV light curves, which, with the limitation of the model, agree reasonably with the observed light curves obtained in multiple AIA channels and EIS lines: they show the same evolution trend, and their magnitudes are comparable within a factor of two. We also compare the computed mean enthalpy flow velocity with the Doppler shifts of EIS lines during the decay phase of the two loops. Our results suggest that the two different loops with different heating functions as inferred from their footpoint UV emission, combined with their different lengths as measured from imaging observations, give rise to different coronal plasma evolution patterns as revealed in both models and observations. With the same method, we further analyze another C4.7 flare. From AIA imaging observations, we can identify two sets of loops in this event. EIS spectroscopic observations reveal blueshifts at the feet of both sets of loops during the impulsive phase. However, the dynamic evolutions of the two sets of loops are quite different. The first set of loops exhibits blueshifts (˜10 km/s) for about 25 minutes followed by redshifts, while the second set shows stronger blueshifts (˜20 km/s) which are maintained for about an hour. The long-lasting blueshifts in the second set of loops are indicative of continuous heating. The UV 1600 Å ~ observation by AIA also shows that the feet of the loops brighten twice with 15 minutes apart. The first set of loops, on the other hand, brighten only once in the UV band. We construct heating functions of the two sets of loops using spatially resolved UV light curves at their footpoints, and model plasma evolution in these loops with the EBTEL model. The results show that, for the first set of loops, the synthetic EUV light curves from the model compare favorably with the observed light curves in six AIA channels and eight EIS spectral lines, and the computed mean enthalpy flow velocities also agree with the Doppler shifts measured in EIS lines. For the second set of loops modeled with twice-heating, there are some discrepancies between modeled and observed EUV light curves at low-temperature lines, and the model does not fully reproduce the prolonged blueshift signatures as observed. The prominent discrepancies between model and observations for the second set of loops may be caused by non-uniform heating localized especially at the loop footpoints which cannot be modeled by the 0D EBTEL model, or by unresolved fine flaring strands in the loops with quite different heating rates and profiles.

  8. Large solar flares - Analysis of the events recorded by the Mont Blanc neutrino detector

    NASA Astrophysics Data System (ADS)

    Aglietta, M.; Badino, G.; Bologna, G.; Castagnoli, C.; Castellina, A.; Dadykin, V. L.; Fulgione, W.; Galeotti, P.; Kalchukov, F. F.; Korolkova, I. V.; Kortchaguin, P. V.; Kudryavtsev, V. A.; Malguin, A. S.; Periale, L.; Ryassny, V. G.; Ryazhskaya, O. G.; Saavedra, O.; Trinchero, G.; Vernetto, S.; Yakushev, V. F.; Zatsepin, G. T.

    1991-11-01

    Analytical results are discussed from events recorded by the Mont Blanc neutrino detector during 19 large solar flares from August 1988 to March 1990, including the powerful flares of September 29 and October 19, 1989. It is found that no significant neutrino signal coincides temporally with solar flares. Upper limits are obtained for the integral neutrino and antineutrino flux of different flavors.

  9. Measurements and modeling of total solar irradiance in X-class solar flares

    SciTech Connect

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

    2014-05-20

    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.

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

    NASA Technical Reports Server (NTRS)

    Moore, Christopher S.; Chamberlin, Phillip Clyde; Hock, Rachel

    2014-01-01

    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.

  11. Flare Particle Escape in 3D Solar Eruptive Events

    NASA Astrophysics Data System (ADS)

    Antiochos, Spiro K.; Masson, Sophie; DeVore, C. R.

    2015-04-01

    Among the most important, but least understood forms of space weather are the so-called Impulsive Solar Energetic Particle (SEP) events, which can be especially hazardous to deep-space astronauts. These energetic particles are generally believed to be produced by the flare reconnection that is the primary driver of solar eruptive events (SEE). A key point is that in the standard model of SEEs, the particles should remain trapped in the coronal flare loops and in the ejected plasmoid, the CME. However, flare-accelerated particles frequently reach the Earth long before the CME does. In previous 2.5D calculations we showed how the external reconnection that is an essential element of the breakout model for CME initiation could lead to the escape of flare-accelerated particles. The problem, however, is that in 2.5D this reconnection also tends to destroy the plasmoid, which disagrees with the observation that SEP events are often associated with well-defined plasmoids at 1 AU known as magnetic clouds. Consequently, we have extended our model to a fully 3D topology that includes a multi-polar coronal field suitable for a breakout SEE near a coronal hole region. We performed high-resolution 3D MHD numerical simulations with the Adaptively Refined MHD Solver (ARMS). Our results demonstrate that the model allows for the effective escape of energetic particles from deep within an ejecting well-defined plasmoid. We show how the complex interactions between the flare and breakout reconnection reproduce all the main observational features of SEEs and SEPs. We discuss the implications of our calculations for the upcoming Solar Orbiter and Solar Probe Plus missions, which will measure SEEs and SEPs near the Sun, thereby, mitigating propagation effects.This research was supported, in part, by the NASA SR&T and TR&T Programs.

  12. On the Origin of Solar and Stellar Flares

    NASA Astrophysics Data System (ADS)

    Ibadov, Subhon

    2015-08-01

    Physical processes connected with falls of comets and evaporating bodies, FEBs, onto stars with cosmic velocities, around 600 km/s, are considered. The processes include aerodynamic crushing of comet nucleus and transversal expansion of crushed mass within the solar chromosphere as well as sharp deceleration of the flattening structure in a relatively very thin layer near the solar/stellar photosphere. Fast thermalization of the body's kinetic energy will be accompanied by impulse generation of a high temperature plasma in the thin layer, i.e., "explosion" and strong "blast" shock wave as well as eruption of the layer ionized material into space above the chromosphere. Impact mechanism is capable to lead to generation of solar/stellar super-flares. Some similarities of this phenomenon with flare activity by magnetic reconnection are also revealed.

  13. Upper limits on the total radiant energy of solar flares

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

    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.

  14. Signatures of current loop coalescence in solar flares

    NASA Technical Reports Server (NTRS)

    Sakai, J.; Nakajima, H.; Zaidman, E.; Tajima, T.; Kosugi, T.; Brunel, F.

    1986-01-01

    The nonlinear coalescence instability of current carrying solar loops can explain many of the characteristics of the solar flares such as their impulsive nature, heating and high energy particle acceleration, amplitude oscillations of electromagnetic emission as well as the characteristics of 2-D microwave images obtained during a solar flare. The physical characteristics of the explosive coalescence of currents are presented in detail through computer simulation and theory. Canonical characteristics of the explosive coalescence are: (1) a large amount of impulsive increase of kinetic energies of electrons and ions; (2) simultaneous heating and acceleration of electrons and ions in high and low energy spectra; (3) ensuing quasi-periodic amplitude oscillations in fields and particle quantities; and (4) the double peak (or triple peak) structure in these profiles, participate in the coalescence process, yielding varieties of phenomena.

  15. An extended superhot solar flare X-ray source

    NASA Technical Reports Server (NTRS)

    Hudson, H. S.; Ohki, K. I.; Tsuneta, S.

    1985-01-01

    A superhot hard X-ray source in a solar flare occulted by the solar limb was identified. Its hard X-ray image was found to show great horizontal extent but little vertical extent. An H alpha brightening at the same limb position about an hour later suggests a multi-component loop prominence system, so that it appears that a superhot source can evolve in the same manner as a normal solar soft X-ray source. The assignment of plausiable values to physical parameters in the source suggests (from the simplest form of classical thermal-conduction theory) that either new physics will be required to suppress conduction, or else that gradual energy release well after the impulsive phase of the flare must occur. In this respect too, the superhot source appears to resemble ordinary soft X-ray sources, except of course that its temperature is higher.

  16. Observational evidence for thermal wave fronts in solar flares

    NASA Technical Reports Server (NTRS)

    Rust, D. M.; Simnett, G. M.; Smith, D. F.

    1985-01-01

    Images in 3.5-30 keV X-rays obtained during the first few minutes of seven solar flares show rapid motions. In each case X-ray emission first appeared at one end of a magnetic field structure, and then propagated along the field at a velocity between 800 and 1700 km/s. The observed X-ray structures were 45,000-230,000 km long. Simultaneous H-alpha images were available in three cases; they showed brightenings when the fast-moving fronts arrived at the chromosphere. The fast-moving fronts are interpreted as electron thermal conduction fronts since their velocities are consistent with conduction at the observed temperatures of 1-3 x 10 to the 7th K. The inferred conductive heat flux of up to 10-billion ergs/s sq cm accounts for most of the energy released in the flares, implying that the flares were primarily thermal phenomena.

  17. The flash phase of solar flares - Satellite observations of electrons

    NASA Technical Reports Server (NTRS)

    Lin, R. P.

    1974-01-01

    Satellite observations of solar electrons bearing on flare particle acceleration and the generation of radio and X-ray emission are reviewed. The observations support a two-stage acceleration process for electrons, one stage commonly occurring at the flare flash phase and accelerating electrons up to about 100 keV, and a second stage occurring only in large proton flares and accelerating electrons up to relativistic energies. The location of the acceleration region appears to be no lower than the lower corona. The accelerated non-relativistic electrons generate type III radio burst emission as they escape from the sun. Direct spacecraft observations of the type III emission generated near 1 AU and the energetic electrons, provide quantitative information on the characteristics of the electrons exciting type III emission, the production of plasma waves, and the conversion from plasma waves to electromagnetic radiation.

  18. X-Class: A Guide to Solar Flares - Duration: 3 minutes, 2 seconds.

    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...

  19. Response of the Mars ionosphere to solar flares: Analysis of MGS radio occultation data

    NASA Astrophysics Data System (ADS)

    Fallows, K.; Withers, P.; Gonzalez, G.

    2015-11-01

    Increased soft X-ray irradiance during solar flares produces increased electron densities in the lower ionosphere of Mars, and the relative changes in electron density during a flare are greater for lower altitudes and larger flares. However, this relationship has not been quantified. This has impeded the validation of simulations of the ionospheric response to flares, which are necessary for developing accurate descriptions of the physical processes governing ionospheric behavior under extreme conditions. Here we develop a response function, a mathematical expression for the change in electron density during a solar flare as a function of the change in solar flux and an optical depth proxy. This function is based on analysis of 20 Mars Global Surveyor (MGS) radio occultation electron density profiles measured during solar flares. We find that characterizing the response as a function of optical depth, rather than altitude, provides the best description of ionospheric variability during a flare. A separate response function, determined from analysis of a numerical simulation of the response to a solar flare, was found to be grossly similar to the observationally based response function, though with a weaker dependence on optical depth. We identify 15 MGS profiles with an apparent solar flare response, but no coincident detected solar flare. We suggest that the observed response function can be used to detect flares not visible from Earth and to give an approximation of their strength. Additionally, it can estimate ionospheric electron densities during a flare; however, precision is limited by a small number of observations.

  20. A Unified Computational Model for Solar and Stellar Flares

    NASA Astrophysics Data System (ADS)

    Allred, Joel C.; Kowalski, Adam F.; Carlsson, Mats

    2015-08-01

    We present a unified computational framework that can be used to describe impulsive flares on the Sun and on dMe stars. The models assume that the flare impulsive phase is caused by a beam of charged particles that is accelerated in the corona and propagates downward depositing energy and momentum along the way. This rapidly heats the lower stellar atmosphere causing it to explosively expand and dramatically brighten. Our models consist of flux tubes that extend from the sub-photosphere into the corona. We simulate how flare-accelerated charged particles propagate down one-dimensional flux tubes and heat the stellar atmosphere using the Fokker-Planck kinetic theory. Detailed radiative transfer is included so that model predictions can be directly compared with observations. The flux of flare-accelerated particles drives return currents which additionally heat the stellar atmosphere. These effects are also included in our models. We examine the impact of the flare-accelerated particle beams on model solar and dMe stellar atmospheres and perform parameter studies varying the injected particle energy spectra. We find the atmospheric response is strongly dependent on the accelerated particle cutoff energy and spectral index.

  1. Temporal Variability of Ion Acceleration and Abundances in Solar Flares

    NASA Technical Reports Server (NTRS)

    Shih, Albert Y.

    2012-01-01

    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.

  2. Temporal Variability of Ion Acceleration and Abundances in Solar Flares

    NASA Technical Reports Server (NTRS)

    Shih, Albert

    2011-01-01

    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.

  3. Energy storage and deposition in a solar flare

    NASA Technical Reports Server (NTRS)

    Vorpahl, J. A.

    1976-01-01

    X-ray pictures of a solar flare taken with the S-056 X-ray telescope aboard Skylab are interpreted in terms of flare energy deposition and storage. The close similarity between calculated magnetic-field lines and the overall structure of the X-ray core is shown to suggest that the flare occurred in an entire arcade of loops. It is found that different X-ray features brightened sequentially as the flare evolved, indicating that some triggering disturbance moved from one side to the other in the flare core. A propagation velocity of 180 to 280 km/s is computed, and it is proposed that the geometry of the loop arcade strongly influenced the propagation of the triggering disturbance as well as the storage and site of the subsequent energy deposition. Some possible physical causes for the sequential X-ray brightening are examined, and a magnetosonic wave is suggested as the triggering disturbance. 'Correct' conditions for energy release are considered

  4. A Unified Computational Model for Solar and Stellar Flares

    NASA Astrophysics Data System (ADS)

    Allred, Joel; Kowalski, Adam; Carlsson, Mats

    2015-04-01

    We describe a unified computational framework which can be used to model impulsive flares on the Sun and on dMe stars. The models are constructed assuming that the flare impulsive phase is caused by a beam of charged particles (primarily electrons and protons) that is accelerated in the corona and propagates downward depositing energy and momentum along the way. This rapidly heats the lower stellar atmosphere causing it to explosively expand and emission to dramatically brighten. Our models consist of flux tubes that extend from the sub-photosphere into the corona. We simulate how these flare-accelerated particles propagate down one dimensional flux tubes and heat the stellar atmosphere using Fokker-Planck kinetic theory. Detailed radiative transfer is included so that model predictions can be directly compared with observations. The flux of flare-accelerated particles drives return currents which additionally heat the stellar atmosphere, and these effects are also included in our models. We examine the impact of the flare-accelerated particle beams on model solar and dMe stellar atmospheres and perform parameter studies varying the injected particle energy spectra. We find the atmospheric response is strongly dependent on the accelerated particle cutoff energy and spectral index.

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

    NASA Technical Reports Server (NTRS)

    Chupp, Edward L.

    1997-01-01

    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.

  6. HMI Observations of Solar Flares in Cycle 24

    NASA Astrophysics Data System (ADS)

    Hoeksema, J. Todd; Bobra, Monica; Couvidat, Sebastien; Sun, Xudong

    2015-08-01

    The Helioseismic and Magnetic Imager (HMI) on NASA’s Solar Dynamics Observatory (SDO) has continuously measured the vector magnetic field, intensity, and Doppler velocity in solar flares and over the entire solar disk since May 2010. The regular cadence of 45 seconds for line-of-sight and 12 minutes for vector measurements enables reliable investigations of photospheric conditions before, during, and after events both locally and globally. Active region indices can be tracked and conditions in the overlying corona can be modeled. A few examples show the utility of the data and demonstrate that some care must be exercised when the HMI data are used to investigate time variations.

  7. Particle acceleration and gamma-emission from solar flares

    NASA Astrophysics Data System (ADS)

    Miroshnichenko, Leonty; Gan, W. Q.; Troitskaia, E. V.

    Experiments on SMM, Yohkoh, GRANAT, Compton GRO, INTEGRAL, RHESSI and CORONAS-F satellites over the past three decades have provided copious data for fundamental research relating to particle acceleration, transport and energetics in flares and to the ambient abun-dance of the corona, chromosphere and photosphere. We summarize main results of solar gamma-astronomy and try to appraise critically a real contribution of those results into modern understanding of solar flares, particle acceleration at the Sun and some properties of the solar atmosphere. Recent findings based on the RHESSI, INTEGRAL and CORONAS-F measure-ments (source locations, spectrum peculiarities, 3He abundance etc.) are especially discussed. Some unusual features of extreme solar events have been found in gamma-ray production and generation of relativistic particles (solar cosmic rays). A number of different plausible assump-tions are considered concerning the details of underlying physical processes during large flares: existence of a steeper distribution of surrounding medium density, enhanced content of the 3He isotope, formation of magnetic trap with specific properties etc. Possible implications of these results are briefly discussed. It is emphasized that real progress in this field may be achieved only by combination of gamma-ray data in different energy ranges with multi-wave and ener-getic particle observations during the same event. We especially note several promising lines for the further studies: 1) resonant acceleration of the 3He ions in the corona; 2) timing of the flare evolution by gamma-ray fluxes in energy range above 90 MeV; 3) separation of gamma-ray fluxes from different sources at/near the Sun (e.g., different acceleration sources/episodes during the same flare, contribution of energetic particles accelerated by the CME-driven shocks etc.); 4) modeling of self-consistent time scenario of the event. Keywords: Sun: atmosphere density, solar flares; Particle acceleration: source location, energy spectrum; Gamma rays: annihilation and de-excitation lines, neutron capture line, pion decay emission

  8. Energy-dependent timing of thermal emission in solar flares

    NASA Astrophysics Data System (ADS)

    Jain, Rajmal; Rajpurohit, Arvind; Awasthi, Arun; Aschwanden, Markus

    A study of thermal emission in solar flares using high-resolution X-ray spectra observed by the Si detector onboard "Solar X-ray Spectrometer" (SOXS) has been conducted. The SOXS onboard GSAT-2 Indian spacecraft was launched by GSLV-D2 rocket on 08 May 2003. With this we investigate the energy dependent timing of thermal emission in solar flares. Firstly we model the spectral-temporal evolution of the X-ray flux F(e,t) assuming multi-temperature plasma governed by thermal conduction cooling. This model is found in agreement with the temperature and emission measure derived from the fitting of the spectra observed by the Si detector. We investigate 10 M-class flares and found that the emission in the energy range e=6 -20 keV is dominated by temperatures T=15 -50 MK while the power-law index (gamma) of the thermal spectrum varies over 2.7 -4.3. The temperature-dependent cooling time varies between 22 and 310 s. The electron density (ne) obtained for the flares under investigation ranges between 0.03 and 5X1011 cm-3 suggests that conduction cooling of thermal X-ray plasma dominates over radiative cooling in the initial phase of the flare. The current study also provides an alternative method for separating thermal from non-thermal spectra, which enables us to measure the break-energy point to be varying between 17 and 220.7 keV.

  9. Ensemble forecasting of major solar flares: First results

    NASA Astrophysics Data System (ADS)

    Guerra, J. A.; Pulkkinen, A.; Uritsky, V. M.

    2015-10-01

    We present the results from the first ensemble prediction model for major solar flares (M and X classes). The primary aim of this investigation is to explore the construction of an ensemble for an initial prototyping of this new concept. Using the probabilistic forecasts from three models hosted at the Community Coordinated Modeling Center (NASA-GSFC) and the NOAA forecasts, we developed an ensemble forecast by linearly combining the flaring probabilities from all four methods. Performance-based combination weights were calculated using a Monte Carlo-type algorithm that applies a decision threshold Pth to the combined probabilities and maximizing the Heidke Skill Score (HSS). Using the data for 13 recent solar active regions between years 2012 and 2014, we found that linear combination methods can improve the overall probabilistic prediction and improve the categorical prediction for certain values of decision thresholds. Combination weights vary with the applied threshold and none of the tested individual forecasting models seem to provide more accurate predictions than the others for all values of Pth. According to the maximum values of HSS, a performance-based weights calculated by averaging over the sample, performed similarly to a equally weighted model. The values Pth for which the ensemble forecast performs the best are 25% for M-class flares and 15% for X-class flares. When the human-adjusted probabilities from NOAA are excluded from the ensemble, the ensemble performance in terms of the Heidke score is reduced.

  10. On the rate of energy input in thermal solar flares

    NASA Technical Reports Server (NTRS)

    Feldman, U.; Doschek, G. A.; Mckenzie, D. L.

    1984-01-01

    The rise phases of solar soft X-ray flares observed by X-ray crystal spectrometers on P78-1 are discussed in terms of the rate of change of X-ray flux as a function of time. It is shown that the flux increases exponentially over most of the rise time. The e-folding time (tau) has a cutoff at approximately 13 s. Soft X-ray flares with smaller values of tau are not observed. It is suggested that this phenomenon is due to the ability of the solar atmosphere to absorb the input energy and convert it into a typical soft X-ray flare, when the value of tau is greater than about 13 s. For energy input rates with tau greater than about 13 s, the temperature attained by the plasma is typically around 2 x 10 to the 7th K, but for values of tau less than 13 s, the gas is heated to much higher temperatures (about 10 to the 8th K), producing a certain class of hard X-ray flares.

  11. A laboratory solar flare simulation using colinear bipolar flux pairs

    NASA Astrophysics Data System (ADS)

    Crockett, G. A.

    1980-08-01

    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.

  12. Modelling the influence of photospheric turbulence on solar flare statistics.

    PubMed

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

    2014-01-01

    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

  13. SHORT-TERM SOLAR FLARE PREDICTION USING MULTIRESOLUTION PREDICTORS

    SciTech Connect

    Yu Daren; Huang Xin; Hu Qinghua; Zhou Rui; Wang Huaning; Cui Yanmei

    2010-01-20

    Multiresolution predictors of solar flares are constructed by a wavelet transform and sequential feature extraction method. Three predictors-the maximum horizontal gradient, the length of neutral line, and the number of singular points-are extracted from Solar and Heliospheric Observatory/Michelson Doppler Imager longitudinal magnetograms. A maximal overlap discrete wavelet transform is used to decompose the sequence of predictors into four frequency bands. In each band, four sequential features-the maximum, the mean, the standard deviation, and the root mean square-are extracted. The multiresolution predictors in the low-frequency band reflect trends in the evolution of newly emerging fluxes. The multiresolution predictors in the high-frequency band reflect the changing rates in emerging flux regions. The variation of emerging fluxes is decoupled by wavelet transform in different frequency bands. The information amount of these multiresolution predictors is evaluated by the information gain ratio. It is found that the multiresolution predictors in the lowest and highest frequency bands contain the most information. Based on these predictors, a C4.5 decision tree algorithm is used to build the short-term solar flare prediction model. It is found that the performance of the short-term solar flare prediction model based on the multiresolution predictors is greatly improved.

  14. Nuclear gamma rays from solar flares. [analysis of theory of gamma ray line emission from solar flares

    NASA Technical Reports Server (NTRS)

    Ramaty, R.; Lingenfelter, R. E.

    1973-01-01

    The theory of gamma-ray line emission from solar flares is reviewed and revised. It is shown that the line emissions at 0.5, 2.2, 4.4, and 6.1 MeV are due to positron annihilation, deuterium deexcitation following neutron capture on hydrogen, and the deexcitation of excited states in carbon and oxygen. From the observed relative line intensities it is possible to determine the spectrum of accelerated protons in the flare region. This spectrum is found to be very similar to that of charged particles from the flare observed near earth. The total number of protons at the sun is deduced from the observed absolute line intensities for various interaction models.

  15. THz photometers for solar flare observations from space

    NASA Astrophysics Data System (ADS)

    Kaufmann, Pierre; Marcon, Rogrio; Abrantes, Andr; Bortolucci, Emilio C.; T. Fernandes, Luis Olavo; Kropotov, Grigory I.; Kudaka, Amauri S.; Machado, Nelson; Marun, Adolfo; Nikolaev, Valery; Silva, Alexandre; da Silva, Claudemir S.; Timofeevsky, Alexander

    2014-11-01

    The search for the still unrevealed spectral shape of the mysterious THz solar flare emissions is one of the current most challenging research issues. The concept, fabrication and performance of a double THz photometer system, named SOLAR-T, is presented. Its innovative optical setup allows observations of the full solar disk and the detection of small burst transients at the same time. The detecting system was constructed 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. Tests have been conducted to confirm the entire system performance, on ambient and low pressure and temperature conditions. An artificial Sun setup was developed to simulate performance on actual observations. The experiment is planned to be on board of two long-duration stratospheric balloon flights over Antarctica and Russia in 2014-2016.

  16. THE THERMAL PROPERTIES OF SOLAR FLARES OVER THREE SOLAR CYCLES USING GOES X-RAY OBSERVATIONS

    SciTech Connect

    Ryan, Daniel F.; Gallagher, Peter T.; Milligan, Ryan O.; Dennis, Brian R.; Kim Tolbert, A.; Schwartz, Richard A.; Alex Young, C.

    2012-10-15

    Solar flare X-ray emission results from rapidly increasing temperatures and emission measures in flaring active region loops. To date, observations from the X-Ray Sensor (XRS) on board the Geostationary Operational Environmental Satellite (GOES) have been used to derive these properties, but have been limited by a number of factors, including the lack of a consistent background subtraction method capable of being automatically applied to large numbers of flares. In this paper, we describe an automated Temperature and Emission measure-Based Background Subtraction method (TEBBS), that builds on the methods of Bornmann. Our algorithm ensures that the derived temperature is always greater than the instrumental limit and the pre-flare background temperature, and that the temperature and emission measure are increasing during the flare rise phase. Additionally, TEBBS utilizes the improved estimates of GOES temperatures and emission measures from White et al. TEBBS was successfully applied to over 50,000 solar flares occurring over nearly three solar cycles (1980-2007), and used to create an extensive catalog of the solar flare thermal properties. We confirm that the peak emission measure and total radiative losses scale with background subtracted GOES X-ray flux as power laws, while the peak temperature scales logarithmically. As expected, the peak emission measure shows an increasing trend with peak temperature, although the total radiative losses do not. While these results are comparable to previous studies, we find that flares of a given GOES class have lower peak temperatures and higher peak emission measures than previously reported. The TEBBS database of flare thermal plasma properties is publicly available at http://www.SolarMonitor.org/TEBBS/.

  17. The Thermal Properties of Solar Flares over Three Solar Cycles Using GOES X-Ray Observations

    NASA Astrophysics Data System (ADS)

    Ryan, Daniel F.; Milligan, Ryan O.; Gallagher, Peter T.; Dennis, Brian R.; Tolbert, A. Kim; Schwartz, Richard A.; Young, C. Alex

    2012-10-01

    Solar flare X-ray emission results from rapidly increasing temperatures and emission measures in flaring active region loops. To date, observations from the X-Ray Sensor (XRS) on board the Geostationary Operational Environmental Satellite (GOES) have been used to derive these properties, but have been limited by a number of factors, including the lack of a consistent background subtraction method capable of being automatically applied to large numbers of flares. In this paper, we describe an automated Temperature and Emission measure-Based Background Subtraction method (TEBBS), that builds on the methods of Bornmann. Our algorithm ensures that the derived temperature is always greater than the instrumental limit and the pre-flare background temperature, and that the temperature and emission measure are increasing during the flare rise phase. Additionally, TEBBS utilizes the improved estimates of GOES temperatures and emission measures from White et al. TEBBS was successfully applied to over 50,000 solar flares occurring over nearly three solar cycles (1980-2007), and used to create an extensive catalog of the solar flare thermal properties. We confirm that the peak emission measure and total radiative losses scale with background subtracted GOES X-ray flux as power laws, while the peak temperature scales logarithmically. As expected, the peak emission measure shows an increasing trend with peak temperature, although the total radiative losses do not. While these results are comparable to previous studies, we find that flares of a given GOES class have lower peak temperatures and higher peak emission measures than previously reported. The TEBBS database of flare thermal plasma properties is publicly available at http://www.SolarMonitor.org/TEBBS/.

  18. The beam-driven chromospheric evaporation model of solar flares - A model not supported by observations from nonimpulsive large flares

    NASA Technical Reports Server (NTRS)

    Feldman, U.

    1990-01-01

    Most large solar flares exhibit hard X-ray emission which is usually impulsive, as well as thermal soft X-ray emission, which is gradual. The beam-driven chromospheric evaporation model of solar flares was proposed to explain the origin of the soft X-ray emitting flare plasma. A careful evaluation of the issue under discussion reveals contradictions between predictions from the theoretical chromospheric evaporation model and actual observations from a set of large X- and M-type flares. It is shown that although the soft X-ray and hard X-ray emissions are a result of the same flare, one is not a result of the other.

  19. Solar Flares and Proton Events driving particle precipitation at higher latitudinal geomagnetic environment

    NASA Astrophysics Data System (ADS)

    Tripathi, S. C.; Khan, P. A.; Gwal, A. K.; Purohit, P. K.

    2013-12-01

    Solar flares, a solar transient producing radiation storm, are thought to be produced at the corona due to magnetic reconnection at solar corona and Solar Energetic particles, another solar transient, are the shower of high energy charged particles and are hazardous to the space environment have good association in their genesis. Spectral analysis of the solar flares associated with the solar proton events make us infer that the solar protons are produced in association with those solar flares which has SHH spectral behavior. These solar protons after interaction with earth's magnetic environment precipitate at the higher latitudinal magnetic environment and have good association with the high latitudinal geomagnetic index PC and its growth rate, which shows that the disturbances in the high latitudinal geomagnetic environment have the close connection with the solar energetic particle events. For the present study 50 solar energetic particle events and their associated flares of 23 solar cycle have been taken into consideration.

  20. High-Energy Aspects of Solar Flares: Observations and Models

    SciTech Connect

    Liu, Wei; Guo, Fan

    2015-07-21

    The paper begins by describing the structure of the Sun, with emphasis on the corona. The Sun is a unique plasma laboratory, which can be probed by Sun-grazing comets, and is the driver of space weather. Energization and particle acceleration mechanisms in solar flares is presented; magnetic reconnection is key is understanding stochastic acceleration mechanisms. Then coupling between kinetic and fluid aspects is taken up; the next step is feedback of atmospheric response to the acceleration process – rapid quenching of acceleration. Future challenges include applications of stochastic acceleration to solar energetic particles (SEPs), Fermi γ-rays observations, fast-mode magnetosonic wave trains in a funnel-shaped wave guide associated with flare pulsations, and the new SMEX mission IRIS (Interface Region Imaging Spectrograph),

  1. RADIO EMISSION FROM ACCELERATION SITES OF SOLAR FLARES

    SciTech Connect

    Li Yixuan; Fleishman, Gregory D. E-mail: gfleishm@njit.edu

    2009-08-10

    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.

