bluuebunny/crossref_metadata_2025 huggingface dataset:
The tectonics of the eastern Mediterranean: A geophysical review
Authors: Lort J. M.
Published: February 2008

A summary is given of present geophysical data available for the eastern Mediterranean, and the structural and tectonic history of the area is interpreted. The western Mediterranean is described in sufficient detail only for comparison.

The region is delineated into plates on the basis of seismic activity at their margins. The African plate is moving northward relative to Europe with crustal destruction and underthrusting occurring along the Crete and Calabrian island arc systems. The intervening Aegean, Apulian, and Turkish plates are small and rapidly moving; they show intense seismicity at the boundaries. All observations (sediment deformation, gravity, magnetics and heat flow) suggest the existence of a zone of compression in the eastern Mediterranean.

Anticlockwise rotation relative to Eurasia of parts of southern Europe occurred during an extensional phase in the west, permitting the development of new oceanic crust and accompanied by compression in the east. What little evidence there is suggests that the crust in the eastern Mediterranean is oceanic, but there are no magnetic stripes to indicate the orientation of the mid‐oceanic ridge from which it developed.
Oceanic volcanism: A review
Authors: McBirney A. R.
Published: February 2008

Recognition of the magnitude and tectonic significance of oceanic volcanism has recently stimulated intensive investigation of the volcanic rocks and structures of the sea floor. An adequate interpretation of these features depends on a thorough understanding of submarine volcanic mechanisms. The pressure of deep water restricts the amount of vesiculation of eruptive magmas so that explosive activity is suppressed. Pillow lavas are probably shorter but thicker than subaerial flows of the same composition. Fragmental hyaloclastites are also important, but seem to be most common at relatively shallow depths. Most lavas and hyaloclastites are basaltic, but more siliceous pyroclastic deposits may be common in shallow seas of the continental shelves.

Circumstantial evidence indicates that most abyssal basalts of the ocean floor were erupted at spreading centers and have been transported laterally. The rate of eruption of lavas is probably related to the mechanism of dike intrusion into a spreading center. Slow spreading rates result in less vertical transfer of heat, so that only relatively thick dikes reach the surface. Thinner dikes are chilled before erupting and cause a differential dilation of the crust that is reflected in shallow normal faulting. With increasing spreading rates, wall rocks are maintained at higher temperatures, and almost all dikes reach the surface to produce lava flows and smoother topography.

Seamounts may begin to grow at ridge crests and continue as the volcano moves outward, but many must begin their activity far from the spreading center. Most of the submarine structure of seamounts must consist of pillow lavas with increasing amounts of hyaloclastites in the upper portion. Injection of dikes and sills adds substantially to the volume of the structure.

Most abyssal basalts erupted at ridge crests are tholeiites, commonly with relatively high alumina contents. Silica‐deficient alkaline basalts become more common outward, especially at the crests of seamounts. The ultramafic rocks dredged from the mid‐Atlantic ridge fall into two classes. Some are clearly cumulate rocks related to associated gabbro and differentiated basalt. Others are strongly depleted in low‐melting components and appear to have been emplaced along fault zones; they may be derived from a residual layer from which basalt was extracted during an earlier episode of partial melting. It is difficult to find conclusive evidence that oceanic volcanism was as intense in pre‐Mesozoic time as it is postulated to be today.
Dynamical characteristics of Phobos and Deimos
Authors: Burns Joseph A.
Published: February 2008

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 models.
Realistic use of two‐error regression treatments as applied to rubidium‐strontium data
Authors: Brooks C. , Hart S. R. , Wendt I.
Published: February 2008

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 an errorchron, 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's t multiplier (derived from the number of replicates used in calculating the experimental errors) should be applied to the final isochron error estimates.
Deformation of the Earth by surface loads
Authors: Farrell W. E.
Published: February 2008

The static deformation of an elastic half‐space by surface pressure is reviewed. A brief mention is made of methods for solving the problem when the medium is plane stratified, but the major emphasis is on the solution for spherical, radially stratified, gravitating earth models. Love‐number calculations are outlined, and from the Love numbers, Green's functions are formed for the surface mass‐load boundary‐value problem. Tables of mass‐load Green's functions, computed for realistic earth models, are given, so that the displacements, tilts, accelerations, and strains at the earth's surface caused by any static load can be found by evaluating a convolution integral over the loaded region.
Observations of the radial gradient of galactic cosmic radiation over a solar cycle
Authors: O’Gallagher J. J.
Published: February 2008

