bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion velocity distributions in the high‐latitude ionosphere
Authors: St‐Maurice J.‐P. , Schunk R. W.
Published: February 2008

The theory and observations relating to ion velocity distributions in the high‐latitude F region are reviewed. The review covers three basic aspects, including methods for calculating ion velocity distributions, experimental evidence for the existence of non‐Maxwellian ion velocity distributions, and the ionospheric consequences of non‐Maxwellian distributions. Specific topics covered include closed form solutions to Boltzmann's equation for a simple collision model, series solutions to the Boltzmann equation for more general collision models, retarding potential analyzer measurements, excitation of VLF electrostatic emissions, ion‐neutral reaction rates, and transport effects.
Ionospheric modification and parametric instabilities
Authors: Fejer J. A.
Published: February 2008

Thresholds and linear growth rates for stimulated Brillouin and Raman scattering and for the parametric decay instability are derived by using arguments of energy transfer. For this purpose an expression for the ponderomotive force is derived. Conditions under which the partial pressure force due to differential dissipation exceeds the ponderomotive force are also discussed. Stimulated Brillouin and Raman scattering are weakly excited by existing incoherent backscatter radars. The parametric decay instability is strongly excited in ionospheric heating experiments. Saturation theories of the parametric decay instability are therefore described. After a brief discussion of the purely growing instability the effect of using several pumps is discussed as well as the effects of inhomogeneity. Turning to detailed theories of ionospheric heating, artificial spread F is discussed in terms of a purely growing instability where the nonlinearity is due to dissipation. Field‐aligned short‐scale striations are explained in terms of dissipation of the parametrically excited Langmuir waves (plasma oscillations); they might be further amplified by an explosive instability (except at the magnetic equator). Broadband absorption is probably due to scattering of the electromagnetic pump wave into Langmuir waves. This absorption is probably responsible for the ‘Overshoot’ effect: the initially observed level of parametrically excited Langmuir waves is much higher than the steady state level.
Models of the Jovian upper atmosphere
Authors: Atreya S. K. , Donahue T. M.
Published: February 2008

Recent developments in photochemical models of the upper atmosphere of Jupiter and Titan are reviewed. Measurements of the Jovian Lyman alpha airglow favor a homopause value of approximately 107 cm² s−1 for the eddy diffusion coefficient. A relatively hot exosphere as implied by the electron density measurements results in an extended atmosphere of hydrogen. Larger than solar C/H and N/H ratios are obtained on reinterpretation of the sunlight reflected from Jupiter; and substantially lower ultraviolet photoabsorption cross sections measured for methane and ethane influence the distribution of CH4, NH3, and their photochemical products. Possible coupling between PH3 and NH3 may inhibit ultraviolet destruction of NH3 on Jupiter. The red color of the Great Red Spot and other minor spots may be due to the presence of red phosphorus crystals formed after photolysis of PH3. The detection of such gases as PH3, GeH4, and CO in the stratosphere of Jupiter gives an indication of the presence of thermochemical nonequilibrium processes, and a strong vertical mixing may be required to explain their large observed upper atmospheric abundances. This argument is further strengthened by a laboratory finding that C2H2 can efficiently scavenge photolysis products of PH3. Other alternate mechanisms to account for the presence of CO in the stratosphere are the oxygen atom transfer from the Galilean satellites to Jupiter either by radial diffusion, or along magnetic flux tubes, or on ablation of meteoroidal material. Subsequent reactions of the thermal oxygen atoms with photolysis products of methane lead to the production of CO. Finally, the discussion of reducing atmospheres is extended to include Titan. It is found that if NH3 has outgassed from Titan and if the surface temperature during the initial phases of its evolution was 150°K or greater, due perhaps to a CH4‐H2 greenhouse, it is inevitable that Titan would have accumulated a thick atmosphere of nitrogen over geologic time. The pressure‐induced thermal opacity of 20 bars of nitrogen can also explain the recently measured 200°K surface temperature of Titan. On the other hand, the composition of Titan's atmosphere would be far less certain if the surface temperature were as low as 100°K.
Ionospheric irregularities
Authors: Ossakow Sidney L.
Published: February 2008

