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1

Universality in solar flare and earthquake occurrence.  

PubMed

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

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

2006-02-10

2

Solar Flares  

NSDL National Science Digital Library

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

Mrs. Verlengia

2011-12-10

3

What flare and CME parameters control the occurrence of solar proton events?  

NASA Astrophysics Data System (ADS)

In this study we examine the occurrence probabilities of solar proton events (SPEs) and their peak fluxes depending on both flare and coronal mass ejection (CME) parameters: flare peak flux, longitude, impulsive time, CME linear speed, and angular width. For this we use the NOAA SPEs, their associated X-ray flares, and CME from 1997 to 2011. We divide the data into 16 subgroups according to the flare and CME parameters and estimate the SPE probabilities for the subgroups. The three highest probabilities are found for the following subgroups: (1) fast full halo (55.3%) and fast partial halo (42.9%) CMEs associated with strong flares from the western region and (2) slow full halo CMEs associated with strong flares from the western region (31.6%). It is noted that the events whose SPE probabilities are nearly 0% belong to the following subgroups: (1) slow and fast partial halo CMEs from the eastern region, (2) slow partial halo CMEs from the western region, and (3) slow full halo CMEs from the eastern region. These results show that important parameters to control SPE occurrences are CME linear speed, angular width, and source longitude, which can be understood by the piston-driven shock formation of fast CMEs and magnetic field connectivity from the source site to the Earth. It is also shown that when the subgroups are separately considered by flare impulsive time and source longitude, the correlation coefficients between the observed and the predicted SPE peak fluxes are greatly improved.

Park, Jinhye; Moon, Y.-J.

2014-12-01

4

Solar Flares  

NSDL National Science Digital Library

This resource is about solar flares, which are tremendous explosions on the surface of the sun that, in a matter of just a few minutes, heat material to many millions of degrees and release as much energy as a billion megatons of TNT. The site discusses the characteristics of the flares, how and why they are observed and who observes them, and their relationship to magnetic shear. Three images of solar flares erupting enhance the discussion.

David Hathaway

5

Solar flares  

NASA Technical Reports Server (NTRS)

General characteristics of solar flares are discussed. They are a spectacular energy release arising from development of magnetic strain and shear, resulting from eruption of new magnetic flux near old. The release of magnetic energy is channeled into hard electrons (and possibly nucleons), which produce a series of other effects. The ultimate source of the magnetic complexity that produces flares is deep in the sun. A number of examples is given, and the difference between various types of flares is discussed.

Zirin, Harold

1990-01-01

6

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

7

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

PubMed

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

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

2006-02-10

8

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

NASA Astrophysics Data System (ADS)

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

Monte-Moreno, Enrique; Hernández-Pajares, Manuel

2014-11-01

9

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

Microsoft Academic Search

Since the launch of the SMM satellite on 1980 February 14, the Gamma-Ray Spectrometer has been monitoring the Sun in the energy range 0.3 - 100 MeV. So far 139 flares have been monitored. The authors report on an analysis of the temporal distribution of these high-energy events to provide information on solar activity and find that, instead of being

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

1984-01-01

10

The relationship between solar flares and solar sector boundaries  

NASA Technical Reports Server (NTRS)

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

Dittmer, P. H.

1974-01-01

11

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

12

Statistical aspects of solar flares  

NASA Technical Reports Server (NTRS)

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

Wilson, Robert M.

1987-01-01

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

Towards Predicting Solar Flares  

NASA Astrophysics Data System (ADS)

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

Winter, Lisa; Balasubramaniam, Karatholuvu S.

2015-04-01

16

Flare models: Chapter 9 of solar flares  

NASA Technical Reports Server (NTRS)

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

Sturrock, P. A. (editor)

1979-01-01

17

Solar Flares: Magnetohydrodynamic Processes  

NASA Astrophysics Data System (ADS)

This paper outlines the current understanding of solar flares, mainly focused on magnetohydrodynamic (MHD) processes responsible for producing a flare. Observations show that flares are one of the most explosive phenomena in the atmosphere of the Sun, releasing a huge amount of energy up to about 10^32 erg on the timescale of hours. Flares involve the heating of plasma, mass ejection, and particle acceleration that generates high-energy particles. The key physical processes for producing a flare are: the emergence of magnetic field from the solar interior to the solar atmosphere (flux emergence), local enhancement of electric current in the corona (formation of a current sheet), and rapid dissipation of electric current (magnetic reconnection) that causes shock heating, mass ejection, and particle acceleration. The evolution toward the onset of a flare is rather quasi-static when free energy is accumulated in the form of coronal electric current (field-aligned current, more precisely), while the dissipation of coronal current proceeds rapidly, producing various dynamic events that affect lower atmospheres such as the chromosphere and photosphere. Flares manifest such rapid dissipation of coronal current, and their theoretical modeling has been developed in accordance with observations, in which numerical simulations proved to be a strong tool reproducing the time-dependent, nonlinear evolution of a flare. We review the models proposed to explain the physical mechanism of flares, giving an comprehensive explanation of the key processes mentioned above. We start with basic properties of flares, then go into the details of energy build-up, release and transport in flares where magnetic reconnection works as the central engine to produce a flare.

Shibata, Kazunari; Magara, Tetsuya

2011-12-01

18

COMPTEL solar flare observations  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

19

The solar flare myth  

NASA Technical Reports Server (NTRS)

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

Gosling, J. T.

1993-01-01

20

The decay phase of solar flare events  

Microsoft Academic Search

A study of the properties of the cosmic radiation of energy ~- 10 MeV generated by solar flares is reported. Data from four Pioneer spacecraft in interplanetary orbits, and separated by ~ 180° in heliocentric longitude are employed. Attention is restricted to the properties evident at times in excess of 1 day after the occurrence of the parent flare. The

K. G. McCracken; U. R. Rao; R. P. Bukata; E. P. Keath

1971-01-01

21

A search for the 154 day periodicity in the occurrence rate of solar flares using Ottawa 2.8 GHz burst data, 1955-1990  

NASA Astrophysics Data System (ADS)

The Ottawa 2.8 GHz burst record from 1955 January to 1990 February has been examined for evidence of a periodicity near 154 days in the occurrence rate of solar flares. This periodicity is found to be statistically significant, at the 1-percent level, only for the years from 1978 to 1983, corresponding to the activity maximum of solar cycle 21. Through 1990 February, the Ottawa data show no evidence for a 154 day period in the current 22d solar cycle that began in 1986 September. A spectral peak near 51 days is found in solar cycle 19 (1955-1964), as had been previously reported based on an examination of CFI data, but its significance is low, at the 33-percent level. It is concluded that, other than for the period in cycle 21 in which it was first discovered, the evidence for the 154 day periodicity from flare-related data sets is contradictory and not compelling. Stronger evidence for the occurrence of the 154 day periodicity outside cycle 21 can be found in recent studies that examine parameters such as sunspot counts and areas that characterize solar active regions.

Kile, J. N.; Cliver, E. W.

1991-03-01

22

Solar flares: an overview.  

PubMed

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

Rust, D M

1992-01-01

23

BATSE Solar Flare Spectroscopy  

NASA Technical Reports Server (NTRS)

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

Schwartz, R. A.

1998-01-01

24

Electron beams in solar flares  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

25

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

26

Solar flares, microflares, nanoflares, and coronal heating  

Microsoft Academic Search

Solar flare occurrence follows a power-law distribution against total flare energy W: dN\\/dW ~ W-a with an index a ~ 1.8 as determined by several studies. This implies (a) that microflares must have a different, steeper distribution if they are energetically significant, and (b) there must be a high-energy cutoff of the observed distribution. We identify the distinct ‘soft’ distribution

H. S. Hudson

1991-01-01

27

Solar flare model atmospheres  

NASA Technical Reports Server (NTRS)

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

Hawley, Suzanne L.; Fisher, George H.

1994-01-01

28

Solar flare model atmospheres  

NASA Technical Reports Server (NTRS)

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

Hawley, Suzanne L.; Fisher, George H.

1993-01-01

29

Solar Flares: Gamma Rays  

E-print Network

We briefly review the theory of gamma ray production in solar flares and present the highlights of the observations and their implications. Specifically: (i) the gamma ray data show that a large fraction of the released flare energy is in accelerated ions, mostly around 1 MeV/nucleon; (ii) the accelerated He-3, heavy ion, and relativistic electron abundances are enriched, implying that the particle acceleration is dominated by stochastic gyroresonant interactions with plasma turbulence; (iii) there is evidence for the enhancement of the abundances of ambient chromospheric elements with low first ionization potentials; (iv) the observed Li-7 and Be-7 lines, at 0.429 MeV and 0.478 MeV due to alpha-alpha interactions, show that both the accelerated alpha particle and the ambient He abundances are significantly enhanced.

Reuven Ramaty; Natalie Mandzhavidze

1998-10-06

30

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

31

Response of TEC to solar flare: latitude and longitude features  

Microsoft Academic Search

The analysis of occurrence of ionospheric electron content to the large solar flare that occurred near 11 00 UT on November 28, 2003 (class X17) is presented. The TEC data were obtained using GPS observations carried by European Permanent Network (EPN) and International GNSS Service (IGS). The detail pictures of TEC response to the solar flare over Europe were obtained

A. Krankowski; I. Shagimuratov; H. Rothkaehl; A. Krypiak-Gregorczyk; I. Zakharenkova; N. Tepenitzyna

2007-01-01

32

Solar chromosphere flare spectrograph  

NASA Astrophysics Data System (ADS)

This paper describes develop of a two channel echelle spectrograph, Solar Chromospheric Flare Spectreograph (SCFC), to observe the optical spectra at the locations of ares and explosive events on the Sun. The SCFS will record are spectra in two channels in the wavelength range of 350-890 nm, which has several chromospheric spectral lines. The SCFS will have a multi-fiber based slit capable of observing at 100 locations of the active region magnetic field polarity inversion lines. The field of view of SCFS will be 80 x 80 arc sec with spatial resolution of 8 arc sec. The spectral resolution of 60,000 will be adequate for measuring Doppler velocities of about 5 km s-1. The instrument is designed using off-the-shelves optical and mechanical parts with minimum fabrication at an in-house machine shop. The SCFS will be integrated with the full-disk Ha telescope at the Big Bear Solar Observatory that is operating semi-automatically around the year except for weather interruptions. The SCFS observations will be mainly used to study the physics of flares, but part of the time will be devoted to classroom educational activities.

Choudhary, Debi Prasad; Yurchyshyn, Vasyl; Gosain, Sanjay

2013-09-01

33

Solar Flare Physics  

NASA Technical Reports Server (NTRS)

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

Schmahl, Edward J.; Kundu, Mukul R.

1998-01-01

34

Solar Flares and Their Prediction  

NASA Technical Reports Server (NTRS)

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

Adams, Mitzi L.

1999-01-01

35

Relativistic electrons from solar flares  

Microsoft Academic Search

Observations of interplanetary relativistic electrons from several solar-flare events monitored through 1964 to mid-1967 are presented. These are the first direct spectral measurements and time histories, made outside the magnetosphere, of solar-flare electrons having relativistic velocities. The 3- to 12-MeV electrons detected have kinetic energies about two orders of magnitude higher than those solar electrons previously studied in space, and

T. L. Cline; F. B. McDonald

1968-01-01

36

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

37

6Li from Solar Flares.  

PubMed

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

Ramaty; Tatischeff; Thibaud; Kozlovsky; Mandzhavidze

2000-05-10

38

Lithium-6 from Solar Flares  

E-print Network

By introducing a hitherto ignored Li-6 producing process, due to accelerated He-3 reactions with He-4, we show that accelerated particle interactions in solar flares produce much more Li-6 than Li-7. By normalizing our calculations to gamma-ray data we demonstrate that the Li-6 produced in solar flares, combined with photospheric Li-7, 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.

R. Ramaty; V. Tatischeff; J. P. Thibaud; B. Kozlovsky; N. Mandzhavidze

2000-03-23

39

Ion acceleration in impulsive solar flares  

NASA Technical Reports Server (NTRS)

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

Steinacker, Jurgen; Jaekel, Uwe; Schlickeiser, Reinhard

1993-01-01

40

Transient particle acceleration associated with solar flares.  

PubMed

Understanding how individual charged particles can be accelerated to extreme energies (10(20) electron volts), remains a foremost problem in astrophysics. Within our solar system, the active sun is capable of producing, on a short time scale, ions with energies higher than 25 gigaelectron volts. Satellite and ground-based observation over the past 30 years have greatly increased our knowledge of the properties of transient bursts of energetic particles emitted from the sun in association with solar flares, but a real understanding of the solar flare particle acceleration process requires greatly refined experimental data. On the practical side, it is also imperative that this problem be solved if man is to venture, for long periods of time, beyond the protective umbrella of Earth's magnetic field, which excludes much of the biologically damaging solar energetic particles. It is only through an understanding of the basic acceleration problem that we can expect to be able to predict the occurrence of a solar flare with lethal solar radiations. For our knowledge of these effects to advance, a new space mission dedicated to studying the high-energy aspects of solar flares at high spatial and energy resolution will be required. PMID:17797307

Chupp, E L

1990-10-12

41

Nuclear processes in solar flares  

NASA Technical Reports Server (NTRS)

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

Ramaty, R.

1982-01-01

42

Parameterization of solar flare dose  

E-print Network

of the adequate shielding to protect against solar flare proton events. Eight flares have been studied covering the period from 1986 to 1994. The results of this research show that the shielding provided by the astronaut's suits is enough to protect them against...

Lamarche, Anne Helene

1995-01-01

43

Current limitation and solar flares  

Microsoft Academic Search

A flare model based on force-free currents in the solar atmosphere is considered. The energy of the flare is supposed to be stored as magnetic energy in the current system. If the current density exceeds a certain critical limit an over-voltage may arise in the circuit which will give rise to a rapid release of the stored energy. At the

P. Carlqvist

1969-01-01

44

Solar Chromosphere Flare Spectrograph  

NASA Astrophysics Data System (ADS)

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

Choudhary, Debi Prasad

45

Particle acceleration in solar flares  

NASA Astrophysics Data System (ADS)

Solar flares are the most powerful explosions in the solar system, and remarkably efficient particle accelerators. About ~10-50% of the energy released in flares goes into tens of keV to 10s of MeV electrons and MeV to GeV ions. Recent hard X-ray and gamma-ray imaging and spectroscopy show that the acceleration of both electrons and ions, and the energy release process in flares is closely related to magnetic reconnection. The solar energetic particles detected near the Earth, however, appear to be accelerated by shocks driven by fast coronal mass ejections, which are almost always associated with a large flare.

Lin, Robert P.

2013-02-01

46

Properties of Solar Flare Clustering  

NASA Astrophysics Data System (ADS)

The continuous full disk observations provided by the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) give an observer the impression that flare and filament eruptions are related. However, both detailed analysis of a number of events as well as a number of statistical studies have provided only rare examples of clear causal behavior. But the mechanisms of flare triggering are not well understood, so the lack of hard evidence is not surprising. Here we have examined the waiting-time statistics of GOES X-ray flares of magnitude C5 or greater during the last sunspot cycle with the aim of assessing the degree to which flares are clustered in time. Clusters are groups of flares in which all successive flares occur within a fixed separation time - the linking window. While many of the flares in a cluster may come from the same active region, the clusters that last more than a disk passage must result from flares in multiple active regions. The longest cluster of the last cycle lasted more than 42 days. None of the flares were separated by more than 36 hours. Since that cluster lasted more than three disk passages, it could not have been caused by a single region. We find that during the last maximum, eight clusters contributed 44% of all flares. All of these clusters spanned multiple disk passages, but occupied only 16.5% of the cycle duration. Two of the clusters provided 34% of the flares. We suggest that this behavior implies that a component of the observed coordinated behavior has its origin in the solar dynamo.

Title, Alan; DeRosa, Marc

47

Largest Solar Flare on Record  

NASA Technical Reports Server (NTRS)

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

2001-01-01

48

Mass motions associated with solar flares  

NASA Technical Reports Server (NTRS)

Mass motions are a principal means by which components of solar flares can be distinguished. Typical patterns of mass motions in H-alpha are described for chromospheric flare ribbons, remote chromospheric flare patches, flare loops, flaring arches, surges, erupting filaments and some expanding coronal features. Interrelationships between these phenomena are discussed and illustrations of each are presented.

Martin, Sara F.

1989-01-01

49

Solar Flare Aimed at Earth  

NASA Technical Reports Server (NTRS)

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

2002-01-01

50

Fine Structure in Solar Flares.  

PubMed

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

Warren

2000-06-20

51

OVERVIEW OF SOLAR FLARES The Yohkoh Perspective  

E-print Network

Chapter 8 OVERVIEW OF SOLAR FLARES The Yohkoh Perspective Hugh Hudson Space Sciences Laboratory, UC This chapter reviews the physics of solar flares, with special emphasis on the past decade. During this decade, corona 153 #12;154 SOLAR AND SPACE WEATHER RADIOPHYSICS 1. Introduction The physics of solar flares seems

California at Berkeley, University of

52

OVERVIEW OF SOLAR FLARES The Yohkoh Perspective  

E-print Network

Chapter 8 OVERVIEW OF SOLAR FLARES The Yohkoh Perspective Hugh Hudson Space Sciences Laboratory, UC This chapter reviews the physics of solar flares, with special emphasis on the past decade. During this decade, corona 1 #12;2 1. Introduction The physics of solar flares seems too broad a subject to review adequately

Hudson, Hugh

53

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

54

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

55

Biggest Solar Flare on Record  

NASA Technical Reports Server (NTRS)

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

2002-01-01

56

RADIO EMISSION FROM SOLAR FLARES  

Microsoft Academic Search

Radio emission from solar flares offers a number of unique diagnostic tools to address long-standing questions about energy release, plasma heating, particle acceleration, and particle transport in magnetized plasmas. At millimeter and centimeter wavelengths, incoherent gyrosynchrotron emission from electrons with energies of tens of kilo electron volts to several mega electron volts plays a dominant role. These electrons carry a

T. S. Bastian; A. O. Benz; D. E. Gary

1998-01-01

57

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

58

Detecting Solar Neutrino Flares and Flavors  

E-print Network

Intense solar flares originated in sun spots produce high energy particles (protons, $\\alpha$) well observable by satellites and ground-based detectors. The flare onset produces signals in different energy bands (radio, X, gamma and neutrons). The most powerful solar flares as the ones occurred on 23 February 1956, 29 September 1989 and the more recent on October 28th, and the 2nd, 4th, 13th of November 2003 released in sharp times the largest flare energies (${E}_{FL} \\simeq {10}^{31}\\div {10}^{32} erg). The high energy solar flare protons scatter within the solar corona and they must be source of a prompt neutrino burst through the production of charged pions. Later on, solar flare particles hitting the atmosphere may marginally increase the atmospheric neutrino flux. The prompt solar neutrino flare may be detected in the largest underground $\

D. Fargion

2004-04-16

59

THE SOLAR FLARE IRON ABUNDANCE  

SciTech Connect

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. [Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking RH6 5NT (United Kingdom); Dennis, B. R., E-mail: kjhp@mssl.ucl.ac.uk, E-mail: Brian.R.Dennis@nasa.gov [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2012-03-20

60

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

61

Ion Acceleration in Solar Flares  

NASA Technical Reports Server (NTRS)

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

Miller, James A.; Weir, Sue B.

