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Implicit large eddy simulation (ILES) has been shown, in the literature, to have some success for three-dimensional flow (e.g. see [Grinstein, F.F., Margolin, L.G. and Rider, W. Implicit Large Eddy Simulation. Cambridge, 2007]), but it has not previously been examined for two-dimensional flow. This thesis investigates whether ILES can be applied successfully to two-dimensional flow. Modified equation analysis is used to demonstrate the similarities between the truncation errors of certain numerical schemes and the subgrid terms of the barotropic vorticity equation (BVE). This presents a theoretical motivation for the numerical testing. Burgers equation is first used as a model problem to develop the ideas and methodology. Numerical schemes that are known to model Burgers equation well (shock capturing schemes) are shown to be implicitly capturing the subgrid terms of the one-dimensional inviscid Burgers equation through their truncation errors. Numerical tests are performed on three equation sets (BVE, Euler equations and the quasi-geostrophic potential vorticity equation) to assess the application of ILES to two-dimensional flow. The results for each of these equation sets show that the schemes considered for ILES are able to capture some of the subgrid terms through their truncation errors. In terms of accuracy, the ILES schemes are comparable (or outperform) schemes with simple explicit subgrid models when comparing vorticity solutions with a high resolution reference vorticity solution. The results suggest that conservation of vorticity is important to the successful application of ILES to two-dimensional flow, whereas conservation of momentum is not. The schemes considered for ILES are able to successfully model the downscale enstrophy transfer, but none of the schemes considered for ILES (or the schemes with simple subgrid models) can model the correct upscale energy transfer from the subgrid to the resolved scales. Energy backscatter models are considered and are used with the ILES schemes. It is shown that it is possible to create an energy conserving and enstrophy dissipating scheme, composed of an ILES scheme and a backscatter model, that improves the accuracy of the vorticity solution (when compared with the corresponding ILES scheme without backscatter).

As the demand for global renewable energy grows, so does the demand for more efficient energy conversion machines and better wind resource assessment. The need to convert as much energy as possible with little cost remains the biggest challenge. In the wind energy sector, the quantity of the resource “wind” is not hard to locate, as with current ground and space based remote sensing technologies, and climate reanalysis techniques, the mapping of average wind speeds across the globe is achievable. The difficulty lies in identifying the “quality” of the wind resource. “Quality” is the measure of the time variant properties of the wind, and time scale here does not represent seasonal, monthly, or the daily variability, but rather the changes within hours, minutes, seconds, and sub‐second periods. Wind possesses a highly unpredictable, and non‐universal character, which is referred to as turbulence. These intermittencies in the wind speed create variable mechanical loads on the structure of wind turbines leading to fatigue, and ultimately failure. Identifying site specific qualities of the wind resource is very crucial in the design and selection process of the wind turbine. Physical theories explaining wind turbulence phenomena over flat terrain have been critiqued and tested by observations, and in general, have achieved reasonable success in explaining surface layer wind dynamics that can be applied universally. This universality, and the extrapolation of flat terrain theories to complex terrain applications, breaks down most of the time due to the newly recognized spatial and temporal spectrum of interaction modes, mechanically and thermodynamically, with the surrounding complex terrain. In terrain as found in New Zealand, most of the wind farm development is carried out over complex terrain, with ridge top and mountainous installations. In this study, an experimental campaign was carried out over a coastal ridge top, proposed for wind farming, to investigate mean and turbulent wind flow features significant for wind turbine selection and placement across the ridge. The steep sloped faces of the ridge, high wind speeds and its proximity to the sea made this location ideal for a benchmark investigation site. Ultra‐sonic ii anemometers, a sodar (sound detection and ranging) wind profiler, and high resolution LES (large eddy simulation) numerical modelling were all utilized separately and in an interconnected way to provide a comprehensive analysis of the wind dynamics over the ridge top. The three principal components of the investigation were: the effect of the upstream topography and the thermal circulation associated with the proximity to the sea on the observed and modelled wind shear vertical profile; the role that the near upwind terrain plays in shaping the turbulence energy spectrum and influencing the predicted spectrum, ultimately affecting isotropy in the flow field and turbulence length scales; turbulence advection from far topography, and the role that far upwind terrain plays in altering the wind turbulence in a measurement area or at a single point. Results showed that the thermal wind circulations and upstream steep topography could dictate the wind shear profile, and consequently have a large impact on wind turbine height selection and placement. The sodar proved to be a very useful tool in identifying vertical shear zones associated with effects of steep upstream terrain, vertical mixing of horizontal momentum, and thermal circulation from the local sea breeze. In complex terrain, the added multi‐directional perturbations from the underlying roughness redistribute the statistical variations (measured by variances) in the three spatial dimensions. Isotropy, based on measured variances, was attained for both sites on the ridge. Isotropy also held true for the energy spectrum via Fourier analysis of the high temporal resolution data, but not for both sites. In general, local isotropy can be attained in cases of higher wind speeds and increased terrain relief. Measured spectral ratios did not converge to the limit suggested by the local isotropy hypothesis. These results identify contradictions in assessing the turbulence isotropy in both real space (statistically through variances) and Fourier space (through power spectrum analysis), which suggests caution in deriving or interpreting turbulence information for wind turbine design and selection. iii 2D‐LES experiments showed that turbulent kinetic energy (TKE) can attain long range memory of underlying terrain, which can then react accordingly with upcoming terrain. Under the high wind speed scenarios, which are suitable for wind farming, and over relatively complex terrain, the flow retained some aspects of terrain information at least 30H (H is the terrain height) upstream and downstream of the terrain. In general, as the turbulence field travels over new terrain it tends to increase in intensity downstream of that feature. The newly modified TKE field acquires geometric features from the underlying terrain; mainly these features register as amplifications in the wave structure of the field at wavelengths comparable to the height of the underlying terrain. The 2D‐LES sensitivity experiments identified key areas of high mean wind speed and turbulence in relation to terrain effects, all of which should be taken into consideration when thinking of locating a wind farm in such areas.

