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  • Cell & Developmental Biology  (1,145)
  • General Chemistry  (1,028)
  • Inorganic Chemistry  (693)
  • METEOROLOGY AND CLIMATOLOGY  (623)
  • LUNAR AND PLANETARY EXPLORATION  (613)
  • Niederschlag
  • 1990-1994  (4,102)
  • 1930-1934
  • 1925-1929
  • 1990  (4,102)
Collection
Keywords
Publisher
Years
  • 1990-1994  (4,102)
  • 1930-1934
  • 1925-1929
Year
  • 1
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    Evolution of tropical circulation anomalies associated with 30-60 day oscillation of globally averaged angular momentum during northern summer (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Lag correlation statistics was used to study intraseasonal variations of upper and lower-level zonal winds, outgoing longwave radiation, and globally averaged angular momentum (GAM) for northern summers of 1977-1984. The temporal and spatial distribution of surface wind stress in the tropics and its relationship with zonal wind anomalies were studied to assess the impact of surface frictional drag on the atmospheric angular momentum. The 30-60 day GAM fluctuation is shown to be accompanied by zonal propagation of convection and 850 mb zonal wind anomalies in the tropical belt. The climatological zonal wind in the tropics affects the magnitude of wind stress anomalies. It is suggested that momentum exchange between the lower and upper troposphere may occur in regions of active convection via vertical momentum transport. The tropical central Pacific is considered to play a key role in linking the atmosphere and the earth through angular momentum exchange on intraseasonal time scales.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Meteorological Society of Japan, Journal (ISSN 0026-1165); 68; 237-249
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  • 2
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    Uranus - The planet, rings and satellites (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The present overview of available data regarding Uranus and its planetary structures encompasses ground- and space-based observations of the planet with specific attention given to the interpretation of Voyager 2 data. A brief examination of historical observations is given which includes its discovery, position determination, and the related discoveries of Uranus' five large satellites and rings. The observational data preceding the Voyager 2 mission are reviewed in terms of the planetary interior, atmosphere, and magnetosphere. The Voyager 2 mission is given detailed treatment with descriptions of NASA's development and deployment of the spacecraft as well as detailed data from the Uranus encounter. Reference is given to structure and composition of Uranus' atmosphere, valid models of the interior, and wave-particle interactions in the magnetosphere. The structures of the rings and satellites are examined with reference to specific observational requirements from future missions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 3
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    Tropical Rainfall Measuring Mission (TRMM) project. III - Japan-U.S. collaborative rain observation experiment using an airborne rain radar (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A collaborative rain-observation experiment using an airborne rain radar was conducted between Communications Research Laboratory (CRL) and Goddard Space Flight Center (GSFC)/NASA. CRL provided an airborne rain-radar/radiometer system and GSFC/NASA provided a NASA P3-A aircraft. Airborne or spaceborne rain-radar echoes have large sea or land-surface echoes. These surface echoes yield rain-estimation algorithms using rain attenuation. The experiment demonstrated the potential of the rain-estimation techniques using rain attenuation.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Communications Research Laboratory, Review (ISSN 0914-9279); 36; 11, J; 35-44
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  • 4
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    Mars Observer's global mapping mission (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The objectives of the Mars Observer global mapping mission are to determine the global elemental and mineralogical character of the Martian surface material, define globally the topography and gravitational field of Mars, establish the nature of Mars's magnetic field, determine the time and space distribution, abundance, sources, and sinks of volatile Martian material and dust over a seasonal cycle, and explore the structure and aspects of the circulation of the Martian atmosphere. The experiments and instruments to be used in this mission are described, and the operations and data analysis are briefly considered.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: EOS (ISSN 0096-3941); 71; 1099
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  • 5
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    Tropical Rainfall Measuring Mission (TRMM) project. V - Scientific background and goals of TRMM (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The scientific goals of TRMM are described. TRMM provides quantitative measurements of tropical rain which can improve the understanding of the global climate. TRMM can also help to improve techniques for measuring rainfall from space.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Communications Research Laboratory, Review (ISSN 0914-9279); 36; 11, J; 57-70
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  • 6
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    Small-scale plasma, magnetic, and neutral density fluctuations in the nightside Venus atmosphere (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The evolution of the Venus small-scale waves as they propagate into the nightsite is examined, and the small-scale structures are compared with the waves in the three components of the magnetic field, magnetic dip angle, and neutral density. It is demonstrated that the small-scale fluctuations evolve between the transterminator and antisolar regions. It is shown that atmospheric gravity waves may also be producing some of the fluctuations observed at longer wavelengths. The electron temperature and density are shown to be approximately 180 deg out of phase and exhibiting the highest correlation of any pair of variables. Waves in the electron and neutral densities are found to be correlated moderately on most orbits, while the average electron temperature is higher when the average magnetic field is more horizontal.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 4085-410
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  • 7
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    Remote sensing of surface turbulence heat flux (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The determination of latent heat-flux variability using spaceborne sensors is discussed. Particular attention is given to the microwave sensors which have all weather capability. The retrieval of surface layer humidity, of wind speed and interfacial humidity, and of sensible heat flux are discussed. Both the indirect retrieval and direct retrieval of latent heat flux are considered.
    Keywords: METEOROLOGY AND CLIMATOLOGY
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  • 8
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    Comment on 'Update on terrestrial ages of Antarctic meteorites' by K. Nishiizumi, D. Elmore and P. W. Kubik (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Earth and Planetary Science Letters (ISSN 0012-821X); 99; 4, Se; 380-382;
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  • 9
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    Geochemistry and genesis of the angrites (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The major and trace elements were analyzed in samples of LEW86010, LEW87051, and Angra dos Reis angrites were analyzed using INAA and fused-bead EMP techniques. Results suggest that all three angrites originated on a volatile-depleted (Na-poor) but oxidized parent body or on several bodies. The combination of low Na and high FeO/MnO found in these samples suggests that the extreme Na depletion was caused by parent-body outgassing during differentiation, rather than by nebular processes. It was also found that the refractory-element abundances observed in LEW86010 and LEW87051 are related via olivine control; it is suggested that LEW86010 may be a residual melt from a LEW87051-like precursor or that LEW87051 formed from a LEW86010-like precursor via olivine accumulation. On the other hand, the Angra dos Reis displayed an unusual refractory element pattern suggesting that either the angrite parent body was heterogeneous or that Angra dos Reis was formed on a parent body different from that of the other two angrites.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 54; 3209-321
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  • 10
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    Zonal motion and structure in Jupiter's upper troposphere from Voyager infrared and imaging observations (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Global digital maps of Jupiter's upper-tropospheric temperature have been generated at the 270- and 150-mb pressure levels, together with IR cloud optical depths at 5 and 45 microns and the ammonia abundance near the 680-mb pressure level, on the basis of Voyager IRIS north-south mapping sequences. Attention is given to the 270-mb and 45 micron data; global digital maps are presented for violet and orange reflectivities. The dominant upper tropospheric thermal structures move at a rate far different from that of the cloud indicators, and are noted to remain stationary relative to the planet's bulk rotation. Strong stationary features are found at a zonal wavenumber of 9 near 15 deg N latitude and of 11 near 20 deg latitude.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 88; 39-72
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  • 11
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    Tidal disruption of solid bodies (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The problem of stress, strain, and breakup in solid satellites and stray bodies subject to tidal perturbations is presently addressed in view of three novel considerations. After presenting a new analytic solution for the stress tensor in a homogeneous and compressible elastic sphere, where the inclusion of compressibility alters stresses by several percent, realistic failure criteria are noted to demonstrate the general failure of such ductile bodies as iron meteoroids by plastic shear, while brittle ice bodies fail by either tensile or shear fracture. A reexamination of crack propagation after initial failure allows the diverse breakup criteria to be reconciled.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 88; 24-38
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  • 12
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    Cloud-tracked winds from Pioneer Venus OCPP images (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Results are presented on the analysis of the Pioneer Venus Orbiter Cloud Photopolarimeter (OCPP) UV images, covering 80-day periods from 1979 to 1985. The analysis provides a method for determining wind speeds at the cloud level, from the motions of cloud UV features. Data used for tracking the cloud feature motions are described along with the analysis method. The results identified four wave modes: a diurnal solar tide, a semidiurnal solar tide, a '4-day equatorial' wave, and a '5-day midlatitude' wave. The features of these wave modes are described.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 47; 2053-208
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  • 13
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    (Ar-39)-(Ar-40) dating of mesosiderites - Evidence for major parent body disruption less than 4 Ga ago (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The (Ar-39) (Ar-40) chronologies were determined for 14 different mesosiderites representing the full range of classification according to recrystallization, and these chronologies were compared with analogous data for other meteorite types and for lunar highland rocks. Results of Ar-Ar chronologies indicate the history of a degassing of Ar due to a major thermal event that occurred less than 3.9 Ga ago; this event is not the metal-silicate mixing event, which is known to have occurred earlier than 4.4 Ga ago. It is suggested that a major collisional disruption-reassembly event less than 3.9 Ga ago took place, leaving the metal-silicate breccias buried under tens of kilometers of rubble, where they cooled slowly through the Ar closure temperatures.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 54; 2549-256
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  • 14
