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NASA NTRS1979

A theory of local and global processes which affect solar wind electrons. 2: Experimental support

The microscopic characteristics of the Coulomb cross section show that there are three natural subpopulations for plasma electrons: the subthermals with local kinetic energy E kT sub c; the transthermals with kT sub c E 7 kT sub c and the extrathermals E 7 kT sub c. Data from three experimental groups on three different spacecraft in the interplanetary medium over a radial range are presented to support the five interrelations projected between solar wind electron properties and changes in the interplanetary medium: (1) subthermals respond primarily to local changes (compression and rarefactions) in stream dynamics; (2) the extrathermal fraction of the ambient electron density should be anti-correlated with the asymptotic bulk speed; (3) the extrathermal "temperature" should be anti-correlated with the local wind speed at 1 AU; (4) the heat flux carried by electrons should be anti-correlated with the local bulk speed; and (5) the extrathermal differential 'temperature' should be nearly independent of radius within 1 AU.

Scudder, J. D.↗

NASA NTRS1979

Release adiabat measurements on minerals: The effect of viscosity

The current inversion of pressure-particle velocity data for release from a high pressure shock state to a pressure-density path is analyzed. It is assumed that the release process is isentropic. It was shown that for geological materials below stresses of 150 GPa, the effective viscosity must be 1000 kg/m/s in order that the viscous (irreversible) work carried out on the material in the shock state remains small compared to the mechanical work recovered upon adiabatic rarefaction. The available data pertaining to the offset of the Rayleigh line from the Hugoniot for minerals, the magnitude of the shear stress in the high pressure shock state for minerals, and the direct measurements of the viscosities of several engineering materials shocked to pressures below 150 GPa yield effective viscosities of 1000 kg/m/s or less. An inferance that this indicates that the conditions for isentropic release of minerals from shock states are achieved, and a conclusion that the application of the Riemann integral to obtain pressure-density states along the release adiabats of minerals in shock experiments is valid are made.

Jeanloz, R.↗

NASA NTRS1978

Stratospheric-related research using the shock tube

The capabilities of shock tubes used in stratospheric-related research are considered, and the results of three independent shock tube research projects are reported. The studies are concerned with the evaluation of stratospheric ozone depletion. In the first experiment, photoabsorption cross sections of Freon 11 and 12 at stratospheric temperatures were measured using rarefaction waves. In the second experiment, reaction-rate coefficients were determined from measurements made behind reflected shock waves. In the third experiment, electronic-transition moments of the O2 Schumann-Runge system and the A2Pi-X2Pi system of ClO were deduced from intensity measurements made behind the incident shock.

Cooper, D. M.↗

NASA NTRS1978

A three-dimensional model of corotating streams in the solar wind. I - Theoretical foundations

The paper is concerned with the development of the theoretical and mathematical background pertinent to the study of steady, corotating solar wind structure in all three spatial dimensions. The dynamical evolution of the plasma in interplanetary space (defined as the region beyond roughly 35 Rs where the flow is supersonic) is approximately described by the nonlinear, single-fluid, polytropic magnetohydrodynamic or hydrodynamic equations. Efficient numerical techniques are outlined for solving this complex system of coupled, hyperbolic partial differential equations. The present formulation is inviscid and nonmagnetic, but the methods used allow for the potential inclusion of both features with only modest modifications. A simple, highly idealized hydrodynamic model stream is examined to illustrate the fundamental processes involved in the three-dimensional dynamics of stream evolution. It is found that spatial variations in the rotational stream interaction mechanism produce small nonradial flows on a global scale that lead to the transport of mass, energy, and momentum away from regions of relative compression and into regions of relative rarefaction. Comparison with simpler models demonstrates the essential nonlinear, multidimensional nature of the interplanetary dynamics.

