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NASA NTRS1983

Middle Atmosphere Program. Handbook for MAP, volume 9

The term Mesosphere-Stratosphere-Troposphere radar (MST) was invented to describe the use of a high power radar transmitter together with a large vertically, or near vertically, pointing antenna to study the dynamics and structure of the atmosphere from about 10 to 100 km, using the very weak coherently scattered radiation returned from small scale irregularities in refractive index. Nine topics were addressed including: meteorological and dynamic requirements for MST radar networks; interpretation of radar returns for clear air; techniques for the measurement of horizontal and vertical velocities; techniques for studying gravity waves and turbulence; capabilities and limitations of existing MST radar; design considerations for high power VHF radar transceivers; optimum radar antenna configurations; and data analysis techniques.

Bowhill, S. A.↗

NASA NTRS1984

A numerical simulation of three-dimensional flow in an adaptive wall wind tunnel

Numerical simulations of three dimensional flows in a prototype adaptive wall wind tunnel are conducted at the Mach number of 0.6 to investigate: (1) wind tunnel wall interference, (2) active streamline control by varying air removal or injection along the walls, and (3) to develop a method for establishing wall boundary conditions for interference free flows. Wind tunnel wall interference could be controlled by using only the vertical velocity components. For the configuration tested, interference free flow with solid sidewalls can be approximated by using only floor and ceiling blowing/suction.

Mendoza, J. P.↗

NASA NTRS1984

Synoptic scale wind field properties from the SEASAT SASS

Dealiased SEASAT SEASAT A Scatterometer System SASS vector winds obtained during the Gulf Of Alaska SEASAT Experiment GOASEX program are processed to obtain superobservations centered on a one degree by one degree grid. The grid. The results provide values for the combined effects of mesoscale variability and communication noise on the individual SASS winds. These superobservations winds are then processed further to obtain estimates of synoptic scale vector winds stress fields, the horizontal divergence of the wind, the curl of the wind stress and the vertical velocity at 200 m above the sea surface, each with appropriate standard deviations of the estimates for each grid point value. They also explain the concentration of water vapor, liquid water and precipitation found by means of the SMMR Scanning Multichannel Microwave Radiometer at fronts and occlusions in terms of strong warm, moist air advection in the warm air sector accompanied by convergence in the friction layer. Their quality is far superior to that of analyses based on conventional data, which are shown to yield many inconsistencies.

Pierson, W. J., Jr.↗

NASA NTRS1983

The use of dynamical constraints in the analysis of mesoscale rawinsonde data

A process for data interpolation which seeks to maintain dynamical consistency is applied to the analysis of mesoscale rawinsonde data obtained from the National Severe Storms Laboratory. The analysis procedure is in two steps: a successive-corrections interpolation to gridpoints, followed by a variational adjustment which uses a set of forecast equations of horizontal momentum as dynamical constraints. The objective analysis is applied in case studies of conditions on May 22, 1966 and June 8, 1966, and it is shown that the adjusted winds and geopotentials have greatly reduced residuals compared to the initial fields. Adjustments to the wind and geopotential fields have root mean square values of 1-2 m/sec and 30-50 sq m/sec per sec, respectively. In addition, the vertical velocity fields computed from the adjusted winds are found to be in closer agreement with actual weather data.

Bloom, S. C.↗

NASA NTRS1984

Maximum likelihood estimation of turbulence spectrum parameters

Estimation of the integral scale and intensity of a generic turbulence record is treated as a statistical problem of parameter estimation. Properties of parameter estimators and the method of maximum likelihood are reviewed. Likelihood equations are derived for estimation of the integral scale and intensity applicable to a general class of turbulence spectra that includes the von Karman and Dryden transverse and longitudinal spectra as special cases. The method is extended to include the Bullen transverse and longitudinal spectra. Coefficients of variation are given for maximum likelihood estimates of the integral scale and intensity of the von Karman spectra. Application of the method is illustrated by estimating the integral scale and intensity of an atmospheric turbulence vertical velocity record assumed to be governed by the von Karman transverse spectrum.

