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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 37 records · Page 2
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NASA NTRS2008

Multispectral Emission of the Sun during the First Whole Sun Month: Magnetohydrodynamic Simulations

We demonstrate that a three-dimensional magnetohydrodynamic (MHD) simulation of the corona can model its global plasma density and temperature structure with sufficient accuracy to reproduce many of the multispectral properties of the corona observed in extreme ultraviolet (EW) and X-ray emission. The key ingredient to this new type of global MHD model is the inclusion of energy transport processes (coronal heating, anisotropic thermal conduction, and radiative losses) in the energy equation. The calculation of these processes has previously been confined to one-dimensional loop models, idealized two-dimensional computations, and three-dimensional active region models. We refer to this as the thermodynamic MHD model, and we apply it to the time period of Carrington rotation 1913 (1996 August 22 to September 18). The form of the coronal heating term strongly affects the plasma density and temperature of the solutions. We perform our calculation for three different empirical heating models: (1) a heating function exponentially decreasing in radius; (2) the model of Schrijver et al.; and (3) a model reproducing the heating properties of the quiet Sun and active regions. We produce synthetic emission images from the density and temperature calculated with these three heating functions and quantitatively compare them with observations from E W Imaging Telescope on the Solar and Heliospheric Observatory and the soft X-ray telescope on Yohkoh. Although none of the heating models provide a perfect match, heating models 2 and 3 provide a reasonable match to the observations.

Lionello, Roberto↗
NASA NTRS2005

Comparison of Two IRI Plasmasphere Extensions with GPS-TEC Observations

Two plasmasphere extensions of the International Reference Ionosphere are made available for the users. It is aimed to estimate the effect of charged particles on technical devices in the Earth's environment and to define the ionosphere-plasmasphere operational conditions compatible with existing and future systems of radio communication, radio navigation and other relevant radio technologies in the ranges of medium and higher frequencies. The Global Core Plasma Model (GCPM-2000) of Gallagher et al. (2000) is an empirical description of thermal plasma densities in the plasmasphere, plasmapause, magnetospheric trough, and polar cap. GCPM-2000 uses the Kp index and is coupled to IRI in the transition region 500-600 km. The IZMIRAN plasmasphere model (Chasovitin et al., 1998; Gulyaeva et al., 2002) is an empirical model based on whistler and satellite observations. It presents global vertical analytical profiles of electron density smoothly fitted to IRI electron density profile at 1000 km altitude and extended towards the plasmapause (up to 36,000 km). For the smooth fitting of the two models, the shape of the IRI topside electron density profile is improved using ISIS 1, ISIS 2, and IK19 satellite inputs (Gulyaeva, 2003). The plasmasphere model depends on solar activity and magnetic activity (kp-index). The two IRI plasmasphere extensions are compared in the present study with the total electron content derived from records of Global Positioning Satellites (GPS-TEC) observations for different latitudinal, solar activity, magnetic activity, diurnal and seasonal conditions. The differences of model TEC with observed TEC in the topside ionosphere and plasmasphere are discussed.

Gulyacva, Tamara↗
NASA NTRS1999

Empirical Modeling of the Plasmasphere

Over 40 years of ground and spacecraft plasmaspheric measurements have resulted in many statistical descriptions of plasmaspheric properties. In some cases, these properties have been represented as analytical descriptions that are valid for specific regions or conditions. For the most part, what has not been done is to extend regional empirical descriptions or models to the plasmasphere as a whole. In contrast, many related investigations depend on the use of representative plasmaspheric conditions throughout the inner magnetosphere. Wave propagation, involving the transport of energy through the magnetosphere, is strongly affected by thermal plasma density and its composition. Ring current collisional and wave particle losses also strongly depend on these quantities, Plasmaspheric also plays a secondary role in influencing radio signals from the Global Positioning System satellites. The Global Core Plasma Model (GCPM) is an attempt to assimilate previous empirical evidence and regional models for plasmaspheric density into a continuous, smooth model of then-nal plasma density in the inner magnetosphere. In that spirit, the International Reference Ionosphere is currently used to complete the low altitude description of density and composition in the model. The models and measurements on which the GCPM is currently based and its relationship to IRI will be discussed.

