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  • Geophysics  (452)
  • Astronomy  (243)
  • 1995-1999  (695)
  • 1935-1939
  • 1999  (695)
  • 1
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    UV irradiation of polycyclic aromatic hydrocarbons in ices: production of alcohols, quinones, and ethers (1999)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1999-02-19
    Description: Polycyclic aromatic hydrocarbons (PAHs) in water ice were exposed to ultraviolet (UV) radiation under astrophysical conditions, and the products were analyzed by infrared spectroscopy and mass spectrometry. Peripheral carbon atoms were oxidized, producing aromatic alcohols, ketones, and ethers, and reduced, producing partially hydrogenated aromatic hydrocarbons, molecules that account for the interstellar 3.4-micrometer emission feature. These classes of compounds are all present in carbonaceous meteorites. Hydrogen and deuterium atoms exchange readily between the PAHs and the ice, which may explain the deuterium enrichments found in certain meteoritic molecules. This work has important implications for extraterrestrial organics in biogenesis.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Bernstein, M P -- Sandford, S A -- Allamandola, L J -- Gillette, J S -- Clemett, S J -- Zare, R N -- New York, N.Y. -- Science. 1999 Feb 19;283(5405):1135-8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉NASA-Ames Research Center, Mail Stop 245-6, Moffett Field, CA 94035-1000, USA. mbernstein@mail.arc.nasa.gov〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10024233" target="_blank"〉PubMed〈/a〉
    Keywords: Alcohols/chemistry ; Astronomical Phenomena ; Astronomy ; Deuterium/chemistry ; Ethers/chemistry ; *Evolution, Chemical ; *Exobiology ; Hydrogen/chemistry ; *Ice ; Mass Spectrometry ; Meteoroids ; Origin of Life ; Oxidation-Reduction ; Photolysis ; Polycyclic Hydrocarbons, Aromatic/*chemistry ; Quinones/chemistry ; Spectrophotometry, Infrared ; *Ultraviolet Rays
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    A barely tested hypothesis (1999)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1999-12-28
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hogg, D W -- New York, N.Y. -- Science. 1999 Nov 26;286(5445):1679.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10610561" target="_blank"〉PubMed〈/a〉
    Keywords: Astronomical Phenomena ; Astronomy ; *Biological Evolution ; Selection, Genetic
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
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    Molecules on a space odyssey (1999)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1999-03-13
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ehrenfreund, P -- New York, N.Y. -- Science. 1999 Feb 19;283(5405):1123-4.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Austrian Academy of Sciences and at Leiden Observatory, Leiden, The Netherlands. pascale@strw.leidenuniv.nl〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10075570" target="_blank"〉PubMed〈/a〉
    Keywords: Astronomical Phenomena ; Astronomy ; *Cosmic Dust ; Deuterium/chemistry ; Earth (Planet) ; *Evolution, Chemical ; *Exobiology ; Hydrogen/chemistry ; Ice ; Meteoroids ; Origin of Life ; Polycyclic Hydrocarbons, Aromatic/*chemistry ; Ultraviolet Rays
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    Goddard Geophysical and Astronomical Observatory (1999)
    In:  CASI
    Details
    Publication Date: 2011-09-13
    Description: This report summarizes the technical parameters and the technical staff of the VLBI system at GGAO. It also gives an overview of VLBI activities during the previous year. The outlook lists the tasks planned for 1999.
    Keywords: Astronomy
    Type: International VLBI Service for Geodesy and Astrometry: 1999 Annual Report; 46-48; NASA/TP-1999-209243
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  • 5
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    Chemistry Experiments (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The purpose of the chemistry component of the model comparison is to assess to what extent differences in the formulation of chemical processes explain the variance between model results. Observed concentrations of chemical compounds are used to estimate to what degree the various models represent realistic situations. For readability, the materials for the chemistry experiment are reported in three separate sections. This section discussed the data used to evaluate the models in their simulation of the source gases and the Nitrogen compounds (NO(y)) and Chlorine compounds (Cl(y)) species.
    Keywords: Geophysics
    Type: Models and Measurements Intercomparison 2; 190-306; NASA/TM-1999-209554
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  • 6
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    Backscatter Modeling at 2.1 Micron Wavelength for Space-Based and Airborne Lidars Using Aerosol Physico-Chemical and Lidar Datasets (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Space-based and airborne coherent Doppler lidars designed for measuring global tropospheric wind profiles in cloud-free air rely on backscatter, beta from aerosols acting as passive wind tracers. Aerosol beta distribution in the vertical can vary over as much as 5-6 orders of magnitude. Thus, the design of a wave length-specific, space-borne or airborne lidar must account for the magnitude of 8 in the region or features of interest. The SPAce Readiness Coherent Lidar Experiment under development by the National Aeronautics and Space Administration (NASA) and scheduled for launch on the Space Shuttle in 2001, will demonstrate wind measurements from space using a solid-state 2 micrometer coherent Doppler lidar. Consequently, there is a critical need to understand variability of aerosol beta at 2.1 micrometers, to evaluate signal detection under varying aerosol loading conditions. Although few direct measurements of beta at 2.1 micrometers exist, extensive datasets, including climatologies in widely-separated locations, do exist for other wavelengths based on CO2 and Nd:YAG lidars. Datasets also exist for the associated microphysical and chemical properties. An example of a multi-parametric dataset is that of the NASA GLObal Backscatter Experiment (GLOBE) in 1990 in which aerosol chemistry and size distributions were measured concurrently with multi-wavelength lidar backscatter observations. More recently, continuous-wave (CW) lidar backscatter measurements at mid-infrared wavelengths have been made during the Multicenter Airborne Coherent Atmospheric Wind Sensor (MACAWS) experiment in 1995. Using Lorenz-Mie theory, these datasets have been used to develop a method to convert lidar backscatter to the 2.1 micrometer wavelength. This paper presents comparison of modeled backscatter at wavelengths for which backscatter measurements exist including converted beta (sub 2.1).
    Keywords: Geophysics
    Type: Tenth Biennial Coherent Laser Radar Technology and Applications Conference; 147-150; NASA/CP-1999-209758
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  • 7
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    Enhanced Fair-Weather Electric Fields Soon After Sunrise (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The typical fair weather electric field at the ground is between -100 and -300 V/m. At the NASA Kennedy Space Center and US Air Force Cape Canaveral Air Station (KSC) the electric field at the ground sometimes reaches -400 to -1200 V/m within an hour or two after sunrise on days that otherwise seem to be fair weather. We refer to the enhanced negative electric fields as the "sunrise enhancement." To investigate the sunrise enhancement at KSC we measured the electric field (E) in the first few hundred meters above the ground before and during several sunrise enhancements. From these E soundings we can infer the presence of charge layers and determine their thickness and charge density.
    Keywords: Geophysics
    Type: 11th International Conference on Atmospheric Electricity; 583-586; NASA/CP-1999-209261
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  • 8
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    Special Diagnostics (1999)
    In:  CASI
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    Publication Date: 2004-12-03
    Description: This section contains a number of special diagnostics that are designed to examine certain mechanisms. Section 1 reports on the method used to test the photochemical partitioning in the models. Sections 2 and 3 represent efforts to examine the model calculated production and removal rates for ozone and how the values are combined with transport rates in the models to produce the simulated ozone distributions. Sections 4 and 5 concentrate on polar processes including the dynamics aspect of vortex confinement and the chemical aspects of chlorine activation.
    Keywords: Geophysics
    Type: Models and Measurements Intercomparison 2; 363-448; NASA/TM-1999-209554
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  • 9
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    Transport Experiments (1999)
    In:  CASI
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    Publication Date: 2004-12-03
    Description: MM II defined a series of experiments to better understand and characterize model transport and to assess the realism of this transport by comparison to observations. Measurements from aircraft, balloon, and satellite, not yet available at the time of MM I [Prather and Remsberg, 1993], provide new and stringent constraints on model transport, and address the limits of our transport modeling abilities. Simulations of the idealized tracers the age spectrum, and propagating boundary conditions, and conserved HSCT-like emissions probe the relative roles of different model transport mechanisms, while simulations of SF6 and C02 make the connection to observations. Some of the tracers are related, and transport diagnostics such as the mean age can be derived from more than one of the experiments for comparison to observations. The goals of the transport experiments are: (1) To isolate the effects of transport in models from other processes; (2) To assess model transport for realistic tracers (such as SF6 and C02) for comparison to observations; (3) To use certain idealized tracers to isolate model mechanisms and relationships to atmospheric chemical perturbations; (4) To identify strengths and weaknesses of the treatment of transport processes in the models; (5) To relate evaluated shortcomings to aspects of model formulation. The following section are included:Executive Summary, Introduction, Age Spectrum, Observation, Tropical Transport in Models, Global Mean Age in Models, Source-Transport Covariance, HSCT "ANOY" Tracer Distributions, and Summary and Conclusions.
