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Surface ecophysiological behavior across vegetation and moisture gradients in tropical South America

Baker, I.T.; Harper, A.B.; Rocha, Humberto Ribeiro da; Denning, A.S.; Araújo, A.C.; Borma, L.S.; Goulden, M.L.; Manzi, A.O.; Miller, S.D.; Nobre, A.D.; Restrepo-Coupe, N.; Saleska, S.R.; Stöckli, R.; Randow, C. von; Wofsy, S.C.; Freitas, H. C.
Fonte: Amsterdam Publicador: Amsterdam
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.48%
Surface ecophysiology at five sites in tropical South America across vegetation and moisture gradients is investigated. From the moist northwest (Manaus) to the relatively dry southeast (Pé de Gigante, state of São Paulo) simulated seasonal cycles of latent and sensible heat, and carbon flux produced with the Simple Biosphere Model (SiB3) are confronted with observational data. In the northwest, abundant moisture is available, suggesting that the ecosystem is light-limited. In these wettest regions, Bowen ratio is consistently low, with little or no annual cycle. Carbon flux shows little or no annual cycle as well; efflux and uptake are determined by high-frequency variability in light and moisture availability. Moving downgradient in annual precipitation amount, dry season length is more clearly defined. In these regions, a dry season sink of carbon is observed and simulated. This sink is the result of the combination of increased photosynthetic production due to higher light levels, and decreased respiratory efflux due to soil drying. The differential response time of photosynthetic and respiratory processes produce observed annual cycles of net carbon flux. In drier regions, moisture and carbon fluxes are in-phase; there is carbon uptake during seasonal rains and efflux during the dry season. At the driest site...

A influência da umidade do substrato no desempenho de revestimentos de piso de edifícios. ; The influence of substrate moisture on performance of floor coatings of buildings.

Lopes, Elizabeth Montefusco
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 05/12/2003 Português
Relevância na Pesquisa
36.33%
Sobre opiso desenvolvem-se todas as atividades a que se destina a edificação. Falhas Em sua execução, tais como, empenamentos, placas soltas, bolhas e manchas têm como conseqüências, desde o desconforto pessoal de andar em uma superfícieirregular, ao risco de acidentes de trabalho, contaminação de produtos por poeira, de salinhamento de equipamentos ou até mesmo a interferência no processo de produção, podendo provocar a paralisação parcial ou total da atividade produtiva da empresa.Tais problemas, muitas vezes são decorrentes do excesso de umidade do substrato de concreto, quando da aplicação do revestimento, por não ter tido o tempo de secagem adequado, de maneira a atingir o nível de umidade ideal. O excesso de água residual decorrente da umidade do substrato é uma das principais causas geradoras de patologias nos pisos de concreto quando utilizados revestimentos suscetíveis à presença de água. O comportamento da umidade do concreto é resultado de uma complexa ação entre a quantidade de água física e quimicamente ligada, durante a hidratação do cimento e a capacidade de transporte de água do sistema de poros do concreto. Neste contexto, o presente trabalho procura contribuir na sistematização do conhecimento sobre o assunto...

Fluxo do CO2 proveniente da respiração do solo em áreas de floresta nativa da Amazônia; CO2 flux from soil respiration in areas of native Amazon forest

Dias, Jadson Dezincourt
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 29/08/2006 Português
Relevância na Pesquisa
36.1%
O sistema climático global e o ciclo do carbono interagem intensamente, e o CO2 constitui um fator dominante na definição do clima, sendo gerado e consumido pelas plantas e pela atividade de microrganismos em ecossistemas aquáticos, terrestres e na atmosfera. Na atmosfera, esse gás contribui para o efeito estufa. Em um ecossistema de floresta tropical, grande parte da produção de CO2 é proveniente da respiração do solo, e os fluxos de CO2 na interface solo-atmosfera dependem de mudanças nas características físicas, químicas e biológicas na superfície do solo. O objetivo desse estudo foi investigar a variabilidade sazonal dos fluxos de CO2, decorrente da respiração do solo de diferentes florestas nativas da Amazônia, localizadas nos municípios de Sinop (MT), Caxiuanã (PA), Manaus (AM) e Santarém (PA), e determinar os principais parâmetros de correlação dos fluxos de CO2 do solo com a temperatura e umidade. As amostragens foram realizadas durante as estações seca e chuvosa em cada local. Os fluxos de CO2 foram medidos por meio de câmaras dinâmicas, que se baseiam na variação da concentração do gás no interior da câmara em função do tempo e foram calculados utilizando-se de equações lineares. Os valores médios encontrados para as regiões estudadas nas estações seca e chuvosa foram respectivamente: Sinop...

