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  • Astronomy  (473)
  • Meteorology and Climatology
  • 1995-1999  (898)
  • 1999  (556)
  • 1997  (342)
  • 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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    Carbon dioxide warming of the early Earth (1997)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Svante Arrhenius' research in atmospheric physics extended beyond the recent past and the near future states of the Earth, which today are at the center of sociopolitical attention. His plan encompassed all of the physical phenomena known at the time to relate to the formation and evolution of stars and planets. His two-volume textbook on cosmic physics is a comprehensive synopsis of the field. The inquiry into the possible cause of the ice ages and the theory of selective wavelength filter control led Arrhenius to consider the surface states of the other terrestrial planets, and of the ancient Earth before it had been modified by the emergence of life. The rapid escape of hydrogen and the equilibration with igneous rocks required that carbon in the early atmosphere prevailed mainly in oxidized form as carbon dioxide, together with other photoactive gases exerting a greenhouse effect orders of magnitude larger than in our present atmosphere. This effect, together with the ensuing chemical processes, would have set the conditions for life to evolve on our planet, seeded from spores spreading through an infinite Universe, and propelled, as Arrhenius thought, by stellar radiation pressure.
    Keywords: Meteorology and Climatology
    Type: Ambio (ISSN 0044-7447); Volume 26; 1; 12-6
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  • 6
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    Background contamination by coplanar polychlorinated biphenyls (PCBs) in trace level high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS) analytical procedures (1997)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The addition of the "dioxin-like" polychlorinated biphenyl (PCB) congeners to the assessment of risk associated with the 2,3,7,8-chlorine substituted dioxins and furans has dramatically increased the number of laboratories worldwide that are developing analytical procedures for their detection and quantitation. Most of these procedures are based on established sample preparation and analytical techniques employing high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS), which are used for the analyses of dioxin/furans at low parts-per-trillion (ppt) levels. A significant and widespread problem that arises when using these sample preparation procedures for the analysis of coplanar PCBs is the presence of background levels of these congeners. Industrial processes, urban incineration, leaking electrical transformers, hazardous waste accidents, and improper waste disposal practices have released appreciable quantities of PCBs into the environment. This contamination has resulted in the global distribution of these compounds via the atmosphere and their ubiquitous presence in ambient air. The background presence of these compounds in method blanks must be addressed when determining the exact concentrations of these and other congeners in environmental samples. In this study reliable procedures were developed to accurately define these background levels and assess their variability over the course of the study. The background subtraction procedures developed and employed increase the probability that the values reported accurately represent the concentrations found in the samples and were not biased due to this background contamination.
    Keywords: Meteorology and Climatology
    Type: Chemosphere (ISSN 0045-6535); Volume 34; 11; 2451-65
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  • 7
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    Ultraviolet radiation from F and K stars and implications for planetary habitability (1997)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Now that extrasolar planets have been found, it is timely to ask whether some of them might be suitable for life. Climatic constraints on planetary habitability indicate that a reasonably wide habitable zone exists around main sequence stars with spectral types in the early-F to mid-K range. However, it has not been demonstrated that planets orbiting such stars would be habitable when biologically-damaging energetic radiation is also considered. The large amounts of UV radiation emitted by early-type stars have been suggested to pose a problem for evolving life in their vicinity. But one might also argue that the real problem lies with late-type stars, which emit proportionally less radiation at the short wavelengths (lambda 〈 200 nm) required to split O2 and initiate ozone formation. We show here that neither of these concerns is necessarily fatal to the evolution of advanced life: Earth-like planets orbiting F and K stars may well receive less harmful UV radiation at their surfaces than does the Earth itself.
    Keywords: Meteorology and Climatology
    Type: Origins of life and evolution of the biosphere : the journal of the International Society for the Study of the Origin of Life (ISSN 0169-6149); Volume 27; 4; 413-20
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  • 8
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    An Optimal Relation of Radar Reflectivity to Lightning Rate (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Thunderstorms separate charge. Most places they lift positive charge or lower negative, a few places they lift negative or lower positive. The electrical generator is stronger in some parts of the cloud than in others. Our long term goal is to map this generator. Cloud physicists tell us that uncharged ice and water particles become charged by collision, and that the charge transferred depends on size, temperature and humidity. There is still some disagreement about exactly how the charge transferred depends on size, temperature, and humidity. In principle, if we knew this ice physics, and also knew the distribution of particles everywhere in the storm, and the winds everywhere and the temperature and humidity everywhere, then we could compute everywhere the electrical power of the thunderstorm generator. In practice it is difficult to know all these things, particularly the distribution of particles, so it is difficult to use real thunderstorms to falsify cloud electrification theories. We here take one small step towards computing that map of electrical generator power, by relating radar reflectivity profiles of 2000 storms to lightning flash rates of those storms. This small step by itself doesn't falsify any existing electrification theories; it merely places weak constraints on the relation of electric generator power to cloud ice.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 719-721; NASA/CP-1999-209261
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  • 9
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    Optical Detection of Lightning from Space (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Two primary detection techniques (optical and RF) have a proven capability for detecting lightning from low earth orbit. However, the lightning processes that generate the optical and RF signals are vastly different providing significantly different information content from each sensor type. Because of the intervening ionosphere, low frequency RF components do not reach satellite altitudes. As a consequence, many of the processes associated with the major energy release of a lightning event (i.e. return strokes, k-changes, recoil streamers, etc), in all likelihood contribute little to the RF signal arriving at the satellite. The optical output from lighting, on the other hand, has been shown to be highly correlated with the energetic, charge-transferring processes mentioned above. On the down side, the optical energy, while essentially unaffected by the atmosphere once it emerges from the cloud, is heavily scattered within the cloud. While there is little absorption by the cloud, the great optical depth makes the total light energy emerging from the cloud to be dependent on where in the cloud the lightning occurred. Analyses suggest that when lightning is confined to the lowest regions of the cloud, the light is strongly attenuated and detection becomes problematic. Fortunately, the vast majority of lightning flashes are comprised of channels that propagate through the middle of the cloud and higher. These flashes produce bright signals at the top of a cloud and are readily detectable. Presently, we have two optical instruments in orbit. The Optical Transient Detector (OTD) has been orbiting the earth since April, 1995, while the Lightning Imaging Sensor (LIS) was launched on the Tropical Rainfall Measuring Mission (TRMM) in November of 1997. Both instruments are relatively small, solid state optical imagers, designed specifically to detect and locate lightning activity from low earth orbit with high detection efficiency and location accuracy.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 715-718; NASA/CP-1999-209261
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  • 10
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    An Intercomparison of Ground, Airborne, and Space Instrumentation Definitions of the Lightning Element (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: For the past century, scientists have made quantitative measurements of lightning discharges. In the process, they refined the definition of a lightning unit, or basic quantum of lightning, in order to base it on observable parameters. In this paper, we will use cluster analysis to derive a basic spatial and temporal definition or scale length for the unit of lightning. We will use data from three different systems that detected pulses from the same storm complex over Central Oklahoma during June, 1998. Since the different instruments detect lightning in different ways with different resolutions, there may not be a single definition of the unit of lightning that can be applied to all three systems. However, common components can be found since all instrumentation are detecting aspects of the same phenomenon.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 166-169; NASA/CP-1999-209261
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  • 11
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    The Next Generation Space Telescope (NGST): Science and technology (1997)
    In:  CASI
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    Publication Date: 2004-12-03
    Description: The scientific requirements and implications for the instruments and telescope design for the Next Generation Space Telescope (NGST) are described. A candidate concept is a deployable, 8 m diameter telescope, optimized for the near infrared region, but featuring instruments capable of observing up to 30 micrometers. The observatory is radiatively cooled to approximately 30 K.
    Keywords: Astronomy
    Type: ; 213-218
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  • 12
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    Simulations of the STIS CCD clear imaging mode PSF (1997)
    In:  CASI
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    Publication Date: 2004-12-03
    Description: Detailed understanding of the properties of the point-spread function (PSF) of Space Telescope Imaging Spectrograph (STIS) imaging modes is necessary to separate real effects of geometrically complex astronomical sources, such as protoplanetary disks surrounding bright stars, from instrumental effects, such as scattering and diffraction. In order to investigate STIS imaging properties we have numerically simulated broadband stellar PSFs generated by STIS in CCD clear imaging mode, including the effects of the Lyot stop and the coronagraphic wedges. The input spectrum is a stellar model atmosphere of the appropriate spectral type, convolved with the pre-flight STIS CCD response function. The PSF modeler generates broadband PSFs by co-adding weighted monochromatic PSFs across the waveband.
    Keywords: Astronomy
    Type: The 1997 HST Calibration Workshop with a New Generation of Instruments; 84-89; NASA/TM-97-208141
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  • 13
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    The UAV: A unique platform for electrodynamic studies of upward lightning in the middle atmosphere (1997)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The use of unmanned aerial vehicles (UAVs), a platform for investigations in an environment hostile to manned spacecraft, is discussed. A program which includes the use of UAVs coupled with ground-based measurements to conduct scientific studies on the electrical state of the atmosphere during electrically active periods is proposed. The radiating power from alternate current and transient components of the storm electrification was investigated.
    Keywords: Meteorology and Climatology
    Type: ; 317-323
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  • 14
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    Correction for the STIS echelle blaze function (1997)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Using the Early Release Observation of 9 Comae, we demonstrate an iterative method for correcting Space Telescope Imaging Spectrograph (STIS) echelle spectra for the effects of the echelle ripple. This analytic approach allows the actual spectrum of interest to be used in the determination of its calibration. The late F star 9 Comae is not an ideal candidate for this method, due to the many absorption lines present in its E230M spectrum, yet, given this difficulty, the method still works quite well.
    Keywords: Astronomy
    Type: The 1997 HST Calibration Workshop with a New Generation of Instruments; 114-119; NASA/TM-97-208141
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  • 15
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    The STIS parallel survey: Introduction and first results (1997)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The installation of the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) allows for the first time two-dimensional optical and ultraviolet slitless spectroscopy of faint objects from space. The STIS Parallel Survey (SPS) routinely obtains broad band images and slitless spectra of random fields in parallel with HST observations using other instruments. The SPS is designed to study a wide variety of astrophysical phenomena, including the rate of star formation in galaxies at intermediate to high redshift through the detection of emission-line galaxies. We present the first results of the SPS, which demonstrate the capability of STIS slitless spectroscopy to detect and identify high-redshift galaxies.
    Keywords: Astronomy
    Type: The 1997 HST Calibration Workshop with a New Generation of Instruments; 94-99; NASA/TM-97-208141
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  • 16
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    An investigation into the milliarcsecond attitude control errors of Hubble Space Telescope (1997)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: An analysis of the fine pointing errors of the Hubble Space Telescope (HST), in the range from 1 to 15 milliarcsecs, is reported on. The emphasis is on the study of the performance characteristics of the pointing control system, fine guidance sensors and the optical telescope assembly, which produce relative attitude and astrometric measurement errors. Since the first servicing mission in December 1993, the HST relative short term position stability is of the order of 3 milliarcsecs RMS when averaged over 1 min intervals. At this level of accuracy, longer term systematic attitude errors in this range can have a noticeable impact on the telescope's observations. The various error sources are described, including: internal temperature effects; spacecraft structure temperature effects; calibration procedures, and computational inaccuracies.
    Keywords: Astronomy
    Type: ; 233-238
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  • 17
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    Global astrometry with the space interferometry mission (1997)
    In:  CASI
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    Publication Date: 2004-12-03
    Description: The prospects for global astrometric measurements with the space interferometry mission (SIM) are discussed. The SIM mission will perform four microarcsec astrometric measurements on objects as faint as 20 mag using the optical interferometry technique with a 10 m baseline. The SIM satellite will perform narrow angle astrometry and global astrometry by means of an astrometric grid. The sensitivities of the SIM global astrometric performance and the grid accuracy versus instrumental parameters and sky coverage schemes are reported on. The problems in finding suitable astrometric grid objects to support microarcsec astrometry, and related ground-based observation programs are discussed.
