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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 793 records · Page 44

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NASA NTRS1987

Vertical temperature gradients on Uranus - Implications for layered convection

Analyses of Voyager IR spectroscopy and radio occultation measurements confirm ground-based observations that the deep lapse rate of Uranus exceeds that for an adiabat of H2 in thermodynamic equilibrium. However, in approximately the same region of the atmosphere, Voyager IR and ground-based observations also indicate that the ratio of ortho to para hydrogen is near the equilibrium value. These two sets of observations can be reconciled by postulating the existence of rapid convective overturning within layers which are thin in comparison to a pressure scale height. Two forms of layered convection are examined. In one case, deposition of kinetic energy results in thin, rapidly overturning layers. Possible kinetic energy sources include braking waves and local instabilities. In the second case considered, molecular-weight discontinuities due to CH4 stratification stabilize the interfaces of thin layers. It is argued that both forms may be important in the convective portion of the Uranus atmosphere.

Gierasch, Peter J.↗

NASA NTRS1988

Soft X-ray emissions, meter-wavelength radio bursts, and particle acceleration in solar flares

A detailed study of the relationship between metric radio bursts and soft X-ray flares has been made using an extensive data set covering 15 yr. It is found that type IV emission is mainly associated with long-duration 1-8 A events that are known to be well associated with coronal mass ejections. In contrast, type II and type III bursts originate primarily in impulsive soft X-ray events that are not necessarily accompanied by mass ejection. Strong type III bursts, in particular, appear to occur only in association with relatively impulsive flares. It is suggested that coronal shocks responsible for type II bursts are blast waves generated in impulsive energy releases.

Cane, H. V.↗

NASA NTRS1989

Low power consumption current transducer

A low power consumption current transducer utilizes a saturable core reactor which includes a pair of opposed gate windings and a control winding. The control winding of the saturable reactor is arranged to receive the current to be measured. A square wave generator is connected to the gate winding of the transformer connected across the square wave generator and the secondary connected in series with the gate windings of the reactor. A full wave rectifier is connected to the gate windings and a resistor is connected across the rectifier to provide a DC voltage to cross it representative of the current flow through the control winding. A DC power supply is provided to supply power to the square wave voltage source. A diode is connected between each end of the primary winding of the transformer and one polarity of the DC power supply to commutate the reactive current resulting from the counter emf generated in the reactor back to the DC supply to eliminate potentially damaging reactive voltage spikes which would otherwise appear at the output of the square wave generator and conserve energy.

W T McLyman↗

NASA NTRS1992

The E-region Rocket/Radar Instability Study (ERRRIS) - Scientific objectives and campaign overview

The plasma instabilities in the low-attitude auroral ionosphere and the sources of free energy that drive these waves have been examined in detail in the framework of the ERRRIS project. Independent sets of experiments were carried out on board three NASA sounding rockets which were flown in conjunction with radar backscatter measurements from Esrange, Sweden, in 1988 and 1989. The backscatter measurements were taken by the 50 MHz CUPRI system for determining the launch conditions. The Eiscat incoherent scatter radar was used to take plasma drift, density, and temperature measurements on board two of the flown rockets. STARE observations of 1 m backscatter echoes were also made. The STARE velocity fields were in agreement with the Eiscat and in situ measured electric fields. Both CUPRI and STARE observed a very dynamic and changing auroral ionosphere over Esrange. It is concluded that the ERRRIS experiments provided valuable data on plasma instabilities in the auroral electrojet, including detailed in situ measurements of the two-stream wave spectrum and phase velocities.

Pfaff, R. F.↗

NASA NTRS1992

Why all stars should possess circumstellar temperature inversions

The paper shows that the circumstellar temperature inversions possessed by all stars are the consequence of the 'velocity filtration' process described by Scudder (1992), according to which a stellar envelope is hotter than its underlying layers. The filtration scenario relies on the theoretically predicted and experimentally determined non-Maxwellian velocity distributions of ions and/or electrons in other sampled astrophysical plasmas and the transition region. The most immediate consequence is that the temperature and quasi-neutral plasma density become anticorrelated with increasing radius in a thin transition region, leaving the temperature profile inverted in excess of 10 exp 6 K up into a corona, without depositing a wave of magnetic field energy into the gas above the base of the transition region.