    Keywords: Geophysics
    Type: Models and Measurements Intercomparison 2; 110-189; NASA/TM-1999-209554
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  • 10
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    Simulation of the Universal-Time Diurnal Variation of the Global Electric Circuit Charging Rate (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: A global lightning model that includes diurnal and annual lightning variation, and total flash density versus latitude for each major land and ocean, has been used as the basis for simulating the global electric circuit charging rate. A particular objective has been to reconcile the difference in amplitude ratios [AR=(max-min)/mean] between global lightning diurnal variation (AR approx. = 0.8) and the diurnal variation of typical atmospheric potential gradient curves (AR approx. = 0.35). A constraint on the simulation is that the annual mean charging current should be about 1000 A. The global lightning model shows that negative ground flashes can contribute, at most, about 10-15% of the required current. For the purpose of the charging rate simulation, it was assumed that each ground flash contributes 5 C to the charging process. It was necessary to assume that all electrified clouds contribute to charging by means other than lightning, that the total flash rate can serve as an indirect indicator of the rate of charge transfer, and that oceanic electrified clouds contribute to charging even though they are relatively inefficient in producing lightning. It was also found necessary to add a diurnally invariant charging current component. By trial and error it was found that charging rate diurnal variation curves in Universal time (UT) could be produced with amplitude ratios and general shapes similar to those of the potential gradient diurnal variation curves measured over ocean and arctic regions during voyages of the Carnegie Institute research vessels.
    Keywords: Geophysics
    Type: 11th International Conference on Atmospheric Electricity; 634-637; NASA/CP-1999-209261
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  • 11
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    An Alternative Lunar Ephemeris Model for On-Board Flight Software Use (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: In calculating the position vector of the Moon in on-board flight software, one often begins by using a series expansion to calculate the ecliptic latitude and longitude of the Moon, referred to the mean ecliptic and equinox of date. One then performs a reduction for precession, followed by a rotation of the position vector from the ecliptic plane to the equator, and a transformation from spherical to Cartesian coordinates before finally arriving at the desired result: equatorial J2000 Cartesian components of the lunar position vector. An alternative method is developed here in which the equatorial J2000 Cartesian components of the lunar position vector are calculated directly by a series expansion, saving valuable onboard computer resources.
    Keywords: Astronomy
    Type: 1999 Flight Mechanics Symposium; 175-184; NASA/CP-1999-209235
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  • 12
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    The "Water-Fountain Nebula" IRAS 16342-3814: Hubble Space Telescope/Very Large Array Study of a Bipolar Protoplanetary Nebula (1999)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: We present Hubble Space Telescope (HST) Wide-Field Planetary Camera 2 images and VLA OH maser emission-line maps of the cold infrared object IRAS 16342-3814, believed to be a protoplanetary nebula. The HST images show an asymmetrical bipolar nebula, with the lobes separated by a dark equatorial waist. The two bright lobes and the dark waist are simply interpreted as bubble-like reflection nebulae illuminated by starlight escaping through polar holes in a dense, flattened, optically thick cocoon of dust, which completely obscures the central star. A faint halo can be seen surrounding each of the lobes. The bubbles are likely to have been created by a fast outflow (evidenced by H2O emission) plowing into a surrounding dense, more slowly expanding, circumstellar envelope of the progenitor asymptotic giant-branch (AGB) star (evidenced by the halo). The IRAS fluxes indicate a circumstellar mass of about 0.7 solar mass (D/2 kpc) and an AGB mass-loss rate of about 10(exp -4) solar mass/yr (V(sub exp)/15 km/s)(D/2 kpc)(sup 2) (assuming a gas-to-dust ratio of 200). OH features with the largest redshifted and blueshifted velocities are concentrated around the bright eastern and western polar lobes, respectively, whereas intermediate-velocity features generally occur at low latitudes, in the dark waist region. We critically examine evidence for the post-AGB classification of IRAS 16342-3814.
    Keywords: Astronomy
    Type: Astrophysical Journal; No. 2
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  • 13
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    Comets: Very Eccentric Characters (1999)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: Astronomical distances, even within our own solar system, are very difficult for anyone, let alone children, to imagine. In this month's space-program-related activity, students have the opportunity to create a visual and kinesthetic model of the solar system on a scale that may begin to inspire an awed comprehension of how big space is and how small Earth is. In addition, they will learn a little basic geometry in demonstrating for themselves the difference between a circular planetary orbit and an elongated elliptical cometary orbit. As a space exploration first the Jet Propulsion Laboratory (JPL), under contract to the National Aeronautics and Space Administration (NASA), is planning to send a spacecraft to rendezvous with and land on a comet. The Space Technology 4/Champollion mission is part of NASA's New Millennium Program, the primary goal of which is to test new technologies for use in 21st century planetary and earth observing missions.
    Keywords: Astronomy
    Type: The Technology Teacher: The Voice of Technology Education; Volume 58; No. 7
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  • 14
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    Atmospheric Multiple Scattering Effects on GLAS Altimetry (1999)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: Estimates of the effect of pulse stretching on satellite laser altimetry in particular the Geoscience Laser Altimeter System (GLAS), by cloud multiple scattering were made from an analytical method and from Monte Carlo calculations. The path delay of the return pulse was found to be largest for low-level clouds with particle radii (3-20 microns). The magnitude of the path delay was affected by several factors including cloud height, cloud optical depth, cloud particle size, particle shape, and receiver field of view. Polar aerosol and Rayleigh scattering usually added less than 1 cm to the overall path delay. Path delay estimates for all cloud conditions would be less if a simple Gaussian fit of the return pulse peak were used to measure the pulse's centroid. However, care must be taken in determining the centroid as factors such as pulse width, surface slope and the fitting method used will affect the estimate. A planned application for laser altimetry is high precision monitoring of the height change of polar ice sheets. In the absence of a correction algorithm, the required GLAS altimetry accuracies will not be achieved unless atmospheric channel information is used to remove profiles that are likely to be heavily contaminated by multiple scattering.
    Keywords: Geophysics
    Type: IEEE Transactions on Remote Sensing
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  • 15
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    The Progenitor of the New COMPTEL/ROSAT Supernova Remnant in Vela (1999)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: We show that (1) the newly discovered supernova remnant (SNR) GROJ0852-4642/RXJ0852.0-4622 was created by a core-collapse supernova of a massive star and (2) the same supernova event that produced the Ti-44 detected by COMPTEL from this source is probably also responsible for a large fraction of the observed Al-26 emission in the Vela region detected by the same instrument. The first conclusion is based on the fact that the remnant is currently expanding too slowly given its young age for it to be caused by a Type la supernova. If the current SNR shell expansion speed is greater than 3000 km/s, a 15 solar mass. Type II supernova with a moderate kinetic energy exploding at about 150 pc away is favored. If the SNR expansion speed is lower than 2000 km/s, as derived naively from X-ray data, a much more energetic supernova is required to have occurred at approximately 250 pc away in a dense environment at the edge of the Gum Nebula. This progenitor has a preferred ejecta mass of less than or equal to 10(Solar Mass), and therefore it is probably a Type Ib or Type Ic supernova. However, the required high ambient density of n(sub H) greater than or equal to 100 cu cm in this scenario is difficult to reconcile with the regional CO data. A combination of our estimates of the age/energetics of the new SNR and the almost perfect positional coincidence of the new SNR with the centroid of the COMPTEL Al-26 emission feature of the Vela region strongly favors a causal connection. If confirmed, this will be the first case in which both Ti-44 and Al-26 are detected from the same young SNR, and together they can be used to select preferred theoretical core-collapse supernova models.
    Keywords: Astronomy
    Type: Astrophysical Journal; Volume 514; 1-4
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  • 16
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    Quantifying the Wave Driving of the Stratosphere (1999)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: The zonal mean eddy heat flux is directly proportional to the wave activity that propagates from the troposphere into the stratosphere. This quantity is a simple eddy diagnostic which is easily calculated from conventional meteorological analyses. Because this "wave driving" of the stratosphere has a strong impact on the stratospheric temperature, it is necessary to compare the impact of the flux with respect to stratospheric radiative changes caused by greenhouse gas changes. Hence, we must understand the precision and accuracy of the heat flux derived from our global meteorological analyses. Herein, we quantify the stratospheric heat flux using five different meteorological analyses, and show that there are 30% differences between these analyses during the disturbed conditions of the northern hemisphere winter. Such large differences result from the planetary differences in the stationary temperature and meridional wind fields. In contrast, planetary transient waves show excellent agreement amongst these five analyses, and this transient heat flux appears to have a long term downward trend.
    Keywords: Geophysics
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  • 17
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    Evidence of Convection as a Dominant Source of Condensation Nuclei in the Northern Midlatitude Upper Troposphere (1999)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: We examine concurrent upper tropospheric measurements of CN (diameter greater than 4 nm). NO, and NO(Y) during the SONEX Experiment over the North Atlantic (Oct.-Nov., 1997). Elevated CN and NO(Y) concentrations observed in the upper troposphere are attributed largely to enhancements in convective outflows. We estimate that less than 7% of observed high-CN plumes (greater than 10000 /cc) may be attributed to aircraft emissions. Dilution of high-CN convective and aircraft plumes appears to be much more rapid than losses of NO(X) and CN by oxidation and coagulation, respectively, and accounts for much of observed CN concentrations. When taking into account of different time scales against dilution for observable aircraft and convective high-CN plumes (estimated to be 1:4), the contribution by aircraft emissions to CN concentrations is significant, about 20% of the convective source. We find no evidence that particle formation in convective plumes is limited by OH oxidation of SO2.
