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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.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

A model for the transient magnetospheric response to sudden solar wind dynamic pressure variations

The evidence for transient variations in the solar wind dynamic pressure, their effect on magnetopause boundary motion, and the signatures they produce within the magnetosphere and at high-latitude auroral ground stations, are examined. A qualitative model for the magnetospheric response to such variations explaining a wide variety of transient magnetopause, magnetospheric and ground signatures is proposed, and its applicability is shown. The model is presented as an alternative explanation for many of the signatures previously interpreted as direct on site evidence of patchy, sporadic, magnetic field merging, namely the flux transfer events (FTEs).

Sibeck, D. G.↗
NASA NTRS1986

Observations of vertical winds and the origin of thermospheric gravity waves launched by auroral substorms and westward travelling surges

Several sequences of observations of strong vertical winds in the upper thermosphere are discussed, in conjunction with models of the generation of such winds. In the auroral oval, the strongest upward winds are observed in or close to regions of intense auroral precipitation and strong ionospheric currents. The strongest winds, of the order of 100 to 200 m/sec are usually upward, and are both localized and of relatively short duration (10 to 20 min). In regions adjacent to those displaying strong upward winds, and following periods of upward winds, downward winds of rather lower magnitude (40 to about 80 m/sec) may be observed. Strong and rapid changes of horizontal winds are correlated with these rapid vertical wind variations. Considered from a large scale viewpoint, this class of strongly time dependent winds propagate globally, and may be considered to be gravity waves launched from an auroral source. During periods of very disturbed geomagnetic activity, there may be regions within and close to the auroral oval where systematic vertical winds of the order of 50 m/sec will occur for periods of several hours. Such persistent winds are part of a very strong large scale horizontal wind circulation set up in the polar regions during a major geomagnetic disturbance. This second class of strong horizontal and vertical winds corresponds more to a standing wave than to a gravity wave, and it is not as effective as the first class in generating large scale propagating gravity waves and correlated horizontal and vertical oscillations. A third class of significant (10 to 30 m/sec) vertical winds can be associated with systematic features of the average geomagnetic energy and momentum input to the polar thermosphere, and appear in statistical studies of the average vertical wind as a function of Universal Time at a given location.

Rees, D.↗
NASA NTRS1989

Thermospheric dynamics during September 18-19, 1984. II - Validation of the NCAR thermospheric general circulation model

The winds, temperatures, and densities predicted by the thermospheric GCM are compared with measurements from the Equinox Transition Study of September 17-24, 1984. Agreement between predictions and observation is good in many respects. The quiet day observations contain a strong semidiurnal wind variation which is mainly due to upward-propagating tides. The storm day wind behavior is significantly different and includes a surge of equatorward winds due to a global propagating disturbance associated with the storm onset. A quantitative statistical comparison of the predicted and measured winds indicates that the equatorward winds in the model are weaker than the observed winds, particularly during storm times. A quiet day phase anomaly in the measured F region winds which is not reproduced by the model suggests the occurrence of an important unmodeled interaction between upward propagating semidiurnal tides and high-latitude effects.

Crowley, G.↗
NASA NTRS2007

Mars-GRAM Applications for Mars Science Laboratory Mission Site Selection Processes

An overview is presented of the Mars-Global Reference Atmospheric Model (Mars-GRAM 2005) and its new features. One important new feature is the "auxiliary profile" option, whereby a simple input file is used to replace mean atmospheric values from Mars-GRAM's conventional (General Circulation Model) climatology. An auxiliary profile can be generated from any source of data or alternate model output. Results are presented using auxiliary profiles produced from mesoscale model output (Southwest Research Institute's Mars Regional Atmospheric Modeling System (MRAMS) model and Oregon State University's Mars mesoscale model (MMM5) model) for three candidate Mars Science Laboratory (MSL) landing sites (Terby Crater, Melas Chasma, and Gale Crater). A global Thermal Emission Spectrometer (TES) database has also been generated for purposes of making 'Mars-GRAM auxiliary profiles. This data base contains averages and standard deviations of temperature, density, and thermal wind components, averaged over 5-by-5 degree latitude bins and 15 degree L(sub S) bins, for each of three Mars years of TES nadir data. Comparisons show reasonably good consistency between Mars-GRAM with low dust optical depth and both TES observed and mesoscale model simulated density at the three study sites. Mean winds differ by a more significant degree. Comparisons of mesoscale and TES standard deviations' with conventional Mars-GRAM values, show that Mars-GRAM density perturbations are somewhat conservative (larger than observed variability), while mesoscale-modeled wind variations are larger than Mars-GRAM model estimates. Input parameters rpscale (for density perturbations) and rwscale (for wind perturbations) can be used to "recalibrate" Mars-GRAM perturbation magnitudes to better replicate observed or mesoscale model variability.

