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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

EXOS-B/Siple station VLF wave-particle interaction experiments. II - Transmitter signals and associated emissions

New observations in the magnetosphere of coherent VLF waves from the Siple Station, Antarctica, transmitter and associated VLF emissions triggered by the transmitter signals are reported. The data analyzed were acquired on the EXOS-B high-altitude satellite during the period July 15-September 7, 1979, during joint VLF wave-injection experiments involving scientists from Kyoto, Tokyo, and Stanford universities. The experiments were carried out to gain a deeper understanding of the interactions between coherent VLF waves and energetic particles in the magnetosphere, in particular, the whistler-mode instability through which both natural and stimulated VLF emissions are produced. Analysis of the emission-triggering events provides strong evidence that the triggering took place inside whistler-mode ducts and that the emissions reached the satellite only after being scattered at one end of the ducts by ionospheric irregularities. It is concluded that in the noon sector of the magnetosphere, the amplitude of nonducted signals from the Siple transmitter is generally less than the threshold level necessary for triggering in the nonducted mode.

Bell, T. F.↗
NASA NTRS1984

The Resonant Count Diagram and Solar g Mode Oscillations

Evidence is provided to support the hypothesis that, because of the particular frequency separations of the solar g modes, resonant three-wave interactions stimulate only a selected few g modes. A resonant count diagram was obtained by plotting the total number of possible resonant three-wave interactions or a given beat frequency against the inverse of the beat frequency (the beat period), within a given frequency tolerance. The 1 = 1, 2, 3, 4 g modes calculated by Christensen-Dalsgaard, Gough and Morgan (1979) for a standard model of the Sun were used. The diagram has a significant peak at 160 minutes as well as other peaks at longer periods. The g modes that Delache and Scherrer (1983) tentatively identified from the Crimea-Stanford data were also plotted. These modes were found to correspond with the other peaks in the diagram. This coincidence between the observed g modes and the peaks in the resonant count diagram suggest that the observed g modes do owe their observability to resonant three-wave interactions.

Guenther, D. B.↗
NASA NTRS1971

Magnetospheric plasma - Sources, wave-particle interactions and acceleration mechanisms.

Some of the basic problems associated with magnetospheric physics are reviewed. The sources of magnetospheric plasma, with auroral particles included as a subset, are discussed. The possible ways in which the solar wind plasma can gain access to the magnetosphere are outlined. Some important consequences of wave-particle interactions are examined. Finally, the basic mechanisms which energize or accelerate particles by reconnection and convection are explained.

Speiser, T. W.↗
NASA NTRS1994

Wave-current interaction study in the Gulf of Alaska for detection of eddies by synthetic aperture radar

High resolution Esa Remote Sensing Satellite-1 (ERS-1) Synthetic Aperture Radar (SAR) images are used to detect a mesoscale eddy. Such features limit dispersal of pollock larvae and therefore likely influence recruitment of fish in the Gulf of Alaska. During high sea states and high winds, the direct surface signature of the eddy was not clearly visible, but the wave refraction in the eddy area was observed. The rays of the wave field are traced out directly from the SAR image. The ray pattern gives information on the refraction pattern and on the relative variation of the wave energy along a ray through wave current interaction. These observations are simulated by a ray-tracing model which incorporates a surface current field associated with the eddy. The numerical results of the model show that the waves are refracted and diverge in the eddy field with energy density decreasing. The model-data comparison for each ray shows the model predictions are in good agreement with the SAR data.

