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At least 307 records · Page 17
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NASA NTRS1976

Coronal holes, solar wind streams, and recurrent geomagnetic disturbances - 1973-1976

Observations of coronal holes, solar-wind streams, and geomagnetic disturbances during 1973-1976 are compared in a 27-day pictorial format which shows their long-term evolution. The results leave little doubt that coronal holes are related to the high-speed streams and their associated recurrent geomagnetic disturbances. In particular, these observations strongly support the hypothesis that coronal holes are the solar origin of the high-speed streams observed in the solar wind near the ecliptic plane.

Sheeley, N. R., Jr.↗
NASA NTRS1977

Nonlinear Alfven waves in high-speed solar wind streams

A nonlinear proton distribution function that is an exact stationary solution of the nonlinear Vlasov equation and Maxwell's equations and which supports a single nonlinear transverse Alfven (ion cyclotron) wave that is circularly polarized and nondispersive is proposed for most of the observations during high-speed solar wind streams. This nonlinear distribution removes the strong Alfven wave instability, inconsistent with the persistence of the observed proton distribution functions in high-speed streams, found by the linear stability analysis. Model temperature anisotropies and drift velocities of the two spatially inhomogeneous bi-Maxwellian components are consistent with typical proton velocity distributions measured in high-speed streams at 1 AU. Two derived relations for each of the wave number and the phase velocity of the wave are obeyed within experimental uncertainties by two typical proton measurements. Our model also predicts that the alpha particle bulk flow velocity exceeds the proton particle bulk flow velocity, as is observed.

Abraham-Shrauner, B.↗
NASA NTRS1977

High coronal structure of high velocity solar wind stream sources

It is shown analytically that the transition from a high-speed stream source to the ambient coronal conditions is quite rapid in longitude in the high corona. This sharp eastern coronal boundary for the solar wind stream sources is strongly suggested by the solar wind 'dwells' which appear in plots of solar wind velocity against constant-radial-velocity-approximation source longitudes. The possibility of a systematic velocity-dependent effect in the constant-radial-velocity approximation, which would cause this boundary to appear sharper than it is, is investigated. A velocity-dependent interplanetary propagation effect or a velocity-dependent 'source altitude' are two possible sources of such a systematic effect. It is shown that, for at least some dwells, significant interplanetary effects are not likely. The variation of the Alfvenic critical radius in solar wind dwells is calculated, showing that the high-velocity stream originates from a significantly lower altitude than the ambient solar wind.

Nolte, J. T.↗
NASA NTRS1977

The radial variation of corotating energetic particle streams in the inner and outer solar system

The radial gradient of long-lived, corotating energetic particle streams was measured using observations of .9-2.2 MeV protons from Helios 1 and 2, IMP 7, Pioneer 10 and Pioneer 11. A positive gradient of approximately 350% per AU is found between .3 AU and 1 AU. Between 1 AU and some 3-5 AU, the gradient is variable with an average value of 100% per AU which is consistent with earlier statistical results. A comparison between measurements at 9 AU and approximately 4 AU shows a negative gradient which is variable from -40 to -100% per AU. Possible solar latitudinal effects on these gradient studies are also discussed. Using solar wind and magnetic field data from Helios 1 between 1 AU and .3 AU, the relation between corotating energetic particle events in the inner solar system and the interplanetary medium is examined. It is found that the energetic particles are contained inside the high speed solar wind stream in a region adjacent to the interaction region between low speed and high speed streams.

Vanhollebeke, M. A. I.↗
NASA NTRS1978

A three-dimensional model of corotating streams in the solar wind. 1: Theoretical foundations

The theoretical and mathematical background pertinent to the study of steady, corotating solar wind structure in all three spatial dimensions (3-D) is discussed. The dynamical evolution of the plasma in interplanetary space (defined as the region beyond roughly 35 solar radii where the flow is supersonic) is approximately described by the nonlinear, single fluid, polytropic (magneto-) hydrodynamic equations. Efficient numerical techniques for solving this complex system of coupled, hyperbolic partial differential equations are outlined. The formulation is inviscid and nonmagnetic, but methods allow for the potential inclusion of both features with only modest modifications. One simple, highly idealized, hydrodynamic model stream is examined to illustrate the fundamental processes involved in the 3-D dynamics of stream evolution. Spatial variations in the rotational stream interaction mechanism were found to 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.

