bluuebunny/crossref_metadata_2025 huggingface dataset:
Lightning electromagnetic radiation field spectra in the interval from 0.2 to 20 MHz
Authors: Willett J. C. , Bailey J. C. , Leteinturier C. , Krider E. P.
Published: February 2008

Average energy spectral densities are presented for the fast transitions in most of the components that produce large radiation field impulses from cloud‐to‐ground lightning: first and subsequent return strokes; stepped, dart‐stepped, and “chaotic” leaders; and “characteristic” cloud pulses. A disagreement in the previous literature about the spectral energy radiated by return strokes at high frequencies is noted and explained. We show that our spectral amplitudes are not seriously distorted by propagation over less than 35 km of seawater, although as much as 45 km of such propagation does appear to produce significant attenuation above about 10 MHz. First and subsequent return strokes produce identical spectra between 0.2 and 20 MHz. The spectra of stepped and dart‐stepped leader steps are nearly identical and are very similar to that of characteristic pulses. The spectra of leader steps also match return stroke spectra above 2–3 MHz after the former are increased by about 7 dB. The shapes of individual spectra do not depend on their amplitude, so the shapes of the average spectra are probably not distorted by the trigger thresholds used in the data acquisition. Return strokes are the strongest sources of radiation from cloud‐to‐ground lightning in the 0.2‐ to 20‐MHz frequency range, although certain intracloud processes are stronger radiators above about 8 MHz.
A model study of the response of mesospheric ozone to short‐term solar ultraviolet flux variations
Authors: Summers M. E. , Strobel D. F. , Bevilacqua R. M. , Zhu Xun , DeLand M. T. , Allen M. , Keating G. M.
Published: February 2008

A one‐dimensional photochemical model and a time‐dependent heat equation which incorporates non‐local thermodynamic equilibrium (non‐LTE) IR radiative transfer are used to study the response of mesospheric ozone concentration to short‐term solar UV flux variations. We compare our model results with the observed ozone response obtained from a statistical analysis of Solar Mesosphre Explorer (SME) data (Keating et al., 1987). Our model with sinusoidal 27‐day‐period forcing of mesospheric chemistry by solar ultraviolet flux, when combined with temperature‐chemistry feed‐back, time‐dependent atmospheric temperature effects, and low eddy mixing rates, reproduces the major characteristics of the observed ozone response but not the observed temperature response. Below 60 km the calculated response shows a strong dependence on the magnitude of the assumed flux modulation in the Hartley region of the spectrum. A comparison of the model O3 response with the SME observations suggests that there is negligible 27‐day variation of solar flux longward of 2400 Å, in agreement with Lean (1987). The magnitude of the computed ozone response to increased solar UV flux in the upper mesosphere (above 70 km) is strongly coupled to the water vapor abundance through the HOx catalytic cycle that removes ozone. Our model predicts the essential aspects of the observed ozone response only when the water vapor mixing ratio and vertical eddy diffusion coefficient are a factor of 5 below observed and inferred mid‐latitude values. But then the model results are in almost complete disagreement with the observed temperature amplitude and phase lag. Calculations performed with imposition of the temperature response observed by Keating et al. (1987) produces an ozone response in the middle mesosphere in severe conflict with observations, suggesting a need for better mesospheric and solar data and further modeling efforts to determine the role of dynamics in the mesospheric ozone and temperature response to solar UV variability.
Possible sources of errors in electrical measurements made in thunderclouds with balloon‐borne instrumentation
Authors: Jonsson Haflidi H.
Published: February 2008

It is possible under some circumstances that the accuracy of data on electrical parameters inside thunderclouds obtained by use of instrumented balloons may sometimes be adversely affected by the balloon platform itself. If the balloon rigging becomes conductive, polarization of the balloon system, corona emissions, and electrical generation of charged water particles may act to alter the parameters that are being measured. Laboratory measurements of conduction currents flowing along nylon monofilaments, sometimes used as insulating supports for instruments carried beneath balloons, revealed a large conductance when the filaments were wet or exposed to high humidity and the ambient temperature was above 0°C. The conductance of a piece of monofilament at high humidity increased by more than 4 orders of magnitude as the air temperature rose from −15°to +20°C. The conductance also depended strongly on the monofilament's surface cleanliness. At 20°C in high humidity, currents of up to 0.3 μA flowed along a piece of monofilament in response to a potential gradient of 2000 V/m. Application of large potential gradients to a monofilament continually wetted, as might be expected as a worst‐case scenario in clouds or rain, produced corona emissions and electrical generation of charged drops. These results indicate that especially in the warmer, lower regions of clouds, currents may flow in the rigging of balloon‐borne instrumentation sufficient to reduce the ambient atmospheric electric fields and to generate a population of artificially charged water particles. In order to ensure credibility of electrical measurements in such situations, it is essential that conduction along the rigging be minimized by the use of hydrophobic materials, and it is desirable that means for monitoring leakage currents be included in the instrumentation.
Benthic foraminiferal δ13C and accumulation rates of organic carbon: Uvigerina Peregrina group and Cibicidoides Wuellerstorfi
Authors: Zahn Rainer , Winn Kyaw , Sarnthein Michael
Published: February 2008

