Science.gov

Sample records for flaring loops effects

  1. The Effects of Including Non-Thermal Particles in Flare Loop Models

    NASA Astrophysics Data System (ADS)

    Reeves, K. K.; Winter, H. D.; Larson, N. L.

    2012-05-01

    In this work, we use HyLoop (Winter et al. 2011), a loop model that can incorporate the effects of both MHD and non-thermal particle populations, to simulate soft X-ray emissions in various situations. First of all, we test the effect of acceleration location on the emission in several XRT filters by simulating a series of post flare loops with different injection points for the non-thermal particle beams. We use an injection distribution peaked at the loop apex to represent a direct acceleration model, and an injection distribution peaked at the footpoints to represent the Alfvén wave interaction model. We find that footpoint injection leads to several early peaks in the apex-to-footpoint emission ratio. Second, we model a loop with cusp-shaped geometry based on the eruption model developed byLin & Forbes (2000) and Reeves & Forbes (2005a), and find that early in the flare, emission in the loop footpoints is much brighter in the XRT filters if non-thermal particles are included in the calculation. Finally, we employ a multi-loop flare model to simulate thermal emission and compare with a previous model where a semi-circular geometry was used (Reeves et al. 2007). We compare the Geostationary Operational Environmental Satellite (GOES) emission from the two models and find that the cusp-shaped geometry leads to a smaller GOES class flare.

  2. Flare loop radiative hydrodynamics. III - Nonlocal radiative transfer effects

    NASA Technical Reports Server (NTRS)

    Canfield, R. C.; Fisher, G. H.; Mcclymont, A. N.

    1983-01-01

    The study has three goals. The first is to demonstrate that processes exist whose intrinsic nonlocal nature cannot be represented by local approximations. The second is to elucidate the physical nature and origins of these nonlocal processes. The third is to suggest that the methods and results described here may prove useful in constructing semiempirical models of the chromosphere by means more efficient than trial and error. Matrices are computed that describe the effect of a temperature perturbation at an arbitrary point in the loop on density, hydrogen ionized fraction, total radiative loss rate, and radiative loss rate of selected hydrogen lines and continua at all other points. It is found that the dominant nonlocal radiative transfer effects can be separated into flux divergence coefficient effects and upper level population effects. The former are most important when the perturbation takes place in a region of significant opacity. Upper level population effects arise in both optically thick and thin regions in response to nonlocal density, ionization, and interlocking effects.

  3. Three-dimensional MHD modeling of flare-induced waves in coronal loops: thermal effects

    NASA Astrophysics Data System (ADS)

    Provornikova, Elena; Ofman, Leon; Wang, Tongjiang

    EUV imaging and spectroscopic observations from several space missions (SOHO, TRACE, Hinode/EIS, SDO/AIA) have revealed the presence of MHD waves in solar coronal loops. Past analysis of SOHO/SUMER data suggested that slow magnetosonic waves in hot coronal loops are excited by flares at the loop`s footpoint. Recent Hinode/EIS observed propagating disturbances in active region loops were interpreted as flows as well as waves most likely generated by plasma outflows or jets. In order to understand dynamics of plasma in coronal loops due to flares or jets at the lower corona boundary, we perform full 3D MHD modeling of an active region and consider different mechanisms of wave excitation. We assume an initial equilibrium of the model active region with dipole magnetic field structure, gravitationally stratified density and temperature obtained from polytropic equation of state of the background coronal plasma. We extend previous isothermal studies by including full energy equation with empirical heating and radiative losses terms in the model. We study waves in both, short and long loops, and consider two excitation mechanisms in the model: impulsive plasma injection into the steady plasma upflow along the magnetic field lines, and impulsive heating at the footpoint of the loop. We show initiation and evolution of flows, excitation and damping of waves and flow-wave interaction in the loops. We compare our new results with previous models and observations.

  4. An interacting loop model of solar flare bursts

    NASA Technical Reports Server (NTRS)

    Emslie, A. G.

    1981-01-01

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

  5. Flare Half-Loops: What Are They?

    NASA Astrophysics Data System (ADS)

    McKenzie, David Eugene; Guidoni, S. E.; Longcope, D. W.; Yoshimura, K.

    2012-05-01

    The M1.4 flare of 28 January 2011 has a remarkable resemblance to the famous "Tsuneta candle-flame" flare of 1992. It was observed with Hinode/XRT, SDO/AIA, and STEREO (A)/EUVI, resulting in higher resolution, greater temperature coverage, and stereoscopic views of this iconic structure. The high temperature images reveal a brightening that grows in size to form a tower-like structure at the top of the arcade. They also show that loops which are successively connected to this tower develop a density increase in one of their legs that can exceed twice the density of the other leg, giving the appearance of "half loops". These jumps in density last for an extended period of time. On the other hand, XRT filter ratios suggest that temperature is approximately uniform along the entire loop. XRT filter-ratio density maps corroborate that the brighter legs have higher density than the fainter halves. The tower is associated with a localized density increase, with even higher densities than either leg of the loop. This spatial variation of density may correspond to a shock at the top of the loops. We use STEREO images to show that the half loop brightening is not a line-of-sight projection effect of the type suggested by Forbes & Acton. This work is supported under contract SP02H3901R from Lockheed-Martin to MSU, and under contract NNM07AB07C with the Harvard-Smithsonian Astrophysical Observatory.

  6. Simultaneous Extreme-Ultraviolet Explorer and Optical Observations of Ad Leonis: Evidence for Large Coronal Loops and the Neupert Effect in Stellar Flares

    NASA Technical Reports Server (NTRS)

    Hawley, Suzanne L.; Fisher, George H.; Simon, Theodore; Cully, Scott L.; Deustua, Susana E.; Jablonski, Marek; Johns-Krull, Christopher; Pettersen, Bjorn R.; Smith, Verne; Spiesman, William J.; Valenti, Jeffrey

    1995-01-01

    We report on the first simultaneous Extreme-Ultraviolet Explorer (EUVE) and optical observations of flares on the dMe flare star AD Leonis. The data show the following features: (1) Two flares (one large and one of moderate size) of several hours duration were observed in the EUV wavelength range; (2) Flare emission observed in the optical precedes the emission seen with EUVE; and (3) Several diminutions (DIMs) in the optical continuum were observed during the period of optical flare activity. To interpret these data, we develop a technique for deriving the coronal loop length from the observed rise and decay behavior of the EUV flare. The technique is generally applicable to existing and future coronal observations of stellar flares. We also determine the pressure, column depth, emission measure, loop cross-sectional area, and peak thermal energy during the two EUV flares, and the temperature, area coverage, and energy of the optical continuum emission. When the optical and coronal data are combined, we find convincing evidence of a stellar 'Neupert effect' which is a strong signature of chromospheric evaporation models. We then argue that the known spatial correlation of white-light emission with hard X-ray emission in solar flares, and the identification of the hard X-ray emission with nonthermal bremsstrahlung produced by accelerated electrons, provides evidence that flare heating on dMe stars is produced by the same electron precipitation mechanism that is inferred to occur on the Sun. We provide a thorough picture of the physical processes that are operative during the largest EUV flare, compare and contrast this picture with the canonical solar flare model, and conclude that the coronal loop length may be the most important factor in determining the flare rise time and energetics.

  7. Heating and Cooling of Flare Loops in a C5.7 Two-ribbon Flare

    NASA Astrophysics Data System (ADS)

    Pearce, Sarah; Qiu, Jiong

    2016-05-01

    Heating and cooling of flare plasmas can be studied using models constrained by observations. In this work, we analyze and model thermal evolution of a C5.7 two-ribbon flare that occurred on December 26, 2011. The flare was observed by AIA. Two hundred flare loops are identified, which formed sequentially during one hour. Light curves of these flare loops in multiple EUV bands are analyzed to derive the duration and timing of flare emission in each bandpass. These timescales usually reflect cooling of flare plasmas from 10~MK to successively lower temperatures. We then use a zero-dimensional enthalpy-based thermal evolution of loops (EBTEL) model to study flare heating and cooling. Several variations on the EBTEL model are assessed. The first model uses an impulsive heating function inferred from the rapid rise of the foot-point UV emission. Synthetic emission from this model evolves and decays more quickly than the observations, as many models do. Two other variations on the model are analyzed, in an attempt to counter this. In one variation the heating function is a combination of an impulsive pulse followed by an extended tail (i.e., continuous heating). The other model uses reduced thermal conduction to slow the flares evolution. These models are compared with one another and the observations, to evaluate effects of different mechanisms governing the thermal evolution of flare plasmas.

  8. The structure, stability and flaring of solar coronal loops

    NASA Technical Reports Server (NTRS)

    Van Hoven, G.

    1982-01-01

    A review is given of recent progress in the theory of the magnetohydrodynamic behavior of coronal loops, beginning with a brief characterization of thy observations. The equilibrium magnetic field is described, along with the consequences of the empirical requirement for short-term, or infinite-conductivity, stability which is shown to be dominated by the end-effect influence of thy quasi-rigid photosphere. A new loop-flare model is then developed, which takes account of the finite loop length. The primary resistive-sausage-mode instability exhibits the necessary threshold behavior, and produces a number of spatially and energetically distinct flare-release manifestations.

  9. Magnetic reconnection and solar flare loops

    NASA Technical Reports Server (NTRS)

    Forbes, T. G.

    1987-01-01

    Reconnection models of the main phase of large solar flares are used to explain the energetics and the motions of the large flare loops that occur during this phase. Correct predictions for the density and temperature of the X-ray emitting loops are obtained by coupling magnetic reconnection with chromospheric ablation. In the reconnection models the ablation is driven by the thermal conduction of heat along magnetic field lines connecting the reconnection shocks in the corona with the flare ribbons in the chromosphere. Combining the compressible reconnection theory of Soward and Priest (1982) with the magnetohydrodynamic (MHD) subshock criteria of Coroniti (1970) shows that the Petschek-type slow-mode shocks in the vicinity of the x-line always dissociate into pairs of isothermal slow-mode subshocks and thermal conduction fronts. The rate of expansion of the loops is a function of the reconnection rate, and loops can be evolving self-similarly in time with their height increasing as sq root t and the reconnection rate decreasing as t to the minus 1.

  10. Comparison Of Simulated And Observed Loop-top Emission In Flares Using The AIA Telescopes On SDO

    NASA Astrophysics Data System (ADS)

    Reeves, Kathy; Engell, A.; Ji, L.; Smith, R.; Golub, L.

    2011-05-01

    We investigate the temporal behavior of loop-top emission in flaring loops observed by AIA's six EUV passbands for several flares of different sizes. These flares are chosen because they exhibit extended periods of loop-top emission in the 193 A channel, thought to be hot emission from Fe XXIV. The flare light curves from this loop-top emission clearly show the progression of flare cooling through the various ionization states of iron that dominate the AIA bands. We use the model of Reeves, Warren & Forbes (2007), which predicts extended periods of loop-top flare emission, to model the flare loop energization, and explore the effects of different energy release rates and durations on the simulated flare light curves. We also explore the conditions under which non-equilibrium ionization effects may be important in these events.

  11. FINE STRUCTURES AND OVERLYING LOOPS OF CONFINED SOLAR FLARES

    SciTech Connect

    Yang, Shuhong; Zhang, Jun; Xiang, Yongyuan

    2014-10-01

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

  12. Flare diagnostics from loop modeling of a stellar flare observed with XMM-Newton

    NASA Astrophysics Data System (ADS)

    Reale, Fabio

    2006-01-01

    XMM-Newton data of an X-ray flare observed on Proxima Centauri provide detailed and challenging constraints for flare modeling. The comparison of the data with the results of time-dependent hydrodynamic loop modeling of this flare allows us to constrain not only the loop morphology, but also the details of the heating function. The results show that even a complex flare event like this can be described with a relatively few though constrained components: two loop systems, i.e., a single loop and an arcade, and two heat components, an intense pulse probably located at the loop footpoints followed by a low gradual decay distributed in the coronal part of the loop. The similarity to at least one solar event (the Bastille Day flare in 2000) indicates that this pattern may be common to solar and stellar flares.

  13. New flare diagnostics from loop modeling of a stellar flare observedwith XMM-Newton

    NASA Astrophysics Data System (ADS)

    Reale, F.

    XMM-Newton data of an X-ray flare observed on Proxima Centauri provide detailed and challenging constraints for flare modeling. The comparison of the data with the results of time-dependent hydrodynamic loop modeling of this flare allows us to constrain not only the loop morphology, but also the details of the heating function. The results show that even a complex flare event like this can be described with a relatively few - though constrained - components: two loop systems, i.e. a single loop and an arcade, and two heat components, an intense pulse probably located at the loop footpoints followed by a low gradual decay distributed in the coronal part of the loop. The similarity to at least one solar event (the Bastille Day flare in 2000) indicate that this pattern may be common to solar and stellar flares.

  14. Large-scale electric fields in post-flare loops

    NASA Technical Reports Server (NTRS)

    Hinata, Satoshi

    1987-01-01

    As the electrical conductivity along the magnetic field in the solar atmosphere is large, parallel electric fields have been neglected in most investigations. The importance of such fields is demonstrated for post-flare loops, and a model for them is introduced which takes into account the effect of parallel electric fields. The electric field calculated from the model is consistent with the electric field observed by Foukal et al. (1983).

  15. HEATING OF FLARE LOOPS WITH OBSERVATIONALLY CONSTRAINED HEATING FUNCTIONS

    SciTech Connect

    Qiu Jiong; Liu Wenjuan; Longcope, Dana W.

    2012-06-20

    We analyze high-cadence high-resolution observations of a C3.2 flare obtained by AIA/SDO on 2010 August 1. The flare is a long-duration event with soft X-ray and EUV radiation lasting for over 4 hr. Analysis suggests that magnetic reconnection and formation of new loops continue for more than 2 hr. Furthermore, the UV 1600 Angstrom-Sign observations show that each of the individual pixels at the feet of flare loops is brightened instantaneously with a timescale of a few minutes, and decays over a much longer timescale of more than 30 minutes. We use these spatially resolved UV light curves during the rise phase to construct empirical heating functions for individual flare loops, and model heating of coronal plasmas in these loops. The total coronal radiation of these flare loops are compared with soft X-ray and EUV radiation fluxes measured by GOES and AIA. This study presents a method to observationally infer heating functions in numerous flare loops that are formed and heated sequentially by reconnection throughout the flare, and provides a very useful constraint to coronal heating models.

  16. The Temperature Structure of Some Typical Flare Loop Systems

    NASA Astrophysics Data System (ADS)

    Gou, T.; Liu, R.; Wang, Y.

    2014-12-01

    Solar flares and coronal mass ejections (CMEs) are the main drivers of disastrous space weather. To understand the physical processes behind solar eruptions is the important base and prerequisite for reliable space weather prediction. Studying thermodynamic properties of flaring structures will help understand the flare energy-release process. Here we show some flares which occur at the solar limb or near the limb and have typical cusp-like flare loops. With high-resolution data provided by six EUV channels of the AIA instrument on board SDO, we utilize the differential emission measure (DEM) method to study the flare loop system, focusing on the temperature of the cusp structure, and the results are compared with previous studies.

  17. Solar flares as cascades of reconnecting magnetic loops.

    PubMed

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

    2003-04-01

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

  18. The formation flare loops by magnetic reconnection and chromospheric ablation

    NASA Technical Reports Server (NTRS)

    Forbes, T. G.; Malherbe, J. M.; Priest, E. R.

    1989-01-01

    Noncoplanar compressible reconnection theory is combined here with simple scaling arguments for ablation and radiative cooling to predict average properties of hot and cool flare loops as a function of the coronal vector magnetic field. For a coronal field strength of 100 G, the temperature of the hot flare loops decreases from 1.2 x 10 to the 7th K to 4.0 x 10 to the 6th K as the component of the coronal magnetic field perpendicular to the plane of the loops increases from 0 percent to 86 percent of the total field. When the perpendicular component exceeds 86 percent of the total field or when the altitude of the reconnection site exceeds 10 to the 6th km, flare loops no longer occur. Shock-enhanced radiative cooling triggers the formation of cool H-alpha flare loops with predicted densities of roughly 10 to the 13th/cu cm, and a small gap of roughly 1000 km is predicted to exist between the footpoints of the cool flare loops and the inner edges of the flare ribbons.

  19. Inferring Flare Loop Parameters with Measurements of Standing Sausage Modes

    NASA Astrophysics Data System (ADS)

    Guo, Ming-Zhe; Chen, Shao-Xia; Li, Bo; Xia, Li-Dong; Yu, Hui

    2016-03-01

    Standing fast sausage modes in flare loops were suggested to account for a considerable number of quasi-periodic pulsations (QPPs) in the light curves of solar flares. This study continues our investigation into the possibility of inverting the measured periods P and damping times τ of sausage modes to deduce the transverse Alfvén time R/v_{Ai}, density contrast ρi/ρe, and the steepness of the density distribution transverse to flare loops. A generic dispersion relation governing linear sausage modes is derived for pressureless cylinders where density inhomogeneity of arbitrary form takes place within the cylinder. We show that in general the inversion problem is under-determined for QPP events where only a single sausage mode exists, whether the measurements are spatially resolved or unresolved. While R/v_{Ai} can be inferred to some extent, the range of possible steepness parameters may be too broad to be useful. However, for spatially resolved measurements where an additional mode is present, it is possible to deduce self-consistently ρi/ρe, the profile steepness, and the internal Alfvén speed v_{Ai}. We show that at least for a recent QPP event that involves a fundamental kink mode in addition to a sausage one, flare loop parameters are well constrained even if the specific form of the transverse density distribution remains unknown. We conclude that spatially resolved, multi-mode QPP measurements need to be pursued to infer flare loop parameters.

  20. FAST CONTRACTION OF CORONAL LOOPS AT THE FLARE PEAK

    SciTech Connect

    Liu Rui; Wang Haimin

    2010-05-01

    On 2005 September 8, a coronal loop overlying the active region NOAA 10808 was observed in TRACE 171 A to contract at {approx}100 km s{sup -1} at the peak of an X5.4-2B flare at 21:05 UT. Prior to the fast contraction, the loop underwent a much slower contraction at {approx}6 km s{sup -1} for about 8 minutes, initiating during the flare preheating phase. The sudden switch to fast contraction is presumably corresponding to the onset of the impulsive phase. The contraction resulted in the oscillation of a group of loops located below, with the period of about 10 minutes. Meanwhile, the contracting loop exhibited a similar oscillatory pattern superimposed on the dominant downward motion. We suggest that the fast contraction reflects a suddenly reduced magnetic pressure underneath due either to (1) the eruption of magnetic structures located at lower altitudes or to (2) the rapid conversion of magnetic free energy in the flare core region. Electrons accelerated in the shrinking trap formed by the contracting loop can theoretically contribute to a late-phase hard X-ray burst, which is associated with Type IV radio emission. To complement the X5.4 flare which was probably confined, a similar event observed in SOHO/EIT 195 A on 2004 July 20 in an eruptive, M8.6 flare is briefly described, in which the contraction was followed by the expansion of the same loop leading up to a halo coronal mass ejection. These observations further substantiate the conjecture of coronal implosion and suggest coronal implosion as a new exciter mechanism for coronal loop oscillations.

  1. ANTI-PHASE SIGNATURE OF FLARE GENERATED TRANSVERSE LOOP OSCILLATIONS

    SciTech Connect

    White, R. S.; Verwichte, E.; Foullon, C.

    2013-09-10

    Transverse loop oscillations observed by the Atmospheric Imaging Assembly instrument on the Solar Dynamics Observatory spacecraft are studied after an impulsive solar flare eruption on 2012 May 8. We have found that a transversely oscillating coronal loop seen in the 171 A bandpass oscillates in anti-phase with respect to adjacent larger loops seen in the 193 A and 211 A bandpasses. These unusual oscillations are analyzed to investigate the excitation mechanism responsible for their initial inwardly directed anti-phase behavior. The transverse oscillations are analyzed by constructing space-time diagrams from cuts made parallel to the projected loop displacements. The displacement time oscillation profiles are background subtracted and fitted with a damped cosine curve that includes a linear change in the period with time. The local magnetic topology of the active region is modeled using potential field source surface extrapolation. It reveals that the loops are anchored in different topological regions with foot point locations identified on either side of the EUV flare peak emission source. In this context, the oscillation characteristics indicate that the excitation mechanism is closely linked to the local magnetic field topology and the reconnection generated wave dynamics in the active region rather than following an external flare blast wave. We discuss how observations such as these may serve to identify reconnection processes in similar quadrupolar active regions.

  2. Decaying long-period oscillations in flaring coronal loops

    NASA Astrophysics Data System (ADS)

    Nakariakov, Valery

    Quasi-periodic rapidly-decaying variations of the Doppler shift of the emission lines associated with the hot plasma were detected in solar flares about ten years ago with the SUMER spectrograph operating in EUV. Later, similar field-aligned flows of the hot plasma in flaring loops were found in the data of Yohkoh/BCS. The oscillations characterised by relatively long periods, in the range 10-20 min, and very short decay times, 15-30 min, are known as “SUMER” oscillations. We present observations of SUMER oscillations in the microwave band with the Nobeyama Radioheliograph and SDO/AIA. Analysis of the microwave data, obtained in the 17 GHz channel during an M1.6 flare revealed the presence of 12.6-min oscillations of the emitting plasma density. The oscillations were seen to decay with the characteristic time of about 15 min. Simultaneously, these oscillations were detected in the variation of the EUV emission intensity measured in the 335A channel of SDO/AIA. Our observational findings support the interpretation of SUMER oscillations in terms of impulsively excited standing acoustic oscillations in flaring loops or arcades, based upon numerical radiative MHD simulations. Moreover, very recently a similar dynamical pattern was detected in the light-curve of a megaflare on the dM4.5e star YZ CMi in the white light band. This result indicates striking similarities between dynamical processes in moderate solar flares and stellar megaflares.

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

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  4. Comparison of simulated and observed loop-top emission in flares using the AIA telescopes on SDO

    NASA Astrophysics Data System (ADS)

    Engell, A.; Reeves, K. K.; Ji, L.; Deluca, E. E.; Smith, R.; Golub, L.

    2010-12-01

    We investigate the spatial and temporal behavior of emission in flaring loops observed by AIA's 193 (Fe XXIV/XII), 131(Fe XX), 094 (Fe XVIII), 335 (Fe XVI), 211 (Fe XIV), and 171 (Fe IX) channels for two C class flares and one M class flare. Plotting light curves from loop-top areas in the six channels reveals the temporal distributions as a function of the ionization stages, with the same characteristic behavior identifiable in all three flares. The order of appearance is from the highest ionization state (FeXXIV) to the lowest (Fe XVI), and the observations are compared with the Reeves, Warren & Forbes (2007) model of flare loop energization, calculated for the various AIA channels. We also model the effects of non-equilibrium ionization on the simulated light curves.

  5. OBSERVATIONS OF RECONNECTING FLARE LOOPS WITH THE ATMOSPHERIC IMAGING ASSEMBLY

    SciTech Connect

    Warren, Harry P.; Sheeley, Neil R. Jr.; O'Brien, Casey M.

    2011-12-01

    Perhaps the most compelling evidence for the role of magnetic reconnection in solar flares comes from the supra-arcade downflows that have been observed above many post-flare loop arcades. These downflows are thought to be related to highly non-potential field lines that have reconnected and are propagating away from the current sheet. We present new observations of supra-arcade downflows taken with the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO). The morphology and dynamics of the downflows observed with AIA provide new evidence for the role of magnetic reconnection in solar flares. With these new observations we are able to measure downflows originating at larger heights than in previous studies. We find, however, that the initial velocities measured here ({approx}144 km s{sup -1}) are well below the Alfven speed expected in the lower corona, and consistent with previous results. We also find no evidence that the downflows brighten with time, as would be expected from chromospheric evaporation. These observations suggest that simple two-dimensional models cannot explain the detailed observations of solar flares.

  6. Signatures of current loop coalescence in solar flares

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

    The nonlinear coalescence instability of current carrying solar loops can explain many of the characteristics of the solar flares such as their impulsive nature, heating and high energy particle acceleration, amplitude oscillations of electromagnetic emission as well as the characteristics of 2-D microwave images obtained during a solar flare. The physical characteristics of the explosive coalescence of currents are presented in detail through computer simulation and theory. Canonical characteristics of the explosive coalescence are: (1) a large amount of impulsive increase of kinetic energies of electrons and ions; (2) simultaneous heating and acceleration of electrons and ions in high and low energy spectra; (3) ensuing quasi-periodic amplitude oscillations in fields and particle quantities; and (4) the double peak (or triple peak) structure in these profiles, participate in the coalescence process, yielding varieties of phenomena.

  7. Hard X-Ray Polarization from Non-vertical Solar Flare Loops

    NASA Astrophysics Data System (ADS)

    Emslie, A. Gordon; Bradsher, Henry L.; McConnell, Mark L.

    2008-02-01

    McConnell et al. have reported preliminary results of hard X-ray polarization measured by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) in an intense solar flare on 2002 July 23. The magnitude of the reported polarization is broadly consistent with the predictions of existing solar flare models which invoke the precipitation of a nonthermal electron beam into a dense chromospheric target. However, the orientation of the polarization vector lies at a substantial angle to the local solar radial direction. This is inconsistent with model predictions of a polarization vector along the local radial direction, a prediction that is a direct consequence of the assumption of a vertical guiding magnetic field. Smith et al., in a study of the same 2002 July 23 event, have suggested that the magnetic structure in which the flare occurs is tilted relative to the local vertical. Motivated by this observation, and by the preliminary nonradial polarization vector reported by McConnell et al., we explore the effect of tilt of the flaring loop on the magnitude and orientation of the predicted polarization vector. We find that allowing loops tilted from the local solar vertical does indeed permit a much wider range of polarization vector orientations than allowed by purely vertical loop geometries. In particular, adding tilt of the magnitude inferred by Smith et al. for the 2002 July 23 event can in principle account for both the magnitude and direction of the polarization vector reported by McConnell et al. for that event.

  8. DETERMINING HEATING RATES IN RECONNECTION FORMED FLARE LOOPS OF THE M8.0 FLARE ON 2005 MAY 13

    SciTech Connect

    Liu Wenjuan; Qiu Jiong; Longcope, Dana W.; Caspi, Amir

    2013-06-20

    We analyze and model an M8.0 flare on 2005 May 13 observed by the Transition Region and Coronal Explorer and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) to determine the energy release rate from magnetic reconnection that forms and heats numerous flare loops. The flare exhibits two ribbons in UV 1600 A emission. Analysis shows that the UV light curve at each flaring pixel rises impulsively within a few minutes, and decays slowly with a timescale longer than 10 minutes. Since the lower atmosphere (the transition region and chromosphere) responds to energy deposit nearly instantaneously, the rapid UV brightening is thought to reflect the energy release process in the newly formed flare loop rooted at the footpoint. In this paper, we utilize the spatially resolved (down to 1'') UV light curves and the thick-target hard X-ray emission to construct heating functions of a few thousand flare loops anchored at the UV footpoints, and compute plasma evolution in these loops using the enthalpy-based thermal evolution of loops model. The modeled coronal temperatures and densities of these flare loops are then used to calculate coronal radiation. The computed soft X-ray spectra and light curves compare favorably with those observed by RHESSI and by the Geostationary Operational Environmental Satellite X-ray Sensor. The time-dependent transition region differential emission measure for each loop during its decay phase is also computed with a simplified model and used to calculate the optically thin C IV line emission, which dominates the UV 1600 A bandpass during the flare. The computed C IV line emission decays at the same rate as observed. This study presents a method to constrain heating of reconnection-formed flare loops using all available observables independently, and provides insight into the physics of energy release and plasma heating during the flare. With this method, the lower limit of the total energy used to heat the flare loops in this event

  9. Well-observed Dynamics of Flaring and Peripheral Coronal Magnetic Loops during an M-class Limb Flare

    NASA Astrophysics Data System (ADS)

    Shen, Jinhua; Zhou, Tuanhui; Ji, Haisheng; Wiegelmann, Thomas; Inhester, Bernd; Feng, Li

    2014-08-01

    In this paper, we present a variety of well-observed dynamic behaviors for the flaring and peripheral magnetic loops of the M6.6 class extreme limb flare that occurred on 2011 February 24 (SOL2011-02-24T07:20) from EUV observations by the Atmospheric Imaging Assembly on the Solar Dynamics Observatory and X-ray observations by RHESSI. The flaring loop motion confirms the earlier contraction-expansion picture. We find that the U-shaped trajectory delineated by the X-ray corona source of the flare roughly follows the direction of a filament eruption associated with the flare. Different temperature structures of the coronal source during the contraction and expansion phases strongly suggest different kinds of magnetic reconnection processes. For some peripheral loops, we discover that their dynamics are closely correlated with the filament eruption. During the slow rising to abrupt, fast rising of the filament, overlying peripheral magnetic loops display different responses. Two magnetic loops on the elbow of the active region had a slow descending motion followed by an abrupt successive fast contraction, while magnetic loops on the top of the filament were pushed outward, slowly being inflated for a while and then erupting as a moving front. We show that the filament activation and eruption play a dominant role in determining the dynamics of the overlying peripheral coronal magnetic loops.

  10. Well-observed dynamics of flaring and peripheral coronal magnetic loops during an M-class limb flare

    SciTech Connect

    Shen, Jinhua; Zhou, Tuanhui; Ji, Haisheng; Feng, Li; Wiegelmann, Thomas; Inhester, Bernd

    2014-08-20

    In this paper, we present a variety of well-observed dynamic behaviors for the flaring and peripheral magnetic loops of the M6.6 class extreme limb flare that occurred on 2011 February 24 (SOL2011-02-24T07:20) from EUV observations by the Atmospheric Imaging Assembly on the Solar Dynamics Observatory and X-ray observations by RHESSI. The flaring loop motion confirms the earlier contraction-expansion picture. We find that the U-shaped trajectory delineated by the X-ray corona source of the flare roughly follows the direction of a filament eruption associated with the flare. Different temperature structures of the coronal source during the contraction and expansion phases strongly suggest different kinds of magnetic reconnection processes. For some peripheral loops, we discover that their dynamics are closely correlated with the filament eruption. During the slow rising to abrupt, fast rising of the filament, overlying peripheral magnetic loops display different responses. Two magnetic loops on the elbow of the active region had a slow descending motion followed by an abrupt successive fast contraction, while magnetic loops on the top of the filament were pushed outward, slowly being inflated for a while and then erupting as a moving front. We show that the filament activation and eruption play a dominant role in determining the dynamics of the overlying peripheral coronal magnetic loops.

  11. A unified view of coronal loop contraction and oscillation in flares

    NASA Astrophysics Data System (ADS)

    Russell, A. J. B.; Simões, P. J. A.; Fletcher, L.

    2015-09-01

    Context. Transverse loop oscillations and loop contractions are commonly associated with solar flares, but the two types of motion have traditionally been regarded as separate phenomena. Aims: We present an observation of coronal loops that contract and oscillate following the onset of a flare. We aim to explain why both behaviours are seen together and why only some of the loops oscillate. Methods: A time sequence of SDO/AIA 171 Å images is analysed to identify the positions of coronal loops following the onset of the M6.4 flare SOL2012-03-09T03:53. We focus on five loops in particular, all of which contract during the flare, with three of them oscillating as well. A simple model is then developed for the contraction and oscillation of a coronal loop. Results: We propose that coronal loop contractions and oscillations can occur in a single response to removal of magnetic energy from the corona. Our model reproduces the various types of loop motion observed and explains why the highest loops oscillate during their contraction, while no oscillation is detected for the shortest contracting loops. The proposed framework suggests that loop motions can be used as a diagnostic for the removal of coronal magnetic energy by flares, while rapid decrease in coronal magnetic energy is a newly identified excitation mechanism for transverse loop oscillations. Appendices are available in electronic form at http://www.aanda.org Warning, no authors found for 2015A&A...581A..14.

  12. Quasi-periodic processes in the flare loop generated by sudden temperature enhancements at loop footpoints

    NASA Astrophysics Data System (ADS)

    Karlický, M.; Jelínek, P.

