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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 433 records · Page 24
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NASA NTRS1985

Satellite observations of sea ice

An overview is presented of Antarctic and Arctic sea ice studies using data from the Nimbus-5 ESMR and the Nimbus-7 SMMR passive microwave radiometers. Four years (1973-1976) of ESMR data for the Antarctic Ocean define the characteristics of the seasonal cycle including regional contrasts and interannual variations. Major advances include the discovery of the Weddell polynya and the presence of substantial areas of open water in the Antarctic winter pack ice. Regional differences in sea ice extent on time-scales of about a month are shown to be associated with variations in surface-wind fields. In the Arctic, the computation of sea ice concentration is complicated by the presence of multiyear ice, but the amount of multiyear ice becomes an important measurable quantity with dual-polarized, multifrequency passive microwave sensors. Analysis of SMMR data demonstrates its advantage for studying the spatial and temporal variability of the Arctic ice cover. Large observed interannual variations in the distribution of the multiyear pack ice and the presence of significant divergent areas in the central Arctic during winter contrast markedly with the classical view of the Arctic pack ice.

Cavalieri, D. J.↗
NASA NTRS1985

Recent results on the Venus atmosphere from Pioneer Venus radio occultations

Temperature structure of the Venus atmosphere was derived from radio occultation data collected by the Pioneer Venus spacecraft during seven occultation seasons in the 1978-1983 period. The measurements, which cover latitudes from both poles to the equator from 40 km to 85 km altitudes, show a latitudinal dependence. At latitudes below 45 deg, there is a smooth temperature transition from the troposphere to the mesosphere. Between 60 and 80 deg, in the 'collar cloud' region, a strong temperature inversion (up to 30 K) appears, which disappears again in the polar areas (80-90 deg), where the mesosphere becomes isothermal without inversion. This temperature behavior is related to the persistent circulation pattern, in which a zonal retrograde motion below 45 deg changes gradually to a circumpolar vortex at the 'collar cloud'. A considerable temporal variability was observed in the thermal structure above the tropopause, suggesting a weather-like variability in the persistent circulation pattern.

Kliore, A. J.↗
NASA NTRS1986

New interstellar masers in nonmetastable ammonia

The first astronomical detections of several ammonia inversion transitions involving nonmetastable levels with energies as high as 1090 K above the ground state are reported. The (J, K) = (9, 6) inversion transition shows maser-like emission in the directions of W51, NGC 7538, W49, and DR 21(OH). The NH3 (6, 3) line exhibits similar characteristics in W51 but is seen in absorption in NGC 7538. These are the first definite detections of ammonia masers in space. The intensities and narrow line widths (0.5-1.5 km/s) for the emission features are in contrast to the previously detected broad, weak, nonmetastable lines attributed to thermal emission in these sources. Temporal variability appears to be evident in the (9, 6) emission in W49 over a 4 month period. The highly excited (J, K) = (9, 6) and (6, 3) ammonia lines are found in regions containig compact H II regions and strongly infrared sources with associated H2O and OH masers; i.e., in regions of active star formation.

Madden, S. C.↗
NASA NTRS1986

Multiple scattering depolarization in marine stratus clouds: Lidar experiments

The depolarization of ruby lidar backscattering caused by multiple scattering in marine stratus clouds was examined systematically from a field site on the southern California coast. Investigated were the effects on the linear depolarization (delta) of lidar receiver field of view (FOV), elevation angle and laser beam pointing errors. An approximately linear increase in maximum delta values was observed with increasing receiver FOV, and the importance of accurate transmitter/receiver beam alignment was demonstrated during experiments in which the laser axis was deliberately misaligned. An elevation angle dependence to the delta values was observed as a consequence of the natural vertical inhomogeneity of water cloud content above the cloud base. Time histories of the depolarization characteristics of dissipating stratus clouds revealed significant spatial and temporal variability in delta values attributed to cloud composition variations. Employing a 1 mrad transmitter FOV, maximum delta values of 0.21 nd 0.33 were observed with 1 and 3 mrad receiver FOVs, respectively, from the low stratus clouds. The fundamental causes and effects on the lidar equation of multiple scattering are also discussed.

