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  • 1
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    The Role of the Interface in Refractory Metal Alloy Composites (1991)
    In:  Other Sources
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    Publication Date: 2011-10-04
    Description: Creep-rupture and tensile tests have been used to evaluate thoriated W-wire reinforced Nb-1 percent Zr alloy matrix composites fabricated via arc-spray monotape technique. A significant creep strength enhancement was observed over the unreinforced matrix alloy while matrix integrity was maintained; the fiber/matrix interface phase is noted to be a strong and ductile W/Nb alloy, which is formed due to the mutual solubility of the constituent metals. High strength, toughness, and thermal stability are demonstrated by this material system, which is also resistant to liquid alkali metal corrosion.
    Keywords: COMPOSITE MATERIALS
    Type: In: Space nuclear power systems; Proceedings of the 8th Symposium, Albuquerque, NM, Jan. 6-10, 1991. Pt. 1 (A93-13751 03-20); p. 186-192.
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  • 2
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    Mechanics of interfaces in fiber reinforced SiC/RBSN ceramic matrix composites (1991)
    In:  Other Sources
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    Publication Date: 2011-12-09
    Description: The mechanical behavior of continuous fiber reinforced SiC/RBSN composites with strong and weak interface characteristics is evaluated. Both catastrophic and noncatastrophic failures are observed in tensile specimens. Effects of fiber/matrix interface debonding (splitting) parallel to the fibers are discussed. Micromechanical models incorporating residual stresses to calculate the critical matrix cracking strength, ultimate strength and work of pull-out are reviewed and used to predict composite response. Experimental results are compared to analytical predictions.
    Keywords: COMPOSITE MATERIALS
    Type: In: Mechanics of composites at elevated and cryogenic temperatures; Proceedings of the Symposium, ASME Applied Mechanics Conference, Columbus, OH, June 16-19, 1991 (A93-32451 12-39); p. 217-229.
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  • 3
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    Reaction of beta-phase Ni-Al alloys with CrB2 (1991)
    In:  Other Sources
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    Publication Date: 2011-12-09
    Description: Reaction of Ni-Al alloys within the beta-NiAl phase with CrB2 was studied at 1473 K as a function of Al concentration in the alloy. Reaction of 49-50 at. pct Al alloys with CrB2 occurred by interdiffusion of Ni into CrB2 and Cr into the alloy without forming a new product phase. On the other hand, a new product phase, rich in Ni and B, formed by the reaction of alloys having Al concentrations 48 at. pct or lower with CrB2. The reaction product was observed both at the CrB2/alloy interface and along the alloy grain boundaries.
    Keywords: COMPOSITE MATERIALS
    Type: Journal of Materials Research (ISSN 0884-2914); 6; 1664-167
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  • 4
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    Estimation of raindrop size distribution parameters from a dual-parameter spaceborne radar measurement (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A method to estimate raindrop size distribution (DSD) parameters from a combined Zm profile and path-integrated attenuation is shown, and a test result of the method using the data from an aircraft experiment is presented. The 'semi' dual-parameter (SDP) measurement is employed to estimate DSD parameters using the data obtained from an aircraft experiment conducted by Communications Research Laboratory, Tokyo, in conjunction with NASA. The validity of estimated DSD parameters is examined using measured Ka-band radar reflectivities. The estimated path-averaged N(0) is consistent with the Ka/X Ze ratio, and the use of estimated DSD shows excellent agreement between the rain rates estimated from the X-band and K-band Zes. The feasibility of estimating DSD parameters from space is confirmed.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: In: International Conference on Radar Meteorology, 25th, Paris, France, June 24-28, 1991, Preprints (A93-37626 15-47); p. 384-387.
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  • 5
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    A potential method for the estimation of drop size distribution from a dual-wavelength airborne radar (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: In order to investigate the role of the drop size distribution (DSD) from a dual-wavelength airborne radar and to recover profiled rain rates, a procedure is described for the purpose of estimating the DSD. The method differs from previous approaches in that it provides 2n + 1 parameters of the profiled DSD (where n is the number of range gates) and it uses a recursive procedure beginning at the range gate near the surface progressing backwards toward the storm top. The method is argued to be useful both as a diagnostic tool and as a means by which more detailed information on the vertical structure of the precipitation can be obtained.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: In: International Conference on Radar Meteorology, 25th, Paris, France, June 24-28, 1991, Preprints (A93-37626 15-47); p. 380-383.
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  • 6
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    Meteorological radar methods for validating space observations of precipitation (1991)
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    Publication Date: 2011-08-24
    Description: Meteorological approaches to verification of space measurements of rainfall are examined; validation of Tropical Rainfall Measuring Mission (TRMM) observations is expected to depend significantly on ground-based radars. Two methods of comparison are initially contemplated. TRMM rainfall data over time periods of a month for large areas (500 x 500 km) are averaged and compared with similarly averaged ground truth measurements. Both the rainfall and height distribution data from TRMM are compared with the instantaneous values observed at one or more 'ground truth' stations and from airborne radar and radiometers as available.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: In: International Conference on Radar Meteorology, 25th, Paris, France, June 24-28, 1991, Preprints (A93-37626 15-47); p. 374-379.
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  • 7
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    Transverse ductility of metal matrix composites (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The role of the fiber matrix interface bond on the transverse ductility of continuous fiber reinforced composites has been investigated. Two specific systems have been considered: an Aluminum alloy matrix reinforced by Alumina fibers, characterized by a strong interface and a Titanium alloy reinforced by coated Silicon Carbide fibers, characterized by a weak interface. A micro-mechanical study indicates that the bond condition has a significant effect on the state of stress in the matrix which in turn dictates the available matrix ductility. The micro-mechanical predictions are in good agreement with the experimental results for the two systems.
    Keywords: COMPOSITE MATERIALS
    Type: In: Failure mechanisms in high temperature composite materials; Proceedings of the Symposium, 112th ASME Winter Annual Meeting, Atlanta, GA, Dec. 1-6, 1991 (A93-31351 11-24); p. 23-30.
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  • 8
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    Comparison of numerically-simulated microphysical characteristics of convective storms with multiparameter radar observations during COHMEX (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The microphysical/dynamical nature and evolution of numerically simulated convective storms observed on July 11, 1986 during the Cooperative Huntsville Meteorological Experiments are investigated with the Goddard Cumulus Ensemble model. The model-simulated hydrometeor and radar reflectivity structure is verified with results derived from the multiparameter radar observations, which includes a description of the reflectivity, differential reflectivity, linear depolarization ratio, and hail signal for two thunderstorm cases analyzed by Fulton and Heymsfield (1990). Radar analysis shows the storm to split with the newer more vigorous cell in the SE quadrant. Echo tops are near 15 km while peak reflectivities exceed 50 dBZ. Preliminary model simulations likewise show a splitting storm with regeneration occurring on the SSE flank. Echo tops are around 14 km with peak reflectivities over 45 dBZ.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: In: International Conference on Radar Meteorology, 25th, Paris, France, June 24-28, 1991, Preprints (A93-37626 15-47); p. 706, 707.
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  • 9
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    Radar and microphysical characteristics of convective storms simulated from a numerical model using a new microphysical parameterization (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The basic features of a new and improved bulk-microphysical parameterization capable of simulating the hydrometeor structure of convective systems in all types of large-scale environments (with minimal adjustment of coefficients) are studied. Reflectivities simulated from the model are compared with radar observations of an intense midlatitude convective system. Simulated reflectivities using the novel four-class ice scheme with a microphysical parameterization rain distribution at 105 min are illustrated. Preliminary results indicate that this new ice scheme works efficiently in simulating midlatitude continental storms.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: In: International Conference on Radar Meteorology, 25th, Paris, France, June 24-28, 1991, Preprints (A93-37626 15-47); p. 782-785.
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  • 10
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    Atmospheric weather regimes over tropical South America (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Infrared radiance measurements by the GOES-6 satellite during April 1986 through April 1987 were used to characterize and identify distinct regimes of persistent large-scale cloudiness patterns over the Amazon Basin. It is suggested that the energetics of the tropical troposphere over the Amazon Basin can be directly related to the GOES large-scale cloudiness patterns. The geometry and persistence of the cloud patterns are influenced by shifts in general circulation features and are likely modulated by 4- to 5-day and 40- to 60-day waves. Diurnal forcing effects are more pronounced during weather regimes characterized by prominently clear skies over land areas.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: ; : Strong shock waves
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  • 11
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    Probabilistic micromechanics and macromechanics of polymer matrix composites (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A probabilistic evaluation of an eight ply graphite-epoxy quasi-isotropic laminate was completed using the Integrated Composite Analyzer (ICAN) in conjunction with Monte Carlo simulation and Fast Probability Integration (FPI) techniques. Probabilistic input included fiber and matrix properties, fiber misalignment, fiber volume ratio, void volume ratio, ply thickness and ply layup angle. Cumulative distribution functions (CDFs) for select laminate properties are given. To reduce the number of simulations, a Fast Probability Integration (FPI) technique was used to generate CDFs for the select properties in the absence of fiber misalignment. These CDFs were compared to a second Monte Carlo simulation done without fiber misalignment effects. It was found that FPI requires fewer simulations to obtain the cumulative distribution functions as opposed to Monte Carlo simulation techniques. Furthermore, FPI provides valuable information regarding the sensitivities of composite properties to the constituent properties, fiber volume ratio and void volume ratio.
    Keywords: COMPOSITE MATERIALS
    Type: In: Composite material technology - 1991; Proceedings of the Symposium, 14th Annual Energy-sources Technology Conference and Exhibition, Houston, TX, Jan. 20-23, 1991 (A93-54676 24-24); p. 285-291.
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  • 12
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    Space Shuttle Orbiter carbon-carbon oxidation performance (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Reusable, oxidation protected reinforced carbon carbon (RCC) has been successfully flown on forty Shuttle Orbiter flights. Thermal testing of the silicon carbide coated, reinforced carbon-carbon to determine its oxidation characteristics has been performed in both radiant and convective (plasma arc jet) heating test facilities. Subsurface oxidation of the RCC substrate as a result of oxygen penetrating micro cracks (fizzures) in the coating was characterized as a function of temperature and pressure for both convective and radiant environments. High temperature testing was performed to establish coating recession for over-temperature flight conditions experienced on abort trajectories. Suggested methods for using these test data to establish multi-mission reuse (i.e., mission life) and single mission limits are presented.
    Keywords: COMPOSITE MATERIALS
    Type: In: Damage and oxidation protection in high temperature composites. Vol. 1; Proceedings of the Symposium, 112th ASME Winter Annual Meeting, Atlanta, GA, Dec. 1-6, 1991 (A93-53937 23-24); p. 47-64.
