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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Analysis of normalized radar cross section (sigma-O) signature of Amazon rain forest using SEASAT scatterometer data

The normalized radar cross section (NRCS) signature of the Amazon rain forest was SEASAT scatterometer data. Statistics of the measured (NRCS) values were determined from multiple orbit passes for three local time periods. Plots of mean normalized radar cross section, dB against incidence angle as a function of beam and polarization show that less than 0.3 dB relative bias exists between all beams over a range of incidence angle from 30 deg to 53 deg. The backscattered measurements analyzed show the Amazon rain forest to be relatively homogeneous, azimuthally isotropic and insensitive to polarization. The return from the rain forest target appears relatively consistent and stable, except for the small diurnal variation (0.75 dB) that occurs at sunrise. Because of the relative stability of the rain forest target and the scatterometer instrument, the response of versus incidence angle was able to detect errors in the estimated yaw altitude angle. Also, small instrument gain biases in some of the processing channels were detected. This led to the development of an improved NRCS algorithm, which uses a more accurate method for estimating the system noise power.

Bracalente, E. M.↗
NASA NTRS1986

The chemical control of soluble phosphorus in the Amazon estuary

The role of sediments in controlling concentrations of soluble phosphorous in the Amazon estuary is examined. The efflux of phosphorous through the estuary is calculated using data collected on field excursions in December 1982 and May 1983, and laboratory mixing experiments. It is observed that soluble phosphorus was released from bottom sediments at a rate of 0.2 micro-M/day, when in seawater and deionizd water mixtures. The relation between release rates and salinity and sediment concentrations is studied. A one-dimensional dispersion model was developed to estimate phosphate inputs to the estuary. The model predicted total fluxes of soluble inorganic phosphorous of 15 x 10 to the 6th mole/day for December 1982 and 27 x 10 to the 6th mole/day for May 1983; the predictions correlate with field observations. It is noted that phosphorous removal is between 0 and 4 ppt at a rate of 0.044 + or - 0.01 micron-M/ppt per day and the annual mean input of phophorous from Amazon to outer-estuary is 23 x 10 to the 6th moles/day.

Fox, L. E.↗
NASA NTRS1986

Emission of methane and other trace gases from the Amazon Varzea

Researchers measured the distributions and fluxes of methane and other trace gases from the various Amazon floodplain environments. These were determined during both a large scale, quasi-synoptic survey along a 2000 km reach of the Amazon river and an intensive local study (by J. Melack, R. Harriss et al.) covering a six-week period. The environments studied included the major rivers, connecting channels (paranas), floating macrophyte beds, flooded forests, open lakes and recently wetted soils. The results are summarized. Measured rates of methane emission averaged about 300 mg m-2 d-1, but with considerable variance, and were comparable to or higher than previously reported emissions from similar temperature zone environments. In general, areas covered by floating macrophytes showed the highest emissions. Individual hotspots had among the highest rates ever observed, over 10 g m-2 d-1. The high methane emissions appear to result because about 50% of the organic matter fixed on the floodplain (either terrestrial or aquatic) that is oxidized in the water is decomposed anaerobically via methanogensis. Measured fluxes of methane to the atmosphere appear to be significantly correlated with surface water dissolved methane concentrations.

Richey, Jeffrey E.↗
NASA NTRS1988

Carbon dioxide in the atmosphere over the Amazon Basin

As a part of the NASA's Amazon Boundary Layer Experiment 2A mission, the cycle of atmospheric CO2 over the Amazon Basin was examined using measured vertical profiles of CO2 concentrations in the canopy and aloft, and direct measurements of CO2 emissions from soils. The results provide a detailed picture of daily exchanges of air between the tropical forest (0-30) and the atmospheric boundary layer (30-2000 m). A comparison of atmospheric CO2 distributions over forests, wetlands, and rivers shows that the lower atmosphere over forests functions separately from that over rivers or wetlands during the night and to some extent during the day; the basic diurnal cycle of CO2 over wetlands is much weaker than over forests, and the cycle is almost absent over rivers. This result is consistent with expectations based on the biogeochemistry of organic carbon in these systems.