1996-01-01

62

Magnetic Flux Transients during Solar Flares  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

63

Electron acceleration in solar flares  

Microsoft Academic Search

For the period September 1978 to December 1982 we have identified 55 solar flare particle events for which our instruments on board the ISEE-3 (ICE) spacecraft detected electrons above 10 MeV. Combining our data with those from the ULEWAT spectrometer (MPI Garching and University of Maryland) electron spectra in the range from 0.1 to 100 MeV were obtained. The observed

Wolfgang Droge; Peter Meyer; Paul Evenson; Dan Moses

1989-01-01

64

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

65

Massively Parallel Simulations of Solar Flares and Plasma Turbulence  

E-print Network

Massively Parallel Simulations of Solar Flares and Plasma Turbulence Lukas Arnold, Christoph Beetz in space- and astrophysical plasmasystems include solar flares and hydro- or magnetohydrodynamic turbulence of solar flares and Lagrangian statistics of compressible and incompress- ible turbulent flows

Grauer, Rainer

66

Solar flares induced D-region ionospheric and geomagnetic perturbations  

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

67

Solar flares controlled by helicity conservation  

NASA Technical Reports Server (NTRS)

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

Gliner, Erast B.; Osherovich, Vladimir A.

1995-01-01

68

A Phase Diagram for Solar Flares  

NASA Astrophysics Data System (ADS)

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

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

2015-04-01

69

Energetic particles from impulsive solar flares  

Microsoft Academic Search

Observations of solar energetic particles from impulsive flares are reviewed. Consideration is given to observations of electron events, He-3 rich events, and heavy-nuclei-rich events. It is found that these observations can be unified into a description of the particles from impulsive flares. The observations are compared with observations of gamma-ray line in impulsive flares and particles in flares and compared

Donald V. Reames

1990-01-01

70

Electron acceleration in solar flares  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

71

Current sheets in solar flares  

NASA Technical Reports Server (NTRS)

Numerical simulations of current sheets in solar flares are described, including new features such as the presence of a shock in Petschek's mechanism and impulsive burst-like reconnection due to secondary tearing and coalescence. The general properties of magnetic reconnection are discussed in connection with the basic requirements of numerical current sheet models. Emphasis is given to the need for realistic criteria for energy balance, the Lundquist number, and line tying in calculations of tearing and reconnection modes. The need for analytical models of current sheet processes to compare with the numerical simulations is also stressed.

Priest, E. R.

1985-01-01

72

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

73

Solar flare leaves sun quaking  

NASA Astrophysics Data System (ADS)

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

1998-05-01

74

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

NASA Astrophysics Data System (ADS)

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

Yang, Ya-Hui

2015-04-01

75

A statistic study of ionospheric solar flare activity indicator  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

76

Automatic prediction of solar flares and super geomagnetic storms  

NASA Astrophysics Data System (ADS)

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

Song, Hui

77

Workshop on Impulsive Solar Flares, 2nd, University of New Hampshire, Durham, Sept. 26-28, 1988, Proceedings  

NASA Technical Reports Server (NTRS)

Papers on impulsive solar flares are presented, covering topics such as the optical properties of impulsive flares, soft X-ray spectroscopy of solar flares, the energy release process in impulsive bursts, high-velocity evaporation and a high-speed shock wave during the impulsive phase of the April 24, 1984 flare, nonpotential magnetic fields at sites of gamma-ray flares, and meter-decimeter and microwave radio observations of solar flares. Other topics include rise times in solar radio bursts, removal of the gradual component in analyses of solar impulsive bursts, ion and relativistic electron transport in solar flares, neutrons and gamma-ray emission on June 3, 1982, emission characteristics of three intense solar flares in cycle 21, and solar flare gamma-ray observations with the Hinotori satellite. Additional topics include spectra of relativistic solar proton ground-level events recorded in Antarctica, a 153-d periodicity in the occurrence of solar flares producing energetic interplanetary electrons, a search for solar neutron response in neutron monitor data, neutral beams in two-ribbon flares and in the geomagnetic tail, beam heating in solar flares, and solar flare gamma-ray line shapes.

1990-01-01

78

Observations of the Effects of Solar Flares on Earth  

E-print Network

Observations of the Effects of Solar Flares on Earth and Mars Paul Withers, Michael Mendillo, Joei and their environments. Solar flares cause sudden ionospheric disturbances at Earth and coronal mass ejections cause of the effects of a solar flare on the upper atmosphere of another planet. A large solar flare on 15 April 2001

Withers, Paul

79

MAGNETIC FIELD STRUCTURES TRIGGERING SOLAR FLARES AND CORONAL MASS EJECTIONS  

SciTech Connect

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

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

2012-11-20

80

Solar flares not producing sudden phase advances  

NASA Astrophysics Data System (ADS)

We present a study of solar flares that do not produce disturbances in the low terrestrial ionosphere, detectable in very low frequency (VLF) low ionosphere propagation as sudden phase advances (SPA). We selected only flares with larger optical H-? importance (equal or larger than 1), occurred near the cycle 22 solar maximum (1987-1989), at times when VLF data were available for long-distance propagation paths entirely illuminated by the Sun. For the 463 optical solar flares selected, we found that 18.8% had no measurable effects on the lower ionosphere. Inversely, all measured SPAs did have a solar counterpart, optical (such a subflare) and/or X-ray fluxes. Among the H-? flares that do not produce measurable disturbances in the low terrestrial ionosphere, there is a surprising selection for events occurred at the solar limbs. On the other hand, the X-ray flux for the H-? flares selected, obtained from GOES for the bands 0.5-4 Å and 1-8 Å exhibited a rather scattered correlation with the SPAs amplitudes. GOES X-rays fluxes for H-? flares not producing SPAs extend over 2-3 orders of magnitude. These results may suggest real physical distinctions between events. Possible explanations suggest the existence of a directional trend for the soft X-ray produced in flares possibly combined with the blockage of ionizing X rays behind the solar limbs.

Kaufmann, Pierre; Rizzo Piazza, Liliana; Fernandez, José Henrique; Rocha da Silva, Márcia

2002-08-01

81

Excitation of XUV radiation in solar flares  

NASA Technical Reports Server (NTRS)

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

Emslie, A. Gordon

1992-01-01

82

The energy spectra of solar flare electrons  

Microsoft Academic Search

A survey of 50 electron energy spectra from .1 to 100 MeV originating from solar flares was made by the combination of data from two spectrometers onboard the International Sun Earth Explorer-3 spacecraft. The observed spectral shapes of flare events can be divided into two classes through the criteria of fit to an acceleration model. This standard two step acceleration

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

1985-01-01

83

Interplanetary shock waves generated by solar flares  

Microsoft Academic Search

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

Murray Dryer

1974-01-01

84

Soliton and strong Langmuir turbulence in solar flare processes  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

85

Energetics of chromospheric evaporation in solar flares  

Microsoft Academic Search

The typical impulsive-phase development of a soft X-ray solar flare is derived from observations of a large set of flares with the Bent Crystal Spectrometer and the Hard X-Ray Burst Spectrometere on the Solar Maximum Mission spacecraft. An indicator of the impulsive phase in soft X-rays in the presence of high-speed plasma upflows with velocities up to 400 km s⁻¹,

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

1984-01-01

86

Soft X-ray Pulsations in Solar Flares  

E-print Network

The soft X-ray emissions of solar flares come mainly from the bright coronal loops at the highest temperatures normally achieved in the flare process. Their ubiquity has led to their use as a standard measure of flare occurrence and energy, although the bulk of the total flare energy goes elsewhere. Recently Dolla et al. (2012) noted quasi-periodic pulsations (QPP) in the soft X-ray signature of the X-class flare SOL2011-02-15, as observed by the standard photometric data from the GOES (Geostationary Operational Environmental Satellite) spacecraft. We analyze the suitability of the GOES data for this kind of analysis and find them to be generally valuable after Sept. 2010 (GOES-15). We then extend Dolla et al. results to a list of X-class flares from Cycle 24, and show that most of them display QPP in the impulsive phase. During the impulsive phase the footpoints of the newly-forming flare loops may also contribute to the observed soft X-ray variations. The QPP show up cleanly in both channels of the GOES dat...

Simões, Paulo J A; Fletcher, Lyndsay

2014-01-01

87

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

88

Solar Eruptions: Coronal Mass Ejections and Flares  

NASA Technical Reports Server (NTRS)

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

Gopalswamy, Nat

2012-01-01

89

Energy release in solar flares  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

90

4Predicting CMEs and Flares Solar flares are violent releases of energy from the sun that last 10 to 20  

E-print Network

4Predicting CMEs and Flares Solar flares are violent releases of energy from the sun that last 10, the following events were recorded: Solar Flares 22 CME s 12 Both flares and CMEs 7 A scientist decides solar flares will happen, and he wants to use flares to predict when CMEs will happen. His first step

91

Ensemble prediction model of solar proton events associated with solar flares and coronal mass ejections  

NASA Astrophysics Data System (ADS)

An ensemble prediction model of solar proton events (SPEs), combining the information of solar flares and coronal mass ejections (CMEs), is built. In this model, solar flares are parameterized by the peak flux, the duration and the longitude. In addition, CMEs are parameterized by the width, the speed and the measurement position angle. The importance of each parameter for the occurrence of SPEs is estimated by the information gain ratio. We find that the CME width and speed are more informative than the flare's peak flux and duration. As the physical mechanism of SPEs is not very clear, a hidden naive Bayes approach, which is a probability-based calculation method from the field of machine learning, is used to build the prediction model from the observational data. As is known, SPEs originate from solar flares and/or shock waves associated with CMEs. Hence, we first build two base prediction models using the properties of solar flares and CMEs, respectively. Then the outputs of these models are combined to generate the ensemble prediction model of SPEs. The ensemble prediction model incorporating the complementary information of solar flares and CMEs achieves better performance than each base prediction model taken separately.

Huang, Xin; Wang, Hua-Ning; Li, Le-Ping

2012-03-01

92

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

93

The local Poisson hypothesis for solar flares  

E-print Network

The question of whether flares occur as a Poisson process has important consequences for flare physics. Recently Lepreti et al. presented evidence for local departure from Poisson statistics in the Geostationary Operational Environmental Satellite (GOES) X-ray flare catalog. Here it is argued that this effect arises from a selection effect inherent in the soft X-ray observations; namely that the slow decay of enhanced flux following a large flare makes detection of subsequent flares less likely. It is also shown that the power-law tail of the GOES waiting-time distribution varies with the solar cycle. This counts against any intrinsic significance to the appearance of a power law, or to the value of its index.

M. S. Wheatland

2001-07-09

94

The effects of solar flares on planetary ionospheres  

E-print Network

1 The effects of solar flares on planetary ionospheres Paul Withers and Michael Mendillo Boston:00-12:30 AOGS Meeting, Singapore #12;Outline · The Sun, solar cycle, solar flares · Observed effects://apod.nasa.gov/apod/image/0712/solarcycle_soho_big.jpg SOHO images at EUV wavelengths (28.4 nm) #12;5 Solar flares http://www

Withers, Paul

95

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

E-print Network

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

Chen, Yuh-Ing

96

The Solar Flare Myth in solar-terrestrial physics  

SciTech Connect

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

Gosling, J.T.

1993-07-01

97

CONTINUUM ELECTROMAGNETIC RADIATION FROM SOLAR FLARES  

Microsoft Academic Search

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

W. A. Stein; E. P. Ney

1963-01-01

98

SOLAR FLARE EFFECTS IN THE IONOSPHERE  

Microsoft Academic Search

content of the ionosphere were observed at four or at five stations, simultaneously with the onset of solar flares on May 21 and 23, 1967. The observations are most readily explained by a large, but brief, enhancement of the solar EUV flux on two occasions. An explanation based on X-ray enhancement only does not appear attractive. Time-correlated values of visual

Owen K. Garriott; Aldo V. da Rosa; Michael J. Davis; O. G. Jr. Villard

1967-01-01

99

Velocity structure of solar flare plasmas  

NASA Astrophysics Data System (ADS)

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

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

100

Multi-thermal Energies of Solar Flares  

NASA Astrophysics Data System (ADS)

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

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

2015-04-01

101

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

102

Solar gamma rays. [of flare origin  

NASA Technical Reports Server (NTRS)

Calculations are presented for the production of gamma-ray lines and continuum emission in solar flares. The interaction models used in the calculations are described, neutron-producing reactions are identified, and formation of the 2.2-MeV line is analyzed. The most important prompt gamma-ray lines that can be observed during solar flares are determined, and the production of gamma-ray continuum emission by electron-proton bremsstrahlung is examined. The results are compared with data on the solar flare of August 4, 1972, to deduce the number and spectrum of accelerated particles at the sun as well as the energy deposited by them in the solar atmosphere. Problems concerning the formation of the 0.51-MeV line by positron annihilation are investigated, and estimates are made for the high-energy gamma-ray and neutron fluxes (at earth) produced by the August 4 flare. The main findings for that flare are: (1) the strongest line, at 2.2 MeV, was due to neutron capture by protons in the photosphere; (2) the intensity of that line depended on the photospheric He-3 abundance; (3) the neutrons were produced mainly in proton-alpha reactions by accelerated particles with energies in excess of 30 MeV/nucleon; and (4) the strongest prompt lines were due to deexcitation of excited states in C-12, O-16, and N-15.

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

1975-01-01

103

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

NASA Astrophysics Data System (ADS)

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

Miller, Richard W.

1988-08-01

104

Detecting Solar Neutrino Flares and Flavors  

NASA Astrophysics Data System (ADS)

Most power-full solar flare as the ones occurred on 23th February 1956, September 29th 1989 and recent ones occurred on 28th October, on 2nd-4th and 13th November 2003 have been respectively recorded by Radio-X- and Cosmic Rays detectors. These flares took place most in the open or in the edge and in the hidden solar disk (as for the September 29th, 1989 beyond 105Wo and for last November 2003 flare events). The 4th November event was the most powerful X event in the highest known rank category X28. The observed and estimated total flare energy E = 1031-1033 erg should be a source also of a prompt secondary neutrino burst originated, by proton-proton-pion production on the sun itself; a more delayed and spread neutrino flux signal arise later on the terrestrial atmosphere. These first earliest prompt solar neutrino burst might be already recorde, in a few neutrino clustered events, in largest neutrino underground detectors as Super-Kamiokande one, in time correlation with the sharp X-Radio flare onset. Our first estimate at the Super-Kamiokande II Laboratory is found to be a few (1-5) events. Their discover (or absence) should constrains the solar flare acceleration, energetic and its inner environment. Any large neutrino flare event might even verify the expected neutrino flavour mixing leading to comparable electron- muon event as well as a comparable energy fluence and spectra. Rare Tau appearence by neutrino muon into tau conversion might also arise.

Fargion, D.

2004-06-01

105

Probabilistic forecasting of solar flares from vector magnetogram data  

E-print Network

Probabilistic forecasting of solar flares from vector magnetogram data G. Barnes,1 K. D. Leka,1 E to solar flare forecasting, adapted to provide the probability that a measurement belongs to either group for solar flare prediction, and to the method employed by the U.S. Space Environment Center (SEC). Although

Barnes, Graham

106

Particle acceleration in solar flares: observations versus numerical simulations  

E-print Network

Particle acceleration in solar flares: observations versus numerical simulations A O Benz, P C@astro.phys.ethz.ch Abstract. Solar flares are generally agreed to be impulsive releases of magnetic energy. Reconnection­ray observations, transit­time damping simulation, reconnection, astrophysics #12; 2 1. Introduction Solar flares

107

Magnetic reconnection configurations and particle acceleration in solar flares  

E-print Network

Magnetic reconnection configurations and particle acceleration in solar flares P. F. Chen, W. J space under different magnetic configurations. Key words: solar flares, magnetic reconnection, particle, for a review). Magnetic reconnection, as the mechanism of solar flares, provides favorite environments for all

Chen, P. F.

108

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

109

Composition of energetic particles from solar flares.  

PubMed

We present a model for composition of heavy ions in the solar energetic particles (SEP). The SEP composition in a typical large solar particle event reflects the composition of the Sun, with adjustments due to fractionation effects which depend on the first ionization potential (FIP) of the ion and on the ratio of ionic charge to mass (Q/M). Flare-to-flare variations in composition are represented by parameters describing these fractionation effects and the distributions of these parameters are presented. PMID:11539996

Garrard, T L; Stone, E C

1994-10-01

110

Study on Triggering Process of Solar Flares Based on Hinode Satellite Observations  

NASA Astrophysics Data System (ADS)

Solar Flares are explosive phenomena driven by magnetic energy stored in the solar corona. Because interplanetary disturbances associated with solar flares sometimes impact terrestrial environments and infrastructure, understanding the flare-triggering conditions is important not only from a solar physics perspective but also for space weather forecasting. There are numerous observational studies and simulations which attempted to reveal the onset mechanism of solar flares. However, because different observations support different models, the underlying mechanism of flare onset remains elusive, and the predictability of flare occurrence remains limited. To elucidate flare-trigger mechanism, we investigated four major flare events that occurred in active regions NOAA 10930 (December 13 and 14, 2006) and NOAA 11158 (February 13 and 15, 2011) by using data obtained by the Solar Optical Telescope (SOT) onboard the Hinode satellite. We analyzed the spatio-temporal correlation between the detailed magnetic field structure and the emission image of the Ca II H line at the central part of flaring regions for several hours prior to the onset of flares. We observed that the magnetic shear angle in the flaring regions exceeded 70 degrees, as well as that characteristic magnetic disturbances developed at the centers of flaring regions in the pre-flare phase. These magnetic disturbances can be classified into two groups depending on the structure of their magnetic polarity inversion lines; to the so-called 'Opposite-Polarity (OP)' and 'Reversed-Shear (RS)' magnetic field recently proposed by Kusano et al. (2012). The result strongly suggests that some major flares are triggered by rather small magnetic disturbances. Furthermore, we study how small magnetic field can work for triggering flares based on the Hinode observations. The results indicate that the critical magnetic flux, which the flare-trigger field has to contain, depends on the magnetic connectivity in the flaring site, and it varies even within an active region. The results indicate that the critical flux for the magnetic disturbance to trigger flare varies even within an active region, and that it might depends on the magnetic connectivity in the flaring site. In addition, Our study indicates that statistical analysis of different flare events based on highly accurate magnetograms and high cadence observations of chromospheric emission (such as Ca II H line emissions) may be a powerful way to resolve these important questions.

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

2013-12-01

111

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

112

36Super-fast solar flares ! NASA's Ramaty High Energy Solar  

E-print Network

36Super-fast solar flares ! NASA's Ramaty High Energy Solar Spectroscopic Imager (RHESSI) satellite has been studying solar flares since 2002. The sequence of figures to the left shows a flaring region hr/3600 sec = 0.98 kilometers/sec. The solar flare blob was traveling at 207 kilometers per second

113

A solar tornado triggered by flares?  