  2. A Statistical Study of Spectral Hardening in Solar Flares and Related Solar Energetic Particle Events

    NASA Astrophysics Data System (ADS)

    Grayson, J.; Krucker, S.; Lin, R. P.

    2009-12-01

    Using hard X-ray observations from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), we investigate the reliability of spectral hardening during solar flares as an indicator of related solar energetic particle (SEP) events at Earth. All RHESSI data are analyzed, from February 2002 through the end of Solar Cycle 23, thereby expanding upon recent work on a smaller sample of flares. Previous investigations have found very high success when associating soft-hard-harder (SHH) spectral behavior with energetic proton events, and confirmation of this link would suggest a correlation between electron acceleration in solar flares and SEPs seen in interplanetary space. In agreement with these past findings, we find that of 37 magnetically well-connected flares (W30-W90), 12 of 18 flares with SHH behavior produced SEP events and none of 19 flares without SHH behavior produced SEPs. This demonstrates a statistically significant dependence of SHH and SEP observations, a link that is unexplained in the standard scenario of SEP acceleration at the shock front of coronal mass ejections, and encourages further investigation of the mechanisms which could be responsible.

  3. A Statistical Study of Spectral Hardening in Solar Flares and Related Solar Energetic Particle Events

    NASA Astrophysics Data System (ADS)

    Grayson, James A.; Krucker, Sm; Lin, R. P.

    2009-12-01

    Using hard X-ray observations from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), we investigate the reliability of spectral hardening during solar flares as an indicator of related solar energetic particle (SEP) events at Earth. All RHESSI data are analyzed, from 2002 February through the end of Solar Cycle 23, thereby expanding upon recent work on a smaller sample of flares. Previous investigations have found very high success when associating soft-hard-harder (SHH) spectral behavior with energetic proton events, and confirmation of this link would suggest a correlation between electron acceleration in solar flares and SEPs seen in interplanetary space. In agreement with these past findings, we find that of 37 magnetically well-connected flares (W30-W90), 12 of 18 flares with SHH behavior produced SEP events and none of 19 flares without SHH behavior produced SEPs. This demonstrates a statistically significant dependence of SHH and SEP observations, a link that is unexplained in the standard scenario of SEP acceleration at the shock front of coronal mass ejections and encourages further investigation of the mechanisms which could be responsible.

  4. A STATISTICAL STUDY OF SPECTRAL HARDENING IN SOLAR FLARES AND RELATED SOLAR ENERGETIC PARTICLE EVENTS

    SciTech Connect

    Grayson, James A.; Krucker, Saem; Lin, R. P. E-mail: krucker@ssl.berkeley.ed

    2009-12-20

    Using hard X-ray observations from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), we investigate the reliability of spectral hardening during solar flares as an indicator of related solar energetic particle (SEP) events at Earth. All RHESSI data are analyzed, from 2002 February through the end of Solar Cycle 23, thereby expanding upon recent work on a smaller sample of flares. Previous investigations have found very high success when associating soft-hard-harder (SHH) spectral behavior with energetic proton events, and confirmation of this link would suggest a correlation between electron acceleration in solar flares and SEPs seen in interplanetary space. In agreement with these past findings, we find that of 37 magnetically well-connected flares (W30-W90), 12 of 18 flares with SHH behavior produced SEP events and none of 19 flares without SHH behavior produced SEPs. This demonstrates a statistically significant dependence of SHH and SEP observations, a link that is unexplained in the standard scenario of SEP acceleration at the shock front of coronal mass ejections and encourages further investigation of the mechanisms which could be responsible.

  5. Far infrared observations of solar flares during the next solar maximum

    NASA Astrophysics Data System (ADS)

    Trottet, G.; Klein, K.-L.; Molodij, G.; Smery, A.

    Observations of the Sun at near-infrared wavelengths brought major advances in our knowledge of magnetic fields in the solar atmosphere and of magnetic structures in the corona The infrared spectrum also holds promise for a better understanding of solar flares However at present there is a gap of two orders of magnitude between solar flare observations at submillimeter and near-infrared wavelengths We propose a pioneer experiment DESIR Detection of Eruptive Solar Infra Red emission dedicated to the first ever measurements of solar flares at far infrared wavelengths There we expect basically two emission processes that provide crucial information on particle acceleration and energy transport in flares the synchrotron emission of relativistic electrons and positrons and the transient thermal emission of the low chromosphere in response to energy transport from coronal flaring regions Observing continuum emission in this range with a typical time resolution of a second will bring us the most stringent test of particle acceleration at the Sun as well as an unprecedented and powerful means to probe the thermal response of low atmospheric layers The scientific rationale of DESIR will be discussed along with very recent first observations of flares at submillimetre wavelengths which show us some glimpses of the processes we may deal with in the far infrared range The DESIR instrument is presently under study It is part of the payload proposed for the project of a French-Chinese microsatellite SMESE which enters phase A studies in June 2006 and which should

  6. Implications of high-energy neutron observations from solar flares

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

    The time-dependent flux of high-energy neutrons discovered from the solar flare of 1980 June 21 provides a new technique for determining the total number and energy spectrum of accelerated protons and nuclei at the sun. The implications of these observations on gamma-ray emission, relativistic electron spectrum and number, proton and electron energy contents, and the location of the interaction region are also examined.

  7. The origin and implications of gamma rays from solar flares

    NASA Technical Reports Server (NTRS)

    Ramaty, R.

    1975-01-01

    Solar flares studied in the gamma ray region provide essential information on accelerated nuclei that can be obtained in no other way. A multitude of physical processes, such as particle acceleration, nuclear reactions, positron and neutron physics, and kinematical line broadening, come into consideration at gamma ray energies. Gamma ray observations are complementary to hard X ray observations, since both provide information on accelerated particles. It appears that only in the gamma ray region do these particles produce distinct spectral lines.

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

    SciTech Connect

    Lobzin, Vasili; Cairns, Iver H.; Robinson, Peter A.

    2011-07-20

    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.

  9. DOES A SCALING LAW EXIST BETWEEN SOLAR ENERGETIC PARTICLE EVENTS AND SOLAR FLARES?

    SciTech Connect

    Kahler, S. W.

    2013-05-20

    Among many other natural processes, the size distributions of solar X-ray flares and solar energetic particle (SEP) events are scale-invariant power laws. The measured distributions of SEP events prove to be distinctly flatter, i.e., have smaller power-law slopes, than those of the flares. This has led to speculation that the two distributions are related through a scaling law, first suggested by Hudson, which implies a direct nonlinear physical connection between the processes producing the flares and those producing the SEP events. We present four arguments against this interpretation. First, a true scaling must relate SEP events to all flare X-ray events, and not to a small subset of the X-ray event population. We also show that the assumed scaling law is not mathematically valid and that although the flare X-ray and SEP event data are correlated, they are highly scattered and not necessarily related through an assumed scaling of the two phenomena. An interpretation of SEP events within the context of a recent model of fractal-diffusive self-organized criticality by Aschwanden provides a physical basis for why the SEP distributions should be flatter than those of solar flares. These arguments provide evidence against a close physical connection of flares with SEP production.

  10. Solar Flare Induced Ionospheric Perturbations Observed by VLF Sferic Propagation

    NASA Astrophysics Data System (ADS)

    McCormick, J.; Cohen, M.

    2014-12-01

    VLF waves are a useful diagnostic for D-region ionospheric disturbances due to their efficient global propagation. The D-region is too high for balloons, too low for satellites, and not ionized enough for radar reflections. Traditionally, ionosphere disturbances have been sensed using dedicated VLF transmitters allowing for only single propagation path analysis since there are only a handful of transmitters. A lightning stroke, however, releases an intense amount of VLF radio energy known as a Radio Atmospheric, or 'sferic' which propagates through the Earth-ionosphere waveguide. Lightning is globally spread and very frequent, so a sferic is therefore also a useful diagnostic of the D-region when ionized by solar flare x-ray bursts.We present observations of lightning-generated sferics during strong solar flares. The advantage to using sferics is that many individual thunderstorms effectively act as separate VLF transmitting sources. During the solar flare there is a significant change in magnitude and frequency content of sferics. This disturbance varies with distance from the source. The difference in magnitude and arrival time of these sferics have local maximums and minimums, and appears to oscillate with distance. We utilize modeling of the Earth-ionosphere system to explain the results.

  11. A brief review of solar flare effects on the ionosphere

    NASA Astrophysics Data System (ADS)

    Tsurutani, B. T.; Verkhoglyadova, O. P.; Mannucci, A. J.; Lakhina, G. S.; Li, G.; Zank, G. P.

    2009-07-01

    The study of solar flare effects (SFEs) on the ionosphere is having a renaissance. The development of GPS ground and satellite data for scientific use has opened up new means for high time resolution research on SFEs. At present, without continuous flare photon spectra (X rays, EUV, UV, and visible) monitoring instrumentation, the best way to model flare spectral changes within a flare is through ionospheric GPS studies. Flare EUV photons can increase the total electron content of the subsolar ionosphere by up to 30% in 5 min. Energetic particles (ions) of 10 keV to GeV energies are accelerated at the flare site. Electrons with energies up to several MeV are also created. A coronal mass ejection (CME) is launched from the Sun at the time of the flare. Fast interplanetary CMEs (ICMEs) have upstream shocks which accelerate ions to 10 keV to 10 MeV. Both sources of particles, when magnetically connected to the Earth's magnetosphere, enter the magnetosphere and the high-latitude and midlatitude ionosphere. Those particles that precipitate into the ionosphere cause rapid increases in the polar atmospheric ionization, disruption of transpolar communication, and cause ozone destruction. Complicating the picture, when the ICME reaches the magnetosphere 1 to 4 days later, shock compression of the magnetosphere energizes preexisting 10-100 keV magnetospheric electrons and ions, causing precipitation into the dayside auroral zone (60-65 MLAT) ionospheres. Shock compression can also trigger supersubstorms in the magnetotail with concomitant energetic particle precipitation into the nightside auroral zones. If the interplanetary sheath or ICME magnetic fields are southwardly directed and last for several hours, a geomagnetic storm will result. A magnetic storm is characterized by the formation of an unstable ring current with energetic particles in the range 10 keV to 500 keV. The ring current decays away by precipitation into the middle latitude ionosphere over timescales of 10 h. A schematic of a time line for the above SFE ionospheric effects is provided. Descriptions of where in the ionosphere and in what time sequence is provided in the body of the text. Much of the terminology presently in use describing solar, interplanetary, magnetospheric, and ionospheric SFE-related phenomena are dated. We suggest physics-based terms be used in the future.

  12. Cosmic ray anisotropies late in a solar flare event

    NASA Technical Reports Server (NTRS)

    Allum, F. R.; Mccracken, K. G.; Rao, U. R.; Palmeira, R. A. R.; Fairfield, D. H.; Gleeson, L. J.

    1974-01-01

    The detailed relationship between the anisotropy characteristics observed during late times in the decay of a solar flare event and the interplanetary magnetic field parameters is investigated. The anisotropy always is from 45 deg east of the earth-sun line. This direction is approximately perpendicular to the nominal Archimedean spiral, independent of the particle energy. The amplitude of the anisotropy increases as the magnetic field azimuthal direction shows greater departure from the radial direction. These results are discussed in terms of current ideas about solar particle propagation in the interplanetary space.

  13. Theoretical aspects related to plasma flows observed in solar flares

    NASA Astrophysics Data System (ADS)

    Somov, Boris

    I review the current state of affairs in the magnetohydrodynamic theories and models for large-scale high-speed plasma flows in solar flares. Main attension is payed to the coronal signatures and their relation to the photosphere and the heliosphere.The large-scale structure and dynamics of coronal plasma flows, as seen in EUV and soft X-rays, can be explained in terms of the three-dimensional reconnection at magnetic separators in the corona. More specifically, this reconnection is determined by the large-scale photospheric flows mainly of two types. First, the shear flows, which are parallel to the photospheric neutral line, increase the length of field lines in the corona an excess of magnetic energy. Second, the converging flows, directed to the neutral line, create the preflare slowly-reconnecting current layers in the corona and provide an excess of energy sufficient to produce a large flare. During the flare, both excesses of energy are released mainly as fast flows of coronal plasma as well as powerful heat fluxes and accelerated particles. The impulsive heating of the upper chromosphere creates a fast expansion of high-temperature plasma upwards into the corona, called the chromospheric `evaporation'. Basic properties of such flows are also reviewed together with draining with cooling. Ref.: Somov B.V., Plasma Astrophysics, Part II, Reconnection and Flares. Second Edition. Springer SBM, New York, 2013.

  14. The impulsive hard X-rays from solar flares

    NASA Technical Reports Server (NTRS)

    Leach, J.

    1984-01-01

    A technique for determining the physical arrangement of a solar flare during the impulsive phase was developed based upon a nonthermal model interpretation of the emitted hard X-rays. Accurate values are obtained for the flare parameters, including those which describe the magnetic field structure and the beaming of the energetic electrons, parameters which have hitherto been mostly inaccessible. The X-ray intensity height structure can be described readily with a single expression based upon a semi-empirical fit to the results from many models. Results show that the degree of linear polarization of the X-rays from a flaring loop does not exceed 25 percent and can easily and naturally be as low as the polarization expected from a thermal model. This is a highly significant result in that it supersedes those based upon less thorough calculations of the electron beam dynamics and requires that a reevaluation of hopes of using polarization measurements to discriminate between categories of flare models.

  15. Solar Flare Impulsive Phase Emission Observed with SDO/EVE

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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.

  16. Solar flare impulsive phase emission observed with SDO/EVE

    SciTech Connect

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

    2013-12-10

    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 T{sub e} = 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.

  17. Ultraviolet spectral diagnostics of solar flares and heating events

    SciTech Connect

    Porter, J.G.

    1984-01-01

    Heating processes in the outer solar atmosphere manifest themselves in continuous and discrete phenomena ranging from the largest solar flares down to the smallest events discernible with present instruments. This thesis addresses two such phenomena as seen in ultraviolet observations of the solar transition zone: data obtained with the Solar Maximum Mission (SMM) satellite are found to reveal the presence of frequent and rapid brightenings in ultraviolet line emission in active regions, and observations obtained with the NRL Slitless Spectroheliograph on Skylab are analyzed to determine the role of the helium resonance lines in the energy balance of a large class M flare. SMM observations with high spatial and temporal resolution at small bright sites in active regions show significant increases in intensity in spectral lines of Si IV and O IV on short time scales. Intensity increases of 20 - 100% are common and typically last 40 - 60s. These characteristics suggest that topological dissipation of energy stored in the magnetic field is occurring more frequently and on smaller spatial scales than previously observed. Such events may constitute a large fraction of the energy budget of the outer solar atmosphere.

  18. Solar flare protection for manned lunar missions - Analysis of the October 1989 proton flare event

    SciTech Connect

    Simonsen, L.C.; Nealy, J.E.; Townsend, L.W.; Sauer, H.H. NOAA, Space Environment Laboratory, Boulder, CL )

    1991-07-01

    Several large solar proton events occurred in the latter half of 1989. For a moderately shielded spacecraft in free space, the potential exposure would have been greatest for the flare which occurred between October 19 to 27, 1989. The temporal variations of the proton energy spectra at approximately 1 AU were monitored by the GOES-7 satellite. These data, recorded and processed at the NOAA-Boulder Space Environment Laboratory, provide the opportunity to analyze dose rates and cumulative doses which might be incurred by astronauts in transit to, or on, the moon. Of particular importance in such an event is the time development of exposure in the early phases of the flare, for which dose rates may range over many orders of magnitude in the first few hours. The cumulative dose as a function of time for the entire event is also predicted. In addition to basic shield calculations, dose rate contours are constructed for flare shelters in free-space and on the lunar surface. 14 refs.

  19. Study on the triggering process of solar flares based on Hinode/SOT observations

    SciTech Connect

    Bamba, Y.; Kusano, K.; Yamamoto, T. T.; Okamoto, T. J.

    2013-11-20

    We investigated four major solar flare events that occurred in active regions NOAA 10930 (2006 December 13 and 14) and NOAA 11158 (2011 February 13 and 15) by using data observed by the Solar Optical Telescope on board the Hinode satellite. To reveal the trigger mechanism of solar flares, we analyzed the spatio-temporal correlation between the detailed magnetic field structure and the emission image of the Ca II H line at the central part of flaring regions for several hours prior to the onset of the flares. In all the flare events, we observed that the magnetic shear angle in the flaring regions exceeded 70°, as well as that characteristic magnetic disturbances developed at the centers of flaring regions in the pre-flare phase. These magnetic disturbances can be classified into two groups depending on the structure of their magnetic polarity inversion lines; the so-called opposite-polarity and reversed-shear magnetic field recently proposed by our group, although the magnetic disturbance in one event of the four samples is too subtle to clearly recognize the detailed structure. The result suggests that some major solar flares are triggered by rather small magnetic disturbances. We also show that the critical size of the flare-trigger field varies among flare events and briefly discuss how the flare-trigger process depends on the evolution of active regions.

  20. Short-Term Solar Flare Prediction Using Predictor Teams

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

    A short-term solar flare prediction model is built using predictor teams rather than an individual set of predictors. The information provided by the set of predictors could be redundant. So it is necessary to generate subsets of predictors which can keep the information constant. These subsets are called predictor teams. In the framework of rough set theory, predictor teams are constructed from sequences of the maximum horizontal gradient, the length of neutral line and the number of singular points extracted from SOHO/MDI longitudinal magnetograms. Because of the instability of the decision tree algorithm, prediction models generated by the C4.5 decision tree for different predictor teams are diverse. The flaring sample, which is incorrectly predicted by one model, can be correctly forecasted by another one. So these base prediction models are used to construct an ensemble prediction model of solar flares by the majority voting rule. The experimental results show that the predictor team can keep the distinguishability of the original set, and the ensemble prediction model can obtain better performance than the model based on the individual set of predictors.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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.

  2. Energetic particles in solar flares. Chapter 4 in the proceedings of the 2nd Skylab Workshop on Solar Flares

    NASA Technical Reports Server (NTRS)

    Ramaty, R.; Colgate, S. A.; Dulk, G. A.; Hoyng, P.; Knight, J. W., III; Lin, R. P.; Melrose, D. B.; Paizis, C.; Orrall, F.; Shapiro, P. R.

    1978-01-01

    The recent direct observational evidence for the acceleration of particles in solar flares, i.e. radio emission, bremsstrahlung X-ray emission, gamma-ray line and continuum emission, as well as direct observations of energetic electrons and ions, are discussed and intercorrelated. At least two distinct phases of acceleration of solar particles exist that can be distinguished in terms of temporal behavior, type and energy of particles accelerated and the acceleration mechanism. Bulk energization seems the likely acceleration mechanism for the first phase while Fermi mechanism is a viable candidate for the second one.

  3. A mechanism for deep chromospheric heating during solar flares

    NASA Technical Reports Server (NTRS)

    Machado, M. E.; Emslie, A. G.; Mauas, P. J.

    1986-01-01

    The role of the negative hydrogen ion, H(-), in the energy balance of the deep solar chromosphere is reexamined and it is found, in contrast with earlier authors, that H(-) is a source of heating at these levels. The response of this region to an ionizing flux of flare-associated UV radiation (1500 to 1900 A) is then addressed: it is found that the excess ionization of Si to Si(+) increases the local electron number density considerably, since most species are largely neutral at deep chromospheric levels. This in turn increases the electron-hydrogen atom association rate, the H(-) abundance, and the rate of absorption of photospheric radiation by this ion. It is found that the excess absorption by this process may lead to a substantial temperature enhancement at temperature minimum levels during flares.

  4. Complex Dynamic Flows in Solar Flare Sheet Structures

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

    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.

  5. GENERIC MODEL FOR MAGNETIC EXPLOSIONS APPLIED TO SOLAR FLARES

    SciTech Connect

    Melrose, D. B.

    2012-04-10

    An accepted model for magnetospheric substorms is proposed as the basis for a generic model for magnetic explosions and is applied to solar flares. The model involves widely separated energy-release and particle-acceleration regions, with energy transported Alfvenically between them. On a global scale, these regions are coupled by a large-scale current that is set up during the explosion by redirection of pre-existing current associated with the stored magnetic energy. The explosion-related current is driven by an electromotive force (EMF) due to the changing magnetic flux enclosed by this current. The current path and the EMF are identified for an idealized quadrupolar model for a flare.

  6. Singly charged energetic helium emitted in solar flares

    NASA Technical Reports Server (NTRS)

    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

    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.

  7. Measurements on a shock wave generated by a solar flare

    NASA Technical Reports Server (NTRS)

    Maxwell, A.; Dryer, M.

    1982-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Canfield, Richard C.; Dennis, Brian R.

    1988-01-01

    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.

  9. A model solar flares and their homologous behavior

    SciTech Connect

    Choe, G.S.; Cheng, C.Z.

    2000-01-27

    A model describing physical processes of solar flares and their homologous behavior is presented based on resistive MHD simulations of magnetic arcade evolution subject to continuous shear-increasing footpoint motions. It is proposed in the model that the individual flaring process encompasses magnetic reconnection of arcade field lines, generation of magnetic islands in the magnetic arcade, and coalescence of magnetic islands. When a magnetic arcade is sheared, a current sheet is formed and magnetic reconnection can take place to form a magnetic island. A continuing increase of magnetic shear can trigger a new reconnection process and create another island in the underlying arcade below the magnetic island. The newborn island rises faster than the preceding island and merges with it to form one island. Before merging with the upper island is completed, the newborn island exhibits two different phases of rising motion: the first phase with a slower rising speed and the second phase wit h a faster rising speed. This is consistent with the Yohkoh observation by Ohyama and Shibata (1998) of X-ray plasma ejecta motion. The first phase, in which reconnection of line-tied field in the underlying arcade is important, can be regarded to be related with the preflare phase. In the second phase, the island coalescence takes place, which creates an elongated current sheet below and enhances the reconnection rate of the line-tied arcade field. This phase is interpreted as the impulsive phase or the flash phase of flares. The obtained reconnection electric field is large enough to accelerate electrons to an energy level higher than 10 keV, which is necessary for observed X-ray emissions. After merging of the islands is completed, magnetic reconnection continues in the current sheet under the integrated island for rather a long period, which can be considered as the main phase of flares. The sequence of all these processes is repeated with some time interval while a shear-increasing motion continues. The authors propose that a series of these flaring processes constitutes a set of homologous flares. The time interval between successive flaring events depends on the energy input rate into the system, which is governed by the nature of the footpoint motion and the flux reconnecting rate. They have also investigated the destruction of a magnetic island in a system undergoing a decrease of magnetic shear. The result suggests that there is a critical value of magnetic shear for existence of a magnetic island in an arcade-like field configuration.

  10. Observations of solar flares with IRIS and SDO

    NASA Astrophysics Data System (ADS)

    Li, D.; Innes, D. E.; Ning, Z. J.

    2016-03-01

    Flare kernels brighten simultaneously in all Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) channels making it difficult to determine their temperature structure. The Interface Region Imaging Spectrograph (IRIS) is able to spectrally resolve Fe xxi emission from cold chromospheric brightenings, so it can be used to infer the amount of Fe xxi emission in the 131 Å AIA channel. We use observations of two small solar flares seen by IRIS and SDO to compare the emission measures (EMs) deduced from the IRIS Fe xxi line and the AIA 131 Å channel to determine the fraction of Fe xxi emission in flare kernels in the 131 Å channel of AIA. Cotemporal and cospatial pseudo-raster AIA images are compared with the IRIS results. We use multi-Gaussian line fitting to separate the blending chromospheric emission so as to derive Fe xxi intensities and Doppler shifts in IRIS spectra. We define loop and kernel regions based on the brightness of the 131 Å and 1600 Å intensities. In the loop regions the Fe xxi EMs are typically 80% of the 131 Å values, and range from 67% to 92%. Much of the scatter is due to small misalignments, but the largest site with low Fe xxi contributions was probably affected by a recent injection of cool plasma into the loop. In flare kernels the contribution of Fe xxi increases from less than 10% at the low-intensity 131 Å sites to 40-80% in the brighter kernels. Here the Fe xxi is superimposed on bright chromospheric emission and the Fe xxi line shows blueshifts, sometimes extending up to the edge of the spectral window, 200 km s-1. The AIA 131 Å emission in flare loops is due to Fe xxi emission with a 10-20% contribution from continuum, Fe xxiii, and cooler background plasma emission. In bright flare kernels up to 52% of the 131 Å is from cooler plasma. The wide range seen in the kernels is caused by significant structure in the kernels, which is seen as sharp gradients in Fe xxi EM at sites of molecular and transition region emission.

  11. SLOW MAGNETOACOUSTIC OSCILLATIONS IN THE MICROWAVE EMISSION OF SOLAR FLARES

    SciTech Connect

    Kim, S.; Shibasaki, K.

    2012-09-10

    Analysis of the microwave data, obtained in the 17 GHz channel of the Nobeyama Radioheliograph during the M1.6 flare on 2010 November 4, revealed the presence of 12.6 minute oscillations of the emitting plasma density. The oscillations decayed with the characteristic time of about 15 minutes. Similar oscillations with the period of about 13.8 minutes and the decay time of 25 minutes are also detected in the variation of EUV emission intensity measured in the 335 A channel of the Solar Dynamics Observatory/Atmospheric Imaging Assembly. The observed properties of the oscillations are consistent with the oscillations of hot loops observed by the Solar and Heliospheric Observatory/Solar Ultraviolet Measurement of Emitted Radiation (SUMER) in the EUV spectra in the form of periodic Doppler shift. Our analysis presents the first direct observations of the slow magnetoacoustic oscillations in the microwave emission of a solar flare, complementing accepted interpretations of SUMER hot loop oscillations as standing slow magnetoacoustic waves.

  12. Energy-Dependent Timing of Thermal Emission in Solar Flares

    NASA Astrophysics Data System (ADS)

    Jain, Rajmal; Awasthi, Arun Kumar; Rajpurohit, Arvind Singh; Aschwanden, Markus J.

    2011-05-01

    We report solar flare plasma to be multi-thermal in nature based on the theoretical model and study of the energy-dependent timing of thermal emission in ten M-class flares. We employ high-resolution X-ray spectra observed by the Si detector of the "Solar X-ray Spectrometer" (SOXS). The SOXS onboard the Indian GSAT-2 spacecraft was launched by the GSLV-D2 rocket on 8 May 2003. Firstly we model the spectral evolution of the X-ray line and continuum emission flux F( ɛ) from the flare by integrating a series of isothermal plasma flux. We find that the multi-temperature integrated flux F( ɛ) is a power-law function of ɛ with a spectral index ( γ)≈-4.65. Next, based on spectral-temporal evolution of the flares we find that the emission in the energy range E=4 - 15 keV is dominated by temperatures of T=12 - 50 MK, while the multi-thermal power-law DEM index ( δ) varies in the range of -4.4 and -5.7. The temporal evolution of the X-ray flux F( ɛ, t) assuming a multi-temperature plasma governed by thermal conduction cooling reveals that the temperature-dependent cooling time varies between 296 and 4640 s and the electron density ( n e) varies in the range of n e=(1.77 - 29.3)×1010 cm-3. Employing temporal evolution technique in the current study as an alternative method for separating thermal from nonthermal components in the energy spectra, we measure the break-energy point, ranging between 14 and 21±1.0 keV.

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

    NASA Technical Reports Server (NTRS)

    Benz, A. O.; Guedel, M.

    1994-01-01

    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.

  14. Solar Flares as Probes of Particle Acceleration Processes

    NASA Astrophysics Data System (ADS)

    Emslie, A. G.

    2004-05-01

    It has been established for some time now that solar flares accelerate copious quantities of charged particles, both electrons and ions. However, the number of particles accelerated and their associated current and energy fluxes, coupled with the relatively short time needed to accomplish the acceleration, continue to offer fundamental challenges to our understanding of the underlying physics. Such challenges include: How can the energy stored in sheared magnetic fields be dissipated on timescales that are orders of magnitude shorter than the classical resistive diffusion time? How can such a large fraction of the stored magnetic energy be converted into low-entropy acceleration rather than high-entropy heating? How can the huge electric currents involved be ``turned on'' in such a short time and without generating unacceptably large magnetic fields? How are the accelerated particles recycled many times through the acceleration process? A variety of theoretical models for particle acceleration in solar flares, ranging from large-scale weak electric fields to small-scale strong electric fields to cascading hydromagnetic turbulence, have been proposed. Each of these models has its particular answers to the above questions and each has its particular predictions regarding the spectrum, directivity, and spatial distribution of the accelerated particles. Discrimination amongst models is, therefore, possible, but only through analysis of the associated radiation fields on time and size scales of physical interest. The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) was designed to perform just this analysis of the X-ray and gamma-ray emissions, and it has indeed started to offer new insights into particle acceleration and transport processes in solar flares.

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

    NASA Technical Reports Server (NTRS)

    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

    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.

  16. Light Element Production in Solar Flares and Present Solar System Abundance of Li, Be, and B

    NASA Astrophysics Data System (ADS)

    Bransford, M. A.; Willson, L. A.