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  • 13
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    Effects of aeroconvective environments on 2D reinforced ceramic matrix composites (1991)
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    Publication Date: 2011-08-24
    Description: The effect of aeroconvective heating environment similar to that observed a spacecraft ascent or reentry from orbit, on the performance of a commercial carbon-reinforced ceramic matrix material specimens of two configurations (orthotropic and quasi-isotropic), fabricated by the Societe Europenne Propulsion (SEP) process was investigated using the NASA Ames Research Center 20 Megawatt Panel Test facility. The performance of the commercial material was compared with the SEP prepared materials. It was found that, whereas the quasi-isotropic SEP specimens exhibited a much higher mass loss rate and a significant dimensional change upon exposure to the thermal environment than did the orthotropic ones, the commercial SEP-like materials did not exhibit these characteristics. There was no greater mass loss rate for the quasi-isotropic specimens, and no dimension changes were observed. The Nicalon reinforced materials in both configurations, as fabricated by SEP or by the commercial source, showed no mass changes and no dimensional changes.
    Keywords: COMPOSITE MATERIALS
    Type: In: Damage and oxidation protection in high temperature composites. Vol. 1; Proceedings of the Symposium, 112th ASME Winter Annual Meeting, Atlanta, GA, Dec. 1-6, 1991 (A93-53937 23-24); p. 35-45.
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  • 14
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    Fatigue of continuous fiber reinforced titanium matrix composites (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Several lay-ups of SCS-6/Ti-15-3 composites were investigated. Static and fatigue tests were conducted for both notched and unnotched specimens at room and elevated temperatures. Test results indicated that the stress in the 0 fibers is the controlling factor in fatigue life. The static and fatigue strength of these materials is shown to be dependent on the level of residual stresses and the fiber/ matrix interfacial strength. Fatigue tests of notched specimens showed that cracks can initiate and grow many fiber spacings in the matrix material without breaking fibers. These matrix cracks can significantly reduce the residual strength of notched composite.
    Keywords: COMPOSITE MATERIALS
    Type: In: Fatigue of advanced materials; Proceedings of the Engineering Foundation International Conference, Santa Barbara, CA, Jan. 13-18, 1991 (A93-38276 15-23); p. 357-377.
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  • 15
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    Multi-parameter airborne rain radar experiment in the western Pacific (1991)
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    Publication Date: 2011-08-24
    Description: The study presents preliminary results from an airborne radar/radiometer experiment (Typhoon Experiment) which was conducted in the western Pacific Ocean during September 1990, with emphasis on the multiparameter radar results. One of the objectives of this experiment is to make radar/radiometer measurements over rain to support the algorithm development and science studies for the Tropical Rainfall Measuring Mission (TRMM) and the spaceborne weather sensors. The extremely high linear depolarization ratio value observed at the melting height is considered to be procured by the melting particle with large eccentricity. It is shown that the multiparameter airborne radar provides valuable information by distinguishing the hydrometeor particles of the rainfall.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: In: International Conference on Radar Meteorology, 25th, Paris, France, June 24-28, 1991, Preprints (A93-37626 15-47); p. 400-403.
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  • 16
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    Ductility of a continuous fiber reinforced aluminum matrix composite (1991)
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    Publication Date: 2011-08-24
    Description: The transverse properties of an aluminum alloy metal matrix composite reinforced by continuous alumina fibers have been investigated. The composite is subjected to both mechanical and cyclic thermal loading. The ductility can vary by an order of magnitude according to the operating conditions. For high mechanical and low thermal loading the ductility is small, for low mechanical and high thermal loading the ductility is an order of magnitude higher. Experiments on a beam in bending confirm that the ductility is strongly dependent on the loading conditions. The observations suggest a means of utilizing the inherent ductility of the matrix.
    Keywords: COMPOSITE MATERIALS
    Type: In: Mechanics of composites at elevated and cryogenic temperatures; Proceedings of the Symposium, ASME Applied Mechanics Conference, Columbus, OH, June 16-19, 1991 (A93-32451 12-39); p. 267-275.
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  • 17
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    Computational characterization of high temperature composites via METCAN (1991)
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    Publication Date: 2011-08-24
    Description: The computer code 'METCAN' (METal matrix Composite ANalyzer) developed at NASA Lewis Research Center can be used to predict the high temperature behavior of metal matrix composites using the room temperature constituent properties. A reference manual that characterizes some common composites is being developed from METCAN generated data. Typical plots found in the manual are shown for graphite/copper. These include plots of stress-strain, elastic and shear moduli, Poisson's ratio, thermal expansion, and thermal conductivity. This manual can be used in the preliminary design of structures and as a guideline for the behavior of other composite systems.
    Keywords: COMPOSITE MATERIALS
    Type: In: Mechanics of composites at elevated and cryogenic temperatures; Proceedings of the Symposium, ASME Applied Mechanics Conference, Columbus, OH, June 16-19, 1991 (A93-32451 12-39); p. 133-143.
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  • 18
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    Observations of fatigue crack initiation and damage growth in notched titanium matrix composites (1991)
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    Publication Date: 2011-08-24
    Description: The purpose was to characterize damage initiation and growth in notched titanium matrix composites at room temperature. Double edge notched or center open hole SCS-6/Ti-15-3 specimens containing 0 deg plies or containing both 0 and 90 deg plies were fatigued. The specimens were tested in the as-fabricated (ASF) and in heat-treated conditions. A local strain criterion using unnotched specimen fatigue data was successful in predicting fatigue damage initiation. The initiation stress level was accurately predicted for both a double edge notched unidirectional specimen and a cross-plied center hole specimen. The fatigue produced long multiple cracks growing from the notches. These fatigue cracks were only in the matrix material and did not break the fibers in their path. The combination of matrix cracking and fiber/matrix debonding appears to greatly reduce the stress concentration around the notches. The laminates that were heat treated showed a different crack growth pattern. In the ASF specimens, matrix cracks had a more tortuous path and showed considerable more crack branching. For the same specimen geometry and cyclic stress, the (0/90/0) laminate with a hole had far superior fatigue resistance than the matrix only specimen with a hole.
    Keywords: COMPOSITE MATERIALS
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  • 19
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    Relevance of impacter shape to nonvisible damage and residual tensile strength of a thick graphite/epoxy laminate (1991)
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    Publication Date: 2011-08-24
    Description: A study was made to determine the relevance of impacter shape to nonvisible damage and tensile residual strength of a 36 mm thick graphite/epoxy motor case. The shapes of the impacters were as follows: 12.7 mm and 25.4 mm diameter hemispheres, a sharp corner, and a 6.3 mm diameter bolt-like rod. The investigation revealed that damage initiated when the contact pressure exceeded a critical level. However, the damage was not visible on the surface until an even higher pressure was exceeded. The impact energy to initiate damage or cause visible damage on the surface increased approximately with impacter diameter to the third power. The reduction in strength for nonvisible damage increased with increasing diameter, 9 and 30 percent for the 12.7 mm and 25.4 mm diameter hemispheres, respectively. The corner impacter made visible damage on the surface for even the smallest impact energy. The rod impacter acted like a punch and sliced through the composite. Even so, the critical level of pressure to initiate damage was the same for the rod and hemispherical impacters. Factors of safety for nonvisible damage increased with increasing kinetic energy of impact. The effects of impacter shape on impact force, damage size, damage visibility, and residual tensile strength were predicted quite well assuming Hertzian contact and using maximum stress criteria and a surface crack analysis.
    Keywords: COMPOSITE MATERIALS
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  • 20
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    Fatigue crack growth in a unidirectional SCS-6/Ti-15-3 composite (1991)
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    Publication Date: 2011-08-24
    Description: An investigation was conducted to characterize and model the fatigue crack growth (FCG) behavior of an SCS-6/Ti-15-3 metal matrix composite. Part of the study was conducted using a fatigue loading stage mounted inside a scanning electron microscope (SEM). The results of the study reveal that the fatigue crack growth behavior of the composite is a function of specimen geometry, fiber orientation, and interaction of local stress fields with the highly anisotropic composite. In the case of (0)8 oriented single edge notch specimens and (90)8 oriented compact tension (CT) specimens, the crack growth was normal to the loading direction. However, for the (0)8 CT specimens, the crack grew mostly parallel to the loading and the fiber direction. The unusual fatigue behavior of the (0)8 CT specimens is attributed to the specimen geometry and the associated high tensile bending stresses perpendicular to the fiber direction.
    Keywords: COMPOSITE MATERIALS
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  • 21
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    Global climate change (1991)
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    Publication Date: 2011-08-24
    Description: Present processes of global climate change are reviewed. The processes determining global temperature are briefly described and the concept of effective temperature is elucidated. The greenhouse effect is examined, including the sources and sinks of greenhouse gases.
    Keywords: METEOROLOGY AND CLIMATOLOGY
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  • 22
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    1200 and 1300 K slow plastic compression properties of Ni-50Al composites (1991)
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    Publication Date: 2011-08-24
    Description: XD synthesis, powder blending, and hot pressing techniques have been utilized to produce NiAl composites containing 4, 7.5, 15, and 25 vol pct alumina whiskers and hybrid composite materials with 15 vol pct Al2O3 + 10 or 20 vol pct, nominally 1 micron TiB2 particles. The resistance to slow plastic flow was determined at 1200 and 1300 K via compression testing in air under constant velocity conditions. The stress-strain behavior of the intermetallic composites depended on the fraction of second phases where the 4 and 7.5 percent Al2O3 materials flowed at a nominally constant stress after about 2 percent deformation, while all the other composites exhibited diffuse yielding followed by strain softening. The flow stress-strain rate properties increased with volume fraction of Al2O3 whiskers except for the 4 and 7.5 percent materials, which had similar strengths. The hybrid composite NiAl + 15Al2O3 + 10TiB2 was substantially stronger than the materials simply containing alumina. Deformation in these composites can be described by the Kelly and Street model of creep in perfectly bonded, rigid, discontinuous fiber materials.
    Keywords: COMPOSITE MATERIALS
    Type: Materials at High Temperatures (ISSN 0960-3409); 9; 1, 19
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  • 23
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    GLOBE backscatter - Climatologies and mission results (1991)
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    Publication Date: 2011-08-24
    Description: The Global Backscatter Experiment (GLOBE) goals require intensive study of the global climatology of atmospheric aerosol backscatter at IR wavelengths. Airborne and ground-based lidars have been developed to measure atmospheric backscatter profiles at CO2 laser wavelengths. Descriptions of the calibration techniques and selected measurement results are presented.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: In: Laser radar VI; Proceedings of the Meeting, Los Angeles, CA, Jan. 23-25, 1991 (A93-17851 05-36); p. 139-146.