    2016-05-01

    Aims: During the impulsive flare phase, the plasma at the flare loop footpoints is rapidly heated by particle beams. In the present paper, we study processes that occur after this sudden heating in a two-dimensional magnetic loop. Methods: We adopt a 2D magnetohydrodynamic (MHD) model, in which we solve a full set of the ideal time-dependent MHD equations by means of the FLASH code, using the adaptive mesh refinement (AMR) method. Periods in the processes are estimated by the wavelet analysis technique. Results: We consider a model of the solar atmosphere with a symmetric magnetic loop. The length of this loop in the corona is approximately 21.5 Mm. At both loop footpoints, at the transition region, we initiate the Gaussian temperature (pressure) perturbation with the maximum temperature 14, 7, or 3.5 times higher than the unperturbed temperature. In the corona, the perturbations produce supersonic blast shocks with the Mach number of about 1.1, but well below Alfvén velocities. We consider cases with the same perturbations at both footpoints (symmetric case) and one with different perturbations (asymmetric case). In the symmetric case, the shocks move along both loop legs upwards to the top of the loop, where they interact and form a transient compressed region. Then they continue in their motion to the transition region at the opposite side of the loop, where they are reflected upwards, and so on. At the top of the loop, the shock appears periodically with the period of about 170 s. In the loop legs during this period, a double peak of the plasma parameters, which is connected with two arrivals of shocks, is detected: firstly, when the shock moves up and then when the shock, propagating from the opposite loop leg, moves down. Increasing the distance of the detection point in the loop leg from the top of the loop, the time interval between these shock arrivals increases. Thus, at these detection points, the processes with shorter periods can be detected. After

  13. Onset of electron acceleration in a flare loop

    SciTech Connect

    Sharykin, Ivan; Liu, Siming; Fletcher, Lyndsay

    2014-09-20

    We carried out a detailed analysis of X-ray and radio observations of a simple flare loop that occurred on 2002 August 12, with the impulsive hard X-ray (HXR) light curves dominated by a single pulse. The emission spectra of the early impulsive phase are consistent with an isothermal model in the coronal loop with a temperature reaching several keV. A power-law high-energy spectral tail is evident near the HXR peak time, in accordance with the appearance of footpoints at high energies, and is well correlated with the radio emission. The energy content of the thermal component keeps increasing gradually after the disappearance of this nonthermal component. These results suggest that electron acceleration only covers the central period of a longer and more gradual energy dissipation process and that the electron transport within the loop plays a crucial role in the formation of the inferred power-law electron distribution. The spectral index of power-law photons shows a very gradual evolution, indicating that the electron accelerator is in a quasi-steady state, which is confirmed by radio observations. These results are consistent with the theory of stochastic electron acceleration from a thermal background. Advanced modeling with coupled electron acceleration and spatial transport processes is needed to explain these observations more quantitatively, which may reveal the dependence of the electron acceleration on the spatial structure of the acceleration region.

  14. Coronal seismology of flare-excited longitudinal slow magnetoacoustic waves in hot coronal loops

    NASA Astrophysics Data System (ADS)

    Wang, T.; Ofman, L.; Sun, X.; Provornikova, E. A.; Davila, J. M.

    2015-12-01

    The flare-excited longitudinal intensity oscillations in hot flaring loops have been recently detected by SDO/AIA in 94 and 131 bandpasses. These oscillations show similar physical properties (such as period, decay time, and trigger) as those slow-mode standing waves previously detected by the SOHO/SUMER spectrometer in Doppler shift of flare lines formed above 6 MK. The multi-wavelength AIA observations with high spatio-temporal resolution and wide temperature coverage enable us to measure both thermal and wave properties of the oscillating hot plasma with unprecedented accuracy. These new measurements can be used to diagnose the complicated energy transport processes in flare plasma by a technique called coronal seismology based on the combination of observations and MHD wave theory. From a detailed case study we have found evidence for thermal conduction suppression in hot loops by measuring the polytropic index and analyzing the phase relationship between the temperature and density wave signals. This result is not only crucial for better understanding the wave dissipation mechanism but also provides an alternative mechanism to explain the puzzles of long-duration events and X-ray loop-top sources which show much slower cooling than expected by the classical Spitzer conductive cooling. This finding may also shed a light on the coronal heating problem because weak thermal conductivity implies slower cooling of hot plasma in nanoflares, so increasing the average coronal temperature for the same heating rate. We will discuss the effects of thermal conduction suppression on the wave damping and loop cooling based on MHD simulations.

  15. KINETIC ALFVEN TURBULENCE AND PARALLEL ELECTRIC FIELDS IN FLARE LOOPS

    SciTech Connect

    Zhao, J. S.; Wu, D. J.; Lu, J. Y.

    2013-04-20

    This study investigates the spectral structure of the kinetic Alfven turbulence in the low-beta plasmas. We consider a strong turbulence resulting from collisions between counterpropagating wavepackets with equal energy. Our results show that (1) the spectra of the magnetic and electric field fluctuations display a transition at the electron inertial length scale, (2) the turbulence cascades mainly toward the magnetic field direction as the cascade scale is smaller than the electron inertial length, and (3) the parallel electric field increases as the turbulent scale decreases. We also show that the parallel electric field in the solar flare loops can be 10{sup 2}-10{sup 4} times the Dreicer field as the turbulence reaches the electron inertial length scale.

  16. Understanding X-Ray Source Motions in a Solar Flare Loop

    NASA Technical Reports Server (NTRS)

    Holman, Gordon D.; Sui, L.; Dennis, B. R.

    2006-01-01

    RHESSI images of a solar flare on 2002 November 28 showed a 3-6 keV hard X-ray source that was initially located at the flare loop top, split and propagated to the foot points of the loop during the flare rise phase, and then propagated back up to the loop top during the declining phase of the flare (Sai, Holman, & Dennis 2006). Higher energy X-ray sources were located lower in the legs of the loop during this period of source evolution, with X-rays above 25 keV seen only at the foot points. Sui, Holman, & Dennis suggested that this spatial evolution reflected the evolution of the spectral index and low-energy cutoff to the distribution of accelerated electrons in the flare. We construct a model flare loop and electron distribution injected at the top of this loop to reproduce the source evolution of the November 28 flare. We determine the constraints on the loop model and the evolution of the accelerated electron distribution. We also study the implications of the model for energy deposition into the loop plasma, and the integrated and imaged X-ray spectra. This work is supported in part by the RHESSI Project and the NASA Guest Investigator Program.

  17. DYNAMICS OF THE FLARING LOOP SYSTEM OF 2005 AUGUST 22 OBSERVED IN MICROWAVES AND HARD X-RAYS

    SciTech Connect

    Reznikova, V. E.; Melnikov, V. F.; Shibasaki, K.

    2010-11-20

    We studied the spatial dynamics of the flaring loop in the 2005 August 22 event using microwave (NoRH) and hard X-ray (RHESSI) observations together with complementary data from SOHO/MDI, SMART at Hida, SOHO/EIT, and TRACE. We have found that (1) the pre-flare morphology of the active region exhibits a strongly sheared arcade seen in H{alpha} and the J-shape filament seen in EUV; (2) energy release and high-energy electron acceleration occur in a sequence along the extensive arcade; (3) the shear angle and the parallel (to the magnetic neutral line) component of the footpoint (FP) distance steadily decrease during the flare process; (4) the radio loop shrinks in length and height during the first emission peak, and later it grows; after the fourth peak the simultaneous descending of the brightest loop and formation of a new microwave loop at a higher altitude occur; (5) the hard X-ray coronal source is located higher than the microwave loop apex and shows faster upward motion; (6) the first peak on microwave time profiles is present in both the loop top and FP regions. However, the emission peaks that follow are present only in the FP regions. We conclude that after the first emission peak the acceleration site is located over the flaring arcade and particles are accelerated along magnetic field lines. We make use of the collapsing magnetic trap model to understand some observational effects.

  18. Above-the-loop-top Oscillation and Quasi-periodic Coronal Wave Generation in Solar Flares

    NASA Astrophysics Data System (ADS)

    Takasao, Shinsuke; Shibata, Kazunari

    2016-06-01

    Observations revealed that various kinds of oscillations are excited in solar flare regions. Quasi-periodic pulsations (QPPs) in flare emissions are commonly observed in a wide range of wavelengths. Recent observations have found that fast-mode magnetohydrodynamic (MHD) waves are quasi-periodically emitted from some flaring sites (quasi-periodic propagating fast-mode magnetoacoustic waves; QPFs). Both QPPs and QPFs imply a cyclic disturbance originating from the flaring sites. However, the physical mechanisms remain puzzling. By performing a set of two-dimensional MHD simulations of a solar flare, we discovered the local oscillation above the loops filled with evaporated plasma (above-the-loop-top region) and the generation of QPFs from such oscillating regions. Unlike all previous models for QPFs, our model includes essential physics for solar flares such as magnetic reconnection, heat conduction, and chromospheric evaporation. We revealed that QPFs can be spontaneously excited by the above-the-loop-top oscillation. We found that this oscillation is controlled by the backflow of the reconnection outflow. The new model revealed that flare loops and the above-the-loop-top region are full of shocks and waves, which is different from the previous expectations based on a standard flare model and previous simulations. In this paper, we show the QPF generation process based on our new picture of flare loops and will briefly discuss a possible relationship between QPFs and QPPs. Our findings will change the current view of solar flares to a new view in which they are a very dynamic phenomenon full of shocks and waves.

  19. Electron Densities in Solar Flare Loops, Chromospheric Evaporation Upflows, and Acceleration Sites

    NASA Technical Reports Server (NTRS)

    Aschwanden, Markus J.; Benz, Arnold O.

    1996-01-01

    We compare electron densities measured at three different locations in solar flares: (1) in Soft X-Ray (SXR) loops, determined from SXR emission measures and loop diameters from Yohkoh Soft X-Ray Telescope maps (n(sub e, sup SXR) = (0.2-2.5) x 10(exp 11)/ cu cm); (2) in chromospheric evaporation upflows, inferred from plasma frequency cutoffs of decimetric radio bursts detected with the 0.1-3 GHz spectrometer Phoenix of ETH Zuerich (n(sub e, sup upflow) = (0.3-11) x 10(exp 10)/cu cm; and (3) in acceleration sites, inferred from the plasma frequency at the separatrix between upward-accelerated (type III bursts) and downward-accelerated (reverse-drift bursts) electron beams [n(sub e, sup acc) = (0.6-10) x 10(exp 9)/cu cm]. The comparison of these density measurements, obtained from 44 flare episodes (during 14 different flares), demonstrates the compatibility of flare plasma density diagnostics with SXR and radio methods. The density in the upflowing plasma is found to be somewhat lower than in the filled loops, having ratios in a range n(sub e, sup upflow)/n(sub e, sup SXR) = 0.02-1.3, and a factor of 3.6 higher behind the upflow front. The acceleration sites are found to have a much lower density than the SXR-bright flare loops, i.e., n(sub e, sup acc)/n(sub e, sup SXR) = 0.005- 0.13, and thus must be physically displaced from the SXR-bright flare loops. The scaling law between electron time-of-flight distances l' and loop half-lengths s, l'/s = 1.4 +/- 0.3, recently established by Aschwanden et al. suggests that the centroid of the acceleration region is located above the SXR-bright flare loop, as envisioned in cusp geometries (e.g., in magnetic reconnection models).

  20. MODELING OF GYROSYNCHROTRON RADIO EMISSION PULSATIONS PRODUCED BY MAGNETOHYDRODYNAMIC LOOP OSCILLATIONS IN SOLAR FLARES

    SciTech Connect

    Mossessian, George; Fleishman, Gregory D.

    2012-04-01

    A quantitative study of the observable radio signatures of the sausage, kink, and torsional magnetohydrodynamic (MHD) oscillation modes in flaring coronal loops is performed. Considering first non-zero order effect of these various MHD oscillation modes on the radio source parameters such as magnetic field, line of sight, plasma density and temperature, electron distribution function, and the source dimensions, we compute time-dependent radio emission (spectra and light curves). The radio light curves (of both flux density and degree of polarization) at all considered radio frequencies are then quantified in both time domain (via computation of the full modulation amplitude as a function of frequency) and in Fourier domain (oscillation spectra, phases, and partial modulation amplitude) to form the signatures specific to a particular oscillation mode and/or source parameter regime. We found that the parameter regime and the involved MHD mode can indeed be distinguished using the quantitative measures derived in the modeling. We apply the developed approach to analyze radio burst recorded by Owens Valley Solar Array and report possible detection of the sausage mode oscillation in one (partly occulted) flare and kink or torsional oscillations in another flare.

  1. Using a reconnection-powered loop to model a real flare

    NASA Astrophysics Data System (ADS)

    Longcope, Dana; Qiu, Jiong; Brewer, Jasmine

    2016-05-01

    Magnetic reconnection has long been invoked to explain the supply of energy for solar flares. In spite of this, few models have been able to capture reconnection-driven energy release at the same time they reproduce other flare-related phenomena, such as chromospheric evaporation. We present a one-dimensional numerical model of flux tube retraction following reconnection. Unlike traditional flare loop models, the energy supply here is not a free parameter but comes self-consistently from the post-reconnection retraction. This model depends on 5 free parameters, two of which can be constrained using pre-flare observations. The remaining three parameters can be varied to fit observations of the actual flare. In this case, they are used to the fit the RHESSI hard X-ray spectrum from a flare on 26 Feb 2004. Once done, the model can be used to reproduce observations from other wavelengths, including their time-evolution. We show that our model agrees with the two different soft X-ray light curves observed by GOES, and the time evolutions observed in various hard X-ray bands observed by RHESSI. The model also predicts hard X-ray emission from the top of the flaring loops, in agreement with hard X-ray images made of the same flare - and many others. While such loop-top sources are well known, their theoretical explanation is still debated. The loop-top source in this model arises from a plug of plasma compressed and heated by slow magnetosonic shocks. This plug persists longer than slow shocks are expected to, giving rise to concentrated source, rather than an elongated jet, and producing considerably more emission than previous models predicted.

  2. Coronal explosions as a signature of current loop coalescence in solar flares

    NASA Astrophysics Data System (ADS)

    Sakai, Jun-Ichi; de Jager, Cornelis

    1989-09-01

    The coronal explosions interpreted by De Jaeger and Boelee (1984) as masnifestations of plasma streaming out of flare kernels are presently reinterpreted as signatures of current loop coalescence in the flaring region. This interpretation can quantitatively explain the various characteristics of the observed coronal explosions. The present model is expected to be very directly addressed by the soft X-ray imaging instrument that will be carried by the Solar-A mission spacecraft due for launch during the next solar maximum.

  3. Post-flare loops embedded in a hot coronal fan-like structure

    NASA Technical Reports Server (NTRS)

    Svestka, Z.; Farnik, F.; Hudson, H. S.; Hick, P.

    1997-01-01

    Limb events were demonstrated on the sun in which rising post-flare loops were embedded in hot structures looking in soft X-rays like fans of rays, formed during the flare and extending high into the corona. One of these structures is analyzed and it is suggested that these fans of rays represent temporary ministreamers, along which mass flows into interplanetary space. This suggestion is supported by maps of solar wind density constructed from scintillation measurements.

  4. SDO/AIA Observation and Modeling of Flare-excited Slow Waves in Hot Coronal Loops

    NASA Astrophysics Data System (ADS)

    Wang, T.; Ofman, L.; Provornikova, E.; Sun, X.; Davila, J. M.

    2014-12-01

    The flare-excited standing slow waves were first detected by SOHO/SUMER as Doppler shift oscillations in hot (>6 MK) coronal loops. It has been suggested that they are excited by small or micro- flares at one loop's footpoint. However, the detailed excitation mechanism remains unclear. In this study, we report an oscillation event observed by SDO/AIA in the 131 channel. The intensity disturbances excited by a C-class flare propagated back and forth along a hot loop for about two period with a strong damping. From the measured oscillation period and loop length, we estimate the wave phase speed to be about 410 km/s. Using a regularized DEM analysis we determine the loop temperature and electron density evolution and find that the loop plasma is heated to a temperature of 8-12 MK with a mean about 9 MK. These measurements support the interpretation as slow magnetoacousic waves. Magnetic field extrapolation suggests that the flare is triggered by slipping and null-point-type reconnections in a fan-spine magnetic topology, and the injected (or impulsively evaporated) hot plasmas flowing along the large spine field lines form the oscillating hot loops. To understand why the propagating waves but not the standing waves as observed previously are excited in this event, we preform simulations using a 3D MHD model based on the observed magnetic configuration including full energy equation. Our simulations indicate that the nature of loop temperature structure is critical for the excitation of whether propagating or standing waves in a hot loop. Our result demonstrates that the slow waves may be used for heating diagnostics of coronal loops with coronal seismology. We also discuss the application of coronal seismology for estimating the average magnetic field strength in the hot loop based on the observed slow waves.

  5. Dark Post-flare Loops Observed by the Solar Dynamics Observatory

    NASA Astrophysics Data System (ADS)

    Song, Qiao; Wang, Jing-Song; Feng, Xueshang; Zhang, Xiaoxin

    2016-04-01

    Solar post-flare loops (PFLs) are arcade-like loop systems that appear during the gradual phases of eruptive flares. The extreme ultraviolet (EUV) observations from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) allow us to investigate the fine structures in PFLs. In this work, we focus on studying the dark post-flare loops (DPFLs) during X-class flares, which are more evident in SDO/AIA data than in previous EUV data. We identify and analyze the DPFLs observed by SDO and find that: (1) the DPFLs of an X5.4 flare have an average lifetime of 10.0 ± 5.5 minutes, an average width of 1022 ± 339 km, and an average maximum length of 33 ± 10 Mm, (2) blob-like falling features with a size close to the resolution of SDO/AIA are identified in the DPFLs and have an average velocity of 76 ± 19 km s‑1, and (3) the average widths of the DPFLs slightly increase with the characteristic temperatures in the AIA 304, 171, 193, and 211 Å channels. Our investigation shows that DPFLs are found in all of the 20 cases within this study, which suggests that they are a common phenomenon in X-class flares and are probably produced by the same mechanism that creates coronal rain.

  6. An equation for the evolution of solar and stellar flare loops

    NASA Technical Reports Server (NTRS)

    Fisher, George H.; Hawley, Suzanne L.

    1990-01-01

    An ordinary differential equation describing the evolution of a coronal loop subjected to a spatially uniform but time-varying heating rate is discussed. It is assumed that the duration of heating is long compared to the sound transit time through the loop, which is assumed to have uniform cross section area. The form of the equation changes as the loop evolves through three states: 'strong evaporation', 'scaling law behavior', and 'strong condensation'. Solutions to the equation may be used to compute the time dependence of the average coronal temperature and emission measure for an assumed temporal variation of the flare heating rate. The results computed from the model agree reasonably well with recent published numerical simulations and may be obtained with far less computational effort. The model is then used to study the May 21, 1980, solar flare observed by SMM and the giant April 12, 1985, flare observed on the star AD Leo.

  7. MAGNETIC RECONNECTION: FROM 'OPEN' EXTREME-ULTRAVIOLET LOOPS TO CLOSED POST-FLARE ONES OBSERVED BY SDO

    SciTech Connect

    Zhang, Jun; Yang, Shuhong; Li, Ting; Zhang, Yuzong; Li, Leping; Jiang, Chaowei E-mail: shuhongyang@nao.cas.cn E-mail: yuzong@nao.cas.cn E-mail: cwjiang@spaceweather.ac.cn

    2013-10-10

    We employ Solar Dynamics Observatory observations and select three well-observed events including two flares and one extreme-ultraviolet (EUV) brightening. During the three events, the EUV loops clearly changed. One event was related to a major solar flare that took place on 2012 July 12 in active region NOAA AR 11520. 'Open' EUV loops rooted in a facula of the AR deflected to the post-flare loops and then merged with them while the flare ribbon approached the facula. Meanwhile, 'open' EUV loops rooted in a pore disappeared from top to bottom as the flare ribbon swept over the pore. The loop evolution was similar in the low-temperature channels (e.g., 171 Å) and the high-temperature channels (e.g., 94 Å). The coronal magnetic fields extrapolated from the photospheric vector magnetograms also show that the fields apparently 'open' prior to the flare become closed after it. The other two events were associated with a B1.1 flare on 2010 May 24 and an EUV brightening on 2013 January 03, respectively. During both of these two events, some 'open' loops either disappeared or darkened before the formation of new closed loops. We suggest that the observations reproduce the picture predicted by the standard magnetic reconnection model: 'open' magnetic fields become closed due to reconnection, manifesting as a transformation from 'open' EUV loops to closed post-flare ones.

  8. Global Sausage Oscillation of Solar Flare Loops Detected by the Interface Region Imaging Spectrograph

    NASA Astrophysics Data System (ADS)

    Tian, Hui; Young, Peter R.; Reeves, Katharine K.; Wang, Tongjiang; Antolin, Patrick; Chen, Bin; He, Jiansen

    2016-05-01

    An observation from the Interface Region Imaging Spectrograph reveals coherent oscillations in the loops of an M1.6 flare on 2015 March 12. Both the intensity and Doppler shift of Fe xxi 1354.08 Å show clear oscillations with a period of ∼25 s. Remarkably similar oscillations were also detected in the soft X-ray flux recorded by the Geostationary Operational Environmental Satellites (GOES). With an estimated phase speed of ∼2420 km s‑1 and a derived electron density of at least 5.4 × 1010 cm‑3, the observed short-period oscillation is most likely the global fast sausage mode of a hot flare loop. We find a phase shift of ∼π/2 (1/4 period) between the Doppler shift oscillation and the intensity/GOES oscillations, which is consistent with a recent forward modeling study of the sausage mode. The observed oscillation requires a density contrast between the flare loop and coronal background of a factor ≥42. The estimated phase speed of the global mode provides a lower limit of the Alfvén speed outside the flare loop. We also find an increase of the oscillation period, which might be caused by the separation of the loop footpoints with time.

  9. The bright knots at the tops of soft X-ray flare loops: Quantitative results from Yohkoh

    NASA Technical Reports Server (NTRS)

    Doschek, G. A.; Strong, K. T.; Tsuneta, S.

    1995-01-01

    Soft X-ray Telescope (SXT) observations from the Japanese Yohkoh spacecraft have shown that confined bright regions are common features at the tops of flare loops throughout most of the duration of the flares. In this paper we present quantitative results for these flare knots, in relation to other flare regions, for four relatively 'simple' flares. Emission measure distributions, electron temperatures, and electron densities are derived from SXT and Yohkoh Bragg Crystal Spectrometer (BCS) observations. The four flares selected are dominated by what appear to be single-loop structures, with bright knots at the loop tops. The flares are neither long-duration nor impulsive events. The spatial distributions of brightness and emission measure in the flares are found to be quite similar for all four events, even though there are significant differences in dynamical behavior between at least two of the events. Temperatures and densities calculated for these flares are consistent with previous results from many solar experiments. An investigation of intensity correlations between adjacent pixels at the tops of the loops suggests the existence of local disturbances in the magnetic loops that occur on spatial scales less than the radii of the loops.

  10. IMPLOSION OF CORONAL LOOPS DURING THE IMPULSIVE PHASE OF A SOLAR FLARE

    SciTech Connect

    Simões, P. J. A.; Fletcher, L.; Hudson, H. S.; Russell, A. J. B. E-mail: lyndsay.fletcher@glasgow.ac.uk E-mail: hhudson@ssl.berkeley.edu

    2013-11-10

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

  11. Modeling an X-ray flare on Proxima Centauri: Evidence of two flaring loop components and of two heating mechanisms at work

    NASA Astrophysics Data System (ADS)

    Reale, F.; Güdel, M.; Peres, G.; Audard, M.

    2004-03-01

    We model in detail a flare observed on Proxima Centauri with the EPIC-PN on board XMM-Newton at high statistics and high time resolution and coverage. Time-dependent hydrodynamic loop modeling is used to describe the rise and peak of the light curve, and a large fraction of the decay, including its change of slope and a secondary maximum, over more than 2 h. The light curve, the emission measure and the temperature derived from the data allow us to constrain the loop morphology and the heating function and to show that this flare can be described with two components: a major one triggered by an intense heat pulse injected in a single flaring loop with half-length ≈1.0 × 1010 cm, the other one by less intense heat pulses released about 1/2 h after the first one in related loop systems, probably arcades, with the same half-length. The heat functions of the two loop systems appear very similar: an intense pulse located at the loop footpoints followed by a low gradual decay distributed in the coronal part of the loop. The latter result and the similarity to at least one solar event (the Bastille Day flare in 2000) indicate that this pattern may be common to solar and stellar flares. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member states and the USA (NASA).

  12. Slow-Mode Oscillations of Hot Loops Excited at Flaring Footpoints

    NASA Astrophysics Data System (ADS)

    Wang, T.; Liu, W.; Ofman, L.; Davila, J.

    2012-05-01

    The analysis of a hot loop oscillation event using SOHO/SUMER, GOES SXI, and RHESSI observations is presented. Damped Doppler shift oscillations were detected in the Fe xix line by SUMER, and interpreted as a fundamental standing slow mode. The evolution of soft X-ray emission from GOES/SXI and hard X-ray sources from RHESSI suggests that the oscillations of a large loop are triggered by a small flare, which may be produced by interaction (local reconnection) of this large loop with a small loop at its footpoint. This study provides clear evidence supporting our early conjecture that the slow-mode standing waves in hot coronal loops are excited by impulsive heating (small or microflares) at the loop's footpoint.

  13. Heating and dynamics of two flare loop systems observed by AIA and EIS

    SciTech Connect

    Li, Y.; Ding, M. D.; Qiu, J.

    2014-02-01

    We investigate heating and evolution of flare loops in a C4.7 two-ribbon flare on 2011 February 13. From Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) imaging observations, we can identify two sets of loops. Hinode/EUV Imaging Spectrometer (EIS) spectroscopic observations reveal blueshifts at the feet of both sets of loops. The evolution and dynamics of the two sets are quite different. The first set of loops exhibits blueshifts for about 25 minutes followed by redshifts, while the second set shows stronger blueshifts, which are maintained for about one hour. The UV 1600 observation by AIA also shows that the feet of the second set of loops brighten twice. These suggest that continuous heating may be present in the second set of loops. We use spatially resolved UV light curves to infer heating rates in the few tens of individual loops comprising the two loop systems. With these heating rates, we then compute plasma evolution in these loops with the 'enthalpy-based thermal evolution of loops' model. The results show that, for the first set of loops, the synthetic EUV light curves from the model compare favorably with the observed light curves in six AIA channels and eight EIS spectral lines, and the computed mean enthalpy flow velocities also agree with the Doppler shift measurements by EIS. For the second set of loops modeled with twice-heating, there are some discrepancies between modeled and observed EUV light curves in low-temperature bands, and the model does not fully produce the prolonged blueshift signatures as observed. We discuss possible causes for the discrepancies.

  14. Acceleration of SEPs in Flaring Loops and CME Driven shocks

    NASA Astrophysics Data System (ADS)

    Petrosian, Vahe; Chen, Qingrong

    2014-06-01

    We consider two stage acceleration of the Solar Energetic Particles (SEPs). The first occurring via the stochastic acceleration mechanism at the flare site in the corona, which produces the so-called impulsive SEPs, with anomalous abundances, as well as nonthermal particles responsible for the observed radiation. The second is re-acceleration the flare accelerated particles at the CME driven shock associated with larger, longer duration events with relatively normal abundances. Turbulence plays a major role in both stages. We will show how stochastic acceleration can explain some of the salient features of the impulsive SEP observations; such as extreme enrichment of 3He (and heavy ions), and the observed broad distributions and ranges of the 3He and 4He fluences. We will then show that the above hybrid mechanism of first stochastic acceleration of ions in the reconnecting coronal magnetic structures and then their re-acceleration in the CME shock can produce the varied shapes of the 3He and 4He spectra observed in all events ranging from weak impulsive to strong gradual events.

  15. Evidence of Multiple Slow Acoustic Oscillations in the Stellar Flaring Loops of Proxima Centauri

    NASA Astrophysics Data System (ADS)

    Srivastava, A. K.; Lalitha, S.; Pandey, J. C.

    2013-12-01

    We present the first observational evidence of multiple slow acoustic oscillations in the post-flaring loops of the corona of Proxima Centauri using XMM-Newton observations. We find the signature of periodic oscillations localized in the decay phase of the flare in its soft (0.3-10.0 keV) X-ray emissions. Using the standard wavelet tool, we find multiple periodicities of 1261 s and 687 s. These bursty oscillations persist for durations of 90 minutes and 50 minutes, respectively, for more than three cycles. The intensity oscillations with a period of 1261 s may be the signature of the fundamental mode of slow magnetoacoustic waves with a phase speed of 119 km s-1 in a loop of length 7.5 × 109 cm, which is initially heated, producing the flare peak temperature of 33 MK and later cooled down in the decay phase and maintained at an average temperature of 7.2 MK. The other period of 687 s may be associated with the first overtone of slow magnetoacoustic oscillations in the flaring loop. The fundamental mode oscillations show dissipation with a damping time of 47 minutes. The period ratio P 1/P 2 is found to be 1.83, indicating that such oscillations are most likely excited in longitudinal density stratified stellar loops. We estimate the density scale height of the stellar loop system as ~23 Mm, which is smaller than the hydrostatic scale height of the hot loop system, and implies the existence of non-equilibrium conditions.

  16. EVIDENCE OF MULTIPLE SLOW ACOUSTIC OSCILLATIONS IN THE STELLAR FLARING LOOPS OF PROXIMA CENTAURI

    SciTech Connect

    Srivastava, A. K.; Pandey, J. C.; Lalitha, S.

    2013-12-01

    We present the first observational evidence of multiple slow acoustic oscillations in the post-flaring loops of the corona of Proxima Centauri using XMM-Newton observations. We find the signature of periodic oscillations localized in the decay phase of the flare in its soft (0.3-10.0 keV) X-ray emissions. Using the standard wavelet tool, we find multiple periodicities of 1261 s and 687 s. These bursty oscillations persist for durations of 90 minutes and 50 minutes, respectively, for more than three cycles. The intensity oscillations with a period of 1261 s may be the signature of the fundamental mode of slow magnetoacoustic waves with a phase speed of 119 km s{sup –1} in a loop of length 7.5 × 10{sup 9} cm, which is initially heated, producing the flare peak temperature of 33 MK and later cooled down in the decay phase and maintained at an average temperature of 7.2 MK. The other period of 687 s may be associated with the first overtone of slow magnetoacoustic oscillations in the flaring loop. The fundamental mode oscillations show dissipation with a damping time of 47 minutes. The period ratio P {sub 1}/P {sub 2} is found to be 1.83, indicating that such oscillations are most likely excited in longitudinal density stratified stellar loops. We estimate the density scale height of the stellar loop system as ∼23 Mm, which is smaller than the hydrostatic scale height of the hot loop system, and implies the existence of non-equilibrium conditions.

  17. The propagation of solar flare particles in a coronal loop

    NASA Technical Reports Server (NTRS)

    Ryan, J. M.

    1986-01-01

    A time-dependent diffusion equation with velocity-dependent diffusion and energy-loss coefficients was solved for the case where energetic solar particles are injected into a coronal loop and then diffuse out the ends of the loop into the lower corona/chromosphere. The solution yields for the case of relativistic electrons, precipitation rates and populations which are necessary for calculating thick and thin target X-ray emission. It follows that the thick target emission is necessarily delayed with respect to the particle acceleration on injection by more than the mere travel time of the particle over the loop length. In addition the time-dependent electron population at the top of the loop is calculated. This is useful in estimating the resulting micron-wave emission. The results show relative timing differences in the different emission processes which are functions of particle species, energy and the point of injection of the particles into the loop. Equivalent quantities are calculated for non-relativistic protons.

  18. The Effects of Flare Definitions on the Statistics of Derived Flare Distrubtions

    NASA Astrophysics Data System (ADS)

    Ryan, Daniel; Dominique, Marie; Seaton, Daniel B.; Stegen, Koen; White, Arthur

    2016-05-01

    The statistical examination of solar flares is crucial to revealing their global characteristics and behaviour. However, statistical flare studies are often performed using standard but basic flare detection algorithms relying on arbitrary thresholds which may affect the derived flare distributions. We explore the effect of the arbitrary thresholds used in the GOES event list and LYRA Flare Finder algorithms. We find that there is a small but significant relationship between the power law exponent of the GOES flare peak flux frequency distribution and the algorithms’ flare start thresholds. We also find that the power law exponents of these distributions are not stable but appear to steepen with increasing peak flux. This implies that the observed flare size distribution may not be a power law at all. We show that depending on the true value of the exponent of the flare size distribution, this deviation from a power law may be due to flares missed by the flare detection algorithms. However, it is not possible determine the true exponent from GOES/XRS observations. Additionally we find that the PROBA2/LYRA flare size distributions are clearly non-power law. We show that this is consistent with an insufficient degradation correction which causes LYRA absolute irradiance values to be unreliable. This means that they should not be used for flare statistics or energetics unless degradation is adequately accounted for. However they can be used to study time variations over shorter timescales and for space weather monitoring.

  19. STATISTICS OF FLARING LOOPS OBSERVED BY THE NOBEYAMA RADIOHELIOGRAPH. III. ASYMMETRY OF TWO FOOTPOINT EMISSIONS

    SciTech Connect

    Huang Guangli; Song Qiwu; Huang Yu

    2010-11-10

    .e., the energy release above a single loop (group 1) and in the coalescence of two flaring loops (group 2). The asymmetry of the two FP emissions cannot simply be explained by the mirroring effect, but it may strongly depend on the asymmetry of the initial pitch angles of nonthermal electrons in the two FPs. The normal or abnormal events are defined as whether a stronger emission corresponds to a stronger or weaker polarization in the two FPs, with a comparable proportion of the normal and abnormal events in the two groups.

