Superstatistics and atmospheric turbulence
NASA Astrophysics Data System (ADS)
Rizzo, S.; Rapisarda, A.
2005-08-01
In this very short contribution we summarize some recent results on wind velocity data recorded at Florence airport. In particular we show that one can describe this example of atmospheric turbulence by means of the superstatistics approach proposed by Beck and Cohen (2003). The latter justifies the successful application of Tsallis generalized statistics in different fields, and more specifically in turbulence experiments.
Measurements of atmospheric turbulence
NASA Technical Reports Server (NTRS)
Murrow, Harold N.
1987-01-01
Various types of atmospheric turbulence measurements are addressed for the purpose of stimulating discussion relative to available data. An outline of these various types of measurements are discussed. Some specific results of detailed characterization studies made at NASA Langley are emphasized. The most recent reports on statistics of turbulence encounters for various types of aircraft operations are summarized. Special severe encounter studies and reference to remote sensing are also included. Wind shear is considered to be a special topic and is not covered.
The problem of atmospheric turbulence
NASA Technical Reports Server (NTRS)
Toomre, J.; HILL; MERRYFIELD; GOUGH
1984-01-01
All ground-based observations of the solar five-minute oscillations are affected by turbulence in the Earth's atmosphere that leads to substantial refractive index variations. The turbulent motions serve to mix an air mass that is thermally stratified in the vertical, thereby producing intermittent thermal fluctuations over a wide range of heights in the atmosphere. These thermal structures yield refractive index changes that deflect the light path in a complicated way, producing intricate variations of amplitude and phase in what might have started out as simple plane waves. Since the fluid turbulence is statistical in nature, so too is the optical turbulence which is an integral measure of the refractive index changes along the light travel path. All of this produces what is usually called atmospheric seeing, which consists of image motion, blurring and distortion across the field of view. The effects of atmospheric seeing upon observations of five-minute oscillations carried out from the ground were assessed. This will help to provide a baseline estimate of the scienctific benefits that might accrue if one were able to observe the same oscillations from a space observatory unfettered by seeing effects.
Review on atmospheric turbulence monitoring
NASA Astrophysics Data System (ADS)
Lombardi, Gianluca; Navarrete, Julio; Sarazin, Marc
2014-07-01
In the past years, intensive Site Characterization campaigns have been performed to chose the sites for the future giant ELTs. Various atmospheric turbulence profilers with different resolution and sensed altitude ranges have been used, as well as climatological tools and satellite data analysis. Mixing long term statistics at low altitude resolution with high resolution data collected during short term campaigns allows to produce the reference profiles as input to the Adaptive Optics instrument performance estimators. In this paper I will perform a brief review of the principal and most used instruments and tools in order to give to the reader a panorama of the work and the efforts to monitor the atmospheric turbulence for astronomical purposes.
Wavelet analysis of atmospheric turbulence
Hudgins, L.H.
1992-12-31
After a brief review of the elementary properties of Fourier Transforms, the Wavelet Transform is defined in Part I. Basic results are given for admissable wavelets. The Multiresolution Analysis, or MRA (a mathematical structure which unifies a large class of wavelets with Quadrature Mirror Filters) is then introduced. Some fundamental aspects of wavelet design are then explored. The Discrete Wavelet Transform is discussed and, in the context of an MRA, is seen to supply a Fast Wavelet Transform which competes with the Fast Fourier Transform for efficiency. In Part II, the Wavelet Transform is developed in terms of the scale number variable s instead of the scale length variable a where a = 1/s. Basic results such as the admissibility condition, conservation of energy, and the reconstruction theorem are proven in this context. After reviewing some motivation for the usual Fourier power spectrum, a definition is given for the wavelet power spectrum. This `spectral density` is then intepreted in the context of spectral estimation theory. Parseval`s theorem for Wavelets then leads naturally to the Wavelet Cross Spectrum, Wavelet Cospectrum, and Wavelet Quadrature Spectrum. Wavelet Transforms are then applied in Part III to the analysis of atmospheric turbulence. Data collected over the ocean is examined in the wavelet transform domain for underlying structure. A brief overview of atmospheric turbulence is provided. Then the overall method of applying Wavelet Transform techniques to time series data is described. A trace study is included, showing some of the aspects of choosing the computational algorithm, and selection of a specific analyzing wavelet. A model for generating synthetic turbulence data is developed, and seen to yield useful results in comparing with real data for structural transitions. Results from the theory of Wavelet Spectral Estimation and Wavelength Cross-Transforms are applied to studying the momentum transport and the heat flux.
NASA Astrophysics Data System (ADS)
Cui, Linyan; Xue, Bindang; Zhou, Fugen
2014-07-01
Infrared optical wave's propagation in marine environment is particularly challenging, not only for scattering and absorption due to high humidity, but also for a different behavior of atmospheric turbulence with respect to terrestrial propagation. In this paper, the marine atmospheric turbulence modulation transfer functions (MTF), which describes the degrading effects of marine atmospheric turbulence on an optical imaging system, is investigated in detail both analytically and numerically. New analytic expressions of the MTF are derived for plane and spherical waves under marine atmospheric turbulence, and they consider physically the influences of finite turbulence inner and outer scales. The final results indicate that, the marine atmospheric turbulence brings more degrading effects on the imaging system than the terrestrial atmospheric turbulence.
New Atmospheric Turbulence Model for Shuttle Applications
NASA Technical Reports Server (NTRS)
Justus, C. G.; Campbell, C. W.; Doubleday, M. K.; Johnson, D. L.
1990-01-01
An updated NASA atmospheric turbulence model, from 0 to 200 km altitude, which was developed to be more realistic and less conservative when applied to space shuttle reentry engineering simulation studies involving control system fuel expenditures is presented. The prior model used extreme turbulence (3 sigma) for all altitudes, whereas in reality severe turbulence is patchy within quiescent atmospheric zones. The updated turublence model presented is designed to be more realistic. The prior turbulence statistics (sigma and L) were updated and were modeled accordingly.
Airplane wing vibrations due to atmospheric turbulence
NASA Technical Reports Server (NTRS)
Pastel, R. L.; Caruthers, J. E.; Frost, W.
1981-01-01
The magnitude of error introduced due to wing vibration when measuring atmospheric turbulence with a wind probe mounted at the wing tip was studied. It was also determined whether accelerometers mounted on the wing tip are needed to correct this error. A spectrum analysis approach is used to determine the error. Estimates of the B-57 wing characteristics are used to simulate the airplane wing, and von Karman's cross spectrum function is used to simulate atmospheric turbulence. It was found that wing vibration introduces large error in measured spectra of turbulence in the frequency's range close to the natural frequencies of the wing.
Laser Doppler systems in atmospheric turbulence
NASA Technical Reports Server (NTRS)
Murty, S. S. R.
1976-01-01
The loss of heterodyne signal power for the Marshall Space Flight Center laser Doppler system due to the random changes in the atmospheric index of refraction is investigated. The current status in the physics of low energy laser propagation through turbulent atmosphere is presented. The analysis and approximate evaluation of the loss of the heterodyne signal power due to the atmospheric absorption, scattering, and turbulence are estimated for the conditions of the January 1973 flight tests. Theoretical and experimental signal to noise values are compared. Maximum and minimum values of the atmospheric attenuation over a two way path of 20 km range are calculated as a function of altitude using models of atmosphere, aerosol concentration, and turbulence.
Impact of Atmospheric Turbulence on Beam Propagation
Strasburg, Jana D.; Harper, Warren W.; William E Thompson & Richard L Brunson
2004-09-08
A trailer-based sensor system has been developed for remote chemical sensing applications. The detection scheme utilizes quantum cascade lasers operating in the long-wave infrared. It has been determined that atmospheric turbulence is the dominating noise source for this system. For this application, horizontal path lengths vary from several hundred meters to several kilometers resulting in weak to moderate to strong turbulence conditions.
Advanced Numerical Modeling of Turbulent Atmospheric Flows
NASA Astrophysics Data System (ADS)
Kühnlein, Christian; Dörnbrack, Andreas; Gerz, Thomas
The present chapter introduces the method of computational simulation to predict and study turbulent atmospheric flows. This includes a description of the fundamental approach to computational simulation and the practical implementation using the technique of large-eddy simulation. In addition, selected contributions from IPA scientists to computational model development and various examples for applications are given. These examples include homogeneous turbulence, convective boundary layers, heated forest canopy, buoyant thermals, and large-scale flows with baroclinic wave instability.
Laser beam propagation in atmospheric turbulence
NASA Technical Reports Server (NTRS)
Murty, S. S. R.
1979-01-01
The optical effects of atmospheric turbulence on the propagation of low power laser beams are reviewed in this paper. The optical effects are produced by the temperature fluctuations which result in fluctuations of the refractive index of air. The commonly-used models of index-of-refraction fluctuations are presented. Laser beams experience fluctuations of beam size, beam position, and intensity distribution within the beam due to refractive turbulence. Some of the observed effects are qualitatively explained by treating the turbulent atmosphere as a collection of moving gaseous lenses of various sizes. Analytical results and experimental verifications of the variance, covariance and probability distribution of intensity fluctuations in weak turbulence are presented. For stronger turbulence, a saturation of the optical scintillations is observed. The saturation of scintillations involves a progressive break-up of the beam into multiple patches; the beam loses some of its lateral coherence. Heterodyne systems operating in a turbulent atmosphere experience a loss of heterodyne signal due to the destruction of coherence.
Optical intensity interferometry through atmospheric turbulence
NASA Astrophysics Data System (ADS)
Tan, P. K.; Chan, A. H.; Kurtsiefer, C.
2016-04-01
Conventional ground-based astronomical observations suffer from image distortion due to atmospheric turbulence. This can be minimized by choosing suitable geographic locations or adaptive optical techniques, and avoided altogether by using orbital platforms outside the atmosphere. One of the promises of optical intensity interferometry is its independence from atmospherically induced phase fluctuations. By performing narrow-band spectral filtering on sunlight and conducting temporal intensity interferometry using actively quenched avalanche photodiodes, the Solar g(2)(τ) signature was directly measured. We observe an averaged photon bunching signal of g(2)(τ) = 1.693 ± 0.003 from the Sun, consistently throughout the day despite fluctuating weather conditions, cloud cover and elevation angle. This demonstrates the robustness of the intensity interferometry technique against atmospheric turbulence and opto-mechanical instabilities, and the feasibility to implement measurement schemes with both large baselines and long integration times.
Atmospheric Turbulence Simulations with Spatial Light Modulators
NASA Astrophysics Data System (ADS)
Bernardi, R.; Kanaan, A.; Mello, A. T.
2014-10-01
Atmospheric turbulence in the optical path of incoming stellar light transforms a plane wavefront into a distorted wavefront. This leads to loss of resolution achievable in a telescope. The correction of these distortions is the goal of adaptive optics. We are designing an experiment to recreate the effects of turbulence on an optical bench. This experiment aims to reproduce the effects observed in an artificial sodium laser star when viewed by a 30m class telescope. The edge of such large telescopes see the sodium artificial star as an elongated rather than a circle. In the bench experiment the turbulence distortions are achieved by directing the light beam through a glass plate whose surface is etched to imitate the phase distortions caused by the atmosphere, this plate is called a phase screen. Phase screens are made much bigger than the incident beam of light and we move this phase plate to simulate the effect of a changing atmosphere. To test new turbulence patterns one needs several different phase screens, which are expensive and hard to make. Our work involves computing numerical simulations of turbulence and testing algorithms to correct the phase distortion.We would then like to test these algorithms on our bench before testing on the telescope. To make these tests more realistic we would like to apply the same simulated turbulence patterns to our phase screen. This is almost impossible to do with phase screens, therefore we are planning to replace phase screens with spatial phase modulators that can be programmed to introduce a phase shift to the incident light at a time resolution of milliseconds. Integration of spatial phase modulators in optical benches as phase screens will allow for much more flexible experiments permitting a perfect correlation between the numerical simulations and the physical experiments.
Simulation of atmospheric turbulence layers with phase screens by JAVA
NASA Astrophysics Data System (ADS)
Zhang, Xiaofang; Chen, Wenqin; Yu, Xin; Yan, Jixiang
2008-03-01
In multiconjugate Adaptive Optics (MCAO), the phase screens are used to simulate atmospheric turbulence layers to study the optimal turbulence delamination and the determination of layer boundary position. In this paper, the method of power spectrum inversion and sub-harmonic compensation were used to simulate atmospheric turbulence layers and results can be shown by grey map. The simulation results showed that, with the increase of turbulence layers, the RMS of adaptive system decreased, but the amplitude diminished. So the atmospheric turbulence can be split into 2-3 layers and be modeled by phase screens. Otherwise, a small simulation atmospheric turbulence delamination system was realized by JAVA.
SNOHATS: Stratified atmospheric turbulence over snow surfaces
NASA Astrophysics Data System (ADS)
Parlange, M. B.; Bou-Zeid, E.; Huwald, H.; Chamecki, M.; Meneveau, C.
2006-12-01
Stably stratified flows present particular challenges for both experimental and numerical studies of the atmosphere and its interaction with the underlying surfaces. Turbulence damping and gravity waves are just two examples of stable flow features that complicate the application of turbulence similarity theories and the formulation of effective turbulence models for subgrid-scales in Large Eddy Simulation (LES). To address these concerns, a field study (SNOHATS) was held at the extensive "Plaine-Morte" glacier in the Swiss Alps (3000 m) from February to April 2006. The snow covered surface is constantly colder than the air guaranteeing stable conditions over long periods. Two horizontal arrays of vertically separated 3D sonic anemometers were deployed. This setup was specifically designed to measure subgrid scale fluxes (upwind uninterrupted fetch of 2 km) and then to assess the success of various models in reproducing these fluxes. We first study the influence of stratification on the spectra and co-spectra of velocity and temperature. Then, we compare dissipation computed using the second order and third order structure functions to the SGS dissipation. Subsequently, the eddy viscosity subgrid scale model is assessed for LES of stably stratified atmospheric flows. Specifically, we measure the Smagorinsky coefficient and the SGS turbulent Prandtl number by matching measured and modeled dissipation rates. Finally, we present the dependence of these coefficients on stability, height above the ground, filter size, and strain rates. Results are compared to previously reported data for stable flows over soil surfaces (HATS, Kleissl et al., 2004; Horst et al., 2004).
Atmospheric turbulence effects on aircraft noise propagation
NASA Technical Reports Server (NTRS)
Chapkis, R. L.
1979-01-01
The Brown and Clifford model for the apparent sound attenuation cuased by atmospheric turbulence was reviewed and extended. Calculations, based on the model, were made for the predicted sound attenuation for a tower-mounted loudspeaker-type sound source and for an airplane sound source. The important parameters in the model are identified and discussed. A model for sound fluctuations is also presented and a practical experimental program to validate the models described.
Atmospheric turbulence measurements at Ali Observatory, Tibet
NASA Astrophysics Data System (ADS)
Liu, Liyong; Yao, Yongqiang; Vernin, Jean; Chadid, Merieme; Wang, Yiping; Wang, Hongshuai; Yin, Jia; Giordano, Christophe; Qian, Xuan
2012-09-01
The atmospheric turbulence characteristics are important to evaluate the quality of ground-based astronomical observatory. In order to characterize Ali observatory, Tibet. we have developed a single star Scidar (SSS) system, which is able to continuously monitor the vertical profiles of both optical turbulence and wind speed. The main SSS configuration includes a 40cm telescope and a CCD camera for fast sampling the star scintillation pattern. The SSS technique analyzes the scintillation patterns in real time, by computing the spatial auto-correlation and at least two cross-correlation images, and retrieves both C2 n (h) and V (h) vertical profiles from the ground up to 30km. This paper presents the first turbulence measurements with SSS at Ali observatory in October, 2011. We have successfully obtained the profiles of optical turbulence and wind speed, as well as the key parameters for adaptive optics, such as seeing, coherence time, and isoplanatic angle. The favourable results indicate that Ali observatory can be an excellent astronomical observatory.
Parallel Computatinal Technology for Atmospheric Turbulence Modeling
NASA Astrophysics Data System (ADS)
Bian, Randy X.
1997-08-01
Desktop Atmospheric Turbulence Diffussion Modeling System (DATDMS) is used by analysts with varied backgrounds for performing air quality assessment and emergency response activities. This modeling system must be robust, well documented, have minimal and well controlled user inputs, and have clear outputs. Existing coarse-grained parallel computers can provide significant increases in computation speed in desktop atmospheric dispersion modeling without considerable increases in hardware cost. This increased speed will allow for significant improvements to be made in the scientific foundations of these applied models, in the form of more advanced diffusion schemes and better representation of the wind and turbulence fields. This is especially attractive for emergency response applications where speed and accuracy are of utmost importance. This presentation describes one particular application of coarse-grained parallel computer technology to a desktop complex terrain atmospheric dispersion modeling system. By comparing performance characteristics of the coarse-grained parallel version of the model with the single-processor version, we will demonstrate that applying coarse-grained parallel computer technology to desktop atmospheric dispersion modeling systems will allow us to address critical issues facing future requirements of this class of dispersion models.
Analysis of non-Kolmogorov weak turbulence effects on infrared imaging by atmospheric turbulence MTF
NASA Astrophysics Data System (ADS)
Xue, Bindang; Cao, Lei; Cui, Linyan; Bai, Xiangzhi; Cao, Xiaoguang; Zhou, Fugen
2013-07-01
The atmospheric turbulence modulation transfer functions (MTF) can be used to describe the degrading effects of atmospheric turbulence on an optical imaging system. In this study, new expressions of long exposure atmospheric turbulence MTF are derived with the generalized atmospheric spectral model for optical waves propagating through non-Kolmogorov weak turbulence with horizontal path. They consider the finite turbulence inner and outer scales, and have a general spectral power law value in the range of 3 to 4 instead of the standard power law value of 11/3. Numerical calculations are conducted to analyze the influence of non-Kolmogorov weak turbulence on the infrared imaging in term of atmospheric turbulence MTF, and results show that the non-Kolmogorov weak turbulence produces less effect on the far infrared imaging.
Gaussian entanglement in the turbulent atmosphere
NASA Astrophysics Data System (ADS)
Bohmann, M.; Semenov, A. A.; Sperling, J.; Vogel, W.
2016-07-01
We provide a rigorous treatment of the entanglement properties of two-mode Gaussian states in atmospheric channels by deriving and analyzing the input-output relations for the corresponding entanglement test. A key feature of such turbulent channels is a nontrivial dependence of the transmitted continuous-variable entanglement on coherent displacements of the quantum state of the input field. Remarkably, this allows one to optimize the entanglement certification by modifying local coherent amplitudes using a finite, but optimal amount of squeezing. In addition, we propose a protocol which, in principle, renders it possible to transfer the Gaussian entanglement through any turbulent channel over arbitrary distances. Therefore, our approach provides the theoretical foundation for advanced applications of Gaussian entanglement in free-space quantum communication.
Rotor noise due to atmospheric turbulence ingestion. I - Fluid mechanics
NASA Technical Reports Server (NTRS)
Simonich, J. C.; Amiet, R. K.; Schlinker, R. H.; Greitzer, E. M.
1986-01-01
In the present analytical procedure for the prediction of helicopter rotor noise generation due to the ingestion of atmospheric turbulence, different models for turbulence fluid mechanics and the ingestion process are combined. The mean flow and turbulence statistics associated with the atmospheric boundary layer are modeled with attention to the effects of atmospheric stability length, windspeed, and altitude. The turbulence field can be modeled as isotropic, locally stationary, and homogeneous. For large mean flow contraction ratios, accurate predictions of turbulence vorticity components at the rotor face requires the incorporation of the differential drift of fluid particles on adjacent streamlines.
Atmospheric turbulence simulation techniques with application to flight analysis
NASA Technical Reports Server (NTRS)
Wang, S. T.; Frost, W.
1980-01-01
Statistical modeling of atmospheric turbulence is discussed. The statistical properties of atmospheric turbulence, in particular the probability distribution, the spectra, and the coherence are reviewed. Different atmospheric turbulence simulation models are investigated, and appropriate statistical analyses are carried out to verify their validity. The models for simulation are incorporated into a computer model of aircraft flight dynamics. Statistical results of computer simulated landings for an aircraft having characteristics of a DC-8 are reported for the different turbulence simulation techniques. The significance of various degrees of sophistication in the turbulence simulation techniques on the landing performance of the aircraft is discussed.
Equilibration of an Atmosphere by Geostrophic Turbulence
NASA Astrophysics Data System (ADS)
Jansen, Malte F.
A major question for climate studies is to quantify the role of turbulent eddy fluxes in maintaining the observed atmospheric mean state. It has been argued that eddy fluxes keep the mid-latitude atmosphere in a state that is marginally critical to the deepest mode of baroclinic instability, which provide's a powerful constraint on the response of the atmosphere to changes in external forcing. A similar criterion does, however not hold in the Southern Ocean, a region whose dynamics are otherwise very similar to the mid-latitude atmosphere. This thesis resolves this apparent contradiction, using a combination of theoretical considerations and eddy-resolving numerical simulations. It is shown that the adjustment of the extra-tropical troposphere to states of marginal criticality does not follow from a fundamental constraint, but is rather the result of the particular parameters characterizing Earth's troposphere. Both marginally critical and strongly supercritical zonal mean flows can be obtained in planetary atmospheres if external parameters are varied. We argue that changes in the equilibrated mean state over a wide range of simulations can better be understood in terms of a balance between the diabatic forcing and the eddy driven overturning circulation. Using a diffusive closure for the eddy flux of potential vorticity, we can relate the eddy-driven overturning transport to properties of the mean flow, and derive scaling relations for both the baroclinicity and vertical stratification of the equilibrated state. (Copies available exclusively from MIT Libraries, libraries.mit.edu/docs - docs mit.edu)
Turbulence effects in radio occultation studies of atmospheric scale heights
NASA Technical Reports Server (NTRS)
Eshleman, V. R.
1975-01-01
Atmospheric scale heights derived from radio occultation measurements of a turbulent planetary atmosphere would be accurate if the average angle of refraction through the turbulent atmosphere were equal to the refraction angle for the corresponding quiescent atmosphere. These two angles are not equal (although their difference may not be large enough to cause significant error). If necessary, it should be possible to correct for the systematic error introduced by this inequality by using measurements of signal spectra to determine characteristics of the turbulence. Sensitive dual-frequency measurements could help define the effects of turbulence in future radio occultation experiments. It does not appear that the angular offset due to turbulence has been important in past experiments, although it may become significant and require corrective analysis when improved equipment is used to probe deep into turbulent atmospheres with greater measurement precision.
Large Eddy Simulation of Aircraft Wake Vortices: Atmospheric Turbulence Effects
NASA Technical Reports Server (NTRS)
Han, Jongil; Lin, Yuh-Lang; Arya, S. Pal; Kao, C.-T.
1997-01-01
Crow instability can develop in most atmospheric turbulence levels, however, the ring vortices may not form in extremely strong turbulence cases due to strong dissipation of the vortices. It appears that strong turbulence tends to accelerate the occurrences of Crow instability. The wavelength of the most unstable mode is estimated to be about 5b(sub 0), which is less than the theoretical value of 8.6b(sub 0) (Crow, 1970) and may be due to limited domain size and highly nonlinear turbulent flow characteristics. Three-dimensional turbulence can decay wake vortices more rapidly. Axial velocity may be developed by vertical distortion of a vortex pair due to Crow instability or large turbulent eddy motion. More experiments with various non-dimensional turbulence levels are necessary to get useful statistics of wake vortex behavior due to turbulence. Need to investigate larger turbulence length scale effects by enlarging domain size or using grid nesting.
Finite-element numerical modeling of atmospheric turbulent boundary layer
NASA Technical Reports Server (NTRS)
Lee, H. N.; Kao, S. K.
1979-01-01
A dynamic turbulent boundary-layer model in the neutral atmosphere is constructed, using a dynamic turbulent equation of the eddy viscosity coefficient for momentum derived from the relationship among the turbulent dissipation rate, the turbulent kinetic energy and the eddy viscosity coefficient, with aid of the turbulent second-order closure scheme. A finite-element technique was used for the numerical integration. In preliminary results, the behavior of the neutral planetary boundary layer agrees well with the available data and with the existing elaborate turbulent models, using a finite-difference scheme. The proposed dynamic formulation of the eddy viscosity coefficient for momentum is particularly attractive and can provide a viable alternative approach to study atmospheric turbulence, diffusion and air pollution.
Effects of ingested atmospheric turbulence on measured tail rotor acoustics
NASA Technical Reports Server (NTRS)
Signor, David B.; Yamauchi, Gloria K.; Mosher, Marianne; Hagen, Martin J.; George, Albert R.
1992-01-01
Results from an outdoor hover test of a full-scale Lynx tail rotor are presented. The investigation was designed to further the understanding of the acoustics of an isolated tail rotor hovering out-of-ground effect in atmospheric turbulence, without the effects of the main rotor wake or other helicopter components. Measurements include simultaneous rotor performance, noise, inflow, and far-field atmospheric turbulence. Results with grid-generated inflow turbulence are also presented. The effects of turbulence ingestion on rotor noise are quantified. Turbulence ingestion noise is found to be the dominant noise mechanism at locations near the rotor axis. At these locations, the sound radiated by the hovering rotor increases with both increasing atmospheric wind speed and ingested rms turbulent velocity.
Calculation of turbulence effects in an upward-refracting atmosphere
NASA Astrophysics Data System (ADS)
Gilbert, Kenneth E.; di, Xiao; Raspet, Richard
1990-06-01
The effect of atmospheric turbulence on sound propagation was investigated for both nonrefractive and refractive atmospheres, using the parabolic equation method of Gilbert and White (1989) in conjunction with a two-dimensional atmospheric turbulence model. The calculations for a nonrefractive atmosphere gave good agreement with experimental data and with Daigle's (1979) theory, while calculations for an upward-refractive atmosphere gave reasonable agreement with the data of Weiner and Keast (1959). It is concluded that, for a receiver deep in a shadow zone and for frequencies greater than a few hundred hertz, the measured sound-pressure level is due almost entirely to the sound scattered into the shadow zone by atmospheric turbulence. Consequently, for upward refraction and frequencies above a few hundred hertz, turbulence must be included in long-range propagation calculations.
Causes of non-Kolmogorov turbulence in the atmosphere.
Lukin, V P; Nosov, E V; Nosov, V V; Torgaev, A V
2016-04-20
In the present work, we briefly describe a model for atmospheric turbulence energy on the basis of experimental data obtained in Siberia. A series of new studies is considered and the results of our long-term experimental observations are summarized. The results of these studies form the basis for an explanation of some effects in interactions between optical waves and atmospheric turbulence. Our numerous experimental results point to the possible generation of so-called coherent turbulence in the atmosphere. When analyzing the problem, we proceeded based on our own experimental data and comprehension that the coherent turbulence is a result of the action of self-organizing nonlinear processes, which run in continuous media, including atmospheric air. The experimental data confirmed the effect of attenuation of light fluctuations in coherent turbulence. PMID:27140124
Hazardous Levels of Commercial Aircraft Response to Atmospheric Turbulence
NASA Astrophysics Data System (ADS)
Chang, Ray C.; Ye, Cun-En; Lan, C. Edward; Guan, Wen-Lin
Jet commercial aircraft in flight are frequently subject to atmospheric turbulence resulting in rapidly varying aerodynamic and flight dynamic characteristics. These varying characteristics not only pose threats to flight safety, but also may cause structural damages and reduce fatigue life. The sudden plunging motion in severe turbulence is the major reason to cause the flight injuries. To express the turbulence intensities as the hazardous levels, the root-mean-square g-load, usually for structural load, has been examined in the past twenty years. The present study is to examine alternative ideas to express the hazardous levels of sudden plunging motion in atmospheric turbulence. The flying-quality parameters of the plunging mode and integrated turbulence-induced downwash will be proposed as more reliable parameters for the turbulence hazard levels.
Entropy studies on beam distortion by atmospheric turbulence
NASA Astrophysics Data System (ADS)
Wu, Chensheng; Ko, Jonathan; Davis, Christopher C.
2015-09-01
When a beam propagates through atmospheric turbulence over a known distance, the target beam profile deviates from the projected profile of the beam on the receiver. Intuitively, the unwanted distortion provides information about the atmospheric turbulence. This information is crucial for guiding adaptive optic systems and improving beam propagation results. In this paper, we propose an entropy study based on the image from a plenoptic sensor to provide a measure of information content of atmospheric turbulence. In general, lower levels of atmospheric turbulence will have a smaller information size while higher levels of atmospheric turbulence will cause significant expansion of the information size, which may exceed the maximum capacity of a sensing system and jeopardize the reliability of an AO system. Therefore, the entropy function can be used to analyze the turbulence distortion and evaluate performance of AO systems. In fact, it serves as a metric that can tell the improvement of beam correction in each iteration step. In addition, it points out the limitation of an AO system at optimized correction as well as the minimum information needed for wavefront sensing to achieve certain levels of correction. In this paper, we will demonstrate the definition of the entropy function and how it is related to evaluating information (randomness) carried by atmospheric turbulence.
Using ground-based GPS to characterize atmospheric turbulence
NASA Astrophysics Data System (ADS)
Nilsson, T.; Davis, J. L.; Hill, E. M.
2009-08-01
A new method for measuring and studying atmospheric turbulence is presented. The method uses data from a local network of GPS receivers. The GPS data are processed in a way that assures that the estimated zenith total delays (ZTD) contain the effects of atmospheric turbulence present in the GPS observations. The turbulence is characterized using the spatial structure function for the atmospheric zenith total delay. The structure function is modeled by an expression with unknown parameters which contains information about the turbulence. The unknown parameters are solved by a fit to the observed ZTD variations. We apply the method to GPS data from the Yucca Mountain network, Nevada, USA. The results show that the magnitude of the turbulent variations in that region have a strong seasonal dependence, with much larger variations in summer compared to winter.
Measurements of atmospheric turbulence effects on tail rotor acoustics
NASA Technical Reports Server (NTRS)
Hagen, Martin J.; Yamauchi, Gloria K.; Signor, David B.; Mosher, Marianne
1994-01-01
Results from an outdoor hover test of a full-scale Lynx tail rotor are presented. The investigation was designed to further the understanding of the acoustics of an isolated tail rotor hovering out-of-ground effect in atmospheric turbulence, without the effects of the main rotor wake or other helicopter components. Measurements include simultaneous rotor performance, noise, inflow, and far-field atmospheric turbulence. Results with grid-generated inflow turbulence are also presented. The effects of atmospheric turbulence ingestion on rotor noise are quantified. In contradiction to current theories, increasing rotor inflow and rotor thrust were found to increase turbulence ingestion noise. This is the final report of Task 13A--Helicopter Tail Rotor Noise, of the NASA/United Kingdom Defense Research Agency cooperative Aeronautics Research Program.
Scattering of sonic booms by anisotropic turbulence in the atmosphere
Kelly; Raspet; Bass
2000-06-01
An earlier paper [J. Acoust. Soc. Am. 98, 3412-3417 (1995)] reported on the comparison of rise times and overpressures of sonic booms calculated with a scattering center model of turbulence to measurements of sonic boom propagation through a well-characterized turbulent layer under moderately turbulent conditions. This detailed simulation used spherically symmetric scatterers to calculate the percentage of occurrence histograms of received overpressures and rise times. In this paper the calculation is extended to include distorted ellipsoidal turbules as scatterers and more accurately incorporates the meteorological data into a determination of the number of scatterers per unit volume. The scattering center calculation overpredicts the shifts in rise times for weak turbulence, and still underpredicts the shift under more turbulent conditions. This indicates that a single-scatter center-based model cannot completely describe sonic boom propagation through atmospheric turbulence. PMID:10875351
Atmospheric turbulence correction using digital holographic detection: experimental results.
Marron, Joseph C; Kendrick, Richard L; Seldomridge, Nathan; Grow, Taylor D; Höft, Thomas A
2009-07-01
The performance of long distance imaging systems is typically degraded by phase errors imparted by atmospheric turbulence. In this paper we apply coherent imaging methods to determine, and remove, these phase errors by digitally processing coherent recordings of the image data. In this manner we are able to remove the effects of atmospheric turbulence without needing a conventional adaptive optical system. Digital holographic detection is used to record the coherent, complex-valued, optical field for a series of atmospheric and object realizations. Correction of atmospheric phase errors is then based on maximizing an image sharpness metric to determine the aberrations present and correct the underlying image. Experimental results that demonstrate image recovery in the presence of turbulence are presented. Results obtained with severe turbulence that gives rise to anisoplanatism are also presented. PMID:19582079
Performance of wind turbines in a turbulent atmosphere
NASA Technical Reports Server (NTRS)
Sundar, R. M.; Sullivan, J. P.
1981-01-01
The effect of atmospheric turbulence on the power fluctuations of large wind turbines was studied. The significance of spatial non-uniformities of the wind is emphasized. The turbulent wind with correlation in time and space is simulated on the computer by Shinozukas method. The wind turbulence is modelled according to the Davenport spectrum with an exponential spatial correlation function. The rotor aerodynamics is modelled by simple blade element theory. Comparison of the spectrum of power output signal between 1-D and 3-D turbulence, shows the significant power fluctuations centered around the blade passage frequency.
Large-eddy simulations of contrails in a turbulent atmosphere
NASA Astrophysics Data System (ADS)
Picot, J.; Paoli, R.; Thouron, O.; Cariolle, D.
2014-11-01
In this work, the evolution of contrails in the vortex and dissipation regimes is studied by means of fully three-dimensional large-eddy simulation (LES) coupled to a Lagrangian particle tracking method to treat the ice phase. This is the first paper where fine-scale atmospheric turbulence is generated and sustained by means of a stochastic forcing that mimics the properties of stably stratified turbulent flows as those occurring in the upper troposphere lower stratosphere. The initial flow-field is composed by the turbulent background flow and a wake flow obtained from separate LES of the jet regime. Atmospheric turbulence is the main driver of the wake instability and the structure of the resulting wake is sensitive to the intensity of the perturbations, primarily in the vertical direction. A stronger turbulence accelerates the onset of the instability, which results in shorter contrail decent and more effective mixing in the interior of the plume. However, the self-induced turbulence that is produced in the wake after the vortex break-up dominates over background turbulence at the end of the vortex regime and dominates the mixing with ambient air. This results in global microphysical characteristics such as ice mass and optical depth that are be slightly affected by the intensity of atmospheric turbulence. On the other hand, the background humidity and temperature have a first order effect on the survival of ice crystals and particle size distribution, which is in line with recent and ongoing studies in the literature.
Helicopter rotor noise due to ingestion of atmospheric turbulence
NASA Astrophysics Data System (ADS)
Simonich, J. C.; Amiet, R. K.; Schlinker, R. H.; Greitzer, E. M.
1986-05-01
A theoretical study was conducted to develop an analytical prediction method for helicopter main rotor noise due to the ingestion of atmospheric turbulence. This study incorporates an atmospheric turbulence model, a rotor mean flow contraction model and a rapid distortion turbulence model which together determine the statistics of the non-isotropic turbulence at the rotor plane. Inputs to the combined mean inflow and turbulence models are controlled by atmospheric wind characteristics and helicopter operating conditions. A generalized acoustic source model was used to predict the far field noise generated by the non-isotropic flow incident on the rotor. Absolute levels for acoustic spectra and directivity patterns were calculated for full scale helicopters, without the use of empirical or adjustable constants. Comparisons between isotropic and non-isotropic turbulence at the rotor face demonstrated pronounced differences in acoustic spectra. Turning and contraction of the flow for hover and low speed vertical ascent cases result in a 3 dB increase in the acoustic spectrum energy and a 10 dB increase in tone levels. Compared to trailing edge noise, turbulence ingestion noise is the dominant noise mechanism below approximately 30 rotor harmonics, while above 100 harmonics, trailing edge noise levels exceed turbulence ingestion noise by 25 dB.
Helicopter rotor noise due to ingestion of atmospheric turbulence
NASA Technical Reports Server (NTRS)
Simonich, J. C.; Amiet, R. K.; Schlinker, R. H.; Greitzer, E. M.
1986-01-01
A theoretical study was conducted to develop an analytical prediction method for helicopter main rotor noise due to the ingestion of atmospheric turbulence. This study incorporates an atmospheric turbulence model, a rotor mean flow contraction model and a rapid distortion turbulence model which together determine the statistics of the non-isotropic turbulence at the rotor plane. Inputs to the combined mean inflow and turbulence models are controlled by atmospheric wind characteristics and helicopter operating conditions. A generalized acoustic source model was used to predict the far field noise generated by the non-isotropic flow incident on the rotor. Absolute levels for acoustic spectra and directivity patterns were calculated for full scale helicopters, without the use of empirical or adjustable constants. Comparisons between isotropic and non-isotropic turbulence at the rotor face demonstrated pronounced differences in acoustic spectra. Turning and contraction of the flow for hover and low speed vertical ascent cases result in a 3 dB increase in the acoustic spectrum energy and a 10 dB increase in tone levels. Compared to trailing edge noise, turbulence ingestion noise is the dominant noise mechanism below approximately 30 rotor harmonics, while above 100 harmonics, trailing edge noise levels exceed turbulence ingestion noise by 25 dB.
Turbulence and diffusion in the atmospheric boundary layer
NASA Astrophysics Data System (ADS)
Baskett, Ronald L.
1990-05-01
This conference addressed recent theoretical advancements of turbulence and diffusion in the atmospheric boundary layer (ABL). Activities were centered on the technical sessions of the conference. Sessions addressed clouds and the marine atmospheric boundary layer, field experimental techniques, physical and numerical simulations, transport and diffusion, surface properties, general boundary layer, stratified turbulence and turbulence in complex terrain. A jointly authored poster on an evaluation of the ARAC emergency response models with and without on-site sound detection and ranging systems (sodars) which measure vertical wind profiles was presented. Several scientists commented on our work and some requested further information. In addition, there was a workshop on dispersion around groups of buildings and a tour of Riso National Laboratory. Developments relevant to our work included work on dispersion model evaluation, especially using Monte Carlo random walk techniques, parameterizations of mixing height and turbulence from remote sensing systems such as sodars and radars, and measurements and parameterizations of enhanced turbulence around groups of buildings.
Turbulence structures in wind turbine wake: Effects of atmospheric stratification
NASA Astrophysics Data System (ADS)
Bhaganagar, Kiran
2014-11-01
Turbulence structure in the wake behind full-scale horizontal-axis WT under the influence of realistic atmospheric turbulent flow conditions has been investigated using actuator-line-model based large-eddy-simulations. Wind turbine simulations have revealed that, in addition to wind shear and ABL turbulence, height-varying wind angle and low-level jets are ABL metrics that influence the structure of turbine wake. Turbulent mixing layer forms downstream of the WT, the strength and size of which decreases with increasing stability. Height dependent wind angle and turbulence are the ABL metrics influencing the lateral wake expansion. Further, ABL metrics strongly impact the evolution of tip and root vortices formed behind the rotor. Two factors play an important role in wake meandering: tip vortex merging due to the mutual inductance form of instability and the corresponding instability of the turbulent mixing layer. NSF CBET Energy for Sustainability.
Atmospheric and Wake Turbulence Impacts on Wind Turbine Fatigue Loadings
Lee, S.; Churchfield, M.; Moriarty, P.; Jonkman, J.; Michalakes, J.
2012-01-01
Large-eddy simulations of atmospheric boundary layers under various stability and surface roughness conditions are performed to investigate the turbulence impact on wind turbines. In particular, the aeroelastic responses of the turbines are studied to characterize the fatigue loading of the turbulence present in the boundary layer and in the wake of the turbines. Two utility-scale 5-MW turbines that are separated by seven rotor diameters are placed in a 3 km by 3 km by 1 km domain. They are subjected to atmospheric turbulent boundary layer flow and data is collected on the structural response of the turbine components. The surface roughness was found to increase the fatigue loads while the atmospheric instability had a small influence. Furthermore, the downstream turbines yielded higher fatigue loads indicating that the turbulent wakes generated from the upstream turbines have significant impact.
Extracting atmospheric turbulence and aerosol characteristics from passive imagery
NASA Astrophysics Data System (ADS)
Reinhardt, Colin N.; Wayne, D.; McBryde, K.; Cauble, G.
2013-09-01
Obtaining accurate, precise and timely information about the local atmospheric turbulence and extinction conditions and aerosol/particulate content remains a difficult problem with incomplete solutions. It has important applications in areas such as optical and IR free-space communications, imaging systems performance, and the propagation of directed energy. The capability to utilize passive imaging data to extract parameters characterizing atmospheric turbulence and aerosol/particulate conditions would represent a valuable addition to the current piecemeal toolset for atmospheric sensing. Our research investigates an application of fundamental results from optical turbulence theory and aerosol extinction theory combined with recent advances in image-quality-metrics (IQM) and image-quality-assessment (IQA) methods. We have developed an algorithm which extracts important parameters used for characterizing atmospheric turbulence and extinction along the propagation channel, such as the refractive-index structure parameter C2n , the Fried atmospheric coherence width r0 , and the atmospheric extinction coefficient βext , from passive image data. We will analyze the algorithm performance using simulations based on modeling with turbulence modulation transfer functions. An experimental field campaign was organized and data were collected from passive imaging through turbulence of Siemens star resolution targets over several short littoral paths in Point Loma, San Diego, under conditions various turbulence intensities. We present initial results of the algorithm's effectiveness using this field data and compare against measurements taken concurrently with other standard atmospheric characterization equipment. We also discuss some of the challenges encountered with the algorithm, tasks currently in progress, and approaches planned for improving the performance in the near future.
Optical measurements of the outer scale of the atmospheric turbulence.
NASA Astrophysics Data System (ADS)
Lukin, V. P.
The light scattering on the turbulence inhomogeneities of the atmosphere is the one of the main mechanism of distortion of the received optical signal. The random spacetime changes of the atmospheric refractive index lead to distortion of the optical beam structure, the fluctuations of the intensity and phase of the optical wave are manifested, in particular, in blurring, shivering and flickering of the source images, as well as in the turbulent extinction of the mean received power of the signal. Several models are compared with measurements of atmospheric parameters.
Atmospheric Quantum Channels with Weak and Strong Turbulence.
Vasylyev, D; Semenov, A A; Vogel, W
2016-08-26
The free-space transfer of high-fidelity optical signals between remote locations has many applications, including both classical and quantum communication, precision navigation, clock synchronization, etc. The physical processes that contribute to signal fading and loss need to be carefully analyzed in the theory of light propagation through the atmospheric turbulence. Here we derive the probability distribution for the atmospheric transmittance including beam wandering, beam shape deformation, and beam-broadening effects. Our model, referred to as the elliptic beam approximation, applies to weak, weak-to-moderate, and strong turbulence and hence to the most important regimes in atmospheric communication scenarios. PMID:27610835
Hyperspectral Image Turbulence Measurements of the Atmosphere
NASA Technical Reports Server (NTRS)
Lane, Sarah E.; West, Leanne L.; Gimmestad, Gary G.; Kireev, Stanislav; Smith, William L., Sr.; Burdette, Edward M.; Daniels, Taumi; Cornman, Larry
2012-01-01
A Forward Looking Interferometer (FLI) sensor has the potential to be used as a means of detecting aviation hazards in flight. One of these hazards is mountain wave turbulence. The results from a data acquisition activity at the University of Colorado s Mountain Research Station will be presented here. Hyperspectral datacubes from a Telops Hyper-Cam are being studied to determine if evidence of a turbulent event can be identified in the data. These data are then being compared with D&P TurboFT data, which are collected at a much higher time resolution and broader spectrum.
On the application of Rice's exceedance statistics to atmospheric turbulence.
NASA Technical Reports Server (NTRS)
Chen, W. Y.
1972-01-01
Discrepancies produced by the application of Rice's exceedance statistics to atmospheric turbulence are examined. First- and second-order densities from several data sources have been measured for this purpose. Particular care was paid to each selection of turbulence that provides stationary mean and variance over the entire segment. Results show that even for a stationary segment of turbulence, the process is still highly non-Gaussian, in spite of a Gaussian appearance for its first-order distribution. Data also indicate strongly non-Gaussian second-order distributions. It is therefore concluded that even stationary atmospheric turbulence with a normal first-order distribution cannot be considered a Gaussian process, and consequently the application of Rice's exceedance statistics should be approached with caution.
An investigation of turbulent transport in the extreme lower atmosphere
NASA Technical Reports Server (NTRS)
Koper, C. A., Jr.; Sadeh, W. Z.
1975-01-01
A model in which the Lagrangian autocorrelation is expressed by a domain integral over a set of usual Eulerian autocorrelations acquired concurrently at all points within a turbulence box is proposed along with a method for ascertaining the statistical stationarity of turbulent velocity by creating an equivalent ensemble to investigate the flow in the extreme lower atmosphere. Simultaneous measurements of turbulent velocity on a turbulence line along the wake axis were carried out utilizing a longitudinal array of five hot-wire anemometers remotely operated. The stationarity test revealed that the turbulent velocity is approximated as a realization of a weakly self-stationary random process. Based on the Lagrangian autocorrelation it is found that: (1) large diffusion time predominated; (2) ratios of Lagrangian to Eulerian time and spatial scales were smaller than unity; and, (3) short and long diffusion time scales and diffusion spatial scales were constrained within their Eulerian counterparts.
Coherent laser radar performance for general atmospheric refractive turbulence
NASA Technical Reports Server (NTRS)
Frehlich, Rod G.; Kavaya, Michael J.
1991-01-01
A general theory for the signal-to-noise ratio (SNR) of a coherent detection laser radar is developed using the path-integral formulation (Fresnel approximation), which is valid for any typical path-integrated atmospheric refractive turbulence. The principal effects of refractive turbulence are discussed, and analytical expressions are presented for the case of untruncated Gaussians for the transmitted field, local oscillator field, and transmitter/receiver optics. The physical mechanisms that reduce heterodyne efficiency are identified.
ATMOSPHERIC TURBULENCE AND POLLUTANT DISPERSION NEAR ROADWAYS
The major objectives of this investigation are: (1) to determine the time and space scales of the eddies generated by the traffic, (2) to study the effects of traffic-induced turbulence on the near-field dispersion of pollutants, (3) to evaluate several commonly used highway air ...
Atmospheric turbulence parameters for modeling wind turbine dynamics
NASA Technical Reports Server (NTRS)
Holley, W. E.; Thresher, R. W.
1982-01-01
A model which can be used to predict the response of wind turbines to atmospheric turbulence is given. The model was developed using linearized aerodynamics for a three-bladed rotor and accounts for three turbulent velocity components as well as velocity gradients across the rotor disk. Typical response power spectral densities are shown. The system response depends critically on three wind and turbulence parameters, and models are presented to predict desired response statistics. An equation error method, which can be used to estimate the required parameters from field data, is also presented.
Why turbulence sustains in supercritically stratified free atmosphere?
NASA Astrophysics Data System (ADS)
Zilitinkevich, Sergej
2016-04-01
It is widely believed that in very stable stratifications, at Richardson numbers (Ri) exceeding critical value Ric ˜ 0.25 turbulence decays and flow becomes laminar. This is so at low Reynolds numbers (Re), e.g., in lab experiments; but this is not true in very-high-Re geophysical flows. Free atmosphere and deep ocean are turbulent in spite of strongly supercritical stratifications: 1 << Ri < 103. Until recently, this paradox remained unexplained. The Energy- and Flux-Budget (EFB) turbulence-closure (Zilitinkevich et al., 2013) has disclosed the following turbulence self-control mechanisms. Until recently, the role of negative buoyancy flux, Fb > 0, in turbulence energetics was treated in terms of the turbulent kinetic energy (TKE) budget equation and understood as just consumption of TKE by the buoyancy forces. This has led to the conclusion that sufficiently strong static stability causes the negative buoyancy flux sufficiently strong to exceed the TKE generation rate and thus to kill turbulence. However, considering TKE equation together with budget equation for turbulent potential energy (TPE proportional to the squared buoyancy fluctuations) shows that the role of Fb in turbulence energetics is nothing but conversion of TKE into TPE (Fb just quantifies the rate of this conversion); so that Fb does not affect total turbulent energy (TTE = TKE + TPE). Moreover, as follows from the buoyancy-flux budget equation, TPE generates positive (directed upward) buoyancy flux irrespective of the sign of the buoyancy gradient. Indeed, the warmer fluid particles (with positive buoyancy fluctuation) rise up, whereas the cooler particles sink down, so that both contribute to the positive buoyancy flux opposing to the usual, negative flux generated by mean buoyancy gradient. In this context, strengthening the negative buoyancy flux leads to decreasing TKE and increasing TPE. The latter enhances the counter-gradient share of the total flux, thus reduces |Fb| and, eventually
Characteristics of turbulent structures in the unstable atmospheric surface layer
NASA Astrophysics Data System (ADS)
Schols, J. L. J.; Jansen, A. E.; Krom, J. G.
1985-10-01
An atmospheric surface-layer (ASL) experiment conducted at a meteorological site in the Oostelijk-Flevoland polder of the Netherlands is described. Turbulent fluctuations of wind velocity, air temperature and static pressure were measured, using three 10 m towers. Simultaneous turbulent signals at several heights on the towers were used to investigate the properties of the turbulent structures which contribute most significantly to the turbulent vertical transports in the unstable ASL. These turbulent structures produce between 30 and 50% of the mean turbulent vertical transport of horizontal alongwind momentum and they contribute to between 40 and 50% of the mean turbulent vertical heat transport; in both cases this occurs during 15 to 20% of the total observation time. The translation speed of the turbulent structures equals the wind speed averaged over the depth of the ASL, which scales on the surface friction velocity. The inclination angle of the temperature interface at the upstream edge of the turbulent structures to the surface is significantly smaller than that of the internal shear layer, which is associated with the temperature interface. The turbulent structures in the unstable ASL are determined by a large-scale temperature field: Convective motions, which encompass the whole depth of the planetary boundary layer (PBL), penetrate into the ASL. The curvature of the vertical profile of mean horizontal alongwind velocity forces the alignment of the convective cells in the flow direction (Kuettner, 1971), which have an average length of several hundreds of metres and an average width of a few tens of metres. This mechanism leads to the formation of turbulent structures, which extend throughout the depth of the ASL.
Characterization, parameter estimation, and aircraft response statistics of atmospheric turbulence
NASA Technical Reports Server (NTRS)
Mark, W. D.
1981-01-01
A nonGaussian three component model of atmospheric turbulence is postulated that accounts for readily observable features of turbulence velocity records, their autocorrelation functions, and their spectra. Methods for computing probability density functions and mean exceedance rates of a generic aircraft response variable are developed using nonGaussian turbulence characterizations readily extracted from velocity recordings. A maximum likelihood method is developed for optimal estimation of the integral scale and intensity of records possessing von Karman transverse of longitudinal spectra. Formulas for the variances of such parameter estimates are developed. The maximum likelihood and least-square approaches are combined to yield a method for estimating the autocorrelation function parameters of a two component model for turbulence.
Irradiance scintillation index on slant atmospheric turbulence: simple approach
NASA Astrophysics Data System (ADS)
Fayed, Heba A.; El Aziz, Ahmed Abd; Aly, Asmaa M.; Aly, Moustafa H.
2016-05-01
Turbulence plays an important role in investigating the irradiance scintillation index (SI) for a free-space optical wave propagating through atmospheric turbulence. The Hufnagel-Valley model is used in most studies, where the SI of the slant path is obtained using numerical analysis. A polynomial is proposed for the refractive index structure parameter, on which a closed form is derived for the irradiance SI of a spherical optical wave propagating through a slant atmospheric turbulence. This is used to study signal-to-noise ratio and bit error rate for system performance evaluation. The obtained results demonstrate the simplicity of using the derived closed form of SI compared to statistical methods. The derived expression takes less computational time for SI, which reflects positively on the system performance, which is an essential issue in vehicular mobile applications, in particular.
Atmospheric turbulence optical model (ATOM) based on fractal theory
NASA Astrophysics Data System (ADS)
Jaenisch, Holger M.; Handley, James W.; Scoggins, Jim; Carroll, Marvin P.
1994-06-01
An Atmospheric Turbulence Optical Model (ATOM) is presented that used cellular automata (CA) rules as the basis for modeling synthetic phase sheets. This method allows image fracture, scintillation and blur to be correctly models using the principle of convolution with a complex kernel derived from CA rules interaction. The model takes into account the changing distribution of turbules from micro-turbule domination at low altitudes to macro-domination at high altitudes. The wavelength of propagating images (such as a coherent laser beam) and the range are taken into account. The ATOM model is written in standard FORTRAN 77 and enables high-speed in-line calculation of atmospheric effects to be performed without resorting to computationally intensive solutions of Navier Stokes equations or Cn2 profiles.
Atmospheric Turbulence Modeling for Aerospace Vehicles: Fractional Order Fit
NASA Technical Reports Server (NTRS)
Kopasakis, George (Inventor)
2015-01-01
An improved model for simulating atmospheric disturbances is disclosed. A scale Kolmogorov spectral may be scaled to convert the Kolmogorov spectral into a finite energy von Karman spectral and a fractional order pole-zero transfer function (TF) may be derived from the von Karman spectral. Fractional order atmospheric turbulence may be approximated with an integer order pole-zero TF fit, and the approximation may be stored in memory.
Inflight data collection for ride quality and atmospheric turbulence research
NASA Technical Reports Server (NTRS)
Kadlec, P. W.; Buckman, R. C.
1974-01-01
A flight test program to investigate the effects of atmospheric turbulence on passenger ride quality in large, wide-body commercial aircraft was conducted. Data were collected on a series of flight on a Boeing 747 aircraft. Atmospheric and aircraft performance data were obtained from special sensors, as well as conventional instruments and avionics systems normally available. Visual observations of meteorlogical conditions encountered were manually recorded during the flights.
Characterising atmospheric optical turbulence using stereo-SCIDAR
NASA Astrophysics Data System (ADS)
Osborn, James; Butterley, Tim; Föhring, Dora; Wilson, Richard
2015-04-01
Stereo-SCIDAR (SCIntillation Detection and Ranging) is a development to the well known SCIDAR method for characterisation of the Earth's atmospheric optical turbulence. Here we present some interesting capabilities, comparisons and results from a recent campaign on the 2.5 m Isaac Newton Telescope on La Palma.
Atmospheric Turbulence Relative to Aviation, Missile, and Space Programs
NASA Technical Reports Server (NTRS)
Camp, Dennis W. (Editor); Frost, Walter (Editor)
1987-01-01
The purpose of the workshop was to bring together various disciplines of the aviation, missile, and space programs involved in predicting, measuring, modeling, and understanding the processes of atmospheric turbulence. Working committees re-examined the current state of knowledge, identified present and future needs, and documented and prioritized integrated and cooperative research programs.
Statistical analysis of low level atmospheric turbulence
NASA Technical Reports Server (NTRS)
Tieleman, H. W.; Chen, W. W. L.
1974-01-01
The statistical properties of low-level wind-turbulence data were obtained with the model 1080 total vector anemometer and the model 1296 dual split-film anemometer, both manufactured by Thermo Systems Incorporated. The data obtained from the above fast-response probes were compared with the results obtained from a pair of Gill propeller anemometers. The digitized time series representing the three velocity components and the temperature were each divided into a number of blocks, the length of which depended on the lowest frequency of interest and also on the storage capacity of the available computer. A moving-average and differencing high-pass filter was used to remove the trend and the low frequency components in the time series. The calculated results for each of the anemometers used are represented in graphical or tabulated form.
The theoretical model of atmospheric turbulence spectrum in surface layer
NASA Astrophysics Data System (ADS)
Liu, Shida; Liu, Shikuo; Xin, Guojun; Liang, Fuming
1994-12-01
It is shown that the slope of energy spectrum obtained from the velocity solution of Kdv—Burgers equation lies between —5/3 and—2 in the dilogarithmic coordinates paper. The spectrum is very close to one of Kolmogorov's isotropic turbulence and Frisch's intermittent turbulence in inertial region. In this paper, the Kdv-Burgers equation to describe atmospheric boundary layer turbulence is obtained. In the equation, the 1 / R e corresponds to dissipative coefficient v, R /2 t to dispersive coefficient β, then ( v/2 β)2 corresponds to 1 / R 2 e • Ri. We prove that the wave number corresponding to maximum energy spectrum S(k) decreases with the decrease of stability (i.e., the increase of ( v / 2 β)2 in eddy—containing region. And the spectrim amplitude decreases with the increase of ( v / 2 β)2 (i.e., the decrease of stability). These results are consistent with actual turbulence spectrum of atmospheric surface layer from turbulence data.
Atmospheric Turbulence Modeling for Aero Vehicles: Fractional Order Fits
NASA Technical Reports Server (NTRS)
Kopasakis, George
2015-01-01
Atmospheric turbulence models are necessary for the design of both inlet/engine and flight controls, as well as for studying coupling between the propulsion and the vehicle structural dynamics for supersonic vehicles. Models based on the Kolmogorov spectrum have been previously utilized to model atmospheric turbulence. In this paper, a more accurate model is developed in its representative fractional order form, typical of atmospheric disturbances. This is accomplished by first scaling the Kolmogorov spectral to convert them into finite energy von Karman forms and then by deriving an explicit fractional circuit-filter type analog for this model. This circuit model is utilized to develop a generalized formulation in frequency domain to approximate the fractional order with the products of first order transfer functions, which enables accurate time domain simulations. The objective of this work is as follows. Given the parameters describing the conditions of atmospheric disturbances, and utilizing the derived formulations, directly compute the transfer function poles and zeros describing these disturbances for acoustic velocity, temperature, pressure, and density. Time domain simulations of representative atmospheric turbulence can then be developed by utilizing these computed transfer functions together with the disturbance frequencies of interest.
Atmospheric Turbulence Modeling for Aero Vehicles: Fractional Order Fits
NASA Technical Reports Server (NTRS)
Kopasakis, George
2010-01-01
Atmospheric turbulence models are necessary for the design of both inlet/engine and flight controls, as well as for studying coupling between the propulsion and the vehicle structural dynamics for supersonic vehicles. Models based on the Kolmogorov spectrum have been previously utilized to model atmospheric turbulence. In this paper, a more accurate model is developed in its representative fractional order form, typical of atmospheric disturbances. This is accomplished by first scaling the Kolmogorov spectral to convert them into finite energy von Karman forms and then by deriving an explicit fractional circuit-filter type analog for this model. This circuit model is utilized to develop a generalized formulation in frequency domain to approximate the fractional order with the products of first order transfer functions, which enables accurate time domain simulations. The objective of this work is as follows. Given the parameters describing the conditions of atmospheric disturbances, and utilizing the derived formulations, directly compute the transfer function poles and zeros describing these disturbances for acoustic velocity, temperature, pressure, and density. Time domain simulations of representative atmospheric turbulence can then be developed by utilizing these computed transfer functions together with the disturbance frequencies of interest.
Programmable simulator for beam propagation in turbulent atmosphere.
Rickenstorff, Carolina; Rodrigo, José A; Alieva, Tatiana
2016-05-01
The study of light propagation though the atmosphere is crucial in different areas such as astronomy, free-space communications, remote sensing, etc. Since outdoors experiments are expensive and difficult to reproduce it is important to develop realistic numerical and experimental simulations. It has been demonstrated that spatial light modulators (SLMs) are well-suited for simulating different turbulent conditions in the laboratory. Here, we present a programmable experimental setup based on liquid crystal SLMs for simulation and analysis of the beam propagation through weak turbulent atmosphere. The simulator allows changing the propagation distances and atmospheric conditions without the need of moving optical elements. Its performance is tested for Gaussian and vortex beams. PMID:27137610
Atmospheric turbulence and sensor system effects on biometric algorithm performance
NASA Astrophysics Data System (ADS)
Espinola, Richard L.; Leonard, Kevin R.; Byrd, Kenneth A.; Potvin, Guy
2015-05-01
Biometric technologies composed of electro-optical/infrared (EO/IR) sensor systems and advanced matching algorithms are being used in various force protection/security and tactical surveillance applications. To date, most of these sensor systems have been widely used in controlled conditions with varying success (e.g., short range, uniform illumination, cooperative subjects). However the limiting conditions of such systems have yet to be fully studied for long range applications and degraded imaging environments. Biometric technologies used for long range applications will invariably suffer from the effects of atmospheric turbulence degradation. Atmospheric turbulence causes blur, distortion and intensity fluctuations that can severely degrade image quality of electro-optic and thermal imaging systems and, for the case of biometrics technology, translate to poor matching algorithm performance. In this paper, we evaluate the effects of atmospheric turbulence and sensor resolution on biometric matching algorithm performance. We use a subset of the Facial Recognition Technology (FERET) database and a commercial algorithm to analyze facial recognition performance on turbulence degraded facial images. The goal of this work is to understand the feasibility of long-range facial recognition in degraded imaging conditions, and the utility of camera parameter trade studies to enable the design of the next generation biometrics sensor systems.
A computer-based simulator of the atmospheric turbulence
NASA Astrophysics Data System (ADS)
Konyaev, Petr A.
2015-11-01
Computer software for modeling the atmospheric turbulence is developed on the basis of a time-varying random medium simulation algorithm and a split-step Fourier transform method for solving a wave propagation equation. A judicious choice of the simulator parameters, like the velocity of the evolution and motion of the medium, turbulence spectrum and scales, enables different effects of a random medium on the optical wavefront to be simulated. The implementation of the simulation software is shown to be simple and efficient due to parallel programming functions from the MKL Intel ® Parallel Studio libraries.
Scattering of coherent sound waves by atmospheric turbulence
NASA Technical Reports Server (NTRS)
Chow, P. L.; Liu, C. H.; Maestrello, L.
1975-01-01
An analytical study of the propagation of coherent sound waves through an atmosphere containing both mean and fluctuating flow variables is presented. The general flow problem is formulated as a time-dependent wave propagation in a half-space containing the turbulent medium. The coherent acoustic waves are analyzed by a smoothing technique, assuming that mean flow variables vary with the height only. The general equations for the coherent waves are derived, and then applied to two special cases, corresponding to uniform and shear mean flow, respectively. The results show that mean shear and turbulence introduce pronounced effects on the propagation of coherent acoustic disturbances.
Restoring atmospheric-turbulence-degraded images.
Furhad, Md Hasan; Tahtali, Murat; Lambert, Andrew
2016-07-01
Image data experiences geometric distortions and spatial-temporal varying blur due to the strong effects of random spatial and temporal variations in the optical refractive index of the communication path. Simultaneously removing these effects from an image is a challenging task. An efficient approach is proposed in this paper to address this problem. The approach consists of four steps. First, a frame selection strategy is employed by proposing an unsupervised k-means clustering technique. Second, a B-spline-based nonrigid image registration is carried out to suppress geometric distortions. Third, a spatiotemporal kernel regression is proposed by introducing the local sharp patch concept to fuse the registered frame sequences into an image. Finally, a blind deconvolution technique is employed to deblur the fused image. Experiments are carried out with synthetic and real-world turbulence-degraded data by implementing the proposed method and two recently reported methods. The proposed method demonstrates significant improvement over the two reported methods in terms of alleviating blur and distortions, as well as improving visual quality. PMID:27409194
Scattering from a rough surface in presence of atmospheric turbulence
NASA Astrophysics Data System (ADS)
Basu, Santasri; Hyde, Milo W.; McCrae, Jack E.; Fiorino, Steven T.
2013-05-01
A Gaussian Schell Model (GSM) might be a convenient way to model extended beacons created on diffuse targets. Earlier, we used a full wave computational technique called the Method of Moments (MoM) to evaluate the scattered field from a rough impedance surface in vacuum. The MoM model showed several deviations from GSM. The present work uses a simulation approach based on physical optics approximation to study the scattering behavior in presence of atmospheric turbulence. A fully coherent beam is propagated through weak turbulence and is incident on the rough surface. The light scattered from the rough surface is again propagated through turbulence back to the source plane and the properties of the scattered radiation are studied through numerical simulations. The simulation results are compared with a GSM.
Higher order correlation beams in atmosphere under strong turbulence conditions.
Avetisyan, H; Monken, C H
2016-02-01
Higher order correlation beams, that is, two-photon beams obtained from the process of spontaneous parametric down-conversion pumped by Hermite-Gauss or Laguerre-Gauss beams of any order, can be used to encode information in many modes, opening the possibility of quantum communication with large alphabets. In this paper we calculate, analytically, the fourth-order correlation function for the Hermite-Gauss and Laguerre-Gauss coherent and partially coherent correlation beams propagating through a strong turbulent medium. We show that fourth-order correlation functions for correlation beams have, under certain conditions, expressions similar to those of intensities of classical beams and are degraded by turbulence in a similar way as the classical beams. Our results can be useful in establishing limits for the use of two-photon beams in quantum communications with larger alphabets under atmospheric turbulence. PMID:26906808
NASA Technical Reports Server (NTRS)
Dewan, E. M.
1986-01-01
The problem of how to empirically distinguish between velocity fluctuations due to turbulence and those due to atmospheric waves is addressed. The physical differences between waves and turbulence are reviewed. New theoretical ideas on the subject of bouyancy range turbulence are presented. A unique scale K sub B is given that allows one to differentiate between waves and turbulence for the special case of theta = 0 (i.e., horizontal propagating waves).
Modeling atmospheric turbulence effects on ground-based telescope systems
Flatte, S.M.; Bradford, L.W.; Max, C.E.
1994-12-31
Bester et al. report measurements of atmospheric fluctuations made with the Infrared Spatial Interferometer, which indicated behavior not in accord with the standard Kolmogorov model with only a single constant wind velocity. The numerical simulations use relatively complex models of the atmosphere to investigate both Kolmogorov and non-Kolmogorov models. The authors find that the measurements of Bester et al. for light passing through the upper atmosphere are within the limits of behavior for Kolmogorov models, but often only if the outer scale of turbulent fluctuations is between 15 to 100 meters. The possibility that the measured behavior might be non-Kolmogorov is not excluded. They also examine measurements made along short paths in the surface boundary layer, where some measurements of Bester et al. showed variations in the atmospheric fluctuations with seeing conditions which appeared to be non-Kolmogorov. These variations can perhaps be explained by standard models, but require that seeing improve with increasing wind speed in the surface layer. They discuss some other measurements which lend some support to that idea. However, they cannot exclude non-Kolmogorov behavior. They find that meteorological data is needed concurrent with astronomical observations, to help constrain the models. The size of the outer scale, the wind velocity profile and the turbulence spectrum are important to the ultimate capabilities of interferometers and other systems with adaptive optics.