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  • 24
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    Effect of a finite outer scale on the Zernike decomposition of atmospheric optical turbulence (1991)
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    Publication Date: 2011-08-24
    Description: Phase distortions in optical systems induced by atmospheric turbulence are investigated with the use of Zernike polynominal decompositions. An analytic solution for the variances of the Zernike coefficients is found for the case of Kolmogorov turbulence with a finite outer-scale length. It is shown that the effect of finite outer scale is to attenuate low-order Zernike components, even when the outer-scale length is much larger than the optical aperture. Effects are investigated for constant outer-scale size and for height-dependent outer scales. It is found that seeing effects on large telescopes are dependent more on the magnitude of the outer scale than on the shape of the outer-scale vertical profile.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Optical Society of America, Journal, A: Optics and Image Science (ISSN 0740-3232); 8; 1568-157
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  • 25
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    Space-based surface wind vectors to aid understanding of air-sea interactions (1991)
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    Publication Date: 2011-08-24
    Description: A novel and unique ocean-surface wind data-set has been derived by combining the Defense Meteorological Satellite Program Special Sensor Microwave Imager data with additional conventional data. The variational analysis used generates a gridded surface wind analysis that minimizes an objective function measuring the misfit of the analysis to the background, the data, and certain a priori constraints. In the present case, the European Center for Medium-Range Weather Forecasts surface-wind analysis is used as the background.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: EOS (ISSN 0096-3941); 72; 201
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  • 26
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    On the wave forcing of the semi-annual zonal wind oscillation (1991)
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    Publication Date: 2011-08-24
    Description: Observational evidence of rather large period waves (23-60 d) in the troposphere/stratosphere, particularly during the winter months, is presented. Wind data collected on a regular basis employing high-altitude balloons and meteorological rockets over the past few years are used. Maximum entropy methods applied to the time series of zonal wind data indicate the presence of 23-60-waves more prominently than shorter-period waves. The waves have substantial amplitudes in the stratosphere and lower mesosphere, often larger than those noted in the troposphere. The mean zonal wind in the troposphere (5-15 km altitude) during December, January, and February exhibits the presence of strong westerlies at latitudes between 8 and 21 deg N.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Atmospheric and Terrestrial Physics (ISSN 0021-9169); 53; 1181-119
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    A nested grid, nonhydrostatic, elastic model using a terrain-following coordinate transformation - The radiative-nesting boundary conditions (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: This study presents a nested-grid nonhydrostatic and elastic model using a terrain-following coordinate transformation as well as a unique application of grid-nesting techniques to the time-splitting elastic model. A simulation of the 10-m-high Witch of Agnesi Mountain provides the control to test this new model. The results show that the model produces the same solution as that derived from a simple linear analytic model. It is demonstrated that the new nested-grid model improves model resolution without resorting to the costly method of placing a fine-resolution grid over the entire domain. Since the wave reflection from the boundaries of the fine-grid model is well controlled, the boundary of the nested fine-grid model can be located even at the wave-active region. The model can be used to simulate various weather systems in which scale interactions are important.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 119; 2852-286
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    A Great Salt Lake waterspout (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Results are presented of observations of a waterspout funnel and spray ring performed under a cumulus line over the Great Salt Lake for about 5 min shortly after sunrise on June 26, 1985. These observations were used as the basis for a study of the initiation and evolution of waterspouts through a series of numerical experiments at two scales, that of a cloud and a waterspout. The cloud scale was simulated using an improved Goddard-Schlesinger model with nearby Salt Lake City soundings. Results showed that for each mode of cloud initiation, the vortex that started at the anticyclonic center grew faster than those started at other centers. This result strongly suggests that the cloud vorticity was important in its initiation. The greatest azimuthal speed for the bubble-initiated cloud was 11 m/s, when the vortex model was started at 28-min cloud time with time-varying boundary conditions, whereas it was 21 m/s when started at 12 min in the line-initiated cloud. The results support the hypothesis that, at least in some circumstances, cloud processes alone can produce waterspouts in the absence of external vorticity sources such as surface convergence lines or other shear features.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 119; 2741-277
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    Diagnostic evaluation of numerical model simulations using the tendency equation (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A procedure is proposed to expand the diagnostic capabilities of the pressure tendency equation of a primitive equation NWP model by computing the pressure tendency in physical coordinates. The advantages of isolating the density advection as a diagnostic tool to understand pressure changes is shown. By simple thermodynamic arguments it is demonstrated that in areas of synoptic-scale cyclonic development, the vertically integrated density advection is more than sufficient to explain the depletion of mass over a growing depression. Consequently, the joint contribution of the net divergence and vertical motion opposes the pressure fall. This is illustrated for a case of rapid cyclogenesis in southern South America.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 119; 2936-295
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  • 30
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    Automated cloud screening of AVHRR imagery using split-and-merge clustering (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Previous methods to segment clouds from ocean in AVHRR imagery have shown varying degrees of success, with nighttime approaches being the most limited. An improved method of automatic image segmentation, the principal component transformation split-and-merge clustering (PCTSMC) algorithm, is presented and applied to cloud screening of both nighttime and daytime AVHRR data. The method combines spectral differencing, the principal component transformation, and split-and-merge clustering to sample objectively the natural classes in the data. This segmentation method is then augmented by supervised classification techniques to screen clouds from the imagery. Comparisons with other nighttime methods demonstrate its improved capability in this application. The sensitivity of the method to clustering parameters is presented; the results show that the method is insensitive to the split-and-merge thresholds.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Remote Sensing of Environment (ISSN 0034-4257); 38; 77-121
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    The effect of matrix mechanical properties on (0)8 unidirectional SiC/Ti composite fatigue resistance (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The relationship between constituent and MMC properties in fatigue loading is investigated with low-cycle fatigue-resistance testing of an alloy Ti-15-3 matrix reinforced with SiC SCS-6 fibers. The fabrication of the composite is described, and specimens are generated that are weak and ductile (WD), strong and moderately ductile (SM), or strong and brittle (SB). Strain is measured during MMC fatigue tests at a constant load amplitude with a load-controlled waveform and during matrix-alloy fatigue tests at a constant strain amplitude using a strain-controlled waveform. The fatigue resistance of the (0)8 SiC/Ti-15-3 composite is found to be slightly influenced by matrix mechanical properties, and the composite- and matrix-alloy fatigue lives are not correlated. This finding is suggested to relate to the different crack-initiation and -growth processes in MMCs and matrix alloys.
    Keywords: COMPOSITE MATERIALS
    Type: Scripta Metallurgica et Materialia (ISSN 0956-716X); 25; 2879-288
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    Combined micromechanical and fabrication process optimization for metal-matrix composites (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A method is presented to minimize the residual matrix stresses in metal matrix composites. Fabrication parameters such as temperature and consolidation pressure are optimized concurrently with the characteristics (i.e., modulus, coefficient of thermal expansion, strength, and interphase thickness) of a fiber-matrix interphase. By including the interphase properties in the fabrication process, lower residual stresses are achievable. Results for an ultra-high modulus graphite (P100)/copper composite show a reduction of 21 percent for the maximum matrix microstress when optimizing the fabrication process alone. Concurrent optimization of the fabrication process and interphase properties show a 41 percent decrease in the maximum microstress. Therefore, this optimization method demonstrates the capability of reducing residual microstresses by altering the temperature and consolidation pressure histories and tailoring the interphase properties for an improved composite material. In addition, the results indicate that the consolidation pressures are the most important fabrication parameters, and the coefficient of thermal expansion is the most critical interphase property.
    Keywords: COMPOSITE MATERIALS
    Type: In: Struceng & Femcad - Structural engineering and optimization (A93-18977 05-39); p. 247-254.
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    Infrared radiation parameterizations in numerical climate models (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This study presents various approaches to parameterizing the broadband transmission functions for utilization in numerical climate models. One-parameter scaling is applied to approximate a nonhomogeneous path with an equivalent homogeneous path, and the diffuse transmittances are either interpolated from precomputed tables or fit by analytical functions. Two-parameter scaling is applied to parameterizing the carbon dioxide and ozone transmission functions in both the lower and middle atmosphere. Parameterizations are given for the nitrous oxide and methane diffuse transmission functions.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Climate (ISSN 0894-8755); 4; 424-437
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    Automatic analysis of stereoscopic satellite image pairs for determination of cloud-top height and structure (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Results are presented on an automatic stereo analysis of cloud-top heights from nearly simultaneous satellite image pairs from the GOES and NOAA satellites, using a massively parallel processor computer. Comparisons of computer-derived height fields and manually analyzed fields show that the automatic analysis technique shows promise for performing routine stereo analysis in a real-time environment, providing a useful forecasting tool by augmenting observational data sets of severe thunderstorms and hurricanes. Simulations using synthetic stereo data show that it is possible to automatically resolve small-scale features such as 4000-m-diam clouds to about 1500 m in the vertical.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Applied Meteorology (ISSN 0894-8763); 30; 257-281
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    Global precipitation estimates from satellite - Using difference fields of outgoing long-wave radiation (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Global precipitation estimates using satellite data are derived using difference fields of outgoing long-wave radiation (OLR). The difference fields consist of clear OLR minus cloudy OLR, which is a measure of long-wave cloud radiative forcing at the top of the earth-atmosphere system; and clear daytime OLR minus clear night-time OLR, which is a measure of the diurnal variation of surface heating. All geophysical parameters used to compute OLR are derived from an analysis of the HIRS2/MSU sounding data. The derived global precipitation estimates show good agreement with collocated raingage data over land.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Atmosphere - Ocean (ISSN 0705-5900); 29; 150-174
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    Continuous fiber-reinforced titanium aluminide composites (1991)
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    Publication Date: 2011-08-19
    Description: An account is given of the fabrication techniques, microstructural characteristics, and mechanical behavior of a lightweight, high service temperature SiC-reinforced alpha-2 Ti-14Al-21Nb intermetallic-matrix composite. Fabrication techniques under investigation to improve the low-temperature ductility and environmental resistance of this material system, while reducing manufacturing costs to competitive levels, encompass powder-cloth processing, foil-fiber-foil processing, and thermal-spray processing. Attention is given to composite microstructure problems associated with fiber distribution and fiber-matrix interfaces, as well as with mismatches of thermal-expansion coefficient; major improvements are noted to be required in tensile properties, thermal cycling effects, mechanical damage, creep, and environmental effects.
