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At least 919 records · Page 51
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NASA NTRS1985

Ultraviolet absorption by highly ionized halo gas near the Galactic center

Initial results are presented for a program to survey highly ionized gas in the Milky Way disk and halo. High-resolution IUE (International Ultraviolet Explorer) far-UV spectra were obtained for 12 stars at galactocentric distances less than 6 kpc. The stars are 0.7-2.2 kpc away from the plane. Most of the spectra contain exceedingly strong and broad interstellar absorption lines of weakly and highly ionized atoms. In addition to the normally strong lines of Si IV and C IV, strong interstellar NV lines have been detected in the spectra of eight stars. The detection of NV absorption (amounting to more than 10 times the predicted NV) provides an important new constraint on models for the origin of Galactic halo gas. A Galactic fountain operating in the presence of known UV and EUV radiation might explain the observations.

Savage, B. D.↗
NASA NTRS1985

In-flight evaluation of pure time delays in pitch and roll

An in-flight investigation of the effect of pure time delays in pitch and roll was undertaken. The evaluation tasks consisted of low lift-to-drag-ratio landings of various levels of difficulty and formation flying. The results indicate that the effect of time delay is strongly dependent on the task. In the pitch axis, in calm air, spot landings from a lateral offset were most strongly influenced by time delay. In the roll axis, in calm air, formation flying was most strongly influenced by time delay. However, when landings were made in turbulence, flying qualities in pitch were only slightly degraded, whereas in roll they were severely degraded.

Berry, D. T.↗
NASA NTRS1985

Lightning on Venus

On the night side of Venus, the plasma wave instrument on the Pioneer-Venus Orbiter frequently detects strong and impulsive low-frequency noise bursts when the local magnetic field is strong and steady and when the field is oriented to point down to the ionosphere. The signals have characteristics of lightning whistlers, and an attempt was made to identify the sources by tracing rays along the B-field from the Orbiter down toward the surface. An extensive data set strongly indicates a clustering of lightning sources near the Beta and Phoebe Regios, with additional significant clustering near the Atla Regio at the eastern edge of Aphrodite Terra. These results suggest that there are localized lightning sources at or near the planetary surface.

Scarf, F. L.↗
NASA NTRS1985

High Resolution Spectrometry of Leaf and Canopy Chemistry for Biochemical Cycling

High-resolution laboratory spectrophotometer and Airborne Imaging Spectrometer (AIS) data were used to analyze forest leaf and canopy chemistry. Fundamental stretching frequencies of organic bonds in the visible, near infrared and short-wave infrared are indicative of concentrations and total content of nitrogen, phosphorous, starch and sugar. Laboratory spectrophotometer measurements showed very strong negative correlations with nitrogen (measured using wet chemistry) in the visible wavelengths. Strong correlations with green wet canopy weight in the atmospheric water absorption windows were observed in the AIS data. A fairly strong negative correlation between the AIS data at 1500 nm and total nitrogen and nitrogen concentration was evident. This relationship corresponds very closely to protein absorption features near 1500 nm.

Spanner, M. A.↗
NASA NTRS1985

Interannual variability of middle atmosphere during northern winter

An investigation was undertaken to examine the characteristics of the interannual variability of the zonal wind and the temperature of the middle atmosphere of the Northern Hemisphere during winter and to search for a relationship of the variability of the middle atmosphere with the activity of the following Indian summer monsoon. For this purpose, the rocketsonde temperature and wind data for 8 stations for a 6-year period for the month of January were collected. It is clear from the results that the interannual variability noticed in the zonal wind of the high latitude middle atmosphere was caused by the differential activity of the long-period planetary waves. In order to examine whether the stability of the polar night jet in the high latitude middle atmosphere has any influence on the spectacular tropospheric weather phenomenon such as the Indian summer monsoon, the rainfall activity for India has been studied. The study revealed that: (1) the strong and stable polar night jet with weak equator to pole temperature gradient at the stratopause in January was linked with the forthcoming weak monsoon activity; and (2) the weak and distorted polar night jet with strong equator-to-pole temperature gradient at the stratopause in January was linked with the forthcoming strong monsoon activity.

