The Quasi-Biennial Oscillation (QBO) is the dominant pattern of variability in the tropical stratosphere. Despite a well established theory regarding its generation in the atmosphere, the simulation in global climate models remains difficult. A set of metrics assessing the quality of model simulations is presented in this study. The QBO simulations in models submitted to the CMIP5 and CCMVal-2 intercomparison projects are characterised and compared to radiosonde observations and reanalysis datasets. Common model biases and their potential causes are addressed. As the QBO has a long intrinsic period, knowing its influences on other parts of the climate system can be used to improve long range forecasts. These teleconnections of the QBO in observations are investigated using composite analysis, multilinear regression and a novel approach called causal effect networks (CEN). Findings from these analyses confirm previous results of the QBO modulating the stratospheric polar vortex and subsequently the North Atlantic Oscillation (NAO). They also suggest that it is important to take the equatorial zonal mean zonal wind vertical profile into account when studying teleconnections, rather than the more traditional method of using just one single level. While QBO influences on the Northern Hemisphere winter polar vortex and the NAO are more clearly established, interactions within the tropics remain inconclusive. Regression analysis does not show a connection between the QBO and the MJO, whereas the CEN analysis does. Further studies are needed to understand the interaction mechanisms near the equator. Finally, following the unprecedented disruption of the QBO cycle in the winter 2015/16, the event is described and a model analogue from the MPI-ESM-MR historical simulation is presented. Future implications are unclear, although model projections indicate more frequent QBO irregularities in a warming climate.

Representing model uncertainty in atmospheric simulators is essential for the production of reliable probabilistic forecasts, and stochastic parametrisation schemes have been proposed for this purpose. Such schemes have been shown to improve the skill of ensemble forecasts, resulting in a growing use of stochastic parametrisation schemes in numerical weather prediction. However, little research has explicitly tested the ability of stochastic parametrisations to represent model uncertainty, since the presence of other sources of forecast uncertainty has complicated the results. This study seeks to provide firm foundations for the use of stochastic parametrisation schemes as a representation of model uncertainty in numerical weather prediction models. Idealised experiments are carried out in the Lorenz `96 (L96) simplified model of the atmosphere, in which all sources of uncertainty apart from model uncertainty can be removed. Stochastic parametrisations are found to be a skilful way of representing model uncertainty in weather forecasts in this system. Stochastic schemes which have a realistic representation of model error produce reliable forecasts, improving on the deterministic and the more "traditional" perturbed parameter schemes tested. The potential of using stochastic parametrisations for simulating the climate is considered, an area in which there has been little research. A significant improvement is observed when stochastic parametrisation schemes are used to represent model uncertainty in climate simulations in the L96 system. This improvement is particularly pronounced when considering the regime behaviour of the L96 system - the stochastic forecast models are significantly more skilful than using a deterministic perturbed parameter ensemble to represent model uncertainty. The reliability of a model at forecasting the weather is found to be linked to that model's ability to simulate the climate, providing some support for the seamless prediction paradigm. The lessons learned in the L96 system are then used to test and develop stochastic and perturbed parameter representations of model uncertainty for use in an operational numerical weather prediction model, the Integrated Forecasting System (IFS). A particular focus is on improving the representation of model uncertainty in the convection parametrisation scheme. Perturbed parameter schemes are tested, which improve on the operational stochastic scheme in some regards, but are not as skilful as a new generalised version of the stochastic scheme. The proposed stochastic scheme has a potentially more realistic representation of model error than the operational scheme, and improves the reliability of the forecasts. While studying the L96 system, it was found that there is a need for a proper score which is particularly sensitive to forecast reliability. A suitable score is proposed and tested, before being used for verification of the forecasts made in the IFS. This study demonstrates the power of using stochastic over perturbed parameter representations of model uncertainty in weather and climate simulations. It is hoped that these results motivate further research into physically-based stochastic parametrisation schemes, as well as triggering the development of stochastic Earth-system models for probabilistic climate prediction.