Mark, W. D.↗

NASA NTRS1984

Short-term climatic fluctuations forced by thermal anomalies

A two level, global, spectral model using pressure as a vertical coordinate was developed. The system of equations describing the model is nonlinear and quasi-geostrophic (linear balance). Static stability is variable in the model. A moisture budget is calculated in the lower layer only. Convective adjustment is used to avoid supercritical temperature lapse rates. The mechanical forcing of topography is introduced as a vertical velocity at the lower boundary. Solar forcing is specified assuming a daily mean zenith angle. The differential diabatic heating between land and sea is parameterized. On land and sea ice surfaces, a steady state thermal energy equation is solved to calculate the surface temperature. On the oceans, the sea surface temperature is specified as the climatological average for January. The model is used to simulate the January, February and March circulations. Previously announced in STAR as N83-14822

Hanna, A. F.↗

NASA NTRS1983

Short-term climatic fluctuations forced by thermal anomalies

Hanna, A. F.↗

NASA NTRS1984

An upper ocean current jet and internal waves in a Gulf Stream warm core ring

On June 22, 1982, the R/V Endeavor, while participating in a multi-ship study of a warm core ring 82B, encountered a strong front in the core of the ring. The vessel was headed on a radial section outward from ring center while a CTD was repeatedly raised and lowered between 10 and 300 m. Current profiles in the upper 100 m were obtained continuously with a Doppler acoustic profiling system. Above the shallow 45 m seasonal thermocline, a current jet of 4 km width was encountered having a central core of relatively light water and a maximum current of 1.1 m/s. This jet was both highly nonlinear and totally unexpected. A high frequency packet of directional internal waves was acoustically observed in the seasonal thermocline at the outer edge of the jet. Vertical velocities were large enough (6 cm/s) as to be directly observable in the Doppler returns. The waves were propagating from the northeast, parallel to the ship track, and orthogonal to the jet toward the center of the warm core ring. While a nonlinear, centrifugal term was required for the force balance of the jet, the high-frequency internal wave packet could be explained with linear, gravest-mode wave dynamics.

Joyce, T. M.↗

NASA NTRS1984

Thunderstorm cloud height-rainfall rate relations for use with satellite rainfall estimation techniques

Observational studies of thunderstorm cloud height-rainfall rate and cloud height-volume rainfall rate relations are reviewed with significant variations being noted among climatological regimes. Analysis of the Florida (summer) and Oklahoma (spring) relations are made using a one-dimensional cloud model to ascertain the important factors in determining the individual cloud-rain relations and the differences between the two regimes. In general, the observed relations are well simulated by the model-based calculations. The generally lower predicted rain rates in Oklahoma (as compared to Florida) result from lower precipitation efficiencies which are due to a combination of larger entrainment (related to larger vertical wind shear) and drier environment. The generally steeper slope of the Oklahoma rain rate height curves is shown to be due to a stronger variation in maximum vertical velocity with cloud top height, which, in turn, is related to the greater static stability in the range of cloud tops. The impact of the regime-to-regime variations on empirical rain estimation schemes based on satellite-observed cloud height or cloud temperature information is discussed and a rain estimation approach based on model-generated cloud-rain relations is outlined.

Adler, R. F.↗

NASA NTRS1984

The design of a model-following control system for helicopters

The design of an explicit model-following control system is described and the results of a ground-based simulation experiment investigating the performance and limitations of this control system for a hingeless-rotor and a teetering-rotor helicopter are reported. The explicit model was a linear, decoupled model such that the pilot commanded pitch attitude with the longitudinal cyclic, roll attitude with the lateral cyclic, yaw rate with the pedals, and earth-fixed vertical velocity with the collective. A new model-following performance criterion was developed to optimize the control-law design and to evaluate the model-following performance. The results of the simulation indicate that the performance of the model-following control system is dependent on the dynamics of the explicit model and on the limitations of the actuating system. Increases in the bandwidth of the explicit model placed higher demands on the control system and resulted in degraded model-following performance. Significant improvements in model-following performance were achieved when a control-law switching feature, which was designed to account for position- or rate-limited actuators, was included in the control system. The excellent overall model-following performance obtained for these two radically different helicopters indicates the flexibility and versatility of this control technique.

Hilbert, K. B.↗

NASA NTRS1984

Evaluation of the Malcolm horizon in a moving-base flight simulator

The efficacy of the Malcolm Horizon (MH) in a controlled, simulated, instrument flight environment was examined. Eight flight parameters were used to compare performance under experimental and control conditions. The parameters studied were pitch attitude, roll attitude, turn rate, airspeed, vertical velocity, heading, altitude, and course deviation. Testing of a commercial realization of the MH concept in a flight simulator revealed strengths and weaknesses of the currently available MH hardware.

Gillingham, K. K.↗

NASA NTRS1984

A global low order spectral model designed for climate sensitivity studies

A two level, global, spectral model using pressure as a vertical coordinate is developed. The system of equations describing the model is nonlinear and quasi-geostrophic. A moisture budget is calculated in the lower layer only with moist convective adjustment between the two layers. The mechanical forcing of topography is introduced as a lower boundary vertical velocity. Solar forcing is specified assuming a daily mean zenith angle. On land and sea ice surfaces a steady state thermal energy equation is solved to calculate the surface temperature. Over the oceans the sea surface temperatures are prescribed from the climatological average of January. The model is integrated to simulate the January climate.