    Keywords: COMPOSITE MATERIALS
    Type: JOM (ISSN 1047-4838); 43; 23-29
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    Comparisons between satellite-derived gradient winds and radar-derived winds from the CIRA-86 (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The zonal and meridional wind contours in the 60-120 km region obtained from satellite radiance data were compared with radar-derived contours of winds obtained from the CIRA-1986 reference atmosphere. It was found that the agreement between the directly observed zonal winds and the zonal mean gradient winds from the reference atmosphere wind model was good, especially below 80 km. However, differences were found in both the Southern and the Northern Hemispheres.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 48; 411-428
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    Air-sea fluxes and surface layer turbulence around a sea surface temperature front (1991)
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    Publication Date: 2011-08-19
    Description: The observed effects of sharp changes in sea surface temperature (SST) on the air-sea fluxes, surface roughness, and the turbulence structure in the surface layer and the marine atmospheric boundary layer are discussed. In situ flux and turbulence observations were carried out from three aircraft and two ships within the FASINEX framework. Three other aircraft used remote sensors to measure waves, microwave backscatter, and lidar signatures of cloud tops. Descriptions of the techniques, intercomparison of aircraft and ship flux data, and use of different methods for analyzing the fluxes from the aircraft data are described. Changing synoptic weather on three successive days yielded cases of wind direction both approximately parallel and perpendicular to a surface temperature front. For the wind perpendicular to the front, wind over both cold-to-warm and warm-to-cold surface temperatures occurred. Model results consistent with the observations suggest that an internal boundary layer forms at the SST.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 8593-860
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    Differences in global data sets of atmospheric and surface parameters and their impact on outgoing longwave radiation and surface downward flux calculations (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 9227-926
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    A simple parameterization of ozone infrared absorption for atmospheric heating rate calculations (1991)
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    Publication Date: 2011-08-19
    Description: A simple parameterization of ozone absorption in the 9.6-micron region which is suitable for two- and three-dimensional stratospheric and tropospheric models is presented. The band is divided into two parts, a brand center region and a band wing region, grouping together regions for which the temperature dependence of absorption is similar. Each of the two regions is modeled with a function having the form of the Goody random model, with pressure and temperature dependent band parameters chosen by empirically fitting line-by-line equivalent widths for pressures between 0.25 and 1000 mbar and ozone absorber amounts between 1.0 x 10 to the -7th and 1.0 cm atm. The model has been applied to calculations of atmospheric heating rates using an absorber amount weighted mean pressure and temperature along the inhomogeneous paths necessary for flux computations. In the stratosphere, maximum errors in the heating rates relative to line-by-line calculations are 0.1 K/d, or 5 percent of the peak cooling at the stratopause. In the troposphere the errors are at most 0.005 K/d.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 9065-907
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    A description of the correlated k distributed method for modeling nongray gaseous absorption, thermal emission, and multiple scattering in vertically inhomogeneous atmospheres (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A radiative transfer method for treating nongray gaseous absorption and thermal emission in vertically inhomogeneous multiple scattering atmospheres is described. Probability density distributions of absorption coefficient strength are derived from line-by-line calculations to construct line-by-line and band model based k distributions. The monotonic ordering of absorption coefficient strengths in these k distributions implicitly preserves the monochromatic structure of the atmosphere at different pressure levels, thus simulating monochromatic spectral integration at a fraction of the line-by-line computing cost. The k distribution approach also permits accurate modeling of overlapping absorption by different atmospheric gases and accurate treatment of nongray absorption in multiple scattering media. It is shown that the correlated k distribution method is capable of achieving numerical accuracy to within 1 percent of cooling rates obtained with line-by-line calculations throughout the troposphere and most of the stratosphere.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 9027-906
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    Calculations of transmission functions in the infrared CO2 and O3 bands (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An efficient method for computing the transmission function in the 15-micron CO2 and the 9.6-micron O3 bands is presented. An inhomogeneous atmospheric path is treated as homogeneous by applying simple pressure and temperature scaling approximations. The transmission functions are then derived from small precomputed tables. Because the atmospheric cooling rate is primarily contributed from adjacent layers, the simple scaling approximations can be used to accurately compute transmission functions in both the middle and lower atmosphere. Applying the parameterization to vastly different atmospheric conditions, the difference with line-by-line calculations is small. In the region between 0.01 mbar and the earth's surface, the cooling rate difference is less than 0.3 C/d in the 15-micron CO2 band and less than 0.1 C/d in the 9.6-micron O3 band.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 9003-901
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    Boundary-layer moisture regimes (1991)
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    Publication Date: 2011-08-19
    Description: Boundary-layer moisture fluctuations are estimated by analyzing HAPEX and FIFE data collected on 52 aircraft flight legs. Moisture fluctuations were given considerable attention in the HAPEX flights, which were 120 km long, and flew 150 m over one area of homogeneous terrain. The repetitions permit statistical consideration of motion characteristics on horizontal scales. Two prototypical boundary layer regimes are discovered: the entrainment-drying boundary layer, and the moistening boundary layer. The latter demonstrates positive moisture skewness close to the surface related to high surface evaporation. The former is characterized by boundary-layer instability, weak surface evaporation, and drier air aloft, leading to unexpected negative moisture skewness. It is noted that 10 km moisture variations with horizontal gradients are often found in narrow zones of horizontal convergence, called mesoscale moisture fronts. A negative moisture to temperature correlation, due to surface energy budget inhomogeneity, is shown to incur large mesoscale variations of relative humidity.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Royal Meteorological Society, Quarterly Journal (ISSN 0035-9009); 117; 151-176
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    Observations of cloud cluster hierarchies over the tropical western Pacific (1991)
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    Publication Date: 2011-08-19
    Description: The structure and propagation of tropical-cloud clusters are investigated during two contrasting periods over the tropical western Pacific in order to determine possible similarities or differences and to compare with previous studies. Three fundamental periodicities are found in tropical convection in the region: 1 day, 2-3 days, and 10-15 days. It is noted that the 10-15-day time scale is closely related to the intraseasonal oscillations propagating from the Indian Ocean to the western Pacific. Large convective complexes, supercloud clusters (SSC) are found to organize in this time scale. The SCC is made up from several cloud clusters generated at 2-3-day intervals. The diurnal variation is found to be most pronounced over the maritime continent, and the amplitude of the diurnal cycle is shown to be modulated by the 2-3-day and 10-15-day oscillations.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 3197-320
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    Reaction of Ti and Ti-Al alloys with alumina (1991)
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    Publication Date: 2011-08-19
    Description: The reaction of single-crystal Al2O3 with pure Ti and Ti-Al alloys with different Al concentrations was examined in the temperature range of 1173 to 1573 K. Significant reaction occurred between Al2O3 and the Ti-Al alloys with Al concentrations lower than that corresponding to the gamma-TiAl phase. The reaction mechanism was determined to be simultaneous diffusion of Al and atomic oxygen from Al2O3 into Ti and the Ti-Al alloys.
    Keywords: COMPOSITE MATERIALS
    Type: Metallurgical Transactions A - Physical Metallurgy and Materials Science (ISSN 0360-2133); 22A; 715-721
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    Surface wind convergence as a short-term predictor of cloud-to-ground lightning at Kennedy Space Center (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Cloud-to-ground lightning is a significant forecast problem at the Kennedy Space Center (KSC) in Florida. In this study, cloud-to-ground lightning is related in time and space to surface convergence for 244 days during the convective seasons of 1985 and 1986 over a 790 sq-km network at KSC. The method uses surface convergence, particularly the average over the area, to identify the potential for new, local thunderstorm growth, and it can be used to specify the likely time and location of lightning during the life cycle of the convection. A threshold of 75 x 10 to the -6th/s change in divergence is the main criterion used to define a convergence event, and a set of flashes less than 30 min apart defines a lightning event. Time intervals are found from the study to be approximately 1 h from beginning convergence to first flash, and another hour to the end of lightning. The influences of low-level winds and midlevel moisture in determining the location and intensity of convection are discussed. This is the first known dynamically-based forecast method for lightning prediction. The technique, currently in use at KSC, has been shown to be a systematic, quantitative tool for predicting lightning onset in situations where conventional analysis tools such as radar and satellite are limited.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Weather and Forecasting (ISSN 0882-8156); 6; 49-64
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    Low-frequency intraseasonal tropical-extratropical interactions (1991)
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    Publication Date: 2011-08-19
    Description: Using seven years (1981-1987) of ECMWF initialized analyses, the low-frequency (20-70 day) intraseasonal variability during Northern Hemisphere winter is examined, with emphasis on the zonal wind variability in the Pacific sector and on its relationship to the tropical convection and the middle-altitude wave propagation. Particular consideration is given to changes in the propagation characteristics associated with variations in the subtropical jet and the implications for low-frequency variability in middle latitudes. Also investigated is the relationship between the Pacific sector u-wind fluctuations and tropical convection anomalies.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 48; 629-650
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    Determination of precipitation profiles from airborne passive microwave radiometric measurements (1991)
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    Publication Date: 2011-08-19
    Description: This study presents the first quantitative retrievals of vertical profiles of precipitation derived from multispectral passive microwave radiometry. Measurements of microwave brightness temperature (Tb) obtained by a NASA high-altitude research aircraft are related to profiles of rainfall rate through a multichannel piecewise-linear statistical regression procedure. Statistics for Tb are obtained from a set of cloud radiative models representing a wide variety of convective, stratiform, and anvil structures. The retrieval scheme itself determines which cloud model best fits the observed meteorological conditions. Retrieved rainfall rate profiles are converted to equivalent radar reflectivity for comparison with observed reflectivities from a ground-based research radar. Results for two case studies, a stratiform rain situation and an intense convective thunderstorm, show that the radiometrically derived profiles capture the major features of the observed vertical structure of hydrometer density.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Atmospheric and Oceanic Technology (ISSN 0739-0572); 8; 148-158
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    Retrieval of monthly rainfall indices from microwave radiometric measurements using probability distribution functions (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An algorithm for the estimation of monthly rain totals for 5 deg cells over the ocean from histograms of SSM/I brightness temperatures has been developed. There are three novel features to this algorithm. First, it uses knowledge of the form of the rainfall intensity probability density function to augment the measurements. Second, a linear combination of the 19.35 and 22.235 GHz channels has been employed to reduce the impact of variability of water vapor. Third, an objective technique has been developed to estimate the rain layer thickness from the 19.35- and 22.235-GHz brightness temperature histograms. Comparison with climatologies and the GATE radar observations suggest that the estimates are reasonable in spite of not having a beam-filling correction. By-products of the retrievals indicate that the SSM/I instrument noise level and calibration stability are quite good.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Atmospheric and Oceanic Technology (ISSN 0739-0572); 8; 118-136
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    Aircraft overflight measurements of midwest severe storms - Implications on geosynchronous satellite interpretations (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The instrumented NASA ER-2 aircraft overflew severe convection with IR V features for the first time in the midwest United States during May 1984. Measurements taken by the ER-2 were: visible and IR imagery, high-frequency passive microwave (92, 183 GHz) imagery, nadir lidar backscattered return, and flight altitude information. The May 7 and May 13, 1984 cases are analyzed in detail and the various data sources are combined and compared with GOES imagery. The high resolution aircraft IR imagery shows that thermal couplets are considerably more pronounced than in GOES imagery. In one of the cases (May 7, 1984) the minimum cloud-top IR temperature was located upshear of the overshooting cloud top in the lidar height field. The IR temperatures in the downshear anvils were as much as 5 C warmer than the ambient air temperatures, implying that the upwelling IR radiance comes from about 0.5-1.0 km below the cloud top. The in situ ER-2 measurements of temperature and air velocity 3-4 km above the overshooting tops showed very intense temperature and vertical velocity, perturbations. These perturbations are suggestive of lee waves generated by the overshooting tops or a cold dome above the squall line possibly due to tropopause lifting by the storms.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 119; 436-456
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    Clouds and the Earth's Radiant Energy System (CERES) - An Earth Observing System experiment (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An overview is presented of the CERES experiment that is designed not only to monitor changes in the earth's radiant energy system and cloud systems but to provide these data with enough accuracy and simultaneity to examine the critical climate/cloud feedback mechanisms which may play a major role in determining future changes in the climate system. CERES will estimate not only the flow of radiation at the top of the atmosphere, but also more complete cloud properties that will permit determination of radiative fluxes within the atmosphere and at the surface. The CERES radiation budget data is also planned for utilization in a wide range of other Earth Observing System interdisciplinary science investigations, including studies of land, biological, ocean and atmospheric processes.
