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

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At least 361 records · Page 20
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NASA NTRS1982

A new look at the Saturn system - The Voyager 2 images

Images of the Saturn system acquired by Voyager 2 in its encounter in August 1981 are presented and information gained from the imagery on the atmosphere, satellites, and rings of Saturn is discussed. The images have shown the Saturn atmosphere to contain persistent oval clouds similar to those of Jupiter, and small irregular features indicative of a pattern of zonal winds that is symmetric about the equator and appears to extend to great depths. The atmosphere of Titan is found to possess an upper haze layer above the main haze, a hemispherical brightness asymmetry, and a dark band in the north polar region. Other satellite observations included relatively high resolution coverage of Enceladus and Tethys, moderate resolution views of Hyperion and Iapetus, and the first observations of Phoebe, as well as views of the eight minor satellites associated with the orbits of Dione, Tethys and Mimas, and the F and A rings. Images of various ring structures were obtained, most notably the birth of a spoke and variable ringlet structures in the outer B ring. The observations may be used to deduce the collisional and thermal history of the rings and satellites.

Smith, B. A.↗
NASA NTRS1982

The spokes in Saturn's rings - A new approach

It is proposed that zonal winds in Saturn's atmosphere cause superrotation of the ionosphere and, by virtue of field-aligned currents, generate a potential of about 16 kV across the B-ring. Such a potential can momentarily polarize 1-10-micron ice particles in a radial sense, and thus create the spectacular spokes. A resulting current flowing radially through the B-ring would give rise to a power of approximately 10 million W, which is close to that dissipated in a Saturn electrostatic discharger burst.

Carbary, J. F.↗
NASA NTRS1982

Pulse asymptotics of the Charney baroclinic instability problem

The asymptotic response of the Charney baroclinic instability problem to a localized perturbation is determined using the formalism of Briggs (1964) and exploiting a recently obtained highly accurate WKB approximate dispersion relation (Lindzen and Rosenthal, 1981). Comparison is made with previous results for two-level and Eady models. Small scales and rapid growth characteristic of the initial stages of cyclogenesis are found and the linear dispersion relation, which can be obtained from observation of zonal wind and stability, emerges as a forecast tool for prediction of geographically local cyclogenesis.

Farrell, B. F.↗
NASA NTRS1982

The role of gravity wave induced drag and diffusion in the momentum budget of the mesosphere

A slight modification of the parameterization suggested by Lindzen (1981) for the zonal drag and eddy diffusion effects generated by breaking internal gravity waves in the mesosphere is tested using a severely truncated midlatitude beta-plane channel model. It is found that realistic mean zonal flow profiles with zonal wind reversals above the mesopause can be simulated for both winter and summer radiative heating conditions provided that a gravity-wave spectrum is assumed which includes both stationary waves and waves of relatively large phase speeds. These results contrast greatly with the unrealistic mean wind profiles produced when Rayleigh friction is used to parameterize the effects of small scale motions on the mean flow.

Holton, J. R.↗
NASA NTRS1982

Parameterization of IR cooling in a middle atmosphere dynamics model. I - Effects on the zonally averaged circulation

A computationally efficient two-stream parameterization of IR cooling is developed for a middle atmosphere dynamics model. The parameterization combines the monochromatic feature of an emissivity formulation with the computational simplicity of a single spatial integral to evaluate the monochromatic transfer equation. Calculations show strong radiative control of the mesopause region and the need for substantial deceleration of the mean zonal winds. Calculated temperatures show good agreement in the summer hemisphere where planetary wave activity is negligible, but in the polar night of the winter hemisphere they are about 30 K too cold, which suggests planetary wave heating must make up the deficit. With observed ozone densities, globally averaged radiative equilibrium temperatures in the 65-75 km region are too cold and an additional heat source about 1 K/day is required.

Apruzese, J. P.↗
NASA NTRS1982

Radiative transfer in realistic planetary atmospheres

Some 40 publications that appeared in scientific journals from 1973 to 1981 as well as 45 scientific reports issued during the grant period are listed by title. Topics cover the development of a matrix operator theory of radiative transfer which made possible the exact model calculations of the radiance as a function of height in planetary atmospheres; calculation of the Mie phase matrix for various types of particles as well as for radiance and polarization in planetary atmospheres; analysis of high dispersion spectroscopic observations of Venus; calculation of curves of growth for Venus; the development of a theory for calculating radiative transfer in spherical shell atmospheres; investigations of zonal winds on Venus; and examination of Rayleigh scattering.