NASA Astrophysics Data System (ADS)
Jeromin, A.; Schaffarczyk, A. P.; Puczylowski, J.; Peinke, J.; Hölling, M.
2014-12-01
For the investigation of atmospheric turbulent flows on small scales a new anemometer was developed, the so-called 2d-Atmospheric Laser Cantilever Anemometer (2d-ALCA). It performs highly resolved measurements with a spatial resolution in millimeter range and temporal resolution in kHz range, thus detecting very small turbulent structures. The anemometer is a redesign of the successfully operating 2d-LCA for laboratory application. The new device was designed to withstand hostile operating environments (rain and saline, humid air). In February 2012, the 2d-ALCA was used for the first time in a test field. The device was mounted in about 53 m above ground level on a lattice tower near the German North Sea coast. Wind speed was measured by the 2d-ALCA at 10 kHz sampling rate and by cup anemometers at 1 Hz. The instantaneous wind speed ranged from 8 m/s to 19 m/s at an average turbulence level of about 7 %. Wind field characteristics were analyzed based on cup anemometer as well as 2d-ALCA. The combination of both devices allowed the study of atmospheric turbulence over several magnitudes in turbulent scales.
Turbulence effects on concentration statistics in the atmospheric surface layer
Biltoft, C.; Bowers, J.; Yee, E.; Klewicki, J.; Metzger, M.
1996-12-31
The dispersion of windborne material released near the earth`s surface is strongly influenced by this impenetrable boundary, which inhibits downward mixing and creates sharp vertical gradients in wind, temperature, turbulence. These strong gradients and the continuous creation of turbulence at the surface cause a rapid evolution of the vertical concentration structure for material released into the atmospheric surface layer (ASL). Recent developments in fast-response instrumentation and an increased realization of potential hazards from the release of common industrial chemicals into the ASL have led to a series of tripartite (US, UK, Canada) field experiments at the US Army Dugway Proving Ground, Utah. This paper contains a preliminary analysis of the data from the most recent follow-on experiments, which included measurements of the vertical profiles of mean and peak concentrations.
NASA Technical Reports Server (NTRS)
Reeves, P. M.; Campbell, G. S.; Ganzer, V. M.; Joppa, R. G.
1974-01-01
A method is described for generating time histories which model the frequency content and certain non-Gaussian probability characteristics of atmospheric turbulence including the large gusts and patchy nature of turbulence. Methods for time histories using either analog or digital computation are described. A STOL airplane was programmed into a 6-degree-of-freedom flight simulator, and turbulence time histories from several atmospheric turbulence models were introduced. The pilots' reactions are described.
Turbulence in a convective marine atmospheric boundary layer
NASA Technical Reports Server (NTRS)
Chou, S.-H.; Atlas, D.; Yeh, E.-N.
1986-01-01
The structure and kinetic energy budget of turbulence in the convective marine atmospheric boundary layer as observed by aircraft during a cold air outbreak have been studied using mixed layer scaling. The results are significantly different from those of previous studies under conditions closer to free convection. The normalized turbulent kinetic energy and turbulent transport are about twice those found during the Air Mass Transformation Experiment (AMTEX). This implies that for a given surface heating the present case is dynamically more active. The difference is mainly due to the greater importance of wind shear in the present case. This case is closer to the roll vortex regime, whereas AMTEX observed mesoscale cellular convection which is closer to free convection. Shear generation is found to provide a significant energy source, in addition to buoyancy production, to maintain a larger normalized turbulent kinetic energy and to balance a larger normalized dissipation. The interaction between turbulent pressure and divergence (i.e., pressure scrambling) is also found to transfer energy from the vertical to the horizontal components, and is expected to be stronger in roll vortices than in m esoscale cells. The sensible heat flux is found to fit well with a linear vertical profile in a clear or subcloud planetary boundary layer (PBL), in good agreement with the results of Lenschow et al., (1980). The heat flux ratio between the PBL top and the surface, derived from the linear fitted curve, is approximately -0.14, in good agreement with that derived from the lidar data for the same case. Near the PBL top, the heat flux profiles are consistent with those of Deardoff (1979) and Deardorff et al. (1980).
Stratified turbulence in the atmosphere and the ocean
NASA Astrophysics Data System (ADS)
Lindborg, E.
2006-12-01
A number of theoretical, observational and numerical studies have been performed by the author in order to understand the mesoscale (wave lengths of 1 - 500 km) wave number energy spectra in the upper troposphere and lower stratosphere. In an observational study some years ago (Cho &Lindborg 2001) it was shown that there is downscale energy cascade in this range of scales, contrary to what has been commonly beleived. In two recent studies (Lindborg 2005; 2006 a) a set of numerical highly resolved box-simulations were carried out of strongly stratified flows. It was demonstrated that the forward energy cascade is a general property of the Boussinesq equations in the limit of strong stratification, provided that the Rossby number is of order unity or larger. These simulations indicated that the mesoscale spectra may be produced by a special type of motion which we call stratified turbulence. The characterisic features of stratified turbulence are extremely elongated flow structures controlled by strong stratification and strongly nonlinear interactions and these flow structures undergo a forward energy cascade. A recent data analysis (Lindborg 2006 b) of velocity structure functions measured in the upper troposphere and lower stratosphere in a previous study (Lindborg 1999), shows that the vortical and wave components of stratified turbulence are of the same order of magnitude with the vortical component generally a little bit larger. This is in accordance with the results from the numerical simulations. In this contribution the recent developments of the concept of stratified turbulence are presented. Moreover, it is also suggested that stratified turbulence may be generally present in the interiour of the ocean, at scales whose dynamics are traditionally though to be dominated by internal gravity waves. A number of oceanic field studies reported in the litterature are referenced to support this suggestion. References: Lindborg 1999 Can the atmospheric energy
Atmospheric turbulence mitigation using complex wavelet-based fusion.
Anantrasirichai, Nantheera; Achim, Alin; Kingsbury, Nick G; Bull, David R
2013-06-01
Restoring a scene distorted by atmospheric turbulence is a challenging problem in video surveillance. The effect, caused by random, spatially varying, perturbations, makes a model-based solution difficult and in most cases, impractical. In this paper, we propose a novel method for mitigating the effects of atmospheric distortion on observed images, particularly airborne turbulence which can severely degrade a region of interest (ROI). In order to extract accurate detail about objects behind the distorting layer, a simple and efficient frame selection method is proposed to select informative ROIs only from good-quality frames. The ROIs in each frame are then registered to further reduce offsets and distortions. We solve the space-varying distortion problem using region-level fusion based on the dual tree complex wavelet transform. Finally, contrast enhancement is applied. We further propose a learning-based metric specifically for image quality assessment in the presence of atmospheric distortion. This is capable of estimating quality in both full- and no-reference scenarios. The proposed method is shown to significantly outperform existing methods, providing enhanced situational awareness in a range of surveillance scenarios. PMID:23475359
Theoretical comparison of subgrid turbulence in the atmosphere and ocean
NASA Astrophysics Data System (ADS)
Kitsios, V.; Frederiksen, J. S.; Zidikheri, M. J.
2015-12-01
Due to the massive disparity between the largest and smallest eddies in the atmosphere and ocean, it is not possible to simulate these flows by explicitly resolving all scales on a computational grid. Instead the large scales are explicitly resolved, and the interactions between the unresolved subgrid turbulence and large resolved scales are parameterised. If these interactions are not properly represented then an increase in resolution will not necessarily improve the accuracy of the large scales. This has been a significant and long standing problem since the earliest climate simulations. Historically subgrid models for the atmosphere and ocean have been developed in isolation, with the structure of each motivated by different physical phenomena. Here we solve the turbulence closure problem by determining the parameterisation coefficients (eddy viscosities) from the subgrid statistics of high resolution quasi-geostrophic atmospheric and oceanic simulations. These subgrid coefficients are characterised into a set of simple unifying scaling laws, for truncations made within the enstrophy cascading inertial range. The ocean additionally has an inverse energy cascading range, within which the subgrid model coefficients have alternative scaling properties. Simulations adopting these scaling laws are shown to reproduce the statistics of the reference benchmark simulations across resolved scales, with orders of magnitude improvement in computational efficiency. This reduction in both resolution dependence and computational effort will improve the efficiency and accuracy of geophysical research and operational activities that require data generated by general circulation models, including: weather, seasonal and climate prediction; transport studies; and understanding natural variability and extreme events.
Group-kinetic theory and modeling of atmospheric turbulence
NASA Technical Reports Server (NTRS)
Tchen, C. M.
1989-01-01
A group kinetic method is developed for analyzing eddy transport properties and relaxation to equilibrium. The purpose is to derive the spectral structure of turbulence in incompressible and compressible media. Of particular interest are: direct and inverse cascade, boundary layer turbulence, Rossby wave turbulence, two phase turbulence; compressible turbulence, and soliton turbulence. Soliton turbulence can be found in large scale turbulence, turbulence connected with surface gravity waves and nonlinear propagation of acoustical and optical waves. By letting the pressure gradient represent the elementary interaction among fluid elements and by raising the Navier-Stokes equation to higher dimensionality, the master equation was obtained for the description of the microdynamical state of turbulence.
Comparative measurements of the level of turbulence atmosphere by optical and acoustic devices
NASA Astrophysics Data System (ADS)
Lukin, V. P.; Botugina, N. N.; Gladkih, V. A.; Emaleev, O. N.; Konyaev, P. A.; Odintsov, S. L.; Torgaev, A. V.
2014-11-01
The complex measurements of level of atmospheric turbulence are conducted by the differential measurement device of turbulence (DMT), wave-front sensor (WFS), and also by ultrasonic weather-stations. Daytime measurements of structure parameters of refractive index of atmospheric turbulence carried out on horizontal optical paths on the Base Experimental Complex (BEC) of V.E. Zuev Institute of Atmospheric Optics SB RAS (IOA). A comparative analysis over of the got results is brought.
Correlation of atmospheric optical turbulence and meteorological measurements
NASA Astrophysics Data System (ADS)
Vaucher, Gail M. Tirrell
1989-06-01
The correlation of meteorological events such as the jet stream, gravity waves and boundary layer circulation with the optical turbulence parameters, the transverse coherence length r sub o and the isoplanatic angle is essential for interpreting and forecasting imaging and laser systems performance. In support of the United States Air Force Relay Mirror Experiment, the Naval Postgraduate School performed a series of six site characterization measurements near Kihei, Maui, during August 1987 to July 1988. Spatial and temporal summaries of atmospheric events corresponding to the optical remote sensor data are presented using meteorological data from the National Weather Service Radiosonde Observation stations, synoptic charts, GOES-WEST infrared satellite images, and four Kihei, Maui rawinsonde datasets. To quantify the correlation between optical turbulence measurements and meteorological phenomena, four methods of calculating C square (T) from rawinsonde data were investigated. Results show that existing rawinsonde systems are inadequate for direct C square (T) calculation. However, moderate improvements in the vertical resolution, the temperature resolution and probe response time, will allow direct calculations of optical turbulence parameters from rawinsonde data.
Compensating image degradation due to atmospheric turbulence in anisoplanatic conditions
NASA Astrophysics Data System (ADS)
Huebner, Claudia S.
2009-05-01
In imaging applications the prevalent effects of atmospheric turbulence comprise image dancing and image blurring. Suggestions from the field of image processing to compensate for these turbulence effects and restore degraded imagery include Motion-Compensated Averaging (MCA) for image sequences. In isoplanatic conditions, such an averaged image can be considered as a non-distorted image that has been blurred by an unknown Point Spread Function (PSF) of the same size as the pixel motions due to the turbulence and a blind deconvolution algorithm can be employed for the final image restoration. However, when imaging over a long horizontal path close to the ground, conditions are likely to be anisoplanatic and image dancing will effect local image displacements between consecutive frames rather than global shifts only. Therefore, in this paper, a locally operating variant of the MCA-procedure is proposed, utilizing Block Matching (BM) in order to identify and re-arrange uniformly displaced image parts. For the final restoration a multistage blind deconvolution algorithm is used and the corresponding deconvolution results are presented and evaluated.
Is 2-D turbulence relevant in the atmosphere?
NASA Astrophysics Data System (ADS)
Lovejoy, Shaun; Schertzer, Daniel
2010-05-01
Starting with (Taylor, 1935), the paradigm of isotropic (and scaling!) turbulence was developed initially for laboratory applications, but following (Kolmogorov, 1941), three dimensional isotropic turbulence was progressively applied to the atmosphere. Since the atmosphere is strongly stratified, a single wide scale range model which is both isotropic and scaling is not possible so that theorists had to immediately choose between the two symmetries: isotropy or scale invariance. Following the development of models of two dimensional isotropic turbulence ((Fjortoft, 1953), but especially (Kraichnan, 1967) and (Charney, 1971)), the mainstream choice was to first make the convenient assumption of isotropy and to drop wide range scale invariance. Starting at the end of the 1970's this "isotropy primary" (IP) paradigm has lead to a series of increasingly complex isotropic 2D/isotropic 3D models of atmospheric dynamics which continue to dominate the theoretical landscape. Justifications for IP approaches have focused almost exclusively on the horizontal statistics of the horizontal wind in both numerical models and analyses and from aircraft campaigns, especially the highly cited GASP (Nastrom and Gage, 1983), (Gage and Nastrom, 1986; Nastrom and Gage, 1985) and MOZAIC (Cho and Lindborg, 2001) experiments. Since understanding the anisotropy clearly requires comparisons between horizontal and vertical statistics/structures this focus has been unfortunate. Over the same thirty year period that 2D/3D isotropic models were being elaborated, evidence slowly accumulated in favour of the opposite theoretical choice: to drop the isotropy assumption but to retain wide range scaling. The models in the alternative paradigm are scaling but strongly anisotropic with vertical sections of structures becoming increasingly stratified at larger and larger scales albeit in a power law manner; we collectively refer to these as "SP" for "scaling primary" approaches. Early authors explicitly
Two-color correlation between intensity fluctuations in atmospheric turbulence
NASA Astrophysics Data System (ADS)
Luo, Meilan; Zhao, Daomu
2016-06-01
The correlation between intensity fluctuations generated by two varying wavelengths through a turbulent medium is investigated, where the influences arising from source correlation and perturbation of atmosphere are mainly emphasized. It is demonstrated that the correlation between intensity fluctuations can be enhanced or reduced by modulating the difference of two incident wavelengths. For shorter wavelength, the correlation between intensity fluctuations is stronger at the far field. In addition, in the case of single wavelength, a relationship λ1z1 =λ2z2 =λnzn holding in free space could be found, from which the distance where the peak value occurs may be inferred. However, it can be destroyed by increasing the strength of atmosphere.
NASA Technical Reports Server (NTRS)
Kopasakis, George
2014-01-01
The presentation covers a recently developed methodology to model atmospheric turbulence as disturbances for aero vehicle gust loads and for controls development like flutter and inlet shock position. The approach models atmospheric turbulence in their natural fractional order form, which provides for more accuracy compared to traditional methods like the Dryden model, especially for high speed vehicle. The presentation provides a historical background on atmospheric turbulence modeling and the approaches utilized for air vehicles. This is followed by the motivation and the methodology utilized to develop the atmospheric turbulence fractional order modeling approach. Some examples covering the application of this method are also provided, followed by concluding remarks.
Is 2-D turbulence relevant in the atmosphere?
NASA Astrophysics Data System (ADS)
Lovejoy, Shaun; Schertzer, Daniel
2010-05-01
Starting with (Taylor, 1935), the paradigm of isotropic (and scaling!) turbulence was developed initially for laboratory applications, but following (Kolmogorov, 1941), three dimensional isotropic turbulence was progressively applied to the atmosphere. Since the atmosphere is strongly stratified, a single wide scale range model which is both isotropic and scaling is not possible so that theorists had to immediately choose between the two symmetries: isotropy or scale invariance. Following the development of models of two dimensional isotropic turbulence ((Fjortoft, 1953), but especially (Kraichnan, 1967) and (Charney, 1971)), the mainstream choice was to first make the convenient assumption of isotropy and to drop wide range scale invariance. Starting at the end of the 1970's this "isotropy primary" (IP) paradigm has lead to a series of increasingly complex isotropic 2D/isotropic 3D models of atmospheric dynamics which continue to dominate the theoretical landscape. Justifications for IP approaches have focused almost exclusively on the horizontal statistics of the horizontal wind in both numerical models and analyses and from aircraft campaigns, especially the highly cited GASP (Nastrom and Gage, 1983), (Gage and Nastrom, 1986; Nastrom and Gage, 1985) and MOZAIC (Cho and Lindborg, 2001) experiments. Since understanding the anisotropy clearly requires comparisons between horizontal and vertical statistics/structures this focus has been unfortunate. Over the same thirty year period that 2D/3D isotropic models were being elaborated, evidence slowly accumulated in favour of the opposite theoretical choice: to drop the isotropy assumption but to retain wide range scaling. The models in the alternative paradigm are scaling but strongly anisotropic with vertical sections of structures becoming increasingly stratified at larger and larger scales albeit in a power law manner; we collectively refer to these as "SP" for "scaling primary" approaches. Early authors explicitly
Turbulent atmospheric flow over a backward-facing step
NASA Technical Reports Server (NTRS)
Kaul, U. K.; Frost, W.
1976-01-01
The phenomenon of atmospheric shear layer separation over a man-made structure such as a building (modeled as a backward-facing step) has been analyzed theoretically by (1) solving the two-dimensional equations of motion in the two variables, stream function and vorticity, and by (2) employing an approximate integral technique. Boundary conditions for the undisturbed flow are that of the turbulent atmospheric shear flow over a rough terrain. In the first approach a two-equation model of turbulence was used. In the second approach an approximate technique was utilized in an attempt to describe the details of the flow in the recirculation zone behind the step. The results predict velocity profiles in sufficient detail that the presence of the corner eddy in the region of negative surface pressure gradient is evident. The magnitude of the reversed flow velocity in the recirculation eddy has been found to agree with that found from experiments. Also, a surface eddy viscosity distribution has been an outgrowth of the method which realistically follows the magnitude of the surface pressure gradient distribution as found experimentally.
Turbulent flux events in a nearly neutral atmospheric boundary layer.
Narasimha, Roddam; Kumar, S Rudra; Prabhu, A; Kailas, S V
2007-03-15
We propose here a novel method of analysing turbulent momentum flux signals. The data for the analysis come from a nearly neutral atmospheric boundary layer and are taken at a height of 4m above ground corresponding to 1.1 x 10(5) wall units, within the log layer for the mean velocity. The method of analysis involves examining the instantaneous flux profiles that exceed a given threshold, for which an optimum value is found to be 1 s.d. of the flux signal. It is found feasible to identify normalized flux variation signatures separately for positive and negative 'flux events'-the sign being determined by that of the flux itself. Using these signatures, the flux signal is transformed to one of events characterized by the time of occurrence, duration and intensity. It is also found that both the average duration and the average time-interval between successive events are of order 1s, about four orders of magnitude higher than a wall unit in time. This episodic description of the turbulence flux in the time domain enables us to identify separately productive, counter-productive and idle periods (accounting, respectively, for 36, 15 and 49% of the time), taking as criterion the generation of the momentum flux. A 'burstiness' index of 0.72 is found for the data. Comparison with laboratory data indicates higher (/lower) ejection (/sweep) quadrant occupancy but lower (/higher) contributions to flux from the ejection (/sweep) quadrant at the high Reynolds numbers of the atmospheric boundary layer. Possible connections with the concept of active and passive motion in a turbulent boundary layer are briefly discussed. PMID:17244581
NASA Technical Reports Server (NTRS)
Simonich, J. C.; Caplin, B.
1989-01-01
A users manual for a computer program for predicting atmospheric turbulence and mean flow and turbulence contraction as part of a noise prediction scheme for nonisotropic turbulence ingestion noise in helicopters is described. Included are descriptions of the various program modules and subroutines, their function, programming structure, and the required input and output variables. This routine is incorporated as one module of NASA's ROTONET helicopter noise prediction program.
Analytical investigation of fan tone noise due to ingested atmospheric turbulence
NASA Technical Reports Server (NTRS)
Ganz, U. W.
1980-01-01
The atmospheric turbulence involved in the fan noise generation is evaluated with an existing model for the atmospheric turbulence and an extended version of an existing model concerned with the effects of a flow contraction on convected turbulence. Fan tone noise due to ingested atmospheric turbulence is evaluated with existing fan noise models. The results indicate that the difference in fan narrowband noise due to atmospheric turbulence between static and flight landing approach conditions is in the order of 30 dB. It is concluded that fan noise due to atmospheric turbulence is insignificant in flight conditions for the fans used in the current high bypass ratio engines. The difference in fan narrowband noise between the two conditions is primarily due to the low intensity of the turbulence involved in fan noise generation in flight conditions. Fan noise due to atmospheric turbulence in static conditions should be reduced below the flight fan broadband noise levels which is best achieved with a reduction in the intensity of the fan inflow turbulence. Such a reduction can be obtained with the use of an inflow control device, low wind velocities, small surface roughness in the test stand environment, and large engine axis height above the ground. Peak sound power levels for fan tone noise due to ingested turbulence occur for transverse integral scales in the order of 25% of the rotor blade spacing in the fan tip region.
NASA Astrophysics Data System (ADS)
Taozheng
2015-08-01
In recent years, due to the high stability and privacy of vortex beam, the optical vortex became the hot spot in research of atmospheric optical transmission .We numerically investigate the propagation of vector elliptical vortex beams in turbulent atmosphere. Numerical simulations are realized with random phase screen. To simulate the vortex beam transport processes in the atmospheric turbulence. Using numerical simulation method to study in the atmospheric turbulence vortex beam transmission characteristics (light intensity, phase, polarization, etc.) Our simulation results show that, vortex beam in the atmospheric transmission distortion is small, make elliptic vortex beam for space communications is a promising strategy.
Spanwise measurements of vertical components of atmospheric turbulence
NASA Technical Reports Server (NTRS)
Sleeper, Robert K.
1990-01-01
Correlation and spectrum magnitude estimates are computed for vertical gust velocity measurements at the nose and wing tips of a NASA B-57B aircraft for six level flight, low speed and low altitude runs and are compared with those of the von Karman atmospheric turbulence model extended for spanwise relationships. The distance between the wing tips was 62.6 ft. Airspeeds ranged from about 330 to 400 ft/sec, heights above the ground ranged from near ground level to about 5250 ft. and gust velocity standard deviations ranged from 4.10 to 8.86 ft/sec. Integral scale lengths, determined by matching measured autocorrelation estimates with those of the model, ranged from 410 to 2050 ft. Digital signals derived from piezoelectric sensors provided continuous pressure and airspeed measurements. Some directional acceleration sensitivity of the sensors was eliminated by sensor orientation, and their performance was spectrally verified for the higher frequencies with supplemental onboard piezoresistive sensors. The model appeared to satisfactorily predict the trends of the measured cross-correlations and cross-spectrum magnitudes, particularly between the nose and wing tips. However, the measured magnitude estimates of the cross-spectra between the wing tips exceeded the predicted levels at the higher frequencies. Causes for the additional power across the wing tips were investigated. Vertical gust velocity components evaluated along and lateral to the flight path implied that the frozen-turbulence-field assumption is a suitable approximation.
Coherent light backscattering by refractive turbulence in the atmosphere
NASA Astrophysics Data System (ADS)
Kopilevich, Yurij I.
1994-12-01
A sharp peak is shown theoretically to exist in angular distribution of light scattered by a layer of ran- dom medium with weak refractive index fluctuations in the vicinity of backward direction. The peak width may be estimated by the ratio of incident radiation wavelength and the turbulence correlation scale. The effect is found to be formed by coherent addition of contributions from elementary layers, and may be considered as an analogue to 'weak photon localisation' phenomena in random media. When the width of scattering layer is large enough compared with the correlation scale of refractive index inhomogeneities, the differential scattering cross-section is composed by the 'coherent' component and 'incoherent' one, obtained earlier by V. I. Tatarski. In the case of visible or IR radiation (in contrast to microwaves) the 'coherent' constituent determines the scattering for large angles close to 180 deg. Quantitative estimates show the backscattering by turbulent layers in atmosphere to produce noticeable contributions to signal registered in remote sensing monostatic lidar experiments, and thus the effect under consideration has to be taken into account when interpretation of laser remote sounding data is carried out.
Investigation of the influence of atmospheric stability and turbulence on land-atmosphere exchange
NASA Astrophysics Data System (ADS)
Osibanjo, O.; Holmes, H.
2015-12-01
Surface energy fluxes are exchanged between the surface of the earth and the atmosphere and impact weather, climate, and air quality. The radiation from the sun triggers the surface-atmosphere interaction during the day as heat is transmitted to the surface and the surface heats the air directly above generating wind (i.e., thermal turbulence) that transports heat, moisture, and momentum in the atmospheric boundary layer (ABL). This process is impacted by greenhouse gasses (i.e., water vapor, carbon dioxide and other trace gases) that absorb heat emitted by the earth's surface. The concentrations of atmospheric greenhouse gasses are increasing leading to changes in ABL dynamics as a result of the changing surface energy balance. The ABL processes are important to characterize because they are difficult to parameterize in global and regional scale atmospheric models. Empirical data can be collected using eddy covariance micrometeorological methods to measure turbulent fluxes (e.g., sensible heat, moisture, and CO2) and quantify the exchange between the surface and the atmosphere. The objective of this work is to calculate surface fluxes using observational data collected during one week in September 2014 from a monitoring site in Echo, Oregon. The site is located in the Columbia Basin with rolling terrain, irrigated farmland, and over 100 wind turbines. The 10m tower was placed in a small valley depression to isolate nighttime cold air pools. This work will present observations of momentum, sensible heat, moisture, and carbon dioxide fluxes from data collected at a sampling frequency of 10Hz at four heights. Atmospheric stability is determined using Monin-Obukov length and flux Richardson number, and the impact of stability on surface-atmosphere exchange is investigated. This work will provide a better understanding of surface fluxes and mixing, particularly during stable ABL periods, and the results can be used to compare with numerical models.
Random bits, true and unbiased, from atmospheric turbulence.
Marangon, Davide G; Vallone, Giuseppe; Villoresi, Paolo
2014-01-01
Random numbers represent a fundamental ingredient for secure communications and numerical simulation as well as to games and in general to Information Science. Physical processes with intrinsic unpredictability may be exploited to generate genuine random numbers. The optical propagation in strong atmospheric turbulence is here taken to this purpose, by observing a laser beam after a 143 km free-space path. In addition, we developed an algorithm to extract the randomness of the beam images at the receiver without post-processing. The numbers passed very selective randomness tests for qualification as genuine random numbers. The extracting algorithm can be easily generalized to random images generated by different physical processes. PMID:24976499
Daily Variation Analysis of Atmospheric Turbulence from Inland to Open Sea
NASA Astrophysics Data System (ADS)
Shao, S. Y.; Li, X. B.; Li, Y. J.; Zhu, W. Y.; Kang, D. Y.; Fan, C. Y.; Weng, N. Q.
2016-02-01
Random fluctuation of turbulence brings random fluctuation of refractive index, which makes atmosphere become a random fluctuation medium and destroys the coherence of light wave especially laser transferring in it. Exploration of atmospheric turbulence is essentially investigation of atmospheric refractive index. The atmospheric structure constant of refractive index is a basic parameter of expressing atmospheric turbulence, and was measured using HTP-2 micro-thermal meter at different areas from inland to open sea. It is analysed that the relation of atmospheric structure constant of refractive index with corresponding temperature and wind speed. The conclusion of turbulence and main influencing factors is to deepen the research in atmospheric optical transmission, and to provide data support for the siting of ship board photoelectric systems.
Characteristics of turbulence driven atmospheric blur over coastal water
NASA Astrophysics Data System (ADS)
de Jong, Arie N.; Schwering, Piet B. W.; Benoist, Koen W.; Gunter, Willem H.; Vrahimis, George; October, Faith J.
2014-10-01
For users of Electro-Optical (EO) sensors at sea, knowledge on their resolution is of key operational importance for the prediction of the obtainable classification ranges. Small targets may be located at ranges of 20 km and more and the present day sensor pixel size may be as small as 10 μrad. In this type of scenarios, sensor resolution will be limited by blur, generated by atmospheric turbulence, easily being greater than 30 μrad (at 20 km range). Predictions of the blur size are generally based upon the theory, developed by Fried [1]. In this theory, the turbulence strength is characterized by the structure parameter for the refractive index Cn 2, of which data are assumed to be available from secondary instruments. The theory predicts the atmospheric Modulation Transfer Function (MTF), which can be incorporated into the total system MTF, used in range performance predictions, as described by Holst [2]. Validation of blur predictions by measurements is a complex effort due to the rapid variations of the blur with time and the problems associated with the simultaneous acquisition of proper Cn 2 data. During the FATMOSE trial, carried out over a range of 15.7 km in the False Bay near Simon's Town (South Africa) from November 2009 to October 2010, these data were collected in a large variety of atmospheric conditions [3]. In stead of the atmospheric MTF, the horizontal and vertical line spread function (LSF) was measured with a camera with 5 μrad resolution. Various methods for the determination of the LSF and the associated problems are discussed in the paper. The width of the LSF is via its Fourier transform directly related to the MTF. Cn 2 data were collected with a standard BLS scintillometer over a nearby range. Additional Cn 2 data were obtained via conversion of the scintillation data from the same camera and from a high speed transmissometer, collecting data over the same range. Comparisons between blur and Beam Wander predictions and measurements from
On the spectral theory of turbulence and atmospheric dispersion
NASA Astrophysics Data System (ADS)
Usman, Shoaib
A new theoretical model has been developed to predict the transport of atmospheric pollutants as they disperse in the environment. The proposed model is the first successful effort to theoretically predict the dispersion coefficient under all six Pasquill stability classes. This new approach is based on the spectral theory of turbulence and Higbie's penetration theory. It is assumed that the fundamental mechanism of mass transfer under the influence of turbulence is similar to the process of molecular diffusion: i.e., the turbulent dispersion coefficient is dependent on the molecular properties. It is also assumed that the rate of diffusion is related to the rate of energy dissipation in the flow field. During this investigation it was realized that there are at least two independent time scales that require consideration in turbulent diffusion modeling. The smaller of the two, the dissipative time scale, is related to the rate of energy dissipation and hence the state of turbulence. On the other hand, a much larger dispersive time scale determined by the size of the largest eddy also plays a critical role in the phenomenon of dispersion. The Penetration Theory is used to obtain an expression for the mass transfer coefficient that is used in conjunction with a dispersive time scale to obtain a final expression for the dispersion coefficient. The dispersive time scale used in this development is based on Gifford's time-dependent velocity autocorrelation function. Therefore, the final expression for the dispersion coefficient contains the two time scales and the molecular diffusivity. In support of Gifford's conclusion, this research has also found that the dispersive time scale is of the same order of magnitude as the Coriolis parameter. The dissipative time scale is the only parameter in the model that requires adjustment to account for the change in atmospheric stability. The new model demonstrates the variability in the diffusion characteristics of various gases
The study of turbulence and optical instability in stably stratified Earth's atmosphere
NASA Astrophysics Data System (ADS)
Kovadlo, P. G.; Shihovtsev, A. Y.
2015-11-01
It is shown that atmospheric turbulence is not suppressed completely in strongly stably stratified conditions when Richardson's number exceeds its critical value. It is worth to note that airflow is laminar according classical ideas of the turbulence theory when Richardson's number values are supercritical. It is shown that in the stably stratified atmospheric surface layer under conditions of large vertical temperature gradients and low wind speeds, atmospheric turbulence is often characterized by intermittent structure and in some parts of space intensity of fluctuations can reach high values. The results of experimental investigations of optical instability conducted out along the horizontal path in the stably stratified atmospheric surface layer are discussed.
BER of Gaussian beam propagation in non-Kolmogorov turbulent atmosphere on slant path
NASA Astrophysics Data System (ADS)
Yang, Rui-ke; Chen, Yuan; Hou, Jie; Chen, Hui
2013-08-01
The propagation characteristic of a Gaussian beam through turbulent atmosphere have been studied in the past several years. The main advantage of Gaussian beam wave model is that the infinite plant wave and a spherical wave are being included. Non-Kolmogorov spectrum can describe generalized turbulent atmosphere environment. The propagation properties of Gaussian beam propagating through the turbulent atmosphere described by non-Kolmogorov spectrum are studied on slant path. The scintillation index is analyzed with the Gaussian beam of different turbulent strength, zenith angle, φ , and the spectral exponent, α, of non-Kolmogorov, respectively. The effect of the turbulent structure constant on the ground on sicntillation is notable. The scintillation index reduces remarkably with zenith angle and structure parameter decrease. At weak turbulenc, scintillation index increases as spectral exponent decreases. The bit error rate (BER) of a Gaussian beam propagating in non-Kolmogorov atmospheric turbulence channel is estimated on Earth-space slant path. By comparing the effect of the spectral power with the structure constant on BER at moderate and strong turbulence, the effect of the spectral power change on BER is small. With turbulence weakening , at the order of 10-15m-2/3 , the relative effect of the spectral power on BER is gradually increase. Hence, at the small structure constant on the ground, or weak turbulence, the effect of the turbulent spectral power on BER is required to take into account.
NASA Astrophysics Data System (ADS)
BozorgMagham, Amir E.; Ross, Shane D.
2015-05-01
To obtain more realistic approximations of atmospheric Lagrangian coherent structures, the material surfaces which form a template for the Lagrangian transport, two concepts are considered. First, the effect of unresolved turbulent motion due to finite spatiotemporal resolution of velocity field data is studied and the resulting qualitative changes on the FTLE field and LCSs are observed. Stochastic simulations show that these changes depend on the probabilistic distribution of position of released virtual particles after backward or forward time integration. We find that even with diffusion included, the LCSs play a role in structuring and bifurcating the probability distribution. Second, the uncertainty of the forecast FTLE fields is analyzed using ensemble forecasting. Unavoidable errors of the forecast velocity data due to the chaotic dynamics of the atmosphere is the salient reason for errors of the flow maps from which the FTLE fields are determined. The common practice for uncertainty analysis is to apply ensemble forecasting and here this approach is extended to FTLE field calculations. Previous work has shown an association between LCS passage and fluctuations in microbial populations and we find that ensemble FTLE forecasts are sufficient to predict such passages one day ahead of time with an accuracy of about 2 h.
Influence of atmospheric turbulence on optical measurement: a case report and review of literature
NASA Astrophysics Data System (ADS)
Yao, Linshen; Shang, Yang; Fu, Dan
2016-01-01
When videogammetry (optical measurement) was carried outdoor or under cruel indoor circumstance, the results would be inevitably affected by the atmosphere turbulence. As a result, the precision of surveying was destroyed. The field of air turbulence's impact on optical measurement was neglected by scholars for a long time, the achievements massed about laser optics and optical communications. The mostly adapted method was noise filtration when the pixel wandering could not be rejected in engineering application, which got little improvement on usual conditions. The principle of influence under atmospheric turbulence on optical measurement is presented in this paper. And experiments data and applications are carried out to announce the impact of atmospheric turbulence. Combining with relevant researches, some essential issues and expectations of the atmospheric turbulence research are proposed.
Influence of atmospheric turbulence on OAM-based FSO system with use of realistic link model
NASA Astrophysics Data System (ADS)
Li, Ming; Yu, Zhongyuan; Cvijetic, Milorad
2016-04-01
We study the influence of atmospheric turbulence on OAM-based free-space optical (FSO) communication by using the Pump turbulence spectrum model which accurately characterizes the realistic FSO link. A comprehensive comparison is made between the Pump and Kolmogorov spectrum models with respect to the turbulence impact. The calculated results show that obtained turbulence-induced crosstalk is lower, which means that a higher channel capacity is projected when the realistic Pump spectrum is used instead of the Kolmogorov spectrum. We believe that our results prove that performance of practical OAM-based FSO is better than one predicted by using the original Kolmogorov turbulence model.
Non-Markovian evolution of photonic quantum states in atmospheric turbulence
NASA Astrophysics Data System (ADS)
Roux, Filippus S.
2016-05-01
The evolution of the spatial degrees of freedom of a photon propagating through atmospheric turbulence is treated as a non-Markovian process. Here, we derive and solve the evolution equation for this process. The turbulent medium is modeled by a sequence of multiple phase screens for general turbulence conditions. The non-Markovian perspective leads to a second-order differential equation with respect to the propagation distance. The solution for this differential equation is obtained with the aid of a perturbative analysis, assuming the turbulence is relatively weak. We also provide another solution for more general turbulence strengths, but where we introduce a simplification to the differential equation.
The Saharan atmospheric boundary layer: Turbulence, stratification and mixing
NASA Astrophysics Data System (ADS)
Garcia-Carreras, Luis; Parker, Douglas J.; Marsham, John H.; Rosenberg, Philip D.; Marenco, Franco; Mcquaid, James B.
2013-04-01
High-resolution large-eddy model simulations, combined with aircraft and radiosonde observations from the Fennec observational campaign are used to describe the vertical structure of the Saharan atmospheric boundary layer (SABL). The SABL, probably the deepest dry convective boundary layer on Earth, is crucial in controlling the vertical redistribution and long-range transport of dust, heat, water and momentum in the Sahara, with significant implications for the large-scale Saharan heat low and West African monsoon systems. The daytime SABL has a unique structure, with an actively growing convective region driven by high sensible heating at the surface, capped by a weak (≤1K) temperature inversion and a deep, near-neutrally stratified Saharan residual layer (SRL) above it, which is mostly well mixed in humidity and temperature and reaches a height of ~500hPa. Large-eddy model (LEM) simulations were initialized with radiosonde data and driven by surface heat flux observations from Fennec supersite-1 at Bordj Bardji Mokhtar (BBM), southern Algeria. Aircraft observations are used to validate the processes of interest identified in the model, as well as providing unprecedented detail of the turbulent characteristics of the SABL. Regular radiosondes from BBM during June 2011 are used to generate a climatology of the day-time SABL structure, providing further evidence that the processes identified with the LEM are recurrent features of the real SABL. The model is shown to reproduce the typical SABL structure from observations, and different tracers are used to illustrate the penetration of the convective boundary layer into the residual layer above as well as mixing processes internal to the residual layer. Despite the homogeneous surface fluxes and tracer initialization, the large characteristic length-scale of the turbulent eddies leads to large horizontal changes in boundary layer depth (which control the formation of clouds) and significant heterogeneity in tracer
Influence of atmospheric turbulence on detecting performance of all-day star sensor
NASA Astrophysics Data System (ADS)
Pan, Yue; Wang, Hu; Shen, Yang; Xue, Yaoke; Liu, Jie
2016-01-01
All-day star sensor makes it possible to observe stars in all-day time in the atmosphere. But the detecting performance is influenced by atmospheric turbulence. According to the characteristic of turbulence in long-exposure model, the modulation transfer function, point spread function and encircled power of the imaging system have been analyzed. Combined with typical star sensor optical system, the signal to noise ratio and the detectable stellar magnitude limit affected by turbulence have been calculated. The result shows the ratio of aperture diameter to atmospheric coherence length is main basis for the evaluation of the impact of turbulence. In condition of medium turbulence in day time, signal to noise ratio of the star sensor with diameter 120mm will drop about 4dB at most in typical work environment, and the detectable stellar limit will drop 1 magnitude.
NASA Technical Reports Server (NTRS)
Rhyne, R. H.; Murrow, H. N.; Sidwell, K.
1976-01-01
Use of power spectral design techniques for supersonic transports requires accurate definition of atmospheric turbulence in the long wavelength region below the knee of the power spectral density function curve. Examples are given of data obtained from a current turbulence flight sampling program. These samples are categorized as (1) convective, (2) wind shear, (3) rotor, and (4) mountain-wave turbulence. Time histories, altitudes, root-mean-square values, statistical degrees of freedom, power spectra, and integral scale values are shown and discussed.
Why turbulence dominates the atmosphere and hydrosphere? (Alfred Wegener Medal Lecture)
NASA Astrophysics Data System (ADS)
Zilitinkevich, Sergej
2015-04-01
It is widely recognised that in very stable stratifications, at Richardson numbers (Ri) exceeding the critical value Ric ~ 0.25, turbulence inevitably decays and the flow becomes laminar. This is so, indeed, in the low-Reynolds-number (Re) flows, e.g., in some laboratory experiments; but this is by no means always the case. Air flows in the free atmosphere and water currents in deep ocean are almost always turbulent in spite of the strongly supercritical stratifications, with typical values of Ri varying in the interval 10 < Ri < 102. Until recently, this paradox has remained unexplained. We demonstrate that the key mechanism of the seemingly paradoxical self-preservation of the very-high-Re geophysical turbulence as a loop including (i) conversion of the turbulent kinetic unto potential energy and (ii) self-control of the negative (down-gradient) turbulent heat flux through efficient generation of the positive (counter-gradient) heat transfer by the turbulent potential energy (Zilitinkevich et al., 2007, 2008, 2009, 2013). Thanks to this loop, turbulence is maintained in supercritical stratifications and, moreover, at Ri > Ric the familiar 'strong-mixing turbulence' regime, typical of boundary-layer flows and characterised by the practically invariable turbulent Prandtl number PrT ~ 1 (the so-called 'Reynolds analogy'), gives way to a previously unknown 'wave-like turbulence' regime, wherein PrT sharply increases with increasing Ri (rather than to the laminar regime as is often the case in lab experiments). It is precisely the wave-like turbulence that dominates the free flows in the atmosphere and ocean. Modellers have long been aware that the turbulent heat transfer in the free atmosphere/ocean is much weaker than the momentum transfer. Our theory gives authentic formulation for this heuristic rule and provides physically grounded method for modelling geophysical turbulence up to very stable startifications.
Analysis of atmospheric turbulence in the upper layers of sea fog
NASA Astrophysics Data System (ADS)
Li, Yongping; Zheng, Yunxia
2015-05-01
Atmospheric turbulence plays a vital role in the formation and dissipation of fog. However, studies of such turbulence are typically limited to observations with ultrasonic anemometers less than 100 m above ground. Thus, the turbulence characteristics of upper fog layers are poorly known. In this paper, we present 4-layers of data, measured by ultrasonic anemometers on a wind tower about 400 m above the sea surface; we use these data to characterize atmospheric turbulence atop a heavy sea fog. Large differences in turbulence during the sea fog episode were recorded. Results showed that the kinetic energy, momentum flux, and sensible heat flux of turbulence increased rapidly during the onset of fog. After onset, high turbulence was observed within the uppermost fog layer. As long as this turbulence did not exceed a critical threshold, it was crucial to enhancing the cooling rate, and maintaining the fog. Vertical momentum flux and sensible heat flux generated by this turbulence weakened wind speed and decreased air temperature during the fog. Towards the end of the fog episode, the vertical distribution of sensible heat flux reversed, contributing to a downward momentum flux in all upper layers. Spatial and temporal scales of the turbulence eddy were greater before and after the fog, than during the fog episode. Turbulence energy was greatest in upper levels, around 430 m and 450 m above mean sea level (AMSL), than in lower levels of the fog (390 m and 410 m AMSL); turbulence energy peaked along the mean wind direction. Our results show that the status of turbulence was complicated within the fog; turbulence caused fluxes of momentum and sensible heat atop the fog layer, affecting the underlying fog by decreasing or increasing average wind speed, as well as promoting or demoting air temperature stratification.
Effects of turbulence in the atmosphere of Venus on Pioneer Venus radio, phase 1
NASA Technical Reports Server (NTRS)
Woo, R.; Kendall, W.; Ishimaru, A.; Berwin, R.
1973-01-01
The prediction of the turbulence effects in the Venus atmosphere on Pioneer Venus radio was investigated. A careful investigation based on a theoretical and experimental study of the power spectrum of the Mariner 5 amplitude fluctuations is carried out and the results contribute considerably to our scientific knowledge of turbulence in the atmosphere of Venus. Fully developed turbulence is seen to exist predominantly in the altitude range of 41 - 49 km. This result is consistent with the high wind shear and wind velocities observed by Venera 4 for altitudes higher than 40 km. The outer scale size of turbulence is on the order of 100 m, the structure constant for the dayside atmosphere 3.9 x 10 to the -7 power m to the -1/3rd power, and that for the nightside atmosphere 2.9 x 10 to the -7 power m to the -1/3rd power.
Statistical properties of visible and infrared beams retroreflected through a turbulent atmosphere
Slatkine, M.; Bensimon, D.; Englander, A.; Shtrikman, S.; Treves, D.
1980-01-01
Statistical properties of HeNe and CO/sub 2/ laser beams retroreflected through a turbulent atmosphere are investigated experimentally for round paths of 1 km and 12 km. Both heterodyne and direct detection are used.
Ring dislocation of a coherence of vortex Bessel beams in turbulent atmosphere
NASA Astrophysics Data System (ADS)
Lukin, Igor P.
2014-11-01
Researches of coherent properties of the vortex Bessel optical beams propagating in turbulent atmosphere are theoretically developed. The degree of coherence of vortex Bessel optical beams depending on beam parameters (crosssection wave number and a topological charge) and characteristics of turbulent atmosphere is in details analysed. It is shown, that at low levels of fluctuations in turbulent atmosphere, the degree of coherence of a vortex Bessel optical beam essentially depends on value of a topological charge of a beam. In the central part of a two-dimensional field of degree of coherence the ring dislocations, which number of rings to equally value of a topological charge of a vortex optical beam, is formed. At high levels of fluctuations in turbulent atmosphere, the degree of coherence of a vortex Bessel beam decreases much faster, than it takes place for the fundamental Bessel beam. And, speed of decrease essentially increases in process of growth of value of a topological charge of a beam.
Formation of a ring dislocation of a coherence of a vortex optical beam in turbulent atmosphere
NASA Astrophysics Data System (ADS)
Lukin, Igor P.
2013-12-01
Researches of coherent properties of the vortex Bessel optical beams propagating in turbulent atmosphere are theoretically developed. The degree of coherence of vortex Bessel optical beams depending on beam parameters (crosssection wave number and a topological charge) and characteristics of turbulent atmosphere is in details analysed. It is shown, that at low levels of fluctuations in turbulent atmosphere, the degree of coherence of an vortex Bessel optical beam essentially depends on value of a topological charge of a beam. In the central part of a two-dimensional field of degree of coherence the ring dislocations, which number of rings to equally value of a topological charge of a vortex optical beam, is formed. At high levels of fluctuations in turbulent atmosphere, the degree of coherence of a vortex Bessel beam decreases much faster, than it takes place for the fundamental Bessel beam. And, speed of decrease essentially increases in process of growth of value of a topological charge of a beam.
Study on the characteristics of different infrared transmission in atmospheric turbulence
NASA Astrophysics Data System (ADS)
Wang, Zhe; Wang, Jing-yuan; Xu, Zhi-yong; Chang, Shuai; Zhao, Ji-yong; Chen, Yi-wang; Wang, Rong; Wei, Yi-mei
2015-10-01
It is known theoretically that the long wavelength infrared has better performance when transmitting in atmospheric turbulence. In order to evaluate the influence of the atmospheric turbulence quantificationally, the characteristics of different infrareds transmission in atmospheric turbulence are simulated and studied. A series of time relevant phase screens of atmospheric turbulence are simulated based on Fourier transform method proposed by McGlamery. Wind speed and direction are introduced in the meantime. Wavefront distortion, image spot dancing and spreading, receive loss of different wavelengths (0.85μm, 3.6μm, 10.6μm) are simulated respectively and compared to each other. The results show that the performances of long wavelength infrared (10.6μm) are the best, mid wavelength infrared (3.6μm) takes the second place and short wavelength infrared (0.85μm) is the worst.
NASA Astrophysics Data System (ADS)
Souza Freire, L.; Chamecki, M.; Kok, J. F.; Martin, R. L.; Samaddar, A.
2015-12-01
Soil dust corresponds to the majority of aerosol particles in the atmosphere, and it plays an important role in radiative transfer and cloud formation, therefore impacting air quality, weather and climate. Dust is primarily emitted by the high-energy impact of larger, less cohesive particles on the soil surface, a process called saltation. Usually, the horizontal saltation flux is modeled as a function of the wind friction velocity, and the dust vertical emission flux is assumed to be a fraction of the saltation flux. In this study, field data collected over sand dunes and a reduced complexity numerical model of turbulence are combined to investigate the interaction between atmospheric turbulence and the process of dust emission. Simultaneous measurements of turbulence from six levels (from 0.5 to 9 meters above ground), dust concentration from four levels (from 0.75 to 6.5 meters) and sand saltation particle counters from nine levels (from 7 to 47 centimeters) are used. A one-dimensional stochastic turbulence model that simulates the time evolution of the atmospheric boundary layer column is used to evaluate different parameterizations of the saltation process as a function of the wind shear on the vertical profiles of dust concentration. The diurnal evolution of dust concentration profiles is then compared with field measurements. The saltation flux data is also used to evaluate the models and to estimate the dust flux directly. Effects of particle size, atmospheric stability and threshold wind speed on dust concentration are also investigated.
Internal gravity wave-atmospheric wind interaction - A cause of clear air turbulence.
NASA Technical Reports Server (NTRS)
Bekofske, K.; Liu, V. C.
1972-01-01
The interaction between an internal gravity wave (IGW) and a vertical wind shear is discussed as a possible cause in the production of clear air turbulence in the free atmosphere. It is shown that under certain typical condition the interaction of an IGW with a background wind shear near a critical level provides a mechanism for depositing sufficient momentum in certain regions of the atmosphere to significantly increase the local mean wind shear and to lead to the production of turbulence.
NASA Technical Reports Server (NTRS)
Jacobson, I. D.; Joshi, D. S.
1976-01-01
The influence of simulated turbulence on aircraft handling qualities was investigated. Pilot opinion of the handling qualities of a light general aviation aircraft were evaluated in a motion-base simulator using a simulated turbulence environment. A realistic representation of turbulence disturbances is described in terms of rms intensity and scale length and their random variations with time. The time histories generated by the proposed turbulence models showed characteristics which appear to be more similar to real turbulence than the frequently-used Gaussian turbulence model. In addition, the proposed turbulence models can flexibly accommodate changes in atmospheric conditions and be easily implemented in flight simulator studies. Six turbulence time histories, including the conventional Gaussian model, were used in an IFR-tracking task. The realism of each of the turbulence models and the handling qualities of the simulated airplane were evaluated. Analysis of pilot opinions shows that at approximately the same rms intensities of turbulence, the handling quality ratings transit from the satisfactory level, for the simple Gaussian model, to an unacceptable level for more realistic and compositely structured turbulence models.
Laser beam scintillation beyond the turbulent atmosphere A numerical computation
NASA Technical Reports Server (NTRS)
Bufton, J. L.; Taylor, L. S.
1976-01-01
The extended Huygens-Fresnel formulation for propagation through turbulence is used to examine scintillation of a finite laser beam. The method is demonstrated analytically for propagation beyond a weak Gaussian phase screen. A numerical integration technique is used to extend the results to a more realistic turbulence model. Results are compared with existing Gaussian beam propagation theory.
Theory and modeling of atmospheric turbulence, part 2
NASA Technical Reports Server (NTRS)
Chen, C. M.
1984-01-01
Two dimensional geostrophic turbulence driven by a random force is investigated. Based on the Liouville equation, which simulates the primitive hydrodynamical equations, a group-kinetic theory of turbulence is developed and the kinetic equation of the scaled singlet distribution is derived. The kinetic equation is transformed into an equation of spectral balance in the equilibrium and non-equilibrium states. Comparison is made between the propagators and the Green's functions in the case of the non-asymptotic quasi-linear equation to prove the equivalence of both kinds of approximations used to describe perturbed trajectories of plasma turbulence. The microdynamical state of fluid turbulence is described by a hydrodynamical system and transformed into a master equation analogous to the Vlasov equation for plasma turbulence. The spectral balance for the velocity fluctuations of individual components shows that the scaled pressure strain correlation and the cascade transfer are two transport functions that play the most important roles.
Wave optics simulation of atmospheric turbulence and reflective speckle effects in CO2 lidar.
Nelson, D H; Walters, D L; Mackerrow, E P; Schmitt, M J; Quick, C R; Porch, W M; Petrin, R R
2000-04-20
Laser speckle can influence lidar measurements from a diffuse hard target. Atmospheric optical turbulence will also affect the lidar return signal. We present a numerical simulation that models the propagation of a lidar beam and accounts for both reflective speckle and atmospheric turbulence effects. Our simulation is based on implementing a Huygens-Fresnel approximation to laser propagation. A series of phase screens, with the appropriate atmospheric statistical characteristics, are used to simulate the effect of atmospheric turbulence. A single random phase screen is used to simulate scattering of the entire beam from a rough surface. We compare the output of our numerical model with separate CO(2) lidar measurements of atmospheric turbulence and reflective speckle. We also compare the output of our model with separate analytical predictions for atmospheric turbulence and reflective speckle. Good agreement was found between the model and the experimental data. Good agreement was also found with analytical predictions. Finally, we present results of a simulation of the combined effects on a finite-aperture lidar system that are qualitatively consistent with previous experimental observations of increasing rms noise with increasing turbulence level. PMID:18345082
A new wind vane for the measurement of atmospheric turbulence
Parker, M.J.; Heverly, M.
1997-02-01
A Cooperative Research and Development Agreement (CRADA) between Met One Instruments, Incorporated (Met One) and Westinghouse Savannah River Company (WSRC) was created to develop a new wind vane that more accurately measures atmospheric turbulence. Through a process that had several phases, Met One created a prototype vane that was designed to attach to the existing Model 1585 Bi-Directional Wind Vane instrument structure. The prototype contained over 20% less mass to enhance responsiveness, which was also increased through the use of a teardrop-shaped fin structure. The prototype vane can be readily manufactured for commercial retail. Tests in wind tunnel of Building 735-7A, the Meteorological Engineering Facility, indicated that the new vane has a superior starting threshold of less than 0.14 meter per second, a delay distance of 0.72 meter, and a damping ratio of 0.4. The relative accuracy of less than one degree is unchanged from the previous design. The vane bias was acceptable at 0.8 degree for the horizontal wind angle, but was slightly high at 1.4 degree for the verticle wind angle. The high value of the verticle wind angle bias can most likely be reduced to the desired less than one degree value with standard manufacturing production techniques. The durability of the prototype vane was not tested in the field but is expected to be slightly less due to the use of hollow rather than foam-filled fins. However, the loss of some durability is more than compensated with increased sensitivity at low wind speeds. Field testing of the prototype is required to test for adequacy of durability.
Effect of turbulent atmosphere on the on-axis average intensity of Pearcey–Gaussian beam
NASA Astrophysics Data System (ADS)
F, Boufalah; L, Dalil-Essakali; H, Nebdi; A, Belafhal
2016-06-01
The propagation characteristics of the Pearcey–Gaussian (PG) beam in turbulent atmosphere are investigated in this paper. The Pearcey beam is a new kind of paraxial beam, based on the Pearcey function of catastrophe theory, which describes diffraction about a cusp caustic. By using the extended Huygens–Fresnel integral formula in the paraxial approximation and the Rytov theory, an analytical expression of axial intensity for the considered beam family is derived. Some numerical results for PG beam propagating in atmospheric turbulence are given by studying the influences of some factors, including incident beam parameters and turbulence strengths.
NASA Astrophysics Data System (ADS)
Li, Bifeng; Wang, Hongxing; Wu, Xiaojun; Song, Bo; Hu, Hao
2015-03-01
A calculation method of scintillation attenuation (SA) for non-line-of-sight (NLOS) ultraviolet (UV) communication is proposed on the basis of weak turbulence theory. To improve the channel model under turbulent environment, the atmospheric extinction coefficient in combination with UV single-scatter approximation model is modified based on SA. The in-depth analysis and interesting conclusion of atmospheric extinction coefficient named the turbulence coefficient versus different factors, including refractive-index structure parameter at the ground with measurement data, transceiver range and transceiver apex angles, are conducted.
The performance of heterodyne detection system for partially coherent beams in turbulent atmosphere
NASA Astrophysics Data System (ADS)
Chengqiang, Li; Tingfeng, Wang; Heyong, Zhang; Jingjiang, Xie; Lisheng, Liu; Shuai, Zhao; Jin, Guo
2015-12-01
The performance of heterodyne system is discussed for partially coherent beams in turbulent atmosphere by introducing turbulence spectrum of refractive-index fluctuations. Several analytic formulae for the heterodyne detection system using the partially coherent Gaussian Schell-model beam are presented. Based on Tatarskii spectrum model, some numerical results are given for the variation in the heterodyne efficiency with the misalignment angle, detector diameter, turbulence conditions, and parameters of the overlapping beams. According to the numerical results, we find that the turbulent atmosphere degrades the heterodyne efficiency significantly, and the variation in heterodyne efficiency is even slower against the misalignment angle in turbulence. For the deterministic received signal and the detector, the performance of the heterodyne detection can be adjusted by controlling the local oscillator signal parameters.
NASA Technical Reports Server (NTRS)
Hubbard, W. B.; Jokipii, J. R.
1977-01-01
Effects of atmospheric turbulence on stellar-occultation inversion procedures are investigated using a heuristic scattering model that is believed to reproduce the essential features of turbulence. A quantitative estimate is made of the size of the error in deducing the mean refractivity profile of a planetary atmosphere, taking into account constant as well as exponential scattering. It is shown that ordinary turbulence has no important effect on the average intensity profile in a stellar occultation but could have an important instantaneous effect. A critical examination of possible manifestations of turbulent scattering during occultations of Beta Sco by Jupiter indicates that all observed phenomena during these events can be understood in terms of scintillations produced by turbulence.
Influence of non-Kolmogorov atmospheric turbulence on the beam quality of vortex beams.
Li, Jinhong; Wang, Weiwei; Duan, Meiling; Wei, Jinlin
2016-09-01
Based on the extended Huygens-Fresnel principle and the definition of second-order moments of the Wigner distribution function (WDF), the analytical expressions for the propagation factors (M^{2}-factors) and Strehl ratio S_{R} of the Gaussian Schell-model (GSM) vortex beams and GSM non-vortex beams propagation through non-Kolmogorov atmospheric turbulence are derived, and used to study the influence of non-Kolmogorov atmospheric turbulence on beam quality of the GSM vortex beams. It is shown that the smaller the generalized structure constant and the outer scale of turbulence are, and the bigger the inner scale of turbulence is, the smaller the normalized propagation factor is, the bigger the Strehl ratio is, and the better the beam quality of GSM vortex beams in atmospheric turbulence is. The variation of beam quality with the generalized exponent α is nonmonotonic, when α = 3.11, the beam quality of the GSM vortex beams is the poorest through non-Kolmogorov atmospheric turbulence. GSM vortex beams is less affected by turbulence than GSM non-vortex beams under certain condition, and will be useful in long-distance free-space optical communications. PMID:27607647
Atmospheric and Wake Turbulence Impacts on Wind Turbine Fatigue Loading: Preprint
Lee, S.; Churchfield, M.; Moriarty, P.; Jonkman, J.; Michalakes, J.
2011-12-01
Large-eddy simulations of atmospheric boundary layers under various stability and surface roughness conditions are performed to investigate the turbulence impact on wind turbines. In particular, the aeroelastic responses of the turbines are studied to characterize the fatigue loading of the turbulence present in the boundary layer and in the wake of the turbines. Two utility-scale 5 MW turbines that are separated by seven rotor diameters are placed in a 3 km by 3 km by 1 km domain. They are subjected to atmospheric turbulent boundary layer flow and data is collected on the structural response of the turbine components. The surface roughness was found to increase the fatigue loads while the atmospheric instability had a small influence. Furthermore, the downstream turbines yielded higher fatigue loads indicating that the turbulent wakes generated from the upstream turbines have significant impact.
NASA Astrophysics Data System (ADS)
Sun, Jielun; Lenschow, Donald; LeMone, Margaret; Mahrt, Larry
2015-04-01
Turbulent fluxes from the Cooperative Atmosphere-Surface Exchange Study in 1999 (CASES-99) field experiment are further analyzed for both day- and nighttime as a follow-on to the investigation of the nighttime turbulence in Sun et al. (2012). The behavior of momentum and heat fluxes is investigated as functions of wind speed and the bulk temperature difference between observation heights and the surface. Vertical variations of momentum and heat flux at a given height z are correlated and are explained in terms of the energy and heat balance in a layer above the ground surface in which the surface heating/cooling and momentum sink need to be included. In addition, the surface also plays an important role in constraining the size of the dominant turbulent eddies, which is directly related to turbulence strength and the length scale of turbulence generation. The turbulence generation is not related to local vertical gradients especially under neutral condition as assumed in Monin-Obukhov similarity theory. Based on the observed relationships between momentum and heat fluxes, a new bulk formula for turbulence parameterization is developed to mainly examine the above-mentioned surface effects on vertical variation of turbulent momentum and heat fluxes. The new understanding of the observed relationships between these turbulent variables and mean variables explains the observed nighttime turbulence regime change observed in Sun et al. (2012) as well as the daytime momentum and heat flux variations with height up to the maximum observation height of 55 m.
Lidar sounding of the optical parameter of atmospheric turbulence
NASA Astrophysics Data System (ADS)
Gurvich, A. S.; Fortus, M. I.
2016-03-01
The operation of a lidar intended for clear air turbulence (CAT) positioning on the basis of the backscatter enhancement (BSE) effect is analyzed using a turbulence model with a power-law spectrum. Systematic distortions occurring due to a need to regularize the lidar positioning problem solution are estimated. It is shown that the effect of molecular viscosity of air on the positioning result can be neglected if the wave parameter, which characterizes the diffraction manifestation, is higher than 3. This corresponds to sounding ranges of more than 1 km for optical or UV lidars. The analysis results show that the BSE lidar positioning accuracy weakly depends on the exponent in the turbulence spectrum in regions of severe turbulence. The results can justify a physical experiment for the design of an aircraft system for the lidar detection of CAT regions ahead of the flight course.
Daytime turbulent exchange between the Amazon forest and the atmosphere
NASA Technical Reports Server (NTRS)
Fitzjarrald, David R.; Moore, Kathleen E.; Cabral, Osvaldo M. R.; Scolar, Jose; Manzi, Antonio
1990-01-01
Detailed observations of turbulence just above and below the crown of the Amazon rain forest during the wet season are presented. The forest canopy is shown to remove high frequency turbulent fluctuations while passing lower frequencies. Filter characteristics of turbulent transfer into the Amazon rain forest canopy are quantified. Simple empirical relations that relate observed turbulent heat fluxes to horizontal wind variance are presented. Changes in the amount of turbulent coupling between the forest and the boundary layer associated with deep convective clouds are presented both as statistical averages and as a series of case studies. These convective processes during the rainy season are shown to alter the diurnal course of turbulent fluxes. In wake of giant coastal systems, no significant heat or moisture fluxes occur for up to a day after the event. Radar data is used to demonstrate that even small raining clouds are capable of evacuating the canopy of substances normally trapped by persistent static stability near the forest floor. Recovery from these events can take more than an hour, even during mid-day. In spite of the ubiquitous presence of clouds and frequent rain during this season, the average horizontal wind speed spectrum is well described by dry CBL similarity hypotheses originally found to apply in flat terrain.
Theory and modeling of atmospheric turbulence, part 1
NASA Technical Reports Server (NTRS)
1984-01-01
The cascade transfer which is the only function to describe the mode coupling as the result of the nonlinear hydrodynamic state of turbulence is discussed. A kinetic theory combined with a scaling procedure was developed. The transfer function governs the non-linear mode coupling in strong turbulence. The master equation is consistent with the hydrodynamical system that describes the microdynamic state of turbulence and has the advantages to be homogeneous and have fewer nonlinear terms. The modes are scaled into groups to decipher the governing transport processes and statistical characteristics. An equation of vorticity transport describes the microdynamic state of two dimensional, isotropic and homogeneous, geostrophic turbulence. The equation of evolution of the macrovorticity is derived from group scaling in the form of the Fokker-Planck equation with memory. The microdynamic state of turbulence is transformed into the Liouville equation to derive the kinetic equation of the singlet distribution in turbulence. The collision integral contains a memory, which is analyzed with pair collision and the multiple collision. Two other kinetic equations are developed in parallel for the propagator and the transition probability for the interaction among the groups.
Daytime turbulent exchange between the Amazon forest and the atmosphere
NASA Technical Reports Server (NTRS)
Fitzjarrald, David R.; Moore, Kathleen E.; Cabral, Osvaldo M. R.; Scolar, Jose; Manzi, Antonio O.; Deabreusa, Leonardo D.
1989-01-01
Detailed observations of turbulence just above and below the crown of the Amazon rain forest during the wet season are presented. The forest canopy is shown to remove high frequency turbulent fluctuations while passing lower frequencies. Filter characteristics of turbulent transfer into the Amazon rain forest canopy are quantified. Simple empirical relations that relate observed turbulent heat fluxes to horizontal wind variance are presented. Changes in the amount of turbulent coupling between the forest and the boundary layer associated with deep convective clouds are presented both as statistical averages and as a series of case studies. These convective processes during the rainy season are shown to alter the diurnal course of turbulent fluxes. In wake of giant coastal systems, no significant heat or moisture fluxes occur for up to a day after the event. Radar data is used to demonstrate that even small raining clouds are capable of evacuating the canopy of substances normally trapped by persistent static stability near the forest floor. Recovery from these events can take more than an hour, even during mid-day. In spite of the ubiquitous presence of clouds and frequent rain during this season, the average horizontal wind speed spectrum is well described by dry CBL similarity hypotheses originally found to apply in flat terrain.
NASA Technical Reports Server (NTRS)
Han, Jongil; Lin, Yuh-Lang; Arya, S. Pal; Proctor, Fred H.
