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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 289 records · Page 16

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NASA NTRS2004

Use of Radon for Evaluation of Atmospheric Transport Models: Sensitivity to Emissions

This paper presents comparative analyses of atmospheric radon (Rn) distributions simulated using different emission scenarios and the observations. Results indicate that the model generally reproduces observed distributions of Rn but there are some biases in the model related to differences in large-scale and convective transport. Simulations presented here use an off-line three-dimensional chemical transport model driven by assimilated winds and two scenarios of Rn fluxes (atom/cm s) from ice-free land surfaces: (A) globally uniform flux of 1.0, and (B) uniform flux of 1.0 between 60 deg. S and 30 deg. N followed by a sharp linear decrease to 0.2 at 70 deg. N. We considered an additional scenario (C) where Rn emissions for case A were uniformly reduced by 28%. Results show that case A overpredicts observed Rn distributions in both hemispheres. Simulated northern hemispheric (NH) Rn distributions from cases B and C compare better with the observations, but are not discernible from each other. In the southern hemisphere, surface Rn distributions from case C compare better with the observations. We performed a synoptic scale source-receptor analysis for surface Rn to locate regions with ratios B/A and B/C less than 0.5. Considering an uncertainty in regional Rn emissions of a factor of two, our analysis indicates that additional measurements of surface Rn particularly during April-October and north of 50 deg. N over the Pacific as well as Atlantic regions would make it possible to determine if the proposed latitude gradient in Rn emissions is superior to a uniform flux scenario.

Gupta, Mohan L.↗

NASA NTRS1988

A two component model for thermal emission from organic grains in Comet Halley

Observations of Comet Halley in the near infrared reveal a triple-peaked emission feature near 3.4 micrometer, characteristic of C-H stretching in hydrocarbons. A variety of plausible cometary materials exhibit these features, including the organic residue of irradiated candidate cometary ices (such as the residue of irradiated methane ice clathrate, and polycyclic aromatic hydrocarbons. Indeed, any molecule containing -CH3 and -CH2 alkanes will emit at 3.4 micrometer under suitable conditions. Therefore tentative identifications must rest on additional evidence, including a plausible account of the origins of the organic material, a plausible model for the infrared emission of this material, and a demonstration that this conjunction of material and model not only matches the 3 to 4 micrometer spectrum, but also does not yield additional emission features where none is observed. In the case of the residue of irradiated low occupancy methane ice clathrate, it is argued that the lab synthesis of the organic residue well simulates the radiation processing experienced by Comet Halley.

Chyba, Christopher↗

NASA NTRS2017

Refined Use of Satellite Aerosol Optical Depth Snapshots to Constrain Biomass Burning Emissions in the GOCART Model

Simulations of biomass burning (BB) emissions in global chemistry and aerosol transport models depend on external inventories, which provide location and strength of burning aerosol sources. Our previous work (Petrenko et al., 2012) shows that satellite snapshots of aerosol optical depth (AOD) near the emitted smoke plume can be used to constrain model-simulated AOD, and effectively, the assumed source strength. We now refine the satellite-snapshot method and investigate applying simple multiplicative emission correction factors for the widely used Global Fire Emission Database version 3 (GFEDv3) emission inventory can achieve regional-scale consistency between MODIS AOD snapshots and the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model. The model and satellite AOD are compared over a set of more than 900 BB cases observed by the MODIS instrument during the 2004, and 2006-2008 biomass burning seasons. The AOD comparison presented here shows that regional discrepancies between the model and satellite are diverse around the globe yet quite consistent within most ecosystems. Additional analysis of including small fire emission correction shows the complimentary nature of correcting for source strength and adding missing sources, and also indicates that in some regions other factors may be significant in explaining model-satellite discrepancies. This work sets the stage for a larger intercomparison within the Aerosol Inter-comparisons between Observations and Models (AeroCom) multi-model biomass burning experiment. We discuss here some of the other possible factors affecting the remaining discrepancies between model simulations and observations, but await comparisons with other AeroCom models to draw further conclusions.

aerosol optical depth↗

NASA NTRS1982

A model for microwave emission from vegetation-covered fields

The measured brightness temperatures over vegetation-covered fields are simulated by a radiative transfer model which treats the vegetation as a uniform canopy with a constant temperature, over a moist soil which emits polarized microwave radiation. The analytic formula for the microwave emission has four parameters: roughness height, polarization mixing factor, effective canopy optical thickness, and single scattering albedo. A good representation has been obtained with the model for both the horizontally and vertically polarized brightness temperatures at 1.4 and 5 GHz frequencies, over fields covered with grass, soybean and corn. A directly proportional relation is found between effective canopy optical thickness and the amount of water present in the vegetation canopy. The effective canopy single scattering albedo depends on vegetation type.