Plass, G. N.↗
NASA NTRS1982

Wave instability in the polar region of Venus

Infrared and radio observations of the upper cloud region of Venus indicate that the north polar region contains features of large thermal contrast. A cold collar, encompassing a region of temperature inversions, lies between latitudes of about 65 and 75 deg, and a pair of warm features, separated by about 180 deg of longitude and centered near 80 deg latitude, rotate about the pole with a period of about 2.9 days. It is shown that the cold temperatures associated with the inversions lead to an enhancement in the mean zonal wind in a localized area near the pole, and that this enhancement makes the mean flow barotropically unstable. Since data for this region are limited, a model for the thermal structure has been used for calculating growth times and phase periods of the unstable modes. Choosing model parameters to agree as closely as possible with available data, it has been determined that the rotating warm features are likely to be manifestations of barotropically unstable waves.

Elson, L. S.↗
NASA NTRS1982

Mg/+/ morphology from visual airglow experiment observations

Observations of low-latitude Mg(+) by the Visual Airglow Experiment on Atmosphere Explorer E were analyzed by a two-dimensional inversion technique. Number density profiles as functions of geographic position were obtained in the F2 region. The profiles represent daytime northern winter, solar maximum conditions and reveal frequent occurrences of large number densities (50-100 per cu cm) at altitudes up to 475 km. Maximum densities are usually found near the equator at 1200-1400 LT. The equatorial density then decreases as the peak concentrations shift to higher latitudes. Longitudinal differences in the time development of the metal ion density appear in the afternoon. These seem to be due to the increasing importance of zonal winds and/or to longitudinal differences in the vertical ion drift velocity.

Fesen, C. G.↗
NASA NTRS1982

Dynamical implications of the observed thermal contrasts in Venus' upper atmosphere

Observational data on the Venusian upper atmosphere are analyzed to determine the dynamical implications of the large pressure change across the terminator, to study the change in diurnal contrast pattern at the 100 km level, and to investigate the viability of the most straightforward explanation of the cooling, radiative emission by CO2 in the 15 micron bands. Evidence is discussed that a major subsidence or downward vertical contraction of the upper atmosphere occurs across the terminator. The observation that supersonic velocities would be induced in horizontal, inviscid flow by the observed pressure distributions affected by the described flow subsidence is investigated by generalizing the equations for adiabatic inviscid flow along streamtubes to the case of nonhorizontal inviscid flow with heat addition. Nightside cooling is discussed, showing variations in cooling rates. Finally, zonal winds below 100 km are considered.

Seiff, A.↗
NASA NTRS1982

Planetary-scale waves in the Venus atmosphere

Observed wave-like cloud features on Venus, which at times form a Y-like structure which encircles the planet, were modelled numerically. Linearized primitive equations for a shallow, hydrostatic atmosphere are defined, along with upper boundary layer conditions for the 4-6 day periods detected in the atmospheric response to forcing. The basic state of the Venus atmosphere was considered to display variations in static stability and the mean zonal wind as a function of altitude. Forcing was introduced over a wide range of frequencies in order to produce the target oscillation modes. Combination of a midlatitude Rossby wave and an equatorial Kelvin wave was found to yield the observed Y-shape, which could be preserved with nonlinear coupling.

Covey, C.↗
NASA NTRS1983

Oceans on Titan?

If global oceans on methane exist on Titan, the atmosphere above them must be within 2 percent of saturation. The two Voyager radio occultation soundings, made at low latitudes, probably occurred over land, since they imply a relative humidity less than or equal to 70 percent near the surface. Oceans might exist at other low-latitude locations if the zonal wind velocities in the lowest 3 kilometers are less than or equal to 4 centimeters per second.

Flasar, F. M.↗
NASA NTRS1984

The simulation of transient statistics of the Southern Hemispheric circulation by the GLAS seasonal cycle model: Preliminary results

The general circulation of the Southern Hemisphere is quite different from that of the Northern Hemisphere in many important ways. These include the barotropic nature of the stationary waves and the presence of a strong barotropic component to the mean zonal wind, the lack of a strong seasonal dependence of the transient eddies, and the dominant role played by eddies with periods less than 10 days compared to longer period fluctuations. Such differences attest to the importance of the altered nature of the orographic and thermal land-sea forcings in the Southern Hemisphere compared to the Northern Hemisphere. Some of the important features of the Southern Hemisphere circulation as simulated by the GLAS Seasonal Cycle Model (SCM) are presented. The geographical patterns of local variability and their seasonal shifts in the SCM are discussed and compared to observations.

