Dissertations / Theses on the topic 'Atmosphere'

The aim of this thesis is to understand if cyanobacteria, grown on an Earth-like planet orbiting around the habitable zone of an M star can survive and use the light coming from the star in a fruitful way, in particular analyzing their gaseous by-products. The organisms chosen usually don't have photopigments capable to photosynthesize the NIR part of the radiation, but can modify their photosynthetic apparatus in order to adapt to different light conditions if exposed in NIR light conditions, producing chlorophyll d and f. The two bacteria highlighted for our purpose are Chlorogloeopsis fritschii and Cyanobacterium Aponinum. The first is known to be able to change its photosynthetic apparatus to cope with new radiation conditions. In particular is capable to generate chlorophyll d and f if exposed to NIR light (720 nm). This feature is call FarLip acclimation. The second bacterium is a well known bacterium but no one has ever tried to understand if it has the same capability. Efforts have been done in order to find the best culture medium and the best growth conditions of temperature and pH. In order to understand how photosynthetic life can handle different radiation doses we ideated and realized a novel and pioneering LED radiation source with dynamical features. Its wavelength intervals (365nm-940nm) overlap the limits of photosynthetic pigment absorption range (280-850 nm) of most common photosynthetic bacteria. Our simulator is composed by an array of 25 different channels corresponding to 25 different wavelengths. Each channel can host a maximum of about 15 LEDs. This simulator has been built thinking to modularity. In fact it is endowed by a mosaic of circuit boards arranged in a pie-chart shape, on the surface of which will be welded the LEDs. This solution allows a rapid change of the damaged LEDs and an easy implementations with other wavelengths. This simulator is capable to reproduce the spectra of main sequence F, G, K and M stars as well as the most common commercial lamps within its wavelength intervals. The control system is composed by a Laptop which controls a LED box and an STS-VIS spectrograph from Ocean Optics with cosine corrector. The first system generate the best fit of the input spectrum and give information to the simulator on how to reproduce it. The spectrometer has the task to control the goodness of the fit and, by means of a closed loop system, to adjust it tuning the LED's power in real time. The stellar simulator bas been subjected to several tests. The power emanated from the radiation source has been estimated to be 106.22 W while the thermal power has been calculated to be 434.05 W. The stellar simulator have been characterized in flux, analyzing the radiation at different distances from the device, from the exit of the source up to 25 cm. Then uniformity measurements have been done, analyzing the flux on a distance of 6.5 cm from the centre. Finally, I calculated the absorption of the optics of the radiation source analyzing the spectra coming out from the stellar simulator and compared it with respect to the spectrum of the single LEDs. In order to lodge the bacteria we built new concept incubator made of a stainless steel cell with the potential to flux a desired gaseous mixture inside it and fill the cell with the desired gas mixture. Four wedged optical windows opens on the lateral surface and needs to allow the oxygen and carbon dioxide concentration inside by means of a Tunable Diode Laser Absorption Spectroscopy (TDLAS) system. The cell is topped by a BOROFLOAT uncoated window to collect the light from the stellar simulator. The cell has been characterized in void and oxygen and carbon dioxide detecting limits have been found. During the experiment, bacteria have been grown in white light conditions at for 24 days at 20 micromol photons/m^2/s and at 30°C in order to understand the growth times and the behaviour in optimal conditions. After that, a new growth experiment have been performed by growing both cyanobacteria species at 30°C and 20 micromol photons/m^2/s and oxymetric measurements have been done after 6 days from the culture start, thus during their exponential growth phases. Then, for the main part of the experiment, eight samples have been used. Two samples of Cyanobacterium aponinum have been grown at 20 micromol photons/m^2/s in white light for 6 days and then at 100 micromol photons/m^2/s for the residual 3 days in white light. Two samples of Chlorogloeopsis fritschii have been grown at 20 micromol photons/m^2/s for 6 days in white light and then at 100 micromol photons/m^2/s for the residual 3 days in white light. Two samples of Cyanobacterium aponinum have been grown at 20 micromol photons/m^2/s for 6 days in white light and then at 100 micromol photons/m^2/s for the residual 3 days using the radiation spectrum of an M7 type star. Two samples of Chlorogloeopsis fritschii have been grown at 20 micromol photons/m^2/s for 6 days in white light and then at 100 micromol photons/m^2/s for the residual 3 days using the radiation spectrum of an M7 type star. The temperature has been kept at 30°C for the samples not exposed to M7 light and at a temperature oscillating from 35°C to 38°C for the samples exposed to M7 light. The higher environmental temperature under the stellar simulator has been due to the over-heating of the LEDs. During the 3 days of different exposure measurements of optical density have been done in order to collect data about the different growth curves. Moreover, O2 production have been calculated for each sample. Finally, a chromatic response have been done, in order to understand if the colour would reflect the vitality of the bacteria
Lo scopo di questa tesi è quello di capire come dei cianobatteri, cresciuti su un pianeta di tipo terrestre orbitante attorno alla zona di abitabilità di una stella M possano sopravvivere ed usare la luce proveniente dalla stella stessa in modo fruttuoso per la loro esistenza. In particolare ci focalizzeremo sullo studio dei gas da essi prodotti. Gli organismi scelti non hanno pigmenti in grado di fotosintetizzare la parte NIR dello spettro di radiazione, ma riescono a modificare il loro apparato fotosintetico per far fronte alle nuove condizioni di luce, se esposti a luce NIR, producendo clorofilla d ed f. I due batteri scelti per i nostri esperimenti sono Chlorogloeopsis fritschii e Cyanobacterium Aponinum. Il primo batterio è certamente in grado di variare il suo apparato fotosintetico in differenti situazioni luminose. In particolare è in grado di produrre clorofilla e ed f se esposto a luce NIR (720 nm). Questa proprietà si chiama acclimatamento FarLip. Il secondo batterio è è abbastanza noto ma non è stata ancora studiata la sua predisposizione a questo tipo di pratica. Per questi batteri sono stati ricercati i terreni di coltura, di temperatura e pH che meglio permettessero il loro sviluppo. Per capire come il foto-acclimatamento possa aver luogo abbiamo ideato e realizzato un nuovo tipo di sorgente a LED con peculiarità dinamiche. L'intervallo di lunghezze d'onda che copre (365nm-940nm) si sovrappone ai limiti di assorbimento dei pigmenti fotosintetici (280-850 nm) dei più comuni batteri. Il simulatore è composto da 25 differenti canali corrispondenti a 25 differenti lunghezze d'onda. Ogni canale può ospitare un massimo di 15 LED. Il simulatore come detto è stato concepito secondo il concetto di modularità. Infatti è composto da un mosaico di piastre in corma circolare divisa a spicchi e su ognuna di tali piastre sono saldati i LED. Questa soluzione permette di cambiare rapidamente i LED danneggiati e permette una facile implementazione con altre lunghezze d'onda. Il simulatore stellare è in grado di riprodurre lo spettro di varie stelle di sequenza principale, F, G, K e M e molte delle più comuni lampade. Il sistema di controllo è composto da un PC che ha il compito di gestire i LED e da uno spettrometro con relativo correttore di coseno che STS-VIS della ditta Ocean Optics. Il PC genera il miglior fit dello spettro da ricreare con l'illuminatore e lgi da informazioni su come riprodurlo. Lo spettrometro invece controlla la bontà del fit ed attraverso un sistema a circuito chiuso, regola la luminosità dei LED in tempo reale. Abbiamo fatto dei test per verificare il corretto funzionamento del simulatore e stimato la potenza totale emanata, 106.22 W e quella termica, 434.05 W. Inoltre la nostra sorgente di radiazione è stata caratterizzata in flusso, analizzando la radiazione a diverse distanze, dalla bocca di apertura fino a 25 cm da essa. Poi sono state fatte misure di uniformità del flusso entro 6.5 cm dal centro. Infine è stato calcolato l'assorbimento dovuto alle ottiche frapposte fra i LED e i campioni. Per alloggiare i batteri abbiamo ideato e costruito in incubatore in acciaio inox con la possibilità di avere un continuo flussaggio di gas o di essere riempita con una miscela desiderata. Sui lati si aprono quattro finestre ottiche che servono per permettere la misura di concentrazione di ossigeno e di anidride carbonica all'interno attraverso un sistema laser chiamato Tunable Diode Laser Absorption Spectroscopy (TDLAS). L'incubatore è dotato anche di una finestra superiore in borosilicato per permettere alla luce di entrarvi. La cella è stata caratterizzata termicamente e sono stati calcolati le quantità minime osservabili sia di ossigeno che di anidride carbonica. Durante la prima fase dell'esperimento, i batteri selezionati sono stati fatti crescere per 24 giorni Durante l'esperimento, i batteri sono stati fatti crescere a 24 days at 20 micromol fotoni/m^2/s e a 30 °C per costruire le curve di crescita ed il loro comportamento in condizioni ottimali. Dopo ciò, è stato condotto un secondo esperimento facendo crescere entrambe se specie di cianobatteri a 30°C e 20 micromol fotoni/m^2/s in luce bianca ed acquisendo dopo 6 giorni le misure di produttività di ossigeno durante la fase esponenziale. Passati sei giorni sono stati ripartite otto colture, quattro di Cyanobacterium aponinum e quattro di Chlorogloeopsis fritschii. Due colture di Cyanobacterium aponinum sono state fattie crescere prima a micromol fotoni/m^2/s per sei giorni e poi a 100 micromol fotoni/m^2/s per altri tre giorni, sempre in luce bianca. La stessa cosa è stata fatta per due campioni di Chlorogloeopsis fritschii. Due colture di Cyanobacterium aponinum sono state fattie crescere prima a micromol fotoni/m^2/s per sei giorni e poi a 100 micromol fotoni/m^2/s per altri tre giorni,con una radiazione che simulava quella di una stella di tipo M7 incidente su un pianeta terrestre. La stessa cosa è stata fatta per Chlorogloeopsis fritschii. La temperatura è stata mantenuta a 30°C per i campioni in luce bianca e fra 35°C e 38°C per gli esemplari illuminati con luce M7. La maggior temperatura nel secondo caso è stata dovuta al calore prodotto dai LED. Durante i tre giorni in cui i campioni sono stati sottoposti a 100 micromol fotoni/m^2/s sono state prese misure di densità ottica e calcolate le curve di crescita. Inoltre per ogni campione è stata calcolata la produzione di ossigeno. Infine i campioni sono stati analizzati anche dal punto di vista del cromatismo per capire come il loro colore fosse collegato alla vitalità

