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At least 415 records · Page 23

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NASA NTRS1979

Observed distribution functions of H, He, C, O, and Fe in corotating energetic particle streams - Implications for interplanetary acceleration and propagation

Distribution functions for H, He, C, O, and Fe derived from our IMP 8 measurements of about 0.15 to 8 MeV per nucleon particles in three corotating streams observed near Earth are shown to have a simple exponential dependence on the particle speed. The e-folding speed, typically 0.01c, is found to be the same for the distribution functions of all elements examined, and varies little from one corotating event to the next. The relative abundances of energetic particles in these events resemble most closely the solar coronal composition and thus, presumably, that of the solar wind. These results may imply that acceleration of these particles, which occurs in corotating interaction regions at several AU from the sun, is by a statistical process.

Gloeckler, G.↗

NASA NTRS1979

The magnetospheric electric field and convective processes as diagnostics of the IMF and solar wind

Indirect measurements of the convection field as well as direct of the ionospheric electric field provide a means to at least monitor quanitatively solar wind processes. For instance, asymmetries in the ionospheric electric field and ionospheric Hall currents over the polar cap reflect the solar wind sector polarity. A stronger electric field, and thus convective flow, is found on the side of the polar cap where the y component of the IMF is parallel to the y component of the geomagnetic field. Additionally, the magnitude of the electric field and convective southward B sub Z and/or solar wind velocity, and thus may indicate the arrival at Earth of an interaction region in the solar wind. It is apparent that processes associated with the convention electric field may be used to predict large scale features in the solar wind; however, with present empirical knowledge it is not possible to make quantitative predictions of individual solar wind or IMF parameters.

Kaye, S. M.↗

NASA NTRS1980

Interaction between a normal shock wave and a turbulent boundary layer at high transonic speeds. Part 1: Pressure distribution. Part 2: Wall shear stress. Part 3: Simplified formulas for the prediction of surface pressures and skin friction

An asymptotic description is derived for the interaction between a shock wave and a turbulent boundary layer in transonic flow, for a particular limiting case. The dimensionless difference between the external flow velocity and critical sound speed is taken to be much smaller than one, but large in comparison with the dimensionless friction velocity. The basic results are derived for a flat plate, and corrections for longitudinal wall curvature and for flow in a circular pipe are also shown. Solutions are given for the wall pressure distribution and the shape of the shock wave. Solutions for the wall shear stress are obtained, and a criterion for incipient separation is derived. Simplified solutions for both the wall pressure and skin friction distributions in the interaction region are given. These results are presented in a form suitable for use in computer programs.

Adamson, T. C., Jr.↗

NASA NTRS1980

Preliminary results on the plasma environment of Saturn from the Pioneer 11 plasma analyzer experiment

The Ames Research Center Pioneer 11 plasma analyzer experiment provided measurements of the solar wind interaction with Saturn and the character of the plasma environment within Saturn's magnetosphere. It is shown that Saturn has a detached bow shock wave and magnetopause quite similar to those at earth and Jupiter. The scale size of the interaction region for Saturn is roughly one-third that at Jupiter, but Saturn's magnetosphere is equally responsive to changes in the solar wind dynamic pressure. Saturn's outer magnetosphere is inflated, as evidenced by the observation of large fluxes of corotating plasma. It is postulated that Saturn's magnetosphere may undergo a large expansion when the solar wind pressure is greatly diminished by the presence of Jupiter's extended magnetospheric tail when the two planets are approximately aligned along the same solar radial vector.

Wolfe, J. H.↗

NASA NTRS1980

On the origin of corotating energetic particle events

The paper examines energetic corotating particle events produced by acceleration at the forward and reverse shock pair which bounds a corotating interaction region by the process of successive multiple reflections. In the steady state, the energetic particle intensity at the shock depends only on the intensity of shock particles, and measurements of energetic particles show systematic variations between intensities at the forward and reverse shocks. It is concluded that the solar wind is the original particle population that is accelerated in the stationary shocks up to several MeV.

Scholer, M.↗

NASA NTRS1980

The propagation of Jovian electrons to earth

An analysis of the Jovian electron flux increases observed by the earth-orbiting satellite Imp 8 throughout five 13 month Jovian synodic years during the period from launch of the satellite in 1973 to 1979 is presented. The analysis defines the characteristics of Jovian propagation to earth. Corotating interaction regions (CIR) that form at the leading edges of fast solar wind streams continue to modulate the propagation of MeV electrons from Jupiter to the orbit of the earth to produce approximately 27 day recurrent variations in the Jovian electron density. The new and significant result of this study is that these time-intensity profiles are more accurately described not by assumption that Jupiter is a constant source of electrons, but rather by assuming that electron emission is initiated with each passage of CIR by Jupiter with the emission continuing for only several days.

