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1

A Comparison of Reported Solar Flare Occurrence Times and Flare Patrol Times, 1955-1964.  

National Technical Information Service (NTIS)

A flare event list that is consistent with flare patrol times is prerequisite to a reliable, unbiased estimate of flare occurrence per unit patrol time. A comparison of the flare occurrence times and flare patrol times reported by 52 solar observatories d...

R. T. Podsiadlo H. R. Baker

1967-01-01

2

Solar Flare Occurrence Rate and Waiting Time Statistics  

NASA Astrophysics Data System (ADS)

We use Renewal Theory for the estimation and interpretation of the flare rate from the Geostationary Operational Environmental Satellite (GOES) soft X-ray flare catalogue. It is found that, in addition to the flare rate variability with the solar cycles, a much faster variation occurs. The fast variation on time scales of days and hours down to minute scale appears to be comparable with time intervals between two successive flares (waiting times). The detected fast non-stationarity of the flaring rate is discussed in the framework of the previously published stochastic models of the waiting time dynamics.

Gorobets, A.; Messerotti, M.

2012-12-01

3

Periodicities in the occurrence of Solar Flare, Coronal Mass Ejection and Sunspot Area in Solar Cycle 23-24  

NASA Astrophysics Data System (ADS)

In order to investigate the relationship between magnetic flux emergence, solar flares and Coronal Mass Ejection (CME), we study the periodicity in the time series of these quantities. It has been known that solar flares, sunspot area and photospheric magnetic flux have a dominant periodicity of about 155 days. However, the time-period relationship obtained using a Morlet wavelet shows that the periodicity is confined to a part of solar cycle and is non repeating. We present the time series analysis of sunspot area, flare and CME occurrence during cycle 23 and the rising phase of cycle 24 from 1996 to 2011. We find that the flux emergence has multiple periodicities. Flares and CMEs, however, do not occur with the same period as the flux emergence. Using the results of this study, we discuss the possible activity sources producing emerging flux.

Choudhary, D. P.

2012-12-01

4

Solar Flares  

NASA Technical Reports Server (NTRS)

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

Savage, Sabrina

2013-01-01

5

Solar Flares  

NASA Technical Reports Server (NTRS)

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

Shih, Albert

2011-01-01

6

Different Periodicities in the Sunspot Area and the Occurrence of Solar Flares and Coronal Mass Ejections in Solar Cycle 23 - 24  

NASA Astrophysics Data System (ADS)

In order to investigate the relationship between magnetic-flux emergence, solar flares, and coronal mass ejections (CMEs), we study the periodicity in the time series of these quantities. It has been known that solar flares, sunspot area, and photospheric magnetic flux have a dominant periodicity of about 155 days, which is confined to a part of the phase of the solar cycle. These periodicities occur at different phases of the solar cycle during successive phases. We present a time-series analysis of sunspot area, flare and CME occurrence during Cycle 23 and the rising phase of Cycle 24 from 1996 to 2011. We find that the flux emergence, represented by sunspot area, has multiple periodicities. Flares and CMEs, however, do not occur with the same period as the flux emergence. Using the results of this study, we discuss the possible activity sources producing emerging flux.

Choudhary, D. P.; Lawrence, J. K.; Norris, M.; Cadavid, A. C.

2014-02-01

7

Parameterization of solar flare dose  

SciTech Connect

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

Lamarche, A.H. [Commissariat a l`Energie Atomique, Fontenay-aux-Roses (France); Poston, J.W. [Texas A& M Univ., College Station, TX (United States)

1996-12-31

8

Frequency dependence of solar flare occurrence rates—inferred from power-law distribution  

NASA Astrophysics Data System (ADS)

Based on the frequency dependence of the power-law distribution of the peak fluxes in 486 radio bursts in 1-35 GHz observed by Nobeyama Radio Polarimeters (see Song et al. in Astrophys. J. 750:160, 2012), we have first suggested in this paper that the events with power-law behaviors may be emitted from the optically-thin regions, which can be considered as a good measure for the flare energy release. This result is supported by that both the power-law and optical-thin events gradually increase with radio frequencies, which are well fitted by a power-law function with similar indices of 0.48 and 0.80, respectively. Moreover, a flare occurrence rate is newly defined by the power-law event number in per unit frequency. Its values in lower frequencies are evidently larger than those in higher frequencies, which just imply that most flares are trigged in higher corona. Hence, the frequency variation of power-law event number may indicate different energy dissipation rates on different coronal heights.

Song, Qiwu; Huang, Guangli; Huang, Yu

2013-09-01

9

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

NASA Technical Reports Server (NTRS)

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

Bai, T.

1993-01-01

10

Predictability of Solar Flares  

NASA Astrophysics Data System (ADS)

Solar flares are significant drivers of space weather. With the availability of high cadence solar chromospheric and photospheric data from the USAF's Optical Solar PAtrol Network (OSPAN; photosphere and chromosphere imaging) Telescope and the Global Oscillations Network Group (GONG; photosphere magnetic imaging), at the National Solar Observatory, we have gained insights into potential uses of the data for solar flare prediction. We apply the Principal Component Analysis (PCA) to parameterize the flaring system and extract consistent observables at solar chromospheric and photospheric layers that indicate a viable recognition of flaring activity. Rather than limiting ourselves to a few known indicators of solar activity, PCA helps us to characterize the entire system using several tens of variables for each observed layer. The components of the Eigen vectors derived from PCA help us recognize and quantify innate characteristics of solar flares and compare them. We will present an analysis of these results to explore the viability of PCA to assist in predicting solar flares.

Mares, Peter; Balasubramaniam, K. S.

2009-05-01

11

Solar flare particle radiation  

NASA Technical Reports Server (NTRS)

The characteristics of the solar particles accelerated by solar flares and subsequently observed near the orbit of the earth are studied. Considered are solar particle intensity-time profiles, the composition and spectra of solar flare events, and the propagation of solar particles in interplanetary space. The effects of solar particles at the earth, riometer observations of polar cap cosmic noise absorption events, and the production of solar cell damage at synchronous altitudes by solar protons are also discussed.

Lanzerotti, L. J.

1972-01-01

12

Understanding Solar Flare Statistics  

NASA Astrophysics Data System (ADS)

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

Wheatland, M. S.

2005-12-01

13

The solar flare myth  

Microsoft Academic Search

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

J. T. Gosling

1993-01-01

14

Solar flares. [plasma physics  

NASA Technical Reports Server (NTRS)

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

Rust, D. M.

1979-01-01

15

Solar Flare Physics  

NASA Technical Reports Server (NTRS)

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

Schmahl, Edward J.; Kundu, Mukul R.

2000-01-01

16

Avalanches and the distribution of solar flares  

NASA Technical Reports Server (NTRS)

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.

Lu, Edward T.; Hamilton, Russell J.

1991-01-01

17

Correlative Studies of Solar Flares  

NASA Technical Reports Server (NTRS)

In October 1992, post-doc Haimin Wang was awarded a Compton GRO Fellowship by NASA to study the flares observed simultaneously by BATSE (Burst and Transient Experiment), OVRO (Owens Valley Radio Observatory), Yohkoh, and BBSO (Big Bear Solar Observatory). During the past four years, a number of flares have been analyzed in detail. Substantial information on the physics of flares came out of these studies.

Zirin, Harold

1996-01-01

18

6Li from Solar Flares  

NASA Astrophysics Data System (ADS)

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.

Ramaty, Reuven; Tatischeff, Vincent; Thibaud, J. P.; Kozlovsky, Benzion; Mandzhavidze, Natalie

2000-05-01

19

Statistical Aspects of Solar Flares.  

National Technical Information Service (NTIS)

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 ...

R. M. Wilson

1987-01-01

20

Particle acceleration in solar flares  

NASA Technical Reports Server (NTRS)

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.

Ramaty, R.; Forman, M. A.

1987-01-01

21

Radiation hydrodynamics in solar flares  

SciTech Connect

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

Fisher, G.H.

1985-10-18

22

Solar Seismology Boosts Flare Predictions  

NASA Astrophysics Data System (ADS)

Predicting when potentially dangerous solar flares will form has always entailed a lot of guesswork. Solar physicists compare active regions of the Sun with what happened after similar activity in the past to come up with forecasts. Now researchers at NOAA's Space Weather Prediction Center, in Boulder, Colo., have designed a new forecasting tool they say is twice as accurate as current methods.

Klotz, Irene

2010-03-01

23

Rapid fluctuations in solar flares  

NASA Technical Reports Server (NTRS)

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

Sturrock, Peter A.

1986-01-01

24

Flares and dynamic aspects. [solar physics  

NASA Technical Reports Server (NTRS)

Theory of the dynamic nature of solar flares, eruptive prominences, and coronal transients is surveyed. Two types of flare are considered: compact eruptions (small flares) which are probably loops, and large eruptions of double filament flares. The physical sense of this classification is justified, using solar observations. Even leaving the question unanswered of whether a coronal transient is a loop of ejected matter or a shock wave, the important, perhaps fundamental, role of mass motion in flare physics is evidenced.

Hanssen, E. T.

1981-01-01

25

Solar flare emissions and geophysical disturbances  

NASA Technical Reports Server (NTRS)

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.

Sakurai, K.

1973-01-01

26

Mass ejections. [during solar flares  

NASA Technical Reports Server (NTRS)

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.

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

27

Interplanetary shock waves associated with solar flares  

NASA Technical Reports Server (NTRS)

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.

Chao, J. K.; Sakurai, K.

1974-01-01

28

Acceleration of electrons in solar flares  

NASA Technical Reports Server (NTRS)

Acceleration of electrons by Langmuir plasma turbulence and by the Fermi mechanism are suggested to explain the two-stage acceleration processes observed in hard X-rays from solar flares. A model for particle acceleration in flares is presented.

Cheng, C.

1971-01-01

29

The Solar Flare Iron Abundance  

NASA Astrophysics Data System (ADS)

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.

Phillips, K. J. H.; Dennis, B. R.

2012-03-01

30

Solar flares and energetic particles.  

PubMed

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

Vilmer, Nicole

2012-07-13

31

Predictions Of The Imminent Flare Occurrence From Photospheric Magnetic Paramenters  

Microsoft Academic Search

With the goal of identifying photospheric magnetic states that likely give rise to solar energetic events (especially, solar flares), we have analyzed three photospheric magnetic parameters, and quantified their correlations with imminent flare productivity of active regions. Three parameters are: (1) total unsigned magnetic flux, which is a measure of an active region's size, (2) the length of strong-gradient neutral

Hui Song; J. Jing; C. Tan; H. Wang

2006-01-01

32

High Resolution Spectra of Solar Flares  

NASA Astrophysics Data System (ADS)

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

Doschek, G. A.

33

FNAS/solar flare energetics  

NASA Technical Reports Server (NTRS)

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.

Machado, M. E.

1992-01-01

34

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

NASA Astrophysics Data System (ADS)

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 ?), 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 ? -rays. The occurrence of solar neutrons appears to be correlated with the intensity of hard X-rays and ? -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 ? -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.

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

35

FLARING SOLAR HALE SECTOR BOUNDARIES  

SciTech Connect

The sector structure that organizes the magnetic field of the solar wind into large-scale domains has a clear pattern in the photospheric magnetic field as well. The rotation rate, 27-28.5 days, implies an effectively rigid rotation originating deeper in the solar interior than the sunspots. The photospheric magnetic field is known to be concentrated near that portion (the Hale boundary) in each solar hemisphere, where the change in magnetic sector polarity matches that between the leading and following sunspot polarities in active regions in the respective hemispheres. We report here that flares and microflares also concentrate at the Hale boundaries, implying that flux emergence and the creation of free magnetic energy in the corona also have a direct cause in the deep interior.

Svalgaard, L. [HEPL, Stanford University, Stanford, CA 94304 (United States); Hannah, I. G.; Hudson, H. S., E-mail: leif@leif.org [School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ (United Kingdom)

2011-05-20

36

Solar gamma rays. [in solar flares  

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

37

Distant Suns: Solar Flares as Proxies for Stellar Flares  

NASA Astrophysics Data System (ADS)

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

Kashyap, Vinay; Reeves, Kathy; Wargelin, Brad

2009-09-01

38

Magnetic theories of solar flares  

Microsoft Academic Search

The basic processes of evaporation and magnetic reconnection have recently been developed in much greater detail. They may be important in the two main types of flaring event, namely simple-loop flares and two-ribbon flares. The first type could be produced by kink instability, thermal nonequilibrium, or emerging flux. The second type is thought to be the result of an eruptive

E. R. Priest

1983-01-01

39

An intelligent method for solar flare observation  

NASA Astrophysics Data System (ADS)

To capture the fine structure of the flare kernel during it's explosive phase, we design a real time flare onset detecting algorithm named Near Saturation Area Threshold(NSAT), And an automatic CCD parameters control algorithm for the observing software. All the data from CCD, 48f/s, could be saved to the hard disk, and the GPS time of the flare onset also be saved in the log. These methods could avoid the data overflow and grab the fine structure data of the flare kernel. The simulation experiment works well and the software will be put into use in Huairou Solar Observatory soon.

Lin, Jia Ben; Guo, Juan; Deng, Yuan Yong

2013-07-01

40

SDO Sees Late Phase in Solar Flares  

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...

41

Solar Flares and Collisions Between Current-Carrying Loops Types and Mechanisms of Solar Flares and Coronal Loop Heating  

NASA Astrophysics Data System (ADS)

This paper deals with the temporal dynamics of solar flares. It gives a systematic description of solar flare models and tries to link the observations to results of simulations. After a review of the development of ideas on flare structure and on theories on current-loop interaction in flares since the pioneering work by Gold and Hoyle (1960), this paper gives first a synthesis of present-days observationally based views on solar flares, essentially describing the developments since the review by de Jager (1986). We distinguish between confined/impulsive and eruptive/dynamic flares (briefly: confined and eruptive). The main difference between these two types is one of field-line topology: ‘closed’ or ‘open’. The ‘grand instability’ in a field-line system opening to space is basic to the relation between eruptive flares, filament instability, and Coronal Mass Ejections. A fair part of the paper deals with the developments in our understanding of the physical processes during collisions between current-carrying loops. After work by Tajima et al. (1982), who introduced the concept of current-loop coalescence in solar flares, using results obtained from two-dimensional particle simulation, it became clear that the current-loop interaction process includes a rich variety of physical mechanisms associated with rapid magnetic energy conversion through partial or complete magnetic reconnection, such as prompt high-energy particle acceleration, plasma heating, shock formation, plasma-jet formation and plasma radiation. This part of the paper concentrates on the developments since the review by Sakai and Ohsawa (1987), dealing with particle acceleration by magnetic reconnection and shocks during current-loop coalescence in solar flares. Theoretical research performed since the above review paper refers to magnetic reconnection, shock formation, particle acceleration and plasma emission during collisions between current-carrying loops. These theoretical developments are compared with observations. The Yohkoh spacecraft, launched August 30, 1991, observed many evidences of two-loops interaction in active regions and a growing number of examples of flares due to coalescence of loops. These observational evidences are reviewed in a systematic way (Section 6), by relating them to the theoretical studies described before. First we describe flares due to interactions of the Y-, X-, and I-types. These can be either confined or eruptive. A new observation is the occurrence of ‘ongoing partial reconnection’ in a flare. Thereafter, we discuss flares due to single-loop instability (these are confined flares), followed by the newly discovered ‘cusp-type’ flares. These are eruptive flares. We end with a description of a typical eruptive flare. In Section 7 we summarize observational and theoretical evidences for our earlier proposed scheme of three different phases of acceleration in flares. The summary in the last section compares flare observations with flare simulations; it deals briefly with the three phases of acceleration, and outlines the present status and prospects of simulation studies and related theoretical research.

Sakai, Jun-Ichi; de Jager, Cornelis

1996-07-01

42

Bayesian model comparison of solar flare spectra  

NASA Astrophysics Data System (ADS)

The detailed understanding of solar flares requires an understanding of the physics of accelerated electrons, since electrons carry a large fraction of the total energy released in a flare. Hard X-ray energy flux spectral observations of solar flares can be fit with different parameterized models of the interaction of the flare-accelerated electrons with the solar plasma. Each model describes different possible physical effects that may occur in solar flares. Bayesian model comparison provides a technique for assessing which model best describes the data. The advantage of this technique over others is that it can fully account for the different number and type of parameters in each model. We demonstrate this using Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spectral data from the GOES (Geostationary Operational Environmental Satellite) X4.8 flare of 23-July-2002. We suggest that the observed spectrum can be reproduced using two different parameterized models of the flare electron content. The first model assumes that the flare-accelerated electron spectrum consisting of a single power law with a fixed low energy cutoff assumed to be below the range of fitted X-ray energies, interacting with a non-uniformly ionized target. The second model assumes that the flare-accelerated electron spectrum has a broken power law and a low energy cutoff, which interacts with a fully ionized target plasma. The low energy cutoff in this model is a parameter used in fitting the data. We will introduce and use Bayesian model comparison techniques to decide which model best explains the observed data. This work is funded by the NASA Solar and Heliospheric Physics program.

Ireland, J.; Holman, G.

2012-12-01

43

Magnetic Variations Associated With Solar Flares  

NASA Technical Reports Server (NTRS)

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.

Petrosian, Vahe

2005-01-01

44

The dependence of flares on the magnetic classification of the source regions in solar cycles 22-23  

NASA Astrophysics Data System (ADS)

Using 28 years of solar X-ray flares and sunspot-group records supplied by the National Geophysical Data Center, we carried a statistical study on the dependence of flares on the magnetic classification of the sunspot groups, and investigated the relationship with the phase in the 22nd and 23rd solar cycles. We found that (1) there are 83.34 per cent X-class flares, 62.35 per cent M-class flares, 43.18 per cent C-class flares, and 25.47 per cent B-class flares occurred in ??? sunspot groups. (2) The occurrence of X-class flares in different sunspot groups shows clear periodic characteristics in phase with the solar cycle: near the two solar maximums, X-class flares occurred in various sunspot groups, but still most X-flares occurred in the ??? sunspot groups. For the other phases, all X-class flare occurred in ??? sunspot groups except 1998. The occurrence of M-class flares in different sunspot groups shows some periodic features in phase with the solar cycle. The occurrence of C-class and B-class flares in different sunspot groups shows weak periodic features with the phase of the solar cycle.

Guo, Juan; Lin, Jiaben; Deng, Yuanyong

2014-07-01

45

Reverse Current in Solar Flares  

NASA Technical Reports Server (NTRS)

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.

Knight, J. W., III

1978-01-01

46

REMOTE OSCILLATORY RESPONSES TO A SOLAR FLARE  

SciTech Connect

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

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

2013-07-20

47

Remote Oscillatory Responses to a Solar Flare  

NASA Astrophysics Data System (ADS)

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.

And¯i?, A.; McAteer, R. T. J.

2013-07-01

48

Solar-terrestrial relations: Flare and solar wind effects  

Microsoft Academic Search

The existence of solar terrestrial relations is clearly shown during solar flare events. During these catastrophic events the enhanced flux of XUV solar radiation as well as the sudden outburst of energetic solar cosmic ray particles induce a series of well identified effects in the Earth's magnetic field, in the terrestrial ionosphere and in the upper atmosphere. These geophysical effects

J. Lemaire

1989-01-01

49

When and where to look to observe major solar flares  

NASA Technical Reports Server (NTRS)

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

Bai, T.

1989-01-01

50

Carbon-poor solar flare events  

NASA Technical Reports Server (NTRS)

Energetic particle flux enhancements over the period October 1973 - December 1977 were surveyed using ULET sensor on the IMP-8 spacecraft. During the four year period the most extreme periods of Fe enrichment compared to oxygen were during solar flare events in February 1974 and May 1974. In these same events, the carbon abundance with respect to oxygen was significantly depleted when compared with a value C:0 is approximately 0.45:1 for typical solar flares. These observations, taken together with previously reported He-3 enrichment in these events, give strong evidence for the importance of a wave-particle interaction in the pre-injection heating of the ambient matter.

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

1979-01-01

51

Positron annihilation radiation from solar flares  

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

52

Deterministically Driven Avalanche Models of Solar Flares  

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

53

On Solar Flares and Cycle 23  

NASA Astrophysics Data System (ADS)

The anomalous character of Solar Cycle 23, which ended in the Summer of 2009, has been pointed out by many authors. It has even been proposed that the solar dynamo is undergoing a transition from a state of “grand maximum” to one of “regular oscillations”. We analyze the temporal distribution of the number and energy of solar flares, and the duration of intervals between them, over Cycles 21 to 23. We consider 32 355 flares of class C2 and larger (C2+) from the GOES catalogue. Daily values of X-ray flux (wavelengths 1 to 8 Å) have been computed by summing the energy proxies of the events. The series of daily numbers of C2+ solar flares are strongly correlated with their daily energy flux. The long duration of Cycle 23 (12.8 years based on sunspots, 13.2 years based on flares) and the long interval with no C2+ flare between the end of Cycle 23, and the start of Cycle 24 (466 days) are remarkable compared to the two earlier cycles. The amplitudes of extreme flares increase when the mean flux decreases. We have calculated running averages of energy flux over intervals going from 7 to 365 days. The singular shape of Cycle 23 is increasingly striking with increasing interval: in the first ? 70% of the cycle (displayed on a logarithmic scale) we see linearly rising maxima, whereas minima are aligned along a descending slope for the latter part of the cycle. The energy flux oscillates between these and takes the shape of a bifurcation, starting near 2002 (a time when it is suggested that photospheric fields were abruptly reduced). Inter-event intervals between successive C2+ flares undergo quasi-periodic (? 11 years) oscillations between two distinct states, which we call “active” and “quiet”, with extremely sharp onset and termination. The ratio of time spent in the active vs. quiet states ranges from 1.8 to 1.4 for Cycles 21 to 23, Cycle 23 having the longest quiet period. It has been proposed that anomalous Cycle 23 resembles Cycle 4, which was followed by reduced Cycles 5 and 6 at the time of the Dalton minimum in solar activity, often associated with a cooler global climate. It will be interesting to monitor the evolution of solar flares in Cycle 24, in order to further our understanding of solar activity during a sequence of possibly weak and decreasing cycles, but also of its potential relation to climate change.

Kossobokov, Vladimir; Le Mouël, Jean-Louis; Courtillot, Vincent

2012-02-01

54

A solar tornado caused by flares  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

55

Investigations of turbulent motions and particle acceleration in solar flares  

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

56

Diagnostics of Solar Flare Energetic Particles  

NASA Astrophysics Data System (ADS)

For work on my thesis dissertation, we have been studying some energetic processes in solar flares. On our work on Hard X-ray (HXR) emission from flares, we have shown that recombination emission can exceed the bremsstrahlung HXR flux for certain flare conditions. We will show some spectral features characteristic of non-thermal recombination HXR emission and will suggest how it plays a significant role in the flare HXR continuum, something that has been ignored in the past. It is important to note that these results could demand a reconsideration of the numbers of accelerated electrons since recombination can be much more efficient in producing HXR photons than bremsstrahlung. In related work on diagnosing particle acceleration in flares, we also have an interest in studying solar neutrons. To this end, we will present our work done with new-age neutron detectors developed by our colleagues at the University of New Hampshire. Using laboratory and simulated data from the detector to produce its response matrix, we then employ regularisation and deconvolution techniques to produce encouraging results for data inversion. As a corollary, we have also been reconsidering the role of inverse Compton (IC) scattering of photospheric photons. Gamma-ray observations clearly show the presence of 100 MeV electrons and positrons in the solar corona, by-products of GeV energy ions. Here we will present results of IC scattering of such photons taking proper account of radiation field geometry near the solar surface. If observed, such radiation would let us determine the number of secondary positrons produced in large flares, contributing to a full picture of ion acceleration and to predicting neutron fluxes to be encountered by future inner heliosphere space missions. This work is supported by a UK STFC Rolling Grant and a Dorothy Hodgkin's Scholarship (PM).

Mallik, Procheta; Brown, J. C.; MacKinnon, A. L.

2009-05-01

57

Absolute Abundance Measurements in Solar Flares  

NASA Astrophysics Data System (ADS)

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

Warren, Harry

2014-06-01

58

Decimetric gyrosynchrotron emission during a solar flare  

Microsoft Academic Search

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

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

1983-01-01

59

Decimetric gyrosynchrotron emission during a solar flare  

Microsoft Academic Search

A decimetric, microwave, and hard X-ray burst has been observed during a solar flare in which the radio spectrum below peak plux fits an f\\/sup +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. Thiis is the first time that gyrosynchrotron radiation

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

1984-01-01

60

On Solar Flares and Cycle 23  

NASA Astrophysics Data System (ADS)

The anomalous character of solar cycle 23 has been pointed out. It is proposed that the solar dynamo is undergoing a transition from a state of "grand maximum" to one of "regular oscillations". In this study, we analyze the time distribution of the number and energy of solar flares, and the duration of intervals between them, from cycle 21 to 23. We consider 32355 flares of class C2 and larger (C2+) from the GOES catalogue. Daily values of X-ray flux (wavelengths 1-8Å) have been computed by summing the energy proxies of the events. The series of daily numbers of C2+ solar flares are strongly correlated to their daily energy flux. The long duration of cycle 23 (~13 years), the long interval with no C2+ flare between the end of cycle 23 and the start of cycle 24 (466 days) are remarkable compared to the two earlier cycles. Amplitudes of extreme flares increase when mean flux decreases. We have calculated running averages of energy flux over intervals going from 7 to 365 days: the singular shape of cycle 23 is increasingly striking with increasing interval: the first ~70% of the cycle display (in logarithmic scale) linearly rising maxima, whereas minima are aligned along a descending slope for the latter part of the cycle. Energy flux oscillates between these and takes the shape of a bifurcation, starting near 2002. Durations of inter-event intervals between successive C2+ flares undergo quasi-periodic (~11yr) oscillations between two distinct states, which we call "active" and "quiet", with sharp onset and termination. The ratio of time spent in the active vs quiet states ranges from 1.8 to 1.4 for cycles 21 to 23, cycle 23 having the longest quiet period. It has been proposed that anomalous cycle 23 resembles cycle 4, which was followed by reduced cycles 5 and 6 at the time of the Dalton-minimum in solar activity, often associated with a cooler global climate. It will be interesting to monitor the evolution of solar flares in cycle 24, in order to further our understanding of solar activity during a sequence of possibly weak and decreasing cycles.

Kossobokov, V. G.; Le Mouel, J.; Courtillot, V.

2011-12-01

61

High energy component of solar flares  

NASA Astrophysics Data System (ADS)

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.

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

62

Periodicity in the most violent solar eruptions: recent observations of coronal mass ejections and flares revisited  

NASA Astrophysics Data System (ADS)

Using the Hilbert-Huang Transform method, we investigate the periodicity in the monthly occurrence numbers and monthly mean energy of coronal mass ejections (CMEs) observed by the Large Angle and Spectrometric Coronagraph Experiment on board the Solar and Heliographic Observatory from 1999 March to 2009 December. We also investigate the periodicity in the monthly occurrence numbers of H? flares and monthly mean flare indices from 1996 January to 2008 December. The results show the following. (1) The period of 5.66 yr is found to be statistically significant in the monthly occurrence numbers of CMEs; the period of 10.5 yr is found to be statistically significant in the monthly mean energy of CMEs. (2) The periods of 3.05 and 8.70yr are found to be statistically significant in the monthly occurrence numbers of H? flares; the period of 9.14yr is found to be statistically significant in the monthly mean flare indices.