Mo, T.↗

NASA NTRS1988

A multicomponent model of the infrared emission from Comet Halley

A model based on a mixture of coated silicates and amorphous carbon grains produces a good spectral match to the available Halley data and is consistent with the compositional and morphological information derived from interplanetary dust particle studies and Halley flyby data. The dark appearance of comets may be due to carbonaceous coatings on the dominant (by mass) silicates. The lack of a 10 micrometer feature may be due to the presence of large silicate grains. The optical properties of pure materials apparently are not representative of cometary materials. The determination of the optical properties of additional silicates and carbonaceous materials would clearly be of use.

Swamy, K. S. Krishna↗

NASA NTRS1992

Outer heliospheric radio emissions. II - Foreshock source models

Observations of LF radio emissions in the range 2-3 kHz by the Voyager spacecraft during the intervals 1983-1987 and 1989 to the present while at heliocentric distances greater than 11 AU are reported. New analyses of the wave data are presented, and the characteristics of the radiation are reviewed and discussed. Two classes of events are distinguished: transient events with varying starting frequencies that drift upward in frequency and a relatively continuous component that remains near 2 kHz. Evidence for multiple transient sources and for extension of the 2-kHz component above the 2.4-kHz interference signal is presented. The transient emissions are interpreted in terms of radiation generated at multiples of the plasma frequency when solar wind density enhancements enter one or more regions of a foreshock sunward of the inner heliospheric shock. Solar wind density enhancements by factors of 4-10 are observed. Propagation effects, the number of radiation sources, and the time variability, frequency drift, and varying starting frequencies of the transient events are discussed in terms of foreshock sources.

Cairns, Iver H.↗

NASA NTRS1985

Models of cometary emission in the 18-cm OH transitions - The predicted behavior of Comet Halley

The return of Halley's comet to the inner solar system in 1985-1986 presents an excellent opportunity to study the behavior of a bright comet, since observations may be planned ahead of time to yield the maximum scientific return. Observations of the OH radical in the 18-cm wavelength Alpha-doublet transitions can be expected to yield significant results to cometary science in a number of areas from the measurement of the production rate of OH parent molecules (water) to the elucidation of the kinematics in the coma. Therefore, models of the OH emission from the comae of comets are presented together with predictions of brightness and spectra of Halley's Comet during the current apparition as an aid to prospective observers. The desirability of certain observational programs, including monitoring, mapping, polarimetry, and occultation experiments, are also discussed.

Schloerb, F. P.↗

NASA NTRS2011

Can the Nanoflare Model Reproduce Observed Emissions?

All theories that attempt to explain the high temperatures observed in the solar corona are based on short bursts of energy release. The intensities and velocities measured in the core of an active, however, can be steady over many hours of observation. One heating scenario that has been proposed to reconcile such observations with models is the "long nanoflare storm," where short duration heating events occur infrequently on many sub-resolutions strands. In this Letter, we examine the emission measure distribution predicted for such a heating scenario by modeling an arcade of strands in an active region core. Comparisons of the computed emission measure distributions with recent observations indicate that that the long nanoflare storm scenario implies much more 1 MK emission than is actually observed for all plausible combinations of loop lengths, heating rates, and abundances. We conjecture that if the plasma had super coronal abundances, the model may be able to match the observations at low temperatures.

Mulu-Moore, Fana M.↗

NASA NTRS1991

Surface scattering properties estimated from modeling airborne multiple emission angle reflectance data

Here, researchers apply the Hapke function to airborne bidirectional reflectance data collected over three terrestrial surfaces. The objectives of the study were to test the range of natural surfaces that the Hapke model fits and to evaluate model parameters in terms of known surface properties. The data used are multispectral and multiple emission angle data collected during the Geologic Remote Sensing Field Experiment (GRSFE) over a mud-cracked playa, an artificially roughened playa, and a basalt cobble strewn playa at Lunar Lake Playa in Nevada. Airborne remote sensing data and associated field measurements were acquired at the same time. The airborne data were acquired by the Advanced Solid State Array Spectroradiometer (ASAS) instrument, a 29-spectral band imaging system. ASAS reflectance data for a cobble-strewn surface and an artificially rough playa surface on Lunar Lake Playa can be explained with the Hanke model. The cobble and rough playa sites are distinguishable by a single scattering albedo, which is controlled by material composition; by the roughness parameter, which appears to be controlled by the surface texture and particle size; and the symmetry factor of the single particle phase function, which is controlled by particle size and shape. A smooth playa surface consisting of compacted, fine-grained particles has reflectance variations that are also distinct from either the cobble site or rough playa site. The smooth playa appears to behave more like a Lambertian surface that cannot be modeled with the Hapke function.

