Search NASA⌕ Search

SEARCH · Search NASA

Results for “wave modes”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS2022

Quasiperiodic Energy Release and Jets at the Base of Solar Coronal Plumes

Coronal plumes are long, ray-like, open structures, which have been considered as possible sources for the solar wind. Their origin in the largely unipolar coronal holes has long been a mystery. Earlier spectroscopic and imaging observations revealed blue-shifted plasma and propagating disturbances (PDs) in plumes that are widely interpreted in terms of flows and/or propagating slow-mode waves, but these interpretations (flows vs waves) remain under debate. Recently we discovered an important clue about plume internal structure: dynamic filamentary features called “plumelets”, which account for most of the plume emission. Here we present highresolution observations from the Solar Dynamics Observatory’s Atmospheric Imaging Assembly (SDO/AIA) and the Interface Region Imaging Spectrograph (IRIS) that revealed numerous, quasiperiodic, tiny jets (so-called “jetlets”) associated with transient brightening, flows, and plasma heating at the chromospheric footpoints of the plumelets. By analogy to larger coronal jets, these jetlets are most likely produced within the plume base by magnetic reconnection between closed and open flux at stressed 3D null points. The jetlet-associated brightenings are in phase with plumelet-associated PDs, and vary with a period of ∼3 to 5 minutes, which is remarkably consistent with the photospheric/chromospheric p-mode oscillation. This reconnection at the open-closed boundary in the chromosphere/transition region is likely modulated or driven by local manifestations of the global p-mode waves. The jetlets extend upward to become plumelets, contribute mass to the solar wind, and may be sources of the switchbacks recently detected by the Parker Solar Probe.

jets↗
NASA NTRS2022

Quasi-periodic Energy Release and Jets at the Base of Solar Coronal Plumes

Coronal plumes are long, ray-like, open structures that have been considered as possible sources of the solar wind. Their origin in the largely unipolar coronal holes has long been a mystery. Earlier spectroscopic and imaging observations revealed blueshifted plasma and propagating disturbances (PDs) in plumes that are widely interpreted in terms of flows and/or propagating slow-mode waves, but these interpretations (flows versus waves) remain under debate. Recently we discovered an important clue about plume internal structure: dynamic filamentary features called plumelets, which account for most of the plume emission. Here we present high-resolution observations from the Solar Dynamics Observatory/Atmospheric Imaging Assembly and the Interface Region Imaging Spectrograph that revealed numerous, quasi-periodic, tiny jets (so-called jetlets) associated with transient brightening, flows, and plasma heating at the chromospheric footpoints of the plumelets. By analogy to larger coronal jets, these jetlets are most likely produced within the plume base by magnetic reconnection between closed and open flux at stressed 3D null points. The jetlet-associated brightenings are in phase with plumelet-associated PDs, and vary with a period of ∼3–5 minutes, which is remarkably consistent with the photospheric/ chromospheric p-mode oscillation. This reconnection at the open-closed boundary in the chromosphere/transition region is likely modulated or driven by local manifestations of the global p-mode waves. The jetlets extend upward to become plumelets, contribute mass to the solar wind, and may be sources of the switchbacks recently detected by the Parker Solar Probe.

jets↗
NASA NTRS2013

Measuring Temperature-Dependent Propagating Disturbances in Coronal Fan Loops Using Multiple SDO-AIA Channels and Surfing Transform Technique

A set of co-aligned high resolution images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) is used to investigate propagating disturbances (PDs) in warm fan loops at the periphery of a non-flaring active region NOAA AR 11082. To measure PD speeds at multiple coronal temperatures, a new data analysis methodology is proposed enabling quantitative description of sub visual coronal motions with low signal-to-noise ratios of the order of 0.1. The technique operates with a set of one-dimensional surfing signals extracted from position-timeplots of several AIA channels through a modified version of Radon transform. The signals are used to evaluate a two-dimensional power spectral density distribution in the frequency - velocity space which exhibits a resonance in the presence of quasi-periodic PDs. By applying this analysis to the same fan loop structures observed in several AIA channels, we found that the traveling velocity of PDs increases with the temperature of the coronal plasma following the square root dependence predicted for the slow mode magneto-acoustic wave which seems to be the dominating wave mode in the studied loop structures. This result extends recent observations by Kiddie et al. (2012) to a more general class of fan loop systems not associated with sunspots and demonstrating consistent slow mode activity in up to four AIA channels.