More than 20 measurements of the heliocentric radial gradient in cosmic‐ray flux have been made and reported between 1960 and 1971. These results are organized so that the important distinction between differential and integral measurements is emphasized and real discrepancies, some as large as 10 times the quoted errors, can be analyzed. Both integral and differential measurements above a few hundred million electron volts are most consistent with a positive gradient (increasing intensity for increasing radial distance) with a magnitude between a few per cent and a few tens of per cent per astronomical unit. On the other hand, below 100 Mev both integral and differential measurements are in wide disagreement, with no consensus even with respect to the sign of the gradient. Some factors that may contribute to these discrepancies are (1) the determination of a reference intensity to remove time variations, (2) the elimination of effects due to particles of solar origin, and (3) proper understanding of the effects of transient fluctuations in intensity.
Solar magnetic fields derived from hydrogen alpha filtergrams
Authors: McIntosh Patrick S.
Published: February 2008

The distribution and polarity of solar magnetic fields can be inferred from photographs taken with narrow band‐pass filters centered on the Hα spectral line. Structures observed in Hα, including filaments, filament channels, fibrils, arch‐filament systems, and plage corridors are used to infer positions of neutral lines in the radial component of the solar magnetic fields. This source of magnetic‐field information, although it is not strictly objective and quantitative, offers a number of important advantages over the solar magnetograph. The inferred data can be obtained with the existing global network of flare patrol observatories at low cost, high speed, and complete reliability from day to day. Patrol films allow the filling of interruptions in magnetograph data and the extension of the magnetic‐field data base back in time to the first spectroheliograms near the beginning of the century. The large‐scale Hα patterns are more precisely outlined than their large‐scale counterparts on magnetograms. The continuity of Hα markers of polarity reversals from active centers to quiescent, large‐scale structures reveals associations and patterns not previously studied. The inferred magnetic data have important applications in solar‐activity forecasting, detection of interplanetary‐sector boundaries, and the inference of structures in the solar corona.
Doppler radar characteristics of precipitation at vertical incidence
Authors: Atlas D. , Srivastava R. C. , Sekhon R. S.
Published: February 2008

A comprehensive review and extension of the theoretical bases for the measurement of the characteristics of rain and snow with vertically pointing Doppler radar are presented. The drop size distribution in rain can be computed from the Doppler spectrum, provided that the updraft can be estimated, but difficulties are involved in the case of snow. Doppler spectra and their moments are computed for rain by using various power law relations of fall speed υ versus particle diameter D and an exponential fit to the actual fall speed data. In the former case, there is no sharp upper bound to the spectra and all the spectral moments increase with rainfall rate R without limit; in the latter case, there is a sharp upper bound of the spectra corresponding to the limiting terminal velocity of raindrops, and the spectral moments approach an asymptote. Accordingly, the power laws are useful approximations over only limited ranges of precipitation rate. A comparison of theoretical and experimental mean Doppler velocity 〈υ〉 as a function of radar reflectivity factor Z shows that the empirical relation 〈υ〉 = 2.6Z0.107 of J. Joss and A. Waldvogel seems to be the only practical relation; even so, the scatter in 〈υ〉 is about ±1 m sec−1. This is also the kind of error to be expected in measuring updraft speeds by present methods. Such updraft errors result in unacceptably large errors in the drop number concentration estimated from Doppler spectra. In the absence of updrafts the mean Doppler velocity 〈υ〉 is uniquely related to Λ, the slope of the exponential drop size distribution. Simultaneous measurements of Z and 〈υ〉 can then be used to estimate N0, Λ, D0, M, and R, where N0 is the intercept of the exponential drop size distribution at D = 0, D0 is the median volume diameter, and M is the liquid‐water content.
Acoustic‐gravity waves in the upper atmosphere
Authors: Yeh K. C. , Liu C. H.
Published: February 2008

