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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 397 records · Page 22
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NASA NTRS1985

Local effects of gravity wave propagation and saturation

In recent years, gravity waves were recognized to play a major role in the dynamics of the middle atmosphere. Perhaps the major effect of such motions are the reversal of the vertical shear of the mean zonal wind and the occurrence of a large turbulent diffusivity in the mesosphere due to gravity wave saturation. Yet, despite the importance of these gravity wave effects, the processes and the consequences of gravity wave propagation and saturation are only beginning to be understood in detail. The linear saturation theory predicts drag and turbulent diffusion due to saturating wave motion. This theory, however, fails to address a number of issues that are certain to be important for gravity wave propagation and saturation in the middle atmosphere. These issues, including wave transience, wave superposition, local convective adjustment, and nonlinearity, are discussed.

Fritts, D. C.↗
NASA NTRS1986

Tidal coupling with the lower atmosphere (invited review)

The various ways are reviewed in which propagating tidal components excited in the mesophere and below affect the structure of the thermosphere and ionosphere above 100 km. Dynamo effects are not treated here. The physical processes affecting the propagation of upward propagating tides are examined and how they are interrelated in the context of a numerical model. Propagating diurnal and semidiurnal tides which reach thermospheric heights are excited primarily by insolation absorption by tropospheric water vapor (0 to 5 km) and stratospheric/mesospheric ozone (40 to 60 km), respectively. Simulation of these oscillations requires consideration of mean zonal winds and meridional temperature gradients, and the damping effects of turbulent and molecular dissipation, radiative cooling, and ion drag. These effects must be considered on a spherical rotating atmosphere extending from the ground to above 300 km, as they are in the model developed by Forbes depicted schematically.

Forbes, J. M.↗
NASA NTRS1985

Temperature structure and dynamics of the middle atmosphere of Venus

Data obtained by the Pioneer Venus Orbiter Infrared Radiometer in late 1978 and early 1979 are presented in tabular form, including, in particular, the mean temperature structure, with complete latitudinal and longitudinal coverage, and zonal-mean cloud properties. The mean thermal and cloud structures can be interpreted in terms of general circulation of the middle atmosphere. The interim results indicate that (1) the zonal winds on Venus fall to very low values above 90 km, (2) there is a strong midlatitude jet which circles the planet approximately every two days, and (3) the observed solar tides are dominated by the semidiurnal component.

Taylor, F. W.↗
NASA NTRS1985

Energy balance constraints on gravity wave induced eddy diffusion in the mesosphere and lower thermosphere

The constraints on turbulence improved by the mesospheric heat budget are reexamined, and the sufficiency of the theoretical evidence to support the hypothesis that the eddy Prandtl number is greater than one in the mesosphere is considered. The mesopause thermal structure is calculated with turbulent diffusion coefficients commonly used in chemical models and deduced from mean zonal wind deceleration. It is shown that extreme mesopause temperatures of less than 100 K are produced by the large net cooling. The results demonstrate the importance of the Prandtl number for mesospheric turbulence.

Strobel, D. F.↗
NASA NTRS1986

The Vega balloon experiment - Initial results from the global radio tracking

A unique global array of 20 radio telescopes provided 24-h telemetry acquisition of meteorological data from the Vega balloons and differential VLBI measurements of their trajectories. Initial Doppler-tracking analysis indicates mean zonal wind velocities of 69 + or - 1 and 66 + or - 1 m/sec at the Vega 1 and Vega 2 float heights, and discloses an anomaly in the Vega 2 trajectory above the mountains in Aphrodite Terra.

Preston, R. A.↗
NASA NTRS1986

Mesoscale waves as a probe of Jupiter's deep atmosphere

Search of the Voyager images of Jupiter reveals a class of mesoscale waves occurring near the extrema of the zonal velocity profile between latitudes 30 deg S and 30 deg N. The average horizontal wavelength is 300 km, compared to an atmospheric scale height of 20 km; the standard deviation about the mean is only 20 percent. The alignment of most wave trains is nearly zonal, i.e., wave crests are north-south. A typical wave packet is 20 wave crests in length and 1300 km wide. Modeling shows that the waves propagate in a duct below the ammonia condensation level (the visible clouds). For selection of one dominant mode, the Richardson number in the duct must be of order unity; this is the first quantitative determination that has ever been made of the stability of Jupiter's atmosphere below its clouds. The duct is topped by a trapping layer, the ammonia clouds, where the Richardson number is less than 0.25. Meridional trapping of the wave packets is due to the shear in the zonal wind. It is speculated that the period of the waves is diurnal and that they do not propagate poleward of latitudes + or - 30 deg because the Coriolis frequency exceeds the duct Brunt frequency. The waves might be excited by diurnal variations of moist convective activity in the ammonia clouds.