The glacial to interglacial δ13C records of the benthic foraminifera Cibicidoides wuellerstorfi and the Uvigerina peregrina group from deep‐sea cores cannot be adjusted by a generally valid constant. The δ13C values of the U. peregrina group largely correlate with the accumulation rates of organic carbon, suggesting a local "habitat effect"; those of C. wuellerstorfi vary independently with respect to the carbon flux and record fluctuations in the δ13C of the ambient bottom water isotopic composition.
Repeated subaerial exposure of subtidal carbonate platforms, Triassic, northern Italy: Evidence for high frequency sea level oscillations on a 104 year scale
Authors: Hardie Lawrence A. , Bosellini Alfonso , Goldhammer Robert K.
Published: February 2008

Triassic carbonate platforms in northern Italy (Ladinian Latemar, Carnian Durrenstein, Norian Dolomia Principale) consist of hundreds of stacked meter‐scale cycles each made of a subtidal unit with a cap rock that carries vadose cements, pisoids, and tepee structures. These diagenetic caps are interpreted to be due to subaerial exposure of the subtidal sediments. The absence of peritidal deposits rules out progradation as the cause of the exposure; i.e., these are not Ginsburg autocycles. Thus the repeated exposure must be the result of relative sea level oscillations, which, based on the number of cycles and time intervals involved, occurred with an average frequency in the 104 ‐year range. We postulate a combination of small‐scale, high‐frequency eustasy and local tectonic movements (e.g., differential subsidence in the Norian and infrequent pulses of uplift in the Ladinian) to explain the cyclicity and its internal variations.
Paleogene geochronology: An integrated approach
Authors: Aubry M. ‐P. , Berggren W. A. , Kent D. V. , Flynn J. J. , Klitgord K. D. , Obradovich J. D. , Prothero D. R.
Published: February 2008

Geochronology is the conceptual division of continuous time as measured (geochronometry) by the progression in an ordinal series of events. This is best achieved by an approach which integrates four independent data sets: magnetostratigraphy, seafloor spreading magnetic lineation patterns, biostratigraphy, and isotopic ages. This integrated approach results in an ordinal framework which can measure time with greater resolution, though perhaps less accuracy, than a radiometric approach alone. A comparative analysis of two recently proposed Paleogene geochronologic time scales is presented.
Surface water response of the equatorial Atlantic Ocean to orbital forcing
Authors: McIntyre Andrew , Ruddiman William F. , Karlin Karen , Mix Alan C.
Published: February 2008

The response of the mixed layer of the equatorial Atlantic to climate change, for times greater than 10 kyr, is predominantly forced by the precessional component of insolation. A zonal transect of three cores analyzed at 1‐kyr intervals documents this response for 0–250 ka The western equatorial Atlantic is characterized by minimal variation in surface water character, indicating temporal stability of the mixed layer, except during intervals of maximum glaciation. In contrast, the eastern region shows marked temporal variations in estimated sea surface temperature and foraminiferal assemblages, with dominant periodicities centered on 23 kyr. At precessional periods, the eastern equatorial Atlantic responds in phase with southern hemisphere sea surface temperature and significantly leads northern hemisphere sea surface temperature and continental ice volume. These signals are the product of orbitally forced variations in (1) trade wind and monsoon‐controlled divergence and (2) advection of heat from high southern latitudes.
The salinity contrast between the Atlantic and Pacific oceans during glacial time
Authors: Broecker W. S.
Published: February 2008

In today's ocean the salinity of low‐latitude surface waters in the Pacific is on the average 1 per mil lower than in the Atlantic. Oxygen isotope records for planktonic foraminifera suggest that an even larger salinity deficit may have existed for Pacific surface water during glacial time. If so, the transport of water vapor from the Atlantic to the Pacific must have been as strong as or even stronger. To balance the tendency toward salt buildup the Atlantic would have had to export, during glacial time, waters saltier than it received from the other oceans.
Pleistocene evolution: Northern hemisphere ice sheets and North Atlantic Ocean
Authors: Ruddiman W. F. , Raymo M. E. , Martinson D. G. , Clement B. M. , Backman J.
Published: February 2008

