bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of the Earth's atmosphere on geomagnetically trapped particles
Authors: Walt Martin , MacDonald William M.
Published: February 2008

The motion of energetic, charged particles trapped in the geomagnetic field is reviewed, and the methods of calculating the effect of the ambient atmosphere on trapped electrons and protons are presented. The results of these theoretical considerations are compared with the available experimental data to determine the spatial regions where collisions of the trapped particles with atmospheric constituents govern the long‐term behavior of the particles. It is concluded that during periods of minimum solar activity atmospheric collisions are the most important loss mechanism for electrons in the region L ⪝ 1.25, where L is McIlwain's magnetic shell parameter. Above this region the behavior of electrons is controlled by other, at present unknown, forces. For protons, it appears that the atmosphere controls the loss rate for the spatial region L ⪝ 1.4, although the evidence for this conclusion must be considered tentative at present.
The rotational splitting of the free oscillations of the Earth, 2
Authors: Gilbert F. , Backus G.
Published: February 2008

Rotational splitting parameters for a large number of low‐order spheroidal and torsional free oscillations of the earth are computed. These results show that rotation introduces serious errors in estimates of density, Lamé parameters, and dissipation obtained from the free oscillations. Methods of correcting for these rotational effects are discussed.
Interfering waves at the surface of an elastic inhomogeneous sphere
Authors: Buldyrev V. S. , Lanin A. I.
Published: February 2008

If a harmonic surface source of SH is applied to a homogeneous sphere, the body waves can be found by ray theory. Attention is focused on the body waves which undergo multiple reflections at shallow angles at the surface of the sphere. When the order of the reflections becomes large, these reflected waves interfere and are identified as surface waves. The surface waves can be computed from the body waves by an application of Watson's lemma and the saddle point method of integration. The extension to an inhomogeneous sphere is not difficult formally.
The gamma‐ray spectrum of the Sun
Authors: Dolan Joseph F. , Fazio G. G.
Published: February 2008

The γ‐ray spectrum (hν > 10 kev) emitted by the sun is investigated and approximate fluxes at the earth are predicted on the basis of a simple solar‐flare model. The object of this paper is to determine what new information about the sun and, in particular, solar flares we can learn from the detection of this radiation. We also investigate which part of the spectrum is most feasibly detectable and which part yields the most direct information on solar‐flare structure. Our calculations indicate the following sources of γ radiation from the sun. The γ radiation emitted by the quiet sun is negligible compared with emission during a solar flare. The most important emission mechanism in the 10‐kev to 1‐Mev energy region is bremsstrahlung by flare‐accelerated electrons. The photon spectrum is continuous and decreases monotonically with energy. Flare‐accelerated protons will interact with carbon, nitrogen, and oxygen nuclei by inelastic scattering and spallation reactions, producing γ radiation as a result of nuclear de‐excitation. Little effort has been made to detect this line emission. Neutrons resulting from spallation reactions will be partially captured by protons to produce deuterium and 2.23‐Mev γ radiation. The intensity of this line emission is proportional to the neutron density in a flare. Line emission at 0.51 Mev results from positron‐electron annihilation. Positrons are produced by β decay of radioactive nuclei generated by spallation reactions and by the decay of π+ mesons produced in proton‐proton reactions. The primary source of photons with energy greater than 50 Mev is the decay of π0 mesons, which are also produced in proton‐proton reactions. The intensity of these photons is very sensitive to the accelerated proton spectrum in the flare. Flux estimates indicate that the detection of γ radiation resulting from a solar flare is feasible and would yield information on nuclear reactions as well as on the intensity and spectrum of high‐energy protons and electrons.
Advances in particles and field research in the satellite era
Authors: Hess W. N. , Mead G. D. , Nakada M. P.
Published: February 2008

The last six years have seen a rapid progress in the exploration of extraterrestrial phenomena. This paper gives a survey of the more important results from investigations of energetic particle radiations, plasmas, and magnetic fields in space. One of the highlights of these investigations was the discovery and study of the continuous flow of plasma away from the sun, the so‐called solar wind. This plasma flow confines the earth's magnetic field within about 10 RE on the day side and is responsible for the magnetospheric tail, which is thought to extend beyond the orbit of the moon. Inside this cavity, large fluxes of magnetically confined energetic charged particles were discovered. Confinement lifetimes in the tail have not yet been established; however, out to roughly 8 RE the particles are trapped and constitute the Van Allen radiation belt. The study of the solar cosmic rays that accompany some solar flares is enhancing our understanding of solar processes and of the interplanetary medium through which the solar protons travel. Continued investigations of cosmic rays are leading to a better knowledge of the heavy particle component, of the low‐energy end (below 100 Mev) of the spectrum, and of the processes responsible for Forbush decreases. On the basis of these discoveries, a new picture is emerging of our environment and, more generally, of the processes in the solar system.
Compilation of deep crustal seismic refraction profiles
Authors: McConnell Robert K. , Gupta Ravindra N. , Wilson J. Tuzo
Published: February 2008