Flasar, F. M.↗
NASA NTRS1987

Jovian seismology

It is hypothesized that observations of the Doppler shifting of IR and UV absorption lines may furnish a powerful method for the detection of 4.5-9 min standing acoustic waves trapped in a wave duct beneath the Jupiter tropopause. Similarly, data could be obtained on Jupiter's thermal and density structure, and on the depth to which its zonal winds penetrate. The present model of standing oscillations in the molecular hydrogen envelope gives attention to theoretical eigenfrequencies and to such forcing functions for wave generation as coupling with turbulent and convective motions, thermal instability due to radiative transfer, wave propagation effects in a saturated atmosphere, and ortho-to-parahydrogen conversion. The small contribution that the forcing mechanisms make to velocity amplitudes implies that the Doppler shifting caused by the waves may only be resolvable through the superposition of oscillation records to enhance S/N ratios.

Bercovici, D.↗
NASA NTRS1986

The behavior of planetary wave 2 in preconditioned zonal flows

The response of linear planetary wave 2 to changes in the isentropic zonally symmetric distribution of potential vorticity (PV) is investigated numerically. Wave 2 is sensitive to the width and position of a region where the meridional derivative of PV is weak, denoted the 'surf zone', in the middle stratosphere. A narrow surf zone leads to an amplification of wave 2, and confines some of its Eliassen-Palm wave activity in high latitudes. For wider surf zones the wave activity is concentrated near the associated critical surface, and the amplitude of the wave decreases. Large changes in the wave amplitude and in the distribution of its activity are associated with the subtle changes in the zonal winds produced by modest modifications in the distribution of PV. Basic states that include regions of reversed meridional gradients of PV lead to wave overreflection and strong poleward focusing of wave activity. The amplitude of wave 2 is enhanced in the presence of negative gradients, with large responses occurring for eastward traveling waves.

Robinson, Walter A.↗
NASA NTRS1986

The quasi-biennial oscillation of ozone in the tropical middle stratosphere - A one-dimensional model

A one-dimensional model of the quasi-biennial oscillation (QBO) of ozone in the tropical middle stratosphere is derived based on assumed (observed) zonal wind QBO in a coupled dynamic, radiative/photochemical system. It is found that the derived vertical variation of the ozone QBO amplitude has two maxima, one at 32 km and the other at 22 km, and a minimum at 28 km. These are in qualitative agreement with observations. In the height interval 30-35 km, the ozone QBO is closely related to temperature dependent photochemistry, and the ozone and temperature variations are out of phase. Below 28 km, where vertical ozone and thermal transports are important, ozone and temperature oscillations are in phase, but both are approximately 270 deg out of phase with the vertical wind variation.

Ling, Xiu-De↗
NASA NTRS1987

Low-frequency atmospheric oscillations over the southeastern Pacific

A 40-50 day atmospheric oscillation has recently been reported in the southeastern Pacific based on analyses of satellite-derived microwave brightness temperature data. Prior to this, such oscillations have not been generally recognized in this region. The purpose of this note is to provide corroboration of the microwave analyses from an independent data set, four years of rawinsonde data from Easter Island. Significant spectral peaks with period 45-53 days were found in the zonal wind near the jet core (300-200 mb) and in the temperature on the underside of the jet. The signal is also present in the 100 mb temperature as shown by strong coherence between 100 and 400 mb temperature perturbations. Direct comparison of the 100 mb temperature perturbations and the microwave data shows good agreement. There is also an indication of a lower frequency signal, about 65-84 day period, in the meridional wind at 1000 mb. This signal appears to be vertically evanescent with maximum amplitude at the surface.

Graves, Charles E.↗
NASA NTRS1987

Planetary atmospheres

Observations and theoretical models of planetary atmospheres published during the period 1983-1986 are reviewed, including Vega and Voyager data and results from ground-based remote sensing. Consideration is given to water-vapor and sulfur-compound distributions, electrical phenomena, and dynamics in the Venus atmosphere; dust storms, water cycles, and water and ice erosion on Mars; the compositions, temperature profiles, and dynamics of the Jovian and Saturnian atmospheres; chemical processes and zonal winds on Titan; and the radiation budgets and chemical compositions of the outer planets.

Leovy, Conway↗
NASA NTRS1987

The response of the tropical atmosphere to low frequency thermal forcing

The tropical response to a localized thermal forcing with approximately 45-day period is investigated for several models of increasing complexity consisting of two equivalent shallow water systems and two fully stratified systems. The fully stratified models appear to be able to reproduce a number of observed features of the tropical 40-50 day oscillation including the modulation of the subtropical jet and the eastward and poleward propagation of zonal wind anomalies.