Chenette, D. L.↗

NASA NTRS1980

The longitudinal galactic cosmic ray intensity modulation in a diffusive and a scatter-free model of the inner heliosphere

Measurements of energetic solar flare electrons, Jovian electrons, and low-energy solar protons have led to the suggestion that the inner heliosphere is essentially scatter free. Consideration is given to a model in which scattering is only important within the corotating interaction regions (CIR's), while the cavity formed by the CIR's in the inner heliosphere is scatter free, as compared to an interplanetary diffusion model wherein scattering is determined by the solar wind and magnetic field microstructure everywhere in the heliosphere. The two models are compared in terms of the solar wind stream associated Forbush decreases at 1 AU and the longitudinal cosmic ray nucleonic intensity variations at larger heliocentric distances (Pioneer 11 measurements at about 3 AU). It is shown that the diffusion model is able to explain consistently all longitudinal galactic cosmic ray intensity modulation measurements.

Morfill, G.↗

NASA NTRS1980

Asymptotic features of shock-wave boundary-layer interaction

A semi-implicit method is applied to solve the Navier-Stokes equations numerically and to evaluate the features of the free-interaction phenomenon that occurs when a shock wave impinges on a Blasius boundary layer. Comparisons are made with predictions of the triple-deck theory and experiment. Results include pressure and skin-friction distribution in the free-interaction region for various values of Reynolds number.

Hussaini, M. Y.↗

NASA NTRS1979

Mechanisms for energetic particle acceleration in the solar wind

Recent work on energetic particle acceleration in the solar wind is reviewed. In particular, it is shown that a statistical mechanism, in which particles interact with magnetosonic waves, may account for particle acceleration in corotating interaction regions, and for the acceleration of the anomalous cosmic-ray component. This mechanism can yield the observed spectra and composition of the accelerated particles.

Fisk, L. A.↗

NASA NTRS1981

Effect of forest canopy closure on incoming solar radiance

In order to better understand the physical processes involved in defoliation assessment from remotely sensed data, a field study was designed to investigate the effect of forest canopy closure and other environmental variables on incoming solar radiation. Diffuse radiation measurements were recorded in red, infrared, and middle infrared wavelengths using the Mark 2 three band field radiometer. Results to date indicate that the percent canopy closure is the single most important variable affecting incoming solar radiation. In the visible and near infrared regions, interaction between time of day and date (defined later as solar zenith angle) also affect radiometric response. Aspect has only limited influence on radiance response. These same variables do not influence middle infrared response, however. Uniformity of the forest canopy appears to be more important. These results are compared to LANDSAT MSS classification results of gypsy moth defoliation.

Dottavio, C. L.↗

NASA NTRS1981

What causes the warp in the heliospheric current sheet

A comparative discussion of the warp in the heliospheric current sheet is presented. Pioneer 10 and 11 data of the interplanetary magnetic field compared with earlier data (Helios 1 and 2) show a good agreement on the phenomenon of the warp; however, the interpretations differ. One theory (Thomas and Smith, 1980) proposes that fast solar wind streams associated with interaction regions may move the current sheet higher to heliospheric latitudes, thus causing the warp; while the earlier theory (1976) adequately explained the phenomenon by using the observed photospheric magnetic field and the Zeeman effect but omitted the solar wind dynamical considerations as part of the computations. It is shown that the Helios data of the polarity of the interplanetary magnetic field are in good agreement with the computed location of the current sheet, confirming the earlier theory.

Wilcox, J. M.↗

NASA NTRS1982

Investigation of passive shock wave-boundary layer control for transonic airfoil drag reduction

The passive drag control concept, consisting of a porous surface with a cavity beneath it, was investigated with a 12-percent-thick circular arc and a 14-percent-thick supercritical airfoil mounted on the test section bottom wall. The porous surface was positioned in the shock wave/boundary layer interaction region. The flow circulating through the porous surface, from the downstream to the upstream of the terminating shock wave location, produced a lambda shock wave system and a pressure decrease in the downstream region minimizing the flow separation. The wake impact pressure data show an appreciably drag reduction with the porous surface at transonic speeds. To determine the optimum size of porosity and cavity, tunnel tests were conducted with different airfoil porosities, cavities and flow Mach numbers. A higher drag reduction was obtained by the 2.5 percent porosity and the 1/4-inch deep cavity.