NASA Astrophysics Data System (ADS)

Context. Solar tornados are dynamical, conspicuously helical magnetic structures that are mainly observed as a prominence activity. Aims: We investigate and propose a triggering mechanism for the solar tornado observed in a prominence cavity by SDO/AIA on September 25, 2011. Methods: High-cadence EUV images from the SDO/AIA and the Ahead spacecraft of STEREO/EUVI are used to correlate three flares in the neighbouring active-region (NOAA 11303) and their EUV waves with the dynamical developments of the tornado. The timings of the flares and EUV waves observed on-disk in 195 Å are analysed in relation to the tornado activities observed at the limb in 171 Å. Results: Each of the three flares and its related EUV wave occurred within ten hours of the onset of the tornado. They have an observed causal relationship with the commencement of activity in the prominence where the tornado develops. Tornado-like rotations along the side of the prominence start after the second flare. The prominence cavity expands with the accelerating tornado motion after the third flare. Conclusions: Flares in the neighbouring active region may have affected the cavity prominence system and triggered the solar tornado. A plausible mechanism is that the active-region coronal field contracted by the "Hudson effect" through the loss of magnetic energy as flares. Subsequently, the cavity expanded by its magnetic pressure to fill the surrounding low corona. We suggest that the tornado is the dynamical response of the helical prominence field to the cavity expansion. Movies are available in electronic form at http://www.aanda.org

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

2013-01-01

114

SORCE Monitors Solar Variability during Record Solar Flares  

NSDL National Science Digital Library

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

Tom Bridgman

2004-02-20

115

SORCE Monitors Solar Variability during Record Solar Flares - Video version  

NSDL National Science Digital Library

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

Tom Bridgman

2004-02-20

116

Carbon-poor solar flare events  

Microsoft Academic Search

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

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

1979-01-01

117

Lyman continuum observations of solar flares  

NASA Technical Reports Server (NTRS)

A study is made of Lyman continuum observations of solar flares, using data obtained by the EUV spectroheliometer on the Apollo Telescope Mount. It is found that there are two main types of flare regions: an overall 'mean' flare coincident with the H-alpha flare region, and transient Lyman continuum kernels which can be identified with the H-alpha and X-ray kernels observed by other authors. It is found that the ground level hydrogen population in flares is closer to LTE than in the quiet sun and active regions, and that the level of Lyman continuum formation is lowered in the atmosphere from a mass column density .000005 g/sq cm in the quiet sun to .0003 g/sq cm in the mean flare, and to .001 g/sq cm in kernels. From these results the amount of chromospheric material 'evaporated' into the high temperature region is derived, which is found to be approximately 10 to the 15th g, in agreement with observations of X-ray emission measures.

Machado, M. E.; Noyes, R. W.

1978-01-01

118

Are there Radio-quiet Solar Flares?  

E-print Network

Some 15% of solar flares having a soft X-ray flux above GOES class C5 are reported to lack coherent radio emission in the 100 - 4000 MHz range (type I - V and decimetric emissions). A detailed study of 29 such events reveals that 22 (76%) of them occurred at a radial distance of more than 800'' from the disk center, indicating that radio waves from the limb may be completely absorbed in some flares. The remaining seven events have statistically significant trends to be weak in GOES class and to have a softer non-thermal X-ray spectrum. All of the non-limb flares that were radio-quiet > 100 MHz were accompanied by metric type III emission below 100 MHz. Out of 201 hard X-ray flares, there was no flare except near the limb (R>800'') without coherent radio emission in the entire meter and decimeter range. We suggest that flares above GOES class C5 generally emit coherent radio waves when observed radially above the source.

Arnold O. Benz; Roman Brajsa; Jasmina Magdalenic

2007-01-19

119

Periodicities of solar flare and its relations  

NASA Technical Reports Server (NTRS)

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

Hady, Ahmed A.

1995-01-01

120

Solar Flare Impacts on Ionospheric Electrodynamics  

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

121

Damping of MHD turbulence in Solar Flares  

E-print Network

(Abridged) We describe the cascade of plasma waves or turbulence injected, presumably by reconnection, at scales comparable to the size of a solar flare loop to scales comparable to particle gyroradii, and evaluate their damping by various mechanisms. We show that the classical viscous damping is unimportant for magnetically dominated or low beta plasmas and the primary damping mechanism is the collisionless damping by the background particles. We show that the damping rate is proportional to the total random momentum density of the particles. For solar flare conditions this means that in most flares, except the very large ones, the damping is dominated by thermal background electrons. For large flares one requires acceleration of essentially all background electrons into a nonthermal distribution so that the accelerated electrons can be important in the damping of the waves. In general, damping by thermal or nonthermal protons is negligible compared to that of electrons except for quasi-perpendicular propagating waves or for rare proton dominated flares with strong nuclear gamma-ray line emission. Using the rate for damping we determine the critical scale below which the damping becomes important and the spectrum of the turbulence steepens. This critical scale, however, has strong dependence on the angle of propagation with respect to the magnetic field direction. The waves can cascade down to very small scales, such as the gyroradii of the particles at small angles (quasi-parallel propagation) and possibly near 90 degree (quasi-perpendicular propagation) giving rise to a highly anisotropic spectral distribution.

Vahe Petrosian; Huirong Yan; Alex Lazarian

2005-08-26

122

Three impulsive solar x-ray flares  

SciTech Connect

In the Soviet-French SIGNE 2M experiment, the Prognoz 7 satellite and the Venera 11 and Venera 12 probes recorded impulsive solar flares at energies E/sub x/>100 keV on 1978 December 3 and 4 and 1979 April 27. The time profiles are described. For the April 27 event the x-ray intensity showed an anisotropy of roughly 20%. For the December 4 flare a lower limit H/sub min/> or =16 000 km is placed on the height of the hard--x-ray emission site above the photosphere.

Dolidze, V.S.; Estulin, I.Z.; Vedrenne, G.; Niel, M.; Talon, A.; Chambon, G.

1982-07-01

123

Ionosphere gives size of greatest solar flare  

Microsoft Academic Search

On 4 November 2003, the largest solar flare ever recorded saturated the GOES X-ray detectors; from these a magnitude of X28 (2.8 mW\\/m2) has been extrapolated (http:\\/\\/sec.noaa.gov\\/weekly\\/pdf\\/prf1471.pdf). However, using the Earth's ionosphere as a giant X-ray detector, we show the magnitude of this flare is consistent with X45 ± 5 (4.5 ± 0.5 mW\\/m2), or more than twice that of

Neil R. Thomson; Craig J. Rodger; Richard L. Dowden

2004-01-01

124

Preliminary Analysis of the distribution of powerful x-ray flares on phases of Solar cycle  

NASA Astrophysics Data System (ADS)

We use all powerful X-ray flares observations from 1976 up to 2013 to study a possible correlation between the moments of occurrence of flares and a phase of a solar cycle. The considered time interval corresponds to cycles 21, 22 and 23 with maximum heights W21=164.5, W22=158.5 and W23=120.8. We find that: 1)Only two of all of 30 flares considered have arisen on a branch of growth of cycles. The others 28 were observed or near to maxima of cycles, or on a decline branch. Probably it is a consequence of a specific field of velocities in a latitudes interval ±15 on the Sun, favorable for work of the reconnection mechanism; 2)The number of powerful flares in a cycle does not correlate with its height: cycles 21 and 22 are almost identical on height (W21=164.5, W22=158.5), but the quantity of flares in them differs almost in 2 times (8 flashes in 21-st cycle and 14 flashes in 22-nd). At the same time cycles 21 and 23, appreciably distinguished on height, gave identical quantity of flashes (8 flares in each cycle); 3)In the lowest 23-rd cycle (W23= 120.8) there were the most powerful flares for all period of observations: two flares of class X17, one flare of class X20 and, apparently, unique for last 144 years super flare of class X28+. The conclusion is made, that approximately up to 2019 it is possible to expect occurrence of M-class flares and X-class flares up to X8. More powerful flares are not excluded as well. Probability of the super power flares on the scale of that in 1859 («Carrington event») is low.

Khlystov, Anatoly

125

Direct Evidence of Solar Flare Modification of Stratospheric Electric Fields  

Microsoft Academic Search

Direct evidence of solar flare modification of stratospheric electric fields is presented through comparison of atmospheric electric field variations with fluxes of solar protons that bombarded the atmosphere during the August 1972 solar flares. Observed order of magnitude variations of the vertical electric field at 30-km altitude in anticorrelation with the intensity of solar protons are quantitatively interpreted in terms

R. H. Holzworth; F. S. Mozer

1979-01-01

126

Characteristics of energetic solar flare electron spectra  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

127

A statistical analysis of hard X-Ray solar flares  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

128

Heating of the solar flare plasma by high energy electrons.  

NASA Technical Reports Server (NTRS)

Discussion of the heating of the ambient plasma by high-energy electrons in solar flares. It is shown that for large flares the heating is enough to produce a thermal plasma with a temperature up to 10 to the 7th K rapidly in the initial phase of the flares. Thus thermal bremsstrahlung in addition to nonthermal bremsstrahlung should be considered for the X-ray emission of solar flares in the initial phase.-

Cheng, C.-C.

1972-01-01

129

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.

130

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

131

Carbon-poor solar flare events  

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

132

Characteristics of energetic solar flare electron spectra  

Microsoft Academic Search

A 55 event survey of energy spectra of 0.1-100 MeV interplanetary electrons originating from solar flares as measured by two spectrometers onboard the ISEE 3 (ICE) spacecraft for the years 1978-1982 has been completed. Spectra generated using the maximum flux of a given event in each energy channel were restricted to events with a well-defined flux rise time. Two broad

Dan Moses; Wolfgang Droege; Peter Meyer; Paul Evenson

1989-01-01

133

High-energy processes in solar flares  

Microsoft Academic Search

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

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

1987-01-01

134

Ion Acceleration and Transport in Solar Flares  

NASA Technical Reports Server (NTRS)

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

Miller, James A.

1995-01-01

135

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

136

SIZE DISTRIBUTIONS OF SOLAR FLARES AND SOLAR ENERGETIC PARTICLE EVENTS  

SciTech Connect

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

Cliver, E. W. [Space Vehicles Directorate, Air Force Research Laboratory, Sunspot, NM 88349 (United States); Ling, A. G. [Atmospheric Environmental Research, Lexington, MA 02421 (United States); Belov, A. [IZMIRAN, Troitsk, Moscow Region 142190 (Russian Federation); Yashiro, S. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2012-09-10

137

Spectrometers for fast neutrons from solar flares.  

PubMed

Neutrons with energies exceeding 1 GeV are emitted in the course of solar flares. Suitable dedicated neutron spectrometers with directional characteristics are necessary for a systematic spectroscopy of solar neutrons. We report here a study of instruments based on the detection of proton recoils from hydrogenous media, with double scattering in order to provide directional information, and also a novel scheme based on the detection of radiation from the neutron magnetic dipole moment, permitting also directional detection of neutrons. Specific designs and detection systems are discussed. PMID:11540017

Slobodrian, R J; Potvin, L; Rioux, C

1994-10-01

138

Umbral flares. [H-alpha solar flare patches  

NASA Technical Reports Server (NTRS)

H-alpha flare patches usually do not occur in sunspot umbrae. Presented here are cases of a type of umbral flare in which the flare patch originated in, and was confined to, the p spot umbra. All are H-alpha subflares. Two of the four flares were accompanied by type III radio bursts. The simplicity and similarity of the magnetic fields of these regions were striking.

Tang, F.

1978-01-01

139

Statistics and investigation of white light solar flares  

Microsoft Academic Search

We discuss the properties of white light flares on the basis of the published accounts of these events, together with the associated Halpha flares, radio bursts, X-ray bursts, proton events and ionosperic distrubances. In addition, spectral plates taken at Purple Mountain Observatory since 1962 have been examined. We found that 5% of the spectrograms of solar flares show variable white-light

Xie-Zhen Chen; Zhen-Yi Wang

1984-01-01

140

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

141

The production of high energy particles in solar flares  

Microsoft Academic Search

A neutral point theory of solar flares might be tenable if sunspots were formed from flux tubes protruding through the photosphere.\\u000a Such a mechanism is consistent with the point-like nature of a flare at its onset, but does not satisfactorily explain the\\u000a positions of flares relative to the components of the spot group.

P. A. Sweet

1958-01-01

142

BATSE flare observations in Solar Cycle 22  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

143

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

144

A slingshot model for solar flares  

NASA Astrophysics Data System (ADS)

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

Benford, Gregory

1991-06-01

145

The Variability of Solar X-Ray Flux and Flare Frequency through a Solar Cycle  

NASA Astrophysics Data System (ADS)

Solar flares are eruptions on the Sun's surface that emit ultraviolet radiation, x-rays, visible light and coronal mass ejections (CMEs). The intensity and frequency of solar flares have been observed to vary over time. To better understand fluctuations in solar flare intensity and frequency, data for various solar flare properties were obtained from satellites, including Geostationary Operational Environmental Satellite (GOES) and Solar TErrestrial RElations Observatory (STEREO) for 2000-2012. Solar flare statistics were analyzed and found to closely follow the 11-year solar cycle, with some deviations. Total daily x-ray flux, comprised of the background radiation and deviations caused by solar flare activity, was also examined for 2000-2012. The magnitude and frequency of the x-ray flux were observed in relation to annual sunspot count. A correlation to other solar activity parameters was observed. These results may help in the understanding and forecasting of solar flare variability.

O'Connell, M.; Marchese, A.; Hirschberger, M.; Mezzafonte, D.; Chen, K.

2013-12-01

146

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

147

Energetic-particle abundances in impulsive solar flare events  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

148

PRODUCTIVITY OF SOLAR FLARES AND MAGNETIC HELICITY INJECTION IN ACTIVE REGIONS  

SciTech Connect

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

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

2010-07-20

149

A Statistical Solar Flare Forecast Method  

E-print Network

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

M. S. Wheatland

2005-05-14

150

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

151

Secondary Flare Ribbons Observed by the Solar Dynamics Observatory  

NASA Astrophysics Data System (ADS)

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

Zhang, Jun; Li, Ting; Yang, Shuhong

2014-02-01

152

The Origin of the Solar Flare Waiting-Time Distribution.  

PubMed

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

Wheatland

2000-06-20

153

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

154

Solar Flare Measurements with STIX and MiSolFA  

E-print Network

Solar flares are the most powerful events in the solar system and the brightest sources of X-rays, often associated with emission of particles reaching the Earth and causing geomagnetic storms, giving problems to communication, airplanes and even black-outs. X-rays emitted by accelerated electrons are the most direct probe of solar flare phenomena. The Micro Solar-Flare Apparatus (MiSolFA) is a proposed compact X-ray detector which will address the two biggest issues in solar flare modeling. Dynamic range limitations prevent simultaneous spectroscopy with a single instrument of all X-ray emitting regions of a flare. In addition, most X-ray observations so far are inconsistent with the high anisotropy predicted by the models usually adopted for solar flares. Operated at the same time as the STIX instrument of the ESA Solar Orbiter mission, at the next solar maximum (2020), they will have the unique opportunity to look at the same flare from two different directions: Solar Orbiter gets very close to the Sun wit...

Casadei, Diego

2014-01-01

155

Deterministically Driven Avalanche Models of Solar Flares  

E-print Network

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 st...

Strugarek, Antoine; Joseph, Richard; Pirot, Dorian

2014-01-01

156

An interacting loop model of solar flare bursts  

NASA Technical Reports Server (NTRS)

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

Emslie, A. G.

1981-01-01

157

Directionality of solar flare hard X rays - Venera 13 observations  

SciTech Connect

An analysis of 79 flares detected by the Venera 13 SIGNE 2 MS gamma-ray telescope is performed to indirectly search for directional effects in the hard (50-300 keV) X rays of solar flares. X-ray spectra were reconstructed assuming a power law fit. From the distribution of X-ray flares with respect to angle of observation and spectral index it is found that the primary-plus-albedo radiation is directive, and that the observed flare spectrum hardens toward the solar limb. 21 references.

Bogovalov, S.V.; Kotov, IU.D.; Zenchenko, V.M.; Vedrenne, G.; Niel, M.

1985-10-01

158

Fine Structures and Overlying Loops of Confined Solar Flares  

NASA Astrophysics Data System (ADS)

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

Yang, Shuhong; Zhang, Jun; Xiang, Yongyuan

2014-10-01

159

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

160

The Effects of Solar Flares on Planetary Ionospheres PAUL WITHERS1  

E-print Network

The Effects of Solar Flares on Planetary Ionospheres PAUL WITHERS1 and MICHAEL MENDILLO1 1 Center 353 1531) During solar flares, the Sun's X-ray irradiance increases dramatically, often within a few during solar flares. Similar increases in plasma densities during solar flares have been observed

Withers, Paul

161

CELLULAR AUTOMATA MODELS AND MHD APPROACH IN THE CONTEXT OF SOLAR FLARES 1  

E-print Network

CELLULAR AUTOMATA MODELS AND MHD APPROACH IN THE CONTEXT OF SOLAR FLARES 1 Anastasios Anastasiadis for the case of solar flares, and compare it to the magnetohydrodynamic (MHD) theory. We consider solar flares the observed statistical properties of solar flaring activity. In Section 2. the basic results

Anastasiadis, Anastasios

162

GAMMA-RAY POLARIMETRY OF TWO X-CLASS SOLAR FLARES Steven E. Boggs,1  

E-print Network

GAMMA-RAY POLARIMETRY OF TWO X-CLASS SOLAR FLARES Steven E. Boggs,1 W. Coburn, and E. Kalemci Space 2005 May 29; accepted 2005 October 18 ABSTRACT We have performed the first polarimetry of solar flare Energy Solar Spectroscopic Imager (RHESSI) for two large flares: the GOES X4.8-class solar flare of 2002

California at Berkeley, University of

163

Solar Flares and the Chromosphere A white paper for the Decadal Survey*  

E-print Network

Solar Flares and the Chromosphere A white paper for the Decadal Survey* L. Fletcher, R. Turkmani, H acceleration (De Pontieu et al. 2007). The need for chromospheric observations of flares: The solar flare of radiation in a solar flare (Canfield et al 1986, Neidig 1989, Woods et al. 2004). In other words, solar

California at Berkeley, University of

164

Observation of H ? line impact polarization in solar flares  

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

165

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

E-print Network

A statistical analysis of the relationship between solar energetic particles (SEPs) and properties of solar flares and coronal mass ejections (CMEs) is presented. SEP events during solar cycle 23 are selected which are associated with solar flares originating on the visible hemisphere of the Sun and at least of magnitude M1. Taking into account all flares and CMEs that occurred during this period, the probability for the occurrence of an SEP event near Earth is determined. A strong rise of this probability is observed for increasing flare intensities, more western locations, larger CME speeds and halo CMEs. The correlations between the proton peak flux and these solar parameters are derived for a low (>10 MeV) and high (>60 MeV) energy range excluding any flux enhancement due to the passage of fast interplanetary shocks. The obtained correlation coefficients are: 0.55+-0.07 (0.63+-0.06) with flare intensity and 0.56+-0.08 (0.40+-0.09) with the CME speed for E>10 MeV (E>60 MeV). For both energy ranges, the cor...