Gallagher, Dennis L.↗
NASA NTRS2001

Determining the Mass Density Along Magnetic Field Lines from Toroida Eigenfrequencies

Toroidal eigenfrequencies can be used to remotely sense the equatorial mass density rho(sub eq) and the density dependence along a magnetic field line. Here we present improvements to the method of Schulz [1996], which allows rho(sub eq) and the power law index alpha (for mass density along a field line proportional to R(sup -alpha), where R is the radial distance from the center of the Earth) to be determined from the y intercept and slope of a plot of toroidal frequency versus toroidal harmonic number n. Our modifications include a model form for eigenfrequencies with a fractional precision of 0.0005 for -6 less than or = alpha less than or = 6 and 2 less than or = L less than or = 8 (accuracy is doubtful beyond L = 5) and an iterative procedure for getting more accurate results than those found using Schulz's method. In addition, we do an analysis of the effect of random measurement errors. Observed frequencies need to be accurate to approx. 6% (3%) of the fundamental frequency in order to determine rho(sub eq) (alpha) to a precision of 30% (unity). We then apply our method to data generated using the Global Core Plasma Model for plasmaspheric mass density; our analysis demonstrates clearly bow the alpha index represents the mass density dependence on the outer part of the field line (R/(LR(sub E)) greater than or approx. 2/3).

Denton, R.↗
NASA NTRS1988

Modeling magnetospheric plasma; Proceedings of the First Huntsville Workshop on Magnetosphere/Ionosphere Plasma Models, Guntersville, AL, Oct. 14-16, 1987

The conference presents papers on the global modeling of magnetospheric plasma processes, the modeling of the midlatitude ionosphere and plasmasphere, the modeling of the auroral zone and boundary layer, the modeling of the polar magnetosphere and ionosphere, and the modeling of the plasma sheet and ring current. Particular attention is given to the kinetic approach in magnetospheric plasma transport modeling, self-consistent neutral point current and fields from single particle dynamics, preliminary statistical survey of plasmaspheric ion properties from observations by DE 1/RIMS, and a model of auroral potential structures based on dynamics explorer plasma data. Other topics include internal shear layers in auroral dynamics, quantitative parameterization of energetic ionospheric ion outflow, and open flux merging in an expanding polarcap model.

Moore, T. E.↗
NASA NTRS2006

Towards the Identification of the Keeper Erosion Cause(s): Numerical Simulations of the Plasma and Neutral Gas Using the Global Cathode Model OrCa2D-II

Numerical simulations with the time-dependent Orificed Cathode (OrCa2D-II) computer code show that classical enhancements of the plasma resistivity can not account for the elevated electron temperatures and steep plasma potential gradients measured in the plume of a 25-27.5 A discharge hollow cathode. The cathode, which employs a 0.11-in diameter orifice, was operated at 5.5 sccm without an applied magnetic field using two different anode geometries. It is found that anomalous resistivity based on electron-driven instabilities improves the comparison between theory and experiment. It is also estimated that other effects such as the Hall-effect from the self-induced magnetic field, not presently included in OrCa2D-II, may contribute to the constriction of the current density streamlines thus explaining the higher plasma densities observed along the centerline.

plasma modeling↗
NASA NTRS1998

Io's Plasma Environment During the Galileo Flyby: Global Three-Dimensional MHD Modeling with Adaptive Mesh Refinement

