Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “spectral modeling”

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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Zonal-Mean Temperature Variations Inferred from SABER Measurements on TIMED Compared with UARS Observations

In the Numerical Spectral Model (NSM, Mayr et al., 2003), small-scale gravity waves propagating in the north/south direction can generate zonal mean (m = 0) meridional wind oscillations with periods between 2 and 4 months. These oscillations tend to be confined to low latitudes and have been interpreted to be the meridional counterpart of the wave-driven Quasi Biennial Oscillation in the zonal circulation. Wave driven meridional winds across the equator should generate, due to dynamical heating and cooling, temperature oscillations with opposite phase in the two hemispheres. We have analyzed SABER temperature measurements in the altitude range between 55 and 95 km to investigate the existence such variations. Because there are also strong tidal signatures (up to approximately 20 K) in the data, our algorithm estimates both mean values and tides together from the data. Based on SABER temperature data, the intra-annual variations with periods between 2 and 4 months can have amplitudes up to 5 K or more, depending on the altitude. Their amplitudes are in qualitative agreement with those inferred Erom UARS data (from different years). The SABER temperature variations also reveal pronounced hemispherical asymmetries, which are qualitatively consistent with wave driven meridional wind oscillations across the equator. Oscillations with similar periods have been seen in the meridional winds based on UARS data (Huang and Reber, 2003).

Huang, Frank T.↗
NASA NTRS2005

The QBO as Potential Amplifier and Conduit to Lower Altitudes of Solar Cycle Influence

In several papers, the solar cycle (SC) effect in the lower atmosphere has been linked to the Quasi-biennial Oscillation (QBO), which is generated primarily by small-scale gravity waves. Salby and Callaghan (2000) analyzed the observed zonal winds of the QBO over more than 40 years and found that it contains a relatively large SC signature at 20 km. Following up on an earlier 2D study with our global-scale Numerical Spectral Model (NSM), we discuss here a 3D study with the QBO under the influence of the SC. For a SC period of 10 years, the amplitude of the relative variations of radiative forcing is taken to vary for simplicity from 0.2% at the surface to 2% at 50 km to 20% at 100 km and above. Covering a limited time span of 40 years, this model produces in the lower stratosphere a relatively large modulation of the QBO, which appears to be related to the SC and is in qualitative agreement with the observations. Some of the energy in the QBO, confined to low latitudes primarily, is redistributed globally by the meridional circulation and planetary waves presumably, so that a measurable SC modulation is generated in the tropospheric temperatures of the polar regions. Further studies are needed, (1) to determine whether the effect is real and prevails in more extensive simulations and whether the results are robust when shorter integration steps are employed, and (2) to explore the mechanism(s) that may ample the apparent SC influence of the UV radiation extending into the lower atmosphere. Quasi-decadal oscillations, generated internally by the QBO interacting with the seasonal cycles, may interfere with or aid the SC effect.

Mayr, Hans G.↗
NASA NTRS2003

Carbon-Nitrogen-Oxygen Line Radiation and the X-ray Bowen Fluorescence Mechanism in Optically Thick, Highly Ionized Media

Radiative transfer effects due to overlapping X-ray lines in a high-temperature, optically thick, highly ionized medium are investigated. One particular example, in which the O VIII Lyalpha doublet (2(sup 2) P(sub 1/2,3/2)-1(sup 2) S(sub 1/2) coincides in frequency with the N VII Lyzeta lines (7(sup 2) P(sub 1/2,3/2)-1(sup 2) S(sub 1/2) is studied in detail to illustrate the effects on the properties of the emergent line spectrum. We solve the radiative transfer equation to study the energy transport of resonance-line radiation in a static, infinite, plane-parallel geometry, which is used to compute the destruction/escape probabilities for each of the lines for various total optical thicknesses of the medium, as well as destruction probabilities by sources of underlying photoelectric opacity. It is found that a large fraction of the O vIII Lyalpha line radiation can be destroyed by N VII, which can result in a reversal of the O VIII Lyalpha/N VII Lyalpha line intensity ratio similar to what may be seen under nonsolar abundances. Photoelectric absorption by ionized carbon and nitrogen can also subsequently increase the emission-line intensities of these ions. We show that line ratios, which are directly proportional to the abundance ratios in optically thin plasmas, are not good indicators of the true CNO abundances. Conversely, global spectral modeling that assumes optically thin conditions may yield incorrect abundance estimates when compared with observations, especially if the optical depth is large. Other potentially important overlapping lines and continua in the X-ray band are also identified, and their possible relevance to recent high-resolution spectroscopic observations with Chandra and XMM-Newton are briefly discussed.

