SEARCH · Engineering Papers

Results for “ATMOSPHERES”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17

All sources NASA NTRS DOE OSTI

NASA NTRS2000

Synthetic spectra of simulated terrestrial atmospheres containing possible biomarker gases

NASA's proposed Terrestrial Planet Finder, a space-based interferometer, will eventually allow spectroscopic analyses of the atmospheres of extrasolar planets. Such analyses would provide information about the existence of life on these planets. One strategy in the search for life is to look for evidence of O3 (and hence O2) in a planet's atmosphere; another is to look for gases that might be present in an atmosphere analogous to that of the inhabited early Earth. In order to investigate these possibilities, we have calculated synthetic spectra for several hypothetical terrestrial-type atmospheres. The model atmospheres represent four different scenarios. The first two, representing inhabited terrestrial planets, are an Earth-like atmosphere containing variable amounts of oxygen and an early Earth-type atmosphere containing methane. In addition, two cases representing Mars-like and early Venus-like atmospheres were evaluated, to provide possible "false positive" spectra. The calculated spectra suggest that ozone could be detected by an instrument like Terrestrial Planet Finder if the O2 concentration in the planet's atmosphere is > or = 200 ppm, or 10(-3) times the present atmospheric level. Methane should be observable on an early-Earth type planet if it is present in concentrations of 100 ppm or more. Methane has both biogenic and abiogenic sources, but concentrations exceeding 1000 ppm, or 0.1% by volume, would be difficult to produce from abiogenic sources alone. High methane concentrations in a planet's atmosphere are therefore another potential indicator for extraterrestrial life.

NASA Discipline Exobiology↗

NASA NTRS2009

Laboratory for Atmospheres 2008 Technical Highlights

The 2008 Technical Highlights describes the efforts of all members of the Laboratory for Atmospheres. Their dedication to advancing Earth Science through conducting research, developing and running models, designing instruments, managing projects, running field campaigns, and numerous other activities, is highlighted in this report. The Laboratory for Atmospheres (Code 613) is part of the Earth Sciences Division (Code 610), formerly the Earth Sun Exploration Division, under the Sciences and Exploration Directorate (Code 600) based at NASA s Goddard Space Flight Center in Greenbelt, Maryland. In line with NASA s Exploration Initiative, the Laboratory executes a comprehensive research and technology development program dedicated to advancing knowledge and understanding of the atmospheres of Earth and other planets. The research program is aimed at understanding the influence of solar variability on the Earth s climate; predicting the weather and climate of Earth; understanding the structure, dynamics, and radiative properties of precipitation, clouds, and aerosols; understanding atmospheric chemistry, especially the role of natural and anthropogenic trace species on the ozone balance in the stratosphere and the troposphere; and advancing our understanding of physical properties of Earth s atmosphere. The research program identifies problems and requirements for atmospheric observations via satellite missions. Laboratory scientists conceive, design, develop, and implement ultraviolet, infrared, optical, radar, laser, and lidar technology for remote sensing of the atmosphere. Laboratory members conduct field measurements for satellite data calibration and validation, and carry out numerous modeling activities. These modeling activities include climate model simulations, modeling the chemistry and transport of trace species on regional-to-global scales, cloud-resolving models, and development of next-generation Earth system models. Interdisciplinary research is carried out in collaboration with other laboratories and research groups within the Earth Sciences Division, across the Sciences and Exploration Directorate, and with partners in universities and other Government agencies. The Laboratory for Atmospheres is a vital participant in NASA s research agenda. Our Laboratory often has relatively large programs, sizable satellite missions, and observational campaigns that require the cooperative and collaborative efforts of many scientists. We ensure an appropriate balance between our scientists responsibility for these large collaborative projects and their need for an active individual research agenda. This balance allows members of the Laboratory to continuously improve their scientific credentials. Members of the Laboratory interact with the general public to support a wide range of interests in the atmospheric sciences. Among other activities, the Laboratory raises the public s awareness of atmospheric science by presenting public lectures and demonstrations, by making scientific data available to wide audiences, by teaching, and by mentoring students and teachers. The Laboratory makes substantial efforts to attract new scientists to the various areas of atmospheric research. We strongly encourage the establishment of partnerships with Federal and state agencies that have operational responsibilities to promote the societal application of our science products. This report describes our role in NASA s mission, gives a broad description of our research, and summarizes our scientists major accomplishments during calendar year 2008. The report also contains useful information on human resources, scientific interactions, and outreach activities.

