INCLUSION OF A TURBULENCE PARAMETERISATION IN A DIAGNOSTIC MASS CONSISTENT MODEL DRIVEN BY A PROGNOSTIC MODEL

Diagnostic atmospheric mass-consistent models generally are used together with turbulence parameterisations defined for flat terrain, thus in principle not able to catch the variability of the turbulence field induced by the presence of complex terrain and inhomogeneous conditions. The possibility of using prognostic turbulence fields produced accounting for the topography is then an appealing approach in inhomogeneous conditions. In this work we test an interpolation procedure applied to the turbulence fields output by a regional atmospheric model to calculate high-resolution fields, which are then coupled with the mean flow produced by a mass-consistent model. We apply this methodology to the RAMS model, using different turbulence closures, and we evaluate the feasibility of using interpolating modules paired up to MINERVE mass-consistent model

Simulação da dispersão de poluentes na camada limite planetária utilizando um sistema de modelos

The meteorological model RAMS and the Lagrangian particle model SPRAY are coupled to simulate the transport and diffusion of tracer released during the project TRACT, realized in the Rhine valley, Central Europe. The simulation results generated by the model system are evaluated against observational data measured in the TRACT experiments. Analysis of the results and the application of statistical indices show that the considered models reproduce well the general behaviour of the contaminant plume, the temporal and spatial distribution of the concentration and the location of the concentration maxima.O modelo meteorológico RAMS e o modelo de partículas Lagrangeano SPRAY são acoplados para simular o transporte e a difusão de um poluente emitido durante o experimento TRACT, realizado no vale do Reno, na Europa Central. Os resultados das simulações geradas pelo sistema de modelos são avaliados contra dados observacionais medidos durante o experimento TRACT. Análises dos resultados e a aplicação de índices estatísticos mostram que os modelos considerados reproduzem bem o comportamento geral da pluma do poluente, a distribuição temporal e espacial da concentração e a localização do máximo de concentração

Decaimento da turbulência convectiva: uma estimativa do coeficiente de difusão turbulento na camada residual

In this work is presented a model that describes the decay of the convective turbulent kinetic energy and that estimates the turbulent diffusion coefficient in the Residual Layer. The dynamic equation for energy spectrum function is obtained from Navier-Stokes equation. The terms that describe the inertial transfer of energy, the production or destruction of energy for thermal effect and the molecular dissipation are considered. The inertial transfer of energy is calculated from the Taylor’s statistical diffusion theory. The Heisenberg’s theory that is based on the concept of a kinematic turbulence viscosity to describe the inertial transfer of energy from the big to the small eddies is used. The term that describes the production or destruction of kinetic energy for thermal effect is obtained from the convective similarity theory considering the Pao’s hypothesis. This hypothesis supposes that energy is extracted of the medium flow in a continuous way, allowing do not explicit a scale of time characteristic. The dynamic equations that describe the turbulent flow are only valid in the three-dimensional space. For this reason it was obtained one spectrum 3-D for convective layer from a model proposed by Kristensen, and of a model for the one-dimensional spectra calculated by Degrazia. The turbulent diffusion coefficient is obtained from the Taylor’s statistical and the similarity convective theories. The results obtained in this work are compared with the LES modelNeste trabalho é apresentado um modelo que descreve o decaimento da energia cinética turbulenta convectiva e estima o coeficiente de difusão turbulento na Camada Residual. A equação dinâmica para a função espectro de energia é obtida da forma clássica a partir da equação de Navier-Stokes. São considerados os termos que descrevem a transferência inercial de energia, a produção ou destruição de energia por efeito térmico e a dissipação molecular. A transferência inercial de energia é parametrizada a partir da teoria estatística de Taylor. Emprega-se a teoria de Heisenberg baseada no conceito de uma viscosidade cinemática turbulenta para descrever a transferência inercial de energia dos grandes para os pequenos turbilhões. O termo que descreve a produção ou destruição de energia cinética por efeito térmico é parametrizado a partir da teoria de similaridade convectiva considerando-se a hipótese de Pao, a qual supõe que a energia é extraída do fluxo médio de forma contínua, o que permite não explicitar uma escala de tempo característica. Pelo fato das equações dinâmicas que descrevem o fluxo turbulento serem válidas somente no espaço tridimensional, foi obtido um espectro 3-D da Camada Convectiva a partir de um modelo proposto por Kristensen, e do modelo para os espectros unidimensionais obtido por Degrazia. O coeficiente de difusão turbulento é determinado a partir da teoria estatística de Taylor e teoria de similaridade convectiva. Os resultados obtidos neste trabalho são comparados com o modelo de LES