    1998-12-01

    If production in stellar flares can be ruled out as a significant source of the Li, Be, and B isotopes observed in stellar atmospheres, then observed abundances provide very stringent constraints on stellar mass loss before and during the main sequence phase. Also, stellar surface abundances of these isotopes are often invoked as constraints on Big Bang nucleosynthesis calculations. Thus, it is important to establish reliable limits on the importance of in situ (flare) production of these isotopes. Indeed, the need for reliable limits is becoming increasingly important in light of several recent observational papers suggesting significant flare production of Li, Be, and B. The question of the possible importance of flare production of these light isotopes may be separated into two specific questions. First, can (or do) solar flares produce Li, Be, and B isotopes in the same ratios as found in the solar photosphere, taking account those slower processes that may modify the abundances ratios after they are formed? Second, are stellar flares energetically capable of producing enough Li, Be, and B to account for the observed abundances? We will present the results of calculations exploring the flare production of these light isotopes, and which address these crucial questions. How do our calculations differ from those in other investigations? The most significant difference is the choice of the mathematical form for the energy spectrum of flare accelerated particles. Calculations have previously employed a power law form, however, it has been shown that the more appropriate form is a modified Bessel function of order 2. One can derive the Bessel function solution from a Fokker-Planck equation for stochastic Fermi acceleration. The Bessel function is our adopted form for the particle energy spectrum. In order to contrast the flare production of Li, Be, B, and the ratios of the isotopes, based on the choice of the particle energy spectrum, we present calculations employing both forms.

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

    NASA Astrophysics Data System (ADS)

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

    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.

  18. The isotopic composition of solar flare accelerated magnesium

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

    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.

  19. Relaxation of magnetic field relative to plasma density during solar flares

    NASA Astrophysics Data System (ADS)

    Yu, Sijie; Yan, Yihua; Tan, Baolin

    2013-07-01

    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.

  20. Solar flare studies. Final scientific report 1 Jul 76-31 Jan 82

    SciTech Connect

    Canfield, R.C.

    1982-03-20

    The primary objective of the research described in this report was increased understanding of solar flares. In the course of the research, many tasks were carried out, which achieved not only the primary objective, but also secondary objectives in related areas. The research program started with active participation in the Skylab Solar Flare Workshop. New observations of solar flare spectra were obtained and interpreted in terms of basic solar flare mechanisms. It was shown that the basic process by which the X-ray radiation of flares is created is by heating the flare plasma to temperatures of about ten million degrees, through evaporation of the chromosphere. This process is driven both by beams of accelerated electrons and by thermal conduction. However, in the major flare for which data were interpreted, the principal energy release mechanism was found to be thermal in nature, implying that most of the flare energy is released in the form of heat, and not charged particles. Theoretical modeling methods were developed for understanding the spectra solar flares. These methods were applied to flare loop dynamics. The spectral signatures of both chromospheric evaporation and beams of accelerated electrons were established. Finally, a theorectical program of theoretical magnetohydrodynamic stability studies was begun.

  1. Measuring and Modeling Solar Flares with SDO EVE

    NASA Technical Reports Server (NTRS)

    Chamberlin, Phillip C.; Woods, Thomas N.; Wilson, Anne; Lindholm, Chris

    2010-01-01

    The Flare Irradiance Spectral Model (FISM) currently provides estimations of the solar Vacuum Ultra-Violet (VUV; 0.1-190 nm) irradiance from 1947 to present at 1 nm bins and 60 second temporal resolution. The accuracy of FISM is limited to 1nm because the TIMED SEE Level 3 and Level 3A measurement, for which the FISM relationships were based on, were at Inm. With the launch of the Solar Dynamics Observatory (SDO) in Feb 2010, the EUV Variability Experiment (EVE) will provide more accurate, increased spectral resolution (0.1 nm) measurements from 6 nm to 106 nm every 10-seconds and almost 100% duty cycle. EVE also observes additional broadband measurements for 0.1-7 nm, some EUV bands from 16 nm to 40 nm, and Hydrogen Lyman alpha at 121.6 nm. Along with the better spectral resolution of EVE leading to similar spectral resolution improvements in FISM, other significant improvements provide by SDO/EVE measurements will be multi-thermal gradual phase decay, impulsive phase center-to-limb variation characterization, non-flare sub-daily variations, and multi-thermal proxies. SDO/EVE observations of various solar flares with different characteristics will be presented, with the discussion theme focused on how EVE observations will help improve the accuracy of the FISM in the future. The final topic will present the updated FISM website that now has easier access to the FISM results and produce real-time updates that are useful for Space Weather studies.

  2. Coronal mass ejection and solar flare initiation processes without appreciable

    NASA Astrophysics Data System (ADS)

    Veselovsky, I.

    TRACE and SOHO/EIT movies clearly show the cases of the coronal mass ejection and solar flare initiations without noticeable large-scale topology modifications in observed features. Instead of this, the appearance of new intermediate scales is often omnipresent in the erupting region structures when the overall configuration is preserved. Examples of this kind are presented and discussed in the light of the existing magnetic field reconnection paradigms. It is demonstrated that spurious large-scale reconnections and detachments are often produced due to the projection effects in poorly resolved images of twisted loops and sheared arcades especially when deformed parts of them are underexposed and not seen in the images only because of this reason. Other parts, which are normally exposed or overexposed, can make the illusion of "islands" or detached elements in these situations though in reality they preserve the initial magnetic connectivity. Spurious "islands" of this kind could be wrongly interpreted as signatures of topological transitions in the large-scale magnetic fields in many instances described in the vast literature in the past based mainly on fuzzy YOHKOH images, which resulted in the myth about universal solar flare models and the scenario of detached magnetic island formations with new null points in the large scale magnetic field. The better visualization with higher resolution and sensitivity limits allowed to clarify this confusion and to avoid this unjustified interpretation. It is concluded that topological changes obviously can happen in the coronal magnetic fields, but these changes are not always necessary ingredients at least of all coronal mass ejections and solar flares. The scenario of the magnetic field opening is not universal for all ejections. Otherwise, expanding ejections with closed magnetic configurations can be produced by the fast E cross B drifts in strong inductive electric fields, which appear due to the emergence of the new magnetic flux. Corresponding theoretical models are presented and discussed.

  3. Ionosphere Transient Response To Solar Flares: Hf Radio Monitoring Observations

    NASA Astrophysics Data System (ADS)

    Lebreton, J.-P.; Telljohann, U.; Witasse, O.; Sanderson, T. R.

    We use a simple and low cost method to monitor the ionospheric reflection of commer- cial HF radio transmissions. It only requires a standard HF radio receiver with Single Side Band capability, a computer with a sound card, and appropriate audio signal spectral analysis software. We tune the radio receiver such that the carrier frequency of the transmission appears as a ~ 1kHz tone at the output of the radio receiver. The output signal of the radio receiver is processed with appropriate software that allows real time recording of high frequency resolution dynamic spectrograms of the audio spectrum in the 0-5 kHz range. Voice modulation is also present in the audio spectrum and appears as both upper and lower side bands but it is not considered in this study. HF radio signals reach the receiving station after being reflected by ionospheric layers. Any change in the ionospheric layers that affects HF wave reflection is detectable. In this paper, we particularly discuss our observations related to the transient response of the ionosphere to solar flare ionizing radiation. Enhanced ionization due to EUV and soft X-rays may produce a transient perturbation of the ionosphere which lasts typically one to few minutes. The signature of the transient response depends upon local time, solar flare intensity and the rise time of the solar flare ionizing radiation. We discuss both a few typical examples and a preliminary analysis of our 1-year sta- tistical analysis of observed events at 17.640 MHz. The method is easily accessible to amateur scientists. Possible use of the method for spaceweather-related research and outreach and educational activities is discussed.

  4. Reconnection in substorms and solar flares: analogies and differences

    SciTech Connect

    Birn, Joachim

    2008-01-01

    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.

  5. Thermodynamic Spectrum of Solar Flares Based on SDO/EVE Observations: Techniques and First Results

    NASA Astrophysics Data System (ADS)

    Wang, Yuming; Zhou, Zhenjun; Zhang, Jie; Liu, Kai; Liu, Rui; Shen, Chenglong; Chamberlin, Phillip C.

    2016-03-01

    The Solar Dynamics Observatory (SDO)/EUV Variability Experiment (EVE) provides rich information on the thermodynamic processes of solar activities, particularly on solar flares. Here, we develop a method to construct thermodynamic spectrum (TDS) charts based on the EVE spectral lines. This tool could potentially be useful for extreme ultraviolet (EUV) astronomy to learn about the eruptive activities on distant astronomical objects. Through several cases, we illustrate what we can learn from the TDS charts. Furthermore, we apply the TDS method to 74 flares equal to or greater than the M5.0 class, and reach the following statistical results. First, EUV peaks are always behind the soft X-ray (SXR) peaks and stronger flares tend to have faster cooling rates. There is a power-law correlation between the peak delay times and the cooling rates, suggesting a coherent cooling process of flares from SXR to EUV emissions. Second, there are two distinct temperature drift patterns, called Type I and Type II. For Type I flares, the enhanced emission drifts from high to low temperature like a quadrilateral, whereas for Type II flares the drift pattern looks like a triangle. Statistical analysis suggests that Type II flares are more impulsive than Type I flares. Third, for late-phase flares, the peak intensity ratio of the late phase to the main phase is roughly correlated with the flare class, and the flares with a strong late phase are all confined. We believe that the re-deposition of the energy carried by a flux rope, which unsuccessfully erupts out, into thermal emissions is responsible for the strong late phase found in a confined flare. Furthermore, we show the signatures of the flare thermodynamic process in the chromosphere and transition region in the TDS charts. These results provide new clues to advance our understanding of the thermodynamic processes of solar flares and associated solar eruptions, e.g., coronal mass ejections.

  6. Space radiation dose analysis for solar flare of August 1989

    SciTech Connect

    Nealy, J.E.; Simonsen, L.C.; Sauer, H.H.; Wilson, J.W.; Townsend, L.W.

    1990-12-01

    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.

  7. Spatial and Spectral Behaviors of Solar Flares Observed in Microwaves

    NASA Astrophysics Data System (ADS)

    Ning, Zongjun; Cao, Wenda

    2009-07-01

    The spatial and spectral behaviors of two solar flares observed by the Nobeyama Radioheliograph (NoRH) on 24 August 2002 and 22 August 2005 are explored. They were observed with a single loop-top source and double footpoint sources at the beginning, then with looplike structures for the rest of the event. NoRH has high spatial and temporal resolution at the two frequencies of 17 and 34 GHz where a nonthermal radio source is often optically thin. Such capabilities give us an opportunity to study the spatial and spectral behaviors of different microwave sources. The 24 August 2002 flare displayed a soft - hard - soft (SHS) spectral pattern in the rising - peak - decay phases at 34 GHz, which was also observed for the spectral behavior of both loop-top and footpoint sources. In contrast, the 22 August 2005 flare showed a soft - hard - harder (SHH) spectral pattern for its both loop-top and footpoint sources. It is interesting that this event showed a harder spectrum in the early rising phase. We found a positive correlation between the spectral index and microwave flux in both the loop-top source and the footpoint sources in both events. The conclusions drawn from the flux index could apply to the electron index as well, because of their simple linear relationship under the assumption of nonthermal gyrosynchrotron mechanism. Such a property of spatial and spectral behaviors of microwave sources gives an observational constraint on the electron acceleration mechanism and electron propagation.

  8. The triggering and subsequent development of a solar flare

    NASA Technical Reports Server (NTRS)

    Vorpahl, J. A.

    1975-01-01

    High temporal and spatial resolution solar X-ray pictures of a flare at 1827 UT on 5 September 1973 were taken with the S-056 telescope on the Apollo telescope mount. Photographs taken at 9 sec intervals allow detailed information to be obtained about the site of the energy release, as well as about the evolution of the flare itself. Observations suggest that the flare occurred in an entire arcade of loops rather than in any single loop. Sequential brightening of different X-ray features indicates that some excitation moved perpendicular to the magnetic field of the arcade at velocities of 180 to 280 km/sec. The most intense X-ray features were located in places where the magnetic field composing the arcade had a small radius of curvature with horizontal field gradients higher than the surroundings region and where the axis of the arcade changed direction. It was felt that the arcade geometry strongly influenced the propagation of the triggering disturbance, as well as the storage and site of the subsequent deposition of energy. A magnetosonic wave is suggested as the propagating mechanism triggering instabilities that may have existed in the preflare structure.

  9. Space radiation dose analysis for solar flare of August 1989

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

    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.

  10. Solar Flare Impulse Broadening from Gamma Ground Survey Network

    NASA Astrophysics Data System (ADS)

    Litz, Marc; Burns, David; Carroll, James; Pereira, Nino

    2012-03-01

    Inexpensive gamma detectors with GPS and wireless communications have been developed and installed to provide a ground survey network for detection of unintended gamma radiation along transport routes. Signals from pedestrian borne and vehicle borne radiation sources have pulse widths that range three orders of magnitude in time from millseconds to seconds. Information collected during the 24/7 operation of this network generated unexpected signals lasting over an hour. These longer time responses have been traced to solar flare events. This paper will discuss the time and intensity correlations with known satellite sensor data. These terrestrial gamma ray flashes will be analysed further as real-time data continues to be collected.

  11. A search for energetic ion directivity in large solar flares

    NASA Technical Reports Server (NTRS)

    Vestrand, W. Thomas

    1993-01-01

    One of the key observational questions for solar flare physics is: What is the number, the energy spectrum, and the angular distribution of flare accelerated ions? The standard method for deriving ion spectral shape employs the ratio of influences observed on the 4-7 MeV band to the narrow neutron capture line at 2.223 MeV. The 4-7 MeV band is dominated by the principal nuclear de-excitation lines from C-12 and O-16 which are generated in the low chromosphere by the direct excitation or spallation of nuclei by energetic ions. In contrast, the narrow 2.223 MeV line is produced by the capture of thermal neutrons on protons in the photosphere. These capture neutrons are generated by energetic ion interactions and thermalized by scattering in the solar atmosphere. In a series of papers, Ramaty, Lingenfelter, and their collaborators have calculated the expected ratio of fluence in the 4-7 MeV band to the 2.223 MeV line for a wide range of energetic ion spectral shapes (see, e.g. Hua and Lingenfelter 1987). Another technique for deriving ion spectral shapes and angular distributions uses the relative strength of the Compton tail associated with the 2.223 MeV neutron capture line (Vestrand 1988, 1990). This technique can independently constrain both the angular and the energy distribution of the energetic parent ions. The combination of this tail/line strength diagnostic with the line/(4-7) MeV fluence ratio can allow one to constrain both properties of the energetic ion distributions. The primary objective of our Solar Maximum Mission (SMM) guest investigator program was to study measurements of neutron capture line emission and prompt nuclear de-excitation for large flares detected by the Solar Maximum Mission/ Gamma-Ray Spectrometer (SMM/GRS) and to use these established line diagnostics to study the properties of flare accelerated ions.

  12. A Comparative Study of Measured Amplitude and Phase Perturbations of VLF and LF Radio Signals Induced by Solar Flares

    NASA Astrophysics Data System (ADS)

    Sulic, D. M.; Sreckovic, V. A.

    2014-06-01

    Very Low Frequency (VLF) and Low Frequency (LF) signal perturbations were examined to study ionospheric disturbances induced by solar X-ray flares in order to understand processes involved in propagation of VLF/LF radio signals over short paths and to estimate specific characteristics of each short path. The receiver at the Belgrade station is constantly monitoring the amplitude and phase of a coherent and subionospherically propagating LF signal operated in Sicily NSC at 45.90 kHz, and a VLF signal operated in Isola di Tavolara ICV at 20.27 kHz, with the great circle distances of 953 km and 976 km, respectively. A significant number of similarities between these short paths is a direct result of both transmitters and the receiver's geographic location. The main difference is in transmitter frequencies. From July 2008 to February 2014 there were about 200 events that were chosen for further examination. All selected examples showed that the amplitude and phase of VLF and LF signals were perturbed by solar X-ray flares occurrence. This six-year period covers both minimum and maximum of solar activity. Simultaneous measurement of amplitude and phase of the VLF/LF signals during a solar flare occurrence was applied to evaluate the electron density profile versus altitude, to carry out the function of time over the middle Europe.

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

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

    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.

  14. Global Energetics of Solar Flares. I. Magnetic Energies

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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.

  15. MEASUREMENTS OF THE CORONAL ACCELERATION REGION OF A SOLAR FLARE

    SciTech Connect

    Krucker, Saem; Hudson, H. S.; Glesener, L.; Lin, R. P.; White, S. M.; Masuda, S.; Wuelser, J.-P.

    2010-05-10

    The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Nobeyama Radioheliograph (NoRH) are used to investigate coronal hard X-ray and microwave emissions in the partially disk-occulted solar flare of 2007 December 31. The STEREO mission provides EUV images of the flare site at different viewing angles, establishing a two-ribbon flare geometry and occultation heights of the RHESSI and NoRH observations of {approx}16 Mm and {approx}25 Mm, respectively. Despite the occultation, intense hard X-ray emission up to {approx}80 keV occurs during the impulsive phase from a coronal source that is also seen in microwaves. The hard X-ray and microwave source during the impulsive phase is located {approx}6 Mm above thermal flare loops seen later at the soft X-ray peak time, similar in location to the above-the-loop-top source in the Masuda flare. A single non-thermal electron population with a power-law distribution (with spectral index of {approx}3.7 from {approx}16 keV up to the MeV range) radiating in both bremsstrahlung and gyrosynchrotron emission can explain the observed hard X-ray and microwave spectrum, respectively. This clearly establishes the non-thermal nature of the above-the-loop-top source. The large hard X-ray intensity requires a very large number (>5 x 10{sup 35} above 16 keV for the derived upper limit of the ambient density of {approx}8 x 10{sup 9} cm{sup -3}) of suprathermal electrons to be present in this above-the-loop-top source. This is of the same order of magnitude as the number of ambient thermal electrons. We show that collisional losses of these accelerated electrons would heat all ambient electrons to superhot temperatures (tens of keV) within seconds. Hence, the standard scenario, with hard X-rays produced by a beam comprising the tail of a dominant thermal core plasma, does not work. Instead, all electrons in the above-the-loop-top source seem to be accelerated, suggesting that the above-the-loop-top source is itself the electron acceleration region.

  16. Global Energetics of Solar Flares: II. Thermal Energies

    NASA Astrophysics Data System (ADS)

    Aschwanden, Markus J.; Boerner, Paul; Ryan, Daniel; Caspi, Amir; McTiernan, James M.; Warren, Harry P.

    2015-03-01

    We present the second 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 the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) during the first 3.5 yr of its mission. In this Paper II we compute the differential emission measure (DEM) distribution functions and associated multithermal energies, using a spatially-synthesized Gaussian DEM forward-fitting method. The multithermal DEM function yields a significantly higher (by an average factor of ≈14), but more comprehensive (multi-)thermal energy than an isothermal energy estimate from the same AIA data. We find a statistical energy ratio of {{E}th}/{{E}diss} ≈ 2-40% between the multithermal energy Eth and the magnetically dissipated energy Ediss, which is an order of magnitude higher than the estimates of Emslie et al. 2012. For the analyzed set of M- and X-class flares we find the following physical parameter ranges: L={{10}8.2}{{-10}9.7} cm for the length scale of the flare areas, {{T}p}={{10}5.7}{{-10}7.4} K for the DEM peak temperature, {{T}w}={{10}6.8}{{-10}7.6} K for the emission measure-weighted temperature, {{n}p}={{10}10.3}-{{10}11.8} cm-3 for the average electron density, E{{M}p}={{10}47.3}-{{10}50.3} cm-3 for the DEM peak emission measure, and {{E}th}={{10}26.8}-{{10}32.0} erg for the multithermal energies. The deduced multithermal energies are consistent with the RTV scaling law {{E}th,RTV}=7.3× {{10}-10} Tp3Lp2, which predicts extremal values of {{E}th,max }≈ 1.5× {{10}33} erg for the largest flare and {{E}th,min }≈ 1× {{10}24} erg for the smallest coronal nanoflare. The size distributions of the spatial parameters exhibit powerlaw tails that are consistent with the predictions of the fractal-diffusive self-organized criticality model combined with the RTV scaling law.

  17. Global energetics of solar flares. I. Magnetic energies

    SciTech Connect

    Aschwanden, Markus J.; Xu, Yan; Jing, Ju E-mail: yan.xu@njit.edu

    2014-12-10

    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 (E{sub p} ), the nonpotential (E {sub np}) or free energies (E {sub free} = E {sub np} – E{sub p} ), and the flare-dissipated magnetic energies (E {sub diss}). We calculate these magnetic parameters using two different NLFFF codes: the COR-NLFFF code uses the line-of-sight magnetic field component B{sub z} 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, E{sub np}∝E{sub p}{sup 1.02}, for the free energy, E{sub free}∝E{sub p}{sup 1.7} and E{sub free}∝B{sub φ}{sup 1.0}L{sup 1.5}, for the dissipated energy, E{sub diss}∝E{sub p}{sup 1.6} and E{sub diss}∝E{sub free}{sup 0.9}, and the energy dissipation volume, V∝E{sub diss}{sup 1.2}. The potential energies vary in the range of E{sub p} = 1 × 10{sup 31}-4 × 10{sup 33} erg, while the free energy has a ratio of E {sub free}/E{sub p} ≈ 1%-25%. The Poynting flux amounts to F {sub flare} ≈ 5 × 10{sup 8}-10{sup 10} erg cm{sup –2} s{sup –1} during flares, which averages to F {sub AR} ≈ 6 × 10{sup 6} erg cm{sup –2} s{sup –1} during the entire observation period and is comparable with the coronal heating rate requirement in active regions.

  18. SOHO Captures CME From X5.4 Solar Flare - Duration: 5 seconds.

    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...

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

    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...

  20. 01.22.12: SDO's View of M8.7 Solar Flare - Duration: 8 seconds.

    NASA Video Gallery

    Solar Dynamics Observatory captured the flare, shown here in teal as that is the color typically used to show light in the 131 Angstrom wavelength, a wavelength in which it is easy to view solar fl...

  1. Extreme Ultra-Violet Spectroscopy of the Lower Solar Atmosphere During Solar Flares (Invited Review)

    NASA Astrophysics Data System (ADS)

    Milligan, Ryan O.

    2015-12-01

    The extreme ultra-violet (EUV) 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, nonthermal broadening, abundance measurements, differential emission measure profiles, continuum temperatures and energetics, among others. In this article I review some of the recent advances that have been made using these techniques to infer physical properties of heated plasma at footpoint and ribbon locations during the initial stages of solar flares. I primarily focus on studies that have utilised spectroscopic EUV data from Hinode/EUV Imaging Spectrometer (EIS) and Solar Dynamics Observatory/EUV Variability Experiment (SDO/EVE), and I also provide some historical background and a summary of future spectroscopic instrumentation.

  2. Solar Chromospheric Flares: Observations in Ly-lpha and Hlpha and Radiative Hydrodynamic Simulations

    NASA Astrophysics Data System (ADS)

    Rubio da Costa, Fatima

    2011-03-01

    This thesis is divided into two main parts: a multiwavelength observational study of solar flares, focusing mainly in the chromosphere in Ly-? and H?, and an application of a radiative transfer code and a radiative hydrodynamic code, to compare the results obtained by observations with the simulated ones. The Ly-? emission is a very interesting line because it is a natural tracer of the solar activity in the chromosphere. The Transition Region And Coronal Explorer satellite observed a small number of flares in the Ly-? passband, but apart from this, these events have not often been observed in this strong chromospheric line. Because TRACE has a broad Ly-? channel, in order to estimate the "pure" Ly? emission, we had to apply an empirical correction. We found that there is a reasonable coverage in TRACE 1216 A and the TRACE 1600 A for two different flares: on 8 September 1999 and on 28 February 1999. Studying them we estimated, for the first time, the pure Ly-? flare signature, being on the order of 10^25 erg/s at the flare peak. The study of the first flare gave us the possibility to calculate the electron energy budget using the X-ray data from Yohkoh/HXT in the context of the collisional thick target model, finding that the Ly-? power is less than 10% of the power inferred by the electrons. The morphology and evolution of the second flare were described in different wavelengths by using imaging data acquired by TRACE and by BBSO in white light and in H?. We studied the magnetic topology using the magnetic field provided by SOHO/MDI, extrapolating the photospheric magnetic field lines, assuming a potential field. We found different morphologies in the magnetic configuration before and after the flare, confirming the occurrence of a reconnection process. The H? line is the most important line in the chromosphere. We studied the H? emission of a flare which occurred on 3 July 2002 using some spectroscopical observations from the Ondrejov Observatory. Analyzing the available data in other wavelengths, we made a morphological study of the active region from three hours before the flare to seven hours after it. The results obtained by observations, both in the form of integrated intensity as a function of time, and detailed line profiles, motivated the second part of the thesis. In this, we used a radiative transfer code (Gouttebroze et al. 1978) applying different atmospheric models as input parameters in order to compute the hydrogen spectral lines and study how they are affected by the temperature and microturbulent stratification. In particular, the intensity of the Ly-? and H? lines is related to the temperature stratification of the atmospheric model, the position of the transition region being a key factor. The variation of the microturbulent velocity does not significantly affect the resulting intensities, but we observed that an increase of the microturbulent velocity broadens the line profiles. The RADYN Radiative HydroDynamic code (Allred et al. 2005) was applied to solar flares, modelling a flare loop from its footpoints in the photosphere to its apex in the corona by adding non-thermal heating at the lower atmosphere and soft X-ray irradiation. The majority of this work was to deal with investigating the dynamical response of the solar chromosphere to energy injected in the form of non-thermal electrons during solar flares. We studied the flare energy transport and radiation production in the chromosphere as well as the H? and Ly-? emission. The Ly-? intensity is affected by the flux of the initial beam of electrons injected at the top of the loop, while the H? intensity appears to be less affected by the flare model. Comparing the observational results in Ly? and H? with the computed ones from the radiative code and the RADYN code, we found that the RADYN code fits better the H? intensities to the observations than the Ly? intensities, concluding that the code gives a better description of processes in the lower chromosphere than those in the upper layers.

  3. Impulsiveness and energetics in solar flares with and without type II radio bursts - A comparison of hard X-ray characteristics for over 2500 solar flares

    NASA Technical Reports Server (NTRS)

    Pearson, Douglas H.; Nelson, Robert; Kojoian, Gabriel; Seal, James

    1989-01-01

    The hard X-ray characteristics of more than 2500 solar flares are used to study the relative size, impulsiveness, and energetics of flares with and without type II radio bursts. A quantitative definition of the hard X-ray impulsiveness is introduced, which may be applied to a large number of events unambiguously. It is found that the flares with type II bursts are generally not significantly larger, more impulsive, or more energetic than those without type II bursts. Also, no evidence is found to suggest a simple classification of the flares as either 'impulsive' or 'gradual'. Because type II bursts are present even in small flares with relatively unimpulsive energy releases, it is concluded that changes in the ambient conditions of the solar atmosphere causing an unusually low Alfven speed may be important in the generation of the shock wave that produces type II radio bursts.

  4. The Human Impact of Solar Flares and Magnetic Storms

    NASA Astrophysics Data System (ADS)

    Joselyn, Jo Ann

    1998-01-01

    The Sun shines, and Earth and its inhabitants benefit. But the Sun radiates more than light, and these radiations are variable over time scales of seconds to days to years. The consequences for people range from glorious celestial displays-auroras-to subtle but potentially damaging effects on the technological systems that are increasingly important for daily living. For example, electric power transmission systems and communication links have proven vulnerable to solar phenomena. And outside of Earth's protective atmosphere and magnetic shield, there is a small but genuine risk of a solar energetic particle burst that would be lethal to satellite sensors and command and control systems and astronauts. It has been known since the time of Galileo that the Sun is neither featureless nor steady. Besides ordinary sunlight, there are three classes of solar emanations that can be directly associated with effects at Earth-photon radiation from solar flares, solar energetic particles, and inhomogeneties in the solar wind that drive magnetic storms. Below, the emanations are summarized and their effects are described.

  5. Fermi Large Area Telescope observations of high-energy gamma-ray emission from solar flares

    NASA Astrophysics Data System (ADS)

    Pesce-Rollins, Melissa; Omodei, N.; Petrosian, V.; Fermi LAT Collaboration

    2014-01-01

    With the current solar cycle reaching its maximum, the Fermi observatory has proven to play an active role in the study of solar flares. The Large Area Telescope (LAT) on-board Fermi has detected >30 MeV gamma-ray emission associated with GOES M-class and X-class X-ray flares accompanied by coronal mass ejections and solar energetic particle events. These detections include both the impulsive and the long duration phases including the ~20 hours of extended emission from the 2012 March 7 X-class flares. Accurate localization with the Fermi LAT of the gamma-ray production site(s) coincide with the solar active region from which X-ray emissions associated with the 2012 March 7 X-class flares originated. In this talk I present an overview of the Fermi solar flare detections over the past five years of operation.

  6. Influence of solar activity on fibrinolysis and fibrinogenolysis. [statistical correlation between solar flare and blood coagulation indices

    NASA Technical Reports Server (NTRS)

    Marchenko, V. I.

    1974-01-01

    During periods of high solar activity fibrinolysis and fibrinogenolysis are increased. A direct correlative relationship is established between the indices of fibrinolysis, fibrinogenolysis and solar flares which were recorded two days before the blood was collected for analysis.

  7. Solar Eruption Model Relating CME Kinematics to Flare Emissions

    NASA Astrophysics Data System (ADS)

    Moats, Stephanie; Reeves, K.

    2010-05-01

    The combination of a loss-of-equilibrium coronal mass ejection (CME) model with a multi-threaded flare loop model is used to develop a model of solar eruptions. The CME kinematics, thermal energy release, and flare emissions are compared in order to understand the relationship between these properties of solar eruptions. CME accelerations and peak x-ray fluxes are modeled for many different cases, and it is found that the timing of the peak flux derivative and the peak acceleration are well correlated when the inflow Alfven Mach number is fast and the magnetic field is high. The total thermal energy release and peak soft x-ray flux are observed to have a power law relationship, where the peak flux is about equal to the thermal energy to the power of alpha (alpha is between 2.54 and 1.54, depending on the reconnection rate). This finding conflicts with theoretical underpinnings of the Neupert Effect, which assumes the soft x-ray flux is proportional to the thermal energy release.