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    Inter- and intra-group compositional variations in Apollo 15 pyroclastic green glass - An electron- and ion-microprobe study (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Results are presented on major- and trace-element abundance analyses of Apollo 15 pyroclastic green glasses from groups A, B, C, D, and E, carried out using electron- and ion-microprobe techniques. The diagrams depicting Sr, Zr, Ba, and Nd vs Co variations indicate the presence of a high-Co trend in groups A and D and a low-Co trend in groups B and C. Group-E glasses were found to be significantly enriched in Sr, relative to the other four glass groups. Chemical data of this study were integrated with previous data to evaluate various magmatic processes that have been proposed in the past to explain chemical variations in the lunar green glass. Results of calculations using a source mixing model suggest that the Apollo 15 green glasses represent multiple eruptive events from three chemically distinct but compositionally variable source regions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 54; 2565-257
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  • 15
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    Evolution of tropical plumes in VAS water vapor imagery (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Synoptic scale tropical plumes are analyzed using satellite data and outgoing longwave radiation data. The evolution of plumes is described and their precursor signals are examined. The horizontal moisture patterns of the plumes are compared with nonplume climatology, and the predictability of plumes based solely on satellite imagery is assessed. The results show that a plume evolves as a stationary, tropical, dry or moist dipole, separated by an exceptionally strong cloud or moisture gradient. Tropical plume evolution is accompanied by a systematic drying of the tropical eastern Pacific atmosphere before development, and moistening and increased cloudiness with development.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 118; 1758-176
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  • 16
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    Energy sources for Triton's geyser-like plumes (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Four geyser-like plumes were discovered near Triton's south pole in areas now in permanent sunlight. Because Triton's southern hemisphere is nearing a maximum summer solstice, insolation as a driver or a trigger for Triton's geyser-like plumes is an attractive hypothesis. Trapping of solar radiation in a translucent, low-conductivity surface layer (in a solid-state greenhouse), which is subsequently released in the form of latent heat of sublimation, could provide the required energy. Both the classical solid-state greenhouse consisting of exponentially absorbed insolation in a gray, translucent layer of solid nitrogen, and the 'super' greenhouse consisting of a relatively transparent solid-nitrogen layer over an opaque, absorbing layer are plausible candidates. Geothermal heat may also play a part if assisted by the added energy input of seasonal cycles of insolation.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 250; 431-435
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  • 17
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    Temperature and thermal emissivity of the surface of Neptune's satellite Triton (1990)
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    Publication Date: 2011-08-19
    Description: Analysis of the preliminary results from the Voyager mission to the Neptune system has provided the scientific community with several methods by which the temperature of Neptune's satellite Triton may be determined. If the 37.5 K surface temperature reported by several Voyager investigations is correct, then the photometry reported by the imaging experiment on Voyager requires that Triton's surface have a remarkably low emissivity. Such a low emissivity is not required in order to explain the photometry from the photopolarimeter experiment on Voyager. A low emissivity would be inconsistent with Triton having a rough surface at the about 100-micron scale as might be expected given the active renewal processes which appear to dominate Triton's surface.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 250; 429-431
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  • 18
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    Subsurface energy storage and transport for solar-powered geysers on Triton (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The location of active geyser-like eruptions and related features close to the current subsolar latitude on Triton suggests a solar energy source for these phenomena. Solid-state greenhouse calculations have shown that sunlight can generate substantially elevated subsurface temperatures. A variety of models for the storage of solar energy in a subgreenhouse layer and for the supply of gas and energy to a geyser are examined. 'Leaky greenhouse' models with only vertical gas transport are inconsistent with the observed upper limit on geyser radius of about 1.5 km. However, lateral transport of energy by gas flow in a porous N2 layer with a block size on the order of a meter can supply the required amount of gas to a source region about 1 km in radius. The decline of gas output to steady state may occur over a period comparable with the inferred active geyser lifetime of 5 earth years. The required subsurface permeability may be maintained by thermal fracturing of the residual N2 polar cap. A lower limit on geyser source radius of about 50 to 100 m predicted by a theory of negatively buoyant jets is not readily attained.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 250; 424-429
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  • 19
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    Triton's geyser-like plumes - Discovery and basic characterization (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: One model for the mechanism driving the plumes of the four active geyser-like eruptions observed by Voyager 2 on Triton is a heating up of nitrogen ice in a subsurface greenhouse environment, where nitrogen gas pressurized by solar heating explosively vents to the surface carrying clouds of ice and dark particles into the atmosphere. A temperature increase of less than 4 K above the ambient surface value of 38 + or - 3 K suffices to drive the plumes to 8-km altitude. Each eruption may last a year or more, over the course of which 0.1 cu km of ice is sublimed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 250; 410-415
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  • 20
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    Satellite observations of instability in the middle atmosphere (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Data from the Limb Infrared Monitor of the Stratosphere (LIMS) have been used to define zonally averaged basic-state temperature and zonal wind fields in the middle atmosphere for several periods during the winter of 1978-79. This basic state has been used to calculate the phase speeds, growth rates, and spatial structures of unstable modes using a linear, quasigeostrophic model. These results have been compared with temperature and ozone variance amplitudes from a spectral analysis of the same LIMS data. The comparison indicates that there is a close match between phase speeds for the most rapidly growing modes predicted by the model and phase speeds for statistically significant temperature and ozone variances. Both calculated and observed modes tend to be limited in latitudinal extent to a few tens of degrees and in vertical extent to about 10 km. These modes also tend to be nondispersive. Examples are given for the Southern Hemisphere near 0.25 mb (60 km) and for low latitudes of the Northern Hemisphere near 15 mb (30 km).
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 47; 1065-107
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  • 21
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    Magellan orbits Venus (1990)
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    Publication Date: 2011-08-19
    Description: Various events surrounding Magellan's orbit of Venus are recounted. Significant events include the successful firing of a solid rocket motor while the spacecraft was behind Venus to transfer it from a solar-centered trajectory to an orbit around the planet. The spacecraft orbits Venus every 3.26 hours at a maximum altitude of 8500 km and minimum altitude of 291 km in an elliptical orbit. The successful August 16 test of the synthetic-aperture radar system is discussed, noting that it produced two strips, each about 20 km x 16,000 km, revealing details as small as 120 m. Two anomalies causing a delay in the start of mapping operations and subsequent breaks in the communication link with earth for 14.5 hours and 17.7 hours are discussed. Protective measures directed from the spacecraft's ROM during breach of contact are listed, and possible causes of the anomalies are suggested, such as solar activity or hardware or software elements, although the actual cause is not yet known.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Spaceflight (ISSN 0038-6340); 32; 334-337
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  • 22
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    Comparative dynamics of the ionospheres of Venus and Mars at large solar zenith angles (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Simple three-ion spectral models of the dynamics and ion chemistry in the upper ionospheres of Venus and Mars have been constructed by including two minor ions, H(+) and O2(+) for Venus and O(+) and CO2(+) for Mars, along with the major ion, O(+) for Venus and O2(+) for Mars. Horizontal flow velocities and ion densities have been calculated in each case and compared with available measured data. For Venus, the present calculations yield results in agreement with earlier finite-difference model studies and with experimental observations. Calculations for Mars are in agreement with the limited observational data obtained by the Viking landers.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Indian Journal of Radio and Space Physics (ISSN 0367-8393); 19; 88-102
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  • 23
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    Albedo and color maps of the Saturnian satellites (1990)
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    Publication Date: 2011-08-19
    Description: The paper discusses the production of maps of the albedos and colors of Mimas, Enceladus, Tethys, Dione, and Rhea over the full range of their imaged surfaces. Voyager images were used to prepare maps of the normal reflectances and color ratios (0.58/0.41 micron) of these satelites.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 87; 339-357
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  • 24
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    Cosmogenic nuclides in extraterrestrial materials (1990)
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    Publication Date: 2011-08-19
    Description: Research on cosmogenic nuclides in extraterrestrial materials is summarized. Methods for determining average production rates in meteorites are considered as well as the composition dependence of production rates. Also discussed are lunar meteorites, solar-gas-rich meteorites, presolar grains, and solar cosmic rays.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Reviews of Geophysics (ISSN 8755-1209); 28; 253-275
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  • 25
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    A model of Saturn's magnetic field based on all available data (1990)
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    Publication Date: 2011-08-19
    Description: A model of Saturn's magnetic field, called Saturn Pioneer Voyager (SPV), is developed on the basis of an analysis of three sets of data: those from the Pioneer 11, the Voyager 1, and the Voyager 2 magnetometers. It is shown that the SPV model fits the data observed between 1.3 and 8.0 Saturn radii from the planet's center with a 1.13 percent weighted rms average of the percent differences between the observed and modeled fields, which is substantially better than the fits yielded by any of the previous models.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 15257-15
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  • 26
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    Backscattering from frost on icy satellites in the outer solar system (1990)
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    Publication Date: 2011-08-19
    Description: Two extreme models are presented of how frost and ice might be intermixed on a typical satellite surface: areal and intimate mixing. Applying such models to selected representative satellite data, it is found that the frost component of the surfaces of these outer satellites must itself be backscattering, unlike its terrestrial counterpart. The difference may arise because frost particles can have much more complex internal textures under the low-temperature and low-gravity conditions of the outer satellites than is the case on earth.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 347; 162-164