Scudder, Jack D.↗

NASA NTRS1993

Numerical quasi-linear study of the critical ionization velocity phenomenon

The critical ionization velocity (CIV) for a neutral barium (Ba) gas cloud moving across the static magnetic field is studied numerically using quasi-linear equations and a parameter range which is typical for the shaped-charge Ba gas release experiments in space. For consistency the charge exchange between the background oxygen ions and neutral atoms and its reverse process, as well as the excitation of the neutral Ba atoms, are included. The numerical results indicate that when the ionization rate due to CIV becomes comparable to the charge exchange rate the energy lost to the ionization and excitation collisions by the superthermal electrons exceeds the energy gain from the waves that are excited by the ion beam. This results in a CIV yield less than the yield by the charge exchange process.

Moghaddam-Taaheri, E.↗

NASA NTRS1993

On possible Mn-53 heterogeneity in the early solar system

The effects of influence of shock wave propagation on the energy spectrum of accelerated particles that lead to different production rates of radionuclides, in particular, Mn-53, on small scales in the early solar system are shown. Search for evidence for extinct Mn-53 has stimulated investigations of Cr isotope anomalies in meteorites. The linear correlation between the magnitude of the Cr-53* excesses and the Mn/Cr ratio that unambiguously proves the in situ decay of Mn-53 was detected, really, in different mineral phases of some carbonaceous and enstatite chondrites, primitive achondrites, pallasites and iron meteorites. However, the data on the Cr-53* excess rarely defines a single linear array on a Mn-53-Cr-52 evolution diagram even for meteorites of the same chemical group. A clear isochron with Mn-53/Mn-55 = 4.4 plus or minus 1.0 x 10(exp -5) (in range of approximately 2.4 to approximately 9 x 10(exp -5)) is observed for CAI of the Allende C3-chondrite while the data for the Murchison C2- and Orgueil C1-chondrites fall much lower corresponding rather to Mn-53/Mn-55 less than 2 x 10(exp -5). In the case of iron meteorites it ranges from less than 5 x 10(exp -8) to less than 5 x 10(exp -5).

Lavrukhina, A. K.↗

NASA NTRS1995

The source of 90-day oscillations at Wake Island

Energetic 90-day oscillations of sea level have been intermittently observed at Wake Island in the western tropical Pacific during the past 2 decades. The oscillations tend to occur about 1.5 years after El Nino-Southern Oscillation events, to have amplitudes of 10-15 cm, and to persist for about 1 year. Sea surface heights from the Geosat altimeter are used to establish that these signals take the form of Rossby waves and have an energy source near the Big Island of Hawaii, which lies 40 deg of longitude to the east. Sea level and upper layer currents from an eddy-resolving numerical model are examined and suggest that the energy source is eddies generated off the Big Island of Hawaii. These eddies appear to be associated with westward currents that intermittently impinge on the island. Several alternate hypotheses are also discussed and rejected.

Mitchum, Gary T.↗

NASA NTRS1996

Advanced Orion Optimized Laser System Analysis

Contractor shall perform a complete analysis of the potential of the solid state laser in the very long pulse mode (100 ns pulse width, 10-30 hz rep-rate) and in the very short pulse mode (100 ps pulse width 10-30 hz rep rate) concentrating on the operation of the device in the 'hot-rod' mode, where no active cooling the laser operation is attempted. Contractor's calculations shall be made of the phase aberrations which develop during the repped-pulse train, and the results shall feed into the adaptive optics analyses. The contractor shall devise solutions to work around ORION track issues. A final report shall be furnished to the MSFC COTR including all calculations and analysis of estimates of bulk phase and intensity aberration distribution in the laser output beam as a function of time during the repped-pulse train for both wave forms (high-energy/long-pulse, as well as low-energy/short-pulse). Recommendations shall be made for mitigating the aberrations by laser re-design and/or changes in operating parameters of optical pump sources and/or designs.