Solar Corona↗
NASA NTRSDate not supplied

Parameterized Study of Heat Load Trends in a Subscale Rotating Detonation Rocket Engine

NASA has developed a subscale rotating detonation rocket engine platform, enabling rapid parameterization of components and their associated performances. A major performance metric of interest for RDREs is the total heat absorbed at a given operating condition and wave mode operation. To investigate this, several sets of hardware were produced to have variation of the contraction ratio, injector geometry, and length. A wide range of total mass flow rates and mixture ratios were also explored using gaseous methane/oxygen. All hardware was produced using laser powder bed fusion GRCop-42, GRX-810, or C-103 alloys depending on the component cooling requirements. Outer and inner body hardware were made from GRCop-42 where heat fluxes were expected to be high and were water cooled through integrated coolant channels. Nozzles were made from C-103 which are radiatively cooled. Finally, the injectors were produced using GRCop-42 or GRX-810 as passive cooling via propellant injection has previously found to be sufficient given the small gap width of exposed injection surface. Total heat load and bulk heat flux measurements to the hot walls are reported. Trends in heat load and heat flux are shown with relation to parameters such as chamber pressure, area ratio, and wave mode. Heat loads between the inner and outer bodies and the chamber and shroud section are compared.

Heat Flux↗
NASA NTRSDate not supplied

Parameterized Study of Heat Load Trends in a Subscale Rotating Detonation Rocket Engine

NASA has developed a subscale rotating detonation rocket engine platform, enabling rapid parameterization of components and their associated performances. A major performance metric of interest for RDREs is the total heat absorbed at a given operating condition and wave mode operation. To investigate this, several sets of hardware were produced to have variation of the contraction ratio, injector geometry, and length. A wide range of total mass flow rates and mixture ratios were also explored using gaseous methane/oxygen. All hardware was produced using laser powder bed fusion GRCop-42, GRX-810, or C-103 alloys depending on the component cooling requirements. Outer and inner body hardware were made from GRCop-42 where heat fluxes were expected to be high and were water cooled through integrated coolant channels. Nozzles were made from C-103 which are radiatively cooled. Finally, the injectors were produced using GRCop-42 or GRX-810 as passive cooling via propellant injection has previously found to be sufficient given the small gap width of exposed injection surface. Total heat load and bulk heat flux measurements to the hot walls are reported. Trends in heat load and heat flux are shown with relation to parameters such as chamber pressure, area ratio, and wave mode. Heat loads between the inner and outer bodies and the chamber and shroud section are compared.

Heat Loads↗
NASA NTRS1974

Amplification of microwaves by superconducting microbridges in a four-wave parametric mode

Parametric amplification of microwaves was observed using thin-film junctions of the Anderson-Dayem type. A series of 80 such junctions were incorporated into the upper conductor of a broadband 50-ohm microstrip transmission line with no DC bias. The amplifier was operated in the 'doubly degenerate' mode with signal, pump, and idler frequencies closely and equally spaced. An electronic gain of 12 dB at 10 GHz was observed. The bandwidth was measured to be 1 GHz and the noise temperature to be less than 20 K.

Parrish, P. T.↗
NASA NTRS1983

Hydromagnetic waves, turbulence, and collisionless processes in the interplanetary medium

An extended discussion is conducted concerning the origin and evolution of interplanetary hydromagnetic waves and turbulence, and their influence on the large scale dynamics of the solar wind. The solar wind is at present the preeminent medium for the study of hydromagnetic waves and turbulence, providing an opportunity for advancement of understanding of the most fundamental processes of the astrophysical plasmas. All interplanetary fluctuations whose time scale is observed to be greater than 1 sec can be regarded as hydromagnetic fluctuations. It has been found to be simplest, and generally very satisfactory, to model interplanetary variations as fluctuations in an MHD fluid. Attention is given to the classification of wave modes, geometrical hydromagnetics, Alfven wave pressure, rugged invariants, and the kinetic theory of collisionless processes.

Barnes, A.↗
NASA NTRS1984

Electromagnetic ion cyclotron mode (ELF) waves generated by auroral electron precipitation

Narrow-banded ELF waves with frequencies between the local hydrogen and the singly-charged helium gyrofrequencies have been seen in the S3-3 satellite electric field wave data at altitudes between 800 and 8000 km. The waves are generated in or just below the auroral acceleration region by the accelerated electron beam and propagate in the Alfven-ion cyclotron branch of the cold electromagnetic dispersion relation as modified by the presence of a two ion H(+)-He(+) plasma.