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  • 27
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    Ubiquitous interstellar diamond and SiC in primitive chondrites - Abundances reflect metamorphism (1990)
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    Publication Date: 2011-08-19
    Description: It is shown here that interstellar diamond and SiC were incorporated into all groups of chondrite meteorites. Abundances rapidly go to zero with increasing metamorphic grade, suggesting that metamorphic destruction is responsible for the apparent absence of these grains in most chondrites. In unmetamorphosed chondrites, abundances normalized to matrix content are similar for different classes. Diamond samples from chondrites of different classes have remarkably similar noble-gas constants and isotropic compositions, although constituent diamonds may have come from many sources. SiC seems to be more diverse, partly because grains are large enough to measure individually, but average characteristics seem to be similar from meteorite to meteorite. These observations suggest that various classes of chondritic meteorites sample the same solar system-wide reservoir of interstellar grains.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 347; 159-162
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  • 28
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    Vertical distribution of water in the atmosphere of Venus - A simple thermochemical explanation (1990)
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    Publication Date: 2011-08-19
    Description: Several lines of evidence concerning the vertical abundance profile of water in the atmosphere of Venus lead to strikingly unusual distributions (the water vapor abundance decreases sharply in the immediate vicinity of the surface) or to serious conflicts in the profiles (different IR bands suggest water abundances that are discrepant by a factor of 2.5 to 10). These data sets can be reconciled if (1) water molecules associate with carbon dioxide and sulfur trioxide to make gaseous carbonic acid and sulfuric acid in the lower atmosphere, and (2) the discrepant 0.94-micrometer water measurements are due to gaseous sulfuric acid, requiring it to be a somewhat stronger absorber than water vapor in this wavelength region. A mean total water abundance of 50 + or - 20 parts/million and a near-surface free water vapor abundance of 10 + or - 4 parts/million are derived.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 249; 1273-127
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    Variations of Mars gravitational field and rotation due to seasonal CO2 exchange (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: About a quarter of the Martian atmospheric mass is exchanged between the atmosphere and the polar caps in the course of a Martian year: CO2 condenses to form (or add to) the polar caps in winter and sublimes into the atmosphere in summer. This paper studies the effect of this CO2 mass redistribution on Martian rotation and gravitational field. Two mechanisms are examined: (1) the waxing and waning of solid CO2 in the polar caps and (2) the geographical distribution of gaseous CO2 in the atmosphere. In particular, the net peak-to-peak changes in J2 and J3 over a Martian year are both found to be as much as about 6 x 10 to the -9th. A simulation suggests that these changes may be detected by the upcoming Mars Observer under favorable but realistic conditions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14755-14
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    Atmospheric measurements at Mars via gamma ray spectroscopy (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper describes three methods for measuring the Martian atmosphere using gamma ray spectroscopy. One method determines atmospheric thickness based on the energy-dependent differential attenuation of gamma-ray line pairs from a common element. Another makes a direct determination based on measurements of the line flux generated in the atmosphere, requires knowledge of the concentration of the component being used. The third, which makes use of a single line emitted from the surface where its flux can be established. The effects of stratigraphy on the differential attenuation method are studied, and calculations are reported which show that the measurement of atmospheric argon will be a sensitive indicator of the atmospheric fractionation accompanying CO2 precipitation in south polar regions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14695-14
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    Infrared radiative transfer in the dust-free Martian atmosphere (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Two theoretical radiative transfer methods are used here to derive synthetic spectra of dust-free Martian atmospheres. One is a versatile, accurate, line-by-line model which completely resolves individual absorption lines to produce high-resolution spectra within gas absorption bands. The other is a fast Voigt quasi-random model which produces accurate results for spectral regions as narrow as 1/cm and is fast enough for routine use in broadband transmission calculations. Synthetic transmission and radiance spectra from these models for dust-free conditions in the Martian atmosphere are used to illustrate the radiative effects of each important absorbing gas and to provide a baseline for comparisons with dust atmosphere spectra.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14577-14
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  • 32
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    Thermal emission spectra of Mars (5.4-10.5 microns) - Evidence for sulfates, carbonates, and hydrates (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Spectra of the Martian thermal emission in the 5.4-10.5 micron region are reported. Emission features at 7.8 and 9.7 microns are attributed to surface silicates, and an emission feature at 6.1 micron is attributed to a molecular water component of the surface material. An absorption band at 8.7 micron and a possible one at 9.8 microns is attributed to sulfate or bisulfate anions probably located at a distorted crystalline site, and an absorption band at 6.7 microns is attributed to carbonate or bicarbonate anions located in a distorted crystalline site. Spectral simulations indicate that the sulfate- and carbonate-bearing minerals are contained in the same particles of airborne dust as the dominant silicate minerals, that the dust optical depth is about 0.6 at a reference wavelength of 0.3 micron over the area of the observed spots, and that sulfates and carbonates constitute 10-15 percent and 1-3 percent by volume of the airborne dust, respectively.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14595-14
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    Origins of Marslike spectral and magnetic properties of a Hawaiian palagonitic soil (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Results are presented on spectral, Moessbauer, static magnetic, petrographic, and compositional data for a Hawaiian palagonitic soil from Mauna Kea (HWMK1). It was found that reflectivity spectra of size separates smaller than 20 microns resemble spectra for Martian bright regions, while spectra of larger size separates show characteristics in common with spectra for Martian dark regions. Data on the HWMK1 soil are consistent with the partitioning of iron among the following minerals: olivine, titanomagnetite, hematite, and a superparamagnetic colored ferric oxide. These mineralogies are heterogeneously distributed within the soil with respect to both particle type and soil-particle diameter. The strongly magnetic titanomagnetite is associated with black particles and is responsible for the magnetic nature of the soil, while the colored weakly magnetic superparamagnetic ferric oxide and minor hematite are associated with orange particles.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14427-14
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    Emplacement of lava flow fields - Application of terrestrial studies to Alba Patera, Mars (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The relationships obtained by Kilburn and Lopes (1988, 1990) for their models of lava flow fields were used to calculate the duration of the emplacement, the average discharge rates, and the average velocities of lavas for the Martian volcano Alba Patera, on which two distinct planimetric types of lava flow field were identified. The validity of using terrestrial analogues for investigating the emplacement conditions of the Alba Patera flow fields is examined. It is concluded that, at least for basaltic-basaltic andesitic compositions, the essential conditions of eruption from Alba Patera may have been similar to those currently observed on earth.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14383-14
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  • 35
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    Fault propagation folds induced by gravitational failure and slumping of the Central Costa Rica volcanic range - Implications for large terrestrial and Martian volcanic edifices (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Maps are presented that describe the compressional tectonic structures found at the base of the Central Costa Rica volcanic range (CCRVR), which comprise thrust faults and related fault propagation folds, only partly covered by syntectonic and posttectonic volcanoclastic deposits. Evidence is presented that these structures formed by gravitational failure and lumping of the flanks of the volcanic range. It is suggested that similar structures may be found at the toe of the southern flank of Kilauea volcano, Hawaii, and along the perimeter scarp of the Olympus Mons volcano on Mars.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14357-14
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    Flank tectonics of Martian volcanoes (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The origin of the numerous terraces on the flanks of the Olympus Mons volcano on Mars, seen on space images to be arranged in a roughly concentric pattern, is investigated. The images of the volcano show that the base of each terrace is marked by a modest but abrupt change in slope, suggesting that these terraces could be thrust faults caused by a compressional failure of the cone. The mechanism of faulting and the possible effect of the interior structure of Olympus Mons was investigated using a numerical model for elastic stresses within a Martian volcano, constructed for that purpose. Results of the analysis supports the view that the terraces on Olympus Mons, as well as on other three Martian volcanoes, including Ascraeus Mons, Arsia Mons, and Pavonis Mons are indeed thrust faults.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14345-14
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    The shallow structure of the Martian lithosphere in the vicinity of the ridged plains (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: On Mars, the most prominent assemblage of regularly spaced plain ridges occurs in the plains of the Coprates and Lunae Planum regions. In this paper, a number of tectonic models is developed and quantitatively evaluated, that relate the regular spacing of these ridges to the shallow internal structure of Mars. It is shown that models with both rigid and deformable megaregolith-basement interface conditions can provide solutions which can explain the ridge spacing within the constraint provided by the estimated thickness of the smooth plains materials. Implications of the models for the structure and state of stress in the Tharsis region at the time of ridge formation are discussed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14215-14
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    Speculations on the origin and evolution of the Utopia-Elysium lowlands of Mars (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper proposes a qualitative model for the origin of the Utopia-Elysium northern lowlands on eastern Mars in terms of the long-term evolution of two large overlapping impact basins. The model, which is consistent with both the observed geologic constraints and more quantitative results obtained by numerical modeling of smaller (Orientale-size) impact basins, is shown to qualitatively account for the major topographic variation seen in the Utopia-Elysium region, including the overall 'lowness' of the area and localized depressions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14203-14
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  • 39
