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1

Universality in Solar Flare and Earthquake Occurrence  

SciTech Connect

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

De Arcangelis, L. [Department of Information Engineering and CNISM, Second University of Naples, 81031 Aversa (CE) (Italy); Godano, C. [Department of Environmental Sciences and CNISM, Second University of Naples, 81100 Caserta (Italy); Lippiello, E. [University of Naples 'Federico II', 80125 Naples (Italy); Nicodemi, M. [Department of Physical Sciences, University of Naples 'Federico II', Coherentia-CNR and INFN, 80125 Naples (Italy)

2006-02-10

2

Universality in solar flare and earthquake occurrence.  

PubMed

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

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

2006-02-06

3

Solar Flare Occurrence Rate and Waiting Time Statistics  

NASA Astrophysics Data System (ADS)

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

Gorobets, A.; Messerotti, M.

2012-12-01

4

Solar Flare Occurrence Rate and Probability in Terms of the Sunspot Classification Supplemented with Sunspot Area and Its Changes  

NASA Astrophysics Data System (ADS)

We investigate the solar flare occurrence rate and daily flare probability in terms of the sunspot classification supplemented with sunspot area and its changes. For this we use the NOAA active region data and GOES solar flare data for 15 years (from January 1996 to December 2010). We consider the most flare-productive 11 sunspot classes in the McIntosh sunspot group classification. Sunspot area and its changes can be a proxy of magnetic flux and its emergence/cancellation, respectively. We classify each sunspot group into two sub-groups by its area: "Large" and "Small". In addition, for each group, we classify it into three sub-groups according to sunspot area changes: "Decrease", "Steady", and "Increase". As a result, in the case of compact groups, their flare occurrence rates and daily flare probabilities noticeably increase with sunspot group area. We also find that the flare occurrence rates and daily flare probabilities for the "Increase" sub-groups are noticeably higher than those for the other sub-groups. In case of the (M+X)-class flares in the `Dkc' group, the flare occurrence rate of the "Increase" sub-group is three times higher than that of the "Steady" sub-group. The mean flare occurrence rates and flare probabilities for all sunspot groups increase with the following order: "Decrease", "Steady", and "Increase". Our results statistically demonstrate that magnetic flux and its emergence enhance the occurrence of major solar flares.

Lee, Kangjin; Moon, Y.-J.; Lee, Jin-Yi; Lee, Kyoung-Sun; Na, Hyeonock

2012-12-01

5

Solar Flares  

NSDL National Science Digital Library

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

Hathaway, David

6

Multiple flare occurrences and the geomagnetic storm characteristics during solar cycle 23  

NASA Astrophysics Data System (ADS)

High solar activity occurred during solar cycle 23, having its solar maximum peak in the years 2000 and 2001. The dual peak occurrence of the solar activity as seen in 2003, during the descending phase of the solar cycle suggests the geo- effective nature of the solar activity following the solar maximum. The most remarkable series of activities were seen during these times. Major flares are invariably followed by an abrupt increase in the solar radiation emissions from the sun. Active regions in the sun gave rise to a sequence of X- & M- class flares, a number of coronal mass ejections and several major solar energetic particle events of varying amplitudes and characteristics. Following these energetic emissions, the geomagnetic field variations recorded on the ground experienced several storm phenomena in 2005 unlike the 2003 geomagnetic storm events. Storm manifestation process as seen in the equatorial and low-latitude digital magnetic records from Indian longitude are explained in association with the prolonged fluctuations in the interplanetary magnetic field during the descending phase of the solar cycle in contrast to intense storm feature of the events in 2003.

Alex, S.; Mukherjee, S.; Pathan, B. M.

7

The Relationship Between Solar Flares and Solar Sector Boundaries.  

National Technical Information Service (NTIS)

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...

P. H. Dittmer

1974-01-01

8

The Relationship Between Solar Flares and Solar Sector Boundaries.  

National Technical Information Service (NTIS)

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 preference for (-+) boundaries ...

P. H. Dittmer

1974-01-01

9

Solar flare nomenclature  

Microsoft Academic Search

The evolution of solar flare nomenclature is reviewed in the context of the paradigm shift, in progress, from flares to coronal mass ejections (CMEs) in solar-terrestrial physics. Emphasis is placed on: the distinction between eruptive (Class II) flares and confined (Class I) flares; and the underlying similarity of eruptive flares inside (two-ribbon flares) and outside (flare-like brightenings accompanying disappearing filaments)

E. W. Cliver

1995-01-01

10

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

11

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

PubMed

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

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

2006-02-06

12

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

13

Solar and Stellar Flares  

NASA Astrophysics Data System (ADS)

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 ?-rays, signifying the common occurrence of particle acceleration to mildly relativistic or higher energies. Abundant direct (the radiation) and indirect information confirms that this particle acceleration is energetically significant, as well as common. We are thus led to the physics of particle distribution functions that may deviate radically from Maxwellian distributions. Stellar observations allow us to study these phenomena across a wide variety of environments, whereas solar and planetary observations allow us to do imaging spectroscopy and thereby get a better understanding of the global structures of the processes. In particular we have spectacular new data from satellite solar observatories such as RHESSI (hard X-rays and ?-rays) and others, most recently the Solar Dynamics Observatory. Of particular interest from the point of view of plasma physics is the flare environment: a low-beta corona linked to a massive body through an intermediate weakly-ionized layer (the chromosphere). The chromosphere is extraordinarily complicated; its behavior is coming again to be recognized as fundamental to the overall flare process, and in this presentation I will attempt to clarify its role.

Hudson, Hugh

2011-04-01

14

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

15

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

16

Solar Flares: Magnetohydrodynamic Processes  

NASA Astrophysics Data System (ADS)

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

Shibata, Kazunari; Magara, Tetsuya

2011-12-01

17

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

18

Solar Flare Physics.  

National Technical Information Service (NTIS)

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 an...

E. J. Schmahl M. R. Kundu

2000-01-01

19

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

20

Solar Flare Physics  

NASA Astrophysics Data System (ADS)

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

Schmahl, Edward J.; Kundu, Mukul R.

2000-03-01

21

Activation of solar flares  

SciTech Connect

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

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

1984-11-01

22

Solar Flare Physics  

NASA Astrophysics Data System (ADS)

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.

2000-12-01

23

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

24

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

25

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

26

Statistical Study of the CME-Solar Flares Associated Events  

NASA Astrophysics Data System (ADS)

The aim of this paper is studying the relation between the coronal mass ejections (CMEs), and their associated solar flares. I used the CMEs data (obtained from CME catalogue) which observed by SOHO/LASCO, during the Solar Cycle 23rd (1996-2006), during this period I selected 12,433 CME records. Also I used the X-ray flares data which provided geostationary operational environmental satellite (GOES), during the same interval in the 1-8 GOES channel, the recorded flare events are 22,688. I filtered these CMEs and solar flare events to select 529 CME-Flare events. I found that there is a moderate relation between the solar flare fluxes and their associated CME energies, where R = 58 %. In addition I found that 61 % of the CME-Flare associated events ejected from the solar surface after the occurrence of the associated flare. Furthermore I found that the CME-Flare relation improved during the period of high solar activity. Finally, I examined the CME association rate as a function of flare longitude and I found that the CME association rate of the total 529 selected CME-Flare events are mostly disk-Flare events.

Youssef, M.

2013-06-01

27

6Li from Solar Flares.  

PubMed

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

Ramaty; Tatischeff; Thibaud; Kozlovsky; Mandzhavidze

2000-05-10

28

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

29

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

30

Application of Stellar Flare Model to Solar Flares  

NASA Astrophysics Data System (ADS)

Solar and stellar flares result from the dynamical rearrangement of magnetic fields, which heats plasma and accelerates particles. Solar flare sizes can be directly measured from space-based observatories, giving insight into the behavior and morphology of the solar magnetic field. With current technology, however, we cannot spatially resolve flares that occur on other stars. Consequently, models have been developed that infer flare sizes using X-ray emission produced by the flare-related plasma heating. One model, the "hydrodynamic method (HM), considers the potential presence of heating during the decay phase of a flare event, along with cooling of the hot material by conduction and radiation. HM assumes that the flare is a single semi-circular loop and that the X-ray emission from the cooling material in the flare declines as a simple exponential. However, several solar and stellar flare observations suggest that this flux decay occurs in two stages, each described by a separate exponential decay timescale. We applied HM to 257 highly energetic, X-class solar flares to determine whether a one or two-stage exponential decay was a better fit for the decay phase. We compared the two fits using a chi-squared minimization technique and F-tests. Through this analysis we determined that 98% of the solar flares in our sample exhibited a two-stage decay phase. Furthermore, of the flares exhibiting a two-stage decay, the flare sizes inferred from stage two were typically much larger than those from stage one, and we found no correlation between them. Given that we do not normally observe significant increases in solar flare sizes during the decay phase _as implied by our results_ the two-stage decay phase in X-class flares may indicate a change in the geometry of the flare region (like the appearance of an "arcade") thus invalidating the results of HM in such instances.

Nunez, Alejandro; Osten, R.

2012-01-01

31

Fine Structure in Solar Flares.  

PubMed

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

Warren

2000-06-20

32

Scattering Polarization in Solar Flares  

NASA Astrophysics Data System (ADS)

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

t?pn, Ji?; Heinzel, Petr

2013-11-01

33

Ion Acceleration in Solar Flares.  

National Technical Information Service (NTIS)

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 ...

J. A. Miller S. B. Weir

1996-01-01

34

Solar flares increased in 1982  

NASA Astrophysics Data System (ADS)

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

35

Statistical Methods for Solar Flare Probability Forecasting.  

National Technical Information Service (NTIS)

The Space Environment Services Center (SESC) of the National Oceanic and Atmospheric Administration provides probability forecasts of regional solar flare disturbances. This report describes a statistical method useful to obtain 24 hour solar flare foreca...

D. F. Vecchia P. V. Tryon G. Caldwell R. H. Jones

1980-01-01

36

Scaling Laws of Solar and Stellar Flares  

NASA Astrophysics Data System (ADS)

In this study we compile for the first time comprehensive data sets of solar and stellar flare parameters, including flare peak temperatures Tp, flare peak volume emission measures EMp, and flare durations ?f from both solar and stellar data, as well as flare length scales L from solar data. Key results are that both the solar and stellar data are consistent with a common scaling law of EMp~T4.7p, but the stellar flares exhibit ~250 times higher emission measures (at the same flare peak temperature). For solar flares we observe also systematic trends for the flare length scale L(Tp)~T0.9p and the flare duration ?F(Tp)~T0.9p as a function of the flare peak temperature. Using the theoretical RTV scaling law and the fractal volume scaling observed for solar flares, i.e., V(L)~L2.4, we predict a scaling law of EMp~T4.3p, which is consistent with observations, and a scaling law for electron densities in flare loops, np~T2p/L~T1.1p. The RTV-predicted electron densities were also found to be consistent with densities inferred from total emission measures, np=(EMp/qVV)1/2, using volume filling factors of qV=0.03-0.08 constrained by fractal dimensions measured in solar flares. Solar and stellar flares are expected to have similar electron densities for equal flare peak temperatures Tp, but the higher emission measures of detected stellar flares most likely represent a selection bias of larger flare volumes and higher volume filling factors, due to low detector sensitivity at higher temperatures. Our results affect also the determination of radiative and conductive cooling times, thermal energies, and frequency distributions of solar and stellar flare energies.

Aschwanden, Markus J.; Stern, Robert A.; Gdel, Manuel

2008-01-01

37

Solar flare proton evaluation at geostationary orbits for engineering applications  

Microsoft Academic Search

Presents the results of novel analyses of spacecraft solar flare proton measurements for solar cycles 20, 21, and 22. Solar events and cycles were classified and ranked by fluence and frequency of occurrence, and events were characterized by the mean energy of the proton spectral distributions. Spacecraft observations permitted a detailed study of event characteristics, such as special consideration of

E. G. Stassinopoulos; G. J. Brucker; D. W. Nakamura; C. A. Stauffer; G. B. Gee; J. L. Barth

1996-01-01

38

The numerical MHD simulation of solar flares  

NASA Astrophysics Data System (ADS)

The 3D MHD calculations carried out above the active region AR 0365 before the flare on May 27, 2003 show solar flare energy accumulation with current sheet (CS) creation in the singular line (SL) vicinity. The maximal radio-emission intensity measured with the SSRT radio telescope (Irkutsk) coincides with the current density maximum in CS. The obtained results confirm the solar flare electrodynamical model and open the possibility for improving the solar flare prognosis.

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

2008-02-01

39

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

40

Exploring Solar Flares with Gamma Rays and Neutrons.  

National Technical Information Service (NTIS)

Gamma-ray and neutron emissions from solar flares carry information about the flaring process and conditions within the flaring magnetic loop. Extraction of this information from solar flare measurements requires an ion- acceleration, transport, and inter...

R. Murphy

2008-01-01

41

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

42

Solar flares and energetic particles.  

PubMed

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

Vilmer, Nicole

2012-07-13

43

Sun Releases X-class Solar Flare  

NASA Video Gallery

This movie shows the July 6, 2012 X1.1 flare in the 171 Angstrom wavelength as captured by NASAs Solar Dynamics Observatory (SDO). AR1515 was the source for this flare. AR1515 has been active all week with multiple M and C class flare.

Holly Zell

2012-07-07

44

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

45

FLARING SOLAR HALE SECTOR BOUNDARIES  

SciTech Connect

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

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

2011-05-20

46

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

47

Automatic Prediction of Solar Flares using Machine Learning: Practical Study on the Halloween Storm  

Microsoft Academic Search

In this paper, a machine learning system that can provide short-term automated prediction for the occurrences of significant solar flares is presented. This system extracts the experts' knowledge embedded in the public NGDC solar catalogues and represents it in learning rules that can be used by computers to predict flares. This work builds on our previous work and the prediction

R. Qahwajil; T. Colak

2007-01-01

48

Solar Flare Myth in solar-terrestrial physics.  

National Technical Information Service (NTIS)

Early observations of associations between solar flares and large non- recurrent geomagnetic storms, large (open quote)solar(close quote) energetic particle events, and transient shock wave disturbances in the solar wind led to a paradigm of cause and eff...

J. T. Gosling

1993-01-01

49

Diagnostics of solar flare reconnection  

NASA Astrophysics Data System (ADS)

We present new diagnostics of the solar flare reconnection, mainly based on the plasma radio emission. We propose that the high-frequency (600-2000 MHz) slowly drifting pulsating structures map the flare magnetic field reconnection. These structures correspond to the radio emission from plasmoids which are formed in the extended current sheet due to tearing and coalescence processes. An increase of the frequency drift of the drifting structures is interpreted as an increase of the reconnection rate. Using this model, time scales of slowly drifting pulsating structure observed during the 12 April 2001 flare by the Trieste radiopolarimeter with high time resolution (1 ms) are interpreted as a radio manifestation of electron beams accelerated in the multi-scale reconnection process. For short periods Fourier spectra of the observed structure have a power-law form with power-law indices in the 1.3-1.6 range. For comparison the 2-D MHD numerical modeling of the multi-scale reconnection is made and it is shown that Fourier spectrum of the reconnection dissipation power has also a power-law form, but with power-law index 2. Furthermore, we compute a time evolution of plasma parameters (density, magnetic field etc) in the 2-D MHD model of the reconnection. Then assuming a plasma radio emission from locations, where the "double-resonance" instability generates the upper-hybrid waves due to unstable distribution function of suprathermal electrons, we model radio spectra. Effects of the MHD turbulence are included. The resulting spectra are compared with those observed. It is found, that depending on model parameters the lace bursts and the decimetric spikes can be reproduced. Thus, it is shown that the model can be used for diagnostics of the flare reconnection process. We also point out possible radio signatures of reconnection outflow termination shocks. They are detected as type II-like herringbone structures in the 200-700 MHz frequency range. Finally, we mention H? spectra of the 18 September 1995 eruptive prominence which indicate the bi-directional plasma flow as expected in the reconnection process.

Karlick, M.; Brta, M.

2004-11-01

50

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

51

Reevaluation of Solar Flares - 1967.  

National Technical Information Service (NTIS)

To bring all flare data for cycle 20 to a reasonably common basis, a reevaluation of flares in 1967 has been carried out at the McMath-Hulbert Observatory. One table presents the resultant finding list of flares of importance greater than or equal to 1, 1...

H. W. Dodson E. R. Hedeman M. R. de Miceli

1972-01-01

52

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

53

Solar Active Region Classification and Flare Forecasting  

NASA Astrophysics Data System (ADS)

There are two sunspot classification systems that are currently being used to forecast the probability of a solar active region flaring, the Mount Wilson magnetic classification system and the Modified Zurich classification system. Once a solar active region emerges on the visible solar disk, it is classified using both of these systems. An individual active region's flaring probability is produced using a well-known table of probabilities (based on the Modified Zurich system), and these probabilities are modified using rules of thumb based on the Mount Wilson system information. A study has been conducted taking solar cycle 23 active regions, re-classifying these regions, and then using the look-up table and legacy rule to provide a probability. These probabilities were then compared to actual flare rates. The presentation will discuss the issues with current classification systems, why look-up table flare forecasting does not work, and where improvements to the current classification systems can be made.

Crown, M.; Balasubramaniam, K. S.; Cooley, K.; Daniels, A.; Mara, J.; Valdez, M.

2010-12-01

54

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

55

Origins and effects of solar flares  

NASA Astrophysics Data System (ADS)

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

Rust, D. M.

56

Understanding solar flares from radio observations  

Microsoft Academic Search

Radio observations are very sensitive to electrons accelerated in solar flares and provide a view of particle acceleration which complements that obtained from hard Xrays and gamma-rays: whereas the latter usually come from accelerated electrons striking the chromosphere, the radio emission comes from electrons gyrating in magnetic fields in the solar corona. The radio emission thus can trace the magnetic

S. White

2002-01-01

57

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

58

C3-class Solar Flare Eruption  

NASA Video Gallery

Just as sunspot 1105 was turning away from Earth on Sept. 8, the active region erupted, producing a C3-class solar flare (peak @ 2330 UT) and a fantastic prominence. This is a three color closeup of the activity taken by Solar Dynamic Observatory (SDO). The accompanying coronal mass ejection (CME) was not directed toward any planets.

Holly Zell

2010-09-09

59

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

60

M-Class Solar Flare Erupts  

NASA Video Gallery

An M-class flare erupted in active sunspot region 1093, peaking at 1824 UTC on August 7, 2010. The eruption hurled a coronal mass ejection (CME) into space. NASA's Solar Dynamics Observatory observed the flare. The CME is not fully directed toward Earth, but some of the plasma cloud may glance the magnetosphere between August 9 and August 10, causing a geomagnetic disturbance and possible aurora

Holly Zell

2010-08-09

61

The Solar Flare Myth in solar-terrestrial physics  

SciTech Connect

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

Gosling, J.T.

1993-07-01

62

Acceleration and Propagation of Solar Flare Energetic Particles.  

National Technical Information Service (NTIS)

Observations and theories of particle acceleration in solar flares are reviewed. The most direct signatures of particle acceleration in flares are gamma rays, X-rays and radio emissions produced by the energetic particles in the solar atmosphere and energ...

M. A. Forman R. Ramaty E. G. Zweibel T. E. Holzer D. Mihalas

1982-01-01

63

Remote Oscillatory Responses to a Solar Flare  

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

64

Detecting Solar Neutrino Flares and Flavors  

NASA Astrophysics Data System (ADS)

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

Fargion, D.

2004-06-01

65

Silicon Abundance from RESIK Solar Flare Observations  

NASA Astrophysics Data System (ADS)

The RESIK instrument on the CORONAS-F spacecraft obtained solar flare and active-region X-ray spectra in four channels covering the wavelength range 3.8 - 6.1 in its operational period between 2001 and 2003. Several highly ionized silicon lines were observed within the range of the long-wavelength channel (5.00 - 6.05 ). The fluxes of the Si xiv Ly- ? line (5.217 ) and the Si xiii 1 s 2 - 1 s3 p line (5.688 ) during 21 flares with optimized pulse-height analyzer settings on RESIK have been analyzed to obtain the silicon abundance relative to hydrogen in flare plasmas. As in previous work, the emitting plasma for each spectrum is assumed to be characterized by a single temperature and emission measure given by the ratio of emission in the two channels of GOES. The silicon abundance is determined to be A(Si)=7.93.21 (Si xiv) and 7.89.13 (Si xiii) on a logarithmic scale with H=12. These values, which vary by only very small amounts from flare to flare and times within flares, are 2.61.3 and 2.40.7 times the photospheric abundance, and are about a factor of three higher than RESIK measurements during a period of very low activity. There is a suggestion that the Si/S abundance ratio increases from active regions to flares.

Sylwester, B.; Phillips, K. J. H.; Sylwester, J.; K?pa, A.

2013-04-01

66

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

67

An objective method for forecasting solar flares  

NASA Astrophysics Data System (ADS)

Solar parameters derived from the region analysis program at the NOAA Space Environment Services Center (SESC) are submitted to a multivariate discriminant analysis (MVDA) in which the parameters relevant to flare prediction are identified and incorporated in a classification procedure to produce a flare forecast. The analysis uses two years of data (6095 solar active region-days). The MVDA forecast is compared with a subjective forecast derived from the SESC forecast during the same period, and is found to have greater accuracy overall. Specific recommendations are made concerning the application of the technique in a forecasting operation, and in the types of data required for future improvement.

Neidig, D. F.; Wiborg, P. H.; Seagraves, P. H.; Hirman, J. W.; Flowers, W. E.

1981-02-01

68

Relationship of flare size and particle anisotropy in solar gamma-ray flares  

SciTech Connect

The effects of radiation directivity on the interpretation of SMM gamma-ray flare observations. If the electron anisotropy is independent of flare size, the size distribution of 300 keV-1 Mev flare is much flatter than that of X-ray flares. This implies that larger flares have, on average, harder electron spectra. Distributions of electrons strongly peaked downward into the solar photosphere are not consistent with the data. 14 references.

Dermer, C.D.

1987-12-01

69

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 ) 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 Moul, Jean-Louis; Courtillot, Vincent

2012-02-01

70

A solar tornado triggered by flares?  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

71

Solar flare proton evaluation at geostationary orbits for engineering applications  

SciTech Connect

This work presents the results of novel analyses of spacecraft solar flare proton measurements for solar cycles 20, 21, and 22. Solar events and cycles were classified and ranked by fluence and frequency of occurrence, and events were characterized by the mean energy of the proton spectral distributions. Spacecraft observations permitted a detailed study of event characteristics, such as special consideration of solar minimum flares and cycle variability. Tables and curves are presented to allow evaluations of potential threats to spacecraft survivability at GEO, particularly for types of flare environments that emulate solar cycle 22. Upsets for major events are calculated for several Bendel A parameter values and shield thicknesses, and effective energy thresholds of events are determined as a function of these variables. Critical fluence levels, required to cause errors, versus A are presented. SEU`s (single event upsets) of 93L422 devices on TDRS-1 are evaluated for various shielding conditions. Finally, upset dependencies on A and shield thickness are correlated with event fluences for threshold energies of >30, >50, and >60 MeV.

Stassinopoulos, E.G.; Barth, J.L. [National Aeronautics and Space Administration, Greenbelt, MD (United States). Goddard Space Flight Center; Brucker, G.J. [Radiation Effects Consultants, West Long Branch, NJ (United States); Nakamura, D.W.; Stauffer, C.A.; Gee, G.B. [SES, Inc., Greenbelt, MD (United States)

1996-04-01

72

Contributions of the solar ultraviolet irradiance to the total solar irradiance during large flares  

Microsoft Academic Search

The solar X-ray radiation varies more than other wavelengths during flares; thus solar X-ray irradiance measurements are relied upon for detecting flare events as well as used to study flare parameters. There is new information about the spectral and temporal variations of flares using solar irradiance measurements from NASA's Solar Radiation and Climate Experiment (SORCE) and the Thermosphere, Ionosphere, Mesosphere,

Thomas N. Woods; Greg Kopp; Phillip C. Chamberlin

2006-01-01

73

On Solar Flares and Cycle 23  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

74

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. Alfvn waves play an important role in transporting energy and potential, and in redistributing current on a global scale.

Melrose, Don

2013-06-01

75

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

76

Three impulsive solar x-ray flares  

SciTech Connect

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

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

1982-07-01

77

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

78

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

79

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

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

80

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

81

The magnetic nature of solar flares  

NASA Astrophysics Data System (ADS)

The main challenge for the theory of solar eruptions has been to understand two basic aspects of large flares. These are the cause of the flare itself and the nature of the morphological features which form during its evolution. Such features include separating ribbons of H? emission joined by a rising arcade of soft x-ray loops, with hard x-ray emission at their summits and at their feet. Two major advances in our understanding of the theory of solar flares have recently occurred. The first is the realisation that a magnetohydrodynamic (MHD) catastrophe is probably responsible for the basic eruption and the second is that the eruption is likely to drive a reconnection process in the field lines stretched out by the eruption. The reconnection is responsible for the ribbons and the set of rising soft x-ray loops, and such a process is well supported by numerical experiments and detailed observations from the Japanese satellite Yohkoh. Magnetic energy conversion by reconnection in two dimensions is relatively well understood, but in three dimensions we are only starting to understand the complexity of the magnetic topology and the MHD dynamics which are involved. How the dynamics lead to particle acceleration is even less well understood. Particle acceleration in flares may in principle occur in a variety of ways, such as stochastic acceleration by MHD turbulence, acceleration by direct electric fields at the reconnection site, or diffusive shock acceleration at the different kinds of MHD shock waves that are produced during the flare. However, which of these processes is most important for producing the energetic particles that strike the solar surface remains a mystery.

Priest, E. R.; Forbes, T. G.

82

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

SciTech Connect

Flare occurrence is statistically associated with changes in several characteristics of the line-of-sight magnetic field in solar active regions (ARs). We calculated magnetic measures throughout the disk passage of 1075 ARs spanning solar cycle 23 to find a statistical relationship between the solar magnetic field and flares. This expansive study of over 71,000 magnetograms and 6000 flares uses superposed epoch (SPE) analysis to investigate changes in several magnetic measures surrounding flares and ARs completely lacking associated flares. The results were used to seek any flare associated signatures with the capability to recover weak systematic signals with SPE analysis. SPE analysis is a method of combining large sets of data series in a manner that yields concise information. This is achieved by aligning the temporal location of a specified flare in each time series, then calculating the statistical moments of the 'overlapping' data. The best-calculated parameter, the gradient-weighted inversion-line length (GWILL), combines the primary polarity inversion line (PIL) length and the gradient across it. Therefore, GWILL is sensitive to complex field structures via the length of the PIL and shearing via the gradient. GWILL shows an average 35% increase during the 40 hr prior to X-class flares, a 16% increase before M-class flares, and 17% increase prior to B-C-class flares. ARs not associated with flares tend to decrease in GWILL during their disk passage. Gilbert and Heidke skill scores are also calculated and show that even GWILL is not a reliable parameter for predicting solar flares in real time.

Mason, J. P.; Hoeksema, J. T., E-mail: JMason86@sun.stanford.ed, E-mail: JTHoeksema@sun.stanford.ed [W. W. Hansen Experimental Physics Laboratory, Stanford University, 450 Serra Mall, Stanford, CA 94305-4085 (United States)

2010-11-01

83

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

84

NASA Sees Fast-Moving Solar Flare  

NASA Video Gallery

One of the fastest coronal mass ejections, or solar flares, in years was captured by the STEREO COR1 telescopes on Aug. 1, 2010. This movie combines COR1-Ahead images with Helium II 304 Angstrom images from the STEREO EUVI telescope. It shows the rapid explosion of material outward, followed by a slower eruption of a polar crown prominence from another part of the sun. This CME headed toward Earth at speeds above 620 miles per second

Robert Garner

2010-08-04

85

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

86

A brief review of ``solar flare effects'' on the ionosphere  

Microsoft Academic Search

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

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

2009-01-01

87

A brief review of solar flare effects on the ionosphere  

Microsoft Academic Search

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

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

2009-01-01

88

Size distributions of solar flares and solar energetic particle events  

NASA Astrophysics Data System (ADS)

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-1) coronal mass ejections (CMEs) that drive coronal/interplanetary shock waves. For the 1996-2005 interval, the slopes (? values) of power-law size distributions of the peak 1-8 fluxes of SXR flares associated with (a) >10 MeV SEP events (with peak fluxes >=1 pr cm-2 s-1 sr-1) and (b) fast CMEs were ~1.3-1.4 compared to ~1.2 for the peak proton fluxes of >10 MeV SEP events and ~2 for the peak 1-8 fluxes of all SXR flares. The difference of ~0.15 between the slopes of the distributions of SEP events and SEP SXR flares is consistent with the observed variation of SEP event peak flux with SXR peak flux.

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

2012-09-01

89

A Study of Connections Between Solar Flares and Subsurface Flow Fields of Active Regions  

NASA Astrophysics Data System (ADS)

We investigate the connections between the occurrence of major solar flares and subsurface dynamic properties of active regions. For this analysis, we select five active regions that produced a total of 11 flares with peak X-ray flux intensity higher than M5.0. The subsurface velocity fields are obtained from time-distance helioseismology analysis using SDO/HMI (Solar Dynamics Observatory/Helioseismic and Magnetic Imager) Doppler observations, and the X-ray flux intensity is taken from GOES (Geostationary Operational Environmental Satellites). It is found that among the eight amplitude bumps in the evolutionary curves of subsurface kinetic helicity, five (62.5%) of them had a flare stronger than M5.0 occurring within 8 hours, either before or after the bumps. Another subsurface parameter is the Normalized Helicity Gradient Variance (NHGV), reflecting kinetic helicity spread in different depth layers; it also shows bumps near the occurrence of these solar flares. Although there is no one-to-one correspondence between the flare and the subsurface properties, these observational phenomena are worth further studies to better understand the flares' subsurface roots, and to investigate whether the subsurface properties can be used for major flare forecasts.

Gao, Yu; Zhao, Junwei; Zhang, Hongqi

2013-04-01

90

Automatic Solar Flare Detection Using MLP, RBF and SVM  

NASA Astrophysics Data System (ADS)

The focus of the automatic solar flare detection is on the development of efficient feature-based classifiers. Three advanced techniques used in this work are Multi-Layer Perceptron (MLP), Radial Basis Function (RBF), and Support Vector Machine (SVM) classifiers. We have experimented and compared these three methods for solar flare detection on the solar H? images obtained from Big Bear Solar Observatory in California. The preprocessing step is to obtain the nine principal features of the solar flares for the classifiers. Experimental results show that by using SVM, we can obtain the best classification rate of the solar flares. Our work would lead to real-time solar flare detection using advanced pattern recognition techniques. The work is supported by National Science Foundation (NSF) under grants ATM 0076602 and ATM 0233931.

Qu, M.; Shih, F.; Jing, J.; Wang, H. M.