Cote, Charles E.↗

NASA NTRS2010

Ultra-High Resolution Spectroscopic Remote Sensing: A Microscope on Planetary Atmospheres

Remote sensing of planetary atmospheres is not complete without studies of all levels of the atmosphere, including the dense cloudy- and haze filled troposphere, relatively clear and important stratosphere and the upper atmosphere, which are the first levels to experience the effects of solar radiation. High-resolution spectroscopy can provide valuable information on these regions of the atmosphere. Ultra-high spectral resolution studies can directly measure atmospheric winds, composition, temperature and non-thermal phenomena, which describe the physics and chemistry of the atmosphere. Spectroscopy in the middle to long infrared wavelengths can also probe levels where dust of haze limit measurements at shorter wavelength or can provide ambiguous results on atmospheric species abundances or winds. A spectroscopic technique in the middle infrared wavelengths analogous to a radio receiver. infrared heterodyne spectroscopy [1], will be describe and used to illustrate the detailed study of atmospheric phenomena not readily possible with other methods. The heterodyne spectral resolution with resolving power greater than 1,000.000 measures the true line shapes of emission and absorption lines in planetary atmospheres. The information on the region of line formation is contained in the line shapes. The absolute frequency of the lines can be measured to I part in 100 ,000,000 and can be used to accurately measure the Doppler frequency shift of the lines, directly measuring the line-of-sight velocity of the gas to --Im/s precision (winds). The technical and analytical methods developed and used to measure and analyze infrared heterodyne measurements will be described. Examples of studies on Titan, Venus, Mars, Earth, and Jupiter will be presented. 'These include atmospheric dynamics on slowly rotating bodies (Titan [2] and Venus [3] and temperature, composition and chemistry on Mars 141, Venus and Earth. The discovery and studies of unique atmospheric phenomena will also be described, such as non-thermal and lasing phenomena on Mars and Venus, mid-infrared aurora on Jupiter [5], and results of small body impacts on Jupiter [6]. The heterodyne technique can also be applied for detailed study of the Earth's stratosphere and mesosphere by measuring trace constituent abundances and temporal and spatial variability as well as winds, which provide information of transport. All ground-based measurements will be described as complementary and supporting studies for on-going and future space missions [7] (Mars Express, Venus Express, Cassini Huygens, JUNO, ExoMars Trace Gas Orbiter, and the Europa Jupiter System Mission, an Earth Science Venture Class missions), Proposed instrument and technology development for a space flight infrared heterodyne spectrometer will be described.

Kostiuk, Theodor↗

NASA NTRS2011

Sulfur Chemistry in the Early and Present Atmosphere of Mars

Atmospheric sulfur species resulting from volcanic emissions impact the composition and chemistry of the atmosphere, impact the climate, and hence, the habitability of Mars and impact the mineralogy and composition of the surface of Mars. The geochemical/ photochemical cycling of sulfur species between the interior (via volcanism), the atmosphere (atmospheric photochemical and chemical processes) and the deposition of sulfuric acid on the surface of Mars is an important, but as yet poorly understood geochemical/ photochemical cycle on Mars. There is no observational evidence to indicate that Mars is volcanically active at the present time, however, there is strong evidence that volcanism was an important and widespread process on early Mars. The chemistry and photochemistry of sulfur species in the early and present atmosphere of Mars will be assessed using a one-dimensional photochemical model. Since it is generally assumed that the atmosphere of early Mars was significantly denser than the present 6-millibar atmosphere, photochemical calculations were performed for the present atmosphere and for the atmosphere of early Mars with assumed surface pressures of 60 and 350-millibars, where higher surface pressure resulted from enhanced atmospheric concentrations of carbon dioxide (CO2). The following sections include the results of earlier modeling studies, a summary of the one-dimensional photochemical model used in this study, a summary of the photochemistry and chemistry of sulfur species in the atmosphere of Mars and some of the results of the calculations.