    Keywords: Geophysics
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  • 18
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    Dual Spacecraft Observations of Lobe Magnetic Field Perturbations Before, During and after Plasmoid Release (1999)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: This study examines a unique data set returned by IMP8 and Geotail on January 29, 1995 during a substorm which resulted in the ejection of a plasmoid. The two spacecraft (s/c) were situated in the north lobe of the tail and both observed a traveling compression region (TCR). From single s/c observations only the length of the plasmoid in X and an estimate of its height in Z can be determined. However, we show that dual s/c measurements of TCRs can be used to model all three dimensions of the underlying plasmoid and to estimate of its rate of expansion or contraction. For this event plasmoid dimensions of Delta(X) approximates 18, Delta(Y) approximates 30, and Delta(Z) approximates 10 R(sub e) are inferred from the IMP8 and Geotail lobe magnetic field measurements. The earthward end of the plasmoid was inferred to be near the mean location of the near-earth neutral line, X approximates -26 R(sub e). Its center was underneath IMP 8 at X approximates -34 R(sub e) and its tailward end appeared to be near X approximates -44 R(sub e). Furthermore, a factor of approximately 2 increase in the amplitude of the TCR occurred in the 1.5 min it took to move from IMP 8 to Geotail. Modeled using conservation of the magnetic flux, this increase in lobe compression implies that the underlying plasmoid was expanding at a rate of approximately 140 km/s. Such an expansion is comparable to recently reported V(sub y) speeds in "young" plasmoids in this region of the tail. Finally, the Geotail measurements indicate that a reconfiguration of the lobe magnetic field closely followed the ejection of the plasmoid which moved magnetic flux tubes into the wake behind the plasmoid where they would convect into the near-earth neutral line and reconnect.
    Keywords: Geophysics
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  • 19
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    Simulation of the December 1998 Stratospheric Major Warming (1999)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: Prior to 1991, major warmings (defined by increasing zonal mean temperatures and zonal mean easterly winds from 60degN to the pole at 10 hPa) typically occurred approximately once every two Arctic winters; a major warming in mid-Dec. 1998 was the first since Feb. 1991. The Dec. 1998 warming was also the second earliest on record. The earliest, and the only other major warming on record before the end of Dec. was in early Dec 1987; prior to that, the earliest was in late Dec./early Jan. 1984-85. The 1984-85 and 1987 warmings resulted in the warmest and weakest lower stratospheric polar vortices in the 20 years before 1998-99. Fig. 1 compares temperatures and vortex strength in 1998-99 with those in the previous 20 years, using the US National Center for Environmental Prediction (NCEP) record; 1987-88 and 1984-85 are also highlighted. The Dec. 1998 warming had a more pronounced effect on mid-stratospheric temperatures than the Dec. 1987 warming (Fig. 1a), although smaller than that of warmings later in winter (e.g., 1984-85). 10-hPa temperatures fell well below average again in late Jan. 1999 and remained unusually low until an early final warming began in late Feb. 840 K PV gradients (Fig. 1c) set a record minimum in Jan. 1999, but were near average in Feb before the final warming. The effect of the Dec. 1998 warming on lower stratospheric temperatures was comparable to that of other major warmings; there was a brief period of record-high minimum 46-hPa temperatures in early Jan 1999 (Fig. 1b), and temperatures then fell to near average for a short period in mid-Feb. Lower stratospheric PV gradients were the weakest on record during the 1998-99 winter (Fig. 1d). The evolution of the vortex and minimum temperatures during 1998-99 was remarkably similar to that during 1987-88, the only previous year when a major warming was observed before the end of Dec.
    Keywords: Geophysics
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  • 20
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    The Astro -E/XRS Calibration Program and Results (1999)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: XRS is the microcalorimeter X-ray detector aboard the US-Japanese ASTRO-E observatory, which is scheduled to be launched in early 2000. XRS is a high resolution spectrometer- with less than 9 eV resolution at 3 keV and better than 14 eV resolution over its bandpass ranging from about 0.3 keV to 15 keV. Here we present the results of our first calibration of the XRS instrument. We describe the methods used to extract detailed information about the detection efficiency and spectral redistribution of the instrument. We also present comparisons of simulations and real data to test our detector models
    Keywords: Astronomy
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  • 21
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    The Low-Mass X-Ray Binary X1832-330 in the Globular Cluster NGC 6652: A Serendipitous ASCA Observation (1999)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Low Mass X-ray Binary (LMXB) X1832-330 in NGC 6652 is one of about 10 bright X-ray sources to have been discovered in Globular Clusters. We report on a serendipitous ASCA observation of this Globular Cluster LMXB, during which a Type I burst was detected and the persistent, non-burst emission of the source was at its brightest level recorded to date. No orbital modulation was detected, which argues against a high inclination for the X1832-330 system. The spectrum of the persistent emission can be fit with a power law plus a partial covering absorber, although other models are not ruled out. Our time-resolved spectral analysis through the burst shows, for the first time, clear evidence for spectral cooling from kT = 2.4 +/- 0.6 keV to kT = 1.0 +/- 0.1 keV during the decay. The measured peak flux during the burst is approximately 10% of the Eddington luminosity for a 1.4 Solar Mass neutron star. These are characteristic of a Type I burst, in the context of the relatively low quiescent luminosity of X1832-330.
    Keywords: Astronomy
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  • 22
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    Direct Measurement of the Supernova Rate in Starburst Galaxies (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: Supernovae play a key role in the dynamics, structure, and chemical evolution of galaxies. The massive stars that end their lives as supernovae live for short times. Many are still associated with dusty star formation regions when they explode, making them difficult to observe at visible wavelengths. In active star forming regions (galactic nuclei and starburst regions), dust extintion is especially severe. Thus, determining the supernova rate in the active star forming regions of galaxies, where the supernova rate can be one or two orders of magnitude higher than the average, has proven to be difficult. From observations of SN1987A, we know that the [NiII] 6.63 micron emission line was the strongest line in the infrared spectrum for a period of a year and a half after the explosion. Since dust extintion is much less at 6.63 pm than at visible wavelengths (A(sub 6.63)/A(sub V) = 0.025), the NiII line can be used as a sensitive probe for the detection of recent supernovae. We have observed a sample of starburst galaxies at 6.63 micron using ISOCAM to search for the NiII emission line characteristic of recent supernovae. We did not detect any NiII line emission brighter than a 5sigma limit of 5 mJy. We can set upper limits to the supernova rate in our sample, scaled to the rate in M82, of less than 0.3 per year at the 90% confidence level using Bayesian methods. Assuming that a supernova would have a NiII with the same luminosity as observed in SN1987A, we find less than 0.09 and 0.15 per year at the 50% and 67% confidence levels. These rates are somewhat less if a more normal type II supernovae has a NiII line luminosity greater than the line in SN1987A.
    Keywords: Astronomy
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    A Catalog of Soft X-Ray Shadows, and More Contemplation of the 1/4 KeV Background (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: This paper presents a catalog of shadows in the 1/4 keV soft X-ray diffuse background 4 (SXRB) that were identified by a comparison between ROSAT All-Sky Survey maps and DIRB&corrected IRAS 100 micron maps. These "shadows" are the negative correlations between the surface brightness of the SXRB and the column density of the Galactic interstellar medium (ISIM) over limited angular regions (a few degrees in extent). We have compiled an extensive but not exhaustive set of 378 shadows in the polar regions of the Galaxy (Absolute value (beta) 〉 and approximately equal 20 deg.), and determined their foreground and background X-ray intensities (relative to the absorbing features), and the respective hardness ratios of that emission. The portion of the sky that was examined to find these shadows was restricted in general to regions where the minimum column density is less than and approximately equal to 4 x 10(exp 20) H/square cm, i.e., relatively high Galactic latitudes, and to regions away from distinct extended features in the SXRB such as supernova remnants and superbubbles. The results for the foreground intensities agree well with the recent results of a general analysis of the local 1/4 KeV emission while the background intensities show additional. but not unexpected scatter. The results also confirm the existence of a gradient in the hardness of the local 1/4 keV emission along a Galactic center/ anticenter axis with a temperature that varies from 10(exp 6.13) K to 10(exp 6.02) K, respectively. The average temperature of the foreground component from this analysis is 10(exp 6.08) K, compared to 10(exp 6.06) K in the previous analysis. Likewise, the average temperature for the distant component for the current and previous analyses are 10(exp 6.06) K and 10(exp 6.02) K, respectively. Finally, the results for the 1/4 keV halo emission are compared to the observed fluxes at 3/4 keV, where the lack of correlation suggests that the Galactic halo's 1/4 keV and 3/4 keV fluxes are likely produced by separate emission regions.
    Keywords: Astronomy
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    Comparisons of Upper Tropospheric Humidity Retrievals from TOVS and METEOSAT (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: Two different methods for retrieving Upper Tropospheric Humidities (UTH) from the TOVS (TIROS Operational Vertical Sounder) instruments aboard NOAA polar orbiting satellites are presented and compared. The first one, from the Environmental Technology Laboratory, computed by J. Bates and D. Jackson (hereafter BJ method), estimates UTH from a simplified radiative transfer analysis of the upper tropospheric infrared water vapor channel at wavelength measured by HIRS (6.3 micrometer). The second one results from a neural network analysis of the TOVS (HIRS and MSU) data developed at, the Laboratoire de Meteorologie Dynamique (hereafter the 3I (Improved Initialization Inversion) method). Although the two methods give very similar retrievals in temperate regions (30-60 N and S), an absolute bias up to 16% appears in the convective zone of the tropics. The two datasets have also been compared with UTH retrievals from infrared radiance measurements in the 6.3 micrometer channel from the geostationary satellite METEOSAT (hereafter MET method). The METEOSAT retrievals are systematically drier than the TOVS-based results by an absolute bias between 5 and 25%. Despite the biases, the spatial and temporal correlations are very good. The purpose of this study is to explain the deviations observed between the three datasets. The sensitivity of UTH to air temperature and humidity profiles is analysed as are the clouds effects. Overall, the comparison of the three retrievals gives an assessment of the current uncertainties in water vapor amounts in the upper troposphere as determined from NOAA and METEOSAT satellites.