    Keywords: Astronomy
    Type: ; 789-793
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  • 18
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    The scientific basis for the space interferometry mission (1997)
    In:  CASI
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    Publication Date: 2004-12-03
    Description: The space interferometry mission (SIM), for launch in 2004, is expected to determine the positions of point sources to a global accuracy of 4 microarcsec, and an accuracy of 1 microarcsec over small angles. The instrument will reach 200 mag in 3 x 10(exp 4) s and has a nominal lifetime of five years. A nulling capability will be provided and synthesis imaging and near-infrared capabilities are being considered. These capabilities will extend those of the Hipparcos mission by almost three orders of magnitude in every sense. The NASA's expectation for the scientific return from the SIM mission is outlined in terms of the areas of stellar physics, galactic structure and extragalactic astrophysics, including the distance scale problem.
    Keywords: Astronomy
    Type: ; 749-753
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  • 19
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    High energy survey of supernova remnants with BATSE (1997)
    In:  CASI
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    Publication Date: 2004-12-03
    Description: The burst and transient source experiment (BATSE) survey of the high energy emission from supernova remnants is reported on. The ability of BATSE to continuously monitor the entire sky in the 20 keV to 2 MeV energy range enables a large group of remnants to by studied at high energies. Preliminary analysis indicates the likely detection of several supernova remnants other than the Crab nebula. Among these are MSH 15-52, Vela, Cas A and possibly HB 9. The techniques employed are discussed together with the status of the survey and its limitations.
    Keywords: Astronomy
    Type: ; 547-550
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  • 20
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    High-resolution spectral measurements of GRO J1655-40 (1997)
    In:  CASI
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    Publication Date: 2004-12-03
    Description: Data from the transient gamma ray germanium detector taken during 1995 provide a limited ability to study the high resolution spectrum of the X-ray transient GRO J1655-40. During a two-day period around the peak intensity, the soft spectrum was measured and found to be consistent with a power law spectrum with photon index -3.0 +/- 0.2. No evidence was found for narrow spectral features in the 50 to 100 keV band or around 511 keV. The 3 sigma upper limit for a narrow emission line at 511 keV is 1.2 x 10(exp -2) phot/cu cm s.
    Keywords: Astronomy
    Type: Proceedings of 2nd INTEGRAL Workshop 'The Transparent Universe'; 229-232; ESA-SP-382
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  • 21
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    Differential Absorption Measurements of Atmospheric Water Vapor with a Coherent Lidar at 2050.532 nm (1999)
    In:  CASI
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    Publication Date: 2004-12-03
    Description: Wind and water vapor are two major factors driving the Earth's atmospheric circulation, and direct measurement of these factors is needed for better understanding of basic atmospheric science, weather forecasting, and climate studies. Coherent lidar has proved to be a valuable tool for Doppler profiling of wind fields, and differential absorption lidar (DIAL) has shown its effectiveness in profiling water vapor. These two lidar techniques are generally considered distinctly different, but this paper explores an experimental combination of the Doppler and DIAL techniques for measuring both wind and water vapor with an eye-safe wavelength based on a solid-state laser material. Researchers have analyzed and demonstrated coherent DIAL water vapor measurements at 10 micrometers wavelength based on CO2 lasers. The hope of the research presented here is that the 2 gm wavelength in a holmium or thulium-based laser may offer smaller packaging and more rugged operation that the CO2-based approach. Researchers have extensively modeled 2 um coherent lasers for water vapor profiling, but no published demonstration is known. Studies have also been made, and results published on the Doppler portion, of a Nd:YAG-based coherent DIAL operating at 1.12 micrometers. Eye-safety of the 1.12 micrometer wavelength may be a concern, whereas the longer 2 micrometer and 10 micrometer systems allow a high level of eyesafety.
    Keywords: Meteorology and Climatology
    Type: Tenth Biennial Coherent Laser Radar Technology and Applications Conference; 68-71; NASA/CP-1999-209758
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  • 22
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    Total Lightning Activity Associated with Tornadic Storms (1999)
    In:  CASI
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    Publication Date: 2004-12-03
    Description: Severe storms often have high flash rates (in excess of one flash per second) and are dominated by intracloud lightning activity. In addition to the extraordinary flash rates, there is a second distinguishing lightning characteristic of severe storms that seems to be important. When the total lightning history is examined, one finds sudden increases in the lightning rate, which we refer to as lightning "jumps," that precede the occurrence of severe weather by ten or more minutes. These jumps are typically 30-60 flashes/min, and are easily identified as anomalously large derivatives in the flash rate. This relationship is associated with updraft intensification and updraft strength is an important factor in storm severity (through the accumulation of condensate aloft and the stretching of vorticity). In several cases, evidence for diminishment of midlevel rotation and the descent of angular momentum from aloft is present prior to the appearance of the surface tornado. Based on our experience with severe and tornadic storms in Central Florida, we believe the total lightning may augment the more traditional use of NEXRAD radars and storm spotters. However, a more rigorous relation of these jumps to storm kinematics is needed if we are to apply total lightning in a decision tree that leads to improved warning lead times and decreased false alarm rates.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 515-518; NASA/CP-1999-209261
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  • 23
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    The Lightning Imaging Sensor (1999)
    In:  CASI
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    Publication Date: 2004-12-03
    Description: The Lightning Imaging Sensor (LIS) is a NASA Earth Observing System (EOS) instrument on the Tropical Rainfall Measuring Mission (TRMM) platform designed to acquire and investigate the distribution and variability of total lightning (i.e., cloud-to-ground and intracloud) between q35' in latitude. Since lightning is one of the responses of the atmosphere to thermodynamic and dynamic forcing, the LIS data is being used to detect deep convection without land-ocean bias, estimate the precipitation mass in the mixed phased region of thunderclouds, and differentiate storms with strong updrafts from those with weak vertical motion.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 746-749; NASA/CP-1999-209261
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  • 24
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    Global Frequency and Distribution of Lightning as Observed by the Optical Transient Detector (OTD) (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The Optical Transient Detector (OTD) is a space-based instrument specifically designed to detect and locate lightning discharges (intracloud and cloud-to-ground) as it orbits the Earth. A statistical examination of OTD lightning data reveals that nearly 1.2 billion flashes occurred over the entire earth during the one year period from September 1995 through August 1996. This translates to an average of 37 lightning flashes occurring around the globe every second, which is well below the traditional estimate of 100 flashes per second. An average of 75% of the global lightning activity during the year occurs between 30' S and 30' N. An analysis of the annual lightning distribution reveals that an average of 82% of the lightning flashes occur over the continents and 18% over the oceans, which translates to an average land-ocean flash density ratio of nearly 11.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 726-729; NASA/CP-1999-209261
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  • 25
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    Determination of Thunderstorm Anvil Ice Contents and Other Cloud Properties from Satellite Observations of Lightning (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The lightning frequency model developed by Baker, Christian and Latham (1995) has been refined and extended, in an effort to provide a more realistic framework from which to examine computationally the relationships that might exist between lightning frequency f (which is now being routinely measured from satellites, using NASA/MSFC devices) and a variety of cloud physical parameters, including precipitation rate, updraught speed and non-precipitating ice content. Model results indicate the existence of a simple relationship between lightning frequency f and the upward flux of ice crystals into the thunderstorm anvil. It follows that, for a particular situation, one can assign a specific mass of non-precipitating ice to an individual lightning stroke. Therefore it may prove possible - using satellite measurements of global lightning - to estimate the atmospheric loading of ice crystals in thunderstorm anvils: a parameter of climatological importance. Early results from this work are presented, together with further studies of the relationships between f and other thundercloud parameters.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 363-366; NASA/CP-1999-209261
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    Charge Transfer Process During Collision of Riming Graupel Pellet with Small Ice Crystals within a Thundercloud (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: A charge transfer process during the collision of a riming graupel pellet and an ice-crystal at low temperature is proposed. During riming, the surface structure of graupel deviates from perfect crystalline structure. A concept of quasi-solid layer (QSL) formation on the surface is introduced. This QSL contains defects formed during riming. In absence of impurities, positively charged X-defect abundance is considered in the outer layer. These defects are assumed to be the charge carriers during the charge transfer process. Some part of the QSL is stripped off by the colliding ice crystals, which thereby gain some positive charge, leaving the graupel pellet negatively charged. With the proposed model, fC to pC of charge transfer is observed per collision. A transition temperature between -10 C to -15 C is also noted beyond which the QSL concept does not hold. This transition temperature is dependent on the bulk liquid water content of the cloud.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 296-299; NASA/CP-1999-209261
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    Cloud-to-Ground Lightning Characteristics of a Major Tropical Cyclone Tornado Outbreak (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: It is well known that most tropical cyclones (TCs) that make landfall along the Gulf coast of the United States spawn at least a few tornadoes. Although most landfalling TCs generate fewer than a dozen such tornadoes, a small proportion produce large swarm outbreaks, with as many as 25 or more tornadoes. Usually, these major outbreaks occur in large, intense hurricane-strength TCs, but on 15-17 August 1994 Tropical Storm Beryl spun off 37 tornadoes along its path from the Florida panhandle through the mid-Atlantic states. Some 32 of these tornadoes occurred on 16 August 1994 from eastern Georgia to southern Virginia, with most of these taking place in South Carolina. Beryl's 37 tornadoes moved it into what was at that time fifth place historically in terms of TC tornado productivity. The Beryl outbreak is especially noteworthy in that at least three of the tornadoes achieved peak intensity of F3 on the Fujita damage intensity scale. Although no fatalities resulted from the Beryl outbreak, at least 50 persons suffered injuries, and property damages totalled more than $50 million . The Beryl outbreak is a good example of a TC whose greatest danger to the public is its post-landfall severe weather. In this respect, and in the character of its swarm outbreak of tornadoes, it resembles another large tornado outbreak spawned by a relatively weak TC, Hurricane Danny of 1985). In the Danny outbreak, numerous shallow mini-supercell storms were found to have occurred, and it was noted that, because of the storms' relatively shallow depth, cloud-to-ground (CG) lightning was negligible. Better observations of future TC tornado outbreaks, especially with modern surveillance tools such as Doppler radars and the National Lightning Detection Network (NLDN), were recommended. Although the Beryl tornado outbreak is not the first set of TC-spawned tornado storms to be observed with the NLDN, it is one of the largest and likely the most intense such outbreak. The purpose of this paper is to document the NLDN-derived CG lightning characteristics of Beryl's tornadic storms, and to see how they compare with observations of CG lightning activity in other types of severe storms. In particular, we attempt to quantify the CG flash rates of TC tornadic cells, and to discover if there are any characteristics of their CG activity that may be useful to operational forecasters seeking to distinguish which cells are most likely to produce severe weather.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 511-514; NASA/CP-1999-209261
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    A Spherical Earth Solution for TOA Lightning Location Retrieval (1999)
    In:  CASI
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    Publication Date: 2004-12-03
    Description: The problem of retrieving ligntning, ground-strike location on a spherical Earth surface using a network of 4 or more time-of-arrival (TOA) sensors is considered, It is shown that this problem has an analytic solution and therefore does not require the use of nonlinear estimation theory (e.g., minimization). The mathematical robustness of the analytic solution is tested using computer-generated lightning sources and simulated TOA measurement errors. A summary of a quasi-analytic extension of the spherical Earth solution to an oblate spheroid Earth geometry is also provided.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 192-195; NASA/CP-1999-209261
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    Optical Observations of Lightning in Northern India, Himalayan Mountain Countries and Tibet (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: This study summarizes the results of an analysis of data from the LIS instrument on the TRMM platform. The data for the Indian summer monsoon season is examined to study the seasonal patterns of the geographic and diurnal distribution of lightning storms. The storms on the Tibetan plateau show a single large diurnal peak at about 1400 local solar time. A region of Northern Pakistan has two storm peaks at 0200 and 1400 local solar time. The morning peak is half the magnitude of the afternoon peak. The region south of the Himalayan Mountains has a combined diurnal cycle in location and time of storm occurrence.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 420-423; NASA/CP-1999-209261