Levine, Joel S.↗

NASA NTRS1969

Models of Earth's Atmosphere (120 to 1000 Km)

Atmospheric conditions encountered by a spacecraft in orbit about the Earth are important factors in space vehicle design, mission planning, and mission operations. Density is the primary atmospheric property that affects the spacecraft's orbital altitude, lifetime, and motion in the altitude range of 120 to 1000 kilometers. Near the lower limit of this range where density is greatest, a spacecraft will generally remain in orbit for a very short time; near the upper limit, the density effect on orbital lifetime is almost negligible. Density directly affects the torques which result from aerodynamic interaction between the space vehicle and the atmosphere; such torques must be considered in design of spacecraft attitude control systems. Density scale height is required in heating calculations for space vehicles re-entering the Earth's upper atmosphere. Density as well as chemical composition and temperature are needed in calculating a spacecraft's drag coefficient. Chemical composition and temperature also are required in the design of experiment sensors to be flown in this altitude range. Because of variability of atmospheric conditions with spatial location and solar condition, invariant models of the Earth's atmosphere (120 to 1000 kilometers) would not be useful for most engineering applications. Therefore, this monograph presents a computerized version of Jacchia's prediction method to provide models of the Earth's atmosphere which vary with solar condition and location. The resulting atmospheric models, which are predicted for particular times and locations, provide atmospheric density, chemical composition, temperature, molecular mass, and density scale height between 120 and 1000 kilometers altitude. In addition to the computerized method, a quick-look prediction method is given that may be used to obtain an estimate of atmospheric density for any time and spatial location without the use of a computer. A sample problem illustrates this method. Both methods provide models of mean density and models having reasonable upper extremes for density. The analytical approaches in both methods are considered to be the best available, but they could be refined considerably by additional data and study. Information contained in this monograph applies to altitudes between 120 and 1000 kilometers; other design criteria monographs in this series will provide atmospheric information below this altitude region.

Weidner, D. K.↗

DOE OSTI2023

The Role of Atmospheric Noise in Decadal SST Variability

Abstract A substantial role for atmospheric noise in simulations of decadal internal variability of SST is demonstrated by a comparison of a multicentury climate model control and a corresponding interactive ensemble (IE) simulation. The IE is designed to reduce atmospheric noise in the heat flux, wind stress, and freshwater flux at the air–sea interface. This comparison suggests that nearly all SST variability on decadal time scales is forced by internal atmospheric variability. The results are examined to determine the relative roles of atmospheric surface heat flux noise and ocean dynamics in the decadal volume-averaged heat budget of the upper ocean. The regional heat budgets in two regions, the South Pacific and the midlatitude North Atlantic, show the net atmospheric surface heat flux to be approximately in equilibrium with the ocean dynamics forcing. The IE and control results are used in the equilibrium heat budget approximation to infer the atmospheric heat flux response to SST, as well as the time series of the control atmospheric noise surface heat flux and ocean dynamics forcings for several regions. The South Pacific region SST is found to be primarily forced by the atmospheric noise surface heat flux and the North Atlantic region SST is forced by the ocean dynamics. Similar strengths for the atmospheric heat flux noise and ocean dynamics forcing, with an interdecadal atmospheric heat flux noise time scale and a centennial ocean dynamics time scale, are found for an Atlantic multidecadal variability region SST.

Meteorology & Atmospheric Sciences↗

NASA NTRS2018

Aerosols in Atmospheric Chemistry and Biogeochemical Cycles of Nutrients

Atmospheric aerosols have complex and variable compositions and properties.While scientific interest is centered on the health and climatic effects of atmospheric aerosols, insufficient attention is given to their involvement in multiphase chemistry that alters their contribution as carriers of nutrients in ecosystems. However, there is experimental proof that the nutrient equilibria of both land and marine ecosystems have been disturbed during the Anthropocene period. This review study first summarizes our current understanding of aerosol chemical processing in the atmosphere as relevant to biogeochemical cycles. Then it binds together results of recent modeling studies based on laboratory and field experiments, focusing on the organic and dust components of aerosols that account for multiphase chemistry, aerosol ageing in the atmosphere, nutrient (N, P, Fe) emissions, atmospheric transport, transformation and deposition. The human-driven contribution to atmospheric deposition of these nutrients, derived by global simulations using past and future anthropogenic emissions of pollutants, is put into perspective with regard to potential changes in nutrient limitations and biodiversity. Atmospheric deposition of nutrients has been suggested to result in human-induced ecosystem limitations with regard to specific nutrients. Such modifications favor the development of certain species against others and affect the overall functioning of ecosystems. Organic forms of nutrients are found to contribute to the atmospheric deposition of the nutrients N, P and Fe by 20%-40%, 35%-45% and 7%-18%, respectively. These have the potential to be key components of the biogeochemical cycles since there is initial proof of their bioavailability to ecosystems. Bioaerosols have been found to make a significant contribution to atmospheric sources of N and P, indicating potentially significant interactions between terrestrial and marine ecosystems. These results deserve further experimental and modeling studies to reduce uncertainties and understand the feedbacks induced by atmospheric deposition of nutrients to ecosystems.

