摘要:

A self‐consistent model for the motions of the neutrals and the plasma within the dynamo region is presented. The mutual coupling between both components, the degree of energy dissipation of the wind and the modification of its horizontal and vertical structure due to the plasma, and finally the electric fields and currents generated by the fundamental diurnal and semidiurnal tidal winds are calculated. The main results are that the diurnal tidal (1, −1) mode, being an evanescent mode in the lower atmosphere, changes into a propagation mode with reduced attenuation within the dynamo region. On the other hand, the semidiurnal (2, 2) mode increases its attenuation there. The electric currents are driven mainly by the divergence‐free part of the electric dynamo fieldv × B. The efficiency of the diurnal wind in generating dynamo currents reduces by a factor of about 2 if the mutual coupling between plasma and neutrals is taken into a

ISSN:0148-0227    

DOI:10.1029/JA081i010p01621

年代:1976

数据来源: WILEY

摘要:

The measurement of the full‐disk solar EUV flux summed over broad spectral bands in this region is shown to be critically dependent on the determination of the level of scattered radiation and other background. The EUV fluxes of some strong lines are reported, as are the total fluxes summed over 10‐Å intervals, based on an Aerobee rocket experiment on November 9, 1971. Significant improvement in the peak‐to‐background ratio was achieved in the measurements below 100 Å. The present state of solar EUV measurements below 205 Å is reviewed, and a summary of the results from several Air Force Cambridge Research Laboratories experiments is presented. The use of EUV flux models scaled with the 10.7‐cm solar radio flux

ISSN:0148-0227    

DOI:10.1029/JA081i010p01629

年代:1976

数据来源: WILEY

摘要:

A mathematical model is presented that describes the squeezing of solar wind plasma out along interplanetary magnetic field lines in the region between the bow shock and the effective planetary boundary (in the case of the earth, the magnetopause). In the absence of local magnetic merging the squeezing process should create a ‘depletion layer,’ a region of very low plasma density just outside the magnetopause. Numerical solutions are obtained for the dimensionless magnetohydrodynamic equations describing this depletion process for the case where the solar wind magnetic field is perpendicular to the solar wind flow direction. For the case of the earth with a magnetopause standoff distance of 10RE, the theory predicts that the density should be reduced by a factor ≥2 in a layer about 700–1300 km thick ifMA, the Alfvén Mach number in the solar wind, is equal to 8. The layer thickness should vary asMA−2and should be approximately uniform for a large area of the magnetopause around the subsolar point. Our computed layer thicknesses are somewhat smaller than those derived from Lees' axisymmetric model. Depletion layers should develop fully only where magnetic merging is locally unimportant. Scaling of the model calculations to Venus and Mars suggests layer thicknesses about 1/10 and 1/15 those of the earth, respectively, neglecting diffusion and ionospher

ISSN:0148-0227    

DOI:10.1029/JA081i010p01636

年代:1976

数据来源: WILEY

摘要:

The point of view that heat‐conduction‐driven plasma instabilities may not be capable of directly modifying the electron heat conduction flux in the solar wind is explored. The electron heat conduction flux is written either as the usual collision‐dominated Spitzer‐Härm flux, −KSH▽∥Te, or as the collisionless heat conduction flux (Hollweg, 1974a), 1.5nekTe(Vsw− ω × r)α. The factor α is of order unity but is only estimated. The former expression pertains close to the sun and far from the sun, where collisions are important, while the latter expression pertains in the intermediate region; the divisions between regions are taken to occur where the radial component of the mean free path equals the radial trapping distance, which is taken to ber/2. Perkins' (1973) term is omitted for three reasons: it is often smaller than the collisionless heat conduction flux; it can be reduced by plasma instabilities; and it is not observed by in situ measurements at 1 AU. The electron‐proton coupling term is also omitted; this means that the electron temperature is overestimated and that the proton temperature must be specified ad hoc. In comparison with solar wind models which use the Spitzer‐Härm flux throughout, the present computations yield the following new features: (1) The electron temperature is elevated in the collision‐dominated region close to the sun. (2) The electron temperature falls off more rapidly in the region where the collisionless heat conduction flux is used, varying asne2/3(1+α)if α = const. (3) The electron temperature and heat conduction flux at 1 AU are lower in the present computations than in models which use only the Spitzer‐Härm flux. (4) The elevated electron temperature close to the sun results in highe

ISSN:0148-0227    

DOI:10.1029/JA081i010p01649

年代:1976

数据来源: WILEY

摘要:

A previous paper (Hollweg, 1974a) discussed a new physical mechanism for accelerating α particles in the solar wind, via their interaction with Alfvén waves. This paper presents numerical calculations of a simple three‐fluid solar wind model, which incorporates the new physical process. The principal result is that the Alfvén waves do effect an important additional coupling between protons and α particles, which tends to equalize their flow speeds at 1 AU. This is in sharp contrast to previous calculations, which gave υα/υp= 0.7–0.8 at 1 AU. But the model calculations still contain two important problems: (1) we do not obtain υα≥ υpat 1 AU, as is frequently observed; and (2) the model calculations give values of υαwhich are unreasonably low near the sun. Thus we conclude that the new physical mechanism is probably sufficiently important to warrant its inclusion in future solar wind models but also that there must be other physical processes working, which still remain