Hanna, A. F.↗

NASA NTRS1984

Dynamical phenomena in sunspots. I - Observing procedures and oscillatory phenomena. II - A moving magnetic feature

High resolution spectra consisting of at least 1 hr periods were obtained of the sunpost atmosphere. The Ca II H and K lines were scanned to characterize umbral oscillations and flashes. The former displayed peaks lasting 150-197 sec, while penumbral oscillations peaked in the 197-300 sec range. Quiet sun oscillations exhibited no peaks under 300 sec. The Ca II K line umbral flashes were ubiquitous for all observational periods and were associated with light bridges in the umbra. Magnetic field, vertical velocity, and chromospheric intensity measurements taken during the 1 hr scans covered moving magnetic features (MMF), which traversed the moats around sunspots. MMF areas increased while the magnetic field intensity decreased with MMF movement away from a sunspot. Bright Ca II K line wings were apparent in the MMFs, but cores of the lines were not observed, suggesting that flux loops generating the line are low in the photosphere.

Thomas, J. H.↗

NASA NTRS1984

Numerical simulation of frontogenesis in a moist atmosphere

This paper describes the effects of condensation and evaporation on mesoscale frontal circulations in a two-dimensional numerical model. Utilizing an explicit scheme for the prediction of water vapor, cloud water and rainwater, the model is used to investigate the interactions between convection and the larger-scale environment. The model results are qualitatively compared with results of theoretical and observational studies, including those from the recent Severe Environmental Storms and Mesoscale Experiment-Atmospheric Variability Experiment (SESAME-AVE). Three major differences are observed in a comparison of the moist and dry simulations: (1) The speed of the upper- and lower-level jets was significantly higher in the moist case, (2) The intensity of the ageostrophic circulations in the moist simulation was much stronger, (3) The vertical velocity field in the moist case was characterized by a banded structure not present in the dry case.

Hsie, E.-Y.↗

NASA NTRS1983

The structure of a microburst - As observed by ground-based and airborne Doppler radar

Attention is given to the microburst observed near Denver, CO, on June 29, 1982, in the course of the Joint Airport Weather Study (JAWS). The JAWS ground radar network was specifically established to furnish high spatial and temporal resolution multiple Doppler data for microburst observations. The data, which were collected from directly above the microburst, permitted direct measurements of vertical velocities to be made. P-3 surveillance aircraft Doppler data was also available for this microburst, whose considerable complexity is noted.

Mueller, C. K.↗

NASA NTRS1985

On the effects of islands' geometry and size on inducing sea breeze circulation

Model scaling of the characteristics of the sea breeze circulation involved with circular and slab elongated-symmetric midlatitude islands was performed. Larger horizontal and vertical velocities were indicated over the small circular islands as compared to those over corresponding elongated islands. The circulation characteristics of both types of islands become similar when the half-width of the island is about the same as the distance of inland penetration of the sea breeze in a nonisland case. Evaluation of the results through a scale analysis is presented.

Mahrer, Y.↗

NASA NTRS1985

Large-scale spectral structure with a gap in the stably stratified atmosphere

The analysis of the large-scale structure of turbulence in a stratified atmosphere is important for the prediction and modelling of turbulence. The Monin-Obukhov similarity consideration is well suited for the modelling of small-scale turbulence. But the large-scale turbulence possesses new features and parameters, as connected with the appearance of a spectral gap in the stably stratified atmosphere, for the understanding of which an analytical investigation is needed. By a group-kinetic method, the anisotropic form of the transfer function and its governing eddy viscosity are derived. On this basis, the spectral laws k to the -5/3rd, k to the -1st, k to the -3rd are obtained for the subranges of inertia, shear, and buoyancy, respectively. A gap connects the last two subranges by the variable anisotropy, as a result of the fall of the spectrum of the vertical velocity fluctuations. The variable anisotropy causes the deviations from the spectral laws k to the -1st and k to the -3rd. An experiment supports the analytical prediction.

Larsen, S. E.↗

NASA NTRS1985

Convection During Unidirectional Solidification

The fluid flow and solute segregation which occur during directional solidification, including effects of gravity and microgravity were studied. The nature of the fluid flow, its effects on the shape of the crystal-metal interface and the resulting distribution of solutes are examined. During solidification of a binary alloy at constant velocity vertically upwards, thermosolutal convection occurs if the solute rejection or preferential incorporation at the crystal-melt interface decreases the density of the melt. Numerical calculations of the solute, temperature, and flow fields are carried out by using previously developed algorithms for Schmidt numbers Sc = 1, 10, 81. The time periodic flow, which occurs over a narrow range of parameters, is investigated.

Coriell, S. R.↗