dust↗

NASA NTRS2023

Importance of Atmospheric Feedbacks in Simulating the Seasonal Cycle of the Antarctic Sea Ice and Its Response to Perturbations

The seasonal cycle of the Antarctic sea ice extent is largely controlled by the evolution of the insolation received at the top of the atmosphere. However, sea ice processes and feedbacks with the ocean and the atmosphere can modulate this seasonal cycle. Here, the atmospheric feedbacks are quantified in a series of idealized sensitivity experiments performed with an eddy-permitting (1/4°) NEMO-LIM3 Southern Ocean configuration, including a representation of ice shelf cavities, in which the model was either driven by an atmospheric reanalysis or coupled to the COSMO-CLM 2 regional atmospheric model. In these experiments, sea ice thermodynamics and dynamics as well as the exchanges with the ocean and atmosphere are strongly perturbed. This perturbation is achieved by modifying snow and ice thermal conductivities, the vertical mixing in the ocean top layers, the effect of freshwater uptake/release upon sea ice growth/melt, ice dynamics and surface albedo. We show that the changes in surface heat fluxes are very different between the configurations driven by the reanalysis and those coupled to the atmosphere. Atmospheric feedbacks enhance the response of the modelled winter ice extent to any of the perturbed processes, and the enhancement is strongest when the albedo is modified. The response of sea ice volume and extent to changes in entrainment of subsurface warm waters to the ocean surface is also greatly amplified by the coupling with the atmosphere. By contrast, the atmospheric feedbacks can damp the impact of the perturbations affecting the heat conductivity through sea ice.

Atmospheric feedbacks↗

DOE OSTI2026

The two radiative states of the Arctic atmosphere and their impacts on the surface energy budget of sea ice

The surface energy budget (SEB) is a central regulator of Arctic climate and sea ice evolution, yet its processes remain poorly constrained due to sparse observations and complex, coupled surface-atmosphere interactions. This study leverages year-long measurements from the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) to provide the most comprehensive assessment to date of the central Arctic SEB and its modulation by atmospheric variability. Ship- and ice-based observations from October 2019 to September 2020 were used to directly measure or tightly constrain each term of the SEB, leading to exceptional energetic closure with the seasonal snow and ice mass balance. The analysis reveals strong seasonal transitions in atmosphere-surface energy transfer that are modulated by the atmospheric state and constrained by the ability of the surface temperature to respond. Classification of the atmosphere into its two dominant radiative states—the semi-transparent (ST) and opaque (OP)—highlights the central role of synoptic-scale variability in clouds. The ST atmospheric state dominated the long winter ice growth season, with limited cloudiness supporting persistent surface radiative cooling and ice growth. The OP state, associated with liquid-containing or thick ice clouds, became dominant in spring, with the combination of increased solar heating and cloud surface longwave warming driving ice and snow melt. Eddy covariance versus bulk approaches for deriving surface turbulent heat fluxes provide vastly different perspectives on the role of turbulence in modulating the SEB. These results establish a high-quality benchmark dataset for Arctic SEB studies and demonstrate how the balance of atmospheric radiative states exerts a first-order control on the annual evolution of the sea ice. The findings have broad implications for advancing observing technologies, understanding Arctic amplification, improving climate models, and predicting future sea ice change.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2024

