摘要:

A general introduction to solar structure and processes is presented. The sun is first viewed as a spherically symmetric steady‐state system, and the energy generated in the core is traced as it flows outward. The various forms and manifestations of this energy flow and the resulting uniquely defined characteristics of different atmospheric layers are described. The sources of solar activity are assumed to be differential rotation and solar magnetic fields. The interaction of these sources to produce the observed solar cycle, active regions, the active‐sun corona, and solar flares is discussed. In describing solar structure and processes, only elementary physical concepts are utilized. This allows people without advanced scientific training to appreciate the subject and provides a rapid orientation for those with more advanced backgrounds who are unfamiliar with solar phenom

ISSN:8755-1209    

DOI:10.1029/RG010i002p00395

年代:1972

数据来源: WILEY

摘要:

The orbital properties of the two small Martian satellites, Phobos and Deimos, are discussed, as well as those dynamical constants of Mars that can be determined from the satellite orbits. A secular acceleration of the mean motion of Phobos was once thought to exist, but now, on the basis of the recent work of G. A. Wilkins, the acceleration is shown to be very small. Of mechanisms that could cause any such acceleration, only tidal friction appears to be important. From the orbital evolution of the Martian satellites under tidal forces, Phobos and Deimos seem to have originated in nearly circular orbits of low inclination fairly close to the distance at which a satellite's orbital period is the planet's rotation period. It is proposed that the Martian satellites were born at the same time as Mars from equatorial dust clouds. The satellites are predicted to be locked in synchronous rotation, with their axes of minimum moment of inertia pointing on the average toward Mars, whereas their maximum axes are approximately normal to their orbit planes. Moderate amplitude physical librations may be observed by Mariner 9 because of resonance effects produced by forcing torques that have roughly the satellite free‐libration period. Observations of the rotational motion of the satellites will permit an evaluation of the ratios of differences in the satellite principal moments of inertia and thus will place constraints on density model

ISSN:8755-1209    

DOI:10.1029/RG010i002p00463

年代:1972

数据来源: WILEY

摘要:

The conservation of potential vorticity of a rotating homogeneous or stratified fluid may, in principle, be used to determine steady‐state field distributions from a given initial state. If the governing equations are linear, if the basic‐state is one of rest, and if the initial field of motion is geostrophically balanced, then no change in this equilibrium state occurs. However, nongeostrophic initial conditions excite transient gravity‐inertia waves that redistribute mass and momentum to ultimately establish a geostrophic steady state, whose potential vorticity is equal to the potential vorticity of the initial state. A steady state may not become established if, for example, hydrodynamic instabilities occur or if wave energy becomes trapped because of inherent refractive properties of the medium. Some examples, which illustrate the properties of geostrophic adjustment and nonadjustment, are presented and discussed. A simple model, which incorporates gross features of atmospheric and ocean flows, is also presented in order to summarize the relationships between the spatial scales associated with the initial conditions and the partition of energy between the allowable modes of oscillation, both transient and steady. The oceanic response to imposed stresses from atmospheric circulation systems and the atmospheric response to sources of wave energy, which includes the introduction of incorrect initial data into numerical simulations, provide practical applications of the t

ISSN:8755-1209    

DOI:10.1029/RG010i002p00485

年代:1972

数据来源: WILEY

摘要:

Recently, absolute isotopic ratios have been published for lead standards. This makes possible for the first time a meaningful comparison of published isotopic ratios of lead from conformable ores with those from oceanic rocks. Such a comparison is interesting because these classes of material exhibit isotopic patterns that may be of worldwide significance. A preliminary study has been made of the adjusted ratios of 18 conformable ores and 22 oceanic volcanic‐rock leads. Each group shows a recognizable pattern such that leads from one regime cannot be obtained by any simple mixture of leads from the other. One widely recognized difference between the patterns is the considerable variation of isotopic ratios for oceanic volcanic samples of similar age, indicative of a heterogeneous source. This contrasts sharply with conformable ores for which isotopic ratios are similar for samples of the same age. Another characteristic, considered to be of equal importance, is the significant deficiency of207Pb in the oceanic volcanic leads. This paper shows that both characteristics can be reproduced by a model in which uranium, thorium, and lead are transferred between two reservoirs. The transport of uranium and thorium must occur more quickly than for lead, and for all elements transport must be sufficiently rapid to reach quasi‐steady state in a time much shorter than the age of the earth. The close relationship between this model and bidirectional transport between the systems is discussed. Two forms of the model are presented. In each, the time‐varying concentrations of204Pb approach asymptotic values exponentially with time. Model A, in which the transport of uranium and thorium is very rapid, provides the most recent beginning of differentiation, at a time 2500 m.y. ago. Model B, in which the transport of uranium and thorium is also exponentially related to time, corresponds to a differentiation beginning 3000 m.y. ago. These seem to be extreme times for the form of the model used. It is suggested that lead‐isotope measurements might be used to identify characteristically oceanic materials now in continental areas as the result of tectonic plate m