1999-01-01
The effects of ambient turbulence on decay and descent of aircraft wake vortices are studied using a validated, three-dimensional: large-eddy simulation model. Numerical simulations are performed in order to isolate the effect of ambient turbulence on the wake vortex decay rate within a neutrally-stratified atmosphere. Simulations are conducted for a range of turbulence intensities, by injecting wake vortex pairs into an approximately homogeneous and isotropic turbulence field. The decay rate of the vortex circulation increases clearly with increasing ambient turbulence level, which is consistent with field observations. Based on the results from the numerical simulations, simple decay models are proposed as functions of dimensionless ambient turbulence intensity (eta) and dimensionless time (T) for the circulation averaged over a range of radial distances. With good agreement with the numerical results, a Gaussian type of vortex decay model is proposed for weak turbulence: while an exponential type of Tortex decay model can be applied for strong turbulence. A relationship for the vortex descent based on above vortex decay model is also proposed. Although the proposed models are based on simulations assuming neutral stratification, the model predictions are compared to Lidar vortex measurements observed during stable, neutral, and unstable atmospheric conditions. In the neutral and unstable atmosphere, the model predictions appear to be in reasonable agreement with the observational data, while in the stably-stratified atmosphere, they largely underestimate the observed circulation decay with consistent overestimation of the observed vortex descent. The underestimation of vortex decay during stably-stratified conditions suggests that stratification has an important influence on vortex decay when ambient levels of turbulence are weak.
NASA Technical Reports Server (NTRS)
Frehlich, Rod; Kavaya, Michael J.
2000-01-01
The explanation for the difference between simulation and the zero-order theory for heterodyne lidar returns in a turbulent atmosphere proposed by Belmonte and Rye is incorrect. The theoretical expansion is not developed under a square- law-structure function approximation (random wedge atmosphere). Agreement between the simulations and the zero-order term of the theoretical expansion is produced for the limit of statistically independent paths (bi-static operation with large transmitter-receiver separation) when the simulations correctly include the large-scale gradients of the turbulent atmosphere.
Influence of atmospheric turbulence on the properties of specular and antispecular beams.
Zhou, Zhaotao; Guo, Mengwen; Zhao, Daomu
2016-08-20
A class of optical fields with specular or antispecular properties can be generated by a Gaussian Schell-model beam passing through a wavefront-folding interferometer. Based on the generalized diffraction integral formula, an analytical expression for the cross-spectral density function of such fields propagating through non-Kolmogorov atmospheric turbulence is derived. It is revealed that the specular and antispecular properties of the beams always maintain during propagation in free space. However, the specularity and antispecularity properties of the beams become different in atmosphere, since they are quickly destroyed by the atmospheric turbulence. PMID:27557000
Analysis of low altitude atmospheric turbulence data measured in flight
NASA Technical Reports Server (NTRS)
Ganzer, V. M.; Joppa, R. G.; Vanderwees, G.
1977-01-01
All three components of turbulence were measured simultaneously in flight at each wing tip of a Beech D-18 aircraft. The flights were conducted at low altitude, 30.5 - 61.0 meters (100-200 ft.), over water in the presence of wind driven turbulence. Statistical properties of flight measured turbulence were compared with Gaussian and non-Gaussian turbulence models. Spatial characteristics of the turbulence were analyzed using the data from flight perpendicular and parallel to the wind. The probability density distributions of the vertical gusts show distinctly non-Gaussian characteristics. The distributions of the longitudinal and lateral gusts are generally Gaussian. The power spectra compare in the inertial subrange at some points better with the Dryden spectrum, while at other points the von Karman spectrum is a better approximation. In the low frequency range the data show peaks or dips in the power spectral density. The cross between vertical gusts in the direction of the mean wind were compared with a matched non-Gaussian model. The real component of the cross spectrum is in general close to the non-Gaussian model. The imaginary component, however, indicated a larger phase shift between these two gust components than was found in previous research.
Daytime turbulent exchange between the Amazon forest and the atmosphere
Fitzjarrald, D.R.; Moore, K.E. ); Cabral, M.R. ); Scolar, J. ); Manzi, A.O.; de Abreau Sa, L.D. )
1990-09-20
Detailed observations of turbulence just above and below the crown of the Amazon rain forest during the wet season are presented. The forest canopy is shown to remove high-frequency turbulent fluctuations while passing lower frequencies. Filter characteristics of turbulent transfer into the Amazon rain forest canopy are quantified. In spite of the ubiquitous presence of clouds and frequent rain during this season, the average horizontal wind speed spectrum and the relationship between the horizontal wind speed and its standard deviation are well described by dry convective boundary layer similarity hypotheses originally found to apply in flat terrain. Diurnal changes in the sign of the vertical velocity skewness observed above and inside the canopy are shown to be plausibly explained by considering the skewness budget. Simple empirical formulas that relate observed turbulent heat fluxes to horizontal wind speed and variance are presented. Changes in the amount of turbulent coupling between the forest and the boundary layer associated with deep convective clouds are presented in three case studies. Even small raining clouds are capable of evacuating the canopy of substances normally trapped by persistent static stability near the forest floor. Recovery from these events can take more than an hour, even during midday.
Automatic parameter estimation for atmospheric turbulence mitigation techniques
NASA Astrophysics Data System (ADS)
Kozacik, Stephen; Paolini, Aaron; Kelmelis, Eric
2015-05-01
Several image processing techniques for turbulence mitigation have been shown to be effective under a wide range of long-range capture conditions; however, complex, dynamic scenes have often required manual interaction with the algorithm's underlying parameters to achieve optimal results. While this level of interaction is sustainable in some workflows, in-field determination of ideal processing parameters greatly diminishes usefulness for many operators. Additionally, some use cases, such as those that rely on unmanned collection, lack human-in-the-loop usage. To address this shortcoming, we have extended a well-known turbulence mitigation algorithm based on bispectral averaging with a number of techniques to greatly reduce (and often eliminate) the need for operator interaction. Automations were made in the areas of turbulence strength estimation (Fried's parameter), as well as the determination of optimal local averaging windows to balance turbulence mitigation and the preservation of dynamic scene content (non-turbulent motions). These modifications deliver a level of enhancement quality that approaches that of manual interaction, without the need for operator interaction. As a consequence, the range of operational scenarios where this technology is of benefit has been significantly expanded.
Modelling atmospheric turbulence effects on ground-based telescope systems
Bradford, L.W.; Flatte, S.M.; Max, C.E.
1993-09-30
Questions still exist concerning the appropriate model for turbulence- induced phase fluctuations seen in ground-based telescopes. Bester et al. used a particular observable (slope of the Allan variance) with an infrared interferometer in an attempt to distinguish models. The authors have calculated that observable for Kolmogorov and {open_quotes}random walk{close_quotes} models with a variety of outer scales and altitude-dependent turbulence and wind velocity. The authors have found that clear distinction between models requires good data on the vertical distribution of wind and turbulence. Furthermore, measurements at time separations of order 60 s are necessary to distinguish the {open_quotes}random walk{close_quotes} model from the Kolmogorov model.
Strong scintillations of pulsed Laguerrian beams in a turbulent atmosphere.
Banakh, Viktor A; Gerasimova, Liliya O
2016-08-22
Turbulent fluctuations of the energy density of broadband pulsed Laguerre-Gaussian beams are studied based on numerical solution of the parabolic wave equation for the complex spectral amplitude of the wave field by the split-step method. It is shown that in the regime of strong scintillations, the relative variance of energy density of the pulsed beams can take values smaller than unity, in contrast to the strong scintillation index of the continuous-wave beams, which tends to unity with increasing the turbulence strength. The level of residual spatial correlation of the energy density of pulsed beams exceeds that for the continuous-wave beams. It increases with shortening of the pulse duration and increasing of the refractive turbulence strength. PMID:27557206
Diffusion of Sound Waves in a Turbulent Atmosphere
NASA Technical Reports Server (NTRS)
Lyon, Richard H.
1960-01-01
The directional and frequency diffusion of a plane monochromatic 2 sound wave in statistically homogeneous, isotropic, and stationary turbulence is analyzed theoretically. The treatment is based on the diffusion equation for the energy density of sound waves, using the scattering cross section derived by Kraichnan for the type of turbulence assumed here. A form for the frequency-wave number spectrum of the turbulence is adopted which contains the pertinent parameters of the flow and is adapted to ease of calculation. A new approach to the evaluation of the characteristic period of the flow is suggested. This spectrum is then related to the scattering cross section. Finally, a diffusion equation is derived as a small-angle scattering approximation to the rigorous transport equation. The rate of spread of the incident wave in frequency and direction is calculated, as well as the power spectrum and autocorrelation for the wave.
Integral momenta of vortex Bessel-Gaussian beams in turbulent atmosphere.
Lukin, Igor P
2016-04-20
The orbital angular momentum of vortex Bessel-Gaussian beams propagating in turbulent atmosphere is studied theoretically. The field of an optical beam is determined through the solution of the paraxial wave equation for a randomly inhomogeneous medium with fluctuations of the refraction index of the turbulent atmosphere. Peculiarities in the behavior of the total power of the vortex Bessel-Gaussian beam at the receiver (or transmitter) are examined. The dependence of the total power of the vortex Bessel-Gaussian beam on optical beam parameters, namely, the transverse wave number of optical radiation, amplitude factor radius, and, especially, topological charge of the optical beam, is analyzed in detail. It turns out that the mean value of the orbital angular momentum of the vortex Bessel-Gaussian beam remains constant during propagation in the turbulent atmosphere. It is shown that the variance of fluctuations of the orbital angular momentum of the vortex Bessel-Gaussian beam propagating in turbulent atmosphere calculated with the "mean-intensity" approximation is equal to zero identically. Thus, it is possible to declare confidently that the variance of fluctuations of the orbital angular momentum of the vortex Bessel-Gaussian beam in turbulent atmosphere is not very large. PMID:27140133
Note: A balloon-borne accelerometer technique for measuring atmospheric turbulence
NASA Astrophysics Data System (ADS)
Marlton, Graeme J.; Giles Harrison, R.; Nicoll, Keri A.; Williams, Paul D.
2015-01-01
A weather balloon and its suspended instrument package behave like a pendulum with a moving pivot. This dynamical system is exploited here for the detection of atmospheric turbulence. By adding an accelerometer to the instrument package, the size of the swings induced by atmospheric turbulence can be measured. In test flights, strong turbulence has induced accelerations greater than 5g, where g = 9.81 m s-2. Calibration of the accelerometer data with a vertically orientated lidar has allowed eddy dissipation rate values of between 10-3 and 10-2 m2 s-3 to be derived from the accelerometer data. The novel use of a whole weather balloon and its adapted instrument package can be used as a new instrument to make standardized in situ measurements of turbulence.
Performance characteristics of a scanning laser imaging system through atmospheric turbulence
NASA Astrophysics Data System (ADS)
Nairat, Mazen; Voelz, David
2012-10-01
The transverse angular (spatial) imaging performance of a laser imaging system through atmospheric turbulence is characterized and described in a practical sense. The system is assumed to scan a far-field scene with a collimated Gaussian beam truncated by a circular aperture and a single channel receiver records the returns. The system point spread function is defined as the average beam profile at the scene and the half-angle beam spread is used to characterize the point spread function. A system modulation transfer function is defined that includes the effects of beam diffraction and turbulence. Spatial sampling of the scene is also considered. A normalized resolution metric (Strehl ratio) is applied to investigate the effects of sampling, beam size, turbulence, and beam truncation. The analysis indicates that resolution will be reduced by more than 90% in homogenous turbulence when the beam waist size is on the order of the atmospheric coherence length. Consistency with conventional imaging performance is discussed.
Shannon capacities and error-correction codes for optical atmospheric turbulent channels
NASA Astrophysics Data System (ADS)
Anguita, Jaime A.; Djordjevic, Ivan B.; Neifeld, Mark A.; Vasic, Bane V.
2005-09-01
Feature Issue on Optical Wireless Communications (OWC) The propagation of an on-off keying modulated optical signal through an optical atmospheric turbulent channel is considered. The intensity fluctuations of the signal observed at the receiver are modeled using a gamma-gamma distribution. The capacity of this channel is determined for a wide range of turbulence conditions. For a zero inner scale, the capacity decreases monotonically as the turbulence strengthens. For non-zero inner scale, the capacity is not monotonic with turbulence strength. Two error-correction schemes, based on low-density parity-check (LDPC) codes, are investigated as a means to improve the bit-error rate (BER) performance of the system. Very large coding gains--ranging from 5.5 to 14 dB, depending on the turbulence conditions--are obtained by these LDPC codes compared with Reed-Solomon error-correction codes of similar rates and lengths.
Analysis of atmospheric flow over a surface protrusion using the turbulence kinetic energy equation
NASA Technical Reports Server (NTRS)
Frost, W.; Harper, W. L.; Fichtl, G. H.
1975-01-01
Atmospheric flow fields resulting from a semi-elliptical surface obstruction in an otherwise horizontally homogeneous statistically stationary flow are modelled with the boundary-layer/Boussinesq-approximation of the governing equation of fluid mechanics. The turbulence kinetic energy equation is used to determine the dissipative effects of turbulent shear on the mean flow. Mean-flow results are compared with those given in a previous paper where the same problem was attacked using a Prandtl mixing-length hypothesis. Iso-lines of turbulence kinetic energy and turbulence intensity are plotted in the plane of the flow. They highlight regions of high turbulence intensity in the stagnation zone and sharp gradients in intensity along the transition from adverse to favourable pressure gradient.
NASA Astrophysics Data System (ADS)
Zamek, Steve; Yitzhaky, Yitzhak
2006-08-01
In remote sensing, atmospheric turbulence and aerosols limit the image quality. For many practical cases turbulence is shown to be dominant, especially for horizontal close-to-earth imaging in hot environments. In a horizontal long-range imaging it is usually impractical to measure path-averaged refractive index structure constant C n2 (which characterizes the turbulence strength) with conventional equipment. In this paper we propose a method for estimation of C n2 based just on the available recorded turbulence-degraded image sequence. The method exploits the turbulence-induced image "dancing". C n2 is extracted from the estimated image shifts variance. Experimental comparison with C n2 measurements using a scintillometer shows reliable estimation results. We also estimate image motion with sub-pixel accuracy for the purpose of obtaining a high-resolution image by applying a simple super-resolution procedure. Results of super-resolution for real imagery are presented.
The nature of large-scale turbulence in the Jovian atmosphere
NASA Technical Reports Server (NTRS)
Mitchell, J. L.
1982-01-01
The energetics and spectral characteristis of quasi-geostrophic turbulence in Jupiter's atmosphere are examined using sequences of Voyager images and infrared temperature soundings. Using global wind measurements momentum transports associated with zonally symmetric stresses and turbulent stresses are quantified. Though a strong up-gradient flux of momentum by eddies was observed, measurements do not preclude the possibility that symmetric stresses play a critical role in maintaining the mean zonal circulation. Strong correlation between the observed meridional distribution of eddy-scale kinetic energy and available potential energy suggests coupling between the observed cloudtop turbulent motions and the upper tropospheric thermodynamics. An Oort energy budget for Jupiter's upper troposphere is formulated.
Effects of turbulent dispersion of atmospheric balance motions of planetary boundary layer
NASA Astrophysics Data System (ADS)
Liu, Shikuo; Huang, Wei; Rong, Pingping
1992-06-01
New Reynolds’ mean momentum equations including both turbulent viscosity and dispersion are used to analyze atmospheric balance motions of the planetary boundary layer. It is pointed out that turbulent dispersion with γ 0 will increase depth of Ekman layer, reduce wind velocity in Ekman layer and produce a more satisfactory Ekman spiral lines fit the observed wind hodograph. The wind profile in the surface layer including turbulent dispersion is still logarithmic but the von Karman constant k is replaced by k 1 = √ 1 — k/2, the wind increases a little more rapidly with height.
New Methods for Applying Statistical State Dynamics to Problems in Atmospheric Turbulence
NASA Astrophysics Data System (ADS)
Farrell, B.; Ioannou, P. J.
2015-12-01
Adopting the perspective of statistical state dynamics (SSD) has led to a number of recent advances inunderstanding and simulating atmospheric turbulence at both boundary layer and planetary scale. Traditionally, realizations have been used to study turbulence and if a statistical quantity was needed it was obtained by averaging. However, it is now becomimg more widely appreciated that there are important advantages to studying the statistical state dynamics (SSD) directly. In turbulent systems statistical quantities are often the most useful and the advantage of obtaining these quantities directly as state variables is obvious. Moreover, quantities such as the probability density function (pdf) are often difficult to obtain accurately by sampling state trajectories. In the event that the pdf is itself time dependent or even chaotic, as is the case in the turbulence of the planetary boundary layer, the pdf can only be obtained as a state variable. However, perhaps the greatest advantage of the SSD approach is that it reveals directly the essential cooperative mechanisms of interaction among spatial and temporal scales that underly the turbulent state. In order to exploit these advantages of the SSD approach to geophysical turbulence, new analytical and computational methods are being developed. Example problems in atmospheric turbulence will be presented in which these new SSD analysis and computational methods are used.
Scattering of sound by atmospheric turbulence predictions in a refractive shadow zone
NASA Technical Reports Server (NTRS)
Mcbride, Walton E.; Bass, Henry E.; Raspet, Richard; Gilbert, Kenneth E.
1990-01-01
According to ray theory, regions exist in an upward refracting atmosphere where no sound should be present. Experiments show, however, that appreciable sound levels penetrate these so-called shadow zones. Two mechanisms contribute to sound in the shadow zone: diffraction and turbulent scattering of sound. Diffractive effects can be pronounced at lower frequencies but are small at high frequencies. In the short wavelength limit, then, scattering due to turbulence should be the predominant mechanism involved in producing the sound levels measured in shadow zones. No existing analytical method includes turbulence effects in the prediction of sound pressure levels in upward refractive shadow zones. In order to obtain quantitative average sound pressure level predictions, a numerical simulation of the effect of atmospheric turbulence on sound propagation is performed. The simulation is based on scattering from randomly distributed scattering centers ('turbules'). Sound pressure levels are computed for many realizations of a turbulent atmosphere. Predictions from the numerical simulation are compared with existing theories and experimental data.
Effect of the atmospheric turbulence on a special correlated radially polarized beam on propagation
NASA Astrophysics Data System (ADS)
Cui, Yan; Wei, Cun; Zhang, Yongtao; Wang, Fei; Cai, Yangjian
2015-11-01
A special correlated radially polarized beam (Phys. Rev. A 89, 013801, 2014) was introduced and demonstrated in experiment recently. In this paper, we investigate the statistical properties of a special correlated radially polarized (SCRP) beam in atmospheric turbulence. Analytical formulas for the average intensity distribution (AID), degree of polarization (DOP) and degree of coherence (DOC) are derived by adopting a beam coherence-polarization (BCP) matrix. With the help of the derived formulas, the evolutions of the AID, DOP and DOC of the SCRP beam in turbulent atmosphere are illustrated through numerical examples in detail, and the results are compared to those of a partially coherent radially polarized (PCRP) beam under equivalent condition. It reveals that the propagation properties of the SCRP beam is much different from those of the PCRP beam in atmosphere, and closely related to the strength of the turbulence and the beam parameters.
Numerical simulation research on sodium laser beacon imagings through the atmosphere turbulence
NASA Astrophysics Data System (ADS)
Liu, Xiangyuan; Qian, Xianmei; Zhang, Suimeng; Zhao, Minfu; Cui, Chaolong; Huang, Honghua
2016-01-01
Based on the relative intensity distributions of Sodium Laser Beacon (SLB) and analysis of the on-axis imaging of incoherent light, considering the effects of atmospheric turbulence and the changes of telescope receiving diameter on the short-exposure SLB imagings on the focal plane, imagings of an extended source SLB are simulated under the three atmospheric turbulence models. Results indicate that sharpness and peak strehl ratio of SLB imagings increase but sharpness radius decrease with the decrease of atmosphere turbulence strengths. Moreover, the changes of telescope diameter from 3.0m to 1.5m cause the decrease of sharpness and peak strehl ratio but the increase of sharpness radius.
NASA Astrophysics Data System (ADS)
Rickenstorff, Carolina; Rodrigo, Jóse A.; Alieva, Tatiana
2016-04-01
Different applications such as astronomy, remote optical sensing and free space optical communications, among others, require both numerical and laboratory experimental simulations of beam propagation through turbulent atmosphere prior to an outdoor test. While rotating phase plates or hot chambers can be applied to such studies, they do not allow changing the atmospheric conditions and the propagation distance in situ. In contrast, the spatial light modulators (SLMs) are a flexible alternative for experimental turbulence simulation. In this work we consider an experimental setup comprising two SLMs for studying laser beam propagation in weak atmospheric turbulence. The changes of atmospheric conditions and propagation distances are properly achieved by the adjustment of the phase screens and the focal distances of digital lenses implemented in both SLMs. The proposed system can be completely automatized and all its elements are in fixed positions avoiding mechanical misalignment. Its design, propagation distance and atmospheric condition adjustment are provided. The setup performance is verified by numerical simulation of Gaussian beam propagation in the weak turbulence regime. The obtained parameters: scintillation index, beam wander and spreading are compared to their theoretical counterparts for different propagation distances and atmospheric conditions.
Cross-frequency coherence and pulse propagation in a turbulent atmosphere.
Ostashev, Vladimir E; Wilson, D Keith; Collier, Sandra L; Cain, Jericho E; Cheinet, Sylvain
2016-07-01
Cross-frequency coherence of acoustic signals in a turbulent atmosphere is an important consideration for source localization with acoustic sensor arrays and for remote sensing of the atmosphere with sodars and tomography techniques. This paper takes as a starting point recently derived, closed-form equations for the spatial-temporal correlation function of a broadband acoustic signal propagating in a turbulent atmosphere with coupled spatial-temporal fluctuations in temperature and wind velocity. This theory is employed to calculate, based on the Rytov approximation, the two-point, two-time, two-frequency mutual coherence function of plane and spherical waves in the weak scattering regime. The cross-frequency coherence for these waveforms is then obtained and compared with that in the geometrical acoustics approximation. The coherence bandwidth is calculated and analyzed for typical meteorological regimes of the atmospheric surface layer and parameters of sound propagation. The results obtained are compared with available experimental data. The cross-frequency coherence is also used to study the effect of atmospheric turbulence on the mean intensity of an acoustic pulse propagating in a turbulent atmosphere. PMID:27475189
Algorithm for Simulating Atmospheric Turbulence and Aeroelastic Effects on Simulator Motion Systems
NASA Technical Reports Server (NTRS)
Ercole, Anthony V.; Cardullo, Frank M.; Kelly, Lon C.; Houck, Jacob A.
2012-01-01
Atmospheric turbulence produces high frequency accelerations in aircraft, typically greater than the response to pilot input. Motion system equipped flight simulators must present cues representative of the aircraft response to turbulence in order to maintain the integrity of the simulation. Currently, turbulence motion cueing produced by flight simulator motion systems has been less than satisfactory because the turbulence profiles have been attenuated by the motion cueing algorithms. This report presents a new turbulence motion cueing algorithm, referred to as the augmented turbulence channel. Like the previous turbulence algorithms, the output of the channel only augments the vertical degree of freedom of motion. This algorithm employs a parallel aircraft model and an optional high bandwidth cueing filter. Simulation of aeroelastic effects is also an area where frequency content must be preserved by the cueing algorithm. The current aeroelastic implementation uses a similar secondary channel that supplements the primary motion cue. Two studies were conducted using the NASA Langley Visual Motion Simulator and Cockpit Motion Facility to evaluate the effect of the turbulence channel and aeroelastic model on pilot control input. Results indicate that the pilot is better correlated with the aircraft response, when the augmented channel is in place.
A qualitative assessment of a random process proposed as an atmospheric turbulence model
NASA Technical Reports Server (NTRS)
Sidwell, K.
1977-01-01
A random process is formed by the product of two Gaussian processes and the sum of that product with a third Gaussian process. The resulting total random process is interpreted as the sum of an amplitude modulated process and a slowly varying, random mean value. The properties of the process are examined, including an interpretation of the process in terms of the physical structure of atmospheric motions. The inclusion of the mean value variation gives an improved representation of the properties of atmospheric motions, since the resulting process can account for the differences in the statistical properties of atmospheric velocity components and their gradients. The application of the process to atmospheric turbulence problems, including the response of aircraft dynamic systems, is examined. The effects of the mean value variation upon aircraft loads are small in most cases, but can be important in the measurement and interpretation of atmospheric turbulence data.
THE MECHANICAL GREENHOUSE: BURIAL OF HEAT BY TURBULENCE IN HOT JUPITER ATMOSPHERES
Youdin, Andrew N.; Mitchell, Jonathan L.
2010-10-01
The intense irradiation received by hot Jupiters suppresses convection in the outer layers of their atmospheres and lowers their cooling rates. 'Inflated' hot Jupiters, i.e., those with anomalously large transit radii, require additional sources of heat or suppressed cooling. We consider the effect of forced turbulent mixing in the radiative layer, which could be driven by atmospheric circulation or by another mechanism. Due to stable stratification in the atmosphere, forced turbulence drives a downward flux of heat. Weak turbulent mixing slows the cooling rate by this process, as if the planet were irradiated more intensely. Stronger turbulent mixing buries heat into the convective interior, provided the turbulence extends to the radiative-convective boundary. This inflates the planet until a balance is reached between the heat buried into and radiated from the interior. We also include the direct injection of heat due to the dissipation of turbulence or other effects. Such heating is already known to slow planetary cooling. We find that dissipation also enhances heat burial from mixing by lowering the threshold for turbulent mixing to drive heat into the interior. Strong turbulent mixing of heavy molecular species such as TiO may be necessary to explain stratospheric thermal inversions. We show that the amount of mixing required to loft TiO may overinflate the planet by our mechanism. This possible refutation of the TiO hypothesis deserves further study. Our inflation mechanism requires a deep stratified layer that only exists when the absorbed stellar flux greatly exceeds the intrinsic emitted flux. Thus, it would be less effective for more luminous brown dwarfs and for longer period gas giants, including Jupiter and Saturn.
Average capacity for PCB propagation in atmospheric turbulence on Earth-space path
NASA Astrophysics Data System (ADS)
Yang, Rui-ke; Hou, Jie; Chen, Yuan; Chen, Hui
2013-08-01
In order to analyze the effect of atmospheric turbulence along Earth-space path on the performance of laser communication system, the change of Kolmogorov spectrum with altitude is taken into account on the basis of the relation of turbulence structure constant with altitude. The scintillation index under the condition of the different coherent degree for optical source are discussed from weak to strong turbulence regime for a partially coherent Gaussian beam (PCB) propagating through turbulent atmosphere. The relation of the scintillation index with elevation is analyzed on Earth-space path. The expressions for the Log-normal and the Gamma-Gamma turbulence channel of irradiance fluctuations are given. The mathematical expression for the evaluation of the average capacity is shown for a Kolmogorov turbulent atmosphere channel. The average capacity of a PCB is calculated under the condition of different coherent length, aperture, on the horizontal and Earth-space path, respectively. The results of scintillation index show that the difference among plane, spherical, and beam wave are obvious from weak to moderate turbulence regime, at strong regime, the results tend to saturation. The degradation of optical source coherence causes scintillation depression at weak turbulence regime. At moderate regime, the scintillation is little increase. The effect of source partially coherence on scintillation is disappear at stronger regime. Based on the Log-normal model in weak turbulent fade channel and the Gamma-Gamma model from weak to strong turbulence fade channel, the average capacities for different initial Gaussian beam radius, partially coherent degree beam are estimated, respectively. The results show that at weak turbulence, the difference between the capacities by Log-normal and Gamma-Gamma distribution is small, and from moderate to strong regime, the difference is gradually increase. At weak regime, the average capacity of partially coherent beam is greater than the
Response of a rigid aircraft to nonstationary atmospheric turbulence.
NASA Technical Reports Server (NTRS)
Verdon, J. M.; Steiner, R.
1973-01-01
The plunging response of an aircraft to a type of nonstationary turbulent excitation is considered. The latter consists of stationary Gaussian noise modulated by a well-defined envelope function. The intent of the investigation is to model the excitation experienced by an airplane flying through turbulence of varying intensity and to examine the influence of intensity variations on exceedance frequencies of the gust velocity and the airplane's plunging velocity and acceleration. One analytical advantage of the proposed model is that the Gaussian assumption for the gust excitation is retained. The analysis described herein is developed in terms of an envelope function of arbitrary form; however, numerical calculations are limited to the case of harmonic modulation.
Performance analysis of coherent wireless optical communications with atmospheric turbulence.
Niu, Mingbo; Song, Xuegui; Cheng, Julian; Holzman, Jonathan F
2012-03-12
Coherent wireless optical communication systems with heterodyne detection are analyzed for binary phase-shift keying (BPSK), differential PSK (DPSK), and M-ary PSK over Gamma-Gamma turbulence channels. Closed-form error rate expressions are derived using a series expansion approach. It is shown that, in the special case of K-distributed turbulence channel, the DPSK incurs a 3 dB signal-to-noise ratio (SNR) penalty compared to BPSK in the large SNR regime. The outage probability is also obtained, and a detailed outage truncation error analysis is presented and used to assess the accuracy in system performance estimation. It is shown that our series error rate expressions are simple to use and highly accurate for practical system performance estimation. PMID:22418534
The propagation characteristics of the conical hollow beams in the turbulent atmosphere
NASA Astrophysics Data System (ADS)
Yuan, Dong; Jin-Qi, He; Shu-Tao, Li; Xi-He, Zhang; Guang-Yong, Jin
2016-08-01
In this paper, by using the Collins formula and the Rytov method, the model used to descript the propagation properties of the conical hollow beams(CHBs) in the turbulent atmosphere is firstly constructed and the simulation is made by the numerical method. The results show that the initial transmission angle has important influence on the propagation properties. Beside these, the index structure constant and the order number also can influence the transverse intensity distribution. So according to the model, the intensity distribution of the conical hollow beams in the turbulent atmosphere can be controlled by adjusting these parameters.
NASA Technical Reports Server (NTRS)
Sparrow, Victor W.; Gionfriddo, Thomas A.
1994-01-01
In this study there were two primary tasks. The first was to develop an algorithm for quantifying the distortion in a sonic boom. Such an algorithm should be somewhat automatic, with minimal human intervention. Once the algorithm was developed, it was used to test the hypothesis that the cause of a sonic boom distortion was due to atmospheric turbulence. This hypothesis testing was the second task. Using readily available sonic boom data, we statistically tested whether there was a correlation between the sonic boom distortion and the distance a boom traveled through atmospheric turbulence.
Using an incoherent target return to adaptively focus through atmospheric turbulence.
Nelson, W; Palastro, J P; Wu, C; Davis, C C
2016-03-15
A laser beam propagating to a remote target through atmospheric turbulence acquires intensity fluctuations. If the target is cooperative and provides a coherent return beam, the phase measured near the beam transmitter and adaptive optics, in principle, can correct these fluctuations. Generally, however, the target is uncooperative. In this case, we show that an incoherent return from the target can be used instead. Using the principle of reciprocity, we derive a novel relation between the field at the target and the returned field at a detector. We simulate an adaptive optics system that utilizes this relation to focus a beam through atmospheric turbulence onto a rough surface. PMID:26977694
Large-eddy simulations of contrail-to-cirrus transition in atmospheric turbulence
NASA Astrophysics Data System (ADS)
Paoli, Roberto; Thouron, Odile; Picot, Joris; Cariolle, Daniel
2012-11-01
Contrails are ice clouds that form by condensation of water vapor exhaust from aircraft engines and develop further in the wake as they are entrained by the airplane trailing vortices. When contrails spread to form cirrus clouds, they can persist for hours and become almost indistinguishable from natural cirrus. This talk focuses on the role of atmospheric turbulence in determining the characteristics of these ``contrail cirrus.'' Large-eddy simulations are carried out using the atmospheric model Meso-NH with the goal of identifying the processes driving the contrail-to-cirrus transition as a function of contrail age. To that end, the effects of atmospheric turbulence, microphysics, and radiative transfer are analyzed separately. Turbulent fields are first generated by means of a stochastic forcing technique that reproduces the atmospheric conditions encountered in the upper troposphere. Contrails generated by a model aircraft are then inserted on the top of these fields. Finally, ice microphysics and radiative transfer are activated to find out on which spatial and temporal scales the vertical motion prevails over the essentially horizontal motion induced by atmospheric turbulent diffusion.
Imaging through atmospheric turbulence for laser based C-RAM systems: an analytical approach
NASA Astrophysics Data System (ADS)
Buske, Ivo; Riede, Wolfgang; Zoz, Jürgen
2013-10-01
High Energy Laser weapons (HEL) have unique attributes which distinguish them from limitations of kinetic energy weapons. HEL weapons engagement process typical starts with identifying the target and selecting the aim point on the target through a high magnification telescope. One scenario for such a HEL system is the countermeasure against rockets, artillery or mortar (RAM) objects to protect ships, camps or other infrastructure from terrorist attacks. For target identification and especially to resolve the aim point it is significant to ensure high resolution imaging of RAM objects. During the whole ballistic flight phase the knowledge about the expectable imaging quality is important to estimate and evaluate the countermeasure system performance. Hereby image quality is mainly influenced by unavoidable atmospheric turbulence. Analytical calculations have been taken to analyze and evaluate image quality parameters during an approaching RAM object. In general, Kolmogorov turbulence theory was implemented to determine atmospheric coherence length and isoplanatic angle. The image acquisition is distinguishing between long and short exposure times to characterize tip/tilt image shift and the impact of high order turbulence fluctuations. Two different observer positions are considered to show the influence of the selected sensor site. Furthermore two different turbulence strengths are investigated to point out the effect of climate or weather condition. It is well known that atmospheric turbulence degenerates image sharpness and creates blurred images. Investigations are done to estimate the effectiveness of simple tip/tilt systems or low order adaptive optics for laser based C-RAM systems.
Profiles of the daytime atmospheric turbulence above Big Bear solar observatory
NASA Astrophysics Data System (ADS)
Kellerer, A.; Gorceix, N.; Marino, J.; Cao, W.; Goode, P. R.
2012-06-01
Context. Space weather has become acutely critical for today's global communication networks. To understand its driving forces we need to observe the Sun with high angular-resolution, and within large fields-of-view, i.e. with multi-conjugate adaptive optics correction. Aims: The design of a multi-conjugate adaptive optical system requires the knowledge of the altitude distribution of atmospheric turbulence. We have therefore measured daytime turbulence profiles above the New Solar Telescope (NST), on Big Bear Lake. Methods: To this purpose, a wide-field wavefront sensor was installed behind the NST. The variation of the wavefront distortions with angular direction allows the reconstruction of the distribution of turbulence. Results: The turbulence is found to have three origins: 1. a ground layer (<500 m) that contains 55-65% of the turbulence, 2. a boundary layer between 1-7 km comprises 30-40% of the turbulent energy, 3. and the remaining ~5% are generated in the tropopause, which is above 12 km in summer and between 8 and 12 km in winter. Conclusions: A multi-conjugate adaptive optical system should thus aim at correcting the ground turbulence, the center of the boundary layer at roughly 3 km altitude and, eventually, the upper boundary layer around 6 km altitude.
Whalley, Richard D; Walsh, James L
2016-01-01
Flowing low temperature atmospheric pressure plasma devices have been used in many technological applications ranging from energy efficient combustion through to wound healing and cancer therapy. The generation of the plasma causes a sudden onset of turbulence in the inhomogeneous axisymmetric jet flow downstream of the plasma plume. The mean turbulent velocity fields are shown to be self-similar and independent of the applied voltage used to generate the plasma. It is proposed that the production of turbulence is related to a combination of the small-amplitude plasma induced body forces and gas heating causing perturbations in the unstable shear layers at the jet exit which grow as they move downstream, creating turbulence. PMID:27561246
Whalley, Richard D.; Walsh, James L.
2016-01-01
Flowing low temperature atmospheric pressure plasma devices have been used in many technological applications ranging from energy efficient combustion through to wound healing and cancer therapy. The generation of the plasma causes a sudden onset of turbulence in the inhomogeneous axisymmetric jet flow downstream of the plasma plume. The mean turbulent velocity fields are shown to be self-similar and independent of the applied voltage used to generate the plasma. It is proposed that the production of turbulence is related to a combination of the small-amplitude plasma induced body forces and gas heating causing perturbations in the unstable shear layers at the jet exit which grow as they move downstream, creating turbulence. PMID:27561246
Salomons, E M
2000-10-01
The validity of the axisymmetric parabolic-equation (PE) method for line-of-sight sound propagation in a turbulent atmosphere is investigated. The axisymmetric PE method is a finite-difference method for solving a 2D parabolic wave equation, which follows from the 3D wave equation by the assumption of axial symmetry around the vertical axis through the source. It is found that this axisymmetric approximation has a considerable spurious effect on the fluctuations of the sound field. This is concluded from analytical expressions for the log-amplitude and phase variances, derived both for isotropic turbulence and for axisymmetric turbulence. The expressions for axisymmetric turbulence are compared with the results of numerical computations with the PE method. PMID:11051480
Evidence for supersonic turbulence in the upper atmosphere of Jupiter.
Emerich, C; Jaffel, L B; Clarke, J T; Prangé, R; Gladstone, G R; Sommeria, J; Ballester, G
1996-08-23
Spectra of the hydrogen Lyman alpha (Ly-alpha) emission line profiles of the jovian dayglow, obtained by the Goddard High Resolution Spectrograph on the Hubble Space Telescope, appear complex and variable on time scales of a few minutes. Dramatic changes occur in the Ly-alpha bulge region at low latitudes, where the line profiles exhibit structures that correspond to supersonic velocities of the order of several to tens of kilometers per second. This behavior, unexpected in a planetary atmosphere, is evidence for the particularly stormy jovian upper atmosphere, not unlike a star's atmosphere. PMID:8688090
Extension of a Kolmogorov Atmospheric Turbulence Model for Time-Based Simulation Implementation
NASA Technical Reports Server (NTRS)
McMinn, John D.
1997-01-01
The development of any super/hypersonic aircraft requires the interaction of a wide variety of technical disciplines to maximize vehicle performance. For flight and engine control system design and development on this class of vehicle, realistic mathematical simulation models of atmospheric turbulence, including winds and the varying thermodynamic properties of the atmosphere, are needed. A model which has been tentatively selected by a government/industry group of flight and engine/inlet controls representatives working on the High Speed Civil Transport is one based on the Kolmogorov spectrum function. This report compares the Dryden and Kolmogorov turbulence forms, and describes enhancements that add functionality to the selected Kolmogorov model. These added features are: an altitude variation of the eddy dissipation rate based on Dryden data, the mapping of the eddy dissipation rate database onto a regular latitude and longitude grid, a method to account for flight at large vehicle attitude angles, and a procedure for transitioning smoothly across turbulence segments.
Zhang, Jiankun; Ding, Shengli; Zhai, Huili; Dang, Anhong
2014-12-29
In wireless optical communications (WOC), polarization multiplexing systems and coherent polarization systems have excellent performance and wide applications, while its state of polarization affected by atmospheric turbulence is not clearly understood. This paper focuses on the polarization fluctuations caused by atmospheric turbulence in a WOC link. Firstly, the relationship between the polarization fluctuations and the index of refraction structure parameter is introduced and the distribution of received polarization angle is obtained through theoretical derivations. Then, turbulent conditions are adjusted and measured elaborately in a wide range of scintillation indexes (SI). As a result, the root-mean-square (RMS) variation and probability distribution function (PDF) of polarization angle conforms closely to that of theoretical model. PMID:25607210
Kotha, A.; Harvey, J.E.; Phillips, R.L.
1994-12-31
A naturally-occurring, conjugate-wave phenomenon in mono-static laser imaging applications is caused by reciprocal scattering paths which experience identical phase delays during the double passage of an electromagnetic wave through a random phase screen or turbulent medium. This ``opposition effect`` or ``enhanced backscatter`` phenomenon is known to be caused by constructive interference between reciprocal multiple scattering paths. Reciprocal path imaging (RPI) is an attempt to exploit this phenomenon for obtaining diffraction-limited images of extended objects obscured by a random phase screen or turbulent atmosphere. The authors report upon their current effort to investigate RPI with sparse array receivers and its potential as a mechanism for achieving high-resolution imaging through a turbulent atmosphere without the use of adaptive optics for image compensation. Preliminary work is reviewed and several RPI concepts to be evaluated in the laboratory are discussed.
NASA Astrophysics Data System (ADS)
Kamardin, A. P.; Nevzorova, I. V.; Odintsov, S. L.
2015-11-01
In the work, we consider estimates of the height of layer of intense turbulent heat exchange in stably stratified atmospheric boundary layer, made with the use of meteorological acoustic radar (sodar). Dependence of this height on temperature gradient is analyzed. Current temperature stratification of the atmosphere in the layer with height up to 1 000 m was determined with the help of MTP-5 meteorological temperature profiler.
Experimental investigation into infrasonic emissions from atmospheric turbulence.
Shams, Qamar A; Zuckerwar, Allan J; Burkett, Cecil G; Weistroffer, George R; Hugo, Derek R
2013-03-01
Clear air turbulence (CAT) is the leading cause of in-flight injuries and in severe cases can result in fatalities. The purpose of this work is to design and develop an infrasonic array network for early warning of clear air turbulence. The infrasonic system consists of an infrasonic three-microphone array, compact windscreens, and data management system. Past experimental efforts to detect acoustic emissions from CAT have been limited. An array of three infrasonic microphones, operating in the field at NASA Langley Research Center, on several occasions received signals interpreted as infrasonic emissions from CAT. Following comparison with current lidar and other past methods, the principle of operation, the experimental methods, and experimental data are presented for case studies and confirmed by pilot reports. The power spectral density of the received signals was found to fit a power law having an exponent of -6 to -7, which is found to be characteristics of infrasonic emissions from CAT, in contrast to findings of the past. PMID:23464000
ACTIVE TURBULENCE AND SCALAR TRANSPORT NEAR THE FOREST-ATMOSPHERE INTERFACE
Turbulent velocity, temperature, water vapor concentration, and other scalars were measured at the canopy-atmosphere interface of a 13–14-m-tall uniform pine forest and a 33-m-tall nonuniform hardwood forest. These measurements were used to investigate whether the mixing la...
Banakh, V A; Marakasov, D A
2008-04-30
An algorithm for the wind profile recovery from spatiotemporal spectra of a laser beam reflected in a turbulent atmosphere is presented. The cases of a spherical wave incident on a diffuse reflector of finite size and a spatially limited beam reflected from an infinite random surface are considered. (laser applications and other topics in quantum electronics)
The effects of atmospheric turbulence on a quadrotor heavy lift airship
NASA Technical Reports Server (NTRS)
Tischler, M. B.; Jex, H. R.
1982-01-01
The response of a quadrotor heavy lift airship to atmospheric turbulence is evaluated using a four-point input model. Results show interaction between gust inputs and the characteristic modes of the vehicle's response. Example loop closures demonstrate tradeoffs between response regulation and structural loads. Vehicle responses to a tuned discrete wave front compare favorably with the linear results and illustrate characteristic HLA motion.
NASA Astrophysics Data System (ADS)
McCrae, Jack E.; Van Zandt, Noah; Cusumano, Salvatore J.; Fiorino, Steven T.
2013-05-01
Beam propagation from a laser phased array system through the turbulent atmosphere is simulated and the ability of such a system to compensate for the atmosphere via piston-only phase control of the sub-apertures is evaluated. Directed energy (DE) applications demand more power than most lasers can produce, consequently many schemes for high power involve combining the beams from many smaller lasers into one. When many smaller lasers are combined into a phased array, phase control of the individual sub-apertures will be necessary to create a high-quality beam. Phase control of these sub-apertures could then be used to do more, such as focus, steer, and compensate for atmospheric turbulence. Atmospheric turbulence is well known to degrade the performance of both imaging systems and laser systems. Adaptive optics can be used to mitigate this degradation. Adaptive optics ordinarily involves a deformable mirror, but with phase control on each sub-aperture the need for a deformable mirror is eliminated. The simulation conducted here evaluates performance gain for a 127 element phased array in a hexagonal pattern with piston-only phase control on each element over an uncompensated array for varying levels of atmospheric turbulence. While most simulations were carried out against a 10 km tactical scenario, the turbulence profile was adjusted so performance could be evaluated as a function of the Fried Parameter (r0) and the log-amplitude variance somewhat independently. This approach is demonstrated to be generally effective with the largest percentage improvement occurring when r0 is close to the sub-aperture diameter.
Turbulent Structures and Coherence in the Atmospheric Surface Layer
NASA Astrophysics Data System (ADS)
Träumner, K.; Damian, Th.; Stawiarski, Ch.; Wieser, A.
2015-01-01
Organized structures in turbulent flow fields are a well-known and still fascinating phenomenon. Although these so-called coherent structures are obvious from visual inspection, quantitative assessment is a challenge and many aspects e.g., formation mechanisms and contribution to turbulent fluxes, are discussed controversially. During the "High Definition Clouds and Precipitation for Advancing Climate Prediction" Observational Prototype Experiment (HOPE) from April to May 2013, an advanced dual Doppler lidar technique was used to image the horizontal wind field near the surface for approximately 300 h. A visual inspection method, as well as a two-dimensional integral length scale analysis, were performed to characterize the observations qualitatively and quantitatively. During situations with forcing due to shear, the wind fields showed characteristic patterns in the form of clearly bordered, elongated areas of enhanced or reduced wind speed, which can be associated with near-surface streaks. During calm situations with strong buoyancy forcing, open cell patterns in the horizontal divergence field were observed. The measurement technique used enables the calculation of integral length scales of both horizontal wind components in the streamwise and cross-stream directions. The individual length scales varied considerably during the observation period but were on average shorter during situations with compared to strongly stable situations. During unstable situations, which were dominated by wind fields with structures, the streamwise length scales increased with increasing wind speed, whereas the cross-stream length scales decreased. Consequently, the anisotropy increased from 1 for calm situations to values of 2-3 for wind speeds of 8-10. During neutral to stable situations, the eddies were on average quite isotropic in the horizontal plane.
The status of military specifications with regard to atmospheric turbulence
NASA Technical Reports Server (NTRS)
Moorhouse, David J.; Heffley, Robert K.
1987-01-01
The features of atmospheric disturbances that are significant to aircraft flying qualities are discussed. Next follows a survey of proposed models. Lastly, there is a discussion of the content and application of the model contained in the current flying qualities specification and the forthcoming MIL-Standard.
Dynamics of the gas flow turbulent front in atmospheric pressure plasma jets
NASA Astrophysics Data System (ADS)
Pei, X.; Ghasemi, M.; Xu, H.; Hasnain, Q.; Wu, S.; Tu, Y.; Lu, X.
2016-06-01
In this paper, dynamic characterizations of the turbulent flow field in atmospheric pressure plasma jets (APPJs) are investigated by focusing on the effect of different APPJ parameters, such as gas flow rate, applied voltage, pulse repetition frequency, and time duration of the pulse. We utilize Schlieren photography and photomultiplier tubes (PMT) as a signal triggering of an intensified charge coupled device (ICCD) and also a high speed camera to examine the formation of the turbulent front and its dynamics. The results reveal that the turbulent front will appear earlier and closer to the tube nozzle by increasing the gas flow rate or the applied voltage amplitude. However, the pulse time duration and repetition frequency cannot change the dynamics and formation of the turbulent front. Further investigation shows that every pulse can excite one turbulent front which is created in a specific position in a laminar region and propagates downstream. It seems that the dominating mechanisms responsible for the formation of turbulent fronts in plasma jets might not be ion momentum transfer.
Sound-wave coherence in atmospheric turbulence with intrinsic and global intermittency.
Wilson, D Keith; Ostashev, Vladimir E; Goedecke, George H
2008-08-01
The coherence function of sound waves propagating through an intermittently turbulent atmosphere is calculated theoretically. Intermittency mechanisms due to both the turbulent energy cascade (intrinsic intermittency) and spatially uneven production (global intermittency) are modeled using ensembles of quasiwavelets (QWs), which are analogous to turbulent eddies. The intrinsic intermittency is associated with decreasing spatial density (packing fraction) of the QWs with decreasing size. Global intermittency is introduced by allowing the local strength of the turbulence, as manifested by the amplitudes of the QWs, to vary in space according to superimposed Markov processes. The resulting turbulence spectrum is then used to evaluate the coherence function of a plane sound wave undergoing line-of-sight propagation. Predictions are made by a general simulation method and by an analytical derivation valid in the limit of Gaussian fluctuations in signal phase. It is shown that the average coherence function increases as a result of both intrinsic and global intermittency. When global intermittency is very strong, signal phase fluctuations become highly non-Gaussian and the average coherence is dominated by episodes with weak turbulence. PMID:18681567
Variability of the atmospheric turbulence in the region lake of Baykal
NASA Astrophysics Data System (ADS)
Botygina, N. N.; Kopylov, E. A.; Lukin, V. P.; Kovadlo, P. G.; Shihovcev, A. Yu.
2015-11-01
The estimations of the fried parameter according to micrometeorological and optical measurements in the atmospheric surface layer in the area of lake Baikal, Baikal astrophysical Observatory. According to the archive of NCEP/NCAR Reanalysis data obtained vertical distribution of temperature pulsations, and revealed the most pronounced atmospheric layers with high turbulence. A comparison of astronomical conditions vision in winter and in summer. By the registration of optical radiation of the Sun with telescopes, ground-based there is a need to compensate for the effects of atmospheric turbulence. Atmospheric turbulence reduces the angular resolution of the observed objects and distorts the structure of the obtained images. To improve image quality, and ideally closer to angular resolution, limited only by diffraction, it is necessary to implement and use adaptive optics system. The specificity of image correction using adaptive optics is that it is necessary not only to compensate for the random jitter of the image as a whole, but also adjust the geometry of the individual parts of the image. Evaluation of atmospheric radius of coherence (Fried parameter) are of interest not only for site-testing research space, but also are the basis for the efficient operation of adaptive optical systems 1 .
NASA Astrophysics Data System (ADS)
Strunin, M. A.; Hiyama, T.
2004-11-01
Instruments that measure atmospheric turbulence for the estimation of turbulent fluxes of heat, water vapor, and carbon dioxide were tested in the laboratory and during in-flight conditions aboard a Russian research Ilyushin-18 aircraft. The response characteristics of the aircraft turbulence sensors were first tested to decrease measurement errors for turbulent heat transfer and fluxes, including water vapour flux, before being installed on the Ilyushin-18 aircraft that was used in joint Russian-Japanese atmospheric boundary-layer research. The results show that the atmospheric turbulence measured in a frequency range of 0.01 to 10 Hz yielded proper estimates of fluxes. Errors in measurements of the turbulence made from the aircraft were also analysed. Aerodynamic distortions linked to the aircraft's body and propellers were determined from flight test experiments. Time lags between vertical wind speed fluctuations and air temperature fluctuations measured by the aircraft thermometer, and those between vertical wind speed fluctuations and air humidity fluctuations measured by an ultraviolet hygrometer (open-path system) and an infrared hygrometer (closed-path system) were estimated. The vertical wind speed and air temperature sensor measurements showed no time lag, but a time lag of 0.6 s occurred between vertical wind speed and ultraviolet hygrometer measurements. The time lag between vertical wind speed and the infrared hygrometer measurements depended on flight conditions due to air pumping load, and had to be defined for each sampling leg. Accounting for the time lag was critical for water vapour flux measurements and helped to eliminate large systematic errors.
NASA Astrophysics Data System (ADS)
Liu, Yang; Zhang, Guo-an
2014-09-01
In order to mitigate atmospheric turbulence, the free space optical (FSO) system model with spatial diversity is analyzed based on intensity detection pulse position modulation (PPM) in the weak turbulence atmosphere. The slot error rate (SER) calculating formula of the system without diversity is derived under pulse position modulation firstly. Then as a benchmark, independent of identical distribution, the average slot error rates of the three linear combining technologies, which are the maximal ratio combining (MRC), equal gain combining (EGC) and selection combining (SelC), are compared. Simulation results show that the performance of system is the best improved by MRC, followed by EGC, and is poor by SelC, but SelC is simpler and more convenient. Spatial diversity is efficient to improve the performance and has strong ability on resistance to atmospheric channel decline. The above scheme is more suitable for optical wireless communication systems.
Large-eddy simulation of turbulence in the free atmosphere and behind aircraft
NASA Astrophysics Data System (ADS)
Schumann, U.; Dörnbrack, A.; Dürbeck, T.; Gerz, T.
1997-02-01
The method of large-eddy simulation has been used for a wide variety of atmospheric flow problems. This paper gives an overview on recent applications of this method to turbulence in the free atmosphere under stably stratified conditions. In particular, flows in the wake of aircraft are studied in light of the potential impact of aircraft exhausts on the chemical and climatological state of the atmosphere. It is shown that different profiles of heat and moisture in the initial conditions of a jet representing engine exhaust gases may cause larger water saturation and hence earlier contrail formation than assumed up to now. The instability of trailing vortices in the wake of an aircraft is simulated up to the fully turbulent regime. The vertical diffusivity of aircraft exhaust is large in the vortex regime and much smaller than horizontal diffusivities in the later diffusion regime. The three-dimensional formation of a critical layer and breaking of gravity waves is simulated.
Target-in-the-loop remote sensing of laser beam and atmospheric turbulence characteristics.
Vorontsov, Mikhail A; Lachinova, Svetlana L; Majumdar, Arun K
2016-07-01
A new target-in-the-loop (TIL) atmospheric sensing concept for in situ remote measurements of major laser beam characteristics and atmospheric turbulence parameters is proposed and analyzed numerically. The technique is based on utilization of an integral relationship between complex amplitudes of the counterpropagating optical waves known as overlapping integral or interference metric, whose value is preserved along the propagation path. It is shown that the interference metric can be directly measured using the proposed TIL sensing system composed of a single-mode fiber-based optical transceiver and a remotely located retro-target. The measured signal allows retrieval of key beam and atmospheric turbulence characteristics including scintillation index and the path-integrated refractive index structure parameter. PMID:27409206
The upper atmosphere of Uranus - A critical test of isotropic turbulence models
NASA Technical Reports Server (NTRS)
French, R. G.; Elliot, J. L.; Sicardy, B.; Nicholson, P.; Matthews, K.
1982-01-01
Observations of the August 15, 1980, Uranus occultation of KM 12, obtained from Cerro Tololo InterAmerican Observatory, European Southern Observatory, and Cerro Las Campanas Observatory, are used to compare the atmospheric structure at points separated by approximately 140 km along the planetary limb. The results reveal striking, but by no means perfect correlation of the light curves, ruling out isotropic turbulence as the cause of the light curve spikes. The atmosphere is strongly layered, and any acceptable turbulence model must accommodate the axial ratios of greater than about 60 which are observed. The mean temperature of the atmosphere is 150 plus or minus 15 K for the region near number density 10 to the 14th per cu cm. Derived temperature variations of vertical scale approximately 130 km and amplitude plus or minus 5 K are in agreement for all stations, and correlated spikes correspond to low-amplitude temperature variations with a vertical scale of several kilometers.
Use of a moiré deflectometer on a telescope for atmospheric turbulence measurements.
Rasouli, Saifollah
2010-05-01
An instrument has been built for the study of the atmospheric turbulence by measuring the fluctuation of the angle of arrival across a telescope aperture using moiré deflectometry. A slightly divergent laser beam passes through a turbulent ground level atmosphere and enters the telescope aperture. The laser beam is recollimated behind the telescope's focal point by means of a collimator. The collimated beam passes through a moiré deflectometer. The fluctuating self-image of the first grating is formed on the second grating of the moiré deflectometer and fluctuating moiré fringes are formed. Using moiré fringe fluctuations we have calculated the fluctuations of the angle of arrival, the Fried's parameter r(0), and the atmospheric refractive index structure constant. Because of the magnifications of the telescope and moiré deflectometry, the precision of the technique can potentially be 1 order of magnitude more precise than previous methods. PMID:20436606
Higher-order laser beam scintillation in weakly turbulent marine atmospheric medium.
Baykal, Yahya
2016-04-01
The atmosphere above the sea or ocean, known as the marine atmosphere, affects optical waves propagating through it in a different manner than the atmosphere above land. Like other system design parameters, intensity fluctuations of laser light propagating in marine atmosphere, quantified by the scintillation index, also show different variations. The on-axis scintillations of higher-order laser beams are formulated and evaluated when such excitations are employed in a weakly turbulent marine atmospheric medium. Variations of the scintillation index with respect to the changes in the Gaussian beam size of the higher-order mode, link length, wavelength, and structure constant are reported. Our results can be used in the design of an optical wireless communication link design operating in marine atmospheres. PMID:27140788
NASA Astrophysics Data System (ADS)
Peng, Yufeng; Peng, Fang; Han, Junpeng
2013-02-01
Based on the laser field from a positive confocal unstable resonator, considering the influence of thermal distortion of the internal resonator mirror on the annular beam, the propagation characteristics of the annular beam through turbulent atmosphere are investigated by means of the fast Fourier transform algorithm (FFT). The intensity distributions of the output laser far-field are obtained to analyze the propagation characteristics of laser annular beam through the turbulent atmosphere, which is a function about different propagation distances. The results show that the peak intensity of the laser pattern becomes depressed and the spread of the far field diagram patterns is broadened under the increasing of the transmission distance and the thermal distortion of the laser resonator. β-parameter and strehl ratio are introduced to estimate the annular beam quality characteristics. It is found that the annular beam through strong turbulence influences much less obviously than the annular beam through weak turbulence on the quality characteristics with thermal distortion. In the same atmospheric conditions with a certain distance, the greater the mirror thermal distortion is, the worse the annular beam quality characteristics is.
A study of key features of the RAE atmospheric turbulence model
NASA Technical Reports Server (NTRS)
Jewell, W. F.; Heffley, R. K.
1978-01-01
A complex atmospheric turbulence model for use in aircraft simulation is analyzed in terms of its temporal, spectral, and statistical characteristics. First, a direct comparison was made between cases of the RAE model and the more conventional Dryden turbulence model. Next the control parameters of the RAE model were systematically varied and the effects noted. The RAE model was found to possess a high degree of flexibility in its characteristics, but the individual control parameters are cross-coupled in terms of their effect on various measures of intensity, bandwidth, and probability distribution.
Statistics of some atmospheric turbulence records relevant to aircraft response calculations
NASA Technical Reports Server (NTRS)
Mark, W. D.; Fischer, R. W.
1981-01-01
Methods for characterizing atmospheric turbulence are described. The methods illustrated include maximum likelihood estimation of the integral scale and intensity of records obeying the von Karman transverse power spectral form, constrained least-squares estimation of the parameters of a parametric representation of autocorrelation functions, estimation of the power spectra density of the instantaneous variance of a record with temporally fluctuating variance, and estimation of the probability density functions of various turbulence components. Descriptions of the computer programs used in the computations are given, and a full listing of these programs is included.
NASA Technical Reports Server (NTRS)
Nerheim, N.
1989-01-01
Blind pointing of the Deep Space Network (DSN) 70-meter antennas can be improved if distortions of the antenna structure caused by unpredictable environmental loads can be measured in real-time, and the resulting boresight shifts evaluated and incorporated into the pointing control loops. The measurement configuration of a proposed pointing compensation system includes an optical range sensor that measures distances to selected points on the antenna surface. The effect of atmospheric turbulence on the accuracy of optical distance measurements and a method to make in-situ determinations of turbulence-induced measurement errors are discussed.
NASA Astrophysics Data System (ADS)
Chan, P. W.
2009-03-01
The Hong Kong International Airport (HKIA) is situated in an area of complex terrain. Turbulent flow due to terrain disruption could occur in the vicinity of HKIA when winds from east to southwest climb over Lantau Island, a mountainous island to the south of the airport. Low-level turbulence is an aviation hazard to the aircraft flying into and out of HKIA. It is closely monitored using remote-sensing instruments including Doppler LIght Detection And Ranging (LIDAR) systems and wind profilers in the airport area. Forecasting of low-level turbulence by numerical weather prediction models would be useful in the provision of timely turbulence warnings to the pilots. The feasibility of forecasting eddy dissipation rate (EDR), a measure of turbulence intensity adopted in the international civil aviation community, is studied in this paper using the Regional Atmospheric Modelling System (RAMS). Super-high resolution simulation (within the regime of large eddy simulation) is performed with a horizontal grid size down to 50 m for some typical cases of turbulent airflow at HKIA, such as spring-time easterly winds in a stable boundary layer and gale-force southeasterly winds associated with a typhoon. Sensitivity of the simulation results with respect to the choice of turbulent kinetic energy (TKE) parameterization scheme in RAMS is also examined. RAMS simulation with Deardorff (1980) TKE scheme is found to give the best result in comparison with actual EDR observations. It has the potential for real-time forecasting of low-level turbulence in short-term aviation applications (viz. for the next several hours).
NASA Astrophysics Data System (ADS)
Puryear, Andrew L.; Shapiro, Jeffrey H.; Parenti, Ronald R.
2012-10-01
Free-space optical communication provides rapidly deployable, dynamic communication links that are capable of very high data rates compared with those of radio-frequency systems. As such, free-space optical communication is ideal for mobile platforms, for platforms that require the additional security afforded by the narrow divergence of a laser beam, and for systems that must be deployed in a relatively short time frame. In clear-weather conditions the data rate and utility of free-space optical communication links are primarily limited by fading caused by micro-scale atmospheric temperature variations that create parts-per-million refractive-index fluctuations known as atmospheric turbulence. Typical communication techniques to overcome turbulence-induced fading, such as interleavers with sophisticated codes, lose viability as the data rate is driven higher or the delay requirement is driven lower. This paper, along with its companion [J. H. Shapiro and A. Puryear, "Reciprocity-Enhanced Optical Communication through Atmospheric Turbulence-Part I: Reciprocity Proofs and Far-Field Power Transfer"], present communication systems and techniques that exploit atmospheric reciprocity to overcome turbulence which are viable for high data rate and low delay requirement systems. Part I proves that reciprocity is exhibited under rather general conditions, and derives the optimal power-transfer phase compensation for far-field operation. The Part II paper presents capacity-achieving architectures that exploit reciprocity to overcome the complexity and delay issues that limit state-of-the art free-space optical communications. Further, this paper uses theoretical turbulence models to determine the performance—delay, throughput, and complexity—of the proposed architectures.
Interaction of the sonic boom with atmospheric turbulence
NASA Technical Reports Server (NTRS)
Rusak, Zvi; Cole, Julian D.
1994-01-01
Theoretical research was carried out to study the effect of free-stream turbulence on sonic boom pressure fields. A new transonic small-disturbance model to analyze the interactions of random disturbances with a weak shock was developed. The model equation has an extended form of the classic small-disturbance equation for unsteady transonic aerodynamics. An alternative approach shows that the pressure field may be described by an equation that has an extended form of the classic nonlinear acoustics equation that describes the propagation of sound beams with narrow angular spectrum. The model shows that diffraction effects, nonlinear steepening effects, focusing and caustic effects and random induced vorticity fluctuations interact simultaneously to determine the development of the shock wave in space and time and the pressure field behind it. A finite-difference algorithm to solve the mixed type elliptic-hyperbolic flows around the shock wave was also developed. Numerical calculations of shock wave interactions with various deterministic and random fluctuations will be presented in a future report.
Thermal shallow water models of geostrophic turbulence in Jovian atmospheres
Warneford, Emma S. Dellar, Paul J.
2014-01-15
Conventional shallow water theory successfully reproduces many key features of the Jovian atmosphere: a mixture of coherent vortices and stable, large-scale, zonal jets whose amplitude decreases with distance from the equator. However, both freely decaying and forced-dissipative simulations of the shallow water equations in Jovian parameter regimes invariably yield retrograde equatorial jets, while Jupiter itself has a strong prograde equatorial jet. Simulations by Scott and Polvani [“Equatorial superrotation in shallow atmospheres,” Geophys. Res. Lett. 35, L24202 (2008)] have produced prograde equatorial jets through the addition of a model for radiative relaxation in the shallow water height equation. However, their model does not conserve mass or momentum in the active layer, and produces mid-latitude jets much weaker than the equatorial jet. We present the thermal shallow water equations as an alternative model for Jovian atmospheres. These equations permit horizontal variations in the thermodynamic properties of the fluid within the active layer. We incorporate a radiative relaxation term in the separate temperature equation, leaving the mass and momentum conservation equations untouched. Simulations of this model in the Jovian regime yield a strong prograde equatorial jet, and larger amplitude mid-latitude jets than the Scott and Polvani model. For both models, the slope of the non-zonal energy spectra is consistent with the classic Kolmogorov scaling, and the slope of the zonal energy spectra is consistent with the much steeper spectrum observed for Jupiter. We also perform simulations of the thermal shallow water equations for Neptunian parameter values, with a radiative relaxation time scale calculated for the same 25 mbar pressure level we used for Jupiter. These Neptunian simulations reproduce the broad, retrograde equatorial jet and prograde mid-latitude jets seen in observations. The much longer radiative time scale for the colder planet Neptune
Statistical analysis of atmospheric turbulence about a simulated block building
NASA Technical Reports Server (NTRS)
Steely, S. L., Jr.
1981-01-01
An array of towers instrumented to measure the three components of wind speed was used to study atmospheric flow about a simulated block building. Two-point spacetime correlations of the longitudinal velocity component were computed along with two-point spatial correlations. These correlations are in good agreement with fundamental concepts of fluid mechanics. The two-point spatial correlations computed directly were compared with correlations predicted by Taylor's hypothesis and excellent agreement was obtained at the higher levels which were out of the building influence. The correlations fall off significantly in the building wake but recover beyond the wake to essentially the same values in the undisturbed, higher regions.
VAWT (Vertical-Axis Wind Turbine) stochastic loads produced by atmospheric turbulence
Homicz, G.F.
