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NASA NTRS1981

Observations of the ionization states of energetic particles accelerated in solar flares

The ionization states and spectra of 0.3 to 2.4 MeV/nuc He, C, O and Fe are measured in a survey of ten solar flare particle events. He(plus) is found to be present in all events, which indicates the common presence of energetic He(plus) in the source material from which solar particles are accelerated. The distribution functions of He(plus), He(plus plus) and heavier elements are represented by simple exponentials of the particle speed times its rigidity to a power n, where n is between 0 and 1, and equal e-folding values. Results are consistent with a model where ions are accelerated in the corona by multi-dimensional shocks out of a population taken from both hot and cold coronal regions.

Gloeckler, G.↗

NASA NTRS1987

The azimuthal and radial distributions of HI and H2 in NGC 6946

A study was completed of the atomic and molecular components of the ISM in NGC 6946. The distribution of molecular clouds was determined from a fully sampled CO map of the inner disk using the 14-meter telescope of the FCRAO. The distribution of atomic gas was derived from VLA observations at 40" resolution in the D configuration. When comparing the global CO and HI properties with other components of the galaxy, it was found that the azimuthally averaged radial distributions of CO, H-alpha, radio continuum and blue light all exhibit similar roughly exponential falloffs, while the azimuthally averaged HI surface densities vary by only a factor of 2 out to R = 16 kpc. This indicates that while the H-alpha/CO ratio is approximately constant with radius, the CO/HI ratio decreases by a factor of 30 from the center of the galaxy to R = 10 kpc.

Tacconi-Garman, Linda J.↗

NASA NTRS1992

Effect of the geomagnetic field on the diffusion of meteor trains

A solution to the problem of the diffusion of a meteor train in the geomagnetic field from an initial line density may be written in closed form in terms of effective diffusion coefficients depending on direction, enabling detailed calculations across the entire range of angle of train to field and relevant heights. While the effective diffusion coefficient in the plane of train and field then remains close to the zero field ambipolar value right up to 90 deg, the effective coefficient in the direction of the normal to plane of train and field drops steadily to its theta = 0 value at theta = 90 deg. At 95 km this corresponds to a change of almost 5 km, in 'diffusion height', that is, the height of an underdense meteor calculated on the basis of the exponential decay of its radar echo. We have estimated the consequent changes in the expected distribution of diffusion heights for various orientations of radar antenna and find the dependence on azimuth is very marked. The effect of the field is relatively minor for a south pointing beam but very strong if the beam is pointing north.

Jones, William↗

NASA NTRS2009

A Method for Retrieving Ground Flash Fraction from Satellite Lightning Imager Data

A general theory for retrieving the fraction of ground flashes in N lightning observed by a satellite-based lightning imager is provided. An "exponential model" is applied as a physically reasonable constraint to describe the measured optical parameter distributions, and population statistics (i.e., mean, variance) are invoked to add additional constraints to the retrieval process. The retrieval itself is expressed in terms of a Bayesian inference, and the Maximum A Posteriori (MAP) solution is obtained. The approach is tested by performing simulated retrievals, and retrieval error statistics are provided. The ability to retrieve ground flash fraction has important benefits to the atmospheric chemistry community. For example, using the method to partition the existing satellite global lightning climatology into separate ground and cloud flash climatologies will improve estimates of lightning nitrogen oxides (NOx) production; this in turn will improve both regional air quality and global chemistry/climate model predictions.

Koshak, William J.↗

NASA NTRS1979

Observed distribution functions of H, He, C, O, and Fe in corotating energetic particle streams: Implications for interplanetary acceleration and propagation

Distribution functions for H, He, C, O, and Fe derived from our IMP 8 measurements of approximately 0.15 to approximately 8 MeV/nucleon particles in three corotating streams observed near earth are shown to have a simple exponential dependence on the particle speed. The e-folding speed, v sub o, is typically 0.01c, is found to be the same for the distribution functions of all elements examined, and varies little from one corotating event to the next. The relative abundances of energetic particles in these events resemble most closely the solar coronal composition and, thus, presumably that of the solar wind. These results may imply that the acceleration of these particles, which occurs in corotating interaction regions at several AU from the sun, is by a statistical process.

