Introduction Very little is known about the fine structure of the E-region of the ionosphere. The pulse method devised by Breit and Tuve is used to study the E-region in detail. Observations were made at Vancouver for the months of July and August 1951. The frequency 1.5 to 5 mc/s. (down to .5 mc/s. after midnight) was swept manually recording in 100 kc/s. intervals the virtual height, h’, to the nearest kilometer. Experimental (h’,t) records were also taken at 15 minute intervals throughout the day on 2 mc/s. The (h’,f) curves were analysed for fine structure details of the region which are not recorded by ionospheric equipment used for routine observations of the entire ionosphere. The following investigations were attempted: 1. Fine Structure of Night-Time E-Region. 2. Diurnal Variation of Fine Structure of E-Region. 3. Sunrise Effects of E-Region. 4. Occurrence of Echoes from Levels Below the E-Region. 5. Diurnal Variation of Critical Penetration Frequency of E-Region. 6. Determination of Scale Height of the E-Region. Results 1. Fine Structure of Night-Time E-Region Throughout the night ionization generally appears as patches from random clouds. Near sunrise short-lived echoes are found between 80 and 200 kms. Few usable results showing fine structure details are found. 2. Diurnal Variation of Fine Structure of E-Region Experimental (h',f) curves are compared to derived curves for a simple parabolic region with an E8 layer appearing as a sharp boundary embedded in the simple region. Good fits to the theoretical curves are normally found below the cusp frequency. The Hail' appearing after the cusp frequency generally has a slope greater then that predicted. Various types of ledges found in the --region are discussed. Moving ledges are often found with an approximate quasi-period (i.e. time to pass through the region) of half an hour. The variation of the penetration frequency of high smooth Es regions also appears to have a similar period. Once during the period of observation both these phenomena occurred together. Very pronounced ledges are sometimes found above the normal maximum. 3. Sunrise Effects of E-Region Day-time ionization of the E-region commences before ground sunrise. Commencement time is found to be approximately that time at which the sun*8 rays strike the E-region after grazing a spherical surface 39 kms. above the earth. 4. Occurrence of Echoes from Levels Below the E-Region Strong indications of region D are found. Often patches of ionization, as though from small ionic clouds, appear at various heights from 80 to 200 kms. No retardation effects are observed for any of these records. 5. Diurnal Variation of Critical Penetration Frequency of E-Region The critical frequency of the E-region is found to obey approximately a law fc = k oosⁿ X where X is the sun's zenith angle. The average morning value for the index, n, is .301 and the average afternoon value is .35. The average morning and afternoon value is .325. Examination of the (log fc , log cos X ) curves show that the afternoon values usually fall more nearly in a straight line. 5. Determination of Scale Height of the E-Region a. Analysis of (h',t) records From plots of the function Ln f(x) = constant + h/H H is found to be 11.3 kms. b. Analysis of (h',f) records From plots of the function h' = hN + φ(f/fc) H is found to be 9.4 kms. When this is corrected for a parabolic assumption giving the best fit to a Chapman distribution, H = 11.28 kms. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

