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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

Electron Jet of Asymmetric Reconnection

We present Magnetospheric Multiscale observations of an electron-scale current sheet and electron outflow jet for asymmetric reconnection with guide field at the subsolar magnetopause. The electron jet observed within the reconnection region has an electron Mach number of 0.35 and is associated with electron agyrotropy. The jet is unstable to an electrostatic instability which generates intense waves with E(sub parallel lines) amplitudes reaching up to 300 mV/m and potentials up to 20% of the electron thermal energy. We see evidence of interaction between the waves and the electron beam, leading to quick thermalization of the beam and stabilization of the instability. The wave phase speed is comparable to the ion thermal speed, suggesting that the instability is of Buneman type, and therefore introduces electron-ion drag and leads to braking of the electron flow. Our observations demonstrate that electrostatic turbulence plays an important role in the electron-scale physics of asymmetric reconnection.

Khotyaintsev, Yu. V.↗
DOE OSTI2024

System and method for wave prediction

A method and system for prediction of wave properties include collecting time series data streams from one or more wave measurement devices and processing the data using a wave-prediction algorithm to identify the frequency components of the data and compute wave parameters. The wave-field is propagated in space and time to predict wave height, speed, and velocity at a target location. A sliding window approach is used to continuously update the prediction in real-time.

Previsic, Mirko↗
NASA NTRS2000

An Altimeter Wind Speed Model Using Both Radar Backscatter and Significant Wave Height

The development and validation of a new altimeter wind speed model will be presented. This algorithm provides a direct mapping of TOPEX-measured backscatter and significant wave height to 10 m wind speed. A large scatterometer/altimeter crossover data set was assembled to develop the routine and several large ancillary data sets have been assembled for validation purposes. Validation results suggest that this two input routine provides marginal, yet measurable improvements over the standard single-parameter MCW algorithm.

Vandemark, D.↗
NASA NTRS2004

Continuous auroral activity related to high speed streams with interplaneraty ALFV&N wave trains

We discuss a type of intense magnetospheric/auroral activity that is not always substorms: High-Intensity, Long-Duration, Continuous AE Activity (HILDCAA) events, which occur during high speed solar wind streams. The high speed streams contain large-amplitude, nonlinear Alfvtn waves. Analyses of POLAR UV images, demonstrate that the AE increases/AL decreases in HILDCAAs are not always substorm expansion phases (although some substorms may occur). The associated auroral W energy deposition is throughout a continuous (360') auroral oval. During some image intervals, the dayside aurora is the most remarkable feature. Our hypothesis is that solar wind energy transfer from the solar wind to the magnetosphere/ionosphere is primarily directly driven due to the finite wavelength Alfv6n waves and the rapid dBz/dt variability.

magnetospheric↗
NASA NTRS1979

A theory of stationary long waves. III - Quasi-normal modes in a singular waveguide

The present paper deals with the fundamental issue of whether one can treat waves as normal modes when critical surface, where the phase speed of the wave matches the zonal wind speed, are present. In particular the question of whether a Rossby critical level (such as the zero-wind line for stationary waves) is absorbing or reflecting is raised and subsequently addressed. It is found that the critical level is never totally absorbing; Rossby waves are partially reflected even if the critical layer is dominated by dissipative processes. The relevance of nonlinearity in planetary-scale Rossby wave critical layers is also discussed and it is found to be the dominant mechanism. With the relative magnitudes of nonlinearity versus viscosity relevant to the earth's atmosphere it is found that the steady-state critical level should be almost perfectly reflecting to incident Rossby waves. Consequently, normal-mode solutions can be found; the quantization condition for these waves is also derived.

Tung, K. K.↗
DOE OSTI2020

Validating simulated mountain wave impacts on hub-height wind speed using SoDAR observations

The ascent of stably stratified air over a mountain barrier can trigger the generation of mountain waves. Mountain waves occur frequently over the Columbia River Gorge in western North America and can impact wind power generation over the area. Therefore, predicting the details of mountain waves events (e.g., dominant wavelength, timing, and duration) can be very valuable for the wind energy community. In this study, the ability of the Weather Research and Forecasting (WRF) model to simulate mountain waves and their impact on hub-height wind speed is investigated. Our results suggest that the WRF model has moderate skill in simulating observed mountain wave. Further, given WRF predictions of wavelength range and wave period, the Fast Fourier Transform can calculate the simulated mountain wave impact on hub-height wind speed. The resulting wind speeds agree well with SoDAR observations in terms of both magnitude and pattern. Finally, for the simulated cases, WRF consistently predicts impacts of significant mountain wave events about an hour earlier than the actual observations. Overall, in this work, the sensitivities as well as uncertainties associated with our methodology are discussed in detail.

