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At least 667 records · Page 37

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NASA NTRS1982

Stable and unstable near-resonant states in multilevel, severely truncated, quasi-geostrophic models

Multilevel, severely truncated, quasi-geostrophic models with damping that extend from the surface to 100 km, are used to study the stationary-wave response to orography and the concomitant feedbacks on the zonal flow. For a typical winter zonal-wind profile, it is shown that large amplitude or resonant planetary waves of intermediate zonal wavenumbers of about 4 or 5 occur with an equivalent barotropic structure. It is also shown that wave-zonal flow interaction with a mountain torque and temperature transport is stable to small perturbations on the low side of resonance and unstable on the high side of resonance. Resonant zonal wavenumbers of lower wave wavenumber also occur for the same zonal profile and have a node in the vertical with a small amplitude maximum near the surface and a larger amplitude maximum in the stratosphere. Instability depends on the presence of the orography and the basic asymmetric state as Newtonian damping and surface friction are sufficient to damp the baroclinic instability associated with a linear inviscid model.

Roads, J. O.↗

NASA NTRS1981

Passive microwave remote sensing for meteorology

The use of passive microwave techniques for the systematic geophysical monitoring of earth from aircraft and space is briefly reviewed. These techniques employ frequencies from approximately 1-300 GHz and have yielded information about atmospheric temperature, composition, and wind profiles. In particular, the application of passive microwave technology to temperature profile determination using the Nimbus 5 and 6 satellites, as well as the Tiros-N operational satellites and the Block 5D satellites, is presented.

Staelin, D. H.↗

NASA NTRS1983

Numerical simulation of the atmosphere during a CAT encounter

In an attempt to determine whether clear air turbulence (CAT) which caused a brief, intense turbulence encounter to a jetliner might have been related to gravity waves generated by a line of thunderstorms, local sounding data taken within two hours of the incident have been used as input to a numerical model designed to simulate stratified flow over obstacles. In the model a rigid obstacle at the lower boundary acted as the source of the gravity waves. The model results show a large amplitude disturbance localized over the obstacle at and above flight level, in regions where CAT would be expected. Stratification studies have been conducted, varying the height and shape of the obstacle and the input wind profile. The success of the experiment leads to the conclusion that atmospheric gravity wave simulation can be useful in understanding and possibly avoiding CAT.

Keller, T. L.↗

NASA NTRS1983

Some properties of a 5-parameter bivariate probability distribution

A five-parameter bivariate gamma distribution having two shape parameters, two location parameters and a correlation parameter was developed. This more general bivariate gamma distribution reduces to the known four-parameter distribution. The five-parameter distribution gives a better fit to the gust data. The statistical properties of this general bivariate gamma distribution and a hypothesis test were investigated. Although these developments have come too late in the Shuttle program to be used directly as design criteria for ascent wind gust loads, the new wind gust model has helped to explain the wind profile conditions which cause large dynamic loads. Other potential applications of the newly developed five-parameter bivariate gamma distribution are in the areas of reliability theory, signal noise, and vibration mechanics.

Tubbs, J. D.↗

NASA NTRS1983

Review of specific antenna configurations: An estimate of cost and performance versus frequency for a simple (10 Lambda)-2 clear-air radar antenna array

The building of operational clear air radar wind profilers is discussed. The choice of operating frequency and antenna configuration for these profilers is examined. The cost and performance of a (10 lambda) 2 antenna array versus operating frequency over the range 30 to 400 MHz is compared. To simplify the comparison the array beam will be fixed and the array will be uniformly fed. Yagi and coaxial collinear (COCO) cable antennas are compared, although other configurations may be competitive. It is assumed that the array is driven by a typical 50 kW peak power, 1 kW average, power transmitter located at the array edge when calculating feedline power handling requirements and when system performance is compared. For this comparison an array aperture of (10 lambda) 2 was chosen since a one way beam width of 5 deg or less is desirable to limit beam spreading effects.

