Characteristics of precipitation in the Santarém study region.

Abstract ID: 80. Publicado também on-line

Watershed response to rainfall events in the Santarém region.

Abstract ID: 28. Publicado também on-line

Análise do Perfil Vertical de co2 em uma Área de Floresta na Amazônia Central

http://dx.doi.org/10.5902/2179460X16210This study aimed to describe the vertical profile of CO2 concentration during least rainy period and rainy periods of 2006 , into an area of tropical forest in the Central Amazon, Brazil . It were used data of CO2, collected at various heights by a system of measures including an infrared gas analyzer (Licor 7000), in a tower with 40 meters of height. From the data collected it was observed that the concentration of CO2 decreases as one moves from the ground to the top of the canopy. This suggests that the largest source of CO2 is from the soil, due to processes such as respiration and decomposition of plant biomass. When is compared the least rainy and the most rainy periods, it is noted significant differences in the amounts of CO2 concentration in these periods. The highest concentrations were observed during least rainy period, with monthly mean values above 440 ppm near the surface.Este estudo teve como objetivo descrever o perfil vertical da concentração de CO2 durante o período menos chuvoso e chuvoso do ano de 2006, em uma área de floresta tropical na Amazônia Central do Brasil.Para tanto, foram utilizados dados da concentração de CO2, coletados em várias alturas por um sistema de medidas incluindo um analisador de gás infravermelho (Licor 7000), em uma torre de 40 metros de altura. A partir dos dados coletados foi possível observar que a concentração de CO2 diminui à medida que se avança do solo ao topo do dossel. O que sugere que a maior fonte de CO2 é proveniente dos solos, em virtude de processos como a respiração e decomposição da biomassa vegetal. Quando se comparam os períodos menos chuvoso e mais chuvoso, nota-se diferenças significativas nos valores de concentração de CO2 entre esses períodos. As maiores concentrações foram observadas durante o período menos chuvoso, com valores médios mensais acima de 440 ppm próximo à superfície

Modelling chemistry in the nocturnal boundary layer above tropical rainforest and a generalised effective nocturnal ozone deposition velocity for sub-ppbv NOx conditions

Measurements of atmospheric composition have been made over a remote rainforest landscape. A box model has previously been demonstrated to model the observed daytime chemistry well. However the box model is unable to explain the nocturnal measurements of relatively high [NO] and [O3], but relatively low observed [NO2]. It is shown that a one-dimensional (1-D) column model with simple O3 -NOx chemistry and a simple representation of vertical transport is able to explain the observed nocturnal concentrations and predict the likely vertical profiles of these species in the nocturnal boundary layer (NBL). Concentrations of tracers carried over from the end of the night can affect the atmospheric chemistry of the following day. To ascertain the anomaly introduced by using the box model to represent the NBL, vertically-averaged NBL concentrations at the end of the night are compared between the 1-D model and the box model. It is found that, under low to medium [NOx] conditions (NOx <1 ppbv), a simple parametrisation can be used to modify the box model deposition velocity of ozone, in order to achieve good agreement between the box and 1-D models for these end-of-night concentrations of NOx and O3. This parametrisation would could also be used in global climate-chemistry models with limited vertical resolution near the surface. Box-model results for the following day differ significantly if this effective nocturnal deposition velocity for ozone is implemented; for instance, there is a 9% increase in the following day’s peak ozone concentration. However under medium to high [NOx] conditions (NOx > 1 ppbv), the effect on the chemistry due to the vertical distribution of the species means no box model can adequately represent chemistry in the NBL without modifying reaction rate constants

Hysteresis phenomenon in turbulent convection

Coherent large-scale circulations of turbulent thermal convection in air have been studied experimentally in a rectangular box heated from below and cooled from above using Particle Image Velocimetry. The hysteresis phenomenon in turbulent convection was found by varying the temperature difference between the bottom and the top walls of the chamber (the Rayleigh number was changed within the range of $10^7 - 10^8$). The hysteresis loop comprises the one-cell and two-cells flow patterns while the aspect ratio is kept constant ($A=2 - 2.23$). We found that the change of the sign of the degree of the anisotropy of turbulence was accompanied by the change of the flow pattern. The developed theory of coherent structures in turbulent convection (Elperin et al. 2002; 2005) is in agreement with the experimental observations. The observed coherent structures are superimposed on a small-scale turbulent convection. The redistribution of the turbulent heat flux plays a crucial role in the formation of coherent large-scale circulations in turbulent convection.Comment: 10 pages, 9 figures, REVTEX4, Experiments in Fluids, 2006, in pres

Características Médias do Vento acima e abaixo do Dossel da Floresta durante o Goamazon em um Sítio Experimental na Amazônia