More than 1000 deep crustal seismic refraction profiles have been compiled in a standard format which gives the location of the profile, summary of seismic results, topographic and physiographic characteristics, reference to where the full interpretation can be found, and, if available, some information on the gravity anomalies. Several maps are given, showing the depths to the Mohorovicic discontinuity as determined from these profiles.
Anelastic properties of the Earth
Authors: Gordon Robert B. , Nelson Carl W.
Published: February 2008

Known mechanisms of internal friction in crystalline materials are examined to find which are likely sources of seismic attenuation in the earth's mantle. Presently available laboratory data on rocks are not useful for this purpose because of the low temperatures and pressures at which they have been determined, but experiments on sintered oxides indicate the important damping mechanisms at high temperature. The sources of seismic attenuation in the order of their probable importance are viscous grain boundary damping, stress‐induced ordering, and dislocation damping. If any parts of the mantle are partially melted, stress‐induced flow of fluid through inter‐granular channels may also cause attenuation. These damping mechanisms characteristically result in internal friction showing a strong frequency dependence. Scattering is almost certainly not an important source of seismic attenuation. The variation with depth of internal friction due to a thermally activated relaxation mechanism is found, and it is shown that such a source of internal friction can account for existing data on the anelasticity of the earth. The low attenuation observed at depths below about 500 km can result from the effect of pressure in decreasing atomic mobility; the observed attenuation decrease is therefore not in itself evidence of a phase change. The relation between damping and the strength of the mantle is developed, and it is shown that seismic attenuation data do not put useful bounds on this quantity.
An analysis of lunar events
Authors: Middlehurst Barbara M.
Published: February 2008

Recently, well‐substantiated reports of color changes and other evidence of lunar activity have led to increased interest in the possibility that the moon is not entirely inert. About 400 events, most in the 18th, 19th, and 20th centuries, are analyzed from the following points of view: (1) type of event; (2) relative frequency and duration; (3) lunar phase; (4) correlation with solar activity; (5) position in the lunar orbit around the earth; (6) positions on the face of the moon of the sites of the events. Evidence is presented suggesting that the onset of a lunar event may be associated with disturbance of the lunar crust. A correlation with lunar tides has been found; the distribution of sites over the lunar surface is consistent with a hypothesis of disturbance of the surface layers through internal causes. Physical conditions in the lunar surface layers are, however, unknown; therefore many uncertainties remain.
Ionospheric ion‐molecule reaction rates
Authors: Ferguson Eldon E.
Published: February 2008

The current status of laboratory measurements of ion‐molecule reactions of ionospheric relevance is reviewed. Rate constants for the atmospheric loss reactions of He+, O+, and N2+ appear to be established to within about a factor of 2 at 300°K. The laboratory rate constants for O+ and N2+ ion loss are compatible with quiet midlatitude E‐ and F‐region requirements. The He+ loss reactions appear to be higher than is compatible with some He+ concentrations observed; however, the laboratory rate constants have been measured by so many investigators that they are unlikely to be seriously in error. In the D region, on the other hand, many of the important reactions are as yet unmeasured. Measurements of the relevant negative ion reactions with neutrals have only recently been started. No in situ atmospheric negative ion composition studies have as yet been carried out to guide the laboratory investigations. Many positive ion reactions of importance in the D region (as well as in sporadic E layers) remain to be measured. Finally, very little information concerning reactions of excited state ions with neutrals has been obtained. This will be important for certain disturbed ionospheric conditions and possibly for a precise analysis of normal ionospheric conditions, when this is merited.
Ionization rates due to the attenuation of 1‐100 Å nonflare solar X rays in the terrestrial atmosphere
Authors: Swider W.
Published: February 2008

Solar fluxes and absorption cross sections are reviewed for 1‐100 Å X rays. Review of the cross sections is extended to 300 Å to more completely validate the cross sections selected at shorter wavelengths. Convenient lists of the solar flux and appropriate cross sections are provided, and simple accurate formulas are given for them. Numerical rates for q, the total ion‐pair production rate, are tabulated for three nonflare solar conditions at various altitudes and solar zenith angles. Production rates due to other ionization sources important at these altitudes and angles are also tabulated. We show that q is distributed as 0.62∶0.17∶0.14∶0.07 for q(N2+)∶ q(O2+)∶ q(N+)∶q (O+) for 1‐100 Å X rays absorbed in normal composition air. The atomic ions result from dissociative ionization, mainly by photoelectrons. About half of these atomic ions are converted immediately into NO+ ions at the altitudes where 1‐100 Å X rays are absorbed, the E and D regions. Preliminary evidence, concerning excited ions directly formed during the atmospheric attenuation of 1‐100 Å X rays, suggests that the ions are ineffective as regards the ultimate ionic composition of the lower ionosphere as compared, for example, with NO+ + e → N + O. This major neutralization process allows atomic nitrogen to be formed in the ²D state. No survey of excited neutrals formed by the X‐ray photoelectrons was undertaken.
Large‐scale atmospheric energetics in the wave‐number domain
Authors: Saltzman Barry
Published: February 2008