2003-05-01

91

High-energy processes in solar flares  

SciTech Connect

A detailed study of high-energy processes in solar flares is reported, including the production of neutrons and pions, and incorporating isobaric and scaling models and a recent compilation of pion production data (Dermer, 1986). The broad-band gamma-ray spectrum resulting from the decay of neutral pions, the bremsstrahlung of positrons and electrons from the decay of charged pions, and the annihilation in flight of positrons is evaluated. Also evaluated is the 0.511 MeV gamma-ray line resulting from the annihilation of the positrons which survive annihilation in flight. Calculations were based on an isotropic, thick-target model using the best available nuclear data and models. Results are compared with extensive observation of the June 3, 1982 flare (10-120 MeV gamma rays), 0.511 and 2.2 MeV line emission, nuclear line emission, high-energy neutrons, and interplanetary charged particles. 75 references.

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

1987-03-01

92

A slingshot model for solar flares  

SciTech Connect

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. 23 refs.

Benford, G. (California, University, Irvine (USA))

1991-06-01

93

Modeling the thermospheric response to solar flares  

NASA Astrophysics Data System (ADS)

Measurements of the incoming solar extreme ultraviolet (EUV) irradiance now allow models to be driven at higher temporal resolution and with better accuracy than with proxy-based models. Using solar irradiance measurements from the Solar EUV Experiment (SEE) instrument to drive the Global Ionosphere-Thermosphere Model, the global thermospheric response to the 28 October 2003 and 6 November 2004 solar flares is presented. The model indicates that the thermospheric density at 400 km can increase by as much as 14.6% in under 2 hours because of the flare and takes 12 hours to settle to close to a nominal state. Intense dayside heating launches nightward propagating gravity waves that transport energy efficiently to the nightside at velocities near the local sound speed plus the bulk wind velocity. Measurements from the Champ satellite indicate that the simulated day to night propagation time is similar to the observed one. Substantial density enhancements occur near the midnight sector as the wave converges on itself. In some locations the nightside perturbations are as large as those on the dayside. The convergence of the wave also leads to significant adiabatic heating of the nightside thermosphere. Eventually, the wave is reflected back toward the dayside but is quickly damped.

Pawlowski, David J.; Ridley, Aaron J.

2008-10-01

94

Impact factor for the ionospheric TEC response to solar flare  

NASA Astrophysics Data System (ADS)

As one of the most fast and severest solar eventssolar flare, that mainly are classified according to the peak flux of soft X-rays (1-8 angstrom) measured on the GOES spacecraft, affects the earth's upper atmosphere seriously. During a flare, the Extreme Ultraviolet (EUV) and X-rays emitted from the solar active region ionize the earth's neutral compositions in the altitudes of ionosphere so to make the extra ionospheric ionization that caused the so-called SIDs. Although the increase of electron density during a flare appears in all ionospheric sub-regions, the increase of electron density in the F region due to the extra ionization of EUV radiation is thought to be responsible for a large fraction of the SITEC so that SITEC can be used as an index to represent the response of the ionospheric F region to solar flares. With the advent of GPS satellite beacon methods for measuring the ionospheric TEC, it has become one of the chief parameters for indicating the strength of the flare effects on ionosphere. Through the study of the ionospheric TEC during different solar flares, the different responses of the ionospheric TEC to the same level solar flares classified according to the soft X-ray peak flux have been noted. Statistical analysis shows that besides the solar X-ray peak flux parameter, the parameter of the flare location on solar disc is also related to the effective strength of the ionospheric response to solar flare. In this study, the relationship between the ionospheric TEC enhancement and the flare location, flare X-ray peak level is analyzed statistically and a primary empirical model is obtained for solar flare's space weather forecast.

Zhang, Donghe; Cai, Lei; Hao, Yongqiang; Xiao, Zuo

95

Solar Flares Fire Up Protons, Make Gamma Rays  

NASA Video Gallery

Solar flares produce gamma rays by several processes, one of which is illustrated here. The energy released in a solar flare rapidly accelerates charged particles. When a high-energy proton strikes matter in the sun's atmosphere and visible surface, the result may be a short-lived particle -- a pion -- that emits gamma rays when it decays. Credit: NASA's Goddard Space Flight Center

gsfcvideo

2012-06-11

96

Doppler study of ionospheric effects of solar flares  

NASA Astrophysics Data System (ADS)

Ionospheric effects arising during solar flares were studied by the Doppler technique on the Fort Collins-Havana path. An approximate electron density profile is determined on the basis of sudden frequency deviation data. Integrated solar flux is determined for the flare of February 15, 1978 at wavelengths of 100-1030 A.

Vazherkin, V. A.; Laso, B.; Lobachevskii, L. A.; Novikov, V. D.; Odintsova, I. N.

1980-12-01

97

Wave-particle interactions in solar flares  

NASA Astrophysics Data System (ADS)

We investigate resonant wave-particle interactions in weakly turbulent low-beta plasmas. We are interested in the scenario in which wave energy is injected at large scales and cascades to smaller scales via three-wave interactions. The resonant interactions between different types of waves and particles are widely different in their efficiency. In this work, the behavior of the resonant interactions are investigated along with the coupled evolution of the anisotropic wave power spectra and particle velocity distributions in 2D numerical simulations. The simulations show that the efficiency of resonant interactions changes as the particle velocity distributions evolve. The implications of our results for solar flares are discussed.

Pongkitiwanichakul, P.; Chandran, B. D.

2010-12-01

98

The Origin of the Solar Flare Waiting-Time Distribution.  

PubMed

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

Wheatland

2000-06-20

99

Flaring time interval distribution and spatial correlation of major X-ray solar flares  

Microsoft Academic Search

A statistical study is performed on X-ray flares stronger than C1 class that erupted during the solar maximum between 1989 and 1991. We have investigated the flaring time interval distribution (waiting-time distribution) and the spatial correlation of successive flare pairs. The observed waiting-time distribution for the whole data is found to be well represented by a nonstationary Poisson probability function

Y.-J. Moon; G. S. Choe; H. S. Yun; Y. D. Park

2001-01-01

100

Ultrarelativistic electrons and solar flare gamma-radiation  

NASA Astrophysics Data System (ADS)

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

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

1985-08-01

101

Multi-wavelength observations of POST flare loops in two long duration solar flares  

Microsoft Academic Search

We have analysed two Long Duration solar Events (LDEs) which produced large systems of Post Flare Loops (PFLs) and which have been observed by Yohkoh and ground-based observatories. Using the Maximum Entropy Method (MEM) image synthesis technique with new modulation patterns we were able to make hard X-ray (HXR) images of the post flare loops recorded in the L Channel

L. K. Harra-Murnion; B. Schmieder; L. van Driel-Gesztelyi; J. Sato; S. P. Plunkett; P. Rudawy; B. Rompolt; M. Akioka; T. Sakao; K. Ichimoto

1998-01-01

102

The standard flare model in three dimensions. II. Upper limit on solar flare energy  

NASA Astrophysics Data System (ADS)

Context. Solar flares strongly affect the Sun's atmosphere as well as the Earth's environment. Quantifying the maximum possible energy of solar flares of the present-day Sun, if any, is thus a key question in heliophysics. Aims: The largest solar flares observed over the past few decades have reached energies of a few times 1032 erg, possibly up to 1033 erg. Flares in active Sun-like stars reach up to about 1036 erg. In the absence of direct observations of solar flares within this range, complementary methods of investigation are needed to assess the probability of solar flares beyond those in the observational record. Methods: Using historical reports for sunspot and solar active region properties in the photosphere, we scaled to observed solar values a realistic dimensionless 3D MHD simulation for eruptive flares, which originate from a highly sheared bipole. This enabled us to calculate the magnetic fluxes and flare energies in the model in a wide paramater space. Results: Firstly, commonly observed solar conditions lead to modeled magnetic fluxes and flare energies that are comparable to those estimated from observations. Secondly, we evaluate from observations that 30% of the area of sunspot groups are typically involved in flares. This is related to the strong fragmentation of these groups, which naturally results from sub-photospheric convection. When the model is scaled to 30% of the area of the largest sunspot group ever reported, with its peak magnetic field being set to the strongest value ever measured in a sunspot, it produces a flare with a maximum energy of ~6 1033 erg. Conclusions: The results of the model suggest that the Sun is able to produce flares up to about six times as energetic in total solar irradiance fluence as the strongest directly observed flare of Nov. 4, 2003. Sunspot groups larger than historically reported would yield superflares for spot pairs that would exceed tens of degrees in extent. We thus conjecture that superflare-productive Sun-like stars should have a much stronger dynamo than in the Sun.

Aulanier, G.; Dmoulin, P.; Schrijver, C. J.; Janvier, M.; Pariat, E.; Schmieder, B.

2013-01-01

103

The Role of Solar Flares in the Variability of the Extreme Ultraviolet Solar Spectral Irradiance  

NASA Astrophysics Data System (ADS)

X-ray and extreme ultraviolet (EUV, 0--121.6 nm) emission from the solar corona has long been used to provide insight into the dynamics and evolution of solar flares. The EUV Variability Experiment (EVE) onboard NASA's Solar Dynamics Observatory (SDO) measures the solar spectral irradiance in the EUV at a wide range of temperatures (7,000 K to 10 MK), capturing the complete evolution of the transition region and corona during solar flares. The goal of this thesis is to use the new observations obtained by EVE to quantify how the EUV spectral irradiance varies in response to solar flares. Most observation-based research on solar flares is done by studying individual, usually large, solar flares. My work takes a different approach. From 1 May 2010 to 31 August 2011, SDO observed over 750 solar flares. I created the EVE flare catalog to examine all of these events to produce a complete picture of the EUV variability of flares. In the process, I discovered that flares can be placed into one of five EUV flare categories. The EUV irradiance signature of these categories is unique and closely related to the magnetic structure of the flare region. Confined flares are the most ubiquitous type of flare. They are non-eruptive flares and appear as the sudden brightening of a coherent bundle of coronal loops. Localized eruptive flares are small point-like flares associated with EUV surges or jets. Arcade flares are the classic CSHKP-type flare and are identified observationally by an eruption followed by arcade of flare loops in the corona and two bright ribbons of footpoint emission in the chromosphere and transition region. EUV late phase flares are characterized by two spatially and temporally separate but related reconnection events. Finally, flares that do not fit into any of the four other flare categories are called "strange" flares. I also used the Enthaply-Based Thermal Evolution of Loops (EBTEL) code to model the heating rate of the corona during flares. By fitting the input parameters of the model to the EVE data, I determined that the rate of energy release during reconnection strongly influences the EUV irradiance signature. Each of these EUV flare categories has a different heating rate profile, which is related to the underlying magnetic structure of the flare region.

Hock, Rachel Allison

104

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

105

Decimetric gyrosynchrotron emission during a solar flare  

NASA Astrophysics Data System (ADS)

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

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

1983-11-01

106

The response of the Mars ionosphere to solar flares  

NASA Astrophysics Data System (ADS)

During a flare, the increase in solar flux at X-ray and EUV wavelengths causes an enhancement in electron densities in planetary ionospheres. Here we identify and analyze a set of 12 Mars Global Surveyor (MGS) radio occultation electron density profiles which have been affected by solar flares. These profiles coincide with flares in GOES XL flux (0.1-0.8 nm), and exhibit electron densities which are significantly enhanced above the daily average, at altitudes where X-ray and EUV flux is absorbed. With an ensemble of flares and enhanced electron density profiles, we investigate the dependence of the ionospheric response on the enhancement in the solar flux at X-ray and EUV wavelengths, and on optical depth. We characterize the relationship between these quantities with a suitable function, and show that the flare-induced enhancement in electron density increases with increasing enhancement in solar flux and with increasing optical depth. We similarly analyze the results of a 1D photochemical model of the response of the Mars ionosphere to a solar flare. We show that the enhancement in model electron densities exhibits the same dependence on solar flux and optical depth as observed in the flare-affected MGS profiles.

Fallows, Kathryn J.; Gonzalez, G.; Withers, P.; Girazian, Z.

2013-10-01

107

AR XIII line ratios in solar flares  

NASA Astrophysics Data System (ADS)

Theoretical Ar XIII electron-density-sensitive emission line ratios, derived using electron impact excitation rates interpolated from accurate R-matrix calculations, are presented for R1 = I/(242.22 A)/I(236.27 A), R2 = I(210.46 A)/I(236.27 A), and R3 = I/(248.68 A)/I(236.27 A). Electron densities deduced from the observed values of R1, R2, and R3 for solar flares obtained with the NRL S082A slitless spectrograph on board Skylab are in excellent agreement, and furthermore compare favorably with those determined from line ratios in Ca XV, which is formed at a similar electron temperature to that of Ar XIII. These results provide experimental support for the accuracy of the atomic data adopted in the analysis, as well as for the techniques used to calculate the line ratios.

Keenan, F. P.; Conlon, E. S.; Foster, V. J.; Aggarwal, K. M.; Widing, K. G.

1993-06-01

108

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

109

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 can harm satellites, communications systems, and even ground-based technologies and power grids.

gsfcvideo

2011-07-20

110

Directionality of bremsstrahlung from relativistic electrons in solar flares  

SciTech Connect

Angular and energy spectra of bremsstrahlung have been calculated from anisotropic electron distributions in solar flares. Results have been compared to observations of gamma-ray limb-brightening and to data on the variation of the gamma-ray spectrum with flare position on the sun.

Dermer, C.D.; Ramaty, R.

1985-09-01

111

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

NASA Astrophysics Data System (ADS)

A stochastic model for the energy of a flaring solar active region is presented, generalizing and extending the approach of Wheatland and Glukhov. 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 downward 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 flarelike 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.

Wheatland, M. S.

2008-06-01

112

The geomagnetic solar flare effect identified by SIIG as an indicator of a solar flare observed by GOES satellites  

NASA Astrophysics Data System (ADS)

This paper studies the efficiency of geomagnetic solar flare effects (gsfe) in X solar flare detection; so during the period 1999-2007 a comparison between solar flare (sf) observed by satellites of the Geostationary Operational Environmental Satellite (GOES) programme and gsfe published by the Service International des Indices Geomagnetiques (SIIG) is made. Solar flares (sfs) are one of the most powerful manifestations of the solar activity. Because the far UV and soft and hard X-ray solar flare radiation is absorbed by the ionosphere, the ionized gas density increases (ionospheric solar flare effect, isfe) and a sudden enhancement of geomagnetic field near Earth surface (geomagnetic solar flare effect, gsfe) is produced. The solar X-ray flux is systematically recorded since 1975 by GOES satellites, and gsfe are declared by geomagnetic observatories since 1957. We corroborate that the identification of sf using gsfe is affected by several factors: the intensity and average growth rate of solar flare radiation when quicker is it more easily the sf is detected as gsfe; the position of the geomagnetic observatory, we found that observatories placed at summer hemisphere identify more easily the sf, so the uneven geographical distribution of observatories make the sf identification difficult; the existing geomagnetic perturbation previous to sf, and the likeness between the gsfe and other geomagnetic variations. This work shows that gsfe recorded as associated to sf is a poor detector of sf even if it is intense. Some of these inconveniences can be avoided if the distribution of the observatories is improved and the identification of a sf is made using simultaneously gsfe, solar wind parameters and isfe.

Van Zele, M. A.; Meza, A.

2011-09-01

113

Toward Reliable Benchmarking of Solar Flare Forecasting Methods  

NASA Astrophysics Data System (ADS)

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.; McAteer, R. T. James; Gallagher, Peter T.

2012-03-01

114

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

115

Disturbance of the photosphere during solar two-ribbon flare  

NASA Astrophysics Data System (ADS)

We study the two-ribbon solar flare on 7 October 1979. As may be seen from the GOES soft X-ray data, the preheating phase preceded the flare impulsive phase. The semiempirical photospheric models for different stages of flare development are calculated on the basis of observed Fraunhofer spectra. The modelling results reveal inhomogeneities of temperature, gas pressure, and other parameters. Disturbances of the matter below undisturbed photosphere base prevailed during the preheating phase. Narrow and cool layers were displaced upwards in the 0.5 min time interval. During the impulsive phase and at the flare maximum the upper and middle photospheric layers were mainly disturbed. This period is characterized by the downward displacement of the lower boundary of wide low-temperature region in the upper photosphere. The photosphere perturbations were still preserved during 25--30 minutes after the flare maximum. The turbulent motions were inhibited throughout the flare.

Alikaeva, K. V.; Kondrashova, N. N.

2006-05-01

116

Solar flare gamma-ray spectroscopy with CGRO-COMPTEL  

NASA Astrophysics Data System (ADS)

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

Young, Christopher Alex

2001-08-01

117

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 s1) 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

118

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

119

GAMMA-RAY BURST FROM A SOLAR FLARE  

Microsoft Academic Search

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

L. E. Peterson; J. R. Winckler

1959-01-01

120

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

121

Studying large solar flares from ultra-long-duration balloons  

Microsoft Academic Search

Balloon flights of up to 100 days over the Antarctic and Arctic could provide a relatively low-cost way to study particle acceleration in large solar flares in the next solar maximum. With the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), we are beginning to study ion acceleration via nuclear line observations with the same level of detail -- imaging,

D. M. Smith

2004-01-01

122

Imaging X-ray Polarimeter for Solar Flares (IXPS)  

NASA Astrophysics Data System (ADS)

We describe the design of a balloon-borne Imaging X-ray Polarimeter for Solar flares (IXPS). 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 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

2011-11-01

123

Solar-Flare-Initiated Shock Waves; Blast Waves Riding on the Solar Wind.  

National Technical Information Service (NTIS)

Consider the speed of the solar flare initiated disturbance as having two separable components. These are: (1) the speed of the blast wave initiated by the impulsive release of energy by the solar flare and (2) the speed of the preexisting solar wind. In ...

D. F. Smart M. A. Shea

1983-01-01

124

Solar Radiance Chain in the April 2002 Series of Flares  

NASA Astrophysics Data System (ADS)

The April 2002 series of solar storms included a number of GOES M- and X-class flares, in particular, a X1.5 flare on April 21 that was observed by many spacecraft - SoHO, TRACE, Wind, and the recently launched RHESSI (Ramaty High Energy Solar Spectroscopic Imager), which is designed to study flare hard X-ray/gamma-ray emissions. At the same time the effects of these emissions on the Earth were observed by an fleet of spacecraft, including TIMED, and by ground-based instrumentation. The effects of the increased energetic photon flux on the Earth's atmosphere during solar flares is usually small in comparison to geomagnetic disturbances, but large X-class flares (such as the one on April 21, 2002) that are several hours in duration can have significant consequences. When the 1 to 10 nm region of the of the solar spectrum is enhanced during a flare, the energy is deposited largely in the E-region of the ionosphere, ~100 to ~120 km altitude, where increases in ion density, photoelectron production, airglow emission, and odd-nitrogen production can result. Higher energy photons (such as observed by RHESSI) penetrate to lower altitudes, where they have less effect on the atmosphere but can still create additional ionization in the D-region of the ionosphere, ~80 to ~100 km altitude, that is disruptive of certain types of radio communication. Here we present the observations of solar photon emissions and their effects on the Earth's ionosphere and atmosphere.

Lin, R. P.; Solomon, S.

2002-12-01

125

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

Microsoft Academic Search

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

Y. Liritzis; B. Petropoulos

1986-01-01

126

A COLD, TENUOUS SOLAR FLARE: ACCELERATION WITHOUT HEATING  

SciTech Connect

We report the observation of an unusual cold, tenuous solar flare, which reveals itself via numerous and prominent non-thermal manifestations, while lacking any noticeable thermal emission signature. RHESSI hard X-rays and 0.1-18 GHz radio data from OVSA and Phoenix-2 show copious electron acceleration (10{sup 35} electrons s{sup -1} above 10 keV) typical for GOES M-class flares with electrons energies up to 100 keV, but GOES temperatures not exceeding 6.1 MK. The imaging, temporal, and spectral characteristics of the flare have led us to a firm conclusion that the bulk of the microwave continuum emission from this flare was produced directly in the acceleration region. The implications of this finding for the flaring energy release and particle acceleration are discussed.

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

2011-04-10

127

Anti-neutrino imprint in solar neutrino flare  

NASA Astrophysics Data System (ADS)

A future neutrino detector at megaton mass might enlarge the neutrino telescope thresholds revealing cosmic supernova background and largest solar flares (SFs) neutrinos. Indeed the solar energetic (Ep>100 MeV) flare particles (protons, ?), while scattering among themselves on solar corona atmosphere must produce prompt charged pions, whose chain decays are source of a solar (electron muon) neutrino 'flare' (at tens or hundreds MeV energy). These brief (minutes) neutrino 'bursts' at largest flare peak may overcome by three to five orders of magnitude the steady atmospheric neutrino noise on the Earth, possibly leading to their detection above detection thresholds (in a full mixed three flavour state). Moreover the birth of anti-neutrinos at a few tens of MeV very clearly flares above a null thermal 'hep' anti-neutrino solar background and also above a tiny supernova relic and atmospheric noise. The largest prompt solar anti-neutrino 'burst' may be well detected in future Super Kamikande (gadolinium implemented) anti-neutrino \\bar\

Fargion, D.

2006-10-01

128

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 flares EUV late phase (Woods et al. 2011). The EUV late phase is most evident in warm coronal emissions (e.g., Fe XVI 33.5 nm). In this Letter, we explore the origin of the EUV late phase through analyzing in detail two late phase flares, M2.9 flare on 2010 October 16 and M1.4 flare on 2011 February 18, using multi-passband imaging observations from Atmospheric Imaing Assembly (AIA) onboard SDO. We find that: (1) the late phase emissions originate from a different magnetic flux system from the main phase flare loop arcade. (2) The two flux systems are magnetically connected in topology, i.e., they share one common polarity magnetic region for one of their two footpoints. (3) The late phase loop arcade appears progressively in time from high to low temperatures, while the main phase arcade reaches the peak at almost the same time for all coronal temperatures. (4) The brightening of the isolated footpoint ribbon of late phase arcade is always tens of seconds later than the main phase ribbons. These results suggest that the late phase EUV emission, while originates from a different magnetic flux system, is possibly triggered by the eruption of the main phase flare through the interconnection of the two magnetic flux systems.

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

2012-05-01

129

Terrestrial response to eruptive solar flares: Geomagnetic storms  

Microsoft Academic Search

During the interval of August 1978 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 at 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-

Walter D. Gonzalez; Bruce T. Tsurutani

130

Diagnosis of Solar Flare Probability from Chromosphere Image Sequences.  

National Technical Information Service (NTIS)

We used optical observations of the solar chromosphere in the diagnosis of flare probability at the observation time. We derived eigenvectors from sequences of hydrogen-alpha (H-alpha) images of sub-regions of selected solar active regions at one-minute i...

D. C. Norquist K. S. Balasubramaniam

2011-01-01

131

M5.3 Labor Day Solar Flare-CME  

NASA Video Gallery

At 9:35 PM ET on September 5, 2011, the sun emitted an Earth-directed M5.3 class flare as measured by the GOES satellite. The flare erupted from a region of the sun that appears close to dead center from Earth's perspective, an active region designated number 1283. A coronal mass ejection (CME) was associated with this flare and is a relatively slow one, traveling at under 200 miles per second. This extreme close-up video was taken by the Solar Dynamics Observatory in 171 angstrom.

Holly Zell

2011-09-06

132

Imaging X-ray Polarimeter for Solar Flares (IXPS)  

Microsoft Academic Search

We describe the design of a balloon-borne Imaging X-ray Polarimeter for Solar flares (IXPS). This novel instrument, a Time\\u000a Projection Chamber (TPC) for photoelectric polarimetry, will be capable of measuring polarization at the few percent level\\u000a in the 2050 keV energy range during an M- or X-class flare, and will provide imaging information at the ?10 arcsec level.\\u000a The primary

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

2011-01-01

133

Effect of a solar flare on a traveling atmospheric disturbance  

NASA Astrophysics Data System (ADS)

It is known that the sudden injection of energy during geomagnetic storms can excite atmospheric gravity waves (AGWs) or traveling atmospheric disturbances (TADs). Together with large-scale circulation, these AGWs/TADs transport energy and momentum away from their sources. In this paper, we investigate possible involvement of AGWs/TADs during solar flares. Model simulations of an X17 flare that occurred on October 28, 2003 shows that AGWs/TADS contributed to flare energy transport from the sunlit South-Pole region to the nightside equatorial region in 3-4 h, resulting in 10% nightside equatorial neutral density enhancement in the upper thermosphere. These nightside AGWs/TADs have a phase speed on the order of 750 m/s and a horizontal wavelength on the order of 4000 km. Enhanced solar heating to the thermosphere through enhanced ionization during flares occurs on the entire dayside, with the spatial scale of the increased solar heating being too large to excite AGWs/TADs. Further analysis revealed that strong localized enhancement of Joule heating was produced during the October 28, 2003 flare. This sudden injection of the localized heating, together with preexisting AGWs/TADs excited by moderate geomagnetic activity prior to the flare, produced intensified AGWs/TADs, which propagated energy and momentum to the equatorial region. On the other hand, model simulations showed that, under assumed geomagnetically quiet conditions, strong localized enhancement of Joule heating and AGWs/TADs were not produced during the flare. This interplay between geomagnetic activity and solar flares can be a challenge to space weather monitoring, specification, and forecasting.

Qian, Liying; Burns, Alan G.; Liu, Hanli; Chamberlin, Phillip C.

2012-10-01

134

Effect of solar flares on electrical parameters of the atmosphere  

Microsoft Academic Search

Variations of the atmospheric electric-field potential gradient Ez near the earth's surface and the level of the regular noise background of VLF radiation at 8.7 kHz are related to solar flares of importance greater than or equal to 2. An increase in Ez is observed a few days before the flare, followed by its decline to the preflare level and

V. G. Moiseev; N. N. Murzaeva; N. G. Skryabin; O. P. Ivanov

1993-01-01

135

Location of narrowband spikes in solar flares  

NASA Astrophysics Data System (ADS)

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

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

2002-02-01

136

Non-Relativistic Electron Beam Stability in Solar Flares  

NASA Astrophysics Data System (ADS)

The thick-target electron beam model has been used for decades as a viable description for the production of solar flare hard X-ray emission. The required very rapid transport of energy to the footpoints during solar flares is achieved in this model by fast electrons traversing the loop to deposit their energy in the dense chromosphere. For some of the largest flares the currents (up to 1017 Amps or 1036 electrons/sec) inferred can significantly exceed the Alfven-Lawson limit suggesting that the assumed electron beam is inherently unstable. In this paper, we use the spectral and spatial resolution of RHESSI to explore whether the conditions for a stable non-thermal electron beam exist in large solar flares. The incident electron spectra at flaring footpoints are derived from the RHESSI photon spectra while an upper limit to the footpoint area is detremined form the hard X-ray images. We determine the electron beam density needed to produce the hard X-ray emission for two large flares, July 17, 2002 (M8.5) and October 28, 2003 (X17.2) and determine whether such beams are viable in these cases. We gratefully acknowledge support from NASA (NAS5-02048).

Daou, A. G.; Alexander, D.; Metcalf, T. R.

2004-05-01

137

Energetic electron distribution in the solar flare  

NASA Astrophysics Data System (ADS)

We investigate the distribution of energetic electrons in the solar flare by means of numerical simulations. First, we study the height distribution under an idealized model of time-varying, potential electromagnetic fields, by solving the drift-kinetic Vlasov equation (Minoshima et al. 2010, ApJ, 714, 332; 2011, ApJ, 732, 111). When pitch-angle scattering is not included, the peak heights of loop-top electrons are constant, regardless of their energy, owing to the continuous acceleration and compression of the electrons via shrinkage of magnetic loops. On the other hand, under pitch-angle scattering, the electron heights are energy-dependent: intermediate-energy electrons are at a higher altitude, whereas lower and higher energy electrons are at lower altitudes. This implies that the intermediate-energy electrons are inhibited from following the shrinking field lines to lower altitudes because pitch-angle scattering causes efficient precipitation of these electrons into the footpoint and their subsequent loss from the loop. This result can explain the energy-dependent height distribution of electrons, as indicated by coronal hard X-ray (HXR) and microwave sources (including the above-the-loop-top HXR source). Next, we perform the test particle simulation under the electromagnetic fields obtained from an MHD simulation of magnetic reconnection with different magnetic Reynolds numbers. When the Reynolds number is low, the reconnected fields are close to the potential one so that the result is very similar to the previous result. On the other hand, with the high Reynolds number, the fields significantly deviate from the potential. A rapid change of the magnetic field topology can violate the second adiabatic invariant of electrons. As a result, an impulsive electron flux appears along the field line, different from the low Reynolds number case. This may contribute to the electron precipitation into the footpoint, as indicated by a rapid temporal change of HXR emissions.

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

2011-12-01

138

The E and F region ionospheric response to solar flares. I - Effects of approximations of solar flare EUV fluxes  

Microsoft Academic Search

SOLRAD and many other satellite systems have provided a large data base showing the time-dependent behavior of broadband solar fluxes in the X-ray and EUV spectral regions. Results are presented of tests performed to determine how this information can best be used to predict the effects of a solar flare on the ionosphere. The approach has been to first adopt

J. T. Mariska; E. S. Oran

1981-01-01

139

The impact of solar flares and magnetic storms on humans  

NASA Astrophysics Data System (ADS)

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.

Joselyn, Jo A.

1992-03-01

140

Comet flares and velocity waves in the solar wind  

SciTech Connect

The flare activity of comets and the structure of the solar wind fluxes are compared with data of measurements of Pioneer-10, -11, Vela-3, IPM-7, and -8 at a heliocentric distance of r approx. = 1-6 AU. It is shown that velocity waves of the solar wind, which evolve into corotating shock waves beyond the orbit of the earth, may be responsible for the flare activity of comets. The work notes a correspondence between the variations of flare activity of comets as a function of heliocentric distance and the behavior of velocity waves in the solar wind, the closeness of the characteristic times of velocity waves (about 7-8 days at r = 1 AU) and the duration of comet flares, and the increase of this characteristic time with increasing r in both cases. The observed distribution of the parameters of comet flare activity in the 11-yr cycle also corresponds well to the distribution of the area of coronal holes and the rate of variation of the area of sunspots ..delta..Sp over the phase of the solar cycle.

Ptitsyna, N.G.; Breus, T.K.; Rikhter, A.K.

1986-05-01

141

Investigation of X-ray and optical solar flare activities during solar cycles 22 and 23  

NASA Astrophysics Data System (ADS)

Daily X-ray flare indices (XFI) for the interval from January 1986 till June 2002 were calculated. The XFI behaviour during solar cycles 22 and 23 was studied. We compare the daily XFI with the daily optical flare indices (OFI) and with the International Relative Sunspot Numbers. The energy emitted by X-ray flares during 77 months of solar cycle 22 is shown to be about five times larger than the analogous value for the present solar cycle. We revealed statistically significant maxima in power spectra of the XFI and OFI. They correspond to periods of 25.5, 36.5, 73, 116, and 150d which presumably are appropriate to characteristic frequencies of the solar flare activity. A hypothesis on an possible effect of Mercury's variable electric charge on the origin of solar flares is proposed and corresponding estimates were made.

