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At least 91 records · Page 5

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NASA NTRS1989

A day-to-day comparison study of Seasat scatterometer winds with winds observed from islands in the tropical Pacific

The winds derived from the Seasat-A Satellite Scatterometer (SASS) measurements have been the subject of great interest since the 1978 mission, because of the promise of radically improved wind observations over the world ocean. Due to the early end of the mission, only a few of the planned ground truth validation experiments could be made, and the subsequent lack of sufficient high quality independent wind data for comparison has limited the ability to resolve critical issues regarding the scatterometer's performance and the correct interpretation of its signal. Operational weather observations were made of ocean winds independent of Seasat mission plans during the Seasat mission period; the results are reported of a comparison study using such observations. Previous verification with in situ winds has been primarily in middle latitudes (GOASEX, JASIN, and NDBO buoys); winds observed from nine tropical Pacific islands are compared with nearly contemporaneous measurements taken by SASS during overpasses of the islands.

Davison, Jerry↗

NASA NTRS1992

Near-nadir microwave specular returns from the sea surface - Altimeter algorithms for wind and wind stress

Two approaches have been adopted to construct altimeter wind algorithms: one is based on the mean-square sea surface slope, and the other is based on the Seasat scatterometer wind. Both types of algorithms are critically reviewed with respect to the mechanism governing near-nadir sea returns and the comparison between altimeter and buoy winds. A new algorithm is proposed; it is deduced on the basis of microwave specular reflection and is finely tuned with buoy-measured winds. On the basis of this algorithm and the formula of the wind-stress coefficient, a simple wind-stress algorithm is also proposed.

Wu, Jin↗

NASA NTRS1993

Wind persistence from 2-18 km using a wind profiler

Existing techniques for quantifying the effects of temporal wind variability on launch vehicles employ very limited sets of wind profile pairs derived from rising balloons. Variability due to spatial differences between the drifting balloon and a vehicle trajectory are traditionally ignored. The authors developed a technique to extract high quality wind profiles at frequent time intervals from a Doppler Radar Wind Profiler. This technique was applied to a limited number of data sets gathered from December 1990 through March 1992 at the Kennedy Space Center using the NASA 50 Mhz Wind Profiler. The authors then used these derived wind profiles to demonstrate techniques for quantifying the effects of temporal and spatial variability.

Wilfong, Timothy L.↗

NASA NTRS1991

Hourly wind profiler observations of the jet stream - Wind shear and pilot reports of turbulence

Hourly wind profiler observations of the jet stream are reported on the basis of over 400 hr of wind and temperature data taken during two prolonged jet stream passages over western and central Pennsylvania during mid-November 1986 and mid-January 1987. The mean wind speed profile with error bars for the 79 hr that the Crown radar was determined to be 'under' the jet stream is shown. A mean speed of 83 m/s for the period was found. A plot of wind shear for the hours of interest is given. Typically, the shear was at a maximum from 3 to 4 km below the level of maximum wind. Thus, an aircraft would have to fly through potentially rough air to reach the fuel savings and relative smoothness of flight at the jet stream level. A good correlation between pilot reports of turbulence and wind shear was found.

Syrett, William J.↗

NASA NTRS1995

Elemental composition in the slow solar wind measured with the MASS instrument on WIND

The MASS instrument on WIND contains the first isochronous time-offlight spectrometer to be flown in the solar wind. The first spectra obtained with this instrument has demonstrated its capability to measure the abundances of several high-and low-FIP elements in the solar wind. The derivation of these abundances requires a careful calibration of the charge exchange efficiencies of the relevant ions in carbon foils. These efficiencies and the corresponding instrument functions have been determined in extensive calibration campaigns at different institutions. We present first and preliminary results obtained in slow solar wind streams and we compare these results with those obtained from previous investigations of solar wind abundances and of coronal abundances as derived from Solar Energetic Particles. Recent models of the FIP related fractionation effect predict a depletion of a factor of typically 4 to 5 for high-FIP elements (He, N, O, Ne, Ar, etc.) relative to low-FIP elements (Mg, Fe, Si, etc.). We also compare our results with the detailed predictions of the different models and we discuss the resulting evidence to validate or to invalidate different physical scenarios explaining the feeding and the acceleration of slow stream solar wind.

Bochsler, P.↗

NASA NTRS1997

Altimeter Estimation of Sea Surface Wind Stress for Light to Moderate Winds

Aircraft altimeter and in situ measurements are used to examine relationships between altimeter backscatter and the magnitude of near-surface wind and friction velocities. Comparison of altimeter radar cross section with wind speed is made through the modified Chelton-Wentz algorithm. Improved agreement is found after correcting 10-m winds for both surface current and atmospheric stability. An altimeter friction velocity algorithm is derived based on the wind speed model and an open-ocean drag coefficient. Close agreement between altimeter- and in situ-derived friction velocities is found. For this dataset, quality of the altimeter inversion to surface friction velocity is comparable to that for adjusted winds and clearly better than the inversion to true 10-m wind speed.