The current capabilities of SASKTRAN – a radiative transfer model at the University of Saskatchewan in Saskatoon, Canada – are to accurately model the scattering of solar radiation within the earth’s atmosphere for the ultraviolet-visible (UV-Vis) and near infra-red (NIR) regions of the electromagnetic spectrum. However, the current model does not account for the radiation emitted by the ground and atmosphere, approximated by the blackbody spectrum. In the UV-Vis, this contribution is unimportant, but when transitioning to wavelengths longer than 2.5 μm, the solar spectrum decreases in intensity while radiation of terrestrial and atmospheric origin increases along the blackbody curve. At wavelengths longer than 5 μm in the far infra-red (FIR), the blackbody radiation is the dominant source in the atmosphere. A modification to the source code of SASKTRAN was made in order to include the additional effect of this “thermal” radiation – with the help of the spectral line database HITRAN – while still maintaining scattering capabilities of solar radiation. This would make SASKTRAN one of the first radiative transfer models with the ability to model radiation in the difficult region between 3 and 5 μm – the mid infra-red (MIR) region – where the solar and thermal radiation sources are equally diminished and are the same order of magnitude. An introduction is given to atmospheric physics with a focus on the science of infra-red active molecules like H2O, CO2, CH4, N2O, O3, and CO – the so-called “greenhouse gases” – and the measurement techniques used to determine their atmospheric distribution. A theoretical basis is then provided for general radiative transfer, and the physics of molecular absorption and emission is examined in detail. A summary of the implementation of thermal radiation within the SASKTRAN framework is given, followed by verification studies where the model’s radiative transfer calculations in the infra-red are compared against measurements, including those made by the ground-based instrument E-AERI, the space-borne instruments IASI and GOSAT, and against model results from the LBLRTM, another well-verified radiative transfer model.

The ocean emission and subsequent oxidation of dimethylsulfide (DMS) provides a source of sulfate in the atmosphere, potentially affecting the amount of solar radiation reaching the Earth's surface through both direct and indirect radiative effects of sulfate aerosols. DMS in the ocean can be quite variable with season and location, which in turn leads to high spatial and temporal variability of ocean DMS emissions. This study tested currently available observational and empirically-based climatologies of DMS concentration in the surface ocean. The exploration of the existing parameterizations mainly reveals the limitations of estimating DMS with an empirical model based on variables such as chlorophyll and mixed layer depth. The different algorithms show significant differences in spatial pattern, and none correlate strongly with observations. There is considerable uncertainty both in terms of the spatiotemporal distribution in DMS concentration and flux, as well as in the global total DMS flux. The present research investigates the influence of DMS on sulfate aerosols and radiative fluxes given different DMS climatologies in the fourth generation of the Canadian Global Atmospheric Climate Model (CanAM4.1). In general, the response in the radiative flux seems to follow the variation in the global mean flux of DMS linearly. Differences in the spatial and temporal structure of oceanic DMS have only a secondary effect on the radiative changes. The overall response of the atmosphere to the presence or absence of structure of DMS in space and time is distinctly smaller compared to the possible uncertainty of this response associated with the magnitude of the annually averaged global flux. / Graduate / 0425 / 0725 / 0416 / jetesdal@uvic.ca

