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NASA NTRS1974

Cosmic ray anisotropies observed late in the decay phase of solar flare events

Data was obtained from instrumentation on Explorers 34 and 41 on cosmic-ray anisotropy and magnetic field vectors during five solar flare events. The analysis was conducted in the energy range from 0.7 to 7.6 MeV, of the late decay phase, to evaluate the dependence of net cosmic-ray anisotropy vector amplitude and direction on the magnetic field azimuth. Results showed that in the late decay phase the direction of the net cosmic-ray anisotropy vector was invariant in relation to the direction of the magnetic field, particle energy, and species. Within the statistical error of the available data the invariant direction was perpendicular to the mean magnetic field direction.

Allum, F. R.↗

NASA NTRS1974

Cosmic ray anisotropies late in a solar flare event

The detailed relationship between the anisotropy characteristics observed during late times in the decay of a solar flare event and the interplanetary magnetic field parameters is investigated. The anisotropy always is from 45 deg east of the earth-sun line. This direction is approximately perpendicular to the nominal Archimedean spiral, independent of the particle energy. The amplitude of the anisotropy increases as the magnetic field azimuthal direction shows greater departure from the radial direction. These results are discussed in terms of current ideas about solar particle propagation in the interplanetary space.

Allum, F. R.↗

NASA NTRS1974

Model of an anisotropy solar proton event

The anisotropy of the particle distribution and its variation with time at 1 AU early in a solar cosmic-ray event can provide information on the pitch-angle scattering of the particles in the interplanetary medium. One proton event (7.6-55 MeV) is described in which the anisotropy remained large well into the decay of the omnidirectional intensity. A Monte Carlo technique which gives the pitch-angle distribution is employed to investigate two models put forward to explain the sustained anisotropy. It is shown that the observed event is consistent with a model in which the injection of particles at the sun reaches a peak 1.5 hours after flare maximum before decaying with an e-folding time of 7 hours. The uniform diffusion coefficient in this model corresponds to a classical mean free path of 1.6 AU.

Palmer, I. D.↗

NASA NTRS1975

On the anisotropies of interplanetary low-energy proton intensities

Explorer 35 proton anisotropic flux data (proton energies between 0.3 and 6.3 MeV) and simultaneous magnetic field measurements were used to supply more information on the propagation characteristics of low-energy protons in the interplanetary medium. During the rising portions of the proton events, large field-aligned anisotropies were observed. During the decaying part of the proton events, either radial anisotropy or near-isotropy was noticed. In addition, certain observations made during the decaying part of the proton events revealed anisotropies deviating significantly from the radial direction.

Pesses, M. E.↗

NASA NTRS1975

The time and spatial behavior of solar flare proton anisotropies observed in deep space on Pioneers 10 and 11

The anisotropy of solar flare protons from the direction of the 'garden hose' magnetic field line has been analyzed for 24 events observed by the University of Chicago experiment on Pioneers 10 and 11 in 1972 and 1973. The anisotropy versus time profiles during individual events are in general consistent with diffusive propagation, but several cases are observed where the decay is better described by an exponential time decay. The anisotropy amplitude evaluated at the time of maximum intensity for each event shows evidence for a gradual decrease with increasing distance from the sun which is qualitatively consistent with diffusive propagation and suggests that the effective interplanetary diffusion coefficient parallel to the magnetic field increases slowly with heliocentric distance.

Mccarthy, J.↗

NASA NTRS1975

Anisotropy measurements of nearly 50 KeV solar protons

The Energetic Particles Experiment on IMP-7 measures the angular distribution of 50-200 keV solar protons in 16 sectors. The velocity of 50 keV protons may be less than 5 times that of the solar wind. A generalized nonlinear Compton-Getting point transformation into the co-moving frame that contains no assumptions as to the angular distribution of either the spectrum or intensity is presented. Nearly 50 keV proton data in the spacecraft frame exhibit an anisotropy ratio that is large (not less than 5) and radial throughout the October 29, 1972 event lasting more than 9 days at this energy. This anisotropy argues against impulsive injection and diffusive decay in the inner solar system. Application of the transformation to the data reveals a long lasting residual anisotropy in the co-moving frame with protons streaming from the sun. Differences between the co-moving frame and solar wind frame velocities suggest residual electric fields upstream from the bow shock.

