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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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108 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Phytoplankton Assemblage Patterns in the Southern Mid-Atlantic Bight

As part of the Wallops Coastal Oceans Observing Laboratory (Wa-COOL) Project, we sampled a time-series transect in the southern Mid-Atlantic Bight (MAB) biweekly. Our 2-year time-series data included physical parameters, nutrient concentrations, and chlorophyll a concentrations. A detailed phytoplankton assemblage structure was examined in the second year. During the 2-year study, chlorophyll a concentration (and ocean color satellite imagery) indicated that phytoplankton blooms occurred in January/February during mixing conditions and in early autumn under stratified conditions. The chlorophyll a concentrations ranged from 0.25 microgram 1(exp -1) to 15.49 microgram 1(exp -1) during the 2-year period. We were able to discriminate approximately 116 different species under phase contrast microscopy. Dominant phytoplankton included Skeletonema costatum, Rhizosolenia spp., and Pseudo-nitzschia pungens. In an attempt to determine phytoplankton species competition/succession within the assemblage, we calculated a Shannon Weaver diversity index for our diatom microscopy data. Diatom diversity was greatest during the winter and minimal during the spring. Diatom diversity was also greater at nearshore stations than at offshore stations. Individual genera appeared patchy, with surface and subsurface patches appearing abruptly and persisting for only 1-2 months at a time. The distribution of individual species differed significantly from bulk variables of the assemblage (chlorophyll a ) and total phytoplankton assemblage (cells), which indicates that phytoplankton species may be limited in growth in ways that differ from those of the total assemblage. Our study demonstrated a highly diverse phytoplankton assemblage throughout the year, with opportunistic species dominating during spring and fall in response to seasonal changes in temperature and nutrients in the southern MAB.

Mid-Atlantic↗
NASA NTRS1992

Dynamically stratified Monte Carlo forecasting

A new method for performing Monte Carlo forecasts is introduced. The method, called dynamic stratification, selects initial perturbations based on a stratification of the error distribution. A simple implementation is presented in which the error distribution used for the stratification is estimated from a linear model derived from a large ensemble of 12-h forecasts with the full dynamic model. The stratification thus obtained is used to choose a small subsample of initial states with which to perform the dynamical Monte Carlo forecasts. Several test cases are studied using a simple two-level general circulation model with uncertain initial conditions. It is found that the method provides substantial reductions in the sampling error of the forecast mean and variance when compared to the more traditional approach of choosing the initial perturbations at random. The degree of improvement, however, is sensitive to the nature of the initial error distribution and to the base state. In practice the method may be viable only if the computational burden involved in obtaining an adequate estimate of the error distribution is shared with the data-assimilation procedure.

Schubert, Siegfried↗
NASA NTRS1999

A Combined Infrared and Microwave Technique for Studying the Diurnal Variation of Rainfall over Amazonia

Over 10 years of continuous data from the Special Sensor microwave Imager (SSM/I) aboard a series of Defense Department satellites has made it possible to construct regional rainfall climatologies at high spatial resolution. Using the Goddard Profiling Algorithm (GPROF), monthly estimates of precipitation were made over the region of northern Brazil, including the Amazon Basin, for 1987 to 1998. GPROF is a physical approach to passive microwave precipitation retrieval, which uses the Goddard Cumulus Ensemble (cloud) model to establish prior probability densities of precipitation structures. Precipitation fields from GPROF were stratified into morning and evening satellite overpasses, and accumulated at monthly intervals at 0.5 degree spatial resolution. Important diurnal effects were noted in the analysis, the most pronounced being a land/sea breeze circulation along the northern coast of Brazil and a mountain/valley circulation along the Andes. There were also indications of morning rainfall maxima along the major rivers, and evening maxima between the rivers. The addition of simultaneous geosynchronous infrared (IR) data leads to the current technique, which takes advantage of the 30 minute sampling and 4 km spatial resolution of the infrared channel and the better physics of the microwave retrieval. The resultant IR method is subsequently used to derive the diurnal variability of rainfall over the Amazon basin, and further, to investigate the relative contribution from its convective and stratiform components.