17 WIND ENERGY↗
NASA NTRS1981

The secondary flow near a baroclinic planetary wave critical line

A critical line (CL) is the surface where the phase speed of a wave in a fluid is equal to the speed of the background flow. The considered investigation is concerned with one aspect of the simplest model of a CL in which the CL is assumed to totally absorb energy from steady, stationary, planetary waves. The aspect of interest is the secondary mean circulation near a CL in a baroclinic atmosphere. The motivation for this study is the observation of the nearly vertical CL by O'Neill and Taylor (1979) which appeared during the sudden warming of 1976/77. Even though the treatment of the CL is highly idealized in the investigation, there is evidence which indicates a very large rate of change in the zonally averaged temperature along a CL may occur. The Lagrangian-mean properties of an idealized baroclinic CL are also examined. It is found that the Lagrangian jets may provide an important transport process for exchange of stratospheric and tropospheric air.

Schoeberl, M. R.↗
NASA NTRS1986

Interferometric phase velocity measurements in the auroral electrojet

A double-probe electric field detector and two spatially separated fixed-bias Langmuir probes were flown on a Taurus-Tomahawk sounding rocket launched from Poker Flat Research Range in March 1982. Interesting wave data have been obtained from about 10s of the downleg portion of the flight during which the rocket passed through the auroral electrojet. Here the electric field receiver and both density fluctuation (delta-n/n) receivers responded to a broad band of turbulence centered at 105 km-altitude and at frequencies generally below 4 kHz. Closer examination of the two delta-n/n turbulent waveforms reveals that they are correlated; from the phase difference between the two signals, the phase velocity of the waves in the rocket reference frame is inferred. The magnitude and direction of the observed phase velocity are consistent either with waves which travel at the ion sound speed or with waves which travel at the electron drift velocity. The observed phase velocity varies by about 50 percent over a 5 km altitude range, an effect which probably results from shear in the zonal neutral wind, although, unfortunately, no simultaneous neutral wind measurements exist to confirm this.

Labelle, J.↗
NASA NTRS1973

Motion of the sources for type 2 and type 4 radio bursts and flare-associated interplanetary disturbances

Shock waves are indirectly observed as the source of type 2 radio brusts, whereas magnetic bottles are identified as the source of moving metric type 4 radio bursts. The difference between the expansion speeds of these waves bottles is examined during their generation and propagation near the flare regions. It is shown that, although generated in the explosive phase of flares, the behavior of the bottles is quite different from that of the waves and that the speed of the former is generally much lower. It is shown that the transit times of disturbances between the sun and the earth give information about the deceleration of shock waves to their local speeds observed near the earth's orbit. A brief discussion is given on the relationship among magnetic bottles, shock waves near the sun, and flare-associated disturbances in interplanetary space.

Sakurai, K.↗
NASA NTRS1981

Measurements of a solar flare-generated shock wave at 13.1 R/0/

The first measurements of the structure of wind speed, electron density, and electron density fluctuations are reported for a shock wave propagating through the acceleration region of the solar wind. Radio scattering observations, consisting of spectral broadening, mean phase and amplitude scintillations, were made on August 18, 1979, 13.1 solar radii east of the sun near the ecliptic plane, using the 2.3 and 8.4 GHz radio signals of Voyager 1. The results show a shock wave speed of about 3,500 km/sec; which, when compared with average transit time speed to 1 AU, shows that substantial deceleration took place with outward propagation from the sun. This result is consistent with a blast wave.

Woo, R.↗
NASA NTRS1991

Relationship between gas exchange, wind speed, and radar backscatter in a large wind-wave tank

The relationships between the gas exchange, wind speed, friction velocity, and radar backscatter from the water surface was investigated using data obtained in a large water tank in the Delft (Netherlands) wind-wave tunnel, filled with water supersaturated with SF6, N2O, and CH4. Results indicate that the gas-transfer velocities of these substances were related to the wind speed with a power law dependence. Microwave backscatter from water surface was found to be related to gas transfer velocities by a relationship in the form k(gas) = a 10 exp (b A0), where k is the gas transfer velocity for the particular gas, the values of a and b are obtained from a least squares fit of the average backscatter cross section and gas transfer at 80 m, and A0 is the directional (azimuthal) averaged return.

