Mon travail porte sur la construction de générateurs aléatoires de conditions de vent en Bretagne. Ces modèles permettent de simuler artificiellement des conditions météorologiques réalistes et sont couramment utilisés pour la gestion des risques liés aux aléas climatiques. Ils sont construits sur la base de données historiques dans le but de produire des simulations cohérentes avec le climat actuel mais peuvent intégrer des scénarios de changement climatique. Les séquences simulées permettent de pallier le manque de données réelles et sont utilisées en entrée de modèles économiques ou écologiques. / This work is aimed at constructing stochastic weather generators. These models enable to simulate artificially weather data that have statistical properties consistent with observed meteorology and climate. Outputs of these models are generally used in impact studies in agriculture or in ecology.

This thesis was funded by the Natural Environment Research Council (NERC) and is presented in an alternative thesis format. The thesis consists of three separate journal articles which form a coherent research project. Paper 1 investigates the development of strong winds in a dry, idealised extratropical cyclone using the horizontal momentum equation. In particular, the southwest wind maximum that develops was found to contain air parcels from three airstreams. The development of the horizontal along-flow forces around the cyclone and along trajectories entering the southwest wind maximum were analysed. An attempt to extend this methodology to a moist, idealised extratropical cyclone was made. However, the effect of adding moisture to the initial condition was found to be negligible. The reasons for this are explored in Paper 2, which documents this finding: that the effect of moisture on the development of an idealised, baroclinic wave is sensitive to the choice of initial condition. Paper 3 applies the horizontal momentum equation diagnostics to an intense, marine extratropical cyclone that brought strong winds to Ireland and the United Kingdom on 12 February 2014. The development of strong winds in Cyclone Tini was investigated by turning off latent heat release and surface fluxes. In the absence of latent heat release a weaker wind maximum developed. However, the simulation without surface fluxes had a very similar vertical structure of the horizontal wind to the full-physics simulation, but a weaker surface wind maximum. The reason for this weaker wind maximum was analysed using the quasigeostrophic omega equation. This analysis demonstrated a maximum in forcing for descent southwest of the low both in the full-physics simulation and in the simulation without surface fluxes, however strong winds were prevented from reaching the surface in the simulation without surface fluxes because of a more stable boundary layer around the bent-back front.

This thesis investigates the relationship between open hexagonal cell cloud motion and surface winds in the northeast Pacific Ocean. Cloud targets are tracked using an automatic scheme fashioned after Barnea and Silverman's (1972) Sequential Similarity Detection Algorithm. The cloud motion vectors obtained are comparable to results obtained by tracking the same cloud targets manually. The well-organized character of open hexagonal cells permits a comparison of various methods of estimating the height of the cloud motion vectors. One method, which uses the minimum infrared pixel value, and a second method, which establishes an arbitrary minimum cloud top temperature, are both found to be unsuitable because of cirrus contamination and partially cloud filled pixels. The cloud motion winds for open hexagonal cells and disorganized cumulus clouds are compared with winds measured at collocated surface buoys. The lack of directional shears between open hexagonal cell movements and surface winds, and directional shears of 14° to 27° for the disorganized cumulus clouds, agree with other observations for the two types of clouds. The differences between the two cloud types suggests that any estimate of surface winds from cloud motion should include cloud type information. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Studies were carried out to determine the circulation of water in the northern basin of Howe Sound, a small fjord on the mainland coast of British Columbia, and to determine the extent of the influence of the winds, the tide and river runoff on the circulation. In one experiment, surface-layer drogues were tracked by radar for four periods each of approximately three days duration. Data sere recorded photographically, then digitized for computer processing. Cubic spline interpolation was used to produce positions, velocities and accelerations at one minute intervals along every drogue track. The interpolated data were averaged in a suitable manner to produce pseudo-Eulerian estimates of velocity. Near the head of the fjord, both wind and tide appeared to cause temporal fluctuations in the surface current of magnitude similar to the expected mean flow due to the river. The river was the cause of spatial inhomogeneity in the flow, but did not appear to be a significant source of temporal variations. Farther down the inlet, wind forcing was the dominant cause of temporal variations in the surface-layer flow of about five times the magnitude of the expected mean river-driven flow. At no distance along the fjord was the velocity observed to be laterally uniform. Lateral gradients of long-channel velocity were strong at the inlet head and decreased away from it, indicating