  8. Multispacecraft Observations of Solar Flare Particles in the Inner Heliosphere

    NASA Technical Reports Server (NTRS)

    Wibberenz, G.; Cane, H. V.

    2007-01-01

    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.

  9. Energy spectra of ions from impulsive solar flares

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    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.

  10. Variations in iron and calcium abundances during solar flares

    NASA Astrophysics Data System (ADS)

    Antonucci, E.; Martin, R.

    1995-07-01

    Evidence for variations in iron and calcium abundances during the impulsive phase of solar flares has been obtained by analyzing the Ca XIX and Fe XXV spectra, detected with the Bent Crystal Spectrometer of the Solar Maximum Mission. The plasma thermal conditions have been investigated by considering different temperature indicators: namely, the temperatures TCa and TFe, derived from the intensity ratios of the dielectronic recombination satellites to the resonance line, and the temperature TCaFe, calculated from the ratio of the resonance lines of Ca XIX and Fe XXV, which is also depending on the Fe/Ca abundance ratio. The observed values of TCa and TFe can be ascribed to the specific characteristics of the plasma therma distribution, the corresponding values of TCaFe can be explained by allowing also for variations in the Fe/Ca abundance ratio relative to the photospheric ratio by a factor within 0.2 and 2.4. According to the observed abundance variations, the events analyzed can be divided in Ca-rich and Fe-rich flares.

  11. Energy spectra of ions from impulsive solar flares

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    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.

  12. Structure of impulsive phase of solar flares from microwave observations

    NASA Technical Reports Server (NTRS)

    Petrosian, V.

    1981-01-01

    Variation of the microwave intensity and spectrum due to gyro-synchrotron radiation from semi-relativistic particles injected at the top of a closed magnetic loop is described. Using the recent high spatial resolution X-ray observations from the HXIS experiment of Solar Maximum Mission and from observations by the Very Large Array (VLA), it is shown that the high microwave brightness observed at the top of the flare loop can come about if (1) the magnetic field from top to footpoints of the loop does not increase very rapidly, and (2) the accelerated particles injected in the loop have a nearly isotropic pitch angle distribution. The limits on the rate of increase of the magnetic field and/or the average pitch angle depend on the geometry and location of the loop on the solar disk.

  13. Terrestrial Response to Eruptive Solar Flares: Geomagnetic Storms

    NASA Technical Reports Server (NTRS)

    Tsurutani, Bruce T.

    1995-01-01

    During the interval of August 1979 - December 1979, 56 unambiguous fast forward shocks were identified using magnetic field and plasma data collected by the ISEE-3 spacecraft. Because this interval is a solar maximum we assume the streams causing these shocks are associated with coronal mass ejections and eruptive solar flares. For these shocks we shall describe the shock-storm relationship for the level of intense storms (Dst < -100 nT). Then, we will discuss the interplanetary structures that are associated with the large-amplitude and long-duration negative Bz fields, which are found in the sheath field and/or driver gas regions of the shock and are thought to be the main cause of the intense storms.

  14. On the Generation of Hydrodynamic Shocks by Mixed Beams and Occurrence of Sunquakes in Flares

    NASA Astrophysics Data System (ADS)

    Zharkova, Valentina; Zharkov, Sergei

    2015-11-01

    Observations of solar flares with sunquakes by space- and ground-based instruments reveal essentially different dynamics of seismic events in different flares. Some sunquakes are found to be closely associated with the locations of hard X-ray (HXR) and white-light (WL) emission, while others are located outside either of them. In this article we investigate possible sources causing a seismic response in a form of hydrodynamic shocks produced by the injection of mixed (electron plus proton) beams, discuss the velocities of these shocks, and the depths where they deposit the bulk of their energy and momentum. The simulation of hydrodynamic shocks in flaring atmospheres induced by electron-rich and proton-rich beams reveals that the linear depth of the shock termination is shifted beneath the level of the quiet solar photosphere on a distance from 200 to 5000 km. The parameters of these atmospheric hydrodynamic shocks are used as initial condition for another hydrodynamic model developed for acoustic-wave propagation in the solar interior (Zharkov, Mon. Not. Roy. Astron. Soc. 431, 3414, 2013). The model reveals that the depth of energy and momentum deposition by the atmospheric shocks strongly affects the propagation velocity of the acoustic-wave packet in the interior. The locations of the first bounces from the photosphere of acoustic waves generated in the vicinity of a flare are seen as ripples on the solar surface, or sunquakes. Mixed proton-dominated beams are found to produce a strong supersonic shock at depths 200 - 300 km under the level of the quiet-Sun photosphere and in this way produce well-observable acoustic waves, while electron-dominated beams create a slightly supersonic shock propagating down to 5000 km under the photosphere. This shock can only generate acoustic waves at the top layers beneath the photosphere since the shock velocity very quickly drops below the local sound speed. The distance ? of the first bounce of the generated acoustic waves is discussed in relation to the minimal phase velocities of wave packets defined by the acoustic cutoff frequency and the parameters of atmospheric shock termination beneath the photosphere.

  15. An upper limit on the hardness of the nonthermal electron spectra produced during the flash phase of solar flares.

    NASA Technical Reports Server (NTRS)

    Kane, S. R.

    1971-01-01

    The observations of impulsive solar-flare X-rays above 10 keV made with OGO-5 satellite have been analyzed in order to study the variation of the nonthermal electron spectrum from one flare to another. The X-ray spectrum at the maxima of 129 impulsive X-ray bursts is represented by KE to the minus-gamma power photons per sq cm per sec per keV, and the frequency of occurrence of bursts with different values of gamma is studied. It is found that for gamma less than 4.0 the frequency of bursts rapidly decreases with the decrease in the value of gamma. The probability of occurrence of a burst with gamma less than 2.3 is extremely small.

  16. PRE-FLARE ACTIVITY AND MAGNETIC RECONNECTION DURING THE EVOLUTIONARY STAGES OF ENERGY RELEASE IN A SOLAR ERUPTIVE FLARE

    SciTech Connect

    Joshi, Bhuwan; Veronig, Astrid M.; Bong, Su-Chan; Cho, Kyung-Suk; Tiwari, Sanjiv Kumar

    2011-12-20

    In this paper, we present a multi-wavelength analysis of an eruptive white-light M3.2 flare that occurred in active region NOAA 10486 on 2003 November 1. The excellent set of high-resolution observations made by RHESSI and the TRACE provides clear evidence of significant pre-flare activities for {approx}9 minutes in the form of an initiation phase observed at EUV/UV wavelengths followed by an X-ray precursor phase. During the initiation phase, we observed localized brightenings in the highly sheared core region close to the filament and interactions among short EUV loops overlying the filament, which led to the opening of magnetic field lines. The X-ray precursor phase is manifested in RHESSI measurements below {approx}30 keV and coincided with the beginning of flux emergence at the flaring location along with early signatures of the eruption. The RHESSI observations reveal that both plasma heating and electron acceleration occurred during the precursor phase. The main flare is consistent with the standard flare model. However, after the impulsive phase, an intense hard X-ray (HXR) looptop source was observed without significant footpoint emission. More intriguingly, for a brief period, the looptop source exhibited strong HXR emission with energies up to {approx}50-100 keV and significant non-thermal characteristics. The present study indicates a causal relation between the activities in the pre-flare and the main flare. We also conclude that pre-flare activities, occurring in the form of subtle magnetic reorganization along with localized magnetic reconnection, played a crucial role in destabilizing the active region filament, leading to a solar eruptive flare and associated large-scale phenomena.

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

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

    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.

  18. Statistics and classification of the microwave zebra patterns associated with solar flares

    SciTech Connect

    Tan, Baolin; Tan, Chengming; Zhang, Yin; Mészárosová, H.; Karlický, M.

    2014-01-10

    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 Ondŕejov 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    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.

  20. Large solar flare radiation shielding requirements for manned interplanetary missions.

    PubMed

    Townsend, L W; Nealy, J E; Wilson, J W; Atwell, W

    1989-01-01

    As the 21st century approaches, there is an ever-increasing interest in launching manned missions to Mars. A major concern to mission planners is exposure of the flight crews to highly penetrating and damaging space radiations. Beyond the protective covering of the Earth's magnetosphere, the two main sources of these radiations are galactic cosmic rays and solar particle events. Preliminary analyses of potential exposures from galactic cosmic rays (GCR's) were presented elsewhere. In this Note, estimates of shielding thicknesses required to protect astronauts on interplanetary missions from the effects of large solar flare events are presented. The calculations use integral proton fluences for the February 1956, November 1960, and August 1972 solar particle events as inputs into the NASA Langley Research Center nucleon transport code BRYNTRN. This deterministic computer code transports primary protons and secondary protons and neutrons through any number of layers of target material of arbitrary thickness and composition. Contributions from target nucleus breakup (fragmentation) and recoil are also included. The results for each flare are presented as estimates of dose equivalent [in units of roentgen equivalent man (rem)] to the skin, eye, and bloodforming organs (BFO) behind various thicknesses of aluminum shielding. These results indicate that the February 1956 event was the most penetrating; however, the August 1972 event, the largest ever recorded, could have been mission- or life-threatening for thinly shielded (< or = 5 g/cm2) spacecraft. Also presented are estimates of the thicknesses of water shielding required to reduce the BFO dose equivalent to currently recommended astronaut exposure limits. These latter results suggest that organic polymers, similar to water, appear to be a much more desirable shielding material than aluminum. PMID:11537157

  1. The 3-D description of vertical current sheets with application to solar flares

    NASA Technical Reports Server (NTRS)

    Fontenla, Juan M.; Davis, J. M.

    1991-01-01

    Following a brief review of the processes which have been suggested for explaining the occurrence of solar flares we suggest a new scenario which builds on the achievements of the previous suggestion that the current sheets, which develop naturally in 3-D cases with gravity from impacting independent magnetic structures (i.e., approaching current systems), do not consist of horizontal currents but are instead predominantly vertical current systems. This suggestion is based on the fact that as the subphotospheric sources of the magnetic field displace the upper photosphere and lower chromosphere regions, where plasma beta is near unity, will experience predominantly horizontal mass motions which will lead to a distorted 3-D configurations of the magnetic field having stored free energy. In our scenario, a vertically flowing current sheet separates the plasma regions associated with either of the subphotospheric sources. This reflects the balanced tension of the two stressed fields which twist around each other. This leads naturally to a metastable or unstable situation as the twisted field emerges into a low beta region where vertical motions are not inhibited by gravity. In our flare scenario the impulsive energy release occurs, initially, not by reconnection but mainly by the rapid change of the magnetic field which has become unstable. During the impulsive phase the field lines contort in such way as to realign the electric current sheet into a minimum energy horizontal flow. This contortion produces very large electric fields which will accelerate particles. As the current evolves to a horizontal configuration the magnetic field expands vertically, which can be accompanied by eruptions of material. The instability of a horizontal current is well known and causes the magnetic field to undergo a rapid outward expansion. In our scenario, fast reconnection is not necessary to trigger the flare, however, slow reconnection would occur continuously in the current layer at the locations of potential flaring. During the initial rearrangement of the field strong plasma turbulence develops. Following the impulsive phase, the final current sheet will experience faster reconnection which we believe responsible for the gradual phase of the flare. The reconnection will dissipate part of the current and will produce sustained and extended heating in the flare region and in the postflare loops.

  2. Evidence for solar flare rare gases in the Khor Temiki aubrite.

    NASA Technical Reports Server (NTRS)

    Rajan, R. S.; Price, P. B.

    1973-01-01

    It has been found by studying a number of gas-rich meteorites, including Khor Temiki that there is a correlation between the abundance of 'track-rich' grains and the concentration of trapped rare gases. The amount of solar flare gas in Khor Temiki is examined. It is pointed out that the Khor Temiki enstatite is an ideal sample in which to look for evidence of solar flare gases because there has been little or no diffusion loss of solar wind gases.

  3. RETURN CURRENTS AND ENERGY TRANSPORT IN THE SOLAR FLARING ATMOSPHERE

    SciTech Connect

    Codispoti, Anna; Torre, Gabriele; Piana, Michele; Pinamonti, Nicola

    2013-08-20

    According to the standard Ohmic perspective, the injection of accelerated electrons into the flaring region violates local charge equilibrium and therefore, in response, return currents are driven by an electric field to equilibrate such charge violation. In this framework, the energy loss rate associated with these local currents has an Ohmic nature and significantly shortens the accelerated electron path. In the present paper, we adopt a different viewpoint and, specifically, we study the impact of the background drift velocity on the energy loss rate of accelerated electrons in solar flares. We first utilize the Rutherford cross-section to derive the formula of the energy loss rate when the collisional target has a finite temperature and the background instantaneously and coherently moves up to equilibrate the electron injection. We then use the continuity equation for electrons and imaging spectroscopy data provided by RHESSI to validate this model. We show that this new formula for the energy loss rate provides a better fit of the experimental data with respect to the model based on the effects of standard Ohmic return currents.

  4. Spatial structure of high energy photon sources in solar flares

    NASA Technical Reports Server (NTRS)

    Kane, S. R.

    1983-01-01

    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.

  5. Joule heating and runaway electron acceleration in a solar flare

    NASA Technical Reports Server (NTRS)

    Holman, Gordon D.; Kundu, Mukul R.; Kane, Sharad R.

    1989-01-01

    The hard and soft x ray and microwave emissions from a solar flare (May 14, 1980) were analyzed and interpreted in terms of Joule heating and runaway electron acceleration in one or more current sheets. It is found that all three emissions can be generated with sub-Dreicer electric fields. The soft x ray emitting plasma can only be heated by a single current sheet if the resistivity in the sheet is well above the classical, collisional resistivity of 10(exp 7) K, 10(exp 11)/cu cm plasma. If the hard x ray emission is from thermal electrons, anomalous resistivity or densities exceeding 3 x 10(exp 12)/cu cm are required. If the hard x ray emission is from nonthermal electrons, the emissions can be produced with classical resistivity in the current sheets if the heating rate is approximately 4 times greater than that deduced from the soft x ray data (with a density of 10(exp 10)/cu cm in the soft x ray emitting region), if there are at least 10(exp 4) current sheets, and if the plasma properties in the sheets are characteristic of the superhot plasma observed in some flares by Lin et al., and with Hinotori. Most of the released energy goes directly into bulk heating, rather than accelerated particles.

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

    NASA Astrophysics Data System (ADS)

    Kaufmann, Pierre; Raulin, Jean-Pierre

    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).

  7. Improving the performance of solar flare prediction using active longitudes information

    NASA Astrophysics Data System (ADS)

    Huang, X.; Zhang, L.; Wang, H.; Li, L.

    2013-01-01

    Context. Solar flare prediction models normally depend on properties of active regions, such as sunspot area, McIntosh classifications, Mount Wilson classifications, and various measures of the magnetic field. Nevertheless, the positional information of active regions has not been used. Aims: We define a metric, DARAL (distance between active regions and predicted active longitudes), to depict the positional relationship between active regions and predicted active longitudes and add DARAL to our solar flare prediction model to improve its performance. Methods: Combining DARAL with other solar magnetic field parameters, we build a solar flare prediction model with the instance-based learning method, which is a simple and effective algorithm in machine learning. We extracted 70 078 active region instances from the Solar and Heliospheric Observatory (SOHO)/Michelson Doppler Imager (MDI) magnetograms containing 1055 National Oceanic and Atmospheric Administration (NOAA) active regions within 30 of the solar disk center from 1996 to 2007 and used them to train and test the solar flare prediction model. Results: Using four performance measures (true positive rate, true negative rate, true skill statistic, and Heidke skill score), we compare performances of the solar flare prediction model with and without DARAL. True positive rate, true negative rate, true skill statistic, and Heidke skill score increase by 6.7% 1.3%, 4.2% 0.5%, 10.8% 1.4% and 8.7% 1.0%, respectively. Conclusions: The comparison indicates that the metric DARAL is beneficial to performances of the solar flare prediction model.

  8. The Magnetic Field Distribution in Active Regions in the Quiet Time and during Large Solar Flares

    NASA Astrophysics Data System (ADS)

    Podgorny, I. M.; Podgorny, A. I; Meshalkina, N. S.

    2014-03-01

    Many controversial results about magnetic field behavior in active regions during solar flares are published. The magnetic field dynamics of active regions that produce large (X class) flares are investigated in this paper. The magnetic flux is obtained by using the results of calculations of the normal magnetic component in the active region. It is shown that the main condition for appearance of an X clas s flare is the big magnetic flux (' > 1022Mx) of active region. This condition is necessary but not a sufficient. The large flare appears above an active region, if the magnetic field distribution is very complex. A simple active region with the bipolar magnetic field distribution does not produce a flare. There are no singular magnetic lines above a bipolar region, which can be responsible for a current sheet creation before the flare. During a solar flare, when the accumulated energy is fast released, the conservation of the magnetic field distribution in the active region during the majority of flares takes place. This surprising fact follows from the analysis of the array data obtained with the SOHO and SDO space crafts. The presented results support the flare theory based on the slow magnetic energy accumulation in the coronal current sheet before a flare and its explosive realize due to current sheet instability. The scheme of the current sheet creation is discussed, which explains the magnetic field dissipation in the corona without perturbations of magnetic field distribution on the Sun surface during

  9. MAGNETIC AND DYNAMICAL PHOTOSPHERIC DISTURBANCES OBSERVED DURING AN M3.2 SOLAR FLARE

    SciTech Connect

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

    2015-02-01

    This Letter reports on a set of full-Stokes spectropolarimetric observations in the near-infrared He i 10830 Å 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 Å 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{sup −3} and ∼10{sup −4} g cm{sup −2} s{sup −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.

  10. Hard x ray/microwave spectroscopy of solar flares

    NASA Technical Reports Server (NTRS)

    Gary, Dale E.

    1992-01-01

    The joint study of hard x ray and microwave observations of solar flares is extremely important because the two complementary ways of viewing the accelerated electrons yield information that cannot be obtained using hard x rays or microwaves alone. The microwaves can provide spatial information lacking in the hard x rays, and the x ray data can give information on the energy distribution of electrons that remove ambiguities in the radio data. A prerequisite for combining the two data-sets, however, is to first understand which range of microwave frequencies correlate best with the hard x rays. This SMM Guest Investigator grant enabled us to combine multi-frequency OVRO data with calibrated hard x ray data to shed light on the relationship between the two emissions. In particular, the questions of which microwave frequencies correspond to which hard x ray energies, and what is the corresponding energy of the electrons that produce both types of emission are investigated.

  11. Evidence for delayed second phase acceleration in solar flares

    NASA Technical Reports Server (NTRS)

    Willett, J. B.; Ling, J. C.; Mahoney, W. A.; Riegler, G. R.; Jacobson, A. S.

    1982-01-01

    Data gathered on solar gamma-ray events by the gamma-ray spectrometer on board the HEAO-3 satellite are discussed. Measurements were made of both hard X-ray and gamma-ray events. A total of 37 flare-like incidences were detected from October 1979 to July 1980. Power law spectra were fitted to the flux energies exceeding 420 keV. The appearance of two events with a 30 sec interval between radiation peaks, a slow rise and quick decay of the high energy component, and the softening of the low energy component are taken for evidence of two acceleration processes, one boosting electrons to hundreds of keV for the X ray bursts, the other producing gamma rays through ions accelerated to tens of MeV.

  12. U.S.-Japan Seminar on Recent Advances in the Understanding of Solar Flares, 2nd, Honolulu, HI, Apr. 7-10, 1987, Proceedings

    NASA Astrophysics Data System (ADS)

    Hudson, H.; Kai, K.

    Papers are presented on solar flare discovery, solar flares and magnetic topology, impulsive and hot thermal solar flares, and plasma dynamics at the very initial phases of flares. Also considered are a magnetodynamic mechanism for loop flares, the propagation and confinement of energetic electrons in solar flares, nuclear processes and accelerated particles in solar flares, and optical observations of solar flares. Other topics include delta spots and great flares, chromospheric downflow velocities as a diagnostic in solar flares, and subphotospheric current systems and flares. Papers are also presented on a long-duration balloon payload for hard X-ray and gamma-ray observations of the sun, the derivation of vector magnetic fields from Stokes profiles, and the Solar-A mission.

  13. A Model of Solar Flares Based on Arcade Field Reconnection and Merging of Magnetic Islands

    SciTech Connect

    G.S. Choe; C.Z. Cheng

    2001-12-12

    Solar flares are intense, abrupt releases of energy in the solar corona. In the impulsive phase of a flare, the intensity of hard X-ray emission reaches a sharp peak indicating the highest reconnection rate. It is often observed that an X-ray emitting plasma ejecta (plasmoid) is launched before the impulsive phase and accelerated throughout the phase. Thus, the plasmoid ejection may not be an effect of fast magnetic reconnection as conventionally assumed, but a cause of fast reconnection. Based on resistive magnetohydrodynamic simulations, a solar flare model is presented, which can explain these observational characteristics of flares. In the model, merging of a newly generated magnetic island and a pre-existing island results in stretching and thinning of a current sheet, in which fast magnetic reconnection is induced. Recurrence of homologous flares naturally arises in this model. Mechanisms of magnetic island formation are also discussed.

  14. Thermal Structure of Supra-Arcade Plasma in Two Solar Flares

    NASA Technical Reports Server (NTRS)

    Reeves, Katharine K.; Savage, Sabrina; McKenzie, David E.; Weber, Mark A.

    2012-01-01

    In this work, we use Hinode/XRT and SDO/AIA data to determine the thermal structure of supra-arcade plasma in two solar flares. The first flare is a Ml.2 flare that occurred on November 5, 2010 on the east limb. This flare was one of a series of flares from AR 11121, published in Reeves & Golub (2011). The second flare is an XI.7 flare that occurred on January 27, 2012 on the west limb. This flare exhibits visible supra-arcade downflows (SADs), where the November 2010 flare does not. For these two flares we combine XRT and AlA data to calculate DEMs of each pixel in the supra-arcade plasma, giving insight into the temperature and density structures in the fan of plasma above the post-flare arcade. We find in each case that the supra-arcade plasma is around 10 MK, and there is a marked decrease in the emission measure in the SADs. We also compare the DEMs calculated with the combined AIA/XRT dataset to those calculated using AIA alone.

  15. Constraints on Energy Storage and Release Models for Astrophysical Transients and Solar Flares

    NASA Astrophysics Data System (ADS)

    Lu, Edward T.

    1995-07-01

    Rosner & Vaiana (1978) proposed an energy storage and release scenario to explain the power-law distributions of transients seen from a wide variety of astrophysical objects including the Sun. We consider whether such a scenario can account for the observed power-law distribution of solar flares. We discuss the quantitative constraints that arise for any physically realizable model of this type and show that such a model is inconsistent with solar flare energy storage in the coronal magnetic field. Not only does this rule out such a model for solar flares, but it also calls into question the application of these models for other astrophysical transients.

  16. Numerical modeling of the energy storage and release in solar flares

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

    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.

  17. Gamma-ray and hard X-ray imaging of solar flares

    NASA Technical Reports Server (NTRS)

    Prince, T. A.; Hurford, G. J.; Hudson, H. S.; Crannell, C. J.

    1988-01-01

    The scientific and technical aspects of high-resolution gamma-ray and X-ray imaging of solar flares are discussed. The scientific necessity for imaging observations of solar flares and the implications of future observations for the study of solar flare electrons and ions are considered. Performance parameters for a future hard X-ray and gamma-ray imager are summarized. Techniques for high-energy photon imaging including direct collimation imaging, coded apertures, and modulation collimators are surveyed. The technique of Fourier-transform imaging is examined. The options for detectors and grid fabrication are reviewed. Several planned future high-energy imagers are described.

  18. Particle densities within the acceleration region of a solar flare

    SciTech Connect

    Krucker, Sm; Battaglia, Marina

    2014-01-01

    The limb flare SOL2012-07-19T05:58 (M7.7) provides the best example of a non-thermal above-the-loop-top hard X-ray source with simultaneous observations by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory. By combining the two sets of observations, we present the first direct measurement of the thermal proton density and non-thermal electron density within the above-the-loop-top source where particle acceleration occurs. We find that both densities are of the same order of magnitude of a few times 10{sup 9} cm{sup 3}, about 30 times lower than the density in the underlying thermal flare loops. The equal densities indicate that the entire electron population within the above-the-loop-top source is energized. While the derived densities depend on the unknown source depth and filling factor, the ratio of these two densities does not. Within the uncertainties, the ratio is one for a low energy cutoff of the non-thermal electron spectrum between 10 and 15 keV. RHESSI observations only constrain the cutoff energy to below ?15 keV, leaving the spectral shape of the electrons within the above-the-loop-top source at lower energies unknown. Nevertheless, these robust results strongly corroborate earlier findings that the above-the-loop-top source is the acceleration region where a bulk energization process acts on all electrons.

  19. DETERMINATION OF STOCHASTIC ACCELERATION MODEL CHARACTERISTICS IN SOLAR FLARES

    SciTech Connect

    Chen, Qingrong; Petrosian, Vah

    2013-11-01

    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.

  20. Model of Electric Energy Accumulation for Solar Flares

    NASA Astrophysics Data System (ADS)

    Krivodubskij, Valery N.

    2015-08-01

    The model of accumulation of energy (in the form of electric charges) for solar flares is proposed. We have named this mechanism as "model of the conditioned electric capacitor". Two magnetohydrodynamics effects play the key role in the proposed model. The essence of the first effect is that the turbulent motion sharply reduces the conductivity coefficient of solar plasma (turbulent conductivity). Meanwhile, a strong magnetic field in some parts of the active regions suppresses turbulence (second effect), thereby neutralizing turbulence impact on conductivity. As a result, near the neutral lines of the magnetic field, the portions of solar plasma will be coexisting with different values of conductivity. The electric current, excited by the large-scale plasma hydrodynamic motions across the mean magnetic field, serves as a source for energy accumulation. The electric charges must be accumulated at the boundaries of the region with reduced turbulent conductivity because of the difference of conductivity values near the neutral magnetic lines ("conditioned capacitor"). The subsequent electrical breakdown in the bulk of "capacitor" will serve as a trigger mechanism for releasing the stored energy.

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

    NASA Technical Reports Server (NTRS)

    Gosling, J. T.

    1995-01-01

    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.

  2. Radio imaging of solar flares using the very large array - New insights into flare process

    NASA Technical Reports Server (NTRS)

    Kundu, M. R.; Schmahl, E. J.; Vlahos, L.; Velusamy, T.

    1982-01-01

    An interpretation of VLA observations of microwave bursts is presented in an attempt to distinguish between certain models of flares. The VLA observations provide information about the pre-flare magnetic field topology and the existence of mildly relativistic electrons accelerated during flares. Examples are shown of changes in magnetic field topology in the hour before flares. In one case, new bipolar loops appear to emerge, which is an essential component of the model developed by Heyvaerts et al. (1977). In another case, a quadrupole structure, suggestive of two juxtaposed bipolar loops, appears to trigger the flare. Because of the observed diversity of magnetic field topologies in microwave bursts, it is believed that the magnetic energy must be dissipated in more than one way. The VLA observations are clearly providing means for sorting out the diverse flare models.

  3. A Two-ribbon White-light Flare Associated with a Failed Solar Eruption Observed by ONSET, SDO, and IRIS

    NASA Astrophysics Data System (ADS)

    Cheng, X.; Hao, Q.; Ding, M. D.; Liu, K.; Chen, P. F.; Fang, C.; Liu, Y. D.

    2015-08-01

    Two-ribbon brightenings are one of the most remarkable characteristics of an eruptive solar flare and are often used to predict the occurrence of coronal mass ejections (CMEs). Nevertheless, it was recently called into question whether all two-ribbon flares are eruptive. In this paper, we investigate a two-ribbon-like white-light (WL) flare that is associated with a failed magnetic flux rope (MFR) eruption on 2015 January 13, which has no accompanying CME in the WL coronagraph. Observations by the Optical and Near-infrared Solar Eruption Tracer and the Solar Dynamics Observatory reveal that with the increase of the flare emission and the acceleration of the unsuccessfully erupting MFR, two isolated kernels appear at the WL 3600 passband and quickly develop into two elongated ribbon-like structures. The evolution of the WL continuum enhancement is completely coincident in time with the variation of Fermi hard X-ray 26-50 keV flux. An increase of continuum emission is also clearly visible at the whole FUV and NUV passbands observed by the Interface Region Imaging Spectrograph. Moreover, in one WL kernel, the Si iv, C ii, and Mg ii h/k lines display significant enhancement and non-thermal broadening. However, their Doppler velocity pattern is location-dependent. At the strongly bright pixels, these lines exhibit a blueshift, while at moderately bright ones, the lines are generally redshifted. These results show that the failed MFR eruption is also able to produce a two-ribbon flare and high-energy electrons that heat the lower atmosphere, causing the enhancement of the WL and FUV/NUV continuum emissions and chromospheric evaporation.

  4. Evidence for a peak in the number of isolated Type III bursts prior to large solar flares

    NASA Technical Reports Server (NTRS)

    Jackson, B. V.; Sheridan, K. V.

    1979-01-01

    Evidence for a broad maximum in the number of isolated metric-wave Type III bursts prior to the large H alpha solar flares observed between May 1973 and February 1974 is reported. The time distribution of isolated Type III bursts within 12.6 h of each of the 111 solar flares of importance 1 or greater recorded during the period is shown to peak approximately 5 h before the time of flare maximum, most markedly in the case of bursts with projected positions near the solar flare position. The examination of H alpha, X-ray and magnetogram data in the vicinity of the flare implies a purely coronal storage and release mechanism for the flare energy. The peak of Type III burst activity is thus suggested as a good indicator of coronal energy input and storage near the time of a large solar flare, although not a reliable flare predictor.

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

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

    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.

  6. The H-alpha/H-beta ratio in solar flares

    NASA Technical Reports Server (NTRS)

    Zirin, H.; Liggett, M.; Patterson, A.