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    High-Altitude Aircraft-Based Electric-Field Measurements Above Thunderstorms (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: We have developed a new set of eight electric field mills that were flown on a NASA ER-2 high-altitude aircraft. During the Third Convection And Moisture EXperiment (CAMEX-3; Fall, 1998), measurements of electric field, storm dynamics, and ice microphysics were made over several hurricanes. Concurrently, the TExas-FLorida UNderflights (TEFLUN) program was being conducted to make the same measurements over Gulf Coast thunderstorms. Sample measurements are shown: typical flight altitude is 20km. Our new mills have an internal 16-bit A/D, with a resolution of 0.25V/m per bit at high gain, with a noise level less than the least significant bit. A second, lower gain channel gives us the ability to measure fields as high as 150 kV/m.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 527-529; NASA/CP-1999-209261
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    Initial Comparison of the Lightning Imaging Sensor (LIS) with Lightning Detection and Ranging (LDAR) (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The mapping of the lightning optical pulses detected by the Lightning Imaging Sensor (LIS) is compared with the radiation sources by Lightning Detection and Ranging (LDAR) and the National Lightning Detection Network (NLDN) for three thunderstorms observed during and overpasses on 15 August 1998. The comparison involves 122 flashes including 42 ground and 80 cloud flashes. For ground flash, the LIS recorded the subsequent strokes and changes inside the cloud. For cloud flashes, LIS recorded those with higher sources in altitude and larger number of sources. The discrepancies between the LIS and LDAR flash locations are about 4.3 km for cloud flashes and 12.2 km for ground flashes. The reason for these differences remain a mystery.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 738-741; NASA/CP-1999-209261
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    Diurnal Lightning Distribution as Observed by the Optical Transient Detector (OTD) (1999)
    In:  CASI
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    Publication Date: 2004-12-03
    Description: Since April 1995, lightning activity around the globe has been monitored with the Optical Transient Detector (OTD). The OTD observations acquired during the one year period from September 1995 through August 1996 have been used to statistically determine the number of flashes that occur over the Earth during each hour of the diurnal cycle, expressed both as a function of local time and universal time. The globally averaged local [il,htnina activity displays a peak in late afternoon (1500-1800 local time) and a minimum in the morning hours (0600- 1000 local time) consistent with convection associated with diurnal heating. No diurnal variation is found for oceanic storms. The diurnal lightning distribution (universal time) for the globe displays a variation of about 35% about its mean as compared to the Carnegie curve which has a variation of only 15% above and below the mean.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 742-745; NASA/CP-1999-209261
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    Optical Transient Detector (OTD) Observations of a Tornadic Thunderstorm (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Total lightning observations made by the Optical Transient Detector (OTD) of a tornadic thunderstorm that occurred over Oklahoma on 17 April 1995 are presented. The average flash rate of the tornadic storm during the 3.2 min observation period was 45 flashes/min, with a flash rate density of 1.16 x 10(exp -4)/s sq km. The total flash rate was almost 18 times higher than the cloud-to-ground rate measured by the National Lightning Detection Network (NLDN). In addition, total lightning rates were observed to decrease prior to tornadic development.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 722-725; NASA/CP-1999-209261
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    Evidence for the Absence of Conductivity Variations Above Thunderstorms (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: In recent years, atmospheric conductivity and electric field measurements over thunderstorms have been made at 20 km with a high altitude aircraft. After compensating for the effects of aircraft charging induced by external electric fields no significant variations in ambient conductivity above thunderstorms have been found. These Gerdien results contrast strongly with the large (and frequent) conductivity variations reported in studies using relaxation probe techniques.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 646-649; NASA/CP-1999-209261
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    The 1997-98 El-Nino Event and Related Lightning Variations in the Southeastern United States (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The El Nino Southern Oscillation (ENSO) is a climate anomaly responsible for world-wide weather impacts ranging from droughts to floods. In the United States, warm episode years are known to produce above normal rainfall along the Southeast US Gulf Coast and into the Gulf of Mexico, with the greatest response observed in the October-March period of the current warm-episode year. The 1997-98 warm episode, notable for being the strongest event since 1982-83, presents our first opportunity to examine the response to a major ENSO event and determine the variation of wintertime thunderstorm activity in this part of the world. Due to the recent launch of a lightning sensor on NASA's Tropical Rainfall Measuring Mission (TRMM) in November 1997 and the expanded coverage of the National Lightning Detection Network (NLDN), we are able to examine such year-to-year changes in lightning activity with far greater detail than ever before.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 519-522; NASA/CP-1999-209261
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    STIS target acquisition (1997)
    In:  CASI
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    Publication Date: 2004-12-03
    Description: We describe the STIS autonomous target acquisition capabilities. We also present the results of dedicated tests executed as part of Cycle 7 calibration, following post-launch improvements to the Space Telescope Imaging Spectrograph (STIS) flight software. The residual pointing error from the acquisitions are 〈 0.5 CCD pixels, which is better than preflight estimates. Execution of peakups show clear improvement of target centering for slits of width 0.1 sec or smaller. These results may be used by Guest Observers in planning target acquisitions for their STIS programs.
    Keywords: Astronomy
    Type: The 1997 HST Calibration Workshop with a New Generation of Instruments; 39-46; NASA/TM-97-208141
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    Thermal motion of the STIS optical bench (1997)
    In:  CASI
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    Publication Date: 2004-12-03
    Description: Various tests have been done of the Space Telescope Imaging Spectrograph (STIS) using internal wavecals to measure thermal motion of the spectral format on the detectors. In most cases, the spectral format moves less than the specification not to exceed 0.2 pixels per hour. Primary causes of the motion are (1) changes to the thermal design dictated by the warmer Aft Shroud environment and (2) on-orbit power cycling of Multi-Anode Microchannel Arrays (MAMA) electronics to minimize the effects of radiation hits on the MAMA detectors. The rear portion of the STIS optical bench is too warm to be held at a constant temperature by internal heaters. Electronics swing in temperature with an orbital and daily frequency. The thermal drift of the optical formats is not negligible, but is well behaved in most circumstances. The observer is advised to examine the trade-off between the most accurate wavelengths with best spectral/spatial resolutions versus increased overheads that directly affect the observing times. A long term concern is that the Aft Shroud thermal environment is predicted to heat up as much as one Centigrade degree per year. Progressively more of the bench would move out of thermal control. Thus the external cooler for STIS, being considered for the Third Servicing Mission is of major importance to the long term operation of STIS.
    Keywords: Astronomy
    Type: The 1997 HST Calibration Workshop with a New Generation of Instruments; 106-113; NASA/TM-97-208141
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    Implications of the broad Al-26 1809 keV line observed by GRIS (1997)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The astrophysical implications of the large width of the 1809 keV gamma ray line from the decay of radioactive Al-26, recently observed with the gamma ray imaging spectrometer (GRIS), are discussed. While there may be no apparent single mechanism that can explain the observed broadening, high speed dust grains, extremely hot superbubbles and a large, low density gaseous halo were identified in the Galactic center region as the possible origins. The implications of these observations on the hot gas content in the interstellar medium are discussed.
    Keywords: Astronomy
    Type: ; 105-108
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    Issues concerning the Orion gamma ray line observations: Line splitting and LiBeB origin (1997)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The phenomenon of broad gamma ray line splitting is discussed, together with a scenario for the suppression of the blue wings of these broad lines due to the geometry of the accelerated particle interaction region. The broad and narrow gamma ray line emissions are compared taking into account the line splitting effect. It is concluded that the observed gamma ray lines from Orion are most likely broad, implying that the low energy cosmic rays which produce this line emission consist mostly of C and heavier ions. The suppression of the proton and alpha particle abundances requires acceleration conditions such as the acceleration of the ejecta of the supernovae before mixing with the interstellar medium. Similar conditions are implied by observations of the B and Be in low metallicity stars formed during the first Gyr of galactic evolution.
    Keywords: Astronomy
    Type: Proceedings of 2nd INTEGRAL Workshop 'The Transparent Universe'; 75-78; ESA-SP-382
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    An Alternative Lunar Ephemeris Model for On-Board Flight Software Use (1999)
    In:  CASI
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    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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    Ozone Depletion, UVB and Atmospheric Chemistry (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The primary constituents of the Earth's atmosphere are molecular nitrogen and molecular oxygen. Ozone is created when ultraviolet light from the sun photodissociates molecular oxygen into two oxygen atoms. The oxygen atoms undergo many collisions but eventually combine with a molecular oxygen to form ozone (O3). The ozone molecules absorb ultraviolet solar radiation, primarily in the wavelength region between 200 and 300 nanometers, resulting in the dissociation of ozone back into atomic oxygen and molecular oxygen. The oxygen atom reattaches to an O2 molecule, reforming ozone which can then absorb another ultraviolet photon. This sequence goes back and forth between atomic oxygen and ozone, each time absorbing a uv photon, until the oxygen atom collides with and ozone molecule to reform two oxygen molecules.
    Keywords: Meteorology and Climatology
    Type: NASA Scientific Forum on Climate Variability and Global Change: UNISPACE 3; 1-14; NASA/CP-1999-209240
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    BATSE as an all-sky monitor for INTEGRAL (1997)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: It is proposed to use data from the burst and transient source experiment (BATSE) onboard the Compton Gamma Ray Observatory (CGRO) as a sensitive, rapid, all sky monitor for the International Gamma Ray Astrophysics Laboratory (INTEGRAL). The all sky earth occultation monitoring and imaging capabilities of BATSE will complement and extend the Galactic plane scans of INTEGRAL as well as provide high latitude Galactic coverage which is inaccessible to INTEGRAL. Examples of transients previously observed by BATSE, its sensitivity, and the response time for these observations are described. Examples of the variability of several of the brighter sources observed by BATSE are shown.
    Keywords: Astronomy
    Type: Proceedings of 2nd INTEGRAL Workshop 'The Transparent Universe'; 537-540; ESA-SP-382
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    Observing gamma-ray bursts with the INTEGRAL spectrometer SPI (1997)
    In:  CASI
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    Publication Date: 2004-12-03
    Description: The spectrometer for INTEGRAL (SPI) is a germanium spectrometer with a wide field of view and will provide the International Gamma Ray Astrophysics Laboratory (INTEGRAL) mission with the opportunity of studying gamma ray bursts. Simulations carried out to assess the response of the instrument using data from real burst data as input are reported on. It is shown that, despite the angular resolution of 3 deg, it is possible to locate the direction of bursts with an accuracy of a few arcmin, while offering the high spectral resolution of the germanium detectors. It is remarked that the SPI field of view is similar to the size of the halo of bursts expected around M 31 on galactic models. The detectability of bursts with such a halo is discussed.
    Keywords: Astronomy
    Type: ; 487-490
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    Gamma-ray observations of BL Lac objects (1997)
    In:  CASI
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    Publication Date: 2004-12-03
    Description: The results from observations of a sample of BL Lac objects by the Compton telescope (COMPTEL) and energetic gamma ray experiment telescope (EGRET) onboard the Compton Gamma Ray Observatory (CGRO) are presented. The main targets in the sample were selected on the basis of their X-ray brightness and apparent spectral hardening at hard X-ray energies. One of the targets, PKS 0521-365 was detected by EGRET, and these data are presented together with contemporaneous ground-based radio data. Subsequent X-ray observations of this source with the Advanced Satellite for Cosomology and Astrophysics (ASCA) demonstrated that, although originally classified as a BL Lac object, it is better described as a flat spectrum radio quasar. Upper limits on the gamma ray flux from all the non-detected BL lacs are presented.
    Keywords: Astronomy
    Type: ; 413-416
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    Radio and X-ray observations of GX 339-4 (1997)
    In:  CASI
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    Publication Date: 2004-12-03
    Description: Observations of the Galactic black hole candidate binary system GX 339-4 at radio, optical and X-ray wavelengths are reviewed. The radio observations reveal a compact, persistent and variable source. On the average, the radio intensity is less than 10 mJy. These data, when compared with previous data, indicate no set correlation between the radio and X-ray emission. The X-ray intensity suggests a 14.5 month cycle. The latest radio observational data are presented together with X-ray data and are discussed in the context of similar correlated observations from other X-ray binaries.