that the fresh water from the river was slowly mixing across the inlet. Another experiment using drogues at three depths in the upper 6 m of the water indicated that the velocity structure was not uniform, either laterally or with depth. Analysis was done on data from six current meters moored in the northern basin of Howe Sound. The mean currents from these meters showed a surface-layer outflow and a return inflow in the waters just below. A mean down-inlet current was seen at 150 m, 80 m below sill depth. Spectra of the currents showed dominant peaks at diurnal and semi-diurnal periods. The wind was coherent with the currents at 3m for periods longer than 10 hours. Below this depth, no consistent relationship was seen. In the diurnal band, the currents were strongest at the surface, indicative of forcing from the surface by the wind. In the semi-diurnal band, the currents were strongest at 10m depth. Both bands also showed a phase variation with depth indicative of a baroclinic structure. These results were compared with some models for surface-layer behaviour. The first model assumed that the wind momentum input was distributed uniformly throughout the surface layer and that the layer was not frictionally coupled to the deeper waters. Drag coefficients calculated from the wind stress and drogue acceleration gave values of 1 to 2x10-3, similar to values measured in other ways. This model was only valid for the first few hours after the onset of the wind. Another model, developed by Farmer (1972), analysed the behaviour of the surface layer of a semi-infinite canal under the influence of a steady wind stress. It predicted correctly the length of time of wind dominance of the flow, the magnitude of the velocity change and the magnitude of the acceleration of the water. A baroclinic tidal model in a two-layer fjord, adapted from Rattray (1960), correctly predicted the phase of the surface-layer currents near the head of a fjord with respect to the height of the tide. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Neste trabalho foi desenvolvido um novo m´etodo de s´ntese espectral para modelar o disco de acres¸cao de vari´aveis catacl´smicas (VCs) nao magn´eticas. O principal objetivo deste trabalho ´e analisar a emissao do cont´nuo e das linhas em uma ampla faixa espectral no ultravioleta (UV). O disco ´e separado em an´eis concentricos e, para cada anel uma atmosfera de disco com vento ´e calculada. Na base, as atmosferas sao calculadas consistemente com o vento, tendo a distribui¸cao de densidade dos modelos de atmosferas de disco de Wade e Hubeny. A estrutura ´e calculada no sistema co-m´ovel com um perfil de velocidade vertical obtido da solu¸cao da equa¸cao de Euler para um disco de acres¸cao. O comportamento das linhas e do cont´nuo como fun¸cao da inclina¸cao orbital ´e consistente com as observa¸coes. Tamb´em foi verificado que a taxa de acres¸cao influi sobre a temperatura do vento levando `as mudan¸cas correspondentes nas intensidades relativas das linhas. Foi encontrado que a massa da prim´aria tem uma forte influencia na profundidade dos perfis de absor¸cao. Tamb´em, encontramos que a os perfis de linha sao fortemente sens´veis ao incremento da taxa de perda de massa, aumentado a intensidade das linhas de emissao. Foram escolhidos dados espectrosc´opicos no UV de duas VCs Nova-like (NL) de baixa inclina¸cao, RW Sex e V3885 Sgr e dois sistemas de alta inclina¸cao, RW Tri e V347 Pup. Uma concordancia dos perfis em emissao dos modelos foi encontrada quando confrontados com os dados no caso de sistemas de alta inclina¸cao. Uma falta de fluxo nas linhas de alta ioniza¸cao Civ ¸¸1548,1551 and Nv ¸¸1238,1242, pode ser o sinal da influencia da boundary layer (BL) ou da influencia da irradia¸cao das regioes externas do vento pelo disco interno. Estas influencias seriam cruciais no caso de sistemas baixa inclina¸cao, mas sao menores no caso de sistemas de alta inclina¸cao. / We have developed a new spectral synthesis method for modeling the accretion disk of non-magnetic cataclysmic variables (CVs). The aim of this work is to analyze the continuum and line emission of disks in a wide ultraviolet (UV) spectral range. The disk is separated in concentric rings, and for each ring a wind plus disk atmosphere are calculated. The wind atmospheres are calculated consistently with a density given by Wade and Hubeny disk-atmosphere models at their base. The structure is calculated in the co-moving frame with a vertical velocity profile defined by the Eulers equation solution for the disk wind. We found that the resulting line and continuum behavior as a function of the orbital inclination is consistent with the observations. We also verify that the accretion rate changes the wind temperature, leading to corresponding trends in the intensity of lines. We found that the primary mass has a strong effect on the absorption profiles depth. It was verified that the lines profiles are strongly sensitive to the wind temperature structure and a rise of mass loss rate increases the line intensity. Selected UV data for two high orbital inclination nova-like (NL) CVs, RW Tri and V347 Pup, were confronted with synthetic spectra. The line widths and profiles are reasonably well reproduced by the models. A lack of flux in some high ionization lines (C iv ¸¸1548,1551 and Nv ¸¸1238,1242) may be the signature of the boundary layer (BL) effect and/or the irradiation of outer wind by inner disk. We also found that for high inclination systems the vertical wind structure is less important than for low inclination system models.

