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NASA NTRS1986

Persistence of solar wind features

Using data from the plasma and magnetometer experiments on board the Voyagers 1 and 2 during the approach to Jupiter, solar wind persistence is investigated over the period from January 1978 (Voyager 1 passing by Voyager 2) through February 1979. The trajectories of both spacecraft provided a unique opportunity to study the radial evolution and variation of the solar wind over about 3 AU, and to analyze the persistence of solar wind features along the radially increasing separation distance of both Voyagers. Some emphasis is placed on a period of DOY (day of year) 152 through 212, 1978, in which the observed propagation delay time of solar wind signatures between both Voyagers significantly deviates from the expected delay time. A decrease in the correlation coefficient of the corresponding Voyager 1 and 2 data profiles indicates a remarkable change of the solar wind flow. This period in question coincides to a great extent with the interval V of June-July 1978, selected by STIP (Study of Travelling Interplanetary Phenomena).

Rucker, H. O.↗
NASA NTRS1975

Development of solar wind shock models with tensor plasma pressure for data analysis

The development of solar wind shock models with tensor plasma pressure and the comparison of some of the shock models with the satellite data from Pioneer 6 through Pioneer 9 are reported. Theoretically, difficulties were found in non-turbulent fluid shock models for tensor pressure plasmas. For microscopic shock theories nonlinear growth caused by plasma instabilities was frequently not clearly demonstrated to lead to the formation of a shock. As a result no clear choice for a shock model for the bow shock or interplanetary tensor pressure shocks emerged.

Abraham-Shrauner, B.↗
NASA NTRS1987

Users of middle atmosphere models remarks

The procedure followed for shuttle operations is to calculate descent trajectories for each potential shuttle landing site using the Global Reference Atmosphere Model (GRAM) to interactively compute density along the flight path 100 times to bound the statistics. The purpose is to analyze the flight dynamics, along with calculations of heat loads during reentry. The analysis program makes use of the modified version of the Jacchia-70 atmosphere, which includes He bulges over the poles and seasonal latitude variations at lower altitudes. For the troposphere, the 4-D Model is used up to 20 km, Groves from 30 km up to 90 km. It is extrapolated over the globe and faired into the Jacchia atmosphere between 90 and 115 km. Since data on the Southern Hemisphere was lacking, what was done was that the data was flipped over and lagged 6 months. Sometimes when winds are calculated from pressure data in the model there appear to be discontinuities. Modelers indicated that the GRAM was not designed to produce winds, but good wind data is needed for the landing phase of shuttle operations. Use of atmospheric models during reentry is one application where it is obvious that a single integrated atmosphere model is required.

Gamble, Joe↗
NASA NTRS1982

Long-term energy capture and the effects of optimizing wind turbine operating strategies

Methods of increasing energy capture without affecting the turbine design were investigated. The emphasis was on optimizing the wind turbine operating strategy. The operating strategy embodies the startup and shutdown algorithm as well as the algorithm for determining when to yaw (rotate) the axis of the turbine more directly into the wind. Using data collected at a number of sites, the time-dependent simulation of a MOD-2 wind turbine using various, site-dependent operating strategies provided evidence that site-specific fine tuning can produce significant increases in long-term energy capture as well as reduce the number of start-stop cycles and yawing maneuvers, which may result in reduced fatigue and subsequent maintenance.

Miller, A. H.↗
NASA NTRS2000

The Dependence of Ocean Surface Emissivity on Wind Vector as Measured with TMR

Global TMR brightness temperature observations at 18, 21, and 37 GHz have been colocated with near-simultaneous SeaWinds wind vector data as well as with a monthly SST climatological product. The combined data allow us to study the dependence of ocean surface emissivity, at each frequency, upon both wind speed and direction. Results show a clear two-branch wind speed dependence; weak and linear below 6 m/s with an abrupt increase in sensitivity above that point. Our analysis also shows that the nadir-view ocean surface emissivity depends on the angle between the wind direction and TMR's antenna polarization orientation.

Tran, N.↗
NASA NTRS1984

Correlations of supersonic boundary-layer transition on cones including effects of large axial variations in wind-tunnel noise

Transition data on sharp tip cones in two pilot low disturbance wind tunnels at Mach numbers of 3.5 and 5 were correlated in terms of noise parameters with data from several conventional wind tunnels and with data from supersonic flight tests on a transition cone. The noise parameters were developed to account for the large axial variations of the free stream noise and the very high frequency noise spectra that occurred in the low disturbance tunnels for some test conditions. The noise could be varied in these tunnels from high levels, approaching those in conventional tunnels, to extremely low levels. The correlations indicated that transition in the low disturbance tunnels was dominated by the local stream noise that was incident on the cone boundary layer unstream of the neutral stability point. The correlation results also suggested that high frequency components of the low disturbance tunnel noise spectra had significant effects on transition when the noise was incident on the boundary layer both upstream and downstream of the neutral stability point.