In this paper we review the theory of acoustic‐gravity waves, the interaction of such waves with the ionosphere, the experimental support for the existence of such waves in the upper atmosphere, and the role played by acoustic‐gravity waves in thermospheric dynamics. After a thorough discussion on the properties of acoustic‐gravity waves in an ideal isothermal atmosphere, the effects produced by horizontal winds, sharp boundary discontinuities, and dissipative processes are discussed. The generation of these waves by stationary or moving sources is then treated. It is shown that the atmospheric response to a stationary impulse source can be described by the emission of three waves: acoustic, buoyancy, and gravity. These discussions are then followed by reviewing propagation effects in a realistic atmosphere for both free waves and guided waves. Recent numerical results are given. When acoustic‐gravity waves propagate through the ionosphere, interaction between the wave and the ionosphere will take place. The physical processes involved in such an interaction are examined. The response of the ionosphere to acoustic‐gravity waves can be fairly complex, but its understanding is necessary to interpret various experimental data. The existing experimental data on traveling disturbances are then reviewed. The existence of acoustic‐gravity waves throughout the atmosphere implies coupling between the lower atmosphere and the upper atmosphere. Transport of both momentum and energy are accompanied by the wave process. The implication of momentum and energy transport on thermospheric dynamics is discussed.
Streamflow generation
Authors: Freeze R. Allan
Published: February 2008

During the past 10 years under the impetus of the International Hydrological Decade there has been a burst of research activity aimed at obtaining better insight into the mechanisms of streamflow generation. The research has focused on an examination of the ways in which water moves from hillslopes into small stream channels during and between rainfall events in upstream tributary basins. The research has been of two types: field measurements in representative experimental drainage basins and theoretical studies using mathematical models of hydrologic processes, carried out with the aid of a digital computer. The field studies have identified the sources of lateral inflow to streams as overland flow, subsurface storm flow, and groundwater flow. They have also proven that most overland flow is generated either on small upland partial areas that are more or less fixed in size and that are controlled by the distribution of soil types or on expanding and contracting ‘variable source areas’ that are adjacent to streams and that are controlled by the topographic and hydrogeologic configuration of the hillslopes. They have shown qualitatively that the relative importance of the different processes depends on such controls as climate, geology, topography, soil characteristics, vegetation, and land use. This variety of field conditions coupled with the complexity of the processes themselves has hindered the growth of generalized interpretations based solely on the field evidence, and hydrologists have increasingly turned to mathematical modeling to isolate the various components of the system. Physically based mathematical models, in the form of boundary value problems based on the partial differential equations of flow, are now available for all the processes involved in streamflow generation. The concepts of open channel hydraulics form the basis for models of flow in a stream channel and for overland flow. The concept of saturated and unsaturated porous media flow has been brought to bear on models of infiltration, subsurface storm flow, and groundwater flow. Applications of these models at field sites and for series of hypothetical cases have identified the physical parameters that control the various observed mechanisms of downslope water movement and for some environments have determined the necessary conditions for the dominance of one mechanism over the others.
Waves and instabilities in the solar wind
Authors: Hollweg Joseph V.
Published: February 2008

We present a review of waves and instabilities in the solar wind, concentrating on those aspects that are likely to play important roles in influencing the dynamic and thermodynamic states of the general solar wind expansion. We consider in particular the roles played by various waves and instabilities in influencing the heating and expansion of the solar wind, the angular momentum of the solar wind, the solar wind thermal anisotropy, the heating and flow of alpha particles in the solar wind, the interstellar neutral particles that become ionized in the solar wind, and the ‘fluidlike behavior’ of the solar wind. We include a brief review of the properties of the hydromagnetic wave modes, concentrating particularly on the Alfvén mode, which has been observed to contribute significantly to the microscale fluctuations of the solar wind. But we also present a summary of observational evidence pertaining to the presence and action in the solar wind of waves and instabilities that are not among the hydromagnetic modes.
The frequency of geomagnetic reversals and the symmetry of the nondipole field
Authors: Cox Allan
Published: February 2008

The average frequency of geomagnetic reversals seen through a sliding window 10 m.y. long typically remains constant or nearly so for intervals of the order of 5 × 107 years and then increases or decreases to another level. Frequency shifts of this type are known from paleomagnetic studies to have occurred at times 107, 86, and 45 m.y. B.P. and at many other times earlier in the earth's history. The most likely cause of the frequency shifts is a change in the topography of the core‐mantle interface or changes in some physical property such as temperature along the interface. If such lateral variations at the base of the mantle exist, if they have changed with time, if they are large enough to create eddies or Taylor columns in the fluid motions of the core, and if these fluid motions affect the operating characteristics of the dynamo, then a simple model is at hand to account for the observed changes in reversal frequency. The generation of fluid eddies in the outer core by irregularities at the core‐mantle interface would also probably induce variations in the nondipole field. These variations should be observable if they include departures of the nondipole field from the zonal symmetry expected solely from rotational effects. Among the candidates for such asymmetrical components of the field are the standing waves that are currently being reported by geomagneticians analyzing the historic field and the apparent northward shift of the main dipole currents of the core dynamo that is suggested by time‐averaged global paleomagnetic data. On the basis of a reexamination of these data the conclusion is here drawn that the apparent northward displacement of the earth's main dipole moment is not the result of a standing zonal field but is rather the result of time averaging individual small excursions of the field caused by the westward drift of major features of the nondipole field. Paleomagnetic results indicate that these features of the nondipole field are not randomly distributed with respect to latitude, as is usually accepted. Instead, it appears that during times of normal polarity, flux usually emerges from the core in localized regions near the equator and reenters the core in localized regions located about 55° from either pole. During times of reversed polarity this entire pattern is reversed, suggesting that when the dipole field reverses, the toroidal field reverses also. The latitudes at which the large features of the nondipole filed are generated by convective cells or other types of fluid motion thus appear to be linked directly to the polarity of the dynamo. These findings are supportive of the reversal mechanism suggested by Parker and Levy.
Snow and ice
Authors: Colbeck S. C. , Thorndike A. S. , Whillans I. M. , Hodge S. M. , Ackley S. F. , Ashton G. D.
Published: February 2008

