Quantitative analysis of flare accelerated electrons through their hard X-ray and microwave radiation

Hard X-ray and microwave modelling that takes into account the temporal evolution of the electron spectrum as well as the inhomogeneity of the magnetic field and the ambient medium in the radio source is presented. This method is illustrated for the June 29 1980 10:41 UT event. The implication on the process of acceleration/injection is discussed

Temporal evolution of an energetic electron population in an inhomogeneous medium: Application to solar hard X-ray bursts

Energetic electrons accelerated during solar flares can be studied through the hard X-ray emission they produce when interacting with the solar ambient atmosphere. In the case of the non thermal hard X-ray emission, the instanteous X-ray flux emitted at one point of the atmosphere is related to the instantaneous fast electron spectrum at that point. A hard X-ray source model then requires the understanding of the evolution in space and time of the fast particle distribution. The physical processes involved here are energy losses due to Coulomb collisions and pitch angle scattering due to both collisions and magnetic field gradients

Radio Spectral Evolution of an X-ray Poor Impulsive Solar Flare: Implications for Plasma Heating and Electron Acceleration

We present radio and X-ray observations of an impulsive solar flare that was moderately intense in microwaves, yet showed very meager EUV and X-ray emission. The flare occurred on 2001 Oct 24 and was well-observed at radio wavelengths by the Nobeyama Radioheliograph (NoRH), the Nobeyama Radio Polarimeters (NoRP), and by the Owens Valley Solar Array (OVSA). It was also observed in EUV and X-ray wavelength bands by the TRACE, GOES, and Yohkoh satellites. We find that the impulsive onset of the radio emission is progressively delayed with increasing frequency relative to the onset of hard X-ray emission. In contrast, the time of flux density maximum is progressively delayed with decreasing frequency. The decay phase is independent of radio frequency. The simple source morphology and the excellent spectral coverage at radio wavelengths allowed us to employ a nonlinear chi-squared minimization scheme to fit the time series of radio spectra to a source model that accounts for the observed radio emission in terms of gyrosynchrotron radiation from MeV-energy electrons in a relatively dense thermal plasma. We discuss plasma heating and electron acceleration in view of the parametric trends implied by the model fitting. We suggest that stochastic acceleration likely plays a role in accelerating the radio-emitting electrons.Comment: 22 pages, 10 figure

Towards a predictive multi-phase model for alpine mass movements and process cascades

Alpine mass movements can generate process cascades involving different materials including rock, ice, snow, and water. Numerical modelling is an essential tool for the quantification of natural hazards. Yet, state-of-the-art operational models are based on parameter back-calculation and thus reach their limits when facing unprecedented or complex events. Here, we advance our predictive capabilities for mass movements and process cascades on the basis of a three-dimensional numerical model, coupling fundamental conservation laws to finite strain elastoplasticity. In this framework, model parameters have a true physical meaning and can be evaluated from material testing, thus conferring to the model a strong predictive nature. Through its hybrid Eulerian–Lagrangian character, our approach naturally reproduces fractures and collisions, erosion/deposition phenomena, and multi-phase interactions, which finally grant accurate simulations of complex dynamics. Four benchmark simulations demonstrate the physical detail of the model and its applicability to real-world full-scale events, including various materials and ranging through five orders of magnitude in volume. In the future, our model can support risk-management strategies through predictions of the impact of potentially catastrophic cascading mass movements at vulnerable sites

Statistical Evidence for Contributions of Flares and Coronal Mass Ejections to Major Solar Energetic Particle Events