  20. Shrinking Loops Observations for the 2008 April 9 Flare

    NASA Astrophysics Data System (ADS)

    Savage, S. L.; McKenzie, D. E.; Reeves, K. K.; Forbes, T. G.

    2012-08-01

    Supra-arcade downflows (SADs) have been observed with Yohkoh/SXT (soft X-rays (SXR)), TRACE (extreme ultra-violet (EUV)), SoHO/LASCO (white light), SoHO/SUMER (EUV spectra), and Hinode/XRT (SXR). Characteristics such as low emissivity and trajectories which slow as they reach the top of the arcade are consistent with post-reconnection magnetic flux tubes. The magnetic flux within the tubes provides pressure against filling with plasma. As with the standard model of reconnection, the tubes retract from a reconnection site high in the corona until they reach a more potential magnetic configuration. Viewed from a perpendicular angle, SADs should appear as shrinking loops rather than downflowing voids. We will present observations of supra-arcade downflowing loops (SADLs) and show that their speeds and decelerations are consistent with those determined for SADs.

  1. Multiple loop activations and continuous energy release in the solar flare of June 15, 1973

    NASA Technical Reports Server (NTRS)

    Widing, K. G.; Dere, K. P.

    1977-01-01

    The spatial and temporal evolution of the high-temperature plasma in the solar flare of June 15, 1973, is studied using XUV spectroheliograms and X-ray filtergrams obtained from Skylab. The analysis focuses on the changing forms and brightness of Fe XXIII 263-A and Fe XXIV 255-A images. Temperatures and emission measures computed for different times during the flare are compared with those derived from Solrad-9 flux data, the electron temperature in the bright compact core of the Fe XXIV image is determined, and a coronal origin is suggested for this bright core. The observational evidence shows that the overall flare event involved a number of different preexisting loops and arches which were activated in succession. The activation and heating are found to have persisted well past the end of the burst phase, implying that the energy release did not end when the impulsive phase was over. The overall development of the flare is summarized on the basis of the observed order of appearance of the loops.

  2. POST-FLARE ULTRAVIOLET LIGHT CURVES EXPLAINED WITH THERMAL INSTABILITY OF LOOP PLASMA

    SciTech Connect

    Reale, F.; Landi, E.; Orlando, S.

    2012-02-10

    In the present work, we study the C8 flare that occurred on 2000 September 26 at 19:49 UT and observed by the Solar and Heliospheric Observatory/Solar Ultraviolet Measurement of Emitted Radiation spectrometer from the beginning of the impulsive phase to well beyond the disappearance in the X-rays. The emission first decayed progressively through equilibrium states until the plasma reached 2-3 MK. Then, a series of cooler lines, i.e., Ca X, Ca VII, Ne VI, O IV, and Si III (formed in the temperature range log T = 4.3-6.3 under equilibrium conditions), are emitted at the same time and all evolve in a similar way. Here, we show that the simultaneous emission of lines with such a different formation temperature is due to thermal instability occurring in the flaring plasma as soon as it has cooled below {approx}2 MK. We can qualitatively reproduce the relative start time of the light curves of each line in the correct order with a simple (and standard) model of a single flaring loop. The agreement with the observed light curves is greatly improved, and a slower evolution of the line emission is predicted, if we assume that the model loop consists of an ensemble of subloops or strands heated at slightly different times. Our analysis can be useful for flare observations with the Solar Dynamics Observatory/Extreme ultraviolet Variability Experiment.

  3. Intercomparison of numerical models of flaring coronal loops

    NASA Technical Reports Server (NTRS)

    Kopp, R. A.; Fisher, G. H.; Macneice, P.; Mcwhirter, R. W. P.; Peres, G.

    1986-01-01

    The proposed Benchmark Problem consists of an infinitesimal magnetic flux tube containing a low-beta plasma. The field strength is assumed to be so large that the plasma can move only along the flux tube, whose shape remains invariant with time (i.e., the fluid motion is essentially one-dimensional). The flux tube cross section is taken to be constant over its entire length. In planar view the flux tube has a semi-circular shape, symmetric about its midpoint s = s sub max and intersecting the chromosphere-corona interface (CCI) perpendicularly at each foot point. The arc length from the loop apex to the CCI is 10,000 km. The flux tube extends an additional 2000 km below the CCI to include the chromosphere, which initially has a uniform temperature of 8000 K. The temperature at the top of the loop was fixed initially at 2 X 1 million K. The plasma is assumed to be a perfect gas (gamma = 5/3), consisting of pure hydrogen which is considered to be fully ionized at all temperatures. For simplicity, moreover, the electron and ion temperatures are taken to be everywhere equal at all times (corresponding to an artificially enhanced electron-ion collisional coupling). While there was more-or-less unanimous agreement as to certain global properties of the system behavior (peak temperature reached, thermal-wave time scales, etc.), no two groups could claim satisfactory accord when a more detailed comparison of solutions was attempted.

  4. Plasma dynamics above solar flare soft x-ray loop tops

    SciTech Connect

    Doschek, G. A.; Warren, H. P.; McKenzie, D. E.

    2014-06-10

    We measure non-thermal motions in flare loop tops and above the loop tops using profiles of highly ionized spectral lines of Fe XXIV and Fe XXIII formed at multimillion-degree temperatures. Non-thermal motions that may be due to turbulence or multiple flow regions along the line of sight are extracted from the line profiles. The non-thermal motions are measured for four flares seen at or close to the solar limb. The profile data are obtained using the Extreme-ultraviolet Imaging Spectrometer on the Hinode spacecraft. The multimillion-degree non-thermal motions are between 20 and 60 km s{sup –1} and appear to increase with height above the loop tops. Motions determined from coronal lines (i.e., lines formed at about 1.5 MK) tend to be smaller. The multimillion-degree temperatures in the loop tops and above range from about 11 MK to 15 MK and also tend to increase with height above the bright X-ray-emitting loop tops. The non-thermal motions measured along the line of sight, as well as their apparent increase with height, are supported by Solar Dynamics Observatory Atmospheric Imaging Assembly measurements of turbulent velocities in the plane of the sky.

  5. On the transport and acceleration of solar flare particles in a coronal loop

    NASA Technical Reports Server (NTRS)

    Ryan, James M.; Lee, Martin A.

    1991-01-01

    The turbulent environment of a flaring solar coronal loop directly affects the population of particles to be accelerated or already accelerated. Under the assumption of a uniform turbulent MHD wave field within the loop, the behavior of a particle distribution as it interacts with the turbulence is discussed, including particle precipitation to the footpoints of the loop and the evolution of the energy distribution as the particles undergo second-order stochastic acceleration. Two cases are discussed in detail: (1) particles spatially diffusing within the loop and precipitating with minimal acceleration in the short time scale of an impulsive event and (2) particles diffusing in both real and momentum space in a long duration event. Collisional losses due to ambient electrons are included. The gamma-ray flare of June 3, 1982 is modeled, and good agreement is obtained between predicted and observed time profiles if the loop length is 100,000 km with an intrinsic spatial diffusion time of 100-450 s. It follows that the production of high-energy neutrons and pi mesons extends over a time scale of 1000 s as observed.

  6. IMAGING OBSERVATIONS OF QUASI-PERIODIC PULSATIONS IN SOLAR FLARE LOOPS WITH SDO/AIA

    SciTech Connect

    Su, J. T.; Mao, X. J.; Shen, Y. D.; Liu, Y.

    2012-08-20

    Quasi-periodic pulsations (QPPs) of flaring emission with periods from a few seconds to tens of minutes have been widely detected from radio bands to {gamma}-ray emissions. However, in the past the spatial information of pulsations could not be utilized well due to the instrument limits. We report here imaging observations of the QPPs in three loop sections during a C1.7 flare with periods of P = 24 s-3 minutes by means of the extreme-ultraviolet 171 A channel of the Atmospheric Imaging Assembly (AIA) instrument on board the Solar Dynamics Observatory. We confirm that the QPPs with the shortest period of 24 s were not of an artifact produced by the Nyquist frequency of the AIA 12 s cadence. The QPPs in the three loop sections were interconnected and closely associated with the flare. The detected perturbations propagated along the loops at speeds of 65-200 km s{sup -1}, close to those of acoustic waves in them. The loops were made up of many bright blobs arranged in alternating bright and dark changes in intensity (spatial periodical distribution) with the wavelengths 2.4-5 Mm (as if they were magnetohydrodynamic waves). Furthermore, in the time-distance diagrams, the detected perturbation wavelengths of the QPPs are estimated to be {approx}10 Mm, which evidently do not fit the above ones of the spatial periodic distributions and produce a difference of a factor of 2-4 with them. It is suggested that the short QPPs with periods P < 60 s were possibly sausage-mode oscillations and the long QPPs with periods P > 60 s were the higher (e.g., >2nd) harmonics of slow magnetoacoustic waves.

  7. High-energy gamma-ray emission from pion decay in a solar flare magnetic loop

    NASA Technical Reports Server (NTRS)

    Mandzhavidze, Natalie; Ramaty, Reuven

    1992-01-01

    The production of high-energy gamma rays resulting from pion decay in a solar flare magnetic loop is investigated. Magnetic mirroring, MHD pitch-angle scattering, and all of the relevant loss processes and photon production mechanisms are taken into account. The transport of both the primary ions and the secondary positrons resulting from the decay of the positive pions, as well as the transport of the produced gamma-ray emission are considered. The distributions of the gamma rays as a function of atmospheric depth, time, emission angle, and photon energy are calculated and the dependence of these distributions on the model parameters are studied. The obtained angular distributions are not sufficiently anisotropic to account for the observed limb brightening of the greater than 10 MeV flare emission, indicating that the bulk of this emission is bremsstrahlung from primary electrons.

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

    SciTech Connect

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

    2011-07-10

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

  9. Flare Hybrids

    NASA Astrophysics Data System (ADS)

    Tomczak, M.; Dubieniecki, P.

    2015-12-01

    On the basis of the Solar Maximum Mission observations, Švestka ( Solar Phys. 121, 399, 1989) introduced a new class of flares, the so-called flare hybrids. When they start, they look like typical compact flares (phase 1), but later on, they look like flares with arcades of magnetic loops (phase 2). We summarize the characteristic features of flare hybrids in soft and hard X-rays as well as in the extreme ultraviolet; these features allow us to distinguish flare hybrids from other flares. In this article, additional energy release or long plasma cooling timescales are suggested as possible causes of phase 2. We estimate the frequency of flare hybrids, and study the magnetic configurations favorable for flare hybrid occurrence. Flare hybrids appear to be quite frequent, and the difference between the lengths of magnetic loops in the two interacting loop systems seem to be a crucial parameter for determining their characteristics.

  10. Standing Sausage Modes in Nonuniform Magnetic Tubes: An Inversion Scheme for Inferring Flare Loop Parameters

    NASA Astrophysics Data System (ADS)

    Chen, Shao-Xia; Li, Bo; Xiong, Ming; Yu, Hui; Guo, Ming-Zhe

    2015-10-01

    Standing sausage modes in flare loops are important for interpreting quasi-periodic pulsations (QPPs) in solar flare light curves. We propose an inversion scheme that consistently uses their periods P and damping times τ to diagnose flare loop parameters. We derive a generic dispersion relation governing linear sausage waves in pressure-less straight tubes, for which the transverse density inhomogeneity takes place in a layer of arbitrary width l and is of arbitrary form. We find that P and τ depend on the combination of [R/{v}{Ai},L/R,l/R,{ρ }{{i}}/{ρ }{{e}}], where R is the loop radius, L is the looplength, vAi is the internal Alfvén speed, and ρi/ρe is the density contrast. For all the density profiles examined, P and τ experience saturation when L/R ≫ 1, yielding an inversion curve in the [R/{v}{Ai},l/R,{ρ }{{i}}/{ρ }{{e}}] space with a specific density profile when L/R is sufficiently large. When applied to a spatially unresolved QPP event, the scheme yields that R/vAi is the best constrained, whereas l/R corresponds to the other extreme. For spatially resolved QPPs, while L/R ≫ 1 cannot be assumed beforehand, an inversion curve remains possible due to additional geometrical constraints. When a spatially resolved QPP event involves another mode, as is the case for a recent event, the full set of [{v}{Ai},l,{ρ }{{i}}/{ρ }{{e}}] can be inferred. We conclude that the proposed scheme provides a useful tool for magneto-seismologically exploiting QPPs.

  11. Large-scale Contraction and Subsequent Disruption of Coronal Loops During Various Phases of the M6.2 Flare Associated with the Confined Flux Rope Eruption

    NASA Astrophysics Data System (ADS)

    Kushwaha, Upendra; Joshi, Bhuwan; Veronig, Astrid M.; Moon, Yong-Jae

    2015-07-01

    We investigate evolutionary phases of an M6.2 flare and the associated confined eruption of a prominence. The pre-flare phase exhibits spectacular large-scale contraction of overlying extreme ultraviolet (EUV) coronal loops during which the loop system was subjected to an altitude decrease of ∼20 Mm (40% of the initial height) for an extended span of ∼30 minutes. This contraction phase is accompanied by sequential EUV brightenings associated with hard X-ray (HXR; up to 25 keV) and microwave (MW) sources from low-lying loops in the core region which together with X-ray spectra indicate strong localized heating in the source region before the filament activation. With the onset of the flare’s impulsive phase, we detect HXR and MW sources that exhibit intricate temporal and spatial evolution in relation to the fast rise of the prominence. Following the flare maximum, the filament eruption slowed down and subsequently became confined within the large overlying active region loops. During the confinement process of the erupting prominence, we detect MW emission from the extended coronal region with multiple emission centroids, which likely represent emission from hot blobs of plasma formed after the collapse of the expanding flux rope and entailing prominence material. RHESSI spectroscopy reveals high plasma temperature (∼30 MK) and substantial non-thermal characteristics (δ ∼ 5) during the impulsive phase of the flare. The time evolution of thermal energy exhibits a good correspondence with the variations in cumulative non-thermal energy, which suggests that the energy of accelerated particles is efficiently converted to hot flare plasma, implying an effective validation of the Neupert effect.

  12. Motion of 3-6 keV Nonthermal Sources Along the Legs of a Flare Loop

    NASA Technical Reports Server (NTRS)

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

    2007-01-01

    Observations of nonthermal X-ray sources me critical to studying electron acceleration and transport in solar flares. Strong thermal emission radiated from the preheated plasma before the flare impulsive phase often makes it difficult to detect low-energy X-ray sources that are produced by relatively low-energy nonthermal electrons. Knowledge of the distribution of these low-energy nonthermal electrons is particularly important in determining the total nonthermal electron energy in solar flares. We report on an 'early impulsive flare' in which impulsive hard X-ray emission was seen early in the flare before the soft X-ray emission had risen significantly, indicating limited plasma pre-heating. Early in the flare, RHESSI < 25 keV images show coronal sources that moved first downward and then upwards along the legs of a flare loop. In particular, the 3-6 keV source appeared as a single coronal source at the start of the flare, and then it involved into two coronal sources moving down along the two legs of the loop. After nearly reaching the two footpoints at the hard X-ray peak, the two sources moved back up to the looptop again. RHESSI images and light curves all indicate that nonthermal emission dominated at energies as low as 3-6 keV. We suggest that the evolution of both the spectral index and the low-energy cutoff of the injected electron distribution could result in the accelerated electrons reaching a lower altitude along the legs of the dense flare loop and hence result in the observed downward and upward motions of the nonthermal sources.

  13. Using Gamma-Ray and Neutron Emission to Determine Solar Flare Accelerated Particle Spectra and Composition and the Conditions within the Flare Magnetic Loop

    NASA Astrophysics Data System (ADS)

    Murphy, R. J.; Kozlovsky, Benzion; Share, G. H.; Hua, X.-M.; Lingenfelter, R. E.

    2007-01-01

    The measurable quantities associated with γ-ray and neutron observations of solar flares are nuclear-deexcitation line shapes, shifts, fluences, and time histories; neutron capture and annihilation line fluences and time histories; and energy-dependent escaping neutron fluence and time history. A comprehensive understanding of these quantities requires a model for ion acceleration, transport, and interaction. In this paper we address transport and interaction using a magnetic loop model that includes energy losses due to Coulomb collisions, removal by nuclear reactions, magnetic mirroring in the convergent flux tube, and MHD pitch-angle scattering in the corona. The accelerated ions are assumed to have a given kinetic energy spectrum and composition. Each measurable quantity depends to varying degree on the parameters of the loop model and of the accelerated ions. We explore these dependences in detail and construct a self-consistent approach to the analysis of high-energy flare data that provides an optimum set of parameters with meaningful uncertainties. To illustrate this approach, the calculations are applied in a comprehensive analysis of the γ-ray and neutron observations of the 1991 June 4 solar flare obtained with OSSE on CGRO. We find that the loop model can account for these observations with physically reasonable values for the parameters. In addition, our analysis of the neutron data shows that the accelerated ion spectrum for this flare was not an unbroken power law but had to steepen sharply above ~125 MeV nucleon-1. The paper also provides yields and yield ratios calculated with assumed abundances and spectral forms currently considered appropriate for solar flares. They can be used by other researchers analyzing high-energy solar flare data.

  14. Slow-Mode Oscillations of Hot Coronal Loops Excited at Flaring Footpoints

    NASA Astrophysics Data System (ADS)

    Wang, Tongjiang; Liu, W.; Ofman, L.; Davila, J. M.

    2011-05-01

    A large number of strongly damped oscillations in hot coronal loops have been observed by SOHO/SUMER in the past decade in Doppler shifts of flaring (>6 MK) lines (Fe XIX and Fe XXI). These oscillations with periods on the order of 10-30 min were interpreted as fundamental standing slow modes. They often manifest features such as recurrence and association with a flow (100-300 km/s) pulse preceding to the oscillation, which suggests that they are likely driven by microflares at the footpoints. With coordinated RHESSI observations, we have found a dozen such events supporting this conjecture. A typical event is presetned here. By analyzing RHESSI hard X-ray and GOES/SXI soft X-ray emissions as well as SUMER Doppler shifts, we identify the flare that triggers the loop oscillations. From RHESSI spectra, we measure physical parameters such as temperature, emission measure, and thermal/non-thermal energy contents as functions of time. We discuss the wave excitation mechanism based on these observations. Our results provide important observational constraints that can be used for improving theoretical models of magnetosonic wave excitation, and for coronal seismology.

  15. Effects of flare definitions on the statistics of derived flare distributions

    NASA Astrophysics Data System (ADS)

    Ryan, D. F.; Dominique, M.; Seaton, D.; Stegen, K.; White, A.

    2016-08-01

    The statistical examination of solar flares is crucial to revealing their global characteristics and behaviour. Such examinations can tackle large-scale science questions or give context to detailed single-event studies. However, they are often performed using standard but basic flare detection algorithms relying on arbitrary thresholds. This arbitrariness may lead to important scientific conclusions being drawn from results caused by subjective choices in algorithms rather than the true nature of the Sun. In this paper, we explore the effect of the arbitrary thresholds used in the Geostationary Operational Environmental Satellite (GOES) event list and Large Yield RAdiometer (LYRA) Flare Finder algorithms. We find that there is a small but significant relationship between the power law exponent of the GOES flare peak flux frequency distribution and the flare start thresholds of the algorithms. We also find that the power law exponents of these distributions are not stable, but appear to steepen with increasing peak flux. This implies that the observed flare size distribution may not be a power law at all. We show that depending on the true value of the exponent of the flare size distribution, this deviation from a power law may be due to flares missed by the flare detection algorithms. However, it is not possible determine the true exponent from GOES/XRS observations. Additionally we find that the PROBA2/LYRA flare size distributions are artificially steep and clearly non-power law. We show that this is consistent with an insufficient degradation correction. This means that PROBA2/LYRA should not be used for flare statistics or energetics unless degradation is adequately accounted for. However, it can be used to study variations over shorter timescales and for space weather monitoring.

  16. Modeling of Reflective Propagating Slow-mode Wave in a Flaring Loop

    NASA Astrophysics Data System (ADS)

    Fang, X.; Yuan, D.; Van Doorsselaere, T.; Keppens, R.; Xia, C.

    2015-11-01

    Quasi-periodic propagating intensity disturbances have been observed in large coronal loops in extreme ultraviolet images over a decade, and are widely accepted to be slow magnetosonic waves. However, spectroscopic observations from Hinode/EIS revealed their association with persistent coronal upflows, making this interpretation debatable. We perform a 2.5D magnetohydrodynamic simulation to imitate the chromospheric evaporation and the following reflected patterns in a flare loop. Our model encompasses the corona, transition region, and chromosphere. We demonstrate that the quasi periodic propagating intensity variations captured by the synthesized Solar Dynamics Observatory/Atmospheric Imaging Assembly 131, 94 Å emission images match the previous observations well. With particle tracers in the simulation, we confirm that these quasi periodic propagating intensity variations consist of reflected slow mode waves and mass flows with an average speed of 310 km s‑1 in an 80 Mm length loop with an average temperature of 9 MK. With the synthesized Doppler shift velocity and intensity maps of the Solar and Heliospheric Observatory/Solar Ultraviolet Measurement of Emitted Radiation Fe xix line emission, we confirm that these reflected slow mode waves are propagating waves.

  17. Simulating Reflective Propagating Slow-wave/flow in a Flaring Loop

    NASA Astrophysics Data System (ADS)

    Fang, X.

    2015-12-01

    Quasi-periodic propagating intensity disturbances have been observed in large coronal loops in EUV images over a decade, and are widely accepted to be slow magnetosonic waves. However, spectroscopic observations from Hinode/EIS revealed their association with persistent coronal upflows, making this interpretation debatable. We perform a 2.5D magnetohydrodynamic simulation to imitate the chromospheric evaporation and the following reflected patterns in a post flare loop. Our model encompasses the corona, transition region, and chromosphere. We demonstrate that the quasi periodic propagating intensity variations captured by our synthesized AIA 131, 94~Å~emission images match the previous observations well. With particle tracers in the simulation, we confirm that these quasi periodic propagating intensity variations consist of reflected slow mode waves and mass flows with an average speed of 310 km/s in an 80 Mm length loop with an average temperature of 9 MK. With the synthesized Doppler shift velocity and intensity maps in SUMER Fe XIX line emission, we confirm that these reflected slow mode waves are propagating waves.

  18. Bright EUV knots on post-flare loops: Are we seeing slow shocks?

    NASA Astrophysics Data System (ADS)

    Unverferth, John; Longcope, Dana; Reeves, Katharine

    2015-04-01

    Post flare loops imaged in the EUV sometimes show bright knots of emission at their apices. Knots from the loops in an arcade often line up to form a bar of coronal emission parallel to the polarity inversion line. These features have been variously interpreted as the results of colliding evaporation flows or volume enhancement at the point of weakest magnetic field. Here we consider the possibility that the features are produced through density enhancement resulting from shock compression during the reconnection process. We present simulations of thin flux tube dynamics following reconnection, which capture the essential physics of Petschek's fast reconnection model. The slow shock present during reconnection and subsequent retraction produce a high density region which persists even after the loop has achieved its ultimate equilibrium configuration. This high density produces enhanced emission at the bottom of the current sheet. Evaporation flows impinge on the high density region resulting in further enhancement to the density and the emission at the same position: the bottom of the current sheet. We compare these results to those from more conventional simulation where ad hoc heating drives evaporation from both feet.

  19. Flare-generated Shock Wave Propagation through Solar Coronal Arcade Loops and an Associated Type II Radio Burst

    NASA Astrophysics Data System (ADS)

    Kumar, Pankaj; Innes, D. E.; Cho, Kyung-Suk

    2016-09-01

    This paper presents multiwavelength observations of a flare-generated type II radio burst. The kinematics of the shock derived from the type II burst closely match a fast extreme ultraviolet (EUV) wave seen propagating through coronal arcade loops. The EUV wave was closely associated with an impulsive M1.0 flare without a related coronal mass ejection, and was triggered at one of the footpoints of the arcade loops in active region NOAA 12035. It was initially observed in the 335 Å images from the Atmospheric Image Assembly with a speed of ∼800 km s‑1 and it accelerated to ∼1490 km s‑1 after passing through the arcade loops. A fan–spine magnetic topology was revealed at the flare site. A small, confined filament eruption (∼340 km s‑1) was also observed moving in the opposite direction to the EUV wave. We suggest that breakout reconnection in the fan–spine topology triggered the flare and associated EUV wave that propagated as a fast shock through the arcade loops.

  20. Flare-generated Shock Wave Propagation through Solar Coronal Arcade Loops and an Associated Type II Radio Burst

    NASA Astrophysics Data System (ADS)

    Kumar, Pankaj; Innes, D. E.; Cho, Kyung-Suk

    2016-09-01

    This paper presents multiwavelength observations of a flare-generated type II radio burst. The kinematics of the shock derived from the type II burst closely match a fast extreme ultraviolet (EUV) wave seen propagating through coronal arcade loops. The EUV wave was closely associated with an impulsive M1.0 flare without a related coronal mass ejection, and was triggered at one of the footpoints of the arcade loops in active region NOAA 12035. It was initially observed in the 335 Å images from the Atmospheric Image Assembly with a speed of ˜800 km s‑1 and it accelerated to ˜1490 km s‑1 after passing through the arcade loops. A fan–spine magnetic topology was revealed at the flare site. A small, confined filament eruption (˜340 km s‑1) was also observed moving in the opposite direction to the EUV wave. We suggest that breakout reconnection in the fan–spine topology triggered the flare and associated EUV wave that propagated as a fast shock through the arcade loops.

  1. Hot spine loops and the nature of a late-phase solar flare

    SciTech Connect

    Sun, Xudong; Todd Hoeksema, J.; Liu, Yang; Aulanier, Guillaume; Su, Yingna; Hannah, Iain G.; Hock, Rachel A.

    2013-12-01

    The fan-spine magnetic topology is believed to be responsible for many curious features in solar explosive events. A spine field line links distinct flux domains, but direct observation of such a feature has been rare. Here we report a unique event observed by the Solar Dynamic Observatory where a set of hot coronal loops (over 10 MK) connected to a quasi-circular chromospheric ribbon at one end and a remote brightening at the other. Magnetic field extrapolation suggests that these loops are partly tracers of the evolving spine field line. Continuous slipping- and null-point-type reconnections were likely at work, energizing the loop plasma and transferring magnetic flux within and across the fan quasi-separatrix layer. We argue that the initial reconnection is of the 'breakout' type, which then transitioned to a more violent flare reconnection with an eruption from the fan dome. Significant magnetic field changes are expected and indeed ensued. This event also features an extreme-ultraviolet (EUV) late phase, i.e., a delayed secondary emission peak in warm EUV lines (about 2-7 MK). We show that this peak comes from the cooling of large post-reconnection loops beside and above the compact fan, a direct product of eruption in such topological settings. The long cooling time of the large arcades contributes to the long delay; additional heating may also be required. Our result demonstrates the critical nature of cross-scale magnetic coupling—topological change in a sub-system may lead to explosions on a much larger scale.

  2. SDO/AIA observations and model of standing waves in hot coronal loops excited by a flare

    NASA Astrophysics Data System (ADS)

    Wang, Tongjiang; Ofman, Leon; Provornikova, Elena; Davila, Joseph M.

    2014-06-01

    The strongly damped Doppler shift oscillations in hot coronal loops were first observed by SOHO/SUMER in flare lines formed at plasma temperature more than 6 MK. They were mainly interpreted as the standing slow magnetosonic waves excited by impulsive energy release at the loop’s footpoint based on the measured properties and on MHD modeling results. Longitudinal waves with similar properties have been recently observed by SDO/AIA in active region loops. In this study, we report a new event that exhibited the flare-excited intensity disturbances propagating back and forth in a hot coronal loop imaged by AIA in 131 bandpass. We measure the physical parameters of the wave and loop plasma, determine the loop geometry, and explore the triggering mechanism. We identify the wave modes (propagating or standing waves) based on these measurements and on 3D MHD modeling. A loop model is constructed with enhanced density in a hydrostatic equilibrium following potential or force-free magnetic field lines extrapolated from the photospheric magnetic field data observed by SDO/HMI. We also discuss the applications of coronal seismology to this event.

  3. Where is the chromospheric response to conductive energy input from a hot pre-flare coronal loop?

    SciTech Connect

    Battaglia, Marina; Fletcher, Lyndsay; Simões, Paulo J. A.

    2014-07-01

    Before the onset of a flare is observed in hard X-rays, there is often a prolonged pre-flare or pre-heating phase with no detectable hard X-ray emission but pronounced soft X-ray emission, which suggests that energy is already being released and deposited into the corona and chromosphere at this stage. This work analyzes the temporal evolution of coronal source heating and the chromospheric response during this pre-heating phase to investigate the origin and nature of early energy release and transport during a solar flare. Simultaneous X-ray, EUV, and microwave observations of a well-observed flare with a prolonged pre-heating phase are analyzed to study the time evolution of the thermal emission and to determine the onset of particle acceleration. During the 20 minute duration of the pre-heating phase we find no hint of accelerated electrons in either hard X-rays or microwave emission. However, the total energy budget during the pre-heating phase suggests that energy must be supplied to the flaring loop to sustain the observed temperature and emission measure. Under the assumption of this energy being transported toward the chromosphere via thermal conduction, significant energy deposition at the chromosphere is expected. However, no detectable increase of the emission in the AIA wavelength channels sensitive to chromospheric temperatures is observed. The observations suggest energy release and deposition in the flaring loop before the onset of particle acceleration, yet a model in which energy is conducted to the chromosphere and subsequent heating of the chromosphere is not supported by the observations.

  4. CHROMOSPHERIC EVAPORATION IN SOLAR FLARE LOOP STRANDS OBSERVED WITH THE EXTREME-ULTRAVIOLET IMAGING SPECTROMETER ON BOARD HINODE

    SciTech Connect

    Brosius, Jeffrey W.

    2013-01-10

    The entire profile of the Fe XXIII line at 263.8 A, formed at temperature Almost-Equal-To 14 MK, was blueshifted by an upward velocity -122 {+-} 33 km s{sup -1} when it was first detected by the Extreme-ultraviolet Imaging Spectrometer operating in rapid cadence (11.18 s) stare mode during a C1 solar flare. The entire profile became even more blueshifted over the next two exposures, when the upward velocity reached its maximum of -208 {+-} 14 km s{sup -1} before decreasing to zero over the next 12 exposures. After that, a weak, secondary blueshifted component appeared for five exposures, reached a maximum upward velocity of -206 {+-} 33 km s{sup -1}, and disappeared after the maximum line intensity (stationary plus blueshifted) was achieved. Velocities were measured relative to the intense stationary profile observed near the flare's peak and early during its decline. The initial episode during which the entire profile was blueshifted lasted about 156 s, while the following episode during which a secondary blueshifted component was detected lasted about 56 s. The first episode likely corresponds to chromospheric evaporation in a single loop strand, while the second corresponds to evaporation in an additional strand, as described in multi-strand flare loop models proposed by Hori et al. and Warren and Doschek. Line emission from progressively cooler ions (Fe XVII, XVI, and XIV) brightened at successively later times, consistent with cooling of flare-heated plasma.

  5. THE SPECIFIC ACCELERATION RATE IN LOOP-STRUCTURED SOLAR FLARES-IMPLICATIONS FOR ELECTRON ACCELERATION MODELS

    SciTech Connect

    Guo, Jingnan; Emslie, A. Gordon; Piana, Michele E-mail: piana@dima.unige.it

    2013-03-20

    We analyze electron flux maps based on RHESSI hard X-ray imaging spectroscopy data for a number of extended coronal-loop flare events. For each event, we determine the variation of the characteristic loop length L with electron energy E, and we fit this observed behavior with models that incorporate an extended acceleration region and an exterior 'propagation' region, and which may include collisional modification of the accelerated electron spectrum inside the acceleration region. The models are characterized by two parameters: the plasma density n in, and the longitudinal extent L{sub 0} of, the acceleration region. Determination of the best-fit values of these parameters permits inference of the volume that encompasses the acceleration region and of the total number of particles within it. It is then straightforward to compute values for the emission filling factor and for the specific acceleration rate (electrons s{sup -1} per ambient electron above a chosen reference energy). For the 24 events studied, the range of inferred filling factors is consistent with a value of unity. The inferred mean value of the specific acceleration rate above E{sub 0} = 20 keV is {approx}10{sup -2} s{sup -1}, with a 1{sigma} spread of about a half-order-of-magnitude above and below this value. We compare these values with the predictions of several models, including acceleration by large-scale, weak (sub-Dreicer) fields, by strong (super-Dreicer) electric fields in a reconnecting current sheet, and by stochastic acceleration processes.

