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1

Accepted by ApJ. Periodicities in Solar Flare Occurrence  

E-print Network

Accepted by ApJ. Periodicities in Solar Flare Occurrence: Analysis of Cycles 19­23 T. Bai Stanford University, Stanford, CA 94305 bai@quake.stanford.edu ABSTRACT Mid-range periodicities in solar flare spectra of major flare occurrence times for the time intervals analyzed by Ozguc & Atac and Bai, strongest

Bai, Taeil

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 ...

Verlengia, Mrs.

2011-12-10

3

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

4

Classification of solar flares  

NASA Technical Reports Server (NTRS)

The historical background of solar flare classification before the SMM launch is reviewed along with recent developments made by observations with SMM, Hinotori, and other contemporary satellite and ground-based observations. Based on these recent findings, solar flares are grouped into five classes: thermal hard X-ray flares, nonthermal hard X-ray flares, impulsive gamma-ray/proton flares, gradual gamma-ray/proton flares, and quiescent filament-eruption flares. The roles of filament eruptions in flare development are examined, and theoretical ideas related to processes occurring in different flare classes are discussed.

Bai, T.; Sturrock, P. A.

1989-01-01

5

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

6

Flare activity and the strength of solar cycles  

Microsoft Academic Search

The paper evaluates the solar flare activity during the last three 11-year cycles (the period 1976 - 2001). The flare occurrence follows the solar cycle (SC) with some particularities for each class of flares and with unexpected \\

Miruna Daniela Popescu; Georgeta Maris; Adrian Oncica; Marilena Mierla

2002-01-01

7

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

NASA Astrophysics Data System (ADS)

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

Song, Qiwu; Huang, Guangli; Huang, Yu

2013-09-01

8

Solar Flare Theory  

NSDL National Science Digital Library

This site offers information related to solar flares. It discusses what a solar flare is, why they are important, and the study of solar flares in hard x-ray. There are many pictures, more websites, and animations in this website. For teachers there is a section with helpful activities

Holman, Gordon

2005-06-07

9

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

NASA Technical Reports Server (NTRS)

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

Bai, T.

1993-01-01

10

Solar flare particle radiation  

NASA Technical Reports Server (NTRS)

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

Lanzerotti, L. J.

1972-01-01

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

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

13

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

14

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

15

Using subsurface helicity measurements to predict flare occurrence  

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

16

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

17

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

18

Soft X-ray solar flare cycles  

Microsoft Academic Search

We present a statistical investigation of soft X-ray (SXR) solar flare occurrence over the last three 11-yr solar cycles (SCs 21-23, corresponding to the period 1976-2003). We studied not only the monthly number of flares, but we also used an index that estimate the energy emitted by flares in the SXR 1-8 Å band (Q_{x}) that we find it better

Georgeta Maris; Miruna Daniela Popescu; Marilena Mierla

2004-01-01

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

Solar Flares--Solar Prominences  

NSDL National Science Digital Library

This colorful Hyperphysics page describes solar flares and prominences and features an image of a particularly large prominence, which is described in the text. The page supplies information on how prominences form.

Nave, Carl R.

2013-03-29

21

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

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

Solar and Stellar Flares  

Microsoft Academic Search

Flares in the atmosphere of the Sun and of many other stars appear to result from the sudden conversion of electromagnetic field energy into a wide array of observable forms. Of these products the definitive modern observations are the X-rays and gamma-rays, signifying the common occurrence of particle acceleration to mildly relativistic or higher energies. Abundant direct (the radiation) and

Hugh Hudson

2011-01-01

24

Solar Flares and particle acceleration  

E-print Network

Solar Flares and particle acceleration Eduard Kontar School of Physics and Astronomy University of Glasgow, UK STFC Summer School, Armagh, 2012 #12;Solar flares: basics X-raysradiowavesParticles1AU Figure and accelerated particles #12;Solar flares and accelerated particles From Emslie et al., 2004, 2005 Free magnetic

25

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

26

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

27

Burst phenomena in solar flares  

Microsoft Academic Search

Solar flares are rapid dissipative processes in which the energy accumulated in the magnetic field is released in the forms of plasma heating, explosive plasma flows with flare shock generations, particle accelerations, and emissions in a very broad range of frequencies ranging from radio waves up to gamma-rays. As solar flares and related phenomena influence not only the processes in

P. Kotrc; Yu. A. Kupryakov; J. Jurcák

2002-01-01

28

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

29

Hard Solar Flare Radiations  

NASA Astrophysics Data System (ADS)

The space craft measurements during a solar flare demonstrate that electron precipitation with energy up to hundreds keV along the magnetic field lines to solar surface takes place. Precipitation of these particles on the solar surface is analogous with particle precipitation in aurora, but the energy in aurora is not so big. The thermal source of X-ray radiation in the corona appears above an active region. Such scenario of the flare is explained by electrodynamical solar flare model based on 3D MHD numerical simulation that demonstrate the energy accumulated in a current sheet can exceed 1e32 erg. The coronal source appears in the current sheet during fast energy release due to magnetic reconnection. The electron beams are accelerated in the field-aligned currents that generated by the Hall electric field produced in the current sheet. The development of neutron monitor data demonstrates two components of solar cosmic rays. The prompt cosmic ray component is generated during main energy release. This component consists of protons moving along the interplanetary magnetic lines. The exponential spectrum of these protons is in agreement with particle acceleration by the Lorenz electric field along the magnetic singular line in a current sheet. The similar effect has been observed in the laboratory experiments with high power discharge - pinch discharge. The similarity and difference of particle acceleration in a linear pinch effect and in the current sheet is discussed. The flares produce also a delayed component with power spectrum E^{-gamma} with gamma ~ 5. Such big gamma is difficult to explain by acceleration in a shock. Apparently, the delayed component spectrum is formed during particle diffusion in the turbulent magnetic field.

Podgorny, I.; Podgorny, A.; Vashenyuk, E.

2008-09-01

30

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

31

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

32

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

33

Solar flare alpha particles  

NASA Technical Reports Server (NTRS)

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

Lanzerotti, L. J.

1973-01-01

34

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

35

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

36

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

37

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

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

Nuclear processes in solar flares  

SciTech Connect

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.

1982-03-01

40

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

41

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

42

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

43

Particle acceleration in solar flares  

NASA Technical Reports Server (NTRS)

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

Ramaty, R.; Forman, M. A.

1987-01-01

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

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

46

Solar flare predictions and warnings  

NASA Technical Reports Server (NTRS)

The real-time solar monitoring information supplied to support SPARCS equipped rocket launches, the routine collection and analysis of 3.3-mm solar radio maps, short-term flare forecasts based on these maps, longer-term forecasts based on the recurrence of active regions, and an extension of the flare forecasting technique are summarized. Forecasts for expectation of a solar flare of class or = 2F are given and compared with observed flares. A total of 52 plage regions produced all the flares of class or = 1N during the study period. The following results are indicated: of the total of 21 positive forecasts, 3 were correct and 18 were incorrect; of the total of 31 negative forecasts, 3 were incorrect and 28 were correct; of a total of 6 plage regions producing large flares, 3 were correctly forecast and 3 were missed; and of 46 regions not producing any large flares, 18 were incorrectly forecast and 28 were correctly forecast.

White, K. P., III

1972-01-01

47

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

48

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

49

Radiation hydrodynamics in solar flares  

SciTech Connect

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

Fisher, G.H.

1985-10-18

50

Solar flare predictions and warnings  

NASA Technical Reports Server (NTRS)

The real-time solar monitoring information supplied to support SPARCS-equipped rocket launches, the routine collection and analysis of 3.3-mm solar radio maps, short-term flare forecasts based on these maps, longer-term forecasts based on the recurrence of active regions, and results of the synoptic study of solar active regions at 3.3-mm wavelength are presented. Forecasted flares in the 24-hour forecasts were 81% accurate, and those in the 28-day forecasts were 97% accurate. Synoptic radio maps at 3.3-mm wavelength are presented for twenty-three solar rotations in 1967 and 1968, as well as synoptic flare charts for the same period.

White, K. P., III; Mayfield, E. B.

1973-01-01

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 1 #12;2 1. Introduction The physics of solar flares seems too broad a subject to review adequately

Hudson, Hugh

52

Mass ejections. [during solar flares  

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

53

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

54

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

55

Energetic particles in solar flares  

NASA Technical Reports Server (NTRS)

The principal properties of energetic particles accelerated in solar flares are reviewed. Particular emphasis is placed on the high-energy flare component whose acceleration is often referred to as second-phase acceleration. Stochastic Fermi acceleration is treated analytically, and the results of the computation are compared with particle and gamma-ray data to deduce information on the timing of the acceleration, the spectrum of the particles, and the energy content of the nucleonic component. A discussion of He-3 and heavy element abundances is also presented.

Ramaty, R.

1979-01-01

56

Cycle 23 Variation in Solar Flare Productivity  

E-print Network

The NOAA listings of solar flares in cycles 21-24, including the GOES soft X-ray magnitudes, enable a simple determination of the number of flares each flaring active region produces over its lifetime. We have studied this measure of flare productivity over the interval 1975-2012. The annual averages of flare productivity remained approximately constant during cycles 21 and 22, at about two reported M or X flares per region, but then increased significantly in the declining phase of cycle 23 (the years 2004-2005). We have confirmed this by using the independent RHESSI flare catalog to check the NOAA events listings where possible. We note that this measure of solar activity does not correlate with the solar cycle. The anomalous peak in flare productivity immediately preceded the long solar minimum between cycles 23 and 24.

Hudson, Hugh; McTiernan, Jim

2014-01-01

57

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

58

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

59

Pulsed acceleration in solar flares  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

60

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

61

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

62

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

63

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 elm-2) and reaches the maximum at 10 TECU/h during M-class flares and 10 TECU/h and 40 TECU/h for X-class flares. ISFAI is closely correlated with the 26-34 nm extreme ultraviolet flux but poorly related to the 0.1-0.8 nm X-ray flux. The central meridian distance (CMD) of flare location is an important reason for depressing relationship between ISFAI and X-ray Flux. Through the CMD effect modification, the ISFAI has a significant dependence on the X-ray flux with a correlation coefficient of 0.76. The ISFAI sensitivity enables to detect the extreme X-class flares, as well as the variations of one order of magnitude or even smaller (such as for C-class flares). Meanwhile, ISFAI is helpful to the calibration of the X-ray flux at 0.1-0.8 nm observed by GOES during some flares. In addition, statistical results demonstrate that ISFAI can detect 80% of all M-class flares and 92% for all X-class ones during 1996-2008. Owing to the high sensitivity and temporal resolution, ISFAI can be utilized as a solar flare detection parameter to monitor space weather.

