SEARCH · Search NASA

Results for “wind direction variability”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6

All sources NASA NTRS DOE OSTI

NASA NTRS1981

The structure of short gravity waves on the ocean surface

A brief review is given of the salient properties of short gravity waves and the way in which their structure is modified by longer waves or swell, by variable currents, and by internal waves. It is noted that an underlying swell produces a mottled pattern in synthetic aperture radar (SAR) imagery, and an expression is derived giving the fractional modulation in backscattering cross section of the ocean surface in terms of the slope of an underlying swell, the wind direction, and the direction of swell propagation relative to the angle of observation. The expression provides the possibility in appropriate circumstances of estimating the swell slope by remote sensing, in addition to the wavelength and direction of propagation, which can be measured directly from the imagery. An account is also given of the refraction of waves in variable currents and internal waves.

Phillips, O. M.↗

NASA NTRS1993

Modeling of topographic effects on Antarctic sea ice using multivariate adaptive regression splines

The role of seafloor topography in the spatial variations of the southern ocean sea ice cover as observed (every other day) by the Nimbus 7 scanning multichannel microwave radiometer satellite in the years 1980, 1983, and 1984 is studied. Bottom bathymetry can affect sea ice surface characteristics because of the basically barotropic circulation of the ocean south of the Antarctic Circumpolar current. The main statistical tool used to quantify this effect is a local nonparametric regression model of sea ice concentration as a function of the depth and its first two derivatives in both meridional and zonal directions. First, we model the relationship of bathymetry to sea ice concentration in two sudy areas, one over the Maud Rise and the other over the Ross Sea shelf region. The multiple correlation coefficient is found to average 44% in the Maud Rise study area and 62% in the Ross Sea study area over the years 1980, 1983, and 1984. Second, a strategy of dividing the entire Antarctic region into an overlapping mosaic of small areas, or windows is considered. Keeping the windows small reduces the correlation of bathymetry with other factors such as wind, sea temperature, and distance to the continent. We find that although the form of the model varies from window to window due to the changing role of other relevant environmental variables, we are left with a spatially consistent ordering of the relative importance of the topographic predictors. For a set of three representative days in the Austral winter of 1980, the analysis shows that an average of 54% of the spatial variation in sea ice concentration over the entire ice cover can be attributed to topographic variables. The results thus support the hypothesis that there is a sea ice to bottom bathymetry link. However this should not undermine the considerable influence of wind, current, and temperature which affect the ice distribution directly and are partly responsible for the observed bathymetric effects.

De Veaux, Richard D.↗

NASA NTRSDate not supplied

Multi-source Estimates of Land / Ocean Moisture Transport Variability over the Satellite Era

It is widely appreciated that atmospheric transport of water from the world’s oceans is a process key to planetary energy balance as well as Earth's habitability. What is not yet clear is the extent of variability in moisture transports, the relative importance of interdecadal variability versus climate change signals, and importantly, our ability to quantify these changes. This work assesses variations in moisture transport variability during the satellite era (~1980 to present) by comparing several different estimates. (i) The most direct estimate is the vertically integrated flux convergence of moisture from reanalyses which use observed wind and moisture information. (ii) One alternative estimate comes from P-ET over land taken from global hydrologic models constrained with precipitation and near-surface meteorology. Here we use an ensemble of six models. An adjunct to this method is to employ satellite derive ET (e.g., GLEAM or DOLCE). (iii) Complementary to this is E-P over the global oceans derived from satellite estimates of P such as TRMM, GPM and GPCP and SeaFlux V3 or J-OFURO3 estimates of E, all relying heavily upon microwave measurements. Transport between land and oceans must essentially balance at monthly scales, i.e., vanish globally. (iv) a fourth perspective comes from estimate of terrestrial RO + storage rate, delta S. G-RUN Ensemble which uses observed streamflow and P measurements to calibrate a statistical model provides the former while GRACE, GRACE-FO provide total water storage anomalies used to calculate storage rate changes. GRACE REC uses GRACE data to train a precipitation-driven statistical model to extend storage estimates before the GRACE era. (All of these alternatives to reanalysis estimates also consider the small atmospheric column water vapor contribution.) We examine the transport changes from these three different methodologies, their relative accuracies and discuss the origin of their differences. Regional trends in moisture flux divergence and their role in multi-decadal trends are considered. Interannual variability arising in connection with ENSO variability is a dominant signal, driven largely by P changes. Trends since 1980 include reductions in moisture delivery to the western U.S., eastern Brazil, and central Africa with recovery of moisture convergence to the Sahel and parts of eastern North America.