Atmospheres play an important role in the habitability of a planet, so understanding and modelling them is an important step in the search for life on other planets. This thesis presents a 1D frequency-dependent radiative-convective code that was written to help determine the temperature-pressure structure of potentially-habitable exoplanets. This code pairs with a chemistry model to determine the chemical composition of these planets' atmospheres. This code is applied to the planets in the TRAPPIST-1 system. The initial atmospheric compositions of the TRAPPIST-1 planets are determined through planet formation history and considered for both outgassed and accreted atmospheres. An interesting result is found when running these initial atmospheric compositions through the chemistry model: when the atmosphere equilibrates, it can change its C/O ratio from equal to that found in the accreted or outgassed volatiles to something lower, because, in temperate conditions, CO$_2$ is favoured over CO. This has the consequence that observed C/O ratios in terrestrial atmospheres cannot be relied on to infer the C/O ratio of the protoplanetary disc in which the planet formed. The initial results of atmospheric modelling for TRAPPIST-1 planets indicate that these planets are likely to have relatively warmer upper atmospheres due to the fact that their host star emits primarily in the infrared, and a portion of this radiation is then absorbed as it enters the top of the atmosphere. These initial results have not been seen in previous work. These initial results are the beginning of a database of potential atmospheres on the TRAPPIST-1 planets. It is hoped that these atmospheres can be compared with observations from future observing missions like the James Webb Space Telescope to help constrain the surface conditions of these potentially-habitable planets and ultimately, to help in the search for life. / Thesis / Master of Science (MSc)

The Earth’s atmosphere constitutes a complex system subject to a large number of forcings of both natural and anthropogenic origin; these influence its evolution on a range of timescales. This thesis makes use of the UMUKCA global chemistry-climate model to explore several aspects relating to the atmospheric response to the 11-year solar cycle forcing and future stratospheric ozone recovery. Firstly, following recent improvements in the model, the atmospheric response to the solar cycle forcing simulated in UMUKCA is discussed. It is shown that while some features show a broad resemblance to observations/reanalysis, there are clear differences with regard to other features; the latter could result from model deficiencies and/or uncertainties in the observed response. The role of analysis method and of interannual variability is also addressed. Secondly, the solar cycle response is separated into the individual contributions from direct radiative heating and from ozone production using a set of sensitivity experiments. It is shown that while the tropical yearly mean responses to the two components are generally linearly additive, this is not necessarily the case in the high latitudes. It is suggested that solar-induced ozone changes could be important for modulating the Southern Hemisphere dynamical response. Thirdly, the role of the representation of the solar ozone response is studied. It is shown that the choice of the solar ozone response prescribed in the radiation scheme in non-interactive ozone experiments has a substantial impact on the simulated temperature response to the solar cycle forcing. The Northern Hemisphere dynamical responses are found to be generally similar within the uncertainty. A comparison with an interactive ozone case is also discussed. Lastly, future ozone recovery is investigated using a seven-member ensemble of 1960- 2099/1980-2080 integrations. The long-term evolution of ozone in different regions is found to be generally consistent with previous modelling studies. The long-term trends and variability in springtime Arctic ozone and its chemical, radiative and dynamical drivers are assessed. It is shown that Arctic ozone increases in the future, consistent with future reduction in stratospheric chlorine, stratospheric cooling and strengthening large-scale circulation. Yet, the large interannual variability is found to continue and to facilitate episodic ozone reductions, with halogen chemistry becoming a smaller but non-negligible driver of future springtime Arctic ozone variability for many decades.

Le système d'upwelling péruvien est l'un des systèmes marins côtiers les plus productifs de l’océan mondial. Le vent de surface le long de la côte est le principal moteur de l'upwelling. Cette thèse vise à étudier la variabilité du vent côtier et ses processus lors du réchauffement de la couche de surface, à différentes échelles de temps: (1) des échelles de temps interannuelles, correspondant aux événements El Niño, et (2) des échelles de temps multi-décadaires résultant du changement climatique régional. Une série de domaines emboités d’un modèle atmosphérique régional est utilisée pour simuler le vent de surface. Dans la première partie de la thèse, on étudie les processus responsables de l'augmentation, contre-intuitive, du vent observée au large du Pérou au cours de la période El Niño 1997-1998. Des expériences de sensibilité montrent que le réchauffement inh de la omogène des eaux de surface, plus important dans le nord, entraîne un gradient de pression accru le long côte, accélérant le vent. Dans une seconde partie de la thèse, l’évolution des vents côtiers est étudiée dans le scénario du «pire cas» du changement climatique RCP8.5. Forcés par le gradient de pression le long de la côte, les vents diminuent en été, tandis qu’ils s’accroissent en hiver, renforçant ainsi légèrement le cycle saisonnier. / The Peruvian upwelling system is one of the most productive coastal marine systems of the world ocean. As in other upwelling systems, alongshore surface wind is the main driver of the coastal upwelling. This thesis aims to study the coastal wind variability and the processes responsible for it during the ocean surface layer warming conditions, at different time scales: (1) interannual time scales, corresponding to El Niño events and (2) multi decadal time scales resulting from regional climate change. A suite of regional atmospheric model embedded domains is used to simulate the surface winds. In the first part of the thesis, the counter-intuitive wind increase observed off Peru during the 1997-1998 El Niño is studied. Sensitivity experiments show that the inhomogenous alongshore surface warming, larger in the north, drives an enhanced alongshore pressure gradient that accelerates the alongshore wind. In the second part of the thesis, the evolution of coastal wind changes is investigated under the “worst case” RCP8.5 climate change scenario. Mainly driven by the alongshore pressure gradient, summer winds decrease whereas winter winds increase, thus slightly reinforcing the seasonal cycle.