1987-01-01
Blade fatigue life is an important element in determining the economic viability of the Vertical-Axis Wind Turbine (VAWT). A principal source of blade fatigue is thought to be the stochastic (i.e., random) aerodynamic loads created by atmospheric turbulence. This paper discusses the development of a model for the simulation of these stochastic loads, given the rotor geometry, operating conditions, and assumed turbulence properties. A Double-Multiple-Streamtube analysis is employed, which includes the effects of wind shear. Reynolds number variations, different airfoil sections and chord lengths along the blade span, and an empirical model for dynamic stall effects. Calculations are presented for the VAWT 34-m Test Bed currently being assembled at Bushland, Texas. Time histories of the loads, as well as their Fourier spectra, are presented and discussed. An unexpected finding is that the average output power is predicted to be more sensitive to turbulence level than had previously been thought. 24 refs., 11 figs.
SWIR sky glow imaging for detection of turbulence in the upper atmosphere
NASA Astrophysics Data System (ADS)
Dayton, David; Nolasco, Rudy; Allen, Jeff; Myers, Mike; Gonglewski, John; Fertig, Gregory; Burns, Dennis; Mons, Ishan
2010-08-01
It is well known that luminance from photo-chemical reactions of hydroxyl ions in the upper atmosphere (~85 km altitude) produces a significant amount of night time radiation in the short wave infra-red (SWIR) band between 0.9 and 1.7 μm wave length. This has been demonstrated as an effective illumination source for night time imaging applications. It addition it has been shown that observation of the spatial and temporal variations of the illumination can be used to characterize atmospheric tidal wave actions in the sky glow region. These spatiotemporal variations manifest themselves as traveling wave patterns whose period and velocity are related to the wind velocity at 85 km as well as the turbulence induced by atmospheric vertical instabilities. Ground to space observation systems especially those employing adaptive optics are adversely affected by high altitude turbulence and winds. In this paper we propose the use of sky glow observations to predict and characterize image system degradation due to upper atmosphere turbulence.
NASA Astrophysics Data System (ADS)
Zou, Xingquan; Hong, Pengda; Ding, Yujie J.
2014-12-01
We demonstrate dynamic recovery of blurred images caused by atmospheric turbulence. In particular, using a phase-conjugate wave generated by a second-order nonlinear crystal or composite, we restore the original quality of the image after the optical radiation forming the image propagates through the turbulent atmosphere. One of the key elements for our experiment is a rotating phase plate being placed in the beam path for simulating turbulent atmosphere. Using the nonlinear composite, we demonstrate that the image recovery is insensitive to the polarization of the optical radiation forming the image.
NASA Technical Reports Server (NTRS)
Woo, R.; Ishimaru, A.
1973-01-01
The purpose of this paper is to analyze the effects of small-scale turbulence on radio waves propagating through a planetary atmosphere. The analysis provides a technique for inferring the turbulence characteristics of a planetary atmosphere from the radio signals received from a spacecraft as it is occulted by the planet. The planetary turbulence is assumed to be localized and smoothly varying, with the structure constant varying exponentially with altitude. Rytov's method is used to derive the variance of log-amplitude and phase fluctuations of a wave propagating through the atmosphere.
Zou, Xingquan; Hong, Pengda; Ding, Yujie J.
2014-12-15
We demonstrate dynamic recovery of blurred images caused by atmospheric turbulence. In particular, using a phase-conjugate wave generated by a second-order nonlinear crystal or composite, we restore the original quality of the image after the optical radiation forming the image propagates through the turbulent atmosphere. One of the key elements for our experiment is a rotating phase plate being placed in the beam path for simulating turbulent atmosphere. Using the nonlinear composite, we demonstrate that the image recovery is insensitive to the polarization of the optical radiation forming the image.
Near-marine boundary layer atmospheric and turbulence measurement and modeling
NASA Astrophysics Data System (ADS)
Manzur, Tariq; Zeller, John; Magee, Eric
2013-06-01
Currently there are extensive modeling and measurement capabilities for the region extending from 100 ft above sea surface to space, but few such capabilities exist for the region extending up to 10 ft above the sea surface. By measuring and characterizing conditions in the marine boundary layer existing below 30 ft above the sea surface such as turbulence and extinction, the optical communication capabilities of maritime vessels when operating at or near the surface may be extended and enhanced. Key physical parameters such as absorption, scattering, and turbulence strength (Cn 2) along the propagation path have a degree of variability on meteorological conditions as well optical wavelength. Modeling of the atmospheric environment is thus critical in order to generate a good understanding of optical propagation through the atmosphere. NUWC is utilizing software provided by MZA to model Cn 2 and resultant beam propagation characteristics through the near-marine boundary layer. We are developing the capability of near-marine boundary layer atmospheric and turbulence measurements and modeling as well as optical laser link testing at outdoor test sites. Measurements are performed with optical laser links (e.g., bit rate error), scintillometer, and particle image velocimetry (PIV) cameras, while turbulence and propagation modeling is achieved using MODTRAN5, ATMTools, NSLOT, LEEDR, and WaveTrain modeling and simulation code. By better understanding the effects of turbulence on optical transmission in the near-marine boundary layer through modeling and experimental measurements, measures can be implemented to reduce the bit error rate and increase data throughput, enabling more efficient and accurate communication link capabilities.
Turbulent Transport Mechanics at the Forest-Atmosphere Interface
NASA Astrophysics Data System (ADS)
Katul, Gabriel
1999-11-01
A new method is developed to estimate momentum and scalar sources and sinks from measured mean concentration profiles within forested canopies (termed as the "Inverse" problem). The method combines many of the practical advantages of a previously proposed Lagrangian Localized Near Field theory and higher order Eulerian closure principles. Particularly, this "hybrid" method successfully combines the essential physics of closure modeling and the robustness of the regression source inversion developed for the Localized Near Field theory. The method is tested using measured mean CO2 concentration and eddy-covariance fluxes collected in a 15 year-old pine forest for a wide range of atmospheric stability conditions and using temperature and sensible heat flux measurements collected in a wind tunnel for a planar heat source. It is demonstrated that the newly proposed method is well suited for routine source and flux distribution inferences within the canopy.
A method of generating atmospheric turbulence with a liquid crystal spatial light modulator
NASA Astrophysics Data System (ADS)
Wilcox, Christopher C.; Santiago, Freddie; Martinez, Ty; Andrews, Jonathan R.; Restaino, Sergio R.; Corley, Melissa; Teare, Scott W.; Agrawal, Brij N.
2010-08-01
The Naval Research Laboratory has developed a new method for generating atmospheric turbulence and a testbed that simulates its aberrations far more inexpensively and with greater fidelity using a Liquid Crystal (LC) Spatial Light Modulator (SLM) than many other methods. This system allows the simulation of atmospheric seeing conditions ranging from very poor to very good and different algorithms may be easily employed on the device for comparison. These simulations can be dynamically generated and modified very quickly and easily. In addition, many models for simulating turbulence often neglect temporal transitions along with different seeing conditions. Using the statistically independent set of Karhunen-Loeve polynomials in conjunction with Kolmogorov statistics in this model provides an accurate spatial and temporal model for simulating turbulence. An added benefit to using a LC SLM is its low cost; and multiple devices can be used to simulate multiple layers of turbulence in a laboratory environment. Current testing with using multiple LC SLMs is under investigation at the Naval Research Laboratory and the Naval Postgraduate School.
Neo, Richard; Goodwin, Michael; Zheng, Jessica; Lawrence, Jon; Leon-Saval, Sergio; Bland-Hawthorn, Joss; Molina-Terriza, Gabriel
2016-02-01
In recent years, there have been a series of proposals to exploit the orbital angular momentum (OAM) of light for astronomical applications. The OAM of light potentially represents a new way in which to probe the universe. The study of this property of light entails the development of new instrumentation and problems which must be addressed. One of the key issues is whether we can overcome the loss of the information carried by OAM due to atmospheric turbulence. We experimentally analyze the effect of atmospheric turbulence on the OAM content of a signal over a range of realistic turbulence strengths typical for astronomical observations. With an adaptive optics system we are able to recover up to 89% power in an initial non-zero OAM mode (ℓ = 1) at low turbulence strengths (0.30" FWHM seeing). However, for poorer seeing conditions (1.1" FWHM seeing), the amount of power recovered is significantly lower (5%), showing that for the terrestrial detection of astronomical OAM, a careful design of the adaptive optics system is needed. PMID:26906859
Zilberman, Arkadi; Golbraikh, Ephim; Kopeika, Norman S
2008-12-01
Turbulence properties of communication links (optical and microwave) in terms of log-amplitude variance are studied on the basis of a three-layer model of refractive index fluctuation spectrum in the free atmosphere. We suggest a model of turbulence spectra (Kolmogorov and non-Kolmogorov) changing with altitude on the basis of obtained experimental and theoretical data for turbulence profile in the troposphere and lower stratosphere. PMID:19037366
Zilberman, Arkadi; Golbraikh, Ephim; Kopeika, Norman S
2008-12-01
Turbulence properties of communication links (optical and microwave) in terms of log-amplitude variance are studied on the basis of a three-layer model of refractive index fluctuation spectrum in the free atmosphere. We suggest a model of turbulence spectra (Kolmogorov and non-Kolmogorov) changing with altitude on the basis of obtained experimental and theoretical data for turbulence profile in the troposphere and lower stratosphere.
NASA Astrophysics Data System (ADS)
Okayama, Hiroshi; Li, Wei
2006-09-01
Atmopheric turbulence is one of the important correction factors to evaluate the earth's surface using a sinsor on a satellite. CO II and aerosol are selected as factors of turbulence. The effects of turbulence caused by CO II and aerosol on the light reflected from the earth's surface are estimated by measuring the degradation of spatial coherence of light in a chamber in which atmospheric turbulence is generated. Dry ice is used to generate carbon dioxide gas. degradation of spatial coherence is measured in relation to the increase of CO II. Turbulence caused by aerosol is measured by density of smoke cigarettes. The spatial coherence of light in the chamber degrades in relation to the increase of aerosol and as a result the turbulence increases. The relation between the turbulence and the degree of spatial coherence is explained in a formula.
NASA Astrophysics Data System (ADS)
Alliss, R.
2014-09-01
Optical turbulence (OT) acts to distort light in the atmosphere, degrading imagery from astronomical telescopes and reducing the data quality of optical imaging and communication links. Some of the degradation due to turbulence can be corrected by adaptive optics. However, the severity of optical turbulence, and thus the amount of correction required, is largely dependent upon the turbulence at the location of interest. Therefore, it is vital to understand the climatology of optical turbulence at such locations. In many cases, it is impractical and expensive to setup instrumentation to characterize the climatology of OT, so numerical simulations become a less expensive and convenient alternative. The strength of OT is characterized by the refractive index structure function Cn2, which in turn is used to calculate atmospheric seeing parameters. While attempts have been made to characterize Cn2 using empirical models, Cn2 can be calculated more directly from Numerical Weather Prediction (NWP) simulations using pressure, temperature, thermal stability, vertical wind shear, turbulent Prandtl number, and turbulence kinetic energy (TKE). In this work we use the Weather Research and Forecast (WRF) NWP model to generate Cn2 climatologies in the planetary boundary layer and free atmosphere, allowing for both point-to-point and ground-to-space seeing estimates of the Fried Coherence length (ro) and other seeing parameters. Simulations are performed using a multi-node linux cluster using the Intel chip architecture. The WRF model is configured to run at 1km horizontal resolution and centered on the Mauna Loa Observatory (MLO) of the Big Island. The vertical resolution varies from 25 meters in the boundary layer to 500 meters in the stratosphere. The model top is 20 km. The Mellor-Yamada-Janjic (MYJ) TKE scheme has been modified to diagnose the turbulent Prandtl number as a function of the Richardson number, following observations by Kondo and others. This modification
Determining beam properties at an inaccessible plane using the reciprocity of atmospheric turbulence
NASA Astrophysics Data System (ADS)
Nelson, W.; Wu, C.; Davis, C. C.
2015-09-01
A turbulent, atmospheric channel can be considered to be reciprocal at any one instance in time. Reciprocity is a powerful property that can be used to compensate for the distortions caused by turbulence such as beam scintillation, spreading, and wander. Here we investigate the use of reciprocity in instances where a beam is propagated to an uncooperative target. Theoretical work [V. P. Lukin and M. I. Charnotskii , Sov. J. Quantum Electron., 12(5), 602 (1982)] has shown that reciprocity principles indicate that properties of the beam incident on a target fluctuate synchronously with the intensity distribution scattered from the target. Here we extend this purely analytical treatment using phase screen simulations. We show that there exists a correlation between the intensity imaged by the receiver and the field incident on the target. Furthermore, we demonstrate that the intensity at a specific location could be used to drive an adaptive optics system that corrects for atmospheric phase distortions.
Slant path average intensity of finite optical beam propagating in turbulent atmosphere
NASA Astrophysics Data System (ADS)
Zhang, Yixin; Wang, Gaogang
2006-10-01
The average intensity of finite laser beam propagating through turbulent atmosphere is calculated from the extended Huygens Fresnel principle. Formulas are presented for the slant path average intensity from an arbitrarily truncated Gaussian beam. The new expressions are derived from the modified von Karman spectrum for refractive-index fluctuations, quadratic approximation of the structure function, and Gaussian approximation for the product of Gaussian function and Bessel function. It is shown that the form of average intensity is not a Gaussian function but a polynomial of the power of the binomial function, Gaussian function, and the incomplete gamma function. The results also show that the mean irradiance of a finite optical beam propagating in slant path turbulent atmosphere not only depends on the effective beam radius at the transmitting aperture plane, propagation distance, and long-term lateral coherence length of spherical wave, but also on the radius of emit aperture.
Cheng, Mingjian; Guo, Lixin; Zhang, Yixin
2015-12-14
Analytic expression of the receiver-aperture-averaged scintillation index (SI) was derived for Gaussian-beam waves propagating through non-Kolmogorov maritime atmospheric environment by establishing a generalized maritime atmospheric spectrum model. The error performance of an intensity-modulated and direct-detection (IM/DD) free-space optical (FSO) system was investigated using the derived SI and log-normal distribution. The combined effects of non-Kolmogorov power-law exponent, turbulence inner scale, structure parameter, propagation distance, receiver aperture, and wavelength were also evaluated. Results show that inner scale and power-law exponent obviously affect SI. Large wavelength and receiver aperture can mitigate the effects of turbulence. The proposed model can be evaluated ship-to-ship/shore FSO system performance. PMID:26699050
Beam wander of J 0- and I 0-Bessel Gaussian beams propagating in turbulent atmosphere
NASA Astrophysics Data System (ADS)
Çil, C. Z.; Eyyuboğlu, H. T.; Baykal, Y.; Korotkova, O.; Cai, Y.
2010-01-01
Root mean square (rms) beam wander of J 0-Bessel Gaussian and I 0-Bessel Gaussian beams, normalized by the rms beam wander of the fundamental Gaussian beam, is evaluated in atmospheric turbulence. Our formulation is based on the first and the second statistical moments obtained from the Rytov series. It is found that after propagating in atmospheric turbulence, the collimated J 0-Bessel Gaussian and the I 0-Bessel Gaussian beams have smaller rms beam wander than that of the Gaussian beam, regardless of the choice of Bessel width parameter. However, the extent of such an advantage depends on the chosen width parameter, Gaussian source size, propagation distance and the wavelength. Focusing at finite distances of the considered beams causes the rms beam wander to decrease sharply at the propagation distances equal to the focusing parameter.
Scintillation statistics caused by atmospheric turbulence and speckle in satellite laser ranging
NASA Technical Reports Server (NTRS)
Bufton, J. L.; Iyer, R. S.; Taylor, L. S.
1977-01-01
We study the statistics of scintillation at the ground-based receiver for the earth-space-earth retroreflector configuration of satellite laser ranging. These statistics are governed by the joint effects of atmospheric turbulence and speckle produced by the retroreflector array. An expression for the probability density function of scintillation is obtained and evaluated numerically. Comparison of the normalized variance of scintillation calculated by using this function shows good agreement with results obtained by other methods.
A method for the analysis of nonlinearities in aircraft dynamic response to atmospheric turbulence
NASA Technical Reports Server (NTRS)
Sidwell, K.
1976-01-01
An analytical method is developed which combines the equivalent linearization technique for the analysis of the response of nonlinear dynamic systems with the amplitude modulated random process (Press model) for atmospheric turbulence. The method is initially applied to a bilinear spring system. The analysis of the response shows good agreement with exact results obtained by the Fokker-Planck equation. The method is then applied to an example of control-surface displacement limiting in an aircraft with a pitch-hold autopilot.
NASA Astrophysics Data System (ADS)
Liu, Dajun; Wang, Yaochuan; Yin, Hongming
2016-04-01
The partially coherent four-petal Gaussian vortex beam is introduced and described by analytical expressions. The analytical propagation equation for partially coherent four-petal Gaussian vortex beam in turbulent atmosphere is derived by using the extended Huygens-Fresnel diffraction integral formula. The influences of refraction index structure, beam order n, topological charge M and the coherence length on the average intensity distributions of beam are investigated by numerical examples.
NASA Astrophysics Data System (ADS)
Vercauteren, N.; Von Larcher, T. G.; Bou-Zeid, E.; Klein, R.; Parlange, M. B.
2013-12-01
Intermittent turbulence is a common feature of stably stratified atmospheric flows, yet its modeling is still problematic. Mesoscale motions such as gravity waves, Kelvin Helmholtz instabilities or density currents may trigger intermittent turbulence and greatly complicate the modeling and measurements of the stable boundary layer (SBL). In this study we investigate the intermittency of turbulence in very stable conditions by applying new statistical analysis tools to the existing SnoHATS dataset, collected in Switzerland over the Glacier de la Plaine Morte in 2006. These tools could then be used to develop stochastic parameterization for the SBL for use in weather or climate models. The SnoHATS dataset includes measurements of atmospheric turbulence collected by horizontal arrays of sonic anemometers. This study applies timeseries analysis tools developed for meteorological data to analyze the SnoHATS dataset with a new perspective. Turbulence in very stable conditions exhibits intermittency, and there is interplay between larger scale atmospheric flow features (at the so-called submesoscales) and onset of turbulence. We investigate the use of statistical tools such as hidden Markov models (HMM) and nonstationary multivariate autoregressive factor models (VARX) as a way to define the interactions between lower frequency modes and turbulence modes. The statistical techniques allow for separation of the data according to metastable states, such as quiet and turbulent periods in the stratified atmosphere.
Study of air-pollution mixing heights and atmospheric turbulence over New York City - data report
SethuRaman, S.; Henderson, C.; Volk, T.; Hoffert, M.I.
1982-08-01
A major factor that affects the variation of ground-level concentration of air pollutants such as particulates, sulfur oxide, nitrogen oxides, carbon monoxide, hydrocarbons, and photochemical oxidants is the mixing height in the earth's atmosphere close to the surface. This is the layer within which processes associated with the atmospheric turbulence generated by the surface roughness and heating dominate. In order to investigate the variation of this mixing height and associated turbulence over New York City, an experiment was performed over the Barney building of New York University located in lower Manhattan. The mixing height was measured continuously with an acoustic sounder for 10 days from the roof of the Barney building estimated to be 50m above the street level. Several meteorological instruments were used on a 16m tower located on the roof of this building to study other atmospheric variables in the mixed layer. A description is given of the instruments and the data acquisition system used in the experiment. The data reveal significant heights of the mixed layer (200 to 400m) during nocturnal conditions which are probably due to urban heat island effects. Horizontal turbulence levels vary between 10 and 20 percent.
A non-gaussian model of continuous atmospheric turbulence for use in aircraft design
NASA Technical Reports Server (NTRS)
Reeves, P. M.; Joppa, R. G.; Ganzer, V. M.
1976-01-01
A non-Gaussian model of atmospheric turbulence is presented and analyzed. The model is restricted to the regions of the atmosphere where the turbulence is steady or continuous, and the assumptions of homogeneity and stationarity are justified. Also spatial distribution of turbulence is neglected, so the model consists of three independent, stationary stochastic processes which represent the vertical, lateral, and longitudinal gust components. The non-Gaussian and Gaussian models are compared with experimental data, and it is shown that the Gaussian model underestimates the number of high velocity gusts which occur in the atmosphere, while the non-Gaussian model can be adjusted to match the observed high velocity gusts more satisfactorily. Application of the proposed model to aircraft response is investigated, with particular attention to the response power spectral density, the probability distribution, and the level crossing frequency. A numerical example is presented which illustrates the application of the non-Gaussian model to the study of an aircraft autopilot system. Listings and sample results of a number of computer programs used in working with the model are included.
NASA Technical Reports Server (NTRS)
Harger, R. O.
1974-01-01
Abstracts are reported relating to the techniques used in the research concerning optical transmission of information. Communication through the turbulent atmosphere, quantum mechanics, and quantum communication theory are discussed along with the results.
Using an atmospheric turbulence model for the stochastic model of geodetic VLBI data analysis
NASA Astrophysics Data System (ADS)
Halsig, Sebastian; Artz, Thomas; Iddink, Andreas; Nothnagel, Axel
2016-06-01
Space-geodetic techniques at radio wavelength, such as global navigation satellite systems and very long baseline interferometry (VLBI), suffer from refractivity of the Earth's atmosphere. These highly dynamic processes, particularly refractivity variations in the neutral atmosphere, contribute considerably to the error budget of these space-geodetic techniques. Here, microscale fluctuations in refractivity lead to elevation-dependent uncertainties and induce physical correlations between the observations. However, up to now such correlations are not considered routinely in the stochastic model of space-geodetic observations, which leads to very optimistic standard deviations of the derived target parameters, such as Earth orientation parameters and station positions. In this study, the standard stochastic model of VLBI observations, which only includes, almost exclusively, the uncertainties from the VLBI correlation process, is now augmented by a variance-covariance matrix derived from an atmospheric turbulence model. Thus, atmospheric refractivity fluctuations in space and time can be quantified. One of the main objectives is to realize a suitable stochastic model of VLBI observations in an operational way. In order to validate the new approach, the turbulence model is applied to several VLBI observation campaigns consisting of different network geometries leading the path for the next-generation VLBI campaigns. It is shown that the stochastic model of VLBI observations can be improved by using high-frequency atmospheric variations and, thus, refining the stochastic model leads to far more realistic standard deviations of the target parameters. The baseline length repeatabilities as a general measure of accuracy of baseline length determinations improve for the turbulence-based solution. Further, this method is well suited for routine VLBI data analysis with limited computational costs.
NASA Astrophysics Data System (ADS)
Kumer, Valerie; Reuder, Joachim
2016-04-01
Wake characteristics are of great importance for wind park performances and turbine loads. Wind tunnel experiments helped to validate wake model simulations under neutral atmospheric conditions. However, recent studies show strongest wake characteristics and power losses in stable atmospheric conditions. Considering all three occurring atmospheric conditions this study presents a turbulence analysis of wind turbine wake flows measured by static and scanning Doppler LiDARs at the coast of the Netherlands. We use data collected by three Windcubes v1, a scanning Windcube 100S and sonic anemometers during the Wind Turbine Wake Experiment - Wieringermeer (WINTWEX-W). Turbulence parameters such as Turbulence Intensity (TI) and turbulent kinetic energy (TKE) are retrieved from the collected raw data. Results show highest turbulence on the flanks of the wake where strong wind shear dominates. On average the spatial turbulence distribution becomes more homogeneous with conical areas of enhanced TI. Highest turbulence and strongest wind deficits occur during stable weather conditions. Despite the ongoing research on the reliability of turbulence retrievals of Doppler LiDAR data, the results are consistent with sonic anemometer measurements and show promising opportunities for a qualitative study of wake characteristics such as wake strength and wake peak frequencies.
NASA Astrophysics Data System (ADS)
Picot, J.; Paoli, R.; Thouron, O.; Cariolle, D.
2015-07-01
In this work, the evolution of contrails in the vortex and dissipation regimes is studied by means of fully three-dimensional large-eddy simulation (LES) coupled to a Lagrangian particle tracking method to treat the ice phase. In this paper, fine-scale atmospheric turbulence is generated and sustained by means of a stochastic forcing that mimics the properties of stably stratified turbulent flows as those occurring in the upper troposphere and lower stratosphere. The initial flow field is composed of the turbulent background flow and a wake flow obtained from separate LES of the jet regime. Atmospheric turbulence is the main driver of the wake instability and the structure of the resulting wake is sensitive to the intensity of the perturbations, primarily in the vertical direction. A stronger turbulence accelerates the onset of the instability, which results in shorter contrail descent and more effective mixing in the interior of the plume. However, the self-induced turbulence that is produced in the wake after the vortex breakup dominates over background turbulence until the end of the vortex regime and controls the mixing with ambient air. This results in mean microphysical characteristics such as ice mass and optical depth that are slightly affected by the intensity of atmospheric turbulence. However, the background humidity and temperature have a first-order effect on the survival of ice crystals and particle size distribution, which is in line with recent studies.
A nonlinear OPC technique for laser beam control in turbulent atmosphere
NASA Astrophysics Data System (ADS)
Markov, V.; Khizhnyak, A.; Sprangle, P.; Ting, A.; DeSandre, L.; Hafizi, B.
2013-05-01
A viable beam control technique is critical for effective laser beam transmission through turbulent atmosphere. Most of the established approaches require information on the impact of perturbations on wavefront propagated waves. Such information can be acquired by measuring the characteristics of the target-scattered light arriving from a small, preferably diffraction-limited, beacon. This paper discusses an innovative beam control approach that can support formation of a tight laser beacon in deep turbulence conditions. The technique employs Brillouin enhanced fourwave mixing (BEFWM) to generate a localized beacon spot on a remote image-resolved target. Formation of the tight beacon doesn't require a wavefront sensor, AO system, or predictive feedback algorithm. Unlike conventional adaptive optics methods which allow wavefront conjugation, the proposed total field conjugation technique is critical for beam control in the presence of strong turbulence and can be achieved by using this non-linear BEFWM technique. The phase information retrieved from the established beacon beam can then be used in conjunction with an AO system to propagate laser beams in deep turbulence.
Quantum polarization fluctuations of an Airy beam in turbulent atmosphere in a slant path.
Yin, Xia; Zhang, Licheng
2016-07-01
Polarization of light has many applications in quantum information processing, including quantum teleportation and dense coding. In this paper, we investigate the polarization fluctuations of Airy beams propagating in a slant turbulent channel under the "few-photon" limit. Using the quantum Stokes parameters and the quantum degree of polarization, we demonstrate that the degree of polarization of Airy beams increases significantly with the large number of the detection photons, and a higher photon-number level can retain the stability of polarization. Numerical simulations show that the longer propagation distance and the stronger turbulence will lead to less oscillatory behaviors and a decrease in the polarization degree of Airy beams, but a bigger exponential truncation factor will cause an increase in the polarization degree of Airy beams. In contrast with Gaussian beams, the degree of polarization of Airy beams is less affected by atmospheric turbulence and propagation distance under the same conditions, which means that Airy beams possess a resilient ability against turbulence-induced perturbations. These results indicate that Airy beams have great potential for applications in long-distance free-space optical communications to improve the performance of a polarization-encoded free-space quantum communication system. PMID:27409692
NASA Astrophysics Data System (ADS)
Spencer, Mark F.; Dragulin, Ivan V.; Cargill, Daniel S.; Steinbock, Michael J.
2015-09-01
Digital holography wave-front sensing in the off-axis image plane recording geometry shows distinct potential for directed-energy and remote-sensing applications. For instance, digital holographic detection provides access to the amplitude and wrapped phase associated with an optical field. From the wrapped phase, one can estimate the atmospheric aberrations present and perform adaptive-optics compensation and high-resolution imaging. This paper develops wave-optics simulations which explore the estimation accuracy of digital holography wave-front sensing in the presence of strong atmospheric turbulence and thermal blooming. Specifically, this paper models spherical-wave propagation through varying atmospheric conditions along a horizontal propagation path and formulates the field-estimated Strehl ratio as a function of the image-plane sampling, the coherence diameter, the log-amplitude variance, and the distortion number. Such results will allow one to assess the number of pixels needed in a detector array when using digital holographic detection in the presence of strong atmospheric turbulence and thermal blooming.
NASA Astrophysics Data System (ADS)
de Jong, Arie N.; Schwering, Piet B. W.; Benoist, Koen W.; Gunter, Willem H.; Vrahimis, George; October, Faith J.
2012-06-01
During the FATMOSE trial, held over the False Bay, South Africa) from November 2009 until October 2010, day and night (24/7) high resolution images were collected of point sources at a range of 15.7 km. Simultaneously, data were collected on atmospheric parameters, as relevant for the turbulence conditions: air- and sea temperature, windspeed, relative humidity and the structure parameter for refractive index: Cn 2. The data provide statistical information on the mean value and the variance of the atmospheric point spread function and the associated modulation transfer function during series of consecutive frames. This information allows the prediction of the range performance for a given sensor, target and atmospheric condition, which is of great importance for the user of optical sensors in related operational areas and for the developers of image processing algorithms. In addition the occurrence of "lucky shots" in series of frames is investigated: occasional frames with locally small blur spots. The simultaneously measured short exposure blur and the beam wander are compared with simultaneously collected scintillation data along the same path and the Cn 2 data from a locally installed scintillometer. By using two vertically separated sources, the correlation is determined between the beam wander in their images, providing information on the spatial extension of the atmospheric turbulence (eddy size). Examples are shown of the appearance of the blur spot, including skewness and astigmatism effects, which manifest themselves in the third moment of the spot and its distortion. An example is given of an experiment for determining the range performance for a given camera and a bar target on an outgoing boat in the False Bay.
Research on theory and technology for improving optical receiver efficiency in turbulent atmosphere
NASA Astrophysics Data System (ADS)
Bie, Rui; Yuan, Xiuhua; Zhao, Ming
2009-08-01
FSO has some significant advantages such as bandwidths, high-data-rate of transfer and less mass, power and volume, and no regulatory restrictions for using frequencies and bandwidths. Atmospheric turbulence is an important factor that constrains the performance of FSO; most of researchers have always been in search of methods to solve this problem. In recent years, the principle and technology of adaptive optics (AO) have been applied to eliminate the influences of turbulent atmosphere. But for a long time, efforts in the traditional AO methods focus on compensating the turbulence on the pupil plane of imaging system, ignoring the differences between the imaging system and FSO. This paper presents a novel space optical receiver that adjusts the wavefront in the rear focal plane of a lens. It is different from common AO technology that system takes the maximum light energy coupled into a fiber as the estimate parameter for reconfiguration wavefront, according to demands for FSO, and realizes a high-speed wavefront compensation receiver without wavefront sensor. Based on these theories, some simulation analysis is implemented and results are compared with traditional AO, it shows that our technique has the better performances than that of general AO. Finally, the farther work and potential application on FSO are discussed in this paper.
NASA Astrophysics Data System (ADS)
Luo, Chun-Ling; Cheng, Jing; Chen, Ai-Xi; Liu, Zhi-Min
2015-10-01
We show that the resolution of the computational ghost imaging (CGI) system through atmospheric turbulence can be significantly improved by modulating a coherent source with high-order cosh-Gaussian functions. The analytical formula for the CGI system with a higher-order cosh-Gaussian source in turbulent atmosphere is derived and can be viewed as the original object convoluted a point-spread function (PSF). The imaging quality is mainly determined by the size of the PSF, which is closely related to the source parameters of the higher-order cosh-Gaussian beam, the turbulent strength and the propagation distance. Numerical examples are given to clearly see the effects of the above system parameters on the PSF and the quality of the CGI system. Compared with the widely used Gaussian source, it is found that the resolution of CGI can be obviously enhanced by properly adjusting the parameters of the higher-order cosh-Gaussian sources. Thus this kind of shaped source can be used to improve the imaging resolution and may be helpful to the CGI real applications.
500 Gb/s free-space optical transmission over strong atmospheric turbulence channels.
Qu, Zhen; Djordjevic, Ivan B
2016-07-15
We experimentally demonstrate a high-spectral-efficiency, large-capacity, featured free-space-optical (FSO) transmission system by using low-density, parity-check (LDPC) coded quadrature phase shift keying (QPSK) combined with orbital angular momentum (OAM) multiplexing. The strong atmospheric turbulence channel is emulated by two spatial light modulators on which four randomly generated azimuthal phase patterns yielding the Andrews spectrum are recorded. The validity of such an approach is verified by reproducing the intensity distribution and irradiance correlation function (ICF) from the full-scale simulator. Excellent agreement of experimental, numerical, and analytical results is found. To reduce the phase distortion induced by the turbulence emulator, the inexpensive wavefront sensorless adaptive optics (AO) is used. To deal with remaining channel impairments, a large-girth LDPC code is used. To further improve the aggregate data rate, the OAM multiplexing is combined with WDM, and 500 Gb/s optical transmission over the strong atmospheric turbulence channels is demonstrated. PMID:27420516
Amplitude Scintillation due to Atmospheric Turbulence for the Deep Space Network Ka-Band Downlink
NASA Technical Reports Server (NTRS)
Ho, C.; Wheelon, A.
2004-01-01
Fast amplitude variations due to atmospheric scintillation are the main concerns for the Deep Space Network (DSN) Ka-band downlink under clear weather conditions. A theoretical study of the amplitude scintillation variances for a finite aperture antenna is presented. Amplitude variances for weak scattering scenarios are examined using turbulence theory to describe atmospheric irregularities. We first apply the Kolmogorov turbulent spectrum to a point receiver for three different turbulent profile models, especially for an exponential model varying with altitude. These analytic solutions then are extended to a receiver with a finite aperture antenna for the three profile models. Smoothing effects of antenna aperture are expressed by gain factors. A group of scaling factor relations is derived to show the dependences of amplitude variances on signal wavelength, antenna size, and elevation angle. Finally, we use these analytic solutions to estimate the scintillation intensity for a DSN Goldstone 34-m receiving station. We find that the (rms) amplitude fluctuation is 0.13 dB at 20-deg elevation angle for an exponential model, while the fluctuation is 0.05 dB at 90 deg. These results will aid us in telecommunication system design and signal-fading prediction. They also provide a theoretical basis for further comparison with other measurements at Ka-band.
NASA Technical Reports Server (NTRS)
Colombatti, G.; Ferri, F.; Angrilli, F.; Fulchignoni, M.
2005-01-01
Experimental results and interpretation of the temperature measurements data retrieved during the balloon campaigns (in 2002 and in 2003) for testing HASI (Huygens Atmospheric Structure Instrument), launched from the Italian Space Agency Base in Trapani (Sicily), are presented. Both ascending and descending phases are analysed; data reveal interesting features near the tropopause (present in the region between 11km-14km), where temperature cooling can be related to layers with strong winds (2002 flight); in the troposphere a multistratified structure of the temperature field is observed and discussed (particularly in the 2003 flight) Finally, stability and turbulence of the atmosphere are analysed; the buoyancy N2 parameters for both the flights show lowers value respect to standard tropospheric values corresponding to a lower stability of the atmosphere; still there is a higher stability above the tropopause. The energy spectrum of temperature data is consistent with the Kolmogorov theory: the characteristic k(sup -5/3) behaviour is reproduced.
Fluctuations of energy density of short-pulse optical radiation in the turbulent atmosphere.
Banakh, V A; Smalikho, I N
2014-09-22
Fluctuations of energy density of short-pulse optical radiation in the turbulent atmosphere have been studied based on numerical solution of the parabolic wave equation for the complex spectral amplitude of the wave field by the split-step method. It has been shown that under conditions of strong optical turbulence, the relative variance of energy density fluctuations of pulsed radiation of femtosecond duration becomes much less than the relative variance of intensity fluctuations of continuous-wave radiation. The spatial structure of fluctuations of the energy density with a decrease of the pulse duration becomes more large-scale and homogeneous. For shorter pulses the maximal value of the probability density distribution of energy density fluctuations tends to the mean value of the energy density. PMID:25321700
Free-space to few-mode-fiber coupling under atmospheric turbulence.
Zheng, Donghao; Li, Yan; Chen, Erhu; Li, Beibei; Kong, Deming; Li, Wei; Wu, Jian
2016-08-01
High speed free space optical communication (FSOC) has taken advantages of components developed for fiber-optic communication systems. Recently, with the rapid development of few-mode-fiber based fiber communication systems, few-mode-fiber components might further promote their applications in FSOC system. The coupling efficiency between free space optical beam and few-mode fibers under atmospheric turbulence effect are investigated in this paper. Both simulation and experimental results show that, compared with single-mode fiber, the coupling efficiencies for a 2-mode fiber and a 4-mode fiber are improved by ~4 dB and ~7 dB respectively in the presence of medium moderate and strong turbulence. Compared with single-mode fiber, the relative standard deviation of received power is restrained by 51% and 66% respectively with a 4-mode and 2-mode fiber. PMID:27505836
NASA Astrophysics Data System (ADS)
Wei, W.; Schmitt, F. G.; Huang, Y. X.; Zhang, H. S.
2016-05-01
Turbulent characteristics in the atmospheric surface layer are investigated using a data-driven method, Hilbert spectral analysis. The results from empirical mode decomposition display a set of intrinsic mode functions whose characteristic scales suggest a dyadic filter-bank property. It can be concluded from the joint probability density function of the intrinsic mode functions that the turbulent properties are totally different under different stratifications: the amplitudes (or energies) are arranged according to the stability parameter [InlineEquation not available: see fulltext.] for stable conditions, but tend to cluster randomly for unstable cases. The intermittency analyses reveal that second-order Hilbert marginal spectra display a power-law behaviour in the inertial subrange, and that the scaling exponent functions deviate from the theoretical values due to the strong intermittency in the stable boundary layer.
NASA Astrophysics Data System (ADS)
Wei, Wei; Schmitt, François G.; Huang, Yongxiang; Zhang, Hongsheng
2016-04-01
Turbulent characteristics in the atmospheric surface layer are investigated using a data-driven method, Hilbert spectral analysis. The results from empirical mode decomposition display a set of intrinsic mode functions whose characteristic scales suggest a dyadic filter-bank property. It can be concluded from the joint probability density function of the intrinsic mode functions that the turbulent properties are totally different under different stratifications: the amplitudes (or energies) are arranged according to the stability parameter z/L for stable conditions, but tend to cluster randomly for unstable cases. The intermittency analyses reveal that second-order Hilbert marginal spectra display a power-law behaviour in the inertial subrange, and that the scaling exponent functions present deviation, from the theoretical values due to the strong intermittency in the stable boundary layer.
Effects of turbulence on average refraction angles in occultations by planetary atmospheres
NASA Technical Reports Server (NTRS)
Eshleman, V. R.; Haugstad, B. S.
1978-01-01
Four separable effects of atmospheric turbulence on average refraction angles in occultation experiments are derived from a simplified analysis, and related to more general formulations by B. S. Haugstad. The major contributors are shown to be due to gradients in height of the strength of the turbulence, and the sense of the resulting changes in refraction angles is explained in terms of Fermat's principle. Because the results of analyses of such gradient effects by W. B. Hubbard and J. R. Jokipii are expressed in other ways, a special effort is made to compare all of the predictions on a common basis. We conclude that there are fundamental differences, and use arguments based on energy conservation and Fermat's principle to help characterize the discrepancies.
Active laser radar systems with stochastic electromagnetic beams in turbulent atmosphere.
Cai, Yangjian; Korotkova, Olga; Eyyuboğlu, Halil T; Baykal, Yahya
2008-09-29
Propagation of stochastic electromagnetic beams through paraxial ABCD optical systems operating through turbulent atmosphere is investigated with the help of the ABCD matrices and the generalized Huygens-Fresnel integral. In particular, the analytic formula is derived for the cross-spectral density matrix of an electromagnetic Gaussian Schell-model (EGSM) beam. We applied our analysis for the ABCD system with a single lens located on the propagation path, representing, in a particular case, the unfolded double-pass propagation scenario of active laser radar. Through a number of numerical examples we investigated the effect of local turbulence strength and lens' parameters on spectral, coherence and polarization properties of the EGSM beam. PMID:18825220
NASA Technical Reports Server (NTRS)
Sidwell, K.
1975-01-01
The random process used to model atmospheric turbulence in aircraft response problems is examined. The first, second, and higher order probability density and characteristic functions were developed. The concepts of the Press model lead to an approximate procedure for the analysis of the response of linear dynamic systems to a class of non-Gaussian random processes. The Press model accounts for both the Gaussian and non-Gaussian forms of measured turbulence data. The nonstationary aspects of measured data are explicitly described by the transition properties of the random process. The effects of the distribution of the intensity process upon calculated exceedances are examined. It is concluded that the press model with a Gaussian intensity distribution gives a conservative prediction of limit load values.
NASA Technical Reports Server (NTRS)
Kirkpatrick, M. P.; Mansour, N. N.; Ackerman, A. S.; Stevens, D. E.
2003-01-01
The use of large eddy simulation, or LES, to study the atmospheric boundary layer dates back to the early 1970s when Deardor (1972) used a three-dimensional simulation to determine velocity and temperature scales in the convective boundary layer. In 1974 he applied LES to the problem of mixing layer entrainment (Deardor 1974) and in 1980 to the cloud-topped boundary layer (Deardor 1980b). Since that time the LES approach has been applied to atmospheric boundary layer problems by numerous authors. While LES has been shown to be relatively robust for simple cases such as a clear, convective boundary layer (Mason 1989), simulation of the cloud-topped boundary layer has proved more of a challenge. The combination of small length scales and anisotropic turbulence coupled with cloud microphysics and radiation effects places a heavy burden on the turbulence model, especially in the cloud-top region. Consequently, over the past few decades considerable effort has been devoted to developing turbulence models that are better able to parameterize these processes. Much of this work has involved taking parameterizations developed for neutral boundary layers and deriving corrections to account for buoyancy effects associated with the background stratification and local buoyancy sources due to radiative and latent heat transfer within the cloud (see Lilly 1962; Deardor 1980a; Mason 1989; MacVean & Mason 1990, for example). In this paper we hope to contribute to this effort by presenting a number of turbulence models in which the model coefficients are calculated dynamically during the simulation rather than being prescribed a priori.
NASA Astrophysics Data System (ADS)
Lyons, G. W.; Murray, N. E.
2015-12-01
Turbulence in the atmospheric boundary layer (ABL) produces fluctuations in the static pressure. The instantaneous pressure at a point depends on an integral over the entire flow; therefore, the effects from turbulence far aloft may be felt at the earth's surface. The statistics of fluctuating pressure at the surface have been studied extensively in the context of wall-bounded engineering-type flows. At best, these neutral flows are a special case of the thermally-stratified ABL, but relatively few experimental studies have considered pressure at the ground under various stability conditions. Here the scaling of pressure statistics at the surface, particularly the spectral density, is reported over a range of convective and stable conditions for both inner and outer turbulence parameters. Measurements of turbulent surface pressure were made using low-frequency microphones buried flush to the ground in a field near Laramie, Wyoming. Simultaneous measurements from three near-surface sonic anemometers and a 50-meter wind tower give estimates of the mean surface-layer parameters. The normalization of the pressure spectrum with the inner scales collapses the spectra along the high-frequency viscous power-law band. The wall shear stress, Obukhov length, L, and horizontal integral scale, λ, are identified as outer scaling parameters for the surface pressure spectrum from an integral solution employing a Monin-Obukhov-similar profile and a simple model of inhomogeneous surface-layer turbulence. Normalization with the outer scales collapses the spectra at low frequencies. Spectral scaling also reveals trends with λ/L in the low-frequency region for both convective and stable boundary layers.
NASA Astrophysics Data System (ADS)
Li, Dan; Katul, Gabriel G.; Bou-Zeid, Elie
2015-10-01
The turbulent energy spectra and cospectra of momentum and sensible heat fluxes are examined theoretically and experimentally with increasing flux Richardson number () in the stable atmospheric surface layer. A cospectral budget model, previously used to explain the bulk relation between the turbulent Prandtl number () and the gradient Richardson number () as well as the relation between and , is employed to interpret field measurements over a lake and a glacier. The shapes of the vertical velocity and temperature spectra, needed for closing the cospectral budget model, are first examined with increasing . In addition, the wavenumber-dependent relaxation time scales for momentum and heat fluxes are inferred from the cospectral budgets and investigated. Using experimental data and proposed extensions to the cospectral budget model, the existence of a `' power-law scaling in the temperature spectra but its absence from the vertical velocity spectra is shown to reduce the magnitude of the maximum flux Richardson number (), which is commonly inferred from the Rf- Ri relation when becomes very large (idealized with ). Moreover, dissimilarity in relaxation time scales between momentum and heat fluxes, also affected by the existence of the `' power-law scaling in the temperature spectra, leads to under near-neutral conditions. It is further shown that the production rate of turbulent kinetic energy decreases more rapidly than that of turbulent potential energy as , which explains the observed disappearance of the inertial subrange in the vertical velocity spectra at a smaller as compared to its counterpart in the temperature spectra. These results further demonstrate novel linkages between the scale-wise turbulent kinetic energy and potential energy distributions and macroscopic relations such as stability correction functions to the mean flow and the - Ri relation.
Tidal and atmospheric influences on near-surface turbulence in an estuary
NASA Astrophysics Data System (ADS)
Orton, Philip M.; Zappa, Christopher J.; McGillis, Wade R.
2010-12-01
Estuarine near-surface turbulence is important for transport, mixing, and air-water exchanges of many important constituents but has rarely been studied in detail. Here, we analyze a unique set of estuarine observations of in situ atmospheric and full water column measurements, estimated air-sea exchanges, and acoustic measurements of several terms in the turbulent kinetic energy (TKE) budget. Observations from a 5.1 m deep site in the Hudson River estuary include dissipation at 50 cm depth (ɛ50), as well as profiles of TKE, shear production of TKE (P), and net turbulent vertical TKE transport (TD). Regressions suggest that the principal controlling factor for ɛ50 was wind (through the surface shear velocity, U*) and that the surface heat flux and tidal currents played a secondary role. For ebb spring tides, the TKE budget at 50 cm depth was closed within noise levels. Ebbs had high ɛ50 due to local shear production, which nearly balanced ɛ50. Floods had TD approaching P in the upper water column but generally weak near-surface shear and turbulence. Examining buoyancy fluxes that impact near-surface stratification and can indirectly control turbulence, solar heat input and tidal straining caused similar buoyancy fluxes on a sunny, calm weather day, promoting ebb tide restratification. Wind-driven mixing was found to dominate during a fall season storm event, and strong overnight heat loss after the storm helped delay restratification afterward. These results demonstrate the utility of combining detailed air-sea interaction and physical oceanographic measurements in future estuary studies.
Turbulent transport in the atmospheric boundary layer with application to wind farm dynamics
NASA Astrophysics Data System (ADS)
Waggy, Scott B.
With the recent push for renewable energy sources, wind energy has emerged as a candidate to replace some of the power produced by traditional fossil fuels. Recent studies, however, have indicated that wind farms may have a direct effect on local meteorology by transporting water vapor away from the Earth's surface. Such turbulent transport could result in an increased drying of soil, and, in turn, negatively affect the productivity of land in the wind farm's immediate vicinity. This numerical study will analyze four scenarios with the goal of understanding turbulence transport in the wake of a turbine: the neutrally-stratified boundary layer with system rotation, the unstably-stratified atmospheric boundary layer, and wind turbine simulations of these previous two cases. For this work, the Ekman layer is used as an approximation of the atmospheric boundary layer and the governing equations are solved using a fully-parallelized direct numerical simulation (DNS). The in-depth studies of the neutrally and unstably-stratified boundary layers without introducing wind farm effects will act to provide a concrete background for the final study concerning turbulent transport due to turbine wakes. Although neutral stratification rarely occurs in the atmospheric boundary layer, it is useful to study the turbulent Ekman layer under such conditions as it provides a limiting case when unstable or stable stratification are weak. In this work, a thorough analysis was completed including turbulent statistics, velocity and pressure autocorrelations, and a calculation of the full turbulent energy budget. The unstably-stratified atmospheric boundary layer was studied under two levels of heating: moderate and vigorous. Under moderate stratification, both buoyancy and shearing contribute significantly to the turbulent dynamics. As the level of stratification increases, the role of shearing is shown to diminish and is confined to the near-wall region only. A recent, multi
NASA Technical Reports Server (NTRS)
Robert, J. Brent; Robertson, Franklin R.; Clayson, Carol Anne; Bosilovich, Michael G.
2012-01-01
Turbulent fluxes of heat and moisture across the atmosphere-ocean interface are fundamental components of the Earth's energy and water balance. Characterizing both the spatiotemporal variability and the fidelity of these exchanges of heat and moisture is critical to understanding the global water and energy cycle variations, quantifying atmosphere-ocean feedbacks, and improving model predictability. This study examines the veracity of the recently completed NASA Modern-Era Retrospective analysis for Research and Applications (MERRA) product with respect to its representation of the surface turbulent heat fluxes. A validation of MERRA turbulent heat fluxes and near-surface bulk variables at local, high-resolution space and time scales is achieved by making comparisons to a large suite of direct observations. Both in situ and satellite-observed gridded surface heat flux estimates are employed to investigate the spatial and temporal variability of the surface fluxes with respect to their annual mean climatologies, their seasonal covariability of near-surface bulk parameters, and their representation of extremes. The impact of data assimilation on the near-surface parameters is assessed through evaluation of incremental analysis update tendencies produced by the assimilation procedure. It is found that MERRA turbulent surface heat fluxes are relatively accurate for typical conditions but have systematically weak vertical gradients in moisture and temperature and have a weaker covariability between the near-surface gradients and wind speed than found in observations. This results in an underestimate of the surface latent and sensible heat fluxes over the western boundary current and storm track regions. The assimilation of observations mostly acts to bring MERRA closer to observational products by increasing moisture and temperature near the surface and decreasing the near-surface wind speeds. The major patterns of spatial and temporal variability of the turbulent heat
NASA Technical Reports Server (NTRS)
Roberts, J. Brent; Robertson, Franklin R.; Clayson, Carol Anne; Bosilovich, Michael G.
2012-01-01
Turbulent fluxes of heat and moisture across the atmosphere-ocean interface are fundamental components of the Earth s energy and water balance. Characterizing both the spatiotemporal variability and the fidelity of these exchanges of heat and moisture is critical to understanding the global water and energy cycle variations, quantifying atmosphere-ocean feedbacks, and improving model predictability. This study examines the veracity of the recently completed NASA Modern-Era Retrospective analysis for Research and Applications (MERRA) product with respect to its representation of the surface turbulent heat fluxes. A validation of MERRA turbulent heat fluxes and near-surface bulk variables at local, high-resolution space and time scales is achieved by making comparisons to a large suite of direct observations. Both in situ and satellite-observed gridded surface heat flux estimates are employed to investigate the spatial and temporal variability of the surface fluxes with respect to their annual mean climatologies, their seasonal covariability of near-surface bulk parameters, and their representation of extremes. The impact of data assimilation on the near-surface parameters is assessed through evaluation of incremental analysis update tendencies produced by the assimilation procedure. It is found that MERRA turbulent surface heat fluxes are relatively accurate for typical conditions but have systematically weak vertical gradients in moisture and temperature and have a weaker covariability between the near-surface gradients and wind speed than found in observations. This results in an underestimate of the surface latent and sensible heat fluxes over the western boundary current and storm track regions. The assimilation of observations mostly acts to bring MERRA closer to observational products by increasing moisture and temperature near the surface and decreasing the near-surface wind speeds. The major patterns of spatial and temporal variability of the turbulent heat
Nelson, D.H.; Petrin, R.R.; MacKerrow, E.P.; Schmitt, M.J.; Quick, C.R.; Zardecki, A.; Porch, W.M.; Whitehead, M.; Walters, D.L.
1998-09-01
The measurement sensitivity of CO{sub 2} differential absorption LIDAR (DIAL) can be affected by a number of different processes. The authors address the interaction of two of these processes: effects due to beam propagation through atmospheric turbulence and effects due to reflective speckle. Atmospheric turbulence affects the beam distribution of energy and phase on target. These effects include beam spreading, beam wander and scintillation which can result in increased shot-to-shot signal noise. In addition, reflective speckle alone has a major impact on the sensitivity of CO{sub 2} DIAL. The interaction of atmospheric turbulence and reflective speckle is of great importance in the performance of a DIAL system. A Huygens-Fresnel wave optics propagation code has previously been developed at the Naval Postgraduate School that models the effects of atmospheric turbulence as propagation through a series of phase screens with appropriate atmospheric statistical characteristics. This code has been modified to include the effects of reflective speckle. The performance of this modified code with respect to the combined effects of atmospheric turbulence and reflective speckle is examined. Results are compared with a combination of experimental data and analytical models.
NASA Astrophysics Data System (ADS)
Nelson, Douglas H.; Petrin, Roger R.; MacKerrow, Edward P.; Schmitt, Mark J.; Quick, Charles R., Jr.; Zardecki, Andrew; Porch, William M.; Whitehead, Michael C.; Walters, Donald L.
1998-09-01
The measurement sensitivity of CO2 differential absorption LIDAR (DIAL) can be affected by a number of different processes. We will address the interaction of two of these processes: effects due to beam propagation through atmospheric turbulence and effects due to reflective speckle. Atmospheric turbulence affects the beam distribution of energy and phase on target. These effects include beam spreading, beam wander and scintillation which can result in increased shot-to-shot signal noise. In addition, reflective speckle alone has a major impact on the sensitivity of CO2 DIAL. The interaction of atmospheric turbulence and reflective speckle is of great importance in the performance of a DIAL system. A Huygens-Fresnel wave optics propagation code has previously been developed at the Naval Postgraduate School that models the effects of atmospheric turbulence as propagation through a series of phase screens with appropriate atmospheric statistical characteristics. This code has been modified to include the effects of reflective speckle. The performance of this modified code with respect to the combined effects of atmospheric turbulence and reflective speckle is examined. Results are compared with a combination of experimental data and analytical models.
Theoretical comparison of subgrid turbulence in atmospheric and oceanic quasi-geostrophic models
NASA Astrophysics Data System (ADS)
Kitsios, Vassili; Frederiksen, Jorgen S.; Zidikheri, Meelis J.
2016-04-01
Due to the massive disparity between the largest and smallest eddies in the atmosphere and ocean, it is not possible to simulate these flows by explicitly resolving all scales on a computational grid. Instead the large scales are explicitly resolved, and the interactions between the unresolved subgrid turbulence and large resolved scales are parameterised. If these interactions are not properly represented then an increase in resolution will not necessarily improve the accuracy of the large scales. This has been a significant and long-standing problem since the earliest climate simulations. Historically subgrid models for the atmosphere and ocean have been developed in isolation, with the structure of each motivated by different physical phenomena. Here we solve the turbulence closure problem by determining the parameterisation coefficients (eddy viscosities) from the subgrid statistics of high-resolution quasi-geostrophic atmospheric and oceanic simulations. These subgrid coefficients are characterised into a set of simple unifying scaling laws, for truncations made within the enstrophy-cascading inertial range. The ocean additionally has an inverse energy cascading range, within which the subgrid model coefficients have different scaling properties. Simulations adopting these scaling laws are shown to reproduce the statistics of the reference benchmark simulations across resolved scales, with orders of magnitude improvement in computational efficiency. This reduction in both resolution dependence and computational effort will improve the efficiency and accuracy of geophysical research and operational activities that require data generated by general circulation models, including weather, seasonal, and climate prediction; transport studies; and understanding natural variability and extreme events.
First results of the PML monitor of atmospheric turbulence profile with high vertical resolution
NASA Astrophysics Data System (ADS)
Ziad, A.; Blary, F.; Borgnino, J.; Fanteï-Caujolle, Y.; Aristidi, E.; Martin, F.; Lantéri, H.; Douet, R.; Bondoux, E.; Mékarnia, D.
2013-11-01
Aims: Future extremely large telescopes will certainly be equipped with wide-field adaptive optics systems. The optimization of the performances of these techniques requires a precise specification of the different components of these AO systems. Most of these technical specifications are related to the atmospheric turbulence parameters, particularly the profile of the refractive index structure constant CN2(h). A new monitor called Profiler of Moon Limb (PML) for the extraction of the CN2(h) profile with high vertical resolution and its first results are presented. Methods: The PML instrument uses an optical method based on the observation of the Moon limb through two subapertures. The use of the lunar limb leads to a continuum of double stars allowing a scan of the whole atmosphere with high resolution in altitude. Results: The first prototype of the PML has been installed at Dome C in Antarctica and the first results of the PML are presented and compared to radio-sounding balloon profiles. In addition to the CN2(h) profile obtained with high vertical resolution, PML is also able to provide other atmospheric turbulence parameters such as the outer scale profile, the total seeing, and the isoplanatic and isopistonic angles.
NASA Technical Reports Server (NTRS)
Haugstad, B. S.
1978-01-01
The nature and magnitude of turbulence-induced errors in atmospheric profiles derived from Doppler measurements made during radio occultations are investigated. It is found that turbulence in planetary atmospheres induces both fluctuating and systematic errors in derived profiles, but the errors of both types are very small. Consideration of the occultation of Mariner 10 by Venus and of the Pioneer occultations by Jupiter shows that the rms fractional errors in the atmospheric profiles derived from these observations were less than 0.01 in both temperature and pressure, while the fractional systematic errors were typically of the order of 1 millionth. The extent to which atmospheric profiles derived from radio and optical intensity measurements are affected by turbulence is also examined. The results indicate that turbulence in planetary atmospheres has only a marginal effect on derived profiles in the weak-scattering limit and that the turbulence-induced errors in this case are always much larger than the corresponding errors in profiles derived from radio Doppler measurements.
NASA Astrophysics Data System (ADS)
Frisch, Uriel
1996-01-01
Written five centuries after the first studies of Leonardo da Vinci and half a century after A.N. Kolmogorov's first attempt to predict the properties of flow, this textbook presents a modern account of turbulence, one of the greatest challenges in physics. "Fully developed turbulence" is ubiquitous in both cosmic and natural environments, in engineering applications and in everyday life. Elementary presentations of dynamical systems ideas, probabilistic methods (including the theory of large deviations) and fractal geometry make this a self-contained textbook. This is the first book on turbulence to use modern ideas from chaos and symmetry breaking. The book will appeal to first-year graduate students in mathematics, physics, astrophysics, geosciences and engineering, as well as professional scientists and engineers.
Aksenov, Valerii P; Kolosov, Valeriy V; Pogutsa, Cheslav E
2014-06-10
The propagation of laser beams having orbital angular momenta (OAM) in the turbulent atmosphere is studied numerically. The variance of random wandering of these beams is investigated with the use of the Monte Carlo technique. It is found that, among various types of vortex laser beams, such as the Laguerre-Gaussian (LG) beam, modified Bessel-Gaussian beam, and hypergeometric Gaussian beam, having identical initial effective radii and OAM, the LG beam occupying the largest effective volume in space is the most stable one. PMID:24921122
Conditions for observation of the enhanced backscattering phenomenon in a turbulent atmosphere
NASA Astrophysics Data System (ADS)
Chrzanowski, Janusz; Kirkiewicz, Jozef; Kravtsov, Yuri A.
2003-11-01
Influence of enhanced backscattering effect on laser measurements of dust and aerosols content in a turbulent atmosphere is discussed. It is shown that doubling of the backscattered light intensity, characteristic for enhanced backscattering, leads to overestimating dust content in the air. To avoid undesirable effect of overestimation, it is recommended to displace receiving aperture sidewise relatively to laser source. Other method to eliminate overestimation is to use wider laser beam and extended receiving aperture as compared to coherence radius of the scattered wave field.
Optical restoration of images blurred by atmospheric turbulence using optimum filter theory.
Horner, J L
1970-01-01
The results of optimum filtering from communications theory have been applied to an image restoration problem. Photographic film imagery, degraded by long-term artificial atmospheric turbulence, has been restored by spatial filters placed in the Fourier transform plane. The time-averaged point spread function was measured and used in designing the filters. Both the simple inverse filter and the optimum least-mean-square filters were used in the restoration experiments. The superiority of the latter is conclusively demonstrated. An optical analog processor was used for the restoration. PMID:20076156
Micropulse lidar for detection of backscatter amplification in the turbulent atmosphere
NASA Astrophysics Data System (ADS)
Banakh, Victor A.; Razenkov, Igor A.
2015-11-01
The design of a two-channel lidar with afocal transceiving telescope receiving the backscattered radiation at the axis of the probing beam and at some distance from the axis is described. The lidar with this design can detect the atmospheric backscatter amplification caused by turbulent fluctuations of the refractive index of air due to the correlation of the probing and scattered radiation. The power ratio of echo signals recorded in two different channels gives the value (coefficient) of backscatter amplification. The developed micropulse two-channel lidar can conduct unattended continuous measurements for a long time.
Numerical Study of the Effects of Atmospheric and Wake Turbulence on Wind Turbine Dynamics
Churchfield, M. J.; Lee, S.; Michalakes, J.; Moriarty, P. J.
2012-01-01
Although the atmospheric sciences community has been studying the effects of atmospheric stability and surface roughness on the planetary boundary layer for some time, their effects on wind turbine dynamics have not been well studied. In this study, we performed numerical experiments to explore some of the effects of atmospheric stability and surface roughness on wind turbine dynamics. We used large-eddy simulation to create atmospheric winds and compute the wind turbine flows, and we modeled the wind turbines as revolving and flexible actuator lines coupled to a wind turbine structural and system dynamic model. We examined the structural moments about the wind turbine blade, low-speed shaft, and nacelle; power production; and wake evolution when large 5-MW turbines are subjected to winds generated from low- and high-surface roughness levels representative of offshore and onshore conditions, respectively, and also neutral and unstable atmospheric conditions. In addition, we placed a second turbine 7 rotor diameters downwind of the first one so that we could explore wake effects under these different conditions. The results show that the turbulent structures generated within the atmospheric boundary layer wind simulations cause isolated loading events at least as significant as when a turbine is waked by an upwind turbine. The root-mean-square (RMS) turbine loads are consistently larger when the surface roughness is higher. The RMS blade-root out-of-plane bending moment and low-speed shaft torque are higher when the atmospheric boundary layer is unstable as compared with when it is neutral. However, the RMS yaw moments are either equal or reduced in the unstable case as compared with the neutral case. For a given surface roughness, the ratio of power produced by the downwind turbine relative to that of the upwind turbine is 15-20% higher when the conditions are unstable as compared with neutral. For a given atmospheric stability, this power ratio is 10% higher with
Statistics of atmospheric turbulence at Cerro Pachon using the GeMS profiler
NASA Astrophysics Data System (ADS)
Rodriguez, Ignacio; Neichel, Benoit; Béchet, Clémentine; Guzmán, Dani; Guesalaga, Andrés.
2014-08-01
The knowledge of the atmospheric turbulence profile directly above the telescope using the telemetry from wide-field Adaptive Optics (AO) measurements can be extremely useful for the optimization of the correction in the new generation of AO systems. For this purpose, two techniques have been recently implemented at the Gemini South MCAO System (GeMS); both based on the SLODAR method. The first technique uses a matrix inversion approach of the slopes covariance matrices and the second deconvolves the cross-correlation functions between all combinations of slopes using the auto-correlation responses. The deconvolution approach has proved to be more reliable that the one based on matrices inversion, so we use it for estimating the profiles from on-sky telemetry gathered over three years (2012 - 2014), obtaining statistical parameters of the turbulence at Cerro Pachón. These results are summarized in this article. Particular attention is paid to the occurrence of turbulence in the dome of the Gemini South telescope.
A low cost, low power, S-band radar for atmospheric turbulence studies
NASA Astrophysics Data System (ADS)
Farrell, Thomas C.
2015-05-01
We present a frequency modulated continuous wave (FMCW) radar capable of measuring atmospheric turbulence profiles within the Earth's surface layer. Due to the low cost and easily automated design, a number of units may be built and deployed to sites of interest around the world. Each unit would be capable of collecting turbulence strength, as a function of altitude, with a range of about 50 meters above the antenna plane. Such data is valuable to developers of directed energy, laser communications, imaging, and other optical systems, where good engineering design is based on an understanding of the details of the turbulence in which those systems will have to operate. The radar is based on the MIT "coffee can" design1,2. It is FCC compliant, operating in the 2.4 GHz instrumentation, science, and medical (ISM) band with less than 1 watt effective isotropic radiated power (EIRP). It is expected to cost less than $1000 per unit and is built from commercial off the shelf parts, along with easily constructed horn antennas. Major modifications to the design in 1,2 are the inclusion of horn antennas for directivity, and a straight forward processing software change that increases integration times to the order of tens of seconds to a minute. Here, a prototype system is described and preliminary data is presented.
Atmospheric turbulence conditions leading to focused and folded sonic boom wave fronts.
Piacsek, Andrew A
2002-01-01
The propagation and subsequent distortion of sonic booms with rippled wave fronts are investigated theoretically using a nonlinear time-domain finite-difference scheme. This work seeks to validate the rippled wave front approach as a method for explaining the significant effects of turbulence on sonic booms [A. S. Pierce and D. J. Maglieri, J. Acoust. Soc. Am. 51, 702-721 (1971)]. A very simple description of turbulence is employed in which velocity perturbations within a shallow layer of the atmosphere form strings of vortices characterized by their size and speed. Passage of a steady-state plane shock front through such a vortex layer produces a periodically rippled wave front which, for the purposes of the present investigation, serves as the initial condition for a finite-difference propagation scheme. Results show that shock strength and ripple curvature determine whether ensuing propagation leads to wave front folding. High resolution images of the computed full wave field provide insights into the spiked and rounded features seen in sonic booms that have propagated through turbulence. PMID:11837957
Sound propagation in a turbulent atmosphere near the ground: a parabolic equation approach.