    Keywords: Astronomy
    Type: Proceedings of 2nd INTEGRAL Workshop 'The Transparent Universe'; 201-204; ESA-SP-382
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    Hard X-ray spectra of neutron stars and black hole candidates (1997)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The hard X-ray behavior of several X-ray binary systems containing a neutron star or a black hole candidate is analyzed in an attempt to determine the specific signature of these categories of compact objects. Limiting the consideration to two subclasses of neutron stars, Atoll sources and non-pulsating Z sources, it appears that only the Atoll sources have a spectral behavior similar to black holes. It is proposed that Atoll sources are weakly magnetized neutron stars, whereas Z sources are small radius moderate magnetized neutron stars. Large magnetic fields funnel the accreting matter, thus preventing spherical accretion and free fall if the neutron star radius is smaller than the last stable accreting orbit. Weak magnetic fields do not have this effect, and blackbody soft photons from the stellar surface are upscattered on the relativistic infalling matter, leading to excess hard X-rays. This excess is visible in two of the observed Atoll sources and in the spectrum of a black hole candidate. In the case of a Z source, a lack of photons was remarked, providing a possible signature to distinguish between these classes of objects.
    Keywords: Astronomy
    Type: Proceedings of 2nd INTEGRAL Workshop 'The Transparent Universe'; 137-139; ESA-SP-382
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    Relation Between Lightning Activity of Summer and Winter Thunderclouds and Surface Electric Field Variation, Japan (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: In winter, active convective clouds frequently form along the coastline of the Hokuriku district, in association with strong advection of Siberian air masses over the Sea of Japan. On the other hand, in summer, many thunderclouds form in the Kanto region in the afternoon every day. Summer and winter thunderclouds were investigated by field works, operation of the C- and X-band weather radars and a car-borne fieldmill. The investigation found a very close relation between the temporal variation of 3-dimensional radar echo and surface electric field magnitude detected by a car-borne fieldmill in the case of summer thunderclouds and winter convective clouds or thunderclouds. The study probed the close relation among radar echoes, quantity of thunderclouds and surface electric field magnitude in the summer and winter seasons. We think that summer thundercloud activity can basically be equated with winter thundercloud lightning activity, except that the magnitude of surface electric field under summer thunderclouds in the case of the Kanto region cannot be equated with that under winter thunderclouds in the case of the Hokuriku district in winter.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 464-467; NASA/CP-1999-209261
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    Characteristics of Thunderstorms and Lightning Flashes Which Produce Mesospheric Transient Luminous Events (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: A six year record of optical observations of lightning-induced mesospheric transient luminous events (TLEs) is available from the Yucca Ridge Field Station (YRFS) near Ft. Collins, CO. Climatological analyses reveal sprites and elves occur in a variety of convective storm types, but principally mesoscale convective systems (MCSs) and squall lines. Severe supercell storms rarely produce TLEs, except during their dissipating stage. Few TLEs are observed during storms with radar echo areas 〈7,500 sq km. Above this size there is a modest correlation with radar areal coverage. A typical High Plains storm produces 45 TLEs over a 143 interval. Sprites and most elves are associated with +CGs. The probability of a TLE increases with peak current. In six storms, 5.1% of +CGs produced TLEs, the number increasing to 32% of +CGs with 〉75 kA and 52% of +CGs with 〉100 kA peak current.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 84-87; NASA/CP-1999-209261
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    Land-Ocean Differences in LIS and OTD Tropical Lightning Observations (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Significant differences are known to exist on a global scale between continental and oceanic total lightning regional flash rates, suggesting differences in the properties of convective storms in these regimes. Lightning properties observed by the Optical Transient Detector (OTD) and Lightning Imaging Sensor (LIS) over land and ocean are compared, limited to analysis over the tropics in order to simplify physical interpretation. We find that the mean flash rates of individual storms over tropical land only exceed those over ocean by a factor of 2 (far less than the observed differences in regional flash rates). However, the average nearest neighbor distance of continental thunderstorms is half that over oceans. Cloud-top lightning optical radiance in oceanic storms is also twice as large as over land, suggesting either more energetic flashes over the oceans or less intervening cloud particles.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 734-737; NASA/CP-1999-209261
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    Lightning Launch Commit Criteria for America's Space Program (1999)
    In:  CASI
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    Publication Date: 2004-12-03
    Description: The danger of natural and triggered lightning significantly impacts space launch operations supported by the USAF. The lightning Launch Commit Criteria (LCC) are used by the USAF to avoid these lightning threats to space launches. This paper presents a brief overview of the LCC.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 238-241; NASA/CP-1999-209261
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    Investigation of a Frequency Spectrum of Discharges Generated by a Charged Aerosol Cloud (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Charged aerosol clouds allow to create strong electric fields which generate discharges. A character of appearance and development of the discharges is similar to thundercloud processes. That is why the charged aerosol clouds are used for experiments on studying of discharges in air. Experimental data on electromagnetic fields investigation produced by discharges between charged cloud and ground are considered.
    Keywords: Meteorology and Climatology
    Type: 11th International Conference on Atmospheric Electricity; 135-137; NASA/CP-1999-209261
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    The Submillimeter Wave Astronomy Satellite: Science objectives and instrument description (1997)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The submillimeter wave astronomy satellite (SWAS) mission is dedicated to the investigation of star formation and interstellar chemistry. In order to perform the mission, SWAS will survey dense molecular clouds within the Milky Way Galaxy in either the ground state or a low-lying transition of five astrophysically-significant species: H2O, H2(18)O, O2, C I and (13)CO. The observation of these lines will: test theories that predict that these species are dominant coolants of molecular clouds during early stages of their collapse to form stars and planets, and supply information concerning the abundance of species central to the chemical models of dense interstellar gas. The SWAS will use two independent Schottky barrier diode mixers and a 53 x 68 sq cm, off-axis Cassegrain antenna.
    Keywords: Astronomy
    Type: ; 189-194
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    [The influence of space flight factors on the growth and development of super dwarf wheat cultivated in greenhouse Svet] (1999)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: In 1996-1997 an experiment with super dwarf wheat (Greenhouse-2) was made aboard the orbital complex MIR as a part of the MIR-NASA space science program. The article deals with the main production and morphometric characteristics of plants that completed their vegetation cycle in the space flight. Lengths of the whole cycle of vegetation and its individual stages were essentially same as in ground control experiments. Dry mass of one plants equal, the number of headed shoots was in 2.7 times less in the flight harvest as compared with the control. The height of shoots was reduced by one half. No seeds were found in the heads formed in space. The architecture of heads was substantially different from what had been observed in the preceeding ground control experiments: mass of the heads was halved and lengths of inflorescence and palea awn shortened. The number of spikelets in a head reduced up to 8-10 vs. 13-14 in the controls, whereas the number of florets per a spikelet averaged 5 vs. 3 in the controls. The experiments showed that mainly the most profound changes in the productive and morphometric parameters of the super dwarf wheat plants were largely caused by the phytotoxic effects of ethylene rather than spaceflight specific factors as its concentrations in the MIR air amount to 0.3-1.8 mg/m3.
    Keywords: Meteorology and Climatology
    Type: Aviakosmicheskaia i ekologicheskaia meditsina = Aerospace and environmental medicine (ISSN 0233-528X); Volume 33; 2; 37-41
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    Urban Heat Islands and Summertime Convective Thunderstorms in Atlanta: Three Case Studies (1999)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: Data from both 27 sites in the Atlanta mesonet surface meteorological network and eight National Weather Service sites were analyzed for the period from 26 July to 3 August 1996. Analysis of the six precipitation events over the city during the period (each on a different day) showed that its urban heat island (UHI) induced a convergence zone that initiated three of the storms at different times of the day, i.e., 0630,0845, and 1445 EDT. Previous analysis has shown that New York City (NYC) effects summer daytime thunderstorm formation and/or movement. That study found that during nearly calm regional flow conditions the NYC UHI initiates convective activity. Moving thunderstorms, however, tended to bifurcate and to move around the city, due to its building barrier effect. The current Atlanta results thus agree with the NYC results with respect to thunderstorm initiation.
    Keywords: Meteorology and Climatology
    Type: Atmospheric Environment (ISSN 1352-2310); Volume 34; 507-516
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  • 55
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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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    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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    Analyses of 1994 Typhoons in the Taiwan Region Using Satellite Data (1997)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: Taiwan is situated in the prevalent typhoon track in the northwestern Pacific. On average, about one third of the island total annual precipitation is due to typhoons, with the other two third being contributed by the summer monsoon, or Meiyu, and wintertime large scale frontal rainfall. While the typhoons bring the needed moisture for agricultural consumption and industrial utilization, heavy rainfall associated with typhoons often result in large scale flooding and land slide. The prediction of the typhoon track and its severity is therefore a high priority topic both for operation and research. The severity of a typhoon can be defined in terms of the wind strength and the moisture content. The Special Sensor Microwave/Imager (SSM/I) on board of the Defense Meteorological Satellite Program (DMSP) satellites measures microwave radiation in 19.4, 22.2, 37, and 85.5 GHz. These measurements provide an opportunity to estimate parameters such as surface wind speed, water vapor and cloud water contents, and rainfall rate over oceans. In 1994, Taiwan experienced an above normal frequency of typhoon hits, five typhoons hit the island in two months. In this report, estimates of the moisture content of these typhoons are made based on the SSM/I measurements. An assessment of the relative strength of the typhoons are made with analyzed data.
    Keywords: Meteorology and Climatology
    Type: Laboratory for Hydrospheric Processes Research Publications; 77-78
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  • 58
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    On the Dramatic Spin-up/Spin-Down Torque Reversals in Accreting Pulsars (1997)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: Dramatic torque reversals between spin-up and spin-down have been observed in half of the persistent X-ray pulsars monitored by the Burst and Transient Space Experiment (BATSE) all-sky monitor on the Compton Gamma Ray Observatory. Theoretical models developed to explain early pulsar timing data can explain spin-down torques via a disk-magnetosphere interaction if the star nearly corotates with the inner accretion disk. To produce the observed BATSE torque reversals, however, these equilibrium models require the disk to alternate between two mass accretion rates, with M+/- producing accretion torques of similar magnitude but always of opposite sign. Moreover, in at least one pulsar (GX 1+4) undergoing secular spin-down, the neutron star spins down faster during brief (approximately 20 day) hard X-ray flares-this is opposite the correlation expected from standard theory, assuming that BATSE pulsed flux increases with mass accretion rate. The 10 day to 10 yr intervals between torque reversals in these systems are much longer than any characteristic magnetic or viscous timescale near the inner disk boundary and are more suggestive of a global disk phenomenon. We discuss possible explanations of the observed torque behavior. Despite the preferred sense of rotation defined by the binary orbit, the BATSE observations are surprisingly consistent with an earlier suggestion for GX 1+4: the disks in these systems somehow alternate between episodes of prograde and retrograde rotation. We are unaware of any mechanism that could produce a stable retrograde disk in a binary undergoing Roche lobe overflow, but such flip-flop behavior does occur in numerical simulations of wind-fed systems. One possibility is that the disks in some of these binaries are fed by an X-ray-excited wind.
    Keywords: Astronomy
    Type: Astrophysical Journal; Volume 488; L117-L120
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    The High Throughput X-ray Spectroscopy (HTXS) Mission (1997)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: The HTXS mission concept combines large effective area (approximately 15,000 sq cm at 1 keV), high spectral resolution (E/Delta(E) approximately 300-3000), and broad energy bandpass (0.25-40 keV and possibly up to 100 keV) by using replicated optics together with a complement of spectroscopic instrumentation including reflection gratings readout by charge-coupled device detectors (CCDs), quantum micro-calorimeters, and cadmium zinc telluride (CZT) or comparable high energy detectors. An essential feature of this concept involves minimization of cost (approximately $350M for development and approximately $500-600M including launches) and risk by building six identical modest satellites to achieve the large area. Current mission and technology studies are targeted towards a new start in the 2002 timeframe, with first launch around 2005-2006. The HTXS mission represents a major advance, providing as much as a factor of 100 increase in sensitivity over currently planned high resolution X ray spectroscopy missions. HTXS will mark the start of a new era when high quality X ray spectra will be obtained for all classes of X ray sources, over a wide range of luminosity and distance. With its increased capabilities, HTXS will address many fundamental astrophysics questions such as the origin and distribution of the elements from carbon to zinc, the formation and evolution of clusters of galaxies, the validity of general relativity in the strong gravity limit, the evolution of supermassive black holes in active galactic nuclei, the details of supernova explosions and their aftermath, and the mechanisms involved in the heating of stellar coronae and driving of stellar winds.
