150 research outputs found
Study of hazes in exoplanetary atmospheres
No full textDe nos jours, l’étude des exoplanètes est devenue un sujet majeur grâce à leur grande diversité de propriétés physiques, procurant un immense laboratoire pour l’exploration des phénomènes atmosphériques. Parmi eux, les brumes et nuages jouent un rôle crucial dans la compréhension de la structure de l’atmosphère via leur interaction avec l’environnement et leur impact sur les observations. Ce travail a pour objectif d’étudier la microphysique des particules de brume et de nuage, leurs interactions et comment ils affectent l’atmosphère et les spectres de transit. Dans ce but, nous utilisons un modèle 1D auto-consistant prenant en compte la microphysique des brumes et nuages, le transfert radiatif/convectif et le déséquilibre chimique, procurant ainsi une vue complète de la composition de l’atmosphère et de sa structure thermique. Nous explorons les conditions de brumes de l’atmosphère de dix Jupiter-chauds en se basant sur des observations du télescope Hubble et trouvons une corrélation entre les conditions de brumes et la température d’équilibre de la planète. Nous développons une paramétrisation pour le transport des particules et espèces chimiques et finalement, nous étudions l’interaction entre les brumes et les nuages, démontrant que les particules de brumes peuvent participer à la formation de nuages dans l’atmosphère de WASP-39 b en utilisant des observations du télescope James Webb.Nowadays, study of exoplanets has become a prime subject owing to their vast diversity in properties providing a fantastic lab to explore atmospheric phenomena. Among them, haze and clouds are expected to play a crucial role in understanding the atmospheric structure via their interaction with the surrounding environment and their impact on the observations. This work aims to study the microphysics of haze and cloud particles, their interactions and how they affect the atmosphere and the transit spectra. In this purpose, we use a 1D self-consistent model accounting for the haze and cloud microphysics, radiative/convective transfer and disequilibrium chemistry, thus providing a complete picture of the atmospheric haze, cloud, chemical composition and thermal structure. We explore the haziness conditions of ten hot-Jupiter exoplanet atmospheres based on HST observations and find a trend of haziness conditions with the planet equilibrium temperature. We develop a parametrization for the transport of particles and chemical species and finally study the interaction between haze and clouds, demonstrating that haze particles can participate to the cloud formation in WASP-39 b utilizing JWST observations
Technogeopolitics of militarization and security in cyberspace:
No full textBased on democratic principles that encourage creation and transmission of information and knowledge using information and communication technologies, the Information Society has become the organizing paradigm for a digital age. Humans residing in digital rich regions of the world rely on cyberspace, the Information Society’s enabling environment, for their business, commerce, education, socialization. Governments and industry are migrating their critical processes into this domain. These trends will intensify as more people realize cyberspace’s utility. However, the promises of the Information Society may never transpire since there is a lack of trust and security in cyberspace. These two concepts are the foundation on which the utility of inter-networked ICTs, such as the Internet, are built. The increasing rate in the occurrence and sophistication of cybercrimes erodes users’ trust in subscribing to networked services Further the militarization of cyberspace by states as a new domain through which they conduct their operations also presents challenges to the Information Society. Both crime and conflict in cyberspace erode trust in digital networks.
