Science.gov

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. Universality in solar flare and earthquake occurrence.

    PubMed

    de Arcangelis, L; Godano, C; Lippiello, E; Nicodemi, M

    2006-02-10

    Earthquakes and solar flares are phenomena involving huge and rapid releases of energy characterized by complex temporal occurrence. By analyzing available experimental catalogs, we show that the stochastic processes underlying these apparently different phenomena have universal properties. Namely, both problems exhibit the same distributions of sizes, interoccurrence times, and the same temporal clustering: We find after flare sequences with power law temporal correlations as the Omori law for seismic sequences. The observed universality suggests a common approach to the interpretation of both phenomena in terms of the same driving physical mechanism. PMID:16486917

  3. A 153 day periodicity in the occurrence of solar flares producing energetic interplanetary electrons

    NASA Technical Reports Server (NTRS)

    Droge, Wolfgang; Gibbs, Kenneth; Grunsfeld, John M.; Meyer, Peter; Newport, Brian J.

    1990-01-01

    The occurrence times of energetic (above 10 MeV) solar flare electron events observed on board the ISEE 3 spacecraft during the years 1978-1982 have been examined; strong evidence is found for a periodicity of 153 + or - 2 days, confirming the discovery of a periodicity in the occurrence of solar flares producing X-rays and gamma rays. The Rayleigh test for periodicity is applied to obtain a probability of less than 10 to the -6th that the times of the electron flares were drawn from a uniform distribution.

  4. 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.

  5. 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.

  6. 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.

  7. Towards understanding solar flares

    NASA Astrophysics Data System (ADS)

    Acton, L. W.

    1982-05-01

    Instrumentation and spacecraft payloads developed at Lockheed for solar flare studies are reviewed, noting the significance of the observations for adding to a data base for eventual prediction of the occurrence of flares and subsequent radiation hazards to people in space. Developmental work on the two solar telescopes on board the Skylab pallet was performed at a Lockheed facility, as was the fabrication of very-large-area proportional counter for flights on the Aerobee rocket in 1967. The rocket work led to the fabrication of the Mapping X Ray Heliometer on the Orbiting Solar Observatory and the X Ray Polychromator for the Solar Maximum Mission. The Polychromator consists of a bent crystal spectrometer for high time resolution flare studies over a wide field of view, and a flat crystal spectrometer for simultaneous polychromatic imaging at 7 different X ray wavelengths.

  8. Intensity thresholds and the statistics of the temporal occurrence of solar flares.

    PubMed

    Baiesi, Marco; Paczuski, Maya; Stella, Attilio L

    2006-02-10

    Introducing thresholds to analyze time series of emission from the Sun enables a new and simple definition of solar flare events and their interoccurrence times. Rescaling time by the rate of events, the waiting and quiet time distributions both conform to scaling functions that are independent of the intensity threshold over a wide range. The scaling functions are well-described by a two-parameter function, with parameters that depend on the phase of the solar cycle. For flares identified according to the current, standard definition, similar behavior is found. PMID:16486918

  9. 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.

  10. 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.

  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. Statistical aspects of solar flares

    NASA Technical Reports Server (NTRS)

    Wilson, Robert M.

    1987-01-01

    A survey of the statistical properties of 850 H alpha solar flares during 1975 is presented. Comparison of the results found here with those reported elsewhere for different epochs is accomplished. Distributions of rise time, decay time, and duration are given, as are the mean, mode, median, and 90th percentile values. Proportions by selected groupings are also determined. For flares in general, mean values for rise time, decay time, and duration are 5.2 + or - 0.4 min, and 18.1 + or 1.1 min, respectively. Subflares, accounting for nearly 90 percent of the flares, had mean values lower than those found for flares of H alpha importance greater than 1, and the differences are statistically significant. Likewise, flares of bright and normal relative brightness have mean values of decay time and duration that are significantly longer than those computed for faint flares, and mass-motion related flares are significantly longer than non-mass-motion related flares. Seventy-three percent of the mass-motion related flares are categorized as being a two-ribbon flare and/or being accompanied by a high-speed dark filament. Slow rise time flares (rise time greater than 5 min) have a mean value for duration that is significantly longer than that computed for fast rise time flares, and long-lived duration flares (duration greater than 18 min) have a mean value for rise time that is significantly longer than that computed for short-lived duration flares, suggesting a positive linear relationship between rise time and duration for flares. Monthly occurrence rates for flares in general and by group are found to be linearly related in a positive sense to monthly sunspot number. Statistical testing reveals the association between sunspot number and numbers of flares to be significant at the 95 percent level of confidence, and the t statistic for slope is significant at greater than 99 percent level of confidence. Dependent upon the specific fit, between 58 percent and 94 percent of the variation can be accounted for with the linear fits. A statistically significant Northern Hemisphere flare excess (P less than 1 percent) was found, as was a Western Hemisphere excess (P approx 3 percent). Subflares were more prolific within 45 deg of central meridian (P less than 1 percent), while flares of H alpha importance or = 1 were more prolific near the limbs greater than 45 deg from central meridian; P approx 2 percent). Two-ribbon flares were more frequent within 45 deg of central meridian (P less than 1 percent). Slow rise time flares occurred more frequently in the western hemisphere (P approx 2 percent), as did short-lived duration flares (P approx 9 percent), but fast rise time flares were not preferentially distributed (in terms of east-west or limb-disk). Long-lived duration flares occurred more often within 45 deg 0 central meridian (P approx 7 percent). Mean durations for subflares and flares of H alpha importance or + 1, found within 45 deg of central meridian, are 14 percent and 70 percent, respectively, longer than those found for flares closer to the limb. As compared to flares occurring near cycle maximum, the flares of 1975 (near solar minimum) have mean values of rise time, decay time, and duration that are significantly shorter. A flare near solar maximum, on average, is about 1.6 times longer than one occurring near solar minimum.

  13. Observations of small solar flares with BATSE

    NASA Astrophysics Data System (ADS)

    Biesecker, D. A.; Ryan, J. M.; Fishman, G. J.

    1994-12-01

    The Burst and Transient Source Experiment on board the Compton Gamma Ray Observatory is being used to observe solar flares. The Large Area Detectors are sensitive to small solar flares. We are searching the BATSE data for solar flares with an automated algorithm that allows for independent confirmation of the event origin. With this search method, we have detected solar flares almost an order of magnitude smaller than those found in a visual search of the BASTE data. We present results that are consistent with the differential distribution of peak flare rates observed by other researchers. These results show that the rate of occurrence of the smallest flares observed by BATSE can be predicted from the rate of occurrence of larger flares.

  14. 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.

  15. Towards Predicting Solar Flares

    NASA Astrophysics Data System (ADS)

    Winter, Lisa; Balasubramaniam, Karatholuvu S.

    2015-04-01

    We present a statistical study of solar X-ray flares observed using GOES X-ray observations of the ~50,000 fares that occurred from 1986 - mid-2014. Observed X-ray parameters are computed for each of the flares, including the 24-hour non-flare X-ray background in the 1-8 A band and the maximum ratio of the short (0.5 - 4 A) to long band (1-8 A) during flares. These parameters, which are linked to the amount of active coronal heating and maximum flare temperature, reveal a separation between the X-, M-, C-, and B- class fares. The separation was quantified and verified through machine-learning algorithms (k nearest neighbor; nearest centroid). Using the solar flare parameters learned from solar cycles 22-23, we apply the models to predict flare categories of solar cycle 24. Skill scores are then used to assess the success of our models, yielding correct predictions for ~80% of M-, C-, and B-class flares and 100% correct predictions for X-flares. We present details of the analysis along with the potential uses of our model in flare forecasting.

  16. 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.

  17. The solar flare myth

    NASA Technical Reports Server (NTRS)

    Gosling, J. T.

    1993-01-01

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

  18. Dimensional Analysis of Solar Flare Distributions

    NASA Astrophysics Data System (ADS)

    Litvinenko, Y.

    2001-05-01

    Dimensional analysis is used to derive the distribution of solar flare energies ~ E-3/2 in accordance with recent observational and numerical results. Several other scalings, notably E ~ t f2 where t f is the flare duration, are obtained as well. Dimensional considerations can also be employed to model the rate of occurrence of solar flares (the flare waiting-time distribution). An analytical estimate for the mean flaring rate λ 0 is obtained, based on the idea that the rate reflects a balance between the processes of energy input into the corona and energy dissipation by flaring. The estimate is shown to be in good agreement with observations of flares by GOES detectors.

  19. Solar flares: an overview.

    PubMed

    Rust, D M

    1992-01-01

    This is a survey of solar phenomena and physical models that may be useful for improving forecasts of solar flares and proton storms in interplanetary space. Knowledge of the physical processes that accelerate protons has advanced because of gamma-ray and X-ray observations from the Solar Maximum Mission telescopes. Protons are accelerated at the onset of flares, but the duration of any subsequent proton storm at 1 AU depends on the structure of the interplanetary fields. X-ray images of the solar corona show possible fast proton escape paths. Magnetographs and high-resolution visible-band images show the magnetic field structure near the acceleration region and the heating effects of sunward-directed protons. Preflare magnetic field growth and shear may be the most important clues to the physical processes that generate high energy solar particles. Any dramatic improvement in flare forecasts will require high resolution solar telescopes in space. Several possibilities for improvements in the art of flare forecasting are presented, among them: the use of acoustic tomography to probe for subsurface magnetic fields; a satellite-borne solar magnetograph; and an X-ray telescope to monitor the corona for eruptions. PMID:11537019

  20. BATSE Solar Flare Spectroscopy

    NASA Technical Reports Server (NTRS)

    Schwartz, R. A.

    1998-01-01

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

  1. Solar Flare Physics

    NASA Astrophysics Data System (ADS)

    Schmahl, Edward J.; Kundu, Mukul R.

    2000-03-01

    In the extended portion of this grant (January 1-March 31, 2000), we have continued our previous efforts (January 1-December 31, 1999) in studies of Fourier imaging methods applied to hard X-ray flares. In particular, we have performed theoretical analysis of the "Forward-Fitting" method in collaboration with Dr. Markus Aschwanden, (Lockheed-Martin Palo Alto Research lab) in support of the HESSI (High Energy Solar Spectroscopic Imager) mission to enable rapid imaging of solar flares in hard X-rays.

  2. Activation of solar flares

    SciTech Connect

    Cargill, P.J.; Migliuolo, S.; Hood, A.W.

    1984-11-01

    The physics of the activation of two-ribbon solar flares via the MHD instability of coronal arcades is presented. The destabilization of a preflare magnetic field is necessary for a rapid energy release, characteristic of the impulsive phase of the flare, to occur. The stability of a number of configurations are examined, and the physical consequences and relative importance of varying pressure profiles and different sets of boundary conditions (involving field-line tying) are discussed. Instability modes, driven unstable by pressure gradients, are candidates for instability. Shearless vs. sheared equilibria are also discussed. (ESA)

  3. 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.

  4. 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.

  5. Solar flare alpha particles

    NASA Technical Reports Server (NTRS)

    Lanzerotti, L. J.

    1973-01-01

    Interplanetary disturbances frequently change the instantaneous values of the low energy solar flare alpha-to-proton flux ratios. The fluxes of alpha particles were integrated over the duration of seven large solar events occurring between May 28, 1967, and November 6, 1969, in order to investigate the total alpha particles fluxes observed at 1 AU resulting from the flares. The spectra of the event integrated alphas are always softer than the spectra of the event integrated protons. As a consequence, the event-integrated alpha-to-proton ratios decrease slightly with increasing energy per nucleon. The He-4/H-1 ratios averaged over the seven events are found to vary as 0.026 (E/nucl) sup -0.2 in the range 1 to 10 MeV/nucleon. The value of the ratio at 1 MeV/nucleon is less than the helium-to-hydrogen abundance determined from spectroscopic studies of prominences and the chromosphere, and is less than the average solar wind helium-to-hydrogen abundance.

  6. 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.

  7. 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.

  8. 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.

  9. 6Li from Solar Flares.

    PubMed

    Ramaty; Tatischeff; Thibaud; Kozlovsky; Mandzhavidze

    2000-05-10

    By introducing a hitherto ignored 6Li producing process, due to accelerated 3He reactions with 4He, we show that accelerated particle interactions in solar flares produce much more 6Li than 7Li. By normalizing our calculations to gamma-ray data, we demonstrate that the 6Li produced in solar flares, combined with photospheric 7Li, can account for the recently determined solar wind lithium isotopic ratio, obtained from measurements in lunar soil, provided that the bulk of the flare-produced lithium is evacuated by the solar wind. Further research in this area could provide unique information on a variety of problems, including solar atmospheric transport and mixing, solar convection and the lithium depletion issue, and solar wind and solar particle acceleration. PMID:10813684

  10. Nuclear processes in solar flares

    NASA Technical Reports Server (NTRS)

    Ramaty, R.

    1982-01-01

    The theory of solar gamma-ray line production is reviewed and new calculations of line production yields are presented. Observations, carried out with gamma-ray spectrometers on OSO-7, HEAO-1, HEAO-3 and SMM are reviewed and compared with theory. These observations provide direct evidence for nuclear reactions in flares and furnish unique information on particle acceleration and flare mechanisms.

  11. Particle acceleration in solar flares

    NASA Technical Reports Server (NTRS)

    Ramaty, R.; Forman, M. A.

    1987-01-01

    The most direct signatures of particle acceleration in flares are energetic particles detected in interplanetary space and in the Earth atmosphere, and gamma rays, neutrons, hard X-rays, and radio emissions produced by the energetic particles in the solar atmosphere. The stochastic and shock acceleration theories in flares are reviewed and the implications of observations on particle energy spectra, particle confinement and escape, multiple acceleration phases, particle anistropies, and solar atmospheric abundances are discussed.

  12. 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.

  13. 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)

  14. 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

  15. Fine Structure in Solar Flares.

    PubMed

    Warren

    2000-06-20

    We present observations of several large two-ribbon flares observed with both the Transition Region and Coronal Explorer (TRACE) and the soft X-ray telescope on Yohkoh. The high spatial resolution TRACE observations show that solar flare plasma is generally not confined to a single loop or even a few isolated loops but to a multitude of fine coronal structures. These observations also suggest that the high-temperature flare plasma generally appears diffuse while the cooler ( less, similar2 MK) postflare plasma is looplike. We conjecture that the diffuse appearance of the high-temperature flare emission seen with TRACE is due to a combination of the emission measure structure of these flares and the instrumental temperature response and does not reflect fundamental differences in plasma morphology at the different temperatures. PMID:10859129

  16. 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.

  17. 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.

  18. Solar flares increased in 1982

    NASA Astrophysics Data System (ADS)

    Geomagnetic storms and solar flares occurred more frequently in 1982 (3 years after the solar maximum of the current 11-year sunspot cycle) than is usual for that portion of the cycle. Among the most notable events were two X-12 flares and one X-7 flare. Although less intense, the X-7 flare triggered the most fierce geomagnetic storm in a decade; it distorted the earth's magnetic field, disrupted long-range communications and low-frequency navigational systems, interfered with ham radio activities, and spread a brilliant auroral display over much of the nation.Solar flares are divided into three classes depending on the output of X radiation: the common C class, the moderate M class, and the intensive X class. The numerical designation indicates the level of radiation intensity; an X-12, which is t h e most intense that instruments can measure, is 12 times more intense than an X-1 . An X-1 flare releases 10 times more radiation than an M-1, and 100 times more than a C-1.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. Periodicities of the LDE-type flare occurrence (1969 - 1992).

    PubMed

    Antalova, A

    1994-10-01

    The power spectrum was calculated for the time series of the LDE-type flare occurrence during the last three solar cycles (the 20-th, the 21-st and the first part of the 22-nd cycle). LDE-type flares (Long Duration Events in SXR) are associated with the interplanetary protons (SEP and STIP as well), energized coronal arches and radio type IV emission. Generally, in all the cycles considered, LDE-type flares mainly originated during a 6-year interval of the respective cycle (2 years before and 4 years after the sunspot cycle maximum). The following significant periodicities were found: in the 20-th cycle: 1.4, 2.1, 2.9, 4.0, 10.7 and 54.2 of month; in the 21-st cycle: 1.2, 1.6, 2.8, 4.9, 7.8 and 44.5 of month; in the 22-nd cycle, till March 1992: 1.4, 1.8, 2.4, 7.2, 8.7, 11.8 and 29.1 of month; in all interval (1969-1992): 1. the longer periodicities: 232.1, 121.1 (the dominant at 10.1 of year), 80.7, 61.9 and 25.6 of month, 2. the shorter periodicities: 4.7, 5.0, 6.8, 7.9, 9.1, 15.8 and 20.4 of month. Solar variability has an extremely complex time dependence. The Sun is a multiperiodic system. The strong periodicities "near 155 and 270 days" were found also in the LDE-type flare occurrence. PMID:11540016

  5. 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.

  6. Magnetic Reconnection in Solar Flares

    NASA Astrophysics Data System (ADS)

    Forbes, Terry G.

    2016-05-01

    Reconnection has at least three possible roles in solar flares: First, it may contribute to the build-up of magnetic energy in the solar corona prior to flare onset; second, it may directly trigger the onset of the flare; and third, it may allow the release of magnetic energy by relaxing the magnetic field configuration to a lower energy state. Although observational support for the first two roles is somewhat limited, there is now ample support for the third. Within the last few years EUV and X-ray instruments have directly observed the kind of plasma flows and heating indicative of reconnection. Continued improvements in instrumentation will greatly help to determine the detailed physics of the reconnection process in the solar atmosphere. Careful measurement of the reconnection outflows will be especially helpful in this regard. Current observations suggest that in some flares the jet outflows are accelerated within a short diffusion region that is more characteristic of Petschek-type reconnection than Sweet-Parker reconnection. Recent resistive MHD theoretical and numerical analyses predict that the length of the diffusion region should be just within the resolution range of current X-ray and EUV telescopes if the resistivity is uniform. On the other hand, if the resistivity is not uniform, the length of the diffusion region could be too short for the outflow acceleration region to be observable.

  7. THE SOLAR FLARE IRON ABUNDANCE

    SciTech Connect

    Phillips, K. J. H.; Dennis, B. R. E-mail: Brian.R.Dennis@nasa.gov

    2012-03-20

    The abundance of iron is measured from emission line complexes at 6.65 keV (Fe line) and 8 keV (Fe/Ni line) in RHESSI X-ray spectra during solar flares. Spectra during long-duration flares with steady declines were selected, with an isothermal assumption and improved data analysis methods over previous work. Two spectral fitting models give comparable results, viz., an iron abundance that is lower than previous coronal values but higher than photospheric values. In the preferred method, the estimated Fe abundance is A(Fe) = 7.91 {+-} 0.10 (on a logarithmic scale, with A(H) = 12) or 2.6 {+-} 0.6 times the photospheric Fe abundance. Our estimate is based on a detailed analysis of 1898 spectra taken during 20 flares. No variation from flare to flare is indicated. This argues for a fractionation mechanism similar to quiet-Sun plasma. The new value of A(Fe) has important implications for radiation loss curves, which are estimated.

  8. Statistical properties of solar flares and coronal mass ejections through the solar cycle

    NASA Astrophysics Data System (ADS)

    Telloni, Daniele; Carbone, Vincenzo; Lepreti, Fabio; Antonucci, Ester

    2016-03-01

    Waiting Time Distributions (WTDs) of solar flares are investigated all through the solar cycle. The same approach applied to Coronal Mass Ejections (CMEs) in a previous work is considered here for flare occurrence. Our analysis reveals that flares and CMEs share some common statistical properties, which result dependent on the level of solar activity. Both flares and CMEs seem to independently occur during minimum solar activity phases, whilst their WTDs significantly deviate from a Poisson function at solar maximum, thus suggesting that these events are correlated. The characteristics of WTDs are constrained by the physical processes generating those eruptions associated with flares and CMEs. A scenario may be drawn in which different mechanisms are actively at work during different phases of the solar cycle. Stochastic processes, most likely related to random magnetic reconnections of the field lines, seem to play a key role during solar minimum periods. On the other hand, persistent processes, like sympathetic eruptions associated to the variability of the photospheric magnetism, are suggested to dominate during periods of high solar activity. Moreover, despite the similar statistical properties shown by flares and CMEs, as it was mentioned above, their WTDs appear different in some aspects. During solar minimum periods, the flare occurrence randomness seems to be more evident than for CMEs. Those persistent mechanisms generating interdependent events during maximum periods of solar activity can be suggested to play a more important role for CMEs than for flares, thus mitigating the competitive action of the random processes, which seem instead strong enough to weaken the correlations among flare event occurrence during solar minimum periods. However, it cannot be excluded that the physical processes at the basis of the origin of the temporal correlation between solar events are different for flares and CMEs, or that, more likely, more sophisticated effects are at work at the same time leading to an even more complex picture. This work represents a first step for further investigations.

  9. Solar flares and energetic particles.

    PubMed

    Vilmer, Nicole

    2012-07-13

    Solar flares are now observed at all wavelengths from γ-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 γ-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/γ-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

  10. 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).

  11. Magnetic Flux Transients during Solar Flares

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  12. 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.