The ice giants, Uranus and Neptune, are the two outermost planets in our solar system. With only one satellite flyby each in the late 1980’s, the ice giants are arguably the least understood of the planets orbiting the Sun. A better understanding of these planets’ atmospheres will not only help satisfy the natural scientific curiosity we have about these distant spheres of gas, but also might provide insight into the dynamics and meteorology of our own planet’s atmosphere. Two new ground-based, near-infrared datasets of the ice giants are studied. Both datasets provide data in a portion of the electromagnetic spectrum that provides good constraint on the size of small scattering particles in the atmospheres’ clouds and haze layers. The broad extent of both telescopes’ spectral coverage allows characterisation of these small particles for a wide range of wavelengths. Both datasets also provide coverage of the 825 nm collision-induced hydrogen-absorption feature, allowing us to disentangle the latitudinal variation of CH4 abundance from the height and vertical extent of clouds in the upper troposphere. A two-cloud model is successfully fitted to IRTF SpeX Uranus data, parameterising both clouds with base altitude, fractional scale height, and total opacity. An optically thick, vertically thin cloud with a base pressure of 1.6 bar, tallest in the midlatitudes, shows strong preference for scattering particles of 1.35 μm radii. Above this cloud lies an optically thin, vertically extended haze extending upward from 1.0 bar and consistent with particles of 0.10 μm radii. An equatorial enrichment of methane abundance and a lower cloud of constant vertical thickness was shown to exist using two independent methods of analysis. Data from Palomar SWIFT of three different latitude regions.

Ensemble calculations for the period from 2000 to 2010 were carried out with the middle and upper atmosphere model (MUAM), and an analysis of the quarterdiurnal tide is performed. The global temporal and latitudinal distributions of the quarterdiurnal tide are modeled with MUAM, and their forcing mechanisms are examined. The quarterdiurnal tides show a similar distribution over the year in the northern and southern hemisphere, with maxima of the amplitude in late winter and spring as well as in autumn. In the latitude-height distribution is also shown that the largest amplitudes of the quarterdiurnal tide are seen at midlatitudes. Due to the decreasing density with height, there is a general increase of the tidal amplitudes with height. The results of the forcing analyses show that direct solar forcing is most important, but also that non-linear forcing and gravity wave interaction with other tides have a non-negligible influence on the quarterdiurnal tide in the middle and upper atmosphere.
Mit dem Modell für die mittlere und obere Atmosphäre MUAM wurden Ensemble-Berechnungen für den Zeitraum 2000 bis 2010 durchgeführt und die vierteltägigen Gezeiten analysiert. Es wird auf die globale zeitliche und räumliche Verteilung der vierteltägigen Gezeiten eingegangen und deren Anregungsmechanismen untersucht. Die vierteltägigen Gezeiten zeigen einen ähnlichen Verlauf über das Jahr auf der Nord- und Südhalbkugel mit Maxima der Amplitude im späten Winter und Frühjahr sowie im Herbst. Ein ähnliches Bild zeigt sich auch für die Verteilung im Breiten-Höhen-Schnitt, wo die größten Amplituden der vierteltätigen Gezeiten in den mittleren Breiten zu finden sind. Aufgrund der abnehmenden Dichte mit der Höhe ist eine allgemeine Zunahme der Amplituden mit der Höhe zu beobachten. Es zeigte sich, dass der direkte solare Antrieb am stärksten ausgeprägt ist, aber auch, dass der nichtlinearer Antrieb und die Interaktion von Schwerewellen mit anderen Gezeiten einen nicht zu vernachlässigenden Einfluss auf die vierteltägigen Gezeiten in der mittleren und oberen Atmosphäre haben.

The naturally-occurring radioactive gases ²²²Rn and ²²⁰Rn are widely used as atmospheric tracers in a variety of applications pertinent to climate and air quality studies, but their use in this context is currently limited by poor knowledge of the spatial and temporal pattern in emissions. The aim of this research was to improve knowledge of ²²²Rn and ²²⁰Rn emissions by investigating their spatial and temporal variation in emissions on various scales. Novel approaches to measuring ²²²Rn and ²²⁰Rn fluxes by the closed chamber method have been developed and compared with some existing methods, and studies of some controlling variables for which there is limited and conflicting information (water table depth, freezing of the soil and snow cover) have been carried out. Studies of the short-term variability in ²²²Rn emissions made with an automatic chamber showed that outside periods of rain the ²²²Rn flux was relatively constant (CV = ~ 25 %), but heavy rainfall may temporarily completely suppress the radon flux if the soil surface becomes saturated. On the seasonal time-scale, flux measurements made on a medium- moisture was found to be the most important factor controlling the variations in radon flux; air pressure and temperature were not important. Field measurements and a laboratory study using a soil monolith showed that water table depth was also an important factor for ²²²Rn flux, but not for ²²⁰Rn, due to its much shorter diffusion length. Freezing of the soil surface layer (~ 5cm depth) did not cause a significant reduction in ²²²Rn or ²²⁰Rn flux. Studies of the spatial variability of ²²²Rn emissions at the local scale showed that ²²²Rn flux is approximately normally distributed (CV = 55 %), and that soil moisture is an important factor. However, measurements made at 15 sites of different soil type and geology across North Britain showed ²²²Rn emissions to be log-normally distributed at this larger scale and highly variable (CV = ~ 200%). The ²²⁶Ra content of the soil, which ranged from <3 Bq kg^-1 to 55 Bq kg^-1 was found to account for a large proportion of the observed variability (~ 80 %). The median ²²²Rn flux was 9.7 Bq m^-2 h^-1, indicating that the average flux from this region is considerably lower than the global average, as would be expected given the large proportion of peat soils and generally high soil water content and shallow water tables. A ²²²Rn flux map produced for North Britain using a GIS and empirical model based on soil and geology classifications was able to reproduce the main spatial pattern in emissions, but on the whole, significantly under- predicted the magnitude of fluxes.