Anderson, John R.↗
NASA NTRS1987

A comparative study of rapidly and slowly rotating dynamical regimes in a terrestrial general circulation model

As a preliminary step in the development of a general circulation model for general planetary use, a simplified vesion of thef GISS Model I GCM has been run at various rotation periods to investigate differences between the dynamical regimes of rapidly and slowly rotating planets. To isolate the dynamical processes, the hydrologic cycle is suppressed and the atmosphere is forced with perpetual annual mean solar heating. All other parameters except the rotation period remain fixed at their terrestrial values. Experiments were conducted for rotation periods of 2/3, 1, 2, 4, 8, 16, 64 and 256 days. The results are in qualitative agreement with similar experiments carried out previously with other GCMs and with certain aspects of one Venus GCM simulation. As rotation rate decreases, the energetics shifts from baroclinc to quasi-barotropic when the Rossby radius of deformation reaches planetary scale. The Hadley cell expands poleward and replaces eddies as the primary mode of large-scale heat transport. Associated with this is a poleward shift of the baroclinic zone and jet stream and a reduction of the equator-pole temperature contrast. Midlatitude jet strength peaks at 8 days period, as does the weak positive equatorial zonal wind which occurs at upper levels at all rotation periods. Eddy momentum transport switches from poleward to equatorward at the same period. Tropospheric mean static stability generally increases in the tropics and decreases in midlatitudes as rotation rate decreases, but the global mean static stability is independent of rotation rate. The peak in the eddy kinetic energy spectrum shifts toward lower wavenumbers, reaching wavenumber 1 at a period of 8 days. Implications of these results for the dynamics of Venus and Titan are discussed. Specifically, it is suggested that the extent of low-level convection determines whether the Gierasch mechanism contributes significantly to equatorial superrotation on these planets.

Del Genio, Anthony D.↗
NASA NTRS1987

Superrotation induced by critical-level absorption of gravity waves on Venus - An assessment

Critical-level absorption of a continuous spectrum of vertically propagating gravity waves is proposed as the mechanism for supporting the superrotation in the deep Venus atmosphere (below the cloud deck). It is shown that the observed westerly zonal wind effectively separates regions where waves of opposite phase speeds are absorbed, leading to westerly mean-flow acceleration below the clouds and easterly above. Using the diagnostic results of Hou and Goody (1985), a quantitative assessment of the required wave spectrum and fluxes of energy and momentum is obtained, and it is shown that they are compatible with observational constraints.

Hou, Arthur Y.↗
NASA NTRS1987

The characteristic Rossby frequency

The characteristic Rossby frequency is defined for a fixed zonal wavenumber perturbation as the variational integral of the Rayleigh-Ritz method. It is a measure of the time scale of the disturbance. For a disturbance which locally has the shape of an eigenfunction but is not global in extent, the characteristic Rossby frequency is very close to the true eigenvalue, and additionally remains unchanged under linear inviscid dynamics. Results are presented for the shallow water equations, both with and without a mean zonal wind. The characteristic Rossby frequency of a wavenumber 1 perturbation having the shape of the second symmetric Rossby mode but confined to the Northern Hemisphere is close to the corresponding Rossby frequency. This finding is helpful in understanding the behavior of the observed wavenumber 1 pattern of January 1979, which propagated westward with nearly the pure Rossby frequency but was discernible only in the Northern Hemisphere (as discussed by Daley and Williamson).

Straus, David M.↗
NASA NTRS1986

Interaction of the Asian summer monsoon and the Southern Hemisphere

The possible role that divergent circulations emanating from regions of large scale organized convection may have on the rotational motions of the subsiding branch of the resulting overturnings is considered. Correspondence is found between the cross-equatorial flow emanating from regions of organized convection in the Northern Hemisphere, and the subtropical jet in the vicinity of Australia. The difference field also reveals a good correspondence between changes in the meridional gravity wave component and changes in the intensity of maximum zonal wind. The results are consistent with the picture of a local ageostrophic Hadley overturning in the entrance region of subtropical jets, and they show the importance of adequate resolution of tropical divergent modes.

Paegle, Julia N.↗
NASA NTRS1988

Verification of regional climates of GISS GCM. Part 1: Winter

Verification is made of the synoptic fields, sea level pressure, precipitation rate, 200 mb zonal wind and the surface resultant wind, generated by two versions of the GISS climate model. The models differ regarding the horizontal resolution of the computational grids and the specification of the sea surface temperatures. Maps of the regional distributions of seasonal variations of the model fields are shown alongside maps showing the observed distributions. Comparisons of the model results with observations are discussed, and also summarized in tables according to geographic regions.

Druyan, Leonard M.↗
NASA NTRS1987

Medium-range numerical forecasts of atmospheric angular momentum

Forecasts of zonal wind fields produced by the medium-range forecast (MRF) model of the National Meteorological Center are used to create predictions of the atmosphere's angular momentum at lead times of 1-10 days. Based on momentum forecasts archived for the period December 1985-November 1986, it is found that, on average, the MRF exhibits positive skill relative to persistence-based forecasts at all lead times. Over the entire one-year study period, the improvement over persistence exceeds 20 percent for 2-6 day forecasts and remains as large as 10 percent even for 10-day forecasts. On the other hand, skill scores for the MRF momentum predictions vary considerably from month to month, and for a sizable fraction of the study period, the MRF is less skillful than persistence.

Rosen, Richard D.↗