Empirical techniques are developed to adjust dynamic model forecasts on the seasonal time scale for southern African summer rainfall. The techniques, called perfect prognosis and model output statistics (MOS), are utilized to statistically "recalibrate" general circulation model (GCM) large-scale fields to three equi-probable rainfall categories for December to February. The recalibration is applied to a GCM experiment where simultaneously observed sea-surface temperature (SST) fields serve as the lower boundary forcing, referred to as the simulation mode experiment. Cross-validation sensitivity tests are first performed over a 28-year climate period to design an optimal canonical correlation analysis (CCA) model for each of the two recalibration methods. After considering several potential predictor fields, the 700 hPa geopotential height field is selected as the single predictor field in the two sets of statistical equations that are subsequently used to produce recalibrated rainfall simulations over a 1 a-year independent test period. Patterns analysis of the predictor and predictand fields suggests that anomalously low (high) 700 hPa geopotential heights over the subcontinent are associated with wet (dry) conditions over land, an association that is supported by observational evidence of rain (drought) producing systems. Additionally, the dominant mode of the recalibration equations is associated with the EI Nino/Southern Oscillation (ENSO) phenomenon. Somewhat higher retro-active skill levels are found using the MOS technique, but the computationally less intensive perfect prognosis technique should also be able to produce usable seasonal rainfall forecasts over southern Africa in an operational forecast environment hampered by the lack of computing resources. / Dissertation (MSc)--University of Pretoria, 2006. / Geography, Geoinformatics and Meteorology / Unrestricted

Brown dwarfs are substellar objects that fall in-between the smallest stars and largest planets in size and temperature. Due to their relatively cool temperatures, the atmospheres of these 'failed stars' have been shown to exhibit interesting properties such as iron, silicate, and salt clouds. Theoretical atmospheric models based on known physics and chemistry can be used as tools to interpret and understand our observations of brown dwarfs. I have fit archival and new infrared spectra of over 300 brown dwarfs with atmospheric models. Using the parameters of the best-fit models as estimates for the physical properties of the brown dwarfs in my sample, I have performed a survey of how brown dwarfs evolve with spectral type and temperature. I present my fit results and observed trends. I use these fit results to note where current atmospheric models are able to well-replicate the data and where the models and data conflict.

Este trabalho trata do estudo do transporte atmosférico de emissões de queimadas na região Amazônica e Centro-Oeste do Brasil. Em consequência da queima de biomasa, gases (CO IND.2, CO, CH IND.4, etc.) e partículas são emitidas para a atmosfera, os quais podem provocar mudanças no equilíbrio climático e biogeo químico do planeta Terra, em várias escalas. O estudo é realizado por meio de simulação numérica dos movimentos da atmosfera utilizando o modelo atmosférico RAMS (Regional Atmospheric Modeling System). São utilizados os métodos Lagrangiano e Euleriano. No método Langrangiano o transporte é estudado por meio do cálculo de trajetórias cinemáticas 3d de massas de ar, utilizando o campo de vento simulado, na escala resolvida. A posição inicial das massas de ar é obtida a partir de mapas de queimadas detectadas por sensores a bordo de satélites como o AVHRR da série NOAA. Uma metodologia simples que contabiliza os efeitos de processos convectivos úmidos da escala sub-grade na velocidade vertical da parcela de ar para modelo atmosféricos de baixa resolução, é introduzida no modelo de trajetórias. No método Euleriano, é resolvida a equação de conservação de massa dos principais elementos emitidos. Para tanto é introduzido um modelo de fontes emissoras de gases/partículas associadas à queimadas em floresta tropical e cerrado da América do Sul, distribuídas espacial e temporalmente através da assimilação diária de mapas de posição de queimadas produzidos por sensoriamento remoto. Os termos de advecção na escala resolvida e o transporte turbulento na escala sub-grade são resolvidos utilizando as parametrizações próprias do modelo RAMS. É introduzida uma parametrização do transporte sub-grade associado às circulações úmidas e profundas não resolvidas explicitamente pelo modelo, devido a baixa resolução