Pizzo, V.↗

NASA NTRS1979

Isentropic decompression of fluids from crustal and mantle pressures

Criteria are derived according to which the flow of single-phase magmatic fluids and the rarefaction expansion of low-viscosity liquids and gases may be considered approximately isentropic. Graphs of entropy vs. density with contours of constant pressure and mass fraction are used to examine the possible thermodynamic histories of H2O and CO2 decompressing isentropically from crustal and upper mantle pressures; these graphs offer a simple visual representation of a number of thermodynamic variables involved in isentropic processes. It is shown how the graphs can be used to examine the behavior of volatiles that (1) ascend in volcanic systems originating at different depths within the earth, and (2) decompress from a shock Hugoniot state. Entropy-density graphs are presented separately for H2O and CO2.

Kieffer, S. W.↗

NASA NTRS1979

Voyager 2 - Energetic ions and electrons in the Jovian magnetosphere

The passage of Voyager 2 through the Jovian magnetosphere demonstrated that this magnetosphere is highly variable, even as close as 10 Jupiter radii from the planet. The cosmic-ray subsystem measured the flux, elemental composition, and anisotropy of energetic particles. Its high sensitivity was particularly valuable during the long passage through the magnetotail, where particle fluxes were orders of magnitude less than in the inner magnetosphere and approached interplanetary values. The new data confirm earlier observations that the Jovian magnetosphere is a giant accelerator of particles - electrons, protons, and heavy ions, including sulfur. Both spatial and temporal changes are observed in the magnetosphere as compared to prior observations with Pioneer 10 and 11 and Voyager 1. It is suggested that the 10-hr modulation of interplanetary Jovian electrons may be associated with the arrival at the dawn magnetopause of a rarefaction region each planetary rotation.

Vogt, R. E.↗

NASA NTRS1979

Release adiabat measurements on minerals - The effect of viscosity

The paper examines the effect of viscosity in the release adiabat measurements on minerals. The current inversion of pressure-particle velocity data for release from a high-pressure shock state to a pressure-density path usually depends critically upon the assumption that the release process is isentropic. It has been shown that the effective viscosity for geological materials below stresses of 150 GPa must be at least 1000 kg/m/s so that viscous work in the shock state remains small compared to mechanical work recovered upon adiabatic rarefaction. The magnitude of the shear stress in the shock state in minerals and viscosities of engineering materials shocked to pressures below 150 GPa show effective viscosities of about 1000 kg/m/s or less indicating that the conditions for isentropic release of materials from shock states are achieved and that the Riemann integral can be applied to obtain pressure-density states along the release adiabats of minerals.

Jeanloz, R.↗

NASA NTRS1981

Dynamic tensile strength of lunar rock types

The dynamic tensile strength of four rocks are determined. A flat plate impact experiment is employed to generate approximately one-microsecond-duration tensile stress pulses in rock samples by superposing rarefaction waves to induce fracture. It is noted that the effect of chemical weathering and other factors has not been explicitly studied. The given tensile strengths are based on a series of experiments on each rock where determination of incipient spallation is made by terminal microscopic examination. The data are generally consistent with previous determinations, at least one of which was for a significantly chemically altered but physically coherent rock.

Cohn, S. N.↗

NASA NTRS1981

Magnetospheric substorm models - Comparison with neutral sheet magnetic field observations

Four models for geomagnetic substorms, a quiet tail model, and models incorporating structural effects of the tail are examined for consistency with magnetic-field data during satellite crossings of the tail neutral sheet/plasma sheet. For this data the tearing mode instability model is always consistent, and inward moving distant neutral line is sometimes consistent, quasi-steady reconnection with slow shock and intermediate wave structure and locally quiet tail rarely consistent, and an outward propagating rarefaction wave is never consistent with the magnetic observations. In several cases structural effects of the tail are consistent with key features of the magnetic signatures.

Speiser, T. W.↗

NASA NTRS1981

Compression of Jupiter's magnetosphere by the solar wind - Reexamination via MHD simulation of evolving corotating interaction regions

Major changes in the solar wind before, during and after the Pioneer 10 and 11 missions' encounter with the Jovian magnetosphere are considered. A numerical simulation of the multiple corotating interaction region (CIR) evolutions from one spacecraft to its sister spacecraft is shown to have confirmed the suggestion by Smith et al (1978) that Jupiter's magnetosphere was compressed by interplanetary CIRs during three out of four of the observed events. The MHD simulation presented suggests that the Jupiter magnetosphere reacts to solar wind rarefactions by expanding. A pair of previously unexplained magnetopause crossings of the Pioneer 11 outbound pass may be due to a delayed reexpansion of the Jupiter magnetosphere from a compression that occurred during the inbound pass.