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

2014-01-01

166

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

167

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

168

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

169

Adiabatic heating in impulsive solar flares  

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

170

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

171

Ultraheavy Element Enrichment in Impulsive Solar Flares  

NASA Astrophysics Data System (ADS)

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

Eichler, David

2014-10-01

172

ELEMENTARY ENERGY RELEASE EVENTS IN SOLAR FLARES  

SciTech Connect

Most theoretical investigations of particle acceleration during solar flares cannot be applied to observations for detailed study of the time evolution. We propose a phenomenological model for turbulence evolution and stochastic particle acceleration that links observations to the energy release and particle acceleration through two coefficients characterizing particle interactions with turbulent electromagnetic fields. In the linear regime the particle distribution does not affect the turbulence energy cascade. It is shown that electron acceleration critically depends on the intensity of small-scale turbulence and an impulsive nonthermal component only appears near the peak of the gradually evolving turbulence intensity. The model naturally reproduces the soft-hard-soft pattern of hard X-ray pulses, and we attribute the observed change in flux and spectral index correlation from the rise to decay phase of some pulses to changes in the background plasma. Detailed modeling of well observed individual events will probe the energy release processes.

Liu Siming; Fletcher, Lyndsay [Department of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ (United Kingdom)], E-mail: sliu@astro.gla.ac.uk

2009-08-10

173

Next-generation EUV imaging spectrometer for solar flare observations  

Microsoft Academic Search

The Naval Research Laboratory Skylab SO82A slitless spectrograph provided solar flare observations that have never been equaled in diagnostic capabilities for interpreting thermal flare physics. Improvements in detector technology, optics and optical coating technology, and almost two decades of analysis of SO82A data can be combined with the basic concept of an EUV objective grating spectrograph to build an instrument

J. Daniel Moses; Guenter E. Brueckner; Kenneth P. Dere; Clarence M. Korendyke; Norman E. Moulton; Dianne K. Prinz; John F. Seely; Dennis G. Socker; Marilyn E. Bruner; James R. Lemen

1996-01-01

174

Driving Major Solar Flares and Eruptions: Carolus J. Schrijver  

E-print Network

Driving Major Solar Flares and Eruptions: A Review Carolus J. Schrijver Lockheed Martin Adv. Techn-rope destabilizations associated with them. I present my summary first, followed by a synthesis scenario for the driving discussed in the text is compiled in Table 1. These flares are all well-observed examples that illustrate

Schrijver, Karel

175

Thermal radio emission of a solar flare during impulsive heating  

SciTech Connect

The thermal gyromagnetic radiation of the plasma in an individual magnetic flux tube with a nonuniform field is calculated from a hydrodynamic solar flare model. The temperature transition layer of the flare will control the dynamic properties of the continuum component of microwave bursts.

Kovalev, V.A.

1981-11-01

176

An unstable arch model of a solar flare  

Microsoft Academic Search

The theoretical consequences of assuming that a current flows along flaring arches consistent with a twist in the field lines of these arches are examined. It is found that a sequence of magneto-hydrodynamic (MHD) and resistive MHD instabilities driven by the assumed current (which we refer to as the toroidal current) can naturally explain most manifestations of a solar flare.

Daniel S. Spicer

1977-01-01

177

Stochastic Particle Acceleration in Impulsive Solar Flares  

NASA Technical Reports Server (NTRS)

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

Miller, James A.

2001-01-01

178

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

179

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

NASA Video Gallery

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

180

TOWARD RELIABLE BENCHMARKING OF SOLAR FLARE FORECASTING METHODS  

SciTech Connect

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

Bloomfield, D. Shaun; Higgins, Paul A.; Gallagher, Peter T. [Astrophysics Research Group, School of Physics, Trinity College Dublin, College Green, Dublin 2 (Ireland); McAteer, R. T. James, E-mail: shaun.bloomfield@tcd.ie [Department of Astronomy, New Mexico State University, Las Cruces, NM 88003-8001 (United States)

2012-03-10

181

Space weather effects on the Mars ionosphere due to solar flares and  

E-print Network

Space weather effects on the Mars ionosphere due to solar flares and meteors Paul Withers1, Michael dotted line marks time of solar flare No data after X14.4 flare on 15 April NmE increased after M7 properties of solar flares and meteors. Can also determine properties of ionosphere that are involved

Withers, Paul

182

Submitted to Ap.J. A Model of Solar Flares and Their Homologous Behavior  

E-print Network

Submitted to Ap.J. A Model of Solar Flares and Their Homologous Behavior G. S. Choe and C. Z. Cheng@pppl.gov ABSTRACT A model describing physical processes of solar flares and their homologous behavior is presented. #12;­ 2 ­ Subject headings: Sun: flares, MHD, methods: numerical 1. INTRODUCTION Solar flares

183

Submitted to Ap.J. A Model of Solar Flares and Their Homologous Behavior  

E-print Network

Submitted to Ap.J. A Model of Solar Flares and Their Homologous Behavior G. S. Choe and C. Z. Cheng@pppl.gov ABSTRACT A model describing physical processes of solar flares and their homologous behavior is presented. #12; -- 2 -- Subject headings: Sun: flares, MHD, methods: numerical 1. INTRODUCTION Solar flares

184

On the absolute abundance of calcium in solar flares  

NASA Technical Reports Server (NTRS)

The abundance of calcium relative to hydrogen in soft X-ray-emitting solar flare plasmas is determined. Results were obtained for 25 flares. An average calcium-to-hydrogen abundance of about 5 x 10 exp -6, which is about a factor of 2 greater than measured for the photosphere, is found. This result is consistent with an enhancement of low first ionization elements in soft X-ray flare plasmas. For one flare, the calcium abundance was higher, at about 1.6 times the average results. It is inferred that the calcium abundance can vary among flares. Significant variations of the calcium abundance during the course of a flare were not detected.

Sterling, Alphonse C.; Doschek, George A.; Feldman, Uri

1993-01-01

185

The chromosphere and transition region. [during solar flare  

NASA Technical Reports Server (NTRS)

The physical processes occurring as a result of the transfer of energy and momentum from the primary solar flare energy release site in the corona to the underlying chromosphere and transition region during the course of the flare are investigated through a comparison of theoretical models and observational data. Static, dynamic and hydrodynamic models of the lower-temperature chromospheric flare are reviewed. The roles of thermal conduction, radiation, fast particles and mass motion in chromosphere-corona interactions are analyzed on the basis of Skylab UV, EUV and X-ray data, and empirical and synthetic models of the chromospheric and upper photospheric responses to flares are developed. The canonical model of chromospheric heating during flares as a result of primary energy release elsewhere is found to be justified in the chromosphere as a whole, although not entirely as the temperature minimum, and a simplified model of horizontal chromospheric flare structure based on results obtained is presented.

Canfield, R. C.; Brown, J. C.; Craig, I. J. D.; Brueckner, G. E.; Cook, J. W.; Doschek, G. A.; Emslie, A. G.; Machado, M. E.; Henoux, J.-C.; Lites, B. W.

1980-01-01

186

GAMMA-RAY BURST FROM A SOLAR FLARE  

Microsoft Academic Search

A burst of high-energy radiation coincident with a solar flare has been ; detected during a balloon flight at 10 g\\/cm² atmosphere depth and 30 deg ; geomagnetic latitude over Cuba. The flare occurred at 1305 UT on March 20, 1958, ; and was associated with solar radio bursts on 1,500 and 10,000 Mc\\/s. Terrestrial ; effects included a SID,

L. E. Peterson; J. R. Winckler

1959-01-01

187

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.

188

Predictive Capabilities of Avalanche Models for Solar Flares  

NASA Astrophysics Data System (ADS)

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

Strugarek, A.; Charbonneau, P.

2014-11-01

189

Predictive Capabilities of Avalanche Models for Solar Flares  

E-print Network

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

Strugarek, Antoine

2014-01-01

190

New component of hard X-rays in solar flares  

Microsoft Academic Search

We present high resolution (approx.1 keV FWHM) spectral measurements from 13 to 300 keV of a solar flare hard X-ray burst observed on 1980 June 27 by a balloon-borne array of cooled germanium planar detectors. At energies below approx.35 keV we identify a new component of solar flare hard X-rays. This component is characterized by an extremely steep spectrum which

R. P. Lin; R. A. Schwartz; R. M. Pelling; K. C. Hurley

1981-01-01

191

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

192

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

193

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

194

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

195

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

196

Solar flare alpha to proton ratio changes following interplanetary disturbances  

Microsoft Academic Search

A discussion is presented on the half hour averaged low energy solar alpha to solar proton flux ratios observed following the three large solar flares of May 23, 1967. One of the large changes observed in the particle ratios (following a sudden commencement (SC) storm observed on the earth) is interpreted as due to a source effect. The second large

L. J. Lanzerotti; M. F. Robbins

1969-01-01

197

High-energy particles associated with solar flares  

NASA Technical Reports Server (NTRS)

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

Sakurai, K.; Klimas, A. J.

1974-01-01

198

Studying the thermal/non-thermal crossover in solar flares  

NASA Technical Reports Server (NTRS)

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

Schwartz, R. A.

1994-01-01

199

The Carrington solar flares of 1859: consequences on life.  

PubMed

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

Muller, C

2014-09-01

200

Gamma-ray observations of solar-flare ion acceleration  

NASA Astrophysics Data System (ADS)

The Sun can produce ions with energies up to tens of GeV and electrons up to hundreds of MeV, in both large solar flares and fast coronal mass ejections (CMEs), and is a useful laboratory to investigate the processes of impulsive energy release and particle acceleration that occur throughout the universe. Solar flares are the most powerful explosions in the solar system, releasing up to 1032-1033 ergs of stored magnetic energy in 100-1,000 seconds, with up to ˜10-50% of this energy going into accelerated electrons and a comparable amount into accelerated >˜1 MeV ions. Flare-accelerated particles are observed through the various types of emission produced as they interact with the ambient solar atmosphere energetic ions produce gamma-ray lines through a variety of processes, while energetic electrons produce bremsstrahlung continuum emission. Gamma-ray observations from the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) probe solar-flare ion acceleration and can compare it to electron acceleration. For RHESSI events, there is a tight linear correlation between ion-associated and electron-associated emissions, implying that the relative acceleration of ions above 30 MeV and electrons above 0.3 MeV is roughly independent of flare size, which provides constraints for acceleration models. This correlation does not hold for all flares at lower electron energies, with some flares exhibiting a relative excess of low-energy electron bremsstrahlung. Also, the ratios of accelerated ions and electrons in flares is comparable to ratios in impulsive solar energetic particle (SEP) events, but much larger than ratios in gradual SEP events. RHESSI gamma-ray observations of the temporal variability of gamma-ray lines suggest the possibility of intriguing changes in the ambient environment (e.g., abundances) as a flare progresses. Finally, open questions about solar-flare ion acceleration will be studied by a new balloon-borne instrument, the Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS), which is being developed at the University of California, Berkeley. GRIPS will use new detector and imaging technologies to produce gamma-ray images at an unprecedented angular resolution and measure gamma-ray polarization, and will prove these technologies for future space-based missions.

Shih, Albert Young-Ming

201

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

202

Imaging X-Ray Polarimeter for Solar Flares (IXPS)  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

203

Relativistic electron transport and bremsstrahlung production in solar flares  

NASA Technical Reports Server (NTRS)

A Monte Carlo simulation of ultrarelativistic electron transport in solar flare magnetic loops has been developed. It includes Coulomb, synchrotron, and bremsstrahlung energy losses; pitch-angle scattering by Alfven and whistler turbulence in the coronal region of the loop; and magnetic mirroring in the converging magnetic flux tubes beneath the transition region. Depth distributions, time profiles, energy spectra, and angular distributions of the resulting bremsstrahlung emission are calculated. It is found that both the preferential detection of solar flares with greater than 10 MeV emission near the limb of the sun and the observation of ultrarelativistic electron bremsstrahlung from flares on the disk are consequences of the loop transport model. The declining portions of the observed time profiles of greater than 10 MeV emission from solar flares can also be accounted for, and it is proposed that these portions are determined by transport and not acceleration.

Miller, James A.; Ramaty, Reuven

1989-01-01

204

Solar flares and avalanches in driven dissipative systems  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

205

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

206

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

207

Prediction of solar flares for the Space Exploration Initiative  

NASA Technical Reports Server (NTRS)

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

Davis, John M.

1994-01-01

208

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

209

Magnetic topology, energetic particles and radiation in solar flares  

NASA Astrophysics Data System (ADS)

Solar active regions are generally regions of great magnetic complexity, and accordingly have complicated topology. Understanding of the magnetic topology of active regions is far from complete, but many theoretical structures such as nulls, spines, fans and (quasi) -separatrix layers can be identified in magnetic fields deduced from data, and are found to be clearly linked to observable features of flaring energy release, such as flare ribbons, and the footpoints where radiation from flare-accelerated particles is produced. Solar flares represent the rapid release of stored magnetic energy in the solar corona, thus the topology of the active region has a crucial bearing on how much free energy a particular structure can store, what changes in connectivity are permitted, and thus the magnitude of a flare. In this talk I will review some basic theoretical ideas and present the observational evidence for the central role of flare magnetic topology in the character and evolution of a flare. I will also discuss the role of the magnetic structures themselves in producing the accelerated particles.

Fletcher, Lyndsay

2010-05-01

210

Implications of RHESSI Observations for Solar Flare Models and Energetics  

NASA Technical Reports Server (NTRS)

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

Holman, Gordon D.

2006-01-01

211

Observations and radiative hydrodynamic simulations of solar and stellar flares  

NASA Astrophysics Data System (ADS)

This dissertation presents an analysis of observations of stellar flares and dynamical simulations of solar and stellar flares. Stellar flares were observed by a collaboration organized by Suzanne Hawley, during March, 2000 on the flare star AD Leo. Simultaneous data were obtained from several ground- and space- based observatories, including observations of eight sizable flares. We discuss chromospheric line broadening and velocity fields observed in several transition region emission lines. These observations are consistent with the solar model of chromospheric evaporation and condensation following impulsive heating by a flux of non-thermal electrons. We calculated several radiative hydrodynamic simulations of solar and M dwarf stellar flares. The flares were simulated by calculating the atmospheric response to a beam of non-thermal electrons injected at the apex of a one- dimensional closed coronal loop, and include heating from thermal soft X-ray, extreme ultraviolet and ultraviolet (XEUV) emission. The equations of radiative transfer and statistical equilibrium were treated in non-LTE and solved for numerous transitions of hydrogen, helium, and Ca II, allowing the calculation of detailed line profiles and continuum emission. The dynamical results for both the solar and M dwarf simulations indicate that flares naturally divide into two phases: an initial gentle phase of near balance between flare heating and radiative cooling, followed by an explosive phase with beam heating dominating over cooling and characterized by strong hydrodynamic waves. We find that the predicted velocities resulting from the explosive heating closely match observations in both the solar and M dwarf cases. The simulations also show elevated coronal and transition region densities resulting in dramatic increases in line and continuum emission in both the UV and optical regions. In the solar case, the optical continuum reaches a peak increase of several percent which is consistent with enhancements observed in solar white light flares. Observations of M dwarfs during flares have shown that the Balmer lines get very broad. Our simulated Balmer line profiles also become very wide as a result of increased Stark broadening, and we conclude that Stark broadening is likely the cause of the observed line broadening.

Allred, Joel C.

2005-11-01

212

Muon and Tau Neutrinos Spectra from Solar Flares  

E-print Network

Solar neutrino flares and mixing are considered. Most power-full solar flare as the ones occurred on 23th February 1956, September 29th 1989, 28th October and on 2nd-4th November 2003 are sources of cosmic rays, X, gamma and neutrino bursts. These flares took place both on front or in the edge and in the hidden solar disk. The observed and estimated total flare energy should be a source of a prompt secondary neutrino burst originated, by proton-proton-pion production on the sun itself; a more delayed and spread neutrino flux signal arise by the solar charged flare particles reaching the terrestrial atmosphere. Our first estimates of neutrino signals in largest underground detectors hint for few events in correlation with, gamma,radio onser. Our approximated spectra for muons and taus from these rare solar eruption are shown over the most common background. The muon and tau signature is very peculiar and characteristic over electron and anti-electron neutrino fluxes. The rise of muon neutrinos will be detectable above the minimal muon threshold of 113 MeV. The rarest tau appearence will be possible only for hardest solar neutrino energies above 3.471 GeV

D. Fargion; F. Moscato

2004-05-03

213

Statistical Assessment of Photospheric Magnetic Features in Imminent Solar Flares Predictions  

E-print Network

Statistical Assessment of Photospheric Magnetic Features in Imminent Solar Flares Predictions Hui is the different level of solar flares magnitude. By analyzing 230 active regions, Lgnl is proved to be the most in solar physics to predict solar flares. 1. Introduction Over the past decades, mankind has become more

214

On the Origin of Solar Flare's EUV Late Phase  

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

215

Modelling the influence of photospheric turbulence on solar flare statistics  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

216

Evidence that solar flares drive global oscillations in the Sun  

E-print Network

Solar flares are large explosions on the Sun's surface caused by a sudden release of magnetic energy. They are known to cause local short-lived oscillations travelling away from the explosion like water rings. Here we show that the energy in the solar acoustic spectrum is correlated with flares. This means that the flares drive global oscillations in the Sun in the same way that the entire Earth is set ringing for several weeks after a major earthquake like the December 2004 Sumatra-Andaman Earthquake. The correlation between flares and energy in the acoustic spectrum of disk-integrated sunlight is stronger for high-frequency waves than for ordinary p-modes which are excited by the turbulence in the near surface convection zone immediately beneath the photosphere.

C. Karoff; H. Kjeldsen

2008-03-21

217

Critical Issues For Understanding Particle Acceleration in Impulsive Solar Flares  

Microsoft Academic Search

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

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

1997-01-01

218

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

219

Sign singularity and flares in solar active region NOAA 11158  

E-print Network

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

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

2015-01-01

220

Excitation of Resonant Helioseimic Modes by Solar Flares  

NASA Astrophysics Data System (ADS)

Flares are known to excite propagating sound waves in the solar atmosphere, and Maurya et al. (2009), using a local analysis (ring diagrams) of the 2003 Halloween flare, showed that they excite resonant p-modes as well. We confirm and extend here these results by: applying the same analysis to other locations on the Sun at the time of the Halloween flare, analyzing other events also showing a signature of p-mode excitation, looking in detail at the results of the ring diagrams analysis in terms of noise fitting and the center-to-limb variation of ring-diagram power.

