Nongray radiating flow about smooth symmetric bodies with large blowing.
Nongray absorption and radiation cooling on smooth symmetric blunt bodies included in modified Maslen flow field method for radiation and large blowing
Olstad, W. B.↗
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Atmospheric Solar Heating in Minor Absorption Bands
Solar radiation is the primary source of energy driving atmospheric and oceanic circulations. Concerned with the huge computing time required for computing radiative transfer in weather and climate models, solar heating in minor absorption bands has often been neglected. The individual contributions of these minor bands to the atmospheric heating is small, but collectively they are not negligible. The solar heating in minor bands includes the absorption due to water vapor in the photosynthetically active radiation (PAR) spectral region from 14284/cm to 25000/cm, the ozone absorption and Rayleigh scattering in the near infrared, as well as the O2 and CO2 absorption in a number of weak bands. Detailed high spectral- and angular-resolution calculations show that the total effect of these minor absorption is to enhance the atmospheric solar heating by approximately 10%. Depending upon the strength of the absorption and the overlapping among gaseous absorption, different approaches are applied to parameterize these minor absorption. The parameterizations are accurate and require little extra time for computing radiative fluxes. They have been efficiently implemented in the various atmospheric models at NASA/Goddard Space Flight Center, including cloud ensemble, mesoscale, and climate models.
Chou, Ming-Dah↗
Mariner-Mars absorptance experiment.
Absorptivity standard instrument to investigate solar absorptance of four surfaces used for spacecraft temperature control for Mariner IV on Mars mission
TEMPERATURE CONTROL↗
Modeling the effects of wind tunnel wall absorption on the acoustic radiation characteristics of propellers
Finite element theory is used to calculate the acoustic field of a propeller in a soft walled circular wind tunnel and to compare the radiation patterns to the same propeller in free space. Parametric solutions are present for a "Gutin" propeller for a variety of flow Mach numbers, admittance values at the wall, microphone position locations, and propeller to duct radius ratios. Wind tunnel boundary layer is not included in this analysis. For wall admittance nearly equal to the characteristic value of free space, the free field and ducted propeller models agree in pressure level and directionality. In addition, the need for experimentally mapping the acoustic field is discussed.
Baumeister, K. J.↗
Modeling the effects of wind tunnel wall absorption on the acoustic radiation characteristics of propellers
Finite element theory is used to calculate the acoustic field of a propeller in a soft walled circular wind tunnel and to compare the radiation patterns to the same propeller in free space. Parametric solutions are present for a 'Gutin' propeller for a variety of flow Mach numbers, admittance values at the wall, microphone position locations, and propeller to duct radius ratios. Wind tunnel boundary layer is not included in this analysis. For wall admittance nearly equal to the characteristic value of free space, the free field and ducted propeller models agree in pressure level and directionality. In addition, the need for experimentally mapping the acoustic field is discussed.
Baumeister, K. J.↗
Perpendicular electron heating by absorption of auroral kilometric radiation
We investigate the possibility of perpendicular heating of electrons and the generation of '90 deg -electron conics' by particle diffusion in velocity space due to wave-particle interaction with intense auroral kilometric radiation. This interaction is made possible by the downward shift in the R-X cutoff below the electron cyclotron frequency that occurs in the presence of warm plasma. We stimulate this condition and solve the diffusion equation using a finite difference algorithm. The results show strong perpendicular electron heating and indicate that the main characteristics of an electron conic distribution can be reproduced under these conditions.
Morgan, D. D.↗
MODIS Aerosol Observations used to Constrain Dust Distributions and Lifecycle in the NASA GEOS-5 Model
Approximately 240 Tg of mineral dust aerosol are transported annually from Saharan Africa to the Atlantic Ocean. Dust affects the Earth radiation budget, and plays direct (through scattering and absorption of radiation) and indirect (through modification of cloud properties and environment) roles in climate. Deposition of dust to the surface provides an important nutrient source to terrestrial and oceanic ecosystems. Dust is additionally a contributor to adverse air quality. Among the tools toward understanding the lifecycle and impacts of mineral dust aerosols are numerical models. Important constraints on these models come from quantitative satellite observations, like those from the space-based Moderate Resolution Imaging Spectroradiometer (MODIS). In particular, Kauhan et al. [2005] used MODIS aerosol observations to infer transport and deposition fluxes of Saharan dust over the Atlantic, Caribbean, and Amazonian basins. Those observations are used here to constrain the transport of dust and its interannual variability simulated in the NASA GEOS-5 general circulation model and data assimilation system. Significant uncertainty exists in the MODIS-derived fluxes, however, due to uncertainty in the wind fields provided by meteorological analyses in this region. That same uncertainty in the wind fields is manifest in our GEOS-5 simulations of dust distributions. Here we use MODIS observations to investigate the seasonality and location of the Saharan dust plume and explore through sensitivity analysis of our model the meteorological controls on the dust distribution, including dust direct radiative effects and sub-gridscale source and sink processes.