The aim of this study was to evaluate the temporal evolution of average characteristics of the vertical profiles of speed and direction above and within of the forest canopy at the Cuieiras experimental site, located about 100 km from the Manaus, Amazonas state, Brazil. We used about 10 months of half-hourly averaged data from 10 sonic anemometers installed at different levels above and within the forest canopy during GoAmazon project in 2014. We found that the vertical wind speed profile varied with the various layers above and below the forest canopy, describing an S-shape type, a form determined by physical obstructions imposed by vertical heterogeneity of the canopy. The predominant wind directions were not constant with height, suggesting that very local circulations can influence the subcanopy flow.O objetivo deste trabalho foi avaliar as características médias da evolução temporal do perfil vertical da velocidade e direção do vento acima e abaixo do dossel da floresta no sítio experimental do Cuieiras, localizado cerca de 100 Km da cidade Manaus, estado do Amazonas, Brasil. Para tanto, foram utilizados aproximadamente 10 meses de dados de 10 anemômetros sônicos instalados em diferentes níveis acima e abaixo do dossel da floresta, durante o projeto GoAmazon, no ano de 2014 . Analisando o conjunto de dados, por meio de médias para cada 30 minutos diários de todo período estudado, foi possível observar que o perfil vertical da velocidade do vento varia de acordo com as diferentes camadas acima e abaixo do dossel da floresta e possui uma forma tipo “S”, definida pelas obstruções físicas impostas pela heterogeneidade vertical da floresta. As direções predominantes do vento não são constantes com a altura, sugerindo que circulações locais podem influenciar o escoamento no sítio experimental estudado

Dry‐Season Greening and Water Stress in Amazonia: The Role of Modeling Leaf Phenology

Large uncertainties on the sensitivity of Amazon forests to drought exist. Even though water stress should suppress photosynthesis and enhance tree mortality, a green‐up has been often observed during the dry season. This interplay between climatic forcing and forest phenology is poorly understood and inadequately represented in most of existing dynamic global vegetation models calling for an improved description of the Amazon seasonal dynamics. Recent findings on tropical leaf phenology are incorporated in the state‐of‐the‐art eco‐hydrological model Thetys & Chloris. The new model accounts for a mechanistic light‐controlled leaf development, synchronized dry‐season litterfall, and an age‐dependent leaf photosynthetic capacity. Simulation results from 32 sites in the Amazon basin over a 15‐year period successfully mimic the seasonality of gross primary productivity; evapotranspiration (ET); as well as leaf area index, leaf age, and leaf productivity. Representation of tropical leaf phenology reproduces the observed dry‐season greening, reduces simulated gross primary productivity, and does not alter ET, when compared with simulations without phenology. Tolerance to dry periods, with the exception of major drought events, is simulated by the model. Deep roots rather than leaf area index regulation mechanisms control the response to short‐term droughts, but legacy effects can exacerbate multiyear water stress. Our results provide a novel mechanistic approach to model leaf phenology and flux seasonality in the tropics, reconciling the generally observed dry‐season greening, ET seasonality, and decreased carbon uptake during severe droughts.Key PointsA mechanistic description of tropical leaf phenology for ecosystem models is presentedModel simulations for 32 sites in the Amazon realistically reproduce carbon/water fluxesLeaf phenology explains dry‐season greening with little impact on evapotranspiration fluxesPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145345/1/jgrg21161_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145345/2/jgrg21161-sup-0001-supplementary.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145345/3/jgrg21161.pd

Observing and Modeling the Vertical Wind Profile at Multiple Sites in and above the Amazon Rain Forest Canopy

We analyzed the vertical wind profile measured at six experimental tower sites in dense forest in the Amazon Basin and examined how well two simple models can reproduce these observations. In general, the vertical wind profile below the canopy is strongly affected by the forest structure. From the forest floor to 0.65h (where h = 35 m is the average height of the forest canopy for sites considered), the wind profile is approximately constant with height with speeds less than 1 ms−1. Above 0.65 to 2.25h, the wind speed increases with height. Testing these data with the Yi and Souza models showed that each was able to reproduce satisfactorily the vertical wind profile for different experimental sites in the Amazon. Using the Souza Model, it was possible to use fewer input variables necessary to simulate the profile

Is friction velocity the most appropriate scale for correcting nocturnal carbon dioxide fluxes?

The use of friction velocity u* as the turbulence scale for correcting eddy-covariance carbon dioxide fluxes in low-mixing conditions is questioned. This is done because u* is, itself, a flux and, therefore, its value is highly dependent on the temporal scale used for the analysis. The multiresolution decomposition is applied to data from three different ecosystems in Brazil, to show that u* is well behaved and related to the turbulent mixing only up to the scale that separates the turbulent mixing from the low-frequency exchange. For larger temporal scales, mesoscale fluxes may induce large variability in the friction velocity, so that time series with low turbulent mixing may show an elevated value for u*, and vice-versa. We propose, as an alternative, the use of σw, the standard-deviation of the vertical velocity fluctuations. It is shown that σw has no variability within the mesoscale range and that, therefore, it is a much better scale to quantify the turbulent exchange than u*. The relationship between the two velocity scales is shown to depend on the scale and to be universal for the scales of the turbulent exchange. It is shown that curves of the turbulent carbon dioxide fluxes as a function of the turbulence scale are smoothed when using the friction velocity. Using σw instead of u* in data filtering procedures has two main consequences: easier determination of the threshold for filtering and larger respiration rates of the series classified as turbulent. The improvement is larger for sites where very stable conditions are common. © 2008 Elsevier B.V. All rights reserved