Pizzo, V. J.↗
NASA NTRS1977

Slender streams with gravity - Outer asymptotic expansions. I, II

The steady, three-dimensional, potential flow (neglecting surface tension) of a slender stream of fluid in the presence of gravity is considered and a description is presented of the first part of an asymptotic theory of such a flow. The theory will provide the ingredients for the construction of the solution to many flow problems involving slender streams. The flows and their boundaries are represented as asymptotic power series in the slenderness ratio of the stream. Attention is given to the formulation of the outer expansion problems, first approximations for a jet, a first approximation for pipe flow, and a first approximation for channel flow.

Geer, J.↗
NASA NTRS1977

Gas stream in Algol

Additional absorption features in the red wings of the Mg II resonance lines near 2800 A are found in observations of Algol made from the Copernicus satellite. The absorption features were clearly seen only during a part of the primary eclipse, in the phase interval 0.90-0.03. The observations are interpreted as being produced by a stream of matter flowing from Algol B in the direction of Algol A. The measured Doppler shifts of the features give the value of 150 km/s as the characteristic velocity of matter in the stream. The mass transfer connected with the stream is estimated to be of the order of 10 to the -13th power solar mass per year.

Cugier, H.↗
NASA NTRS1978

Solar wind stream interfaces

Results are presented for a superposed epoch analysis of discontinuous solar wind interfaces. The average time-space profiles of stream interfaces are discussed with reference to fluid properties (flow speed, pressure ridge, density, electron and proton temperatures) and kinetic properties (electron core and halo, flow speed fluctuations, electron heat flux, alpha particles). Other aspects of stream interfaces are described, such as the persistence of individual interfaces, shock associations, the sector boundaries of the interplanetary magnetic field, and sudden impulses in the geomagnetic field. Interface position is considered in terms of the observed temperature jump. A conceptual model of high-speed stream evolution is proposed.

Gosling, J. T.↗
NASA NTRS1978

Excitation of low frequency waves by streaming ions via anomalous cyclotron resonance

The effect of a small population of streaming ions on low-frequency waves with frequencies below the ion cyclotron frequency is analyzed for three modes of interest: Alfven waves, magnetosonic waves, and ion-cyclotron waves. The instability mechanism is the anomalous cyclotron resonance of the waves with the streaming ions. Conditions for excitation of the three types of waves are derived and expressions for the growth rates are obtained. Excitation of Alfven waves is possible even if the ratio of the densities of the streaming ions to the thermal ions is very small. For magnetosonic waves, excitation can easily occur if waves are propagating parallel or nearly parallel to the ambient magnetic field. As for ion-cyclotron waves, it is found that for the ion-whistler branch the excitation is suppressed over a broader range of wave frequencies than for the fast magnetosonic branch.

Wu, C. S.↗
NASA NTRS1977

Detection and interpretation of ocean roughness variations across the Gulf Stream inferred from radar cross section observations

Radar cross section data shows that the Gulf Stream has a higher cross section per unit area (interpreted here as a greater roughness) than the water on the continental shelf. A steep gradient in cross section was often seen at the expected location of the western boundary. There were also longer-scale (10-20 km) gradual fluctuations within the stream of significant magnitude. These roughness variations are correlated with the surface shear stress that the local wind imposes on the sea. Using the available surface-truth information concerning the wind speed and direction, an assumed Gulf Stream velocity profile, and high-resolution ocean-surface temperature data obtained by the VHRR onboard a NOAA-NESS polar-orbiting satellite, the present study demonstrates that the computed surface stress variation bears a striking resemblance to the measured radar cross-section variations.

Weissman, D. E.↗
NASA NTRS1978

Large-scale Gulf Stream frontal study using GEOS 3 radar altimeter data

From data obtained by the GEOS 3 radar altimeter, sea surface heights are found by both editing and filtering the raw sea surface height measurements and then referencing these processed data to a 5 foot by 5 foot geoid. Any trend between the processed data and the geoid is removed by subtracting out a linear fit to the residuals in the open ocean. Data from individual passes are further processed by applying a minimum variance technique at the subsatellite crossing points to produce surface topography maps for the 6 months and an overall mean map which reveal important details about the Gulf Stream system. The differences between the monthly mean and the overall mean are calculated for each of the 6 months to show the temporal and spatial changes of the Gulf Stream front and spawned eddies. The standard deviation map is even more informative and shows preferred locations of Gulf Stream meanders.

Huang, N. E.↗
NASA NTRS1978

Dynamic MHD modeling of solar wind corotating stream interaction regions observed by Pioneer 10 and 11

The use of the Pioneer 10 and 11 projects to test an MHD one-dimensional time-dependent model of corotating solar wind streams during the period from Sept. 30 to Nov. 25, 1973 is described. During this period, five or six corotating interaction regions streamed past the two spacecraft, and, as a result of multiple-spacecraft radial alignment and temporally varying conditions at the solar wind source, the pattern predicted by the Steinolfson et al. (1975) model could be compared with observations. The results, in general, support the validity of the model, although the neglect of thermal energy exchange leads to incorrect values for the proton temperature. A detailed analysis of a stream is discussed.