Akimov, L. A.; Belkina, I. L.; Bushueva, T. P.

2003-02-01

142

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

143

Solar flare intermittency and the earth's temperature anomalies.  

PubMed

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

Scafetta, Nicola; West, Bruce J

2003-06-17

144

Solar flares as cascades of reconnecting magnetic loops.  

PubMed

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

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

2003-03-31

145

Ionospheric Electron Concentration Enhancement during a Solar Flare  

NASA Astrophysics Data System (ADS)

DURING solar flares, sudden increases of extreme ultraviolet (EUV) and X-ray flux produce abrupt increases of electron concentration (Ne) in the sunlit part of the ionosphere. Because of their relatively short duration and the accompanying blackout in h.f. propagation, these enhancements of Ne have hitherto been difficult to investigate, especially in the E region. We report here some results of applying a new technique, incoherent scatter radar, to this problem. The observations were made at Malvern (52.1 N, 2.3 W) during a solar flare on February 20, 1970.

Taylor, G. N.; Watkiks, C. D.

1970-11-01

146

Multiwavelength Analysis of a Solar Flare on 2002 April 15  

NASA Astrophysics Data System (ADS)

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 further 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 Radioheliograph (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

2005-11-01

147

Vertical inhomogenuity of the magnetic field in the solar flares  

NASA Astrophysics Data System (ADS)

The magnetic field is of primary importance in the physics of the Sun and Solar flare. We present the results of investigation of the solar flares of 25 October 2003 and 5 November 2004. The Echelle Zeeman-spectrograms of the flare were obtained on horizontal solar telescope of Astronomical Observatory of Kyiv Shevchenko University. Ten spectral lines of FeI, FeII, ScII and CrII were investigated to diagnose the small-scale magnetic field structures. We compared the data for 2 photometrical sections of these lines. It was shown, that magnetic field range was from 100 G to about 1000 G for both flares. There is an evidence on the spatially unresolved magnetic field sructure with kG local magnetic fields. We have built the dependence of magnetic fields and height formation for both flares. This proves the existence of the middle photosphere level (250-300 km), where the change of the height gradient sign of the magnetic field is observed.

Osyka, O.; Lozitsky, V.

2005-04-01

148

Radio Studies of Electron Acceleration and Transport During Solar Flares  

NASA Astrophysics Data System (ADS)

At centimeter wavelengths solar flare radiation is dominated by incoherent gyrosynchrotron emissions from 10 keV to several MeV electrons. Due to unique sensitivity of the gyrosynchrotron radiation to electron momentum distribution and ambient magnetic field, the radio observations at these wavelengths can provide important clues to the evolution of high-energy electrons residing in the flaring loops. In this talk I review some of recent progress made primarily using the Owens Valley Solar Array (OVSA) to understand acceleration, trapping, and precipitation of electrons during solar flares. These works are extensions of the traditional, correlative studies of temporal and spatial morphologies of radio bursts versus those of other flare radiations (X-rays, UV/EUV, and H? ) to exploit the multi-frequencies of the OVSA. The results demonstrate additional advantages of radio observations as a flare diagnostic tool when both spatial and spectral resolutions are available, and provide a major initiative in building the Frequency-Agile Radio Telescope (FASR). This work has been supported by NASA grant NAG5-10891. The OVSA is supported by NSF grant AST-9987366 to New Jersey Institute of Technology.

Lee, J.

2002-05-01

149

Laboratory Study of Solar Flare Dynamics in MRX  

NASA Astrophysics Data System (ADS)

We will present an experimental study of the dynamics of half-toroidal plasma arcs relevant to solar coronal activities utilizing the existing MRX facility [1,2]. A set of electrodes are inserted in MRX to generate a variety of plasma flux loops which contain variable toroidal guide field. Three dimensional evolution of the simulated flares is monitored by an ultra fast framing camera. The time evolution of discharges with Argon, Helium and Hydrogen with currents of 5-15 kA show the stability condition for a line-tied plasma flux loop similar to those on the solar surface. With the initial data it is shown that the q value, which describes the rotational transform of field lines, is the key for characterizing the global stability. Our experimental results will contribute to the understanding of evolution of magnetic topology of the solar flare including concepts such as current sheets, stability of current carrying flares, and line-tying, which are vitally important for understanding the Solar/Heliospheric and Interplanetary Environment. [1] M. Yamada, H. Ji, S. Hsu, T. Carter, R. Kulsrud, N. Bretz, F. Jobes, Y. Ono, and F. Perkins. Study of driven magnetic reconnection in a laboratory plasma. Phys. Plasmas, 4:1936, 1997. [2] V.S. Titov and P. D'emoulin. Basic topology of twisted magnetic configurations in solar flares. Astron.and Astrophys., 351:707, 1999.

Oz, E.; Yamada, M.; McGeehan, B.; Dorfman, S.; Ji, H.

2008-12-01

150

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

NASA Astrophysics Data System (ADS)

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

Huang, Z.; Roussel-Dupre, R.

2004-12-01

151

A RECONNECTING CURRENT SHEET IMAGED IN A SOLAR FLARE  

SciTech Connect

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

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

2010-11-01

152

Solar proton flares with weak impulsive phases  

SciTech Connect

The current picture of a proton flare includes a well-defined impulsive phase characterized by a prominent hard X-ray (or microwave) peak. Lin and Hudson have argued that the correlation between intense flare hard X-ray bursts and large proton events is evidenced that the second stage of particle acceleration, during which the protons observed at 1 AU are thought to be accelerated, is fueled by energy originally contained in flash phase 10--100 keV electrons. In our examination of large (J(>10 MeV)< or =10 protons cm/sup -2/ s/sup -1/ sr/sup -1/), prompt, proton events occurring between 1965--1979, however, we found several events that originated in flares with relatively weak (Sp(9 GHz)<100 sfu) impulsive phases. Various lines of evidence indicate that these flares were associated with mass ejection events which, given the absence of a prominent flash phase, appear to have been magnetically driven.

Cliver, E.W.; Kahler, S.W.; McIntosh, P.S.

1983-01-15

153

SDO Captures M6.9 Class Solar Flare  

NASA Video Gallery

This movie shows an M6.9 class flare on July 7, 2012 as captured by NASA's Solar Dynamics Observatory (SDO) in a combination of the 131, 171, and 304 Angstrom wavelengths. It has been colorized in yellow and red. The movie covers the time frame from 12:00 PM EDT to 1:30 PM.

Holly Zell

2012-07-09

154

Sites of flares and filaments in solar active regions  

Microsoft Academic Search

We applied a method developed to derive from magnetic field data the location of energy release in solar active regions. This method has been applied to two sets of data (June 13-15 1980 and June 23-25 1989) using magnetograms (Meudon, MSFC, Potsdam) and Halpha data (Debrecen, MSDP Meudon). The Halpha flares are located at intersections of the separatrices with the

B. Schmieder; L. van-Driel; A. Hofmann; P. Dmoulin; J. C. Hnoux; M. Hagyard

1993-01-01

155

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

National Technical Information Service (NTIS)

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

G. M. Simnett

1992-01-01

156

Analysis of digital H-alpha solar flare measurements  

Microsoft Academic Search

H-alpha data from a digital solar flare measurement system using semiautomated computer-video techniques are examined. Periodically from early 1971, two systems were run simultaneously. The measurements are consistent to within 10 per cent. Many events show area enhancements in lower brightness levels minutes before the peak brightness in the region changes, indicating an initial heating phenomenon. Our data show a

P. E. Argo; V. E. Hildebrand; M. P. Bleiweiss

1974-01-01

157

Investigation of Fe xv Emission Lines in Solar Flare Spectra.  

National Technical Information Service (NTIS)

Previously, large discrepancies have been found between theory and observation for Fe xv emission line ratios in solar flare spectra covering the 224-327 Angstrom wavelength range, obtained by the Naval Research Laboratory's S082A instrument on board Skyl...

A. Z. Msezane D. S. Bloomfield F. P. Keenan K. G. Widing K. M. Aggarwal

2008-01-01

158

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

159

Fuzzy forecast of flood disaster caused by solar proton flares.  

NASA Astrophysics Data System (ADS)

The flood disaster caused by solar proton flares is forecasted using the theory of fuzzy mathematics. The index system and standards of fuzzy evaluation, as well as the membership function are proposed. A practical software of computer data processing for forecasting flood disaster is given.

Han, Zhengzhong; Tang, Yuhua

1999-01-01

160

Interplanetary transport of decay protons from solar flare neutrons  

Microsoft Academic Search

Models for the propagation of protons produced by the decay of solar flare neutrons have been developed. These models are applied to the observation of such protons on 1982 June 3 and 1984 April 25. Numerical simulations treating the deposition, pitch-angle scattering, and adiabatic focusing of neutron-decay protons have been performed. Fitting these simulations to the measurements of the time

D. Ruffolo

1991-01-01

161

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

National Technical Information Service (NTIS)

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 2...

A. G. Emslie A. Y. Shih B. R. Dennis C. E. Urba J. E. Hill J. K. Black K. Jahoda M. Hosack P. Deines-Jones

2011-01-01

162

The cooling of flare produced plasmas in the solar corona  

Microsoft Academic Search

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

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

1970-01-01

163

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

164

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

165

Max '91: flare research at the next solar maximum  

SciTech Connect

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

Dennis, B.; Canfield, R.; Bruner, M.; Emslie, G.; Hildner, E.; Hudson, H.; Hurford, G.; Lin, R.; Novick, R.; Tarbell, T.

1988-01-01

166

Vector Magnetograph Observations by the Solar Flare Telescope at Boao  

Microsoft Academic Search

We report that the vector magnetograph(VMG) observations of the solar photosphere are being carried out by the Solar Flare Telescope(SOFT) in BOAO(Bohyunsan Optical Astronomical Observatory) of Korea Astronomy Observatory. The VMG uses a narrow band Lyot filter (FWHM = 0.125A) for observations of Stokes parameters(I,Q,U,V) to obtain longitudinal and transversal fields. The Stokes images are acquired by Sony XC -77

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

1999-01-01

167

Statistical properties of solar gamma-ray flares  

Microsoft Academic Search

We studied the 120 solar gamma-ray events observed by the gamma-ray spectrometer (GRS) on board the SMM satellite between 1980 March and 1983 June with particular emphasis on the basic properties of the active regions producing such events. Combined with observed data of Type-II and Type-IV metre wave radio bursts, we further discussed the physical mechanisms in solar flares. Our

Ao-Ao Xu; Chun-Lin Yin; He-Qi Zhang; S. T. Wu

1991-01-01

168

Solar flare impulsive phase observations from SDO and other observatories  

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

169

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

170

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

171

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

172

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

Microsoft Academic Search

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

Joan Feynman; Arthur J. Hundhausen

1994-01-01

173

Muon and Tau Neutrinos Spectra from Solar Flares  

NASA Astrophysics Data System (ADS)

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

Fargion, Daniele; Moscato, Federica

2003-12-01

174

Effects of solar flares on the ionosphere of Mars.  

PubMed

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

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

2006-02-24

175

An extended superhot solar flare X-ray source  

NASA Astrophysics Data System (ADS)

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

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

1985-08-01

176

Automated Feature Detection and Solar Flare Prediction Using SDO Data  

NASA Astrophysics Data System (ADS)

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

Qahwaji, Rami; Ahmed, Omar; Colak, Tufan

177

Gradient spectral analysis of solar radio flare superevents  

NASA Astrophysics Data System (ADS)

Some of complex solar active regions exhibit rare and sudden transitions that occur over time intervals that are short compared to the characteristic time scales of their evolution. Usually, extreme radio emission is driven by a latent nonlinear process involving magnetic reconnection among coronal loops and such extreme events (e.g., X-class flares and coronal mass ejections) express the presence of plasma and magnetic activity usually hidden inside the solar convective layer. Recently, the scaling exponent obtained from Detrended Fluctuation Analysis has been used to characterize the formation of solar flare superevents - SFS (integrated flux of radiation greater than 1.5 J/m2) when it is observed in the decimetric range of 1-3 GHz (Veronese et al., 2011). Here, we show a complementary computational analisys of four X-class solar flares observed in 17GHz from Nobeyama Radioheliograph. Our analysis is based on the combination of DFA and Gradient Spectral Analysis (GSA) which can be used to characterize the evolution of SFSs under the condition that the emission threshold is large enough (fmax > 300 S.F.U.) and the solar flux unit variability is greater than 50% of the average taken from the minimum flux to the extreme value. Preliminary studies of the gradient spectra of Nobeyama data in 17 GHz can be found in Sawant et al. (JASTP 73(11), 2011). Future applications of GSA on the images which will be observed from the Brazilian Decimetric Array (BDA) are discusssed.

Rosa, R. R.; Veronese, T. B.; Sych, R. A.; Bolzan, M. A.; Sandri, S. A.; Drummond, I. A.; Becceneri, J. C.; Sawant, H. S.

2011-12-01

178

Solar flare mechanism based on magnetic arcade reconnection and island merging.  

National Technical Information Service (NTIS)

The authors propose a model describing physical processes of solar flares based on resistive reconnection of magnetic field subject to continuous increase of magnetic shear in the arcade. The individual flaring process consists of magnetic reconnection of...

C. Z. Chen G. S. Choe

2000-01-01

179

Ionospheric Response to Solar Flares Using an Improved Version of SAMI2.  

National Technical Information Service (NTIS)

Solar flare-induced disturbances in the ionosphere can affect the propagation of electromagnetic waves, causing errors in GPS navigation, false radar echoes, and loss of HF radio communications. Accurately modeling the ionospheric response to flares is th...

I. J. Reich

2008-01-01

180

Relationship of solar flare accelerated particles to solar energetic particles (SEPs) observed in the interplanetary medium  

SciTech Connect

Observations of hard X-ray (HXR)/gamma-ray continuum and gamma-ray lines produced by energetic electrons and ions, respectively, colliding with the solar atmosphere, have shown that large solar flares can accelerate ions up to many GeV and electrons up to hundreds of MeV. Solar energetic particles (SEPs) are observed by spacecraft near 1 AU and by ground-based instrumentation to extend up to similar energies, but these appear to be accelerated by shocks associated with fast Coronal Mass Ejections (CMEs). The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) mission provides high-resolution spectroscopy and imaging of flare HXRs and gamma-rays. Here we review RHESSI observations for large solar flares and SEP events. The 23 July gamma-ray line flare was associated with a fast, wide CME but no SEPs were observed, while the 21 April 2002 flare had no detectable gamma-ray line emission but a fast CME and strong SEP event were observed. The October- November 2003 series of large flares and associated fast CMEs produced both gamma-ray line emission and strong SEP events. The spectra of flare-accelerated protons, inferred from the gamma-ray line emission observed by RHESSI, is found to be essentially identical to the spectra of the SEPs observed near 1 AU for the well-connected 2 November and 20 January events.

Lin, R.P. [Physics Department, University of California, Berkeley, CA 94720-7450 (United States); Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450 (United States)

2005-08-01

181

The development and cooling of a solar limb-flare  

NASA Astrophysics Data System (ADS)

Observations of a flare that began in soft X-rays at 20:37 UT on 1980 April 12, at the west limb of the Sun are discussed. The Solar Maximum Mission (SMM) satellite was used to obtain X-ray images before the flare and for a period during the decay phase. H? photographs and the soft X-ray flux measured by the GOES-3 satellite are available throughout the flare. Some alternative models are discussed but insufficient data are available for a full treatment. Overall, the observations are best fitted qualitatively by a model where pre-existing magnetic loop structures are perturbed by the intrusion of new magnetic flux.

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

1984-09-01

182

Ionospheric response to the solar flare of 14 July 2000  

NASA Astrophysics Data System (ADS)

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

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

2004-02-01

183

Temporal Variability of Ion Acceleration and Abundances in Solar Flares  

NASA Astrophysics Data System (ADS)

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

Shih, Albert Y.; Smith, D. M.; Lin, R. P.

2011-05-01

184

Solar flares and focused energy transport by MHD waves  

NASA Astrophysics Data System (ADS)

Context. Transport of flare energy from the corona to the chromosphere has traditionally been assigned to electron beams; however, interest has recently been renewed in magnetohydrodynamic (MHD) waves as a complementary or alternative mechanism. Aims: We determine whether, and under what conditions, MHD waves deliver spatially localised energy to the chromosphere, as required if MHD waves are to contribute to emission from flare ribbons and kernels. This paper also highlights several properties of MHD waves that are relevant to solar flares and demonstrates their application to the flare problem. Methods: Transport is investigated using a magnetic arcade model and 2.5D MHD simulations. Different wave polarisations are considered and the effect of fine structuring transverse to the magnetic field is also examined. Ray tracing provides additional insight into the evolution of waveguided fast waves. Results: Alfvn waves are very effective at delivering energy fluxes to small areas of chromosphere, localisation being enhanced by magnetic field convergence and phase mixing. Fast waves, in the absence of fine coronal structure, are more suited to powering emission from diffuse rather than compact sources; however, fast waves can be strongly localised by coronal waveguides, in which case focused energy is best transported to the chromosphere when waveguides are directly excited by the energy release. Conclusions: MHD waves pass an important test for inclusion in future flare models.

Russell, A. J. B.; Stackhouse, D. J.

2013-10-01

185

Particle acceleration and gamma-emission from solar flares  

NASA Astrophysics Data System (ADS)

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

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

186

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

187

SHORT-TERM SOLAR FLARE PREDICTION USING MULTIRESOLUTION PREDICTORS  

SciTech Connect

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

Yu Daren; Huang Xin; Hu Qinghua; Zhou Rui [Harbin Institute of Technology, No. 92 West Da-Zhi Street, Harbin, Heilongjiang Province (China); Wang Huaning [National Astronomical Observatories, 20A Datun Road, Chaoyang District, Beijing (China); Cui Yanmei, E-mail: huangxinhit@yahoo.com.c [Center for Space Science and Applied Research, No. 1 Nanertiao, Zhongguancun, Haidian District, Beijing (China)

2010-01-20

188

Short-term Solar Flare Prediction Using Multiresolution Predictors  

NASA Astrophysics Data System (ADS)

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

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

2010-01-01

189

The Association of Solar Flares with Coronal Mass Ejections During the Extended Solar Minimum  

NASA Astrophysics Data System (ADS)

We study the association of solar flares with coronal mass ejections (CMEs) during the deep, extended solar minimum of 2007 - 2009, using extreme-ultraviolet (EUV) and white-light (coronagraph) images from the Solar Terrestrial Relations Observatory (STEREO). Although all of the fast (v>900 km s-1), wide (?>100?) CMEs are associated with a flare that is at least identified in GOES soft X-ray light curves, a majority of flares with relatively high X-ray intensity for the deep solar minimum (e.g. ?110-6 W m-2 or C1) are not associated with CMEs. Intense flares tend to occur in active regions with a strong and complex photospheric magnetic field, but the active regions that produce CME-associated flares tend to be small, including those that have no sunspots and therefore no NOAA active-region numbers. Other factors on scales similar to and larger than active regions seem to exist that contribute to the association of flares with CMEs. We find the possible low coronal signatures of CMEs, namely eruptions, dimmings, EUV waves, and Type III bursts, in 91 %, 74 %, 57 %, and 74 %, respectively, of the 35 flares that we associate with CMEs. None of these observables can fully replace direct observations of CMEs by coronagraphs.

Nitta, N. V.; Aschwanden, M. J.; Freeland, S. L.; Lemen, J. R.; Wlser, J.-P.; Zarro, D. M.

2013-09-01

190

Fermi Detects Solar Flare's Gamma Rays  

NASA Video Gallery

During a powerful solar blast in March, NASA's Fermi Gamma-ray Space Telescope detected the highest-energy light ever associated with an eruption on the sun. The discovery heralds Fermi's new role as a solar observatory, a powerful new tool for understanding solar outbursts during the sun's maximum period of activity. Credit: NASA's Goddard Space Flight Center > Related story > Download high-res video

gsfcvideo

2012-06-12

191

Analysis of flares observed during the solar maximum year  

NASA Astrophysics Data System (ADS)

This report encompasses three major projects: (1) Qualitative characterization of the H-alpha profiles of the flare of 5 November 1980 at 2233 UT; (2) Construction of a film projector/digitizer for the purpose of projecting half-frame 35mm images onto a television camera detector; (3) Images of solar plages near the limb in broadband continuum, and analysis thereof. These projects are described in the respective three sections of this report.

Zirin, H.; Martin, S. F.; Walton, S. R.

1982-11-01

192

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

193

Time evolution of the size of solar flare plasma loops along the main sequence  

NASA Astrophysics Data System (ADS)

Our Sun is about 4.6 billion years old. Richard C. Carrington made the first flare observations in the 19th century, and we have thus observed solar flares for 10-8 part of its age. Solar flares could be an important factor in the evolution of the solar system. I therefore attempt to paint an evolutionary picture of solar flares based on existing solar observations, original observations of young suns at the beginning of the main sequence and stellar flares. My primary focus will be on deriving the sizes of solar flare plasma loops when the Sun was young. I will also briefly discuss the implications of this picture to particle acceleration and transport in the heliosphere and beyond. ?

Vnnen, Mikko

2008-08-01

194

Three-Dimensional Adaptive Magnetohydrodynamic Simulations of Eruptive Solar Flares  

NASA Astrophysics Data System (ADS)

The violent expulsion of mass, energy, and magnetic flux from the Sun in eruptive flares constitutes the most dramatic and energetic phenomenon routinely affecting the Earth's near-space environment. About once a day at sunspot maximum, the Sun ejects into interplanetary space a billion tons of matter moving at a million miles per hour. Understanding and predicting these eruptions and their effects are major goals of research in solar and space physics. A critical component of this understanding is a mechanism for the sudden, explosive release of energy in the eruptive flare, following its slow accumulation and storage in solar magnetic structures. One candidate for this mechanism is the onset of rapid, sustained reconnection at magnetic null points between the restraining fields of the erupting region and the background field of the surrounding atmosphere. Key issues in computer simulations of the events are the rate of numerical dissipation realized, its dependence on the grids and algorithms employed, and its extrapolation to the low physical values expected in the highly conducting solar plasma. To address these matters, we have developed a three-dimensional, time-dependent, magnetohydrodynamic simulation code using dynamically adaptive grids. Numerical magnetic reconnection at the grid scale is controlled by varying the number of allowed levels of grid refinement. We will present results for simulated eruptive flares within our model and discuss their application to the Sun. This research was supported by DoD and NASA.

DeVore, C. Richard; Antiochos, Spiro K.

2002-08-01

195

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

PubMed

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

Smart, D F; Shea, M A

1992-01-01

196

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

Microsoft Academic Search

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

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

1989-01-01

197

Radial velocities of the photospheric matter in a solar flare with matter ejection  

Microsoft Academic Search

We present results of a study of photospheric horizontal motions at the initial and main phases of the solar flare which happened\\u000a on September 4, 1990, near the solar limb. The flare was accompanied by matter ejection. Spectra of the flare were obtained\\u000a using the AZU-26 horizontal solar telescope at the MAO NAS (Terskol observatory). We found variations of the

N. N. Kondrashova; M. N. Pasechnik

2010-01-01

198

Spectral Diagnostics and Radiative Hydrodynamics of Solar Flares  

NASA Astrophysics Data System (ADS)

Solar flares are one of the most significant active phenomena in the solar atmosphere. It is involved in very complicated physical processes, including energy release, plasma instability, acceleration and propagation of energetic particles, radiation and dynamics of the flaring atmosphere, mass motions and ejections, and so on. Enhanced radiation during flares spans virtually the entire electromagnetic spectrum originating from different layers of the solar atmosphere. High energetic particles and strong radiations that are produced during the flare eruptions play a major role in space weather. Therefore, it is very important and necessary to study the mechanisms of solar flares. In this thesis, combined with ground and space observations, the theoretical calculations are used to study the spectral features and radiation mechanisms of solar flares. In particular, our research is concentrated on the diagnostics of non-thermal processes and origin of the white-light flares. The main contents are described as follows: (1) Different chromospheric lines are used to diagnose the heating mechanisms in flares. We calculate the H? and Ca II 8542 line profiles based on four different atmospheric models, including the effects of non-thermal electron beams with various energy fluxes. These two lines have different responses to the thermal and non-thermal effects, and can be used to diagnose the thermal and non-thermal heating processes. We apply our method to an X-class flare occurred on 2001 October 19 and find that the non-thermal effects at the outer edge of the flare ribbon are more notable than that at the inner edge, while the temperature at the inner edge seems higher. On the other hand, the results show that non-thermal effects increase rapidly in the rise phase and decrease quickly in the decay phase, but the atmospheric temperature can still keep relatively high for some time after getting to its maximum. For the two kernels that we analyze, the maximum energy fluxes of the electron beams are approximately 1010 erg cm-2 s-1 and 1011 erg cm-2 s-1, respectively. However, the atmospheric temperatures are not so high, i.e., lower than or slightly higher than that of the weak flare model F1 at the two kernels. We discuss the implications of the results for the two-ribbon flare models. (2) The white-light emission in solar flares is studied by radiative hydrodynamic simulations. It is believed that solar white-light flares (WLFs) originate from the lower chromosphere and upper photosphere. In particular, some recently observed WLFs show a very large continuum enhancement at 1.56 ?m where the opacity reaches its minimum. Therefore, it is important to make clear how the energy is transferred to the lower layers responsible for the production of WLFs. Based on radiative hydrodynamic simulations, we study the role of non-thermal electron beams in increasing the continuum emission. We vary the parameters of the electron beams and disk positions and compare the results with observations. The electron beam heated model can explain most of the observational white-light enhancements. (3) The effect of periodic non-thermal electron beam on chromospheric lines is studied. Heated by the periodic non-thermal electrons, the H? line center and wings show the same periodicity as the injected electrons. The line center and wings have different time delays compared to the bombarded electron beam. The line center has a relatively small phase difference. The red and blue wings also show different time delays. The blue wing shows a smaller phase difference compared to the red wing. The phase differences between the line center and wings can be explained by their different formation layers. However, the phase difference between the red and blue wings can not be fully explained in this manner. A possible explanation is that the macroscopic velocity field changes the emission and absorption features at the red and blue wings. The above results provide useful information for diagnosing the heating processes by using the fine time structures observ

Cheng, J. X.

2011-03-01

199

Iron K. cap alpha. fluorescence due to solar flares  

SciTech Connect

A relatively simple expression is obtained for the flux of K..cap alpha.. photons of weakly ionized iron emitted in the process of reprocessing of hard radiation (h..nu..>7 keV) of a solar flare in dense layers of the solar atmosphere. An exact solution of the problem of radiation transfer is used for this. The efficiency of K..cap alpha.. fluorescence is compared in detail with the efficiency of excitation by electron impact. The information which observations of K..cap alpha.. emission of iron in the 1.93--1.94 A range can provide is discussed briefly.

Basko, M.M.

1979-03-01

200

Soft X-ray Transient is Likely a Reflected Solar Flare  

NASA Astrophysics Data System (ADS)

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

Smith, D. A.; Remillard, R.

2003-03-01

201

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 Nanay 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

202

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 Nanay 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

203

Direct Observation of Prompt Solar Flare Perturbation to Stratospheric Electrodynamics  

NASA Astrophysics Data System (ADS)

Several solar flare events were observed during the MINIS balloon experiment from SANAE station Antarctica, January 2005. The balloon payloads carried a large number of particle and field instruments which clearly identified several direct one-to-one perturbations between energetic particle flux enhancements, and the stratospheric electric field. Previous stratospheric electric field experiments have also detected one to one correlations with solar flares of both enormous size (August 1972) and quite small (February 1984). The flares during the MINIS flights produced a surprising influence on both the vertical electric field (as in the previous experiments) as well as on the horizontal electric field. The dramatic vertical electric field reductions, seen by MINIS as well as the earlier flights, may be directly related to the global circuit return currents and the influence of changing electrical conductivity. However, during the MINIS flight, we will show that the horizontal electric field also dropped to near zero. This could be caused by an abrupt cessation in large scale convection (at least locally), or by a rapid reconfiguration of the magnetosphere, perturbing the mapping of electric fields from the magnetosphere to the latitude of the balloon.

Holzworth, R. H.; Bering, E. A.; Kokorowski, M.; Reddell, B. D.; McCarthy, M. P.; Bale, S.; Blake, J. B.; Collier, A. B.; Hughes, A. R.; Lay, E.; Lin, R. P.; Millan, R. M.; Moraal, H.; O'Brien, T. P.; Parks, G. K.; Pulupa, M.; Sample, J. G.; Smith, D. M.; Stoker, P.; Woodger, L.

2005-12-01

204

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

2010-05-01

205

Next-generation EUV imaging spectrometer for solar flare observations  

NASA Astrophysics Data System (ADS)

The Naval Research Laboratory Skylab SO82A slitless spectrograph provided solar flare observations that have never been equaled in diagnostic capabilities for interpreting thermal flare physics. Improvements in detector technology, optics and optical coating technology, and almost two decades of analysis of SO82A data can be combined with the basic concept of an EUV objective grating spectrograph to build an instrument to address many of the remaining mysteries of solar flares. This next generation instrument incorporates two sets of two identical, orthogonally mounted slitless spectrographic Cassegrain telescopes. Each telescope consists of a multilayer coated, Wadsworth mount objective grating and multilayer coated spherical secondary mirror; a backside illuminated CCD detector is installed at the focal plane. The orthogonal mounting changes the dispersion direction by 90 degrees on the disk image; processing on the two resulting images allows recovery of the undispersed disk image and spectral line profiles. The resulting instrument will obtain high time cadence, spectrally-dispersed images with improved spatial resolution, dynamic range, signal-to-noise ratio, and velocity discrimination.

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

1996-11-01

206

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

Microsoft Academic Search

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

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

1972-01-01

207

The Periodicities of Solar X-ray Flares and Coronal Mass ejections during Solar Cycle 23  

Microsoft Academic Search

The Events of energetic particles from solar X-ray flares and shock waves have been studied. The data were taken from the National Geophysical data center (NGDC) in Boulder, Colorado, USA, Where the data were taken during the solar cycle 23rd. The 23rd cycle is the present one, that started in April 1996, and its maximum was in May 2001, and

Ahmed Abdel Hady

2004-01-01

208

Stochastic particle acceleration by helical turbulence in solar flares  

NASA Astrophysics Data System (ADS)

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

Fleishman, Gregory D.; Toptygin, Igor N.

2013-03-01

209

Generic Model for Magnetic Explosions Applied to Solar Flares  

NASA Astrophysics Data System (ADS)

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

Melrose, D. B.