Justh, Hilary↗
NASA NTRS1986

Solar cycle variations in the solar wind

The solar cycle variations of various solar wind parameters are reviewed. It is shown that there is a gradual decrease in the duration of high-speed streams from the declining phase of solar cycle 20 through the ascending phase of cycle 21 and a corresponding decrease in the annual average of the proton speed toward solar maximum. Beta, the ratio of the proton thermal pressure to magnetic pressure, undergoes a significant solar cycle variation, as expected from the variation in the IMF. Individual hourly averages of beta often exceed unity with 20 cases exceeding 10 and one case as high as 25. The Alfven Mach number shows a solar cycle variation similar to beta, lower aboard solar maximum. High-speed streams can be seen clearly in epsilon and the y component of the interplanetary magnetic field.

Freeman, John W.↗
NASA NTRS1987

The Giotto three-dimensional positive ion analyser

An instrument to measure the three-dimensional energy distribution of positive ions in order to study the interaction between the solar wind and ionized Halley cometary particles was designed. Two sensors measure the distribution from 10 eV to 20 keV once per spacecraft spin and the distribution from 90 eV to 90 keV, with coarse mass discrimination, once every 32 spins. The instrument was turned on September 8, 1985. The performance throughout all testing was nominal. The spacecraft was greater than 10 million km from the earth in the solar wind. The only population identified is the solar wind. The Fast Ion Sensor follows solar wind variations with its autoranging capability. The Implanted Ion Sensor identifies higher mass ions such as O(6+) and O(5+) in the solar wind.

Johnstone, A. D.↗
NASA NTRS1978

Magnetic flux transfer associated with expansions and contractions of the dayside magnetosphere

The paper shows that the use of an empirical ellipsoidal model of the sunward magnetopause - which uses Ogo 5 magnetometer data, solar wind data from three satellites, and auroral zone magnetic indices - yields quantitative statistical estimates of the relative values of magnetopause displacements due to solar wind variation, flux transfers, and other causes. While the displacements due to flux transfers are smaller on the average, they are clearly comparable with those due solar wind fluctuations. The fact that expansion and contraction events are observed throughout the region accessible to Ogo 5 satellite on the sunward magnetopause suggests that the entire sunward magnetosphere is affected by flux erosion and return.

Holzer, R. E.↗
NASA NTRS1981

Evaluation of Nimbus 7 SMMR sensor with airborne radiometers and surface observations in the Norwegian Sea

Measurements made by the Nimbus 7 SMMR are compared with near simultaneous observations using the airborne SMMR simulator and with surface observations. The area of the test is in the Norwegian Sea between Bear Island and Northern Norway. It is noted that during the observation period two low-pressure systems were located in the test area, giving a spatial wind variation from 3-20 m/s. It is shown that the use of the currently available brightness temperatures and algorithms for SMMR does not give universally satisfactory results for SST and wind speed under extreme weather conditions. In addition, the SMMR simulator results are seen as indicating the need for more work on calibration.

Gloersen, P.↗
NASA NTRS1990

Barotropic instability with divergence - Theory and applications to Venus

IR images of Venus reveal a curious double-lobed hot spot in the polar region. Elson (1982) has suggested that this dipole represents a barotropic instability associated with a high-latitude jet. Unfortunately, the classical theory of barotropic instability cannot predict temperature variations. This paper generalizes the theory to include horizontal divergence, vertical motions, and temperature variations, and applies it to the stratosphere of Venus. The fastest-growing barotropic instability in the nominal model matches the observed dipole in period and horizontal temperature pattern. The accompanying wind variations are comparable to the speed of the mean jet, indicating strong nonlinear effects. It is concluded that the Venus dipole may represent the self-limited stage of a barotropic instability with divergence.