Guinness, Edward A.↗

NASA NTRS1987

A model for the infrared emission from the bulge of our Galaxy

A quantitative model for the IR emission from the bulge of the Galaxy is constructed using a sequence of models for circumstellar dust shells around late-type stars. The luminosity function for asymptotic giant branch stars and the distribution function for the dust-shell optical depth are derived. The total bolometric luminosity of the bulge population is 170 million solar luminosities and the total mass loss rate is 0.0083 solar mass/yr. The 12 microns and most of the 25 microns flux from the inner part of M31 can be understood as emission from a bulge population similar to that in the Galaxy. A simple model for the IR emission from late-type stars in the disk of the Galaxy is also given.

Rowan-Robinson, M.↗

NASA NTRS1991

Surface scattering properties estimated from modeling ASAS multiple emission angle reflectance data over the lunar crater volcanic field, Nevada

ASAS multispectral data were acquired over Lunar Lake playa at 12 different lighting and viewing geometries. Atmospheric models and field-based data demonstrate that atmospheric contributions to ASAS data were relatively small and were thus ignored in analyses of surface photometric properties. ASAS data of an artificially roughened playa and cobble-strewn surfaces exhibit trends of increasing reflectance as phase angle decreases. The reflectance of a natural playa surface exhibits Lambertian scattering properties that cannot be replicated with the Hapke (1986) photometric function. The Hapke model does fit the rough and cobble-strewn playa data with single-scattering albedo, asymmetry factor, and roughness terms consistent with known properties of these surfaces. No published photometric model explains the reflectance variations of all three surfaces.

Guinness, Edward A.↗

NASA NTRS1975

Solar radio continuum storms and a breathing magnetic field model

Radio noise continuum emissions observed in metric and decametric wave frequencies are, in general, associated with actively varying sunspot groups accompanied by the S-component of microwave radio emissions. These continuum emission sources, often called type I storm sources, are often associated with type III burst storm activity from metric to hectometric wave frequencies. This storm activity is, therefore, closely connected with the development of these continuum emission sources. It is shown that the S-component emission in microwave frequencies generally precedes, by several days, the emission of these noise continuum storms of lower frequencies. In order for these storms to develop, the growth of sunspot groups into complex types is very important in addition to the increase of the average magnetic field intensity and area of these groups. After giving a review on the theory of these noise continuum storm emissions, a model is briefly considered to explain the relation of the emissions to the storms.

Source record↗

NASA NTRS2013

Inverse Modeling of Texas NOx Emissions Using Space-Based and Ground-Based NO2 Observations

Inverse modeling of nitrogen oxide (NOx) emissions using satellite-based NO2 observations has become more prevalent in recent years, but has rarely been applied to regulatory modeling at regional scales. In this study, OMI satellite observations of NO2 column densities are used to conduct inverse modeling of NOx emission inventories for two Texas State Implementation Plan (SIP) modeling episodes. Addition of lightning, aircraft, and soil NOx emissions to the regulatory inventory narrowed but did not close the gap between modeled and satellite observed NO2 over rural regions. Satellitebased top-down emission inventories are created with the regional Comprehensive Air Quality Model with extensions (CAMx) using two techniques: the direct scaling method and discrete Kalman filter (DKF) with Decoupled Direct Method (DDM) sensitivity analysis. The simulations with satellite-inverted inventories are compared to the modeling results using the a priori inventory as well as an inventory created by a ground-level NO2 based DKF inversion. The DKF inversions yield conflicting results: the satellite based inversion scales up the a priori NOx emissions in most regions by factors of 1.02 to 1.84, leading to 3-55% increase in modeled NO2 column densities and 1-7 ppb increase in ground 8 h ozone concentrations, while the ground-based inversion indicates the a priori NOx emissions should be scaled by factors of 0.34 to 0.57 in each region. However, none of the inversions improve the model performance in simulating aircraft-observed NO2 or ground-level ozone (O3) concentrations.