Les novæ naines permettent, depuis presque 50 ans maintenant, de tester les modèles d’accrétion. Ces systèmes montrent des éruptions en optique d’une durée de l’ordre de la semaine avec des temps de récurrence de l’ordre du mois. Ces éruptions sont communément attribuées à une instabilité thermo-visqueuse au sein du disque d’accrétion entourant la naine blanche. Les temps caractéristiques de ces éruptions posent de fortes contraintes sur les mécanismes de transport de moment cinétique pilotant l’accrétion dans le disque, mécanismes qui constituent l’objet de cette thèse. Il est souvent admis que l’instabilité magnéto-rotationnelle (MRI) est responsable du transport de moment cinétique via la turbulence qu’elle produit. Cependant, je montre ici, à l’aide de simulations locales de disque d’accrétion avec transfert radiatif, que le transport turbulent produit par la MRI ne permet pas de reproduire les courbes de lumière. En quiescence, où le disque est peu ionisé, il est même peu probable que de la turbulence MRI puisse survivre. Un des résultats majeurs de cette thèse est d’avoir mis en lumière que la MRI ne participe pas qu’au transport turbulent mais peut également lancer des vents magnéto-hydrodynamiques (MHD) qui transportent également du moment cinétique, voire dominent le transport dans l’état quiescent. Ces vents MHD induisent un couple magnétique de surface sur le disque et ne peuvent être réduits à une turbulence effective, en partie car ceux-ci ne déposent pas d’énergie thermique localement mais en emportent contrairement au transport turbulent. Nous avons inclus le transport de moment cinétique dû au couple du vent MHD dans un modèle d’instabilité de disque, modèle classiquement utilisé pour reproduire les éruptions de novæ naines. Avec ce nouveau modèle, nous avons montré qu’il est possible de reproduire les courbes de lumière des éruptions de novæ naines, en utilisant un champ magnétique à la surface de la naine blanche compatible avec ce qui est attendu. C’est la première fois que les éruptions de novæ naines sont modélisées avec succès en utilisant des prescriptions pour le transport de moment cinétique basées sur des simulations MHD et non sur les observations. / Dwarf novæ have been used for almost 50 years now as a test for the theory of accretion. These systems exhibit eruptions in optical light lasting approximately a week with a recurrence time scale of a month. Eruptions are thought to be due to a thermal-viscous instability in the accretion disk surrounding the white dwarf. This model has long been known to put constraints on the mechanisms transporting angular momentum in the disk, which will be the subject of this thesis. Traditionally, transport is presumed to be turbulent where turbulence is due to the magneto-rotational instability (MRI). However, I show here, using local simulations of accretion disks with radiative transfer that there exists a discrepancy between observations and light curves obtained with MRI turbulence only. In quiescence, where the disk is poorly ionised, it is very unlikely that MRI can even survive. One of the key results of this thesis is that MRI do not participate to turbulent angular momentum transport only, but is also able to drive MHD outflows which extract angular momentum very efficiently, especially in quiescence. Wind-driven transport is, by nature, very different from turbulent transport, it induces a surface-torque on the disk and do not deposit thermal energy locally but extract energy from the disk instead. We included MHD wind-driven angular momentum transport in a disk instability model, model which is usually used to reproduce light curves of dwarf novæ. Using this new model, we were able to retrieve light curves looking alike observations, with a magnetic field consistent with what is expected from the dipolar magnetic field of a white dwarf. It is the first time that eruptions of dwarf novæ are modeled with success using prescriptions for angular momentum transport derived from first principles instead of ad hoc parameters.