We analyze five high‐resolution time series spanning the last 1.65 m.y.: benthic foraminiferal δ18O and δ13O, percent CaCO3, and estimated sea surface temperature (SST) at North Atlantic Deep Sea Drilling Project site 607 and percent CaCO3 at site 609. Each record is a multicore composite verified for continuity by splicing among multiple holes. These climatic indices portray changes in northern hemisphere ice sheet size and in North Atlantic surface and deep circulation. By tuning obliquity and precession components in the δ18O record to orbital variations, we have devised a time scale (TP607) for the entire Pleistocene that agrees in age with all K/Ar‐dated magnetic reversals to within 1.5%. The Brunhes time scale is taken from Imbrie et al. [1984], except for differences near the stage 17/16 transition (0.70 to 0.64 Ma). All indicators show a similar evolution from the Matuyama to the Brunhes chrons: orbital eccentricity and precession responses increased in amplitude; those at orbital obliquity decreased. The change in dominance from obliquity to eccentricity occurred over several hundred thousand years, with fastest changes around 0.7 to 0.6 Ma. The coherent, in‐phase responses of δ18O, δ13O, CaCO3 and SST at these rhythms indicate that northern hemisphere ice volume changes have controlled most of the North Atlantic surface‐ocean and deep‐ocean responses for the last 1.6 m.y. The δ13O, percent CaCO3, and SST records at site 607 also show prominent changes at low frequencies, including a prominent long‐wavelength oscillation toward glacial conditions that is centered between 0.9 and 0.6 Ma. These changes appear to be associated neither with orbital forcing nor with changes in ice volume.
Growth rate variations of manganese nodules and crusts induced by paleoceanographic events
Authors: Segl M. , Mangini A. , Beer J. , Bonani G. , Suter M. , Wölfli W.
Published: February 2008

Time markers at about 3 Ma., 6.5 Ma., and 14 Ma. are common to 16 manganese nodules and crusts from different localities in the world oceans. These time markers correspond to variations in the growth rates, in the inner structure, and in the chemistry of the samples. The observed time markers could be related to (1) changes of the bottom water velocity and (2) variations in the manganese and iron contents in the deep ocean. The time markers were determined by high‐resolution 10Be dating, applying the accelerator mass spectrometry facility at the Eidgenössische Technische Hochschule Zürich.
Lithium‐to‐calcium ratios in Modern, Cenozoic, and Paleozoic articulate brachiopod shells
Authors: Delaney M. L. , Popp B. N. , Lepzelter C. G. , Anderson T. F.
Published: February 2008

Li/Ca ratios in modern brachiopod shells generally correlate inversely with growth temperature, ranging from ∼20 µmol/mol at 30°C to ∼50 µmol/mol at 0°C with no apparent interspecific offsets. Causes of the temperature effect on Li/Ca ratios are not yet understood. Cenozoic brachiopod Li/Ca ratios average ∼30 µmol/mol, similar to the average observed in modern brachiopods. Relatively constant Li/Ca ratios for Eocene to Pleistocene nonluminescent brachiopod shells, consistent with previous observations of Cenozoic planktonic foraminifera, support the conclusion of little variation in Cenozoic seawater Li/Ca. Nonluminescent portions of Permian and Carboniferous brachiopods have Li/Ca ratios substantially lower (generally <10 µmol/mol) than modern, Cenozoic, or Devonian samples. Mass balance considerations, constrained by δ18O of brachiopods, suggest that low Li concentrations in Permo‐Carboniferous seawater could be the result of a lower flux of dissolved Li from the continents and/or a higher flux of Li from seawater to clastic marine sediments. Nonluminescent Devonian brachiopods from a single hand specimen have Li/Ca ratios around 70% of the modern average. These Li/Ca ratios can be explained by either somewhat higher temperature with constant seawater Li/Ca, somewhat lower seawater Li/Ca at constant temperature, or a combination of slightly elevated temperature and slightly lower seawater Li/Ca.
The influence of microhabitats on the carbon isotopic composition of deep‐sea benthic foraminifera
Authors: McCorkle Daniel C. , Keigwin Lloyd D. , Corliss Bruce H. , Emerson Steven R.
Published: February 2008

We report δ13C and δ18O values for Rose Bengal‐stained benthic foraminifera from a set of box cores from continental margin environments in the Atlantic and Pacific oceans. These isotopic results are compared with foraminiferal distribution data and pore water δ13C profiles to evaluate the importance of environmental (microhabitat) effects on the carbon isotopic composition of benthic foraminifera. The δ13C values of infaunal taxa are consistently lower than those of epifaunal taxa, suggesting that microhabitat effects on test composition do exist. The δ13C differences between foraminiferal carbonate and bottom water dissolved inorganic carbon are not correlated with the δ18O differences between benthic foraminifera tests and equilibrium calcite, but they do correlate with variations in the chemistry of sediment pore waters. However, interspecific δ18O differences as well as δ13C differences between species with similar vertical distributions in the sediments indicate that taxon‐specific “vital” effects also influence test composition.
Late Gauss to Early Matuyama invasions of Neogloboquadrina Atlantica in the Mediterranean and associated record of climatic change
Authors: Zachariasse W. J. , Gudjonsson L. , Hilgen F. J. , Langereis C. G. , Lourens L. J. , Verhallen P. J. J. M. , Zijderveld J. D. A.
Published: February 2008