Analogues were developed for Interplanetary Dust Particles (IDPs) and Meteoric Smoke Particles (MSPs). Candidate materials were characterised and compared to the present understanding of the nature of IDPs and MSPs. Knowledge and understanding from meteoritics was used to inform open questions in atmospheric chemistry. The elemental composition, structural, surface and size distribution properties of the candidates was compared to micrometeorites and remote measurements of MSPs. Both relatively rare carbonaceous and the more common ordinary chondritic meteorites and terrestrial minerals were shown to be useful analogues for IDPs, whilst synthetic materials were identified as analogues for MSPs. Uptake of HNO3 and HO2, based on laboratory experiments, was implemented in a global modelling study. The uptake processes were assessed to determine the region(s) and season(s) in which they would affect atmospheric chemistry. This heterogeneous chemistry augmented previous understanding of gas-phase chemistry, with a view to understanding all sources and sinks of atmospheric species. Whole Atmosphere Community Climate Model (WACCM) runs including uptake were compared to control runs with only gas-phase chemistry. Uptake of both HNO3 and HO2 was shown to alter chemistry in the polar vortex, including effects on many secondary species and feedbacks on each other. Heterogeneous nucleation kinetics of nitric acid hydrates in Polar Stratospheric Clouds (PSCs) was investigated in the laboratory. SiO2 particles were used as analogues for MSPs processed in acidic solution and the phase which formed was investigated. A newly developed drop freeze assay capable of quantifying heterogeneous nucleation kinetics was used. Nucleation events observed in μl droplets were parameterised using current theoretical models and the results compared to atmospheric observations. The measured heterogeneous nucleation kinetics of the Dihydrate, which then readily converts to the Trihydrate, on SiO2 were shown to be capable of explaining the concentrations of crystals observed in the atmosphere.

The new CRISP filter at the Swedish 1-m Solar Telescope provides opportunities for observing the solar atmosphere with unprecedented spatial resolution and cadence. In order to benefit from the high quality of observational data from this instrument, we have developed methods for calibrating and restoring polarized Stokes images, obtained at optical and near infrared wavelengths, taking into account field-of-view variations of the filter properties. In order to facilitate velocity measurements, a time series from a 3D hydrodynamical granulation simulation is used to compute quiet Sun spectral line profiles at different heliocentric angles. The synthetic line profiles, with their convective blueshifts, can be used as absolute references for line-of-sight velocities. Observations of the Ca II 8542 Å line are used to study magnetic fields in chromospheric fibrils. The line wings show the granulation pattern at mid-photospheric heights whereas the overlying chromosphere is seen in the core of the line. Using full Stokes data, we have attempted to observationally verify the alignment of chromospheric fibrils with the magnetic field. Our results suggest that in most cases fibrils are aligned along the magnetic field direction, but we also find examples where this is not the case. Detailed interpretation of Stokes data from spectral lines formed in the chromospheric data can be made using non-LTE inversion codes. For the first time, we use a realistic 3D MHD chromospheric simulation of the quiet Sun to assess how well NLTE inversions recover physical quantities from spectropolarimetric observations of Ca II 8542 Å. We demonstrate that inversions provide realistic estimates of depth-averaged quantities in the chromosphere, although high spectral resolution and high sensitivity are needed to measure quiet Sun chromospheric magnetic fields.
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Submitted. Paper 2: Manuscript. Paper 3: Submitted. Paper 4: Submitted.

Thesis (M.F.A.)--West Virginia University, 2002.
Title from document title page. Document formatted into pages; contains iv, 52 p. : col. ill. Vita. Includes abstract. Includes bibliographical references (p. 32).

Recently, an increasing number of modelling and observational studies have looked at the signatures of small-scale waves, such as gravity waves (GWs) of meteorological origin, in the upper atmosphere. General circulation models require an appropriate GW parameterisation to reproduce a realistic global circulation. Existing schemes implemented into GCMs lack a physically proper wave dissipation mechanism above the turbopause. For more self-consistent wave propagation in GCMs, and to estimate their dynamic and energetic importance in the upper atmosphere, it is crucial to account for realistic upper atmospheric dissipation processes. The UCL Coupled Middle Atmosphere-Thermosphere-2 (CMAT2) general circulation model was developed in order to investigate atmospheric vertical coupling. This model is an updated version of its predecessor CMAT. Three GW parameterisations of different characteristics have been implemented into CMAT2. While they all, to some extent, reproduce the necessary mesosphere and lower thermosphere (MLT) dynamics, artificial dissipation above the turbopause is a problem in all these schemes. Therefore, an extended spectral non-linear GW parameterisation, which incorporates more physically realistic GW dissipation, has been developed. Using an offline column model, the sensitivity of GW propagation and dissipation in the thermosphere-ionosphere has been studied. Considerable GW propagation into the upper atmosphere is demonstrated. The associated wave forcing and heating are significant. This new extended scheme has been implemented in CMAT2. Its dynamical effects on the circulation of the upper atmosphere have been investigated. Results demonstrate the importance of GW momentum flux divergence in the thermosphere-ionosphere. The extended scheme improves the model simulations markedly with respect to an empirical model.

