摘要:

We have solved the two‐dimensional time‐dependent diffusion‐convection equation numerically to obtain the distribution and anisotropy of cosmic rays in the heliosphere. We have assumed that the parallel and perpendicular mean free paths are proportional to the particle Larmor radius, and we have treated each proportionality constant (a, b) as a parameter. We have found that the set (a, b) = (4, 2) gives the steady state solution compatible with observations on the intensity and the solar diurnal anisotropy of cosmic rays in 0.5‐ to 10‐GeV range as obtained at the earth. This set of (a, b) corresponds to the ratio of the diffusion coefficientsD∥/D⊥= 10. In our solution the intensity for the (pre‐1980) interplanetary magnetic field (IMF) state where the solar magnetic dipole and the angular velocity vector are parallel is higher than for the (post‐1980) state where they are antiparallel, while the phase of the diurnal anisotropy is about 15 hours for the parallel state and about 18 hours for the antiparallel state. We have also reproduced the observed small radial gradient for each IMF state. We discuss the nature of the solution in order to understand the effect of the density gradient drift motion on the cosmic

ISSN:0148-0227    

DOI:10.1029/JA091iA01p00001

年代:1986

数据来源: WILEY

摘要:

A numerical model of the cosmic ray storm in the two‐dimensional heliosphere is constructed incorporating the drift effect. We estimate the effect of a flare‐associated interplanetary shock and the disturbed region behind it (characterized by enhancement in velocity and magnetic field, and decrease in mean free path) on the density and anisotropy of cosmic rays in the heliosphere. As the disturbance propagates outward, a density enhancement appears on the front side, and a density depression region is produced on the rear side. The effect of drift on the cosmic ray storm appears most clearly in the higher‐latitude region. For the parallel (antiparallel) state of the solar magnetic field which corresponds to the pre‐(post‐) 1980 period, the density in the higher‐latitude region decreases (increases) before the shock arrival. The maximum density depression near the earth for the parallel state is greater than for the antiparallel state, and the energy spectrum of the density depression in percentage is softer for the parallel state than for the antiparallel state. Prior to the arrival of the shock, the phase of solar diurnal anisotropy begins to shift to the earlier hours, and its amplitude becomes greater for both polarity states. North‐south anisotropy also becomes greater because of the enhanced drift for both po

ISSN:0148-0227    

DOI:10.1029/JA091iA01p00013

年代:1986

数据来源: WILEY

摘要:

Measurements of the direction of propagation of 29 coronal mass ejection events observed during the Skylab epoch (1973–1974) and 19 events observed during the SMM epoch (1980) reveal that the former undergo an average 2.2° equatorward deflection, while the latter do not deviate significantly from radial motion. No differences between eruptive prominence‐associated or flare‐associated events can be detected for either epoch. The results suggest that coronal mass ejection events are influenced by the background coronal magnetic and flow patterns; the nonradial forces affecting the Skylab epoch mass ejections arise from the large‐scale dipolar magnetic field and flow configuration present at t

ISSN:0148-0227    

DOI:10.1029/JA091iA01p00031

年代:1986

数据来源: WILEY

摘要:

A new, definitive, reliable and fast iterative method is described for determining the geometrical properties of a shock (i.e., θBn,n,VsandMA), the conservation constants and the self‐consistent asymptotic magnetofluid variables using the Rankine‐Hugoniot conservation equations. The technique uses the three dimensional magnetic field and plasma observations. The method is well conditioned and reliable at all θBnangles regardless of the shock strength or geometry. Explicit proof of “uniqueness” of the shock geometry solution by either analytical or graphical methods is given. The method is applied to synthetic and real interplanetary shocks, including a bow shock event and the results are then compared with those determined by preaveraging methods and other iterative schemes. A complete analysis of the confidence region and error bounds of the solution is also

ISSN:0148-0227    

DOI:10.1029/JA091iA01p00039

年代:1986

数据来源: WILEY

摘要:

A method for calculating ensemble averages from magnetic field data is described. A data set comprising approximately sixteen months of nearly continuous ISEE‐3 magnetic field data is used in this study. Individual subintervals of this data, ranging from 15 hours to 15.6 days comprise the ensemble. The sole condition for including each subinterval in the averages is the degree to which it represents a weakly time‐stationary process. Averages obtained by this method are appropriate for a turbulence description of the interplanetary medium. The ensemble average correlation length obtained from all subintervals is found to be 4.9×1011cm. The average value of the variances of the magnetic field components are in the approximate ratio 8∶9∶10, where the third component is the local mean field direction. The correlation lengths and variances are found to have a systematic variation with subinterval duration, reflecting the important role of low‐frequency fluctuations in the interplanet

ISSN:0148-0227    

DOI:10.1029/JA091iA01p00059

年代:1986

数据来源: WILEY

摘要:

The calculation of a reasonable global average temperature structure is the first step in the simulation of the dynamics and observed characteristics of Venus's upper mesosphere and thermosphere. Various physical processes that influence Venus temperatures are examined using updated inputs and new parameterizations. We demonstrate, using a one‐dimensional NLTE radiative transfer code, that temperatures observed during the Pioneer Venus mission can be reproduced using an O‐CO2collisional excitation rate coefficient of 4×10−13cm³ s−1for strong 15‐µm cooling balanced by 9.5%‐efficient EUV heating. Cooling by eddy mixing is at best a minor contribution to the total cooling required. Exospheric temperatures are calculated to vary by 60 K or less over a solar cycle, in rough agreement with observations. We conclude that CO2cooling effectively buffers against such solar perturbations, due to its nonlinear temperat

ISSN:0148-0227    

DOI:10.1029/JA091iA01p00070

年代:1986

数据来源: WILEY

摘要:

We extend the Lee (1982) self‐consistent theory of upstream wave excitation and particle energization to address observations by Voyager 2 of sunward propagating MHD waves and diffuse suprathermal particle populations upstream of the Jovian bow shock. Two new ideas are incorporated into the theory. First, the interplanetary seed wave population is taken to be an equal admixture of waves propagating both toward and away from the shock parallel to the interplanetary magnetic field. Second, finite connection times are incorporated approximately into the theory in an effort to understand whether the particle spectra at high energy are limited by particle escape or finite connection time. It is found that finite connection times dominate the particle distribution at energies above 40 keV. In this manner the suprathermal proton distributions can be accounted for by a multiple reflection, shock acceleration theory. We find that the theory can also account for the low‐frequency waves observed upstream of the shock in conjunction with the suprathermal i

ISSN:0148-0227    

DOI:10.1029/JA091iA01p00081

年代:1986

数据来源: WILEY

摘要:

Study of ISEE 2 fast plasma data reveals that many suprathermal ion events that in previous studies would have been identified as intermediate ion events are actually gyrating ion events. Of 190 apparently intermediate ion events selected on the basis of their signature in energy‐time spectrograms, half are actually found to be gyrating ion events. Using a model bow shock, the shock geometries and spacecraft locations for the observed gyrating and intermediate ion events are compared and found to be quite similar. Both gyrating and intermediate ion events are found to be associated with upstream MHD‐like wave activity. Most gyrating ion events are associated with large‐amplitude, monochromatic, weakly compressive waves, whereas many intermediate ion events are associated with smaller‐amplitude, nonmonochromatic, weakly compressive waves. Some intermediate ion events are found to have no associated waves. Detailed study of the gyrating ion distributions reveals that the distributions are typically gyrotropic within ∼4REof the bow shock, whereas at larger distances (up to ∼10RE) upstream from the shock the distributions are frequently “gyrophase bunched.” In light of these observational characteristics it is concluded that gyrating ion distributions are most likely generated both through coherent wave disruption of field‐aligned beams and through reflection of solar wind i

ISSN:0148-0227    

DOI:10.1029/JA091iA01p00091

年代:1986

数据来源: WILEY

摘要:

The generation of nonoscillatory mirror waves is studied using a one‐dimensional periodic hybrid electromagnetic simulation. The ion dynamics are treated exactly; the electrons are approximated as a finite pressure, massless fluid. Compression of the flux tubes in the magnetosheath causes a large pressure anisotropy, and it has been proposed that this anisotropy drives a mirror instability. The mirror waves have been identified by large amplitude fluctuations of the magnetic field, anticorrelated with pressure fluctuations. The simulations are initiated in a homogeneous high beta (beta = 2.5) plasma with the ambient magnetic field at various angles to the simulation axis. It is found that ion cyclotron waves are also driven by the pressure anisotropy, in competition with the nonoscillatory mirror waves. Simulations indicate that in a pure ¹H+plasma the much faster growing ion cyclotron waves absorb the free energy in the anisotropy to the extent that mirror waves should not be observed. Analysis of the dispersion relations of mirror waves and ion cyclotron waves in the multi‐component plasma indicates that4He2+and16O6+ions in the solar wind should stabilize the ion cyclotron waves sufficiently that the mirror waves become the dominant instabi

ISSN:0148-0227    

DOI:10.1029/JA091iA01p00101

年代:1986

数据来源: WILEY

摘要:

A two‐dimensional magnetoinductive particle‐in‐cell code is used to compare the stability of isotropic and anisotropic current layers in a collisionless plasma. We find, in agreement with recent theories, that temperature anisotropy withT⊥>T∥significantly enhances the instability. The simulation growth rates agree well with analytical predictions of growth rates in the linear phase. Nonlinear growth rates are significantly larger than linear growth rates and are apparently the result of coalescence instability. For a fixed system length the influence of coalescence on the growth rates increases with anisotropy. This is evidently because of a shift in the most unstable mode to shorter wavelength with increasing anisotropy. Thus anisotropic current layers tend to produce large amplitude small wavelength islands which rapi

ISSN:0148-0227    

DOI:10.1029/JA091iA01p00113

年代:1986

数据来源: WILEY