Nitrogen dioxide↗

NASA NTRS2004

Use of IRI to Model the Effect of Ionosphere Emission on Earth Remote Sensing at L-Band

Microwave remote sensing in the window at 1.413 GHz (L-band) set aside for passive use only is important for monitoring sea surface salinity and soil moisture. These parameters are important for understanding ocean dynamics and energy exchange between the surface and atmosphere, and both NASA and ESA plan to launch satellite sensors to monitor these parameters at L-band (Aquarius, Hydros and SMOS). The ionosphere is an important source of error for passive remote sensing at this frequency. In addition to Faraday rotation, emission from the ionosphere is also a potential source of error at L-band. As an aid for correcting for emission, a regression model is presented that relates ionosphere emission to the integrated electron density (TEC). The goal is to use TEC from sources such as TOPEX, JASON or GPS to obtain estimates of emission over the oceans where the electron density profiles needed to compute emission are not available. In addition, data will also be presented to evaluate the use of the IRI for computing emission over the ocean.

Abraham, Saji↗

NASA NTRS1991

A model for the infrared emission from an OB star cluster environment

A model for the infrared emission from the neighborhood of an OB star cluster is described. The distribution of gas and dust around the stars, properties of the dust, and the cluster and interstellar radiation fields are variable. The model can be applied to regions around clusters embedded to various degrees in their parental molecular clouds (i.e., compact H II regions, blister-type H II regions, and the tenuous H II regions ionized by naked O stars). The model is used to simulate IRAS observations of a typical blister H II region. Infrared surface brightness and spectral energy distributions are predicted and the impact of limited spatial resolution is illustrated. The model results are shown to be consistent with observations of the exemplary outer Galaxy OB cluster NGC 7380. It is planned to use the model as a diagnostic tool to probe the physical conditions and dust properties in star-formation regions and, ultimately, in an interpretation of the spectral energy distributions of spiral galaxies.

Leisawitz, D.↗

NASA NTRS2004

Interstellar Dust Models Consistent with Extinction, Emission, and Abundance Constraints

We present new interstellar dust models which have been derived by simultaneously fitting the far ultraviolet to near infrared extinction, the diffuse infrared emission, and, unlike previous models, the elemental abundances in dust for the diffuse interstellar medium. We found that dust models consisting of a mixture of spherical graphite and silicate grains, polycyclic aromatic hydrocarbon (PAH) molecules, in addition to porous composite particles containing silicate, organic refractory, and water ice, provide an improved .t to the UV-to-infrared extinction and infrared emission measurements, while consuming the amounts of elements well within the uncertainties of adopted interstellar abundances, including B star abundances. These models are a signi.cant improvement over the recent Li & Draine (2001, ApJ, 554, 778) model which requires an excessive amount of silicon to be locked up in dust: 48 ppm (atoms per million of H atoms), considerably more than the solar abundance of 34 ppm or the B star abundance of 19 ppm.

Zubko, Viktor↗

NASA NTRS1986

Models for aurora and airglow emissions from other planetary atmospheres

Models for aurora and airglow emissions from planetary atmospheres other than the earth are surveyed, with emphasis on accomplishments of the last seven years. The goals of modeling the terrestrial planets and modeling the outer planets are very different. Because less is known about the atmospheres of the outer planets, models of their luminosity seek to provide information about the basic structure of the atmospheres and to identify the major production mechanisms. Models of the terrestrial planets have recently begun to address more complex questions about the abundances of trace and minor constituents, about transport phenomena, and about spatial and temporal variations in the atmosphere and in the processes that produce the emissions. In addition, there are a few instances in which models have been used to elucidate atomic and molecular processes that are difficult to study either in the terrestrial atmosphere or in the laboratory.

Fox, J. L.↗

NASA NTRS1978

Ultraviolet and optical spectral variability in the Be star Gamma Cassiopeiae - A coronal model for the emission

This paper reports the presence of Mg II emission, the probable presence of Si IV emission, and the possible presence of N V absorption in the UV spectrum of the B0.5 IVe star Gamma Cas. Changes in these features on time scales of several months are described. The detached-ring and mass-exchange binary models are briefly discussed and shown to be inadequate for Gamma Cas. An ad hoc generalization of the detailed stellar-wind model of Poeckert and Marlborough (1978) is presented and suggested as being qualitatively compatible with the UV data as well as with photoelectric H-alpha observations and the X-ray outburst observed in 1976. The presence of a 1-solar-mass neutron star companion with an orbital period of about 4 yr is hypothesized.

Marlborough, J. M.↗