No abstract

The Pampa‐2016 experimental campaign was performed in a typical Pampa lowland South American region. It consisted of both surface flux measurements (at 3 and 29 m) and a radiosonde launched every 3 h. The resulting meteorological observations allowed for the analysis of turbulent properties associated with both a stable and a convective boundary layer. The combined analysis of the surface data and vertical soundings has revealed some general characteristics of the atmospheric boundary layer for both the nocturnal stable conditions and the daytime convective environment. The continuous surface measurements showed that the nocturnal stable inversion, occurring in calm winds, is basically generated by the radiative cooling mechanism that is established after the late afternoon transition. The analysis of night‐time surface data also showed that, under stable conditions in the case of vanishing wind speed, the friction velocity has unrealistic values that are very close to zero. This situation is undesirable for numerical models that generally use this quantity as a lower boundary condition. The analysis of night‐time temperature profiles revealed two contrasting patterns in agreement with the classical classification of radiative night (a very stable boundary layer) and a turbulent night (a weakly stable boundary layer). In contrast, the analysis of the daytime temperature profiles provided an estimation of the convective time scale that is of the order of 10 min, in agreement with experimental values. A spectral analysis and the consequent estimation of the spectral peaks under unstable and stable conditions were in agreement with literature values.

This paper presents a development and validation of a 3D numerical model for the advection-diffusion equation. Atmospheric flow field generated by mesoscale circulation model is used as input for the wind speed. As the mesoscale model gives information at scale higher than the necessary for description of a plume trajectory a weighted linear average proper interpolation was developed for intermediate these distances. Diffusion coefficients are variables in time and space and are different for lateral and vertical directions. This assumption is important and considers that the turbulence is not isotropic. Numerical scheme is explicit and conservative and has small implicit diffusion in the advection part of the model. Boundary conditions are open at lateral domain and normal in the bottom and at the top of the Planetary Boundary Layer (PBL) height. Output of the model can be viewed at any time step as well as the concentration distributions are showed at horizontal or vertical surfaces. For validation of the model two experiments were carried out near a thermoelectric power plant located in the south of Brazil. Each experiment was forty days longer. Hourly SO 2 concentrations were collected in four receptors around the power plant. During the experiments micrometeorological measurements and tethered balloons were also used in order to describe properly the local atmospheric circulation and PBL characteristics. Various static indices indicate that the model works very well at least for the source and the terrain were it is located, i.e. continuous emission and homogeneous topography.

No abstract

Paddy fields are significant anthropogenic sources of methane (CH4) emissions. In southern Brazil, rice is grown in lowland flooded areas once a year, followed by a long fallow period. This study aimed to measure CH4 fluxes in a rice paddy field in southern Brazil during the rice-growing season of 2015/2016 and the following fallow period. The fluxes were estimated using the eddy covariance (EC) technique and soil chamber (SC). Diurnal and seasonal variations of CH4 fluxes and potential meteorological drivers were analyzed. The CH4 fluxes showed distinct diurnal variations in each analyzed subperiod (vegetative, reproductive, pre-harvest, no rice, and land preparation), characterized by a single-peak diurnal pattern. The variables that most influenced methane emissions were air and surface temperatures. In the growing season, the rice vegetative stage was responsible for most of the measured emissions. The accumulated annual emission estimated was 44.88 g CH4 m−2 y−1, being 64% (28.50 g CH4 m−2) due to the rice-growing season and 36% (16.38 g CH4 m−2) due to the fallow period. These results show the importance of including fallow periods in strategies to mitigate methane emissions in flood irrigated rice-growing areas.

A partir de dados observacionais de temperatura do solo e do ar, é obtida uma equação para descrever a temperatura do solo a 5 cm de profundidade em função da temperatura do ar para uma região de cultivo de arroz irrigado. A região do estudo apresenta períodos de alagamento. A equação obtida descreve de forma satisfatório os períodos secos. PALAVRAS-CHAVE: temperatura do solo, temperatura do ar.

RESUMONeste trabalho, realiza-se a análise da eficiência da utilização da luz pela cultura do milho cultivado com plantio direto e preparo convencional. Relacionou-se a produção primaria bruta obtida pelo método de covariância de vórtices turbulentos, com a radiação fotossinteticamente ativa absorvida pelo dossel das plantas de milho, obtendo-se a eficiência da utilização da luz. A análise mostrou que há uma boa correlação entre a produção primária bruta e a radiação fotossinteticamente ativa absorvida para ambos os sistemas de plantio da cultura do milho. O plantio direto mostrou-se mais eficiente na utilização da luz para a produção primária bruta. ABSTRACTIn this work we analyzed the efficiency of light utilization by corn grown under no-tillage and conventional tillage. Related to gross primary production obtained by the method of eddy covariance, with photosynthetically active radiation absorbed by the canopy of corn plants, resulting in the efficient use of light. The analysis showed that there is a good correlation between gross primary production and photosynthetic active radiation absorbed for both tillage systems of corn. The tillage was more efficient in the use of light for gross primary production. INTRODUÇÃOO conceito de eficiência na utilização de luz (LUE) é a base subjacente para estimar a troca de carbono em muitos modelos de ecossistema, especialmente os modelos que utilizam o sensoriamento remoto para restringir as estimativas de fotossíntese do dossel (JENKINS, 2007). O entendimento da eficiência na utilização de luz pela vegetação para a produção primária bruta (GPP) é de interesse para aplicação de dados de satélite para monitorar a GPP e a troca líquida de carbono a nível regional para escalas globais (TURNER,2003). O objetivo é avaliar a eficiência de utilização da luz pela cultura do milho em dois diferentes sistemas de preparo do solo.

In the last 15-20 years has greatly increased research on the problem of climate change, necessitating a demand for reliable measurements of absorption and emission of carbon dioxide, methane, as well as the impact on water resources. In the biome Pampa are the largest continuous natural field extensions, requiring a monitoring of water and temperature regime on the ground. The water content of the soil has spatial and temporal variability affecting many hydrological processes and determining this is needed since the soil store and provide the water and nutrients for the plants, thus involving relationships water-soil-plant-atmosphere. In this work, we compared the water content behavior of the soil at depths of 10, 30 and 50 cm, the temperature of the soil at depths of 5, 15 and 30 cm, heat flux in soil installed 10 cm deep and the thermal conductivity was determined in two experimental sites in the Pampa biome, for the period 01.01.2015 to 06.31.2015. It was found that there are differences between the sites in the capacity to retain moisture in the soil and in the ability to store energy in the soil for the study period.