Search NASA⌕ Search

SEARCH · Search NASA

Results for “localized emission”

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.

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

At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

POLAR-UVI and other Coordinated Observations of a Traveling Convection Vortex Event Observed on 24 July 1996

Coordinated analysis of data from the POLAR UVI instrument, ground magnetometers, incoherent scatter radar, solar wind monitors IMP-8 and WIND, and DMSP satellite is focused on a traveling convection vortex (TCV) event on 24 July 1966. Starting at 10:48 UT, ground magnetometers in Greenland and eastern Canada measure pulsations consistent with the passing overhead of a series of alternating TCV field-aligned current pairs. Sondrestrom incoherent scatter radar measures strong modulation of the strength and direction of ionospheric plasma flow, The magnetometer pulsations grow in magnitude over the next hour, peaking in intensity at 11:39 UT, at which time the UVI instrument measures a localized intensification of auroral emissions over central and western Greenland. Subsequent images show the intensification grow in strength and propagate westward (tailward) until approximately 11:58 UT at which time the emissions fade. These observations are consistent with the westward passage of two pairs of moderately intense TCVs over central Greenland followed by a third very intense TCV pair. The intensification of auroral emissions at 11:39 UT is associated with the trailing vortex of the third TCV pair, thought to be the result of an upward field-aligned current. Measurements of the solar wind suggest that a pressure change may be responsible for triggering the first two pairs of TCVS, and that a subsequent sudden change in orientation of the IMF may have produced the intensification of the third TCV pair and the associated aurora] brightening. DMSP particle data indicate that the TCVs occur on field lines which map to the boundary plasma sheet or outer edge of the low latitude boundary layer.

Clauer, C. R.↗
NASA NTRS1998

Multi-Instrument Analysis of a Traveling Convection Vortex Event on July 24, 1996 Coordinated with the Polar UVI

We present the analysis of a coordinated set of observations from the POLAR Ultraviolet Imager (UVI), ground magnetometers, incoherent scatter radar, solar wind monitors, DMSP and GOES satellites, focused on a traveling convection vortex (TCV) event on 24th July 1996. Starting at approximately 10:48 UT, around magnetometers in Greenland and northern Canada observe pulsations consistent with the passing overhead of a series of alternating TCV filed-aligned current pairs. Azimuthal scans by the Sondrestrom incoherent scatter radar located near Kangerlussuaq (formerly Sondrestrom), Greenland, at this time show strong modulation in the strength and direction of ionospheric plasma flow. The magnetometer pulsations grow in magnitude over the next hour, peaking in intensity at 11:39 UT, at which time images form the UVI instrument show a localized intensification of auroral emissions over central and western Greenland. Subsequent images show the intensification grow in strength and propagate westward (tailward) until approximately 11:58 UT at which time the intensification fades. These observations are consistent with the westward passage of two pairs of moderately intense TCVs over central Greenland followed by a third very intense TCV pair. The intensification of auroral emissions at 11:39 UT is associated with the trailing vortex of the third TCV pair, thought to be the result of an upward field aligned current. The modulated flow observed by the radar is the result of the strong electric fields associated with the impulsive TCV related field aligned current systems as they pass through the field of view of the radar. Measurements of the solar wind from the V;IND and IMP-8 spacecraft suggest that a pressure change may be responsible for triggering the first two pairs of TCVS, and that a subsequent sudden change in the orientation of the interplanetary magnetic field may have produced the intensification of the third TCV pair and the associated auroral brightening. Magnetometer data from the GOES satellite located over the eastern United States at geostationary orbit is consistent with a series of field-aligned moving tailward past the satellite. DMSP particle data indicated that the TCVs occur on field lines which map to the boundary plasma sheet (BPS).