Gao, Peng-Xin; Xie, Jing-Lan; Liang, Hong-Fei

2012-03-01

63

Solar Flare and Cme Prediction From Photospheric Magnetic Field Measurements  

Microsoft Academic Search

The coronal mass ejection that associated with a solar flare produces powerful mag- netospheric disturbances. The numerical 3D MHD model for prediction of CME and flares is proposed. The photospheric magnetic measurements are used as boundary conditions. The scenario of vertical current sheet creation is demonstrated for several solar flares. The new version of the PERSVET code is developed for

A. I. Podgorny; I. M. Podgorny

2002-01-01

64

Solar flares, proton showers, and the space shuttle  

Microsoft Academic Search

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

D. M. Rust

1982-01-01

65

Study of periodicities of solar nuclear gamma ray flares and sunspots  

NASA Astrophysics Data System (ADS)

A power-spectrum analysis of solar nuclear gamma-ray (NGR) flares observed by SMM and HINOTORI satellites was carried out. The solar NGR flares show a periodicity of 152 days, confirming the existence of a 152-158 days periodicity in the occurrence of solar activity phenomena and also indicating that the NGR flares are a separate class of solar flares. The power-spectrum analysis of the daily sunspot areas on the sun for the period 1980-1982 shows a peak around 159 days, while sunspot number data do not show any periodicity (Verma and Joshi, 1987). Therefore, only sunspot area data should be treated as an indicator of solar activity and not the daily sunspot number data.

Verma, V. K.; Joshi, G. C.; Paliwal, D. C.

1992-03-01

66

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

NASA Astrophysics Data System (ADS)

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.

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

2013-03-01

67

Ion Acceleration in Solar Flares Determined by Solar Neutron Observations  

NASA Astrophysics Data System (ADS)

Large amounts of particles can be accelerated to relativistic energy in association with solar flares and/or accompanying phenomena (e.g., CME-driven shocks), and they sometimes reach very near the Earth and penetrate the Earth's atmosphere. These particles are observed by ground-based detectors (e.g., neutron monitors) as Ground Level Enhancements (GLEs). Some of the GLEs originate from high energy solar neutrons which are produced in association with solar flares. These neutrons are also observed by ground-based neutron monitors and solar neutron telescopes. Recently, some of the solar neutron detectors have also been operating in space. By observing these solar neutrons, we can obtain information about ion acceleration in solar flares. Such neutrons were observed in association with some X-class flares in solar cycle 23, and sometimes they were observed by two different types of detectors. For example, on 2005 September 7, large solar neutron signals were observed by the neutron monitor at Mt. Chacaltaya in Bolivia and Mexico City, and by the solar neutron telescopes at Chacaltaya and Mt. Sierra Negra in Mexico in association with an X17.0 flare. The neutron signal continued for more than 20 minutes with high statistical significance. Intense gamma-ray emission was also registered by INTEGRAL, and by RHESSI during the decay phase. We analyzed these data using the solar-flare magnetic-loop transport and interaction model of Hua et al. (2002), and found that the model could successfully fit the data with intermediate values of loop magnetic convergence and pitch angle scattering parameters. These results indicate that solar neutrons were produced at the same time as the gamma-ray line emission and that ions were continuously accelerated at the emission site. In this paper, we introduce some of the solar neutron observations in solar cycle 23, and discuss the tendencies of the physical parameters of solar neutron GLEs, and the energy spectrum and population of the accelerated particles produced in these solar flares, etc. We also report recent solar neutron observations by the Space Environment Data Acquisition equipment-Attached Payload (SEDA-AP) which has been installed on the international space station, and introduce the plan for the new solar neutron detector of the SciBar for the Cosmic Ray Telescope (SciCRT) at Mt. Sierra Negra in Mexico.

Watanabe, K.; Solar Neutron Observation Group

2013-05-01

68

Observations of particle acceleration in solar flares  

NASA Technical Reports Server (NTRS)

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

Hudson, H. S.

1979-01-01

69

Measurements of Absolute Abundances in Solar Flares  

NASA Astrophysics Data System (ADS)

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

Warren, Harry P.

2014-05-01

70

X-ray Candles: Solar Flares on Your Birthday  

NSDL National Science Digital Library

In this activity, middle school students discover the solar cycle through an investigation of solar X-ray flares. Using X-ray data from the Geostationary Operational Environmental Satellite (GOES), they record the total number of flares in their birth month over 11 years. Students then compute the percentage of high class flares which occur for each year and graph their findings to help identify the long term pattern of flare activity on the Sun. The site offers a solar flare introduction section, which includes information about solar flares and GOES, as the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) satellite has not yet collected data. The section also shows how to read the data along with the X-ray flare classification system.

71

Gyrosynchrotron Microwave Emission From Solar Flares  

NASA Astrophysics Data System (ADS)

The subject of this research is decimetric and microwave emission from solar flares. The research deals with gyrosynchrotron emission from a population of fast electrons. Two frequency ranges are investigated: low multiples (1-3) of the cyclotron frequency nu_B , and high multiples ( 6 nu_B and above) of the cyclotron frequency. In the high frequency range a simple geometrical model of a flare loop is investigated. We show that our simple model reproduces observed microwave fluxes and spectra, and present a fit for the microwave spectrum and time evolution of the flare of June 4th 1991. We conclude that the flare spectrum can be explained with a simple model, and that even the time evolution can be fit by changing a single parameter at a time. We also investigate how the observed flare spectrum changes for different locations of the flare on the sun, a question not dealt with previously. The shape of the spectrum is quantified by the ratio of the flux at 10 GHz to the flux at 4 GHz, and this ratio is shown to change by an order of magnitude as the same flare model is moved from the Limb to the Disk center. In the low frequency range we investigate amplification through the Electron Cyclotron Maser (ECM) mechanism in the range 0.5 < nu_p / nu_B < 2, where nu_p is the plasma frequency. The ECM process is widely assumed to produce solar microwave millisecond spike emission. Most previous studies concentrated on the region nu_p / nu_B<1, and claim that spikes are produced there. We show that maser emission should be produced at the foot-points of the flare, where nu_p / nu_B > 1. Previous studies claim emission at 70 degrees to the magnetic field,or more, and emission at the first or second harmonic. We show that spike emission from the foot-points should appear at angles of 30-70 degrees to the magnetic field, and at frequencies near the second cyclotron harmonic, usually at 2.06 nu_B. We also find that ECM emission depends on the temperature and that the unobservable Z-mode quenchs the maser for temperatures above 10(7) Kelvin. These conclusions can be checked by observations of high spatial resolution, especially if performed simultaneously with observations from which the temperature can be estimated.

Stupp, A.

1999-04-01

72

The coalescence instability in solar flares  

NASA Technical Reports Server (NTRS)

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.

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

1985-01-01

73

The Ulysses Catalog of Solar Hard X-Ray Flares  

NASA Astrophysics Data System (ADS)

Ulysses was launched in October 1990, and its Solar X-ray/Cosmic Gamma-Ray Burst Experiment (GRB) has provided more than 13 years of uninterrupted observations of solar X-ray flare activity. Due to the large variation of the relative solar latitude and longitude of the spacecraft orbit with respect to the Earth, the perspective of the GRB instrument often differed significantly from that of X-ray instruments on Earth-orbiting satellites. During extended periods the GRB experiment made direct observations of flares on the hidden face of the Sun, providing a unique record of events not visible to other instruments. The small detector area of GRB and its optimization for very high counting rates minimized the effects of pulse pile-up. We interpret the spectra, time histories, and occurrence distribution patterns of GRB data in terms of “thermal feed-through”, the confusion of thermal soft X-rays and non-thermal hard X-rays. This effect is a systematic problem for scintillation-counter spectrometers observing the solar hard X-ray spectrum. This paper provides a definitive catalog of the Ulysses X-ray flare observations and discusses various features of this unique database. For the equivalent GOES range X2 - X25, we find a power-law fit for the (differential) occurrence frequency at >25 keV with slope -1.61±0.04, with no evidence for a downturn at the highest event magnitudes (for the relatively small sample of such events available in this study). If the nine most intense events are excluded because of concerns about the effects of pulse pile-up, the slope steepens to -1.75±0.08.

Tranquille, C.; Hurley, K.; Hudson, H. S.

2009-08-01

74

Investigating ``Precursor Flows'' in Solar Flares  

NASA Astrophysics Data System (ADS)

Despite some measure of theoretical and predictive success of the electron-heated model of solar flares, observations of low levels of soft X-ray emission prior to the detection of hard X-rays in most flares present a problem for the paradigm, since it suggests some sort of ``preheating'' of the chromospheric plasma before electron acceleration. Particularly troublesome are assertions that plasma flows have been observed prior to hard X-ray emission, because they imply significant and rapid energy input by some agent without leaving a (currently) detectable hard X-ray signature. Given this challenge to a prevailing paradigm, it is imperative to investigate more comprehensively the existence of ``precursor flows'' manifested in the asymmetry of X-ray spectral lines. In this paper, we examine a sample of 50 disk-center flares observed by the Yohkoh Bragg Crystal Spectrometer (BCS) between 1991 and 1993, and determine with the velocity differential emission measure the extent to which ``precursor flows'' occur. We explore specifically the possibility that these ``precursor flows'' are only apparent, arising from the existence of more than one emission region on the solar disk. The spatial separation between regions could cause the emission to be registered by the detector in a wavelength bin that is shifted relative to the line's nominal location, giving rise to line asymmetries. In our sample, we find that only five flares manifest ``precursor flows,'' three of which can be explained definitively by the presence of other active regions. It also appears plausible that the remaining two events can be explained in terms of such spatial effects, although the evidence is more circumstantial. We conclude, therefore, that one can reasonably question the existence of ``precursor flows'' in our sample and that the observations to date cannot contribute decisively to the electron versus proton debate. These results are contrasted with those of Plunkett & Simnett, who identified 14 precursor events in a sample of 35 flares and hence concluded, without further analysis, that protons, rather than electrons, must be the primary energy carriers in flares. Our paper's sample included eight of Plunkett & Simnett's 14 precursor events, and yet our analysis, which employed substantially different methods, identified only one of these eight as a ``precursor'' event. The remaining seven were either troubled by BCS data dropout or failed to exceed the 10% threshold required to classify a flare as a``precursor'' event.

Newton, Elizabeth K.

1997-07-01

75

Flare models. [solar physics current status review  

NASA Technical Reports Server (NTRS)

The current status of solar flare modeling is reviewed. Primary and secondary observational features that a proposed flare model should be capable of explaining are discussed, including energy storage and release, particle acceleration, mass ejection, heating of the temperature minimum region, X-ray, EUV, UV, visible and radio emission and mass flow. Consideration is then given to the twisted flux tube paramagnetic recombination model of Gold and Hoyle (1960), the current model of Alfven and Carlqvist (1967), closed current-sheet models such as those of Syrovatskii (1966, 1969, 1977) and Uchida and Sakurai (1977), open-field models such as those of Carmichael (1964) and Barnes and Sturrock (1972), the emerging flux model of Heyvaerts and Priest (1974, 1977, 1978) and the loop-flare models of Spicer (1977) and Colgate (1978). It is noted that no one model can yet account for all the observational features, and that there may turn out to be several types of flare, each requiring its own explanation.

Sturrock, P. A.

1980-01-01

76

Acceleration of electrons during the flash phase of solar flares  

NASA Technical Reports Server (NTRS)

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

Kane, S. R.

1974-01-01

77

Size Distributions of Solar Flares and Solar Energetic Particle Events  

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

78

A brief review of “solar flare effects” on the ionosphere  

Microsoft Academic Search

The study of solar flare effects (SFEs) on the ionosphere is having a renaissance. The development of GPS ground and satellite data for scientific use has opened up new means for high time resolution research on SFEs. At present, without continuous flare photon spectra (X rays, EUV, UV, and visible) monitoring instrumentation, the best way to model flare spectral changes

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

2009-01-01

79

Acceleration of runaway electrons in solar flares  

NASA Technical Reports Server (NTRS)

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.

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

1990-01-01

80

Relationships Between Photospheric Flows and Solar Flares  

NASA Astrophysics Data System (ADS)

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.

Welsch, B. T.; Li, Y.

2013-12-01

81

High-energy processes in solar flares  

NASA Technical Reports Server (NTRS)

A detailed study of high-energy processes in solar flares is reported, including the production of neutrons and pions, and incorporating isobaric and scaling models and a recent compilation of pion production data (Dermer, 1986). The broad-band gamma-ray spectrum resulting from the decay of neutral pions, the bremsstrahlung of positrons and electrons from the decay of charged pions, and the annihilation in flight of positrons is evaluated. Also evaluated is the 0.511 MeV gamma-ray line resulting from the annihilation of the positrons which survive annihilation in flight. Calculations were based on an isotropic, thick-target model using the best available nuclear data and models. Results are compared with extensive observation of the June 3, 1982 flare (10-120 MeV gamma rays), 0.511 and 2.2 MeV line emission, nuclear line emission, high-energy neutrons, and interplanetary charged particles.

Murphy, R. J.; Dermer, C. D.; Ramaty, R.

1987-01-01

82

Study of the behaviour of the equatorial ionization anomaly (EIA) during solar flares  

NASA Astrophysics Data System (ADS)

A solar flare occurring in the sun's chromosphere is observed in various wavebands (radio to x-rays). The response of the solar flare which causes sudden changes in the earth's ionosphere is not yet well understood though investigations suggested that its impact depends on the size and location of occurrence of solar flare on sun. Considering this, we have carried an investigation to study the response of two strong and gradual solar flares: 2 Apr 2001 (X20, limb) and 7 Feb 2010 (M6.4, disk) on the earth's equatorial-low latitude regions using multi-technique observations of satellite and ground-based instruments. We found a weakening of strength of equatorial ionization anomaly (EIA) in total electron content during both the flares as observed by TOPEX, JASON-1 and JASON-2 altimeter measurements. The H component of the geomagnetic field also shows a sudden change at equatorial and low latitude stations in the sunlit hemisphere during the flare. The observations of ionosonde at low-latitudes indicate a strong absorption of higher-frequency radio signals. The detail response of these flare on EIA of the earth's ionosphere will be presented and discussed.

Aggarwal, Malini; Astafyeva, Elvira

2014-05-01

83

Observation System of Solar Flare Telescope  

NASA Astrophysics Data System (ADS)

SOFT(Solar Flare Telescope) installed at BOAO(Bohyunsan Optical Astronomy Observatory) is purposed for observing solar active regions using four refractors on a single mount with a 400" x 300" field of view: Two refractors with a diameter of 15cm(f15) observe the white light and H?, and the other two refractors with a diameter of 20cm(f8) observe the magnetic field distribution and Doppler shifts at the solar chromosphere. Three Lyot filters, one of the most important observational instruments, are installed on the optical rails for VMG, LMG, and H? that possible to very narrow pass band observation under high precision stability of temperature. From the combination of KD*P and quarter wave plate in the Lyot filter possible observe the magnetic fields strength and doppler shifts by using the characteristics of polarization components. In this paper, we introduce the basic characteristics, optical system, and monitor system of the SOFT.

Park, Young Deuk; Moon, Yong-Jae; Jang, Be-Ho; Sim, Kyung Jin

1997-12-01

84

Nuclear gamma rays from solar flares  

NASA Technical Reports Server (NTRS)

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.

Ramaty, R.; Lingenfelter, R. E.

1973-01-01

85

Gamma ray emission and solar flares  

NASA Technical Reports Server (NTRS)

Solar gamma ray line and continuum emission provide information about particle acceleration and its temporal behavior; the energy spectrum, composition and directivity of the accelerated particles; and the composition, density and temperatures of the ambient medium. These data, coupled with the comprehensive photon and particle observations available for the sun, give a detailed picture of the particle acceleration and flare energy release processes. Additional information on elemental and isotopic abundances, surface nuclear reactions and coronal heating mechanisms can be obtained. Implications of present observations and the potential return from future observational are discussed.

Lin, R. P.; Ramaty, R.

1978-01-01

86

Heat Transport Problem in Solar Flares  

NASA Astrophysics Data System (ADS)

We develop mathematical models describing plasma heating in the corona by heat fluxes from a super-hot (T ? 108 K) reconnecting current layer in solar flares. The effect of collisional relaxation is shown to be important in these conditions. Taking this effect into account, we have computed the electron-temperature distributions in the vicinity of the current layer, differential and integral emission measures of the heated plasma, the intensities of spectral lines Fe XXVI (1.78 and 1.51 Å) and Ni XXVII (1.59 Å). The theoretical results are compared with observations.

Oreshina, A. V.; Somov, B. V.

2012-06-01

87

Adiabatic heating in impulsive solar flares  

NASA Technical Reports Server (NTRS)

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.

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

1977-01-01

88

Current loop coalescence model of solar flares  

NASA Technical Reports Server (NTRS)

A computer simulation and theoretical study of the physical characteristics of the explosive coalescence of current-carrying loops is presented. Characteristics of the explosive coalescence include a large impulsive increase of the kinetic energies of electrons and ions, the simultaneous heating and acceleration of electrons and ions in high and low energy ranges, and a break in the energy spectra of electrons and ions. A characteristic double subpeak structure is found in the quasi-periodic oscillations found in the time profiles of the solar flares of June 7, 1980 and November 26, 1982 which can be explained in terms of the coalescence instability of two current loops.

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

1987-01-01

89

Solar flare prediction using highly stressed longitudinal magnetic field parameters  

NASA Astrophysics Data System (ADS)

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.

Huang, Xin; Wang, Hua-Ning

2013-03-01

90

Solar flare and sudden change of earth's rotation  

Microsoft Academic Search

The conditions for solar flares to produce effects on the earth's rotation are analytically determined. It is shown that a sudden change in the earth's rotation can occur only when, in a shock pair produced by a large solar flare, the following shock moves appreciably faster than the leading shock.

Bo Feng

1991-01-01

91

Explosive hydrogen-burning model of solar flares  

Microsoft Academic Search

A model of solar flare is proposed, taking into account the high temperature (~109K) produced by the shock wave generated by the hydromagnetic wave at the junction of sunspot and the area just outside it and subsequent explosive hydrogen burning, producing the desired 1028–29 ergs of a solar flare.

L. Manihar Singh; L. Randhoni Devi

1990-01-01

92

Explosive Hydrogen-Burning Model of Solar Flares  

Microsoft Academic Search

A model of solar flare is proposed, taking into account the high temperature (˜109K) produced by the shock wave generated by the hydromagnetic wave at the junction of sunspot and the area just outside it and subsequent explosive hydrogen burning, producing the desired 1028 29 ergs of a solar flare.

L. Manihar Singh; L. Randhoni Devi

1990-01-01

93

Ionic charge distributions of energetic particles from solar flares  

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

94

SDO's View of May 5, 2010 Solar Flare - Without Timeline  

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, 171).

95

Solar flare forecasting based on sequential sunspot data  

NASA Astrophysics Data System (ADS)

It is widely believed that the evolution of solar active regions leads to solar flares. However, information about the evolution of solar active regions is not employed in most existing solar flare forecasting models. In the current work, a short-term solar flare forecasting model is proposed, in which sequential sunspot data, including three days of information about evolution from active regions, are taken as one of the basic predictors. The sunspot area, the McIntosh classification, the magnetic classification and the radio flux are extracted and converted to a numerical format that is suitable for the current forecasting model. Based on these parameters, the sliding-window method is used to form the sequential data by adding three days of information about evolution. Then, multi-layer perceptron and learning vector quantization are employed to predict the flare level within 48h. Experimental results indicate that the performance of the proposed flare forecasting model works better than previous models.

Li, Rong; Zhu, Jie

2013-09-01

96

Spectrum synthesis of EUV solar flare line profiles  

NASA Technical Reports Server (NTRS)

A classic double ribbon flare of importance 1B occurred at approximately 1405 UT on June 15, 1973, reached an H alpha maximum at 1413 UT, and ended at 1455 UT. The flare occurred in an old and simplifying bipolar region at N18 W32. This flare was studied due to the extensive temporal data available. A total of 136 spectra of wavelength ranges from 1100 to 3000 A were taken during the flare's duration by the Naval Research Laboratory normal incidence slit spectrograph. Using this data the nature of the solar chromosphere of a flare event as a function of time was determined.

Tripp, D. A.

1980-01-01

97

Spectrum synthesis of EUV solar flare line profiles  

NASA Astrophysics Data System (ADS)

A classic double ribbon flare of importance 1B occurred at approximately 1405 UT on June 15, 1973, reached an H alpha maximum at 1413 UT, and ended at 1455 UT. The flare occurred in an old and simplifying bipolar region at N18 W32. This flare was studied due to the extensive temporal data available. A total of 136 spectra of wavelength ranges from 1100 to 3000 A were taken during the flare's duration by the Naval Research Laboratory normal incidence slit spectrograph. Using this data the nature of the solar chromosphere of a flare event as a function of time was determined.

Tripp, D. A.

1980-07-01

98

High-resolution X-ray spectra of solar flares  

NASA Astrophysics Data System (ADS)

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

Doschek, G. A.

2006-01-01

99

Soft X-ray Irradiance during a Solar Flare  

NASA Astrophysics Data System (ADS)

Solar soft X-ray irradiance provides a highly variable energy source to the lower thermosphere. Solar flares are a dramatic source of this variability. Observations from the NASA satellite mission Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics - Solar Extreme Ultraviolet Experiment (TIMED-SEE) are being analyzed to determine how the solar soft X-ray energy deposition varies during a solar flare. The XUV Photometer System (XPS) aboard TIMED-SEE observes the solar soft X-ray irradiance between 0.1 and 27 nm for a 3 minute period approximately every 96 minutes. Contrary to initial assumptions based on the nature and infrequency of solar flares, XPS observations have shown that flares significantly impact the daily averaged energy input and thus the atmospheric chemistry of the lower thermosphere. The XPS observed, on average, eight solar flares of various strengths per month during a five month period in 2002 while the Student Nitric Oxide Explorer (SNOE) observed nitric oxide (NO) between 95 and 135 km. It has been shown that SNOE observed a significant increase in NO during the April 21, 2002 solar flare that was observed by the XPS. The eight XPS photodiodes are broadband detectors and a reference spectrum is required to interpret the signal because the sensitivity varies within each detector bandpass. A solar flare spectrum is inferred from the XPS detectors by an algorithm that iterates through differential emission measures until they produce a model spectrum that can reproduce the XPS detector observations. These flare spectra will be used to determine the soft X-ray energy input to Earth's lower thermosphere during a solar flare. Results and a description of this analysis will be presented.

Rodgers, E. M.; Bailey, S. M.; Woods, T. N.; Eparvier, F. G.

2005-05-01

100

Are solar gamma-ray-line flares different from other large flares?  

NASA Technical Reports Server (NTRS)

We reevaluate evidence indicating that gamma-ray-line (GRL) flares are fundamentally different from other large flares without detectable GRL emission and find no compelling support for this proposition. For large flares observed by the Solar Maximum Mission (SMM) from 1980 to 1982, we obtain a reasonably good correlation between 4-8 MeV GRL fluences and greater than 50 keV hard X-ray fluences and find no evidence for a distinct population of large hard X-ray flares that lack commensurate GRL emission. Our results are consistent with the acceleration of the bulk of the approximately 100 keV electrons and approximately 10 MeV protons (i.e., the populations of these species that interact in the solar atmosphere to produce hard X-ray and GRL emission) by a common process in large flares of both long and short durations.

Cliver, E. W.; Crosby, N. B.; Dennis, B. R.

1994-01-01

101

Decimetric gyrosynchrotron emission during a solar flare  

NASA Technical Reports Server (NTRS)

The implications of high time-resolution observations of a decimetric, microwave, and hard X-ray burst during a solar flare in which the 900-998 MHz, 8.4 GHz, and 10.4 GHz peak fluxes fit the optically thick spectrum of a homogeneous, thermal gyrosynchrotron source are reported and discussed. The hard X-ray spectrum from 30 to 463 keV is well represented by a thermal bremsstrahlung function, and a temperature derived from this spectrum is used to find the source area of about 10 to the 18th sq cm. An electron density of less than about 7 x 10 to the 9th/cu cm and a magnetic field of roughly 120 gauss are deduced from elementary plasma physics considerations and the lack of Razin-Tsytovich absorption of the 900-998 MHz flux. These conditions place the gyrosynchrotron source at high altitude in a coronal loop, in agreement with VLA observations of other flares.

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

1984-01-01

102

Decimetric gyrosynchrotron emission during a solar flare  

NASA Astrophysics Data System (ADS)

The implications of high time-resolution observations of a decimetric, microwave, and hard X-ray burst during a solar flare in which the 900-998 MHz, 8.4 GHz, and 10.4 GHz peak fluxes fit the optically thick spectrum of a homogeneous, thermal gyrosynchrotron source are reported and discussed. The hard X-ray spectrum from 30 to 463 keV is well represented by a thermal bremsstrahlung function, and a temperature derived from this spectrum is used to find the source area of about 10 to the 18th sq cm. An electron density of less than about 7 x 10 to the 9th/cu cm and a magnetic field of roughly 120 gauss are deduced from elementary plasma physics considerations and the lack of Razin-Tsytovich absorption of the 900-998 MHz flux. These conditions place the gyrosynchrotron source at high altitude in a coronal loop, in agreement with VLA observations of other flares.

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

1984-05-01

103

Testing Solar Flare Models with BATSE  

NASA Technical Reports Server (NTRS)

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

Zarro, Dominic M.

1995-01-01

104

Testing Solar Flare Models with BATSE  

NASA Astrophysics Data System (ADS)

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

Zarro, Dominic M.

1995-07-01

105

Decimetric gyrosynchrotron emission during a solar flare  

NASA Astrophysics Data System (ADS)

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.

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

1983-11-01

106

Decimetric gyrosynchrotron emission during a solar flare  

NASA Technical Reports Server (NTRS)

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.

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

1983-01-01

107

Existence of thresholds in proton flares and application to solar energetic particle alerts  

Microsoft Academic Search

This article discusses our statistical investigations into the occurrence of proton events for solar energetic particle (SEP) alerts in space weather forecasts. We analyzed X-ray flux and proton intensity data obtained with the GOES satellite in the 23rd solar cycle. We found that the total soft X-ray flux (1-8Å) of almost all flares related to proton events exceeded a threshold

Yuki Kubo; Maki Akioka

2004-01-01

108

Existence of thresholds in proton flares and application to solar energetic particle alerts  

Microsoft Academic Search

This article discusses our statistical investigations into the occurrence of proton events for solar energetic particle (SEP) alerts in space weather forecasts. We analyzed X-ray flux and proton intensity data obtained with the GOES satellite in the 23rd solar cycle. We found that the total soft X-ray flux (1–8Å) of almost all flares related to proton events exceeded a threshold

Y?ki Kubo; Maki Akioka

2004-01-01

109

IRIS Observations of the Solar Atmospheric Response to Flares  

NASA Astrophysics Data System (ADS)

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.

Wuelser, Jean-Pierre

2014-06-01

110

Insights Into Categorization Of Solar Flares Using Principal Component Analysis  

NASA Astrophysics Data System (ADS)

Using time sequences of solar chromospheric images acquired using the USAF/NSO Improved Solar Observing Network (ISOON) prototype telescope, we have applied principal component analysis (PCA) to time-series of both erupting and non-erupting active regions. Our primary purpose is to develop an advanced data driven model for solar flare prediction using machine learning algorithms, with principal components as the input. Using the principal components we show a clear separation in the Eigen vectors. Eigen vectors fall into three major flaring categories: weak flares (GOES peak intensity < C4.0; intermediary flares (GOES peak intensity between C4.0 and C8.0) and, strong flares (GOES peak intensity > C8.0). In this paper, we will provide insights into implications for the underlying physical mechanisms that describe these three distinct categories. This work funded by the U. S. Air Force Office of Scientific Research (AFOSR).

