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At least 1,621 records · Page 90
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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 NTRS1982

Planetary-scale characteristics of the atmospheric circulation during January and February 1979

The global scale mass and wind fields observed during FGGE special observing period (SOP) are studied, with attention given to the time variation and vertical structure of the ultralong waves. A spherical harmonic representation is developed for the global fields. The tropical circulation is found to imprint more amplitude on the lower-order components than the midlatitude circulation does. High amplitude oscillations are determined to be present in the divergent fields on all time scales, i.e., diurnal to monthly. The global scale wind was found to change on scales approaching a week. Good agreement with teleconnection predictions was demonstrated for the cross-equatorial divergent and zonal rotational flow changes. The global scale was concluded to resemble force modes of linear tidal theory, with important contributions from longitudinal heating gradients.

Paegle, J.↗
NASA NTRS1982

A simple method to compute the change in earth-atmosphere radiative balance due to a stratospheric aerosol layer

A computer code was developed in terms of a three-layer model for the earth-atmosphere system, using a two-stream approximation for the troposphere and stratosphere. The analysis was limited to variable atmosphere loading by solar radiation over an unperturbed section of the atmosphere. The scattering atmosphere above a Lambertian ground layer was considered in order to derive the planar albedo and the spherical albedo. Attention was given to the influence of the aerosol optical thickness in the stratosphere, the single scattering albedo and asymmetry factor, and the sublayer albedo. Calculations were performed of the zonal albedo and the planetary radiation balance, taking into account a stratospheric aerosol layer containing H2SO4 droplets and volcanic ash. The resulting ground temperature disturbance was computed using a Budyko (1969) climate model. Local decreases in the albedo in the summer were observed in high latitudes, implying a heating effect of the aerosol. An accompanying energy loss of 23-27 W/sq m was projected, which translates to surface temperature decreases of either 1.1 and 0.45 C, respectively, for background and volcanic aerosols.

Lenoble, J.↗
NASA NTRS1982

Climate studies with a multi-layer energy balance model. I - Model description and sensitivity to the solar constant. II - The role of feedback mechanisms in the CO2 problem

A nine-layer zonally averaged, steady-state model, based upon thermal energy balance, is developed for use in climate sensitivity studies and includes an accurate treatment of radiative transfer, parameterized meridional and vertical energy transport, and thermodynamic interaction between the surface and the atmosphere. A high degree of nonlinearity is exhibited by the model in a study of sensitivity to changes in the solar constant. The change in the hemispheric mean surface temperature is +3.1 C in response to a 2% increase in the solar constant and -4.3 C in response to a 2% decrease in the solar constant. The sensitivity varies with latitude, and the response of atmospheric temperature varies with height. In addition, the model is used to study the sensitivity of climate to a doubling of the atmospheric CO2 content. It is found that the tropospheric temperature lapse rate decreases at low latitudes but increases at high latitudes in response to a doubled CO2 content. Averaged over the Northern Hemisphere, the change is +2.3 C in the surface temperature and +0.47 C in the earth's brightness temperature. The effects of some feedback mechanisms on the climate sensitivity to a doubled CO2 content show that the sensitivity of surface temperature approximately doubles at all latitudes due to the change in water vapor content.

Peng, L.↗
NASA NTRS1982

Numerical simulation of the development of mean monsoon circulation in July

Eight different experiments are carried out, ranging from 8 to 20 days, with a primitive equation model consisting of five atmospheric layers and one oceanic layer. The purpose is to investigate the relative importance of radiative heating and deep cumulus condensation, orography, and initial conditions for the development of the mean monsoon circulation from June to July in the 0-180 deg E, 25 deg S - 55 deg N region. Two alternative initial states are used, one based on the observed monthly mean June pressure distribution, the other on the mean June zonal average pressure distribution. Whereas large-scale condensation and actual land and sea distributions are included in every experiment, deep cumulus cone condensation and radiative heating are always taken together. It is found that the means sea level pressure distribution and low-level flow pattern produced by these simulations are in the main determined by the diabatic heating distribution and are influenced somewhat by orography; they are, however, almost independent of the initial state. The low pressure systems are found to develop faster when diurnal variation of solar radiation is allowed for; this is thought to be due mainly to the more vigorous cumulus activity during the day.

Kuo, H. L.↗
NASA NTRS1983

Equatorial long waves in geostationary satellite observations and in a multichannel sea surface temperature analysis

Geostationary satellite observations of a zonally oriented sea surface temperature front in the eastern equatorial Pacific were made between 1975 and 1981. Long waves appeared along the front mainly during the summer and fall, except during 1976, the year of an El Nino. The waves have averaged periods of 25 days and wavelengths of 1000 km. At the end of 1981, the long waves also were detected in a new sea surface temperature analysis based on multichannel infrared measurements from a polar-orbiting satellite. This quantitative analysis may improve the ability to resolve low-frequency equatorial wave motions from satellite observations.