Discussion: Presentation of Atmospheric 14 C O2 data

ABSTRACT Observations of radiocarbon ( 14 C) in Earth’s atmosphere and other carbon reservoirs are important to quantify exchanges of CO 2 between reservoirs. The amount of 14 C is commonly reported in the so-called Delta notation, i.e., Δ 14 C, the decay- and fractionation-corrected departure of the ratio of 14 C to total C from that ratio in an absolute international standard; this Delta notation permits direct comparison of 14 C/C ratios in the several reservoirs. However, as Δ 14 C of atmospheric CO 2 , Δ 14 CO 2 is based on the ratio of 14 CO 2 to total atmospheric CO 2 , its value can and does change not just because of change in the amount of atmospheric 14 CO 2 but also because of change in the amount of total atmospheric CO 2 , complicating ascription of change in Δ 14 CO 2 to change in one or the other quantity. Here we suggest that presentation of atmospheric 14 CO 2 amount as mole fraction relative to dry air (moles of 14 CO 2 per moles of dry air in Earth’s atmosphere), or as moles or molecules of 14 CO 2 in Earth’s atmosphere, all readily calculated from Δ 14 CO 2 and the amount of atmospheric CO 2 (with slight dependence on δ 13 CO 2 ), complements presentation only as Δ 14 CO 2 , and can provide valuable insight into the evolving budget and distribution of atmospheric 14 CO 2 .

Geochemistry & Geophysics↗

DOE OSTI2020

Chemically distinct regions of Venus’s atmosphere revealed by measured N 2 concentrations

A defining characteristic of the planet Venus is its thick, CO 2 -dominated atmosphere. Despite over 50 years of robotic exploration of Venus, including thirteen successful atmospheric probes and landers, our knowledge of N 2 , the second most abundant compound in the atmosphere, is highly uncertain. We report the first measurement of the nitrogen content of Venus’s atmosphere at altitudes between 60 and 100 km. Our result, 5.0 ± 0.4 v% N 2 , is 40% higher than the value of 3.5 v% N 2 reported for the lower atmosphere (<50 km altitude). Our discovery of altitude-dependent variations in the N 2 content of the atmosphere defies early expectations of homogeneous composition below 100 km (for example, see ref. 1), and necessitates complete chemical modelling to investigate chemical versus physical explanations for the enhanced N 2 in the upper atmosphere. Furthermore, the existence of chemically distinct lower and upper atmosphere regions complicates the use of remote sensing measurements of the upper atmosphere to infer the properties of the lower atmosphere and surface, an important lesson that also extends to the growing field of exoplanet astronomy.

99 GENERAL AND MISCELLANEOUS↗

DOE OSTI2023

Cross-Scale Land-Atmosphere Experiment (CSLAEX) (Final Report)

It is now well recognized that land-atmosphere interactions play an important role in both weather and climate. These interactions take place over a wide range of spatial and temporal scales. Most of the current formulations of the momentum, heat and moisture transport laws are informed by observations with a limited temporal or spatial scale, and hence may have limited applicability. The objective of this work is to improve the multi-scale representation of the near-surface heat transfer in the ground and in the atmosphere using a combination of modeling and field observations. Our knowledge and predictive capacity in land-atmosphere coupling is limited by our capacity to observe the full-scale spectrum at play. In order to bridge this fundamental gap in our observation capacity I will work to: create the first long-term Integrated Cross-Scale land-Atmosphere Experiment (CSLAEX) since I will work to: measure the components of the surface energy balance at a spatial scale relevant to remote sensing and meteorological applications (5km), along with observations of the nested subscale processes with Distributed Temperature Sensors (DTS). This proposal aims to fill the gaps in modeling and observing land-atmosphere interactions across scales via a novel Cross-Scale Land-Atmosphere Experiment (CSLAEX) to be implemented as part of the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site near Lamont, Oklahoma. The proposed research effort aims at exploring land-atmosphere processes across multiple spatial scales and to investigate the effect of landscape heterogeneity using Distributed Temperature Sensor measurements. The novel instrumentation of the Surface Energy Balance and simultaneous observations of the atmospheric state (boundary layer, cloud, convection) available at the DOE ARM SGP site will be used to create CSLAEX. This dataset will be used to frame and evaluate new transport laws and parameterizations for the boundary layer and the land surface, which can be implemented into the Weather and Research Forecasting (WRF) model and Community Atmospheric Model (CAM). The result of this study should impact multiple fields: meteorology, climate, and hydrology.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2022