Balasubramaniam, K. S.; Norquist, D. C.

2012-05-01

111

Solar flares, proton showers, and the space shuttle.  

PubMed

The space shuttle era will focus renewed attention on the hazards of the space environment to human habitation. 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 druing 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. PMID:17809050

Rust, D M

1982-05-28

112

Solar flare perturbations in stratospheric current systems  

SciTech Connect

Electric field, conductivity, and ionization rate data were collected on two balloon payloads at 26 km in the southern hemisphere stratosphere during the solar flare of 16 February 1984. Both polarities of the conductivity were enhanced by a factor of two at a payload with an invariant latitude (..lambda..) of -56.3/sup 0/ (Rigidity = 1.4GV). At the same time no transient effects were seen in any of these parameters by a more equatorially located payload at ..lambda.. = -48.8/sup 0/ (Rigidity = 2.8 GV). The two payloads were separated by 5 hours of local time. The vertical current density (J/sub z/) at the poleward most payload was enhanced by over a factor of two, while no J/sub z/ variations were seen by the equatorward payload. Interpretation of these observations suggests that a simple RC time constant analysis of the global circuit may be incorrect. copyright American Geophysical Union 1987

Holzworth, R.H.; Norville, K.W.; Williamson, P.R.

1987-08-01

113

Stochastic acceleration of solar flare protons  

NASA Technical Reports Server (NTRS)

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

Barbosa, D. D.

1978-01-01

114

The double solar flare of October 6, 1977  

NASA Astrophysics Data System (ADS)

Prognoz-6 data are used to examine the energetic and temporal characteristics of the 1N double solar flare of October 6, 1977. The energetic characteristics are determined on the basis of an analysis of the parameters of charged-particle propagation in interplanetary space. The energy yield of the flare in the region of thermal and bremsstrahlung X-rays is calculated.

Valnichek, B.; Vedrenne, G.; Kuznetsov, A. V.; Likin, O. B.; Morozova, E. I.; Niel, M.; Pisarenko, N. F.; Farnik, F.; Hurley, K.; Chambon, G.

115

Relationship between solare flare productivity and photospheric magnetic field properties  

Microsoft Academic Search

From a large number of magnetograms we compute several physical measures including the maximum horizontal gradient the length of neutral line etc These measures are used to describe photospheric magnetic field properties such as nonpotentiality and complexity which is believed to be closely related with flare production Our statistical results suggest that solar flare productivity increases with nonpotentiality and complexity

Y. M. Cui; H. N. Wang

2006-01-01

116

Changes in the photospheric magnetic field associated with solar flares  

Microsoft Academic Search

The flare-related, persistent and abrupt changes in the photospheric magnetic field have been reported by many authors during recent years. These bewildering observational results pose a challenge to the current flare theories in which the photospheric magnetic field usually remains unchanged in the eruption. In this paper, changes in the photosphere magnetic field during the solar eruption are investigated based

Zhixing Mei; Jun Lin

2008-01-01

117

Capabilities of GRO/OSSE for observing solar flares  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

118

Nuclear processes and neutrino production in solar flares  

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

119

Dependence of the aurora borealis occurrences on the solar-terrestrial parameters  

Microsoft Academic Search

The recent measurements made by satellites of the aurorae in connection with solar phenomena have increased interest in auroral research. In the present investigation, we establish that, for the 20th solar cycle, the occurrence of visual discrete aurorae A, deduced from a complete set of data, is significantly related to the sunspot numbers Rz, the number of flares F (of

Y. Liritzis; B. Petropoulos

1986-01-01

120

Constraining Solar Flare Differential Emission Measures with EVE and RHESSI  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

121

Relation between the active region magnetic field and solar flares  

NASA Astrophysics Data System (ADS)

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.

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

2013-11-01

122

Antarctic O3 Depletion and its Correlation with Solar Flare Index  

Microsoft Academic Search

The paper presents the effect of solar flare index on Antarctic O3 depletion. Solar flare index is the actual representative of energy output of any flare event. A calibration curve between solar flare index and relative sunspot number is drawn. (A straight line is obtained and correlation coefficient between two variables is 0.95, n = 27, P < 0.01).The equation

S. K. Midya; S. C. Ganda; S. N. Sahu

1997-01-01

123

EVIDENCE FOR HOT FAST FLOW ABOVE A SOLAR FLARE ARCADE  

SciTech Connect

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

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

2013-10-10

124

Models of the Solar Atmospheric Response to Flare Heating  

NASA Technical Reports Server (NTRS)

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

Allred, Joel

2011-01-01

125

Signatures of the coalescence instability in solar flares  

NASA Technical Reports Server (NTRS)

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.

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

1984-01-01

126

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

NASA Astrophysics Data System (ADS)

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.

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

127

Magnetic Energy and the Cause of Solar Flares  

NSDL National Science Digital Library

This is a lesson about how magnetism causes solar flares. Learners will set up an electrical circuit with magnets to examine magnetic fields and their similarities to magnetic fields seen on the Sun. Learners should have a conceptual understanding of magnetism prior to exploring this lesson. This activity requires special materials including a galvanometer, copper wire, and sandpaper. This is Activity 2 in the Exploring Magnetism in Solar Flares teachers guide.

128

High energy phenomena during solar flares  

NASA Astrophysics Data System (ADS)

The main purpose is to analyze the characteristics of peculiar solar events that could be produced by ultrarelativistic electrons and try to define the new boundary conditions for the primary energy release during impulsive phase. It seems that submillimeter emission in solar flares is not a rare phenomenon, there is not much evidence, due to the lack of observations in this range of the spectrum. During May 1984 the Sun was observed at 90 GHz with high time resolution and high sensitivity, and evidence was obtained. The May 21, 1984 event, at 1326 UT is the best example of the high energy manifestation during the spectrum and gave us new boundary conditions for the physical phenomena in the Sun. The May 21 event required a detailed analysis of the current interpretation models and suggested the presence of relativistic electrons during the impulsive phase. In this case Syncrotron/inverse compton mechanism was suggested to explain submillimeter/x ray emission and short pulse duration. The new boundary conditions for primary energy release favored Tajima and Sakai's model, based in magnetic island coalescence theory.

Correia, Emilia

1989-11-01

129

Energetic electrons in impulsive solar flares  

NASA Technical Reports Server (NTRS)

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.

Batchelor, D. A.

1984-01-01

130

High energy gamma-emission of faint solar flares  

NASA Astrophysics Data System (ADS)

Hard X-ray and gamma-ray emission in energy band E¿50 keV was first observed by AVS-F apparatus onboard CORONAS-F satellite (detector SONG-D) during some solar flares classes B and C by GOES classification. Such hard component registered in flares with duration less than 30 min. According to AVS-F data about 50High energy gamma-emission up to several tens of MeV was observed during some classes B and C flares, which temporal profiles were not corresponded to Neupert effect. For example, during class B2.3 limb solar flare January 7, 2005 maximum observed energy was Emax 36 MeV and during class B4.6 disk solar flare January 12, 2005 maximum observed energy was Emax 12 MeV. Properties of temporal profiles and energy spectra of faint solar flares, during which high energy gamma-emission were registered discussed in the presented work. There is not any strong correlation between presence or absence of hard X-ray and gamma-ray emission and the intensity of soft X-ray emission during solar flares. It was not observed any statistically significant count rate exceed above background level was during some class M flares, for example, during event November 8, 2001 (class M4.2, flare lasts from 14:59 UT up to 16:00 UT, maximum of soft X-ray emission was at 15:35 UT on GOES data).

Arkhangelskaja, Irene; Kotov, Yury; Glyanenko, Alexander; Arkhangelsky, Andrey; Kolchina, Mary; Kirichenko, Alexey

131

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

132

Unique solar flare of September 22, 2011: The suction effect  

NASA Astrophysics Data System (ADS)

The specific features in the development of an X1 solar flare, which occurred on September 22, 2011, and was registered with the Atmospheric Imaging Assembly (AIA) device onboard the Solar Dynamics Observatory (SDO) in the UV line (? = 304 Å, He II), are analyzed. During the flare, which lasted about 12 h, cold plasma was sucked up with an increasing velocity from a very distant region into the low-lying hot region of flare energy release along a flat helical trajectory. This phenomenon fundamentally differs from a surge ejection, when matter previously ejected from the flare region returns to the flare hot zone under the action of gravity. Suction of cold plasma "from outside" into the hot flare region is interpreted in the scope of the rope flare mechanism, according to which an extremely inhomogeneous plasma density distribution in the cross-section originates in an emerging magnetic rope. In the region with a sharply decreased density (which is the suction region), the drift velocity in the current chanel can reach the ion thermal velocity, which inevitably results in the excitation of plasma turbulence and anomalous resistance, i.e., in the development of a flare.

Solov'ev, A. A.; Kirichek, E. A.; Ganiev, V. V.

2013-12-01

133

F-region enhancements induced by solar flares  

NASA Technical Reports Server (NTRS)

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.

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

1976-01-01

134

Magnetic Energy Dissipation in 200 Solar Flares Measured with SDO  

NASA Astrophysics Data System (ADS)

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

Aschwanden, Markus J.

2014-06-01

135

Imaging Spectroscopy of a White-Light Solar Flare  

NASA Astrophysics Data System (ADS)

We report observations of a white-light solar flare ( SOL2010-06-12T00:57, M2.0) observed by the Helioseismic Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO) and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The HMI data give us the first space-based high-resolution imaging spectroscopy of a white-light flare, including continuum, Doppler, and magnetic signatures for the photospheric Fe i line at 6173.34 Å and its neighboring continuum. In the impulsive phase of the flare, a bright white-light kernel appears in each of the two magnetic footpoints. When the flare occurred, the spectral coverage of the HMI filtergrams (six equidistant samples spanning ±172 mÅ around nominal line center) encompassed the line core and the blue continuum sufficiently far from the core to eliminate significant Doppler crosstalk in the latter, which is otherwise a possibility for the extreme conditions in a white-light flare. RHESSI obtained complete hard X-ray and ?-ray spectra (this was the first ?-ray flare of Cycle 24). The Fe i line appears to be shifted to the blue during the flare but does not go into emission; the contrast is nearly constant across the line profile. We did not detect a seismic wave from this event. The HMI data suggest stepwise changes of the line-of-sight magnetic field in the white-light footpoints.

Martínez Oliveros, J. C.; Couvidat, S.; Schou, J.; Krucker, S.; Lindsey, C.; Hudson, H. S.; Scherrer, P.

2011-04-01

136

EGRET observations of X-class solar flares.  

NASA Astrophysics Data System (ADS)

A series of X-class solar flares in the first week of June from the same region of the Sun prompted the action of making the Sun a Target of Opportunity for the Compton Observatory. The high energy capabilities of the EGRET instrument provided an opportunity to investigate the energetic solar flare processes for these flares. During the June 11, 1991 flare, the EGRET spark chamber obtained spectral and temporal measurements of high energy gamma-ray emissions to greater than 1GeV lasting hours after the initial impulsive phase of the flare. Spectral fits of the spark chamber data allow bremsstrahlung and pion decay contributions to the extended delayed emission to be determined. Spectral fits of the EGRET NaI data for the 1-200MeV energy range allow the solar line fluences of the 2.23 and 4.43MeV radiation to be determined for four of the June flares. Another series of X-class flare that occurred in late October 1991 were observed by the EGRET NaI detector and similar analyses were performed.

Schneid, E. J.; Bertsch, D. L.; Dingus, B. L.; Esposito, J. A.; Fichtel, C. E.; Hartman, R. C.; Hunter, S. D.; Kanbach, G.; Kniffen, D. A.; Lin, Y. C.; Mayer-Hasselwander, H. A.; Michelson, P. F.; von Montigny, C.; Mukherjee, R.; Nolan, P. L.; Sreekumar, P.; Thompson, D. J.

1996-12-01

137

Solar flare acceleration of solar wind: influence of active region magnetic field.  

PubMed

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. PMID:17790539

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

1981-06-26

138

Prediction of solar flares for the Space Exploration Initiative  

NASA Astrophysics Data System (ADS)

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

Davis, John M.

1994-06-01

139

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

SciTech Connect

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

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

2013-09-10

140

Another giant solar explosion follows Tuesday's enormous solar flare  

NASA Astrophysics Data System (ADS)

The activity started on Tuesday with a giant solar flare - the second biggest ever seen by SOHO, the ESA-NASA solar observatory that maintains a constant watch on the Sun, monitoring these events as they happen. A few minutes later, spacecraft circling the Earth began to detect high levels of energetic radiation, capable of blinding satellites and causing increased radiation levels down to normal aircraft cruising altitudes. About 24 hours after the solar flare was observed, an accompanying coronal mass ejection - a giant cloud of magnetised plasma - reached the Earth, causing rapid changes in the Earth's magnetic field and what is known as a geomagnetic storm. This storm caused widespread disruption to communications; both satellite-based and HF radio. These events are truly sporadic and extremely difficult to predict. On Wednesday it appeared that radiation levels were decreasing. However, a second flare overnight has caused a further sharp increase in radiation levels. Here on Earth, the disruption continues today with a further coronal mass ejection expected to reach the Earth tomorrow in time for Halloween. Solar eruptions of this type together with the associated increased radiation levels and electromagnetic disturbances around the Earth have real immediate and long-term economic impacts. During the last few days, space weather related problems have been detected on spacecraft operated by a range of agencies across the globe and operations teams are on alert. On Earth, telecommunication links have been disrupted and steps have been taken to safeguard aircraft, which including some changes in scheduling. Effects have also been detected in high latitude power grids and are being carefully monitored. The increased dependency of our society on systems which are directly or indirectly influenced by solar and other events seen in space raises concerns about our ability to monitor and anticipate these events and the resulting changes collectively referred to as space weather. At the European Space Agency these issues are being handled jointly in the Electromagnetics and Space Environment Division by Dr Eamonn Daly’s group for the specifications of spacecraft protection and in the spacecraft operations teams. In addition, Europe-wide coordination is currently being set up together with the European Union via its COST (Coordination in Science and Technology) programme and ESA’s General Studies Programme. This coordination aims to optimise our existing resources (together with our international partners) in order to develop an operational resource which will enable society to respond effectively to immediate as well as long-term changes in our space weather. Websites on space weather: http://www.esa.int/spaceweather/

2003-10-01

141

The energetics of chromospheric evaporation in solar flares  

NASA Technical Reports Server (NTRS)

The Solar Maximum Mission (SMM) spacecraft has provided high time resolution observational data regarding the soft X-ray emission from solar-flare plasma during 1980. The present investigation is concerned with the characteristics of a soft X-ray flare and the energetics of the impulsive phase on the basis of the data collected with the aid of two of the instruments on board the SMM, taking into account the Hard X-ray Burst Spectrometer (HXRBS) and the Bent Crystal Spectrometer (BCS). Attention is given to an analysis of soft X-ray flare spectra, the relative motion of the soft X-ray sources, the phenomenology of the soft X-ray flare, energy and mass transport during the impulsive phase, and energy deposition in the chromosphere during evaporation.

Antonucci, E.; Gabriel, A. H.; Dennis, B. R.

1984-01-01

142

Particle kinematics in solar flares: observations and theory  

NASA Astrophysics Data System (ADS)

This thesis is devoted to the study of particle acceleration and propagation processes in solar flares. Solar flares are amongst the most powerful and energetic activity phenomena our Sun exhibits. They release energy of the order of 10(32) erg in seconds to minutes. In the process, electrons and protons are accelerated to relativistic energies, making flares very efficient particle accelerators. The most compelling observational signatures of flares can be found in X-rays and extreme ultra-violet wavelengths. Due to atmospheric absorption, those wavelengths can only be studied from space. Since the beginning of the space age, countless flares have been observed by satellites. The present work is largely based on observations by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), an X-ray satellite which has been observing the Sun since February 2002. It is a NASA mission with substantial Swiss hardware and software contribution. Using RHESSI observations of flares of different intensity, a deeper understanding of the particle transport and energy transport processes in flare loops, as well as the acceleration site and acceleration mechanism is sought. The time evolution of images and spectra is studied along with the quantitative relations between X-ray sources observed in the corona (coronal sources) and from the chromosphere (footpoints). The spectral relations found between coronal sources and footpoints are compared to the so-called ``intermediate thin-thick target model'', which was based on observations by the satellite Yohkoh. We show that the spectral relations between coronal sources and footpoints observed with RHESSI cannot be explained by the intermediate thin-thick target model. In a next step, return currents in the flare loop were considered. With this extension to the existing model, the spectra of the coronal source and the footpoints, as well as the relations between them can be explained, indicating the importance of return currents in flare loops. In a second part, observations of so-called ``pre-flares'' are presented. This earliest phase of a flare cannot be explained by the standard flare model of chromospheric evaporation which involves energy transport and deposition in the chromosphere by beams of accelerated electrons. In pre-flares, an increase in density and emission measure is observed, indicating that chromospheric evaporation is occurring. However, no observational signatures of fast electrons are found. We show that if energy is transported by means of thermal conduction instead of an electron beam, the observations can explained.

Battaglia, Marina

2008-12-01

143

Identification of the ionospheric activities in the solar flare  

NASA Astrophysics Data System (ADS)

With the continuous observations of different explosive activities on the sun by the NASA/GOES satellite it has become possible to calibrate various events. Enhanced X-ray and UV flux from solar events increases the degree of ionization in the ionosphere. This modulates the VLF signals emitted from various call stations throughout the globe. We present examples of VLF signals received at CSP antennas from such stations due to a few recent solar flares and compare them with the profiles of the solar flares directly observed by GOES. Such results could be used to study the composition of thebreak ionosphere.

Sasmal, S.; Saha, M.; Khan, R.; Chakrabarti, S.; Chakrabarti, S. K.

144

Predicting Arrival Of Protons Emitted In Solar Flares  

NASA Technical Reports Server (NTRS)

Visual Utility for Localization of Corona Accelerated Nuclei (VULCAN) computer program provides both advance warnings and insight for post-event analyses of effects of solar flares. Using measurements of peak fluxes, times of detection, flare location, solar wind velocities, and x-ray emissions from Sun, as electronically sent by NOAA (National Oceanographic and Atmospheric Administration), VULCAN predicts resulting intensities of proton fluxes at various user-chosen points (spacecraft or planets) of solar system. Also predicts times of onset of fluxes of protons and peak values of fluxes.

Spagnuolo, John N., Jr.; Schwuttke, Ursula M.; Han, Cecilia S.; Hervias, Felipe

1996-01-01

145

Unusual Sunquake Events Challenge the Standard Model of Solar Flares  

NASA Astrophysics Data System (ADS)

"Sunquakes" represent helioseismic waves excited by solar flares. According to the standard flare model, sunquakes are associated with the hydrodynamic response of the low atmosphere to beams of flare-accelerated particles. Observations with the HMI instrument on Solar Dynamics Observatory have shown that sunquakes are a much more common phenomenon than this was found from the previous SOHO/MDI observations. The HMI observations reveal that sunquakes may occur not only during strong X-class flare but also in relatively weak flares of low M-class (as low as M1). It is particularly surprising that, in some cases, the sunquake initiating impacts are observed in the early impulsive or even pre-heating phase, prior to the main hard X-ray impulse and even without a significant hard X-ray signal. We examine properties of such sunquake events, present a detailed analysis of M2.8 flare of February 17, 2013, using HMI, AIA, GOES and RHESSI data, and discuss implications for the standard flare model.

Kosovichev, Alexander G.; Sharykin, Ivan; Zimovets, Ivan

2014-06-01

146

Capabilities of Gro/Osse for Observing Solar Flares.  

National Technical Information Service (NTIS)

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 som...

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

1989-01-01

147

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

NASA Astrophysics Data System (ADS)

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 ?-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.

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

148

Energetic electron distribution in the solar flare  

NASA Astrophysics Data System (ADS)

We investigate the distribution of energetic electrons in the solar flare by means of numerical simulations. First, we study the height distribution under an idealized model of time-varying, potential electromagnetic fields, by solving the drift-kinetic Vlasov equation (Minoshima et al. 2010, ApJ, 714, 332; 2011, ApJ, 732, 111). 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 can explain the energy-dependent height distribution of electrons, as indicated by coronal hard X-ray (HXR) and microwave sources (including the above-the-loop-top HXR source). Next, we perform the test particle simulation under the electromagnetic fields obtained from an MHD simulation of magnetic reconnection with different magnetic Reynolds numbers. When the Reynolds number is low, the reconnected fields are close to the potential one so that the result is very similar to the previous result. On the other hand, with the high Reynolds number, the fields significantly deviate from the potential. A rapid change of the magnetic field topology can violate the second adiabatic invariant of electrons. As a result, an impulsive electron flux appears along the field line, different from the low Reynolds number case. This may contribute to the electron precipitation into the footpoint, as indicated by a rapid temporal change of HXR emissions.

Minoshima, T.; Masuda, S.; Miyoshi, Y.; Miyoshi, T.; Kusano, K.

2011-12-01

149

Lunar surface cosmic ray experiment. [including solar flare studies  

NASA Technical Reports Server (NTRS)

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

Price, P. B.

1974-01-01

150

Conduction-driven chromospheric evaporation in a solar flare  

NASA Technical Reports Server (NTRS)

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

Zarro, Dominic M.; Lemen, James R.

1988-01-01

151

Common SphinX and RHESSI observations of solar flares  

NASA Astrophysics Data System (ADS)

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

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

152

Periodicities in the occurrence rate of solar proton events  

NASA Technical Reports Server (NTRS)

Power spectral analyses of the time series of solar proton events during the past three solar cycles reveal a periodicity around 154 days. This feature is prominent in all of the cycles combined, cycles 19 and 21 individually, but is only weak in cycle 20. These results are consistent with the presence of similar periodicities between 152 and 155 days in the occurrence rate of major solar flares, the sunspot blocking function (Ps), the 10.7 cm radio flux (F10.7), and the sunspot number (Rz). This suggests that the circa 154-days periodicity may be a fundamental characteristic of the sun. Periods around 50-52 days are also found in the combined data set and in the three individual cycles, in general agreement with the detection of this periodicity in major flares in cycle 19, and in Ps, F10.7, and Rz in cycle 21. The cause of the 155 day period remains unknown. The spectra contain lines (or show power at frequencies) consistent with a model in which the periodicity is caused by differential rotation of active zones and a model in which it is related to beat frequencies between solar oscillations, as proposed by Wolff (1974, 1983).

Gabriel, S.; Evans, R.; Feynman, J.

1990-01-01

153

Periodicities in the occurrence rate of solar proton events  

NASA Astrophysics Data System (ADS)

Power spectral analyses of the time series of solar proton events during the past three solar cycles reveal a periodicity around 154 days. This feature is prominent in all of the cycles combined, cycles 19 and 21 individually, but is only weak in cycle 20. These results are consistent with the presence of similar periodicities between 152 and 155 days in the occurrence rate of major solar flares, the sunspot blocking function (Ps), the 10.7 cm radio flux (F10.7), and the sunspot number (Rz). This suggests that the circa 154-days periodicity may be a fundamental characteristic of the sun. Periods around 50-52 days are also found in the combined data set and in the three individual cycles, in general agreement with the detection of this periodicity in major flares in cycle 19, and in Ps, F10.7, and Rz in cycle 21. The cause of the 155 day period remains unknown. The spectra contain lines (or show power at frequencies) consistent with a model in which the periodicity is caused by differential rotation of active zones and a model in which it is related to beat frequencies between solar oscillations, as proposed by Wolff (1974, 1983).

Gabriel, S.; Evans, R.; Feynman, J.

1990-08-01

154

Magnetic-field variations and solar flare activity  

NASA Astrophysics Data System (ADS)

Solar filtergrams obtained at the Crimean Astrophysical Observatory at the center and wings of the H ? 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.

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

2012-11-01

155

The Periodicities of Solar Flares during Solar Cycle 23  

NASA Astrophysics Data System (ADS)

The Events of energetic particles from solar flares and CME have been studied. The data were taken from National Geophysical data center (NGDC) in Boulder Colorado USA. The data of these events were given during the solar cycle 23rd. The 23rd cycle is the present one started in April 1996 and its maximum was in May 2001 and will be decayed during year 2007. Power spectrum methods have been applied for analysis of the data given to find the short and intermediate periodicities. The periodicity around 14 days has been appeared in this analysis. This has important implications for understanding and predicting the effects of solar activity on the Earth and earth’s atmosphere. If a CME’ hit the Earth it can excite a geomagnetic storm. Large geomagnetic storms have among other things will cause electrical power which damage satellites communications. In space CME typically drive shock waves that produce energetic particles that can damag both electronic equipment and astronauts that are outside the protection of the Earth's magnetic field. So the prediction of the high energetic particle events is of vital importance for space navigation and airline disasters.

Abdhady, Ahmed

156

Energetic Correlation Between Solar Flares and Coronal Mass Ejections  

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

157

A thermal/nonthermal approach to solar flares  

NASA Technical Reports Server (NTRS)

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

Benka, Stephen G.

1991-01-01

158

Variability of Thermosphere and Ionosphere Responses to Solar Flares  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

159

A RECONNECTING CURRENT SHEET IMAGED IN A SOLAR FLARE  

SciTech Connect

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

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

2010-11-01

160

Ion acceleration and positron production and annihilation in solar flares  

NASA Astrophysics Data System (ADS)

I first review: a) the current state of knowledge of ion acceleration in solar flares; b) the physics of positron production and annihilation; and c) recent RHESSI data on solar flare annihilation radiation. I then show how the modeling of the positron production and annihilation in the chromosphere, coupled with the newly available high-resolution data on the 511 keV annihilation line, can have important physical implications w. r. t. the models: a) information on the temperature and density of the chromosphere; b) constraints on some of the physical characteristics of the flare and to some extent on the acceleration process.Although I do mention past instruments (SMM and Yohkoh), this review focuses on the RHESSI satellite, considering the quantum leap it has constituted in the quality of the data it is providing and consequently the constraints it can place on models (of ion acceleration, annihilation environment, etc.).

Guessoum, Nidhal

161

The acceleration of heavy nuclei in solar flares  

NASA Technical Reports Server (NTRS)

The overabundance of heavy nuclei in solar cosmic rays of energy approximately 5 Mev/nucleon is explained by taking into account the pre-flare ionization states of these nuclei in the region where they are accelerated. A model is proposed which considers two-step accelerations associated with the initial development of solar flares. The first step is closely related to the triggering process of flares, while the second one starts with the development of the explosive phase. Further ionization of medium and heavy nuclei occurs through their interaction with Kev electrons accelerated by the first-step acceleration. It is suggested that the role of these electrons is important in producing fully ionized atoms in the acceleration regions.

Sakurai, K.

1974-01-01

162

The acceleration of heavy nuclei in solar flares  

NASA Technical Reports Server (NTRS)

The overabundance of heavy nuclei in solar cosmic rays of energy below about 10 MeV/nucleon is explained by taking into account the pre-flare ionization states of these nuclei in the region where they are accelerated. A model is proposed which considers two-step accelerations associated with the initial development of solar flares. The first step is closely related to the triggering process of flares, while the second one starts with the development of the explosive phase. Further ionization of medium and heavy nuclei occurs through their interaction with keV electrons accelerated by the first-step acceleration. It is suggested that the role of these electrons is important in producing fully ionized atoms in the acceleration regions.

Sakurai, K.