Source record↗

NASA NTRS1998

Magnetospheric Substorms and Tail Dynamics

This grant funded several studies of magnetospheric substorms and their effect on the dynamics of the earth's geomagnetic tail. We completed an extensive study of plasmoids, plasma/magnetic field structures that travel rapidly down the tail, using data from the ISEE 3 and IMP 8 spacecraft. This study formed the PhD thesis of Mark Moldwin. We found that magnetically plasmoids are better described as flux-ropes (twisted magnetic flux tubes) rather than plasma bubbles, as had been generally regarded up to that point (Moldwin and Hughes, 1990; 1991). We published several examples of plasmoids observed first in the near tail by IMP 8 and later in the distant tail by ISEE 3, confirming their velocities down tail. We showed how the passage of plasmoids distorts the plasma sheet. We completed the first extensive statistical survey of plasmoids that showed how plasmoids evolve as they move down tail from their formation around 30 RE to ISEE 3 apogee at 240 RE. We established a one-to-one correspondence between the observation of plasmoids in the distant tail and substorm onsets at earth or in the near tail. And we showed that there is a class of plasmoid-like structures that move slowly earthward, especially following weak substorms during northward IMF. Collectively this work constituted the most extensive study of plasmoids prior to the work that has now been done with the GEOTAIL spacecraft. Following our work on plasmoids, we turned our attention to signatures of substorm onset observed in the inner magnetosphere near geosynchronous orbit, especially signatures observed by the CRRES satellite. Using data from the magnetometer, electric field probe, plasma wave instrument, and low energy plasma instrument on CRRES we were able to better document substorm onsets in the inner magnetosphere than had been possible previously. Detailed calculation of the Poynting flux showed energy exchange between the magnetosphere and ionosphere, and a short burst of tailward convective flow just prior to onset, suggesting the active role of the ionosphere in the onset process, and adding credibility to the ballooning instability theory of substorm onset. This grant also supported a number of other substorm studies and reviews. These are represented by the list of publications and meeting presentations resulting out of this grant.

Hughes, W. Jeffrey↗

NASA NTRS1997

Rendering Three-Dimensional Solar Coronal Structures

An X-ray or EUV image of the corona or chromosphere is a 2D representation of an extended 3D complex for which a general inversion process is impossible. A specific model must be incorporated in order to understand the full 3D structure. We approach this problem by modeling a set of optically-thin 3D plasma flux tubes which we render these as synthetic images. The resulting images allow the interpretation of the X-ray/EUV observations to obtain information on (1) the 3D structure of X-ray images, i.e., the geometric structure of the flux tubes, and on (2) the internal structure using specific plasma characteristics, i.e., the physical structure of the flux tubes. The data-analysis technique uses magnetograms to characterize photospheric magnetic fields and extrapolation techniques to form the field lines. Using a new set of software tools, we have generated 3D flux tube structures around these field lines and integrated the plasma emission along the line of sight to obtain a rendered image. A set of individual flux-tube images is selected by a non-negative least-squares technique to Provide a match with an observed X-ray image. The scheme minimizes the squares of the differences between the synthesized image and the observed image with a non-negative constraint on the coefficients of the brightness of the individual flux-tube loops. The derived images are used to determine the specific photospheric foot points and physical data, i.e., scaling laws for densities and loop lengths. The development has led to Computer efficient integration and display software that is compatible for comparison with observations (e.g., Yohkoh SXT data, NIXT, or EIT). This analysis is important in determining directly the magnetic field configuration, which provides the structure of coronal loops, and indirectly the electric currents or waves, which provide the energy for the heating of the plasma. We have used very simple assumptions (i.e., potential magnetic fields and isothermal corona) to provide an initial test of the techniques before complex models are introduced. We have separated the physical and geometric contributions of the emission for a set of flux tubes and concentrated, in this initial study, on the geometric contributions by making approximations to the physical contributions. The initial results are consistent with the scaling laws derived from Yohkoh SXT data.