Franklin Robertson↗

NASA NTRS1958

Characteristics of the Langley 8-foot Transonic Tunnel with Slotted Test Section

A large wind tunnel, approximately 8 feet in diameter, has been converted to transonic operation by means of slots in the boundary extending in the direction of flow. The usefulness of such a slotted wind tunnel, already known with respect to the reduction of the subsonic blockage interference and the production of continuously variable supersonic flows, has been augmented by devising a slot shape with which a supersonic test region with excellent flow quality could be produced. Experimental locations of detached shock waves ahead of axially symmetric bodies at low supersonic speeds in the slotted test section agreed satisfactorily with predictions obtained by use of existing approximate methods.

Wright, Ray H↗

NASA NTRS2024

High Spectral Resolution Lidar – Generation 2 (HSRL-2) Retrievals of Ocean Surface Wind Speed: Methodology and Evaluation

Ocean surface wind speed (i.e., wind speed 10 m above sea level) is a critical parameter used by atmospheric models to estimate the state of the marine atmospheric boundary layer (MABL). Accurate surface wind speed measurements in diverse locations are required to improve characterization of MABL dynamics and assess how models simulate large-scale phenomena related to climate change and global weather patterns. To provide these measurements, this study introduces and evaluates a new surface wind speed data product from the NASA Langley Research Center nadir-viewing High Spectral Resolution Lidar – generation 2 (HSRL-2) using data collected as part of the NASA Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) mission. The HSRL-2 can directly measure vertically resolved aerosol backscatter and extinction profiles without additional constraints or assumptions, enabling the instrument to accurately derive atmospheric attenuation and directly determine surface reflectance (i.e., surface backscatter). Also, the high horizontal spatial resolution of the HSRL-2 retrievals (0.5 s or ∼ 75 m along track) allows the instrument to probe the fine-scale spatial variability in surface wind speeds over time along the flight track and over breaks in broken cloud fields. A rigorous evaluation of these retrievals is performed by comparing coincident HSRL-2 and National Center for Atmospheric Research (NCAR) Airborne Vertical Atmosphere Profiling System (AVAPS) dropsonde data, owing to the joint deployment of these two instruments on the ACTIVATE King Air aircraft. These comparisons show correlations of 0.89, slopes of 1.04 and 1.17, and y intercepts of −0.13 and −1.05 m s−1 for linear and bisector regressions, respectively, and the overall accuracy is calculated to be 0.15 ± 1.80 m s−1. It is also shown that the dropsonde surface wind speed data most closely follow the HSRL-2 distribution of wave slope variance using the distribution proposed by Hu et al. (2008) rather than the ones proposed by Cox and Munk (1954) and Wu (1990) for surface wind speeds below 7 m s−1, with this category comprising most of the ACTIVATE data set. The retrievals are then evaluated separately for surface wind speeds below 7 m s−1 and between 7 and 13.3 m s−1 and show that the HSRL-2 retrieves surface wind speeds with a bias of ∼ 0.5 m s−1 and an error of ∼ 1.5 m s−1, a finding not apparent in the cumulative comparisons. Also, it is shown that the HSRL-2 retrievals are more accurate in the summer (−0.18 ± 1.52 m s−1) than in the winter (0.63 ± 2.07 m s−1), but the HSRL-2 is still able to make numerous (N=236) accurate retrievals in the winter. Overall, this study highlights the abilities and assesses the performance of the HSRL-2 surface wind speed retrievals, and it is hoped that further evaluation of these retrievals will be performed using other airborne and satellite data sets.

Sanja Dmitrovic↗

NASA NTRS1998

Variations in Upper-Level Water Vapor Transport Diagnosed from Climatological Satellite Data

GOES-7 VAS measurements during the Pathfinder period (1987-88) have been analysed to reveal seasonal and interannual variations in moisture transport. Long term measurements of quality winds and humidity from satellite estimates show superior benefit in diagnosing middle and upper tropospheric large scale climate variations such as ENSO events and direct circulation systems such as the Hadley Cell. A water Vapor Transport Index (WVTI) has been developed to diagnose preferred regions of strong moisture transport and to gauge the seasonal and interannual intensities detected in the GOES viewing area. Second-order variables that may be derived from GOES winds will be also discussed on the poster.