Liu, Antony K.↗
NASA NTRS1996

Mixing and Transition Control Studied

Considerable progress in understanding nonlinear phenomena in both unbounded and wallbounded shear flow transition has been made through the use of a combination of high- Reynolds-number asymptotic and numerical methods. The objective of this continuing work is to fully understand the nonlinear dynamics so that ultimately (1) an effective means of mixing and transition control can be developed and (2) the source terms in the aeroacoustic noise problem can be modeled more accurately. Two important aspects of the work are that (1) the disturbances evolve from strictly linear instability waves on weakly nonparallel mean flows so that the proper upstream conditions are applied in the nonlinear or wave-interaction streamwise region and (2) the asymptotic formulations lead to parabolic problems so that the question of proper out-flow boundary conditions--still a research issue for direct numerical simulations of convectively unstable shear flows--does not arise. Composite expansion techniques are used to obtain solutions that account for both mean-flow-evolution and nonlinear effects. A previously derived theory for the amplitude evolution of a two-dimensional instability wave in an incompressible mixing layer (which is in quantitative agreement with available experimental data for the first nonlinear saturation stage for a plane-jet shear layer, a circular-jet shear layer, and a mixing layer behind a splitter plate) have been extended to include a wave-interaction stage with a three-dimensional subharmonic. The ultimate wave interaction effects can either give rise to explosive growth or an equilibrium solution, both of which are intimately associated with the nonlinear self-interaction of the three dimensional component. The extended theory is being evaluated numerically. In contrast to the mixing-layer situation, earlier comparisons of theoretical predictions based on asymptotic methods and experiments in wall-bounded shear-flow transition have been somewhat lacking in one aspect or another. The current work strongly suggests that the main weakness is the underlying asymptotic representation of the linear "part" of the problem and not the explicit modeling of the nonlinear/wave-interaction effects. Consequently, the long-wave-length/high-Reynolds-number asymptotic limit for the Blasius boundary-layer stability problem was reexamined, and a new dispersion relationship for the instability waves that is uniformly valid for both the upper- and lower branch regions to the required order of approximation was obtained. A comparison with numerical results, obtained by solving the Orr-Sommerfeld stability problem, shows that the asymptotic formula provides surprisingly good results, even for values of the frequency parameter usually encountered in experimental investigations. This is particularly evident in the dynamically important upper-branch region, where much of the nonlinear interactions in transition experiments are believed to take place. The result is important in that it can be used to greatly improve the accuracy of weakly nonlinear critical-layer-based theories, and a consistent nonlinear theory is currently under evaluation.

Source record↗
NASA NTRS1990

Gyroresonant wave-particle interactions in a dynamic magnetosphere

The response of the interaction mechanism to time-dependent perturbations in the magnetic field was examined using the global field compressions that occur during sudden commencements. This study was performed to assess the effect of nonequilibrium or dynamic magnetospheric processes on wave-particle interactions (WPI). It is shown that current theories of gyroresonant WPI, when modified to include a time-dependent magnetic field, can be used to predict the properties of WPI in a dynamic magnetospheric environment.

Gail, W. B.↗
NASA NTRS1981

Wave-particle interactions at the magnetopause - Contributions to the dayside aurora

The observations on ISEE 1 and ISEE 2 correlate the presence of intense electromagnetic and electrostatic emissions with enhanced fluxes of 1-6 keV electrons at the earth's magnetopause. The measured proton to electron ratio in the 1-10 keV energy range indicates the presence of substantial fluxes of electrons at energies below 1 keV. The 1.3-1.7 keV proton flux was essentially unchanged as the spacecraft moved from the magnetosheath into the wave-particle layer at and inside the magnetopause. The consequences of the magnetopause wave-particle interactions reported are consistent with the known features of the dayside aurora.

Tsurutani, B. T.↗
NASA NTRSDate not supplied

As Seen by Parker Solar Probe: In-Situ Signatures of Wave-Particle Interactions Driven by Solar Ejecta

Parker Solar Probe (PSP) is sampling regions of the inner heliosphere never seen before to address where and why energy flows between the Sun and earth. With the onset of solar maximum, recent encounters have witnessed the increase in solar activity. We present in-situ signatures of coronal mass ejections and other smaller transients of coronal origin. Using simultaneous measurements from the SWEAP and FIELDS instrument suite, both ion and electron-scale dynamics are investigated in coincidence with both lower frequency electromagnetic and higher frequency electrostatic waves. We present an overview of these wave-particle interaction observations and hypothesize on their role in plasma energization and subsequent solar wind heating.