Wofsy, Steven C.↗
NASA NTRS1988

Measurements of atmospheric hydrocarbons and biogenic emission fluxes in the Amazon boundary layer

Tropospheric mixing ratios of methane, C2-C10 hydrocarbons, and carbon monoxide were measured over the Amazon tropical forest near Manaus, Amazonas, Brazil, in July and August 1985. The measurements, consisting mostly of altitude profiles of these gases, were all made within the atmospheric boundary layer up to an altitude of 1000 m above ground level. Data characterize the diurnal hydrocarbon composition of the boundary layer. Biogenic emissions of isoprene control hydroxyl radical concentrations over the forest. Biogenic emission fluxes of isoprene and terpenes are estimated to be 25,000 micrograms/sq m per day and 5600 micrograms/sq m per day, respectively. This isoprene emission is equivalent to 2 percent of the net primary productivity of the tropical forest. Atmospheric oxidation of biogenic isoprene and terpenes emissions from the Amazon forest may account for daily increases of 8-13 ppb for carbon monoxide in the planetary boundary layer.

Zimmerman, P. R.↗
NASA NTRS1988

The cycle of biogenic sulfur compounds over the Amazon Basin. I - Dry season

The concentrations of SO2, methylmercaptan, dimethylsulfide, H2S, aerosol sulfate, and methanesulfonate over the Amazon Basin during the July/August dry season were determined from samples collected by the NASA research aircraft. The results indicate that biogenic emissions represent an important, if not the dominant, source of sulfur to the atmosphere over Amazonia. Per unit area, the wet continental tropics appear to have about the same reduced sulfur emission flux as the oceanic area average (about 6 nmol/sq m per min), consistent with the fact that the aerosol sulfate concentration over the Amazon Basin is similar to the excess sulfate levels over the remote oceans. However, since the wet tropical continents represent only about 3 percent of the earth's surface, their global contribution is modest; it is also small relative to the anthropogenic emissions from fossil fuel burning.

Andreae, M. O.↗
NASA NTRS1988

Regional aerosol chemistry of the Amazon Basin during the dry season

The distribution and chemical composition of the atmospheric aerosol over the Amazon Basin forest were determined during the 1985 July-August dry season, using data on the aerosol chemical constituent concentration collected during the NASA Global Tropospheric Experiment Amazon Boundary Layer Experiment 2A mission. The results of the analyses suggest that there is a remarkable compositional and spatial homogeneity of the atmospheric aerosol on an extensive regional scale. Particulate organic carbon is the dominant component of the atmospheric aerosol, exhibiting an average concentration of about 740 nmol/cu m in the mixed layer and about 220 nmol/cu m in free tropospheric air. Oxalate and SO4(2-) exhibited the greatest enrichment in the mixed layer, while Cl(-) showed essentially no enrichment. The aerosol in the Amazonian atmosphere is essentially acid-base neutral, primarily as a result of incorporation of NH(+), which is presumably derived from NH3 released by the forest ecosystem.

Talbot, R. W.↗
NASA NTRS1988

Methane emissions to the troposphere from the Amazon floodplain

The magnitudes of CH4 emissions to the troposphere from the Amazon River floodplain and the mechanism of these emissions were investigated using the data of 94 individual flux measurements made along a 1700-km stretch of the river during July/August 1985. The overall average rate of CH4 emission from wetlands was found to be 390 mg CH4/sq m per day, with the highest emissions (590 mg CH4/sq m per day) attributed to the water surfaces covered by aquatic macrophytes. Ebullition was the dominant mechanism of emission, accounting for 85 percent of the total. Surface-water CH4 concentrations were highly supersaturated, averaging 6.4 micromolar. The annual emission of CH4 from the Amazon Basin to the troposphere, estimated from the area and the known emission rate, is about 10 CH4 Tg/yr, indicating the importance of the area in the global atmospheric CH4 cycle.

Devol, Allen H.↗
NASA NTRS1988

The dispersal of the Amazon's water

New information obtained with NASA's Coastal Zone Color Scanner and with drifting buoys reveals that the discharge of the Amazon is carried offshore around a retroflection of the North Brazil Current and into the North Equatorial Countercurrent towards Africa between June and January each year. From about February to May, the countercurrent and the retroflection weaken or vanish, and Amazon water flows northwestward toward the Caribbean Sea.

