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  • 1
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    Global-scale waves in the Venus atmosphere (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The nature of global-scale waves that can exist in the atmosphere of Venus is examined. A linear three-dimensional model atmosphere with spherical geometry is used to study large-scale forced and free waves. Solutions are obtained numerically with grid points in the vertical and a spherical harmonic expansion in the horizontal. Observations have shown a global-scale traveling wave with phase speed near the cloud-top wind velocity. Global-scale wave modes are found to exist in the model at this velocity. When a radiative-dynamic cloud feedback is added to the model, the most unstable wave mode is found to have the same phase speed as the observed wave. The horizontal structure of this wave is consistent with the observed horizontal structure of the 'Y' feature seen in ultraviolet images of the Venus cloud top.
    Keywords: SPACE SCIENCES (GENERAL)
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 50; 24; p. 4080-4096
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  • 2
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    Zonal motion and structure in Jupiter's upper troposphere from Voyager infrared and imaging observations (1990)
    In:  Other Sources
    Details
    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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  • 3
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    Use of fellowships (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The effective use of Space Grant Program fellowships are critical in meeting program objectives. In the first year of operation, the 21 colleges/consortia will expend from 30-40 percent of their grants for fellowships; program policy will allow up to 50 percent to be spent for fellowships. Thus, fellowship policy must be carefully implemented and monitored.
    Keywords: SOCIAL SCIENCES (GENERAL)
    Type: JHU, First National Space Grant Conference Report; p 94-98
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  • 4
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    Jupiter's Atmospheric Temperatures: From Voyager IRIS to Cassini CIRS (2004)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: Retrievals run on Cassini Composite Infrared Spectrometer data obtained during the distant Jupiter flyby have been used to generate global temperature maps of the planet in the troposphere and stratosphere. Similar retrievals were performed on Voyager 1 IRIS data and have provided the first detailed IRIS map of the stratosphere. In both data sets, high latitude troposphere temperatures are presented for the first time, and the meridional gradients indicate the presence of circumpolar jets. Thermal winds were calculated for each data set and show strong vertical shears in the zonal winds at low latitudes. The temperatures retrieved from the two spacecraft were also compared with yearly ground-based data obtained over the intervening two decades. Tropospheric temperatures reveal gradual changes at low latitudes, with little obvious seasonal or short-term variation (Orton et al. 1994). Stratospheric temperatures show much more complicated behavior over short timescales, consistent with quasi-quadrennial oscillations at low latitudes, as suggested in prior analyses of shorter intervals of ground- based data (Orton et al. 1991, Friedson 1999). A scaling analysis indicates that meridional motions, mechanically forced by wave or eddy convergence, play an important role in modulating the temperatures and winds in the upper troposphere and stratosphere on seasonal and shorter time scales. At latitudes away from the equator, the mechanical forcing can be derived simply from a temporal record of temperature and its vertical derivative. Ground-based observations with improved vertical resolution and/or long-term monitoring from spacecraft are required for this purpose.
    Keywords: Lunar and Planetary Science and Exploration
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  • 5
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    Temporal Variations of Titan's Middle-Atmospheric Temperatures from 2004 to 2009 Observed by Cassini/CIRS (2011)
    In:  Other Sources
    Details
    Publication Date: 2018-06-06
    Description: We use five and one-half years of limb- and nadir-viewing temperature mapping observations by the Composite Infrared Radiometer-Spectrometer (CIRS) on the Cassini Saturn orbiter, taken between July 2004 and December 2009 (Ls from 293 deg. to 48 deg.; northern mid-winter to just after northern spring equinox), to monitor temperature changes in the upper stratosphere and lower mesosphere of Titan. The largest changes are in the northern (winter) polar stratopause, which has declined in temperature by over 20 K between 2005 and 2009. Throughout the rest of the mid to upper stratosphere and lower mesosphere, temperature changes are less than 5 K. In the southern hemisphere, temperatures in the middle stratosphere near 1 mbar increased by 1-2 K from 2004 through early 2007, then declined by 2-4 K throughout 2008 and 2009, with the changes being larger at more polar latitudes. Middle stratospheric temperatures at mid-northern latitudes show a small 1-2 K increase from 2005 through 2009, at north polar latitudes within the polar vortex, temperatures in the middle stratosphere show an approximately 4 K increase during 2007, followed by a comparable decrease in temperatures in 2008 and into early 2009. The observed temperature changes in the north polar region are consistent with a weakening of the subsidence within the descending branch of the middle atmosphere meridional circulation.