2012-04-01

210

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

211

A rope-shaped solar filament and a IIIb flare  

NASA Astrophysics Data System (ADS)

On September 14-18, 2000, a medium-small solar active region was observed at Ganyu Station of Purple Mountain Observatory. Its spots were not large, but it had a peculiar active filament. On Sep.16, a flare of importance IIIb with rather intense geophysical effects was produced. Our computation of the magnetic structure of the active region reveals that the rope-shaped filament was concerned with a low magnetic arc close to magnetic neutral line. An intense shear of magnetic field occurred near magnetic rope. The QSL analysis shows that a 3-D magnetic reconnection might appear in the vicinity of filament, and this can be used to interpret the formation of a large flare.

Zhang, Yan-An; Song, Mu-Tao; Ji, Hai-Sheng

212

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

213

Continuum analysis of an avalanche model for solar flares.  

PubMed

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

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

2002-11-19

214

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

215

Observations of Solar Flares from GHz to THz Frequencies  

NASA Astrophysics Data System (ADS)

The discovery of a new solar burst spectral component with sub-THz fluxes increasing with frequency, simultaneous but separated from the well known microwave component, brings serious constraints for interpretation. Suggested explanations are briefly reviewed. They are inconclusive indicating that further progresses on the understanding of nature of the emission mechanisms involved require the knowledge of GHz to THz continuum burst spectral shapes. New 45 and 90 GHz high sensitivity solar polarimeters are being installed at El Leoncito high altitude observatory, where sub-THz (0.2 and 0.4 THz) solar flare flux data are being obtained regularly since several years. Solar flare THz photometry in the continuum should be carried in space or at few selected frequency windows at exceptional ground-based sites. A dual photometer system, operating at 3 and 7 THz, is being constructed to be flown in a long duration stratospheric balloon flight in Antarctica (summer 2013-2014) in cooperation with University of California, Berkeley, together with GRIPS experiment. One test flight is planned for the fall 2012 in USA. Another long duration balloon flight over Russia is considered (2015-2016), in a cooperation with Moscow Lebedev Physics Institute.

Kaufmann, Pierre

216

The extreme Halloween 2003 solar flares (and Bastille Day, 2000 Flare), ICMEs, and resultant extreme ionospheric effects: A review  

Microsoft Academic Search

Extreme solar flares can cause extreme ionospheric effects. The Oct 28, 2003 flare caused a ?25 TECU (a total electron content unit is 1016electron\\/m2 column density), or a ?30%, increase in the local noon equatorial ionospheric column density. This enhancement occurred within ?5min. This TEC increase was ?5 times the TEC increases detected for the Oct 29, 2003, Nov 4,

B. T. Tsurutani; A. J. Mannucci; B. Iijima; F. L. Guarnieri; W. D. Gonzalez; D. L. Judge; P. Gangopadhyay; J. Pap

2006-01-01

217

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

SciTech Connect

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

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

2011-07-20

218

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

219

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

220

Relaxation of magnetic field relative to plasma density during solar flares  

NASA Astrophysics Data System (ADS)

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

Yu, Sijie; Yan, Yihua; Tan, Baolin

2013-07-01

221

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

222

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

223

Gamma ray measurements of the 1991 November 15 solar flare  

NASA Astrophysics Data System (ADS)

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

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

2000-04-01

224

Fermi GBM and LAT Solar Flare X Ray and ? Ray Observations  

NASA Astrophysics Data System (ADS)

Our Fermi GI program will make GBM (8 keV - 30 MeV) and LAT (10 MeV - 10 GeV) solar flare data and our IDL analysis software tools readily available to the international solar physics community. The observations will provide information on the highest energy flare-accelerated electrons and ions. The quicklook displays and spectral analysis tools are all based on RHESSI mission software. We are creating the following online products: IDL tools for joint spectral and time series analysis using OSPEX in SolarSoftWare. Solar flare list including which GBM detector observed the flare, as well as the usual flare parameters Quicklook plots of GBM light curves for each orbit Event FITS files containing GBM and LAT solar flare data and detector response matrices for GBM triggered and untriggered events. We have already prepared a method to identify solar flares in the GBM data stream that can reliably identify hard x-ray flares corresponding to a GOES C1-class event. The full GBM data stream will be available for download through the FERMI public data archive on an as-needed basis as we do for RHESSI. For the gamma-ray flares we will prepare data files of the LAT data and the response matrix files that can be used with OSPEX that will include the parameterized high energy emission models.

Schwartz, Richard A.; Dennis, B.; Tolbert, A. K.; Murphy, R.; Share, G.; Fishman, G.; Briggs, M.; Longo, F.; Diehl, R.; Wijers, R.

2010-05-01

225

Solar flare effect preceding Halloween storm (28 October 2003): Results of a worldwide analysis  

Microsoft Academic Search

On 28 October 2003 an extreme solar flare with significant increases in the EUV and X-ray flux caused increased photoionization effects in the dayside ionosphere and determined a remarkable solar flare effect (SFE) manifestation that preceded Halloween storm. An analysis conducted at 53 stations revealed that the geomagnetic disturbance had greatest amplitude and longest duration at lowest latitudes in the

U. Villante; M. Regi

2008-01-01

226

Universality in solar flare, magnetic storm and earthquake dynamics using Tsallis statistical mechanics  

Microsoft Academic Search

The universal character of the dynamics of various extreme phenomena is an outstanding scientific challenge. We show that X-ray flux and Dst time series during powerful solar flares and intense magnetic storms, respectively, obey a nonextensive energy distribution function for earthquake dynamics with similar values for the Tsallis entropic index q. Thus, evidence for universality in solar flares, magnetic storms

Georgios Balasis; Ioannis A. Daglis; Anastasios Anastasiadis; Constantinos Papadimitriou; Mioara Mandea; Konstantinos Eftaxias

2011-01-01

227

Predicted solar flare activity for the 1990s - Possible effects on navigation systems  

Microsoft Academic Search

The current solar cycle, which began in September 1986, may prove to be the highest ever, as measured by sunspot numbers and radio flux. The cycle's frequent and strong solar flare activity can be illustrated by the March 1989 episode, which caused many problems for navigation systems. Flares and the geomagnetic storms that sometimes accompany them can disrupt low-frequency systems

J. M. Kunches; J. W. Hirman

1990-01-01

228

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

NSDL National Science Digital Library

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

2011-04-20

229

Solar Flare Impulse Broadening from Gamma Ground Survey Network  

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

230

MEASUREMENTS OF THE CORONAL ACCELERATION REGION OF A SOLAR FLARE  

SciTech Connect

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

Krucker, Saem; Hudson, H. S.; Glesener, L.; Lin, R. P. [Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450 (United States); White, S. M. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Masuda, S. [Solar-Terrestrial Environment Laboratory, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601 (Japan); Wuelser, J.-P., E-mail: krucker@ssl.berkeley.ed [Solar and Astrophysics Laboratory, Lockheed Martin ATC, 3251 Hanover Street, Palo Alto, CA 94304 (United States)

2010-05-10

231

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

SciTech Connect

The hard X-ray characteristics of more than 2500 solar flares are used to study the relative size, impulsiveness, and energetics of flares with and without type II radio bursts. A quantitative definition of the hard X-ray impulsiveness is introduced, which may be applied to a large number of events unambiguously. It is found that the flares with type II bursts are generally not significantly larger, more impulsive, or more energetic than those without type II bursts. Also, no evidence is found to suggest a simple classification of the flares as either impulsive or gradual. Because type II bursts are present even in small flares with relatively unimpulsive energy releases, it is concluded that changes in the ambient conditions of the solar atmosphere causing an unusually low Alfven speed may be important in the generation of the shock wave that produces type II radio bursts. 22 references.

Pearson, D.H.; Nelson, R.; Kojoian, G.; Seal, J.

1989-01-01

232

The Human Impact of Solar Flares and Magnetic Storms  

NASA Astrophysics Data System (ADS)

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

Joselyn, Jo Ann

1998-01-01

233

Variations in iron and calcium abundances during solar flares  

NASA Astrophysics Data System (ADS)

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

Antonucci, E.; Martin, R.

1995-07-01

234

The debate on protons and electrons in solar flares  

NASA Astrophysics Data System (ADS)

The series of articles in Eos (September 10, 1996) on particles in solar flares caught my eye. As I am not directly working in, but certainly am interested in, the field of particle acceleration in solar flares, I expected comprehensive, easy to understand summaries of two conflicting points of view I had read about before. The introduction by Peter Cargill set the stage perfectly for such a discussion.Too bad the debate did not fulfill my expectations. It became very clear as I read the articles that [the authors of the debate] were not dealing with the subject on an equal basis. Clearly, the article by George M. Simnett about protons had been written without prior insight into the opposing view. Unfortunately, the case for the electrons by A. Gordon Emslie was basically a reply to the proton case, sometimes specifically citing parts of the article. This would have been appropriate if Simnett had had the chance to reply, but unfortunately no such reply was added to the series.

Zurbuchen, Thomas H.

235

Temporal variations of the CaXIX spectra in solar flares  

NASA Astrophysics Data System (ADS)

Aims. The standard model of solar flares comprises a bulk expansion and a rise of abruptly heated plasma (chromospheric evaporation). Emission from plasma ascending along loops rooted in the visible solar disk often should be dominated, at least temporally, by a blue-shifted emission. However, there is only a very limited number of published observations of solar flares having spectra in which the blue-shifted component dominates the stationary one. In this work we compare observed X-ray spectra of three solar flares recorded during their impulsive phases and relevant synthetic spectra calculated using one-dimensional hydro-dynamic numerical model of these flares. The main aim of the work is to explain why many flares do not show blue-shifted spectra. Methods: We synthetised time series of Bragg Crystal Spectrometer (BCS) spectra of three solar flares at various moments of their evolution from the beginning of the impulsive phases to beyond maxima of the X-ray emission using a 1D numerical model of the solar flares and standard software to calculate BCS synthetic spectra of the flaring plasma. The models of the flares were calculated using observed energy distributions of the non-thermal electron beams injected into the loops, initial values of the main physical parameters of the plasma confined in the loops and geometrical properties of the loops estimated using available observational data. The synthesized BCS spectra of the flares were compared with the relevant observed BCS spectra. Results: Taking into account the geometrical dependences of the line-of-sight velocities of the plasma moving along the flaring loop inclined toward the solar surface as well as a distribution of the investigated flares over the solar disk, we conclude that the stationary component of the spectrum should be observed for almost all flares during their early phases of evolution. On the contrary, the blue-shifted component of the spectrum could not be detected in flares having plasma rising along the flaring loop even with high velocity due to the geometric dependences only. Our simulations based on realistic heating rates of plasma by non-thermal electrons indicate that the upper chromosphere is heated by non-thermal electrons a few seconds before the beginning of noticeable high-velocity bulk motion, and before this time plasma emits the stationary component of the spectrum only. After the start of the upward flow, the blue-shifted component temporally dominates the synthetic spectra of the investigated flares in their early phases.

Falewicz, R.; Rudawy, P.; Siarkowski, M.

2009-12-01

236

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

NASA Astrophysics Data System (ADS)

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

Su, Jiangtao; Liu, Yu; Shen, Yuandeng

2013-07-01

237

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

NASA Astrophysics Data System (ADS)

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

Verma, V. K.

2011-07-01

238

Simulations of the response of the Mars ionosphere to solar flares and solar energetic particle events  

NASA Astrophysics Data System (ADS)

Recent observations by the Mars Global Surveyor and Mars Express spacecraft have shown that the ionosphere of Mars responds strongly to solar flares and solar energetic particle events. Radio occultation observations of vertical electron density profiles show that increases in extreme ultraviolet and soft X-ray emission during solar flares cause electron densities below about 120 km to increase significantly. The relative enhancement in electron density increases with decreasing altitude, consistent with the hardening of the solar spectrum during a flare. MARSIS topside radar sounder measurements of radio wave attenuation show that the low altitude (below 130 km) plasma content of the ionosphere increases during solar energetic particle events, although these observations alone do not constrain the magnitude or vertical extent of the enhancement in plasma densities. Here we report the results of two projects simulating these effects. We investigate the ionospheric effects of a solar energetic particle (SEP) event at Mars, specifically the 29 September 1989 event. We use its energy spectrum and a steady-state ionospheric model to simulate vertical profiles of ion and electron densities. The ionospheric response to this large event would have been readily observable. It caused electron densities to exceed 1E4 per cubic centimeter at 30-170 km, much larger densities than typically observed below 100 km. It also increased the ionosphere's total electron content by half of its subsolar value and would have caused strong attenuation of radio waves. The simulated attenuation is 462 dB at 5 MHz, which demonstrates that SEP events can cause sufficient attenuation (> 13 dB) to explain the lack of surface reflections in some MARSIS topside radar sounder observations. We modify an existing model of the ionosphere of Mars to incorporate time-dependent solar irradiances and use it to simulate ionospheric conditions during the X14.4 and M7.8 solar flares of 15 and 26 April 2001, respectively. Simulations were validated by comparison to Mars Global Surveyor radio occultation measurements of vertical profiles of ionospheric electron density. Adjustments to the model's representation of the neutral atmosphere and electron-impact ionization were required to adequately reproduce the observations before and during these solar flares. Simulated enhancements in the electron density are largest and persist the longest in the M1 region. We predict that the peak electron density in the M1 region can exceed that of the M2 region for short periods during intense solar flares.

Withers, P.

2012-04-01

239

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

NASA Astrophysics Data System (ADS)

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

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

1988-07-01

240

On the energy released in the extreme ultraviolet range by solar flares  

NASA Astrophysics Data System (ADS)

As the result of different physical processes taking place at various heights in the solar atmosphere, solar flares radiate energy at all wavelengths with different contrast and absolute energy. Because of the lack of simultaneous observations for many flares, the spectral distribution of the flare energy and its dependence on the flare magnitude are still poorly know. In this work, we perform a statistical analysis of many flares observed by the SDO/EVE instrument, which measures the Sun-as-a-star extreme-ultraviolet spectrum with unprecedented temporal and spectral resolution. In particular, we will estimate the energy released in various part sof the EUV spectrum and look at its dependance on the flare magnitude.

Kretzschmar, Matthieu

2013-04-01

241

Large solar flare radiation shielding requirements for manned interplanetary missions.  

PubMed

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

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

242

X-ray observations of solar flares with the Einstein Observatory  

Microsoft Academic Search

The first Einstein Observatory Imaging Proportional Counter (IPC) observations of solar flares are presented. These flares were detected in scattered X-ray light when the X-ray telescope was pointed at the sunlit earth. The propagation and scattering of solar X-rays in the earth's atmosphere are discussed in order to be able to deduce the solar X-ray flux incident on top of

J. H. M. M. Schmitt; H. Fink

1987-01-01

243

A New Self-Organized Criticality Model of Solar Flaring Using Reconnection at Magnetic Separators  

Microsoft Academic Search

Several authors have proposed solar flare models in the form of cellular automota, sometimes called sandpile models (Lu and Hamilton 1991, Vlahos et al. 1995). Such models are chiefly motivated by the observation that flare-frequency is related to flare-amplitude by a power-law. We propose an alternative derivation for a cellular automoton model, based on reconnection along separators in a complex

E. J. Noonan; D. W. Longcope

1999-01-01

244

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

245

Return Currents and Energy Transport in the Solar Flaring Atmosphere  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

246

Magnetography of Solar Flaring Loops with Microwave Imaging Spectropolarimetry  

NASA Astrophysics Data System (ADS)

We have developed a general framework for modeling gyrosynchrotron and free-free emission from solar flaring loops and used it to test the premise that 2D maps of source parameters, particularly the magnetic field, can be deduced from spatially resolved microwave spectropolarimetry data. We show quantitative results for a flaring loop with a realistic magnetic geometry, derived from a magnetic-field extrapolation, and containing an electron distribution with typical thermal and nonthermal parameters, after folding through the instrumental profile of a realistic interferometric array. We compare the parameters generated from forward-fitting a homogeneous source model to each line of sight through the folded image data cube both with the original parameters used in the model and with parameters generated from forward-fitting a homogeneous source model to the original (unfolded) image data cube. We find excellent agreement in general, but with systematic effects that can be understood as due to the finite resolution in the folded images and the variation of parameters along the line of sight, which are ignored in the homogeneous source model. We discuss the use of such 2D parameter maps within a larger framework of 3D modeling, and the prospects for applying these methods to data from a new generation of multifrequency radio arrays now or soon to be available.

Gary, D. E.; Fleishman, G. D.; Nita, G. M.

2013-04-01

247

Two Solar Flares that Became X-ray Plasma Ejections  

NASA Astrophysics Data System (ADS)

Solar flares and X-ray plasma ejections (XPEs) occur simultaneously but usually are separated spatially. We present two exceptional events observed by Yohkoh in 2001 October 2 (event 1) and 2000 October 16 (event 2), in which features of flares and XPEs are mixed. Namely, the soft and hard X-ray images show intense sources of emission that move dynamically. Both events occurred inside broad active regions showing complicated multi-level structure reaching up to 200 Mm high. Both events show also similar four-stages evolution: (1) a fast rise of a system of loops, (2) sudden changes in their emission distribution, (3) a reconfiguration leading to liberation of large amounts of plasma, (4) a small, static loop as the final remnant. Nevertheless, the events are probably caused by different physical processes: emerging magnetic flux plus reconnection (event 1) and reconnection plus ballooning instability (event 2). Different is also the final destination of the ejected plasma: in the event 1 overlying magnetic fields stop the ejection, in the event 2 the ejection destabilizes the overall magnetic structure and forms a coronal mass ejection (CME).

Tomczak, M.

248

Solar Flare Probability depending on Sunspot Classification, Its Area, and Its Area Change  

NASA Astrophysics Data System (ADS)

We have investigated solar flare probability depending on sunspot classification, its area, and its area change using only solar white light data. For this we used the McIntosh sunspot group classification and then selected most flare-productive six sunspot groups : DKI, DKC, EKI, EKC, FKI and FKC. For each group, we classified it into three sub-groups according to sunspot area change : increase, steady, and decrease. For sunspot data, we used the NOAA active region information for 19 years (from January 1992 to December 2010): daily sunspot class and its area corrected for the projection effect. As a result, we find that the mean flare rates and the flare probabilities for the "increase" sub-groups are noticeably higher than those for other sub-groups. In the case of the (M+X)-class flares of `kc groups, the mean flare rates of the "increase"sub-groups are more than two times than those of the "steady"sub-groups. In the case of DKC sunspot group, the (M+X)-class flare probability of the "increase" sub-group is 53% while the "decrease" and "steady" sub-groups are 27% and 24%, respectively. This is statistical evidence that magnetic flux emergence is an very important mechanism for triggering solar flares since sunspot area can be a good proxy of magnetic flux. In addition, we are examining the relationship between sunspot area and solar flare probability. For this, we classified each sunspot group into two sub-groups: large and small. In the case of compact group, the solar flare probabilities noticeably increase with its area. We are going to develop a flare probability model depending on sunspot class, its area, and its area change.

Lee, Kang-Jin; Moon, Y.

2011-05-01

249

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

SciTech Connect

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

G.S. Choe; C.Z. Cheng

2001-12-12

250

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

251

On the information content of ionospheric solar flare effect observations - II. Some model considerations on the interpretation of solar flare effects in the ionosphere  

Microsoft Academic Search

Analysis of records of LF sudden field anomaly (SFA) effects, together ; with the SOLRAD-9 records of the corresponding solar x-ray flare, shows that the ; quasi-phase height interpretation of the SFA effects is justified and that ; relatively simple model assumptions are able to provide a quantitative ; interpretation of these effects and their dependence on solar zenith angle

J. Taubenheim; G. Entzian; R. Knuth; K.-H. Ohle

1974-01-01

252

New interactive solar flare modeling and advanced radio diagnostics tools  

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

253

Influence of solar flare's location and heliospheric current sheet on the associated shock's arrival at Earth  

NASA Astrophysics Data System (ADS)

We study the source locations of 130 solar flare-type II radio burst events with the associated interplanetary shocks observed by L1 spacecraft (type A events) and 217 flare-type II events without such shocks observed at L1 (type B events) during February 1997-August 2002. In particular, we investigate the relative positions between the flare sources, the heliospheric current sheet (HCS), and the Earth. We found the following results: (1) Solar flares are usually distributed within [S30, N30] in heliographic latitude and [S30, N30] [E10, W30] is the predominant source region on the solar disk that includes the majority of geoeffective solar flares. (2) The shocks with the associated flares located near the HCS would have a lower probably of reaching the Earth. For the Earth-encountered shocks, their initial speeds are distinctly higher when their associated flares are located near the HCS. (3) The angular distance from the flare source to the Earth (defined as ? below) also contributes to the probability of the associated shock being observed at the Earth. The shock arrival probability decreases with the increment of ? and the mean initial shock speed increases with ? for those Earth-encountered shocks. (4) The so-called "same-opposite side effect" of the HCS is confirmed to exist. That is, the shocks whose associated flares are located on the same side of the HCS as the Earth (called as "same side events") have a greater chance of reaching the Earth than those shocks with their associated flares on the opposite side ("opposite side events"). Here for the first time, a comprehensive sample of solar transient events of both arriving and nonarriving ones (at Earth) is used to testify to the same-opposite side effect. These results would be valuable in understanding the solar-terrestrial relations, and helpful for space weather prediction.

Zhao, Xinhua; Feng, Xueshang; Wu, Chin-Chun

2007-06-01

254

Solar Flare 4: 10 keV X-ray Spectrum.  

National Technical Information Service (NTIS)

The 4-10 keV solar flare spectrum includes highly excited lines of stripped Ca, Fe, and Ni ions as well as a continuum steeply falling with energy. Groups of lines at approximately 7 keV and approximately 8 keV, observed during flares by the broad-band RH...

K. J. H. Phillips

2004-01-01

255

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

256

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

257

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

NASA Astrophysics Data System (ADS)

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

HernNdez-Pajares, M.; GarcA-Rigo, A.; Juan, J. M.; Sanz, J.; Monte, E.; Aragn-Ngel, A.

2012-12-01

258

Determination of Stochastic Acceleration Model Characteristics in Solar Flares  

NASA Astrophysics Data System (ADS)

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

Chen, Qingrong; Petrosian, Vah

2013-11-01

259

Observations of solar flare transition zone plasmas from the solar maximum mission  

SciTech Connect

We present observations of the 1980 April 8 flare in the Si IV 1401 A lines, obtained with the Ultraviolet Spectrometer and Polarimeter on Solar Maximum Mission. We have studied the spatial and temporal evolution of the Si IV. O IV intensity, density, and mass motions in the preflare and flare transition zone plasmas. The density is determined from the observed intensity ratio between the Si IV resonance line and the O IV intersystem line, and this diagnostic method is discussed in detail. The principal results are as follows: (1) The UV flare observed in the Si IV and O IV lines is unambiguously identified as occurring in a low-lying preexisting transition zone loop. The loop spanned the magnetic neutral line which separated a larger leader spot and a newly emerged isolated spot of opposite polarity. (2) At the onset of the flare, the easternmost footpoint, which are anchored in an isolated spot region of high longtidunal magnetic field gradient, suddenly showed impulsive brightening.This flaring kernel previously had been inconspicuous. (3) The density of the transition zone plasma at a temperature of approx.10/sup 5/ k at the flaring footpoint increased an order of magnitude from its preflare value of 2 x 10/sup 11/ cm/sup -3/ to 3 x 10/sup 12/ cm/sup -3/ during the impulsive brightening. (4) The large intensity and density increases in the flaring kernel were associated with a downward mass motion with a velocity of approx.20 km s/sup -1/. The other part of the loop remained relatively stationary. (5) The emission from the high temperature flare plama, as observed in the soft x-ray Fe XXV lines, was concentrated in a cloud overlying the whole Si IV/O IV loop, indicating that the flare energy was released in a low-lying loop or loops, including the observed Si IV/O IV loop. The released flare energy was transported by way of large-scale connecting field lines to other parts of the active region, producing the hot plasma and H..cap alpha.. kernels observed near the trailing spot.

Cheng, C.; Bruner, E.C.; Tandbert-Hanssen, E.; Woodgate, B.E.; Shine, R.A.; Kenny, P.J.; Henze, W.; Poletto, G.

1982-02-01

260

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

Microsoft Academic Search

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

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

1989-01-01

261

Rossby-Type Wave-Induced Periodicities in Flare Activities and Sunspot Areas or Groups during Solar Maxima  

Microsoft Academic Search

The Gamma-Ray Spectrometer (GRS) aboard the Solar Maximum Mission (SMM) discovered a 154 day periodicity in solar flare rates. Subsequently, periodicities in various solar flare activities and in sunspot areas or groups during a few years around solar maxima have been extensively monitored using different diagnostics and at many electromagnetic wavelengths. Notable periods are ~154, 128, 102, 78, and 51

Yu-Qing Lou

2000-01-01

262

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

263

Spectrum Synthesis of EUV Solar Flare Line Profiles.  

National Technical Information Service (NTIS)

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 ...

D. A. Tripp

1980-01-01

264

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

National Technical Information Service (NTIS)

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

H. Zirin

1997-01-01

265

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

NASA Astrophysics Data System (ADS)

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.

1989-07-01

266

Magnetic Fields and Thermodynamic Conditions at Photospheric Level of Two Solar Flares  

NASA Astrophysics Data System (ADS)

Two solar flares, on July 19, 2000 and August 4, 2005 of importance M6.4/3N and C8.4/1N, respectively, were studied using the echelle Zeeman spectrograms obtained with horizontal solar telescope at the Astronomical Observatory of Kyiv Shevchenko National University. The Stokes I V profiles were compared for about ten lines of FeI, FeII, CrII, SrII and TiII. The direct magnetic field measurements using the `center of gravity' method had shown the non-monotonous magnetic field gradient in area of first flare contrary to usual weak negative gradient outside flare emission. Semi-empirical models of flares were calculated close to maximums using Baranovsky's (1993) program are in good agreement with these direct measurements. In particular, for flare of July, 2000, a very narrow (? 100 km) and sharp magnetic field peak at photospheric level (lg ?[5 ]? -2) was discovered. This peculiarity indicates likely the local magnetic field amplification due to any specific process during the flare. Once more interesting detail is two discrete hot flare layers related to the middle photosphere and temperature minimum zone. The turbulent velocities had one or two peaks placed close to named peaks of temperature. In more weak flare on August 4, 2005 the magnetic field increased along with depth of the photosphere without peculiarities. Baranovsky E.A. Semiempirical LTE modelling of solar photosphere layers.I. Theoretical background. Contrib. Astron. Obs. Skalnate Pleso. 1993. V.23. P.107-117.

Lozitsky, V. G.; Kurochka, E. V.; Osyka, O. B.

2006-08-01

267

What RHESSI Annihilation-Radiation Observations Tell Us About The Flaring Solar Atmosphere  

NASA Astrophysics Data System (ADS)

The electron-positron annihilation line and continuum below the line provide information on the density, temperature, and ionization state of the medium in which the positrons annihilate. The positrons originate from radioactive decay of nuclei and from pions created when flare-accelerated ions interact deep in the solar atmosphere and photosphere. The width of line has been found to be highly variable from flare-flare and during individual flares; during the 2003 October 28 flare the line width changed from ~ 6 keV to 1 keV in 2 - 3 minutes. This suggests that the temperature in the high density region where the line formed changed rapidly from ? 2 105 K to < 104 K. There is evidence that this change might be associated with cooling of small regions near the photosphere late in the flare. We review RHESSI observations of annihilation radiation in five solar flares and implications for the state of the flaring solar atmosphere. This work was supported by NASA DPR 10049 and NNG04ED181.

Share, G. H.; Murphy, R. J.; Smith, D. M.; Shih, A. Y.; Lin, R. P.; Schwartz, R. A.

2005-12-01

268

10100 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

269

Delayed X- and Gamma-Ray Line Emission from Solar Flare Radioactivity  

Microsoft Academic Search

We have studied the radioactive line emission expected from solar active regions after large flares, following the production of long-lived radioisotopes by nuclear interactions of flare-accelerated ions. This delayed X- and gamma-ray line emission can provide unique information on the accelerated particle composition and energy spectrum, as well as on mixing processes in the solar atmosphere. Total cross sections for

V. Tatischeff; B. Kozlovsky; J. Kiener; R. J. Murphy

2006-01-01

270

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

PubMed

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

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

2008-03-28

271

Magnetic fields and Fe I line profiles in the major solar flare on October 28, 2003  

Microsoft Academic Search

Strong (kilogauss) small-scale magnetic fields were detected outside a sunspot near the seismic source of the major X17.2\\/4B\\u000a solar flare on October 28, 2003. Echelle Zeeman spectrograms of the flare were obtained with the horizontal solar telescope\\u000a at the Astronomical Observatory of the Taras Shevchenko Kiev National University. Analysis of the Stokes I V profiles for the Fe I

V. G. Lozitsky

2009-01-01

272

Logistic Avalanche Processes, Elementary Time Structures, and Frequency Distributions in Solar Flares  

Microsoft Academic Search

We analyze the elementary time structures (on timescales of ~0.1-3.0 s) and their frequency distributions in solar flares using hard X-ray (HXR) data from the Compton Gamma Ray Observatory (CGRO) and radio data from the radio spectrometers of Eidgenoessische Technische Hochschule (ETH) Zurich. The four analyzed data sets are gathered from over 600 different solar flares and include about (1)

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

1998-01-01

273

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

274

NUMERICAL SIMULATION OF FLARE-GENERATED DISTURBANCES IN THE SOLAR WIND  

Microsoft Academic Search

The propagation of flare-generated shock waves through the solar wind is examined using numerical solutions of the time-dependent hydrodynamic equations. These solutions are valid for all shock strengths, including the intermediate values that have been observed in the solar wind, and take into account the variation of the properties of the ambient solar wind. The entire range of time scales

A. J. Hundhausen; R. A. Gentry

1969-01-01

275

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

276

X-ray observations of solar flares with the Einstein Observatory  

SciTech Connect

The first Einstein Observatory Imaging Proportional Counter (IPC) observations of solar flares are presented. These flares were detected in scattered X-ray light when the X-ray telescope was pointed at the sunlit earth. The propagation and scattering of solar X-rays in the earth's atmosphere are discussed in order to be able to deduce the solar X-ray flux incident on top of the atmosphere from scattered X-ray intensity measurements. After this correction, the scattered X-ray data are interpreted as full-disk observations of the sun obtained with the same instrumentation used for observations of flares on other stars. Employing the same data analysis and interpretation techniques, extremely good agreement is found between the physical flare parameters deduced from IPC observations and known properties of compact loop flares. This agreement demonstrates that flare observations with the IPC can reveal physical parameters such as temperature and density quite accurately in the solar case and therefore suggests that the interpretations of stellar X-ray flare observations are on a physically sound basis. 26 references.

Schmitt, J.H.M.M.; Fink, H.; Harnden, F.R. Jr.