  13. Solar neutron events associated with large solar flares in solar cycle 23

    NASA Astrophysics Data System (ADS)

    Watanabe, K.; Muraki, Y.; Matsubara, Y.; Sako, T.; Masuda, S.; Sakai, T.; Tsuchiya, H.; Shibata, S.; Yoshimori, M.; Ohmori, N.; Velarde, A.; Ticona, R.; Martinic, N.; Miranda, P.; Kakimoto, F.; Ogio, S.; Tsunesada, Y.; Tokuno, H.; Shirasaki, Y.; Valdés-Galicia, J. F.; Hurtado, A.; Musalem, O.; Ogasawara, R.; Mizumoto, Y.; Nakagiri, M.; Miyasita, A.; Stoker, P. H.; Lopate, C.; Kudela, K.; Gros, M.

    2005-12-01

    We have investigated ion acceleration mechanisms in solar flares by observing solar neutrons produced by in association with these solar flares. Solar neutrons are observed by means of ground-based neutron monitors and solar neutron telescopes which form an international network for solar neutron observations. Observations of solar neutrons have been made during solar cycle 23 using this network. More than a hundred X class flares have been recorded in solar cycle 23. Corresponding to these, five solar neutron events were observed by ground-based neutron monitors from the flares of November 24, 2000, August 25, 2001, October 28, November 2 and 4, 2003. The statistical significances of all these events were, very significant (more than 5 σ), and the excesses were clear. These solar neutron events observed in solar cycle 23 were detected in association with strong emissions of hard X-rays and γ -rays. The occurrence of solar neutrons appears to be correlated with the intensity of hard X-rays and γ -rays emitted by the associated solar flare as observed by the Yohkoh, RHESSI and INTEGRAL satellites. Assuming that solar neutrons are produced at the same time as the emission of these γ -rays, a good correlation is found between the production times of solar neutrons and the observed excesses of neutron monitors. The corresponding energy spectra of solar neutrons at the solar surface is well described by a power law. The spectral indexes of the solar neutron events we have observed in solar cycle 23 are typical for the solar neutron events observed so far, being between -3 and -4, although the fluxes are fainter than those observed in earlier events. From the spectra of solar neutrons, the energy spectra of accelerated ions can be deduced and these are found to be softer than the neutron spectra, which have spectral indexes between -4 and -5. The corresponding number of protons above 30 MeV was estimated to be between 1030 and 1033 for these events.

  14. Pulsed acceleration in solar flares

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

    We study the nonlinear dynamics of particle acceleration in solar flares by analyzing the time series of various quasi-periodic radio signatures during flares. In particular we present the radio and hard X-ray data of three flares which suppport the following tentative conclusions: (1) Particle acceleration and injection into magnetic structures occurs intrinsically in a pulsed mode (with a typical period of 1-2 s), produced by a single, spatially coherent, nonlinear system, rather than by a stochastic system with many spatially independent components ('statistical flare' produced by a fragmented primary energy release). (2) The nonlinear (quasi-periodic) mode of pulsed particle acceleration and injection into a coronal loop can be stabilized by phase locking with an MHD wave (oscillation) mode, if both periods are close to each other. (3) Pulsed injection of electron beams into a coronal loop may trigger nonlinear relaxational oscillations of wave-particle interactions. This is particularly likely when the limit cycles of both systems are similar.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Activated solar filaments and flares

    NASA Technical Reports Server (NTRS)

    Svestka, Z.

    1980-01-01

    Skylab observations have shown that activations and disruptions of dark H-alpha filaments are one of the basic and most important mechanisms of solar activity. The Kopp-Pneuman theory of post-flare loops shows that the process which disrupts a filament opens the magnetic field and causes a greatly enhanced mass flow along the field lines. The open field lines subsequently reconnect, starting from the bottom of the corona and proceeding upwards. This process can last for many hours. Hot loops are first seen in X-rays, then in extreme UV lines, and, after an appropriate cooling time, in H-alpha as the loop prominence systems.

  3. 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

  4. Millimeter emission of solar flares

    NASA Astrophysics Data System (ADS)

    Nagnibeda, V. G.; Smirnova, V. V.; Ryzhov, V. S.; Zhiltsov, A. V.

    2013-06-01

    We analyzed two unique radio observations of millimeter solar flares at 93 and 140 GHz with the THz component in these spectra. Data were obtained from ground-based radio-telescope RT-7.5 operated by Bauman Moscow State Technical University (BMSTU) with the spacial resolution of 2.5 and 1.5 arc-minutes. We analyzed temporal structure of observed radio-bursts and their dynamics in comparison with soft and hard X-ray light-curves obtained from GOES and RHESSI space-based observations. It was found the 140 GHz emission enhancement at the spectra that is new independent confirmation of the THz component existance. Also, we analyzed data of microwave solar flares with the emission enhanced at 35 GHz obtained from Nobeyama radioheliograph (NoRH) and radiopolarimeter (NoRP). It was found that the maximum of the flux density spectra was shifted toward high frequencies that didn't agree with the model spectrum obtained from microwave observations. We assumed, that such kind of spectra are associated with the gyro-synchrotron radiation of the significant number of high-energetic electrons emission with energies of about 500 keV. The emission mechanism at millimeter waves is the gyro-synchrotron radiation. However, if the energetic electrons are not enough the thermal emission mechanism could be dominant factor at millimeter radiation that could also explain the spectral maximum shift to high frequencies.

  5. 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.

  6. 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.

  7. 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.

  8. Automatic prediction of solar flares and super geomagnetic storms

    NASA Astrophysics Data System (ADS)

    Song, Hui

    Space weather is the response of our space environment to the constantly changing Sun. As the new technology advances, mankind has become more and more dependent on space system, satellite-based services. A geomagnetic storm, a disturbance in Earth's magnetosphere, may produce many harmful effects on Earth. Solar flares and Coronal Mass Ejections (CMEs) are believed to be the major causes of geomagnetic storms. Thus, establishing a real time forecasting method for them is very important in space weather study. The topics covered in this dissertation are: the relationship between magnetic gradient and magnetic shear of solar active regions; the relationship between solar flare index and magnetic features of solar active regions; based on these relationships a statistical ordinal logistic regression model is developed to predict the probability of solar flare occurrences in the next 24 hours; and finally the relationship between magnetic structures of CME source regions and geomagnetic storms, in particular, the super storms when the D st index decreases below -200 nT is studied and proved to be able to predict those super storms. The results are briefly summarized as follows: (1) There is a significant correlation between magnetic gradient and magnetic shear of active region. Furthermore, compared with magnetic shear, magnetic gradient might be a better proxy to locate where a large flare occurs. It appears to be more accurate in identification of sources of X-class flares than M-class flares; (2) Flare index, defined by weighting the SXR flares, is proved to have positive correlation with three magnetic features of active region; (3) A statistical ordinal logistic regression model is proposed for solar flare prediction. The results are much better than those data published in the NASA/SDAC service, and comparable to the data provided by the NOAA/SEC complicated expert system. To our knowledge, this is the first time that logistic regression model has been applied in solar physics to predict flare occurrences; (4) The magnetic orientation angle [straight theta], determined from a potential field model, is proved to be able to predict the probability of super geomagnetic storms (D= st <=-200nT). The results show that those active regions associated with | [straight theta]| < 90° are more likely to cause a super geomagnetic storm.

  9. Solar flares and magnetic topology

    NASA Technical Reports Server (NTRS)

    Sturrock, P. A.

    1987-01-01

    This article is a very brief review and comparison of the observational properties of flares and theoretical concepts of models of flares, especially the concepts of magnetic topology and its evolution. We examine the environmental aspects of flare behavior. Some of these aspects must be consequences of unknown processes occurring below the photosphere. Other aspects involve structures - such as filaments - that are closely related to flares. We then examine properties of flares to try to distinguish the different phases of energy release that can occur in the course of a flare. Finally a schematic scenario is offered to interpret these phases in terms of this scenario.

  10. 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.

  11. 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.

  12. Excitation of XUV radiation in solar flares

    NASA Technical Reports Server (NTRS)

    Emslie, A. Gordon

    1992-01-01

    The goal of the proposed research was to understand the means by which XUV radiation in solar flares is excited, and to use this radiation as diagnostics of the energy release and transport processes occurring in the flare. Significant progress in both of these areas, as described, was made.

  13. 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.

  14. 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

  15. 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.

  16. 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

  17. Magnetic Variations Associated With Solar Flares

    NASA Technical Reports Server (NTRS)

    Petrosian, Vahe

    2005-01-01

    A report summarizes an investigation of helioseismic waves and magnetic variations associated with solar flares, involving analysis of data acquired by the Michelson Doppler Imager (MDI) aboard the Solar and Heliocentric Observatory (SOHO) spacecraft, the Yohkoh spacecraft, and the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft. Reconstruction of x-ray flare images from RHESSI data and comparison of them with MDI magnetic maps were performed in an attempt to infer the changes in the geometry of the magnetic field. It was established that in most flares observed with MDI, downward propagating shocks were much weaker than was one observed in the July 9, 1996 flare, which caused a strong helioseismic response. It was concluded that most of the observed impulsive variations result from direct impact of high-energy particles. Computer codes were developed for further study of these phenomena.

  18. 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.

  19. 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.

  20. 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.

  1. Automatic Prediction of Super Geomagnetic Storms and Solar Flares

    NASA Astrophysics Data System (ADS)

    Song, Hui; Yurchyshyn, V.; Tan, C.; Jing, J.; Wang, H.

    2007-05-01

    In this study we first investigated the relationship between magnetic structures of coronal mass ejection (CME) source regions and geomagnetic storms, in particular, the super storms when the Dst index decreases below -200 nT. By examining all full halo CMEs that erupted between 1996 and 2004, we selected 73 events associated with M-class and X-class solar flares, which have a clearly identifiable source region. By analyzing daily full-disk MDI magnetograms, we found that the horizontal gradient of the line-of-sight magnetic field is a viable parameter to identify a flaring magnetic neutral line and thus can be used to predict the possible source region of CMEs. We report that for about 92% of super storms the orientation angle of the magnetic structures of source regions was found to be southward. Our findings demonstrate that this approach can be used to perform an automatic prediction of the occurrence of large X-class flares and super geomagnetic storms. In order to further extend our prediction of flares, we next used the ordinal logistic regression method to establish a prediction model, which estimates the probability for each active region to produce X-, M- or C-class flares during the next 1-day time period. Three predictive parameters are: total unsigned magnetic flux Tflux, the length of strong gradient neutral line Lgnl, and total magnetic dissipation Ediss. The ordinal response variable is the different level of solar flares magnitude. Compared the results with the current predictions methods used by NASA SDAC and NOAA SEC, the ordinal logistic model using Lgnl and Tflux as predictors demonstrated its automaticity, simpleness and fairly high prediction accuracy. To our knowledge, this is the first time the ordinal logistic regression model was used in solar physics to predict solar flares.

  2. 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.

  3. Origins and effects of solar flares

    SciTech Connect

    Rust, D.M.

    1993-12-31

    During the 1989 - 1991 peak of solar activity, geomagnetic storms from interplanetary shocks caused a massive failure in the Canadian power grid, minor failures in other power eqipment, and many communications disruptions and satellite malfunctions. The proton storms would have been lethal for unshielded space travellers. Had the power managers been given a credible, timely forecast of the solar storm, they could have protected their generating equipment and the grid. They do not keep protective circuits in place full-time because that reduces efficiency and increases the cost of power distribution. Nor will astronauts on the moon or in deep space confine themselves full-time to thick-walled, radiation-resistant closets. To enable manned deep space exploration we have to find a way to determine what happens in solar flares. Only this will improve the forecasts. Expensive and restrictive protective measures would then have to be applied only when a major flare is clearly imminent. There is no generally accepted flare theory or description of the pre-flare state or of the instabilities. The Solar Maximum Mission (SMM) cleared up many questions about electromagnetic flare emissions and the structure of the flaring atmosphere, but the dynamic of the magnetic fields is still a mystery.

  4. 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.

  5. 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.

  6. Acceleration of electrons in solar flares

    NASA Technical Reports Server (NTRS)

    Lin, R. P.

    1973-01-01

    Observations pertaining to the acceleration and emission of 10 to 100 keV electrons in small solar flares are reviewed. The energy spectrum of the accelerated electrons is obtained from observations of X-rays and escaping electrons. The loss of the electrons through various processes, such as collisions with the ambient medium, escape to the interplanetary medium, and emission of X-rays and radio waves, is considered, and quantitative energy loss estimates obtained for each process. The role of the accelerated electrons in the overall flare mechanism is examined and an attempt is made to develop a consistent picture of a small electron flare.

  7. Neutrino Generation in Powerful Solar Flares

    NASA Astrophysics Data System (ADS)

    Bazilevskaya, G. A.; Nikolsky, S. I.; Stozhkov, Y. I.; Charakhchyan, T. N.

    The combined analysis of data from the solar neutrino Cl-Ar detector and those on powerful solar cosmic ray and solar γ-bursts showed that: (1) The powerful solar cosmic ray bursts with a 24-hr averaged solar proton intensity I(≥150 MeV) ≥ 3 cm-2s-1sr-1 are the source of neutrino fluxes sufficient for a significant contribution to the 37Ar production in the Cl-Ar experiment. (2) The increased neutrino generation is observed in the solar flares in which high-energy γ-quanta were observed. (3). The flares on the back side of the sun do not contribute to the production rate of 37Ar in the neutrino experiment although they can produce a significant flux of high-energy solar particles at the Earth.

  8. 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.

  9. 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.

  10. Dependence of Sunspot Properties on Flare Occurrence and Flare-CME Association

    NASA Astrophysics Data System (ADS)

    Yang, Ya-Hui

    2015-04-01

    Previous studies showed that the intense flares tend to erupt from the large sunspot region with complex magnetic configuration and strong magnetic field. However, note that not all the active regions (ARs) classified as βγδ would produce X-class flares. To clarify the significance of sunspot properties on solar explosive events, we reexamine the dependence of flare magnitude on sunspot size and magnetic type during 1996-2014 based on the report of NOAA Solar Region Summary and the measurements of GOES soft X-ray flux. In particular, we focus on the βγδ-type ARs to relate the flare productivity to the sunspot area and magnetic field strength by means of the line-of-sight magnetograms from SOHO/MDI and SDO/HMI. Two flare-productive ARs, 10486 and 12192, with βγδ magnetic configuration during most periods of their disk passages are further investigated to characterize the sunspots and flare-CME association.

  11. Multi-thermal Energies of Solar Flares

    NASA Astrophysics Data System (ADS)

    Ryan, Daniel; Aschwanden, Markus; Boerner, Paul; Caspi, Amir; McTiernan, James; Warren, Harry

    2015-04-01

    Measuring energy partition in solar eruptions is key to understanding how different processes affect their evolution. In order to improve our knowledge on this topic, we are participating in a multi-study project to measure the energy partition of 400 M- and X-class flares and associated coronal mass ejections (CMEs). In this study we focus on the flare thermal energies of 391 of these events. We improve upon previous studies in the following ways: 1) We determine thermal energy using spatially resolved multi-thermal differential emission measures (DEMs) determined from AIA (Atmospheric Imaging Assembly) rather than relying on the isothermal assumption; 2) We determine flare volumes by thresholding these DEM maps rather than relying on single passband observations which may not show the full flare volume; 3) We analyze a greater number of events than previous similar studies to increase the statistical reliability of our results. We find that the thermal energies of these flares lie in the range 10^26.8—10^32 erg. These results are compared to those of Aschwanden et al. (2014) who examined a subset of these events. They determined the dissipated non-potential magnetic energy which is thought to be the total energy available to drive solar eruptions. For the 171 events common to both studies, we find that the ratio of flare thermal energy to dissipated magnetic energy ranges from 2%—40%. This is an order of magnitude higher than previously found by Emslie et al. (2012). This may be because Emslie et al. (2012) had to assume the amount of non-potential magnetic energy, or that they relied on the isothermal assumption to determine flare thermal energies. The improved results found here will help us better understand the role played by flare thermal processes in dissipating the overall energy of solar eruptions.

  12. REMOTE OSCILLATORY RESPONSES TO A SOLAR FLARE

    SciTech Connect

    Andic, A.; McAteer, R. T. J.

    2013-07-20

    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.

  13. 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

  14. Positron annihilation radiation from solar flares

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

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

  15. 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.

  16. 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 Å are analysed in relation to the tornado activities observed at the limb in 171 Å. 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

  17. WOLF - A computer expert system for sunspot classification and solar-flare prediction

    NASA Astrophysics Data System (ADS)

    Miller, Richard W.

    1988-08-01

    An expert systmem, WOLF, has been developed that acts as an expert in analyzing solar active regions and predicting the probable occurrence of solar flares. The system has a knowledge base consisting of a set of IF-THEN rules and an inference engine which applies the rules. WOLF asks questions concerning an observed solar active region and uses the answers to determine the McIntosh (1968) sunspot classification. WOLF then indicates the probability of that group producing a flare of specified X-ray intensity based on the statistical analysis of past flare activity of similar groups.

  18. 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.

  19. Investigations of turbulent motions and particle acceleration in solar flares

    NASA Technical Reports Server (NTRS)

    Jakimiec, J.; Fludra, A.; Lemen, J. R.; Dennis, B. R.; Sylwester, J.

    1986-01-01

    Investigations of X-raya spectra of solar flares show that intense random (turbulent) motions are present in hot flare plasma. Here it is argued that the turbulent motions are of great importance for flare development. They can efficiently enhance flare energy release and accelerate particles to high energies.

  20. 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.

  1. 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.

  2. 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.

  3. Periodicities of solar flare and its relations

    NASA Technical Reports Server (NTRS)

    Hady, Ahmed A.

    1995-01-01

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

  4. 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.

  5. 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.

  6. Solar Flare Prediction Using Advanced Feature Extraction, Machine Learning, and Feature Selection

    NASA Astrophysics Data System (ADS)

    Ahmed, Omar W.; Qahwaji, Rami; Colak, Tufan; Higgins, Paul A.; Gallagher, Peter T.; Bloomfield, D. Shaun

    2013-03-01

    Novel machine-learning and feature-selection algorithms have been developed to study: i) the flare-prediction-capability of magnetic feature (MF) properties generated by the recently developed Solar Monitor Active Region Tracker ( SMART); ii) SMART's MF properties that are most significantly related to flare occurrence. Spatiotemporal association algorithms are developed to associate MFs with flares from April 1996 to December 2010 in order to differentiate flaring and non-flaring MFs and enable the application of machine-learning and feature-selection algorithms. A machine-learning algorithm is applied to the associated datasets to determine the flare-prediction-capability of all 21 SMART MF properties. The prediction performance is assessed using standard forecast-verification measures and compared with the prediction measures of one of the standard technologies for flare-prediction that is also based on machine-learning: Automated Solar Activity Prediction ( ASAP). The comparison shows that the combination of SMART MFs with machine-learning has the potential to achieve more accurate flare-prediction than ASAP. Feature-selection algorithms are then applied to determine the MF properties that are most related to flare occurrence. It is found that a reduced set of six MF properties can achieve a similar degree of prediction accuracy as the full set of 21 SMART MF properties.

  7. Spectral Diagnostics and Radiative Hydrodynamics of Solar Flares

    NASA Astrophysics Data System (ADS)

    Cheng, J. X.

    2011-03-01

    Solar flares are one of the most significant active phenomena in the solar atmosphere. It is involved in very complicated physical processes, including energy release, plasma instability, acceleration and propagation of energetic particles, radiation and dynamics of the flaring atmosphere, mass motions and ejections, and so on. Enhanced radiation during flares spans virtually the entire electromagnetic spectrum originating from different layers of the solar atmosphere. High energetic particles and strong radiations that are produced during the flare eruptions play a major role in space weather. Therefore, it is very important and necessary to study the mechanisms of solar flares. In this thesis, combined with ground and space observations, the theoretical calculations are used to study the spectral features and radiation mechanisms of solar flares. In particular, our research is concentrated on the diagnostics of non-thermal processes and origin of the white-light flares. The main contents are described as follows: (1) Different chromospheric lines are used to diagnose the heating mechanisms in flares. We calculate the Hα and Ca II 8542 Å line profiles based on four different atmospheric models, including the effects of non-thermal electron beams with various energy fluxes. These two lines have different responses to the thermal and non-thermal effects, and can be used to diagnose the thermal and non-thermal heating processes. We apply our method to an X-class flare occurred on 2001 October 19 and find that the non-thermal effects at the outer edge of the flare ribbon are more notable than that at the inner edge, while the temperature at the inner edge seems higher. On the other hand, the results show that non-thermal effects increase rapidly in the rise phase and decrease quickly in the decay phase, but the atmospheric temperature can still keep relatively high for some time after getting to its maximum. For the two kernels that we analyze, the maximum energy fluxes of the electron beams are approximately 1010 erg cm-2 s-1 and 1011 erg cm-2 s-1, respectively. However, the atmospheric temperatures are not so high, i.e., lower than or slightly higher than that of the weak flare model F1 at the two kernels. We discuss the implications of the results for the two-ribbon flare models. (2) The white-light emission in solar flares is studied by radiative hydrodynamic simulations. It is believed that solar white-light flares (WLFs) originate from the lower chromosphere and upper photosphere. In particular, some recently observed WLFs show a very large continuum enhancement at 1.56 μm where the opacity reaches its minimum. Therefore, it is important to make clear how the energy is transferred to the lower layers responsible for the production of WLFs. Based on radiative hydrodynamic simulations, we study the role of non-thermal electron beams in increasing the continuum emission. We vary the parameters of the electron beams and disk positions and compare the results with observations. The electron beam heated model can explain most of the observational white-light enhancements. (3) The effect of periodic non-thermal electron beam on chromospheric lines is studied. Heated by the periodic non-thermal electrons, the Hα line center and wings show the same periodicity as the injected electrons. The line center and wings have different time delays compared to the bombarded electron beam. The line center has a relatively small phase difference. The red and blue wings also show different time delays. The blue wing shows a smaller phase difference compared to the red wing. The phase differences between the line center and wings can be explained by their different formation layers. However, the phase difference between the red and blue wings can not be fully explained in this manner. A possible explanation is that the macroscopic velocity field changes the emission and absorption features at the red and blue wings. The above results provide useful information for diagnosing the heating processes by using the fine time structures observed in chromospheric lines. (4) A statistical study of RHESSI hard X-ray spikes is made. The spikes refer to fine time structures on time scales of seconds to milliseconds in hard X-ray time profiles during solar flares. We get a preliminary statistical result of temporal and spectral properties of hard X-ray spikes. About one fifth of the spikes can be detected in photon energies higher than 100 keV. Some main properties of the spikes are as follows: (i) Spikes are produced in both impulsive flares and long-duration flares with nearly the same occurrence rates. 90% of the spikes occur during the rise phase of the flares, and about 70% occur around the peaks of the flares. (ii) The durations of the spikes vary from 0.2 s to 2 s, with an average being 1.3 s, which is independent of photon energies. The spikes exhibit symmetric time profiles with no significant difference between the rise and decay phases. (iii) Among the most energetic spikes, about two thirds of them have harder count spectra than their underlying slow-varying components. There is also a weak indication that spikes exhibiting time lags in high-energy emissions tend to have harder spectra than spikes with time lags in low-energy emissions.