A well‐dated, high‐resolution record of climatic change is presented for the late Pliocene Mediterranean. Principal component analysis on abundances of 14 planktonic foraminiferal species reveals a series of late Gauss to early Matuyama surface water cooling events which can be correlated with North Atlantic glacial isotope stages 108 to 94. The abundance record of the benthic foraminifer Trifarina angulosa suggests lowered bottom water temperatures at times of surface water cooling. The record of surface water oxygen and carbon isotopes shows an inverse pattern with δ18O maxima and δ13C minima at times of cool sea surface temperature conditions. Concomitant decrease in P/B value and increased admixtures of clastic material suggest that late Gauss to early Matuyama surface water cooling events in the Mediterranean are accompanied with glacioeustatic sea level low‐stands. Major surface water cooling events are associated with invasions of Neogloboquadrina atlantica. This North Atlantic mid‐ to high‐latitude species is at 2.55 Ma close to the Gibraltar portal whereafter it could invade the Mediterranean repeatedly during periods of climatic cooling until it disappears from all over the North Atlantic and Mediterranean at the end of glacial stage 96.
Reconstructing tropical Atlantic hydrography using planktontic foraminifera and an ocean model
Authors: Ravelo A. C. , Fairbanks R. G. , Philander S. G. H.
Published: February 2008

In the tropical Atlantic, planktonic foraminfera species are vertically distributed with highest abundances occurring in the photic zone (approximately 0–100 m). The tropical Atlantic thermocline dips from east to west and varies seasonally due to changes in the southeast and northeast trade winds. In the east, the thermocline is in the photic zone, and in the west, the well‐mixed surface layer extends below the photic zone most of the year. As expected from species vertical distributions in plankton tows, the species assemblages on the seafloor are correlated to the hydrographic conditions of the overlying surface ocean layer. A new technique to reconstruct past tropical Atlantic (20°N to 20°S) photic zone hydrography and surface wind field uses faunal assemblage data from deep‐sea cores. Planktonic foraminifera abundances in core tops correlate with observations of modern photic zone hydrography defined here as seasonal temperature variation and mixed layer depth. The hydrography is mathematically described using empirical orthogonal function (EOF) analysis of annual temperature range as a function of depth. Factor analysis of 29 species of planktonic foraminifera from 118 core tops produces three factors. The factors correlate to mixed layer depth and the two EOF modes. The ocean model of the Atlantic ocean produces similar map patterns of the EOF modes. Therefore the model can be used to simulate hydrographic changes to compare with faunal predicted past hydrographic changes. Since the ocean model is wind driven, this approach provides a way of evaluating the validity of estimates of past wind stress changes and the contribution of these changes to the faunal changes in the past. A double wind stress run indicates that the central and eastern equatorial and southeast regions of the study area are most sensitive to wind stress increases. Factor analysis of the foraminifera abundances from the last glacial maximum (LGM) shows that species associations change downcore and demonstrates how the methods developed in this study can be applied. Comparison of the double wind stress experiment and the LGM faunal changes indicates some areas of significant agreement suggesting that faunal changes may reflect thermocline structure response to the LGM wind field. Discrepancies may reflect the fact that uniform changes in the north and south trade wind strengths did not occur at the LGM.
Salinity history of the northern Atlantic during the last deglaciation
Authors: Broecker Wallace S.
Published: February 2008

The claim has been made (see Broecker et al., 1988) that production of North Atlantic Deep Water terminated during Younger Dryas time and that the onset of this termination occurred about 11,000 years ago when the flow of meltwater from a large segment of the southern margin of the Laurentide ice sheet was diverted from the Mississippi to the St. Lawrence drainage. Fairbanks [1989] points out a serious weakness in this argument. Based on a sea level curve derived from radiocarbon dates on coral obtained from borings made off the Barbados coast, he suggests that a lull in the melting of the ice caps during Younger Dryas time may have more than compensated for the impact of the diversion. The purpose of this paper is to reassess the situation regarding the origin of the Younger Dryas in light of this new evidence. Currently the salinity of surface waters in the northern Atlantic is influenced by three fluxes. Water vapor transport from the Atlantic drainage basin to the Pacific‐Indian basin tends to raise the salinity of the entire Atlantic. The excess over evaporation of precipitation and runoff poleward of 40°N tends to reduce the salinity of waters in this region relative to the Atlantic average. The conveyor circulation of the Atlantic trades more salty waters of the Atlantic with less salty waters outside the Atlantic tending to drive down the Atlantic's salinity. The conveyor circulation also flushes the northern Atlantic, pushing its salinity toward the mean for the Atlantic. During the period of deglaciation meltwater emanating from the Laurentide and Scandinavian ice sheets was also important. This flux tended to lower not only the salinity of the entire Atlantic but also the salinity of surface waters in the northern Atlantic relative to the Atlantic's mean. As deepwater formation in the northern Atlantic depends critically on the salinity of surface waters, the interactions among these fluxes can change the strength of the conveyor.
A salt oscillator in the glacial Atlantic? 2. A “scale analysis” model
Authors: Birchfield G. Edward , Broecker Wallace S.
Published: February 2008