Wanninkhof, Richard H.↗
NASA NTRS1976

Interplanetary magnetic field power spectra - Mean field radial or perpendicular to radial

A detailed frequency analysis of Pioneer-6 interplanetary magnetic field data is carried out for 5 to 15 hour periods during which the mean interplanetary field is approximately radial or perpendicular to radial. The reason why these data sets were chosen is that by making the usual assumption that the phase speed of any wave present is much less than the mean solar wind speed, the measured frequency spectra can be interpreted in terms of the wave number parallel or perpendicular to the mean field, without such additional assumptions as isotropy or the dominance of a particular mode and without measurements of velocity and density. The details of the calculation of the magnetic field power spectra, coherencies, and correlation functions are discussed, along with results obtained directly from the data (such as spectra, slopes, anisotropies, and coherencies). The results are interpreted in terms of MHD theory, and are related to work in other areas.

Sari, J. W.↗
NASA NTRS2023

Breaking Wave Field Statistics With A Multi-Layer Model

The statistics of breaking wave fields are characterised within a novel multi-layer framework, which generalises the single-layer Saint-Venant system into a multi-layer and non-hydrostatic formulation of the Navier–Stokes equations. We simulate an ensemble of phase-resolved surface wave fields in physical space, where strong nonlinearities, including directional wave breaking and the subsequent highly rotational flow motion, are modelled, without surface overturning. We extract the kinematics of wave breaking by identifying breaking fronts and their speed, for freely evolving wave fields initialised with typical wind wave spectra. The Λ(c) distribution, defined as the length of breaking fronts (per unit area) moving with speed c to c + dc following Phillips (J. Fluid Mech., vol. 156, 1985, pp. 505–531), is reported for a broad range of conditions. We recover the Λ(c) ∝ c−6 scaling without wind forcing for sufficiently steep wave fields. A scaling of Λ(c) based solely on the root-mean-square slope and peak wave phase speed is shown to describe the modelled breaking distributions well. The modelled breaking distributions are in good agreement with field measurements and the proposed scaling can be applied successfully to the observational data sets. The present work paves the way for simulations of the turbulent upper ocean directly coupled to a realistic breaking wave dynamics, including Langmuir turbulence, and other sub-mesoscale processes.

Jiarong Wu↗
NASA NTRS1978

On phase and ray directions of magnetosonic waves

The behavior of phase speed for 'slow' and 'fast' magnetosonic waves is well documented in the literature. Not so well documented is the behavior of the ray direction and its relation to the phase direction - indeed the ray behavior recorded in most of the standard plasma physics texts has not been found. This situation is rectified, and some of the curiosities associated with the direction of the 'slow' ray relative to the direction of the 'slow' phase wave are indicated. These calculations have been performed as a necessary basis for discussion of phase and ray evolution of magnetosonic waves in differentially shearing plasmas.

Lerche, I.↗
NASA NTRS1980

Deceleration of the solar wind upstream from the earth's bow shock and the origin of diffuse upstream ions

Observations with the Los Alamos Scientific Laboratory/Max-Planck-Institut crossed-fan solar wind ion experiment on ISEE I reveal that the solar wind is decelerated and deflected away from the direction of the earth's bow shock as it enters that portion of the upstream region populated by diffuse bow shock ions and long-period (10-60 s) waves. Typically, the average directed velocity vector changes by 7-10 km/s as it enters the wave region. At times, average speed changes as large as 25-40 km/s are observed. Superposed upon these changes in average flow speed are large amplitude (+ or - 15) fluctuations in flow speed associated with the waves themselves. The observations suggest that the solar wind deceleration is the result of momentum transfer from reflected bow shock ions to the wind via the long-period waves as the reflected ion beams go unstable. The broad angular distributions of the diffuse ions thus appear to be produced as a consequence of the disruption of reflected ion beams.

Bame, S. J.↗
NASA NTRS1990

Highly nonlinear magnetic pulses at Comet Giacobini-Zinner

Nonlinear solitary magnetic pulses have been detected near the outbound bow shock/wave of Comet Giacobini-Zinner. The pulses have peak field-to-background compression ratios ranging from 2.3 to 7.0 and full-width half-maximum durations from 12 to 72s, comparable to the H2O group ion gyroperiod. Because all of the solitary waves have the same spacecraft-frame polarizations, it is suggested that the waves may have phase speeds greater than the solar wind speed. The role that the waves may play with the bow shock is discussed briefly.

Tsurutani, Bruce T.↗
NASA NTRS1981

Gulf of Mexico satellite radar altimetry

The dynamic topography of the sea surface was measured. The radar altimeter measurements yield average ocean topographic data which are mapped. Seasonal deviations from a 3 year mean topography are presented. The altimeters are also instrumented with sample and hold gates which provide information about the shape and amplitude of the return waveform. Parameters including ocean surface wind speed and the significant wave height are determined. One hundred eighty six wind speed and significant wave height histograms are presented.

Parra, C. G.↗