摘要:

A prerequisite for thermodynamic modeling of silicate melts is a knowledge of basic thermodynamic data for glasses and liquids. The recent advances in the measurement and rationalization of these data are thus reviewed in this paper, with particular emphasis on the influence of the thermal history of glasses on their various thermochemical properties. Above room temperature the heat capacities of glasses (Cpg) do not depend sensitively on thermal history. They are almost additive functions of the chemical composition, which can now be empirically calculated to within about 1%. In contrast, the heat capacities of liquids (Cpl) do not generally vary linearly with composition, especially for aluminosilicates. But more experimental data would be useful to improve the accuracy of the models proposed for calculating the heat capacity of molten rocks. The available enthalpies of fusion (ΔHf), which depend measurably on the thermal history of the glasses used in solution calorimetry measurements, are summarized for silicates of geochemical or theoretical interest, and new values have been derived for some additional compositions. The usefulness of these data for calculating the entropies of liquids is pointed out, in particular for calculating the entropies and configurational entropies of the liquids. Finally, available enthalpies of mixing of glasses and liquids are also summarized. A few examples are used to illustrate the major influence of the thermal history of glasses on their mixing properties, and it is suggested that the ternary excess enthalpies of mixing observed in simple systems could be a spurious consequence of neglecting this influence

ISSN:8755-1209    

DOI:10.1029/RG024i001p00001

年代:1986

数据来源: WILEY

摘要:

The shape of a deep seismic zone is thought to represent that of the descending slab of lithosphere. The lithosphere before subduction is a spherical shell, and the shape of the descending slab is the result of the deformation of the spherical lithosphere at the subduction zone. Upon bending a spherical shell often deforms in a very different way from a simple plate. We examine whether the actual shape of the descending slab can be explained by a simple bending of an inextensible spherical shell, which shows little surface deformation under moderate stress. This examination is made region by region for most of the subduction zones in the world by means of an analogue method. The lithosphere is simulated by an inextensible spherical shell made of polyvinyl chloride resin. The Wadati‐Benioff zone is shaped by plaster by referring to the reliable hypocentral data selected from the International Seismological Centre (ISC) bulletins. The spherical shell is forced to fit the miniature of the Wadati‐Benioff zone. Fitting is first attempted only by bending. If a good fit is not attainable and if a discontinuity or gap in seismic activity is observed in the relevant region, the spherical shell is torn along this discontinuity or gap, and the goodness of fit is reexamined. The results of the analysis are summarized as follows: (1) The shape of the Wadati‐Benioff zone can be simulated largely by a simple bending of a spherical shell without surface deformation. (2) In almost all of the regions of poor fit with bending, a good fit can be achieved by tearing the spherical shell along the trace of low seismicity. The sphericity of the lithosphere and the inextensibility upon deformation are the two essential factors in controlling the slab shape. This means that the lateral constraint is most important for understanding the geometry of the downgoing slab of lithosphere and the stress state within it. Further, several problems related to the deformational characteristics of the spherical lithosphere are also reviewed and discussed in connection with subduction tect

ISSN:8755-1209    

DOI:10.1029/RG024i001p00027

年代:1986

数据来源: WILEY

摘要:

Studies of the solar wind controlled Pc 3, 4 pulsations by early and recent researchers are highlighted. The review focuses on the recent observations, which cover the time during the International Magnetospheric Study (IMS). Results from early and recent observations agree on one point, that is, that the Pc 3, 4 pulsations are influenced by three main solar wind parameters, namely, the solar wind velocityVsw, the IMF orientation θxB, and magnitudeB. The results can be interpreted, preferably, in terms of an external origin for Pc 3, 4 pulsations. This implies, essentially, the signal model, which means that the pulsations originate in the upstream waves (in the interplanetary medium) and are transported by convection to the magnetopause, where they couple to oscillations of the magnetospheric field lines

ISSN:8755-1209    

DOI:10.1029/RG024i001p00055

年代:1986

数据来源: WILEY

摘要:

The theory of surface operators is described and applied to four surface operators on spheres: the dimensionless surface gradient, ▽1=r▽‐r∂r; the dimensionless surface curl,Λ1=rˆ×▽1; the dimensionless surface Laplacian, ▽1²=▽1· ▽1; and the Funk‐Hecke operators, integral operators with axisymmetric kernels. Three methods are given for solving ▽1²g=fasg=▽1−2f; one method works numerically whenfhas a rapidly convergent expansion in spherical harmonics, the second works whenfis smooth in longitude but not latitude, and the third (a Funk‐Hecke operation) works whenfis rough in all directions. With this apparatus, a complete proof is given of the Helmholtz representation of an arbitrary vector fieldvS(r), the spherical surface of radiusrcentered on the origin: there are unique scalar fieldsf, g, honS(r) such thatv=rˆf+▽1g+Λ1hand 〈g〉r=〈h〉r=0. Here 〈g〉ris the average value ofgonS(r). From the Helmholtz representation on spherical surfaces, the Mie or poloidal‐toroidal representation in spherical shells is deduced. SupposeS(a,c) is the spherical shell whose inner and outer boundaries areS(a) andS(c). SupposeBis solenoidal inS(a,c), i.e., ▽·B=0 and 〈Br〉a=0. Then there are unique scalar fieldsPandQinS(a,c) such thatB=▽ × Λ1P+ Λ1Qand 〈P〉r=〈Q〉r=0 fora⪕r⪕c. The fieldsP= ▽ × Λ1PandQ=Λ1Qare the poloidal and toroidal parts ofB. Applications of this formalism to geomagnetic field modeling are discussed. Gauss's resolution of the geomagnetic fieldBonS(b) into internal and external parts is generalized; if the radial currentJrdoes not vanish onS(b), then to Gauss's expression must be added a toroidal field onS(b) due entirely toJronS(b). A simple proof is given of Runcorn's theorem that to first order in susceptibility no external magnetic field results from magnetization in a horizontally homogeneous spherical shell polarized by sources inside the shell. A Funk‐Hecke‐based method of modeling ionospheric currents is described, which may be more accurate than truncated spherical harmonic expansions and easier to use than Biot‐Savart integrals. Finally, the formalism makes possible the modeling of satellite samples of the geomagnetic field in a spherical shellS(a,c) where electric currents cannot be neglected. Two approximation schemes are described. One is a truncated power series expansion in (c‐a)/H, whereHis the radial length scale of the currents. The other assumes that most ofBinS(a,c) is not due to the currents betweenS(a) andS(c), and that the currents inS(a,c) are field‐aligned. Then the collection of physically possible magnetic fields inS(a,c) is only 50% larger, in a well‐defined sens

ISSN:8755-1209    

DOI:10.1029/RG024i001p00075

年代:1986

数据来源: WILEY

摘要:

We review the various natural and anthropogenic factors that may affect the climate. The purpose is to summarize our understanding of these factors and their potential future climatic effects so that CO2‐induced climate change can be viewed in a proper context. The factors we discuss include trace gases, anthropogenic and volcanic aerosols, variation of solar constant, change of surface characteristics, and releases of waste heat. We discuss the origins of the various natural and anthropogenic perturbations, the physical and chemical processes and their interactions, model sensitivity calculations, and model projections of their potential future climatic effects. The discussions center on trace gases because of their potentially large climatic effects. It appears that the increases of atmospheric trace gases of other kinds in addition to CO2could have important climatic effects. The model calculations suggest that the combined effect of these other trace gases, and the associated change of atmospheric ozone and water vapor distributions, could potentially warm the climate by an amount comparable in magnitude to the effect of doubling the CO2. Aerosols of anthropogenic origins may have substantial effects on regional climate, while the volcanic aerosols may have an effect on large‐scale climate for up to a few years after injection. Changes of surface characteristics and releases of waste heat may also have substantial effects on the regional climate, but these effects are most likely to be small when compared with the effect of CO2increase. Changes of solar constant could have an effect on the global scale, but the time scale is much longer. There is much more that needs to be learned with regard to the above mentioned natural and anthropogenic factors that may affect the climate. A brief summary of those needs is presen

ISSN:8755-1209    

DOI:10.1029/RG024i001p00110

年代:1986

数据来源: WILEY

摘要:

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ISSN:8755-1209    

DOI:10.1029/RG024i001p00141

年代:1986

数据来源: WILEY