1987-11-01

277

Short-Term Solar Flare Prediction Using a Sequential Supervised Learning Method  

NASA Astrophysics Data System (ADS)

Solar flares are powered by the energy stored in magnetic fields, so evolutionary information of the magnetic field is important for short-term prediction of solar flares. However, the existing solar flare prediction models only use the current information of the active region. A sequential supervised learning method is introduced to add the evolutionary information of the active region into a prediction model. The maximum horizontal gradient, the length of the neutral line, and the number of singular points extracted from SOHO/MDI longitudinal magnetograms are used in the model to describe the nonpotentiality and complexity of the photospheric magnetic field. The evolutionary characteristics of the predictors are analyzed by using autocorrelation functions and mutual information functions. The analysis results indicate that a flare is influenced by the 3-day photospheric magnetic field information before flare eruption. A sliding-window method is used to add evolutionary information of the predictors into machine learning algorithms, then C4.5 decision tree and learning vector quantization are employed to predict the flare level within 48 hours. Experimental results indicate that the performance of the short-term solar flare prediction model within the sequential supervised learning framework is significantly improved.

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

2009-03-01

278

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

279

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--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.

2013-09-01

280

Flare productivity of newly-emerged paired and isolated solar active regions  

NASA Astrophysics Data System (ADS)

Aims:We investigate whether sunspot regions that emerge near existing ones are more flare productive than those that emerge isolated. Methods: We analyse a sample of 2115 new regions obtained from the USAF/Mount Wilson catalogue of sunspot regions. For our analysis we use AstroGrid, a Virtual Observatory developed in the UK, to build a series of workflows that perform queries to catalogues of solar regions and flares, and operations on the results of the queries. If a new region emerged through the solar surface within 12 of a pre-existing one, we classify it as paired, otherwise as isolated. Results: We find that paired regions are more flare productive than isolated ones, although this is a small effect. Here only soft X-ray flares of magnitude greater than C1.0 are considered, and flare productivity is characterised by the percentage of regions that produced at least one flare over 4 days since emergence, and by the average number of flares over the same period. For paired regions, we also consider the flare productivity of the nearby companion region and find that if a flare does happen within the pair, it will more likely take place in the companion region than in the newly-emerged one. Our results show that although emergence in proximity to another region can slightly increase the probability of a flare taking place, presumably by increasing the likelihood of magnetic reconnection and significant change in magnetic topology, this is not a large effect. It appears that intrinsic properties of the region are the key factor in determining whether or not it will produce flares, as opposed to interaction with pre-existing regions.

Dalla, S.; Fletcher, L.; Walton, N. A.

2007-06-01

281

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

282

VLF Remote Sensing of the Lower Ionosphere with AWESOME Receivers: Solar Flares, Lightning-induced Electron Precipitation, Sudden Ionospheric Disturbances, Sprites, Gravity Waves and Gamma-ray Flares  

Microsoft Academic Search

Stanford University Very Low Frequency (VLF) radio receivers have been used extensively for remote sensing of the ionosphere and the magnetosphere. Among the phenomena that can be uniquely measured via VLF receivers are radio atmospherics, whistlers, electron precipitation, solar flares, sudden ionospheric disturbances, gravity waves, sprites, and cosmic gamma-ray flares. With the use of simple square air-core magnetic loop antennas

M. Cohen; P. Scherrer; D. Scherrer

2006-01-01

283

Solar X-ray flare hazards on the surface of Mars  

NASA Astrophysics Data System (ADS)

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

Smith, David S.; Scalo, John

2007-03-01

284

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

285

Bulk Energization of Electrons in Solar Flares by Alfvn Waves  

NASA Astrophysics Data System (ADS)

Bulk energization of electrons to 10 - 20 keV in solar flares is attributed to dissipation of Alfvn waves that transport energy and potential downward to an acceleration region near the chromosphere. The acceleration involves the parallel electric field that develops in the limit of inertial Alfvn waves (IAWs). A two-potential model for IAWs is used to relate the parallel potential to the cross-field potential transported by the waves. We identify a maximum parallel potential in terms of a maximum current density that corresponds to the threshold for the onset of anomalous resistivity. This maximum is of order 10 kV when the threshold is that for the Buneman instability. We argue that this restricts the cross-field potential in an Alfvn wave to about 10 kV. Effective dissipation requires a large number of up- and down-current paths associated with multiple Alfvn waves. The electron acceleration occurs in localized, transient, anomalously conducting regions (LTACRs) and is associated with the parallel electric field determined by Ohm's law with an anomalous resistivity. We introduce an idealized model in which the LTACRs are (upward-)current sheets, a few skin depths in thickness, separated by much larger regions of weaker return current. We show that this model can account semi-quantitatively for bulk energization.

Melrose, D. B.; Wheatland, M. S.

2013-08-01

286

Perspectives of current-layer diagnostics in solar flares  

NASA Astrophysics Data System (ADS)

Context. 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. Aims: 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. Methods: The method is based on a simple mathematical model of a super-hot (T ? 108 K) turbulent-current layer (SHTCL) and a model of plasma heating by the layer. Results: 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 1.51 ) and Ni xxvii (1.59 ). This method provides a theoretical basis for determining parameters of the current layer from observations. Conclusions: Observations of SHTCLs are difficult, because the spectral line intensities are faint, but it is theoretically possible in the future. Observations in X-ray range 1.5-1.8 with high spectral resolution (better than 0.01 ) and high temporal resolution (seconds) are needed. It is also very important to interpret the observations using a multi-temperature approach instead of the usual single or double temperature method.

Oreshina, A. V.; Oreshina, I. V.

2013-10-01

287

Fine structure of the sources of quasi-periodic pulsations in "single-loop" solar flares  

NASA Astrophysics Data System (ADS)

Analysis of the observational data obtained with a high angular resolution in the ranges of vacuum ultraviolet (1?, TRACE) and hard X-ray (4?, RHESSI) emissions in some solar flares previously considered "single-loop" ones shows that they are not such flares. The thick single loops with a diameter of 13?-21? observed in these flares in the microwave range with an angular resolution of 5?-10? (NoRH) are actually arcades of thinner loops with a diameter of less than 3?. In this case, the observed quasi-periodic pulsations of microwave emission are not a consequence of the oscillations of an isolated thick loop, as is usually assumed, but a result of the successive involvement of many relatively thinner loops in the process of flare energy release. The established facts impose significant constraints on the generation models of pulsations in flares.

Zimovets, I. V.; Kuznetsov, S. A.; Struminsky, A. B.

2013-04-01

288

A Critical Examination of the Fundamental Assumptions of Solar Flare and Coronal Mass Ejection Models  

NASA Astrophysics Data System (ADS)

The fundamental assumptions of conventional solar flare and coronal mass ejection (CME) theory are re-examined. In particular, the common theoretical assumption that magnetic energy that drives flares and CMEs can be stored in situ in the corona with sufficient energy density is found wanting. In addition, the observational constraint that flares and CMEs produce non-thermal electrons with fluxes of order 1034-1036 electrons s-1, with energies of order 10-20 keV, must also be explained. This constraint when imposed on the "standard model" for flares and CMEs is found to miss the mark by many orders of magnitude. We suggest, in conclusion, there are really only two possible ways to explain the requirements of observations and theory: flares and CMEs are caused by mass-loaded prominences or driven directly by emerging magnetized flux.

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

2013-05-01

289

Stimulated dissipation of magnetic discontinuities and the origin of solar flares  

NASA Astrophysics Data System (ADS)

It is proposed that the principal cause of the confined solar flare is the dissipation of magnetic energy at the many small-scale pre-existing tangential discontinuities in the local bipolar magnetic field. The discontinuities are a consequence of the continuous shuffling and intermixing of the footpoints of the bipolar field by the turbulent photospheric granules. The X-ray corona within the bipolar field is presumed to be a consequence of the continuing dissipation by reconnection at these discontinuities. A flare results when static deformation and/or internal agitation of the field stimulates the onset of rapid reconnection at the many small internal discontinuities. The discontinuities are partially exhausted by the flare, so that the post-flare X-ray emission of that particular loop is substantially below the pre-flare level for a period of some hours while the discontinuities are being rejuvenated.

Parker, E. N.

1987-09-01

290

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

SciTech Connect

In this paper, we analyze the energy budgets of two single-loop solar flares under the assumption that non-thermal electrons (NTEs) are the only source of plasma heating during all phases of both events. The flares were observed by RHESSI and GOES on 2002 September 20 and 2002 March 17, respectively. For both investigated flares we derived the energy fluxes contained in NTE beams from the RHESSI observational data constrained by observed GOES light curves. We showed that energy delivered by NTEs was fully sufficient to fulfill the energy budgets of the plasma during the pre-heating and impulsive phases of both flares as well as during the decay phase of one of them. We concluded that in the case of the investigated flares there was no need to use any additional ad hoc heating mechanisms other than heating by NTEs.

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

2011-05-20

291

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

292

The effects of different solar flare characteristics on the global thermosphere  

NASA Astrophysics Data System (ADS)

Given the ability of global models of the upper atmosphere to utilize high-resolution solar spectra to specify the solar soft X-ray and EUV irradiance, researchers now have the ability to perform detailed theoretical analysis of the response of the upper atmosphere to dynamic solar forcing more completely than ever before. Therefore, it is possible to develop a more quantitative understanding of the response of the thermosphere to solar flares. In this study, the effect of different characteristics of solar flares on the thermosphere is investigated. This is done in a theoretical manner, using synthetic solar irradiance data that is based on observations as input to the global ionosphere-thermosphere model (GITM). Specifically, the neutral response to the total incident energy, peak flare magnitude, background irradiance magnitude, duration of the impulsive phase, and decay time is investigated. It is found that the density response at 400 km altitude is linearly dependent on the total integrated energy above the background level being deposited into the atmosphere, and that the day-side response is strongly dependent on both the total incident energy into the system and the peak flare magnitude. Also, the decay time of the flare is important in determining the time at which the maximum global response occurs. Finally, the duration of the impulsive phase is found to have little effect on the global response of the system.

Pawlowski, David J.; Ridley, Aaron J.

2011-08-01

293

The study of relations between kilometric radiobursts and energetic electrons during powerful solar flares: INTERBALL-1  

NASA Astrophysics Data System (ADS)

The observational data of the long wave radiobursts and energetic electrons, registered on satellite INTERBALL-1 during large chromospheric flares have been analyzed. Radioemission was observed at the frequency range 100-1500 kHz with multi-channel spectroanalyser with passband 10 kHz. Electrons have been registered with DOK-2 at energy range E = 20-450 keV. The temporal profiles of solar radiobursts and electron fluxes and spectra were investigated. The onset and increase of radiobursts coincided with explosive phase of the flare and characterized by high drift velocity, typical to the radiobursts of III type and the duration within several minutes. It is known that the generation of radiobursts was caused by the energetic electrons, accelerated at solar flare and spreading to the outer corona up to the Earth orbit. The energetic electrons after solar flares, which we analyzed, have been observed near the Earth with energy E~100 keV, that sufficed to generate the kilometric radiobursts at near-solar space. For some events we valued the time of spreading of electrons to the Earth. Also the question about possible origin of long wave radioemission from accelerated electrons in connection with CME was considered. Besides the solar events we analyzed the AKR, the radioemission of magnetospheric origin, observed during the geomagnetic disturbances after analyzed solar flares.

Kurilchik, V.; Prokudina, V.; Kudela, K.; Slivka, M.

2003-09-01

294

Association of magnetic topology and radiative emissions in solar flares  

Microsoft Academic Search

We relate the energetic process in flares to the detailed topology, dynamics and evolution of magnetic field for NOAA active region 10720, which proved to be the most flare productive region of Cycle 23. We obtain the locations of quasi-separatrix layers (QSLs) from photospheric vector magnetic field observations based on the squashing degree, Q of Titov et al. (2002)and compare

D. Alexander; L. Tian; A. Coyner

2008-01-01

295

Effects of Solar Flares on Earth and Mars  

Microsoft Academic Search

Flares on the Sun have long been known to cause changes in the Earth's ionosphere. At other planets, ionospheric observations are far less common, and certainly not continuous, making the detection of short-lived flare effects not easy to demonstrate. The Mars Global Surveyor (MGS) radio science experiment has now made 4896 measurements of the electron density profiles at Mars since

M. Mendillo; P. Withers

2006-01-01

296

Seismic Emission from the Solar Flares of 2003 October 28 and 29  

NASA Astrophysics Data System (ADS)

We report the detection of seismic waves emitted from powerful solar flares that occurred in NOAA Active Region 10486 on 2003 October 28 and 29. We used helioseismic holography to image the seismic sources of the waves. This technique was previously used to image the source of seismic emission from the large solar flare of 1996 July 9. Egression power maps at 6 mHz with a 2 mHz bandwidth reveal multiple compact acoustic sources strongly associated with the footpoints of a coronal loop that hosted the flares. The total acoustic energy in the flare signatures is a very small fraction of the total energy radiated by the flares. The acoustic signatures are co-aligned with hard X-ray signatures, suggesting a direct link between energetic particles accelerated during the flare and the acoustic waves as a hydrodynamic response of the chromosphere, or possibly the underlying photosphere, to these particles at the footpoints of the loop. There is also evidence of high-energy protons impinging onto the chromosphere in the neighborhoods of the acoustic sources. Observations of emission in the D1 line of neutral sodium at the onset of the October 29 flare show evidence of a downward-propagating shock/condensation at the onset of the flare. Concurrent Global Oscillation Network Group (GONG) intensity observations show significant radiative emission with a sudden onset in the compact region encompassing the acoustic signature. Most flares appear to be acoustically inactive. Photospheric heating by high-energy protons is likely to be a major factor in seismic emission from acoustically active flares.

Donea, A.-C.; Lindsey, C.

2005-09-01

297

Implications for energy transport in solar flares from the recent observations of sun-quakes  

NASA Astrophysics Data System (ADS)

Analysis of seismic emission (sun-quakes) induced in the solar interior in the vicinity of flares offers us an opportunity to explore the physical processes of energy transport in flaring atmospheres. Only about 17 M and X-class flares have been reported to show seismic signatures in the form or ripples or egression sources, revealing that some of the most powerful flares often do not produce any seismic signatures. In addition, the most powerful signatures were recorded from an M-class flare. This raises important questions about how the flare energy and momentum are transported to the solar surface and interior in order to produce sun-quakes. Observations of ripples associated with the first few sun-quakes suggested that hydrodynamic shocks arising from a hydrodynamic response of the ambient plasma to precipitation of energetic particles (electrons or protons) are plausible sources of the seismic emission. Later, noting that sun-quakes are often co-spatial with hard X-ray and white light, another source of seismic emission was proposed related to back-warming of the photosphere by the enhanced chromospheric and coronal radiation caused by physical processes in flares. A third mechanism proposed to account for sun-quakes is related to possible Lorentz force transients that occur as a result of the coronal restructuring of the magnetic field in flares. Recent work comparing samples of white-light flares with and without sun-quakes, and new observations with GONG, Hinode and SDO of seismic emission associated with the X-class flares of 14 December 2006 and 15 February 2011 demonstrate inconsistencies with some existing models. In this paper these inconsistencies are explored and possible alternative scenarios are discussed.

Matthews, S. A.; Zharkov, S.; Zharkova, V. V.; Green, L.; Pedram, E.

2011-12-01

298

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

PubMed

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

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

2002-04-04

299

An Automated Algorithm to Distinguish and Characterize Solar Flares and Associated Sequential Chromospheric Brightenings  

NASA Astrophysics Data System (ADS)

We present a new automated algorithm to identify, track, and characterize small-scale brightening associated with solar eruptive phenomena observed in H?. The temporal, spatially localized changes in chromospheric intensities can be separated into two categories: flare ribbons and sequential chromospheric brightenings (SCBs). Within each category of brightening we determine the smallest resolvable locus of pixels, a kernel, and track the temporal evolution of the position and intensity of each kernel. This tracking is accomplished by isolating the eruptive features, identifying kernels, and linking detections between frames into trajectories of kernels. We fully characterize the evolving intensity and morphology of the flare ribbons by observing the tracked flare kernels in aggregate. With the location of SCB and flare kernels identified, they can easily be overlaid on complementary data sets to extract Doppler velocities and magnetic-field intensities underlying the kernels. This algorithm is adaptable to any dataset to identify and track solar features.

Kirk, M. S.; Balasubramaniam, K. S.; Jackiewicz, J.; McNamara, B. J.; McAteer, R. T. J.

2013-03-01

300

The heliolongitudinal distribution of solar flares associated with solar proton events.  

PubMed

We find that the heliolongitudinal distribution of solar flares associated with earth-observed solar proton events is a function of the particle measurement energy. For solar proton events containing fluxes with energies exceeding 1 GeV, we find a Gaussian distribution about the probable root of the Archimedean spiral favorable propagation path leading from the earth to the sun. This distribution is modified as the detection threshold is lowered. For > 100 MeV solar proton events with fluxes > or = 10 protons (cm2-sec-ster)-1 we find the distribution becomes wider with a secondary peak near the solar central meridian. When the threshold is lowered to 10 MeV the distribution further evolves. For > 10 MeV solar proton events having a flux threshold at 10 protons (cm2-sec-ster)-1 the distribution can be considered to be a composite of two Gaussians. One distribution is centered about the probable root of the Archimedean spiral favorable propagation path leading from the earth to the sun, and the other is centered about the solar central meridian. For large flux solar proton events, those with flux threshold of 1000 (cm2-sec-ster)-1 at energies > 10 MeV, we find the distribution is rather flat for about 40 degrees either side of central meridian. PMID:11540356

Smart, D F; Shea, M A

1996-01-01

301

The heliolongitudinal distribution of solar flares associated with solar proton events  

NASA Astrophysics Data System (ADS)

We find that the heliolongitudinal distribution of solar flares associated with earth-observed solar proton events is a function of the particle measurement energy. For solar proton events containing fluxes with energies exceeding 1 GeV, we find a Gaussian distribution about the probable root of the Archimedean spiral favorable propagation path leading from the earth to the sun. This distribution is modified as the detection threshold is lowered. For greater than 100 MeV solar proton events with fluxes greater than or = 10 protons/(sq cm-sec-ster) we find the distribution becomes wider with a secondary peak near the solar central meridan. When the threshold is lowered to 10 MeV the distribution further evolves. For greater than 10 MeV solar proton events having a flux threshold at 10 protons/(sq cm-sec-ster) the distribution can be considered to be a composite of two Gaussians. One distribution is centered about the probable root of the Archimedean spiral favorable propagation path leading from the earth to the sun, and the other is centered about the solar central meridian. For large flux solar proton events, those with flux threshold of 1000/(sq cm-sec-ster) at energies greater than 10 MeV, we find the distribution is rather flat for about 40 degrees either side of central meridian.

Smart, D. F.; Shea, M. A.

302

Multiple Views of X1.4 Solar Flare on July 12, 2012  

NASA Video Gallery

This video shows the July 12, 2012 X1.4 class solar flare in a variety of wavelength; 131- Teal colored, 335 - blue colored, 171 - yellow colored and finally a combined wavelength view. All video was captured by the Solar Dynamic Observatory's (SDO) AIA instrument.

Holly Zell

2012-07-13

303

Nonplanar mhd model for solar flare-generated disturbances in the heliospheric equatorial plane  

Microsoft Academic Search

An analysis, with a representative (canonical) example of solar-flare-generated equatorial disturbances, is presented for the temporal and spatial changes in the solar wind plasma and magnetic field environment between the Sun and one astronomical unit (AU). Our objective is to search for first order global consequences rather than to make a parametric study. The analysis - an extension of earlier

S. T. Wu; M. Dryer; S. M. Han

1983-01-01

304

Improved Modeling Of Atmospheric Effects Of The September 1859 Solar Flare  

Microsoft Academic Search

The atmospheric effects of the 1859 solar flare known as the Carrington event have previously been studied by two different groups. In Thomas et al. 2007, the event was studied with a 2D atmospheric chemistry and dynamics model, using a proton fluence estimate derived from ice core records, and ionization scaled from the 1989 solar proton event. In Rodger et

Keith Arkenberg; B. Thomas

2011-01-01

305

The escape of trapped electrons in the decay phase of solar flare  

NASA Astrophysics Data System (ADS)

From the observations of radio and HXR bursts, the escape rate of energetic electrons trapped in the flare loops is studied based on the trap-plus-precipitation model for the kinematics of energetic electrons in solar flares. Coulomb collision is regarded as the main pitch angle scattering of trapped electrons in the decay phase of the event on 2004 December 1. The escape rate of trapped electrons decreases firstly and then increases, which indicates the evolution of the plasma density in the flare loops during the decay phase.

Huang, Jing

2013-07-01

306

A solar flare X-ray polarimeter for the space shuttle  

Microsoft Academic Search

We have recently built and tested an instrument designed to measure the polarization of the hard (530 keV) X-ray emission from solar flares, and thereby to investigate the energy release mechanism and constrain flare models. In particular, these measurements will help to determine whether hard X-ray bursts are produced by nonthermal or by thermal electrons. The polarimeter makes use of

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

1982-01-01

307

GRAPE: A Balloon-Borne Hard X-ray Polarimeter for Solar Flares  

Microsoft Academic Search

We present the current status of the gamma-ray polarimetry experiment (GRAPE) project to measure linear polarization in solar flares in the hard X-ray range (50-300 keV). Polarimetry measurements offer a new way to measure the extent to which energetic electrons in flares are beamed, which has important implications for particle acceleration models. Each GRAPE detector consists of an array of

Peter F. Bloser; M. L. McConnell; J. S. Legere; J. R. Macri; J. M. Ryan; T. Narita

2006-01-01

308

A Solar Flare X-Ray Polarimeter for the Space Shuttle  

Microsoft Academic Search

We have recently built and tested an instrument designed to measure the polarization of the hard (5 30 keV) X-ray emission from solar flares, and thereby to investigate the energy release mechanism and constrain flare models. In particular, these measurements will help to determine whether hard X-ray bursts are produced by nonthermal or by thermal electrons. The polarimeter makes use

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

1982-01-01

309

A Model for the Escape of Solar-flare-accelerated Particles  

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

310

ELECTRON DENSITY ENHANCEMENTS IN THE E AND F REGIONS OF THE IONOSPHERE DURING SOLAR FLARES  

Microsoft Academic Search

Using the method of Thomson scatter, it has been possible to observe detailed ionospheric effects due to solar flares. Observations have been limited to four 2B flares, and two of these events have been examined intensively. The two events that have been studied exhibit very similar characteristics, i.e., a strong and long-lasting E-region electron density enhancemcnt, a moderate and shorter

G. D. Thome; L. S. Wagner

1971-01-01

311

Hard X-ray imaging observations of solar hot thermal flares with the HINOTORI spacecraft  

Microsoft Academic Search

Two solar hard X-ray bursts of a new type (hot thermal flare) were observed with hard X-ray imaging telescopes and other instruments on Japanese spacecraft Hinotori. The flares have no clear impulsive phase below 40 keV and emit intense hard X-rays (10-50 keV) with extremely steep spectra from a small region with size (FWHM) of 10-20 arcsec. This source contains

S. Tsuneta; N. Nitta; T. Takakura; K. Makishima; T. Murakami; M. Oda; Y. Ogawara; K. Ohki; K. Tanaka

1984-01-01

312

Ionospheric effects of the solar flares as deduced from global GPS network data  

Microsoft Academic Search

Results derived from analysing the ionosphere response to faint and bright\\u000asolar flares are presented. The analysis used technology of a global detection\\u000aof ionospheric effects from solar flares as developed by the authors, on the\\u000abasis of phase measurements of the total electron content (TEC) in the\\u000aionosphere using an international GPS network. The essence of the method is

L. A. Leonovich; A. T. Altynsev; V. V. Grechnev; E. L. Afraimovich

2001-01-01

313

Waiting-Time Distribution and Angular Correlation Function of Solar X-ray Flares  

Microsoft Academic Search

A statistical study is performed on X-ray flares stronger than C1 class that erupted during the solar maximum between 1989 and 1991. We have investigated the waiting-time distribution and the angular correlation function of successive flare pairs. The observed waiting-time distribution for the whole data is found to be well represented by a nonstationary Poisson probability function with time-varying mean

Y. Moon; G. S. Choe; H. S. Yun; Y. D. Park

2001-01-01

314

Modeling the Solar Atmospheric Response to Flare-Accelerated Ion Beams  

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

315

Directionality of continuum gamma rays from solar flares  

SciTech Connect

Hard x-ray-burst spectrometer total counts as calibration are used to investigate how the brightness of gamma rays above 300 keV changes as a function of the heliocentric angle of a flare. The normalized gamma-ray brightness, on the average, increases with the heliocentric angle; a flare at the limb is estimated to be 13 times brighter in gamma rays than a similar flare near the central meridian. Both pancake-like electron distributions and downward beam distributions can be adjusted to produce the deduced limb brightening.

Bai, T.

1988-11-15

316

Directionality of continuum gamma rays from solar flares  

SciTech Connect

Using hard X-ray burst spectrometer total counts as calibration, the changes in the brightness of gamma rays above 300 keV as a function of the heliocentric angle of a flare are investigated. The normalized gamma-ray brightness, on the average, increases with the heliocentric angle; a flare at the limb is estimated to be 13 times brighter in beam gamma rays than a similar flare near the central meridian. Both pancakelike electron distributions and downward beam distributions can be adjusted to produce the deduced limb brightening. 14 references.

Bai, T.

1988-11-01

317

Directionality of continuum gamma rays from solar flares  

SciTech Connect

The hard-x-ray spectrometer total counts are used as calibration to investigate how the brightness of gamma rays above 300 keV changes as a function of the heliocentric angle of a flare. The normalized gamma-ray brightness, on the average, increases with the heliocentric angle; a flare at the limb is estimated to be 13 times brighter in gamma rays than a similar flare near the central meridian. Both pancake-like electron distributions and downward beam distributions can be adjusted to produce the deduced limb brightening.

Bai, T.

1988-04-01

318

Quantitative Analysis of Solar Flare Characteristics as Observed in the Solar Observing Optical Network and the Global Oscillation Network Group.  

National Technical Information Service (NTIS)

This study consists of a quantitative comparison of H-alpha solar flare area and brightness as recorded by the Solar Observing Optical Network (SOON) and the Global Oscillation Network Group (GONG) from March 11 through November 30, 2011. The Air Force ut...

T. M. Wittman

2012-01-01

319

A loop-top hard X-ray source in a compact solar flare as evidence for magnetic reconnection  

Microsoft Academic Search

SOLAR flares are thought to be the result of magnetic reconnection --- the merging of antiparallel magnetic fields and the consequent release of magnetic energy. Flares are classified into two types1: compact and two-ribbon. The two-ribbon flares, which appear as slowly-developing, long-lived large loops, are understood theoretically2-6 as arising from an eruption of a solar prominence that pulls magnetic field

S. Masuda; T. Kosugi; H. Hara; S. Tsuneta; Y. Ogawara

1994-01-01

320

Solar Flare Doppler Blueshifted Soft X-Ray Emission and Hard X-Ray Bursts  

NASA Astrophysics Data System (ADS)

Hard X-ray emission and the dynamics of soft X-ray emitting plasma are among the most immediate manifestations of solar flare energy release. To understand better the early impulsive phase of solar flare energy release, we have examined Ca XIX and Fe XXV soft X-ray resonance line spectra that exhibit strong blue-wing asymmetries from 32 flares. These spectra were obtained with the Bragg Crystal Spectrometer on the Japanese Yohkoh spacecraft, which is up to 10 times more sensitive than previously flown crystal spectrometers. The increased sensitivity allowed the comparison of Doppler blueshifted X-ray emission to hard X-ray emission observed with the Compton Gamma Ray Observatory's Burst and Transient Source Experiment, the Yohkoh Wide Band Spectrometer, and Yohkoh Hard X-Ray Telescope. We found that (1) hard X-ray burst light curves and resonance line blue-wing light curves are similar for most flares that exhibit strong blueshifts; (2) the time evolution of the intensity ratio of the blue wing to the peak unshifted spectral component resembles higher energy hard X-ray emission more closely than the blue-wing light curve alone; (3) though many flares had blue-wing/resonance peak ratios that resembled or peaked at the same time as the hard X-ray burst, nearly one-third of the flares exhibited ratio curves that either were nonzero before the detection of burst hard X-rays or peaked before the hard X-ray burst peaked-a few of these flares exhibited small blueshifted line profiles before the detection of hard X-ray emission; (4) a few flares with strong blueshifts had little or no detectable emission above 30 keV; and (5) the time derivative of the resonance peak emission usually resembles the blue-wing light curve. The implication of these results for current flare models is discussed.

Rilee, M. L.; Doschek, G. A.

2001-06-01

321

Filament Eruptions and the Impulsive Phase of Solar Flares.  

National Technical Information Service (NTIS)

We examine the observed development of filament eruptions in the impulsive phase of flares for evidence of how the eruption is driven. A possibility sometimes adopted as working hypothesis is that the filament eruption and accompanying coronal mass ejecti...

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

1988-01-01

322

Structure and Dynamics of Magnetic Reconnection in a Solar Flare  

Microsoft Academic Search

We report a detailed analysis of the temperature structure of a prototypical flare that occurred on 1992 February 21. In the decay phase of this flare, the outer loops systematically have higher temperatures, reaching the peak (12 MK) far outside the apparent bright X-ray loop where the X-ray intensity is only 2%-5% of the peak. In between the high-temperature ridges,

Saku Tsuneta

1996-01-01

323

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

NASA Astrophysics Data System (ADS)

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

Cecatto, Jose Roberto

1994-11-01

324

Predicted solar flare activity for the 1990s - Possible effects on navigation systems  

SciTech Connect

The current solar cycle, which began in September 1986, may prove to be the highest ever, as measured by sunspot numbers and radio flux. The cycle's frequent and strong solar flare activity can be illustrated by the March 1989 episode, which caused many problems for navigation systems. Flares and the geomagnetic storms that sometimes accompany them can disrupt low-frequency systems such as Loran-C, as well as the satellite-borne GPS. Although the maximum of the solar cycle is expected during the first quarter of 1990, flare activity is likely to persist at high levels for a few years to follow. Geomagnetic activity may occur at any time in the cycle, and thus geomagnetic disruptions are possible at any point in the 1990s. 5 refs.

Kunches, J.M.; Hirman, J.W. (NOAA, Boulder, CO (USA))

1990-01-01

325

Predicted solar flare activity for the 1990s - Possible effects on navigation systems  

NASA Astrophysics Data System (ADS)

The current solar cycle, which began in September 1986, may prove to be the highest ever, as measured by sunspot numbers and radio flux. The cycle's frequent and strong solar flare activity can be illustrated by the March 1989 episode, which caused many problems for navigation systems. Flares and the geomagnetic storms that sometimes accompany them can disrupt low-frequency systems such as Loran-C, as well as the satellite-borne GPS. Although the maximum of the solar cycle is expected during the first quarter of 1990, flare activity is likely to persist at high levels for a few years to follow. Geomagnetic activity may occur at any time in the cycle, and thus geomagnetic disruptions are possible at any point in the 1990s.