Lerner, Jeffrey A↗

NASA NTRS2002

Statistical Short-Range Guidance for Peak Wind Speed Forecasts on Kennedy Space Center/Cape Canaveral Air Force Station: Phase I Results

This report describes the results of the ANU's (Applied Meteorology Unit) Short-Range Statistical Forecasting task for peak winds. The peak wind speeds are an important forecast element for the Space Shuttle and Expendable Launch Vehicle programs. The Keith Weather Squadron and the Spaceflight Meteorology Group indicate that peak winds are challenging to forecast. The Applied Meteorology Unit was tasked to develop tools that aid in short-range forecasts of peak winds at tower sites of operational interest. A 7 year record of wind tower data was used in the analysis. Hourly and directional climatologies by tower and month were developed to determine the seasonal behavior of the average and peak winds. In all climatologies, the average and peak wind speeds were highly variable in time. This indicated that the development of a peak wind forecasting tool would be difficult. Probability density functions (PDF) of peak wind speed were calculated to determine the distribution of peak speed with average speed. These provide forecasters with a means of determining the probability of meeting or exceeding a certain peak wind given an observed or forecast average speed. The climatologies and PDFs provide tools with which to make peak wind forecasts that are critical to safe operations.

Lambert, Winifred C.↗

NASA NTRS1993

Experimental aerodynamic characteristics of a generic hypersonic accelerator configuration at Mach numbers 1.5 and 2.0

An experimental investigation of the static longitudinal and lateral-directional aerodynamic characteristics of a generic hypersonic research vehicle was conducted in the Langley Unitary Plan Wind Tunnel (UPWT). A parametric study was performed to determine the interference effects of various model components. Configuration variables included delta and trapezoidal canards; large and small centerline-mounted vertical tails, along with a set of wing-mounted vertical tails; and a set of model noses with different degrees of bluntness. Wing position was varied by changing the longitudinal location and the incidence angle. The test Mach numbers were 1.5 and 2.0 at Reynolds numbers of 1 x 10(exp 6) per foot, 2 x 10(exp 6) per foot, and 4 x 10(exp 6) per foot. Angle of attack was varied from -4 degrees to 27 degrees, and sideslip angle was varied from -8 degrees to 8 degrees. Generally, the effect of Reynolds number did not deviate from conventional trends. The longitudinal stability and lift-curve slope decreased with increasing Mach number. As the wing was shifted rearward, the lift-curve slope decreased and the longitudinal stability increased. Also, the wing-mounted vertical tails resulted in a more longitudinally stable configuration. In general, the lift-drag ratio was not significantly affected by vertical-tail arrangement. The best lateral-directional stability was achieved with the large centerline-mounted tail, although the wing-mounted vertical tails exhibited the most favorable characteristics at the higher angles of attack.

Walker, Ira J.↗

NASA NTRS1994

A variable cross-section model of the bow shock of Venus

Magnetohydrodynamics (MHD) parameters like the Alfvenic and the sonic Mach numbers and the direction of the interplanetary magnetic field profoundly affect the interaction of the solar wind with nonmagnetized conducting objects like Venus. The size of the bow shock depends on the two Mach numbers, whereas asymmetries in its shape are governed by the direction of the magnetic field. This paper introduces a new class of bow shock models in which both the shape and the size are controlled by the upstream plasma and field conditions. We use insights from the MHD theory of shocks for point objects and empirical information from actual bow shock crossings to obtain a semiempirical, semitheoretical model of the Cytherean bow shock. The model was developed from a limited data set obtained from the Galileo flyby of Venus but is also in substantial agreement with Pioneer Venus Orbiter observations. It is shown that the dozen bow shock crossing observed by Galileo under steady conditions of solar wind flow and density were caused by changes in the cross section of the bow shock induced by the changing direction of the interplanetary magnetic field.

Khurana, Krishan K.↗

NASA NTRS1992

Variation in energy balance components from six sites in a native prairie for three years

Six automatic stations were used to evaluate the surface energy and radiation balances on a native prairie near Manhattan, Kansas, using the Bowen ratio technique for a total of 300 days. Data were taken during the periods from May 26 to October 16, 1987, May 10 to September 18, 1988, and July 21 to August 13, 1989. The station site locations were selected to represent burned and unburned treatments on ridges, valley bottoms, and slopes with various aspects. The measured variables were (1) air and wet bulb temperatures at two heights, (2) net radiation, (3) solar radiation (up and down), (4) total hemispherical radiation (up and down), (5) diffuse radiation, (6) soil heat flow and soil temperature, (7) wind speed, (8) wind direction, and (9) precipitation. Energy balance components at the sites were compared for the 3 years. The variation between sites and years was small, even though some sites were as much as 10 km apart and the years had different rainfall amounts. The average values for the four summer intensive field campaigns (IFCs) were as follows: albedo, 0.2; ratio of net radiation to solar radiation, 62 percent; evaporation equivalent, 4 mm/d; Bowen ratio, 0.32; evaporation fraction, 70 percent; and the ratio of evaporation to solar energy, 40 percent. These values were different for the fall IFC. The latent and sensible heat fluxes were more variable than the radiation terms reflecting soil moisture differences between IFCs.

