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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Turbulent exchanges between near-inertial waves and balanced flows

Wind generated near-inertial waves are ubiquitous in the upper ocean. An improved understanding of near-inertial wave dynamics following their excitation in the ocean and their subsequent interaction with mesoscale geostrophic balanced flows is key to decoding oceanic energy flow pathways. In this regard, multiple oceanic data sets accumulated over the past few decades reveal that the relative strength of near-inertial waves and geostrophic balanced eddy fields is highly variable, both geographically and seasonally. Inspired by these observations, we investigate turbulent interactions and energy exchanges between near-inertial waves and balanced flows using freely evolving numerical simulations of the non-hydrostatic Boussinesq equations. Here, we find accelerated vertical propagation and dissipation of the waves in regimes where balanced and wave fields have comparable strengths. In such regimes we also find that near-inertial waves directly extract energy from balanced flows, with O(10%) being the amount of balanced energy loss. In contrast, we find that near-inertial waves transfer energy to balanced flows in regimes where balance-to-wave energy ratio is small, with the gain in balanced energy being dependent on the relative strength of waves. Furthermore, these regimes are characterized by relatively weaker vertical propagation and dissipation of the near-inertial wave field. One of the key outcomes of this study is the demonstration of the lack of a unique direction for near-inertial wave-balanced flow energy transfers. Depending on the balance-to-wave energy ratio, near-inertial waves can act as an energy sink or energy source for the geostrophic balanced flow.

58 GEOSCIENCES↗
NASA NTRS1985

The ICE project

The International Cometary Explorer (ICE) spacecraft passed through the plasma tail of Comet Giacobini-Zinner (G/Z) on Sept. 11, 1985, and made in situ measurements of particles, fields, and waves. The scientific results indicate that Alfven's magnetic-field capture and draping model is correct; that the comet/solar-wind interaction produces energetic ions (probably by the pick-up process), and that the bow wave, as seen on the flanks, is not a shock but an extended interaction region. It is concluded that the ICE spacecraft survived the encounter virtually unscathed and made field and particle measurements upstream of Comet Halley, actually detecting the comet via plasma wave and energetic particle measurements.

Brandt, J. C.↗
NASA NTRS2013

Ponderomotive Force in the Presence of Electric Fields

This paper presents averaged equations of particle motion in an electromagnetic wave of arbitrary frequency with its wave vector directed along the ambient magnetic field. The particle is also subjected to an E cross B drift and a background electric field slowly changing in space and acting along the magnetic field line. The fields, wave amplitude, and the wave vector depend on the coordinate along the magnetic field line. The derivations of the ponderomotive forces are done by assuming that the drift velocity in the ambient magnetic field is comparable to the particle velocity. Such a scenario leads to new ponderomotive forces, dependent on the wave magnetic field intensity, and, as a result, to the additional energy exchange between the wave and the plasma particles. It is found that the parallel electric field can lead to the change of the particle-wave energy exchange rate comparable to that produced by the previously discussed ponderomotive forces.

Plasmas↗
NASA NTRS1972

Physical picture for the anomalous progagation of ordinary electromagnetic waves in a plasma

It is shown that the physical mechanism for the anomalous propagation of electromagnetic waves at frequencies below the plasma frequency is due to the deflection of particle thermal motions by the wave magnetic field, leading to a density perturbation which can be large when enhanced by some resonance. In presence of an external magnetic field, cyclotron resonance provides the enhancement for ordinary waves. A waveparticle resonance gives rise to anomalous propagation if the velocity distribution is anisotropic with respect to the wave vector, which allows slow electromagnetic waves, with phase velocity less than the velocity of light.