    Keywords: Astronomy
    Type: The Next Generation of X-Ray Observatories; 173-189; XRA97/02
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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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    The Effect of Clouds on Water Vapor Profiling from the Millimeter-Wave Radiometric Measurements (1997)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: Simultaneous measurements with the millimeter-wave imaging radiometer (MIR), cloud lidar system (CLS), and the MODIS airborne simulator (MAS) were made aboard the NASA ER-2 aircraft over the western Pacific Ocean on 17-18 January 1993. These measurements were used to study the effects of clouds on water vapor profile retrievals based on millimeter-wave radiometer measurements. The CLS backscatter measurements (at 0.532 and 1.064 am) provided information on the heights and a detailed structure of cloud layers; the types of clouds could be positively identified. All 12 MAS channels (0.6-13 Am) essentially respond to all types of clouds, while the six MIR channels (89-220 GHz) show little sensitivity to cirrus clouds. The radiances from the 12-/Am and 0.875-gm channels of the MAS and the 89-GHz channel of the MIR were used to gauge the performance of the retrieval of water vapor profiles from the MIR observations under cloudy conditions. It was found that, for cirrus and absorptive (liquid) clouds, better than 80% of the retrieval was convergent when one of the three criteria was satisfied; that is, the radiance at 0.875 Am is less than 100 W/cm.sr, or the brightness at 12 Am is greater than 260 K, or brightness at 89 GHz is less than 270 K (equivalent to cloud liquid water of less than 0.04 g/cm). The range of these radiances for convergent retrieval increases markedly when the condition for convergent retrieval was somewhat relaxed. The algorithm of water vapor profiling from the MIR measurements could not perform adequately over the areas of storm-related clouds that scatter radiation at millimeter wavelengths.
    Keywords: Meteorology and Climatology
    Type: Laboratory for Hydrospheric Processes Research Publications; 165-166
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    Friction Velocity Estimation Using Dual-Frequency Altimeter Data (1997)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: Global estimation of wind speeds near the sea-surface can be obtained using normalized radar cross sections sigma(o) from satellite-borne single-frequency altimeters. Indeed recent validation studies of Geosat altimeter-derived wind speeds show that several often cited semiempirical algorithms yield linear trends between wind-speeds from altimeter data and wind speeds from (a) ships of opportunity (Etcheto 1992), (b) buoys (Carter 1992), and (c) atmospheric models (Guillaume 1992). Although the linear trends are striking, there is considerable scatter since the range of standard deviations is from 1.5 to 3 m/s. In fact, the scatter of some particular measurements about the regressions is striking because they depart from the 'standard' by as much as +/- 5 m/s, which is large - even for full gale winds of 20 m/s. These anomalies can cause serious problems for gas exchange, heat, and aerosol estimates. They can also induce considerable errors in wind-driven oceanic circulation models and sea-surface wave models. This paper explores the possibility of improving the accuracy of wind speed estimation using dual-frequency altimeters.
    Keywords: Meteorology and Climatology
    Type: Laboratory for Hydrospheric Processes Research Publications; 117-118
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    Global Oceanic Precipitation: A Joint View by TOPEX and the TOPEX Microwave Radiometer (1997)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: The TOPEX/POSEIDON mission offers the first opportunity to observe rain cells over the ocean by a dual-frequency radar altimeter (TOPEX) and simultaneously observe their natural radiative properties by a three-frequency radiometer (TOPEX microwave radiometer (TMR)). This work is a feasibility study aimed at understanding the capability and potential of the active/passive TOPEX/TMR system for oceanic rainfall detection. On the basis of past experiences in rain flagging, a joint TOPEX/TMR rain probability index is proposed. This index integrates several advantages of the two sensors and provides a more reliable rain estimate than the radiometer alone. One year's TOPEX/TMR data are used to test the performance of the index. The resulting rain frequency statistics show quantitative agreement with those obtained from the Comprehensive Ocean-Atmosphere Data Set (COADS) in the Intertropical Convergence Zone (ITCZ), while qualitative agreement is found for other regions of the world ocean. A recent finding that the latitudinal frequency of precipitation over the Southern Ocean increases steadily toward the Antarctic continent is confirmed by our result. Annual and seasonal precipitation maps are derived from the index. Notable features revealed include an overall similarity in rainfall pattern from the Pacific, the Atlantic, and the Indian Oceans and a general phase reversal between the two hemispheres, as well as a number of regional anomalies in terms of rain intensity. Comparisons with simultaneous Global Precipitation Climatology Project (GPCP) multisatellite precipitation rate and COADS rain climatology suggest that systematic differences also exist. One example is that the maximum rainfall in the ITCZ of the Indian Ocean appears to be more intensive and concentrated in our result compared to that of the GPCP. Another example is that the annual precipitation produced by TOPEX/TMR is constantly higher than those from GPCP and COADS in the extratropical regions of the northern hemisphere, especially in the northwest Pacific Ocean. Analyses of the seasonal variations of prominent rainy and dry zones in the tropics and subtropics show various behaviors such as systematic migration, expansion and contraction, merging and breakup, and pure intensity variations. The seasonality of regional features is largely influenced by local atmospheric events such as monsoon, storm, or snow activities. The results of this study suggest that TOPEX and its follow-on may serve as a complementary sensor to the special sensor microwave/imager in observing global oceanic precipitation.
    Keywords: Meteorology and Climatology
    Type: Laboratory for Hydrospheric Processes Research Processes; 25-26
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    Uncertainty in Satellite Rainfall Estimates: Time Series Comparison (1997)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: We examined nine satellite rainfall algorithms and compared the rain fields produced from these algorithms for the period of August 1987 to December 1988. Preliminary results show algorithms which use the same satellite sensor data tend to be similar, suggesting the importance of sampling. Oceanic global mean rainfall ranges from 2.7 to 3.6 mm/d. The variability in zonal mean rain rate is about 1.5-2 mm/d for these algorithms.
    Keywords: Meteorology and Climatology
    Type: Laboratory for Hydrospheric Processes Research Publications; 123-124
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    Cabauw Experimental Results from the Project for Intercomparison of Land-Surface Parameterization Schemes (1997)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: In the Project for Intercomparison of Land-Surface Parameterization Schemes phase 2a experiment, meteorological data for the year 1987 from Cabauw, the Netherlands, were used as inputs to 23 land-surface flux schemes designed for use in climate and weather models. Schemes were evaluated by comparing their outputs with long-term measurements of surface sensible heat fluxes into the atmosphere and the ground, and of upward longwave radiation and total net radiative fluxes, and also comparing them with latent heat fluxes derived from a surface energy balance. Tuning of schemes by use of the observed flux data was not permitted. On an annual basis, the predicted surface radiative temperature exhibits a range of 2 K across schemes, consistent with the range of about 10 W/m in predicted surface net radiation. Most modeled values of monthly net radiation differ from the observations by less than the estimated maximum monthly observational error (+/- 10 W/sq m). However, modeled radiative surface temperature appears to have a systematic positive bias in most schemes; this might be explained by an error in assumed emissivity and by models' neglect of canopy thermal heterogeneity. Annual means of sensible and latent heat fluxes, into which net radiation is partitioned, have ranges across schemes of 30 W/sq m and 25 W/sq m, respectively. Annual totals of evapotranspiration and runoff, into which the precipitation is partitioned, both have ranges of 315 mm. These ranges in annual heat and water fluxes were approximately halved upon exclusion of the three schemes that have no stomatal resistance under non-water-stressed conditions. Many schemes tend to underestimate latent heat flux and overestimate sensible heat flux in summer, with a reverse tendency in winter. For six schemes, root-mean-square deviations of predictions from monthly observations are less than the estimated upper bounds on observation errors (5 W/m for sensible beat flux and 10 W/m for latent heat flux). Actual runoff at the site is believed to be dominated by vertical drainage to ground water, but several schemes produced significant amounts of runoff as overland flow or interflow. There is a range across schemes of 184 mm (40% of total pore volume) in the simulated annual mean root-zone soil moisture. Unfortunately, no measurements of soil moisture were available for model evaluation. A theoretical analysis suggested that differences in boundary conditions used in various schemes are not sufficient to explain the large variance in soil moisture. However, many of the extreme values of soil moisture could be explained in terms of the particulars of experimental setup or excessive evapotranspiration.
    Keywords: Meteorology and Climatology
    Type: Laboratory for Hydrospheric Processes Research Publications; 27-28
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    A Correlation Between Length of Strong-Shear Neutral Lines and Total X-Ray Brightness in Active Regions (1997)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: From a sample of 7 MSFC vector magnetograms,of active regions and 17 Yohkoh SXT soft X-ray images of these active regions, we have found that the total x-ray brightness of an entire active region is correlated with the total length of neutral lines on which the magnetic field is both strong (less than 250 G) and strongly sheared (shear angle greater than 75 deg) in the same active region. This correlation, if not fortuitous, is additional evidence of the importance of strong-shear strong-field neutral lines to strong heating in active regions.
    Keywords: Astronomy
    Type: Solar Physics; Volume 176; 123-126
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    Cloud 3D Effects Evidenced in Landsat Power Spectra and Autocorrelation Functions (1999)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: An analysis of nadir reflectivity Fourier spatial power spectra and autocorrelation functions at solar wavelengths and for cloudy conditions has been carried out. The data come from Landsat Thematic Mapper (TM) observations, while Monte Carlo (MC) simulations are used to aid the interpretation of the Landsat results. We show that radiative processes produce consistent signatures on power spectra and autocorrelation functions. The former take a variety of forms not shown or explained in previous observational studies. We demonstrate that the TM spectra can potentially be affected by both radiative "roughening" at intermediate scales (approx. 1 -5 km), being more prevalent at large solar zenith angles, and the already documented radiative "smoothing" at small scales (less than 1 km). These processes are wavelength dependent, as shown by systematic differences between conservative (for cloud droplets) TM band 4 (approx. 0.8 microns) and absorbing band 7 (approx. 2.2 microns): band 7 exhibits more roughening and less smoothing. This is confirmed quantitatively by comparing least-squared fitted power spectral slopes for the two bands. It is also corroborated by a slower decrease with distance of autocorrelation function values for band 4 compared to band 7. The appearance of roughening at large solar zenith angles is a result of side illumination and shadowing and adds an additional complexity to the power spectra. MC spectra are useful in illustrating that scale invariant optical depth fields can produce complex power spectra that take a variety of shapes under different conditions. We show that radiative roughening increases with the decrease of single scattering albedo and with the increase of solar zenith angle (as in the observations). For high Sun there is also a clear shift of the radiative smoothing scale to smaller values as droplet absorption increases. The shape of the power spectrum is sensitive to the magnitude and type of cloud top height variability, with the spectral signatures of decorrelation between reflectance and optical depth at large scales becoming stronger as the magnitude of cloud top variations increase. Finally, the usefulness of power spectral analysis in evaluating the skill of novel optical depth retrieval techniques in removing 3D radiative effects is demonstrated. New techniques using inverse Non-local Independent Pixel Approximation (NIPA) and Normalized Difference of Nadir Reflectivity (NDNR) yield optical depth fields which better match the scale-by-scale variability of the true optical depth field.
    Keywords: Meteorology and Climatology
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    Cloud Liquid Water, Mean Droplet Radius and Number Density Measurements Using a Raman Lidar (1999)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: A new technique for measuring cloud liquid water, mean droplet radius and droplet number density is outlined. The technique is based on simultaneously measuring Raman and Mie scattering from cloud liquid droplets using a Raman lidar. Laboratory experiments on liquid micro-spheres have shown that the intensity of Raman scattering is proportional to the amount of liquid present in the spheres. This fact is used as a constraint on calculated Mie intensity assuming a gamma function particle size distribution. The resulting retrieval technique is shown to give stable solutions with no false minima. It is tested using Raman lidar data where the liquid water signal was seen as an enhancement to the water vapor signal. The general relationship of retrieved average radius and number density is consistent with traditional cloud physics models. Sensitivity to the assumed maximum cloud liquid water amount and the water vapor mixing ratio calibration are tested. Improvements to the technique are suggested.