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

64

Magnetic reconnection configurations and particle acceleration in solar flares  

E-print Network

types of solar flares. Upper panel: two-ribbon flares; Lower panel: compact flares. The color showsMagnetic 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

Chen, P. F.

65

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

66

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

67

Transition Region Luminosities of Solar Flares  

NASA Astrophysics Data System (ADS)

The energy released in a solar flare includes contributions from both thermal and nonthermal particle motions. We estimate the transition region luminosity during the impulsive phase of solar flares using SOHO/UVCS observations of O VI photons scattered by the corona. GOES data is used to analyze the thermal X-ray emission of the flare, and we use these results to compare the transition region and X-ray luminosities of the flare. This study increases the event sample size by a factor of 5 from a previous study by Raymond et al. (2007) and includes events behind the limb.

Johnson, H.; Raymond, J. C.; Murphy, N. A.

2010-12-01

68

A 154 day periodicity in the occurrence rate of proton flares  

NASA Technical Reports Server (NTRS)

We have analyzed periodicities in the occurrence rate of proton flares for solar cycles 19 through 21 (1955 to 1986) and have identified two epochs that exhibit a 154-day periodicity. These epochs are a 14-year interval from 1958 January through 1971 December and a 5.5-year interval from 1978 February to 1983 August. The best-determined period is 154.6. We have found that the phase of this periodicity changed between the above-mentioned two epochs by about one half of a period. It appears that the occurrence rate of proton flares is more sensitive to the 154-day periodicity than the occurrence rate of flares selected by other criteria.

Bai, Taeil; Cliver, E. W.

1990-01-01

69

A statistic study of ionospheric solar flare activity indicator  

NASA Astrophysics Data System (ADS)

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

70

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

71

Sunquakes: helioseismic response to solar flares  

E-print Network

Sunquakes observed in the form of expanding wave ripples on the surface of the Sun during solar flares represent packets of acoustic waves excited by flare impacts and traveling through the solar interior. The excitation impacts strongly correlate with the impulsive flare phase, and are caused by the energy and momentum transported from the energy release sites. The flare energy is released in the form of energetic particles, waves, mass motions, and radiation. However, the exact mechanism of the localized hydrodynamic impacts which generate sunquakes is unknown. Solving the problem of the sunquake mechanism will substantially improve our understanding of the flare physics. In addition, sunquakes offer a unique opportunity for studying the interaction of acoustic waves with magnetic fields and flows in flaring active regions, and for developing new approaches to helioseismic acoustic tomography.

Kosovichev, Alexander G

2014-01-01

72

Explosive evaporation in solar flares  

NASA Technical Reports Server (NTRS)

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

Fisher, George H.

1987-01-01

73

Transient particle acceleration associated with solar flares  

NASA Technical Reports Server (NTRS)

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

Chupp, E. L.

1990-01-01

74

Model solar flares and their homologous behavior  

Microsoft Academic Search

A model describing physical processes of solar flares and their homologous behavior is presented based on resistive MHD simulations of magnetic arcade evolution subject to continuous shear-increasing footpoint motions. It is proposed in the model that the individual flaring process encompasses magnetic reconnection of arcade field lines, generation of magnetic islands in the magnetic arcade, and coalescence of magnetic islands.

G. S. Choe; C. Z. Cheng

2000-01-01

75

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

76

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

77

Composition of energetic particles from solar flares  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

78

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

79

Bayesian model comparison of solar flare spectra  

NASA Astrophysics Data System (ADS)

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

Ireland, J.; Holman, G.

2012-12-01

80

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

81

Secular variations in solar flare proton fluxes  

NASA Technical Reports Server (NTRS)

Proton fluences in contemporary solar-flare events (1965-82) are analyzed to obtain values of average flux and characteristic rigidity R0 (MV). Both proton fluences F (E greater than 10MeV) and R0 (in the energy interval 10-30 MeV) values for individual events follow log-normal distribution. Comparison of contemporary average flux and R0 values with long-term averaged values, based on lunar sample data, indicate that the ancient solar-flare proton spectra were harder compared to that observed in contemporary flares. The contemporary and long-term (greater than 10,000 yr) averaged fluxes are similar, although such a comparison may not be meaningful because the contemporary averages suffer from uncertainty due to statistics of a single event. The long-term average data suggests a secular variation in solar-flare activity with enhanced proton fluxes during the last 100,000 years.

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

1983-01-01

82

Magnetic Variations Associated With Solar Flares  

NASA Technical Reports Server (NTRS)

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

Petrosian, Vahe

2005-01-01

83

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

84

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

85

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

86

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

87

An Observational Overview of Solar Flares  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

88

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

89

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

90

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

91

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

92

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

93

When and where to look to observe major solar flares  

NASA Technical Reports Server (NTRS)

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

Bai, T.

1989-01-01

94

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

95

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

96

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 of the electron energy spectrum during solar flares. It turns out that the model reproduces the soft: magnetic fields PACS: 96.60.qe, 96.50.Pw, 96.60.Hv 1 Introduction Particle acceleration in solar flares

Chen, P. F.

97

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

98

On Solar Flares and Cycle 23  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

99

Solar flare gamma-ray line shapes  

NASA Technical Reports Server (NTRS)

A computer code has been developed which is used to calculate ab initio the laboratory shapes and energy shifts of gamma-ray lines from (C-12)(p, gamma/4.438/)p-prime(C-12) and (O-16)(p, gamma/6.129/)p-prime(O-16) reactions and to calculate the expected shapes of these lines from solar flares. The sensitivity of observable solar flare gamma-ray line shapes to the directionality of the incident particles is investigated for several projectile angular distributions. Shapes of the carbon and oxygen lines are calculated assuming realistic proton energy spectra for particles in circular orbits at the mirror points of magnetic loops, for particle beams directed downward into the photosphere, and for isotropic particle distributions. Line shapes for flare sites near the center of the sun and on the limb are shown for both thin-target and thick-target interaction models.

Werntz, C.; Kim, Y. E.; Lang, Frederick L.

1990-01-01

100

Investigations of turbulent motions and particle acceleration in solar flares  

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

101

The influence of active region information on the prediction of solar flares: an empirical model using data mining  

NASA Astrophysics Data System (ADS)

Predicting the occurrence of solar flares is a challenge of great importance for many space weather scientists and users. We introduce a data mining approach, called Behavior Pattern Learning (BPL), for automatically discovering correlations between solar flares and active region data, in order to predict the former. The goal of BPL is to predict the interval of time to the next solar flare and provide a confidence value for the associated prediction. The discovered correlations are described in terms of easy-to-read rules. The results indicate that active region dynamics is essential for predicting solar flares.

Núñez, M.; Fidalgo, R.; Baena, M.; Morales, R.

2005-11-01

102

Solar flare X-ray polarimetry  

NASA Technical Reports Server (NTRS)

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

Chanan, G. A.; Novick, R.

1986-01-01

103

Absolute Abundance Measurements in Solar Flares  

NASA Astrophysics Data System (ADS)

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

Warren, Harry

2014-06-01

104

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

105

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

106

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

107

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

108

SORCE Monitors Solar Variability during Record Solar Flares  

NSDL National Science Digital Library

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

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

2004-02-20

109

SORCE Monitors Solar Variability during Record Solar Flares - Video version  

NSDL National Science Digital Library

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

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

2004-02-20

110

Global aspects of solar flares  

NASA Astrophysics Data System (ADS)

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

Melrose, Don

2013-06-01

111

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

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 observed on November 3, 2003. This flare was rated as 'X3.9' making it an extremely powerful event

113

X-Class: A Guide to Solar Flares  

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...

114

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

115

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

116

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

117

A solar tornado triggered by flares?  

E-print Network

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

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

2012-01-01

118

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.

119

Solar activity parameters and their interrelationship: Continuous decrease in flare activity from solar cycles 20 to 23  

NASA Astrophysics Data System (ADS)

The paper gives an insight regarding the interrelationship among a variety of solar activity (SA) parameters. A detailed correlative study has been performed using the monthly data of various solar activity parameters, for example, sunspot numbers (SSN), solar flux (SF, 10.7 cm), grouped solar flares (GSF), solar flare index (SFI), coronal index (CI), and tilt angle (TA) for the solar cycles 19 to 23, the present cycle. Though in general SSN shows a high degree of correlation with other SA parameters, the relationship between SSN and flare indices (GSF and SFI) is not straightforward. The slope of the regression lines between SSN and GSF (for cycles 20 to 23) and those between SSN and SFI (for cycles 21 to 23) is found to decrease continuously with the progression of cycles, without any associated unidirectional change in the correlation coefficient between these indices. In conformity, the similar feature is also observed from the peak values of SSN and flare indices. It is not seen, however, in the case of other SA parameters. The different trend of regression lines between SSN-GSF and SSN-SFI has been explained on the basis of the duration of the major solar flares. The present analysis also includes the statistical/numerical investigations of the occurrence of flares (imp ? 1B) over the span of solar cycles 20 to 23. These findings shed new light on the underlying physical processes responsible for solar activity and their generic relationship.

Gupta, Meera; Mishra, V. K.; Mishra, A. P.

2007-05-01

120

A phenomenological model of solar flares  

NASA Technical Reports Server (NTRS)

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

Colgate, S. A.

1978-01-01

121

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

122

Impulsive phase explosive dynamics. [of solar flares  

NASA Technical Reports Server (NTRS)

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

Canfield, Richard C.

1986-01-01

123

Explosive plasma flows in a solar flare  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

124

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

125

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

126

Investigating ``Precursor Flows'' in Solar Flares  

NASA Astrophysics Data System (ADS)

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

Newton, Elizabeth K.

1997-07-01

127

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

128

Solar Flare Photons and Energetic Particles in Space  

Microsoft Academic Search

I review the evolution of research on solar energetic particle events, beginning with Forbush's report of the ground level event of 1946, through the most recent observations of the Advanced Composition Explorer (ACE). The emphasis is on research that attempted to link solar flare electromagnetic emissions with the solar energetic particles (SEPs) observed in space following flares. The evolution of

E. W. Cliver

2006-01-01

129

Acceleration of electrons during the flash phase of solar flares  

NASA Technical Reports Server (NTRS)

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

Kane, S. R.

1974-01-01

130

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

131

Influence of solar flares on the X-ray corona  

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

132

A slingshot model for solar flares  

NASA Technical Reports Server (NTRS)

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

Benford, Gregory

1991-01-01

133

Relationships Between Photospheric Flows and Solar Flares  

NASA Astrophysics Data System (ADS)

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

Welsch, B. T.; Li, Y.

