摘要:

The diurnal anisotropy of cosmic ray intensity has been investigated over the interval 1973–1978 by using neutron monitor data from Calgary, Deep River, Goose Bay, and Inuvik. It is observed that in general, the 27‐day variation in the diurnal anisotropy is greater for the component perpendicular to the nominal interplanetary magnetic field (IMF) in comparison with the parallel (or field aligned) component, which has very little ‘power’. However, the direction of the average anisotropy vector is aligned almost perpendicular (within the hour) to the IMF. The results are discussed in terms of alternate possibilities: the ‘power’ with 27‐day period and its harmonics arise from fluctuations in the amplitude aligned in the direction (a) of the total vector itself (≈ 16 hours) (b) perpendic

ISSN:0148-0227    

DOI:10.1029/JA086iA13p11093

年代:1981

数据来源: WILEY

摘要:

All spectra measured with the High Energy Resolution Gamma‐Ray Spectroscopy Experiment (HEAO C‐1) on the third High Energy Astronomy Observatory (HEAO 3) contain a strong line at 511 keV resulting from positron annihilation. This line originates in the instrument itself, the earth's atmosphere, and cosmic sources, possibly including the diffuse cosmic background. In order to understand the emission from cosmic sources, the atmospheric positron annihilation line emission has been determined as a function of geomagnetic latitude and zenith angle. Although the intensity of the line increases with increasing latitude, it was found that variations with zenith angle can be satisfactorily explained only if the atmospheric emission exhibits significant limb darkening. The atmospheric line has an energy of 511.07±0.10 keV and a net width of 2.29±0.30 keV FWHM. Characteristics of the instrument background have allowed an upper limit of 9.4 × 10−3photons/cm² ‐sec‐sr to be placed on any narrow (≲3 keV) diffuse cosmic emis

ISSN:0148-0227    

DOI:10.1029/JA086iA13p11098

年代:1981

数据来源: WILEY

摘要:

An analysis is presented of the Pioneer 10 and 11 magnetic field data, with regard to the sector structure in the interplanetary magnetic field. For the 3–4 years leading up to the last solar minimum, the data are shown to be consistent with the existence of a wavy equatorial current sheet in the heliosphere. Two sectors are shown to dominate the long term field structure, and each sector is shown to adopt a Parker spiral geometry in the outflowing solar wind. This observation is consistent with the existence of a tilted current sheet that is approximately flat near the sun but that develops a large scale wavy structure owing to the solar rotation. The recurrence pattern of the sector structure suggests an inertial rotation rate of 26.1 days (with a confidence limit of approximately 0.2 day) an observation which may indicate that the source of the low‐latitude solar wind is at mid‐latitudes on the sun. Corotating interaction regions are shown to be capable of modifying the structure of the current sheet. In particular it is suggested that they can absorb the current sheet by overtaking the nearest fold in its wavy stru

ISSN:0148-0227    

DOI:10.1029/JA086iA13p11105

年代:1981

数据来源: WILEY

摘要:

Although proton acceleration often is observed at interplanetary shocks, electron acceleration rarely has been reported. In contrast, many of the shocks identified so far by instruments on the ISEE 3 spacecraft show significant increases in the spin averaged electron flux at energies greater than 2 keV. At 2 keV, the spin averaged electron flux usually increased by a factor of 2 to 3 but on several occasions increased to more than 10 times its preshock level. Often, the behavior of the electrons is similar to higher energy (several MeV) proton spikes: the electrons are field aligned before the shock and are highly anisotropic with the flux maximum perpendicular to the magnetic field at the shock and immediately after the shock. This is the signature of the shock drift model of acceleration where the gradient in the magnetic field causes the particles to move in the direction of lower potential energy in the convection electric field. Given that a primary assumption of the shock drift model is that the gyroradius is much larger than the shock thickness, and that this assumption is invalid for electrons, it is initially surprising that electrons and ions can act similarly at shocks. A closer look shows that by conserving the first adiabatic invariant, electrons obey the same expressions for reflected and transmitted particles as ions.

ISSN:0148-0227    

DOI:10.1029/JA086iA13p11111

年代:1981

数据来源: WILEY

摘要:

The formalism for deriving ‘two‐dimensional’ magnetostatic equilibria is extended to spherical coordinates and applied to magnetic fields that are functions of radius and polar angle. A family of analytic solutions is readily found. The basic properties of these solutions are displayed for a dipole magnetic field at the base of the atmosphere and for physical parameters appropriate to the solar corona. Variation of the concentration of plasma at the ‘magnetic equator’ illustrates the distortion of a simple dipole magnetic field by the electric currents required to maintain force balance in the presence of the imposed pressure gradients in the polar direction. The deviation of the magnetostatic field lines from the simple dipole configuration depends on the parameter (Peq–Ppole)/(B0²/8π), wherePeqandPpoleare the equatorial and polar plasma pressures andB0is the dipole field strength at the base of the corona. Reasonable choices of these physical quantities give a value for this parameter of about 1/2, implying deviations in the large‐scale coronal magnetic field geometry from the commonly used potential field that are not negligible. These deviations lead to field lines that are more nearly vertical at the base of the corona and to more magnetic flux on open field lines than in potential field models with the same magnetic boun