Sassen, K.↗
NASA NTRS1985

Studies of humid continental haze during SPACE

A concept for a solar radiometer network to provide supporting data during the Satellite Preciptiation and Cloud Experiment (SPACE) was developed. Each of the 9 prime and 10 supplementary SPACE ground sites will be equipped with an upward pointing global solar pyranometer. About half of the sites will also be equipped with upward pointing diffuse (shade ring) solar pyranometers, and a downward pointing global albedo pyranometer. These radiometers will be used to monitor the spatial and temporal variability of solar insolation and haze optical depth. The insolation data will ultimately be input to numerical models of the pre-storm and near-storm boundary layer. The optical depth data will be compared with simultaneous measurements from airborne and satellite-based passive visible radiometers and airborne lidars.

Bowdle, D. A.↗
NASA NTRS1986

Thermal infrared imaging of Comet Halley

Thermal infrared images (10.8, 12.8, and 19.2 microns) of comet Halley were obtained on 1986 Mar. 28.7, 29.7 and 30.7 UT using the NASA-MSFC 20-pixel bolometer array at the NASA Infrared Telescope Facility. Analysis of the observations shows: the presence of spatial structure indicative of dust ejection occurring mainly on the sunward side of the nucleus; a dust coma deficient in large particles (radius greater than 100 microns) compared with that of Comet P/Giacobini-Zinner, temporal variability consistent with an extrapolation of a quasi-sinusoidal light curve observed by IUE on 1986 March 23, 24, and 25; and a maximum at the nuclear condensation of the color temperature and the strength of the silicate emission feature.

Campins, H.↗
NASA NTRS1986

Ultraviolet observations of Be stars. II - Superionization in Be stars of different spectral types

The results of an investigation of the dependence of the strength/presence of lines from superionized species (N V, C IV, Si IV) on spectral type and v sin i in the ultraviolet spectra of Be stars are presented. No evidence is found for N V in stars later than B2; this apparent absence may, however, simply reflect problems with the IUE reduction procedure. The C IV and Si IV lines pervade the ultraviolet spectra of all B subtypes, with a trend toward increasing strength with increasing effective temperature. A similar trend in the 'edge velocity' of the feature with spectral type is found. The data also suggest a possible trend toward the presence of stronger C IV and a higher edge velocity in stars with larger values of v sin i. The observed temporal variability in N V, C IV, and Si IV in some Be stars is discussed.

Marlborough, J. M.↗
NASA NTRS1987

Simultaneous field measurements of biogenic emissions of nitric oxide and nitrous oxide

Seasonal and diurnal emissions of NO and N2O from agricultural sites in Jamestown, Virginia and Boulder, Colorado are estimated in terms of soil temperature; percent moisture; and exchangeable nitrate, nitrite, and ammonium concentrations. The techniques and procedures used to analyze the soil parameters are described. The spatial and temporal variability of the NO and N2O emissions is studied. A correlation between NO fluxes in the Virginia sample and nitrate concentration, temperature, and percent moisture is detected, and NO fluxes for the Colorado site correspond with temperature and moisture. It is observed that the N2O emissions are only present when percent moisture approaches or exceeds the field capacity of the soil. The data suggest that NO is produced primarily by nitrification in aerobic soils, and N2O is formed by denitrification in anaerobic soils.

Anderson, Iris Cofman↗
NASA NTRS1987

Chemistry of the global troposphere - Fluorocarbons as tracers of air motion

Winds and convective mixing from a general circulation model of the atmosphere have been applied in a chemical tracer model (CTM) to simulate the global distribution and temporal variability of chlorofluorocarbons (CFCs). The seasonal cycle in moist convection, with maximum activity over continents in summer, leads to an annual cycle in the surface concentration of CFCs. Emissions are retained in the lowest levels of the atmosphere during winter, and surface concentrations peak near sources. In this season, CFCs from European sources are carried by low-level winds into the Arctic. During summer, vertical exchange is more efficient, and pollutants are transported more rapidly to the middle atmosphere. Consequently, concentrations of CFCs during summer are relatively low near the surface and elevated in the middle troposphere. Time series analysis of data from Adrigole, Ireland, indicates that the model accurately simulates long-range transport of air pollution. The model reproduces global distributions and trends for CFC-11 and CFC-12 observed by the ALE experiment; however, subgrid diffusion must be introduced into the model in order to reproduce the observed interhemispheric gradient. Interhemispheric exchange occurs mainly in the upper tropical troposphere, producing a profile which increases with altitude in the Southern Hemisphere, in agreement with observations. The distribution of CFCs is such that it is necessary to apply important corrections to observations at surface stations in order to derive global distributions.

