摘要:

An analysis of electromagnetic lower hybrid waves or hybrid whistlers that propagate nearly perpendicular to the magnetic field lines in the solar wind is described. Doppler‐shifted, these waves have a broadband nature when observed in the spacecraft frame depending on the direction of propagation and the supersonic flow velocity of the wind. Lower hybrid waves can energize ions normal to the interpletary magnetic field. They may occasionally be responsible for the observed temperature anisotropy in high speed streams and possibly for the acceleration of heavier ions such as the oxygen ions, alpha particles, etc. These modes are probably driven unstable by the anisotropic halos of the solar wind electron distributions exhibiting ‘heat flux’ pro

ISSN:0148-0227    

DOI:10.1029/JA088iA09p06869

年代:1983

数据来源: WILEY

摘要:

A theoretical model of suprathermal halo or strahl solar wind electrons, including both binary collisions and conservative force fields, is proposed. From this model we derive the collisionally modified electron pitch angle distribution and compare it with relevant measurements made in the solar wind at 1 AU by using the Los Alamos IMP 8 plasma analyzer. Although the collisionally modified distribution is more isotropic than that predicted by simple exospheric theory, it is not isotropic enough to describe the measurements.

ISSN:0148-0227    

DOI:10.1029/JA088iA09p06881

年代:1983

数据来源: WILEY

摘要:

A compact, quantitative model of the distribution of charged particles between 1 eV and several MeV in the Jovian magnetosphere is presented. The model is based primarily on in situ data returned by experiments on the Pioneer and Voyager spacecraft, supplemented where necessary by earth‐based observations and theoretical considerations. Thermal plasma parameters, notably convection speed, number density, and characteristic energy, are specified as functions of position for electrons and several ion species (H+, O+, O++, S+, S++, S+++, and Na+). At intermediate energy the electron and proton populations are modeled using kappa distributions, which join smoothly onto the radiation belt spectra at high energies (E>100 keV). At these energies the radiation belt intensity spectra include angular distributions for energetic electrons inside 16RJand protons inside 12RJ. Major features of the magnetic field, thermal plasma, and trapped particle distributions are modeled, such as ring and satellite absorption signatures and corotational flow within the Io plasma torus and the current disk. Within each plasma region the model results are compared with observed spectra, showing that the model represents the data typically to within a factor of 2±1except where time variations, neglected in the model, are known to be significant. Several practical applications of the model to spacecraft near Jupiter are illustrated with sample results from radiation analyses and electrostatic charging calculatio

ISSN:0148-0227    

DOI:10.1029/JA088iA09p06889

年代:1983

数据来源: WILEY

摘要:

During the interval from about May through August 1981, when Voyager 2 was inbound to Saturn, the planetary radio astronomy instrument measured repeated, dramatic decreases in the intensity of the Saturn kilometric radiation (SKR). The emission dropouts averaged two orders of magnitude below mean energy levels and varied from about 1 to 10 Saturn rotations in duration. Comparison with pre‐Saturn encounter Voyager 1 observations (June to November 1980) shows that the SKR dropouts were unique to the Voyager 2 observing interval, consistent with the closer proximity of Saturn to Jupiter's distant magnetotail in 1981. Further, the dropouts occurred on the average at times when Voyager 2 is known to have been within or near Jupiter's magnetic tail. Interpretation of these events as the radio signatures of successive Saturn immersions into Jupiter's tail or wake region is consistent with the independent evidence that the SKR radio source is driven externally by the solar wind ram pressure. The dropouts are identical to the one observed just after Voyager 2 closest approach to Saturn, providing the best evidence that Saturn was within Jupiter's tail at the time of the encounter. The sequence of events during this Saturn tail encounter is deduce

ISSN:0148-0227    

DOI:10.1029/JA088iA09p06904

年代:1983

数据来源: WILEY

摘要:

A restudy has been made of Pioneer 11 data on the distribution of energetic protonsEp>80 MeV in Saturn's inner magnetosphere. An improved value of the ratio of the cosmic ray albedo neutron decay source strength $ to the radial diffusion coefficientDis 6.9 × 10−24cm−5atr∼ 2.67Rs(1Rs= Saturn's equatorial radius = 60,000 km). Using the recently calculated lower limit on $ by Blake et al., one finds an upper limit on the mean residence timeTagainst diffusion of 4.6 × 108s (15 years) in the major peak of the distribution, whereas using our earlier estimate of $, one findsT∼ 2.2 × 108s (7.0 years). The two corresponding determinations ofDare>1.3 × 10−11and ∼ 2.8 × 10−11Rs² s−1, respectively. A generous upper limit onDis 2 × 10−10Rs² s−1as found from study of the slot region associated with the co‐orbiting satellites 1979 S2 (1980 S3) and 1980 S1. The mean lifetime τ of energetic protons against absorption by particulate matter in Ring G is1.4 × 10−6g cm−2, and an areal number densityn<8 × 10−3cm−2. It is unlikely thatRexceeds 0.1 cm. The foregoing values ofR(for assumed spherical particulates of water ice, all of the same size) are in effect the ratio 〈R³〉/〈R²〉 for a distribution of sizes, where the angle brackets denote the mean value over the distribution. It is reasonably certain that there are no satellites having radii of the order of a kilometer or larger associated with Ring G and that objects having radii of ≳10 cm contribute less

ISSN:0148-0227    

DOI:10.1029/JA088iA09p06911

年代:1983

数据来源: WILEY

摘要:

Quasi‐parallel bowshock structures are simulated by using a one‐dimensional nonperiodic hybrid code in which the ion dynamics are treated exactly while the electron dynamics are omitted by neglecting the electron inertia (me= 0) and pressure. The simulations are initialized with the upstream condition specified by θ1= 10°, β1= 0.5, andMA1= 2 to 4 with 0.5 increment while the downstream condition is obtained from the Rankine‐Hugoniot relations, where θ1is the angle between the shock normal and the magnetic field, β1is the ratio of kinetic to magnetic pressures, andMA1is the Alfvén Mach number. The main results of our simulations follow: (1) ForMA1,3, the magnetic field profile of the shock is turbulent. The upstream waves are again right‐hand polarized whistlers with wavelengths varying from λ ∼ 310 km upstream to λ ≳ 1250 km downstream. The downstream waves are predominantly the right‐hand polarized fast magnetosonic waves (ω ≲ Ωi). (3) The transition from the laminar (subcritical) to the turbulent (supercritical) shock structures is shown to result from the firehose instability which occurs whenMA1≳ 3. (4) The dissipation mechanism for the quasi‐parallel shock in our simulation is identified with the nonadiabatic compression of ions streaming through the low frequency whistler waves (ω ≳ Ωi), resulting in conversion of ion streaming energy to ion thermal energy. (5) Significant ion heat flux flowing upstream occurs whenMA1≳ 3 due primarily to the bac

ISSN:0148-0227    

DOI:10.1029/JA088iA09p06919

年代:1983

数据来源: WILEY

摘要:

To examine the basic characteristics of reconnection on the dayside magnetopause, we have numerically studied the reconnection process at an interface where the total pressure is in balance but where the thermal pressure is higher on one side than on the other. Reconnection is caused by anomalous resistivity that is assumed to operate only in a localized region at the interface. Boundaries are assumed to be free boundaries, but reflection of the perturbations originating from inside the simulation region is suppressed by placement of an absorbing region. Results can be expressed as follows, denoting the high‐pressure and low‐pressure regions as magnetosheath and magnetosphere, respectively. (1) a slow shock is formed in magnetosheath and a slow expansion fan is formed in magnetosphere; (2) at the slow shock the Lorentz force and pressure gradient are of comparable importance in accelerating plasma, but at the expansion fan the pressure gradient has the dominant effect, and (3) the acceleration depends on the direction of the interplanetary magnetic field (IMF) and when the reconnection line is assumed to be directed at the half angle (θ/2) between IMF and geomagnetic field, the velocity of the accelerated plasma is roughly proportional to sin² (θ/2) + sin

ISSN:0148-0227    

DOI:10.1029/JA088iA09p06926

年代:1983

数据来源: WILEY

摘要:

We have analyzed phase space density observations of ring current protons (30–130 keV) during a magnetopause crossing of ISEE 1 on July 5, 1978. Plasma and magnetic field data obtained during this crossing have been reported to be consistent with quasi‐steady reconnection and a reconnection line south of the satellite crossing (Sonnerup et al., 1981). We find that within the magnetosphere the phase space densities of ∼30‐ to ∼65‐keV protons are higher for particles streaming parallel to the field (i.e., inflowing particles) than antiparallel to the field (i.e., outward flowing particles). In the magnetosheath the phase space densities parallel to the field are higher than the densities of both outward and inward flowing particles parallel to the field within the magnetosphere. The observations are discussed in terms of acceleration of the reflected and transmitted ring current protons in the magnetopause cu

ISSN:0148-0227    

DOI:10.1029/JA088iA09p06937

年代:1983

数据来源: WILEY

摘要:

Low‐energy (<100 eV) ion data from the plasma composition experiment on ISEE 1 are examined statistically to study pitch angle distributions in all local times of the magnetosphere (L= 3–10). The pitch angle distributions in the data set used here can be classified into seven types; however, there are four major types, i.e., isotropic distribution, bi‐directional field‐aligned distribution, unidirectional field‐aligned distribution, and low flux. The isotropic distribution that consists of very low energy (typically<10 eV) ions is a persistent feature in the inner region. It is frequently observed with an accompanying loss cone‐like structure. The bi‐directional field‐aligned distribution consisting of warm ions (⩾10 eV) is a persistent feature on the outer dayside and it is seen just outside the isotropic distribution region of the nightside. It is noted that the loss cone‐like structure is also a common feature of this type of distribution in the noon sector. On the outer nightside the unidirectional field‐aligned distribution consisting of warm ions is the dominant signature, but in some cases only the low flux (no appreciable flux) is observed. The ‘sources’ of ions in various regions are discussed on the basis of

ISSN:0148-0227    

DOI:10.1029/JA088iA09p06944

年代:1983

数据来源: WILEY

摘要:

We have investigated the effect of local perturbations of the geomagnetic field on the vertical cosmic ray cutoff rigidities at Jungfraujoch and Kiel as representative mid‐latitude neutron monitor stations. The main, effective, and Störmer vertical cutoff rigidities and their changes were determined by utilizing the trajectory‐tracing technique in a magnetic field which is modeled as a simple dipole field to which the disturbance field is superposed. It was found that the cosmic ray cutoff rigidities are most sensitive to variations of thezcomponent of the geomagnetic field at geomagnetic latitudes −20°<Λ<+30° and at longitudes within 90° to the east of these northern hemisphere stations. Furthermore, cutoff rigidity variations at Kiel are predominantly due to changes of the geomagnetic field within geocentric distances 2.5RE

ISSN:0148-0227    

DOI:10.1029/JA088iA09p06961

年代:1983

数据来源: WILEY