  8. 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.

  9. A statistical analysis of hard X-Ray solar flares

    NASA Technical Reports Server (NTRS)

    Pearce, G.; Rowe, A. K.; Yeung, J.

    1993-01-01

    In this study we perform a statistical study on, 8319 X-Ray solar flares observed with the Hard X-Ray Spectrometer (HXRBS) on the Solar Maximum Mission satellite (SMM). The events are examined in terms of the durations, maximum intensities, and intensity profiles. It is concluded that there is no evidence for a correlation between flare intensity, flare duration, and flare asymmetry. However, we do find evidence for a rapid fall-of in the number of short-duration events.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Statistical study of spatio-temporal distribution of precursor solar flares associated with major flares

    NASA Astrophysics Data System (ADS)

    Gyenge, N.; Ballai, I.; Baranyi, T.

    2016-04-01

    The aim of the present investigation is to study the spatio-temporal distribution of precursor flares during the 24-hour interval preceding M- and X-class major flares and the evolution of follower flares. Information on associated (precursor and follower) flares is provided by Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). Flare List, while the major flares are observed by the Geostationary Operational Environmental Satellite (GOES) system satellites between 2002 and 2014. There are distinct evolutionary differences between the spatio-temporal distributions of associated flares in about one day period depending on the type of the main flare. The spatial distribution was characterised by the normalised frequency distribution of the quantity δ (the distance between the major flare and its precursor flare normalised by the sunspot group diameter) in four 6-hour time intervals before the major event. The precursors of X-class flares have a double-peaked spatial distribution for more than half a day prior to the major flare, but it changes to a lognormal-like distribution roughly 6 hours prior to the event. The precursors of M-class flares show lognormal-like distribution in each 6-hour subinterval. The most frequent sites of the precursors in the active region are within a distance of about 0.1 diameter of sunspot group from the site of the major flare in each case. Our investigation shows that the build-up of energy is more effective than the release of energy because of precursors.

  2. 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.

  3. 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.

  4. Stochastic Acceleration of Electrons in Solar Flares

    NASA Astrophysics Data System (ADS)

    Pongkitiwanichakul, P.; Chandran, B. D.

    2012-12-01

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

  5. 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.

  6. Relationships Between Photospheric Flows and Solar Flares

    NASA Astrophysics Data System (ADS)

    Welsch, B. T.; Li, Y.

    2013-12-01

    Fourier Local Correlation Tracking (FLCT) has been applied to the entire database of 96-minute cadence line-of-sight (LOS) magnetograms from the SOHO/MDI mission, to derive photospheric transverse velocities (u_x,u_y). In a previous study, we applied FLCT to a few dozen active regions (ARs), and found that the "proxy Poynting flux" (PPF) --- the product u B^2, where u is the FLCT flow speed and B is the LOS field divided by the cosine of viewing angle, integrated over each AR --- was statistically related to flare activity. We will present preliminary results of our investigation of the relationship between PPF and flare activity from NOAA's GOES catalog for several hundred ARs identified in NOAA's daily Solar Region Summaries.

  7. Nonlocal thermal transport in solar flares

    NASA Technical Reports Server (NTRS)

    Karpen, Judith T.; Devore, C. Richard

    1987-01-01

    A flaring solar atmosphere is modeled assuming classical thermal transport, locally limited thermal transport, and nonlocal thermal transport. The classical, local, and nonlocal expressions for the heat flux yield significantly different temperature, density, and velocity profiles throughout the rise phase of the flare. Evaporation of chromospheric material begins earlier in the nonlocal case than in the classical or local calculations, but reaches much lower upward velocities. Much higher coronal temperatures are achieved in the nonlocal calculations owing to the combined effects of delocalization and flux limiting. The peak velocity and momentum are roughly the same in all three cases. A more impulsive energy release influences the evolution of the nonlocal model more than the classical and locally limited cases.

  8. 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.

  9. 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.

  10. Nuclear gamma rays 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 recently observed (Chupp et al., 1972) 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 the charged particles from the flare observed near earth. The total numbers of protons at the sun is deduced from the observed absolute line intensities for various interaction models. It is found that if the protons at the sun have a spectrum which is an exponential in rigidity, the total energy in protons is a few times 10 to the 28th power ergs if the gamma rays are produced by protons moving down into the sun; and about 10 to the 30th power ergs if the gamma rays are produced at the site of the acceleration.

  11. 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.

  12. 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.

  13. An essay on sunspots and solar flares

    NASA Astrophysics Data System (ADS)

    Akasofu, S.-I.

    1984-11-01

    The author reviews some of the recent findings on large-scale magnetic fields and sunspots. Then, instead of relying on the hypothetical flux tube beneath the photosphere, he considers an amplification process of the observed large-scale fields by a dynamo process on the basis of the observed and possible photospheric shear flows. Thus, the photosphere is considered as an active medium, rather than the passive medium through which the hypothetical flux tube merely penetrates. Specifically, the author considers the dynamo process associated with vortex motions which can supply the power needed for the formation of sunspots from the observed weak field and the power needed for solar flares.

  14. The acceleration and propagation of solar flare energetic particles

    NASA Technical Reports Server (NTRS)

    Forman, M. A.; Ramaty, R.; Zweibel, E. G.

    1986-01-01

    A review of the most pertinent data on solar energetic particles is presented, and the implications of the data are discussed, taking into account radio emissions, hard X-rays, gamma rays, energy spectra and electron-proton correlations, chemical compositions, and isotopic and ionic compositions. The mechanisms of solar flare particle acceleration are considered along with solar flare particle spectra in interplanetary space. Attention is given to stochastic acceleration, shock acceleration, acceleration in direct electric fields, the mean free paths of solar electrons and protons in interplanetary space, and an illustration of the probable effect of adiabatic deceleration on the spectra of solar flare ions at the time of maximum.

  15. 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.

  16. Solar flare prediction using highly stressed longitudinal magnetic field parameters

    NASA Astrophysics Data System (ADS)

    Huang, Xin; Wang, Hua-Ning

    2013-03-01

    Three new longitudinal magnetic field parameters are extracted from SOHO/MDI magnetograms to characterize properties of the stressed magnetic field in active regions, and their flare productivities are calculated for 1055 active regions. We find that the proposed parameters can be used to distinguish flaring samples from non-flaring samples. Using the long-term accumulated MDI data, we build the solar flare prediction model by using a data mining method. Furthermore, the decision boundary, which is used to divide flaring from non-flaring samples, is determined by the decision tree algorithm. Finally, the performance of the prediction model is evaluated by 10-fold cross validation technology. We conclude that an efficient solar flare prediction model can be built by the proposed longitudinal magnetic field parameters with the data mining method.

  17. 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.

  18. The Origin of the Solar Flare Waiting-Time Distribution.

    PubMed

    Wheatland

    2000-06-20

    It was recently pointed out that the distribution of times between solar flares (the flare waiting-time distribution) follows a power law for long waiting times. Based on 25 years of soft X-ray flares observed by Geostationary Operational Environmental Satellite instruments, it is shown that (1) the waiting-time distribution of flares is consistent with a time-dependent Poisson process and (2) the fraction of time the Sun spends with different flaring rates approximately follows an exponential distribution. The second result is a new phenomenological law for flares. It is shown analytically how the observed power-law behavior of the waiting times originates in the exponential distribution of flaring rates. These results are argued to be consistent with a nonstationary avalanche model for flares. PMID:10859130

  19. 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.

  20. An interacting loop model of solar flare bursts

    NASA Technical Reports Server (NTRS)

    Emslie, A. G.

    1981-01-01

    As a result of the strong heating produced at chromospheric levels during a solar flare burst, the local gas pressure can transiently attain very large values in certain regions. The effectiveness of the surrounding magnetic field at confining this high pressure plasma is therefore reduced and the flaring loop becomes free to expand laterally. In so doing it may drive magnetic field lines into neighboring, nonflaring, loops in the same active region, causing magnetic reconnection to take place and triggering another flare burst. The features of this interacting loop model are found to be in good agreement with the energetics and time structure of flare associated solar hard X-ray bursts.

  1. 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.

  2. 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.

  3. 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.

  4. The Effects Od Solar Protons Flares On The Navigation Systems of Aircrafts and Resulting Accents During 20th Cencury

    NASA Astrophysics Data System (ADS)

    Shaltout, M.; Hady, A.

    In early study for the authors, from the analysis of 802 important accents of the air- craft's which occurred during the period (1920-2000) all over the world. It is found that the number of occurrence of the accents increases at the solar maximum activity, and decrease with decreasing the solar activity on the annual scale. There is a doubt the geomagnetic storms due to the charged particles, which come from the sun as a cloud after two or three days from the high energetic flares occurrence. Which affected on the navigation system of the aircraft's, especially for aircraft's which pass through the polar regions of the earth, at the high latitudes. The aim of the present study is to analysis more than one handed solar protons flares (1970-2000) of energies more than 10 MeV observed by the artificial satellites GOES and published in solar Geophysical Data, NOAA, Boulder, Colorado, USA. A com- parison studies between the proton flares occurrence and the important accents of the aircraft's, which occur after two days to one week, from the high energetic proton flares occurrence, or case by case, in an attempt to confirm the relation between the solar activities and aircraft accents due to disturbance in the Navigation systems. Also, we not Ignore in our study the effects of the geomagnetic field on the flying staff, due to the occurrence of the solar proton flares , as indicated by other authors in early studies.

  5. 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.

  6. 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.

  7. 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.

  8. Decimetric gyrosynchrotron emission during a solar flare

    NASA Technical Reports Server (NTRS)

    Batchelor, D. A.; Benz, A. O.; Wiehl, H. J.

    1983-01-01

    A decimetric, microwave, and hard X-ray burst was observed during a solar flare in which the radio spectrum below peak flux fits an f+2 power law over more than a decade in frequency. The spectrum is interpreted to mean that the radio emission originated in a homogeneous, thermal, gyrosynchrotron source. This is the first time that gyrosynchrotron radiation has been identified at such low decimetric frequencies (900-998) MHz). The radio emission was cotemporal with the largest single hard X-ray spike burst ever reported. The spectrum of the hard X-ray burst can be well represented by a thermal bremsstrahlung function over the energy range from 30 to 463 keV at the time of maximum flux. The temporal coincidence and thermal form of both the X-ray and radio spectra suggest a common source electron distribution. The unusual low-frequency extent of the single-temperature thermal radio spectrum and its association with the hard X-ray burst imply that the source had an area approx. 10(18) sq cm a temperature approx 5x10(8) K, an electron density approx. 7.10(9) cu cm and a magnetic field of approx. 120 G. H(alpha) and 400-800 MHz evidence suggest that a loop structure of length 10,000 km existed in the flare active region which could have been the common, thermal source of the observed impulsive emissions.

  9. 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.

  10. Stochastic acceleration of electrons in solar flares

    NASA Technical Reports Server (NTRS)

    Benz, A. O.; Smith, D. F.

    1987-01-01

    The generation of lower-hybrid waves by cross-field currents is applied to reconnection processes proposed for solar flares. Recent observations on fragmentation of energy release and acceleration, and on hard X-ray (HXR) spectra are taken into account to develop a model for electron acceleration by resonant stochastic interactions with lower-hybrid turbulence. The continuity of the velocity distribution is solved including collisions and escape from the turbulence region. It describes acceleration as a diffusion process in velocity space. The result indicates two regimes that are determined by the energy of the accelerating electrons which may explain the double power-law often observed in HXR spectra. The model further predicts an anticorrelation between HXR flux and spectral index in agreement with observations.

  11. 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.

  12. 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.

  13. 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.

  14. Long-period geomagnetic pulsations as solar flare precursors

    NASA Astrophysics Data System (ADS)

    Barkhatov, N. A.; Obridko, V. N.; Revunov, S. E.; Snegirev, S. D.; Shadrukov, D. V.; Sheiner, O. A.

    2016-03-01

    We compare long-period pulsations of the horizontal component of the geomagnetic field at intervals that precede extreme solar flares. To this end, we use the wavelet-skeleton technique to process the geomagnetic field disturbances recorded at magnetic stations over a wide geographical range. The synchronization times of wavelet-skeleton spectral distributions of long-period pulsations of geomagnetic oscillations over all magnetic stations are shown as normalized histograms. A few days before an intense solar flare, the histograms show extremes. This means that these extremes can be regarded as flare precursors. The same technique is used to analyze the parameters of near-Earth space. The histograms obtained in this case are free of the aforementioned extrema and, therefore, cannot point to an upcoming flare. The goal of this study is to construct a correlation-spectral method for the short-term prediction of solar flare activity.

  15. 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

  16. Understanding flaring solar-type stars seen by Kepler

    NASA Astrophysics Data System (ADS)

    Soderblom, David

    2012-02-01

    The early Kepler data show unambiguous and dramatic evidence of large-scale, massive white-light stellar flares on G and early-K dwarfs. The energies released in these flares are at least 103?104 times that of the largest solar flares ever seen, meaning that they put substantial energy into their circumstellar environments, and much of that energy may be in hard x-rays. At the same time, it is not clear from the Kepler data alone why these particular stars flare because there are many other stars with no evident flares that have similar rotation periods and amplitudes of variation. Are bouts of massive flaring episodic? Do the flaring stars have other properties (activity, v sin i, lithium, inter alia) that distinguish them? Are the flaring stars in close binaries? Keck HIRES spectra can address all these questions and more, and help us to more fully understand this important phenomenon that has critical implications for the formation and evolution of planets and, e! specially, for chemistry and astrobiology in those regions. These stars are also of potential great importance for understanding the flaring behavior of the Sun because white-light flares have not been seen on G stars before, and it is crucial to understand if these flaring stars are unusually young, in close pairs, or if they represent a broader phenomenon that has not yet been appreciated.

  17. 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.

  18. 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).

  19. 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 ...

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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...

  9. 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...

  10. The Efficiency of Solar Flares With Gamma-ray Emission of Solar Cosmic Rays Production.

    NASA Astrophysics Data System (ADS)

    Belov, A. V.; Kurt, V. G.; Mavromichalaki, H.

    A statistical analysis of solar flares with gamma-ray emission measured by SMM (W.T. Westrand, at al.,1999, Ap.J, Suppl. Series, 409) and proton events occurrence based on the proton events catalog (A.Belov, at al.2001, Proc. 27th ICRC 2001, Ham- burg, 3465) was performed. We obtained the probabilities of the appearence of pro- ton fluxes near the Earth from the different fluence values of gamma-line emission, bremsstrahlung emissions and soft X-ray emission of the parent flares. This statisti- cal approach allows us to obtain if not precise than at least proper quantitative ratios than relate the flares with obvious evidences for proton production with the escaped from the Sun viciniy. We than look at the available data of soft X-ray flares time behaviour and show the exact timing of proton acceleration and probably shock for- mation comparing the soft X-ray injection function. The shock wave influence on the proton escaping process is shortly discussed.

  11. 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.

  12. Study of 1991 November 02 Solar Flare

    NASA Astrophysics Data System (ADS)

    Lee, C. Y.; Wang, H.

    1996-05-01

    We analyzed hard X-ray and microwave data for the solar flare BATSE #1791, which started at 1611UT and ended at 1656UT, on 2 November 1991. Data are available simultaneously from BATSE/LAD X-ray and OVRA microwave data base. This flare was particularly interesting, because of the deep cyclic intensity variation. We quantitatively compare the time variations in X-ray photon index and microwave spectral index (both high and low frequency), as well as microwave peak frequency at which the gyro-synchrotron radiation transits from optically-thin to optically thick. Using the time profile of the BASTE/LAD 25-50 KeV flux as a reference, the X-ray photon index profile is out of phase with it as expected; in addition, the microwave peak frequency profile and the low frequency slope profile are observed to be correlated with it. Interesting enough, the high frequency slope profile correlated with X-ray flux before the main peak and anti-correlated with it after the main peak. The relationship between X-ray photon peak counts and microwave peak fluxes is also studied. A plot of microwave peak flux versus X-ray photon peak count produces a curve tracing a tilted ellipse counter-clockwisely. This indicates that the X-ray peak counts arrive earlier than the corresponding microwave peak fluxes. Finally, we studied the time delays between X-ray and microwave flux peak as a function of frequency and found that delay increases as the frequency increases. The maximum delay time is found for the main peak, it is of about 72 seconds. Shorter delays are found for the other five sub-peaks.

  13. Solar flare cosmic rays at and beyond the modulation boundary.

    NASA Technical Reports Server (NTRS)

    Jokipii, J. R.; Stone, E. C.

    1973-01-01

    Consideration of the characteristics of solar flare cosmic ray events observed beyond a postulated modulation boundary, should any such boundary exist. It is pointed out that observations of solar flare particles at great distances from the sun provide a sensitive and precise diagnostic for any such boundary. Such considerations are of substantial interest in view of the probable penetration of deep space probes to distances of the order of 10 AU in the near future.

  14. Signatures of the coalescence instability in solar flares

    SciTech Connect

    Nakajima, H.; Tajima, T.; Brunel, F.

    1984-11-01

    Double sub-peak structures in the quasi periodic oscillations in the time profiles of solar flares in 1980 and 1982 are discussed. Computer simulations of the coalescence instability of two current loops agree with observations of the (widely differing) flares. The simultaneous accelerations of electrons and ions, and the double sub-peak structure in quasi periodic pulses are well explained. The double sub-peak structure is more pronounced when the currents in the two loops are sufficient for fast coalescence to occur. This corresponds to the 1980 flare. When the currents are insufficient for fast coalescence, the double sub-peak structure is less pronounced, as in the 1982 flare. Observations suggest the collision of the two microwave sources for the 1982 event. It is argued that this mechanism is a plausible particle acceleration mechanism in solar flares. (ESA)

  15. 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.

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

    NASA Astrophysics Data System (ADS)

    Young, Christopher Alex

    2001-08-01

    The X-ray and γ-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 γ-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.

  17. 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.

  18. 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.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

    Schwartz, R. A.

    1994-12-01

    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.

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. Dynamics of magnetic fields of active regions in pre-flare states and during solar flares

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    Solar flares observed in the active regions NOAA 10656, NOAA 11429, and NOAA 10930 are analyzed. The magnetic fluxes were constant to within 2% during these flares, as well as the distribution of the magnetic fields in the active regions. The analysis supports earlier conclusions that large (class X) solar flares arise when the magnetic fluxes of the active regions exceed 1022 Mx. The observation of a high magnetic flux in an active region is not sufficient for the appearance of a large flare: complex ßγδ field structures must also be observed before flares. Such active regions can generate singular lines of the magnetic field in the corona, in whose vicinities current sheets form. Magnetic-field lines above simple dipolar active regions have arched forms; singular lines are absent and no current sheets are created. Dipolar-type active regions do not generate flares. Imbalances in the magnetic flux of an active region and the growth rate of the magnetic flux are not any indications of the imminent appearance of a flare.

  7. Solar Flare Hard X-ray Spikes Observed by RHESSI: a Statistical Study

    NASA Astrophysics Data System (ADS)

    Cheng, Jianxia; Qiu, J.; Ding, M.; Wang, H.

    2013-07-01

    Hard X-ray (HXR) spikes refer to fine time structures on timescales of seconds to milliseconds in high-energy HXR emission profiles during solar flare eruptions. We present a preliminary statistical investigation of temporal and spectral properties of HXR spikes. Using a three-sigma spike selection rule, we detected 184 spikes in 94 out of 322 flares with significant counts at given photon energies, which were detected from demodulated HXR light curves obtained by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). About one fifth of these spikes are also detected at photon energies higher than 100 keV. The statistical properties of the spikes are as follows. (1) HXR spikes are produced in both impulsive flares and long-duration flares with nearly the same occurrence rates. Ninety percent of the spikes occur during the rise phase of the flares, and about 70% occur around the peak times of the flares. (2) The time durations of the spikes vary from 0.2 to 2 s, with the mean being 1.0 s, which is not dependent on photon energies. The spikes exhibit symmetric time profiles with no significant difference between rise and decay times.(3) Among the most energetic spikes, nearly all of them have harder count spectra than their underlying slow-varying components. There is also a weak indication that spikes exhibiting time lags in high-energy emissions tend to have harder spectra than spikes with time lags in low-energy emissions.