Observational studies of the atmospheric energy cycle involving large‐scale components of the general circulation, as measured by wave number around latitude circles, are reviewed. The relevant equations are set down in full form for a closed global system. All pertinent observational studies of the terms arising in these equations are listed chronologically, and the results of the most comprehensive of these studies are displayed in energy flow diagrams for winter and summer average conditions. The need for further work is suggested by the imbalances and omissions and the inadequacies of data coverage.
Wave propagation in a periodic medium with application to the ocean
Authors: Rhines P. B.
Published: February 2008

The problem of linear wave motion in a medium with sinusoidal spatial variations is considered. For properties with small enough variation (measured by the parameter q), a Mathieu equation is often obtained; a full dispersion relation is constructed, which includes resonant (linear) interaction between two waves aided by the medium. Gaps (the classic ‘stopping bands’ of Brillouin) appear in the dispersion curve, implying that no solutions, everywhere finite in an unbounded medium, exist within certain bands of frequency. Various combinations of normal modes exhibit temporal and spatial modulations; the spatial modulations represent trapping of wave energy in a band lying along contours of the medium. This feature was anticipated by O. Phillips with a qualitative argument. The simple analysis also encompasses the approaches to exact resonance. If the wave numbers are detuned by a fraction q, for example, the energy transferred between waves is reduced by 9/10. Solutions in the ‘forbidden’ band of frequencies, appropriate to a bounded medium, are given. The wave field is then confined to the neighborhood of a fixed or moving wall. Three examples relevant to the ocean are considered: internal gravity waves in a sinusoidal shear flow (for large Richardson number), long gravity waves over a sinusoidal bottom (for small fractional depth changes, δ) and Rossby waves over a sinusoidal bottom (for small δ/λ, where λ is the frequency in cycles per day, itself small).
Smoothing, filtering, and boundary effects
Authors: Shapiro Ralph
Published: February 2008

Numerical integrations of finite‐difference analogs of systems of nonlinear partial differential equations, such as those arising in atmospheric dynamics, are subject to computational instability from a variety of causes. One type of instability is produced by a spurious, nonlinear growth of high‐frequency components that may be introduced by roundoff, truncation, and observational error. This type of instability, first discussed by N. A. Phillips, can be suppressed by a suitable choice of finite‐difference method or by the use of a filter that selectively damps the high‐frequency components. Though much effort is being devoted to the development of stable finite‐difference procedures, and considerable success has been achieved, all such methods involve high‐frequency smoothing either implicitly or explicitly. It is therefore important that the effects of such filtering be fully understood. Filtering and smoothing operators are developed for use in conjunction with the numerical integration of nonlinear systems and for other purposes. The general procedure is demonstrated for simple one‐dimensional operators and the properties of such operators are thoroughly explored. The development is then expanded to allow for compound operators designed to suit some particular requirement and further extended to more than one dimension. Both real and complex operators are discussed. Reverse smoothers or wave amplifiers are introduced, and some of the problems associated with their use are discussed. A general procedure is outlined for the construction of an ‘ideal’ low‐pass filter; that is, a filter that removes the shortest resolvable wave component (the 2‐grid‐interval wave) but restores all other wave components as close as is desired to their original amplitudes without amplifying or changing the phase of any wave component. Finally, the effects, sometimes disastrous, of finite domains on the properties of the smoothing operators are explored for a variety of common boundary assumptions.
Seismic radiation from explosions in prestressed media and the measurement of tectonic stress in the Earth
Authors: Archambeau Charles , Sammis Charles
Published: February 2008