Fried, B. D.↗
NASA NTRS1982

Collaborative research in tunneling and field emission pumped surface wave local oscillators and amplifiers for infrared and submillimeter wavelengths under director's discretionary fund

Progress is reported in work towards the development of surface wave sources for the infrared and sub-millimeter portion of the spectrum to be based upon electron pumping by tunneling electrons in metal-barrier-metal or metal-barrier-semiconductor devices. Tunneling phenomena and the coupling of radiation to tunnel junctions were studied. The propagation characteristics of surface electro-magnetic modes in metal-insulator-p(++) semiconductor structures as a function of frequency were calculated. A model for the gain process based upon Tucker's formalism was developed and used to estimate what low frequency gain might be expected from such structures. The question of gain was addressed from a more fundamental viewpoint using the method of Lasher and Stern.

Gustafson, T. K.↗
NASA NTRS1988

Fundamental problem in computing radiating flow fields with thick shock waves

Possible reasons for the failure of the Navier-Stokes equations to yield realistic profiles of the temperature and density through the structure of a hypersonic shock wave are investigated. Models for bulk viscosity in a monatomic gas are examined which yield a realistic thickness for the shock-wave density profile, but not the temperature profile, and hence are not satisfactory. A tentative computational model for nitrogen is explored which yields considerably more realistic results than the Navier-Stokes equations. This model involves a nonlinear stress-strain tensor, nonlinear heat flux vector, and nonequilibrium rotational energy.

Chapman, Dean R.↗
NASA NTRS1991

Enhancement of wave growth for warm plasmas with a high-energy tail distribution

The classical linear theory of electromagnetic wave growth in a warm plasma is considered for waves propagating parallel to a uniform ambient magnetic field. Wave-growth rates are calculated for ion-driven right-hand mode waves for Kappa and Maxwellian particle distribution functions and for various values of the spectral index, the temperature anisotropy, and the ratio of plasma pressure to magnetic pressure appropriate to the solar wind. When the anisotropy is low the wave growth is limited to frequencies below the proton gyrofrequency and the growth rate increases dramatically as the spectral index is reduced. The growth rate for any Kappa distribution greatly exceeds that for a Maxwellian with the same bulk properties. For large thermal anisotropy the growth rate from either distribution is greatly enhanced. The growth rates from a Kappa distribution are generally larger than for a Maxwellian distribution, and significant wave growth occurs over a broader range of frequencies.

Thorne, Richard M.↗
NASA NTRS1977

On the existence of finite amplitude, transverse Alfven waves in the interplanetary magnetic field

Interplanetary magnetic field data from the Mariner 10 spacecraft were examined for evidence of small and finite amplitude transverse Alfven waves, general finite amplitude Alfven waves, and magnetosonic waves. No evidence for transverse Alfven waves was found. Instead, the field fluctuations were found to be dominated by the general finite amplitude Alfven wave. Such wave modes correspond to non-plane-wave solutions of the nonlinear magnetohydrodynamic equations.

Sari, J. W.↗
NASA NTRS2012

Interpretation of Vector Electric Field Measurements of Bursty Langmuir Waves in the Cusp

An analysis of auroral Langmuir waves in the cusp observed by two high-frequency electric field instruments on the TRICE high-flyer sounding rocket shows many examples of Langmuir wave bursts modulated at approximately 10 kHz. Previous studies have explained these and similar observations as the result of beating between waves with very close frequencies near the Langmuir cutoff, resulting from either wave-wave interactions or independent linear excitations. The unique three-dimensional (3-D) data set provided by the NASA Goddard Space Flight Center TAEFWD instrument shows that up to 25% of waveforms selected from the most intense bursts exhibit anisotropic modulations, i.e., the beat nulls and peaks are not aligned in time across the three perpendicular electric field components. Modulations of this type arise when superposed wave normal modes possess differing polarizations, and simulations using wave modes calculated with the J-WHAMP numerical dispersion code show (1) that waves with differing polarizations can exist in conditions like those observed by TRICE-High and (2) that superpositions of such waves can produce anisotropic modulation. Fourier analysis of the 3-D waveform data suggests that both linear and elliptically polarized waves are present near the Langmuir cutoff at these times. These observations illustrate how 3-D measurements can give valuable insight into the nature of wave interactions in the auroral plasma environment.

Dombrowski, M. P.↗