Sub-terahertz, microwaves and high energy emissions during the December 6, 2006 flare, at 18:40 UT

The presence of a solar burst spectral component with flux density increasing with frequency in the sub-terahertz range, spectrally separated from the well-known microwave spectral component, bring new possibilities to explore the flaring physical processes, both observational and theoretical. The solar event of 6 December 2006, starting at about 18:30 UT, exhibited a particularly well-defined double spectral structure, with the sub-THz spectral component detected at 212 and 405 GHz by SST and microwaves (1-18 GHz) observed by the Owens Valley Solar Array (OVSA). Emissions obtained by instruments in satellites are discussed with emphasis to ultra-violet (UV) obtained by the Transition Region And Coronal Explorer (TRACE), soft X-rays from the Geostationary Operational Environmental Satellites (GOES) and X- and gamma-rays from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The sub-THz impulsive component had its closer temporal counterpart only in the higher energy X- and gamma-rays ranges. The spatial positions of the centers of emission at 212 GHz for the first flux enhancement were clearly displaced by more than one arc-minute from positions at the following phases. The observed sub-THz fluxes and burst source plasma parameters were found difficult to be reconciled to a purely thermal emission component. We discuss possible mechanisms to explain the double spectral components at microwaves and in the THz ranges.Comment: Accepted version for publication in Solar Physic

Physics of Solar Prominences: I - Spectral Diagnostics and Non-LTE Modelling

This review paper outlines background information and covers recent advances made via the analysis of spectra and images of prominence plasma and the increased sophistication of non-LTE (ie when there is a departure from Local Thermodynamic Equilibrium) radiative transfer models. We first describe the spectral inversion techniques that have been used to infer the plasma parameters important for the general properties of the prominence plasma in both its cool core and the hotter prominence-corona transition region. We also review studies devoted to the observation of bulk motions of the prominence plasma and to the determination of prominence mass. However, a simple inversion of spectroscopic data usually fails when the lines become optically thick at certain wavelengths. Therefore, complex non-LTE models become necessary. We thus present the basics of non-LTE radiative transfer theory and the associated multi-level radiative transfer problems. The main results of one- and two-dimensional models of the prominences and their fine-structures are presented. We then discuss the energy balance in various prominence models. Finally, we outline the outstanding observational and theoretical questions, and the directions for future progress in our understanding of solar prominences.Comment: 96 pages, 37 figures, Space Science Reviews. Some figures may have a better resolution in the published version. New version reflects minor changes brought after proof editin

Oracle-based optimization applied to climate model calibration

In this paper, we show how oracle-based optimization can be effectively used for the calibration of an intermediate complexity climate model. In a fully developed example, we estimate the 12 principal parameters of the C-GOLDSTEIN climate model by using an oracle- based optimization tool, Proximal-ACCPM. The oracle is a procedure that finds, for each query point, a value for the goodness-of-fit function and an evaluation of its gradient. The difficulty in the model calibration problem stems from the need to undertake costly calculations for each simulation and also from the fact that the error function used to assess the goodness-of-fit is not convex. The method converges to a Fbest fit_ estimate over 10 times faster than a comparable test using the ensemble Kalman filter. The approach is simple to implement and potentially useful in calibrating computationally demanding models based on temporal integration (simulation), for which functional derivative information is not readily available

Transfer inside pairs of Pr3+ in LaF3 studied by up-conversion fluorescence

Experimental results are reported which show for the first time a transfer inside pairs of ions after their selective excitation by a pulsed laser. This transfer is studied in Pr3+ : LaF3 by monitoring the time dependence of an up-conversion fluorescence. The results show that two mechanisms must be considered, depending upon the distance between the ions of the pairs, to explain the transfer rates measured on 11 different pairs.Ce travail présente des résultats expérimentaux montrant, pour la première fois, un transfert à l'intérieur d'une paire d'ions à la suite d'une excitation sélective par un laser pulsé. Ce transfert est étudié avec Pr3+ : LaF3 en mesurant la dynamique d'une fluorescence de up-conversion. Les résultats montrent que deux mécanismes doivent être invoqués, selon la distance qui sépare les deux ions de chaque paire, pour expliquer les taux de transfert mesurés sur 11 paires différentes

Interaction strength of weakly coupled pairs measured by a two laser spectroscopy technique