Smith, Z. K.↗

NASA NTRS1981

Comparison of theory and in situ observations for electron and ion distributions in the near wake of the Explorer 31 and AE-C satellites

Measurements of electron density, plasma potential, and mean ion mass from the Explorer 31 satellite, and measurements of ion current, plasma potential, and ion composition from the Atmosphere Explorer C satellite were used in a comparative study with Parker's theory regarding the charged particle distribution in the near wake of an ionospheric satellite (1976). It is shown that theory and experiment agree fairly well in the angle-of-attack range between 90 and 135 deg. In the maximum rarefaction zone (between 145 and 180 deg), however, the theoretical model overestimates the measured ion depletion by several orders of magnitude. A comparison between theory and the Explorer 31 electron measurements shows that the theory again overestimates the electron depletion. These discrepancies are mainly due to the use of a steady-state theory and a single ion equation (using a mean ion mass). Improved agreement between theory and experiment can be obtained by the use of the time-dependent Vlasov-Poisson equations with separate equations for the various ion species.

Samir, U.↗

NASA NTRS1980

Impact-induced water loss from serpentine, nontronite and kernite

Preliminary experiments have been conducted to study shock-release of volatiles from minerals. Impact-induced loss of bound water from hydrous minerals has been observed, using infrared absorption and X-ray powder diffractometer techniques. Serpentine (Mg3Si2O5(OH)4) and nontronite (.5Ca(0.7)Fe4/(Si(7.3)Al(0.7))O20/(OH)4.nH2O) were shocked and recovered from pressures of up to 38 GPa, using one-dimensional shock reverberation techniques. Kernite (Na2B4O7.4H2O) was impacted by a spherical pyrex projectile traveling at 4.89 km/sec, which produced a peak pressure of approximately 33 GPa. The infrared absorption spectra indicate that some of the bound water from these three minerals was released as a result of shock compression and subsequent rarefaction. This evidence is supported by the recovery of small amounts of vapor from the serpentine shocked to 23.5 GPa and the nontronite shocked to 18 GPa. The recovered vapor is inferred to be water from the shocked minerals. X-ray diffraction spectra indicate no major changes in the unit cell dimensions of the two silicates, except for a decrease in the lattice constant in the c-direction of the nontronite, consistent with the loss of interlayer water.

Boslough, M. B.↗

NASA NTRS1982

Detonation propulsion experiments and theory

Test data are presented for the use of a single detonation of explosives in long-cone, short-cone, straight, and firing-plug nozzles to provide propulsion in a simulated Jupiter atmosphere, as well as the ambient gases N, CO2 and He. The long-cone nozzle yielded a progressive increase with ambient pressure for the higher molecular weight gases CO2 and N, while the lower molecular weight He and simulated Jupiter atmosphere showed a specific pulse decrease with increasing ambient pressure. The short-plug nozzle yielded a small specific impulse reduction with increasing ambient pressure, and its results were found to be nearly independent of ambient gas molecular weight. All data gathered are analyzed by using first principles, approximate blast wave theory predictions, and two-dimensional numerical calculations. Rarefaction and oscillatory wave phenomena are found to significantly influence specific impulse.

Back, L. H.↗

NASA NTRS1982

Numerical calculations relevant to the initial expansion of the polar wind

The results of a numerical simulation of the expansion of an H(+)-0(+) electron plasma into a vacuum are reported. Variations were introduced in the ionic density ratios, the scale lengths for the density gradient at the plasma-vacuum interface, and the initial electron-ion temperature ratio. Conditions of a gravitationally bound O(+) plasma were also considered. It was found that if H(+) is a major ion, the H(+) density profile in the expansion region is always concave, with a phase-space divided into three regions, i.e., an undisturbed plasma, a rarefaction region, and an expansion region in which ions are accelerated. When the H(+) is a minor ion, the O(+) ions accelerate the H(+) ions, the H(+) phase-space is divided into five regions, and the increased electron temperatures produce enhanced electrostatic potentials and H(+) drifts in the expansion region.