Solar energetic particle (SEP) events are related to flares and coronal mass ejections (CMEs). This work is a new investigation of statistical relationships between SEP peak intensities - deka-MeV protons and near-relativistic electrons - and characteristic quantities of the associated solar activity. We consider the speed of the CME and quantities describing the flare-related energy release: peak flux and fluence of soft X-ray (SXR) emission, fluence of microwave emission. The sample comprises 38 SEP events associated with strong SXR bursts (classes M and X) in the western solar hemisphere between 1997 and 2006, and where the flare-related particle acceleration is accompanied by radio bursts indicating electron escape to the interplanetary space. The main distinction of the present statistical analysis from earlier work is that besides the classical Pearson correlation coefficient the partial correlation coefficients are calculated in order to disentangle the effects of correlations between the solar parameters themselves. The classical correlation analysis shows the usual picture of correlations with broad scatter between SEP peak intensities and the different parameters of solar activity, and strong correlations between the solar activity parameters themselves. The partial correlation analysis shows that the only parameters that affect significantly the SEP intensity are the CME speed and the SXR fluence. The SXR peak flux and the microwave fluence have no additional contribution. We conclude that these findings bring statistical evidence that both flare acceleration and CME shock acceleration contribute to the deka-MeV proton and near-relativistic electron populations in large SEP events.Comment: The final publication is available at Springer via http://dx.doi.org/10.1007/s11207-014-0628-

A burst with double radio spectrum observed up to 212 GHz

We study a solar flare that occurred on September 10, 2002, in active region NOAA 10105 starting around 14:52 UT and lasting approximately 5 minutes in the radio range. The event was classified as M2.9 in X-rays and 1N in H\alpha. Solar Submillimeter Telescope observations, in addition to microwave data give us a good spectral coverage between 1.415 and 212 GHz. We combine these data with ultraviolet images, hard and soft X-rays observations and full-disk magnetograms. Images obtained from Ramaty High Energy Solar Spectroscopic Imaging data are used to identify the locations of X-ray sources at different energies and to determine the X-ray spectrum, while ultra violet images allow us to characterize the coronal flaring region. The magnetic field evolution of the active region is analyzed using Michelson Doppler Imager magnetograms. The burst is detected at all available radio-frequencies. X-ray images (between 12 keV and 300 keV) reveal two compact sources and 212 GHz data, used to estimate the radio source position, show a single compact source displaced by 25" from one of the hard X-ray footpoints. We model the radio spectra using two homogeneous sources, and combine this analysis with that of hard X-rays to understand the dynamics of the particles. Relativistic particles, observed at radio wavelengths above 50 GHz, have an electron index evolving with the typical soft-hard-soft behaviour.Comment: Submitted to Solar Physics, 20 pages, 8 fugure

Caractérisation de sources de résistance à la fusariose chez le blé dur

National audienceFacing the increasing problem of Fusarium head blight with durum wheat caused by different species of Fusarium, a study was undertaken with the help of the Ministry in charge for agriculture. This study made it possible to assess the resistance of different sub-species of Triticum turgidum. The populations with the most resistant accessions belong to the sub-species T. turgidum dicoccum. Going deeper into this study showed that this resistance was a type 2 one: slow progression of necrosis after contamination of one spikelet per spike. One accession, TRI2215, exhibited very high level of resistance, but it is very high and very late accession, this will make this accession difficult to be used in breeding. This justifies a QTL search for Fusarium resistance. The analysis of the determinant for Fusarium aggressiveness confirmed that a great part was linked with the production of mycotoxins. Several phenol compounds seemed to play a part in the resistance of the plant. A qualitative analysis of the Fusarium flora on the spikes allowed identifying six major Fusarium species and to associate them with the different mycotoxins. A close genus, Microdochium, did not produce mycotoxins. We also showed that the amount of mycotoxins in an organ was related to the fungus DNA in the organ.Face au problème croissant chez le blé dur de la fusariose des épis causée par différentes espèces de Fusarium sp., une étude a été entreprise, avec le concours du Ministère chargé de l’Agriculture. Cette étude a permis d’évaluer la résistance de différentes sous-espèces de Triticum turgidum. Les populations contenant le plus d’individus résistants sont issues de la sous-espèce T. turgidum dicoccum. Une étude plus approfondie a permis de montrer cette résistance était de type 2 : faible progression des symptômes après la contamination d’un épillet par épi. Un géniteur, TRI2215, montre un niveau de résistance particulièrement intéressant, mais est très haut et très tardif, ce qui le rendra difficile à utiliser. C’est pourquoi une recherche de QTL a été entreprise sur ce géniteur. L’analyse des déterminants de l’agressivité des Fusarium confirme qu’elle vient en grande partie des mycotoxines. Différents composés phénoliques semblent aussi jouer un rôle dans la résistance de la plante. Une analyse qualitative de la flore fusarienne des épis a permis d’identifier six espèces majeures de Fusarium et de les associer avec les différentes mycotoxines, et qu’un genre proche, Microdochium, ne produisait pas de mycotoxines. Il a montré aussi que la quantité de mycotoxines dans un organe était proportionnelle à la quantité d’ADN du champignon dans l’organe

