摘要:

We have used steady state modulation models of increasing complexity, with emphasis on drift models, to establish to what extent these models can simulate the observed cosmic ray integral radial gradient (energy ≥60–70 MeV/nucleon) in the heliosphere from 1977 to 1986. Special attention has been given to the apparent asymmetric behavior of the radial gradient with respect to the recent interplanetary magnetic field polarity reversal, and the remarkable constant radial gradient for the years 1977–1982. Instead of using differential intensities at specific energies, we presented integral radial gradients calculated from the computed integral intensities which made comparison with observations more realistic. We found that nondrift models had difficulties producing constant radial gradients over several years of increasing solar activity, because these models depend primarily on changes of the radial diffusion coefficientKrrto simulate an 11‐year cycle and therefore produce, in general, radial gradients symmetric with respect to solar maximum activity. Making these models independent of changes inKrrneeds, in our opinion, unrealistic changes in the conventional modulation parameters. Drift models, on the other hand, could produce a constant radial gradient for the period 1977‐1982 and account for the asymmetric behavior of the radial gradient. But because of the inherent insensitivity of these models to changes in modulation parameters during this period, the radial gradient remained less than 1% per AU, even with the effects of a wavy neutral sheet incorporated. In an attempt to increase it, we scaled drift effects down by a factor of 10 over the entire heliosphere and found a radial gradient remarkably compatible with observations. This reduction of drift has the advantage that the models produce drift effects closer to what has actually been observed, and it retains effects which apparently need drift as an explanation, for example, charge‐dependent modulation. With diminished drift effects a polarity reversal (as in 1981) produced an increase in the radial gradient in the inner heliosphere but a decrease in the outer heliosphere (r≥ 25 AU). For the period after the polarity reversal, drift models accounted remarkably well for the behavior of the integral radial gradient; the magnitude and change in the radial dependence could be obtained, even without scaling drift down. With the effects of a wavy neutral sheet incorporated, the gradient responded, at first, slowly to changes in the waviness of the neutral sheet with the tilt angle α ≥ 45°, but significantly and nonlinearly when α droppe

ISSN:0148-0227    

DOI:10.1029/JA094iA03p02323

年代:1989

数据来源: WILEY

摘要:

As part of an ongoing program to determine the processes which lead to the launch of solar coronal mass ejections (CMEs) we present a thorough examination of periods where there are observations from the hard X ray imaging spectrometer on the Solar Maximum Mission which are complementary to observations made by the MkIII K‐coronameter on Hawaii. At the time of the observations no attempt was made to produce compatible data sets so the analysis is hampered by unfortunate timing and pointing. Nevertheless, with the analysis of six events we are able to draw some useful conclusions which agree with the findings of our previous work but dispute the scenarios presented by most theoretical models of the CME launch and the CME/flare relationship. To summarize briefly our results: (1) None of the CME launches occur in coincidence with a flare onset, (2) flares which do occur in the vicinity of a CME launch site occur both after the CME onset and in one foot of the CME structure, (3) there is weak X ray activity also associated with the footpoints of the CME structures and these indicate the presence of large coronal structures which underlie the CME structures, (4) there are X ray enhancements after all of the CME onsets; in some cases these are bright enough to be classed as flares, and in others they are lesser brightenings which we refer to as subflare

ISSN:0148-0227    

DOI:10.1029/JA094iA03p02333

年代:1989

数据来源: WILEY

摘要:

Plasma data from Helios A and B, IMP, ISEE 3, Pioneer 10 and 11, and Voyager 1 and 2, together with an MHD simulation model, have been used to study on a global scale the temporal and radial evolution of the solar wind's thermodynamic properties (temperature T, number density n, and entropy s). The study has given the following results: (1) Near and inside 1 AU, T and n are negatively correlated almost all the time. Outside ≈5 AU, the T,n relation evolves to become positively correlated. (2) At 1 AU, T, p, n, and βiare dependent on the sunspot number. During the minimum of the sunspot cycle, the negative correlations between T and n are very strong. (3) The radial evolution of temperature and entropy shows that a heating process takes place for the heliospheric plasma. Between 1 and 10 AU, the entropy increases by ≈4×10−16erg/K/proton. In addition, from the combined Voyager 1 and 2 observations between 1 AU and 10 AU, the solar rotation average proton temperature was found to decrease as r−0.46±0.09, a rate much slower than the r−4/3rate predicted by the adiabatic expansion of the solar wind. We interpret this heating to be largely due to the cumulative effect of the shock process with increasing distance from the Sun. (4) The simulation model is also used to extrapolate the thermodynamic properties of the solar wind from Voyager 2 to the region of the outer heliosphere bounded by the termination shock. As the heliocentric distance increases by a factor of 10, the temperature decreases by a factor of 3, and the shock process raises the entropy by 4×10