  6. Influence of magnetic field structure on the conduction cooling of flare loops

    NASA Technical Reports Server (NTRS)

    Antiochos, S. K.; Sturrock, P. A.

    1976-01-01

    A simple model facilitates calculation of the influence of magnetic-field configuration on the conduction cooling rate of a hot post-flare coronal plasma. The magnetic field is taken to be that produced by a line dipole or point dipole at an arbitrary depth below the chromosphere. For the high temperatures (at least 10 million K) produced by flares, the plasma may remain static and isobaric. The influence of the field is such as to increase the heat flux (per unit area) into the chromosphere, but to decrease the total conduction cooling of the flare plasma. This leads to a significant enhancement of the total energy radiated by the flare plasma.

  7. TEMPORAL VARIATIONS OF X-RAY SOLAR FLARE LOOPS: LENGTH, CORPULENCE, POSITION, TEMPERATURE, PLASMA PRESSURE, AND SPECTRA

    SciTech Connect

    Jeffrey, Natasha L. S.; Kontar, Eduard P.

    2013-04-01

    The spatial and spectral properties of three solar flare coronal X-ray loops are studied before, during, and after the peak X-ray emission. Using observations from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), we deduce the temporal changes in emitting X-ray length, corpulence, volume, position, number density, and thermal pressure. We observe a decrease in the loop length, width, and volume before the X-ray peak, and an increasing number density and thermal pressure. After the X-ray peak, volume increases and loop corpulence grows due to increasing width. The volume variations are more pronounced than the position variations, often known as magnetic field line contraction. We believe this is the first dedicated study examining the temporal evolution of X-ray loop lengths and widths. Collectively, the observations also show for the first time three temporal phases given by peaks in temperature, X-ray emission, and thermal pressure, with the minimum volume coinciding with the X-ray peak. Although the volume of the flaring plasma decreases before the peak in X-ray emission, the relationship between temperature and volume does not support simple compressive heating in a collapsing magnetic trap model. Within a low {beta} plasma, shrinking loop widths perpendicular to the guiding field can be explained by squeezing the magnetic field threading the region. Plasma heating leads to chromospheric evaporation and growing number density. This produces increasing thermal pressure and decreasing loop lengths as electrons interact at shorter distances and we believe after the X-ray peak, the increasing loop corpulence.

  8. Origins and effects of solar flares

    SciTech Connect

    Rust, D.M. ||

    1993-12-31

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

  9. Evaporative cooling of flare plasma

    NASA Technical Reports Server (NTRS)

    Antiochos, S. K.; Sturrock, P. A.

    1978-01-01

    We investigate a one-dimensional loop model for the evaporative cooling of the coronal flare plasma. The important assumptions are that conductive losses dominate radiative cooling and that the evaporative velocities are small compared with the sound speed. We calculate the profile and evolution of the temperature and verify the accuracy of our assumptions for plasma parameters typical of flare regions. The model is in agreement with soft X-ray observations on the evolution of flare temperatures and emission measures. The effect of evaporation is to greatly reduce the conductive heat flux into the chromosphere and to enhance the EUV emission from the coronal flare plasma.

  10. Using coronal loops to reconstruct the magnetic field of an active region before and after a major flare

    SciTech Connect

    Malanushenko, A.; Schrijver, C. J.; DeRosa, M. L.; Wheatland, M. S.

    2014-03-10

    The shapes of solar coronal loops are sensitive to the presence of electrical currents that are the carriers of the non-potential energy available for impulsive activity. We use this information in a new method for modeling the coronal magnetic field of active region (AR) 11158 as a nonlinear force-free field (NLFFF). The observations used are coronal images around the time of major flare activity on 2011 February 15, together with the surface line-of-sight magnetic field measurements. The data are from the Helioseismic and Magnetic Imager and Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. The model fields are constrained to approximate the coronal loop configurations as closely as possible, while also being subject to the force-free constraints. The method does not use transverse photospheric magnetic field components as input and is thereby distinct from methods for modeling NLFFFs based on photospheric vector magnetograms. We validate the method using observations of AR 11158 at a time well before major flaring and subsequently review the field evolution just prior to and following an X2.2 flare and associated eruption. The models indicate that the energy released during the instability is about 1 × 10{sup 32} erg, consistent with what is needed to power such a large eruptive flare. Immediately prior to the eruption, the model field contains a compact sigmoid bundle of twisted flux that is not present in the post-eruption models, which is consistent with the observations. The core of that model structure is twisted by ≈0.9 full turns about its axis.

  11. Modelling the effects of a solar flare on INTEGRAL

    NASA Astrophysics Data System (ADS)

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

    2001-09-01

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

  12. Closed coronal structures. V - Gasdynamic models of flaring loops and comparison with SMM observations

    NASA Technical Reports Server (NTRS)

    Peres, G.; Serio, S.; Vaiana, G.; Acton, L.; Leibacher, J.; Rosner, R.; Pallavicini, R.

    1983-01-01

    A time-dependent one-dimensional code incorporating energy, momentum and mass conservation equations, and taking the entire solar atmospheric structure into account, is used to investigate the hydrodynamic response of confined magnetic structures to strong heating perturbations. Model calculation results are compared with flare observations which include the light curves of spectral lines formed over a wide range of coronal flare temperatures, as well as determinations of Doppler shifts for the high temperature plasma. It is shown that the numerical simulation predictions are in good overall agreement with the observed flare coronal plasma evolution, correctly reproducing the temporal profile of X-ray spectral lines and their relative intensities. The predicted upflow velocities support the interpretation of the blueshifts as due to evaporation of chromospheric material.

  13. Effects of Solar Flares on Earth and Mars

    NASA Astrophysics Data System (ADS)

    Mendillo, M.; Withers, P.

    2006-05-01

    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 1998; recent analyses have shown large electron density enhancements to be due unambiguously to flares. In this paper, we will review briefly the types of flare effects seen in the Earth's ionosphere, and relate them to the EUV and X-ray flare emissions that cause enhancements to the F-layer's total electron content (TEC) and to the E-layer's peak density, respectively. We will contrast these with effects now being seen at Mars, assessing both TEC variations and changes in Mars' secondary ionospheric layer. The different roles of ionization by photo-electrons at the two planets are major factors in understanding solar-terrestrial-martian relationships.

  14. Solar and Stellar Flares over Time: Effects on Hosted Planets

    NASA Astrophysics Data System (ADS)

    Guinan, Edward F.; DeWarf, Laurence E.; Engle, Scott G.; Gropp, Jeffrey

    2016-01-01

    The effects of flares from the Sun on Earth and other solar-system planets are presented. Also discussed are the flare properties of cooler, commonplace main-sequence K-M stars. Data from our "Sun in Time" program are used to study the flare properties of the Sun and solar-type stars from youth to old age. These studies are based on ground-based observations, UV and X-ray space missions (IUE & HST, ROSAT & Chandra) as well as a wealth of data from the Kepler Mission. The ultra-high precision photometry available from the Kepler Mission (and K2) has made it possible to study starspots, flare properties, and rotations of thousands of G, K, M stars. Superflares (defined as E > 10+33 ergs ~X-100 flares) on hundreds of mostly G and K stars have been found. (See e.g. Shibayama et al. 2013; Maehara et al. 2015; Notsu et al. 2013/15; Saar et al. 2015; Guinan et al. 2015). Using our Age-Rotation relations, we determine correlations of flares properties of the Sun and solar-type over a wide range of ages. We also compare these flare histories with the cooler, more common K- and M-type stars. The analysis of these datasets imply that the young Sun had numerous, very powerful flares that may have played major roles the evolution of the early atmospheres of Earth and other terrestrial planets. The strong X-UV fluxes and proton fluences from flares and associated plasmas from coronal mass ejection events can greatly affect the photochemistry of planetary atmospheres as well as ionizing and possibly eroding their atmospheres. Some examples are given. Also discussed are the effects of superflares from the present Sun on the Earth. Even though solar superflares are rarer (~1 per 300-500 yrs) than from the young Sun (> 1-2 per year), they could cause significant damage to our communication and satellite systems, electrical networks, and threaten the lives of astronauts in space..This research is supported by grants from NSF/RUI and NASA: NSF, AST 1009903; Chandra GO2-13020X, HST GO

  15. Solar Flare Effects on the Thermosphere and Ionosphere

    NASA Astrophysics Data System (ADS)

    Solomon, S.; Qian, L.; Rodgers, E.; Bailey, S.

    The Solar Extreme-ultraviolet Experiment SEE on the TIMED satellite and by the X-ray Photometer System XPS on the SORCE satellite provide the first comprehensive irradiance measurements of the complete solar spectrum during large solar flares However the soft X-ray portion of these observations are performed using silicon photodiodes coated with metallic filters to provide photometric measurements with multiple band passes which leads to complexities in obtaining spectral information A new analysis technique developed specifically for flare conditions is used to infer flare spectra in this region These are combined with spectrographic measurements in the extreme ultraviolet and far ultraviolet and applied to the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model TIE-GCM The electron content neutral density and airglow response to large flares during the declining phase of solar cycle 23 are calculated using this model and compared to several measurement sets obtaining good agreement This supports both the validity of the solar X-ray analysis and the modeling methodology showing that although flare-driven effects in the upper atmosphere are significant they are shorter and of much smaller magnitude than geomagnetic disturbances

  16. Evidence of Thermal Conduction Suppression in a Solar Flaring Loop by Coronal Seismology of Slow-mode Waves

    NASA Astrophysics Data System (ADS)

    Wang, Tongjiang; Ofman, Leon; Sun, Xudong; Provornikova, Elena; Davila, Joseph M.

    2015-09-01

    Analysis of a longitudinal wave event observed by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory is presented. A time sequence of 131 Å images reveals that a C-class flare occurred at one footpoint of a large loop and triggered an intensity disturbance (enhancement) propagating along it. The spatial features and temporal evolution suggest that a fundamental standing slow-mode wave could be set up quickly after meeting of two initial disturbances from the opposite footpoints. The oscillations have a period of ˜12 minutes and a decay time of ˜9 minutes. The measured phase speed of 500 ± 50 km s‑1 matches the sound speed in the heated loop of ˜10 MK, confirming that the observed waves are of slow mode. We derive the time-dependent temperature and electron density wave signals from six AIA extreme-ultraviolet channels, and find that they are nearly in phase. The measured polytropic index from the temperature and density perturbations is 1.64 ± 0.08 close to the adiabatic index of 5/3 for an ideal monatomic gas. The interpretation based on a 1D linear MHD model suggests that the thermal conductivity is suppressed by at least a factor of 3 in the hot flare loop at 9 MK and above. The viscosity coefficient is determined by coronal seismology from the observed wave when only considering the compressive viscosity dissipation. We find that to interpret the rapid wave damping, the classical compressive viscosity coefficient needs to be enhanced by a factor of 15 as the upper limit.

  17. Effects of solar flares on the ionosphere of Mars.

    PubMed

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

    2006-02-24

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

  18. Plasma motions and non-thermal line broadening in flaring twisted coronal loops

    NASA Astrophysics Data System (ADS)

    Gordovskyy, M.; Kontar, E. P.; Browning, P. K.

    2016-05-01

    Context. Observation of coronal extreme ultra-violet (EUV) spectral lines sensitive to different temperatures offers an opportunity to evaluate the thermal structure and flows in flaring atmospheres. This, in turn, can be used to estimate the partitioning between the thermal and kinetic energies released in flares. Aims: Our aim is to forward-model large-scale (50-10 000 km) velocity distributions to interpret non-thermal broadening of different spectral EUV lines observed in flares. The developed models allow us to understand the origin of the observed spectral line shifts and broadening, and link these features to particular physical phenomena in flaring atmospheres. Methods: We use ideal magnetohydrodynamics (MHD) to derive unstable twisted magnetic fluxtube configurations in a gravitationally stratified atmosphere. The evolution of these twisted fluxtubes is followed using resistive MHD with anomalous resistivity depending on the local density and temperature. The model also takes thermal conduction and radiative losses in the continuum into account. The model allows us to evaluate average velocities and velocity dispersions, which would be interpreted as non-thermal velocities in observations, at different temperatures for different parts of the models. Results: Our models show qualitative and quantitative agreement with observations. Thus, the line-of-sight (LOS) velocity dispersions demonstrate substantial correlation with the temperature, increasing from about 20-30 km s-1 around 1 MK to about 200-400 km s-1 near 10-20 MK. The average LOS velocities also correlate with velocity dispersions, although they demonstrate a very strong scattering compared to the observations. We also note that near footpoints the velocity dispersions across the magnetic field are systematically lower than those along the field. We conclude that the correlation between the flow velocities, velocity dispersions, and temperatures are likely to indicate that the same heating

  19. Solar flare model atmospheres

    NASA Technical Reports Server (NTRS)

    Hawley, Suzanne L.; Fisher, George H.

    1993-01-01

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

  20. Effect of flares on the chemical composition of exoplanets atmospheres

    NASA Astrophysics Data System (ADS)

    Venot, O.; Decin, L.

    2015-10-01

    M stars are very abundant in our Galaxy, and very likely harbour the majority of planetary systems. But a particularity of M stars is that they are the most active class of stars. Indeed, they experience stellar variability such as flares. These violent and unpredictable outbursts originate from the photosphere and are caused by magnetic processus. During such an event, the energy emitted by the star can vary by several orders of magnitude for the whole wavelength range. It results in an enhancement of the H# emission and of the continuum. Different studies on the effect of flares on exoplanets have already been conducted [1, 2]. Here we are interested in the effect of a flare on the atmospheric composition of a warm Neptune orbiting around an M star. Using the stellar flux of AD Leo recorded during a flare event [1] and the chemical model of [3], we have studied the impact on the atmosphere. We have also computed the synthetic spectra assuming that such an event occurs during a transit. We will present these results.

  1. Evaporative cooling of flare plasma

    NASA Technical Reports Server (NTRS)

    Antiochos, S. K.; Sturrock, P. A.

    1976-01-01

    A one-dimensional loop model for the evaporative cooling of the coronal flare plasma was investigated. Conductive losses dominated radiative cooling, and the evaporative velocities were small compared to the sound speed. The profile and evolution of the temperature were calculated. The model was in agreement with soft X-ray observations on the evolution of flare temperatures and emission measures. The effect of evaporation was to greatly reduce the conductive heat flux into the chromosphere and to enhance the EUV emission from the coronal flare plasma.

  2. Non-thermal Motions in and Above Flare Loop Tops Measured by the Extreme-ultraviolet Imaging Spectrometer (EIS) on Hinode

    NASA Astrophysics Data System (ADS)

    Doschek, George A.; McKenzie, David Eugene; Warren, Harry P

    2014-06-01

    The plasma volume above the soft X-ray emitting loop tops is of particular interest for studying the formation of flare loops. We present EIS observations of non-thermal motions (turbulence) determined from spectral line profiles of Fe XXIII and Fe XXIV ions for three well-observed flares near the solar limb. We compare the non-thermal motions at temperatures near 10 MK with the motions along the same lines-of-sight determined from lines of coronal ions such as Fe XII, Fe XIV, and Fe XV formed at 1-2 MK. The take-away is that the non-thermal motions obtained from Fe XXIII and Fe XXIV lines increase with height towards the reconnection region, up to speeds of about 50-60 km/s for the largest heights that we can observe. The implication is that considerable plasma heating occurs outside the reconnection region. In addition, we discuss the implications of results obtained for flares from earlier X-ray Yohkoh observations of line profiles of Fe XXV and Ca XIX on the current results from EIS and AIA. Fe XXV is formed at significantly higher temperatures than any strong flare EUV spectral line observed by EIS or by imaging telescopes such as AIA or TRACE. This work is supported by NASA grants.

  3. Effects of time delay and pitch control sensitivity in the flared landing

    NASA Technical Reports Server (NTRS)

    Berthe, C. J.; Chalk, C. R.; Wingarten, N. C.; Grantham, W.

    1986-01-01

    Between December 1985 and January 1986, a flared landing program was conducted, using the USAF Total In-Flight simulator airplane, to examine time delay effects in a formal manner. Results show that as pitch sensitivity is increased, tolerance to time delay decreases. With the proper selection of pitch sensitivity, Level I performance was maintained with time delays ranging from 150 milliseconds to greater than 300 milliseconds. With higher sensitivity, configurations with Level I performance at 150 milliseconds degraded to level 2 at 200 milliseconds. When metrics of time delay and pitch sensitivity effects are applied to enhance previously developed predictive criteria, the result is an improved prediction technique which accounts for significant closed loop items.

  4. The universal one-loop effective action

    NASA Astrophysics Data System (ADS)

    Drozd, Aleksandra; Ellis, John; Quevillon, Jérémie; You, Tevong

    2016-03-01

    We present the universal one-loop effective action for all operators of dimension up to six obtained by integrating out massive, non-degenerate multiplets. Our general expression may be applied to loops of heavy fermions or bosons, and has been checked against partial results available in the literature. The broad applicability of this approach simplifies one-loop matching from an ultraviolet model to a lower-energy effective field theory (EFT), a procedure which is now reduced to the evaluation of a combination of matrices in our universal expression, without any loop integrals to evaluate. We illustrate the relationship of our results to the Standard Model (SM) EFT, using as an example the supersymmetric stop and sbottom squark Lagrangian and extracting from our universal expression the Wilson coefficients of dimension-six operators composed of SM fields.

  5. Effects of X-ray flares on the aeronomy of Mars: Simultaneous measurements of ionospheric effects of X-ray flares on Earth and Mars

    NASA Astrophysics Data System (ADS)

    Haider, Syed A.; Machado Santos, Angela; Abdu, Mangalathayil A.; Batista, Inez S.; Shah, Siddhi Y.; Thirupathaiah, P.

    2016-07-01

    MIRI: Validation and Testing Requirements We have studied X-ray aeronomy in the ionospheric E region of Mars during six X-ray flares that occurred on 28 March and 6 April, 2001; 17,18 March and 21 April, 2003 and 19 February, 2005 respectively. These flares were responded by the corresponding electron density profiles of Mars Global Surveyor (MGS). The time series of photoionization rate, photoelectron impact ionization rate, photoelectron flux, ion density, electron density and total Electron Content (TEC) are predicted for each flare day. The estimated production rate, flux and densities are increased by 1-2 orders of magnitude due to effects of these flares in the E region ionosphere of Mars. The normalized estimated TEC are compared with the normalized measured TEC of MGS profiles. At the peak flare time the normalized estimated and normalized measured TEC were enhanced by a factor of 5-10 and 2 respectively. The effects of these flares were also registered in the D region equatorial ionosphere of Earth at Fortaleza observatory. The flares of 6 April, 2001, 17 March and 21 April, 2003 also produced electron density enhancement in the E region ionosphere of Earth at College AK and Cachoeira Paulista observatories. The minimum frequency fmin, recorded in ionogram, increased by 100% (due to D region absorption) while the foE increased by 20%, in the Earth's ionosphere.

  6. Heat transport in steep temperature gradients. I - Small flaring solar loops

    NASA Technical Reports Server (NTRS)

    Smith, D. F.

    1986-01-01

    Results on nonlocal heat transport which properly takes into account the presence of fast electrons with mean free paths much longer than the temperature scale height L are reviewed. In terms of the mean free path for the slow bulk electrons, lambda(s), the nonlocal effects are important whenever lambda(s)/L greater than 0.001, with the following consequences. The heat flux in the hot part of the gradient is reduced relative to the Spitzer-Haerm value q(SH) which does not take into account the heat carried away by the fast electrons. The heat flux in the cold part of the gradient is enhanced relative to the value q(SH) which does not take into account the heat deposited by the fast electrons. These quite general results, which should have several applications in astrophysics, are applied to the problem of thermal hard X-ray burst models. It is shown that heat is not bottled up as effectively as in some past models, and temperatures achieved for realistic energy input rates are consequently not as high. As a result such sources can be effective only in the soft part (10-30 keV) of the hard X-ray range for energy input rates up to 6,400 ergs/cu cm s. The analysis is based on a fluid model and does not consider the X-ray signature of fast electrons which escape to distances far beyond the conduction fronts formed. It is shown that such electrons could at most be effective in the soft part of the hard X-ray range.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  8. FLARES PRODUCING WELL-ORGANIZED POST-FLARE ARCADES (SLINKIES) HAVE EARLY PRECURSORS

    SciTech Connect

    Ryutova, M. P.

    2011-06-01

    Exploding loop systems producing X-ray flares often, but not always, bifurcate into a long-living, well-organized system of multi-threaded loop arcades resembling solenoidal slinkies. The physical conditions that cause or prevent this process are not known. To address this problem, we examined most of the major (X-class) flares that occurred during the last decade and found that the flares that bifurcate into long-living slinky arcades have different signatures than those that do not 'produce' such structures. The most striking difference is that, in all cases of slinky formation, GOES high energy proton flux becomes significantly enhanced 10-24 hr before the flare occurs. No such effect was found prior to the 'non-slinky' flares. This fact may be associated with the difference between energy production by a given active region and the amount of energy required to bring the entire system into the form of well-organized, self-similar loop arcades. As an example illustrating the process of post-flare slinky formation, we present observations taken with the Hinode satellite, in several wavelengths, showing a time sequence of pre-flare and flare activity, followed by the formation of dynamically stable, well-organized structures. One of the important features revealed is that post-flare coronal slinky formation is preceded by scale invariant structure formation in the underlying chromosphere/transition region. We suggest that the observed regularities can be understood within the framework of self-organized critical dynamics characterized by scale invariant structure formation with critical parameters largely determined by energy saturation level. The observed regularities per se may serve as a long-term precursor of strong flares and may help to study predictability of system behavior.

  9. Solar and Stellar Flares and Their Effects on Planets

    NASA Astrophysics Data System (ADS)

    Shibata, Kazunari

    2015-08-01

    Recent space observations of the Sun revealed that the solar atmosphere is full of explosions, such as flares and flare-like phenomena. These flares generate not only strong electromagnetic emissions but also nonthermal particles and bulk plasma ejections, which sometimes lead to geomagnetic storms and affect terrestrial environment and our civilization, damaging satellite, power-grids, radio communication etc. Solar flares are prototype of various explosions in our universe, and hence are important not only for geophysics and environmental science but also for astrophysics. The energy source of solar flares is now established to be magnetic energy stored near sunspots. There is now increasing observational evidence that solar flares are caused by magnetic reconnection, merging of anti-parallel magnetic field lines and associated magneto-plasma dynamics (Shibata and Magara 2011, Living Review). It has also been known that many stars show flares similar to solar flares, and often such stellar flares are much more energetic than solar flares. The total energy of a solar flare is typically 10^29 - 10^32 erg. On the other hand, there are much more energetic flares (10^33 - 10^38 erg) in stars, especially in young stars. These are called superflares. We argue that these superflares on stars can also be understood in a unified way based on the reconnection mechanism. Finally we show evidence of occurrence of superflares on Sun-like stars according to recent stellar observations (Maehara et al. 2012, Nature, Shibayama et al. 2013), which revealed that superflares with energy of 10^34 - 10^35 erg (100 - 1000 times of the largest solar flares) occur with frequency of once in 800 - 5000 years on Sun-like stars which are very similar to our Sun. Against the previous belief, these new observations as well as theory (Shibata et al. 2013) suggest that we cannot deny the possibility of superflares on the present Sun. Finally, we shall discuss possible impacts of these superflares

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

    NASA Technical Reports Server (NTRS)

    Das, Uma; Pallamraju, Duggirala; Chakrabarti, Supriya

    2010-01-01

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

  11. String theory effective action; String loop corrections

    SciTech Connect

    Tseytlin, A.A. )

    1988-01-01

    The authors discuss the general ideology of the computation of string loop corrections to the effective action for the massless modes of the string. Both the S-matrix and the sigma-model approaches are presented. It is emphasized that the effective action is more general and better defined object than the S-matrix. In particular, it is finite in spite of modular infinities that may be present in loop amplitudes computed near a wrong vacuum. The case of the disc topology in the open-closed string theory is treated in some detail. Some issues concerning the soft dilation vertex operators related to the infinities of the string amplitudes are discussed.

  12. Effects of camera location on the reconstruction of 3D flare trajectory with two cameras

    NASA Astrophysics Data System (ADS)

    Özsaraç, Seçkin; Yeşilkaya, Muhammed

    2015-05-01

    Flares are used as valuable electronic warfare assets for the battle against infrared guided missiles. The trajectory of the flare is one of the most important factors that determine the effectiveness of the counter measure. Reconstruction of the three dimensional (3D) position of a point, which is seen by multiple cameras, is a common problem. Camera placement, camera calibration, corresponding pixel determination in between the images of different cameras and also the triangulation algorithm affect the performance of 3D position estimation. In this paper, we specifically investigate the effects of camera placement on the flare trajectory estimation performance by simulations. Firstly, 3D trajectory of a flare and also the aircraft, which dispenses the flare, are generated with simple motion models. Then, we place two virtual ideal pinhole camera models on different locations. Assuming the cameras are tracking the aircraft perfectly, the view vectors of the cameras are computed. Afterwards, using the view vector of each camera and also the 3D position of the flare, image plane coordinates of the flare on both cameras are computed using the field of view (FOV) values. To increase the fidelity of the simulation, we have used two sources of error. One is used to model the uncertainties in the determination of the camera view vectors, i.e. the orientations of the cameras are measured noisy. Second noise source is used to model the imperfections of the corresponding pixel determination of the flare in between the two cameras. Finally, 3D position of the flare is estimated using the corresponding pixel indices, view vector and also the FOV of the cameras by triangulation. All the processes mentioned so far are repeated for different relative camera placements so that the optimum estimation error performance is found for the given aircraft and are trajectories.

  13. One-loop effective lagrangians after matching

    NASA Astrophysics Data System (ADS)

    del Aguila, F.; Kunszt, Z.; Santiago, J.

    2016-05-01

    We discuss the limitations of the covariant derivative expansion prescription advocated to compute the one-loop Standard Model (SM) effective lagrangian when the heavy fields couple linearly to the SM. In particular, one-loop contributions resulting from the exchange of both heavy and light fields must be explicitly taken into account through matching because the proposed functional approach alone does not account for them. We review a simple case with a heavy scalar singlet of charge -1 to illustrate the argument. As two other examples where this matching is needed and this functional method gives a vanishing result, up to renormalization of the heavy sector parameters, we re-evaluate the one-loop corrections to the T-parameter due to a heavy scalar triplet with vanishing hypercharge coupling to the Brout-Englert-Higgs boson and to a heavy vector-like quark singlet of charged 2 / 3 mixing with the top quark, respectively. In all cases we make use of a new code for matching fundamental and effective theories in models with arbitrary heavy field additions.

  14. Leptogenesis from loop effects in curved spacetime

    NASA Astrophysics Data System (ADS)

    McDonald, Jamie I.; Shore, Graham M.

    2016-04-01

    We describe a new mechanism — radiatively-induced gravitational leptogenesis — for generating the matter-antimatter asymmetry of the Universe. We show how quantum loop effects in C and CP violating theories cause matter and antimatter to propagate differently in the presence of gravity, and prove this is forbidden in flat space by CPT and translation symmetry. This generates a curvature-dependent chemical potential for leptons, allowing a matter-antimatter asymmetry to be generated in thermal equilibrium in the early Universe. The time-dependent dynamics necessary for leptogenesis is provided by the interaction of the virtual self-energy cloud of the leptons with the expanding curved spacetime background, which violates the strong equivalence principle and allows a distinction between matter and antimatter. We show here how this mechanism is realised in a particular BSM theory, the see-saw model, where the quantum loops involve the heavy sterile neutrinos responsible for light neutrino masses. We demonstrate by explicit computation of the relevant two-loop Feynman diagrams how the size of the radiative corrections relevant for leptogenesis becomes enhanced by increasing the mass hierarchy of the sterile neutrinos, and show how the induced lepton asymmetry may be sufficiently large to play an important rôle in determining the baryon-to-photon ratio of the Universe.

  15. Generalized effective description of loop quantum cosmology

    NASA Astrophysics Data System (ADS)

    Ashtekar, Abhay; Gupt, Brajesh

    2015-10-01

    The effective description of loop quantum cosmology (LQC) has proved to be a convenient platform to study phenomenological implications of the quantum bounce that resolves the classical big bang singularity. Originally, this description was derived using Gaussian quantum states with small dispersions. In this paper we present a generalization to incorporate states with large dispersions. Specifically, we derive the generalized effective Friedmann and Raychaudhuri equations and propose a generalized effective Hamiltonian which are being used in an ongoing study of the phenomenological consequences of a broad class of quantum geometries. We also discuss an interesting interplay between the physics of states with larger dispersions in standard LQC, and of sharply peaked states in (hypothetical) LQC theories with larger area gap.

  16. The flare kernel in the impulsive phase

    NASA Technical Reports Server (NTRS)

    Dejager, C.

    1986-01-01

    The impulsive phase of a flare is characterized by impulsive bursts of X-ray and microwave radiation, related to impulsive footpoint heating up to 50 or 60 MK, by upward gas velocities (150 to 400 km/sec) and by a gradual increase of the flare's thermal energy content. These phenomena, as well as non-thermal effects, are all related to the impulsive energy injection into the flare. The available observations are also quantitatively consistent with a model in which energy is injected into the flare by beams of energetic electrons, causing ablation of chromospheric gas, followed by convective rise of gas. Thus, a hole is burned into the chromosphere; at the end of impulsive phase of an average flare the lower part of that hole is situated about 1800 km above the photosphere. H alpha and other optical and UV line emission is radiated by a thin layer (approx. 20 km) at the bottom of the flare kernel. The upward rising and outward streaming gas cools down by conduction in about 45 s. The non-thermal effects in the initial phase are due to curtailing of the energy distribution function by escape of energetic electrons. The single flux tube model of a flare does not fit with these observations; instead we propose the spaghetti-bundle model. Microwave and gamma-ray observations suggest the occurrence of dense flare knots of approx. 800 km diameter, and of high temperature. Future observations should concentrate on locating the microwave/gamma-ray sources, and on determining the kernel's fine structure and the related multi-loop structure of the flaring area.

  17. Effect of enhanced x-ray flux on the ionosphere over Cyprus during solar flares

    NASA Astrophysics Data System (ADS)

    Mostafa, Md. Golam; Haralambous, Haris

    2015-06-01

    In this work we study the effect of solar flares on the ionosphere over Cyprus. Solar flares are impulsive solar activity events usually coupled with Coronal Mass Ejection (CME). The arrival and the subsequent impact of solar flares on geospace, following an eruption on the Sun's surface is almost immediate (around 9 min) whereas the impact of CMEs is rather delayed (2-3 days) as the former is based on X-ray radiation whereas the latter phenomenon is related with particles and magnetic fields travelling at lower speeds via the Solar Wind. The penetration of X-rays down to the Dregion following such an event enhances the electron density. This increase can be monitored by ionosondes, which measure the electron density up to the maximum electron density NmF2. The significance of this increase lies on the increase of signal absorption causing limited window of operating frequencies for HF communications. In this study the effect of enhanced X-ray flux on the ionosphere over Cyprus during solar flares has been investigated. To establish the correlation and extent of impact on different layers, data of X-ray intensity from Geostationary Operational Environmental Satellite (GOES) and ionospheric characteristics (D & F layer) over Nicosia station (35° N, 33° E) were examined for all solar flares during the period 2011-2014. The analysis revealed a positive and good correlation between frequency of minimum reflection, fmin and X-ray intensity for D layer demonstrating that X-rays play a dominant role in the ionization of lower ionosphere. Hence, X-ray flux can be used as a good proxy for studying the solar flare effects on lower ionosphere. The correlation coefficient between maximum electron density of F layer, NmF2 and X-ray intensity was found to be poor.

  18. Assessing out-of-band flare effects at the wafer level for EUV lithography

    SciTech Connect

    George, Simi; Naulleau, Patrick; Kemp, Charles; Denham, Paul; Rekawa, Senajith

    2010-01-25

    To accurately estimate the flare contribution from the out-of-band (OOB), the integration of a DUV source into the SEMATECH Berkeley 0.3-NA Micro-field Exposure tool is proposed, enabling precisely controlled exposures along with the EUV patterning of resists in vacuum. First measurements evaluating the impact of bandwidth selected exposures with a table-top set-up and subsequent EUV patterning show significant impact on line-edge roughness and process performance. We outline a simulation-based method for computing the effective flare from resist sensitive wavelengths as a function of mask pattern types and sizes. This simulation method is benchmarked against measured OOB flare measurements and the results obtained are in agreement.

  19. Quantitative assessment of the effects of pupillary dilation on aqueous flare in eyes with chronic anterior uveitis using laser flare photometry.