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    Discontinuities in the shallow Martian crust at Lunae, Syria, and Sinai Plana (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Detailed photoclinometric data are presented for a variety of surface features (pits, troughs, wall valleys, and grabens) within three study areas in the western equatorial regions of Mars (Lunae, Syria, and Sinai Plana) that provide evidence for mechanical discontinuities within the shallow Martian crust in these regions. The data's relation to some of the previously proposed mechanical discontinuities within the Martian crust is discussed, and the geologic significance of these features is speculated upon.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14231-14
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  • 40
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    A new survey of multiring impact basins on Mars (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Literature data on Martian multiring impact basins with diameters greater than 500 km are summarized, and evidence is found for eight new such basins. The pattern of changes of basin morphology with increasing basin size suggests three subclasses of multiring basins: (1) multiring basins with diameters up to about 1850 km, which are characterized by the Orientale type concentric structure and cumulative frequency power law slope of -0.75; (2) the Argyre-type basins (with diameters between 1850 and 3600 km, defined by rugged concentric annnuli and a power law slope of nearly -2.0; and (3) the Chryse-type basins (with diameters greater than 3600 km), which exhibit multiple concentric rings and very shallow topographic profiles. Multiring basins are found in all parts of Mars, including the northern lowlands, Tharsis, and surrounding highlands, and are associated with much of the subsequent resurfacing of cratered terrain.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14175-14
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  • 41
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    Mars gravity field error analysis from simulated radio tracking of Mars Observer (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Results are presented on the analysis of the recovery of the Martian gravity field from tracking data in the presence of unmodeled error effects associated with different orbit orientations. The analysis was based on the mission plan for the Mars Observer (MO) radio tracking data from the Deep Space Network. From the analysis, a conservative estimate of the gravitational accuracy for the entire mission could be obtained. The results suggest that, because the atmospheric drag is the dominant error source, the spacecraft orbit could possibly be raised in altitude without a significant loss of gravitational signal. A change in altitude will also alleviate the large effects seen in the spectrum the satellite resonant orders.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14155-14
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  • 42
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    Martian impact craters - Correlations of ejecta and interior morphologies with diameter, latitude, and terrain (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An effort is made to establish the ability of a correlation between crater morphology and latitude, diameter, and terrain, to discriminate among the effects of impact energy, atmosphere, and subsurface volatiles in 3819 larger-than-8 km diameter craters distributed over the Martian surface. It is noted that changes in ejecta and interior morphology correlate with increases in crater diameter, and that while many of the interior structures exhibit distributions interpretable as terrain-dependent, central peak and peak ring interior morphologies exhibit minimal relationships with planetary properties.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 87; 156-179
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    Sun and dust versus greenhouse gases - An assessment of their relative roles in global climate change (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Many mechanisms, including variations in solar radiation and atmospheric aerosol concentrations, compete with anthropogenic greenhouse gases as causes of global climate change. Comparisons of available data show that solar variability will not counteract greenhouse warming and that future observations will need to be made to quantify the role of tropospheric aerosols, for example.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Nature (ISSN 0028-0836); 346; 713-719
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    A goal and strategy for human exploration of the moon and Mars (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Eventual settlement of the solar system, beginning with the moon and Mars, is proposed, and a strategy for the exploration of and initial settlement of the moon and Mars, based on the model of European settlement of the Americas, is discussed. Strategies suggest an allocation of functions between humans and telerobots to conduct the exploration and initial settlement.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Space Policy (ISSN 0265-9646); 6; 195-208
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  • 45
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    Large-scale patterns of eolian sediment transport on Venus - Predictions for Magellan (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The atmosphere of Venus is likely to exert a major influence on the surface. Arecibo and Venera 15/16 observations of the population of impact craters with bright halos give direct evidence of surface modification, on the scale of centimeters, to smooth the surface on time scales of 50 - 250 my. Both chemical and mechanical modifications probably occur. Diurnal winds in the planetary boundary layer can transport particles. Using boundary layer theory, including the effects of topography, surface stresses and resulting transport and deposition of sand-size particles are calculated. Regional slopes are sites of largest surface stresses. Sand will be generally transported downhill, although there is a preferential net transport from east to west, in the same direction as the atmospheric superrotation. It is predicted here that streaks may be seen in the Magellan radar images which will indicate directions of net eolian transport on the surface of Venus.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1365-136
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  • 46
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    Small domes on Venus - Probable analogs of Icelandic lava shields (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: On the basis of observed shapes and volumetric estimates, small, dome-like features on radar images of Venus are interpreted to be analogs of Icelandic lava-shield volcanoes. Morphometric data for Venusian domes in Aubele and Slyuta as well as measurements of representative dome volumes and areas from Tethus Regio are used to demonstrate that the characteristic aspect ratios and flank slopes of these features are consistent with a subclass of low Icelandic lava-shield volcanoes (LILS).
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1381-138
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  • 47
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    Geologic evidence of hotspot activity of Venus - Predictions for Magellan (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A number of distinctive types of geologic features have been identified on Venus that are interpreted to be related to thermal plumes including domal rises, coronae, and major composite shield volcanoes. The basic characteristics of these features as well as their distribution are documented. The three types of features have related morphologies and are interpreted to represent a continuum of features formed by mantle plumes at scales from 100s to over 1000 km. The Artemis structure, located in Aphrodite Terra, is proposed to be a large corona. If crustal spreading processes are operating on Venus, hotspot features should form chains on the surface as seen in terrestrial ocean basins. On the basis of current data on hotspot-related feature distribution on Venus, no clear evidence exists for hotspot chains. The complete distribution of hotspot features in Magellan data will be used to understand better the relationship between interior processes and surface features, as well as to provide a test for the crustal spreading hypothesis.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1377-138
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  • 48
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    Radar characteristics of the equatorial plains of Venus from Goldstone observations - Implications for interpretation of Magellan data (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Based on analyses of recent high resolution observations of the approximately 1000 km diameter Heng-O ring structure by the Goldstone Solar System Radar, it is predicted that the structure is a large corona. Calibrated values of radar backscatter coefficient indicate lateral variations of a factor of 4 in Fresnel reflectivity in the vicinity of Heng-O, as well as in other areas of the plains, at scales of tens of km. It is predicted that areas with very low reflectivity values, which occur in a variety of geological settings, are soil-dominated, with bulk densities as low as 1.5 g/cu cm.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1357-136
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  • 49
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    Titan and other icy satellites - Dielectric properties of constituent materials and implications for radar sounding (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Radar sounding observations of Titan and the other outer solar system icy satellites have been conducted in order to ascertain the materials present, their dielectric properties, and the degree of radar signal penetration. Deep penetration is possible at long wavelengths, while strong reflections may occur due to pockets or layers of H2O-NH3 solution. Attention is given to the case of Titan, using models to calculate radar reflection S/N ratios; the models involve H2O ice covered by a 100-m thick layer of organic sediments that are overlain by an ocean of liquid CH4-C2H6-N2. At 13.6-cm wavelength, a greater-than-10 dB S/N is computed from the ocean-sediment and sediment-ice interfaces, suggesting that the geology of Titan may be investigated by such a sounding mode despite deep ocean coverage of the satellite.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 86; 336-354
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    Transitions from Hadley to Rossby flows in internally forced rotating spherical systems (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The possibility of global-scale transitions between the Hadley and Rossby atmospheric regimes is investiated using a simple three-dimensional rotating spherical model without a boundary layer structure, bottom topography, or cumulus friction, and the expected occurrence of the Hadley to Rossby transition is demonstrated. It is shown that a transition from Hadley flow to wavenumber-5 Rossby flow is preferred, in agreement with standard baroclinic instability results. This result gives a reasonable Rossby wave bifurcation from the Hadley solution. For the cases examined, it was found that the upper symmetric Hadley regime does not exist and that the Hadley to Rossby transition depends on the values of the eddy viscosities.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 47; 1041-105
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    The deep atmosphere of Venus revealed by high-resolution nightside spectra (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The first high-resolution spectroscopic observations of the night side of Venus obtained in two narrow spectral windows centered at 1.74 and 2.3 microns, where the nightside is anomalously bright, are reported. Absorption features from CO2, CO, H2O, HDO, HCl, HF, and COS are detected, and there are a number of unidentified features. A preliminary analysis indicates that the observed radiation is thermal emission from atmospheric layers in the eight-bar pressure region for the 2.3 micron window and even deeper at 1.7 micron. The derived CO and H2O abundances agree with in situ Pioneer measurements in the deep troposphere and are consistent with the high deuterium enrichment inferred from Pioneer data. The first measurements of HCl and HF below the clouds are reported along with the first firm detection of COS.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 345; 508-511
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  • 52