Exciting developments in the understanding of ionospheric irregularities have occurred during the 1975–1978 time frame. Advances in experimental and in theoretical and computer simulation techniques have provided the tools for this progress. Major successes have been attained in the understanding of equatorial spread F phenomena. This report dwells heavily in this area. In addition, the areas of irregularities generated by the artificial release of ionospheric plasma clouds and equatorial E region electrojet irregularities are reviewed. Although work has been done in other areas (treated in the bibliography), a comparable understanding of ionospheric irregularities at mid‐latitude and high latitude, with respect to the above mentioned three areas, does not exist. Much work, especially theoretical and computational, in mid‐latitude and high latitude ionospheric irregularity phenomena is needed in the years ahead. In addition, work in the three areas summarized in this report requires further fine tuning.
Physics of the solar wind for the 1975–1978 IUUG Quadrennial Report
Authors: Barnes Aaron
Published: February 2008

The quadrennium 1975–1978 was a period of great advance for solar‐wind studies, a period that combined exploration of new regions with increased maturity in established fields of study. The Helios, Pioneer, and Voyager spacecraft have been exploring the inner and outer regions of the solar wind. There has been a rebirth of the study of possible relations between solar variability and Earth's climate and weather, stimulated largely by Eddy's [1976] investigation of the Maunder Minimum; the solar wind may well prove to be a significant link in solar‐terrestrial relations. Unique coronal data from the SKYLAB 1973–1974 mission, in combination with satellite and ground‐based observations, provided the basis for identification of coronal holes as the main source of high‐speed solar wind.
Theoretical petrology
Authors: Stolper Edward
Published: February 2008

The central issues in petrology have remained remarkably unchanged in the last 50 years. In igneous petrology, the focus is on understanding the nature and cause of diversity in igneous rocks: on identifying primary magma types and constraints on the compositional and mineralogical characteristics, the physical conditions, and the evolutions of their source regions and on establishing the processes by which derivative magmas evolve from primary magmas. In metamorphic petrology, the major concern is with understanding the conditions and processes experienced by a rock in reaching its present state. In both igneous and metamorphic petrology, the ultimate goal is the integration of petrological constraints with those from other branches of earth science into regional and global theories of earth history. What has changed over the years, however, is the framework within which these issues are addressed: the backdrop provided by plate tectonics and geophysical constraints, the growing sophistication of chemical and physical models of rock systems, the ever increasing inputs from trace element and isotopic geochemistry, the sophistication and complexity of experimental approaches to petrological problems, and the growing body of detailed petrological studies of specific rock suites and associations from all over the world. What I will attempt in this report is to pinpoint and briefly review those areas of growing interest and emphasis in American efforts in petrology during the 1975–1978 quadrennium and the ways in which they were shaped by this framework.
Convection
Authors: Turcotte Donald L.
Published: February 2008

The lithospheric plates of plate tectonics are created from hot mantle rock at ocean ridges and descend into the mantle at ocean trenches. The plates are by definition, part of mantle convection cells. A fluid heated from within or from below and cooled from above convects thermally if the Rayleigh number exceeds a critical value. The earth's mantle is heated from within due to the decay of radioactive isotopes and is heated from below by heat generation in the core.
High temperature deformation of rocks and minerals
Authors: Tullis J. A.
Published: February 2008

The goal of research on the high temperature deformation of rocks and minerals is to determine the stress and strain history of the crust and mantle—to interpret the structures observed in naturally deformed rocks, to interpret geophysical measurements, and to allow accurate modelling. This research thus includes experimental and theoretical studies, as well as studies of naturally deformed rocks. In the four years since the review by Carter [1975] the importance of this field has been emphasized by a number of special conferences, including a Royal Society Discussion on Creep of Engineering Materials and of the Earth [1977; Phil. Trans. Roy. Soc. London, series A, v. 288, 1–236] and a C.N.R.S. International Colloquium on Deformation Mechanisms in Minerals and Rocks [1979; Bull. Fr. Soc. Min. Crist., v. 102]. This field was reviewed by Carter [1976] and treated extensively in a book by Nicolas and Poirier [1976], but there have been a number of significant advances in our understanding in the past few years.
Marine gravimetry
Authors: Cochran James R. , Talwani Manik
Published: February 2008

The first continuous shipboard gravity measurements were made just over 20 years ago on board U.S.S. Compass Island (Worzel, 1958) and, since about 1961, gravity measurements have been routinely made by several institutions as part of marine geophysical surveys.