  8. 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.

  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. F-region enhancements induced by solar flares

    NASA Technical Reports Server (NTRS)

    Donnelly, R. F.; Davies, K.; Grubb, R. N.; Fritz, R. B.

    1976-01-01

    ATS-6 total electron content (NT) observations during solar flares exhibit four types of response: (1) a sudden increase in NT (SITEC) for about 2 min with several maxima in growth rate, then a maximum or a distinct slowing in growth, followed by a slow smooth increase to a flat peak, and finally a slow decay in NT; (2) a SITEC that occurs during ionospheric storms, where NT decays abruptly after the first maximum; (3) slow enhancements devoid of distinct impulsive structure in growth rate; and (4) no distinct response in NT, even for relatively large soft X-ray flares. Flare-induced increases in NT are dominated by low-loss F2 ionization produced by 90-911-A emission. The impulsive flare component is relatively intense in the 90-911-A range, but is short lived and weak for flares near the edge of the visible solar disk and for certain slow flares. The impulsive flare component produces the rapid rise, the sharp maxima in growth rate, and the first maximum in SITECs. The slow flare components are strong in the 1-90-A range but relatively weak in the 90-911-A range and accumulatively contribute to the second maximum in type 1 and 3 events, except during storms when F2 loss rates are abnormally high in type 2 events.

  11. Solar flare acceleration of solar wind - Influence of active region magnetic field

    NASA Technical Reports Server (NTRS)

    Lundstedt, H.; Wilcox, J. M.; Scherrer, P. H.

    1981-01-01

    The direction of the photospheric magnetic field at the site of a solar flare is a good predictor of whether the flare will accelerate solar wind plasma. If the field has a southward component, high-speed solar wind plasma is usually observed near the earth about 4 days later. If the field has a northward component, such high-speed solar wind is almost never observed. Southward-field flares may then be expected to have much larger terrestrial effects than northward flares.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Origin of the Universal Correlation between the Flare Temperature and the Emission Measure for Solar and Stellar Flares.

    PubMed

    Shibata; Yokoyama

    1999-11-20

    We present a theory to explain the observed universal correlation between flare temperature T and emission measure EM=n2V for solar and stellar flares (including solar microflares observed by Yohkoh as well as protostellar flares observed by ASCA), where n is the electron density and V is the volume. The theory is based on a magnetic reconnection model with heat conduction and chromospheric evaporation, assuming that the gas pressure of a flare loop is comparable to the magnetic pressure. This theory predicts the relation EM~B-5T17/2, which explains well the observed correlation between EM and T in the range of 6x106 K < T<108 K and 1044solar microflares to protostellar flares, if the magnetic field strength B of a flare loop is nearly constant for solar and stellar flares. PMID:10534459

  17. 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.

  18. Magnetic Shear in Two-ribbon Solar Flares

    NASA Astrophysics Data System (ADS)

    Su, Y. N.

    2010-04-01

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

  19. 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

  20. Solar flare nuclear gamma rays and interplanetary proton events

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

  1. 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.

  2. Statistics of Multi-Wavelength Solar Flare Observations

    NASA Astrophysics Data System (ADS)

    Milligan, Ryan O.

    2016-05-01

    Our current fleet of space-based solar observatories offer us a wealth of opportunities to study solar flares over a range of wavelengths, and the greatest advances in our understanding of flare physics often come from coordinated observations between different instruments. However, despite considerable effort to try and coordinate this armada of instruments over the years (e.g. through the Max Millennium Program of Solar Flare Research), there are frustratingly few solar flares that have been well and truly observed by most or all instruments simultaneously. This is due to a range of factors such as instruments having a limited field of view, satellites in low-Earth orbit going into eclipse, and observing schedules being uploaded days in advance. I shall describe a new technique to retrospectively search archival databases for flares jointly observed by RHESSI, SDO/EVE, Hinode/EIS+SOT, and IRIS. I shall also present a summary of how many flares have been observed by different configurations of these instruments since the launch of SDO.

  3. Evolutionary aspects and north-south asymmetry of soft X-ray flare index during solar cycles 21, 22, and 23

    NASA Astrophysics Data System (ADS)

    Joshi, B.; Bhattacharyya, R.; Pandey, K. K.; Kushwaha, U.; Moon, Yong-Jae

    2015-10-01

    Aims: In this paper, we investigate the temporal evolution and north-south (N-S) asymmetry in the occurrence of solar flares during cycle 21, 22, and 23, and compare the results with traditional solar activity indices. Methods: The flare activity is characterized by a soft X-ray (SXR) flare index, which incorporates information about flare occurrences during a selected interval along with the peak intensity of individual events. Results: The SXR flare index correlates well with other conventional parameters of solar activity. Further, it exhibits a significantly higher correlation with sunspot area over sunspot number, which suggests the variations in sunspot area to be more closely linked with the transient energy release in the solar corona. The cumulative plots of the flare index indicate a slight excess of activity in the northern hemisphere during cycle 21, while a southern excess clearly prevails for cycles 22 and 23. The study reveals a significant N-S asymmetry, which exhibits variations with the phases of solar cycle. The reliability and persistency of this asymmetry significantly increases when the data is averaged over longer periods, while an optimal level is achieved when data is binned for 13 Carrington rotations. The time evolution of the flare index further confirms evolution of dual peaks in solar cycles during the solar maxima and violation of Gnevyshev-Ohl rule for the pair of solar cycles 22 and 23. Conclusions: The SXR flare index in the northern and the southern hemispheres of the Sun exhibits significant asymmetry during the evolutionary phases of the solar cycle, which implies that N-S asymmetry of solar flares is manifested in terms of the flare counts as well as the intensity of flare events.

  4. 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.

  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. Electron Kappa Distributions in Solar Flares and the Earth's Magnetotail

    NASA Astrophysics Data System (ADS)

    Oka, M.; Krucker, S.; Phan, T.

    2013-12-01

    Explosive phenomena in the solar corona and the Earth's magnetotail produce non-thermal, energetic electrons of up to tens of MeV and hundreds of keV, respectively. While power-law energy spectra have been observed in both environments, similarities and differences of the power-law features remain unclear. Here we propose to use kappa distribution to compare the power-law spectral indices obtained by hard X-ray observations during solar flares as well as in-situ electron measurements in the Earth's magnetotail. We will present RHESSI solar flare observations in which foot-points of the flare loop were behind the solar limb so that the photon spectra of the hard X-ray coronal source could be studied without much contamination by photons from the foot-points. As a reference, we will also show a THEMIS observation of electron kappa distribution in the reconnection flow-braking region within the Earth's magnetotail.

  7. Location of narrowband spikes in solar flares

    NASA Astrophysics Data System (ADS)

    Benz, A. O.; Saint-Hilaire, P.; Vilmer, N.

    2002-02-01

    Narrowband spikes of the decimeter type have been identified in dynamic spectrograms of Phoenix-2 of ETH Zurich and located in position with the Nançay Radioheliograph at the same frequency. The spike positions have been compared with the location of hard X-ray emission and the thermal flare plasma in soft X-rays and EUV lines. The decimetric spikes are found to be single sources located some 20 arcsec to 400 arcsec away from the flare site in hard or soft X-rays. In most cases there is no bright footpoint nearby. In at least two cases the spikes are near loop tops. These observations do not confirm the widely held view that the spike emission is produced by some loss-cone instability masering near the footpoints of flare loops. On the other hand, the large distance to the flare sites and the fact that these spikes are all observed in the flare decay phase make the analyzed spike sources questionable sites for the main flare electron acceleration. They possibly indicate coronal post-flare acceleration sites.

  8. Solar neutron events in association with large solar flares in November 2003

    NASA Astrophysics Data System (ADS)

    Watanabe, K.; Muraki, Y.; Matsubara, Y.; Murakami, K.; Sako, T.; Miranda, P.; Ticona, R.; Velarde, A.; Kakimoto, F.; Ogio, S.; Tokuno, H.; Tsuchiya, H.; Shibata, S.; Sakai, T.; Mizumoto, Y.; Ogasawara, R.; Nakagiri, M.; Miyashita, A.; Lopate, C.

    2006-01-01

    The Sun was intensely active from late October to the beginning of November 2003. A series of 11 X class solar flares occurred in NOAA regions 484, 486 and 488. Unique among this series of flares were those occurring on November 2 and 4 in which solar neutrons were observed by the ground based neutron monitors located at Mt. Chacaltaya, Bolivia and Haleakala, Hawaii, respectively. In these flares, intense emission of hard X-rays and γ-rays have been observed by the satellites. It seems that production of solar neutrons coincided with the production of the hard electromagnetic radiations of these two flares.

  9. STATISTICAL ANALYSES ON THERMAL ASPECTS OF SOLAR FLARES

    SciTech Connect

    Li, Y. P.; Gan, W. Q.; Feng, L.

    2012-03-10

    The frequency distribution of flare energies provides a crucial diagnostic to calculate the overall energy residing in flares and to estimate the role of flares in coronal heating. It often takes a power law as its functional form. We have analyzed various variables, including the thermal energies E{sub th} of 1843 flares at their peak time. They were recorded by both Geostationary Operational Environmental Satellites and Reuven Ramaty High-Energy Solar Spectroscopic Imager during the time period from 2002 to 2009 and are classified as flares greater than C 1.0. The relationship between different flare parameters is investigated. It is found that fitting the frequency distribution of E{sub th} to a power law results in an index of -2.38. We also investigate the corrected thermal energy E{sub cth}, which represents the flare total thermal energy including the energy loss in the rising phase. Its corresponding power-law slope is -2.35. Compilation of the frequency distributions of the thermal energies from nanoflares, microflares, and flares in the present work and from other authors shows that power-law indices below -2.0 have covered the range from 10{sup 24} to 10{sup 32} erg. Whether this frequency distribution can provide sufficient energy to coronal heatings in active regions and the quiet Sun is discussed.

  10. 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.

  11. 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.

  12. 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...

  13. Observations and modeling of plasma flows driven by solar flares

    NASA Astrophysics Data System (ADS)

    Brannon, Sean Robert

    One of the fundamental statements that can be made about the solar atmosphere is that it is structured. This structuring is generally believed to be the result of both the arrangement of the magnetic field in the corona and the distribution of plasma along magnetic loops. The standard model of solar flares involves plasma transported into coronal loops via a process known as chromospheric evaporation, and the resulting evolution of the flare loops is believed to be sensitive to the physical mechanism of energy input into the chromosphere by the flare. We present here the results of three investigations into chromospheric plasma flows driven by solar flare energy release and transport. First, we develop a 1-D hydrodynamic code to simulate the response of a simplified model chromosphere to energy input via thermal conduction from reconnection-driven shocks. We use the results from a set of simulations spanning a parameter space in both shock speed and chromospheric-to-coronal temperature ratio to infer power-law relationships between these quantities and observable evaporation properties. Second, we use imaging and spectral observations of a quasi-periodic oscillation of a flare ribbon to determine the phase relationship between Doppler shifts of the ribbon plasma and the oscillation. The phase difference we find leads us to suggest an origin in a current sheet instability. Finally, we use imaging and spectral data of an on-disk flare event and resulting flare loop plasma flows to generally validate the standard picture of flare loop evolution, including evaporation, cooling time, and draining downflows, and we use a simple free-fall model to produce the first direct comparison between observed and synthetic downflow spectra.

  14. On Our Ability to Predict Major Solar Flares

    NASA Astrophysics Data System (ADS)

    Georgoulis, Manolis K.

    We discuss the outstanding problem of solar flare prediction and briefly overview the various methods that have been developed to address it. A class of these methods, relying on the fractal and multifractal nature of solar magnetic fields, are shown to be inadequate for flare prediction. More promise seems delivered by morphological methods applying mostly to the photospheric magnetic configuration of solar active regions but a definitive assessment of their veracity is subject to a number of caveats. Statistical and artificial-intelligence methods are also briefly discussed, together with their possible shortcomings. The central importance of proper validation procedures for any viable method is also highlighted, together with the need for future studies that will finally judge whether practically meaningful flare prediction will ever become possible, if only purely probabilistic.

  15. 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.

  16. Collisionless Three-dimensional Reconnection In Impulsive Solar Flares

    NASA Astrophysics Data System (ADS)

    Somov, Boris V.; Kosugi, Takeo; Sakao, Taro

    1998-04-01

    Two subclasses of impulsive solar flares, observed with the Hard X-Ray Telescope (HXT) onboard Yohkoh, have been discovered by Sakao et al. The two subclasses can be characterized as more impulsive (MI) and less impulsive (LI) flares, the former having a shorter total duration of the impulsive phase in the hard X-ray emission than the latter. We assume that in both subclasses, the collisionless three-dimensional reconnection process occurs at the separator with a longitudinal magnetic field. The high-temperature turbulent-current sheet (HTTCS), located along the separator, generates accelerated particles and fast outflows of ``superhot'' (T >= 30 MK) plasma. Powerful anomalous heat-conductive fluxes along the reconnected field lines maintain a high temperature in the superhot plasma. The difference between the LI and MI flares presumably appears because the footpoint separation (the distance between two brightest hard X-ray sources) increases in time in the LI flares, but decreases in the MI flares. According to our model, in the LI flares the three-dimensional reconnection process accompanies an increase in the longitudinal magnetic field at the separator. In contrast, in the MI flares the reconnection proceeds with a decrease of the longitudinal field; hence, the reconnection rate is higher in the MI flares. Since reconnection in the MI flares proceeds with a decrease of the longitudinal field, the reconnected field lines become shorter in this process. As the reconnected lines become shorter, accelerated electron beams arrive at the upper chromosphere faster. So, in the MI flares chromospheric evaporation begins earlier than in the LI flares. The evaporation process driven by accelerated electron beams generates upflows of ``warm'' (T <= 10 MK) plasma that interacts with downflows of superhot plasma and can switch off the accumulation of superhot plasma in the MI flares during the impulsive phase. In the LI flares, however, an observable amount of superhot plasma is accumulated even during the impulsive phase. Moreover, since the cooling timescales increase with the length of the reconnected field lines, our argument for the association of superhot plasma with longer lines may remain valid to a reasonable extent even if the chromospheric evaporated plasma mixes with the reconnected outflow and superhot temperatures are reached in this mixture. Further analysis of the Yohkoh data obtained simultaneously with the Hard and Soft X-Ray Telescopes and the bent crystal spectrometer (BCS) is necessary to distinguish the superhot components of chromospheric and coronal origins in different classes of flares as well as at different phases of their development.

  17. 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.

  18. Solar flares detection and warning by space network

    NASA Astrophysics Data System (ADS)

    Melkonian, G.; Boschat, J.; Lantos, P.; Bourrieau, J.

    1991-10-01

    The solar flares produce magnetic storms and charged particle bursts which induce ground and space systems damage with heavy economic consequences. In order to apply countermeasures in due time, an early detection network is proposed. The paper presents an overview of the solar activity, the earth-sun relation, and the present knowledge about the propagation of solar protons in space medium. The proposed network is based on the utilization of several satellites measuring proton fluxes and transmitting corresponding data to the earth.

  19. Distinguishing Between Different Types of Prominences Associated with Solar Flares

    NASA Astrophysics Data System (ADS)

    Martin, Sara F.; Engvold, Oddbjorn; Lin, Yong

    2015-08-01

    In the early days of solar astronomy, any feature that extended above the solar limb was called a prominence. However, many such coronal features have been sufficiently studied to justify more specific names such as flare loops, surges, and flaring arches. Each of these named phenomena has different properties and involves different physical processes from other solar prominences. If we exclude these well-identified phenomena, we find that the majority of the remaining prominences can be grouped into only two categories that are distinctly different from each other. The main two types are (1) channel prominences or channel filaments when seen against the solar disk and (2) coronal cloud prominences, including narrow, down-flows named coronal rain. We illustrate the many significant differences between channel prominences and coronal cloud prominences. One of the fundamental differences is that channel prominences often have patterns of mass motions useful in anticipating many flares while coronal cloud prominences tend to occur hours after major solar flares. We also raise the question of whether the much taller coronal cloud prominences could have a counterpart in prominences on solar-like stars with magnetic fields of greater magnitude than the Sun.

  20. Magnetic-field variations and solar flare activity

    NASA Astrophysics Data System (ADS)

    Grigor'eva, I. Yu.; Shakhovskaya, A. N.; Livshits, M. A.; Knyazeva, I. S.

    2012-11-01

    Solar filtergrams obtained at the Crimean Astrophysical Observatory at the center and wings of the H α line are used to study variations in filaments, in particular, in arch filament systems (AFSs). These are considered as an indicator of emerging new magnetic flux, providing information about the spatial locations of magnetic-field elements. Magnetic-field maps for the active region NOAA 10030 are analyzed as an example. A method developed earlier for detecting elements of emerging flux using SOHO/MDI magnetograms indicates a close link between the increase in flare activity in theNOAA 10030 group during July 14-18, 2002 and variations in the topological disconnectedness of the magnetograms. Moreover, variations in the flare activity one day before a flare event are correlated with variations in the topological complexity of the field (the Euler characteristic) in regions with high field strengths (more than 700 G). Analysis of multi-wavelength polarization observations on the RATAN-600 radio telescope during July 13-17, 2002 indicate dominance of the radio emission above the central spot associated with the increase in flare activity. In addition to the flare site near the large spot in the group, numerous weak flares developed along an extended local neutral line, far from the central line of the large-scale field. The statistical characteristics of the magnetic-field maps analyzed were determined, and show flare activity of both types, i.e., localized in spot penumbras and above the neutral line of the field.

  1. 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.

  2. 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.

  3. Solar flares as cascades of reconnecting magnetic loops.

    PubMed

    Hughes, D; Paczuski, M; Dendy, R O; Helander, P; McClements, K G

    2003-04-01

    A model for the solar coronal magnetic field is proposed where multiple directed loops evolve in space and time. Loops injected at small scales are anchored by footpoints of opposite polarity moving randomly on a surface. Nearby footpoints of the same polarity aggregate, and loops can reconnect when they collide. This may trigger a cascade of further reconnection, representing a solar flare. Numerical simulations show that a power law distribution of flare energies emerges, associated with a scale-free network of loops, indicating self-organized criticality. PMID:12689272

  4. Solar flare intermittency and the earth's temperature anomalies.

    PubMed

    Scafetta, Nicola; West, Bruce J

    2003-06-20

    We argue that Earth's short-term temperature anomalies and the solar flare intermittency are linked. The analysis is based upon the study of the scaling of both the spreading and the entropy of the diffusion generated by the fluctuations of the temperature time series. The joint use of these two methods evidences the presence of a Lévy component in the temporal persistence of the temperature data sets that corresponds to the one that would be induced by the solar flare intermittency. The mean monthly temperature data sets cover the period from 1856 to 2002. PMID:12857233

  5. 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.

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

    NASA Technical Reports Server (NTRS)

    Townsend, Lawrence W.; Nealy, John E.; Wilson, John W.; Atwell, William

    1989-01-01

    Estimates are given for the radiation shielding thicknesses required to protect astronauts on interplanetary missions from the effects of large solar flares, on the basis of the integral proton fluences for several past solar particle events. NASA-Langley's nucleon transport deterministic computer code, BRYNTRN, is used to transport primary protons and secondary protons and neutrons through any number of layers of target material of arbitrary thickness and composition. The results of each flare are presented as estimates of dose equivalents to the skin, eyes, and blood-forming organs behind various thicknesses of aluminum shielding.

  7. 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.

  8. 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.

  9. 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.

  10. Energetic Correlation Between Solar Flares and Coronal Mass Ejections

    NASA Technical Reports Server (NTRS)

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

    2007-01-01

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

  11. MULTIWAVELENGTH ANALYSIS OF A SOLAR FLARE ON 2002 APRIL 15

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

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

  13. 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.

  14. The Response of Mid-Latitude Ionospheric TEC to Geomagnetic Storms and Solar Flares

    NASA Astrophysics Data System (ADS)

    Huang, Z.; Roussel-Dupre, R.

    2004-12-01

    The effects of geomagnetic storms and solar flares on the ionosphere are manifested as large magnitude sudden fluctuations in the Total Electron Content (TEC). In this study, the broadband VHF signal (30-100MHz) data from the Los Alamos Portable Pulser (LAPP) received by the FORTE (Fast Onboard Recording of Transient Events) satellite during the period of 1997-2002 are used to investigate the mean TEC variation response to geomagnetic storm. A total of 14 geomagnetic storms are selected where FORTE-LAPP data are available to derive average TECs during extended storm-time and non-storm time for a given storm. The variations in the ionospheric TECs at Los Alamos, New Mexico are investigated for the 14 selected geomagnetic storms. In most cases (12 out of 14), we see overall enhancements in TEC as a result of geomagnetic storm impact at Los Alamos. The relative enhancements in TEC at Los Alamos due to a geomagnetic storm can reach as high as 3-fold of the normal TEC values. The overall absolute enhancements in TEC at Los Alamos are up to about 30 TECU. The magnitude of TEC enhancements is diversified over all storm categories without a clean-cut relationship between the storm intensity and the TEC enhancement. The mean TEC variation response to geomagnetic storm can be complicated when several consecutive storms occurred in a row and a net TEC reduction may be seen. Data of continuous GPS TEC measurements are collected at a 1-minute time resolution during July 2004 when 5 X-class solar flares occurred from two Allen Osborne Associates ICS-4000Z GPS receivers mounted at the Physics Building at Los Alamos National Laboratory. In detecting effects of solar flares on the ionospheric TEC, we apply appropriate filtering to remove the linear trend of TEC and a coherent processing of TEC variations simultaneously for all the visible GPS satellites in a given time interval. The responses of ionospheric TEC at minute time scale to these powerful impulsive solar flares are investigated. The onset time of the ionospheric response and the magnitude of the TEC fluctuations and its time derivative are examined along with their relationships with the solar flux characteristics, duration of the flare and location of the flare on the Sun, X-ray emission variations during the flares, and local time of the flare occurrence.

