SEARCH · Search NASA
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Rainfall modification of scatterometer response from the sea surface was simulated in wind-wave tank experiments. Data show that for a given wind speed, radar cross section increases as rainfall rate increases, but this effect decreases as wind speed increases. An empirical model accounts for these observations.
The following monthly mean global distributions for 1990 are proposed with a common color scale and geographical map: 10-m height wind speed estimated from the Special Sensor Microwave Imager (SSMI) on a United States (US) Air Force Defense Meteorological Satellite Program (DMSP) spacecraft; sea surface temperature estimated from the advanced very high resolution radiometer (AVHRR/2) on a U.S. National Oceanic and Atmospheric Administration (NOAA) spacecraft; Cartesian components of free drifting buoys which are tracked by the ARGOS navigation system on NOAA satellites; and Cartesian components on the 10-m height wind vector computed by the European Center for Medium-Range Weather Forecasting (ECMWF). Charts of monthly mean value, sampling distribution, and standard deviation values are displayed. Annual mean distributions are displayed.
The following monthly mean global distributions for 1991 are presented with a common color scale and geographical map: 10-m height wind speed estimated from the Special Sensor Microwave Imager (SSMI) on a United States Air Force Defense Meteorological Satellite Program (DMSP) spacecraft; sea surface temperature estimated from the advanced very high resolution radiometer (AVHRR/2) on a U.S. National Oceanic and Atmospheric Administration (NOAA) spacecraft; Cartesian components of free-drifting buoys which are tracked by the ARGOS navigation system on NOAA satellites; and Cartesian components of the 10-m height wind vector computed by the European Center for Medium-Range Weather Forecasting (ECMWF). Charts of monthly mean value, sampling distribution, and standard deviation value are displayed. Annual mean distributions are displayed.
The GEOS 3 significant waveheight and ground wind speed estimation algorithms are derived and then applied to all GEOS 3 data in the South Atlantic Bight. The investigation area is divided into five geographical sectors and significant waveheight and wind speed histograms are presented in each sector by month and by season. In the discussion of the histograms, definite seasonal trends are identified and examined.
Following completion of the 9- by 15-Foot Low Speed Wind Tunnel acoustic improvement modification project, a characterization of the flow field throughout the 9- by 15-foot test section was conducted in 2019. The acoustic improvement modifications project included several large-scale tunnel loop modifications and reconstruction of the 9- by 15-Foot Low Speed Wind Tunnel test section and diffuser to decrease the noise floor in the test section. Data were collected at three cross-sectional planes in the 9- by 15-ft test section using a 15-foot traversing calibration rake and a set of eight boundary layer rakes. The data from the characterization test were used to generate calibration relationships for facility operation and understand the flow quality in the new test section, including uniformity, flow angularity, turbulence intensity, and boundary layer characteristics. Additionally, the subsonic quick check rake was used to baseline the check calibration data set for the new test section.
The potential of very-long-baseline interferometry (VLBI) is examined for use in the determination of wind speeds in Venus' lower atmosphere via the differential tracking of entry probes. A simplified mathematical model is presented in detail. An incomplete error analysis based on this model permits an educated guess to be made: an uncertainty in wind speed determination of no more than about 100/t m/sec, where t l is the corresponding time resolution in seconds, is an achievable goal, without the use of transponders on the miniprobes. If transponders are available on all probes, there should be little difficulty in estimating wind speeds with useful precision.
The aa index can be decomposed into two separate components: the leading sporadic component due to solar activity as measured by sunspot number and the residual or recurrent component due to interplanetary disturbances, such as coronal holes. For the interval 1964-2006, a highly statistically important correlation (r = 0.749) is found between annual averages of the aa index and the solar wind speed (especially between the residual component of aa and the solar wind speed, r = 0.865). Because cyclic averages of aa (and the residual component) have trended upward during cycles 11-23, cyclic averages of solar wind speed are inferred to have also trended upward.
The methods and results of measurements for wind speed and atmospheric turbulence in the clouds of Venus are described, and compared with earlier results. The distribution of wind speed obtained from the data of Venera 12 is in good conformity with the data of the preceding Venera and Pioneer probes, indicating the existence of a constant and powerful zonal movement of the troposphere.
The first Advanced Microwave Sounding Unit temperature sounder (AMSU-A) was launched on the NOAA-15 satellite on 13 May 1998. The AMSU-A's higher spatial and radiometric resolutions provide more useful information on the strength of the middle- and upper-tropospheric warm cores associated with tropical cyclones than have previous microwave temperature sounders. The gradient wind relationship suggests that the temperature gradient near the core of tropical cyclones increases nonlinearly with wind speed. The gradient wind equation is recast to include AMSU-A-derived variables, Stepwise regression is used to determine which of these variables is most closely related to maximum sustained winds (V(sub max)). The satellite variables investigated include the radially averaged gradients at two spatial resolutions of AMSU-A channels 1-10 T(sub b) data (delta(sub r)T(sub B)), the squares of these gradients, a channel-15-based scattering index (SI(sub 89)), and area-averaged T(sub B). Calculations of T(sub B) and delta(sub r)T(sub B) from mesoscale model simulations of Andrew reveal the effects of the AMSU spatial sampling on the cyclone warm core presentation. Stepwise regression of 66 AMSU-A terms against National Hurricane Center V(sub max) estimates from the 1998 and 1999 Atlantic hurricane season confirms the existence of a nonlinear relationship between wind speed and radially averaged temperature gradients near the cyclone warm core. Of six regression terms, four are dominated by temperature information, and two are interpreted as correcting for hydrometeor contamination. Jackknifed regressions were performed to estimate the algorithm performance on independent data. For the 82 cases that had in situ measurements of V(sub max), the average error standard deviation was 4.7 m/s. For 108 cases without in situ wind data, the average error standard deviation was 7.5 m/s Operational considerations, including the detection of weak cyclones and false alarm reduction, are also discussed.