    Keywords: Geophysics
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  • 25
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    Magnetism of Carbonados (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: Carbonados are porous polycrystalline (with crystal sizes up to 100 micrometer) diamonds. Carbonado is found only in alluvial deposits in Bahia, Brazil and in the Central African Republic (CAR). Alluvial deposit host is 1.5 Ga while the carbonados are between 2.6 - 3.8 Ga. The process of fusing the carbonado microcrystals together is not fully understood, partly due to fact that the origin of these carbonado, is not known. Several modes of origins are proposed for carbonado. First, a crustal origin. Carbonados have a light carbon and helium isotopic signature. They contain an enrichment of the rare-earth elements (REE). Carbonados have tightly trapped atmospheric noble gases and contain an evidence of high He content despite the carbonado expected depletion of He at mantle temperatures. Carbonados have high porosity incompatible with high pressure mantle conditions. Second, a mantle origin is proposed based on similar REE pattern to kimberlites. The presence of nitrogen platelet (by IR spectra) indicates high temperature origin and syngenetic inclusions of rutile, ilmenite, and magnetite indicates high pressure and high temperature conditions consistent with mantle origin as well. Third, it is proposed that carbonado diamonds are a result of early impacts into crustal rocks. This is indicated by the rare and controversial occurrence of high pressure diamond polymorph, londsdaleite, frequently found in diamonds from meteorite impact sites, and by observation of planar deformation features, possibly indicating shock events. Finally, it is suggested that carbonados have an extraterrestrial origin, as indicated by a long term annealing based on observation of a zero-phonon line, attributed to paired nitrogen atoms in association with a vacancy.
    Keywords: Geophysics
    Type: Lunar and Planetary Science Conference; United States
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    Extremely Low Ionospheric Peak Altitudes in the Polar-Hole Region (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: Vertical electron-density (N (sub e)) profiles, deduced from newly-available ISIS-II digital ionospheric topside-sounder data, are used to investigate the "polar-hole" region within the winter, nighttime polar cap ionosphere during solar minimum. The hole region is located around 0200 MLT near the poleward side of the auroral oval. Earlier investigations had revealed very low N (sub e) values in this region (down to 200/cu cm near 300 km). In the present study, such low N, values (approx. 100/cu cm) were only found near the ISIS (International Satellite for Ionospheric Study)-II altitude of 1400 km. The peak ionospheric concentration below the spacecraft remained fairly constant (approx. 10 (exp 5)/cu cm across the hole region but the altitude of the peak dropped dramatically. This peak dropped, surprisingly, to the vicinity of 100 km. These observations suggest that the earlier satellite in situ measurements, interpreted as deep holes in the ionospheric F-region concentration, could have been made during conditions of an extreme decrease in the altitude of the ionospheric N (sub e) peak. The observations, in combination with other data, indicate that the absence of an F-layer peak may be a frequent occurrence at high latitudes.
    Keywords: Geophysics
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    Crustal Uplift in the Southcentral Alaska Subduction Zones: A New Analysis and Interpretation of Tide Gauge Observations (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: We have examined the sea level height tide records at seven tide gauge sites in the region of southcentral Alaska that were affected by the 1964 Prince William Sound earthquake to determine the history of crustal uplift subsequent to the earthquake. There is considerable variation in the behavior depending on the location of the site relative to the 1964 rupture. At Seward, on the eastern side of the Kenai Peninsula we find a slow uplift that is consistent with elastic strain accumulation while at Seldovia and Nikiski on the western side of the Kenai we find a persistent rapid uplift of about 1 cm/yr that most likely represents a long term transient response to the earthquake, but which cannot be sustained over the expected recurrence interval for a great earthquake of several hundred years. Further to the southwest, at Kodiak, we find evidence that the rate of uplift, which is still several mm/yr, has slowed significantly over the past three and a half decades. To the east of the Kenai Peninsula we find subsidence at Cordova and an uncertain behavior at Valdez. At both of these sites there is a mathematically significant time-dependence to the uplift behavior, but the data confirming this time dependence are not as convincing as at Kodiak. At Anchorage, to the north there is little evidence of vertical motion since the earthquake. We compare these long term tide gauge records to recent GPS observations. In general there is reasonable consistency except at Anchorage and Cordova where the GPS measurement indicate somewhat more rapid uplift and subsidence, respectively.
    Keywords: Geophysics
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    Future Radiation Damage in Space Due to South Atlantic Anomaly (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: The geographic limits of the South Atlantic Anomaly, as defined by radiation damage, are compared to contours of geomagnetic total field intensity, as defined by the 1995 IGRF, for the present and recent past. The most likely secular variation of the geomagnetic field is estimated and used to extrapolate the geomagnetic field to the year 2100. This indicates that radiation damage to spacecraft and humans in space will likely increase and to cover a much larger geographic area.
    Keywords: Geophysics
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    Influence of Transport on Two-Dimensional Model Simulation: 2. Stratospheric Aircraft Perturbations (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: We have adopted the transport scenarios used in Part 1 to examine the sensitivity of stratospheric aircraft perturbations to transport changes in our 2-D model. Changes to the strength of the residual circulation in the upper troposphere and stratosphere and changes to the lower stratospheric K(sub zz) had similar effects in that increasing the transport rates decreased the overall stratospheric residence time and reduced the magnitude of the negative perturbation response in total ozone. Increasing the stratospheric K(sub yy) increased the residence time and enhanced the global scale negative total ozone response. However, increasing K(sub yy) along with self-consistent increases in the corresponding planetary wave drive, which leads to a stronger residual circulation, more than compensates for the K(sub yy)-effect, and results in a significantly weaker perturbation response, relative to the base case, throughout the stratosphere. We found a relatively minor model perturbation response sensitivity to the magnitude of K(sub yy) in the tropical stratosphere, and only a very small sensitivity to the magnitude of the horizontal mixing across the tropopause and to the strength of the mesospheric gravity wave drag and diffusion. These transport simulations also revealed a generally strong correlation between passive NO(sub y) accumulation and age of air throughout the stratosphere, such that faster transport rates resulted in a younger mean age and a smaller NO(y) mass accumulation. However, specific variations in K(sub yy) and mesospheric gravity wave strength exhibited very little NO(sub y)-age correlation in the lower stratosphere, similar to 3-D model simulations performed in the recent NASA "Models and Measurements" II analysis. The base model transport, which gives the most favorable overall comparison with inert tracer observations, simulated a global/annual mean total ozone response of -0.59%, with only a slightly larger response in the northern compared to the southern hemisphere. For transport scenarios which gave tracer simulations within some agreement with measurements, the annual/globally averaged total ozone response ranged from -0.45% to -0.70%. Our previous 1995 model exhibited overly fast transport rates, resulting in a global/annually averaged perturbation total ozone response of -0.25%, which is significantly weaker compared to the 1999 model. This illustrates how transport deficiencies can bias model simulations of stratospheric aircraft.
    Keywords: Geophysics
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    Viscoelastic Postseismic Rebound to Strike-Slip Earthquakes in Regions of Oblique Plate Convergence (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: According to the slip partitioning concept, the trench parallel component of relative plate motion in regions of oblique convergence is accommodated by strike-slip faulting in the overriding continental lithosphere. The pattern of postseismic surface deformation due to viscoelastic flow in the lower crust and asthenosphere following a major earthquake on such a fault is modified from that predicted from the conventual elastic layer over viscoelastic halfspace model by the presence of the subducting slab. The predicted effects, such as a partial suppression of the postseismic velocities by 1 cm/yr or more immediately following a moderate to great earthquake, are potentially detectable using contemporary geodetic techniques.
    Keywords: Geophysics
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    A Digital Tectonic Activity Map of the Earth (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: The subject of neotectonics, covering the structures and structural activity of the last 5 million years (i.e., post-Miocene) is a well-recognized field, including "active tectonics," focussed on the last 500,000 years in a 1986 National Research Council report of that title. However, there is a cartographic gap between tectonic maps, generally showing all features regardless of age, and maps of current seismic or volcanic activity. We have compiled a map intended to bridge this gap, using modern data bases and computer-aided cartographic techniques. The maps presented here are conceptually descended from an earlier map showing tectonic and volcanic activity of the last one million years. Drawn by hand with the National Geographic Society's 1975 "The Physical World" map as a base, the 1981 map in various revisions has been widely reproduced in textbooks and various technical publications. However, two decades of progress call for a completely new map that can take advantage of new knowledge and cartographic techniques. The digital tectonic activity map (DTM), presented in shaded relief (Fig. 1) and schematic (Fig. 2) versions, is the result. The DTM is intended to show tectonism and volcanism of the last one million years, a period long enough to be representative of global activity, but short enough that features such as fault scarps and volcanos are still geomorphically recognizable. Data Sources and Cartographic Methods The DTM is based on a wide range of sources, summarized in Table 1. The most important is the digital elevation model, used to construct a shaded relief map. The bathymetry is largely from satellite altimetry, specifically the marine gravity compilations by Smith and Sandwell (1996). The shaded relief map was designed to match the new National Geographic Society world physical map (1992), although drawn independently, from the digital elevation model. The Robinson Projection is used instead of the earlier Van der Grinten one. Although neither conformal nor equal-area, the Robinson Projection provides a reasonable compromise and retains useful detail at high latitudes.