The radiation field from explosions in a prestressed medium can be theoretically predicted on the basis of a dynamical theory of stress relaxation in the vicinity of the shock‐induced fracture zone created by an explosion. The field consists of the normal compressional wave field resulting from the conversion of the shock wave to an elastic wave plus an anomalous part due to the release of strain energy. In this study we consider the nature of the radiation field to be expected from such a source in an inhomogenous earth and determine the stress field required to explain the observations from a large underground explosion. The field is described in terms of radiation patterns as functions of frequency or alternately as the amplitude and phase spectrums at particular distances. These theoretical predictions are compared to the Love‐ and Rayleigh‐wave radiation patterns and spectra from the nuclear explosion Bilby. Using the known source parameters, we obtain agreement between the observed radiation patterns and the predicted patterns for a pure shear prestress field equivalent to a shear couple oriented approximately N10°W. Using the amplitude spectrum of the observed field adjusted for propagational effects, we find that the prestress was 70 ± 20 bars in the source area. We conclude that this approach can be utilized as a means of systematically measuring the stress field of the earth.
Sliding motion of glaciers: Theory and observation
Authors: Kamb Barclay
Published: February 2008

The sliding motion of glacier ice over bedrock, which contributes about half the flow velocity of temperate glaciers, is analyzed for arbitrary bedrock topography of low roughness. Fourier‐analyzed topography is represented by a roughness spectral function ζ(h, k) defined in terms of the mean square topographic amplitude. From an essentially exact solution of the sliding problem for linear ice‐flow rheology, an approximate solution for the actual nonlinear rheology is built on the assumption that the second strain‐rate invariant depends only on distance from the ice‐bedrock contact. The transition wavelength λ0 between regelation and plastic flow, constant in the linear theory, is replaced in the nonlinear theory by a velocity‐ and roughness‐dependent parameter λα that plays a similar role. Detailed results are given for three special types of ζ(h, k): (1) white roughness (|ζ| constant); (2) truncated white roughness (|ζ| constant for all wavelengths above a certain lower limit); (3) a single wavelength; and (4) cross‐corrugated sinusoidal waves. The results are tested against field observations of sliding. Given sliding velocity υ, basal shear stress τ, and rheological parameters, the theory predicts roughness values ζ for the different types of ζ(h, k). When compared with ζ values inferred from observed bedrock outcrops, predicted values for white roughness are somewhat too small, whereas for white roughness truncated at 3.53 meters, they are of the expected size (ζ ∼ 0.05). Predicted λα values range from 3 to 112 cm; high υ (>20 m yr−1) generally gives λα in the range 10–40 cm, and low υ (<6 m yr−1) 30–70 cm. The predicted thickness of the regelation layer (1–10 mm) agrees with observation, but the predicted λα values appear to be somewhat too small. Extensive separation of the ice sole from bedrock, due to tensile stresses set up in sliding, is predicted in icefalls, whereas for valley glaciers little separation is predicted, unless meltwater under a head of pressure comparable to half the glacier thickness has access to the bed. Extensive separation is not needed to account for typical sliding velocities, provided that the roughness spectrum is truncated. Observed features of glaciated bedrock indicate truncation, which results from glacial abrasion. For the truncated spectrum, the predicted dependence of υ on τ is much more highly nonlinear than for the full white spectrum; this implies a relatively high sensitivity of sliding velocity to changes in glacier thickness or surface slope.
New polar magnetic disturbances: Sqp, SP, DPC, and DP 2
Authors: Nishida A. , Kokubun S.
Published: February 2008

The analyses that have led to the finding of a new polar magnetic disturbance are reviewed, and a unified picture is presented. Although the new disturbance has been reported under various names, an essential common feature is that the disturbance does not originate from the auroral electrojet. The high correlation observed between the disturbance and the orientation of the interplanetary magnetic field suggests that the disturbance reflects a basic interaction process between the solar wind and the magnetosphere.
Geomagnetic field distortions and their effects on radiation belt particles
Authors: Roederer Juan G.
Published: February 2008

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 all changes occur slowly, i.e., adiabatically).
Bombardment of the polar‐cap ionosphere by solar cosmic rays
Authors: Zmuda A. J. , Potemra T. A.
Published: February 2008

Solar flares often produce bursts of energetic particles (mainly protons but also heavier nuclei and electrons). Protons from these flares with energies greater than about 0.8 Mev are of interest because they enter the earth's atmosphere at polar latitudes and produce ionization below 90‐km altitude at a rate that far exceeds the ionization rate due to normal solar and galactic sources. This increased ionization produces many interesting ionospheric effects. Comparison of ion and electron concentration profiles in the lower ionosphere (specifically in the D region) with inferences drawn from both ground‐based radio data and satellite particle data lead to the conclusion that the ion chemistry at such times is much simpler than during undisturbed times. The diverse methods seem to be compatible in defining major characteristics and reactions of the D region during periods when it is bombarded by solar‐flare protons. Thus these events provide the framework for a detailed investigation of D region chemical processes.
On what ionospheric workers should know about the plasmapause‐plasmasphere
Authors: Carpenter D. L. , Park C. G.
Published: February 2008