Les processus chimiques de l'atmosphère dense de CO2 de Vénus sont contrôlés par des gaz à traces tels que SO2, O3, H2O, CO, etc. Parmi ces composants atmosphériques, un groupe de composés soufrés et oxygènés occupe une place centrale.L'objectif de cette thèse concerne l'étude du dioxyde de soufre et de l'ozone présents du côté nuit de la haute mésosphère de Vénus entre 85 et 110 km d’altitude. La chimie et la dynamique sont très actives dans cette région et le cycle chimique du soufre dans cette région conduit à la formation de l’épaisse couche nuageuse entre 47 et 70 km d’altitude tout autour de la planète. En outre, on n'a pas encore déterminé exactement quelles interactions chimiques étaient responsables de l'équilibre sur le long terme du CO2. Une réelle difficulté subsiste en effet quant à notre capacité à évaluer la capacité d'oxydation de l'atmosphère vénusienne, du fait de l'absence de mesures directes de la quantité d'oxygène moléculaire. Cependant, des estimations indirectes de l'O2 peuvent être faites sur la base des dérivés de cette molécule, dont l'un en particulier est l'ozone. On s’attend à ce que l’ozone soit impliqué dans des réactions avec des espèces principalement chlorées très présentes sur Vénus.Mon travail de recherche est basé sur les données obtenues par le canal UV du spectromètre SPICAV à bord de l'orbiteur Venus Express qui a opéré entre 2006 et 2014. SPICAV est un instrument particulièrement bien adapté à la mesure de CO2, SO2 et O3 du côté nuit de l'atmosphère de Vénus au-dessus de la couche nuageuse. Mon étude comprend également une ré-évaluation détaillée de la précision des méthodes de traitement des données spectrales employées jusqu’alors pour déterminer les distributions verticales de la concentrations de gaz dans l'atmosphère. Il s'agit principalement d'une séparation entre la lumière d’une étoile utilisée pour la mesure et celle d’émissions UV provenant de différentes sources, que l’on considère comme parasitant l’interprétation des données obtenues lors des occultations stellaires. Une influence très forte de la calibration en longueur d'onde a pu être mise en évidence, et a abouti à une modification de la technique de calibration se basant sur la comparaison de la position des raies stellaires avec une base de données de référence. Ainsi, cela a permis d'établir des profils de SO2 de 85 km à 100 km principalement localisés dans les latitudes moyennes. Ces profils suggèrent que SO2 est uniformément mélangé dans cette gamme d’altitude et qu’il est soumis à une variabilité forte sur de faibles échelles de temps. Cependant, une faible augmentation a été constatée entre le matin et le soir dans les zones du terminateur vénusien et à une altitude de 90-95 km. Enfin, après la découverte de la couche d'ozone sur Vénus faite par Montmessin et al. (2011), la présence de l’ozone a pu être confirmée dans plus de 100 séances d'occultation. L'étude actuelle montre également que les valeurs d'ozone détecté correspondent à ses valeurs maximales plutôt qu'à l'épaisse couche stable que l’on trouve près du sommet des nuages. Ces résultats représentent la première base de données sur la distribution verticale détaillée de la teneur en SO2 et O3 dans la mésosphère supérieure du côté nuit, ce qui ouvre de nouvelles perspective pour la compréhension théorique des processus se produisant dans l'atmosphère de Vénus
Chemical processes of the dense CO2-atmosphere of Venus are determined by trace gases such as SO2, O3, H2O, CO, etc. Among these atmospheric components, a group of sulfur and oxygen compounds occupies a central position. The objective of this thesis is a study of sulfur dioxide and ozone at the night side of Venus' upper mesosphere that is related to altitudes from 85 to 110 km. Chemistry and dynamics of this altitude range is very active. The sulfuric chemical cycle in the mesosphere leads to a formation of the thick cloud deck at 47-70 km globally enshrouding the planet. Furthermore, it has not yet been determined exactly which chemical interactions are responsible for stabilizing the equilibrium in the chemical cycles of the atmosphere, and maintaining a high mixing ratio of CO2. The difficulty of evaluating the oxidizing capacity of the atmosphere, due to the lack of direct measurements of the amount of molecular oxygen, is one reason for this. However, indirect O2 estimations can be made based on derivatives of this molecule, and one of them is ozone. This gas is involved in reactions with species, probably mainly chlorinated compounds, leading to the general chemical cycles.The research is based on the data obtained from the first stellar occultation experiment released for Venus. It was performed by the UV channel of the SPICAV spectrometer onboard Venus Express orbiter working in 2006-2014. This is a powerful instrument to measure absorption of CO2, SO2 and O3 at the night side of Venus’ atmosphere above the cloud layer. This study also includes a detailed assessment of the accuracy of the spectral data processing methods used to retrieve vertical atmospheric gas concentration distributions. Mainly it concerns a separation of a stellar light from UV emission signal originated from different spread sources, which is a parasitic light for the stellar occultation data investigation. A significant influence of a calibration assignment of wavelength to a digital pixel number was obtained. The required accuracy was achieved by a determination of stellar lines position for a large set of stars' spectra measuring in each observational session. Thus, it allowed to establish a profile of the SO2 content from 85 km to 100 km mainly devoted to mid-latitudinal range. On average, it shows a stable mixing ratio with altitude. For this gas, a prevailed short-period variability has been confirmed. However, a weak possible increase of SO2 abundance with local time is noticed from the morning to the evening terminator at 90-95 km. After the discovery of the ozone layer on Venus made by Montmessin et al. (2011), the ozone content was confirmed in more than 100 occultation sessions. The current study also shows that the detected ozone values correspond to its maximum values rather than to the thick stable layer. These results are the first detailed vertical distribution of the SO2 and O3 content in the upper mesosphere on the night side, which opens up new possibilities for the theoretical description of processes occurring in the atmosphere of Venus

Cette thèse étudie la formation et l'évolution des jets et des vortexdans les atmosphères planétaires turbulentes, à l'aide d'une doubleapproche de simulations numériques et d'expériences delaboratoire. Pour l'approche numérique, un modèle en fluidesshallow-water quasi-géostrophique à deux couches dans le plan betaavec des conditions canal a été utilisé. Comme dans Panetta (1988), onimplémente un cisaillement vertical pour représenter le gradientlatitudinal de température moyenné spatialement, qui est partiellementmaintenu par un forçage thermique. Les instabilités baroclinesaffaiblissent le gradient de température, alors que le forçagethermique le restaure, ce qui crée une dynamique non-linéaire trèsriche.Tout d'abord, nous avons considéré l'écoulement sur un fond plat, etavons modélisé les mouvements convectifs par des paires decyclones/anticyclones ou `hetons' comme dans Thomson (2016). Nousobtenons ainsi des jets principalement baroclines, oscillants entredes phases calmes et des phases turbulentes, où l'écoulement perd sazonalité. Des vortex se forment à partir des jets méandreux etl'énergie zonale diminue alors que l'énergie tourbillonnaireaugmente. Ces phases turbulentes durent typiquement pendant unepériode de relaxation du forçage thermique. On étudie les effets ducisaillement vertical, du forçage thermique et des hetons, enregardant les transferts d'énergie entre les énergies cinétiques etpotentielles, leurs composantes barotropes et baroclines ainsi queleurs composantes zonales et tourbillonnaires. Ceci nous amène àrepenser le paradigme classique des transferts d'énergie présenté dansSalmon (1982). De plus, nous étudions comment une analyse de stabilitélinéaire de l'écoulement zonal instantané est reliée aux phases calmeset turbulentes.Ensuite, nous considérons l'effet d'une topographie de grande échelle,comme une première approche pour comprendre le rôle de la topographiedans la formation des jets et des vortex. Nous utilisons le mêmemodèle que dans la première étude mais nous ajoutons un fondtopographique linéaire méridionalement, qui a l'avantage de dépendred'un seul paramètre, la pente. Une pente négative approfondit lacouche inférieure par rapport à un fond plat, ce qui augmente lepotentiel des instabilités baroclines, alors qu'une pente positive aun effet stabilisateur. Nous supprimons le forçage par les hetons etperturbons l'écoulement grâce à une zone de Rossby de faibleamplitude dans la couche inférieure à l'instant initial. L'effetprincipal du forçage par les hetons est d'agir comme une sorted'amortissement : les fluctuations de l'énergie sont constamment plusextrêmes que sans forçage. Une analyse de stabilité linéaire esteffectuée afin de déterminer les zones de stabilité etd'instabilité.Pour l'étude expérimentale, nous utilisons une cuve tournanteremplie par deux couches de fluides avec une stratification au sel etun couvercle rigide en rotation différentielle. Nous étudions unfront barocliniquement instable dans le régime des vacillationsd'amplitude, qui est caractérisé par l'émergence et ladisparition de vortex de grande échelle. L'analyse de deuxexpériences à la limite de la géostrophie, avec des nombres deRossby de Ro=0.4 et Ro=0.6, montre des comportement trèsdifférents. Pour un faible nombre de Rossby, nous observons desdipôles baroclines alors que pour un large nombre de Rossby nousobtenons des vortex barotropes. Nous examinons l'activité des ondesde petite échelle par différentes méthodes qui révèlent laprésence d'ondes d'inertie gravité comme précurseures del'émergence des vortex.Afin de poursuivre nos recherches sur les fronts à l'interface entredeux couches de fluides immiscibles, nous avons développé unenouvelle méthode de détection de la hauteur et de la pente baséesur les lois optiques de la réfraction. Les équations théoriquesassociées sont résolues numériquement et validées à l'aidede plusieurs situations idéalisées
This thesis investigates the formation and evolution of jets andvortices in turbulent planetary atmospheres using a dual approach ofhigh-resolution numerical simulations and novel laboratoryexperiments. A two-layer quasi-geostrophic beta-channel shallow watermodel is used for the numerical study. As in Panetta (1988), avertical shear is implemented to represent a spatially-meanlatitudinal temperature gradient, which is partially maintained bythermal damping. Baroclinic instabilities work to erode thetemperature gradient, while thermal damping acts to restore it. Asthe basic state vertical shear is unstable, the thermal damping cannotlead to a full recovery, thus modifying subsequent instabilities andleading to rich nonlinear dynamical behaviour.First, we consider flow over a flat bottom, and model convectivemotions like those thought to occur on Jupiter by pairs ofcyclones/anti-cyclones or `hetons' as in Thomson (2016). We therebyobtain predominantly baroclinic jets, oscillating between quiescentphases, when jets are zonal and the energy is nearly stationary, andturbulent phases, when the flow loses its zonality, vortices pinch offfrom the meandering jets, and zonal energy components drop while eddyenergy components increase. These turbulent phases typically last fora thermal damping relaxation period. The impacts of vertical shear(baroclinicity), thermal damping and heton forcing are comprehensivelyinvestigated by considering the energy transfers occurring betweenkinetic and potential energy, their barotropic and baroclinic parts aswell as their zonal and eddy parts. This leads to a rethinking of theclassic paradigm of energy transfer presented by Salmon (1982), asthis paradigm is too simplistic to explain the results found.Then, we consider the effect of large-scale bottom topography, as afirst approach to understanding the role of topography in jet andvortex formation. We use the same model as in the first study butinclude a linearly sloping topography which has the advantage of beingcharacterised by a single parameter, the slope. We omit the hetonforcing and instead perturb the flow with a small amplitude Rossbywave initially. The main effect of heton forcing is actually to act asa kind of damping: energy fluctuations are consistently less extremethan when no forcing is used. A linear stability analysis is carriedout to motivate a series of nonlinear simulations investigating theeffect of topography, in particular, differences from the flat bottomcase previously examined. We find that destabilising topography makesthe jets more dynamic.In the experimental part, a two-layer salt-stratified fluid is used ina rotating tank with a differentially rotating lid to generate theshear across the interface. We consider a baroclinically unstablefront in the regime of amplitude vacillation, which is found to becharacterised by the sequential emergence and disappearance of alarge-scale vortex. Analysing two similar experiments at the limit ofgeostrophy, with different Rossby numbers Ro=0.4 and Ro=0.6, showssurprisingly different behaviours, with a baroclinic dipole for small,and a barotropic vortex for the large Rossby number. The small-scalewave activity is explored using different methods, and the resultssuggest small, spontaneously-arising inertia-gravity waves precedingthe emergence of the vortex which stirs the interface, thus having animpact on the mixing between the two layers. The recovery period ofthe amplitude vacillation, as well as the intensity of the vortex,increases with the Rossby number.For further research on fronts at two-layer immiscible interfaces, avery accurate novel optical method has been developed to detect theheight and slope, based on the refractive laws of optics. Theassociated theoretical equations are solved numerically and validatedin various idealised situations