ISSN:0148-0227    

DOI:10.1029/JA086iA13p11117

年代:1981

数据来源: WILEY

摘要:

The noise voltage found at the terminals of an electric dipole antenna immersed in a hot plasma is calculated. The plasma is assumed stable and at rest. It is described as made of two maxwellian electron populations. A grid of calculated noise spectra is presented in normalized coordinates, and we give analytical expressions valid for frequencies much lower or larger than the plasma frequencyfpor close to the noise peak. The antenna impedance is also calculated; in contrast to the noise spectrum, it is found to be very weakly dependent upon the hot population parameters. From these results one can calculate the response of a receiving system, thus enabling the actual measurement of the plasma parameters from the noise spectrum. Using ISEE 3 SBH experimental data, it is shown that the observations do fit the theoretical predictions over most of the frequency range. Plasma parameters are obtained and found in good agreement with results from the Los Alamos plasma analyzer on the same spacecraft. It appears that the high energy tail of the particle distribution function accounts for the peak noise voltages of several times 10−12V²Hz−1found at the terminals of a 45‐m half‐length dipole. The interpretation of these observations does not therefore require an unstable plasma. We discuss these results and show that more work should be done to explain an unpredicted increase of the spectrum belowfpand to explain the weak spin modulation. Solving these remaining problems requires the introduction of ions and of the bulk and/or drift velocity into the calculations. Appendix A contains a partial justification of the assumption of a triangular current distribution on the antenna. The calculations are presented in ap

ISSN:0148-0227    

DOI:10.1029/JA086iA13p11127

年代:1981

数据来源: WILEY

摘要:

This paper presents calculations of transport in a Vlasov plasma due to weak electrostatic microfluctuations driven unstable by a shear in a bulk flow. The flow velocity is parallel to a uniform magnetic field and wave propagation is in the plane perpendicular to the shear direction. A consistent procedure is used to evaluate transport of the momentum and the kinetic energy tensor due to the electrostatic flow shear instability. The transport reduces the free energy driving the instability. The wave‐particle momentum loss rate scales as the cube of the inverse shear scale length, suggesting that it may be difficult to attain an asymptotically large Reynolds number for macroscopic turbulence in a collisionless plasm

ISSN:0148-0227    

DOI:10.1029/JA086iA13p11139

年代:1981

数据来源: WILEY

摘要:

A mechanism of narrow band VLF hiss emissions above the local half cyclotron frequency observed in the outer magnetosphere by satellites is proposed. The proposed mechanism is a kind of Harris type electrostatic instability for whistler mode waves with short wavelengths and large wave normal angles in a bi‐Maxwellian hot plasma. The free energy of the instability originates from the anisotropy of the plasma whose temperature is as low as several electron volts. This wave mode has both an electrostatic and an electromagnetic nature. The growth rate of this instability and the frequency limit, below which the waves grow, are strictly dependent on the anisotropy factor A of the plasma. A type of narrow band hiss is considered to be generated in a region where A is maximum. When this hiss propagates from the source, the band of frequency becomes narrower because the upper limit frequency decreases due to a decrease of A. Extremely narrow band hiss observed by the satellite OGO 5 can be explained by a combination of the above instability and propagation effect

ISSN:0148-0227    

DOI:10.1029/JA086iA13p11148

年代:1981

数据来源: WILEY

摘要:

We present observations of the detailed temporal development of particle intensities, composition, and density gradient anisotropies for protons and heavier ions during several diffuse ion events observed upstream of the earth's bow shock. The measurements, covering the energy range ∼16 keV/Q to ∼130 keV/Q, were made with the ultra‐low energy charge analyzer sensor of the Max‐Planck‐Institut/University of Maryland experiment on ISEE 1. Composition ratios are found to be constant as a function of energy per charge not only during the equilibrium intensity levels of these events, but also during their onset and decay phases. We interpret our measurements in terms of temporal and spatial structures in the upstream region produced by a time dependent first‐order Fermi acceleratio

ISSN:0148-0227    

DOI:10.1029/JA086iA13p11153

年代:1981

数据来源: WILEY

摘要:

Measurements of ion current, electron temperature, and density and values of satellite potential from the U.S. Air Force Satellite S3‐2 together with ion composition measurements from the Atmosphere Explorer (AE‐E) satellite were used to examine the variation of the ratio α=[I+(wake)]/[I+(ambient)]| (whereI+is the ion current) with altitude and to examine the significance of the parametric interplay between ionic Mach number, normalized body sizeRD(=R0/λD, whereR0is the satellite radius and λDis the ambient debye length) and normalized body potential ϕN(=eϕS/KTe, where ϕsis the satellite potential,Teis the electron temperature, andeandKare constants). It was possible to separate between the influence ofRDand ϕNon α for a specific range of plasma parameters. Uncertainty, however, remains regarding the competition betweenRDandS(H+) andS(O+) (whereS(O+) andS(H+) are oxygen and hydrogen ionic Mach numbers, respectively) in determining the ion distribution in the nearest vicinity to the satellite surface. A brief discussion relevant to future experiments in the area of body plasma flow interactions to be conducted on board the Shuttle/Spacelab facility, is al

ISSN:0148-0227    

DOI:10.1029/JA086iA13p11161

年代:1981

数据来源: WILEY