Large-eddy Simulation in Low Wind Conditions

Os resultados preliminares de uma simulação dos grandes turbilhões (LES) em uma camada limite convectiva com vento fraco são apresentados. Uma simulação LES foi realizada incluindo, na superfície, a teoria de similaridade de Monin-Obukhov e a teoria de convecção natural. Os resultados foram comparados com radiossondagens e observações superficiais realizadas no CNR (Italian National Research Council) de Torino (em 22 de setembro de 2007), Itália. O modelo LES mostrou-se capaz de descrever uma condição atmosférica de baixa velocidade do vento

Proposal of a new autocorrelation function in low wind speed conditions

Abstract In this study a new mathematical expression to describe the observed meandering autocorrelation functions in low-wind speed is proposed. The analysis utilizes a large number of best fit curves to show that the proposed theoretical function well reproduces the general form and the negative lobes characterizing the experimental meandering autocorrelation function. Further, the good agreement of the measured autocorrelation curves with the proposed algebraic autocorrelation function allows to calculate the magnitudes of the meandering period and of the loop parameter. The results agree with the values presented and discussed in the literature. Therefore, the new formulation describing experimental meandering autocorrelation functions can be used to simulate the dispersion of contaminant during low wind episodes and to determine relevant meandering parameters

Estimando a Magnitude do Parâmetro de Looping do Meandro do Vento Horizontal

The looping parameter m is the main value to characterize the meandering phenomenon. This parameter is relationship with negative lobes in the observed autocorrelation function generated from components of horizontal speed. In this work, we present a study comparing the mean values of the looping parameter between 2 diverse sites in the Brazilian sector.A magnitude do parâmetro de looping m é o principal critério utilizado para caracterizar o meandro do vento do horizontal. Este parâmetro está associado à magnitude do lóbulo negativo da função de autocorrelação experimental das componentes horizontais da velocidade. Neste trabalho apresenta-se um estudo dos valores médios do parâmetro de looping m do meandro do vento horizontal utilizando dados de 2 sítios situados em diferentes latitudes

Trend of Ozone in the Free Troposphere above Europe

Ozone observation were made one century ago by the Schoenbein technique at meteorological observatories in the alpine region.Within the intrinsic limitations of the technique,historical readings have been converted to present-time concentrations(ppbv). The evalueted ozone level in the free trposphere(17 ppbv) was twice as large as at the surface;comparable values were obtained by chemical and spectroscopic techniques in the first half of our century.Furthermore,the reconstrued ozone trend in the free troposphere shows a sharp increase after the '50s,as already observed at the surface at mid-latitudes of the northern hemisphere.JRC.(EI)-Environment Institut

Interaction of Submeso Motions in the Antarctic Stable Boundary Layer

Submesomotions add complexities to the structure of the stable boundary layer. Such motions include horizontal meandering and gravity waves, in particular when the large-scale flow is weak. The coexistence and interaction of such submeso motions is investigated through the analysis of data collected in Antarctica, in persistent conditions of strong atmospheric stratification. Detected horizontal meandering is frequently associated with temperature oscillations characterized by similar time scales (30 min) at all levels (2, 4.5 and 10 m). In contrast, dirty gravity waves superimposed on horizontal meandering are detected only at the highest level, characterized by time scales of a few minutes. The meandering produces an energy peak in the low-frequency spectral range, well fitted by a spectral model previously proposed for low wind speeds. The coexistence of horizontal and vertical oscillations is observed in the presence of large wind-direction shifts superimposed on the gradual flow meandering. Such shifts are often related to the variation of the mean flow dynamics, but also to intermittent events, localized in time, which do not produce a variation in the mean wind direction and that are associated with sharp decreases in wind speed and temperature. The noisy gravity waves coexisting with horizontal meandering persist only for a few cycles and produce bursts of turbulentmixing close to the ground, affecting the exchange processes between the surface and the stable boundary layer. The results confirm the importance of sharp wind-direction changes at lowwind speed in the stable atmosphere and suggest a possible correlation between observed gravity waves and dynamical instabilities modulated by horizontal meandering

Entropic Approach for Emission Rate Estimation of Area Pollutant Sources

Abstract The estimat ion of the area source pollutant strength is a relevant issue for atmospheric environ ment. Th is characterizes an inverse problem in the atmospheric pollution dispersion. In the inverse analysis, an area source domain is considered, where the strength of such area source term is assumed unknown. The inverse problem is formu lated as a non-linear optimization approach, whose objective function is given by the square difference between the measured pollutant concentration and the mathematical models, associated with a regularization operator. The forward problem is addressed by a source-receptor scheme, where a regressive Lagrangian model is applied to co mpute the transition matrix. A quasi-Newton method is emp loyed for minimizing the object ive function. The second order maximu m entropy regularizat ion is used, and the regularizat ion parameter is calculated by the L-curve technique. This inverse problem methodology is tested with synthetic observational data, producing good inverse solutions