The high level of snow and ice research activity of the preceding 15 yr has been maintained partly by increased interest in cold regions engineering by commercial interests. The mobility of ships in the Arctic Ocean, mining in and around glaciers, and industrial applications of ice have added incentive to the existing concerns over water supply, recreational facilities, and basic scientific knowledge. Much of the financial support for individual investigators is now directed through large projects (e.g., Arctic Ice Dynamics Joint Experiment (AIDJEX), Ross Ice Shelf Project (RISP), and Greenland Ice Sheet Program (GISP)) which define scientific objectives, arrange logistical support, and promote international and interagency cooperation. Coordinated efforts are notably lacking in some areas (e.g., snow, avalanche, and temperate glacier research) where research funds are either lacking or spread over many disjointed projects. Many of the significant research advances are due to the large projects and/or the use of remote sensing imagery.
Ionospheric irregularities
Authors: Perkins F. W.
Published: February 2008

Ionospheric irregularities are small‐scale structures in the ionospheric plasma density generally oriented so that the plasma density variations occur rapidly across the geomagnetic field but slowly (or not at all) along the geomagnetic field. On the practical side, they play an important role in satellite communication systems [Utlaut, 1974].

The scale length of ionospheric irregularities can range from a few meters to several kilometers across the magnetic field. A vast literature of radio wave studies has produced a fairly complete morphological picture of their occurrence pattern [Herman, 1966; Aarons and Allen, 1971]. Briefly, they occur in the auroral and polar cap F region almost all the time [Aarons, 1973], in the auroral E region in times of geomagnetic activity [Greenwald et al., 1973], in the equatorial E region [Balsley and Farley, 1973], and in the equatorial F region at night [Farley et al., 1970]. Ionospheric irregularities occur at temperate latitudes only in the nighttime F region during times of geomagnetic activity [Herman, 1966]. Often the occurrence of F region irregularities is called ‘spread F,’ a term derived from the appearance of ionograms under conditions when irregularities occur. Ionospheric irregularities have also been generated artificially by barium plasma releases [Rosenburg, 1971] and radio wave heating experiments [Utlaut and Cohen, 1971].
Parameterization of the planetary boundary layer in atmospheric general circulation models
Authors: Bhumralkar Chandrakant M.
Published: February 2008

The interaction between the atmosphere and the underlying surface occurs through the planetary boundary layer. The basic information required for describing the large‐scale processes in terms of the boundary layer processes relates to the turbulent fluxes of momentum, heat, and moisture, the height of the boundary layer, and surface parameters such as soil moisture content and topography.

The numerical models of the atmospheric general circulation incorporate the (statistical) effects of the boundary layer processes in terms of the large‐scale parameters computed by the model through parameterization techniques. This paper reviews various parameterization techniques used in current general circulation models and suggests the need for a sensitivity test to find the best one.
Some basic stress diffusion solutions for fluid‐saturated elastic porous media with compressible constituents
Authors: Rice James R. , Cleary Michael P.
Published: February 2008