    Keywords: Geophysics
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    Photometric Observations of 6000 Stars in the Cygnus Field (1999)
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    Publication Date: 2013-08-29
    Description: A small photometer to detect transits by extrasolar planets has been assembled and is being tested at Lick Observatory on Mt. Hamilton, California. The Vulcan photometer is constructed from a 30 cm focal length, F/2.5 AeroEktar reconnaissance lens and Photometrics PXL16800 CCD camera. A spectral filter is used to confine the pass band from 480 to 763 mn. It simultaneously monitors 6000 stars brighter than 12th magnitude within a single star field in the galactic plane. When the data are folded and phased to discover low amplitude transits, the relative precision of one-hour samples is about 1 part per thousand (10 x l0(exp -3)) for many of the brighter stars. This precision is sufficient to find jovian-size planets orbiting solar-like stars, which have signal amplitudes from 5 to 30 x l0(exp -3) depending on the inflation of the planet and the size of the star. Based on the frequency of giant inner-planets discovered by Doppler-velocity method, one or two planets should be detectable in a rich star field. The goal of the observations is to obtain the sizes of giant extrasolar planets in short-period orbits and to combine these with masses determined from Doppler velocity measurements to determine the densities of these planets. A further goal is to compare the measured planetary diameters with those predicted from theoretical models. From August 10 through September 30 of 1998, a forty nine square degree field in the Cygnus constellation centered at RA and DEC of 19 hr 47 min, +36 deg 55 min was observed. Useful data were obtained on twenty-nine nights. Nearly fifty stars showed some evidence of transits with periods between 0.3 and 8 days. Most had amplitudes too large to be associated with planetary transits. However, several stars showed low amplitude transits. The data for several transits of each of these two stars have been folded and been folded into 30 minute periods. Only Cygl433 shows any evidence of a flattened bottom that is expected when a small object transits a much larger primary. However when high-resolution spectra were obtained for both stars, the stars were found to be double-lined binaries so similar in size as to have indistinguishable transit depths. The low amplitude of the transits is explained if the stellar orbital planes are tipped approximately 5 degrees from the line of sight causing both binaries to show grazing transits. The two absorption lines, due to the H(sub beta) feature in each star, are apparent and indicate the presence of a binary system with similar components.
    Keywords: Astronomy
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    Exploration of Uncertainty in Glacier Modelling (1999)
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    Publication Date: 2013-08-29
    Description: There are procedures and methods for verification of coding algebra and for validations of models and calculations that are in use in the aerospace computational fluid dynamics (CFD) community. These methods would be efficacious if used by the glacier dynamics modelling community. This paper is a presentation of some of those methods, and how they might be applied to uncertainty management supporting code verification and model validation for glacier dynamics. The similarities and differences between their use in CFD analysis and the proposed application of these methods to glacier modelling are discussed. After establishing sources of uncertainty and methods for code verification, the paper looks at a representative sampling of verification and validation efforts that are underway in the glacier modelling community, and establishes a context for these within overall solution quality assessment. Finally, an information architecture and interactive interface is introduced and advocated. This Integrated Cryospheric Exploration (ICE) Environment is proposed for exploring and managing sources of uncertainty in glacier modelling codes and methods, and for supporting scientific numerical exploration and verification. The details and functionality of this Environment are described based on modifications of a system already developed for CFD modelling and analysis.
    Keywords: Geophysics
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    Mesospheric Odd Nitrogen Enhancements During Relativistic Electron Precipitation Events (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: The behavior of mesospheric odd nitrogen species during and following relativistic and diffuse auroral precipitation events is simulated, Below 75 km nitric oxide is enhanced in proportion to the ion pair production function associated with the electron precipitation and the length of the event. Nitrogen dioxide and nitric acid are also enhanced. At 65 km the percentage of odd nitrogen for N is 0.1%, HNO3 is 1.6%, NO2 is 15%, and NO is 83.3%. Between 75 and 85 km NO is depleted during particle events due to the faster destruction of NO by N relative to the production of NO by N reacting with O2. Recovery of NO depends on transport from the lower thermosphere, where NO is produced in abundant amounts during particle events.
    Keywords: Geophysics
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    Statistical Perspectives on Stratospheric Transport (1999)
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    Publication Date: 2013-08-29
    Description: Long-lived tropospheric source gases, such as nitrous oxide, enter the stratosphere through the tropical tropopause, are transported throughout the stratosphere by the Brewer-Dobson circulation, and are photochemically destroyed in the upper stratosphere. These chemical constituents, or "tracers" can be used to track mixing and transport by the stratospheric winds. Much of our understanding about the stratospheric circulation is based on large scale gradients and other spatial features in tracer fields constructed from satellite measurements. The point of view presented in this paper is different, but complementary, in that transport is described in terms of tracer probability distribution functions (PDFs). The PDF is computed from the measurements, and is proportional to the area occupied by tracer values in a given range. The flavor of this paper is tutorial, and the ideas are illustrated with several examples of transport-related phenomena, annotated with remarks that summarize the main point or suggest new directions. One example shows how the multimodal shape of the PDF gives information about the different branches of the circulation. Another example shows how the statistics of fluctuations from the most probable tracer value give insight into mixing between different regions of the atmosphere. Also included is an analysis of the time-dependence of the PDF during the onset and decline of the winter circulation, and a study of how "bursts" in the circulation are reflected in transient periods of rapid evolution of the PDF. The dependence of the statistics on location and time are also shown to be important for practical problems related to statistical robustness and satellite sampling. The examples illustrate how physically-based statistical analysis can shed some light on aspects of stratospheric transport that may not be obvious or quantifiable with other types of analyses. An important motivation for the work presented here is the need for synthesis of the large and growing database of observations of the atmosphere and the vast quantities of output generated by atmospheric models.
    Keywords: Geophysics
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    Thermal Sensitivity of MD Hematite: Implication for Magnetic Anomalies (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: Magnetic remanence of crustal rocks can reside in three common rock-forming magnetic minerals: magnetite, pyrrhotite, and hematite. Thermoremanent magnetization (TRM) of magnetite and pyrrhotite is carried mostly by single domain (SD) grains. The TRM of hematite grains, however, is carried mostly by multidomain (NM) grains. This characteristic is illustrated by TRM acquisition curves for hematite of variable grainsizes. The transition between truly NM behavior and tendency towards SD behavior his been established between hematite grainsizes of 0. 1 and 0.05 mm. Coarse grainsize of lower crustal rocks and the large sensitivity of MD hematite grains to acquire TRM indicates that hematite could be a significant contributor to long-wavelength magnetic anomalies.
    Keywords: Geophysics
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    Properties of QBO and SAO Generated by Gravity Waves (1999)
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    Publication Date: 2013-08-29
    Description: We present an extension for the 2D (zonal mean) version of our Numerical Spectral Mode (NSM) that incorporates Hines' Doppler spread parameterization (DSP) for small scale gravity waves (GW). This model is applied to describe the seasonal variations and the semi-annual and quasi-biennial oscillations (SAO and QBO). Our earlier model reproduced the salient features of the mean zonal circulation in the middle atmosphere, including the QBO extension into the upper mesosphere inferred from UARS measurements. In the present model we incorporate also tropospheric heating to reproduce the upwelling at equatorial latitudes associated with the Brewer-Dobson circulation that affects significantly the dynamics of the stratosphere as Dunkerton had pointed out. Upward vertical winds increase the period of the QBO observed from the ground. To compensate for that, one needs to increase the eddy diffusivity and the GW momentum flux, bringing the latter closer to values recommended in the DSP. The QBO period in the model is 30 months (mo), which is conducive to synchronize this oscillation with the seasonal cycle of solar forcing. Multi-year interannual oscillations are generated through wave filtering by the solar driven annual oscillation in the zonal circulation. Quadratic non-linearities generate interseasonal variations to produce a complicated pattern of variability associated with the QBO. The computed temperature amplitudes for the SAO and QBO are in substantial agreement with observations at equatorial and extratropical latitudes. At high latitudes, however, the observed QBO amplitudes are significantly larger, which may be a signature of propagating planetary waves not included in the present model. The assumption of hydrostatic equilibrium not being imposed, we find that the effects from the vertical Coriolis force associated with the equatorial oscillations are large for the vertical winds and significant for the temperature variations even outside the tropics but are relatively small for the zonal winds.