Sitar, R. J.↗
NASA NTRS2009

The Development of Directional Decohesion Finite Elements for Multiscale Failure Analysis of Metallic Polycrystals

Atomistic simulations of intergranular fracture have indicated that grain-scale crack growth in polycrystalline metals can be direction dependent. At these material length scales, the atomic environment greatly influences the nature of intergranular crack propagation, through either brittle or ductile mechanisms, that are a function of adjacent grain orientation and direction of crack propagation. Methods have been developed to obtain cohesive zone models (CZM) directly from molecular dynamics simulations. These CZMs may be incorporated into decohesion finite element formulations to simulate fracture at larger length scales. A new directional decohesion element is presented that calculates the direction of Mode I opening and incorporates a material criterion for dislocation emission based on the local crystallographic environment to automatically select the CZM that best represents crack growth. The simulation of fracture in 2-D and 3-D aluminum polycrystals is used to illustrate the effect of parameterized CZMs and the effectiveness of directional decohesion finite elements.

Saether, Erik↗
NASA NTRS2010

Interferometry in the Era of Very Large Telescopes

Research in modern stellar interferometry has focused primarily on ground-based observatories, with very long baselines or large apertures, that have benefited from recent advances in fringe tracking, phase reconstruction, adaptive optics, guided optics, and modern detectors. As one example, a great deal of effort has been put into development of ground-based nulling interferometers. The nulling technique is the sparse aperture equivalent of conventional coronography used in filled aperture telescopes. In this mode the stellar light itself is suppressed by a destructive fringe, effectively enhancing the contrast of the circumstellar material located near the star. Nulling interferometry has helped to advance our understanding of the astrophysics of many distant objects by providing the spatial resolution necessary to localize the various faint emission sources near bright objects. We illustrate the current capabilities of this technique by describing the first scientific results from the Keck Interferometer Nuller that combines the light from the two largest optical telescopes in the world including new, unpublished measurements of exozodiacal dust disks. We discuss prospects in the near future for interferometry in general, the capabilities of secondary masking interferometry on very large telescopes, and of nulling interferometry using outriggers on very large telescopes. We discuss future development of a simplified space-borne NIR nulling architecture, the Fourier-Kelvin Stellar Interferometer, capable of detecting and characterizing an Earth twin in the near future and how such a mission would benefit from the optical wavelength coverage offered by large, ground-based instruments.

Barry, Richard K.↗
NASA NTRS2013

A First Search for Coincident Gravitational Waves and High Energy Neutrinos Using LIGO, Virgo and ANTARES Data from 2007

We present the results of the first search for gravitational wave bursts associated with high energy neutrinos. Together, these messengers could reveal new, hidden sources that are not observed by conventional photon astronomy, particularly at high energy. Our search uses neutrinos detected by the underwater neutrino telescope ANTARES in its 5 line configuration during the period January - September 2007, which coincided with the fifth and first science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed for candidate gravitational-wave signals coincident in time and direction with the neutrino events. No significant coincident events were observed. We place limits on the density of joint high energy neutrino - gravitational wave emission events in the local universe, and compare them with densities of merger and core-collapse events.

using LIGO↗
NASA NTRS2016

Unique Spectroscopy and Imaging of Mars with the James Webb Space Telescope

In this paper, we summarize the main capabilities of the James Webb Space Telescope (JWST) for performing observations of Mars. The distinctive vantage point of JWST at the Sun-Earth Lagrange point (L2) will allow sampling the full observable disk, permitting the study of short-term phenomena, diurnal processes (across the east-west axis), and latitudinal processes between the hemispheres (including seasonal effects) with excellent spatial resolutions (0.''07 at 2 micron). Spectroscopic observations will be achievable in the 0.7-5 micron spectral region with NIRSpec at a maximum resolving power of 2700 and with 8000 in the 1-1.25 micron range. Imaging will be attainable with the Near-Infrared Camera at 4.3 micrometers and with two narrow filters near 2 micron, while the nightside will be accessible with several filters in 0.5 to 2 micron. Such a powerful suite of instruments will be a major asset for the exploration and characterization of Mars. Some science cases include the mapping of the water D/H ratio, investigations of the Martian mesosphere via the characterization of the non-local thermodynamic equilibrium CO2 emission at 4.3 micron, studies of chemical transport via observations of the O2 nightglow at 1.27 micron, high-cadence mapping of the variability dust and water-ice clouds, and sensitive searches for trace species and hydrated features on the Martian surface. In-flight characterization of the instruments may allow for additional science opportunities.