The development of a comprehensive international law for cyberspace is essential to govern state and non-state actor behavior in this global commonage. The formation of the World Summit on the Information Society (WSIS) in the early twenty-first century marks the first time that state and non-state actors convened to develop plans of action to guide the development of in the digital world. This project examines the negotiating positions of the United States, Russia and China in the area of cybersecurity through the lens of technogeopolitics. It is shown how the political and military interests of each affect their negotiating positions in the WSIS. The methods of content analyses on material from diplomatic archives, participant-observation at international conferences and interview surveys of participants at these conferences are used to investigate the reasons why decision are made or not made in the field of international cybersecurity cooperation.Ph.D.Includes bibliographical references (p. 225-248)by Panayotis Alexander Yannakogeorgo
Analysis of Titan's Detached Haze Layer with Cassini/ISS instrument
No full textChargée de brume photochimique, l'atmosphère de Titan est le siège d'une activité dynamique complexe évoluant lentement au gré des saisons. Tout comme la couche d'ozone sur Terre, la couche détachée sur Titan est une fine bande d'aérosols englobant la partie la plus externe de son atmosphère. Depuis sa découverte par les sondes Voyager dans les années 80, elle attise les curiosités quant à sa composition et ses mécanismes de formation.Grâce à la sonde Cassini, en orbite autour de Saturne depuis 2004, nous avons une opportunité unique de l'observer sur près d'une demie année titanienne. Cette thèse vise à réaliser un suivi détaillé de la couche détachée sur l'ensemble de cette mission en s'appuyant sur les relevés réalisés par l'instrument ISS.Dans un premier temps, nous présentons la procédure de traitement mise en place pour calibrer et géo-référencer les données du PDS.Puis, nous réalisons une caractérisation des propriétés optiques des aérosols présents dans la couche détachée en couplant un modèle de diffusion par des agrégats fractals avec un modèle de transfert radiatif simplifié.Par la suite, ces nouvelles contraintes sont réutilisées pour réaliser une inversion globale des profils d'extinction de la brume en s'appuyant sur un modèle plus complexe de transfert radiatif au limbe. Ces relevés systématiques nous permettent de suivre l'évolution spatiale et temporelle de la couche détachée tout au long de la mission Cassini.Enfin, nous nous penchons tout particulièrement sur la disparition de la couche détachée au passage de l'équinoxe de printemps, suivi de sa réapparition en 2016, peu de temps avant le solstice d'été.Loaded with photochemical haze, Titan's dynamical atmosphere is slowly evolving through the seasons. Like the ozone layer on Earth, Titan's detached haze layer is a thin coat of aerosols surrounding the upper part of its atmosphere. Since its discovery in the 80's by Voyagers' flybys, it has raised many questions on its content and origin. Thanks to the Cassini mission orbiting around Saturn since 2004, we have the chance to track it over half a Titan year. This thesis carries out a complet survey on Titan's detached haze layer observations taken continuously by the ISS instrument during the whole mission.At first, we present the processing pipeline developed to calibrate and navigate the raw data coming the PDS.Then, we characterize the aerosols optical properties seen inside the detached haze layer by coupling a fractal aggregate model with a simplified version of the radiative transfer equation.Thereafter, these new constrains are used as input into a more complex radiative transfer model in the limb geometry in order to extract globally the extinction profiles of the haze in the upper atmosphere. These systematic surveys allow us to follow the spatial and temporal evolution of the detached haze layer from the beginning to the end of the Cassini mission.Finally, we took a special care on the disappearance of the detached haze after the vernal equinox and its recent reappearance in 2016, just before the summer solstice
Impact of the International Coffee Agreement's export quota system on the World's coffee market