Connaitre précisément la structure interne des corps célestes est indispensable pour, à la fois, comprendre la physique qui régit leur existence et le processus qui leur a donné naissance. La sismologie, d’abord appliquée à la Terre puis au soleil, s’est révélée être un outil très efficace pour sonder leurs intérieurs. Dans les années 70 (Vorontsov et al 1976), des premiers travaux théoriques ont étudié la possibilité d’une sismologie des planètes géantes gazeuses. Les premières tentatives de mesures d’oscillations ont eu lieu à la fin des années 80. La détection des modes d’oscillations de Jupiter s’est avérée une entreprise très délicate en raison de sa rotation rapide. Pour augmenter les chances de détection, un instrument spécifique a été construit au début des années 2000 à l’OCA. Cet instrument, appelé SYMPA, est un spectromètre imageur de type Mach-Zehnder capable de produire une carte de vitesse radiale de Jupiter. Une détection de modes d’oscillations sur Jupiter par cet instrument a été publiée par Gaulme et al en 2011. Une version améliorée de l’instrument (appelé DSI) a été proposée pour la mission spatiale JUICE à destination de Jupiter, et un nouveau prototype a été construit dans ce but. Par la suite, le projet s’est réorienté vers un programme d’observation depuis le sol sous la forme d’un réseau de trois télescopes répartis en longitude (USA, France, Japon) et financé par l’ANR à partir de 2015 (ANR JOVIAL). L’intérêt de la mise en réseau est d’assurer la continuité des données (météo mise à part). L’instrument étant capable de produire des cartes de vitesse radiales, le projet permet également l’étude de la dynamique atmosphérique des planètes géantes. Ce travail de thèse s’inscrit dans le contexte de préparation de JOVIAL, avec pour objectif de caractériser l’instrument en laboratoire et d’identifier les problèmes liés aux conditions réelles d’observation. Les mesures en laboratoires ont montré des performances conformes aux attentes, avec un bruit de mesure propre à l’instrument inférieur au bruit de photon attendu sur Jupiter. Les premières mesures sur le ciel avec un télescope ont mis en évidence une sensibilité de l’instrument au degré de polarisation de la lumière ainsi qu’une dérive de la vitesse mesurée liée aux instabilités de position de la pupille pendant les observations. Le design de l’instrument et de son interface avec le télescope a été revu pour résoudre ces problèmes. Plusieurs campagnes d’observations de Jupiter ont été réalisées, permettant de mettre sur pied une chaine complète de traitement des données, dont la validité a été vérifiée par des simulations réalistes. Les observations de Jupiter ont donné des résultats scientifiques particulièrement intéressants. L’analyse des données de deux campagnes de 2015 et 2016 a fourni des séquences temporelles de cartes de vitesses radiales de Jupiter. Une première étude a consisté à chercher dans ces cartes la signature des vents zonaux et de les comparer aux mesures réalisées par suivi des nuages sur des images résolues (cloud-tracking). Une telle mesure n’avait jamais été faite par effet Doppler. Le résultat, bien qu’affecté par des biais de mesures identifiés, montre des profils de vents stables d’une année sur l’autre et en cohérence avec les valeurs issues du cloud-tracking, sauf au niveau de la partie nord de la bande équatoriale de Jupiter. La mesure Doppler suggère en effet une vitesse de vent bien inférieure à la vitesse apparente dans cette zone, ce qui a potentiellement des implications sur les modèles de dynamique atmosphérique. Ces résultats sont très importants pour mieux comprendre les mesures de la sonde Juno, actuellement en orbite autour de Jupiter. L’analyse fréquentielle des données temporelles a été abordée en fin de thèse. Les analyses préliminaires ne semblent pas pour l’instant reproduire la détection de SYMPA. Une analyse plus poussée est nécessaire avant de conclure à une absence du signal. / To know precisely the internal structure of the celestial bodies is essential to both to understand the physics which governs their existence, and the process which gave them birth. First applied to the Earth and then to the sun, seismology has proven to be a very effective tool to sound their interiors. It has become natural and legitimate to question the possibility of seismology of gaseous giant planets. The first theoretical work was carried out in the 1970s (Vorontsov et al. 