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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 / The work of this thesis enters in the frame of the development of a scientific program named S.E.T.U.P. (a french acronym for Theoretical and Experimental Simulations Useful for Planetology) whose objective is to perform representative laboratory simulations of Titan's atmosphere. The study seeks to highlight the mechanisms responsible for the evolution of region of the stratosphere where a neutral chemistry is involved. With this aim, an experimental device has been built. The coupled N2/CH4 chemistry is initiated, in a flow reactor, by both electrons (microwave plasma discharge) and photons (irradiation by a continuous lamp or a excimer pulsed laser). In addition, laser spectroscopy technique is used in order to identify and quantify the products allowing the in situ analysis of the evolution of the resulting gas phase. First, I have studied methane photolysis at two different wavelengths. Indeed, in simulation experiments, methane photo-dissociation could involve photons either at 121.6 nm (Lyman-α) or at 248 nm respectively delivered by a H2/He lamp or a pulsed KrF excimer laser (this latter should enable kinetic studies of transient species). Irradiation experiments of pure CH4 and of N2/CH4 mixtures at both wavelengths have been conducted; afterwards, they have been simulated by a 0D photochemical model. Results obtained from the CH4 irradiations at Lyman-α indicate that additional works were needed to understand the differences between experimental and theoretical profiles for all the species formed during irradiation. In particular, the emission spectrum of the UV lamp has to be recorded, then, it turns out that its particular shape, as the intensity is not centered at but is spread in a wide range of wavelengths, has to be taken-Lyman- into account in the model. The latter has thus be improved allowing to better reconcile experimental and theoretical data. Results obtained for the 248 nm irradiations suggest that CH4 is not only dissociated but also ionized. Therefore, although this radiation could be interesting to study ionospheric processes held in Titan’s atmosphere, it is definitely not suitable to study the neutral chemistry we are interested in, therefore, the use of a laser delivering, this time, a radiation should be then considered if we want to pursue with -Lyman- fast kinetic studies. Secondly, I have implemented three types of preliminary experimental simulations of Titan's atmosphere: i) N2/CH4 discharge simulation experiments ii) N2/CH4 post-discharge simulation experiments, i.e. CH4 is introduced downstream of the flowing afterglow of a pure N2 discharge iii) coupled simulation simulations i.e. CH4, introduced downstream of the flowing afterglow of pure N2 microwave discharge is irradiated by a H2/He lamp (121.6 nm). Ex-situ qualitative and quantitative analysis of the resulting gas mixture recovered in a cold trap has been performed, for the first time, by IRTF spectroscopy. In N2/CH4 discharge experiments, more or less similar to those commonly conducted (the difference lies in the type of plasma used), the obtained products are HCN, NH3, HC3N, HC5N, C2H2, C2H4, C2H6, C3H4, C4H2 and C6H2 with abundances compatible with those retrieved from observations of Titan’s high atmosphere in the range between 900 to 1200 km. More surprisingly, in the N2/CH4 post discharges experiments, only HCN and NH3 are observed and this regardless the fact that methane is photolyzed or not. This result is explained by the fact that CH4’s photodissociation appears to be less efficient than N2’s dissociation in the plasma preventing the formation of hydrocarbons. It is therefore necessary to increase the radiation flux of radiation. The use of a radiation would allow reaching thislaser delivering a Lyman- objective. The results obtained with this “step by step” methodology helped to highlight the essential parameters that we have to master for the implementation of relevant experimental simulations of Titan's atmosphere. They also define the direction for the future developments of SETUP project

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.