espacial. Termos sumidouros associados a processos genéricos de remoção/transformação de gases/partículas são ) também parametrizadas e inseridos na equação de conservação de massa. A metodologia é aplicada a um estudo de caso ocorrido no mês de julho de 1993. São modelados o transporte turbulento na camada limite planetária, os efeitos transientes associados à entrada de frentes frias vindo do sul do continente e à convecção na bacia Amazônica no transporte convectivo de poluentes, bem como o transporte associado aos sistemas de larga escala. São observados padrões de exportação continental de poluentes, com saídas ocorrendo a noroeste da América do Sul em direção ao oceano Pacífico, e a sudeste em direção ao oceano Atlântico. / A study about the atmospheric transport f biomass burning emissions in the Amazon and the Central of Brazil is presented. Gases (CO IND.2, CO, CH IND.4, etc.) and particles emitted to the atmosphere due the biomass burning are responsible for the climatic and biogeochemical budget changes in the Earth planet, in many scales. This study is carried out through a numerical simulation of the atmospheric motions using the atmospheric models RAMS (Regional Atmospheric Modeling System). Lagragian and Eulerian methods are used. In the Lagrangian method the transport is studied through 3D kinematic air mass trajectories calculation, using simulated wind fields, in a resolved scale. The initial position of the air masses is obtained from biomass burning spots maps, derived from satellite sensors (AVHRR from NOAA series). A simple methodology to take into account the sub-grid effects of wet convective process in the vertical velocity of the air parcels, for low resolution atmospheric models is introduced in the trajectory model. In the Eulerian method the mass conservation equation is resolved for the main elements emitted. A model of gases and particles sources emissions is introduced associated with biomass burning in South America tropical forest and savanna, spatially and temporally distributed and daily assimilated, according to the biomass burning spots defined by remote sensing. The advection in a resolved scale and turbulent transport, in a sub-grid parameterization associated to wet and deep circulation not explicitly resolved by the model due its low spatial resolution is introduced. Sinks associated with generic process of removal/transformation of gases/particles are parameterized and introduced in the mass conservation equation. The methodology is applied to a case study on July 1993. The turbulent transport in the planetary boundary layer the transient effects in the convective transport of pollutants associated with cold fronts from the south and convection in the Amazon basin and the transport associated with the large scale systems are modeled. Patterns of pollutant exportation are observed with a corridor to the Pacific Ocean in the South America Northwest and another in the Southeast to the Atlantic Ocean.

Este trabalho trata do estudo do transporte atmosférico de emissões de queimadas na região Amazônica e Centro-Oeste do Brasil. Em consequência da queima de biomasa, gases (CO IND.2, CO, CH IND.4, etc.) e partículas são emitidas para a atmosfera, os quais podem provocar mudanças no equilíbrio climático e biogeo químico do planeta Terra, em várias escalas. O estudo é realizado por meio de simulação numérica dos movimentos da atmosfera utilizando o modelo atmosférico RAMS (Regional Atmospheric Modeling System). São utilizados os métodos Lagrangiano e Euleriano. No método Langrangiano o transporte é estudado por meio do cálculo de trajetórias cinemáticas 3d de massas de ar, utilizando o campo de vento simulado, na escala resolvida. A posição inicial das massas de ar é obtida a partir de mapas de queimadas detectadas por sensores a bordo de satélites como o AVHRR da série NOAA. Uma metodologia simples que contabiliza os efeitos de processos convectivos úmidos da escala sub-grade na velocidade vertical da parcela de ar para modelo atmosféricos de baixa resolução, é introduzida no modelo de trajetórias. No método Euleriano, é resolvida a equação de conservação de massa dos principais elementos emitidos. Para tanto é introduzido um modelo de fontes emissoras de gases/partículas associadas à queimadas em floresta tropical e cerrado da América do Sul, distribuídas espacial e temporalmente através da assimilação diária de mapas de posição de queimadas produzidos por sensoriamento remoto. Os termos de advecção na escala resolvida e o transporte turbulento na escala sub-grade são resolvidos utilizando as parametrizações próprias do modelo RAMS. É introduzida uma