摘要:

We have performed a detailed analysis of the published Venus IR maps and have obtained a number of new results. The global contour map of the average temperature variations in the vicinity of 6120 km reveals the existence of saddle points along the equator at dawn, at noon, and just before sunset. The hot spots observed at 4:30–4:40 A.M. at 65°–68°S latitude appear to be in the vicinity of the coldest region from which the 8‐ to 14‐µm emissions originate. At large earth zenith angles the limb darkening curves show a hump which is attributed primarily to a single patchy haze layer in the vicinity of 6123 km and with a thickness of the order of 3 km. We obtain an average IR source region temperature of 250°K at the equator. At the poles the same altitude region is

ISSN:0148-0227    

DOI:10.1029/JA083iA07p03113

年代:1978

数据来源: WILEY

摘要:

Computations of the group velocity of whistlers in a two‐ion plasma show that a quasi‐longitudinal (QL) right‐handed polarized wave (electron wave) has a minimum group velocity at the so‐called crossover frequency; a QL left‐handed polarized wave has a maximum group velocity at the same frequency. A quasi‐transverse (QT) electron wave has a minimum group velocity at the ion hybrid frequency. In an oxygen/hydrogen plasma this minimum occurs only for almost perpendicular waves, whereas in a helium/hydrogen plasma it occurs also for waves propagating off perpendicular to the magnetic field. We also find that a small concentration of helium in a hydrogen plasma introduces a ‘stop band’ for quasi‐transverse waves with frequencies just above the helium gyrofrequency. The theoretical results are used to interpret satellite observations of quasi‐transverse low

ISSN:0148-0227    

DOI:10.1029/JA083iA07p03125

年代:1978

数据来源: WILEY

摘要:

Whistler data are used to present a statistical view of equatorial plasmaspheric electron density neqand associated tube electron content NT(defined as the number of electrons in a geomagnetic flux tube of 1cm² cross‐sectional area at 1000km altitude and extending to the magnetic equator). The data were acquired between 1959 and 1973 at Byrd (L ≃ 7), Eights (L ≃ 4), and Siple (L ≃ 4), Antarctica, which are within 1 hour of the same geomagnetic meridian, and from Stanford, California (L ≃ 2). The plasmaspheric neqprofile beyond L ≃ 3 is dominated by variations associated with magnetic disturbances and subsequent recovery. In the aftermath of disturbances the plasmasphere tends to be divided into an inner ‘saturated’ region, which is in equilibrium with the underlying ionosphere in a diurnal average sense, and an outer ‘unsaturated’ region, which is still filling with plasma from below. In the outer plasmasphere byond ˜3.5 RE, diurnal variations appear as relatively small effects superimposed on larger storm‐associated variations. Large numbers of whistler traces (as many as 3000 in some cases) were scaled for each of several months. These data sets form the basis for approximations to neqprofiles to form log10(neq) = aL + b. These profiles are offered for reference use in estimating plasmasphere density levels. The previously reported annual and solar cycle variations are further documented by new evidence that these effects diminish with in

ISSN:0148-0227    

DOI:10.1029/JA083iA07p03137

年代:1978

数据来源: WILEY

摘要:

It is shown that corotation of charged particles in the azimuthally asymmetric magnetic field of the Jovian magnetosphere leads to a pitch‐angle‐dependent energy loss and gain of particles that drift from noon to midnight and midnight to noon, respectively. An isotropic pitch angle distribution at noon would become dumbbell‐like at midnight. Nonadiabatic scattering relaxes the dumbbell distribution toward isotropy without changing the particle's energy. This scattering represents an increase of the first adiabatic invariantM. As the particles drift back toward noon at an increased value ofM, they gain more energy than they lost during their drift from noon to midnight. The overall energy gain per rotation can be as large as a factor of 2, and in 10 rotations the total energy may be increased by several orders of magnitude. The model can account for the 10‐hour modulation of spectral index and makes a number of testable pred

ISSN:0148-0227    

DOI:10.1029/JA083iA07p03145

年代:1978

数据来源: WILEY

摘要:

The distinctive ‘hat shape’ of equatorial pitch angle distributions constructed from Pioneer 10 and 11 Jupiter observations of energetic electronsEe>21 MeV andEe>31 MeV atL= 3 is examined from the point of view of pitch angle diffusion by resonant interaction with a band‐limited spectrum of whistler mode noise. In this picture, the pitch angle profiles are consistent with whistler mode noise limited to frequencies below an upper cutoff frequency 2.8 ≲fc≲ 4.6 kHz. Equatorial linear growth rates of parallel propagating whistlers are evaluated in a fully relativistic manner for the inner region 3

ISSN:0148-0227    

DOI:10.1029/JA083iA07p03151

年代:1978

数据来源: WILEY

摘要:

The ecliptic plane components of the pressure tensors for low‐energy (<30 keV) electrons and protons have been examined for more than 400 hours of quiet time plasma sheet data from Imp 6 and Imp 8. Individual high time resolution (≲100 s) measurements show that while at times the tensors may be clearly anisotropic with the pressure parallel to the magnetic field (P∥) being as much as 1.5–2.0 times the pressure perpendicular (P⊥), the anisotropies are not usually of this magnitude and are typically below the value thought necessary to balance the tension of the magnetic field. One‐hour averages of the particle counts have also been calculated. While these averages mask more rapid changes due to variations in the distributions and the magnetic field and can yield only a lower limit to the true anisotropy, examinations of the individual measurements indicate that they do provide a reasonable summary. On this time scale, the protons are nearly isotropic: the ratio of the maximum ecliptic component of the proton pressure tensor to the minimum is typically ≲1.1, and there is no apparent tendency for the distributions to be field aligned. On the same time scale, the electron distributions do show a tendency to be field aligned with P∥/P⊥≥ 1.2 approximately 25% of the time. Due to the low energy density of the electrons, however, this anisotropy is not itself sufficient to balance the tension of

ISSN:0148-0227    

DOI:10.1029/JA083iA07p03166

年代:1978

数据来源: WILEY

摘要:

Refraction of electrostatic noise in the whistler and upper hybrid modes out of the spatially limited amplification region of the auroral electron beam limits the amplitude of the noise produced. Power flux spectra are calculated by using the linear electrostatic growth rate and allowing for ray refraction in the direction perpendicular to the auroral arc. A graphical algorithm is developed for predicting the power flux spectra of whistler and upper hybrid noise for a wide range of ionospheric and beam parameters. Predicted power flux spectral shapes and intensities for the whistler mode are in good agreement with observations of VLF hiss. The power flux in the upper hybrid mode can exceed the whistler mode power flux in the region of the ionosphere where the electron plasma frequency is larger than the electron cyclotron frequency. A distinction based on the beam intensity is made between quiet and intense arcs. Quasi‐linear and nonlinear processes are not important in quiet arcs but may produce observable effects in intense arcs. In particular, intense electrostatic noise near the plasma frequency may produce deep density cavities that radiate electromagnetic kilometric radiatio

ISSN:0148-0227    

DOI:10.1029/JA083iA07p03173

年代:1978

数据来源: WILEY

摘要:

Analytic results on the nonlinear evolution of the Rayleigh‐Taylor instability into equatorial spreadFbubbles are presented. The nonlinear saturation amplitude andkspectrum of the inertia‐dominated Rayleigh‐Taylor instability is computed in two dimensions (east‐west and vertical). Analogous to the collisional case, the dominant nonlinearity is found to be two dimensional. The linearly most unstable modes which are primarily horizontal (kx

ISSN:0148-0227    

DOI:10.1029/JA083iA07p03189

年代:1978

数据来源: WILEY

摘要:

Further Heos 2 plasma and magnetic field data obtained in the frontside boundary layers of the magnetosphere are presented. They reveal that the low‐latitude extension of the entry layer is of a somewhat different nature. The most pronounced difference with respect to the entry layer in the cusp region is the substantial density jump at the magnetopause. Furthermore, the low‐latitude boundary layer tends to be thinner and less turbulent, and the flow velocity inside the layer is always lower than that of the adjacent magnetosheath. This observation excludes large‐scale reconnection at the front of the magnetosphere as the origin of the layer. It is suggested that diffusive entry of magnetosheath plasma and/or heating of detached plasma from the plasmasphere leads to the formation of the layer. It appears likely that reconnection is dominantly occurring as a transient process in the cusp region and accompanies the eddy convection inside the entry layer. As a consequence, magnetic flux is being eroded from the front of the magnetosphere. This is in agreement with the signature of short‐term large‐amplitude magnetic perturbations observed in the low‐latitude bou

ISSN:0148-0227    

DOI:10.1029/JA083iA07p03195

年代:1978

数据来源: WILEY

摘要:

Electron densities and temperatures as well as omnidirectional fluxes of hyperthermal positive ions (E>28 eV) were measured by means of spherical Langmuir probes aboard Injun 5 at altitudes of>2000 km during a major geomagnetic storm. The electron density in the mid‐latitude trough decreased and the temperatures increased during the early phases of the storm. As the storm progressed, the trough's position moved equatorward, plasma depletions being observed to an invariant latitude of 40° during the early recovery phase. Hyperthermal ions detected in the vicinity of the trough were ring current particles reaching to the satellite's altitude. The minimum thermal electron densities in the trough were found to be within 1° of latitude of the maximum ring current flux. Maximum electron temperatures were measured several degrees equatorward of this position. Injun 5 electron temperatures are compared with those measured by Alouette 2 over the reported positions of stable auroral red arcs. The observations are also used to evaluate further a method developed by Cole (1970) for calculating the position of the ring current by using ground magnetic fluctuati

ISSN:0148-0227    

DOI:10.1029/JA083iA07p03217

年代:1978

数据来源: WILEY