Gold, R. E.↗

NASA NTRS1976

Critical electron pitch angle anisotropy necessary for chorus generation

Simultaneous wave, resonant-particle, and ambient-plasma data from OGO 5 for chorus emissions on August 15, 1968, were found consistent with the theoretical critical pitch-angle-anisotropy condition for whistler-mode instability by Doppler-shifted electron cyclotron resonance. Local generation, as determined by wave normal measurements, occurred only when the pitch-angle anisotropy of resonant electrons required for instability substantially exceeded the critical anisotropy defined by Kennel and Petschek (1966).

Burton, R. K.↗

NASA NTRS1979

Aether drift and the isotropy of the universe: a measurement of anisotropies in the primordial black-body radiation

This experiment detected and mapped large-angular-scale anisotropies in the 3 K primordial black-body radiation with a sensitivity of 2x.0001k and an angular resolution of about 10 degs. It measured the motion of the Earth with respect to the distant matter of the Universe (Aether Drift), and probed the homogeneity and isotropy of the Universe (the Cosmological Principle). The experiment used two Dicke radiometers, one at 33 GHz to detect the cosmic anisotropy, and one at 54 GHz to detect anisotropies in the residual oxygen above the detectors. The system was installed in the NASA-Ames Earth Survey Aircraft (U-2), and operated successfully in a series of flights.

Muller, R. A.↗

NASA NTRS1979

Anisotropies in the fluxes of Pioneer 10 protons

One-hour-averaged fluxes of 1.8- to 2.15-MeV protons observed by the LET2 detector on Pioneer 10 on the inbound trajectory showed anisotropies attributable to corotation of Jupiter's magnetodisc only when Pioneer was near the dipole equator. Most of the time the anisotropy greatly exceeded the value expected from corotation. Gradients in the distribution function can be used to account for this excess anisotropy, but the amount of gradient required is unacceptably large by 1-2 orders of magnitude. If they were taken as real, these gradients would predict almost complete disappearance of these protons from Jupiter's magnetosphere in a matter of hours. The remedy is to introduce into the model of the distribution function proton flow along field lines away from the equator into both the southern and the northern hemisphere. The parallel flux at the southernmost latitudes reached by Pioneer can reach 25% of the product of proton density and velocity, i.e., 25% of the maximum possible.

Northrop, T. G.↗

NASA NTRS1979

Southern Hemisphere measurements of the anisotropy in the cosmic microwave background radiation

A recent airborne measurement of the large-angular-scale anisotropy in the cosmic background radiation from the Southern Hemisphere (Lima, Peru) is in essential agreement with previous measurements from the northern hemisphere. The net anisotropy from the combined data can be described by a first-order spherical harmonic (Doppler) anisotropy of amplitude 3.1 plus or minus 0.4 mK with a quadrupole component of less than 1 mK. Additional ground-based measurements of the linear polarization yield an upper limit of l mK, or one part in 3000, at 95% confidence level for the amplitudes of any spherical harmonic through third order.

Smoot, G. F.↗

NASA NTRS1980

Effect of molecular anisotropy on the intensity and degree of polarization of light scattered from model atmospheres

Computations of the properties of sunlight scattered from models of the earth-atmosphere system are presented to show the effect of molecular anisotropy on the intensity, flux, and degree of polarization of the scattered light. The values of these parameters change significantly when the anisotropy factor is neglected in the molecular optical thickness and scattering phase matrix. However, if the Rayleigh scattering optical thickness is kept constant and the molecular anisotropy factor is included only in the Rayleigh phase matrix, the flux does not change, the intensity changes by a small amount, but the changes in the degree of polarization are still significant.

Bahethi, O. P.↗

NASA NTRS1980

Sudden disappearance of anisotropies in the September 23, 1978 solar flare

Shortly after the onset of the particle event associated with the September 23, 1978 solar flare the University of Chicago instrument on the ISEE-3 spacecraft was measuring large anisotropies in the flux of protons with energies between 32 and 150 MeV. Several hours after the onset, the anisotropy nearly disappeared on a timescale of minutes. We present the time history of the anisotropy in this event and discuss it in terms of available information on the solar and interplanetary conditions at that time.