The first results for applying a three-dimensional multimedia ideal MHD model for the mass-loaded flow of Jupiter's corotating magnetospheric plasma past Io are presented. The model is able to consider simultaneously physically realistic conditions for ion mass loading, ion-neutral drag, and intrinsic magnetic field in a full global calculation without imposing artificial dissipation. Io is modeled with an extended neutral atmosphere which loads the corotating plasma torus flow with mass, momentum, and energy. The governing equations are solved using adaptive mesh refinement on an unstructured Cartesian grid using an upwind scheme for AHMED. For the work described in this paper we explored a range of models without an intrinsic magnetic field for Io. We compare our results with particle and field measurements made during the December 7, 1995, flyby of to, as published by the Galileo Orbiter experiment teams. For two extreme cases of lower boundary conditions at Io, our model can quantitatively explain the variation of density along the spacecraft trajectory and can reproduce the general appearance of the variations of magnetic field and ion pressure and temperature. The net fresh ion mass-loading rates are in the range of approximately 300-650 kg/s, and equivalent charge exchange mass-loading rates are in the range approximately 540-1150 kg/s in the vicinity of Io.

Combi, M. R.↗
NASA NTRS2023

The Gamma-Ray Pulsar Phenomenology in View of 3D Kinetic Global Magnetosphere Models

We develop kinetic plasma models of pulsar magnetospheres with magnetic-field-line-dependent plasma injection that reveal the importance of various magnetosphere regions in regulating the gamma-ray emission. We set different particle injection rates for the so-called open, closed, and separatrix zones. Moderate particle injection rates in open and closed zones ensure a global field structure close to the force-free one, while the dissipation occurs mainly in and around the equatorial current sheet. The particles injected in the separatrix zone affect the particle populations that enter the equatorial current sheet region and, therefore, the corresponding accelerating electric fields, particle energies, the spectral cutoff energy, and gamma-ray efficiency. The separatrix zone models reproduce the recently discovered fundamental plane of gamma-ray pulsars consistent with curvature radiation emission, the gamma-ray light-curve shapes, and the radio-lag vs. peak-separation correlation reported in the Fermi second pulsar catalog. The model beaming factors indicate that the pulsar total gamma-ray luminosities listed in the Fermi catalogs are overestimations of the actual ones. We find that the radiation reaction limited regime starts ceasing to govern the high-energy emission for spin-down powers less than 1034 erg/s. Our results also indicate that toward high magnetic inclination angles, the "Y point" around the rotational equator migrates well inside the light cylinder sparking additional peaks in the gamma-ray pulse profiles. We find that an equivalent enhanced particle injection beyond the Y point strengthens these features making the model gamma-ray light curves inconsistent with those observed.

Neutron stars↗
NASA NTRS1995

Microscale Effects from Global Hot Plasma Imagery

We have used a three-dimensional model of recovery phase storm hot plasmas to explore the signatures of pitch angle distributions (PADS) in global fast atom imagery of the magnetosphere. The model computes mass, energy, and position-dependent PADs based on drift effects, charge exchange losses, and Coulomb drag. The hot plasma PAD strongly influences both the storm current system carried by the hot plasma and its time evolution. In turn, the PAD is strongly influenced by plasma waves through pitch angle diffusion, a microscale effect. We report the first simulated neutral atom images that account for anisotropic PADs within the hot plasma. They exhibit spatial distribution features that correspond directly to the PADs along the lines of sight. We investigate the use of image brightness distributions along tangent-shell field lines to infer equatorial PADS. In tangent-shell regions with minimal spatial gradients, reasonably accurate PADs are inferred from simulated images. They demonstrate the importance of modeling PADs for image inversion and show that comparisons of models with real storm plasma images will reveal the global effects of these microscale processes.