    Keywords: Geophysics
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    Stratospheric Temperature Changes: Observations and Model Simulations (1999)
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    Publication Date: 2013-08-29
    Description: This paper reviews observations of stratospheric temperatures that have been made over a period of several decades. Those observed temperatures have been used to assess variations and trends in stratospheric temperatures. A wide range of observation datasets have been used, comprising measurements by radiosonde (1940s to the present), satellite (1979 - present), lidar (1979 - present) and rocketsonde (periods varying with location, but most terminating by about the mid-1990s). In addition, trends have also been assessed from meteorological analyses, based on radiosonde and/or satellite data, and products based on assimilating observations into a general circulation model. Radiosonde and satellite data indicate a cooling trend of the annual-mean lower stratosphere since about 1980. Over the period 1979-1994, the trend is 0.6K/decade. For the period prior to 1980, the radiosonde data exhibit a substantially weaker long-term cooling trend. In the northern hemisphere, the cooling trend is about 0.75K/decade in the lower stratosphere, with a reduction in the cooling in mid-stratosphere (near 35 km), and increased cooling in the upper stratosphere (approximately 2 K per decade at 50 km). Model simulations indicate that the depletion of lower stratospheric ozone is the dominant factor in the observed lower stratospheric cooling. In the middle and upper stratosphere both the well-mixed greenhouse gases (such as CO) and ozone changes contribute in an important manner to the cooling.
    Keywords: Geophysics
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    Seasonal and Interannual Variabilities in Tropical Tropospheric Ozone (1999)
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    Publication Date: 2013-08-29
    Description: This paper presents a detailed characterization of seasonal and interannual variability in tropical tropospheric column ozone (TCO). TCO time series are derived from 20 years (1979-1998) of total ozone mapping spectrometer (TOMS) data using the convective cloud differential (CCD) method. Our study identifies three regions in the tropics with distinctly different zonal characteristics related to seasonal and interannual variability. These three regions are the eastern Pacific, Atlantic, and western Pacific. Results show that in both the eastern and western Pacific seasonal-cycle variability of northern hemisphere (NH) TCO exhibits maximum amount during NH spring whereas largest amount in southern hemisphere (SH) TCO occurs during SH spring. In the Atlantic, maximum TCO in both hemispheres occurs in SH spring. These seasonal cycles are shown to be comparable to seasonal cycles present in ground-based ozonesonde measurements. Interannual variability in the Atlantic region indicates a quasi-biennial oscillation (QBO) signal that is out of phase with the QBO present in stratospheric column ozone (SCO). This is consistent with high pollution and high concentrations of mid-to-upper tropospheric O3-producing precursors in this region. The out of phase relation suggests a UV modulation of tropospheric photochemistry caused by the QBO in stratospheric O3. During El Nino events there is anomalously low TCO in the eastern Pacific and high values in the western Pacific, indicating the effects of convectively-driven transport of low-value boundary layer O3 (reducing TCO) and O3 precursors including H2O and OH. A simplified technique is proposed to derive high-resolution maps of TCO in the tropics even in the absence of tropopause-level clouds. This promising approach requires only total ozone gridded measurements and utilizes the small variability observed in TCO near the dateline. This technique has an advantage compared to the CCD method because the latter requires high-resolution footprint measurements of both reflectivity and total ozone in the presence of tropopause-level cloud tops.
    Keywords: Geophysics
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    A New NASA Data Product: Tropospheric and Stratospheric Column Ozone in the Tropics Derived from TOMS Measurements (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: Tropospheric column ozone (TCO) and stratospheric column ozone (SCO) gridded data in the tropics for 1979-present are now available from NASA Goddard Space Flight Center via either direct ftp, world-NN,ide-NN,eb, or electronic mail. This note provides a brief overview of the method used to derive the data set including validation and adjustments.
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    A Highly Doppler Blueshifted Fe-K Emission Line in the High-Redshift QSO PKS 2149-306 (1999)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: We report the results from an ASCA observation of the high-luminosity, radioloud quasar PKS 2149-306 (redshift 2.345), covering the approximately 1.7 - 30 keV band in the quasar-frame. We find the source to have a luminosity of approximately 6 x 10(exp 47) ergs/s in the 2 - 10 keV band (quasar frame). We detect an emission line centered at approximately 17 keV in the quasar frame. Line emission at this energy has not been observed in any other active galaxy or quasar to date. We present evidence rejecting the possibility that this line is the result of instrumental artifacts, or a serendipitous source. The most likely explanation is blueshifted Fe-K emission (the equivalent width, is EW approximately 300 +/- 200 eV, quasar frame). Bulk velocities of the order of 0.75c are implied by the data. We show that Fe-K line photons originating in an accretion disk and Compton-scattering off a leptonic jet aligned along the disk axis can account for the emission line. Curiously. if the emission-line feature recently discovered in another quasar (PKS 0637-752, z = 0.654) at 1.6 keV in the quasar frame, is due to blueshifted OVII emission, the Doppler blueshifting factor in both quasars is similar (approximately 2.7 - 2.8).
    Keywords: Astronomy
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    Influence of Transport on Two-Dimensional Model Simulation. Tracer Sensitivity to 2-D Model Transport (1999)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: In this study, we examine the sensitivity of long lived tracers to changes in the base transport components in our 2-D model. Changes to the strength of the residual circulation in the upper troposphere and stratosphere and changes to the lower stratospheric K(sub zz) had similar effects in that increasing the transport rates decreased the overall stratospheric mean age, and increased the rate of removal of material from the stratosphere. Increasing the stratospheric K(sub yy) increased the mean age due to the greater recycling of air parcels through the middle atmosphere, via the residual circulation, before returning to the troposphere. However, increasing K(sub yy) along with self-consistent increases in the corresponding planetary wave drive, which leads to a stronger residual circulation, more than compensates for the K(sub yy)-effect, and produces significantly younger ages throughout the stratosphere. Simulations with very small tropical stratospheric K(sub yy) decreased the globally averaged age of air by as much as 25% in the middle and upper stratosphere, and resulted in substantially weaker vertical age gradients above 20 km in the extratropics. We found only very small stratospheric tracer sensitivity to the magnitude of the horizontal mixing across the tropopause, and to the strength of the mesospheric gravity wave drag and diffusion used in the model. We also investigated the transport influence on chemically active tracers and found a strong age-tracer correlation, both in concentration and calculated lifetimes. The base model transport gives the most favorable overall comparison with a variety of inert tracer observations, and provides a significant improvement over our previous 1995 model transport. Moderate changes to the base transport were found to provide modest agreement with some of the measurements. Transport scenarios with residence times ranging from moderately shorter to slightly longer relative to the base case simulated N2O lifetimes that were within the observational estimates of Volk et al. [1997]. However, only scenarios with rather fast transport rates were comparable with the Volk et al. estimates of CFCl3 lifetimes. This is inconsistent with model-measurement comparisons of mean age in which the base model or slightly slower transport rates compared the most favorably with balloon SF6 data. For all comparisons shown, large transport changes away from the base case resulted in simulations that were outside the range of measurements, and in many cases, far outside this range.
    Keywords: Geophysics
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    Interrelationships Between Aerosol Characteristics and Light Scattering During Late-winter in a Eastern Mediterranean Arid Environment (1999)
    In:  CASI
    Details
    Publication Date: 2013-04-10
    Description: An intensive field campaign involving measurement of various aerosol physical, chemical, and radiative properties was conducted at Sde Boker in the Negev Desert of Israel, from 18 February to 15 March 1997. Nephelometer measurements gave average background scattering coefficient values of about 25 M/m at 550 nm wavelength, but strong dust events caused the value of this parameter to rise up to about 800 M/m Backscattering fractions did not depend on aerosol loading, and generally fell in the range of 0.1 to 0.25, comparable to values reported for marine and Arctic environments. Chemical analysis of the aerosol revealed that, in the coarse size range (2 - 10 micrometer equivalent aerodynamic diameter (EAD)), calcium (Ca) was by far the most abundant element followed by silicon (Si), both of which are indicators for mineral dust. In the fine size fraction (〈 2 micrometers EAD), sulfur (S) generally was the dominant element, except during high dust episodes when Ca and Si were again the most abundant. Furthermore, fine black carbon (BC) correlates with S, suggesting that they may have originated from the same sources or source regions. An indication of the short-term effect of aerosol loading on radiative forcing was provided by measurements of global and diffuse solar radiation, which showed that during high turbidity periods (strong dust events) almost all of the solar radiation reaching the area is scattered or absorbed.
    Keywords: Geophysics
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    Breadth of Scientific Activities and Network Station Specifications in the IGS (1999)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: This presentation provides a brief overview of the scientific activities of the International GPS Service (IGS). This was an approved activity of the International Association of Geodesy (IAG) with official start of service on 1 Jan 1994. The mission of the IGS is "To provide a service to support geodetic and geophysical research activities, through GPS data and data products." The presentation explains the concept of the IGS working group, and pilot projects, and reviews the current working groups and pilot projects.