1975-01-01

163

Peak flux density spectra of large solar radio bursts and proton emission from flares  

NASA Astrophysics Data System (ADS)

Castelli et al. (1967) proposed that the 'U-shaped' peak flux density radio spectrum with high flux densities at meter and centimeter wavelengths and a minimum in the decimeter range is the 'preferred spectrum' for major solar proton flares. Evidence was presented indicating that the U-shaped spectrum was a necessary or almost necessary condition for a solar flare to produce a polar cap absorption (PCA) event. The present study is concerned with a classification of the peak flux density spectra of all large radio bursts observed from 1965-1979, taking into account also a comparison of the associations of bursts of different spectral classes with interplanetary proton events and type II/IV bursts. In addition an examination is conducted of the nature of the low-frequency branch of the U-shaped spectrum. A search is performed regarding the necessary conditions in the radio domain for the occurrence of a significant proton event.

Cliver, E. W.; McNamara, L. F.; Gentile, L. C.

1985-07-01

164

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

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

165

Antarctic O 3 Depletion and its Correlation with Solar Flare Index  

Microsoft Academic Search

The paper presents the effect of solar flare index on Antarctic O3 depletion. Solar flare index is the actual representative of energy output of any flare event. A calibration curve between\\u000a solar flare index and relative sunspot number is drawn. (A straight line is obtained and correlation coefficient between two\\u000a variables is 0.95, n = 27, P < 0.01).The equation

S. K. Midya; S. C. Ganda; S. N. Sahu

1997-01-01

166

Laboratory simulation of energy release in solar flares  

Microsoft Academic Search

A laboratory simulation method is proposed for energy release processes occurring in a fragment of the flare current sheet on the Sun. The method relies on the assumption that the spatial scale of such processes is represented by the current sheet's thickness whose values can be close for both the solar and laboratory conditions. It is shown that in an

A. T. Altyntsev; V. M. Bardakov; V. I. Krasov; N. V. Lebedev; V. L. Papernyi

1986-01-01

167

Explosive hydrogen-burning model of solar flares  

Microsoft Academic Search

A solar-flare model is proposed, based on the 'explosive burning' concept of Wallace and Woosely (1981), which takes into account the high temperature (10 to the 9th K) produced by the shock wave generated by the hydromagnetic wave at the junction of the sunspot and the area outside it. According to this model, the increase of the magnetic field during

L. Manihar Singh; L. Randhoni Devi

1990-01-01

168

Energy Build-Up, Transport, and Release in Solar Flares.  

National Technical Information Service (NTIS)

With the advent of the new observatories, it is becoming more evident that the solar flare is a more global phenomenon than previously thought. It is only the high temperature/high density manifestations that are confined to a small part of an active regi...

G. M. Simnett

1992-01-01

169

The cooling of flare produced plasmas in the solar corona  

Microsoft Academic Search

Solar flare X-rays, at energies less than 10 keV, are emitted by hot plasmas located in the corona. Three plasma cooling models are examined in detail. The cooling of the electrons by Coulomb collisions with ions at a lower temperature would require the observed material to occupy very large volumes. Cooling could take place by conduction or by radiation and

J. L. Culhane; J. F. Vesecky; K. J. H. Phillips

1970-01-01

170

Hydromagnetic interpretation of short time scale structures in solar flares  

Microsoft Academic Search

Hydromagnetic interpretation of the solar flare short time scale structure indicated in microwave and hard X-ray emission during the impulsive phase is presented. The main assumption is that the plasma ejection from the current sheet may be considered as a forced convection by an isolated source. From this point of view some analogies with small scale short lasting hydrodynamic and

V. M. Dermendjiev

1986-01-01

171

Statistical Properties of Super-hot Solar Flares  

NASA Astrophysics Data System (ADS)

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 ? and volume filling factor f cannot be much less than unity in the super-hot region.

Caspi, Amir; Krucker, Säm; Lin, R. P.

2014-01-01

172

Correlation Between Solar Flare Productivity and Photospheric Magnetic Field Properties  

Microsoft Academic Search

From a large number of SOHO\\/MDI longitudinal magnetograms, three physical measures including the maximum horizontal gradient,\\u000a the length of the neutral line, and the number of singular points are computed. These measures are used to describe photospheric\\u000a magnetic field properties including nonpotentiality and complexity, which is believed to be closely related to solar flares.\\u000a Our statistical results demonstrate that solar

Yanmei Cui; Rong Li; Liyun Zhang; Yulin He; Huaning Wang

2006-01-01

173

Max '91: Flare research at the next solar maximum  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

174

Theoretical studies on rapid fluctuations in solar flares  

NASA Technical Reports Server (NTRS)

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

Vlahos, Loukas

1986-01-01

175

Bulk Acceleration of Electrons in Solar Flares?  

NASA Astrophysics Data System (ADS)

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

Holman, Gordon D.

2014-06-01

176

Solar flare impulsive phase observations from SDO and other observatories  

NASA Astrophysics Data System (ADS)

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

Chamberlin, P. C.; Woods, T. N.; Schrijver, C. J.; Warren, H. P.; Milligan, R. O.; Christe, S.; Brosius, J. W.

2010-12-01

177

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

NASA Astrophysics Data System (ADS)

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 ?. In this flare, the intense emission of hard X-rays and ?-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 ?-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.

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

178

The preferential acceleration of heavy nuclei in solar flares.  

NASA Technical Reports Server (NTRS)

A two-stage model is proposed for the mechanism of heavy nuclei (Z greater than 8) accelerated in solar flares. In the first stage, fully stripped ions are first accelerated to suprathermal energies. In the second stage, a fraction of these ions are Fermi-accelerated to higher energies. Transport to the Fermi-acceleration region involves electron pickup, while injection into Fermi acceleration is rigidity dependent. The degree of enhancement of the abundance of heavy nuclei may be expected to vary for each individual flare.

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

1972-01-01

179

Solar Atmopheric Abundances and Energy Content in Flare Accelerated Ions from Gamma-Ray Spectroscopy  

Microsoft Academic Search

We used SMM gamma-ray data from 19 solar flares to study ambient elemental abundances in the solar atmosphere. We found that the abundance ratios of low FIP (first ionization potential) to high FIP elements are enhanced relative to photospheric abundances, but that the variability of these ratios from flare to flare is limited to a narrower range than that inferred

Reuven Ramaty; Natalie Mandzhavidze; Benzion Kozlovsky; Ronald J. Murphy

1995-01-01

180

Large Solar Flares and Sheared Magnetic Field Configuration  

NASA Technical Reports Server (NTRS)

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.

Choudhary, Debi Prasad

2001-01-01

181

Signatures of current loop coalescence in solar flares  

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

182

Ground-based Observations of Large Solar Flares Precursors  

NASA Astrophysics Data System (ADS)

The importance problem of Solar-terrestrial physics is regular forecasting of solar activity phenomena, which negatively influence the human's health, operating safety, communication, radar sets and others. The opportunity of development of short-term forecasting technique of geoeffective solar flares is presented in this study. This technique is based on the effect of growth of pulsations of horizontal component of geomagnetic field before the solar proton flares. The long-period (30-60 minutes) pulsations of H-component of geomagnetic field are detected for the events of different intensity on March 22, 1991, November 4, 2001, and November 17, 2001 using the method of wavelet-analysis. Amplitudes of fluctuations of horizontal component of geomagnetic field with the 30-60 minute's periods grow at the most of tested stations during 0.5-3.5 days before the solar flares. The particularities of spectral component are studied for the stations situated on different latitudes. The assumptions about the reason of such precursors-fluctuations appearance are made.

Sheyner, Olga; Smirnova, Anna; Snegirev, Sergey

2010-05-01

183

Automated Feature Detection and Solar Flare Prediction Using SDO Data  

NASA Astrophysics Data System (ADS)

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

Qahwaji, Rami; Ahmed, Omar; Colak, Tufan

184

An emerging flux model for the solar flare phenomenon  

NASA Technical Reports Server (NTRS)

An outline is presented of the physical processes involved in the emerging flux model, which appears to explain naturally many solar flare observations. The separate physical phases of the basic model include a preflare heating phase as the new flux emerges, an impulsive phase as high-energy particles are accelerated, a flash (or explosive) phase when the H-alpha intensity increases, and a main phase while it decreases. The extent and morphology of the main phase emission depend on the structure of the magnetic field region in which the new flux finds itself imbedded. It is suggested that a (small) simple loop flare occurs if the new flux appears in a region where no great amount of magnetic energy in excess of potential is stored. A two-ribbon flare occurs if the flux emerges near the polarity inversion line of an active region that has begun to develop filaments.

Heyvaerts, J.; Priest, E. R.; Rust, D. M.

1977-01-01

185

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

186

Ionospheric response to the solar flare of 14 July 2000  

NASA Astrophysics Data System (ADS)

We present our observations of the global ionospheric response to the X-class solar flare that started the Bastille Day storm on 14 June 2000. The observations were made using the Low-Resolution Airglow and Aurora Spectrograph (LORAAS) instrument on the Advanced Research and Global Observation Satellite (ARGOS). The ARGOS is in a Sun-synchronous orbit at 0230/1430 LT at approximately 840 km altitude. During the daytime the LORAAS observes the 911-Å emission; this emission is produced by radiative recombination of F region O+ and electrons. We simultaneously invert approximately one-half of an orbit of 911-Å limb scans (approximately 30-45 min of observing) using a tomographic inversion technique to produce dayside electron density maps in the orbit plane. We compare our observations of orbits immediately before and after the flare to the orbit in which the flare occurred. We observed a 41% increase in the average 911-Å brightness during the flare orbit compared to the orbits before and after the flare. This corresponds to an overall increase of electron density by ˜20%. This density enhancement has largely decayed by the next orbit. At altitudes near the F region peak, 250-450 km, the density enhancement has decayed to the preflare value. An enhancement of the electron densities at approximately -50° geomagnetic latitude has moved northward in the flare orbit, which may be indicative of enhanced meridional transport postflare. We compared our results to output from the SAMI-2 model, which was run for the flare study presents in the work of [2002].

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

2004-02-01

187

A Multiwavelength Study of Three Solar Flares  

NASA Astrophysics Data System (ADS)

In this paper we seek a self-consistent model for three strong limb flares observed at 17 and 34 GHz by the Nobeyama radioheliograph and also in soft X-rays and hard X-rays by the Yohkoh SXT (Soft X-Ray Telescope) and HXT (Hard X-Ray Telescope) instruments. Additional radio spectral data were provided by the Nobeyama polarimeter. The flare geometry is simple, with one well-defined flaring loop in each event. The 17 and 34 GHz emissions are optically thin gyrosynchrotron radiation from energetic electrons that outlines the flaring loops and peaks close to the loop tops. We infer that the variation of magnetic field along the loops is very small. We try to reproduce the observed radio morphologies and fluxes using a model gyrosynchrotron loop. The results of our modeling rely on the model magnetic field geometry that we choose. Although the exact loop geometry cannot be constrained from a two-dimensional snapshot, we choose for simplicity a line-dipole magnetic field, and the model field lines are circular. The SXT/HXT images are used to provide the physical parameters of the model loops. The high-frequency polarimeter data give the energy spectral index of the radio-emitting electrons. We could not reconcile the observed radio morphologies and fluxes using classic dipole magnetic field models. The best-fit model that uses the same input parameters for both frequencies and partly reconciles the observed 17 and 34 GHz morphologies and fluxes is produced when we invoke a magnetic field with constant strength along the model loop. These model loops have uniform thickness. The derived densities of the radio-emitting electrons are (1-6)×104 cm-3 with energy limits between 60 and 5000 keV. These models are the best fits we can get under the best assumptions we can justify, but they do not in fact match the radio morphologies very well; their problems and limitations are discussed.

Kundu, M. R.; Nindos, A.; White, S. M.; Grechnev, V. V.

2001-08-01

188

Temporal Variability of Ion Acceleration and Abundances in Solar Flares  

NASA Technical Reports Server (NTRS)

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

Shih, Albert

2011-01-01

189

Elemental abundances of flaring solar plasma - Enhanced neon and sulfur  

NASA Technical Reports Server (NTRS)

Elemental abundances of two flares observed with the SMM Flat Crystal Spectrometer are compared and contrasted. The first had a gradual rise and a slow decay, while the second was much more impulsive. Simultaneous spectra of seven bright soft X-ray resonance lines provide information over a broad temperature range and are available throughout both flares, making these events unique in the SMM data base. For the first flare, the plasma seemed to be characterized by coronal abundances but, for the second, the plasma composition could not be coronal, photospheric, or a linear combination of both. A good differential emission measure fit required enhanced neon such that Ne/O = 0.32 +/- 0.02, a value which is inconsistent with the current models of coronal abundances based on the elemental first-ionization potential. Similar values of enhanced neon are found for flaring plasma observed by the SMM gamma-ray spectrometer, in (He-3)-rich solar energetic particle events, and in the decay phase of several long duration soft X-ray events. Sulfur is also enhanced in the impulsive flare, but not as dramatically as neon. These events are compared with two models which attempt to explain the enhanced values of neon and sulfur.

Schmelz, J. T.

1993-01-01

190

Statistical analysis of thermospheric and ionospheric response to solar flares in solar cycle 23  

NASA Astrophysics Data System (ADS)

In the present study, we first explored the thermospheric response to all X-class solar flares during 2001-2006 by analyzing CHAMP and GRACE measurements. The observed results show that X5 and stronger solar flares can induce an average enhancement of 10-13% in thermospheric density in latitude 50°S-50°N within ~4 hours after the flare onset. Many important lines and continua in solar EUV region are optically thick, thus EUV enhancements are smaller for flares located near the solar limb due to absorption by the solar atmosphere. Limb flares induce smaller thermospheric responses, due to the limb effect of solar EUV. The thermospheric density enhancement is much more correlated with integrated EUV flux than with peak EUV flux, with a high correlation coefficient of 0.91, which suggests that thermospheric response is strongly dependent on the total integrated energy into the thermosphere. Then we studied the ionospheric responses to solar flares during 1999-2006 by using the GOES 0.1-0.8nm X-ray, 26-34nm EUV, and GPS/TEC in the worldwide. The statistical results show the TEC enhancements are highly related to the solar zenith angle (SZA). The smaller SZA would result in the greater TEC responses. The TEC response is not highly related with the X-ray flux (the correlation coefficient 0.6), which is due to that the ionospheric response is not only related to the X-ray flux level, but also related to the flare location on solar disc. The limb flare has less effect on the ionosphere than the central flare. The reason for this is that the main ionization source EUV flux has such flare location dependence. The statistical results show that the flare location effect decreases with decreasing flare X-ray class. The results also show that the TEC enhancement does not linearly increase with X-ray flux. Its uprising amplitude increases with X-ray flux. The TEC response also has slight latitude dependence: it decrease with latitude. And the TEC response has significant seasonal dependence. The maximum response occurred at equinox and the minimum response at summer.

Le, Huijun; Liu, Libo; Chen, Yiding; Wan, Weixing

2013-04-01

191

Particle acceleration and gamma-emission from solar flares  

NASA Astrophysics Data System (ADS)

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

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

192

Flares on DMe Stars: IUE (International Ultraviolet Explorer) and Optical Observations of At Mic, and Comparison of Far-Ultraviolet Stellar and Solar Flares.  

National Technical Information Service (NTIS)

The paper concerns observations of a large flare event on the dMe star At Mic, detected by the International Ultraviolet Explorer. The far-ultraviolet spectra of the flare is compared with those of other stellar flares, and also with a large solar flare r...

G. E. Bromage K. J. H. Phillips P. L. Dufton A. E. Kingston

1986-01-01

193

Dielectronic satellite lines and double layers in solar flares  

NASA Astrophysics Data System (ADS)

Context. Particle acceleration during solar flares results in departures of the distribution of particle energies from the Maxwellian distribution. Apart from the high-energy tail, the bulk of the distribution was recently also found to be significantly affected, due, e.g., to the presence of double layers. Aims: We investigate the influence of several proposed non-Maxwellian distribution functions on the X-ray flare line spectra. The distribution functions considered are sharply peaked and include the n-distribution, the moving Maxwellian distribution, and the distribution formed in strong double layers in the flaring plasma. Methods: Synthetic Si xiid-Si xiv spectra involving allowed and dielectronic transitions at 5 - 6 Å are calculated numerically. The parameters chosen for the calculations correspond to the impulsive phase of solar flares, as inferred by previous authors. Results: The Si xiid ?5.56/Si xiii ?5.68 and Si xiid ?5.82/Si xiii ?5.68 ratios depend on the relative number of electrons at energies corresponding to the formation of the Si xiid lines. Therefore, these ratios increase with the increasing narrowness of the peak of the electron distribution function. The highest ratios are achieved for the distribution formed in double layers, while the moving Maxwellian distribution is less likely to reproduce the observed enhancement of Si xiid intensities. However, the ratio of the allowed Si xiv ?5.22/Si xiii ?5.68 transitions depends on the ionization equilibrium. This ratio is very small for the double-layer distribution. Combination of the double-layer distribution with a Maxwellian distribution with the same mean energy significantly enhances this ratio, while keeping the Si xiid intensities sufficiently increased to explain the characteristics of the observed spectra. Conclusions: These results support the presence of double layers in the plasma during impulsive phase of solar flares.

Dzif?áková, E.; Karlický, M.; Dudík, J.

2013-02-01

194

Flare-excited Waves in the Solar Interior and Atmosphere  

NASA Astrophysics Data System (ADS)

The X2.2 flare of February 15, 2011, produced powerful waves traveling in the solar interior and atmosphere, which were observed with the HMI and AIA instruments on SDO. These data provide a unique opportunity for high-resolution spatial and spectral analyses of the helioseismic and atmospheric responses and their relationship to the flare energy release. In particular, the analysis of the SDO/HMI and X-ray data from RHESSI shows that the helioseismic waves were initiated by the photospheric impact in the early impulsive phase, observed prior to the hard X-ray (50-100 keV) impulse, and were probably associated with atmospheric heating by relatively low-energy electrons (6-50 keV) and heat flux transport. The impact caused a short wave-like motion in the sunspot penumbra prior to the appearance of the helioseismic wave. The AIA observations revealed for the first time the propagation of this wave in the upper atmosphere, and the accompanying shock wave. The multi-instrument observations of the flare-excited waves open new perspectives for studying the energy release and transport in solar flares, and also for the magnetic field seismology in active regions.

Kosovichev, Alexander G.

2011-05-01

195

Plasma heating during the rise phases of the solar flares  

NASA Astrophysics Data System (ADS)

In our poster we analyze soft X-ray (SXR) and hard X-ray (HXR) emissions of two solar flares observed by the RHESSI and GOES satellites, where SXR emission precedes the onset of the main bulk HXR emissions by few minutes. RHESSI spectra indicate a presence of the non-thermal electrons also before the impulsive phases of both events. This suggests that an additional heating mechanism of the plasma may be at work at the early beginning of the flares. Assuming that a dominant energy transport mechanism during the rise phase of solar flares is electron-beam-driven evaporation, we used non-thermal electron beams derived from RHESSI spectra as the heating source in a hydrodynamic models of the analyzed flares. We showed that energy delivered by non-thermal electron beams is sufficient to heat the are loops to temperatures in which they emit SXR closely following the GOES light curves. Additionally we analyze the number of non-thermal electrons, the low-energy cutoffs, electron spectral indices, and the changes of these parameters with time.

Rudawy, Pawel; Falewicz, Robert; Siarkowski, Marek

196

Flux emergence, flux imbalance, magnetic free energy and solar flares  

NASA Astrophysics Data System (ADS)

Emergence of complex magnetic flux in the solar active regions lead to several observational effects such as a change in sunspot area and flux embalance in photospheric magnetograms. The flux emergence also results in twisted magnetic field lines that add to free energy content. The magnetic field configuration of these active regions relax to near potential-field configuration after energy release through solar flares and coronal mass ejections. In this paper, we study the relation of flare productivity of active regions with their evolution of magnetic flux emergence, flux imbalance and free energy content. We use the sunspot area and number for flux emergence study as they contain most of the concentrated magnetic flux in the active region. The magnetic flux imbalance and the free energy are estimated using the HMI/SDO magnetograms and Virial theorem method. We find that the active regions that undergo large changes in sunspot area are most flare productive. The active regions become flary when the free energy content exceeds 50% of the total energy. Although, the flary active regions show magnetic flux imbalance, it is hard to predict flare activity based on this parameter alone.

Choudhary, Debi Prasad; Gosain, Sanjay; Gopalswamy, Nat; Manoharan, P. K.; Chandra, R.; Uddin, W.; Srivastava, A. K.; Yashiro, S.; Joshi, N. C.; Kayshap, P.; Dwivedi, V. C.; Mahalakshmi, K.; Elamathi, E.; Norris, Max; Awasthi, A. K.; Jain, R.

2013-10-01

197

Flare.  

National Technical Information Service (NTIS)

The patent application relates to flares which are designed to reach maximum or near maximum infrared output as quickly as possible after ignition, i.e., flares with very fast rise times. Constructing a flare grain with a plurality of longitudinal opening...

K. K. Foote

1974-01-01

198

D-region electron density evaluated from VLF amplitude time delay during X-ray solar flares  

NASA Astrophysics Data System (ADS)

VLF amplitude enhancements of the NAA/24.0 kHz signal (Maine, USA), registered by the Belgrade AbsPAL facility during solar flares, have been related to solar X-ray fluxes measured by the GOES-12 satellite. The observed regular appearance of the VLF amplitude/phase peak behind the peak of the corresponding X-ray flux has been characterized by the time delay assigned to each of the 97 out of 114 flare-induced distinct amplitude/phase enhancement events analysed. The measurements reported pertain to the period May August of the years 2004 and 2005 and have been used to model the electron density enhancements of the D-region during solar flares. On the grounds of the continuity equation for the electron component and the amplitude time delay, the effective recombination coefficient has been estimated to range from 10m/s to 10m/s, depending on the X-ray maximum flux. By integrating the continuity equation, the time variation of the electron density during solar flare occurrence has been restored. Enhancements up to two orders of magnitude, for X-class flares, with respect to undisturbed conditions were predicted. The results obtained have been found to be in good agreement with measurements by different techniques, as well as with the independent estimates of ? and H. Errors introduced by the applied approach have been critically examined to place the uncertainty of the results arrived at between 10% and 20%.

Žigman, V.; Grubor, D.; Šuli?, D.

2007-05-01

199

THz photometers for solar flare observations from space  

NASA Astrophysics Data System (ADS)

The search for the still unrevealed spectral shape of the mysterious THz solar flare emissions is one of the current most challenging research issues. The concept, fabrication and performance of a double THz photometer system, named SOLAR-T, is presented. Its innovative optical setup allows observations of the full solar disk and the detection of small burst transients at the same time. The detecting system was constructed to observe solar flare THz emissions on board of stratospheric balloons. The system has been integrated to data acquisition and telemetry modules for this application. SOLAR-T uses two Golay cell detectors preceded by low-pass filters made of rough surface primary mirrors and membranes, 3 and 7 THz band-pass filters, and choppers. Its photometers can detect small solar bursts (tens of solar flux units) with sub second time resolution. Tests have been conducted to confirm the entire system performance, on ambient and low pressure and temperature conditions. An artificial Sun setup was developed to simulate performance on actual observations. The experiment is planned to be on board of two long-duration stratospheric balloon flights over Antarctica and Russia in 2014-2016.

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

2014-05-01

200

Probable solar flare doses encountered on an interplanetary mission as calculated by the MCFLARE code  

NASA Technical Reports Server (NTRS)

The computer program, MCFLARE, uses Monte Carlo methods to simulate solar flare occurrences during an interplanetary space voyage. The total biological dose inside a shielded crew compartment due to the flares encountered during the voyage is determined. The computer program evaluates the doses obtained on a large number of trips having identical trajectories. From these results, a dose D sub p having a probability p of not being exceeded during the voyage can be determined as a function of p for any shield material configuration. To illustrate the use of the code, a trip to Mars and return is calculated, and estimated doses behind several thicknesses of aluminum shield and water shield are presented.

Lahti, G. P.; Karp, I. M.

1972-01-01

201

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

NASA Astrophysics Data System (ADS)

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/.

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

2012-10-01

202

Chromospheric Evaporation Manifested by Microwave Source of a Solar Flare  

NASA Astrophysics Data System (ADS)

Being the key ingredient of standard scenario of solar flares, chromospheric evaporation has been gotten more and more observational supports, from the blue-shifted ultraviolet lines in early SMM time to the movement of hard X-ray sources in the RHESSI time. However there seems to have less work related microwave imaging observations to the chromospheric evaporation. We present in this paper the detailed source evaluation at 17 and 34 GHz for a solar flare observed with Nobeyama Radioheliograph, which appears first at the footpoints, then expands along the loop upward, and finally fills up the loop. We discuss the mechanism of this expanding microwave source and point out that it is in fact a reflection of chromospheric evaporation, through changing the pitch-angle of gyrosynchrotron electrons.

Gan, Weiqun; Li, Youping

2012-07-01

203

Solar Cycle Variations of the Occurrence of Coronal Type III Radio Bursts and a New Solar Activity Index  

NASA Astrophysics Data System (ADS)

The results of studies of solar cycle variations of the occurrence rate of coronal type III radio bursts are presented. 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 (ARBIS). Access to data from other RSTN sites will allow processing 24-hour radio spectra in near-real time and estimating true daily values of this index. It is also shown that coronal type III bursts can even occur when there are no visible sunspots on the Sun. However, no evidence is found that the bursts are not associated with active regions. It is also concluded that the type III burst productivity of active regions exhibits solar cycle variations.

Lobzin, V. V.; Cairns, I. H.; Robinson, P. A.

2011-12-01

204

Current Fragmentation and Particle Acceleration in Solar Flares  

NASA Astrophysics Data System (ADS)

Particle acceleration in solar flares remains an outstanding problem in plasma physics and space science. While the observed particle energies and timescales can perhaps be understood in terms of acceleration at a simple current sheet or turbulence site, the vast number of accelerated particles, and the fraction of flare energy in them, defies any simple explanation. The nature of energy storage and dissipation in the global coronal magnetic field is essential for understanding flare acceleration. Scenarios where the coronal field is stressed by complex photospheric motions lead to the formation of multiple current sheets, rather than the single monolithic current sheet proposed by some. The currents sheets in turn can fragment into multiple, smaller dissipation sites. MHD, kinetic and cellular automata models are used to demonstrate this feature. Particle acceleration in this environment thus involves interaction with many distributed accelerators. A series of examples demonstrate how acceleration works in such an environment. As required, acceleration is fast, and relativistic energies are readily attained. It is also shown that accelerated particles do indeed interact with multiple acceleration sites. Test particle models also demonstrate that a large number of particles can be accelerated, with a significant fraction of the flare energy associated with them. However, in the absence of feedback, and with limited numerical resolution, these results need to be viewed with caution. Particle in cell models can incorporate feedback and in one scenario suggest that acceleration can be limited by the energetic particles reaching the condition for firehose marginal stability. Contemporary issues such as footpoint particle acceleration are also discussed. It is also noted that the idea of a "standard flare model" is ill-conceived when the entire distribution of flare energies is considered.

Cargill, P. J.; Vlahos, L.; Baumann, G.; Drake, J. F.; Nordlund, Å.

2012-11-01

205

Ionospheric response to the solar flare of 14 July 2000  

Microsoft Academic Search

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

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

2004-01-01

206

The origin and implications of gamma rays from solar flares  

NASA Technical Reports Server (NTRS)

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

Ramaty, R.

1975-01-01

207

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

NASA Technical Reports Server (NTRS)

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

Cane, H. V.

2004-01-01

208

Do Flares Contribute to Total Solar Irradiance Variability ?  