2013-12-01

134

Model solar flares and their homologous behavior  

NASA Astrophysics Data System (ADS)

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

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

2000-01-01

135

The impact of solar flares and magnetic storms on humans  

SciTech Connect

Photon radiation from solar flares, solar energetic particles, and inhomogeneities in the solar wind that drives magnetic storms are presently considered from the viewpoint of their effects on human society. Attention is given to solar-flare RF blackout effects, the penetration of high-energy particles into living tissues, and the earth's response to blasts of solar wind, through energization of populations of magnetospheric electrons and ions. 8 refs.

Joselyn, J.A. (NOAA, Space Environment Lab., Boulder, CO (United States))

1992-02-01

136

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

137

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

138

Gamma ray emission and solar flares  

NASA Technical Reports Server (NTRS)

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

Lin, R. P.; Ramaty, R.

1978-01-01

139

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

140

SDO's View of May 5, 2010 Solar Flare - With Timeline  

NASA Video Gallery

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

141

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

142

Spectrum synthesis of EUV solar flare line profiles  

NASA Technical Reports Server (NTRS)

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

Tripp, D. A.

1980-01-01

143

Spectrum synthesis of EUV solar flare line profiles  

NASA Astrophysics Data System (ADS)

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

Tripp, D. A.

1980-07-01

144

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

145

Stochastic Fermi acceleration in solar flares  

NASA Technical Reports Server (NTRS)

Proton spectra, valid from non- to ultra-relativistic energies, resulting from stochastic Fermi acceleration in solar flares are calculated. These spectra were obtained by numerically solving the Fokker-Planck equation, in which the escape of the particles from the acceleration region is characterized by an energy-independent escape time. In addition to equilibrium spectra, time-dependent energy spectra showing the approach to equilibrium are also presented. These numerical equilibrium spectra are compared with previous results which were obtained either by Monte Carlo simulations or approximate analytical treatments. There are no analytic solutions valid in the transrelativistic regime, which is very important for the production of pions and neutrons in solar flares. The acceleration efficiency is related to physical parameters, in particular the energy density in either magnetosonic or Alfven waves, and a lower limit is placed on either of these energy densities from acceleration times implied by gamma-ray observations. Also discussed is the physical interpretation of the escape time.

Miller, James A.; Guessoum, Nidhal; Ramaty, Reuven

1990-01-01

146

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

147

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

148

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

149

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

E-print Network

the observed statistical properties of solar flaring activity. In Section 2. the basic results of the statistical studies of the solar flaring activity are presented, together with a discussion on the MHD and CA Solar flares as complex dynamical systems Solar flares are the manifestation of an energy release

Anastasiadis, Anastasios

150

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

151

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

152

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

153

The Energetics of a Flaring Solar Active Region, and Observed Flare Statistics  

E-print Network

A stochastic model for the energy of a flaring solar active region is presented, generalising and extending the approach of Wheatland & Glukhov (1998). The probability distribution for the free energy of an active region is described by the solution to a master equation involving deterministic energy input and random jump transitions downwards in energy (solar flares). It is shown how two observable distributions, the flare frequency-energy distribution and the flare waiting-time distribution, may be derived from the steady-state solution to the master equation, for given choices for the energy input and for the rates of flare transitions. An efficient method of numerical solution of the steady-state master equation is presented. Solutions appropriate for flaring, involving a constant rate of energy input and power-law distributed jump transition rates, are numerically investigated. The flare-like solutions exhibit power-law flare frequency-energy distributions below a high energy rollover, set by the largest energy the active region is likely to have. The solutions also exhibit approximately exponential (i.e. Poisson) waiting-time distributions, despite the rate of flaring depending on the free energy of the system.

M. S. Wheatland

2008-02-26

154

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

155

Investigations of turbulent and directed motions in solar flares  

NASA Technical Reports Server (NTRS)

A method is presented for fitting asymmetric line profiles from spectrally resolved observations of solar flares obtained during the past solar maximum. The method is applied to more than 40 flares observed with the Bent Crystal Spectrometer on the Solar Maximum Mission. Correlations between turbulent and directed motions are discussed. From ratios of Ca XIX and Fe XXV line intensities, the temperature of the upflowing component is inferred separately from the stationary component.

Lemen, J. R.; Fludra, A.; Jakimiec, J.

1988-01-01

156

Filament eruptions and the impulsive phase of solar flares  

Microsoft Academic Search

Filament motion during the onset of the solar flare impulsive phase is examined. The impulsive phase onset is established from profiles of about 30 keV X-ray fluxes and the rapid flare brightenings characteristic of the H-alpha flash phase. The filament motion begins several minutes before the impulsive or flash phase of the flare. No new accleration is observed in the

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

1988-01-01

157

Impact of flares on the solar terrestrial environment  

SciTech Connect

The current knowledge of the flare process and its particle and photon emissions is summarized. The impact of flares on the different regions of the solar-terrestrial environment, in order of their distance from the Sun to Earth: the heliosphere, the magnetosphere, the ionosphere, and atmosphere are considered. The effect of flares on modern technology and manned spaceflight is described. In all cases, an attempt is made to distinguish clearly what is known, what is suspected, and is unknown.

Not Available

1984-06-01

158

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

159

An interacting loop model for solar flare bursts  

NASA Technical Reports Server (NTRS)

A schematic model is presented which attempts to explain the quasi-periodic behavior (on a timescale of less than or approximately equal to 10 s) frequency observed in solar hard X-ray bursts. It is shown how, as a result of the strong heating produced during a solar flare burst, the local gas pressure can transiently attain very large values in regions corresponding to the upper preflare chromosphere. 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, non-flaring, 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

160

Flares as fingerprints of inner solar darkness  

E-print Network

X-ray flares and other solar brightenings have been discarded as potential axion signatures. An axion X-ray signal must appear exclusively near the disk centre, and its spectrum must peak at ~4.2keV, contrary to observation. We argue here that due to Compton scattering off the (plasma) electrons the outward propagation of X-rays from axions converted near the Sun's surface can explain energy distribution and non direcivity. Simulation points at the photosphere as the birth place of the presumed axion conversion, implying an axion rest mass of ~0.01eV. At present, even optimistic parameter values can not reproduce the measured intensities. The simulated photon spectrum peaks at low energies. Quiet Sun hard X-rays are in favour of massive and/or light axion involvement.

K. Zioutas; M. Tsagri; Y. Semertzidis; T. Papaevangelou

2008-08-11

161

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

162

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

163

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

164

Correlation between solar flare productivity and photospheric vector magnetic fields  

NASA Astrophysics Data System (ADS)

Studying the statistical correlation between the solar flare productivity and photospheric magnetic fields is very important and necessary. It is helpful to set up a practical flare forecast model based on magnetic properties and improve the physical understanding of solar flare eruptions. In the previous study ([Cui, Y.M., Li, R., Zhang, L.Y., He, Y.L., Wang, H.N. Correlation between solar flare productivity and photospheric magnetic field properties 1. Maximum horizontal gradient, length of neutral line, number of singular points. Sol. Phys. 237, 45 59, 2006]; from now on we refer to this paper as ‘Paper I’), three measures of the maximum horizontal gradient, the length of the neutral line, and the number of singular points are computed from 23990 SOHO/MDI longitudinal magnetograms. The statistical relationship between the solar flare productivity and these three measures is well fitted with sigmoid functions. In the current work, the three measures of the length of strong-shear neutral line, total unsigned current, and total unsigned current helicity are computed from 1353 vector magnetograms observed at Huairou Solar Observing Station. The relationship between the solar flare productivity and the current three measures can also be well fitted with sigmoid functions. These results are expected to be beneficial to future operational flare forecasting models.

Cui, Yanmei; Wang, Huaning

2008-11-01

165

A Model of Solar Flares and Their Homologous Behavior  

Microsoft Academic Search

A model describing physical processes of solar flares and their homologous behavior is proposed based on resistive MHD simulations of magnetic arcade evolution. The individual flaring process encompasses magnetic reconnection of arcade field, generation of magnetic islands, and coalescence of magnetic islands. When the magnetic shear of the arcade field is increased over a threshold (via footpoint motion or flux

C. Z. Cheng; G. S. Choe

2000-01-01

166

A Model of Solar Flares and Their Homologous Behavior  

Microsoft Academic Search

A model describing physical processes of solar flares and their homologous behavior is presented based on resistive MHD simulations of magnetic arcade evolution subject to continuous shear-increasing footpoint motions. It is proposed in our model that the individual flaring process encompasses magnetic reconnection of arcade field lines, generation of magnetic islands in the magnetic arcade, and coalescence of magnetic islands.

G. S. Choe; C. Z. Cheng

2000-01-01

167

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

168

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

169

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

170

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

171

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

172

The probability of SWF occurrence in relation to solar activity  

NASA Technical Reports Server (NTRS)

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

Morozova, L. P.

1989-01-01

173

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

174

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

175

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

176

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

177

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

178

Magnetic Field Evolution Leading to Solar Flares II. Cases with High Magnetic Shear and Flare-Related Shear Change  

NASA Astrophysics Data System (ADS)

Following Paper I in which we considered five solar flares, we have selected another three solar flares greater than GOES X-ray class M/H? importance 1. The three active regions discussed here are characterized by high magnetic shear. We investigated the spatial relationships among H? flare ribbons, soft X-ray (SXR) flare loops, and magnetic configurations for the three flares produced in these active regions. Our results show that only one of these three flares satisfies the sufficient conditions for a flare to occur proposed by Hagyard (1990, AAA 052.075.047). We also discuss the magnetic shear changes around the flaring time only along the neutral lines associated with the studied flares and over the whole flaring area. The flare-related changes on the neutral line are small (2deg-4deg) and the association of these changes with the flares is not conclusive. The average shear in the flaring areas of the flares associated with high shear decreases significantly after the flares and it may be a better parameter to characterize the flare-related shear changes in such cases.

Li, Hui; Sakurai, Takashi; Ichimoto, Kiyoshi; UeNo, Satoru

2000-06-01

179

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

180

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

181

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

182

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.

183

Evidence for Hot Fast Flow above a Solar Flare Arcade  

NASA Astrophysics Data System (ADS)

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-1) component was located above the flare loop. This is consistent with magnetic reconnection taking place above the flare loop.

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

2013-10-01

184

Initial phase of chromospheric evaporation in a solar flare  

NASA Technical Reports Server (NTRS)

Attention is given to the initial phase of chromospheric evaporation in the solar flare observed by the Solar Maximum Mission's Hard X-ray Imaging Spectrometer, on May 21, 1980. Images of the flaring region in the 3.5-8.0 and 16-30 keV energy bands indicate that both the soft and hard X-ray emissions are localized near the footpoints early in the event, while they are weaker from the rest of the flaring loop system; this implies that there is no heating taking place at the top of the loops, while energy is primarily deposited at their base. Observations of the energy deposition in the chromosphere by electrons accelerated in the flare region to energies above 25 keV furnish further support for an interpretation of plasma upflows as the mechanism responsible for the formation of the soft X-ray flare, identified with chromospheric evaporation.