    Keywords: Geophysics
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    Near-Simultaneous Spectroscopic and Broadband Polarimetric Observations of Be Stars (1999)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: Near simultaneous optical spectroscopic (on four nights) and broadband linear continuum (B, V, R, and I bands) polarimetric (on seven nights) observations of 29 Be stars were carried out during 1993 November-December. The program Be stars displayed wavelength dependence of intrinsic polarizations with no frequency dependence of polarimetric position angles. Some of the Be stars displayed long-term polarization variability. The Be and Be-shell stars could not be distinguished from one another solely on the basis of their polarization values. Full widths at half-maximum of the H.alpha profiles and the intrinsic linear continuum polarizations are closely correlated with the projected rotational velocities of the program stars. Photospheric-absorption-corrected equivalent widths of H.alpha profiles [W(alpha)] and the radii of H.alpha-emitting or -absorbing envelopes (R(sub e) or R(sub a)) are nonlinearly correlated with the intrinsic continuum polarizations of these stars. However, W(alpha) and R(sub e) are linearly correlated. With large uncertainties, there is a trend of spectral dependence of polarization. Detailed discussion of these results is presented in this paper.
    Keywords: Astronomy
    Type: Astronomical Journal; Volume 118; 1061-1072
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    Bright Points and Subflares in Ultraviolet Lines and X-Rays (1999)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: We have analyzed an active region which was observed in H.alpha (Multichannel Subtractive Double Pass Spectrograph), in UV lines (SMM/UVSP), and in X-rays (SMM/HXIS). In this active region there were only a few subflares and many small bright points visible in UV and in X-rays. Using an extrapolation based on the Fourier transform, we have computed magnetic field lines connecting different photospheric magnetic polarities from ground-based magnetograms. Along the magnetic inversion lines we find two different zones: (1) a high-shear region (〉 70 deg) where subflares occur, and (2) a low-shear region along the magnetic inversion line where UV bright points are observed. In these latter regions the magnetic topology is complex with a mixture of polarities. According to the velocity field observed in the Si IV lamda.1402 line and the extrapolation of the magnetic field, we notice that each UV bright point is consistent with emission from low-rising loops with downflows at both ends. We notice some hard X-ray emissions above the bright-point regions with temperatures up to 8 x 10(exp 6) K, which suggests some induced reconnection due to continuous emergence of new flux. This reconnection is also enhanced by neighboring subflares.
    Keywords: Astronomy
    Type: Astrophysical Journal; Volume 510; 474-484
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    An Unusual Supernova in the Error Box of the Gamma-Ray Burst of 25 April 1998 (1999)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: The discovery of afterglows associated with gamma-ray bursts at X-ray, optical and radio wavelengths and the measurement of the redshifts of some of these events has established that gamma-ray bursts lie at extreme distances, making them the most powerful photon-emitters known in the Universe. Here we report the discovery of transient optical emission in the error box of the gamma-ray burst GRB980425, the light curve of which was very different from that of previous optical afterglows associated with gamma-ray bursts. The optical transient is located in a spiral arm of the galaxy ESO 184-GS2, which has a redshift velocity of only 2,550 km/ s. Its optical spectrum and location indicate that it is a very luminous supernova, which has been identified as SN1998bw. If this supernova and GRB980425 are indeed associated, the energy radiated in gamma-rays is at least four orders of magnitude less than in other gamma-ray bursts, although its appearance was otherwise unremarkable: this indicates that very different mechanisms can give rise to gamma-ray bursts. But independent of this association, the supernova is itself unusual, exhibiting an unusual light curve at radio wavelengths that requires that the gas emitting the radio photons be expanding relativistically.
    Keywords: Astronomy
    Type: Nature; Volume 395; 670-672
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    Topographic Profiles Across Wrinkle Ridges Indicate Subsurface Faults (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Geophysics
    Type: American Geophysical Union Fall Meeting; San Francisco, CA; United States
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    Probing Europa's Hidden Ocean from Tidal Effects on Orbital Dynamics (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: Division for Planetary Sciences Meeting of the American Astronomical Society; Padua; Italy
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    Sulfuric Acid on Europa's Surface and the Radiolytic Sulfur Cycle (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: Galileo infrared spectra of Europa's surface show distorted water bands that have been attributed to hydrated evaporite salts (McCord et al., J. Geophys. Res. 104, 11827, 1999) or to the scattering properties of ice (Dalton and Clark, Bull. Am. Astron. Soc. 30, 1081, 1998).
    Keywords: Astronomy
    Type: Division for Planetary Sciences Meeting of the American Astronomical Society; Padua; Italy
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    The Gravity Field and Interior Structure of Callisto (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: Division for Planetary Sciences Meeting of the American Astronomical Society; Padua; Italy
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    Towards an Understanding of the Mid-Infrared Surface Brightness of Normal Galaxies (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: We report a mid-infrared color and surface brightness analysis of IC 10, NGC 1313, and NGC 6946, three of the nearby galaxies studied under the Infrared Space Observatory Key Project on Normal Galaxies.
    Keywords: Astronomy
    Type: Astronomical Journal
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    Ground-based Observations of Arctic O(sub 3) Loss During Spring and Summer 1997 (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: Ground-based solar absorption spectra were measured from Fairbanks, Alaska (65 degrees North, 148 degrees West) and from Ny Alesund, Spitsbergen, (79 degrees North, 12 degrees East) from March to September 1997 by Fourier Transform Infra-Red (FTIR) spectrometers.
    Keywords: Geophysics
    Type: Journal of Geophysical Research (Atmospheres)
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    Variations in the Free Chlorine Content of the Stratosphere (1991-1997): Anthropogenic an Volcanic Influences (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: Remote sensing of chlorine monoxide (CIO) by the Microwave Limb Sounder (MLS) experiment aboard the Upper Atmosphere Research Satellite (UARS) has provided global measurements of variations in stratospheric free chlorine (for 1991 to 1997).
    Keywords: Geophysics
    Type: Journal of Geophysical Research
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    The Etched Hourglass Nebula MyCn18: I. Hubble Space Telescope (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: Astronomical Journal
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    SSMI Wind Speed Climatology of the Time of Monsoon Wind Onset in the Western Arabian Sea (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Geophysics
    Type: International Union of Geology and Geophysics (IOGG); Birmingham; United Kingdom
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  • 57
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    Improving NSCAT Winds for Tropical Cyclones (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: There has been a question on whether it is possible to measure the surface wind speeds of tropical cyclones with a spaceborne Ku-band scatterometer.
    Keywords: Geophysics
    Type: Journal of Geophysical Research-Ocean
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  • 58
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    Monitoring Global Geophysical Fluids with Respect to Large-Scale Geodynamic Properties (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Geophysics
    Type: American Geophysical Union; Boston, MA; United States
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  • 59
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    Energetic Particle Transport at Corotating Interaction Regions (CIRs) (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: We examine energetic particle transport at or near Corotating Interaction Regions (CIRs).
    Keywords: Geophysics
    Type: Journal of Geophysical Research
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    Markarian 421's Unusual Satellite Galaxy (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: We present Hubble Space Telescope (HST) imagery, and ground-based spectroscopy and CCD photometry of the active galaxy Markarian 421 and its companion galaxy 14 arcsec to the ENE.
    Keywords: Astronomy
    Type: Astronomical Journal
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    Influence of Shock-Induced Ionospheric Conductivity Enhancements on Storm Main Phase Intensities (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Geophysics
    Type: International Union of Geodesy and Geophysics (IUGG) '99; Birmingham; United Kingdom
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    Estimating the Motion of Atmospheric Water Vapor Using the Global Positioning System (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Geophysics
    Type: International Symposium on GPS: Application To Earth Sciences and Interaction with Other Space Geodetic Techniques, 1999; Tsukubu, Ibaraki; Japan
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    HST/NICMOS Imaging of Disks and Envelopes Around Very Young Stars (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: We present HST/NICMOS observations with ~ 0''.1 = 15 AU resolution of six young stellar objects in the Taurus star-formation region.
    Keywords: Astronomy
    Type: Astronomical Journal
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    Coronal Hole Myth (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: AAS, Bulletin of American Astronomical Society; Chicago, IL; United States
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  • 65
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    Near/Mid Infrared-Wavelength Study of the Interacting Galaxy Pair UGC 12914/5 -- Taffy (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: The system consists of two counter-rotating spirals having suffered a nearly face-on collsion only ~10(sup 7) years ago.
    Keywords: Astronomy
    Type: Astronomical Journal
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    Autonomous, Free-Flying Nanospacecraft for Space Physics Measurements (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Geophysics
    Type: American Geophysical Union; Boston, MA; United States
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    Glacial Isostatic Adjustment Observed with VLBI and SLR (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: In global geodetic solutions vertical rates of site motion are usually estimated relative to the geocenter (center of figure) of the solid earth. The velocity of the geocenter is estimated assuming that the plates are rigid, that the velocities of the plates equal those in NUVEL-1A (DeMets et al. 1990, 1994) and that the uplift, subsidence, and intraplate deformation due to glacial isostatic adjustment is negligible.
    Keywords: Geophysics
    Type: Journal of Geophysical Research
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    Fluctuation of SST and CHL-a Concentration Caused by Baroclinic Inertia-Gravity Waves (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Geophysics
    Type: International Union of Geodesy and Geophysics (IUGG) 1999 Meeting; Birmingham; United Kingdom
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    Observations of Convective and Dynamical Instabilities in Tropospause Folds and their Contributions to Stratosphere-Trophosphere Exchange (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: With aircraft-mounted in-situ and remote sensing instruments for dynamical, thermal, and chemical measurements, we studied two cases of tropopause folding.
