摘要:

Observations of protons, alpha particles, and medium group nuclei (C,N,O) have been made with particle counters aboard the IMP 7 and 8 (Explorer 47 and 50) spacecraft for the time period from October 1972 to the present. Since this interval includes nearly the complete solar cycle 21, and the data coverage is high, it is now possible to characterize the entirety of solar and interplanetary particles in the vicinity of the earth. Extensive and detailed catalogs of identified solar flare events have been prepared for two periods of time, classified as Solar Minimum (day 300 of 1974 through day 200 of 1977) and Solar Active (day 1 of 1978 through day 365 of 1981). Histograms of daily averaged particle fluxes have been prepared for three types of subintervals of the Solar Minimum and Active periods. These subintervals were for flare particle‐dominated times, quiet times, and the residual (nonflare, nonquiet). Comparison of these histograms yields a variety of salient differences between the compositions and intensities of particles in these subintervals. During Solar Minimum, for example, each type of subinterval displays distinctly different compositions both in the median and in the distribution, with flare times showing by far the greatest variability of proton/alpha and alpha/medium ratios. During Solar Active time there does not appear to be a compositionally distinct signature of flare times as compared to nonflare, nonquiet times. We discuss and characterize these results and other quantitative measures of solar and interplanetary charged particle fluxes in solar cycle 2

ISSN:0148-0227    

DOI:10.1029/JA090iA10p09439

年代:1985

数据来源: WILEY

摘要:

We report observations of 35 interplanetary shocks detected at heliocentric distances between 6.5 and 9.4 AU in mid‐1980 by the Voyager 1, Voyager 2, and Pioneer 11 spacecraft. These shocks were all evidently generated by the interaction of corotating streams. Measurements of the pre‐ and postshock plasma parameters are used to determine the shock normals and speeds for each shock. Twelve of these 35 events are observed at all three spacecraft. The shock parameters at each spacecraft are compared to determine the time history for the 12 shocks. The single‐spacecraft determinations of shock normal and speed are compared with the results of several techniques for determining shock velocities using all three spacecraft. We find that shocks undergo significant evolution as they travel past the three spacecraft. Every shock seen by both end spacecraft was also seen by the middle spacecraft. Shock formation possibly may be occurring at a heliocentric distance as great as ∼7 AU. It appears that the shock surfaces have a complex three‐dimensional structure with “ripples” on a scale of

ISSN:0148-0227    

DOI:10.1029/JA090iA10p09454

年代:1985

数据来源: WILEY

摘要:

A kinematic analysis of the previously neglected effect of velocity inhomogeneity on the topology of the heliospheric current sheet in a radially flowing solar wind shows how the originally smooth current sheet becomes “ruffled.” In the highly idealized case of a totally uniform, radial, steady solar wind, the shape of the current sheet is independent of distance from the sun. However, the real solar wind is inhomogeneous; the velocity varies from point to point along the current sheet, causing a distortion in the current sheet of progressively greater amplitude with increasing distance from the sun. This is true even for purely radial flow. Significant and observable distortion is produced by relatively small gradients in velocity; thus to predict or understand the shape of the heliospheric current sheet it is essential to know the solar wind in which the current sheet is embedded. We give examples of mild velocity gradients which demonstrate the principles, the magnitude, and the character of the effect; deformation of the actual heliospheric current sheet in the highly variable solar wind is expected to be of far greater amplitude and complexity than in the simplified, tutorial examples. We also derive a new expression for the inclination of the current sheet as a function of velocity inhomogeneity and distance from the sun that is easily applied to the interpretation of solar wind d

ISSN:0148-0227    

DOI:10.1029/JA090iA10p09461

年代:1985

数据来源: WILEY

摘要:

The plasma state of the hot torus is studied with a local, homogeneous, steady state model described by a set of coupled quasi‐linear equations for the distribution functions of S+, S++, S+++, O+, and O++. The equations contain model Fokker‐Planck operators for ion‐ion and ion‐electron collisions, a species‐ and energy‐independent loss rate τ−1, impact ionization of S, S+, S++, O, and O+, recombination of S+++, and 11 charge exchange reactions. The only free parameters, which are not governed by physical processes contained in the model, are the ion confinement or residence lifetime τ and the neutral densities of sulfur,nS, and oxygen,nO. Equivalently, ifnS,nO, and the electron densityneare adopted as parameters, then τ is determined by imposing charge neutrality. Under the constraints that the pickup mechanism for newly created ions is the dominant energy source and that the torus is in equilibrium between collisional energy loss from ions to electrons and radiative UV loss from ions excited by ion‐electron collisions, the densities, average energies, and distribution functions of all ion species and the temperature of the electrons, which are assumed to be Maxwellian, are calculated as functions of the input parameters. Among the results are the following: (1) The ion velocity distributions are significantly non‐Maxwellian for the major species, with high‐energy tails extending to the pickup energy. A quasi‐thermal core exists for the O+and/or S+ion velocity distribution functions only if the EUV luminosity of the torus is less than 0.2 eV cm−3s−1. The core “temperature” is at mostTi∼ 100 eV; the average energy of the total distribution is generally less than 0.5 of the pickup energy. The ion velocity distributions do not drive the ion loss cone instability for parameters generally typical of the torus. (2) The EUV luminosity of the torus during the Voyager 1 encounter was ∼0.15 eV cm−3S−1, a factor of ∼1.8 less than that reported by Shemansky and Smith (1981). This downward revision in the EUV intensities is in agreement with calibration adjustments adopted by Holberg et al. (1982) at longer wavelengths (912–1050 Å). (3) During the Voyager 1 encounter the approximate average torus ion densities were S+:<350, S++: 420, S+++: 10–20; O+: 660, O++: 40–80 cm−33 withTe∼ 4.8 eV, τ ∼ 60 days, andne∼ 2000 cm−3. The average neutral torus densities werenS∼ 6 andnO∼ 30 cm−3and consistent with an SO2source. (4) The upper limit obtained by Brown et al. (1983b) on O++concentrations is only applicable to short duration periods when transient, large eruptions of sulfur‐driven volcanoes occur on the surface of Io (McEwen and Soderblom, 1983) and mass loading of the neutral torus is preferentially by sulfur. The resultant plasma torus contains S+and S++densities of ∼600, O+∼120, O

ISSN:0148-0227    

DOI:10.1029/JA090iA10p09469

年代:1985

数据来源: WILEY

摘要:

This paper considers the quasi‐linear theory of the right‐ and left‐hand resonant electromagnetic instabilities driven by a hot ion beam streaming parallel to a magnetic field in a homogeneous Vlasov plasma. Using the single‐mode approximation, the time evolutions of important parameters are obtained to show that for the range of parameters considered, reduction of the beam speed and formation of temperature anisotropies are the most significant factors in the quasi‐linear stabilization process. Combining both instabilities in a quasi‐linear study is found to produce a roughly equal mixture of both polarizations and relatively isotropic conditions for tenuous beam densities and low initial beam drift speeds. Computer simulations are used to compare with the quasi‐linear results. The simulations justify the single‐mode assumption, verify that quasi‐linear changes are the means of saturation for the parameter range of concern, and check the nonlinear evolution of the system when both

ISSN:0148-0227    

DOI:10.1029/JA090iA10p09494

年代:1985

数据来源: WILEY

摘要:

Using laboratory simulation experiments, we investigate plasma flow in the vicinity of the model magnetosphere, especially in the tail region. Luminous thermal plasma is injected by means of a newly designed plasma emitter called the powered double probe (PDP). Time exposure photographs show luminosity along the magnetic field lines which cross the position of the PDP. The results obtained from different positions of the PDP show four regions of illumination. The dependence of the illumination width of such artificial plasma on the PDP positions yields information on energetic particles and their diamagnetic effect. Artificial plasma injection illuminates trajectories of energetic particles produced in the nightside magnetosphere. In particular, when the PDP is located in the tail at a geocentric distance corresponding to about 15 to 18 RE, an especially bright luminous line was found to form. It is suggested that this phenomenon results from plasma intrusion into the magnetosphere through the dayside cusp region. In order to examine the effect of the intrusion of the interplanetary magnetic field (IMF) into the magnetosphere, an external quasi‐static magnetic field is applied that simulates the IMF. The result reveals the structural form of magnetic field lines which indicate characteristics of a stable “open” magnetosphere. In the presence of southward IMF, a neutral line was formed at about the location where the linear sum of the external vaccum magnetic field (IMF) and the distorted dipole field BM(without BZ) becomes null. This result seems to imply a direct IMF control of energy coupling between the solar wind and the magnetos

ISSN:0148-0227    

DOI:10.1029/JA090iA10p09503

年代:1985

数据来源: WILEY

摘要:

Detailed analyses of 18 ISEE 1 magnetopause crossings have been made using three‐dimensional plasma data obtained by the University of Iowa LEPEDEA's which detect ions and electrons from 1 eV to 45 keV. Crossings were examined that occurred on both the dawn and dusk flanks near the sunward, outer magnetospheric boundary. Nearly all cases show a de‐energization of magnetosheath plasma after this plasma crosses the magnetopause to produce the magnetospheric boundary layer. The bulk plasma flow frequently changes direction as it crosses the magnetopause, resulting in boundary layer flow that has an enhanced cross‐field flow component without, typically, any increase in speed. These observed flow directions are consistent withEp× Bdrifts imposed by polarization fieldsEpestablished near the forward extent of penetrating magnetosheath irregularities which are producing the boundary layer. Our three‐dimensional observations of plasma flow demonstrate that these polarization fields are present and significant. In addition, we directly observe the field‐aligned depolarizing currents linked to this dynamo region, which is likely a primary generator for the cusp region and system 1 field‐aligned currents. A few exceptional crossings do show plasma energization in the boundary layer, a condition that occasionally results from Maxwell stresses on impulsively injected magnetosheath plasma. However, some principal cases of such energized plasma appear to occur on closed field lines, so that the reconnection mechanism is not necessarily involved in these exceptional crossings. The reconnection hypothesis also predicts that plasma is energized at the expense of field energy density. However, our study demonstrates that the dominant process in the solar wind‐magnetosphere interaction results in plasma de‐energization as magnetosheath plasma crosses the magnetopause to supply the magnetospheri

ISSN:0148-0227    

DOI:10.1029/JA090iA10p09519

年代:1985

数据来源: WILEY

摘要:

A comprehensive survey of ISEE and IMP LEPEDEA plasma measurements in the earth's magnetotail reveals that the magnetospheric boundary layer and the plasma sheet boundary layer are the primary transport regions there. These plasma measurements also distinguish various components of the plama sheet, including the central plasma sheet and plasma sheet boundary layer. A significant new result reported here is the existence of cold‐and hot‐plasma components that are spatially copresent within the central plasma sheet. Such plasma components cannot be explained merely by temporal variations in spectra involving the entire plasma sheet. Contributions to a low‐temperature component of the plasma sheet enter directly from the boundary layer located along the magnetotail flanks. Field‐aligned flows predominate within the plasma sheet boundary layer, which is almost always present and is located near the northern and southern border of the plasma sheet. The plasma sheet boundary layer comprises highly anisotropic ion distributions, including counterstreaming ion beams, that evolve into the hot, isotropic component of the plasma sheet. Tailward acceleration regions generate these ion beams with plasma input from the magnetospheric boundary layer. Antisunward flowing ion beams, atE/q<1 kV and of ionospheric composition, are frequently observed in the plasma sheet boundary layer and in the tail lobes. These ion beams are likely accelerated at low altitude over the polar cap and especially along auroral field lines. An ionospheric component of the plasma sheet is supplied from this source via the plasma sheet boundary layer. On the basis of a survey of ∼2000 three‐dimensional velocity distribution functions sampled by the ISEE LEPEDEA in the magnetotail we find that interpretations based solely on moments parameters are inevitably inadequate for inferring plasma sources and acceleration processes. We find that earthward flowing ions or counterstreaming beams are often observed near expansive phase onset under conditions for which antisunward ion flow is predicted by the near‐earth neutral line model of magnetospheric substorms. Magnetotail plasma flows sampled out to 38REand reported as typical of onset and recovery of magnetospheric substorms can only be adequately understood by considering spatial and temporal variations of the boundary layers de

ISSN:0148-0227    

DOI:10.1029/JA090iA10p09541

年代:1985

数据来源: WILEY

摘要:

Models incorporating merging between dayside magnetosheath and magnetosphere field lines predict the location of the magnetotail boundary layer and bending of magnetotail field lines in the direction of the IMF. We review previous observations supporting these models and reexamine a case of dense magnetotail boundary layer plasma and strongly bent field lines observed by ISEE 3. We discuss observations of boundary layer plasma within a tangential discontinuity magnetopause. Our model to explain this phenomenon requires that interconnected magnetotail and magnetosheath field lines leave the magnetotail via a narrow “window.” Field lines in the dense boundary layer plasma veer away from the aberrated x axis more than those in the void magnetotail lobes in order to pass through the windows. Magnetosheath plasma must enter the magnetotail lobes through the windows at all downstream distances in order to supply the observed tailward flux of lobe pla

ISSN:0148-0227    

DOI:10.1029/JA090iA10p09561

年代:1985

数据来源: WILEY

摘要:

The temporal dynamics of a plasmoid is numerically studied on the basis of the plasmoid that is in due course formed when magnetic reconnection is coupled to anomalous resistivity. No external agency is imposed, so that the temporal behavior of the plasmoid, defined by three neutral points, X1, O, and X2(X1

ISSN:0148-0227    

DOI:10.1029/JA090iA10p09576

年代:1985

数据来源: WILEY