J. L. Verniero↗
NASA NTRS2004

Gravity Wave Forcing of the Mesosphere and Lower Thermosphere: Mountain and Convective Waves Ascending Vertically (MaCWAVE)

The specific objectives of this research effort included the following: 1) Quantification of gravity wave propagation throughout the lower and middle atmosphere in order to define the roles of topographic and convective sources and filtering by mean and low-frequency winds in defining the wave field and wave fluxes at greater altitudes; 2) The influences of wave instability processes in constraining wave amplitudes and fluxes and generating turbulence and transport; 3) Gravity wave forcing of the mean circulation and thermal structure in the presence of variable motion fields and wave-wave interactions, since the mean forcing may be a small residual when wave interactions, anisotropy, and momentum and heat fluxes are large; 4) The statistical forcing and variability imposed on the thermosphere at greater altitudes by the strong wave forcing and interactions occurring in the MLTI.

Fritts, David C.↗
NASA NTRS1991

Non-linear interaction of a detonation/vorticity wave

The interaction of an oblique, overdriven detonation wave with a vorticity disturbance is investigated by a direct two-dimensional numerical simulation using a multi-domain, finite-difference solution of the compressible Euler equations. The results are compared to those of linear theory, which predict that the effect of exothermicity on the interaction is relatively small except possibly near a critical angle where linear theory no longer holds. It is found that the steady-state computational results agree with the results of linear theory. However, for cases with incident angle near the critical angle, moderate disturbance amplitudes, and/or sudden transient encounter with a disturbance, the effects of exothermicity are more pronounced than predicted by linear theory. Finally, it is found that linear theory correctly determines the critical angle.

Lasseigne, D. G.↗
NASA NTRS2004

Wave-Particle Interactions As a Driving Mechanism for the Solar Wind

Our research has been focusing on a highly experimentally relevant issue: intermittency of the fluctuating fields in outflowing plasmas. We have contributed to both the theoretical and experimental research of the topic. In particular, we have developed a theoretical model and data analyzing programs to examine the issue of intermittency in space plasma outflows, including the solar wind. As fluctuating electric fields in the solar wind are likely to provide a heating and acceleration mechanism for the ions, our studies of the intermittency in turbulence in space plasma outflows help us toward achieving the goal of comparing major physical mechanisms that contribute to the driving of the fast solar wind. Our new theoretical model extends the utilities of our global hybrid model, which has allowed us to follow the kinetic evolution of the particle distributions along an inhomogeneous field line while the particles are subjected to various physical mechanisms. The physical effects that were considered in the global hybrid model included wave-particle interactions, an ambipolar electric field that was consistent with the particle distributions themselves, and Coulomb collisions. With an earlier version of the global hybrid model, we examined the overall impact on the solar wind flow due to the combination of these physical effects. In particular, we studied the combined effects of two major mechanisms that had been proposed as the drivers of the fast solar wind: (1) velocity filtration effect due to suprathermal electrons; (2) ion cyclotron resonance. Since the approval of this research grant, we have updated the model such that the effects due to these two driving mechanisms can be examined separately, thereby allowing us to compare their contributions to the acceleration of the solar wind. In the next section, we shall demonstrate that the velocity filtration effect is rather insignificant in comparison with that due to ion cyclotron resonance.

Wagner, William J.↗
NASA NTRS2004

On the Origin of Whistler Mode Radiation in the Plasmasphere

The origin of whistler mode radiation in the plasmasphere is examined from three years of plasma wave observations from the Dynamics Explorer and three years from the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft. These data are used to construct plasma wave intensity maps of whistler mode radiation in the plasmasphere. The highest average intensities of the radiation in the wave maps show source locations and/or sites of wave amplification. Each type of emission is classified based on its magnetic latitude and longitude rather than any spectral feature. Equatorial electromagnetic (EM) emissions (approx. 30-330 Hz), plasmaspheric hiss (approx. 330 Hz - 3.3 kHz), chorus (approx. 2 kHz - 6 kHz), and VLF transmitters (approx. 10-50 kHz) are the main types of waves that are clearly delineated in the plasma wave maps. Observations of the equatorial EM emissions show that the most intense region is on or near the magnetic equator in the afternoon sector and that during times of negative B(sub z) (interplanetary magnetic field),the maximum intensity moves from L values of 3 to less than 2. These observations are consistent with the origin of this emission being particle-wave interactions in or near the magnetic equator. Plasmaspheric hiss shows high intensity at high latitudes and low altitudes (L shells from 2 to 4) and in the magnetic equator over L values from 2 to 3 in the early afternoon sector. The longitudinal distribution of the hiss intensity (excluding the enhancement at the equator) is similar to the distribution of lightning: stronger over continents than over the ocean, stronger in the summer than winter, and stronger on the dayside than nightside. These observations strongly support lightning as the dominant source for plasmaspheric hiss, which through particle-wave interactions, maintains the slot region in the radiation belts. The enhancement of hiss at the magnetic equator is consistent with particle-wave interactions. The chorus emissions are most intense on the morning side as previously reported. At frequencies from approx. 10-50 kHz VLF transmitters dominate the spectrum. The maximum intensity of the VLF transmitters is in the late evening or early morning with enhancements all along L shells from 1.8 to 3.