Straus, D. M.↗
NASA NTRS1984

Two contrasting Northern Hemisphere winters: 1980 - 1981 and 1981 - 1982

Seasonal statistics calculated from daily operational analyses by the European Centre for Medium Range Weather Forecasts for December 1980 - February 1981 (season 1) and December 1981 - February 1982 (season 2) were used to contrast the two seasonal mean circulation patterns present in the Northern Hemisphere and to investigate possible causes for the differences. The vertically averaged seasonal mean zonal wind and E-vector, a measure of the anisotropy of the transient eddies over the Pacific is shown for season 1 and season 2. The pattern in season 2, but not season 1, resembles that found in a modeling study of barotropic instability. One possible explanation for the differences between season 1 and 2 is a weak change in tropical heating associated with the southern oscillation, the effect of which in midlatitude was amplified by the occurrence of barotropic instability over the Pacific in season 2, but not season 1.

White, G. H.↗
NASA NTRS1983

Stratospheric water vapor variability for Washington, DC/Boulder, CO - 1964-82

Measurements for Washington, DC and Boulder, CO are combined to provide a time series of midlatitude stratospheric water vapor data for the period 1964-82. The mean concentration for the data period is shown to be nearly constant with altitude for the low stratospheric layer between 16-22 km with a mass mixing ratio for the layer of 2.5-2.6 ppmm. Above 22 km the mixing ratio increases slightly with altitude. Evident in the 60 mb level time series is an annual cycle, a quasi-biennial cycle and a long-term nonlinear trend. The quasi-biennial cycle in water vapor at midlatitudes is consistent with variations in tropical stratosphere zonal winds and temperature and total ozone and suggests a modulation of the Hadley cell circulation. The long-term trend shows mixing ratio increasing during the 1960s and decreasing in the 1970s after 1972.

Mastenbrook, H. J.↗
NASA NTRS1984

The earth's thermospheric superrotation from Dynamics Explorer 2

Neutral thermospheric zonal winds measured from the Wind and Temperature Experiment on Dynamics Explorer 2 have been analyzed to provide a measure of the superrotation of the neutral thermosphere. The data were averaged in local time in 10 degree bands from the equator to 40 degrees latitude. The results show an average wind velocity on the order of 18 m/s to the East at the equator and a westward wind of the same magnitude at mid latitudes. Within the range of altitudes of the data base (200 to 700 km) no evidence of any significant altitude dependence was found. Averaging our data over the latitude bands studied indicates a net corotation of the thermosphere. This result is not in agreement with the superrotation value reported by King-Hele and Walker on the basis of satellite drag analysis.

Wharton, L. E.↗
NASA NTRS1984

Tropical response to lateral forcing with a latitudinally and zonally nonuniform basic state

The dynamics of lateral forcing of a stable tropical atmosphere by incident waves from the midlatitudes are examined. Attention is focused on conditions where the WKB method is invalid, and only given to barotropic flows. The tropical atmosphere is treated as a steady planetary wave and a zonal shear flow. The 200 mb level is investigated in terms of a midlatitude wave with self-compatible parametric values that is constrained to satisfy the radiation conditions at the boundary. Wave modes are found to be susceptible to trapping between two turning points in the equatorial zone in the presence of a zonal shear flow. Quasi-resonant waves can then appear over a wide range of parametric conditions of the forcing wave and the basic state. The zonal wind structure determines the resonance conditions.

Wilson, J. D.↗
NASA NTRS1983

The simulation of the seasonal cycle of the Southern Hemispheric circulation by the GLAS Seasonal Cycle Model and a comparison to observations

The general circulation of the Southern Hemisphere is quite different from that of the Northern Hemisphere in many important ways. These include the barotropic nature of the stationary waves and the presence of a strong barotropic component to the mean zonal wind, the lack of a strong seasonal dependence of the transient eddies, and the dominant role played by eddies with periods less than 10 days compared to longer period fluctuations. Such differences attest to the importance of the altered nature of the orographic and thermal land-sea forcings in the Southern Hemisphere compared to the Northern Hemisphere. Some of the important features of the Southern Hemisphere circulation as simulated by the GLAS Seasonal Cycle Model (SCM) are presented. The geographical patterns of local variability and their seasonal shifts in the SCM are discussed and compared to observations.

Straus, D. M.↗
NASA NTRS1983

Modes of inter-hemispheric wave propagation

Attention is given to observations made in connection with the First GARP (Global Atmospheric Research Program) Global Experiment (FGGE), taking into account the average 200 mb zonal wind for two periods during the First Special Observing Period of FGGE, and the 200 mb velocity potential. The meridional linkages implied in the observations involve sources south of 15 deg N, and the most active extratropical patterns are collocated with regions of tropical easterlies. The possibility is investigated that the theory of reduced Rossby wave propagation through easterlies is not sufficiently general to cover the considered observations, taking into account a shallow water model. It is found that the meridional interactions cannot be associated with Rossby waves because these waves connot be generated in the regions of zero absolute vorticity gradient within which the forcing is embedded.

Paegle, J.↗