Singh, N.↗

NASA NTRS1982

Chromospheric evaporation in a well-observed compact flare

Hudson and Ohki (1972) pointed out that the increase of the soft X-ray emission measure during flares might be accounted for in two different ways, either by 'coronal condensation', or by what they termed 'chromospheric rarefaction', now more commonly called 'chromospheric evaporation'. They ruled out coronal condensation on the basis of cornal mass content arguments. Moore et al. (1980) found it highly probable that the bulk of the mass of the soft X-ray emitting plasma is supplied during the rise phase by chromospheric evaporation from the feet of the soft X-ray loops. On the other hand, Cheng et al. (1981) argued that chromospheric evaporation is not important as a source of soft X-ray plasma. The present investigation is concerned with an event in which direct chromospheric observations contradict the conclusions reached by Cheng et al. Up to now chromospheric evaporation has always been an inference, without compelling positive evidence. In the current investigation, observations are considered which constitute such evidence.

Acton, L. W.↗

NASA NTRS1982

Plasma turbulence in the downstream ionosheath of Venus

Observations made by the Pioneer Venus Orbiter plasma analyzer and the plasma wave instrument in the Venus ionosheath are compared. Large increases in plasma wave turbulence levels appear to be connected with changing plasma distributions and interpenetrating plasma beams. Some of these plasma waves are identified as Doppler - shifted ion acoustic waves due to beam/beam interactions, but it is noted that different forms of instabilities are probably also operative. The changes in the temperature, intensity and energy of the peak in the PVO plasma distributions are similar to those observed by Venera 10 closer to the planet and appear to be evidence for rarefaction and compression in the downstream ionosheath. Some of the changes in the PVO plasma distributions may be related to the presence of a second ion population or the acceleration of protons.

Intriligator, D. S.↗

NASA NTRS1983

The expansion of a plasma into a vacuum - Basic phenomena and processes and applications to space plasma physics

In this review attention is called to basic phenomena and physical processes involved in the expansion of a plasma into a vacuum, or the expansion of a plasma into a more tenuous plasma, in particular the fact that upon the expansion, ions are accelerated and reach energies well above their thermal energy. Also, in the process of the expansion a rarefaction wave propagates into the ambient plasma, an ion front moves into the expansion volume, and discontinuities in plasma parameters occur. The physical processes which cause the above phenomena are discussed, and their possible application is suggested for the case of the distribution of ions and electrons (hence plasma potential and electric fields) in the wake region behind artificial and natural obstacles moving supersonically in a rarefied space plasma. To illustrate this, some in situ results are reexamined. Directions for future work in this area via the utilization of the Space Shuttle and laboratory work are also mentioned.

Wright, K. H., Jr.↗

NASA NTRS1983

Conductive damping of coronal motions

Time-dependent motions in the solar corona are subject to modification through conductive transport of thermal energy away from compression regions and into rarefaction regions. The evolution depends on how the energy is introduced - by an essentially thermal perturbation or by a density perturbation. The net effect of thermal conduction is to convert local kinetic energy in the transient into widely distributed thermal energy, which then may in turn be partially converted into kinetic energy of the bulk flow. Local motion in the transient is thereby damped. These effects are modeled here using a numerical solution of the time-dependent solar wind equations for single-fluid thermally conductive flow. The simulations of transient phenomena are made for ordinary collisional thermal conduction and compared with similar simulations done using polytropic flow. Between one and five solar radii, the gross character in the two cases is very similar. However, there are effects with thermal conduction that cannot be modeled with polytropic flow, illustrated here by temperature and velocity forerunners and a delayed and large-amplitude trailing velocity low. If thermal conduction is artificially inhibited by simple reduction of the thermal conduction coefficient, relative velocity amplitudes remain larger in approximate proportion to the amount the coefficient is reduced.

Suess, S. T.↗