Gloeckler, G.↗

NASA NTRS1986

Consideration of some factors affecting low-frequency fuselage noise transmission for propeller aircraft

Possible reasons for disagreement between measured and predicted trends of sidewall noise transmission at low frequency are investigated using simplified analysis methods. An analytical model combining incident plane acoustic waves with an infinite flat panel is used to study the effects of sound incidence angle, plate structural properties, frequency, absorption, and the difference between noise reduction and transmission loss. Analysis shows that these factors have significant effects on noise transmission but they do not account for the differences between measured and predicted trends at low frequencies. An analytical model combining an infinite flat plate with a normally incident acoustic wave having exponentially decaying magnitude along one coordinate is used to study the effect of a localized source distribution such as is associated with propeller noise. Results show that the localization brings the predicted low-frequency trend of noise transmission into better agreement with measured propeller results. This effect is independent of low-frequency stiffness effects that have been previously reported to be associated with boundary conditions.

Mixson, J. S.↗

NASA NTRS1987

Linear and nonlinear dynamic instability of rotating polytropes

A three-dimensional hydrodynamic computer program is used to study the growth of nonaxisymmetric structures in rapidly rotating, self-gravitating polytropes. Models with polytropic index n = 0.8, 1.0, 1.3, 1.5, and 1.8 are studied. The initially axisymmetric equilibria are constructed by the Ostriker-Mark self-consistent-field method. The nonaxisymmetric pattern that develops out of low-amplitude random noise is a two-armed spiral with a well-defined pattern speed and growth rate which closely match properties of the toroidal mode predicted from the linear, second-order tensor-virial equation. A Fourier analysis of each polytrope's azimuthal density distribution shows that, even in the linear amplitude regime, higher-order angular patterns also develop exponentially in time. The higher-order patterns ultimately move in synchronization with the broad two-armed spiral, creating a narrow two-armed spiral. As the polytropic index is decreased, a more open and centrally more barlike pattern develops.

Williams, Harold A.↗

NASA NTRS2010

A Ground Flash Fraction Retrieval Algorithm for GLM

A Bayesian inversion method is introduced for retrieving the fraction of ground flashes in a set of N lightning observed by a satellite lightning imager (such as the Geostationary Lightning Mapper, GLM). An exponential model is applied as a physically reasonable constraint to describe the measured lightning optical parameter distributions. Population statistics (i.e., the mean and variance) are invoked to add additional constraints to the retrieval process. The Maximum A Posteriori (MAP) solution is employed. The approach is tested by performing simulated retrievals, and retrieval error statistics are provided. The approach is feasible for N greater than 2000, and retrieval errors decrease as N is increased.

Koshak, William J.↗

NASA NTRS2011

The Impacts of an Observationally-Based Cloud Fraction and Condensate Overlap Parameterization on a GCM's Cloud Radiative Effect

It has been shown that the details of how cloud fraction overlap is treated in GCMs has substantial impact on shortwave and longwave fluxes. Because cloud condensate is also horizontally heterogeneous at GCM grid scales, another aspect of cloud overlap should in principle also be assessed, namely the vertical overlap of hydrometeor distributions. This type of overlap is usually examined in terms of rank correlations, i.e., linear correlations between hydrometeor amount ranks of the overlapping parts of cloud layers at specific separation distances. The cloud fraction overlap parameter and the rank correlation of hydrometeor amounts can be both expressed as inverse exponential functions of separation distance characterized by their respective decorrelation lengths (e-folding distances). Larger decorrelation lengths mean that hydrometeor fractions and probability distribution functions have high levels of vertical alignment. An analysis of CloudSat and CALIPSO data reveals that the two aspects of cloud overlap are related and their respective decorrelation lengths have a distinct dependence on latitude that can be parameterized and included in a GCM. In our presentation we will contrast the Cloud Radiative Effect (CRE) of the GEOS-5 atmospheric GCM (AGCM) when the observationally-based parameterization of decorrelation lengths is used to represent overlap versus the simpler cases of maximum-random overlap and globally constant decorrelation lengths. The effects of specific overlap representations will be examined for both diagnostic and interactive radiation runs in GEOS-5 and comparisons will be made with observed CREs from CERES and CloudSat (2B-FLXHR product). Since the radiative effects of overlap depend on the cloud property distributions of the AGCM, the availability of two different cloud schemes in GEOS-5 will give us the opportunity to assess a wide range of potential cloud overlap consequences on the model's climate.