Evenson, P.↗

NASA NTRS1980

Theory of scan plane flux anisotropies

When a spacecraft detector measures particle flux as a function of look direction in a plane (the scan plane), anisotropy is often seen. This anisotropy is caused by spatial gradients, by E x B particle drift, and by various spectral and geometric effects. This paper treats all of these effects systematically, starting from the nonrelativistic Vlasov equation. The general analysis is applied to a simple model of an anisotropic distribution to give a relation between the E x B drift, the gradient and the experimentally observed first, second, and third harmonics of the flux as a function of angle in the scan plane. Even with an assumed model, anisotropy observations in one plane alone do not suffice to determine the E x B drift velocity and the spatial gradient independently. If the E x B velocity is assumed (e.g., the corotational velocity in a rotating planetary magnetosphere), the spatial gradient may be deduced, and from it the time rate of change of flux in a nonrotating frame of reference.

Northrop, T. G.↗

NASA NTRS1981

Large-angular-scale anisotropy in the cosmic background radiation

Results of an extended series of airborne measurements of large-angular-scale anisotropy in the 3-K cosmic background radiation are reported. A dual-antenna microwave radiometer operating at 33 GHz flown aboard a U-2 aircraft to 20-km altitude on 11 flights between December 1976 and May 1978 measured differential intensity between pairs of directions distributed over most of the Northern Hemisphere. Measurements show clear evidence of anisotropy that is readily interpreted as due to the solar motion relative to the sources of the radiation. The anisotropy is well fitted by a first order spherical harmonic of amplitude 3.6 + or - 0.5 mK, corresponding to a velocity of 360 + or - 50 km/s toward the direction 11.2 + or - 0.5 hours of right ascension and 19 deg + or - 8 deg declination.

Gorenstein, M. V.↗

NASA NTRS1981

Ion temperature anisotropy and heat flow in the Venus lower ionosphere

Motivated by the recent observations of supersonic ion flow in the Venus ionosphere near the terminator, the paper studies the extent to which such a flow can induce an ion temperature anisotropy and a diffusion-thermal heat flow. Calculations indicate that appreciable ion temperature anisotropies can be induced at altitudes below about 220 km. The temperature anisotropy is with respect to the ion-neutral relative drift velocity vector, with the ion temperature parallel to the relative drift velocity greater than the perpendicular ion temperature. The parallel to perpendicular ion temperature ratio is likely to be in the range of from 2 to 4, depending on the ionospheric conditions. It is also found that in the same ionospheric region the ion neutral relative drift induces a diffusion-thermal heat flow that is considerably more important than ordinary ion thermal conduction.

Schunk, R. W.↗

NASA NTRS1981

Anisotropy of the cosmic microwave background radiation

Theoretical predictions of the angular anisotropy in the cosmic microwave background radiation on both small and large angular scales are presented, and the effect of massive neutrinos on both the background radiation anisotropy and on the galaxy correlation function over very large scales is reviewed. Current observations show that the quadrupole anisotropy provides the greatest constraint on theory, and the values for the gravitational potential fluctuations indicate that small amplitude but sufficiently large-scale density fluctuations, both at the present epoch and on the surface of last scattering, can produce significant large angular scale variations in the radiation temperature. Most importantly, it is proposed that the quadrupole moment is most simply and elegantly interpreted in terms of the density fluctuations on very large scales whose presence is inferred from the requirement that an initial fluctuation spectrum is required in order for structure to develop.

Silk, J.↗

NASA NTRS1982

Anisotropy in MHD turbulence due to a mean magnetic field

The development of anisotropy in an initially isotropic spectrum is studied numerically for two-dimensional magnetohydrodynamic turbulence. The anisotropy develops due to the combined effects of an externally imposed dc magnetic field and viscous and resistive dissipation at high wave numbers. The effect is most pronounced at high mechanical and magnetic Reynolds numbers. The anisotropy is greater at the higher wave numbers.

Shebalin, J. V.↗

NASA NTRS1983

Anisotropy in MHD turbulence due to a mean magnetic field

Shebalin, J. V.↗