Gary, G. Allen↗

NASA NTRS1999

Recent Development on O(+)-O Collision Frequency and Ionosphere-Middle Atmosphere Coupling

The collision frequency between an oxygen atom and its singly charged ion controls the transfer of energy between the solar radiation and the thermosphere. There were a long standing discrepancy, extending over a decade, between the theoretical and empirical determination of this frequency, and the empirical value of this frequency exceeded the theoretical value by a factor of 1.7. Recent improvements in theory were obtained by using accurate oxygen ion-oxygen atom potential energy curves, and partial wave quantum mechanical calculations. Similarly, recently three independent statistical methods were applied to the empirical determination of this frequency. These methods give results consistent with each other, and together with the recent theoretical improvements, bring the ratio close to unity, as it should be. It will be shown that the old statistical method for this determination contained accumulative errors, leading to a larger value for this ratio. The recent improvements lead to an average value of the empirical to the theoretical ratio equal to 0.98, with an uncertainty of +/- 8%, resolving the old discrepancy between theory and observations. The main source of uncertainties are errors in the profile of the oxygen atom density, which is of the order of 11 %. An alternative method to find the oxygen atom density is being suggested.

Omidvar, K.↗

NASA NTRS1999

Recent Development on O(+) - O Collision Frequency and Ionosphere-Thermosphere Coupling

The collision frequency between an oxygen atom and its singly charged ion controls the momentum transfer between the ionosphere and the thermosphere. There has been a long standing discrepancy, extending over a decade, between the theoretical and empirical determination of this frequency: the empirical value of this frequency exceeded the theoretical value by a factor of 1.7. Recent improvements in theory were obtained by using accurate oxygen ion-oxygen atom potential energy curves, and partial wave quantum mechanical calculations. We now have applied three independent statistical methods to the observational data, obtained at the MIT/Millstone Hill Observatory, consisting of two sets A and B. These methods give results consistent with each other, and together with the recent theoretical improvements, bring the ratio close to unity, as it should be. The three statistical methods lead to an average for the ratio of the empirical to the theoretical values equal to 0.98, with an uncertainty of +/-8%, resolving the old discrepancy between theory and observation. The Hines statistics, and the lognormal distribution statistics, both give lower and upper bounds for the Set A equal to 0.89 and 1.02, respectively. The related bounds for the Set B are 1.06 and 1.17. The average values of these bounds thus bracket the ideal value of the ratio which should be equal to unity. The main source of uncertainties are errors in the profile of the oxygen atom density, which is of the order of 11%. An alternative method to find the oxygen atom density is being suggested.

Omidvar, K.↗

NASA NTRS2000

Theory of Type 3 and Type 2 Solar Radio Emissions

The main features of some current theories of type III and type II bursts are outlined. Among the most common solar radio bursts, type III bursts are produced at frequencies of 10 kHz to a few GHz when electron beams are ejected from solar active regions, entering the corona and solar wind at typical speeds of 0.1c. These beams provide energy to generate Langmuir waves via a streaming instability. In the current stochastic-growth theory, Langmuir waves grow in clumps associated with random low-frequency density fluctuations, leading to the observed spiky waves. Nonlinear wave-wave interactions then lead to secondary emission of observable radio waves near the fundamental and harmonic of the plasma frequency. Subsequent scattering processes modify the dynamic radio spectra, while back-reaction of Langmuir waves on the beam causes it to fluctuate about a state of marginal stability. Theories based on these ideas can account for the observed properties of type III bursts, including the in situ waves and the dynamic spectra of the radiation. Type 11 bursts are associated with shock waves propagating through the corona and interplanetary space and radiating from roughly 30 kHz to 1 GHz. Their basic emission mechanisms are believed to be similar to those of type III events and radiation from Earth's foreshock. However, several sub-classes of type II bursts may exist with different source regions and detailed characteristics. Theoretical models for type II bursts are briefly reviewed, focusing on a model with emission from a foreshock region upstream of the shock for which observational evidence has just been reported.