Moore, T. E.↗
NASA NTRS1994

The whistler heat flux instability: Threshold conditions in the solar wind

Solar wind electrons are observed often to consist of two components: a core and a halo. The anisotropics and relative average speeds of these components correspond to a heat flux that has the potential to excite several different electromagetic instabilities; wave-particle scattering by the resulting enhanced fluctuations can limit this heat flux. This manuscript describes theoretical studies using the linear Vlasco dispersion equation for drifting bi-Maxwellian component distributions in a homogeneous plasma to examine the threshold of the whistler heat flux instability. Expressions for this threshold are obtained from two different parametric baselines: a local model that yields scalings as functions of local dimensionless plasma paramaters, and a global model based on average electron properties observed during the in-eliptic phase of the Ulysses mission. The latter model yields an expression for the heat flux at threshold of the whistler instability as a function of helisopheric radius that scales in the same way as the average heat flux observed form Ulysses and that provides an approximate upper bound for that same quantity. This theoretical scaling is combined with the observational results to yield a semi-empirical closure relation for the average electron heat flux in the solar wind between 1 and 5 AU.

Gary, S. Peter↗
NASA NTRS2021

Core-Plasma Refilling and Erosion: Science Justification

Global magnetospheric models do not currently couple dynamic plasmaspheric plasma due to computational limitations that will be overcome by 2050. A true GGCM will need to include a dynamic plasmasphere for both physics and space weather prediction. Such inclusion requires that we answer longstanding, fundamental questions about the life cycle of core (<10 eV, plasmaspheric) plasma: how it gets into the inner magnetosphere, and how it is eroded. Erosion and refilling are processes controlling a fundamental space plasma population. During every geomagnetic disturbance, tens of metric tons of plasma are rapidly eroded away, then slowly and unevenly replenished. After several decades we still do not understand the cross-scale mechanisms proposed to be responsible for these 2 processes. Removal and replacement of this enormous plasma mass is as important to the dynamics of the magnetosphere as solar-wind driving. Our community must dedicate the resources and effort needed to solve this enduring puzzle. Other white papers submitted in response to the HP2050 call are discussing cold plasma and ionospheric outflow in more general contexts. This white paper deals specifically with the science justification for studying refilling and erosion.

Plasmasphere, core-plasma, erosion, refilling↗
NASA NTRS1996

Kinetic Space Weather: Toward a Global Hybrid Model of the Polar Ionosphere-Lower Magnetosphere Plasma Transport

During the indicated period of performance, we had a number of publications concerned with kinetic polar ionosphere-lower magnetosphere plasma transport. For the IUGG 1991-4 Quadrennial Report, we reviewed aspects of U.S. accomplishments concerned with polar plasma transport, among other issues. In another review, we examined the computer simulations of multiple-scale processes in space plasmas, including polar plasma outflow and transport. We also examined specifically multiscale processes in ionospheric outflows. We developed a Generalized Semi-Kinetic(GSK) model for the topside-lower magnetosphere which explored the synergistic action of wave heating and electric potentials in the formation of auroral Ion conics, in particular the "pressure cooker" mechanism. We extended the GSK model all the way down to 120 km and applied this code to illustrate the response of the ionosphere- magnetosphere to soft-electron precipitation and convection-driven frictional ion heating, respectively. Later, the convection-driven heating work was extended to a paper for the Journal of Geophysical Research. In addition to the above full published papers, we also presented the first developments of the coupled fluid-semikinetic model for polar plasma transport during this period. The results from a steady-state treatment were presented, with the second presentation being concerned with the effects of photo-electrons on the polar wind, and the first garnering an outstanding student paper award from the American Geophysical Union. We presented the first results from a time-dependent version of this coupled fluid-semikinetic model.

Horwitz, James L.↗
NASA NTRS1987

Modeling of the magnetosphere

The derivation of the magnetosphere configuration is discussed, with consideration given to both descriptive models, which represent the observed magnetic field B and perhaps the electric field E, and physical models, which also include plasma effects. Consideration is given to global field models, static physical magnetohydrostatic models, slowly variable E, and MHD tail models, and to the type of data used for their derivation. It is emphasized that the current trend in derivation of magnetospheric models is for incorporating more physics( e.g., V x B) to match regions of observed current flow, plasma pressure obeying equilibrium conditions, E linked to interplanetary sources, and time-dependent convective flows.