ISSN:0148-0227    

DOI:10.1029/JA094iA03p02345

年代:1989

数据来源: WILEY

摘要:

Using data from the ISEE‐3 ion composition instrument (ICI), velocities and abundances of silicon ions in the solar wind have been determined. The period of investigation covers the maximum of solar cycle 21, beginning with launch of ISEE‐3 in August 1978 and ending at the removal of the spacecraft from the Lagrangian Point L1 in June 1982. The results generally confirm previous ICI observations of iron, the other heavy element with a low first ionization potential measured with the ICI. Silicon ions (and other ions in the sameM/Qrange) tend to stream at the bulk velocity of4He++in low‐speed solar wind. At high‐speed solar wind, Si lags by up to or about 20 km/s after4He++. By means of a minimum variance estimation technique, fluxes (and densities) of silicon in the solar wind have been obtained free of bias. An average Si/O flux ratio of 0.19±0.04 is derived. This value is larger by a factor of 3 or 4 than the Si/O abundance ratio at the solar

ISSN:0148-0227    

DOI:10.1029/JA094iA03p02365

年代:1989

数据来源: WILEY

摘要:

An analysis of available experimental data and theoretical concepts indicates that the interaction of the solar wind (SW) on the subsolar side with Venus, which has no intrinsic magnetic field, and with Mars, which has a small intrinsic magnetic field, is determined by the solar wind dynamic pressure with a contribution from the neutral planetary atmosphere to this interaction. The pattern of the SW interaction with these planets is different in principle for high and low dynamic pressures of the SW and is related to the varying intensity of ion formation processes (the SW Mass loading effect) in the vicinity of the SW obstacle boundary, which moves for different SW dynamic pressures into regions of different neutral atmosphere density. For moderate or high SW dynamic pressures, the subsolar Martian magnetosphere is also affected by this process. Results of numerical simulations of the SW‐Mars interaction for a magnetospheric obstacle boundary at an altitude of 300 km are presented. To estimate the relative role of photoionization and charge exchange processes and their effect on the shock front position, different versions of the mass loading effect were separately calculate

ISSN:0148-0227    

DOI:10.1029/JA094iA03p02375

年代:1989

数据来源: WILEY

摘要:

This study uses Pioneer Venus orbiter (PVO) magnetometer and plasma analyzer measurements to investigate the draped‐field tail of Venus with an emphasis on determining the magnetic field and plasma conditions within the various tail regions and their dependence upon interplanetary magnetic field (IMF) orientation. For this purpose PVO orbits during which the spacecraft's high inclination trajectory took it through the central magnetotail were identified. The criteria used to select these orbits were the existence of relatively complete magnetic field and plasma data during crossings of the magnetotail which lasted more than 3 hours. Examination of observations from four PVO tail seasons in 1981–1983 produced 12 orbits meeting these requirements. Analysis of the observations taken during those orbits indicates that the distribution of plasma within the magnetotail is highly asymmetric and controlled by the orientation of the IMF. In the plasma sheet and adjacent lobe regions downstream of the Venus hemisphere over which the solar wind motional electric field,Esw= −Vsw×Bsw, is directed away from the planet, PVO observed increasing fluxes of H+and O+as the spacecraft moves away from the tail axis toward the outer boundary of the tail. The greatest concentration of these O+ions was found in the vicinity of the cross‐tail current layer downstream of this Venus hemisphere. No O+ions were observed outside of the magnetotail based upon the magnetic field data and the definitions adopted in this study. However, only slow,<310 km/s, antisolar directed O+is detectable by the PVO plasma analyzer and this factor may be the reason for the frequent observation of O+in the cross‐tail current and the absence of measurable O+outside of the magnetotail where the bulk flow speeds are significantly slower than in the distant ionosheath. Downstream of the Venus hemisphere over which the solar wind motional electric field is directed in toward the planet, PVO does not usually observe significant fluxes ofE/Q= 0–8 kV ions, except sometimes directly adjacent to the outer boundary of the tail. The outer boundary of the Venus magnetotail downstream of this hemisphere is typically a well‐defined magnetopauselike current layer. The magnetotail‐ionosheath interface downstream of Venus hemisphere over which the solar wind motional electric field is outward, however, is very broad and resembles a slow mode expansion fan with field strength slowly decreasing and plasma density gradually increasing as PVO moves outward and enters the ionosheath. These results are interpreted as being due to the more efficient pick‐up of newly ionized atmospheric neutrals over the Venus hemisphere where the initial gyromotion takes the newly created ions away from the dense, lower atmosphere where they might be lost due to scattering (Cloutier et al., 1974). The implications of these findings for the formation and maintenance of the Venus magneto