    1982-01-01

    The present investigation involves the study of an extensive body of data accumulated of simultaneous H-alpha and H-beta cinematography of flares. The data were obtained with two telescopes simultaneously photographing flares in H-alpha and H-beta. The results of measurements in a number of flares are presented in a table. The flares were selected purely by optical quality of the data. That the measured ratios are not too different from those in stellar flares is suggested by the last two columns of the table. These columns show that a variety of possible line width ratios could give an integrated intensity ratio of less than unity.

  7. MULTI-WAVELENGTH OBSERVATIONS OF SOLAR FLARES WITH A CONSTRAINED PEAK X-RAY FLUX

    SciTech Connect

    Bowen, Trevor A.; Testa, Paola; Reeves, Katharine K.

    2013-06-20

    We present an analysis of soft X-ray (SXR) and extreme-ultraviolet (EUV) observations of solar flares with an approximate C8 Geostationary Operational Environmental Satellite (GOES) class. Our constraint on peak GOES SXR flux allows for the investigation of correlations between various flare parameters. We show that the duration of the decay phase of a flare is proportional to the duration of its rise phase. Additionally, we show significant correlations between the radiation emitted in the flare rise and decay phases. These results suggest that the total radiated energy of a given flare is proportional to the energy radiated during the rise phase alone. This partitioning of radiated energy between the rise and decay phases is observed in both SXR and EUV wavelengths. Though observations from the EUV Variability Experiment show significant variation in the behavior of individual EUV spectral lines during different C8 events, this work suggests that broadband EUV emission is well constrained. Furthermore, GOES and Atmospheric Imaging Assembly data allow us to determine several thermal parameters (e.g., temperature, volume, density, and emission measure) for the flares within our sample. Analysis of these parameters demonstrate that, within this constrained GOES class, the longer duration solar flares are cooler events with larger volumes capable of emitting vast amounts of radiation. The shortest C8 flares are typically the hottest events, smaller in physical size, and have lower associated total energies. These relationships are directly comparable with several scaling laws and flare loop models.

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

    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.

  9. Multiple Views of X1.4 Solar Flare on July 12, 2012 - Duration: 60 seconds.

    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...

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

    NASA Astrophysics Data System (ADS)

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

    1989-07-01

    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.

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

    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...

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

    NASA Technical Reports Server (NTRS)

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

    1973-01-01

    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.

  13. Transient ionization and solar flare X-ray spectra

    NASA Technical Reports Server (NTRS)

    Doschek, G. A.; Tanaka, K.

    1987-01-01

    In this paper the effects of a transiently ionizing solar flare plasma on the X-ray spectrum of iron between 1.85 and 1.92 A are considered. The atomic physics of the nonequilibrium spectrum is discussed, and reasons for differences in appearance from ionization equilibrium spectra are explained. The effect of spectral resolution on the ability to detect transient ionization in the iron X-ray spectrum is illustrated by synthetic spectra. A synthetic transiently ionizing spectrum is applied to the interpretation of spectra obtained from the SOX 1 spectrometer on the Japanese Hinotori spacecraft. Some indications of transient ionization are found, although counting statistics negate a strong conclusion. A hypothetical spectrometer with about one order of magnitude more sensitivity than the SOX 1 Hinotori or the bent crystal spectrometer flown on the Solar Maximum Mission (SMM) is also considered. The ranges of plasma parameters such as plasma emission measure and density that are necessary for transient ionization to be detected by such an instrument are discussed.

  14. THE SOLAR FLARE SULFUR ABUNDANCE FROM RESIK OBSERVATIONS

    SciTech Connect

    Sylwester, J.; Sylwester, B.; Phillips, K. J. H.; Kuznetsov, V. D. E-mail: bs@cbk.pan.wroc.pl E-mail: kvd@izmiran.ru

    2012-06-01

    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.

  15. Flares and Antiflares on Young Solar Analog EK Draconis

    NASA Astrophysics Data System (ADS)

    Ayres, Thomas R.

    2015-01-01

    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.

  16. Solar Flare Element Abundances from the Solar Assembly for X-Rays (SAX) on MESSENGER

    NASA Astrophysics Data System (ADS)

    Dennis, Brian R.; Phillips, Kenneth J. H.; Schwartz, Richard A.; Tolbert, Anne K.; Starr, Richard D.; Nittler, Larry R.

    2015-04-01

    X-ray spectra in the range 1.5-8.5 keV have been analyzed for 526 large flares detected with the Solar Assembly for X-rays (SAX) on the Mercury MESSENGER spacecraft between 2007 and 2013. For each flare, the temperature and emission measure of the emitting plasma were determined from the spectrum of the continuum. In addition, with the SAX energy resolution of 0.6 keV (FWHM) at 6 keV, the intensities of the clearly resolved Fe-line complex at 6.7 keV and the Ca-line complex at 3.9 keV were determined, along with those of unresolved line complexes from S, Si, and Ar at lower energies. Comparisons of these line intensities with theoretical spectra allow the abundances of these elements relative to hydrogen to be derived, with uncertainties due to instrument calibration and the unknown temperature distribution of the emitting plasma. While significant deviations are found for the abundances of Fe and Ca from flare to flare, the abundances averaged over all flares are found to be enhanced over photospheric values by factors of 1.66 0.34 (Fe), 3.89 0.76 (Ca), 1.23 0.45 (S), 1.64 0.66 (Si), and 2.48 0.90 (Ar). These factors differ from previous reported values for Fe and Si at least. They suggest a more complex relation of abundance enhancement with the first ionization potential (FIP) of the element than previously considered, with the possibility that fractionation occurs in flares for elements with an FIP of less than 7 eV rather than 10 eV.

  17. Gamma-ray and microwave evidence for two phases of acceleration in solar flares

    NASA Technical Reports Server (NTRS)

    Bai, T.; Ramaty, R.

    1976-01-01

    Relativistic electrons in large solar flares produce gamma ray continuum by bremsstrahlung and microwave emission by gyrosynchrotron radiation. Using observations of the 1972, August 4 flare, the electron spectrum and the physical properties of the common emitting region of these radiations were evaluated. Information was also obtained on energetic protons in this flare by using gamma ray lines. From the electron spectrum, the proton-to-electron ratio, and the time dependences of the microwave emission, the 2.2 MeV line and the gamma ray continuum, it was concluded that in large solar flares relativistic electrons and energetic nuclei are accelerated by a mechanism which is different from the mechanism which accelerates approximately less than 100 keV electrons in flares.

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

    NASA Technical Reports Server (NTRS)

    Das, Uma; Pallamraju, Duggirala; Chakrabarti, Supriya

    2010-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Das, Uma; Pallamraju, Duggirala; Chakrabarti, Supriya

    2010-08-01

    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 (23.16°S, 70.66°W), 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.

  20. Spectral Analysis on Solar Flares with an Emission > 300 keV

    NASA Astrophysics Data System (ADS)

    Vargas, R.; Connaughton, V.

    2013-12-01

    The continuum gamma-ray emission from solar flares is caused when a population of electrons is accelerated to relativistic speeds and interacts with the solar plasma. However, it has been theorized that the gamma-ray emission from some brighter flares comes from two populations of electrons. Using the Gamma-Ray Burst Monitor (GBM), we studied the gamma-ray emission spectra of solar flares and paid special attention to the solar flares that showed emission above 300 keV. We found that the emission above 300 keV was better fit with a broken power-law than a single power-law, evidence that the gamma-ray emission from certain solar flares involved two populations of electrons. Specifically, our best model involved a broken power law that had a steeper slope before the break in energy than after. We studied the spectral parameters as a function of time during the period of the high-energy emission. We also found that solar flares with emission above 300 keV form a small subset (~4%) of flares that trigger GBM above 20 keV. One of the flares with an emission greater than 300 keV was fitted with a Broken Power Law model. Only data from the BGO detector was used in making the plots. Various parameters of the fit have been plotted vs. time with the top two graphs representing the light curves of the flare from different detectors (BGO-0 and NaI-4). A spectral fit for bn100612038 for the time interval of [45s-50s] using only the BGO (0) detector file. Data from this fit was used in creating the other plots.

  1. Heavy solar cosmic rays in the January 25, 1971 solar flares

    NASA Technical Reports Server (NTRS)

    Pellerin, C. J., Jr.

    1974-01-01

    A detailed study of the charge composition of heavy solar cosmic rays measured in the January 25, 1971 solar flare including differential fluxes for the even charged nuclei from carbon through argon is presented. The measurements are obtained for varying energy intervals for each nuclear species in the energy range from 10 to 35 MeV/nucleon. In addition, abundances relative to oxygen are computed for all the above nuclei in the single energy interval from 15 to 25 MeV/nucleon. This interval contains measurements for all of the species and as a result requires no spectral extrapolations. An upper limit for the abundance of calcium nuclei is also presented. These measurements, when combined with other experimental results, enable the energy dependence of abundance measurements as a function of nuclear charge to be discussed. It is seen that at energies above about 10 MeV/nucleon, the variations of abundance ratios are limited to about a factor of 3 from flare to flare, in spite of large variations in other characteristics of these solar events.

  2. 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)

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

    2013-05-01

    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.

  3. Stereoscopic observations of hard x ray sources in solar flares made with GRO and other spacecraft

    NASA Technical Reports Server (NTRS)

    Kane, S. R.; Hurley, K.; Mctiernan, J. M.; Laros, J. G.

    1992-01-01

    Since the launch of the Gamma Ray Observatory (GRO) in Apr. 1991, the Burst and Transient Source Experiment (BATSE) instrument on GRO has recorded a large number of solar flares. Some of these flares have also been observed by the Gamma-Ray Burst Detector on the Pioneer Venus Orbiter (PVO) and/or by the Solar X-Ray/Cosmic Gamma-Ray Burst Experiment on the Ulysses spacecraft. A preliminary list of common flares observed during the period May-Jun. 1991 is presented and the possible joint studies are indicated.

  4. OSO-8 observations of the impulsive phase of solar flares in the transition-zone and corona

    NASA Technical Reports Server (NTRS)

    Lites, B. W.; Bruner, E. C., Jr.; Wolfson, C. J.

    1981-01-01

    Several solar flares were observed from their onset in C IV 1548.2 A and 1-8 A X-rays using instruments on OSO-8. It is found that impulsive brightening in C IV is often accompanied by redshifts, interpreted as downflows, of the order of 80 km/s. The maximum soft X-ray intensity usually arrives several minutes after the maximum C IV intensity. The most energetic C IV event observed shows a small blueshift just before reaching maximum intensity; estimates of the mass flux associated with this upflow through the transition zone are consistent with the increase of mass in the coronal loops as observed in soft X-rays. Finally, it is suggested that the frequent occurrence of violent dynamical processes at the onset of the flare is associated with the initial energy release mechanism.

  5. Upgraded Siberian Solar Radio Telescope: new opportunities to diagnose energetic particles in solar flares

    NASA Astrophysics Data System (ADS)

    Kuznetsov, Alexey; Altyntsev, Alexander; Sergey, Lesovoi; Fleishman, Gregory

    Energetic electrons are a key factor of solar flares and therefore knowing their parameters is highly important for understanding the flare mechanisms and verifying the flare models. Radio emission offers multiple promising diagnostic tools, because this emission is produced by these energetic particles in the corona, at or near the particle acceleration sites. However, high diagnostic potential of radio observations has not yet been fully utilized due to two main reasons: (1) lack of well-calibrated observations with high spatial, spectral, and temporal resolutions and (2) lack of accurate and reliable theoretical models and fast numerical tools capable of recovering the emission source parameters from the radio data. Here we report on the recent and anticipated progress in both these science components - instrumentation and modeling. To this end the Siberian Solar Radio Telescope (Badary, Russia) is now being significantly upgraded in order to convert this instrument into a multi-wavelength imaging spectropolarimetry radioheliograph. At stage 1, the instrument will produce two-dimensional images of the Sun with high temporal and spatial resolution at five frequencies simultaneously in the 4-8 GHz range; this stage will be completed in 2015. Final (stage 2) configuration of the Upgraded Siberian Solar Radio Telescope (expected to be completed in 2019) will perform imaging observations at 15 frequencies in the 3-24 GHz range. At the same time, we are developing new theoretical methods and computer codes to analyze and interpret the anticipated observational data; the recent achievements include the "fast gyrosynchrotron codes", gyroresonance codes, and the 3D simulation tool "GX Simulator" freely available via the SSW distribution. In this presentation, we discuss the approaches to diagnosing the solar energetic particles with radio observations, including the recent advances and the opportunities coming from the construction of the Multiwavelength Siberian Solar Radio Telescope. We also discuss some unsolved problems in this field, which require cooperative efforts of the solar physics community.

  6. Tsallis non-extensive statistics, intermittent turbulence, SOC and chaos in the solar plasma. Part two: Solar flares dynamics

    NASA Astrophysics Data System (ADS)

    Karakatsanis, L. P.; Pavlos, G. P.; Xenakis, M. N.

    2013-09-01

    In this study which is the continuation of the first part (Pavlos et al. 2012) [1], the nonlinear analysis of the solar flares index is embedded in the non-extensive statistical theory of Tsallis (1988) [3]. The q-triplet of Tsallis, as well as the correlation dimension and the Lyapunov exponent spectrum were estimated for the singular value decomposition (SVD) components of the solar flares timeseries. Also the multifractal scaling exponent spectrum f(a), the generalized Renyi dimension spectrum D(q) and the spectrum J(p) of the structure function exponents were estimated experimentally and theoretically by using theq-entropy principle included in Tsallis non-extensive statistical theory, following Arimitsu and Arimitsu (2000) [25]. Our analysis showed clearly the following: (a) a phase transition process in the solar flare dynamics from a high dimensional non-Gaussian self-organized critical (SOC) state to a low dimensional also non-Gaussian chaotic state, (b) strong intermittent solar corona turbulence and an anomalous (multifractal) diffusion solar corona process, which is strengthened as the solar corona dynamics makes a phase transition to low dimensional chaos, (c) faithful agreement of Tsallis non-equilibrium statistical theory with the experimental estimations of the functions: (i) non-Gaussian probability distribution function P(x), (ii) f(a) and D(q), and (iii) J(p) for the solar flares timeseries and its underlying non-equilibrium solar dynamics, and (d) the solar flare dynamical profile is revealed similar to the dynamical profile of the solar corona zone as far as the phase transition process from self-organized criticality (SOC) to chaos state. However the solar low corona (solar flare) dynamical characteristics can be clearly discriminated from the dynamical characteristics of the solar convection zone.

  7. Observations of solar-flare ionization in the mesosphere using coherent-scatter radar

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

    Observations of solar-flare ionization in the mesosphere can be made using coherent-scatter radar systems. The scattered power profiles they measure in the 60-90 km altitude region is a function of the ion concentration gradient and the intensity of turbulent mixing at each altitude. By comparing the power profiles before, during and after a solar flare, it is possible to estimate the ion production rate during the flare as a function of altitude and time. This analysis is used to compare the ion production rates with generally accepted ion-chemical models. Comparisons are made with ion production rates estimated from the solar X-ray flux for the same flare made by geostationary satellites.

  8. Implications of X-Ray Observations for Electron Acceleration and Propagation in Solar Flares

    NASA Technical Reports Server (NTRS)

    Holman, G. D.; Aschwanden, M. J.; Aurass, H.; Battaglia, M.; Grigis, P. C.; Kontar, E. P.; Liu, W.; Saint-Hilaire, P.; Zharkova, V. V.

    2011-01-01

    High-energy X-rays and gamma-rays from solar flares were discovered just over fifty years ago. Since that time, the standard for the interpretation of spatially integrated flare X-ray spectra at energies above several tens of keV has been the collisional thick-target model. After the launch of the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) in early 2002, X-ray spectra and images have been of sufficient quality to allow a greater focus on the energetic electrons responsible for the X-ray emission, including their origin and their interactions with the flare plasma and magnetic field. The result has been new insights into the flaring process, as well as more quantitative models for both electron acceleration and propagation, and for the flare environment with which the electrons interact. In this article we review our current understanding of electron acceleration, energy loss, and propagation in flares. Implications of these new results for the collisional thick-target model, for general flare models, and for future flare studies are discussed.

  9. A comparison between statistical properties of solar X-ray flares and avalanche predictions in cellular automata statistical flare models

    NASA Astrophysics Data System (ADS)

    Georgoulis, M. K.; Vilmer, N.; Crosby, N. B.

    2001-02-01

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

  10. Slipping magnetic reconnection during an X-class solar flare observed by SDO/AIA

    SciTech Connect

    Dudk, J.; Del Zanna, G.; Mason, H. E.; Janvier, M.; Aulanier, G.; Schmieder, B.; Karlick, M. E-mail: mjanvier@maths.dundee.ac.uk

    2014-04-01

    We present SDO/AIA observations of an eruptive X-class flare of 2012 July 12, and compare its evolution with the predictions of a three-dimensional (3D) numerical simulation. We focus on the dynamics of flare loops that are seen to undergo slipping reconnection during the flare. In the Atmospheric Imaging Assembly (AIA) 131 observations, lower parts of 10 MK flare loops exhibit an apparent motion with velocities of several tens of km s{sup 1} along the developing flare ribbons. In the early stages of the flare, flare ribbons consist of compact, localized bright transition-region emission from the footpoints of the flare loops. A differential emission measure analysis shows that the flare loops have temperatures up to the formation of Fe XXIV. A series of very long, S-shaped loops erupt, leading to a coronal mass ejection observed by STEREO. The observed dynamics are compared with the evolution of magnetic structures in the 'standard solar flare model in 3D.' This model matches the observations well, reproducing the apparently slipping flare loops, S-shaped erupting loops, and the evolution of flare ribbons. All of these processes are explained via 3D reconnection mechanisms resulting from the expansion of a torus-unstable flux rope. The AIA observations and the numerical model are complemented by radio observations showing a noise storm in the metric range. Dm-drifting pulsation structures occurring during the eruption indicate plasmoid ejection and enhancement of the reconnection rate. The bursty nature of radio emission shows that the slipping reconnection is still intermittent, although it is observed to persist for more than an hour.

  11. Trigger of a Blowout Jet in a Solar Coronal Mass Ejection Associated with a Flare

    NASA Astrophysics Data System (ADS)

    Li, Xiaohong; Yang, Shuhong; Chen, Huadong; Li, Ting; Zhang, Jun

    2015-11-01

    Using the multi-wavelength images and the photospheric magnetograms from the Solar Dynamics Observatory, we study the flare that was associated with the only coronal mass ejection (CME) in active region (AR) 12192. The eruption of a filament caused a blowout jet, and then an M4.0 class flare occurred. This flare was located at the edge of the AR instead of in the core region. The flare was close to the apparently open fields, appearing as extreme-ultraviolet structures that fan out rapidly. Due to the interaction between flare materials and open fields, the flare became an eruptive flare, leading to the CME. Then, at the same site of the first eruption, another small filament erupted. With the high spatial and temporal resolution H? data from the New Vacuum Solar Telescope at the Fuxian Solar Observatory, we investigate the interaction between the second filament and the nearby open lines. The filament reconnected with the open lines, forming a new system. To our knowledge, the detailed process of this kind of interaction is reported for the first time. Then the new system rotated due to the untwisting motion of the filament, implying that the twist was transferred from the closed filament system to the open system. In addition, the twist seemed to propagate from the lower atmosphere to the upper layers and was eventually spread by the CME to the interplanetary space.

  12. New observational facts about particle acceleration and transport during solar flares

    NASA Technical Reports Server (NTRS)

    Trottel, G.

    1996-01-01

    Extensive hard X-ray (HXR)/gamma-ray (GR) observations of solar flares, performed during solar cycles 21 and 22 have led to important new discoveries. These data, combined with observations obtained in other parts of the electromagnetic spectrum (soft X-ray, Hard X-ray, optical, and radio) largley contributed to get a better understanding and to develop new ideas on particle acceleration and transport during solar flares. This review presents new observational facts relevant to hard X-ray/gamma-ray producing flares. Among these are the frequent presence of sub-second time structure in the hard X-ray emission, the variability in hard X-ray and radio spatial distributions during a flare and from flare to flare, the evidence for strong gamma-ray line emission from the Corona and the existence of extended phases of the gamma-ray emission lasting for several hours after the flare onset. This ensemble of observations indicates that particle acceleration takes place at different sites in a complex and dynamic magnetic field environment.

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

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

    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.

  14. MHD discontinuities in solar flares: Continuous transitions and plasma heating

    NASA Astrophysics Data System (ADS)

    Ledentsov, L. S.; Somov, B. V.

    2015-12-01

    The boundary conditions for the ideal MHD equations on a plane discontinuity surface are investigated. It is shown that, for a given mass flux through a discontinuity, its type depends only on the relation between inclination angles of a magnetic field. Moreover, the conservation laws on a surface of discontinuity allow changing a discontinuity type with gradual (continuous) changes in the conditions of plasma flow. Then there are the so-called transition solutions that satisfy simultaneously two types of discontinuities. We obtain all transition solutions on the basis of the complete system of boundary conditions for the MHD equations. We also found the expression describing a jump of internal energy of the plasma flowing through the discontinuity. Firstly, this allows constructing a generalized scheme of possible continuous transitions between MHD discontinuities. Secondly, it enables the examination of the dependence of plasma heating by plasma density and configuration of the magnetic field near the discontinuity surface, i.e., by the type of the MHD discontinuity. It is shown that the best conditions for heating are carried out in the vicinity of a reconnecting current layer near the areas of reverse currents. The result can be helpful in explaining the temperature distributions inside the active regions in the solar corona during flares observed by modern space observatories in soft and hard X-rays.

  15. Solar Flare Abundances of Potassium, Argon, and Sulphur

    NASA Technical Reports Server (NTRS)

    Oegerle, William (Technical Monitor); Phillips, K. J. H.; Sylwester, J.; Sylwester, B.; Landi, E.

    2003-01-01

    The absolute coronal abundances of potassium has been determined for the first time from X-ray solar flare line and continuous spectra together with absolute and relative abundances of Ar and S. Potassium is of importance in the continuing debate concerning the nature of the coronal/photospheric element abundance ratios which are widely considered to depend on first ionization potential since it has the lowest FIP of any common element in the Sun. The measurements were obtained with the RESIK crystal spectrometer on the Coronas-F spacecraft. A differential emission measure DEM = const. x exp (-(beta)T(sub e) was found to be the most consistent with the data out of three models considered. We find that the coronal ratio [K/H] = 3.7 x 10(exp - 7), a factor 3 times photospheric, in agreement with other observations using line-to-line ratios. Our measured value for the coronal ratio [Ar/H] = 1.5 x 10(exp -6) is significantly less than photospheric, indicating that there is a slight depletion of this high-FIP element in the corona. For S (an intermediate-FIP element) we obtained [S/H] = 2.2 x 10(exp - 5), approximately the same as in previous work.

  16. Magnetic shielding of interplanetary spacecraft against solar flare radiation

    NASA Technical Reports Server (NTRS)

    Cocks, Franklin H.; Watkins, Seth

    1993-01-01

    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.

  17. Optimal Electron Energies for Driving Chromospheric Evaporation in Solar Flares

    NASA Astrophysics Data System (ADS)

    Reep, J. W.; Bradshaw, S. J.; Alexander, D.

    2015-08-01

    In the standard model of solar flares, energy deposition by a beam of electrons drives strong chromospheric evaporation leading to a significantly denser corona and much brighter emission across the spectrum. Chromospheric evaporation was examined in great detail by Fisher et al., who described a distinction between two different regimes, termed explosive and gentle evaporation. In this work, we examine the importance of electron energy and stopping depths on the two regimes and on the atmospheric response. We find that with explosive evaporation, the atmospheric response does not depend strongly on electron energy. In the case of gentle evaporation, lower energy electrons are significantly more efficient at heating the atmosphere and driving up-flows sooner than higher energy electrons. We also find that the threshold between explosive and gentle evaporation is not fixed at a given beam energy flux, but also depends strongly on the electron energy and duration of heating. Further, at low electron energies, a much weaker beam flux is required to drive explosive evaporation.

  18. Search for evidence of low energy protons in solar flares

    NASA Astrophysics Data System (ADS)

    Metcalf, Thomas R.; Wuelser, Jean-Pierre; Canfield, Richard C.; Hudson, Hugh S.

    1992-02-01

    We searched for linear polarization in the H alpha line using the Stokes Polarimeter at Mees Solar Observatory and present observations of a flare from NOAA active region 6659 which began at 01:30 UT on 14 Jun. 1991. Our dataset also includes H alpha spectra from the Mees charge coupled device (MCCD) imaging spectrograph as well as hard x ray observations from the Burst and Transient Source Experiment (BATSE) instrument on board the Gamma Ray Observatory (GRO). The polarimeter scanned a 40 x 40 inch field of view using 16 raster points in a 4 x 4 grid. Each scan took about 30 seconds with 2 seconds at each raster point. The polarimeter stopped 8.5 inches between raster points and each point covered a 6 inch region. This sparse sampling increased the total field of view without reducing the temporal cadence. At each raster point, an H alpha spectrum with 20 mA spectral sampling is obtained covering 2.6 A centered on H alpha line center. The preliminary conclusions from the research are presented.

  19. A CLASSIFICATION SCHEME FOR TURBULENT ACCELERATION PROCESSES IN SOLAR FLARES

    SciTech Connect

    Bian, Nicolas; Kontar, Eduard P.; Emslie, A. Gordon E-mail: eduard@astro.gla.ac.uk

    2012-08-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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

  1. High-energy Gamma-Ray Emission from Solar Flares: Summary of Fermi Large Area Telescope Detections and Analysis of Two M-class Flares

    NASA Astrophysics Data System (ADS)

    Ackermann, M.; Ajello, M.; Albert, A.; Allafort, A.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Bissaldi, E.; Bonamente, E.; Bottacini, E.; Bouvier, A.; Brandt, T. J.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Cecchi, C.; Charles, E.; Chekhtman, A.; Chen, Q.; Chiang, J.; Chiaro, G.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Cutini, S.; D'Ammando, F.; de Angelis, A.; de Palma, F.; Dermer, C. D.; Desiante, R.; Digel, S. W.; Di Venere, L.; Silva, E. do Couto e.; Drell, P. S.; Drlica-Wagner, A.; Favuzzi, C.; Fegan, S. J.; Focke, W. B.; Franckowiak, A.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Germani, S.; Giglietto, N.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grenier, I. A.; Grove, J. E.; Guiriec, S.; Hadasch, D.; Hayashida, M.; Hays, E.; Horan, D.; Hughes, R. E.; Inoue, Y.; Jackson, M. S.; Jogler, T.; Jhannesson, G.; Johnson, W. N.; Kamae, T.; Kawano, T.; Kndlseder, J.; Kuss, M.; Lande, J.; Larsson, S.; Latronico, L.; Lemoine-Goumard, M.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Mayer, M.; Mazziotta, M. N.; McEnery, J. E.; Michelson, P. F.; Mizuno, T.; Moiseev, A. A.; Monte, C.; Monzani, M. E.; Moretti, E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Murphy, R.; Nemmen, R.; Nuss, E.; Ohno, M.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orienti, M.; Orlando, E.; Ormes, J. F.; Paneque, D.; Panetta, J. H.; Perkins, J. S.; Pesce-Rollins, M.; Petrosian, V.; Piron, F.; Pivato, G.; Porter, T. A.; Rain, S.; Rando, R.; Razzano, M.; Reimer, A.; Reimer, O.; Ritz, S.; Schulz, A.; Sgr, C.; Siskind, E. J.; Spandre, G.; Spinelli, P.; Takahashi, H.; Takeuchi, Y.; Tanaka, Y.; Thayer, J. G.; Thayer, J. B.; Thompson, D. J.; Tibaldo, L.; Tinivella, M.; Tosti, G.; Troja, E.; Tronconi, V.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Vianello, G.; Vitale, V.; Werner, M.; Winer, B. L.; Wood, D. L.; Wood, K. S.; Wood, M.; Yang, Z.

    2014-05-01

    We present the detections of 18 solar flares detected in high-energy ?-rays (above 100 MeV) with the Fermi Large Area Telescope (LAT) during its first 4 yr of operation. This work suggests that particle acceleration up to very high energies in solar flares is more common than previously thought, occurring even in modest flares, and for longer durations. Interestingly, all these flares are associated with fairly fast coronal mass ejections (CMEs). We then describe the detailed temporal, spatial, and spectral characteristics of the first two long-lasting events: the 2011 March 7 flare, a moderate (M3.7) impulsive flare followed by slowly varying ?-ray emission over 13 hr, and the 2011 June 7 M2.5 flare, which was followed by ?-ray emission lasting for 2 hr. We compare the Fermi LAT data with X-ray and proton data measurements from GOES and RHESSI. We argue that the ?-rays are more likely produced through pion decay than electron bremsstrahlung, and we find that the energy spectrum of the proton distribution softens during the extended emission of the 2011 March 7 flare. This would disfavor a trapping scenario for particles accelerated during the impulsive phase of the flare and point to a continuous acceleration process at play for the duration of the flares. CME shocks are known for accelerating the solar energetic particles (SEPs) observed in situ on similar timescales, but it might be challenging to explain the production of ?-rays at the surface of the Sun while the CME is halfway to the Earth. A stochastic turbulence acceleration process occurring in the solar corona is another likely scenario. Detailed comparison of characteristics of SEPs and ?-ray-emitting particles for several flares will be helpful to distinguish between these two possibilities.