Villanueva, Geronimo L.↗
NASA NTRSDate not supplied

Observation of Pollution Events at Low Altitude During TRACER-AQ – The Advantage of Adaptive Resolution Lidar

The TRACER-AQ campaign happened in August-September 2021 in Houston, Texas. Its objective was to better understand the pollution events in the coastal environment and to evaluate models and satellite observations. As a supporting instrument, NASA’s Langley Mobile Ozone Lidar (LMOL) was installed on the Houston campus, adjacent to University of Houston’s air-quality site, and performed observations of ozone and aerosols. Co-located instrumentation included a Pandora spectrophotometer, in-situ trace-gas measurements, and ozonesonde launches. Thanks to an adaptive resolution retrieval scheme, LMOL was able to detect thin-layer O3 structures at low (~200m) altitude that are not captured by the ozonesondes, and would ordinarily be missed with traditional coarse TOLNet lidar vertical averaging. We show that some of these features are not present in the models and are likely coming from local, industry-generated, emissions.

Guillaume Gronoff↗
NASA NTRS1981

The 2f/p/ circumterrestrial radio radiation as seen from ISEE 3

A narrowband highly spin-modulated radio source has been observed with the radio astronomy experiment on ISEE 3 from a position 0.01 AU upstream of the earth. The source is interpreted as radio line emission generated at twice the local plasma frequency in the vicinity of the earth's bow shock by energetic particles. The bandwidth of the 2f(p) emission varies from less than 3 kHz to more than 20 kHz and is probably broadened by solar wind density variations across the source region. The 2f(p) source is visible about 50% of the time, and the true position of its centroid is usually located within 30 earth radii of the subsolar point, but at times is observed at a distance of up to 60 earth radii. But most of these variations might result from changes in the orientation of the polarization vector in a partially polarized source or from refraction across an electron density front.

Hoang, S.↗
NASA NTRS1998

X-Ray Emission from the Unidentified Gamma Ray Transient GRO J1838-0415 and X-Ray Localization of Gamma-Ray Transients near the Galactic Plane

The investigation was focused on studying the residual X-ray emission from possible counterparts of enigmatic gamma-ray transients near the Galactic plane. These sources (discovered by our group at Columbia) are highly variable gamma-ray sources with no radio-loud spectrally flat blazar in their approx 1 deg. diameter error box. BSAX Narrow Field Instruments pointed the gamma-ray error box of the prominent non-blazar Energetic Gamma Ray Experiment Telescope (EGRET) source GRO 1838-04 twice on April 17, 1997, and on April 20, 1997. Most of the EGRET error box was imaged and several faint X-ray sources were detected. BSAX Wide Field Camera data were also obtained for a variety of sources near the Galactic plane, including GRO J1838-04.

Tavani, Marco↗
NASA NTRS1994

The Uranian aurora and its relationship to the magnetosphere

About 32 h of Voyager Ultraviolet Spectrometer (UVS) observations of Uranus H2 band airglow emission (875 less than or equal to lambda less than or equal to 1115 A) have been analyzed using the singular value decomposition (SVD) approach to inversion, producing an intensity map showing aurora at both magnetic poles. An H Lyman alpha aurora may also be present but is difficult to separate from scattered solar and local interstellar medium components. SVD analysis of variance shows that the intensity estimate is significantly larger than the error estimate over both Uranographic poles and part of the equatorial region, fortuitously including both magnetic polar regions. The Goddard Space Flight Center Q(sub 3) magnetic field model correctly predicts that the aurora should be larger in area and emit more power at the weaker N magnetic pole than at the stronger S magnetic pole. However, the auroral emissions are quite localized in magnetic longitude and so do not form complete auroral ovals. The brightest auroral emission at each magnetic pole is confined to a range of approximately 90 deg of magnetic longitude centered on the magnetotail direction, at moderate magnetic L parameter (5 less than or equal to L less than or equal to 10), but some emission at each pole is distributed over a range of more than 180 deg of longitude. The magnetic longitudes of the aurora are completely inconsistent with the 'windshield wiper' effect for either ions or electrons, indicating that some other effect, such as rapid depletion of the population of precipitating particles of highly localized strong pitch-angle diffusion, may be acting to localize emission. The low apparent L of the precipitating particles indicates that their energies may be less than or equal to 10 keV. Hence magnetospheric convection is likely to be important, and thus particles exciting the aurora may not remain on constant L shells. The precipitating particles may be a relatively low-energy population at high L that is heated to aurora-exciting energy by adiabatic compression during convection to low L. We estimate that the total auroral power output at H Lyman alpha and shorter wavelengths is about 3 x 10(exp 9) to 7 x 10(exp 9) W, requiring about 10 times that much power for excitation.