Antonucci, E.; Dennis, B. R.; Gabriel, A. H.; Simnett, G. M.

1985-01-01

185

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

186

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

187

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

188

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

189

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

190

Rapid Penumbral Decay following Three X-Class Solar Flares  

NASA Astrophysics Data System (ADS)

We show strong evidence that penumbral segments decayed rapidly and permanently right after three X-class solar flares. Two of the three events occurred very recently in NOAA Active Region 10486, an X17 flare on 2003 October 28 and an X10 flare on 2003 October 29. The third X2.3 flare was observed in solar active region NOAA AR 9026 on 2000 June 6. The locus of penumbral decay is related to flare emission, albeit with distinct differences for each event. We present difference images highlighting the rapid changes between pre- and postflare states of the flaring active region, which show distinct decaying penumbral segments and neighboring umbral cores becoming darker. Because of the lack of spectroscopic data, we cannot exclude the possibility that the observed changes are due to changes in the temperature structure of the flaring atmosphere, or to a corresponding reduction in opacity for a section of both umbra and penumbra. However, we argue against this possibility because the observed intensity changes are permanent, not transient. We instead propose a possible explanation that magnetic fields change from a highly inclined to a more vertical configuration within approximately 1 hr after the flares; i.e., part of the penumbral magnetic field is converted into umbral fields.

Wang, H.; Liu, C.; Qiu, J.; Deng, N.; Goode, P. R.; Denker, C.

2004-02-01

191

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

192

Proton versus electron heating in solar flares  

Microsoft Academic Search

Proton and electron heating of a flaring atmosphere is compared in a kinetic approach for the particles ejected from a non-neutral reconnecting current sheet (RCS) located above the top of reconnected flaring loops in a two-ribbon flare. Two kinds of high-energy particles are considered: particles accelerated by a super-Dreicer electric field and those ejected from the reconnection region as neutral

M. Gordovskyy; V. V. Zharkova; Yu. M. Voitenko; M. Goossens

2005-01-01

193

Ionospheric Currents Flowing along the Terminator during Solar Flares  

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

194

Constraining Solar Flare Differential Emission Measures with EVE and RHESSI  

E-print Network

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 $\\lesssim$2 to $\\gtrsim$50 MK. We present a new technique, combining extreme ultraviolet (EUV) spectra from the EUV Variability Experiment (EVE) onboard the Solar Dynamics Observatory with X-ray spectra from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), to derive, for the first time, a self-consistent, well-constrained DEM for jointly-observed solar flares. EVE is sensitive to ~2-25 MK thermal plasma emission, and RHESSI to $\\gtrsim$10 MK; together, the two instruments cover the full range of flare coronal plasma temperatures. We have validated the new technique on artificial test data, and apply it to two X-class flares from solar cycle 24 to determine the flare DEM and its temporal evolution; the constraints on the thermal emission derived from ...

Caspi, Amir; Warren, Harry P

2014-01-01

195

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

196

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

197

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

198

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

199

Another giant solar explosion follows Tuesday's enormous solar flare  

NASA Astrophysics Data System (ADS)

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

2003-10-01

200

Detecting Solar Neutrino Flare in Megaton and km3 detectors  

NASA Astrophysics Data System (ADS)

To foresee a solar flare neutrino signal we infer its upper and lower bound. The upper bound was derived since a few years by general energy equipartition arguments on observed solar particle flare. The lower bound, the most compelling one for any guarantee neutrino signal, is derived by most recent records of hard Gamma bump due to solar flare on January 2005 (by neutral pion decay). Because neutral and charged pions (made by hadron scattering in the flare) are born on the same foot, their link is compelling: the observed gamma flux [Grechnev V.V. et al., arXiv:0806.4424, Solar Physics, Vol. 1, October, (2008), 252] reflects into a corresponding one for the neutrinos, almost one to one. Moreover while gamma photons might be absorbed (in deep corona) or at least reduced inside the flaring plasma, the secondaries neutrino are not. So pion neutrinos should be even more abundant than gamma ones. Tens-hundred MeV neutrinos may cross undisturbed the whole Sun, doubling at least their rate respect a unique solar-side for gamma flare. Therefore we obtain minimal bounds opening a windows for neutrino astronomy, already at the edge of present but quite within near future Megaton neutrino detectors. Such detectors are considered mostly to reveal cosmic supernova background or rare Local Group (few Mpc) Supernovas events [Matthew D. Kistler et al. 0810.1959v1]. However rarest (once a decade), brief (a few minutes) powerful solar neutrino “flare” may shine and they may overcome by two to three order of magnitude the corresponding steady atmospheric neutrino noise on the Earth, leading in largest Neutrino detector at least to one or to meaning-full few events clustered signals. The voice of such a solar anti-neutrino flare component at a few tens MeVs may induce an inverse beta decay over a vanishing anti-neutrino solar background. Megaton or even inner ten Megaton Ice Cube detector at ten GeV threshold may also reveal traces in hardest energy of solar flares. Icecube, marginally, too. Solar neutrino flavors may shine light on neutrino mixing angles. Not only on orbit satellites but even human astronauts in Space may exploit underground neutrino detectors for the prompt alert on (otherwise) fast and maybe lethal solar explosions.

Fargion, Daniele; di Giacomo, Paola

2009-03-01

201

Solar flare nuclear gamma rays and interplanetary proton events  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

202

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

203

GEOMAGNETIC CONSEQUENCES OF THE SOLAR FLARES DURING THE LAST HALE SOLAR CYCLE (II)  

E-print Network

magnetosphere; this is in the form of high-energy solar particles that may originate from solar flares, eruptive is the solar plasma that may originate from solar eruptive phenomena that take their energy from magnetic field, and indirectly, through the induced geomagnetic variations. Solar radiation monitoring and studies of solar

204

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

205

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

206

Solar flare particles - Energy-dependent composition and relationship to solar composition  

NASA Technical Reports Server (NTRS)

Plastic and glass track detectors on rockets and Apollo spacecraft have been used to determine the composition of particles from He to Ni at energies from 0.1 to 50 MeV per nucleon in several solar flares of widely varying intensities. At low energies the composition of solar particles is enriched in heavy elements by an amount, relative to the asymptotic high-energy composition, that increases with atomic number from Z = 2 up to at least Z = 50, that decreases with energy, and that varies from flare to flare. At high energies (usually beyond an energy of 5 to 20 MeV per nucleon) the composition becomes independent of energy and, though somewhat variable from flare to flare, approximates the composition of the solar atmosphere. A table of abundances of the even-Z elements from He to Ni (plus N) in solar particles is constructed by averaging the asymptotic high-energy abundances in several flares.

Crawford, H. J.; Price, P. B.; Cartwright, B. G.; Sullivan, J. D.

1975-01-01

207

Predicting Arrival Of Protons Emitted In Solar Flares  

NASA Technical Reports Server (NTRS)

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

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

1996-01-01

208

The energetics of chromospheric evaporation in solar flares  

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

209

Solar flares, proton showers, and the Space Shuttle  

NASA Technical Reports Server (NTRS)

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

Rust, D. M.

1982-01-01

210

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

211

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

212

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

213

Modelling the influence of photospheric turbulence on solar flare statistics  

E-print Network

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 encoura...

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

2014-01-01

214

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

215

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

216

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

217

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

218

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

219

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

220

The impact of solar flares and magnetic storms on humans  

SciTech Connect

Three classes of solar emanations, namely, photon radiation from solar flares, solar energetic particles, and inhomogeneities in the solar wind that drive magnetic storms, are examined, and their effects on humans and technological systems are discussed. Solar flares may disrupt radio communications in the HF and VLF ranges. Energetic particles pose a special hazard at low-earth orbit and above, where they can penetrate barriers such as spacesuits and aluminum and destroy cells and solid state electronics. Energetic solar particles also influence terrestrial radio waves propagating through polar regions. Magnetic storms may disturb the operation of navigation instruments, power lines and pipelines, and satellites; they give rise to ionospheric storms which affect radio communication at all latitudes. There is also a growing body of evidence that changes in the geomagnetic field affect biological systems. 3 refs.

Joselyn, J.A. (NOAA, Space Environment Laboratory, Boulder, CO (United States))

1992-03-01

221

Common SphinX and RHESSI observations of solar flares  

NASA Astrophysics Data System (ADS)

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

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

222

On the magnetic reconnection of electric currents in solar flares  

NASA Astrophysics Data System (ADS)

The role of the electric currents distributed over the volume of an active region on the Sun is considered from the standpoint of solar flare physics. We suggest including the electric currents in a topological model of the magnetic field in an active region. Typical values of the mutual inductance and the interaction energy of the coronal electric currents flowing along magnetic loops have been estimated for the M7/1N flare on April 27, 2006. We show that if these currents actually make a significant contribution to the flare energetics, then they must manifest themselves in the photosphericmagnetic fields. Depending on their orientation, the distributed currents can both help and hinder reconnection in the current layer at the separator during the flare. Asymmetric reconnection of the currents is accompanied by their interruption and an inductive change in energy. The reconnection of currents in flares differs significantly from the ordinary coalescence instability of magnetic islands in current layers. Highly accurate measurements of the magnetic fields in active regions are needed for a quantitative analysis of the role of distributed currents in solar flares.

Somov, B. V.