Ecklund, W. L.↗

NASA NTRS1983

Voyager 2 observations of Saturn's northern mid-latitude cloud features - Morphology, motions, and evolution

Voyager 2 images provide a basis for detailed study of the morphology and circulation of Saturn's northern midlatitudes. Both Saturn's large-scale cloud bands and the distribution of its local cloud features have a characteristic zonal organization. The region between 30 N and 45 N contains two oppositely directed jets in close proximity, with many bright, active features in the westward jet, and an unusual ribbonlike wave feature encircling the planet in the eastward jet. Several of the smaller features within the westward jet do not remain at fixed latitudes and interact with each other. One group of v-shaped features is found to have periods of high activity correlated with the passage of a cyclonic bright spot. The ribbon wave was Fourier analyzed to determine its spectral composition. The greatest power is near wave number 9, with significant additional peaks appearing at planetary wave numbers 19, 25-27, 35-38, and 47-51. The phase velocity increases with wave number but is not well described by a Rossby-Haurwitz dispersion relation. The curvature of the mean wind profile obtained from cloud tracking indicates that the westward jet exceeds the standard barotropic instability condition, while the eastward jet marginally exceeds the deep-circulation instability condition of Ingersoll and Pollard (1982). The rms eddy velocities on Saturn are less than half as large as those observed on Jupiter.

Sromovsky, L. A.↗

NASA NTRS1983

The response of stationary planetary waves to tropospheric forcing

The lower boundary forcing of airflow over topography, and the internal forcing that results from the geographical distribution of diabatic heating, are studied in light of a steady state, linear, quasi-geostrophic model of stationary waves on a sphere. The lower boundary vertical motions forced by airflow over topography depend on whether the horizontal deflection of airflow around topographic features is taken into account, the level of the wind profile at which flow over topography is assumed to take place, and the topographic data set that was used in the forcing formulation. The lower boundary forcing is taken to be given by the observed stationary planetary wave in lower boundary geopotential height, and the internal forcing is computed using the planetary wave propagation equation on the observed wave structure.

Alpert, J. C.↗

NASA NTRS1984

Testing and optimizing MST coaxial collinear arrays, part 6.4A

Many clear-air VHF wind profiles use coaxial collinear (COCO) arrays for their antenna. A COCO array is composed of long lines of half-wave dipoles spaced one-half wavelength apart. An inexpensive method of checking a COCO array is described and its performance is optimized by measuring and then correcting the relative rf phase among its lines at their feed point. This method also gives an estimate of the rf current amplitude among the lines. The strength and location of the sidelobes in the H-plane of the array can be estimated.

Warnock, J. M.↗

NASA NTRS1984

A further study of gravity wave induced drag and diffusion in the mesosphere

Lindzen's (1967) parameterization for the drag and eddy diffusion produced by breaking internal gravity waves in the mesosphere and lower thermosphere is applied to a modified version of the beta-plane channel model of Holton (1982) in which an isotropic source spectrum of waves is specified similar to that given in 1982 by Matsuno (1982). The transmission for each wave component is influenced by Newtonian cooling and by eddy diffusion induced by the breaking of other wave components. In general the waves with smallest Doppler-shifted phase speeds break first and produce sufficient eddy diffusion to significantly raise the breaking heights for the higher speed components. Thus, the wave drag and diffusion is spread through a deep layer and the resulting mean wind profiles for both summer and winter solstice conditions are more realistic than those computed previously by Holton.

Holton, J. R.↗

NASA NTRS1984

Structure and dynamics of Saturn's atmosphere

The large-scale structure and dynamics of Saturn's atmosphere, as revealed in the visible markings, wind patterns, and horizontal variation of temperature, are discussed. The large-scale thermal structure is addressed, including the mean vertical structure and the seasons and jets of the horizontal temperature structure. Earth-based and Voyager wind observations are used to discuss the internal rate of rotation, the zonal wind profile, the eddies, and the eddy transport. Dynamic models of the atmospheric circulation are reviewed, discussing the depth of the zonal flow, upwelling and downwelling, deep convection, eddy-mean flow interactions, long-lived ovals, and the zonal velocity profile.

Ingersoll, A. P.↗

NASA NTRS1985

Diagnostic requirements for the superrotation on Venus

The eddy source pattern required to maintain zonally averaged circulation in the solar heating and zonal wind profiles of the Venus atmosphere below 80 km has been calculated. The calculated residual meridional circulation in the cloud top region corresponds to multiple direct and indirect cells in the vertical, whose depths are controlled by the scales of solar heating and eddy sources. In the presence of mean meridional transports, the observed zonal superrotation can be supported by alternating layers of eddy sources and sinks, which may be due to thermal tides.

Hou, A. Y.↗

NASA NTRS1985

Gravity Waves

In recent years it has been widely recognized that vertically propagating gravity waves play an important role in the dynamics of the middle atmosphere in partly determining the large scale temperature and wind structure through their energy and momentum transport. In particular, the meridional temperature distribution and the mean wind profile in the upper mesosphere are considered to be largely affected by the turbulence diffusion and friction that gravity waves induce through their breaking. For an understanding of the middle atmosphere circulation, it is therefore very important to know the global distribution and temporal variation of gravity waves in a climatological sense. The results of the statistics for gravity wave activity in the stratosphere and mesosphere are presented as a function of latitude and month, with the aid of meteorological rocket network observations.