    Keywords: METEOROLOGY AND CLIMATOLOGY
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    Aircraft multifrequency passive microwave observations of light precipitation over the ocean (1991)
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    Publication Date: 2011-08-19
    Description: Aircraft passive microwave observations at 18, 37, 92, and 183 GHz of light oceanic precipitation are studied in conjunction with visible and infrared observations and ground-based radar data. Microwave signatures for clear, cloudy, and precipitating conditions are defined, with results in general agreement with previous theoretical results. Emission signatures are evident at 18, 37, and 92 GHz with clouds and precipitation producing an increase in brightness temperature over that observed over the low-emissivity ocean background. Polarization differences at 18 and 37 GHz also decrease in precipitation areas to minima of 30 K at 18 GHz and 15 K at 37 GHz. The 92-GHz brightness temperature shows a double-valued relationship, with an increase in cloudy and very lightly raining areas and a subsequent decrease for higher rain rates and deeper clouds where the ice scattering process becomes important. The 183-GHz observations display a distinct sensitivity to small amounts of ice. Simple channel differences are shown to compare favorably to the rain field, including polarization differences at 18 and 37 GHz and frequency differences between 92 and 37 GHz and between 183 and 92 GHz.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Atmospheric and Oceanic Technology (ISSN 0739-0572); 8; 201-220
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    Cold-air outbreak during GALE - Lidar observations and modeling of boundary layer dynamics (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Two cold-air outbreaks were studied during the Genesis of Atlantic Lows Experiment. A lidar system was operated to observe the boundary layer evolution and the development of clouds. On the first day (January 30, 1986) boundary layer rise was less than 50 percent of the value for the second day (March 2, 1986). On the first day only a thin broken cloud cover formed, while on the second day a thick solid cloud deck formed - although the average moisture content was 60 percent of that on the first day. A trajectory slab model was employed to simulate the evolution of the layer over the ocean near the east Atlantic shore. The model allows for vertical gradients in conservative variables under neutrally buoyant conditions. The primary effect of these assumptions, which are based on observed thermodynamic profiles, is to reduce cloudiness to be more in line with observations. Boundary-layer depth was reasonably well predicted as was sensible and latent heat flux.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 119; 1132-115
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    Shortwave shape factor inversion of earth radiation budget observations (1991)
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    Publication Date: 2011-08-19
    Description: Results are presented on an investigation of the effects of various assumptions (including assumptions of a constant flux field, a constant albedo field, and a variable albedo field) used for deriving the shortwave shape factor on the estimates, from radiometric measurements, of the albedo at the top of the atmosphere. The accuracies and the resolutions of the shape-factor-flux estimates obtained using these assumptions are determined by simulating the shape factor inversion technique with scanner data from the Earth Radiation Budget Experiment (ERBE). The resulting biases and variances are given for both the ERBE medium-field-of-view and wide-field-of-view radiometers.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 48; 390-402
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    Fluctuations of high clouds and 500-mb geopotential heights in baroclinic waveguides (1991)
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    Publication Date: 2011-08-19
    Description: The spatial phase relationship between the atmospheric circulation and the bandpass fluctuations in cloudiness are investigated using satellite retrievals of high cloud areas reported by Stowe et al. (1988, 1989) NMC 500-mb geopotential heights in northern extratropics. Results of the analysis suggest that the high-cloud structures of baroclinic waves are less spatially coherent than the internal geopotential-height structures. It is shown that over the North Pacific, small-scale (latitudinal wavenumber 13-18) fluctuations in geopotential play a greater role in forcing high cloudiness than do medium-scale (latitudinal wavenumber 7-12) fluctuations in geopotential.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 119; 73-83
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    Analysis of a general circulation model simulation of the atmospheric response to the observed sea surface temperature anomalies of January and February 1983 (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A new version of the Goddard Laboratory for Atmospheres GCM is utilized to simulate the influence of an observed sea surface temperature anomaly on rainfall and atmospheric circulation. The model can reproduce many essential features of the observed tropical rainfall and circulation anomalies during January-February 1983. Particularly, the model simulates realistic patterns of tropical anomalies of sea level pressure, 200 mb geopotential heights, and horizontal winds at the 200 and 850 mb levels. The model-simulated tropical precipitation anomaly patterns appear realistic, although the precipitation is rather excessive and the atmosphere is too energetic.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Climate (ISSN 0894-8755); 4; 107-115
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    Thermochemical analysis of chemical processes relevant to the stability and processing of SiC-reinforced Si3N4 composite (1991)
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    Publication Date: 2011-08-19
    Description: Chemical processes relevant to the stability and processing of SiC-reinforced Si3N4 composites have been examined from thermochemical considerations. The thermodynamic stabilities of various interfaces, such as SiC-Si3N4, SiC-Si3N4-Si2ON2, and SiC-Si3N4-SiO2, have been examined as a function of temperature, and the temperatures above which these interfaces become unstable have been calculated. The degradation of SiC during the processing of the composite has been examined. The processing routes considered in this study include the reaction bonded silicon nitride (RBSN) process and the pressure-assisted sintering processes with suitable sintering additives.
    Keywords: COMPOSITE MATERIALS
    Type: Ceramic Engineering and Science Proceedings (ISSN 0196-6219); 12; 1873-188
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    Dual-parameter radar rainfall measurement from space - A test result from an aircraft experiment (1991)
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    Publication Date: 2011-08-19
    Description: An aircraft experiment has been conducted with a dual-frequency (X/Ka-bands) radar to test various rainfall retrieval methods from space. The authors test a method to derive raindrop size distribution (DSD) parameters from the combination of a radar reflectivity profile and a path-integrated attenuation derived from surface return, which may be available from most spaceborne radars. The estimated DSD parameters are reasonable in that the values generally fall within the range of commonly measured ones and that shifts in DSD parameters appear to be correlated with changes in storm type. The validity of the estimation result is also demonstrated by a consistency check using the Ka-band reflectivity profile which is independent of the DSD estimation process. Although errors may occur in the cases of nonuniform beam filling, these test results indicate the feasibility of the dual-parameter radar measurement from space in achieving a better accuracy in quantitative rainfall remote measurements.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); 29; 690-703
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    Horizontal wind fluctuations in the stratosphere during large-scale cyclogenesis (1991)
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    Publication Date: 2011-08-19
    Description: The meteorological measurement system (MMS) on the U-2 aircraft measured pressure, temperature, and the horizontal wind during a cyclogenesis event over western United States on April 20, 1984. The mean horizontal wind in the stratosphere decreases monotonically with altitude. Superimposed on the mean stratospheric wind is a perturbation wind vector, which is an elliptically polarized wave with an amplitude of 4 to 10 m/s and a vertical wavelength of 2 to 3 km. The perturbation wind vector rotates anticyclonically (clockwise) with altitude and produces alternating advection in the plane of the aircraft flight path. This differential advection folds surfaces of constant tracer mixing ratio and contributes to the observed tracer laminar structures and inferred cross-jet transport.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 17
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    Estimation of the diurnal cycle of oceanic precipitation from SSM/I data (1991)
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    Publication Date: 2011-08-19
    Description: A study of differences between the morning and evening monthly rainfall for 5 x 5 deg cells over the oceans from the SSM/I data has been conducted. The monthly rainfalls are estimated from the technique given by Wilheit et al. The difference between the morning and evening monthly rainfall arises due to the various random errors involved in the retrieval process, the sampling error in the observations, and the diurnal component of oceanic rainfall. The diurnal component is weak but clearly visible when averaged over large areas and for long time periods. The analysis shows that morning rainfall is consistently greater than evening rainfall. The Northern Hemisphere seem to have a larger diurnal variation than does the Southern Hemisphere. The maximum ratio between the morning and evening monthly rainfall is 1.7 while 1.2 is the more typical value.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 119; 2168-217
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    The 27-28 October 1986 FIRE Cirrus case study - Retrieval of cloud particle sizes and optical depths from comparative analyses of aircraft and satellite-based infrared measurements (1991)
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    Publication Date: 2011-08-19
    Description: Infrared radiance measurements were acquired from a narrow-field nadir-viewing radiometer based on the NASA ER-2 aircraft during a coincident Landsat 5 overpass on October 28, 1986 as part of the FIRE Cirrus IFO in the vicinity of Lake Michigan. The spectral bandpasses are 9.90-10.87 microns for the ER-2-based radiometer and 10.40-12.50 microns for the Landsat thematic mapper band. After adjusting for spatial and temporal differences, a comparative study using data from these two instruments is undertaken in order to retrieve cirrus cloud ice-crystal sizes and optical depths. Retrieval is achieved by analysis of measurement correlations between the two spectral bands and comparison to multistream radiative transfer model calculations. The results indicate that the equivalent sphere radii of the cirrus ice crystals were typically less than 30 microns. Such particles were too small to be measured by the available in situ instrumentation. Cloud optical depths at a reference wavelength of 11.4 microns ranged from 0.3 to 2.0 for this case study. Supplemental results in support of this study are described using radiation measurements from the King Air aircraft, which was also in near coincidence with the Landsat overpass.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 119; 1673-169
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    Comparison of ice-phase microphysical parameterization schemes using numerical simulations of tropical convection (1991)
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    Publication Date: 2011-08-19
    Description: The performance of several ice parameterizations has been evaluated through a numerical cloud model. Ice effects using different schemes are contrasted with each other and with an ice-free control by incorporating them into the cloud model and by applying them to simulations of tropical squall systems. The latter are simulated in 2D so that a large domain can be used to incorporate a complete anvil. Nonsquall-type convective lines are simulated in 3D owing to their smaller horizontal scale. It is concluded that inclusion of ice microphysics in the cloud model enhanced the agreement of the simulated convection with some features of observed convection, including the proportion of surface rainfall in the anvil region and the intensity and structure of the radar brightband near the melting level in the anvil. In the experiments with bulk microphysics, three ice categories produced much better results than two ice categories, which in turn was better than no ice. For the tropical squall-type and nonsquall-type systems the optimal mix was ice, snow, and graupel.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Applied Meteorology (ISSN 0894-8763); 30; 985-1004
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    On the dependence of travelling wave stability on basic state wave phase speed (1991)
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    Publication Date: 2011-08-19
    Description: The dependence of stability on basic state wave phase speed is examined in a nondivergent barotropic model on a sphere for planetary scale waves with phase speeds typical of waves observed in the atmosphere. Triad interactions are examined analytically and compared to numerical results from a full spectral model. A number of triads may result in growth of the perturbation components for each basic state wave; for each triad there is a basic state wave phase speed where it is resonant, identified as the point where the critical amplitude for instability to that perturbation becomes zero. Critical amplitudes for instability obtained using the full spectral model generally agree well with triad results. Since the basic state wave phase speed determines which triad will grow, spatial structure and critical amplitudes for instability for the growing disturbances depend strongly on basic state wave phase speed. The results of this idealized study suggest that phase speed may be an important factor in determining the stability of planetary scale waves in the atmosphere.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Royal Meteorological Society, Quarterly Journal (ISSN 0035-9009); 117; 319-331
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    Preliminary studies on NiAl/Nb2Be17 reaction and effectiveness of BeO as an interfacial reaction barrier (1991)
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    Publication Date: 2011-08-19
    Description: The interfacial reaction between NiAl and Nb2Be17 (used as a reinforcement for the alloy) was studied by measuring diffusion bonding of NiAl and Nb2Be17 plates in a hot press under a vacuum of 10 exp -5 atm. It was found that, after 2 hrs of hot pressing at 1373 K, the reaction between NiAl and Nb2Be17 was extensive. A 40 to 50-micron-thick reaction zone consisted of three distinct layers at the NiAl/Nb2Be17 interface: layer A next to Nb2Be17, layer B in the middle, and layer C next to NiAl. Results of analysis of the reaction layers using energy dispersive spectroscopy (EDS) were inconclusive because of the inabiliaty of EDS to detect Be.