Ostashev, V E; Salomons, E M; Clifford, S F; Lataitis, R J; Wilson, D K; Blanc-Benon, P; Juvé, D
2001-05-01
The interference of the direct wave from the point source to the receiver and the wave reflected from the impedance ground in a turbulent atmosphere is studied. A parabolic equation approach for calculating the sound pressure p at the receiver is formulated. Then, the parabolic equation is solved by the Rytov method yielding expressions for the complex phases of direct and ground-reflected waves. Using these expressions, a formula for the mean squared sound pressure [absolute value(p)2] is derived for the case of anisotropic spectra of temperature and wind velocity fluctuations. This formula contains the "coherence factor," which characterizes the coherence between direct and ground-reflected waves. It is shown that the coherence factor is equal to the normalized coherence function of a spherical sound wave for line-of-sight propagation. For the case of isotropic turbulence, this result allows one to obtain analytical formulas for [absolute value(p)2] for the Kolmogorov, Gaussian, and von Karman spectra of temperature and wind velocity fluctuations. Using these formulas, the effects of temperature and wind velocity fluctuations, and the effects of different spectra of these fluctuations on the mean squared sound pressure, are numerically studied. Also the effect of turbulent anisotropy on the interference of direct and ground reflected waves is numerically studied. Finally, it is shown that the mean squared sound pressure [absolute value(p)2] calculated for the von Karman spectrum of temperature fluctuations agrees well with experimental data obtained in a laboratory experiment. PMID:11386544
Scaling laws of turbulence intermittency in the atmospheric boundary layer: the role of stability
NASA Astrophysics Data System (ADS)
Paradisi, Paolo; Cesari, Rita; Allegrini, Paolo
2015-09-01
Bursting and intermittent behavior is a fundamental feature of turbulence, especially in the vicinity of solid obstacles. This is associated with the dynamics of turbulent energy production and dissipation, which can be described in terms of coherent motion structures. These structures are generated at random times and remain stable for long times, after which they become suddenly unstable and undergo a rapid decay event. This intermittent behavior is described as a birth-death point process of self-organization, i.e., a sequence of critical events. The Inter-Event Time (IET) distribution, associated with intermittent self-organization, is typically a power-law decay, whose power exponent is known as complexity index and characterizes the complexity of the system, i.e., the ability to develop self-organized, metastable motion structures. We use a method, based on diffusion scaling, for the estimation of system's complexity. The method is applied to turbulence velocity data in the atmospheric boundary layer. A neutral condition is compared with a stable one, finding that the complexity index is lower in the neutral case with respect to the stable one. As a consequence, the crucial birth-death events are more rare in the stable case, and this could be associated with a less efficient transport dynamics.
Temporal decorrelation of optical turbulence as a function of altitude in the atmosphere
NASA Astrophysics Data System (ADS)
Avilés, J. L.; Avila, R.; Carrasco, E.; Sánchez, L. J.; Chun, M.; Butterley, T.; Wilson, R.; Urbiola, F. J.
2016-05-01
Here, we propose a new method to evaluate the Taylor's frozen-flow hypothesis with the Generalized SCIntillation Detection And Ranging technique (G-SCIDAR). Unlike the work previously reported in the literature, we take into consideration the wind-speed fluctuation effects when examining the spatiotemporal cross-covariance functions computed according to the G-SCIDAR method. We show that under the assumption of having turbulent layers driven by fluctuating wind-velocity vectors, it is correct examining the encircled volume of smeared cross-covariance peaks. The method was used to process 60 spatiotemporal cross-covariance functions of the stellar scintillation patterns retrieved at the 2.2 m telescope of the University of Hawaii along a two hours observation run. We found that most of the time the structure of atmospheric refraction-index inhomogeneities decorrelates linearly with time for individual turbulent layers. Moreover, contrary to the behaviour expected under the assumption of having a slowly evolving structure of turbulent eddies, being translated by a much greater wind-velocity vector, which should strengthen the hypothesis of a frozen flow, we found that the temporal decorrelation of such structure increases as the overall layer displacement velocity increases.
NASA Technical Reports Server (NTRS)
Frost, W.; Harper, W. L.
1975-01-01
Flow over surface obstructions can produce significantly large wind shears such that adverse flying conditions can occur for aeronautical systems (helicopters, STOL vehicles, etc.). Atmospheric flow fields resulting from a semi-elliptical surface obstruction in an otherwise horizontally homogeneous statistically stationary flow are modelled with the boundary-layer/Boussinesq-approximation of the governing equation of fluid mechanics. The turbulence kinetic energy equation is used to determine the dissipative effects of turbulent shear on the mean flow. Iso-lines of turbulence kinetic energy and turbulence intensity are plotted in the plane of the flow and highlight regions of high turbulence intensity in the stagnation zone and sharp gradients in intensity along the transition from adverse to favourable pressure gradient. Discussion of the effects of the disturbed wind field in CTOL and STOL aircraft flight path and obstruction clearance standards is given. The results indicate that closer inspection of these presently recommended standards as influenced by wind over irregular terrains is required.
Impact of ice cover in the Arctic on ocean-atmosphere turbulent heat fluxes
NASA Astrophysics Data System (ADS)
Selivanova, J. V.; Tilinina, N. D.; Gulev, S. K.; Dobrolubov, S. A.
2016-01-01
The impact of spatiotemporal variability of the ice-covered area in the Arctic on the value and interannual dynamics of turbulent heat fluxes on the ocean-atmosphere border is considered. An expected inverse dependence of the heat fluxes integrated over the Arctic area and the area of ice is not detected. The largest interannual oscillations of heat fluxes from the ocean to the atmosphere are timed to the varying position of the ice edge and, to a lesser extent, are connected with total area of ice. The role of the marginal ice zone in oceanic heat transfer is analyzed. In particular, it is shown that while moving along the marginal zone from the ice-free surface to the surface with an ice concentration of 0.8, latent and sensible heat fluxes are reduced by a factor of 2.5-3.
J. KAO; D. COOPER; ET AL
2000-11-01
As lidar technology is able to provide fast data collection at a resolution of meters in an atmospheric volume, it is imperative to promote a modeling counterpart of the lidar capability. This paper describes an integrated capability based on data from a scanning water vapor lidar and a high-resolution hydrodynamic model (HIGRAD) equipped with a visualization routine (VIEWER) that simulates the lidar scanning. The purpose is to better understand the spatial and temporal representativeness of the lidar measurements and, in turn, to extend their utility in studying turbulence fields in the atmospheric boundary layer. Raman lidar water vapor data collected over the Pacific warm pool and the simulations with the HIGRAD code are used for identifying the underlying physics and potential aliasing effects of spatially resolved lidar measurements. This capability also helps improve the trade-off between spatial-temporal resolution and coverage of the lidar measurements.
NASA Technical Reports Server (NTRS)
Han, Jongil; Arya, S. Pal; Shaohua, Shen; Lin, Yuh-Lang; Proctor, Fred H. (Technical Monitor)
2000-01-01
Algorithms are developed to extract atmospheric boundary layer profiles for turbulence kinetic energy (TKE) and energy dissipation rate (EDR), with data from a meteorological tower as input. The profiles are based on similarity theory and scalings for the atmospheric boundary layer. The calculated profiles of EDR and TKE are required to match the observed values at 5 and 40 m. The algorithms are coded for operational use and yield plausible profiles over the diurnal variation of the atmospheric boundary layer.
The vertical turbulence structure of the coastal marine atmospheric boundary layer
Tjernstroem, M.; Smedman, A.S. )
1993-03-15
The vertical turbulence structure in the marine atmosphere along a shoreline has been investigated using data from tower and aircraft measurements performed along the Baltic coast in the southeast of Sweden. Two properties make the Baltic Sea particularly interesting. It is surrounded by land in all directions within moderate advection distances, and it features a significant annual lag in sea surface temperature as compared with inland surface temperature. The present data were collected mostly during spring or early summer, when the water is cool, i.e., with a stably or neutrally stratified marine boundary layer usually capped by an inversion. Substantial daytime heating over the land area results in a considerable horizontal thermal contrast. Measurements were made on a small island, on a tower with a good sea fetch, and with an airborne instrument package. The profile data from the aircraft is from 25 slant soundings performed in connection to low level boundary layer flights. The results from the profiles are extracted through filtering techniques on individual time (space) series (individual profiles), applying different normalization and finally averaging over all or over groups of profiles. The land-based data are from a low tower situated on the shoreline of a small island with a wide sector of unobstructed sea fetch. Several factors are found that add to the apparent complexity of the coastal marine environment: the state of the sea appears to have a major impact on the turbulence structure of the surface layer, jet-shaped wind speed profiles were very common at the top of the boundary layer (in about 50% of the cases) and distinct layers with increased turbulence were frequently found well above the boundary layer (in about 80% of the cases). The present paper will concentrate on a description of the experiment, the analysis methods, and a general description of the boundary layer turbulence structure over the Baltic Sea. 40 refs., 16 figs., 2 tabs.
Atmospheric turbulence in urban environments: large-eddy simulation and experiment
NASA Astrophysics Data System (ADS)
Hertwig, D.; Nguyen van yen, R.; Patnaik, G.; Leitl, B.
2012-04-01
The description of atmospheric turbulence in densely built urban environments is a major theoretical challenge, which has wide-ranging practical implications - regarding for example pollutant dispersion, wind comfort, and many other micro-climatic issues. The traditional approach to adopt obstacle-resolving micro-scale meteorological models based on Reynolds-averaged equations is strongly limited by its inherent inability to provide spatio-temporal data. Although more advanced models, such as large-eddy simulation (LES), are now technically applicable to this problem, the precise validation of their output is still a matter of ongoing investigation, which is particularly challenging due to the time-dependent nature of the problem. In this work, we undertake a systematic comparison between results of urban LES computations and boundary-layer wind-tunnel measurements of turbulent flow in the inner city of Hamburg, Germany. The experimental data were acquired for neutral atmospheric stratification within an urban model on a scale of 1:350, under well-defined and documented boundary constraints. Background information about the atmospheric inflow conditions for both the physical and numerical model was deduced from suburban field site measurements. LES computations were conducted by the U.S. Naval Research Laboratory using the code FAST3D-CT that is based on the monotone integrated LES methodology (MILES). The validation focuses on the comparison of time-series information and the characterization of turbulent flow structures within and above the urban canopy. Densely spaced measurements in vertical profiles and horizontal flow layers allow for the investigation of the urban boundary-layer development across the city. Typical obstacle-induced urban flow scenarios provide further test cases for detailed analyses. Besides mean flow and turbulence statistics, velocity histograms, fluctuation time scales, spectral information and statistics of the Reynolds stress
NASA Astrophysics Data System (ADS)
Chatterjee, Monish R.; Mohamed, Fathi H. A.
2016-05-01
In a parallel approach to recently-used transfer function formalism, a study involving diffraction of modulated electromagnetic (EM) waves through uniform and phase-turbulent atmospheres is reported in this paper. Specifically, the input wave is treated as a modulated optical carrier, represented by use of a sinusoidal phasor with a slowly timevarying envelope. Using phasors and (spatial) Fourier transforms, the complex phasor wave is transmitted across a uniform or turbulent medium using the Kirchhoff-Fresnel integral and the random phase screen. Some preliminary results are presented comparing non-chaotic and chaotic information transmission through turbulence, outlining possible improvement in performance utilizing the robust features of chaos.
Polarization of radiation of point-like source reflected from turbulent magnetized atmosphere
NASA Astrophysics Data System (ADS)
Silant'ev, N. A.; Gnedin, Yu. N.
2008-04-01
We consider the multiple scattering of the light from a point-like source located above the semi-infinite electron, turbulent, and magnetized atmospheres. The frozen magnetic field has both the regular B0 and stochastic B' components (B= B_0+ B'). The stochastic Faraday rotations due to fluctuations B' decrease the intensity of each separate polarized beam (the extinction factor is proportional to λ^4< B'^2>). This decrease at large λ dominates the usual decrease (∝λ^2B_0 cosΘ_0) caused by summing beams with very different Faraday's rotation angles. This effect changes the spectrum of polarization degree as compared with what is influenced by the regular magnetic field. We calculated the integral (observed) polarization of the reflected radiation with the inclusion of unpolarized radiation going directly from the point-like source. We present the observed polarization for various degrees of true absorption of the radiation into the atmosphere and the values of magnetic energy fluctuations. The spectra of polarization in the optical (λ =0-1 μm), infrared (λ =1-5 μ m), and X-ray (E=1-50 keV) regions of the wavelengths are presented. We discuss the possibility of estimating parameters of magnetic field fluctuations from the observation of the spectra of polarization in AGNs with the X-ray excesses and in the turbulent accretion disk in NGC 4258.
Transition from geostrophic turbulence to inertia-gravity waves in the atmospheric energy spectrum.
Callies, Jörn; Ferrari, Raffaele; Bühler, Oliver
2014-12-01
Midlatitude fluctuations of the atmospheric winds on scales of thousands of kilometers, the most energetic of such fluctuations, are strongly constrained by the Earth's rotation and the atmosphere's stratification. As a result of these constraints, the flow is quasi-2D and energy is trapped at large scales—nonlinear turbulent interactions transfer energy to larger scales, but not to smaller scales. Aircraft observations of wind and temperature near the tropopause indicate that fluctuations at horizontal scales smaller than about 500 km are more energetic than expected from these quasi-2D dynamics. We present an analysis of the observations that indicates that these smaller-scale motions are due to approximately linear inertia-gravity waves, contrary to recent claims that these scales are strongly turbulent. Specifically, the aircraft velocity and temperature measurements are separated into two components: one due to the quasi-2D dynamics and one due to linear inertia-gravity waves. Quasi-2D dynamics dominate at scales larger than 500 km; inertia-gravity waves dominate at scales smaller than 500 km. PMID:25404349
Study of Transitions in the Atmospheric Boundary Layer Using Explicit Algebraic Turbulence Models
NASA Astrophysics Data System (ADS)
Lazeroms, W. M. J.; Svensson, G.; Bazile, E.; Brethouwer, G.; Wallin, S.; Johansson, A. V.
2016-08-01
We test a recently developed engineering turbulence model, a so-called explicit algebraic Reynolds-stress (EARS) model, in the context of the atmospheric boundary layer. First of all, we consider a stable boundary layer used as the well-known first test case from the Global Energy and Water Cycle Experiment Atmospheric Boundary Layer Study (GABLS1). The model is shown to agree well with data from large-eddy simulations (LES), and this agreement is significantly better than for a standard operational scheme with a prognostic equation for turbulent kinetic energy. Furthermore, we apply the model to a case with a (idealized) diurnal cycle and make a qualitative comparison with a simpler first-order model. Some interesting features of the model are highlighted, pertaining to its stronger foundation on physical principles. In particular, the use of more prognostic equations in the model is shown to give a more realistic dynamical behaviour. This qualitative study is the first step towards a more detailed comparison, for which additional LES data are needed.
Wichern, Gordon; Azimi-Sadjadi, Mahmood R; Mungiole, Michael
2007-05-01
An environmentally adaptive system for prediction of acoustic transmission loss (TL) in the atmosphere is developed in this paper. This system uses several back propagation neural network predictors, each corresponding to a specific environmental condition. The outputs of the expert predictors are combined using a fuzzy confidence measure and a nonlinear fusion system. Using this prediction methodology the computational intractability of traditional acoustic model-based approaches is eliminated. The proposed TL prediction system is tested on two synthetic acoustic data sets for a wide range of geometrical, source and environmental conditions including both nonturbulent and turbulent atmospheres. Test results of the system showed root mean square (RMS) errors of 1.84 dB for the nonturbulent and 1.36 dB for the turbulent conditions, respectively, which are acceptable levels for near real-time performance. Additionally, the environmentally adaptive system demonstrated improved TL prediction accuracy at high frequencies and large values of horizontal separation between source and receiver. PMID:17521880
A simplified free-space adaptive optics system against atmospheric turbulence
NASA Astrophysics Data System (ADS)
Sharma, Sanjay
2012-03-01
Optical free-space communications have the distinct advantages over conventional radio frequency and microwave systems in terms of information capacity and increased security. However, optical carrier frequencies drastically suffer due to atmospheric turbulence. This effect is a random process and time-varying process; therefore, it is very difficult to overcome the effect. Adaptive optics is the technology used to mitigate chaotic optical wave-front distortions in real time by measuring the wave-front distortion with the help of a sensor and then adapting the wave-front corrector to lessen the phase distortions and ultimately to recover a closely approximated signal to its original counterpart. But these systems are too expensive and large. This study employs the various aspects of Adaptive Optics system, such as wave-front corrector, wave-front sensors and analytical analysis of open and closed-loop systems using loop equations, in order to make free-space optics communication links more vulnerable against atmospheric turbulence and wave-front phase distributions. The purpose of this study is to investigate a wave-front sensorless adaptive optics system, which would provide reduced complexity, size and cost.
Effect of large eddies on atmospheric surface layer turbulence and the underlying wave field
NASA Astrophysics Data System (ADS)
Savtchenko, Andrey
1999-02-01
To improve existing models for air-sea interaction, a better understanding of the energy transfer across the boundary layer and in particular of the coupling of large atmospheric eddies with the air-sea interface is needed. Recent investigations have already shown a possible coupling of large structures in atmospheric turbulence and surface ripples. This was done using synthetic aperture radar (SAR) imagery of ocean surface and almost simultaneous advanced very high resolution radiometer (AVHRR) imagery of cloud streets at a cold-air outbreak. The intent of our study is to further validate this hypothesis in a general case of coastal circulation. For this purpose we analyze a suite of collocated simultaneous records of airflow, radar return, and surface elevations from a coastal platform. We investigate the influence of large eddies (20-60 min) on the turbulent properties of the airflow in the first 2 m above the ocean surface. The analysis shows very prominent peaks in the magnitude of 12- to 16-min fluctuations which are further modulated in 20- to 40-min intervals. These scales and modulations are characteristic for all variables of interest here. The detected scales and their modulation suggest significant interaction of surface layer within the first 1-2 m with large eddies of scales of O(1) and O(10) km. The intermittent structure of turbulence responds by alternating contributions from bursts and sweeps; the frequency of occurrence of bursts and sweeps also reveals the influence of large structures. The instantaneous cross correlation between the shorter scales of momentum flux and radar return, corresponding to the individual burst events, can be 4 times as strong as the overall cross correlation.
An atmospheric turbulence generator for dynamic tests with LINC-NIRVANA's adaptive optics system
NASA Astrophysics Data System (ADS)
Meschke, D.; Bizenberger, P.; Gaessler, W.; Zhang, X.; Mohr, L.; Baumeister, H.; Diolaiti, E.
2010-07-01
LINC-NIRVANA[1] (LN) is an instrument for the Large Binocular Telescope[2] (LBT). Its purpose is to combine the light coming from the two primary mirrors in a Fizeau-type interferometer. In order to compensate turbulence-induced dynamic aberrations, the layer oriented adaptive optics system of LN[3] consists of two major subsystems for each side: the Ground-Layer-Wavefront sensor (GLWS) and the Mid- and High-Layer Wavefront sensor (MHLWS). The MHLWS is currently set up in a laboratory at the Max-Planck-Institute for Astronomy in Heidelberg. To test the multi-conjugate AO with multiple simulated stars in the laboratory and to develop the necessary control software, a dedicated light source is needed. For this reason, we designed an optical system, operating in visible as well as in infrared light, which imitates the telescope's optical train (f-ratio, pupil position and size, field curvature). By inserting rotating surface etched glass phase screens, artificial aberrations corresponding to the atmospheric turbulence are introduced. In addition, different turbulence altitudes can be simulated depending on the position of these screens along the optical axis. In this way, it is possible to comprehensively test the complete system, including electronics and software, in the laboratory before integration into the final LINC-NIRVANA setup. Combined with an atmospheric piston simulator, also this effect can be taken into account. Since we are building two identical sets, it is possible to feed the complete instrument with light for the interferometric combination during the assembly phase in the integration laboratory.
NASA Astrophysics Data System (ADS)
Fortuniak, K.
2010-09-01
Knowledge of the structure of turbulence is essential for many practical applications including atmospheric dispersion. In accordance of Monin-Obukhov (M-O) similarity theory, over homogenous surface both spectra and normalized velocity standard deviations, should depend on stability parameter, z/L, where L is Obukhov length and z sensor height. In the urban atmosphere applicability of M-O is still questionable because shrinking of inertial sublayer where this theory is supposed to work. The objective of this study is to investigate spectral turbulence statistics at two urban measurement points located in Łódź, central Poland (population ca 750,000). Turbulent fluxes were measured with the aid of fast respond sensors (sonic anemometers and gas analyzers) at two points in the city centre. At the firs point data were collected in years 2000-2003 and at the second point measurements are continued since 2005. At both stations sensors were mounted at thin masts at the level (37m and 42m above ground) significantly exciding mean building height (11m and 17m respectively). Calculated spectral characteristics include spectra and cospectra in different stability classes focused on verification of the Monin-Obukhov relationships. Results show that power spectra of wind components for close to neutral conditions fit to reference spectrum based on Kansas experiment. For a non-neutral stability wind spectral peaks show a shift to lower frequencies as instability increases. Results for a temperature spectra and cospectra do not lead to clear conclusion on spectral function shape and applicability of M-O theory.
NASA Astrophysics Data System (ADS)
Lukin, Igor P.
2015-11-01
In this paper results of theoretical consideration of behavior of degree of coherence of the coherent vortex Bessel optical beam propagating in turbulent atmosphere are presented. It is shown, that at low levels of fluctuations, in the central part of a two-dimensional field of degree of coherence of the vortex Bessel optical beams the ring dislocation is formed, the number of rings in which is equal to value of a topological charge of an optical beam. The structure of a ring dislocation of degree of coherence of the vortex Bessel optical beams in turbulent atmosphere is studied in detail. For this purpose two characteristics of a ring dislocation are entered: its spatial coordinates and width of a ring. Influence of parameters of an optical beam (a cross-section wave number and a topological charge) and atmospheric turbulence on these characteristics of a ring dislocation of degree of coherence of the vortex Bessel optical beam is considered.
On the origin of jets and vortices in turbulent planetary atmospheres.
NASA Astrophysics Data System (ADS)
Jougla, Thibault; Dritschel, David G.
2016-04-01
Stratified rotating fluids tend to form large scale coherent structures. These structures are present in many different geophysical fluids, for example jet streams in the Earth's atmosphere, the famous and conspicuous jets in the Jovian atmosphere, and oceanic jets like the latent jets and the well-known main currents including the Gulf stream and Kuroshio. Observations, numerical models, and laboratory experiments have sought to explain their origins and their evolutions. To investigate the coexistence, evolution and vertical structure of jets and vortices in turbulent planetary atmospheres, we make use of the widely studied two-layer quasi-geostrophic shallow water model on the β-plane. Numerical simulations at ultra-high resolution are carried out with the Combined Lagrangian Advection Method [1]. Following Panetta 1988 [2], to characterise the pole to equator heating variation on a planet, a vertical shear is imposed and maintained by thermal damping. To crudely represent convection from the bottom layer to the top layer, hetons are constantly added to the flow. Many numerical simulations covering a large range of parameters have been run. The thermal damping and vertical shear dependence has been widely studied and analysed. The baroclinicity of the flow is clearly evident in all cases studied. Moreover, the flow is strongly dependent on thermal damping. There is a competition between baroclinic instabilities trying to reduce the imposed vertical shear and thermal damping trying to maintain the vertical shear. Without any thermal damping, the imposed vertical shear quickly erodes. On the other hand if the thermal damping is very high, the flow is mainly dominated by incoherent, small-scale turbulence. For weaker thermal damping, the competition between baroclinic instability and thermal damping may lead to oscillations between stable and turbulent phases. However, thermal damping does not have a significant impact on the number of homogeneous regions and jets
NASA Astrophysics Data System (ADS)
Brasseur, James; Vijayakumar, Ganesh; Lavely, Adam; Jayaraman, Balaji; Paterson, Eric; Sullivan, Peter
2014-11-01
Loading transients on wind turbine blades underlie premature component failure. We research the underlying causes of nonsteady blade loadings from interactions with atmospheric eddies in the atmospheric boundary layer (ABL) using combinations of blade-boundary-layer-resolving HPC simulation and lower-order blade models (ALM, BEMT). A daytime ABL simulated with a 760 760 256 pseudo-spectral LES interacts with a 62 m rotating wind turbine blade, simulated with advanced finite-volume-based algorithms in two complex multi-grid/scale domains in relative motion. We focus on two key discoveries: (1) Whereas nonsteady blade loadings are generally interpreted as in response to nonsteadiness in wind speed, time changes in wind vector direction are a much greater contributor to load transients, and strongly impact boundary layer dynamics; (2) Large temporal variations in loadings occur within two disparate time scales, an advective time scale associated with atmospheric eddy passage, and a sub blade-rotation time scale associated with turbulence-induced forcings as the blades traverse internal atmospheric eddy structure. The latter generates the strongest transients; the former modulates the response. Supported by DOE & NSF. Computer resources by XSEDE, OLCF, NREL.
NASA Astrophysics Data System (ADS)
Herman, Agnieszka
2015-10-01
Ocean-atmosphere interactions are complex and extend over a wide range of temporal and spatial scales. Among the key components of these interactions is the ocean-atmosphere (latent and sensible) turbulent heat flux (THF). Here, based on daily optimally-interpolated data from the extratropical Southern Hemisphere (south of 30°S) from a period 1985-2013, we analyze short-term variability and trends in THF and variables influencing it. It is shown that, in spite of climate-change-related positive trends in surface wind speeds over large parts of the Southern Ocean, the range of the THF variability has been decreasing due to decreasing air-water temperature and humidity differences. Occurrence frequency of very large heat flux events decreased accordingly. Remarkably, spectral analysis of the THF data reveals, in certain regions, robust periodicity at frequencies 0.03-0.04 day-1, corresponding exactly to frequencies of the baroclinic annular mode (BAM). Finally, it is shown that the THF is correlated with the position of the major fronts in sections of the Antarctic Circumpolar Current where the fronts are not constrained by the bottom topography and can adjust their position to the atmospheric and oceanic forcing, suggesting differential response of various sections of the Southern Ocean to the changing atmospheric forcing.
Can we estimate the fog-top height from atmospheric turbulent measurements at surface?
NASA Astrophysics Data System (ADS)
Román-Cascón, Carlos; Yagüe, Carlos; Steeneveld, Gert-Jan; Sastre, Mariano; Arrillaga, Jon A.; Maqueda, Gregorio
2016-04-01
The knowledge of the fog-top height (fog thickness) can be very meaningful for aircraft maneuvers, data assimilation/validation of Numerical Weather Prediction models or nowcasting of fog dissipation. However, its value is usually difficult to determine and it is sometimes approximated with satellite data, ground remote-sensing instruments or atmospheric soundings. These instruments are expensive and their data not always available. In this work, we show how the fog-top height shows a linear correlation with atmospheric turbulent variables measured close to the surface. This relation is statistically calculated from observational data of several radiation-fog events at two research sites: The Research Centre for the Lower Atmosphere (CIBA) in Spain and the Cabauw Experimental Site for Atmospheric Research (CESAR) in The Netherlands. Thus, surface friction velocity and buoyancy heat flux are presented as potential indicators of fog thickness. These methods are also evaluated over a long-lasting radiation-fog event at CESAR. The proposed methods could be operationally implemented for providing a continuous estimation of fog-top height through the deployment of a sonic anemometer close to the surface.
NASA Astrophysics Data System (ADS)
Fattal, Eyal; Gavze, Ehud
2014-05-01
The modeling of pollutant dispersion in the atmospheric boundary layer depends on an adequate description of the turbulent processes. Since turbulence is a multi-scale phenomenon characterized by a high degree of disorder, a statistical approach is needed. Among the statistical approaches, Lagrangian stochastic particle models provide a well established theoretical framework for the description of pollutant dispersion in different atmospheric boundary layer scenarios. Usually turbulent structure in the surface layer is described in terms of Monin-Obukhov similarity theory (MOST) using universal relationships between scaling parameters. These relationships have been shown to be valid in the case of horizontal homogeneity for stationary turbulence. The description of the turbulent processes above rough surfaces, such as over canopies, is a more complex case. For the urban canopy it was found that under developed stationary turbulence conditions MOST relations are approximately valid (in some cases, with extensions). An even more complex case is that of rough surfaces over topography, as no similarity theory has been established to properly describe the turbulence exchange over heterogeneous surfaces in complex terrain. We show Lagrangian stochastic model simulations based on MOST against measurements in urban canopy over complex terrain. Comparison gives good agreement with direct tracer measurements, in cases of neutral and convective stratifications. It is shown that in conditions of developed stationary turbulence, at most areas, there is in an agreement with MOST predictions. However, in very low wind conditions the turbulent nocturnal boundary layer is not necessarily stationary and is spatially non-homogeneous. This results in larger horizontal velocity standard deviation than expected in regular stable regime, as manifested in the pollutant pattern.
NASA Astrophysics Data System (ADS)
Linn, R.; Koo, E.; Kelley, N. D.; Jonkman, B.; Lundquist, J. K.; Canfield, J.
2010-12-01
In order to increase our efficiency of energy capture in wind farms, optimize turbine arrangements, and adapt wind-turbine technology to optimal performance in common atmospheric conditions such as low level jets (LLJ), it is critical to understand the dynamic interactions between turbulence and multiple wind turbines. Ambient atmospheric turbulence interacts with spinning turbines producing the critical mechanism for the recovery of the wind field behind a wind turbine. This turbine-influenced turbulent wind field creates the environment surrounding downstream turbines in a wind farm, thus controlling the amount of wind energy available for harvesting as well as the nature of the wear and tear that downwind turbines endure. The strength of the turbulent structures and their length-scales evolve downstream. Thus, the conditions to which downstream turbines are exposed, their productivity, and potentially their lifespan is a function of their position within the turbulent wake of upstream turbines. A numerical technique, WindBlade, has been developed for characterizing the interaction of spinning wind turbines and unsteady/heterogeneous atmospheric boundary layers at length scales ranging from blade-chord-scale (meters) to turbine-array-scale (multiple kilometers). This implementation of this technique combines an R&D100 winning numerical tool, HIGRAD/FIRETEC, a fully-compressible atmospheric hydrodynamics model with novel techniques to capture forces exchanged between the atmosphere and turbine as it rotates. The blade-induced forces on the wind field over the along the span of spinning turbine blades interacts with any oncoming atmospheric turbulence or shear, thus producing turbine wakes which are functions of turbine blade geometry and pitch, rotation speed, topographic and vegetation influences, and of course ambient wind speed, direction, shear, and turbulence. TurbSim, which creates vertical planes of three-dimensional turbulent wind fields based on empirical
Chen, Chunyi; Yang, Huamin
2016-08-22
The changes in the radial content of orbital-angular-momentum (OAM) photonic states described by Laguerre-Gaussian (LG) modes with a radial index of zero, suffering from turbulence-induced distortions, are explored by numerical simulations. For a single-photon field with a given LG mode propagating through weak-to-strong atmospheric turbulence, both the average LG and OAM mode densities are dependent only on two nondimensional parameters, i.e., the Fresnel ratio and coherence-width-to-beam-radius (CWBR) ratio. It is found that atmospheric turbulence causes the radially-adjacent-mode mixing, besides the azimuthally-adjacent-mode mixing, in the propagated photonic states; the former is relatively slighter than the latter. With the same Fresnel ratio, the probabilities that a photon can be found in the zero-index radial mode of intended OAM states in terms of the relative turbulence strength behave very similarly; a smaller Fresnel ratio leads to a slower decrease in the probabilities as the relative turbulence strength increases. A photon can be found in various radial modes with approximately equal probability when the relative turbulence strength turns great enough. The use of a single-mode fiber in OAM measurements can result in photon loss and hence alter the observed transition probability between various OAM states. The bit error probability in OAM-based free-space optical communication systems that transmit photonic modes belonging to the same orthogonal LG basis may depend on what digit is sent. PMID:27557248
Dissipation of buoyancy waves and turbulence in the atmosphere of venus
NASA Astrophysics Data System (ADS)
Izakov, M. N.
2010-12-01
The turbulent energy dissipation rate and the coefficients of turbulent diffusion and viscosity caused by breaking buoyancy waves (BWs) have been calculated. From the comparison of these values with other data, the contribution of BWs to the generation of turbulence has been determined. The comparison confirms the validity of the turbulence characteristics of the Venusian troposphere previously calculated from experimental data.
NASA Technical Reports Server (NTRS)
Gilbert, Kenneth E.; Di, Xiao; Wang, Lintao
1990-01-01
Weiner and Keast observed that in an upward-refracting atmosphere, the relative sound pressure level versus range follows a characteristic 'step' function. The observed step function has recently been predicted qualitatively and quantitatively by including the effects of small-scale turbulence in a parabolic equation (PE) calculation. (Gilbert et al., J. Acoust. Soc. Am. 87, 2428-2437 (1990)). The PE results to single-scattering calculations based on the distorted-wave Born approximation (DWBA) are compared. The purpose is to obtain a better understanding of the physical mechanisms that produce the step-function. The PE calculations and DWBA calculations are compared to each other and to the data of Weiner and Keast for upwind propagation (strong upward refraction) and crosswind propagation (weak upward refraction) at frequencies of 424 Hz and 848 Hz. The DWBA calculations, which include only single scattering from turbulence, agree with the PE calculations and with the data in all cases except for upwind propagation at 848 Hz. Consequently, it appears that in all cases except one, the observed step function can be understood in terms of single scattering from an upward-refracted 'skywave' into the refractive shadow zone. For upwind propagation at 848 Hz, the DWBA calculation gives levels in the shadow zone that are much below both the PE and the data.
Transition from geostrophic turbulence to inertia–gravity waves in the atmospheric energy spectrum
Callies, Jörn; Ferrari, Raffaele; Bühler, Oliver
2014-01-01
Midlatitude fluctuations of the atmospheric winds on scales of thousands of kilometers, the most energetic of such fluctuations, are strongly constrained by the Earth’s rotation and the atmosphere’s stratification. As a result of these constraints, the flow is quasi-2D and energy is trapped at large scales—nonlinear turbulent interactions transfer energy to larger scales, but not to smaller scales. Aircraft observations of wind and temperature near the tropopause indicate that fluctuations at horizontal scales smaller than about 500 km are more energetic than expected from these quasi-2D dynamics. We present an analysis of the observations that indicates that these smaller-scale motions are due to approximately linear inertia–gravity waves, contrary to recent claims that these scales are strongly turbulent. Specifically, the aircraft velocity and temperature measurements are separated into two components: one due to the quasi-2D dynamics and one due to linear inertia–gravity waves. Quasi-2D dynamics dominate at scales larger than 500 km; inertia–gravity waves dominate at scales smaller than 500 km. PMID:25404349
Reduced-order FSI simulation of NREL 5 MW wind turbine in atmospheric boundary layer turbulence
NASA Astrophysics Data System (ADS)
Motta-Mena, Javier; Campbell, Robert; Lavely, Adam; Jha, Pankaj
2015-11-01
A partitioned fluid-structure interaction (FSI) solver based on an actuator-line method solver and a finite-element modal-dynamic structural solver is used to evaluate the effect of blade deformation in the presence of a day-time, moderately convective atmospheric boundary layer (ABL). The solver components were validated separately and the integrated solver was partially validated against FAST. An overview of the solver is provided in addition to results of the validation study. A finite element model of the NREL 5 MW rotor was developed for use in the present simulations. The effect of blade pitching moment and the inherent bend/twist coupling of the rotor blades are assessed for both uniform inflow and the ABL turbulence cases. The results suggest that blade twisting in response to pitching moment and the bend/twist coupling can have a significant impact on rotor out-of-plane bending moment and power generated for both the uniform inflow and the ABL turbulence cases.
NASA Astrophysics Data System (ADS)
Xu, Yonggen; Li, Yude; Dan, Youquan; Du, Quan; Wang, Shijian
2016-07-01
The Wigner distribution function (WDF) has been used to study the propagation properties of partially coherent Laguerre Gaussian (PCLG) beams through atmospheric turbulence. Based on the extended Huygens-Fresnel principle, an analytical formula of the propagation matrixes in terms of the second-order moments of the WDF for PCLG Beams in the receiving plane is derived. And then the analytical formulae for the curvature radii of PCLG Beams propagating in turbulence are given by the second-order moments of the WDF. The numerical results indicate that the curvature radius of PCLG Beams changes more rapidly in turbulence than that in the free space. The influence of the transverse coherence width and the beam waist width on the curvature radius of PCLG Beams is obvious, while the laser wavelength and the inner scale of turbulence have a slight effect. The study results may be useful for remote sensing and free space optical communications.
NASA Astrophysics Data System (ADS)
Ghassemlooy, Zabih; Popoola, Wasiu O.; Ahmadi, Vahid; Leitgeb, Erich
In this paper, we analyse the error performance of transmitter/receiver array free-space optical (FSO) communication system employing binary phase shift keying (BPSK) subcarrier intensity modulation (SIM) in clear but turbulent atmospheric channel. Subcarrier modulation is employed to eliminate the need for adaptive threshold detector. Direct detection is employed at the receiver and each subcarrier is subsequently demodulated coherently. The effect of irradiance fading is mitigated with an array of lasers and photodetectors. The received signals are linearly combined using the optimal maximum ratio combining (MRC), the equal gain combining (EGC) and the selection combining (SelC). The bit error rate (BER) equations are derived considering additive white Gaussian noise and log normal intensity fluctuations. This work is part of the EU COST actions and EU projects.
Scintillation reduction for combined Gaussian-vortex beam propagating through turbulent atmosphere
Berman, Gennady P; Gorshkov, V. N.; Torous, S. V.
2010-12-14
We numerically examine the spatial evolution of the structure of coherent and partially coherent laser beams (PCBs), including the optical vortices, propagating in turbulent atmospheres, The influence of beam fragmentation and wandering relative to the axis of propagation (z-axis) on the value of the scintillation index (SI) of the signal at the detector is analyzed. A method for significantly reducing the SI, by averaging the signal at the detector over a set of PCBs, is described, This novel method is to generate the PCBs by combining two laser beams - Gaussian and vortex beams, with different frequencies (the difference between these two frequencies being significantly smaller than the frequencies themselves). In this case, the SI is effectively suppressed without any high-frequency modulators.
NASA Technical Reports Server (NTRS)
Lichtenstein, J. H.
1974-01-01
A method of computing the power spectral densities of the lateral response of airplanes to random atmospheric turbulence was adapted to an electronic digital computer. By use of this program, the power spectral densities of the lateral roll, yaw, and sideslip angular displacement of several conventional and STOL airplanes were computed. The results show that for the conventional airplanes, the roll response is more prominent than that for yaw or sideslip response. For the STOL airplanes, on the other hand, the yaw and sideslip responses were larger than the roll response. The response frequency of the STOL airplanes generally is higher than that for the conventional airplanes. This combination of greater sensitivity of the STOL airplanes in yaw and sideslip and the frequency at which they occur could be a factor causing the poor riding qualities of this class of airplanes.
NASA Astrophysics Data System (ADS)
Shao, Lina; Cao, Zhaoliang; Mu, Quanquan; Zhang, Peiguang; Yao, Lishuang; Wang, Shaoxin; Hu, Lifa; Xuan, Li
2016-05-01
An experimental analysis was conducted to investigate the fitting error of diffractive liquid crystal wavefront correctors (LCWFCs). First, an experiment was performed to validate the theoretical equations presented in our previous work Cao et al., 2009 [9]. The results showed an apparent discrepancy between the theoretical and measured results for the fitting error. This difference was examined and the influence of nonlinearities and rounding errors generated by the LCWFC was analyzed and discussed. Finally, the fitting error formula of the LCWFC was modified to obtain a more effective tool for the design of LCWFCs for atmospheric turbulence correction. These results will be useful for researchers who design liquid crystal adaptive optics systems for large-aperture ground-based telescopes.
NASA Technical Reports Server (NTRS)
Press, Harry; Meadows, May T; Hadlock, Ivan
1956-01-01
The available information on the spectrum of atmospheric turbulence is first briefly reviewed. On the basis of these results, methods are developed for the conversion of available gust statistics normally given in terms of counts of gusts or acceleration peaks into a form appropriate for use in spectral calculations. The fundamental quantity for this purpose appears to be the probability distribution of the root-mean-square gust velocity. Estimates of this distribution are derived from data for a number of load histories of transport operations; also, estimates of the variation of this distribution with altitude and weather condition are derived from available data and the method of applying these results to the calculation of airplane gust-response histories in operations is also outlined. (author)
PML/PBL: A new generalized monitor of atmospheric turbulence profiles
NASA Astrophysics Data System (ADS)
Ziad, Aziz; Blary, Flavien; Borgnino, Julien; Fanteï-Caujolle, Yan; Aristidi, Eric; Martin, François; Lantéri, Henri; Douet, Richard; Bondoux, Erick; Mekarnia, Djamel
2013-12-01
The futures large telescopes will be certainly equipped with Multi-Conjugate Adaptive Optics systems. The optimization of the performances of these techniques requires a precise specification of the different components of these systems. Major of these technical specifications are related to the atmospheric turbulence particularly the structure constante of the refractive index Cn2(h) and the outer scale L0(h). New techniques based on the moon limb observation for the monitoring of the Cn2(h) and L0(h) profiles with high vertical resolution will be presented. A new monitor PBL (Profileur Bord Lunaire) for the extraction of the Cn2(h) profile with high vertical resolution has been developed. This instrument uses an optical method based on observation of the moon limb with a DIMM configuration (Differential Image Motion Monitor). Indeed, in the PBL the lunar limb is observed through two sub-apertures of 6cm separated by a base of ~30cm. The moon limb offers a continuum of stars at different angular separations allowing the scan the atmosphere with a very high resolution. The angular correlation along the lunar limb between of the differential distance between the two images of the lunar edge leads to the Cn2(h) profile. The other parameters of turbulence are also accessible from this instrument as the profile of outer scale, the seeing and isoplanatic & isopistonicdomains. The PBL succeeded to our first moon limb profiler MOSP (Monitor of Outer Scale Profile) which was developed mainly for outer scale profile extraction. Several campaigns have been carried out with MOSP particularly at Mauna Kea Observatory (Hawaii) and Cerro Paranal in Chile. The PBL instrument has been installed at Dome C in Antarctica since January 2011. In addition to this winterized PBL for Dome C, a second copy of this instrument has been developed for mid-latitude sites. A first campaign with this light version of PBL, was carried out at the South African Large Telescope (SALT) Observatory in
NASA Astrophysics Data System (ADS)
Ji, Xiaoling; Chen, Hong; Ji, Guangming
2016-08-01
Characteristics of annular beams propagating through atmospheric turbulence along a downlink path and an uplink path are studied in detail by using numerical simulation method. It is found that in downlink the influence of atmospheric turbulence on the characteristics is quite different from that in uplink because of the altitude-dependent index structure constant. It is shown that, when the zenith angle θ is not large enough, it is always σ_{{I {{up}}}}2 > σ_{{I {{down}}}}2 on propagation whatever the value of the obscure ratio ɛ is, where σ_{{I {{up}}}}2 and σ_{{I {{down}}}}2 are the on-axis scintillation index in uplink and downlink, respectively. However, when θ is large enough, σ_{{I {{down}}}}2 is close to σ_{{I {{up}}}}2 as the propagation distance z increases, and σ_{{I {{up}}}}2 and σ_{{I {{down}}}}2 overlap each other as ɛ increases. Furthermore, as z increases, σ_{{I {{up}}}}2 approaches an asymptotical value when θ is not large enough, and the saturation phenomenon of σ_{{I {{up}}}}2 appears when θ is large enough. But the asymptotical value and the saturation phenomenon of σ_{{I {{down}}}}2 never appear. On the other hand, the energy focusability in downlink is better than that in uplink, and the difference of energy focusability between a downlink and an uplink increases with increasing θ or decreasing ɛ. In addition, in downlink there may exist sidelobes of intensity distributions when θ is not large enough, but the sidelobes never appear in uplink.
NASA Astrophysics Data System (ADS)
Tilinina, N. D.; Gulev, S. K.; Gavrikov, A. V.
2016-01-01
The role of extreme surface turbulent fluxes in total oceanic heat loss in the North Atlantic is studied. The atmospheric circulation patterns enhancing ocean-atmosphere heat flux in regions with significant contributions of the extreme heat fluxes (up to 60% of the net heat loss) are analyzed. It is shown that extreme heat fluxes in the Gulf Stream and the Greenland and Labrador Seas occur in zones with maximal air pressure gradients, i.e., in cyclone-anticyclone interaction zones.
PIV Measurements of Atmospheric Turbulence and Pollen Dispersal Above a Corn Canopy
NASA Astrophysics Data System (ADS)
Zhu, W.; van Hout, R.; Luznik, L.; Katz, J.
2003-12-01
Dispersal of pollen grains by wind and gravity (Anemophilous) is one of the oldest means of plant fertilization available in nature. Recently, the growth of genetically modified foods has raised questions on the range of pollen dispersal in order to limit cross-fertilization between organically grown and transgenic crops. The distance that a pollen grain can travel once released from the anther is determined, among others, by the aerodynamic parameters of the pollen and the characteristics of turbulence in the atmosphere in which it is released. Turbulence characteristics of the flow above a pollinating corn field were measured using Particle Image Velocimetry (PIV). The measurements were performed on the eastern shore of the Chesapeake Bay, in Maryland, during July 2003. Two PIV systems were used simultaneously, each with an overall sample area of 18x18 cm. The spacing between samples was about equal to the field of view. The PIV instrumentation, including CCD cameras, power supply and laser sheets forming optics were mounted on a measurement platform, consisting of a hydraulic telescopic arm that could be extended up to 10m. The whole system could be rotated in order to align it with the flow. The flow was seeded with smoke generated about 30m upstream of the sample areas. Measurements were carried out at several elevations, from just below canopy height up to 1m above canopy. The local meteorological conditions around the test site were monitored by other sensors including sonic anemometers, Rotorod pollen counters and temperature sensors. Each processed PIV image provides an instantaneous velocity distribution containing 64x64 vectors with a vector spacing of ~3mm. The pollen grains (~100mm) can be clearly distinguished from the smoke particles (~1mm) based on their size difference. The acquired PIV data enables calculation of the mean flow and turbulence characteristics including Reynolds stresses, spectra, turbulent kinetic energy and dissipation rate. Data
NASA Technical Reports Server (NTRS)
Devasirvatham, D. M. J.; Hodge, D. B.
1981-01-01
A model of the microwave and millimeter wave link in the presence of atmospheric turbulence is presented with emphasis on satellite communications systems. The analysis is based on standard methods of statistical theory. The results are directly usable by the design engineer.
Solar seeing monitor MISOLFA: A new method for estimating atmospheric turbulence parameters
NASA Astrophysics Data System (ADS)
Irbah, A.; Borgnino, J.; Djafer, D.; Damé, L.; Keckhut, P.
2016-07-01
Aims: Daily observation conditions are needed when observing the Sun at high angular resolution. MISOLFA is a daytime seeing monitor developed for this purpose that allows the estimation of the spatial and temporal parameters of atmospheric turbulence. This information is necessary, for instance, for astrometric measurements of the solar radius performed at Calern Observatory (France) with SODISM II, the ground-based version of the SODISM instrument of the PICARD mission. Methods: We present a new way to estimate the spatial parameters of atmospheric turbulence for daily observations. This method is less sensitive to vibrations and guiding defaults of the telescope since it uses short-exposure images. It is based on the comparison of the optical transfer function obtained from solar data and the theoretical values deduced from the Kolmogorov and Von Kàrmàn models. This method, previously tested on simulated solar images, is applied to real data recorded at Calern Observatory in July 2013 with the MISOLFA monitor. Results: First, we use data recorded in the pupil plane mode of MISOLFA and evaluate the turbulence characteristic times of angle-of-arrival fluctuations: between 5 and 16 ms. Second, we use the focal plane mode of MISOLFA to simultaneously record solar images to obtain isoplanatic angles: ranging from 1 to 5 arcsec (in agreement with previously published values). These images and our new method allow Fried's parameter to be measured; it ranges from 0.5 cm to 4.7 cm with a mean value of 1.5 cm when Kolmogorov's model is considered, and from less than 0.5 to 2.6 cm with a mean value of 1.3 cm for the Von Kàrmàn model. Measurements of the spatial coherence outer scale parameter are also obtained when using the Von Kàrmàn model; it ranges from 0.25 to 13 m with a mean value of 3.4 m for the four days of observation that we analyzed. We found that its value can undergo large variations in only a few hours and that more data analysis is needed to better
NASA Astrophysics Data System (ADS)
Ban, Junmei; Gao, Zhiqiu; Lenschow, Donald H.
2010-01-01
This study examines climate simulations with the National Center for Atmospheric Research Community Atmosphere Model version 3 (NCAR CAM3) using a new air-sea turbulent flux parameterization scheme. The current air-sea turbulent flux scheme in CAM3 consists of three basic bulk flux equations that are solved simultaneously by an iterative computational technique. We recently developed a new turbulent flux parameterization scheme where the Obukhov stability length is parameterized directly by using a bulk Richardson number, an aerodynamic roughness length, and a heat roughness length. Its advantages are that it (1) avoids the iterative process and thus increases the computational efficiency, (2) takes account of the difference between z0m and z0h and allows large z0m/z0h, and (3) preserves the accuracy of iteration. An offline test using Tropical Ocean-Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) data shows that the original scheme overestimates the surface fluxes under very weak winds but the new scheme gives better results. Under identical initial and boundary conditions, the original CAM3 and CAM3 coupled with the new turbulent flux scheme are used to simulate the global distribution of air-sea surface turbulent fluxes, and precipitation. Comparisons of model outputs against the European Remote Sensing Satellites (ERS), the Objectively Analyzed air-sea Fluxes (OAFlux), and Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) show that: (1) the new scheme produces more realistic surface wind stress in the North Pacific and North Atlantic trade wind belts and wintertime extratropical storm track regions; (2) the latent heat flux in the Northern Hemisphere trade wind zones shows modest improvement in the new scheme, and the latent heat flux bias in the western boundary current region of the Gulf Stream is reduced; and (3) the simulated precipitation in the new scheme is closer to observation in the Asian monsoon
NASA Astrophysics Data System (ADS)
Kim, Mu J.; Hyde, Milo W.
2012-10-01
An improved binary material-classification algorithm using passive polarimetric imagery degraded by atmospheric turbulence is presented. The technique implements a modified version of an existing polarimetric blind-deconvolution algorithm in order to remove atmospheric distortion and correctly classify the unknown object. The classification decision, dielectric or metal in this case, is based on degree of linear polarization (DoLP) estimates provided by the blind-deconvolution algorithm augmented by two DoLP priors - one statistically modeling the polarization behavior of metals and the other statistically modeling the polarization behavior of dielectrics. The DoLP estimate which maximizes the log-likelihood function determines the image pixel's classification. The method presented here significantly improves upon a similar published polarimetric classification method by adaptively updating the DoLP priors as more information becomes available about the scene. This new adaptive method significantly extends the range of validity of the existing polarimetric classification technique to near-normal collection geometries where most polarimetric material classifiers perform poorly. In this paper, brief reviews of the polarimetric blind-deconvolution algorithm and the functional forms of the DoLP priors are provided. Also provided is the methodology for making the algorithm adaptive including three techniques for updating the DoLP priors using in-progress DoLP estimates. Lastly, the proposed technique is experimentally validated by comparing classification results of two dielectric and metallic samples obtained using the new method to those obtained using the existing technique.
Friedrich, K.; Lundquist, J. K.; Aitken, M.; Kalina, E. A.; Marshall, R. F.
2012-01-01
When monitoring winds and atmospheric stability for wind energy applications, remote sensing instruments present some advantages to in-situ instrumentation such as larger vertical extent, in some cases easy installation and maintenance, measurements of vertical humidity profiles throughout the boundary layer, and no restrictions on prevailing wind directions. In this study, we compare remote sensing devices, Windcube lidar and microwave radiometer, to meteorological in-situ tower measurements to demonstrate the accuracy of these measurements and to assess the utility of the remote sensing instruments in overcoming tower limitations. We compare temperature and wind observations, as well as calculations of Brunt-Vaisala frequency and Richardson numbers for the instrument deployment period in May-June 2011 at the U.S. Department of Energy National Renewable Energy Laboratory's National Wind Technology Center near Boulder, Colorado. The study reveals that a lidar and radiometer measure wind and temperature with the same accuracy as tower instruments, while also providing advantages for monitoring stability and turbulence. We demonstrate that the atmospheric stability is determined more accurately when the liquid-water mixing ratio derived from the vertical humidity profile is considered under moist-adiabatic conditions.
Propagation properties of quantized Laguerre-Gaussian beams in atmospheric turbulence
NASA Astrophysics Data System (ADS)
Saito, Aya; Tanabe, Ayano; Kurihara, Makoto; Hashimoto, Nobuyuki; Ogawa, Kayo
2016-03-01
Effect of scintillations is serious problems in optical systems which require the atmospheric propagation, the optimization of optical system to minimize the effects of scintillation have been examined using the simulation of propagation in atmospheric turbulence. The analytic studies of scintillation index of LG beams show that LG beams have less scintillation than Gaussian beams. However, in these researches, the diameter of receiving aperture was set as point receiver without considering the effects of aperture averaging, which is phenomenon that reduced scintillations over finite aperture. In this paper, considering size of a receiving aperture, the propagation losses and the scintillation index of LG beams are simulated. Also, for practical applications, propagation properties of "quantized" LG(5,1) beams simulated. As a result of the examination, the propagation losses and the scintillation index of LG beams is smaller than those of Gaussian beams. By applying LG beams for optical wireless communications, it is expected to improve better the effect of scintillations than using Gaussian beams. The result is that the scintillation index of quantized LG beams is equal to those of LG beams, and it suggested that quantized LG beams can be treat the quantized LG beams the same as LG beams.
Costigan, K.R.
1998-11-01
Deseret Chemical Depot is one of the US Army`s storage facilities for its stockpile of chemical weapon agents. Congress has directed the Department of Defense to eliminate the aging stockpiles, which have existed since the end of World War II, and the US Army is destroying these lethal chemical munitions. Although the danger is slight, accurate predictions of the wind field in the valley are necessary for dispersion calculations in the event of an accident involving toxic chemicals at the depot. There are several small communities in Rush and Tooele valleys, including the town of Tooele, and Salt Lake City is located 65 km to the Northeast of Deseret Chemical Depot South area, at 1,300 m MSL and beyond the Oquirrh Mountains. The purpose of this report is to carry out three-dimensional numerical simulations of the atmospheric circulations in the region around Deseret Chemical Depot with the Higher Order Turbulence Model for Atmospheric Circulations (HOTMAC) and to evaluate the performance of the model. The code had been modified to assimilate local meteorological observations through the use of Newtonian nudging. The nudging scheme takes advantage of the extensive network of local observations in the valley.
NASA Astrophysics Data System (ADS)
Friedrich, Katja; Lundquist, Julie K.; Aitken, Matthew; Kalina, Evan A.; Marshall, Robert F.
2012-02-01
When monitoring winds and atmospheric stability for wind energy applications, remote sensing instruments present some advantages to in-situ instrumentation such as larger vertical extent, in some cases easy installation and maintenance, measurements of vertical humidity profiles throughout the boundary layer, and no restrictions on prevailing wind directions. In this study, we compare remote sensing devices, Windcube lidar and microwave radiometer, to meteorological in-situ tower measurements to demonstrate the accuracy of these measurements and to assess the utility of the remote sensing instruments in overcoming tower limitations. We compare temperature and wind observations, as well as calculations of Brunt-Väisälä frequency and Richardson numbers for the instrument deployment period in May-June 2011 at the U.S. Department of Energy National Renewable Energy Laboratory's National Wind Technology Center near Boulder, Colorado. The study reveals that a lidar and radiometer measure wind and temperature with the same accuracy as tower instruments, while also providing advantages for monitoring stability and turbulence. We demonstrate that the atmospheric stability is determined more accurately when the liquid-water mixing ratio derived from the vertical humidity profile is considered under moist-adiabatic conditions.
Chen, Chunyi; Yang, Huamin; Tong, Shoufeng; Lou, Yan
2016-04-01
The radial average-power distribution and normalized average power of orbital-angular-momentum (OAM) modes in a vortex Gaussian beam after passing through weak-to-strong atmospheric turbulence are theoretically formulated. Based on numerical calculations, the role of the intrinsic mode index, initial beam radius and turbulence strength in OAM-mode variations of a propagated vortex Gaussian beam is explored, and the validity of the pure-phase-perturbation approximation employed in existing theoretical studies is examined. Comparison between turbulence-induced OAM-mode scrambling of vortex Gaussian beams and that of either Laguerre-Gaussian (LG) beams or pure vortex beams has been made. Analysis shows that the normalized average power of OAM modes changes with increasing receiver-aperture size until it approaches a nearly stable value. For a receiver-aperture size of practical interest, OAM-mode scrambling is severer with a larger mode index or smaller initial beam radius besides stronger turbulence. Under moderate-to-strong turbulence condition, for two symmetrically-neighboring extrinsic OAM modes, the normalized average power of the one with an index closer to zero may be greater than that of the other one. The validity of the pure-phase-perturbation approximation is determined by the intrinsic mode index, initial beam radius and turbulence strength. It makes sense to jointly control the amplitude and phase of a fundamental Gaussian beam for producing an OAM-carrying beam. PMID:27136990
NASA Astrophysics Data System (ADS)
Valley, M. T.; Dudorov, V. V.; Kolosov, V. V.; Filimonov, G. A.
2006-11-01
The error caused by atmospheric turbulence, in determining the orientation angle of an object (a series of reflectors) has been studied. The orientation angle was determined by studying the image of the object. Numerical modeling was performed involving construction of the image of a series of reflectors as if they were observed through a turbulent medium, calculation of the coordinates of reflector mass centers, finding of the line closest to the reflector mass centers, and determination of its slope angle. Variance of the slope angle fluctuations is calculated.
NASA Astrophysics Data System (ADS)
Jha, Pankaj Kumar
Wind energy is becoming one of the most significant sources of renewable energy. With its growing use, and social and political awareness, efforts are being made to harness it in the most efficient manner. However, a number of challenges preclude efficient and optimum operation of wind farms. Wind resource forecasting over a long operation window of a wind farm, development of wind farms over a complex terrain on-shore, and air/wave interaction off-shore all pose difficulties in materializing the goal of the efficient harnessing of wind energy. These difficulties are further amplified when wind turbine wakes interact directly with turbines located downstream and in adjacent rows in a turbulent atmospheric boundary layer (ABL). In the present study, an ABL solver is used to simulate different atmospheric stability states over a diurnal cycle. The effect of the turbines is modeled by using actuator methods, in particular the state-of-the-art actuator line method (ALM) and an improved ALM are used for the simulation of the turbine arrays. The two ALM approaches are used either with uniform inflow or are coupled with the ABL solver. In the latter case, a precursor simulation is first obtained and data saved at the inflow planes for the duration the turbines are anticipated to be simulated. The coupled ABL-ALM solver is then used to simulate the turbine arrays operating in atmospheric turbulence. A detailed accuracy assessment of the state-of-the-art ALM is performed by applying it to different rotors. A discrepancy regarding over-prediction of tip loads and an artificial tip correction is identified. A new proposed ALM* is developed and validated for the NREL Phase VI rotor. This is also applied to the NREL 5-MW turbine, and guidelines to obtain consistent results with ALM* are developed. Both the ALM approaches are then applied to study a turbine-turbine interaction problem consisting of two NREL 5-MW turbines. The simulations are performed for two ABL stability
NASA Astrophysics Data System (ADS)
Li, Ye; Zhang, Yixin; Wang, Donglin; Shan, Lei; Xia, Mingchao; Zhao, Yuanhang
2016-05-01
The effects of strong turbulence on the orbital angular momentum (OAM) states of infrared and non-diffraction beam propagation in a terrestrial atmosphere are investigated. A new probability density model for OAM states of Bessel-Gaussian-Schell beam in the paraxial and strong turbulent channel is modeled based on the modified Rytov approximation. We find that the normalization energy weight of signal OAM modes at each OAM level is approximate equivalence in strong turbulence regime, one can constitute multiple mode channels by choosing OAM modes with large energy level difference between modes to reduce mode interference, and one can utilize BGS beam with OAM modes increasing the channel capacity of optical communications.
NASA Astrophysics Data System (ADS)
Faranda, Davide; Defrance, Dimitri
2016-06-01
The modifications of atmospheric circulation induced by anthropogenic effects are difficult to capture because wind fields feature a complex spectrum where the signal of large-scale coherent structures (planetary, baroclinic waves and other long-term oscillations) is mixed up with turbulence. Our purpose is to study the effects of climate changes on these two components separately by applying a wavelet analysis to the 700 hPa wind fields obtained in climate simulations for different forcing scenarios. We study the coherent component of the signal via a correlation analysis to detect the persistence of large-scale or long-lasting structures, whereas we use the theory of autoregressive moving-average stochastic processes to measure the spectral complexity of the turbulent component. Under strong anthropogenic forcing, we detect a significant climate change signal. The analysis suggests that coherent structures will play a dominant role in future climate, whereas turbulent spectra will approach a classical Kolmogorov behaviour.
NASA Technical Reports Server (NTRS)
Haugstad, B. S.; Eshleman, V. R.
1979-01-01
The dependence of the effects of planetary atmospheric turbulence on radio or optical wavelength in occultation experiments is discussed, and the analysis of Hubbard and Jokipii (1977) is criticized. It is argued that in deriving a necessary condition for the applicability of their method, Hubbard and Jokipii neglect a factor proportional to the square of the ratio of atmospheric or local Fresnel zone radius and the inner scale of turbulence, and fail to establish sufficient conditions, thereby omitting the square of the ratio of atmospheric scale height and the local Fresnel zone radius. The total discrepancy is said to mean that the results correspond to geometrical optics instead of wave optics, as claimed, thus being inapplicable in a dicussion of wavelength dependence. Calculations based on geometrical optics show that the bias in the average bending angle depends on the wavelength in the same way as does the bias in phase path caused by turbulence in a homogeneous atmosphere. Hubbard and Jokipii comment that the criterion of Haugstad and Eshleman is incorrect and show that there is a large wave optical domain where the results are independent of wavelength.
NASA Astrophysics Data System (ADS)
Wilson, Jordan M.
This research focuses on the dynamics of turbulent mixing under stably stratified flow conditions. Velocity fluctuations and instabilities are suppressed by buoyancy forces limiting mixing as stability increases and turbulence decreases until the flow relaminarizes. Theories that ubiquitously assume turbulence collapse above a critical value of the gradient Richardson number (e.g. Ri > Ric) are common in meteorological and oceanographic communities. However, most theories were developed from results of small-scale laboratory and numerical experiments with energetic levels several orders of magnitude less than geophysical flows. Geophysical flows exhibit strong turbulence that enhances the transport of momentum and scalars. The mixing length for the turbulent momentum field, L M, serves as a key parameter in assessing large-scale, energy-containing motions. For a stably stratified turbulent shear flow, the shear production of turbulent kinetic energy, P, is here considered to be of greater relevance than the dissipation rate of turbulent kinetic energy, epsilon. Thus, the turbulent Reynolds number can be recast as Re ≡ k2/(nuP) where k is the turbulent kinetic energy, allowing for a new perspective on flow energetics. Using an ensemble data set of high quality direct numerical simulation (DNS) results, large-eddy simulation (LES) results, laboratory experiments, and observational field data of the stable atmospheric boundary layer (SABL), the dichotomy of data becomes apparent. High mixing rates persist to strong stability (e.g. Ri ≈ 10) in the SABL whereas numerical and laboratory results confirm turbulence collapse for Ri ˜ O(1). While this behavior has been alluded to in literature, this direct comparison of data elucidates the disparity in universal theories of stably stratified turbulence. From this theoretical perspective, a Reynolds-averaged framework is employed to develop and evaluate parameterizations of turbulent mixing based on the competing forces
The role of atmospheric stability/turbulence on wakes at the Egmond aan Zee offshore wind farm
NASA Astrophysics Data System (ADS)
Barthelmie, R. J.; Churchfield, M. J.; Moriarty, P. J.; Lundquist, J. K.; Oxley, G. S.; Hahn, S.; Pryor, S. C.
2015-06-01
The aim of the paper is to present results from the NREL SOWFA project that compares simulations from models of different fidelity to meteorological and turbine data from the Egmond aan Zee wind farm. Initial results illustrate that wake behavior and impacts are strongly impacted by turbulence intensity [1]. This includes both power losses from wakes and loading illustrated by the out of plane bending moment. Here we focus on understanding the relationship between turbulence and atmospheric stability and whether power losses due to wakes can effectively be characterized by measures of turbulence alone or whether atmospheric stability as a whole plays a fundamental role in wake behavior. The study defines atmospheric stability using the Monin-Obukhov length estimated based on the temperature difference between 116 and 70 m. The data subset selected using this method for the calculation of the Monin-Obukhov length indicate little diurnal or directional dependence of the stability classes but a dominance of stable classes in the spring/unstable classes in fall and of near-neutral classes at high wind speeds (Figure 2). The analysis is complicated by the need to define turbulence intensity. We can select the ratio of the standard deviation of wind speed to mean wind speed in each observation period using data from the meteorological mast, in which case a substantial amount of data must be excluded due to the presence of the wind farm. An alternative is to use data from the wind turbines which could provide a larger data set for analysis. These approaches are examined and compared to illustrate their robustness. Finally, power losses from wakes are categorized according to stability and/or turbulence in order to understand their relative importance in determining the behavior of wind turbine wakes.
NASA Astrophysics Data System (ADS)
Thayer-Calder, K.; Larson, V. E.; Gettelman, A.; Craig, C.; Goldhaber, S.; Schanen, D.
2013-12-01
Global climate models (GCMs) have long had trouble representing climate variability that is highly dependent on convective variability. Convective clouds operate on scales far too small to actually simulate on a large GCM grid. To rectify these issues, GCM development is moving in several directions simultaneously. While much work is focusing on improved convective parameterizations, some modelers are increasing resolution to the point where deep convective clouds can be resolved on the grid scale. Others are using a super-parameterized approach, where small-scale models are embedded within the large-scale grid. Our study utilizes a new approach to modeling convective variability that attempts to model coupled convective and microphysics processes more explicitly than traditional parameterizations. Using the new Community Atmosphere Model (CAM) subcolumn framework, we create several instances of local cloudy or clear air profiles within the large-scale GCM grid. Each sub-column is instantiated through Latin-Hypercube sampling of double-gaussian PDFs predicted by a higher-order closure cloud parameterization known as CLUBB (Cloud Layers Unified By Binormals). The CAM microphysics code then runs with each instance, and the resulting heat and moisture tendencies are averaged and returned to the GCM in the same way as traditional parameterizations. Here, we present results from single-column simulations of CAM using this sub-column approach to coupling the moist turbulence parameterization to the microphysics scheme.