Mukherjee, B. K.↗
NASA NTRS1986

Self-consistent modelling of the polar thermosphere and ionosphere to magnetospheric convection and precipitation (invited review)

It has recently been demonstrated that the dramatic effects of plasma precipitation and convection on the composition and dynamics of the polar thermosphere and ionosphere include a number of strong interactive, or feedback, processes. To aid the evaluation of these feedback processes, a joint three dimensional time dependent global model of the Earth's thermosphere and ionosphere was developed in a collaboration between University College London and Sheffield University. This model includes self consistent coupling between the thermosphere and the ionosphere in the polar regions. Some of the major features in the polar ionosphere, which the initial simulations indicate are due to the strong coupling of ions and neutrals in the presence of strong electric fields and energetic electron precipitation are reviewed. The model is also able to simulate seasonal and Universal time variations in the polar thermosphere and ionospheric regions which are due to the variations of solar photoionization in specific geomagnetic regions such as the cusp and polar cap.

Rees, D.↗
NASA NTRS1985

CO detections and IRAS observations of bright radio spiral galaxies at cz equal or less than 9000 kilometers per second

CO emission has been detected from 20 of 21 bright radio spirals with strong extended nuclear sources, including the most distant (NGC 7674) and the most luminous (IC 4553 = Arp 220, NGC 6240) galaxies yet detected in CO. All of these galaxies are rich in molecular gas, with M total(H2) = 3 x 10 to the 8th - 2 x 10 to the 10th solar masses. IRAS observations show that they have a strong far-infrared (FIR) excess, with L(FIR)/L(B) approximately equal to 1-35 and L(FIR) (40-400 microns) approximately equal to 10 to the 10th - 10 to the 12th L solar masses. The primary luminosity source for these radio cores appears to be star formation in molecular clouds. A strong correlation is found between the FIR and extended 21 cm continuum flux, implying that the fraction of massive stars formed is independent of the star formation rate. The ratio L(FIR)/M(H2) provides a measure of the current rate of star formation, which is found to be a factor 3-20 larger in these galaxies than for the ensemble of molecular clouds in the Milky Way. At these rates their molecular gas will be depleted in about 10 to the 8th yr.

Sanders, D. B.↗
NASA NTRS1985

Review of recent laboratory double layer experiments

Recent laboratory measurements of double layers are reviewed. Most experiments that are considered employed triple plasma devices or Q-machines. It is shown that a variety of both one and three dimensional phenomena have been achieved. Stationary one and three dimensional structures consist of monotonic double layers, very weak, weak, strong and very strong double layers with potential steps e(phi)/T(e) equal to about 1, less than, greater than, and much greater than 10, respectively. Multiple double layers consist of structures with large potential dips on the low potential side and stairstep double layers. Two and three dimensional structures include multiple double layers, which resemble U shaped double layers, and ionization produced strong double layers. Moving double layers include ion acoustic double layers and double layers which are the result of drifting species and mismatches at plasma boundaries. It appears that double layers can be BGK solutions or related to turbulence. Double layer creation can occur in a variety of different ways. Ionization can sometimes be important and sometimes play no role at all.

Hershkowitz, N.↗
NASA NTRS1985

An evaluation and comparison of vertical profile data from the VISSR Atmospheric Sounder (VAS)

A statistical evaluation is used to compared vertical profiles of temperature and moisture derived from VISSR Atmospheric Sounder (VAS) with three different algorithms to that of corresponding rawinsonde measurements for a clear cold environment. To account for time and space discrepancies between the data sets, rawinsonde data were adjusted to be representative of the satellite sounding times. Both rawinsonde and satellite sounding data were objectively analyzed onto a mesoscale grid. These grid point values were compared at 50 mb pressure increments from the surface up to 100 mb. The data were analyzed for horizontal and vertical structure, representatives of derived parameters, and significant departure (improvement) from the apriori (first guess) information. Results indicate some rather strong temperature and moisture biases exist in the satellite soundings. Temperature biases of 1 to 4 C and dewpoint biases of 2 to 6 C generally occur in layers where strong inversions are present and vary with time as these atmospheric features evolve. The biases also changes as a function retrieval scheme suggesting limitations and restrictions on the applications of the various techniques. Standard temperature deviations range from 1 to 2 C for each retrieval scheme with maximum values around 800 and 400 mb. Derived parameters (precipitable water and thickness) suffer from similar biases, though to a somewhat lesser extent. Gradients of basic and derived parameters are generally weaker but have good horizontal structure where magnitudes of the parameters are relatively strong. Integrated thermal (temperature) and moisture (precipitable water) parameters show mixed results.