Robinson, P. A.↗

NASA NTRS2000

Mesosphere Dynamics with Gravity Wave Forcing: Planetary Waves - 2

We present results from a non-linear, 3D, time dependent numerical spectral model (NSM) which extends from the ground up into the thermosphere and incorporates Hines' Doppler Spread Parameterization for small-scale gravity waves (GW). Our focal point is the mesosphere where wave interactions are playing a dominant role. We discuss planetary waves in the present paper and diurnal and semi-diurnal tides in the companion paper. Without external time dependent energy or momentum sources, planetary waves (PWs) are generated in the model for zonal wavenumbers 1 to 4, which have amplitudes in the mesosphere above 50 km as large as 30 m/s and periods between 2 and 50 days. The waves are generated primarily during solstice conditions, which indicates that the baroclinic instability (associated with the GW driven reversal in the latitudinal temperature gradient) is playing an important role. Results from a numerical experiment show that GWs are also involved directly in generating the PWs. For the zonal wavenumber m = 1, the predominant wave periods in summer are around 4 days and in winter between 6 and 10 days. For m = 2, the periods are in summer and close to 2.5 and 3.5 days respectively For m = 3, 4 the predominant wave periods are in both seasons close to two days. The latter waves have the characteristics of Rossby gravity waves with meridional winds at equatorial latitudes. A common feature of the PWs (m = 1 to 4) generated in summer and winter is that their vertical wavelengths throughout the mesosphere are large which indicates that the waves are not propagating freely but are generated throughout the region. Another common feature is that the PWs propagate preferentially westward in summer and eastward in winter, being launched from the westward and eastward zonal winds that prevail respectively in summer and winter altitudes below 80 km. During spring and fall, for m = 1 and 2 eastward propagating long period PWs are generated that are launched from the smaller eastward zonal winds that prevail in these seasons. PWs generated in the model produce large amplitude modulations of the diurnal tides at altitudes above 80 km and contribute to their seasonal variations.

Mayr, H. G.↗

NASA NTRS2001

Enhanced Climatic Warming in the Tibetan Plateau Due to Double CO2: A Model Study

The NCAR (National Center for Atmospheric Research) regional climate model (RegCM2) with time-dependent lateral meteorological fields provided by a 130-year transient increasing CO2 simulation of the NCAR Climate System Model (CSM) has been used to investigate the mechanism of enhanced ground temperature warming over the TP (Tibetan Plateau). From our model results, a remarkable tendency of warming increasing with elevation is found for the winter season, and elevation dependency of warming is not clearly recognized in the summer season. This simulated feature of elevation dependency of ground temperature is consistent with observations. Based on an analysis of surface energy budget, the short wave solar radiation absorbed at the surface plus downward long wave flux reaching the surface shows a strong elevation dependency, and is mostly responsible for enhanced surface warming over the TP. At lower elevations, the precipitation forced by topography is enhanced due to an increase in water vapor supply resulted from a warming in the atmosphere induced by doubling CO2. This precipitation enhancement must be associated with an increase in clouds, which results in a decline in solar flux reaching surface. At higher elevations, large snow depletion is detected in the 2xCO2run. It leads to a decrease in albedo, therefore more solar flux is absorbed at the surface. On the other hand, much more uniform increase in downward long wave flux reaching the surface is found. The combination of these effects (i.e. decrease in solar flux at lower elevations, increase in solar flux at higher elevation and more uniform increase in downward long wave flux) results in elevation dependency of enhanced ground temperature warming over the TP.

Chen, Baode↗

NASA NTRS2000

A Shocking New Pump

Hydro Dynamics, Inc. received a technical helping hand from NASA that made their Hydrosonic Pump (HPump) a reality. Marshall engineers resolved a bearing problem in the rotor of the pump and recommended new bearings, housings and mounting hardware as a solution. The resulting HPump is able to heat liquids with greater energy efficiency using shock waves to generate heat.

Source record↗

NASA NTRS2004

Unresolved Issues With Inner Magnetosphere-Ionosphere Coupling

Dipolarization and the release of stored magnetic energy is strongly evident in the energized plasma sheet electrons and ions injected earthward from the magnetotail. While some of these plasma are presumed lost into the dayside magnetosheath, much of the energy is dissipated into the ionosphere through electric currents, through collisions into low energy plasma, and into plasma waves, which then go on to heat and energize plasma of the inner magnetosphere. Many mechanisms for the transfer of energy and the consequences to inner magnetospheric plasma populations have been proposed. The sophistication of theoretical models to represent the interdependencies between plasma populations is rapidly increasing. However without the restraint and reality imposed on theory by relevant measurements, the degree to which specific mechanisms participate in the exchange of energy as a function of location and time cannot be known. ORBITALS offers this capability. Some of the outstanding problems in inner magnetospheric physics and the opportunities presented by the ORBITAL concept to solve problems will be discussed.

Gallagher, D. L.↗