    PubMed

    Ikeji, Felicia; Pavesio, Carlos; Bunce, Catey; White, Edward

    2010-10-01

    The purpose of this study is to determine whether pupillary dilation has any effect on anterior chamber flare measurements using a Kowa laser flare meter (FM-500) in patients with chronic anterior uveitis (CAU). Twenty-five eyes of 25 consecutive patients with CAU were assessed for anterior chamber inflammation by an experienced operator using the Kowa laser flare meter. Ten measurements were taken in total, with the highest and the lowest measurements deducted. The mean value and standard deviation was then recorded. One drop of tropicamide 1% and phenylephrine 2.5% was then applied and after 30 min the measurements were repeated and the results recorded. Sixteen women (64%) and nine men (36%) were recruited. The majority of patients were white Caucasian (68%). Fifteen left and ten right eyes were studied and the median (interquartile range: IQR) visual acuity was 6/9 (6/6-6/18). Iris colour was classified as brown, blue, grey/hazel and hazel. Thirteen eyes (52%) had brown irises, eight (32%) had blue, two had grey and the remainder were grey/hazel and hazel. The mean (SD) age was 50.8 (12.59) years. The median (IQR) flare reading before dilation was 17.93 (8.33-29.93) and after dilation was 15.97 (10.17-29.4). The mean change was -0.74 which was not a statistically significantly different to 0 (P=0.25) and the 95% limits of agreements ranged from -6.91 to 5.43. This study showed little evidence of any systematic difference between dilated and undilated flare measurements. The measurement of flare was not affected by the dilation of the pupil and measurements could be taken before or after papillary dilation for the purpose of patient follow-up data and clinical studies. PMID:20502943

  20. The Time-Dependent Effect of a Stellar Flare on Terrestrial Planet Habitability and Biosignatures

    NASA Astrophysics Data System (ADS)

    Walkowicz, Lucianne M.; Segura, A.; Meadows, V.; Kasting, J.; Hawley, S.

    2009-01-01

    Due to their low stellar luminosities, M dwarf habitable zones (as defined by Kasting et al. 1993) lie very near the star ( 0.2 AU or less), making planets in the habitable zone especially vulnerable to the effects of stellar activity. Although M dwarfs emit the bulk of their flux in the optical and near infrared, activity on these stars produces energetic radiation, from X rays to ultraviolet (UV), that may be dangerous for life on a planet in the habitable zone (HZ) of the star. In particular, stellar activity is a concern for the continuity of habitability on the planetary surface, as starspots or flares may cause the stellar irradiance to vary strongly with time. Using a convective/radiative model coupled to a photochemical model, we simulated the atmosphere of an Earth-like planet located in the habitable zone of the active M dwarf AD Leo over the course of a large flare. We present the time-dependent atmospheric temperature and composition profiles for water, methane and ozone, finding that while water and ozone are photolyzed in the stratosphere, the temperature profile and methane column depth are relatively unperturbed. Ozone number density decreases in the stratosphere during the impulsive phase of the flare, but quickly recovers to preflare levels thereafter. While the UV flux at the planetary surface changes with the ozone concentration during the flare, we find that the planetary surface UV flux is less than that received on Earth's surface except during the very peak of the flare. We conclude that even large flares may not be detrimental to life on planets with Earth-like atmospheres.

  1. Xrt And Shinx Joint Flare Study: Ar 11024

    NASA Astrophysics Data System (ADS)

    Engell, Alexander; Sylwester, J.; Siarkowski, M.

    2010-05-01

    From 12:00 UT on July 3 through July 7, 2009 SphinX (Solar Photometer IN X-rays) observes 130 flares with active region (AR) 11024 being the only AR on disk. XRT (X-Ray Telescope) is able to observe 64 of these flare events. The combination of both instruments results in a flare study revealing (1) a relationship between flux emergence and flare rate, (2) that the presence of active region loops typically results in different flare morphologies (single and multiple loop flares) then when there is a lack of an active region loop environment where more cusp and point-like flares are observed, (3) cusp and point-like flares often originate from the same location, and (4) a distribution of flare temperatures corresponding to the different flare morphologies. The differences between the observed flare morphologies may occur as the result of the heated plasma through the flaring process being confined by the proximity of loop structures as for the single and multiple loop flares, while for cusp and point-like flares they occur in an early-phase environment that lack loop presence. The continuing flux emergence of AR 11024 likely provides different magnetic interactions and may be the source responsible for all of the flares.

  2. Inverse spin Hall effect in a closed loop circuit

    SciTech Connect

    Omori, Y.; Auvray, F.; Wakamura, T.; Niimi, Y.; Fert, A.

    2014-06-16

    We present measurements of inverse spin Hall effects (ISHEs), in which the conversion of a spin current into a charge current via the ISHE is detected not as a voltage in a standard open circuit but directly as the charge current generated in a closed loop. The method is applied to the ISHEs of Bi-doped Cu and Pt. The derived expression of ISHE for the loop structure can relate the charge current flowing into the loop to the spin Hall angle of the SHE material and the resistance of the loop.

  3. The Effects of Looping on Perceived Values and Academic Achievement

    ERIC Educational Resources Information Center

    Rodriguez, Carmen; Arenz, Bernard

    2007-01-01

    This study was designed to examine the effects of looping, a practice whereby teachers and students stay together for more than one year, on perceived values and academic achievement in language arts at a Fresno Unified School District elementary school in Fresno, CA. Looping has many perceived advantages, such as the development of long-term…

  4. Effect of a Radiation Cooling and Heating Function on Standing Longitudinal Oscillations in Coronal Loops

    NASA Astrophysics Data System (ADS)

    Kumar, S.; Nakariakov, V. M.; Moon, Y.-J.

    2016-06-01

    Standing long-period (with periods longer than several minutes) oscillations in large, hot (with a temperature higher than 3 MK) coronal loops have been observed as the quasi-periodic modulation of the EUV and microwave intensity emission and the Doppler shift of coronal emission lines, and they have been interpreted as standing slow magnetoacoustic (longitudinal) oscillations. Quasi-periodic pulsations of shorter periods, detected in thermal and non-thermal emissions in solar flares could be produced by a similar mechanism. We present theoretical modeling of the standing slow magnetoacoustic mode, showing that this mode of oscillation is highly sensitive to peculiarities of the radiative cooling and heating function. We generalized the theoretical model of standing slow magnetoacoustic oscillations in a hot plasma, including the effects of the radiative losses and accounting for plasma heating. The heating mechanism is not specified and taken empirically to compensate the cooling by radiation and thermal conduction. It is shown that the evolution of the oscillations is described by a generalized Burgers equation. The numerical solution of an initial value problem for the evolutionary equation demonstrates that different dependences of the radiative cooling and plasma heating on the temperature lead to different regimes of the oscillations, including growing, quasi-stationary, and rapidly decaying. Our findings provide a theoretical foundation for probing the coronal heating function and may explain the observations of decayless long-period, quasi-periodic pulsations in flares. The hydrodynamic approach employed in this study should be considered with caution in the modeling of non-thermal emission associated with flares, because it misses potentially important non-hydrodynamic effects.

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

    NASA Astrophysics Data System (ADS)

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

    2010-10-01

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

  6. IMAGE-FUV observations of the October-November 2003 flare and magnetic storm effects on Earth

    NASA Astrophysics Data System (ADS)

    Immel, T. T.; Ostgaard, N.; Strickland, D. J.; Frey, H. U.; Mende, S. B.; Lu, G.

    2004-05-01

    The series of solar flares and coronal mass ejections that occurred between October 26 and November 4, 2003 had extraordinary effects on Earth's upper atmospheric and space environments. In several areas these effects can be quantified by space-based global imagers such as the Far Ultraviolet Imager on the NASA-IMAGE satellite. The immediate effects of the X-Ray and EUV components of the solar flares on terrestrial photoelectron fluxes are evident in the rapid, global variations in FUV brightness. IMAGE was favorably positioned in its 14-hour orbit to monitor the time variation of the photoelectron flux enhancement during four of the X-class flares, including the two greatest flares of the period, providing an indirect measure of the solar EUV irradiance enhancements. Also measured indirectly by the FUV geocoronal imager is the enhancement in the solar FUV HI Lyman alpha irradiance during each of the four flares. The October 28, 2003 flare produced an estimated 20% enhancement in the solar Lyman alpha irradiance at Earth, the largest increase ever observed. The global FUV imager also is able to determine the effects of the CME induced magnetic storms on thermospheric composition, with accurate global measurements of the FUV emissions of OI at 135.6 nm. A global survey of the O/N2 ratios through the entire period of activity is therefore possible. Comparisons with TIMED-GUVI flare observations and NCAR TIMEGCM O/N2 will be made for cross-validation purposes.

  7. Fine Structure in Solar Flares.

    PubMed

    Warren

    2000-06-20

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

  8. EXTREME-ULTRAVIOLET MULTI-WAVELENGTH OBSERVATIONS OF QUASI-PERIODIC PULSATIONS IN A SOLAR POST-FLARE CUSP-SHAPE LOOP WITH SDO/AIA

    SciTech Connect

    Su, J. T.; Shen, Y. D.; Liu, Y.

    2012-07-20

    We present extreme-ultraviolet multi-wavelength observations with the SDO/AIA instruments of quasi-periodic pulsations (QPPs) propagating along a cusp-shaped loop formed after an M2.2 flare on the Sun. Our motivation is to detect whether there were slow-mode magnetoacoustic waves propagating along its protruding flux tube. To this end, with fast Fourier transform we extract the short (<3 minutes) and long (>3 minutes) period components of the QPPs from time-space diagrams of the tube slices. We find that velocity differences did exist among the short/long-period components of different wavelengths, but only one event in the long-period ones showed they were greater than the measurement errors (e.g., 65 km s{sup -1}), which were 330 km s{sup -1} detected in 171 A, 590 km s{sup -1} in 211 A, and 180 km s{sup -1} in 304 A. The intensity modulation in all wavelengths is found to be very large, e.g., {approx}60% of the emission trend for an event in the 171 A passband, which would be an order of magnitude higher than the perturbation of the plasma density in the slow-mode magnetoacoustic waves. Moreover, only the QPPs with upward velocities of 50-300 km s{sup -1} are found in the tube, and the downward ones of several tens of kilometers are never unambiguously detected. Therefore, most of the QPP events under study were likely the episodic outflows along the tube, and the one with a supersonic speed of 590 km s{sup -1} may be a kink wave.

  9. Solar flares. [plasma physics

    NASA Technical Reports Server (NTRS)

    Rust, D. M.

    1979-01-01

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

  10. Flare model sensitivity of the Balmer spectrum

    NASA Technical Reports Server (NTRS)

    Falchi, A.; Falciani, R.; Smaldone, L. A.; Tozzi, G. P.

    1989-01-01

    Careful studies of various chromospheric spectral signatures are very important in order to explore their possible sensitivity to the modifications of the thermodynamic quantities produced by the flare occurrence. Pioneer work of Canfield and co-workers have shown how the H alpha behavior is able to indicate different changes in the atmospheric parameters structure associated to the flare event. It was decided to study the behavior of the highest Balmer lines and of the Balmer continuum in different solar flare model atmospheres. These spectral features, originating in the deep photosphere in a quiet area, may have a sensitivity different from H alpha to the modification of a flare atmosphere. The details of the method used to compute the Stark profile of the higher Balmer line (n is greater than or equal to 6) and their merging were extensively given elsewhere (Donati-Falchi et al., 1985; Falchi et al., 1989). The models used were developed by Ricchiazzi in his thesis (1982) evaluating the chromospheric response to both the nonthermal electron flux, for energy greater than 20 kev, (F sub 20) and to the thermal conduction, (F sub c). The effect of the coronal pressure values (P sub O) at the apex of the flare loop is also included.

  11. Examination of Prompt Effects of Solar X-ray Flares on Ionospheric Electrodynamics

    NASA Astrophysics Data System (ADS)

    Eccles, J. V.

    2007-12-01

    Photons from solar X-ray flares arrive at the Earth only eight minutes after emission. The short wavelength region of the solar spectrum is effective in modifying the ionization of the dayside upper atmosphere. For periods like the 2003 Halloween Solar events, the solar flares enhanced the E and D regions significantly over the quiet time background ionosphere. The effects of these enhancements on HF and VLF signal propagation and absorption are well understood and widely known. We present studies of the space weather impacts of sustained, elevated solar x-ray and EUV levels of the background spectrum during solar active times related to the changes in the dayside conductivities. We show that not only the dayside conductivities sustain at an order of magnitude higher values than background levels, but the Pedersen-to-Hall conductivity ratio increases by a factor of 2 to 3 during high solar X-ray periods when compared to quiet periods. The effects of prompt changes of the dayside conductivities associated with a solar flare event on the dynamo electric fields and ionospheric currents are then systematically examined by using a model of the low-latitude ionospheric electrodynamics.

  12. The Role of Entropic Effects on DNA Loop Formation

    NASA Astrophysics Data System (ADS)

    Wilson, David; Tkachenko, Alexei; Lillian, Todd; Perkins, Noel; Meiners, Jens Christian

    2009-03-01

    The formation of protein mediated DNA loops often regulates gene expression. Typically, a protein is simultaneously bound to two DNA operator sites. An example is the lactose repressor which binds to the Lac operon of E. coli. We characterize the mechanics of this system by calculating the free energy cost of loop formation. We construct a Hamiltonian that describes the change in DNA bending energy due to linear perturbations about the looped and open states, starting from a non-linear mechanical rod model that determines the shape and bending energy of the inter-operator DNA loop while capturing the intrinsic curvature and sequence-dependent elasticity of the DNA. The crystal structure of the LacI protein provides the boundary conditions for the DNA. We then calculate normal modes of the open and closed loops to account for the thermal fluctuations. The ratio of determinants of the two Hamiltonians yields the partition function, and the enthalphic and entropic cost of looping. This calculation goes beyond standard elastic energy models because it fully accounts for the substantial entropic differences between the two states. It also includes effects of sequence dependent curvature and stiffness and allows anisotropic variations in persistence length. From the free energy we then calculate the J-factor and ratio of loop lifetimes.

  13. The Effects of Hairpin loops on Ligand-DNA Interactions

    PubMed Central

    Nguyen, Binh; Wilson, W. David

    2009-01-01

    Hairpin nucleic acids are frequently used in physical studies due to their greater thermal stability compared to their equivalent duplex structures. They are also good models for more complex loop-containing structures such as quadruplexes, i-motifs, cruciforms, and molecular beacons. Although a connecting loop can increase stability, there is little information on how the loop influences the interactions of small molecules with attached base-paired nucleic acid regions. In this study, the effects of different hairpin loops on the interactions of A/T specific DNA minor groove binding agents with a common stem sequence have been investigated by spectroscopic and surface plasmon resonance (SPR) biosensor methods. The results indicate that the hairpin loop has little influence on the specific site interactions on the stem but significantly affects nonspecific binding. The use of a non-nucleotide loop (with a reduced negative charge) not only enhances the thermal stability of the hairpin but also reduces the non-specific binding at the loop without compromising the primary binding affinity on the stem. PMID:19778070

  14. Solar flares

    NASA Technical Reports Server (NTRS)

    Zirin, H.

    1974-01-01

    A review of the knowledge about solar flares which has been obtained through observations from the earth and from space by various methods. High-resolution cinematography is best carried out at H-alpha wavelengths to reveal the structure, time history, and location of flares. The classification flares in H alpha according to either physical or morphological criteria is discussed. The study of flare morphology, which shows where, when, and how flares occur, is important for evaluating theories of flares. Consideration is given to studies of flares by optical spectroscopy, radio emissions, and at X-ray and XUV wavelengths. Research has shown where and possibly why flares occur, but the physics of the instability involved, of the particle acceleration, and of the heating are still not understood.

  15. Anemone structure of Active Region NOAA 10798 and related geo-effective flares/ CMEs

    NASA Astrophysics Data System (ADS)

    Asai, A.; Ishii, T. T.; Shibata, K.; Gopalswamy, N.

    2006-08-01

    Introduction: We report the evolution and the coronal features of an active region NOAA 10798, and the related magnetic storms. Method: We examined in detail the photospheric and coronal features of the active region by using observational data in soft X-rays, in extreme ultraviolet images, and in magnetogram obtained with GOES, SOHO satellites. We also examined the interplanetary disturbances from the ACE data. Results: This active region was located in the middle of a small coronal hole, and generated 3 M-class flares. The flares are associated with high speed CMEs up to 2000 km/s. The interplanetary disturbances also show a structure with southward strong magnetic field. These produced a magnetic storm on 2005 August 24. Conclusions: The anemone structure may play a role for producing the high-speed and geo-effective CMEs even the near limb locations.

  16. Analysis of flares in the chromosphere and corona of main- and pre-main-sequence M-type stars

    NASA Astrophysics Data System (ADS)

    Crespo-Chacón, I.

    2015-11-01

    having an accretion disk) we carry out a detailed analysis of an extremely long rise phase and of a shorter, weaker flare (allowing us to compare the results with those reported for young stars but surrounded by disks). Assuming multitemperature models to describe the coronal flaring plasma, we have calculated the metal abundance, the electron temperatures and the respective emission measures by fitting the spectra with the Astrophysical Plasma Emission Code included in the XSPEC software, which calculates spectral models for hot, optically thin plasmas. Moreover, we are able to estimate the size of the flaring loops by using theoretical models. These sizes give us an idea about the extent of the corona. For those flares in which heating does not entirely drive the flare evolution we use the models reported by Reale (2007) and Reale et al. (1997) for the rise and decay phases, respectively, including the effect of sustained heating during the decay. Instead, the stellar version of the Kopp & Poletto (1984)'s solar two-ribbon flare model (Poletto et al. 1988) is used when the residual heating completely drives the flare over the plasma cooling. Later, we apply the so-called RTV scaling laws (Rosner et al. 1978) and other fundamental laws of physics to determine additional characteristics of the plasma contained in the flaring loops (electron density and pressure), as well as the volume of the flaring region, the heating rate per unit volume, and the strength of the magnetic field required to confine this plasma. Making some assumptions we are also able to estimate the number of loops involved in the observed flares and the kind of magnetic structures present in the atmosphere of these types of stars. Finally, we discuss and interpret the results in the context of solar and stellar flares reported so far.

  17. The effects of Kelvin-Helmholtz instability on resonance absorption layers in coronal loops

    NASA Technical Reports Server (NTRS)

    Karpen, Judith T.; Dahlburg, Russell B.; Davila, Joseph M.

    1994-01-01

    One of the long-standing uncertainties in the wave-resonance theory of coronal heating is the stability of the resonance layer. The wave motions in the resonance layer produce highly localized shear flows which vary sinusoidally in time with the resonance period. This configuration is potentially susceptible to the Kelvin-Helmholtz instability (KHI), which can enhance small-scale structure and turbulent broadening of shear layers on relatively rapid ideal timescales. We have investigated numerically the response of a characteristic velocity profile, derived from resonance absorption models, to finite fluid perturbations comparable to photospheric fluctuations. We find that the KHI primarily should affect long (approximately greater than 6 x 10(exp 4) km) loops where higher velocity flows (M approximately greater than 0.2) exist in resonance layers of order 100 km wide. There, the Kelvin-Helmholtz growth time is comparable to or less than the resonance quarter-period, and the potentially stabilizing magnetic effects are not felt until the instability is well past the linear growth stage. Not only is the resonance layer broadened by the KHI, but also the convective energy transport out of the resonance layer is increased, thus adding to the efficiency of the wave-resonance heating process. In shorter loops, e.g., those in bright points and compact flares, the stabilization due to the magnetic field and the high resonance frequency inhibit the growth of the Kelvin-Helmholtz instability beyond a minimal level.

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  19. SECONDARY FLARE RIBBONS OBSERVED BY THE SOLAR DYNAMICS OBSERVATORY

    SciTech Connect

    Zhang, Jun; Li, Ting; Yang, Shuhong E-mail: liting@nao.cas.cn

    2014-02-20

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

  20. Flares in childhood eczema.

    PubMed

    Langan, S M

    2009-01-01

    Eczema is a major public health problem affecting children worldwide. Few studies have directly assessed triggers for disease flares. This paper presents evidence from a published systematic review and a prospective cohort study looking at flare factors in eczema. This systematic review suggested that foodstuffs in selected groups, dust exposure, unfamiliar pets, seasonal variation, stress, and irritants may be important in eczema flares. We performed a prospective cohort study that focused on environmental factors and identified associations between exposure to nylon clothing, dust, unfamiliar pets, sweating, shampoo, and eczema flares. Results from this study also demonstrated some new key findings. First, the effect of shampoo was found to increase in cold weather, and second, combinations of environmental factors were associated with disease exacerbation, supporting a multiple component disease model. This information is likely to be useful to families and may lead to the ability to reduce disease flares in the future. PMID:20054505

  1. Loop and water effect on stability of intertriplex DNA

    NASA Astrophysics Data System (ADS)

    Yang, Linjing; Lee, Imshik; Wang, Chen; Li, Qing; Bai, Chunli

    1998-02-01

    Stability of four intratriplexes and one intertriplex influenced by loops and water have been investigated by molecular mechanics calculation. The four intratriplexes are 5'-d(TC) 6-d(T) m-d(CT) 6-d(C) n-d(AG) 6-3' ( m, n = 3 or 4), the corresponding intertriplex is d(TC) 6∗d(AG) 6·d(CT) 6 (·, Watson-Crick hydrogen bond; ∗, Hoogsteen hydrogen bond). We studied in detail how loops and water would effect intra- and interstrand interactions of the five triplexes, respectively. The results showed that the existence of loops may have limited impact on the stability of the concerned triplex structures, regardless of water environment. In contrast, water molecules do have appreciable effects on triplex stability. Sugar conformations of the five triplexes were also discussed in this paper. The theoretical results are in good agreement with the FT-IR experiments.

  2. On the Convergence in Effective Loop Quantum Cosmology

    SciTech Connect

    Corichi, Alejandro; Vukasinac, Tatjana; Zapata, Jose Antonio

    2010-07-12

    In Loop Quantum Cosmology (LQC) there is a discreteness parameter {lambda}, that has been heuristically associated to a fundamental granularity of quantum geometry. It is also possible to consider {lambda} as a regulator in the same spirit as that used in lattice field theory, where it specifies a regular lattice in the real line. A particular quantization of the k = 0 FLRW loop cosmological model yields a completely solvable model, known as solvable loop quantum cosmology(sLQC). In this contribution, we consider effective classical theories motivated by sLQC and study their {lambda}-dependence, with a special interest on the limit {lambda}{yields}0 and the role of the evolution parameter in the convergence of such limit.

  3. Completely inverted hysteresis loops: Inhomogeneity effects or experimental artifacts

    SciTech Connect

    Song, C. Cui, B.; Pan, F.; Yu, H. Y.

    2013-11-14

    Completely inverted hysteresis loops (IHL) are obtained by the superconducting quantum interference device with large cooling fields (>10 kOe) in (La,Sr)MnO{sub 3} films with self-assembled LaSrMnO{sub 4}, an antiferromagnetic interface. Although the behaviours of measured loops show many features characteristic to the IHL, its origin, however, is not due to the exchange coupling between (La,Sr)MnO{sub 3}/LaSrMnO{sub 4}, an often accepted view on IHL. Instead, we demonstrate that the negative remanence arises from the hysteresis of superconducting coils, which drops abruptly when lower cooling fields are utilized. Hence the completely inverted hysteresis loops are experimental artifacts rather than previously proposed inhomogeneity effects in complicated materials.

  4. One Loop Superstring Effective Actions and d = 4 Supergravity

    SciTech Connect

    Moura, Filipe

    2008-06-25

    We review our recent work on the existence of a new independent R{sup 4} term, at one loop, in the type IIA and heterotic effective actions, after reduction to four dimensions, besides the usual square of the Bel-Robinson tensor. We discuss its supersymmetrization.

  5. Effective action for hard thermal loops in gravitational fields

    NASA Astrophysics Data System (ADS)

    Francisco, R. R.; Frenkel, J.; Taylor, J. C.

    2016-05-01

    We examine, through a Boltzmann equation approach, the generating action of hard thermal loops in the background of gravitational fields. Using the gauge and Weyl invariance of the theory at high temperature, we derive an explicit closed-form expression for the effective action.

  6. The flares of August 1972. [solar flare characteristics and spectra

    NASA Technical Reports Server (NTRS)

    Zirin, H.; Tanaka, K.

    1973-01-01

    Observations of the August, 1972 flares at Big Bear and Tel Aviv, involving monochromatic movies, magnetograms, and spectra, are analyzed. The region (McMath 11976) showed inverted polarity from its inception on July 11; the great activity was due to extremely high shear and gradients in the magnetic field, as well as a constant invasion of one polarity into the opposite; observations in lambda 3835 show remarkable fast flashes in the impulsive flare of 18:38 UT on Aug. 2 with lifetimes of 5 sec, which may be due to dumping of particles in the lower chromosphere. Flare loops show evolutionary increases of their tilts to the neutral line in the flares of Aug. 4 and 7. Spectroscopic observations show red asymmetry and red shift of the H alpha emission in the flash phase of the Aug. 7 flare, as well as substantial velocity shear in the photosphere during the flare, somewhat like earthquake movement along a fault. Finally the total H alpha emission of the Aug. 7 flare could be measured accurately as about 2.5 x 10 to the 30th power erg, considerably less than coarser previous estimates for great flares.

  7. Solar flare effects on the thermosphere and E-layer as observed by GRACE and DEMETER

    NASA Astrophysics Data System (ADS)

    Boudjada, Mohammed Y.; Krauss, Sandro; Sawas, Sami; Hausleitner, Walter; Parrot, Michel; Voller, Wolfgang

    2013-04-01

    We investigate the effect of solar flares on the lower thermosphere and ionosphere of the Earth. For this study we select solar flares which occurred in the period from Nov. 2004 to Sept. 2005. We combine the measurements of the GRACE and DEMETER satellites which lead us to estimate, respectively, the atmospheric density and the electric field variation at an altitude of about 100 km. The accelerometer measurements from GRACE orbiting at an altitude of about 450 km comprise all non gravitational forces acting on the satellite and may be used to determine the atmospheric neutral density. The intensity variation of the transmitter ground signals is detected by DEMETER at an altitude in the order of 700 km. In this study we insist on an atmosphere-ionosphere coupling effect which may appear at an altitude of about 100 km. This crucial altitude corresponds to critical regions where important changes are observed in the atmosphere (Mesosphere/Thermosphere) and in the ionosphere (D/E layers). We discuss the possible correlation between the measurements of GRACE and DEMETER observations, where both the local and global effects are taken into consideration.

  8. COMPTEL solar flare observations

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

  9. Effective nonrenormalizable theories at one loop

    SciTech Connect

    Gaillard, M.K.

    1987-10-12

    The paper focuses on a nonrenormalizable theory that is more closely related to those suggested by superstrings, namely a gauged nonlinear delta-model, but one which can also be obtained analytically in a particular limit of a parameter (m/sub H/ ..-->.. infinity) of the standard, renormalizable electroweak theory. This will provide another laboratory for testing the validity of calculations using the effective theory. We find (as for certain superstring inspired models to be discussed later) features similar to those for the Fermi theory: quadratic divergences can be reinterpreted as renormalizations, while new terms are generated at the level of logarithmic divergences. Also introduced in the context of more familiar physics are notions such as scalar metric, scalar curvature and nonlinear symmetries, that play an important role in formal aspects of string theories. 58 refs., 12 figs.

  10. Radio flares of compact binary mergers: the effect of non-trivial outflow geometry

    NASA Astrophysics Data System (ADS)

    Margalit, Ben; Piran, Tsvi

    2015-10-01

    The next generation gravitational waves (GW) detectors are most sensitive to GW emitted by compact (neutron star/black hole) binary mergers. If one of those is a neutron star the merger will also emit electromagnetic radiation via three possible channels: gamma-ray bursts and their (possibly orphan) afterglows, Li-Paczynski Macronovae and radio flares. This accompanying electromagnetic radiation is vitally important in confirming the GW detections. It could also reveal a wealth of information regarding the merger and will open a window towards multimessenger astronomy. Identifying and characterizing these counterparts is therefore of utmost importance. In this work, we explore late time radio flares emitted by the dynamically ejected outflows. We build upon previous work and consider the effect of the outflow's non-trivial geometry. Using an approximate method, we estimate the radio light-curves for several ejected matter distributions obtained in numerical simulations. Our method provides an upper limit to the effect of non-sphericity. Together with the spherical estimates, the resulting light curves bound the actual signal. We find that while non-spherical geometries can in principle lead to an enhanced emission, in most cases they result in an increase in the time-scale compared with a corresponding spherical configuration. This would weaken somewhat these signals and might decrease the detection prospects.

  11. Solar Flares

    NASA Technical Reports Server (NTRS)

    Savage, Sabrina

    2013-01-01

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

  12. Solar Flares

    NASA Technical Reports Server (NTRS)

    Shih, Albert

    2011-01-01

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

  13. SDO Sees Late Phase in Solar Flares

    NASA Video Gallery

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

  14. THE EFFECTS OF WAVE ESCAPE ON FAST MAGNETOSONIC WAVE TURBULENCE IN SOLAR FLARES

    SciTech Connect

    Pongkitiwanichakul, Peera; Chandran, Benjamin D. G.; Karpen, Judith T.; DeVore, C. Richard E-mail: benjamin.chandran@unh.edu E-mail: devore@nrl.navy.mil

    2012-09-20

    One of the leading models for electron acceleration in solar flares is stochastic acceleration by weakly turbulent fast magnetosonic waves ({sup f}ast waves{sup )}. In this model, large-scale flows triggered by magnetic reconnection excite large-wavelength fast waves, and fast-wave energy then cascades from large wavelengths to small wavelengths. Electron acceleration by large-wavelength fast waves is weak, and so the model relies on the small-wavelength waves produced by the turbulent cascade. In order for the model to work, the energy cascade time for large-wavelength fast waves must be shorter than the time required for the waves to propagate out of the solar-flare acceleration region. To investigate the effects of wave escape, we solve the wave kinetic equation for fast waves in weak turbulence theory, supplemented with a homogeneous wave-loss term. We find that the amplitude of large-wavelength fast waves must exceed a minimum threshold in order for a significant fraction of the wave energy to cascade to small wavelengths before the waves leave the acceleration region. We evaluate this threshold as a function of the dominant wavelength of the fast waves that are initially excited by reconnection outflows.

  15. The Effects of Wave Escape on Fast Magnetosonic Wave Turbulence in Solar Flares

    NASA Technical Reports Server (NTRS)

    Pongkitiwanichakul, Peera; Chandran, Benjamin D. G.; Karpen, Judith T.; DeVore, C. Richard

    2012-01-01

    One of the leading models for electron acceleration in solar flares is stochastic acceleration by weakly turbulent fast magnetosonic waves ("fast waves"). In this model, large-scale flows triggered by magnetic reconnection excite large-wavelength fast waves, and fast-wave energy then cascades from large wavelengths to small wavelengths. Electron acceleration by large-wavelength fast-waves is weak, and so the model relies on the small-wavelength waves produced by the turbulent cascade. In order for the model to work, the energy cascade time for large-wavelength fast waves must be shorter than the time required for the waves to propagate out of the solar-flare acceleration region. To investigate the effects of wave escape, we solve the wave kinetic equation for fast waves in weak turbulence theory, supplemented with a homogeneous wave-loss term.We find that the amplitude of large-wavelength fast waves must exceed a minimum threshold in order for a significant fraction of the wave energy to cascade to small wavelengths before the waves leave the acceleration region.We evaluate this threshold as a function of the dominant wavelength of the fast waves that are initially excited by reconnection outflows.

  16. Solar flare particle radiation

    NASA Technical Reports Server (NTRS)

    Lanzerotti, L. J.

    1972-01-01

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

  17. Flares from small to large: X-ray spectroscopy of Proxima Centauri with XMM-Newton

    NASA Astrophysics Data System (ADS)

    Güdel, M.; Audard, M.; Reale, F.; Skinner, S. L.; Linsky, J. L.