Evolução dos eventos El Niños em fases distintas da Oscilação Decadal do Pacífico: impactos no Jato de Baixos Níveis a leste dos Andes e nos ciclones extratropicais da América do Sul; El Niño events and their evolution in different phases of the Pacific Decadal Oscillation: impacts on the Low Level Jet east of the Andes and extratropical cyclones on the South America.

Silva, Gyrlene Aparecida Mendes da
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 11/08/2009 Português
Relevância na Pesquisa
46.48%
Neste trabalho foi investigado o impacto da evolução dos eventos El Niño (EN) de acordo com as fases distintas da Oscilação Decadal do Pacífico (positiva, ODP(+) e negativa, ODP(-)) nas mudanças no transporte de umidade sobre o Sudeste da América do Sul (SEAS) durante o verão austral de 1950-1999. A resposta da variabilidade do Jato de Baixos Níveis a leste do Andes (JBN) e de algumas propriedades dos ciclones extratropicais sobre o cone sul do continente as modificações na circulação associadas aos eventos mencionados acima foi analisada. Foi mostrado que existem poucas mudanças significativas no regime de precipitação sobre a América do Sul ao se considerar a influência dos anos neutros do Pacífico Equatorial durante a ODP(+) quando comparado com os anos da ODP(- ). Entretanto, os eventos EN da ODP(+) indicam diferenças no padrão de anômalo de ondas em altos níveis em resposta as diferentes anomalias de Temperatura de Superfície do Mar (TSM) dos oceanos Pacífico e Atlântico Equatorial quando comparado com os eventos da ODP(-). Como conseqüência foram observadas anomalias positivas de precipitação no SEAS associadas à intensificação do fluxo convergente de umidade em baixos níveis oriundo do Atlântico Equatorial e região Amazônica para esta região durante os eventos EN da ODP(+). Todavia...

Estimation of soil moisture in the root-zone from remote sensing data

Bezerra,Bergson Guedes; Santos,Carlos Antonio Costa dos; Silva,Bernardo Barbosa da; Perez-Marin,Aldrin Martin; Bezerra,Marcus Vinícius Cândido; Bezerra,José Renato Cortez; Rao,Tantravahi Venkata Ramana
Fonte: Sociedade Brasileira de Ciência do Solo Publicador: Sociedade Brasileira de Ciência do Solo
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2013 Português
Relevância na Pesquisa
36.26%
Field-based soil moisture measurements are cumbersome. Thus, remote sensing techniques are needed because allows field and landscape-scale mapping of soil moisture depth-averaged through the root zone of existing vegetation. The objective of the study was to evaluate the accuracy of an empirical relationship to calculate soil moisture from remote sensing data of irrigated soils of the Apodi Plateau, in the Brazilian semiarid region. The empirical relationship had previously been tested for irrigated soils in Mexico, Egypt, and Pakistan, with promising results. In this study, the relationship was evaluated from experimental data collected from a cotton field. The experiment was carried out in an area of 5 ha with irrigated cotton. The energy balance and evaporative fraction (Λ) were measured by the Bowen ratio method. Soil moisture (θ) data were collected using a PR2 - Profile Probe (Delta-T Devices Ltd). The empirical relationship was tested using experimentally collected Λ and θ values and was applied using the Λ values obtained from the Surface Energy Balance Algorithm for Land (SEBAL) and three TM - Landsat 5 images. There was a close correlation between measured and estimated θ values (p<0.05, R² = 0.84) and there were no significant differences according to the Student t-test (p<0.01). The statistical analyses showed that the empirical relationship can be applied to estimate the root-zone soil moisture of irrigated soils...