Dobrovolskis, Anthony R.↗
NASA NTRS1995

Calculation of design load for the MOD-5A 7.3 mW wind turbine system

Design loads are presented for the General Electric MOD-SA wind turbine. The MOD-SA system consists of a 400 ft. diameter, upwind, two-bladed, teetered rotor connected to a 7.3 mW variable-speed generator. Fatigue loads are specified in the form of histograms for the 30 year life of the machine, while limit (or maximum) loads have been derived from transient dynamic analysis at critical operating conditions. Loads prediction was accomplished using state of the art aeroelastic analyses developed at General Electric. Features of the primary predictive tool - the Transient Rotor Analysis Code (TRAC) are described in the paper. Key to the load predictions are the following wind models: (1) yearly mean wind distribution; (2) mean wind variations during operation; (3) number of start/shutdown cycles; (4) spatially large gusts; and (5) spatially small gusts (local turbulence). The methods used to develop statistical distributions from load calculations represent an extension of procedures used in past wind programs and are believed to be a significant contribution to Wind Turbine Generator analysis. Test/theory correlations are presented to demonstrate code load predictive capability and to support the wind models used in the analysis. In addition MOD-5A loads are compared with those of existing machines. The MOD-5A design was performed by the General Electric Company, Advanced Energy Program Department, under Contract DEN3-153 with NASA Lewis Research Center and sponsored by the Department of Energy.

Mirandy, L.↗
NASA NTRS1993

Prediction of geomagnetic activity

A simple analytic model for the directly driven, adiabatic solar wind-magnetosphere-ionosphere coupling is derived on the basis of frontside reconnection and force balance in the tail. Magnetosphere-ionosphere coupling occurs through Alfven waves which are driven by changes of electric fields in the magnetosphere. The model provides an algorithm which calculates the directly driven part of the auroral electrojets from an observed solar wind variation. For two days in May 1979 the cross correlation between the prediction and observation of AE is greater than 0.9. This suggests that most of the geomagnetic activity during these two days was directly driven by the solar wind.

Goertz, C. K.↗
NASA NTRS1996

Effects of the solar wind conditions on the global magnetospheric configuration as deduced from data-based field models

The results of data based modeling of the magnetospheric configuration and its response to changes in the solar wind dynamical pressure and the interplanetary magnetic field (IMF) are described. Previous models did not have a pre-defined magnetopause and were calibrated by the Kp index, and therefore did not correctly model the solar wind effects. Models are presented which include the effects of the solar wind-controlled magnetopause, the region 1 and 2 Birkeland currents, and the interconnection of the magnetospheric and solar wind fields at the boundary. They predict the most significant effects of solar wind variation on the global magnetospheric structure. On the dayside, the region 1 Birkeland currents cause major changes of the magnetic configuration as the IMF turns southward. The tail current intensity is controlled mainly by the pressure of the solar wind, although the influence of the southward IMF is clearly seen. The effects of the IMF-induced interconnection field were found to be significant.

Tsyganenko, N. A.↗
DOE OSTI2025

Wind and solar energy droughts: Potential impacts on energy system dynamics and research needs

This Perspective article provides a brief overview of the topic of wind and solar energy droughts (henceforth WSDs). It does not attempt to provide a complete literature review of the subject but rather highlights some of the main concepts associated with WSDs. These include wind and solar energy drought definitions and metrics; meteorological conditions producing WSDs; a comparison of their characteristics with hydrologic droughts and hydropower droughts; model-based and observational datasets useful for WSD analyses; the linkage of WSDs to transmission, storage, and demand response; the potential impacts of WSDs vs energy demand variations; wind and solar flood events; WSD predictability; WSD dependency on climate modes of variability; climate change impacts on WSDs; and the special challenge of evaluating the characteristics of WSDs in developing countries that have limited historical data available. Finally, the manuscript identifies research areas that the authors believe would provide immediate benefit to energy system planners.

14 SOLAR ENERGY↗
NASA NTRS1982

Magnesium emission variability among late-type giant stars

Profiles of the Mg II h and k emission features in the spectra of 21 late-type giant stars were obtained. Emission strengths were separately measured in the shortward (S) and longward (L) components. Variations in total emission intensity (S + L) can be interpreted as evidence for variations in the rate of mechanical energy deposition in the chromosphere. Mass loss processes in the corona/outer atmosphere may be strong enough to affect the ratio of S/L: thus, rapid mass loss causes S/L to be less than unity. Rapid mass loss is likely caused by deposition of mechanical energy by stellar wind. Variations in S/L are a measure of variations in the rate of mechanical energy deposition in the corona/outer atmosphere. The stellar sample variations were divided into four classes: (1) variations in S/L; (2) variations in the circumstellar absorption components; (3) variations in the total flux; and (4) no evidence for variations found on the time scales used.

Mullan, D. J.↗