Kunches, J. M.; Hirman, J. W.

326

Can microbunch instability on solar flare accelerated electron beams account for bright broadband coherent synchrotron microwaves?  

SciTech Connect

The physical processes producing bright broadband coherent synchrotron radiation (CSR) bursts in laboratory accelerators are proposed to happen also in solar flares, bringing a plausible explanation to serious interpretation constraints raised by the discovery of a solar flare sub-mm-wave spectral emission component peaking in the terahertz (THz) range simultaneous to the well-known microwaves component. The THz component is due to incoherent synchrotron radiation (ISR) produced by a beam of ultrarelativistic electrons. Beam density perturbations, on a scale of the order of or smaller than the emitting wavelength, sets a microbunch instability producing the intense CSR at lower frequencies. Hard x-ray/{gamma}-ray emissions may include a significant synchrotron emission component from the same ISR spectrum, bringing a new possibility to explain the so called ''solar flare electron number paradox'.

Kaufmann, Pierre; Raulin, Jean-Pierre [Centro de Radio-Astronomia e Astrofisica-CRAAM-Escola de Engenharia, Universidade Presbiteriana Mackenzie, Sao Paulo, SP (Brazil)

2006-07-15

327

The Sun near of the solar cycle 24 maximum: the geoeffective flare phenomena, the evolution and the development forecast  

NASA Astrophysics Data System (ADS)

The main characteristics and course of the current solar cycle XXIV evolution after 3.8 years of development and some signs suggesting that the current cycle is in a phase of maximum are considered. At the same time, the curve of the current solar cycle evolution is similar to the solar cycle XIV - the lowest of the authentic solar cycles. During the current solar cycle 30 large solar flares have occurred up to now, among which two flares with the class X> 5 and 13 flares with class X>=1.0. The number of geoeffective solar flare events and coronal holes is abnormally low. During the period no several magnetic storms (Ap >= 100), only one major magnetic storm (Ap >= 70), two solar proton event (Epr> 10 MeV) with a flux of protons greater than 1000 p.f.u. and only one GLE event were registered.

Ishkov, V. N.

2013-02-01

328

Ionospheric and magnetospheric effects of solar flares monitored by ground-based riometer and magnetometers  

NASA Astrophysics Data System (ADS)

The solar flare incidence follows a behavior similar to the solar cycle activity, which results in periodic disturbances on the Earth's ionosphere and magnetosphere. The correlation of this phenomenon can provide important information about the magnetosphere, the Sun/Earth interaction, as well as events occurring in the ionosphere which can, for instance, generate disturbances in telecommunications, small satellites or even in the space weather. Riometer and magnetometers data analysis can provide useful way for measuring and understanding the effects of solar flare radiation in the ionosphere and magnetosphere. The Solar Flare effect (SFE) is associated with the sudden change of ionospheric currents caused by the extra ionization produced by soft X-ray (0.1 to 9.0 nm) and EUV (9.0 to 100.0 nm) radiation from the solar flare. The objective of this work is to present the correlation of the ionospheric and magnetospheric (H, D, Z) sudden disturbances due to high-intensity solar flares (M and X class), that can emit up to 1032 ergs of energy. For this purpose, analysis were performed for the riometer and magnetometers dedicated to study the Solar-Earth interactions at the Southern Space Observatory (SSO/CRS/INPE -MCT), (29.4 S, 53.8 W, 480m a.s.l), So Martinho da a Serra, RS, Brazil. To identify and investigate the sudden radiation increase caused by the solar flare, the X-ray data (0.1 to 0.8 nm) from GOES Satellites and the EUV data (26.0 to 34.0 nm and 0.1 to 50.0 nm) from the Solar EUV Monitor (SEM) on the SOHO spacecraft are correlated. With the analysis of these ground-based instruments and spacecrafts data, the correlation of the solar activity and the magnetospheric and ionospheric disturbances were performed, as for the Sudden Ionospheric Disturbance (SID) and Magnetic Crochet about 60% D-component variation during a large solar flare was observed.

Ronan Coelho Stekel, Tardelli; Schuch, Nelson Jorge; Echer, Ezequiel; Guarnieri, Fernando; Makita, Kazuo; Espindola Antunes, Cassio; Moro, Juliano; Machado Paulo, Claudio

329

The characteristics of the X-ray flares (1 - 8 , GOES) of the different classes and their variations in two cycles of solar activity  

Microsoft Academic Search

The X-ray (1 - 8 ) flux data of the solar flares are analyzed. The data used were obtained on GOES satellite during the solar cyles 21 and 22. The total number of the flares is more than 33000. The flare distributions according to their X-ray-classes, durations and intensities are constructed. The evolution of these distributions in solar cycle as

R. T. Sotnikova

1999-01-01

330

Statistical Studies on the Excess Peak Flux in Soft X-rays and EUV Bands from Solar Flares  

NASA Astrophysics Data System (ADS)

Based on the solar X-ray data in the band of 0.1 - 0.8 nm observed by Geostationary Operational Environmental Satellites (GOES), the XUV and EUV data in the bands of 26 - 34 nm and 0.1 - 50 nm observed by the Solar EUV Monitor (SEM) onboard the Solar and Heliospheric Observatory (SOHO), a statistical analysis on the excess peak flux (the pre-flare flux is subtracted) in two SEM bands during M- and X-class flares from 1998 to 2007 is given. The average ratio of the excess peak flux to the pre-flare flux for the M-class flares is 5.5 %3.7 % and that for the X-class flares is 16 %11 %. The excess peak fluxes in two SEM bands are positively correlated with the X-ray flare class; with the increase in the X-ray flare class, the excess peak flux in two SEM bands increases. However, a large dispersion in the excess peak flux in the SEM bands and their ratio is found for the same X-ray flare class. The relationship between the excess peak fluxes of the two SEM bands also shows large dispersion. It is considered that the diversity we found in the flare spectral irradiance is caused by many variable factors related to the structure and evolution of solar flares.

Zhang, D. H.; Cai, L.; Ercha, A.; Hao, Y. Q.; Xiao, Z.

2012-09-01

331

ABRUPT LONGITUDINAL MAGNETIC FIELD CHANGES AND ULTRAVIOLET EMISSIONS ACCOMPANYING SOLAR FLARES  

SciTech Connect

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

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

2012-11-20

332

Solar Flare and CME Observations with STEREO/EUVI  

NASA Astrophysics Data System (ADS)

STEREO/EUVI observed 185 flare events (detected above the GOES class C1 level or at > 25 keV with RHESSI) during the first two years of the mission (December 2006 - November 2008), while coronal mass ejections (CMEs) were reported in about a third of these events. We compile a comprehensive catalog of these EUVI-observed events, containing the peak fluxes in soft X rays, hard X rays, and EUV, as well as a classification and statistics of prominent EUV features: 79% show impulsive EUV emission (coincident with hard X rays), 73% show delayed EUV emission from postflare loops and arcades, 24% represent occulted flares, 17% exhibit EUV dimming, 5% show loop oscillations or propagating waves, and at least 3% show erupting filaments. We analyze an example of each EUV feature by stereoscopic modeling of its 3D geometry. We find that EUV emission can be dominated by impulsive emission from a heated, highly sheared, noneruptive filament, in addition to the more common impulsive EUV emission from flare ribbons or the delayed postflare EUV emission that results from cooling of the soft-X-ray-emitting flare loops. Occulted flares allow us to determine CME-related coronal dimming uncontaminated from flare-related EUV emission. From modeling the time evolution of EUV dimming we can accurately quantify the initial expansion of CMEs and determine their masses. Further, we find evidence that coronal loop oscillations are excited by the rapid initial expansion of CMEs. These examples demonstrate that stereoscopic EUV data provide powerful new methods to model the 3D aspects in the hydrodynamics of flares and kinematics of CMEs.

Aschwanden, M. J.; Wuelser, J. P.; Nitta, N. V.; Lemen, J. R.

2009-05-01

333

Study of Three Homologous Solar Flares Observed from Active Region NOAA 9033 on 12th June 2000  

NASA Astrophysics Data System (ADS)

In the paper, we present a study of three homologous H flares observed on 12th June 2000 in active region (AR) NOAA 9033. During the observation of AR NOAA 9033 on 12th June 2000, we observed 1st solar flare between 0135-0155 UT, 2nd flare between 0236-0253 UT and 3rd flare between 0259-0323 UT. The present study supports the quadrapolar reconnection scenario presented by Machado et al. (1983) and also shows the presence of 26.7 min periodicity in intensity data estimated from the site of the homologous flares.

Verma, V. K.; Vats, Hari Om

2003-03-01

334

Generalization of the Neupert effect over the solar flare plasma cooling  

NASA Astrophysics Data System (ADS)

We investigate 10 M-class flares observed by the SOXS mission to study the influence of the solar flare plasma cooling on the Neupert effect. We study the temporal evolution of 1s cadence X-ray emission in 7-10 keV and 10-30 keV representing the SXR and HXR emission respectively. We model the cooling as a function of time by the ratio of time-derivative of SXR with the HXR flux. We report that the ratio is exponentially decaying in rise phase of the flare, which, however, saturates after the impulsive phase. We estimate the cooling time scale in the rise phase for the flares and found to be varying between 39 and 525 s.

Awasthi, Arun Kumar; Jain, Rajmal

2013-07-01

335

Speed Distributions of Merging X-Ray Sources During Chromospheric Evaporation in Solar Flares  

NASA Astrophysics Data System (ADS)

We explore the speed distributions of X-ray source motions after the start of chromospheric evaporation in two Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) flares. First, we make CLEAN images at 15 energy bands with a 12 second integration window; then, we outline a flaring loop geometry to cover the looptop and footpoint sources as much as possible. Consistent with the previous steps, we find converging motion of the double footpoint sources along the flaring loop in these two events. This motion is dependent on the energy band and time and is typically seen at 3 - 25 keV, indicating a chromospheric evaporation origin. The speed distributions at various energy bands are measured for the 10 September 2002 flare, which exhibits a separation-to-mergence motion pattern well correlated with the rising-to-decay phases at 50 - 100 keV.

Ning, Zongjun

2011-10-01

336

The wide band spectrometer for the solar flare satellite SOLAR-A  

NASA Astrophysics Data System (ADS)

The Wide Band Spectrometer (WBS) for the solar flare satellite SOLAR-A scheduled for launch in 1991 consists of three kinds of detectors to observe the wide band spectrum from soft X-rays to gamma-rays. The soft X-ray spectrometer (gas proportional counter), hard X-ray spectrometer (NaI scintillation counter and gamma-ray spectrometer (two BGO scintillation counters) cover the 2-30 keV, 20-400 keV and 0.2-100 MeV bands, respectively. Further, the WBS contains a radiation belt monitor consisting of a NaI scintillation counter which is capable of detecting cosmic gamma-ray bursts. The details of these detectors, electronics systems and data collection are described.

Yoshimori, Masato; Okudaira, Kiyoaki; Hirasima, Yo; Yanagimachi, Tomoki; Kondo, Ichiro; Ohki, Ken-Ichiro; Watanabe, Tetsuya; Nishimura, Jun; Yamagami, Takamasa; Murakami, Toshio; Ito, Masayuki; Yoshida, Atsumasa

1988-02-01

337

EVIDENCE OF SOLAR FLARE TRIGGERING DUE TO LOOP-LOOP INTERACTION CAUSED BY FOOTPOINT SHEAR MOTION  

SciTech Connect

We analyze multi-wavelength data of an M7.9/1N class solar flare which occurred on 2006 April 27 in AR NOAA 10875. GOES soft X-ray images provide the most likely signature of two interacting loops and their reconnection, which triggers the solar flare. TRACE 195 A images also reveal the loop-loop interaction and the formation of 'X' points with converging motion ({approx}30 km s{sup -1}) at the reconnection site in between this interacting loop system. This provides evidence of progressive reconnection and flare maximization at the interaction site in the active region. The absence of type III radio bursts during this time period indicates no opening of magnetic field lines during the flare energy release, which implies that the change of field line connectivity/orientation occurred only during the loop-loop interaction and reconnection process. The Ondrejov dynamic radio spectrum shows an intense decimetric (DCIM) radio burst (2.5-4.5 GHz, duration {approx}3 minutes) during the flare initiation, which reveals the signature of particle acceleration from the reconnection site during loop-loop interaction. The double-peak structures at 4.9 and 8.8 GHz provide the most likely confirmatory signature of the loop-loop interaction at the flare site in the active region. RHESSI hard X-ray images also show the loop-top and footpoint sources of the corresponding two-loop system, which act like current-carrying flux tubes with resultant opposite magnetic fields and net force of attraction, and their coalescence during the flare maximum. We also suggest that the shear motion/rotation of the footpoint of the smaller loop, which is anchored in the opposite polarity spot, may be responsible for the flare energy buildup and its eventual release due to the loop-loop interaction.

Kumar, Pankaj; Srivastava, A. K.; Uddin, Wahab [Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital-263129 (India); Somov, B. V. [Astronomical Institute, Moscow State University, Universitetskij Prospekt 13, Moscow 119992 (Russian Federation); Manoharan, P. K. [Radio Astronomy Centre, NCRA, Tata Institute of Fundamental Research, Udhagamandalam (Ooty) 643 001 (India); Erdelyi, R., E-mail: pkumar@aries.res.i, E-mail: aks@aries.res.i [Solar Physics and Space Plasma Research Centre (SP2RC), Department of Applied Mathematics, University of Sheffield, Sheffield S3 7RH (United Kingdom)

2010-11-10

338

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

339

GEMSIS-Sun: Modeling of Particle Acceleration and Transport in Solar Flares  

NASA Astrophysics Data System (ADS)

GEMSIS (Geospace Environment Modeling System for Integrated Studies) is one of projects in Solar- Terrestrial Environment Laboratory, Nagoya University. Its final goal is to build a geospace-environment model based on various (satellite and ground-based) observational facts in order to understand the dynamic energy-transport-processes taking place in geospace. In the first three years (2007.4 - 2010.3), we set a few individual scientific targets as fundamental elements/information for the final model. One of them is to know how particles are accelerated, transported, and lose their energies in solar flares. It is evident from many observations such as X-rays, gamma-rays, and microwaves that a large amount of high-energy particles are produced in solar flares. However, the dynamics of these particles is not completely understood so far. The GEMSIS-Sun group approaches this research topic through integrated studies, i.e., an empirical modeling of particle dynamics and analyses of various data observed with Hinode, RHESSI, Nobeyama Radioheliograph, and so on. It is widely believed that a solar flare is a consequence of magnetic reconnection. Based on the magnetic reconnection model, we are developing a numerical model for particle acceleration and transport in the flare region. Since the temporal and spatial scales of particles are much shorter than the flare scale (roughly by ten to the six for ions), the full-particle approach is yet unrealistic for the empirical understanding. We therefore employ the guiding-center kinetic equation of particles so that we can perform the calculation in the coronal actual parameter range. By the direct comparison between observations and the calculation, we will empirically discuss the acceleration and transport mechanisms of particles in solar flares.

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

2008-12-01

340

Ionospheric Solar Flare Effects Monitored by the Ground-based GPS Receivers V Theory and Observation  

NASA Astrophysics Data System (ADS)

A theoretical model for monitoring ionospheric solar flare effects by using ground-based receivers of the global positioning system (GPS) has been developed and reviewed in this paper. The physical representations and meanings of two GPS quantities, variations in the total electron content (TEC) and their time rate of changes (rTEC), are examined and discussed. The theoretical and mathematical derivations show that the rTEC practically represent the frequency deviation of the GPS signals. Meanwhile, worldwide ground based GPS receivers are used to derive the TEC and associated rTEC to monitor the ionospheric solar flare effect on 14 July (Bastille Day) 2000. It is found that ionospheric solar flare effects can be observed from pre-dawn to post-dusk regions, and the most pronounced signatures appear in the midday area. The agreement between theoretical predications and observations demonstrates that the GPS TEC is suitable to monitor the overall variations of flare X-ray radiations while the rTEC is capable to detect sudden changes in flare X-ray radiations.

Liu, J. Y.; Lin, C. H.; Tsai, H. F.; Liou, Y. A.

2002-05-01

341

A Method to Calculate Background-Subtracted Flare Plasma Parameters Using GOES Over Three Solar Cycles  

NASA Astrophysics Data System (ADS)

The GOES solar flare catalogue is the largest, self-consistent listing currently available covering three solar cycles - #21, 22, and 23 - from 1974 to the present. Solar X-ray flux integrated over the full solar disk is recorded every 3s in each of the two GOES channels (long; 1-8 and short; 0.5-4). By taking the ratio of the flux in the two passbands, parameters of the SXR-emitting plasma (e.g. temperature, emission measure, radiative loss rate etc.) can be derived, as well as the timescales over which they change. In doing so, it is vital to perform a suitable background subtraction to remove the influence of flux not associated with the flaring plasma. Using the method outlined in Bornmann 1990, we have developed a technique to systematically derive the flare parameters for all GOES flares from 1980 to present after accounting for background emission. This then allows us to make statistically meaningful comparisons between events observed over the course of the past three solar cycles. This research is generously funded by the Irish Research Council for Science, Engineering and Technology (IRCSET).

Ryan, Daniel; Gallagher, P. T.; Milligan, R. O.; Young, C. A.

2010-05-01

342

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

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

343

Modeling solar flare hard X-ray images and spectra observed with RHESSI  

NASA Astrophysics Data System (ADS)

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

Sui, Linhui

2004-12-01

344

Polarization of Hard X-Rays in October-November, 2003 Solar Flares Observed Onboard CORONAS-F Satellite  

NASA Astrophysics Data System (ADS)

Hard X-ray radiation from several powerful solar flares was detected in October-November, 2003 by the SPR-N hard X-ray polarimeter onboard CORONAS-F satellite. In the October, 29 solar flare (20:40 - 21:00 UT) the X-ray radiation was strongly polarized (more than 70% of photons with energies 40-100 keV). In the flares 28.10.03 and 04.11.03 the emission was not polarized. The upper limits for the part of polarized photons at the level of tens percents were obtained in these flares.

Bogomolov, A. V.; Denisov, Yu. I.; Logachev, Yu. I.; Morozov, O. V.; Myagkova, I. N.; Svertilov, S. I.; Zhitnik, I. A.; Ignat'ev, A. P.; Oparin, S. N.; Pertsov, A. A.

345

WHAT IS THE RELATIONSHIP BETWEEN PHOTOSPHERIC FLOW FIELDS AND SOLAR FLARES?  

SciTech Connect

We estimated photospheric velocities by separately applying the Fourier Local Correlation Tracking and Differential Affine Velocity Estimator methods to 2708 co-registered pairs of SOHO/MDI magnetograms, with nominal 96 minute cadence and approx2'' pixels, from 46 active regions (ARs) from 1996 to 1998 over the time interval tau{sub 45} when each AR was within 45{sup 0} of disk center. For each magnetogram pair, we computed the reprojected, average estimated radial magnetic field, B-tilde{sub R}; and each tracking method produced an independently estimated flow field, u. We then quantitatively characterized these magnetic and flow fields by computing several extensive and intensive properties of each; extensive properties scale with AR size, while intensive properties do not depend directly on AR size. Intensive flow properties included moments of speeds, horizontal divergences, and radial curls; extensive flow properties included sums of these properties over each AR, and a crude proxy for the ideal Poynting flux, S{sub R}=SIGMA|u|B-tilde{sub R}{sup 2}. Several quantities derived from B-tilde{sub R} were also computed, including: PHI, the total unsigned flux; R, a measure of the unsigned flux near strong-field polarity inversion lines; and SIGMAB-tilde{sub R}{sup 2}. Next, using correlation and discriminant analysis, we investigated the associations between these properties and flares from the GOES flare catalog, when averaged over both tau{sub 45} and shorter time windows of 6 and 24 hr. Our AR sample included both flaring and flare-quiet ARs; the latter did not flare above GOES C1.0 level during tau{sub 45}. Among magnetic properties, we found R to be most strongly associated with flare flux. Among extensive flow properties, the proxy Poynting flux, S{sub R} , was most strongly associated with flare flux, at a level comparable to that of R. All intensive flow properties studied were more poorly associated with flare flux than these extensive properties. Past flare activity was also associated with future flare occurrence. The largest coefficients of determination from correlations with flare flux that we performed are approx0.25, implying no single variable that we considered can explain the majority of variability in average flare flux.

Welsch, Brian T.; Li Yan; Fisher, George H. [Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450 (United States); Schuck, Peter W., E-mail: welsch@ssl.berkeley.ed [Heliophysics Science Division, Space Weather Laboratory, Code 674, NASA Goddard Space Flight Center, 8801 Greenbelt Road, Greenbelt, MD 20771 (United States)

2009-11-01

346

Yohkoh observations of plasma upflows during solar flares  

NASA Astrophysics Data System (ADS)

Observations of two flares, an M 2.2 event on 16 December, 1991 and the precursor to an X1 flare on 15 November, 1991 are presented. Spectra obtained with the Bragg Crystal Spectrometer (BCS) are compared with data from the Hard and Soft X-ray Telescopes (HXT, SXT) and the Wide Band Spectrometer (WBS) on the satellite. For both events the creation of upflowing plasma is detected. While the first event seems to conform well to the chromospheric evaporation model for high temperature plasma production, the behaviour for the second event is more complex.

Culhane, J. L.; Phillips, A. T.; Pike, C. D.; Fludra, A.; Bentley, R. D.; Bromage, B.; Doschek, G. A.; Hiei, E.; Inda, M.; Mariska, J. T.; Phillips, K. J. H.; Sterling, A. C.; Watanabe, T.

1993-09-01

347

RELAXATION OF MAGNETIC FIELD RELATIVE TO PLASMA DENSITY REVEALED FROM MICROWAVE ZEBRA PATTERNS ASSOCIATED WITH SOLAR FLARES  

SciTech Connect

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

Yu Sijie; Yan Yihua; Tan Baolin, E-mail: sjyu@nao.cas.cn, E-mail: yyh@nao.cas.cn, E-mail: bltan@nao.cas.cn [Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

2012-12-20

348

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

NASA Astrophysics Data System (ADS)

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

Yu, Sijie; Yan, Yihua; Tan, Baolin

2012-12-01

349

High temporal resolution measurements of linear polarization in solar flare's H? line.  

NASA Astrophysics Data System (ADS)

Since the summer season 1998 a system consisting of a Wollaston prism and ?/2 plate is experimentally tested in the complex of video cameras used both in the image and in the spectral data acquisition of the Ond?ejov Multichannel Flare Spectrograph. In addition to the slit-jaw camera and to the three other video cameras working in H?, H? (resp. in He D3) and in the Ca II 854.2 nm another CCD video camera for measurements of linear polarization in H? spectral line has been added. The main purpose of this set of fast detectors is to observe solar flare spectra and images and to detect fast variations of intensity and linear polarization expected at the beginning and during initial phases of solar flares. Main advantages and limitations of the system are briefly described from the points of view of its scientific philosophy, intends and outputs. Some obtained results, experience and future prospects are discussed.

Kotr?, P.

350

The Relationship between Extreme Ultraviolet Non-thermal Line Broadening and High-energy Particles during Solar Flares  

NASA Astrophysics Data System (ADS)

We have studied the relationship between the location of EUV non-thermal broadening and high-energy particles during large flares using the EUV Imaging Spectrometer on board Hinode, the Nobeyama Radio Polarimeter, the Nobeyama Radioheliograph, and the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory. We have analyzed five large flare events that contain thermal-rich, intermediate, and thermal-poor flares classified by the definition discussed in the paper. We found that, in the case of thermal-rich flares, the non-thermal broadening of Fe XXIV occurred at the top of the flaring loop at the beginning of the flares. The source of 17 GHz microwaves is located at the footpoint of the flare loop. On the other hand, in the case of intermediate/thermal-poor flares, the non-thermal broadening of Fe XXIV occurred at the footpoint of the flare loop at the beginning of the flares. The source of 17 GHz microwaves is located at the top of the flaring loop. We discussed the difference between thermal-rich and intermediate/thermal-poor flares based on the spatial information of non-thermal broadening, which may provide clues that the presence of turbulence plays an important role in the pitch angle scattering of high-energy electrons.

Kawate, T.; Imada, S.

2013-10-01

351

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

SciTech Connect

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

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

2011-06-10

352

Quasi-Separatrix layers in solar flares. I. Method  

Microsoft Academic Search

Magnetic reconnection is usually thought to be linked to the presence of magnetic null points and to be accompanied by the transport of magnetic field lines across separatrices, the set of field lines where the mapping of field lines is discontinuous. In view of the variety of observed flaring configurations, we show that this view is too restrictive. Instead, Priest

P. Demoulin; J. C. Henoux; E. R. Priest; C. H. Mandrini

1996-01-01

353

Stochastic Particle Acceleration by Helical Turbulence in Solar Flares  

NASA Astrophysics Data System (ADS)

Modern X-ray and radio observations favor a stochastic (Fermi) acceleration mechanism of fast particles produced in flares, which implies that an accelerating turbulence must somehow be generated by the primary flare energy release. The very release of free magnetic energy is only possible if the magnetic field deviates from a potential one. We show that this magnetic field nonpotentiality, via its corresponding current helicity, necessarily results in a noticeable kinetic helicity of the turbulence generated at the flare site by the primary energy release. We study the role of the turbulence helicity on the particle acceleration and find that a nonzero turbulence helicity has a remarkably strong effect on the particle acceleration. The main reason for this strong helicity effect is that the helical component of the turbulence induces, through a well-known alpha-effect, a regular large-scale electric field capable of directly accelerating charged particles (like in the models with DC field acceleration). We estimate the turbulence kinetic helicity based on measured photospheric and extrapolated values of the current helicity and take into consideration the helical turbulence effect on stochastic particle acceleration. We find that this induced large-scale electric field can be comparable with the electron and estimated effective ion Dreicer fields, which has an immediate effect on charged particle extraction from the thermal pool and their injection into stochastic acceleration process. We have discovered that this, so far missing but highly important, ingredient of the particle stochastic acceleration by turbulence at the flare site is naturally consistent with such puzzling flare manifestations as spatial separation of electron and proton emission sites, electron beam formation, and enrichment of the accelerated particle population by 3He and other tiny ions. This work was supported in part by NSF grant AGS-0961867 and NASA grant NNX10AF27G to New Jersey Institute of Technology.

Fleishman, Gregory D.; Toptygin, I. N.

2012-05-01

354

Simulation Studies of Electron Acceleration by Ion Ring Distributions in Solar Flares.  

National Technical Information Service (NTIS)

Using a 2 1/2-D fully relativistic electromagnetic particle-in-cell code (PIC), the authors have investigated a potential electron acceleration mechanism in solar flares. The free energy is provided by ions which have a ring velocity distribution about th...

K. G. McClements J. J. Su R. Bingham J. M. Dawson D. S. Spicer

1990-01-01

355

Particle Motion in Collapsing Magnetic Traps in Solar Flares. I. Kinematic Theory of Collapsing Magnetic Traps  

Microsoft Academic Search

We present a model of collapsing magnetic traps in magnetic field configurations associated with solar flares. The model is based on a kinematic description of the magnetic field obeying the ideal Ohm's law. The dynamic evolution of the models is given in terms of a time-dependent transformation from Eulerian to Lagrangian coordinates. The transformation can be used to determine the

Paolo Giuliani; Thomas Neukirch; Paul Wood

2005-01-01

356

Incoherent scatter observations of the ionospheric response to a large solar flare  

Microsoft Academic Search

Incoherent scatter observations at Millstone Hill were made during the ; importance 3B solar flare which occurred at 15:00 UT on 7 August 1972. ; Measurements were obtained of the electron density profile over the height range ; 125 to 1200 km, together with observations of the electron temperature, ion ; temperature, and vertical drift velocity above 225 km. The

Michael Mendillo; John V. Evans

1974-01-01

357

X-Ray Observations of Motions and Structure above a Solar Flare Arcade  

Microsoft Academic Search

In this Letter, we describe a solar flare that was observed by Yohkoh in 1999 January 20. This long-duration event is notable because the Yohkoh images show not only the formation of the arcade associated with the coronal mass ejection but also a considerable amount of motion above the arcade in the region normally identified with a large-scale current sheet

D. E. McKenzie; H. S. Hudson

1999-01-01

358

Low-Energy Cosmic-Ray Events Associated with Solar Flares  

Microsoft Academic Search

As a result of the IGY riometer program, it has been found that the measure- ment of ionospheric absorption in arctic regions is a sensitive method of detecting low-energy cosmic rays associated with solar flares. The normal morphology of these events is described, and details are given of the 24 such events that have been detected in the period from

George C. Reid; Harold Leinbach

1959-01-01

359

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

National Technical Information Service (NTIS)

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

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

1980-01-01

360

Turbulence as a Contributor to Intermediate Energy Storage During Solar Flares,  

National Technical Information Service (NTIS)

Turbulence is considered as a method for converting the energy observed as mass motions during the impulsive phase into thermal energy observed during the gradual phase of solar flares. The kinetic energy of the large-scale eddies driven by the upflowing ...

P. L. Bornmann

1987-01-01

361

Turbulence as a Proposed Intermediate Energy Storage Mechanism during Solar Flares.  

National Technical Information Service (NTIS)

Turbulence is proposed as a method for converting the energy observed as mass motions during the impulsive phase into thermal energy and the subsequent thermal radiation observed during the gradual phase of solar flares. The kinetic energy in the large sc...

P. L. Bornmann

1986-01-01

362

Quasi-Separatrix Layers: Refined Theory and its Application to Solar Flares  

Microsoft Academic Search

Although the analysis of observational data indicates that quasi-separatrix layers (QSLs) have to play an important role in magnetic configurations of solar flares, the corresponding theory is only at an initial stage so far. In particular, there is still a need in a proper definition of QSL. This problem is analyzed here on the basis of geometrical properties of the

V. S. Titov; P. Demoulin; G. Hornig

1999-01-01

363

Ionospheric and stratopsheric effects of a proton flare during unusual solar activity - 22 November 1977  

Microsoft Academic Search

The effect of the proton flare of 22 November 1977 on the various levels in the middle atmosphere and the bottom-side ionosphere is studied in order to compare synchronous phenomena in the middle atmosphere with phenomena in upper regions and to investigate the response of middle atmosphere to the penetration of high energy solar particles and radiation.

P. Velinov; G. Nestorov; Kh. Spasov; Ts. Dachev; Y. Tasev

1984-01-01

364

Radioactivity Induced in Apollo 11 Lunar Surface Material by Solar Flare Protons  

Microsoft Academic Search

Comparison of values of the specific radioactivities reported for lunar surface material from the Apollo 11 mission with analogous data for stone meteorites suggests that energetic particles from the solar flare of 12 April 1969 may have produced most of the cobalt-56 observed.

H. R. Heydegger; Anthony Turkevich

1970-01-01

365

Li-7 and Be-7 Deexcitation Lines: Probes for Accelerated Particle Transport Models in Solar Flares.  