Prather, Michael↗
NASA NTRS1988

The detection and interpretation of long-term changes in ozone from space

Long-term measurements of backscattered ultraviolet radiances, now being acquired by orbiting monochromators, will provide the basis for seeking trends in atmospheric ozone. The unambiguous detection of ozone trends on decadal time scales demands a data set that is essentially free of instrument drifts. Periodic flights of an ultraviolet monochromator on the space shuttle will provide an independent means of evaluating the long-term stability of identical instruments operating on free-flying satellites. A successful calibration of the free-flying sensors using the shuttle instrument places strict demands on calibration repeatability from one flight to the next. In addition, spatial and temporal variability in cloud cover could pose further complications in carrying out these in-flight calibrations.

Frederick, John E.↗
NASA NTRS1987

Far-field mission planning for nap-of-the-earth flight

In the face of numerically superior hostile forces, deployment of individual vehicles to the right place, at the right time, and the ability to plan missions with less conservatism, will become significant force multipliers. Far-field mission planning is one of the enabling technologies that will facilitate force coordination through management of mission timeline, vehicle survivability and fuel constraints. On-board replanning is required to deal responsively with departures from nominal plan execution that result from imperfect knowledge of and temporal variability in the mission environment. The far-field planning problem is posed as a constrained optimization problem and algorithms and structural organization are proposed for the solution.

Deutsch, Owen L.↗
NASA NTRS1988

Estimating soil wetness using satellite data

Improved estimates of soil wetness were obtained using observations from both the NIMBUS-7 Scanning Multichannel Microwave Radiometer (SMMR) and the NOAA-7 Advanced Very High Resolution Radiometer (AVHRR). SMMR 66 GHz frequency, horizontal polarization, brightness temperature T(BH) was first correlated with soil wetness, as computed using an Antecedent Precipitation Index (API) model, for a number of SMMR ground resolution areas involving a fairly wide range of vegetation densities. The API generally accounted for more than 70 percent of the observed temporal variability in T(BH), with linear correlations being significant at the 1 percent level. The regression slope of T(BH) versus API correlated well, at the 1 percent level, with a vegetation index derived from AVHRR visible and near-infrared observations. The regression intercept was found to correlate less satisfactorily, but was significant at the 5 percent level. These linear regression results were used to develop a diagnostic model for soil wetness using SMMR and AVHRR data only.

Choudhury, Bhaskar J.↗
NASA NTRS1989

Antarctic Ocean polynyas

The spatial and temporal variability of sea ice concentrations derived from Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) brightness temperatures are presented. Emphasis is on the continental shelf region of the Ross Sea during 1984, when supporting data were obtained from oceanographic stations and moored instruments. The effects of the large spring polynya in the Ross Sea on summer insolation, surface heat layer storage, and late autumn ice formation are described.

Jacobs, Stanley S.↗
NASA NTRS1989

Rocket measurements of electron density irregularities during MAC/SINE

Four Super Arcas rockets were launched at the Andoya Rocket Range, Norway, as part of the MAC/SINE campaign to measure electron density irregularities with high spatial resolution in the cold summer polar mesosphere. They were launched as part of two salvos: the turbulent/gravity wave salvo (3 rockets) and the EISCAT/SOUSY radar salvo (one rocket). In both salvos meteorological rockets, measuring temperature and winds, were also launched and the SOUSY radar, located near the launch site, measured mesospheric turbulence. Electron density irregularities and strong gradients were measured by the rocket probes in the region of most intense backscatter observed by the radar. The electron density profiles (8 to 4 on ascent and 4 on descent) show very different characteristics in the peak scattering region and show marked spatial and temporal variability. These data are intercompared and discussed.