Sako, Masao↗
NASA NTRS2003

Atomic Data for the K-vacancy States of Fe XXIV

As part of a project to compute improved atomic data for the spectral modeling of iron K lines, we report extensive calculations and comparisons of atomic data for K-vacancy states in Fe XXIV. The data sets include: (i) energy levels, line wavelengths, radiative and Auger rates; (ii) inner-shell electron impact excitation rates and (iii) fine structure inner-shell photoionization cross sections. The calculations of energy levels and radiative and Auger rates have involved a detailed study of orbital representations, core relaxation, configuration interaction, relativistic corrections, cancellation effects and semi-empirical corrections. It is shown that a formal treatment of the Breit interaction is essential to render the important magnetic correlations that take part in the decay pathways of this ion. As a result, the accuracy of the present A-values is firmly ranked at better than 10% while that of the Auger rates at only 15%. The calculations of collisional excitation and photoionization cross sections take into account the effects of radiation and spectator Auger dampings. In the former, these effects cause significant attenuation of resonances leading to a good agreement with a simpler method where resonances are excluded. In the latter, resonances converging to the K threshold display symmetric profiles of constant width that causes edge smearing.

Bautista, M. A.↗
NASA NTRS2005

The High Energy Spectrum of NGC 4151

We present first INTEGRAL observations of the type 1.5 Seyfert galaxy NGC 4151. Combining several INTEGRAL observations performed during 2003, totaling approximately 400 ksec of exposure time, allow us to study the spectrum in the 3 - 300 keV range. The measurements presented here reveal an overall spectrum from X-rays up to the soft gamma-rays that can be described by an absorbed (N(sub H) approximately equal to 5 x 10(exp 22) per square centimeter) and non-variable thermal component, plus a Fe Kalpha line, and an exponential cutoff occurs at 110 keV, consistent with earlier claims. The Galactic hydrogen column density in the line of sight is N(sub H), Gal approximately equal to 2.1 x 10 (exp 20) per square centimeter. The time resolved analysis shows little variation of the spectral parameters. The comparison with CGRO/OSSE data shows that the same spectral model can be applied over a time span of 15 years, while the flux varied by a factor of 2. Applying a Compton reflection component improves the model fit to the INTEGRAL data. Nonetheless the data available to date cannot significantly confirm or exclude the existence of reflection, nor is a high iron overabundance in the absorber, as had been previously suggested, clearly detectable.

Beckmann, V.↗
NASA NTRS2005

The QBO as Potential Amplifier and Conduit to Lower Altitudes of Solar Cycle Influence

The solar cycle (SC) effect in the lower atmosphere has been linked observationally to the Quasi-biennial Oscillation (QBO), which is generated primarily by small-scale gravity waves. Salby and Callaghan analyzed the QBO observations covering more than 40 years and found that it contains a relatively large SC signature at 20 km. Following up on a 2D study with our Numerical Spectral Model (NSM), we discuss here a 3D study in which we simulated the QBO under the influence of the SC. For a SC period of 10 years, the amplitude of the relative variations of radiative forcing is taken to vary from 0.2% at the surface to 2% at 50 km to 20% at 100 km and above. This model produces in the lower stratosphere a relatively large modulation of the QBO, which appears to be related to the SC and is in qualitative agreement with the observations. Further studies are needed, (1) to determine whether the effect is real and the results are robust and (2) to explore the mechanism(s) that may amplify the SC effect. Quasi-decadal oscillations, generated internally by the QBO interacting with the seasonal cycles, may interfere with or aid the SC effect.

Mayr, Hans G.↗
NASA NTRS2007

Quantifying the Complete Mineral Assemblages in Rocks of GUSEV Crater, Mars

Determining the complete mineralogy of Mars rocks by remote sensing has remained a challenge, because of inherent limitations in the minerals that can be detected and uncertainties in spectral modeling. A subset of the igneous rocks of Gusev crater provide a unique opportunity to determine modal mineralogy, because of limited alteration and the analytical capabilities of the Athena instrument package. Here we estimate the absolute (wt. %) abundances of Fe-bearing minerals from Moessbauer spectra (previously reported only as "areas for component subspectra"), and compare these results to the normative mineralogy calculated from APXS elemental analyses. We also test our preferred mineralogy by comparison of Mini-TES spectra with synthetic thermal emission spectra.

McSween, H. Y.↗
NASA NTRS2008

Using Space Weather Variability in Evaluating the Environment Design Specifications for NASA'S Constellation Program

Spectral models of solar particle events and trapped radiation belts are necessary for the design requirements of total ionizing radiation dose, single event effects, and spacecraft charging. Space radiation and plasma environment specifications for hardware design are necessarily conservative to assure system robustness for a wide range of space environments.