Negri, Andrew J.↗
NASA NTRS1978

Heat Transfer and Fluid Mechanics Institute, Meeting, 26th, Washington State University, Pullman, Wash., June 26-28, 1978, Proceedings

Papers are presented on the heat transfer and fluid mechanics in energy systems including diesel combustion analysis using rapid sampling and the numerical simulation of thermal response of architectural structures. Experiments associated with hypersonic boundary layers, the prediction of nozzle-wall pressure distribution, and the effects of nozzle geometry on an axisymmetric thrust augmentor are outlined. Predictions are made of film thickness on a roll-metering device and the thermal characteristics of multiple-surface submerged condenser modules are described. Numerical studies are made of the interaction between natural and forced convection in a complex geometry and of pressure drop and holdup in two-phase stratified flow. A numerical solution is given for viscous flows at high Reynolds numbers and for compressible boundary layer flows near separation or reattachment. The structure and transport properties in turbulent shear flows are reviewed along with the spectra of Reynolds stresses in a developing pipe flow.

Crowe, C. T.↗
NASA NTRS1994

Multiwavelength Search for Correlated Time Variations in the Brightest EGRET Blazars

We have found that the emission in the blazar jets is highly stratified, as evidenced by time delays between the peaks of the flares at different wavebands. This fits well with the predictions of the jet models. Not all of the blazars have yet been observed long enough with the VLBA to determine the motions of their components. However, for those 39 blazars for which this analysis is possible as of August 1997, the apparent superluminal speeds are very high, ranging from about 10 to 35c (for a Hubble constant of 65 km/s Mpc. If this trend holds for the remainder of the sample (to be determined after the results of observations in July 1997 are analyzed along with those from previous epochs), the implication is that the EGRET-detected blazars have stronger relativistic beaming than does the general radio-bright blazar population.

Marscher, Alan P.↗
NASA NTRS1992

The constitution of the atmospheric layers and the extreme ultraviolet spectrum of hot hydrogen-rich white dwarfs

An analysis is presented of the atmospheric properties of hot, H-rich, DA white dwarfs that is based on optical, UV, and X-ray observations aimed at predicting detailed spectral properties of these stars in the range 80-800 A. The divergences between observations from a sample of 15 hot DA white dwarfs emitting in the EUV/soft X-ray range and pure H synthetic spectra calculated from a grid of model atmospheres characterized by Teff and g are examined. Seven out of 15 DA stars are found to consistently exhibit pure hydrogen atmospheres, the remaining seven stars showing inconsistency between FUV and EUV/soft X-ray data that can be explained by the presence of trace EUV/soft X-ray absorbers. Synthetic data are computed assuming two other possible chemical structures: photospheric traces of radiatively levitated heavy elements and a stratified hydrogen/helium distribution. Predictions about forthcoming medium-resolution observations of the EUV spectrum of selected hot H-rich white dwarfs are made.

Vennes, Stephane↗
NASA NTRS2008

Completion of the Edward Air Force Base Statistical Guidance Wind Tool

The goal of this task was to develop a GUI using EAFB wind tower data similar to the KSC SLF peak wind tool that is already in operations at SMG. In 2004, MSFC personnel began work to replicate the KSC SLF tool using several wind towers at EAFB. They completed the analysis and QC of the data, but due to higher priority work did not start development of the GUI. MSFC personnel calculated wind climatologies and probabilities of 10-minute peak wind occurrence based on the 2-minute average wind speed for several EAFB wind towers. Once the data were QC'ed and analyzed the climatologies were calculated following the methodology outlined in Lambert (2003). The climatologies were calculated for each tower and month, and then were stratified by hour, direction (10" sectors), and direction (45" sectors)/hour. For all climatologies, MSFC calculated the mean, standard deviation and observation counts of the Zminute average and 10-minute peak wind speeds. MSFC personnel also calculated empirical and modeled probabilities of meeting or exceeding specific 10- minute peak wind speeds using PDFs. The empirical PDFs were asymmetrical and bounded on the left by the 2- minute average wind speed. They calculated the parametric PDFs by fitting the GEV distribution to the empirical distributions. Parametric PDFs were calculated in order to smooth and interpolate over variations in the observed values due to possible under-sampling of certain peak winds and to estimate probabilities associated with average winds outside the observed range. MSFC calculated the individual probabilities of meeting or exceeding specific 10- minute peak wind speeds by integrating the area under each curve. The probabilities assist SMG forecasters in assessing the shuttle FR for various Zminute average wind speeds. The A M ' obtained the processed EAFB data from Dr. Lee Bums of MSFC and reformatted them for input to Excel PivotTables, which allow users to display different values with point-click-drag techniques. The GUI was created from the PivotTables using VBA code. It is run through a macro within Excel and allows forecasters to quickly display and interpret peak wind climatology and probabilities in a fast-paced operational environment. The GUI was designed to look and operate exactly the same as the KSC SLF tool since SMG forecasters were already familiar with that product. SMG feedback was continually incorporated into the GUI ensuring the end product met their needs. The final version of the GUI along with all climatologies, PDFs, and probabilities has been delivered to SMG and will be put into operational use.