This is a study of the formulation, some basic solutions, and applications of the Biot linearized quasistatic elasticity theory of fluid‐infiltrated porous materials. Whereas most previously solved problems are based on idealizing the fluid and solid constituents as separately incompressible, full account is taken here of constituent compressibility. Previous studies are reviewed and the Biot constitutive equations relating strain and fluid mass content to stress and pore pressure are recast in terms of new material parameters, more directly open to physical interpretation as the Poisson ratio and induced pore pressure coefficient in undrained deformation. Different formulations of the coupled deformation/diffusion field equations and their analogues in coupled thermoelasticity are discussed, and a new formulation with stress and pore pressure as basic variables is presented that leads, for plane problems, to a convenient complex variable representation of solutions. The problems solved include those of the suddenly introduced edge dislocation and concentrated line force and of the suddenly pressurized cylindrical and spherical cavity. The dislocation solution is employed to represent that for quasi‐static motions along a shear fault, and a discussion is given, based on fracture mechanics models for fault propagation, of phenomena involving coupled behavior between the rupturing solid and its pore fluid, which could serve to stabilize a fault against rapid spreading. Also, the solution for a pressurized cylindrical cavity leads to a time‐dependent stress field near the cavity wall, and its relevance to time effects in the inception of hydraulic fractures from boreholes, or from drilled holes in laboratory specimens, is discussed. Various limiting cases are identified, and numerical values of the controlling porous media elastic parameters are given for several rocks.
Steady state flow of rocks
Authors: Carter Neville L.
Published: February 2008

Experimentally determined steady state flow properties and processes of important rock‐forming materials are reviewed in reference to those of metals and ceramics and to physical conditions in the earth's crust and upper mantle. Dislocation motion controls the creep rate over a wide range of steady state conditions in the experiments, and the observation that the same processes have operated during natural deformations permits extrapolations of the mechanical data. Under these conditions, strain rate is related to stress raised to the power 2–9, depending on the material and conditions, and the resulting flow stresses and equivalent viscosities are compared at a representative geological strain rate of 10−14/s. The results are applied in brief discussions of diapirism, growth of folds, and flow in the upper mantle.
Magnetometers using RF‐driven squids and their applications in rock magnetism and paleomagnetism
Authors: Goree W. S. , Fuller M.
Published: February 2008

A variety of magnetometer systems have been constructed utilizing superconducting quantum interference device (Squid) sensors. The magnetometers have high sensitivity and fast response times and eliminate the need for spinning or vibrating the sample to make measurements. The magnetometers have superconducting sense coils in which a dc persistent current is induced by the insertion of the sample. The current gives, via a flux transformer, a field at the Squid sensor, which is detected as the measure of the magnetization of the sample. The sense coils, the transformer, and the detector are housed within a superconducting shield. It was the advent of the Josephson junction devices which permitted the use of critical currents so small that flux‐switching sensors such as those used in the magnetometers could be developed. The particular Squid used in these magnetometers is an RF‐driven weak link sensor. The magnetometers have been used to observe magnetic transitions to identify magnetic phases. A high‐field susceptometer with a superconducting magnet permits determination of saturation magnetization and magnetic characteristics. Standard paleomagnetic samples can be measured at a magnetic moment sensitivity of 10−8 G cm³. Small samples have been measured with a 3‐mm access system whose noise level is 2 × 10−10 G cm³. Long cores can be measured by using a horizontal open access system. Continuous thermal demagnetization and intensity determinations are being developed.
Retrieval of atmospheric temperature and composition from remote measurements of thermal radiation
Authors: Rodgers C. D.
Published: February 2008

This paper reviews the methods which may be used to estimate the state of the atmosphere, i.e., the distribution of temperature and composition, from measurements of emitted thermal radiation such as are made by remote sounding instruments on satellites. The principles of estimation theory are applied to a linear version of the problem, and it is shown that many of the apparently different methods to be found in the literature are particular cases of the same general method. As an aid to understanding, the optimum linear solution is described in terms of the geometry of n dimensions, with n = 3 for illustration. In generalizing the approach to the nonlinear problem there are two stages: (1) finding any member of the infinite family of possible solutions, which may be done by any convenient iterative method, and (2) finding the optimum solution by satisfying appropriate constraints.
West Antarctic ice streams
Authors: Hughes T.
Published: February 2008