Fritschen, Leo J.↗

NASA NTRS1985

Method for evaluating wind turbine wake effects on wind farm performance

A method of testing the performance of a cluster of wind turbine units an data analysis equations are presented which together form a simple and direct procedure for determining the reduction in energy output caused by the wake of an upwind turbine. This method appears to solve the problems presented by data scatter and wind variability. Test data from the three-unit Mod-2 wind turbine cluster at Goldendale, Washington, are analyzed to illustrate the application of the proposed method. In this sample case the reduction in energy was found to be about 10 percent when the Mod-2 units were separated a distance equal to seven diameters and winds were below rated.

Neustadter, H. E.↗

NASA NTRS1999

Backscatter Modeling at 2.1 Micron Wavelength for Space-Based and Airborne Lidars Using Aerosol Physico-Chemical and Lidar Datasets

Space-based and airborne coherent Doppler lidars designed for measuring global tropospheric wind profiles in cloud-free air rely on backscatter, beta from aerosols acting as passive wind tracers. Aerosol beta distribution in the vertical can vary over as much as 5-6 orders of magnitude. Thus, the design of a wave length-specific, space-borne or airborne lidar must account for the magnitude of 8 in the region or features of interest. The SPAce Readiness Coherent Lidar Experiment under development by the National Aeronautics and Space Administration (NASA) and scheduled for launch on the Space Shuttle in 2001, will demonstrate wind measurements from space using a solid-state 2 micrometer coherent Doppler lidar. Consequently, there is a critical need to understand variability of aerosol beta at 2.1 micrometers, to evaluate signal detection under varying aerosol loading conditions. Although few direct measurements of beta at 2.1 micrometers exist, extensive datasets, including climatologies in widely-separated locations, do exist for other wavelengths based on CO2 and Nd:YAG lidars. Datasets also exist for the associated microphysical and chemical properties. An example of a multi-parametric dataset is that of the NASA GLObal Backscatter Experiment (GLOBE) in 1990 in which aerosol chemistry and size distributions were measured concurrently with multi-wavelength lidar backscatter observations. More recently, continuous-wave (CW) lidar backscatter measurements at mid-infrared wavelengths have been made during the Multicenter Airborne Coherent Atmospheric Wind Sensor (MACAWS) experiment in 1995. Using Lorenz-Mie theory, these datasets have been used to develop a method to convert lidar backscatter to the 2.1 micrometer wavelength. This paper presents comparison of modeled backscatter at wavelengths for which backscatter measurements exist including converted beta (sub 2.1).

Srivastava, V.↗

NASA NTRS2004

Examples of Current and Future Uses of Neural-Net Image Processing for Aerospace Applications

Feed forward artificial neural networks are very convenient for performing correlated interpolation of pairs of complex noisy data sets as well as detecting small changes in image data. Image-to-image, image-to-variable and image-to-index applications have been tested at Glenn. Early demonstration applications are summarized including image-directed alignment of optics, tomography, flow-visualization control of wind-tunnel operations and structural-model-trained neural networks. A practical application is reviewed that employs neural-net detection of structural damage from interference fringe patterns. Both sensor-based and optics-only calibration procedures are available for this technique. These accomplishments have generated the knowledge necessary to suggest some other applications for NASA and Government programs. A tomography application is discussed to support Glenn's Icing Research tomography effort. The self-regularizing capability of a neural net is shown to predict the expected performance of the tomography geometry and to augment fast data processing. Other potential applications involve the quantum technologies. It may be possible to use a neural net as an image-to-image controller of an optical tweezers being used for diagnostics of isolated nano structures. The image-to-image transformation properties also offer the potential for simulating quantum computing. Computer resources are detailed for implementing the black box calibration features of the neural nets.

Decker, Arthur J.↗

NASA NTRS1997

Origin of the Ubiquitous Fast Solar Wind

The solar wind is a direct manifestation of the coronal heating processes which continue to elude us. For over three decades, observations in interplanetary space have identified two types of wind: a slow component with highly variable physical properties also characterized by speeds typically beow 500 kn/s, and a much less variable fast wind flowing on average at 750 km/s1.

solar wind↗

NASA NTRSDate not supplied

Synergy of Satellite Radiation, Precipitation, and Other Meteorological Variable Observations for Global Mean Sea Surface Turbulent Heat Flux Estimation