Temerin, M.↗
NASA NTRS1986

Surface generation and detection of coupled fiber-matrix mode acoustic wave propagation in fiber-reinforced composites

A technique is described that makes it possible to transmit and receive bulk ultrasonic waves launched from the same surface of a composite sheet by means of transducers mounted on variable angle blocks. A straightforward approach to measure the velocity and attenuation of this wave is presented. A bulk compressional wave of 930,000 cm/sec velocity was launched and received in this manner in an 8-ply unidirectional T-300-5208 epoxy composite. Preliminary results indicate that parameters associated with this wave might be sensitive to accumulated damage in a composite; thus, the technique has a potential for NDE in structures made from composite materials.

Yost, W. T.↗
NASA NTRS1996

Evidence of Boundary Reflection of Kelvin and First-Mode Rossby Waves

TOPEX/POSEIDON sea level data leads to new opportunities to investigate some theoretical mechanisms suggested to be involved in the El Nino/Southern Oscillation phenomenon in the tropical Pacific ocean. In particular, we are interested in studying the western boundary reflection, a process crucial for the delayed action oscillator theory, by using the TOPEX/POSEIDON data from November 1992 to May 1995.

boundary reflection TOPEX/POSEIDON↗
NASA NTRS2010

Heat Entrapment Effects Within Liquid Acquisition Devices

We introduce a model problem to address heat entrapment effects or the local accumulation of thermal energy within liquid acquisition devices. We show that the parametric space consists of six parameters, namely the Rayleigh and Prandtl numbers, the aspect ratio, and heat flux ratios for the bottom, side, and top boundaries of the enclosure. For the range of Ra considered 1 to 10(sup 9), beyond Ra on the order of 10(sup 5), convective instability is the dominant mode of convection in comparison to natural convection. The flow field transitions to asymmetric modes at Ra on the order of 10(sup 7). Direct numerical simulation of a large geometric length scale prototype for Ra on the order of 10(sup 9) shows that the flow field evolves from small wavelength instability which gives rise to nonlinear growth of thermals, propagation of the instability occurs via growth of secondary and tertiary modes, and a travelling wave mode occurs prior to asymmetry. The effect of a large aspect ratio is to increase the number of modes in the vertical direction. Due to the slow diffusion of heat in the prototype, asymptotic states are not readily attained, we show that dynamical similarity can be used for a model which allows the attainment of asymptotic states and that transition to a chaotic state occurs for Ra on the order of 10(sup 9) via a broadband power spectrum. These dynamical events show that for the baseline condition in which heat is absorbed from background laboratory environment, higher heat flux is absorbed at the top and bottom boundaries of the enclosure than a nominal value of 34.9 ergs per square centimeter -second.

Duval, W. M. B.↗
NASA NTRS2010

Acceleration of Magnetospheric Relativistic Electrons by Ultra-Low Frequency Waves: A Comparison between Two Cases Observed by Cluster and LANL Satellites

Understanding the origin and acceleration of magnetospheric relativistic electrons (MREs) in the Earth's radiation belt during geomagnetic storms is an important subject and yet one of outstanding questions in space physics. It has been statistically suggested that during geomagnetic storms, ultra-low-frequency (ULF) Pc-5 wave activities in the magnetosphere are correlated with order of magnitude increase of MRE fluxes in the outer radiation belt. Yet, physical and observational understandings of resonant interactions between ULF waves and MREs remain minimum. In this paper, we show two events during storms on September 25, 2001 and November 25, 2001, the solar wind speeds in both cases were > 500 km/s while Cluster observations indicate presence of strong ULF waves in the magnetosphere at noon and dusk, respectively, during a approx. 3-hour period. MRE observations by the Los Alamos (LANL) spacecraft show a quadrupling of 1.1-1.5 MeV electron fluxes in the September 25, 2001 event, but only a negligible increase in the November 2.5, 2001 event. We present a detailed comparison between these two events. Our results suggest that the effectiveness of MRE acceleration during the September 25, 2001 event can be attributed to the compressional wave mode with strong ULF wave activities and the physical origin of MRE acceleration depends more on the distribution of toroidal and poloidal ULF waves in the outer radiation belt.