Leibacher, John William; Baudin, Frédéric; Rabello Soares, Maria Cristina

2015-04-01

221

STATISTICAL ANALYSES ON THERMAL ASPECTS OF SOLAR FLARES  

SciTech Connect

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

Li, Y. P.; Gan, W. Q.; Feng, L., E-mail: wqgan@pmo.ac.cn [Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, 210008 Nanjing (China)

2012-03-10

222

Prediction of Solar Flares from a Statistical Analysis of Events during Solar Cycle 23  

E-print Network

Ways to give medium- and short-term predictions of solar flares are proposed according to the statistical analysis of events during solar cycle 23. On one hand, the time distribution of both C and M class flares shows two main periods of 13.2 and 26.4 months in this cycle by wavelet analysis. On the other hand, active regions of specific magnetic configurations and their evolutions give high productivity of C class flares but relatively low productivity of energetic (M and X class) flares. Furthermore, by considering the measurable kinetic features of active regions, i.e., the rotation of the sunspots, some active regions of specified types are observed to have high energetic flare productivity, above 66%. The periodicity of the activity revealed can be used for medium-term C and M class flare forecasting and the high productivity of active regions forms the basis for short-term prediction of individual energetic flares.

Z. Q. Qu

2008-11-14

223

TRANSITION REGION EMISSION FROM SOLAR FLARES DURING THE IMPULSIVE PHASE  

SciTech Connect

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

Johnson, H.; Raymond, J. C.; Murphy, N. A.; Suleiman, R. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Giordano, S. [INAF-Osservatorio Astronomico di Torino, via Osservatorio 20, 10025 Pino Torinese (Italy); Ko, Y.-K. [Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States); Ciaravella, A. [INAF-Osservatorio Astronomico di Palermo, P.za Parlamento 1, 90134 Palermo (Italy)

2011-07-10

224

Fine Structures and Overlying Loops of Confined Solar Flares  

E-print Network

Using the H$\\alpha$ observations from the New Vacuum Solar Telescope at Fuxian Solar Observatory, we focus on the fine structures of three confined flares and the issue why all the three flares are confined instead of eruptive. All the three confined flares take place successively at the same location and have similar morphologies, so can be termed homologous confined flares. In the simultaneous images obtained by the Solar Dynamics Observatory, many large-scale coronal loops above the confined flares are clearly observed in multi-wavelengths. At the pre-flare stage, two dipoles emerge near the negative sunspot, and the dipolar patches are connected by small loops appearing as arch-shaped H$\\alpha$ fibrils. There exists a reconnection between the small loops, and thus the H$\\alpha$ fibrils change their configuration. The reconnection also occurs between a set of emerging H$\\alpha$ fibrils and a set of pre-existing large loops, which are rooted in the negative sunspot, a nearby positive patch, and some remote ...

Yang, Shuhong; Xiang, Yongyuan

2014-01-01

225

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

NASA Video Gallery

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

226

PROPERTIES OF THE ACCELERATION REGIONS IN SEVERAL LOOP-STRUCTURED SOLAR FLARES  

E-print Network

PROPERTIES OF THE ACCELERATION REGIONS IN SEVERAL LOOP-STRUCTURED SOLAR FLARES Jingnan Guo1 , A-energy electrons accelerated in solar flares is the hard X-ray bremsstrahlung that they produce as they propagate

Piana, Michele

227

Can we explain atypical solar flares?  

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

228

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

SciTech Connect

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

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

2011-07-20

229

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

E-print Network

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

Scafetta, Nicola

230

Simulations of the effects of extreme solar flares on technological systems  

E-print Network

Simulations of the effects of extreme solar flares on technological systems at Mars Paul Withers, then vanished · His results vanished too · So progress has been slower than desired #12;Solar Flares (1) · Peak plasma densities increases by tens of percent during X-class solar flare · MARSIS topside radar sounder

Withers, Paul

231

Radio emission from acceleration sites of solar flares , Gregory D. Fleishman1,2  

E-print Network

Radio emission from acceleration sites of solar flares Yixuan Li1 , Gregory D. Fleishman1 acceleration site of a solar flare. Specifically, we calculate incoherent radio emission produced within two microwave and decimeter continuum bursts may be a signature of the stochastic acceleration in solar flares

232

15Data Corruption by High-Energy Particles Solar flares can severely affect sensitive instruments in  

E-print Network

15Data Corruption by High-Energy Particles Solar flares can severely affect sensitive instruments the approximate times of the events. Problem 1: At about what time did the solar flare first erupt on the sun://spacemath.gsfc.nasa.gov #12;15 Answer Key: Problem 1: At about what time did the solar flare first erupt on the sun? Answer

233

The Soft XRay/Microwave Ratio of Solar and Stellar Flares and Coronae  

E-print Network

We have carried out plasma diagnostics of solar flares using soft X­ray (SXR) and simultaneous microwave observations and have compared the ratio of X­ray to microwave luminosities of solar flares as thermal radiations of coronal plasmas. On the other hand, the microwave emission of stars and solar flares

Guedel, Manuel

234

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

E-print Network

Early Abnormal Temperature Structure of X-ray Looptop Source of Solar Flares Jinhua Shen1 processes in the contraction and expansion phases of these solar flares are different. Subject headings: Sun lines reconnect at higher and higher altitudes. However, the contraction of solar flare loops

235

The study of solar flares with the extended cellular automaton (XCA) model  

E-print Network

The study of solar flares with the extended cellular automaton (X­CA) model H. Isliker 1 , A of cellular automaton (CA) model, the extended CA (X­CA), for the study of solar flares. The X­CA model distributions of total energy, peak flux, and duration of solar flares. We present and discuss the relevant

Anastasiadis, Anastasios

236

The Effects of Solar Flares on the Ionospheres of Earth and Mars  

E-print Network

The Effects of Solar Flares on the Ionospheres of Earth and Mars Paul Withers Boston University.10.31 (withers@bu.edu) #12;Solar Flares http://www ionosphere to solar flares taught us a lot about the terrestrial ionosphere - the same will be true for Mars

Withers, Paul

237

Simulations of the effects of extreme solar flares on technological systems  

E-print Network

Simulations of the effects of extreme solar flares on technological systems at Mars Paul Withers profiles · Simulations from models · Normal conditions · Solar flares · Energetic particle events and models · "Harder" models ­ Time-dependent solar flare ­ Additional SEP events and improved analysis #12;

Withers, Paul

238

Space weather effects on the Mars ionosphere due to solar flares and meteors  

E-print Network

Space weather effects on the Mars ionosphere due to solar flares and meteors P. Withers (1), M observed two aspects of space weather at Mars. Following solar flares of both moderate to strong magnitude the simultaneous responses of the ionospheres of Earth and Mars to solar flares, highlighting the importance

Withers, Paul

239

PLASMA HEATING IN THE VERY EARLY PHASE OF SOLAR FLARES  

SciTech Connect

In this Letter, we analyze soft X-ray (SXR) and hard X-ray (HXR) emission of the 2002 September 20 M1.8 GOES class solar flare observed by the RHESSI and GOES satellites. In this flare event, SXR emission precedes the onset of the main bulk HXR emission by approx5 minutes. This suggests that an additional heating mechanism may be at work at the early beginning of the flare. However, RHESSI spectra indicate a presence of the non-thermal electrons also before the impulsive phase. So, we assumed 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 model of the analyzed flare. We showed that energy delivered by non-thermal electron beams is sufficient to heat the flare loop to temperatures in which it emits SXR closely following the GOES 1-8 A light curve. We also analyze the number of non-thermal electrons, the low-energy cutoff, electron spectral indices, and the changes of these parameters with time.

Siarkowski, M. [Space Research Centre, Polish Academy of Sciences, 51-622 Wroclaw, ul. Kopernika 11 (Poland); Falewicz, R.; Rudawy, P., E-mail: ms@cbk.pan.wroc.p, E-mail: falewicz@astro.uni.wroc.p, E-mail: rudawy@astro.uni.wroc.p [Astronomical Institute, University of Wroclaw, 51-622 Wroclaw, ul. Kopernika 11 (Poland)

2009-11-10

240

The acceleration and propagation of solar flare energetic particles  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

241

Solar flares as cascades of reconnecting magnetic loops.  

PubMed

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

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

2003-04-01

242

Gamma-Ray Polarimetry of Two X-Class Solar Flares  

E-print Network

We have performed the first polarimetry of solar flare emission at gamma-ray energies (0.2-1 MeV). These observations were performed with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) for two large flares: the GOES X4.8-class solar flare of 2002 July 23, and the X17-class flare of 2003 October 28. We have marginal polarization detections in both flares, at levels of 21% +/- 9% and -11% +/- 5% respectively. These measurements significantly constrain the levels and directions of solar flare gamma-ray polarization, and begin to probe the underlying electron distributions.

Steven E. Boggs; W. Coburn; E. Kalemci

2005-10-19

243

Modelling the effects of a solar flare on INTEGRAL  

NASA Astrophysics Data System (ADS)

The delayed effects of a large solar flare proton flux on the ?-ray instruments on-board INTEGRAL have been modelled. We simulated exposing INTEGRAL to a varying flux over a period of five days. The total integrated input proton flux for the flare chosen was 1.5×1014 protons. The induced count rates due to this proton flux over an energy range of 30 MeV - 2 GeV one minute after the end of the flare are 345.9+/-0.5 c/s for IBIS (the imager) and 10.03+/-0.06 c/s for SPI (the spectrometer). Spectra one minute after the end of the flare are shown for each instrument. The most significant spectral lines have been identified and the isotopic half-lives compared to the half-lives of the total count rates.

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

2001-09-01

244

A static model of chromospheric heating in solar flares  

NASA Technical Reports Server (NTRS)

The response of the solar chromosphere to flare processes, namely nonthermal electrons, thermal conduction, and coronal pressure, is modeled. Finite difference methods employing linearization and iteration are used in obtaining simultaneous solutions to the equations of steady-state energy balance, hydrostatic equilibrium, radiative transfer, and atomic statistical equilibrium. The atmospheric response is assumed to be confined to one dimension by a strong vertical magnetic field. A solution is obtained to the radiative transfer equation for the most important optically thick transitions of hydrogen, magnesium, and calcium. The theoretical atmospheres discussed here are seen as elucidating the role of various physical processes in establishing the structure of flare chromospheres. At low coronal pressures, conduction is found to be more important than nonthermal electrons in establishing the position of the transition region. Only thermal conduction can adequately account for the chromospheric evaporation in compact flares. Of the mechanisms considered, only nonthermal electrons bring about significant heating below the flare transition region.

Ricchiazzi, P. J.; Canfield, R. C.

1983-01-01

245

Electron Firehose instability and acceleration of electrons in solar flares  

E-print Network

An electron distribution with a temperature anisotropy T_par/T_perp > 1 can lead to the Electron Firehose instability (Here par and perp denote directions relative to the background magnetic field B_0). Since possible particle acceleration mechanisms in solar flares exhibit a preference of energizing particles in parallel direction, such an anisotropy is expected during the impulsive phase of a flare. The properties of the excited waves and the thresholds for instability are investigated by using linearized kinetic theory. These thresholds were connected to the pre-flare plasma parameters by assuming an acceleration model acting exclusively in parallel direction. For usually assumed pre-flare plasma conditions the electrons become unstable during the acceleration process and lefthand circularly polarized waves with frequencies of about the proton gyrofrequency are excited at parallel propagation. Indications have been found, that the largest growth rates occur at oblique propagation and the according frequencies lie well above the proton gyrofrequency.

Gunnar Paesold; Arnold O. Benz

2000-01-14

246

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

247

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

248

MULTIWAVELENGTH ANALYSIS OF A SOLAR FLARE ON 2002 APRIL 15  

NASA Technical Reports Server (NTRS)

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

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

2005-01-01

249

High Energy Gamma Ray Lines from Solar Flares  

NASA Technical Reports Server (NTRS)

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

Crannell, Carol Jo

2000-01-01

250

Evolution of electron energy spectrum during solar flares  

E-print Network

Evolution of electron energy spectrum during solar flares W. J. Liu, P. F. Chen, C. Fang, M. D simulations as done in Chen and Shibata (2000). This paper is organized as follows. A description/CMEs, Chen and Shibata (2000) performed 2-dimensional MHD simulations and proposed an emerging flux trigger

Chen, P. F.

251

THz solar telescope for detection flare synchrotron radiation  

Microsoft Academic Search

Recent solar flare observations have shown the existence of a spectral component exhibiting fluxes increasing with frequency in the sub-THz spectrum simultaneously with the well known spectral component peaking at microwaves bringing challenging constraints for interpretation. This double spectral feature cannot be well explained by existing models. One possibility is to associate the high frequency emissions to incoherent synchrotron radiation

Pierre Kaufmann; J. Michael Klopf

2011-01-01

252

Emerging flux model for the solar flare phenomenon  

Microsoft Academic Search

It is suggested that many solar flares occur in three stages when loops of magnetic flux emerge from below the photosphere and interact with the overlying field. First of all, during the preflare heating phase, continuous reconnection occurs in the current sheet that forms between the new and old flux. Waves which radiate from the ends of the sheet heat

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

1977-01-01

253

Non-thermal processes in large solar flares  

Microsoft Academic Search

We analyze particle acceleration processes in large solar flares, using observations of the August, 1972, series of large events. The energetic particle populations are estimated from the hard X-ray and ?-ray emission, and from direct interplanetary particle observations. The collisional energy losses of these particles are computed as a function of height, assuming that the particles are accelerated high in

R. P. Lin; H. S. Hudson

1976-01-01

254

Numerical Study of Magnetic Reconnection Processes in Solar Flares  

E-print Network

(1965) said "fluid mechanics is especially rich in nonlinearities". In this sense, I might as well say, Ms. H. Li, G. X. Liu, X. X. liu, and so on, gave me generous help. Our librarian, Mr. L. Q. Cheng;Extended Abstract The solar flare represents a sudden release of energy (1029­1033 erg within 100­1000 s

Chen, P. F.

255

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

NASA Astrophysics Data System (ADS)

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

Caballero, C.; Aranda, M. C.

2014-05-01

256

Solar flare hard X-ray spikes observed by RHESSI: a statistical study  

NASA Astrophysics Data System (ADS)

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

Cheng, J. X.; Qiu, J.; Ding, M. D.; Wang, H.

2012-11-01

257

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

NASA Technical Reports Server (NTRS)

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

Holman, Gordon D.

2004-01-01

258

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

259

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

260

Small Scale Microwave Bursts in Long-duration Solar Flares  

E-print Network

Solar small scale microwave bursts (SMBs), including microwave dot, spike, and narrow band type III bursts, are characterized with very short timescales, narrow frequency bandwidth, and very high brightness temperatures. Based on observations of the Chinese Solar Broadband Radio Spectrometer at Huairou with superhigh cadence and frequency resolution, this work presents an intensive investigation of SMBs in several flares occurred in active region NOAA 10720 during 2005 Jan 14-21. Especially long-duration flares, SMBs occurred not only in early rising and impulsive phase, but also in the flare decay phase, and even in time of after the flare ending. These SMBs are strong bursts with inferred brightness temperature at least 8.18*10^11 - 1.92*10^13 K, very short lifetime of 5-18 ms, relative frequency bandwidths of 0.7-3.5%, and superhigh frequency drifting rates. Together with their obviously different polarizations from the background emission (the quiet Sun, and the underlying flaring broadband continuum), su...

Tan, Baolin

2013-01-01

261

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

262

Solar Flare Impulsive Phase Observations from SDO and Other Observatories  

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

263

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

264

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

NASA Technical Reports Server (NTRS)

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

Chupp, Edward L.

1998-01-01

265

Muon and Tau Neutrinos Spectra from Solar Flares  

NASA Astrophysics Data System (ADS)

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

Fargion, Daniele; Moscato, Federica

2003-12-01

266

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

267

The development and cooling of a solar limb-flare  

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

268

Acceleration of runaway electrons and Joule heating in solar flares  

NASA Technical Reports Server (NTRS)

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

Holman, G. D.

1984-01-01

269

Acceleration of runaway electrons and Joule heating in solar flares  

NASA Technical Reports Server (NTRS)

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

Holman, G. D.

1985-01-01

270

Effects of solar flares on the ionosphere of Mars.  

PubMed

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

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

2006-02-24

271

Frequency distributions and correlations of solar X-ray flare parameters  

Microsoft Academic Search

We have determined frequency distributions of flare parameters from over 12000 solar flares recorded with the Hard X-Ray Burst Spectrometer (HXRBS) on the Solar Maximum Mission (SMM) satellite. These parameters include the flare duration, the peak counting rate, the peak hard X-ray flux, the total energy in electrons, and the peak energy flux in electrons (the latter two computed assuming

Norma B. Crosby; Markus J. Aschwanden; Brian R. Dennis

1993-01-01

272

THE SOLAR-FLARE PHENOMENON AND THE THEORY OF RECONNECTION AND ANNIHILATION OF MAGNETIC FIELDS  

Microsoft Academic Search

A study of contemporary theory and observation of the solar-flare ; phenomenon is presented for the purpose of forming some judgment of the popular ; notion that the solar flare is explained by the annihilation of magnetic fields ; in the site of the visible flare. The discussion deals principally with the ; basic energy consideration. The energy output of

E. N. Parker

1963-01-01

273

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

274

Solar flares and magnetic reconnection in quasi-separatrix layers  

NASA Astrophysics Data System (ADS)

Magnetic reconnection is a fundamental plasma physics process which is believed to be responsible for the bulk of energy release in solar flares. One the one hand, the onset of fast reconnection in high-Reynolds plasmas has long since been regarded as, perhaps, the major issue to understand. On the other hand, little attention has relatively been given to the three-dimensional nature of this phenomenon. Up to very recently, the latter has mostly been addressed by the solar physics community, presumably due to the wealth of space-borne and ground-based observations of three-dimensional solar coronal features during flares. Among other 3D concept, finite-B ``quasi-separatrix layers'' (QSLs) have been introduced in the nineties, as a generalization of the concept of true separatrices emanating from null-points. In this talk, I will show how both solar and experimental physics have revealed that these QSLs physically behave like true separatrices, in terms of current sheet formation and magnetic reconnection, albeit for the continuous slippage of field lines during the process. I will then show how this ``slip-running reconnection'' occurs in the wake of flux-ropes erupting from the solar corona towrds the heliosphere, and how it it eventually forms the observed post-flare loops in the Sun's corona.

Aulanier, G.; Demoulin, P.; Janvier, M.; Masson, S.; Pariat, E.

2012-10-01

275

Flare Particle Escape in 3D Solar Eruptive Events  

NASA Astrophysics Data System (ADS)

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

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

2015-04-01

276

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

277

Sign Singularity and Flares in Solar Active Region NOAA 11158  

NASA Astrophysics Data System (ADS)

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

Sorriso-Valvo, L.; De Vita, G.; Kazachenko, M. D.; Krucker, S.; Primavera, L.; Servidio, S.; Vecchio, A.; Welsch, B. T.; Fisher, G. H.; Lepreti, F.; Carbone, V.

2015-03-01

278

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

NASA Video Gallery

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

279

Extreme Ultra-Violet Spectroscopy of the Flaring Solar Chromosphere  

E-print Network

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

Milligan, Ryan O

2015-01-01

280

What produces the high densities observed in solar flare plasmas  

NASA Technical Reports Server (NTRS)

Attention is drawn to the implications of the high densities observed in flare plasmas in the wide temperature range from 10 to the 4th K to more than 10 to the 7th K. The chromospheric evaporation theory for the decay phase is discussed, and it is found that it is not consistent with the observations. It is pointed out that all the flare mechanisms proposed so far, e.g., magnetic field reconnection in various geometries, have entirely ignored the fundamental problem of how the high densities arise in the first place, and, in fact, they are unable to answer this question. It is suggested that compressional heatings of a flaring loop might be responsible for the density and emission measure (EM) increases observed in flare plasmas. Chromospheric evaporation associated with local heating in the initial rising phase of the flare, in distinction to the existing evaporation theory which assumes a coronal heating source, is also discussed. Possible observational tests, utilizing the newly launched Solar Maximum Mission (SMM) satellite, are presented.