Hirota, I.↗

NASA NTRS1985

Simulation studies related to the design of post-FGGE observing systems

The results of three detailed simulation studies are presented. The first study consists of a comparative assessment of the performance of an advanced moisture/temperature sounder (AMTS) being proposed by NASA as a follow-on replacement to the current HIRS-2 operational sounder aboard the NOAA weather satellites. The second study was concerned with assessing the relative accuracies of inferred atmospheric states for idealized lidar wind profiling systems, temperature profiling systems, temperature profiling systems, surface pressure systems, and composite systems. The third study incorporated the above systems into a highly realistic data analysis/forecast cycle from which a series of forecast impact studies were conducted. These studies, taken together, give us a picture of the potential that emerging technoloies can offer in the determination of the basic atmospheric variables required for long-range numerical weather and climate prediction.

Halem, M.↗

NASA NTRS1985

Some studies of zonal and meridional wind characteristics at low latitude Indian stations

At the beginning of the Indian Middle Atmosphere Programme (IMAP), it was decided that the preparation of consolidation reports of already available parameters for the middle atmosphere would be useful. Atmospheric wind data obtained by rockets and balloons constituted one such parameter which had to be consolidated. The present paper summaries the results of this consolidation study. Both zonal and meridional components of winds at four low latitude Indian stations namely Thumba, Shar, Hyderabad, and Balasore, have been analyzed to yield reference wind profiles for each month. The montly mean values have been used to bring out the amplitudes and phases of the annual, semiannual and quasi-biennial oscillations.

Nagpal, O. P.↗

NASA NTRS1985

Doppler lidar wind measurement on Eos

A polar-orbiting platform segment of the Earth Observing System (EOS) could carry a CO2-laser based Doppler lidar for recording global wind profiles. Development goals would include the manufacture of a 10 J laser with a 2 yr operational life, space-rating the optics and associated software, and the definition of models for global aerosol distributions. Techniques will be needed for optimal scanning and generating computer simulations which will provide adequately accurate weather predictions.

Fitzjarrald, D.↗

NASA NTRS1986

On satellite scatterometer capabilities in air-sea interaction

The verified capabilities and some practical usage of the satellite scatterometer in geophysical data production have demonstrated the value of this instrument. This evaluation of scatterometer ability to measure marine winds includes the scatterometer verification data, the state of the art planetary boundary layer model relating the wind profile in the atmosphere to the surface stress, and the pertinent results of the Storms Response Experiment.

Brown, R. A.↗

NASA NTRS1986

Observations and a model of gravity-wave variability in the middle atmosphere

A major goal was to determine what portion of the gravity-wave frequency spectrum accounted for the majority of the momentum flux and divergence, as this has important implications for the middle atmosphere response. It was found that approx. 70% of the total flux and divergence was due to wave motions with observed periods less than 1 hour, consistent with expectations based on the shape of the observed gravity-wave spectrum (FrItts, 1984). This dominance of the momentum flux and divergence by high-frequency motions implies a potential for the modulation of those quantities by large-amplitude motions at lower frequencies. A second, striking aspect of the velocity and momentum flux data is its dramatic diurnal variability, particularly at certain levels. This variability is illustrated with the momentum flux, computed in 8-hr blocks. The dominant contributions here are due to waves with periods less than 1 hr. The variability with height and size of the mean square velocity in the west beam and the momentum flux, energed over the 3-day period. A detailed analysis of the various tidal motions present during this data interval was performed, and it was determined that variations in the zontal wind profile imposed by the diurnal tidal motion are probably responsible for the modulation of the gravity-wave amplitudes and momentum fluxes.

Fritts, D. C.↗

NASA NTRS1986

Scientific reasons for a network of ST radars and cooperative campaigns

Due to their capabilities of measuring wind profiles in the troposphere and stratosphere with good time and height resolution, whatever the weather conditions, stratosphere-troposphere (ST) radars are well adapted to carry out atmospheric research in many fields as well as to fulfill the meteorological forecasting needs. Examples are presented from previous and future national or international campaigns planned in France. The ST radars were used first by themselves with the adjunction of radiosonde data. Then networks were built and used to get horizontal parameters. It appears that ST radar networks should naturally be included in cooperative campaigns.

Petitdidier, M.↗