  15. Soft X-ray spectroscopy of solar flares - An overview

    NASA Technical Reports Server (NTRS)

    Doschek, G. A.

    1990-01-01

    An overview of the current status of high spectral resolution soft X-ray observations of solar flares is given. The review concentrates primarily on recent results and interpretations of results obtained from orbiting Bragg crystal spectrometers flow during the last solar maximum on the US DoD P78-1 spacecraft, the NASA SMM, and the ISAS Hinotori spacecraft. Results and several key issues regarding interpretation of the spectra are presented. Specifically, the dynamics of coronal flare plasmas as revealed by X-ray line profiles and wavelength shifts are discussed. Recent results concerning the theory of chromospheric evaporation are given. The temperature of coronal flare plasma is discussed within the context of a differential mission measure. Results concerning electron density measurements, nonequilibrium processes, and relative element abundances are also reviewed.

  16. 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.

  17. High Energy Gamma Ray Lines from Solar Flares

    NASA Technical Reports Server (NTRS)

    Crannell, Carol Jo

    2000-01-01

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

  18. The effects of solar protons flares on the navigation systems of aircraft s and the resulting accents during 20th century

    NASA Astrophysics Data System (ADS)

    Shaltout, M.; Hady, A.

    In early study for the authors, from the analysis of 802 important accents of the aircraft's which occurred during the period (1920 -2000) all over the world. It is found that the number of occurrence of the accents increases at the solar maximum activity, and decrease with decreasing the solar activity on the annual scale. There is a doubt the geomagnetic storms due to the charged particles, which come from the s un as a cloud after two or three days from the high energetic flares occurrence. Which affected on the navigation system of the aircraft's, especially for aircraft's which pass through the polar regions of the earth, at the high latitudes. The aim of the present study is to analysis more than one handed solar protons flares (1970-2000) of energies more than 10 MeV observed by the artificial satellite! GOES and published in solar Geophysical Data, NOAA, Boulder, Colorado, USA. A comparison studies between the proton flares occurrence and the important accents of the aircraft's, which occur after two days to one week, from the high energetic proton flares occurrence, or case by case, in an attempt to confirm the relation between the solar activities and aircraft accents due to disturbance in the Navigation systems. Also, we not Ignore in our study the effects of the geomagnetic field on the flying staff, due to the occurrence of the solar proton flares, as indicated by other authors in early studies.

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. EVIDENCE THAT TEMPORAL CHANGES IN SOLAR SUBSURFACE HELICITY PRECEDE ACTIVE REGION FLARING

    SciTech Connect

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

    2010-02-20

    We report on the analysis of subsurface vorticity/helicity measurements for flare producing and quiet active regions. We have developed a parameter to investigate whether large, decreasing kinetic helicity density commonly occurs prior to active region flaring. This new parameter is effective at separating flaring and non-flaring active regions and even separates among C-, M-, and X-class flare producing regions. In addition, this parameter provides advance notice of flare occurrence, as it increases 2-3 days before the flare occurs. These results are striking on an average basis, though on an individual basis there is still considerable overlap between flare associated and non-flare associated values. We propose the following qualitative scenario for flare production: subsurface rotational kinetic energy twists the magnetic field lines into an unstable configuration, resulting in explosive reconnection and a flare.

  7. Evidence That Temporal Changes in Solar Subsurface Helicity Precede Active Region Flaring

    NASA Astrophysics Data System (ADS)

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

    2010-02-01

    We report on the analysis of subsurface vorticity/helicity measurements for flare producing and quiet active regions. We have developed a parameter to investigate whether large, decreasing kinetic helicity density commonly occurs prior to active region flaring. This new parameter is effective at separating flaring and non-flaring active regions and even separates among C-, M-, and X-class flare producing regions. In addition, this parameter provides advance notice of flare occurrence, as it increases 2-3 days before the flare occurs. These results are striking on an average basis, though on an individual basis there is still considerable overlap between flare associated and non-flare associated values. We propose the following qualitative scenario for flare production: subsurface rotational kinetic energy twists the magnetic field lines into an unstable configuration, resulting in explosive reconnection and a flare.

  8. 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.

  9. Three-Dimensional Analysis of the Magnetic Structure Producing the X and M Class Flares in the Solar Active Region 11158

    NASA Astrophysics Data System (ADS)

    Inoue, S.; Magara, T.; Hayashi, K.; Choe, G.

    2012-12-01

    The solar active region NOAA 11158 is an attractive object to study the solar flares because it produced one X-class flare and several M-class flares. Solar physics satellite "Solar Dynamics Observatory" (SDO) continuously observed vector-field data and EUV images of this active region with unprecedented time resolution, covering pre-flare phase, onset and post- flare flares of these solar flares. In this study, we analyze the three-dimensional (3D) magnetic structure to clarify the occurrence conditions of the X2.2 flares occurred at Feb. 15, 2011 and several M flares corresponding to M6.6, M1.0, M1.1 occurred at Feb. 13 and 16, 2011 in this active region. 3D magnetic field are extrapolated by the MHD-Relaxation method developed by Inoue et al. 2011 and 2012, based on the Helioseismic and Magnetic Imager (HMI) on board the SDO. We focus on the magnetic twist obtained from 3D magnetic field lines because this is key value of the stability of the magnetic configuration and strongly related to the occurrence conditions of flares. We found that the twist values of the strong twisted lines just before the X2.2 and M6.6 flares correspond to the range from half-turn to one-turn which disappear after these flares while the magnetic twists less than half turn are almost remained through the both flares. This result suggests that the build up of the magnetic twisted lines over the half turn is key issue generating the larger flares. On the other hand, although the strong twisted field lines are also built up just before the M1.0 and M1.1 flares, these are almost remained even after the flares. Topology analysis of the 3D field lines suggests the overlying field lines formed after the X2.2 flare play an important role to confine the dynamics due to the strong twisted lines. Moreover, based on these results, we discuss the favorable magnetic configuration generating X and M class flares.

  10. Solar Neutron Event in Association with a Large Solar Flare on 2000 November 24

    NASA Astrophysics Data System (ADS)

    Watanabe, K.; Muraki, Y.; Matsubara, Y.; Murakami, K.; Sako, T.; Tsuchiya, H.; Masuda, S.; Yoshimori, M.; Ohmori, N.; Miranda, P.; Martinic, N.; Ticona, R.; Velarde, A.; Kakimoto, F.; Ogio, S.; Tsunesada, Y.; Tokuno, H.; Shirasaki, Y.

    2003-07-01

    Solar neutrons have been detected using the neutron monitor located at Mount Chacaltaya, Bolivia, in association with a large solar flare on 2000 November 24. This is the first detection of solar neutrons by a neutron monitor that has been reported so far in solar cycle 23. The statistical significance of the detection is 5.5 σ. In this flare, the intense emission of hard X-rays and γ-rays has been observed by the Yohkoh Hard X-ray Telescope (HXT) and Gamma Ray Spectrometer (GRS), respectively. The production time of solar neutrons is better correlated with those of hard X-rays and γ-rays than with the production time of soft X-rays. The observations of the solar neutrons on the ground have been limited to solar flares with soft X-ray class greater than X8 in former solar cycles. In this cycle, however, neutrons were detected associated with an X2.3 solar flare on 2000 November 24. This is the first report of the detection of solar neutrons on the ground associated with a solar flare with an X-ray class smaller than X8.

  11. 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.

  12. Solar Flares Observed with the Ramaty High Energy Solar Spectroscopic Imager (RHESSI)

    NASA Technical Reports Server (NTRS)

    Holman, Gordon D.

    2004-01-01

    Solar flares are impressive examples of explosive energy release in unconfined, magnetized plasma. It is generally believed that the flare energy is derived from the coronal magnetic field. However, we have not been able to establish the specific energy release mechanism(s) or the relative partitioning of the released energy between heating, particle acceleration (electrons and ions), and mass motions. NASA's RHESSI Mission was designed to study the acceleration and evolution of electrons and ions in flares by observing the X-ray and gamma-ray emissions these energetic particles produce. This is accomplished through the combination of high-resolution spectroscopy and spectroscopic imaging, including the first images of flares in gamma rays. RHESSI has observed over 12,000 solar flares since its launch on February 5, 2002. I will demonstrate how we use the RHESSI spectra to deduce physical properties of accelerated electrons and hot plasma in flares. Using images to estimate volumes, w e typically find that the total energy in accelerated electrons is comparable to that in the thermal plasma. I will also present flare observations that provide strong support for the presence of magnetic reconnection in a large-scale, vertical current sheet in the solar corona. RHESSI observations such as these are allowing us to probe more deeply into the physics of solar flares.

  13. Muon and Tau Neutrinos Spectra from Solar Flares

    NASA Astrophysics Data System (ADS)

    Fargion, Daniele; Moscato, Federica

    2003-12-01

    Most power-full solar flare as the ones occurred on 23th February 1956, September 29th 1989, 28th October and on 2nd-4th November 2003 are sources of cosmic rays, X, gamma and neutrino bursts. These flares took place both on front or in the edge and in the hidden solar disk. The 4th November event was the most powerful X event in the highest known rank category X28 just at horizons. The observed and estimated total flare energy (EFL ≃ 1031div 1033 erg) should be a source of a prompt secondary neutrino burst originated, by proton-proton-pion production on the sun itself; a more delayed and spread neutrino flux signal arise by the solar charged flare particles reaching the terrestrial atmosphere. These first earliest prompt solar neutrino burst might be observed, in a few neutrino clustered events, in present or future largest neutrino underground detectors as Super-Kamiokande one, in time correlation with the X-Radio flare. The onset in time correlation has great statistical significance. Our first estimate on the neutrino number events detection at the Super-Kamiokande II Laboratory for horizontal or hidden flare is found to be few events: NeV_bar{ν}_e≃ 0.63&etae ()/(35 MeV) ()/(1031 erg); and NeV_bar{ν}μ ≃ 3.58()/(200 MeV) ()/(1031erg) η,SUB>μ, where η≃ 1, Eνμ > 113 MeV. Our first estimates of neutrino signals in largest underground detectors hint for few events in correlation with X, gamma, radio onser. Our approximated spectra for muons and taus from these rare solar eruption are shown over the most common background. The muon and tau signature is very peculiar and characteristic over electron and anti-electron neutrino fluxes. The rise of muon neutrinos will be detectable above the minimal muon threshold Eν ≃ 113 MeV energy, or above the pion and Δ ° thresholds (Eν≃ 151 and 484 MeV). Any large neutrino flare event record might also verify the expected neutrino flavour mixing leading to a few as well as a comparable, νe, νμ, bar{ν}e, bar{ν}μ energy fluence and spectra. The rarest tau appearance will be possible only for hardest solar neutrino energies above 3.471 GeV.

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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...

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. A Unified Computational Model for Solar and Stellar Flares

    NASA Technical Reports Server (NTRS)

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

    2015-01-01

    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.

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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/.

  8. 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.

  9. 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),

  10. Beam-return current systems in solar flares

    NASA Technical Reports Server (NTRS)

    Spicer, D. S.; Sudan, R. N.

    1984-01-01

    It is demonstrated that the common assumption made in solar flare beam transport theory that the beam-accompanied return current is purely electrostatically driven is incorrect, and that the return current is both electrostatically and inductively driven, in accordance with Lenz's law, with the inductive effects dominating for times greater than a few plasma periods. In addition, it is shown that a beam can only exist in a solar plasma for a finite time which is much smaller than the inductive return current dissipation time. The importance of accounting for the role of the acceleration mechanism in forming the beam is discussed. In addition, the role of return current driven anomalous resistivity and its subsequent anomalous Joule heating during the flare process is elucidated.

  11. 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.

  12. 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

  13. 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.

  14. X-ray and Gamma-ray Observations of Solar Flares and SEP Events

    NASA Astrophysics Data System (ADS)

    Winter, Lisa M.

    2016-05-01

    We present a statistical analysis of the X-ray and gamma ray observations of C, M, and X-class flares from solar cycle 24. Extending upon the Winter & Balasubramaniam 2015 study of the GOES XIS observations of 50,000 flares from 1986 to the present, we include Fermi GBM and LAT data from the Fermi solar flare catalogs. As in the previous work, we use machine-learning techniques to determine whether the higher energy data reveal further temperature diagnostics to establish clustering of flare properties. Additionally, we compare the X-ray and gamma ray intensities and flare timing with the intensity and timing of solar energetic particle events.

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

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  16. 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.

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

    NASA Technical Reports Server (NTRS)

    Cane, H. V.

    2004-01-01

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

  18. The Energetic Importance of Accelerated Electrons in Solar Flares

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

  19. Internal and External Reconnection Series Homologous Solar Flares

    NASA Technical Reports Server (NTRS)

    Sterling, Alphonse C.; Moore, Ronald L.

    2001-01-01

    Using data from the extreme ultraviolet imaging telescope (EIT) on SOHO and the soft X-ray telescope (SXT) on Yohkoh, we examine a series of morphologically homologous solar flares occurring in National Oceanic and Atmospheric Administration (NOAA) active region 8210 over May 1-2, 1998. An emerging flux region (EFR) impacted against a sunspot to the west and next to a coronal hole to the east is the source of the repeated flaring. An SXT sigmoid parallels the EFR's neutral line at the site of the initial flaring in soft X rays. In EIT each flaring episode begins with the formation of a crinkle pattern external to the EFR. These EIT crinkles move out from, and then in toward, the EFR with velocities approx. 20 km/ s. A shrinking and expansion of the width of the coronal hole coincides with the crinkle activity, and generation and evolution of a postflare loop system begins near the time of crinkle formation. Using a schematic based on magnetograms of the region, we suggest that these observations are consistent with the standard reconnection-based model for solar eruptions but are modified by the presence of the additional magnetic fields of the sunspot and coronal hole. In the schematic, internal reconnection begins inside of the EFR-associated fields, unleashing a flare, postflare loops, and a coronal mass ejection (CME). External reconnection, first occurring between the escaping CME and the coronal hole field and second occurring between fields formed as a result of the first external reconnection, results in the EIT crinkles and changes in the coronal hole boundary. By the end of the second external reconnection, the initial setup is reinstated; thus the sequence can repeat, resulting in morphologically homologous eruptions. Our inferred magnetic topology is similar to that suggested in the "breakout model" of eruptions although we cannot determine if our eruptions are released primarily by the breakout mechanism (external reconnection) or, alternatively, primarily by the internal reconnection.

  20. Modeling the time-intensity profile of solar flare generated particle fluxes in the inner heliosphere.

    PubMed

    Smart, D F; Shea, M A

    1992-01-01

    It is possible to model the time-intensity profile of solar particles expected in space after the occurrence of a significant solar flare on the sun. After the particles are accelerated in the flare process, if conditions are favorable, they may be released into the solar corona and then into space. The heliolongitudinal gradients observed in the inner heliosphere are extremely variable, reflecting the major magnetic structures in the solar corona which extend into space. These magnetic structures control the particle gradients in the inner heliosphere. The most extensive solar particle measurements are those observed by earth-orbiting spacecraft, and forecast and prediction procedures are best for the position of the earth. There is no consensus of how to extend the earth-based models to other locations in space. Local interplanetary conditions and structures exert considerable influence on the time-intensity profiles observed. The interplanetary shock may either reduce or enhance the particle intensity observed at a specific point in space and the observed effects are very dependent on energy. PMID:11537020

  1. Location of Decimetric Pulsations in Solar Flares

    NASA Astrophysics Data System (ADS)

    Benz, Arnold O.; Battaglia, Marina; Vilmer, Nicole

    2011-11-01

    This work investigates the spatial relation between coronal X-ray sources and coherent radio emissions, both generally thought to be signatures of particle acceleration. Two limb events were selected during which the radio emission was well correlated in time with hard X-rays. The radio emissions were of the type of decimetric pulsations as determined from the spectrogram observed by Phoenix-2 of ETH Zurich. The radio positions were measured from observations with the Nançay Radioheliograph between 236 and 432 MHz and compared to the position of the coronal X-ray source imaged with RHESSI. The radio pulsations originated at least 30 - 240 Mm above the coronal hard X-ray source. The altitude of the radio emission increases generally with lower frequency. The average positions at different frequencies are on a line pointing approximately to the coronal hard X-ray source. Thus, the pulsations cannot be caused by electrons trapped in the flare loops, but are consistent with emission from a current sheet above the coronal source.

  2. Location of Decimetric Pulsations in Solar Flares

    NASA Astrophysics Data System (ADS)

    Benz, Arnold O.; Battaglia, Marina; Vilmer, Nicole

    This work investigates the spatial relation between coronal X-ray sources and coherent radio emissions, both generally thought to be signatures of particle acceleration. Two limb events were selected during which the radio emission was well correlated in time with hard X-rays. The radio emissions were of the type of decimetric pulsations as determined from the spectrogram observed by Phoenix-2 of ETH Zurich. The radio positions were measured from observations with the Nançay Radioheliograph between 236 and 432 MHz and compared to the position of the coronal X-ray source imaged with RHESSI. The radio pulsations originated at least 30 - 240 Mm above the coronal hard X-ray source. The altitude of the radio emission increases generally with lower frequency. The average positions at different frequencies are on a line pointing approximately to the coronal hard X-ray source. Thus, the pulsations cannot be caused by electrons trapped in the flare loops, but are consistent with emission from a current sheet above the coronal source.

  3. Imaging spectroscopy of solar microwave radiation. 1: Flaring emission

    NASA Technical Reports Server (NTRS)

    Lim, Jeremy; Gary, Dale E.; Hurford, Gordon J.; Lemen, James R.

    1994-01-01

    We present observations of an impulsive microwave burst on the Sun with both high spatial and spectral resolution, made with the Solar Array at the Owens Valley Radio Observatory (OVRO). We used the measured brightness temperature spectrum to infer the emission process responsible for each microwave source, and to derive physical conditions in the source region. We confimed our predictions using soft X-ray measurements from Geostationary Operational Environmental Satellite (GOES), soft X-ray images from Yohkoh, and H-alpha flare images together with sunspots and magnetogram images from the Big Bear Solar Observatory.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. ANATOMY OF A SOLAR FLARE: MEASUREMENTS OF THE 2006 DECEMBER 14 X-CLASS FLARE WITH GONG, HINODE, AND RHESSI

    SciTech Connect

    Matthews, S. A.; Zharkov, S.; Zharkova, V. V.

    2011-10-01

    Some of the most challenging observations to explain in the context of existing flare models are those related to the lower atmosphere and below the solar surface. Such observations, including changes in the photospheric magnetic field and seismic emission, indicate the poorly understood connections between energy release in the corona and its impact in the photosphere and the solar interior. Using data from Hinode, TRACE, RHESSI, and GONG we study the temporal and spatial evolution of the 2006 December 14 X-class flare in the chromosphere, photosphere, and the solar interior. We investigate the connections between the emission at various atmospheric depths, including acoustic signatures obtained by time-distance and holography methods from the GONG data. We report the horizontal displacements observed in the photosphere linked to the timing and locations of the acoustic signatures we believe to be associated with this flare, their vertical and horizontal displacement velocities, and their potential implications for current models of flare dynamics.

  9. Solar Neutron Event in Association with a Large Solar Flare on August 25, 2001

    NASA Astrophysics Data System (ADS)

    Watanabe, K.; Muraki, Y.; Matsubara, Y.; Murakami, K.; Sako, T.; Tsuchiya, H.; Masuda, S.; Yoshimori, M.; Ohmori, N.; Miranda, P.; Martinic, N.; Ticona, R.; Velarde, A.; Kakimoto, F.; Ogio, S.; Tsunesada, Y.; Tokuno, H.; Shirasaki, Y.

    2003-07-01

    Solar neutrons have been detected using the neutron monitor located at Mt. Chacaltaya, Bolivia, in association with a large solar flare on August 25, 2001. The statistical significance of the detection is 4.7 σ . In this flare, intense emission of hard X-rays and γ -rays was observed by the Yohkoh Hard X-ray telescope (HXT) and Gamma Ray spectrometer (GRS), respectively. The time of solar neutron production is better correlated with that of hard X-rays and γ -rays than with the production time of soft X-rays.

  10. 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.

  11. Turbulent and directed plasma motions in solar flares

    NASA Technical Reports Server (NTRS)

    Fludra, A.; Bentley, R. D.; Lemen, J. R.; Jakimiec, J.; Sylwester, J.

