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At least 1,045 records · Page 58

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NASA NTRS1984

Self-deactivation of water vapor - Role of the dimer

A phenomenological multiple-relaxation theory of the deactivation rate constant for the nu-2 (1 - 0) bending mode of water vapor is presented which incorporates the role not only of the excited monomer but also of the bound molecular complex, in particular the dimer. The deactivation takes place by means of three parallel processes: (1) collisional deexcitation of the excited monomer, (2) a two-step reaction involving association and spontaneous redissociation of an H2O collision complex, and (3) spontaneous dissociation of the stably bound H2O dimer. Oxygen, but not nitrogen or argon, serves as an effective chaperon for the formation of the activated complex. This observation explains the impurity dependence of the self-deactivation rate constant of water vapor. Analysis of an ultrasonic absorption peak based on the third process yields values for the standard entropy and enthalpy of dissociation of the stably bound H2O dimer.

Zuckerwar, A. J.↗

NASA NTRS1984

Investigation of light source and scattering medium related to vapor-screen flow visualization in a supersonic wind tunnel

Methods for increasing the radiant in light sheets used for vapor screen set-ups were investigated. Both high-pressure mercury arc lamps and lasers were considered. Pulsed operation of the air-cooled 1-kW lamps increased the light output but decreased reliability. An ellipsoidal mirror improved the output of the air-cooled lamps by concentrating the light but increased the complexity of the housing. Water-cooled-4-kW lamps coupled with high-aperture Fresnel lenses provided reasonable improvements over the air-cooled lamps. Fanned laser beams measurements of scattered light versus dew point made in conjunction with successful attempts to control the fluid injection. A number of smoke generators are described and test results comparing smoke and vapor screens are shown. Finally, one test included a periscope system to relay the image to a camera outside the flow.

Snow, W. L.↗

NASA NTRS1984

Metal vapor arc switch electromagnetic accelerator technology

A multielectrode device housed in an insulator vacuum vessel, the metal vapor vacuum switch has high power capability and can hold off voltages up to the 100 kilovolt level. Such switches can be electronically triggered and can interrupt or commutate at a zero current crossing. The physics of arc initiation, arc conduction, and interruption are examined, including material considerations; inefficiencies; arc modes; magnetic field effects; passive and forced extinction; and voltage recovery. Heating, electrode lifetime, device configuration, and external circuit configuration are discussed. The metal vapor vacuum switch is compared with SCRs, GTOs, spark gaps, ignitrons, and mechanical breakers.

Mongeau, P. P.↗

NASA NTRS1983

Water vapor profile retrievals from the HIRS/MSU sounder

The present physically based water vapor profile retrieval system for the HIRS/MSU sounding instrument is capable of producing accurate atmospheric and surface temperature retrievals, as well as accurate measurements of cloud fields on the basis of radiance values. In order to establish the extent of useful water vapor information in channels 8, 10, 11 and 12 of the HIRS instrument, studies have been conducted in which simultaneous temperature/humidity retrievals were performed on the basis of radiances simulated for clear and cloudy conditions.

Reuter, D.↗

NASA NTRS1984

Vertical displacement of the mid-tropospheric water vapor boundary in the tropics derived from the VISSR Atmospheric Sounder (VAS) 6.7-micron channel

A technique for locating areas of upward or downward motion of the upper boundary of the midtropospheric water-vapor envelope over tropical oceans on the basis of GOES Visible/IR Spin-Scan Radiometer (VISSR) Atmospheric Sounder (VAS) 6.7-micron brightness temperatures is developed and demonstrated. The technique employs an analogy to the method developed by Schoeberl and Krueger (1983) for the bottom of the ozone layer and depends on the relationship investigated by Chesters and Uccellini (1982) between 6.7-micron brightness temperature and the pressure of the water-vapor upper boundary. The results of analysis of VAS data for the North Atlantic (20-40 deg N and 35-75 deg W) on September 5-7, 1982, are presented in maps which are shown to be physically consistent and in agreement with conventional upper-air measurements. Refinement of the method to account for horizontal advection and diffusion is suggested.

Stout, J.↗

NASA NTRS1984

Nimbus 7 SMMR derived seasonal variations in the water vapor, liquid water, and surface winds over the global oceans

A study based on monthly mean maps of atmospheric water vapor, liquid water, and surface wind derived from Nimbus-7 SMMR over the oceans for 13 months, is examined. A discussion of the retrieval technique used to derive the parameters is presented. The seasonal changes in the strength and position of several of the parameter features are revealed by the December 1978 and June 1979 maps. Zonal averages of the water vapor, liquid water, and surface wind for December and June are compared with information derived from conventional measurements and the results are presented in graphs.