    Keywords: COMPOSITE MATERIALS
    Type: Metallurgical Transactions A - Physical Metallurgy and Materials Science (ISSN 0360-2133); 22A; 2535-253
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    Micromechanical analysis of filamentary metal matrix composites under longitudinal loading (1991)
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    Publication Date: 2011-08-19
    Description: A two-material composite cylinder model (CCM) was considered for the study of the mechanical behavior at different temperatures of a fiber-reinforced silicon carbide/aluminum (SiC/Al) composite. An elastoplastic analysis of the model was performed in which the fiber was assumed to be linear elastic and the matrix elastoplastic with work-hardening. The analysis was based on the deformation theory of plasticity in conjunction with the von-Mises yield criterion. Experimental stress-strain curves of an SiC/Al composite were obtained at 24 and 288 C (75 and 550 F). The complete three-dimensional stress distribution in the composite using the CCM was determined. It was found that, in addition to longitudinal stresses, transverse stresses in both the fiber and the matrix were developed as a result of the different Poisson's ratios of the two materials. The transverse stresses, although much smaller than the longitudinal stresses, contributed to the plastic deformation of the matrix. The experimental stress-strain curves were favorably compared with the theoretical predictions.
    Keywords: COMPOSITE MATERIALS
    Type: Journal of Composites Technology and Research (ISSN 0885-6804); 13; 168-174
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    Satellite observations of variations in tropical cyclone convection caused by upper-tropospheric troughs (1991)
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    Publication Date: 2011-08-19
    Description: Satellite observations and numerical model results have been used to study the relationship between upper-tropospheric forcing and the oscillation of convection of tropical cyclones Florence (1988) and Irene (1981) during their mature stage over open warm oceans (SST greater than or equal to 26 C). It is suggested that the initiation and maintenance of intense convective outbreaks in tropical cyclones are related to the channeling and strengthening of their outflow by upper-tropospheric troughs. It is possible to enhance the convection in response to the outflow jet-induced import of eddy relative angular momentum and ascending motion associated with the thermally direct circulation. Both Florence and Irene are found to intensify after the onset of these convective episodes. It is also suggested that the cessation in the convection of the two tropical cyclones occurs when the upper-tropospheric troughs move near or over the tropical cyclones, resulting in the weakening of their outflow and the entrainment of dry upper-tropospheric air into their inner core.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Applied Meteorology (ISSN 0894-8763); 30; 1163-118
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    The derivation of cloud parameters from satellite-measured radiances for use in surface radiation calculations (1991)
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    Publication Date: 2011-08-19
    Description: A simple scheme is developed for calculating the cloud amount, optical thickness, and height from satellite-measured radiances and is applied to the International Satellite Cloud Climatology Project B3 radiance data to compute the surface radiative fluxes over the tropical and subtropical western Pacific regions for July 1983, using a radiative transfer model. Results are presented on the sensitivity of surface radiation to the cloud scheme. In addition, the validity of an empirical relationship between the solar fluxes at the surface and at the top of the atmosphere is examined.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 48; 1549-155
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    Contributions to the implementation of the Arakawa-Schubert cumulus parameterization in the GLA GCM (1991)
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    Publication Date: 2011-08-19
    Description: The roles of the Critical Cloud Work Function (CCWF) data set and the upper and lower bounds on entrainment by cumulus plumes in the Arakawa-Schubert cumulus parameterization (ASCP) in the GLA GCM (Geller et al., 1988) were investigated in two sets of experiments. It was found that the horizontal and vertical distribution of cumulus heating can be altered in ASCP by adjusting these parameters. These changes can have a strong influence on the vertical structure of condensation heating, water vapor distribution, temperature, and rainfall. The CCWF is an important limiting parameter that controls the onset of different cloud types; increasing the threshold values of CCWF for all clouds tends to concentrate the rainfall into a narrower ITCZ and affects the rainfall during the initial adjustment period.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 48; 1573-158
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    The effect of snow cover on the climate (1991)
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    Publication Date: 2011-08-19
    Description: Large-scale snow cover anomalies are thought to cause significant changes in the diabatic heating of the earth's surface in such a way as to produce substantial local cooling in the surface temperatures. This theory was tested using the GISS 3D GCM (General Circulation Model). The results of the GCM experiment showed that snow cover caused only a short term local decrease in the surface temperature. In the surface energy budget, reduction in absorbed shortwave radiation and the increased latent heat sink of melting snow contributed to lower temperatures. However, all the remaining heating terms contribute to increasing the net heating over a snow covered surface. The results emphasize the negative feedback which limits the impact of snow cover anomalies over longer time scales.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Climate (ISSN 0894-8755); 4; 689-706
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    Heat fluxes and roll circulations over the western Gulf Stream during an intense cold-air outbreak (1991)
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    Publication Date: 2011-08-19
    Description: Turbulence and heat fluxes in the marine atmospheric boundary layer (MABL) for three aircraft stacks near the western Gulf Stream front, observed during the Genesis of Atlantic Lows Experiment (GALE) January 28, 1986 cold-air outbreak, has been studied using mixed-layer scaling. The GOES image and stability parameter indicates that these three stacks were in the roll vortex regime. The turbulence structure in the MABL is studied for this case, as well as the significance of roll vortices to heat fluxes. The roll circulations are shown to contribute significantly to the sensible (temperature) and latent heat (moisture) fluxes with importance increasing upward. The results suggest that the entrainment at the MABL top might affect the the budgets of temperature and humidity fluxes in the lower MABL, but not in the unstable surface layer.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Boundary-Layer Meteorology (ISSN 0006-8314); 55; 3, Ma
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    Effective thermal conductivity of composites with fibre-matrix debonding (1991)
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    Publication Date: 2011-08-19
    Description: Debonding of the fiber-matrix interface is a major cause for the degradation of the mechanical properties and the loss of thermal conductivity of fiber-reinforced composites. This paper discusses two analytical approaches for modeling the thermal conduction problem of composites. One is based on the concept of modeling the thermal barrier by an equivalent heat transfer coefficient at the fiber-matrix interface, as described by Hasselman and Johnson (1987) and Benveniste and Miloh (1986). The other approach, suggested by Hatta and Taya (1986), is by treating a composite with debonded interface as a coated-fiber composite. The major advantage of the latter aproach is that the thickness of the fiber coating can be realistically modeled depending upon the extent of degradation of the composite with the thermal conductivity of the coating as that of air.
    Keywords: COMPOSITE MATERIALS
    Type: Journal of Materials Science Letters (ISSN 0261-8028); 10; 682-684
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    The radiative effects of clouds and their impact on climate (1991)
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    Publication Date: 2011-08-19
    Description: The radiative effects of clouds on the climate system are reviewed on the basis of data published over the last 15-20 years and some relevant unpublished model studies. Emphasis is placed on the impact of clouds on the incoming and outgoing radiation at the top of the atmosphere and the two-way interaction of clouds with other variables of the climate system, i.e., the cloud/climate feedback problem, as revealed by climate model simulations. Investigations aimed at determining the overall effects of clouds on the climate system (climate forcing) show that clouds have a net cooling effect. Two estimates of the global annual average effect of clouds on the net flux at the top of the atmosphere, based on recent satellite observations, show wide discrepancies. The sign of cloud feedback is found to be positive when the spatial distribution of clouds is allowed to vary in response to climate change. It is concluded that clouds may have a strong influence on climate change, but the magnitude of this influence is unknown.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: American Meteorological Society, Bulletin (ISSN 0003-0007); 72; 795-813
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    Microwave sounding units and global warming (1991)
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    Publication Date: 2011-08-19
    Description: A recent work of Spencer and Christy (1990) on precise monitoring of global temperature trends from satellites is critically examined. It is tentatively concluded in the present comment that remote sensing using satellite microwave radiometers can in fact provide a means for the monitoring of troposphere-averaged air temperature. However, for this to be successful more than one decade of data will be required to overcome the apparent inherent variability of global average air temperature. It is argued that the data set reported by Spencer and Christy should be subjected to careful review before it is interpreted as evidence of the presence or absence of global warming. In a reply, Christy provides specific responses to the commenters' objections.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Science (ISSN 0036-8075); 251; 316; Rep
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    Infrared cooling rate calculations in operational general circulation models - Comparisons with benchmark computations (1991)
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    Publication Date: 2011-08-19
    Description: The performance of several parameterized models is described with respect to numerical prediction and climate research at GFDL, NCAR, and GISS. The radiation codes of the models were compared to benchmark calculations and other codes for the intercomparison of radiation codes in climate models (ICRCCM). Cooling rates and fluxes calculated from the models are examined in terms of their application to established general circulation models (GCMs) from the three research institutions. The newest radiation parameterization techniques show the most significant agreement with the benchmark line-by-line (LBL) results. The LBL cooling rates correspond to cooling rate profiles from the models, but the parameterization of the water vapor continuum demonstrates uncertain results. These uncertainties affect the understanding of some lower tropospheric cooling, and therefore more accurate parameterization of the water vapor continuum, as well as the weaker absorption bands of CO2 and O3 is recommended.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 9105-912
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    Time-cumulated visible and infrared radiance histograms used as descriptors of surface and cloud variations (1991)
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    Publication Date: 2011-08-19
    Description: The spatial and temporal stability of the distributions of satellite-measured visible and infrared radiances, caused by variations in clouds and surfaces, are investigated using bidimensional and monodimensional histograms and time-composite images. Similar analysis of the histograms of the original and time-composite images provides separation of the contributions of the space and time variations to the total variations. The variability of both the surfaces and clouds is found to be larger at scales much larger than the minimum resolved by satellite imagery. This study shows that the shapes of these histograms are distinctive characteristics of the different climate regimes and that particular attributes of these histograms can be related to several general, though not universal, properties of clouds and surface variations at regional and synoptic scales. There are also significant exceptions to these relationships in particular climate regimes. The characteristics of these radiance histograms provide a stable well defined descriptor of the cloud and surface properties.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: International Journal of Remote Sensing (ISSN 0143-1161); 12; 877-920
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    Lightning flash mensuration using video from the Space Shuttle Columbia (STS-32) (1991)
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    Publication Date: 2011-08-19
    Description: Using the payload bay television cameras from various Space Shuttle missions, a study was performed to investigate the relationship between the size and duration of lightning flashes, though separated by 1-100 km, that appeared to be flashing in synchronization. The area, duration, and rate of propagation of the lightning in these storms was also studied. By employing the analytical methods described, the use of deinterlaced video of lightning observed from STS-32 provides the highest sampling rate ever utilized for this purpose from space (1 image each 16.7 m/sec).