Dual-Doppler radar is a relatively new technology in the wind energy community and thus not yet studied vastly. This paper aims to compare horizontal wind speed and direction data retrieved from dual-Doppler radar and profiling lidars within the American WAKE experimeNt (AWAKEN) to investigate the influence of measurement height, wind direction and speed on the comparison. The 10-min averaged data show a better agreement of the measurements for higher altitudes, especially at faster wind speeds. For the wind direction, two sectors of larger differences in the measurements were detected: around 270° transient winds occur with a higher frequency than in other sectors. To explain the different measurement values in the wind direction sector around 90°, further studies, e.g. on the influence of atmospheric stability, are necessary.
A new method to construct a horizontal resolution-dependent wind speed adjustment factor for evaluating tropical cyclones (TCs) in global climate models (GCMs) is presented here. In contrast to the previous studies that used idealized axisymmetric wind fields, this study analyzes 48 hours of 10-second surface wind fields from 1-km TC simulations. The adjustment factor is derived from filtering the simulated TC wind fields onto various horizontal grid spacings typical of those used in GCMs. The new adjustment factor leads to TCs with greater intensity than the existing adjustment factors for horizontal grid spacings smaller than 30 km. This difference is attributed to more realistic wind fields in the TC simulations that contain highly asymmetric, localized patches of higher wind speeds instead of axisymmetric wind fields. Applying the new adjustment factor to select GCM simulations suggests the common interpretation of low-intensity bias in GCM-simulated TCs might be slightly exaggerated.
The microwave brightness temperature measurements for Nimbus-5 electrically scanned microwave radiometer and Nimbus E microwave spectrometer are used to retrieve the atmospheric water vapor, liquid water and wind speed by a quasi-statistical retrieval technique. It is shown that the brightness temperature can be utilized to yield these parameters under various weather conditions. Observations at 19.35 GHz, 22.235 GHz and 31.4 GHz were input to the regression equations. The retrieved values of these parameters for portions of two Nimbus-5 orbits are presented. Then comparison between the retrieved parameters and the available observations on the total water vapor content and the surface wind speed are made. The estimated errors for retrieval are approximately 0.15 g/sq cm for water vapor content, 6.5 mg/sq cm for liquid water content and 6.6 m/sec for surface wind speed.
Long-term enhancements in solar wind speed over timescales on the order of a year appear to be a common feature throughout the heliosphere over heliocentric distances that range from less than 0.72 AU to greater than 60. The origin of these events remains to be determined, but they are almost certainly associated with long-term variations at the solar wind source, in contrast with smaller-scale structures such as CIRs, MIRs, and GMIRs which are dynamical in origin. We present a survey of the long-term speed enhancements observed at the Pioneer Venus Orbiter (PVO), IMP 8, Voyager 2, and Pioneer 10 between 1974 and 1994 and compare this with published reports of smaller-scale events such as MIRs. We examine several of these long-term speed enhancements in detail to identify and characterize aspects of their structure, then describe how that structure evolves with heliocentric distance. Finally we discuss some of the implications of these events.
Microwave remote sensing observations of hurricanes, from NOAA and USAF hurricane surveillance aircraft, provide vital data for hurricane research and operations, for forecasting the intensity and track of tropical storms. The current operational standard for hurricane wind speed and rain rate measurements is the Stepped Frequency Microwave Radiometer (SFMR), which is a nadir viewing passive microwave airborne remote sensor. The Hurricane Imaging Radiometer, HIRAD, will extend the nadir viewing SFMR capability to provide wide swath images of wind speed and rain rate, while flying on a high altitude aircraft. HIRAD was first flown in the Genesis and Rapid Intensification Processes, GRIP, NASA hurricane field experiment in 2010. This paper reports on geophysical retrieval results and provides hurricane images from GRIP flights. An overview of the HIRAD instrument and the radiative transfer theory based, wind speed/rain rate retrieval algorithm is included. Results are presented for hurricane wind speed and rain rate for Earl and Karl, with comparison to collocated SFMR retrievals and WP3D Fuselage Radar images for validation purposes.
Empirical studies suggest a close relationship between the solar-wind speed near the earth and the magnetic structure of the solar corona. The correlation can be used to infer the latitudinal distribution of wind speed at different phases of the sunspot cycle, and to identify the sources of fast, high-latitude wind streams such as those that might be encountered by the Ulysses spacecraft on its journey toward the solar poles during 1992-1995.
Aircraft observed radiances were used to measure surface wind speed and aerosol thickness. Results show that the surface wind speed is related to the width of the glitter pattern.
Map surface wind speed over wide swath (approximately 50-60 km, for aircraft greater than FL600) in hurricanes. Provide research data for understanding hurricane structure, and intensity change. Enable improved forecasts, warnings, and decision support.
The first Special Sensor Microwave Imager (SSMI) was launched on the Defence Meteorological Satellite Program (DMSP) F8 spacecraft in July 1987, and wind speed was no longer retrieved after December 1991. A second SSMI was launched on DMSP F10 in December 1990. Interpretation of the 1987 - 1993 (or longer)SSMI wind speed time series is dependent upon the space and time characteristics of the differences between F8 and F10 SSMI measurements.