A proposal has been made by Broecker et al. (1990) that rapid changes on a time scale of a thousand years or so, seen over much of the last major glacial in the Greenland ice core record, represent significant climate changes and are caused by a salt oscillator in the glacial Atlantic. This proposal is examined in terms of a rudimentary quantitative model. Scale analysis asserts that heat transported to the high‐latitude atmosphere when the thermohaline circulation is turned on, is large enough to produce the melting rates found by Fairbanks (1989) for the time interval around that of the Younger Dryas event and that these melting rates are of the same order of magnitude as the mass flux associated with water vapor flux to the Pacific Ocean estimated by Broecker (1989). Scale analysis also suggests that the salinity fluxes associated with 1) the water vapor flux mechanism, 2) the rapid melting episodes of Fairbanks, 3) possibly ice sheet growth events, 4) net transport by the thermohaline circulation and 5) net transport by turbulent eddy mixing are roughly of the same order of magnitude and therefore may be important mechanisms for producing salinity oscillations on a time scale of a few thousands of years, (see Broecker, 1990). By integration of simple salt conservation equations, it is found that model oscillations with a period of a few thousand years occur over a significant range of salinity fluxes; estimated fluxes fall well within the range for which oscillations exist. The model also suggests that there may exist close coupling between the European‐Scandinavian ice sheets and the bimodal response of the oscillator; that is, significant increases or decreases in continental ice volume may accompany each complete cycle of the oscillator. In addition, it appears that continental ice may be required for the salt oscillator to function. A crucial element, which cannot adequately be investigated with the present model, concerns the local effect of salinity source/sinks associated with melt water production. The proximity of these source regions on the neighboring ice sheets to the local regions where production of deep water occurs may play a critical role in the functioning of the proposed salt oscillator. In addition, further treatment of thermodynamics is needed to investigate the feasibility of a salinity driven oscillator.
Stable isotope evidence for gradual environmental changes and species survivorship across the Cretaceous/Tertiary Boundary
Authors: Barrera Enriqueta , Keller Gerta
Published: February 2008

High‐resolution δ13C and δ18O records have been generated from analyses of the planktonic foraminiferal species Heterohelix globulosa and the benthonic foraminiferal taxon Lenticulina spp from 3 m of a cored section spanning the Cretaceous/Tertiary (K/T) boundary at Brazos River, Texas. These are the first stable isotope records across the K/T boundary based on monospecific and monogeneric foraminiferal samples. They show a gradual decrease in δ13C values of about 2.5 permil beginning at the K/T boundary, as defined by the first appearance of Tertiary planktonic foraminifera, and continuing 17–20 cm above the boundary, approximately 40,000 years later. Gradual 13C depletion contrasts with the sudden δ13C drop at the K/T boundary observed in many deep‐sea sections. The surface‐to‐bottom δ13C gradient decreased to less than zero approximately 25,000–30,000 years after the K/T boundary and remained negative for at least the next 140,000 years. Concomitant with change in δ13C values is a gradual decrease of about 2.5 permil in δ18C values which has not been observed at other localities. This 18O depletion suggests changes in temperature and/or salinity in the earliest Paleocene Gulf of Mexico. No extinction of foraminiferal species is associated with the K/T boundary or the onset of 18O and 13C depletions. Instead, two phases of Cretaceous species extinctions occur. One extinction phase is below the K/T boundary and below the tsunami bed of Bourgeois et al. [1988] and may be linked to sea level regression and environmental perturbations. The second extinction phase coincides with the minimum in δ13C and δ18O values in the Early Danian (Zone P0/Pla) and appears directly related to environmental changes reflected in the isotopic record. H. globulosa, which is commonly present in Maastrichtian and Danian sediments, exhibits significantly lower 18O/16O and 13C/12C ratios in Tertiary sediments relative to specimens from Maastrichtian sediments, demonstrating the survival of this important Cretaceous taxon after the K/T boundary event.
Comets and cometary debris in the solar system
Authors: Beard David B.
Published: February 2008

The orbital behavior, size, surface temperature, and surface vapor pressure of comets are shown to be determined from and by their observed rapid evolution of gas and dust while they are visible. The numerical density and size distribution of the cometary and asteroidal debris that freights the solar system are inferred from solar eclipse observations, and the probable history of the dust particles is reviewed. The erosion of space‐vehicle surfaces by microscopic dust predicted to condense on the planets and space‐vehicle surface penetration by stones are shown to be either nonexistent or easily surmountable problems.
Adiabatic charged‐particle motion
Authors: Northrop Theodore G.
Published: February 2008