Recent research on the structure and dynamics of the magnetospheric thermal plasma indicates that the vast region above an altitude of ∼1000 km rivals the underlying ionosphere in complexity and that it is coupled to the lower region in complicated, physically important ways. An example involves the relation of the electron content of magnetospheric tubes of ionization to the electron content of the regular ionosphere. Tube volume between ∼1000 km and the magnetic equator varies rapidly over a relatively small range of tube end point latitudes, which gives rise to correspondingly rapid variations with latitude in coupled effects that involve interchange of ionization between the upper and lower regions. In the past, some correlative studies involving the plasmapause have been hindered by lack of information concerning (1) the unsteady nature of the process by which the disturbed‐time plasmapause profile is established and (2) the fact that at most times and at most locations the plasmasphere‐plasmapause system is in a state of recovery. A series of equatorial density profiles is shown to illustrate the reduction of plasmapause radius during brief periods of increased disturbance and the recovery of the plasmasphere by various processes, particularly by filling from the underlying ionosphere. A number of research results are presented as part of a ‘quick‐reference guide’ to the plasmasphere. To the ionospheric observer, the plasmapause should appear to have a complex but generally predictable geometry as well as characteristic motions. A crude predictor of plasmapause L value (Lpp) in the post‐midnight period as a function of magnetic disturbance is the formula Lpp = 5.7‐0.47Kp, where Kp is the maximum 3‐hour Kp value in the preceding 12 hours. A ground station at L ∼ 3.7 is recommended as optimum for observation of plasmapause‐associated effects directly overhead. The plasmasphere is regularly perturbed by substorm‐associated convection electric fields, and these apparently have important effects on the nightside ionosphere at middle latitudes. Other known departures of the plasmasphere from corotation are expected to have their counterparts in the ionosphere.
Magnetospheric substorms: Some problems and controversies
Authors: Vasyliunas V. M. , Wolf R. A.
Published: February 2008

This description of the present status of work on magnetospheric substorms is based on the talks and discussions that occurred at the Rice University‐AGU Conference on Magnetospheric Substorms. Various types of new data were presented, including, for example, Isis 2 scanning photometer observations of the aurora from above and lunar shadowing observations made from the Apollo 15 subsatellite. The subject of greatest controversy at the conference was the substorm growth phase: gaps in the network of ground magnetometer stations can result in the expansion phase of one substorm being mistaken for the growth phase of another, and there was considerable debate over whether this observational ambiguity could invalidate popular ideas about the growth phase and its signatures. Correlations between magnetospheric phenomena and the direction of the interplanetary magnetic field constituted another area of considerable discussion: the picture appears complicated, with different magnetospheric phenomena correlating with different components of the interplanetary magnetic field. Two areas in which previous controversies have been closed for some time now are the question of whether the magnetosphere is open or closed and the general pattern of the average magnetospheric electric field: it now seems generally agreed that there is direct connection between interplanetary and magnetospheric magnetic field lines, although the details of the connection process remain uncertain, and electric‐field measurements from balloons and satellites have convincingly verified the existence of systematic magnetospheric convection, with dawn‐to‐dusk electric fields over the polar caps. A variety of theoretical approaches to the substorm problem are being pursued, with, as yet, no commonly accepted unifying concept.
Measurement of electric charge of cloud droplets, drizzle, and raindrops
Authors: Takahashi Tsutomu
Published: February 2008

The purpose of this review is to survey recent work on the electricity of cloud droplets, drizzle, and raindrops and, in particular, to describe the instruments used in such observations. The review begins with a number of basic definitions and key questions in this area of cloud physics. A detailed description of instruments for the measurement of drop size and charge, both at the ground and in clouds, follows. The third section presents and interprets some of the data gathered with these instruments. We then sketch ongoing attempts to observe the charge distribution of the particles in relation to the cloud life cycle and to determine the size range of the particles that constitute the main charge carrier in the cloud. We conclude with a statement of three current goals of investigation.
Martian dust storms
Authors: Gierasch Peter J.
Published: February 2008

A brief survey is presented of observational evidence and theoretical speculations concerning Martian dust storms. The observations fall into two major classes: earth‐based photographic records and Mariner 9 infrared spectra. Among the conclusions reached are that: the mechanism for loss of particles from the atmosphere is not Stokes‐Cunningham fallout, more experiments are necessary in order to reach an understanding of injection processes, observations of storm genesis from Mars orbit will probably be necessary to distinguish between different theories of storm dynamics.
Stable isotope geochemistry
Authors: Taylor Hugh P.
Published: February 2008

This review is intended principally to be a reasonably comprehensive bibliography. It covers papers by workers in stable isotope geochemistry in the United States that have been published or presented at national meetings since the last quadrennial report. The titles of the papers in the bibliography are in most cases indicative of the general content, so only the highlights are described below.
Mesozoic reversal sequence
Authors: Larson Roger L. , Helsley Charles E.
Published: February 2008

