摘要:

Cosmic ray data from IMP 8, Voyager 1 and 2, Pioneer 10 are used to investigate the heliocentric radial dependence of the characteristics of about 20 Forbush‐type transient decreases which occurred from 1978 to 1984. These characteristics include (1) the recovery time, (2) the amplitude, and (3) the time to decrease to minimum. It is found that the average recovery time is about 5 times longer atR= 30 AU than at 1 AU. The magnitudes of the transient decreases are observed to decrease about 1.5%/AU on average so that the magnitude of the decrease is half as great atR∼ 30 AU as at 1 AU. The time for the cosmic ray intensity to decrease to the minimum in the transient decrease is found to be greater at larger distances and is about 5 times longer atR= 30 AU than at 1 AU. The behavior of these effects as a function of radius is obviously related to the evolution of the disturbances causing the transient decreases as they propagate outward. A model of the Forbush‐type decrease is proposed to explain the observed radial dependence of the recovery time and time to minimum of the decrease. The implications of these results for understanding the relationship between Forbush‐type decreases and the 11‐year variation are

ISSN:0148-0227    

DOI:10.1029/JA091iA04p04103

年代:1986

数据来源: WILEY

摘要:

Previous wave‐driven solar wind models (Hollweg, 1978) have been extended by including a new hypothesis for the nonlinear wave dissipation. The hypothesis is that the waves dissipate via a turbulent cascade at the rate given by (1) and the waves evolve according to (16). A subhypothesis is that the relevant correlation length scales as the distance between magnetic field lines. This hypothesis allows us to treat the corona and the solar wind on an equal footing; unlike in previous wave‐driven models, we do not assume that the coronal heating takes place below the base of the model. The models exhibit the correct qualitative features, viz., a steep temperature rise (the transition region) to a maximum coronal temperature in excess of 106K, and a substantial solar wind mass flux in excess of 3.5×108cm−2s−1at 1 AU. However, the model fails in detail. Parameters that yield a high‐speed flow at 1 AU have base pressures that are too low; parameters that yield correct base pressures have low solar wind flow speeds. However, the model “comes close.” Thus although we have not shown that the initial hypothesis is consistent with available data, we feel that there are sufficient uncertainties both in the model and in the data to preclude outright rejection of the hypothe

ISSN:0148-0227    

DOI:10.1029/JA091iA04p04111

年代:1986

数据来源: WILEY

摘要:

The effects of viscosity on a steady, radial, spherically symmetric solar wind with an embedded, non‐radial magnetic field are reconsidered. The correct expression for the classical viscosity in the presence of a non‐radial magnetic field is shown to be different from that used in the past, and a means of describing non‐classical viscosity is presented. A physical interpretation of the classical and nonclassical descriptions of viscosity is provided, and observational inferences are used in discussing the nature and degree of viscous effects in the solar

ISSN:0148-0227    

DOI:10.1029/JA091iA04p04126

年代:1986

数据来源: WILEY

摘要:

We present solar wind Fe charge state and density measurements from two time periods of high‐speed solar wind occurring during a flare‐associated driver plasma and two time periods during coronal hole‐associated high‐speed streams. This constitutes the first reported measurements of Fe charge states in coronal hole‐associated high‐speed streams. The observations, made with the ultralow energy charge analyzer (ULECA) sensor on ISEE 3, indicate that the iron in the driver plasma solar wind was predominately of charge state 15 or 16, indicative of an unusually high coronal temperature (∼4×106K). In contrast, the Fe charge state distributions in the coronal hole‐associated high‐speed streams peak at 9 or 10, indicating a much lower coronal temperature (∼1.4×106K). We also present the charge state distribution of the CNO group in one coronal hole‐associated stream and find an ionization temperature of (1.3±0.3) × 106K. Combining the ULECA measurements with proton observations made with the Los Alamos National Laboratory solar wind instrument on ISEE 3, we find that the speed of solar wind iron is equal to that of hydrogen in the driver plasma but is substantially higher (by about the Alfvén speed) in the coronal hole flows. Both the iron‐hydrogen velocity difference and the calculated temperature gradient from the corona to 1 AU suggest that although the driver plasma expansion was nearly adiabatic, an extended energy input existed for the coronal hole flows. The abundance ratio Fe/H, relative to the nominal interstream value, is found to be enhanced by a factor of ∼2 in the driver plasma and depressed by a factor of ∼2 in the co

ISSN:0148-0227    

DOI:10.1029/JA091iA04p04133

年代:1986

数据来源: WILEY

摘要:

The kinematic and pitch angle scattering constraints for multiple shock encounters to occur are investigated. The results suggest that (1) large particle anisotropies and a large number of shock encounters are not mutually exclusive and (2) solar wind ions are not directly injected into the nearly perpendicular interplanetary shock acceleration process. Also, the average number of shock encounters required to accelerate an ion between two energies is calculated. The results are consistent with the shock geometry dependence observed in interplanetary shock spike and corotating interaction region associated energetic ion events.