The adiabatic theory of charged‐particle motion is developed systematically in this review. We present the essentials of the theory without giving all the analysis in detail. The general expressions for guiding‐center motion and particle energy change are given, with application to the Van Allen radiation and to Fermi acceleration. It is shown that Fermi acceleration and betatron acceleration should not be regarded as distinct processes. Modifications of the nonrelativistic theory that are necessary when the particle is relativistic are discussed. Proofs are given of the invariance to lowest order of the first and second adiabatic invariants for the case of static fields. Finally, applications are made to the theory of plasmas.
The deep structure of continents
Authors: MacDonald Gordon J. F.
Published: February 2008

Gravity and heat flow observations demonstrate that, on the average, mass and radioactivity per unit area are equal under continents and oceans. A global representation of the anomalies in the heat flow and gravity fields shows many similarities, and horizontal gradients in both fields are correlated with earthquake zones. The regional variations of Rayleigh and Love wave velocities provide evidence additional to that of gravity and heat flow that the mantle under continents differs from that under oceans to a depth of 400 to 700 km. Taken together the observations of the planetary fields imply that vertical segregation has been the dominant feature of the process of continent formation. The significance of deep structure of continents and oceans is explored by a number of numerical experiments. The difference in radioactivity between continents and oceans results in a concentration of thermal stresses at the continent‐ocean boundary. The ensuing fault zones provide a preferred location for the release of strain energy accumulated by dynamic processes such as those associated with changes in the earth's rotation. The decay of radioactivity implies a past rate of heat production in excess of the heat loss. During the first two to three aeons, the earth expanded at an average rate of about 10 km aeon−1. The resulting fracturing of the outer surface with accompanying upward flow of matter led to the localization of the early continents. Continental growth proceeded by secular differentiation of the subjacent mantle.
Whistler measurements of electron density in the magnetosphere
Authors: Carpenter D. L. , Smith R. L.
Published: February 2008

It is the purpose of this paper to discuss the whistler method of measuring electron density in the magnetosphere. Particular attention is devoted to certain questions that may have been perplexing to workers outside the whistler field. Profiles of equatorial electron density deduced from whistlers are compared and are found to be in general agreement. Whistler results on the ‘knee’ in the equatorial electron density profile and on values of electron density near 2 earth radii geocentric distance are found to agree with corresponding results obtained by independent methods of measurement.
Low‐frequency electromagnetic oscillations of the Earth‐ionosphere cavity
Authors: Madden T. , Thompson W.
Published: February 2008

The observational and theoretical work on the low‐frequency electromagnetic oscillations of the earth‐ionosphere cavity, known as the Schumann resonances, is reviewed. Additional theoretical considerations are introduced to allow the models to incorporate the asymmetries of the actual cavity. These models are used to explain the observed variations of the power and of the apparent frequency of the resonant modes. The theoretical studies show that the structure of the low D or C region of the ionosphere is critical to these resonances, and the observed frequencies must rule out certain proposed ionospheric models. The perturbations of the cavity are also studied, and comparisons are made between different types of perturbations. The resonance data from July 9, 1962, are used to confirm the tremendous extent of the ionospheric perturbations caused by the Starfish high‐altitude nuclear explosion. The possible effects of natural perturbations are also examined.
Trapped orbits in a magnetic dipole field
Authors: Dragt A. J.
Published: February 2008

This article is a review of the trapped motion of a charged particle in a dipole magnetic field. It provides an extensive discussion of the equations of motion in various coordinate systems and of their solution by approximate and analytically exact methods. Wherever possible, approximate solutions are compared with exact solutions obtained by numerical integration.
Terrestrial and solar neutrons
Authors: Haymes R. C.
Published: February 2008

The study of neutrons in the solar system is reviewed, and the theories and experiments that relate to this study are described. Neutron capture in the atmosphere produces among other isotopes carbon 14 and tritium. The earth's neutron albedo is also a source of Van Allen radiation. The importance of the source is, however, in doubt; therefore, some studies of geomagnetically trapped charged radiation are also reviewed to emphasize the areas of greatest uncertainty in the theory of injection by the neutron albedo. There are conflicting data on the absolute value of the albedo itself, although there is now better agreement on neutron fluxes within the atmosphere. Hence a critical review of the techniques employed in neutron experiments is undertaken, and some possible ways of resolving some of the difficulties are suggested. The search for solar neutrons is also described, and some possible solar‐neutron experiments are suggested. In the study of both Van Allen and solar problems, high‐energy neutrons are most interesting, and yet this energy region is the least explored.
Recent developments in the theory of radiative transfer in planetary atmospheres
Authors: Sekera Zdenek
Published: February 2008

