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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Emission of nitric oxide (NO) from tropical forest soils and exchange of NO between the forest canopy and atmospheric boundary layers

Emissions of NO from soils in the Amazon rain forest were measured at 66 locations using an enclosure technique, and continuous vertical profiles of NO and O3 were measured between the ground and 41-m altitude. Fluxes of NO averaged 8.9 (+ or - 1.5) x 10 to the 9th molecules/sq cm per sec from the dominant (yellow clay) soils of the region, with larger fluxes observed from adjacent white sand soils. Fluxes from clay soils were lower by more than a factor of 5 than fluxes observed during the dry season at a nearby site. Low soil emission rates were reflected in lower concentrations of NO at the top of the forest canopy in the wet season, only 30-50 parts per trillion by volume during the daytime. The measured fluxes are consistent with chemical mass balances for NO within the forest canopy, calculated from the NO and O3 profiles taken at night, and with observations of NO between 150 and 5000 m altitude. Measurements of NO emission rates from soil plots fertilized using NaNO3, NH4Cl, or sucrose indicated that a reductive pathway (denitrification) may have been primarily responsible for production of the NO released by both clay and sand soils.

Bakwin, Peter S.↗
NASA NTRS1990

Measurements of reactive nitrogen oxides (NO/y/) within and above a tropical forest canopy in the wet season

Measurements of ambient concentrations of reactive nitrogen oxides were made in the Amazon rain forest, near Manaus, Brazil, continuously at 39 m (above the canopy), and on several days and nights at 19 m (within the canopy). Concentrations were very low, typically 100-700 pptv, except for brief periods when up to 5000 pptv of NO(y) was observed, indicating polluted air from the urban area of Manaus. The forest was a net sink for NO(y) with the NO(y) flux = -7.6 + or - 5.0) x 10 to the 9th molecules/sq cm per sec in unpolluted periods, even though soils emitted NO at a significant rate (8.9 + or - 1.5 x 10 to the 9th molecules/sq cm per sec). The deposition rate for NO(y) appeared to be much larger during the daytime than at night, suggesting that uptake was controlled either by plant processes (stomatal opening) or by supply of reactive components of NO(y) (e.g., HNO3) during the daytime. Implications for regional and global atmospheric chemistry are discussed.

Bakwin, Peter S.↗
NASA NTRS1990

Sources of variation in nitrous oxide flux from Amazonian ecosystems

Nitrous oxide flux and soil nutrient characteristics were measured in three undisturbed tropical ecosystem types, in cleared and burned areas, and in areas of forest converted to pasture near Manaus, Brazil. Nitrogen mineralization, nitrification, and soil nitrogen pools were high in upland forests on clay soils (terra firme) and low in the sand-type and floodplain (varzea) soils. Nitrous oxide flux followed the same pattern, with an average flux of 1.9 ng/sq cm per hr in terra firme, 0.3 in sand types, and 0.1 in varzea. Flux from recently cleared and burned areas did not differ from terra firme forest, but pastures had significantly elevated fluxes (10.3 ng/sq cm per hr). These data were combined with satellite data-based areal estimates of land cover classes to estimate total N2O-N flux from the intensive study area used by the Amazon Boundary Layer Experiment. Total N2O-N flux from the area was 22.9 kg/h; pastures covered 11 percent of the area but accounted for over 40 percent of the flux.

Matson, P. A.↗
NASA NTRS1990

Ozone measurements in Amazonia - Dry season versus wet season

Recent ozone measurements taken in the Amazonian rain forest environment during the wet season (April-May 1987) are described, revealling new aspects of the regional atmospheric chemistry. The measurements were part of the Amazon Boundary Layer Experiment (ABLE 2B) mission and utilized UV absorption as a measurement technique to obtain surface ozone data; 20 ozonesondes were launched in order to obtain vertical ozone profiles used to describe the upper troposphere and stratosphere. The major differences in comparison to a previous dry season experiment, which found ozone concentrations to be lower in the whole troposphere by nearly a factor of 2, are stressed.