No full textEx-post simulations of the global coffee model over the recent period of operation of the International Coffee Agreement's export quota system, (1981-86) show the following. The quota system had a stabilizing effect on world coffee prices in the 1981-85 period. In 1986, when coffee prices increased sharply due to the drought in Brazil and the export quotas were suspended, prices would have been 24 percent higher in the absence of quotas over the 1981-85 period. However, the quotas have reduced export revenues (in real terms), except for such large producers as Brazil and Colombia. These countries gained form the scheme because they face very small or even zero marginal export revenues from increased exports, due to their large market shares. In projections of the coffee market, with and without the export quota system, prices would be substantially lower during the first half of the 1990s if the quota system were suspended in 1990. But prices would recover in the second half of the decade as production and exports declined in lagged response to the very low prices of the first half.Economic Theory&Research,Environmental Economics&Policies,Markets and Market Access,Access to Markets,Crops&Crop Management Systems
Aerosols optical properties in Titan's Detached Haze Layer
No full textInternational audienceTitan's Detached Haze Layer (DHL) was first observed in 1983 by Rages and Pollack during the Voyager 2 is a consistent spherical haze feature surrounding Titan's upper atmosphere and detached from the main haze. Since 2005, the Imaging Science Subsystem (ISS) instrument on board the Cassini mission performs a continuous survey of the Titan's atmosphere and confirmed its persistence at 500 km up to the equinox (2009) before its drop and disappearance in 2012 (West et al. 2011). Previous analyses showed, that this layer corresponds to the transition area between small spherical aerosols and large fractal aggregates and play a key role in the aerosols formation in Titan's atmosphere (Rannou et al. 2000, Lavvas et al. 2009, Cours et al. 2011).In this talk we will present the UV photometric analyses based on radiative transfer inversion to retrieve aerosols particles properties in the DHL (bulk and monomer radius and local density) performed on ISS observations taken from 2005 to 2007.References:- Rages and Pollach, Icarus 55 (1983)- West, et al., Icarus 38 (2011)- Rannou, et al., Icarus 147 (2000)- Lavvas, et al., Icarus 201 (2009)- Cours, et al., ApJ Lett. 741 (2015
A physically derived eddy parametrization for giant planet atmospheres with application on hot-Jupiters
No full textInternational audienceWe present a parameterization for the eddy diffusion profile of gas giant exoplanets based on physical phenomena and we explore how the parameterized eddy profile impacts the chemical composition, the thermal structure, the haze microphysics, and the transit spectra of 8 hot-Jupiters. Our eddy parameterization depends on the planetary intrinsic temperature (T int), we thus evaluate how the increase of this parameter to values higher than those typically used (∼100K) impacts the atmospheric structure and composition. Our investigation demonstrates that despite the strong impact of T int on the chemical composition of the deep atmosphere, the upper atmosphere is not affected for T eq > 1300 K owing to high altitude quench levels at these conditions. Below this threshold, however, the larger atmospheric temperatures produced by increasing T int affect the quenched chemical composition. Our parameterization depends on two parameters, the eddy magnitude at the radiative-convective boundary (K 0) and the corresponding magnitude at the homopause (K top). We demonstrate that, when using common K 0 and K top values among most of the different planet cases studied, we derive transit spectra consistent with Hubble Space Telescope observations. Moreover, our simulations show that increasing the eddy profile enhances the photochemical production of haze particles and reduces their average radius, thus providing a steeper UV-Visible slope. Finally, we demonstrate for WASP-39b that the James Webb Space Telescope observations provide improved constraints for the hazes and clouds and we show that both components seem necessary to interpret the combined transit spectrum from HST and JWST observations