Dryer, M.↗
NASA NTRS1978

The prediction of fast stream front arrivals at the earth on the basis of solar wind measurements at smaller solar distances

The problems involved in the prediction of the arrival of fast solar wind streams at the earth on the basis of measurements made by space probes in the region between 0.3 and 1 AU are discussed. It is shown that arrival time predictions accurate to within a few hours that can be made at least as long as the large scale conditions on the Sun are relatively stationary as observed near the time of solar minimum. However, the latitudinal extent of the respective high speed streams is found to be important for making quantitative predictions. Coronal data sufficient for locating the sources of high speed streams can improve the precision of these predictions.

Rosenbauer, H.↗
NASA NTRS1978

Electron heating within interaction zones of simple high-speed solar wind streams

In the present paper, electron heating within the high-speed portions of three simple stream-stream interaction zones is studied to further our understanding of the physics of heat flux regulation in interplanetary space. To this end, the thermal signals present in the compressions at the leading edges of the simple high-speed streams are analyzed, showing that the data are inconsistent with the Spitzer conductivity. Instead, a polynomial law is found to apply. Its implication concerning the mechanism of interplanetary heat conduction is discussed, and the results of applying this conductivity law to high-speed flows inside of 1 AU are studied. A self-consistent model of the radial evolution of electrons in the high-speed solar wind is proposed.

Feldman, W. C.↗
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 NTRS1978

The relationship between Jovian electrons and solar wind stream structure

Near-earth observations of above-0.22-MeV Jovian electrons by the APL/JHU experiments on IMP-7 and 8 during 1972-1975, a period of stable recurrent solar wind, reveals 19 of 26 events in good association with solar wind streams. This pattern of positive correlation with solar wind streams is also observed in 3-6 MeV data from 1965-1972 during well-defined electron events. During their pre-encounter periods Pioneers 10 and 11 were nearly radially aligned with Jupiter and direct magnetic connection was highly unlikely. Jovian electrons above about 5 MeV in the UCSD experiments on Pioneers 10 and 11 were anticorrelated with solar wind velocity from about 3-4 AU until encounter. Reconstructions of the large-scale interplanetary magnetic field suggest that the near-earth events result from direct connection with the Jovian magnetotail and corotation of quasi-trapped populations while for Pioneer events electrons propagate out from the magnetosphere to a solar wind stream interaction, in along the interaction, then in to Pioneer on undisturbed field lines.

Gold, R. E.↗
NASA NTRS1979

Pitot pressure measurements in flow fields behind circular-arc nozzles with exhaust jets at subsonic free-stream Mach numbers

The flow field behind a circular arc nozzle with exhaust jet was studied at subsonic free stream Mach numbers. A conical probe was used to measure the pitot pressure in the jet and free stream regions. Pressure data were recorded for two nozzle configurations at nozzle pressure ratios of 2.0, 2.9, and 5.0. At each set of test conditions, the probe was traversed from the jet center line into the free stream region at seven data acquisition stations. The survey began at the nozzle exit and extended downstream at intervals. The pitot pressure data may be applied to the evaluation of computational flow field models, as illustrated by a comparison of the flow field data with results of inviscid jet plume theory.

Mason, M. L.↗
NASA NTRS1980

Wind tunnel investigation of the Titan Forward Skirt compartment vent from a free-stream Mach number of 0.80 to 1.96

A test was conducted to determine the flow characteristics of the Titan forward skirt compartment vent over a free stream Mach number range of 0.80 to 1.96. The vent was mounted in a flat plate and the plate was flush mounted to the tunnel side wall with coinciding center lines. Air was discharged from a duct, located on the tunnel side wall behind the plate, through a canted aft 30 deg honeycomb vent into the free stream. Data for the analysis of the Titan forward skirt compartment venting during ascent through the atmosphere are provided. Full scale simulated flight hardware, such as the honeycomb vent, duct corrugations and field joint ring were used. Boundary layer thicknesses were used to vary boundary height. The highest vent discharge coefficient for any given Mach number and vent pressure ratio generally occurred at the maximum displacement thickness. With no vent flow the static pressure in the vent region was generally less than the free stream static pressure. With vent flow, the static pressures upstream of the vent increased, and those downstream of the vent decreased.

Johns, A. L.↗