Green, James L.↗
NASA NTRS1991

Nonlinear interaction of a detonation/vorticity wave

The interaction of an oblique, over driven detonation wave with a vorticity disturbance is investigated by a direct two-dimensional numerical simulation using a multi-domain, finite-difference solution of the compressible Euler equations. The results are compared to those of linear theory, which predict that the effect of exothermicity on the interaction is relatively small except possibly near a critical angle where linear theory no longer holds. It is found that the steady-state computational results agree with the results of linear theory. However, for cases with incident angle near the critical angle, moderate disturbance amplitudes, and/or sudden transient encounter with a disturbance, the effects of exothermicity are more pronounced than predicted by linear theory. Finally, it is found that linear theory correctly determines the critical angle.

Lasseigne, D. G.↗
NASA NTRS1991

Ion pickup by the solar wind via wave-particle interactions

Ion pickup by the solar wind is a topic of current interest. In situ observations and theoretical studies establish a fairly good understanding of the physics of the ion-pickup process. In a weakly turbulent solar wind, hydromagnetic waves that are either intrinsic or excited by the newborn ions can lead to pitch-angle diffusion which can be approximately described by the quasi-linear theory with or without incorporating the resonance-broadening mechanism due to weak turbulence. According to the weak turbulence theory, the pickup ions do not form a complete spherical shell distribution in the time-asymptotic state unless the wave field is sufficiently strong. In some cases the ions only possess a partial or incomplete shell. When the solar wind is highly turbulent, direct interaction between the wave fields and the newborn ions can result in rapid pitch-angle scattering leading to swift formation of a spherical shell distribution on the time scale of an ion gyro-period.

Yoon, Peter H.↗
NASA NTRS1988

Wave particle interactions in the foot of the Saturnian bow shock

Voyager 1 plasma wave data show that the quasi-perpendicular, supercritical bow shock of Saturn exhibits the same plasma wave phenomenology observed near Jupiter. Using a quasi-linear model developed for the Jovian bow shock, it is shown that plasma waves at Saturn can generate a significant portion of the totalelectron temperature jump measured across the shock. In this respect, Saturn's bow shock more closely resembles Jupiter's than the earth's, where plasma waves contribute negligibly to the total electron temperature jump.

Moses, S. L.↗
NASA NTRS1993

Development of separation due to interaction between a shock wave and a turbulent boundary layer perturbed by rarefaction waves

The interaction of a turbulent boundary layer with rarefaction and shock waves in flows past inclined steps was investigated experimentally and theoretically. The experiments were carried out in supersonic wind tunnels with test sections of 0.6 x 0.6 m and 0.2 x 0.2 m, with adiabatic conditions on the surface model. Based on detailed measurements of pressure fields, velocity, and surface friction, combined with results of optical visualization and analysis of limiting flow lines, three characteristic flow regimes are identified. These are (1) nonseparated flow at small step angles, (2) formation of a local separation zone with a free separation point at moderate step angles, and (3) formation of a large-scale separated flow with a fixed separation point at sufficiently large step angles. The quantitative gasdynamic schemes and surface pressure distributions for these flow regimes are shown for Mach 2.85.

Zheltovodov, A. A.↗