Muller-Karger, Frank E.↗
NASA NTRS1989

Daytime turbulent exchange between the Amazon forest and the atmosphere

Detailed observations of turbulence just above and below the crown of the Amazon rain forest during the wet season are presented. The forest canopy is shown to remove high frequency turbulent fluctuations while passing lower frequencies. Filter characteristics of turbulent transfer into the Amazon rain forest canopy are quantified. Simple empirical relations that relate observed turbulent heat fluxes to horizontal wind variance are presented. Changes in the amount of turbulent coupling between the forest and the boundary layer associated with deep convective clouds are presented both as statistical averages and as a series of case studies. These convective processes during the rainy season are shown to alter the diurnal course of turbulent fluxes. In wake of giant coastal systems, no significant heat or moisture fluxes occur for up to a day after the event. Radar data is used to demonstrate that even small raining clouds are capable of evacuating the canopy of substances normally trapped by persistent static stability near the forest floor. Recovery from these events can take more than an hour, even during mid-day. In spite of the ubiquitous presence of clouds and frequent rain during this season, the average horizontal wind speed spectrum is well described by dry CBL similarity hypotheses originally found to apply in flat terrain.

Fitzjarrald, David R.↗
NASA NTRS1989

Amazon capims (floating grassmats) - A source of C-13 enriched methane to the troposphere

The C-13 isotopic composition of methane emitted to the troposphere from Amazon capims (floating grassmats) ranged from -36.9 to -48.0, per mil averaging -44.4 + or - 4.2 per mil. All pools of methane associated with the grassmats were enriched; methane withdrawn from plant stems ranged from -39 to -49 per mil while bubbles stirred from the root mat averaged -41.4 per mil. As the CH4 flux from these habitats makes up some 40 percent of the total flux from the Amazon floodplain, methane emissions from the region as a whole must be enriched in.

Chanton, Jeffrey↗
NASA NTRS1989

C-13/C-12 of atmospheric CO2 in the Amazon basin - Forest and river sources

Results are presented of measurements of the CO2 concentrations and C-13/C-12 ratios in CO2 in air samples collected from within the Amazonian rain forest and over the Amazon river between 1982 and 1987. Results indicate the presence of a diurnal cycle in the CO2 concentration and the C-13/C-12 ratio. It was found that the CO2 input to air in the forest was derived from the soil respiration, and the CO2 input to air over the Amazon river was derived from the degassing of CO2 from the river. It was also found that plants growing at heights lower than 7 m assimilate soil-derived CO2 with a low C-13/C-12 ratio.

Quay, Paul↗
NASA NTRS1990

The Amazon Boundary Layer Experiment - Wet season 1987

This paper describes the overall experimental design for the Amazon Boundary Layer Experiment (ABLE 2B), which used data from aircraft, ground-based, and satellite platforms to characterize the chemistry and dynamics of the lower atmosphere over the Amazon Basin during wet season conditions in April-May 1987. The ABLE 2B focused on determining the spatial and temporal scales of variability in trace gases and aerosols in the lower and midtroposphere over the Amazonian rain forest during wet season conditions, and assessing the role of local-to-regional atmospheric scales of motion on determining the distribution of atmospheric chemical species and their photochemical environment. A summary of the results from the combined ABLE 2A and ABLE 2B are presented.

Harriss, R. C.↗
NASA NTRS1990

Budgets of reactive nitrogen, hydrocarbons, and ozone over the Amazon forest during the wet season

The atmospheric composition over the Amazon forest during the wet season is simulated with a one-dimensional photochemical model for the planetary boundary layer (PBL) extending from the ground to 2000-m altitude. The model is constrained and evaluated using observations from the Amazon Boundary Layer Experiment 2B field expedition. Results indicate that only about 20 percent of NO(x) emitted by soils is exported to the atmosphere above the forest canopy. The balance is deposited to vegetation before leaving the canopy layer. The small NO(x) flux that escapes from the canopy is nevertheless sufficient to account for the low NO concentrations observed in the PBL. Soil emission can account for only a portion of NO(y) observed over the forest. Organic nitrates of nonbiogenic origin likely account for the balance of NO(y). Enhancements of CO observed in the PBL appear to reflect direct emission of CO by the forest ecosystem. Concentrations of O3 in the PBL are regulated largely by transport from aloft and deposition to the canopy, with little net influence from photochemistry. Ozone is photochemically produced immediately above the forest where NO concentrations are relatively high, but is photochemically consumed in the upper portion of the PBL.