Coffey, Victoria N.↗
NASA NTRS2007

Inter-annual and Long-term Temperature Variations in the Mesopause Region at High Latitudes Generated by the Stratospheric QBO

The Numerical Spectral Model (NSM) simulates the Quasi-biennial Oscillation (QBO) that dominates the zonal circulation of the lower stratosphere at low latitudes. In the model, the QBO is generated with parameterized small-scale gravity waves (GW), which are partially augmented in 3D with planetary waves owing to baroclinic instability. Due to GW filtering, the QBO extends into the upper mesosphere, evident in UARS zonal wind and TIMED temperature measurements. While the QBO zonal winds are confined to equatorial latitudes, even in simulations with latitude-independent wave source, the associated temperature variations extend to high latitudes. The meridional circulation redistributes some of the QBO energy to focus it partially onto the Polar Regions. The resulting QBO temperature variations away from the equator tend to increase at higher altitudes to produce inter-annual variations that can exceed 5 K in the polar mesopause region -- and our 3D model simulations show that the effect is variable from year to year and can produce large differences between the two hemispheres, presumably due to interactions involving the seasonal variations. Modeling studies with the NSM have shown that long-term variations can also be generated by the QBO interacting with the seasonal cycles through OW node-filtering. A 30-month QBO, optimally synchronized by the 6-month Semi-Annual Oscillation (SAO), thus produces a 5-year or semi-decadal (SD) oscillation -- and observational evidence for that has been provided by a recent analysis of stratospheric NCEP data. In a simulation with the 2D version of the NSM, this SD oscillation extends into the upper mesosphere, and we present results to show that the related temperature variations could contribute significantly to the long-term variations of the polar mesopause region. Quasi-decadal variations could furthermore arise from the modeled solar cycle modulations of the QBO and 12-month annual oscillation. Our numerical results are discussed in the context of the observed low summer temperatures reproduced by the model, to demonstrate that the above interannual and long-term variations could contribute significantly to the climatology of Polar Mesospheric Clouds (PMC) investigated by the Aeronomy of Ice in the Mesosphere (AIM) mission.

Mayr, Hans G.↗
NASA NTRS2006

Intra-seasonal Oscillations Inferred from SABER (TIMED) and MLS (UARS) Temperature Measurements

In the zonal mean meridional winds of the upper mesosphere, intra-seasonal oscillations with periods between 1 and 4 months have been inferred from UARS measurements and independently predicted with the Numerical Spectral Model WSM). The wind oscillations tend to be confined to low latitudes and appear to be driven, at least in part, by small-scale gravity waves propagating in the meridional direction. Winds across the equator should generate, due to dynamical heating and cooling, temperature oscillations with opposite phase in the two hemispheres. Investigating this phenomenon, we have analyzed SABER temperatures from TIMED in the altitude range between 55 and 95 km to delineate with an empirical model, the year-long variability of the migrating tides and zonal mean components. The inferred seasonal variations of the diurnal tide, characterized by amplitude maxima near equinox, are in substantial agreement with UARS observations and results from the NSM. For the zonal mean, the dominant seasonal variations in the SABER temperatures, with annual (12 months) and semiannual (6 months) periodicities, agree well with those derived from UARS measurements. The intra-seasonal variations with periods between 2 and 4 months have amplitudes close to 2 K, almost half as large as those for the dominant seasonal variations. Their amplitudes are in qualitative agreement with the corresponding values inferred from UARS during different years. The SABER and UARS temperature variations reveal pronounced hemispherical asymmetries, consistent with meridional wind oscillations across the equator. The phase of the semi-annual temperature oscillations from the NSM agrees with the observations from UARS and SABER. But the amplitudes are systematically smaller, which may indicate that planetary waves are more important than is allowed for in the model. For the shorter-period intra-seasonal variations, which can be generated by gravity wave drag, the model results are generally in better agreement with the observations.