Herbert, Floyd↗
NASA NTRS1988

Prospects for exploring the local galaxies through the study of their high-energy gamma-ray emission

In the near future, high-energy (E greater than 20 MeV) gamma-ray astronomy offers the promise of a new means of examining the closest galaxies. Three local galaxies, the SMCs, LMCs, and M31, should be visible to the high-energy gamma-ray telescope on the Gamma Ray Observatory and the first two should be seen by GAMMA-1. It is expected that the intensity and the structure of both of the Magellanic Clouds can be examined in sufficient detail to study the cosmic-ray density and its variation, and, thereby, to determine the relevant scale of coupling for the cosmic rays and diffuse matter. With the assumptions of adequate sources and reasonable magnetic field strengths, both of which should likely be satisfied, very specific predictions of the gamma-ray emission can be made separating the three current cosmic-ray containment concepts, namely that it is on the scale of one to a few kiloparsec mass clustering, the whole galaxy, or some much larger scale. Further, because of the markedly different distributions of molecular and atomic hydrogen in the galaxies and the differences between the galaxies, an independent measure of the normalization of the diffuse molecular hydrogen density is possible.

Ozel, Mehmet E.↗
NASA NTRS2001

Continued Analysis of EUVE Solar System Observations

This is the final report for this project. We proposed to continue our work on extracting important results from the EUVE (Extreme UltraViolet Explorer) archive of lunar and jovian system observations. In particular, we planned to: (1) produce several monochromatic images of the Moon at the wavelengths of the brightest solar EUV emission lines; (2) search for evidence of soft X-ray emissions from the Moon and/or X-ray fluorescence at specific EUV wavelengths; (3) search for localized EUV and soft X-ray emissions associated with each of the Galilean satellites; (4) search for correlations between localized Io Plasma Torus (IPT) brightness and volcanic activity on Io; (5) search for soft X-ray emissions from Jupiter; and (6) determine the long term variability of He 58.4 nm emissions from Jupiter, and relate these to solar variability. However, the ADP review panel suggested that the work concentrate on the Jupiter/IPT observations, and provided half the requested funding. Thus we have performed no work on the first two tasks, and instead concentrated on the last three. In addition we used funds from this project to support reduction and analysis of EUVE observations of Venus. While this was not part of the original statement of work, it is entirely in keeping with extracting important results from EUVE solar system observations.

Gladstone, G. Randall↗
NASA NTRS2020

Local and Remote Mean and Extreme Temperature Response to Regional Aerosol Emissions Reductions