A three-dimensional mechanistic model of the middle atmosphere is used to model various classes of equatorial wave motions that are observed in the atmosphere. These waves are thought to be largely responsible for the forcing of the quasi-biennial oscillation (QBO) in the tropical lower stratosphere. By generating a combination of different classes of equatorial waves in the model, an oscillation which has many similarities to the observed QBO is produced in the model. The numerical model used is run in a variety of configurations, including running it at different vertical resolutions and with two different radiation parameterisation schemes. It is found that model used in the project must be modified to allow the accurate modelling of equatorial waves. Several modelling problems are encountered while applying the modifications necessary in the model; the steps necessary to rectify these problems are detailed in this thesis. Equatorial waves are then forced in this modified model under a range of conditions and their interaction with the mean flow is observed. Their dissipation mechanisms and the influence of changes in model conditions on these waves are investigated. The model is found to be generally very successful in modelling these equatorial waves. Modelling of the QBO is one of the principle aims of this project and a QBO is successfully generated in a variety of model configurations. The modelled QBO is found to be sensitive to changes in the temperature structure of the model (brought about by changes in the model's radiation scheme) and several experiments are performed in order to learn what processes affect this sensitivity. A QBO is then generated in series of model runs where the state of the model is varied from very idealised (where temperatures in the model are relaxed towards an isothermal state by the radiation scheme) to a state that is far more realistic (a perpetual January run with realistic boundary information). A fairly realistic QBO is generated throughout many of the experiments. The properties of this QBO are investigated and compared to the observed QBO. The model is then run with planetary waves forced in addition to the QBO. The interaction between the planetary waves and the QBO is investigated. It is found that the planetary waves have little effect on the QBO propagation. The QBO however has a fairly strong modulating effect on the planetary waves in certain regions.

Thesis (Ph.D.)--George Mason University, 2008.
Vita: p. 190. Thesis director: Edwin K. Schneider. Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Climate Dynamics. Title from PDF t.p. (viewed Mar. 9, 2009). Includes bibliographical references (p. 181-189). Also issued in print.

Cette thèse se penche sur la propagation d’ondes au sein du système coupléTerre-océan-atmosphère. La compréhension de ces phénomènes a une importance majeure pour l’étude de perturbations sismiques et d’explosions atmosphériques notamment dans le cadre de missions spatiales planétaires. Les formes d’ondes issues du couplage fluide-solide permettent d’obtenir de précieuses informations sur la source du signal ou les propriétés des milieux de propagation. On développe donc deux outils numériques d’ordre élevé pour la propagation d’ondes acoustiques et de gravité. L'u en différences finies et se concentre sur le milieu atmosphérique et la propagation d’ondes linéaires dans un milieu stratifié visqueux et avec du vent. Cette méthode linéaire est validée par des solutions quasi-analytiques reposant sur les équations de dispersion dans une atmosphère stratifiée. Elle est aussi appliquée à deux cas d’études : la propagation d’ondes liée à l’impact d’une météorite à la surface de Mars (mission NASA INSIGHT), et la propagation d’ondes atmosphériques liées au tsunami de Sumatra en 2004. La seconde méthode résout la propagation non-linéaire d’ondes gravito-acoustiques dans une atmosphère couplée, avec topographie, à la propagation d’ondes élastiques dans un solide visco-élastique. Cette méthode repose sur sur le couplage d’une formulation en éléments finis discontinus, pour résoudre les équations de Navier-Stokes la partie fluide, par éléments finis continus pour résoudre les équations de l’élastodynamique dans la partie solide. Elle a été validée grâce à des solutions analytiques ainsi que par des comparaisons avec les résultats de la méthode par différences finies
This thesis deals with the wave propagation problem within the Earth-ocean-atmosphere coupled system. A good understanding of the these phenomena has a major importance for seismic and atmospheric explosion studies, especially for planetary missions. Atmospheric wave-forms generated by explosions or surface oscillations can bring valuable information about the source mechanism or the properties of the various propagation media. We develop two new numerical full-wave high-order modeling tools to model the propagation of acoustic and gravity waves in realistic atmospheres. The first one relies on a high-order staggered finite difference method and focus only on the atmosphere. It enables the simultaneous propagation of linear acoustic and gravity waves in stratified viscous and windy atmosphere. This method is validated against quasi-analytical solutions based on the dispersion equations for a stratified atmosphere. It has also been employed to investigate two cases : the atmospheric propagation generated by a meteor impact on Mars for the INSIGHT NASA mission and for the study of tsunami-induced acoutic and gravity waves following the 2004 Sumatra tsunami. The second numerical method resolves the non-linear acoustic and gravity wave propagation in a realistic atmosphere coupled, with topography, to the elastic wave propagation in a visco-elastic solid. This numerical tool relies on a discontinuous Galerkin method to solve the full Navier-Stokes equations in the fluid domain and a continuous Galerkin method to solve the elastodynamics equations in the solid domain. It is validated against analytical solutions and numerical results provided by the finite-difference method

We investigate the effect of wind clumping on the dynamics of Wolf-Rayet winds, by means of the Potsdam Wolf-Rayet (PoWR) hydrodynamic atmosphere models. In the limit of microclumping the radiative acceleration is generally enhanced. We examine the reasons for this effect and show that the resulting wind structure depends critically on the assumed radial dependence of the clumping factor D(r). The observed terminal wind velocities for WR stars imply that D(r) increases to very large values in the outer part of the wind, in agreement with the assumption of detached expanding shells.