Kirchhoff, V. W. J. H.↗
NASA NTRS1990

Precipitation chemistry in central Amazonia

Rain samples from three sites in central Amazonia were collected over a period of 6 weeks during the 1987 wet season and analyzed for ionic species and dissolved organic carbon. A continuous record of precipitation chemistry and amount was obtained at two of these sites, which were free from local or regional pollution, for a time period of over 1 month. The volume-weighted mean concentrations of most species were found to be about a factor of 5 lower during the wet season compared with previous results from the dry season. Only sodium, potassium, and chloride showed similar concentrations in both seasons. When the seasonal difference in rainfall amount is taken into consideration, the deposition fluxes are only slightly lower for most species during the wet season than during the dry season, again with the exception of chloride, potassium, and sodium. Sodium and chloride are present in the same ratio as in sea salt; rapid advection of air masses of marine origin to the central Amazon Basin during the wet season may be responsible for the observed higher deposition flux of these species. Statistical analysis suggests that sulfate is, to a large extent, of marine (sea salt and biogenic) origin, but that long-range transport of combustion-derived aerosols also makes a significant contribution to sulfate and nitrate levels in Amazonian rain. Organic acid concentrations in rain were responsible for a large fraction of the observed precipitation acidity; their concentration was strongly influenced by gas/liquid interactions.

Andreae, M. O.↗
NASA NTRS1990

Cloud draft structure and trace gas transport

During the second Amazon Boundary Layer Experiment (ABLE 2B), meteorological observations, chemical measurements, and model simulations are utilized in order to interpret convective cloud draft structure and to analyze its role in transport and vertical distribution of trace gases. One-dimensional photochemical model results suggest that the observed poststorm changes in ozone concentration can be attributed to convective transports rather than photochemical production and the results of a two-dimensional time-dependent cloud model simulation are presented for the May 6, 1987 squall system. The mesoscale convective system exhibited evidence of significant midlevel detrainment in addition to transports to anvil heights. Chemical measurements of O3 and CO obtained in the convective environment are used to predict photochemical production within the troposphere and to corroborate the cloud model results.

Scala, John R.↗
NASA NTRS1990

Recent flood lavas in the Elysium region of Mars

A volcanic origin is presently suggested for the 'Cerberus Formation' region of smooth plains in the southeastern Elysium region of Mars, on the basis of its surface morphology, lobate edges, vents, and an embayment relation of the unit with adjacent, older units. The low viscosity lavas that filled a topographic depression in southeastern Elysium subsequently flowed into western Amazonic Planitia via channels formed by an earlier fluvial episode. A young, upper Amazonian dating is indicated by crater frequencies and stratigraphic relations, implying that large-scale eruptions of low-viscosity lava were still possible late in Martian history.

Plescia, J. B.↗
NASA NTRS1990

Remote sensing of the biosphere; Proceedings of the Meeting, Orlando, FL, Apr. 19, 20, 1990

The global context and monitoring of the biological aspects relevant to the EOS program are addressed, the large-scale regional field experiments required to understand ecosystem functioning in more detail and to calibrate the application of remote-sensing techniques for extracting flux and state information are covered, and sensors of the proposed EOS platform are discussed. Attention is given to terrestrial productivity, both tropical-forest and semiarid environments, coastal environments, and global oceanic productivity. Focus is placed on the First International Field Experiment (FIFE) in Kansas, the HAPEX field experiment in France, the ABLE-2 experiment in the Amazon, and the Forest Ecosystem Study in Maine. The proposed electro-optical instruments for EOS including both MODIS-N and MODIS-T, the AIRS and MISR instruments, the ITIR, and ERBE calibration issues are considered.

Smith, James A.↗
NASA NTRS1990

Differential absorption lidar detection of ozone in the troposphere and lower stratosphere

The DIAL technique for deriving O3 profiles from lidar measurements is discussed. Examples of a variety of O3 and aerosol measurements are presented from studies of (1) photochemically produced O3 in the summertime over the eastern United States and in biomass burning plumes during the dry season over the Amazon Basin of Brazil; (2) vertical O3 transport from the mixed layer into the free troposphere via cloud dynamics and from the stratosphere into the troposphere via tropopause fold events; and (3) O3 depletion in the O3 hole over Antarctica. The NASA airborne DIAL system is considered to be an advanced field system.

Browell, E. V.↗
NASA NTRS1991

Global biomass burning - Atmospheric, climatic, and biospheric implications

The present volume discusses the biomass burning (BMB) studies of the International Global Atmospheric Chemistry project, GEO satellite estimation of Amazonian BMB, remote sensing of BMB in West Africa with NOAA-AVHRR, an orbital view of the great Chinese fire of 1987, BMB's role in tropical rainforest reduction, CO and O3 measurements of BMB in the Amazon, effects of vegetation burning on the atmospheric chemistry of the Venezuelan savanna, an assessment of annually-burned biomass in Africa, and light hydrocarbon emissions from African savanna burnings. Also discussed are BMB in India, trace gas and particulate emissions from BMB in temperate ecosystems, ammonia and nitric acid emissions from wetlands and boreal forest fires, combustion emissions and satellite imagery of BMB, BMB in the perspective of the global carbon cycle, modeling trace-gas emissions from BMB, NO(x) emissions from BMB, and cloud-condensation nuclei from BMB.