NASA Astrophysics Data System (ADS)

The Total Solar Irradiance (TSI) varies on all time scales and a major fraction of its variability can be reproduced by considering the appearance and disappearance of features, such as sunspots and faculae, on the solar disk. Other effects (e.g. the so called network), however, are contributing to the variability of the TSI, as evidenced by its unusually low level during the last solar minimum. Here we show that flares of various amplitudes also have a significant impact on the TSI. In contrast to standard belief, the dominant contribution comes from the visible domain. We next estimate the probability distribution of flares versus their total radiative output; previous estimates were restricted to a specific spectral range only (e.g. in the soft X-ray or radio domain) whereas we consider the total energy. The obtained distribution follows a power law; we investigate the possibility of small flares to have a major contribution to the TSI variability. The research leading to these results has received funding from the European Commission's Seventh Framework Programme (FP7/2007-2013) under the grant agreement SOTERIA (project n° 218816, www.soteria-space.eu)

Kretzschmar, M.; Dudok de Wit, T.

2010-12-01

209

Does a Scaling Law Exist between Solar Energetic Particle Events and Solar Flares?  

NASA Astrophysics Data System (ADS)

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.

Kahler, S. W.

2013-05-01

210

Anatomy of a Solar Flare: Measurements of the 2006 December 14 X-class Flare with GONG, Hinode, and RHESSI  

NASA Astrophysics Data System (ADS)

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.

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

2011-10-01

211

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

SciTech Connect

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.

Matthews, S. A.; Zharkov, S. [UCL Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, RH5 6NT UK (United Kingdom); Zharkova, V. V. [Horton D Building, Department of Mathematics, University of Bradford, Bradford, BD7 1DP (United Kingdom)

2011-10-01

212

The isotopic composition of solar flare accelerated neon  

NASA Technical Reports Server (NTRS)

The individual isotopes of neon in energetic solar-flare particles have been clearly resolved with a rms mass resolution of 0.20 amu. The ratios found are Ne-20/Ne-22 = 7.6 (+2.0, -1.8) and Ne-21/Ne-22 of no more than about 0.11 in the 11-26 MeV per nucleon interval. This isotopic composition is essentially the same as that of meteoritic planetary neon-A and is significantly different from that of the solar wind.

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

1979-01-01

213

Lattice Models for Solar Flares and Coronal Heating  

NASA Astrophysics Data System (ADS)

Solar coronal heating is a complex problem due to the variety of scales and physical phenomena involved, and intricacy of “boundary conditions”. Lattice models and self-organized criticality provide means to model phenomenologically some of the physics involved over a wide range of scales, and reproduce certain statistical features of solar flares. Furthermore, these models offer a basis for the study of Parker's hypothesis of coronal heating by nanoflares. We provide a short review of this approach pioneered by Lu & Hamilton (1991) and related more recent works involving lattice models.

Podladchikova, O.; Lefebvre, B.

214

Time behavior of solar flare particles to 5 AU  

NASA Technical Reports Server (NTRS)

A simple model of solar flare radiation event particle transport is developed to permit the calculation of fluxes and related quantities as a function of distance from the sun (R). This model assumes the particles spiral around the solar magnetic field lines with a constant pitch angle. The particle angular distributions and onset plus arrival times as functions of energy at 1 AU agree with observations if the pitch angle distribution peaks near 90 deg. As a consequence the time dependence factor is essentially proportional to R/1.7, (R in AU), and the event flux is proportional to R/2.

Haffner, J. W.

1972-01-01

215

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

SciTech Connect

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

Simonsen, L.C.; Nealy, J.E.; Townsend, L.W.; Sauer, H.H. (NASA, Langley Research Center, Hampton, VA (United States) NOAA, Space Environment Laboratory, Boulder, CL (United States))

1991-07-01

216

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

NASA Astrophysics Data System (ADS)

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

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

1991-07-01

217

Solar gamma rays from a over-the-limb' flare  

SciTech Connect

On 1989 September 29 a remarkable gamma-ray flare occurred on the sun. This event was first detected at [approximately] 10:47 UT by soft x-ray detectors on a GOES satellite which subsequently recorded a peak (X9.8) at 11:33 UT and persistent emission lasting until about 14:35 UT. The soft x-ray peak was followed at 11:45 UT by the largest cosmic-ray ground level event (GLE) observed by neutron monitors since 1956. Those ground level measurements indicate that solar protons with rigidities of up to [approximately]25 GV were present. The H-alpha observations for this period do not show any flare on the visible solar disk that is likely to be associated with such a large event. Instead, the flare has been associated with an active region (NOAA region 698) beyond the southwestern limb (W105) whose giant flare loops indicated powerful activity. When the Gamma-Ray Spectrometer (GRS) on SMM emerged from an SAA pass at 11:33 UT, intense gamma-ray emission extending to energies > 50 MeV was measured until the satellite entered orbital night at 11:50 UT. The rich spectra obtained during this interval show evidence for prompt nuclear emission in the 4-7 MeV band and a surprisingly strong line at 2.2 MeV from neutron capture on hydrogen. The relative strength of the neutron capture line requires a large fraction of the observed emission to be generated on the visible disk well away from AR 5698. This requires the transport and/or acceleration of energetic particles in a region covering more than [approximately] 25[degrees] in solar longitude. These observations give the first clues about the spatial scale of extented-phase gamma-ray emission.

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

1992-01-01

218

Some Comments on the East-West Solar Flare Distribution During the 1976-1985 Period.  

National Technical Information Service (NTIS)

We present the results of an analysis of the east-west asymmetry in the solar flare distribution, observed during the years from 1976 to 1985. We conclude that flare events, all type of H alpha flares, are not uniformly spread in heliolongitude over the s...

A. M. Heras B. Sanahuja D. F. Smart M. A. Shea

1990-01-01

219

Soft X-ray Transient is Likely a Reflected Solar Flare  

NASA Astrophysics Data System (ADS)

It was pointed out to us that there was a solar flare measured by GOES, precisely consistant in both start time and duration with the flare seen in the ASM data. Given that the moon's position was within a half-degree of our best-fit position for the transient, we conclude that this event was most likely a solar flare reflected off the moon, and not an event originating outside our solar system. Thanks to David Smith for pointing out the contemporaneous solar flare.

Smith, D. A.; Remillard, R.

2003-03-01

220

Turbulent and directed plasma motions in solar flares  

NASA Technical Reports Server (NTRS)

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.

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

1989-01-01

221

Source Flares of Type II Solar Radio Bursts During Solar Cycle 21  

NASA Astrophysics Data System (ADS)

A preliminary analysis of type II and complex type II + IV Solar Radio Bursts (SRBs) during solar cycle (SC) 21 was done in a previous paper (Maris and Tifrea, 1994). The yearly distributions of these SRBs as well as the yearly and heliographic distributions of their source flares are, in this paper, discussed. the yearly distributions of analyzed phenomena present more than one maximum during SC 21. The heliographic distributions of the source flares, in latitude and longitude, were also not uniform, but they are in good agreement with the distributions of other solar activity phenomena.

Maris, Georgeta; Tifrea, Emilia

222

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

NASA Astrophysics Data System (ADS)

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 ? . In this flare, intense emission of hard X-rays and ? -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 ? -rays than with the production time of soft X-rays.

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

223

Stochastic particle acceleration by helical turbulence in solar flares  

NASA Astrophysics Data System (ADS)

Flaring release of magnetic energy in solar corona is only possible if the magnetic field deviates from a potential one. We show that the linear magnetohydrodynamic (MHD) modes excited on top of the non-potential magnetic field possess a non-zero kinetic helicity. Accordingly, this necessarily results in a noticeable kinetic helicity of the turbulence, composed of these linear modes with various scales and random phases, generated at the flare site by the primary energy release, which may be important for many applications. In particular, a non-zero turbulence helicity has a potentially strong effect on the particle acceleration because the helical component of the turbulence induces a mean regular large-scale (DC) electric field capable of directly accelerating the charged particles in addition to the commonly considered stochastic turbulent electric field. In this paper, we derive the kinetic helicity density of the linear MHD modes excited on top of a twisted large-scale magnetic field, estimate the corresponding turbulence helicity and take its effect on stochastic particle acceleration by the turbulence into consideration; in particular, we compare this induced mean electric field with the electron and estimated effective ion Dreicer fields. We have discovered that this, so far missing but highly important, ingredient of the turbulence at the flare site can be responsible for the thermal-to-non-thermal energy partition in flares by controlling the process of particle extraction from the thermal pool and formation of the seed particle population to be then stochastically accelerated to higher energies. In addition, it is naturally consistent with such puzzling flare manifestations as spatial separation of electron and proton emission sites, electron beam formation, and enrichment of the accelerated particle population by 3He and other rare ions.

Fleishman, Gregory D.; Toptygin, Igor N.

2013-03-01

224

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

NASA Technical Reports Server (NTRS)

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

Canfield, Richard C.; Dennis, Brian R.

1988-01-01

225

SUB-THz RADIATION MECHANISMS IN SOLAR FLARES  

SciTech Connect

Observations in the sub-THz range of large solar flares have revealed a mysterious spectral component increasing with frequency and hence distinct from the microwave component commonly accepted to be produced by gyrosynchrotron (GS) emission from accelerated electrons. Evidently, having a distinct sub-THz component requires either a distinct emission mechanism (compared to the GS one), or different properties of electrons and location, or both. We find, however, that the list of possible emission mechanisms is incomplete. This Letter proposes a more complete list of emission mechanisms, capable of producing a sub-THz component, both well known and new in this context, and calculates a representative set of their spectra produced by (1) free-free emission, (2) GS emission, (3) synchrotron emission from relativistic positrons/electrons, (4) diffusive radiation, and (5) Cherenkov emission. We discuss the possible role of the mechanisms in forming the sub-THz emission and emphasize their diagnostics potential for flares.

Fleishman, Gregory D. [Center for Solar-Terrestrial Research, New Jersey Institute of Technology, Newark, NJ 07102 (United States); Kontar, Eduard P. [Department of Physics and Astronomy, University of Glasgow, G12 8QQ (United Kingdom)], E-mail: gfleishm@njit.edu

2010-02-01

226

Generic Model for Magnetic Explosions Applied to Solar Flares  

NASA Astrophysics Data System (ADS)

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 Alfvénically 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.

Melrose, D. B.

2012-04-01

227

A model solar flares and their homologous behavior  

SciTech Connect

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.

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

2000-01-27

228

Frequency of Solar Spotless Days and Flare Index as Indices of Solar Cycle Activity  

NASA Astrophysics Data System (ADS)

There was a research on the prolongation of solar cycle 23 by the solar cyclic variation of solar, interplanetary geomagnetic parameters by Oh & Kim (2013). They also suggested that the sunspot number cannot typically explain the variation of total solar irradiance any more. Instead of the sunspot number, a new index is introduced to explain the degree of solar activity. We have analyzed the frequency of sunspot appearance, the length of solar cycle, and the rise time to a solar maximum as the characteristics of solar cycle. Then, we have examined the predictability of solar activity by the characteristics of preceding solar cycle. We have also investigated the hemispheric variation of flare index for the periods that the leading sunspot has the same magnetic polarity. As a result, it was found that there was a good correlation between the length of preceding solar cycle and spotless days. When the length of preceding solar cycle gets longer, the spotless days increase. It is also shown that the shorter rise time to a solar maximum is highly correlated with the increase of sunspots at a solar maximum. Therefore, the appearance frequency of spotless days and the length of solar cycle are more significant than the general sunspot number as an index of declining solar activity. Additionally, the activity of flares leads in the northern hemisphere and is stronger in the hemisphere with leading sunspots in positive polarity than in the hemisphere with leading sunspots in negative polarity. This result suggests that it is necessary to analyze the magnetic polarity¡¯s effect on the flares and to interpret the period from the solar maximum to solar maximum as the definition of solar cycle.

Oh, Suyeon

2014-06-01

229

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

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

230

Numerical simulations of impulsively heated solar flares  

SciTech Connect

The response of a model solar atmosphere to heating by an electron beam has been studied for electron beam flux spectra which are power laws with low-energy knees (rising linearly with time to a peak at 30 s and then falling linearly to 0 at 60 s) ranging from 10 to 20 keV. The results indicate that high peak electron beam fluxes, low-energy knees, and larger spectral indices all move the atmospheric response toward greater enhancements of the parameters in the coronal regions of the atmosphere. Coronal responses can thus be used as a diagnostic of the parameters of the electron beam. 23 refs.

Mariska, J.T.; Emslie, A.G.; Li, P. (E. O. Hulburt Center for Space Research, Washington, DC (USA); Alabama Univ., Huntsville (USA))

1989-06-01

231

The effect of anisotropy of accelerated electrons on hard X-ray spectra of solar flares  

NASA Astrophysics Data System (ADS)

The calculations of X-ray spectra of solar flares were made analytically taking account of electron multiple scattering and radiation reflection from the photosphere. They showed a strong dependence of the radiation spectrum shape on the heliocentric angle of the flares. The analysis of the mean radiation spectra hardness versus the observation angle of the flares detected by SIGN-2M3 instruments in the range of 50 - 300 keV revealed a systematical softening of the spectra towards the centre of the solar disk. The comparison of the calculated radiation spectra with the observed ones points to the generation of electrons with anisotropic angular distribution in solar flares.

Bogovalov, S. V.; Kel'Ner, S. R.; Kotov, Iu. D.; Zenchenko, V. M.; Vedrenne, G.

232

Relaxation of magnetic field relative to plasma density during solar flares  

NASA Astrophysics Data System (ADS)

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

Yu, Sijie; Yan, Yihua; Tan, Baolin

2013-07-01

233

The isotopic composition of solar flare accelerated magnesium  

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

234

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

Microsoft Academic Search

We are developing empirical space weather (solar flares, solar proton events, and geomagnetic storms) forecast models based on solar information. These models have been set up with the concept of probabilistic forecast using historical events. Major findings can be summarized as follows. First, we presented a concept of storm probability map depending on CME parameters as well as contingency tables

Y. Moon; R. Kim

2010-01-01

235

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

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

236

Measuring and Modeling Solar Flares with SDO EVE  

NASA Technical Reports Server (NTRS)

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.

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

2010-01-01

237

Reconnection in substorms and solar flares: analogies and differences  

SciTech Connect

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

Birn, Joachim [Los Alamos National Laboratory

2008-01-01

238

Gamma Ray Observations of the June 1991 Solar Flares  

NASA Astrophysics Data System (ADS)

The EGRET instrument on the Compton Gamma Ray Observatory observed four of the X-class solar flares that occurred from the same region of the Sun on June 4, 6, 9, and 11 in 1991. All four exhibited nuclear line emission in spectra from the EGRET energy calorimeter. Spectra from 1 to 200 MeV are given along with the time profile of the 2.22 and 4.4 Mev line intensities. The flare on June 11 was especially significant in that the EGRET spark chamber detected emission to over 1000 MeV, and the time-scale of emission above 50 MeV persisted for 8 hours. An M-class flare 18 hours later produced a second increase above 50 MeV. The high energy spectra are well-fit by a combination of a bremsstrahlung and pion decay spectra. The time-scale of the bremsstrahlung component is as long or longer than the nuclear component suggesting that the acceleration process must be extended or episodic during the 8 hour period.

Bertsch, D.; Hartman, R.; Hunter, S.; Thompson, D.; Dingus, B.; Esposito, J.; Sreekumar, P.; Mukherjee, R.; von Montigny, C.; Lin, Y.; Michelson, P.; Nolan, P.; Kanbach, G.; Mayer Hasselwander, H.; Kniffen, D.; Schneid, E.

1997-05-01

239

Substorm occurrence during quiet solar wind driving  

NASA Astrophysics Data System (ADS)

We examine the OMNI database and International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer chain records to study the substorm occurrence and characteristics during quiet solar driving periods, especially during the solar minimum period in 2009. We define substorm-like activations as periods where the hourly average AL is below -200 nT. Using the OMNI data set, we demonstrate that there are limiting solar wind speed, interplanetary magnetic field magnitude, and driving electric field values below which substorm-like activations (AL < 200 nT, intensification and decay of the electrojet) do not occur. These minimum parameter values are V < 266 km/s, B < 1.4 nT, and E < 0.025 mV/m such low values are observed less than 1% of the time. We also show that for the same level of driving solar wind electric field, the electrojet intensity is smaller (by few tens of nT), and the electrojet resides farther poleward (by over 1°) during extended quiet solar driving in 2009 than during average solar activity conditions. During the solar minimum period in 2009, we demonstrate that substorm-like activations can be identified from the IMAGE magnetometer chain observations during periods when the hourly average IL index is below -100 nT. When the hourly IL activity is smaller than that, which covers 87% of the nighttime observations, the electrojet does not show coherent behavior. We thus conclude that substorm recurrence time during very quiet solar wind driving conditions is about 5-8 h, which is almost double that of the average solar activity conditions.

Pulkkinen, T. I.; Partamies, N.; Kilpua, E. K. J.

2014-04-01

240

Solar Flare Impulse Broadening from Gamma Ground Survey Network  

NASA Astrophysics Data System (ADS)

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.

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

2012-03-01

241

The reason for magnetospheric substorms and solar flares  

NASA Astrophysics Data System (ADS)

The author suggests that magnetospheric substorms and solar flares are manifestations of the same physical process, namely the escape (or attempted escape) of plasma from a region of closed magnetic field lines. This plasma is being slowly energized and supports a discrete auroral arc. It is enclosed by a magnetic bottle to prevent its escape. However, the author presents an alternative (and in many ways complementary) description to Schindler's (1976) to indicate how simple physics in three dimensions can help elucidate a number of problems, such as the production of bursts of very energetic particles, and the sudden development of field aligned current tubes.

Heikkila, W. J.

1983-10-01

242

Flare index of solar activity and global geomagnetic variability.  

NASA Astrophysics Data System (ADS)

The associations of solar flare index (SFI) and global geomagnetic variability (Ap) with annual mean sunspot number (SSN) during the period 1986 - 96 have been analysed. It is found that the SFI in the northern hemisphere, southern hemisphere and total disk surface of the Sun shows close correspondence with the SSN on long- and short-term basis. An internal association between SSN, SFI and Ap has also been analysed. The authors have found that Ap poorly correlated with SFI and SSN during the aforesaid period.

Dubey, S. C.; Mishra, A. P.

2000-06-01

243

Compton scattering polarimeter "PENGUIN" for solar flares polarimetry  

NASA Astrophysics Data System (ADS)

Compton scattering polarimeter is discussed. This instrument will be used for linear polarization measurements of solar flares in energy range from 20keV to 150keV. Scattering detector consists of a number of p-terphenil crystals with total square 120cm2 and thickness 3cm. The detectors of scattered radiation are CsJ(Na)-based crystals. All detectors are enclosed anticoincidence shields in order to avoid charge particle background. The estimations of efficiency are made by means of Monte-Carlo simulation. Proposed accuracy of polarization measurements is near 10±1%. The stabilization system is used to keep threshold levels not more 1%.

Kotov, Y. D.; Kruglov, E. M.; Khmylko, V. V.; Chichikaluk, Y. A.

2001-08-01

244

The U.S. Max '91 program of flare research at the next solar maximum  

NASA Technical Reports Server (NTRS)

A brief summary is presented of Max '91, a proposed program to study the problems of flare physics during the next solar maximum. The program uses instruments on spacecraft, rockets, balloons, and ground-based observations to study the processes of particle acceleration and energy storage, release, and transport in solar flares. The space missions, instruments, and experiments included in the program are outlined.

Dennis, Brian R.

1988-01-01

245

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

NSDL National Science Digital Library

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

2011-04-20

246

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

Microsoft Academic Search

Aims.Several experiments have reported observations on possible correlations between the flux of high energy muons and intense solar flares. If confirmed, these observations would have significant implications for acceleration processes in the heliosphere able to accelerate protons and other ions to energies of at least tens of GeV. Methods: The solar flare of the 14 of July 2000 offered a

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

2006-01-01

247

Ionic charge distributions of energetic particles from solar flares. Semiannual Report, 1 July-31 December 1985  

SciTech Connect

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.

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

1986-03-01

248

Gamma-ray emission and electron acceleration in solar flares  

NASA Technical Reports Server (NTRS)

Recent observations have extended the spectra of the impulsive phase of flares to the GeV range. Such high-energy photons can be produced either by electron bremsstrahlung or by decay of pions produced by accelerated protons. In this paper we investigate the effects of processes which become important at high energies. We examine the effects of synchrotron losses during the transport of electrons as they travel from the acceleration region in the corona to the gamma-ray emission sites deep in the chromosphere and photosphere, and the effects of scattering and absorption of gamma rays on their way from the photosphere to space instruments. These results are compared with the spectra from so-called electron-dominated flares, observed by GRS on the Solar Maximum Mission, which show negligible or no detectable contribution from accelerated protons. The spectra of these flares show a distinct steepening at energies below 100 keV and a rapid falloff at energies above 50 MeV. Following our earlier results based on lower energy gamma-ray flare emission we have modeled these spectra. We show that neither the radiative transfer effects, which are expected to become important at higher energies, nor the transport effects (Coulomb collisions, synchrotron losses, or magnetic field convergence) can explain such sharp spectral deviations from a simple power law. These spectral deviations from a power law are therefore attributed to the acceleration process. In a stochastic acceleration model the low-energy steepening can be attributed to Coulomb collision and the rapid high-energy steepening can result from synchrotron losses during the acceleration process.

Petrosian, Vahe; Mctiernan, James M.; Marschhauser, Holger

1994-01-01

249

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

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

250

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)

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.

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

1989-01-01

251

Magnetic Structure Producing X- and M-class Solar Flares in Solar Active Region 11158  

NASA Astrophysics Data System (ADS)

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.

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

2013-06-01

252

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

NASA Technical Reports Server (NTRS)

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.

Marchenko, V. I.

1974-01-01

253

The Formation of Accelerated Electron Distributions in Solar Flares  

NASA Astrophysics Data System (ADS)

Driven by RHESSI observations of dense compact coronal hard X-ray sources in solar flares, we study electron acceleration in such regions. We consider the acceleration of electrons by a stochastic process that is characterized by a diffusion coefficient D_turb ~ 1/v in a collisional medium of finite length. If electron escape can be neglected, the electron distribution function is determined by a balance between stochastic acceleration and collisional friction. Such a scenario admits a stationary solution for the electron distribution function that takes the form of a kappa-distribution. We show how the growth toward this stationary distribution can be described as a "wave"' propagating forwards in velocity space, so that electrons of higher energy E are accelerated later than lower-energy ones; quantitatively, the acceleration time ? scales with E according to ? ~ E^{3/2}. Since such an approach towards a stationary kappa distribution becomes progressively slower at high energies, escape from the acceleration region (of finite length L) will, at sufficiently high energies, eventually dominate over collisions, and a different stationary solution, corresponding to a balance between diffusive acceleration and particle escape, is applicable in this energy range. Using a numerical treatment, we derive the time evolution toward the stationary solution for a range of parameters appropriate to the solar flare situation.

Emslie, A. Gordon; Bian, Nicolas; Kontar, Eduard

2014-06-01

254

Particle Densities within the Acceleration Region of a Solar Flare  

NASA Astrophysics Data System (ADS)

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 109 cm-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.

Krucker, Säm; Battaglia, Marina

2014-01-01

255

Solar Irradiance Variations and Flare Frequencies during the Interesting Solar Cycle 24  

NASA Astrophysics Data System (ADS)

The current solar cycle 24 has had a slow rise during its first three years, more than a factor of two slower than recent solar cycles. While solar maximum may not have yet been reached for this cycle, the solar irradiance remains significantly lower than the previous cycle 23 maximum level. In spite of a lower activity cycle, there have been episodes of intense and frequent solar storms, such as in February and March 2011. However, these storms appear to be weaker than previous cycles, and a decrease in storm frequency appears to have started back in the late 1990s because the solar flares during solar cycle 23 are about a factor of two less frequent than those in solar cycles 21 and 22. Much of the activity in cycle 24 has been from the solar northern hemisphere, and only recently has the southern hemisphere become more active. This north-south asymmetry in solar activity may influence a slow rise for this cycle, as well as lower activity level, because both hemispheres are not contributing at the same time. These topics will be discussed using data from several different solar irradiance sensors and the GOES X-ray flare monitor over the past four solar cycles.

Woods, T. N.

2012-12-01

256

Vector magnetograph observations by the solar flare telescope at BOAO.  

NASA Astrophysics Data System (ADS)

The authors report that vector magnetograph (VMG) observations of the solar photosphere are being carried out by the Solar Flare Telescope (SOFT) at BOAO. The VMG uses a narrow band Lyot filter (FWHM = 0.125 A) for Stokes parameter (I,Q,U,V) observations to obtain longitudinal and transverse fields. The authors have obtained a filter-convolved line profile of Fe I 6302.5 for VMG by changing the central wavelength of the Lyot filter, which is consistent with the Sacramento Peak spectral atlas data. Using the line profile, the authors have determined calibration coefficients of longitudinal and transverse fields by the line slope method. Then they have compared vector fields of AR 8422 observed at BOAO with those at Mitaka. The comparison shows that longitudinal fields are very similar to each other, but transverse fields are a little different.

Park, Y. D.; Moon, Y.-J.; Yun, H. S.

1999-12-01

257

Structure of impulsive phase of solar flares from microwave observations  

NASA Technical Reports Server (NTRS)

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

Petrosian, V.

1981-01-01

258

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

259

What we think we know and do not know about solar flares  

NASA Technical Reports Server (NTRS)

Solar-terrestrial relations begin in the convective zone of the sun. A combination of nonuniform rotation and cyclonic convection generates magnetic fields in migratory waves, which can account for the observed 22-year solar magnetic cycle. The magnetic fields are the active agent in creating the active magnetic regions, with sunspots, prominences, and flares. The present status of knowledge regarding the solar flare phenomenon is reviewed, giving attention to the extraordinary complexity of the solar flare and the broad spectrum of theoretical ideas that have been generated to meet the challenge.

Parker, E. N.

1973-01-01

260

Changing photospheric vector magnetic fields associated with a B4.2-class solar flare  

NASA Astrophysics Data System (ADS)

Recent observations have provided evidence that the solar photospheric magnetic fields could have rapid and permanent changes in both longitudinal and transverse components associated with large (X- or M-class) solar flares. However, few observations have been reported about small flares. In this paper we find the observational evidence of changing photospheric vector magnetic fields associated with a B4.2-class flare obtained with the Solar Magnetic Field Telescope (SMFT) installed at Huairou Solar Observing Station (HSOS) of Nation Astronomical Observatories of Chinese Academy of Sciences.

Su, Jiangtao; Liu, Yu; Shen, Yuandeng

2013-07-01

261

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

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

262

Directivity of High-Energy Emission from Solar Flares: Solar Maximum Mission Observations,  

National Technical Information Service (NTIS)

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 strongly indicate that the high-energy e...

W. T. Vestrand D. J. Forrest E. L. Chupp E. Rieger G. H. Share

1987-01-01

263

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

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

264

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

265

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

266

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

NASA Technical Reports Server (NTRS)

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.

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

1991-01-01

267

Solar flare particle fluences during solar cycles 19, 20 and 21  

Microsoft Academic Search

Satellite data for solar flare particle events during solar cycle 21 (up to July 1982) have been analyzed to obtain event-integrated fluxes of energetic protons and alpha particles. Thirty nine events with proton fluences (E greater than 10 MeV) greater than 10-million\\/sq cm occurred during 1976-1982. The average flux of protons with kinetic energy greater than 10 MeV is 65

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

1983-01-01

268

Complex Dynamic Flows in Solar Flare Sheet Structures  

NASA Astrophysics Data System (ADS)

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. This work is supported by NASA under contract SP02H3901R from Lockheed-Martin to MSU (DMcK), contract SP02H1701R from Lockheed-Martin to SAO (KKR), and contract NNM07AB07C with the Harvard-Smithsonian Astrophysical Observatory. SLS is supported via a NASA/GSFC NPP appointment administered by Oak Ridge Associated Universities and under the mentorship of G. Holman.