ISSN:8755-1209    

DOI:10.1029/RG010i002p00529

年代:1972

数据来源: WILEY

摘要:

Four two‐error linear regression treatments have been reported in the literature for use in Rb‐Sr geochronology. We have made a general comparison of these treatments and have examined some of the assumptions and concepts implied in their use. For certain cases we show that analytical errors involved in Rb‐Sr measurement are normally distributed and uncorrelated and may thus be regressed with any of the four published treatments. Furthermore, by the use of simulated test data, we show that all treatments provide essentially identical regression parameters (slope, intercept, and associated error estimates), provided that the observed scatter can be accounted for solely in terms of the experimental error. Such data are said to define an isochron. Data that possess scatter in excess of experimental error (i.e., geological error) are said to define anerrorchron, and for such data the existing treatments may not furnish reliable regression parameters. One of the most important provisions of several of the treatments is a statistical index for distinguishing between isochrons and errorchrons. Use of this index requires an allowance for small‐sample statistics based both on the number of samples regressed and on the number of replicates used in calculating the experimental error. As the value chosen for the experimental error also directly affects the final isochron error estimate, a Student'stmultiplier (derived from the number of replicates used in calculating the experimental errors) should be applied to the final isochron error es

ISSN:8755-1209    

DOI:10.1029/RG010i002p00551

年代:1972

数据来源: WILEY

摘要:

The dispersion relationship for hydromagnetic waves in a rotating system indicates that, under plausible assumptions concerning the strength of the toroidal magnetic field in the earth's liquid core, the periods associated with slow planetary‐scale waves in the core would be comparable with the characteristic time scales found in the geomagnetic secular variation, decades to centuries, and it now seems likely that such waves could also play a key role in the production of the geomagnetic field by the ‘dynamo’ process. Attempts to interpret specific features of the field in terms of hydromagnetic oscillations of the core (or of any other type of fluid motion, for that matter) have not yet proved entirely successful, for they encounter serious and in some cases fundamental mathematical difficulties. The present paper reviews theoretical work on free hydromagnetic oscillations of a bounded rotating fluid in the context of the geomagnetic pr

ISSN:8755-1209    

DOI:10.1029/RG010i002p00579

年代:1972

数据来源: WILEY

摘要:

The study of trapped‐particle motion in the earth's magnetic field is usually geared toward building the foundation of radiation‐belt dynamics (particle injection, acceleration, diffusion, and loss). In this article we turn the situation around and use trapped‐particle motion to explore the properties of the geomagnetic field itself. One of the quadrupole terms in the main geomagnetic field is found to contribute to a north‐south ‘shear distortion’ of the particle‐drift shells, whereas one of the octupole components causes a longitude‐dependent radial deformation and associated ‘drift‐shell splitting.’ The collective action of all higher multipoles on trapped‐particle motion is then used to analyze the ‘true’ anomalies or distortions of the internal geomagnetic field that are independent of the quadrupole‐related eccentricity of the main dipole. These ‘true’ anomalies must originate in upper‐mantle or crustal perturbations that lie relatively near the earth's surface on both sides of the mid‐Atlantic ridge; they influence trapped‐particle drift shells only where the latter have their closest approach to the earth (South Atlantic and South African areas). The quadrupole and octupole perturbations, on the other hand, obviously originate deep in the earth's core. The most adequate space and particle coordinate systems are introduced, and their validity is briefly analyzed. In the final part of this review, we discuss the effects of external magnetospheric currents. A time‐dependent symmetric ring current causes drift shells to be displaced radially, with associated particle acceleration; magnetopause currents introduce a day‐night asymmetry, causing shell splitting. Time dependence of these effects introduces further complications; an invariant particle coordinate system is discussed that can be used for particle‐flux representations that are independent of the particular instantaneous field configuration (provided that the latter is known and that a

ISSN:8755-1209    

DOI:10.1029/RG010i002p00599

年代:1972

数据来源: WILEY

摘要:

This review deals with the propagation of waves, especially radio waves in the ionosphere. In the macroscopic electromagnetic theory, the mathematical structure of wave propagation problems depends entirely on the properties of the dielectric operator in a magnetically nonpermeable medium. These properties can be deduced from general discussions of symmetry and considerations of physical principles. When the medium is specifically the ionosphere, various physical phenomena may occur. Because of a large number of parameters, it is desirable to define a parameter space. A point in the parameter space corresponds to a specific plasma. The parameter space is subdivided into regions whose boundaries correspond to conditions of resonance and cutoff. As the point crosses these boundaries, the refractive index surface transforms continuously. The medium in which the propagation takes place may influence the wave in many different ways. Specific experiments can be designed to probe the medium to learn its properties.

ISSN:8755-1209    

DOI:10.1029/RG010i002p00631

年代:1972

数据来源: WILEY