When the coupling between two ions associated in pair exceeds a given value, the excitation of both ions of the pair is impossible when using a single narrow laser. This double excitation was obtained with two lasers of different wavelengths. A narrowing of the inhomogeneous broadened lines is observed which gives information on the strain field in the crystal. From the difference between the wavelengths, the order of magnitude of the coupling is deduced and compared with phonon assisted transfer rates.Lorsque le couplage entre les deux ions d'une paire dépasse une certaine valeur, l'excitation des deux ions est impossible avec un seul laser fin. Cette double excitation est réalisée avec deux lasers de différente longueur d'onde. Un rétrécissement des raies inhomogènes est observé et apporte des informations sur le champ de contrainte dans le cristal. L'ordre de grandeur du couplage est déduit de la différence entre les longueurs d'onde et comparé à des taux de transferts assistés de phonons

Evidence for energy transfer induced by superexchange in LaF 3 : Pr3+

Direct measurement of fluorescence quenching rates for various Pr 3+ pairs in weakly doped LaF3 are reported. Since few pairs only are quenched, the transfer mechanism is short range. From the rate values, the shape of the fluorescence decay for heavily doped samples is predicted. The good agreement with the observed decay proves the interest of the connection between microscopic and macroscopic measurements. Finally arguments are developed to prove that the transfer mechanism is superexchange.Les taux d'extinction pour plusieurs paires de Pr3+ dans LaF 3 faiblement dopé ont été mesurés directement. Puisqu'ils sont significatifs pour quelques paires seulement, le mécanisme est à courte portée. A partir des valeurs mesurées, la forme du déclin de la fluorescence de cristaux fortement dopés est prévue. Le bon accord avec l'expérience montre l'intérêt de relier les mesures microscopiques et macroscopiques. Enfin, des arguments sont avancés pour prouver que le mécanisme de transfert est le superéchange

PHOTON GATED HOLE BURNING IN THE 7F0 ? 5D2 ABSORPTION OF BaCIF : Sm2+

Spectral hole burning in solids is a selective bleaching of a small portion of an inhomogeneously broadened optical transition by a laser. In the photon gated holeburning process spectral holes are burned in two steps. The first is provided by a narrow band laser resonant with the inhomogeneously broadened transition and the second (gating) can be initiated by a broad band light source. Photon gated spectral hole burning was reported recently in 7F0→5D0 and 7F0→5D1 absorption lines of Sm2+ in BaClF(1). In this poster we report on the spectral holeburning behaviour of 1F0→5D2 transition. We found that even in absence of additional light source for gating, permanent holes can be burned. This self gating behaviour is consistent with the observation that the optimum frequency following 5D0 excitation is ≈ 22 000cm-1 so that two photons of energy 5D2 - 7F0 are sufficient to produce photoionisation. We have analysed the light intensity dependance of hole area and a simple model indicate that the electron transfer following the photoionisation is strongly dependant on the ion - electron trap distance

OPTICAL PROPERTIES OF Nd3+ ION PAIRS IN LiYF4 CRYSTAL

Les paires d'ions Nd3+ ont été étudiées par des techniques optiques sur un cristal de LiYF4. Les transferts non radiatifs ont été analysés grâce à la fluorescence de up-conversion et au quenching du niveau 4F3/2. Les spectres d'excitation à haute-résolution et de fluorescence permettent d'attribuer les raies satellites à 6 catégories de paires constituées d'ions les plus proches. Le mécanisme responsable du transfert est à courte portée et le super-échange est invoqué pour l'expliquer.The Nd3+ ion pairs are studied by optical techniques in a weakly doped, LiYF4 crystal. Non radiative energy transfers are analysed thanks to up-conversion fluorescence and to fluorescence quenchin of the 4F3/2 level. High resolution selective excitation and fluorescence spectra allow an assignment of satellite lines with 6 classes of pairs made of ions in the nearest neighbour positions. The mechanism responsible for the transfer is short range and the superexchange is suggested to explain it

LINE NARROWING CAPABILITIES OF Nd3+ PAIRS IN LiYF4

Les paires d'ions Nd3+ dans LiYF4 sont utilisées pour mesurer la corrélation entre les distributions inhomogènes des deux transitions successives nécessaires à leurs doubles excitations. Les profils et les intensités des raies sont bien interprétés. Nous déduisons une faible largeur homogène qui est proche de celle qui peut être déduite du temps de vie des états excités.Pairs of Nd3+ ions in LiYF4 are used to test the correlation between the inhomogeneous distributions of the two successive transitions needed for their double excitation. The experimental line shape and line intensities are well accounted for by a single model. We measure a small homogeneous linewidth which can be connected to the lifetime of the excited levels