parametrização do transporte sub-grade associado às circulações úmidas e profundas não resolvidas explicitamente pelo modelo, devido a baixa resolução espacial. Termos sumidouros associados a processos genéricos de remoção/transformação de gases/partículas são ) também parametrizadas e inseridos na equação de conservação de massa. A metodologia é aplicada a um estudo de caso ocorrido no mês de julho de 1993. São modelados o transporte turbulento na camada limite planetária, os efeitos transientes associados à entrada de frentes frias vindo do sul do continente e à convecção na bacia Amazônica no transporte convectivo de poluentes, bem como o transporte associado aos sistemas de larga escala. São observados padrões de exportação continental de poluentes, com saídas ocorrendo a noroeste da América do Sul em direção ao oceano Pacífico, e a sudeste em direção ao oceano Atlântico. / A study about the atmospheric transport f biomass burning emissions in the Amazon and the Central of Brazil is presented. Gases (CO IND.2, CO, CH IND.4, etc.) and particles emitted to the atmosphere due the biomass burning are responsible for the climatic and biogeochemical budget changes in the Earth planet, in many scales. This study is carried out through a numerical simulation of the atmospheric motions using the atmospheric models RAMS (Regional Atmospheric Modeling System). Lagragian and Eulerian methods are used. In the Lagrangian method the transport is studied through 3D kinematic air mass trajectories calculation, using simulated wind fields, in a resolved scale. The initial position of the air masses is obtained from biomass burning spots maps, derived from satellite sensors (AVHRR from NOAA series). A simple methodology to take into account the sub-grid effects of wet convective process in the vertical velocity of the air parcels, for low resolution atmospheric models is introduced in the trajectory model. In the Eulerian method the mass conservation equation is resolved for the main elements emitted. A model of gases and particles sources emissions is introduced associated with biomass burning in South America tropical forest and savanna, spatially and temporally distributed and daily assimilated, according to the biomass burning spots defined by remote sensing. The advection in a resolved scale and turbulent transport, in a sub-grid parameterization associated to wet and deep circulation not explicitly resolved by the model due its low spatial resolution is introduced. Sinks associated with generic process of removal/transformation of gases/particles are parameterized and introduced in the mass conservation equation. The methodology is applied to a case study on July 1993. The turbulent transport in the planetary boundary layer the transient effects in the convective transport of pollutants associated with cold fronts from the south and convection in the Amazon basin and the transport associated with the large scale systems are modeled. Patterns of pollutant exportation are observed with a corridor to the Pacific Ocean in the South America Northwest and another in the Southeast to the Atlantic Ocean.

Approved for public release, distribution is unlimited / The objective of this thesis is to investigate the forecastability of optical turbulence using the U.S. Navy's Coupled Ocean Atmosphere Mesoscale Prediction System (COAMPS). First, a detailed synoptic study was performed over the Eastern Pacific region for observation periods in October 2001 and March 2002 to focus on mesoscale features affecting Vandenberg AFB. Second, a modified version of COAMPS version 2.0.16 model output was evaluated to ensure reasonable modeling of the mesoscale. Next, temperature and dewpoint temperature vertical profiles of COAMPS, modified with the Turbulent Kinetic Energy (TKE) Method, were compared with balloon-launched rawinsondes, initially, then with higher resolution thermosondes. Optical turbulence parameters were then calculated from the data and a comparison between synthetic profiles and thermosonde-derived profiles were qualitatively and quantitatively studied. Then the vertical resolution of the model was increased for selected forecasts to determine the potential for forecast improvement. / Lieutenant Commander, United States Navy