Comparison of 30 THz impulsive burst time development to microwaves, H-alpha, EUV, and GOES soft X-rays

The recent discovery of impulsive solar burst emission in the 30 THz band is raising new interpretation challenges. One event associated with a GOES M2 class flare has been observed simultaneously in microwaves, H-alpha, EUV, and soft X-ray bands. Although these new observations confirm some features found in the two prior known events, they exhibit time profile structure discrepancies between 30 THz, microwaves, and hard X-rays (as inferred from the Neupert effect). These results suggest a more complex relationship between 30 THz emission and radiation produced at other wavelength ranges. The multiple frequency emissions in the impulsive phase are likely to be produced at a common flaring site lower in the chromosphere. The 30 THz burst emission may be either part of a nonthermal radiation mechanism or due to the rapid thermal response to a beam of high-energy particles bombarding the dense solar atmosphere.Comment: accepted to Astronomy and Astrophysic

Particle Acceleration in Multiple Dissipation Regions

The sharp magnetic discontinuities which naturally appear in solar magnetic flux tubes driven by turbulent photospheric motions are associated with intense currents. \citet{Par83} proposed that these currents can become unstable to a variety of microscopic processes, with the net result of dramatically enhanced resistivity and heating (nanoflares). The electric fields associated with such ``hot spots'' are also expected to enhance particle acceleration. We test this hypothesis by exact relativistic orbit simulations in strong random phase magnetohydrodynamic (MHD) turbulence which is forming localized super-Dreicer Ohm electric fields ($E_\Omega/E_D$ = $10^2 ... 10^5$) occurring in 2..15 % of the volume. It is found that these fields indeed yield a large amplification of acceleration of electrons and ions, and can effectively overcome the injection problem. We suggest in this article that nanoflare heating will be associated with sporadic particle acceleration.Comment: 12 pages, 5 figures, to appear in ApJ

Origin of the submillimeter radio emission during the time-extended phase of a solar flare

Solar flares observed in the 200-400 GHz radio domain may exhibit a slowly varying and time-extended component which follows a short (few minutes) impulsive phase and which lasts for a few tens of minutes to more than one hour. The few examples discussed in the literature indicate that such long-lasting submillimeter emission is most likely thermal bremsstrahlung. We present a detailed analysis of the time-extended phase of the 2003 October 27 (M6.7) flare, combining 1-345 GHz total-flux radio measurements with X-ray, EUV, and H{\alpha} observations. We find that the time-extended radio emission is, as expected, radiated by thermal bremsstrahlung. Up to 230 GHz, it is entirely produced in the corona by hot and cool materials at 7-16 MK and 1-3 MK, respectively. At 345 GHz, there is an additional contribution from chromospheric material at a few 10^4 K. These results, which may also apply to other millimeter-submillimeter radio events, are not consistent with the expectations from standard semi-empirical models of the chromosphere and transition region during flares, which predict observable radio emission from the chromosphere at all frequencies where the corona is transparent.Comment: 27 pages, 7 figure