Ionization processes in the atmosphere of Titan. II. Electron precipitation along magnetic field lines

International audienceThe Cassini probe regularly passes the vicinity of Titan, providing new insights into particle precipitation by use of its electron and ion spectrometers. A discrepancy between precipitation models and observations of electron fluxes has been found. This discrepancy was suspected to be caused by the geometry of the magnetic field. Aims. In this article, we compute the electron impact ionization in the nightside ionosphere of Titan, assuming non-trivial geometry for the magnetic field lines. Methods. We use the TransTitan model, modified to take into account the magnetic field line geometry in the nightside, and we compare these results with the electron flux measurements during the T5 fly-by of Cassini. We use several magnetic field line geometries, including one produced by hybrid simulations. Results. The geometry of the lines implies a longer path of the electron inside the atmosphere of Titan. The electron fluxes are therefore modified considerably compared to the vertical precipitation hypothesis. At an altitude of 1200 km, the electron flux can be divided up to ten times with a field line resulting from hybrid simulation. Thanks to the use of more accurate field lines, the model reproduces the experiment well without any further adjustment of the precipitated measured electron flux. Conclusions. Several hypothesis had been suggested to explain the discrepancies between the different models and the observation of the electron flux during the T5 fly-by of Cassini. Our approach shows that the most probable explanation is the magnetic field line geometry. This work shows that the computation of ion production by electron impact in the atmosphere of Titan needs the consideration of both magnetic field and the input electron fluxes. Based on these considerations, our model can compute the conditions for future fly-by, and could be used to compare models with experiments

Modélisation des émissions aurorales de Jupiter dans l'ultraviolet. Modélisation de l'émission Lyman de Jupier chauds

La première partie de cette thèse présente une modélisation des émissions aurorales de Jupiter dans l'ultraviolet. Le but de ce travail est de quantifier comment ces émissions permettent de contraindre l'énergie des électrons qui précipitent dans la haute atmosphère polaire de la planète. Deux types d'émissions sont étudiés : celle de la raie Lyman alpha de l'hydrogène atomique ainsi que celles de H2. Les précipitations d'électrons aurorales sont modélisées à l'aide d'un code de transport cinétique. Le profil et l'intensité de la raie H Lyman alpha sont obtenus avec un code de transfert radiatif. Des spectres synthétiques des émissions de H2 sont calculés. En étudiant la variabilité des raies en fonction de l'énergie des électrons nous montrons que seules des observations à très haute résolution permettront de contraindre fortement les précipitations d'électrons. La deuxième partie de cette thèse présente la première modélisation de l'émission H Lyman alpha d'un Jupiter chaud jamais réalisée. Si elle était détectée, cette raie permettrait de caractériser l'environnement des planètes extrasolaires. L'émission de l'étoile est beaucoup plus intense que celle de la planète, ce qui rend la détection de la raie planétaire très difficile. Les seules estimations de contraste qui avaient été réalisées jusqu'à présent découlaient d'extrapolations basées sur l'émission de Jupiter. Nous introduisons ici des outils appropriés au calcul des émissions des Jupiter chauds, en tenant compte des spécificités de leur haute atmosphère, et notamment leur forte ionisation et leurs températures qui dépassent les 10 000 K. Nous évaluons l'émission Lyman alpha de deux Jupiter chauds, en tenant compte de plusieurs sources d'excitation des particules : les émissions aurorales et thermiques sont calculées, ainsi que l'émission excitée par le rayonnement de l'étoile. Nous montrons que, dans le cas du Jupiter chaud HD 209458b, la détection de l'émission planétaire n'est pas possible avec les instruments actuels. En revanche la raie Lyman alpha du Jupiter chaud HD 189733b semble pouvoir être détectée avec l'instrument STIS du télescope spatial Hubble.The first part of this thesis describes a modeling of the auroral emission of Jupiter in the ultraviolet. The aim of this work is to quantify how these emissions allow to constrain the energy of the electrons that precipitate in the upper atmosphere of the planet at polar latitudes. Two kinds of emissions are studied : the one of the Lyman alpha line of atomic hydrogen and those of H2. The auroral electron precipitation is modeled with a kinetic transport code. The H Lyman alpha line profile and intensity are obtained with a radiative transfer code. Synthetic spectra of H2 emissions are calculated. By studying the variability of the lines as a function of the energy of the precipitating electrons, we show that only high resolution observations will allow to put strong constraints on the electron precipitation. The second part of this thesis presents the first calculation of the H Lyman alpha emission of a hot Jupiter ever realized. If it were detected, this line would allow to constrain the environment of the extrasolar planets. The stars' emission is much more intense than that of the planet, which transforms the detection of the planetary line in a very difficult challenge. Up to now, the only estimations of contrast that have been realized are based on extrapolations of Jupiter's emission. Here we present tools that are adequate to calculate the emission of hot Jupiters. They take into account the particularities of their atmosphere, like their high ionization degree and their temperatures that exceed 10,000 K. We calculate the Lyman alpha emission of two hot Jupiters, by taking into account the auroral, thermal and dayglow contributions. In the case of the hot Jupiter HD 209458b, we show that current facilities do not allow to detect the planetary emission. On the other hand, the detection of the Lyman alpha line of the planet HD 189733b seems to be within reach of the Hubble Space Telescope.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