Dreher, Joseph G.↗
NASA NTRS2014

Water in the Cratonic Mantle: Insights from FTIR Data on Lac De Gras Xenoliths (Slave Craton, Canada)

The mantle lithosphere beneath the cratonic part of continents is the deepest (> 200 km) and oldest (>2-3 Ga) on Earth, remaining a conundrum as to how these cratonic roots could have resisted delamination by asthenospheric convection over time. Water, or trace H incorporated in mineral defects, could be a key player in the evolution of continental lithosphere because it influences melting and rheology of the mantle. Mantle xenoliths from the Lac de Gras kimberlite in the Slave craton were analyzed by FTIR. The cratonic mantle beneath Lac de Gras is stratified with shallow (<145 km) oxidized ultradepleted peridotites and pyroxenites with evidence for carbonatitic metasomatism, underlain by reduced and less depleted peridotites metasomatized by kimberlite melts. Peridotites analyzed so far have H O contents in ppm weight of 7-100 in their olivines, 58 to 255 in their orthopyroxenes (opx), 11 to 84 in their garnet, and 139 in one clinopyroxene. A pyroxenite contains 58 ppm H2O in opx and 5 ppm H2O in its olivine and garnet. Olivine and garnet from the deep peridotites have a range of water contents extending to higher values than those from the shallow ones. The FTIR spectra of olivines from the shallow samples have more prominent Group II OH bands compared to the olivines from the deep samples, consistent with a more oxidized mantle environment. The range of olivine water content is similar to that observed in Kaapvaal craton peridotites at the same depths (129-184 km) but does not extend to as high values as those from Udachnaya (Siberian craton). The Slave, Kaapvaal and Siberian cratons will be compared in terms of water content distribution, controls and role in cratonic root longevity.

Peslier, Anne H.↗
NASA NTRS2015

A Prototype Hail Detection Algorithm and Hail Climatology Developed with the Advanced Microwave Sounding Unit (AMSU)

In previous studies published in the open literature, a strong relationship between the occurrence of hail and the microwave brightness temperatures (primarily at 37 and 85 GHz) was documented. These studies were performed with the Nimbus‐7 SMMR, the TRMM Microwave Imager (TMI) and most recently, the Aqua AMSR‐E sensor. This lead to climatologies of hail frequency from TMI and AMSR‐E, however, limitations include geographical domain of the TMI sensor (35 S to 35 N) and the overpass time of the Aqua satellite (130 am/pm local time), both of which reduce an accurate mapping of hail events over the global domain and the full diurnal cycle. Nonetheless, these studies presented exciting, new applications for passive microwave sensors. Since 1998, NOAA and EUMETSAT have been operating the AMSU‐A/B and the MHS on several operational satellites: NOAA‐15 through NOAA‐19; MetOp‐A and ‐B. With multiple satellites in operation since 2000, the AMSU/MHS sensors provide near global coverage every 4 hours, thus, offering a much larger time and temporal sampling than TRMM or AMSR‐E. With similar observation frequencies near 30 and 85 GHz and additionally three at the 183 GHz water vapor band, the potential to detect strong convection associated with severe storms on a more comprehensive time and space scale exists. In this study, we develop a prototype AMSU‐based hail detection algorithm through the use of collocated satellite and surface hail reports over the continental U.S. for a 12‐year period (2000‐2011). Compared with the surface observations, the algorithm detects approximately 40 percent of hail occurrences. The simple threshold algorithm is then used to generate a hail climatology that is based on all available AMSU observations during 2000‐11 that is stratified in several ways, including total hail occurrence by month (March through September), total annual, and over the diurnal cycle. Independent comparisons are made compared to similar data sets derived from other satellite, ground radar and surface reports. The algorithm was also applied to global land measurements for a single year and showed close agreement with other satellite based hail climatologies. Such a product could serve as a prototype for use with a future geostationary based microwave sensor such as NASA's proposed PATH mission.

