Atmospheric downward longwave radiation flux (L↓) is a variable that directly influences the surface net radiation and consequently, weather and climatic conditions. Measurements of L↓ are scarce, and the use of classical models depending on some atmospheric variables may be an alternative. In this paper, we analyzed L↓ measured over the Brazilian Pampa biome. This region is located in a humid subtropical climate zone and characterized by well defined seasons and well distributed precipitation. Furthermore, we evaluated the performance of the eleven classical L↓ models for clear sky with one-year experimental data collected in the Santa Maria experimental site (SMA) over native vegetation and high relative humidity throughout the year. Most of the L↓ estimations, using the original coefficients, underestimated the experimental data. We performed the local calibration of the L↓ equations coefficients over an annual period and separated them into different sky cover classifications: clear sky, partly cloudy sky, and cloudy sky. The calibrations decreased the errors, especially in cloudy sky classification. We also proposed the joint calibration between the clear sky emissivity equations and cloud sky correction function to reduce errors and evaluate different sky classifications. The results found after these calibrations presented better statistical indexes. Additionally, we presented a new empirical model to estimate L↓ based on multiple regression analysis using water vapor pressure and air temperature. The new equation well represents partial and cloudy sky, even without including the cloud cover parameterization, and was validated with the following five years in SMA and two years in the Cachoeira do Sul experimental site (CAS). The new equation proposed herein presents a root mean square error ranging from 13 to 21 Wm⁻² and correlation coefficient from 0.68 to 0.83 for different sky cover classifications. Therefore, we recommend using the novel equation to calculate L↓ over the Pampa biome under these specific climatic conditions.

Considering the influence of the downslope windstorm called “Vento Norte” (VNOR; Portuguese for “North Wind”) in planetary boundary layer turbulent features, a new set of turbulent parameterizations, which are to be used in atmospheric dispersion models, has been derived. Taylor’s statistical diffusion theory, velocity spectra obtained at four levels (3, 6, 14, and 30 m) in a micrometeorological tower, and the energy-containing eddy scales are used to calculate neutral planetary boundary layer turbulent parameters. Vertical profile formulations of the wind velocity variances and Lagrangian decorrelation time scales are proposed, and to validate this new parameterization, it is applied in a Lagrangian Stochastic Particle Dispersion Model to simulate the Prairie Grass concentration experiments. The simulated concentration results were shown to agree with those observed.

Neste trabalho investiga-se a camada limite atmosférica marinha diurna empregando a simulação dos grandes turbilhões (LES) e observações atmosféricas do Ligurian Air-Sea Interaction Experiment (LASIE). O código LES utilizado neste trabalho foi modificado para descrever a evolução da camada limite sobe o mar. Os resultados da análise mostram que o modelo LES realístico é adequado para simular a camada limite atmosférica marinha.

The objective of this paper was to calibrate and validate the CERES-Rice model in relation to the productivity estimate for the cultivar IRGA 424 in Rio Grande do Sul, using only information found in the literature. CERES-Rice is a model that simulates the development and productivity of a cultivar. To achieve this goal, it is necessary to obtain the genetic coefficients of the cultivar through the calibration process. The genetic coefficients describe the behavior of the plant in the soil-plant-atmosphere system. The GENCALC module present in the DSSAT was used for the calibration. After the calibration process with 30% of the assembled experiments, the validation was performed in the others. The results for productivity were considered acceptable, since most of the values were below 15%, only one of the results showed an error of 16,88%. Note that the model did not consider neither phenological stages nor fertilization or water issues in the calibration and validation process.

O presente trabalho tem como objetivo apresentar uma solução analı́tica para a equação de advecção-difusão tridimensional em condições de vento fraco em uma camada limite estável dominada por cisalhamento. O modelo inclui a difusão longitudinal que não pode ser negligenciada sobre condições de vento fraco. A solução da equação de advecção-difusão é obtida aplicando a técnica da transformada integral. Para validar a presente metodologia, dados coletados durante o experimento clássico Prairie Grass foram empregados. Para verificar o desempenho do modelo, neste trabalho foram utilizados coeficientes de difusão com formulação integral e algébrica para parametrizar a turbulência. O perfil do vento é descrito por uma lei de potência e similaridade.