Evaluating the Contribution of Climate Forcing and Forest Dynamics to Accelerating Carbon Sequestration by Forest Ecosystems in the Northeastern U.S.

We used 10 Hz eddy flux signals and 0.2 Hz incident radiation (global shortwave and PAR) records from Harvard Forest (Massachusetts) and Tapajos National Forest (Brazil) to establish empirical relationships among directly measured cloud type and cover percentage and corresponding PAR fluctuations and its diffuse fraction. In future work such a cloud characterization will be related to water and light use efficiency estimates for each of these ecosystems. We developed empirical relationships to link sky cover type and fraction (measured with the ceilometer) to incident direct and diffuse PAR. We developed a methodology for constructing synthetic incident solar radiation time series based on operational reports of sky cover and cloud type from National Weather Service METAR reports. The aim of this work is to document the temporal and spectral properties radiation incident on the canopy, as a first step toward developing a sky-type parameterization for the net carbon uptake models

SECA E A SAÚDE DAS POPULAÇÕES RESIDENTES EM REGIÕES DA AMAZÔNIA BRASILEIRA NOS ANOS DE 2005, 2010 E 2015

O objetivo deste trabalho é verificar os impactos ocasionados pelos três últimos eventos de seca na saúde da população de catorze municípios na Amazônia, agrupados em quatro grupos com características pluviométricas homogêneas. Utilizaram-se dados diários e mensais de precipitação e temperatura do ar disponibilizado pelo Banco de Dados Meteorológicos para Ensino e Pesquisa do Instituto Nacional de Meteorologia e de internações por doenças respiratórias do Sistema Único de Saúde, DATASUS, do período de 2000 a 2015. Levando-se em consideração as especificidades dos dados em estudo utilizou-se a modelagem via Equações de Estimação Generalizada para captar associações significativas e o risco relativo de aumento da ocorrência das internações da população exposta a ausência de chuva. Os resultados mostraram que as estações que muito sofreram com a seca de 2005 (região A) localizada a sudoeste da Amazônia também foram pouco afetadas negativamente pelo evento de 2015. Embora o evento de seca de 2010 tenha sido mais extenso espacialmente do que 2005, o efeito da diminuição das chuvas a partir dos dados observados de um evento pra outro só se mostrou perceptível nas estações da região B, mais ao centro da Amazônia. Já a seca de 2015 teve maior impacto nas estações das regiões C e D. As populações consideradas mais vulneráveis por meio dos riscos captados pelo modelo foram Itaituba (região C), Monte Alegre e Porto de Moz (região D). Conclui-se que ao comparar as regiões percebe-se que os três eventos de seca afetam de forma diferente os quatros grupos, o que provavelmente está associado ao efeito diferencial dos mecanismos causadores das secas nas diferentes áreas da Amazônia.

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

Evaluating the Contribution of Climate Forcing and Forest Dynamics to Accelerating Carbon Sequestration by Forest Ecosystems in the Northeastern U.S.

We used 10 Hz eddy flux signals and 0.2 Hz incident radiation (global shortwave and PAR) records from Harvard Forest (Massachusetts) and Tapajos National Forest (Brazil) to establish empirical relationships among directly measured cloud type and cover percentage and corresponding PAR fluctuations and its diffuse fraction. In future work such a cloud characterization will be related to water and light use efficiency estimates for each of these ecosystems. We developed empirical relationships to link sky cover type and fraction (measured with the ceilometer) to incident direct and diffuse PAR. We developed a methodology for constructing synthetic incident solar radiation time series based on operational reports of sky cover and cloud type from National Weather Service METAR reports. The aim of this work is to document the temporal and spectral properties radiation incident on the canopy, as a first step toward developing a sky-type parameterization for the net carbon uptake models

Amazon Rainforest Exchange of Carbon and Subcanopy Air Flow: Manaus LBA Site—A Complex Terrain Condition