National Technical Information Service (NTIS)

The photon energy spectrum of a spectral feature composed of the 429 and 478 keV gamma-ray lines from Li-7 and Be-7 (produced by interactions of flare-accelerated alpha particles with ambient He in the solar atmosphere) depends on the angular distribution...

R. J. Murphy X. Hua B. Kozlovsky R. Ramaty

1989-01-01

366

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

Microsoft Academic Search

Jenkins and Fischbach (Astroparticle Physics, 31, 407, 2009) have recently found evidence for fluctuations in the decay rates of radioactive isotopes in association with solar flares. Jenkins et al. (Astroparticle Physics, 32, 42, 2010) have also found strong evidence for annual variations in measurements of decay rates acquired at the Brookhaven National Laboratory (BNL) and at the Physikalisch-Technische Bundesanstalt (PTB)

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

2009-01-01

367

Photospheric Model Transformation In The Course Of A Solar Two -Ribbon Flare  

NASA Astrophysics Data System (ADS)

We study the two-ribbon solar flare on 7 October 1979. As may be seen from the GOES soft X-ray data, the preheating phase preceded the flare impulsive phase. The semiempirical photospheric models for different stages of flare development are calculated on the basis of observed Fraunhofer spectra. The temporal variations of the magnetic field strength and the inclination of the magnetic field vector are obtained as well. The modelling results reveal inhomogeneities of temperature, gas pressure, and other parameters. Disturbances of the matter below undisturbed photosphere base prevailed during the preheating phase. Narrow and cool layers were displaced upwards in the 0.5 min time interval. During the impulsive phase and at the flare maximum the upper and middle photospheric layers were mainly disturbed. For this period the downward displacement of the lower boundary of wide low-temperature region in the upper photosphere took place. The photosphere perturbations were still preserved at 25-30 minutes after the flare maximum. The turbulent motions were inhibited during the flare.

Alikaeva, K. V.; Kondrashova, N. N.

2006-08-01

368

Impulsive 2-10 keV solar electron events not associated with flares  

NASA Astrophysics Data System (ADS)

Data from the ISEE 3 satellite reveal a class of impulsive solar electron events with no measurable increase in flux above 10-20 keV. The flux histories and angular distributions indicate that the electrons propagate through interplanetary space with little or no scattering. The smooth extension of the power-law energy spectra down to the limit of the observations at 2 keV indicates that the electrons are accelerated at altitudes greater than 0.5 solar radii in the solar corona. Although these events occur more frequently than any other type of impulsive solar particle event observed, no correlation is found with flares or flare-related activity. However, there is a close correlation with low-frequency type III radio bursts.

Potter, D. W.; Lin, R. P.; Anderson, K. A.

1980-03-01

369

High-energy solar flare observations at the Y2K maximum  

NASA Astrophysics Data System (ADS)

Solar flares afford an opportunity to observe processes associated with the acceleration and propagation of high-energy particles at a level of detail not accessible in any other astrophysical source. I will review some key results from previous high-energy solar flare observations, including those from the Compton Gamma-Ray Observatory, and the problems that they pose for our understanding of energy release and particle acceleration processes in the astrophysical environment. I will then discuss a program of high-energy observations to be carried out during the upcoming 2000-2001 solar maximum that is aimed at addressing and resolving these issues. A key element in this observational program is the High Energy Solar Spectroscopic Imager (HESSI) spacecraft, which will provide imaging spectroscopic observations with spatial, temporal, and energy resolutions commensurate with the physical processes believed to be operating, and will in addition provide the first true gamma-ray spectroscopy of an astrophysical source. .

Emslie, A. Gordon

2000-04-01

370

HARD X-RAY AND MICROWAVE EMISSIONS FROM SOLAR FLARES WITH HARD SPECTRAL INDICES  

SciTech Connect

We analyze 10 flare events that radiate intense hard X-ray (HXR) emission with significant photons over 300 keV to verify that the electrons that have a common origin of acceleration mechanism and energy power-law distribution with solar flares emit HXRs and microwaves. Most of these events have the following characteristics. HXRs emanate from the footpoints of flare loops, while microwaves emanate from the tops of flare loops. The time profiles of the microwave emission show delays of peak with respect to those of the corresponding HXR emission. The spectral indices of microwave emissions show gradual hardening in all events, while the spectral indices of the corresponding HXR emissions are roughly constant in most of the events, though rather rapid hardening is simultaneously observed in some for both indices during the onset time and the peak time. These characteristics suggest that the microwave emission emanates from the trapped electrons. Then, taking into account the role of the trapping of electrons for the microwave emission, we compare the observed microwave spectra with the model spectra calculated by a gyrosynchrotron code. As a result, we successfully reproduce the eight microwave spectra. From this result, we conclude that the electrons that have a common acceleration and a common energy distribution with solar flares emit both HXR and microwave emissions in the eight events, though microwave emission is contributed to by electrons with much higher energy than HXR emission.

Kawate, T. [Kwasan and Hida Observatory, Kitashirakawa-oiwakecho, Sakyo, Kyoto 606-8502 (Japan); Nishizuka, N. [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 229-8510 (Japan); Oi, A. [College of Science, Ibaraki University, Mito, Ibaraki 310-8512 (Japan); Ohyama, M. [Faculty of Education, Shiga University, 2-5-1 Hiratsu, Otsu, Shiga 1-1, Baba Hikone city, Siga 522-8522 (Japan); Nakajima, H., E-mail: kawate@kusastro.kyoto-u.ac.jp [Nobeyama Solar Radio Observatory, NAOJ, Nobeyama, Minamisaku, Nagano 384-1305 (Japan)

2012-03-10

371

Continuum Contributions to the SDO/AIA Passbands during Solar Flares  

NASA Astrophysics Data System (ADS)

Data from the Multiple EUV Grating Spectrograph component of the Extreme-ultraviolet Variability Experiment (EVE) on board the Solar Dynamics Observatory (SDO) were used to quantify the contribution of continuum emission to each of the extreme ultraviolet (EUV) channels of the Atmospheric Imaging Assembly (AIA), also on SDO, during an X-class solar flare that occurred on 2011 February 15. Both the pre-flare-subtracted EVE spectra and fits to the associated free-free continuum were convolved with the AIA response functions of the seven EUV passbands at 10 s cadence throughout the course of the flare. It was found that 10%-25% of the total emission in the 94 , 131 , 193 , and 335 passbands throughout the main phase of the flare was due to free-free emission. Reliable measurements could not be made for the 171 channel, while the continuum contribution to the 304 channel was negligible due to the presence of the strong He II emission line. Up to 50% of the emission in the 211 channel was found to be due to free-free emission around the peak of the flare, while an additional 20% was due to the recombination continuum of He II. The analysis was extended to a number of M- and X-class flares and it was found that the level of free-free emission contributing to both the 171 and 211 passbands increased with increasing GOES class. These results suggest that the amount of continuum emission that contributes to AIA observations during flares is more significant than stated in previous studies which used synthetic, rather than observed, spectra. These findings highlight the importance of spectroscopic observations carried out in conjunction with those from imaging instruments so that the data are interpreted correctly.

Milligan, Ryan O.; McElroy, Sarah A.

2013-11-01

372

On the Origin of the Extreme-ultraviolet Late Phase of Solar Flares  

NASA Astrophysics Data System (ADS)

Solar flares typically have an impulsive phase that is followed by a gradual phase as best seen in soft X-ray emissions. A recent discovery based on the EUV Variability Experiment observations on board the Solar Dynamics Observatory (SDO) reveals that some flares exhibit a second large peak separated from the first main phase peak by tens of minutes to hours, which is coined as the flare's EUV late phase. In this paper, we address the origin of the EUV late phase by analyzing in detail two late phase flares, an M2.9 flare on 2010 October 16 and an M1.4 flare on 2011 February 18, using multi-passband imaging observations from the Atmospheric Imaging Assembly on board SDO. We find that (1) the late phase emission originates from a different magnetic loop system, which is much larger and higher than the main phase loop system. (2) The two loop systems have different thermal evolution. While the late phase loop arcade reaches its peak brightness progressively at a later time spanning for more than one hour from high to low temperatures, the main phase loop arcade reaches its peak brightness at almost the same time (within several minutes) in all temperatures. (3) Nevertheless, the two loop systems seem to be connected magnetically, forming an asymmetric magnetic quadruple configuration. (4) Further, the footpoint brightenings in UV wavelengths show a systematic delay of about one minute from the main flare region to the remote footpoint of the late phase arcade system. We argue that the EUV late phase is the result of a long-lasting cooling process in the larger magnetic arcade system.

Liu, Kai; Zhang, Jie; Wang, Yuming; Cheng, Xin

2013-05-01

373

CONVERSION FROM EXPLOSIVE TO GENTLE CHROMOSPHERIC EVAPORATION DURING A SOLAR FLARE  

SciTech Connect

A GOES M1.5 solar flare was observed in NOAA AR 10652 on 2004 July 27 around 20:00 UT with the Coronal Diagnostic Spectrometer (CDS) aboard the Solar and Heliospheric Observatory (SOHO) spacecraft. Images obtained with SOHO's Extreme-ultraviolet Imaging Telescope and with the Transition Region And Coronal Explorer satellite show that the CDS slit was positioned within the flare, whose emission extended 1 arcmin along the slit. Rapid cadence (9.8 s) stare spectra obtained with CDS include emission from the upper chromosphere (He I at 584.3 A), transition region (O V at 629.7 A), corona (Si XII at 520.7 A), and hot flare plasma (Fe XIX at 592.2 A), and reveal that (1) the flare brightened in its southern parts before it did so in the north; (2) chromospheric evaporation was 'explosive' during the first rapid intensity increase observed in Fe XIX, but converted to 'gentle' during the second; (3) chromospheric evaporation did not occur in the northern portion of the flare observed by CDS: the brightening observed there was due to flare material moving into that location from elsewhere. We speculate that the initial slow, steady increase of Fe XIX intensity that was observed to start several minutes before its rapid increase was due to direct coronal heating. The change from explosive to gentle evaporation was likely due to either an increased absorption of beam energy during the gentle event because the beam passed through an atmosphere modified by the earlier explosive event, or to a weakening of the coronal magnetic field's ability to accelerate nonthermal particle beams (via reconnection) as the flare progressed, or both.

Brosius, Jeffrey W. [Catholic University of America at NASA Goddard Space Flight Center, Solar Physics Laboratory, Code 671, Greenbelt, MD 20771 (United States)], E-mail: Jeffrey.W.Brosius@nasa.gov

2009-08-20

374

High time resolution observations of solar H? flares. II. Search for signatures of electron beam heating  

NASA Astrophysics Data System (ADS)

Aims: The H? emission of solar flare kernels and associated hard X-ray (HXR) emission often show similar time variations but their light curves are shifted in time by energy transfer mechanisms. We searched for fast radiative response of the chromosphere in the H? line as a signature of electron beam heating. Methods: We investigate the time differences with sub-second resolution between the H? line emission observed with a Multi-channel Subtractive Double Pass (MSDP) spectrograph on the Large Coronagraph and Horizontal Telescope at Bia?kw Observatory, Poland, and HXR emission recorded by the RHESSI spacecraft during several flares, greatly extending our earlier analysis (Paper I) to flares between 2003 and 2005. Results: For 16 H? flaring kernels, observed in 12 solar flares, we made 72 measurements of time delays between local maxima of the RHESSI X-ray and H? emissions. For most kernels, there is an excellent correlation between time variations in the H? line emission (at line centre and in the line wings) and HXR (20-50 keV) flux, with the H? emission following features in the HXR light curves generally by a short time lapse ?t = 1-2 s, sometimes significantly longer (10-18 s). We also found a strong spatial correlation. Conclusions: Owing to our larger number of time measurements than in previous studies, the distribution of ?t values shows a much clearer pattern, with many examples of short (1-2 s) delays of the H? emission, but with some flares showing longer (10-18 s) delays. The former are consistent with energy transfer along the flaring loop legs by non-thermal electron beams, the latter to the passage of conduction fronts.

Radziszewski, K.; Rudawy, P.; Phillips, K. J. H.

2011-11-01

375

1980 to 1989 Observations of Nuclear Gamma-Rays from Solar Flares  

NASA Astrophysics Data System (ADS)

We present a study of background-corrected spectra, 0.3 <= E_? <=8.5 MeV, observed by the Gamma Ray Spectrometer on the Solar Maximum Mission satellite from 1980 to 1989. A total of 192 spectra covering the impulsive phases of these flares were fit by a model containing a power-law electron bremsstrahlung component and a nuclear component. The nuclear model was derived from the 1981 April 27 flare (Murphy et al. 1990). About 60\\ the flares exhibit evidence for a nuclear component in addition to bremsstrahlung. We have summed spectra from flares into 16 groups according to their observed bremsstrahlung flux, extending over a dynamic range of 100. These summed spectra were fit once again with the two component model to compare average nuclear and bremsstrahlung emissions. The average nuclear and bremstrahlung fluxes are strongly correlated over the full range of study. On average we find evidence for nuclear emission even for the lowest range of bremsstrahlung fluxes observable >=300 keV ( ~ 5 times 10(-2) gamma cm(-2) s(-1) ). We also find that the average nuclear/bremsstrahlung ratio decreases and the average bremsstrahlung spectrum hardens with increasing heliocentric angle. This is consistent with earlier studies suggesting that the electrons producing the bremsstrahlung are not isotropically distributed. On the other hand the nuclear/bremsstrahlung ratio exhibits large scatter from flare to flare. A study of the temporal variations of the prompt nuclear and bremsstrahlung emissions, and of the delayed lines at 0.511 and 2.223 MeV, within individual flares is in progress. The nuclear/bremsstrahlung ratio exhibits significant variation during some of the flares. This work is supported under NASA DPR's W-17,972 and W-17,973. Murphy, R.J., et al. 1990, Ap. J., 358, 298.

Share, G. H.; Murphy, R. J.; MacKinnon, R. J.

1992-05-01

376

Asymmetry of Hard X-Ray Emissions at Conjugate Footpoints in Solar Flares  

NASA Astrophysics Data System (ADS)

The chromospheric double hard X-ray (HXR) sources generally appear at the conjugate footpoints of flaring loops with asymmetric flux distributions. The behavior of such HXR footpoint asymmetry should be affected by several effects simultaneously and cannot be attributed to a single effect easily. In this study, we attempt to address the properties of photospheric magnetic fields in the areas coinciding with asymmetric HXR footpoints based on RHESSI observations during 2002-2009. A total of 172 time intervals in 22 flares closed to the solar disk center with available pre-flare MDI magnetograms are investigated. The strong HXR footpoint is found to preferentially (75%) locate at the region with weak magnetic field strength, which is qualitatively consistent with the asymmetric magnetic mirror scenario. The HXR footpoint fluxes become more asymmetric when the footpoints move to the areas with more asymmetric field strength. A feature of asymmetry reversal between different energy ranges is observed in some flares, although no significant energy dependence of footpoint asymmetry is found in our statistical results. We also investigated the possible causes of time-dependent HXR footpoint asymmetry by examining the 2004 November 4 M5.4 flare and the 2004 November 6 M3.6 flare. By comparing the estimated asymmetry quantities with the HXR light curves, the asymmetry reversal in the late period of the M5.4 flare is mainly attributed to the difference of coronal energy release or acceleration processes in different periods, while it is associated with the location changes of HXR footpoints moving to different magnetic field regions in the M3.6 flare.

Yang, Ya-Hui; Cheng, C. Z.; Krucker, Sm; Hsieh, Min-Shiu; Chen, Nai-Hwa

2012-09-01

377

Nonplanar MHD model for solar flare-generated disturbances in the heliospheric equatorial plane  

Microsoft Academic Search

An analysis, with a representative (canonical) example of solar-flare-generated equatorial disturbances, is made for the temporal and spatial changes in the solar wind plasma and magnetic field environment between the sun and 1 AU. The goal is to search for first-order global consequences rather than to make a parametric study. The analysis treats all three plasma velocity and magnetic field

S. T. Wu; M. Dryer; S. M. Han

1983-01-01

378

The emission and propagation of ? 40keV solar flare electrons  

Microsoft Academic Search

Observations of prompt ~ 40 keV solar flare electron events by the IMP series of satellites in the period August, 1966 to December, 1967 are tabulated along with prompt energetic solar proton events in the period 19641967. The interrelationship of the various types of energetic particle emission by the sun, including relativistic energy electrons reported by Cline and McDonald (1968)

R. P. Lin

1970-01-01

379

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

380

A Comprehensive View of the Temperature Distribution in Solar Flares from EVE and RHESSI  

NASA Astrophysics Data System (ADS)

Solar flares accelerate electrons up to hundreds of MeV and heat plasma up to tens of MK, but the physical processes behind these phenomena remain poorly understood. While the ubiquitous 10-25 MK plasma is commonly accepted to result from chromospheric evaporation, evidence suggests that in intense (GOES M- and X-class) flares, the hottest, 20-50 MK plasma is directly heated in the corona, although the heating mechanism and its connection to the flare-accelerated non-thermal electrons is not yet understood. While observations of hard X-ray bremmstrahlung directly probe the non-thermal electron population, the spectra below 20-30 keV are typically dominated by strong thermal emission. The low-energy extent of the non-thermal spectrum can thus be only loosely quantified, which has significant implications for calculating flare energy budgets and for constraining possible acceleration mechanisms. Hence, a precise characterization of the thermal electron population is imperative. New extreme ultraviolet observations from the EUV Variability Experiment (EVE) on-board the Solar Dynamics Observatory (SDO), combined with X-ray data from the Reuven Ramaty High Energy Spectroscopic Imager (RHESSI), offer the most comprehensive view into the flare temperature distribution to date. EVE observes a wealth of EUV emission lines with peak formation temperatures of 2-20 MK, while RHESSI observes the X-ray bremsstrahlung of hot, 10-50 MK plasmas; combined, the two instruments have excellent temperature sampling and coverage over the full range of flare plasma temperatures. We have calculated differential emission measures (DEMs) using EVE and RHESSI independently, for separately observed events. We present a novel method of combining simultaneous EVE and RHESSI observations to determine the flare DEM, and its evolution, over the full 1-100 MK range during intense M/X flares. We present preliminary results from the 2011-Feb-15 X2.2 flare, and compare with the RHESSI non-thermal emission to discuss the implications for flare plasma heating.

Caspi, Amir; McTiernan, J. M.; Warren, H. P.

2012-05-01

381

Runaway electron acceleration by DC electric fields in impulsive solar flares  

NASA Astrophysics Data System (ADS)

Impulsive solar flares occupy a unique position in the realm of energetic transient astrophysical phenomena, releasing up to 1032 ergs of energy over times that range from a few minutes to a few hours. A large fraction of the energy is contained in suprathermal particles that remain trapped at the sun or escape into the corona. A major signature of a solar flare is the hard X-ray emission generated by 100 keV electrons which interact with the ambient plasma to produce continuum radiation that ranges from radio, to microwave, soft X-rays and occasionally gamma-rays. We investigate time-dependent solar flare electron acceleration by large-scale sub-Dreicer fields, taking into account spatial transport, current closure, Coulomb collisions, and plasma waves. In this process, the particles are energized directly out of the thermal coronal plasma, where they can produce hard X-rays. We show that a bump-on-tail distribution readily develops if the current closure is localized near the ends of the current channel and we study the resultant wave-particle interactions. We then incorporate Joule heating and thermal conduction to explore the temperature evolution of the electron distribution. We study the conditions under which electric fields can produce the hard X-ray inferred fluxes of >20 keV electrons. We are able to successfully fit the high-energy hard X-ray spectrum from the 1980 June 27 solar flare using the numerically calculated hard X-ray spectrum generated from a solar flare that contained a superpositioning of filaments with different lengths and densities.

Sommer, James Clarence

2002-09-01

382

Solar flare hard and soft X ray relationship determined from SMM HXRBS and BCS data  

NASA Astrophysics Data System (ADS)

The exact nature of the solar flare process is still somewhat a mystery. A key element to understanding flares if the relationship between the hard x rays emitted by the most energetic portions of the flare and the soft x rays from other areas and times. This relationship was studied by comparing hard x ray light curved from the Hard X-Ray Burst Spectrometer (HXRBS) with the soft x ray light curve and its derivation from the Bent Crystal Spectrometer (BCS) which is part of the X-Ray Polychrometer (XRP), these instruments being on the Solar Maximum Mission spacecraft (SMM). Data sample was taken from flares observed with the above instruments during 1980, the peak of the previous maximum of solar activity. Flares were chosen based on complete coverage of the event by several instruments. The HXRBS data covers the x ray spectrum from about 25 keV to about 440 keV in 15 spectral channels, while the BCS data used covers a region of the Spectrum around 3 angstroms including emission from the Ca XIX ion. Both sets of data were summed over their spectral ranges and plotted against time at a maximum time resolution of around 3 seconds. The most popular theory of flares holds that a beam of electrons produces the hard x rays by bremsstrahlung while the soft x rays are the thermal response to this energy deposition. The question is whether the rate of change of soft x ray emission might reflect the variability of the electron beam and hence the variability of the hard x rays. To address this, we took the time derivative of the soft x ray light curve and compared it to the hard flares, 12 of them showed very closed agreement between the soft x ray derivative and the hard x ray light curve. The other five did not show this behavior but were similar to each other in general soft x ray behavior. Efforts to determine basic differences between the two kinds of flares continue. In addition the behavior of soft x ray temperature of flares was examined.

Toot, G. David

1989-09-01

383

Ionospheric response to the X-class solar flare on 7 September 2005  

NASA Astrophysics Data System (ADS)

We investigate the extreme ionospheric effect during the intense solar flare (X17.0/3B) that occurred on 7 September 2005. A strong E region electron density enhancement is observed by the incoherent scatter radars at Millstone Hill, Sondrestrom, and Troms, as well as by the radio occultation experiment on board the CHAMP satellite. The observations from both Millstone Hill and Sondrestrom stations show the average percentage enhancements of electron density during 17:40-18:10 UT are more than 200% near the E region peak height but only about 10% near the F region peak height; as a result, it leads to an unusual phenomenon where the E region electron density exceeds the F region electron density. We ascribe the unusual response to weak enhancement in EUV flux and strong enhancement in X-ray flux during this flare. To further understand this unusual feature, we analyze in detail the E region response by comparing the electron production rates derived from the measurements with those fitted by the Chapman production function. Our results demonstrate that the Chapman production theory fits the observations better in the flare time than in the nonflare time, which is attributed to the obvious difference in the solar radiation spectra at flare and nonflare times. Owing to the strong enhancement in X-ray flux during this flare, the E region electron production is more dominated by the X-ray, and the Chapman ionization theory is more applicable in the flare time than in the nonflare time. In addition, we propose a method to estimate the effective solar radiation flux from the ionospheric observations of electron density profiles. The radiation flux derived with our method agrees well with the X-ray flux at 0.1-0.8 nm observed by GOES 12.

Xiong, Bo; Wan, Weixing

2013-04-01

384

MAGNETIC RECONNECTION DURING THE TWO-PHASE EVOLUTION OF A SOLAR ERUPTIVE FLARE  

SciTech Connect

We present a detailed multi-wavelength analysis and interpretation of the evolution of an M7.6 flare that occurred near the southeast limb on 2003 October 24. Pre-flare images at TRACE 195 A show that the bright and complex system of coronal loops already existed at the flaring site. The X-ray observations of the flare taken from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft reveal two phases of the flare evolution. The first phase is characterized by the altitude decrease of the X-ray looptop (LT) source for approx11 minutes. Such a long duration of the descending LT source motion is reported for the first time. The EUV loops, located below the X-ray LT source, also undergo contraction with similar speed (approx15 km s{sup -1}) in this interval. During the second phase the two distinct hard X-ray footpoint (FP) sources are observed which correlate well with UV and Halpha flare ribbons. The X-ray LT source now exhibits upward motion as anticipated from the standard flare model. The RHESSI spectra during the first phase are soft and indicative of hot thermal emission from flaring loops with temperatures T > 25 MK at the early stage. On the other hand, the spectra at high energies (epsilon approx> 25 keV) follow hard power laws during the second phase (gamma = 2.6-2.8). We show that the observed motion of the LT and FP sources can be understood as a consequence of three-dimensional magnetic reconnection at a separator in the corona. During the first phase of the flare, the reconnection releases an excess of magnetic energy related to the magnetic tensions generated before a flare by the shear flows in the photosphere. The relaxation of the associated magnetic shear in the corona by the reconnection process explains the descending motion of the LT source. During the second phase, the ordinary reconnection process dominates describing the energy release in terms of the standard model of large eruptive flares with increasing FP separation and upward motion of the LT source.

Joshi, Bhuwan; Cho, K.-S.; Bong, S.-C.; Kim, Y.-H. [Korea Astronomy and Space Science Institute, Daejeon 305-348 (Korea, Republic of); Veronig, Astrid [IGAM/Institute of Physics, University of Graz, Universitaetsplatz 5, A-8010 Graz (Austria); Somov, B. V. [Astronomical Institute, Moscow State University, Universitetskij Prospekt 13, Moscow 119992 (Russian Federation); Moon, Y.-J. [School of Space Research, Kyung Hee University, Yongin 446-701 (Korea, Republic of); Lee, Jeongwoo [Physics Department, New Jersey Institute of Technology, 161 Warren Street, Newark, NJ 07102 (United States); Manoharan, P. K., E-mail: bhuwan@prl.res.i [Radio Astronomy Centre, Tata Institute of Fundamental Research, Udhagamandalam (Ooty) 643 001 (India)

2009-12-01

385

YOHKOH observations of high temperature plasma in solar flares  

Microsoft Academic Search

After a summary of results from previous misisons and of H-aplha observations, results from Yohkoh are presented. These deal with plasma motions, impulsive soft-X-ray footprint brightenings, and the distribution of X-ray emitting plasma in flaring coronal loops. The observations suggest that soft X-ray emissions originates from locally heated gas and from plasma that flows up from the chromosphere following energy

J. L. Culhane

1996-01-01

386

Observed signatures of magnetic energy conversion in solar flares and microflares  

NASA Astrophysics Data System (ADS)

A study of the evolution of X-ray output in different bipolar structures (Machado et al., 1988) is extended to weaker microflare activity in active regions. It is shown that, in solar flares and in weak flare-like transient brightenings, the energy release is triggered by the interaction of impacted bipolar regions. The results suggest that transient microflares may be responsible for a large fraction of the coronal heating in active regions. It is proposed that reconnection may act as a catalyst for the release of stored magnetic energy.

Mandrini, C. H.; Hernandez, A. M.; Rovira, M. G.; Machado, M. E.

387

Jan. 19, 2012 - M3.2 Solar Flare and CME  

NASA Video Gallery

Our increasing active sun let loose a long duration M3.2 class flare and coronal mass ejection (CME) between 15:15 and 16:30 UT today. The CME is Earth directed with impact predicted for Jan. 21, 2012. This video taken by the Solar Dynamics Observatory, shows a close-up of sunspot 1401 region as the flare erupts. The CME cloud lifting off is visible just past midway in the video. Across the top is a graph of corresponding X-ray measurements taken by the GOES 15 satellite.

Holly Zell

2012-01-19

388

Electron densities in a solar flare derived from X-ray spectra  

NASA Astrophysics Data System (ADS)

A major solar flare was observed with the RAP crystal of the SOLEX B spectrometer. The spectra were obtained by scanning back and forth between Bragg angles of 17.4 deg and 61.7 deg (7.8 to 23 A) at a rate of 0.525 degrees-.15. A full scan took 84.5 sec. A line list identifying more than 100 lines observed in this flare was compiled. Measurements of the density sensitive O 7 lines near 22 A are discussed.

McKenzie, D. L.; Broussard, R. M.; Landecker, P. B.; Rugge, H. R.; Young, R. M.; Doschek, G. A.; Feldman, U.

1982-01-01

389

Automated Solar Activity Prediction: A hybrid computer platform using machine learning and solar imaging for automated prediction of solar flares  

NASA Astrophysics Data System (ADS)

The importance of real-time processing of solar data especially for space weather applications is increasing continuously. In this paper, we present an automated hybrid computer platform for the short-term prediction of significant solar flares using SOHO/Michelson Doppler Imager images. This platform is called the Automated Solar Activity Prediction tool (ASAP). This system integrates image processing and machine learning to deliver these predictions. A machine learning-based system is designed to analyze years of sunspot and flare data to create associations that can be represented using computer-based learning rules. An imaging-based real-time system that provides automated detection, grouping, and then classification of recent sunspots based on the McIntosh classification is also created and integrated within this system. The properties of the sunspot regions are extracted automatically by the imaging system and processed using the machine learning rules to generate the real-time predictions. Several performance measurement criteria are used and the results are provided in this paper. Also, quadratic score is used to compare the prediction results of ASAP with NOAA Space Weather Prediction Center (SWPC) between 1999 and 2002, and it is shown that ASAP generates more accurate predictions compared to SWPC.

Colak, T.; Qahwaji, R.

2009-06-01

390

Response of the low ionosphere to X-ray and Lyman-? solar flare emissions  

NASA Astrophysics Data System (ADS)

Using soft X-ray measurements from detectors onboard the Geostationary Operational Environmental Satellite (GOES) and simultaneous high-cadence Lyman-? observations from the Large Yield Radiometer (LYRA) onboard the Project for On-Board Autonomy 2 (PROBA2) ESA spacecraft, we study the response of the lower part of the ionosphere, the D region, to seven moderate to medium-size solar flares that occurred in February and March of 2010. The ionospheric disturbances are analyzed by monitoring the resulting sub-ionospheric wave propagation anomalies detected by the South America Very Low Frequency (VLF) Network (SAVNET). We find that the ionospheric disturbances, which are characterized by changes of the VLF wave phase, do not depend on the presence of Lyman-? radiation excesses during the flares. Indeed, Lyman-? excesses associated with flares do not produce measurable phase changes. Our results are in agreement with what is expected in terms of forcing of the lower ionosphere by quiescent Lyman-? emission along the solar activity cycle. Therefore, while phase changes using the VLF technique may be a good indicator of quiescent Lyman-? variations along the solar cycle, they cannot be used to scale explosive Lyman-? emission during flares.

Raulin, Jean-Pierre; Trottet, GRard; Kretzschmar, Matthieu; Macotela, Edith L.; Pacini, Alessandra; Bertoni, Fernando C. P.; Dammasch, Ingolf E.

2013-01-01

391

Spatial coherence of solar flares and the latitude-time structure of some activity indices in cycles 17-19  

NASA Astrophysics Data System (ADS)

Latitudinal displacements of flare centroids with respect to sunspots are calculated. The displacements are presented in the form of latitude-time butterfly vector diagrams for three 11-year solar cycles, 17-19 (1935-1964). Results point to the global-scale excitation of flares by wavelike disturbances in the chromosphere associated with sunspot inpulses.

Kasinskii, V. V.