2012-02-01

223

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

224

Statistical Properties of Solar Flares and Comparison to Other Impulsive Energy Release Events  

Microsoft Academic Search

Impulsive energy release events are observed in many natural systems. Solar flares are certainly among the most remarkable examples of such processes. In the last years the study of solar flare statistical properties has received considerable attention in the context of solar flare models based on different approaches, such as Self Organized Criticality (SOC) or magnetohydrodynamic (MHD) turbulence. In this

Fabio Lepreti; Vladimir G. Kossobokov; Vincenzo Carbone

2009-01-01

225

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

E-print Network

) and the reproduction of the observed solar flare statistics. On the other hand the energy release process has been to explain the solar flare statistics derived from observations. These models simulate the storage events, which leads to poor statistics for comparison to solar flares. We present here preliminary

Anastasiadis, Anastasios

226

Automatic Solar Flare Detection Using MLP, RBF and SVM , Frank Y. Shih1  

E-print Network

in light curves. In the mean time, solar flares also emit high velocity charged particles that take one1 Automatic Solar Flare Detection Using MLP, RBF and SVM Ming Qu1 , Frank Y. Shih1 , Ju Jing2. The focus of the automatic solar flare detection is on the development of efficient feature

227

PRODUCTIVITY OF SOLAR FLARES AND MAGNETIC HELICITY INJECTION IN ACTIVE REGIONS  

E-print Network

PRODUCTIVITY OF SOLAR FLARES AND MAGNETIC HELICITY INJECTION IN ACTIVE REGIONS SUNG-HONG PARK,1 and Astronomy, Seoul National University, Seoul 151-742, Korea. #12;­ 2 ­ 1. INTRODUCTION A solar flare). Solar flares produce high energy particles, radiation, and erupting magnetic structures that are related

228

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

229

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

230

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

231

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

232

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

233

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

234

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

235

Time-dependent coronal shock acceleration of energetic solar flare particles  

Microsoft Academic Search

A global time-dependent model is presented for the coronal and interplanetary shock acceleration and propagation of energetic solar flare particles. The calculations are carried out to help prove that coronal shock acceleration of solar flare particles is responsible for energetic solar flare event data gathered in interplanetary space. The model is based on the theory of diffusive shock acceleration, and

M. A. Lee; J. M. Ryan

1986-01-01

236

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

237

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

238

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

239

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

240

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

241

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

242

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

243

Fractal behavior of ionospheric TEC during solar X-ray flares  

NASA Astrophysics Data System (ADS)

The Earth's ionosphere is generated by the ionization produced by the solar ultraviolet radiation upon arriving to the top of the atmosphere. However, the variations of the total electron content (TEC) of the ionosphere is mainly associated with geomagnetic storms occurring with the arrival of coronal mass ejections (CMEs) to the Earth's environment. In spite of the fact that the high energy electromagnetic radiations like ultraviolet and X-rays intensifies during intense solar flares, their impact on the diurnal variation of TEC is of little importance. Therefore, the purpose of this work is to carry out a fractal analysis of the TEC time series during several days around the time of occurrence of 75 X-ray flares from 2000 to the present, in order to show that the impact of the electromagnetic radiation on the ionosphere is given more in a change of the "rugosity" of the time series than in an increase in the amplitude of the variation.

Lopez-Montes, R.; Rodriguez-Martinez, M.; Perez-Enriquez, R.

2011-12-01

244

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

E-print Network

The microwave zebra pattern (ZP) is the most interesting, intriguing, and complex spectral structure frequently observed in solar flares. A comprehensive statistical study will certainly help us to understand the formation mechanism, which is not exactly clear now. This work presents a comprehensive statistical analysis on a big sample with 202 ZP events collected from observations at the Chinese Solar Broadband Radio Spectrometer at Huairou and the Ondrejov Radiospectrograph in Czech Republic at frequencies of 1.00 - 7.60 GHz during 2000 - 2013. After investigating the parameter properties of ZPs, such as the occurrence in flare phase, frequency range, polarization degree, duration, etc., we find that the variation of zebra stripe frequency separation with respect to frequency is the best indicator for a physical classification of ZPs. Microwave ZPs can be classified into 3 types: equidistant ZP, variable-distant ZP, and growing-distant ZP, possibly corresponding to mechanisms of Bernstein wave model, whistl...

Tan, Baolin; Zhang, Yin; Meszarosova, H; Karlicky, M

2013-01-01

245

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

246

Magnetic Shear in Two-ribbon Solar Flares  

NASA Astrophysics Data System (ADS)

In this thesis, we study the evolution of the highly sheared magnetic fields before, during, and after solar flares, in order to address the fundamental questions in solar flare research: how does the magnetic free energy stored and released? The work primarily focuses on the analysis of multi-wavelength data, while non-linear force free field (NLFFF) modeling of one active region is also explored. A detailed analysis of the strong-to-weak shear motion of the flare footpoints (TRACE) in an X17 flare (2003 Oct 28) shows that the cessation of this shear change occurs in the middle of the impulsive phase. The observations are interpreted in terms of the splitting of the sheared envelope field of the greatly sheared core rope during the early phase of the flare, based on a 3D version of the standard flare model. This shear motion of the footpoints has been found to be common, i.e., 43 out of 50 of the well-observed (by TRACE) two-ribbon flares we studied show this shear motion, this type of flares are called type I flare. We also found that: for a subset of 24 type I flares, the initial and final shear angles of the footpoints are mainly in the range from 50° to 80° and 15° to 55°, respectively; in 10 of the 14 flares having both measured shear angle and corresponding hard X-ray observations, the cessation of shear change is 0--2 minutes earlier than the end of the impulsive phase, which may suggest that the change from impulsive to gradual phase is related to magnetic shear change. For a sample of 18 Type I flares associated with CMEs, we found that the magnetic flux and the change of shear angle of the foopoints significantly correlated with the intensity of flare/CME events, while the initial shear angle of the foopoints does not. This observation indicates that the intensity of flare/CME events may depend on the released magnetic free energy rather than the total free energy stored prior to the flare. We also found that a linear combination of several parameters shows a much better correlation with the intensity of flare/CME events than each parameter itself. The aforementioned work are mainly based on TRACE observations, in which we infer the sheared field information from the flare footpoints. However, the X-ray telescope (XRT) on board the newly launched Hinode spacecraft provides direct observations of highly sheared coronal loops at various stages. XRT observations of two X-class flares occurred last December show that part of the sheared core field erupted, and another part of the sheared core field stayed behind during the flares, which may explain why a large part of the filament is still seen by TRACE after the flare. We also find that the post-flare core field is clearly less sheared than the pre-flare core field, which is consistent with the idea that the energy released during the flares is stored in the highly sheared fields prior to the flare. At last, we explored the NLFFF modeling of a simple bipolar active region (NOAA 10953), which produced several small flares (mostly B class and one C8.5 class) and filament activations from April 30 to May 3 in 2007. These events appear to be associated with the frequent flux cancellations (SOHO/MDI) that occurred in the region close to the polarity inversion line. We constructed a series of NLFFF models for this active region at three times, using the flux-rope insertion method. The models are constructed based on MDI magetograms, and constrained by H? filaments and highly sheared loops observed by XRT. We find good NLFFF models that fit the observations before the C8.5 flare, but not for the case after the flare. The flux rope contains highly sheared but weakly twisted magnetic fields. Before the C8.5 flare, this active region is close to an eruptive state: the axial flux in the flux rope is close to the upper limit for eruption.

Su, Yingna

2007-12-01

247

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

248

Manifestations of energetic electrons with anisotropic distributions in solar flares  

E-print Network

magnetic field from those of self-induced electric field for beams with different initial energy fluxesManifestations of energetic electrons with anisotropic distributions in solar flares II in collisions and Ohmic losses induced by a self-induced electric field. We separate the effects of converging

249

Far-IR and Radio Continua in Solar Flares  

Microsoft Academic Search

With the invention of new far-infrared (FIR) and radio mm and sub-mm instruments (DESIR on SMESE satellite, ESO ALMA), there is a growing interest in observations and analysis of solar flares in this so far unexplored wavelength region. Two principal radition mechanisms play a role: the synchrotron emission due to accelerated particle beams moving in the magnetic field and the

P. Heinzel; J. Kasparova; M. Varady; M. Karlicky; Z. Moravec

2008-01-01

250

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

251

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

NASA Technical Reports Server (NTRS)

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

Gloeckler, G.

1975-01-01

252

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

253

Filament eruptions and the impulsive phase of solar flares  

SciTech Connect

Filament motion during the onset of the solar flare impulsive phase is examined. The impulsive phase onset is established from profiles of about 30 keV X-ray fluxes and the rapid flare brightenings characteristic of the H-alpha flash phase. The filament motion begins several minutes before the impulsive or flash phase of the flare. No new accleration is observed in the motion of the filament during the onset of the impulsive phase for at least two of the four flares. The most common H-alpha brightenings associated with the impulsive phase lie near the magnetic inversion line roughly centered under the erupting filament. Filament speeds at the onset of the impulsive or flash phase lie in the range 30-180 km/s. These characteristics indicate that the filament eruption is not driven by the flare plasma pressure, but instead marks an eruption of magnetic field driven by a global MHD instability of the field configuration in the region of the flare. 36 references.

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

1988-05-01

254

Filament eruptions and the impulsive phase of solar flares  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

255

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

256

High energy particles in solar flares: observations, mechanisms and transport  

NASA Astrophysics Data System (ADS)

We review the observations bearing on electron and ion acceleration in solar flares, and the key challenges they pose to theory. Solar flare hard X-rays testify to the presence of accelerated electrons, with energies extending from thermal to the MeV range and possibly beyond. A variety of line and continuum signatures in the gamma-ray range reveal properties of energetic ions, from MeV to GeV energies. We review the ideas of the thick target and local reacceleration models for source regions and their implications for overall pictures of the flare energy release. Attainment of the highest particle energies poses a different sort of challenge to theory. Using the nuclear transport code FLUKA we show examples of the transport and radiation of ~GeV energy ions and their secondaries, and consider some of the questions raised by long-lasting high-energy continuum after flares. The further constraints offered by radio and sub-mm observations are discussed, sub-mm in particular both posing new questions and offering new insights. We conclude by identifying a few key questions for future flare studies.

MacKinnon, Alexander

257

NEW SOLAR EXTREME-ULTRAVIOLET IRRADIANCE OBSERVATIONS DURING FLARES  

SciTech Connect

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

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

2011-10-01

258

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

259

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

260

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

261

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

262

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

263

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

264

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

265

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

266

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

267

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

268

Low-latitude Ionospheric Heating during Solar Flares  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

269

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

270

Observational evidence for thermal wave fronts in solar flares  

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

271

On the Origin of Linear Polarization in Solar Flares  

NASA Astrophysics Data System (ADS)

A significant degree of linear polarization (up to few percent) of some spectral lines is occasionally reported from the observations of solar flares. This polarization is often found at the edges of the flare ribbons and it is usually radial or tangential. The mechanism usually considered as being responsible for this effect is the impact polarization by electron and/or proton beams bombarding the chromosphere. We point out that resonant scattering polarization in a multi-dimensional geometry of the chromosphere has to be considered as an important ingredient of the problem. The significant horizontal inhomogeneities at the boundaries of the flare ribbons causes a considerable change in the radiation field anisotropy which may lead to emission of strongly linearly polarized spectral lines. For more details see Št?pán, & Heinzel (2013)

Št?pán, J.; Heinzel, P.