The review of the recent advances made in the western part of the world in the theory of radiative transfer relates to the studies of the only physically realistic models of a planetary atmosphere in which both multiple scattering and polarization are taken fully into consideration. In the mathematical formulation of radiative transfer problems, the meaningful advances have been made in the emphasis on better physical interpretation of the mathematical analysis and of the used parameters that have resulted in the renaissance of the original Chapman's approach, based on a source matrix and on the solution of auxiliary equations for this matrix. This procedure is demonstrated in the derivation of this equation for the inhomogeneous case of imperfect scattering (i.e., the case with absorption and scattering with variable albedo of single scattering within the medium). The integrodifferential equations for the reflection and transmission matrices for this case are presented, and their reduction is demonstrated for the separable phase matrix in which the directional parameters of the incident and scattered radiation can be separated. For such a phase matrix the integrodifferential equations can be reduced to the solution of a pair of integral equations forXand Y matrices that for homogeneous cases assume forms identical to those for the X and Y functions introduced by Chandrasekhar. Considerable advances have been made in the analysis of these functions, especially in the solution of the problem of their non‐uniqueness. With the use of the theory of singular integral equations applied to the nonlinear integral equation for X and Y function, transformed into a singular form, a method has been recently developed that enables rapidly converging iteration for large optical thickness, leading even to asymptotic expressions for large τ. The review is concluded with the list of problems that can be expected to be solved in the near future without great or basic difficulties.
Statistical prediction of earthquakes
Authors: Lomnitz C.
Published: February 2008

Statistical prediction is an extension of Fourier spectrum analysis of time series. Historical attempts at prediction of earthquakes have centered on the question of periodicity. A survey of work in this field is given, both preceding and following critical investigations by Jeffreys. Present evidence indicates earthquakes to be uncorrelated events; observed deviations from the Poisson distribution, previously attributed to dependence in time, may be an effect of spatial inhomogeneity. It is fallacious to infer properties of the earthquake process on the basis of the shape of the distribution function of number of events in time. Some restrictions are shown to apply to the use of direct extrapolation methods in earthquake time series. Multiple prediction is a possibility; however, the actual measurement of geophysical variables for prediction purposes has progressed very slowly. Direct measurements of stresses and strains at depth are needed; values based on the theoretical release of strains by earthquakes are insufficient. Plotting the square roots of earthquake energies yields no specific strain information of predictive value. The estimation of earthquake risks is different, in principle, from the prediction problem. Mathematical techniques are available for risk estimation. A simplified model of the earthquake process is suggested, which may satisfy elementary requirements for purposes of engineering, city planning, and earthquake insurance.
Dilatancy and the seismic focal mechanism
Authors: Orowan E.
Published: February 2008

In a recent paper F. C. Frank suggested that the seismic focal stress drop might by the consequence of a mechanical instability of deformation due to dilatancy of the crust and mantle. A more complete calculation shows that the instability attributed to dilatancy is a familiar general property of compacted granular masses independent of dilatancy. The rapid propagation of the seismic fault attributed to shear melting by elastic energy release would depend on the assumed absence of friction between the walls of an initial Griffith crack. Since the length of the thin Griffith crack was estimated at 5 km, friction could be absent only if the crack were filled with a pore fluid of pressure equal to the total pressure; in this case the shear strength would be zero and seismic shocks could not arise.
Solar wind and interplanetary magnetic field
Authors: Dessler A. J.
Published: February 2008

A brief history is presented of some of our ideas regarding the solar wind. The basic physical principles of supersonic expansion are discussed. An analogy is drawn with the flow of an ideal gas through a rocket‐engine nozzle. Supersonic expansion of a stellar corona requires a stellar and coronal temperature lower than a specified maximum. For temperatures above this maximum, subsonic expansion should result. The thermal structure of the sun is such that only supersonic expanion occurs although subsonic expansion is, in principal, allowed.

The present status of relevant experiments and theory regarding the solar wind and interplanetary magnetic field is discussed. In particular, attention is drawn to a comparison between theoretical predictions and actual measurements. It is concluded that measurements are consistent with theory for the component of field projected on the ecliptic plane. However, a serious discrepancy is noted between theory and experiment with regard to a possible component perpendicular to the sun's equatorial plane.

Wave motion in the solar wind is discussed briefly. It is shown that, under certain conditions, relative wave amplitudes should grow with increasing heliocentric distance.

Finally, ideas concerning the ultimate fate of the supersonic solar wind are reviewed.
Measurement of gravity at sea and in the air
Authors: Lacoste Lucien J. B.
Published: February 2008

General problems of gravity measurement at sea are discussed. A treatment of the effects of vertical accelerations shows that gravity meter nonlinearities cause errors that ordinarily are proportional to the square of the vertical acceleration. In a treatment of horizontal accelerations, similarities and differences that exist between gimbal supported and stabilized platform gravity meters are pointed out. It is shown that optimization of the parameters of a stabilized reference can reduce gravity meter errors by two or more orders of magnitude at long periods. A method for correcting for inadequate period of a stabilized reference is given. The Schuler‐tuned stabilized platform is briefly described. The theory of inherent type cross coupling and examples of imperfection type cross coupling are given.