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Geocarto International (ISSN 1010-6049); 6; 61-68
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    Structure of an internal bore and dissipating gravity current as revealed by Raman lidar (1991)
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    Publication Date: 2011-08-19
    Description: The Raman lidar observations of a weak gravity current and an internal bore associated with a thunderstorm gust front are presented. These observations have been complemented by conventional surface meteorologial analyses, special radiosonde data, spectral and bandpass filter analysis of barograph data, and infrared satellite imagery. Results obtained reveal the time-space continuity and dynamic nature of two boundary-layer disturbances seen in the lidar data. A comparison of the lidar display with the rawinsonde data makes it possible to determine the thermal fields associated with these disturbances at high temporal resolution (2 min) and an altitude of 6 km. The airflow associated with the disturbances was inferred by synthesizing the lidar and rawinsonde data. One of the two disturbances represents a dissipating outflow boundary (gust front) and can be characterized as a gravity current. The second disturbance represents an internal bore propagating ahead of the gravity current on a surface-based stable layer, which acted as a waveguide. The lidar revealed a mean bore depth of 1.9 km, observed and calculated speeds were in good agreement (about + or - 20 percent).
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 119; 857-887
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    Evaluation of thermomechanical damage in silicon carbide/titanium composites (1991)
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    Publication Date: 2011-08-19
    Keywords: COMPOSITE MATERIALS
    Type: AIAA Journal (ISSN 0001-1452); 29; 992-997
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    Crosslinking-property relationships in PMR polyimide composites. I (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The effect of the crosslink density of the matrix on physical and mechanical properties of a graphite-fiber-reinforced PMR (for polymerization of monomer reactants) polyimide composites during isothermal aging was investigated in experiments where unidirectional composite specimens of Celion 6000/PMR-P1 were isothermally exposed at 288 C in air for various time periods up to 5000 hrs. It was found that, as the crosslink density increased, the glass transition temperature, density, and elevated-temperature interlaminar shear strength of a composite increased, while the initial moisture absorption and the coefficient of thermal expansion decreased. However, after reaching the highest possible matrix crosslink density, several of the composite properties began to deteriorate rapidly.
    Keywords: COMPOSITE MATERIALS
    Type: Polymer Composites (ISSN 0272-8397); 12; 126-132
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    Dynamic mechanical properties of N-phenylnadimide modified PMR polyimide composites (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Temperature-frequency dependence of alpha, beta, and gamma transitions was determined using a Rheometrics dynamic spectrometer on a series of unidirectional Celion 6000/N-phenylnadimide (PN) modified PMR polyimide composites. The objective was to see if any correlations exist between crosslinked network structure and dynamic mechanical properties. Variation in crosslinked network structures was achieved by altering the polyimide formulation through addition of various quantities of PN into the standard PMR-15 composition. As a control, PMR-15 composite system exhibited well-defined alpha, beta, and gamma transitions in the regions of 360, 100, and -120 C, respectively. Their activation energies were estimated to be 232, 60, and 14 kcal/mole, respectively. Increasing the amount of PN concentration caused lowering of the activation energies of the three relaxations, a decrease of the glass transition temperature, and increasing intensities of the three damping peaks, compared to the control PMR-15 counterpart. These dynamic mechanical responses were in agreement with formation of a more flexible copolymer from PN and PMR-15 prepolymer.
    Keywords: COMPOSITE MATERIALS
    Type: Polymer Composites (ISSN 0272-8397); 12; 133-136
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    Simulations of the HDO and H2O-18 atmospheric cycles using the NASA GISS general circulation model - Sensitivity experiments for present-day conditions (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Incorporating the full geochemical cycles of stable water isotopes (HDO and H2O-18) into an atmospheric general circulation model (GCM) allows an improved understanding of global delta-D and delta-O-18 distributions and might even allow an analysis of the GCM's hydrological cycle. A detailed sensitivity analysis using the NASA/Goddard Institute for Space Studies (GISS) model II GCM is presented that examines the nature of isotope modeling. The tests indicate that delta-D and delta-O-18 values in nonpolar regions are not strongly sensitive to details in the model precipitation parameterizations. This result, while implying that isotope modeling has limited potential use in the calibration of GCM convection schemes, also suggests that certain necessarily arbitrary aspects of these schemes are adequate for many isotope studies. Deuterium excess, a second-order variable, does show some sensitivity to precipitation parameterization and thus may be more useful for GCM calibration.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 7495-750
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    A numerical study of thunderstorm electrification - Model development and case study (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A numerical model was developed for examining the thunderstorm electrification process in which it is assumed that the electrification is entirely due to noninductive charge transfer between colliding ice crystals and hail. Since this ice-hail charge mechanism is very dependent on particle sizes and distributions, an explicit microphysical framework is used. To maintain simplicity, the electrification model is kinematic; thus the temperature and velocity fields are input into the electrification model. The cloud model of Taylor (1989) was used to generate the temperature and velocity fields to examine the July 19, 1981, Cooperative Convective Precipitation Experiment thundercloud. Using these fields, the electrification model produced time-dependent ice particle concentrations, radar reflectivities, charge, and vertical electric field distributions in good general agreement with those observed. The model produced a maximum electric field strength of 1.27 kV/cm, which is on the order of that needed for lightning initiation, and this maximum occurred very close to the time of the observed discharge. Thus, the ice-hail charge mechanism appears to have played an important role in the electrical development of the July 19 cloud.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 7463-748
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    Increased ocean heat transports and warmer climate (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The impact of an increased ocean heat transport on climate is investigated in the framework of the GISS GMC model described by Hansen et al. (1983), using two scenarios: one starting from warmer polar temperatures/no sea ice and the other from the current ocean conditions. A 20-percent increase in cross-equatorial heat transport was sufficient to melt all sea ice; it resulted in a climate that was 2 C warmer for the global average, with values some 20-deg warmer at high altitudes and 1-deg warmer near the equator. It is suggested that the hydrological and dynamical changes associated with this different climate regime may be self-sustaining and, as such, would account for the high-latitude warmth of climates in the Mesozoic and Tertiary periods and the decadenal-scale climate fluctuations during the Holocene.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 7437-746
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    Vertical eddy heat fluxes from model simulations (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Vertical eddy fluxes of heat are calculated from simulations with a variety of climate models, ranging from three-dimensional GCMs to a one-dimensional radiative-convective model. The models' total eddy flux in the lower troposphere is found to agree well with Hantel's analysis from observations, but in the mid and upper troposphere the models' values are systematically 30 percent to 50 percent smaller than Hantel's. The models nevertheless give very good results for the global temperature profile, and the reason for the discrepancy is unclear. The model results show that the manner in which the vertical eddy flux is carried is very sensitive to the parameterization of moist convection. When a moist adiabatic adjustment scheme with a critical value for the relative humidity of 100 percent is used, the vertical transports by large-scale eddies and small-scale convection on a global basis are equal: but when a penetrative convection scheme is used, the large-scale flux on a global basis is only about one-fifth to one-fourth the small-scale flux. Comparison of the model results with observations indicates that the results with the latter scheme are more realistic. However, even in this case, in mid and high latitudes the large and small-scale vertical eddy fluxes of heat are comparable in magnitude above the planetary boundary layer.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Climate (ISSN 0894-8755); 4; 304-317
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    Hysteresis and the transition between axisymmetric flow and wave flow in the baroclinic annulus (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A numerical model is employed to establish the transitions between axisymmetric flow and wave flow in the rotating, differentially heated annulus experiments of Fein for both rigid lid and free surface cases. It is shown that, for most of the transitions, the method of computing a steady axisymmetric flow and then testing its linear stability to wave disturbance results in good agreement with the experiments. Implications for the investigation of the dynamics of the earth's atmosphere are considered.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 48; 811-823
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    Effects of satellite data resolution on measuring the space/time variations of surfaces and clouds (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The correlated distributions of satellite-measured visible and infrared radiances, caused by spatial and temporal variations in clouds and surfaces, have been found to be characteristic of the major climate regimes and can be described by the attributes of bidimensional and monodimensional histograms and time-composite images. Most of the variability of both the surfaces and clouds is found to occur at scales larger than the minimum resolved by satellite imagery. Since satellite imaging data sets are difficult to analyze because of their large volumes, many studies reduce the volume by various sampling or averaging schemes. The effects of data resolution and sampling on the radiance histogram statistics and on the time-composite image characteristics are examined. In particular, the sampling strategy used by the International Satellite Cloud Climatology Project is tested. This sampling strategy is found to preserve the statistics of smaller cloud variations for most regions, with the exception of very rare events, if they are accumulated over large enough areas (at least 500 km in dimension) and long enough time periods (at least one month).