2014-10-01

272

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

273

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

E-print Network

A STATISTICAL STUDY OF SPECTRAL HARDENING IN SOLAR FLARES AND RELATED SOLAR ENERGETIC PARTICLE Ramaty High Energy Solar Spectroscopic Imager (RHESSI), we investigate the reliability of spectral 2009. The American Astronomical Society. All rights reserved. Printed in the U.S.A. A STATISTICAL STUDY

California at Berkeley, University of

274

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

275

Solar X-ray flare hazards on the surface of Mars  

Microsoft Academic Search

Putative organisms on the Martian surface would be exposed to potentially high doses of ionizing radiation during strong solar X-ray flares. We extrapolate the observed flare frequency-energy release scaling relation to total X-ray energies much larger than seen so far for the Sun, an assumption supported by observations of flares on other solar- and subsolar-mass main sequence stars. Flare spectra

David S. Smith; John M. Scalo

2007-01-01

276

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

277

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

278

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

279

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

280

THz photometers for solar flare observations from space  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

281

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

282

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

283

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

284

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

2008-01-24

285

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

286

Far-IR and Radio Thermal Continua in Solar Flares  

Microsoft Academic Search

With the invention of new far-infrared (FIR) and radio mm and sub-mm instruments (DESIR on SMESE satellite, ESO-ALMA), there is a growing interest in observations and analysis of solar flares in this so far unexplored wavelength region. Two principal radiation mechanisms play a role: the synchrotron emission due to accelerated particle beams moving in the magnetic field and the thermal

J. Kasparová; P. Heinzel; M. Karlický; Z. Moravec; M. Varady

2009-01-01

287

Solar-Flare Shielding With Regolith at  

E-print Network

the Moon steadily from sources outside the solar system. Unlike on Earth, lunar inhabitants will not have, the dose at 5-cm depth is considered represen- tative of the dose to the blood-forming organs (BFO dose

Rathbun, Julie A.

288

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

289

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

Microsoft Academic Search

We analyse the North-South (N-S) asymmetry of soft X-ray (SXR) solar flares during the 11-year solar cycle (SC). After reviewing the literature on flare dominance in the northern and southern hemispheres of the solar disk for SCs 17-23, we analyse the SXR flare distribution in the two hemispheres during the period 1976-2001. The analysis was made using the number of

Georgeta Maris; Miruna Daniela Popescu; Marilena Mierla

2002-01-01

290

THE NORTH-SOUTH ASYMMETRY OF SOFT X-RAY SOLAR FLARES  

Microsoft Academic Search

We analyse the North-South (N-S) asymmetry of soft X-ray (SXR) solar flares during the 11-year solar cycle (SC). After reviewing the literature on flare dominance in the northern and southern hemispheres of the solar disk for SCs 17-23, we analyse the SXR flare distribution in the two hemispheres during the period 1976- 2001. The analysis was made using the number

MIRUNA DANIELA POPESCU; MARILENA MIERLA; N. Ireland

2002-01-01

291

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

292

Solar flare electron acceleration: comparing theories and observations  

E-print Network

A popular scenario for electron acceleration in solar flares is transit-time damping of low-frequency MHD waves excited by reconnection and its outflows. The scenario requires several processes in sequence to yield energetic electrons of the observed large number. Until now there was very little evidence for this scenario, as it is even not clear where the flare energy is released. RHESSI measurements of bremsstrahlung by non-thermal flare electrons yield energy estimates as well as the position where the energy is deposited. Thus quantitative measurements can be put into the frame of the global magnetic field configuration as seen in coronal EUV line observations. We present RHESSI observations combined with TRACE data that suggest primary energy inputs mostly into electron acceleration and to a minor fraction into coronal heating and primary motion. The more sensitive and lower energy X-ray observations by RHESSI have found also small events (C class) at the time of the acceleration of electron beams exciting meter wave Type III bursts. However, not all RHESSI flares involve Type III radio emissions. The association of other decimeter radio emissions, such as narrowband spikes and pulsations, with X-rays is summarized in view of electron acceleration

Arnold O. Benz; Pascal Saint-Hilaire

2003-08-19

293

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

294

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

295

Location of Decimetric Pulsations in Solar Flares  

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

296

Location of Decimetric Pulsations in Solar Flares  

NASA Astrophysics Data System (ADS)

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

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

297

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

298

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

299

Detection and Analysis of Neutron Emissions from Solar Flares  

NASA Astrophysics Data System (ADS)

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

Valdes-Galicia, J. F.

2013-05-01

300

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

NASA Astrophysics Data System (ADS)

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

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

1991-07-01

301

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

302

Turbulent and directed plasma motions in solar flares  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

303

Short-term solar flare prediction using predictor teams  

NASA Astrophysics Data System (ADS)

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

Huang, Xin; Wang, Huaning

304

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

305

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

306

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

307

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

308

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

309

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

310

A model solar flares and their homologous behavior  

SciTech Connect

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

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

2000-01-27

311

A Model of Solar Flares and Their Homologous Behavior  

NASA Astrophysics Data System (ADS)

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

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

2000-09-01

312

A Model of Solar Flares and Their Homologous Behavior  

NASA Astrophysics Data System (ADS)

A model describing physical processes of solar flares and their homologous behavior is proposed based on resistive MHD simulations of magnetic arcade evolution. The individual flaring process encompasses magnetic reconnection of arcade field, generation of magnetic islands, and coalescence of magnetic islands. When the magnetic shear of the arcade field is increased over a threshold (via footpoint motion or flux emergence or both), a current sheet is formed and magnetic reconnection takes place to form a magnetic island. In the underlying arcade below the magnetic island, a new reconnection process can be triggered by a continuing increase of magnetic shear to create a new island. The newborn island rises faster than the preceding island and merges with it to form one island. Before the island merging process is completed, the newborn island exhibits two different phases of rising motion: the first phase with a slower rising speed and the second phase with a faster rising speed. This is consistent with the Yohkoh observation of the upward motion of X-ray plasma ejecta by Ohyama and Shibata [1998]. The first phase, in which reconnection of line-tied fields in the underlying arcade is important, is considered to be the preflare phase. In the second phase, the island coalescence process creates an elongated current sheet in the underlying arcade and enhances the reconnection of line-tied arcade fields. This phase is considered as the impulsive phase or the flash phase of flares. The reconnection electric field during the second phase is large enough to accelerate electrons to an energy level greater than 10 keV necessary for hard X-ray production. After the island merging is completed, magnetic reconnection continues in the current sheet under the integrated island for a longer period which is considered as the main phase of flares. The sequence of all these processes is repeated with some time interval while the magnetic shear is increased. A series of these flaring processes is considered to constitute a set of homologous flares. The time interval between successive flaring events depends on the magnetic energy input rate into the system, which is governed by the nature of magnetic shear increase and the plasma dissipation rate.

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

2000-05-01

313

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

314

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

315

The Scaling of Solar Flare Hard X-ray Emission to Other Flaring Objects in the Universe  

NASA Astrophysics Data System (ADS)

Fletcher & Martens have successfully modeled solar hard X-ray sources observed at the top and footpoints of flaring magnetic loops with a Fokker-Planck type particle transport code. I show here that there are invariances in the Fokker-Planck equations that make these results applicable to environments with vastly different physical parameters, such as hard X-ray flares in accretion disks in active galactic nuclei, and in RS CVn and ALGOL type binaries.

Martens, P. C. H.

2000-05-01

316

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

NASA Astrophysics Data System (ADS)

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

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

317

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

318

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

319

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

320

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

321

Space radiation dose analysis for solar flare of August 1989  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

322

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

323

Hard X rays of relativistic electrons accelerated in solar flares  

NASA Astrophysics Data System (ADS)

The direction and polarization degree of hard X rays (HXRs) in solar flares are studied. The continuous injection of relativistic electrons, which is implemented in powerful flares, is considered. The stationary relativistic kinetic equation is studied by using the method of expansion in terms of the Legendre polynomial and by integrating the equations for the expansion coefficients. The HXR characteristics are calculated using the bremsstrahlung relativistic cross-section for different angular and energetic electron distributions in the acceleration region. A high linear polarization degree of HXRs (˜35%) has been obtained for narrow (˜cos6?) beams of electrons with a soft spectrum (˜ E -6); the polarization degree decreases with increasing quanta energy, whereas the directivity of a high-energy emission increases. This effect is absent for a nonrelativistic approximation. The considered model is applied to one of the most powerful flares in cycle 23, registered on October 28, 2003. The measured polarization degree values at relativistic energies (0.2-0.4 and 0.4-1 MeV) agree with the results achieved in the considered model when the electron energy spectrum index (? = 2.5), angular distribution part (˜cos6?), and the spectrum cutoff energy ( E max = 1.3 MeV) were specified.

Kudryavtsev, I. V.; Charikov, Yu. E.

2012-12-01

324

Space radiation dose analysis for solar flare of August 1989  

NASA Astrophysics Data System (ADS)

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

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

1990-12-01

325

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.

326

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

E-print Network

Earth Planets Space, 00, 000--000, 2000 Solar Flare Mechanism Based on Magnetic Arcade Reconnection of solar flares based on re­ sistive reconnection of magnetic field subject to continuous increase field lines, generation of magnetic islands in the magnetic arcade, and coalescence of magnetic islands

327

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

328

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

329

A query into the source of proton emission from solar flares, report 2  

NASA Technical Reports Server (NTRS)

Seven solar flares that were followed by major proton events were examined to determine the diverse and common properties of major flares. The most probable site of primary proton acceleration is cospatial with the site and instant of formation of coronal loops. Because loop formation occurs through the entire duration of major solar flares over significantly large areas of active centers, it is proposed that proton injection occurs from a relatively large volume of space in the corona of active centers and is continuous throughout, and possibly even after, the visible duration of the related chromospheric flare. The flare veil is hypothesized to occur as a result of proton charge exchange taking place in the white-light transient. The Kopp and Pneuman model of loop formation by magnetic reconnection is suggested as an adequate and satisfactory model for all major flares with the provision that the beginning of rapid magnetic field reconnection is coincident with flare start.

Martin, S. F.

1979-01-01

330

01.22.12: SDO's View of M8.7 Solar Flare  

NASA Video Gallery

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

331

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

332

Gamma-ray emission and electron acceleration in solar flares  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

333

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

334

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

335

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

336

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

337

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

338

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

339

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

E-print Network

ABSTRACT STUDIES OF SOLAR WHITE-LIGHT FLARES AND SMALL-SCALE MAGNETIC STRUCTURES OBSERVED, detailed study of solar white-light flares and small magnetic structures, such as faculae and pores of near infrared (NIR) solar physics: (1) the first detection and understanding of white-light flares

340

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

NASA Technical Reports Server (NTRS)

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

Marchenko, V. I.

1974-01-01

341

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

342

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

343

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

344

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

345

Energy spectra of ions from impulsive solar flares  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

346

Terrestrial Response to Eruptive Solar Flares: Geomagnetic Storms  

NASA Technical Reports Server (NTRS)

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

Tsurutani, Bruce T.