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    Mars ionopause during solar minimum - A lesson from Venus (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The ion densities measured by the Viking landers (Hanson et al., 1977) do not show an abrupt falloff with height, giving the false impression that Mars has no ionopause. On the basis of knowledge gained from the solar wind interaction at Venus during solar minimum, it is demonstrated that the observed O2 profile above about 160 km on Mars is a distributed photodynamical ionosphere and can produce an ionopause at around 325 km, similar to that observed on Venus during solar minimum. It is concluded that the solar wind interacts directly with the Mars ionosphere, suggesting that the planet does not have an intrinsic magnetic field of any consequence.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 8265-826
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    A method for estimating eruption rates of planetary lava flows (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The eruption rates of single-lobed planetary lava flows are presently accounted for by a model for radiative losses from a partially crusted hotter core, assuming thermal characteristics similar to terrestrial flows. Eruption rates are within this framework expressible as functions of (1) exposed core area fraction, (2) initial core temperature, (3) core temperature upon cessation of flow, (3) crust thickness, and (4) the lava's density and heat capacity.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 85; 512-515
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    CH4 nonlocal thermodynamic equilibrium in the atmospheres of the giant planets (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The present consideration of methane's vibrational relaxation in the Giant Planets' upper stratospheres employs a model for the thermalization of solar energy absorbed under non-LTE conditions, at the 1.7, 2.3. and 3.3 micron-centered CH4 band groups. On this basis, a range of model atmospheres was produced, reflecting current uncertainties concerning CH4 collisional excitation rates. At 0.1 mbar, all of the non-LTE models are within 2 K of the LTE reference models; the extreme non-LTE models steadily depart from reference LTE ones, however, and reach about + or - 20 K at 0,1 mbar.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 85; 355-379
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    Titan's stratospheric temperatures - A case for dynamical inertia? (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Voyager IRIS spectral radiances in the nu4-band of CH4 for the Titan atmosphere exhibit a hemispheric asymmetry. While asymmetry in the meridional distribution of opacity about the equator cannot be discounted, attention is given to the need for angular momentum transport concurrent with seasonally varying temperatures in the Titan stratosphere, which would maintain the cyclostrophic thermal wind relation between zonal winds and temperatures. The adiabatic heating and cooling associated with these motions can produce the observed temperature asymmetry.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 85; 346-354
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    The extraordinary radar echoes from Europa, Ganymede, and Callisto - A geological perspective (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Electromagnetic echo-scattering models, empirical and theoretical considerations on regolith formation, and ice physics, are presently invoked in a geologic treatment of the anomalous radar properties of the icy Galilean satellites. These are held to arise because of the electrical differences between ice and silicates, and the absence of icy regoliths' ice-density structures in silicate regoliths. Icy regoliths may uniquely smooth out discontinuities between solid ejecta fragments and more porous surroundings, forming refraction-scattering 'lenses'; high-order multiple scatterings will thereby become more likely responsible for the echoes than low-order scattering.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 85; 335-345
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    On the effect of X rays on the color of elemental sulfur - Implications for Jupiter's satellite Io (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Absorption features arose at 0.42 and 0.52 microns when spectral reflectance measurements were conducted for elemental sulfur allotrope mixtures produced by the exposure of the cyclooctal S(8) allotrope of sulfur to X-rays; while these features due to the presence of short-chain molecules are stable at low temperatures, they fade upon warming of the sample. The hypothesis that X-rays in the Jovian environment would cause other allotropic forms of sulfur to revert to S(8) is contradicted by the fact that these features are not present in S(8) at the same temperature that had not been exposed to X-rays.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 85; 326-334
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    Internal structure of Io and the global distribution of its topography (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A global topography is presently calculated for two multilayer Io models in which dissipation occurs in a viscous asthenosphere and a solid mantle: (1) a 'thermal swell' model, in which topography and heat flow are positively correlated, and (2) a 'differentiated lithosphere' model, in which topography and heat flow are negatively correlated. Both the polar topography and the hypsometric distribution of elevations in the differentiated lithosphere model are better matched with observations than the thermal swell model. The shift of the equatorial basin-swell pattern indicates a recent zonal rotation of about 25 deg for Io's lithosphere.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 85; 309-325
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  • 59
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    TV observations of Phobos - First results (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: From February to March, 1989, Phobos-2 acquired 37 TV images of Phobos at distances from 200 to 1100 km. These images will be used to update the figure model and topographic and geological maps of Phobos, its spectral characteristics and scattering law, the surface composition and texture, and the parameters of the orbital motion and forced libration.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Pis'ma v Astronomicheskii Zhurnal (ISSN 0320-0108); 16; 378-388
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  • 60
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    A numerical study of the onset of baroclinic instabilities in spherical geometry (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The onset of instabilities in a fluid contained in a rotating hemispherical shell, driven by thermal gradients imposed upon the hemispherical boundaries and by a spherically symmetric radial body force, is numerically studied. Computations are presented for a range of Taylor and thermal Rossby numbers. The analysis indicates the presence of an instability dependent upon the spherically radial gravity alone when the warmest temperatures are at the pole and an additional centrifugal buoyant instability for weak imposed gravity and fast rotation when the temperature decreases poleward.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Geophysical and Astrophysical Fluid Dynamics (ISSN 0309-1929); 52; 25-43
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  • 61
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    A simple two-system-parameter model for surface-effected warming of the planetary boundary layer (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The transabsorptivity concept which specifies the heat input into the PBL resulting from surface-atmosphere interactions is discussed. This concept is examined in terms of governing equations, and transabsorptivity is defined as the product of the surface absorptivity and the transfer efficiency. It is proposed that the climatic effects of surface changes be formulated in terms of changes in the transabsorptivity. A diagram of the surface-atmosphere interactions is provided.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Boundary-Layer Meteorology (ISSN 0006-8314); 51; 3, Ma; 213-227
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  • 62
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    Charge-coupled device spectra of asteroids. I - Near-earth and 3:1 resonance asteroids (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Main-belt asteroids and cometary nuclei are both frequently suggested sources of the relatively short-lived near-earth asteroids (NEAs). The asteroidal origin hypothesis is studied by obtaining new high-quality reflectivity spectra of 19 NEAs and 23 asteroids near the 3:1 resonance, and by performing a systematic comparison of these two groups of spectra. Nonparametric statistical tests are used to check for consistency between the color distributions of the two populations. The tests indicate that the difference between the two distributions is generally not significant at the 3 sigma level. However, this conclusion is dependent on the (unknown) size distribution of the NEAs. The observations are compatible with the hypothesis that the NEAs are derived from the 3:1 resonance region, but do not imply that this is the only possible source region.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astronomical Journal (ISSN 0004-6256); 99; 1985-201
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  • 63
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    Mars - Change in axial tilt due to climate? (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The average tilt of Mars' equator with respect to its orbital plane may have increased significantly over the age of the solar system. Obliquity oscillations might have induced changes in the climate, which altered the mass distribution and hence the solar torque on the planet. Viscous deformation attributable to loading by the large polar caps expected at low obliquity may have induced secular changes in the axial tilt. Earth-like effective viscosities can account for virtually the entire present obliquity of 24.4 degrees. Thus the present average tilt of Mars may not be primordial.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 248; 720
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  • 64
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    Degradation of the lunar vacuum by a moon base (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Several industrial processes requiring high and ultra-high vacuum similar to the lunar vacuum are outlined. The effects of a 20-person lunar base and a 250-person industrial facility on this vacuum are discussed. It is shown that exhaust from transport spacecraft and leakage from the habitat will be comparable to the daytime gas pressure for the 20-person base, and will degrade the vacuum to the range of 2 x 10 to the -9th torr for the use of 250-person facility. This will result in replacing the mostly nonreactive gases hydrogen, helium, and neon with more reactive gases containing carbon and oxygen. This vacuum is still good enough to perform many important vacuum processes such as plasma-deposition of amorphous silicon for solar cells, but processes such as molecular beam epitaxy or locating an intersecting beam accelerator on the moon will require additional vacuum pumping.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Acta Astronautica (ISSN 0094-5765); 21; 183-187
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  • 65
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    The dynamics of the ionosphere of Mars at large solar zenith angles (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A model of the ion chemistry and dynamics of the ionosphere of Mars at large solar zenith angles has been constructed using techniques previously developed for Venus. It is found that a substantial nighttime ionosphere should occur even when the ionopause height is as low as 250 km. At low altitudes the interaction of the plasma flow with the neutral atmosphere appears to result in considerable 'noise' in the flow patterns. Transterminator plasma velocities are smaller than for Venus, although they may exceed the local sonic speed. The effect of a nocturnal source of suprathermal electrons is also discussed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 6263-626
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  • 66