  2. High-energy gamma-ray emission from solar flares: Summary of Fermi large area telescope detections and analysis of two M-class flares

    SciTech Connect

    Ackermann, M.; Ajello, M.; Albert, A.; Allafort, A.; Bechtol, K.; Bottacini, E.; Buehler, R.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Buson, S.; Bellazzini, R.; Bregeon, J.; Bissaldi, E.; Bonamente, E.; Bouvier, A.; Brandt, T. J.; Brigida, M.; Bruel, P.; and others

    2014-05-20

    We present the detections of 18 solar flares detected in high-energy γ-rays (above 100 MeV) with the Fermi Large Area Telescope (LAT) during its first 4 yr of operation. This work suggests that particle acceleration up to very high energies in solar flares is more common than previously thought, occurring even in modest flares, and for longer durations. Interestingly, all these flares are associated with fairly fast coronal mass ejections (CMEs). We then describe the detailed temporal, spatial, and spectral characteristics of the first two long-lasting events: the 2011 March 7 flare, a moderate (M3.7) impulsive flare followed by slowly varying γ-ray emission over 13 hr, and the 2011 June 7 M2.5 flare, which was followed by γ-ray emission lasting for 2 hr. We compare the Fermi LAT data with X-ray and proton data measurements from GOES and RHESSI. We argue that the γ-rays are more likely produced through pion decay than electron bremsstrahlung, and we find that the energy spectrum of the proton distribution softens during the extended emission of the 2011 March 7 flare. This would disfavor a trapping scenario for particles accelerated during the impulsive phase of the flare and point to a continuous acceleration process at play for the duration of the flares. CME shocks are known for accelerating the solar energetic particles (SEPs) observed in situ on similar timescales, but it might be challenging to explain the production of γ-rays at the surface of the Sun while the CME is halfway to the Earth. A stochastic turbulence acceleration process occurring in the solar corona is another likely scenario. Detailed comparison of characteristics of SEPs and γ-ray-emitting particles for several flares will be helpful to distinguish between these two possibilities.

  3. Dynamic evolution of the transition zone plasma in solar flares and active region transients

    NASA Technical Reports Server (NTRS)

    Cheng, Chung-Chieh; Tandberg-Hanssen, E.

    1986-01-01

    The dynamic evolution of flares and of transient brightenings in active regions observed during the Solar Maximum Mission (SMM) in the UV lines of Si IV and O IV were studied. Transient brightenings in active regions and in flares occur in small points or kernels, not necessarily the initially bright regions. There is no apparent velocity pattern in which flaring or transient brightenings preferentially occur. At the flaring point, the velocity of the transition zone plasma tends to show larger downflow in the rise phase, and after the peak UV emission the downflow decreases or may even reverse and become upflow. This anticorrelation between velocity and UV intensity holds for some of the transient bright points but is more apparent for the flaring points.

  4. PLASMA HEATING IN THE VERY EARLY AND DECAY PHASES OF SOLAR FLARES

    SciTech Connect

    Falewicz, R.; Rudawy, P.; Siarkowski, M. E-mail: rudawy@astro.uni.wroc.pl

    2011-05-20

    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.

  5. Spatial and temporal evolution of soft and hard X-ray emission in a solar flare

    NASA Technical Reports Server (NTRS)

    Machado, M. E.; Duijveman, A.; Dennis, B. R.

    1982-01-01

    Hard X-ray burst spectrometer and imaging spectrometer data are used to study the spatial and temporal characteristics of the 3.5-30.0 keV emission in an Apr. 10, 1980 solar flare. It is found that: (1) continuous energy release is needed to sustain the increase of the emission through the flare's rising phase, before and after the impulsive phase in hard X-rays, and the release is characterized by the production of 50 million-150 million K thermal regions within the flare loop structures; (2) the observational parameters which characterize the impulsive burst indicate that it is probably associated with nonthermal processes, such as particle acceleration; and (3) the continuous energy release is associated with strong chromospheric evaporation, in view of spectral line behavior. Both particle acceleration and chromospheric evaporation stop just before flare maximum, and the subsequent evolution is probably governed by the radiative cooling of the flare plasma.

  6. A CRITICAL EXAMINATION OF THE FUNDAMENTAL ASSUMPTIONS OF SOLAR FLARE AND CORONAL MASS EJECTION MODELS

    SciTech Connect

    Spicer, D. S.; Bingham, R.; Harrison, R.

    2013-05-01

    The fundamental assumptions of conventional solar flare and coronal mass ejection (CME) theory are re-examined. In particular, the common theoretical assumption that magnetic energy that drives flares and CMEs can be stored in situ in the corona with sufficient energy density is found wanting. In addition, the observational constraint that flares and CMEs produce non-thermal electrons with fluxes of order 10{sup 34}-10{sup 36} electrons s{sup -1}, with energies of order 10-20 keV, must also be explained. This constraint when imposed on the ''standard model'' for flares and CMEs is found to miss the mark by many orders of magnitude. We suggest, in conclusion, there are really only two possible ways to explain the requirements of observations and theory: flares and CMEs are caused by mass-loaded prominences or driven directly by emerging magnetized flux.

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

    NASA Technical Reports Server (NTRS)

    Wilson, R. M.

    1977-01-01

    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.

  8. The Relation between Solar Eruption Topologies and Observed Flare Features. II. Dynamical Evolution

    NASA Astrophysics Data System (ADS)

    Savcheva, A.; Pariat, E.; McKillop, S.; McCauley, P.; Hanson, E.; Su, Y.; DeLuca, E. E.

    2016-01-01

    A long-established goal of solar physics is to build understanding of solar eruptions and develop flare and coronal mass ejection (CME) forecasting models. In this paper, we continue our investigation of nonlinear forces free field (NLFFF) models by comparing topological properties of the solutions to the evolution of the flare ribbons. In particular, we show that data-constrained NLFFF models of three erupting sigmoid regions (SOL2010-04-08, SOL2010-08-07, and SOL2012-05-12) built to reproduce the active region magnetic field in the pre-flare state can be rendered unstable and the subsequent sequence of unstable solutions produces quasi-separatrix layers that match the flare ribbon evolution as observed by SDO/AIA. We begin with a best-fit equilibrium model for the pre-flare active region. We then add axial flux to the flux rope in the model to move it across the stability boundary. At this point, the magnetofrictional code no longer converges to an equilibrium solution. The flux rope rises as the solutions are iterated. We interpret the sequence of magnetofrictional steps as an evolution of the active region as the flare/CME begins. The magnetic field solutions at different steps are compared with the flare ribbons. The results are fully consistent with the three-dimensional extension of the standard flare/CME model. Our ability to capture essential topological features of flaring active regions with a non-dynamic magnetofrictional code strongly suggests that the pre-flare, large-scale topological structures are preserved as the flux rope becomes unstable and lifts off.

  9. Solar Energy-An Everyday Occurrence

    ERIC Educational Resources Information Center

    Keister, Carole; Cornell, Lu Beth

    1978-01-01

    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)

  10. Electron impact polarization expected in solar EUV lines from flaring chromospheres/transition regions

    NASA Technical Reports Server (NTRS)

    Fineschi, S.; Fontenla, Juan M.; Macneice, P.; Ljepojevic, N. N.

    1991-01-01

    We have evaluated lower bounds on the degree of impact Extreme Ultraviolet/Ultraviolet (EUV/UV) line polarization expected during solar flares. This polarization arises from collisional excitation by energetic electrons with non-Maxwellian velocity distributions. Linear polarization was observed in the S I 1437 A line by the Ultraviolet Spectrometer and Polarimeter/Solar Maximum Mission (UVSP/SMM) during a flare on 15 July 1980. An early interpretation suggested that impact excitation by electrons propagating through the steep temperature gradient of the flaring transition region/high chromosphere produced this polarization. Our calculations show that the observed polarization in this UV line cannot be due to this effect. We find instead that, in some flare models, the energetic electrons can produce an impact polarization of a few percent in EUV neutral helium lines (i.e., lambda lambda 522, 537, and 584 A).

  11. Statistical Study of Free Magnetic Energy and Flare Productivity of Solar Active Regions

    NASA Astrophysics Data System (ADS)

    Su, J. T.; Jing, J.; Wang, S.; Wiegelmann, T.; Wang, H. M.

    2014-06-01

    Photospheric vector magnetograms from the Helioseismic and Magnetic Imager on board the Solar Dynamic Observatory are utilized as the boundary conditions to extrapolate both nonlinear force-free and potential magnetic fields in solar corona. Based on the extrapolations, we are able to determine the free magnetic energy (FME) stored in active regions (ARs). Over 3000 vector magnetograms in 61 ARs were analyzed. We compare FME with the ARs' flare index (FI) and find that there is a weak correlation (<60%) between FME and FI. FME shows slightly improved flare predictability relative to the total unsigned magnetic flux of ARs in the following two aspects: (1) the flare productivity predicted by FME is higher than that predicted by magnetic flux and (2) the correlation between FI and FME is higher than that between FI and magnetic flux. However, this improvement is not significant enough to make a substantial difference in time-accumulated FI, rather than individual flare, predictions.

  12. Statistical study of free magnetic energy and flare productivity of solar active regions

    SciTech Connect

    Su, J. T.; Jing, J.; Wang, S.; Wang, H. M.; Wiegelmann, T.

    2014-06-20

    Photospheric vector magnetograms from the Helioseismic and Magnetic Imager on board the Solar Dynamic Observatory are utilized as the boundary conditions to extrapolate both nonlinear force-free and potential magnetic fields in solar corona. Based on the extrapolations, we are able to determine the free magnetic energy (FME) stored in active regions (ARs). Over 3000 vector magnetograms in 61 ARs were analyzed. We compare FME with the ARs' flare index (FI) and find that there is a weak correlation (<60%) between FME and FI. FME shows slightly improved flare predictability relative to the total unsigned magnetic flux of ARs in the following two aspects: (1) the flare productivity predicted by FME is higher than that predicted by magnetic flux and (2) the correlation between FI and FME is higher than that between FI and magnetic flux. However, this improvement is not significant enough to make a substantial difference in time-accumulated FI, rather than individual flare, predictions.

  13. Estimates of the neutron emission during large solar flares in the rising and maximum period of solar cycle 24

    NASA Astrophysics Data System (ADS)

    Lopez, D.; Matsubara, Y.; Muraki, Y.; Sako, T.; Valdés-Galicia, J. F.

    2016-03-01

    We searched for solar neutrons using the data collected by six detectors from the International Network of Solar Neutron Telescopes and one Neutron Monitor between January 2010 and December 2014. We considered the peak time of the X-ray intensity of thirty five ≥ X1.0 class flares detected by GOES satellite as the most probable production time of solar neutrons. We prepared a light-curve of the solar neutron telescopes and the neutron monitor for each flare, spanning ± 3 h from the peak time of GOES. Based on these light curves, we performed a statistical analysis for each flare. Setting a significance level at greater than 3σ, we report that no statistically significant signals due to solar neutrons were found. Therefore, upper limits are determined by the background level and solar angle of these thirty five solar flares. Our calculation assumed a power-law neutron energy spectrum and an impulsive emission profile at the Sun. The estimated upper limits of the neutron emission are consistent within the order of magnitude of the successful detections of solar neutrons made in solar cycle 23.

  14. Energetic solar particle fluxes out to 3 AU during the 7 May 1978 flare event

    NASA Technical Reports Server (NTRS)

    Lockwood, J. A.; Debrunner, H.

    1985-01-01

    Simultaneous solar proton flux measurements on IMP 7 and by the world wide neutron monitor network during the May 7, 1978 flare event led to conclusions that in the energy range from 50 MeV to 10 GeV: (1) the propagation of the flare particles in the interplanetary magnetic field (IMF) between the Sun and the Earth was nearly scatter free; and (2) therefore, the intensity time (IT) profiles of the solar proton fluxes observed at Earth for about one hour after onset represent the solar injection profiles even to energies as low as 50 MeV. Observations of the IMF at Helios A indicate that the IMF was undisturbed between the Sun and Helios A at the time of the May 7, 1978 flare event; and, therefore, the solar particle propagation was also scatter free from the Sun to Helios A.

  15. COMPTEL Gamma-Ray Observations of the C4 Solar Flare on 20 January 2000

    NASA Astrophysics Data System (ADS)

    Ryan, J. M.; Arndt, M.; Lockwood, J. A.; McConnell, M. L.; Miller, R.; Young, C. A.; Diehl, R.; Rank, G.; Schoenfelder, V.; Bennett, K.; Winkler, C.; Debrunner, H.

    2000-05-01

    In response to a BACODINE cosmic gamma-ray burst alert, COMPTEL on the Compton Gamma Ray Observatory recorded gamma rays above 1 MeV from the C4 flare at 0221 UT 20 January 2000. Although the candidate burst was, in fact, the solar flare, the COMPTEL analysis system produced an image of the transient centered within statistics on the Sun. A preliminary combined BATSE/COMPTEL spectrum shows a bremsstrahlung continuum with a power law index of approximately -3.1, on top of which rides a nuclear line component that falls off at the expected energy of 8 MeV. Although subject to the uncertain extrapolation of the bremsstrahlung continuum, the ratio of the nuclear component to the bremsstrahlung component tends to be higher than the same ratio for the distribution of flares measured with SMM. Only one C flare exhibited gamma-ray emission above 1 MeV in the SMM atlas. However, the fact that a "normal" solar flare gamma-ray spectrum can originate from a C4 flare, throws into question the concept of a minimum flare size for proton or relativistic electron acceleration. This work was in part supported by NASA NAS5-26645, the German government 50 Q 9096 8 and the Swiss National Science Foundation 20-50697.97.

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    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.

  17. Fermi Large Area Telescope observation of high-energy solar flares: constraining emission scenarios

    NASA Astrophysics Data System (ADS)

    Omodei, Nicola; Pesce-Rollins, Melissa; Petrosian, Vahe; Liu, Wei; Rubio da Costa, Fatima

    2015-08-01

    The Fermi Large Area Telescope (LAT) is the most sensitive instrument ever deployed in space for observing gamma-ray emission >100 MeV. This has also been demonstrated by its detection of quiescent gamma-ray emission from pions produced by cosmic-ray protons interacting in the solar atmosphere, and from cosmic-ray electron interactions with solar optical photons. The Fermi LAT has also detected high-energy gamma-ray emission associated with GOES M-class and X-class X-ray flares, each accompanied by a coronal mass ejection and a solar energetic particle event increasing the number of detected solar flares by almost a factor of 10 with respect to previous space observations. During the impulsive phase, gamma rays with energies up to several hundreds of MeV have been recorded by the LAT. Emission up to GeV energies lasting several hours after the flare has also been recorded by the LAT. Of particular interest are the recent detections of two solar flares whose position behind the limb was confirmed by the STEREO-B satellite. While gamma-ray emission up to tens of MeV resulting from proton interactions has been detected before from occulted solar flares, the significance of these particular events lies in the fact that these are the first detections of >100 MeV gamma-ray emission from footpoint-occulted flares. We will present the Fermi-LAT, RHESSI and STEREO observations of these flares and discuss the various emission scenarios for these sources.

  18. The structure of high-temperature solar flare plasma in non-thermal flare models

    NASA Technical Reports Server (NTRS)

    Emslie, A. G.

    1985-01-01

    Analytic differential emission measure distributions have been derived for coronal plasma in flare loops heated both by collisions of high-energy suprathermal electrons with background plasma, and by ohmic heating by the beam-normalizing return current. For low densities, reverse current heating predominates, while for higher densities collisional heating predominates. There is thus a minimum peak temperature in an electron-heated loop. In contrast to previous approximate analyses, it is found that a stable reverse current can dominate the heating rate in a flare loop, especially in the low corona. Two 'scaling laws' are found which relate the peak temperature in the loop to the suprathermal electron flux. These laws are testable observationally and constitute a new diagnostic procedure for examining modes of energy transport in flaring loops.

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

    NASA Technical Reports Server (NTRS)

    Shih, Albert Y.

    2010-01-01

    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.

  20. Solar Flare Predictions Using Time Series of SDO/HMI Observations and Machine Learning Methods

    NASA Astrophysics Data System (ADS)

    Ilonidis, Stathis; Bobra, Monica; Couvidat, Sebastien

    2015-08-01

    Solar active regions are dynamic systems that can rapidly evolve in time and produce flare eruptions. The temporal evolution of an active region can provide important information about its potential to produce major flares. In this study, we build a flare forecasting model using supervised machine learning methods and time series of SDO/HMI data for all the flaring regions with magnitude M1.0 or higher that have been observed with HMI and several thousand non-flaring regions. We define and compute hundreds of features that characterize the temporal evolution of physical properties related to the size, non-potentiality, and complexity of the active region, as well as its flaring history, for several days before the flare eruption. Using these features, we implement and test the performance of several machine learning algorithms, including support vector machines, neural networks, decision trees, discriminant analysis, and others. We also apply feature selection algorithms that aim to discard features with low predictive power and improve the performance of the machine learning methods. Our results show that support vector machines provide the best forecasts for the next 24 hours, achieving a True Skill Statistic of 0.923, an accuracy of 0.985, and a Heidke skill score of 0.861, which improve the scores obtained by Bobra and Couvidat (2015). The results of this study contribute to the development of a more reliable and fully automated data-driven flare forecasting system.

  1. Solar flare and IMF sector structure effects in the lower ionosphere

    SciTech Connect

    Lastovicka, J.

    1984-05-01

    About 1% of all sudden ionospheric disturbances (SIDs) observed at the Panska Ves Observatory (Czechoslovakia), were found to be not of solar-XUV origin. Among them, the very rare SWF events (observed at L 2.4) of corpuscular origin are the most interesting. The IMF sector structure effects in the midlatitude lower ionosphere are minor in comparison with effects of solar flares, geomagnetic storms, etc. There are two basic types of effects. The first type is a disturbance, best developed in geomagnetic activity, and observed in the night-time ionosphere. It can be interpreted as a response to sector structure related changes of geomagnetic (magnetospheric) activity. The other type is best developed in the tropospheric vorticity area index and is also observed in the day-time ionosphere in winter. This effect is quietening in the ionosphere as well as troposphere. While the occurrence of the former type is persistent in time, the latter is severely diminished in some periods. All the stratosphere, the 10-mb level temperature and height above Berlin-Tempelhof do not display any observable IMF section structure effect.

  2. Solar flare and IMF sector structure effects in the lower ionosphere

    NASA Astrophysics Data System (ADS)

    Lastovicka, J.

    1984-05-01

    About 1% of all sudden ionospheric disturbances (SIDs) observed at the Panska Ves Observatory (Czechoslovakia), were found to be not of solar-XUV origin. Among them, the very rare SWF events (observed at L = 2.4) of corpuscular origin are the most interesting. The IMF sector structure effects in the midlatitude lower ionosphere are minor in comparison with effects of solar flares, geomagnetic storms, etc. There are two basic types of effects. The first type is a disturbance, best developed in geomagnetic activity, and observed in the night-time ionosphere. It can be interpreted as a response to sector structure related changes of geomagnetic (= magnetospheric) activity. The other type is best developed in the tropospheric vorticity area index and is also observed in the day-time ionosphere in winter. This effect is quietening in the ionosphere as well as troposphere. While the occurrence of the former type is persistent in time, the latter is severely diminished in some periods. All the stratosphere, the 10-mb level temperature and height above Berlin-Tempelhof do not display any observable IMF section structure effect.

  3. Solar Flare and IMF Sector Structure Effects in the Lower Ionosphere

    NASA Technical Reports Server (NTRS)

    Lastovicka, J.

    1984-01-01

    About 1% of all sudden ionospheric disturbances (SIDs) observed at the Panska Ves Observatory (Czechoslovakia), were found to be not of solar-XUV origin. Among them, the very rare SWF events (observed at L = 2.4) of corpuscular origin are the most interesting. The IMF sector structure effects in the midlatitude lower ionosphere are minor in comparison with effects of solar flares, geomagnetic storms, etc. There are two basic types of effects. The first type is a disturbance, best developed in geomagnetic activity, and observed in the night-time ionosphere. It can be interpreted as a response to sector structure related changes of geomagnetic (= magnetospheric) activity. The other type is best developed in the tropospheric vorticity area index and is also observed in the day-time ionosphere in winter. This effect is quietening in the ionosphere as well as troposphere. While the occurrence of the former type is persistent in time, the latter is severely diminished in some periods. All the stratosphere, the 10-mb level temperature and height above Berlin-Tempelhof do not display any observable IMF section structure effect.

  4. Investigation of solar-flare effects by the oblique sounding of the ionosphere

    NASA Astrophysics Data System (ADS)

    Blagoveshchenskaia, N. F.; Bubnov, V. A.; Ustinovich, V. T.

    1989-01-01

    The paper examines results of an investigation of solar-flare effects by the oblique sounding of the ionosphere on a subauroral path about 9000 km long during 1981-1982. Oblique sounding data are compared with investigations of SWF, SPA, SEA, and SFD sudden ionospheric disturbances, as well as with solar-radio emission parameters in the 650-15,000 MHz range.

  5. High energy neutron and gamma-radiation generated during the solar flares

    NASA Technical Reports Server (NTRS)

    Kocharov, G. E.; Mandzhavidze, N. Z.

    1985-01-01

    The problem of high energy neutrons and gamma rays generation in the solar conditions is considered. It is shown that due to a peculiarity of generation and propagation of neutrons corresponding solar flares should be localized at high helio-longitudes.

  6. A dominant role for protons at the onset of solar flares

    NASA Technical Reports Server (NTRS)

    Simnett, G. M.

    1985-01-01

    It is suggested that recent observations have cast considerable doubt on the generally accepted explanation that non-thermal electron beams transfer most of the flare energy during the onset of solar flares. It is argued that non-thermal protons in the energy region 100 to 1000 keV are a more probable energy transfer mechanism. An important consequence of this hypothesis is that the hard X-ray burst must be thermal.

  7. A MODEL FOR THE ESCAPE OF SOLAR-FLARE-ACCELERATED PARTICLES

    SciTech Connect

    Masson, S.; Antiochos, S. K.; DeVore, C. R.

    2013-07-10

    We address the problem of how particles are accelerated by solar flares can escape into the heliosphere on timescales of an hour or less. Impulsive solar energetic particle (SEP) bursts are generally observed in association with so-called eruptive flares consisting of a coronal mass ejection (CME) and a flare. These fast SEPs are believed to be accelerated directly by the flare, rather than by the CME shock. However, the precise mechanism by which the particles are accelerated remains controversial. Regardless of the origin of the acceleration, the particles should remain trapped in the closed magnetic fields of the coronal flare loops and the ejected flux rope, given the magnetic geometry of the standard eruptive-flare model. In this case, the particles would reach the Earth only after a delay of many hours to a few days (coincident with the bulk ejecta arriving at Earth). We propose that the external magnetic reconnection intrinsic to the breakout model for CME initiation can naturally account for the prompt escape of flare-accelerated energetic particles onto open interplanetary magnetic flux tubes. We present detailed 2.5-dimensional magnetohydrodynamic simulations of a breakout CME/flare event with a background isothermal solar wind. Our calculations demonstrate that if the event occurs sufficiently near a coronal-hole boundary, interchange reconnection between open and closed fields can occur. This process allows particles from deep inside the ejected flux rope to access solar wind field lines soon after eruption. We compare these results to standard observations of impulsive SEPs and discuss the implications of the model on further observations and calculations.

  8. Spectral lines observed in solar flares between 171 and 630 angstroms

    NASA Technical Reports Server (NTRS)

    Dere, K. P.

    1978-01-01

    Several hundred spectral lines emitted in solar flares between 171 and 630 A have been recorded by the Naval Research Laboratory spectroheliograph aboard Skylab. The wavelengths, identifications, and intensity estimates of these lines are presented, based on measurements of all of the suitable flare plates. Nearly 100 new and unidentified lines have been observed. Identifications of three Fe XXI and two Fe XVII lines are suggested.

  9. Fermi LAT High-Energy Gamma-Ray Observations of Solar Flares

    NASA Astrophysics Data System (ADS)

    Allafort, A.; Omodei, N.; Chen, Q.; Petrosian, V.

    2013-12-01

    The Fermi Large Area Telescope (LAT) has open a new window in solar physics as it is the most sensitive instrument ever for observing high-energy gamma-ray emission. Eighteen solar flares have been observed above 100 MeV from August 2008 to August 2012. A few flares are detected only in their impulsive phase, but most of them show sustained emission up to GeV energies lasting from a few to 20 hours. Interestingly all Fermi LAT detected flares are associated with fairly fast coronal mass ejections and most with solar energetic particles. From the detailed analyses of the longest and brightest flares detected by the Fermi LAT so far, the 2011 March 7 and 2012 March 7 flares, a continuous acceleration process seems required to explain the long duration of the high-energy gamma-ray emission. Moreover the gamma-ray spectra are consistent with pion interactions from accelerated protons up to GeV energies. We will present an updated list of the solar flares detected by the Fermi LAT with their general characteristics, as well as progress made in the interpretation of these phenomena, focusing on a multi wavelength approach. Gamma-ray lightcurve for the 2011 March 7 flare. Emission lasted more than 13 hours (Ackermann et al. 2013, arXiv:1304.3749) Localization of the gamma-ray source, integrated over the 20 hours of emission that followed the March 7, 2012 flares (Ajello et al. 2013, arXiv:1304.5559).

  10. Effect of enhanced x-ray flux on the ionosphere over Cyprus during solar flares

    NASA Astrophysics Data System (ADS)

    Mostafa, Md. Golam; Haralambous, Haris

    2015-06-01

    In this work we study the effect of solar flares on the ionosphere over Cyprus. Solar flares are impulsive solar activity events usually coupled with Coronal Mass Ejection (CME). The arrival and the subsequent impact of solar flares on geospace, following an eruption on the Sun's surface is almost immediate (around 9 min) whereas the impact of CMEs is rather delayed (2-3 days) as the former is based on X-ray radiation whereas the latter phenomenon is related with particles and magnetic fields travelling at lower speeds via the Solar Wind. The penetration of X-rays down to the Dregion following such an event enhances the electron density. This increase can be monitored by ionosondes, which measure the electron density up to the maximum electron density NmF2. The significance of this increase lies on the increase of signal absorption causing limited window of operating frequencies for HF communications. In this study the effect of enhanced X-ray flux on the ionosphere over Cyprus during solar flares has been investigated. To establish the correlation and extent of impact on different layers, data of X-ray intensity from Geostationary Operational Environmental Satellite (GOES) and ionospheric characteristics (D & F layer) over Nicosia station (35 N, 33 E) were examined for all solar flares during the period 2011-2014. The analysis revealed a positive and good correlation between frequency of minimum reflection, fmin and X-ray intensity for D layer demonstrating that X-rays play a dominant role in the ionization of lower ionosphere. Hence, X-ray flux can be used as a good proxy for studying the solar flare effects on lower ionosphere. The correlation coefficient between maximum electron density of F layer, NmF2 and X-ray intensity was found to be poor.

  11. SOLAR-T: terahertz photometers to observe solar flare emission on stratospheric balloon flights

    NASA Astrophysics Data System (ADS)

    Kaufmann, P.; Abrantes, A.; Bortolucci, E. C.; Correia, E.; Diniz, J. A.; Fernandez, G.; Fernandes, L. O. T.; Gimnez de Castro, C. G.; Godoy, R.; Hurford, G.; Kudaka, A. S.; Lebedev, M.; Lin, R. P.; Machado, N.; Makhmutov, V. S.; Marcon, R.; Marun, A.; Nicolaev, V. A.; Pereyra, P.; Raulin, J.-P.; da Silva, C. M.; Shih, A.; Stozhkov, Y. I.; Swart, J. W.; Timofeevsky, A. V.; Valio, A.; Villela, T.; Zakia, M. B.

    2012-09-01

    A new solar flare spectral component has been found with intensities increasing for larger sub-THz frequencies, spectrally separated from the well known microwaves component, bringing challenging constraints for interpretation. Higher THz frequencies observations are needed to understand the nature of the mechanisms occurring in flares. A twofrequency THz photometer system was developed to observe outside the terrestrial atmosphere on stratospheric balloons or satellites, or at exceptionally transparent ground stations. 76 mm diameter telescopes were designed to observe the whole solar disk detecting small relative changes in input temperature caused by flares at localized positions at 3 and 7 THz. Golay cell detectors are preceded by low-pass filters to suppress visible and near IR radiation, band-pass filters, and choppers. It can detect temperature variations smaller than 1 K with time resolution of a fraction of a second, corresponding to small burst intensities. The telescopes are being assembled in a thermal controlled box to which a data conditioning and acquisition unit is coupled. While all observations are stored on board, a telemetry system will forward solar activity compact data to the ground station. The experiment is planned to fly on board of long-duration stratospheric balloon flights some time in 2013-2015. One will be coupled to the GRIPS gamma-ray experiment in cooperation with University of California, Berkeley, USA. One engineering flight will be flown in the USA, and a 2 weeks flight is planned over Antarctica in southern hemisphere summer. Another long duration stratospheric balloon flight over Russia (one week) is planned in cooperation with the Lebedev Physics Institute, Moscow, in northern hemisphere summer.

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

    NASA Technical Reports Server (NTRS)

    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

    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.

  13. Acceleration of solar cosmic rays in a flare current sheet and their propagation in interplanetary space

    NASA Astrophysics Data System (ADS)

    Podgorny, A. I.; Podgorny, I. M.

    2015-09-01

    Analyses of GOES spacecraft data show that the prompt component of high-energy protons arrive at the Earth after a time corresponding to their generation in flares in the western part of the solar disk, while the delayed component is detected several hours later. All protons in flares are accelerated by a single mechanism. The particles of the prompt component propagate along magnetic lines of the Archimedean spiral connectng the flare with the Earth. The prompt component generated by flares in the eastern part of the solar disk is not observed at the Earth, since particles accelerated by these flares do not intersect magnetic-field lines connecting the flare with the Earth. These particles arrive at the Earth via their motion across the interplanetary magnetic field. These particles are trapped by the magnetic field and transported by the solar wind, since the interplanetary magnetic field is frozen in the wind plasma, and these particles also diffuse across the field. The duration of the delay reaches several days.

  14. A very small and super strong zebra pattern burst at the beginning of a solar flare

    SciTech Connect

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

    2014-08-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    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.

  16. Sub-arcsecond Structure and Dynamics of Flare Ribbons Observed with New Solar Telescope

    NASA Astrophysics Data System (ADS)

    Sharykin, Ivan; Kosovichev, Alexander G.