Huang, F. T.↗
NASA NTRS2006

SABER (TIMED) and MLS (UARS) Temperature Observations of Mesospheric and Stratospheric QBO and Related Tidal Variations

More than three years of temperature observations from the SABER (TIMED) and MLS WARS) instruments are analyzed to study the annual and inter-annual variations extending from the stratosphere into the upper mesosphere. The SABER measurements provide data from a wide altitude range (15 to 95 km) for the years 2002 to 2004, while the MLS data were taken in the 16 to 55 km altitude range a decade earlier. Because of the sampling properties of SABER and MLS, the variations with local solar time must be accounted for when estimating the zonal mean variations. An algorithm is thus applied that delineates with Fourier analysis the year-long variations of the migrating tides and zonal mean component. The amplitude of the diurnal tide near the equator shows a strong semiannual periodicity with maxima near equinox, which vary from year to year to indicate the influence from the Quasi-biennial Oscillation (QBO) in the zonal circulation. The zonal mean QBO temperature variations are analyzed over a range of latitudes and altitudes, and the results are presented for latitudes from 48"s to 48"N. New results are obtained for the QBO, especially in the upper stratosphere and mesosphere, and at mid-latitudes. At Equatorial latitudes, the QBO amplitudes show local peaks, albeit small, that occur at different altitudes. From about 20 to 40 km, and within about 15" of the Equator, the amplitudes can approach 3S K for the stratospheric QBO or SQBO. For the mesospheric QBO or MQBO, we find peaks near 70 km, with temperature amplitudes reaching 3.5"K, and near 85 km, the amplitudes approach 2.5OK. Morphologically, the amplitude and phase variations derived from the SABER and MLS measurements are in qualitative agreement. The QBO amplitudes tend to peak at the Equator but then increase again pole-ward of about 15" to 20'. The phase progression with altitude varies more gradually at the Equator than at mid-latitudes. A comparison of the observations with results from the Numerical Spectral Model (NSM) reveals that there is qualitative agreement. The NSM generates the QBO extending from the stratosphere into the upper mesosphere, with temperature variations extending to mid latitudes, but the predicted amplitudes are smaller than those observed.

Huang, Frank T.↗
NASA NTRS2011

The Microquasar Cyg X-1: A Short Review

We review the spectral properties of the black hole candidate Cygnus X-I. Specifically, we discuss two recent sets of multi-satellite observations. One comprises a 0.5-500 keY spectrum, obtained with eve!)' flying X-ray satellite at that time, that is among the hardest Cyg X-I spectra observed to date. The second set is comprised of 0.5-40 keV Chandra-HETG plus RXTE-PCA spectra from a radio-quiet, spectrally soft state. We first discuss the "messy astrophysics" often neglected in the study of Cyg X-I, i.e., ionized absorption from the wind of the secondary and the foreground dust scattering halo. We then discuss components common to both state extremes: a low temperature accretion disk, and a relativistically broadened Fe line and reflection. Hard state spectral models indicate that the disk inner edge does not extend beyond > or approx.= 40 GM/sq c , and may even approach as close as approx. = 6GM/sq c. The soft state exhibits a much more prominent disk component; however, its very low normalization plausibly indicates a spinning black hole in the Cyg X-I system. Key words. accretion, accretion disks - black hole physics - X-rays:binaries

Nowak, M. A.↗
NASA NTRS2011

Confirmation of IGR J01363 plus 6610 as a Be X-Ray Binary with Very Low Quiescent X-Ray Luminosity

The field containing the candidate High Mass X-ray Binary IGR J01 363+6610 was observed by XMM-Newton on 2009 July 31 for 28 ks. A Be star was previously suggested as the possible counterpart of the INTEGRAL source, and although Chandra, during a 2007 observation, did not detect an X-ray source at the position of the Be star, we find a variable source (XMMU 101 3549.5+661243) with an average X-ray flux of 2 x 10(exp -13)ergs/sq cm/s (0.2-12 keV, unabsorbed) at this position with XMM-Newton. The spectrum of this source is consistent with a hard power law with a photon index of r = 1.4+/-0.3 and a column density of N(sub H) = (15(+0.7/-0.5)) x 10(exp 22)/sq cm (90% confidence errors). These results, along with our optical investigation of other X-ray sources in the field, make the association with the Be star very likely, and the 2 kpc distance estimate for the Be star indicates an X-ray luminosity of 9.1 x 10(exp 31) ergs/s. This is lower than typical for a Be X-ray binary, and the upper limit on the luminosity was even lower ( < 1.4 x 10(exp 3)ergs/s assuming the same spectral model) during the Chandra observation. We discuss possible implications of the very low quiescent luminosity for the physical properties of IGR 101363+6610.