Vandemark, Douglas↗

NASA NTRS2006

Physics-based Tests to Identify the Accuracy of Solar Wind Ion Measurements: A Case Study with the Wind Faraday Cups

We present techniques for comparing measurements of velocity, temperature, and density with constraints imposed by the plasma physics of magnetized bi-Maxwellian ions. Deviations from these physics-based constraints are interpreted as arising from measurement errors. Two million ion spectra from the Solar Wind Experiment Faraday Cup instruments on the Wind spacecraft are used as a case study. The accuracy of velocity measurements is determined by the fact that differential flow between hydrogen and helium should be aligned with the ambient magnetic field. Modeling the breakdown of field alignment suggests velocity uncertainties are less than 0.16% in magnitude and 3deg in direction. Temperature uncertainty is found by examining the distribution of observed temperature anisotropies in high-beta solar wind intervals where the firehose, mirror, and cyclotron microinstabilities should drive the distribution to isotropy. The presence of a finite anisotropy at high beta suggests overall temperature uncertainties of 8%. Hydrogen and helium number densities are compared with the electron density inferred from observations of the local electron plasma frequency as a function of solar wind speed and year. We find that after accounting for the contribution of minor ions, the results are consistent with a systematic offset between the two instruments of 34%. The temperature and density methods are sensitive to non-Maxwellian features such as heat flux and proton beams and as a result are more suited to slow solar wind where these features are rare. These procedures are of general use in identifying the accuracy of observations from any solar wind ion instrument.

Kasper, J. C.↗

NASA NTRS2013

Integrating Wind Profiling Radars and Radiosonde Observations with Model Point Data to Develop a Decision Support Tool to Assess Upper-Level Winds for Space Launch

On the day of launch, the 45th Weather Squadron (45 WS) Launch Weather Officers (LWOs) monitor the upper-level winds for their launch customers. During launch operations, the payload/launch team sometimes asks the LWOs if they expect the upper-level winds to change during the countdown. The LWOs used numerical weather prediction model point forecasts to provide the information, but did not have the capability to quickly retrieve or adequately display the upper-level observations and compare them directly in the same display to the model point forecasts to help them determine which model performed the best. The LWOs requested the Applied Meteorology Unit (AMU) develop a graphical user interface (GUI) that will plot upper-level wind speed and direction observations from the Cape Canaveral Air Force Station (CCAFS) Automated Meteorological Profiling System (AMPS) rawinsondes with point forecast wind profiles from the National Centers for Environmental Prediction (NCEP) North American Mesoscale (NAM), Rapid Refresh (RAP) and Global Forecast System (GFS) models to assess the performance of these models. The AMU suggested adding observations from the NASA 50 MHz wind profiler and one of the US Air Force 915 MHz wind profilers, both located near the Kennedy Space Center (KSC) Shuttle Landing Facility, to supplement the AMPS observations with more frequent upper-level profiles. Figure 1 shows a map of KSC/CCAFS with the locations of the observation sites and the model point forecasts.

Bauman, William H., III↗

NASA NTRS2012

Quality Control Algorithms for the Kennedy Space Center 50-Megahertz Doppler Radar Wind Profiler Winds Database

This paper presents the process used by the Marshall Space Flight Center Natural Environments Branch (EV44) to quality control (QC) data from the Kennedy Space Center's 50-MHz Doppler Radar Wind Profiler for use in vehicle wind loads and steering commands. The database has been built to mitigate limitations of using the currently archived databases from weather balloons. The DRWP database contains wind measurements from approximately 2.7-18.6 km altitude at roughly five minute intervals for the August 1997 to December 2009 period of record, and the extensive QC process was designed to remove spurious data from various forms of atmospheric and non-atmospheric artifacts. The QC process is largely based on DRWP literature, but two new algorithms have been developed to remove data contaminated by convection and excessive first guess propagations from the Median Filter First Guess Algorithm. In addition to describing the automated and manual QC process in detail, this paper describes the extent of the data retained. Roughly 58% of all possible wind observations exist in the database, with approximately 100 times as many complete profile sets existing relative to the EV44 balloon databases. This increased sample of near-continuous wind profile measurements may help increase launch availability by reducing the uncertainty of wind changes during launch countdown

Barbre, Robert E., Jr.↗

NASA NTRS2014

Three-Dimensional Wind Profiling of Offshore Wind Energy Areas With Airborne Doppler Lidar

A technique has been developed for imaging the wind field over offshore areas being considered for wind farming. This is accomplished with an eye-safe 2-micrometer wavelength coherent Doppler lidar installed in an aircraft. By raster scanning the aircraft over the wind energy area (WEA), a three-dimensional map of the wind vector can be made. This technique was evaluated in 11 flights over the Virginia and Maryland offshore WEAs. Heights above the ocean surface planned for wind turbines are shown to be within the marine boundary layer, and the wind vector is seen to show variation across the geographical area of interest at turbine heights.