Reduced Atmospheres of Post-impact Worlds: The Early Earth

Impacts may have had a significant effect on the atmospheric chemistry of the early Earth. Reduced phases in the impactor (e.g., metallic iron) can reduce the planet's H 2 O inventory to produce massive atmospheres rich in H 2 . While previous studies have focused on the interactions between the impactor and atmosphere in such scenarios, we investigate two further effects: (1) the distribution of the impactor's iron inventory during impact between the target interior, target atmosphere, and escaping the target; and (2) interactions between the post-impact atmosphere and the impact-generated melt phase. We find that these two effects can potentially counterbalance each other, with the melt–atmosphere interactions acting to restore reducing power to the atmosphere that was initially accreted by the melt phase. For a ~10 22 kg impactor, when the iron accreted by the melt phase is fully available to reduce this melt, we find an equilibrium atmosphere with H 2 column density ~10 4 moles cm –2 (pH 2 ~ 120 bars, X H2 ~ 0.77), consistent with previous estimates. However, when the iron is not available to reduce the melt (e.g., sinking out in large diameter blobs), we find significantly less H 2 (7 × 10 2 – 5 × 10 3 moles cm –2 , pH 2 ≲ 60 bars, X H2 ≲ 0.41). These lower H 2 abundances are sufficiently high that species important to prebiotic chemistry can form (e.g., NH 3 , HCN), but sufficiently low that the greenhouse heating effects associated with highly reducing atmospheres, which are problematic to such chemistry, are suppressed. The manner in which iron is accreted by the impact-generated melt phase is critical in determining the reducing power of the atmosphere and resolidified melt pool in the aftermath of impact.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1983

Planetary atmospheres

During the period from 1979 to 1982, Pioneer and Voyager missions to Venus, Jupiter, and Saturn combined with ongoing analysis and data collection from the Viking-Mars mission have contributed greatly to an understanding of planetary atmospheres. Research concerning the atmosphere of Venus is discussed, taking into account the atmospheric composition, the isotopic ratios of noble gases, data concerning temperature and pressure, information regarding various atmospheric layers, atmospheric density data, and models regarding the dynamical properties of Venus' atmosphere. Information concerning the atmosphere of Mars is also examined. Isotopic ratios of carbon and oxygen are considered along with altitude profiles, diurnal heating and cooling, and thermal tides and their relationship to dust storms. Attention is given to the temperature structure of the Jovian atmosphere, the morphology of Jovian cloud features, features in the Saturnian atmosphere, information with respect to the atmosphere of Titan, the rotation rates of Uranus, masses and densities of Uranus and Neptune, and the identification of Pluto as a small icy body.

Beebe, R.↗

NASA NTRS1986

The production of trace gases by photochemistry and lightning in the early atmosphere

Recent atmospheric calculation suggest that the prebiological atmosphere was most probably composed of nitrogen, carbon dioxide, and water vapor, resulting from volatile outgassing, as opposed to the older view of a strongly reducing early atmosphere composed of methane, ammonia, and hydrogen. Photochemical calculations indicate that methane would have been readily destroyed via reaction with the hydroxyl radical produced from water vapor and that ammonia would have been readily lost via photolysis and rainout. The rapid loss of methane and ammonia, coupled with the absence of a significant source of these gases, suggest that atmospheric methane and ammonia were very short lived, if they were present at all. An early atmosphere of N2, CO2, and H2O is stable and leads to the chemical production of a number of atmospheric species of biological significance, including oxygen, ozone, carbon monoxide, formaldehyde, and hydrogen cyanide. Using a photochemical model of the early atmosphere, the chemical productionof these species over a wide range of atmospheric parameters were investigated. These calculations indicate that early atmospheric levels of O3 were significantly below the levels needed to provide UV shielding. The fate of volcanically emitted sulfur species, e.g., sulfur dioxide and hydrogen sulfide, was investigated in the early atmosphere to assess their UV shielding properties. The photochemical calculations show that these species were of insufficient levels, due in part to their short photochemical lifetimes, to provide UV shielding.

Levine, J. S.↗

NASA NTRS1995

Calculation of surface and top of atmosphere radiative fluxes from physical quantities based on ISCCP data sets. 2: Validation and first results