Χωρικές και χρονικές μεταβολές των ιδιοτήτων της ατμόσφαιρας και της επιφάνειας του Τιτάνα: προσομοίωση και ερμηνεία μέσω διαστημικών και επιγείων παρατηρήσεων
No full textA new 1D coupled Radiative / Convective - Photochemical – Microphysical model for a planetary atmosphere was developed and applied to the investigation of the spatial and temporal variability of Titan's atmosphere, and in particular to photochemical haze production. The spatial variability corresponds to the vertical structure of the atmosphere and the way this is determined by the different physical, chemical and radiative processes that take place. The temporal variability, addresses the impact of the 11-year solar cycle on the vertical structure of the atmosphere. The model incorporates detailed radiation transfer calculations for the description of the shortwave and longwave fluxes which provide the vertical structure of the radiation field and determine the temperature profile. These are used for the generation of the photochemical and haze structure in the atmosphere, initiated by the photolysis of Titan's main constituents, nitrogen (N₂) and methane (CH₄). The resulting hydrocarbons and nitriles are used for the production of the haze precursors, whose evolution is described by the microphysical part of the model. The calculated aerosol and gas opacities are iteratively included in the radiation transfer calculations in order to investigate their effect on the resulting temperature profile and geometric albedo. The main purpose of this model is to help in the understanding of the missing link between the production of gaseous species and their transformation to haze particles in Titan's atmosphere. The model generates the haze structure from the gaseous species photochemistry. Model results are presented for the species vertical concentration profiles, haze formation and its radiative properties, vertical temperature/density profiles and geometric albedo. These are validated against the very recent Cassini/Huygens observations and also against other ground-based and space-borne measurements. The model reproduces well most of the latest measurements from the Cassini/Huygens instruments for the chemical composition of Titan's atmosphere and the vertical profiles of the observed species. For the haze production, we have included pathways that are based on pure hydrocarbons, pure nitriles and hydrocarbon/nitrile copolymers. From these, the nitrile and copolymer pathways provide the stronger contribution, in agreement with the results from the ACP instrument, which support the incorporation of nitrogen in the pyrolised haze structures. The haze model reveals a new second major peak in the vertical profile of haze production rate between 500 and 900 km. This peak is produced by the copolymer family used and has important ramifications for the vertical atmospheric temperature profile and geometric albedo. In particular, the existence of this second peak determines the vertical profile of haze extinction. The solar cycle variability affects the species vertical profiles and eventually results in increase in the haze production of about 60% from solar minimum to solar maximum. This has further effects on the geometric albedo and the vertical temperature structure. The model results have been compared with the DISR retrieved haze extinction profiles and are found to be in very good agreement. Furthermore, heterogeneous chemistry on the haze particles that converts atomic hydrogen to molecular hydrogen has been incorporated in the model. The resultant H₂ profile is closer to the INMS measurements, while the vertical profile of the diacetylene formed is found to be closer to that of the CIRS profile when this heterogeneous chemistry is included.