1995-01-01

347

Energy spectra of ions from impulsive solar flares  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

348

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

349

On the reconstruction of the energy distribution of electrons accelerated in solar flares  

NASA Astrophysics Data System (ADS)

A technique for reconstructing energy spectra of electrons accelerated in solar flares is suggested that is based on the rigorous solution of the inverse problem considering their X-ray bremsstrahlung. Model calculations are made for various spectra, and it is proved that this technique makes it possible to find the electron energy distribution in real flare events. The energy distribution of high-energy electrons accelerated in the solar flare observed on July 26, 2002, is reconstructed. It is shown that the hard X-ray spectrum of the flare may result from the bremsstrahlung of three groups of high-energy electrons.

Motorina, G. G.; Koudriavtsev, I. V.; Lazutkov, V. P.; Matveev, G. A.; Savchenko, M. I.; Skorodumov, D. V.; Charikov, Yu. E.

2012-12-01

350

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

351

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

SciTech Connect

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

Joshi, Bhuwan [Udaipur Solar Observatory, Physical Research Laboratory, Udaipur 313 001 (India); Veronig, Astrid M. [IGAM/Institute of Physics, University of Graz, A-8010 Graz (Austria); Lee, Jeongwoo [Physics Department, New Jersey Institute of Technology, Newark, NJ 07102 (United States); Bong, Su-Chan; Cho, Kyung-Suk [Korea Astronomy and Space Science Institute, Daejeon 305-348 (Korea, Republic of); Tiwari, Sanjiv Kumar [Max-Planck-Institut fuer Sonnensystemforschung, 37191 Katlenburg-Lindau (Germany)

2011-12-20

352

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

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

353

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

354

Solar flare neon composition and solar cosmic-ray exposure ages based on lunar mineral separates  

Microsoft Academic Search

Etched pyroxene grain-size separates from lunar soils 14148 and 24087 and etched feldspar grain-size separates from soil 61221 are analyzed for neon isotopic and elemental composition, and the procedures to isolate the implanted solar flare (SF) neon and solar and Galactic cosmic-ray (SCR and GCR)-produced Ne components in these samples are discussed. These results indicate that the SF neon composition

C. M. Nautiyal; J. T. Padia; M. N. Rao; T. R. Venkatesan

1986-01-01

355

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

NASA Astrophysics Data System (ADS)

The GOES C7.5 flare on 20 February 2002 at 11:07 UT is one of the first solar flares observed by RHESSI at X-ray wavelengths. It was simultaneously observed at metric/decimetric wavelengths by the Nançay radioheliograph (NRH) which provided images of the flare between 450 and 150 MHz. We present a first comparison of the hard X-ray images observed with RHESSI and of the radio emission sites observed by the NRH. This first analysis shows that: (1) there is a close occurrence between the production of the HXR-radiating most energetic electrons and the injection of radio-emitting non-thermal electrons at all heights in the corona, (2) modifications with time in the pattern of the HXR sources above 25 keV and of the decimetric radio sources at 410 MHz are observed occurring on similar time periods, (3) in the late phase of the most energetic HXR peak, a weak radio source is observed at high frequencies, overlying the EUV magnetic loops seen in the vicinity of the X-ray flaring sites above 12 keV. These preliminary results illustrate the potential of combining RHESSI and NRH images for the study of electron acceleration and transport in flares.

Vilmer, N.; Krucker, S.; Lin, R. P.; Rhessi Team

2002-11-01

356

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

357

Composition and azimuthal spread of solar energetic particles from impulsive and gradual flares  

NASA Astrophysics Data System (ADS)

A list of 77 flare-associated solar energetic particle (SEP) parent flares are classified as impulsive (25 cases) or gradual (52 cases) on the basis of their soft X-ray durations. The intensities of the prompt component of about 0.5 MeV electrons, about 10 MeV protons, and about 10 MeV per nucleon helium for the two classes of SEP flares are compared. SEPs from gradual flares have higher intensities than SEPs from impulsive flares. These differences are most pronounced for protons (about two orders of magnitude), and less for electrons (about one order of magnitude), and helium (about a factor of 5). The SEPs from impulsive flares have a 'cone of emission' of +/- 50 deg vs +/- 120 deg for gradual flares.

Kallenrode, M.-B.; Cliver, E. W.; Wibberenz, G.

1992-05-01

358

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

359

Multi-Wavelength Observations of Solar Flares with Emphasis on the Millimeter Emission  

Microsoft Academic Search

In this work, we study a total of 10 solar flares observed by the Berkeley-Illinois-Maryland millimeter interferometer (BIMA). All flares were simultaneously observed in soft X-rays, and some of the events were also detected in hard X-rays, Halpha, and at microwave wavelengths. The great majority of flares for which images were available showed multiple sources whose physical characteristics varied considerably

Adriana Valio Roque da Silva

1995-01-01

360

Far-IR and Radio Continua in Solar Flares  

NASA Astrophysics Data System (ADS)

With the invention of new far-infrared (FIR) and radio mm and sub-mm instruments (DESIR on SMESE satellite, ESO ALMA), there is a growing interest in observations and analysis of solar flares in this so far unexplored wavelength region. Two principal radition mechanisms play a role: the synchrotron emission due to accelerated particle beams moving in the magnetic field and the thermal emission due to energy deposit in the lower atmospheric layers. The latter one was recently explored for the case of semiempirical flare models, without considering the temporal evolution. However, as the radiation-hydrodynamical simulations do show, the lower atmosphere heated by beams exhibits fast temporal changes which are typically reflected in variations of spectral-line intensities. In this contribution we explore the time-dependent effects of beams on FIR and radio continua. We show how and where these continua are formed in the presence of time dependent beam heating and non-thermal excitation/ionization of the chromospheric hydrogen plasma. Our results should contribute to planning of new observations in FIR and radio domain.

Heinzel, P.; Kasparova, J.; Varady, M.; Karlicky, M.; Moravec, Z.

2008-09-01

361

Spectroscopy of Reconnection Inflow and Outflow in Solar Flares  

NASA Astrophysics Data System (ADS)

We report reconnection inflow and outflow structures in a type of solar flares that were observed by spectroscopic observations with the Hinode EUV Imaging Spectrometer. A dark outflow has been found by EIS raster scan observations in hot emission lines like Fe XXIII and Fe XXIV as a structure extended from a site above a bright flare loop. The outflow structure is heated to ~10 MK, and the electron density of the outflow is enhanced by about a factor of 2 from the surrounding corona. The hot emission lines in the outflow structure show a large excess width, which may imply the presence of an internal flow structure or the plasma in a turbulent state. A high-density blob structure that appears above the loop-top region where the reconnection outflow collides shows the Doppler motion toward the low-altitude direction. The reconnection rate is estimated to be 0.01-0.1 in combination with the signature of reconnection inflow from the Doppler velocity measurement.

Hara, Hirohisa

362

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

363

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

364

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

365

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

366

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

367

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

368

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

369

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

E-print Network

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

Tan, Baolin; Zhang, Yin; Huang, Jing; Meszarosova, Hana; Karlicky, Marian; Yan, Yihua

2014-01-01

370

Far-IR and radio thermal continua in solar flares  

E-print Network

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

Kašparová, J; Karlický, M; Moravec, Z; Varady, M

2009-01-01

371

Far-IR and Radio Thermal Continua in Solar Flares  

NASA Astrophysics Data System (ADS)

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

Kašparová, J.; Heinzel, P.; Karlický, M.; Moravec, Z.; Varady, M.

372

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

373

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

374

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

375

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

376

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

377

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

378

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

379

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

380

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

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

381

Energy release in solar flares - critical analysis of the current approach  

NASA Astrophysics Data System (ADS)

We review current approach to solar flare origin with critical analysis of different aspects of this problem: 1. Pre-flare equilibrium state: role of observed ultra fine structure of the force-free magnetic fields of active region (problem of magnetic ropes equilibrium). 2. Loss of pre-flare equilibrium: absence of adequate mechanisms for description of this catastrophic transition from previous force free equilibrium to singular state with concentration of dispersed currents into very thin current sheet & string, where anomalous magnetic dissipation and reconnection. 3. Flare energy release itself: problem of "survival" of flare's current sheet caused by its strong (threshold-like) sensitivity to current density, by effects of current's region overheating and by "splitting" of current sheet. We present some possible solution on the base of "percolation approach" to current propagation in unstable turbulent current sheet and show that this approach is able to explain naturally both threshold-like start of flare energy release, power-like frequency-amplitude spectra of flare bursts and power-like energetic spectra of accelerated particles. We present possible scheme of solar-terrestrial connection (space weather influence) based on reason-sequence chain "solar activity" - "coronal heating" - "solar wind enhanced generation" - "modulation of cosmic ray flux by solar wind and correspondent change of its penetration into atmosphere" & "modulation of magnetosphere activity" - "modulation of atmospheric state in regions with unstable state of atmospheric processes (cloudiness, atmospheric circulation)". We present observational data confirmed reality of these expected effects of space weather influence.

Pustil'Nik, Lev

382

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

383

SDO Captures Release of X1.2 Class Solar Flare  

NASA Video Gallery

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

384

Statistical Properties of Solar Flares and Comparison to Other Impulsive Energy Release Events  

NASA Astrophysics Data System (ADS)

Impulsive energy release events are observed in many natural systems. Solar flares are certainly among the most remarkable examples of such processes. In the last years the study of solar flare statistical properties has received considerable attention in the context of solar flare models based on different approaches, such as Self Organized Criticality (SOC) or magnetohydrodynamic (MHD) turbulence. In this talk the main statistical properties of solar flares will be presented and compared to those of other well known impulsive processes, such as earthquakes and soft ?-ray flashes occurring on neutron stars. It is shown that the these phenomena are characterized by different statistics that cannot be rescaled onto a single, universal curve and that this holds even for the same phenomenon, when observed in different periods or at different locations. Our results indicate apparent complexity of impulsive energy release processes, which neither follow a common behavior nor could be attributed to a universal physical mechanism.

Lepreti, Fabio; Kossobokov, Vladimir G.; Carbone, Vincenzo

385

Hard X-ray Imaging of Solar Flares Using Interpolated Visibilities  

Microsoft Academic Search

RHESSI produces solar flare images with the finest angular and spectral resolutions ever achieved at hard X-ray energies. Because this instrument uses indirect, collimator-based imaging techniques, the \\

Anna Maria Massone; A. Gordon Emslie; G. J. Hurford; Marco Prato; Eduard P. Kontar; Michele Piana

2009-01-01

386

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

387

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

388

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

389

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

390

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

391

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

392

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

393

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

394

Transient ionization and solar flare X-ray spectra  

NASA Astrophysics Data System (ADS)

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

Doschek, G. A.; Tanaka, K.

1987-12-01

395

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

396

Solar Eruptive Flares: from Physical Understanding to Probabilistic Forecasting  

NASA Astrophysics Data System (ADS)

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

Georgoulis, M. K.