Levine, Joel S.↗
NASA NTRS1992

Smoke and fire characteristics for cerrado and deforestation burns in Brazil - BASE-B experiment

Five test fires were performed during August and September 1990 in the cerrado (savannalike region) in central Brazil (three fires) and tropical moist forest (two fires) in the eastern Amazon. This paper details the gases released, the ratios of the gases to each other and to particulate matter, fuel loads, and the fraction consumed (combustion factors), and the fire behavior associated with biomass consumption. Models are presented for evaluating emission factors for CH4, CO2, CO, H2, and particles less than 2.5 micron diam (PM2.5) as a function of combustion efficiency. The ratio of carbon released as CO2 (combustion efficiency) for the cerrado fires averaged 0.94 and for the deforestation fires it decreased from 0.88 for the flaming phase to less than 0.80 during the smoldering phase of combustion. For tropical ecosystems, emissions of most products of incomplete combustion are projected to be lower than previous estimates for savanna ecosystems and somewhat higher for fires used for deforestation purposes.

Ward, D. E.↗
NASA NTRS1991

Airborne lidar measurements of ozone and aerosols in the summertime Arctic troposphere

Ozone (O3) and aerosol distributions were remotely measured from an aircraft using a differential absorption lidar (DIAL) system as part of the 1988 NASA Global Tropospheric Experiment - Arctic Boundary Layer Experiment (ABLE-3A). The airborne DIAL system made simultaneous measurements of O3 and aerosols from the surface to above the tropopause. These measurements were made in a broad range of atmospheric conditions over the tundra, ice, and ocean regions near Barrow and Bethel, Alaska, during July and August 1988. The tropospheric composition over the Arctic was found to be strongly influenced by stratospheric intrusions. Regions of low aerosol scattering and enhanced O3 mixing ratios were usually correlated with descending air from the upper troposphere or lower stratosphere. Several cases of enhanced O3 were observed during ABLE-3A in conjunction with enhanced aerosol layers in the free troposphere resulting from biomass burning. As was found in the Amazon, the products of biomass burning can significantly alter O3 concentrations in the troposphere. This paper describes the NASA airborne DIAL system and discusses the large-scale variations of O3 and aerosols observed with the airborne DIAL system during ABLE-3A.

Browell, Edward V.↗
NASA NTRS1993

Estimation of the fractional coverage of rainfall in climate models

The fraction of the grid cell area covered by rainfall, mu, is an essential parameter in descriptions of land surface hydrology in climate models. A simple procedure is presented for estimating this fraction, based on extensive observations of storm areas and rainfall volumes. Storm area and rainfall volume are often linearly related; this relation can be used to compute the storm area from the volume of rainfall simulated by a climate model. A formula is developed for computing mu, which describes the dependence of the fractional coverage of rainfall on the season of the year, the geographical region, rainfall volume, and the spatial and temporal resolution of the model. The new formula is applied in computing mu over the Amazon region. Significant temporal variability in the fractional coverage of rainfall is demonstrated. The implications of this variability for the modeling of land surface hydrology in climate models are discussed.

Eltahir, E. A. B.↗
NASA NTRS1993

On the response of the tropical atmosphere to large-scale deforestation

Recent studies on the Amazon deforestation problem predict that removal of the forest will result in a higher surface temperature, a significant reduction in evaporation and precipitation, and possibly significant changes in the tropical circulation. Here, we discuss the basic mechanisms contributing to the response of the tropical atmosphere to deforestation. A simple linear model of the tropical atmosphere is used in studying the effects of deforestation on climate. It is suggested that the impact of large-scale deforestation on the circulation of the tropical atmosphere consists of two components: the response of the tropical circulation to the negative change in precipitation (heating), and the response of the same circulation to the positive change in surface temperature. Owing to their different signs, the changes in predicted temperature and precipitation excite competing responses working in opposite directions. The predicted change in tropical circulation determines the change, if any, in atmospheric moisture convergence, which is equivalent to the change in run-off. The dependence of run-off predictions on the relative magnitudes of the predicted changes in precipitation and surface temperature implies that the predictions about run-off are highly sensitive, which explains, at least partly, the disagreement between the different models concerning the sign of the predicted change in Amazonian run-off.