Stern, David P.↗
NASA NTRS1998

Beta in Streamers

Streamers are generally described as regions of the corona in which the density is higher than in coronal holes because the plasma is trapped by closed loops of magnetic flux. In contrast, MHD models of the global corona show the plasma beta in streamers above siml.2R_S (heliocentric). There are three recent contributions to this topic. The first is that heating near the cusp further drives beta up and results in release of new slow solar wind plasma from the top of the streamer. The second is SOHO/UVCS observations, in combination with a potential field/source surface model of the magnetic field, that show beta above 1.2R_S in a streamer observed near solar sunspot minimum. The third is a magnetic field reconstruction technique that uses field deforming algorithms and is more versatile for local fields than potential field models . The field reconstruction algorithm was applied to an isolated active region (AR 7999) and to the Pneuman Kopp global MHD model (beta has never been published for their model). In the active region, beta becomes larger than unity at siml.2 R_S. In the Pneuman & Kopp model, beta at the base of the streamer and rises with increasing height, becoming 15-20 at 1.6R_S and 35- 50 at 1.7R_S. Global simulations go on to show that the reason streamers do not simply explode under such high beta conditions is that they are held down by pressure from the sides due to the magnetic fields (and low beta) in adjacent coronal holes. The main role of the closed magnetic loop near the cusp is to keep the steamer from continuously leaking plasma, as otherwise happens in a magnetic pinch which is similar but has no closed loops. Awareness of MHD physical conditions in streamers is causing us to focus more attention on the details of the heating. On obvious suggestion is that heating is at much lower heights in streamers than in coronal holes. Also, energy which is directly delivered as momentum in coronal holes might all be deposited as heat in streamers.

Suess, Steven T.↗
NASA NTRS2006

Global Aspects of Heliosphere-Geosphere Coupling

The magnetosphere serves both to hold off the solar wind and to couple it selectively to the Earth through the auroral zones. It has long been understood that the plasmasphere consists of geogenic plasmas that expand out of the sunlit low latitude ionosphere, but it was initially assumed that the hot low density plasma beyond the plasmasphere is largely of solar wind origin with a minor admixture of ionospheric plasmas, discovered via mass spectrometric observations in the early 70's. Since then, elaborate simulation models have been developed that have taken us from an era of cartoon physics to a new era of quantitative global comparisons between observations and theory. In most current global circulation models of the magnetosphere, the ionospheric load on the system is taken to lie exclusively in the thin F layer of the ionosphere. This layer is coupled with solar wind and magnetospheric plasmas via Maxwell stresses communicated by field aligned current systems, and with the thermosphere via ion-neutral charge exchange and Coulomb collisions. However, recent observations have shown us that ionospheric plasmas flow sporadically in various forms into the plasmasphere and up into the high latitude circulation cells of the outer magnetosphere, as driven by the solar wind and its variable intensity and magnetic field. Under some conditions, ionospheric material is observed to be the principal component of plasmas at the dayside magnetopause and in the plasma sheet and ring current regions. Given a global model of magnetospheric circulation, it is relatively straightforward to investigate the behaviors of ionospheric plasmas in response to solar wind drivers, and we report the results of such efforts here. We find that ionospheric plasmas dominate the plasma pressure in the magnetosphere in some regions, particularly when the solar wind is especially intense and-or southward directed. This result violates the assumption that the ionospheric load is confined to the F layer, and shows that the ionosphere is often an important dynamic element of the solar wind-ionosphere system throughout the magnetosphere, especially during larger geospace storms. This means that future global circulation models must account for ionospheric plasma inertia, heat capacity, and pressure, to be quantitatively credible.