    1989-01-01

    An improved method for fitting asymmetric soft X-ray line profiles from solar flares is presented. A two-component model is used where one component represents the total emission from directed upflow plasma and the other the emission from the plasma at rest. Unlike previous methods, the width of the moving component is independent from that of the stationary component. Time variations of flare plasma characteristics (i.e., temperature, emission measure of moving and stationary plasma, upflow and turbulent velocities) are derived from the Ca XIX and Fe XXV spectra recorded by the Bent Crystal Spectrometer on the Solar Maximum Mission. The fitting technique provides a statistical estimation for the uncertainties in the fitting parameters. The relationship between the directed and turbulent motions has been studied, and a correlation of the random and directed motions has been found in some flares with intensive plasma upflows. Mean temperatures of the upflowing and stationary plasmas are compared for the first time from ratios of calcium to iron X-ray line intensities. Finally, evidence for turbulent motions and the possibility of plasma upflow late into the decay phase is presented and discussed.

  12. RHESSI Investigations of the Neupert Effect in Solar Flares

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

    In many solar flares the time integral of the hard X-ray emission closely matches the temporal variation of the soft X-ray emission. This is known as the Neupert Effect and is believed to result when the same accelerated electrons that produce the bremsstrahlung hard X-rays also heat the plasma that produces the thermal bremsstrahlung soft X-rays. The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is uniquely capable of investigating this effect since is covers the soft (down to 3 keV) and hard X-ray energy ranges with keV energy resolution, arcsecond-class angular resolution, and sub-second time resolution. Several GOES M-class flares have already been detected that show this general effect, but the detailed time histories suggest that there must be other heating mechanisms besides the thermalization of accelerated electrons that are heating the soft X-ray emitting plasma, even during the impulsive phase. Spatially-resolved hard and soft X-ray observations of these flares are also being investigated to determine what fraction of the heating is produced by the accelerated electrons.

  13. 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.

  14. 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.

  15. 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.

  16. Continuum analysis of an avalanche model for solar flares.

    PubMed

    Liu, Han-Li; Charbonneau, Paul; Pouquet, Annick; Bogdan, Thomas; McIntosh, Scott

    2002-11-01

    We investigate the continuum limit of a class of self-organized critical lattice models for solar flares. Such models differ from the classical numerical sandpile model in their formulation of stability criteria in terms of the curvature of the nodal field, and are known to belong to a different universality class. A fourth-order nonlinear hyperdiffusion equation is reverse engineered from the discrete model's redistribution rule. A dynamical renormalization-group analysis of the equation yields scaling exponents that compare favorably with those measured in the discrete lattice model within the relevant spectral range dictated by the sizes of the domain and the lattice grid. We argue that the fourth-order nonlinear diffusion equation that models the behavior of the discrete model in the continuum limit is, in fact, compatible with magnetohydrodynamics (MHD) of the flaring phenomenon in the regime of strong magnetic field and the effective magnetic diffusivity characteristic of strong MHD turbulence. PMID:12513560

  17. 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.

  18. 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.

  19. A Novel Forecasting System for Solar Particle Events and Flares (FORSPEF)

    NASA Astrophysics Data System (ADS)

    Papaioannou, A.; Anastasiadis, A.; Sandberg, I.; Georgoulis, M. K.; Tsiropoula, G.; Tziotziou, K.; Jiggens, P.; Hilgers, A.

    2015-08-01

    Solar Energetic Particles (SEPs) result from intense solar eruptive events such as solar flares and coronal mass ejections (CMEs) and pose a significant threat for both personnel and infrastructure in space conditions. In this work, we present FORSPEF (Forecasting Solar Particle Events and Flares), a novel dual system, designed to perform forecasting of SEPs based on forecasting of solar flares, as well as independent SEP nowcasting. An overview of flare and SEP forecasting methods of choice is presented. Concerning SEP events, we make use for the first time of the newly re-calibrated GOES proton data within the energy range 6.0-243 MeV and we build our statistics on an extensive time interval that includes roughly 3 solar cycles (1984-2013). A new comprehensive catalogue of SEP events based on these data has been compiled including solar associations in terms of flare (magnitude, location) and CME (width, velocity) characteristics.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. High-Speed Imaging System for Solar-Flare Research at Hida Observatory

    NASA Astrophysics Data System (ADS)

    Ishii, Takako T.; Kawate, Tomoko; Nakatani, Yoshikazu; Morita, Satoshi; Ichimoto, Kiyoshi; Masuda, Satoshi

    2013-04-01

    A high-speed imaging system for observing solar flares in the continuum and Hα wavelengths was installed on a φ 25 cm telescope of the Solar Magnetic Activity Research Telescope (SMART) at Hida observatory of Kyoto University. The aim of this system is to diagnose the spatio-temporal evolution of high-energy particles in solar flares by capturing the explosive evolution of chromospheric and photospheric flare kernels. The system acquires flare images covering a field of view of 344" × 258" with a spatial sampling of 0.215" pixel-1 and a frame rate of 25 frames s-1 . Initial data, including two white-light flares, demonstrate the diffraction-limited performance of the system. Observations have been in regular operation since 2011 November. The system is expected to provide a data set that is highly complementary with Hinode/SOT, SDO/AIA, and other ground-based instruments for upcoming solar-flare research.

  10. 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.

  11. 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.

  12. Source dynamics of the microwave emission during a solar flare

    NASA Astrophysics Data System (ADS)

    Begum Shaik, Shaheda; Gary, Dale E.; Nita, Gelu M.

    2016-05-01

    Determining the microwave burst source characteristics is important to understand the parameters of the flare process which produce the microwave emission. Previous studies show that the microwave solar bursts do typically exhibit a single source of emission but also often show inhomogeneous sources as a function of frequency at some periods during the burst. This study focuses on the spectral and spatial dynamics of the microwave gyrosynchrotron source through the microwave spectral and imaging analysis. We report the source characteristics of few impulsive flare events observed by the newly upgraded Expanded Owens Valley Solar Array (EOVSA) in the frequency range of 2.5 to 18 GHz and from the complimentary data of (Nobeyama Radioheliograph / Nobeyama Radio Polarimeters) NoRH / NoRP. The low frequency optically thick part of the microwave spectrum is an indicator of spatial inhomogeneity and complexity of the sources. We concentrate in the dynamics of the low frequency spectrum (intensity and spectral index) measured by EOVSA, and compare it to the corresponding spatial propoerties of the NoRH sources observed at 17 GHz and to the loop structures seen in the EUV (Extreme Ultraviolet) images with SDO (Solar Dynamics Observatory).

  13. 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.

  14. 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.

  15. The mean ionic charge of silicon in 3HE-rich solar flares

    NASA Technical Reports Server (NTRS)

    Luhn, A.; Klecker, B.; Hovestadt, E.; Moebius, E.

    1985-01-01

    Mean ionic charge of iron in 3He-rich solar flares and the average mean charge of Silicon for 23 #He-rich periods during the time interval from September 1978 to October 1979 were determined. It is indicated that the value of the mean charge state of Silicon is higher than the normal flare average by approximately 3 units and in perticular it is higher then the value predicted by resonant heating models for 3He-rich solar flares.

  16. 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.

  17. Electron-cyclotron maser emission during solar and stellar flares

    NASA Technical Reports Server (NTRS)

    Winglee, R. M.

    1985-01-01

    Radio bursts, with high brightness temperature 10 to the 10th power K and high degree of polarization, and the heating of the solar and stellar coronae during flares have been attributed to emission from the semirelativistic maser instability. In plasmas where the electron-plasma frequency, p, omega sub p, and the electron-cyclotron frequency, Omega sub e, are such that omega sup 2 sub p/Omega sup 2 sub e 1, x-mode growth dominates while z-mode growth dominates if omega sup 2 sub p/Omega sup 2 sub e is of order unity. The actual value of omega sup 2 sub p/Omega sup 2 sub e at which x-mode growth dominates is shown to be dependent on the plasma temperature with x-mode growth dominating at higher omega sub p/Omega sub e as the plasma temperature increases. Observations from a set of 20 impulsive flares indicate that the derived conditions for the dominance of x-mode growth are satisfied in about 75 percent of the flares.

  18. Atmospheric occultation of a solar flare in hard x rays

    NASA Technical Reports Server (NTRS)

    Chen, Kwan-Yu

    1989-01-01

    The objective of this study is two-fold: to investigate the absorption of hard x rays along a tangential path through the terrestrial atmosphere, and to locate, other than the use of imaging devices, the flare source of x ray emission in the sun. Observational data were taken with the Hard X Ray Burst Spectrometer (HXRBS) on board the Solar Maximum Mission satellite (SMM). The occultation event chosen for investigation is the flare on 14 October 1981. Night fell on SMM during the decaying phase of the flare. In about fifteen seconds, the x ray flux decreased to zero. The model for computing synthetic light curve, which is directly comparable to the observed curve, consists of two computing programs. One is a modified version of an existing code, which compute the coordinates of the tangent points of the SMM-sun lines. The other program computed the atmospheric densities along the angles (N to S and E to W) measured from the center of the sun. The various model also depends on the destination of the terrestrial atmosphere at geocentric positions of SMM and the sun, the mean atmospheric densities at different heights and latitudes, and the x ray absorption cross of nitrogen, oxygen, and argon. The optical length, at a given time and for a x ray energy, is computed with the two angular parameters. The fit of a particular synthetic light, curve, i.e., the exponentials of the optical lengths, to the observed eclipse curve, yields the desired angular parameters.

  19. Impulsive phase solar flare X-ray polarimetry

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  20. Gamma ray measurements of the 1991 November 15 solar flare

    NASA Astrophysics Data System (ADS)

    Arndt, Martina B.; Bennett, Kevin; Connors, Alanna; McConnell, Mark; Rank, Gerhard; Ryan, James M.; Schönfelder, Volker; Suleiman, Raid; Young, C. Alex

    2000-04-01

    The 1991 November 15 X1.5 flare was a well observed solar event. Comprehensive data from ground-based observatories and spacecraft provide the basis for a contextual interpretation of gamma-ray spectra from the Compton Gamma Ray Observatory (CGRO). In particular, spectral, spatial, and temporal data at several energies are necessary to understand the particle dynamics and the acceleration mechanism(s) within this flare. X-ray images, radio, Ca XIX data and magnetograms provide morphological information on the acceleration region [4,5], while gamma-ray spectral data provide information on the parent ion spectrum. Furthermore, time profiles in hard X-rays and gamma-rays provide valuable information on temporal characteristics of the energetic particles. We report the results of our analysis of the evolution of this flare as a function of energy (~25 keV-2.5 MeV) and time. These results, together with other high energy data (e.g. from experiments on Yohkoh, Ulysses, and PVO) may assist in identifying and understanding the acceleration mechanism(s) taking place in this event. .

  1. 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.

  2. 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.

  3. Stochastic three-wave interaction in flaring solar loops

    NASA Technical Reports Server (NTRS)

    Vlahos, L.; Sharma, R. R.; Papadopoulos, K.

    1983-01-01

    A model is proposed for the dynamic structure of high-frequency microwave bursts. The dynamic component is attributed to beams of precipitating electrons which generate electrostatic waves in the upper hybrid branch. Coherent upconversion of the electrostatic waves to electromagnetic waves produces an intrinsically stochastic emission component which is superposed on the gyrosynchrotron continuum generated by stably trapped electron fluxes. The role of the density and temperature of the ambient plasma in the wave growth and the transition of the three wave upconversion to stochastic, despite the stationarity of the energy source, are discussed in detail. The model appears to reproduce the observational features for reasonable parameters of the solar flare plasma.

  4. Energetic-particle abundances in impulsive solar flares

    NASA Technical Reports Server (NTRS)

    Reames, D. V.; Cane, H. V.; Von Rosenvinge, T. T.

    1990-01-01

    The abundances of elements and of He-3 in 90 solar electron events have been examined. It is found that the events fall into two distinct groups based upon their F/C ratio. Events in the F-rich group frequently have high He-3/He-4 ratios and are associated with type III and type V radio bursts in the parent flare. The F-poor events are associated with type IV bursts. These results on individual events support the conclusions of earlier work done with daily-averaged abundances.

  5. 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.

  6. Unprecedented Fine Structure of a Solar Flare Revealed by the 1.6 m New Solar Telescope

    NASA Astrophysics Data System (ADS)

    Jing, Ju; Xu, Yan; Cao, Wenda; Liu, Chang; Gary, Dale; Wang, Haimin

    2016-04-01

    Solar flares signify the sudden release of magnetic energy and are sources of so called space weather. The fine structures (below 500 km) of flares are rarely observed and are accessible to only a few instruments world-wide. Here we present observation of a solar flare using exceptionally high resolution images from the 1.6 m New Solar Telescope (NST) equipped with high order adaptive optics at Big Bear Solar Observatory (BBSO). The observation reveals the process of the flare in unprecedented detail, including the flare ribbon propagating across the sunspots, coronal rain (made of condensing plasma) streaming down along the post-flare loops, and the chromosphere’s response to the impact of coronal rain, showing fine-scale brightenings at the footpoints of the falling plasma. Taking advantage of the resolving power of the NST, we measure the cross-sectional widths of flare ribbons, post-flare loops and footpoint brighenings, which generally lie in the range of 80–200 km, well below the resolution of most current instruments used for flare studies. Confining the scale of such fine structure provides an essential piece of information in modeling the energy transport mechanism of flares, which is an important issue in solar and plasma physics.

  7. Unprecedented Fine Structure of a Solar Flare Revealed by the 1.6 m New Solar Telescope.

    PubMed

    Jing, Ju; Xu, Yan; Cao, Wenda; Liu, Chang; Gary, Dale; Wang, Haimin

    2016-01-01

    Solar flares signify the sudden release of magnetic energy and are sources of so called space weather. The fine structures (below 500 km) of flares are rarely observed and are accessible to only a few instruments world-wide. Here we present observation of a solar flare using exceptionally high resolution images from the 1.6 m New Solar Telescope (NST) equipped with high order adaptive optics at Big Bear Solar Observatory (BBSO). The observation reveals the process of the flare in unprecedented detail, including the flare ribbon propagating across the sunspots, coronal rain (made of condensing plasma) streaming down along the post-flare loops, and the chromosphere's response to the impact of coronal rain, showing fine-scale brightenings at the footpoints of the falling plasma. Taking advantage of the resolving power of the NST, we measure the cross-sectional widths of flare ribbons, post-flare loops and footpoint brighenings, which generally lie in the range of 80-200 km, well below the resolution of most current instruments used for flare studies. Confining the scale of such fine structure provides an essential piece of information in modeling the energy transport mechanism of flares, which is an important issue in solar and plasma physics. PMID:27071459

  8. Unprecedented Fine Structure of a Solar Flare Revealed by the 1.6 m New Solar Telescope

    PubMed Central

    Jing, Ju; Xu, Yan; Cao, Wenda; Liu, Chang; Gary, Dale; Wang, Haimin

    2016-01-01

    Solar flares signify the sudden release of magnetic energy and are sources of so called space weather. The fine structures (below 500 km) of flares are rarely observed and are accessible to only a few instruments world-wide. Here we present observation of a solar flare using exceptionally high resolution images from the 1.6 m New Solar Telescope (NST) equipped with high order adaptive optics at Big Bear Solar Observatory (BBSO). The observation reveals the process of the flare in unprecedented detail, including the flare ribbon propagating across the sunspots, coronal rain (made of condensing plasma) streaming down along the post-flare loops, and the chromosphere’s response to the impact of coronal rain, showing fine-scale brightenings at the footpoints of the falling plasma. Taking advantage of the resolving power of the NST, we measure the cross-sectional widths of flare ribbons, post-flare loops and footpoint brighenings, which generally lie in the range of 80–200 km, well below the resolution of most current instruments used for flare studies. Confining the scale of such fine structure provides an essential piece of information in modeling the energy transport mechanism of flares, which is an important issue in solar and plasma physics. PMID:27071459

  9. Unprecedented Fine Structure of a Solar Flare Revealed by the 1.6~m New Solar Telescope

    NASA Astrophysics Data System (ADS)

    Jing, Ju; Xu, Yan; Cao, Wenda; Liu, Chang; Gary, Dale E.; Wang, Haimin

    2016-05-01

    Solar flares signify the sudden release of magnetic energy and are sources of so called space weather. The fine structures (below 500 km) of flares are rarely observed and are accessible to only a few instruments world-wide. Here we present observation of a solar flare using exceptionally high resolution images from the 1.6~m New Solar Telescope (NST) equipped with high order adaptive optics at Big Bear Solar Observatory (BBSO). The observation reveals the process of the flare in unprecedented detail, including the flare ribbon propagating across the sunspots, coronal rain (made of condensing plasma) streaming down along the post-flare loops, and the chromosphere's response to the impact of coronal rain, showing fine-scale brightenings at the footpoints of the falling plasma. Taking advantage of the resolving power of the NST, we measure the cross-sectional widths of flare ribbons, post-flare loops and footpoint brighenings, which generally lie in the range of 80-200 km, well below the resolution of most current instruments used for flare studies. Confining the scale of such fine structure provides an essential piece of information in modeling the energy transport mechanism of flares, which is an important issue in solar and plasma physics.

  10. 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.

  11. 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.

  12. 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.

  13. A modeling study of global ionospheric and thermospheric responses to extreme solar flare

    NASA Astrophysics Data System (ADS)

    Le, Huijun; Liu, Libo; Ren, Zhipeng; Chen, Yiding; Zhang, Hui; Wan, Weixing

    2016-01-01

    In this study, we employed a thermosphere and ionosphere coupling model to investigate ionospheric and thermospheric responses to an extreme solar flare of X40. The simulated results show that the peak enhancement of total electron content reaches about 35 TECU (total electron content unit, 1 TECU = 1016 el m-2), and there are as long as more than 4 h ionospheric disturbances induced by the extreme solar flare. At the same time, the extreme solar flare causes significant disturbances in the thermosphere. The peak enhancement of neutral density at 400 km reaches more than 100%, and the peak enhancement in neutral temperature at 400 km is about 250 K. Several numerical experiments for different class solar flares were further carried out to study the ionosphere and thermosphere variations with solar flare level. The results show that the increasing amplitude of electron density at low altitude decreases with increasing flare level; however, the increasing amplitude of electron density at topside ionosphere increases with increasing flare level. The thermosphere density has the same variation trends with flare level. These results suggest that the extreme solar flare would cause the strong disturbances at high height.

  14. Solar neutron events in association with large solar flares in November 2003

    NASA Astrophysics Data System (ADS)

    Watanabe, K.; Muraki, Y.; Matsubara, Y.; Murakami, K.; Sako, T.; Miranda, P.; Ticona, R.; Velarde, A.; Kakimoto, F.; Ogio, S.; Solar Neutron Observation Group

    The Sun was intensely active from the late October to the beginning of November 2003. A series of eleven X-class solar flares were observed during October 19 and November 5, 2003, in NOAA regions 484, 486 and 488. Among them, in the flares on November 2, 3 and 4, solar neutrons were observed by the ground based neutron monitors and the solar neutron telescopes located around the world. At 17:03 UT on November 2, 2003, an X8.3 class solar flare was occurred in NOAA active region 486. Solar neutrons in association with this flare were detected by the neutron monitor located at Mt. Chacaltaya, Bolivia (292.0°E, 16.2°S, 5250 m a.s.l.). The statistical significance of this event was 4.5 σ. The solar neutron event of November 3, 2003, was detected by the Hawaii solar neutron telescope located at Mauna Kea (203.7°E, 19.8°N, 4200 m a.s.l.), in association with an X2.7 class flare occurred at 1:09 UT. The statistical significance of this event was 4.7 σ. Excesses for this event were detected from the direction of the sun. On November 4, 2003, an X28 class solar flare, which is the largest flare on record, was detected at 19:29 UT. Solar neutrons were also observed by the neutron monitor at Mt. Haleakala, Hawaii (20.7°N, 203.7°E, 3030 m a.s.l.). The statistical significance of this event was 5.3 σ. In these flares, intense emission of hard X-rays and γ-rays have been observed by the RHESSI satellite. At the solar neutron event of November 2, 2003, the 800-7000 keV high energy channel of the RHESSI satellite observed clear excesses. And in particular, a large amount of 2.223 MeV neutron capture line γ-rays was observed. On November 3, 2003, there was no significant enhancement of 2.223 MeV γ-rays, however, the intense emission of 300 - 800 keV γ-rays has been observed. During the solar flare occurred on November 4, 2003, RHESSI satellite could not observe the solar flare because it was the night side of the Earth. However, GOES satellite observed rapid increase of soft X-rays at 19:42 UT. It seems that solar neutrons were produced at the same time as the production time of these hard electromagnetic radiations. In this paper, we report these solar neutron events and describe analysis results.

  15. 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.

  16. 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...

  17. 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...

  18. 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...

  19. MAGNETIC STRUCTURE PRODUCING X- AND M-CLASS SOLAR FLARES IN SOLAR ACTIVE REGION 11158

    SciTech Connect

    Inoue, S.; Magara, T.; Choe, G. S.; Hayashi, K.; Shiota, D.

    2013-06-10

    We study the three-dimensional magnetic structure of the solar active region 11158, which produced one X-class and several M-class flares on 2011 February 13-16. We focus on the magnetic twist in four flare events, M6.6, X2.2, M1.0, and M1.1. The magnetic twist is estimated from the nonlinear force-free field extrapolated from the vector fields obtained from the Helioseismic and Magnetic Imager on board the Solar Dynamic Observatory using the magnetohydrodynamic relaxation method developed by Inoue et al. We found that strongly twisted lines ranging from half-turn to one-turn twists were built up just before the M6.6 and X2.2 flares and disappeared after that. Because most of the twists remaining after these flares were less than a half-turn twist, this result suggests that the buildup of magnetic twist over the half-turn twist is a key process in the production of large flares. On the other hand, even though these strong twists were also built up just before the M1.0 and M1.1 flares, most of them remained afterward. Careful topological analysis before the M1.0 and M1.1 flares shows that the strongly twisted lines were surrounded mostly by the weakly twisted lines formed in accordance with the clockwise motion of the positive sunspot, whose footpoints are rooted in strong magnetic flux regions. These results imply that these weakly twisted lines might suppress the activity of the strongly twisted lines in the last two M-class flares.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Laboratory solar flare simulation using colinear bipolar flux pairs

    SciTech Connect

    Crockett, G.A.