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: International Journal of Remote Sensing (ISSN 0143-1161); 12; 921-952
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    Simulations of the effect of a warmer climate on atmospheric humidity (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Increases in the concentration of water vapor constitute the single largest positive feedback in models of global climate warming caused by greenhouse gases. It has been suggested that sinking air in the regions surrounding deep cumulus clouds will dry the upper troposphere and eliminate or reverse the direction of water vapor feedback. This hypothesis has been tested by performing an idealized simulation of climate change with two different versions of a climate model which both incorporate drying due to subsidence of clear air but differ in their parameterization of moist convection and stratiform clouds. Despite increased drying of the upper troposphere by cumulus clouds, upper-level humidity increases in the warmer climate because of enhanced upward moisture transport by the general circulation and increased accumulation of water vapor and ice at cumulus cloud tops.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Nature (ISSN 0028-0836); 351; 382-385
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    Microphysical and radiative characteristics of convective clouds during COHMEX (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper has two purposes: first, to document the structure and evolution of two strong thunderstorms in Alabama using radar multiparameter data; and second, to relate the inferred microphysics to the resulting upwelling microwave radiance observed concurrently by high altitude aircraft. These measurements were collected during the COHMEX field program in the summer of 1986. The radar analysis includes a description of the parameters reflectivity Z, differential reflectivity Z(DR), linear depolarization ratio LDR, and hail signal HS for two thunderstorm cases on July 11, 1986. The simultaneous aircraft data include passive microwave brightness temperature, T(B), measurements at four frequencies ranging from 18 to 183 GHz, as well as visible and infrared data. The remote radar observations reveal the existence of large ice particles within the storms, which is likely to have caused the observed low microwave brightness temperatures. By relating the evolution of the radar measureables to the microwave T(B)s it has been found that knowledge of the storm microphysics and its evolution is important to adequately understand the microwave T(B)s.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Applied Meteorology (ISSN 0894-8763); 30; 98-116
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    Saturation point representation of cloud-top entrainment instability (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Cloud-top entrainment instability was investigated using a mixing line analysis. Mixing time scales are closely related to the actual size of the parcel, so that local instabilities are largely dependent on the scales of mixing near the cloud top. Given a fixed transport velocity, variation over a small range of parcel length scales (parcel mixing velocities) turns an energy-producing mixing process into an energy-consuming mixing process. It is suggested that a single criterion for cloud-top entrainment instability will not be found due to the role of at least three factors operating more or less independently; the stability of the mixing line, the entrainment speed, and the strength of the internal boundary-layer circulation.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 48; 2426-243
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    Simulations of microphysical, radiative, and dynamical processes in a continental-scale forest fire smoke plume (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The impact of a large forest fire smoke plume on atmospheric processes is studied through a numerical model of meteorology, aerosols, and radiative transfer. The simulated smoke optical depths at 0.63-micron wavelength are in agreement with analyses of satellite data and show values as high as 1.8. The smoke has an albedo of 35 percent, or more than double the clear-sky value, and cools the surface by as much as 5 K. An imaginary refractive index, n sub im, of 0.01 yields results which closely match the observed cooling, single scattering albedo, and the Angstrom wavelength exponent. An n exp im of 0.1, typical of smoke from urban fires, produces 9 K cooling. Coagulation causes the geometric mean radius by number to increase from the initial value of 0.08 micron to a final value of 0.15 micron, while the specific extinction and absorption increase by 40 and 25 percent, respectively.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 22
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    Examination of the relationship between outgoing infrared window and total longwave fluxes using satellite data (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The relationship between narrowband and broadband thermal radiances is explored to determine the accuracy of outgoing longwave radiation derived from narrowband data. Infrared window (10.2-12.2 microns) data from the Geostationary Operational Environment Satellite are correlated with longwave (5.0-50.0 microns) data from the Earth Radiation Budget Experiment. A simple quadratic fit between the narrowband and longwave fluxes results in standard errors of 4.4-5.3 percent for data that are matched closely in time and space. The use of matched regional flux data with temporal differences up to 59 minutes yields standard errors of 4.1-5.4 percent. About 30 percent of the error may be attributed to limb darkening and spatial and temporal differences in the matched fluxes. The relationship shows a statistically significant dependence on the relative humidity of the atmosphere above the radiating surface. Although this dependency accounts for only about 1 percent of the standard error, it reduces the monthly mean regional errors by more than 10 percent. Data taken over land produced a relationship slightly different from data taken over water. The differences appear to be primarily due to daytime heating of the land surface.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Climate (ISSN 0894-8755); 4; 1114-113
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    A model for predicting high-temperature fatigue failure of a W/Cu composite (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The material studied, a tungsten-fiber-reinforced, copper-matrix composite, is a candidate material for rocket nozzle liner applications. It was shown that at high temperatures, fatigue cracks initiate and propagate inside the copper matrix through a process of initiation, growth, and coalescence of grain boundary cavities. The ductile tungsten fibers neck and rupture locally after the surrounding matrix fails, and complete failure of the composite then ensues. A simple fatigue life prediction model is presented for the tungsten/copper composite system.
    Keywords: COMPOSITE MATERIALS
    Type: Structural Integrity and Durability of Reusable Space Propulsion Systems; p 207-218
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    An overview of the crash dynamics failure behavior of metal and composite aircraft structures (1991)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: An overview of failure behavior results is presented from some of the crash dynamics research conducted with concepts of aircraft elements and substructure not necessarily designed or optimized for energy absorption or crash loading considerations. Experimental and analytical data are presented that indicate some general trends in the failure behavior of a class of composite structures that includes fuselage panels, individual fuselage sections, fuselage frames, skeleton subfloors with stringers and floor beams without skin covering, and subfloors with skin added to the frame stringer structure. Although the behavior is complex, a strong similarity in the static/dynamic failure behavior among these structures is illustrated through photographs of the experimental results and through analytical data of generic composite structural models.
    Keywords: COMPOSITE MATERIALS
    Type: First NASA Advanced Composites Technology Conference, Part 2; p 1005-1035
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    Evaluation of some scale effects in the response and failure of composite beams (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The feasibility of using scale model testing for predicting full-scale behavior of composite beams loaded in tension and flexure was investigated. Classical laws of similitude were applied to fabricate and test replica model beams to identify scaling effects in the load response, strength, and mode of failure. Experiments were conducted using graphite-epoxy composite beams having different laminate stacking sequences and a range of scaled sizes. Results indicated that the elastic response of scaled composite beams was independent of specimen size. However, a significant scale effect in strength was observed. In addition, a transition in failure mode was observed among scaled beams of certain laminate stacking sequences. Weibull statistical and fracture mechanics based models were applied to predict the strength scale effect since standard failure criteria cannot account for the influence of absolute specimen size in failure.
    Keywords: COMPOSITE MATERIALS
    Type: NASA. Langley Research Center, First NASA Advanced Composites Technology Conference, Part 2; p 979-1003
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    Structural response of bead-stiffened thermoplastic shear webs (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The results of an experimental and analytical study of the structural response and failure characteristics of selected bead-stiffened thermoplastic shear-webs are presented. Results are given for specimens with one stiffeneer, with two stiffeners, and different stiffener geometries. Selected analytical results that were obtained with the Computational Structural Mechanics (CSM) Testbed computer code are presented. Analytical results that describe normal and transverse shear stress are also presented.
    Keywords: COMPOSITE MATERIALS
    Type: First NASA Advanced Composites Technology Conference, Part 2; p 969-977
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    Experimental behavior of graphite-epoxy Y-stiffened specimens loaded in compression (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: An experimental investigation of the behavior of graphite-epoxy Y-stiffened specimens loaded in compression is presented. Experimental results are presented for element specimens with a single stiffener and for panel specimens with three stiffeners. Response and failure characteristics of the specimens are described. Effects of impact damage on structural response for both specimen configurations are also presented. Results indicate that impact location may significantly affect the residual strength of the Y-stiffened specimens. The failure results indicate that the critical failure mode is buckling of the stiffener webs for Y-stiffened element specimens and buckling of both stiffener web and stiffener blade for the Y-stiffened panel specimens.
    Keywords: COMPOSITE MATERIALS
    Type: First NASA Advanced Composites Technology Conference, Part 2; p 953-968
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    Probabilistic composite analysis (1991)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Formal procedures are described which are used to computationally simulate the probabilistic behavior of composite structures. The computational simulation starts with the uncertainties associated with all aspects of a composite structure (constituents, fabrication, assembling, etc.) and encompasses all aspects of composite behavior (micromechanics, macromechanics, combined stress failure, laminate theory, structural response, and tailoring) optimization. Typical cases are included to illustrate the formal procedure for computational simulation. The collective results of the sample cases demonstrate that uncertainties in composite behavior and structural response can be probabilistically quantified.
    Keywords: COMPOSITE MATERIALS
    Type: NASA. Langley Research Center, First NASA Advanced Composites Technology Conference, Part 2; p 891-900
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    Effects of bolt-hole contact on bearing-bypass damage-onset strength (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A combined experimental and analytical study was conducted to investigate the effects of bolt-hole contact on the bearing bypass strength of a graphite-epoxy laminate. Tests were conducted on specimens consisting of 16-ply quasi-isotropic T300/5208 laminates with a centrally located hole. Bearing loads were applied through a clearance-fit steel bolt. Damage onset strength and damage mode were determined for each test case. A finite element procedure was used to calculate the bolt-hole stresses and bolt contact for each test case. A finite element procedure was used to calculate the bolt-hole stresses and bolt contact for each measured damage-onset strength. For the tension bearing-bypass cases tested, the bolt contact half-angle was approximately 60 degrees at damage onset. For compression, the contact angle was 20 degrees as the bypass load increased. A corresponding decrease in the bearing damage onset strength was attributed to the decrease in contact angle which made the bearing loads more severe. Hole boundary stresses were also computed by superimposing stresses for separate bearing and bypass loading. Stresses at the specimen net section were accurately approximated by the superposition procedure. However, the peak bearing stresses had large errors because the bolt contact angles were not represented correctly. For compression, peak bearing stress errors of nearly 50 percent were calculated.
    Keywords: COMPOSITE MATERIALS
    Type: First NASA Advanced Composites Technology Conference, Part 2; p 921-937
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    Multiple methods integration for structural mechanics analysis and design (1991)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: A new research area of multiple methods integration is proposed for joining diverse methods of structural mechanics analysis which interact with one another. Three categories of multiple methods are defined: those in which a physical interface are well defined; those in which a physical interface is not well-defined, but selected; and those in which the interface is a mathematical transformation. Two fundamental integration procedures are presented that can be extended to integrate various methods (e.g., finite elements, Rayleigh Ritz, Galerkin, and integral methods) with one another. Since the finite element method will likely be the major method to be integrated, its enhanced robustness under element distortion is also examined and a new robust shell element is demonstrated.
    Keywords: COMPOSITE MATERIALS
    Type: First NASA Advanced Composites Technology Conference, Part 2; p 875-889
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    Progressive failure methodologies for predicting residual strength and life of laminated composites (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Two progressive failure methodologies currently under development by the Mechanics of Materials Branch at NASA Langley Research Center are discussed. The damage tolerance/fail safety methodology developed by O'Brien is an engineering approach to ensuring adequate durability and damage tolerance by treating only delamination onset and the subsequent delamination accumulation through the laminate thickness. The continuum damage model developed by Allen and Harris employs continuum damage laws to predict laminate strength and life. The philosophy, mechanics framework, and current implementation status of each methodology are presented.
    Keywords: COMPOSITE MATERIALS
    Type: First NASA Advanced Composites Technology Conference, Part 2; p 843-873
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