    2004-03-01

    We report results from a comprehensive study of the nearby M dwarf Proxima Centauri with the XMM-Newton satellite, using simultaneously its X-ray detectors and the Optical Monitor with its U band filter. We find strongly variable coronal X-ray emission, with flares ranging over a factor of 100 in peak flux. The low-level emission is found to be continuously variable on at least three time scales (a slow decay of several hours, modulation on a time scale of 1 hr, and weak flares with time scales of a few minutes). Several weak flares are characteristically preceded by an optical burst, compatible with predictions from standard solar flare models. We propose that the U band bursts are proxies for the elusive stellar non-thermal hard X-ray bursts suggested from solar observations. In the course of the observation, a very large X-ray flare started and was observed essentially in its entirety. Its peak luminosity reached 3.9× 1028 erg s-1 [0.15-10 keV], and the total X-ray energy released in the same band is derived to be 1.5× 1032 ergs. This flare has for the first time allowed to measure significant density variations across several phases of the flare from X-ray spectroscopy of the O VII He-like triplet; we find peak densities reaching up to 4× 1011 cm-3 for plasma of about 1-5 MK. Abundance ratios show little variability in time, with a tendency of elements with a high first ionization potential to be overabundant relative to solar photospheric values. Using Fe XVII lines with different oscillator strengths, we do not find significant effects due to opacity during the flare, indicating that large opacity increases are not the rule even in extreme flares. We model the large flare in terms of an analytic 2-Ribbon flare model and find that the flaring loop system should have large characteristic sizes (≈ 1R*) within the framework of this simplistic model. These results are supported by full hydrodynamic simulations. Comparing the large flare to flares of similar

  18. Nonequilibrium ionization effects in asymmetrically heated loops. [in solar corona

    NASA Technical Reports Server (NTRS)

    Spadaro, D.; Antiochos, Spiro K.; Mariska, J. T.

    1991-01-01

    The effects of nonequilibrium ionization on magnetic loop models with a steady siphon flow that is driven by a nonuniform heating rate are investigated. The model developed by Mariska (1988) to explain the observed redshifts of transition region emission lines is examined, and the number densities of the ions of carbon and oxygen along the loop are computed, with and without the approximation of ionization equilibrium. Considerable deviations from equilibrium were found. In order to determine the consequences of these nonequilibrium effects on the characteristics of the EUV emission from the loop plasma, the profiles and wavelength positions of all the important emission lines due to carbon and oxygen were calculated. The calculations are in broad agreement with Mariska's conclusions, although they show a significant diminution of the Doppler shifts, as well as modifications to the line widths. It is concluded that the inclusion of nonequilibrium effects make it more difficult to reproduce the observed characteristics of the solar transition region by means of the asymmetric-heating models.

  19. The solar flare myth

    NASA Technical Reports Server (NTRS)

    Gosling, J. T.

    1993-01-01

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

  20. Teachers' Attitudes and Perceptions of Looping and the Effect of Looping on Students' Academic Achievement

    ERIC Educational Resources Information Center

    Williams-Wright, Vera

    2013-01-01

    The purpose of this research study was two-fold. The first purpose was to investigate the impact of looping on academic achievement of students in selected public schools in Mississippi. The students' results on the 2010 and 2011 Mississippi Curriculum Test, Second Edition (MCT2) were used to determine whether looping students score differently in…

  1. The cooling and condensation of flare coronal plasma

    NASA Technical Reports Server (NTRS)

    Antiochos, S. K.; Sturrock, P. A.

    1981-01-01

    A model is investigated for the decay of flare heated coronal loops in which rapid radiative cooling at the loop base creates strong pressure gradients which, in turn, generate large (supersonic) downward flows. The coronal material cools and 'condenses' onto the flare chromosphere. The features which distinguish this model from previous models of flare cooling are: (1) most of the thermal energy of the coronal plasma may be lost by mass motion rather than by conduction or coronal radiation; (2) flare loops are not isobaric during their decay phase, and large downward velocities are present near the footpoints; (3) the differential emission measure q has a strong temperature dependence.

  2. Covariant effective action for loop quantum cosmology a la Palatini

    SciTech Connect

    Olmo, Gonzalo J.; Singh, Parampreet E-mail: psingh@perimeterinstitute.ca

    2009-01-15

    In loop quantum cosmology, non-perturbative quantum gravity effects lead to the resolution of the big bang singularity by a quantum bounce without introducing any new degrees of freedom. Though fundamentally discrete, the theory admits a continuum description in terms of an effective Hamiltonian. Here we provide an algorithm to obtain the corresponding effective action, establishing in this way the covariance of the theory for the first time. This result provides new insights on the continuum properties of the discrete structure of quantum geometry and opens new avenues to extract physical predictions such as those related to gauge invariant cosmological perturbations.

  3. Model of slowly evolving flare.

    NASA Astrophysics Data System (ADS)

    Chiuderi Drago, F.; Landini, M.; Monsignori Fossi, B. C.

    A gradual rise and fall flare with a duration of about one hour was observed on June 10, 1980 in the radio (Toyokawa and VLA), optical (Bing Bear) and XUV (SMM satellite) ranges of wavelengths. The flare developed as a large loop connecting two regions of opposite polarity in a pre-existing active region. A model of the differential emission measure of the loop observed at three different stages of the flare is deduced from the analysis of the XUV images in C IV (1549 Å), O VIII (18.97 Å), Ne IX (13.45 Å), Mg XI (9.17 Å) and Si XIII (6.65 Å) emission lines. The differential emission measure as a function of temperature is controlled by the conductive flux via the temperature gradient; the evaluation of the divergence of the conductive flux is used in the energy balance to have information on the power deposition function.

  4. Isotopic overabundances and the energetic particle model of solar flares

    NASA Technical Reports Server (NTRS)

    Perez-Enriquez, R.; Bravo, S.

    1985-01-01

    According to the energetic particle model of solar flares particles are efficiently accelerated in the magnetic field loop of an active region (AR) by hydromagnetic turbulence. It is demonstrated that the isotopic overabundances observed in some flares are not a consequence of the flare itself but are characteristic of the plasma in the AR. Only when a flare releases the plasma into the interplanetary space it is possible to observe this anomalous composition at spacecraft locations.

  5. Flares on Mira stars?

    NASA Technical Reports Server (NTRS)

    Schaefer, Bradley E.

    1991-01-01

    Fourteen cases of flares reported on Mira type stars have been collected. These flares typically have an amplitude of over half a magnitude, a rise time of minutes, and a duration of tens of minutes. Nine of the 11 stars represent a normal cross section of the Mira population, while the remaining two are in symbiotic systems (CH Cyg and RX Pup). The flares were observed photographically (five cases), photometrically (three cases), visually (three cases), and with radio telescopes (two cases), while CH Cyg has had flares observed by many techniques. The evidence for the existence of flares on Miras is strong but not definitive. It is possible to hypothesize a variety of background or instrumental effects that could explain all 14 events; however, there is no evidence that suggests the data should be taken at other than face value, and there are good arguments for rejecting the possibility of artifacts. It is felt that the current data warrant systematic observational and theoretical investigation of the possibility of flares on Mira stars.

  6. Thermal Fronts in Solar Flares

    NASA Astrophysics Data System (ADS)

    Karlický, Marian

    2015-12-01

    We studied the formation of a thermal front during the expansion of hot plasma into colder plasma. We used a three-dimensional electromagnetic particle-in-cell model that includes inductive effects. In early phases, in the area of the expanding hot plasma, we found several thermal fronts, which are defined as a sudden decrease of the local electron kinetic energy. The fronts formed a cascade. Thermal fronts with higher temperature contrast were located near plasma density depressions, generated during the hot plasma expansion. The formation of the main thermal front was associated with the return-current process induced by hot electron expansion and electrons backscattered at the front. A part of the hot plasma was trapped by the thermal front while another part, mainly with the most energetic electrons, escaped and generated Langmuir and electromagnetic waves in front of the thermal front, as shown by the dispersion diagrams. Considering all of these processes and those described in the literature, we show that anomalous electric resistivity is produced at the location of the thermal front. Thus, the thermal front can contribute to energy dissipation in the current-carrying loops of solar flares. We estimated the values of such anomalous resistivity in the solar atmosphere together with collisional resistivity and electric fields. We propose that the slowly drifting reverse drift bursts, observed at the beginning of some solar flares, could be signatures of the thermal front.

  7. Effect of coronal structure on loop oscillations: exponential profiles

    NASA Astrophysics Data System (ADS)

    Díaz, A. J.; Donnelly, G. R.; Roberts, B.

    2007-12-01

    Aims:The role of longitudinal structuring of the surrounding corona on the modes of oscillation of a coronal magnetic flux tube was studied in Donnelly et al. (2006) for a piecewise uniform profile. Here we investigate whether a more realistic continuous exponential profile changes the conclusions drawn from that paper. Methods: A partial differential equation is derived for the total pressure perturbation of the fast modes, which is then decomposed by separation of variables. The longitudinal part is solved numerically, obtaining a dispersion relation. These results are supported by an analytical investigation in terms of Bessel functions of purely imaginary order. Results: Structure in the interior of the loop shifts the frequencies of the modes (and may trap higher harmonics), an effect which can be understood by taking an averaged profile with a suitable weight. Structure in the environment modifies only slightly the frequencies, but displaces the cutoff frequency. The shift due to the structure in the fundamental period is small, but the ratio between the periods of the fundamental mode and its harmonics can be used to probe the structure. Conclusions: The results support our previous study in a more realistic, continuously varying profile and provide limits to the conclusions drawn in coronal seismology if an unstructured loop is used. Also, the ratio between the period of the fundamental kink (even) mode and its first (odd) harmonic is proven as an extra seismological tool for coronal loops.

  8. Coronal behavior before the large flare onset

    NASA Astrophysics Data System (ADS)

    Imada, Shinsuke; Bamba, Yumi; Kusano, Kanya

    2014-12-01

    Flares are a major explosive event in our solar system. They are often followed by a coronal mass ejection that has the potential to trigger geomagnetic storms. There are various studies aiming to predict when and where the flares are likely to occur. Most of these studies mainly discuss the photospheric and chromospheric activity before the flare onset. In this paper we study the coronal features before the famous large flare occurrence on 2006 December 13. Using the data from Hinode/Extreme ultraviolet Imaging Spectrometer (EIS), X-Ray Telescope (XRT), and Solar and Heliospheric Observatory (SOHO)/Extreme ultraviolet Imaging Telescope (EIT), we discuss the coronal features in the large scale (a few 100″) before the flare onset. Our findings are as follows. (1) The upflows in and around the active region start growing from ˜ 10 to 30 km s-1 a day before the flare. (2) The expanding coronal loops are clearly observed a few hours before the flare. (3) Soft X-ray and extreme ultraviolet intensity are gradually reduced. (4) The upflows are further enhanced after the flare. From these observed signatures, we conclude that the outer part of active region loops with low density was expanding a day before the flare onset, and the inner part with high density was expanding a few hours before the onset.

  9. Effect of post type and restorative techniques on the strain and fracture resistance of flared incisor roots.

    PubMed

    Silva, Gisele Rodrigues da; Santos-Filho, Paulo César de Freitas; Simamoto-Júnior, Paulo Cézar; Martins, Luis Roberto Marcondes; Mota, Adérito Soares da; Soares, Carlos José

    2011-01-01

    Restoring flared endodontically treated teeth continues to be a challenge for clinicians. This study evaluated the effect of post types and restorative techniques on the strain, fracture resistance, and fracture mode of incisors with weakened roots. One hundred five endodontically treated bovine incisors roots (15 mm) were divided into 7 groups (n=15). The two control groups were (C) intact roots restored with Cpc (cast posts and core) or Gfp (glass fiber posts). The five experimental groups were (F) flared roots restored with GfpAp (Gfp associated with accessory glass fiber posts), GfpRc (anatomic Gfp, relined with composite resin), and GfpRcAp (anatomized Gfp with resin and accessory glass fiber posts). All teeth were restored with metal crowns. Mechanical fatigue was performed with 3x10(5)/50 N. Specimens were loaded at 45º, and the strain values (μS) were obtained on root buccal and proximal surfaces. Following that, the fracture resistance (N) was measured. One-way ANOVA and Tukey's HSD tests (α=0.05) were applied, and failure mode was checked. No significant difference in strain values among the groups was found. Cpc presented lower fracture resistance and more catastrophic failures in flared roots. Gfp associated with composite resin or accessory glass fiber posts seems to be an effective method to improve the biomechanical behavior of flared roots. PMID:21915521

  10. THE ABRUPT CHANGES IN THE PHOTOSPHERIC MAGNETIC AND LORENTZ FORCE VECTORS DURING SIX MAJOR NEUTRAL-LINE FLARES

    SciTech Connect

    Petrie, G. J. D.

    2012-11-01

    We analyze the spatial and temporal variations of the abrupt photospheric magnetic changes associated with six major flares using 12 minute, 0.''5 pixel{sup -1} vector magnetograms from NASA's Helioseismic and Magnetic Imager instrument on the Solar Dynamics Observatory satellite. The six major flares occurred near the main magnetic neutral lines of four active regions, NOAA 11158, 11166, 11283, and 11429. During all six flares the neutral-line field vectors became stronger and more horizontal, in each case almost entirely due to strengthening of the horizontal field components parallel to the neutral line. In all six cases the neutral-line pre-flare fields were more vertical than the reference potential fields, and collapsed abruptly and permanently closer to potential-field tilt angles during every flare, implying that the relaxation of magnetic stress associated with non-potential tilt angles plays a major role during major flares. The shear angle with respect to the reference potential field did not show such a pattern, demonstrating that flare processes do not generally relieve magnetic stresses associated with photospheric magnetic shear. The horizontal fields became significantly and permanently more aligned with the neutral line during the four largest flares, suggesting that the collapsing field is on average more aligned with the neutral line than the pre-flare neutral-line field. The vertical Lorentz force had a large, abrupt, permanent downward change during each of the flares, consistent with loop collapse. The horizontal Lorentz force changes acted mostly parallel to the neutral line in opposite directions on each side, a signature of the fields contracting during the flare, pulling the two sides of the neutral line toward each other. The greater effect of the flares on field tilt than on shear may be explained by photospheric line-tying.

  11. Analysis of sampling and quantization effects on the performance of PN code tracking loops

    NASA Technical Reports Server (NTRS)

    Quirk, K. J.; Srinivasan, M.

    2002-01-01

    Pseudonoise (PN) code tracking loops in direct-sequence spread-spectrum systems are often implemented using digital hardware. Performance degradation due to quantization and sampling effects is not adequately characterized by the traditional analog system feedback loop analysis.

  12. Characteristics of gamma-ray line flares

    NASA Technical Reports Server (NTRS)

    Bai, T.; Dennis, B.

    1983-01-01

    Observations of solar gamma rays by the Solar Maximum Mission (SMM) demonstrate that energetic protons and ions are rapidly accelerated during the impulsive phase. To understand the acceleration mechanisms for these particles, the characteristics of the gamma ray line flares observed by SMM were studied. Some very intense hard X-ray flares without detectable gamma ray lines were also investigated. Gamma ray line flares are distinguished from other flares by: (1) intense hard X-ray and microwave emissions; (2) delay of high energy hard X-rays; (3) emission of type 2 and/or type 4 radio bursts; and (4) flat hard X-ray spectra (average power law index: 3.1). The majority of the gamma ray line flares shared all these characteristics, and the remainder shared at least three of them. Positive correlations were found between durations of spike bursts and spatial sizes of flare loops as well as between delay times and durations of spike bursts.

  13. X-Ray Flares of Sun-like Young Stellar Objects and Their Effects on Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Glassgold, A. E.; Feigelson, E. D.; Montmerle, T.; Wolk, S.

    2005-12-01

    Astronomical observations of flares from analogs of the early Sun have the potential to give critical insights into the high energy irradiation environment of protoplanetary disks. Solar-mass young stellar objects are significantly more X-ray luminous than the typical low-mass T Tauri star. They undergo frequent strong flaring on a several day time scale. Very powerful flares also occur, but on a longer time frame. The hard X-ray spectrum of these stars become even harder during flaring. The X-rays from these Sun-like young stellar objects have the potential to ionize circumstellar material at a level greater than galactic cosmic rays out to distances ˜104 AU. Their characteristic hard spectra imply that, on encountering this material, they penetrate to fairly large surface densities of the order of 1 g psqcm or more. Three specific illustrations are given of the effects of the X-rays: The physics and chemistry of the atmospheres of the inner accretion disks; the ionization level at the disk midplane, important for the viability of the magnetorotational instability; and the nuclear fluence in the irradiation zone just interior to the inner edge of the disk, important in local irradiation scenarios for producing the short-lived radionuclides found in meteorites.

  14. Adalimumab effectively reduces the rate of anterior uveitis flares in patients with active ankylosing spondylitis: results of a prospective open-label study

    PubMed Central

    Rudwaleit, M; Rødevand, E; Holck, P; Vanhoof, J; Kron, M; Kary, S; Kupper, H

    2009-01-01

    Objective: To evaluate the effect of adalimumab on the frequency of anterior uveitis (AU) flares in patients with active ankylosing spondylitis (AS). Methods: We determined the history of ophthalmologist-diagnosed AU in 1250 patients with active AS who were enrolled in a multinational, open-label, uncontrolled clinical study of treatment with adalimumab, 40 mg every other week for up to 20 weeks. All AU flares were documented throughout the adalimumab treatment period plus 70 days. We compared the rates of AU flares per 100 patient years (PYs) reported during the year before adalimumab treatment with rates during adalimumab treatment, in total and by patient subgroups. Results: The AU flare rates before adalimumab treatment were 15/100 PYs in all patients (n = 1250), 68.4/100 PYs in 274 patients with a history of AU flares, 176.9/100 PYs in 106 patients with a recent history of AU flares, 192.9/100 PYs in 28 patients with symptomatic AU at baseline and 129.1/100 PYs in 43 patients with a history of chronic uveitis. During adalimumab treatment, the rate of AU flares was reduced by 51% in all patients, by 58% in 274 patients with a history of AU, by 68% in 106 patients with a recent history of AU, by 50% in 28 patients with symptomatic AU at baseline and by 45% in 43 patients with chronic uveitis. AU flares during adalimumab treatment were predominantly mild. Two patients with periods of high AS disease activity had new-onset AU during the treatment period. Conclusions: Results of this prospective open-label study suggest that adalimumab had a substantial preventive effect on AU flares in patients with active AS, including patients with a recent history of AU flares. Clinical trials: ClinicalTrials.gov Identifier: NCT00478660. PMID:18662932

  15. Solar Flare and IMF Sector Structure Effects in the Lower Ionosphere

    NASA Technical Reports Server (NTRS)

    Lastovicka, J.

    1984-01-01

    About 1% of all sudden ionospheric disturbances (SIDs) observed at the Panska Ves Observatory (Czechoslovakia), were found to be not of solar-XUV origin. Among them, the very rare SWF events (observed at L = 2.4) of corpuscular origin are the most interesting. The IMF sector structure effects in the midlatitude lower ionosphere are minor in comparison with effects of solar flares, geomagnetic storms, etc. There are two basic types of effects. The first type is a disturbance, best developed in geomagnetic activity, and observed in the night-time ionosphere. It can be interpreted as a response to sector structure related changes of geomagnetic (= magnetospheric) activity. The other type is best developed in the tropospheric vorticity area index and is also observed in the day-time ionosphere in winter. This effect is quietening in the ionosphere as well as troposphere. While the occurrence of the former type is persistent in time, the latter is severely diminished in some periods. All the stratosphere, the 10-mb level temperature and height above Berlin-Tempelhof do not display any observable IMF section structure effect.

  16. Solar flare and IMF sector structure effects in the lower ionosphere

    SciTech Connect

    Lastovicka, J.

    1984-05-01

    About 1% of all sudden ionospheric disturbances (SIDs) observed at the Panska Ves Observatory (Czechoslovakia), were found to be not of solar-XUV origin. Among them, the very rare SWF events (observed at L 2.4) of corpuscular origin are the most interesting. The IMF sector structure effects in the midlatitude lower ionosphere are minor in comparison with effects of solar flares, geomagnetic storms, etc. There are two basic types of effects. The first type is a disturbance, best developed in geomagnetic activity, and observed in the night-time ionosphere. It can be interpreted as a response to sector structure related changes of geomagnetic (magnetospheric) activity. The other type is best developed in the tropospheric vorticity area index and is also observed in the day-time ionosphere in winter. This effect is quietening in the ionosphere as well as troposphere. While the occurrence of the former type is persistent in time, the latter is severely diminished in some periods. All the stratosphere, the 10-mb level temperature and height above Berlin-Tempelhof do not display any observable IMF section structure effect.

  17. Solar Flares

    NASA Astrophysics Data System (ADS)

    Rust, David

    1998-01-01

    The Sun is constantly changing. Not an hour goes by without a rise or fall in solar x-radiation or radio emission. Not a day goes by without a solar flare. Our active star, this inconsistent Sun, this gaseous cloud that blows in all directions, warms the air we breathe and nourishes the food we eat. From Earth, it seems the very model of stability, but in space it often creates havoc. Over the past century, solar physicists have learned how to detect even the weakest of solar outbursts or flares. We know that flares must surely trace their origins to the magnetic strands stretched and tangled by the rolling plasma of the solar interior. Although a century of astrophysical research has produced widely accepted, fundamental understanding about the Sun, we have yet to predict successfully the emergence of any magnetic fields from inside the Sun or the ignition of any flare. As in any physical experiment, the ability to predict events not only validates the scientific ideas, it also has practical value. In astrophysics, a demonstrated understanding of sunspots, flares, and ejections of plasma would allow us to approach many other mysteries, such as stellar X-ray bursters, with tested theories.

  18. TEMPERATURE AND ELECTRON DENSITY DIAGNOSTICS OF A CANDLE-FLAME-SHAPED FLARE

    SciTech Connect

    Guidoni, S. E.; Plowman, J. E.

    2015-02-10

    Candle-flame-shaped flares are archetypical structures that provide indirect evidence of magnetic reconnection. A flare resembling Tsuneta's famous 1992 candle-flame flare occurred on 2011 January 28; we present its temperature and electron density diagnostics. This flare was observed with Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA), Hinode/X-Ray Telescope (XRT), and Solar Terrestrial Relations Observatory Ahead (STEREO-A)/Extreme Ultraviolet Imager, resulting in high-resolution, broad temperature coverage, and stereoscopic views of this iconic structure. The high-temperature images reveal a brightening that grows in size to form a tower-like structure at the top of the posteruption flare arcade, a feature that has been observed in other long-duration events. Despite the extensive work on the standard reconnection scenario, there is no complete agreement among models regarding the nature of this high-intensity elongated structure. Electron density maps reveal that reconnected loops that are successively connected at their tops to the tower develop a density asymmetry of about a factor of two between the two legs, giving the appearance of ''half-loops''. We calculate average temperatures with a new fast differential emission measure (DEM) method that uses SDO/AIA data and analyze the heating and cooling of salient features of the flare. Using STEREO observations, we show that the tower and the half-loop brightenings are not a line-of-sight projection effect of the type studied by Forbes and Acton. This conclusion opens the door for physics-based explanations of these puzzling, recurrent solar flare features, previously attributed to projection effects. We corroborate the results of our DEM analysis by comparing them with temperature analyses from Hinode/XRT.

  19. Temperature and Electron Density Diagnostics of a Candle-flame-shaped Flare

    NASA Astrophysics Data System (ADS)

    Guidoni, S. E.; McKenzie, D. E.; Longcope, D. W.; Plowman, J. E.; Yoshimura, K.

    2015-02-01

    Candle-flame-shaped flares are archetypical structures that provide indirect evidence of magnetic reconnection. A flare resembling Tsuneta's famous 1992 candle-flame flare occurred on 2011 January 28; we present its temperature and electron density diagnostics. This flare was observed with Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA), Hinode/X-Ray Telescope (XRT), and Solar Terrestrial Relations Observatory Ahead (STEREO-A)/Extreme Ultraviolet Imager, resulting in high-resolution, broad temperature coverage, and stereoscopic views of this iconic structure. The high-temperature images reveal a brightening that grows in size to form a tower-like structure at the top of the posteruption flare arcade, a feature that has been observed in other long-duration events. Despite the extensive work on the standard reconnection scenario, there is no complete agreement among models regarding the nature of this high-intensity elongated structure. Electron density maps reveal that reconnected loops that are successively connected at their tops to the tower develop a density asymmetry of about a factor of two between the two legs, giving the appearance of "half-loops." We calculate average temperatures with a new fast differential emission measure (DEM) method that uses SDO/AIA data and analyze the heating and cooling of salient features of the flare. Using STEREO observations, we show that the tower and the half-loop brightenings are not a line-of-sight projection effect of the type studied by Forbes & Acton. This conclusion opens the door for physics-based explanations of these puzzling, recurrent solar flare features, previously attributed to projection effects. We corroborate the results of our DEM analysis by comparing them with temperature analyses from Hinode/XRT.

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

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  1. Flares and habitability

    NASA Astrophysics Data System (ADS)

    Abrevaya, Ximena C.; Cortón, Eduardo; Mauas, Pablo J. D.

    2012-07-01

    At present, dwarf M stars are being considered as potential hosts for habitable planets. However, an important fraction of these stars are flare stars, which among other kind of radiation, emit large amounts of UV radiation during flares, and it is unknown how this events can affect life, since biological systems are particularly vulnerable to UV. In this work we evaluate a well known dMe star, EV Lacertae (GJ 873) as a potential host for the emergence and evolution of life, focusing on the effects of the UV emission associated with flare activity. Since UV-C is particularly harmful for living organisms, we studied the effect of UV-C radiation on halophile archaea cultures. The halophile archaea or haloarchaea are extremophile microorganisms, which inhabit in hypersaline environments and which show several mechanisms to cope with UV radiation since they are naturally exposed to intense solar UV radiation on Earth. To select the irradiance to be tested, we considered a moderate flare on this star. We obtained the mean value for the UV-C irradiance integrating the IUE spectrum in the impulsive phase, and considering a hypothetical planet in the center of the liquid water habitability zone. To select the irradiation times we took the most frequent duration of flares on this star which is from 9 to 27 minutes. Our results show that even after considerable UV damage, the haloarchaeal cells survive at the tested doses, showing that this kind of life could survive in a relatively hostile UV environment.

  2. Effect of calcium hydroxide and triple antibiotic paste as intracanal medicaments on the incidence of inter-appointment flare-up in diabetic patients: An in vivo study

    PubMed Central

    Pai, Swathi; Vivekananda Pai, A. R.; Thomas, Manuel S.; Bhat, Vishal

    2014-01-01

    Aim: To evaluate and compare the effect of antibacterial intracanal medicaments on inter-appointment flare-up in diabetic patients. Materials and Methods: Fifty diabetic patients requiring root canal treatment were assigned into groups I, II, and III. In group I, no intracanal medicament was placed. In groups II and III, calcium hydroxide and triple antibiotic pastes were placed as intracanal medicaments, respectively. Patients were instructed to record their pain on days 1, 2, 3, 7, and 14. Inter-appointment flare-up was evaluated using verbal rating scale (VRS). Results: Overall incidence of inter-appointment flare-up among diabetic patients was found to be 16%. In group I, 50% of the patients and in group II, 15% of the patients developed inter-appointment flare-up. However, no patients in group III developed inter-appointment flare-up. The comparison of these results was found to be statistically significant (P = 0.002; χ2 = 12.426). However, with respect to intergroup comparison, only the difference between groups I and III was found to be statistically significant (P = 0.002; χ2 = 12.00). Conclusions: Calcium hydroxide and triple antibiotic paste are effective for managing inter-appointment flare-ups in diabetic patients. Triple antibiotic paste is more effective than calcium hydroxide in preventing the occurrence of flare-up in diabetic patients. PMID:24944440

  3. Thermal instability in post-flare plasmas

    NASA Technical Reports Server (NTRS)

    Antiochos, S. K.

    1976-01-01

    The cooling of post-flare plasmas is discussed and the formation of loop prominences is explained as due to a thermal instability. A one-dimensional model was developed for active loop prominences. Only the motion and heat fluxes parallel to the existing magnetic fields are considered. The relevant size scales and time scales are such that single-fluid MHD equations are valid. The effects of gravity, the geometry of the field and conduction losses to the chromosphere are included. A computer code was constructed to solve the model equations. Basically, the system is treated as an initial value problem (with certain boundary conditions at the chromosphere-corona transition region), and a two-step time differencing scheme is used.

  4. The Effect of Magnetic Topology on the Escape of Flare Particles

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

    Magnetic reconnection in the solar atmosphere is believed to be the driver of most solar explosive phenomena. Therefore, the topology of the coronal magnetic field is central to understanding the solar drivers of space weather. Of particular importance to space weather are the impulsive Solar Energetic particles that are associated with some CME/eruptive flare events. Observationally, the magnetic configuration of active regions where solar eruptions originate appears to agree with the standard eruptive flare model. According to this model, particles accelerated at the flare reconnection site should remain trapped in the corona and the ejected plasmoid. However, flare-accelerated particles frequently reach the Earth long before the CME does. We present a model that may account for the injection of energetic particles onto open magnetic flux tubes connecting to the Earth. Our model is based on the well-known 2.5D breakout topology, which has a coronal null point (null line) and a four-flux system. A key new addition, however, is that we include an isothermal solar wind with open-flux regions. Depending on the location of the open flux with respect to the null point, we find that the flare reconnection can consist of two distinct phases. At first, the flare reconnection involves only closed field, but if the eruption occurs close to the open field, we find a second phase involving interchange reconnection between open and closed. We argue that this second reconnection episode is responsible for the injection of flare-accelerated particles into the interplanetary medium. We will report on our recent work toward understanding how flare particles escape to the heliosphere. This work uses high-resolution 2.5D MHD numerical simulations performed with the Adaptively Refined MHD Solver (ARMS).

  5. Anemone structure of AR NOAA 10798 and related geo-effective flares and CMEs

    NASA Astrophysics Data System (ADS)

    Asai, A.; Ishii, T. T.; Shibata, K.; Gopalswamy, N.

    We report coronal features of an active region NOAA 10798 This active region was located in the middle of a small coronal hole and generated 3 M-class flares The flares are associated with high speed CMEs which produced a magnetic storm on 2005 August 24 We examined the coronal features by using observational data in soft X-rays in extreme ultraviolets and in microwaves obtained with GOES SOHO TRACE satellites and Nobeyama Radioheliograph

  6. Effective dynamics in Bianchi type II loop quantum cosmology

    NASA Astrophysics Data System (ADS)

    Corichi, Alejandro; Montoya, Edison

    2012-05-01

    We numerically investigate the solutions to the effective equations of the Bianchi II model within the “improved” loop quantum cosmology dynamics. The matter source is a massless scalar field. We perform a systematic study of the space of solutions, and focus on the behavior of several geometrical observables. We show that the big bang singularity is replaced by a bounce and the pointlike singularities do not saturate the energy density bound. There are up to three directional bounces in the scale factors, one global bounce in the expansion, the shear presents up to four local maxima and can be zero at the bounce. This allows for solutions with density larger than the maximal density for the isotropic and Bianchi I cases. The asymptotic behavior is shown to behave like that of a Bianchi I model, and the effective solutions connect anisotropic solutions even when the shear is zero at the bounce. All known facts of Bianchi I are reproduced. In the “vacuum limit,” solutions are such that almost all the dynamics is due to the anisotropies. Since Bianchi II plays an important role in the Bianchi IX model and the Belinskii, Khalatnikov, Lifshitz conjecture, our results can provide an intuitive understanding of the behavior in the vicinity of general spacelike singularities, when loop-geometric corrections are present.

  7. FLARES AND THEIR UNDERLYING MAGNETIC COMPLEXITY

    SciTech Connect

    Engell, Alexander J.; Golub, Leon; Korreck, Kelly; Siarkowski, Marek; Gryciuk, Magda; Sylwester, Janusz; Sylwester, Barbara; Cirtain, Jonathan

    2011-01-01

    SphinX (Solar PHotometer IN X-rays), a full-disk-integrated spectrometer, observed 137 flare-like/transient events with active region (AR) 11024 being the only AR on disk. The Hinode X-Ray Telescope (XRT) and Solar Optical Telescope observe 67 of these events and identified their location from 12:00 UT on July 3 through 24:00 UT 2009 July 7. We find that the predominant mechanisms for flares observed by XRT are (1) flux cancellation and (2) the shearing of underlying magnetic elements. Point- and cusp-like flare morphologies seen by XRT all occur in a magnetic environment where one polarity is impeded by the opposite polarity and vice versa, forcing the flux cancellation process. The shearing is either caused by flux emergence at the center of the AR and separation of polarities along a neutral line or by individual magnetic elements having a rotational motion. Both mechanisms are observed to contribute to single- and multiple-loop flares. We observe that most loop flares occur along a large portion of a polarity inversion line. Point- and cusp-like flares become more infrequent as the AR becomes organized with separation of the positive and negative polarities. SphinX, which allows us to identify when these flares occur, provides us with a statistically significant temperature and emission scaling law for A and B class flares: EM = 6.1 x 10{sup 33} T{sup 1.9{+-}0.1}.

