Andréa U. Timm

Energy Partitioning and Evapotranspiration over a Rice Paddy in Southern Brazil

AbstractDuring approximately 80% of its growing season, lowland flooded irrigated rice ecosystems in southern Brazil are kept within a 5–10-cm water layer. These anaerobic conditions have an influence on the partitioning of the energy and water balance components. Furthermore, this cropping system differs substantially from any other upland nonirrigated or irrigated crop ecosystems. In this study, daily, seasonal, and annual dynamics of the energy and water balance components were analyzed over a paddy rice farm in a subtropical location in southern Brazil using eddy covariance measurements. In this region, rice is grown once a year in low wetlands while the ground is kept fallow during the remaining of the year. Results show that the energy budget residual corresponded to up to 20% of the net radiation during the rice-growing season and around 10% for the remainder of the year (fallow). The energy and water balance analysis also showed that because of the high water table in the region, soil was near sat...

Employing a Lagrangian stochastic dispersion model and classical diffusion experiments to evaluate two turbulence parameterization schemes

Considering a Lagrangian stochastic particle dispersion model and diffusion experiments, two turbulence parameterizations have been tested. The parameters obtained from the Taylor turbulence parameterization are derived from observed spectral properties and characteristics of energy containing eddies. Taylor turbulence scheme provides continuous values for the turbulent parameters in the planetary boundary layer. Hanna turbulence parameterization is obtained from theoretical considerations and second–order closure models and it does not provide continuous vertical profiles for the turbulent parameters. The predicted values by a Lagrangian diffusion model utilizing Taylor turbulence parameterization and the Hanna turbulence scheme are compared with observed concentration data from diffusion experiments. The use of Taylor turbulence scheme resulted in better results.

Seasonality of soil water exchange in the soybean growing season in southern Brazil

The processes of water transfer in the soil-plant-atmosphere system are strongly affected by soil use and management. Differences in the dynamics of soil water transfer between no-tillage (NT) and conventional tillage (CT) practices during a soybean (Glycine max) growing season in southern Brazil were assessed in this study. All the water balance components were analyzed during the soybean growing season (2009/2010). Rainfall, runoff, soil water storage and hydro-physical soil properties were analyzed under two tillage systems. The land-atmosphere water vapor exchanges, obtained from eddy covariance stations, were analyzed with regard to the soybean agroecosystem. Characterizations of soil water storage were also formulated in the 2006/2007 and 2008/2009 soybean growing seasons under the NT system. During the periods without rain, the soil water content under NT was greater than under CT. The soil superficial layer, more porous under NT, contributed to less runoff during rainy events. Moreover, under NT conditions the water supply was always high, between 0.2 - 0.5 m. The total evapotranspiration in the soybean agroecosystem growing season was 410.8 mm.

ESTUDO DO COMPORTAMENTO DE VARIÁVEIS DE SOLO UTILIZANDO O MODELO NOAH PARA UMA CULTURA DE ARROZ IRRIGADO

This study aims to evaluate the performance of the land surface model Noah by simulating soil data and compare them with observed data in a region with rice in southern Brazil. From the results, it is observed that the Noah model needs adjustments, especially when analyzing the parameter volumetric soil moisture.

DESEMPENHO DO MODELO DE SUPERFÍCIE NOAH PARA SIMULAÇÕES DE SOLO EM UMA REGIÃO COM AGRICULTURA

O objetivo deste estudo e avaliar o desempenho do modelo de superficie Noah atraves da simulacao de dados de solo e compara-los com dados observados em uma regiao com agricultura no sul do Brasil. A partir dos resultados, observou-se que o modelo Noah representa satisfatoriamente as quantidades avaliadas. Porem, necessita de algumas parametrizacoes, uma vez que o Noah simula a temperatura do solo como se a radiacao incidisse diretamente na superficie.

ANÁLISE DA EVAPOTRANSPIRAÇÃO E ÍNDICE DE ÁREA FOLIAR NUMA CULTURA DE SOJA SOB DOIS SISTEMAS DE MANEJO

Neste trabalho sao analisados resultados da evapotranspiracao (ET) e do indice de area foliar (IAF) obtidos durante a estacao de cultivo (2009/2010) para os sistemas de plantio direto (PD) e plantio convencional (PC) no ciclo da cultura da soja, no municipio de Cruz Alta, Rio Grande do Sul (RS).