Thermohaline circulation stability : a box model

Lucarini, Valerio
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 97 leaves; 3949967 bytes; 3949774 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
26.44%
A thorough analysis of the stability of uncoupled and coupled versions of an inter-hemispheric 3-box model of Thermohaline Circulation (THC) is presented. The model consists of a northern high latitudes box, a tropical box, and a southern high latitudes box, which respectively can be thought as corresponding to the northern, tropical and southern Atlantic ocean. We study how the strength of THC changes when the system undergoes forcings that are analogous to those of global warming conditions. In each class of experiments, we determine, using suitably defined metrics, the boundary dividing the set of forcing scenarios that lead the system to equilibria characterized by a THC pattern similar to the present one, from those that drive the system to equilibria where the THC is reversed. In the case of the uncoupled model, we apply to the equilibrium state perturbations to the moisture and heat fluxes into the three boxes. High rates of increase in the moisture flux into the northern high-latitude box lead to a THC breakdown at smaller total final increases in the moisture flux than low rates, while the presence of moisture flux increases into the southern high-latitude box strongly inhibit the breakdown and can prevent it, in the case of slow rates in the Northern Hemisphere. Similarly...

Surface ecophysiological behavior across vegetation and moisture gradients in tropical South America.

BAKER, I. T.; HARPER, A. B.; ROCHA, H. R. da; DENNING, A. S.; ARAUJO, A. C.; BORMA, L. S.; FREITAS, H. C.; GOULDE, M. L.; MANZI, A. O.; MILLER, S. D.; NOBRE, A. D.; RESTREPO-COUPE, N.; SALESKA, S. R.; STÖCKLI, R.; RANDOW, C. von; WOFSY, S. C.
Fonte: Agricultural and Forest Meteorology, v. 182-183, p. 177-188, Dec. 2013. Publicador: Agricultural and Forest Meteorology, v. 182-183, p. 177-188, Dec. 2013.
Tipo: Artigo em periódico indexado (ALICE)
Português
Relevância na Pesquisa
26.48%
Surface ecophysiology at five sites in tropical South America across vegetation and moisture gradients is investigated. From the moist northwest (Manaus) to the relatively dry southeast (Pé de Gigante, state of São Paulo) simulated seasonal cycles of latent and sensible heat, and carbon flux produced with the Simple Biosphere Model (SiB3) are confronted with observational data. In the northwest, abundant moisture is available, suggesting that the ecosystem is light-limited. In these wettest regions, Bowen ratio is consistently low, with little or no annual cycle. Carbon flux shows little or no annual cycle as well; efflux and uptake are determined by high-frequency variability in light and moisture availability. Moving downgradient in annual precipitation amount, dry season length is more clearly defined. In these regions, a dry season sink of carbon is observed and simulated. This sink is the result of the combination of increased photosynthetic production due to higher light levels, and decreased respiratory efflux due to soil drying. The differential response time of photosynthetic and respiratory processes produce observed annual cycles of net carbon flux. In drier regions, moisture and carbon fluxes are in-phase; there is carbon uptake during seasonal rains and efflux during the dry season. At the driest site...

A Bayesian analysis of sensible heat flux estimation: quantifying uncertainty in meteorological forcing to improve model prediction

Ershadi, A.; McCabe, M.; Evans, J.; Mariethoz, G.; Kavetski, D.
Fonte: American Geophysical Union Publicador: American Geophysical Union
Tipo: Artigo de Revista Científica
Publicado em //2013 Português
Relevância na Pesquisa
36.15%
The influence of uncertainty in land surface temperature, air temperature, and wind speed on the estimation of sensible heat flux is analyzed using a Bayesian inference technique applied to the Surface Energy Balance System (SEBS) model. The Bayesian approach allows for an explicit quantification of the uncertainties in input variables: a source of error generally ignored in surface heat flux estimation. An application using field measurements from the Soil Moisture Experiment 2002 is presented. The spatial variability of selected input meteorological variables in a multitower site is used to formulate the prior estimates for the sampling uncertainties, and the likelihood function is formulated assuming Gaussian errors in the SEBS model. Land surface temperature, air temperature, and wind speed were estimated by sampling their posterior distribution using a Markov chain Monte Carlo algorithm. Results verify that Bayesian-inferred air temperature and wind speed were generally consistent with those observed at the towers, suggesting that local observations of these variables were spatially representative. Uncertainties in the land surface temperature appear to have the strongest effect on the estimated sensible heat flux, with Bayesian-inferred values differing by up to ±5°C from the observed data. These differences suggest that the footprint of the in situ measured land surface temperature is not representative of the larger-scale variability. As such...