During the 1960's much effort went into developing and refining instruments and into understanding the mechanical and environmental factors affecting them. A major factor in improving the reliability of gravity measurements was the introduction in the late 196O's of satellite navigation systems which meant that accurate positions, speeds, and courses, all necessary to compute the theoretical gravity value and the Eotvos correction, could be obtained.
Geodetic interferometry submission for the IUGG Quadrennial Report Reviews of Geophysics and Space Physics
Authors: Clark Thomas A.
Published: February 2008

In the previous Quadrennial Report, Counselman [1975] discussed the developments of Very Long Baseline Interferometry (VLBI) from the inception of the technique in 1967 through circa 1974 as they apply to disciplines related to Geodesy. Other review papers and bibliographic sources which provide valuable reference material to document the developments in VLBI include Benjauthrit [1978], Cohen [1973], Counselman [1973, 1976], Fanselow [1978], and Moran [1975, 1976]. In this report, we will review the development of VLBI instrumentation and analytical techniques, the efforts to provide “absolute” calibration and verify the inherent accuracy of interferometric techniques and the applications of these techniques to problems of geodesy, geophysics and related disciplines. Finally we will discuss the present and future programs which will use radio interferometry as a measurement tool, including some forecasts of the future.
Planetary geodesy
Authors: Michael William H.
Published: February 2008

Research in planetary geodesy in the United States during the period 1975–1978 has benefitted from data obtained by a number of U.S. planetary spacecraft and from some exciting ground‐based and aircraft‐based observations. Continuing analyses of data from the Mariner 9 orbiter of Mars obtained in 1971 and 1972, the Pioneer 10 and 11 fly‐bys of Jupiter in 1973 and 1974, the Mariner 10 fly‐bys of Venus and Mercury in 1974 and 1975, plus analyses of new data from the Viking orbiters and landers since 1976, have produced many of the highlights in planetary geodesy for this period. In addition, although results are not available for reporting herein, the Pioneer Venus orbiter and multiprobe spacecraft were scheduled for arrival at Venus in December 1978 and two Voyager spacecraft are enroute to encounters with Jupiter, Saturn, and Uranus. This review, of work subsequent to that reported by Anderson (1975), pertains to the typical geodetic topics of the masses, gravity fields, figures, topography, and rotational dynamics of the planets and, where applicable, of their satellites.
Polar oceanography II: Southern Ocean
Authors: Baker D. James
Published: February 2008

The results of experiments started in the Southern Ocean during the past four years have led to a large increase in the number of papers for this report.

Long‐term measurements in both the Drake Passage and Weddell Sea have led to new insights into processes in the Antarctic Circumpolar Current and polar front zone and into processes of mixing and transport of various Antarctic water masses. A number of theoretical studies on ocean models relevant to the region and studies of air‐sea interaction and southern hemisphere climate effects have appeared.
Theoretical studies of atmospheric tides
Authors: Forbes Jeffrey M. , Garrett Henry B.
Published: February 2008

Advances in the theory of atmospheric tides since the monograph by Chapman and Lindzen (1970) are comprehensively reviewed. Major developments include investigations of the effects of mean zonal winds and meridional temperature gradients, molecular viscosity and thermal conductivity, radiative damping, composition variations, and hydromagnetic coupling, including seasonal and solar cycle effects. Linearized inviscid and viscid equations of general applicability are documented in this review, and a number of quantitative studies of atmospheric tides are considered as simplifications or modifications of these equations. Recent calculations of thermal excitation due to insolation absorption by H2O and O3 below 80 km, UV and EUV absorption in the lower thermosphere, and latent heat release in the tropical troposphere are presented. Although no attempt is made to exhaustively review incoherent scatter, meteor radar, and satellite mass spectrometer contributions to the study of atmospheric tides, representative wind, temperature, and composition data from these sources are interpreted within the framework of the most recent quantitative models, and the current status of our understanding of atmospheric tides is assessed. Some potentially fruitful areas of future research are also presented.
Seismic detection of gravitational radiation
Authors: Jensen O. G.
Published: February 2008

The theory of resonance absorption of plane gravitational waves incident on a layered earth is developed and applied in the analysis of the response of various crustal models. In comparison with a homogeneous half‐space model, crustal layering is found to enhance, greatly, the radiation‐generated surface seismic motions at certain resonant frequencies. Under particular conditions the resonance quality Q is limited only by the absorption of elastic energy in the crustal materials. These results suggest that well‐located seismograph systems might provide an effective means for the detection of gravitational radiation in the 0.1‐ to 10‐Hz band. The possibility of the incidental discovery of gravitational wave bursts by the community of seismologists is discussed. Furthermore, the response of the earth to gravitational radiation with very long and ultralong periods is discussed in terms of the current understanding of the earth's elastic and fluid mechanical motions. Experiments in seismic detection of gravitational radiation are reviewed.
Planetary magnetism
Authors: Russell C. T.
Published: February 2008