On the moderately complex terrain covered by dense tropical Amazon Rainforest (Reserva Biologica do Cuieiras—ZF2—02°36′17.1′′ S, 60°12′24.4′′ W), subcanopy horizontal and vertical gradients of the air temperature, CO2 concentration and wind field were measured for the dry and wet periods in 2006. We tested the hypothesis that horizontal drainage flow over this study area is significant and can affect the interpretation of the high carbon uptake rates reported by previous works at this site. A similar experimental design as the one by Tóta et al. (2008) was used with a network of wind, air temperature, and CO2 sensors above and below the forest canopy. A persistent and systematic subcanopy nighttime upslope (positive buoyancy) and daytime downslope (negative buoyancy) flow pattern on a moderately inclined slope (12%) was observed. The microcirculations observed above the canopy (38 m) over the sloping area during nighttime presents a downward motion indicating vertical convergence and correspondent horizontal divergence toward the valley area. During the daytime an inverse pattern was observed. The micro-circulations above the canopy were driven mainly by buoyancy balancing the pressure gradient forces. In the subcanopy space the microcirculations were also driven by the same physical mechanisms but probably with the stress forcing contribution. The results also indicated that the horizontal and vertical scalar gradients (e.g., CO2) were modulated by these micro-circulations above and below the canopy, suggesting that estimates of advection using previous experimental approaches are not appropriate due to the tridimensional nature of the vertical and horizontal transport locally. This work also indicates that carbon budget from tower-based measurement is not enough to close the system, and one needs to include horizontal and vertical advection transport of CO2 into those estimates

Atmosphere-biosphere exchange of CO 2 and O 3 in the central Amazon Forest

Measurements of vertical fluxes for CO2 and O3 were made at a level 10 m above the canopy of the Amazon forest during the wet season, using eddy correlation techniques. Vertical profiles of CO2 and O3 were recorded continuously from above the canopy to the soil surface, and forest floor respiration was measured using soil enclosures. Nocturnal respiration of CO2 by the forest ecosystem averaged 2.57 kgC/ha/h, with about 85% from the forest floor. During the daytime, CO2 was taken up at a mean rate of 4.4 kgC/ha/h. Net ecosystem uptake of carbon dioxide increased with solar flux by 0.015 (kgC/ha/h)/(W m−2), corresponding to fixation of 0.0076 moles CO2 per mole photons (about 0.017 moles CO2 per mole of absorbed photons at photosynthetically active wavelengths). The relationship between net ecosystem exchange and solar flux was virtually the same in the Amazon forest as in forests in Canada (Desjardins et al., 1982, 1985) and Tennessee (Baldocchi et al., 1987a,b). The relatively high efficiency for utilization of light (about 30% of the theoretical maximum) and the strong dependence of net CO2 uptake on solar flux suggest that light may significantly regulate net ecosystem exchange and carbon storage in the tropical forest. Changes in the distribution of cloud cover, associated for example with climatic shifts, might induce globally significant changes in carbon storage. Rates for uptake of O3 averaged 2.3×1011 molecules cm−2s−1 in the daytime (10 hours, 700–1700 hours), dropping by roughly a factor of 10 during the 14 hours from dusk to dawn. The mean O3 deposition velocity at 40 m was 0.26 cm s−1 in the night and 1.8 cm s−1 in the day. Diurnal variation of O3 deposition was regulated both by stratification of the atmospheric boundary layer and by stomatal response to light and water deficit. The total flux of O3 to the forest was limited largely by supply from the free troposphere above. Deposition of O3 to the forest canopy appears to be a regionally, and perhaps globally, important sink for tropospheric O3.Engineering and Applied Science

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

Amazon rain forest subcanopy flow and the carbon budget: Santarém LBA-ECO site

Horizontal and vertical CO2 fluxes and gradients were made in an Amazon tropical rain forest, the Tapajós National Forest Reserve (FLONA-Tapajós: 54°58'W, 2°51'S). Two observational campaigns in 2003 and 2004 were conducted to describe subcanopy flows, clarify their relationship to winds above the forest, and estimate how they may transport CO2 horizontally. It is now recognized that subcanopy transport of respired CO2 is missed by budgets that rely only on single point eddy covariance measurements, with the error being most important under nocturnal calm conditions. We tested the hypothesis that horizontal mean transport, not previously measured in tropical forests, may account for the missing CO 2 in such conditions. A subcanopy network of wind and CO2 sensors was installed. Significant horizontal transport of CO2 was observed in the lowest 10 m of the canopy. Results indicate that CO2 advection accounted for 73% and 71%, respectively, of the carbon budget for all calm nights evaluated during dry and wet periods. We found that horizontal advection is likely important to the canopy CO2 budget even for conditions with the above-canopy friction velocity higher than commonly used thresholds. Copyright 2008 by the American Geophysical Union