    2014-06-01

    Emission of solar flares across the electromagnetic spectrum is often observed in the form of two expanding ribbons. The standard flare model explains the flare ribbons as footpoints of magnetic arcades, emitting due to the interaction of energetic particles with the chromospheric plasma. However, the physics of this interaction and properties of the accelerated particles are still unknown. We present results of multiwavelength observations of C2.1 flare of August 15, 2011, observed with the 1.6-meter New Solar Telescope of Big Bear Solar Observatory. These unique data are characterized by the great spatial resolution reaching the telescope diffraction limit with good spectral scanning of H-alpha line, and photospheric imaging. The observations reveal previously unresolved sub-arcsecond structure of the flare ribbons in regions of strong magnetic field. We discuss the fine structure of the flare ribbons, their dynamics, and possible mechanisms of the energy release and transport, using also data from SDO, GOES and FERMI spacecraft.

  17. Directivity of 100 keV-1 MeV photon sources in solar flares

    NASA Technical Reports Server (NTRS)

    Kane, S. R.; Fenimore, E. E.; Klebesadel, R. W.; Laros, J. G.

    1988-01-01

    Stereoscopic observations of 0.1-1.0 MeV photon sources in solar flares made with spectrometers aboard the ISEE 3 and PVO (Pioneer Venus Orbiter) have been analyzed to determine the directivity of the photon sources and its possible dependence on photon energy. During the period October 1, 1978-October 31, 1980, a total of 44 solar flares were observed simultaneously by the two instruments. Of these, 39 flares were in full view of both the instruments, the remaining five being partially occulted by the photosphere from the line of sight of at least one instrument. The view angles theta(P) and theta(I) of the PVO and ISEE 3 instruments with respect to the outward solar radius at the flare site varied from one flare to another and were in the range 9-88 deg. The difference between the two view angles varied from 1 deg to 66 deg. The observations of differential photon energy spectra averaged over more than about 16 s do not indicate any systematic directivity. In most flares the directivity of 0.1-1.0 MeV photon sources is found to be less than about 2.5.

  18. Correlated observations of impulsive UV and hard X-ray bursts in solar flares from the solar maximum mission

    NASA Technical Reports Server (NTRS)

    Cheng, C.-C.; Tandberg-Hanssen, E.; Orwig, L. E.

    1984-01-01

    An investigation is conducted of the temporal and spatial structures of UV and hard X-ray bursts in a disk and a limb flare observed with instruments on the Solar Maximum Mission satellite. Attention is given to the transient UV brightening before the flare, the impulsive enhancement of UV continuum emission, the relationship between emission source region and particle acceleration region, and large scale excitations. The most active part of the active region appears to be the most flare-productive region. These regions exhibit high UV activities with numerous UV transient bursts occurring in many small kernels.

  19. Solar modulation of cosmic ray intensity and solar flare events inferred from (14)C contents in dated tree rings

    NASA Technical Reports Server (NTRS)

    Fan, C. Y.; Chen, T. M.; Yun, S. X.; Dai, K. M.

    1985-01-01

    The delta 14C values in 42 rings of a white spruce grown in Mackenzie Delta was measured as a continuing effort of tracing the history of solar modulation of cosmic ray intensity. The delta 14C values in six rings were measured, in search of a 14C increase due to two large solar flares that occurred in 1942. The results are presented.

  20. Investigation of Solar Flares Using Spectrally, Spatially, and Temporally Resolved Observations in Gamma Rays, Hard X Rays, and Microwaves

    NASA Technical Reports Server (NTRS)

    Crannell, Carol Jo; Oegerle, William (Technical Monitor)

    2003-01-01

    The high-energy components of solar flares radiate at a wide range of wavelengths. We are using spatially, spectrally, and temporally resolved hard X-ray, gamma-ray, and microwave observations of solar flares to investigate flare models and to understand the flare acceleration process. The hard X-ray and gamma-ray observations are obtained with the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) spacecraft that was launched on February 5, 2002. The microwave observations are obtained with the Owens Valley Radio Observatory (OVRO), which has been dedicated to daily observations of solar flares in microwaves with a five-element interferometer since June 1992. These studies are expected to yield exciting new insights into the fundamental physics of the flare acceleration processes.

  1. Thermal Evolution of Solar Flares During the First Year of SDO as Seen by the EVE Instrument

    NASA Technical Reports Server (NTRS)

    Chamberlin, Phillip C.; Woods, Thomas N.

    2011-01-01

    It is very evident during the first year of the Solar Dynamics Observatory (SDO) that the Sun awoke from its prolonged minimum and is well into solar cycle 24. There has been tens of moderate M-class flares and a large X-class event (as of abstract submission), with more surely to come as the solar cycle activity increases. With SDO's 24/7 observations, every single flare has been observed through their entire evolution, providing new insights in the thermal evolution of every flare. It is evident that this evolution is extremely different for many of the flares, even for flares with similar X-ray magnitude classifications. Presented and discussed will be these different flares with their varying thermal evolution profiles as observed by the Extreme ultraviolet Variability Experiment (EVE) onboard the Solar Dynamics Observatory (SDO).

  2. Solar wind disturbances in th outer heliosphere caused by successive solar flares from the same active region

    NASA Technical Reports Server (NTRS)

    Akasofu, S. I.; Hakamada, K.

    1983-01-01

    Solar wind disturbances caused by successive flares from the same active region are traced to about 20 AU, using the modeling method developed by Hakamada and Akasofu (1982). It is shown that the flare-generated shock waves coalesce with the co-rotating interaction region of the interplanetary magnetic field, resulting in a large-scale magnetic field structure in the outer heliosphere. Such a structure may have considerable effects on the propagation of galactic cosmic rays.

  3. Energy partitions and evolution in a purely thermal solar flare

    NASA Astrophysics Data System (ADS)

    Fleishman, Gregory; Nita, Gelu M.; Gary, Dale E.

    2015-04-01

    A conventional way of producing a hot plasma in the flaring loops is via the impact of the nonthermal particles accelerated in flares due to release of the excessive magnetic energy, which has come to be known as the Neupert effect. We know, however, that in many events the heating starts clearly before the particle acceleration, which implies that no accelerated particles may be required for this heating. To this end, we present here a flare whose microwave emission is consistent with a purely thermal distribution of electrons, based on the 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. We conclude that the apparent decrease of the magnetic field in the radio source over the rise phase of the flare requires an upward propagating magnetic reconnection/plasma heating process, such as in the standard flare scenario, but with one remarkable difference: the absence of any significant nonthermal electron generation. We expect that the study of these rare thermal flares will better clarify the origin of such purely thermal events, characterized by significant energy release observed through the plasma heating, but without any measurable acceleration of the charged particles.This work was partially supported by NSF grants AGS-1250374 and AGS-1262772, and NASA grant NNX14AC87G.

  4. New Observations of Balmer Continuum Flux in Solar Flares - Instrument Description and First Results

    NASA Astrophysics Data System (ADS)

    Kotrč, P.; Procházka, O.; Heinzel, P.

    2016-02-01

    Increase in the Balmer continuum radiation during solar flares was predicted by various authors, but has never been firmly confirmed observationally using ground-based slit spectrographs. Here we describe a new post-focal instrument, the image selector, with which the Balmer continuum flux can be measured from the whole flare area, in analogy to successful detections of flaring dMe stars. The system was developed and put into operation at the horizontal solar telescope HSFA2 of the Ondřejov Observatory. We measure the total flux by a fast spectrometer from a limited but well-defined region on the solar disk. Using a system of diaphragms, the disturbing contribution of a bright solar disk can be eliminated as much as possible. Light curves of the measured flux in the spectral range 350 - 440 nm are processed, together with the H\\upalpha images of the flaring area delimited by the appropriate diaphragm. The spectral flux data are flat-fielded, calibrated, and processed to be compared with model predictions. Our analysis of the data proves that the described device is sufficiently sensitive to detect variations in the Balmer continuum during solar flares. Assuming that the Balmer-continuum kernels have at least a similar size as those visible in H\\upalpha, we find the flux increase in the Balmer continuum to reach 230 - 550 % of the quiet continuum during the observed X-class flare. We also found temporal changes in the Balmer continuum flux starting well before the onset of the flare in H\\upalpha.

  5. Estimating Flaring Probability from High-Cadence Images of the Solar Chromosphere

    NASA Astrophysics Data System (ADS)

    Norquist, Donald C.; Balasubramaniam, K.

    2011-05-01

    We applied principal component analysis to 8-10 hour sequences of chromospheric H? images of selected solar active regions as observed by the U. S. Air Force Improved Solar Optical Observation Network (ISOON) telescope at Sacramento Peak, NM at one-minute intervals. A covariance matrix of all combinations of image time pairs was computed from the picture element H? intensities from each image sequence, and eigenvalues and eigenvectors were computed. Computation of explained variance from the eigenvalues indicated that 99.9% of the characteristics were represented by the first 50 eigenvectors or so. The leading eigenvectors were matched at each image time with a flare category indicator deduced from coincident active region area-average H? intensity and 1-8 GOES X-ray flux measurements at one-minute intervals. Multivariate discriminant analysis (MVDA) was applied to the eigenvector elements and flaring indicators from a training set of image sequences to compute a vector of coefficients whose linear combination with the eigenvector predictors maximizes the distinction among flaring groups. The discriminant function, computed from the dot product of the coefficients with the eigenvectors of an independent ISOON case, is used to compute the probability of each flaring group at each measurement time. Flare category indicators from independent case times are used to assess the flaring probability estimates. Multivariate logistic regression (MVLR) was also applied to the subset of eigenvectors in the training data, and the derived coefficients were also dotted with the independent eigenvalues to generate a separate flaring probability estimate. A total of 47 ISOON image sequences were available for training and flaring probability estimation. Preliminary results showed that the MVLR was competitive with MVDA in skill of diagnosing flaring probability. If this approach shows promise in a diagnostic mode, efforts will be made to extend it to short-term (1-3 hour) prognostic mode.

  6. Radiative hydrodynamic modelling and observations of the X-class solar flare on 2011 March 9

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    Aims: We investigated the response of the solar atmosphere to non-thermal electron beam heating using the radiative transfer and hydrodynamics modelling code RADYN. The temporal evolution of the parameters that describe the non-thermal electron energy distribution were derived from hard X-ray observations of a particular flare, and we compared the modelled and observed parameters. Methods: The evolution of the non-thermal electron beam parameters during the X1.5 solar flare on 2011 March 9 were obtained from analysis of RHESSI X-ray spectra. The RADYN flare model was allowed to evolve for 110 s, after which the electron beam heating was ended, and was then allowed to continue evolving for a further 300 s. The modelled flare parameters were compared to the observed parameters determined from extreme-ultraviolet spectroscopy. Results: The model produced a hotter and denser flare loop than that observed and also cooled more rapidly, suggesting that additional energy input in the decay phase of the flare is required. In the explosive evaporation phase a region of high-density cool material propagated upward through the corona. This material underwent a rapid increase in temperature as it was unable to radiate away all of the energy deposited across it by the non-thermal electron beam and via thermal conduction. A narrow and high-density (ne ? 1015 cm-3) region at the base of the flare transition region was the source of optical line emission in the model atmosphere. The collision-stopping depth of electrons was calculated throughout the evolution of the flare, and it was found that the compression of the lower atmosphere may permit electrons to penetrate farther into a flaring atmosphere compared to a quiet Sun atmosphere.

  7. High Resolution Millimeter Wavelength Radiometer and Temporal Fragmentation of the Solar Flare in the Millimeter Wavelength

    NASA Astrophysics Data System (ADS)

    Cecatto, Jose Roberto

    1994-11-01

    High-sensitivity, high-spectral-resolution solar observations in the millimeter wavelength are scanty. A sensitive radiometer with I GHz resolution, operating in the frequency range of 18 and 23 GHz in conjunction with 13.7 m diameter antenna has been developed by the author initially, in 1987, for the observations of the solar active regions and later on modified for the bursts observations. At present each frequency is sampled for 100 ms. Details of this instrumentation, including the process of calibration, data acquisition, and reduction are described. The author has participated in the international solar observation campaigns. Sixty seven groups of the solar bursts have been observed by this instrument, 9 observed simultaneously with hard X-ray burst spectrometer on board of Solar Maximum Mission satellite and 5 observed with Frequency Agile Interferometer, operating in the frequency range of (1-18) GHz, of the CALTECH. There is a suggestion that solar flares are composed of small flares named as elementary flare bursts. The counterpart of these bursts in the millimeter wave band is known as "Simple Bursts" of the duration of the order of seconds exhibiting single peak. Occurrence of such burst is rare. Eleven of these bursts have been investigated in detail for their spectral behaviour for the f-irst time. The observed parameters of these bursts are as follows: average rise time approx. 4 s, spectral index varied between - 1.8 and -3.2, and time evolution of the spectral index shows soft-hard-soft behaviour. Short rise time together with observed spectral behaviour suggest the mechanism of the acceleration and injection of the electrons as of impulsive type. High spectral resolution observations in the optically thin part of the spectra permitted to estimate precise spectral index. Observed spectral index and estimated magnetic field suggest that higher energy, approx. 200 keV electrons are involved in the generation of these bursts. Possible mechanism of the acceleration has been also discussed. Source parameters (B = 570 G; E = 100-300 keV; NT = 1033 - 1036 electrons and ET = 1025 - 1027 erg) of the EFB are nearly similar to 'hot points'. We have made first order estimate of millimeter wave emission from such source. Simultaneous investigations of the eight complex millimeter bursts, exhibiting more than one peak, with hard X-rays, have been carried out for the f-irst time with high spectral and temporal resolutions. Here, for the first time we have shown at least in three cases that highest energy of X-rays simultaneously peaking with millimeter wavelength bursts was about 300 keV thus indicating that higher energy electrons up to (200-400) keV are responsible for the generation of the millimeter wavelength bursts. Also estimated are source parameters of the X-ray and microwave sources. In one case we have observed turnover frequency enabling us to estimate more accurate magnetic field and other source parameters.

  8. Characteristics of the photospheric magnetic field associated with solar flare initiation

    SciTech Connect

    Yang, Ya-Hui; Chen, P. F.; Hsieh, Min-Shiu; Wu, S. T.; He, Han; Tsai, Tsung-Che E-mail: chenpf@nju.edu.cn E-mail: wus@uah.edu E-mail: tctsai@narlabs.org.tw

    2014-05-01

    The physical environment governing the solar flare initiation is not fully understood, although there are significant efforts to address the relationship between magnetic non-potential parameters and early flare signatures. In this study, we attempt to characterize the flare initiation based on the processed Helioseismic and Magnetic Imager vector magnetograms, Atmospheric Imaging Assembly 1600 , and RHESSI hard X-ray observations. Three flare events, the M6.6 flare on 2011 February 13, the X2.2 flare on 2011 February 15, and the X2.1 flare on 2011 September 6, in two active regions AR 11158 and AR 11283 are investigated. We analyze the source field strength in the photosphere, which is defined as the magnitude of the observed magnetic field deviation from the potential field. It is found that one of the strong source field regions above the magnetic polarity inversion line well connects the initial bright kernels of two conjugate ribbons. The results imply that the distribution of the photospheric source field strength can be used to locate the initiation site of flaring loops regardless of the configuration of pre-flare magnetic fields or the evolution of active regions. Moreover, the field configuration in the strong source field regions tends to become more inclined after flares, which is consistent with the coronal implosion scenario. We also employ a fast method to derive the total current density from the photospheric vector magnetogram in the framework of force-free field. This method can provide fast estimation of photospheric current density within a reasonable accuracy without appealing for the more accurate calculation from a model extrapolation.

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

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

    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.

  10. Comparison between IBIS Observations and Radiative Transfer Hydrodynamic Simulations of a Solar Flare

    NASA Astrophysics Data System (ADS)

    Rubio da Costa, F.; Kleint, L.; Liu, W.; Sainz Dalda, A.; Petrosian, V.

    2014-12-01

    High-resolution spectroscopic observations of solar flares are rare but can provide valuable diagnostics. On September 24, 2011 an M3.0 class flare was observed by the Interferometric BIdimensional Spectropolarimeter (IBIS) in chromospheric H? and CaII 8542 lines and by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) in X-rays. We fitted the RHESSI spectra at different times with a power-law plus isothermal component. We then used the fitted real-time spectral parameters of nonthermal electrons as the input to the RADYN radiative hydrodynamic code (Carlsson et al, 1992, 1996; Allred et al, 2005) to simulate the low-chromospheric response to collisional heating by energetic electrons. We synthesized both the H? and CaII 8542 lines from the simulation results and compare them with the IBIS observations. We discuss the constraints from this comparison on particle acceleration mechanisms in solar flares.

  11. Energy supply processes for magnetospheric substorms and solar flares - Tippy bucket model or pitcher model?

    NASA Technical Reports Server (NTRS)

    Akasofu, S.-I.

    1985-01-01

    In the past, both magnetospheric substorms and solar flares have almost exclusively been discussed in terms of explosive magnetic reconnection. Such a model may conceptually be illustrated by the so-called 'tippy-bucket model', which causes sudden unloading processes, namely a sudden (catastrophic, stochastic, and unpredictable) conversion of stored magnetic energy. However, recent observations indicate that magnetospheric substorms can be understood as a result of a directly driven process which can conceptually be illustrated by the 'pitcher model' in which the output rate varies in harmony with the input rate. It is also possible that solar flare phenomena are directly driven by a photospheric dynamo. Thus, explosive magnetic reconnection may simply be an unworkable hypothesis and may not be a puzzle to be solved as the primary energy supply process for magnetospheric substorms and solar flares.

  12. Energetics and dynamics in a large solar flare of 1989 March

    NASA Technical Reports Server (NTRS)

    Wulser, Jean-Pierre; Canfield, Richard C.; Zarro, Dominic M.

    1992-01-01

    Solar Maximum Mission X-ray observations and National Solar Observatory/Sacramento Peak H alpha spectra are combined in a large (X1.2) solar flare to test predictions of chromospheric heating and evaporation by nonthermal thick-target electrons. It is demonstrated that the ratio of H alpha flare energy flux to the energy flux deposited by thick-target electrons obeys a power-law dependence on electron heating flux, with a slope that is consistent with that predicted by a thick-target electron transport and heating model in a 1D hydrostatic atmosphere. It is concluded that the thick-target model satisfactorily accounts for the observed magnitude of chromospheric H alpha emission, and the amplitudes and timing of oppositely directed plasma motions during the impulsive phase of this X flare.

  13. A Catalog of Suzaku/WAM Hard X-Ray Solar Flares

    NASA Astrophysics Data System (ADS)

    Endo, Akira; Minoshima, Takashi; Morigami, Kouichi; Suzuki, Masanobu; Shimamori, Atsushi; Sato, Yumi; Terada, Yukikatsu; Tashiro, Makoto S.; Urata, Yuji; Sonoda, Eri; Yamaoka, Kazutaka; Sugita, Satoshi; Watanabe, Kyoko

    2010-10-01

    We developed a catalog of solar flares in the hard X-ray band observed with the Wide-band All-sky Monitor (WAM) onboard the Suzaku satellite between 2005 July and 2009 November. During this period, 105 solar flares (GOES class X: 13, M: 29, C: 47, B: 16) were detected with WAM, including 10% of GOES-class C events reported during the same period. The observed photon flux ranged between 9 10-5 and 9 10-1 photons s-1 cm-2 keV-2 at 100 keV. The averaged hard X-ray spectrum for each solar flare was evaluated for 70 of the 105 events, and 43 of them were well fitted with a single power-law model with a photon index ranging between -7 and -3. We observed a weak trend where events with longer durations exhibited harder spectral slopes.

  14. Can microbunch instability on solar flare accelerated electron beams account for bright broadband coherent synchrotron microwaves?

    SciTech Connect

    Kaufmann, Pierre; Raulin, Jean-Pierre

    2006-07-15

    The physical processes producing bright broadband coherent synchrotron radiation (CSR) bursts in laboratory accelerators are proposed to happen also in solar flares, bringing a plausible explanation to serious interpretation constraints raised by the discovery of a solar flare sub-mm-wave spectral emission component peaking in the terahertz (THz) range simultaneous to the well-known microwaves component. The THz component is due to incoherent synchrotron radiation (ISR) produced by a beam of ultrarelativistic electrons. Beam density perturbations, on a scale of the order of or smaller than the emitting wavelength, sets a microbunch instability producing the intense CSR at lower frequencies. Hard x-ray/{gamma}-ray emissions may include a significant synchrotron emission component from the same ISR spectrum, bringing a new possibility to explain the so called ''solar flare electron number paradox'.

  15. Can microbunch instability on solar flare accelerated electron beams account for bright broadband coherent synchrotron microwaves?

    NASA Astrophysics Data System (ADS)

    Kaufmann, Pierre; Raulin, Jean-Pierre

    2006-07-01

    The physical processes producing bright broadband coherent synchrotron radiation (CSR) bursts in laboratory accelerators are proposed to happen also in solar flares, bringing a plausible explanation to serious interpretation constraints raised by the discovery of a solar flare sub-mm-wave spectral emission component peaking in the terahertz (THz) range simultaneous to the well-known microwaves component. The THz component is due to incoherent synchrotron radiation (ISR) produced by a beam of ultrarelativistic electrons. Beam density perturbations, on a scale of the order of or smaller than the emitting wavelength, sets a microbunch instability producing the intense CSR at lower frequencies. Hard x-ray/?-ray emissions may include a significant synchrotron emission component from the same ISR spectrum, bringing a new possibility to explain the so called ``solar flare electron number paradox.''

  16. Table-top solar flares produced with laser driven magnetic reconnections

    NASA Astrophysics Data System (ADS)

    Zhong, J. Y.; Li, Y. T.; Wang, X. G.; Wang, J. Q.; Dong, Q. L.; Liu, X.; Lin, X. X.; Yuan, D. W.; Du, F.; Wang, S. J.; Zhang, L.; An, L.; Xiao, C. J.; Wei, H. G.; Zhang, K.; Wang, F. L.; Jiang, S. E.; Ding, Y. K.; Cao, Z. R.; Yuan, Z.; Zhang, H. Y.; Yang, Z. W.; Zhu, J. Q.; He, X. T.; Cai, H. B.; Zhao, G.; Zhang, J.

    2013-11-01

    The American Nuclear Society (ANS) has presented the prestigious Edward Teller award to Dr. Bruce A. Remington during the 2011 IFSA conference due to his "pioneering scientific work in the fields of inertial confinement fusion (ICF), and especially developing an international effort in high energy density laboratory astrophysics" [1,2]. This is a great acknowledgement to the subject of high energy density laboratory astrophysics. In this context, we report here one experiment conducted to model solar flares in the laboratory with intense lasers [3]. The mega-gauss -scale magnetic fields produced by laser produced plasmas can be used to make magnetic reconnection topology. We have produced one table-top solar flare in our laboratory experiment with the same geometric setup as associated with solar flares.

  17. The super-hot thermal component in the decay phase of solar flares

    NASA Technical Reports Server (NTRS)

    Lin, H.-A.; Lin, R. P.; Kane, S. R.

    1985-01-01

    Solar X-ray observations from balloons and from the SMM and Hinotori spacecraft have revealed evidence for a superhot thermal component with a temperature of more than about 3 x 10 to the 7th K in many solar flares, in addition to the usual 10-20 x 10 to the 6th K soft X-ray flare plasma. The decay phase of 35 solar flare X-ray events observed by ISEE-3 during 1980 was systematically studied. Based on fits to the continuum X-ray spectrum in the 4.8-14 keV range and to the intensity of the 1.9 A feature of iron lines, it was found that 15 (about 43) of the analyzed events have a superhot thermla component in the decay phase of the flare. In this paper, the important properties of the superhot thermal component in the decay phase are summarized. It is found that an additional input of energy is required to maintain the superhot thermal components. Finally, it is suggested that the superhot thermal component in the decay phase is created through the reconnection of the magnetic field during the decay phase of solar flares.

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

    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.

  19. X-class Flares at the Maximum of Solar Cycle 24

    NASA Astrophysics Data System (ADS)

    Fisher, Richard R.; Rock, Kristine A.

    2015-04-01

    17 instruments on 7 spacecraft were used to examine NOAA GOES X-class solar flares. This data set has unique spatial and temporal coverage of solar activity occurring from 15 February 2011 to 10 September 2014 and includes 32 X-class flare events.In 32 of 32 cases EUV running difference sequences of Fe XII disk images show the initiation of an LCPF (Nitta et al., 2013) at or near the time of flare onset. These features are generally seen moving upward and away from the X-flare site. In 28 of 32 cases the SWAVES instruments on the STEREO A & B spacecraft detected Type III radio bursts coincident in time with the flare initiation. The four flares that are exceptions are characterized as brief peaks in integrated X-ray flux.In 31 of 32 of the X-class flare events Cor1 imagers (1.04-4.0 Ro) initially show a rising arch followed by a cavity. In 27of 32 cases at increased heights from three vantage points STEREO and SOHO time sequences follow the development of the outward expansion of structure from 4.0-20 Ro.It is concluded from the imagery that the LCPF is a shock front (likely MHD fast mode) that surrounds CME and prominence material as structures rise and expand. Using measurements from the CME on 20110307, X5.4, mach number estimates of the shock strength range from 1.7-3.2 over the combined fields of view.For 25 of 32 events the CMEs detected were either characterized as halo events or demonstrated latitudinal and longitudinal expansion characteristics that would have created a halo for an observer located along the axis between the flare and the nose of the expanding shock. This configuration of a CME can be characterized as a bubble. It is concluded that bubble CMEs were associated with 78% of X-class flares during the maximum of solar cycle 24.In 6 of 32 cases all NASA proton detectors located at 1 AU distance from the sun were impacted by flare generated protons.Nitta, N. V., C. J. Schrijver, A. M. Title, W. Liu (2013) Large-scale Coronal Propagating Fronts in Solar Eruptions as Observed by the Atmospheric Imaging Assembly on Board the Solar Dynamics Observatory--an Ensemble Study, ApJ, 776:58 (13pp).

  20. Solar Extreme Ultraviolet (EUV) Flare Observations and Findings from the Solar Dynamics Observatory (SDO) EUV Variability Experiment (EVE)

    NASA Astrophysics Data System (ADS)

    Woods, Thomas N.; Mason, James; Eparvier, Francis; Jones, Andrew

    2015-08-01

    There have been more than six thousand flares observed by the Solar Dynamics Observatory (SDO) since it launched in February 2010. The SDO mission is ideal for studying flares with 24/7 operations from its geosynchronous orbit (GEO) and with some 7000 TeraBytes of data taken so far. These data include more than 100,000,000 images of coronal full-disk images from the Atmospheric Imaging Assembly (AIA) and Dopplergrams and magnetograms from the Helioseismic and Magnetic Imager (HMI) and over 15,000,000 spectra of the solar EUV irradiance from the EUV Variability Experiment (EVE). This presentation will focus primarily on the EVE flare observations and a couple key flare findings involving both AIA and EVE observations. One of these findings includes the discovery of the EUV late phase that occur in about 15% of flares. The EUV late phase is the brightening of warm coronal emissions in the EUV that starts much later after the main X-ray bright phase, lasts up to several hours, and can emit more total energy than the EUV radiation during the X-ray phase. The combination of EVE and AIA observations have revealed that the cause for the EUV late phase is a second set of post-flare coronal loops that form much higher than the primary post-flare loops near the source of the flare. This second set of loops is much longer and thus has a much slower cooling rate; consequently, the radiation from these loops appears much later after the main X-ray flare phase. Another key finding is that the EVE solar EUV irradiance observations in cool coronal emissions have dimming during and following eruptive flare events, which is often associated with coronal mass ejections (CMEs). Furthermore, the magnitude of the EVE coronal dimming is consistent with the amount of mass lost, as observed near the flaring region by AIA. This result could be important for space weather operations because EVEs near-realtime data products of its on-disk (Earth-facing) flare observations may provide an early warning that a CME has occurred and could be heading towards Earth.

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

    NASA Technical Reports Server (NTRS)

    Reshetov, V. D.

    1979-01-01

    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.

  2. ON THE RELATION OF ABOVE-THE-LOOP AND FOOTPOINT HARD X-RAY SOURCES IN SOLAR FLARES

    SciTech Connect

    Ishikawa, S.; Krucker, Saem; Lin, R. P.; Takahashi, T.

    2011-08-20

    We report on the most prominent example of an above-the-loop hard X-ray source in the extensive solar flare database of RHESSI. The limb flare of 2003 October 22 around 20 UT resembles the famous Masuda flare, except that only one of the footpoint sources is visible with the other one occulted. However, even for this very prominent event, the above-the-loop source is only visible during one of the four hard X-ray peaks, highlighting the rare occurrence of above-the-loop sources that are equally bright as footpoint sources. The relative timing between the above-the-loop and footpoint sources shows that the coronal source peaks about 10 s before the footpoint source and decays during the time the footpoint source is most prominent. Furthermore, the derived number of non-thermal electrons within the above-the-loop source is large enough to provide the needed number of precipitating electrons to account for the footpoint emission over the duration of the hard X-ray peak. Hence, these observations support the simple scenario where bulk energization is accelerating all electrons within the above-the-loop source and precipitating electrons are emptying out of the above-the-loop source to produce the footpoint emissions.

  3. On the Relation of Above-the-loop and Footpoint Hard X-Ray Sources in Solar Flares

    NASA Astrophysics Data System (ADS)

    Ishikawa, S.; Krucker, Sm; Takahashi, T.; Lin, R. P.

    2011-08-01

    We report on the most prominent example of an above-the-loop hard X-ray source in the extensive solar flare database of RHESSI. The limb flare of 2003 October 22 around 20 UT resembles the famous Masuda flare, except that only one of the footpoint sources is visible with the other one occulted. However, even for this very prominent event, the above-the-loop source is only visible during one of the four hard X-ray peaks, highlighting the rare occurrence of above-the-loop sources that are equally bright as footpoint sources. The relative timing between the above-the-loop and footpoint sources shows that the coronal source peaks about 10 s before the footpoint source and decays during the time the footpoint source is most prominent. Furthermore, the derived number of non-thermal electrons within the above-the-loop source is large enough to provide the needed number of precipitating electrons to account for the footpoint emission over the duration of the hard X-ray peak. Hence, these observations support the simple scenario where bulk energization is accelerating all electrons within the above-the-loop source and precipitating electrons are emptying out of the above-the-loop source to produce the footpoint emissions.