The climatic implications of regional aerosol and precursor emissions reductions implemented to protect human health are poorly understood. We investigate the mean and extreme temperature response to regional changes in aerosol emissions using three coupled chemistry–climate models: NOAA GFDL CM3, NCAR CESM1, and NASA GISS-E2. Our approach contrasts a long present-day control simulation from each model (up to 400 years with perpetual year 2000 or 2005 emissions) with 14 individual aerosol emissions perturbation simulations (160–240 years each). We perturb emissions of sulfur dioxide (SO2) and/or carbonaceous aerosol within six world regions and assess the statistical significance of mean and extreme temperature responses relative to internal variability determined by the control simulation and across the models. In all models, the global mean surface temperature response (perturbation minus control) to SO2 and/or carbonaceous aerosol is mostly positive (warming) and statistically significant and ranges from +0.17 K (Europe SO2) to -0.06 K (US BC). The warming response to SO2 reductions is strongest in the US and Europe perturbation simulations, both globally and regionally, with Arctic warming up to 1 K due to a removal of European anthropogenic SO2 emissions alone; however, even emissions from regions remote to the Arctic, such as SO2 from India, significantly warm the Arctic by up to 0.5 K. Arctic warming is the most robust response across each model and several aerosol emissions perturbations. The temperature response in the Northern Hemisphere midlatitudes is most sensitive to emissions perturbations within that region. In the tropics, however, the temperature response to emissions perturbations is roughly the same in magnitude as emissions perturbations either within or outside of the tropics. We find that climate sensitivity to regional aerosol perturbations ranges from 0.5 to 1.0 K (W m(exp -2))(exp -1) depending on the region and aerosol composition and is larger than the climate sensitivity to a doubling of CO2 in two of three models. We update previous estimates of regional temperature potential (RTP), a metric for estimating the regional temperature responses to a regional emissions perturbation that can facilitate assessment of climate impacts with integrated assessment models without requiring computationally demanding coupled climate model simulations. These calculations indicate a robust regional response to aerosol forcing within the Northern Hemisphere midlatitudes, regardless of where the aerosol forcing is located longitudinally. We show that regional aerosol perturbations can significantly increase extreme temperatures on the regional scale. Except in the Arctic in the summer, extreme temperature responses largely mirror mean temperature responses to regional aerosol perturbations through a shift of the temperature distributions and are mostly dominated by local rather than remote aerosol forcing.

Westervelt, Daniel M.↗
NASA NTRS1999

Ultraviolet, Optical and X-Ray Imaging of Selected Cygnus Loop Fields

During the Astro-1 and Astro-2 Space Shuttle missions in 1990 and 1995, far ultraviolet (FUV) images of five 40 ft diameter fields around the rim of the Cygnus Loop Super Nova Remnants (SNR) were observed with the Ultraviolet Imaging Telescope (UIT). These fields sample a broad range of SNR conditions including both radiative and non-radiative shocks in various geometries and scales. The UIT B5 band images discussed here sample predominantly ion-C4 lambda 1550 and the 2-photon continuum. Smaller contributions are made by emission lines of ion He-2 lambda 1640 and ion 03 lambda 1666. A unique aspect of the B5 band is its ability to sample the hydrogen 2-photon continuum from regions where the gas is recombining. We present these new FUV images and compare them with optical H-alpha and [ion O13], and ROSAT HRI X-ray images. In non-radiative shocks, existing 2-photon flux measurements from spectra and the H-alpha images suggest we are seeing approximately equal contributions from 2-photon and ion C4 emission. In radiative filaments, however, shock models and our images suggest ion C4 should dominate while spectra of specific locations seem to indicate that 2-photon emission dominates. We surmise that spectral observations on specific bright filaments have decreased locally-observed levels of ion C41 emission due to resonance scattering in that line.

Danforth, C. W.↗
NASA NTRS2018

Su Lyn: Diagnosing the Boundary Layer with UV and Hard X-Ray Data

Symbiotic stars in which the symbiotic phenomenon is powered solely by accretion, often at an average rate that is higher than in cataclysmic variable stars, provide an important opportunity to diagnose boundary layers around disk-accreting white dwarfs. Here, we investigate SU Lyncis (SU Lyn), a recently discovered example of a purely accretion-powered symbiotic star, using the first reliable X-ray spectroscopy, obtained with NuSTAR, and ultraviolet (UV) photometry obtained with Swift. SU Lyn has hard, thermal, X-ray emission that is strongly affected by a variable local absorber that has little impact on the UV emission. Its X-ray spectrum is described well using a plasma cooling from kT ≈ 21 keV, with a 3-30 keV luminosity of approximately 4.9 × 10(exp 32) erg s(exp -1). The spectrum is also consistent with the presence of reflection with an amplitude of 1.0, although in that case, the bestfit plasma temperature is 20%-25% lower. The UV to X-ray luminosity ratio of SU Lyn changed significantly between 2015 and 2016. We interpret this as a consequence of a drop by almost 90% in the accretion rate. Whereas the UV luminosity of the disk responded linearly, the luminosity of the optically thin (hard X-ray) emission from the boundary layer remained roughly constant because the boundary layer changed from partially optically thick to almost completely optically thin. Under this interpretation, we place a lower limit on the white dwarf mass of 0.7 solar mass (0.8 solar mass if we neglect reflection).