Solar heat is the acknowledged driving force for climatic change. However, ice sheets are also capable of causing climatic change. This property of ice sheets derives from the facts that ice and rock are crystalline whereas the oceans and atmosphere are fluids and that ice sheets are massive enough to depress the earth's crust well below sea level. These features allow time constants for glacial flow and isostatic compensation to be much larger than those for ocean and atmospheric circulation and therefore somewhat independent of the solar variations that control this circulation. This review examines the nature of dynamic processes in ice streams that give ice sheets their degree of independent behavior and emphasizes the consequences of viscoplastic instability inherent in anisotropic polycrystalline solids such as glacial ice. Viscoplastic instability and subglacial topography are responsible for the formation of ice streams near ice sheet margins grounded below sea level. As a result the West Antarctic marine ice sheet is inherently unstable and can be rapidly carved away by calving bays which migrate up surging ice streams. Analyses of tidal flexure along floating ice stream margins, stress and velocity fields in ice streams, and ice stream boundary conditions are presented and used to interpret ERTS 1 photomosaics for West Antarctica in terms of characteristic ice sheet crevasse patterns that can be used to monitor ice stream surges and to study calving bay dynamics.
On the orientation of hydromagnetic waves in the magnetosphere
Authors: Hasegawa Akira , Lanzerotti L. J.
Published: February 2008

We review evidence gathered from theoretical considerations and from measurements on the ground and in space for a 90° rotation of the major axis of the polarization ellipse of geomagnetic pulsation signals between the geomagnetic equator and the ground. The evidence at present supports the existence of the rotation phenomenon, although more observational work is needed. The rotation arises from the nonconducting air on the ground surface and the highly conducting plasma in space.
A critical look at long‐term Sun‐weather relationships
Authors: Pittock A. B.
Published: February 2008

Many and varied claims have been made over many years for a relationship between weather or climate and solar variations, notably sunspot cycles. Those relating primarily to the single and double sunspot cycles (of about 11‐ and 22‐year quasi‐periodicities) are critically reviewed in the light of what is known about solar variations, the observed variability of weather and climate, and possible physical connections between the two. Various pitfalls in the application or lack of application of statistics to the problem are discussed and illustrated from the literature. Following a survey of the literature it is concluded that despite the great number of recent papers on the subject, little convincing evidence has yet been produced for real correlations between sunspot cycles and the weather/climate on the 11‐ and 22‐year time scales, although evidence for correlations with solar events on time scales of days appears to exist. The state of the literature in this particularly controversial area must raise doubts as to the prevailing standards of objectivity and critical analysis in other areas of science as well. Clearly, in the case of sun‐weather relationships, further research requires much higher standards of objectivity, with the rigorous and critical application of statistics, and step by step investigation of hypothetical mechanisms. This criticism is not addressed to the recent studies of apparently significant correlations between certain meteorological indices and the passage of interplanetary magnetic sector boundaries; however, the relevance of such correlations to time scales of climatic interest has yet to be demonstrated.
A survey of lightning energy estimates
Authors: Hill R. D.
Published: February 2008

This survey attempts first, briefly, to identify typical lightning and then to compare the methods used for evaluating the energy dissipated in a return stroke. Energy values obtained from a large number of measurements, estimates, and theoretical models are tabulated. An attempt is made to find a typical average value.
Compositions of energetic particle populations in interplanetary space
Authors: Gloeckler George
Published: February 2008

Although the study of the composition of low‐energy particles in the interplanetary medium is a relatively new subject, our knowledge in this field has been advancing rapidly. Discoveries of pronounced anomalies in the compositions of solar flare particles and low‐energy “cosmic‐rays”, and of large‐scale interplanetary acceleration regions beyond several AU have been followed by more systematic investigations aimed at characterizing each of the components of the interplanetary energetic particle population.

The discoveries may be attributed to a combination of three favorable circumstances: (a) availability of sophisticated instruments capable of performing composition measurements at low energies, (b) properly instrumented deep space probes exploring the outer and inner heliosphere, and (c) a favorable time period in the solar activity cycle during which the discovered phenomena were especially prominent. Composition measurements not only have played a key role in the initial discoveries, but have also contributed significantly to our understanding of the acceleration processes responsible for the production of energetic particles which populate interplanetary space.
Seismic wave attenuation in rocks
Authors: Mavko Gerald , Kjartansson Einar , Winkler Kenneth
Published: February 2008

A fundamental feature associated with the propagation of stress waves in all solids is absorption of energy, which usually results in a change of the shape of transient waveforms. Despite its importance, the processes by which mechanical wave energy is converted into heat, and its effect on seismic observations, have been poorly understood. Although considerable progress has been made during the past few years, seismic attenuation remains a controversial subject as there is still considerable disagreement between different authors about some of its most fundamental aspects.