Theory and significant details of construction are given for the LaCoste and Romberg (L&R) gravity meter and stabilized platform. Tests on L&R air‐Sea gravity meters made during the last decade are discussed. The largest error in earlier work is shown to have been due to vertical accelerations. A method of correcting for these errors is described. Tests indicate that presently attainable accuracy of L&R gravity meters is appreciably better than 1 mgal.
Low‐frequency waves in the magnetosphere
Authors: Helliwell R. A.
Published: February 2008

In the magnetosphere are found low‐frequency (100–100,000 Hz) electromagnetic waves generated externally by lightning and ground‐based transmitters and internally by energetic charged particles. Dispersion and anisotropy characterize the medium, and both ducted and nonducted paths of propagation are found. Lightning‐generated ducted ‘whistlers,’ observed on the ground, give information on the distribution of electrons and the latitudinal drift motions of ducts in the magnetosphere. Nonducted whistlers observed in satellites give information on electron and ion concentrations, the earth's magnetic field, and wave damping by energetic particles.

Noise generated in the magnetosphere (or ionosphere) includes steady noise, or hiss, and the structured forms known as discrete emissions. In the auroral zone, hiss is seen in close association with the aurora and over a frequency range of at least 4 kHz to several hundred kHz. It has been attributed tentatively to incoherent Cerenkov radiation from the incoming auroral particles. At middle latitudes, noise from the magnetosphere is mostly of the discrete type with associated hiss and appears to be limited to frequencies below the minimum gyrofrequency on the path of propagation. A related type of noise, called ‘polar chorus,’ appears at high latitudes below about 1500 Hz. Discrete emissions may occur spontaneously or be triggered by whistlers or man‐made signals from the ground. The upper cutoff frequency is controlled by the minimum gyrofrequency on the path of propagation, indicating that the region of generation lies in the equatorial plane. Discrete emissions have been attributed to cyclotron resonance between whistler‐mode waves and electrons. Emissions offer new possibilities for studying wave‐particle interactions in the earth's magnetosphere and in other plasmas, both natural and man‐made.
Propagators of atmospheric motions 1. Excitation by point impulses
Authors: Dickinson Robert E.
Published: February 2008

Linear equations for the motions of inviscid ideal gas atmospheres are considered, a brief description of the climatology of the relevant propagation parameters being given. An operational formalism is developed for obtaining elementary solutions for point impulse sources. The propagation of a pulse according to the Boussinesq gravity wave model is analyzed in terms of convergent series solutions for small time and in terms of asymptotic series solutions for large time. Elementary propagators for the gravity wave mode and buoyancy oscillation mode are defined by contour integrals about the singularities of the propagator operator. The theory is extended to the propagation of a pulse in a stratified compressible atmosphere. All motion is then confined within an acoustic front expanding radially with the speed of sound. Series solution in powers of the distance behind the front is described. Sufficiently far behind the front, the motion is given by an acoustic oscillation, buoyancy oscillation, and gravity wave mode. Consideration of the analogous problem, except for a hydrostatic atmosphere on a rotating plane, indicates when and where the assumptions of hydrostatic balance and absence of rotation are tenable. With rotation, a potential vorticity mode describing time‐independent motion also occurs, or, if the variation of the earth's vorticity is included in the model, Rossby waves occur. Addition of a lower boundary is discussed with emphasis on the horizontal propagation of the Lamb wave mode. Impulsive addition of heat excites a Lamb pressure wave pulse strongly modulated by buoyancy oscillations.
Production and prediction of sporadic E
Authors: Whitehead J. D.
Published: February 2008

This is a survey of the experimental observations and theories of formation of all types of sporadic E. The wind‐shear theory is most likely to explain temperate‐zone sporadic E. In the equatorial zone, VHF reflections are most probably due to the two‐stream plasma instability, though gradient instabilities may play a part in producing the irregularities that cause HF vertical‐incidence reflection. In the auroral zone, energetic particles dumped by any one of a variety of mechanisms cause ionization. This ionization has to be moved into thin layers of irregularities to cause auroral sporadic E and radio aurora reflections. Many recommendations are made to further the understanding of and the prediction of sporadic E for communication purposes.
The creep strength of the Earth's mantle
Authors: Weertman J.
Published: February 2008

In this paper we show that it is probable that at stresses greater than about 10−2 bar creep in the earth's mantle is caused by dislocation motion rather than by the mass transport of atoms through diffusion from one grain boundary to another. The latter process leads to Nabarro‐Herring creep. Only at very low stresses (<10−2 bar) should Nabarro‐Herring creep be dominant. Dislocation creep equations (which are nonlinear in stress) are used to estimate the ‘effective viscosity,’ at a constant creep rate of 10−16 sec−1, of the moon, Mars, and the mantles of Venus and the earth. The effective viscosity of the mantles of Venus and the earth diminishes with increasing depth, goes through a minimum, and then increases continuously up to the mantle‐core boundary. The effective viscosity in the lower mantle is much smaller than estimates derived from the Nabarro‐Herring creep equation. The effective viscosity in the deep interior of the moon is approximately constant and does not increase appreciable with depth. The effective viscosity of Mars is intermediate in behavior between that of the earth and of the moon.