1976), and the first attempts to measure oscillations at the end of the 1980s. The detection of Jupiter's oscillating modes turned out to be very difficult (reduced flux, small apparent diameter, fast rotation ...). To increase the chances of detection, a specific instrument was built in the early 2000s at the OCA. This instrument, called SYMPA, is a Mach-Zehnder-type imaging spectrometer enable to produce radial velocity maps of Jupiter. A first detection of acoustic modes on Jupiter with this instrument was published by Gaulme et al in 2011. An improved version of the instrument (called DSI), based on the same principle, was built in the wake, with the primary objective of boarding a spacecraft to Jupiter. The project was finally reoriented towards an observation program from the ground in the form of a network of three telescopes equidistant in longitude (USA, France, Japan) and supported by the ANR fund starting in 2015 (ANR JOVIAL). The interest of the network is to ensure the continuity of data (weather apart). The instrument being able to produce radial velocity maps, the project also aims to study the atmospheric dynamics of giant planets. This thesis work is part of a preparation for JOVIAL, with the aim of characterizing the instrument and identifying the problems related to real observations conditions. Laboratory measurements showed expected performances with an instrumental noise level (related to thermal fluctuations) lower than expected photon noise on Jupiter. The first measurements on the sky with a telescope showed a sensitivity of the instrument to the degree of polarization of the light as well as drifts of the velocity measurements due the motions of the pupil position. Some adjustments of the design of the instrument and its interface with the telescope were necessary to solve these issues. Several Jupiter observation campaigns were carried out during the thesis, allowing the development of full data processing software. The complete procedure was tested against simulated data and validated. Two observations runs in 2015 and 2016 were analyzed to produce time sequences of radial velocity maps of Jupiter, providing very interesting scientific results. First, the maps were analyzed to look for the signature of the zonal winds and to compare them with the measurements made by cloud-tracking. Such measurements by Doppler effect were never made before. The result, albeit affected by measurement biases, showed stable year-to-year wind patterns and coherent results with cloud-tracking measurements, except at the northern part of the Jovian’s equatorial band. The Doppler measurement indeed suggests a wind speed well below the apparent speed in this area, which potentially has implications for the theory of atmospheric dynamics and will be helpful to interpret the Juno (a spacecraft presently orbiting Jupiter) measurements. Frequency analysis of temporal data was undertaken at the end of the thesis. The preliminary results do not seem for the moment to reproduce the SYMPA detection. Further analysis is necessary before concluding if the signal is absent or attenuated.

No description available.

Clumped structures in wind flows have substantially altered our interpretations of multiwavelength data for understanding mass loss from massive stars. Embedded wind shocks have long been the favored explanation for the hot plasma production and X-ray generation in massive star winds. This contribution reports on line profile shapes fromthe clump bowshock model and summarizes the temperature and emission measure distributions throughout the wind for this model with a focus on results that can be tested against observations.The authors acknowledge funding support for this work from a NASA grant(NNH09CF39C

Massive star winds are understood to be structured. Structures can come in the form of co-rotating interaction regions, which are globally organized flow streams that thread the winds. Structures can also be stochastic in nature, generically referred to as "clumps". The theory for interpreting the radio emissions from randomly distributed microclumps in single star winds is established. Results are presented here for macroclumping, in which the radiative transfer is sensitive to the clump geometry. Two cases are compared: spherical clumps and pancake-like fragments. The geometry of macroclumps can influence the power-law slope of the long wavelength spectral energy distribution.