Gravity waves are ubiquitous at the surface of the ocean and play a key role in the coupled ocean-atmosphere system. These wind generated waves, for which gravity provides the restoring force, influence the kinematics and dynamics of the upper ocean and lower atmosphere. Their breaking injects turbulence into the upper ocean, generates bubble plumes and sea-spray thus transferring energy, momentum, heat and mass between the atmosphere and the ocean. In the anthropocene, with CO2 driving the warming trend and the ocean acting as the main carbon sink, it is imperative to understand the complex physical controls of air-sea gas transfer. Large uncertainties still remain under high wind speed conditions where wave breaking processes are dominant. This dissertation seeks to shed light onto the dependence of wave breaking and air-sea gas transfer on environmental parameters. It further explores process based models of air-sea gas transfer that explicitly account for the breaking related processes. Air entraining breaking waves are easily detectable as bright features on the ocean surface composed of foam and subsurface bubble plumes. These features, termed whitecaps, arise at wind speed as as low as 3 m s−1 . The whitecap coverage (W) has been recognized as a useful proxy for quantifying wave breaking related processes. It can be determined from shipboard, air-borne and satellite remote sensing. W is most commonly parameterized as a function of wind speed, but previous parameterizations display over three orders of magnitude scatter. Concurrent wave field and flux measurements acquired during the Southern Ocean Gas Exchange (SO GasEx) and the High Wind Gas exchange Study (HiWinGS) projects permitted evaluation of the dependence of W on wind speed, wave age, wave steepness, mean square slope, as well as on wave-wind and breaking Reynolds numbers. W was determined from over 600 high frequency visible imagery recordings of 20 minutes each. Wave statistics were computed from in situ and remotely sensed data as well as from a WAVEWATCH-III® hind cast. The first ship-borne estimates of W under sustained wind speeds (U10N ) of 25 m s−1 were obtained during HiWinGS. These measurements suggest that W levels off at high wind speed, not exceeding 10% when averaged over 20 minutes. Combining wind speed and wave height in the form of the wave-wind Reynolds number resulted in closely agreeing models for both datasets, individually and combined. These are also in good agreement with two previous studies. When expressing W in terms of wave field statistics only or wave age, larger scatter is observed and/or there is little agreement between SO GasEx, HiWinGS, and previously published data. The wind–speed-only parameterizations deduced from the SO GasEx and HiWinGS datasets agree closely and capture more of the observed W variability than Reynolds number parameterizations. However, these wind-speed-only models do not agree as well with previous studies than the wind-wave Reynolds numbers. The ability to quantify air-sea gas transfer hinges on parameterizations of the gas transfer velocity k. k represents physical mass transfer mechanisms and is usually parameterized as a non-linear function of wind forcing. Previous eddy-covariance measurements and models based on the global radio carbon inventory led to diverging parameterizations with both cubic and quadratic wind speed dependence. At wind speeds above 10 m s−1 these parameterizations differ considerably and measurements display large scatter. In an attempt to reduce uncertainties in k, explored empirical parameterizations that incorporate both wind speed and sea state dependence via breaking and wave-wind Reynolds numbers, were explored. Analysis of concurrent eddy covariance gas transfer and measured wave field statistics supplemented by wave model hindcasts shows for the first time that wave-related Reynold numbers collapse four open ocean datasets that have a wind speed dependence of CO2 transfer velocity ranging from lower than quadratic to cubic. Wave-related Reynolds number and wind speed show comparable performance for parametrizing DMS which, because of its higher solubility, is less affected by bubble-mediated exchange associated with wave breaking. While single parameter models may be readily used in climate studies, their application is gas specific and may be limited to select environments. Physically based parameterizations that incorporate multiple forcing factors allow to model the gas transfer of gases with differing solubility for a wide range of environmental conditions. Existing mechanistic models were tested and a novel framework to model gas transfer in the open ocean in the presence of breaking waves is put forward. This analysis allowed to update NOAA’s Coupled OceanAtmosphere Response Experiment Gas transfer algorithm (COAREG) and exposed limitation of other existing physically based parameterizations. The newly proposed mechanistic model incorporates both the turbulence and bubble mediated transfer. It is based on various statistics determined from the breaking crest length distribution (Λ(c)). Λ(c) was obtained by tracking the advancing front of breaking waves in the high frequency videos taken during HiWinGS. Testing the mechanistic model with the HiWinGS dataset shows promising results for both CO2 and DMS, though it does not perform better than COAREG. Uncertainties remain in the quantification of bubble cloud which are at the core of the formulation of the bubble mediated transfer and additional field measurements are necessary to characterize bubble plume properties in the open ocean.

Thesis (Ph. D.)--University of Rhode Island, 2003. / Typescript. Includes bibliographical references (leaves 211-224).

Thesis (Ph. D.)--University of South Florida, 2003. / Includes vita. Title from PDF of title page. Document formatted into pages; contains 119 pages. Includes bibliographical references.

Typescript (photocopy) / 1 v. (various paging) : ill. ; 30 cm / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics, 1982

Thesis (Ph.D.) -- University of Adelaide, Dept. of Physics, 1982. / Typescript (photocopy).