Jedlovec, G. J.↗
NASA NTRS1986

Evolution of the net surface shortwave radiation over the Indian Ocean during summer MONEX (1979) - A satellite description

The evolution of the net shortwave (NSW) radiation fields during the monsoon of 1979 was analyzed, using geostationary satellite data, collected before, during, and after the monsoon onset. It is seen, from the time sequence of NSW fields, that during the preonset phase the characteristics of the NSW field are dominated by a strong maximum in the entire Arabian Sea and by a strong minimum in the central and eastern equatorial Indian Ocean, the minimum being associated with the intense convective activity occurring in that region. As the season evolves, the minima of NSW associated with the large scale convective activity propagate westward in the equatorial ocean. During the monsoon onset, there occurs an explosive onset of the convection activity in the Arabian Sea: the maximum has retreated towards the Somalia coast, and most of the sea then experiences a strong minimum of NSW associated with the intense precipitation occurring along the southwestern coast of the Indian subcontinent.

Gautier, C.↗
NASA NTRS1986

Observations of neutral atoms in the Rho Ophiuchi cloud

New observations of lines from neutral atoms in the lines of sight to three stars in the Rho Oph cloud are combined with literature data to look for evidence of density-enhanced regions with higher elemental depletions than those characterizing the cloud as a whole. The depletions inferred from neutral species, however, are comparable to those measured directly from observations of ions, suggesting that no strong density enhancements exist in the observed lines of sight. This conclusion is supported by electron densities derived from the observed ionization fractions, which also show no evidence for a strong variation of density with depth in the cloud. It appears that the overall density (and overall level of depletion) in the cloud is higher than in typical diffuse clouds, despite the apparent lack of strong condensations with enhanced relative depletions.

Snow, T. P.↗
NASA NTRS1986

High-pressure ruby and diamond fluorescence - Observations at 0.21 to 0.55 terapascal

A diamond-anvil, high-pressure apparatus was used to extend the upper pressure limit of static laboratory experiments. Shifts of the R1 strong fluorescent line of ruby were observed that correspond to static pressures of 0.21 to 0.55 terapascal (2.1 to 5.5 megabars) at 25 C. Sensitive spectroscopic techniques in the pressure range 0.15 to 0.28 terapascal were used to observe ruby and diamond fluorescence separately; these two fluorescent emissions overlap strongly at high pressures. At pressures greater than approximately 0.28 terapascal, the diamond fluorescence diminished and the ruby fluorescence reappeared strongly. Pressure was determined by extrapolation of the calibrated shift of the ruby R1 line.

Xu, J. A.↗
NASA NTRS1986

Infrared observations of planetary atmospheres

Infrared data was obtained on planetary atmospheres which provides critical information on atmospheric structure, composition, and cloud properties in support of planetary missions such as Voyager and Galileo. Mapping of Jupiter and Saturn in thermal and reflected solar radiation is a high-priority monitoring and exploratory activity. Some of these images of Jupiter are shown. Radiation at 17.8 micrometer probes the upper tropospheric temperature structure where spatial structure bears a strong resemblance to visible and near-infrared reflected sunlight such as at 2.0 micrometer. At 7.8 micrometer, stratospheric temperatures appear to have a three-banded structure, enhancements near the magnetic poles and occasional transient features such as the equatorial filament near the right limb. Clouds or hazes are observed high in the stratosphere looking at wavelengths such as 2.2 micrometer, where gaseous opacity is very strong. Other maps examine cloud properties from thermal radiation not strongly influenced by gaseous opacity and the distribution of condensable gases, such as ammonia. Millimeter and submillimeter filtered radiometric observations were made of Jupiter, Uranus and Neptune via collaborative work. Radiometric observations of Uranus and Neptune at 21 and 32 micrometer were acquired and analyzed as well as grating array spectra in the ranges of 8 to 14 micrometer, 16 to 23 micrometer, and 18 to 32 micrometer. These showed evidence for C2H2 in the stratosphere of Uranus and C2H4 in the stratosphere of Neptune.