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    Petrogenesis of mesosiderites. I - Origin of mafic lithologies and comparison with basaltic achondrites (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: New petrologic and trace element data on basaltic and gabbroic clasts in mesosiderites and basaltic achondrites, combined with existing petrologic and trace element data, have served as a basis for interpretation of the petrogenesis of mesosiderite clasts. Compared with the basaltic achondrites, the mesosiderite basaltic and gabbroic clasts contain more abundant modal tridymite and merrilite, and more commonly contain augite as a late magmatic phase. Their pyroxenes tend to be more MgO-rich, and have lower Fe/Mn ratios which are positively correlated with the Fe/Mg ratio. Some of the mesosiderite basaltic and gabbroic clasts contain xenocrystic plagioclase. The basaltic clasts commonly show superchondritic Eu/Sm ratios and slight LREE depletions. The cumulate gabbro clasts are extremely depleted in LIL, have very high Eu/Sm ratios and high Lu/Sm ratios. All of these features can be explained by a model in which the mafic lithologies of mesosiderites were formed by remelting of a mixed basalt-cumulate gabbro-metal source region near the parent body surface.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 54; 1165-117
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    Suggestions for the measurement and derivation of fluxes and flux divergences from a satellite (1990)
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    Publication Date: 2011-08-19
    Description: Consideration is given to the determination of the optimal bands for measuring and deriving the total outgoing longwave radiation (OLR), surface downward flux (SDF), and cooling rates (CRs) using linear regression. The optimal bands are determined from scatter plots of total fluxes and cooling rates associated with the various bands. It is found that the best band for OLR is between 800 and 1200/cm, while the best band for SDF is between 500 and 660/cm or between 660 and 800/cm. For CRs, it is shown that the best band is also between 660 and 800/cm. It is noted that the AVHRR OLR is damped compared with the Nimbus-7 earth radiation budget (ERB) OLR derived from the broadband, narrow FOV ERB instrument.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 5257-527
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    Matrix effects for reflectivity spectra of dispersed nanophase (superparamagnetic) hematite with application to Martian spectral data (1990)
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    Publication Date: 2011-08-19
    Description: The effect of the matrix on the reflectivity spectra of nanophase (superparamagnetic) hematite (np-Hm) dispersed within the matrix was investigated in four series of powder samples containing np-Hm dispersed within discrete powder particles (of two size ranges) of silica gel and activated alumina. The spectral data show that matrix effects are large. Samples with the same Fe2O3 content can have np-Hm absorption edges characterized by very different positions and curvature and slope indices, while samples with equivalent absorption edges can have very different Fe2O3 concentrations. Thus, quantitative relationships between the positions of ferric absorption edges and Fe2O3 concentrations are unreliable without knowledge of matrix properties of the system. It is shown that it was possible to match the Fe2O3 concentration, magnetic properties, and spectral data for Martian surface material with a laboratory mixture whose only ferric-bearing phase was hematite.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 5101-510
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    A comparison of Solar Mesosphere Explorer and Stratosphere Aerosol and Gas Experiment II ozone densities near the stratopause (1990)
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    Publication Date: 2011-08-19
    Description: Ozone measurements made by the SME UV Spectrometer and the Stratosphere Aerosol and Gas Experiment II (SAGE II) spectometer are compared at 1.0 mbar for the time period from October 1984 to December 1986, using a model of the diurnal variation of ozone to correct for the difference in local times of the two measurements. The absolute values of the ozone mixing ratio measured by the two spectrometers were found to agree to better than 5 percent, with no significant divergence between the instruments. It is concluded that, since the SAGE II data are not dependent on the absolute calibration of the instrument, these data can be used as time-dependent 'ground truth' measurements for comparisons with other instruments.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 3533-353
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  • 70
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    Influence of the solar wind/interplanetary medium on Saturnian kilometric radiation (1990)
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    Publication Date: 2011-08-19
    Description: Previous studies on the periodicities of the Saturnian kilometric radiation (SKR) suggested a considerable solar wind influence on the occurrence of SKR, so it was obvious to investigate the relationship between parameters of the solar wind/interplanetary medium and this Saturnian radio component. Voyager 2 data from the Plasma Science experiment, the Magnetometer experiment and the Planetary Radio Astronomy experiment were used to analyze the external control of SKR. Out of the examined quantities known to be important in controlling magnetospheric processes this investigation yielded a dominance of the solar wind momentum, ram pressure and kinetic energy flux, in stimulating SKR and controlling its activity and emitted energy, and confirmed the results of the Voyager 1 analysis.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geomagnetism and Geoelectricity (ISSN 0022-1392); 42; 12, 1
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    Thermospheric gravity waves - Observations and interpretation using the transfer function model (TFM) (1990)
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    Publication Date: 2011-08-19
    Description: This paper presents some numerical experiments performed with the TFM to study the various wave components excited in the auroral regions that propagate through the thermosphere and lower atmosphere, and to demonstrate the properties of realistic source geometries. The model is applied to the interpretation of satellite measurements, and gravity waves seen in the thermosphere of Venus are discussed. Gravity waves are prominent in the terrestrial thermosphere polar region and can be excited by perturbations in Joule heating and Lorentz force due to magnetospheric processes. Observations from the Dynamics Explorer-2 satellite are used to illustrate the complexity of the phenomenon and to review the TFM that is utilized.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Space Science Reviews (ISSN 0038-6308); 54; 297-375
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    Deep optically thin cirrus clouds in the polar regions. I - Infrared extinction characteristics (1990)
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    Publication Date: 2011-08-19
    Description: The spectral data obtained by the infrared interferometer Spectrometer (IRIS) flown on Nimbus 4 satellite in 1970 indicated the existence of optically thin ice clouds in the upper troposphere that probably extended into lower stratosphere, in the polar regions, during winter and early spring. The spectral features of these clouds differ somewhat from that of the optically thin cirrus clouds in the tropics. From theoretical simulation of the infrared spectra in the 8-25 micron region, it is inferred that these polar clouds have a vertical stratification in particle size, with larger particles (about 12 microns) in the bottom of the cloud and smaller ones (less than 1 micron) aloft. Radiative transfer calculations also suggest that the equivalent ice-water content of these polar clouds is of the order of 1 mg/sq cm.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Applied Meteorology (ISSN 0894-8763); 29; 1313-132
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    Cirrus structure and radiative parameters from airborne lidar and spectral radiometer observations - The 28 October 1986 FIRE study (1990)
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    Publication Date: 2011-08-19
    Description: A description is presented of cirrus based on results from a FIRE observation flight in central Wisconsin on October 28, 1986. Cirrus structure and radiative parameters as determined by the ER-2 lidar and imaging spectral radiometers are presented. From the lidar observations a complex structure was shown with differing cloud layers extending over six kilometers of altitude range. Both thin and dense cirrus layers were present and mixed phase clouds were found at lower altitudes. As indicated by the cloud structure, precipitation of crystals from high, but vertically thin, layers produces a significant fraction of the lower cirrus. Multiple layers should be considered as normal for cirrus formations. It is noted that the cloud height is an important factor for satellite cloud retrievals and cloud climatology.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 118; 2329-234
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  • 74
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    A comparative study of Venus and Mars - Upper atmospheres, ionospheres and solar wind interactions (1990)
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    Publication Date: 2011-08-19
    Description: The neutral atmospheres of Mars and Venus are discussed. A comparative study is presented of the upper atmospheres, ionospheres, and solar wind interactions of these two planets. The review is mainly concerned with the region about 100 km above the surface of the planets.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Indian Journal of Radio and Space Physics (ISSN 0367-8393); 19; 444-465
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    The global budget of impact-derived sediments on Venus (1990)
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    Publication Date: 2011-08-19
    Description: The sedimentary cycle of Venus is examined, with specific attention to the contribution from impact events. The observed record of impact craters on the surface of Venus can be used to calculate the contribution of fine materials generated by impact processes to the global sedimentary cycle. Ejecta volume calculations carried out on the basis of various crater population scenarios suggest that the maximum global ejecta layer thickness over the past 1 Gyr is about 1-2 mm. This would translate to a global accumulation rate of only 0.002 to 0.01 micron per year. Moreover, most of this material could never have been available for global transport; it is projected that over 90 percent of the ejecta would be deposited within 1-3 radii of the crater rim, and only 0.02-0.05 percent could be available as fine dust for global sedimentary cycle. Therefore, the global layer thickness of transportable impact-derived dust can be no more than a few mm over the past 1 Gyr.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Earth, Moon, and Planets (ISSN 0167-9295); 50-51; 175-190
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    An increase of early rains in southern Israel following land-use change? (1990)
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    Publication Date: 2011-08-19
    Description: Rains at the onset of the October-April rainy season in southern Israel have steeply increased in the last 25 years relative to the previous 20 years, and are accompanied by an appreciable general increase of rainy-season rainfall. This increase in precipitation is specifically attributable to an intensification of the convection and advection processes due to afforestation and increased cultivation-induced enhancement of the daytime sensible heat flux from the generally dry surface; the enhancement proceeds from both the reduced surface albedo and the reduced soil heat flux in October, when insolation is strong. Greater daytime convection can lead to penetration of inversions capping the planetary boundary layer, while strengthened advection can furnish moist air from the Mediterranean.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Boundary-Layer Meteorology (ISSN 0006-8314); 53; 333-351
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    In situ measurement of interstellar silicon carbide in two CM chondrite meteorites (1990)
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    Publication Date: 2011-08-19
    Description: The first in situ observations of isotopically anomalous SiC are reported. The grains were found by X-ray mapping of polished sections of two chondritic meteorites, Cold Bokkeveld and Murchison. Ion microprobe measurements showed C-13 enrichments, delta C-13, from 199 to 2800 per mil, proving that the grains are indigenous. SiC grains are revealed only as isolated matrix particles, ruling out the possibility that SiC grains were brought into the solar system as inclusions in larger grains, which protected them from destruction in the solar nebula. Several of the SiC grains are cracked, suggesting that the etching treatment may result in size distributions biased toward smaller grains.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 348; 715-717