NASA Astrophysics Data System (ADS)
De Bruin, Henk; Hartogensis, Oscar
2015-04-01
In this study we will investigate the assumption that in the atmospheric surface layer the outer scale (L0) is proportional to the height above the surface, under dry convective conditions. For this purpose we analyzed raw sonic anemometers data collected at 3.5 m and at 9 m in a field campaign at the Santa Cruz Flats (32040.3190'N, 111032.641'W, 526 m of elevation) near Eloy, Arizona. For simplicity, we define the L0 as that separation distance at which the spatial correlation coefficient of air temperature at two points in the surface layer is 0.5. Then, according to the 2/3-Kolmogorov scaling law in the inertial sub-range, L0 is determined by the variance and the structure parameter of T . It is found that L0 does not scale with height. Possible reasons for this negative result will be discussed, by considering the methodology to determine structure parameters, Taylor's frozen turbulence hypothesis, effects of intermittency and Monin-Obukhov flux relationships for variance and structure parameter for T . The question is asked whether the concept of surface constant flux layer still holds under strong convective condition.
NASA Astrophysics Data System (ADS)
Li, Qinglei; Fu, Zuntao
2016-04-01
How to quantify the effects of non-stationarity on organization of atmospheric turbulent eddy motions has drawn less attention in recent literatures. Here Benford's law (BL), which states that the first digit (1 through 9) in many datasets follows a monotonically decreasing logarithmic distribution, is used to address this issue for the first time. A quantifier called multi-scale first digit entropy (MFDE) is adopted, which is based on the deviation of BL from the practical first digit distribution of multi-scaled vertical velocity increments, and marked differences are detected in stationary and non-stationary series. The MFDE values of stationary records do not change much with different scales while increase significantly for non-stationary ones as time scales increase. Due to the close relationship between MFDE and the multi-scale Shannon entropy (MSSE), the above results indicate that the non-stationary series are more organized than the stationary ones. Especially, the MFDE can also be used to quantify the different organization degrees of the multi-scaled structures existing in surface vertical velocity records.
Chen, Chunyi; Yang, Huamin; Tong, Shoufeng; Lou, Yan
2015-06-20
A theoretical formulation of the spherical-wave two-frequency mutual coherence function (MCF) for a propagation path characterized by a complex ABCD matrix with anisotropic atmospheric turbulence existing somewhere is developed. A specialization of this formulation leads to an expression for the two-frequency MCF of an equivalent pulsed Gaussian beam propagating in weak anisotropic atmospheric turbulence along a horizontal line-of-sight path; relevant closed-form analytical solutions under both near- and far-field conditions are obtained. The small- and large-scale solutions for both the plane- and spherical-wave spatial-coherence radii in either horizontal or vertical direction are derived. Analysis shows that the formula for the on-axis two-frequency MCF of a pulsed Gaussian beam under the weak-turbulence condition in both the near- and far-field regions is distinguished from that applicable in the strong-turbulence limit only by whether the turbulence-induced beam broadening can be thought of as negligible. Under both the near- and far-field conditions, the turbulence-induced increment of the mean-square temporal-pulse half-width is proportional to the effective anisotropy factor of turbulence. The MCF becomes statistically anisotropic due to the anisotropy of turbulence. For the spatial coherence radius of either a plane or spherical wave propagating along a horizontal line-of-sight path in anisotropic atmospheric turbulence, the corresponding small-scale solution is proportional to that for the plane-wave spatial-coherence radius in the isotropic-turbulence case with a proportionality coefficient depending only on the effective anisotropy factor of turbulence. The corresponding large-scale solution is proportional to that for the plane-wave spatial-coherence radius in the isotropic-turbulence case with a proportionality coefficient that depends on both the effective anisotropy factor and spectral index of turbulence. PMID:26193032
NASA Astrophysics Data System (ADS)
Khallaf, Haitham S.; Garrido-Balsells, José M.; Shalaby, Hossam M. H.; Sampei, Seiichi
2015-12-01
The performance of multiple-input multiple-output free space optical (MIMO-FSO) communication systems, that adopt multipulse pulse position modulation (MPPM) techniques, is analyzed. Both exact and approximate symbol-error rates (SERs) are derived for both cases of uncorrelated and correlated channels. The effects of background noise, receiver shot-noise, and atmospheric turbulence are taken into consideration in our analysis. The random fluctuations of the received optical irradiance, produced by the atmospheric turbulence, is modeled by the widely used gamma-gamma statistical distribution. Uncorrelated MIMO channels are modeled by the α-μ distribution. A closed-form expression for the probability density function of the optical received irradiance is derived for the case of correlated MIMO channels. Using our analytical expressions, the degradation of the system performance with the increment of the correlation coefficients between MIMO channels is corroborated.
Ma, Jing; Li, Kangning; Tan, Liying; Yu, Siyuan; Cao, Yubin
2015-09-01
The performances of satellite-to-ground downlink optical communications over Gamma-Gamma distributed atmospheric turbulence are studied for a coherent detection receiving system with spatial diversity. Maximum ratio combining (MRC) and selection combining (SC) techniques are considered as practical schemes to mitigate the atmospheric turbulence. Bit-error rate (BER) performances for binary phase-shift keying modulated coherent detection and outage probabilities are analyzed and compared for SC diversity using analytical results and for MRC diversity through an approximation method with different numbers of receiving aperture each with the same aperture area. To show the net diversity gain of a multiple aperture receiver system, BER performances and outage probabilities of MRC and SC multiple aperture receiver systems are compared with a single monolithic aperture with the same total aperture area (same total average incident optical power) for satellite-to-ground downlink optical communications. All the numerical results are verified by Monte-Carlo simulations. PMID:26368880
NASA Technical Reports Server (NTRS)
Chan, Kin P.; Killinger, Dennis K.
1992-01-01
A coherent 1-micron Nd:YAG lidar system is employed to measure directly the reduced spatial coherence length rho 0 of the lidar returns caused by atmospheric turbulence. The experiments were conducted by using a 2 x 2 heterodyne detector array, which permitted real-time spatial correlation measurements of the lidar returns at two different detector spacings. The spatial correlation coefficients and spatial coherence length of the lidar returns from a hard target were measured during a day-to-night time period when the atmospheric turbulence parameter, Cn-squared, was measured to vary from 2 x 10 exp -13 to 2 x 10 exp -4 m exp -2/3. These directly measured values of rho 0 as a function of Cn-squared were found to be in good agreement with theoretical predictions.
NASA Astrophysics Data System (ADS)
Chrzanowski, J.; Kirkiewicz, J.; Kravtsov, Yu. A.
2002-07-01
Influence of enhanced backscattering effect on laser measurements of dust and aerosols content in a turbulent atmosphere is discussed. It is shown that doubling of the backscattered light intensity, characteristic for enhanced backscattering leads to overestimating dust content in the air. To avoid undesirable effect of overestimation of dust and aerosols it is recommended to displace receiving aperture sidewise relatively to source and to use wider laser beam and extended receiving aperture as compared to coherence radius of the scattered wave field.
An experimental study of high Reynolds number turbulence in the atmosphere
NASA Astrophysics Data System (ADS)
Dhruva, Brindesh R.
2000-11-01
High Reynolds number turbulence in the atmospheric boundary layer has been investigated using constant temperature hot-wire anemometry. The Taylor microscale Reynolds numbers (Rλ) were typically between 5 × 103 at 2 meters in the salt flats of Western Utah and 2 × 104 at 35 meters on the meterological tower of Brookhaven National Laboratory in Long Island. The measurements were used to study the statistical properties of inertial range quantities, Reynolds stress and wind direction. The identification of possible self- similar behavior in the inertial range is a primary goal in turbulence research. To motivate the need for high Reynolds number measurements we demonstrate the Reynolds number effect on the existence and extent of the inertial range. We find that the inertial range is non-existent at typical laboratory Reynolds numbers. We thus turn to high Reynolds numbers and analyze the asymmetry in the probability distribution function (pdf) of the longitudinal velocity increment. We compute the scaling exponents of the positive and negative structure functions and find that the negative exponents are more anomalous than the positive ones. Furthermore, we quantify the contribution to the asymmetry-or the skewness-from different regions of the pdf. We find that the core region of the pdf is more or less symmetric and the skewness comes primarily from the rare large amplitude events contained in the tails of the pdf. We discuss this result in the context of the down-scale cascade of energy. Next it is shown that even at Rλ ~ 20,000 the structure functions do not scale unambiguously-although the situation is far better than that at low Reynolds numbers. By applying various filtering techniques and conditional sampling it is shown that this lack of strict scaling even at very high Reynolds numbers is due to large scale ``corrupting effects'' on the inertial range. We propose a plausible scheme to remove the large scale effects. Next, we characterize the
Ke, Xizheng; Lei, Sichen
2016-05-20
Maksutov-Cassegrains are widely used in free-space optical communication. The coupling efficiency and variance of a Maksutov-Cassegrain fiber (single-mode) system distorted by atmospheric turbulence are numerically evaluated using second-order and fourth-order moments under a Von Karman spectrum. Considering the limited cost and size of the equipment, the Maksutov-Cassegrain aperture should satisfy D_{A}/ρ_{S}≈7 (ρ_{S} approximates the characteristic atmospheric coherence length), and the obscuration ratio should be no more than 0.2. PMID:27411112
Zharkova, Valentina V.; Siversky, Taras V. E-mail: taras.siversky@gmail.com
2011-05-20
The precipitation of an electron beam injected into the solar atmosphere is studied for the generation of Langmuir wave turbulence in the presence of collisional and Ohmic losses. The system of quasi-linear time-dependent kinetic equations describing the evolution of beams and Langmuir waves is solved by using the summary approximation method. It is found that at upper atmospheric levels the self-induced electric field suppresses the generation of Langmuir turbulence to very small regions below injection. With further precipitation into deeper atmosphere the initial single power-law distributions of beam electrons are transformed into energy distributions with maxima at lower energies formed by collisional and Ohmic energy depletion. The electrons with lower energies (<20 keV) generate on large spatial scales intense low-hybrid and high-hybrid Langmuir waves with well-defined patterns in the corona while higher energy electrons generate moderate low-hybrid waves in the chromosphere. The maximum wave density appears at the maximum of the ambient density. The self-induced electric field reduces the level and makes the regions with low-hybrid Langmuir turbulence narrower in the corona and upper chromosphere. The higher the beam energy flux or its self-induced electric field, the narrower the regions with Langmuir turbulence. High-hybrid Langmuir waves in the form of multiple patterns in space (in the corona) and energy (below 20 keV) are found to be generated only by a very intense electron beam. The number of patterns in both dimensions is also shown to be significantly reduced by the self-induced electric field.
NASA Technical Reports Server (NTRS)
Bilanin, A. J.; Teske, M. E.; Hirsh, J. E.
1978-01-01
Enhanced dispersion of two-dimensional trailed vortex pairs within simplified neutral atmospheric backgrounds is studied numerically for three conditions: when the pair is imbedded in a constant turbulent bath (constant dissipation); when the pair is subjected to a mean cross-wind shear; and when the pair is near the ground. Turbulent transport is modeled using second-order closure turbulent transport theory. The turbulent background fields are constructed using a superequilibrium approximation. The computed results allow several general conclusions to be drawn with regard to the reduction in circulation of the vortex pair and the rolling moment induced on a following aircraft: (1) the rate of decay of a vortex pair increases with increasing background dissipation rate; (2) cross-wind shear disperses the vortex whose vorticity is opposite to the background; and (3) the proximity of a ground plane reduces the hazard of the pair by scrubbing. The phenomenon of vortex bounce is explained in terms of secondary vorticity produced at the ground plane. Qualitative comparisons are made with available experimental data, and inferences of these results upon the persistence of aircraft trailing vortices are discussed.
NASA Astrophysics Data System (ADS)
Erven, C.; Heim, B.; Meyer-Scott, E.; Bourgoin, J. P.; Laflamme, R.; Weihs, G.; Jennewein, T.
2012-12-01
The statistical fluctuations in free-space links in the turbulent atmosphere are important for the distribution of quantum signals. To that end, we first study statistics generated by the turbulent atmosphere in an entanglement-based free-space quantum key distribution (QKD) system. Using the insights gained from this analysis, we study the effect of link fluctuations on the security and key generation rate of decoy state QKD concluding that it has minimal effect in the typical operating regimes. We then investigate the novel idea of using these turbulent fluctuations to our advantage in QKD experiments. We implement a signal-to-noise ratio filter (SNRF) in our QKD system which rejects measurements during periods of low transmission efficiency, where the measured quantum bit error rate is temporarily elevated. Using this, we increase the total secret key generated by the system from 78 009 bits to 97 678 bits, representing an increase of 25.2% in the final secure key rate, generated from the same raw signals. Lastly, we present simulations of a QKD exchange with an orbiting low earth orbit satellite and show that an SNRF will be extremely useful in such a situation, allowing many more passes to extract a secret key than would otherwise be possible.
NASA Astrophysics Data System (ADS)
Vijayakumar, Ganesh
Modern commercial megawatt-scale wind turbines occupy the lower 15-20% of the atmospheric boundary layer (ABL), the atmospheric surface layer (ASL). The current trend of increasing wind turbine diameter and hub height increases the interaction of the wind turbines with the upper ASL which contains spatio-temporal velocity variations over a wide range of length and time scales. Our interest is the interaction of the wind turbine with the energetic integral-scale eddies, since these cause the largest temporal variations in blade loadings. The rotation of a wind turbine blade through the ABL causes fluctuations in the local velocity magnitude and angle of attack at different sections along the blade. The blade boundary layer responds to these fluctuations and in turn causes temporal transients in local sectional loads and integrated blade and shaft bending moments. While the integral scales of the atmospheric boundary layer are ˜ O(10--100m) in the horizontal with advection time scales of order tens of seconds, the viscous surface layer of the blade boundary layer is ˜ O(10 -- 100 mum) with time scales of order milliseconds. Thus, the response of wind turbine blade loadings to atmospheric turbulence is the result of the interaction between two turbulence dynamical systems at extremely disparate ranges of length and time scales. A deeper understanding of this interaction can impact future approaches to improve the reliability of wind turbines in wind farms, and can underlie future improvements. My thesis centers on the development of a computational framework to simulate the interaction between the atmospheric and wind turbine blade turbulence dynamical systems using a two step one-way coupled approach. Pseudo-spectral large eddy simulation (LES) is used to generate a true (equilibrium) atmospheric boundary layer over a flat land with specified surface roughness and heating consistent with the stability state of the daytime lower troposphere. Using the data from the
NASA Astrophysics Data System (ADS)
Li, Kangning; Ma, Jing; Belmonte, Aniceto; Tan, Liying; Yu, Siyuan
2015-12-01
The performances of satellite-to-ground downlink optical communications over Gamma-Gamma distributed turbulence are studied for a multiple-aperture receiver system. Equal gain-combining (EGC) and selection-combining (SC) techniques are considered as practical schemes to mitigate the atmospheric turbulence under thermal-noise-limited conditions. Bit-error rate (BER) performances for on-off keying-modulated direct detection and outage probabilities are analyzed and compared for SC diversity receptions using analytical results and for EGC diversity receptions through an approximation method. To show the net diversity gain of a multiple-aperture receiver system, BER performances and outage probabilities of EGC and SC receiver systems are compared with a single monolithic-aperture receiver system with the same total aperture area (same average total incident optical power) for satellite-to-ground downlink optical communications. All the numerical results are also verified by Monte-Carlo simulations.
NASA Astrophysics Data System (ADS)
Zhao, Yuanhang; Zhang, Yixin; Hu, Zhengda; Li, Ye; Wang, Donglin
2016-07-01
Polarization and spatial coherence of quantization Gaussian Schell-beams propagating through the anisotropic non-Kolmogorov turbulence of marine-atmosphere channel are studied based on the quantized Huygens-Fresnel principle and the degree of quantum polarization. The spatial coherence length and the polarization degree of linearly polarization quantization Gaussian Schell-beams are developed. The effects of outer scale on the lateral coherence length are not obvious as same as the effects of wavelength on the degree of polarization. The degree of polarization decreases as the source transverse coherent width, anisotropic factor, the number of received photons, spectral index, the inner scale of turbulent eddies and source transverse radius decrease or generalized refractive-index structure parameter increases. The refractive-index structure parameter, spectral index and inner scale have also effect on the changes of lateral coherence length. Those results can be used to improve the performance of a polarization-encoded quantum communication system.
NASA Astrophysics Data System (ADS)
Valley, M. T.; Dudorov, V. V.; Kolosov, V. V.; Filimonov, G. A.
2006-11-01
The paper considers the error caused by atmospheric turbulence, in determining the motion speed of an object by using its successive images recorded on a matrix of a digital camera. Numerical modeling of the image of a moving object in successive time moments is performed. Fluctuation variance of the image mass centre affecting the measurement error is calculated. Error dependences on the distance to the object and path slope angle are obtained for different turbulence models. Considered are the situations, when the angular displacement of the object between two immediate shots of the digital camera is greater than the isoplanatism angle as well as the situations when the angular displacement is smaller than this angle.
NASA Astrophysics Data System (ADS)
Eberhard, Wynn L.
1992-11-01
Techniques for extraction of boundary layer parameters from measurements of a short pulse (~0.4 μs) CO2 Doppler lidar (λ=10.6 μm) are described. The lidar is operated by the National Oceanic and Atmospheric Administration (NOAA) Wave Propagation Laboratory (WPL). The measurements are those collected during the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE). The recorded radial velocity measurements have a range resolution of 150 m. With a pulse repetition rate of 20 Hz it is possible to perform scannings in two perpendicular vertical planes (x-z and y-z) in approximately 72 s. By continuously operating the lidar for about an hour, one can extract stable statistics of the radial velocities. Assuming that the turbulence is horizontally homogeneous, we have estimated the mean wind, its standard deviations, and the momentum fluxes. We have estimated the first, second, and, third moments of the vertically velocity from the vertical pointing beam. Spectral analysis of the radial velocities is also performed, from which (by examining the amplitude of the power spectrum at the inertial range) we have deduced the kinetic energy dissipation. Finally, using the statistical form of the Navier-Stokes equations, the surface heat flux is derived as the residual balance between the vertical gradient of the third moment of the vertical velocity and the kinetic energy dissipation. With the exception of the vertically pointing beam an individual radial velocity estimate is accurate only to +/-0.7 ms-1. Combining many measurements would normally reduce the error, provided that it is unbiased and uncorrelated. The nature of some of the algorithms, however, is such that biased and correlated errors may be generated even though the ``raw'' measurements are not. We have developed data processing procedures that eliminate bias and minimize error correlation. Once bias and error correlations are accounted for, the large sample size is
NASA Astrophysics Data System (ADS)
Gal-Chen, Tzvi; Xu, Mei; Eberhard, Wynn L.
1992-11-01
Techniques for extraction of boundary layer parameters from measurements of a short pulse (≈0.4 μs) CO2 Doppler lidar (λ = 10.6 μm) are described. The lidar is operated by the National Oceanic and Atmospheric Administration (NOAA) Wave Propagation Laboratory (WPL). The measurements are those collected during the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE). The recorded radial velocity measurements have a range resolution of 150 m. With a pulse repetition rate of 20 Hz it is possible to perform scannings in two perpendicular vertical planes (x-z and y-z) in approximately 72 s. By continuously operating the lidar for about an hour, one can extract stable statistics of the radial velocities. Assuming that the turbulence is horizontally homogeneous, we have estimated the mean wind, its standard deviations, and the momentum fluxes. We have estimated the first, second, and, third moments of the vertical velocity from the vertically pointing beam. Spectral analysis of the radial velocities is also performed, from which (by examining the amplitude of the power spectrum at the inertial range) we have deduced the kinetic energy dissipation. Finally, using the statistical form of the Navier-Stokes equations, the surface heat flux is derived as the residual balance between the vertical gradient of the third moment of the vertical velocity and the kinetic energy dissipation. With the exception of the vertically pointing beam an individual radial velocity estimate is accurate only to ±0.7 m s-1. Combining many measurements would normally reduce the error, provided that it is unbiased and uncorrelated. The nature of some of the algorithms, however, is such that biased and correlated errors may be generated even though the "raw" measurements are not. We have developed data processing procedures that eliminate bias and minimize error correlation. Once bias and error correlations are accounted for, the large sample size is
Representation of the grey zone of turbulence in the atmospheric boundary layer
NASA Astrophysics Data System (ADS)
Honnert, Rachel
2016-04-01
Numerical weather prediction model forecasts at horizontal grid lengths in the range of 100 to 1 km are now possible. This range of scales is the "grey zone of turbulence". Previous studies, based on large-eddy simulation (LES) analysis from the MésoNH model, showed that some assumptions of some turbulence schemes on boundary-layer structures are not valid. Indeed, boundary-layer thermals are now partly resolved, and the subgrid remaining part of the thermals is possibly largely or completely absent from the model columns. First, some modifications of the equations of the shallow convection scheme have been tested in the MésoNH model and in an idealized version of the operational AROME model at resolutions coarser than 500 m. Secondly, although the turbulence is mainly vertical at mesoscale (> 2 km resolution), it is isotropic in LES (< 100 m resolution). It has been proved by LES analysis that, in convective boundary layers, the horizontal production of turbulence cannot be neglected at resolutions finer than half of the boundary-layer height. Thus, in the grey zone, fully unidirectional turbulence scheme should become tridirectional around 500 m resolution. At Météo-France, the dynamical turbulence is modelled by a K-gradient in LES as well as at mesoscale in both MésoNH and AROME, which needs mixing lengths in the formulation. Vertical and horizontal mixing lengths have been calculated from LES of neutral and convective cases at resolutions in the grey zone.
Turbulent Transfer Between Street Canyons and the Overlying Atmospheric Boundary Layer
NASA Astrophysics Data System (ADS)
Salizzoni, Pietro; Marro, Massimo; Soulhac, Lionel; Grosjean, Nathalie; Perkins, Richard J.
2011-12-01
The turbulent exchange of momentum between a two-dimensional cavity and the overlying boundary layer has been studied experimentally, using hot-wire anemometry and particle image velocimetry (PIV). Conditions within the boundary layer were varied by changing the width of the canyons upstream of the test canyon, whilst maintaining the square geometry of the test canyon. The results show that turbulent transfer is due to the coupling between the instabilities generated in the shear layer above the canyons and the turbulent structures in the oncoming boundary layer. As a result, there is no single, unique velocity scale that correctly characterizes all the processes involved in the turbulent exchange of momentum across the boundary layer. Similarly, there is no single velocity scale that can characterize the different properties of the turbulent flow within the canyon, which depends strongly on the way in which turbulence from the outer flow is entrained into the cavity and carried round by the mean flow. The results from this study will be useful in developing simple parametrizations for momentum exchange in the urban canopy, in situations where the street geometry consists principally of relatively long, uniform streets arranged in grid-like patterns; they are unlikely to be applicable to sparse geometries composed of isolated three-dimensional obstacles.
NASA Astrophysics Data System (ADS)
Lavely, Adam; Vijayakumar, Ganesh; Brasseur, James; Paterson, Eric; Kinzel, Michael
2011-11-01
Using large-eddy simulation (LES) of the neutral and moderately convective atmospheric boundary layers (NBL, MCBL), we analyze the impact of coherent turbulence structure of the atmospheric surface layer on the short-time statistics that are commonly collected from wind turbines. The incoming winds are conditionally sampled with a filtering and thresholding algorithm into high/low horizontal and vertical velocity fluctuation coherent events. The time scales of these events are ~5 - 20 blade rotations and are roughly twice as long in the MCBL as the NBL. Horizontal velocity events are associated with greater variability in rotor power, lift and blade-bending moment than vertical velocity events. The variability in the industry standard 10 minute average for rotor power, sectional lift and wind velocity had a standard deviation of ~ 5% relative to the ``infinite time'' statistics for the NBL and ~10% for the MCBL. We conclude that turbulence structure associated with atmospheric stability state contributes considerable, quantifiable, variability to wind turbine statistics. Supported by NSF and DOE.
The flux tube paradigm and its role in MHD turbulence in the solar atmosphere
NASA Astrophysics Data System (ADS)
Matthaeus, W. H.; Greco, A.; Servidio, S.; Wan, M.; Osman, K.; Ruffolo, D. J.
2011-12-01
Descriptions of magnetic field and plasma structures in terms of flux tubes, plasmoids and other bundles of magnetic field lines are familiar in the vocabulary of observational and theoretical space physics. "Spaghetti models" and flux ropes are well known examples. Flux tubes and families of field lines can also be defined in a medium that admits magnetic fluctuations, including strong MHD turbulence, but their behavior can become complicated. In 3D fluctuations the smooth flux tube description itself becomes in some sense unstable, as nearby field lines diverge and flux surfaces shred. This lends complexity to the structure of flux tubes, and can give rise to temporarily trapped field lines and charged test particle trajectories, with immediate implications for transport, e.g., of solar energetic particles. The properties of the turbulent magnetic field can also be strongly influenced by the dynamics of turbulence. Large scale self organizing behavior, or inverse cascade, can enhance very long wavelength structure, favoring Bohm scaling of diffusion coefficients. Meanwhile smaller scale flux tube structures are integral features of the inertial range of turbulence, giving rise to a cellularization of the plasma due to rapid dynamical relaxation processes. These drive the turbulent system locally towards low-acceleration states, including Alfvenic, Beltrami and force-free states. Cell boundaries are natural positions for formation of near discontinuous boundaries, where dynamical activity can be enhanced. A primary example is appearance of numerous discontinuities and active reconnection sites in turbulence, which appear to support a wide distribution of reconnection rates associated with coherent current structures. These discontinuities are also potential sites of enhanced heating, as expected in Kolmogorov's Refined Similarity Hypothesis. All of these features are related to self organization, cascade and intermittency of the turbulence. Examples of these
Structure of atmospheric turbulence in the friction layer below 500 meters
NASA Technical Reports Server (NTRS)
Maas, S. J.; Scoggins, J. R.
1976-01-01
Measurements of wind direction and speed, vertical velocity, and temperature were made from several levels of the 444 m tower near Oklahoma City. Turbulence quantities were calculated from the covariances between observed variables over periods ranging from 5 min to 1 hr. It was found that in some cases parameters such as mean wind speed, shearing stress, and vertical heat flux could be expressed by simple equations for periods of 15 min to 1 hr. Changes in these quantities with time are related to changes in vertical motion and stability. Power spectra were calculated for sequential 15 min, 30 min, and 1 hr periods. The effects of stability, wind speed, and surface roughness on the spectra of longitudinal and lateral velocity were examined, along with the effect of height on the spectrum of vertical velocity. This region was shown to be composed of a lower region in which mechanical turbulence dominates and an upper region dominated by convective turbulence.
Transmission analysis of CPolM-based OFDM FSO system in atmospheric turbulence
NASA Astrophysics Data System (ADS)
Su, Yuwei; Bai, Fan; Sato, Takuro
2016-06-01
In this paper, we propose to implement a consecutive polarization modulation (CPolM) scheme to transmit orthogonal frequency division multiplexing (OFDM) signal over the turbulent free-space optical (FSO) links. We analyze the fluctuation of polarization states of an optical wave while propagating through the turbulence channel of which the refractive-index property is described by Kolmogorov spectrum. The transmission performance in terms of signal-to-noise-ratio (SNR), symbol-error-ratio (SER) and outage probability of the proposed system are evaluated. The proposed system provides a more efficient way to compensate scintillation effects in a comparison with the intensity modulation (IM) based OFDM FSO system under a varying degrees of turbulence strength regimes.
NASA Astrophysics Data System (ADS)
Litt, Maxime; Sicart, Jean-Emmanuel; Helgason, Warren D.; Wagnon, Patrick
2015-03-01
We investigate properties of the turbulent flow and sensible heat fluxes in the atmospheric surface layer of the high elevation tropical Zongo glacier ( m a.s.l., S, Bolivia) from data collected in the dry season from July to August 2007, with an eddy-covariance system and a 6-m mast for wind speed and temperature profiles. Focus is on the predominant downslope wind regime. A low-level wind-speed maximum, around a height of m, is detected in low wind conditions (37 % of the time). In strong wind conditions (39 % of the time), no wind-speed maximum is detected. Statistical and spectral analyses reveal low frequency oscillations of the horizontal wind speed that increase vertical mixing. In strong winds, wavelet analysis shows that coherent structures systematically enhance the turbulent sensible heat fluxes, accounting for 44-52 % of the flux. In contrast, in low wind conditions, the katabatic flow is perturbed by its slow oscillations or meandering motions, inducing erratic turbulent sensible heat fluxes. These motions account for 37-43 % of the flux. On tropical glaciers, the commonly used bulk aerodynamic profile method underestimates the eddy-covariance-based flux, probably because it does not account for low frequency disturbances that influence the surface flow in both wind regimes.
Remote sensing of turbulence in the clear atmosphere with 2-micron lidars
NASA Technical Reports Server (NTRS)
Martinson, Robert J.; Flint, John H.
1994-01-01
The development of an eye-safe, airborne LIDAR that exploits the decorrelation of the heterodyne signal to detect clear air turbulence is reported. A one watt average power transmitter is capable of detecting clear air turbulence to over 20 km is subvisual cirrus (an environment highly correlated with instabilities of sratified shear layers). In the absence of subvisual cirrus, a 4 km detection range is maintained. A table depicting the warning time in seconds with respect to the aircraft speed and instrument range (in kilometers) is presented.
NASA Astrophysics Data System (ADS)
Bolinger, William K.
1987-06-01
An experimental flow visualization study was performed on a rectangular block and other elements that could be assembled in the form of a generic destroyer ship model. The purpose of the study was to visually analyze the flow field around the model in a simulated open ocean atmospheric boundary layer. To ensure correct simulation of the atmospheric boundary layer, both velocity profile and longitudinal turbulence intensities were matched. For the actual flow visualization studies, two techniques were used. During the on-body portion of the study, the ultraviolet lighting/fluorescent minituft technique was used. For the off-body portion, helium bubble system, with a neutral density centrifuge, was utilized. Both techniques produced excellent photographic results and allowed for direct comparison of the flow fields using the two flow visualization techniques.
NASA Astrophysics Data System (ADS)
Kadygrov, Evgeny N.; Shur, Genrih N.; Viazankin, Anton S.
2003-06-01
The MTP-5, a microwave temperature profiler, has been widely used since 1991 for investigation of the atmospheric boundary layer (ABL). The MTP-5 is an angular scanning single-channel instrument with a central frequency of about 60 GHz, designed to provide continuous, unattended observations. It can measure the thermal emission of the atmosphere with high sensitivity (0.03 K at 1 s integration time) from different zenith angles. On the basis of this measurement, it is possible to retrieve temperature profiles at the altitude range up to 600 m, to calculate wind speed and wind direction at the lowest 250 m, and to get information about some parameters of atmospheric turbulence. This report presents some applications of the MTP-5 instrument data collected in 1998-2001 within a number of international field projects: the dynamics of ABL temperature inversion in a mountain valley (Mesoscale Alpine Program (MAP)), as well as along an island coast (north part of Sakhalin Island, Russia-Japan Project); continuous measurements of the ABL temperature profile provided from a special scientific train that crossed the territory of Russia (the Transcontinental Observations of the Chemistry of the Atmosphere Project (TROICA)); and simultaneous measurements of the ABL temperature profile provided over the central and northern part of Moscow in a continuous mode (the Global Urban Research Meteorology and Environment Project (GURME)). In 1999, two MTP-5 instruments were installed on a platform that was rotating in the azimuth direction at the 310 m Obninsk Meteorological Research Tower (Meteo Tower) to validate the method and microwave equipment for measurement of wind speed and wind direction and investigation of atmospheric turbulence. Spectral analyses of the integrated signal provided an opportunity to estimate the inertial subrange low-frequency limit and its height dependence for thermal turbulence at the lowest 200 m layer. Wavelet analysis of the signal made it possible to
NASA Astrophysics Data System (ADS)
Sjöholm, Mikael; Kapp, Stefan; Kristensen, Leif; Mikkelsen, Torben
2011-11-01
Affordable coherent wind lidars based on modern telecom components have recently emerged on the wind energy market spurred by high demand of the industry for compact and accurate remote sensing wind and turbulence profilers. Today, hundreds of ground based wind lidars that achieve the range resolution by either focusing a continuous-wave laser beam or by gating a pulsed laser beam are used for measuring mean wind and turbulence profiles in the lower atmospheric boundary-layer. However, detailed understanding of the influence of the spatial filtering of the lidars on their precise assessment of turbulence is still a challenge. For assessment of the fine structure turbulence, and in particular for the easy and fast assessment of the dissipation rate of turbulent kinetic energy from measurements in the Kolmogorov inertial subrange, we havemodeled the atmospheric velocity structure functions and spectra obtainable from fixed-orientation along-beam wind measurements by these lidars. The dissipation rate retrieval model is experimentally evaluated with data obtained with a pulsed lidar pointing horizontally into horizontally homogeneous turbulence encountered at the top level of a 125 m tall meteorological tower, equipped with an in-situ turbulence measurement device (a three-dimensional sonic anemometer) for intercomparison. Our experimental study has revealed that the easily manageable analytical model accounts well for the observed fine structure turbulent spectra and their dependence on the pointing direction of the lidar beam relative to the mean wind direction. The results demonstrate that turbulence dissipation rates, and hence boundary-layer turbulence, can easily be obtained from wind lidar-based fine structure measurements.
NASA Astrophysics Data System (ADS)
Mohamed, A.; Clothier, R.; Watkins, S.; Sabatini, R.; Abdulrahim, M.
2014-10-01
Fixed-wing Micro-Aerial Vehicles (MAVs) need effective sensors that can rapidly detect turbulence induced motion perturbations. Current MAV attitude control systems rely on inertial sensors. These systems can be described as reactive; detecting the disturbance only after the aircraft has responded to the disturbing phenomena. In this part of the paper, the current state of the art in reactive attitude sensing for fixed-wing MAVs are reviewed. A scheme for classifying the range of existing and emerging sensing techniques is presented. The features and performance of the sensing approaches are discussed in the context of their application to MAV attitude control systems in turbulent environments. It is found that the use of single sensors is insufficient for MAV control in the presence of turbulence and that potential gains can be realised from multi-sensor systems. A successive paper to be published in this journal will investigate novel attitude sensors which have the potential to improve attitude control of MAVs in Turbulence.
NASA Astrophysics Data System (ADS)
Kopeć, Jacek M.; Kwiatkowski, Kamil; de Haan, Siebren; Malinowski, Szymon P.
2016-05-01
Navigational information broadcast by commercial aircraft in the form of Mode-S EHS (Mode-S Enhanced Surveillance) and ADS-B (Automatic Dependent Surveillance-Broadcast) messages can be considered a new source of upper tropospheric and lower stratospheric turbulence estimates. A set of three processing methods is proposed and analysed using a quality record of turbulence encounters made by a research aircraft.The proposed methods are based on processing the vertical acceleration or the background wind into the eddy dissipation rate. Turbulence intensity can be estimated using the standard content of the Mode-S EHS/ADS-B.The results are based on a Mode-S EHS/ADS-B data set generated synthetically based on the transmissions from the research aircraft. This data set was validated using the overlapping record of the Mode-S EHS/ADS-B received from the same research aircraft. The turbulence intensity, meaning the eddy dissipation rate, obtained from the proposed methods based on the Mode-S EHS/ADS-B is compared with the value obtained using on-board accelerometer. The results of the comparison indicate the potential of the methods. The advantages and limitation of the presented approaches are discussed.
NASA Astrophysics Data System (ADS)
Djordjevic, Goran T.; Petkovic, Milica I.
2016-04-01
This paper presents the exact average bit error rate (BER) analysis of the free-space optical system employing subcarrier intensity modulation (SIM) with Gray-coded quadrature amplitude modulation (QAM). The intensity fluctuations of the received optical signal are caused by the path loss, atmospheric turbulence and pointing errors. The exact closed-form analytical expressions for the average BER are derived assuming the SIM-QAM with arbitrary constellation size in the presence of the Gamma-Gamma scintillation. The simple approximate average BER expressions are also provided, considering only the dominant term in the finite summations of obtained expressions. Derived expressions are reduced to the special case when optical signal transmission is affected only by the atmospheric turbulence. Numerical results are presented in order to illustrate usefulness of the derived expressions and also to give insights into the effects of different modulation, channel and receiver parameters on the average BER performance. The results show that the misalignment between the transmitter laser and receiver detector has the strong effect on the average BER value, especially in the range of the high values of the average electrical signal-to-noise ratio.
Reynolds, Kate V; Thomas, Adrian L R; Taylor, Graham K
2014-12-01
Turbulent atmospheric conditions represent a challenge to stable flight in soaring birds, which are often seen to drop their wings in a transient motion that we call a tuck. Here, we investigate the mechanics, occurrence and causation of wing tucking in a captive steppe eagle Aquila nipalensis, using ground-based video and onboard inertial instrumentation. Statistical analysis of 2594 tucks, identified automatically from 45 flights, reveals that wing tucks occur more frequently under conditions of higher atmospheric turbulence. Furthermore, wing tucks are usually preceded by transient increases in airspeed, load factor and pitch rate, consistent with the bird encountering a headwind gust. The tuck itself immediately follows a rapid drop in angle of attack, caused by a downdraft or nose-down pitch motion, which produces a rapid drop in load factor. Positive aerodynamic loading acts to elevate the wings, and the resulting aerodynamic moment must therefore be balanced in soaring by an opposing musculoskeletal moment. Wing tucking presumably occurs when the reduction in the aerodynamic moment caused by a drop in load factor is not met by an equivalent reduction in the applied musculoskeletal moment. We conclude that wing tucks represent a gust response precipitated by a transient drop in aerodynamic loading. PMID:25320064
Salar, Ali Reza; Ahmadi, Fazlollah; Navipour, Hassan
2016-01-01
Background: Nursing management is the most important aspect for providing high-quality nursing care. Therefore, skillful nursing managers, such as head nurses, are required to accomplish this goal. High-quality nursing care is one of the most important principles of health organizations to ensure society’s health. Objectives: The goal of the conventional content analysis is to explain the dominant experienced-based behavior of the head nurses in clinical wards. Materials and Methods: This study was conducted by applying a quality study approach with a common content analysis model (Granheim and Lundmen). The participants were 25 head nurses who were working in the wards of various hospitals in Zahedan City. They were selected via the purposeful sampling method. The data were collected thoroughly and continued until a saturation stage was reached. Results: The result of data analysis was the theme “turbulent atmosphere-based management,” which consists of five categories as follows: the work culture of the ward, job burnout, negligent evaluation, job conflict, and decision making with limited effects. Conclusions: The analysis of the findings of the present study through considering the defined categories demonstrated that, to modify and correct the turbulent atmosphere-based management, several important measures are required and need to be continually monitored. PMID:27186386
NASA Astrophysics Data System (ADS)
Ostashev, Vladimir E.; Collier, Sandra L.; Keith Wilson, D.
Using the narrow-angle and Markov approximations, a formula for the transverse-longitudinal coherence function of a sound field propagating in a turbulent atmosphere with temperature and wind velocity fluctuations is derived. This function, which applies to observation points that are arbitrarily located in space, generalizes the transverse coherence function (coherence when the observation points are in a plane perpendicular to the sound propagation path), which has been studied extensively. The new result is expressed in terms of the transverse coherence function and the extinction coefficient of the mean sound field. The transverse-longitudinal coherence function of a plane sound wave is then calculated and studied in detail for the Gaussian and von Kármán spectra of temperature and wind velocity fluctuations. It is shown, for relatively small propagation distances, that the magnitude of the coherence function decreases in the longitudinal direction but remains almost constant in the transverse direction. On the other hand, for moderate and large propagation distances, the magnitude of the coherence decreases faster in the transverse direction than in the longitudinal. For some parameters of the problem, the coherence function has relatively large local maxima and minima as the transverse and longitudinal coordinates are varied. With small modifications, many results obtained in the paper can be applied to studies of electromagnetic wave propagation in a turbulent atmosphere.
Reynolds, Kate V.; Thomas, Adrian L. R.; Taylor, Graham K.
2014-01-01
Turbulent atmospheric conditions represent a challenge to stable flight in soaring birds, which are often seen to drop their wings in a transient motion that we call a tuck. Here, we investigate the mechanics, occurrence and causation of wing tucking in a captive steppe eagle Aquila nipalensis, using ground-based video and onboard inertial instrumentation. Statistical analysis of 2594 tucks, identified automatically from 45 flights, reveals that wing tucks occur more frequently under conditions of higher atmospheric turbulence. Furthermore, wing tucks are usually preceded by transient increases in airspeed, load factor and pitch rate, consistent with the bird encountering a headwind gust. The tuck itself immediately follows a rapid drop in angle of attack, caused by a downdraft or nose-down pitch motion, which produces a rapid drop in load factor. Positive aerodynamic loading acts to elevate the wings, and the resulting aerodynamic moment must therefore be balanced in soaring by an opposing musculoskeletal moment. Wing tucking presumably occurs when the reduction in the aerodynamic moment caused by a drop in load factor is not met by an equivalent reduction in the applied musculoskeletal moment. We conclude that wing tucks represent a gust response precipitated by a transient drop in aerodynamic loading. PMID:25320064
Turbulence and chemistry in the atmosphere of a central Amazonian forest
NASA Astrophysics Data System (ADS)
Fuentes, J. D.; Chamecki, M.; Gerken, T.; Nascimento dos Santos, R. M.; Stoy, P. C.; Trowbridge, A.; Tota, J.; Katul, G. G.; Manzi, A. O.; Jardine, A.; Jardine, K.; Chambers, J. Q.
2014-12-01
This presentation provides an overview of a field project in the rainforest of the Brazilian Amazon region conducted during April to July 2014. Objectives were to investigate turbulent transport and chemical processing of vegetation emitted gases to assess the role of the forest in aerosol production. Turbulence within and above the 35-m forest was investigated with 10 sonic anemometers deployed on a 50-m tower. Temporal and spatial distribution of plant-emitted hydrocarbons, and reactive chemical species such as ozone, carbon monoxide, sulfur dioxide, and nitrogen oxides were determined using gas analyzers and mass spectrometers to estimate aerosol yields from hydrocarbon photo-oxidation. Particle sizes and concentrations were investigated with aerosol spectrometers. The upper canopy experienced strong turbulence, with standard deviation of vertical velocity normalized by the friction velocity similar to values above the forest. The lower canopy maintained a quiescent state with turbulence being four times weaker than near the canopy top. Such weak turbulent state is conducive to the development of strong and pronounced hydrocarbon mixing ratio mean gradients within the canopy, with highest gas levels within the forest crown responding to strong emissions. The forest emitted monoterpenes, resulting in a total sum exceeding one parts per billion (ppb). Ozone levels ranged from 5 to 10 ppb. Such low ozone mixing ratios can be attributed to the frequent presence of clouds and precipitation. However, following the passage of mesoscale convective storms, ozone levels abruptly increased in response to downward transport from aloft and reached maximum levels of 30 ppb. Photochemical process remained suppressed and resulted in low particle concentrations (<104 particles cm-3), dominated by small diameter (< 400 nanometers) particles. Oxidants remained at sufficient levels to allow reactions of the locally produced hydrocarbons to generate particles. One conclusion is that
NASA Astrophysics Data System (ADS)
Ličer, Matjaž; Smerkol, Peter; Fettich, Anja; Ravdas, Michalis; Papapostolou, Alexandros; Mantziafou, Anneta; Strajnar, Benedikt; Cedilnik, Jure; Jeromel, Maja; Jerman, Jure; Petan, Sašo; Benetazzo, Alvise; Carniel, Sandro; Malačič, Vlado; Sofianos, Sarantis
2016-04-01
We have studied the performances of (a) a two-way coupled atmosphere-ocean modeling system and (b) one-way coupled ocean model (forced by the atmosphere model), as compared to the available in situ measurements during and after a strong Adriatic Bora wind event in February 2012, which led to extreme air-sea interactions. The simulations span the period between January and March 2012. The models used were ALADIN (4.4 km resolution) on the atmosphere side and Adriatic setup of POM (1°/30 × 1°/30 angular resolution) on the ocean side. The atmosphere-ocean coupling was implemented using the OASIS3-MCT model coupling toolkit. Two-way coupling ocean feedback to the atmosphere is limited to sea surface temperature. We have compared modeled atmosphere-ocean fluxes (computed using modified Louis scheme) and sea temperatures from both setups to platform and CTD measurements of fluxes (computed using COARE scheme) and temperatures from three observational platforms (Vida, Paloma, Acqua Alta) in the Northern Adriatic. We show that turbulent fluxes from both setups differ up to 20% during the Bora but not significantly before and after the event. The impact of the coupling on the ocean is significant while the impact on the atmosphere is less pronounced. When compared to observations, two way coupling ocean temperatures exhibit a four times lower RMSE than those from one-way coupled system. Two-way coupling improves sensible heat fluxes at all stations but does not improve latent heat loss.
NASA Astrophysics Data System (ADS)
Bashkin, A. S.; Beznozdrev, V. N.; Pirogov, N. A.
2003-01-01
A simplified model of the propagation of intense laser beams in the turbulent Earth's atmosphere along horizontal and oblique paths is improved. The model takes into account the basic mechanisms of interaction of laser radiation with the Earth's atmosphere (molecular absorption, aerosol extinction, turbulence-induced beam spread and wander). The application of this model demonstrates a general approach to determining the optimal radiation wavelengths for attaining the maximum intensity of focused laser radiation at a stationary object depending on the path length, angle of the path inclination, weather conditions, and diameter of the laser output beam. A simple physical interpretation of the dependences obtained is presented. The efficiencies of propagation of various high-power laser beams through the turbulent Earth's atmosphere are compared. Specific features of the energy transfer from various lasers to moving objects are analysed. It is shown that, when weather conditions change over a wide range, it is expedient to use radiation from a cw chemical DF laser.
NASA Astrophysics Data System (ADS)
Hicks, Micheal M.
A comprehensive analysis of surface-atmosphere flux exchanges over a mixed rural and urban convective environment is conducted at Howard University Beltsville, MD Research Campus. This heterogeneous site consists of rural, suburban and industrial surface covers to its south, east and west, within a 2 km radius of a flux sensor. The eddy covariance method is utilized to estimate surface-atmosphere flux exchanges of momentum, heat and moisture. The attributes of these surface flux exchanges are contrasted to those of classical homogeneous sites and assessed for accuracy, to evaluate the following: (I) their similarity to conventional convective boundary layer (CBL) processes and (II) their representativeness of the surrounding environment's turbulent properties. Both evaluations are performed as a function of upwind surface conditions. In particular, the flux estimates' obedience to spectrum power laws and similarity theory relationships is used for performing the first evaluation, and their ability to close the surface energy balance and accurately model CBL heights is used for the latter. An algorithm that estimates atmospheric boundary layer heights from observed lidar extinction backscatter was developed, tested and applied in this study. The derived lidar based CBL heights compared well with those derived from balloon borne soundings, with an overall Pearson correlation coefficient and standard deviation of 0.85 and 223 m, respectively. This algorithm assisted in the evaluation of the response of CBL processes to surface heterogeneity, by deriving high temporal CBL heights and using them as independent references of the surrounding area averaged sensible heat fluxes. This study found that the heterogeneous site under evaluation was rougher than classical homogeneous sites, with slower dissipation rates of turbulent kinetic energy. Flux measurements downwind of the industrial complexes exhibited enhanced efficiency in surface-atmosphere momentum, heat, and
Veligdan, James T.
1993-01-01
Atmospheric effects on sighting measurements are compensated for by adjusting any sighting measurements using a correction factor that does not depend on atmospheric state conditions such as temperature, pressure, density or turbulence. The correction factor is accurately determined using a precisely measured physical separation between two color components of a light beam (or beams) that has been generated using either a two-color laser or two lasers that project different colored beams. The physical separation is precisely measured by fixing the position of a short beam pulse and measuring the physical separation between the two fixed-in-position components of the beam. This precisely measured physical separation is then used in a relationship that includes the indexes of refraction for each of the two colors of the laser beam in the atmosphere through which the beam is projected, thereby to determine the absolute displacement of one wavelength component of the laser beam from a straight line of sight for that projected component of the beam. This absolute displacement is useful to correct optical measurements, such as those developed in surveying measurements that are made in a test area that includes the same dispersion effects of the atmosphere on the optical measurements. The means and method of the invention are suitable for use with either single-ended systems or a double-ended systems.
NASA Astrophysics Data System (ADS)
Christen, A.; Oldroyd, H. J.; Diebold, M.; Huwald, H.; Parlange, M. B.
2013-12-01
Land surfaces with a low thermal admittance, such as snow, experience fluctuations in their surface temperature (Ts) not only due to the diurnal course of the energy balance, but also on much shorter time-scales as the consequence of turbulent heat exchange between the surface and the atmospheric surface layer. High-frequency fluctuations in Ts, as reported for selected land-surfaces in the literature, are the imprint of coherent turbulent structures transporting heat away or towards the surface in the atmospheric surface layer. Our hypothesis is that spatially coherent perturbations in Ts on a snowpack can be mapped using time-sequential thermography (TST) - time series of thermal images sampled using state-of-the-art thermal cameras. The low thermal admittance of fresh snow implies that snow should respond with higher amplitudes in Ts to atmospheric forcing than many other land-surfaces, where fluctuations in Ts can be below the radiometric resolution of common thermal camera systems. On February 13 and 14, 2013 we operated an uncooled thermal camera (A320, FLIR, Wilsonville, OR, USA) over a snow covered glacier (';Glacier de la Plaine Morte', 46°22'37"N, 7°29'16" E, 2720 m a.s.l.). The thermal camera was mounted on a short 3 m mast to provide an oblique view of a uniform and flat part of the glacier upstream of the tower, with a filed of view (FOV) of 25 x 19° at 320 x 240 pixel resolution. Thermal images of the apparent surface temperature were acquired with ~5Hz and complemented by 20 Hz measurements of the atmospheric flow with three ultrasonic anemometer-thermometers (CSAT-3, CSI, Logan, UT, USA), of which one was installed in the FOV of the thermal camera. During the measurement campaign, the atmospheric surface layer was stably stratified (clear skies, air temperatures -15 to -10°C), and Ts ranged between -21 and -10°C. The snow-surface exhibited quite large fluctuations in Ts up to ×3 K over short time (within ~10-30 seconds). The extracted spatio
Chen, Chunyi; Yang, Huamin; Tong, Shoufeng; Lou, Yan
2015-09-21
The mean-square angle-of-arrival (AOA) difference between two counter-propagating spherical waves in atmospheric turbulence is theoretically formulated. Closed-form expressions for the path weighting functions are obtained. It is found that the diffraction and refraction effects of turbulent cells make negative and positive contributions to the mean-square AOA difference, respectively, and the turbulent cells located at the midpoint of the propagation path have no contributions to the mean-square AOA difference. If the mean-square AOA difference is separated into the refraction and diffraction parts, the refraction part always dominates the diffraction one, and the ratio of the diffraction part to the refraction one is never larger than 0.5 for any turbulence spectrum. Based on the expressions for the mean-square AOA difference, formulae for the correlation coefficient between the angles of arrival of two counter-propagating spherical waves in atmospheric turbulence are derived. Numerical calculations are carried out by considering that the turbulence spectrum has no path dependence. It is shown that the mean-square AOA difference always approximates to the variance of AOA fluctuations. It is found that the correlation coefficient between the angles of arrival in the x or y direction of two counter-propagating spherical waves ranges from 0.46 to 0.5, implying that the instantaneous angles of arrival of two counter-propagating spherical waves in atmospheric turbulence are far from being perfectly correlated even when the turbulence spectrum does not vary along the path. PMID:26406667
NASA Astrophysics Data System (ADS)
Yan, Xiang; Zhang, Peng-Fei; Zhang, Jing-Hui; Qiao, Chun-Hong; Fan, Cheng-Yu
2016-08-01
Non-classical polarization properties of dark hollow beams propagating through non-Kolmogorov turbulence are studied. The analytic equation for the polarization degree of the quantization partially coherent dark hollow beams is obtained. It is found that the polarization fluctuations of the quantization partially coherent dark hollow beams are dependent on the turbulence factors and beam parameters with the detection photon numbers. Furthermore, an investigation of the changes in the on-axis propagation point and off-axis propagation point shows that the polarization degree of the quantization partially coherent dark hollow beams presents oscillation for a short propagation distance and gradually returns to zero for a sufficiently long distance. Project supported by the Major Research Plan of the National Natural Science Foundation of China (Grant No. 61405205).
NASA Technical Reports Server (NTRS)
Hocking, W. K.
1983-01-01
A theory is developed for the extraction of r.m.s. velocities of scatterer motions from spectra measured with a Doppler backscatter radar. The effects of finite beam-widths, finite pulse lengths, beam broadening, shear broadening, and the other such spectral contaminants are considered. It is shown that these contaminants can play a major role in determining the measured spectral widths (and, equivalently, the signal fading time), and so must be properly considered if the spectral widths are to be used to extract the r.m.s. motions of the scatterers. It is also shown that these r.m.s. motions can be used to estimate turbulence intensities, in those cases where turbulence is the dominant cause of the scatterer motions.
NASA Technical Reports Server (NTRS)
Chan, Kin P.; Killinger, Dennis K.
1992-01-01
Calculations of the integrated effect of atmospheric refractive turbulence on 1-, 2-, and 10-micron coherent lidar performance are presented for a series of different lidar propagation geometries. The effective lidar receiver telescope diameter is evaluated for each case. The results indicate that atmospheric turbulence should not be a significant factor in the performance of a downward-looking high-altitude or satellite-borne coherent lidar system. It is also shown that ground-based 1-2-micron coherent lidars may be limited in their useful telescope aperture, especially for horizontal or nearly horizontal path measurements near the ground.
NASA Technical Reports Server (NTRS)
DeCroix, David; Lin, Yuh-Lang; Arya, S. Pal; Kao, C.-T.; Shen, S.
1997-01-01
The vortices produced by an aircraft in flight are a complex phenomena created from a 'sheet of vorticity' leaving the trailing edge of the aircraft surfaces. This sheet tends to roll-up into two counter-rotating vortices. After a few spans downstream of the aircraft, the roll-up process is complete and the vortex pair may be characterized in a simple manner for modeling purposes. Our research will focus on what happens to these post roll-up vortices in the vicinity of an airport terminal. As the aircraft wake vortices descend, they are transported by the air mass which they are embedded and are decayed by both internal and external processes. In the vicinity of the airport, these external influences are usually due to planetary boundary layer (PBL) turbulence. Using large-eddy simulation (LES), one may simulate a variety of PBL conditions. In the LES method, turbulence is generated in the PBL as a response to surface heat flux, horizontal pressure gradient, wind shear, and/or stratification, and may produce convective or unstably stratified, neutral, or stably stratified PBL's. Each of these PBL types can occur during a typical diurnal cycle of the PBL. Thus it is important to be able to characterize these conditions with the LES method. Once this turbulent environment has been generated, a vortex pair will be introduced and the interactions are observed. The objective is to be able to quantify the PBL turbulence vortex interaction and be able to draw some conclusions of vortex behavior from the various scale interactions. This research is ongoing, and we will focus on what has been accomplished to date and the future direction of this research. We will discuss the model being used, show results that validate its use in the PBL, and present a nested-grid method proposed to analyze the entire PBL and vortex pair simultaneously.
Venusian atmospheric turbulence evaluated from cloud brightness distribution in VEX UV images
NASA Astrophysics Data System (ADS)
Teraguchi, T.; Kasaba, Y.; Hoshino, N.; Sato, T. M.; Takahashi, Y.; Watanabe, S.; Yamada, M.; Matsuda, Y.; Kouyama, T.; Titov, D.; Markiewicz, W.
2011-10-01
This study suggested following points: (1) The power spectra mostly contained the inflection. The slope at lower wavenumbers was steeper than that at higher wavenumbers. Such a feature agrees with the characteristics in the kinetic energy spectra shon Earth (Nastrom et al., 1984; Nastrom and Gage, 1985). (2) The slopes at planetary wavenumbers K < 50 (0.001 /km at the latitude of 20S) had intermediate value between the theoretical ones, -3 and -5/3. It agrees well with the previous Venusian studies (e.g. Peralta et al., 2007). This feature was common over three years. (3) We first derived the slope at higher wavenumbers, 0.002 - 0.01 /km, which was due to the high spatial resolution of VMC. However, it was sometimes close to 0, which might be affected by instrumental noise. We are doing further checks. (4) We found some temporal and spatial changes of the slopes in short interval as several hours. This result also suggests that the PSD slope has a large variability in the individual latitude. (5) The wavenumbers at the inflection point were 0.001 - 0.003 /km. Kitamura and Matsuda (2006) suggested that the inflection point at 330 - 1000km can be a border between 2D and 3D turbulences. Our result indicates a possibility to have enstrophy forward cascade in 2D turbulence at lower wavenumbers and the energy forward cascade in 3D turbulence at higher wavenumbers.
NASA Astrophysics Data System (ADS)
Yang, Hu; Liu, Jiping; Lohmann, Gerrit; Shi, Xiaoxu; Hu, Yongyun; Chen, Xueen
2016-03-01
Three prominent features of ocean surface turbulent heat fluxes (THF) trends during 1958-2013 are identified based on the Objectively Analyzed air-sea Fluxes (OAFlux) data set. The associated ocean-atmosphere dynamics changes are further investigated based on the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis. First, the THF are enhanced over the mid-latitude expansions of the subtropical western boundary currents (WBCs). An intensified oceanic heat transport, forced by stronger near-surface zonal wind, is likely to be the cause of such THF tendency. Second, the THF are reduced over the tropical eastern Pacific Ocean, which is primarily caused by the decreasing near-surface wind speed and sea surface temperature (SST), associated with a local coupled ocean-atmosphere cooling mode. Finally, the THF are reduced over the northern tropical Atlantic Ocean, which is attributed to the decreasing air-sea humidity and temperature differences as a result of the convergence of near-surface air and the divergence of ocean currents (upwelling).
NASA Astrophysics Data System (ADS)
Brugger, Peter; Träumner, Katja; Stawiarski, Christina
2016-04-01
Doppler LIDARs have a systematic bias in measurements of the turbulent wind field, which leads to a turbulence reduction in Doppler LIDAR measurements. The bias is caused by the spatial extend of the laser pulse and the sampling frequency of the backscattered light from the atmosphere. This error is an inherent effect of the Doppler LIDAR measurement principle and becomes especially important for powerful Doppler LIDARs with a large range, which are most useful for dual or triple Doppler LIDAR measurements of virtual towers. In case of our Wind Tracer system from Lockheed Martin Coherent Technology the bias without any corrections for the variance of the turbulent velocity fluctuations was 47% in comparison of time series with an ultrasonic anemometer. A theoretical analysis of this bias was done by Frehlich (1997) and a correction procedure was developed by Frehlich and Cornman (2002). Although the correction procedure was already used on data from field experiments, a validation by a high frequency in-situ measurement near a range gate center of a Doppler LIDAR was still missing. We show a comparison of turbulent velocity fluctuation variances and the outer scales of turbulence from an ultrasonic anemometer with those from our Doppler LIDAR to validate the correction procedure. The correction procedure could reduce the bias of the velocity variance by 29% and for the outer scale of turbulence by 43%. Both turbulence parameters had a remaining bias, which could not be explained.
NASA Astrophysics Data System (ADS)
Prabu, K.; Kumar, D. Sriram
2015-05-01
An optical wireless communication system is an alternative to radio frequency communication, but atmospheric turbulence induced fading and misalignment fading are the main impairments affecting an optical signal when propagating through the turbulence channel. The resultant of misalignment fading is the pointing errors, it degrades the bit error rate (BER) performance of the free space optics (FSO) system. In this paper, we study the BER performance of the multiple-input multiple-output (MIMO) FSO system employing coherent binary polarization shift keying (BPOLSK) in gamma-gamma (G-G) channel with pointing errors. The BER performance of the BPOLSK based MIMO FSO system is compared with the single-input single-output (SISO) system. Also, the average BER performance of the systems is analyzed and compared with and without pointing errors. A novel closed form expressions of BER are derived for MIMO FSO system with maximal ratio combining (MRC) and equal gain combining (EGC) diversity techniques. The analytical results show that the pointing errors can severely degrade the performance of the system.
NASA Astrophysics Data System (ADS)
Sun, Kang; Li, Dan; Tao, Lei; Zhao, Zhongkuo; Zondlo, Mark A.
2015-10-01
The influence of random errors in turbulence measurements on scalar similarity for temperature, water vapour, , and is investigated using two eddy-covariance datasets collected over a lake and a cattle feedlot. Three measures of scalar similarity, namely, the similarity constant in the flux-variance relationship, the correlation coefficient between two scalars and the relative transport efficiency, are examined. The uncertainty in the similarity constant in the flux-variance relationship resulting from random errors in turbulence measurements is quantified based on error propagation analyses and a Monte-Carlo sampling method, which yields a distribution instead of a single value for . For different scalars, the distributions of are found to significantly overlap, implying that scalars are transported similarly under strongly unstable conditions. The random errors in the correlation coefficients between scalars and the relative transport efficiencies are also quantified through error propagation analyses, and they increase as the atmosphere departs from neutral conditions. Furthermore, the correlation coefficients between three scalars (water vapour, , and ) are statistically different from unity while the relative transport efficiencies are not, which highlights the difference between these two measures of scalar similarity. The results suggest that uncertainties in these measures of scalar similarity need to be quantified when using them to diagnose the existence of dissimilarity among different scalars.
NASA Astrophysics Data System (ADS)
Golmohammady, Sh; Ghafary, B.
2016-06-01
In this study, generalized Stokes parameters of a phase-locked partially coherent flat-topped array beam based on the extended Huygens–Fresnel principle and the unified theory of coherence and polarization have been reported. Analytical formulas for 2 × 2 cross-spectral density matrix elements, and consequently Stokes parameters of a phase-locked partially coherent flat-topped array beam propagating through the turbulent atmosphere have been formulated. Effects of many physical attributes such as wavelength, turbulence strength, flatness order and other source parameters on the Stokes parameters, and therefore spectral degree of polarization upon propagation have been studied thoroughly. The behaviour of the spectral degree of coherence of a delineated beam for different source conditions has been investigated. It can be shown that four generalized Stokes parameters increase by raising the flatness order at the same propagation distance. Increasing the number of beams leads to a decrease in the Stokes parameters to zero slowly. The results are of utmost importance for optical communications.
Turbulent Helicity and Potential Vorticity in Lower 25 meters of Atmosphere
NASA Astrophysics Data System (ADS)
Koprov, B.; Koprov, V.; Kurganskiy, M. V.; Chkhetiani, O.
2015-12-01
The measuring procedure developed and results obtained as related to turbulent flux of vorticity
NASA Technical Reports Server (NTRS)
Cliff, W. C.; Skarda, J. R.
1987-01-01
NASA's Airborne Doppler Lidar System has been used to obtain a detailed 'instantaneous' mapping of horizontal spatial wind fields at 600-800 m elevations on the east side of the San Gorgonio Pass in California, in the form of checkerboard-fashion horizontal wind vectors spaced at 300 m intervals along and normal to the flight path. Spatial autocorrelations for the lateral and longitudinal components are ensemble-averaged, and integral turbulent length scales are computed for the wind fields' longitudinal and lateral directions. The flow in the region studied does not appear to be isotropic.
NASA Technical Reports Server (NTRS)
Johnson, E. H.
1975-01-01
The optimal design was investigated of simple structures subjected to dynamic loads, with constraints on the structures' responses. Optimal designs were examined for one dimensional structures excited by harmonically oscillating loads, similar structures excited by white noise, and a wing in the presence of continuous atmospheric turbulence. The first has constraints on the maximum allowable stress while the last two place bounds on the probability of failure of the structure. Approximations were made to replace the time parameter with a frequency parameter. For the first problem, this involved the steady state response, and in the remaining cases, power spectral techniques were employed to find the root mean square values of the responses. Optimal solutions were found by using computer algorithms which combined finite elements methods with optimization techniques based on mathematical programming. It was found that the inertial loads for these dynamic problems result in optimal structures that are radically different from those obtained for structures loaded statically by forces of comparable magnitude.
NASA Astrophysics Data System (ADS)
Sun, Xiaole; Djordjevic, Ivan B.; Neifeld, Mark A.
2016-03-01
Free-space optical (FSO) channels can be characterized by random power fluctuations due to atmospheric turbulence, which is known as scintillation. Weak coherent source based FSO quantum key distribution (QKD) systems suffer from the scintillation effect because during the deep channel fading the expected detection rate drops, which then gives an eavesdropper opportunity to get additional information about protocol by performing photon number splitting (PNS) attack and blocking single-photon pulses without changing QBER. To overcome this problem, in this paper, we study a large-alphabet QKD protocol, which is achieved by using pulse-position modulation (PPM)-like approach that utilizes the time-frequency uncertainty relation of the weak coherent photon state, called here TF-PPM-QKD protocol. We first complete finite size analysis for TF-PPM-QKD protocol to give practical bounds against non-negligible statistical fluctuation due to finite resources in practical implementations. The impact of scintillation under strong atmospheric turbulence regime is studied then. To overcome the secure key rate performance degradation of TF-PPM-QKD caused by scintillation, we propose an adaptation method for compensating the scintillation impact. By changing source intensity according to the channel state information (CSI), obtained by classical channel, the adaptation method improves the performance of QKD system with respect to the secret key rate. The CSI of a time-varying channel can be predicted using stochastic models, such as autoregressive (AR) models. Based on the channel state predictions, we change the source intensity to the optimal value to achieve a higher secret key rate. We demonstrate that the improvement of the adaptation method is dependent on the prediction accuracy.