A moisture transport and precipitation parameterization for energy balance climate models

Chu, Shaoping
Fonte: Universidade Rice Publicador: Universidade Rice
Português
Relevância na Pesquisa
36.26%
The spatial distribution of water in all its three phases is an important factor in determining the climate. The interactions among temperature, water vapor, infrared emission and solar radiation form a series of feedback mechanisms, which play a very important role in the climate system. In order to trace moisture flow through the climate system and examine its impact on climate, a parameterization for the computation of moisture transport and precipitation is developed, one that will eventually be incorporated into a coupled energy balance climate-thermodynamic sea ice model (the CCSI model). This parameterization is tested by comparing computed energy transports and precipitation rates with available observations and by evaluating its sensitivity to variations in the values of specified parameters. The results of these studies indicate that the moisture parameterization is somewhat sensitive to variations in wind speed, surface air temperature and moisture flux, while it is relatively insensitive to changes in relative humidity. In general this parameterization does a good job in simulating the seasonal cycle and latitudinal distribution of the wind speed, moisture transport and precipitation when compared to the observed data and general circulation model (GCM) results.

Matéria orgânica, fluxo de CO2 e índice Q10 em dois latossolos com texturas contrastantes sob diferentes usos no cerrado; Organic matter, CO2 flux and Q10 index in two Typic acrustox with contrastant soil textures under different uses at savanna

Vinhal-Freitas, Isabel Cristina
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
36.23%
A introdução de sistemas agrícolas no Cerrado, com o uso intensivo do solo causa impactos nos atributos químicos, físicos e biológicos do solo, acarretando rápida degradação e desbalanço nos processos biológicos e ciclagem de nutrientes. A textura do solo e a sazonalidade também interferem nesses processos. Os objetivos deste trabalho foram determinar as alterações causadas no metabolismo do solo em agroecossistemas sobre Latossolos de diferentes texturas, avaliar os efeitos da sazonalidade na atividade microbiana e no fluxo de CO2 com a aplicação de modelos, e avaliar a sensibilidade da respiração do solo em função do aumento da temperatura. A fração orgânica, a biomassa microbiana e as enzimas extracelulares (β-glicosidase, urease, fosfatase ácida e FDA) foram avaliadas. A respiração do solo, a temperatura do solo e a umidade gravimétrica do solo foram avaliadas em campo quinzenalmente, no ano de 2012. A precipitação pluviométrica e temperatura do ar também foram monitoradas. Bioensaios em laboratório foram realizados para determinação do C-CO2 liberado por incubação estática com temperaturas induzidas de 20, 25 e 30oC. Modelos lineares, quadráticos e exponenciais foram aplicados com o intuito de modelar como o fator umidade do solo e a combinação de umidade e temperatura na emissão de CO2. Para determinação do índice Q10...

Modeling the impact of atmospheric moisture transport on global ice volume

Nisancioglu, Kerim Hestnes, 1975-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 154 leaves; 3334069 bytes; 3376332 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
36.4%
Following Milankovitch's original hypothesis most model studies of changes in global ice volume on orbital time scales have focused on the impact of ablation on ice sheet mass balance. In most cases, poleward moisture flux is fixed and accumulation of snow only depends on local temperature. In this study, a simple coupled atmosphere-ice process model is introduced. An improved representation of the atmospheric hydrological cycle is included, and accumulation is related to the meridional flux of moisture by large scale baroclinic eddies. The ice sheets in the Northern Hemisphere respond to both precession and obliquity frequencies when the model is forced with seasonal insolation. Obliquity variations are introduced by the impact of earth's tilt on the meridional temperature gradient and the poleward flux of moisture, whereas precession governs surface melting by regulating summer temperatures. The response of the ice sheet to obliquity and precession is comparable, and significantly smaller than what is observed in the oxygen isotope record of the late Pliocene and early Pleistocene (2.7 - 0.8 Ma BP). This suggests that in order to successfully reproduce the strong 41 Ka periodicity observed in the record, other mechanisms must be involved such as nonlinear self-sustained...