Colarco, P.↗
Tribological and Radiation Shielding Response of Novel Titanium-Boron Nitride Coatings for Lunar Structural Components
Aluminum (Al) and titanium (Ti) lightweight alloys play a crucial role in space systems due to their exceptional strength-to-weight ratio. However, their premature failure in the presence of lunar regolith and their lack of neutron shielding ability are significant challenges. To address these issues, we have developed air and vacuum plasma-sprayed hBN (hexagonal Boron Nitride) -reinforced titanium coatings with 2 and 10 vol% of hBN. Tribological studies conducted with JSC-1 A lunar regolith simulant revealed a 90 % reduction in wear volume for the Ti/2 vol% hBN coatings compared to conventional materials due to the synergistic action of harder secondary phases and solid lubrication effect of hBN. Additionally, a 27 % enhancement in radiation shielding is obtained based on the mass absorption coefficient (radiation absorbed per sample density and thickness) for VPS Ti/2 vol% hBN coatings.
Wear↗
X-ray Absorption Spectroscopy Experiments of Radiatively Ionized Argon gas
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Kelso, Kwyntero↗
A novel approach to characterize the full spectrum and radiative properties of aerosols
Organic aerosols play a significant role in the absorption and radiative budget of the atmosphere, but current modeling approaches do not adequately capture the photo-chemical and oxidative bleaching that occurs during their lifetimes. Most climate models inaccurately assume constant optical properties of these particles, therefore leading to errors in their predictions. In this study we present an approach to better parameterize the optical properties of atmospheric aerosols, including brown carbon (BrC). Using thin-film spectrometry, the full spectrum of reflectivity and emissivity was used to calculate the complex refractive index for multiple species of organic aerosols. This is in contrast to previous techniques which only probe single wavelengths. Since BrC is a complex molecular mixture, we initially focused on single species absorption using four molecular surrogates. Dye-doped polyacrylic-acid thin-films were prepared on glass slides and compared to an aerosolized collection method. Verification of the collection method will open the door to characterizing the complex refractive index of smoke and ambient aerosol.
58 GEOSCIENCES↗
Adaptive materials and systems for manipulation of electromagnetic radiation
Fully artificial, adaptive composite materials and systems, having variable transmittance, reflectance, and/or absorptance to radiation in visible, infrared, or other desired region of the electromagnetic spectrum, and methods of the manufacture and use thereof are provided. The adaptive composite materials and systems possess an unprecedented combination of properties and are, therefore, poised to enable a broad range of practical applications. The adaptive composite material incorporates at least one size-variable active area having a variable transmittance, reflectance, and/or absorptance in at least a portion of the electromagnetic spectrum and comprises at least: an elastomer substrate, a texturizing layer disposed on top of the substrate, and an optional reflective coating disposed on top of the texturizing layer. In operation, the stretching and relaxation of the elastomer substrate causes changes in the surface morphology of the texturized layers (e.g., the change in the size and depth of surface features in the texturizing layer), this in turn results in the increased or decreased transmittivity, reflectivity, and/or absorptivity of the active area.
Gorodetsky, Alon A.↗
High temperature solar photon engines
High temperature heat engines designed to make maximum use of the thermodynamic potential of concentrated solar radiation are described. Plasmas between 2000 K and 4000 K can be achieved by volumetric absorption of radiation in alkali metal vapors, leading to thermal efficiencies up to 75% for terrestrial solar power plants and up to 50% for space power plants. Two machines capable of expanding hot plasmas using practical technology are discussed. A binary Rankine cycle uses fluid mechanical energy transfer in a device known as the 'Comprex' or 'energy exchanger.' The second machine utilizes magnetohydrodynamics in a Brayton cycle for space applications. Absorption of solar energy and plasma radiation losses are investigated for a solar superheater using potassium vapor.