Legeckis, R.↗
NASA NTRS1983

The role of latent heat release in baroclinic waves - Without beta-effect

An attempt is made to understand the role of latent heat release in the development of baroclinic waves by developing the analytical theory of two-level, quasi-geostrophic baroclinic waves proposed by Phillips (1954) without beta effect, for the case of an atmosphere initially saturated with water vapor and subject to pseudo-adiabatic lifting and dry adiabatic subsistence. The saturated atmosphere condition precludes consideration of conditional convective instability. A consideration of disturbances at each level which depends only on the zonal coordinates and time results in a set of differential equations which is linear in all respects except for the latent heating term in the thermodynamic energy equation. A fundamental nonlinearity is present in this model which is due to heating via the release of latent heat when vertical motion is upward.

Tang, C.-M.↗
NASA NTRS1983

Southern ocean mean monthly waves and surface winds for winter 1978 by Seasat radar altimeter

Data acquired by the SEASAT radar altimeter during the 3 month satellite lifetime are analyzed in a study of the sea state of the southern hemisphere oceans. The lifetime of the SEASAT satellite, July 7 to October 10, 1978, corresponds to the Antarctic winter. Mean monthly maps of wind speed, significant wave height, and swell have been generated from the altimeter measurements along the satellite tracks. These maps delineate spatial and temporal differences of these parameters in the Atlantic, Indian, and Pacific oceans. Several features of the Southern Ocean wind and wave fields agree with conventional descriptions. For example, the principle zonal wind regimes established by the Southeast Trades and Westerlies are clearly evident in the monthly averages. Significant wave height and swell also exhibit minima near the Doldrums at low latitudes with steady increases southward to the latitudes of the Westerlies. However, superimposed on these general patterns is significant variability with horizontal scales as small as 1000 km. The maps also document a gradual migration of the region of absolute maximum wind and wave from the Atlantic eastward to the Indian Ocean and finally into the Pacific.

Mognard, N. M.↗
NASA NTRS1983

On the nonlinear versus linearized lower boundary conditions for topographically forced stationary long waves

For quasi-geostraphic stationary long waves forced by topography, the nonlinear lower boundary condition is derived in terms of the geopotential height and compared with the linearized version. The common practice of replacing terms describing the flow over and around a mountain by upstream zonal flow over the mountain and evaluating the resulting condition at sea level is found to be a good approximation for the cases considered and does not need to be modified as sometimes suggested. Specifically, it is found that this approximation does not affect, for most cases, the lower boundary condition expressed in terms of the geopotential height provided that the stationary wave is not near resonance. At resonance, the eddy advection terms may become important for large-amplitude waves when dissipation and surface diabatic heating are taken into account.

Tung, K. K.↗
NASA NTRS1982

Climatic influence of background and volcanic stratosphere aerosol models

A simple modelization of the earth atmosphere system including tropospheric and stratospheric aerosols has been derived and tested. Analytical expressions are obtained for the albedo variation due to a thin stratospheric aerosol layer. Also outlined are the physical procedures and the respective influence of the main parameters: aerosol optical thickness, single scattering albedo and asymmetry factor, and sublayer albedo. The method is applied to compute the variation of the zonal and planetary albedos due to a stratospheric layer of background H2SO4 particles and of volcanic ash.

Deschamps, P. Y.↗
NASA NTRS1982

Conference on Complex Turbulent Flows: Comparison of Computation and Experiment, Stanford University, Stanford, CA, September 14-18, 1981, Proceedings. Volume 2 - Taxonomies, reporters' summaries, evaluation, and conclusions

Computational techniques for simulating turbulent flows were explored, together with the results of experimental investigations. Particular attention was devoted to the possibility of defining a universal closure model, applicable for all turbulence situations; however, conclusions were drawn that zonal models, describing localized structures, were the most promising techniques to date. The taxonomy of turbulent flows was summarized, as were algebraic, differential, integral, and partial differential methods for numerical depiction of turbulent flows. Numerous comparisons of theoretically predicted and experimentally obtained data for wall pressure distributions, velocity profiles, turbulent kinetic energy profiles, Reynolds shear stress profiles, and flows around transonic airfoils were presented. Simplifying techniques for reducing the necessary computational time for modeling complex flowfields were surveyed, together with the industrial requirements and applications of computational fluid dynamics techniques.

Kline, S. J.↗
NASA NTRS1983

A general circulation model of a Venus-like atmosphere

Heat and momentum budgets are investigated for a three-dimensional general circulation model of a Venus-like, massive and slowly rotating atmosphere which is forced with an axisymmetric radiative heating/cooling distribution. Model results confirm the suggestions of Gierasch (1975) and Rossow and Williams (1979), with a mean meridional circulation which, despite its multicellular form, interacts with quasi-barotropic eddies produced by zonal flow shear instability to yield a weak superrotation of the entire model atmosphere. This process is sufficiently general to encourage the conclusion that it will occur in all slowly rotating atmospheres. Whether it can accelerate wind speeds as large as those observed on Venus cannot presently be determined.