Koch, Grady J.↗

NASA NTRS2015

Quality Control of Wind Data from 50-MHz Doppler Radar Wind Profiler

Upper-level wind profiles obtained from a 50-MHz Doppler Radar Wind Profiler (DRWP) instrument at Kennedy Space Center are incorporated in space launch vehicle design and day-of-launch operations to assess wind effects on the vehicle during ascent. Automated and manual quality control (QC) techniques are implemented to remove spurious data in the upper-level wind profiles caused from atmospheric and non-atmospheric artifacts over the 2010-2012 period of record (POR). By adding the new quality controlled profiles with older profiles from 1997-2009, a robust database will be constructed of upper-level wind characteristics. Statistical analysis will determine the maximum, minimum, and 95th percentile of the wind components from the DRWP profiles over recent POR and compare against the older database. Additionally, this study identifies specific QC flags triggered during the QC process to understand how much data is retained and removed from the profiles.

Vacek, Austin D.↗

NASA NTRS2015

Quality Control of Wind Data from 50-MHz Doppler Radar Wind Profiler

Vacek, Austin↗

NASA NTRS2016

Quality Control of Wind Data from 50-MHz Doppler Radar Wind Profiler

Vacek, Austin↗

NASA NTRSDate not supplied

Novel Mars In-situ Wind & Wind-Blown Particle Measurement Instruments

Mars Sonic Anemometer We have developed the Mars Sonic Anemometer: an in-situ wind measuring instrument. It uses transducers to transmit ‘chirps’ through a volume of atmosphere and measures wind direction, speed, and temperature based on the chirp travel times when received by a paired transducer (fig 1). This method can rapidly take multiple samples of wind (~20 Hz) and can measure gentler wind speeds (~0.05 m/s) than current planetary weather stations (~1Hz and ~2m/s) and is more durable than recent Mars wind sensors. The Sonic Anemometer opens new avenues of research into Mars surface-to-atmosphere exchange (e.g., of heat, momentum or trace gases). It also can be recast as a hydrogen ortho-para sensor for a giant planet descent probe or as an infrasound detector for Earth or Venus. The performance of the sensor at Mars-like conditions of 6mbar of CO2 was validated at the Danish Mars Wind Tunnel.

Donald J Banfield↗

NASA NTRS1976

Wind tunnel measurements of the tower shadow on models of the ERDA/NASA 100 KW wind turbine tower

Detailed wind speed profile measurements were made in the wake of 1/25 scale and 1/48 scale tower models to determine the magnitude of the speed reduction (the tower shadow). The 1/25 scale tower modeled closely the actual wind turbine including the service stairway and the equipment elevator rails on one face. The 1/48 scale model was made of all tubular members. Measurements were made on the 1/25 scale model with and without the stairway and elevator rails, and on the 1/48 all tube model without stairs and rails. The test results show that the stairs and rails were a major source of wind flow blockage. The all tubular 1/48 scale tower was found to offer less resistance to the wind than the 1/25 scale model that contained a large number of square sections. Shadow photos are included to show the extent of the blockage offered to the wind from various directions.

Savino, J. M.↗

NASA NTRS1977

Possible origins of time variability in Jupiter's outer magnetosphere. I - Variations in solar wind dynamic pressure. II - Variations in solar wind magnetic field

Attention is given to the effect of changes in the dynamic pressure of the solar wind on the structure of a centrifugally driven planetary wind from Jupiter. It is suggested that dynamic pressure variations can induce a transition between a super-Alfvenic wind and a sub-Alfvenic wind breeze on Jupiter's dayside. This could possibly account for the observed large-scale changes in the structure of Jupiter's outer magnetosphere. An attempt is then made to conceptually merge planetary wind models of Jupiter's outer magnetosphere with reconnection models of Jupiter's outer magnetosphere.

Coroniti, F. V.↗

NASA NTRS1978

Synchronization of wind turbine generators against an infinite bus under gusting wind conditions

Studies of synchronizing a wind turbine generator against an infinite bus are performed on a digital computer. In the digital simulation, wind gusts of different magnitudes and durations are hypothesized. Prior to the synchronization, differences of the frequency and phase position between voltages of the alternator and the bus are also included in the simulation. Solutions for rotor speed, generator power angle, electromagnetic torque, wind turbine torque, wind turbine blade pitch angle, and armature current are simulated and presented graphically. The ERDA-NASA 100-kW wind turbine is used as a case study. The results so obtained will thus have immediate applications.

Hwang, H. H.↗

NASA NTRS1978

A comparison of cloud motion winds from ATS 6 images with coinciding SMS 1 winds

A methodology is developed for accurate measurement of cloud motion winds from the geosynchronous ATS 6 image data. Attitude changes between consecutive images (as a function of scan-line number) are accounted for in wind computations through measurement of the earth-edge displacements between the successive infrared images. Also, an image matching procedure is used to remove obvious and distracting image distortions. The availability of SMS imagery coinciding with ATS 6 imagery makes SMS an excellent reference against which the quality of ATS 6 winds can be tested. The resulting winds inferred from cloud displacement measurements taken from a sequence of the corrected images are found to agree better than 2 m/sec rms with winds measured from coincident SMS 1 imagery.

Kuhlow, W. W.↗