McKenzie, David Eugene; Reeves, K. K.; Savage, S. L.

2012-05-01

269

Return Currents and Energy Transport in the Solar Flaring Atmosphere  

NASA Astrophysics Data System (ADS)

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.

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

2013-08-01

270

Spatial structure of high energy photon sources in solar flares  

NASA Technical Reports Server (NTRS)

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

Kane, S. R.

1983-01-01

271

Characteristics of CMEs associated with solar flares and DH type II radio bursts based on source position  

NASA Astrophysics Data System (ADS)

We studied the characteristics of Coronal Mass Ejections (CMEs) associated with solar flares and Deca-Hectometric (DH) type II radio bursts, based on source position during 23rd solar cycle (1997-2007). We classified these CME events into three groups using solar flare locations as, (i) disk events (0-30?); (ii) intermediate events (31-60?) and (iii) limb events (61-90?). Main results from this studies are, (i) the number of CMEs associated with solar flares and DH-type IIs decreases as the source position approaches from disk to limb, (ii) most of the DH CMEs are halo (72%) in disk events and the number of occurrence of halo CMEs decreases from disk to limb, (iii) the average width and speed of limb events (164? and 1447 km s-1) are higher than those of disk events (134? and 1035 km s-1) and intermediate events (146? and 1170 km s-1) and (iv) the average accelerations for disk, intermediate and limb events are -8.2 m s-2, -10.3 m s-2 and -4.5 m s-2 respectively. These analysis of CMEs properties show more dependency on longitude and it gives strong evidence for projection effect.

Lakshmi, M. Anna; Umapathy, S.

2012-04-01

272

Partial Effects on VLF Data due to a Solar Flare During 2010 Annular Solar Eclipse  

NASA Astrophysics Data System (ADS)

The VLF radio waves propagate through the Earth-ionosphere waveguide. Irregularities caused by excesses or deficient soft X-rays which sustain the ionosphere changes the waveguide properties and hence the signals are modified. We report the results of our monitoring of the NWC transmitter from Khukurdaha (~80 km away from Kolkata) during the partial solar eclipse (75%) of 15th January, 2010. The receiving station and the transmitter were on two opposite sides of the annular eclipse belt. We got clear depression in the data during the period of partial eclipse. There was also a solar flare (spot no. 1040) on that day during the time the eclipse was near maximum. The flare started from B, reaching maximum to C1.3 (as observed by GOES 14 satellite). We saw the partial effect of this flare since a part of the active region was blocked by the moon. To our knowledge this is the first such incident where the solar flare was observed through lunar occultation.

Maji, Surya K.; Chakrabarti, Sandip K.; Mondal, Sushanta K.

2010-10-01

273

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

274

Improving the performance of solar flare prediction using active longitudes information  

NASA Astrophysics Data System (ADS)

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.

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

2013-01-01

275

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

NASA Technical Reports Server (NTRS)

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

Feynman, Joan; Hundhausen, Arthur J.

1994-01-01

276

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

NASA Astrophysics Data System (ADS)

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

Feynman, Joan; Hundhausen, Arthur J.

1994-05-01

277

Thermal Structure of Supra-Arcade Plasma in Two Solar Flares  

NASA Technical Reports Server (NTRS)

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.

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

2012-01-01

278

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

SciTech Connect

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.

G.S. Choe; C.Z. Cheng

2001-12-12

279

Is there a limit on solar flare proton fluxes  

NASA Technical Reports Server (NTRS)

The possibility that solar flare proton fluxes are limited in magnitude by saturation effects inherent to the acceleration mechanism is explored. If cyclotron damping of Alfven waves acts to accelerate protons, the criterion that the damping time is comparable to the acceleration time provides a fast particle number density at which protons load the wave spectrum. The limiting flux at 1 AU is obtained by a volume integration over the acceleration region and redistribution into an interplanetary emission cone. A simplified explosion model permits a delineation between volume and surface acceleration mechanisms in terms of a temporal parameter, the effective duration of acceleration. It is concluded that the limiting flux may be a realistic concept, but that further investigation is warranted to sharpen the criterion.

Barbosa, D. D.

1980-01-01

280

Determination of Stochastic Acceleration Model Characteristics in Solar Flares  

NASA Astrophysics Data System (ADS)

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

Chen, Qingrong; Petrosian, Vahé

2013-11-01

281

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

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

282

Magnetic field configuration associated with solar gamma ray flares in June, 1991  

NASA Technical Reports Server (NTRS)

The vector magnetic field configuration of the solar active region AR 6659 that produced very high levels of flare activity in Jun. 1991 is described. The morphology and evolution of the photospheric fields are described for the period 7-10 Jun., and the flares taking place around these dates and their locations relative to the photospheric fields are indicated. By comparing the observed vector field with the potential field calculated from the observed line-of-sight flux, we identify the nonpotential characteristics of the fields along the magnetic neutral lines where the flares were observed. These results are compared with those from the earlier study of gamma-ray flares.

Hagyard, M. J.; West, E. A.; Smith, J. E.; Trussart, F.-M.; Kenney, E. G.

1992-01-01

283

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

NASA Astrophysics Data System (ADS)

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.

Hamidi, Zety Sharizat Binti

2013-11-01

284

Solar flare gamma-ray and hard X ray imaging with the GRID-on-a-balloon  

Microsoft Academic Search

A primary scientific objective for solar flare research during the rapidly approaching maximum in solar activity is the imaging of gamma-ray and hard x ray sources of solar flare emissions. These goals will be pursued by the Gamma Ray Imaging Device (GRID) instrument, one of three instruments recently selected for NASA's Max '91 Solar Balloon Program. The GRID instrument is

Larry E. Orwig; C. J. Crannell; Brian R. Dennis; R. Starr; G. J. Hurford; H. S. Hudson; F. Vanbeek; M. E. Greene; W. N. Johnson; J. P. Norris

1989-01-01

285

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

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

286

Properties of solar X-ray flares and proton event forecasting  

NASA Astrophysics Data System (ADS)

X-ray flares and acceleration processes are in one complex of sporadic solar events (together with CMEs, radio bursts, magnetic field dissipation and reconnection). This supposes the connection (if not physical, but at least statistical) between characteristics of the solar energetic proton events and flares. The statistical analysis indicates that probability and magnitude of the near-Earth proton enhancement depends heavily on the flare importance and their heliolongitude. These relations may be used for elaboration of the forecasting models, which allow us to calculate probability of the solar proton events from the X-ray observations. The models of probability for different kinds of solar proton events are obtained on the basis of all accumulated data of X-ray flares on the Sun and solar proton enhancements near the Earth. These models describe well enough the available data, are suitable for practical use and, really, are already utilized in the IZMIRAN prognostic practice. However, we should remember about the limitation of accumulated statistics. X-ray flares and proton enhancements have been observed for so short time that any new burst of solar activity is able to add something to our understanding of the relation “solar flares - proton enhancements”.

Belov, A.

2009-02-01

287

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

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

288

Correlative Studies of Solar Flares. Report for September 14, 1992 to September 14, 1996.  

National Technical Information Service (NTIS)

In October 1992, post-doc Haimin Wang was awarded a Compton GRO Fellowship by NASA to study the flares observed simultaneously by BATSE (Burst and Transient Experiment), OVRO (Owens Valley Radio Observatory), Yohkoh, and BBSO (Big Bear Solar Observatory)....

H. Zirin

1997-01-01

289

SDO Captures Release of X1.2 Class Solar Flare  

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...

290

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

291

Energetic analysis of the white light emission associated to seismically active flares in solar cycle 24  

NASA Astrophysics Data System (ADS)

Solar flares are explosive phenomena, thought to be driven by magnetic free energy accumulated in the solar corona. Some flares release seismic transients, "sunquakes", into the Sun's interior. Different mechanisms are being considered to explain how sunquakes are generated. We are conducting an analysis of white-light emission associated with those seismically active solar flares that have been reported by different authors within the current solar cycle. Seismic diagnostics are based upon standard time-distance techniques, including seismic holography, applied to Dopplergrams obtained by SDO/HMI and GONG. The relation between white-light emissions and seismic activity may provide important information on impulsive chromospheric heating during flares, a prospective contributor to seismic transient emission, at least in some instances. We develop a method to get an estimation of Energy associated whit white-light emission and compare those results whit values of energy needed to generate a sunquake according with holographic helioseismology techniques.

Buitrago-Casas, Juan Camilo; Martinez Oliveros, Juan Carlos; Glesener, Lindsay; Krucker, Sam

2014-06-01

292

Explosion of sungrazing comets in the solar atmosphere and solar flares  

NASA Astrophysics Data System (ADS)

Explosive evolution of nuclei of sungrazing comets near the solar surface, which occurs at conditions of intense interaction between the solar atmosphere and falling high-velocity comet nuclei as well as the relation of the phenomenon to the character of solar activity are analytically considered. It is found that, due to aerodynamic fragmentation of the falling body in the solar chromosphere and transversal expansion of the fragmented mass under the action of pressure gradient on the frontal surface, thermalization of the kinetic energy of the body occurs by sharp stopping of the disklike hypervelocity fragmented mass near the solar surface within a relatively very thin subphotospheric layer and has, therefore, an essentially impulsive and strongly explosive character. The specific energy release in the explosion region, erg/g, considerably exceeds the evaporation/sublimation heat of the body so that the process is accompanied by production of a high-temperature plasma. The energetics of such an explosive process corresponds to that of very large solar flares for falling bodies having masses equal to the mass of the nucleus of Comet Halley. Spectral observations of sungrazing comets by SOHO-like telescopes in a wide spectral range, including X rays, with a high time resolution, of the order of 0.1-10 s, are important for revealing solar activity in the form of an impact-generated photospheric flare.

Ibadov, S.; Ibodov, F. S.; Grigorian, S. S.

2009-03-01

293

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

294

Current state of the problem of solar flares: New observations and new models  

NASA Astrophysics Data System (ADS)

A review of current questions related to the problem of large solar flares is given. The basic physical principles applied in numerical simulation of flares are presented and illustrated. The main attention is given to the phenomenon of magnetic reconnection in large-scale current layers at separators of magnetic field in the corona. This phenomenon is demonstrated within the framework of the Rainbow topological model. The model provides the possibility of explaining specific features of large-scale reconnection as a physical process that makes it possible to accumulate large energy in the form of the magnetic energy of current layers before a flare and to quickly transform this energy to the kinetic energy of particles during a flare. The secondary effects in the solar atmosphere caused by energy fluxes from reconnecting current layers are also discussed. These consequences of the primary energy release are responsible for the flare pattern observed in X-ray, optical, UV, and other spectral ranges.

Somov, B. V.

2006-03-01

295

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

NASA Technical Reports Server (NTRS)

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.

Bai, T.; Ramaty, R.

1976-01-01

296

Recent Laboratory Tests of a Hard X-Ray Solar Flare Polarimeter  

Microsoft Academic Search

We report on the development of a Compton scatter polarimeter for measuring the linear polarization of hard X-rays (50-300 keV) from solar flares. Such measurements would be useful for studying the directivity (or beaming) of the electrons that are accelerated in solar flares. We initially used a simple prototype polarimeter to successfully demonstrate the reliability of our Monte Carlo simulation

M. L. McConnell; J. R. Macri; M. McClish; J. Ryan

297

Signature of an Avalanche in Solar Flares as Measured by Photospheric Magnetic Fields  

Microsoft Academic Search

We analyzed time variations of turbulent parameters of the photospheric magnetic field of four active regions obtained during the course of major solar flares using longitudinal magnetograms from the Big Bear Solar Observatory and from SOHO\\/MDI full-disk measurements. Analysis of the data indicated that, before each flare, the degree of intermittency of the magnetic field had been increasing for 6-33

V. I. Abramenko; V. B. Yurchyshyn; H. Wang; T. J. Spirock; P. R. Goode

2003-01-01

298

Correlation between Solar Flare Productivity and Photospheric Magnetic Field Properties II. Magnetic Gradient and Magnetic Shear  

Microsoft Academic Search

With 1353 vector magnetograms observed at Huairou Solar Observing Station (HSOS), a statistical analysis is made on the relationship\\u000a among solar flares, magnetic gradient, and magnetic shear. The results suggest that flare productivity has positive correlations\\u000a with the gradient and the shear, which can be well fitted by the Boltzmann sigmoidal function. In the vicinity of neutral\\u000a lines, high gradient

Yanmei Cui; Rong Li; Huaning Wang; Han He

2007-01-01

299

Neutron and electromagnetic emissions during the 1990 May 24 solar flare  

SciTech Connect

In this paper, the authors are primarily concerned with the solar neutron emission during the 1990 May 24 flare, utilizing the counting rate of the climax neutron monitor and the time profiles of hard X-rays and gamma-rays obtained with the GRANAT satellite. They compare the derived neutron injection function with macroscopic parameters of the flare region as obtained from the Halpha and microwave observations made at the Big Bear Solar Observatory and the Owens Valley Radio Observatory, respectively.

Kocharov, L.G.; Lee, J.W.; Zirin, H.; Kovaltsov, G.A.; Usoskin, I.G.

1996-12-13

300

Solar Flare Soft X-ray Irradiance and its Impact on the Earth's Upper Atmosphere  

NASA Astrophysics Data System (ADS)

Solar flare soft X-ray irradiance provides a highly variable energy source to the lower thermosphere. Observations from three NASA satellite missions, the Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics - Solar Extreme Ultraviolet Experiment (TIMED-SEE), the Solar Radiation and Climate Experiment (SORCE) and the Student Nitric Oxide Explorer (SNOE) are analyzed to determine how solar soft X-ray irradiance varies during a solar flare and how this irradiance affects the Earth's lower thermosphere. Solar soft X-rays are one of the principal energy sources that lead to the production of thermospheric nitric oxide (NO) through the dissociation of odd-nitrogen. NO is an important source of radiative cooling in the thermosphere and therefore performs an important role in the energy balance. The XUV Photometer System (XPS) aboard TIMED-SEE and the XPS aboard SORCE both include a suite of photodiode detectors that measure the solar soft X-ray irradiance in broadband channels from 0.1 to 27 nm. The TIMED-SEE XPS observed 29 flares of various strengths over a six month period in 2002 and the SORCE XPS observed several large flares during the fall of 2003. An emission measure technique is used to interpret the broadband observations and determine a solar flare spectrum with a model that calculates theoretical spectra for input differential emission measures (DEM). The DEMs are iterated until the resulting spectrum reproduces the XPS observations. These solar flare spectra are used to determine the soft X-ray energy input to the Earth's lower thermosphere. Most of the solar flare soft X-ray irradiance comes from the 1 - 2 nm range and is deposited near 106 km. The abundance of NO peaks near 106 km and responds dramatically to energy deposited in the upper atmosphere. SNOE observed a significant increase in thermospheric NO following the X17 solar flare on 28 October 2003. Analysis of solar flare NO density enhancements and a comparison to results from a photochemical model will be presented along with a description of the solar flare spectral analysis.

Rodgers, E. M.; Bailey, S. M.; Warren, H. P.; Woods, T. N.; Eparvier, F. G.

2006-05-01

301

Vector Magnetograph Observations by the Solar Flare Telescope at Boao  

NASA Astrophysics Data System (ADS)

We report that the vector magnetograph(VMG) observations of the solar photosphere are being carried out by the Solar Flare Telescope(SOFT) in BOAO(Bohyunsan Optical Astronomical Observatory) of Korea Astronomy Observatory. The VMG uses a narrow band Lyot filter (FWHM = 0.125A) for observations of Stokes parameters(I,Q,U,V) to obtain longitudinal and transversal fields. The Stokes images are acquired by Sony XC -77 video CCD cameras which are digitized in 8-bit by an image processor, MVC 150/40 manufactured by ITI(Image Technology Incorporate). The digitized images are saved in 16 bit after integration (up to 256 frames) or in 8-bit multiple frames for analysis. Since the transmission wavelength of Lyot filter is very sensitive to environmental temperature (0.35A/deg), it requires a careful temperature control of the filter interior. For this, we have made a continuous effort to maintain the temperature stability within the accuracy of less than 0.05 deg. with NAIRC (Nanjing Astronomical Instrument Research Center) team. We have obtained clean line profiles of FeI 6302.5 from our VMG by scanning the individual profiles by changing the central wavelength of the Lyot filter. We present some of our observed VMG observations, which are compared with those made with similar vector magnetographs at other observatories.

Park, Y. D.; Moon, Y.-J.

302

Solar Eruptive Flares: from Physical Understanding to Probabilistic Forecasting  

NASA Astrophysics Data System (ADS)

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.

Georgoulis, M. K.

2013-12-01

303

Solar Atmospheric and Solar Flare Accelerated Helium Abundances from Gamma-Ray Spectroscopy  

Microsoft Academic Search

From the measured fluences of alpha alpha and narrow gamma-ray lines we derive He abundances (He\\/O) in the gamma-ray production region of solar flares, most likely subcoronal regions located above the photosphere. The alpha alpha line is a spectral feature due to de-excitations in 7Li and 7Be produced by the interactions of alpha -particles with He. We find that the

Natalie Mandzhavidze; Reuven Ramaty; Benzion Kozlovsky

1997-01-01

304

The High Energy Photons Emission from Solar Flares Observed by SZ2-XD  

NASA Astrophysics Data System (ADS)

The spectra and light curve of near a hundred Solar X-ray Flare events, which were observed by SZ2/XD in the energy band of 10-800 keV during 2001, have been investigated. The events covered from C to X-class flares, which are shown different characters of high energy photons emission. The results will be presented in this paper. The discussions will be made especially for 3 of the brightest X-class solar flares SF010402(X20),SF010406(X5.6) and SF010415 (X14.4, a GLE event).

Wang, Huanyu; Li, Xinqiao; Ma, Yuqian; et al.

305

Spatial coherency of solar flares in the activity cycles 17 and 18 (1934 - 1954).  

NASA Astrophysics Data System (ADS)

Mean locations of flares with respect to the centers of gravity of sunspot groups on latitude-time diagrams for 1934 - 1955 are calculated. The results are presented as vector diagrams of flare displacements R?(?,t). Combining the wings of butterfly diagrams of two adjacent cycles (17 and 18) of solar activity indicates a high spatial coherency of the directions of vectors pointing to the ?-t diagram center. This has been interpreted as being due to a global trigger mechanism for solar flares.

Kasinskij, V. V.

306

Acceleration, containment, and emission of very low energy solar flare particles  

NASA Technical Reports Server (NTRS)

We present the first observations of protons down to 44 keV and electrons down to less than about 2 keV emitted in an impulsive solar particle event. The observations are from the Apollo 15 Subsatellite during a flare event which began on September 1, 1971. We obtain a lower limit estimate of the energy contained in protons above about 0.05 MeV in the flare. The effects of adiabatic deceleration in the interplanetary medium and dE/dx energy loss in the corona are discussed. We conclude that energetic protons may constitute a major energy release in large solar flares.

Lin, R. P.; Mcguire, R. E.; Anderson, K. A.

1974-01-01

307

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

308

Probing Magnetic Energy Release in a Solar Flare with Radio Dynamic Imaging Spectroscopy  

NASA Astrophysics Data System (ADS)

Solar flares involve sudden release of magnetic energy that is previously stored in the Sun's corona. Yet details of the flare energy release processes are still poorly understood. Solar radio bursts are intense and short-lived radio emissions that occur in solar flares. They are believed to be intimately related to flare energy release processes. However, their potential in diagnosing flare energy release has been greatly limited by the lack of simultaneous spatial information. The upgraded Karl G. Jansky Very Large Array (VLA) provides the first opportunity of radio synthesis imaging along with high spectral and temporal resolution, making the new technique of radio dynamic imaging spectroscopy possible. We report VLA observations of a solar flare event using this new technique, during which a rich variety of radio bursts are recorded. With the help of concurrent data in extreme ultra-violet and X-ray wavelengths, these observations allow us to establish the relation between the bursts and flare energy release, and use them to probe physical properties of the energy release site.

Chen, Bin; Bastian, T. S.; Gary, D. E.; White, S. M.

2014-01-01

309

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

NASA Astrophysics Data System (ADS)

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.

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

2013-09-01

310

Effect of solar flares in radiochemical measurements of solar neutrino intensity  

NASA Astrophysics Data System (ADS)

The effect of chromospheric flares at the end of the exposure has been studied for all radiochemical facilities measuring the flux of solar neutrino. For chlorine-argon measurements (Brookheaven), it has been found that the development of flared results in the count rate acceleration to 4.7 ± 1.2 SNU. The effect of this growth is fictitious; this is an increase in the effectiveness of reaction product extraction from the target matter under the action of the ULF electromagnetic disturbance induced by the flare X-rays rather than an increase in the flux. The indications that a similar effect is present in the SAGE gallium-germanium measurement have been obtained. For the GALLEX gallium-germanium experiment, the effect of flares has not been found; the sign of this effect possibly differs from that of the Brookheaven and SAGE measurements. The found difference agrees with the conclusion that the results of the SAGE and GALLEX measurements anticorrelate for the exposures that end simultaneously.

Vladimirskii, B. M.; Bruns, A. V.

2007-12-01

311

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

NASA Technical Reports Server (NTRS)

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.

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

312

Clear Evidence of Reconnection Inflow of a Solar Flare  

Microsoft Academic Search

We found an important piece of evidence for magnetic reconnection inflow in a flare on 1999 March 18. The flare occurred on the northeast limb, displaying a nice cusp-shaped soft X-ray loop and a plasmoid ejection typical for the long-duration events. The EUV observation of the same flare shows us a bubble-like void ejection. The core of this EUV void

T. Yokoyama; K. Akita; T. Morimoto; K. Inoue; J. Newmark

2001-01-01

313

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

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

314

Magnetic Field Changes in SDO/HMI Line-of-sight Magnetograms during Large Solar Flares  

NASA Astrophysics Data System (ADS)

Photospheric magnetic fields are often used to study the topology of a flaring active region as well as to predict when a flare will happen. We examined SDO/HMI line-of-sight magnetograms for forty flares (M5.0 or larger) from 2010 to 2013. Using the full-resolution (0.5 arcsecond/pixel) and high time cadence (45-second), observations, we identified three types of changes in line-of-sight magnetic flux near the flaring region during large solar flares: First, discreet jumps or steps in the line-of-sight magnetic flux are often observed when examining magnetograms before and after the flare. Second, spikes or rapid and transient changes lasting just a few minutes occur during the rise of the flare, coinciding with the impulsive phase. Finally, in a few flares, moderate-scale waves in magnetograms, similar to Moreton or EIT waves, are seen propagating away from the flaring region. In this study, we provide statistics on these different apparent magnetic flux changes as well as offer possible physical explanations.

Balasubramaniam, K. S.; Hock, Rachel

2014-06-01

315

Simulating the Effects of Initial Pitch-angle Distributions on Solar Flares  

NASA Astrophysics Data System (ADS)

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.

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

2011-07-01

316

An active role for magnetic fields in solar flares  

NASA Technical Reports Server (NTRS)

Observations of photospheric magnetic fields are reviewed to determine whether changes in such fields can be related to flare activity, assuming that magnetic fields play an active role in providing flare energy. An intimate relation between emerging fields and bright flare knots is noted, and it is shown that the activation and eruption of an H-alpha filament is indicative of a major disruption of a magnetic field just prior to a flare. Observations of twisting motions in a filament just before a flare are discussed, erupting untwisting filaments are taken as unambiguous evidence for restructuring of the magnetic fields associated with flares, and it is argued that magnetic-field changes in the midst of most flares are obvious. It is concluded that successive brightenings in a family of loops may be evidence for the spread of a magnetic-field reconnection point from one field concentration to another and that flares may well take place in regions of field-line reconnection. This latter conclusion is illustrated using an empirical flare model that involves field-line reconnection, filament activation, and emerging magnetic flux.

Rust, D. M.

1976-01-01

317

Flares on dMe Stars: IUE (International Ultraviolet Explorer) and Optical Observations of AT Mic, and Comparison of Far-Ultraviolet Stellar and Solar Flares.  

National Technical Information Service (NTIS)

In the paper the authors describe observations and analysis of a large flare event on a dMe star, detected by the International Ultraviolet Explorer (IUE). They compare its far-ultraviolet spectrum with those of other stellar flares and also a large solar...

G. E. Bromage K. J. H. Phillips P. L. Dufton A. E. Kingston

1986-01-01

318

The energetic relationship among geoeffective solar flares, associated CMEs and SEPs  

NASA Astrophysics Data System (ADS)

Major solar eruptions (flares, coronal mass ejections (CMEs) and solar energetic particles (SEPs)) strongly influence geospace and space weather. Currently, the mechanism of their influence on space weather is not well understood and requires a detailed study of the energetic relationship among these eruptive phenomena. From this perspective, we investigate 30 flares (observed by RHESSI), followed by weak to strong geomagnetic storms. Spectral analysis of these flares suggests a new power-law relationship (r ~ 0.79) between the hard X-ray (HXR) spectral index (before flare-peak) and linear speed of the associated CME observed by LASCO/SOHO. For 12 flares which were followed by SEP enhancement near Earth, HXR and SEP spectral analysis reveals a new scaling law (r ~ 0.9) between the hardest X-ray flare spectrum and the hardest SEP spectrum. Furthermore, a strong correlation is obtained between the linear speed of the CME and the hardest spectrum of the corresponding SEP event (r ~ 0.96). We propose that the potentially geoeffective flare and associated CME and SEP are well-connected through a possible feedback mechanism, and should be regarded within the framework of a solar eruption. Owing to their space weather effects, these new results will help improve our current understanding of the Sun-Earth relationship, which is a major goal of research programs in heliophysics.

Bhatt, Nipa J.; Jain, Rajmal; Awasthi, Arun Kumar

2013-08-01

319

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

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

320

New observational facts about particle acceleration and transport during solar flares  

NASA Technical Reports Server (NTRS)

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.

Trottel, G.

1996-01-01

321

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

NASA Technical Reports Server (NTRS)

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.

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

1973-01-01

322

The composition of corotating energetic particle streams. [nucleons in solar wind and flares  

NASA Technical Reports Server (NTRS)

The relative abundances of 1.5-23 MeV per nucleon ions in corotating nucleon streams are compared with ion abundances in particle events associated with solar flares and with solar and solar wind abundances. He/O and C/O ratios are found to be a factor of the order 2-3 greater in corotating streams than in flare-associated events. The distribution of H/He ratios in corotating streams is found to be much narrower and of lower average value than in flare-associated events. H/He in corotating energetic particle streams compares favorably in both lack of variability and numerical value with H/He in high-speed solar wind plasma streams. The lack of variability suggests that the source population for the corotating energetic particles is the solar wind, a suggestion consistent with acceleration of the corotating particles in interplanetary space.

Mcguire, R. E.; Von Rosenvinge, T. T.; Mcdonald, F. B.

1978-01-01

323

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

NASA Astrophysics Data System (ADS)

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.

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

324

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

325

CORONAL ELECTRON DISTRIBUTION IN SOLAR FLARES: DRIFT-KINETIC MODEL  

SciTech Connect

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.

