摘要:

The hydromagnetic flow configurations associated with the cosmic ray modulation in 1977–1980 were determined using solar wind plasma and magnetic field data from Voyager 1 and 2 and Helios 1. The modulation was related to two types of large‐scale systems of flows: one containing a number of transients such as shocks and postshock flows, the other consisting primarily of a series of quasi‐stationary flows following interaction regions containing a stream interface and often bounded by a forward‐reverse shock pair. Each of three major episodes of cosmic ray modulation was associated with the passage of a system of transient flows. Plateaus in the cosmic ray intensity‐time profile were associated with the passage of systems of corotatin

ISSN:0148-0227    

DOI:10.1029/JA089iA08p06579

年代:1984

数据来源: WILEY

摘要:

The purpose of the present study is to confirm the view of a heliospheric current sheet moving with respect to the solar equator, in relation to the solar cycle phases. For this reason, we have analyzed both observed and high‐accuracy inferred daily interplanetary magnetic field (IMF) polarities between the maxima of solar cycles 18 and 21 (1947–1980). Statistically significant north‐south and “away”‐“toward” differences of the IMF mean sector widths (MSW) have been detected around the solar activity minima while no significant differences have been observed around the maxima or the solar polarity reversals. This peculiar variability of the MSW differences in the solar activity extrema can be finally interpreted by assuming a variable placement of the heliospheric current sheet with respect to the solar equator and the solar cycle phases. Actually, in the epochs of the solar polarity reversal our observations are consistent with a current sheet located symmetrically to the solar equator, almost vertical to it and extending to high heliolatitudes. In the opposite, in the epochs of the solar minima the interpretation of our observations could be due to a current sheet which is southward depressed in the northern but symmetrical in the southern hemisphere. The various placements of the current sheet on both sides of the solar equator in relation to the solar cycle phases, are supposed to originate in north‐south asymmetric solar activity which has been found by several authors to predominate in the solar minima. The MSW differences detected in the last minimum (1975–1977) of the time span under consideration give reasons to venture the prediction that in the solar minima of the time period 1976–1998 the heliospheric current sheet will appear northward depressed in the southern hemisphere but symmetrical in the northern hemisphere. Systematic meridional and high‐latitude observations of both solar wind parameters and IMF patterns would contribute significantly in giving a final answer to the question of possible heliospheric current sheet displacements during th

ISSN:0148-0227    

DOI:10.1029/JA089iA08p06588

年代:1984

数据来源: WILEY

摘要:

Helios particle and magnetic field observations between 0.3 and 1 AU are used to determine plasma parameters that characterize the bulk and internal energy state of the solar wind. Quantities expected to be conserved in a time‐stationary flow with local spherical symmetry in the ecliptic plane are actually found to be invariant within measurement uncertainties. These are the total mass, energy, and angular momentum fluxes for the anisotropic solar wind plasma composited by electrons, protons, and alphas. Although individual species have nonthermal velocity distributions, the total plasma pressure is almost isotropic (p⊥/p∥= 0.9). The total heat flux divided by the mass fluxQr/ρuris markedly smaller than thermal speeds squared υ∥,⊥² =p∥,⊥/ρ. By this reason an appropriately defined polytropic index γ is found to be almost 5/3 and rather insensitive to heliocentric distance and flow speed. This index γ does not include terms due to wave turbulence or external heat sources but is solely based on the total particle heat flux. These observational findings indicate that the heat flux beyond 0.3 AU is observationally too small to cause a strong departure from adiabaticity. The solar wind expansion may be conceived in terms of a “single particle” moving in the binding gravitational potential and in the accelerating thermal (enthalpy and heat fluxes) and magnetorotational (azimuthal kinetic energy and Poynting flux) potentials. The radial profiles of these potentials are de

ISSN:0148-0227    

DOI:10.1029/JA089iA08p06599

年代:1984

数据来源: WILEY

摘要:

This paper is an extension of recent work by Isenberg and Hollweg dealing with the preferential acceleration and heating of solar wind heavy ions by a resonant cyclotron interaction with a turbulent spectrum of ion‐cyclotron waves. Two major approximations of the previous work are eliminated: that of isotropic ion distributions, and that of nondispersive waves. The wave action flux of finite‐amplitude Alfvén waves in a multi‐ion, differentially flowing, gyrotropic plasma is derived. This quantity is incorporated into the wave‐driven solar wind model of Isenberg and Hollweg, which is then applied to gyrotropic protons and alpha particles. It is found that allowing for nonisotropic ions yields enhanced preferential acceleration of alpha particles. However, when dispersion is included in the resonant interaction, the preferential effects are again reduced. These more realistic calculations show that the observations of solar wind alpha particles cannot be explained by a resonant cyclotron int

ISSN:0148-0227    

DOI:10.1029/JA089iA08p06613

年代:1984

数据来源: WILEY

摘要:

The excitation mechanism of the upstream low‐frequency waves (0.01–0.05 Hz) is investigated based on the wave observations. We compared the observed wave frequencies with the frequencies expected from the ion (proton) beam‐cyclotron instability process. We estimated the beam velocity from the solar wind parameters using Sonnerup’s formula. Our analysis supports the hypothesis that these waves are excited by the resonant beam‐cyclotron instability. For the waves observed in the deep foreshock region, however, we found it necessary to include the solar wind convection effect on the wave pr

ISSN:0148-0227    

DOI:10.1029/JA089iA08p06623

年代:1984

数据来源: WILEY

摘要:

A detailed study of electron plasma waves observed upstream of the earth’s bow shock and of their relationships to the position of the satellite in the foreshock and to the electron measurements has been carried out. The wave characteristics depend on the position in the electron foreshock: a narrow‐band (a few percent) and intense (a few millivolts per meter) noise is observed at the plasma frequency at the edge of the foreshock while the spectrum widens (Δf/f ≃ 0.3) at the same time as the power decreases (hundreds of microvolts per meter) deeper (a few earth radii) inside the foreshock. Signals below the plasma frequency are also observed. These waves are polarized along the magnetic field, with long wavelengths below and at the plasma frequency and short wavelengths above it. They appear as short bursts, the duration of which depends on the frequency: longer close to the plasma frequency (50 ms), they shorten with increasing separation from the plasma frequency, the usual duration being 15 ms. While the correlation of the wave characteristics with the reflected electrons is good as the satellite moves inside the foreshock, no evolution is found with the distance to the bow shock, neither for the noise nor for the particles. These results are discussed in the frame of various mechanisms which have been proposed to explain these upstream waves but no satisfactory agreement is found with any o

ISSN:0148-0227    

DOI:10.1029/JA089iA08p06631

年代:1984

数据来源: WILEY

摘要:

In collisionless magnetosonic shock waves, ions are commonly thought to be decelerated by a dc electrostatic cross‐shock electric field along the shock normal , where γ is the effective polytrope index for electrons. By observation this ratio is ∼1/10 at the earth’s bow shock. When viewed in the de Hoffman‐Teller frame, corresponding changes in the ion kinematics occur. Since thee[ϕ*HT] is an order of magnitude smaller than the ion energy, the ions are not significantly affected by the electrostatic force. They are instead primarily retarded in this frame by the magnetic force. Since this latter force is proportional to the component ofBout of the coplanarity plane, infinitesimally thin shock models may not be realistic for the study of the ion and electron dynamics in the de Hoffman‐T

ISSN:0148-0227    

DOI:10.1029/JA089iA08p06654

年代:1984

数据来源: WILEY

摘要:

The Jovian magnetospheric field measured by Pioneer 10 and 11 can be well modeled by a combination of current systems composing an azimuthally symmetric current disc, a dusk‐dawn current sheet in both the dayside and the nightside magnetosphere, and an image dipole to represent the effects of currents on the magnetopause. The inclusion of a dusk‐dawn current sheet in the dayside magnetosphere allows observations obtained both inbound and outbound to be simultaneously fit by an azimuthally symmetric current disc (i.e., without the need for local time dependent current densities). Similar disc current intensities are found to describe both Pioneer 10 and Pioneer 11 encounters. During the Pioneer 10 inbound passage the magnetopause was rapidly pushed inside the spacecraft position by a solar wind compression event. The changes that occurred in the magnetospheric field at this time can be described by relatively simple changes in our model parameters. When the field lines of our model are extended beyond the region of fitting, both the Pioneer 10 and the Pioneer 11 encounters give similar profiles with magnetopause distances that are consistent with the actual encounters. The most striking feature of the models is that they suggest that the Jovian cusp is at much lower latitudes than is the case with the earth’s magnetos

ISSN:0148-0227    

DOI:10.1029/JA089iA08p06663

年代:1984

数据来源: WILEY

摘要:

The spatial and seasonal distributions of Martian atmospheric clouds, organized according to simple morphologic criteria, exhibit distinct patterns. When interpreted self‐consistently using analogies to terrestrial cloud forms and Martian temperature, wind direction, and water vapor measurements, patterns of cloud occurrence provide some loose constraints on global‐scale near‐surface wind speed, static stability, and humidity. We have examined all Mariner 9 and Viking Orbiter images for this study; we concentrate primarily on the larger Viking data set. Whenever observations are possible, relatively high near‐surface winds appear to follow the seasonal cap edges during early fall, late winter, and spring. Moderate to high winds are also inferred in mid‐latitudes for mid southern winter and in low latitudes, mainly in the steeply sloping areas of Tharsis, near the solstices. At other times, lower winds are suspected. Hemispheric asymmetries are traced to differences in atmospheric hydration state and to global dust storm related effects on the atmospheric temperature structure and the north polar cap recession schedule. Cloud occurrence data suggest that the near‐surface daytime static stability is low in the northern hemisphere during summer and at low latitudes during mid northern spring. Relatively high static stability is deduced near the winter poles and globally during the dust storm season. In spite of low atmospheric temperatures, the correspondingly low absolute humidity apparently precludes the formation of thick water ice clouds at high latitudes in mid to late autumn and winter in both hemispheres and in southern mid‐latitudes during early winter. During northern spring and summer, saturation conditions seem to be easily achieved at mid‐latitudes, and condensate clouds are abundant; the situation is complicated by atmospheric dust in southern spring and summer. Low latitudes generally appear to be farther from saturation than mid‐latitudes, and clouds generally form more easily in the northern hemisphere than in the south during corr

ISSN:0148-0227    

DOI:10.1029/JA089iA08p06671

年代:1984

数据来源: WILEY

摘要:

Magnetic field profiles across the dayside magnetopause, obtained during the first five years (1977–1981) of the ISEE mission have been examined in boundary normal coordinates to determine the spatial distribution and controlling factors of flux transfer events (FTE’s). Owing to the natural evolution of the orbital plane of the spacecraft, the dayside magnetopause region is eventually sampled both above and below the magnetic equator. Nevertheless, at the end of the period surveyed, the satellites still had not yet reached latitudes as far south of the equator as they were initially north of the equator. Two types of magnetic signature in the component normal to the magnetopause are regularly observed when an FTE passes the spacecraft. In the northern dawn quadrant the perturbation along the normal direction is usually first outward and then inward, whereas in the southern dusk quadrant the reverse behavior occurs. The dividing line between the two signatures is tilted somewhat with respect to the equator along a south dawn‐north dusk direction. However deviations from this simple pattern are observed in both hemispheres. Examination of simultaneous IMP 8 and ISEE 3 interplanetary data reveals that FTE’s occur almost exclusively during southward interplanetary magnetic field (IMF) conditions. FTE’s occur about 45% of the time when the IMF has a southward component, with the highest rates of occurrence for due southward IMF. The sign of the east‐west component of the IMF does not exert control on the rate of FTE

ISSN:0148-0227    

DOI:10.1029/JA089iA08p06689

年代:1984

数据来源: WILEY