Cheng, C.-C.; Feldman, U.; Doschek, G. A.

1981-01-01

281

Thermal and non-thermal energies in solar flares  

E-print Network

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

Pascal Saint-Hilaire; Arnold O. Benz

2005-03-03

282

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

283

A Unified Computational Model for Solar and Stellar Flares  

NASA Astrophysics Data System (ADS)

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

Allred, Joel; Kowalski, Adam; Carlsson, Mats

2015-04-01

284

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

285

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.

286

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

SciTech Connect

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.; Gallagher, Peter T. [School of Physics, Trinity College Dublin, Dublin 2 (Ireland); Milligan, Ryan O.; Dennis, Brian R.; Kim Tolbert, A.; Schwartz, Richard A.; Alex Young, C. [Solar Physics Laboratory (Code 671), Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2012-10-15

287

What Gamma-Ray Deexcitation Lines Reveal about Solar Flares R. J. Murphy and G. H. Share  

E-print Network

What Gamma-Ray Deexcitation Lines Reveal about Solar Flares R. J. Murphy and G. H. Share E. O of the calculations to flare observations by both SMM and RHESSI are also presented. Keywords: solar flares; gamma that the energy source for particle acceleration in solar flares is related to reconnection of coronal magnetic

Share, Gerald

288

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

289

Short-term Solar Flare Prediction Using Multiresolution Predictors  

NASA Astrophysics Data System (ADS)

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

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

2010-01-01

290

Modelling the influence of photospheric turbulence on solar flare statistics.  

PubMed

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

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

2014-01-01

291

On the rate of energy input in thermal solar flares  

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

292

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

NASA Technical Reports Server (NTRS)

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

Chupp, Edward L.

1997-01-01

293

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.; T. Fernandes, Luis Olavo; Kropotov, Grigory I.; Kudaka, Amauri S.; Machado, Nelson; Marun, Adolfo; Nikolaev, Valery; Silva, Alexandre; da Silva, Claudemir S.; Timofeevsky, Alexander

2014-11-01

294

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

SciTech Connect

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

Grayson, James A.; Krucker, Saem [Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450 (United States); Lin, R. P., E-mail: jgrayson@berkeley.ed, E-mail: krucker@ssl.berkeley.ed, E-mail: rlin@ssl.berkeley.ed [Also at Department of Physics, University of California, Berkeley, CA 94720-7300 (United States)

2009-12-20

295

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

SciTech Connect

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., E-mail: AFRL.RVB.PA@kirtland.af.mil [Air Force Research Laboratory, Space Vehicles Directorate, 3550 Aberdeen Ave., Kirtland AFB, NM 87117 (United States)

2013-05-20

296

RADIO EMISSION FROM ACCELERATION SITES OF SOLAR FLARES  

SciTech Connect

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

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

2009-08-10

297

THE ACCELERATION OF IONS IN SOLAR FLARES DURING MAGNETIC RECONNECTION  

SciTech Connect

The acceleration of solar flare ions during magnetic reconnection is explored via particle-in-cell simulations that self-consistently and simultaneously follow the motions of both protons and {alpha} particles. We show that the dominant heating of thermal ions during guide field reconnection, the usual type in the solar corona, results from pickup behavior during the entry into reconnection exhausts. In contrast to anti-parallel reconnection, the temperature increment is dominantly transverse, rather than parallel, to the local magnetic field. A comparison of protons and {alpha} reveals a mass-to-charge (M/Q) threshold in pickup behavior that favors the heating of high-M/Q ions, which is consistent with impulsive flare observations.

Knizhnik, K. [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Swisdak, M.; Drake, J. F., E-mail: kknizhni@pha.jhu.edu, E-mail: swisdak@umd.edu, E-mail: drake@umd.edu [Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742 (United States)

2011-12-20

298

Particle Acceleration by Fast Modes in Solar Flares  

E-print Network

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

Huirong Yan; A. Lazarian; V. Petrosian

2008-05-08

299

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

NASA Technical Reports Server (NTRS)

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

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

2005-01-01

300

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

301

Plasma heating during the rise phases of the solar flares  

Microsoft Academic Search

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

Pawel Rudawy; Robert Falewicz; Marek Siarkowski

2010-01-01

302

Ion and relativistic electron transport in solar flares  

NASA Technical Reports Server (NTRS)

Recent models for the ion and relativistic electron transport in solar flare magnetic loops are reviewed, focusing on the ways in which the models handle loop structure, particle acceleration, and particle transport. Results are presented from Monte Carlo simulations of ion and relativistic ion transport. Consideration is given to results concerning the depth distributions of gamma-ray production, the attenuation of gamma-ray lines, the time dependences of the various emissions and the angular distribution of the bremsstrahlung.

Ramaty, R.; Miller, J. A.; Hua, X.-M.; Lingenfelter, R. E.

1990-01-01

303

The Energetic Importance of Accelerated Electrons in Solar Flares  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

304

Imaging spectroscopy of solar microwave radiation. 1: Flaring emission  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

305

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

306

Electron-Electron Bremsstrahlung Emission and the Inference of Electron Flux Spectra in Solar Flares  

E-print Network

to the hard X-ray emission from solar flares, the latter is normally ignored. Such an omission in the study of hard X-ray spectra from solar flares. With the high-resolution hard X- ray spectra madeElectron-Electron Bremsstrahlung Emission and the Inference of Electron Flux Spectra in Solar

Piana, Michele

307

Anisotropic Bremsstrahlung Emission and the form of Regularized Electron Flux Spectra in Solar Flares  

E-print Network

,3 , & John C. Brown4 ABSTRACT The cross-section for bremsstrahlung photon emission in solar flares is in gen a regularized inversion technique to high- resolution hard X-ray spectra from solar flares in order to recoverAnisotropic Bremsstrahlung Emission and the form of Regularized Electron Flux Spectra in Solar

Piana, Michele

308

Global Energetics of Solar Flares: II. Thermal Energies  

E-print Network

We present the second part of a project on the global energetics of solar flares and CMEs that includes about 400 M- and X-class flares observed with AIA/SDO during the first 3.5 years of its mission. In this Paper II we compute the differential emission measure (DEM) distribution functions and associated multi-thermal energies, using a spatially-synthesized Gaussian DEM forward-fitting method. The multi-thermal DEM function yields a significantly higher (by an average factor of $\\approx 14$), but more comprehensive (multi-)thermal energy than an isothermal energy estimate from the same AIA data. We find a statistical energy ratio of $E_{th}/E_{diss} \\approx 2\\%-40\\%$ between the multi-thermal energy $E_{th}$ and the magnetically dissipated energy $E_{diss}$, which is an order of magnitude higher than the estimates of Emslie et al.~2012. For the analyzed set of M and X-class flares we find the following physical parameter ranges: $L=10^{8.2}-10^{9.7}$ cm for the length scale of the flare areas, $T_p=10^{5.7}-...

Aschwanden, M J; Ryan, D; Caspi, A; McTiernan, J M; Warren, H P

2015-01-01

309

Theoretical aspects related to plasma flows observed in solar flares  

NASA Astrophysics Data System (ADS)

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

Somov, Boris

310

The impulsive hard X-rays from solar flares  

NASA Technical Reports Server (NTRS)

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

Leach, J.

1984-01-01

311

Plasma Turbulence and Stochastic Acceleration in Solar Flares  

E-print Network

Observational aspects of solar flares relevant to the acceleration process of electrons and protons are reviewed and it is shown that most of these observations can be explained by the interaction with flare plasma of a power law energy distribution of electrons (and protons) that are injected at the top of a flaring loop, in the so-called thick target model. Some new observations that do not agree with this model are described and it is shown that these can be explained most naturally if most of the energy released by the reconnection process goes first into the generation of plasma turbulence, which accelerates, scatters and traps the ambient electrons near the top of the loop stochastically. The resultant bremsstrahlung photon spectral and spatial distributions agree with the new observations. This model is also justified by some theoretical arguments. Results from numerical evaluation of the spectra of the accelerated electrons and their bremsstrahlung emission are compared with observations and shown how one can constrain the model parameters describing the flare plasma and the spectrum and the energy density of the turbulence.

Vahe Petrosian

1999-11-18

312

Relative timing of solar flares observed at different wavelengths  

E-print Network

The timing of 503 solar flares observed simultaneously in hard X-rays, soft X-rays and H-alpha is analyzed. We investigated the start and the peak time differences in different wavelengths, as well as the differences between the end of the hard X-ray emission and the maximum of the soft X-ray and H-alpha emission. In more than 90% of the analyzed events, a thermal preheating seen in soft X-rays is present prior to the impulsive flare phase. On average, the soft X-ray emission starts 3 min before the hard X-ray and the H-alpha emission. No correlation between the duration of the preheating phase and the importance of the subsequent flare is found. Furthermore, the duration of the preheating phase does not differ for impulsive and gradual flares. For at least half of the events, the end of the nonthermal emission coincides well with the maximum of the thermal emission, consistent with the beam-driven evaporation model. On the other hand, for about 25% of the events there is strong evidence for prolonged evaporation beyond the end of the hard X-rays. For these events, the presence of an additional energy transport mechanism, most probably thermal conduction, seems to play an important role.

A. Veronig; B. Vrsnak; M. Temmer; A. Hanslmeier

2002-08-05

313

Solar flares and solar wind helium enrichments: July 1965–July 1967  

Microsoft Academic Search

It has previously been suggested that the very high relative abundances of helium occasionally observed in the solar wind mark the plasma accelerated by major solar flares. To confirm this hypothesis, we have studied the 43 spectra with He\\/H ? 15% that were observed among 10300 spectra collected by Vela 3 between July 1965–July 1967. The 43 spectra were distributed

J. Hirshberg; S. J. Bame; D. E. Robbins

1972-01-01

314

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

315

Directivity of high-energy emission from solar flares: solar-maximum mission observations  

Microsoft Academic Search

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 emission from flares is anisotropic. They are the following: the fraction of events detected at energies > 300 keV near the limb

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

1987-01-01

316

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

317

Frequency distributions and correlations of solar X-ray flare parameters  

NASA Technical Reports Server (NTRS)

Frequency distributions of flare parameters are determined from over 12,000 solar flares. The flare duration, the peak counting rate, the peak hard X-ray flux, the total energy in electrons, and the peak energy flux in electrons are among the parameters studied. Linear regression fits, as well as the slopes of the frequency distributions, are used to determine the correlations between these parameters. The relationship between the variations of the frequency distributions and the solar activity cycle is also investigated. Theoretical models for the frequency distribution of flare parameters are dependent on the probability of flaring and the temporal evolution of the flare energy build-up. The results of this study are consistent with stochastic flaring and exponential energy build-up. The average build-up time constant is found to be 0.5 times the mean time between flares.

Crosby, Norma B.; Aschwanden, Markus J.; Dennis, Brian R.

1993-01-01

318

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

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

319

Heating rates in X-ray flares: From solar microflares to stellar events  

NASA Astrophysics Data System (ADS)

Soft X-ray solar and stellar flares appear in the coronae of solar-like stars due to abrupt release of energy accumulated in magnetic fields. To build a quantitatively correct model of a flare we need to know how much energy is released in flares of different sizes and strengths. Here we estimate and compare the energy release rate in flares as different as microflares occurring over the quiet Sun and strong stellar events in RS CVn systems. We find one simple scaling law which describes flares differing one from another by 10 orders of magnitude in the amount of emission measure.

Pre?, P.; Falewicz, R.; Jakimiec, J.

320

STUDIES OF SOLAR WHITE-LIGHT FLARES AND SMALL-SCALE MAGNETIC STRUCTURES OBSERVED IN THE NEAR INFRARED  

E-print Network

of near infrared (NIR) solar physics: (1) the first detection and understanding of white-light flares for comparison. For flare study, the very first near-infrared observations of two white-light flares;STUDIES OF SOLAR WHITE-LIGHT FLARES AND SMALL-SCALE MAGNETIC STRUCTURES OBSERVED IN THE NEAR INFRARED

321

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

322

ELECTROMAGNETIC AND CORPUSCULAR EMISSION FROM THE SOLAR FLARE OF 1991 JUNE 15: CONTINUOUS ACCELERATON OF  

E-print Network

emission from the powerful flare of 1991 June 15. During this flare, high-energy 3'-ray emission up to 2 Ge in the active region 6659, which was a source of a number of very powerful solar flares connectedwith strong° cm. According to GOES observations in the soft X-ray band (1-8 A, 0.5-4 A) the flare had an onset

Usoskin, Ilya G.

323

Continuum emission in the 1980 July 1 solar flare  

NASA Technical Reports Server (NTRS)

Comparison of continuum measurements of the July 1, 1980 flare at Big Bear Solar Observatory and Sacramento Peak Observatory show strong blue emission kernels with the ratio of Balmer continuum (Bac):3862 A continuum:continuum above 4275 A to be about 10:5:1. The blue continuum at 3862 A is too strong to be explained by unresolved lines. The Bac intensity was 2.5 times the photosphere and the strongest 3826 A continuum was 2 times the photosphere. The brightest continuum kernel occurred late in the flare, after the hard X-ray peak and related in time to an isolated peak in the 2.2 MeV line, suggesting that that continuum was excited by protons above 20 MeV.

Zirin, H.; Neidig, D. F.

1981-01-01

324

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

325

Singly charged energetic helium emitted in solar flares  

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

326

A mechanism for deep chromospheric heating during solar flares  

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

327

Complex Dynamic Flows in Solar Flare Sheet Structures  

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

328

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

329

X-Ray Polarization of Solar Flares Measured with Rhessi  

E-print Network

The degree of linear polarization in solar flares has not yet been precisely determined despite multiple attempts to measure it with different missions. The high energy range in particular has very rarely been explored, due to its greater instrumental difficulties. We approached the subject using the Reuven Ramaty High Energy Spectroscopic Imager (RHESSI) satellite to study 6 X-class and 1 M-class flares in the energy range between 100 keV and 350 keV. Using RHESSI as a polarimeter requires the application of strict cuts to the event list in order to extract those photons that are Compton scattered between two detectors. Our measurements show polarization values between 2% and 54%, with errors ranging from 10% to 26% in 1 sigma level. In view of the large uncertainties in both the magnitude and direction of the polarization vector, the results can only reject source models with extreme properties.

E. Suarez-Garcia; W. Hajdas; C. Wigger; K. Arzner; M. Guedel; A. Zehnder; P. Grigis

2006-09-28

330

Continuum analysis of an avalanche model for solar flares.  

PubMed

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

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

2002-11-01

331

GENERIC MODEL FOR MAGNETIC EXPLOSIONS APPLIED TO SOLAR FLARES  

SciTech Connect

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

Melrose, D. B. [Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006 (Australia)

2012-04-10

332

SLOW MAGNETOACOUSTIC OSCILLATIONS IN THE MICROWAVE EMISSION OF SOLAR FLARES  

SciTech Connect

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

Kim, S.; Shibasaki, K. [Nobeyama Solar Radio Observatory/NAOJ, Nagano 384-1305 (Japan); Nakariakov, V. M., E-mail: sjkim@nro.nao.ac.jp [Physics Department, University of Warwick, Coventry, CV4 7AL (United Kingdom)

2012-09-10

333

North and South Major Flare Periodicities During Solar Cycle 20  

NASA Astrophysics Data System (ADS)

The periodicities of monthly values of major flare numbers and comprehensive major flare index (CFI) have been studied for the 20th solar cycle. It has been proved that the periodicity 152 days exists also in the southern (S) solar hemisphere. This periodicity has been previously defined in the earlier cycles to be a northern (N) periodicity, but it has migrated to the southern hemisphere (S) during the cycles 19, 20, 21. For the whole solar disk data, it has been found that the periodicity at 78.43d is much remarkable than its first harmonic at 156.86d. We have also detected very strong periodicity at 548.96d in N-hemisphere while a strong one has been found near 100d in both solar hemispheres. The detected periodicities at 80±2d and 101-+1d seems to have a global origin . The 87.1d periodicity is present and it is suggested that it is related to 88d periodicity attributed to the tidal influence of the planet Mercury on sunspots. Both hemispheres present their periodicities independently.

Galal, A. A.; Yousef, Shahinaz; Bebars, E.

1995-06-01

334

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

NASA Technical Reports Server (NTRS)

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

Benz, A. O.; Guedel, M.

1994-01-01

335

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

336

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

337

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

338

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

Microsoft Academic Search

Event-integrated fluxes of protons and alpha particles in solar-flare-associated particle events during solar cycle 21 (1976--1986) are determined from data obtained by detectors on board the IMP-7 and IMP-8 satellites. Sixty-three solar particle events with proton fluence (E>10 MeV)>10⁷ cm⁻² were identified from October 1972 to March 1987. The average omnidirectional flux of protons with kinetic energy>10 MeV for cycle

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

1988-01-01

339

Solar-stellar connection - the relationship between flaring rates, flare power, and quiescent X-ray background  

SciTech Connect

The flaring rates, flare powers, and quiescent X-ray luminosities of dMe (red dwarf) stars are compared with those of solar active regions. In dMe stars, these properties are found to be closely related, and this may have a significant influence on the understanding of the flare process and coronal heating. For example, a correlation between flare rate and quiescent X-ray luminosity suggests that both may be driven by similar processes on a differing scale. It is a natural extension of this work to investigate similar relationships for the sun. The results are mixed. The relationships between the various parameters are certainly not as clear for the sun as for the dMe stars. Some solar properties appear to vary in a manner similar to the dMe analysis, and some contradict the dMe case. The implications of this are discussed. 14 references.

Harrison, R.A.; Pearce, G.; Skumanich, A.

1988-09-01

340

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

341

A high-resolution study of the isotopes of solar flare nuclei  

NASA Technical Reports Server (NTRS)

Individual isotopes of the elements He, C, N, O, Ne, and Mg with energies from 5 to 50 MeV per nucleon have been resolved in energetic flare particles during the September 23, 1978 solar flare event. In addition, an earlier determination of Ne-22/Ne-20 in this flare was improved on by extending the energy interval for isotope analysis. A significant difference between the isotopic composition of solar flare and solar wind neon is found, which is compared to similar evidence from studies of solar energetic particles implanted in lunar and meteoritic samples. Although limited by statistics, the measurements of He, C, N, O, and Mg isotopes are consistent with typical isotopic abundances found in other samples of solar system material. The ensemble of these results is used to test for the possibility of mass-dependent fractionation during solar flare acceleration and propagation.

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

1984-01-01

342

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

343

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

344

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

345

Reconnection in substorms and solar flares: analogies and differences  

NASA Astrophysics Data System (ADS)

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 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 a 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. Further similarities might exist in the role of collapsing magnetic flux tubes, as a consequence of reconnection, in the heating and acceleration of charged particles.