Research directed toward the development of a magnetic polarity reversal sequence for the Mesozoic has been very active during the past few years, having been stimulated by the successful delineation of a polarity reversal sequence for the Tertiary by Heirtzler et al. [1968]. This research naturally divides itself into two parts: (1) the study of the magnetic record preserved in the oceanic crust and observed as anomalies of the earth's magnetic field and (2) the magnetic record preserved in individual igneous and sedimentary rock units and observed by paleomagnetic techniques. Both aspects of this work are made more difficult by the incomplete preservation of the record which has been locally destroyed by hiatuses or by subsequent tectonic activity. Thus it has been necessary to patch together a record that has been developed independently at many different localities. The sea floor record is now fairly well known back to 153 m.y. (Late Jurassic), and studies on land‐based sections and DSDP cores have resulted in the development of polarity reversal sequences for the latest Late Cretaceous, the Late Jurassic, and the Early and Late Triassic. The following discussion summarizes and attempts to integrate the two diverse data sets.
Core motions and the geodynamo
Authors: Busse F. H.
Published: February 2008

Although the earth's core represents only about one sixth of the earth's mass, it is the origin of a variety of geophysical phenomena. By far the most important is the phenomenon of geomagnetism. It is generally accepted today that the earth's magnetic field is generated by motions in the liquid outer core. The dynamo theory of geomagnetism has become one of the most active areas of mathematical geophysics in recent years. Other phenomena related to motions in the core are the wobble of the earth and the changes in the length of the day that occur on a time scale of the order of a decade. In the following discussion, recent progress in the dynamics of the core and the origin of geomagnetism will be reviewed. In general the attention can be restricted to the past 3 years, since the article by Cox and Cain [1972] has reviewed nearly all the literature through 1971.
Theoretical seismology
Authors: Richards Paul G.
Published: February 2008

An outstanding achievement of the last 4 years in U.S. research into theoretical seismology is the identification of how much information (about earth structure) is contained in a given set of seismic data. This work, an extension of earler successes in inverse theory, should find wide application in other branches of physical science and in the biological sciences. Advances have also been made in studies of the effect of lateral heterogeneities on short‐period waves, the theoretical effect (on seismic waves) of departures from the usual laws of isotropic linear elasticity, the spectral content of short‐period waves by using maximum entropy methods and homomorphic deconvolution, and the use of finite difference and finite element codes. A beginning has been made in the study of wave scattering in random media. These research fields are all fairly new in relation to the traditional occupation of generating theoretical seismograms in ever more complex earth models, assumed to be spherically symmetric; this classical endeavor too has seen breakthroughs in the last 4 years. Seismic source theory, now taking probably more than half the research effort of theoreticians, is reviewed in a separate report.
Project Famous
Authors: Heirtzler J. R.
Published: February 2008

A National Academy of Science workshop held in January 1972 outlined a number of timely studies that could be made of the Atlantic Ocean floor. One recommended study was a detailed multidisciplinary investigation of the axis of the Mid‐Atlantic Ridge. Toward that end, plans, initially begun earlier by institutions in France and the United States, were finalized and put on a viable funding basis, and the project was called Famous (French American Midocean Undersea Study).

The purpose of this project was to study and understand the geological and geophysical processes operative at the axis of the Mid‐Atlantic Ridge spreading center. Broad regional surveys were made with more detailed, smaller area surveys following. A number of specialized surface and deep‐towed instruments were employed. These included the Scripps deep tow fish, accurately navigated dredges, photographs, water temperature sensors, and heat flow instruments. Special large area bottom cameras were employed. Contour charts of about 10 km were made of the bottom by using narrow beam echo sounders. A sonar side scan image of the whole area was made with a powerful surface‐towed side scan device. Bottom seismographs and accurately tracked surface sonobuoy arrays were used to study natural seismicity and to undertake refraction experiments. The final study was made by specially trained scientific divers in manned submersibles in the summer of 1974. In the study area, which was a section of the rift valley southwest of the Azores, 47 dives were made to the inner rift valley floor.
Analytical and numerical studies of ocean circulation
Authors: Reid Robert O.
Published: February 2008

This report, while concerning primarily those analytical and numerical models of quasi‐steady circulation of the oceans and adjacent seas, also recognizes similar important studies pertaining to lakes, estuaries, and the continental shelf. (Note, however, that coastal upwelling studies are covered in a separate report.) The accompanying bibliography includes representative papers from abroad as well as from the United States. Several review papers are included with the new contributions, published since the beginning of 1971; moreover, the list includes some papers that this reporter is aware of which will be published in 1975. Several of the latter, although carrying the date 1975, are papers presented at the Symposium on Numerical Models of Ocean Circulation which was held in October 1972, at Durham, New Hampshire; the proceedings will appear as a publication of the U.S. National Academy of Science.
A report on the continental shelf circulation and coastal upwelling
Authors: Niiler Pearn P.
Published: February 2008