Oreopoulos, Lazaros↗

NASA NTRS2000

Southern Alaska as an Example of the Long-Term Consequences of Mountain Building Under the Influence of Glaciers

Southern Alaska is a continent-scale region of ongoing crustal deformation within the Pacific-North American plate boundary zone. Glaciers and glacial erosion have dictated patterns of denudation in the orogen over the last approx. 5 My. The orogen comprises three discrete topographic domains from south to north, respectively: (1) the Chugach/St. Elias Range; (2) the Wrangell Mountains; and (3) the eastern Alaska Range. Although present deformation is distributed across the orogen, much of the shortening and uplift are concentrated in the Chugach/St. Elias Range. A systematic increase in topographic wavelength of the range from east to west reflects east-to-west increases in the width of a shallowly-dipping segment of the plate interface, separation of major upper plate structures, and a decrease in the obliquity of plate motion relative to the plate boundary. Mean elevation decays exponentially from approx. 2500 m to approx. 1100 m from east to west, respectively. Topographic control on the present and past distribution of glaciers is indicated by close correspondence along the range between mean elevation and the modern equilibrium line altitude of glaciers (ELA) and differences in the modern ELA, mean annual precipitation and temperature across the range between the windward, southern and leeward, northern flanks. Net, range- scale erosion is the sum of: (1) primary bedrock erosion by glaciers and (2) erosion in areas of the landscape that are ice-marginal and are deglaciated at glacial minima. Oscillations between glacial and interglacial climates controls ice height and distribution, which, in turn, modulates the locus and mode of erosion in the landscape. Mean topography and the mean position of the ELA are coupled because of the competition between rock uplift, which tends to raise the ELA, and enhanced orographic precipitation accompanying mountain building, which tends to lower the ELA. Mean topography is controlled both by the 60 deg latitude and maritime setting of active deformation and by the feedback between shortening and uplift, glacial erosion, and orographic effects on climate accompanying mountain building.

Meigs, Andrew↗

NASA NTRS1992

A Gaussian measure of quantum phase noise

We study the width of the semiclassical phase distribution of a quantum state in its dependence on the average number of photons (m) in this state. As a measure of phase noise, we choose the width, delta phi, of the best Gaussian approximation to the dominant peak of this probability curve. For a coherent state, this width decreases with the square root of (m), whereas for a truncated phase state it decreases linearly with increasing (m). For an optimal phase state, delta phi decreases exponentially but so does the area caught underneath the peak: all the probability is stored in the broad wings of the distribution.

Schleich, Wolfgang P.↗

NASA NTRS1982

Radar scattering laws for the lunar surface

Bistatic radar observations of quasi-specular scatter from the lunar surface at 13 and 116 cm wavelengths have been expressed in terms of probability densities of the underlying surface slope distributions. These show best agreement with a Hagfors scattering function, although other forms having predominantly Gaussian or exponential characteristics also occur. Estimates of root mean square (rms) surface slope derived from these function range from 4 deg rms in maria to at least 8 deg rms in highlands. These are values appropriate to 25 m horizontal scales and represent averages over tens of square kilometers of surface area. The effective scattering roughness varies with wavelength, most strongly in maria, where its behavior is consistent with that expected from an immature, i.e., unsaturated cratered surface. There is very little variation in scattering roughness with wavelength in highlands area.

Simpson, R. A.↗

NASA NTRS1985

Effect of flow oscillations on cavity drag and a technique for their control

Experiments to relate the state of the shear layer to cavity drag have been performed in a water channel using a 4" axisymmetric cavity model. Detailed flow measurements in various cavity flow oscillation phases, amplitude amplification along the flow direction, distribution of shear stress, and other momentum flux obtained by laser Doppler velocimeter are presented. Measurements show exponential dependence of cavity drag on the length of the cavity. A jump in the cavity drag coefficient is observed as the cavity flow shows a bluff body wake type behavior. Natural and forced oscillations are introduced by a sinusoidally heated thin-film strip which excites the Tollmein-Schlichting waves in the boundary layer upstream of the gap. For a large gap, self-sustained periodic oscillations are observed, while for smaller gaps, which do not oscillate naturally, periodical oscillations can be obtained by external forcing through the strip heater. The drag of the cavity can be increased by one order of magnitude in the non-oscillating case through external forcing. Also, it is possible to completely eliminate mode switching by external forcing. For the first time, it is demonstrated that amplitude of cavity flow Kelvin-Helmholtz wave is dampened or cancelled by introduction of external perturbation of natural flow frequency but different phase.