Ferraro, Ralph↗
NASA NTRSDate not supplied

Seasonal, Spectral, and Regional Characterization of Deep Convective Clouds Top-of-Atmosphere Bidirectional Reflectance for Improved Satellite Intercalibration

The NASA CERES project provides the scientific community with regional broadband fluxes designed for long-term climate monitoring. The CERES climate quality dataset requires that the CERES instrument, as well as the MODIS and VIIRS imager records to be radiometrically stable over time. Deep Convective Clouds (DCCs) are spectrally uniform, near-Lambertian natural diffusers offering high signal-to-noise ratio and stable radiometric response in the VIS-NIR spectrum. For shortwave infrared (SWIR) wavelengths greater than 1.2µm, the DCC response is significantly influenced by cloud particle size and atmospheric absorption. Previous studies improved the characterization of the SWIR band DCC radiance, by using channel specific monthly empirical BRDFs as well as using the probability density function mean statistic to track the SWIR band stability. Also, that the DCC radiance is greater over land than over ocean and that the TWP DCC radiance has the lowest tropical DCC radiance. This study confirms and improves upon the previous studies. The study stratified the tropics regionally into land and ocean domains and applied their respective ocean-only and land-only empirical monthly BRDFs and normalized the land DCC BRDF corrected radiances with their ocean counterpart. This approach provided the most stable DCC response. The DCC BRDF corrected radiance monthly standard error was 0.24%, 0.62%, 0.59%, and 0.43% for the 1.24µm, 1.37µm, 1.61µm, and 2.25µm SWIR bands, which reduced the standard error 20%, 13%, 24%, and 26%, respectively when compared with the all-surface approach. The same approach was attempted over the Tropical Western Pacific and found not to be an improvement over the tropical domain. Further stratification of the tropical domain will need to balance sufficient sampling while accounting for regional DCC radiance differences.

Prathana Khakurel↗
NASA NTRS1996

CM-like Interplanetary Dust Particles in Lower Stratosphere During 1989 October and 1991 June/July

The stratospheric interplanetary dust particles L2005T12 and L2011O3 are linked to CM chondrite matrix. Particle L2005T12 is dominated by tabular grains of partially dehydrated greenalite-rich serpentine. Its amorphous matrix contains abundant smectite nanocrystals and annular Fe,Ni,S units. A uniquely stratified (partial) maghemite rim occurs only on S-rich parts of the matrix. Formation of this rim and Mg depletions in the matrix occurred during atmospheric entry heating of this particle. Particle L2011O3 has large iron sulfide and magnesiowustite grains in an amorphous low-Al, ferromagnesiosilica matrix. Hydrous crystallisation of this matrix produced ultrafine-grained smectites and disseminated iron sulfides. Atmospheric entry heating of both particles is indicated by the partial iron oxide rim, vesicular sulfides, and the scatter of matrix compositions due to loss of Mg. While many uncertainties remain, the high incidence of chondritic rough particles, which include an unknown amount of CM-like particles, in the lower stratosphere during 1984, 1989, and 1991 suggests annual variations in their abundances. The timing of lower stratospheric dust samplings is critical to collect these particles.