La influencia del estado del suelo en los procesos asociados a la precipitación en la región del monzón sudamericano

Collini, Estela Angela
Fonte: Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires Publicador: Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires
Tipo: info:eu-repo/semantics/doctoralThesis; tesis doctoral; info:eu-repo/semantics/publishedVersion Formato: application/pdf
Publicado em //2008 Português
Relevância na Pesquisa
36.32%
El tema principal de esta tesis es la investigación de los procesos de realimentación suelo-atmósfera, que tienen lugar dentro del sistema monzónico de Sudamérica. Este estudio utiliza simulaciones con un modelo regional para responder una serie de interrogantes: a) cual es el rol de las condiciones de superficie en el desarrollo del monzón?; b) cuales son las sinergias entre la humedad del suelo y la precipitación?; c) cómo son afectadas las circulaciones regionales como resultado de los efectos de superficie?. Con el modelo regional Eta (Mesinger 1997; Mesinger et al. 1988; Black, 1994), sobre un dominio de integración que cubre toda la América del Sur y parte de América Central, utilizando como campos iniciales y condiciones de contorno los reanálisis del Proyecto de Reanálisis NCAR-NCEP (Kalnay et. al., 1996), se realizaron distintos experimentos de sensibilidad a las condiciones iniciales de superficie. Los resultados de las simulaciones permiten concluir que, aunque las modificaciones en las condiciones de superficie, se imponen en el inicio de las integraciones del modelo, el efecto sobre todas las variables analizadas se observa en todo el periodo de integración. Las simulaciones se realizaron para distintos meses de octubre...

Mechanisms linking plant productivity and water status for a temperate Eucalyptus forest flux site: analysis over wet and dry years with a simple model

Pepper, David A.; McMurtrie, Ross; Medlyn, Belinda E.; Keith, Heather; Eamus, Derek
Fonte: CSIRO Publishing Publicador: CSIRO Publishing
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
36.33%
A simple process-based model was applied to a tall Eucalyptus forest site over consecutive wet and dry years to examine the importance of different mechanisms linking productivity and water availability. Measured soil moisture, gas flux (CO2, H2O) and met

Dependence of hillslope moisture content on downhill saturation

November, L. J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.53%
We derive steady equilibria for lateral downslope moisture flow in an idealized thin closed layer as a solution to the 1D Richards' Equation. The equilibria are determined by two free parameters: the downslope flux and a boundary condition. Solutions exhibit a constant downslope flow speed and moisture content for the constant equilibrium flux, which is the product of the two. However where an isolated zone of fixed saturation degree exists representing a boundary condition, the flow speed immediately upslope is reduced and the moisture content correspondingly increased to preserve the constant equilibrium flux. The capillary head jump at the saturated zone produces a blockage that gives a high moisture content back upslope through a pooling distance determined by the equilibrium condition that the downslope flux is constant. In our numerical integrations, the vertically projected pooling height is more than 10 km for a fully saturated zone in mixed silty or clay soils, but decreases by about an order of magnitude with every 10% decrease in the boundary-zone saturation degree. The drying of downhill saturated zones with the increased speed of mountain moisture outflow and corresponding decreased mountain moisture content gives a viable explanation for the mysterious ~69% unaccounted drop seen in the spring outflow in the La Luz / Fresnal Watershed at Alamogordo's upstream spring-box diversions in the semiarid southeastern New Mexico USA.; Comment: 8 pages...

