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  • LUNAR AND PLANETARY EXPLORATION  (4)
  • METEOROLOGY AND CLIMATOLOGY  (2)
  • 1985-1989  (6)
  • 1
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    Microdunes and Other Aeolian Bedforms on Venus: Wind Tunnel Simulations (1985)
    In:  CASI
    Details
    Publication Date: 2014-10-08
    Description: The development of aeolian bedforms in the simulated Venusian environment has been experimentally studied in the Venus Wind tunnel. It is found that the development of specific bedforms, including ripples, dunes, and waves, as well as their geometry, are controlled by a combination of factors including particle size, wind speed, and atmospheric density. Microdunes are formed which are analogous to full-size terrestrial dunes and are characterized by the development of slip faces, internal cross-bedding, a low ratio of saltation path length to dune length, and a lack of particle-size sorting. They begin to develop at wind speeds just above saltation threshold and evolve into waves at higher velocities. At wind speeds of about 1.5 m/sec and higher, the bed is flat and featureless. This evolution is explained by a model based on the interaction of alternating zones of erosion and deposition and particle saltation distances.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington Repts. of Planetary Geol. and Geophys. Program; p 309
    Format: text
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  • 2
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    Potential Bedforms on Venus: Wind Tunnel Simulations (1985)
    In:  CASI
    Details
    Publication Date: 2014-10-08
    Description: Wind tunnel studies involving mixtures of particle sizes (bimodal and multimodal distributions) indicate the microdunes and related ridge- and wave-like structures can occur over a wider range of conditions. The results indicate that the bedforms develop as a consequence of the effective sorting capability of the high-density Venusian atmosphere. Four mixtures of different particle-size distributions were investigated. The results of these experiments suggest that: (1) small-scale bedforms on Venus may be more common than previously anticipated from simulations involving only unimodal sands; (2) small particles are rapidly sorted on Venus if winds slightly above threshold are available; (3) coarse particles are transported in traction within the bedforms as well as rolled by saltating fines, suggesting that the capacity of wind on Venus to transport material is greater than anticipated from previous flux studies and (4) microdunes and related ridges and waves with coarse and fine layers can be produced during sorting.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington Repts. of Planetary Geol. and Geophys. Program; p 307-308
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  • 3
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    Aeolian abrasion on Venus: Preliminary results from the Venus simulator (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The role of atmospheric pressure on aeolian abrasion was examined in the Venus Simulator with a constant temperature of 737 K. Both the rock target and the impactor were fine-grained basalt. The impactor was a 3 mm diameter angular particle chosen to represent a size of material that is entrainable by the dense Venusian atmosphere and potentially abrasive by virtue of its mass. It was projected at the target 10 to the 5 power times at a velocity of 0.7 m/s. The impactor showed a weight loss of approximately 1.2 x 10 to the -9 power gm per impact with the attrition occurring only at the edges. Results from scanning electron microscope analysis, profilometry, and weight measurement are summarized. It is concluded that particles can incur abrasion at Venusian temperatures even with low impact velocities expected for Venus.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1986; p 279-281
    Format: application/pdf
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  • 4
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    Transport of Venusian rolling 'stones' by wind? (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Simulations of Venusian wind processes are described which show that particles are moved by 'rolling' at wind speeds as much as 30 percent lower than those required for saltation threshold. This mode of wind transport is only observed for sustained periods in water on earth; thus, there are similarities between aqueous fluid transport on earth and atmospheric transport on Venus. The formation of small sand ridges and grooves oriented parallel to the wind direction is associated with the rolling of grains in Venusian simulations and these structures may be unique aeolian features on Venus.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 313; 771-773
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  • 5
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    Limb effects in satellite temperature sounding (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: To date, operational satellite temperature retrievals from the TIROS-N/NOAA A-G series of satellites and a large percentage of those produced for research purposes have used statistical techniques to estimate limb effects in satellite-observed radiances. In this study, temperature profiles were derived using the radiative transfer equation in a form which properly takes into account the angle of observation. These temperature profiles were then compared to those derived using the radiative transfer equation with 'nadir radiances' produced by a statistical limb correction technique similar to those now used operationally. This comparison revealed significant differences in the derived temperature profiles at large viewing angles, particularly in the case of strong meridional temperature gradients. Overall, the results suggest that for the calculation of temperature profiles from nonnadir observations, the more proper physical solution is the preferred procedure for deriving temperature fields.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Climate and Applied Meteorology (ISSN 0733-3021); 24; 287-290
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  • 6
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    Hurricane Debby - An illustration of the complementary nature of VAS soundings and cloud and water vapor motion winds (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The utility of VISSR Atmospheric Sounder (VAS) temperature and moisture soundings and cloud and water vapor motion winds in defining a storm and its surroundings at subsynoptic scales has been examined using a numerical analysis and prognosis system. It is shown that the VAS temperature and moisture data, which specify temperature and moisture well in cloud-free areas, are complemented by cloud and water vapor motion data generated in the cloudy areas. The cloud and water vapor 'winds' provide thermal gradient information for interpolating the soundings across cloudy regions. The loss of analysis integrity due to the reduction of VAS sounding density in the cloudy regions associated with synoptic activity is ameliorated by using cloud and water vapor motion winds. The improvement in numerical forecasts resulting from the addition of these data to the numerical analysis is recorded.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: American Meteorological Society, Bulletin (ISSN 0003-0007); 66; 258-263
    Format: text
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