Rietmeijer, Frans J. M.↗
NASA NTRS2017

Northwest Africa 10758: A New CV3 Chondrite Bearing a Giant CAI with Hibonite-Rich Wark-Lovering Rim

Northwest Africa (NWA) 10758 is a newly identified carbonaceous chondrite that is a Bali-like oxidized CV3. The large Ca-Al rich inclusion (CAI) in this sample is approx. 2.4 x 1.4 cm. The CAI is transitional in composition between type A and type B, with interior mineralogy dominated by melilite, plus less abundant spinel and Al-Ti rich diopside, and only very minor anorthite (Fig. 1A). This CAI is largely free of secondary alteration in the exposed section we examined, with almost no nepheline, sodalite or Ca-Fe silicates. The Wark-Lovering (WL) rim on this CAI is dominated by hibonite, with lower abundances of spinel and perovskite, and with hibonite locally overlain by melilite plus perovskite (as in Fig. 1B). Note that the example shown in 1B is exceptional. Around most of the CAI, hibonite + spinel + perovskite form the WL rim, without overlying melilite. The WL rim can be unusually thick, ranging from approx.20 microns up to approx. 150 microns. A well-developed, stratified accretionary rim infills embayments of the CAI, and thins over protuberances in the convoluted CAI surface.

Ross, D. K.↗
NASA NTRS2017

NWA10758: A New CV3 Chondrite Bearing a Giant CAI with Hibonite-Rich Wark-Lovering Rim

Northwest Africa (NWA) 10758 is a newly identified carbonaceous chondrite that is a Bali-like oxidized CV3. The large Ca-Al rich inclusion (CAI) in this sample is approx. 2.4 x 1.4 cm. The CAI is transitional in composition between type A and type B, with interior mineralogy dominated by melilite, plus less abundant spinel and Al-Ti rich diopside, and only very minor anorthite (Fig. 1A). This CAI is largely free of secondary alteration in the exposed section we examined, with almost no nepheline, sodalite or Ca-Fe silicates. The Wark-Lovering (WL) rim on this CAI is dominated by hibonite, with lower abundances of spinel and perovskite, and with hibonite locally overlain by melilite plus perovskite (as in Fig. 1B). Note that the example shown in 1B is exceptional. Around most of the CAI, hibonite + spinel + perovskite form the WL rim, without overlying melilite. The WL rim can be unusually thick, ranging from approx. 20 microns up to approx. 150 microns. A well-developed, stratified accretionary rim infills embayments of the CAI, and thins over protuberances in the convoluted CAI surface.

Ross, D. K.↗
NASA NTRS2018

Formation of the UV Spectrum of Molecular Hydrogen in the Sun

Ultraviolet (UV) lines of molecular hydrogen have been observed in solar spectra for almost four decades, but the behavior of the molecular spectrum and its implications for solar atmospheric structure are not fully understood. Data from the High-Resolution Telescope Spectrometer (HRTS) instrument revealed that H2 emission forms in particular regions, selectively excited by a bright UV transition region and chromospheric lines. We test the conditions under which H2 emission can originate by studying non-LTE models, sampling a broad range of temperature stratifications and radiation conditions. Stratification plays the dominant role in determining the population densities of H2, which forms in greatest abundance near the continuum photosphere. However, opacity due to the photoionization of Si and other neutrals determines the depth to which UV radiation can penetrate to excite the H2. Thus the majority of H2 emission forms in a narrow region, at about 650 km in standard one dimensional (1D) models of the quiet Sun, near the tau = 1 opacity surface for the exciting UV radiation, generally coming from above. When irradiated from above using observed intensities of bright UV emission lines, detailed non-LTE calculations show that the spectrum of H2 seen in the quiet-Sun Solar Ultraviolet Measurement of Emitted Radiation atlas spectrum and HRTS light-bridge spectrum can be satisfactorily reproduced in 1D stratified atmospheres, without including three-dimensional or time-dependent thermal structures. A detailed comparison to observations from 1205 to 1550 Angstroms is presented, and the success of this 1D approach to modeling solar UV H2 emission is illustrated by the identification of previously unidentified lines and upper levels in HRTS spectra.