2013-12-01

397

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

398

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

399

Point process models for astronomy: Quasars, coronal mass ejections, and solar flares  

Microsoft Academic Search

This thesis presents a statistical analysis of two interesting astronomical applications that involve point process data. The first chapter presents an application in solar physics that looks at two types of solar events: solar flares and coronal mass ejections (CMEs). The data are viewed as a marked point process in time, and the analysis seeks to determine whether there is

Angela Beth Hugeback

2007-01-01

400

SEP Temporal Fluctuations Related to Extreme Solar Flare Events Detected by SOHO/CELIAS/SEM  

E-print Network

SEP Temporal Fluctuations Related to Extreme Solar Flare Events Detected by SOHO/CELIAS/SEM Leonid, Pacific Palisades, CA 90272, USA The SOHO CELIAS/SEM measurements of the solar Extreme Ultraviolet (EUV of Solar Energetic Particles (SEP). A model of the SEM response to a quasi-isotropic SEP fluence allowed us

Didkovsky, Leonid

401

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

402

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

NASA Astrophysics Data System (ADS)

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

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

403

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

404

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

405

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

406

SAR arc occurrence frequency during cycle 23 of solar activity  

Microsoft Academic Search

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

V. N. Alekseev; I. B. Ievenko

2008-01-01

407

Evidence for extended acceleration of solar flare ions from 18 MeV solar neutrons detected with the MESSENGER Neutron Spectrometer  

E-print Network

Evidence for extended acceleration of solar flare ions from 1­8 MeV solar neutrons detected are the first detection of solar neutrons inside 1 AU. This flare contained multiple acceleration episodesV solar neutrons detected with the MESSENGER Neutron Spectrometer, J. Geophys. Res., 115, A01102, doi:10

California at Berkeley, University of

408

Energetic Solar Flares and x-ray Burst during last 3 cycles  

NASA Astrophysics Data System (ADS)

Grouped Solar flares and energetic flares during its entire period (launch on Aug. 1966 to re-entry on Dec. 2006) were given. The data were obtained from Solar Geophysical data reports by the US Department of Commerce, hard X-ray burst spectrometer (HXRBS) during the solar cycle21,22 and 23. The bursts emitted from solar coronal atmosphere, and extended to the outer layers of the sun, were also studied. Power spectrum analyses method were used for the data treatments, to find the intermediate and intermediate-term periodicities, 14, 28, 35 are significant. Long term periodicities periodicity 311 days appeared, and confirmed with the other results.

Abdel Hady, A.

2009-04-01

409

On the acceleration of high-energy particles in solar flares  

NASA Technical Reports Server (NTRS)

The relationship is discussed between some characteristics of microwave Type 4 radio bursts and solar cosmic ray protons of MeV energy. It is shown that the peak flux intensity of those bursts is almost linearly correlated with MeV proton peak flux observed by satellites near the earth and that protons and electrons would be accelerated simultaneously by a similar mechanism during the explosive phase of solar flares. Brief discussion is given on the propagation of solar cosmic rays in the solar envelope after ejection from the flare regions.

Sakurai, K.

1972-01-01

410

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

SciTech Connect

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

Winter, Henry D.; Reeves, Katharine K. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 58, Cambridge, MA 02138 (United States); Martens, Petrus, E-mail: hwinter@cfa.harvard.edu [Department of Physics, Montana State University, P.O. Box 173840, Bozeman, MT 59717 (United States)

2011-07-10

411

Looptop Hard X-Ray Emission in Solar Flares: Images and Statistics  

E-print Network

The discovery of hard X-ray sources near the top of a flaring loop by the HXT instrument on board the YOHKOH satellite represents a significant progress towards the understanding of the basic processes driving solar flares. In this paper we extend the previous study of limb flares by Masuda (1994) by including all YOHKOH observations up through August 1998. We report that from October 1991 to August 1998, YOHKOH observed 20 X-ray bright limb flares (where we use the same selection criteria as Masuda), of which we have sufficient data to analyze 18 events, including 8 previously unanalyzed flares. Of these 18 events, 15 show detectable impulsive looptop emission. Considering that the finite dynamic range (about a decade) of the detection introduces a strong bias against observing comparatively weak looptop sources, we conclude that looptop emission is a common feature of all flares. We summarize the observations of the footpoint to looptop flux ratio and the spectral indices. We present light curves and images of all the important newly analyzed limb flares. Whenever possible we present results for individual pulses in multipeak flares and for different loops for multiloop flares. We then discuss the statistics of the fluxes and spectral indices of the looptop and footpoint sources taking into account observational selection biases. The importance of these observations (and those expected from the scheduled HESSI satellite with its superior angular spectral and temporal resolution) in constraining acceleration models and parameters is discussed briefly.

Vahe' Petrosian; Timothy Q. Donaghy; James M. McTiernan

2001-12-14

412

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

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

413

Solar flare induced D-region ionospheric perturbations evaluated from VLF measurements  

NASA Astrophysics Data System (ADS)

The results of very low frequency (VLF) wave amplitude measurements carried out at the low latitude station Varanasi (geom. lat. 14?55'N, long. 154?E), India during solar flares are presented for the first time. The VLF waves (19.8 kHz) transmitted from the NWC-transmitter, Australia propagated in the Earth-ionosphere waveguide to long distances and were recorded at Varanasi. Data are analyzed and the reflection height H' and the sharpness factor ? are evaluated. It is found that the reflection height decreases whereas sharpness factor increases with the increase of solar flare power. The H' is found to be higher and ? smaller at low latitudes than the corresponding values at mid and high latitudes. The sunspot numbers were low during the considered period 2011-2012, being the rising phase of solar cycle 24 and as a result cosmic rays may impact the D-region ionosphere. The increased ionization from the flare lowers the effective reflecting height, H', of the D-region roughly in proportion to the logarithm of the X-ray flare intensity from a typical mid-day unperturbed value of about 71-72 km down to about 65 km for an X class flare. The sharpness ( ?) of the lower edge of the D-region is also significantly increased by the flare but reaches a clear saturation value of about 0.48 km-1 for flares of magnitude greater than about X1 class.

Singh, Ashutosh K.; Singh, A. K.; Singh, Rajesh; Singh, R. P.

2014-03-01

414

New observational facts about particle acceleration and transport during solar flares  

NASA Technical Reports Server (NTRS)

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

Trottel, G.

1996-01-01

415

Solar Flare Abundances of Potassium, Argon, and Sulphur  

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

416

A CLASSIFICATION SCHEME FOR TURBULENT ACCELERATION PROCESSES IN SOLAR FLARES  

SciTech Connect

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

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

2012-08-01

417

Magnetic shielding of interplanetary spacecraft against solar flare radiation  

NASA Technical Reports Server (NTRS)

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

Cocks, Franklin H.; Watkins, Seth

1993-01-01

418

Ulysses particle observations of the March 1991 solar flare events  

NASA Technical Reports Server (NTRS)

Observations of energetic ions from the COSPIN instrument on the Ulysses spacecraft at 2.5 AU during the March 1991 series of solar flare events arae presented. The intensity profiles observed during this sequence of events were affected both by the presence of interplanetary shocks and large-scale discontinuities in the magnetic field, the low-energy (about 1 MeV) protons being influenced mainly by the shocks and the discontinuities, and the high-energy (about 100 MeV) protons by the discontinuities. The first shock observed at Ulysses was followed by several discontinuities and a Coronal Mass Ejection (CME) which were probably moving with the shock. Particles following this shock were prevented from propagating freely into the heliosphere by the structure moving with the shock, and were carried along with it. A second shock was followed by a region containing bi-directional particle anisotropies. A subsequent enhancement of low-energy particles suggests the passage of another shock. This was followed by a slow intensity decay which coincided with a second CME and where bi-directional particle anisotropies were again observed.

Sanderson, T. R.; Marsden, R. G.; Heras, A. M.; Wenzel, K.-P.; Anglin, J. D.; Balogh, A.; Forsyth, R.

1992-01-01

419

High-sensitivity observations of solar flare decimeter radiation  

E-print Network

A new acousto-optic radio spectrometer has observed the 1 - 2 GHz radio emission of solar flares with unprecedented sensitivity. The number of detected decimeter type III bursts is greatly enhanced compared to observations by conventional spectrometers observing only one frequency at the time. The observations indicate a large number of electron beams propagating in dense plasmas. For the first time, we report weak, reversed drifting type III bursts at frequencies above simultaneous narrowband decimeter spikes. The type III bursts are reliable signatures of electron beams propagating downward in the corona, apparently away from the source of the spikes. The observations contradict the most popular spike model that places the spike sources at the footpoints of loops. Conspicuous also was an apparent bidirectional type U burst forming a fish-like pattern. It occurs simultaneously with an intense U-burst at 600-370 MHz observed in Tremsdorf. We suggest that it intermodulated with strong terrestrial interference (cellular phones) causing a spurious symmetric pattern in the spectrogram at 1.4 GHz. Symmetric features in the 1 - 2 GHz range, some already reported in the literature, therefore must be considered with utmost caution.

Arnold O. Benz; Peter Messmer; Christian Monstein

2000-12-05

420

Perspectives of current-layer diagnostics in solar flares  

E-print Network

A reconnecting current layer is a `heart' of a solar flare, because it is a place of magnetic-field energy release. However there are no direct observations of these layers. The aim of our work is to understand why we actually do not directly observe current layers and what we need to do it in the future. The method is based on a simple mathematical model of a super-hot (T ~ 1E8 K) turbulent-current layer (SHTCL) and a model of plasma heating by the layer. The models allow us to study a correspondence between the main characteristics of the layer, such as temperature and dimensions, and the observational features, such as differential and integral emission measure of heated plasma, intensity of spectral lines Fe XXVI (1.78 and 1.51A) and Ni XXVII (1.59 A). This method provides a theoretical basis for determining parameters of the current layer from observations. Observations of SHTCLs are difficult, because the spectral line intensities are faint, but it is theoretically possible in the future. Observations i...

Oreshina, A V

2014-01-01

421

CORONAL ELECTRON DISTRIBUTION IN SOLAR FLARES: DRIFT-KINETIC MODEL  

SciTech Connect

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

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

2011-05-10

422

ON THE MECHANICAL ENERGY AVAILABLE TO DRIVE SOLAR FLARES A. N. McClymont and G. H. Fisher  

E-print Network

ON THE MECHANICAL ENERGY AVAILABLE TO DRIVE SOLAR FLARES A. N. McClymont and G. H. Fisher Institute specifically, assuming that the ultimate source of flare energy is mechanical energy in the convection zone to the energy source may limit this mechanism to moderate sized flares; and that emerging magnetic flux tubes

Fisher, George H.

423

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01