Tomsick, John A.↗
NASA NTRS2012

A Suzaku View of Cyclotron Line Sources and Candidates

Seventeen accreting neutron star pulsars, mostly high mass X-ray binaries with half of them Be-type transients, are known to exhibit Cyclotron Resonance Scattering Features (CRSFs) in their X-ray spectra, with characteristic line energies from 10 to 60 keY. To date about two thirds of them, plus a few similar systems without known CRSFs, have been observed with Suzaku. We present an overview of results from these observations, including the discovery of a CRSF in the transient IA1118-61 and pulse phase resolved spectroscopy of OX 301-2. These observations allow for the determination of cyclotron line parameters to an unprecedented degree of accuracy within a moderate amount of observing time. This is important since these parameters vary - e.g., with orbital phase, pulse phase, or luminosity - depending on the geometry of the magnetic field of the pulsar and the properties of the accretion column at the magnetic poles. We briefly introduce a spectral model for CRSFs that is currently being developed and that for the first time is based on these physical properties. In addition to cyclotron line measurements, selected highlights from the Suzaku analyses include dip and flare studies, e.g., of 4U 1907+09 and Vela X-I, which show clumpy wind effects (like partial absorption and/or a decrease in the mass accretion rate supplied by the wind) and may also display magnetospheric gating effects.

Pottschmidt, K.↗
NASA NTRS2012

Global Energetics of Large Solar Eruptive Events

We have evaluated the energetics of the larger solar eruptive events recorded with a variety of spacecraft instruments between February 2002 and December 2006. All of the energetically important components of the flares and of the accompanying coronal mass ejections and solar energetic particles have been evaluated as accurately as the observations allow. These components include the following : (1) the total energy in the high temperature plasma determined from the RHESSI thermal X-ray observations; (2) the total energies in accelerated electrons above 20 keV and ions above 1 MeV from RHESSI hard X-ray and gamma-ray observations, respectively; (3) the potential and kinetic energies of the CME from SOHO/LASCO observations; (4) the solar energetic particle (SEP) energy estimates from in situ measurements on ACE, GOES, and SOHO; (5) the total radiated energy from the SORCEITSI measurements where available, and otherwise from the Flare Irradiance Spectral Model (FISM). The results are assimilated and discussed relative to the probable amount of non potential magnetic energy estimated to be available in the flaring active regions from MDI line-of-sight magnetograms.

Dennis, Brian R.↗
NASA NTRS2011

Suzaku Detection of Diffuse Hard X-Ray Emission Outside Vela X

Vela X is a large, 3 deg x 2 deg, radio-emitting pulsar wind nebula (PWN) powered by the Vela pulsar in the Vela supernova remnant. Using four Suzaku/XIS observations pointed just outside Vela X, we find hard X-ray emission extending throughout the fields of view. The hard X-ray spectra are well represented by a power-law. The photon index is measured to be constant at Gamma approximates 2.4, similar to that of the southern outer part of Vela X. The power-law flux decreases with increasing distance from the pulsar. These properties lead us to propose that the hard X-ray emission is associated with the Vela PWN. The larger X-ray extension found in this work strongly suggests that distinct populations relativistic electrons form the X-ray PWN and Vela X, as was recently inferred from multiwavelength spectral modeling of Vela X.

Katsuda, Satoru↗
NASA NTRS2012

Wavelength Dependence of Solar Flare Irradiation and its Influence on the Thermosphere

The wavelength dependence of solar flare enhancement is one of the important factors determining how the Thermosphere-Ionosphere (T-I) system response to flares. To investigate the wavelength dependence of solar flare, the Flare Irradiance Spectral Model (FISM) has been run for 34 X-class flares. The results show that the percentage increases of solar irradiance at flare peak comparing to pre-flare condition have a clear wavelength dependence. In the wavelength range between 0 - 195 nm, it can vary from 1% to 10000%. The solar irradiance enhancement is largest ( 1000%) in the XUV range (0 - 25 nm), and is about 100% in EUV range (25 - 120 nm). The influence of different wavebands on the T-I system during the October 28th, 2003 flare (X17.2-class) has also been examined using the latest version of National Center for Atmospheric Research (NCAR) Thermosphere- Ionosphere-Electrodynamics General Circulation Model (TIE-GCM). While the globally integrated solar energy deposition is largest in the 0 - 14 nm waveband, the impact of solar irradiance enhancement on the thermosphere at 400 km is largest for 25 - 105 nm waveband. The effect of 122 - 195 nm is small in magnitude, but it decays slowly.

Huang, Yanshi↗
NASA NTRS2014

Surface Spectroscopy Center Of Excellence Project

We propose to develop a national center of excellence in Regolith Radiative Transfer (RRT), i.e., in modeling spectral reflectivity and emissivity of grainy or structured surfaces. The focus is the regime where the structural elements of grainy surfaces have grain sizes and separations of tens of microns, comparable to the wavelengths carrying diagnostic compositional information. This regime is of fundamental interest to remote sensing of planetary and terrestrial surfaces.

Regolith Radiative Transfer (RRT)↗