  8. Flares and Their Underlying Magnetic Complexity

    NASA Astrophysics Data System (ADS)

    Engell, Alexander J.; Siarkowski, Marek; Gryciuk, Magda; Sylwester, Janusz; Sylwester, Barbara; Golub, Leon; Korreck, Kelly; Cirtain, Jonathan

    2011-01-01

    SphinX (Solar PHotometer IN X-rays), a full-disk-integrated spectrometer, observed 137 flare-like/transient events with active region (AR) 11024 being the only AR on disk. The Hinode X-Ray Telescope (XRT) and Solar Optical Telescope observe 67 of these events and identified their location from 12:00 UT on July 3 through 24:00 UT 2009 July 7. We find that the predominant mechanisms for flares observed by XRT are (1) flux cancellation and (2) the shearing of underlying magnetic elements. Point- and cusp-like flare morphologies seen by XRT all occur in a magnetic environment where one polarity is impeded by the opposite polarity and vice versa, forcing the flux cancellation process. The shearing is either caused by flux emergence at the center of the AR and separation of polarities along a neutral line or by individual magnetic elements having a rotational motion. Both mechanisms are observed to contribute to single- and multiple-loop flares. We observe that most loop flares occur along a large portion of a polarity inversion line. Point- and cusp-like flares become more infrequent as the AR becomes organized with separation of the positive and negative polarities. SphinX, which allows us to identify when these flares occur, provides us with a statistically significant temperature and emission scaling law for A and B class flares: EM = 6.1 × 1033 T 1.9±0.1.

  9. The Effect of Nonspecific Binding of Lambda Repressor on DNA Looping Dynamics

    PubMed Central

    Manzo, Carlo; Zurla, Chiara; Dunlap, David D.; Finzi, Laura

    2012-01-01

    The λ repressor (CI) protein-induced DNA loop maintains stable lysogeny, yet allows efficient switching to lysis. Herein, the kinetics of loop formation and breakdown has been characterized at various concentrations of protein using tethered particle microscopy and a novel, to our knowledge, method of analysis. Our results show that a broad distribution of rate constants and complex kinetics underlie loop formation and breakdown. In addition, comparison of the kinetics of looping in wild-type DNA and DNA with mutated o3 operators showed that these sites may trigger nucleation of nonspecific binding at the closure of the loop. The average activation energy calculated from the rate constant distribution is consistent with a model in which nonspecific binding of CI between the operators shortens their effective separation, thereby lowering the energy barrier for loop formation and broadening the rate constant distribution for looping. Similarly, nonspecific binding affects the kinetics of loop breakdown by increasing the number of loop-securing protein interactions, and broadens the rate constant distribution for this reaction. Therefore, simultaneous increase of the rate constant for loop formation and reduction of that for loop breakdown stabilizes lysogeny. Given these simultaneous changes, the frequency of transitions between the looped and the unlooped state remains nearly constant. Although the loop becomes more stable thermodynamically with increasing CI concentration, it still opens periodically, conferring sensitivity to environmental changes, which may require switching to lytic conditions. PMID:23083719

  10. ELF effects caused by the giant gamma-flare of Dec. 27, 2004

    NASA Astrophysics Data System (ADS)

    Nickolaenko, Alexander; Hobara, Yasuhide; Kudintseva, Irina; Pechony, Olga; Hayakawa, Masashi; Schekotov, Alexander; Sátori, Gabriella; Bór, József; Neska, Mariusz

    The report presents extremely low frequency (ELF) observations associated with the giant gamma-ray flare from SGR 1806-20 on Dec. 27, 2004. Electromagnetic signals were treated in the frequency band of the global electromagnetic (Schumann) resonance. The gamma flare lowered the ionosphere over the dayside of the globe and thus modified the Schumann resonance spectra. We exploited the continuous ELF data recorded at the Moshiri observatory, Japan (44.37° N and 142.24° E) at the moment of flare. Sonograms were compared with the model data describing the expected modifications. Simultaneous abrupt changes were present in the observed resonance pattern. The gamma quanta also modified the global electric circuit and thus caused a ‘parametric’ ELF transient, which was globally detected by Schumann resonance observatories. We show the GPS synchronized experimental records of ELF pulses relevant to the gamma flare collected at Moshiri, Japan (44.37° N and 142.24° E), Onagawa, Japan (38.43° N; 141.48° E), Esrange, Sweden (67.83° N; 21.1° E), Karimshino, Russia (52.83° N; 158.13° E), Nagycenk, Hungary (47.6° N; 16.7° E), and Polish station Hornsund, Spitzbergen, (77.0°N; 15.5°E). Data demonstrate an exceptional similarity and contain a pair of characteristic pulses around the occurrence time of gamma flare. Wavelet processing showed that: - pulses arrived around the time of gamma flare; - the lowest Schumann resonance mode dominated in the spectra; - the source bearings corresponded to the position of sub-flare point; - polarity of the source current was positive; - the radio wave polarization was close to linear. These properties are in accord with the concept of a parametric electromagnetic pulse originating from a sizeable modification of the global electric circuit. Model results were compared with records revealing changes in the global electric circuit.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  13. Fields, Flares, And Forecasts

    NASA Astrophysics Data System (ADS)

    Boucheron, L.; Al-Ghraibah, Amani; McAteer, J.; Cao, H.; Jackiewicz, J.; McNamara, B.; Voelz, D.; Calabro, B.; DeGrave, K.; Kirk, M.; Madadi, A.; Petsov, A.; Taylor, G.

    2011-05-01

    Solar active regions are the source of many energetic and geo-effective events such as solar flares and coronal mass ejections (CMEs). Understanding how these complex source regions evolve and produce these events is of fundamental importance, not only to solar physics, but also to the demands of space weather forecasting. We propose to investigate the physical properties of active region magnetic fields using fractal-, gradient-, neutral line-, emerging flux-, wavelet- and general image-based techniques, and to correlate them to solar activity. The combination of these projects with solarmonitor.org and the international Max Millenium Campaign presents an opportunity for accurate and timely flare predictions for the first time. Many studies have attempted to relate solar flares to their concomitant magnetic field distributions. However, a consistent, causal relationship between the magnetic field on the photosphere and the production of solar flares is unknown. Often the local properties of the active region magnetic field - critical in many theories of activity - are lost in the global definition of their diagnostics, in effect smoothing out variations that occur on small spatial scales. Mindful of this, our overall goal is to create measures that are sensitive to both the global and the small-scale nature of energy storage and release in the solar atmosphere in order to study solar flare prediction. This set of active region characteristics will be automatically explored for discriminating features through the use of feature selection methods. Such methods search a feature space while optimizing a criterion - the prediction of a flare in this case. The large size of the datasets used in this project make it well suited for an exploration of a large feature space. This work is funded through a New Mexico State University Interdisciplinary Research Grant.

  14. Outer Atmospheres of Low Mass Stars — Flare Characteristics.

    NASA Astrophysics Data System (ADS)

    Lalitha, S.; Schmitt, J. H. M. M.

    2013-04-01

    We compare the coronal properties during flares on active low mass stars CN Leonis, AB Doradus A and Proxima Centauri observed with XMM-Newton. From the X-ray data we analyze the temporal evolution of temperature, emission measure and coronal abundance. The nature of these flares are with secondary events following the first flare peak in the light curve, raising the question regarding the involved magnetic structure. We infer from the plasma properties and the geometry of the flaring structure that the flare originates from a compact arcade rather than in a single loop.

  15. Flare models: Chapter 9 of solar flares

    NASA Technical Reports Server (NTRS)

    Sturrock, P. A. (Editor)

    1979-01-01

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

  16. One loop superstring effective actions and N=8 supergravity

    SciTech Connect

    Moura, Filipe

    2008-06-15

    In a previous article we have shown the existence of a new independent R{sup 4} term, at one loop, in the type IIA and heterotic effective actions, after reduction to four dimensions, besides the usual square of the Bel-Robinson tensor. It had been shown that such a term could not be directly supersymmetrized, but we showed that was possible after coupling to a scalar chiral multiplet. In this article, we study the extended (N=8) supersymmetrization of this term, where no other coupling can be taken. We show that such supersymmetrization cannot be achieved at the linearized level. This is in conflict with the theory one gets after toroidal compactification of type II superstrings being N=8 supersymmetric. We interpret this result in the face of the recent claim that perturbative supergravity cannot be decoupled from string theory in d{>=}4, and N=8, d=4 supergravity is in the swampland.

  17. Study of the effect of solar flares on VLF signals during D-layer preparation or disappearance time

    NASA Astrophysics Data System (ADS)

    Ray, Suman; Chakrabarti, Sandip Kumar; Palit, Sourav

    2016-07-01

    "Very Low Frequency" (VLF) is one of the bands of the Radio waves having frequency 3-30 KHz, which propagates through the Earth-ionosphere wave-guide. In relation to propagation of radio waves through ionosphere, low mass and high mobility cause electrons to play a vital role. Electrons are not distributed uniformly in the ionosphere and depending on this factor, ionosphere has different layers namely D, E and F. Different ionospheric layers generally exist during day and night time. During day-time when the main source of the ionization of the ionosphere is Sun, the lower most layer of ionosphere is D-layer. But during the night-time when Sun is absent and cosmic ray is the main source of the ionization of the ionosphere, this D-layer disappears and E-layer becomes the lower most region of the ionosphere. Normally, patterns of VLF signal depend on regular solar flux variations. However, during solar flares extra energetic particles are released from Sun, which makes the changes in the ionization of the ionosphere and these changes can perturb VLF signal amplitude. Usually if a solar flare occurs during any time of day, it only affects the amplitude and phase of the VLF signals. But in the present work, we found the if the flare occurs during D-layer preparation / disappearance time, then it will not only affect to amplitude and phase of the VLF signals but also to terminator times of VLF signals. We have observed that the sun set terminator time of the VLF signals shifted towards night time due to the effect of a M-class solar flare which occurred during the D-layer disappearance time. The shift is so high that it crossed 5σ level. We are now trying to a make model using the ion-chemistry and LWPC code to explain this observed effect.

  18. Analyzing the effectiveness of flare dispensing programs against pulse width modulation seekers using self-organizing maps

    NASA Astrophysics Data System (ADS)

    Şahingil, Mehmet C.; Aslan, Murat Š.

    2013-10-01

    Infrared guided missile seekers utilizing pulse width modulation in target tracking is one of the threats against air platforms. To be able to achieve a "soft-kill" protection of own platform against these type of threats, one needs to examine carefully the seeker operating principle with its special electronic counter-counter measure (ECCM) capability. One of the cost-effective ways of soft kill protection is to use flare decoys in accordance with an optimized dispensing program. Such an optimization requires a good understanding of the threat seeker, capabilities of the air platform and engagement scenario information between them. Modeling and simulation is very powerful tool to achieve a valuable insight and understand the underlying phenomenology. A careful interpretation of simulation results is crucial to infer valuable conclusions from the data. In such an interpretation there are lots of factors (features) which affect the results. Therefore, powerful statistical tools and pattern recognition algorithms are of special interest in the analysis. In this paper, we show how self-organizing maps (SOMs), which is one of those powerful tools, can be used in analyzing the effectiveness of various flare dispensing programs against a PWM seeker. We perform several Monte Carlo runs for a typical engagement scenario in a MATLAB-based simulation environment. In each run, we randomly change the flare dispending program and obtain corresponding class: "successful" or "unsuccessful", depending on whether the corresponding flare dispensing program deceives the seeker or not, respectively. Then, in the analysis phase, we use SOMs to interpret and visualize the results.

  19. The smallest hard X-ray flare?

    NASA Astrophysics Data System (ADS)

    Glesener, Lindsay; Krucker, Sam; Hannah, Iain; Smith, David M.; Grefenstette, Brian; Marsh, Andrew; Hudson, Hugh S.; White, Stephen M.; Chen, Bin

    2016-05-01

    We report a NuSTAR observation of a small solar flare on 2015 September 1, estimated to be on the order of a GOES class A.05 flare in brightness. This flare is fainter than any hard X-ray (HXR) flares in the existing literature, and with a peak rate of only ∼5 counts s‑1 detector‑1 observed by RHESSI, is effectively the smallest that can just barely be detected by the current standard (indirectly imaging) solar HXR instrumentation, though we expect that smaller flares will continue to be discovered as instrumental and observational techniques progress. The flare occurred during a solar observation by the highly sensitive NuSTAR astrophysical HXR spacecraft, which used its direct focusing optics to produce detailed flare spectra and images. The flare exhibits properties commonly observed in larger flares, including a fast rise and more gradual decay, and similar spatial dimensions to the RHESSI microflares. We will discuss the presence of non-thermal (flare-accelerated) electrons during the impulsive phase. The flare is small in emission measure, temperature, and energy, though not in physical dimensions. Its presence is an indication that flares do indeed scale down to smaller energies and retain what we customarily think of as “flarelike” properties.

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

    SciTech Connect

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

    1990-01-01

    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.

  1. The Myth of Long Duration Flare Emission: Slow Heating or Slow Cooling?

    NASA Astrophysics Data System (ADS)

    Qiu, Jiong; Longcope, Dana; Klimchuk, James A.

    2015-04-01

    Long duration flare emissions lasting for a few hours are likely governed by magnetic reconnection that continuously heats flare plasmas in continuously formed flare loops. In this study, we confirm that this process leads to the long-duration total emission for up to four hours in a C2.9 flare on 2011 September 13. Observed by AIA, the flare exhibits an ordered spread of flare UV ribbons along the polarity inversion line, followed by the sequential formation of post-flare loops in EUV emissions. We infer heating rates of thousands of flare loops from the UV light curves at the flare foot-points, and model the flare total emission with the 0d EBTEL model, which reproduces the global evolution pattern of the long-duration flare EUV emissions as the result of superposition of continuously formed and heated flare loops. However, observations at single loop pixels also show long duration EUV emission at 10 MK, long cooling time from 10 MK to 3 MK, and later on very short duration of EUV emission at 1-2 MK. All of these signatures cannot be produced by superposition of multiple impulsive heating events. Our experiments, with both the 0d EBTEL model and a 1d hydrodynamic model, have demonstrated that a heating profile in a single loop consisting of two parts, an intense impulsive heating followed by a low-rate heating 1-2 orders of magnitude smaller that is attenuated over 20-30 minutes, is required to produce the observed time evolution signatures in a single loop. The total energy in the gradual heating phase is comparable with that in the impulsive heating phase in a flare loop. We discuss viable physical mechanisms for such two-phase heating in a post-reconnection flare loop.

  2. Laser energy deposition effectiveness on shock-wave boundary-layer interactions over cylinder-flare combinations

    NASA Astrophysics Data System (ADS)

    Osuka, T.; Erdem, E.; Hasegawa, N.; Majima, R.; Tamba, T.; Yokota, S.; Sasoh, A.; Kontis, K.

    2014-09-01

    The effects of repetitive laser-pulse energy depositions (5.5 mJ/pulse) onto a shock wave-boundary layer interaction region over cylinder-flare model in a Mach 1.92 flow are experimentally investigated. Depending on the nose shape and the flare angle, the flow patterns are subdivided to two; separated flow in which a slip line and a strong separation shock wave originated in the nose-cylinder junction appears, and a non-separated flow in which a slip line is not observed and the re-attachment shock wave is much weaker. At flare angles around 30°, the separation can be suppressed by laser energy deposition even of down to 5 kHz. The Schlieren-visualized flow patterns are well correlated to the drag characteristics, in which a larger drag is obtained without separation. A possible scenario of the separation control is that the disturbance introduced by the baroclinic vortex ring induced the boundary layer transition so that it became robust against the adverse pressure gradient. Under marginal conditions, dual mode flow patterns, that is, a partial and full suppression modes are obtained under the same operation conditions.

  3. The Effects of Low- and High-Energy Cutoffs on Solar Flare Microwave and Hard X-Ray Spectra

    NASA Technical Reports Server (NTRS)

    Holman, G. D.; Oegerle, William (Technical Monitor)

    2002-01-01

    Microwave and hard x-ray spectra provide crucial information about energetic electrons and their environment in solar flares. These spectra are becoming better determined with the Owens Valley Solar Array (OVSA) and the recent launch of the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The proposed Frequency Agile Solar Radiotelescope (FASR) promises even greater advances in radio observations of solar flares. Both microwave and hard x-ray spectra are sensitive to cutoffs in the electron distribution function. The determination of the high-energy cutoff from these spectra establishes the highest electron energies produced by the acceleration mechanism, while determination of the low-energy cutoff is crucial to establishing the total energy in accelerated electrons. This paper will show computations of the effects of both high- and low-energy cutoffs on microwave and hard x-ray spectra. The optically thick portion of a microwave spectrum is enhanced and smoothed by a low-energy cutoff, while a hard x-ray spectrum is flattened below the cutoff energy. A high-energy cutoff steepens the microwave spectrum and increases the wavelength at which the spectrum peaks, while the hard x-ray spectrum begins to steepen at photon energies roughly an order of magnitude below the electron cutoff energy. This work discusses how flare microwave and hard x-ray spectra can be analyzed together to determine these electron cutoff energies. This work is supported in part by the NASA Sun-Earth Connection Program.

  4. THE COOLING OF CORONAL PLASMAS. IV. CATASTROPHIC COOLING OF LOOPS

    SciTech Connect

    Cargill, P. J.; Bradshaw, S. J.

    2013-07-20

    We examine the radiative cooling of coronal loops and demonstrate that the recently identified catastrophic cooling is due to the inability of a loop to sustain radiative/enthalpy cooling below a critical temperature, which can be >1 MK in flares, 0.5-1 MK in active regions, and 0.1 MK in long tenuous loops. Catastrophic cooling is characterized by a rapid fall in coronal temperature, while the coronal density changes by a small amount. Analytic expressions for the critical temperature are derived and show good agreement with numerical results. This effect considerably limits the lifetime of coronal plasmas below the critical temperature.

  5. Effects of inflation on a cosmic string loop population

    SciTech Connect

    Avelino, P. P.; Martins, C. J. A. P.; Shellard, E. P. S.

    2007-10-15

    We study the evolution of simple cosmic string loop solutions in an inflationary universe. We show, for the particular case of circular loops, that periodic solutions do exist in a de Sitter universe, below a critical loop radius R{sub c}H=1/2. On the other hand, larger loops freeze in comoving coordinates, and we explicitly show that they can survive more e-foldings of inflation than pointlike objects. We discuss the implications of these findings for the survival of realistic cosmic string loops during inflation and for the general characteristics of post-inflationary cosmic string networks. We also consider the analogous solutions for domain walls, in which case the critical radius is R{sub c}H=2/3.

  6. The Structure and Dynamics of the Coronal Part of the 06.11.1979 Flare by Ground Spectral Observation

    NASA Astrophysics Data System (ADS)

    Ograpishvili, N. B.; Maghradze, D. A.

    2014-12-01

    The analysis of observational data obtained in the Abastumani Astrophysical Observatory in the form of spectrograms and filter images of formations, related to the limb flare of November, 6th, 1979, is presented. The flare loops system, a late stage development of bright flare loops and post-flare coronal loops received in Hα and coronal lines, were studied. Physical parameters of observable structures, as well as their sizes and interposition were defined. Doppler speeds at different heights are measured. The primary direction of movement of a matter in flare loops upwards from below is revealed.

  7. Pulsed acceleration in solar flares

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  8. Observational Evidence for Loop-Loop Interaction

    NASA Astrophysics Data System (ADS)

    Guiping, W.; Guangli, H.; Yuhua, T.; Aoao, X.

    2004-01-01

    Through analysis of the data including the hard x-ray(BASTE) microwave(NoRP) and magnetogram(MDI from SOHO) as well as the images of soft x-ray(YHKOH) and EIT(SOHO) on Apr. 151998 solar flare in the active region 8203(N30W12) we found: (1) there are similar quasi period oscillation in the profile of hard x-ray flux (25-5050-100keV) and microwave flux(1GHz) with duration of 85+/-25s every peak includes two sub-peak structures; (2) in the preheat phase of the flare active magnetic field changes apparently and a s-pole spot emerges ; (3) several EIT and soft x-ray loops exist and turn into bright . All of these may suggest that loop-loop interaction indeed exist. Through reconnection the electrons may be accelerated and the hard x-ray and microwave emission take place.

  9. Effects of Scenery, Lighting, Glideslope, and Experience on Timing the Landing Flare

    ERIC Educational Resources Information Center

    Palmisano, Stephen; Favelle, Simone; Sachtler, W. L.

    2008-01-01

    This study examined three visual strategies for timing the initiation of the landing flare based on perceptions of either: (a) a critical height above ground level; (b) a critical runway width angle ([psi]); or (c) a critical time-to-contact (TTC) with the runway. Visual displays simulated landing approaches with trial-to-trial variations in…

  10. SCATTERING POLARIZATION IN SOLAR FLARES

    SciTech Connect

    Štěpán, Jiří; Heinzel, Petr

    2013-11-20

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

  11. Spatially resolved hard X-ray polarization in solar flares: effects of Compton scattering and bremsstrahlung

    NASA Astrophysics Data System (ADS)

    Jeffrey, N. L. S.; Kontar, E. P.

    2011-12-01

    Aims: We study the polarization of hard X-ray (HXR) sources in the solar atmosphere, including Compton backscattering of photons in the photosphere (the albedo effect) and the spatial distribution of polarization across the source. Methods: HXR photon polarization and spectra produced via electron-ion bremsstrahlung emission are calculated from various electron distributions typical for solar flares. Compton scattering and photoelectric absorption are then modelled using Monte Carlo simulations of photon transport in the photosphere to study the observed (primary and albedo) sources. Polarization maps across HXR sources (primary and albedo components) for each of the modelled electron distributions are calculated at various source locations from the solar centre to the limb. Results: We show that Compton scattering produces a distinct polarization variation across the albedo patch at peak albedo energies of 20-50 keV for all anisotropies modelled. The results show that there are distinct spatial polarization changes in both the radial and perpendicular to radial directions across the extent of the HXR source at a given disk location. In the radial direction, the polarization magnitude and direction at specific positions along the HXR source will either increase or decrease with increased photon distribution directivity towards the photosphere. We also show how high electron cutoff energies influence the direction of polarization at above ~100 keV. Conclusions: Spatially resolved HXR polarization measurements can provide important information about the directivity and energetics of the electron distribution. Our results indicate the preferred angular resolution of polarization measurements required to distinguish between the scattered and primary components. We also show how spatially resolved polarization measurements could be used to probe the emission pattern of an HXR source, using both the magnitude and the direction of the polarization.

  12. The landing flare: An analysis and flight-test investigation

    NASA Technical Reports Server (NTRS)

    Seckel, E.

    1975-01-01

    Results are given of an extensive investigation of conventional landing flares in general aviation type airplanes. A wide range of parameters influencing flare behavior are simulated in experimental landings in a variable-stability Navion. The most important feature of the flare is found to be the airplane's deceleration in the flare. Various effects on this are correlated in terms of the average flare load factor. Piloting technique is extensively discussed. Design criteria are presented.

  13. How Did a Major Confined Flare Occur in Super Solar Active Region 12192?

    NASA Astrophysics Data System (ADS)

    Jiang, Chaowei; Wu, S. T.; Yurchyshyn, Vasyl; Wang, Haiming; Feng, Xueshang; Hu, Qiang

    2016-09-01

    We study the physical mechanism of a major X-class solar flare that occurred in the super NOAA active region (AR) 12192 using data-driven numerical magnetohydrodynamic (MHD) modeling complemented with observations. With the evolving magnetic fields observed at the solar surface as bottom boundary input, we drive an MHD system to evolve self-consistently in correspondence with the realistic coronal evolution. During a two-day time interval, the modeled coronal field has been slowly stressed by the photospheric field evolution, which gradually created a large-scale coronal current sheet, i.e., a narrow layer with intense current, in the core of the AR. The current layer was successively enhanced until it became so thin that a tether-cutting reconnection between the sheared magnetic arcades was set in, which led to a flare. The modeled reconnecting field lines and their footpoints match well the observed hot flaring loops and the flare ribbons, respectively, suggesting that the model has successfully “reproduced” the macroscopic magnetic process of the flare. In particular, with simulation, we explained why this event is a confined eruption—the consequence of the reconnection is a shared arcade instead of a newly formed flux rope. We also found a much weaker magnetic implosion effect compared to many other X-class flares.

  14. Particle propagation, wave growth and energy dissipation in a flaring flux tube

    NASA Technical Reports Server (NTRS)

    White, S. M.; Melrose, D. B.; Dulk, G. A.

    1986-01-01

    Wave amplification by downgoing particles in a common flare model is investigated. The flare is assumed to occur at the top of a coronal magnetic flux loop, and results in the heating of plasma in the flaring region. The hot electrons propagate down the legs of the flux tube towards increasing magnetic field. It is simple to demonstrate that the velocity distributions which result in this model are unstable to both beam instabilities and cyclotron maser action. An explanation is presented for the propagation effects on the distribution, and the properties of the resulting amplified waves are explored, concentrating on cyclotron maser action, which has properties (emission in the z mode below the local gyrofrequency) quite different from maser action by other distributions considered in the context of solar flares. The z mode waves will be damped in the coronal plasma surrounding the flaring flux tube and lead to heating there. This process may be important in the overall energy budget of the flare. The downgoing maser is compared with the loss cone maser, which is more likely to produce observable bursts.

  15. Effect of Interaction between Chromatin Loops on Cell-to-Cell Variability in Gene Expression

    PubMed Central

    Zhou, Tianshou

    2016-01-01

    According to recent experimental evidence, the interaction between chromatin loops, which can be characterized by three factors—connection pattern, distance between regulatory elements, and communication form, play an important role in determining the level of cell-to-cell variability in gene expression. These quantitative experiments call for a corresponding modeling effect that addresses the question of how changes in these factors affect variability at the expression level in a systematic rather than case-by-case fashion. Here we make such an effort, based on a mechanic model that maps three fundamental patterns for two interacting DNA loops into a 4–state model of stochastic transcription. We first show that in contrast to side-by-side loops, nested loops enhance mRNA expression and reduce expression noise whereas alternating loops have just opposite effects. Then, we compare effects of facilitated tracking and direct looping on gene expression. We find that the former performs better than the latter in controlling mean expression and in tuning expression noise, but this control or tuning is distance–dependent, remarkable for moderate loop lengths, and there is a limit loop length such that the difference in effect between two communication forms almost disappears. Our analysis and results justify the facilitated chromatin–looping hypothesis. PMID:27153118

  16. The Effect of Radiative Cooling on Coronal Loop Oscillations

    NASA Astrophysics Data System (ADS)

    Aschwanden, Markus J.; Terradas, Jaume

    2008-10-01

    Coronal loops that exhibit kink-mode oscillations have generally been assumed to have a constant density and temperature during the observed time interval. Analyzing their intensities in an EUV wave band, however, clearly shows that their brightness varies in a way that is consistent with a temperature cooling through the EUV passband, which limits their detection time, observed damping time, and number of observable periods. We study kink-mode oscillations of eight loops observed during the so-called harmonica event on 2001 April 15, 21:58-22:27 UT in the 171 Å band. We find loop densities of ne = (1.4 +/- 0.6) × 109 cm-3, loop widths of w = 2.0 +/- 2.6 Mm, and e-folding cooling times of τcool = 17 +/- 7 minutes, when they cool through the peak temperature T = 0.95 MK of the 171 Å band. We conclude that oscillations of a single loop cannot be detected longer than 10-20 minutes in one single filter and appropriate light curve modeling is necessary to disentangle the subsequent oscillation phases of multiple near-cospatial loops.

  17. A multiwavelength study of a double impulsive flare

    NASA Technical Reports Server (NTRS)

    Strong, K. T.; Benz, A. O.; Dennis, B. R.; Poland, A. I.; Leibacher, J. W.; Mewe, R.; Schrijver, J.; Simnett, G.; Smith, J. B., Jr.; Sylwester, J.

    1984-01-01

    Solar Maximum Mission (SMM) and ground-based observations are given for two flares which occurred 3 min apart in the same section of the active region. The physical characteristics of the two flares are derived and compared, and the main difference between them is noted to be in the preflare state of the coronal plasma at the flare site. These data suggest that the plasma filling the flaring loops absorbed most of the energy released during the impulsive phase of the second flare, so that only a fraction of the energy could reach the chromosphere to produce mass motions and turbulence. Since a study of the brightest flares observed by SMM shows that at least 43 percent of them are multiple, the situation presently studied may be quite common, and the difference in initial plasma conditions could explain at least some of the large variations in observed flare parameters.

  18. Solar flare nomenclature

    NASA Astrophysics Data System (ADS)

    Cliver, E. W.

    1995-03-01

    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) of active regions. A list of reserach questions/ problems raised, or brought into focus, by the new paradigm is suggested; in general, these questions bear on the inter- relationships and associations of the two classes (or phases) or flares. Terms such as 'eruptive flare' and 'eruption' (defined to encompass both the CME and its associated eruptive flare) may be useful as nominal links between opposing viewpoints in the 'flares vs CMEs' controversy.

  19. Effect of Variable Emittance Coatings on the Operation of a Miniature Loop Heat Pipe

    NASA Astrophysics Data System (ADS)

    Douglas, Donya M.; Ku, Jentung; Ottenstein, Laura; Swanson, Theodore; Hess, Steve; Darrin, Ann

    2005-02-01

    As the size of spacecraft shrink to accommodate small and more efficient instruments, smaller launch vehicles, and constellation missions, all subsystems must also be made smaller. Under NASA NRA 03-OSS-02, Space Technology-8 (ST 8), NASA Goddard Space Flight Center and Jet Propulsion Laboratory jointly conducted a Concept Definition study to develop a miniature loop heat pipe (loop heat pipe) thermal management system design suitable for future small spacecraft. The proposed loop heat pipe thermal management system consists of a miniature loop heat pipe (LHP) and deployable radiators that are coated with variable emittance coatings (VECs). As part of the Phase A study and proof of the design concept, variable emittance coatings were integrated with a breadboard miniature loop heat pipe. The entire system was tested under vacuum at various temperature extremes and power loads. This paper summarizes the results of this testing and shows the effect of the VEC on the operation of a miniature loop heat pipe.

  20. Energy Transport Effects in Flaring Atmospheres Heated by Mixed Particle Beams

    NASA Astrophysics Data System (ADS)

    Zharkova, Valentina; Zharkov, Sergei; Macrae, Connor; Druett, Malcolm; Scullion, Eamon

    2016-07-01

    We investigate energy and particle transport in the whole flaring atmosphere from the corona to the photosphere and interior for the flaring events on the 1st July 2012, 6 and 7 September 2011 by using the RHESSI and SDO instruments as well as high-resolution observations from the Swedish 1-metre Solar Telescope (SST3) CRISP4 (CRisp Imaging Spectro-polarimeter). The observations include hard and soft X-ray emission, chromospheric emission in both H-alpha 656.3 nm core and continuum, as well as, in the near infra-red triplet Ca II 854.2 nm core and continuum channels and local helioseismic responses (sunquakes). The observations are compared with the simulations of hard X-ray emission and tested by hydrodynamic simulations of flaring atmospheres of the Sun heated by mixed particle beams. The temperature, density and macro-velocity variations of the ambient atmospheres are calculated for heating by mixed beams and the seismic response of the solar interior to generation of supersonic shocks moving into the solar interior. We investigate the termination depths of these shocks beneath the quiet photosphere levels and compare them with the parameters of seismic responses in the interior, or sunquakes (Zharkova and Zharkov, 2015). We also present an investigation of radiative conditions modelled in a full non-LTE approach for hydrogen during flare onsets with particular focus on Balmer and Paschen emission in the visible, near UV and near IR ranges and compare them with observations. The links between different observational features derived from HXR, optical and seismic emission are interpreted by different particle transport models that will allow independent evaluation of the particle transport scenarios.

  1. Spatial Size and Plasma Variables of RHESSI Flares

    NASA Astrophysics Data System (ADS)

    Väänänen, Mikko; Pohjolainen, Silja

    2007-04-01

    We have analysed 64 flares observed with GOES and RHESSI in the 3.1 24.8 keV band (0.5 4 Å). Flares were randomly chosen to represent different GOES classes, between B1 and M6. RHESSI was used to image the flaring region on the surface of the Sun. We derived the spatial area of the flare on the surface of the Sun from the imaging observations, scaled it dimensionally to volume, and used the spectroscopically derived emission measure to obtain several flare parameters. We experimented with several imaging methods and selected the use of 50% maximum image photon flux contours to define the flare area ( F 50%). Most of the flares showed a single spherical loop-top source. The volume measurement for V, temperature T, and electron density N produced power indices that showed no correlation within the boundaries of error. Larger flares by loop-top source volume are thus neither hotter nor denser. The background-subtracted GOES flux RHESSI Total Emission Measure ( TEM RHESSI) and TEM GOES TEM RHESSI dependencies were in agreement with the instrument characteristics and earlier studies. Nonthermal flux was noticed to increase with thermal energy and TEM, which can be said to agree with the “Big Flare Syndrome,” with nonthermal photon flux being considered as one flare manifestation.

  2. 2PI effective action at four loop order in φ4 theory

    NASA Astrophysics Data System (ADS)

    Carrington, M. E.; Meggison, B. A.; Pickering, D.