Minoshima, Takashi; Kusano, Kanya [Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 3173-25, Syowa-machi, Kanazawaku, Yokohama 236-0001 (Japan); Masuda, Satoshi; Miyoshi, Yoshizumi, E-mail: minoshim@jamstec.go.jp [Solar-Terrestrial Environment Laboratory, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601 (Japan)

2011-05-10

326

Magnetic shielding of interplanetary spacecraft against solar flare radiation  

NASA Astrophysics Data System (ADS)

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

Cocks, Franklin H.; Watkins, Seth

1993-07-01

327

Solar X-ray flare hazards on the surface of Mars  

NASA Astrophysics Data System (ADS)

Putative organisms on the Martian surface would be exposed to potentially high doses of ionizing radiation during strong solar X-ray flares. We extrapolate the observed flare frequency-energy release scaling relation to total X-ray energies much larger than seen so far for the Sun, an assumption supported by observations of flares on other solar- and subsolar-mass main sequence stars. Flare spectra are taken as power laws, with the logarithmic slope a parameter based on the observed statistics of the most energetic hard X-ray flare spectra. We calculate surface spectra using a Monte Carlo code we developed for the transport of X-rays and gamma rays, including photoabsorption and detailed Compton scattering. Biological doses from indirect genome damage are calculated for each parameterized flare spectrum by integration over the X-ray opacity of water. The resulting doses depend sensitively on spectral slope, which varies greatly and unsystematically for solar flares. Using the roughly uniform observed distribution of spectral slopes, we estimate the mean waiting time for solar flares producing a given biological dose of ionizing radiation on Mars and compare with lethal dose data for a wide range of terrestrial organisms. These timescales range from decades for significant human health risk to 0.5 Myr for D. radiodurans lethality. Such doses require total flare energies of 1033- 1038 erg, the lower range of which has been observed for other stars. Flares are intermittent bursts, so acute lethality will only occur on the sunward hemisphere during a sufficiently energetic flare, unlike low-dose-rate, extended damage by cosmic rays. We estimate the soil and CO2 ice columns required to provide 1/e shielding as 4-9gcm-2, depending on flare mean energy and atmospheric column density. Topographic altitude variations give a factor of two variation in dose for a given flare. Life in ice layers that may exist ˜100gcm-2 below the surface would be well protected. Finally, we point out that designing spacesuits to sufficiently block this radiation on Mars missions may be difficult, given the conflict between solutions for lightweight protection from energetic particles and those from X-rays.

Smith, David S.; Scalo, John

2007-03-01

328

The photospheric magnetic field response to a solar flare  

Microsoft Academic Search

Using the vector magnetic field measurements the authors have studied the scaling of photospheric magnetic field and current helicity Bz·(?×B)z during the periods of high flare activity in two active regions. The results allow to assume that from the very onset of a flare the transverse photospheric magnetic field undergoes significant changes, namely, the fluctuations energy is reduced as well

V. I. Abramenko; V. B. Yurchishin; V. Carbone

1998-01-01

329

Collected and Corrected Solar Flare Reports, 1955-1964.  

National Technical Information Service (NTIS)

The flare data were compiled primarily from the flare lists of the IAU Quarterly Bulletin and a magnetic tape obtained from the Institute for Telecommunication Sciences and Aeronomy (ITSA). This tape was assembled from the CRPL-F Part B series (1955 throu...

H. J. E. Fischer D. C. Jensen

1966-01-01

330

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

NASA Technical Reports Server (NTRS)

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.

Holman, Gordon D.

2011-01-01

331

The North-South Asymmetry of Soft X-Ray Solar Flares  

NASA Astrophysics Data System (ADS)

We analyse the North-South (N-S) asymmetry of soft X-ray (SXR) solar flares during the 11-year solar cycle (SC). After reviewing the literature on flare dominance in the northern and southern hemispheres of the solar disk for SCs 17-23, we analyse the SXR flare distribution in the two hemispheres during the period 1976-2001. The analysis was made using the number of flares (N) and Qx index, which evaluates the energy emitted by flares in soft X-ray. The monthly and annual N-S asymmetry values computed by us for the mentioned period are in agreement with the results from the literature. The degree of the N-S asymmetry for both N and Qx indices confirmed the antiphase of SXR flare emergence for spectral classes M and X, and class C, respectively, noted by Maris et al. (2000). Finally, we consider that the detailed study of the descending and minimum phases of the SCs, at the stage when magnetic phenomena from both the old and the new cycle interact in the solar atmosphere, would be useful for inferring information about the activity level of the next cycle.

Maris, Georgeta; Popescu, Miruna Daniela; Mierla, Marilena

332

Anomaly in Chromospheric Evaporation/ Neupert Effect observed in Impulsive versus Gradual Solar flares  

NASA Astrophysics Data System (ADS)

We investigate the physical implication of Neupert effect in 12 M-class solar flares observed by "Solar X-ray Spectrometer" (SOXS) onboard GSAT-2 Indian spacecraft that launched in 2003. The chromospheric evaporation model describing origin of Neupert effect in solar flares is a major tool for quantitative estimation of energy released in the form of soft and hard X-rays. The quantification of the fraction (Qf) of total energy converted to thermal and non-thermal components is the goal of current investigation, which may improve our current understanding of energy release processes in solar flares. We employ 3s spectra from Si and CZT detectors of SOXS experiment for the current investigation. Our data sample includes 5 impulsive and 7 gradual flares. We find Qf in impulsive flares to be 0.8 at peak emission, which suggests that approximately 80 percent of the energy of the accelerated electrons is deposited in chromo-spheres during thick-target bremsstrahlung. On the other hand, Qf is ¿1 for all gradual flares .This suggests origin of thermal i.e. SXR emission cannot be well explained by chromospheric evaporation model and needs detailed investigation.

Jain, Rajmal; Awasthi, Arun

333

Physical Properties of Solar Flares: New Results from EVE/SDO  

NASA Astrophysics Data System (ADS)

Much of our current understanding of the temperature and density structure of solar flares has been derived from broad band X-ray instruments, such as RHESSI, GOES, and SXT/Yohkoh, or the observation of isolated emission lines, such as from BCS/Yohkoh. This has lead to uncertainties in determining the distribution of temperatures and densities in a flare. The EUV Variability Experiment (EVE) on the Solar Dynamics Observatory (SDO) provides an unprecedented opportunity to observe a very wide range of high-temperature emission lines at high cadence (10 s) and relatively high spectral resolution (1 A). The spectral range between 90 and 200 Angstroms is particularly rich in emission lines from Fe that are formed at temperatures above 7 MK (Fe XVIII - Fe XXIV). This range also includes one of the few density diagnostics (Fe XXI 145.66/128.75) that is useful in solar flare observations. Our initial calculations suggest very broad differential emission measure distributions and indicate high densities (Log Ne as high as 11.7), which implies a very rapid cooling of flare plasma. These observations are broadly consistent with flare models that allow for the release of energy on many independent threads and we will discuss these results in the context of current theories of solar flares.

Warren, H. P.; Mariska, J. T.; Doschek, G. A.; Eve Team

2010-12-01

334

The thermal phase of a large solar flare. [Skylab observations  

NASA Technical Reports Server (NTRS)

EUV and X-ray observations are used to derive the differential emission measures, temperatures, densities, radiative and conductive cooling rates, and thermal energy content of a class 2B flare that occurred on September 7, 1973. The results of the analysis indicate that (1) most of the flare plasma was at temperatures between 3 and 10 million degrees; (2) the peak temperature decreased with time from about 8 million K to 5 million K over a period of 3.5 hours; (3) the differential emission measure steadily decreased with time at nearly all temperatures; (4) both radiation and conduction were important cooling mechanisms for the plasma at temperatures above 100,000 K; and (5) a substantial amount of energy, of the order of 3 x 10 to the 31st power ergs, was deposited in the flare loops after flare maximum. The empirically determined flare parameters are compared with similar parameters derived from a simple theoretical loop model.

Withbroe, G. L.

1978-01-01

335

Relationship between unusual features in umbrae and flares  

NASA Astrophysics Data System (ADS)

The influence of photospheric and chromospheric dynamics and morphologies on flare activity are still unclear. We present a study of two flaring active regions (ARs) with complementary instruments (DST/IBIS, Hinode/SOT-SP, SDO/HMI and SDO/AIA) to investigate the temporal evolution of the sunspots and their magnetic and thermodynamic properties. In spite of vast differences in flare occurrence and flare magnitudes, both ARs show similar features in the lower solar atmosphere during flares. We investigate common magnetic topologies and dynamics, which may favor flare activity.

Sainz Dalda, Alberto; Kleint, Lucia

2014-06-01

336

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

NASA Technical Reports Server (NTRS)

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).

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

1991-01-01

337

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

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

338

Automated Classification of Flaring Behavior in Solar Active Regions: Preliminary Results  

NASA Astrophysics Data System (ADS)

Solar active events are the source of many energetic and geo-effective events such as solar flares and coronal mass ejections (CMEs). Understanding how these complex source regions evolve and produce these events is of fundamental importance, not only to solar physics but also the demands of space weather forecasting. In this poster, we present preliminary results from our analysis of the physical properties of active region magnetic fields using fractal-, gradient-, neutral line-, emerging flux-, and wavelet-based techniques. These analyses look to use the defined physical measures to form a predictive model for flaring behavior in active regions.

Al-Ghraibah, Amani; Boucheron, L. E.; McAteer, R.; Cao, H.; Jackiewicz, J.; McNamara, B.; Voelz, D.; Calabro, B.; DeGrave, K.; Hao, Y.; Kirk, M.; Pevtsov, A.; Mckeever, J.; Taylor, G.

2012-01-01

339

Solar flare and IMF sector structure effects in the lower ionosphere  

NASA Technical Reports Server (NTRS)

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.

Lastovicka, J.

1984-01-01

340

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

341

The High Energy Photons Emission from Solar Flares Observed by SZ2-XD  

Microsoft Academic Search

The spectra and light curve of near a hundred Solar X-ray Flare events, which were observed by SZ2\\/XD in the energy band of 10-800 keV during 2001, have been investigated. The events covered from C to X-class flares, which are shown different characters of high energy photons emission. The results will be presented in this paper. The discussions will be

Huanyu Wang; Xinqiao Li; Yuqian Ma

2008-01-01

342

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

SciTech Connect

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.

Masson, S.; Antiochos, S. K. [Space Weather Laboratory, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771 (United States); DeVore, C. R., E-mail: sophie.masson@nasa.gov [Laboratory for Computational Physics and Fluid Dynamics, Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375 (United States)

2013-07-10

343

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

Microsoft Academic Search

Solar Maximum Mission observations of three flares that impose stringent constraints on physical models of the hard X-ray production during the impulsive phase are presented. Hard X-ray imaging observations of the flares on 1980 November 5 at 22:33 UT show two patches in the 16 to 30 keV images that are separated by 70,000 km and that brighten simultaneously to

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

1985-01-01

344

Solar Energy-An Everyday Occurrence  

ERIC Educational Resources Information Center

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

Keister, Carole; Cornell, Lu Beth

1978-01-01

345

Energetics and dynamics of simple impulsive solar flares  

NASA Technical Reports Server (NTRS)

Flare energetics and dynamics were studied using observations of simple impulsive spike bursts. A large, homogeneous set of events was selected to enable the most definite tests possible of competing flare models, in the absence of spatially resolved observations. The emission mechanisms and specific flare models that were considered in this investigation are described, and the derivations of the parameters that were tested are presented. Results of the correlation analysis between soft and hard X-ray energetics are also presented. The ion conduction front model and tests of that model with the well-observed spike bursts are described. Finally, conclusions drawn from this investigation and suggestions for future studies are discussed.

Starr, R.; Heindl, W. A.; Crannell, C. J.; Thomas, R. J.; Batchelor, D. A.; Magun, A.

1987-01-01

346

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

NASA Astrophysics Data System (ADS)

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

Berlicki, A.; Heinzel, P.

2004-06-01

347

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

NASA Astrophysics Data System (ADS)

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.

Sharykin, Ivan; Kosovichev, Alexander G.

2014-06-01

348

Modeling the Solar Atmospheric Response to Flare-Accelerated Ion Beams  

NASA Astrophysics Data System (ADS)

In the standard model of the impulsive phase of flares, particles accelerated to high energy at the flare reconnection site are the main source of heating in the lower atmosphere. These particles travel down magnetic flux tubes transferring their energy to the ambient plasma along the way through Coulomb collisions. It is likely that electrons as well as ions are accelerated by flare reconnection, and much work has been done understanding the response of the solar atmosphere to electron beam heating. However, since the presence of ions is much more difficult to directly detect than electrons, their role in flare heating is less understood. To better understand this, we have performed simulations of the solar atmospheric response to ion beam heating. Our models solve the equations of non-LTE radiation hydrodynamics for the conditions of the flaring solar atmosphere with an ion beam energy source term. Radiative transfer is solved in detail for many important optically thick hydrogen and helium transitions and numerous optically thin EUV lines. Thus, these models are ideally suited to study the emission that is produced during flares. We will pay special attention to understanding how key EUV lines respond to ion beam heating. We will compare these results to simulations performed with electron beam heating.

Allred, Joel C.; Holman, G. D.

2012-05-01

349

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

NASA Technical Reports Server (NTRS)

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).

Chamberlin, Phillip C.; Woods, Thomas N.

2011-01-01

350

The homologous flare sites and the general solar activity  

NASA Astrophysics Data System (ADS)

The homologous flares observed in the same region of a spotgroup testify the existence and the duration of a permanent instability. However, they also attest that the general magnetic configuration is not destroyed by these flares and that it changes slowly up to the death of the site. The study of every flaring sites where more than ten flares occur has been performed in Meudon for the 1974-1980 period. One hundred and sixty-six sites have been analysed from the rotation where the A.R. is observed up to five rotations ahead. The basis of the study are the ``Synoptic Maps''. A relation is found between the presence of crossing of ``filament-phantom'' corridors and the location of the homologous flare sites. The specific analysis concerning every active regions observed in 1980 and selected for the ``homologous flares'' study, i.e. A.R. nr. 2363; 2372; 2478; 2466-69-79; 2490; 2507; 2516-17; 2522; 2570; 2629; 2646; were grouped into a composite figure which was presented and explained during the Symposium.

Martres, M.-J.; Mouradian, Z.; Soru-Escaut, I.

351

Energy release topology in a multiple-loop solar flare  

NASA Technical Reports Server (NTRS)

The temporal and spatial structures of the UV and X-ray emissions and the magnetic field configuration in the November 12, 1980 flare observed from SMM have been studied. The UV observations were done in the O V and Fe XXI lines with a spatial resolution of 10 arcsec. The observations show that the impulsive UV bursts, and also the hard X-ray bursts by their temporal correlation with the impulsive O V emission, occurred in small localized kernels. By comparing the O V, Fe XXI, and X-ray raster images of the flare with the magnetogram, these emission kernels were identified as footpoints of interacting magnetic flux loops. The temporal evolution of the O V/Fe XXI emission shows that there was considerable preheating in the flare plasma some 8-9 minutes prior to the onset of the main hard X-ray bursts. The results are interpreted as indicating that the primary flare energy release occurred in a highly sheared multiloop structure, which lies along a magnetic neutral line. By either beam particle propagation or convective motion, flare energy is transported via a common footpoint to another loop which brightened later. The preheating of the flare plasma is shown to create a more favorable environment for energetic particle acceleration which resulted in the main impulsive hard X-ray bursts.

Cheng, C.-C.; Pallavicini, R.; Acton, L. W.; Tandberg-Hanssen, E.

1985-01-01

352

Characteristics of the Photospheric Magnetic Field Associated with Solar Flare Initiation  

NASA Astrophysics Data System (ADS)

The physical environment governing the solar flare initiation is not fully understood, although there are significant efforts to address the relationship between magnetic non-potential parameters and early flare signatures. In this study, we attempt to characterize the flare initiation based on the processed Helioseismic and Magnetic Imager vector magnetograms, Atmospheric Imaging Assembly 1600 Å, and RHESSI hard X-ray observations. Three flare events, the M6.6 flare on 2011 February 13, the X2.2 flare on 2011 February 15, and the X2.1 flare on 2011 September 6, in two active regions AR 11158 and AR 11283 are investigated. We analyze the source field strength in the photosphere, which is defined as the magnitude of the observed magnetic field deviation from the potential field. It is found that one of the strong source field regions above the magnetic polarity inversion line well connects the initial bright kernels of two conjugate ribbons. The results imply that the distribution of the photospheric source field strength can be used to locate the initiation site of flaring loops regardless of the configuration of pre-flare magnetic fields or the evolution of active regions. Moreover, the field configuration in the strong source field regions tends to become more inclined after flares, which is consistent with the coronal implosion scenario. We also employ a fast method to derive the total current density from the photospheric vector magnetogram in the framework of force-free field. This method can provide fast estimation of photospheric current density within a reasonable accuracy without appealing for the more accurate calculation from a model extrapolation.

Yang, Ya-Hui; Chen, P. F.; Hsieh, Min-Shiu; Wu, S. T.; He, Han; Tsai, Tsung-Che

2014-05-01

353

The 73-DAY Periodicity of the Flare Index during the Current SOLAR-CYCLE-22  

NASA Astrophysics Data System (ADS)

The flare index of the current solar cycle 22 is analysed to detect intermediate-term periodicities from Sep. 1, 1986 to Dec. 31, 1991. Power spectral analysis of the time series of solar flare index data reveals a periodicity around 73 and 53 days. We find that a periodicity of 73 days was in operation from 1988 November to the end of 1991 December. We also find that when the 73-day periodicity or the 154-day periodicity is in operation, the flare index is well correlated with the relative sunspot numbers. As a conclusion, we do not expect to see a resumption of the 154-day or 73-day periodicity, but we do expect only one of the periodicity near the integral multiples of 25d.8 in the next solar cycles.

Özgüç, Atila; Ataç, Tamer

1994-06-01

354

Table-top solar flares produced with laser driven magnetic reconnections  

NASA Astrophysics Data System (ADS)

The American Nuclear Society (ANS) has presented the prestigious Edward Teller award to Dr. Bruce A. Remington during the 2011 IFSA conference due to his "pioneering scientific work in the fields of inertial confinement fusion (ICF), and especially developing an international effort in high energy density laboratory astrophysics" [1,2]. This is a great acknowledgement to the subject of high energy density laboratory astrophysics. In this context, we report here one experiment conducted to model solar flares in the laboratory with intense lasers [3]. The mega-gauss -scale magnetic fields produced by laser produced plasmas can be used to make magnetic reconnection topology. We have produced one table-top solar flare in our laboratory experiment with the same geometric setup as associated with solar flares.

Zhong, J. Y.; Li, Y. T.; Wang, X. G.; Wang, J. Q.; Dong, Q. L.; Liu, X.; Lin, X. X.; Yuan, D. W.; Du, F.; Wang, S. J.; Zhang, L.; An, L.; Xiao, C. J.; Wei, H. G.; Zhang, K.; Wang, F. L.; Jiang, S. E.; Ding, Y. K.; Cao, Z. R.; Yuan, Z.; Zhang, H. Y.; Yang, Z. W.; Zhu, J. Q.; He, X. T.; Cai, H. B.; Zhao, G.; Zhang, J.

2013-11-01

355

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

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

356

Longitudinal Distribution of Solar Flares and Their Association with Coronal Mass Ejections and Forbush Decreases  

NASA Astrophysics Data System (ADS)

Major H ? solar-flare events of high optical importance have been employed to study their heliographic distribution in longitude around the Sun for the period of 2001 to 2006. A statistical analysis was performed to obtain their relationship with halo/partial-halo CMEs and Forbush decreases (Fds) of cosmic-ray intensity. Our analysis indicates that 63% of the solar flares associated with halo CMEs and Fds occur in the western hemisphere and of 37% of such flares occur in the eastern hemisphere. Similarly, we found that nearly 60% of the solar flares associated with partial- halo CMEs and Fds occur in the western hemisphere and the rest (40%) occur in the eastern hemisphere. Finally, we conclude that the flares in association with CMEs and located in the western hemisphere of the solar disk are more effective in producing Fds. The magnitudes of Fds are observed to be higher when in association of halo CMEs. A slight excess in the eastern hemisphere is found for both the halo and partial-halo CMEs.

Shrivastava, Pankaj K.; Jothe, Mukesh K.; Singh, Mahendra

2011-04-01

357

Hybrid Kinetic and Radiative Hydrodynamic Simulations of Solar Flares and Comparison With Multiwavelength Observations  

NASA Astrophysics Data System (ADS)

We present a unified simulation which combines two physical processes: how the particles are accelerated and the energy is transported along a coronal loop, and how the atmosphere responds. The “flare” code from Stanford University (Petrosian et al, 2001) models the stochastic acceleration and transport of particles and radiation of solar flares. It includes pitch angle diffusion and energy loss, and computes collisional heating to the background plasma and bremsstrahlung emission along the loop. The radiative hydrodynamic RADYN Code (Carlsson et al, 1992, 1996; Allred et al, 2005) computes the energy transport by the injected non-thermal electrons at the top of a 1D coronal loop. Recently, we have combined the two codes by updating the non-thermal heating in the RADYN code from the "flare" code, allowing us to develop a self-consistent simulation. In addition, we can now model more realistically the multi-wavelength emission of solar flares and compare it with observations, e.g., at optical wavelengths from IBIS at the Dunn Solar Telescope and in X-rays from RHESSI. The high resolution UV observations from the recently launched IRIS imaging spectrograph will be particularly useful in this regard. These will allow us to compare numerically modeled and observed emissions of solar flares in several lines using more robust simulations than possible before.

Rubio Da Costa, Fatima; Petrosian, Vahe; Liu, Wei; Carlsson, Mats; Kleint, Lucia

2014-06-01

358

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

Microsoft Academic Search

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

B. V. Jackson; K. V. Sheridan

1979-01-01

359

Recent development of The Gamma Ray Imager/Polarimeter for Solar Flares (GRIPS) instrument  

NASA Astrophysics Data System (ADS)

The sun is an efficient and powerful particle accelerator. Flares can release up to 10^33 ergs in 10-1000 seconds, imparting 10s of percent of energy released into particles. Ions and electrons are proportionally accelerated, with ions reaching energies of 10s of GeV. Moving particles emit spectra which encode key information about acceleration processes and ambient plasma parameters, providing a powerful tool to study particle dynamics. The mechanisms by which the energy stored in solar magnetic fields is released and used to accelerate particles are poorly understood. In the last solar cycle, the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) satellite found the location of ion emission sources were significantly displaced from electron sources in the flare footpoints of the two best observed flares. This result is surprising; the standard flare model predicts that ions and electrons are accelerated 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 provide enhanced spectroscopy and imaging of the gamma/HXR spectrum over wide ranges of energy and spatial resolutions to address particle acceleration in flares. GRIPS is optimized to provide high-resolution imaging, spectroscopy and polarimetry of gamma/HXR flare emissions from ~20 keV to >~10MeV. GRIPS' novel three dimensional germanium detector (3D-GeD) enables the use of a single grid imaging system, the multi-pitch rotating modulator (MPRM), that creates a nearly ideal point response function with quasi-continuous resolution from 12.5-162 arcsecs. This design has a two-fold increased sensitivity over a bi-grid design like RHESSI, significantly enhancing counting statistics in a regime which is usually plagued by low counts. Here, we present the recent progress and development of GRIPS imaging system.

Duncan, N. A.; Hurford, G. J.; Donakowski, B.; Shih, A. Y.; Lin, R. P.

2012-12-01

360

Diagnostics of electron-heated solar flare models. III - Effects of tapered loop geometry and preheating  

NASA Technical Reports Server (NTRS)

A series of hydrodynamic numerical simulations of nonthermal electron-heated solar flare atmospheres and their corresponding soft X-ray Ca XIX emission-line profiles, under the conditions of tapered flare loop geometry and/or a preheated atmosphere, is presented. The degree of tapering is parameterized by the magnetic mirror ratio, while the preheated atmosphere is parameterized by the initial upper chromospheric pressure. In a tapered flare loop, it is found that the upward motion of evaporated material is faster compared with the case where the flare loop is uniform. This is due to the diverging nozzle seen by the upflowing material. In the case where the flare atmosphere is preheated and the flare geometry is uniform, the response of the atmosphere to the electron collisional heating is slow. The upward velocity of the hydrodynamic gas is reduced due not only to the large coronal column depth, but also to the increased inertia of the overlying material. It is concluded that the only possible electron-heated scenario in which the predicted Ca XIX line profiles agree with the BCS observations is when the impulsive flare starts in a preheated dense corona.

Emslie, A. G.; Li, Peng; Mariska, John T.

1992-01-01

361

ABRUPT LONGITUDINAL MAGNETIC FIELD CHANGES AND ULTRAVIOLET EMISSIONS ACCOMPANYING SOLAR FLARES  

SciTech Connect

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

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

2012-11-20

362

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

NASA Technical Reports Server (NTRS)

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

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

2005-01-01

363

Solar Flare Kernel Observations with Integral Field Spectroscopy in H-alpha Line and SDO  

NASA Astrophysics Data System (ADS)

We developed a field integral spectroscopic instrument using a micro-lens array at the Domeless Solar Telescope, Hida Obervatory. and obtained data of H-alpha flares in X-ray C- and M-class flares taking place on 3 Nov 2011. The field of view was about 10 arc seconds square and time cadence was 12 seconds. The data demonstrate that simultaneous spectroscopic observations over extended solar structures, at a high spatial resolution and temporal cadence, are important to track and understand the physics of transient phenomena happening in impulsive flare kernels. With two-dimensional field spectral data, we made monochromatic images at given wavelengths in the H-alpha line and nearby continuum to co-align with X-ray and UV images from SDO. We also carried out line profile analysis to derive 2-D distribution of atmospheric parameters. Obtained H-alpha spectra clearly show the rapid development of red asymmetry at the flare kernels, giving a large downward Doppler shift of up to 50 km/sec. The accompanied formation of coronal flaring loop structures are consistent with a scenario of downward motion of compressed chromospheric flare kernels due do impulsive heat flow from the corona to the chromosphere and simultaneous evaporation of the chromospheric material into the corona.

Suematsu, Y.

2013-12-01

364

Statistical relationship between the succeeding solar flares detected by the RHESSI satellite  

NASA Astrophysics Data System (ADS)

The Reuven Ramaty High Energy Solar Spectroscopic Imager has observed more than 80 000 solar energetic events since its launch on 2002 February 12. Using this large sample of observed flares, we studied the spatiotemporal relationship between succeeding flares. Our results show that the statistical relationship between the temporal and spatial differences of succeeding flares can be described as a power law of the form R(t) ˜ tp with p = 0.327 ± 0.007. We discuss the possible interpretations of this result as a characteristic function of a supposed underlying physics. Different scenarios are considered to explain this relation, including the case where the connectivity between succeeding events is realized through a shock wave in the post Sedov-Taylor phase or where the spatial and temporal relationship between flares is supposed to be provided by an expanding flare area in the sub-diffusive regime. Furthermore, we cannot exclude the possibility that the physical process behind the statistical relationship is the reordering of the magnetic field by the flare or it is due to some unknown processes.

Balázs, L. G.; Gyenge, N.; Korsós, M. B.; Baranyi, T.; Forgács-Dajka, E.; Ballai, I.

2014-06-01

365

Deuterium and tritium from solar flares at approximately 10 MeV per nucleon  

NASA Technical Reports Server (NTRS)

It is indicated that the observations with the high-resolution solid-state charged-particle telescopes of the IMP-5 and IMP-6 earth satellites have resolved all the hydrogen and helium isotopes of solar-flare origin in groups of solar flares during the period from September, 1969, through November, 1972. The values obtained for the average isotope ratios are given and are compared with previous values. It is concluded that the observed high yields of H(2), H(3) and He(3) can be explained only by high-energy nuclear interactions and that an acceleration process must have taken place in the chromosphere at that time.