Eltahir, E. A. B.↗
NASA NTRS1992

Strategies for detection of floodplain inundation with multi-frequency polarimetric SAR

Mapping of floodplain inundation patterns is a key element in developing hydrological and biogeochemical models for large tropical river basins such as the Amazon. Knowledge of the time sequence of inundation is necessary to determine both water routing and biogenic gas fluxes. Synthetic Aperture Radar (SAR) is uniquely suited for this application because of its ability to penetrate cloud cover and, in many cases, to detect flooding beneath a forest or herbaceous canopy. A procedure for discriminating flooded forest, flooded herbaceous vegetation, and open water from other cover types for a coastal wetland site on the lower Altamaha floodplain, Georgia, emphasizing robust classifiers that are not site-specific is currently being developed.

Hess, Laura L.↗
NASA NTRS1994

Completing below-ground carbon budgets for pastures, recovering forests, and mature forests of Amazonia

The objective of this grant was to complete below-ground carbon budgets for pastures and forest soils in the Amazon. Profiles of radon and carbon dioxide were used to estimate depth distribution of CO2 production in soil. This information is necessary for determining the importance of deep roots as sources of carbon inputs. Samples were collected for measuring root biomass from new research sites at Santana de Araguaia and Trombetas. Soil gases will be analyzed for CO2 and (14)CO2, and soil organic matter will be analyzed for C-14. Estimates of soil texture from the RADAMBRASIL database were merged with climate data to calculate soil water extraction by forest canopies during the dry season. In addition, a preliminary map of areas where deep roots are needed for deep soil water was produced. A list of manuscripts and papers prepared during the reporting periods is given.

Davidson, Eric A.↗
NASA NTRS1994

Albedo as a modulator of climate response to tropical deforestation

An atmospheric general circulation model with land surface properties represented by the simplified Simple Biosphere model is used to investigate the effects on local climate due to tropical deforestation for the Amazon basin. One control and three anomaly integrations of 4 years' duration are performed. In the anomaly integrations, rain forest in South America is replaced by degraded grassland. The anomaly integrations differ only in the optical properties of the grassland vegetation, with net surface albedos ranging from the same as to 0.09 lighter than that of rain forest. It is found that the change in climate, particularly rainfall, is strongly dependent on the change in surface albedo that accompanies deforestation. Replacement of forest by grass causes a reduction in transpiration and reduces frictional convergence by decreasing surface roughness. However, precipitation averaged over the deforested area is not necessarily reduced. Average precipitation decreases when the increase in albedo is greater than 0.03. If surface albedo is not increased appreciably as a result of deforestation, moisture flux convergence driven by the increase in surface temperature can offset the other effects, and average precipitation increases. As albedo is increased, surface temperature does not change, but surface latent and sensible heat flux decreases due to reduced radiational energy absorbed at the surface, resulting in a reduction in convection and precipitation. A change in the distribution of precipitation due to deforestation that appears to be independent of the albedo is observed.

Dirmeyer, Paul A.↗
NASA NTRS1994

TOPEX/POSEIDON microwave radiometer performance and in-flight calibration

Results of the in-flight calibration and performance evaluation campaign for the TOPEX/POSEIDON microwave radiometer (TMR) are presented. Intercomparisons are made between TMR and various sources of ground truth, including ground-based microwave water vapor radiometers, radiosondes, global climatological models, special sensor microwave imager data over the Amazon rain forest, and models of clear, calm, subpolar ocean regions. After correction for preflight errors in the processing of thermal/vacuum data, relative channel offsets in the open ocean TMR brightness temperatures were noted at the approximately = 1 K level for the three TMR frequencies. Larger absolute offsets of 6-9 K over the rain forest indicated a approximately = 5% gain error in the three channel calibrations. This was corrected by adjusting the antenna pattern correction (APC) algorithm. AS 10% scale error in the TMR path delay estimates, relative to coincident radiosondes, was corrected in part by the APC adjustment and in part by a 5% modification to the value assumed for the 22.235 FGHz water vapor line strength in the path delay retrieval algorithm. After all in-flight corrections to the calibration, TMR global retrieval accuracy for the wet tropospheric range correction is estimated at 1.1 cm root mean square (RMS) with consistent peformance under clear, cloudy, and windy conditions.

Ruf, C. S.↗