ISSN:0148-0227    

DOI:10.1029/JA094iA03p02383

年代:1989

数据来源: WILEY

摘要:

The major observational characteristics of the smooth, narrow bandwidth component of Uranus' radio emissions are well described by sources radiating near the local electron gyrofrequency, confined to the magnetic equatorial plane and encircling the planet at radial distances of approximately 2 to 3RU. The most intense emission appears to be generated in association with the ε ring at 2.0RUradial distance. We infer a cold electron density of ≤4 cm−3in this re

ISSN:0148-0227    

DOI:10.1029/JA094iA03p02399

年代:1989

数据来源: WILEY

摘要:

This paper provides the essential tools for deriving quickly the quasi‐thermal noise spectrum or the impedance of a given electric antenna near the plasma frequency, for calibration or diagnosis in space plasmas. We give simple analytical expressions and numerical results for either wire or sphere dipoles in an isotropic plasma with one or two Maxwellian electron populations. We include the contribution of the particles collected and/or emitted by the antenna surface. We also indicate some modifications brought about by using more complicated antenna geometries, and a drifting or a magnetized plasma. Finally, we give some conclusions for antenna design or data interpretation in plasma wave experiment

ISSN:0148-0227    

DOI:10.1029/JA094iA03p02405

年代:1989

数据来源: WILEY

摘要:

The purpose of the present study is to present a new approach to the problem of reconstructing the wave distribution function from observed frequency spectra. A method which does not rely on cold plasma theory is developed. We use numerical methods to solve the dispersion relation for waves in a warm, homogeneous, anisotropic, and multicomponent plasma. This allows us to treat almost any linear wave mode and also to handle a large variety of plasma models, including warm plasma. Doppler effects are taken into account, and reconstruction is performed over a wide frequency range simultaneously. To define a solution to the inverse underdetermined problem occurring in the reconstruction, we use the method of maximum‐entropy. As a test of our method, we solve a model problem with simulated dat

ISSN:0148-0227    

DOI:10.1029/JA094iA03p02417

年代:1989

数据来源: WILEY

摘要:

The linear dispersion relation and the quasi‐linear evolution of the electron beam‐plasma instability are studied in intermediate regimes between the limits of the gentle bump‐on‐tail instability of Langmuir waves and purely reactive instability. The ranges of beam and plasma parameters which correspond to narrow‐banded plasma waves, broadband waves and waves with frequencies substantially below the electron plasma frequency are determined in a systematic and practical manner. The transition between these regimes and the changes in the topology of the dispersion relation are described by analytic theory and by detailed numerical solutions. All branches of the dispersion relation, including weakly damped modes which may be important in nonlinear wave coupling, are considered. Dissipative and reactive instability mechanisms are differentiated analytically and by comparing solutions of the exact dispersion relation with hybrid models using fluid components. Consequences for observations, especially in the electron foreshock, and for the design and analysis of simulation experiments are pointed out. The theory is also applicable to instabilities with ion beams or current driven instabilities. The study of the effects of increasing bulk temperature (or decreasing drift) applies in particular to the evolution from reactive Buneman instability to kinetic ion sound in

ISSN:0148-0227    

DOI:10.1029/JA094iA03p02429

年代:1989

数据来源: WILEY