    Keywords: Meteorology and Climatology
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    The Prospect for Remote Sensing of Cirrus Clouds with a Submillimeter-Wave Spectrometer (1999)
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    Publication Date: 2011-08-23
    Description: Given the substantial radiative effects of cirrus clouds and the need to validate cirrus cloud mass in climate models, it is important to measure the global distribution of cirrus properties with satellite remote sensing. Existing cirrus remote sensing techniques, such as solar reflectance methods, measure cirrus ice water path (IWP) rather indirectly and with limited accuracy. Submillimeter/wave radiometry is an independent method of cirrus remote sensing based on ice particles scattering the upwelling radiance emitted by the lower atmosphere. A new aircraft instrument, the Far Infrared Sensor for Cirrus (FIRSC), is described. The FIRSC employs a Fourier Transform Spectrometer (FTS). which measures the upwelling radiance across the whole submillimeter region (0.1 1.0-mm wavelength). This wide spectral coverage gives high sensitivity to most cirrus particle sizes and allows accurate determination of the characteristic particle size. Radiative transfer modeling is performed to analyze the capabilities of the submillimeter FTS technique. A linear inversion analysis is done to show that cirrus IWP, particle size, and upper-tropospheric temperature and water vapor may be accurately measured, A nonlinear statistical algorithm is developed using a database of 20000 spectra simulated by randomly varying most relevant cirrus and atmospheric parameters. An empirical orthogonal function analysis reduces the 500-point spectrum (20 - 70/cm) to 15 "pseudo-channels" that are then input to a neural network to retrieve cirrus IWP and median particle diameter. A Monte Carlo accuracy study is performed with simulated spectra having realistic noise. The retrieval errors are low for IWP (rms less than a factor of 1.5) and for particle sizes (rins less than 30%) for IWP greater than 5 g/sq m and a wide range of median particle sizes. This detailed modeling indicates that there is good potential to accurately measure cirrus properties with a submillimeter FTS.
    Keywords: Meteorology and Climatology
    Type: Journal of Applied Meteorology; Volume 38; 514-525
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    Prospects for the Next Generation of X-ray Astronomy (1997)
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    Publication Date: 2011-08-23
    Description: This rapporteur contribution attempts to summarize the discussions at this conference in the context of current funding realities.
    Keywords: Astronomy
    Type: The Next Generation of X-Ray Observatories; 221-226; XRA97/02
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    Scatterometer Observes Extratropical Transition of Pacific Typhoons (1997)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: From September 15 to 25, 1996, NASA's scatterometer (NSCAT) monitored the evolution of twin typhoons, Violet and Tom, as they moved north from the western tropical Pacific, acquiring features of mid-latitude storms. The typhoons developed frontal structures, increased asymmetry, and dry air was introduced into their cores. Violet hit Japan, causing death and destruction (Figure 1), and Tom merged with a mid-latitude trough and evolved into a large extratropical storm with gale-force winds (Figure 2). We understand relatively little about the extratropical transition of tropical cyclones because of the complex thermodynamics involved [e.g., Sinclair, 1993], but we do know that the mid-latitude storms resulting from tropical cyclones usually generate strong winds and heavy precipitation. Since the transition usually occurs over the ocean, few measurements have been made. The transition is a fascinating science problem, but it also has important economic consequences. The transition occurs over the busiest trans-ocean shipping lanes, and when the resulting storms hit land, they usually devastate populated areas. NSCAT was successfully launched into a near-polar, sun-synchronous orbit on the Japanese Advanced Earth Observing Satellite (ADEOS) in August 1996 from Tanegashima Space Center in Japan. NSCAT's six antennas send microwave pulses at a frequency of 14 GHz to the Earth's surface and measure the backscatter. The antennas scan two 600-km bands of the ocean, which are separated by a 330-km data gap. From NSCAT observations, surface wind vectors can be derived at 25-km spatial resolution, covering 77% of the ice-free ocean in one day and 97% of the ocean in two days, under both clear and cloudy conditions.
    Keywords: Meteorology and Climatology
    Type: EOS, Transactions (ISSN 0096-3941); Volume 78; No. 23; 237, 240
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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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    Estimating the Uncertainty in Passive-Microwave Rain-Retrievals (1997)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Current passive-microwave rain-retrieval methods are largely based on databases built off-line using cloud models. The vertical distribution of hydrometeors within the cloud has a large impact on upwelling brightness temperatures ([31,[5]). Thus, a forward radiative transfer model can predict off-line the radiance associated with different rain scenarios. To estimate the rain from measured brightness temperatures, one simply looks for the rain scenario whose associated radiances are closest to the measurements. To understand the uncertainties in this process, we first study the dependence of the simulated brightness temperatures on different hydrometeor size distribution (DSD) models. We then analyze the marginal and joint distributions of the radiances observed by the Tropical Rainfall Measuring Mission satellite and of those in the databases used in the TRMM rain retrievals. We finally calculate the covariances of the rain profiles and brightness temperatures in the TRMM passive-microwave database and derive a simple parametric model for the conditional uncertainty, given measured radiances. These results are used to characterize the uncertainty inherent in the passive-microwave retrieval.
    Keywords: Meteorology and Climatology
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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
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    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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    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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    The Tropical Rainfall Measuring Mission (TRMM) (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: Recognizing the importance of rain in the tropics and the accompanying latent heat release, NASA for the U.S. and NASDA for Japan have partnered in the design, construction and flight of an Earth Probe satellite to measure tropical rainfall and calculate the associated heating. Primary mission goals are: 1) the understanding of crucial links in climate variability by the hydrological cycle, 2) improvement in the large-scale models of weather and climate, and 3) improvement in understanding cloud ensembles and their impacts on larger scale circulations. The linkage with the tropical oceans and landmasses are also emphasized. The Tropical Rainfall Measuring Mission (TRMM) satellite was launched in November 1997 with fuel enough to obtain a four to five year data set of rainfall over the global tropics from 37 deg N to 37 deg S. This paper reports progress from launch date through the spring of 1999. The data system and its products and their access is described, as are the algorithms used to obtain the data. Some exciting early results from TRMM are described. Some important algorithm improvements are shown. These will be used in the first total data reprocessing, scheduled to be complete in early 2000. The reader is given information on how to access and use the data.
    Keywords: Meteorology and Climatology
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    Environmental Forcing of Super Typhoon Paka's (1997) Latent Heat Structure (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: The distribution and intensity of total (i.e., combined stratified and convective processes) rainrate/latent heat release (LHR) were derived for tropical cyclone Paka during the period 9-21 December, 1997 from the F-10, F-11, F-13, and F-14 Defense Meteorological Satellite Special Sensor Microwave/Imager and the Tropical Rain Measurement Mission Microwave Imager observations. These observations were frequent enough to capture three episodes of inner core convective bursts that preceded periods of rapid intensification and a convective rainband (CRB) cycle. During these periods of convective bursts, satellite sensors revealed that the rainrates/LHR: 1) increased within the inner eye wall region; 2) were mainly convectively generated (nearly a 65% contribution), 3) propagated inwards; 4) extended upwards within the middle and upper-troposphere, and 5) became electrically charged. These factors may have caused the eye wall region to become more buoyant within the middle and upper-troposphere, creating greater cyclonic angular momentum, and, thereby, warming the center and intensifying the system. Radiosonde measurements from Kwajalein Atoll and Guam, sea surface temperature observations, and the European Center for Medium Range Forecast analyses were used to examine the necessary and sufficient condition for initiating and maintaining these inner core convective bursts. For example, the necessary conditions such as the atmospheric thermodynamics (i.e., cold tropopause temperatures, moist troposphere, and warm SSTs [greater than 26 deg]) suggested that the atmosphere was ideal for Paka's maximum potential intensity (MPI) to approach super-typhoon strength. Further, Paka encountered weak vertical wind shear (less than 15 m/s ) before interacting with the westerlies on 21 December. The sufficient conditions, on the other hand, appeared to have some influence on Paka's convective burst, but the horizontal moisture flux convergence values in the outer core were weaker than some of the previously examined tropical cyclones. Also, the upper tropospheric outflow generation of eddy relative angular momentum flux convergence was 4D much less than that found during moderate tropical cyclone/trough interaction. These results indicated how important the external necessary condition and the internal forcing (i.e., CRB cycle) were in generating Paka's convective bursts as compared to the external sufficient forcing mechanisms found in higher latitude tropical cyclones. Later, as Paka began to interact with the westerlies, both the necessary (i.e., strong vertical shear and colder SSTs) and sufficient (i.e., dry air intrusion) external forcing mechanisms helped to decrease Paka's rainrate.
    Keywords: Meteorology and Climatology
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    Winter to Spring Transition in Europe 48-45 degrees N: From Temperature Control by Advection to Control by Insolation (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: As established in previous studies, and analyzed further herein for the years 1988-1998, warm advection from the North Atlantic is the predominant control of the surface-air temperature in northern-latitude Europe in late winter. This thesis is supported by the substantial correlation Cti between the speed of the southwesterly surface winds over the eastern North Atlantic, as quantified by a specific Index Ina, and the 2-meter level temperature Ts over central Europe (48-54 deg N; 5-25 deg E), for January, February and early March. In mid-March and subsequently, the correlation Cti drops drastically (quite often it is negative). The change in the relationship between Ts and Ina marks a transition in the control of the surface-air temperature. As (a) the sun rises higher in the sky, (b) the snows melt (the surface absorptivity can increase by a factor of 3.0), (c) the ocean-surface winds weaken, and (d) the temperature difference between land and ocean (which we analyze) becomes small, absorption of insolation replaces the warm advection as the dominant control of the continental temperature. We define the onset of spring by this transition, which evaluated for the period of our study occurs at pentad 16 (Julian Date 76, that is, March 16). The control by insolation means that the surface is cooler under cloudy conditions than under clear skies. This control produces a much smaller interannual variability of the surface temperature and of the lapse rate than prevailing in winter, when the control is by advection. Regional climatic data would be of greatest value for agriculture and forestry if compiled for well-defined seasons. For continental northern latitudes, analysis presented here of factors controlling the surface temperature appears an appropriate tool for this task.
    Keywords: Meteorology and Climatology
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    A Solar Reflectance Method for Retrieving Cloud Optical Thickness and Droplet Size Over Snow and Ice Surfaces (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: Cloud optical thickness and effective radius retrievals from solar reflectance measurements are traditionally implemented using a combination of spectral channels that are absorbing and non-absorbing for water particles. Reflectances in non-absorbing channels (e.g., 0.67, 0.86, 1.2 micron spectral window bands) are largely dependent on cloud optical thickness, while longer wavelength absorbing channels (1.6, 2. 1, and 3.7 micron window bands) provide cloud particle size information. Cloud retrievals over ice and snow surfaces present serious difficulties. At the shorter wavelengths, ice is bright and highly variable, both characteristics acting to significantly increase cloud retrieval uncertainty. In contrast, reflectances at the longer wavelengths are relatively small and may be comparable to that of dark open water. A modification to the traditional cloud retrieval technique is devised. The new algorithm uses only a combination of absorbing spectral channels for which the snow/ice albedo is relatively small. Using this approach, retrievals have been made with the MODIS Airborne Simulator (MAS) imager flown aboard the NASA ER-2 from May - June 1998 during the Arctic FIRE-ACE field deployment. Data from several coordinated ER-2 and University of Washington CV-580 in situ aircraft observations of liquid water stratus clouds are examined. MAS retrievals of optical thickness, droplet effective radius, and liquid water path are shown to be in good agreement with the in situ measurements. The initial success of the technique has implications for future operational satellite cloud retrieval algorithms in polar and wintertime regions.