Chen, F. J.↗
NASA NTRS1994

On the problem of measuring interannual wind speed variations using SSMI data

The first Special Sensor Microwave Imager (SSMI) was launched on the Defense 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. The 10 deg-zonal averaged monthly mean F8-F10 wind speed difference was negative (positive) for wind speeds less (greater) than 7.9 m/s, reaching -0.43 (0.32) m/s at 5(10) m/s. Between 60 deg S and 60 deg N the 10 deg-zonal averaged monthly mean F8-F10 wind speed bias was greater than +/- 0.5 m/s on several occasions. From 60 deg S - 60 deg N the 1991 average value of the monthly mean root-mean-square difference between daily F8 and F10 wind speeds in 10 deg-longitudinal bands was 2.0 m/s.In the 60 deg S - 60 deg N region, about 50% of the daily F8 and F10 wind speed differences was caused by measurement non-simultaneity and about 50% of the difference was attributed to other factors, such as instrument noise and the different azimuthal orientations of each SSMI.

Halpern, David↗
NASA NTRS1993

On the Problem of Measuring Interannual Wind Speed Variations Using SSMI Data

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.

SSMI↗
NASA NTRS1988

Moisture and latent heat flux variabilities in the tropical Pacific derived from satellite data

This paper describes a method of determining latent heat flux and the ocean-atmosphere moisture from sea surface temperature, precipitable water, and surface wind speed data derived from 1980-1983 observations of SMMR aboard Nimbus 7 above tropical Pacific. The observation period included a very intense El Nino-Southern Oscillation (ENSO) episode. It was found that, during the early phase of the 1982-1983 ENSO, a surface convergence center moved east leading the anomalous equatorial westerlies. At this center, the low wind and high humidity caused negative (low) latent heat flux anomalies, despite anomalously high sea surface temperatures. Latent heat flux was found to play an important role in the seasonal cooling of the upper ocean, except in areas covered by major surface convergence zones and in areas of ocean upwelling.

Liu, W. Timothy↗
NASA NTRS1993

Satellite altimeter measurements of surface wind

Recent analyses of wind speed measurements by the Geosat altimeter showed that the radar cross section is affected by oceanographic factors, particularly by the degree of sea development, which are not directly accounted for in the geophysical model functions (GMF). In the present work, two new GMFs which account for the effects of the actual degree of sea development are proposed. Along with the radar cross section, these models use significant wave height information. One particular version is recommended for applications in oceanographic and climate studies where wind speed (or wind stress) data have to be binned (i.e., averaged over time and/or space intervals). The accuracy of this GMF (overall bias of 0.1 m/s and rms error of about 1.6 m/s) is higher than the accuracy of commonly employed GMFs, while the wave-age-related trend is reduced to a geophysically insignificant level. Finally, the wind speed histograms for the collocated data set are derived and compared with the ground truth data as well as with the histograms yielded by presently known GMFs. It is also shown that the accuracy of altimeter measurements could be increased even further if some additional information on the wave field were available from independent sources (e.g., the dominant wavelength from synthetic aperture radar images).

Glazman, Roman E.↗
NASA NTRS1987

Latitudinal dependence of solar wind speed

The data of King (1979, 1983) and of Hoeksema et al. (1982, 1983) are used to investigate the solar-cycle evolution of solar wind bulk speed as a function of source magnetic field strength. The effects of solar transient events are removed. The data suggest that the latitudinal gradient in background solar wind speed is steepest at solar minimum and broadest at solar maximum. The lowest and highest background speeds are found to remain fairly constant throughout the solar cycle. A function developed for the background solar wind speed is inserted into the improved kinematic code of Hakamada and Akasofu (1982), and solar wind speed and IMF are simulated for two periods in the solar cycle. The observed parameters for specific coronal hole passage are well reproduced by the analysis.

Fry, C. D.↗
NASA NTRS1972

Flow interference in a variable porosity trisonic wind tunnel.

Pressure data from a 20-degree cone-cylinder in a variable porosity wind tunnel for the Mach range 0.2 to 5.0 are compared to an interference free standard in order to determine wall interference effects. Four 20-degree cone-cylinder models representing an approximate range of percent blockage from one to six were compared to curve-fits of the interference free standard at each Mach number and errors determined at each pressure tap location. The average of the absolute values of the percent error over the length of the model was determined and used as the criterion for evaluating model blockage interference effects. The results are presented in the form of the percent error as a function of model blockage and Mach number.

Davis, J. W.↗
NASA NTRS1986

Bidirectional solar wind electron heat flux and hemispherically symmetric polar rain

THe paper examines ISEE 3 solar wind electron data obtained concurrent with reported symmetric polar rain events and it is found that a bidirectional solar wind electron heat flux is present whenever such polar cap events occur. In contrast to the normal situation when only one of the earth's polar caps is magnetically connected to the sun, during hemispherically symmetric polar rain events either both of the earth's polar caps are magnetically connected to the sun, or else both are connected to a magnetic loop which is entirely disconnected from the sun. The relative timing between bidirectional solar wind heat flux and symmetrical polar rain events can be utilized to determine certain magnetospheric quantities such as the cross-tail convection speed.