Gharib, M.↗

NASA NTRS1986

Rain cell size statistics derived from radar observations at Wallops Island, Virginia

An investigation of two-dimensional rain cell size statistics has analyzed regression relations relating radar-determined rain rates to disdrometer data. This has yielded least-squares fits of radar reflectivity factors, and the application of a contouring program has generated 22,000 contours in which each isopleth belongs to predefined rain-rate intervals. An abundance of total and cell contours were observed belonging to all rain-rate categories. Both the computed number distributions and the conditional cumulative distributions as a function of contour diameter were found to be represented with good approximation by given exponential functions.

Goldhirsh, J.↗

NASA NTRS1991

Nongray radiative gas analyses using the S-N discrete ordinates method

The S-N discrete ordinates method is applied to analyze radiative heat transfer in nongray gases. Spectral correlation between the terms in the equation of transfer is considered for black or nearly nonreflecting walls. Formulations to apply the S-N method using a narrow-band or the exponential wide-band model are presented. The net radiative wall heat fluxes and the radiative source distributions are obtained for uniform, parabolic, and boundary layer-type temperature profiles, as well as for a parabolic concentration profile. The narrow- and wide-band nongray solutions are compared with gray-band approximations using the same band models. The computational speed of the gray-band approximation is obtained at the expense of accuracy in the internal fluxes and radiative source distributions. The wall radiative flux predictions by the gray-band approximation are satisfactory.

Kim, T. K.↗

NASA NTRS2018

A Concept of Operations for Earth Science Data Archive and Distribution in the Cloud

Science data systems can enable more comprehensive Earth system research by evolving to take advantage of advances in commercial computer technology services. Since their inception twenty five years ago, NASA's Earth Observing System Data and Information System (EOSDIS) Distributed Active Archive Centers (DAACs) have periodically evolved to utilize new technology and expand research using the exponential growth and diversity of Earth observations. Recently, with the advent of a maturing commercial compute services industry and upcoming high data volume missions such as the Surface Water and Ocean Topography (SWOT) mission and the NASA-Indian Space Research Organization Synthetic Aperture Radar (NISAR) mission, options were explored and a decision made to utilize commercial compute and storage services. This paper presents an overview of the concept of operations under development for the DAACs in the Cloud. We highlight the goals and expected advantages of utilizing Cloud services. We outline EOSDIS operations tenets and driving principles. A high-level view of EOSDIS system of systems target architecture serves as context for describing principle interactions. Concepts for key DAAC system and EOSDIS enterprise functions characterize automated end-to-end operations but mark nominal check and recovery points. Concepts are presented for managing Cloud resources, including organizational roles and responsibilities of the NASA project and DAAC personnel. Scenarios we use to further distinguish between what the system will do and what configuration and controls operators will have. Examples include interactions with data providers and data consumers with both in-cloud and on-premise facilities.

Moses, John F.↗

NASA NTRS1990

Stationary orbits of satellites of disk galaxies

The satellite of an S-galaxy will experience opposing dynamical-friction forces from the stars of the disk and the halo. If these forces are in balance, the satellite may travel in a stable, near-circular orbit whose radius, for a wide range of physical parameters, should be limited to a zone 1.2 to 1.4 times the disk radius, much as is observed. The idea is very simple. The dynamical friction acting on a small satellite, moving through a stellar galactic halo, makes this satellite slow down. On the other hand, a stellar disk, rotating faster than a satellite, makes it speed up. But the density distributions in radius for disk's and halo's stars in real flat galaxies are quite different (respectively, exponential and power-law). Moreover, the observational data show that the exponential profile for disk's surface density drops abruptly at some radius (r sub d). So it is natural to expect that a stationary orbit could be near the edge of a disk (where two effects are mutually compensated).

Polyachenko, Valerij L.↗

NASA NTRS1991

Galactic structure from the Spacelab infrared telescope. II - Luminosity models of the Milky Way

A 2.4-micron map of the northern Galactic plan is used to determine the 3D luminosity distribution of the Milky Way. The radial surface brightness profile of the disk is found to have an exponential scale length of 3.0 kpc. In the solar neighborhood, the scale height is about 247 pc, which is in agreement with star counts perpendicular to the Galactic plane. The scale height is not constant with the radius but decreases to about 165 pc. To the first order, the bulge can be represented by an oblate spheroid with an axis ratio of 0.61. The 2.2-micron/12-micron flux ratio for the bulge is typical of other dust-free spheroidal systems. Luminosity fluctuations along the Galactic plane are found to be caused chiefly by variations in the line-of-sight extinction.

Kent, S. M.↗