NASA Astrophysics Data System (ADS)
Elperin, T.; Kleeorin, N.; Krasovitov, B.; Kulmala, M.; Liberman, M.; Rogachevskii, I.; Zilitinkevich, S.
2015-07-01
Condensation of water vapor on active cloud condensation nuclei produces micron-size water droplets. To form rain, they must grow rapidly into at least 50- to 100 -μ m droplets. Observations show that this process takes only 15-20 min. The unexplained physical mechanism of such fast growth is crucial for understanding and modeling of rain and known as "condensation-coalescence bottleneck in rain formation." We show that the recently discovered phenomenon of the tangling clustering instability of small droplets in temperature-stratified turbulence [Phys. Fluids 25, 085104 (2013), 10.1063/1.4816643] results in the formation of droplet clusters with drastically increased droplet number densities. The mechanism of the tangling clustering instability is much more effective than the previously considered by us the inertial clustering instability caused by the centrifugal effect of turbulent vortices. This is the reason of strong enhancement of the collision-coalescence rate inside the clusters. The mean-field theory of the droplet growth developed in this study can be useful for explanation of the observed fast growth of cloud droplets in warm clouds from the initial 1 -μ m -size droplets to 40- to 50 -μ m -size droplets within 15-20 min.
Elperin, T; Kleeorin, N; Krasovitov, B; Kulmala, M; Liberman, M; Rogachevskii, I; Zilitinkevich, S
2015-07-01
Condensation of water vapor on active cloud condensation nuclei produces micron-size water droplets. To form rain, they must grow rapidly into at least 50- to 100-μm droplets. Observations show that this process takes only 15-20 min. The unexplained physical mechanism of such fast growth is crucial for understanding and modeling of rain and known as "condensation-coalescence bottleneck in rain formation." We show that the recently discovered phenomenon of the tangling clustering instability of small droplets in temperature-stratified turbulence [Phys. Fluids 25, 085104 (2013)] results in the formation of droplet clusters with drastically increased droplet number densities. The mechanism of the tangling clustering instability is much more effective than the previously considered by us the inertial clustering instability caused by the centrifugal effect of turbulent vortices. This is the reason of strong enhancement of the collision-coalescence rate inside the clusters. The mean-field theory of the droplet growth developed in this study can be useful for explanation of the observed fast growth of cloud droplets in warm clouds from the initial 1-μm-size droplets to 40- to 50-μm-size droplets within 15-20 min. PMID:26274274
Atmospheric turbulence remote sensing by cw and pulsed CO2 Doppler lidars
NASA Astrophysics Data System (ADS)
Kurochkin, Nikolay N.; Gordienko, Vyacheslav M.; Priezzhev, Alexander V.; Poutivski, Iouri Y.
1994-12-01
The theoretical basis for wind velocity field parameters' measurements using CW Doppler Lidars (DL) is outlined. The instant power spectrum of photocurrent is shown to be histogram of velocity projection field with a weight depending on Dl's parameters. A non-destructive long-range method is presented for measuring the structure constant of the wind velocity field. The essence of the method is (the constancy of the backscatter coefficient is assumed): the average square width of the DL photocurrent power spectrum is the averaged structure function of the wind velocity weighted with a function depending on the DL parameters, the measurement time and the average wind velocity. Consequently, it is proportional to velocity structure constant with a factor depending on the DL parameters, the measurement time, the average wind velocity, the internal and external scales of turbulence. At certain DL parameters and measurement time the factor is shown to be practically independent from the average wind velocity, the internal and external scales of turbulence, thus a priori estimate can be successfully used instead of their real values. The differences between structures of CW and pulsed DL signal are discussed. The described above method is applied for pulsed DL.
NASA Astrophysics Data System (ADS)
Cheng, A.; Xu, K.
2013-12-01
This presentation describes the implementation and testing of an advanced third-order turbulence closure, an intermediately-prognostic higher-order turbulence closure (IPHOC), into the Community Atmosphere Model version 5 (CAM5). The third-order turbulence closure introduces a joint double-Gaussian distribution of liquid water potential temperature, total water mixing ratio, and vertical velocity to represent the subgrid scale variations including skewed turbulence circulations. The distribution is inferred from the first-, second-, and third-order moments of the variables given above and is used to diagnose cloud fraction and grid-mean liquid water mixing ratio, as well as the buoyancy term and fourth-order terms in the equations describing the evolution of the second- and third-order moments. In addition, a diagnostic planetary boundary layer (PBL) height approach has been incorporated in IPHOC in order to resolve the strong inversion above PBL for the coarse general circulation model (GCM) vertical grid-spacing. The IPHOC replaces PBL, shallow convection, and cloud macrophysics parameterizations in CAM5. The coupling of CAM5 with IPHOC (CAM5-IP) represents a more unified treatment of boundary layer and shallow convective processes. Results from global climate simulations are presented and suggest that CAM5-IP can provide a better treatment of boundary layer clouds and processes when compared to CAM5. The global annual mean low cloud fraction and precipitation are compared among CAM5, CAM5-IP, and a multi-scale modeling framework model with IPHOC (MMF-IP). The low cloud amounts near the west coast of the subtropical continents are well produced in CAM5-IP and are more abundant than in other two models. The global mean liquid water path is the closest to the SSM/I observation. The cloud structures from CAM5-IP, represented by the cloud fraction and cloud water content at 15°S transect, compare well with the CloudSat/CALIPSO observations. The shallow cumulus
Nelson, D.H.; Petrin, R.R.; MacKerrow, E.P.; Schmitt, M.J.; Foy, B.R.; Koskelo, A.C.; McVey, B.D.; Quick, C.R.; Porch, W.M.; Tiee, J.J.; Fite, C.B.; Archuleta, F.A.; Whitehead, M.C.; Walters, D.L.
1999-03-23
The measurement sensitivity of CO{sub 2} differential absorption lidar (DIAL) can be affected by a number of different processes. We have previously developed a Huygens-Fresnel wave optics propagation code to simulate the effects of two of these process: effects caused by beam propagation through atmospheric optical turbulence and effects caused by reflective speckle. Atmospheric optical turbulence affects the beam distribution of energy and phase on target. These effects include beam spreading, beam wander and scintillation which can result in increased shot-to-shot signal noise. In addition, reflective speckle alone has been shown to have a major impact on the sensitivity of CO{sub 2} DIAL. However, in real DIAL systems it is a combination of these phenomena, the interaction of atmospheric optical turbulence and reflective speckle, that influences the results. In this work, we briefly review a description of our model including the limitations along with previous simulation s of individual effects. The performance of our modified code with respect to experimental measurements affected by atmospheric optical turbulence and reflective speckle is examined. The results of computer simulations are directly compared with lidar measurements and show good agreement. In addition, advanced studies have been performed to demonstrate the utility of our model in assessing the effects for different lidar geometries on RMS noise and correlation ''size'' in the receiver plane.
Nelson, D.; Petrin, R.; MacKerrow, E.; Schmitt, M.; Foy, B.; Koskelo, A.; McVey, B.; Quick, C.; Porch, W.; Fite, C.; Archuleta, F.; Whitehead, M.; Tiee, J.; Walters, D.
1999-04-01
The measurement sensitivity of CO{sub 2} differential absorption lidar (DIAL) can be affected by a number of different processes. The authors have previously developed a Huygens-Fresnel wave optics propagation code to simulate the effects of two of these processes: effects caused by beam propagation through atmospheric optical turbulence and effects caused by reflective speckle. Atmospheric optical turbulence affects the beam distribution of energy and phase on target. These effects include beam spreading, beam wander and scintillation which can result in increased shot-to-shot signal noise. In addition, reflective speckle alone has been shown to have a major impact on the sensitivity of CO{sub 2} DIAL. However, in real DIAL systems it is a combination of these phenomena, the interaction of atmospheric optical turbulence and reflective speckle, that influences the results. The performance of the modified code with respect to experimental measurements affected by atmospheric optical turbulence and reflective speckle is examined. The results of computer simulations are directly compared with lidar measurements. The limitations of the model are also discussed. In addition, studies have been performed to determine the importance of key parameters in the simulation. The results of these studies and their impact on the overall results will be presented.
NASA Astrophysics Data System (ADS)
Braendholt, Andreas; Steenberg Larsen, Klaus; Ibrom, Andreas; Pilegaard, Kim
2016-04-01
Precise quantification of the diurnal and seasonal variation of soil respiration (Rs) is crucial to correctly estimate annual soil carbon fluxes as well as to correctly interpret the response of Rs to biotic and abiotic factors on different time scale. In this study we found a systematic effect of low atmospheric turbulence on continuous hourly Rs measurements with closed chambers throughout one year in a temperate Danish beech forest. Using friction velocity (u⋆) measured at the site above the canopy, we filtered out chamber flux data measured at low atmospheric turbulence. The non-filtered data showed a clear diurnal pattern of Rs across all seasons with highest fluxes during night time suggesting an implausible negative temperature sensitivity of Rs. When filtering out data at low turbulence, the annually averaged diurnal pattern changed, such that the highest Rs fluxes were seen during day time, i.e. following the course of soil temperatures. This effect on the diurnal pattern was due to low turbulence primarily occurring during night time. We calculated different annual Rs budgets by filtering out fluxes for different levels of u⋆. The highest annual Rs budget was found when including all data and it decreased with an increasing u⋆ filter threshold. Our results show that Rs was overestimated at low atmospheric turbulence throughout the year and that this overestimation considerably biased the diurnal pattern of Rs and led to an overestimation of the annual Rs budget. Thus we recommend that that any analysis of the diurnal pattern of Rs must consider overestimation of Rs at low atmospheric turbulence, to yield unbiased diurnal patterns. This is crucial when investigating temperature responses and potential links between CO2 production and Rs on a short time scale, but also for correct estimation of annual Rs budgets. Acknowledgements: This study was funded by the free Danish Ministry for Research, Innovation and higher Education, the free Danish Research
Rasouli, Saifollah; Tavassoly, M Taghi
2006-11-15
There are several methods for measuring ground-level atmospheric turbulence parameters, such as the refractive index profile and its fluctuations, correlations of the fluctuations in space and time, and the atmospheric refractive-index structure constant. These methods are based mainly on the measurement of fluctuations in intensity and location of an image formed by light propagating in the turbulent atmosphere or the fluctuations in impinging points of narrow light beams traversing the ground-level atmosphere. Exploiting the moiré technique, we suggest a high-precision approach for determining fluctuaions in the angle of arrival. When a low-frequency grating (carrier grating) is installed at a suitable distance from a telescope, its image, practically, forms on the focal plane of the telescope objective. Superimposing a physical grating (probe grating) of the same pitch as the image grating on the image forms the moiré pattern. The atmospheric turbulence distorts the image grating. Processing the fluctuations of successive moiré fringes can yield the mentioned parameters across a rather large cross section of the atmosphere with high accuracy, because of the moiré technique's magnifying character and access to a large volume of data, and does so in a comparatively simple and reliable manner. PMID:17072395
NASA Astrophysics Data System (ADS)
Zhu, Ping; Wang, Yuting; Chen, Shuyi S.; Curcic, Milan; Gao, Cen
2016-01-01
Roll vortices in the atmospheric boundary layer (ABL) are important to oil operation and oil spill transport. This study investigates the impact of storm-induced sea surface temperature (SST) cooling on the roll vortices generated by the convective and dynamic instability in the ABL of Hurricane Isaac (2012) and the roll induced transport using hindcasting large eddy simulations (LESs) configured from the multiply nested Weather Research & Forecasting model. Two experiments are performed: one forced by the Unified Wave INterface - Coupled Model and the other with the SST replaced by the NCEP FNL analysis that does not include the storm-induced SST cooling. The simulations show that the roll vortices are the prevalent eddy circulations in the ABL of Isaac. The storm-induced SST cooling causes the ABL stability falls in a range that satisfies the empirical criterion of roll generation by dynamic instability, whereas the ABL stability without considering the storm-induced SST cooling meets the criterion of roll generation by convective instability. The ABL roll is skewed and the increase of convective instability enhances the skewness. Large convective instability leads to large vertical transport of heat and moisture; whereas the dominant dynamic instability results in large turbulent kinetic energy but relatively weak heat and moisture transport. This study suggests that failure to consider roll vortices or incorrect initiation of dynamic and convective instability of rolls in simulations may substantially affect the transport of momentum, energy, and pollutants in the ABL and the dispersion/advection of oil spill fume at the ocean surface.
Software-based mitigation of image degradation due to atmospheric turbulence
NASA Astrophysics Data System (ADS)
Huebner, Claudia S.; Scheifling, Corinne
2010-10-01
Motion-Compensated Averaging (MCA) with blind deconvolution has proven successful in mitigating turbulence effects like image dancing and blurring. In this paper an image quality control according to the "Lucky Imaging" principle is combined with the MCA-procedure, weighting good frames more heavily than bad ones, skipping a given percentage of extremely degraded frames entirely. To account for local isoplanatism, when image dancing will effect local displacements between consecutive frames rather than global shifts only, a locally operating MCA variant with block matching, proposed in earlier work, is employed. In order to reduce loss of detail due to normal averaging, various combinations of temporal mode, median and mean are tested as reference image. The respective restoration results by means of a weighted blind deconvolution algorithm are presented and evaluated.
NASA Technical Reports Server (NTRS)
Stothers, Richard B.
1989-01-01
The theory of turbulent plumes maintained above steady line sources of buoyancy is worked out in detail within the limitations of Taylor's entrainment assumption. It is applied to the structure of a pure plume injected into a stably stratified atmosphere. Volcanic basalt eruptions that develop from long, narrow vents create line source plumes, which rise well above the magmatic fire fountains playing near the ground level. The eruption of Laki in 1783 may provide an example of this style of eruption. Flood basalts are more ancient examples. Evidence of enormous fissure eruptions that occurred in the past on Mars and Venus also exists. Owing to the different properties of the atmospheres on these two planets from those on the earth, heights of line source plumes are expected to vary in the ratios 1:6:0.6 (earth:Mars:Venus). It is very unlikely that the observed increase of sulfur dioxide above the Venusian cloud deck in 1978 could have been due to a line source volcanic eruption, even if it had been a flood basalt eruption.
Correlation of velocity and velocity-density turbulence in the exhaust of an atmospheric burner
NASA Technical Reports Server (NTRS)
Fralick, Gustave C.
1985-01-01
In the experiment described herein, temperature (density) and velocity are measured separately but simultaneously as functions of time so that it is possible to determine the relationships among velocity, density, and the product of density and velocity. An atmospheric burner rig was used to provide the flow for the experiment.
Atmospheric Turbulence Measurements With the Automatic Mini UAV 'M2AV Carolo'
NASA Astrophysics Data System (ADS)
Bange, J.; van den Kroonenberg, A. C.; Spieß, T.; Buschmann, M.; Krüger, L.; Heindorf, A.; Vörsmann, P.
2007-05-01
The limitations of manned airborne meteorological measurements led to the development of an autonomously operating mini aircraft, the Meteorological Mini-UAV (M2AV), at the Institute of Aerospace Systems, Technical University of Braunschweig, Germany. The task was to develop, test and verify a meteorological sensor package as payload for an already available automatic carrier aircraft, the UAV 'Carolo T200', which operates autonomously i.e. without remote control. The M2AV is a self constructed model aircraft with two electrically powered engines and a wingspan of two meters. The maximum take-off weight is 4.5~kg (the M2AV is therefore classified as an model plane which simplifies authority issues), including 1.5~kg of payload. It is hand-launched which makes operation of the aircraft easy. With an endurance of approximately 50 minutes, the range accounts for 60 km at a cruising speed of 20~m/s. The M2AV is capable of performing turbulence measurements (wind vector, temperature and humidity) within the troposphere and offers an economic component during meteorological campaigns. The meteorological sensors are mounted on a noseboom to minimise the aircraft's influence on the measurements and to position the sensors closely to each other. Wind is measured via a small five-hole probe, an inertia measurement unit and GPS. The flight mission (waypoints, altitudes, airspeed) is planned and assigned to the aircraft before the semi- automatic launch. The flight is only controlled by the on-board autopilot system which only communicates with a ground station (laptop PC) for the exchange of measured data and command updates like new waypoints etc. The talk gives details on the technical items, calibration and first missions. Results from first field experiments like the LAUNCH-2005 campaign near Berlin are used for data quality assessment by comparison with simultaneous lidar and sodar measurements. An in situ comparison with the highly accurate helicopter-borne turbulence
NASA Astrophysics Data System (ADS)
Kaser, L.; Karl, T.; Yuan, B.; Mauldin, R. L.; Cantrell, C. A.; Guenther, A. B.; Patton, E. G.; Weinheimer, A. J.; Knote, C.; Orlando, J.; Emmons, L.; Apel, E.; Hornbrook, R.; Shertz, S.; Ullmann, K.; Hall, S.; Graus, M.; Gouw, J.; Zhou, X.; Ye, C.
2015-12-01
The hydroxyl radical (OH) is the most important oxidant in the atmosphere and the primary sink for isoprene, the dominant volatile organic compound emitted by vegetation. Recent research on the atmospheric oxidation capacity in isoprene-dominated environments has suggested missing radical sources leading to significant overestimation of the lifetime of isoprene. Here we report, for the first time, a comprehensive experimental budget of isoprene in the planetary boundary layer based on airborne flux measurements along with in situ OH observations in the Southeast and Central U.S. Our findings show that surface heterogeneity of isoprene emissions lead to a physical separation of isoprene and OH resulting in an effective slowdown in the chemistry. Depending on surface heterogeneity, the intensity of segregation (Is) could locally slow down isoprene chemistry up to 30%. The effect of segregated reactants in the planetary boundary layer on average has an influence on modeled OH radicals that is comparable to that of recently proposed radical recycling mechanisms.
The correlation of the displacements of the images of point sources in the turbulent atmosphere
NASA Astrophysics Data System (ADS)
Marakasov, Dmitri A.
2015-11-01
We consider the problem of determining of the transverse wind speed on atmospheric path from the temporal correlation of the displacements of the centroids of the images of point sources shifted in the transverse. In the framework of the first approximation of the method of small perturbations expressions for correlation functions are outlined. The possibility of estimation of the wind velocity averaged over the optical path is shown.
NASA Astrophysics Data System (ADS)
Zhang, Rongwang; Huang, Jian; Wang, Xin; Zhang, Jun A.; Huang, Fei
2016-06-01
Effects caused by precipitation on the measurements of three-dimensional sonic anemometer are analyzed based on a field observational experiment conducted in Maoming, Guangdong Province, China. Obvious fluctuations induced by precipitation are observed for the outputs of sonic anemometer-derived temperature and wind velocity components. A technique of turbulence spectra and cospectra normalized in the framework of similarity theory is utilized to validate the measured variables and calculated fluxes. It is found that the sensitivity of sonic anemometer-derived temperature to precipitation is significant, compared with that of the wind velocity components. The spectra of wind velocity and cospectra of momentum flux resemble the standard universal shape with the slopes of the spectra and cospectra at the inertial subrange, following the -2/3 and -4/3 power law, respectively, even under the condition of heavy rain. Contaminated by precipitation, however, the spectra of temperature and cospectra of sensible heat flux do not exhibit a universal shape and have obvious frequency loss at the inertial subrange. From the physical structure and working principle of sonic anemometer, a possible explanation is proposed to describe this difference, which is found to be related to the variations of precipitation particles. Corrections for errors of sonic anemometer-derived temperature under precipitation is needed, which is still under exploration.
Muñoz-Esparza, D.; Kosović, B.; Beeck, J. van; Mirocha, J.
2015-03-15
Despite the variety of existing methods, efficient generation of turbulent inflow conditions for large-eddy simulation (LES) models remains a challenging and active research area. Herein, we extend our previous research on the cell perturbation method, which uses a novel stochastic approach based upon finite amplitude perturbations of the potential temperature field applied within a region near the inflow boundaries of the LES domain [Muñoz-Esparza et al., “Bridging the transition from mesoscale to microscale turbulence in numerical weather prediction models,” Boundary-Layer Meteorol., 153, 409–440 (2014)]. The objective was twofold: (i) to identify the governing parameters of the method and their optimum values and (ii) to generalize the results over a broad range of atmospheric large-scale forcing conditions, U{sub g} = 5 − 25 m s{sup −1}, where U{sub g} is the geostrophic wind. We identified the perturbation Eckert number, Ec=U{sub g}{sup 2}/ρc{sub p}θ{sup ~}{sub pm}, to be the parameter governing the flow transition to turbulence in neutrally stratified boundary layers. Here, θ{sup ~}{sub pm} is the maximum perturbation amplitude applied, c{sub p} is the specific heat capacity at constant pressure, and ρ is the density. The optimal Eckert number was found for nonlinear perturbations allowed by Ec ≈ 0.16, which instigate formation of hairpin-like vortices that most rapidly transition to a developed turbulent state. Larger Ec numbers (linear small-amplitude perturbations) result in streaky structures requiring larger fetches to reach the quasi-equilibrium solution, while smaller Ec numbers lead to buoyancy dominated perturbations exhibiting difficulties for hairpin-like vortices to emerge. Cell perturbations with wavelengths within the inertial range of three-dimensional turbulence achieved identical quasi-equilibrium values of resolved turbulent kinetic energy, q, and Reynolds-shear stress,
Baker, K L; Stappaerts, E A; Gavel, D; Tucker, J; Silva, D A; Wilks, S C; Olivier, S S; Olsen, J
2004-08-25
An adaptive optical system used to correct horizontal beam propagation paths has been demonstrated. This system utilizes an interferometric wave-front sensor and a large-actuator-number MEMS-based spatial light modulator to correct the aberrations incurred by the beam after propagation along the path. Horizontal path correction presents a severe challenge to adaptive optics systems due to the short atmospheric transverse coherence length and the high degree of scintillation incurred by laser propagation along these paths. Unlike wave-front sensors that detect phase gradients, however, the interferometric wave-front sensor measures the wrapped phase directly. Because the system operates with nearly monochromatic light and uses a segmented spatial light modulator, it does not require that the phase be unwrapped to provide a correction and it also does not require a global reconstruction of the wave-front to determine the phase as required by gradient detecting wave-front sensors. As a result, issues with branch points are eliminated. Because the atmospheric probe beam is mixed with a large amplitude reference beam, it can be made to operate in a photon noise limited regime making its performance relatively unaffected by scintillation. The MEMS-based spatial light modulator in the system contains 1024 pixels and is controlled to speeds in excess of 800 Hz, enabling its use for correction of horizontal path beam propagation. In this article results are shown of both atmospheric characterization with the system and open loop horizontal path correction of a 1.53 micron laser by the system. To date Strehl ratios of greater than 0.5 have been achieved.
Ren, Yongxiong; Wang, Zhe; Xie, Guodong; Li, Long; Willner, Asher J; Cao, Yinwen; Zhao, Zhe; Yan, Yan; Ahmed, Nisar; Ashrafi, Nima; Ashrafi, Solyman; Bock, Robert; Tur, Moshe; Willner, Alan E
2016-06-01
We explore the mitigation of atmospheric turbulence effects for orbital angular momentum (OAM)-based free-space optical (FSO) communications with multiple-input multiple-output (MIMO) architecture. Such a system employs multiple spatially separated aperture elements at the transmitter/receiver, and each transmitter aperture contains multiplexed data-carrying OAM beams. We propose to use spatial diversity combined with MIMO equalization to mitigate both weak and strong turbulence distortions. In a 2×2 FSO link with each transmitter aperture containing two multiplexed OAM modes of ℓ=+1 and ℓ=+3, we experimentally show that at least two OAM data channels could be recovered under both weak and strong turbulence distortions using selection diversity assisted with MIMO equalization. PMID:27244375
NASA Astrophysics Data System (ADS)
Brilouet, Pierre-Etienne; Canut, Guylaine; Durand, Pierre
2015-04-01
During winter, the North Western Mediterranean Sea is characterised by intense air-sea exchanges linked to regional strong winds (Mistral or Tramontana) which bring cold and dry continental air over a warmer sea. The HyMeX-ASICS-MED field campaign, devoted to intense sea-atmosphere exchange and deep oceanic convection analysis took place in the Gulf of Lion during winter 2013. The French ATR42 aircraft was operated to document the mean and turbulent structure of the atmospheric boundary layer (ABL) during strong wind conditions. The aircraft was equipped to measure turbulence fluctuations, thus allowing the computation of turbulence parameters. The flight strategy consisted of stacked horizontal legs oriented along and across the wind direction, in order to obtain information about the isotropy of the turbulent field and about coherent structures. Strong wind events were documented with 11 flights during which latent heat flux up to 600 W.m-2 were observed. The structure of the turbulent field is analysed through the integral length scale and the wavelength of the spectrum peak of the vertical velocity which represent the size of the large and the most energetic eddies, respectively. It reveals a stretching of turbulent eddies along the mean wind. This kind of organized structures plays a major role by modulating the transfers inside the ABL. In particular, this non-isotropic behaviour alters the flux estimates from along-wind samples. This last point is critical because surface and entrainment fluxes, deduced from extrapolation of the flux profiles, are essential parameters to characterise the coupling between air-sea exchanges and the ABL structure.
NASA Astrophysics Data System (ADS)
Mukhartova, Juliya; Levashova, Natalia; Volkova, Elena; Olchev, Alexander
2016-04-01
vegetation and land-use types are situated far enough from the domain boundaries. It enabled us to assume that near these boundaries the values of vertical and horizontal wind components are independent on x coordinate. To quantify the possible effects of relief and vegetation heterogeneity on CO2 fluxes the three transects crossing the study area were chosen. For each transect the 2D patterns of wind speed components, turbulent exchange coefficients, CO2 concentrations and fluxes were calculated. The modeled vertical CO2 fluxes were compared with the fluxes calculated without allowing for turbulent disturbances due to relief and vegetation heterogeneity. All modeling experiments were provided for different weather conditions. The results of modeling experiments for different transects under various meteorological conditions showed that relief and vegetation heterogeneity have a significant impact on CO2 fluxes within the atmospheric surface layer and their ignoring can results in uncertainties in flux estimations. This study was supported by the Russian Science Foundation (Grant 14-14-00956).
R. L. Street; F. L. Ludwig; Y. Chen
2005-04-11
Our DOE project is one of the efforts comprising the Vertical Transport and Mixing Program of the Environmental Sciences Division of the Office of Biological and Environmental Research in Department of Energy. We used ARPS to simulate flow in the Salt Lake Valley. We simulated the physical processes more accurately so that we can better understand the physics of flow in complex terrain and its effects at larger scales. The simulations provided evidence that atmospheric forcing interacts with the Jordan Narrows, the Traverse Range and other complex mountain terrain at the south end of the Salt Lake Valley to produce lee rotors, hydraulic jumps and other effects. While we have successfully used ARPS to simulate VTMX 2000 flows, we have also used observed data to test the model and identify some of its weaknesses. Those are being addressed in a continuation project supported by DOE.
NASA Astrophysics Data System (ADS)
Mohamed, A.; Watkins, S.; Clothier, R.; Abdulrahim, M.; Massey, K.; Sabatini, R.
2014-11-01
Challenges associated with flight control of agile fixed-wing Micro Air Vehicles (MAVs) operating in complex environments is significantly different to any larger scale vehicle. The micro-scale of MAVs can make them particularly sensitive to atmospheric disturbances thus limiting their operation. As described in Part 1, current conventional reactive attitude sensing systems lack the necessary response times for attitude control in high turbulence environments. This paper reviews in greater detail novel and emerging biologically inspired sensors, which can sense the disturbances before a perturbation is induced. A number of biological mechanoreceptors used by flying animals are explored for their utility in MAVs. Man-made attempts of replicating mechanoreceptors have thus been reviewed. Bio-inspired flow and pressure-based sensors were found to be the most promising for complementing or replacing current inertial-based reactive attitude sensors. Achieving practical implementations that meet the size, weight and power constraints of MAVs remains a significant challenge. Biological systems were found to rely on multiple sensors, potentially implying a number of research opportunities in the exploration of heterogeneous bio-inspired sensing solutions.
NASA Astrophysics Data System (ADS)
Rodrigues, C. Veiga; Palma, J. M. L. M.; Rodrigues, Á. H.
2016-05-01
The atmospheric flow over a mountainous region has been simulated using a model-chain approach, whereby the flow in a larger region was simulated using a mesoscale model with three nesting levels, down to a 3-km horizontal resolution, within which a fourth nesting level was set with a microscale flow solver and a domain with varying horizontal resolution, around 300 m at the site of interest. Two periods in the summer (July) and autumn (November-December) 2005, each with a duration of two weeks, were selected to test the present approach. Two sites were chosen, comprising a total of seven meteorological masts with wind vanes and anemometers at two heights. The microscale solver improved the wind-speed prediction of the mesoscale model in 10 of the 14 anemometers and replicated the high wind speeds, which were under-predicted in the mesoscale model. The wind conditions in summer varied with the daily cycle, related to regional-scale sea breezes and their interaction with local circulations induced by the topography. Regarding the turbulence intensity, the predicted decay with wind-speed increase was in agreement with the measurements. This study shows the need of both models: the microscale model captures the details of the boundary-layer physics, which would not be possible without the boundary conditions provided by the mesoscale model.
Liu, Chao; Hu, Lifa; Mu, Quanquan; Cao, Zhaoliang; Xuan, Li
2011-01-01
We present an open-loop adaptive optics (AO) system based on two liquid-crystal spatial light modulators (LCSLMs) that profit from high precision wavefront generation and good repeatability. A wide optical bandwidth of 300 nm is designed for the system, and a new open-loop optical layout is invented to conveniently switch between the open and closed loop. The corresponding control algorithm is introduced with a loop frequency (the reciprocal of the total time delay of a correction loop) of 103 Hz. The system was mounted onto a 2.16 m telescope for vertical atmospheric turbulence correction. The full width at half-maximum of the image of the star α Boo reached 0.636 arc sec after the open-loop correction, while it was 2.12 arc sec before the correction. The result indicates that the open-loop AO system based on LCSLMs potentially has the ability to be used for general astronomical applications. PMID:21221164
NASA Astrophysics Data System (ADS)
Arrasmith, William W.; Sullivan, Sean F.
2008-04-01
Phase diversity imaging methods work well in removing atmospheric turbulence and some system effects from predominantly near-field imaging systems. However, phase diversity approaches can be computationally intensive and slow. We present a recently adapted, high-speed phase diversity method using a conventional, software-based neural network paradigm. This phase-diversity method has the advantage of eliminating many time consuming, computationally heavy calculations and directly estimates the optical transfer function from the entrance pupil phases or phase differences. Additionally, this method is more accurate than conventional Zernike-based, phase diversity approaches and lends itself to implementation on parallel software or hardware architectures. We use computer simulation to demonstrate how this high-speed, phase diverse imaging method can be implemented on a parallel, highspeed, neural network-based architecture-specifically the Cellular Neural Network (CNN). The CNN architecture was chosen as a representative, neural network-based processing environment because 1) the CNN can be implemented in 2-D or 3-D processing schemes, 2) it can be implemented in hardware or software, 3) recent 2-D implementations of CNN technology have shown a 3 orders of magnitude superiority in speed, area, or power over equivalent digital representations, and 4) a complete development environment exists. We also provide a short discussion on processing speed.
Raj, A Arockia Bazil; Selvi, J Arputha Vijaya; Kumar, D; Sivakumaran, N
2014-06-10
In free-space optical link (FSOL), atmospheric turbulence causes fluctuations in both intensity and phase of the received beam and impairing link performance. The beam motion is one of the main causes for major power loss. This paper presents an investigation on the performance of two types of controller designed for aiming a laser beam to be at a particular spot under dynamic disturbances. The multiple experiment observability nonlinear input-output data mapping is used as the principal components for controllers design. The first design is based on the Taguchi method while the second is artificial neural network method. These controllers process the beam location information from a static linear map of 2D plane: optoelectronic position detector, as observer, and then generate the necessary outputs to steer the beam with a microelectromechanical mirror: fast steering mirror. The beam centroid is computed using monopulse algorithm. Evidence of suitability and effectiveness of the proposed controllers are comprehensively assessed and quantitatively measured in terms of coefficient of correlation, correction speed, control exactness, centroid displacement, and stability of the receiver signal through the experimental results from the FSO link setup established for the horizontal range of 0.5 km at an altitude of 15.25 m. The test field type is open flat terrain, grass, and few isolated obstacles. PMID:24921147
NASA Astrophysics Data System (ADS)
Torres, Olivier; Braconnot, Pascale; Gainusa-Bogdan, Alina; Hourdin, Frédéric; Marti, Olivier; Pelletier, Charles
2016-04-01
The turbulent fluxes across the ocean/atmosphere interface represent one of the principal driving forces of the global atmospheric and oceanic circulation and are also responsible for various phenomena like the water supply to the atmospheric column, which itself is extremely important for atmospheric convection. Although the representation of these fluxes has been the subject of major studies, it still remains a very challenging problem. Our aim is to better understand the role of these fluxes in climate change experiments and in the equator-pole redistribution of heat and water by the oceanic and atmospheric circulation. For this, we are developing a methodology starting from idealized 1D experiments and going all the way up to fully coupled ocean-atmosphere simulations of past and future climates. The poster will propose a synthesis of different simulations we have performed with a 1D version of the LMDz atmosphere model towards a first objective of understanding how different parameterizations of the turbulent fluxes affect the moisture content of the atmosphere and the feedback with the atmospheric boundary layer and convection schemes. Air-sea fluxes are not directly resolved by the models because they are subgrid-scale phenomena and are therefore represented by parametrizations. We investigate the differences between several 1D simulations of the TOGA-COARE campaign (1992-1993, Pacific warm pool region), for which 1D boundary conditions and observations are available to test the results of atmospheric models. Each simulation considers a different version of the LMDz model in terms of bulk formula (four) used to compute the turbulent fluxes. We also consider how the representation of gustiness in these parameterizations affects the results. The use of this LMDz test case (very constrained within an idealized framework) allows us to determine how the response of surface fluxes helps to reinforce or damp the atmospheric water vapor content or cloud feedbacks
Thayer-Calder, K.; Gettelman, A.; Craig, C.; Goldhaber, S.; Bogenschutz, P. A.; Chen, C.-C.; Morrison, H.; Höft, J.; Raut, E.; Griffin, B. M.; et al
2015-06-30
Most global climate models parameterize separate cloud types using separate parameterizations. This approach has several disadvantages, including obscure interactions between parameterizations and inaccurate triggering of cumulus parameterizations. Alternatively, a unified cloud parameterization uses one equation set to represent all cloud types. Such cloud types include stratiform liquid and ice cloud, shallow convective cloud, and deep convective cloud. Vital to the success of a unified parameterization is a general interface between clouds and microphysics. One such interface involves drawing Monte Carlo samples of subgrid variability of temperature, water vapor, cloud liquid, and cloud ice, and feeding the sample points into amore » microphysics scheme. This study evaluates a unified cloud parameterization and a Monte Carlo microphysics interface that has been implemented in the Community Atmosphere Model (CAM) version 5.3. Results describing the mean climate and tropical variability from global simulations are presented. The new model shows a degradation in precipitation skill but improvements in short-wave cloud forcing, liquid water path, long-wave cloud forcing, precipitable water, and tropical wave simulation. Also presented are estimations of computational expense and investigation of sensitivity to number of subcolumns.« less
Thayer-Calder, K.; Gettelman, A.; Craig, C.; Goldhaber, S.; Bogenschutz, P. A.; Chen, C.-C.; Morrison, H.; Höft, J.; Raut, E.; Griffin, B. M.; et al
2015-12-01
Most global climate models parameterize separate cloud types using separate parameterizations. This approach has several disadvantages, including obscure interactions between parameterizations and inaccurate triggering of cumulus parameterizations. Alternatively, a unified cloud parameterization uses one equation set to represent all cloud types. Such cloud types include stratiform liquid and ice cloud, shallow convective cloud, and deep convective cloud. Vital to the success of a unified parameterization is a general interface between clouds and microphysics. One such interface involves drawing Monte Carlo samples of subgrid variability of temperature, water vapor, cloud liquid, and cloud ice, and feeding the sample points into amore » microphysics scheme. This study evaluates a unified cloud parameterization and a Monte Carlo microphysics interface that has been implemented in the Community Atmosphere Model (CAM) version 5.3. Model computational expense is estimated, and sensitivity to the number of subcolumns is investigated. Results describing the mean climate and tropical variability from global simulations are presented. The new model shows a degradation in precipitation skill but improvements in shortwave cloud forcing, liquid water path, long-wave cloud forcing, precipitable water, and tropical wave simulation.« less
NASA Technical Reports Server (NTRS)
Romanski, Joy; Hameed, Sultan
2015-01-01
Interannual variations of latent heat fluxes (LHF) and sensible heat fluxes (SHF) over the Mediterranean for the boreal winter season (DJF) show positive trends during 1958-2011. Using reanalysis and satellite-based products, the variability and trends in the heat fluxes are compared with variations in three atmospheric teleconnection patterns: the North Atlantic Oscillation (NAO), the pressure and position of the Azores High (AH), and the East Atlantic-West Russia teleconnection pattern (EAWR). Comparison of correlations between the heat fluxes and teleconnections, along with analysis of composites of surface temperature, humidity, and wind fields for different teleconnection states, demonstrates that the AH explains the heat flux changes more successfully than NAO and EAWR. Trends in pressure and longitude of the Azores High show a strengthening and an eastward shift. Variations of the Azores High occur along an axis defined by lower pressure and westward location at one extreme and higher pressure and eastward location at the other extreme. The shift of the AH from predominance of the low/west state to the high/east state induces trends in Mediterranean Sea surface winds, temperature, and moisture. These, combined with sea surface warming trends, produce trends in wintertime sensible and latent heat fluxes.
Thayer-Calder, Katherine; Gettelman, A.; Craig, Cheryl; Goldhaber, Steve; Bogenschutz, Peter; Chen, Chih-Chieh; Morrison, H.; Hoft, Jan; Raut, E.; Griffin, Brian M.; Weber, J. K.; Larson, Vincent E.; Wyant, M. C.; Wang, Minghuai; Guo, Zhun; Ghan, Steven J.
2015-12-01
Most global climate models parameterize separate cloud types using separate parameterizations.This approach has several disadvantages, including obscure interactions between parameterizations and inaccurate triggering of cumulus parameterizations. Alternatively, a unified cloud parameterization uses one equation set to represent all cloud types. Such cloud types include stratiform liquid and ice cloud, shallow convective cloud, and deep convective cloud. Vital to the success of a unified parameterization is a general interface between clouds and microphysics. One such interface involves drawing Monte Carlo samples of subgrid variability of temperature, water vapor, cloud liquid, and cloud ice, and feeding the sample points into a microphysics scheme. This study evaluates a unified cloud parameterization and a Monte Carlo microphysics interface that has been implemented in the Community Atmosphere Model (CAM) version 5.3. Results describing the mean climate and tropical variability from global simulations are presented. The new model shows a degradation in precipitation skill but improvements in short-wave cloud forcing, liquid water path, long-wave cloud forcing, perceptible water, and tropical wave simulation. Also presented are estimations of computational expense and investigation of sensitivity to number of subcolumns.
NASA Astrophysics Data System (ADS)
Thayer-Calder, K.; Gettelman, A.; Craig, C.; Goldhaber, S.; Bogenschutz, P. A.; Chen, C.-C.; Morrison, H.; Höft, J.; Raut, E.; Griffin, B. M.; Weber, J. K.; Larson, V. E.; Wyant, M. C.; Wang, M.; Guo, Z.; Ghan, S. J.
2015-12-01
Most global climate models parameterize separate cloud types using separate parameterizations. This approach has several disadvantages, including obscure interactions between parameterizations and inaccurate triggering of cumulus parameterizations. Alternatively, a unified cloud parameterization uses one equation set to represent all cloud types. Such cloud types include stratiform liquid and ice cloud, shallow convective cloud, and deep convective cloud. Vital to the success of a unified parameterization is a general interface between clouds and microphysics. One such interface involves drawing Monte Carlo samples of subgrid variability of temperature, water vapor, cloud liquid, and cloud ice, and feeding the sample points into a microphysics scheme. This study evaluates a unified cloud parameterization and a Monte Carlo microphysics interface that has been implemented in the Community Atmosphere Model (CAM) version 5.3. Model computational expense is estimated, and sensitivity to the number of subcolumns is investigated. Results describing the mean climate and tropical variability from global simulations are presented. The new model shows a degradation in precipitation skill but improvements in shortwave cloud forcing, liquid water path, long-wave cloud forcing, precipitable water, and tropical wave simulation.
NASA Astrophysics Data System (ADS)
Singh, Maneesh Kumar; Kapoor, Vinod
2011-10-01
Since last two decades free-space optical communication (FSO) has become more and more interesting as an alternative to radio frequency communication. This paper gives an overview of the power budget of an FSO system, designer has to consider while designing an FSO link. In this paper we have calculated the power needed for the transmission of a signal in free space. The received power and distance graph shows that more power needed when the link distances increases; also power and Bit Rate graph obtained at a distance 500 meter. In order to evaluate the power vs. Bit Rate graph we consider a link of distance 500 meter, optical window 1550 nm and three different atmospheric condition 10 dB/Km, 40 dB/Km and 60 dB/Km. The VCSEL laser is used for direct line of sight communication and at the receiver side the APD is used for power reception. The NRZ-OOK modulation format is used for laser beam modulation.
NASA Astrophysics Data System (ADS)
Thayer-Calder, K.; Gettelman, A.; Craig, C.; Goldhaber, S.; Bogenschutz, P. A.; Chen, C.-C.; Morrison, H.; Höft, J.; Raut, E.; Griffin, B. M.; Weber, J. K.; Larson, V. E.; Wyant, M. C.; Wang, M.; Guo, Z.; Ghan, S. J.
2015-06-01
Most global climate models parameterize separate cloud types using separate parameterizations. This approach has several disadvantages, including obscure interactions between parameterizations and inaccurate triggering of cumulus parameterizations. Alternatively, a unified cloud parameterization uses one equation set to represent all cloud types. Such cloud types include stratiform liquid and ice cloud, shallow convective cloud, and deep convective cloud. Vital to the success of a unified parameterization is a general interface between clouds and microphysics. One such interface involves drawing Monte Carlo samples of subgrid variability of temperature, water vapor, cloud liquid, and cloud ice, and feeding the sample points into a microphysics scheme. This study evaluates a unified cloud parameterization and a Monte Carlo microphysics interface that has been implemented in the Community Atmosphere Model (CAM) version 5.3. Results describing the mean climate and tropical variability from global simulations are presented. The new model shows a degradation in precipitation skill but improvements in short-wave cloud forcing, liquid water path, long-wave cloud forcing, precipitable water, and tropical wave simulation. Also presented are estimations of computational expense and investigation of sensitivity to number of subcolumns.
Geophysical and astrophysical turbulence
NASA Astrophysics Data System (ADS)
Moffatt, H. K.
Spiral structures in two-dimensional turbulence are studied and a theory (Moffatt, 1985, 1986) which regards fully three-dimensional turbulence as an agglomeration of 'random vortex sheets and coherent helical structures' is reviewed. Consideration is given to the process by which current-sheet discontinuities may appear during magnetic relaxation. Within the framework of dynamo theory, the determination of the generation coefficient and the turbulent diffusivity in mean-field electrodynamics for turbulence with helicity in the limit of a large magnetic Reynolds number is discussed. Certain features of 'chromospheric turbulence' (i.e., turbulence in the solar atmosphere outside the photosphere) are also examined.
NASA Astrophysics Data System (ADS)
Ding, Zhangwei; Ma, Yaoming; Wen, Zhiping; Ma, Weiqiang; Chen, Shiji
2016-03-01
Banana plantation and alpine meadow ecosystems in southern China and the Tibetan Plateau (TP) are unique in the underlying surfaces they exhibit. In this study, we used eddy covariance and a micrometeorological tower to examine the characteristics of land surface energy exchanges over a banana plantation in southern China and an alpine meadow in the Tibetan Plateau from May 2010 to August 2012. The results showed that the diurnal and seasonal variations in upward shortwave radiation flux and surface soil heat flux were larger over the alpine meadow than over the banana plantation surface. Dominant energy partitioning varied with season. Latent heat flux was the main consumer of net radiation flux in the growing season, whereas sensible heat flux was the main consumer during other periods. The Monin-Obukhov similarity theory was employed for comparative purposes, using sonic anemometer observations of flow over the surfaces of banana plantations in the humid southern China monsoon region and the semi-arid areas of the TP, and was found to be applicable. Over banana plantation and alpine meadow areas, the average surface albedo and surface aerodynamic roughness lengths under neutral atmospheric conditions were ˜0.128 and 0.47 m, and ˜0.223 and 0.01 m, respectively. During the measuring period, the mean annual bulk transfer coefficients for momentum and sensible heat were 1.47 × 10-2 and 7.13 × 10-3, and 2.91 × 10-3 and 1.96 × 10-3, for banana plantation and alpine meadow areas, respectively.
NASA Astrophysics Data System (ADS)
Ding, Zhangwei; Ma, Yaoming; Wen, Zhiping; Ma, Weiqiang
2016-04-01
Banana plantation and alpine meadow ecosystems in southern China and the Tibetan Plateau are unique in the underlying surfaces they exhibit. In this study, we used eddy covariance and a micrometeorological tower to examine the characteristics of land surface energy exchanges over a banana plantation in southern China and an alpine meadow in the Tibetan Plateau from May 2010 to August 2012. The results showed that the diurnal and seasonal variations in upward shortwave radiation flux and surface soil heat flux were larger over the alpine meadow than over the banana plantation surface. Dominant energy partitioning varied with season. Latent heat flux was the main consumer of net radiation flux in the growing season, whereas sensible heat flux was the main consumer during other periods. The Monin-Obukhov similarity theory was employed for comparative purposes, using sonic anemometer observations of flow over the surfaces of banana plantations in the humid southern China monsoon region and the semi-arid areas of the TP, and was found to be applicable. Over banana plantation and alpine meadow areas, the average surface albedo and surface aerodynamic roughness lengths under neutral atmospheric conditions were ~0.128 and 0.47m, and ~0.223 and 0.01m, respectively. During the measuring period, the mean annual bulk transfer coefficients for momentum and sensible heat were 1.47×10-2 and 7.13×10-3, and 2.91×10-3 and 1.96×10-3, for banana plantation and alpine meadow areas, respectively. This is the first time in Asia that long-term open field measurements have been taken with the specific aim of making comparisons between banana plantation and alpine meadow surfaces.
NASA Technical Reports Server (NTRS)
Tchen, C. M.
1986-01-01
Theoretical and numerical works in atmospheric turbulence have used the Navier-Stokes fluid equations exclusively for describing large-scale motions. Controversy over the existence of an average temperature gradient for the very large eddies in the atmosphere suggested that a new theoretical basis for describing large-scale turbulence was necessary. A new soliton formalism as a fluid analogue that generalizes the Schrodinger equation and the Zakharov equations has been developed. This formalism, processing all the nonlinearities including those from modulation provided by the density fluctuations and from convection due to the emission of finite sound waves by velocity fluctuations, treats large-scale turbulence as coalescing and colliding solitons. The new soliton system describes large-scale instabilities more explicitly than the Navier-Stokes system because it has a nonlinearity of the gradient type, while the Navier-Stokes has a nonlinearity of the non-gradient type. The forced Schrodinger equation for strong fluctuations describes the micro-hydrodynamical state of soliton turbulence and is valid for large-scale turbulence in fluids and plasmas where internal waves can interact with velocity fluctuations.
NASA Astrophysics Data System (ADS)
Madala, Srikanth; Satyanarayana A. N., V.; Srinivas C., V.; Boadh, Rahul; Pinaka Pani V. V. S., N.; Kumar, Manoj
2015-04-01
The complex terrain region of Patratu, Jharkhand in southern Chota Nagpur of eastern India has high air pollution problems besides complex mesoscale flow and meteorology. The FLEXPART-WRF mesoscale Lagrangian Particle dispersion model is used to simulate the dispersion of elevated effluent releases of nitrogen dioxide (NO2) and suspended particulate matter (SPM) from Patratu thermal power plant over Patratu at a high resolution of 1 km. The WRF is integrated with nested domains (27, 9, 3 km resolutions, 51 vertical levels). The relationships for turbulent intensities in the default diffusion parameterization of the Hanna scheme of FLEXPART is modified with new empirical relationships derived as a function of atmospheric stability from one year fast response turbulence measurements from a nearby observational site at Ranchi. The pollutant dispersion simulated by FLEXPART is evaluated with modified version of the model and using the WRF simulated atmospheric flow field and thermodynamical structure with three alternative PBL schemes [Yonsei University (YSU), Asymmetric Convective Model version 2 (ACM2) and Mellor- Yamada Nakanishi and Niino Level 2.5 PBL (MYNN2]. Results indicate that the new turbulence intensity relationships in FLEXPART provide better comparisons for concentrations of NO2 and SPM with available observations relative to the default relationships. Further, the meteorological parameters simulated using YSU significantly reduces the bias in modeled pollutant concentrations in terms of lesser mean absolute error (MAE), root mean square error (RMSE), normalized mean square error (NMSE), fractional bias (FB) and FAC2 (Factor of 2). These parametric tests enabled to fine tune and validate the FLEXPART-WRF dispersion model with YSU PBL physics and improved Hanna relationships to realistically simulate pollution dispersion over complex terrain of the study region. The study demonstrates the utility of high quality turbulence measurements in pollution
Tactical missile turbulence problems
NASA Technical Reports Server (NTRS)
Dickson, Richard E.
1987-01-01
Of particular interest is atmospheric turbulence in the atmospheric boundary layer, since this affects both the launch and terminal phase of flight, and the total flight for direct fire systems. Brief discussions are presented on rocket artillery boost wind problems, mean wind correction, turbulent boost wind correction, the Dynamically Aimed Free Flight Rocket (DAFFR) wind filter, the DAFFR test, and rocket wake turbulence problems. It is concluded that many of the turbulence problems of rockets and missiles are common to those of aircraft, such as structural loading and control system design. However, these problems have not been solved at this time.
NASA Astrophysics Data System (ADS)
Xia, Geng; Zhou, Liming; Freedman, Jeffrey M.; Roy, Somnath Baidya; Harris, Ronald A.; Cervarich, Matthew Charles
2016-04-01
Recent studies using satellite observations show that operational wind farms in west-central Texas increase local nighttime land surface temperature (LST) by 0.31-0.70 °C, but no noticeable impact is detected during daytime, and that the diurnal and seasonal variations in the magnitude of this warming are likely determined by those in the magnitude of wind speed. This paper further explores these findings by using the data from a year-long field campaign and nearby radiosonde observations to investigate how thermodynamic profiles and surface-atmosphere exchange processes work in tandem with the presence of wind farms to affect the local climate. Combined with satellite data analyses, we find that wind farm impacts on LST are predominantly determined by the relative ratio of turbulence kinetic energy (TKE) induced by the wind turbines compared to the background TKE. This ratio explains not only the day-night contrast of the wind farm impact and the warming magnitude of nighttime LST over the wind farms, but also most of the seasonal variations in the nighttime LST changes. These results indicate that the diurnal and seasonal variations in the turbine-induced turbulence relative to the background TKE play an essential role in determining those in the magnitude of LST changes over the wind farms. In addition, atmospheric stability determines the sign and strength of the net downward heat transport as well as the magnitude of the background TKE. The study highlights the need for better understanding of atmospheric boundary layer and wind farm interactions, and for better parameterizations of sub-grid scale turbulent mixing in numerical weather prediction and climate models.
NASA Technical Reports Server (NTRS)
Helfand, H. M.; Labraga, J. C.
1988-01-01
The suitability of applying the Mellor and Yamada (1974, 1982) Level 2.5 second-order turbulence closure model to general circulation models is investigated by examining not only the scheme's simulation of fully (or nearly fully) developed turbulence, but also its simulation of rapidly growing or strongly decaying turbulence. The behavior of the model is presented over its entire domain of definition, with special consideration given to the pathologies of the model. The model is then modified for the case of growing turbulence to rectify some of its physical shortcomings for that case, and to remove the pathologies that prohibit its use in a general circulation model. The performance of the modified Level 2.5 model is compared to the performance of various other modified versions through the numerical simulation for a growing convective PBL. The results show that the modified Level 2.5 model is a viable candidate for the prediction of turbulence and the simulation of the PBL in general circulation models.
Mechem, D.B.; Kogan, Y.L.; Childers, M.E.; Donner, K.M.
2005-03-18
Numerous observational studies of marine stratocumulus have demonstrated a pronounced diurnal cycle. At night, longwave flux divergence at the top of the cloud drives negatively buoyant eddies that tend to keep the boundary layer well mixed. During the day, solar absorption by the cloud tends to reduce the turbulent intensity and often decouples the planetary boundary layer (PBL) into cloud- and sub-cloud circulations. The delicate balance between turbulent intensity, entrainment, and fluxes dictates cloud geometry and persistence, which can significantly impact the shortwave radiation budget. Millimeter-wavelength cloud radars (MMCRs) have been used to study the turbulent structure of boundary layer stratocumulus (e.g. Frisch et al. 1995; Kollias and Albrecht 2000). Analysis is confined to nondrizzling or lightly drizzling cloud systems for which precipitation contamination is negligible. Under such assumptions the Doppler velocity field becomes a proxy for vertical velocity. Prior research has mainly consisted of a few case studies of specific cloud systems using radar scan strategies optimized for this particular cloud type. The MMCR operating at the Southern Great Plains Atmospheric Radiation Measurement Climate Research Facility is broadly configured to be able to detect many different cloud types over a broad range of reflectivities and altitudes, so it is not specifically optimized for PBL clouds. Being in more-or-less continuous operation since the end of 1996, it does, however, have the advantage of long data coverage, which suggests that statistically significant measures of the diurnal cycle of turbulence should be attainable. This abstract summarizes the first few steps toward this goal, using 7 months of cold season MMCR data.
NASA Technical Reports Server (NTRS)
Oehman, W. I.
1976-01-01
A gust alleviation system for aircraft flying in turbulent air was analyzed. A vane sensor (with noise) was used to measure vertical gusts, and elevators and flaps were used to reduce the root-mean-square value of the normal accelerations associated with the aircraft response to gusts. Since turbulence has stochastic properties, stochastic control theory was used in the analysis. A quadratic performance-index function involving normal acceleration and control deflections was minimized. Application of the analysis was illustrated by a short take-off and landing (STOL) airplane in flight through turbulent air. Effects of varying the noise characteristics of the vane sensor and of a weighting matrix in the performance-index function were determined. Calculations were performed as required by stochastic control theory to obtain the root-mean-square response of the airplane to turbulence. Results show that good alleviation was calculated when the intensity of the measurement noise was about 3.6 percent of the vane deflection angles.
NASA Astrophysics Data System (ADS)
Jackson, Christopher Robert
"Lucky-region" fusion (LRF) is a synthetic imaging technique that has proven successful in enhancing the quality of images distorted by atmospheric turbulence. The LRF algorithm selects sharp regions of an image obtained from a series of short exposure frames, and fuses the sharp regions into a final, improved image. In previous research, the LRF algorithm had been implemented on a PC using the C programming language. However, the PC did not have sufficient sequential processing power to handle real-time extraction, processing and reduction required when the LRF algorithm was applied to real-time video from fast, high-resolution image sensors. This thesis describes two hardware implementations of the LRF algorithm to achieve real-time image processing. The first was created with a VIRTEX-7 field programmable gate array (FPGA). The other developed using the graphics processing unit (GPU) of a NVIDIA GeForce GTX 690 video card. The novelty in the FPGA approach is the creation of a "black box" LRF video processing system with a general camera link input, a user controller interface, and a camera link video output. We also describe a custom hardware simulation environment we have built to test the FPGA LRF implementation. The advantage of the GPU approach is significantly improved development time, integration of image stabilization into the system, and comparable atmospheric turbulence mitigation.
Lawson, J K; Carrano, C J
2006-06-20
Image data collected near the ground, in the boundary layer, or from low altitude planes must contend with the detrimental effects of atmospheric turbulence on the image quality. So it is useful to predict operating regimes (wavelength, height of target, height of detector, total path distance, day vs. night viewing, etc.) where atmospheric turbulence is expected to play a significant role in image degradation. In these regimes, image enhancement techniques such as speckle processing, deconvolution and Wiener filtering methods can be utilized to recover near instrument-limited resolution in degraded images. We conducted a literature survey of various boundary layer and lower troposphere models for the structure coefficient of the index of refraction (C{sub n}{sup 2}). Using these models, we constructed a spreadsheet tool to estimate the Fried parameter (r{sub 0}) for different scenarios, including slant and horizontal path trajectories. We also created a tool for scenarios where the height along the path crudely accounted for the topology of the path. This would be of particular interest in mountain-based viewing platforms surveying ground targets. The tools that we developed utilized Visual Basic{reg_sign} programming in an Excel{reg_sign} spreadsheet environment for accessibility and ease of use. In this paper, we will discuss the C{sub n}{sup 2} profile models used, describe the tools developed and compare the results obtained for the Fried parameter with those estimated from experimental data.
NASA Astrophysics Data System (ADS)
Mihailovic, D. T.; Alapaty, K.; Lalic, B.; Arsenic, I.; Rajkovic, B.; Malinovic, S.
2004-10-01
A method for estimating profiles of turbulent transfer coefficients inside a vegetation canopy and their use in calculating the air temperature inside tall grass canopies in land surface schemes for environmental modeling is presented. The proposed method, based on K theory, is assessed using data measured in a maize canopy. The air temperature inside the canopy is determined diagnostically by a method based on detailed consideration of 1) calculations of turbulent fluxes, 2) the shape of the wind and turbulent transfer coefficient profiles, and 3) calculation of the aerodynamic resistances inside tall grass canopies. An expression for calculating the turbulent transfer coefficient inside sparse tall grass canopies is also suggested, including modification of the corresponding equation for the wind profile inside the canopy. The proposed calculations of K-theory parameters are tested using the Land Air Parameterization Scheme (LAPS). Model outputs of air temperature inside the canopy for 8 17 July 2002 are compared with micrometeorological measurements inside a sunflower field at the Rimski Sancevi experimental site (Serbia). To demonstrate how changes in the specification of canopy density affect the simulation of air temperature inside tall grass canopies and, thus, alter the growth of PBL height, numerical experiments are performed with LAPS coupled with a one-dimensional PBL model over a sunflower field. To examine how the turbulent transfer coefficient inside tall grass canopies over a large domain represents the influence of the underlying surface on the air layer above, sensitivity tests are performed using a coupled system consisting of the NCEP Nonhydrostatic Mesoscale Model and LAPS.
NASA Astrophysics Data System (ADS)
Balsley, Ben B.; Lawrence, Dale A.; Woodman, Ronald F.; Fritts, David C.
2013-04-01
We report results of preliminary high-resolution in situ atmospheric measurements through the boundary layer and lower atmosphere over the southern coast of Perú. This region of the coast is of particular interest because it lies adjacent to the northern coastal edge of the sub-tropical south-eastern Pacific, a very large area of ocean having a persistent stratus deck located just below the marine boundary layer (MBL) inversion. Typically, the boundary layer in this region during winter is topped by a quasi-permanent, well-defined, and very large temperature gradient. The data presented herein examine fine-scale details of the coastal atmosphere at a point where the edge of this MBL extends over the coastline as a result of persistent onshore flow. Atmospheric data were gathered using a recently-developed in-house constructed, GPS-controlled, micro-autonomous-vehicle aircraft (the DataHawk). Measured quantities include high-resolution profiles of temperature, wind, and turbulence structure from the surface to 1,300 m.
NASA Astrophysics Data System (ADS)
Ma, Jing; Li, Kangning; Tan, Liying; Yu, Siyuan; Cao, Yubin
2016-02-01
The error rate performances and outage probabilities of free-space optical (FSO) communications with spatial diversity are studied for Gamma-Gamma turbulent environments. Equal gain combining (EGC) and selection combining (SC) diversity are considered as practical schemes to mitigate turbulence. The exact bit-error rate (BER) expression and outage probability are derived for direct detection EGC multiple aperture receiver system. BER performances and outage probabilities are analyzed and compared for different number of sub-apertures each having aperture area A with EGC and SC techniques. BER performances and outage probabilities of a single monolithic aperture and multiple aperture receiver system with the same total aperture area are compared under thermal-noise-limited and background-noise-limited conditions. It is shown that multiple aperture receiver system can greatly improve the system communication performances. And these analytical tools are useful in providing highly accurate error rate estimation for FSO communication systems.
NASA Technical Reports Server (NTRS)
Chiu, Y. T.; Straus, J. M.
1974-01-01
Photographs of global scale auroral forms taken by scanning radiometers onboard weather satellites in 1972 show that auroral bands exhibit well organized wave motion with typical zonal wave number of 5 or so. The scale size of these waves is in agreement with that of well organized neutral wind fields in the 150- to 200-km region during the geomagnetic storm of May 27, 1967. Further, the horizontal scale size revealed by these observations are in agreement with that of high altitude traveling ionospheric disturbances. It is conjectured that the geomagnetic storm is a source of planetary and synoptic scale neutral atmospheric waves in the middle atmosphere. Although there is, at present, no observation of substorm related waves of this scale size at mesospheric and stratospheric altitudes, the possible existence of a new source of waves of the proper scale size to trigger instabilities in middle atmospheric circulation systems may be significant in the study of lower atmospheric response to geomagnetic activity.
NASA Astrophysics Data System (ADS)
Archer, C. L.; Xie, S.; Ghaisas, N.
2014-12-01
Large-eddy simulations (LES) have been successfully utilized in many atmospheric turbulence studies. In LES, grid spacing acts like a low-pass filter such that flow features larger than the grid spacing can be resolved, whereas the effects of smaller, sub-grid scale (SGS) eddies are modeled. Therefore, a well-designed SGS model plays a vital role in a successful LES. One of the most sophisticated SGS models is the Lagrangian scale-dependent (LASD) model, in which the scale-dependence of the Smagorinsky coefficient CS is taken into account by performing two explicit filtering processes with different filter widths. Then Lagrangian averaging in time along flow trajectories is used to eliminate the numerical instability caused by backscattering. The LASD model has been successfully implemented in atmospheric boundary layer (ABL) studies using the spectral/pseudo-spectral methods. However, it has not been coupled with finite-difference methods. In this study, the finite-difference method is used for the first time in LES of the ABL using an LASD subgrid scale model. First, a-posteriori tests with a fully conservative 4th-order scheme are performed by simulating turbulent channel flows with . Vertical profiles of mean wind velocity, turbulence intensity, and momentum fluxes, and 1-D spectra of streamwise velocity are compared to those from an existing direct numerical simulation (DNS) database. Several different SGS models are compared and a sensitivity test of spatial resolution is also performed. Second, LES of a neutral ABL with (i.e., molecular viscosity is negligible) are performed using the same numerical methods. The classic logarithmic profile of the streamwise velocity in the inertial subrange is examined in particular. Third, the numerical methods are extended to LES of a stable ABL where the buoyancy effect is considered by using the Boussinesq approximation. The SGS heat flux is calculated via an LASD model similar to that for the SGS stress. The results are
NASA Astrophysics Data System (ADS)
Guala, M.
2013-12-01
Reproducing the different thermal stability regimes of the atmospheric boundary layer (ABL) in wind tunnel experiments requires accurate control of the free stream air and wall temperatures and a test section long enough to ensure the establishment of fully developed conditions. Such requirements are met in the SAFL atmospheric wind tunnel, with some limitations on the achievable range of z/L, confined between the weakly stratified and weakly convective boundary layers. A number of statistical checks based on Reynolds, Monin-Obukhov similarities, Kolmogorov small scale universality, temperature and velocity variance balance equations, are available to assess the quality of the measurements, flow and estimate of the scaling parameters. However, limited work has been devoted to the comparison of the spatio-temporal structure of turbulent flows from the laboratory to the field scale. Specifically, the vertical extent, scaling and statistical relevance of different structural types pose some scalability issues and deserve further investigation. PIV and triple wire measurements from the SAFL Wind Tunnel will be presented and compared with measurements in the atmospheric surface layer. Particular care is devoted to the contributions of large and very-large scale motions to the momentum and heat fluxes, and to their role in near-surface processes and wind energy.
NASA Astrophysics Data System (ADS)
Bakhmetieva, Nataliya V.; Grigoriev; Tolmacheva, Ariadna V.
Artificial periodic irregularities (API) formed by the powerful standing radio waves in the ionospheric plasma give the good chance for the lower ionosphere comprehensive studies. In this paper we present some applications of the API technique for experimental studies of sporadic E-layers (E _{s}), internal gravity waves and turbulent events in the lower ionosphere. API are formed in the field of the standing radio wave produced by interference of the incident wave and reflected one from the ionosphere (in more details about the API technique one can see in the book Belikovich et al., Ionospheric Research by Means of Artificial Periodic Irregularities - Katlenburg-Lindau, Germany. 2002. Copernicus GmbH. ISBN 3-936586-03-9). The spatial period of the irregular structure is equal to the standing wavelength Lambda or one-half the powerful wavelength lambda/2. API diagnostics are carried out at the API relaxation or decay stage by their sounding of probing radio pulses. Based on the measurement of an amplitude and a phase of the API scattered signal their relaxation time and regular vertical plasma velocity are measured. In the E-region of the ionosphere API are formed as a result of the diffusion redistribution of the non-uniformly heated plasma. The relaxation of the periodic structure is specified by the ambipolar diffusion process. The diffusion time is tau=(K (2) D _{a}) (-1) where K=2pi/Lambda and D _{a} is the ambipolar diffusion rate. The atmospheric turbulence causes reduction of the API relaxation time in comparison the diffusion time. Determination of the turbulent velocity is based on this fact. The vertical plasma velocity is determined by measuring the phase of the scattered signal. Atmospheric waves having the periods from 5-10 minutes to 5-6 hours give the contribution to temporal variations of the velocity. Parameters and effects of atmospheric waves and the turbulence on the API relaxation process are presented. Determination of the masses of the
NASA Technical Reports Server (NTRS)
Fritts, D. C.; Geller, M. A.; Balsley, B. B.; Chanin, M. L.; Hirota, I.; Holton, J. R.; Kato, S.; Lindzen, R. S.; Schoeberl, M. R.; Vincent, R. A.