Jaeggli, S. A.↗
NASA NTRS2013

Unification of X-ray Winds in Seyfert Galaxies: From Ultra-fast Outflows to Warm Absorbers

The existence of ionized X-ray absorbing layers of gas along the line of sight to the nuclei of Seyfert galaxies is a well established observational fact. This material is systematically outflowing and shows a large range in parameters. However, its actual nature and dynamics are still not clear. In order to gain insights into these important issues we performed a literature search for papers reporting the parameters of the soft X-ray warm absorbers (WAs) in 35 type 1 Seyferts and compared their properties to those of the ultra-fast outflows (UFOs) detected in the same sample. The fraction of sources with WAs is >60 per cent, consistent with previous studies. The fraction of sources with UFOs is >34 per cent, >67 per cent of which also show WAs. The large dynamic range obtained when considering all the absorbers together, spanning several orders of magnitude in ionization, column, velocity and distance allows us, for the first time, to investigate general relations among them. In particular, we find significant correlations indicating that the closer the absorber is to the central black hole, the higher the ionization, column, outflow velocity and consequently the mechanical power. In all the cases, the absorbers continuously populate the whole parameter space, with the WAs and the UFOs lying always at the two ends of the distribution. These evidence strongly suggest that these absorbers, often considered of different types, could actually represent parts of a single large-scale stratified outflow observed at different locations from the black hole. The UFOs are likely launched from the inner accretion disc and the WAs at larger distances, such as the outer disc and/or torus. We argue that the observed parameters and correlations are, to date, consistent with both radiation pressure through Compton scattering and magnetohydrodynamic processes contributing to the outflow acceleration, the latter playing a major role. Most of the absorbers, especially the UFOs, show a sufficiently high mechanical power (at least approx 0.5 per cent of the bolometric luminosity) to provide a significant contribution to active galactic nuclei (AGN) feedback and thus to the evolution of the host galaxy. In this regard, we find possible evidence for the interaction of the AGN wind with the surrounding environment on large scales.

Unification↗
NASA NTRS1993

A regional rainfall climatology over Mexico and the southwest United States derived from passive microwave and geosynchronous infrared data

A three-year climatology of satellite-estimated rainfall for the warm season for the southwest United States and Mexico has been derived from data from the Special Sensor Microwave Imager (SSM/I). The microwave data have been stratified by month (June, July, August), year (1988, 1989, 1990), and time of day (morning and evening orbits). A rain algorithm was employed that relates 86-GHz brightness temperatures to rain rate using a coupled cloud-radiative transfer model. Results identify an early evening maximum in rainfall along the western slope of the Sierra Madre Occidental during all three months. A prominent morning rainfall maximum was found off the western Mexican coast near Mazatlan in July and August. Substantial differences between morning and evening estimates were noted. To the extent that three years constitute a climatology, results of interannual variability are presented. Results are compared and contrasted to high-resolution (8 km, hourly) infrared cloud climatologies, which consist of the frequency of occurrence of cloud colder than -38 C and -58 C. This comparison has broad implications for the estimation of rainfall by simple (cloud threshold) techniques. By sampling the infrared data to approximate the time and space resolution of the microwave, we produce ratios (or adjustment factors) by which we can adjust the infrared rain estimation schemes. This produces a combined microwave/infrared rain algorithm for monthly rainfall. Using a limited set of raingage data as ground truth, an improvement (lower bias and root-mean-square error) was demonstrated by this combined technique when compared to either method alone. The diurnal variability of convection during July 1990 was examined using hourly rain estimates from the Geostationary Operational Environmental Satellite (GOES) precipitation index and the convective stratiform technique, revealing a maximum in estimated rainfall from 1800 to 2100 local time. It is in this time period when the SSM/I evening orbit occurs. A high-resolution topographic database was available to aid in interpreting the influence of topography on the rainfall patterns.