ISSN:0148-0227    

DOI:10.1029/JA081i010p01659

年代:1976

数据来源: WILEY

摘要:

Lyman α imagery of the hydrogen geocorona was obtained from the lunar surface during the Apollo 16 mission. The images are of 20° diameter fields, with 2 arc min limiting resolution, centered on the earth and about 12° upsun of the earth. The data confirm that the hydrogen geocorona is detectable above the interplanetary Lyman α background to more than 15REin the upsun direction. In the antisolar direction there is a pronounced ‘geotail’ effect due to solar Lyman α radiation pressure, which is markedly asymmetric about the sun line. Comparison of the data with theoretical models shows quite good agreement, particularly in the vicinity of 3RE. In agreement with other observations the hydrogen density is lower than the theoretical density in the far‐upsun direction, and very close to the earth there is a buildup of hydrogen on the

ISSN:0148-0227    

DOI:10.1029/JA081i010p01664

年代:1976

数据来源: WILEY

摘要:

Rocket observations of auroral electrons are compared with the predictions of a number of theoretical acceleration mechanisms that involve an electric field parallel to the earth's magnetic field. The theoretical models are discussed in terms of required plasma sources, the location of the acceleration region, and properties of necessary wave‐particle scattering mechanisms. We have been unable to find any steady state scatter‐free electric field configuration that predicts electron flux distributions in agreement with the observations. The addition of a fluctuating electric field or wave‐particle scattering several thousand kilometers above the rocket can modify the theoretical flux distributions so that they agree with measurements. The presence of very narrow energy peaks in the flux contours implies a characteristic temperature of several tens of electron volts or less for the source of field‐aligned auroral electrons and a temperature of several hundred electron volts or less for the relatively isotropic ‘monoenergetic’ auroral electrons. The temperature of the field‐aligned electrons is more representative of the magnetosheath or possibly the ionosphere as a source region than of the

ISSN:0148-0227    

DOI:10.1029/JA081i010p01673

年代:1976

数据来源: WILEY

摘要:

Far ultraviolet spectra of the terrestrial airglow were obtained from the lunar surface during the Apollo 16 mission. The spectra cover the wavelength range 490–1600 Å with a resolution of about 40 Å and the wavelength range 1050–1600 Å with a resolution of 30 Å. Features recorded spectrographically for the first time include He 584 Å, O+834 Å, H Lyman β 1026 Å, and N+1086 Å. The maximum intensities, and the variations of intensity across the disk, have been determined for individual observed features. Optical depth effects are evident in the disk profiles. Comparisons with previous observations reveal general agreement, but further observations are needed with higher spatial and spectral resolution, particularly in the wavelength range

ISSN:0148-0227    

DOI:10.1029/JA081i010p01683

年代:1976

数据来源: WILEY

摘要:

An electrostatic analyzer, a Lepedea, was employed on the low‐altitude satellite Ariel 4 in order to gain pitch angle distributions of electron intensities with good temporal resolution within the energy range 205 eV to 12.5 keV over the day side auroral oval. Two major precipitation zones were encountered: an equatorward zone of broad spectra with intensities of ∼ 104el (cm² s sr eV)−1and a poleward zone, the polar cusp, with intensities typical of those of the magnetosheath. Angular distributions within the equatorward zone are generally isotropic outside of the atmospheric backscatter cone. The precipitation mechanism would appear to be pitch angle scattering near the distant magnetic equator. In contrast, pitch angle distributions within the polar cusp are often found to be strongly field aligned with intensities within the atmospheric loss cone greater by factors of ∼ 10 than the mirroring intensities. These angular distributions within the day side polar cusp are qualitatively similar to those for the inverted V precipitation events at later local times and probably share a common acceleration mechanism with the inverted V ph

ISSN:0148-0227    

DOI:10.1029/JA081i010p01695

年代:1976

数据来源: WILEY

摘要:

A new method to study dynamic behavior of the ionosphere‐protonosphere coupling within the plasmasphere is developed and used to calculate ion distributions above 500 km using observed electron densities at 500 km. The method is based on the relation between the total magnetic flux tube content of H+above some reference height (e.g., 3000 km) and the H+flux at that height, which is uniquely determined by the coupled momentum and continuity equations for the quasi‐steady state. The O+profile is perturbed from diffusive equilibrium only by ion drag with H+. The time dependency is taken into account by applying self‐consistent boundary conditions which are obtained from the solution of the time‐dependent equation for the tube content of H+. Calculations are carried out for two models. The first model deals with the ion dynamics in a tube of force which rotates with the earth. In the second model, effects of the cross‐Lplasma drifts are considered. Both models produce diurnal variations of H+and O+densities near 1000 km similar to observational results. While the corotating model yields upward flow of H+in the daytime and downward flow in the nighttime, the inclusion of the cross‐Lplasma motion gives rise to significant changes in the tube content and alters the diurnal variation of the H+flux as well as the direction of flow in the evening sector. Although this effect is not very significant in the inner portion of the plasmasphere, the cross‐Lmotion of plasma will play a more important role in the outer portion of the

ISSN:0148-0227    

DOI:10.1029/JA081i010p01700

年代:1976

数据来源: WILEY