    Keywords: Geophysics
    Type: Geophysical Research Letters
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    The Dark Side of Iapetus and Hyperion: One and the Same? (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: Division for Planetary Sciences Meeting of the American Astronomical Society; Padova; Italy
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    Photochemical Modeling of HOx in the Terrestrial Mesosphere and Comparison to OH Column Measurements from the JPL Table Mountain Facility (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Geophysics
    Type: American Geophysical Union Fall Meeting; San Francisco, CA; United States
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    C II 158 ??bservations of a Sample of Late-type Galaxies from the Virgo Cluster (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: We have observed 19 Virgo cluster spiral galaxies with the Long Wavelength Spectrometer (LWS) onboard ESAs Infrared Space Observatory (ISO) obtaining spectra around the [CII] 157.741 ??ine structure line.
    Keywords: Astronomy
    Type: Monthly Notices of the Royal Astronomical Society
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    Estimating the Uncertainty in Passive-Microwave Rain Retrievals (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: Current passive-microwave rain-retrieval methods are largely based on databases built off-line using cloud models.
    Keywords: Geophysics
    Type: Journal of Geophysics Research - Atmospheres
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    Shortening and Thickening of Metropolitan Los Angeles Measured and Inferred Using Geodesy (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: Geodetic measurements using the Global Positioning System and other techniques show north-south shortening near Los Angeles to be fastest across the northern part of the metropolitan area, where an ESE-striking, 5- to 40-km-wide belt lying to the south of San Gabriel Mountains and to the north of downtown and West Los Angeles is shortening at 5 mm/yr.
    Keywords: Geophysics
    Type: Geology
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    Calibrating Spaceborne Microwave Radiometers with GPS (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: Data from terrestrial GPS receivers are being used in growing numbers of applications requiring precise tropospheric sensing. One emerging application is the calibration of water vapor measurements from spaceborne microwave radiometers.
    Keywords: Geophysics
    Type: International Union of Geodesy and Geophysics General Assembly; Birmingham; United Kingdom
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    Polar Vortex Dynamics During Spring and Fall Diagnosed Using ATMOS Trace Gas Observation (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: Trace gases measured by the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument during the Mar/Apr 1992(AT-1), Apr 1993(AT-2), and Nov 1994(AT-3) space-shuttle missions have been mapped into equivalent latitude/potential temperature (EqL/0) coordinates.
    Keywords: Geophysics
    Type: Journal of Geophysical Research
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    Studies of Polar Processes in the Lower Stratosphere Using UARS MLS Observations (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Geophysics
    Type: International Union of Geodesy & Geophysics; Birmingham; United Kingdom
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    Simple Models for Late Holocene and Present-day Patagonian Glacier Fluctuation and Predictions of a Geodtically Detectable Isostatic Response (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: The late Holocene glacial moraine chronology in the southernmost South American Andes includes four (sup 14)C dated Neoglacial advances and retreats.
    Keywords: Geophysics
    Type: Geophysical Journal International
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    Impact of Aircraft Emissions on NO(sub x) in the Lowermost Stratosphere at Northern Midlatitudes (1999)
    In:  Other Sources
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    Publication Date: 2018-06-11
    Description: Airborne measurements of NO, total reactive nitrogen(NO(sub y)), O(sub 3), and condensation nuclei (CN) were made, together with other tracers such as CO and H(sub 2)O, within air traffic corridors over the U.S. and North Atlantic regions in October and November 1997.
    Keywords: Geophysics
    Type: Geophysical Research Letters
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    A New Estimate of Hubble's Constant From The Gravitational Lens PKS 1830-211 (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: American Astronomical Society - Astronomy; Austin, TX; United States
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    Ground and Space-based Optical & IR Stellar Interferometry (1999)
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    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: Japan National Astronomical Observatory; Tokyo; Japan
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    Substorms, Pseudobreakups and Quiescent Events Caused by Interplanetary Shocks (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: We use WIND solar wind data and POLAR UV imaging data to study magnetospheric responses and substorm triggering mechanisms during and after interplanetary (IP) shock events.
    Keywords: Geophysics
    Type: Journal of Geophysical Research
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  • 83
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    The Co- and Immediate Post-seismic Geodetic Signature of the 1999 Hector Mine Earthquake (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: The M7.1 Hector Mine earthquake ruptured the Lavic Lake fault near Twentynine Palms, CA at 09:46 UTC October 16, 1999.
    Keywords: Geophysics
    Type: EOS
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  • 84
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    The Etched Hourglass Nebula MyCn18: II A Spatio-Kinematic Model (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: We have observed MyCn18, a young Planetary Nebulae with HST/WFPC2 and presented the observational results in an earlier paper. Here we present a detailed spatial/kinematical model of H alpha emission from the nebula.
    Keywords: Astronomy
    Type: Astronomical Journal
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  • 85
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    Deployment of Autonomous GPS Stations in Marie Byrd Land, Antartica (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: During the 1998-1999 Antarctic field season, we installed three autonomous GPS stations in Marie Byrd Land, West Antarctica to measure glacio-isostatic rebound and rates of spreading across the West Antartic Rift System.
    Keywords: Geophysics
    Type: Geophysical Research Letters
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  • 86
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    Secular PGR Stokes Coefficients Via Ice Model Improvements, Quarter Century-Long Data Records and High Degeree and Order Field Recovery (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Geophysics
    Type: European Geophysical Society General Meeting; Nice; France
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  • 87
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    Present Constraints and Future Observations of Postglacial Rebound in Antarctica (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Geophysics
    Type: European Geophysical Society General Meeting; Nice; France
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  • 88
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    The Astronomical Low Frequency Array: A Proposed Explorer Mission for Radio Astronomy (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: A radio interferometer array in space providing high dynamic range images with unprecedented angular resolution over the broad frequency range from 0.030 - 30 MHz will open new vistas in solar, terrestial, galactic, and extragalactic astrophysics.
    Keywords: Astronomy
    Type: American Geophysical Union; United States
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  • 89
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    Cryocooler Options for Next Generation Space Telescope (NGST) and Other Space Applications (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: We present a summary of cryocoolers that are presently available or in development and would be suitable for support of mid-infrared camera on the Next Generation Space Telescope.
    Keywords: Astronomy
    Type: Publications of the Astronomical Society of the Pacific
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  • 90
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    New VLA Observations for the HH 1-2 Region: Evidence for Density Enhancements Moving Along the Axis of the VLA 1 Radio Jet (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: Using the Very Large Array, we have carried out new, sensitive radio continuum observations at 6 and 3.6 cm of the HH 1-2 region. The comparison between the 6 cm maps made from data taken in 1986.2 and 1992.9 indicates that VLA 1, the exciting source of the HH 1-2 flow, has suffered a morphological change that is attributed to the motion of a symmetric pair of knots along the axis of the radio jet.
    Keywords: Astronomy
    Type: Astronomical Journal
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  • 91
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    K/Ar Ages From the Guerrero Transect Date Four Thermotectonic Events Affecting the North America Plate in Mexico from 301 Ma to 29 Ma (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: Because of questions regarding the validity of proposed accreted terranes, the tectonostratigraphic evolution of the southern margin of North America plate in Mexico remains controversial.
    Keywords: Geophysics
    Type: American Geophysical Union; United States
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  • 92
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    Microarcsecond Astrometry as a Probe of Circumstellar Structure (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: 195th American Astronomical Society; Atlanta, GA; United States
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  • 93
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    JPL Solution for the Co- and Immediate Post-Seismic Displacements of SCIGN Stations in the 1999 Hector Mine Earthquake (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Geophysics
    Type: American Geophysical Union Fall Meeting; San Francisco, CA; United States
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  • 94
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    Differential Astrometry of the 61 Cygni System with the Palomar Testbed Interferometer (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: American Astronomical Society; Atlanta, GA; United States
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  • 95
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    Differential Astrometry with the Keck Interferometer (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: Among the Keck Interferometer's high priority science programs will be the differential astrometric detection of planetary companions to nearby stars.
    Keywords: Astronomy
    Type: Working on the Fringe Conference; Dana Point, CA; United States
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  • 96
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    Predicting Stellar Angular Sizes (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: Reliable prediction of stellar diameters, particularly angular diameters, is a useful and necessary tool for the increasing number of milliarcsecond resolution studies being carried out in the astronomical community.
    Keywords: Astronomy
    Type: Working on the Fringe Conference; Dana Point, CA; United States
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  • 97
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    Importance of Salinity Measurements in the Heat Storage Estimation from Topex/Poseidon (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: Sea surface height anomaly signals from satellite altimeter data are used to estimate heat storage. Since variability in sea surface height is mostly due to expansion and contraction of the water column it can be correlated with variations in the heat and salt content.
    Keywords: Geophysics
    Type: Geophysical Research Letters
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  • 98
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    Visualization of Dynamic Volcanic Phenomena: The Advance of Lava Flows on the Kamoamoa Flow Field, Kilauea Volcano, Hawaii (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Geophysics
    Type: American Geophysical Union Fall Meeting; San Francisco, CA; United States
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  • 99
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    Estimating the Motion of Atmospheric Water Vapor Using the Global Positioning System (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Geophysics
    Type: International Symposium on GPS: Applications to Earth Sciences and Interaction with Other Space Geodetic Techniques; Tsubuka; Japan
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  • 100
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    Ferrate (VI) as a Possible Oxidant on the Martian Surface (1999)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: Proceedings of Bio-Astronomy|Bio-Astronomy; United States
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