Ένα νέο μονοδιάστατο υπολογιστικό μοντέλο το οποίο συνδέει τη διάδοση της ακτινοβολίας, τη φωτοχημεία και τη μικροφυσική σε μια πλανητική ατμόσφαιρα, κατασκευάστηκε και εφαρμόστηκε για τη μελέτη των χωρικών και χρονικών μεταβολών της ατμόσφαιρας του Τιτάνα, και ειδικότερα τη φωτοχημική παραγωγή των αερολυμάτων της ατμοσφαιράς του. Οι χωρικές μεταβολές αφορούν την καθ' ύψος δομή της ατμόσφαιρας όπως αυτή καθορίζεται από τις διαφορετικές φυσικές και χημικές διεργασίες καθώς και τη διάδοση της ακτινοβολίας που λαμβάνουν χώρα. Οι χρονικές μεταβολές αφορούν την επίδραση του 11-ετoύς ηλιακού κύκλου στη καθ' ύψος δομή της ατμόσφαιρας. Το μοντέλο περιλαμβάνει λεπτομερείς υπολογισμούς για τη ροή της ακτινοβολίας για τα μικρά (υπεριώδες, ορατό και κοντινό υπέρυθρο) και μεγάλα (υπέρυθρο) μήκη κύματος, που παρέχουν τη καθ' ύψος δομή του πεδίου της ακτινοβολίας και καθορίζουν τη δομή της θερμοκρασίας. Αυτές χρησιμοποιούνται για τη περιγραφή της δημιουργίας της φωτοχημικής σύστασης και της δομής των αερολυμάτων οι οποίες ξεκινούν με τη φωτόλυση των κυρίων συστατικών της ατμόσφαιρας του Τιτάνα, του αζώτου και του μεθανίου. Τα χημικά στοιχεία που δημιουργούνται χρησιμοποιούνται για την παραγωγή των δομικών δομών των αερολυμάτων, η εξέλιξη των οποίων περιγράφεται από το μικροφυσικό τμήμα του μοντέλου. Οι υπολογισμένες δομές της χημικής σύστασης και αυτή των αερολυμάτων στη συνέχεια εισέρχονται στους υπολογισμούς της διάδοσης της ακτινοβολίας και στη γεωμετρική ανάκλαση της ατμόσφαιρας. Ο βασικός στόχος αυτού του υπολογιστικού μοντέλου είναι η κατανόηση του άγνωστου μέχρι στιγμής κρίκου μεταξύ της παραγωγής των αερίων στοιχείων στην ατμόσφαιρα του Τιτάνα και της μετατροπής τους στα παρατηρούμενα αερολύματα. Το μοντέλο δημιουργεί τη δομή των αερολυμάτων από την αέρια φωτοχημεία. Τα αποτελέσματα του μοντέλου για τη καθ' ύψος συγκέντρωση του κάθε στοιχείου, τη δημιουργία των αερολυμάτων και τις οπτικές τους ιδιότητες, τη καθ' ύψος δομή της θερμοκρασίας και της ατμοσφαιρικής πυκνότητας και τη γεωμετρική ανάκλαση παρουσιάζονται και συγκρίνονται με τα τελευταία αποτελέσματα από τη διαστημική αποστολή Cassini/Huygens καθώς και με προηγούμενες επίγειες και διαστημικές παρατηρήσεις. Το μοντέλο καταφέρνει να αναπαράγει σωστά τις περισσότερες από τις τελευταίες μετρήσεις για τη συγκέντρωση και καθ' ύψος δομή των χημικών στοιχείων της ατμόσφαιρας του Τιτάνα. Για την παραγωγή των αερολυμάτων χρησιμοποιήθηκαν διαδικασίες οι οποίες περιλαμβάνουν καθαρούς υδρογονάνθρακες, αζωτούχους υδρογονάνθρακες καθώς και συνδυασμούς των δύο (συν-πολυμερή). Από αυτούς, οι αζωτούχοι υδρογονάνθρακες και τα συν-πολυμερή, βρέθηκαν να έχουν τη σημαντικότερη συνεισφορά στη παραγωγή των αερολυμάτων. Αυτό το αποτέλεσμα είναι σε συμφωνία με τις μετρήσεις από το όργανο ACP της ακάτου Huygens, το οποίο έδωσε ενδείξεις για την ύπαρξη αζώτου στη δομή των αερολυμάτων. Το μοντέλο αποκαλύπτει την ύπαρξη μιας νέας σημαντικής ζώνης παραγωγής αερολυμάτων μεταξύ 500 και 900 χλμ. η οποία προέρχεται από τα συν-πολυμερή και η οποία έχει σημαντικές επιδράσεις για τη δομή της θερμοκρασίας και τη γεωμετρική ανάκλαση. Πιο συγκεκριμένα, η ύπαρξη αυτής της δεύτερης κορυφής καθορίζει την καθ’ ύψος παραγωγή των αερολυμάτων. Ο 11-ετής ηλιακός κύκλος επηρεάζει τη δομή των χημικών στοιχείων και τελικά έχει ως αποτέλεσμα την αύξηση της παραγωγής αερολυμάτων κατά 60% μεταξύ ηλιακού ελαχίστου και μεγίστου. Αυτό έχει περαιτέρω επιδράσεις στη δομή της θερμοκρασίας και στη γεωμετρική ανάκλαση. Τα αποτελέσματα του μοντέλου συγκρίθηκαν και με τη καθ' ύψος δομή των οπτικών ιδιοτήτων των αερολυμάτων, όπως αυτή μετρήθηκε από το όργανο DISR, με την οποία βρέθηκε να είναι σε καλή συμφωνία. Επίσης, ετερογενής χημικές διαδικασίες στην επιφάνεια των αερολυμάτων, οι οποίες μετατρέπουν ατομικό υδρογόνο σε μοριακό, συμπεριλήφθηκαν στο μοντέλο. Αυτές είχαν σαν αποτέλεσμα τη βελτίωση των αποτελεσμάτων για το μοριακό υδρογόνο σε σχέση με τις μετρήσεις από το όργανο INMS και για τη δι-ασετιλίνη με βάση τις μετρήσεις από το όργανο CIRS
Coupling haze and cloud microphysics in WASP-39b's atmosphere based on JWST observations
No full textWe present a study on the coupling of haze and clouds in the atmosphere of
WASP-39b. We developed a cloud microphysics model simulating the formation of
Na2S and MgSiO3 condensates over photochemical hazes in gas giant atmospheres.
We apply this model to WASP-39b, recently observed with the JWST to study how
these heterogeneous components may affect the transit spectrum. We simulate
both morning and evening terminators independently and average their transit
spectra. While MgSiO3 formation has negligible impact on the spectrum, Na2S
condensates produce gray opacities in the water band, in agreement with HST and
JWST observations. Moreover, the formation of Na2S on the morning side depletes
the atmosphere of its sodium content, decreasing the strength of the Na line.