Jacob, Daniel J.↗
NASA NTRS1990

Methane flux from the Amazon River floodplain - Emissions during rising water

Methane flux data obtained during a period of high and falling water level in the course of the dry season of 1985 (the Amazon Boundary Layer Experiment, ABLE 2A) and a period of moderate and rising water during the wet season of 1987 (ABLE 2B) were used to characterize the influence of seasonal variations in the vegetation, water column depth, and chemistry, as well as atmospheric dynamics, on the methane flux from the Amazon River floodplain. It was found that the annual estimate of methane from wetlands is identical to the annual estimate made by Matthews and Fung (1987) (both at 111 Tg). However, it was found that peatlands between 50 and 70 N contribute 39 Tg, with the large areas of forested and nonforested bogs making up 37 Tg of this figure, while the figures of Matthews and Fung were 63 and 62 Tg, respectively.

Bartlett, Karen B.↗
NASA NTRS1990

The atmospheric sulfur cycle over the Amazon Basin. II - Wet season

The fluxes and concentrations of atmospheric sulfur species were determined at ground level and from aircraft over the Amazon Basin during the 1987 wet season, providing a comprehensive description of the sulfur cycle over a remote tropical region. The vertical profile of dimethylsulfide (DMS) during the wet season was found to be very similar to that measured during the dry season, suggesting little seasonal variation in DMS fluxes. The concentrations of H2S were almost an order of magnitude higher than those of DMS, which makes H2S the most important biogenic source species in the atmosheric sulfur cycle over the Amazon Basin. Using the gradient-flux approach, the flux of DMS at the top of the tree canopy was estimated. The canopy was a source of DMS during the day, and a weak sink during the night. Measurements of sulfur gas emissions from soils, using the chamber method, showed very small fluxes, consistent with the hypothesis that the forest canopy is the major source of sulfur gases. The observed soil and canopy emission fluxes are similar to those measured in temperate regions. The concentrations of SO2 and sulfate aerosol in the wet season atmosphere were similar to dry season values.

Andreae, M. O.↗
NASA NTRS1990

Daytime turbulent exchange between the Amazon forest and the atmosphere

Detailed observations of turbulence just above and below the crown of the Amazon rain forest during the wet season are presented. The forest canopy is shown to remove high frequency turbulent fluctuations while passing lower frequencies. Filter characteristics of turbulent transfer into the Amazon rain forest canopy are quantified. Simple empirical relations that relate observed turbulent heat fluxes to horizontal wind variance are presented. Changes in the amount of turbulent coupling between the forest and the boundary layer associated with deep convective clouds are presented both as statistical averages and as a series of case studies. These convective processes during the rainy season are shown to alter the diurnal course of turbulent fluxes. In wake of giant coastal systems, no significant heat or moisture fluxes occur for up to a day after the event. Radar data is used to demonstrate that even small raining clouds are capable of evacuating the canopy of substances normally trapped by persistent static stability near the forest floor. Recovery from these events can take more than an hour, even during mid-day. In spite of the ubiquitous presence of clouds and frequent rain during this season, the average horizontal wind speed spectrum is well described by dry CBL similarity hypotheses originally found to apply in flat terrain.

Fitzjarrald, David R.↗
NASA NTRS1990

Atmosphere-biosphere exchange of CO2 and O3 in the Central Amazon Forest

An eddy correlation measurement of O3 deposition and CO2 exchange at a level 10 m above the canopy of the Amazon forest, conducted as part of the NASA/INPE ABLE2b mission during the wet season of 1987, is presented. It was found that the ecosystem exchange of CO2 undergoes a well-defined diurnal variation driven by the input of solar radiation. A curvilinear relationship was found between solar irradiance and uptake of CO2, with net CO2 uptake at a given solar irradiance equal to rates observed over forests in other climate zones. The carbon balance of the system appeared sensitive to cloud cover on the time scale of the experiment, suggesting that global carbon storage might be affected by changes in insolation associated with tropical climate fluctuations. The forest was found to be an efficient sink for O3 during the day, and evidence indicates that the Amazon forests could be a significant sink for global ozone during the nine-month wet period and that deforestation could dramatically alter O3 budgets.

Fan, Song-Miao↗