Shao, X.↗
NASA NTRS2024

The Global Mapping of Electron Precipitation and Ionospheric Conductance From Whistler-Mode Chorus Waves

Auroral precipitation is the second major energy source after solar irradiation that ionizes the Earth’s upper atmosphere. Diffuse electron aurora caused by wave-particle interaction in the inner magnetosphere (L < 8) takes over 60% of total auroral energy flux, strongly contributing to the ionospheric conductance and thus to the ionosphere-thermosphere dynamics. This paper quantifies the impact of chorus waves on the diffuse aurora and the ionospheric conductance during quiet, medium, and strong geomagnetic activities, parameterized by AE <100, 100 < AE < 300, and AE > 300, respectively. Using chorus wave statistics and inner-magnetosphere plasma conditions from Timed History Events and Macroscale Interactions during Substorms (THEMIS) observations, we directly derive the energy spectrum of diffuse electron precipitation under quasi-linear theory. We then calculate the height-integrated conductance from the wave-driven aurora spectrum using the electron impact ionization model of Fang et al. (Geophys. Res. Lett., 2010, 37) and the MSIS atmosphere model. By utilizing Fang’s ionization model, the US Naval Research Laboratory Mass Spectrometer and Incoherent Scattar Radar (NRLMSISE-00) model from 2000s for the neutral atmosphere components, and the University of California, Los Angeles (UCLA) Full Diffusion Code, we improve upon the standard generalization of Maxwellian diffuse electron precipitation patterns and their resulting ionosphere conductance. Our study of global auroral precipitation and ionospheric conductance from chorus wave statistics is the first statistical model of its kind. We show that the total electron flux and conductance pattern from our results agree with those of Ovation Prime model over the pre-midnight to post-dawn sector as geomagnetic activity increases. Our study examines the relative contributions of upper band chorus (UBC) and lower band chorus wave (LBC) driven conductance in the ionosphere. We found LBC waves drove diffuse electron precipitation significantly more than UBC waves, however it is possible that THEMIS data may have underestimated the upper chorus band wave observations for magnetic latitudes below 65 degrees. ° .

diffuse auroral precipitation↗
NASA NTRS1990

Measurement of the electron beam mode in earth's foreshock

High frequency electric field measurements from the AMPTE IRM plasma wave receiver are used to identify three simultaneously excited electrostatic wave modes in the earth's foreshock region: the electron beam mode, the Langmuir mode, and the ion acoustic mode. A technique is developed which allows the rest frame frequecy and wave number of the electron beam waves to be determined. It is shown that the experimentally determined rest frame frequency and wave number agree well with the most unstable frequency and wave number predicted by linear homogeneous Vlasov theory for a plasma with Maxwellian background electrons and a Lorentzian electron beam. From a comparison of the experimentally determined and theoretical values, approximate limits are put on the electron foreshock beam temperatures. A possible generation mechanism for ion acoustic waves involving mode coupling between the electron beam and Langmuir modes is also discussed.

Onsager, T. G.↗
NASA NTRS1992

Secondary instability of high-speed flows and the influence of wall cooling and suction

The periodic streamwise modulation of the supersonic and hypersonic boundary layers by a two dimensional first mode or second mode wave makes the resulting base flow susceptible to a broadband spanwise-periodic three dimensional type of instability. The principal parametric resonance of this instability (subharmonic) was analyzed using Floquet theory. The effect of Mach number and the effectiveness of wall cooling or wall suction in controlling the onset, the growth rate, and the vortical nature of the subharmonic secondary instability are assessed for both a first mode and a second mode primary wave. Results indicate that the secondary subharmonic instability of the insulated wall boundary layer is weakened as Mach number increases. Cooling of the wall destabilizes the secondary subharmonic of a second mode primary wave, but stabilizes it when the primary wave is a first mode. Suction stabilizes the secondary subharmonic at all Mach numbers.

El-Hady, Nabil M.↗
NASA NTRS1992

Secondary instability of high-speed flows and the influence of wall cooling and suction

The periodic streamwise modulation of the supersonic and hypersonic boundary layers by a two-dimensional first-mode or second-mode wave makes the resulting base flow susceptible to a broadband spanwise-periodic three-dimensional type of instability. The principal parametric resonance of this instability (subharmonic) has been analyzed using Floquet theory. The effect of Mach number and the effectiveness of wall cooling or wall suction in controlling the onset, the growth rate, and the vortical structure of the subharmonic secondary instability are assessed for both a first-mode and a second-mode primary wave. Results indicate that the secondary subharmonic instability of an insulated wall boundary layer is weakened as Mach number increases. Cooling of the wall destabilizes the secondary subharmonic of a second-mode primary wave, but stabilizes it when the primary wave is a first mode. Suction stabilizes the secondary subharmonic at all Mach numbers.

El-Hady, Nabil M.↗