Nagamatsu, H. T.↗

NASA NTRS1981

On the acceleration of ions by interplanetary shock waves. 3: High time resolution observations of CIR proton events

Observations within + or - 3 hours of corotating interaction region (CIR) shock waves of proton intensities, pitch angle distribution and crude differential energy spectra of the range of 0.6 E sub p 3.4 MeV are presented. The principle result is the evidence for the persistent flow of particles away from the shock. The observations are found to be in good agreement with the hypothesis of local interplanetary shock acceleration by the shock drift and compression mechanisms. The same set of observations strongly suggest that transit time damping does not play an important role in the acceleration of protons to 1 MeV in the immediate vicinity of CIR shocks.

Pesses, M. E.↗

NASA NTRS1981

On the origin of the MeV energy nucleon flux associated with CIRs

Measurements of recurrent enhancements of interplanetary nucleon flux in the MeV energy range are presented and interpreted. The features recur at the solar rotation period in association with stream-stream plasma interaction regions corotating with the sun. At distances from the sun less than 1 AU, the maximum intensities of the hydrogen and helium components increase with increasing distance between 300%/AU and 600%/AU. A model is proposed which predicts the acceleration of nuclei from keV plasma energies to MeV energies by means of transit time damping of magnetosonic waves as solar wind plasma flows from the sun. Numerical solutions of the transport equation are derived to demonstrate that the model does not reproduce radial variations of hydrogen and helium fluxes, and estimates are made of the radial diffusive mean free path. Finally, the observations are found to be consistent with nucleon acceleration at the CIR shocks beyond 1 AU with subsequent diffusion toward the sun.

Christon, S. P.↗

NASA NTRS1982

Three-dimensional flow calculations including boundary layer effects for supersonic inlets at angle of attack

An analysis is presented for calculating the steady three-dimensional flow field in supersonic mixed-compression inlets at incidence. A zonal modeling approach is employed to obtain the solution. The supersonic core flow is computed using a second-order pentahedral bicharacteristic algorithm. The bow shock wave and the reflected internal shock train are determined using a three-dimensional discrete shock fitting procedure. The boundary layer flow adjacent to both the centerbody and the cowl is computed using a second-order implicit finite difference method. The flow in a shock wave-boundary layer interaction region is computed using an integral formulation. The culmination of the present research effort is the development of a production-type computer program capable of analyzing flow in a variety of mixed-compression aircraft inlets. Numerical results and experimental correlations are presented to illustrate application of the analysis.

Vadyak, J.↗

NASA NTRS1982

Impulsive plasma transport through the magnetopause

The considered investigation is concerned with a study of the process of localized plasma entry on the basis of first principles. Since the magnetopause often moves at high velocities, an induction electric field must be involved. Attention is given to the case in which the adjacent magnetopause is at rest. Occasionally, a frame moving with the magnetopause in the interaction region is also considered. The employed model is based on the observations provided by ISEE. The considered plasma irregularity, which is denominated a 'cloud', may not have to be a large enhancement in number density or velocity. An examination of the involved physical relations shows that the plasma will create its own electric field, via a polarization current, to make possible a penetration through the magnetopause by the cloud. At the magnetopause the polarization current creates a charge separation electric field which promotes (rather than inhibits) continued flow through the moving magnetopause.

Heikkila, W. J.↗

NASA NTRS1981

A theoretical interpretation of Forbush decreases

An analysis is presented of the intensity variations of relativistic cosmic rays, at 1 AU, which are associated with the passage of a flare shock wave. The magnitude and time profile obtained is similar to that observed in flare-induced Forbush decreases, and the principal cause of the energy reduction is an increase in adiabatic cooling of the arriving particles due to prolonged containment behind the compressed field of the flare shock wave. The large decreases calculated for the smaller diffusion coefficients are inconsistent with observation, implying larger mean free paths than those traditionally assumed at these rigidities. The method presented may be used to study intensity variations associated with other large-scale structures of the interplanetary field, such as corotating interaction regions.

Gall, R.↗

NASA NTRS1982

Amplitudes of solar modulation of low energy cosmic rays

There have been differences of opinion regarding the origin and behavior of the solar modulation of galactic cosmic rays. It has been shown that the return to solar maximum intensity levels beginning in early 1978 was dominated by Forbush decreases. These Forbush decreases were caused by radially moving interplanetary shocks resulting from large solar flares. The present investigation is concerned with solar modulation effects which were observed during the previous solar minimum. The effects were associated with high-speed streams in the solar wind. These streams caused the formation of corotating interaction regions with both forward and reverse shocks. The modulation effects seen near earth are intimately connected with these shocks.

Von Rosenvinge, T. T.↗