摘要:

The adiabatic theory of charged‐particle motion is developed systematically in this review. We present the essentials of the theory without giving all the analysis in detail. The general expressions for guiding‐center motion and particle energy change are given, with application to the Van Allen radiation and to Fermi acceleration. It is shown that Fermi acceleration and betatron acceleration should not be regarded as distinct processes. Modifications of the nonrelativistic theory that are necessary when the particle is relativistic are discussed. Proofs are given of the invariance to lowest order of the first and second adiabatic invariants for the case of static fields. Finally, applications are made to the theory of plas

ISSN:8755-1209    

DOI:10.1029/RG001i003p00283

年代:1963

数据来源: WILEY

摘要:

The rate of influx of helium 4 from the earth's crust into the atmosphere is about 2 × 106atoms cm−2sec−1. The average rate of thermal escape averaged over the last solar cycle is 6 × 104atoms cm−2sec−1. The present abundance of helium in the atmosphere would accumulate in about two million years. Either some nonthermal mechanism permits at present a greater rate of escape of helium or the rate of escape has varied in time. This paper is concerned with an examination of possible changes in the escape rate due to variations in the earth's magnetic field. Problems associated with the heat balance in the upper atmosphere are reviewed. Statistical analysis of drag on satellites and solar decimeter flux establishes that the 27‐day variation in atmospheric density results from fluctuations in the intensity of the solar wind. It is considered likely that a heat source over and beyond that provided by ultraviolet radiation is required to account for both the day‐night variations in upper atmosphere densities and the 27‐day variation. Various mechanisms by which energy density in the solar wind can be transferred into the upper atmosphere are considered. It is suggested that, if the additional heat source is indeed due to the solar plasma, historical fluctuations in the earth's magnetic field could result in a greater escape rate for helium. The establishment and identification of the additional heat source is necessary for a full understanding of the escape of helium. The terrestrial economy of helium 3 is reviewed. The contribution by solar cosmic rays to the abundance of helium 3 remains a major problem. The rate of influx of helium 3, about 10 atoms cm−2sec−1, is greater than the escape rate averaged over the last solar cycle, about 4 atoms cm−2sec−1, if solar cosmic rays contain abo

ISSN:8755-1209    

DOI:10.1029/RG001i003p00305

年代:1963

数据来源: WILEY

摘要:

This review is concerned with the variation of compressional and shear‐wave velocities with depth in the earth's upper mantle. Information about the compressional velocities is obtained from a study of body waves of thePtype. MostP‐wave studies have been limited to continental regions. These studies suggest that there is no pronounced shadow zone forPwaves resulting from a low‐velocity channel in the upper mantle, except in tectonically active regions such as California‐Nevada, Japan, Andes, etc. Information about the shear velocities is obtained from studies of body waves of theStype and of Rayleigh and Love surface waves. Surface‐wave studies have been made for both continental and oceanic regions. The surface‐ andS‐wave studies suggest that there is an earth‐encircling, low‐velocity channel for shear waves in the upper mantle. The shear velocities in this channel are lower than average in oceanic regions, and higher than average in continent

ISSN:8755-1209    

DOI:10.1029/RG001i003p00351

年代:1963

数据来源: WILEY

摘要:

The qualitative effects of anisotropy on elastic waves propagating in a solid medium were well known to Lord Kelvin. Having been recognized, however, these effects were neglected as being of secondary importance in the dynamics of elastic mediums. This relegation of anisotropy to a secondary role in the dynamics of elastic mediums was undoubtedly justified, particularly in view of the relatively primitive state of experimental elasticity and seismology during Kelvin's time. It was not until after World War 2 that the effects of anisotropy again received serious attention. This was primarily because of the development of ultrasonic techniques for the measurement of dynamic elastic constants of pure crystals. In such experimental problems anisotropy no longer plays a secondary role. The study of how a disturbance, generated by a transducer on the surface of a crystal, spreads through the crystal led to the discovery, by Musgrave, that the wave surface, which forms the boundary of the spreading disturbance, could have cuspidal singularities. This had not been previously predicted, although it could have been predicted by Kelvin had he been more familiar with algebraic geometry. In another area of research (seismology), the post World War 2 years also saw a rise of interest in anisotropy, particularly in the effect of possible continental anisotropy on the propagation of Rayleigh waves. The increased experimental activity in crystal dynamics and the improvement of experimental seismology to the point where secondary effects became important resulted in a number of theoretical investigations into the propagation of plane, time harmonic waves in anisotropic mediums. By 1959 the state of the theoretical and experimental understanding of anisotropic elastic wave propagation had advanced to the point where rigorous wave theoretical calculations were in order. All the simple, solvable problems of isotropic dynamic elasticity, i.e. the initial value problem for an unbounded homogeneous medium, the mixed initial and boundary value problem for a surface line source on a half‐space, the normal mode problem for an elastic wave guide, etc., can be formulated and solved in detail in the anisotropic case. Furthermore, the solutions can be obtained by extensions of the usual transform methods used in isotropic problems. The results can be physically interpreted by means of classical differential geometry. This review summarizes those anisotropic problems treated since 1959 and the techniques developed to solve the

ISSN:8755-1209    

DOI:10.1029/RG001i003p00401

年代:1963

数据来源: WILEY

摘要:

Six hundred and eighty‐seven heat flow data from more than 780 individual determinations and estimations were compiled. Of these, 634 data were analyzed. The range of the present heat flow per unit area is approximately 0 to 8 µcal/cm2sec. The world's arithmetic mean is 1.62, and the standard deviation of a datum is 1.21. The data do not seem to form any simple distribution. Since the sampling is poor and biased, a weighted mean technique is developed. On the basis of three assumptions, the world's average heat flow per unit area was found to be 1.5 ± 10 per cent at 95 per cent confidence. This is significantly higher than the value 1.2 suggested in 1954. There is no simple dependence of heat flow per unit area on latitude and longitude. A spherical harmonic analysis indicates that all the coefficients of the harmonics are at least an order of magnitude less than the mean of about 1.5. Heat flow and geological parameters, as well as difficulties in heat flow research and sources of heat, are briefly discussed. The purpose of this study is to summarize all the available data in a comprehensive list with extensive bibliographies and to set up computer programs for data analysis that can be used in the fut

ISSN:8755-1209    

DOI:10.1029/RG001i003p00449

年代:1963

数据来源: WILEY