Can current moisture responses predict soil CO₂ efflux under altered precipitation regimes? A synthesis of manipulation experiments

Vicca, S.; Bahn, M.; Estiarte, Marc; Loon, E. E. van; Vargas, R.; Alberti, G.; Ambus, P; Arain, M. A.; Beier, Claus; Bentley, L. P.; Borken, W.; Buchmann, N.; Collins, S. L.; De Dato, G.; Dukes, Jeffrey S.; Escolar, C.; Fay, P; Guidolotti, G; Hanson, P. J
Fonte: Universidade Autônoma de Barcelona Publicador: Universidade Autônoma de Barcelona
Tipo: Artigo de Revista Científica Formato: application/pdf; application/pdf
Publicado em //2014 Português
Relevância na Pesquisa
36.23%
As a key component of the carbon cycle, soil CO₂ efflux (SCE) is being increasingly studied to improve our mechanistic understanding of this important carbon flux. Predicting ecosystem responses to climate change often depends on extrapolation of current relationships between ecosystem processes and their climatic drivers to conditions not yet experienced by the ecosystem. This raises the question of to what extent these relationships remain unaltered beyond the current climatic window for which observations are available to constrain the relationships. Here, we evaluate whether current responses of SCE to fluctuations in soil temperature and soil water content can be used to predict SCE under altered rainfall patterns. Of the 58 experiments for which we gathered SCE data, 20 were discarded because either too few data were available or inconsistencies precluded their incorporation in the analyses. The 38 remaining experiments were used to test the hypothesis that a model parameterized with data from the control plots (using soil temperature and water content as predictor variables) could adequately predict SCE measured in the manipulated treatment. Only for 7 of these 38 experiments was this hypothesis rejected. Importantly, these were the experiments with the most reliable data sets...

Stochastic Models for the Kinematics of Moisture Transport and Condensation in Homogeneous Turbulent Flows

O'Gorman, Paul A.; Schneider, Tapio
Fonte: American Meteorological Society Publicador: American Meteorological Society
Tipo: Article; PeerReviewed Formato: application/pdf; other; other; other; other; other
Publicado em /11/2006 Português
Relevância na Pesquisa
36.63%
The transport of a condensing passive scalar is studied as a prototype model for the kinematics of moisture transport on isentropic surfaces. Condensation occurs whenever the scalar concentration exceeds a specified local saturation value. Since condensation rates are strongly nonlinear functions of moisture content, the mean moisture flux is generally not diffusive. To relate the mean moisture content, mean condensation rate, and mean moisture flux to statistics of the advecting velocity field, a one-dimensional stochastic model is developed in which the Lagrangian velocities of air parcels are independent Ornstein–Uhlenbeck (Gaussian colored noise) processes. The mean moisture evolution equation for the stochastic model is derived in the Brownian and ballistic limits of small and large Lagrangian velocity correlation time. The evolution equation involves expressions for the mean moisture flux and mean condensation rate that are nonlocal but remarkably simple. In a series of simulations of homogeneous two-dimensional turbulence, the dependence of mean moisture flux and mean condensation rate on mean saturation deficit is shown to be reproducible by the one-dimensional stochastic model, provided eddy length and time scales are taken as given. For nonzero Lagrangian velocity correlation times...

Land-atmosphere Interaction: from Atmospheric Boundary Layer to Soil Moisture Dynamics

Yin, Jun
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2015 Português
Relevância na Pesquisa
36.39%

Accurate modeling of land-atmosphere interaction would help us understand the persistent weather conditions and further contribute to the skill of seasonal climate prediction. In this study, seasonal variations in radiation and precipitation forcing are included in a stochastic soil water balance model to explore the seasonal evolution of soil moisture probabilistic structure. The theoretical results show soil moisture tends to exhibit bimodal behavior only in summer when there are strong positive feedback from soil moisture to subsequent rainfall. Besides the statistical analysis of soil moisture – rainfall feedback, simplified mixed-layer models, coupled with soil-plant-atmosphere continuum, are also used to study heat flux partitioning, cloud initiation, and strength of moist convection. Approximate analytical solutions to the mixed-layer model are derived by applying Penman-Monteith approach, which help explain the roles of equilibrium evaporation and vapor pressure deficit in controlling the diurnal evolution of boundary layer. Results from mixed-layer model also define four regimes for possible convection in terms of cloud/no-cloud formation and low/high convection intensity. Finally, cloud-topped mixed-layer model is developed to simulate the boundary-layer dynamics after the cloud formation...

