On the momentum fluxes associated with mountain waves in directionally sheared flows

The direct impact of mountain waves on the atmospheric circulation is due to the deposition of wave momentum at critical levels, or levels where the waves break. The first process is treated analytically in this study within the framework of linear theory. The variation of the momentum flux with height is investigated for relatively large shears, extending the authors’ previous calculations of the surface gravity wave drag to the whole atmosphere. A Wentzel–Kramers–Brillouin (WKB) approximation is used to treat inviscid, steady, nonrotating, hydrostatic flow with directional shear over a circular mesoscale mountain, for generic wind profiles. This approximation must be extended to third order to obtain momentum flux expressions that are accurate to second order. Since the momentum flux only varies because of wave filtering by critical levels, the application of contour integration techniques enables it to be expressed in terms of simple 1D integrals. On the other hand, the momentum flux divergence (which corresponds to the force on the atmosphere that must be represented in gravity wave drag parameterizations) is given in closed analytical form. The momentum flux expressions are tested for idealized wind profiles, where they become a function of the Richardson number (Ri). These expressions tend, for high Ri, to results by previous authors, where wind profile effects on the surface drag were neglected and critical levels acted as perfect absorbers. The linear results are compared with linear and nonlinear numerical simulations, showing a considerable improvement upon corresponding results derived for higher Ri

ESTUDO DE IMPACTE AMBIENTAL DO ALQUEVA - CLIMA

A circulação atmosférica é fortemente influenciada pela superfície da Terra, reflectindo a estrutura espacial da orografia, das massas de água e da cobertura do solo. As heterogeneidades observadas na superfície do planeta são uma das razões da existência de energia disponível, a partir da qual se pode manter um ciclo de conversões de Energia e Entropia, que estão na base da circulação observada. Não quer isto dizer, no entanto, que qualquer alteração significativa e permanente da superfície se traduza necessariamente numa correspondente alteração climática. Na verdade, existem certos condicionamentos dinâmicos que favorecem o efeito das grandes e médias escalas horizontais, de tal modo que uma alteração intensa mas localizada no espaço pode ter um efeito desprezável, enquanto uma outra alteração mais ténue mas extensa pode ser muito mais significativa. O conceito de escala tem por isso um papel central na Meteorologia. Convencionalmente fala-se em quatro escalas distintas na dinâmica da Atmosfera - a Escala Planetária (dezenas de milhares de km), a Escala Sinóptica (milhares de km), a Mesoscala (dezenas de km) e a Microscala - verificando-se que as duas escalas intermédias têm um papel fundamental na definição do clima observado em cada local. Na latitude de Portugal, em particular, observa-se que os regimes de circulação médios e a precipitação são em grande medida condicionados pela escala sinóptica, especialmente no período de Inverno, em que ocorre a maior parte da precipitação sob a forma de precipitação frontal. No entanto é também bem conhecida a influência de circulações de mesoscala no estabelecimento de diferenciação climática entre locais relativamente próximos. Por outro lado, o valor local de diversos parâmetros atmosféricos é muitas vezes fortemente condicionado por condições que ocorrem numa escala horizontal ainda mais pequena, influenciando por exemplo a exposição ao Sol ou ao Vento com consequências, por vezes significativas, em termos de Temperatura. O empreendimento do Alqueva, dada a natureza das alterações introduzidas e a sua extensão horizontal, implicará com certeza alterações microclimáticas e poderá implicar alterações na circulação de mesoscala da região envolvente. Na verdade, é aparentemente um dos poucos empreendimentos localizados capaz de ter efeito à escala regional, em termos climáticos

The Raman Spectrum of the Squarate (C4O4-2 ) Anion: An Ab Initio Basis Set Dependence Study

The Raman excitation profile of the squarate anion, C4O4-2 , was calculated using ab initio methods at the Hartree-Fock using Linear Response Theory (LRT) for six excitation frequencies: 632.5, 514.5, 488.0, 457.9, 363.8 and 337.1 nm. Five basis set functions (6-31G*, 6-31+G*, cc-pVDZ, aug-cc-pVDZ and Sadlej's polarizability basis set) were investigated aiming to evaluate the performance of the 6-31G* set for numerical convergence and computational cost in relation to the larger basis sets. All basis sets reproduce the main spectroscopic features of the Raman spectrum of this anion for the excitation interval investigated. The 6-31G* basis set presented, on average, the same accuracy of numerical results as the larger sets but at a fraction of the computational cost showing that it is suitable for the theoretical investigation of the squarate dianion and its complexes and derivatives.O perfil de excitação Raman do anion esquarato, C4O4-2 , foi calculado por métodos ab initio no nível de teoria Hartree-Fock utilizando a Teoria de Resposta Linear (TRL) para seis frequências de excitação: 632,5, 514,5, 488,0, 457,9, 363,8 e 337,1 nm. Um total de cinco conjuntos de funções de base (6-31G*, 6-31+G*, cc-pVDZ, aug-cc-pVDZ e bases de Sadlej) foi investigado visando comparar o desempenho da base 6-31G*, em termos de convergência numérica dos resultados e custo computacional, com os dos demais conjuntos de base. Todos os conjuntos de base testados reproduzem as principais características do espectro Raman do anion esquarato no intervalo de excitação estudado. A base 6-31G* apresentou, em média, o mesmo desempenho nos resultados numéricos dos conjuntos de base maiores mas a uma fração do custo computacional mostrando-se apropriada para o estudo teórico dos derivados e complexos deste anion.324331Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Mountain waves in two-layer sheared flows: critical-level effects, wave reflection, and drag enhancement