    Keywords: Meteorology and Climatology
    Type: Icarus (ISSN 0019-1035); Volume 211; Issue 1; 686-698
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  • 6
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    Dynamics of the atmospheres of the outer planets (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Current knowledge about dynamics and the thermal structure of the outer planets is reviewed with the aim of identifying important measurements which should be made in the post-Voyager era. The existence of jets and cloud bands is the puzzle that underlies all others. The discussion focuses on the particular case of Jupiter because the documentation is the most complete. It is argued that the gross dynamical parameters of the outer planetary atmospheres are the keys to their behaviors, rather than the particular specifics of radiative forcing, cloud distributions, or thermodynamic transformations. Voyager data has shown that the jet systems decay with height in the region above the visible clouds. Therefore, the highest priority must be given to establishing dynamical parameters that characterize levels within and beneath the clouds. These require the determination of the deep structure of the jets, of the density stratification, and of the horizontal density contrasts. The deep regions are not easily accessible and these measurements present challenging opportunities. Indirect inferences about the controlling processes may sometimes be possible by observing waves and other activity in the more easily accessible stratosphere.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-190084 , NAS 1.26:190084
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  • 7
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    Temporal Variations of Titan's Middle-Atmospheric Temperatures From 2004-2009 Observed by Cassini/CIRS (2010)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: We use five and one-half years of limb- and nadir-viewing temperature mapping observations by the Composite Infrared Radiometer-Spectrometer (CIRS) on the Cassini Saturn orbiter, taken between July 2004 and December 2009 (Ls from 293deg to 4deg; northern mid-winter to just after northern spring equinox), to monitor temperature changes in the upper stratosphere and lower mesosphere of Titan. The largest changes are in the northern (winter) polar stratopause, which has declined in temperature by over 20 K between 2005 and 2009. Throughout the rest of the mid to upper stratosphere and lower mesosphere, temperature changes are less than 5 K. In the southern hemisphere, temperatures in the middle stratosphere near 1 mbar increased by 1 to 2K from 2004 through early 2007, then declined by 2 to 4K throughout 2008 and 2009, with the changes, being larger at more, polar latitudes. Middle stratospheric temperatures at mid-northern latitudes show a small 1 to 2K increase, from 2005 through 2009. At north polar latitudes within the polar vortex, temperatures in the middle stratosphe=re show a approx. 4 K increase during 2007, followed by a comparable decrease in temperatures in 2008 and into early 2009. The observed temperature. changes in the north polar region are consistent with a weakening of the subsidence within the descending branch of the middle atmosphere meridional circulation.
    Keywords: Astronomy
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  • 8
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    On the Long-Term Variability of Jupiter's Winds and Brightness as Observed from Hubble (2010)
    In:  Other Sources
    Details
    Publication Date: 2018-06-06
    Description: Hubble Space Telescope Wide Field Planetary Camera 2 imaging data of Jupiter were combined with wind profiles from Voyager and Cassini data to study long-term variability in Jupiter's winds and cloud brightness. Searches for evidence of wind velocity periodicity yielded a few latitudes with potential variability; the most significant periods were found nearly symmetrically about the equator at 0 deg., 10-12 deg. N, and 14-18 deg. S planetographic latitude. The low to mid-latitude signals have components consistent with the measured stratospheric temperature Quasi-Quadrennial Oscillation (QQO) period of-5 years, while the equatorial signal is approximately seasonal and could be tied to mesoscale wave formation, robustness tests indicate that a constant or continuously varying periodic signal near 4.5 years would appear with high significance in the data periodograms as long as uncertainties or noise in the data are not of greater magnitude. However, the lack of a consistent signal over many latitudes makes it difficult to interpret as a QQO-related change. In addition, further analyses of calibrated 410-nm and 953-nm brightness scans found few corresponding changes in troposphere haze and cloud structure on QQO timescales. However, stratospheric haze reflectance at 255-nm did appear to vary on seasonal timescales, though the data do not have enough temporal coverage or photometric accuracy to be conclusive. Sufficient temporal coverage and spacing, as well as data quality, are critical to this type of search.
    Keywords: Astronomy
    Type: Icarus; Volume 210; Issue 1; 258-269
    Format: text
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  • 9
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    A global traveling wave on Venus (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The dominant large-scale pattern in the clouds of Venus has been described as a 'Y' or 'Psi' and tentatively identified by earlier workers as a Kelvin wave. A detailed calculation of linear wave modes in the Venus atmosphere verifies this identification. Cloud feedback by infrared heating fluctuations is a plausible excitation mechanism. Modulation of the large-scale pattern by the wave is a possible explanation for the Y. Momentum transfer by the wave could contribute to sustaining the general circulation.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-194356 , NAS 1.26:194356
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  • 10
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    Temperature and circulation in the stratospheres of the outer planets (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A zonally symmetric, linear radiative-dynamical model is compared with observations of the upper tropospheres and stratospheres of the outer planets. Seasonal variation is included in the model. Friction is parameterized by linear drag (Rayleigh friction). Gas opacities are accounted for but aerosols are omitted. Horizontal temperature gradients are small on all the planets. Seasonal effects are strongest on Saturn and Neptune but are weak even in these cases, because the latitudinal gradient of radiative heating is weak. Seasonal effects on Uranus are extremely weak because the radiative time constant is longer that the orbital period. One free parameter in the model is the frictional time constant. Comparison with observed temperature perturbations over zonal currents in the troposphere shows that the frictional time constant is on the same order as the radiative time constant for all these objects. Vertical motions predicted by the model are extremely weak. They are much smaller than one scale height per orbital period, except in the immediate neighborhood of tropospheric and zonal currents.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-184826 , NAS 1.26:184826
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