NuSTAR↗
NASA NTRSDate not supplied

High resolution assimilation of multiple satellite retrievals with emissions adjustment to improve air quality forecasting with WRF-Chem/DART

We will present results from medium (15km, 6hr cycling) and high (4 km, 6 hr cycling) spatiotemporal resolution applications of the WRF-Chem/DART ensemble, regional, air quality (AQ) forecast/assimilation system.The medium-resolution setup is applied to the Discover AQ/Front Range Air Pollution and Photochemistry Experiment (FRAPPE) domain from July 14 to July 29, 2014. The high-resolution setup is applied to a Colorado domain from July 14 to July 29, 2020. For the FRAPPE application, we assimilate MOPITT CO; IASI CO;MODIS AOD; OMI O3, NO2; and AirNow CO, O3, NO2, SO2, PM10, and PM2.5. For the Colorado application, we assimilate the same MOPITT, MODIS, and AirNow constituents as in the FRAPPE application and TROPOMI CO, O3, NO2; and synthetic TEMPO O3and NO2. WRF-Chem/DART integrates the Weather Research and Forecast (WRF) model with on-line chemistry (WRF-Chem) into the Data Assimilation Research Testbed (DART). It assimilates AirNow CO, O3, NO2, SO2, PM10, and PM2.5 measurements, MOPITT CO; IASI CO, O3; OMI O3, NO2, SO2; TROPOMI CO, O3, NO2, SO2; MODIS AOD; and synthetic TEMPO O3 and NO2 total/partial column and/or profile retrievals.WRF-Chem/DART uses: (i) the state augmentation method for adjusting emissions; (ii) state-space localization; and (iii) a near-real time scripting system. We use the medium-resolution FRAPPE application to demonstrate the incremental benefits from assimilating OMI observations with emissions adjustment and the high-resolution Colorado application to demonstrate the incremental benefits from assimilating syntheticTEMPO observations with emissions adjustment. For both applications, we expect that: (i) assimilating chemical observations will increaseAQ forecast skill; (ii) including emissions adjustment will increase forecast skill/predictability; and (iii) including assimilation of synthetic TEMPO observations will further increase forecast skill/predictability.

High resolution↗
NASA NTRS1995

A localized excess of diffuse gamma radiation

Using archival Energetic Gamma Ray Experiment Telescope (EGRET) gamma-ray data and atomic hydrogen (H I) column densities derived from 21 cm radio observations, we have found a large irregular region in the northern Galactic hemisphere extending from (l approximately 90 deg, b approximately 52 deg) to (l approximately 45 deg, b approximately 77 deg) with a significant enhancement in the gamma-ray emissivity compared to the surrounding sky. The region contains no previously identified gamma-ray point sources. The emission may arise from a localized enhancement in cosmic-ray density or from the presence of matter other than H I. If the emission is due to unseen matter, a column density enhancement equivalent to approximately 2 x 10(exp 20) H-atoms/sq cm is required.

Chen, A.↗
NASA NTRS1976

Source location measurements of terrestrial kilometric radiation obtained from lunar orbit

Two-dimensional source locations of individual terrestrial kilometric radiation (TKR) events have been measured by the Radio Astronomy Explorer-2 (RAE-2) spacecraft in lunar orbit. Although the average source location at 250 kHz is above the polar regions near the earth (r nearly 2-3 earth radii), approximately 10% of the events occur at a distance larger than 7 earth radii from the earth. Furthermore, there is considerable evidence for multiple sources and source motion over the time scale of tens of minutes. Recent TKR mechanism theories which assume that the emission occurs at or near the local electron plasma or gyrofrequency would predict generation much closer to the earth's surface. Alternative emission mechanisms or special propagation conditions are required to explain many TKR events.

Kaiser, M. L.↗