A Terrella Device for Simulating Aurora-Like Phenomena in a Box

International audience; A Terrella device was developed and setup in Trieste in 2006 to be used as an experimental training device during practicum sessions of the Advanced International School on Space Weather at ICTP. The Terrella consisted of a vacuum chamber, where an aluminum sphere with an embedded permanent magnet bar mimics the Earth (Terrella) and its magnetic field, and a system of electrodes is set to a high potential difference to generate an electron flow (particle wind) that ionizes the residual air around the sphere. This results in aurora-like glowing patterns whose geometry is dependent on the orientation and distance of the bar magnet, so that various configurations can be experimented. This Terrella device proved to be an effective tool not only for academic but also for outreach purposes. We will briefly present both applications, focusing in particular on the latter, and on the planned use for IHY EPO activities

The EUV Sun as the superposition of elementary Suns

International audienceAims. Many studies assume that the solar irradiance in the EUV can be decomposed into different contributions, which makes modelling the spectral variability considerably easier. We consider a different approach in which these contributions are not imposed a priori but effectively and robustly inferred from spectral irradiance measurements. Methods. This is a source separation problem with a positivity constraint, for which we use a Bayesian solution. Results. Using five years of daily EUV spectra recorded by the TIMED/SEE satellite, we show that the spectral irradiance can be decomposed into three elementary spectra. Our results suggest that they describe different layers of the solar atmosphere rather than specific regions. The temporal variability of these spectra is discussed

JSWSC: recent developments and further advances

International audienceNo abstract availabl

Exploitation, dissemination, education and outreach in the frame of the COST action ES0803 "developing space weather products and services in Europe"

COST (European Cooperation in Science and Technology) is one of the longest-running European frameworks supporting cooperation among scientists and researchers across Europe. Its action ES0803 "Developing Space Weather Products and Services in Europe" involves the task "Exploitation, Dissemination, Education and Outreach". To meet the objectives of this task, we describe how we developed and maintained the Space Weather Portal, initiated the electronic Journal of Space Weather and Space Climate, took care of the scientific organization of the annual European Space Weather Week conference and of two schools for scientists and students from the space weather community. We also describe several dissemination projects supported by the action, which target the non-specialist in the field of space weather

Le soleil comme superposition de soleils élémentaires

Le but de ce travail est la décomposition de l'activité solaire en des activités élémentaires interprétables physiquement. Nous utilisons les mesures du spectre solaire issues de l'instrument SEE embarqué par le satellite TIMED. Les mesures journalières du spectre VUV obtenues sur cinq années autorisent l'utilisation d'un algorithme MCMC de séparation bayésienne de sources positives. Nous montrons que le spectre solaire peut être décomposé en la somme pondérée de trois spectres élémentaires, deux étant clairement représentatifs de zones différentes du soleil, le dernier étant plus difficilement interprétable

Planetary space weather: scientific aspects and future perspectives

International audienceIn this paper, we review the scientific aspects of planetary space weather at different regions of our Solar System, performing a comparative planetology analysis that includes a direct reference to the circum-terrestrial case. Through an interdisciplinary analysis of existing results based both on observational data and theoretical models, we review the nature of the interactions between the environment of a Solar System body other than the Earth and the impinging plasma/radiation, and we offer some considerations related to the planning of future space observations. We highlight the importance of such comparative studies for data interpretations in the context of future space missions (e.g. ESA JUICE; ESA/JAXA BEPI COLOMBO). Moreover, we discuss how the study of planetary space weather can provide feedback for better understanding the traditional circum-terrestrial space weather. Finally, a strategy for future global investigations related to this thematic is proposed

Earth’s climate response to a changing Sun

For centuries, scientists have been fascinated by the role of the Sun in the Earth’s climate system. Recent discoveries, outlined in this book, have gradually unveiled a complex picture, in which our variable Sun a¬ffects the climate variability via a number of subtle pathways, the implications of which are only now becoming clear. This handbook provides the scientifically curious, from undergraduate students to policy makers with a complete and accessible panorama of our present understanding of the Sun-climate connection. 61 experts from di¬fferent communities have contributed to it, which reflects the highly multidisciplinary nature of this topic. The handbook is organised as a mosaic of short chapters, each of which addresses a specific aspect, and can be read independently. The reader will learn about the assumptions, the data, the models, and the unknowns behind each mechanism by which solar variability may impact climate variability. None of these mechanisms can adequately explain global warming observed since the 1950s. However, several of them do impact climate variability, in particular on a regional level. This handbook aims at addressing these issues in a factual way, and thereby challenge the reader to sharpen his/her critical thinking in a debate that is frequently distorted by unfounded claims