    1980-01-01

    The plasma physics process of magnetic field line reconnection is experimentally studied in a Double Solenoid Device (DSD). The DSD incorporates the magnetic topology that Sweet (1958) postulated as necessary for a process where the magnetic fields of two bipolar sun spot groups 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 ..mu..f high voltage capacitor bank through four linear 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 (200 millitorr) Argon gas filling the bell jar above the solenoids. The total magnetic field, difference magnetic field, and current densities were measured in the central vertical plane containing the solenoid spots. The magnetic fields reconnected in a quiescent fashion with only a weak and diffuse collisional current system induced near the neutral point region. The currents concentrated above each bipolar flux pair and was explained by an MHD Hall generator effect. The difference magnetic field showed only rough agreement with Sweet's prediction that there should be an O-type topology coincident with the x-topology. The measured reconnected plasma flux lagged the vacuum flux until 20 ..mu..s, i.e. near the end of the first quarter cycle, when they became equal.

  5. 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 Δ 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.

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

    NASA Technical Reports Server (NTRS)

    Newton, Elizabeth; Giblin, Timothy

    1999-01-01

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

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Magnetic Reconnection of Solar Flare Detected by Solar Radio Burst Type III

    NASA Astrophysics Data System (ADS)

    Hamidi, Z. S.; Shariff, N. N. M.; Ibrahim, Z. A.; Monstein, C.; Zulkifli, W. N. A. Wan; Ibrahim, M. B.; Arifin, N. S.; Amran, N. A.

    2014-10-01

    The Sun is an ideal object of a blackbody with a large and complex magnetic field. In solar activity specifically solar flare phenomenon, the magnetic reconnection is one of the most significant factors of the Sun that can simplify a better understanding of our nearest star. This factor is due to the motion of the plasma and other particles through the convection mechanism inside the Sun. In our work, we will highlight one of the solar burst events that associated with solar flares. This event occurred on 13th November 2012 from 2:00:03 UT till 2:00:06 UT. It peaked with M2.0 solar flare at 2.04 UT. Within short time intervals of about l02 ~ 103s, large quantities of energy of 1022 ~ 1026J are emancipated. The changing magnetic field converts magnetic potential energy into kinetic energy by accelerating plasmas in the solar corona. It is believed that the plasma is channelled by the magnetic field up and away from the Sun. It is also accelerated back down along the magnetic field into the chromosphere. In conclusion, we showed that the structure of the solar radio burst type III is an indicator of a starting point of magnetic reconnection.

  13. 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.

  14. Solar flare protons and alpha particles during the last three solar cycles

    NASA Technical Reports Server (NTRS)

    Goswami, J. N.; Mcguire, R. E.; Reedy, R. C.; Lal, D.; Jha, R.

    1988-01-01

    This paper presents solar-flare-associated proton and alpha-particle fluxes determined for major events from October 1972 through March 1987 (the period that represents the last part of solar cycle 20 and the whole of solar cycle 21), using data obtained by detectors on board the IMP-7 and IMP-8 satellites, along with earlier obtained data for cycle 20. It was found that the average omnidirectional flux of protons with kinetic energy above 10 MeV for cycle 21 (64/sq cm per sec) is lower than the corresponding number for cycle 20 (92/sq cm per sec) and for the cycle 19 (378/sq cm per sec). No definitive correlation was found to exist between cycle-averaged solar flare proton fluxes and peak sunspot numbers.

  15. Relativistic-Electron-Dominated Solar Flares Observed by Fermi/GBM

    NASA Astrophysics Data System (ADS)

    Shih, A. Y.; Schwartz, R. A.; Dennis, B. R.

    2013-12-01

    Up to tens of percent of the energy released in solar flares goes into accelerating electrons above ~10 keV and ions above ~1 MeV, and the impulsive heating of the ambient solar atmosphere by these particles is partially or wholly responsible for the production of hot flare plasmas (up to ~50 MK). Although flares can accelerate electrons to relativistic energies, in even large flares the typical falling power-law energy spectrum means that the plasma is primarily heated by the much larger number of low-energy electrons. However, there have been flares observed where the electron energy spectra have high low-energy cutoffs (well above ~100 keV), which significantly changes the electron energies responsible for heating and modifies the usual conception of energy transport in a flare. A systematic study of a range of relativistic-electron-dominated flares can improve our understanding of the relevant acceleration processes and how they may differ from those in "typical" flares. We search the Fermi/GBM data set for such flares based on the electron-associated X-ray/gamma-ray bremsstrahlung emission, making use of an improved background-subtraction approach to improve the ability to detect weaker flares. We present the fitted parameters for the relativistic-electron spectrum and their evolution over time, and compare against RHESSI observations and other instruments when available. We also discuss these events in the context of previously observed correlations between relativistic-electron acceleration and ion acceleration in flares.

  16. A STATISTICAL STUDY OF THE RELATIONSHIP BETWEEN THE TRANSPORT RATE OF MAGNETIC HELICITY AND SOLAR FLARES

    SciTech Connect

    Zhang Yin; Tan Baolin; Yan Yihua

    2009-10-20

    We present a statistical study which is aimed at understanding the fact that some flares (type I flare) are associated with sharp variations of the transport rate of magnetic helicity (dH/dt) while others are not (type II flare). The sample consists of 49 M-class and X-class flares which were produced by nine isolated active regions. Using high temporal magnetograms obtained by the Michelson Doppler Imager instrument on the Solar and Heliospheric Observatory, we calculate the temporal variation of dH/dt during the flaring time, and compare its profile with the soft X-ray flux. We find that type I flares have longer duration and higher peak flux in soft X-ray than type II flares. Furthermore, the ratio of the total unsigned magnetic flux of the host active region to that of the visible solar disk is also higher for type I flares, while the total flux itself is independent of the flare type. Our results show that whether the flare is associated with sharp variations of dH/dt depends on the properties of the flare and of its host active region. The relationship between dH/dt and microwave bursts is also discussed.

  17. 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.

  18. Relationship of great soft X-ray flares with other solar activity phenomena

    NASA Astrophysics Data System (ADS)

    Verma, V. K.

    2011-07-01

    We present study of relationship of GSXR flares with H α flares, hard X-ray (HXR) bursts, microwave (MW) bursts at 15.4 GHz, type II/IV radio bursts, coronal mass ejections (CMEs), protons flares (>10 MeV) and ground level enhancement (GLE) events we find that about 85.7%, 93%, 97%, 69%, 60%, 11.1%, 79%, 46%, and 23%% GSXR flares are related/associated with observed H α flares, HXR bursts, MW bursts at 15.4 GHz, type II radio bursts, type IV radio bursts, GLE events, CMEs, halo CMEs, and proton flares (>10 MeV), respectively. In the paper we have studied the onset time delay of GSXR flares with H α flares, HXR, and MW bursts which shows the during majority GSXR flares SXR emissions start before the H α, HXR and MW emissions, respectively while during 15-20% of GSXR flares the SXR emissions start after the onset of H α, HXT and MW emissions, respectively indicating two types of solar flares. The, onset time interval between SXR emissions and type II radio bursts, type IV radio bursts, GLE events CMEs, halo CMEs, and protons flares are 1-15 min, 1-20 min, 21-30 min, 21-40 min, 21-40 min, and 1-4 hrs, respectively. Following the majority results we are of the view that the present investigations support solar flares models which suggest flare triggering first in the corona and then move to chromospheres/ photosphere to starts emissions in other wavelengths. The result of the present work is largely consistent with "big flare syndrome" proposed by Kahler (1982).

  19. 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.

  20. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  2. 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

  3. 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.

  4. 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).

  5. Multi-scale Numerical Approach to Solar Flare Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Bárta, M.; Karlický, M.; Nickeler, D.

    2008-09-01

    Magnetic reconnection - considered now commonly as the engine of solar flares - spans over many mutually coupled scales from the global flare dimensions (approximately 10 Mm) down to the scale, where dissipation through kinetic effects take place (approximately 10 m). Direct numerical simulation covering all the scales is therefore impossible for obvious reasons: full 3D numerical model would have to involve 1018 grid points. Nevertheless, the filamentary nature of the current sheet fragmentation give us the chance to describe the process of reconnection with highly reduced request for number of grid points. As the smaller-scale dynamics is interesting only in regions of enhanced current sheet filamentation, we can focus just on these areas, which occupy only a small fraction of the total volume. Generally, as the fragmentation continues, it forms a cascade (finished by the kinetic dissipation) where information relevant for description of the smaller-scale level occupies only a small fraction of grid points describing the higher level. Thus, one can subsequently zoom-in onto the regions of continuing current filamentation. Anticipated current-sheet-fragmentation cascade supposes multiple dissipative regions formed in a single current sheet - this fact can play a key role for direct particle acceleration in reconnection. The numerical algorithm implementing this 'zooming' technique and the first results will be presented.

  6. 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.

  7. 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.

  8. New interactive solar flare modeling and advanced radio diagnostics tools

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

    The coming years will see routine use of solar data of unprecedented spatial and spectral resolution, time cadence, and completeness in the wavelength domain. To capitalize on the soon to be available radio facilities such as the expanded OVSA, SSRT and FASR, and the challenges they present in the visualization and synthesis of the multi-frequency datasets, we propose that realistic, sophisticated 3D active region and flare modeling is timely now and will be a forefront of coronal studies over the coming years. Here we summarize our 3D modeling efforts, aimed at forward fitting of imaging spectroscopy data, and describe currently available 3D modeling tools. We also discuss plans for future generalization of our modeling tools.

  9. 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.

  10. Time extended production of neutrons during a solar flare

    NASA Technical Reports Server (NTRS)

    Chupp, E. L.; Forrest, D. J.; Vestrand, W. T.; Dubrunner, H.; Flueckiger, E. O.; Cooper, J. F.; Kanbach, G.; Reppin, C.; Share, G. H.

    1985-01-01

    The most energetic neutral emissions expected from solar flares are gamma rays (10 MeV) from relativistic primary and secondary electron bremsstrahlung,from approx 0 meson decay, and from neutrons ( 50 MeV). Bremsstrahlung photon energies extend to that of the highest energy electron present, but the shape of the pi sup 0 gamma ray spectrum, peaking at 69 MeV, does not depend strongly on the proton spectrum above threshold, which is approx. 292 MeV for meson production on protons. The highest energy neutrons observed indicate directly the highest energy ions which interact at the Sun, and the presence or absence of anergy cutoff in the acceleration process. The high-energy proton spectrum shape can be determined from the neutron spectrum.

  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. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

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

    SciTech Connect

    Krucker, Säm; 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.

  18. DETERMINATION OF STOCHASTIC ACCELERATION MODEL CHARACTERISTICS IN SOLAR FLARES

    SciTech Connect

    Chen, Qingrong; Petrosian, Vahé

    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.

  19. 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.

  20. Automatic Short-Term Solar Flare Prediction Using Machine Learning and Sunspot Associations

    NASA Astrophysics Data System (ADS)

    Qahwaji, R.; Colak, T.

    2007-03-01

    In this paper, a machine-learning-based system that could provide automated short-term solar flare prediction is presented. This system accepts two sets of inputs: McIntosh classification of sunspot groups and solar cycle data. In order to establish a correlation between solar flares and sunspot groups, the system explores the publicly available solar catalogues from the National Geophysical Data Center to associate sunspots with their corresponding flares based on their timing and NOAA numbers. The McIntosh classification for every relevant sunspot is extracted and converted to a numerical format that is suitable for machine learning algorithms. Using this system we aim to predict whether a certain sunspot class at a certain time is likely to produce a significant flare within six hours time and if so whether this flare is going to be an X or M flare. Machine learning algorithms such as Cascade-Correlation Neural Networks (CCNNs), Support Vector Machines (SVMs) and Radial Basis Function Networks (RBFN) are optimised and then compared to determine the learning algorithm that would provide the best prediction performance. It is concluded that SVMs provide the best performance for predicting whether a McIntosh classified sunspot group is going to flare or not but CCNNs are more capable of predicting the class of the flare to erupt. A hybrid system that combines a SVM and a CCNN is suggested for future use.

  1. Solar Particle Acceleration and The Gamma Ray Imager/Polarimeter for Solar Flares (GRIPS) Instrument

    NASA Astrophysics Data System (ADS)

    Duncan, Nicole; Shih, A. Y.; Hurford, G. J.; Saint-Hilaire, P.; Bain, H.; Zoglauer, A.; Lin, R. P.; Boggs, S. E.

    2013-04-01

    Flares accelerate ions and relativistic electrons proportionally; the ratio of their fluences has been shown to remain constant over three orders of magnitude, a correlation that is independent of flare size. This evidence suggests that ion and electron populations are accelerated together, and possibly by similar mechanisms. In two of the best-observed flares of the last cycle, the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) satellite found the centroids of ion and relativistic electron associated emission to be significantly displaced from one another. This result is surprising; ions and electrons that are accelerated in the same region are thought to be transported along the same field lines, implying that they would enter the chromosphere together and have similar emission source locations. The Gamma-Ray Imager/Polarimeter for Solar Flares (GRIPS) instrument is designed to address particle transport questions by providing enhanced imaging, spectroscopy and polarimetry of gamma/HXR flare emissions 20 keV to > 10MeV). GRIPS’ key technological improvements over the current solar state of the art in HXR/gamma ray energies (RHESSI) include the use of three dimensional germanium detectors (3D-GeDs) and a single grid modulation collimator design, the multi-pitch rotating modulator (MPRM). The 3D-GeDs allow GRIPS to Compton track energy deposition within the crystal, providing significant background reduction and solar polarization measurements. Imaging will be primarily accomplished through the MPRM grid system. The single grid design provides quasi-continuous resolution from 12.5 - 162arcsecs with 2x the throughput of a dual grid imaging system like RHESSI. This spatial resolution will be capable of imaging the separate footpoints of many flare sizes. In comparison, RHESSI images with a minimum of 35arcsecs at HXR/gamma ray energies, making the footpoints resolvable in only the largest of flares. Here, we present a discussion of GRIPS science goals, an instrument overview and recent developments in GRIPS' imaging and detector systems. GRIPS is scheduled for an engineering flight from Fort Sumner in September of this year, followed by two long duration balloon flights from Antarctica.

  2. GNSS measurement of EUV photons flux rate during strong and mid solar flares

    NASA Astrophysics Data System (ADS)

    HernáNdez-Pajares, M.; GarcíA-Rigo, A.; Juan, J. M.; Sanz, J.; Monte, E.; Aragón-ÀNgel, A.

    2012-12-01

    A new GNSS Solar Flare Activity Indicator (GSFLAI) is presented, given by the gradient of the ionospheric Vertical Total Electron Content (VTEC) rate, in terms of the solar-zenithal angle, measured from a global network of dual-frequency GPS receivers. It is highly correlated with the Extreme Ultraviolet (EUV) photons flux rate at the 26-34 nm spectral band, which is geo-effective in the ionization of the mono-atomic oxygen in the Earth's atmosphere. The results are supported by the comparison of GSFLAI with direct EUV observations provided by SEM instrument of SOHO spacecraft, for all the X-class solar flares occurring between 2001 and 2011 (more than 1000 direct comparisons at the 15 s SEM EUV sampling rate). The GSFLAI sensitivity enables detection of not only extreme X-class flares, but also of variations of one order of magnitude or even smaller (such as for M-class flares). Moreover, an optimal detection algorithm (SISTED), sharing the same physical fundamentals as GSFLAI, is also presented, providing 100% successful detection for all the X-class solar flares during 2000-2006 with registered location outside of the solar limb (i.e., detection of 94% of all of X-class solar-flares) and about 65% for M-class ones. As a final conclusion, GSFLAI is proposed as a new potential proxy of solar EUV photons flux rate for strong and mid solar flares, presenting high sensitivity with high temporal resolution (1 Hz, greater than previous solar EUV irradiance instruments), using existing ground GNSS facilities, and with the potential use as a solar flare detection parameter.

  3. 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.

  4. 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.

  5. Dynamical structure of solar radio burst type III as evidence of energy of solar flares

    NASA Astrophysics Data System (ADS)

    Hamidi, Zety Sharizat Binti

    2013-11-01

    Observations of low frequency solar type III radio bursts associated with the ejection of plasma oscillations localized disturbance is due to excitation atoms in the plasma frequency incoherent radiations play a dominant role at the meter and decimeter wavelengths. Here, we report the results of the dynamical structure of solar flare type III that occurred on 9th March 2012 at National Space Centre, Sg Lang, Selangor, Malaysia by using the CALLISTO system. These bursts are associated with solar flare type M6 which suddenly ejected in the active region AR 1429 starting at 03:32 UT and ending at 05:00 UT with the peak at 04:12 UT. The observation showed an initial strong burst occurred due to strong signal at the beginning of the phase. We also found that both solar burst and flares tend to be a numerous on the same day and probability of chance coincidence is high. It is clearly seen that an impulsive lace burst was detected at 4:24 UT and it is more plausible that the energies are confined to the top of the loop when we compared with X-ray results. Associated with this event was type II with velocities 1285 km/s and type IV radio sweeps along with a full halo Coronal Mass Ejections (CMEs) first seen in SOHO/LASCO C2 imagery at 09/0426 Z. We concluded that the significance of study solar burst type III lies in the fact that the emission at decimetric wavelength comes from the role of magnetic field in active region that may provide the key to the energy release mechanism in a flare.

  6. 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.

  7. 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.

  8. High energy neutron and pion-decay gamma-ray emissions from solar flares

    NASA Astrophysics Data System (ADS)

    Chupp, Edward L.; Ryan, James M.

    2009-01-01

    Solar flare gamma-ray emissions from energetic ions and electrons have been detected and measured to GeV energies since 1980. In addition, neutrons produced in solar flares with 100 MeV to GeV energies have been observed at the Earth. These emissions are produced by the highest energy ions and electrons accelerated at the Sun and they provide our only direct (albeit secondary) knowledge about the properties of the accelerator(s) acting in a solar flare. The solar flares, which have direct evidence for pion-decay gamma-rays, are unique and are the focus of this paper. We review our current knowledge of the highest energy solar emissions, and how the characteristics of the acceleration process are deduced from the observations. Results from the RHESSI, INTEGRAL and CORONAS missions will also be covered. The review will also cover the solar flare capabilities of the new mission, FERMI GAMMA RAY SPACE TELESCOPE, launched on 2008 June 11. Finally, we discuss the requirements for future missions to advance this vital area of solar flare physics.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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...

  14. 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...

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

    NASA Technical Reports Server (NTRS)

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

    1980-01-01

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

  16. Directivity and its energy dependence in solar flare energetic emission

    NASA Technical Reports Server (NTRS)

    Li, Peng

    1995-01-01

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

  17. Solar Eruptive Flares: from Physical Understanding to Probabilistic Forecasting

    NASA Astrophysics Data System (ADS)

    Georgoulis, M. K.

    2013-12-01

    We describe a new, emerging physical picture of the triggering of major solar eruptions. First, we discuss and aim to interpret the single distinguishing feature of tight, shear-ridden magnetic polarity inversion lines (PILs) in solar active regions, where most of these eruptions occur. Then we analyze the repercussions of this feature, that acts to form increasingly helical pre-eruption structures. Eruptions, with the CME progenitor preceding the flare, tend to release parts of the accumulated magnetic free energy and helicity that are always much smaller than the respective budgets of the source active region. These eruption-related decreases, however, are not optimal for eruption forecasting - this role is claimed by physically intuitive proxy parameters that could show increased pre-eruption sensitivity at time scales practical for prediction. Concluding, we show how reconciling this new information - jointly enabled by the exceptional resolution and quality of Hinode and cadence of SDO data - can lead to advances in understanding that outline the current state-of-the-art of our eruption-forecasting capability.

  18. 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.

  19. 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.

  20. 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.

  1. Molecular models need to be tested: the case of a solar flares discoidal HDL model.

    PubMed

    Shih, Amy Y; Sligar, Stephen G; Schulten, Klaus

    2008-06-01

    In the absence of atomic structures of high-density lipoproteins in their lipid-bound states, many molecular models have been produced based on experimental data. Using molecular dynamics, we show that a recently proposed "solar-flares" model of discoidal high-density lipoprotein is implausible. Our simulations show a collapse of the protruding solar-flare loops and a notable protein rearrangement due to an energetically unfavorable orientation of the hydrophobic protein surface toward the aqueous solvent. PMID:18375520

  2. Radio and soft X-ray investigation of the solar flares of February 4, 1986

    NASA Technical Reports Server (NTRS)

    Ji, Shuchen; Ding, Youji; Chen, Guoqiang; Cao, Wenda

    1993-01-01

    The 3B flare of February 4, 1986 is studied comprehensively. The escape electrons accelerated to 10-100 keV at the top of coronal loop are confirmed by type III bursts. The energetic electron beams moved downward trigger the eruptions in the lower layer of the solar atmosphere. The radio and soft X-ray bursts are interpreted, respectively, by the maser mechanism and evaporation effect. Finally, the important role of energetic electron beams in solar flares is pointed out.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Heavy solar cosmic rays in the January 25, 1971 solar flare

    NASA Technical Reports Server (NTRS)

    Pellerin, C. J., Jr.