Orton, G. S.↗
NASA NTRS1985

Numerical simulation of convective response to mesoscale forcing

A two-dimensional mesoscale model was used to initialize a two-dimensional cloud model with both mesoscale thermodynamic and dynamic information utilized in the initialization. The Mesoscale-cloud mdoel linkage was used to examine differential convective response due to mesoscale variations for the April 24, 1982 Atmospheric Variability Experiment-Vertical Atmospheric Sounder (AVE-VAS), Case 4. On this day both data analyses and mesoscale model simulations indicated strong variations in thermodynamic and dynamic structure across the panhandle of Texas where a moderately strong convective line formed. Using the cloud model, the current research has shown a preferred area for strong convection to occur due to concomitant mesoscale convergence and mesoscale destabilization of the atmosphere.

Mcnider, R. T.↗
NASA NTRS1986

Optical spectroscopy of HH-exciting stars from scattered light continua

Optical spectra of the reflected light continua visible in parts of several Herbig-Haro objects are presented. HH 100 unmistakably scatters the chromospheric spectrum of a strong emission-line T Tau star. HH 48S also reflects a T Tau stellar spectrum, as perhaps do HH 24 and HH 55, but less convincingly. HH 55 reveals photospheric absorption features too, corresponding to an M3.5 T Tau star. The continuum in HH 120 (= CG 30 HH) is unclassifiable while that in HH 46A has dimmed considerably (by a factor of order 20) although, only 7 yr ago, it clearly reflected a strong-line T Tau spectrum. It is concluded that at least some of the stars that excite Herbig-Haro nebulae, even when those stars are not directly visible, pass through a strong-line T Tau phase, and can undergo abrupt and dramatic changes in visual luminosity.

Cohen, M.↗
NASA NTRS1986

Thermal coupling of conjugate ionospheres and the tilt of the earth's magnetic field

The effect of thermal coupling and the tilt of the earth's magnetic field on interhemispheric coupling is investigated, and, due to a longitudinal displacement in the conjugate points, it is found that the tilt significantly effects the upward flow of H(+) flux such that the maximum upward flux can occur several hours before local sunrise. Heating from the conjugate atmosphere, which accompanies solar illumination in one hemisphere, produces electron temperatures 1000 K higher in the dark than in the sunlit hemisphere, and the morning upward H(+) fluxes in the dark ionosphere are as large as the daytime fluxes. A strong symmetry is also noted in the overall behavior of the H(+) fluxes due to the differing day lengths at the conjugate points, which are separated by 15 deg in latitude. Electron temperatures in the conjugate hemispheres are found to be strongly coupled above the F region peaks, though in the vicinity of the peaks near 250 km, the coupling is weak during the day and strong during the night.

Richards, P. G.↗
NASA NTRS1987

Unusual electron distribution functions in the solar wind derived from the Helios plasma experiment - Double-strahl distributions and distributions with an extremely anisotropic core

Electron distribution functions with unusual features, which have been observed on rare occasions in the solar wind by the Helios probes, are presented. Two examples show a strong symmetric bidirectional anisotropy in the energy regime of the halo up to particle energies of 800 eV (double-strahl distributions). Another example shows an unusually strong bidirectional anisotropy in the energy regime of the core (below 150 eV). The infrequently observed double-strahl distributions provide evidence that magnetic field loops can exist in the solar wind where electrons are trapped. In addition, they provide evidence that in the case of electrons trapped in closed magnetic field structures the break in the energy spectrum separating the core from the halo is produced only by collisions. On the other hand, the class of distribution functions with strongly anisotropic cores indicates that in the case of 'open' magnetic field lines the break between core and halo is largely determined both by the interplanetary electrostatic potential and by collisions.

Pilipp, W. G.↗
NASA NTRS1987

The effects of interactions on spiral galaxies. II - Disk star-formation rates

H-alpha emission-line and IRAS far-IR observations of interacting spiral and irregular galaxies are here used to assess the influence of interactions on their global star-formation rates. Two samples of interacting galaxies were observed: a complete sample of close pairs, and an Arp atlas sample of peculiar systems. When compared to a control sample of single galaxies, both samples of interacting systems exhibit systematically higher levels of H-alpha and infrared emission on average, and a larger dispersion in emission properties. Emission levels in the very active system are much more strongly correlated with the properties of the interaction than with the internal properties of the galaxies themselves. Strong disk emission is almost always accompanied by unusually strong nuclear activity. Simple star-formation burst models can reproduce the observed H-alpha equivalent widths and broadband colors of most of the galaxies. The bursts are relatively short (few times 10 million yr) and rarely involve more than 1-2 percent of a galaxy's total mass.

Kennicutt, Robert C., Jr.↗