Rossow, W. B.↗
NASA NTRS1983

Global mesoscale variability from collinear tracks of SEASAT altimeter data

Eight to nine sets of global collinear altimeter data with a cross-track grid spacing of approximately 900 km at the equator and 600 km at midlatitude have been obtained from the last 25 days of the 1978 SEASAT mission. Since the geoid is time-invariant, such observations can reveal sea surface height variability caused by dynamic ocean phenomena. Variations due to deep ocean mesoscale features are presently solved for by eliminating the longer wavelength deviations, yielding sea height profiles with an accuracy of a few cm, and a global variability map constructed from these data which reveal an exceptionally realistic perspective of mesoscale energetics. The dominance of exceedingly small variability over extensive regions of the oceans is noted. In both the Atlantic and the Pacific, the North Equatorial Current systems were clearly expressed as zonal bands of higher variability.

Cheney, R. E.↗
NASA NTRS1982

Neutral winds in the polar thermosphere as measured from Dynamics Explorer

Remote sensing measurements of the meridional thermospheric neutral wind using the Fabry-Perot Interferometer on Dynamics Explorer have been combined with in-situ measurements of the zonal component using the Wind and Temperature Spectrometer on the same spacecraft. The two data sets with appropriate spatial phasing and averaging determine the vector wind along the track of the polar orbiting spacecraft. A study of fifty-eight passes over the Southern (sunlit) pole has enabled the average Universal Time dependence of the wind field to be determined for essentially a single solar local time cut. The results show the presence of a 'back-ground' wind field driven by solar EUV heating upon which is superposed a circulating wind field driven by high latitude momentum and energy sources.

Killeen, T. L.↗
NASA NTRS1982

The variability of stratospheric nitrogen compounds observed by LIMS in the winter of 1978-1979

The LIMS experiment was launched on the Nimbus 7 satellite for the purpose of sounding the vertical structure of temperature and key upper atmosphere trace gases on a global scale. The technique of thermal infrared limb sounding was used to obtain measurements of O3, H2O, NO2, and HNO3. LIMS collected data almost continuously from late October to late May over the latitude range from 64 deg S to 84 deg N. Two of the gases, NO2 and HNO3, are important elements in the NO(x) chain of chemical reactions leading to ozone destruction. Results for these gases are described in terms of zonal mean profiles and latitudinal distributions. The period selected for study is January-May 1979, when a major stratospheric warming occurred.

Russell, J. M., III↗
NASA NTRS1983

Stratospheric sudden coolings and the role of nonlinear wave interactions in preconditioning the circumpolar flow

The mechanisms responsible for the transition of the circumpolar flow from its normal midwinter state to the preconditioned state that should evolve before a wavenumber-2 major warming are investigated, through a combination of observational, numerical and theoretical studies. Observations of Eliassen-Palm flux cross sections indicate that while wave zonal mean flow interaction theory could account for the qualitative evolution of the circumpolar flow during the warming, substantial nonlinear wave interactions were active during the cooling period, and these interactions significantly influenced the evolution of the circumpolar flow. Numerical experiments employing a truncated, semispectral model indicate that this cooling phenomenon is realistically reproducible in an idealized integration in which wave-wave interactions are present. Two different mechanisms are proposed to account for these nonlinearities.

Palmer, T. N.↗
NASA NTRS1983

Latitudinal variation of tropospheric ozone in a photochemical model

A zonally, vertically, and annually averaged numerical model of trace gases in the troposphere is used to examine the variation of ozone as a function of latitude. Processes included in the ozone budget are a source due to downward transport of ozone from the stratosphere, deposition at earth's surface, north-south diffusive transport, and photochemical reactions. Sensitivity of calculated ozone concentrations to the latitude variation and magnitude of the stratospheric source is presented. The model indicates a net photochemical source of ozone in the Northern Hemisphere and a net chemical sink in the tropical latitudes. Calculated variation of ozone concentration with latitude is in qualitative agreement with observations.

Hameed, S.↗
NASA NTRS1983

Progress toward the analysis of supersonic inlet flows

A zonal flow analysis procedure was developed to predict the flow through the supersonic diffuser of an axisymmetric mixed compression inlet at angle-of-attack. In this analysis, the inlet flow is divided into three types of regions, each with different dominant flow phenomena. These are the inviscid supersonic core, boundary layer, and shock/boundary layer interaction flows. An appropriate analysis was selected or developed for the three-dimensional flow in each type of region. Procedures were developed to interface these analyses for the overall inlet flow analysis. This analysis was applied to an inlet operating at M = 2.58 at several angle-of-attack conditions. Comparisons are presented between computed and measured flow properties for the inlet and for the component analysis flows. Extensions of the present procedure to include the terminal shock and subsonic diffuser flows are recommended. Desirable experiments for evaluation of the inlet analysis procedure or the component analyses and to support improved modeling or extension of the inlet analysis are defined and recommended.

Paynter, G. C.↗