Ulwick, J. C.↗
NASA NTRS1988

A Near-Infrared Mapping Spectrometer for investigation of Jupiter and its satellites

The Near-Infrared-Mapping Spectrometer (NIMS) is one of the science instruments in the Galileo mission, which will explore Jupiter and its satellites in the mid-1990's. The NIMS experiment will map geological units on the surfaces of the Jovian satellites and characterize their mineral content; and, for the atmosphere of Jupiter, investigate cloud properties and the spatial and temporal variability of molecular abundances. The optics are gold-coated reflective and consist of a telescope and a grating spectrometer. The balance of the instrument includes a 17-detector (silicon and indium antimonide) focal plane array, a tuning fork chopper, microprocessor-controlled electronics, and a passive radiative cooler. A wobbling secondary mirror in the telescope provides 20 pixels in one dimension of spatial scanning in a pushbroom mode with 0.5 mr x 0.5 mr instantaneous field of view. The spectral range is 0.7-5.2 microns; resolution is 0.025 micron. NIMS is the first infrared experiment to combine both spatial and spectral mapping capability in one instrument.

Aptaker, Irving M.↗
NASA NTRS1989

Airborne infrared spectroscopy of Comet Wilson (1986l) and comparisons with Comet Halley

H2O and possibly CH4 have been detected in near-infrared spectra of Comet Wilson (1986l). The observed number and relative intensities of cometary H2O lines in the nu3 band at 2.65 microns were consistent with fluorescent excitation pumped by solar infrared photons. The H2O production rate in Comet Wilson was approximately 3 x 10 to the 29th/s at R = 1.2 AU; no pronounced temporal variability was observed. Lines in the nu3 band of CH4 at 3.3 microns were possibly detected at the 3 sigma confidence level. The CH4 abundance is in the range CH4/H2O = 0.014-0.045; the uncertainty is due primarily to the assumed effective excitation temperature of CH4. The CH4 abundance in this dynamically 'new' comet is similar to that observed in P/Halley. These values are low for equilibrium compositional models and very high for disequilibrium condensation in the solar nebula.

Larson, Harold P.↗
NASA NTRS1989

Ozone precursors and ozone photochemistry over eastern North Pacific during the spring of 1984 based on the NASA GTE/CITE 1 airborne observations

Simultaneous high-resolution measurements of O3, NO, CO, dew point temperature, and UV flux obtained during the NASA Global Tropospheric Experiment Chemical Instrumentation Test and Evaluation (GTE/CITE 1) spring 1984 airborne field exercise over the eastern North Pacific Ocean are analyzed. Mid-tropospheric CO, O3, and NO mixing ratios averaged about 120 parts per billion by volume (ppbv), 50 ppbv, and 10 parts per trillion by volume (pptv), respectively. Statistical analysis of the high-resolution data indicates the existence of two ozone sources, one related to the downward transport of ozone-rich air from the upper troposphere and stratosphere, and the other to the transport of ozone-rich air from the continents. Modeling calculations based on these average levels imply that, from the surface to about 8 km, photochemical reactions probably supplied a net sink of ozone to the region overlying the eastern North Pacific Ocean during the sampling period. However, because the NO levels measured during the flights were frequently at or near the detection limit of the instruments and because the results are very sensitive to the absolute NO levels and their temporal variability, the conclusion must be considered provisional.

Chameides, W. L.↗
NASA NTRS1989

On the identification of formaldehyde in Halley's comet

The v1 and v5 infrared bands of formaldehyde in Halley's comet have been synthesized, using a line-by-line model for solar infrared fluorescence from low-temperature H2CO. Fully resolved spectra were convolved to spectral resolutions comparable with those used on the IKS spectrometer on the Vega 1 spacecraft. Excellent agreement is obtained between the observed and modeled spectra, permitting a definite identification of H2CO in Halley's comet. The retrieved production rate is 4.5 + or - 0.5 x 10 to the 28th molecules/s, and the rotational temperature is probably less than 150 K, with a best-fit value of about 50 K. Production rates (or upper limits) are also retrieved from ground-based spectra of Comets Halley and Wilson (1986), and it is shown that the production rate of H2CO exhibits significant temporal variability, relative to H2O, in Comet Halley.

Mumma, Michael J.↗