The bathymetry and hydrography of the coastal regime of continents are a complex maze which belies their physical description in simple shapes and coherent water masses. Each river outflow, shelf canyon, bay, harbor, and sandbar has its distinct character and depending on a variety of atmospheric conditions, is bordered by a distinct water mass. The shallow beach zone has been a region of intense study which has been led by coastal engineers for several decades. In reviewing the advances in research in coastal oceanography it is heartening to find that a significant body of unifying ideas and models for the deeper continental shelf emerges. This indeed must be inevitable because the dynamic structure of the oceanic water mass is constrained by Newton's laws of high Reynolds number and the second law of thermodynamics of high Peclet number in which the variety of local conditions become hydrodynamically similar. However, such an overview has been a long time coming in the United States because only in the past 10 years have direct observations of continental shelf water motions been made in a manner by which the variability of the hydrodynamic regime on the shelf can be clearly documented. The most significant advance is that coastal oceanographers have begun measuring, describing, and modeling the long‐wave shallow water turbulence on the continental shelf. Past interpretation of sea surface and sea bed drifter statistics and the classical hydrographic file implies that the synoptic continental shelf circulation patterns are a morass; however, a more focused picture emerges from long time series of direct current measurements, closely spaced and frequently sampled hydrographic surveys, and infrared and color satellite imagery. It is found that continental shelf circulation principally varies with the (1) local variations in the atmospheric wind stress and thermohaline forcing on both synoptic and seasonal time scales, (2) eddies and long waves which impinge from the deep sea, and (3) tidal phenomena.
Weather‐climate modification
Authors: Mordy Wendell A.
Published: February 2008

Although modern efforts to modify weather date from 1946, the field of weather modification is separately described in this quadrennial report for the first time. Nevertheless, the scope of the remarks which follow is confined, insofar as possible, to developments from 1971 to 1974; for those outside meteorology, attention is drawn to several works which describe the background and early work in the field [McDonald, 1958; Mason, 1961; Battan, 1969; Droessler, 1972; Hess, 1974].

During the past 4 yr, activities in this field have come to embrace studies of what has happened or is happening to the weather and climate as a result of human activities not intended to alter the weather, as well as experiments and operations designed to alter atmospheric phenomena. Furthermore, in addition to physical and technical studies of deliberate and inadvertent weather modification by meteorologists, mathematicians, physicists, chemists, and engineers, many concurrent investigations have recently been undertaken of the implications of weather modification, involving the fields of geography, ecology, economics, law, political science, and sociology. The latter endeavors are ultimately for the purpose of providing guidance in the formulation of public policy in regard to weather modification, which can have profound implications for society under modern population and technological conditions. While some sort of ‘atmospheric management’ is coming to be regarded as a necessity for the future, scientists are beginning to raise questions about the wisdom of projecting climate control as a goal. A recent article weighing the pros and cons of the idea of climate stabilization [Kellogg and Schneider, 1974] concludes that at the least, an important social goal is the development, through interdisciplinary studies, of the ability to understand and anticipate natural, inadvertent, and purposeful climate change and its social consequences.
Advances in magnetospheric physics: Energetic particles
Authors: West Harry I.
Published: February 2008

An account is given of energetic particle research in magnetospheric physics for the time period 1971–1974. Emphasis is on relating the various aspects of energetic particles to magnetospheric processes.
Plasma processes in the expansion of the solar wind and in the interplanetary medium
Authors: Barnes Aaron
Published: February 2008

This article is aimed at reviewing research in plasma processes in the expansion of the solar wind and in the interplanetary medium for the period 1971–1974. However, this report is not a comprehensive review of the field, which would not be in the spirit of this series of reports; in any case, considerations of time and length prohibit such a review article. On the other hand, it would be inappropriate to present nothing more than a bibliography. The middle ground, adopted for this article, is to emphasize those research developments which, in the author's judgment, have been most important in the past 4 years, in addition to a complete bibliography of the field. Obviously, such a policy means that a number of significant papers will not be mentioned in the text. Therefore it is proper to offer a brief explanation of how the emphasis in the text was chosen.
Composition of the solar wind: Present and past
Authors: Hirshberg J.
Published: February 2008

Studies of the elemental, isotopic, and ionic composition of the solar wind are vital to an understanding of the interactions of plasma species both in the solar wind and at its source, the solar corona. Such studies are also of importance to more general problems of solar physics and the history of the solar system. Although the heavier component of the solar wind is much more difficult to observe than the proton component, data have been collected from plasma probes, from lunar foil experiments, and from lunar samples, and the analysis of these data has been undertaken in many studies with unexpected results. Less effort has been devoted to the theoretical understanding of the observations, although it has been well established for many years that the observations cannot be explained by the theoretical models.
Neutron and γ ray emissions from the Sun
Authors: Duggal S. P.
Published: February 2008

The contributions of U.S. researchers made during the period from 1971 to 1974 concerning neutron and γ ray emission associated with solar flares are summarized in this report.