Prabhakara, C.↗

NASA NTRS1984

Satellite derived atmosphere water vapor as a tracer of large scale interactions between the atmosphere and ocean

Two water-vapor distributions and the accompanying circulation patterns which occurred over the North and South Atlantic Ocean during February 1979 are described. It is shown that scanning multichannel microwave radiometer observations from the Nimbus-7 satellite are used to remotely sense the vertically integrated atmospheric water vapor and liquid water, and the surface wind speed over the ocean and that they provide information on the ocean-atmosphere interaction. To provide evidence of the events revealed in the satellite observations, FGGE data are used.

Short, D. A.↗

NASA NTRS1985

Noctilucent cloud formation and the effects of water vapor variability on temperatures in the middle atmosphere

To investigate the occurrence of low temperatures and the formation of noctilucent clouds in the summer mesosphere, a one-dimensional time-dependent photochemical-thermal numerical model of the atmosphere between 50 and 120 km has been constructed. The model self-consistently solves the coupled photochemical and thermal equations as perturbation equations from a reference state assumed to be in equilibrium and is used to consider the effect of variability in water vapor in the lower mesosphere on the temperature in the region of noctilucent cloud formation. It is found that change in water vapor from an equilibrium value of 5 ppm at 50 km to a value of 10 ppm, a variation consistent with observations, can produce a roughly 15 K drop in temperature at 82 km. It is suggested that this process may produce weeks of cold temperatures and influence noctilucent cloud formation.

Mckay, C. P.↗

NASA NTRS1985

A new instrument for the determination of radio path delay due to atmospheric water vapor

A new water-vapor radiometer is being developed to determine atmospheric path-delay corrections for geodynamics applications. The radiometer has microwave channels at 20.7, 22.2, and 31.4 GHz, and includes new features which should promote radiometric precision while at the same time reduce instrument complexity. The instrument will be compact, portable, and will possess a self-diagnostic capability to ensure reliability. The performance objective is the determination of the line-of-sight path delay through the atmosphere due to water vapor with a one-sigma error less than 0.5 cm at the zenith.

Janssen, M. A.↗

NASA NTRS1985

Vapor Growth of Alloy-Type Semiconductor Crystals

The present effort is part of a continuing research program directed towards the investigation of basic vapor transport phenomena and of crystal growth properties of electronic materials. The primary purpose of ground-based studies is the development and definition of optimum experimental parameters for flight experiments. The ground-based effort includes the investigation of gravity-driven convection effects on mass transport rates and on crystal morphology for different orientations of the density gradient with respect to the gravity vector, and as a function of pressure and of temperature. In addition to the experimental tasks, theoretical efforts involve the quantitative thermodynamic analysis of the systems under investigation, the computation of fluid dynamic parameters, and the consideration of other possible effects on fluid flow under vertical, stabilizing and microgravity conditions. The specific experiments to be performed in a microgravity environment include the investigation of vapor transport and crystal growth phenomena of the GeSe-Xenon system and of the mass flux and growth of bulk and layer-type crystals of Hg sub (1-x) Cd sub x Te using HgI as a transport agent.

Wiedemeier, H.↗

NASA NTRS1986

Liquid-vapor interface locations in a spheroidal container under low gravity

As a part of the general study of liquid behavior in low gravity environments, an experimental investigation was conducted to determine if there are equilibrium liquid-vapor interface configurations that can exist at more than one location in oblate spheroidal containers under reduced gravity conditions. Static contact angles of the test liquids on the spheroid surface were restricted to near 0 deg. The experiments were conducted in a low gravity environment. An oblate spheroidal tank was tested with an eccentricity of 0.68 and a semimajor axis of 2.0 cm. Both quantitative and qualitative data were obtained on the liquid-vapor interface configuration and position inside the container. The results of these data, and their impat on previous work in this area, are discussed. Of particular interest are those equilibrium interface configurations that can exist at multiple locations in the container.

Carney, M. J.↗

NASA NTRS1986

Senstitivity analysis of horizontal heat and vapor transfer coefficients for a cloud-topped marine boundary layer during cold-air outbreaks

The effects of external parameters on the surface heat and vapor fluxes into the marine atmospheric boundary layer (MABL) during cold-air outbreaks are investigated using the numerical model of Stage and Businger (1981a). These fluxes are nondimensionalized using the horizontal heat (g1) and vapor (g2) transfer coefficient method first suggested by Chou and Atlas (1982) and further formulated by Stage (1983a). In order to simplify the problem, the boundary layer is assumed to be well mixed and horizontally homogeneous, and to have linear shoreline soundings of equivalent potential temperature and mixing ratio. Modifications of initial surface flux estimates, time step limitation, and termination conditions are made to the MABL model to obtain accurate computations. The dependence of g1 and g2 in the cloud topped boundary layer on the external parameters (wind speed, divergence, sea surface temperature, radiative sky temperature, cloud top radiation cooling, and initial shoreline soundings of temperature, and mixing ratio) is studied by a sensitivity analysis, which shows that the uncertainties of horizontal transfer coefficients caused by changes in the parameters are reasonably small.