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    Estimation of synoptic fields of middle atmosphere parameters from Nimbus-7 LIMS profile data (1990)
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    Publication Date: 2011-08-19
    Description: The most widely used version of the Nimbus-7 middle atmosphere dataset is the set of high quality, daily, and zonal Fourier coefficients that resolve information out to six wavenumbers at 12 UTC. A Kalman filter algorithm was applied to the original profile data in order to generate those fields for the data archive or LAMAT product. The characteristics and implementation of the algorithm are described in some detail, along with examples of the output for each of the LIMS parameters.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Atmospheric and Oceanic Technology (ISSN 0739-0572); 7; 689-705
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    Vertical structure and characteristics of 23-60 day (zonal) oscillations over the tropical latitudes during the winter months of 1986 - Results of equatorial wave campaign-II (1990)
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    Publication Date: 2011-08-19
    Description: Results are presented of the equatorial wave campaign-II, a meteorological rocket study which was part of the Indian Middle Atmosphere Program. The equatorial wave campaign-II was conducted from Shar, India (13.7 deg N, 80.2 deg E) from January 15-February 28, 1986. By means of high altitude balloon and the RH-200 meteorological rocket, winds were measured from ground level up to 60 km altitude once each day during the 45-day period. The oscillation frequencies of the deviations in the east-west component of the winds from their mean at each 1-km height interval are obtained by the maximum entropy method. The phases and amplitudes of these frequencies are determined by use of the least squares method on the wind variation time series. Enhanced wave activity is shown to take place in the troposphere and lower mesosphere. The tropospheric waves observed suggest themselves to be Rossby waves of extratropical origin penetrating to tropical latitudes. The observed stratospheric/mesospheric waves appear to emanate from a source around the stratopause.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: (ISSN 0253-4126); 99; 413-423
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    Discovery of hotspots on Io using disk-resolved infrared imaging (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: First results are presented using two new techniques for ground-based observation of Io's hotspots. An IR array camera was used to obtain direct IR images of Io with resolution better than 0.5 arcsec, so that more than one hotspot is seen on Io in Jupiter eclipse. The camera was also used to make the first observations of the Jupiter occultation of the hotspots. These new techniques have revealed and located at least three hotspots and will now permit routine ground-based monitoring of the locations, temperatures, and sizes of multiple hotspots on Io.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 348; 618-621
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    Parameterization of eddy sensible heat transports in a zonally averaged dynamic model of the atmosphere (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A Charney-Branscome based parameterization has been tested as a way of representing the eddy sensible heat transports missing in a zonally averaged dynamic model (ZADM) of the atmosphere. The ZADM used is a zonally averaged version of a general circulation model (GCM). The parameterized transports in the ZADM are gaged against the corresponding fluxes explicitly simulated in the GCM, using the same zonally averaged boundary conditions in both models. The Charney-Branscome approach neglects stationary eddies and transient barotropic disturbances and relies on a set of simplifying assumptions, including the linear appoximation, to describe growing transient baroclinic eddies. Nevertheless, fairly satisfactory results are obtained when the parameterization is performed interactively with the model. Compared with noninteractive tests, a very efficient restoring feedback effect between the modeled zonal-mean climate and the parameterized meridional eddy transport is identified.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 47; 2475-248
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    Behavior of deep convective clouds in the tropical Pacific deduced from ISCCP radiances (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The characteristic features, the diurnal cycle, and the spatial distribution of deep convection over the equatorial Pacific and the relationship of deep convection to SST and surface-wind convergence were examined using a combined visible-IR (VS-IR) threshold method and an IR-only threshold method for diagnosing deep convection clouds (DCCs). Results suggest that deep convection is latitudinally confined to a much smaller spatial scale than that suggested by maps of outgoing long-wave radiation. The results suggested that there are two types of relationships between deep convection, SST, and surface-wind convergence: the west Pacific type and the east Pacific type. The latter relationship is observed in the east Pacific only when SST is not abnormally warm.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Climate (ISSN 0894-8755); 3; 1129-115
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    Global atmospheric temperature monitoring with satellite microwave measurements - Method and results 1979-84 (1990)
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    Publication Date: 2011-08-19
    Description: This paper describes a method for determining global atmospheric-temperature anomalies by means of satellite microwave radiometry. It is shown that microwave measurements of molecular oxygen thermal emission by the Microwave Sounding Units (MSUs) flying aboard the NOAA-6 and NOAA-7 can be used to monitor tropospheric temperature anomalies on global basis to a high level of precision. Comparisons between monthly MSU-derived hemispheric temperature anomalies with those computed from surface thermometer data show a very good agreement over the United States, although not for the hemispheres, especially the Southern Hemisphere. In this latter case, the poor agreement is ascribed to weaker thermal coupling between the ocean and the deep troposphere than that over the U.S. Annual anomalies for the hemispheres exhibit better correlations than do monthly anomalies.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Climate (ISSN 0894-8755); 3; 1111-112
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    A simple inertial model for Neptune's zonal circulation (1990)
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    Publication Date: 2011-08-19
    Description: Voyager imaging observations of zonal cloud-tracked winds on Neptune revealed a strongly subrotational equatorial jet with a speed approaching 500 m/s and generally decreasing retrograde motion toward the poles. The wind data are interpreted with a speculative but revealingly simple model based on steady gradient flow balance and an assumed global homogenization of potential vorticity for shallow layer motion. The prescribed model flow profile relates the equatorial velocity to the mid-latitude shear, in reasonable agreement with the available data, and implies a global horizontal deformation scale L(D) of about 3000 km.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 2269-227
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  • 85
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    Determination of cloud liquid water content using the SSM/I (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: As part of a calibration/validation effort for the special sensor microwave/imager (SSM/I), coincident observations of SSM/I brightness temperatures and surface-based observations of cloud liquid water were obtained. These observations were used to validate initial algorithms and to derive an improved algorithm. The initial algorithms were divided into latitudinal-, seasonal-, and surface-type zones. It was found that these initial algorithms, which were of the D-matrix type, did not yield sufficiently accurate results. The surface-based measurements of channels were investigated; however, the 85V channel was excluded because of excessive noise. It was found that there is no significant correlation between the SSM/I brightness temperatures and the surface-based cloud liquid water determination when the background surface is land or snow. A high correlation was found between brightness temperatures and ground-based measurements over the ocean.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); 28; 817-822
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  • 86
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    Field-independent source localization of Neptune's radio bursts (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: During the Voyager 2 encounter with Neptune, a narrowbanded bursty radio component was observed between 500 and 1326 kHz by the Planetary Radio Astronomy instrument. Based on the emission occurrence pattern, the radio source has been localized without the explicit use of the Neptunian offset-tilted dipole magnetic field model, which is accurate only at distances greater than 4 R(N) (Neptune radii) from the planet. Only assumptions based upon the general nature of radio wave propagation in planetary magnetospheres were used. A number of different candidate radial positions were sampled. For example, at 1.5 R(N), the derived source location was positioned only about 10 deg from the south magnetic pole. The radiation from this source was beamed into a cone of 77.5 + or - 6.3 deg half-angle that was tilted about 10 deg from the radial direction to the north-northeast. At other sampled radial positions, similar source locations were obtained. Due to its proximity to the south magnetic pole, the kilometric emission radio source is believed to be associated with an active auroral region, similar in nature to those found at earth and Saturn.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 19143-19
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  • 87
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    The surface of Venus (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: NASA's Magellan spacecraft first revealed the true nature of Venus's surface when it began to transmit photos in September 1990, and it continues its planned mission to map the whole surface of the planet. The very sharp images obtained and processed to date leave the overall impression that Venus is a dynamic world that has been shaped by processes fundamentally similar to those that have taken place on earth, but often with dramatically different results. Magellan's synthetic aperture radar reveals details as small as 120 meters across, one tenth the size of those detected previously. Venus will be mapped eight times over the next five years, which will improve the resolution and fill in missing areas. A number of images are provided along with explanatory descriptions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Scientific American (ISSN 0036-8733); 263; 60-65
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  • 88
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    Seasonal variation of cloud radiative forcing derived from the Earth Radiation Budget Experiment (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The impact of clouds on the earth's radiation balance is assessed in terms of longwave, shortwave, and net cloud forcing by using monthly averaged clear-sky and cloudy-sky flux data derived from the NASA Earth Radiation Budget Experiment (ERBE). Emphasis is placed on regional measurements, regional cloud forcing, zonal cloud forcing, and snow and ice contributions. It is shown that the global mean cooling varied from 14 to 21 W/sq m between April 1985 and January 1986; hemispherically, the longwave and shortwave cloud forcing nearly cancel each other in the winter hemisphere, while in the summer the negative shortwave cloud forcing is significantly lower than the longwave cloud forcing, producing a strong cooling. The ERBE data reveal that globally, hemispherically, and zonally, clouds have a significant effect on the radiative heating gradients.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 18687-18
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  • 89