    Keywords: Meteorology and Climatology
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    A TRMM Microwave Radiometer Rain Rate Estimation Method with Convective and Stratiform Discrimination (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) radiometer brightness temperature data in the 85 GHz channel (T85) reveal distinct local minima (T85min) in a regional map containing a Mesoscale Convective System (MCS). This is because of relatively small footprint size (approximately 5.5 km) and strong extinction properties in this channel of the TMI. A map of surface rain rate for that region, deduced from simultaneous measurements made by the Precipitation Radar (PR) on board the TRMM satellite, reveals that these T85(sub min), produced by scattering, correspond to local PR rain maxima. Utilizing the PR rain rate map as a guide, we infer empirically from TMI data the presence of three different kinds of thunderstorms or Cbs. These Cbs are classified as young, mature, and decaying types, and are assumed to have a scale of about 20 km on the average. Two parameters are used to classify these three kinds of Cbs based on the T85 data: a) the magnitude of scattering depression deduced from local T85(sub min) and b) the mean horizontal gradient of T85 around such minima. Knowing the category of a given Cb, we can estimate the rain rate associated with it. Such estimation is done with the help of relationships linking T85min to rain rate in each Cb type. Similarly, a weak background rain rate in all the areas where T85 is less than 260 K is deduced with another relationship linking T85 to rain rate. In our rain retrieval model, this background rain constitutes stratiform rain where the Cbs are absent. Initially, these relationships are optimized or tuned utilizing the PR and TMI data of a few MCS events. After such tuning, the model is applied to independent MCS cases. The areal distribution of light (1-10 mm/hr), moderate (10-20 mm/hr), and intense (〉= 20 mm/hr) rain rates are retrieved satisfactorily. Accuracy in the estimates of the light, moderate, and intense rain areas and the mean rain rates associated with such areas in these independent MCS cases is on the average about 15 %. Taking advantage of this ability of our retrieval method, one could derive the latent heat input into the atmosphere over the 760 km wide swath of the TMI radiometer in the tropics.
    Keywords: Meteorology and Climatology
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    Global Precipitation during the 1997-98 El Nino and Initiation of the 1998-99 La Nina (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: The 1997-99 ENSO (El nino Southern Oscillation) cycle was very powerful, but also well observed. The best satellite rainfall estimates combined with gauge observations allow for a global analysis of precipitation anomalies accompanying the 1997-98 El Nino and initiation of the 1998-99 La Nina. For the period April 1997 to March 1998 the central to eastern Pacific, southeastern and western U.S., Argentina, eastern Africa, South China, eastern Russia, and North Atlantic were all more than two standard deviations wetter than normal. During the same year the Maritime Continent, eastern Indian Ocean, subtropical North Pacific, northeastern South America, and much of the mid- latitude southern oceans were more than two standard deviations drier than normal. An analysis of the evolution of the El Nino and accompanying precipitation anomalies revealed that a dry Maritime Continent led the formation of the El Nino SST (Sea Surface Temperature), while in the central Pacific, precipitation anomalies lagged the El Nino SST by a season. A rapid transition from El Nino to La Nina occurred in May 1998, but as early as October-November 1997 precipitation indices captured precursor changes in Pacific rainfall anomalies. Differences were found between observed and modeled [NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis] precipitation anomalies for 1997 and 98. In particular, the model had a bias towards positive precipitation anomalies and the magnitudes of the anomalies in the equatorial Pacific were small compared to the observations. Also, the evolution of the precipitation field, including the drying of the Maritime Continent and eastward progression of rainfall in the equatorial Pacific, was less pronounced for the model compared to the observations. One degree daily estimates of rainfall show clearly the MaddenJulian Oscillation and related westerly wind burst events over the Maritime Continent, which are key indicators for the onset of El Nino.
    Keywords: Meteorology and Climatology
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    TRMM Precipitation Radar Reflectivity Profiles Compared to High-Resolution Airborne and Ground-Based Radar Measurements (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: In this paper, TRMM (Tropical Rainfall Measuring Mission Satellite) Precipitation Radar (PR) products are evaluated by means of simultaneous comparisons with data from the high-altitude ER-2 Doppler Radar (EDOP), as well as ground-based radars. The comparison is aimed primarily at the vertical reflectivity structure, which is of key importance in TRMM rain type classification and latent heating estimation. The radars used in this study have considerably different viewing geometries and resolutions, demanding non-trivial mapping procedures in common earth-relative coordinates. Mapped vertical cross sections and mean profiles of reflectivity from the PR, EDOP, and ground-based radars are compared for six cases. These cases cover a stratiform frontal rainband, convective cells of various sizes and stages, and a hurricane. For precipitating systems that are large relative to the PR footprint size, PR reflectivity profiles compare very well to high-resolution measurements thresholded to the PR minimum reflectivity, and derived variables such as bright band height and rain types are accurate, even at high PR incidence angles. It was found that for, the PR reflectivity of convective cells small relative to the PR footprint is weaker than in reality. Some of these differences can be explained by non-uniform beam filling. For other cases where strong reflectivity gradients occur within a PR footprint, the reflectivity distribution is spread out due to filtering by the PR antenna illumination pattern. In these cases, rain type classification may err and be biased towards the stratiform type, and the average reflectivity tends to be underestimated. The limited sensitivity of the PR implies that the upper regions of precipitation systems remain undetected and that the PR storm top height estimate is unreliable, usually underestimating the actual storm top height. This applies to all cases but the discrepancy is larger for smaller cells where limited sensitivity is compounded by incomplete beam filling. Users of level three TRMM PR products should be aware of this scale dependency.
    Keywords: Meteorology and Climatology
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    Determination of Radiative Forcing of Saharan Dust using Combined TOMS and ERBE Data (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: The direct radiative forcing of Saharan dust aerosols has been determined by combining aerosol information derived from Nimbus-7 TOMS with radiation measurements observed at the top of atmosphere (TOA) by NOAA-9 ERBE made during February-July 1985. Cloud parameters and precipitable water derived from the NOAA-9 HIRS2 instrument were used to aid in screening for clouds and water vapor in the analyses. Our results indicate that under "cloud-free" and "dry" conditions there is a good correlation between the ERBE TOA outgoing longwave fluxes and the TOMS aerosol index measurements over both land and ocean in areas under the influence of airborne Saharan dust. The ERBE TOA outgoing shortwave fluxes were also found to correlate well with the dust loading derived from TOMS over ocean. However, the calculated shortwave forcing of Saharan dust aerosols is very weak and noisy over land for the range of solar zenith angle viewed by the NOAA-9 ERBE in 1985. Sensitivity factors of the TOA outgoing fluxes to changes in aerosol index were estimated using a linear regression fit to the ERBE and TOMS measurements. The ratio of the shortwave-to-longwave response to changes in dust loading over the ocean is found to be roughly 2 to 3, but opposite in sign. The monthly averaged "clear-sky" TOA direct forcing of airborne Saharan dust was also calculated by multiplying these sensitivity factors by the TOMS monthly averaged "clear-sky" aerosol index. Both the observational and theoretical analyses indicate that the dust layer height, ambient moisture content as well as the presence of cloud all play an important role in determining the TOA direct radiative forcing due to mineral aerosols.
    Keywords: Meteorology and Climatology
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    ASCA Observation of the Dipping X-Ray Source X1916-053 (1997)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: We present the results of timing and spectral studies of the dipping X-ray source X1916-053, observed by ASCA during its Performance Verification phase. The detected dipping activity is consistent with previous observations, with a period of 3008s and an intermittent secondary dip observed roughly 0.4 out of phase with the primary dip. The energy spectra of different intensity states are fitted with a power law with partial covering fraction absorption and interstellar absorption. The increase in the hardness ratio during the primary and secondary dips, and the increase in the covering fraction and column density with decreasing X-ray intensity, all imply that the dipping is caused by the photo-absorbing materials which have been suggested to be where the accreted flow hits the outer edge of the disk materials. The spectra at all intensity levels show no apparent evidence for Fe or Ne emission lines. This may be due to the low metal abundance in the accretion flow. Alternatively, the X-ray luminosity of the central source may be too weak to excite emission lines, which are assumed to be produced by X-ray photoionization of the disk materials.
    Keywords: Astronomy
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    Cold Reversal on Kodiak Island, Alaska, Correlated with the European Younger Dryas by Using Variations of Atmospheric C-14 Content (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: High-resolution AMS (accelerator-mass-spectrometer) radiocarbon dating was performed on late-glacial macrofossils in lake sediments from Kodiak Island, Alaska, and on shells in marine sediments from southwest Sweden. In both records, a dramatic drop in radiocarbon ages equivalent to a rise in the atmospheric C-14 by approximately 70%. coincides with the beginning of the cold period at 11000 yr B.P. (C-14 age). Thus our results show that a close correlation between climatic records around the globe is possible by using a global signature of changes in atmospheric C-14 content.
    Keywords: Meteorology and Climatology
    Type: Geology
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    Photometric Observations of 6000 Stars in the Cygnus Field (1999)
    In:  CASI
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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.
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    Effects of Precipitation on Ocean Mixed-Layer Temperature and Salinity as Simulated in a 2-D Coupled Ocean-Cloud Resolving Atmosphere Model (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: A two-dimensional coupled ocean-cloud resolving atmosphere model is used to investigate possible roles of convective scale ocean disturbances induced by atmospheric precipitation on ocean mixed-layer heat and salt budgets. The model couples a cloud resolving model with an embedded mixed layer-ocean circulation model. Five experiment are performed under imposed large-scale atmospheric forcing in terms of vertical velocity derived from the TOGA COARE observations during a selected seven-day period. The dominant variability of mixed-layer temperature and salinity are simulated by the coupled model with imposed large-scale forcing. The mixed-layer temperatures in the coupled experiments with 1-D and 2-D ocean models show similar variations when salinity effects are not included. When salinity effects are included, however, differences in the domain-mean mixed-layer salinity and temperature between coupled experiments with 1-D and 2-D ocean models could be as large as 0.3 PSU and 0.4 C respectively. Without fresh water effects, the nocturnal heat loss over ocean surface causes deep mixed layers and weak cooling rates so that the nocturnal mixed-layer temperatures tend to be horizontally-uniform. The fresh water flux, however, causes shallow mixed layers over convective areas while the nocturnal heat loss causes deep mixed layer over convection-free areas so that the mixed-layer temperatures have large horizontal fluctuations. Furthermore, fresh water flux exhibits larger spatial fluctuations than surface heat flux because heavy rainfall occurs over convective areas embedded in broad non-convective or clear areas, whereas diurnal signals over whole model areas yield high spatial correlation of surface heat flux. As a result, mixed-layer salinities contribute more to the density differences than do mixed-layer temperatures.
    Keywords: Meteorology and Climatology
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    Unstable Air-Sea Interaction in the Extratropical North Atlantic (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: The possibility of coupled modes in the extratropical North Atlantic has fascinated the climate community since 1960's. A significant aspect of such modes is an unstable air-sea interaction, also called positive feedback, where disturbances between the atmosphere and ocean grow unbound. If a delayed response exists before the negative feedback takes effect, an oscillatory behaviour will develop. Here we explore the relationship between heat flux (positive upward) and sea surface temperature (SST). Positive feedback is characterized by a cross-correlation between the two where correlation maintains a negative sign whether SST or heat flux leads. We use model results and observations to argue that in the North Atlantic there exist regions with positive feedback. The two main locations coincide with the well-known north-south SST dipole where anomalies of opposite sign occupy areas east of Florida and north-east of Newfoundland. We show that oceanic dynamics, wave propagation and advection, give rise to oceanic anomalies in these regions. Subsequently these anomalies are amplified by atmosphere- ocean interaction: thus a positive feedback.
    Keywords: Meteorology and Climatology
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  • 90
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    Wind Speed Measurement from Bistatically Scattered GPS Signals (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: Instrumentation and retrieval algorithms are described which use the forward, or bistatically scattered range-coded signals from the Global Positioning System (GPS) radio navigation system for the measurement of sea surface roughness. This roughness is known to be related directly to the surface wind speed. Experiments were conducted from aircraft along the TOPEX ground track, and over experimental surface truth buoys. These flights used a receiver capable of recording the cross correlation power in the reflected signal. The shape of this power distribution was then compared against analytical models derived from geometric optics. Two techniques for matching these functions were studied. The first recognized the most significant information content in the reflected signal is contained in the trailing edge slope of the waveform. The second attempted to match the complete shape of the waveform by approximating it as a series expansion and obtaining the nonlinear least squares estimate. Discussion is also presented on anomalies in the receiver operation and their identification and correction.