Combining morning and evening profiles results in a good fit of the Na
observations. These nominal results assume a small Na2S/haze contact angle
(5.7{\deg}). Using a larger value (61{\deg}) reduces the cloud density and
opacity, but the effect on the Na profile and spectral line remains identical.
In addition, the presence of haze in the upper atmosphere reproduces the
UV-visible slope observed in the HST and VLT data and contributes to the
opacity between the water bands at wavelengths below 2 microns. The averaged
spectra are rather insensitive to the variation of eddy diffusion and haze mass
flux tested in this study, though the UV-visible slope, probing the haze layer
above the clouds, is affected. Finally, our disequilibrium chemistry model,
including photochemistry, reproduces the SO2 and CO2 absorption features
observed.Comment: 19 pages, 16 figure
A physically derived eddy parameterization for giant planet atmospheres with application on hot-Jupiter atmospheres
No full textWe present a parameterization for the eddy diffusion profile of gas giant
exoplanets based on physical phenomena and we explore how the parameterized
eddy profile impacts the chemical composition, the thermal structure, the haze
microphysics, and the transit spectra of 8 hot-Jupiters. Our eddy
parameterization depends on the planetary intrinsic temperature (T ),
we thus evaluate how the increase of this parameter to values higher than those
typically used (100K) impacts the atmospheric structure and composition.
Our investigation demonstrates that despite the strong impact of T on
the chemical composition of the deep atmosphere, the upper atmosphere is not
affected for T 1300 K owing to high altitude quench levels at these
conditions. Below this threshold, however, the larger atmospheric temperatures
produced by increasing T affect the quenched chemical composition. Our
parameterization depends on two parameters, the eddy magnitude at the
radiative-convective boundary (K) and the corresponding magnitude at the
homopause (K). We demonstrate that, when using common K and
K values among most of the different planet cases studied, we derive
transit spectra consistent with Hubble Space Telescope observations. Moreover,
our simulations show that increasing the eddy profile enhances the
photochemical production of haze particles and reduces their average radius,
thus providing a steeper UV-Visible slope. Finally, we demonstrate for WASP-39b
that the James Webb Space Telescope observations provide improved constraints
for the hazes and clouds and we show that both components seem necessary to
interpret the combined transit spectrum from HST and JWST observations.Comment: 19 pages, 12 figure
A large range of haziness conditions in hot-Jupiter atmospheres
No full textWe present a study of photochemical hazes of exoplanet atmospheres based on a
self-consistent model including haze microphysics, disequilibrium chemistry,
and radiative feedbacks. We derive the haze properties required to match HST
observations of ten hot-Jupiters. HAT-P-12b, HD-189733b, HD-209458b and WASP-6b
require haze mass fluxes between 5x10 and 9x10
to match the observations. WASP-12b and WASP-19b with equilibrium temperatures
above 2000 K are incompatible with the presence of haze and are better fitted
by heavy metals. HAT-P-1b and WASP-31b do not show clear evidence for the
presence of hazes with upper mass fluxes of 10 and
10, respectively, while WASP-17b and WASP-39b present
an upper mass flux limit of 10. We discuss the
implications of the self-consistent model and we derive upper limits for the
haze abundances based on photochemistry results. Our results suggest HCN as the
main haze precursor up to 1300 K effective temperatures and CO above. Our
derived haze mass fluxes based on the fit to the observations are consistent
with the photochemistry with formation yields up to 6.4\%. Disequilibrium
chemistry has negligible impact on the spectra considering the low resolution
observations used but impacts the chemical composition and temperature
profiles. We find that hazes produce hotter upper atmosphere temperatures with
a detectable impact on the spectra. Clouds may have implications for
interpreting the transit spectra of HD-209458b, WASP-31b and WASP-39b.
Nevertheless, the presence of silicate and iron clouds is expected in all
studied atmospheres except WASP-12b and WASP-19b.Comment: 29 pages, 25 figure
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