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

1973-01-01

366

Solar gamma-ray lines as probes of accelerated particle directionalities in flares  

NASA Technical Reports Server (NTRS)

Anisotropies of charged particles accelerated in solar flares were studied by observing Doppler shifts of selected gamma-ray lines. The spectral shape was calculated of the 6.1-MeV line of O-16. If the accelerated particles are isotropic, the line remains centered at e sub 0 = 6129.4 keV, and its width (FWHM) is about 100 keV. For particle anisotropies that may be produced in solar flares, the line is shifted to lower energies by about 30 to 40 keV.

Ramaty, R.; Crannell, C. J.

1975-01-01

367

On Fine Structure in Solar Flares from SDO, RHESSI and TRACE Observations  

NASA Astrophysics Data System (ADS)

Data on white-light flares (WLFs) on the Sun have been collected. Results of observations in H?, UV, near infrared (NIR), X-ray and white-light (WL) on the ground and aboard SDO, RHESSI, Hinode, TRACE SOHO and STEREO are analyzed. Characteristics of flares and relation be tween continuum emission and Hard X-rays (HXRs) are considered. Usually WL and HXR origin in the footpoints of flaring loops in lower dense layers of the solar atmosphere; however, if the loop density is high enough, WL, HXR and radio emission can originate in the flaring arch itself. Continuum enhancement varies in a wide range. The problem of the heights, where the WL and HXR are formed, is discussed. Observational and theoretical aspects are considered.

Porfir'eva, G. A.; Yakunina, G. V.

2014-03-01

368

Constraints for electron acceleration models in solar flares from microwave observations with high spatial resolution  

NASA Astrophysics Data System (ADS)

Different theoretical models of particle acceleration in solar flares predict different accelera-tion/injection sites in flaring loops, as well as different pitch-angle distributions of accelerated electrons. In this study we solve the non-stationary Fokker-Plank kinetic equation with differ-ent assumptions on the injection site and pitch-angle anisotropy of energetic electrons in order to find their spatial, energy, and pitch-angle distributions, and calculate corresponding gyrosyn-chrotron emission properties. We show that different locations of acceleration/injection sites in flaring loops may produce different types of pitch-angle distributions of accelerated electrons and, as a consequence, very different spatial, spectral and polarization properties of the loop microwave emission. It is shown that these properties can be detected using spatially resolved microwave observations of specific flaring loops and be used to choose the most suitable electron acceleration model. The conclusion is illustrated by Nobeyama Radioheliograph observations.

Melnikov, Victor

369

Prompt particle acceleration around moving X-point magnetic field during impulsive phase of solar flares  

NASA Technical Reports Server (NTRS)

We present a model for high-energy solar flares to explain prompt proton and electron acceleration, which occurs around moving X-point magnetic field during the implosion phase of the current sheet. We derive the electromagnetic fields during the strong implosion phase of the current sheets, which is driven by the converging flow derived from the magnetohydrodynamic equations. It is shown that both protons and electrons can be promptly (within 1 second) accelerated to approximately 70 MeV and approximately 200 MeV, respectively. This acceleration mechanism can be applicable for the impulsive phase of the gradual gamma ray and proton flares (gradual GR/P flare), which have been called two-ribbon flares.

Sakai, Jun-Ichi

1992-01-01

370

Ionic charge states of solar energetic particles - Effects of flare X-rays  

NASA Technical Reports Server (NTRS)

Ionic charge states of solar energetic particles (SEP) from three flares have been reported by Luhn et al. (1984). Interpretations of the mean charges in terms of a source temperature Ts (assuming collisional ionization equilibrium) yield inconsistent results. For Mg, the required Ts (up to 8 x 10 to the 6th K) are larger than for N and Si by factors of up to 5. Here it is pointed out that flare X-rays photoionize the ambient corona, causing apparent ionization temperatures there to exceed the local electron temperature, Te. Using realistic flare X-ray fluxes, it is shown that the charge data for six elements (C, N, Ne, Mg, Si, and S) can be fitted if the source is at coronal temperatures (Te = 1-2 x 10 to the 6th K), but the ionization equilibrium is radiation dominated. For oxygen, a slight inconsistency persists in the three flares.

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

1986-01-01

371

The effect of solar flare index on the seasonal variation of 5577 Å line intensity at Calcutta.  

NASA Astrophysics Data System (ADS)

Twilight and night airglow observation of 5577 Å line was observed by Dunn-Manring type photometer for the period 1983 - 1987. This paper presents the seasonal variation of 5577 Å line intensity (A?) and its variation with solar flare index (If) which is calculated considering all the flares which occurred during a particular month for which airglow intensity is considered. It is concluded that the variation of the intensity of airglow line (5577 Å) with solar flare index (If) shows a periodic trend. Average period of 5577 Å line intensity with monthly mean of flare index are compared for lower and higher values of solar flare index (If). A possible explanation of such type of variation is invoked by considering the formation and destruction of O3 by ultraviolet rays during flare time.

Midya, S. K.; Tarafdar, G.; Sen, A. K.; Ghosh, S. N.

1999-10-01

372

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

NASA Astrophysics Data System (ADS)

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

Kolarski, Aleksandra; Grubor, Davorka

2014-06-01

373

Modeling the Secondary Flare Irradiance Measured by Solar Dynamic Observatory (SDO) Extreme ultraviolet Variability Experiment (EVE)  

NASA Astrophysics Data System (ADS)

NASA’s Solar Dynamic Observatory (SDO) launched on 11 February 2010 and normal operations for all three instruments began 1 May 2010. Since then numerous small and moderate (C- and M-class) flares have been observed. One interesting feature observed by the Extreme ultraviolet Variability Experiment (EVE) is the enhancement of 2-3 million K emission several hours after the flare’s soft x-ray emission. From the Atmospheric Imaging Assembly (AIA) images, we can tell that these secondary emissions occur in the same active region as the flare but not in same coronal loops. Here, we examine the C8.8 flare that occurred on 5 May 2010. The flare occurred in Active Region 11069, a small magnetically complex region near the western limb of the Sun. The gradual phase of the flare is clearly seen in both GOES soft X-rays and the hot coronal emissions (>2 million K) measured by EVE. The secondary flare emission starts 30 minutes after the peak in gradual phase and slowly increases over an hour before decaying to the pre-flare levels. It is most strongly seen in Fe XV and Fe XVI (2-3 million K). Using the Enthalpy-Based Thermal Evolution of Loops (EBTEL) model, we are able calculate the EUV irradiance of a set of coronal loops for a given heating function. This allows us to determine the best-fit heating profile as a function of time for the C8.8 flare. The heating profile for this event clearly shows that there are two separate phases of heating. The first phase involves traditional post-flare loops. The field reconnects after erupting, and the energy released during the reconnection heats the plasma to very high temperatures. As the loops cool, emissions are seen in progressively cooler lines from 10 to 1 million K. The second phase is very different. A large number of coronal loops are heated only modestly-. The plasma in each loop, instead of reaching 10 million K, reaches 3 million K. The heating is also spread out over an hour generating the long secondary flare emission profile. We discuss the nature of this secondary flare emission, which seems to be an important component of many events.

Hock, R. A.; Woods, T. N.; Klimchuk, J. A.; Eparvier, F. G.

2010-12-01

374

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

375

Magnetic field structure changes in the vicinity of solar flares  

SciTech Connect

Changes in the structure of the sunspot group and its magnetic field are studied in Hale Region 17644 (May 1981) in connection with the May 16 3B/X1 flare. The characteristic changes, also found in HR 16850 (May 1980) and HR 17098 (September 1980), are the following: rapid motions of umbrae of opposite polarity in the vicinity of the magnetic zero line, parallel to this line, but in opposite direction. Appearance of new small spots before the flare, leading to a more complicated field structure. Simplification of the magnetic structure after the flare in some days, i.e., decrease of spot areas in the affected territory and the straightening of the magnetic zero line. 15 references.

Kalman, B.

1984-01-01

376

Solar Flare Detection With SWIFT and Real-time GONG H-alpha Images  

NASA Astrophysics Data System (ADS)

The Air Force Weather Agency (AFWA) has begun the process of upgrading the Solar Observing Optical Network (SOON) with an Improved-SOON (ISOON). During the interim period, AFWA is supporting the addition and operation of a solar H-alpha (Hydrogen-alpha, 656.3 nm) full-disk image network utilizing the light feed from the National Solar Observatory's existing GONG (Global Oscillation Network Group) instruments. The H-alpha instruments at the GONG sites have been in operation collectively since the beginning of 2011, providing one to three H-alpha images per minute. Cross-site comparison and calibration of flare detection has begun using an image analysis tool called SWIFT (SWFL/ISOON Flare-cast Tool). SWIFT is a unique and versatile software package, designed originally for ISOON data, that has been attuned to ingest and display GONG H-alpha images in real-time. The SWIFT software allows a user to detect and analyze optical flares from solar active regions. The SWIFT software is in the process of being beta-tested at AFWA in collaboration with the Space Weather Center of Excellence's SWFL (Space Weather Forecasting Laboratory) to better forecast space weather events. Solar flares are of great interest to the Air Force Research Laboratory's Space Vehicles Directorate because they can trigger energetic particle events or coronal mass ejection events that impact the Earth's magnetosphere creating geomagnetic storms. Such events can result in satellite charging damage, increased satellite drag, power grid disruption, navigation system anomalies, and communication fadeouts. An overview of SWIFT, along with preliminary flare detection comparisons between GONG sites and the SOON flare reports, will be presented.

Henney, Carl John; MacKenzie, D.; Hill, F.; Mills, B.; Pietrzak, J.

2011-05-01

377

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

NASA Astrophysics Data System (ADS)

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

Murray, Sophie A.

2013-01-01

378

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

379

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

NASA Technical Reports Server (NTRS)

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

Chupp, E. L.

1987-01-01

380

What is the relationship between photospheric flow [|#12#|]fields and solar flares?  

NASA Astrophysics Data System (ADS)

We estimated photospheric velocities by separately applying the Fourier Local Correlation Tracking (FLCT) and Differential Affine Velocity Estimator (DAVE) methods to 2708 co-registered pairs of SOHO/MDI magnetograms, with nominal 96-minute cadence and ~2'' pixels, from 46 active regions (ARs) from 1996-1998 over the time interval t_45 when each AR was within 45 degrees of disk center. For each magnetogram pair, we computed the reprojected, average estimated radial magnetic field, B_R; and each tracking method produced an independently estimated flow field, u. We then quantitatively characterized these magnetic and flow fields by computing several extensive and intensive properties of each; extensive properties scale with AR size, while intensive properties do not depend directly on AR size. Intensive flow properties included moments of speeds, horizontal divergences, and radial curls; extensive flow properties included sums of these properties over each AR, and a crude proxy for the ideal Poynting flux, S_R, equal to the sum of (u B_R^2) over a magnetogram. Several quantities derived from B_R were also computed, including: total unsigned flux; a measure of the amount of unsigned flux near strong-field polarity inversion lines (SPILs), R; and the sum of B_R^2 over each magnetogram. Next, using correlation and discriminant analysis, we investigated the associations between these properties and flares from the GOES flare catalog, when averaged over both t_45 and shorter time windows, of 6 and 24 hours. Our AR sample included both flaring and flare-quiet ARs; the latter did not flare above GOES C1.0 level during t_45. Among magnetic properties, we found R to be most strongly associated with flare flux. Among extensive flow properties, the proxy Poynting flux, S_R, was most strongly associated with flare flux, at a level comparable to that of R. All intensive flow properties studied were more poorly associated with flare flux than these extensive properties. Past flare activity was also associated with future flare occurrence. The largest coefficients of determination from correlations with flare flux that we performed are ~0.25, implying no single variable that we considered can explain variations in average flare flux.

Welsch, B. T.; Li, Y.; Schuck, P. W.; Fisher, G. H.

2009-12-01

381

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

SciTech Connect

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

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

2011-06-01

382

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

NASA Technical Reports Server (NTRS)

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

Holman, Gordon D.

2004-01-01

383

Modeling Solar Flare Hard X-ray Images and Spectra Observed with RHESSI  

NASA Technical Reports Server (NTRS)

Observations obtained with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) of a flare on February 20, 2002 indicate a hard X-ray (HXR) coronal source at or near the top of a flare loop (called a HXR looptop source). The existence of the HXR looptop source suggests that magnetic reconnection, which is believed to power flares, occurs above the loop. In order to explain this HXR looptop source, I created a steady-state particle transport model, in which high-energy electrons are continuously injected at the top of a semicircular flare loop. Based on the simulation results, I find that the model predictions are consistent with the RHESSI observations in many respects, but the spectrum of the looptop source obtained from the model is steeper than that from the RHESSI data. This suggests that, instead of being accelerated above the loop as generally believed, the particles might be accelerated in the looptop itself. RHESSI-observations of three other homologous flares that occurred between April 14 and 16, 2002, provide strong evidence for the presence of a large scale current sheet above a flare loop, which is the basis of standard flare models. The most convincing finding is the presence of the temperature distribution of a separate coronal source above the flare loops: the hotter part of the coronal source was located lower in altitude the cooler part. Together with the fact that the hotter flare loops are higher than the cooler loops, the observations support the existence of a large-scale current sheet between the top of the flare loops and the coronal source above. Blob-Like sources along a line above the loop in the decay phase of the April 15, 2002, flare, which are suggestive of magnetic islands initiated by the tearing-mode instability, and the observation of a cusp structure in microwaves, further support the presence of the current sheet. The observations of the three homologous flares reveal two other features which are beyond the predictions of the standard flare models: the downward motion of flare loops in the early impulsive phase of each flare, and an initially stationary coronal source above the loops. These features me believed to be related to the formation and development of a current sheet. In particular, the downward loop motion seem to be a common phenomenon in flares, suggesting the necessity for modifications to the existing standard flare. models. Finally, thanks to the broad energy coverage of the RHESSI spectra, a low-energy cutoff of 28 (plus or minus 2) keV in the nonthermal electron distribution was determined for the April 15, 2002, flare. As a result, the energy carried by the nonthermal electrons is found to be comparable to the thermal energy of the flare, but one order of magnitude larger than the kinetic energy of the associated coronal mass ejection. The method used to deduce the electron low-energy cutoff will be useful in the analyses of similar events.

Sui, Linhui

2005-01-01

384

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

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

385

Particle Acceleration and Propagation in Strong Flares without Major Solar Energetic Particle Events  

NASA Astrophysics Data System (ADS)

Solar energetic particles (SEPs) detected in space are statistically associated with flares and coronal mass ejections (CMEs). But it is not clear how these processes actually contribute to the acceleration and transport of the particles. The present work addresses the question why flares accompanied by intense soft X-ray bursts may not produce SEPs detected by observations with the GOES spacecraft. We consider all X-class X-ray bursts between 1996 and 2006 from the western solar hemisphere. 21 out of 69 have no signature in GOES proton intensities above 10 MeV, despite being significant accelerators of electrons, as shown by their radio emission at cm wavelengths. The majority (11/20) has no type III radio bursts from electron beams escaping towards interplanetary space during the impulsive flare phase. Together with other radio properties, this indicates that the electrons accelerated during the impulsive flare phase remain confined in the low corona. This occurs in flares with and without a CME. Although GOES saw no protons above 10 MeV at geosynchronous orbit, energetic particles were detected in some (4/11) confined events at Lagrangian point L1 aboard ACE or SoHO. These events have, besides the confined microwave emission, dm-m wave type II and type IV bursts indicating an independent accelerator in the corona. Three of them are accompanied by CMEs. We conclude that the principal reason why major solar flares in the western hemisphere are not associated with SEPs is the confinement of particles accelerated in the impulsive phase. A coronal shock wave or the restructuring of the magnetically stressed corona, indicated by the type II and IV bursts, can explain the detection of SEPs when flare-accelerated particles do not reach open magnetic field lines. But the mere presence of these radio signatures, especially of a metric type II burst, is not a sufficient condition for a major SEP event.

Klein, K.-L.; Trottet, G.; Samwel, S.; Malandraki, O.

2011-04-01

386

Spectrometer IRIS: Investigation of the Time Structure and Energy Spectra of X-Ray Emission from Solar Flares  

NASA Astrophysics Data System (ADS)

The research program underlying the IRIS experiment (Russian acronym for Investigation of Solar X-Ray Emission) encompasses investigation of the characteristics of X-ray emission from solar flares and of their precursors in the 2-200-keV range, which would form a basis for development of physical models describing the process of buildup and explosive release of energy in a solar flare, as well as accumulation of experimental data to serve in devising techniques for forecasting the solar flare activity

Matveev, G. A.; Dmitriev, P. B.; Kudryavtsev, I. V.; Lazutkov, V. P.; Savchenko, M. I.; Skorodumov, D. V.; Charikov, Yu. E.

387

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

NASA Astrophysics Data System (ADS)

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

Yu, Sijie; Yan, Yihua; Tan, Baolin

2012-12-01

388

The solar flares of February 1986 and the ensuing intense geomagnetic storm  

NASA Astrophysics Data System (ADS)

A very intense geomagnetic storm, the largest observed in 26 years, was observed in early February 1986 having just been preceded by a series of six solar flares during the period 3 - 7 February. The storm and its antecedent flares are currently a subject of great interest because of the unusually large magnitude of the various geomagnetic effects that obtained. The fact that the flares were moderate to large in soft X-ray intensity, but much smaller than the largest that the Sun is capable of producing, coupled with the fact that these events occurred near the minimum of the current solar activity cycle, adds to the uniqueness of the overall episode. This paper describes the special circumstances surrounding these events and offers an interpretation of the cause and effect relationships through a numerical simulation of the dynamical evolutionary processes that may have occurred in interplanetary space.

Garcia, Howard A.; Dryer, Murray

1987-09-01

389

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

390

A solar flare X-ray polarimeter for the Space Shuttle  

NASA Technical Reports Server (NTRS)

An instrument has recently been built and tested which is designed to measure the polarization of the hard (5-30 keV) X-ray emission from solar flares, and thereby to investigate the energy release mechanism and constrain flare models. In particular, these measurements will help to determine whether hard X-ray bursts are produced by nonthermal or by thermal electrons. The polarimeter makes use of the angular dependence of Thomson scattering from targets of metallic lithium. It has an energy resolution of a few keV, a time resolution of 5 s, and sufficient sensitivity to measure polarization levels (3 sigma) of a few percent in about 10 s for a moderate strength solar flare. The instrumental polarization has been directly measured and found to be within the design goal of approximately 1%. This polarimeter is scheduled to be flown as part of the OSS-1 pallet on an early Space Shuttle mission.

Lemen, J. R.; Chanan, G. A.; Hughes, J. P.; Laser, M. R.; Novick, R.; Rochwarger, I. T.; Sackson, M.; Tramiel, L. J.

1982-01-01

391

Flare Size  

NSDL National Science Digital Library

This is an activity about determining the size of a solar flare. Learners will measure the diameter of a solar flare by making calculations using transparency grids overlaid on images of the Sun. This is the third activity as part of the "How Does HESSI Take a Picture" lesson.

392

Modeling of Solar Flare Plasma and Its Radiation  

Microsoft Academic Search

We present a modular and highly versatile test particle-radiative hydrodynamic code which simultaneously models the particle beam energy transport and deposition, the corresponding explosive response of the flare atmosphere and the NLTE (NLTE, plasma and radiation out of the local thermodynamic equilibrium) radiative transfer for partly ionized hydrogen in the chromosphere and photosphere. The computational domain covers the photosphere, the

Michal Varady; Jana Kasparova; Zdenek Moravec; Petr Heinzel; Marian Karlicky

2010-01-01

393

Morphology and physical parameters of a solar flare  

NASA Technical Reports Server (NTRS)

The chromospheric and coronal morphology of the flare of June 15, 1973, (1B/M3) in NOAA active region 131 (McMath 12379) is discussed, and results of quantitative analysis of Skylab soft X-ray observations of the event are presented. H-alpha and white-light observations reveal evidence of emerging flux near the site of the H-alpha flare onset. Preflare and early flare filament activity and its spatial and temporal correlation with the flare are discussed. Spatially resolved soft X-rays are compared with H-alpha and magnetic-field measurements. Full-disk high-temporal-resolution soft X-ray flux measurements and time profiles of the resultant temperature and density calculations are also presented which yield a peak temperature of about 14.2 million K and a peak electron density of approximately 3.5 deg 10 to the -10th power per cu cm and show a preflash-phase temperature rise to about 9 million K. The peak values should be compared with the respective values of approximately 25 million K and 4.5 by 10 to the -10th power per cu cm deduced from the spatially resolved data.

Smith, J. B., Jr.; Wilson, R. M.; Henze, W., Jr.

1977-01-01

394

Modeling of the Solar Flare's Chromosphere and Photosphere  

NASA Astrophysics Data System (ADS)

The flare of importance 2 is studied in the H?, H?, H?, H Ca II, the lines of He I, D3 and ? 4471 Å, and photospheric lines using the spectra obtained on the echelle spectrograph of the Crimean Astrophysical Observatory.

Baranovsky, E. A.; Shoumko, A. V.

395

Plasma Heating in Solar Flares and their Soft and Hard X-Ray Emissions  

NASA Astrophysics Data System (ADS)

In this paper, the energy budgets of two single-loop-like flares observed in X-ray are analyzed under the assumption that nonthermal 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 February 20 and June 2, respectively. Using a one-dimensional (1D) hydrodynamic code for both flares, the energy deposited in the chromosphere was derived applying RHESSI observational data. The use of the Fokker-Planck formalism permits the calculation of distributions of the NTEs in flaring loops and thus spatial distributions of the X-ray nonthermal emissions and integral fluxes for the selected energy ranges that were compared with the observed ones. Additionally, a comparative analysis of the spatial distributions of the signals in the RHESSI images was conducted for the footpoints and for all the flare loops in selected energy ranges with these quantities' fluxes obtained from the models. The best compatibility of the model and observations was obtained for the 2002 June 2 event in the 0.5-4 Å GOES range and total fluxes in the 6-12 keV, 12-25 keV, 20-25 keV, and 50-100 keV energy bands. Results of photometry of the individual flaring structures in a high energy range show that the best compliance occurred for the 2002 June 2 flare, where the synthesized emissions were at least 30% higher than the observed emissions. For the 2002 February 20 flare, synthesized emission is about four times lower than the observed one. However, in the low energy range the best conformity was obtained for the 2002 February 20 flare, where emission from the model is about 11% lower than the observed one. The larger inconsistency occurs for the 2002 June 2 solar flare, where synthesized emission is about 12 times greater or even more than the observed emission. Some part of these differences may be caused by inevitable flaws of the applied methodology, like by an assumption that the model of the flare is symmetric and there are no differences in the emissions originating from the feet of the flares loop and by relative simplicity of the applied numerical 1D code and procedures. No doubt a significant refinement of the applied numerical models and more sophisticated implementation of the various physical mechanisms involved are required to achieve a better agreement. Despite these problems, a collation of modeled results with observations shows that soft and hard X-ray emissions observed for analyzed single-loop-like events may be fully explained by electron-beam-driven evaporation only.

Falewicz, R.

2014-07-01

396

HELIOSEISMIC RESPONSE TO THE X2.2 SOLAR FLARE OF 2011 FEBRUARY 15  

SciTech Connect

The X2.2-class solar flare of 2011 February 15 produced a powerful 'sunquake' event, representing a helioseismic response to the flare impact in the solar photosphere, which was observed with the Helioseismic and Magnetic Imager (HMI) instrument on board the Solar Dynamics Observatory (SDO). The impulsively excited acoustic waves formed a compact wave packet traveling through the solar interior and appearing on the surface as expanding wave ripples. The initial flare impacts were observed in the form of compact and rapid variations of the Doppler velocity, line-of-sight magnetic field, and continuum intensity. These variations formed a typical two-ribbon flare structure, and are believed to be associated with thermal and hydrodynamic effects of high-energy particles heating the lower atmosphere. The analysis of the SDO/HMI and X-ray data from RHESSI shows that the helioseismic waves were initiated by the photospheric impact in the early impulsive phase, observed prior to the hard X-ray (50-100 keV) impulse, and were probably associated with atmospheric heating by relatively low-energy electrons ({approx}6-50 keV) and heat flux transport. The impact caused a short motion in the sunspot penumbra prior to the appearance of the helioseismic wave. It is found that the helioseismic wave front traveling through a sunspot had a lower amplitude and was significantly delayed relative to the front traveling outside the spot. These observations open new perspectives for studying the flare photospheric impacts and for using the flare-excited waves for sunspot seismology.

Kosovichev, A. G. [W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305 (United States)

2011-06-10

397

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

398

Wavelets, Intermittency and Solar Flare Hard X-rays 2. LIM Analysis of High Time Resolution BATSE Data  

NASA Astrophysics Data System (ADS)

We apply local intermittency measure (LIM) analysis to 64 ms time resolved BATSE measurements of hard X-rays from several solar flares. LIM analysis yields information on the character of the processes giving rise to fluctuations in light curves, e.g. avalanche vs. cascade pictures. We present LIM scaleograms for several flares and summarise scaleogram morphological features. More detailed descriptions are given of the behaviour in the flare of 13 January 1992 (the well-known `Masuda flare') and an interesting event on 22 November 1998. All flares display episodes of intermittency across a range of scales. LIM scaleogram features may be consistent with both `top-down' and `bottom-up' scenarios for the development of small-scale structure, sometimes within the same flare. Thus neither class of model captures the totality of the events in a flare.

Dinkelaker, A. N.; MacKinnon, A. L.

2013-02-01

399

Muon excess at sea level from solar flares in association with the Fermi GBM spacecraft detector  

NASA Astrophysics Data System (ADS)

This paper presents results of an ongoing survey on the association between muon excesses at ground level, registered by the Tupi telescopes, and transient solar events, whose gamma-ray and x-ray emissions were reported by the Fermi Gamma Burst Monitor and the Geostationary Operational Environmental Satellite 14, respectively. We show that solar flares of small scale, those with prompt x-ray emission classified by the Geostationary Operational Environmental Satellite as C-Class with power 10-6 to 10-5Wattsm-2 at 1 AU, may give rise to muon excess probably associated with solar protons and ions emitted by the flare and arriving at the Earth as a coherent particle pulse. The Tupi telescopes are within the central region of the South Atlantic Anomaly, where the geomagnetic field intensity is the lowest on the Earth. Here we argue for the possibility of a “scale-free” power-law energy spectrum of particles accelerated by solar flares. For energies around and exceeding the pion production, large and small scale flares have the same power-law energy spectrum. The difference is only in the intensity. The Tupi events give support to this conjecture.

Augusto, C. R. A.; Navia, C. E.; Shigueoka, H.; Tsui, K. H.; Fauth, A. C.

2011-08-01

400

A 2.2 Mev gamma Ray Line Observed During a SN Solar Flare.  

National Technical Information Service (NTIS)

On December 15, 1978, an omnidirectional gamma ray detector was flown during day time. Around noon time, when the sun was in the field of view of the detector, a solar flare of magnitude SN was observed. The flux of 2.2 MeV line showed enhancement during ...

K. R. Rao I. M. Martin J. O. D. Jardim U. B. Jayanthi

1980-01-01

401

Thermal and nonthermal contributions to the solar flare x-ray flux  

Microsoft Academic Search

The relative thermal and nonthermal contributions to the total energy budget of a solar flare are being determined through analysis of RHESSI X-ray imaging and spectral observations in the energy range from ˜ 5 to ˜ 50 keV. The classic ways of differentiating betwee