  4. On Halo CMEs relation with Solar Flares and Coronal Holes observed during 1996-2008

    NASA Astrophysics Data System (ADS)

    Verma, V. K.

    2012-07-01

    In the present paper we have studied the reconnection of chromospheric active regions events and uni-polar regions (Coronal Holes/CH) leading to the production of solar halo coronal mass ejections (HCMEs). To carry out this study we have used HCMEs data for the period April 1996 and December 2008 observed by LASCO/ SOHO and the daily solar CH maps observed and CH synoptic chart prepared at KPNO for the same period. We also used solar activity events data recorded by EIT instruments aboard SOHO, X-ray images of Sun recorded by Yohkoh mission, solar activity events recorded in Hα emission from various ground based-based observatories. To understand the role of CH maps in 10830 A and Chromospheric solar active region events we first matched time of onset of HCMEs with time of solar events in Hα or EIT data. Secondly we looked for the spatial location of solar activity phenomena and CH maps on the solar disk. From this study we find that 29.5% HCMEs were observed when there were CHs within 1-10 degree of flares locations, 26.5% H-CMEs were observed when there were CHs within 11-20 degree of flares locations, 17.9% HCMEs were observed when there were CHs within 21-30 degree of flares locations, 14.5% H-CMEs were observed when there were CHs within 31-40 degree of flares locations, and 11.6% H-CMEs were observed when there were CHs within > 40 and ˜60 degree of flares locations. We are of the view that the HCMEs have been produced by some mechanism, in which the mass ejected by some solar flares or active prominences, gets connected with the open magnetic lines of CHs (source of high speed solar wind streams) and moves along them to appear as suggested earlier by Verma and Pande (1989) and Verma (1998). References: Verma, V. K. & Pande, M. C. (1989) Proc. IAU Colloq. 104 Solar and Stellar Flares (Poster Papers), Stanford University, Stanford, USA, p.239. Verma, V. K.(1998) Journal of Geophysical Indian Union, 2, 65.

  5. High-temperature solar flare plasma behaviour from crystal spectrometer observations

    NASA Astrophysics Data System (ADS)

    Sylwester, Barbara; Sylwester, Janusz; Phillips, Kenneth J. H.; Kepa, Anna; Mrozek, Tomasz

    2015-08-01

    We discuss an analysis of spectra obtained from the Polish RESIK instrument flown on the CORONAS-F satellite. RESIK was a bent crystal spectrometer operating in the 3.36.1 range at high spectral and time resolution during flares over the 20022003 period, at the peak of the last solar cycle. Unlike many previous spectrometers, RESIK was accurately (20%) calibrated and crystal fluorescence was either eliminated or reduced to a minimum. The emission lines and continuum observed are formed at high temperatures (T > 3 MK) that are commonly present in active regions and flares. The spectra were observed during flares ranging in GOES importance from B and C up to multiples of X and with durations that were short and impulsive up to several hours. An analysis of absolute and relative intensities of lines and continuum that we performed for 33 flare events allowed the determination of the plasma composition (abundances of Si, S, Ar, K, and even the low-abundance element Cl) as well as a detailed study of the time evolution of the flare temperature structure from the differential emission measure (DEM). We will present the typical DEM evolutionary patterns of the flares seen and discuss their thermodynamics which helps our understanding of flares.

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

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

    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.

  7. ABRUPT LONGITUDINAL MAGNETIC FIELD CHANGES AND ULTRAVIOLET EMISSIONS ACCOMPANYING SOLAR FLARES

    SciTech Connect

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

    2012-11-20

    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.

  8. The Solar Flare 4: 10 keV X-ray Spectrum

    NASA Technical Reports Server (NTRS)

    Phillips, K. J. H.

    2004-01-01

    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.

  9. Magnetic-island Contraction and Particle Acceleration in Simulated Eruptive Solar Flares

    NASA Astrophysics Data System (ADS)

    Guidoni, S. E.; DeVore, C. R.; Karpen, J. T.; Lynch, B. J.

    2016-03-01

    The mechanism that accelerates particles to the energies required to produce the observed high-energy impulsive emission in solar flares is not well understood. Drake et al. proposed a mechanism for accelerating electrons in contracting magnetic islands formed by kinetic reconnection in multi-layered current sheets (CSs). We apply these ideas to sunward-moving flux ropes (2.5D magnetic islands) formed during fast reconnection in a simulated eruptive flare. A simple analytic model is used to calculate the energy gain of particles orbiting the field lines of the contracting magnetic islands in our ultrahigh-resolution 2.5D numerical simulation. We find that the estimated energy gains in a single island range up to a factor of five. This is higher than that found by Drake et al. for islands in the terrestrial magnetosphere and at the heliopause, due to strong plasma compression that occurs at the flare CS. In order to increase their energy by two orders of magnitude and plausibly account for the observed high-energy flare emission, the electrons must visit multiple contracting islands. This mechanism should produce sporadic emission because island formation is intermittent. Moreover, a large number of particles could be accelerated in each magnetohydrodynamic-scale island, which may explain the inferred rates of energetic-electron production in flares. We conclude that island contraction in the flare CS is a promising candidate for electron acceleration in solar eruptions.

  10. Correlation of Hard X-Ray and White Light Emission in Solar Flares

    NASA Astrophysics Data System (ADS)

    Kuhar, Matej; Krucker, Säm; Martínez Oliveros, Juan Carlos; Battaglia, Marina; Kleint, Lucia; Casadei, Diego; Hudson, Hugh S.

    2016-01-01

    A statistical study of the correlation between hard X-ray and white light emission in solar flares is performed in order to search for a link between flare-accelerated electrons and white light formation. We analyze 43 flares spanning GOES classes M and X using observations from the Reuven Ramaty High Energy Solar Spectroscopic Imager and Helioseismic and Magnetic Imager. We calculate X-ray fluxes at 30 keV and white light fluxes at 6173 Å summed over the hard X-ray flare ribbons with an integration time of 45 s around the peak hard-X ray time. We find a good correlation between hard X-ray fluxes and excess white light fluxes, with a highest correlation coefficient of 0.68 for photons with energy of 30 keV. Assuming the thick target model, a similar correlation is found between the deposited power by flare-accelerated electrons and the white light fluxes. The correlation coefficient is found to be largest for energy deposition by electrons above ∼50 keV. At higher electron energies the correlation decreases gradually while a rapid decrease is seen if the energy provided by low-energy electrons is added. This suggests that flare-accelerated electrons of energy ∼50 keV are the main source for white light production.

  11. Statistical relationship between the succeeding solar flares detected by the RHESSI satellite

    NASA Astrophysics Data System (ADS)

    Balzs, L. G.; Gyenge, N.; Korss, M. B.; Baranyi, T.; Forgcs-Dajka, E.; Ballai, I.

    2014-06-01

    The Reuven Ramaty High Energy Solar Spectroscopic Imager has observed more than 80 000 solar energetic events since its launch on 2002 February 12. Using this large sample of observed flares, we studied the spatiotemporal relationship between succeeding flares. Our results show that the statistical relationship between the temporal and spatial differences of succeeding flares can be described as a power law of the form R(t) tp with p = 0.327 0.007. We discuss the possible interpretations of this result as a characteristic function of a supposed underlying physics. Different scenarios are considered to explain this relation, including the case where the connectivity between succeeding events is realized through a shock wave in the post Sedov-Taylor phase or where the spatial and temporal relationship between flares is supposed to be provided by an expanding flare area in the sub-diffusive regime. Furthermore, we cannot exclude the possibility that the physical process behind the statistical relationship is the reordering of the magnetic field by the flare or it is due to some unknown processes.

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

    NASA Astrophysics Data System (ADS)

    Kraaikamp, Emil; Verbeeck, Cis

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

    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.

  14. Deuterium and tritium from solar flares at approximately 10 MeV per nucleon

    NASA Technical Reports Server (NTRS)

    Anglin, J. D.; Dietrich, W. F.; Simpson, J. A.

    1973-01-01

    It is indicated that the observations with the high-resolution solid-state charged-particle telescopes of the IMP-5 and IMP-6 earth satellites have resolved all the hydrogen and helium isotopes of solar-flare origin in groups of solar flares during the period from September, 1969, through November, 1972. The values obtained for the average isotope ratios are given and are compared with previous values. It is concluded that the observed high yields of H(2), H(3) and He(3) can be explained only by high-energy nuclear interactions and that an acceleration process must have taken place in the chromosphere at that time.

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

    NASA Technical Reports Server (NTRS)

    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

    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.

  16. Prompt particle acceleration around moving X-point magnetic field during impulsive phase of solar flares

    NASA Technical Reports Server (NTRS)

    Sakai, Jun-Ichi

    1992-01-01

    We present a model for high-energy solar flares to explain prompt proton and electron acceleration, which occurs around moving X-point magnetic field during the implosion phase of the current sheet. We derive the electromagnetic fields during the strong implosion phase of the current sheets, which is driven by the converging flow derived from the magnetohydrodynamic equations. It is shown that both protons and electrons can be promptly (within 1 second) accelerated to approximately 70 MeV and approximately 200 MeV, respectively. This acceleration mechanism can be applicable for the impulsive phase of the gradual gamma ray and proton flares (gradual GR/P flare), which have been called two-ribbon flares.

  17. Solar Flare Impulsive Phase Footpoint Emission Observed with SDO/EVE

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

    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.

  18. Numerical simulations of loops heated to solar flare temperatures. III - Asymmetrical heating

    NASA Technical Reports Server (NTRS)

    Cheng, C.-C.; Doschek, G. A.; Karpen, J. T.

    1984-01-01

    A numerical model is defined for asymmetric full solar flare loop heating and comparisons are made with observational data. The Dynamic Flux Tube Model is used to describe the heating process in terms of one-dimensional, two fluid conservation equations of mass, energy and momentum. An adaptive grid allows for the downward movement of the transition region caused by an advancing conduction front. A loop 20,000 km long is considered, along with a flare heating system and the hydrodynamic evolution of the loop. The model was applied to generating line profiles and spatial X-ray and UV line distributions, which were compared with SMM, P78-1 and Hintori data for Fe, Ca and Mg spectra. Little agreement was obtained, and it is suggested that flares be treated as multi-loop phenomena. Finally, it is concluded that chromospheric evaporation is not an effective mechanism for generating the soft X-ray bursts associated with flares.

  19. Observations of solar flare photon energy spectra from 20 keV to 7 MeV

    NASA Technical Reports Server (NTRS)

    Yoshimori, M.; Watanabe, H.; Nitta, N.

    1985-01-01

    Solar flare photon energy spectra in the 20 keV to 7 MeV range are derived from the Apr. 1, Apr. 4, apr. 27 and May 13, 1981 flares. The flares were observed with a hard X-ray and a gamma-ray spectrometers on board the Hinotori satellite. The results show that the spectral shape varies from flare to flare and the spectra harden in energies above about 400 keV. Effects of nuclear line emission on the continuum and of higher energy electron bremsstrahlung are considered to explain the spectral hardening.

  20. IRIS Observations of the Mg II h & k Lines During a Solar Flare

    NASA Astrophysics Data System (ADS)

    Kerr, Graham Stewart; Simões, Paulo J. A.; Qiu, Jiong; Fletcher, Lyndsay

    2015-04-01

    The bulk of the radiative output of a solar flare is radiated from the chromosphere. We have, until very recently, lacked routine observations of one of the strongest chromospheric lines: the MgII h&k resonance lines. These optically thick lines sample the atmosphere from the upper photosphere to the upper chromosphere and have been shown to be important diagnostics of the atmosphere in the non flaring features (quiet Sun, plage, network, sunspots, and prominences). However, only one flare observation of these lines has been reported (Lemaire et al 1984). With the launch of the IRIS solar telescope we are in a position to routinely observe the MgII h&k lines during flares, and we present a detailed study of the response of these lines to a solar flare. The spatial and temporal behaviour of the integrated intensities, k/h line ratios, line of sight velocities, line widths and line asymmetries were investigated during an M class flare, using a nonparametric quartiles approach. Redshifts of ~20km/s and line broadenings are observed at times of significant intensity enhancements, at the outer edge of the flare ribbons. The lines show blue asymmetry in only the most intense sources. Interestingly the characteristic central reversal feature that is ubiquitous in quiet Sun observations is absent in flaring profiles. Subordinate lines in the MgII passband are observed to be in emission within flaring sources, brightening and cooling in sync with the resonance lines. Additionally, we present the results of initial experiments with advanced numerical models to aid in the physical interpretation of these observed properties. This was achieved using the radiation hydrodynamic code RADYN that simulates the response of the solar atmosphere to flare energy input (we used a range of beam parameters to investigate energy injection to the atmosphere). RADYN provides both the hydrodynamic response of the atmosphere and the radiative response in energetically important lines and continua. The hydrodynamic output from RADYN was used as input to the radiative transfer code RH that solves the MgII resonance lines using partial redistributon.

  1. Two types of electron events in solar flares

    NASA Technical Reports Server (NTRS)

    Daibog, E. I.; Kurt, V. G.; Logachev, Y. I.; Stolpovsky, V. G.

    1985-01-01

    The fluxes and spectra of the flare electrons measured on board Venera-I3 and I4 space probes are compared with the parameters of the hard (E sub x approximately 55 keV) and thermal X-ray bursts. The electron flux amplitude has been found to correlate with flare importance in the thermal X-ray range (r approximately 0.8). The following two types of flare events have been found in the electron component of SCR. The electron flux increase is accompanied by a hard X-ray burst and the electron spectrum index in the approximately 25 to 200 keV energy range is gamma approximately 2 to 3. The electron flux increase is not accompanied by a hard X-ray burst and the electron spectrum is softer (Delta gamma approximately 0.7 to 1.0).

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

    NASA Technical Reports Server (NTRS)

    Chupp, E. L.

    1987-01-01

    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.

  3. Study of intensive solar flares in the rise phase of solar cycle 23 and 24 and other activities

    NASA Astrophysics Data System (ADS)

    Subramanian, S. Prasanna; Shanmugaraju, A.

    2016-02-01

    We present a statistical study and comparison on the properties of intensive solar flares (>M5.0 X-ray flare), decameter-hectometric (DH) wavelength [frequency, 1-14 MHz] type II radio bursts and solar energetic particle (SEP) events during the rising phase of solar cycles 23 and 24. The period of study is May 1996-November 2000 for solar cycle 23 and December 2008-June 2013 for solar cycle 24. Apart from reported weakness of solar cycle 24 compared to the cycle 23, we noted the following differences between the two cycles on the properties of these activities associated with intensive flares: (i) The reduction in the number of intensive flares (>M5.0 class) in cycle 24 is ˜34 %, similar to the reduction in sunspot number reported by Gopalswamy et al. (2014a); (ii) The slightly higher mean starting-frequency (4.15 MHz) and lower ending frequency (0.58 MHz) in cycle 24 compared to those of cycle 23 (2.63 and 0.89 MHz, respectively) indicate that the radio emission of this cycle started closer to the Sun and the CME-shock travelled farther away from the Sun in cycle 24; (iv) Cycle 23 produced a nearly equal number of SEP events as cycle 24 during the rising phase. The correlation between SEP intensity and CME speed is more prominent in cycle 23 (CC=0.7) than in cycle 24 (CC=0.3).

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

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

    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.

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

    SciTech Connect

    Simes, P. J. A.; Fletcher, L.; Hudson, H. S.; Russell, A. J. B. E-mail: lyndsay.fletcher@glasgow.ac.uk E-mail: hhudson@ssl.berkeley.edu

    2013-11-10

    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.

  6. IRIS observations of the Mg ii h and k lines during a solar flare

    NASA Astrophysics Data System (ADS)

    Kerr, G. S.; Simões, P. J. A.; Qiu, J.; Fletcher, L.

    2015-10-01

    The bulk of the radiative output of a solar flare is emitted from the chromosphere, which produces enhancements in the optical and UV continuum, and in many lines, both optically thick and thin. We have, until very recently, lacked observations of two of the strongest of these lines: the Mg ii h and k resonance lines. We present a detailed study of the response of these lines to a solar flare. The spatial and temporal behaviour of the integrated intensities, k/h line ratios, line of sight velocities, line widths and line asymmetries were investigated during an M class flare (SOL2014-02-13T01:40). Very intense, spatially localised energy input at the outer edge of the ribbon is observed, resulting in redshifts equivalent to velocities of ~15-26 km s-1, line broadenings, and a blue asymmetry in the most intense sources. The characteristic central reversal feature that is ubiquitous in quiet Sun observations is absent in flaring profiles, indicating that the source function increases with height during the flare. Despite the absence of the central reversal feature, the k/h line ratio indicates that the lines remain optically thick during the flare. Subordinate lines in the Mg ii passband are observed to be in emission in flaring sources, brightening and cooling with similar timescales to the resonance lines. This work represents a first analysis of potential diagnostic information of the flaring atmosphere using these lines, and provides observations to which synthetic spectra from advanced radiative transfer codes can be compared.

  7. The structure, stability and flaring of solar coronal loops

    NASA Technical Reports Server (NTRS)

    Van Hoven, G.

    1982-01-01

    A review is given of recent progress in the theory of the magnetohydrodynamic behavior of coronal loops, beginning with a brief characterization of thy observations. The equilibrium magnetic field is described, along with the consequences of the empirical requirement for short-term, or infinite-conductivity, stability which is shown to be dominated by the end-effect influence of thy quasi-rigid photosphere. A new loop-flare model is then developed, which takes account of the finite loop length. The primary resistive-sausage-mode instability exhibits the necessary threshold behavior, and produces a number of spatially and energetically distinct flare-release manifestations.

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

    NASA Astrophysics Data System (ADS)

    Murray, Sophie A.

    2013-01-01

    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.

  9. STUDY OF TWO SUCCESSIVE THREE-RIBBON SOLAR FLARES ON 2012 JULY 6

    SciTech Connect

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

    2014-01-20

    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 12-25keV 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.

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

    NASA Technical Reports Server (NTRS)

    Lin, R. P.

    2003-01-01

    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.

  11. What is the relationship between photospheric flow [|#12#|]fields and solar flares?

    NASA Astrophysics Data System (ADS)

    Welsch, B. T.; Li, Y.; Schuck, P. W.; Fisher, G. H.

    2009-12-01

    We estimated photospheric velocities by separately applying the Fourier Local Correlation Tracking (FLCT) and Differential Affine Velocity Estimator (DAVE) methods to 2708 co-registered pairs of SOHO/MDI magnetograms, with nominal 96-minute cadence and ~2'' pixels, from 46 active regions (ARs) from 1996-1998 over the time interval t_45 when each AR was within 45 degrees of disk center. For each magnetogram pair, we computed the reprojected, average estimated radial magnetic field, B_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_R, equal to the sum of (u B_R^2) over a magnetogram. Several quantities derived from B_R were also computed, including: total unsigned flux; a measure of the amount of unsigned flux near strong-field polarity inversion lines (SPILs), R; and the sum of B_R^2 over each magnetogram. Next, using correlation and discriminant analysis, we investigated the associations between these properties and flares from the GOES flare catalog, when averaged over both t_45 and shorter time windows, of 6 and 24 hours. Our AR sample included both flaring and flare-quiet ARs; the latter did not flare above GOES C1.0 level during t_45. Among magnetic properties, we found R to be most strongly associated with flare flux. Among extensive flow properties, the proxy Poynting flux, S_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 ~0.25, implying no single variable that we considered can explain variations in average flare flux.

  12. Modeling Solar Flare Hard X-ray Images and Spectra Observed with RHESSI

    NASA Technical Reports Server (NTRS)

    Sui, Linhui

    2005-01-01

    Observations obtained with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) of a flare on February 20, 2002 indicate a hard X-ray (HXR) coronal source at or near the top of a flare loop (called a HXR looptop source). The existence of the HXR looptop source suggests that magnetic reconnection, which is believed to power flares, occurs above the loop. In order to explain this HXR looptop source, I created a steady-state particle transport model, in which high-energy electrons are continuously injected at the top of a semicircular flare loop. Based on the simulation results, I find that the model predictions are consistent with the RHESSI observations in many respects, but the spectrum of the looptop source obtained from the model is steeper than that from the RHESSI data. This suggests that, instead of being accelerated above the loop as generally believed, the particles might be accelerated in the looptop itself. RHESSI-observations of three other homologous flares that occurred between April 14 and 16, 2002, provide strong evidence for the presence of a large scale current sheet above a flare loop, which is the basis of standard flare models. The most convincing finding is the presence of the temperature distribution of a separate coronal source above the flare loops: the hotter part of the coronal source was located lower in altitude the cooler part. Together with the fact that the hotter flare loops are higher than the cooler loops, the observations support the existence of a large-scale current sheet between the top of the flare loops and the coronal source above. Blob-Like sources along a line above the loop in the decay phase of the April 15, 2002, flare, which are suggestive of magnetic islands initiated by the tearing-mode instability, and the observation of a cusp structure in microwaves, further support the presence of the current sheet. The observations of the three homologous flares reveal two other features which are beyond the predictions of the standard flare models: the downward motion of flare loops in the early impulsive phase of each flare, and an initially stationary coronal source above the loops. These features me believed to be related to the formation and development of a current sheet. In particular, the downward loop motion seem to be a common phenomenon in flares, suggesting the necessity for modifications to the existing standard flare. models. Finally, thanks to the broad energy coverage of the RHESSI spectra, a low-energy cutoff of 28 (plus or minus 2) keV in the nonthermal electron distribution was determined for the April 15, 2002, flare. As a result, the energy carried by the nonthermal electrons is found to be comparable to the thermal energy of the flare, but one order of magnitude larger than the kinetic energy of the associated coronal mass ejection. The method used to deduce the electron low-energy cutoff will be useful in the analyses of similar events.

  13. Gamma-ray spectroscopy of the 2003 October 29 solar flare using RHESSI imaging

    NASA Astrophysics Data System (ADS)

    Duncan, N. A.; Shih, A. Y.; Hurford, G. J.; Lin, R. P.

    2011-12-01

    The solar system's most powerful explosions occur at the Sun, capable of releasing up to 10^33 ergs. The most powerful of these explosions release high-energy gamma rays and hard X-rays which encode key information about particle acceleration as well as the ambient solar environment. Here we present a study of one of the largest solar flares (GOES class X10) to have been captured by the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) instrument, occurring on October 29, 2003. This flare had previously been obscured by high background counts due to the magnetospheric response of another large flare that occurred the previous day. In this study, we use a Fourier-imaging technique to eliminate background before performing spectroscopy using the imaged flux. RHESSI's bi-collimated grid design phase modulates incoming solar photons before they are collected by the spectrometer. A back-projection technique is used to reconstruct an image from knowledge of grid orientation and detector counts. Since background counts are not phase modulated, they are generally insignificant in the back-projected image's derived flux. In this study we present spectra from the October 29 event, place this event in context with other large flares by adding this event to the correlation plots from Shih et al. (2009) and examine the limitations of this method.

  14. Global thermospheric disturbances induced by a solar flare: a modeling study

    NASA Astrophysics Data System (ADS)

    Le, Huijun; Ren, Zhipeng; Liu, Libo; Chen, Yiding; Zhang, Hui

    2015-12-01

    This study focuses on the global thermosphere disturbances during a solar flare by a theoretical model of thermosphere and ionosphere. The simulated results show significant enhancements in thermospheric density and temperature in dayside hemisphere. The greatest thermospheric response occurs at the subsolar point, which shows the important effect of solar zenith angle. The results show that there are also significant enhancements in nightside hemisphere. The sudden heating due to the solar flare disturbs the global thermosphere circulation, which results in the significant change in horizontal wind. There is a significant convergence process to the antisolar point and thus the strong disturbances in the nightside occur at the antisolar point. The peak enhancements of the neutral density around antisolar point occur at about 4 h after solar flare onset. The simulated results show that thermospheric response to a solar flare mainly depends on the total integrated energy into the thermosphere, not the peak value of EUV flux. The simulated results are basically consistent with the observations derived from the CHAMP satellite, which verified the results of this modeling study.

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

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

    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.

  16. MICROWAVE ZEBRA PATTERN STRUCTURES IN THE X2.2 SOLAR FLARE ON 2011 FEBRUARY 15

    SciTech Connect

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

    2012-01-10

    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.

  17. A Method to Calculate Background-Subtracted Flare Plasma Parameters Using GOES Over Three Solar Cycles

    NASA Astrophysics Data System (ADS)

    Ryan, Daniel; Gallagher, P. T.; Milligan, R. O.; Young, C. A.

    2010-05-01

    The GOES solar flare catalogue is the largest, self-consistent listing currently available covering three solar cycles - #21, 22, and 23 - from 1974 to the present. Solar X-ray flux integrated over the full solar disk is recorded every 3s in each of the two GOES channels (long; 1-8 and short; 0.5-4). By taking the ratio of the flux in the two passbands, parameters of the SXR-emitting plasma (e.g. temperature, emission measure, radiative loss rate etc.) can be derived, as well as the timescales over which they change. In doing so, it is vital to perform a suitable background subtraction to remove the influence of flux not associated with the flaring plasma. Using the method outlined in Bornmann 1990, we have developed a technique to systematically derive the flare parameters for all GOES flares from 1980 to present after accounting for background emission. This then allows us to make statistically meaningful comparisons between events observed over the course of the past three solar cycles. This research is generously funded by the Irish Research Council for Science, Engineering and Technology (IRCSET).

  18. Properties of Chromospheric Evaporation and Plasma Dynamics of a Solar Flare from Iris

    NASA Astrophysics Data System (ADS)

    Sadykov, Viacheslav M.; Vargas Dominguez, Santiago; Kosovichev, Alexander G.; Sharykin, Ivan N.; Struminsky, Alexei B.; Zimovets, Ivan

    2015-06-01

    The dynamics of hot chromospheric plasma of solar flares is a key to understanding the mechanisms of flare energy release and particle acceleration. A moderate M1.0 class flare of 2014 June 12, (SOL2014-06-12T21:12) was simultaneously observed by NASA's Interface Region Imaging Spectrograph (IRIS) and other spacecraft, and also by the New Solar Telescope at the BBSO. This paper presents the first part of our investigation focused on analysis of the IRIS data. Our analysis of the IRIS data in different spectral lines reveals a strong redshifted jet-like flow with a speed of 100 km s-1 of the chromospheric material before the flare. Strong nonthermal emission of the C ii k 1334.5 line, formed in the chromosphere-corona transition region, is observed at the beginning of the impulsive phase in several small (with a size of 1?) points. It is also found that the C ii k line is redshifted across the flaring region before, during, and after the impulsive phase. A peak of integrated emission of the hot (1.1 107 K) plasma in the Fe xxi 1354.1 line is detected approximately five minutes after the integrated emission peak of the lower temperature C ii k. A strong blueshift of the Fe xxi line across the flaring region corresponds to evaporation flows of the hot chromospheric plasma with a speed of 50 km s-1. Additional analysis of the RHESSI data supports the idea that the upper chromospheric dynamics observed by IRIS has features of gentle evaporation driven by heating of the solar chromosphere by accelerated electrons and by a heat flux from the flare energy release site.

  19. QUASI-PERIODIC PULSATIONS IN SOLAR AND STELLAR FLARES: RE-EVALUATING THEIR NATURE IN THE CONTEXT OF POWER-LAW FLARE FOURIER SPECTRA

    SciTech Connect

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

    2015-01-10

    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.

  20. Analysis of coronal and chromospheric hard X-ray sources in an eruptive solar flare

    NASA Astrophysics Data System (ADS)

    Zimovets, Ivan; Golovin, Dmitry; Livshits, Moisey; Vybornov, Vadim; Sadykov, Viacheslav; Mitrofanov, Igor

    We have analyzed hard X-ray emission of an eruptive solar flare on 3 November 2010. The entire flare region was observed by the STEREO-B spacecraft. This gave us an information that chromospheric footpoints of flare magnetic loops were behind the east solar limb for an earth observer. Hard X-ray emission from the entire flare region was detected by the High Energy Neutron Detector (HEND) onboard the 2001 Mars Odyssey spacecraft while hard X-rays from the coronal part of the flare region were detected by the RHESSI. This rare situation has allowed us to investigate both coronal and chromospheric sources of hard X-ray emission separately. Flare impulsive phase was accompanied by eruption of a magnetic flux rope and formation of a plasmoid detected by the AIA/SDO in the EUV range. Two coronal hard X-ray sources (S_{1} and S_{2}) were detected by the RHESSI. The upper source S_{1} coincided with the plasmoid and the lower source S_{2} was near the tops of the underlying flare loops that is in accordance with the standard model of eruptive flares. Imaging spectroscopy with the RHESSI has allowed to measure energetic spectra of hard X-ray emission from the S_{1} and S_{2} sources. At the impulsive phase peak they have power-law shape above ? 15 keV with spectral slopes gamma_{S_{1}}=3.46 1.58 and gamma_{S_{2}}=4.64 0.12. Subtracting spatially integrated spectrum of coronal hard X-ray emission measured by the RHESSI from the spectrum measured by the HEND we found spectrum of hard X-rays emitted from the footpoints of the flare loops (source S_{0}). This spectrum has a power-law shape with gamma_{S_{0}}=2.21 0.57. It is shown that it is not possible to explain the measured spectra of the S_{2} and S_{0} sources in frames of the thin and thick target models respectively if we assume that electrons were accelerated in the energy release site situated below the plasmoid and above the flare loops as suggested by the standard flare model. To resolve the contradiction the Coulomb energy losses by non-thermal electrons in the corona should be taken into consideration. Hard X-ray spectrum of the upper coronal source S_{1} can be explained by continuous injection model of non-thermal electrons from the acceleration site into the plasmoid which should be considered as an ideal magnetic trap.