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    Isotope mass fractionation during evaporation of Mg2SiO4 (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Synthetic forsterite (Mg2SiO4) was partially evaporated in vacuum for various durations and at different temperatures. The residual charges obtained when molten Mg2SiO4 was evaporated to 12 percent of its initial mass were enriched in heavy isotopes by about 20, 30, and 15 per mil/amu for O, Mg, and Si, respectively, whereas solid forsterite evaporated to a similar residual mass fraction showed negligible fractionations. These results imply that calcium and aluminum-rich refractory inclusions in carbonaceous chondrites must have been at least partially molten in the primordial solar nebula if the observed large mass fractionation effects were caused by evaporation processes in the nebula.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 347; 655-658
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  • 90
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    Xenon fractionation in porous planetesimals (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The distinctively fractionated Xe on Mars and earth may have its root in a common source from which both planets accreted. Beginning with Ozima and Nakazawa's (1980) hypothesis that terrestrial Xe fractionation was caused by gravitational separation of adsorbed solar nebular gases inside large porous planetesimals, it is pointed out that Xe would have been trapped as the planetesimal grew and pores were squeezed shut by lithostatic pressure. It is shown that enough fractionated Xe to supply the earth could have been trapped this way. The degree of fractionation is controlled by the lithostatic pressure at the pore-closing front and so would have been roughly the same for all large planetesimals. The predicted degree of fractionation agrees well with that preserved in terrestrial and Martian Xe. Relative to Xe, this source is strongly depleted in other noble gases. In contrast to the original Ozima and Nakazawa hypothesis, the present hypothesis predicts the observed fractionation, and it allows planetary accretion to occur after the dissipation of the solar nebula.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geochimica et Cosmochimica Acta (ISSN 0016-7037); 54; 2577-258
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  • 91
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    Surface and airborne evidence for plumes and winds on Triton (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Aeolian features on Triton that were imaged during the Voyager Mission have been grouped. The term 'aeolian feature' is broadly defined as features produced by or blown by the wind, including surface and airborne materials. Observations of the latitudinal distributions of the features probably associated with current activity (known plumes, crescent streaks, fixed terminator clouds, and limb haze with overshoot) all occur from latitude -37 deg to latitude -62 deg. Likely indicators of previous activity (dark surface streaks) occur from latitude -5 deg to -70 deg, but are most abundant from -15 deg to -45 deg, generally north of currently active features. Those indicators which give information on wind direction and speed have been measured. Wind direction is a function of altitude. The predominant direction of the surface wind streaks is found to be between 40 deg and 80 deg measured clockwise from north. The average orientation of streaks in the northeast quadrant is 59 deg. Winds at 1- to 3-kilometer altitude are eastward, while those at more than 8 kilometers blow west.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 250; 421-424
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  • 92
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    Global color and albedo variations on Triton (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Global multispectral mosaics of Triton have been produced from Voyager approach images; six spectral units are defined and mapped. The margin of the south polar cap (SPC) is scalloped and ranges in latitude from + 10 deg to -30 deg. A bright fringe is closely associated with the cap's margin; form it, diffuse bright rays extend north-northeast for hundreds of kilometers. Thus, the rays may consist of fringe materials that were redistributed by northward-going Coriolis-deflected winds. From 1977 to 1989, Triton's full-disk spectrum changed from markedly red and UV-dark to nearly neutral white and UV-bright. This spectral change can be explained by new deposition of nitrogen frost over both the northern hemisphere and parts of a formerly redder SPC. Frost deposition in the southern hemisphere during southern summer is possible over relatively high albedo areas of the cap (Stansberry et al., 1990), which helps to explain the apparent stability of the unexpectedly large SPC and the presence of the bright fringe.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1765-176
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  • 93
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    Observations of Neptunian rings by Voyager Photopolarimeter Experiment (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The Voyager Photopolarimeter Experiment detected the Neptunian rings 1989N1R and possibly 1989N2R. These rings were also photographed by the Voyager imaging cameras in August 1989. The firm detection of 1989N1R has an equivalent depth (the product of the radial width and mean normal optical depth) of 0.77 + or - 0.13 km, while a less certain detection of 1989N2R has an equivalent depth of 0.7 km + or - 0.2 km. Several statistical techniques were used to search for additional material in the Neptune ring system, and none was identified at a high confidence level.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1745-174
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  • 94
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    Nitrogen ion clusters in Triton's atmosphere (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The nitrogen ion chemistry that controls Triton's ionospheric composition and may be responsible for the hazes detected by the Voyager spacecraft are discussed. In particular, it is shown that nitrogen cluster ion formation should readily occur in Triton's thin cold atmosphere. The very low temperatures of Triton's atmosphere imply that these clustered ions can nucleate into solid nitrogen particles, creating the extended visible hazes. A model based on the chemical kinetics of nitrogen ions predicts a dense ionosphere at 200-400 km, as detected by Voyager radio occultation measurements.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1725-172
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  • 95
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    Airborne flux measurements and budget estimates of trace species over the Amazon Basin during the GTE/ABLE 2B expedition (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In situ airborne measurements of turbulent heat, moisture, momentum, ozone, and carbon monoxide fluxes in a convective boundary layer were obtained over a tropical rain forest between 1100 and 1630 LT on May 4, 1987. The aircraft flight path was chosen so as to fly over the tower site at the Ducke Forest Reserve near Manaus, Amazonas, Brazil. Both turbulence statistics and mean quantities were used to study the budgets of heat, water vapor, ozone, and carbon monoxide. The ozone budget study shows an accumulation rate in the boundary layer of 0.3 + or - 0.2 ppbv/h. The surface resistance to ozone during this flight was determined to be 0.06 + or - 0.03 s/cm, while the aerodynamic resistance was 0.14-0.17 s/cm. Results from the CO budget analysis show a midday accumulation rate of 0.6 + or - 0.3 ppbv/h in the Amazonian boundary layer. The evidence suggests production of CO in the PBL. A source of CO may exist below the lowest flight level (about 150 m), although it was not possible to determine what part of the flux at flight level was due to chemical production and what part may be due to surface emission.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 16875-16
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  • 96
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    Determination of atmospheric optical properties during the First International Satellite Land Surface Climatology Project Field Experiment (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 27; 373-379
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  • 97
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    Origin of low frequency (intraseasonal) oscillations in the tropical atmosphere. III - Monsoon dynamics (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The issue of the interaction of the monsoon large-scale circulation and intraseasonal oscillations is addressed, showing that, as a result of the interaction of the large scale monsoon flow with the near-equatorial intraseasonal oscillation, unstable baroclinic disturbances are generated over the monsoon region. From a linear stability analysis of quasi-geostrophic motion in a two-level model, it is shown that the westward propagating disturbances generated over the monsoon region are the manifestation of heat-induced unstable Rossby waves. The instability is favored in the region with large vertical wind shear and reduced effective static stability. The monsoon large scale circulation over India and southeast Asia and the plentiful supply of moisture in the region appear to be favorable for the development of these unstable waves.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 47; 1443-146
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  • 98
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    Meteorological conditions during the summer 1986 CITE 2 flight series (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An overview of meteorological conditions during the NASA Global Tropospheric Experiment/Chemical Instrumentation Testing and Evaluation (GTE/CITE 2) summer 1986 flight series is presented. Computer-generated isentropic trajectories are used to trace the history of air masses encountered along each aircraft flight path. The synoptic-scale wind fields are depicted based on Montgomery stream function analyses. Time series of aircraft-measured temperature, dew point, ozone, and altitude are shown to depict air mass variability. Observed differences between maritime tropical and maritime polar air masses are discussed.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 10055-10
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  • 99
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    Potential evapotranspiration and the likelihood of future drought (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The possibility that the greenhouse warming predicted by the GISS general-circulation model and other GCMs could lead to severe droughts is investigated by means of numerical simulations, with a focus on the role of potential evapotranspiration E(P). The relationships between precipitation (P), E(P), soil moisture, and vegetation changes in GCMs are discussed; the empirically derived Palmer drought-intensity index and a new supply-demand index (SDDI) based on changes in P - E(P) are described; and simulation results for the period 1960-2060 are presented in extensive tables, graphs, and computer-generated color maps. Simulations with both drought indices predict increasing drought frequency for the U.S., with effects already apparent in the 1990s and a 50-percent frequency of severe droughts by the 2050s. Analyses of arid periods during the Mesozoic and Cenozoic are shown to support the use of the SDDI in GCM drought prediction.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 9983-100
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  • 100
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    Aircraft microwave observations and simulations of deep convection from 18 to 183 GHz. II - Model results (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In this June 29, 1986 case study, a radiative transfer model is used to simulate the aircraft multichannel microwave brightness temperatures presented in the Adler et al. (1990) paper and to study the convective storm structure. Ground-based radar data are used to derive hydrometeor profiles of the storm, based on which the microwave upwelling brightness temperatures are calculated. Various vertical hydrometeor phase profiles and the Marshall and Palmer (M-P, 1948) and Sekhon and Srivastava (S-S, 1970) ice particle size distributions are experimented in the model. The results are compared with the aircraft radiometric data. The comparison reveals that the M-P distribution well represents the ice particle size distribution, especially in the upper tropospheric portion of the cloud; the S-S distribution appears to better simulate the ice particle size at the lower portion of the cloud, which has a greater effect on the low-frequency microwave upwelling brightness temperatures; and that, in deep convective regions, significant supercooled liquid water (about 0.5 g/cu m) may be present up to the -30 C layer, while in less convective areas, frozen hydrometeors are predominant above -10 C level.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Atmospheric and Oceanic Technology (ISSN 0739-0572); 7; 392-410
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