    1975-01-01

    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 per nucleon. In addition, abundances relative to oxygen are computed for all the above nuclei in the single energy interval from 15 to 25 MeV per 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 per 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.

  8. 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.

  9. 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.

  10. Observational and theoretical interpretation of energetic particle transport in solar flares

    NASA Astrophysics Data System (ADS)

    Daou, Antoun Georges

    The combination of excellent space-based remote sensing, and image reconstruction techniques, as well as improvements in numerical modeling, help enhance our understanding of particle transport in solar flares. We conduct a rigorous analysis of flare hard X-ray emission using the unprecedented spectral and spatial resolution of the RHESSI telescope data in order to better understand the spectral properties of the emitting electron population in solar flares. We complete our study with a forward-fit to the data using a Fokker- Planck kinetic code, to numerically model the particle transport in phase-space in realistic magnetic geometries and for different particle injection profiles.

  11. 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.

  12. How can we interpret and understand pulsations in solar flare emission? A Bayesian model comparison approach.

    NASA Astrophysics Data System (ADS)

    Inglis, Andrew; Ireland, Jack; Dominique, Marie

    2015-04-01

    Recent work has shown that power-law-like Fourier power spectra are an intrinsic property of solar and stellar flare signals, similarly to other astrophysical objects such as gamma-ray bursts and magnetars. It is therefore critical to account for this in order to understand the nature and significance of short-timescale fluctuations in flares.We present the results of a Bayesian model comparison method for investigating flare time series, fully considering these Fourier power-law properties. 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 'quasi-periodic puslation (QPP)' events. While emphasising that the observed fluctuations are real and of solar origin, we find that, for all but one event tested, an explicit oscillation is not required to explain the observations. Instead, the observed flare signals are adequately described as a manifestation of a power law in the Fourier power spectrum. This evaluation of the QPP phenomenon is markedly different from much of the prior literature.We conclude that the prevalence of oscillatory signatures in solar and stellar flares may be less than previously believed. Furthermore, studying the slope of the observed Fourier power spectrum as a function of energy may provide us with a diagnostic window into the fundamental nature of solar flares.

  13. 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.

  14. The contraction of flare loops and its impact on the solar lower atmosphere

    NASA Astrophysics Data System (ADS)

    Ji, H.

    2012-06-01

    This short reviewing article is intended to introduce a possibly existing relevance for three important macroscopic behaviors of solar flares. The behaviors include the contraction of flare loops (implosion), the rapid change of magnetic fields and seismic waves during flares. We show that the phenomena basically reflects a process of rapid restructuring of sheared magnetic field by a release of free magnetic energy. The contraction and rapid magnetic changes might be the direct consequences of the restructuring. Also the flattening of magnetic loops caused by the contraction in the corona will impart momentum down to the photosphere even to the solar interior. Part of the energy transported by the downward momentum can account for seismic waves. All phenomena, putting together, show that the magnetic reconnection process during the early impulsive phase is quite different from during the gradual phase and plays a dominant role in powering solar flares.

  15. 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.

  16. 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.

  17. 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)

  18. Wavelength dependence of solar flare irradiance enhancement and its influence on the thermosphere-ionosphere system

    NASA Astrophysics Data System (ADS)

    Huang, Y.; Richmond, A. D.; Deng, Y.; Qian, L.; Solomon, S. C.; Chamberlin, P. C.

    2012-12-01

    The wavelength dependence of irradiance enhancement during solar flare is one of the important factors in determining how the Thermosphere-Ionosphere (T-I) system responds to flares. To investigate the wavelength dependence of irradiance, the Flare Irradiance Spectral Model (FISM) was run for 34 X-class flares. The results show that the percentage increases of solar irradiance at flare peak 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 the 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 the National Center for Atmospheric Research (NCAR) Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM). While the enhancement of the globally integrated solar energy deposition is largest in the 0 - 14 nm waveband, the impact of solar irradiance enhancement on the thermosphere at 400km is largest for the 25 - 105 nm waveband. The effect of the enhancement of the 122 - 195 nm waveband is small in magnitude, but it decays slowly.

  19. SIMULATING THE EFFECTS OF INITIAL PITCH-ANGLE DISTRIBUTIONS ON SOLAR FLARES

    SciTech Connect

    Winter, Henry D.; Reeves, Katharine K.; Martens, Petrus

    2011-07-10

    In this work, we model both the thermal and non-thermal components of solar flares. The model we use, HYLOOP, combines a hydrodynamic equation solver with a non-thermal particle tracking code to simulate the thermal and non-thermal dynamics and emission of solar flares. In order to test the effects of pitch-angle distribution on flare dynamics and emission, a series of flares is simulated with non-thermal electron beams injected at the loop apex. The pitch-angle distribution of each beam is described by a single parameter and allowed to vary from flare to flare. We use the results of these simulations to generate synthetic hard and soft X-ray emissions (HXR and SXR). The light curves of the flares in Hinode's X-ray Telescope passbands show a distinct signal that is highly dependent on pitch-angle distribution. The simulated HXR emission in the 3-6 keV bandpass shows the formation and evolution of emission sources that correspond well to the observations of pre-impulsive flares. This ability to test theoretical models of thermal and non-thermal flare dynamics directly with observations allows for the investigation of a wide range of physical processes governing the evolution of solar flares. We find that the initial pitch-angle distribution of non-thermal particle populations has a profound effect on loop top HXR and SXR emission and that apparent motion of HXR is a natural consequence of non-thermal particle evolution in a magnetic trap.

  20. Forecasting SEP events with same active region prior flares

    NASA Astrophysics Data System (ADS)

    Kahler, S. W.; Ling, A.; White, S. M.

    2015-02-01

    Forecasting large solar energetic (E > 10 MeV) particle (SEP) events is currently based on observed solar X-ray flare peak fluxes or fluences. Recent work has indicated that the probability of a solar eruptive event in an active region (AR) is enhanced when a large flare has occurred in that AR during the previous day. In addition, peak intensities Sp of SEP events associated with fast coronal mass ejections (CMEs) are larger for CMEs with prior CMEs from the same associated ARs in the previous day. This suggests that the associated SEP event probability and/or Sp may be higher for a given solar X-ray flare with a recent prior major flare in the same AR. We use data sets of NOAA flares and SEP events from solar cycles 22-24 to test this idea statistically for periods of prior flares ranging from 12 to 48 h. The occurrence probabilities and Sp of large SEP events for flares with prior same AR major (≥ M2) flares are not significantly higher than for flares without the prior flares; hence, prior flare occurrence is not a useful SEP event forecasting tool. The flare-based occurrence probabilities are higher for cycle 24 than for cycles 22 and 23, but the dependence of Sp on X-ray fluence appears unchanged. We show an example of a recent flare-prolific AR for which the SEP-associated flares are spatially distinct from the numerous non-SEP associated flares, indicating how prior AR flares may be unrelated to SEP-associated flares.

  1. Observations of Neutrons in Association with the Large Solar Flare of 6 November 1997

    NASA Astrophysics Data System (ADS)

    Tsuchiya, H.; Matsubara, Y.; Muraki, Y.; Murakami, K.; Sako, T.; Kakimoto, F.; Ogio, S.; Tsunesada, Y.; Tokuno, H.; Yoshii, H.; Tajima, N.; Martinic, N.; Miranda, P.; Ticona, R.; Velarde, A.

    2001-08-01

    Solar neutrons were detected by the Mt. Chacaltaya neutron detector in Bolivia (S E, 5250 m above sea level) in association with solar flares on 1997 November 6th. A clear signal was observed in association with a C4.7 solar flare which occurred at about 10 minutes before the X9.4 large solar flare. Previously, there have been no observation of solar neutrons in association with C class solar flares. Moreover, the signal was detected at early in the morning(7:41 Local Time). Therefore, solar neutrons which arrive at the earth must travel through a thick atmosphere to reach the detector because of large incident angle (?) to the atmosphere. In the thick atmosphere, it has been believed that solar neutrons could not arrive at the detector if we applied the usual attenuation model. However, calculations based on a new attenuation model for solar neutrons in the atmosphere, which takes account of multiple and/or large scattering, gives us a new possibility for us detecting solar neutrons under extreme conditions.

  2. Solar flare accelerated isotopes of hydrogen and helium. [observed by IMP-4 and IMP-5

    NASA Technical Reports Server (NTRS)

    Anglin, J. D.; Dietrich, W. F.; Simpson, J. A.

    1973-01-01

    Measurements of solar flare hydrogen, deuterium, tritium, helium-3, and helium-4 in the energy range approximately 10 to 50 MeV per nucleon obtained with instrumentation on the IMP-4 and IMP-5 satellites are reported and studies based on these results which place several constraints on theories of solar flare particle acceleration are discussed. A brief review of previous work and the difficulties in studying the rare isotopes of hydrogen and helium is also included. Particular emphasis is placed on the fact that the information to be obtained from the solar flare products of high energy interactions is not available through either solar wind observations where both the acceleration mechanism and the coronal source of the nuclear species are different, or optical measurements of solar active regions.

  3. 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 Hα 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.

  4. 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.

  5. 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.

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

    SciTech Connect

    Dudík, J.; Del Zanna, G.; Mason, H. E.; Janvier, M.; Aulanier, G.; Schmieder, B.; Karlický, 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 Å 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.

  7. 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.

  8. 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.

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    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.

  10. CORONAL ELECTRON DISTRIBUTION IN SOLAR FLARES: DRIFT-KINETIC MODEL

    SciTech Connect

    Minoshima, Takashi; Kusano, Kanya; Masuda, Satoshi; Miyoshi, Yoshizumi

    2011-05-10

    Using a model of particle acceleration and transport in solar flares, we investigate the height distribution of coronal electrons by focusing on the energy-dependent pitch-angle scattering. When pitch-angle scattering is not included, the peak heights of loop-top electrons are constant, regardless of their energy, owing to the continuous acceleration and compression of the electrons via shrinkage of magnetic loops. On the other hand, under pitch-angle scattering, the electron heights are energy-dependent: intermediate-energy electrons are at a higher altitude, whereas lower and higher energy electrons are at lower altitudes. This implies that the intermediate-energy electrons are inhibited from following the shrinking field lines to lower altitudes because pitch-angle scattering causes efficient precipitation of these electrons into the footpoint and their subsequent loss from the loop. This result is qualitatively consistent with the position of the above-the-loop-top hard X-ray (HXR) source that is located above coronal HXR loops emitted by lower energy electrons and microwaves emitted by higher energy electrons. Quantitative agreement with observations might be achieved by considering primary acceleration before the onset of loop shrinkage and additional pitch-angle scattering via wave-particle interactions.

  11. 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.

  12. 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.

  13. Search for solar neutrons associated with series of X-class flares during the declining period of solar cycle 23

    NASA Astrophysics Data System (ADS)

    Matsubara, Y.; Muraki, Y.; Sako, T.; Watanabe, K.; Sakai, T.; Shibata, S.; Flueckiger, E.; Buetikofer, R.; Chilingarian, A.; Hovsepyan, G.; Tan, Y.H.; Yuda, T.; Ohonishi, M.; Tsuchiya, H.; Katayose, Y.; Ogasawara, R.; Mizumoto, Y.; Kakimoto, F.; Tsunesada, Y.; Velarde, A.; Ticona, R.; Martinic, N.; Miranda, P.; Valdes-Galicia, J.F.; Gonzalez, L.X.; Hurtado, A.; Musale, O.

    It was surprising that Gigantic solar flares exceeding X-class occurred 10 times in September, 2005, because the activity of the Sun had already been in the declining period. More surprisingly, 4 X-class solar flares occurred in December, 2006, when the activity of the Sun was at the minimum. It is expected that some of these flares were accompanied by the acceleration of ions, which would be observed as solar neutrons or GLEs on the ground. Solar neutron telescopes, which are dedicated to observe solar neutrons and to measure their energies, have been operating during solar cycle 23. Distributed in a worldwide network covering all longitudes they watch the Sun 24 hours a day. In this paper, we report on results of the search for solar neutron events associated with these 14 X-class flares, using data obtained by this international network of solar neutron telescopes. There was no clear evidence for detecting solar neutrons within these periods, except for the significant detection of solar neutrons on September 7, 2005. Details of this particular event will be presented by Sako et al. during this Conference.

  14. 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

  15. 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.

  16. The Impact of Return-Current Losses on the Observed Emissions from Solar Flares

    NASA Technical Reports Server (NTRS)

    Holman, Gordon D.

    2011-01-01

    Electrons accelerated in solar flares are expected to drive a co-spatial return current in the ambient plasma when they escape the acceleration region. This return current maintains plasma neutrality and the stability of the beam of streaming electrons. The electric field that drives this return current also decelerates the energetic electrons in the beam. The corresponding energy loss experienced by the accelerated electrons can affect the observed properties of the X-ray and radio emissions from flares and the evolution of the thermal flare plasma. I will discuss the properties of the flare emissions expected in a classical, steady-state model. As part of this discussion, I will examine Gordon Emslie's 1980 conjecture that return-current losses result in a maximum brightness for the hard X-ray emission from flares.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Geometrical properties of avalanches in self-organized critical models of solar flares.

    PubMed

    McIntosh, Scott W; Charbonneau, Paul; Bogdan, Thomas J; Liu, Han-Li; Norman, James P

    2002-04-01

    We investigate the geometrical properties of avalanches in self-organized critical models of solar flares. Traditionally, such models differ from the classical sandpile model in their formulation of stability criteria in terms of the curvature of the nodal field, and belong to a distinct universality class. With a view toward comparing these properties to those inferred from spatially and temporally resolved flare observations, we consider the properties of avalanche peak snapshots, time-integrated avalanches in two and three dimensions, and the two-dimensional projections of the latter. The nature of the relationship between the avalanching volume and its projected area is an issue of particular interest in the solar flare context. Using our simulation results we investigate this relationship, and demonstrate that proper accounting of the fractal nature of avalanches can bring into agreement hitherto discrepant results of observational analyses based on simple, nonfractal geometries for the flaring volume. PMID:12005944

  5. Temporal and spatial relationships between O V and Fe XXI emissions in solar flares

    NASA Technical Reports Server (NTRS)

    Cheng, Chung-Chieh; Pallavicini, Roberto

    1988-01-01

    The temporal-spatial structure of simple solar flares observed with the Ultraviolet Spectrometer and Polarimeter of the Solar Maximum mission satellite has been studied in order to investigate the relationships between the impulsive O V and the gradual Fe XXI emissions. The point-like flares are characterized by the cotemporal evolution of the O V and Fe XXI emissions. The simple loop flares have a much larger spatial extent and show two distinctive phases: an initial impulsive phase with its emission localized in loop footpoints, and a gradual phase with its emission distributed in the loop. The temporal evolution of the Fe XXI and O V emissions in a flare is found to be closely related to its spatial structure.

  6. 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.

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

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

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

  8. 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).

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Comparison of long-term trend of solar radius with sunspot activity and flare index

    NASA Astrophysics Data System (ADS)

    Kilic, H.; Golbasi, O.

    2011-07-01

    Results are presented from a study of solar radius measurements taken with the solar astrolabe at the TUBITAK National Observatory (TUG) over seven years, 2001-2007. The data series with standard deviation of 0.35 arcsec shows the long-term variational trend with 0.04 arcsec/year. On the other hand, the data series of solar radius are compared with the data of sunspot activity and H- α flare index for the same period. Over the seven year trend, we have found significant linear anti-correlations between the solar radius and other indicators such as sunspot numbers, sunspot areas, and H- α flare index. While the solar radius displays the strongest anti-correlation (-0.7676) with sunspot numbers, it shows a significant anti-correlation of -0.6365 with sunspot areas. But, the anti-correlation between the solar radius and H- α flare index is found to be -0.4975, slightly lower than others. In addition, we computed Hurst exponent of the data sets ranging between 0.7214 and 0.7996, exhibiting the persistent behavior for the long term trend. In the light of the strong correlations with high significance, we may suggest that there are a causal relationship between the solar radius and solar time series such as sunspot activity and H- α flare index.

  17. 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.

  18. Spectral response of the solar atmosphere to an X-class flare event

    NASA Astrophysics Data System (ADS)

    Lacatus, Daniela Adriana; Donea, Alina

    2016-05-01

    The only X-class flare of 2015 observed by IRIS occurred at 16:22 UT on 11 March 2015, in AR 12297. This flare generated significant seismic transients in the photosphere at the eastern location of the flare. IRIS observations of the chromosphere and transition region help us understand the physics of the sunquake. In this work we will analyse this event using data from IRIS, SDO, and RHESSI. The IRIS rasters scanned the area between the main footpoints of the solar flare, and a wealth of chromospheric information has been inferred about the dynamics of the event. The main X-ray emission dominates the eastern flare footpoint, being missed by the IRIS slit. Significant enhancements in the chromospheric and TR lines intensities were identified. The forbidden line of Fe XXI 1354.1 Å is detected after the flare peak revealing the coronal responses to the flare. Plasma downflows of up to 300 km/s were identified in the majority of the observed lines, consistent with magnetic field local reconfiguration. We have also analysed an erupting filament developing at an earlier time, which moved rapidly towards the eastern part of the active region. We discuss the possibility that this filament might have pre-conditioned the chromosphere for the flare process.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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).

  5. 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.

  6. 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.

  7. The origins of space weather: recent advances in understanding solar flares

    NASA Astrophysics Data System (ADS)

    Browning, Philippa

    “Space weather” events affecting the terrestrial magnetosphere have their origins in explosive events in the solar atmosphere, notably solar flares. Solar flares may affect the magnetosphere through EUV/X-ray radiation and energetic charged particles (both ions and electrons) , as well as the production of Coronal Mass Ejections (CMEs). A brief overview of our current theoretical and observational understanding of solar flares will be given, focusing on the generation of radiation, particles and CMEs. Recent new models of the acceleration of charged particles by magnetic reconnection in large-scale current sheets solar flares will be described, showing how populations of both trapped and escaping non-thermal particles are generated - the latter propagating into the heliosphere. Test particle and particle-in-cell modelling allow prediction of the time evolution of energy spectra and pitch angles of energetic particles, and their spatial distributions. Smaller, confined flares may occur due to instabilities in twisted magnetic loops. Recent modelling of the heating and particle acceleration in unstable twisted loops will be described, using a coupled magnetohydrodynamic and test particle approach. The time dependence of the radiation in EUV and soft X-rays, due to plasma heating, as well as the Hard X-rays associated with the non-thermal particles are forward-modelled, allowing comparison with data from SDO and RHESSI, and radio instruments.

  8. 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.

  9. 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.

  10. 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.

  11. 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; Mészárosová, Hana; Karlický, 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.

  12. 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; Mészárosová, Hana; Karlický, 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.

  13. Hydrogen over helium enhancement in successive solar flare particle events from the same active region

    NASA Technical Reports Server (NTRS)

    Briggs, P. R.; Armstrong, T. P.; Krimigis, S. M.

    1979-01-01

    An analysis of all of the identified solar-flare-associated energetic particle events in the 1972-1975 period observed with instruments aboard the IMP 7 and IMP 8 satellites has revealed at least eight occasions when more than one particle-producing flare occurred within the same McMath active plage region during its transit of the visible solar disk. A strong tendency for second flares to produce hydrogen over helium (p/alpha) enhanced energetic particle fluxes when compared with the first flare in the 1.8-10.0 MeV per nucleon range emerged in these multiflare regions. The p/alpha enhancement is apparently transient, and for flares separated by at least about 100 hours the p/alpha ratio tends toward its preflare value. It is suggested that the substrate plasma in an active region may be enriched prior to a flare in elements heavier than hydrogen and the composition may not be significantly altered during subsequent acceleration, escape, and propagation. Thus, the preflare history of the active region must be added to the list of factors influencing observed solar-particle-event composition.

  14. 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.

  15. 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.

  16. 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).

  17. 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.

  18. 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.

  19. 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.

    2016-03-01

    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 Hα 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 Hα, 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 Hα.

  20. Hα Linear Polarization Observations of Solar Flares: The Search for Proton Beams

    NASA Astrophysics Data System (ADS)

    Johns-Krull, C. M.; Fisher, G. H.; Varsik, J.; Marquette, W.

    2000-05-01

    The role of ~ 100 keV proton beams in flare energy transport is currently unknown. Claims in the literature range from an energetically negligible role for such protons during flares to claims that 100 keV proton beams carry the majority of the energy released in the corona to the photosphere during a solar flare. Much of the uncertainty concerning protons is due to the fact that 100 keV protons produce very few distinguishable radiative emissions. One such distinguishing emission is the production of linear polarization in the core of the Hα emission line during the impulsive phase of a solar flare. This linear polarization is produced as accelerated, directed, protons collide with ambient hydrogen atoms in the solar chromosphere. The geometry of the situation is such that the linear polarization should be strongest at the limb of the Sun and vanish at disk center, while the orientation of the polarization should always be along the line between the flare location and disk center. The expected signal is 5 -- 10% linear polarization at the limb. We have modified the Big Bear Solar Observatory (BBSO) video magnetograph (VMG) to operate in the core of the Hα line. Here, we present observations of a handful of solar flares using this system. We show that our sensitivity level is ~ 1%, and we discuss in detail observations of a long duration GOES class M2 flare observed at the West limb on 5 August 1999. CMJ-K would like to acknowledge partial funding support of this work by CalSpace.