This investigation is driven by the desire to find an alternative method of obtaining fresh water. More specifically, fresh water is to be obtained by condensation of atmospheric water vapor on a surface maintained below the dew point by a radiative heat loss from its surface to the night sky. To properly simulate the condensation process, an accurate estimation of the effective sky temperature is required. To estimate the effective night sky temperature an experimental system, consisting of a series of metal plates embedded on a heat transfer panel, a weather station and a control system, was built. The temperature of each plate was controlled using an electric flat-plate heater. A control loop was implemented to ensure that the heat transfer panel was adjusted automatically to always be oriented perpendicular to the wind direction. In addition to the effective night sky temperature, the experimental system was designed to estimate the convective heat transfer coefficient between the plates and ambient air as well as the surface emissivity of the plates. The results obtained from theoretical analyses and preliminary experiments are presented and discussed. Special emphasis was given to mathematical solution of the system of equations that need to be solved to obtain the effective sky temperature. It was shown that, although the solution of the system of equations was straightforward for the direct heat transfer problem, there was a serious difficulty to solve the inverse heat transfer problem to retrieve the desired parameters.

Whilst the underlying mechanisms of atmospheric turbulence are complex, the observed effects on imaging can be described in simpler terms. In this thesis, I address the effects seen as geometric distortions in anisoplanatic imaging and propose new digital restorations techniques that are real-time capable and predictive. The anisoplanatic problem arises in wide-field telescopic imaging and in new ventures of astronomy such as giant telescopes that process wide-field imagery. The methods proposed here, both digital and digital-optical hybrid, remove the position dependent distortions as a precursor to image analysis. Previous existing digital restoration techniques have used a prototype formed by averaging an image time sequence for image registration where valuable high frequencies information is lost due to the low-pass filtering effect of averaging. The proposed techniques are capable of using any arbitrary frame in the sequence as prototype, thus circumventing the low pass filtering effect and also allowing real-time implementation. Furthermore, these techniques are made predictive by the use of Kalman filtering. The predictive capabilities of these techniques open a new path to the combination of digital processing and adaptive optics that can result in hybrid systems. The key to adoption of hybrid systems is to reduce the complexity and expense of the optics and couple this with digital processing prediction. To this end I also propose a new type of inexpensive and fast piezoelectric deformable mirror based on the vibration modes of circular PVDF membranes that exhibit striking similarities to Zernike polynomials. It requires only two electrodes for actuation and a very simple driving signal generator, therefore constituting an inexpensive and viable alternative to existing deformable mirrors. With the emergence of multi-conjugate adaptive optics (MCAO) and multiobject adaptive optics (MOAO) in astronomy, and the more demanding correction required for long range surveillance imaging, this inexpensive deformable mirror and the real-time capable digital algorithms are promising building blocks for a hybrid solution to the anisoplanatic imaging problem.

Thesis (Ph. D.)--University of California, San Diego, 2007.
Title from first page of PDF file (viewed July 10, 2007). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 138-152).

It is generally accepted that ice clouds are of significant importance when considering the Earth's atmosphere with regards to the radiation budget and precipitation processes. This thesis explores three aspects of ice cloud processes: ice nucleation, ice aggregation and ice development inside growing cumulus congestus.

Studies were made of the dynamics of the atmosphere at heights of between 65 km and 102.5 km at Birdlings Flat over a period of 2½ years. Variance profiles for internal gravity waves were calculated for each month in the 2½ year period. These profiles were similar for each month. The variances remained reasonably steady in most months at heights below 80 km, but increased steadily above 80 km to a maximum at heights between 92.5 km and 97.5 km. various models were developed to explain this and other features of internal gravity wave behaviour. A simple saturation model explained most of the observed features of internal gravity wave behaviour in this region. The isotropy of internal gravity waves was also considered. Isotropic behaviour was generally observed below 80 km, but strong anisotropies were observed to occur between 80 km and 95 km. These anisotropies occurred in the same direction in every month at all heights between 80 km and 95 km. Above 95 km the anisotropies were less pronounced. Various explanations for this behaviour have been considered, but no explanation has proved to be entirely adequate. Some consequence of this behaviour have also been discussed.

Spacecraft that orbit in Low Earth Orbit travel through a tenuous atmosphere and hence experience aerodynamic forces that can become quite significant, specially at low altitudes. The presence of these forces can become a major design driver for missions that fly at very low altitudes. Unfortunately, spacecraft aerodynamics are not well understood. In this dissertation, a CubeSat mission is proposed which will study rarefied-gas aerodynamics, with the objective of determining the effect of surface composition, surface finishing and flow incidence angle on the drag and lift coefficients with an error of less than 5% using a novel method. The CubeSat, has been named ΔDsat, because this study, will be performed using differential measurements of drag and lift coefficients in order to eliminate any measurement bias. ΔDsat carries 4 deployable fins that can rotate independently and expose different surface types to the flow at different incident angles. In addition, in the dissertation four methods to exploit the aerodynamic forces for the missions advantage are proposed and described in detail. The first one is aerostability, which by shaping the spacecraft appropriately, the resulting aerodynamic torques stabilise the attitude spacecraft with respect to the flow. The second method uses aerodynamic drag and lift to change de inclination of a decaying spacecraft in order to maintain the Sun-synchronous aspect of an orbit whilst decaying. The required lift to drag ratio is in the order of 1.0-1.6, which is not currently achievable (it is theoretically possible), but it could be achieved if drag compensating propulsion is used (thus becoming a fuel saving strategy). The third method controls the atmospheric re¬entry interface (the location of the burn-up) by modulating the drag, hence controlling the decay profile. When applied to ΔDsat an error of less than 200 km 3cr on the re-entry location is achieved. Finally, aerostable spacecraft can be used to perform in-situ measurements of the atmospheric winds, by observing their attitude evolution. The aerostable ΔDsat CubeSat would be capable of determining the cross-track winds with an error of less 4 m/s 3cr.

This dissertation combines several new observations of the Io sodium cloud to create a consistent picture of the extended Io atmosphere and its interaction with the Jovian plasma torus. I used the LPL echelle spectrograph to obtain three types of high-resolution spectra of the extended sodium cloud at the sodium D-lines (5890, 5896Å). The first class of observations made use of the mutual satellite eclipses of 1985 to probe the density profile of the atmosphere in the range 1.4 to 10 Io radii, a previously unstudied region. The second type of observation examined the sodium emission in Io's immediate vicinity, allowing an accurate measurement of the velocity structure around Io. The final method employed a high-sensitivity detector to study faint jets of high-speed sodium farther out in the extended cloud. The synthesis of these three data sets results in a better understanding of how sodium is distributed about Io as a function of position and velocity. Io's extended atmosphere is composed of many kinematically distinct components. The distribution in space is linked to their characteristic velocities, with low-energy sodium confined near Io and faster atoms (10 to 100 km sec⁻¹) prevalent beyond ∼25 Io radii. The sodium density profile is steep near Io and shallower outside 5.6 Io radii, the effective limit of Io's gravity. The data indicate that the atmosphere is collisionally thick near the surface, but becomes thin by an altitude of ∼700 km. The upper limit of the exobase location is derived from reliable sodium density measurements made during the satellite eclipses. The lower limit is indirectly inferred from the velocity distribution of sodium near Io and the nature of high-speed jets far from Io. The high-speed sodium jets reveal a new type of close interaction between the corotating plasma and Io's atmosphere. The morphology and brightness of the jets require a two-reaction process, in which atmospheric sodium is ionized, accelerated to high speeds, and then charge-exchanges with other sodium atoms. These processes must occur near the atmospheric exobase, indicating that Io's atmosphere is not completely protected from the plasma flow.