In the first section of this paper the progress in arriving at a general phenomenological description of wave propagation and related effects such as the frequency dependence of the elastic moduli and transient creep will be covered. It turns out that for most attenuation mechanisms that are significant in rocks, this can be treated relatively independent of the details of the particular physical mechanisms responsible for the energy dissipation, which are treated in the second section. The third section gives a review of experimental results.
Climatic change
Authors: Barry R. G. , Hecht A. D. , Kutzbach J. E. , Sellers W. D. , Webb T. , Wright P. B.
Published: February 2008

Activity and progress in research on climate change has been substantial during the past four years. A number of factors seem to be responsible for the surge of interest and progress in this field during the 1970's, and the momentum should continue into the 1980's. In this introduction, we will mention some of these factors in each of three areas: paleoclimates, short‐term climate fluctuations, and climate simulations. These same three areas will be reviewed in subsequent sections.
Observing, analyzing, and modeling mesoscale weather phenomena
Authors: Kreitzberg Carl W.
Published: February 2008

Recent progress and current research in this field are placed in perspective, along with key problems to be addressed in the coming years. Modeling has progressed further than analysis because mesoscale analysis requires assimilation of information from diverse observing systems. Physical equations are essential tools in data analysis; four‐dimensional dynamic assimilation is a powerful but complex tool. Dynamic model predictions permit observations at different times to be interpreted in a consistent manner.

Key observing systems and field programs are discussed briefly. Analysis techniques are discussed in relation to dynamic models with which they interact. Different classes of dynamic models are discussed, including prediction models, simulation models, and parameterization schemes. The relation of research on different classes of models is described. The emphasis throughout is on systems of models that use real data and can be verified against real data. Subsections are included dealing with communications among researchers and analysis of precipitation.

The conclusion is that even more rapid progress is likely in the coming years, but the key problem will be four‐dimensional data assimilation. The challenge is to efficiently combine diverse types of data and provide for effective collaboration of diverse scientific specialties. When the challenge is met, this field will have advanced to the point that operational applications will be feasible and productive.

An extended bibliography is included and sources of important technical reports are identified.
Inductive electric fields in the Ionosphere‐Magnetosphere System
Authors: Kim J. S. , Graham D. A. , Wang C. S.
Published: February 2008

In recent years, there has been increasing awareness of the importance of large‐scale electric fields in the earth's magnetosphere. Much attention has been directed to the quasi‐static electric field associated with charge separations generated by solar wind‐magnetosphere interaction, but these seem inadequate to explain many important processes. This paper reviews the evidence for the inclusion of electric fields of inductive origin, i.e., those due to time‐dependent currents in the magnetosphere‐ionosphere system. Attention is focused on processes associated with magnetospheric substorms, as they are well characterized by various types of evidence and do involve events such as energetic particle precipitation which require explanation beyond that provided by static electric field models. It is found that inductive electric fields are significant at times and should be included for a proper description of observed events.
Gravity fields of the terrestrial planets: Long‐wavelength anomalies and tectonics
Authors: Phillips Roger J. , Lambeck Kurt
Published: February 2008

We present a review of the long‐wavelength gravity fields of the terrestrial planets, earth, moon, Mars, and Venus with particular emphasis placed on the interrelationship between gravity anomalies and tectonic processes. After first summarizing appropriate statistical formulas, we discuss the relevant continuum mechanical solutions for elastic, viscoelastic, and convecting media in terms of the relationship to the gravity field both for predicting gravity anomalies and for the use of gravity as a constraining boundary condition. Gravity data can provide a strong constraint for the first two classes of solutions, but a significant ambiguity exists in convection interpretations because of the competing effects from flow and boundary deformation. The question of finite strength of crustal and mantle materials plays a paramount role in gravity studies because of the possibility of model discrimination based on stress states. A variety of evidence is reviewed, and it is concluded that the finite strength of the terrestrial planets is unlikely to exceed a kilobar when subject to loads over long geologic periods. Isostasy plays a dominant role in any discussion of the lithospheric contribution to planetary gravity fields. Since it tends to minimize stresses, it is a basic state to be expected, and most useful discussions of the gravity fields are centered on departures from the isostatic state, either due to dynamic forces or to finite strength. For the earth the long‐wavelength anomalies arise largely from beneath the lithosphere and are related to mantle flow. Apart from the obvious correlation of gravity to the plate boundaries, the specific relationships between the gravity field and relevant flow parameters are complex, and there are at present no systematic relationships established between geophysical observables in the intraplate regions. On the moon, most of the contributions to the gravity field arise from the lithosphere and are supported by the finite strength of that layer. The mascons are due to a combination of several kilometer thick basalt layers and crustal collapse at the time of impact, forming ring structures and mantle uplift. Mars appears to be intermediate between the earth and moon and is dominated by the Tharsis anomaly, with the possibility that gravity anomalies arise from both lithospheric and sublithospheric regions. If the Tharsis Province is supported entirely by the lithosphere, then stress levels are of the order of 1 kbar, even with isostasy, which may imply partial dynamic support. Preliminary analysis of Venus gravity data suggests a power spectrum grossly similar to that of the earth, but systematic discrepancies among some harmonics may indicate differences in the nature of interior processes for the two planets. In particular, there appears to be a higher correlation of long‐wavelength gravity with topography for Venus.
A new look at the seismic velocity structure of the oceanic crust
Authors: Spudich Paul , Orcutt John
Published: February 2008