Gosling, J. T.↗
NASA NTRS1991

Mach 3.5 boundary-layer transition on a cone at angle of attack

Boundary-layer transition on a sharp 5-deg half-angle cone at incidence was investigated at Mach 3.5 in NASA's Supersonic Low-Disturbance Pilot Tunnel. The tests were conducted with low and high levels of freestream acoustic disturbance, and four angles of attack (alpha/theta-c = 0, 0.12, 0.4, and 0.8). Transition data, obtained with and without significantly reduced freestream acoustic disturbance levels, are compared with conventional ('noisy') wind-tunnel data. It was found that, under quiet flow conditions, there was no significant unit Reynolds number effect, whereas with noisy flow conditions, a significant unit Reynolds number effect was measured on and near the windward ray for alpha/theta-c values 0.4 and 0.8.

King, Rudolph A.↗
NASA NTRS2011

Data Driven Model Development for the SuperSonic SemiSpan Transport (S(sup 4)T)

In this report, we will investigate two common approaches to model development for robust control synthesis in the aerospace community; namely, reduced order aeroservoelastic modelling based on structural finite-element and computational fluid dynamics based aerodynamic models, and a data-driven system identification procedure. It is shown via analysis of experimental SuperSonic SemiSpan Transport (S4T) wind-tunnel data that by using a system identification approach it is possible to estimate a model at a fixed Mach, which is parsimonious and robust across varying dynamic pressures.

Kukreja, Sunil L.↗
NASA NTRS1993

Longitudinal structure in atomic oxygen concentrations observed with WINDII on UARS

WINDII, the Wind Imaging Interferometer on the Upper Atmosphere Research Satellite, began atmospheric observations on September 28, 1991 and since then has been collecting data on winds, temperatures and emissions rates from atomic, molecular and ionized oxygen species, as well as hydroxyl. The validation of winds and temperatures is not yet complete, and scientific interpretation has barely begun, but the dominant characteristic of these data so far is the remarkable structure in the emission rate from the excited species produced by the recombination of atomic oxygen. The latitudinal and temporal variability has been noted before by many others. In this preliminary report on WINDII results we draw attention to the dramatic longitudinal variations of planetary wave character in atomic oxygen concentration, as reflected in the OI 557.7 nm emission, and to similar variations seen in the Meine1 hydroxyl band emission.

Shepherd, G. G.↗
NASA NTRS2006

Antarctic Circumpolar Current Transport Variability during 2003-05 from GRACE

Gravity Recovery and Climate Experiment (GRACE) gravity data spanning January 2003 - November 2005 are used as proxies for ocean bottom pressure (BP) averaged over 1 month, spherical Gaussian caps 500 km in radius, and along paths bracketing the Antarctic Circumpolar Current's various fronts. The GRACE BP signals are compared with those derived from the Estimating the Circulation and Climate of the Ocean (ECCO) ocean modeling-assimilation system, and to a non-Boussinesq version of the Regional Ocean Model System (ROMS). The discrepancy found between GRACE and the models is 1.7 cm(sub H2O) (1 cm(sub H2O) similar to 1 hPa), slightly lower than the 1.9 cm(sub H2O) estimated by the authors independently from propagation of GRACE errors. The northern signals are weak and uncorrelated among basins. The southern signals are strong, with a common seasonality. The seasonal cycle GRACE data observed in the Pacific and Indian Ocean sectors of the ACC are consistent, with annual and semiannual amplitudes of 3.6 and 0.6 cm(sub H2O) (1.1 and 0.6 cm(sub H2O) with ECCO), the average over the full southern path peaks (stronger ACC) in the southern winter, on days of year 197 and 97 for the annual and semiannual components, respectively; the Atlantic Ocean annual peak is 20 days earlier. An approximate conversion factor of 3.1 Sv ( Sv equivalent to 10(exp 6) m(exp 3) s(exp -1)) of barotropic transport variability per cm(sub H2O) of BP change is estimated. Wind stress data time series from the Quick Scatterometer (QuikSCAT), averaged monthly, zonally, and over the latitude band 40 de - 65 deg S, are also constructed and subsampled at the same months as with the GRACE data. The annual and semiannual harmonics of the wind stress peak on days 198 and 82, respectively. A decreasing trend over the 3 yr is observed in the three data types.

oceanographic regions↗
NASA NTRS1986

The real-time use of wind profilers in nowcasting

The program for Regional Observing and Forecasting Services (PROFS) has been using wind profile data in experimental forecast applications for over two years, mostly in the form of real-time color displays on the PROFS forecast workstation. The most ambitious test of the workstation to date, the 1985 PROFS Real-Time Experiment (RT-85), ran from 15 May to 23 August, 1985. The use of wind profiler products during this and previous experiments is described. Data from the experimental profiler network in Colorado and from the profiler in Oklahoma are in the form of hourly averages. Arriving data frequently contain errors whose origins range from interference by aircraft in the beams to highway truck traffic. Most of the irregularities are apparent through visual inspection of profiler wind observations plotted on a time-height cross section, but this method of quality control is inadequate if the intended uses of the data involve numerical calculations.

Smith, T. L.↗