    2016-07-01

    It is well known that perturbative pressure calculations show poor convergence. Calculations using a two-particle irreducible (2PI) effective action show improved convergence at the 3 loop level, but no calculations have been done at 4 loops. We consider the 2PI effective theory for a symmetric scalar theory with quartic coupling in four dimensions. We calculate the pressure and two different nonperturbative vertices as functions of coupling and temperature. Our results show that the 4 loop contribution can become larger than the 3 loop term when the coupling is large. This indicates a breakdown of the 2PI approach, and the need for higher order n PI approximations. In addition, our results demonstrate the renormalizability of 2PI calculations at the 4 loop level. This is interesting because the counterterm structure of the 2PI theory at 4 loops is different from the structure at n ≤3 loops. Two vertex counterterms are required at the 4 loop level, but not at lower loop order. This unique feature of the 2PI theory has never been verified numerically.

  3. A Cold Flare with Delayed Heating

    NASA Astrophysics Data System (ADS)

    Fleishman, Gregory D.; Pal'shin, Valentin D.; Meshalkina, Natalia; Lysenko, Alexandra L.; Kashapova, Larisa K.; Altyntsev, Alexander T.

    2016-05-01

    Recently, a number of peculiar flares have been reported that demonstrate significant nonthermal particle signatures with low, if any, thermal emission, which implies a close association of the observed emission with the primary energy release/electron acceleration region. This paper presents a flare that appears “cold” at the impulsive phase, while displaying delayed heating later on. Using hard X-ray data from Konus-Wind, microwave observations by SSRT, RSTN, NoRH, and NoRP, context observations, and three-dimensional modeling, we study the energy release, particle acceleration, and transport, and the relationships between the nonthermal and thermal signatures. The flaring process is found to involve the interaction between a small loop and a big loop with the accelerated particles divided roughly equally between them. Precipitation of the electrons from the small loop produced only a weak thermal response because the loop volume was small, while the electrons trapped in the big loop lost most of their energy in the coronal part of the loop, which resulted in coronal plasma heating but no or only weak chromospheric evaporation, and thus unusually weak soft X-ray emission. The energy losses of the fast electrons in the big tenuous loop were slow, which resulted in the observed delay of the plasma heating. We determined that the impulsively accelerated electron population had a beamed angular distribution in the direction of the electric force along the magnetic field of the small loop. The accelerated particle transport in the big loop was primarily mediated by turbulent waves, which is similar to other reported cold flares.

  4. The effect of a strong stellar flare on the atmospheric chemistry of an earth-like planet orbiting an M dwarf.

    PubMed

    Segura, Antígona; Walkowicz, Lucianne M; Meadows, Victoria; Kasting, James; Hawley, Suzanne

    2010-09-01

    Main sequence M stars pose an interesting problem for astrobiology: their abundance in our galaxy makes them likely targets in the hunt for habitable planets, but their strong chromospheric activity produces high-energy radiation and charged particles that may be detrimental to life. We studied the impact of the 1985 April 12 flare from the M dwarf AD Leonis (AD Leo), simulating the effects from both UV radiation and protons on the atmospheric chemistry of a hypothetical, Earth-like planet located within its habitable zone. Based on observations of solar proton events and the Neupert effect, we estimated a proton flux associated with the flare of 5.9 × 10⁸ protons cm⁻² sr⁻¹ s⁻¹ for particles with energies >10 MeV. Then we calculated the abundance of nitrogen oxides produced by the flare by scaling the production of these compounds during a large solar proton event called the Carrington event. The simulations were performed with a 1-D photochemical model coupled to a 1-D radiative/convective model. Our results indicate that the UV radiation emitted during the flare does not produce a significant change in the ozone column depth of the planet. When the action of protons is included, the ozone depletion reaches a maximum of 94% two years after the flare for a planet with no magnetic field. At the peak of the flare, the calculated UV fluxes that reach the surface, in the wavelength ranges that are damaging for life, exceed those received on Earth during less than 100 s. Therefore, flares may not present a direct hazard for life on the surface of an orbiting habitable planet. Given that AD Leo is one of the most magnetically active M dwarfs known, this conclusion should apply to planets around other M dwarfs with lower levels of chromospheric activity. PMID:20879863

  5. The Effect of a Strong Stellar Flare on the Atmospheric Chemistry of an Earth-like Planet Orbiting an M Dwarf

    PubMed Central

    Walkowicz, Lucianne M.; Meadows, Victoria; Kasting, James; Hawley, Suzanne

    2010-01-01

    Abstract Main sequence M stars pose an interesting problem for astrobiology: their abundance in our galaxy makes them likely targets in the hunt for habitable planets, but their strong chromospheric activity produces high-energy radiation and charged particles that may be detrimental to life. We studied the impact of the 1985 April 12 flare from the M dwarf AD Leonis (AD Leo), simulating the effects from both UV radiation and protons on the atmospheric chemistry of a hypothetical, Earth-like planet located within its habitable zone. Based on observations of solar proton events and the Neupert effect, we estimated a proton flux associated with the flare of 5.9 × 108 protons cm−2 sr−1 s−1 for particles with energies >10 MeV. Then we calculated the abundance of nitrogen oxides produced by the flare by scaling the production of these compounds during a large solar proton event called the Carrington event. The simulations were performed with a 1-D photochemical model coupled to a 1-D radiative/convective model. Our results indicate that the UV radiation emitted during the flare does not produce a significant change in the ozone column depth of the planet. When the action of protons is included, the ozone depletion reaches a maximum of 94% two years after the flare for a planet with no magnetic field. At the peak of the flare, the calculated UV fluxes that reach the surface, in the wavelength ranges that are damaging for life, exceed those received on Earth during less than 100 s. Therefore, flares may not present a direct hazard for life on the surface of an orbiting habitable planet. Given that AD Leo is one of the most magnetically active M dwarfs known, this conclusion should apply to planets around other M dwarfs with lower levels of chromospheric activity. Key Words: M dwarf—Flare—Habitable zone—Planetary atmospheres. Astrobiology 10, 751–771. PMID:20879863

  6. COMBUSTION EFFICIENCY OF FLARES

    EPA Science Inventory

    The paper gives results of a study to provide data on industrial flare emissions. (Emissions of incompletely burned hydrocarbons from industrial flares may contribute to air pollution. Available data on flare emissions are sparse, and methods to sample operating flares are unavai...

  7. Multichannel spectrophotometry of stellar flares

    NASA Technical Reports Server (NTRS)

    Mochnacki, S. W.; Zirin, H.

    1980-01-01

    Stellar flares have been observed using the 32 channel spectrophotometer on the 5 m telescope. Net flare fluxes in the region 3200-7000 A are presented. A simple model of blackbody radiation and hydrogen recombination emission appears to fit the continuum points well. Owing to vignetting problems, only the region between 4200 and 7000 A was used for a detailed fit to the Planck function to obtain apparent temperatures and effective areas. The rise of each flare was associated with an increase of the area, while the initial steep decline of the light was associated with a similar decrease of the blackbody temperature. The maximum temperatures, coincident with maximum light, were 7500-9500 K, similar to values for solar flares. The hydrogen line emission rose simultaneously with the continuum but declined more slowly. The ratio of H sub gamma to H sub alpha was about 1.5 at the peak, declining to about 1.0 after the peak.

  8. A Rayleigh Scatter-Based Ocular Flare Analysis Meter for Flare Photometry of the Anterior Chamber

    PubMed Central

    Lam, Deborah L.; Axtelle, Jim; Rath, Susan; Dyer, Andrew; Harrison, Benjamin; Rogers, Claude; Menon, Naresh; Van Gelder, Russell N.

    2015-01-01

    Purpose Existing flare photometers are based on the Tyndall effect, which requires sophisticated laser photometry. The ocular flare analysis meter (OFAM) is a nonlaser photometer that uses quantitative Rayleigh scatter and absorption from visible light to compute a flare value. This study is designed to correlate OFAM measurements with qualitative measurements of flare in vitro and in vivo. Methods Following validation of the device on artificial anterior chambers containing known protein concentrations, flare readings were obtained from 90 subjects (46 with and 44 without uveitis) in one eye. Subjects were graded by the Standardization of Uveitis Nomenclature (SUN) working group flare scoring system and received the OFAM flare measurements. Results The OFAM showed linear response in vitro to protein concentrations ranging from 0 to 0.5 mg/ml. In clinical use in subjects ranging from SUN flare scores of 0+ to 2+, OFAM showed statistically significant measurement accuracy (P = 0.0008 of flare 0 versus flare 2; P = 0.031 of flare 0 versus flare 1). Distinction of SUN scores 1 and 2 was borderline significant (P = 0.057). Conclusion The OFAM photometry correlates with the standard SUN scoring system. This method may provide an objective method to diagnosis and monitor uveitis. Further longitudinal studies are warranted. Translational Relevance Currently, ocular flare is assessed qualitatively in most clinical settings. The existing methodology uses only Tyndall effect to measure flare. The OFAM uses an alternate, nonlaser means for measurement of anterior chamber flare by measure of Raleigh scatter. This pilot clinical study suggests that the OFAM device may be useful in measurement of uveitis activity. PMID:26688778

  9. Stochastic acceleration of electrons by fast magnetosonic waves in solar flares: the effects of anisotropy in velocity and wavenumber space

    SciTech Connect

    Pongkitiwanichakul, Peera; Chandran, Benjamin D. G.

    2014-11-20

    We develop a model for stochastic acceleration of electrons in solar flares. As in several previous models, the electrons are accelerated by turbulent fast magnetosonic waves ({sup f}ast waves{sup )} via transit-time-damping (TTD) interactions. (In TTD interactions, fast waves act like moving magnetic mirrors that push the electrons parallel or anti-parallel to the magnetic field). We also include the effects of Coulomb collisions and the waves' parallel electric fields. Unlike previous models, our model is two-dimensional in both momentum space and wavenumber space and takes into account the anisotropy of the wave power spectrum F{sub k} and electron distribution function f {sub e}. We use weak turbulence theory and quasilinear theory to obtain a set of equations that describes the coupled evolution of F{sub k} and f {sub e}. We solve these equations numerically and find that the electron distribution function develops a power-law-like non-thermal tail within a restricted range of energies E in (E {sub nt}, E {sub max}). We obtain approximate analytic expressions for E {sub nt} and E {sub max}, which describe how these minimum and maximum energies depend upon parameters such as the electron number density and the rate at which fast-wave energy is injected into the acceleration region at large scales. We contrast our results with previous studies that assume that F{sub k} and f {sub e} are isotropic, and we compare one of our numerical calculations with the time-dependent hard-X-ray spectrum observed during the 1980 June 27 flare. In our numerical calculations, the electron energy spectra are softer (steeper) than in models with isotropic F{sub k} and f {sub e} and closer to the values inferred from observations of solar flares.

  10. Flare Particle Escape in 3D Solar Eruptive Events

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  11. INVESTIGATION OF CHROMOSPHERIC EVAPORATION IN A NEUPERT-TYPE SOLAR FLARE

    SciTech Connect

    Ning Zongjun; Cao Wenda

    2010-07-10

    The Neupert effect implies a flare model in which the hard X-rays (HXRs) are produced by energetic electrons via electron-ion bremsstrahlung as they lose their energies in the chromosphere, while the soft X-rays (SXRs) are produced by thermal bremsstrahlung from 'chromospheric evaporation' due to plasma being heated by those same electrons. Based on this concept, we investigate the evidence for chromospheric evaporation in a Neupert-type flare on 2004 October 30. First, we demonstrate that this event is consistent with the Neupert effect. Using the RHESSI data, both thermal and nonthermal energies are derived after the onset of this flare. The high correlation between the derivative of the SXRs and HXRs and between the derivative of the thermal energy and nonthermal energy indicates that the 2004 October 30 flare is a Neupert-type event. Second, chromospheric evaporation is necessarily expected during the flare's rising phase. We analyze RHESSI images at different energies and different times around the flare maximum. The HXR emission tends to move the footpoints close to each other, finally merging them into a single source with the same position as the loop-top source. When the projection effect (due to this event being near the disk center) is taken into account, this fact can be regarded as the signature of chromospheric evaporation in the X-ray observations. RHESSI observations show three kinds of evidence that are consistent with the evaporation model. First, at a given instant, the higher energy X-rays originate from the deeper layers of the atmosphere or further away from the loop top. Second, in a given energy band, i.e., at 20-30 keV, the earlier X-rays originate from the deeper layers or further away from the loop top. Third, the X-ray footpoint sources at higher energies disappear at later times. Based on these characteristics, chromospheric evaporation took about 100 s for the 2004 October 30 flare. X-rays at all energy bands do not show evidence of

  12. Simulating VIIRS Observed Gas Flare

    NASA Astrophysics Data System (ADS)

    Hsu, F. C.

    2015-12-01

    VIIRS Nightfire (VNF) had been proved being able to effectively detect gas flares at night, and characterize their temperature and source size. [1] However, limited access to generally confidential gas flare operation measurements made it difficult to verify the output. Although flared gas volume is occasionally available, it is not common to log the temperature and flames size which directly links to VNF output. To understand the mechanism of gas flare and how VIIRS perceives the event, a platform is proposed to simulate the gas flare being observed by VIIRS. The methodology can be described in three steps. (1) Use CFD simulation software ISIS-3D to simulate a simple gas flare. [2] Scalar fields of temperature and species concentration related to combustion are extracted from the simulation. The instantaneous scalar can be determined from time-averaging or guess by stochastic time and space series (TASS) from single-point statistics [3]. (2) Model spectral radiance intensity of simulated gas flare using RADCAL. [4] RADCAL developed by NIST can accurately model the spectral radiance emitted on the direction of lineof-sight given the spatial profile of temperature and concentration of species. (3) Use radiative transfer modeling to calculate the energy propagated to VIIRS. The modeled radiation will then be weighted by the MODTRAN [5] modeled transmissivity over predefined atmosphere to the satellite, with geometrical effects considered. Such platform can help understanding how exactly VNF is measuring gas flares, and thus lead to more precise characterization of combustion events. [1] C. D. Elvidge et al, Remote Sensing, 2013[2] IRSN ISIS-3D[3] M. E. Kounalakis et al, ASME J. Heat Transfer, 1991 [4] W. L. Grosshandler, NIST Technical Note 1402, 1993 [5] A. Berk et al, MODTRAN 5.2.0.0 User's Manual

  13. Evidence of thermal conduction depression in hot coronal loops

    NASA Astrophysics Data System (ADS)

    Wang, Tongjiang; Ofman, Leon; Sun, Xudong; Provornikova, Elena; Davila, Joseph

    2015-08-01

    Slow magnetoacoustic waves were first detected in hot (>6 MK) flare loops by the SOHO/SUMER spectrometer as Doppler shift oscillations in Fe XIX and Fe XXI lines. These oscillations are identified as standing slow-mode waves because the estimated phase speeds are close to the sound speed in the loop and some cases show a quarter period phase shift between velocity and intensity oscillations. The observed very rapid excitation and damping of standing slow mode waves have been studied by many authors using theories and numerical simulations, however, the exact mechanisms remain not well understood. Recently, flare-induced longitudinal intensity oscillations in hot post-flare loops have been detected by SDO/AIA. These oscillations have the similar physical properties as SUMER loop oscillations, and have been interpreted as the slow-mode waves. The multi-wavelength AIA observations with high spatio-temporal resolution and wide temperature coverage allow us to explore the wave excitation and damping mechanisms with an unprecedented detail to develope new coronal seismology. In this paper, we present accurate measurements of the effective adiabatic index (γeff) in the hot plasma from the electron temperature and density wave signals of a flare-induced longitudinal wave event using SDO/AIA data. Our results strikingly and clearly reveal that thermal conduction is highly depressed in hot (˜10 MK) post-flare loops and suggest that the compressive viscosity is the dominant wave damping mechanism which allows determination of the viscosity coefficient from the observables by coronal seismology. This new finding challenges our current understanding of thermal energy transport in solar and stellar flares, and may provide an alternative explanation of long-duration events and enhance our understand of coronal heating mechanism. We will discuss our results based on non-ideal MHD theory and simulations. We will also discuss the flare trigger mechanism based on magnetic topology

  14. Analysis of ultraviolet and X-ray observations of three homologous solar flares from SMM

    NASA Technical Reports Server (NTRS)

    Cheng, Chung-Chieh; Pallavicini, Roberto

    1987-01-01

    Three homologous flares observed in the UV lines of Fe XXI and O V and in X-rays from the SMM were studied. It was found that: (1) the homology of the flares was most noticeable in Fe XXI and soft X-ray emissions; (2) the three flares shared many of the same loop footprints which were located in O V bright kernals associated with hard X-ray bursts; and (3) in spite of the strong spatial homology, the temporal evolution in UV and X-ray emissions varied from flare to flare. A comparison between the UV observations and photospheric magnetograms revealed that the basic flare configuration was a complex loop system consisting of many loops or bundles of loops.

  15. LYRA Observations of Two Oscillation Modes in a Single Flare

    NASA Astrophysics Data System (ADS)

    Van Doorsselaere, T.; De Groof, A.; Zender, J.; Berghmans, D.; Goossens, M.

    2011-10-01

    We analyze light curves from the LYRA irradiance experiment on board PROBA2 during the flare of 2010 February 8. We see both long- and short-period oscillations during the flare. The long-period oscillation is interpreted in terms of standing slow sausage modes; the short-period oscillation is thought to be a standing fast sausage mode. The simultaneous presence of two oscillation modes in the same flaring structure allows for new coronal seismological applications. The periods are used to find seismological estimates of the plasma-β and the density contrast of the flaring loop. Also the wave mode number is estimated from the observed periods.

  16. Suppression of Parallel Transport in Turbulent Magnetized Plasmas and Its Impact on the Non-thermal and Thermal Aspects of Solar Flares

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    The transport of the energy contained in electrons, both thermal and suprathermal, in solar flares plays a key role in our understanding of many aspects of the flare phenomenon, from the spatial distribution of hard X-ray emission to global energetics. Motivated by recent RHESSI observations that point to the existence of a mechanism that confines electrons to the coronal parts of flare loops more effectively than Coulomb collisions, we here consider the impact of pitch-angle scattering off turbulent magnetic fluctuations on the parallel transport of electrons in flaring coronal loops. It is shown that the presence of such a scattering mechanism in addition to Coulomb collisional scattering can significantly reduce the parallel thermal and electrical conductivities relative to their collisional values. We provide illustrative expressions for the resulting thermoelectric coefficients that relate the thermal flux and electrical current density to the temperature gradient and the applied electric field. We then evaluate the effect of these modified transport coefficients on the flare coronal temperature that can be attained, on the post-impulsive-phase cooling of heated coronal plasma, and on the importance of the beam-neutralizing return current on both ambient heating and the energy loss rate of accelerated electrons. We also discuss the possible ways in which anomalous transport processes have an impact on the required overall energy associated with accelerated electrons in solar flares.

  17. FNAS/solar flare energetics

    NASA Technical Reports Server (NTRS)

    Machado, M. E.

    1992-01-01

    We have performed an extensive study of solar flare energy buildup and release, concentrating in two aspects: (1) relationship with 3D field topology and measured electric currents; and (2) flare onset characteristics as determined from combined x ray and ultraviolet observations. We extended our previous studies on the characteristic topology of flaring regions, by following the evolution of an active region over three consecutive days. From comparison with flare observations in x rays and h alpha, we found further support for the hypothesis that flares were triggered by taking place at the separators (3D generalization of and x-type neutral point). Furthermore, we found that emerging in flux at a site within the active regions where no (or little) activity was previously observed, caused the appearance of a secondary separator and thereon continuous triggering of activity at such site. Our topology arguments were then applied to a study of sympathetic activity between two regions within an active complex. Here again we found that interacting field structures along separators and separatrices, which act as pathways for recurrent flaring to spread between the regions, could be used to understand how activity spread to potentially explosive sites with the complex. We also finished our study of flare onset characteristics as determined from combined x ray and ultraviolet observations. Using a quasi-static modeling approach, we find that this phase is characterized by a relatively low level of energy release, 10 exp 26-27 erg/s, which is sufficient to produce 'gentle' evaporation, a shift in the location of the transition zone as compared to pre-flare conditions, and an increase in the temperature and density of coronal loops. All these changes have profound implications on the observed signatures of impulsive phase phenomena, which had been neglected in the past. As a follow-up of this investigation, we now plan to apply our results to the interpretation of high

  18. Computed tomography evaluation of residual root thickness after pre-flaring using gates Glidden drills: The sequence effect

    PubMed Central

    Akhlaghi, Nahid M; Naghdi, Amirali; Bajgiran, Laleh Mohammadian; Behrooz, Elahe

    2014-01-01

    Aim: The aim of the present study is to evaluate the residual root thickness in mesiolingual (ML) canals of mandibular molars after pre-flaring using different sequences of Gates-Glidden (GG) drills. Materials and Methods: Computed tomography (CT) scans of the ML canals of 60 mandibular first molars were provided from areas within 1, 2, 3 and 4 mm of the furcation area and minimum initial root thickness (MIRT) of concave areas was measured at each level. The samples were divided into two groups (G1 and G2) which were prepared by the step-back and crown-down techniques, respectively. In both groups, anti-curvature filing was used. On secondary CT images of the samples in the same position, the minimum residual root thickness (MRRT) and the amount of removed dentin were analyzed by t-test and ANOVA. Results: There was no significant difference for MIRT between the two groups. The MRRT was greater in the G2 group in all the sections, with no significant difference between them. The average of MRRT was not <0.5 mm in any of the groups or sections. Conclusion: Based on the results of this study when the appropriate root thickness is present initially, GG drills used in any sequence may be suitable, safe and cost effective for pre-flaring of mesial canals of mandibular first molars with preserving the root thickness of furcation areas. PMID:24778510

  19. Effect of Thermal Conduction on Acoustic Waves in Coronal Loops

    NASA Astrophysics Data System (ADS)

    Bogdan, T. J.

    2006-05-01

    The influence of classical (Spitzer) thermal conduction on longitudinal acoustic waves in a coronal loop is determined through an idealized but exactly solvable model. The model consists of an isothermal, stratified (constant gravity) atmosphere in which a monochromatic acoustic wave, traveling in the direction of decreasing density, is imposed throughout the lower half of the atmosphere. Based on the linearized equations of motion, the complete steady state (t-->∞) solution is obtained. In addition to the imposed driving wave, the solution also contains reflected and transmitted acoustic and thermal conduction waves. The mode transformation and mixing occurs in the vicinity of the atmospheric layer where the gas pressure passes through a critical value set by the magnitude of the thermal conduction and other model parameters. For 5 minute waves in a million degree loop, this critical pressure is on the order of 8×10-4 in cgs units. Since the apex gas pressure of many coronal loops of current interest is thought to be comfortably in excess of this value, mode mixing and transformation is not likely to be a relevant factor for understanding acoustic waves in these structures. On the other hand, enhanced thermal conductivity as a result of plasma instabilities, for example, could revive the importance of this mechanism for coronal loops. If this mixing layer is present, the calculations show that the pair of thermal conduction waves invariably gains the overwhelming majority of the energy flux of the incoming acoustic wave. This energy is rapidly dissipated in the neighborhood of the mixing layer.

  20. Signatures of the coalescence instability in solar flares

    SciTech Connect

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

    1984-11-01

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

  1. EVIDENCE FOR HOT FAST FLOW ABOVE A SOLAR FLARE ARCADE

    SciTech Connect

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

    2013-10-10

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

  2. Effects of grain size, hardness, and stress on the magnetic hysteresis loops of ferromagnetic steels

    NASA Astrophysics Data System (ADS)

    Kwun, H.; Burkhardt, G. L.

    1987-02-01

    Effects of grain size, hardness, and stress on the magnetic hysteresis loops of AISI 410 stainless steel and SAE 4340 steel specimens were investigated experimentally. It was observed that both hardness and stress significantly influenced the hysteresis loops, while the grain size had a minimal effect. For each material, the mechanically harder specimen was more difficult to magnetize. Upon application of uniaxial stress, the magnetic induction increased under tension and decreased under compression, with the sides of the hysteresis loops becoming inclined more toward the vertical axis under tension and the horizontal axis under compression. For each material, the effects of stress on the hysteresis loops were greater for the mechanically softer specimen and exhibited an inverse relationship to the hardness. The effects of stress were not dependent on grain size.

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

    SciTech Connect

    Dudík, J.; Del Zanna, G.; Mason, H. E.; Janvier, M.; Aulanier, G.; Schmieder, B.; Karlický, M. E-mail: mjanvier@maths.dundee.ac.uk

    2014-04-01

    We present SDO/AIA observations of an eruptive X-class flare of 2012 July 12, and compare its evolution with the predictions of a three-dimensional (3D) numerical simulation. We focus on the dynamics of flare loops that are seen to undergo slipping reconnection during the flare. In the Atmospheric Imaging Assembly (AIA) 131 Å observations, lower parts of 10 MK flare loops exhibit an apparent motion with velocities of several tens of km s{sup –1} along the developing flare ribbons. In the early stages of the flare, flare ribbons consist of compact, localized bright transition-region emission from the footpoints of the flare loops. A differential emission measure analysis shows that the flare loops have temperatures up to the formation of Fe XXIV. A series of very long, S-shaped loops erupt, leading to a coronal mass ejection observed by STEREO. The observed dynamics are compared with the evolution of magnetic structures in the 'standard solar flare model in 3D.' This model matches the observations well, reproducing the apparently slipping flare loops, S-shaped erupting loops, and the evolution of flare ribbons. All of these processes are explained via 3D reconnection mechanisms resulting from the expansion of a torus-unstable flux rope. The AIA observations and the numerical model are complemented by radio observations showing a noise storm in the metric range. Dm-drifting pulsation structures occurring during the eruption indicate plasmoid ejection and enhancement of the reconnection rate. The bursty nature of radio emission shows that the slipping reconnection is still intermittent, although it is observed to persist for more than an hour.

  4. The effects of spaceflight on open-loop and closed-loop postural control mechanisms: human neurovestibular studies on SLS-2

    NASA Technical Reports Server (NTRS)

    Collins, J. J.; De Luca, C. J.; Pavlik, A. E.; Roy, S. H.; Emley, M. S.; Young, L. R. (Principal Investigator)

    1995-01-01

    Stabilogram-diffusion analysis was used to examine how prolonged periods in microgravity affect the open-loop and closed-loop postural control mechanisms. It was hypothesized that following spaceflight: (1) the effective stochastic activity of the open-loop postural control schemes in astronauts is increased; (2) the effective stochastic activity and uncorrelated behavior, respectively, of the closed-loop postural control mechanisms in astronauts are increased; and (3) astronauts utilized open-loop postural controls schemes for shorter time intervals and smaller displacements. Four crew members and two alternates from the 14-day Spacelab Life Sciences 2 Mission were included in the study. Each subject was tested under eyes-open, quiet-standing conditions on multiple preflight and postflight days. The subjects' center-of-pressure trajectories were measured with a force platform and analyzed according to stabilogram-diffusion analysis. It was found that the effective stochastic activity of the open-loop postural control schemes in three of the four crew members was increased following spaceflight. This result is interpreted as an indication that there may be in-flight adaptations to higher-level descending postural control pathways, e.g., a postflight increase in the tonic activation of postural muscles. This change may also be the consequence of a compensatory (e.g., "stiffening") postural control strategy that is adopted by astronauts to account for general feeling of postflight unsteadiness. The crew members, as a group, did not exhibit any consistent preflight/postflight differences in the steady-state behavior of their closed-loop postural control mechanisms or in the functional interaction of their open-loop and closed-loop postural control mechanisms. These results are interpreted as indications that although there may be in-flight adaptations to the vestibular system and/or proprioceptive system, input from the visual system can compensate for such changes

  5. Understanding Solar Flare Statistics

    NASA Astrophysics Data System (ADS)

    Wheatland, M. S.

    2005-12-01

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

  6. Observations and Modeling of Solar Flare Atmospheric Dynamics

    NASA Astrophysics Data System (ADS)

    Li, Y.

    2015-09-01

    Solar flares are one of the most energetic events in solar atmosphere, which last minutes to tens of minutes. The eruption of a solar flare involves energy release, plasma heating, particle acceleration, mass flows, waves, etc. A solar flare releases a large amount of energy, and its emission spans a wide wavelength range. Solar flares are usually accompanied by coronal mass ejections (CMEs); therefore they could significantly affect the space environments between the Earth and the Sun. At present, we do not fully understand the whole flare process. There are still many important questions to be resolved, such as when and where is the energy released? How long does the energy release last? What are the main ways of energy release? And how does the solar atmosphere respond to the energy release? To address these questions, we study in detail the flare heating and dynamic evolution. We first give a brief review of previous flare studies (Chapter 1), and introduce the observing instruments (Chapter 2) and the modeling method (Chapter 3) related to this thesis work. Then we use spectral data to investigate the chromospheric evaporation (Chapter 4). Based on the results, we further explore the flare heating problem. With observationally inferred heating functions, we model two flare loops, and compare the results with observations (Chapter 5). A consistency is achieved between modeling and observations. In addition, we model two different sets of flare loop systems with quite different heating profiles and dynamic evolutions (Chapter 6). The details are described as below. Firstly, we investigate the chromospheric evaporation in the flare on 2007 January 16 using line profiles observed by the Extreme-ultraviolet (EUV) Imaging Spectrometer (EIS) on board Hinode. Three points with different magnetic polarities at flare ribbons are analyzed in detail. We find that the three points show different patterns of upflows and downflows in the impulsive phase of the flare. The

  7. An X-ray flare from 47 Cas

    SciTech Connect

    Pandey, Jeewan C.; Karmakar, Subhajeet

    2015-02-01

    Using XMM-Newton observations, we investigate properties of a flare from the very active but poorly known stellar system 47 Cas. The luminosity at the peak of the flare is found to be 3.54 × 10{sup 30} erg s{sup −1}, which is ∼2 times higher than that at a quiescent state. The quiescent state corona of 47 Cas can be represented by two temperature plasma: 3.7 and 11.0 MK. The time-resolved X-ray spectroscopy of the flare show the variable nature of the temperature, the emission measure, and the abundance. The maximum temperature during the flare is derived as 72.8 MK. We infer the length of a flaring loop to be 3.3 × 10{sup 10} cm using a hydrodynamic loop model. Using the RGS spectra, the density during the flare is estimated as 4.0 × 10{sup 10} cm{sup −3}. The loop scaling laws are also applied when deriving physical parameters of the flaring plasma.

  8. THE RELATIONSHIP BETWEEN EXTREME ULTRAVIOLET NON-THERMAL LINE BROADENING AND HIGH-ENERGY PARTICLES DURING SOLAR FLARES

    SciTech Connect

    Kawate, T.; Imada, S.

    2013-10-01

    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.

  9. Contact effects and quantum interference in engineered dangling bond loops on silicon surfaces.

    PubMed

    Kleshchonok, Andrii; Gutierrez, Rafael; Cuniberti, Gianaurelio

    2015-09-01

    Dangling bond structures created on H-passivated silicon surfaces offer a novel platform for engineering planar nanoscale circuits, compatible with conventional semiconductor technologies. In this investigation we focus on the electronic structure and quantum transport signatures of dangling bond loops built on H-passivated Si(100) surfaces contacted by carbon nanoribbons, thus leading to a two-terminal planar, nanoscale setup. The computational studies were carried out to rationalize the influence of the local atomic-scale contacts of the dangling bond system to the mesoscopic electrodes as well as the possibility of revealing quantum interference effects in the dangling bond loops. Our results reveal a strong sensitivity of the low-energy quantum transmission to the loop topology and to the atomistic details of the electrode-loop contact. Varying the length of the loop or the spatial position of at least one of the electrodes has a drastic impact on the quantum interference pattern; depending on whether constructive or destructive interference within the loop takes place, the conductance of the system can be tuned over several orders of magnitude, thus suggesting the possibility of exploiting such quantum mechanical effects in the design of two-dimensional, atomic-scale electronic devices such as logic gates. PMID:26228007

  10. Magnetic reconnection in solar flares

    NASA Technical Reports Server (NTRS)

    Forbes, T. G.

    1991-01-01

    The magnetic energy stored in the corona is the only plausible source for the energy released during large solar flares. During the last 20 years most theoretical work has concentrated on models which store magnetic energy in the corona in the form of electrical currents, and a major goal of present day research is to understand how these currents are created, and then later dissipated during a flare. Another important goal is to find a flare model which can eject magnetic flux into interplanetary space. Although many flares do not eject magnetic flux, those which do are of special importance for solar-terrestrial relations since the ejected flux can have dramatic effects if it hits the Earth's magnetosphere. Three flare models which have been extensively investigated are the emerging-flux model, the sheared-arcade model, and the magnetic-flux-rope model. All of these models can store and release magnetic energy efficiently provided that rapid magnetic reconnection occurs. However, only the magnetic-flux-rope model appears to provide a plausible mechanism for ejecting magnetic flux into interplanetary space.