Hertzberg, A.↗
Thermospheric densities and temperatures from EUV absorption measurements by OSO-III.
Thermospheric densities and temperatures from solar EUV radiation atmospheric absorption measurements by OSO 3 satellite monochromator, comparing satellite and rocket data
Hall, L. A.↗
The 27-day versus 13.5-day variations in the solar Lyman-alpha radiation and the radio wave absorption in the lower ionosphere over Europe
In order to clarify the question of solar periods in absorption, the pattern was studied of the solar Lyman-alpha radiation (the principal ionizing agent of the lower ionosphere) and of the radio wave absorption at five widely spaced places in Europe. When the solar Lyman-alpha flux variability is very well developed, then it dominates in the lower ionospheric variability. The most pronounced Lyman-alpha variation on time scale day-month is the solar rotation variation (about 27 days). When the Lyman-alpha variability is developed rather poorly, as it is typical for periods dominated by the 13.5 day variability, then the lower ionospheric variability appears to be dominated by variations of meteorological origin. The conclusions hold for all five widely spaced placed in Europe.
Delamorena, B. A.↗
Solar radiation incident on the Martian surface
Calculations indicate that the maximum daily solar radiation reaching the Martian surface is about 325 cal/sq cm during southern hemisphere summer at latitude of about 40 deg S. In the ultraviolet region of the spectrum, the radiation reaching the surface at wavelengths greater than 2800 A is within 10% of the radiation incident on the atmosphere. There is significant extinction of radiation in the spectral region near 2500 A in mid and high latitudes due to absorption of radiation by ozone; radiation reaching the surface may be reduced to one one-thousandth of that incident on the atmosphere during winter. Virtually no radiation of wavelengths less than 1900 A reaches the surface because of absorption by the large column abundance of carbon dioxide. Daily and latitudinal distributions of radiation are presented for wavelengths of 3000, 2500 and 2000 A.
Kuhn, W. R.↗
Efficient Line-by-Line Calculation of Absorption Coefficients to High Numerical Accuracy
A simple yet efficient method is presented for calculating spectral absorption coefficients to high numerical accuracy. The accuracy achieved is independent of the sampling interval. The method is applicable to any analytic model of the spectral line shape.
spectral absorption absorption coefiecients spectr↗
Water vapor absorption of carbon dioxide laser radiation
An optoacoustic detector or spectrophone has been used to perform detailed measurements of the absorptivity of mixtures of water vapor in air. A (C-12) (O-16)2 laser was used as the source, and measurements were made at forty-nine different wavelengths from 9.2 to 10.7 microns. The details of the optoacoustic detector and its calibration are presented, along with a discussion of its performance characteristics. The results of the measurements of water vapor absorption show that the continuum absorption in the wavelength range covered is 5-10% lower than previous measurements.
Shumate, M. S.↗
The role of radiative acceleration in outflows from broad absorption line QSOs. 1: Comparison with O star winds
We investigate the role of radiation pressure in accelerating the broad absorption line (BAL) outflows in QSOs by comparing their properties with those of radiatively driven O star winds. We find that, owing to their lower column densities and higher velocity spreads, BAL outflows have only a few tens of strong resonance lines that are dynamically important, as compared with 10(exp 3) - 10(exp 4) lines in O star winds. We show that the combined radiative force (the 'force multiplier') declines more rapidly as a function of column density for BAL outflows than for O star winds. This is mainly attributed to the absence of lines from excited states in the BAL region. The absorbing gas in BAL outflows must have a small filling factor in order for radiative acceleration to be important dynamically. This allows the absorbing material to remain at a high enough density to maintain the ion species necessary for efficient radiative acceleration as well (as those responsible for the observed absorption), without the average flow density becoming so large that the absorbing matter cannot be accelerated by an increment larger than its own sound speed. The latter condition is necessary if the outflow is to tap a large portion of the incident photon momentum. Once a small filling factor is assumed, radiative acceleration can be more efficient in BAL outflows than in O stars. We show that terminal velocities of a few times 10(exp 4) km/sec can be expected, provided that the absorbing matter does not have to drag with it a much heavier substrate.
Arav, Nahum↗