ISSN:0148-0227    

DOI:10.1029/JA091iA04p04143

年代:1986

数据来源: WILEY

摘要:

We develop the theory for the generalized first invariant for adiabatic motion of charged particles in regions where there are large gradients in magnetic or electric fields. The general condition for an invariant to exist in such regions is that the potential well in which the particle oscillates change its shape slowly as the particle drifts. We show how the Kruskal (1962) procedure can be applied to obtain expressions for the invariant and for drift velocities that are asymptotic in a smallness parameter ε. We illustrate the procedure by obtaining the invariant and drift velocities for particles traversing a perpendicular shock, and we compare the generalized invariant with the magnetic moment, and the drift orbits with the actual orbits, for a particular case. In contrast to the magnetic moment, the generalized first invariant is better for large gyroradii (large kinetic energies) than for small gyroradii. We also give expressions for the invariant when an electrostatic potential jump is imposed across the perpendicular shock, and when the particle traverses a rotational shear layer with a small normal component of the magnetic field

ISSN:0148-0227    

DOI:10.1029/JA091iA04p04149

年代:1986

数据来源: WILEY

摘要:

To identify observed plasma and magnetic field discontinuities in interplanetary space as magnetohydrodynamic shocks requires fitting the plasma and magnetic field data to Rankine‐Hugoniot conditions. By statistics and specific samples we show that unless the fluctuations in the observed parameters in the preshock and postshock regions are seriously taken into consideration, careful fitting may still lead to erroneous identification and description of a shock. An approach to the unbiased choice of the preshock and postshock values is to systematically consider all possible combinations of preshock and postshock parameters averaged over different time intervals measured away from the shoc

ISSN:0148-0227    

DOI:10.1029/JA091iA04p04157

年代:1986

数据来源: WILEY

摘要:

A test particle model is used to study the motion of ions specularly reflected off a shock in the presence of large‐amplitude, monochromatic, transverse MHD waves. The characteristics of the motion depend on the frequency, wavelength, phase, and amplitude of the wave that is being convected into the shock. For low wave frequencies and long wavelengths (ω′ ≪ ion gyrofrequency, λ ≫ ion gyroradius), the ion motion depends only upon θBn(ϕ0), the instantaneous angle between the total magnetic field at the shock (ambient + wave) and the shock normal. For high wave frequencies and short wavelengths (ω′ ≫ ion gyrofrequency, λ ≪ ion gyroradius), the ion motion depends only upon θBn0, the angle between the ambient magnetic field and the shock normal. For intermediate frequencies and wavelengths, including those of interest in the region upstream from the earth';s bow shock (ω′ ∼ ion gyrofrequency, λ ∼ ion gyroradius), no simple θBn0or θBn(ϕ0)criterion for the ion motion is found. For example, at intermediate frequencies, the motion depends both on θBn(ϕ0) and θBn0as well as uponb/B, the ratio of the wave amplitude to ambient magnetic field strength. In general, the presence of upstream waves inhibits the escape of specularly reflected ions from the shock, the effect being greatest when the wave amplitude is large. Other properties of ion motion that are affected by the presence of an MHD wave include the propagation time of an ion from the shock to a given upstream distance, the time variation of the gyrospeed and guiding center speed, and t

ISSN:0148-0227    

DOI:10.1029/JA091iA04p04163

年代:1986

数据来源: WILEY

摘要:

By means of a numerical simulation, nonlinear evolution of large amplitude dispersive Alfven waves is studied. An energy transfer from the parent wave to two daughter Alfven‐like waves and a soundlike wave is observed (a stimulated Brillouin scattering process). The observed growth rates and propagation characteristics of these daughter waves agree with the analytical results, which we obtain by extending the previous treatments by Goldstein, Derby, Sakai, and Sonnerup. Ions are first trapped by the electrostatic potential of the daughter soundlike waves. Along with the eventual decay (ion Landau damping) of the soundlike waves, ions are phase‐mixed and left heated in the parallel direction. The increased parallel energy of ions is transferred to the perpendicular thermal energy through the nonresonant scattering process in the colliding Alfven waves (parent and daughter waves). We further observe that the daughter Alfven waves, which still have a large amplitude, are also unstable for further decay, and that the wave energy is continuously transferred to the longer wavelength regime (inverse cascading proce

ISSN:0148-0227    

DOI:10.1029/JA091iA04p04171

年代:1986

数据来源: WILEY

摘要:

Electromagnetic instabilities driven by a relatively cool ion beam are studied by one‐dimensional hybrid computer simulations. Both the beam and the instabilities propagate parallel or antiparallel to a uniform magnetic field. At relatively small beam‐core relative drift speeds, similar to conditions predicted for ion beams upstream of slow shocks in the magnetotail, the right‐hand resonant instability exhibits quasi‐linear behavior. In particular, instability saturation is due to a reduction in the beam‐core relative drift speed as well as to an increase in the perpendicular‐to‐parallel beam temperature. For tenuous beams in this quasi‐linear regime the fluctuating magnetic field amplitude at saturation scales as the beam drift kinetic energy. At higher drift speeds, including parameters similar to those upstream of the quasi‐perpendicular bow shock, the right‐hand resonant and nonresonant instabilities both lead to phase bunching of the ion beam. The relative phase between the fluctuating velocity vector of the beam and the fluctuating magnetic field is examined; computed values agree with both linear theory during the early growth phase and nonlinear arguments at saturation. In this nonlinear regime both instabilities saturate when approximately half the initial beam drift kinetic energy density is converted to fluctuating magnetic f

ISSN:0148-0227    

DOI:10.1029/JA091iA04p04188

年代:1986

数据来源: WILEY