    Keywords: Meteorology and Climatology
    Type: IEEE Transactions on Geoscience and Remote Sensing; Volume 20; No. Y; 100-130
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  • 91
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    A Study of the December 1992 Westerly Wind Burst Event during TOGA COARE (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: Using the Penn State/NCAR MM5 mesoscale model, a westerly wind burst (WWB) that occurred during the period from 19 to 30 December 1992 over the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) has been simulated and compared with observation. This event is characterized by the presence of super cloud clusters and the occurrence of a major WWB that extended over the western and central Pacific Ocean. Although several of the observed convective systems were not precisely simulated by MM5, the model did capture many other observed characteristics, such as the explosive development of convection, the cyclonic circulation and the WWB. The WWB resulted from the coalescence of three types of tropical disturbances. The first type was a low-level westerly jet (LWJ) that developed at the equator and may be associated with the eastward propagation of an ISO (Intraseasonal Oscillation). The second type featured an easterly wave-like disturbance that originated in the south central Pacific Ocean and propagated westward. Finally, the third type involved a cross-equatorial flow that deflected Northern Hemispheric easterlies into the Southern Hemisphere and may be caused by inertial instability. These disturbances worked in concert, resulting in intense convection over the TOGA COARE region. Once intense convection developed, a large-scale circulation was produced over the western Pacific warm pool, propagated eastward, and initiated a WWB.
    Keywords: Meteorology and Climatology
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  • 92
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    Seasonal and Interannual Variations of Evaporation and their Relations with Precipitation, Net Radiation, and Net Carbon Accumulation for the Gediz Basin Area (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: A model combining the rate of carbon assimilation with water and energy balance equations has been run using satellite and ancillary data for a period of 60 months (January 1986 to December 1990). Calculations for the Gediz basin area give mean annual evaporation as 395 mm, which is composed of 45% transpiration, 42% soil evaporation and 13% interception. The coefficient of interannual variation of evaporation is found to be 6%, while that for precipitation and net radiation are, respectively, 16% and 2%, illustrating that net radiation has an important effect in modulating interannual variation of evaporation. The mean annual water use efficiency (i.e., the ratio of net carbon accumulation and total evaporation) is ca. 1 g/sq m/mm, and has a coefficient of interannual variation of 5%. A comparison of the mean water use efficiency with field observations suggests that evaporation over the area is utilized well for biomass production. The reference crop evaporation for irrigated areas has annual mean and coefficient of variation as, respectively, 1176 mm and 3%. The total evaporation during three summer months of peak evaporation (June-August) is estimated to be about 575 mm for irrigated crops like maize and cotton. Seasonal variations of the fluxes are presented.
    Keywords: Meteorology and Climatology
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  • 93
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    Raman LIDAR Detection of Cloud Base (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: Advantages introduced by Raman lidar systems for cloud base determination during precipitating periods are explored using two case studies of light rain and virga conditions. A combination of the Raman lidar derived profiles of water vapor mixing ratio and aerosol scattering ratio, together with the Raman scattered signals from liquid drops, can minimize or even eliminate some of the problems associated with cloud boundary detection using elastic backscatter lidars.
    Keywords: Meteorology and Climatology
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  • 94
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    Variance and Predictability of Precipitation at Seasonal-to-Interannual Timescales (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: A series of atmospheric general circulation model (AGCM) simulations, spanning a total of several thousand years, is used to assess the impact of land-surface and ocean boundary conditions on the seasonal-to-interannual variability and predictability of precipitation in a coupled modeling system. In the first half of the analysis, which focuses on precipitation variance, we show that the contributions of ocean, atmosphere, and land processes to this variance can be characterized, to first order, with a simple linear model. This allows a clean separation of the contributions, from which we find: (1) land and ocean processes have essentially different domains of influence, i.e., the amplification of precipitation variance by land-atmosphere feedback is most important outside of the regions (mainly in the tropics) that are most affected by sea surface temperatures; and (2) the strength of land-atmosphere feedback in a given region is largely controlled by the relative availability of energy and water there. In the second half of the analysis, the potential for seasonal-to-interannual predictability of precipitation is quantified under the assumption that all relevant surface boundary conditions (in the ocean and on land) are known perfectly into the future. We find that the chaotic nature of the atmospheric circulation imposes fundamental limits on predictability in many extratropical regions. Associated with this result is an indication that soil moisture initialization or assimilation in a seasonal-to-interannual forecasting system would be beneficial mainly in transition zones between dry and humid regions.
    Keywords: Meteorology and Climatology
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  • 95
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    Interaction Between Tropical Convection and its Embedding Environment: An Energetics Analysis of a 2-D Cloud Resolving Simulation (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: The phase relation between the perturbation kinetic energy (K') associated with the tropical convection and the horizontal-mean moist available potential energy (bar-P) associated with environmental conditions is investigated by an energetics analysis of a numerical experiment. This experiment is performed using a 2-D cloud resolving model forced by the TOGA-COARE derived vertical velocity. The imposed upward motion leads to a decrease of bar-P directly through the associated vertical advective cooling, and to an increase of K' directly through cloud related processes, feeding the convection. The maximum K' and its maximum growth rate lags and leads, respectively, the maximum imposed large-scale upward motion by about 1-2 hours, indicating that convection is phase locked with large-scale forcing. The dominant life cycle of the simulated convection is about 9 hours, whereas the time scales of the imposed large-scale forcing are longer than the diurnal cycle. In the convective events, maximum growth of K' leads maximum decay of the perturbation moist available potential energy (P') by about 3 hours through vertical heat transport by perturbation circulation, and perturbation cloud heating. Maximum decay of P' leads maximum decay of bar-P by about one hour through the perturbation radiative, processes, the horizontal-mean cloud heating, and the large-scale vertical advective cooling. Therefore, maximum gain of K' occurs about 4-5 hours before maximum decay of bar-P.
    Keywords: Meteorology and Climatology
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  • 96
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    Tropical Rainfall Distributions Determined Using TRMM Combined with other Satellite and Raingauge Information (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: Abstract A technique is described to use Tropical Rain Measuring Mission (TRMM) combined radar/radiometer information to adjust geosynchronous infrared satellite data (the TRMM Adjusted GOES Precipitation Index, or TRMM AGPI). The AGPI is then merged with rain gauge information (mostly over land; the TRMM merged product) to provide fine- scale (1 deg latitude/longitude) pentad and monthly analyses, respectively. The TRMM merged estimates are 10% higher than those from the Global Precipitation Climatology Project (GPCP) when integrated over the tropical oceans (37 deg N-S) for 1998, with 20% differences noted in the most heavily raining areas. In the dry subtropics the TRMM values are smaller than the GPCP estimates. The TRMM merged-product tropical-mean estimates for 1998 are 3.3 mm/ day over ocean and 3.1 mm/ day over land and ocean combined. Regional differences are noted between the western and eastern Pacific Ocean maxima when TRMM and GPCP are compared. In the eastern Pacific rain maximum the TRMM and GPCP mean values are nearly equal, very different from the other tropical rainy areas where TRMM merged-product estimates are higher. This regional difference may indicate that TRMM is better at taking in to account the vertical structure of the rain systems and the difference in structure between the western and eastern (shallower) Pacific convection. Comparisons of these TRMM merged analysis estimates with surface data sets shows varied results; the bias is near zero when compared to western Pacific Ocean atoll raingauge data, but significantly positive compared to Kwajalein radar estimates (adjusted by rain gauges). Over land the TRMM estimates also show a significant positive bias. The inclusion of gauge information in the final merged product significantly reduces the bias over land, as expected. The monthly precipitation patterns produced by the TRMM merged data process clearly show the evolution of the ENSO tropical precipitation pattern from early 1998 (El Nino) through early 1999 (La Nina) and beyond. The El Nino minus La Nina difference map shows the eastern Pacific maximum, the maritime continent minima and other tropical and mid-latitude features. The differences in the Pacific are very similar to those detected by the GPCP analyses. However, summing the El Nino minus La Nina differences over the global tropical oceans yields divergent answers from TRMM, GPCP and other estimates. This emphasizes the need for additional validation and analysis before it is feasible to understand the relations between global precipitation anomalies and Pacific Ocean ENSO temperature changes.
    Keywords: Meteorology and Climatology
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    Sensitivity of High-Resolution Simulations of Hurricane Bob (1991) to Planetary Boundary Layer Parameterizations (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: The MM5 mesoscale model is used to simulate Hurricane Bob (1991) using grids nested to high resolution (4 km). Tests are conducted to determine the sensitivity of the simulation to the available planetary boundary layer parameterizations, including the bulk-aerodynamic, Blackadar, Medium-RanGe Forecast (MRF) model, and Burk-Thompson boundary-layer schemes. Significant sensitivity is seen, with minimum central pressures varying by up to 17 mb. The Burk-Thompson and bulk-aerodynamic boundary-layer schemes produced the strongest storms while the MRF scheme produced the weakest storm. Precipitation structure of the simulated hurricanes also varied substantially with the boundary layer parameterizations. Diagnostics of boundary-layer variables indicated that the intensity of the simulated hurricanes generally increased as the ratio of the surface exchange coefficients for heat and momentum, C(sub h)/C(sub M), although the manner in which the vertical mixing takes place was also important. Findings specific to the boundary-layer schemes include: 1) the MRF scheme produces mixing that is too deep and causes drying of the lower boundary layer in the inner-core region of the hurricane; 2) the bulk-aerodynamic scheme produces mixing that is probably too shallow, but results in a strong hurricane because of a large value of C(sub h)/C(sub M) (approximately 1.3); 3) the MRF and Blackadar schemes are weak partly because of smaller surface moisture fluxes that result in a reduced value of C(sub h)/C(sub M) (approximately 0.7); 4) the Burk-Thompson scheme produces a strong storm with C(sub h)/C(sub M) approximately 1; and 5) the formulation of the wind-speed dependence of the surface roughness parameter, z(sub 0), is important for getting appropriate values of the surface exchange coefficients in hurricanes based upon current estimates of these parameters.
    Keywords: Meteorology and Climatology
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  • 98
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    Data Assimilation in the Presence of Forecast Bias: The GEOS Moisture Analysis (1999)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: We describe the application of the unbiased sequential analysis algorithm developed by Dee and da Silva (1998) to the GEOS DAS moisture analysis. The algorithm estimates the persistent component of model error using rawinsonde observations and adjusts the first-guess moisture field accordingly. Results of two seasonal data assimilation cycles show that moisture analysis bias is almost completely eliminated in all observed regions. The improved analyses cause a sizable reduction in the 6h-forecast bias and a marginal improvement in the error standard deviations.
    Keywords: Meteorology and Climatology
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  • 99
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    A Highly Doppler Blueshifted Fe-K Emission Line in the High-Redshift QSO PKS 2149-306 (1999)
    In:  CASI
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    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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  • 100
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    ALDF Data Retrieval Algorithms for Validating the Optical Transient Detector (OTD) and the Lightning Imaging Sensor (LIS) (1997)
    In:  CASI
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    Publication Date: 2013-08-29
    Description: A linear algebraic solution is provided for the problem of retrieving the location and time of occurrence of lightning ground strikes from in Advanced Lightning Direction Finder (ALDF) network. The ALDF network measures field strength, magnetic bearing, and arrival time of lightning radio emissions and solutions for the plane (i.e.. no Earth curvature) are provided that implement all of these measurements. The accuracy of the retrieval method is tested using computer-simulated data sets and the relative influence of bearing and arrival time data on the outcome of the final solution is formally demonstrated. The algorithm is sufficiently accurate to validate NASA's Optical Transient Detector (OTD) and Lightning Imaging System (LIS). We also introduce a quadratic planar solution that is useful when only three arrival time measurements are available. The algebra of the quadratic root results are examined in detail to clarify what portions of the analysis region lead to fundamental ambiguities in source location. Complex root results are shown to be associated with the presence of measurement errors when the lightning source lies near an outer sensor baseline of the ALDF network. For arbitrary noncollinear network geometries and in the absence of measurement errors, it is shown that the two quadratic roots are equivalent (no source location ambiguity) on the outer sensor baselines. The accuracy of the quadratic planar method is tested with computer-generated data sets and the results are generally better than those obtained from the three station linear planar method when bearing errors are about 2 degrees.
    Keywords: Meteorology and Climatology
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