We use global, multiyear observations of the properties of clouds, the atmosphere, and the surface to calculate global shortwave (SW) and longwave (LW) fluxes at the top of the atmosphere and at the surface at a resolution of 280 km and 3 hours for every third month from April 1985 to January 1989. Our validation studies suggest that the specification of cloud effects is no longer the dominant uncertainty in reconstructing the radiative fluxes at the top of atmosphere and at the surface. Rather cloud property uncertainties are now roughly equal contributors to the flux uncertainty, along with surface and atmospheric properties. The resulting SW and LW flux data sets suggest the following conclusions: (1) The net SW heating of Earth appears predominantly at the surface, whereas the net LW cooling arises predominantly from the atmosphere. The net cooling effect of clouds on top of atmospheric radiation appears primarily at the surface rather than in the atmosphere. (2) Clouds have almost no net effect on the global mean radiation balance of the atmosphere, but they enhance the latitudinal gradient in the LW cooling and reinforce the radiative forcing for the mean atmospheric circulation. Clouds act to mute seasonal contrasts however. (3) Clouds enhance the land-ocean contrasts of the atmospheric cooling, reinforcing the growth of standing eddy motions; but reduce land-ocean contrasts of the surface heating.

Rossow, W. B.↗

NASA NTRS1998

The Atmospheric Structure of Triton and Pluto

The goal of this research was to better determine the atmospheric structures of Triton and Pluto through further analysis of three occultation data sets obtained with the Kuiper Airborne Observatory (KAO.) As the research progressed, we concentrated our efforts on the Triton data, as this appeared to be the most fruitful. Three papers have been prepared as a result of this research. The first paper presents new results about Triton's atmospheric structure from the analysis of all ground-based stellar occultation data recorded to date, including one single-chord occultation recorded on 1993 July 10 and nine occultation lightcurves from the double-star event on 1995 August 14. These stellar occultation observations made both in the visible and in the infrared have good spatial coverage of Triton, including the first Triton central-flash observations, and are the first data to probe the altitude level 20-100 km on Triton. The small-planet lightcurve model of J. L. Elliot and L. A. Young was generalized to include stellar flux refracted by the far limb, and then fitted to the data. Values of the pressure, derived from separate immersion and emersion chords, show no significant trends with latitude, indicating that Triton's atmosphere is spherically symmetric at approximately 50 km altitude to within the error of the measurements; however, asymmetry observed in the central flash indicates the atmosphere is not homogenous at the lowest levels probed (approximately 20 km altitude). From the average of the 1995 occultation data, the equivalent isothermal temperature of the atmosphere is 47 plus or minus 1 K and the atmospheric pressure at 1400 km radius (approximately 50 km altitude) is 1.4 plus or minus 0.1 microbar. Both of these are not consistent with a model based on Voyager UVS and RSS observations in 1989. The atmospheric temperature from the occultation is 5 K colder than that predicted by the model and the observed pressure is a factor of 1.8 greater than the model. In our opinion, the disagreement in temperature and pressure is probably due to modeling problems at the microbar level, since measurements at this level have not previously been made. Alternatively, the difference could be due to seasonal change in Triton's atmospheric structure. The second paper reports observations of a recent stellar occultation by Triton which, when combined with earlier results, show that Triton has undergone a period of global warming since 1989. The most conservative estimates of the rate of temperature and surface-pressure increase during this period imply that the atmosphere is doubling in bulk every 10 years -- significantly faster than predicted by published frost model for Triton. Our results suggests that permanent polar caps on Triton play a dominant role in regulating seasonal atmospheric changes. Similar processes should also be active on Pluto. A third paper 'Global Warming on Triton' will appear in a the January 1999 issue of Sky and Telescope.

Elliot, James L.↗

NASA NTRS2002

Prebiotic Synthesis from CO Atmospheres: Implications for the origins of life

Most models of the primitive atmosphere around the time life originated suggest that the atmosphere was dominated by carbon dioxide, largely based on the notion that the atmosphere was derived via volcanic outgassing, and that those gases were similar to those found in modern volcanic effluent. These models tend to downplay the possibility of a strongly reducing atmosphere, which had been thought to be important for prebiotic synthesis and thus the origin of life. However, there is no definitive geologic evidence for the oxidation state of the early atmosphere and bioorganic compounds are not efficiently synthesized from CO2 atmospheres. In the present study, it was shown that a CO-CO2-N2-H2O atmosphere can give a variety of bioorganic compounds with yields comparable to those obtained from a strongly reducing atmosphere. Atmospheres containing carbon monoxide might therefore have been conducive to prebiotic synthesis and perhaps the origin of life. CO-dominant atmospheres could have existed if the production rate of CO from impacts of extraterrestrial materials were high or if the upper mantle had been more reduced than today.

Meyer, Michael↗