Microorganisms are critical to the functioning of terrestrial and aquatic ecosystems and may also play a role in the functioning of the atmosphere. However, little is known about the diversity and function of microorganisms in the atmosphere. To investigate the forces driving the assembly of bacterial microbial communities in the atmosphere, I measured temporal variation in bacterial diversity and composition over diurnal and inter-day time scales. Results suggest that bacterial communities in the atmosphere markedly vary over diurnal time scales and are likely structured by inputs from both local terrestrial and long-distance sources. To assess the potential functions of bacteria and fungi in the atmosphere, I characterized total and potentially active communities using both RNA- and DNA-based data. Results suggest there are metabolically active microorganisms in the atmosphere that may affect atmospheric functions including precipitation development and carbon cycling. This dissertation includes previously published and unpublished co-authored material.

Mit Hilfe numerischer Simulationen wird gezeigt, dass manche Änderungen des klimatologischen Hintergrundwindfeldes zu instabilem mittleren Zonalwind in der mittleren Atmosphäre Sommerhemisphäre führen. Diese Instabilität treibt Oszillationen mit einer Periode um 2 Tage an, welche eine zonale Wellenzahl von s = 3 oder 4 aufweisen. Beobachtete Variationen des mittleren Windes stehen in Verbindung mit diesen numerisch gefundenen Schwingungen. Starke 2-Tage-Wellen wiederum sind instabil und können daher Wellen längerer Periodendauer und kleinerer Wellanzahl anregen. Dieser Effekt ist jedoch nur für sehr starke 2-Tage-Wellen signifikant. Effektiver ist ein Prozess, bei dem nichtlineare Wechselwirkung zwischen einer 10-14-Tage-Welle und der 2-Tage-Welle der zonalen Wellenzahl 4 eine neue quasi-2-Tage-Welle mit einer Periodendauer von 55-60 Stunden anregt. Diese Welle generiert sekundäre Wellen effektiver als die ursprüngliche 2-Tage-Wellen; die sekundären Wellen können beobachtet werden
Basing on numerical calculations we have demonstrated that some changing of the climatological background atmosphere could lead to an unstable mean zonal wind distribution in the summer middle atmosphere. This instability forces oscillations propagating westward with a period of about 2 days and zonal wavenumbers s = 3 and/or 4. There are variations in the mean zonal wind distribution due to the excitation and transient propagation of these waves and numerical results correspond to features of these changes obtained in experimental studies. Strong 2-day waves in turn are unstable and can generate secondary waves with longer periods and lower zonal wavenumbers. This effect is significant only for very strong 2-day waves. It is shown that the 2-day wave with s=3 forced by non-linear interaction between 10-14 day planetary waves and the 2-day wave of zonal wave number 4 is unstable. This wave generates secondary waves of lower zonal wavenumbers more easily than the primary 2-day waves and these secondary waves may be observed

A mesoscale non-hydrostatic atmospheric model was extended by including both a chemical transport module (CTM) for the chemical triade NO, N02, and 0 3, and an explicit surface-subgrid module (ESSM) for a subscale resolution of the topographical surface. CTEM: The simulated time-dependent concentration fields result from the following processes involved: anthropogenic emission at different heights, biogenic emission, dry deposition on the receptive surface, chemical reactions, turbulent diffusion, and passive transport according to the model dynamics. The calculations in the lowest model layer, usually treated as a constant-flux layer, are now performed on a vertical subgrid that was inserted to better resolve the often observed high concentration gradients within the surface layer. ESSM: Moreover, an equidistant horizontal-subgrid is introduced for finer resolving the topography. The surface fluxes of momentum, sensible and latent heat, long-wave radiation, soil heat flux and wetness as well as the surf ace-energy balance are calculated in the usual approximations, however, employing the individual surface and soil properties of the subgrid cells. The averaged subgrid quantities serve as boundary values required for the model-grid calculations. Within the CTM the ESSM method leads to an intersection of the horizontal ESSM subgrid and the vertical CTM subgrid. Preliminary results representing an interim realization state of the ESSM demonstrate partially strong changes of the dry deposition rates caused by subgrid-resolved surface properties
Ein mesoskaliges nicht-hydrostatisches Atmosphärenmodell ist um ein Chemie-TransportModul (CTM) zur Berücksichtigung der Triaden-Komponenten NO, N02 und 03 sowie um ein Verfahren zur verfeinerten Auflösung der topographischen Unterlage (explicit surface-subgrid modul ESSM) erweitert worden. CTM: Die simulierten zeitabhängigen Konzentrationsfelder sind das Resultat folgender modellierter Prozesse: Anthropogene Emission in verschiedenen Höhenschichten, biogene Emission, trockene Deposition (Rezeption), die speziellen chemischen Umwandlungen, turbulente Diffusion und passiver Transport. Da der Schwerpunkt der Prozesse und die höchsten Konzentrationsgradienten innerhalb der bodennahen ersten Modellschicht vorliegen, werden die Berechnungen in dieser Schicht auf einem verfeinerten vertikalen Untergitter durchgeführt. ESSM: Unabhängig von den Eigenheiten des CTM wird für alle untergrundbezogenen meteorologischen Größen ein regelmäßiges horizontales Untergitter zwecks Berücksichtigung des subskalig aufgelösten topographischen Untergrundes eingeführt. Auf diesem Untergitter werden in den bisherigen Näherungen alle Oberflächenflüsse für Impuls, fühlbare und latente Wärme, langwellige Strahlung, der Bodenwärmefluß, die Bodenfeuchte sowie die Energiebilanz am Boden berechnet. Die über die Untergitterzellen gemittelten Werte dienen den weiteren Berechnungen im normalen Modellgitter als die erforderlichen Randwerte. Innerhalb des CTM führt die ESSM-Methode zu einer Überlagerung des vertikalen CTM-Untergitters mit dem horizontalen Untergitter des ESSM. Erste Simulationsergebnisse, die dem derzeitigen Stand in der Realisierung des ESSM entsprechen, erbringen teilweise stark veränderte Depositionsraten infolge der Berücksichtigung der horizontal feiner aufgelösten Topographie