The observations of neutrons from the quiet sun which are important for models of storage of protons in the solar magnetic field have not been included in this report [Heidbreder et al., 1970; Cortellessa et al., 1971; Daniel et al., 1971; Eyles et al., 1971, 1972; Simnett, 1971; Sood, 1972; Lockwood, 1973; Lockwood et al., 1973; Hovestadt, 1973; Moon et al., 1973]. Furthermore, we shall confine this summary to primary emissions only; thus the neutron and γ ray production processes in the earth's atmosphere are not discussed [Armstrong et al., 1973; Klumpar and Lockwood, 1973; Klumpar et al., 1973; Lockwood, 1973; Mendell et al., 1973; Preszler et al., 1974; Reppin et al., 1973a; Dahlbacka et al., 1973; Daniel and Stephens, 1974; Kinzer et al., 1974; Peterson et al., 1973; Seeman et al., 1973; Staib et al., 1973, 1974; Stecker, 1973; Thompson, 1974; Thompson et al., 1973].
Low‐energy solar cosmic rays: A bibliography
Authors: Roelof E. C. , Krimigis S. M.
Published: February 2008

This report has been prepared as a topical bibliography on low‐energy solar cosmic rays, and the following overview is in no sense intended as a review. Rather, we have included in the bibliography and indicated by asterisks recent comprehensive reviews on each main topic. The bibliography itself is the result of culling the journals (1971–1974) in which low‐energy cosmic ray research is customarily published: Geophysical Research Letters, Journal of Geophysical Research, Planetary and Space Science, Reviews of Geophysics and Space Physics, Solar Physics, Space Science Reviews. Articles from other journals are cited, but no systematic search of them was made. We have generally not included articles from topical conferences, since their proceedings are usually not as widely disseminated as are journals and since the work reported is often preliminary in nature. However, these conferences contain a dense concentration of current results, so we include a listing of recent proceedings at the end of this section.
The theory of whistler propagation
Authors: Walker A. D. M.
Published: February 2008

Naturally occurring whistlers provide a powerful ground‐based technique for probing the magnetosphere. The major features of the theory of whistler propagation in ducts in the plasmasphere are well understood. The details of how the whistler propagates upward from its source and excites the duct and how it escapes from the duct and reaches the ground are not so clear. Recent direction‐finding experiments are designed to find the point at which the signal emerges from the lower ionosphere; from this the motion in longitude of the duct in which the whistler has propagated is inferred. It is thus important to understand the propagation of the signal between the duct and the lower ionosphere in order to interpret direction‐finding experiments. Another problem of current interest is the amplification of whistlers. In this paper, existing theoretical understanding of the propagation of whistlers is reviewed. The region between the lower ionosphere and the ducts and the mechanisms of excitation of and leakage from the ducts are discussed. An attempt is made to identify those problems which require solution if the whistler technique is to be used to its full effect.
Advances in atmospheric acoustics
Authors: Brown Edmund H. , Hall Freeman F.
Published: February 2008

We give a detailed review of developments in atmospheric acoustics of the last decade. These developments include new ways to use refractive effects, studies of phase and amplitude fluctuations during propagation of sound along a path, nonlinear effects near high‐powered acoustic antennas, problems related to noise, insights into large‐scale atmospheric processes gained from infrasound, applications dependent on the Doppler frequency shift, and hybrid devices using both acoustic and electromagnetic waves. The introduction of the echosonde approximately 10 years ago results in the considerable emphasis given to advances in active acoustic remote sensing of atmospheric structure.
Tropical waves
Authors: Beer Tom
Published: February 2008

On a flat equatorial beta plane the equations of fluid motion and continuity have low‐frequency wavelike solutions that are separable into vertical and horizontal modes. The horizontal modal structure is the same in the case of a compressible fluid in hydrostatic equilibrium (the usual meteorological case) and in the case of an incompressible fluid under the Boussinesq approximation (the usual oceanographic case), but the vertical modal structure, normally expressed in terms of an equivalent depth, is different in the two cases. The theory of low‐frequency tropical waves (excluding tides) is used to highlight the similarities and the disparities in the oceanographic and meteorological approaches to them. This is followed by a brief review of the observational evidence for the existence of these low‐frequency waves in the oceans, atmosphere, and ionosphere of the tropics.