摘要:

The Millstone Hill radar, Westford, Massachusetts (Λ = 56°), has been upgraded for observations in support of the International Magnetospheric Study (IMS) by means of the addition of a 150‐ft. diameter fully steerable antenna. This antenna allows measurements of F‐region ion drifts, from which F‐region electric fields can be derived, using the existing UHF (68‐cm wavelength) radar. This paper describes analytical models of the mean electric field behavior in the auroral zone over the interval 60°<Λ<75° as determined from our measurements made during the year 1978. There was a greater preponderance of summer data in our 1978 observations and also more periods in which the inferred interplanetary magnetic field was directed toward the sun. A separate model is obtained for each of the three Kp ranges (3o). Each model incorporates a polynomial description of intensity with invariant latitude and a sinusoidal harmonic variation in local time with 102 degrees of freedom for each of the perpendicular electric field components. Coefficients of this model are provided for numerical computation by users. Tabulations of these fields and a computer program to calculate fields and potentials are available on request from the authors. The results are compared with models published by Heppner [1977]. Each of these average field models is consistent with a two‐cell convection pattern having antisunward plasma flow over the pole and return paths eastward and westward through the dawn and dusk meridians. The centers of the vortices are near the far limit of observation (Λ = 75°). The entire convection pattern appears to be rotated by as much as two hours toward earlier local times from the nominal noon‐midnight over‐the‐pole flow direction, though this conclusion is influenced strongly by our least reliable (highest latitude) data. The dusk cell is dominant in size and strength; however, both the pattern rotation and cell dissimilarity lessen as Kp increases. The Harang discontinuity, which was recognizable on individual days, is largely absent in the average patterns, presumably as a result of the variability in its position. Nevertheless, we do see a residual, low‐speed, late‐evening protrusion of the dusk cell extending toward lower latitudes with increasing local time, reaching as far as 0300 LT for low Kp but only to midnight for high Kp. For low Kp, we observe a region of very small average flow from dawn to noon, apparently disconnected from the overall convection pattern. The dawn cell encroaches into this region as Kp increases, but the 1000–1200 LT sector maintains its low‐speed character even for high Kp. The cross‐polar‐cap potential varies linearly with Kp as V = 10.06 + 14.44 Kp kV, but the smoothing in our observations may have caused this to be an underestimate. Penetration of auroral electric fields to mid‐latitudes is most likely to occur a

ISSN:0148-0227    

DOI:10.1029/JA088iA07p05505

年代:1983

数据来源: WILEY

摘要:

The subject of the present study is to analyze the characteristic variations of the ionospheric slab thickness observed at Lunping Observatory. The slab thickness data obtained from March 1977 to February 1982 were used to analyze the diurnal, seasonal, and solar cycle variations. The diurnal variation showed an unusually large peak that appeared in pre‐sunrise hours, especially during winter time. Lunar variations of slab thickness were obtained by Chapman‐Miller method and discussed. The storm time variation and disturbance daily variation of slab thickness were obtained by selecting 138 strong and weak geomagnetic storms. Superposed epoch method was also used to analyze the geomagnetic activity effect on the variation of slab thickn

ISSN:0148-0227    

DOI:10.1029/JA088iA07p05517

年代:1983

数据来源: WILEY

摘要:

The geomagnetic daily variations at the Nigerian dip equator are analyzed to find the thickness of the nonconducting layer in this zone. To do so, the external current system was determined from the external part of the geomagnetic daily variations by using a method discussed in a previous work. The field induced by this system was calculated assuming a two‐layer model for the earth conductivity. Fitting this induced field to the internal part of the geomagnetic daily variations yielded a thickness of 500 km for the nonconducting layer in the interval of 100 km south to 500 km north of the dip equator. However, there is evidence showing a latitudinal gradient in the thickness south of this interva

ISSN:0148-0227    

DOI:10.1029/JA088iA07p05523

年代:1983

数据来源: WILEY

摘要:

A multi‐bubble model is developed to study the morphology of a finite array of plasma density depletions (bubbles) in the context of equatorialF‐region irregularities during spreadF. The Pedersen current conservation equation with quasi‐neutrality is solved analytically by using an electrostatic analogy. The solution is exact with no a priori assumption regarding the separation distance. A two‐bubble system with a piecewise constant density profile is first analyzed, and the technique is then applied to multi‐bubble systems to calculate the polarization electric field and the rise velocities. It is shown that the influence of the neighboring bubbles is relatively short ranged and that a small number of bubbles can adequately model the essential physics in a large array of bubbles. For moderately short separation distances, it is found that theE×Brise velocity is substantially reduced in comparison with the single‐bubble case and that the rise velocity is strongly sheared resulting in deformation of the contours. It is found that these results compare favorably with observational evidence. The implications of the new morphological results on the stability and dynamical behavior of the bubbles are discussed. The theory is also applied to multi‐plasma density enhancements such as one might encounter in plasma cloud str

ISSN:0148-0227    

DOI:10.1029/JA088iA07p05528

年代:1983

数据来源: WILEY

摘要:

Observations of 1 to 20 MeV/nuc oxygen, sodium, and sulfur ions in the Jovian magnetosphere are reported. Measurements made by the cosmic ray subsystem on Voyager 1 and 2 are used to calculate abundances and energy spectra in the region from 5 to 20 Jovian radii (RJ). The phase space density of the oxygen ions calculated from the spectra has a positive radial gradient between 6 and 17RJ, indicating an inward diffusive flow. The upper limit for the diffusion coefficientDat 9RJis ∼10−5s−1. This limit, combined with the analysis of Voyager plasma observations by Siscoe et al. (1981), implies an upper limit to the production rate of oxygen and sulfur ions from Io of ∼1028ions/s. IfD(9RJ) is ∼4×10−6s−1, then ∼2×1024oxygen and sulfur ions with>70 MeV/nuc‐G are lost per second as they diffuse inward from 12 to 8RJ. Assuming these ions are scattered into the loss cone, they deliver ∼4×1012W to the Jovian atmosphere. Extrapolations to lower magnetic moments suggest that the 1013–1014W required to produce the observed ultraviolet auroral emissions could result from the precipitation of ∼1026oxygen and sulfur ions/s with magnetic moments ≳10 to 30 MeV/nuc‐G (≳35 to 100 keV/nuc at 10RJ). The ions with ≳70 MeV/nuc‐G deposit their energy between ∼67° and ∼72° magnetic latitude at an average depth of ∼1019cm−2of H2(∼500‐km altitude), which is above the homopause. If the extrapolated spectrum extends down to ∼10 MeV/nuc‐G, then 10 times more energy (∼1013W) is carried inward across 10RJby the energetic oxygen and sulfur ions than flows outward with the plasma, indicating the presence

ISSN:0148-0227    

DOI:10.1029/JA088iA07p05537

年代:1983

数据来源: WILEY

摘要:

Voyager 2's passage through the downstream corotation region of Ganymede found disturbances in the field and particle environment. Large fluctuations in the intensities and energy spectra of ions in the 0.1‐ to 4.0‐MeV interval were also observed with the low energy charged particle experiment. All ion species were evidently affected, up through medium (C, N, O) nuclei. Electrons intensities while disturbed, did not behave similarly to the ions. These effects are probably associated with the wake, produced by the absorption of Jovian magnetospheric corotating plasma by Ganymede. We propose a two‐dimensional theoretical model for perturbed field in the wake region and show by direct numerical simulation of exact particle trajectories that such perturbations are capable of modulating the charged particle energies to about the observed amount for the observed magnetic and plasma parameters. Analysis shows that the energization process is dependent on the pitch angles of the energetic ions and the process itself is non‐adiabatic (the Larmor radius is approximately the size of the disturbance

ISSN:0148-0227    

DOI:10.1029/JA088iA07p05551

年代:1983

数据来源: WILEY

摘要:

Laboratory observations of electron flux disruption by the potential well of a large‐amplitude ion cyclotron wave, which can be interpreted as electron trapping, are reported for the first time. Associated with trapping of more than 50% of the electron distribution is the existence of a weak electric field parallel to the external magnetic field. The significance of these observations, particularly to magnetospheric phenomena, is discusse

ISSN:0148-0227    

DOI:10.1029/JA088iA07p05564

年代:1983

数据来源: WILEY

摘要:

Saturn's broad E ring, the narrow G ring, and the structured and apparently time‐variable F ring(s) contain many micron and submicron‐sized particles, which make up the ‘visible’ component. These rings (or ring systems) are in direct contact with magnetospheric plasma. Fluctuations in the plasma density and/or mean energy, due to magnetospheric and solar wind processes, may induce stochastic charge variations on the dust particles, which in turn lead to an orbit perturbation and spatial diffusion. In addition, Coulomb drag forces may be important, in particular for the E ring. The possibility that electromagnetic effects may play a role in determining the F ring structure, and its possible time variations, is critically examined. Sputtering of micron‐sized dust particles in the E ring by magnetospheric ions yields lifetimes of 10² to 104years. This effect as well as the plasma induced transport processes require an active source for the E ring, probably

ISSN:0148-0227    

DOI:10.1029/JA088iA07p05573

年代:1983

数据来源: WILEY

摘要:

As Voyager 2 approached Jupiter's bow shock, large‐amplitude fluctuations were seen in both the magnetic field and plasma fluid velocity. These fluctuations generally coincided with the occurrence of long‐lived energetic particle events similar to the upstream waves often observed near the earth's bow shock. In this paper we present an analysis of the magnetic field and plasma observations using spectral methods. The characteristic spectral features related to the upstream waves are generally seen near 1 mHz. The measured correlation lengths of these fluctuations suggest that they are coherent over only a few wavelengths. Our analysis is consistent with the hypothesis that these fluctuations are driven by streaming ions, possibly protons. No evidence for the existence of whistler waves is found. We argue that some of the observed spectral features suggest that dynamical turbulent processes are occurring in the upstream wave region, including a possible observation of an inverse cascade of magnetic helicity to large spatial sca

ISSN:0148-0227    

DOI:10.1029/JA088iA07p05581

年代:1983

数据来源: WILEY

摘要:

A substantial nightside ionosphere has been observed on Venus during most orbits of the Pioneer Venus Orbiter. However, on some orbits during which the solar wind dynamic pressure was large, the nightside ionosphere seems to have almost disappeared, existing only as irregular patches of low‐density plasma. We interpret these observational results using a two‐dimensional theoretical model of the ionosphere of Venus in which empirical horizontal velocities are adopted. We show that the degree to which horizontal transport of ions from day to night can maintain the nightside ionosphere depends on two parameters: (1) the flow velocities and (2) the ionopause height at the terminator. We also investigate the role of electron precipitation in supporting a nightside ionosphere. Our model also provides indirect evidence for an enhanced deuterium to hydrogen ratio on Ve

ISSN:0148-0227    

DOI:10.1029/JA088iA07p05595

年代:1983

数据来源: WILEY