Negri, Andrew J.↗
NASA NTRS1994

Regional rainfall climatologies derived from Special Sensor Microwave Imager (SSM/I) data

Climatologies of convective precipitation were derived from passive microwave observations from the Special Sensor Microwave Imager using a scattering-based algorithm of Adler et al. Data were aggregated over periods of 3-5 months using data from 4 to 5 years. Data were also stratified by satellite overpass times (primarily 06 00 and 18 00 local time). Four regions (Mexico, Amazonia, western Africa, and the western equatorial Pacific Ocean (TOGA COARE area) were chosen for their meteorological interest and relative paucity of conventional observations. The strong diurnal variation over Mexico and the southern United States was the most striking aspect of the climatologies. Pronounced morning maxima occured offshore, often in concativities in the coastline, the result of the increased convergence caused by the coastline shape. The major feature of the evening rain field was a linear-shaped maximum along the western slope of the Sierra Madre Occidental. Topography exerted a strong control on the rainfall in other areas, particularly near the Nicaragua/Honduras border and in Guatemala, where maxima in excess of 700 mm/month were located adjacent to local maxima in terrain. The correlation between the estimates and monthly gage data over the southern United States was low (0.45), due mainly to poor temporal sampling in any month and an inadequate sampling of the diurnal cycle. Over the Amazon Basin the differences in morning versus evening rainfall were complex, with an alternating series of morning/evening maxima aligned southwest to northeast from the Andes to the northeast Brazilian coast. A real extent of rainfall in Amazonia was slightly higher in the evening, but a maximum in morning precipitation was found on the Amazon River just east of Manaus. Precipitation over the water in the intertropical convergence zone (ITCZ) north of Brazil was more pronounced in the morning, and a pronounced land-/sea-breeze circulation was found along the northeast coast of Brazil. Inter-comparison of four years revealed 1992 to be the driest over Amazonia, with about a 23% decrease in mean rate compared to the 4-year mean estimated rain rate.

Negri, Andrew J.↗
NASA NTRS1995

Molecular indicators for palaeoenvironmental change in a Messinian evaporitic sequence (Vena del Gesso, Italy). II: High-resolution variations in abundances and 13C contents of free and sulphur-bound carbon skeletons in a single marl bed

The extractable organic matter of 10 immature samples from a marl bed of one evaporitic cycle of the Vena del Gesso sediments (Gessoso-solfifera Fm., Messinian, Italy) was analyzed quantitatively for free hydrocarbons and organic sulphur compounds. Nickel boride was used as a desulphurizing agent to recover sulphur-bound lipids from the polar and asphaltene fractions. Carbon isotopic compositions (delta vs PDB) of free hydrocarbons and of S-bound hydrocarbons were also measured. Relationships between these carbon skeletons, precursor biolipids, and the organisms producing them could then be examined. Concentrations of S-bound lipids and free hydrocarbons and their delta values were plotted vs depth in the marl bed and the profiles were interpreted in terms of variations in source organisms, 13 C contents of the carbon source, and environmentally induced changes in isotopic fractionation. The overall range of delta values measured was 24.7%, from -11.6% for a component derived from green sulphur bacteria (Chlorobiaceae) to -36.3% for a lipid derived from purple sulphur bacteria (Chromatiaceae). Deconvolution of mixtures of components deriving from multiple sources (green and purple sulphur bacteria, coccolithophorids, microalgae and higher plants) was sometimes possible because both quantitative and isotopic data were available and because either the free or S-bound pool sometimes appeared to contain material from a single source. Several free n-alkanes and S-bound lipids appeared to be specific products of upper-water-column primary producers (i.e. algae and cyanobacteria). Others derived from anaerobic photoautotrophs and from heterotrophic protozoa (ciliates), which apparently fed partly on Chlorobiaceae. Four groups of n-alkanes produced by algae or cyanobacteria were also recognized based on systematic variations of abundance and isotopic composition with depth. For hydrocarbons probably derived from microalgae, isotopic variations are well correlated with those of total organic carbon. A resistant aliphatic biomacromolecule produced by microalgae is, therefore, probably an important component of the kerogen. These variations reflect changes in the depositional environment and early diagenetic transformations. Changes in the concentrations of S-bound lipids induced by variations in conditions favourable for sulphurization were discriminated from those related to variations in primary producer assemblages. The water column of the lagoonal basin was stratified and photic zone anoxia occurred during the early and middle stages of marl deposition. During the last stage of the marl deposition the stratification collapsed due to a significant shallowing of the water column. Contributions from anaerobic photoautotrophs were apparently associated with variations in depth of the chemocline.

Non-NASA Center↗