1984-01-01
Internal gravity waves are disturbances whose intrinsic frequencies k(c - u) are smaller than the Brunt-Vaisala frequency (N). Their importance arises because: they are the major components of the total flow and temperature variability fields of the mesosphere (i.e., shears and lapse rates) and hence constitute the likely sources of turbulence; and they are associated with fluxes of momentum that communicate stresses over large distances. For example, gravity waves exert a drag on the flow in the upper mesosphere. However, in order for gravity waves to exert a net drag on the atmosphere, they must be attenuated. There are two general types of processes that seek to attenuate gravity waves: dissipation and saturation. Dissipation is any process that is effective independent of the wave amplitude, while saturation occurs when certain wave amplitude conditions are met. Radiative damping is an example of dissipation, while convective overturning is an example of saturation. The two processes are not mutually exclusive.
NASA Astrophysics Data System (ADS)
Lundquist, J. K.; Handschy, M.
2013-12-01
During the year 2012, the cumulative wind power capacity installed in the United States could provide roughly 4.4% of electricity demand. Although the wind resource can provide many times over the entire US electrical needs, and costs for onshore wind deployment are continually dropping, the variability of the wind represents one of the greatest remaining barriers to wide-scale wind deployment. This study focuses on the nature of this variability. We quantify the axiom 'geographic diversity reduces variability' (of wind generation) by relating resource variability characteristics to the well-understood physical phenomena of turbulence in the Earth's atmosphere. Many existing studies focus on datasets of a few years' duration in a particular geographic area; such results are difficult to generalize. Our approach builds on the fundamental nonlinear characteristics of turbulence in the atmosphere to characterize wind speed and power generation correlations between wind plants from local to continental scales. The resulting general principles enable estimation of the benefits of geographic aggregation absent detailed site-specific historical data, thereby enabling more efficient transmission grid models, expediting transmission plans, and providing a framework for evaluating the requirements and benefits of electric storage at higher wind penetrations. To validate these general principles, we compare them to observed inter-station correlations in a number of wind-speed data sets, including a 40-year Canadian dataset that spans the continent of North America, as well as shorter-duration datasets in smaller regions within the United States. This presentation will present general rules for the dependence of correlation between wind turbines on separation and time scale. We suggest these general rules could help shift renewable integration planning from simulation towards optimization.
NASA Technical Reports Server (NTRS)
Kao, S. K.; Lordi, N. J.
1977-01-01
Analyses of the meteorological rocket data obtained from an experiment conducted at 3-hour intervals at 8 western meridional rocket stations are presented. Large variations in the meridional wind contribute substantially to overall turbulence in the tropical stratosphere. The solar semidiurnal component of wind oscillations in the tropics was observed to be much higher than predicted by theory, often exceeding the magnitude of the diurnal amplitude throughout the stratosphere. The observed value of the solar diurnal amplitude in the stratosphere was in line with theoretical prediction. The solar terdiurnal amplitudes for temperature, meridional and zonal winds were non-negligible and must be considered in any harmonic analysis. Phase angle variation with height was rapid for all harmonics; however, there was general agreement between predicted and observed phase angles. Because of large changes in the mean winds in the mesosphere with season, harmonic determinations are difficult. There appear to be large zonal wind changes even within the same season as mentioned previously. Turbulence diffusivity in the upper stratosphere is greater near the equator than in the mid-latitudes.
NASA Technical Reports Server (NTRS)
Fried, D. L.
1975-01-01
Laser scintillation data obtained by the NASA Goddard Space Flight Center balloon flight no. 5 from White Sands Missile Range on 19 October 1973 are analyzed. The measurement data, taken with various size receiver apertures, were related to predictions of aperture averaging theory, and it is concluded that the data are in reasonable agreement with theory. The following parameters are assigned to the vertical distribution of the strength of turbulence during the period of the measurements (daytime), for lambda = 0.633 microns, and the source at the zenith; the aperture averaging length is d sub o = 0.125 m, and the log-amplitude variance is (beta sub l)2 = 0.084 square nepers. This corresponds to a normalized point intensity variance of 0.40.
NASA Technical Reports Server (NTRS)
Bennett, Floyd V.; Yntema, Robert T.
1959-01-01
Several approximate procedures for calculating the bending-moment response of flexible airplanes to continuous isotropic turbulence are presented and evaluated. The modal methods (the mode-displacement and force-summation methods) and a matrix method (segmented-wing method) are considered. These approximate procedures are applied to a simplified airplane for which an exact solution to the equation of motion can be obtained. The simplified airplane consists of a uniform beam with a concentrated fuselage mass at the center. Airplane motions are limited to vertical rigid-body translation and symmetrical wing bending deflections. Output power spectra of wing bending moments based on the exact transfer-function solutions are used as a basis for the evaluation of the approximate methods. It is shown that the force-summation and the matrix methods give satisfactory accuracy and that the mode-displacement method gives unsatisfactory accuracy.
Hollweg, Joseph V.; Chandran, Benjamin D. G.; Kaghashvili, Edisher Kh. E-mail: ekaghash@aer.com
2013-06-01
We analytically consider how velocity shear in the corona and solar wind can cause an initial Alfven wave to drive up other propagating signals. The process is similar to the familiar coupling into other modes induced by non-WKB refraction in an inhomogeneous plasma, except here the refraction is a consequence of velocity shear. We limit our discussion to a low-beta plasma, and ignore couplings into signals resembling the slow mode. If the initial Alfven wave is propagating nearly parallel to the background magnetic field, then the induced signals are mainly a forward-going (i.e., propagating in the same sense as the original Alfven wave) fast mode, and a driven signal propagating like a forward-going Alfven wave but polarized like the fast mode; both signals are compressive and subject to damping by the Landau resonance. For an initial Alfven wave propagating obliquely with respect to the magnetic field, the induced signals are mainly forward- and backward-going fast modes, and a driven signal propagating like a forward-going Alfven wave but polarized like the fast mode; these signals are all compressive and subject to damping by the Landau resonance. A backward-going Alfven wave, thought to be important in the development of MHD turbulence, is also produced, but it is very weak. However, we suggest that for oblique propagation of the initial Alfven wave the induced fast-polarized signal propagating like a forward-going Alfven wave may interact coherently with the initial Alfven wave and distort it at a strong-turbulence-like rate.
NASA Astrophysics Data System (ADS)
Vorontsov, M.; Gudimetla, V.; Carhart, G.; Weyrauch, T.; Lachinova, S.; Polnau, E.; Reierson, J.; Beresnev, L.; Liu, J.; Riker, J.
2011-09-01
We report results of the experimental analysis of atmospheric effects on laser beam propagation over two distinctive propagation paths: a long-range (149 km) propagation path between Mauna Loa (Island of Hawaii) and Haleakala (Island of Maui) mountains, and a tactical-range (7 km) propagation path between the roof of the Dayton Veterans Administration Medical Center (VAMC) and the Intelligent Optics Laboratory (IOL/UD) located on the 5th floor of the University of Dayton College Park Center building. Both testbeds include three laser beacons operating at wavelengths 532 nm, 1064 nm, and 1550 nm and a set of identical optical receiver systems with fast-framing IR cameras for simultaneous measurements of pupil and focal plane intensity distributions. The results reported here are focused on analysis of intensity scintillations that were simultaneously measured at three wavelengths. Comparison of experimental results shows significant differences in the physics of atmospheric turbulence impact on laser beam propagation over the long- and tactical-range distances.
NASA Astrophysics Data System (ADS)
Sérazin, Guillaume; Penduff, Thierry; Terray, Laurent; Grégorio, Sandy; Barnier, Bernard; Molines, Jean-Marc
2015-04-01
Ocean-atmosphere heat fluxes are particularly strong in Western Boundary Current (WBC) regions where SST front variations influence basin-scale climate variability. Observed low-frequency fluctuations in latitude and strength of these oceanic jets are classically thought to be essentially atmospherically-driven by wind stress curl variability via the oceanic Rossby wave adjustment. Yet academic eddy-resolving process-oriented models with double-gyre configurations have revealed that an idealized WBC may exhibit low-frequency intrinsic fluctuations without low-frequency external forcing (e.g. Berloff et al., 2007, Dijkstra and Ghil, 2005, etc). Experiments with eddying Ocean General Circulation Models (OGCMs) have also shown that the amount of low-frequency Sea Level Anomaly (SLA) variability is largely intrinsic in WBCs (Penduff et al. 2011; Sérazin et al 2014) and that the frontal-scale (<10°) pattern of the Kuroshio Extension (KE) variability is similar to intrinsic modes (Taguchi et al. 2010). Based on a pair of atmospherically-forced 1/12° OGCM experiments that simulate with accuracy either the intrinsic variability (seasonally-forced) or the observed total variability (forced with the full range of atmospheric timescales), Empirical Orthogonal Function analysis is performed on zonally-averaged SLA fields of four main WBCs (e.g. Gulf Stream, Kuroshio Extension, Agulhas Current and East Australian Current). The first two modes of the KE and GS exhibit a similar spatial structure that is shaped by oceanic intrinsic processes. The frequency content is however different between the intrinsic and total Principal Components, the former containing a wide range of timescales similar to a red noise and the latter being more autocorrelated at interannual-to-decadal timescales. These modes are compared with those obtained from the 20 years of altimetry observation and relationships with low-frequency westward propagative features in the respective oceanic basin are
Stirring turbulence with turbulence
NASA Astrophysics Data System (ADS)
Cekli, Hakki Ergun; Joosten, René; van de Water, Willem
2015-12-01
We stir wind-tunnel turbulence with an active grid that consists of rods with attached vanes. The time-varying angle of these rods is controlled by random numbers. We study the response of turbulence on the statistical properties of these random numbers. The random numbers are generated by the Gledzer-Ohkitani-Yamada shell model, which is a simple dynamical model of turbulence that produces a velocity field displaying inertial-range scaling behavior. The range of scales can be adjusted by selection of shells. We find that the largest energy input and the smallest anisotropy are reached when the time scale of the random numbers matches that of the largest eddies of the wind-tunnel turbulence. A large mismatch of these times creates a highly intermittent random flow with interesting but quite anomalous statistics.
Turbulence compensation: an overview
NASA Astrophysics Data System (ADS)
van Eekeren, Adam W. M.; Schutte, Klamer; Dijk, Judith; Schwering, Piet B. W.; van Iersel, Miranda; Doelman, Niek J.
2012-06-01
In general, long range visual detection, recognition and identification are hampered by turbulence caused by atmospheric conditions. Much research has been devoted to the field of turbulence compensation. One of the main advantages of turbulence compensation is that it enables visual identification over larger distances. In many (military) scenarios this is of crucial importance. In this paper we give an overview of several software and hardware approaches to compensate for the visual artifacts caused by turbulence. These approaches are very diverse and range from the use of dedicated hardware, such as adaptive optics, to the use of software methods, such as deconvolution and lucky imaging. For each approach the pros and cons are given and it is indicated for which scenario this approach is useful. In more detail we describe the turbulence compensation methods TNO has developed in the last years and place them in the context of the different turbulence compensation approaches and TNO's turbulence compensation roadmap. Furthermore we look forward and indicate the upcoming challenges in the field of turbulence compensation.
NASA Astrophysics Data System (ADS)
Fairall, C. W.; Bariteau, L.; Grachev, A. A.; Hill, R. J.; Wolfe, D. E.; Brewer, W. A.; Tucker, S. C.; Hare, J. E.; Angevine, W. M.
2006-12-01
In this paper, we examine observations of shallow, stable boundary layers in the cool waters of the Gulf of Maine between Cape Cod, Massachusetts, and Nova Scotia, obtained in the 2004 New England Air Quality Study (NEAQS-04), which was part of the International Consortium for Atmospheric Research into Transport and Transformation (ICARTT). The observations described herein were made from the NOAA Research Vessel Ronald H. Brown. The ship was instrumented for measurements of meteorological, gas-phase and aerosol atmospheric chemistry variables. Meteorological instrumentation included a Doppler lidar, a radar wind profiler, rawinsonde equipment, and a surface flux package. In this study, we focus on direct comparisons of the NEAQS-04 flux observations with the COARE bulk flux algorithm to investigate possible coastal influences on air-sea interactions. We found significant suppression of the transfer coefficients for momentum, sensible heat, and latent heat; the suppression was correlated with lighter winds, more stable surface layers, S-SE wind direction, and lower boundary layer heights. Analysis of the details shows the suppression is not a measurement, stability correction, or surface wave effect. The correlation with boundary layer height is consistent with an interpretation that our measurements at 18-m height do not realize the full surface flux in shallow boundary layers. We also find that a bulk Richardson number threshold of 0.1 gives a better estimate of boundary layer height than 0.25 or 0.5. Mean ozone deposition velocity is estimated as 0.44 mm s-1, corresponding to a boundary removal timescale of about 1 day.
NASA Technical Reports Server (NTRS)
Burke, J. J.; Breckinridge, J. B.
1978-01-01
The signal-to-noise (S/N) ratio to be expected when a 180 deg rotationally shearing interferometer is used for image recovery at the diffraction limit of a large telescope is computed. The variance and covariance of the irradiance fluctuations at the detector array are shown to yield measures of the high-frequency spatial spectrum of the source. Four fundamental sources of noise are considered: temporal fluctuations of the source, space-time fluctuations of the atmosphere, shot noise in the detected photocurrents, and the effects of finite sampling. S/N is found to be directly proportional to the angular resolution of the telescope, the single-frame integration time, the square root of the number of frames, the cube of the operating wavelength, the quantum efficiency of the detector, and the average spectral irradiance from the source on the pupil. It is inversely proportional to the cube of the field angle subtended by the source (or part thereof) under study.
NASA Astrophysics Data System (ADS)
Carper, Matthew A.; Porté-Agel, Fernando
2004-11-01
A field experiment was designed and carried out to study the role of coherent structures on the local transfers of energy and temperature variance between resolved and subfilter (unresolved) scales relevant to large-eddy simulation of high-Reynolds-number boundary layers. In particular, 16 sonic anemometers were used in an arrangement with a 6 m high vertical array (ten anemometers) that intersected a 3 m wide horizontal array (seven anemometers). The data collected are used to calculate the subfilter-scale (SFS) stresses and fluxes, and the SFS dissipation rate (transfer rate between resolved and subfilter scales) of energy and temperature variance. With these quantities, conditional averaging is used to study the relation of strong positive (forward-scatter) and negative (backscatter) SFS dissipation events to local features of the flow. The conditionally averaged vertical and horizontal flow fields reveal vortical structures, inclined downwind at angles close to 16° during near-neutral atmospheric stability, and as large as 34° during convective conditions. These inclined vortical structures agree with the concept of a hairpin vortex (with head and trailing legs) around which sweep and ejection events are found. Localized regions of large forward-scatter are found on the upper trailing edge of these structures, whereas localized regions of large backscatter are found on the lower leading edge of the same type of structures.
NASA Astrophysics Data System (ADS)
Gemmrich, J.; Farmer, D.
2003-04-01
Breaking surface waves are believed to provide a major pathway for the energy input from the atmosphere to the ocean and are a source of enhanced turbulent kinetic energy levels in the near-surface layer. Increased turbulence levels relate to enhanced air-sea exchange processes. The ocean surface is a complex system with a wide range of relevant scales. We use direct measurement of the small-scale velocity field as a first step to evaluate near-surface turbulence. At wind speed up to 14 m/s, velocity profiles were obtained with pulse-to-pulse coherent acoustic Doppler profilers. Based on wavenumber spectra calculated with the empirical mode decomposition, dissipation of turbulent kinetic energy at ~1m beneath the free surface and 1 Hz sampling rate is estimated. In addition, bubble size distributions were obtained from acoustic resonator measurements and whitecap occurrence was monitored with video cameras. High turbulence levels with dissipation rates more than four orders larger than the background dissipation are linked to wave breaking. The decay and depth-dependence of the wave-induced turbulence are examined and implications for turbulence models are discussed. In individual breaking waves, the onset of enhanced dissipation occurs up to a quarter wave period prior to the air entrainment. Magnitude and occurrence of the pre-breaking turbulence are consistent with wave-turbulence interaction in a rotational wave field. The detailed structure of the turbulence and bubble field associated with breaking waves will be presented. Implications for air-sea exchange processes will be discussed.
NASA Astrophysics Data System (ADS)
Yamada, Hiromasa; Yamagishi, Yusuke; Sakakita, Hajime; Tsunoda, Syuichiro; Kasahara, Jiro; Fujiwara, Masanori; Kato, Susumu; Itagaki, Hirotomo; Kim, Jaeho; Kiyama, Satoru; Fujiwara, Yutaka; Ikehara, Yuzuru; Ikehara, Sanae; Nakanishi, Hayao; Shimizu, Nobuyuki
2016-01-01
To understand the mechanism of turbulent enhancement phenomena of a neutral gas flow containing plasma ejected from the nozzle of plasma equipment, the schlieren optical method was performed to visualize the neutral gas behavior. It was confirmed that the turbulent starting point became closer to the nozzle exit, as the amplitude of discharge voltage (electric field) increased. To study the effect of electric field on turbulent enhancement, two sets of external electrodes were arranged in parallel, and the gas from the nozzle was allowed to flow between the upper and lower electrodes. It was found that the neutral gas flow was bent, and the bending angle increased as the amplitude of the external electric field increased. The results obtained using a simple model analysis roughly coincide with experimental data. These results indicate that momentum transport from drifted ions induced by the electric field to neutral particles is an important factor that enhances turbulence.
Turbulence in Natural Environments
NASA Astrophysics Data System (ADS)
Banerjee, Tirtha
Problems in the area of land/biosphere-atmosphere interaction, hydrology, climate modeling etc. can be systematically organized as a study of turbulent flow in presence of boundary conditions in an increasing order of complexity. The present work is an attempt to study a few subsets of this general problem of turbulence in natural environments- in the context of neutral and thermally stratified atmospheric surface layer, the presence of a heterogeneous vegetation canopy and the interaction between air flow and a static water body in presence of flexible protruding vegetation. The main issue addressed in the context of turbulence in the atmospheric surface layer is whether it is possible to describe the macro-states of turbulence such as mean velocity and turbulent velocity variance in terms of the micro-states of the turbulent flow, i.e., a distribution of turbulent kinetic energy across a multitude of scales. This has been achieved by a `spectral budget approach' which is extended for thermal stratification scenarios as well, in the process unifying the seemingly different and unrelated theories of turbulence such as Kolmogorov's hypothesis, Heisenberg's eddy viscosity, Monin Obukhov Similarity Theory (MOST) etc. under a common framework. In the case of a more complex scenario such as presence of a vegetation canopy with edges and gaps, the question that is addressed is in what detail the turbulence is needed to be resolved in order to capture the bulk flow features such as recirculation patterns. This issue is addressed by a simple numerical framework and it has been found out that an explicit prescription of turbulence is not necessary in presence of heterogeneities such as edges and gaps where the interplay between advection, pressure gradients and drag forces are sufficient to capture the first order dynamics. This result can be very important for eddy-covariance flux calibration strategies in non-ideal environments and the developed numerical model can be
Abarzhi, S I; Sreenivasan, K R
2010-04-13
Turbulence is a supermixer. Turbulent mixing has immense consequences for physical phenomena spanning astrophysical to atomistic scales under both high- and low-energy-density conditions. It influences thermonuclear fusion in inertial and magnetic confinement systems; governs dynamics of supernovae, accretion disks and explosions; dominates stellar convection, planetary interiors and mantle-lithosphere tectonics; affects premixed and non-premixed combustion; controls standard turbulent flows (wall-bounded and free-subsonic, supersonic as well as hypersonic); as well as atmospheric and oceanic phenomena (which themselves have important effects on climate). In most of these circumstances, the mixing phenomena are driven by non-equilibrium dynamics. While each article in this collection dwells on a specific problem, the purpose here is to seek a few unified themes amongst diverse phenomena. PMID:20211872
Rasouli, Saifollah; Tavassoly, M Taghi
2008-05-01
When a slightly divergent laser beam passes through a turbulent ground level atmosphere and strikes a linear grating, fluctuating self-images are formed at Talbot distances. By superimposing a similar grating on one of the self-images, even for the case of parallel gratings' lines, fluctuating moiré fringes are formed owing to the beam divergence. Recording the successive moiré patterns by a CCD camera and feeding them to a computer, after filtering the higher spatial frequencies, produces highly magnified fluctuations of the laser beam. Using moiré fringe fluctuations we have calculated the fluctuations of the angle of arrival and the atmospheric refractive index structure constant. The implementation of the technique is straightforward, a telescope is not required, fluctuations can be magnified more than ten times, and the precision of the technique is similar to that reported in our previous work. PMID:18451959
Scintillation index in strong oceanic turbulence
NASA Astrophysics Data System (ADS)
Baykal, Yahya
2016-09-01
Scintillation index of spherical wave in strongly turbulent oceanic medium is evaluated. In the evaluation, modified Rytov solution and our recent formulation that expresses the oceanic turbulence parameters by the atmospheric turbulence structure constant, are employed. Variations of the scintillation index in strong oceanic turbulence are examined versus the oceanic turbulence parameters such as the rate of dissipation of kinetic energy per unit mass of fluid, the rate of dissipation of mean-squared temperature, viscosity, wavelength, the link length, and the ratio of temperature to salinity contributions to the refractive index spectrum.
Horton, W.; Hu, G.
1998-07-01
The origin of plasma turbulence from currents and spatial gradients in plasmas is described and shown to lead to the dominant transport mechanism in many plasma regimes. A wide variety of turbulent transport mechanism exists in plasmas. In this survey the authors summarize some of the universally observed plasma transport rates.
NASA Astrophysics Data System (ADS)
Madala, Srikanth; Satyanarayana, A. N. V.; Srinivas, C. V.
2015-12-01
Accurate representation of air pollutant dispersion is essential for environmental management and planning purposes. In this study, semi-empirical relationships of turbulence intensity (σu/u*, σv/u* and σw/u*) as a function of surface layer scaling and local stability are developed following boundary layer similarity concepts at Ranchi, a complex terrain in Jharkhand, Eastern India for various seasons. The impact of the new turbulence parameterization for air pollution dispersion simulation is studied by incorporating the same in the Hanna scheme of FLEXPART-WRF Lagrangian Particle dispersion model over study region. The model is used to estimate the ground level concentrations of nitrogen oxides (NOx) due to industrial and vehicular sources in study region. The meteorological parameters needed in air-quality simulation are simulated using the Advanced Research WRF (ARW) mesoscale model at high resolution (3 km). Three turbulence schemes (YSU, MYNN2 and ACM2) in ARW are alternatively tested in dispersion simulation and comparisons are made with available air quality data for eight days in different seasons (winter, pre-monsoon, monsoon and post-monsoon). Simulations with FLEXPART revealed distinct seasonal variation of dispersion patterns. It has been found that the new turbulence intensity relationships in FLEXPART improved the NOx concentration estimates by reducing the negative bias seen with default Hanna scheme. Further, the ARW simulated meteorological parameters using ACM2 and MYNN2 significantly reduced the bias in modeled pollutant concentrations. The study demonstrates the utility of high quality seasonal turbulence measurements in pollution dispersion model for better diffusion parameterization needed in air quality modeling.
Remote Sensing of Turbulence in Natural Fluids
NASA Astrophysics Data System (ADS)
Gibson, Carl H.
2010-11-01
It is generally agreed that natural fluids including the atmosphere, ocean, and astrophysical objects are mixed by turbulence against the forces of gravity. However, the basic mechanisms, definition, and even the direction of the turbulence kinetic energy cascade remain controversial. Broadband remote sensing gives strong evidence to resolve such questions. Turbulence is found to be an eddy-like state of fluid motion where the inertial-vortex forces of the eddies are larger than any other forces that tend to damp the eddies out. Irrotational flows are non-turbulent by definition. Because turbulent vorticity is always produced at the Kolmogorov scale, the direction of the turbulent energy cascade is always from small scales to large. Fossilization of the turbulence occurs at its largest scales. Fossil turbulence is any perturbation of a hydrophysical field produced by turbulence that is no longer turbulent at the scale of the perturbation. In the ocean, fossil vorticity turbulence internal waves carry bottom turbulence energy to the sea surface by means of beamed zombie turbulence maser action mixing chimneys, a generic process of natural fluids. Spectral analysis of the sea surface brightness from space satellites combined with simultaneous ocean microstructure sea truth reveals the generic mechanism, also supported by recent astrophysical observations http://arxiv.org/abs/1005.2772v4.
An overview of turbulence compensation
NASA Astrophysics Data System (ADS)
Schutte, Klamer; van Eekeren, Adam W. M.; Dijk, Judith; Schwering, Piet B. W.; van Iersel, Miranda; Doelman, Niek J.
2012-09-01
In general, long range visual detection, recognition and identification are hampered by turbulence caused by atmospheric conditions. Much research has been devoted to the field of turbulence compensation. One of the main advantages of turbulence compensation is that it enables visual identification over larger distances. In many (military) scenarios this is of crucial importance. In this paper we give an overview of several software and hardware approaches to compensate for the visual artifacts caused by turbulence. These approaches are very diverse and range from the use of dedicated hardware, such as adaptive optics, to the use of software methods, such as deconvolution and lucky imaging. For each approach the pros and cons are given and it is indicated for which type of scenario this approach is useful. In more detail we describe the turbulence compensation methods TNO has developed in the last years and place them in the context of the different turbulence compensation approaches and TNO's turbulence compensation roadmap. Furthermore we look forward and indicate the upcoming challenges in the field of turbulence compensation.
NASA Astrophysics Data System (ADS)
Kunz, G. J.; van Eijk, A. M. J.; Tsintikidis, D.; Hammel, S. M.
2005-08-01
EOSTAR, a PC based Windows application, integrates the required modules necessary to calculate the electro-optical sensor performance on the basis of standard meteorological data. The primary output of EOSTAR consists of the synthetic sensor image ("what does the sensor see?") and a coverage diagram ("detection probability versus range"). As part of the EOSTAR validation effort, the refraction and turbulence modules are being evaluated against literature data, similar models and experimental results. It is shown that the EOSTAR model can predict with reasonable success the occurrence of optical turbulence and refraction phenomena such as mirages. The major cause for discrepancies between the various models is attributed to the underlying micrometeorological bulk modules, whereas the sensitivity of the predictions on the values of the meteorological input parameters is held responsible for the discrepancies between model predictions and measurements.
Global Variation of Meteor Trail Plasma Turbulence
NASA Technical Reports Server (NTRS)
Dyrud, L. P.; Hinrichs, J.; Urbina, J.
2011-01-01
We present the first global simulations on the occurrence of meteor trail plasma irregularities. These results seek to answer the following questions: when a meteoroid disintegrates in the atmosphere will the resulting trail become plasma turbulent, what are the factors influencing the development of turbulence, and how do they vary on a global scale. Understanding meteor trail plasma turbulence is important because turbulent meteor trails are visible as non-specular trails to coherent radars, and turbulence influences the evolution of specular radar meteor trails, particularly regarding the inference of mesospheric temperatures from trail diffusion rates, and their usage for meteor burst communication. We provide evidence of the significant effect that neutral atmospheric winds and density, and ionospheric plasma density have on the variability of meteor trail evolution and the observation of nonspecular meteor trails, and demonstrate that trails are far less likely to become and remain turbulent in daylight, explaining several observational trends using non-specular and specular meteor trails.
Using Indirect Turbulence Measurements for Real-Time Parameter Estimation in Turbulent Air
NASA Technical Reports Server (NTRS)
Martos, Borja; Morelli, Eugene A.
2012-01-01
The use of indirect turbulence measurements for real-time estimation of parameters in a linear longitudinal dynamics model in atmospheric turbulence was studied. It is shown that measuring the atmospheric turbulence makes it possible to treat the turbulence as a measured explanatory variable in the parameter estimation problem. Commercial off-the-shelf sensors were researched and evaluated, then compared to air data booms. Sources of colored noise in the explanatory variables resulting from typical turbulence measurement techniques were identified and studied. A major source of colored noise in the explanatory variables was identified as frequency dependent upwash and time delay. The resulting upwash and time delay corrections were analyzed and compared to previous time shift dynamic modeling research. Simulation data as well as flight test data in atmospheric turbulence were used to verify the time delay behavior. Recommendations are given for follow on flight research and instrumentation.
Coherence in Turbulence: New Perspective
NASA Astrophysics Data System (ADS)
Levich, Eugene
2009-07-01
It is claimed that turbulence in fluids is inherently coherent phenomenon. The coherence shows up clearly as strongly correlated helicity fluctuations of opposite sign. The helicity fluctuations have cellular structure forming clusters that are actually observed as vorticity bands and coherent structures in laboratory turbulence, direct numerical simulations and most obviously in atmospheric turbulence. The clusters are named BCC - Beltrami Cellular Clusters - because of the observed nearly total alignment of the velocity and vorticity fields in each particular cell, and hence nearly maximal possible helicity in each cell; although when averaged over all the cells the residual mean helicity in general is small and does not play active dynamical role. The Beltrami like fluctuations are short-lived and stabilize only in small and generally contiguous sub-domains that are tending to a (multi)fractal in the asymptotic limit of large Reynolds numbers, Re → ∞. For the model of homogeneous isotropic turbulence the theory predicts the leading fractal dimension of BCC to be: DF = 2.5. This particular BCC is responsible for generating the Kolmogorov -5/3 power law energy spectrum. The most obvious role that BCC play dynamically is that the nonlinear interactions in them are relatively reduced, due to strong spatial alignment between the velocity field v(r, t) and the vorticity field ω(r, t) = curlv(r, t), while the physical quantities typically best characterizing turbulence intermittency, such as entrophy, vorticity stretching and generation, and energy dissipation are maximized in and near them. The theory quantitatively relates the reduction of nonlinear inter-actions to the BCC fractal dimension DF and subsequent turbulence intermittency. It is further asserted that BCC is a fundamental feature of all turbulent flows, e.g., wall bounded turbulent flows, atmospheric and oceanic flows, and their leading fractal dimension remains invariant and universal in these flows
ERIC Educational Resources Information Center
Hanratty, Thomas J.
1980-01-01
This paper gives an account of research on the structure of turbulence close to a solid boundary. Included is a method to study the flow close to the wall of a pipe without interferring with it. (Author/JN)
NASA Astrophysics Data System (ADS)
Nazarenko, Sergey
2015-07-01
Wave turbulence is the statistical mechanics of random waves with a broadband spectrum interacting via non-linearity. To understand its difference from non-random well-tuned coherent waves, one could compare the sound of thunder to a piece of classical music. Wave turbulence is surprisingly common and important in a great variety of physical settings, starting with the most familiar ocean waves to waves at quantum scales or to much longer waves in astrophysics. We will provide a basic overview of the wave turbulence ideas, approaches and main results emphasising the physics of the phenomena and using qualitative descriptions avoiding, whenever possible, involved mathematical derivations. In particular, dimensional analysis will be used for obtaining the key scaling solutions in wave turbulence - Kolmogorov-Zakharov (KZ) spectra.
Will climate change increase transatlantic aviation turbulence?
NASA Astrophysics Data System (ADS)
Williams, Paul; Joshi, Manoj
2013-04-01
Atmospheric turbulence causes most weather-related aircraft incidents. Commercial aircraft encounter moderate-or-greater turbulence tens of thousands of times each year world-wide, injuring probably hundreds of passengers (occasionally fatally), costing airlines tens of millions of dollars, and causing structural damage to planes. Clear-air turbulence is especially difficult to avoid, because it cannot be seen by pilots or detected by satellites or on-board radar. Clear-air turbulence is linked to atmospheric jet streams, which are projected to be strengthened by anthropogenic climate change. However, the response of clear-air turbulence to climate change has not previously been studied. Here we show using computer simulations that clear-air turbulence changes significantly within the transatlantic flight corridor when the concentration of carbon dioxide in the atmosphere is doubled. At cruise altitudes within 50-75°N and 10-60°W in winter, most clear-air turbulence measures show a 10-40% increase in the median strength of turbulence and a 40-170% increase in the frequency of occurrence of moderate-or-greater turbulence. Our results suggest that climate change will lead to bumpier transatlantic flights by the middle of this century. Journey times may lengthen and fuel consumption and emissions may increase. Aviation is partly responsible for changing the climate, but our findings show for the first time how climate change could affect aviation.
Will Climate Change Increase Transatlantic Aviation Turbulence?
NASA Astrophysics Data System (ADS)
Williams, P. D.; Joshi, M. M.
2013-12-01
Atmospheric turbulence causes most weather-related aircraft incidents. Commercial aircraft encounter moderate-or-greater turbulence tens of thousands of times each year world-wide, injuring probably hundreds of passengers (occasionally fatally), costing airlines tens of millions of dollars, and causing structural damage to planes. Clear-air turbulence is especially difficult to avoid, because it cannot be seen by pilots or detected by satellites or on-board radar. Clear-air turbulence is linked to atmospheric storm tracks and jet streams, which are projected to be strengthened by anthropogenic climate change. However, the response of clear-air turbulence to climate change has not previously been studied. Here we show using computer simulations that clear-air turbulence changes significantly within the transatlantic flight corridor when the concentration of carbon dioxide in the atmosphere is doubled. At cruise altitudes within 50-75°N and 10-60°W in winter, most clear-air turbulence measures show a 10-40% increase in the median strength of turbulence and a 40-170% increase in the frequency of occurrence of moderate-or-greater turbulence. Our results suggest that climate change will lead to bumpier transatlantic flights by the middle of this century. Journey times may lengthen and fuel consumption and emissions may increase. Aviation is partly responsible for changing the climate, but our findings show for the first time how climate change could affect aviation.
TURBULENCE MODELING APPLIED TO BUOYANT PLUMES
A viable computer model was developed that is based on second-order closure of the turbulent correlation equations for predicting the fate of nonchemically reacting contaminants released in the atmospheric boundary layer. The invariant turbulence model discussed in previous repor...
NASA Technical Reports Server (NTRS)
Safren, H. G.
1987-01-01
The effect of atmospheric turbulence on the bit error rate of a space-to-ground near infrared laser communications link is investigated, for a link using binary pulse position modulation and an avalanche photodiode detector. Formulas are presented for the mean and variance of the bit error rate as a function of signal strength. Because these formulas require numerical integration, they are of limited practical use. Approximate formulas are derived which are easy to compute and sufficiently accurate for system feasibility studies, as shown by numerical comparison with the exact formulas. A very simple formula is derived for the bit error rate as a function of signal strength, which requires only the evaluation of an error function. It is shown by numerical calculations that, for realistic values of the system parameters, the increase in the bit error rate due to turbulence does not exceed about thirty percent for signal strengths of four hundred photons per bit or less. The increase in signal strength required to maintain an error rate of one in 10 million is about one or two tenths of a db.
Ma, Jing; Ma, Lie; Yang, Qingbo; Ran, Qiwen
2015-11-01
The average efficiency of spatial light coupling into a single-mode optical fiber is widely used but cannot estimate the signal-to-noise ratio (SNR) and bit error rate (BER) in free-space optical communication. We provide a statistical model for coupling efficiency and derive the exact expression of the probability density function (PDF). The simulation results confirm that the model is reasonable in the condition of different turbulence intensities and wavefront compensation terms, which is also consistent with our outdoor experiment. We also estimate the average SNR and BER using the PDF. The model is quite useful in a satellite-to-ground laser communication downlink. PMID:26560584
Lipkens, B; Blackstock, D T
1998-09-01
A model experiment was reported to be successful in simulating the propagation of sonic booms through a turbulent atmosphere [B. Lipkens and D. T. Blackstock, J. Acoust. Soc. Am. 103, 148-158 (1998)]. In this study the effect on N wave characteristics of turbulence intensity and propagation distance through turbulence are investigated. The main parameters of interest are the rise time and the peak pressure. The effect of turbulence intensity and propagation distance is to flatten the rise time and peak pressure distributions. Rise time and peak pressure distributions always have positive skewness after propagation through turbulence. Average rise time grows with turbulence intensity and propagation distance. The scattering of rise time data is one-sided, i.e., rise times are almost always increased by turbulence. Average peak pressure decreases slowly with turbulence intensity and propagation distance. For the reported data a threefold increase in average rise time is observed and a maximum decrease of about 20% in average peak pressure. Rise times more than ten times that of the no turbulence value are observed. At most, the maximum peak pressure doubles after propagation through turbulence, and the minimum peak pressure values are about one-half the no-turbulence values. Rounded waveforms are always more common than peaked waveforms. PMID:9745733
Characteristics of ultraviolet scattering and turbulent channels.
Wang, Peng; Xu, Zhengyuan
2013-08-01
The nonline of sight (NLOS) ultraviolet (UV) scattering communication channel and atmospheric optical turbulent channel have been extensively but independently studied in the rich literature. However, the new characteristics of NLOS UV scattering and turbulent channels have not been comprehensively investigated. We propose a configurable framework, unifying the traditional line of sight turbulence theory and the Monte Carlo simulation framework for random scattering of photons. Results show that the scattering link geometry can significantly alter the received signal distribution. Irradiance fluctuations at the receiver may become much weaker due to the smoothing effect of impinging photons from different scattering paths, even though each scattering path undergoes strong turbulence. PMID:23903138
Adams, Allan; Chesler, Paul M; Liu, Hong
2014-04-18
We construct turbulent black holes in asymptotically AdS4 spacetime by numerically solving Einstein's equations. Using the AdS/CFT correspondence we find that both the dual holographic fluid and bulk geometry display signatures of an inverse cascade with the bulk geometry being well approximated by the fluid-gravity gradient expansion. We argue that statistically steady-state black holes dual to d dimensional turbulent flows have horizons whose area growth has a fractal-like structure with fractal dimension D=d+4/3. PMID:24785028
Turbulence in Compressible Flows
NASA Technical Reports Server (NTRS)
1997-01-01
Lecture notes for the AGARD Fluid Dynamics Panel (FDP) Special Course on 'Turbulence in Compressible Flows' have been assembled in this report. The following topics were covered: Compressible Turbulent Boundary Layers, Compressible Turbulent Free Shear Layers, Turbulent Combustion, DNS/LES and RANS Simulations of Compressible Turbulent Flows, and Case Studies of Applications of Turbulence Models in Aerospace.
NASA Technical Reports Server (NTRS)
Bardina, Jorge E.
1995-01-01
The objective of this work is to develop, verify, and incorporate the baseline two-equation turbulence models which account for the effects of compressibility into the three-dimensional Reynolds averaged Navier-Stokes (RANS) code and to provide documented descriptions of the models and their numerical procedures so that they can be implemented into 3-D CFD codes for engineering applications.
Talbot, L.; Cheng, R.K.
1993-12-01
Turbulent combustion is the dominant process in heat and power generating systems. Its most significant aspect is to enhance the burning rate and volumetric power density. Turbulent mixing, however, also influences the chemical rates and has a direct effect on the formation of pollutants, flame ignition and extinction. Therefore, research and development of modern combustion systems for power generation, waste incineration and material synthesis must rely on a fundamental understanding of the physical effect of turbulence on combustion to develop theoretical models that can be used as design tools. The overall objective of this program is to investigate, primarily experimentally, the interaction and coupling between turbulence and combustion. These processes are complex and are characterized by scalar and velocity fluctuations with time and length scales spanning several orders of magnitude. They are also influenced by the so-called {open_quotes}field{close_quotes} effects associated with the characteristics of the flow and burner geometries. The authors` approach is to gain a fundamental understanding by investigating idealized laboratory flames. Laboratory flames are amenable to detailed interrogation by laser diagnostics and their flow geometries are chosen to simplify numerical modeling and simulations and to facilitate comparison between experiments and theory.
Submerged turbulence detection with optical satellites
NASA Astrophysics Data System (ADS)
Gibson, Carl H.; Keeler, R. Norris; Bondur, Valery G.; Leung, Pak T.; Prandke, H.; Vithanage, D.
2007-09-01
During fall periods in 2002, 2003 and 2004 three major oceanographic expeditions were carried out in Mamala Bay, Hawaii. These were part of the RASP Remote Anthropogenic Sensing Program. Ikonos and Quickbird optical satellite images of sea surface glint revealed ~100 m spectral anomalies in km2 averaging patches in regions leading from the Honolulu Sand Island Municipal Outfall diffuser to distances up to 20 km. To determine the mechanisms behind this phenomenon, the RASP expeditions monitored the waters adjacent to the outfall with an array of hydrographic, optical and turbulence microstructure sensors in anomaly and ambient background regions. Drogue tracks and mean turbulence parameters for 2 × 10 4 microstructure patches were analyzed to understand complex turbulence, fossil turbulence and zombie turbulence near-vertical internal wave transport processes. The dominant mechanism appears to be generic to stratified natural fluids including planet and star atmospheres and is termed beamed zombie turbulence maser action (BZTMA). Most of the bottom turbulent kinetic energy is converted to ~ 100 m fossil turbulence waves. These activate secondary (zombie) turbulence in outfall fossil turbulence patches that transmit heat, mass, chemical species, momentum and information vertically to the sea surface for detection in an efficient maser action. The transport is beamed in intermittent mixing chimneys.
Submerged turbulence detection with optical satellites
NASA Astrophysics Data System (ADS)
Gibson, Carl H.; Keeler, R. Norris; Bondur, Valery G.; Leung, Pak T.; Prandke, H.; Vithanage, D.
2013-01-01
During fall periods in 2002, 2003 and 2004 three major oceanographic expeditions were carried out in Mamala Bay, Hawaii. These were part of the RASP Remote Anthropogenic Sensing Program. Ikonos and Quickbird optical satellite images of sea surface glint revealed !100 m spectral anomalies in km2 averaging patches in regions leading from the Honolulu Sand Island Municipal Outfall diffuser to distances up to 20 km. To determine the mechanisms behind this phenomenon, the RASP expeditions monitored the waters adjacent to the outfall with an array of hydrographic, optical and turbulence microstructure sensors in anomaly and ambient background regions. Drogue tracks and mean turbulence parameters for 2 ! 104 microstructure patches were analyzed to understand complex turbulence, fossil turbulence and zombie turbulence near-vertical internal wave transport processes. The dominant mechanism appears to be generic to stratified natural fluids including planet and star atmospheres and is termed beamed zombie turbulence maser action (BZTMA). Most of the bottom turbulent kinetic energy is converted to ! 100 m fossil turbulence waves. These activate secondary (zombie) turbulence in outfall fossil turbulence patches that transmit heat, mass, chemical species, momentum and information vertically to the sea surface for detection in an efficient maser action. The transport is beamed in intermittent mixing chimneys.
NASA Technical Reports Server (NTRS)
Embleton, Tony F. W.; Daigle, Gilles A.
1991-01-01
Reviewed here is the current state of knowledge with respect to each basic mechanism of sound propagation in the atmosphere and how each mechanism changes the spectral or temporal characteristics of the sound received at a distance from the source. Some of the basic processes affecting sound wave propagation which are present in any situation are discussed. They are geometrical spreading, molecular absorption, and turbulent scattering. In geometrical spreading, sound levels decrease with increasing distance from the source; there is no frequency dependence. In molecular absorption, sound energy is converted into heat as the sound wave propagates through the air; there is a strong dependence on frequency. In turbulent scattering, local variations in wind velocity and temperature induce fluctuations in phase and amplitude of the sound waves as they propagate through an inhomogeneous medium; there is a moderate dependence on frequency.
NASA Technical Reports Server (NTRS)
Rubesin, Morris W.
1987-01-01
Recent developments at several levels of statistical turbulence modeling applicable to aerodynamics are briefly surveyed. Emphasis is on examples of model improvements for transonic, two-dimensional flows. Experience with the development of these improved models is cited to suggest methods of accelerating the modeling process necessary to keep abreast of the rapid movement of computational fluid dynamics into the computation of complex three-dimensional flows.
NASA Astrophysics Data System (ADS)
Kühnen, Jakob; Hof, Björn
2015-11-01
We show that a simple modification of the velocity profile in a pipe can lead to a complete collapse of turbulence and the flow fully relaminarises. The annihilation of turbulence is achieved by a steady manipulation of the streamwise velocity component alone, greatly reducing control efforts. Several different control techniques are presented: one with a local modification of the flow profile by means of a stationary obstacle, one employing a nozzle injecting fluid through a small gap at the pipe wall and one with a moving wall, where a part of the pipe is shifted in the streamwise direction. All control techniques act on the flow such that the streamwise velocity profile becomes more flat and turbulence gradually grows faint and disappears. In a smooth straight pipe the flow remains laminar downstream of the control. Hence a reduction in skin friction by a factor of 8 and more can be accomplished. Stereoscopic PIV-measurements and movies of the development of the flow during relaminarisation are presented.
NASA Astrophysics Data System (ADS)
Griessbaum, F.; Narita, Y.; Held, A.; Klemm, O.; Uematsu, M.
2006-12-01
Recent studies of emission and deposition of atmospheric aerosols employing the eddy covariance technique (EC) have been conducted in the terrestrial and marine boundary layer, the latter mainly limited to fixed platforms in the coastal domain. The captioned approach enables us to study the sinks and sources of atmospheric aerosols and their impact on the sea/air exchange of materials and on the direct and indirect radiation effect in the marine boundary layer from moving platforms, such as vessels. Measurements of atmospheric parameters from a ship are challenging especially due to the flow distortion caused by the ship's superstructure and the vessel's motions. It is known from recent work employing computational fluid dynamics (CFD) on the geometry of vessels, that the most suitable place for undistorted measurements is at the very bow and the most elevated location, commonly the foremast. For this reason, the entire eddy covariance instrumentation was fixed at the very top of the foremast, consisting of: sonic anemometer, condensation particle counter (CPC, from 5 nm particle diameter), fog droplet spectrometer (2 to 50 μm droplet diameter), CO{_2}/H{_2}O Analyser and an inertial sensing system. In order to operate the CPC also while the vessel is underway or in rough sea conditions, the max tilt angle (rolling and pitching) of the CPC was technically improved from 10° up to over 30°. This EC-measurement was conducted over the high primary productive region with high frequency of sea fog appearance during the cruise MR06-4 on R/V Mirai from Hokkaido, Japan, to the Chukchi Sea in Arctic Ocean, lasting from August 2 through September 29, 2006. Initial results will be presented and discussed.
Learning to soar in turbulent environments.
Reddy, Gautam; Celani, Antonio; Sejnowski, Terrence J; Vergassola, Massimo
2016-08-16
Birds and gliders exploit warm, rising atmospheric currents (thermals) to reach heights comparable to low-lying clouds with a reduced expenditure of energy. This strategy of flight (thermal soaring) is frequently used by migratory birds. Soaring provides a remarkable instance of complex decision making in biology and requires a long-term strategy to effectively use the ascending thermals. Furthermore, the problem is technologically relevant to extend the flying range of autonomous gliders. Thermal soaring is commonly observed in the atmospheric convective boundary layer on warm, sunny days. The formation of thermals unavoidably generates strong turbulent fluctuations, which constitute an essential element of soaring. Here, we approach soaring flight as a problem of learning to navigate complex, highly fluctuating turbulent environments. We simulate the atmospheric boundary layer by numerical models of turbulent convective flow and combine them with model-free, experience-based, reinforcement learning algorithms to train the gliders. For the learned policies in the regimes of moderate and strong turbulence levels, the glider adopts an increasingly conservative policy as turbulence levels increase, quantifying the degree of risk affordable in turbulent environments. Reinforcement learning uncovers those sensorimotor cues that permit effective control over soaring in turbulent environments. PMID:27482099
Neutral surface layer turbulence over complex terrain
Bowen, B.M.
1995-09-01
Accurate turbulence estimates are important input to atmospheric dispersion models since they characterize downwind dispersion and hence, potential pollutant concentrations. When only basic wind information is available, an atmospheric modeler must first estimate roughness length (z{sub 0},) at the location of interest, ({mu}*) from similarity theory using average wind speed ({mu}) and z{sub 0}, and finally apply experimentally derived relationships to determine the turbulence intensities. Even when turbulence coefficients are measured, the turbulence profile must be estimated in the surface layer, using, for example, the power law recommended in a US Environmental Protection Agency guidance document. In this study, turbulent intensities and wind profiles are analyzed in eight direction sectors during near neutral stability. ``Local`` and ``regional`` roughness lengths are calculated from wind speed profiles and from longitudinal turbulence intensities ({sigma}{sub {mu}}) at both sites. With ``regional`` roughness length, complex terrain features are in effect the roughness elements. Profiles of median, 15-minute averaged turbulence intensities {sigma}{sub {mu}}, {sigma}{sub {nu}} and {sigma}{sub w} are calculated at both sites. Profiles of median {sigma}{sub {theta}} and {sigma}{sub {phi}} are also calculated using four mean values of regional z{sub 0} at both sites. Finally, differences between widely-used turbulence relationships and the relationships determined in this study, and their possible effect on model results, are discussed.
Baker, K; Stappaerts, E; Gavel, D; Wilks, S; Tucker, J; Silva, D; Olsen, J; Olivier, S; Young, P; Kartz, M; Flath, L; Kruelivitch, P; Crawford, J; Azucena, O
2004-03-04
Atmospheric propagation results for a high-speed, large-actuator-number, adaptive optics system are presented. The system uses a MEMS-based spatial light modulator correction device with 1024 actuators. Tests over a 1.35 km path achieved correction speeds in excess of 800 Hz and Strehl ratios close to 0.5. The wave-front sensor was based on a quadrature interferometer that directly measures phase. This technique does not require global wave-front reconstruction, making it relatively insensitive to scintillation and phase residues. The results demonstrate the potential of large actuator number MEMS-based spatial light modulators to replace conventional deformable mirrors.
NASA Technical Reports Server (NTRS)
Manning, Robert M.
2005-01-01
Solutions are derived for the generalized mutual coherence function (MCF), i.e., the second order moment, of a random wave field propagating through a random medium within the context of the extended parabolic equation. Here, "generalized" connotes the consideration of both the transverse as well as the longitudinal second order moments (with respect to the direction of propagation). Such solutions will afford a comparison between the results of the parabolic equation within the pararaxial approximation and those of the wide-angle extended theory. To this end, a statistical operator method is developed which gives a general equation for an arbitrary spatial statistical moment of the wave field. The generality of the operator method allows one to obtain an expression for the second order field moment in the direction longitudinal to the direction of propagation. Analytical solutions to these equations are derived for the Kolmogorov and Tatarskii spectra of atmospheric permittivity fluctuations within the Markov approximation.
An investigation of turbulence structure in a low-Reynolds-number incompressible turbulent boundary
NASA Technical Reports Server (NTRS)
White, B. R.; Strataridakis, C. J.
1987-01-01
An existing high turbulence intensity level (5%) atmospheric boundary-layer wind tunnel has been successfully converted to a relatively low level turbulence (0.3%) wind tunnel through extensive modification, testing, and calibration. A splitter plate was designed, built, and installed into the wind-tunnel facility to create thick, mature, two-dimensional turbulent boundary layer flow at zero pressure gradient. Single and cross hot-wire measurements show turbulent boundary layer characteristics of good quality with unusually large physical size, i.e., viscous sublayer of the order of 1 mm high. These confirm the potential ability of the tunnel to be utilized for future high-quality near-wall turbulent boundary layer measurements. It compares very favorably with many low turbulence research tunnels.
Magnetohydrodynamic Turbulence
NASA Astrophysics Data System (ADS)
Montgomery, David C.
2004-01-01
Magnetohydrodynamic (MHD) turbulence theory is modeled on neutral fluid (Navier-Stokes) turbulence theory, but with some important differences. There have been essentially no repeatable laboratory MHD experiments wherein the boundary conditions could be controlled or varied and a full set of diagnostics implemented. The equations of MHD are convincingly derivable only in the limit of small ratio of collision mean-free-paths to macroscopic length scales, an inequality that often goes the other way for magnetofluids of interest. Finally, accurate information on the MHD transport coefficients-and thus, the Reynolds-like numbers that order magnetofluid behavior-is largely lacking; indeed, the algebraic expressions used for such ingredients as the viscous stress tensor are often little more than wishful borrowing from fluid mechanics. The one accurate thing that has been done extensively and well is to solve the (strongly nonlinear) MHD equations numerically, usually in the presence of rectangular periodic boundary conditions, and then hope for the best when drawing inferences from the computations for those astrophysical and geophysical MHD systems for which some indisputably turbulent detailed data are available, such as the solar wind or solar prominences. This has led to what is perhaps the first field of physics for which computer simulations are regarded as more central to validating conclusions than is any kind of measurement. Things have evolved in this way due to a mixture of the inevitable and the bureaucratic, but that is the way it is, and those of us who want to work on the subject have to live with it. It is the only game in town, and theories that have promised more-often on the basis of some alleged ``instability''-have turned out to be illusory.
Explosive turbulent magnetic reconnection.
Higashimori, K; Yokoi, N; Hoshino, M
2013-06-21
We report simulation results for turbulent magnetic reconnection obtained using a newly developed Reynolds-averaged magnetohydrodynamics model. We find that the initial Harris current sheet develops in three ways, depending on the strength of turbulence: laminar reconnection, turbulent reconnection, and turbulent diffusion. The turbulent reconnection explosively converts the magnetic field energy into both kinetic and thermal energy of plasmas, and generates open fast reconnection jets. This fast turbulent reconnection is achieved by the localization of turbulent diffusion. Additionally, localized structure forms through the interaction of the mean field and turbulence. PMID:23829741
Middle Atmosphere Program. Handbook for MAP. Volume 18: Extended abstracts
NASA Technical Reports Server (NTRS)
Kato, S. (Editor)
1985-01-01
Various topics related to middle atmosphere research are discussed. Variability of the middle atmosphere during winter, climatology, gravity waves, atmospheric turbulence, transport processes of trace species and aerosols, and research in the Antarctic are among the topics covered.
What is turbulence and which way does it cascade?
NASA Astrophysics Data System (ADS)
Gibson, Carl H.
2009-11-01
Turbulence is defined as an eddy-like state of fluid motion where the inertial vortex forces of the eddies are larger than any of the other forces that tend to damp the eddies out. Inertial vortex forces vxw are zero for irrotational flows, so irrotational flows are not turbulent by definition even though they may be random and induced by turbulence. Because the vorticity w is always produced at small scales, turbulence always cascades from small scales to large. Turbulence growth is limited by vertical buoyancy forces at the Ozmidov scale of fossilization and by horizontal Coriolis forces at the Hopfinger scale of fossilization. Fossil turbulence is defined as a perturbation in any hydrophysical field produced by turbulence that persists after the fluid is no longer turbulent at the scale of the perturbation. Most turbulent mixing in the ocean and atmosphere occurs in fossil turbulence patches where most of the turbulent kinetic energy of the patch has radiated near vertically as fossil turbulence waves. Vertical heat, mass, momentum and information transport in the ocean is dominated by an intermittent generic process termed beamed zombie turbulence maser action mixing chimneys (see http: //maeresearch.ucsd.edu /˜cgibson /Documents2007 /GibsonBB08Nov26Alist.htm).
Imaging through turbulence using a plenoptic sensor
NASA Astrophysics Data System (ADS)
Wu, Chensheng; Ko, Jonathan; Davis, Christopher C.
2015-09-01
Atmospheric turbulence can significantly affect imaging through paths near the ground. Atmospheric turbulence is generally treated as a time varying inhomogeneity of the refractive index of the air, which disrupts the propagation of optical signals from the object to the viewer. Under circumstances of deep or strong turbulence, the object is hard to recognize through direct imaging. Conventional imaging methods can't handle those problems efficiently. The required time for lucky imaging can be increased significantly and the image processing approaches require much more complex and iterative de-blurring algorithms. We propose an alternative approach using a plenoptic sensor to resample and analyze the image distortions. The plenoptic sensor uses a shared objective lens and a microlens array to form a mini Keplerian telescope array. Therefore, the image obtained by a conventional method will be separated into an array of images that contain multiple copies of the object's image and less correlated turbulence disturbances. Then a highdimensional lucky imaging algorithm can be performed based on the collected video on the plenoptic sensor. The corresponding algorithm will select the most stable pixels from various image cells and reconstruct the object's image as if there is only weak turbulence effect. Then, by comparing the reconstructed image with the recorded images in each MLA cell, the difference can be regarded as the turbulence effects. As a result, the retrieval of the object's image and extraction of turbulence effect can be performed simultaneously.
Signal modeling of turbulence-distorted imagery
NASA Astrophysics Data System (ADS)
Young, S. Susan; Driggers, Ronald G.; Krapels, Keith; Espinola, Richard L.; Reynolds, Joseph P.; Cha, Jae
2009-05-01
Understanding turbulence effects on wave propagation and imaging systems has been an active research area for more than 50 years. Conventional atmospheric optics methods use statistical models to analyze image degradation effects that are caused by turbulence. In this paper, we intend to understand atmospheric turbulence effects using a deterministic signal processing and imaging theory point of view and modeling. The model simulates the formed imagery by a lens by tracing the optical rays from the target through a band of turbulence. We examine the nature of the turbulence-degraded image, and identify its characteristics as the parameters of the band of turbulence, e.g., its width, angle, and index of refraction, are varied. Image degradation effects due to turbulence, such as image blurring and image dancing, are revealed by this signal modeling. We show that in fact these phenomena can be related not only to phase errors in the frequency domain of the image but also a 2D modulation effect in the image spectrum. Results with simulated and realistic data are provided.
Statistical turbulence theory and turbulence phenomenology
NASA Technical Reports Server (NTRS)
Herring, J. R.
1973-01-01
The application of deductive turbulence theory for validity determination of turbulence phenomenology at the level of second-order, single-point moments is considered. Particular emphasis is placed on the phenomenological formula relating the dissipation to the turbulence energy and the Rotta-type formula for the return to isotropy. Methods which deal directly with most or all the scales of motion explicitly are reviewed briefly. The statistical theory of turbulence is presented as an expansion about randomness. Two concepts are involved: (1) a modeling of the turbulence as nearly multipoint Gaussian, and (2) a simultaneous introduction of a generalized eddy viscosity operator.
Correction methods for underwater turbulence degraded imaging
NASA Astrophysics Data System (ADS)
Kanaev, A. V.; Hou, W.; Restaino, S. R.; Matt, S.; Gładysz, S.
2014-10-01
The use of remote sensing techniques such as adaptive optics and image restoration post processing to correct for aberrations in a wavefront of light propagating through turbulent environment has become customary for many areas including astronomy, medical imaging, and industrial applications. EO imaging underwater has been mainly concentrated on overcoming scattering effects rather than dealing with underwater turbulence. However, the effects of turbulence have crucial impact over long image-transmission ranges and under extreme turbulence conditions become important over path length of a few feet. Our group has developed a program that attempts to define under which circumstances application of atmospheric remote sensing techniques could be envisioned. In our experiments we employ the NRL Rayleigh-Bénard convection tank for simulated turbulence environment at Stennis Space Center, MS. A 5m long water tank is equipped with heating and cooling plates that generate a well measured thermal gradient that in turn produces various degrees of turbulence. The image or laser beam spot can be propagated along the tank's length where it is distorted by induced turbulence. In this work we report on the experimental and theoretical findings of the ongoing program. The paper will introduce the experimental setup, the techniques used, and the measurements made as well as describe novel methods for postprocessing and correction of images degraded by underwater turbulence.
Cui, Linyan; Xue, Bindang; Zhou, Fugen
2015-11-16
Theoretical and experimental investigations have shown that the atmospheric turbulence exhibits both anisotropic and non-Kolmogorov properties. In this work, two theoretical atmosphere refractive-index fluctuations spectral models are derived for optical waves propagating through anisotropic non-Kolmogorov atmospheric turbulence. They consider simultaneously the finite turbulence inner and outer scales and the asymmetric property of turbulence eddies in the orthogonal xy-plane throughout the path. Two anisotropy factors which parameterize the asymmetry of turbulence eddies in both horizontal and vertical directions are introduced in the orthogonal xy-plane, so that the circular symmetry assumption of turbulence eddies in the xy-plane is no longer required. Deviations from the classic 11/3 power law behavior in the spectrum model are also allowed by assuming power law value variations between 3 and 4. Based on the derived anisotropic spectral model and the Rytov approximation theory, expressions for the variance of angle of arrival (AOA) fluctuations are derived for optical plane and spherical waves propagating through weak anisotropic non-Kolmogorov turbulence. Calculations are performed to analyze the derived spectral models and the variance of AOA fluctuations. PMID:26698490
Measurements of turbulence and its evolution and variability during MAP
NASA Technical Reports Server (NTRS)
Hocking, W. K.
1989-01-01
The understanding of turbulence in the middle atmosphere has improved considerably during the MAP period. For a theoretical viewpoint, several advances were made including understanding the ways in which turbulence is generated, and the differences between the rates of diffusion of momentum and heat. Experimentally, a proper understanding of how radars can be used to measure turbulence has emerged, and turbulent energy dissipation rates in the middle atmosphere were measured with MF, HF, and VHF radars. New rocket techniques were developed which have enabled detailed studies of the fine structure of turbulence to be made. While some discrepancies between techniques still exist, these will undoubtedly be resolved soon, and these different techniques are already providing a great improvement in the understanding of turbulence on a global scale.
Mountain wave-induced turbulence: Elevated turbulence zones over a double mountain ridge
NASA Astrophysics Data System (ADS)
Strauss, Lukas; Grubišić, Vanda; Serafin, Stefano
2015-04-01
In their seminal 1974 paper on "Lower Turbulent Zones Associated with Mountain Lee Waves", P. F. Lester and W. A. Fingerhut attempted to characterize regions of low-level turbulence in the lee of mountain ranges, using in situ measurements by research aircraft. Their "Lower Turbulent Zones" (LTZs), associated with large-amplitude mountain waves and ensuing atmospheric rotors, encompass the turbulent flow on the lee side of an obstacle that reaches all the way to the ground. This work is based on aircraft measurements collected during the Terrain-Induced Rotor Experiment (T-REX, Sierra Nevada, California, 2006) that was focused on the investigation of the coupled mountain-wave, rotor, and boundary-layer system. The analysis of airflow during several T-REX Intensive Observation Periods (IOPs) reveals a variety of mountain-flow scenarios, underlining the influence of the secondary orographic obstacle (the White and Inyo Mountains east of the Sierra Nevada) on the formation of wave-induced turbulence zones. In the present contribution, we focus on a scenario characterized by an inversion-capped valley atmosphere documented during T-REX IOPs 1 and 2. The valley inversion imposes an additional positive buoyancy force on the downslope flow in the lee of the primary ridge and prevents it from penetrating deep into the valley. Consequently, the flow separates higher up along the lee slope, forming an elevated turbulence zone that resides above the "virtual valley floor", represented by the inversion. The elevated turbulence zone shares some characteristics of the well-known low-level turbulence zone such as turbulence intensity being highest below the ascending part of the lee wave. However, clear indication of flow reversal at the bottom of the turbulent region, suggestive of a rotor circulation, is missing. For sufficiently short wavelength of the lee wave, multiple wave crests can fit between the primary and secondary mountain ridge and can give rise to several elevated
PREFACE: Turbulent Mixing and Beyond Turbulent Mixing and Beyond
NASA Astrophysics Data System (ADS)
Abarzhi, Snezhana I.; Gauthier, Serge; Rosner, Robert
2008-10-01
The goals of the International Conference `Turbulent Mixing and Beyond' are to expose the generic problem of Turbulence and Turbulent Mixing in Unsteady Flows to a wide scientific community, to promote the development of new ideas in tackling the fundamental aspects of the problem, to assist in the application of novel approaches in a broad range of phenomena, where the non-canonical turbulent processes occur, and to have a potential impact on technology. The Conference provides the opportunity to bring together scientists from the areas which include, but are not limited to, high energy density physics, plasmas, fluid dynamics, turbulence, combustion, material science, geophysics, astrophysics, optics and telecommunications, applied mathematics, probability and statistics, and to have their attention focused on the long-standing formidable task. The Turbulent Mixing and Turbulence in Unsteady Flows, including multiphase flows, plays a key role in a wide variety of phenomena, ranging from astrophysical to nano-scales, under either high or low energy density conditions. Inertial confinement and magnetic fusion, light-matter interaction and non-equilibrium heat transfer, properties of materials under high strain rates, strong shocks, explosions, blast waves, supernovae and accretion disks, stellar non-Boussinesq and magneto-convection, planetary interiors and mantle-lithosphere tectonics, premixed and non-premixed combustion, oceanography, atmospheric flows, unsteady boundary layers, hypersonic and supersonic flows, are a few examples to list. A grip on unsteady turbulent processes is crucial for cutting-edge technology such as laser-micromachining and free-space optical telecommunications, and for industrial applications in aeronautics. Unsteady Turbulent Processes are anisotropic, non-local and multi-scale, and their fundamental scaling, spectral and invariant properties depart from the classical Kolmogorov scenario. The singular aspects and similarity of the
Atmospheric and adaptive optics
NASA Astrophysics Data System (ADS)
Hickson, Paul
2014-11-01
Atmospheric optics is the study of optical effects induced by the atmosphere on light propagating from distant sources. Of particular concern to astronomers is atmospheric turbulence, which limits the performance of ground-based telescopes. The past two decades have seen remarkable growth in the capabilities and performance of adaptive optics (AO) systems. These opto-mechanical systems actively compensate for the blurring effect of the Earth's turbulent atmosphere. By sensing, and correcting, wavefront distortion introduced by atmospheric index-of-refraction variations, AO systems can produce images with resolution approaching the diffraction limit of the telescope at near-infrared wavelengths. This review highlights the physical processes and fundamental relations of atmospheric optics that are most relevant to astronomy, and discusses the techniques used to characterize atmospheric turbulence. The fundamentals of AO are then introduced and the many types of advanced AO systems that have been developed are described. The principles of each are outlined, and the performance and limitations are examined. Aspects of photometric and astrometric measurements of AO-corrected images are considered. The paper concludes with a discussion of some of the challenges related to current and future AO systems, particularly those that will equip the next generation of large, ground-based optical and infrared telescopes.