Internal gravity waves generated in two-layer stratified shear flows over mountains are investigated here using linear theory and numerical simulations. The impact on the gravity wave drag of wind profiles with constant unidirectional or directional shear up to a certain height and zero shear above, with and without critical levels, is evaluated. This kind of wind profile, which is more realistic than the constant shear extending indefinitely assumed in many analytical studies, leads to important modifications in the drag behavior due to wave reflection at the shear discontinuity and wave filtering by critical levels. In inviscid, nonrotating, and hydrostatic conditions, linear theory predicts that the drag behaves asymmetrically for backward and forward shear flows. These differences primarily depend on the fraction of wavenumbers that pass through their critical level before they are reflected by the shear discontinuity. If this fraction is large, the drag variation is not too different from that predicted for an unbounded shear layer, while if it is small the differences are marked, with the drag being enhanced by a considerable factor at low Richardson numbers (Ri). The drag may be further enhanced by nonlinear processes, but its qualitative variation for relatively low Ri is essentially unchanged. However, nonlinear processes seem to interact constructively with shear, so that the drag for a noninfinite but relatively high Ri is considerably larger than the drag without any shear at all

Stress Analysis on a “L” shape Truss Optimization

The metal construction market in Brazil has grown significantly over the past few years. The weight reductions and performance increase of mechanical pieces obtained by using optimization techniques are significant to the point that currently its use is critical to define that competitiveness of the metal-mechanical engineering industries, and its undeniable importance in reducing costs. The optimization applied in the mechanical part design consists of using computational methods for dimensions, shape or optimal topology of parts. This study aims to propose a study methodology to analyse the stress distribution thought the use of mathematical software and photoelasticity techniques, to propose a new structural profile, lighter and more efficient, which may be used as solution to overcome the current constructive limitations

Estimation of the friction velocity in stably stratified boundary-layer flows over hills

A method is suggested for the calculation of the friction velocity for stable turbulent boundary-layer flow over hills. The method is tested using a continuous upstream mean velocity profile compatible with the propagation of gravity waves, and is incorporated into the linear model of Hunt, Leibovich and Richards with the modification proposed by Hunt, Richards and Brighton to include the effects of stability, and the reformulated solution of Weng for the near-surface region. Those theoretical results are compared with results from simulations using a non-hydrostatic microscale-mesoscale two-dimensional numerical model, and with field observations for different values of stability. These comparisons show a considerable improvement in the behaviour of the theoretical model when the friction velocity is calculated using the method proposed here, leading to a consistent variation of the boundary-layer structure with stability, and better agreement with observational and numerical data

InSAR Meteorology: High-Resolution Geodetic Data Can Increase Atmospheric Predictability

AbstractThe present study assesses the added value of high‐resolution maps of precipitable water vapor, computed from synthetic aperture radar interferograms , in short‐range atmospheric predictability. A large set of images, in different weather conditions, produced by Sentinel‐1A in a very well monitored region near the Appalachian Mountains, are assimilated by the Weather Research and Forecast (WRF) model. Results covering more than 2 years of operation indicate a consistent improvement of the water vapor predictability up to a range comparable with the transit time of the air mass in the synthetic aperture radar interferograms footprint, an overall improvement in the forecast of different precipitation events, and better representation of the spatial distribution of precipitation. This result highlights the significant potential for increasing short‐range atmospheric predictability from improved high‐resolution precipitable water vapor initial data, which can be obtained from new high‐resolution all‐weather microwave sensors

Infrared sounding of the trade-wind boundary layer: AIRS and the RICO experiment

The new generation of remote sensors on board NASA's A-Train constellation offers the possibility of observing the atmospheric boundary layer in different regimes, with or without clouds. In this study we use data from the Atmospheric InfraRed Sounder (AIRS) and of the Rain In Cumulus over the Ocean (RICO) campaign, to verify the accuracy and precision of the AIRS Version 5 Level 2 support product. This AIRS product has an improved vertical sampling that is necessary for the estimation of boundary layer properties. Good agreement is found between AIRS and RICO data, in a regime of oceanic shallow cumulus that is known to be difficult to analyze with other remote sensing data, and also shows a low sensitivity to cloud or land fraction. This suggests that AIRS data may be used for global boundary layer studies to support parameterization development in regions of difficult in-situ observation