Moore, Thomas E.↗
NASA NTRS1993

Dispersed ion structures at the poleward edge of the auroral oval: Low-altitude observations and numerical modeling

We have compared the AUREOL 3 (A3) observations of auroral ion precipitation, particularly ion beams, with the results from the global kinetic model of magnetotail plasma of Ashour-Abdalla et al. (1993). We have identified 101 energetic keV H(+) velocity dispersed precipitating ion structures (VDIS) with fluxes above 10(exp -3) ergs./sq cm./s in the A3 record between the end of 1981 and mid-1984. These beams display a systematic increase in energy with increasing latitude and were observed in a narrow region within less than 1 deg in latitude of the polar cap boundary. The VDIS are the most distinctive feature in the auroral zone of the plasma sheet boundary layer. We report first on a statistical analysis of the possible ralationships between magnetic activity or substorm phase and the VDIS properties. Our particle simulations of the precipitating ions have been extended by using a series of modified versions of the Tsyganenko (1989) magnetic field model and by varying the cross-magnetosphere electric field. In the simulations, plasma from a mantle source is subject to strong nonlinear acceleration, forming beams which flow along the PSBL. Only 3 to 4% of these beams precipitate into the ionosphere to form the VDIS while the majority return to the equatorial plane after mirroring and form the thermalized central plasma sheet. The final energy and the dispersion of the beams in the model depend on the amplitude of the cross-tail electric field. Two unsual observations of low-energy (less than 5 keV) O(+) VDIS, shifted by 4 deg 5 deg in invariant latitude equatorward of H(+) VDIS are analyzed in detail. The sparsity of such O(+) events and the absence of the changes in the flux and frequency of occurrence indicate a solar wind origin for the plasma. Finally, large-scale kinetic modeling, even with its simplifications and assumptions (e.g., static magnetic field, solar wind source), reproduces low-altitude auroral ion features fairly well; it may therefore be presented as an appropriate framework into which data on energization and transport of the hot plasma, obtained in the equatorial plane, could be inserted in the near future.

Bosqued, J. M.↗
NASA NTRSDate not supplied

Tracking the Subsolar Bow Shock and Magnetopause

Global magnetohydrodynamic models predict that plasma velocities vary almost linearly from 0 km s-1 along the stagnation streamline leading from the nose of the stationary magnetopause to 0.25 Vsw at the nose of the bow shock, where Vsw is the solar wind velocity. This paper presents a proof-of-concept study showing how two-point measurements of the plasma velocity in the subsolar magnetosheath can be used to determine gradients in the plasma velocity and consequently the steady-state or slowly-moving locations of both the nose of the magnetopause and the nose of the bow shock. The results may be of use to those binning magnetosheath observations to develop empirical models, those testing models for magnetopause erosion or deposition in response to magnetic reconnection, and those determining the stand-off distance of the bow shock as a function of solar wind conditions.

David Sibeck↗
NASA NTRS2008

Image-Based Empirical Modeling of the Plasmasphere

A new suite of empirical models of plasmaspheric plasma based on remote, global images from the IMAGE EUV instrument is proposed for development. The purpose of these empirical models is to establish the statistical properties of the plasmasphere as a function of conditions. This suite of models will mark the first time the plasmaspheric plume is included in an empirical model. Development of these empirical plasmaspheric models will support synoptic studies (such as for wave propagation and growth, energetic particle loss through collisions and dust transport as influenced by charging) and serves as a benchmark against which physical models can be tested. The ability to know that a specific global density distribution occurs in response to specific magnetospheric and solar wind factors is a huge advantage over all previous in-situ based empirical models. The consequence of creating these new plasmaspheric models will be to provide much higher fidelity and much richer quantitative descriptions of the statistical properties of plasmaspheric plasma in the inner magnetosphere, whether that plasma is in the main body of the plasmasphere, nearby during recovery or in the plasmaspheric plume. Model products to be presented include statistical probabilities for being in the plasmasphere, near thermal He+ density boundaries and the complexity of its spatial structure.

Adrian, Mark L.↗