Birn, J.; Hesse, M.

2009-03-01

346

Extremely Large EUV Late Phase of Solar Flares  

NASA Astrophysics Data System (ADS)

The second peak in the Fe xvi 33.5 nm line irradiance observed during solar flares by the Extreme-Ultraviolet Variability Experiment (EVE) is known as the EUV late phase. Our previous paper in 2013 by Liu et al. found that the main emissions in the late phase are originated from large-scale loop arcades that are closely connected to but different from the post-flare loops (PFLs), and we also proposed that a long cooling process without additional heating could explain the late phase. In this paper, we define the extremely large late phase because it not only has a bigger peak in the warm 33.5 irradiance profile, but also releases more EUV radiative energy than the main phase. Through detailed inspection of the EUV images from three points of view, it was discovered that aside from the later-phase loop arcades, the main contributor of the extremely large late phase is a hot structure that fails to erupt. This hot structure is identified as a flux rope, which is quickly energized by the flare reconnection and later on continuously produces the thermal energy during the gradual phase. Together with the late-phase loop arcades, the flux rope failing to erupt with the additional heating create the extremely large EUV late phase.

Liu, Kai; Wang, Yuming; Zhang, Jie; Cheng, Xin; Liu, Rui; Shen, Chenglong

2015-03-01

347

Global Energetics of Solar Flares: I. Magnetic Energies  

E-print Network

We present the first part of a project on the global energetics of solar flares and coronal mass ejections (CMEs) that includes about 400 M- and X-class flares observed with AIA and HMI onboard SDO. We calculate the potential energy, free energy, and the flare-dissipated magnetic energy. We calculate these magnetic parameters using two different NLFFF codes: The COR-NLFFF code uses the line-of-sight magnetic field component $B_z$ from HMI to define the potential field, and the 2D coordinates of automatically detected coronal loops in 6 coronal wavelengths from AIA to measure the helical twist of coronal loops caused by vertical currents, while the PHOT-NLFFF code extrapolates the photospheric 3D vector fields. We find agreement between the two codes in the measurement of free energies and dissipated energies within a factor of $ \\approx 3$. The size distributions of magnetic parameters exhibit powerlaw slopes that are approximately consistent with the fractal-diffusive self-organized criticality model. The ma...

Aschwanden, Markus J; Jing, Ju

2014-01-01

348

A search for energetic ion directivity in large solar flares  

NASA Technical Reports Server (NTRS)

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

Vestrand, W. Thomas

1993-01-01

349

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

NASA Technical Reports Server (NTRS)

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

Kane, S. R.

1971-01-01

350

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

SciTech Connect

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.; Magara, T.; Choe, G. S. [School of Space Research, Kyung Hee University 1, Seocheon-dong, Giheung-gu, Yongin, Gyeonggi-do 446-701 (Korea, Republic of); Hayashi, K. [W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305 (United States); Shiota, D., E-mail: inosato@khu.ac.kr [Solar-Terrestrial Environment Laboratory, Nagoya University Furo-cho, Chikusa-ku, Nagoya 464-8601 (Japan)

2013-06-10

351

NEUTRON AND ELECTROMAGNETIC EMISSIONS DURING THE 1990 MAY 24 SOLAR FLARE  

E-print Network

NEUTRON AND ELECTROMAGNETIC EMISSIONS DURING THE 1990 MAY 24 SOLAR FLARE L. G. KOCHAROV,* JEONGWOO revised form 15 July, 1994) Abstract. In this paper, we are primarilyconcerned with the solar neutron emission during the 1990 May 24 flare, utilizing the counting rate of the Climax neutron monitor

Usoskin, Ilya G.

352

HARD X-RAY AND MICROWAVE FLUX SPECTRA OF THE 2 NOVEMBER 1991 SOLAR FLARE  

E-print Network

HARD X-RAY AND MICROWAVE FLUX SPECTRA OF THE 2 NOVEMBER 1991 SOLAR FLARE CHIK-YIN LEE1,2 and HAIMIN analysed the hard X-ray and microwave flux spectra of the solar flare (BATSE No. 1791) on 2 November 1991/LAD hard X-ray and 45-frequency OVRO microwave database. We quantitatively compare the time variations

353

Evidence for gentle chromospheric evaporation during the gradual phase of large solar flares  

Microsoft Academic Search

The Multichannel Subtractive Double Pass Spectrograph of the Meudon solar tower is used to obtain high spatial resolution H-alpha line profiles during the gradual phase of three solar flares. In all cases, small blueshifts lasting for several hours are observed in the flare ribbons. By contrast, the region between the two ribbons exhibits large redshifts that are typical of H-alpha

B. Schmieder; T. G. Forbes; J. M. Malherbe; M. E. Machado

1987-01-01

354

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

355

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

356

MICROWAVE AND HARD XRAY OBSERVATIONS OF FOOTPOINT EMISSION FROM SOLAR FLARES  

E-print Network

radio and X­ray imaging data for two solar flares in order to test the idea that asymmetric on the Yohkoh spacecraft, and by the Nobeyama 17 GHz radioheliograph. The hard X­ray images in one case show twoMICROWAVE AND HARD X­RAY OBSERVATIONS OF FOOTPOINT EMISSION FROM SOLAR FLARES M. R. KUNDU Dept

White, Stephen

357

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

NASA Video Gallery

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

358

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

NASA Video Gallery

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

359

Global Energetics of Solar Flares: II. Thermal Energies  

NASA Astrophysics Data System (ADS)

We present the second part of a project on the global energetics of solar flares and coronal mass ejections that includes about 400 M- and X-class flares observed with the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) during the first 3.5 yr of its mission. In this Paper II we compute the differential emission measure (DEM) distribution functions and associated multithermal energies, using a spatially-synthesized Gaussian DEM forward-fitting method. The multithermal DEM function yields a significantly higher (by an average factor of ?14), but more comprehensive (multi-)thermal energy than an isothermal energy estimate from the same AIA data. We find a statistical energy ratio of {{E}th}/{{E}diss} ? 2-40% between the multithermal energy Eth and the magnetically dissipated energy Ediss, which is an order of magnitude higher than the estimates of Emslie et al. 2012. For the analyzed set of M- and X-class flares we find the following physical parameter ranges: L={{10}8.2}{{-10}9.7} cm for the length scale of the flare areas, {{T}p}={{10}5.7}{{-10}7.4} K for the DEM peak temperature, {{T}w}={{10}6.8}{{-10}7.6} K for the emission measure-weighted temperature, {{n}p}={{10}10.3}-{{10}11.8} cm-3 for the average electron density, E{{M}p}={{10}47.3}-{{10}50.3} cm-3 for the DEM peak emission measure, and {{E}th}={{10}26.8}-{{10}32.0} erg for the multithermal energies. The deduced multithermal energies are consistent with the RTV scaling law {{E}th,RTV}=7.3× {{10}-10} Tp3Lp2, which predicts extremal values of {{E}th,max }? 1.5× {{10}33} erg for the largest flare and {{E}th,min }? 1× {{10}24} erg for the smallest coronal nanoflare. The size distributions of the spatial parameters exhibit powerlaw tails that are consistent with the predictions of the fractal-diffusive self-organized criticality model combined with the RTV scaling law.

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

2015-03-01

360

Global Energetics of Solar Flares. I. Magnetic Energies  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

361

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

362

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

E-print Network

This Letter is to investigate the physics of a newly discovered phenomenon -- contracting flare loops in the early phase of solar flares. In classical flare models, which were constructed based on the phenomenon of expansion of flare loops, an energy releasing site is put above flare loops. These models can predict that there is a vertical temperature gradient in the top of flare loops due to heat conduction and cooling effects. Therefore, the centroid of an X-ray looptop source at higher energy bands will be higher in altitude, for which we can define as normal temperature distribution. With observations made by {\\it RHESSI}, we analyzed 10 M- or X-class flares (9 limb flares). For all these flares, the movement of looptop sources shows an obvious U-shaped trajectory, which we take as the signature of contraction-to-expansion of flare loops. We find that, for all these flares, normal temperature distribution does exist, but only along the path of expansion. The temperature distribution along the path of contraction is abnormal, showing no spatial order at all. The result suggests that magnetic reconnection processes in the contraction and expansion phases of these solar flares are different.

Jinhua Shen; Tuanhui Zhou; Haisheng Ji; Na Wang; Wenda Cao; Haimin Wang

2008-08-29

363

The topology of magnetic reconnection in solar flares  

NASA Astrophysics Data System (ADS)

In order to better understand the location and evolution of magnetic reconnection, which is thought to be the energy release mechanism in solar flares, I combine the analysis of hard X-ray (HXR) sources observed by RHESSI with a three-dimensional, quantitative magnetic charge topology (MCT) model. I first examine the evolution of reconnection by analyzing the relationship between observed HXR footpoint motions and a topological feature called spine lines. With a high degree of confidence, I find that the HXR footpoints sources moved along the spine lines. The standard two dimensional flare model cannot explain this relationship. Therefore, I present a three dimensional model in which the movement of footpoints along spine lines can be understood. To better analyze the location of reconnection, I developed a more detailed method for representing photospheric magnetic fields in the MCT model. This new method can portray internal changes and rotations of photospheric magnetic flux regions, which was not possible with the original method. I then examine the location of reconnection by assuming a relationship between the build-up of energy in stressed coronal magnetic fields and the measurement of the change in separator flux per unit length. I find that the value of this quantity is larger on the separators that connect the HXR footpoint sources than the value on the separators that do not. Therefore, I conclude that we are able to understand the location of HXR sources observed in flares in terms of a physical and mathematical model of the topology of the active region. In summary, based on the success of the MCT model in relating the motion of HXR sources to the evolution of magnetic reconnection on coronal separators, as well as my mathematical and physical model of energy storage at separators, I conclude the MCT model gives useful insight into the relationship between sites of HXR emission and the topology of flare productive active regions.

Des Jardins, Angela Colman

364

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

365

Diffusion entropy and waiting time statistics of hard-x-ray solar flares Paolo Grigolini,1,2,3  

E-print Network

Diffusion entropy and waiting time statistics of hard-x-ray solar flares Paolo Grigolini,1 of the distribution of time distance between two nearest-neighbor solar flares. This traditional part of the analysis reveals the presence of memory effects induced by the time dependence of the solar flare rate. When

Scafetta, Nicola

366

ELECTRON FLUX SPECTRAL IMAGING OF SOLAR FLARES THROUGH REGULARIZED ANALYSIS OF HARD X-RAY SOURCE VISIBILITIES  

E-print Network

ELECTRON FLUX SPECTRAL IMAGING OF SOLAR FLARES THROUGH REGULARIZED ANALYSIS OF HARD X-RAY SOURCE method for imaging spectroscopy analysis of hard X-ray emission during solar flares. The method avoids then yields images of the elec- tron flux that vary smoothly with energy. We apply the method to a solar flare

California at Berkeley, University of

367

Large Solar Flares and their Ionospheric D-region Enhancements Neil R. Thomson and Craig J. Rodger  

E-print Network

1 Large Solar Flares and their Ionospheric D-region Enhancements Neil R. Thomson and Craig J Division, British Antarctic Survey, Cambridge, UK On 4 November 2003, the largest solar flare ever recorded solar flares the X-ray flux received at the Earth increases dramatically, often within a few minutes

Otago, University of

368

ELECTRON FLUX SPECTRAL IMAGING OF SOLAR FLARES THROUGH REGULARIZED ANALYSIS OF HARD X-RAY SOURCE VISIBILITIES  

E-print Network

ELECTRON FLUX SPECTRAL IMAGING OF SOLAR FLARES THROUGH REGULARIZED ANALYSIS OF HARD X-RAY SOURCE a new method for imaging spectroscopy analysis of hard X-ray emission during solar flares. The method the method to a solar flare observed on 2002 February 20 by the RHESSI instrument. The event is characterized

Piana, Michele

369

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

370

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

NASA Technical Reports Server (NTRS)

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

Newton, Elizabeth; Giblin, Timothy

1999-01-01

371

Solar flare proton spectrum averaged over the last 5000 years  

NASA Technical Reports Server (NTRS)

The solar flare differential energy spectrum and integral proton flux above 10 MeV averaged over the last several thousand years are derived from thermoluminescence (TL) data. The dose-rate depth profile is obtained using a new TL equilibrium technique which is independent of the TL decay kinetics. The dose-rate depth profile produced by solar flare protons with a differential energy spectrum of the form dJ/dE = KE to the minus gamma power is calculated for arbitrary gamma. The best fit to the TL data in rock 14310 is obtained for gamma = 2.3 plus or minus 0.2 and an omnidirectional (4 pi) integral flux above 10 MeV of 40 to 80 prot/sq cm/sec. The TL half-life is determined to be 2000 yr. These results are compared to those for Na-22 (half-life of. 2.6 yr) and Al-26 (half-life of 740,000 yr) obtained by Wahlen et al. (1972) and Rancitelli et al. (1972), and it is concluded that the spectral shape and flux of protons in the interval from 25 to 100 MeV is the same within experimental errors when averaged over these three very different time periods.

Hoyt, H. P., Jr.; Walker, R. M.; Zimmerman, D. W.

1973-01-01

372

Multispacecraft Observations of Solar Flare Particles in the Inner Heliosphere  

NASA Technical Reports Server (NTRS)

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

Wibberenz, G.; Cane, H. V.

2007-01-01

373

Solar Eruption Model Relating CME Kinematics to Flare Emissions  

NASA Astrophysics Data System (ADS)

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

Moats, Stephanie; Reeves, K.

2010-05-01

374

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

375

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

376

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

377

Large solar flare radiation shielding requirements for manned interplanetary missions.  

PubMed

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

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

1989-01-01

378

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

NASA Astrophysics Data System (ADS)

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

Kaufmann, Pierre; Raulin, Jean-Pierre

379

Relationship between Magnetic Power Spectrum and Flare Productivity in Solar Active Regions  

Microsoft Academic Search

Power spectra of the line-of-sight magnetograms were calculated for 16 active regions of different flare activity. Data obtained by the Michelson Doppler Imager instrument on board the Solar and Heliospheric Observatory in high-resolution mode were used in this study. For each active region, the daily soft X-ray flare index, A, was calculated. This index characterizes the flare productivity of an

V. I. Abramenko

2005-01-01

380

GPS global detection of the ionospheric response to solar flares  

NASA Astrophysics Data System (ADS)

This author suggests the concept of a new technology for global detection (GLOBDET) of atmospheric disturbances of natural and technogenic origin, on the basis of phase measurements of the total electron content (TEC) in the ionosphere using an international GPS network. Temporal dependencies of TEC are obtained for a set of spaced receivers of the GPS network simultaneously for the entire set of "visible" (over a given time interval) GPS satellites (up to 5-10 satellites). These series are subjected to filtering in the selected range of oscillation periods using algorithms for spatiotemporal analysis of signals of nonequidistant GPS phased antenna arrays which are adequate to the detected disturbance. An analysis is made of the possibilities of using the GLOBDET when detecting the ionospheric response of solar flares. In this case it is best to make the coherent summation of the filtered series of TEC. Powerful impulsive flares of July 29, 1999, and December 28, 1999, were chosen to illustrate the practical implementation of the proposed method.

Afraimovich, E. L.

2000-11-01

381

Joule heating and runaway electron acceleration in a solar flare  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

382

MHD discontinuities in solar flares: continuous transitions and plasma heating  

NASA Astrophysics Data System (ADS)

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

Ledentsov, Leonid; Somov, Boris

383

RETURN CURRENTS AND ENERGY TRANSPORT IN THE SOLAR FLARING ATMOSPHERE  

SciTech Connect

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 [Dipartimento di Matematica, Universita di Genova, via Dodecaneso 35, I-16146 Genova (Italy)

2013-08-20

384

Electron versus Proton Timing Delays in Solar Flares  

E-print Network

Both electrons and ions are accelerated in solar flares and carry nonthermal energy from the acceleration site to the chromospheric energy loss site, but the relative amount of energy carried by electrons versus ions is subject of debate. In this {\\sl Letter} we test whether the observed energy-dependent timing delays of 20-200 keV HXR emission can be explained in terms of propagating electrons versus protons. For a typical flare, we show that the timing delays of fast ($\\lapprox 1$ s) {\\sl HXR pulses} is consistent with time-of-flight differences of directly precipitating electrons, while the timing delays of the {\\sl smooth HXR} flux is consistent with collisional deflection times of trapped electrons. We show that these HXR timing delays cannot be explained either by $\\le 1$ MeV protons (as proposed in a model by Simnett \\& Haines 1990), because of their longer propagation and trapping times, or by $\\approx 40$ MeV protons (which have the same velocity as $\\approx 20$ keV electrons), because of their longer trapping times and the excessive fluxes required to generate the HXRs. Thus, the HXR timing results clearly rule out protons as the primary generators of $\\ge 20$ keV HXR emission.

Markus J. Aschwanden

1996-07-31

385

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

386

Recent observations and theories of solar flares; Second Flares 22 Workshop, Ottawa, Canada, May 22-28, 1993  

NASA Technical Reports Server (NTRS)

A conference on recent observations and theories of solar flares produced papers in the areas of particle acceleration, energy storage, energy release, energy transport, and material ejection. The results from new ground-based and space-based facilities were also prominent in these papers.

Gaizauskas, Victor (editor); Machado, Marcus E. (editor)

1994-01-01

387

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

388

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

389

Solar Flare Element Abundances from the Solar Assembly for X-rays (SAX) on MESSENGER  

E-print Network

X-ray spectra in the range $1.5-8.5$~keV have been analyzed for 526 large flares detected with the Solar Assembly for X-rays (SAX) on the Mercury {\\em MESSENGER} spacecraft between 2007 and 2013. For each flare, the temperature and emission measure of the emitting plasma were determined from the spectrum of the continuum. In addition, with the SAX energy resolution of 0.6 keV (FWHM) at 6~keV, the intensities of the clearly resolved Fe-line complex at 6.7~keV and the Ca-line complex at 3.9~keV were determined, along with those of unresolved line complexes from S, Si, and Ar at lower energies. Comparisons of these line intensities with theoretical spectra allow the abundances of these elements relative to hydrogen to be derived, with uncertainties due to instrument calibration and the unknown temperature distribution of the emitting plasma. While significant deviations are found for the abundances of Fe and Ca from flare to flare, the abundances averaged over all flares are found to be enhanced over photospheri...