Meandering Dispersion Model Applied to Air Pollution

Generally in stable conditions, during situations of low wind speed (u ≤ 1− 2ms−1), low-frequency horizontal wind oscillations (meandering) are observed in a nocturnal Planetary Boundary Layer (PBL). The study of lowwind speed conditions is of interest, partly because the simulation of airborne pollutant dispersion in these conditions is rather difficult. In fact, most of the existing regulatory dispersion models become unreliable as u approaches zero, so that their application is generally limited to (u > 2ms−1). The meandering movements are clearly distinct from those associated to a full developed turbulence, which are responsible for the pollutants dispersion in a PBL. Even when the stability reduces the vertical dispersion and the instantaneous plume may be thin, meandering disperses the plume over a rather wide angular sector. As a consequence, any air pollution operational dispersion model to be reliable must take into account the transport effect provocated by the meandering. Transport phenomenon in turbulence, including the diffusion of passive scalars and the dispersion of pollutants in the PBL, are controlled by the advection processes associated with the action of stochastic velocity fluctuations in time and space. As a consequence, a Lagrangian description following the movement of infinitesimal fluid particles, as they are carried by the velocity turbulent fluctuations, is conceptually correct and from practical point of view useful for describing turbulent transport (Yeung, 2002). Lagrangian stochastic particle models are powerful computational tools for the investigation of the atmospheric dispersion process (Rodean, 1996). In these models, the fluid particle displacements are produced by stochastic velocities and the movement evolution of a particle can be considerate a Markov process (Wang, 1945), in which past and future are statistically independent when the present is known. This method is based on Langevin equation, which is derived from the hypothesis that the velocity is given by the combination between a deterministic and a stochastic term (Chandrasekhar, 1943). Each fluid particle moves taking into account the transport due to the mean wind velocity and the turbulent fluctuations of the wind velocity components. From the spatial distribution of the particles it is possible to determine the pollutant concentrations. The implementation of the Lagrangian stochastic dispersion model in air pollution problems permits to take into account complex situations such as turbulent flows generated above inhomogeneous topo-graphy (different terrains) (Carvalho et al., 2002), in non-stationary situations associated with the evolutionary transition 4

ESTUDO DO BALANÇO DE ÁGUA PARA O CULTIVO DE SOJA SOB DOIS SISTEMAS DE PLANTIO

1. Introdução O desenvolvimento de novas tecnologias e de técnicas de manejo do solo possibilitaram a expansão da área de cultivo da soja (Glycine max (L.) Merril), nas últimas décadas no Brasil. As mudanças nas formas dos manejos alteram as propriedades físicas e hídricas do solo, sendo que a disponibilidade hídrica é a maior causa de variabilidade dos rendimentos de grãos observados a cada ano nas diversas regiões produtoras brasileiras. Também é o principal fator limitante à obtenção de rendimentos próximos ao potencial produtivo da espécie (Farias, 2004). Com isso o conhecimento do balanço de água de uma área plantada é importante para a avaliação da disponibilidade hídrica.

Difusão de contaminantes em condições de vento fraco empregando um modelo estocástico Lagrangeano

A Lagrangian stochastic particle model is utilized to simulate the dispersion and the transport of contaminants under low wind stable conditions in the tracer experiment carried in the Idaho National Engineering Laboratory (INEL). In this work a new parameterization for the parameters representing the frequencies associated to the meandering phenomenon is tested. The new parameterization is expressed in terms of a non-dimensional quantity that controls the frequencies of the meandering oscillation and of the time scale associated to a coherent structure in a fully developed turbulence. The simulations show that the considered Lagrangian model, incorporating this new parameterization, reproduces correctly the diffusion of passive scalars in a low wind speed stable atmospheric boundary layer.

ESTIMATIVA DOS FLUXOS SUPERFICIAIS DE ENERGIA UTILIZANDO O MODELO DE SUPERFÍCIE NOAH

This study aims to compare the surface flows of energy (sensibleheat and latent) obtained from Candiota07 micrometeorologicalexperiment with the results estimated by the Noah surface model.According to the results, the Noah surface model presents a goodagreement with observed data, except for the flow of latent heat duringthe night.