Le travail de cette thèse s'inscrit dans le cadre du développement du programme S.E.T.U.P. (Simulations Expérimentale et Théorique Utiles à la planétologie) dont l'objectif est d'effectuer des simulations représentatives de l'atmosphère de Titan et de déterminer les processus physico-chimiques qui y sont impliqués. Pour ce faire, un dispositif expérimental combine deux types de dépôts d'énergie (électrons et photons) représentatifs des processus de dissociation des molécules N2 et CH4 qui composent majoritairement l'atmosphère de Titan. De plus, une technique d'analyse par spectroscopie laser doit permettre d'identifier et de quantifier des produits et donc de suivre l'évolution du mélange réactionnel in situ en temps réel.La méthodologie adoptée pour la mise en œuvre des expériences de simulations a été de caractériser l'ensemble des étapes depuis les sources énergétiques jusqu'à l'analyse des produits et de développer les outils de modélisation nécessaires à l'interprétation des expériences.Dans un premier temps, il s'est agit de mieux caractériser les deux types de photolyse du méthane envisagés. En effet, il est prévu d'utiliser soit une lampe UV délivrant un rayonnement à Lyman-α (121,6 nm) soit un laser excimère KrF pulsé délivrant un rayonnement à 248 nm. Ce dernier doit en effet permettre des études cinétiques concernant les espèces à courte durée de vie. Des expériences d'irradiation de CH4 et d'un mélange N2/CH4 aux deux longueurs d'onde ont été menées puis simulées grâce à un modèle 0D.L'analyse fine des résultats issus des irradiations de CH4 à Lyman-α montre que des travaux complémentaires sont nécessaires pour comprendre les différences entre les expériences et le modèle chimique. En particulier, une caractérisation de l'émission de la lampe s'est avérée indispensable et a été réalisée afin d'améliorer la compréhension de la chimie mise en jeu. Les résultats obtenus lors de l'irradiation à 248 nm suggèrent que la source laser utilisée pourrait provoquer l'ionisation de CH4 et induire une chimie ionique qui n'était pas envisagée au départ. Ce type d'irradiation pourrait se révéler intéressant pour étudier les processus ionosphériques de l'atmosphère de Titan. En revanche, cette source doit être abandonnée pour l'étude de la chimie des neutres. Une source pulsée à Lyman-α devra être développée.Dans un deuxième temps, trois types d'expériences préliminaires de simulations de l'atmosphère de Titan ont été effectuées. Afin de mieux comprendre l'importance relative de chaque source énergétique, des expériences dites de " plasma " où N2 et CH4 sont dissociés simultanément dans un plasma crée par décharge microonde, ont tout d'abord été menées. Ensuite, des expériences dites de " post-décharge " où CH4 est introduit dans l'enceinte après la dissociation de N2 par plasma, ont été conduites. Et enfin, des expériences dites de " couplage ", censées mieux représenter les processus de l'atmosphère de Titan où CH4, toujours introduit en post-décharge, est cette fois photodissocié à Lyman-α, ont été réalisées.Lors des expériences " plasma ", dix composés sont identifiés : HCN, NH3, HC3N, C2H2, C2H4, C2H6, C3H4, C4H2, HC5N et C6H2. Leur abondance est globalement en bon accord avec celle déterminée par les observations de la haute atmosphère de Titan dans la zone comprise entre 900 et 1200 km d'altitude validant ainsi le module plasma du dispositif. Lors des expériences " post-décharge " et " couplage ", seuls les composés azotés HCN et NH3 sont formés et cela indépendamment du fait que le CH4 subisse ou pas une irradiation UV. Ce résultat s'explique par le fait que le taux de photodissociation du CH4 se révèle très inférieur à la dissociation de N2 par les électrons, ce qui empêche une complexification chimique des hydrocarbures dans les simulations. Il s'avère donc indispensable de modifier la source de rayonnement à Lyman-α afin d'être beaucoup plus efficace en terme de flux.Les résultats acquis grâce à cette méthodologie " étape par étape " ont permis de mettre en évidence les paramètres qu'il faut impérativement maîtriser pour la mise en œuvre de simulations pertinentes de l'atmosphère de Titan. Ils définissent aussi l'orientation des futurs développements du projet SETUP

Thesis (Ph. D.) -- University of Maryland, College Park, 2007.
Thesis research directed by: Civil Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

The Middle and Upper Atmosphere Model (MUAM) is used to implement a modern whole atmosphere gravity wave (GW) parameterization (Yigit et al., 2008). To adjust the resulting model climatology to observations, we compare two different spectra of GW phase speeds and the related momentum fluxes included in this parameterization.The first spectrum, termed Spectrum1, which is more narrow, covers phase speeds up to ±80 m s−1 and the second one, Spectrum2, goes up to ±95 m s−1. We analyzed the zonal GW drag, the acceleration of the zonal mean flow owing to breaking GWs, and the resulting background circulation. We also examined zonal wind amplitudes of the diurnal and semidiurnal migrating solar tide. As a result, we find that both GW phase speed spectra have their advantages and disadvantages. For example, Spectrum1 reproduces the zonal wind reversal in the mesosphere correctly, but it does not lead to a reversed zonal GW drag in the lower thermosphere. While the amplitudes of the diurnal tide tend to be more realistic for Spectrum1, those of the semidiurnal tide are more representational for Spectrum2. Overall, the new GW parameterization is a substantial improvement to the MUAM model.
Das Modell für die mittlere und obere Atmosphäre (MUAM) wird für die Implementierung einer neuen Schwerewellenparametrisierung, die für die gesamte Atmosphäre geeignet ist, verwendet (Yigit et al., 2008). Um die Klimatologie des Modells basierend auf der neuen Parametrisierung an Beobachtungen anzupassen, werden zwei verschiedene Spektren für die Phasengeschwindigkeiten von Schwerewellen und deren Impulsflüsse verglichen. Das erste Spektrum, als Spectrum1 bezeichnet, das einen schmaleren Bereich von Phasengeschwindigkeiten abdeckt, geht bis zu ±80 m s−1 und das zweite, Spectrum2, geht bis zu ±95 m s−1. Wir analysieren die Beschleunigung des mittleren Zonalwindes durch brechende Schwerewellen und die daraus resultierende Hintergrundzirkulation. Wir untersuchen ebenfalls die Zonalwindamplituden der ganztägigen und halbtätigen migrierenden solaren Gezeiten. Das Ergebnis dieses Experiments zeigt, dass beide Phasengeschwindigkeitsspektren ihre Vor- sowie Nachteile haben. Beispielsweise reproduziert Spectrum1 die Umkehr des Zonalwindes in der Mesosphäre korrekt, jedoch führt es nicht zu einer umgekehrten zonalen Beschleunigung durch Schwerewellen in der Thermosphäre. Während die Amplituden der ganztägigen Gezeit bezüglich Spectrum1 wesentlich realistischer zu sein scheinen, sind jene der halbtägigen Gezeit bezüglich Spectrum2 repräsentativer. Insgesamt ist die neue Parameterisierung eine erhebliche Verbesserung des MUAM Modells.

Dans un environnement urbain pollué, les altérations qui affectent les verres du patrimoine dépendent de facteurs intrinsèques, extrinsèques et temporels. Afin de caractériser les altérations atmosphériques résultant des interactions entre ces différents facteurs une stratégie de recherche prenant en compte un environnement multiphasique, le matériau (composition et surface) et le temps a été mise en place. Pour ce faire une étude complémentaire est menée sur des verres de vitraux exposés plusieurs centaines d'année et de verres modèles exposés en site réel et altéré artificiellement en laboratoire. Une approche multi-instrumentale et multi-échelle a été mise en place. Elle a permis d'identifier des mécanismes d'évolution de la couche d'altération (CA) notamment par la formation de lamines concentriques de ~10 nm (anciens fronts d'altération probables). L'exploration de l'impact des eaux de ruissellement montre que l'évolution de l'épaisseur de CA est dépendante à la fois d'une cinétique de diffusion (√t) et de dissolution (t). Enfin l'influence indirecte des produits néoformés sur l'altération semble jouer un rôle majeur à la fois en condition de ruissellement, avec la présence de CaCO3 qui précipite le détachement des écailles, et en milieu abrité, où la présence de K2CO3 est mise en cause dans la dissolution du réseau vitreux
In a polluted urban environment, alterations affecting heritage glasses depend on intrinsic and extrinsic factors as well as time. In order to characterize the atmospheric alteration resulting from the interactions occurring between these factors, a research strategy has been set up, taking into account the multi-phase environment, the material (composition and surface) and time. In order to do so, a complementary study was conducted on stained glasses displaying several hundred years of alterations and model-glasses exposed in-situ for a few years or artificially altered in the lab. A multi-instrument and multi-scale approach was used in this study. It allowed the identification of the mechanisms responsible for the evolution of the leached layer (LL), especially the presence of concentric 10nm thick laminae (probable traces of alteration front). The exploration of the run-off impact on alteration shows a dependency of LL thickness on both diffusion type kinetics (√t) and dissolution kinetics. Finally, the indirect impact of neoformed alteration products seems to take a major part both in run-off conditions, CaCO3 hastens the scaling, and in sheltered conditions, where K2CO3 can be cause for glass network dissolution