Dennis, B R; Schwartz, R A; Tolbert, A K; Starr, R D; Nittler, L R

2015-01-01

390

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

E-print Network

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

Eduard P. Kontar; Alexander L. MacKinnon

2005-06-05

391

Numerical modeling of the energy storage and release in solar flares  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

392

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

E-print Network

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

Daniele Fargion

2011-06-19

393

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

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

394

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

E-print Network

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

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

2014-01-01

395

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

396

DETERMINATION OF STOCHASTIC ACCELERATION MODEL CHARACTERISTICS IN SOLAR FLARES  

SciTech Connect

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

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

2013-11-01

397

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

SciTech Connect

Event-integrated fluxes of protons and alpha particles in solar-flare-associated particle events during solar cycle 21 (1976--1986) are determined from data obtained by detectors on board the IMP-7 and IMP-8 satellites. Sixty-three solar particle events with proton fluence (E>10 MeV)>10/sup 7/ cm/sup -2/ were identified from October 1972 to March 1987. The average omnidirectional flux of protons with kinetic energy>10 MeV for cycle 21, 64 cm/sup -2/ s/sup -1/, is lower than the corresponding number for cycle 20 (92 cm/sup -2/ s/sup -1/) based on satellite data and for the cycle 19 (378 cm/sup -2/ s/sup -1/) based on lunar sample data. Six large events contributed 70% of the total proton fluence during solar cycle 21. Several events in early 1981 with high proton fluences could account for much of the high /sup 56/Co radioactivities observed in the small-sized Salem meteorite. The event-averaged alpha-particle to proton ratio in the energy interval 1--10 MeV/nucleon varies from 0.006 to 0.05, with an average value of 0.02 for the whole cycle. The events during solar cycle 21 are characterized by softer spectra for both protons and alpha particles compared to those in earlier solar cycles. No definitive correlation exists between cycle-averaged solar flare proton fluxes and peak sunspot numbers. A comparison with long-term (million year) averaged data for these parameters, obtained from lunar sample data, shows that the contemporary solar flare proton spectra are characterized by softer spectra (lower R/sub 0/ values). A similar comparison cannot be made for the mean long-term averaged flux, as the contemporary average suffers from uncertainty due to statistics of single events.

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

1988-07-01

398

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

399

Discrepancies between empirical and theoretical models of the flaring solar chromosphere and their possible resolution  

NASA Technical Reports Server (NTRS)

Models of the solar chromosphere during flaring deduced theoretically or empirically are compared. Marked discrepancies are noted and various reasons are offered to explain their existence. A means is presented for testing theoretical heating models (electron heating) by analyzing the net energy loss rates in (observed) empirical atmospheres and inverting the flare energy equation to deduce the parameters of the supposed heating mechanism.

Emslie, G. A.; Brown, J. C.; Machado, M. E.

1980-01-01

400

EVIDENCES OF CHROMOSPHERIC EVAPORATIONS IN THE DECEMBER 1, 2004 SOLAR FLARE  

E-print Network

EVIDENCES OF CHROMOSPHERIC EVAPORATIONS IN THE DECEMBER 1, 2004 SOLAR FLARE ZONGJUN NING1 , WENDA and hard X-ray evidences of chromospheric evaporation during an M1.0 flare which occurred on December 1 explain these decimetric bursts in terms of chromospheric evaporation. On the other hand, RHESSI

401

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

NASA Technical Reports Server (NTRS)

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

Gosling, J. T.

1995-01-01

402

TRITIUM AND HELIUM3 IN SOLAR FLARES AND LOSS OF HELIUM FROM THE EARTH'S ATMOSPHERE  

Microsoft Academic Search

He³ and Ha³in the casing of the earth satellite Discoverer ; XVII flown following the Nov. 12, 1960, solar flare are probably due to the ; satellite intercepting some of the flare radiation. The results indicate that a ; large part of the He³ and a significant fraction of the H³ in the ; earth's atmosphere are accreted from the

E. Flamm; R. E. Lingenfelter; J. F. MacDonald; W. F. Libby

1962-01-01

403

Solar flare induced ionospheric D-region enhancements from VLF phase and amplitude observations  

Microsoft Academic Search

Ionospheric perturbations due to solar flares, measured at VLF in both phase and amplitude on long subionospheric paths, are used to determine the accompanying D-region electron density enhancements as a function of the flare X-ray fluxes measured by the GOES satellites. The electron densities are characterised by the two traditional parameters, H? and ? (being measures of the ionospheric height

Wayne M. McRae; Neil R. Thomson

2004-01-01

404

Solar flare proton rigidity spectra deduced from cosmic ray neutron monitor observations  

Microsoft Academic Search

The solar flare proton rigidity spectra for several flares occurring between 1967 and 1972 have been deduced from the ground level cosmic ray neutron monitor observations. To obtain consistent agreement for all the ground level events (GLE's) analyzed, the specific yield functions of Lockwood and Webber (1967) must be reduced slightly below P = 1.6 GV. The typical spectral indices

J. A. Lockwood; W. R. Webber; L. Hsieh

1974-01-01

405

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

E-print Network

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

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

2005-08-30

406

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

Microsoft Academic Search

High-resolution x-ray spectra of class M flares have been recorded by four Bragg crystal spectrometers (SOLFLEX = solar flare x-rays) flown by NRL on an Air Force spacecraft. The wavelength ranges are 1.82 to 1.97 A, 2.98 to 3.07 A, 3.14 to 3.24 A, and 8.26 to 8.53 A. Electron temperatures are derived from dielectronic satellite-line-to-resonance-line ratios as a function

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

1980-01-01

407

Are Solar Active Regions with Major Flares More Fractal, Multifractal, or Turbulent Than Others?  

NASA Astrophysics Data System (ADS)

Multiple recent investigations of solar magnetic-field measurements have raised claims that the scale-free (fractal) or multiscale (multifractal) parameters inferred from the studied magnetograms may help assess the eruptive potential of solar active regions, or may even help predict major flaring activity stemming from these regions. We investigate these claims here, by testing three widely used scale-free and multiscale parameters, namely, the fractal dimension, the multifractal structure function and its inertial-range exponent, and the turbulent power spectrum and its power-law index, on a comprehensive data set of 370 timeseries of active-region magnetograms (17 733 magnetograms in total) observed by SOHO’s Michelson Doppler Imager (MDI) over the entire Solar Cycle 23. We find that both flaring and non-flaring active regions exhibit significant fractality, multifractality, and non-Kolmogorov turbulence but none of the three tested parameters manages to distinguish active regions with major flares from flare-quiet ones. We also find that the multiscale parameters, but not the scale-free fractal dimension, depend sensitively on the spatial resolution and perhaps the observational characteristics of the studied magnetograms. Extending previous works, we attribute the flare-forecasting inability of fractal and multifractal parameters to i) a widespread multiscale complexity caused by a possible underlying self-organization in turbulent solar magnetic structures, flaring and non-flaring alike, and ii) a lack of correlation between the fractal properties of the photosphere and overlying layers, where solar eruptions occur. However useful for understanding solar magnetism, therefore, scale-free and multiscale measures may not be optimal tools for active-region characterization in terms of eruptive ability or, ultimately, for major solar-flare prediction.

Georgoulis, Manolis K.

2012-02-01

408

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

409

Upper limits on the solar-neutron flux at the Yangbajing neutron monitor from BATSE-detected solar flares  

E-print Network

The purpose of this work is to search the Yangbajing neutron monitor data obtained between 1998 October and 2000 June for solar neutrons associated with solar flares. Using the onset times of 166 BATSE-detected flares with the GOES peak flux (1 -- 8 \\AA) higher than $1.0 \\times 10^{-5}$ $\\mathrm{Wm^{-2}}$, we prepare for each flare a light curve of the Yangbajing neutron monitor, spanning $\\pm$ 1.5 hours from the BATSE onset time. Based on the light curves, a systematic search for solar neutrons in energies above 100 MeV from the 166 flares was performed. No statistically significant signals due to solar neutrons were found in the present work. Therefore, we put upper limits on the $>$ 100 MeV solar-neutron flux for 18 events consisting of 2 X and 16 M class flares. The calculation assumed a power-law shaped neutron energy spectrum and three types of neutron emission profiles at the Sun. Compared with the other positive neutron detections associated with X-class flares, typical 95% confidence level upper limits for the two X-class flares are found to be comparable to the lowest and second lowest neutron fluxes at the top of the atmosphere.In addition, the upper limits for M-class flares scatter in the range of $10^{-2}$ to 1 neutrons $\\mathrm{cm^{-2}s^{-1}}$. This provides the first upper limits on the solar-neutron flux from M-class solar flares, using space observatories as well as ground-based neutron monitors.

H. Tsuchiya; H. Miyasaka; E. Takahashi; S. Shimoda; Y. Yamada; I. Kondo; K. Makishima; F. Zhu; Y. Tan; H. Hu; Y. Tang; J. Zhang; H. Lu; X. Meng

2007-03-16

410

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

411

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

NASA Video Gallery

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

412

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

NASA Video Gallery

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

413

Particle Acceleration in Solar Flares and Enrichment of 3He and Heavy Ions  

E-print Network

We discuss possible mechanisms of acceleration of particles in solar flares and show that turbulence plays an important role in all the mechanism. It is also argued that stochastic particle acceleration by turbulent plasma waves is the most likely mechanism for production of the high energy electrons and ions responsible for observed radiative signatures of solar flares and for solar energetic particle or SEPs, and that the predictions of this model agrees well with many past and recent high spectral and temporal observations of solar flares. It is shown that, in addition, the model explains many features of SEPs that accompany flares. In particular we show that it can successfully explain the observed extreme enhancement, relative to photospheric values, of $^3$He ions and the relative spectra of $^3$He and $^4$He. It has also the potential of explaining the relative abundances of most ions including the increasing enhancements of heavy ions with ion mass or mass-to-charge ratio.

Vahe' Petrosian

2008-08-13

414

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

SciTech Connect

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

Bowen, Trevor A.; Testa, Paola; Reeves, Katharine K., E-mail: tbowen@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 58, Cambridge, MA 02138 (United States)

2013-06-20

415

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

NASA Astrophysics Data System (ADS)

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

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

2015-04-01

416

Recurrence of flare energy releases in solar active regions (Cycle 23)  

NASA Astrophysics Data System (ADS)

The following results have been achieved in this work. The distribution of the recurrence times of solar flare events is generally lognormal. The typical flare recurrence times at the cycle 23 minimum and maximum are different: the average times (100-200 min) are most typical of the maximum; at the same time, the minimum is simultaneously characterized by short (several tens of seconds) and long (from several hundreds to a thousand of minutes). The minimal flare recurrence time tends to decrease in an active region with increasing sunspot group area in this region. The average flare recurrence times in an active region have typical values of 120m, 210m, 300m, 400m, and 530m, which is close to the typical periods of long-period sunspot oscillations. The total number of flares in an active region depends on the sunspot area in this region and the flare energy release rate.

Nagovitsyn, Yu. A.; Kuleshova, A. I.

2013-12-01

417

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

NASA Astrophysics Data System (ADS)

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

Basak, Tamal; Chakrabarti, Sandip Kumar

418

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

NASA Astrophysics Data System (ADS)

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

Basak, Tamal; Chakrabarti, Sandip K.

2013-12-01

419

Study on Triggering Process of Solar Flares Based on Hinode/SOT Observations  

E-print Network

We investigated four major solar flare events that occurred in active regions NOAA 10930 (December 13 and 14, 2006) and NOAA 11158 (February 13 and 15, 2011) by using data observed by the Solar Optical Telescope (SOT) onboard the Hinode satellite. To reveal the trigger mechanism of solar flares, we analyzed the spatio-temporal correlation between the detailed magnetic field structure and the emission image of the Ca H line at the central part of flaring regions for several hours prior to the onset of flares. We observed in all the flare events that the magnetic shear angle in the flaring regions exceeded 70 degrees, as well as that characteristic magnetic disturbances developed at the centers of flaring regions in the pre-flare phase. These magnetic disturbances can be classified into two groups depending on the structure of their magnetic polarity inversion lines; the so-called "Opposite-Polarity" and "Reversed-Shear" magnetic field recently proposed by our group, although the magnetic disturbance in one eve...

Bamba, Y; Yamamoto, T T; Okamoto, T J

2013-01-01

420

High-temperature phase transition in a plasma and the mechanism of powerful solar flares  

E-print Network

It is shown that the high- temperature phase transition in a plasma gives the mechanism of transition from the highly conductive state to the highly resistive state of a plasma in the `electric circuit' model of solar flares which was first introduced by H.Alfven and P.Carlqvist in 1967. With this addendum, the modern version of the electric circuit model can explain both the fast dissipation of energy and the acceleration of particles in a solar flare.

Fedor V. Prigara

2006-05-04

421

10–100 keV electron acceleration and emission from solar flares  

Microsoft Academic Search

We present an analysis of spacecraft observations of non-thermal X-rays and escaping electrons for 5 selected small solar flares in 1967. OSO-3 multi-channel energetic X-ray measurements during the non-thermal component of the solar flare X-ray bursts are used to derive the parent electron spectrum and emission measure. IMP-4 and Explorer-35 observations of > 22 keV and > 45 keV electrons

R. P. Lin; H. S. Hudson

1971-01-01

422

Molecular Models Need to be Tested: The Case of a Solar Flares Discoidal HDL Model  

PubMed Central

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

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

2008-01-01

423

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

PubMed

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

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

2008-06-01

424

Power Laws in Solar Flares: Self-Organized Criticality or Turbulence?  

Microsoft Academic Search

The statistics of quiescent times tauL between successive bursts of solar flares activity, performed using 20 years of data, displays a power law distribution with exponent alpha~=2.4. This is an indication of an underlying complex dynamics with long correlation times. The observed scaling behavior is in contradiction with the self-organized criticality models of solar flares which predict Poisson-like statistics. Chaotic

Guido Boffetta; Vincenzo Carbone; Paolo Giuliani; Pierluigi Veltri; Angelo Vulpiani

1999-01-01

425

Directivity and its energy dependence in solar flare energetic emission  

NASA Technical Reports Server (NTRS)

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

Li, Peng

1995-01-01

426

THE SOLAR FLARE SULFUR ABUNDANCE FROM RESIK OBSERVATIONS  

SciTech Connect

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

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

2012-06-01

427

Flares and Antiflares on Young Solar Analog EK Draconis  

NASA Astrophysics Data System (ADS)

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

Ayres, Thomas R.

2015-01-01

428

Statistical properties of X-class flares and their relationship with super active regions during solar cycles 21-23  

NASA Astrophysics Data System (ADS)

We investigate the statistical distribution of X-class flares and their relationship with super active regions (SARs) during solar cycles 21-23. Analysis results show that X1.0-X1.9 flares accounted for 52.71 % of all X-class flares, with X2.0-X2.9 flares at 20.59 %, X3.0-X4.9 at 13.57 %, X5-X9.9 at 8.37 % and ? X10 at 4.75 %. All X-class flares occurred around the solar maximum during solar cycle 22, while in solar cycle 23, X-class flares were scattered in distribution. In solar cycle 21, X-class flares were distributed neither in a concentrated manner like cycle 22 nor in a scattered manner as cycle 23. During solar cycles 21-23, 32.2 % of the X1.0-X1.9 flares, 31.9 % of the X2.0-X2.9 flares, 43.3 % of the X3.0-X4.9 flares, 81.08 % of the X5.0-X9.9 flares, and 95.2 % of the ? X10 flares were produced by SARs.

Le, Guiming; Yang, Xingxing; Liu, Yonghua; Li, Peng; Yin, Zhiqiang; Chen, Yulin

2014-04-01

429

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

NASA Technical Reports Server (NTRS)

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

Das, Uma; Pallamraju, Duggirala; Chakrabarti, Supriya

2010-01-01

430

20Measuring the Speed of a Solar Tsunami! Moments after a major class X-6 solar flare  

E-print Network

20Measuring the Speed of a Solar Tsunami! Moments after a major class X-6 solar flare erupted at 18:43 captured a movie of a shock wave 'tsunami' emerging from Sunspot 930 and traveling across the solar surface be seen. You can watch the entire movie and see it more clearly (http

431

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

NASA Astrophysics Data System (ADS)

Recent work has shown that power-law-like Fourier power spectra are an intrinsic property of solar and stellar flare signals, similarly to other astrophysical objects such as gamma-ray bursts and magnetars. It is therefore critical to account for this in order to understand the nature and significance of short-timescale fluctuations in flares.We present the results of a Bayesian model comparison method for investigating flare time series, fully considering these Fourier power-law properties. Using data from the PROBA2/Large Yield Radiometer, Fermi/Gamma-ray Burst Monitor, Nobeyama Radioheliograph, and Yohkoh/HXT instruments, we study a selection of flares from the literature identified as 'quasi-periodic puslation (QPP)' events. While emphasising that the observed fluctuations are real and of solar origin, we find that, for all but one event tested, an explicit oscillation is not required to explain the observations. Instead, the observed flare signals are adequately described as a manifestation of a power law in the Fourier power spectrum. This evaluation of the QPP phenomenon is markedly different from much of the prior literature.We conclude that the prevalence of oscillatory signatures in solar and stellar flares may be less than previously believed. Furthermore, studying the slope of the observed Fourier power spectrum as a function of energy may provide us with a diagnostic window into the fundamental nature of solar flares.

Inglis, Andrew; Ireland, Jack; Dominique, Marie

2015-04-01

432

Correction of SOHO CELIAS/SEM EUV Measurements saturated by extreme solar flare events  

E-print Network

The solar irradiance in the Extreme Ultraviolet (EUV) spectral bands has been observed with a 15 sec cadence by the SOHO Solar EUV Monitor (SEM) since 1995. During remarkably intense solar flares the SEM EUV measurements are saturated in the central (zero) order channel (0.1 -- 50.0 nm) by the flare soft X-ray and EUV flux. The first order EUV channel (26 -- 34 nm) is not saturated by the flare flux because of its limited bandwidth, but it is sensitive to the arrival of Solar Energetic Particles (SEP). While both channels detect nearly equal SEP fluxes, their contributions to the count rate is sensibly negligible in the zero order channel but must be accounted for and removed from the first channel count rate. SEP contribution to the measured SEM signals usually follows the EUV peak for the gradual solar flare events. Correcting the extreme solar flare SEM EUV measurements may reveal currently unclear relations between the flare magnitude, dynamics observed in different EUV spectral bands, and the measured Earth atmosphere response. A simple and effective correction technique based on analysis of SEM count-rate profiles, GOES X-ray, and GOES proton data has been developed and used for correcting EUV measurements for the five extreme solar flare events of July 14, 2000, October 28, November 2, November 4, 2003, and January 20, 2005. Although none of the 2000 and 2003 flare peaks were contaminated by the presence of SEPs, the January 20, 2005 SEPs were unusually prompt and contaminated the peak. The estimated accuracy of the correction is about 7.5% for large X-class events.

L. V. Didkovsky; D. L. Judge; A. R. Jones; S. Wieman; B. T. Tsurutani; D. McMullin

2006-10-04

433

Forecasting SEP events with same active region prior flares  

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

434

Flare Clustering  

NASA Astrophysics Data System (ADS)

In this study we tested for groups of flares (flare clusters) in which successive flares occur within a fixed time - the linking window. The data set used is the flare waiting times provided by the X-ray flare detectors on the Geostationary Operational Environmental Satellites (GOES). The study was limited to flares of magnitude C5 and greater obtained during cycle 23. While many flares in a cluster may come from the same active region, the larger clusters often have origins in multiple regions. The longest cluster of the last cycle lasted more than 42 days with an average time separation between successive flares of 5 hours, where no two flares were separated by more than 36 hours. The flare rate in clusters is 4 to 6 time greater than the rate in solar maximum outside of flares. The are indications that flare clustering is associated with periods of multiple sunspo