Sea surface turbulent heat flux is one of the key components in global freshwater and energy balances and plays an important role in atmospheric dynamics, thermodynamics and general circulation. This turbulent heat flux is dominantly decided by sea surface latent heat release with some contribution from sensible heat exchange. The flux and its anomaly could significantly affect ocean heat storage and ocean circulation. They are part of and have great impacts on climate variability. Though the turbulent heat flux is extremely important for the climate and weather systems, only very limited ship and buoy observations of the flux are available over open oceans. There are no global, operational, direct measurements of this crucial meteorological variable. Global estimates are, basically, indirectly calculated from bulk turbulent flux parameterization with a combination of satellite column water vapor, sea surface water temperature, and wind speed observations. Critical parameters such as sea surface air temperature and humidity are estimated from empirical relations of theses variables with the water vapor and sea surface water temperature, respectively. Lacking accurate knowledge on surface air temperature and humidity, uncertainties in the parameterization and potential changes in the non-linear turbulent processes with long-term climate variations could cause large errors in estimated long-term turbulent fluxes from the indirect method as shown in current global sea surface turbulent flux datasets. This study uses synergized data of satellite global radiation, precipitation, and other meteorological variable observations to estimate sea surface turbulent heat fluxes. The radiation observations are made by the satellite Clouds and the Earth’s Radiant Energy System (CERES) sensors, while the global precipitation data is from NASA’s satellite Global Precipitation Climatology Project (GPCP). Other data includes satellite sea surface water temperature and wind speed observations. These datasets are obtained from a wide range of space sensors from passive to active instruments and from visible and near infrared to thermal infrared and microwave spectral sounders. One significant feature of these datasets is that they have multi-decades long climate records. Top-of-atmosphere (TOA) radiation and its anomaly represents the net heat energy input to the climate system, and the oceanic precipitation and ocean-land moisture transport can be used to quantify sea surface latent heat release. Based on the synergized datasets and the principle of global water and energy balances, global mean turbulent heat fluxes are estimated. The turbulent heat anomalies for the first two decades of the 21st century are, then, obtained mainly from global CERES radiation and GPCP precipitation anomalies, along with CERES derived ocean-land heat transports. Analysis indicates that the uncertainties in the estimated turbulent flux anomalies may be reduced considerably. The results suggest a strong needs in synchronized and synergized observations of atmospheric radiation, precipitation, and oceanic meteorological variables for long-term climate studies.

Bing Lin↗

NASA NTRS1970

Aerodynamic characteristics of a six-jet V/STOL configuration with four swing-out lift jets in the transition speed range

A wind-tunnel investigation has been made of the longitudinal aerodynamic characteristics and jet-interference effects of a model of a jet V/STOL variable-sweep fighter airplane that employs four direct-lift engines which swing out from the fuselage and two lift-cruise engines located in the rear part of the fuselage. Data were obtained with two wing areas for various forward speeds and power conditions in the transition speed range. The data are presented without analysis or discussion.

Carter, A. W.↗

NASA NTRS2002

Obtaining Reliable Predictions of Terrestrial Energy Coupling From Real-Time Solar Wind Measurements

Measurements of the interplanetary magnetic field (IMF) from the ACE (Advanced Composition Explorer), Wind, IMP-8 (Interplanetary Monitoring Platform), and Geotail spacecraft have revealed that the IMF variations are contained in phase planes that are tilted with respect to the propagation direction, resulting in continuously variable changes in propagation times between spacecraft, and therefore, to the Earth. Techniques for using 'minimum variance analysis' have been developed in order to be able to measure the phase front tilt angles, and better predict the actual propagation times from the L1 orbit to the Earth, using only the real-time IMF measurements from one spacecraft. The use of empirical models with the IMF measurements at L1 from ACE (or future satellites) for predicting 'space weather' effects has also been demonstrated.

Weimer, Daniel R.↗

NASA NTRS1986

Noise radiation directivity from a wind-tunnel inlet with inlet vanes and duct wall linings

The acoustic radiation patterns from a 1/15th scale model of the Ames 80- by 120-Ft Wind Tunnel test section and inlet have been measured with a noise source installed in the test section. Data were acquired without airflow in the duct. Sound-absorbent inlet vanes oriented parallel to each other, or splayed with a variable incidence relative to the duct long axis, were evaluated along with duct wall linings. Results show that splayed vans tend to spread the sound to greater angles than those measured with the open inlet. Parallel vanes narrowed the high-frequency radiation pattern. Duct wall linings had a strong effect on acoustic directivity by attenuating wall reflections. Vane insertion loss was measured. Directivity results are compared with existing data from square ducts. Two prediction methods for duct radiation directivity are described: one is an empirical method based on the test data, and the other is a analytical method based on ray acoustics.

Soderman, P. T.↗