392

Stochastic Acceleration of Protons and Electrons: Gamma-Ray Emissions from LT and FP of Solar Flares  

Microsoft Academic Search

Stochastic acceleration by turbulent plasma waves, induced perhaps by magnetic reconnection or shocks near the top of flaring loops, seems to be the most viable scenario for the production of nonthermal particles detected during the impulsive phase of solar flares. Previous studies mostly focused either on electron acceleration or on that of protons. A comprehensive comparative study of the two

V. Petrosian; S. Liu

2003-01-01

393

Solar Gamma-Ray-Line Flares, Type II Radio Bursts, and Coronal Mass Ejections. (Reannouncement with New Availability Information).  

National Technical Information Service (NTIS)

We use a Big Flare Syndrome (BFS) test to substantiate earlier reports of a statistically significant association between nuclear gamma-ray-line (GRL) flares (observed by the Gamma Ray Spectrometer on the Solar Maximum Mission) and metric type 2 bursts fr...

E. W. Cliver H. V. Cane D. J. Forrest M. J. Koomen R. A. Howard

1991-01-01

394

The helium-3 rich solar flares and the bursts of electromagnetic radiations  

NASA Astrophysics Data System (ADS)

Kocharov et al. (1980) and Kocharov (1980, 1981) have proposed a model of a helium-3 rich solar flare which takes into account a mechanism for the separation of helium isotopes in the solar atmosphere due to plasma effects. The present investigation is concerned with a study of the observable events occurring in connection with the model characteristics. According to the model, hard X rays are emitted as bremsstrahlung by beams of accelerated electrons. Qualitative and quantitative relations between the parameters of helium-3 rich events and X-ray emission are considered. Soft X rays emitted in connection with the start of a helium-3 rich event are discussed, giving attention to the electron temperature of the radiating plasma, thermal energy requirements the electron concentration, and the volume of the radiating region. Relations between the flare and the solar wind structure are also considered.

Kocharov, G. E.; Charikov, Iu. F.; Kocharov, L. G.

395

STATISTICAL STUDY of HARD X-RAY SPECTRAL CHARACTERISTICS OF SOLAR FLARES  

NASA Astrophysics Data System (ADS)

We investigate the spectral characteristics of 75 solar flares at the hard X-ray peak time observed by RHESSI (Ramaty High Energy Solar Spectroscopic Imager) in the energy range 12-150keV. At energies above 40keV, the Hard X-ray emission is mostly produced by bremsstrahlung of suprathermal electrons as they interact with the ambient plasma in the chromosphere. The observed photon spectra therefore provide diagnostics of electron acceleration processes in Solar flares. We will present statistical results of spectral fitting using two models: a broken power law plus a thermal component which is a direct fit of the photon spectrum and a thick target model plus a thermal component which is a fit of the photon spectra with assumptions on the electrons emitting bremsstrahlung in the thick target approximation.

Alaoui, M.; Krucker, S.; Saint-Hilaire, P.; Lin, R. P.

2009-12-01

396

Solar flare model: Comparison of the results of numerical simulations and observations  

NASA Astrophysics Data System (ADS)

The electrodynamic flare model is based on numerical 3D simulations with the real magnetic field of an active region. An energy of 1032 erg necessary for a solar flare is shown to accumulate in the magnetic field of a coronal current sheet. The thermal X-ray source in the corona results from plasma heating in the current sheet upon reconnection. The hard X-ray sources are located on the solar surface at the loop foot-points. They are produced by the precipitation of electron beams accelerated in field-aligned currents. Solar cosmic rays appear upon acceleration in the electric field along a singular magnetic X-type line. The generation mechanism of the delayed cosmic-ray component is also discussed.

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

2009-12-01

397

New evidence of EIBS & IINF model on energy release in solar flare  

NASA Astrophysics Data System (ADS)

I developed a model named electron-ion bound state and its introducing nuclear fusion EIBS IINF in 1994 It met thoroughly and widely doubt The EIBS IINF model give the idea for solar flare energy release as following these are two independent processes of emission in solar flare p-e-p sim 12 5keV soft X-ray and p-e-A sim 25keV are source of soft X-ray sim 12 5keV or 25keV mainly d -e-d sim 25keV and d d fusion and secondary reactions producing gamma -ray are source of hard X-ray sim 13keV Widely accepted Neupert effect model or evaporation model or thick target model is contradiction to observations New observations by BATSE SPEC and LAD especially by RHESSI provide firmly evidences indicating that the EIBS IINF model is suitable to explain the mechanism of energy release in solar flare Reference 1 R P Lin P T Fetter and R A Schwartz APJ557 L125-L128 2001 2 S Krucker and R P Lin Solar Phys 210 229-243 2002 3 A O Benz and P C Grigis Solar Physics 210 431-444 2002

Lu, Run Bao

398

Influence of solar flare X-rays on the habitability on the Mars  

NASA Astrophysics Data System (ADS)

We probe the lethality of X-rays from solar flares to organisms on Mars based on the observations of 10 solar flares. We, firstly, estimate the doses produced by the strong flares observed by the RHESSI and GOES missions during the descending phase of sunspot cycle 23. Next, in order to realize the dependence of dose on flux and steepness of spectra, we model the incident spectra over a wide range of spectral index to estimate dose values and compare them with the observed doses. We calculate the distribution of surficial spectra visible to organisms on the martian surface by employing attenuation of X-rays due to CO2 column densities distribution over the South Pole. The surficial flux distribution after folding with the opacity of water enables us to estimate the dose distribution over the South Pole. The dose measured from the surficial spectrum produced by the observed 10 flares corresponding to the latitudes 50-60, 60-70, 70-80 and 80-90S varies in the range of 6.39 10-9-1.80 10-6; 4.89 10-10-5.21 10-8; 5.10 10-11-5.20 10-9 and 4.42 10-10-4.89 10-12 gray (1 gray = 104 erg/g) respectively. Comparing the measured as well as the modeled doses with those proposed to be lethal for various organisms by Smith and Scalo (Smith, D.S., Scalo, J. [2007]. Planet. Space Sci. 55, 517-527); we report that the habitability of life on the South Pole remains unaffected even by the strongest solar flare occurred during descending phase of solar cycle 23. Further, the monthly integrated energy released by the solar flares in the most productive month viz. October 2003 and January 2005 from the GOES soft X-ray observations is estimated to be 8.43 and 3.32 1032 ergs respectively, which is almost equal in order to the typical energy released by a single strong X-class flare. Therefore, we propose the life near the South Pole region on the Mars remain uninfluenced by X-ray emission even during monster phenomena of energy release on the Sun and/or Star.

Jain, Rajmal; Awasthi, Arun K.; Tripathi, Sharad C.; Bhatt, Nipa J.; Khan, Parvaiz A.

2012-08-01

399

On the heat conduction in a high-temperature plasma in solar flares  

NASA Astrophysics Data System (ADS)

We have developed three types of mathematical models to describe the mechanisms of plasma heating in the corona by intense heat fluxes from a super-hot ( T e ? 108 K) reconnecting current layer in connection with the problem of energy transport in solar flares. We show that the heat fluxes calculated within the framework of self-similar solutions using Fourier's classical law exceed considerably the real energy fluxes known from present-day multi-wavelength observations of flares. This is because the conditions for the applicability of ordinary heat conduction due to Coulomb collisions of thermal plasma electrons are violated. Introducing anomalous heat conduction due to the interaction of thermal runaway electrons with ion-acoustic turbulence does not give a simple solution of the problem, because it produces unstable temperature profiles. Themodels incorporating the effect of collisional heat flux relaxation describe better the heat transport in flares than Fourier's law and anomalous heat conduction.

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

2011-10-01

400

Thermal and Magnetic Parameters in Solar Flares Derived from GOES X-Ray Light Curves  

NASA Astrophysics Data System (ADS)

The purpose of this study is to reproduce the GOES X-ray (1-8 ) light curves of the impulsive phase of 20 solar flares and to estimate the thermal and magnetic parameters in flare loops. The expected X-ray light curves are calculated from the values of the coronal field strength and inflow velocity under some assumptions. We used the magnetic reconnection heating model of Shibata and Yokoyama (2002, ApJ, 577, 422), photospheric vector magnetic field data, and a simple 1-D flare loop model. It is found the maximum inflow velocities are 107cm s-1, and that the maximum magnetic reconnection rates are 0.006-0.9, and further that the characteristic coronal field strengths are 6-100 G. Using the thermal and magnetic parameters derived, we found that geometrically our calculated flare loops are higher than the potential fields that model the postflare loops, and are also higher than the preflare loops containing magnetic free energy that is large enough to provide the thermal energy of a flare. Hence, we conclude that the plasma ? value would be near unity in the flare loops we studied, and the magnetic field lines shrunk during the decay phase. The downward velocities of the field-line shrinkage are estimated to be 106-107cm s-1 except one event. The height of the reconnection point was roughly estimated to be from 1010cm to 4 1010cm. We propose a new interpretation of the Neupert effect, and also discuss a temporal relationship between the X-ray flux and the flare loop heating.

Yamamoto, Tetsuya T.; Sakurai, Takashi

2010-06-01

401

Flare and CME Properties and Rates at Sunspot Minimum  

Microsoft Academic Search

The corona at solar minimum generally differs greatly from that during active times. We discuss the current Cycle 23\\/24 minimum from the point of view of the occurrence of flares and CMEs (coronal mass ejections). By comparison with the previous minimum, the flare\\/CME ratio diminished by almost an order of magnitude. This suggests that the environmental effect in flare\\/CME association

H. S. Hudson; Yan Li

2010-01-01

402

Flare and CME Properties and Rates at Sunspot Minimum  

NASA Astrophysics Data System (ADS)

The corona at solar minimum generally differs greatly from that during active times. We discuss the current Cycle 23/24 minimum from the point of view of the occurrence of flares and CMEs (coronal mass ejections). By comparison with the previous minimum, the flare/CME ratio diminished by almost an order of magnitude. This suggests that the environmental effect in flare/CME association differed in the sense that the Cycle 23/24 minimum corona was relatively easy to disrupt.

Hudson, H. S.; Li, Y.

2010-06-01

403

A new approach to model particle acceleration and energy transfer in solar flares  

NASA Astrophysics Data System (ADS)

Motivated by available observations of two different flares in Ly? and H?, we model the conditions of the solar atmosphere using a radiation hydrodynamics code (RADYN, Carlsson & Stein, 1992) and analyze the energy transport carried by a beam of non-thermal electrons injected at the top of a 1D coronal loop. The numerical Ly? and H? intensities match with the observations. The electron energy distribution is assumed to follow a power law of the form (E/Ec )-? for energies greater than a cutoff value of Ec. Abbett & Hawley (1999) and Allred et al. (2005) assumed that the non-thermal electrons flux injected at the top of a flaring loop, the cut-off energy and the power law index are constant over time. An improvement was achieved by Allred & Hawley (2006), who modified the RADYN code in such a way that the input parameters were time dependent. Their inputs were based on observations of a flare obtained with RHESSI. By combining RADYN with the flare code from Stanford University which models the acceleration and transport of particles and radiation of solar flares in non-LTE regime, we can calculate the non-thermal electrons flux, the cut-off energy and the power law index at every simulated time step. The atmospheric parameters calculated by RADYN could in turn be used as updated inputs for "flare", providing several advantages over the results from Liu et al. (2009), who combined the particle acceleration code with a 1-D hydrodynamic code, improving the atmospheric conditions.

Rubio Da Costa, Fatima; Zuccarello, F.; Fletcher, L.; Labrosse, N.; Kasparova, J.; Proseck, T.; Carlsson, M.; Petrosian, V.; Liu, W.

2013-07-01

404

X-ray and ultraviolet investigation into the magnetic connectivity of a solar flare  

NASA Astrophysics Data System (ADS)

We investigate the X-ray and UV emission detected by RHESSI and TRACE in the context of a solar flare on the 16th November 2002 with the goal of better understanding the evolution of the flare. We analysed the characteristics of the X-ray emission in the 12-25 and 25-50 keV energy range while we looked at the UV emission at 1600 . The flare appears to have two distinct phases of emission separated by a 25-s time delay, with the first phase being energetically more important. We found good temporal and spatial agreement between the 25-50 keV X-rays and the most intense areas of the 1600 UV emission. We also observed an extended 100-arcsec < 25 keV source that appears coronal in nature and connects two separated UV ribbons later in the flare. Using the observational properties in X-ray and UV wavelengths, we propose two explanations for the flare evolution in relation to the spine/fan magnetic field topology and the accelerated electrons. We find that a combination of quasi separatrix layer reconnection and null-point reconnection is required to account for the observed properties of the X-ray and UV emission.

Reid, H. A. S.; Vilmer, N.; Aulanier, G.; Pariat, E.

2012-11-01

405

The Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS)  

NASA Astrophysics Data System (ADS)

The balloon-borne Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS) instrument will provide a near-optimal combination of high-resolution imaging, spectroscopy, and polarimetry of solar-flare gamma-ray/hard X-ray emissions from ~20 keV to >~10 MeV. GRIPS will address questions raised by recent solar flare observations regarding particle acceleration and energy release, such as: What causes the spatial separation between energetic electrons producing hard X-rays and energetic ions producing gamma-ray lines? How anisotropic are the relativistic electrons, and why can they dominate in the corona? How do the compositions of accelerated and ambient material vary with space and time, and why? The spectrometer/polarimeter consists of sixteen 3D position-sensitive germanium detectors (3D-GeDs), where each energy deposition is individually recorded with an energy resolution of a few keV FWHM and a spatial resolution of <0.1 mm3. Imaging is accomplished by a single multi-pitch rotating modulator (MPRM), a 2.5-cm thick tungstenalloy slit/slat grid with pitches that range quasi-continuously from 1 to 13 mm. The MPRM is situated 8 meters from the spectrometer to provide excellent image quality and unparalleled angular resolution at gamma-ray energies (12.5 arcsec FWHM), sufficient to separate 2.2 MeV footpoint sources for almost all flares. Polarimetry is accomplished by analyzing the anisotropy of reconstructed Compton scattering in the 3D-GeDs (i.e., as an active scatterer), with an estimated minimum detectable polarization of a few percent at 150-650 keV in an X-class flare. GRIPS is scheduled for a continental-US engineering test flight in fall 2013, followed by long or ultra-long duration balloon flights in Antarctica.

Shih, Albert Y.; Lin, Robert P.; Hurford, Gordon J.; Duncan, Nicole A.; Saint-Hilaire, Pascal; Bain, Hazel M.; Boggs, Steven E.; Zoglauer, Andreas C.; Smith, David M.; Tajima, Hiroyasu; Amman, Mark S.; Takahashi, Tadayuki

2012-09-01

406

Magnetic Energy Spectrum and Intermittency in Solar Active Regions of Different Flare Productivity  

NASA Astrophysics Data System (ADS)

Solar photosphere is in a state of highly developed turbulence owing to the sub-photospheric convection. The strength and growth of turbulence determines eventually the degree of complexity of the magnetic field. Complexity is thought to be responsible for the flaring productivity of an active region (AR). Due to the inherently non-linear nature of turbulence, complexity hardly can be adequately presented by a single scalar parameter. Rather a spectrum of values representing the behavior of the field at different scales should be analyzed. Here the results of analysis of the magnetic energy spectra and intermittency spectra for 186 ARs observed during 2000-2006 with SOHO/MDI in the high-resolution mode are presented. We thus found that steeper energy spectra are related to higher flaring productivity (the correlation coefficient CC=0.69). The intermittency spectrum was determined via a hyper flatness function (ratio of the 6th-order structure function to the squared 3rd-order structure function) for a set of spatial scales. It was found that the range of scales where the hyper-flatness decreases (a signature of intermittency and multifractality) can vary for different ARs, however, there is a strong tendency for ARs with higher flare productivity to posses steeper and broader intermittency spectrum at small scales (below 10-20 Mm). Very steep and broad intermittency spectra found for several ARs showing extremely high flaring activity seem to be related to shredded magnetic fields along the neutral line of a delta-structure. Our results indicate that the capability of an active region to produce solar flares is directly related to the development of intermittent structures in an active region magnetic field. Prospects of applying this approach to new high resolution data from Hinode, SDO and NST acquired during the oncoming solar maximum will be also discussed.

Abramenko, Valentyna

2010-05-01

407

COMBINED STEREO/RHESSI STUDY OF CORONAL MASS EJECTION ACCELERATION AND PARTICLE ACCELERATION IN SOLAR FLARES  

SciTech Connect

Using the potential of two unprecedented missions, Solar Terrestrial Relations Observatory (STEREO) and Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI), we study three well-observed fast coronal mass ejections (CMEs) that occurred close to the limb together with their associated high-energy flare emissions in terms of RHESSI hard X-ray (HXR) spectra and flux evolution. From STEREO/EUVI and STEREO/COR1 data, the full CME kinematics of the impulsive acceleration phase up to {approx}4 R{sub sun} is measured with a high time cadence of <=2.5 minutes. For deriving CME velocity and acceleration, we apply and test a new algorithm based on regularization methods. The CME maximum acceleration is achieved at heights h <= 0.4 R{sub sun}, and the peak velocity at h <= 2.1 R{sub sun} (in one case, as small as 0.5 R{sub sun}). We find that the CME acceleration profile and the flare energy release as evidenced in the RHESSI HXR flux evolve in a synchronized manner. These results support the 'standard' flare/CME model which is characterized by a feedback relationship between the large-scale CME acceleration process and the energy release in the associated flare.

Temmer, M.; Veronig, A. M. [IGAM/Kanzelhoehe Observatory, Institute of Physics, Universitaet Graz, Universitaetsplatz 5, A-8010 Graz (Austria); Kontar, E. P. [Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Krucker, S. [Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450 (United States); Vrsnak, B., E-mail: mat@igam.uni-graz.a, E-mail: asv@igam.uni-graz.a, E-mail: eduard@astro.gla.ac.u, E-mail: krucker@ssl.berkeley.ed, E-mail: bvrsnak@gmail.co [Hvar Observatory, Faculty of Geodesy, University of Zagreb, Kaciceva 26, HR-10000 Zagreb (Croatia)

2010-04-01

408

Solar flares X-ray polarimetry in a wide energy band  

NASA Astrophysics Data System (ADS)

Polarimetry of solar flares X-ray emission is an additional tool for investigating particles dynamics within the solar atmosphere. Accelerated electrons by magnetic reconnection in the corona produce bremsstrahlung radiation as primary emission in the footpoints of a solar flare which has moreover the possibility to be Compton backscattered resulting in albedo emission. Non-thermal bremsstrahlung emission is expected to be a significant above 15 keV and highly polarized. The albedo component peaks between 20 and 50 keV, its polarization properties depend on the Compton scattering angle. Such a diffusion modifies the spectrum and the polarization of the primary bremsstrahlung emission. Hard X-ray polarimetry, spectroscopy and imaging are therefore necessary to disentangle and modeling the different components in a solar flare. We present a non imaging Compton polarimeter sensitive from 20 keV designed as a single scattering unit surrounded by absorbers of high atomic number. A photelectric polarimeter based on the Gas Pixel Detector technology sensitive in the 15-35 keV energy band can be coupled for imaging.

Fabiani, Sergio; Campana, Riccardo; Costa, Enrico; Muleri, Fabio; Bellazzini, Ronaldo; Soffitta, Paolo; Del Monte, Ettore; Rubini, Alda

2012-07-01

409

SHORT-TERM SOLAR FLARE LEVEL PREDICTION USING A BAYESIAN NETWORK APPROACH  

SciTech Connect

A Bayesian network approach for short-term solar flare level prediction has been proposed based on three sequences of photospheric magnetic field parameters extracted from Solar and Heliospheric Observatory/Michelson Doppler Imager longitudinal magnetograms. The magnetic measures, the maximum horizontal gradient, the length of neutral line, and the number of singular points do not have determinate relationships with solar flares, so the solar flare level prediction is considered as an uncertainty reasoning process modeled by the Bayesian network. The qualitative network structure which describes conditional independent relationships among magnetic field parameters and the quantitative conditional probability tables which determine the probabilistic values for each variable are learned from the data set. Seven sequential features-the maximum, the mean, the root mean square, the standard deviation, the shape factor, the crest factor, and the pulse factor-are extracted to reduce the dimensions of the raw sequences. Two Bayesian network models are built using raw sequential data (BN{sub R}) and feature extracted data (BN{sub F}), respectively. The explanations of these models are consistent with physical analyses of experts. The performances of the BN{sub R} and the BN{sub F} appear comparable with other methods. More importantly, the comprehensibility of the Bayesian network models is better than other methods.

Yu Daren; Huang Xin; Hu Qinghua; Zhou Rui [Harbin Institute of Technology, No. 92 West Da Zhi Street, Harbin, Heilongjiang Province 150001 (China); Wang Huaning [National Astronomical Observatories, 20A Datun Road, Chaoyang District, Beijing 100012 (China); Cui Yanmei, E-mail: huangxinhit@yahoo.com.c [Center for Space Science and Applied Research, No. 1 Nanertiao, Zhongguancun, Haidian District, Beijing 100080 (China)

2010-02-10

410

Short-term Solar Flare Level Prediction Using a Bayesian Network Approach  

NASA Astrophysics Data System (ADS)

A Bayesian network approach for short-term solar flare level prediction has been proposed based on three sequences of photospheric magnetic field parameters extracted from Solar and Heliospheric Observatory/Michelson Doppler Imager longitudinal magnetograms. The magnetic measures, the maximum horizontal gradient, the length of neutral line, and the number of singular points do not have determinate relationships with solar flares, so the solar flare level prediction is considered as an uncertainty reasoning process modeled by the Bayesian network. The qualitative network structure which describes conditional independent relationships among magnetic field parameters and the quantitative conditional probability tables which determine the probabilistic values for each variable are learned from the data set. Seven sequential featuresthe maximum, the mean, the root mean square, the standard deviation, the shape factor, the crest factor, and the pulse factorare extracted to reduce the dimensions of the raw sequences. Two Bayesian network models are built using raw sequential data (BN_R) and feature extracted data (BN_F), respectively. The explanations of these models are consistent with physical analyses of experts. The performances of the BN_R and the BN_F appear comparable with other methods. More importantly, the comprehensibility of the Bayesian network models is better than other methods.

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

2010-02-01

411

Empirical models of solar flare X ray and EUV emission for use in studying their E and F region effects  

Microsoft Academic Search

The time structure and spectra of X ray and extreme ultraviolet (EUV) bursts during solar flares are described from the viewpoint of evaluating their ionospheric effects. The impulsive flare component is strong in emission from solar source regions with temperatures in the range 10⁴degreeK--10⁶degreeK, which are strong in the 90- to 1027-A range. The strength of the impulsive EUV emissions

R. F. Donnelly

1976-01-01

412

A statistical study on photospheric active-region magnetic nonpotentiality and associated flares during solar cycles 22 - 23  

NASA Astrophysics Data System (ADS)

Using photospheric data obtained by vector magnetograph in Huairou Solar Observing Station of China, we have statistically studied the strength evolution of several magnetic nonpotentiality measures, along with a quantified parameter characterizing the active-region magnetic complexity - effective distance, and their relationship with associated flares during the latest 22nd and 23rd solar cycles. And the flare-prediction performance of these magnetic nonpotentiality and complexity parameters is verified by a machine learning technique.

Yang, Xiao; Zhang, HongQi; Lin, GangHua; Gao, Yu; Guo, Juan

2013-07-01

413

The Solar Maximum Mission Atlas of Gamma?Ray Flares  

Microsoft Academic Search

We present a compilation of data for all 258 gamma-ray ares detected above 300 keV by the Gamma Ray Spectrometer (GRS) aboard the Solar Maximum Mission satellite. This gamma-ray are sample was collected during the period from 1980 February to 1989 November; covering the latter half of the 21st solar sunspot cycle and the onset of the 22d solar sunspot

W. Thomas Vestrand; Gerald H. Share; Ronald J. Murphy; David J. Forrest; Erich Rieger; Edward L. Chupp; Gottfried Kanbach

1999-01-01

414

AVS-F observations of ?-ray emission during January 20, 2005 solar flare up to 140 MeV  

NASA Astrophysics Data System (ADS)

The solar flare of January 20, 2005 (X7.1, 06:36-07:26 UT, maximum at 07:01 UT by the GOES soft X-ray data) was the most powerful one in January 2005 series. The AVS-F apparatus onboard CORONAS-F registered ?-emission during soft X-ray rising phase of this flare in two energy ranges of 0.1-20 MeV and 2-140 MeV. The highest ?-ray energy registered during this flare was 140 MeV. Six spectral features were registered in energy spectrum of this solar flare: annihilation + ?? (0.4-0.6 MeV), 24Mg + 20Ne + 28Si + neutron capture (1.7-2.3 MeV), 21Ne + 22Ne + 16O + 12? (3.2-5.0 MeV), 16O (5.3-6.9 MeV), one from neutral pions decay (25-110 MeV) and one in energy band 15-21 MeV. Four of them contain typical for solar flares lines - annihilation, nuclear de-excitation and neutron capture at 1H. Spectral feature caused by neutral pions decay was registered during several flares too. Some spectral peculiarities in the region of 15-21 MeV were first observed in solar flare energy spectrum.

Arkhangelskaja, I. V.; Arkhangelsky, A. I.; Kotov, Yu. D.; Kalmykov, P. A.; Glyanenko, A. S.

2009-02-01

415

Multi-wavelength observations and modelling of a canonical solar flare  

NASA Astrophysics Data System (ADS)

Aims: We investigate the temporal evolution of temperature, emission measure, energy loss, and velocity in a C-class solar flare from both observational and theoretical perspectives. Methods: The properties of the flare were derived by following the systematic cooling of the plasma through the response functions of a number of instruments - the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI; >5 MK), GOES-12 (5-30 MK), the Transition Region and Coronal Explorer (TRACE 171 ; 1 MK), and the Coronal Diagnostic Spectrometer (CDS; ~0.03-8 MK). These measurements were studied in combination with simulations from the 0-D enthalpy based thermal evolution of loops (EBTEL) model. Results: At the flare onset, upflows of ~90 km s-1 and low-level emission were observed in Fe XIX, consistent with pre-flare heating and gentle chromospheric evaporation. During the impulsive phase, upflows of ~80 km s-1 in Fe XIX and simultaneous downflows of ~20 km s-1 in He I and O V were observed, indicating explosive chromospheric evaporation. The plasma was subsequently found to reach a peak temperature of ?13 MK in approximately 10 min. Using EBTEL, conduction was found to be the dominant loss mechanism during the initial ~300 s of the decay phase. It was also found to be responsible for driving gentle chromospheric evaporation during this period. As the temperature fell below ~8 MK, and for the next ~4000 s, radiative losses were determined to dominate over conductive losses. The radiative loss phase was accompanied by significant downflows of ?40 km s-1 in O V. Conclusions: This is the first extensive study of the evolution of a canonical solar flare using both spectroscopic and broad-band instruments in conjunction with a 0-D hydrodynamic model. While our results are in broad agreement with the standard flare model, the simulations suggest that both conductive and non-thermal beam heating play important roles in heating the flare plasma during the impulsive phase of at least this event.

Raftery, C. L.; Gallagher, P. T.; Milligan, R. O.; Klimchuk, J. A.

2009-02-01

416

Formation of the charge spectrum and composition of particles accelerated in solar flares  

SciTech Connect

The charge and mass selectivity of the four most probable mechanisms of acceleration in solar flares (the Fermi and betatron mechanisms and acceleration by the electric field and by Langmuir waves) and the influence of collisions on the charge spectrum and composition of the particles are analyzed. It is shown that it is possible to qualitatively explain the composition of solar cosmic rays by the action of two mechanisms in different parts of the acceleration region, one of which is characterized by a very high intensity and acts directly during the flash phase of the flare while the other mechanism, considerably slower, acts before the flash phase. The action of the latter leads to the accumulation of heavy particles in the low-energy region. The influence of collisions of the particles with protons and the role of the proton loss maximum are studied. The conditions for the establishment of an equilibrium charge of the accelerated particles are discussed.

Korchak, A.A.; Filippov, B.P.

1979-05-01

417

Magnetic fields and Fe I line profiles in the major solar flare on October 28, 2003  

NASA Astrophysics Data System (ADS)

Strong (kilogauss) small-scale magnetic fields were detected outside a sunspot near the seismic source of the major X17.2/4B solar flare on October 28, 2003. Echelle Zeeman spectrograms of the flare were obtained with the horizontal solar telescope at the Astronomical Observatory of the Taras Shevchenko Kiev National University. Analysis of the Stokes I V profiles for the Fe I 5232.9, 5247.1, 5250.2, and 5397.1 lines has revealed a number of characteristic spectral features. These are indicative of both background fields with a strength of ?300 G and small-scale fields with a strength of 1300 3100 G. Evidence for the presence of another small-scale field component of opposite polarity with a strength of 8 10 kG has been found. A redshift (downflow) with a velocity of 1 km s-1 was observed in the latter component.

Lozitsky, V. G.

2009-02-01

418

Direct observation of solar neutrons following the 0118 UT flare on 1980 June 21  

SciTech Connect

Energetic solar neutrons (>50 MeV) have been detected at the Earth following a solar flare which occurred on the west limb on 1980 June 21 at 01:18:20 UT. Impulsive photon emission from 10 keV to greater than 65 MeV lasting over a period of approx.66 s was followed by a transient flux of approx.50-600 MeV neutrons incident over a approx.17 minute period. The peak counting rate corresponds to an average flux at the Earth of (3.8 +- 0.6) x 10/sup -2/ neutrons cm/sup -2/s/sup -1/ at approx.130 MeV. These observations indicate the emission of approx.3 x 10/sup 28/ neutrons sr/sup -1/ with energies > or approx. =50 MeV requiring the rapid acceleration (<<60 s) of protons to approx.GeV energies during the impulsive phase of the flare.

Chupp, E.L.; Forrest, D.J.; Ryan, J.M.; Heslin, J.; Reppin, C.; Pinkau, K.; Kanbach, G.; Reiger, E.; Share, G.H.

1982-12-15

419

The solar flare of 18 August 1979: Incoherent scatter radar data and photochemical model comparisons  

SciTech Connect

Measurements of electron density at seven D-region altidues were made with the Arecibo radar during a Class-X solar flare on 18 August 1979. Measurements of solar x-ray fluxes during the same period were available from the GOES-2 satellite (0.5 to 4 /angstrom/ and 1 to 8 /angstrom/) and from ISEE-3 (in four bands between 26 and 400 keV). From the x-ray flux data we computed ionization rates in the D-region and the associated chemical changes, using a coupled atmospheric chemistry and diffusion model (with 836 chemical reactions and 19 vertical levels). The computed electron densities matched the data fairly well after we had adjusted the rate coefficients of two reactions. We discuss the hierarchies among the many flare-induced chemical reactions in two altitude ranges within the D-region and the effects of adjusting several other rate coefficients. 51 refs., 6 figs., 3 tabs.

Zinn, J.; Sutherland, C.D.; Fenimore, E.E.; Ganguly, S.

1988-04-01