Chang, Y. V.↗

NASA NTRS1985

20-micron transparency and atmospheric water vapor at the Wyoming Infrared Observatory

The atmospheric transparency at 19.5 and 23 microns from the Wyoming Infrared Observatory over the past six years has been examined. It is found that the transparency is largely controlled by the season. Four months: June, July, August, and September have very poor 20-micron transparency. During the rest of the year the transparency is usually quite good at 19.5 microns and moderately good at 23 microns. Using rawinsonde data and theoretical calculations for the expected infrared transparency, the measures of 20-micron transparency were calibrated in terms of atmospheric water-vapor content. The water vapor over the Wyoming Infrared Observatory is found to compare favorably with that above other proposed or developed sites: Mauna Kea, Mount Graham, and Wheeler Peak.

Grasdalen, G. L.↗

NASA NTRS1985

Turbulent flow model for vapor collection efficiency of a high-purity silicon reactor

In this study a mathematical model and a computer code based on this model was developed to allow prediction of the product distribution in chemical reactors for converting gaseous silicon compounds to condensed-phase silicon. Specifically, the model formulated describes the silicon vapor separation/collection from the developing turbulent flow stream within reactors of the Westinghouse type. Migration of the silicon vapor to the reactor walls was described by the parametric solutions presented here, in order to reduce the experimentation necessary in the design of such reactors. Calculations relating to the collection efficiencies of such reactors are presented as a function of the reactor throughflow and distance along its length.

Srivastava, R.↗

NASA NTRS1985

Shock vaporization and the accretion of the icy satellites of Jupiter and Saturn

The known properties of water and ice over a wide range of pressures and temperatures are applied to describe constraints on the shock vaporization processes for water and ice in the solar system. In particular, the role of impact vaporization acting during the formation of the Jovian and Saturnian satellites is examined in an attempt to explain the observed density in terms of composition of these rock and ice objects. A possible model of accretion of icy satellites is considered which predicts that the amount of ice devolatilization is related to planetary size.

Ahrens, T. J.↗

NASA NTRS1985

Seasonal variability of mesospheric water vapor

Ground-based spectral line measurements of the 22.2 GHz atmospheric water vapor line in emission were made at the JPL in order to obtain data in a dry climate, and to confirm similar measurements made at the Haystack Observatory. The results obtained from March 1984 to July 1984 and from December 1984 to May 1985, were based on data recorded by a HP9816 microcomputer. The instrument spectrometer was a 64 channel, 62.5 kHz resolution filter bank. Data indicates the existence of a seasonal variation in the abundance of water vapor in the upper mesosphere, with mixing ratios higher in summer than in spring. This is consistent with recent theoretical and observational results. In the area of semiannual oscillation, Haystack data are more consistent than those of JPL, indicating an annual cycle with abundances at maximum in summer and minimum in winter.

Schwartz, P. R.↗

NASA NTRS1986

Experimental studies of the vapor phase nucleation of refractory compounds. III - The condensation of silver

Measurements are reported of the critical supersaturation necessary to initiate the vapor phase nucleation of silver over the ambient temperature range 500-950 K at total pressures of 250 and 500 torr of hydrogen. The results are compared with the predictions of both classical nucleation theory and the theory of a physical spinodal developed by Rasmussen (1982), neither of which adequately describes the present observations. The nucleation of silver appears to be dependent on the total pressure of the system in a manner which suggests that three-body reactions are necessary in order to form the initial silver cluster (e.g., dimers) from the monoatomic vapor.

Nuth, J. A.↗

NASA NTRS1986

A new algorithm for microwave delay estimation from water vapor radiometer data

A new algorithm has been developed for the estimation of tropospheric microwave path delays from water vapor radiometer (WVR) data, which does not require site and weather dependent empirical parameters to produce high accuracy. Instead of taking the conventional linear approach, the new algorithm first uses the observables with an emission model to determine an approximate form of the vertical water vapor distribution which is then explicitly integrated to estimate wet path delays, in a second step. The intrinsic accuracy of this algorithm has been examined for two channel WVR data using path delays and stimulated observables computed from archived radiosonde data. It is found that annual RMS errors for a wide range of sites are in the range from 1.3 mm to 2.3 mm, in the absence of clouds. This is comparable to the best overall accuracy obtainable from conventional linear algorithms, which must be tailored to site and weather conditions using large radiosonde data bases. The new algorithm's accuracy and flexibility are indications that it may be a good candidate for almost all WVR data interpretation.

Robinson, S. E.↗