Sensitivity of the Australian Monsoon to insolation and vegetation: Implications for human impact on continental moisture balance

Miller, Gifford Hubbs; Mangan, Jennifer; Pollard, David; Thompson, Stanley; Felzer, Benjamin; Magee, John
Fonte: Geological Society of America Inc Publicador: Geological Society of America Inc
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
46.19%
General circulation model experiments test the geologically based correlation of high monsoon rainfall over interior Australia with Northern Hemisphere insolation and evaluate the sensitivity of the Australian Monsoon to ecosystem change. Our results suggest that Northern Hemisphere insolation control on the intensity of the Siberian High, rather than summer insolation over the Australian continent, determines the strength of the Australian Monsoon on millennial time scales, unlike a classic monsoon regime. Additional simulations show that the penetration of monsoon moisture into the interior is sensitive to biosphere-atmosphere feedbacks linked to vegetation type and soil properties. This sensitivity offers a resolution to the observed failure of the Australian Monsoon to penetrate the interior in the Holocene. Postulated regular burning practiced by early humans may have converted a tree-shrub-grassland mosaic across the semiarid zone to the modern desert scrub, thereby weakening biospheric feedbacks and resulting in long-term desertification of the continent.

Soil and canopy CO2, 13CO2, H2O and sensible heat flux partitions in a forest canopy inferred from concentration measurements

Styles, Julie; Raupach, Michael R; Farquhar, Graham; Kolle, Olaf; Lawton, Kieran; Brand, W A; Wen, L; Jordan, A; Schulze, Detlef; Shibistova, O; Lloyd, Jonathan
Fonte: Munksgaard International Publishers Publicador: Munksgaard International Publishers
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
36.1%
A canopy scale model is presented that utilises Lagrangian dispersal theory to describe the relationship between source distribution and concentration within the canopy. The present study differs from previous studies in three ways: (1) source/sink distributions are solved simultaneously for CO2, 13CO2, H2O and sensible heat to find a solution consistent with leaf-level constraints imposed by photosynthetic capacity, stomatal and boundary layer conductance, available energy and carbon isotopic discrimination during diffusion and carboxylation; (2) the model is used to solve for parameters controlling the nonlinear source interactions rather than the sources themselves; and (3) this study used plant physiological principles to allow the incorporation of within- and above-canopy measurements of the 13C/12C ratios of CO2 as an additional constraint. Source strengths of CO2, H2O, sensible heat and 13CO2 within a Siberian mixed-coniferous forest were constrained by biochemical and energy-balance principles applied to sun and shaded leaves throughout the canopy. Parameters relating to maximum photosynthetic capacity, stomatal conductance, radiation penetration and turbulence structure were determined by the optimisation procedure to match modelled and measured concentration profiles...

Sensitivity of simulated convection to soil moisture in a region in central Amazon

Mendina,M.; Terra,R.
Fonte: Centro de Ciencias de la Atmósfera, UNAM Publicador: Centro de Ciencias de la Atmósfera, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/07/2012 Português
Relevância na Pesquisa
36.23%
We study the sensitivity of convective precipitation to soil moisture in a continental region in Central Amazon based on Atmospheric General Circulation Model (AGCM) simulations and further analyze the physical processes involved, in particular those related to the diurnal cycle. The region was selected based on the analysis of perpetual January simulations with the University of California at Los Angeles AGCM. It shows a uniform and differentiated behavior in the diurnal cycle of convection, which is strongly associated to surface forcing and in opposite phase to large scale ascending motion. Sensitivity to ground wetness was explored based on a control parameter (which varies between 0 and 1) that multiplies evaporation. Results show that the largest sensitivity appears for relatively dry conditions, confirming previous studies. Although evaporation decreases monotonically as the control parameter is reduced, a slight increase in moisture convergence maintains precipitation almost unchanged up to a value of 0.3 of the parameter. The daily maxima in moisture convergence (excluding the extreme case with no evaporation within the region), convective precipitation, and large scale ascending motion at 500 mb are reached in the simulation with a value of 0.4 of the control parameter. Soil and surface temperature increase with decreasing sensitivity parameter...