Within the last decade a new picture of the oceanic crust has emerged from advances in seismic experimental design, instrumentation, and analysis techniques. In this new picture, layer 2 is a region in which velocity increases rapidly with depth. While there is evidence of finer structure within layer 2, the exact nature of this structure is still poorly resolved. Layer 3 is much more homogeneous vertically than layer 2 and appears to have gentle vertical velocity gradients and occasional low‐velocity zones in νp and νs. Although it has been observed at several sites, the widespread existence of a high‐velocity basal crustal layer is in doubt. The thickness of the crust‐mantle transition has been observed to vary between 0 and 2 km from site to site, and even at flat lying, uncomplicated sites, seismic evidence for lateral heterogeneities on a scale of a few kilometers can be found. This seismic picture of the crust is in good agreement with the seismic velocities of rocks from ophiolite complexes and is consistent with the theoretically expected behavior of seismic velocities in porous, water‐saturated rocks at elevated pressures. A review of velocity results obtained from use of synthetic seismogram modeling techniques is given, and the types of synthetic techniques suitable for marine work are described.
Longitudinal instabilities and secondary flows in the planetary boundary layer: A review
Authors: Brown R. A.
Published: February 2008

Within the past decade, satellite pictures have shown persistent cloud patterns which indicate that the flow in the atmospheric planetary boundary layer is often organized into helical secondary circulations aligned parallel to the mean flow. Theory and observation agree that both convection in the presence of shear and the dynamic inflection point instabilities of the Ekman layer lead to these flow patterns. The observations and theory are reviewed with emphasis on the dynamics‐dominated flow.
Comparison of some methods for the detailed representation of the Earth’s gravity field
Authors: Tscherning C. C.
Published: February 2008

Currently, two types of methods are used for the detailed representation of the earth’s gravity potential, namely, integral formulae and approximation techniques. The theoretical advantages and disadvantages of the methods (or of a combination of the methods) are discussed, and the results obtained are compared. If the methods are judged according to their general applicability, flexibility, and possibilities for obtaining error estimates, then approximation techniques like least squares or minimum norm collocation must be preferred. Integral formulae techniques are, on the other hand, well suited in areas with a homogeneous data coverage.
Local and global gravity field representation
Authors: Groten E.
Published: February 2008

Gravity fields applied in geodesy are usually built up by (1) a global satellite (low harmonics) part obtained from altimetry and/or differential orbit improvement (in the future, satellite to satellite tracking techniques will also contribute), (2) a regional part obtained from conventional terrestrial material, and (3) a local part of ±1‐mGal accuracy. Whenever four‐dimensional considerations are of interest, ±0.001‐mGal accuracy is necessary. The combination of these parts is considered; attention is also paid to the zero‐degree term in view of very accurate modern absolute measurements of gravity. Integral equation solutions dominated by kernel functions such asl−nas well as collocation formulas lend themselves to useful combinations of high‐precision regional and low‐precision global parts where many difficulties arise in practical applications. But no ideal method is available in order to overcome deficient knowledge of the gravity field. Detailed applications of Stokes‐ and Poisson‐type solutions are discussed. In spite of the fact that a lot of local information is averaged out because of its random behavior, valuable information on systematic effects gets lost unless local parameters are incorporated. Model considerations are based on Kaula’s rule of thumb for high harmonics.
Sampling function and finite element method representation of the gravity field
Authors: Schmidt H. F.
Published: February 2008

After introducing the fundamental method of interpolation and approximation of functions using sampling functions, some examples of one‐dimensional models are demonstrated. Then a method of sampling functions for the representation and determination of the earth’s gravity field—based on spherical harmonics and an arrangement of sampling points on a sphere—is described and discussed by investigating its mathematical implication. Additionally, this method is compared with the finite element method, with a view to the interpolation and modeling of the gravity field of the earth.