Una característica propia de las precipitaciones en el área del Mediterráneo Occidental es la torrencialidad. En el marco de unas precipitaciones anuales no muy abundantes, típicas del clima mediterráneo, se registran fenómenos de precipitaciones torrenciales intensas en muchas zonas del Mediterráneo Occidental que provocan grandes daños económicos e incluso, en ocasiones, víctimas. La cuenca mediterránea está conformada por un mar profundo y semicerrado rodeado por una serie de cadenas montañosas, especialmente en su mitad occidental. Esta configuración favorece el desarrollo de una dinámica atmosférica propia con algunos comportamientos particulares de esta región. Uno de los factores que pueden ser importantes en la génesis y desarrollo de las precipitaciones torrenciales es la interacción entre el mar y la atmósfera con intercambios de humedad y calor que pueden inestabilizar la masa de aire que se desplaza sobre el mar. El Mediterráneo es un mar semicerrado con una circulación propia y poco intercambio de masas de agua con otros mares u océanos. A partir de datos de satélites se ha elaborado una climatología de la temperatura superficial del Mediterráneo y se ha estudiado sus patrones de distribución espacial en las diferentes épocas del año. Como resultado de este análisis, se ha determinado la existencia de dos regímenes principales de distribución de la temperatura superficial de mar en las épocas invernal y estival, con dos periodos de transición entre ambas en primavera y otoño. A partir del conocimiento de la climatología de la temperatura superficial del mar y, especialmente, de su distribución espacial se han seleccionado tres eventos de precipitaciones torrenciales en la Comunidad Valenciana para estudiar el efecto de las diferentes distribuciones de temperatura del mar en la simulación de las lluvias torrenciales. Para ello, se ha seleccionado episodios de lluvia correspondientes a los regímenes invernal, estival y de transición en otoño. Para todos los eventos se ha realizado una simulación de control con los datos de temperatura superficial del mar originales que actúa como simulación de control. Posteriormente se ha realizado simulaciones de cada evento en las que se perturbaba la temperatura superficial del mar en las zonas por las que se desplazaba la masa de aire que originaba las lluvias torrenciales a lo largo de su trayectoria en los días previos. Se ha comprobado en los resultados del modelo meteorológico que la variación de la temperatura superficial del mar en determinadas zonas, indicadas por su régimen de distribución espacial, provoca importantes cambios en la precipitación acumulada. Se ha podido identificar, por tanto, la existencia de áreas de recarga donde la interacción mar-atmósfera favorece el desarrollo de precipitaciones torrenciales en diferentes puntos de la cuenca mediterránea, en este caso la Comunidad Valenciana. / Torrentiality is a known feature of rainfall in the Western Mediterranean. As part of a typical Mediterranean climate, heavy rain events are recorded in many areas of the Western Mediterranean that cause major economic damage and even sometimes human casualties. The Mediterranean basin is formed by a deep and almost closed sea and surrounded by a series of mountain ranges, especially in its western basin. This configuration favors the development of its own atmospheric dynamic behavior. A main factor in the genesis and development of torrential rainfall are the ocean and atmosphere exchanges of moisture and heat that can destabilize the air mass that travels over the sea. The Mediterranean is a semi-enclosed sea with its own oceanic circulation and little exchange of water masses with other seas. A surface temperature climatology of the Mediterranean has been built from satellite data so its spatial distribution patterns have been studied. As a result of this analysis, we have determined the existence of two main distribution modes for sea surface temperature in winter and summer, with transitional periods in spring and autumn. From the knowledge of sea surface temperature climatology and, especially, from its spatial distribution three heavy precipitation events have been selected in Valencia to study the effect of different sea temperature distributions in the simulation of torrential rains. To this end, we selected rainfall events for winter and summer regimes and for fall transition. For all events a simulation with the unperturbed sea surface temperature data was performed as control simulation. Then, simulations of each event were run in which sea surface temperature was modified in areas along the air mass path. It has been found that the variation of sea surface temperature in certain areas, indicated by its spatial distribution scheme, causes significant changes in the precipitation accumulated in the simulation. Therefore, the existence of recharge areas where the air-sea interaction favors the development of torrential rainfall in different parts of the Mediterranean, in this case Valencia, has been shown.