Planetary spacecraft have now probed the magnetic fields of all the terrestrial planets, the moon, Jupiter, and Saturn. These measurements reveal that dynamos are active in at least four of the planets, Mercury, the earth, Jupiter, and Saturn but that Venus and Mars appear to have at most only very weak planetary magnetic fields. The moon may have once possessed an internal dynamo, for the surface rocks are magnetized. The large satellites of the outer solar system are candidates for dynamo action in addition to the large planets themselves. Of these satellites the one most likely to generate its own internal magnetic field is Io.
Estimations from irregular arrays
Authors: Bretherton Francis P. , McWilliams James C.
Published: February 2008

A general approach is presented for estimating statistics of a random process from a finite data set from an irregularly spaced array of measurement locations. Particular attention is focused upon estimation of the spectrum under circumstances where it is smooth (i.e., broadband). A procedure is proposed based upon the technique of optimal linear estimation or generalized least squares fits in order to estimate coefficients of spectral features of interest to the investigator. Selection of which features are appropriate for estimation from a given array and set of measurements is made within the formalism of Bayesian statistical inference. The converse problem is also addressed: given a set of spectral features and a fixed number of possible measurements, which configuration of measurement locations will yield the most information about the amplitudes of those features? Finally, an assessment is made of the efficiency (i.e., the bias and accuracy) of various previously proposed methods of spectral estimation from irregular arrays.
Mechanisms for auroral precipitation: A review
Authors: Swift Daniel W.
Published: February 2008

Theories for and observations relating to auroral precipitation are reviewed for purposes of assessing our understanding of the aurora and of identifying those processes which play the most important role in auroral precipitation. For purposes of the review, four categories of auroral forms are defined: (1) the diffuse aurora, which usually forms the equatorward boundary of the auroral oval, (2) auroral patches and pulsations, which appear most commonly within the morning sector of the diffuse aurora, (3) the discrete aurora, most prominently observed in the evening and poleward sectors of the auroral oval, and (4) the ‘inverted‐V’ aurora, which appears in the same regions as discrete aurora but with much larger size scales. One principal conclusion is that the diffuse aurora, likely caused by both proton and electron precipitation, is the result of pitch angle scattering by electrostatic cyclotron waves. Another is that the auroral pulsations and patches are the result of pitch angle scattering of more energetic electrons by electromagnetic whistler mode waves. The patches may represent flux tubes of enhanced ionization tied to the lower ionosphere. The discrete aurora is the result of electron acceleration parallel to the magnetic field by the quasi‐static electric field of a current‐driven laminar electrostatic V shock. The theory for inverted‐V precipitation is not well developed, but observations strongly suggest that it is related to ion cyclotron anomalous resistivity.
The equatorial electrojet
Authors: Forbes Jeffrey M.
Published: February 2008

An integrated treatment of observations and models of the undisturbed equatorial electrojet is presented. Previous reviews have concentrated on particular aspects of the electrojet phenomenon, such as ground magnetic variations, the counterelectrojet, or E region electron density irregularities and associated plasma instabilities. Here accomplishments during the past 15 years involving all aspects of the phenomenon are covered and, where possible, interrelated. Observational and theoretical studies during recent years have emphasized the local time, longitude, vertical, and latitudinal structure of electric fields and currents in the electrojet; this review similarly places its emphasis along these lines and by necessity involves a detailed examination of electrodynamic coupling with the neutral atmosphere tidal oscillations in temperature, composition, and winds. The review concludes with an assessment of current knowledge concerning the equatorial electrojet and suggestions for the future direction of observational and theoretical research on electrodynamical processes in the equatorial ionosphere.
An overview of seasonal snow metamorphism
Authors: Colbeck S. C.
Published: February 2008

The grains in seasonal snow undergo rapid and radical transformations in size, shape, and cohesion. These grain characteristics affect all of the basic properties of snow. Snow is characterized as either wet or dry depending on the presence of liquid water. Wet snow is markedly different at low and high liquid contents. Dry snow is characterized as either an equilibrium form or a kinetic growth form; that is, it is either well rounded or faceted. Of course, many snow grains display either transitional features between two of these categories or features which arise from other processes. Snow is classified depending on the dominant processes of its metamorphism.
Three‐dimensional seismic inhomogeneities in the lithosphere and asthenosphere: Evidence for decoupling in the lithosphere and flow in the asthenosphere
Authors: Aki Keiiti
Published: February 2008

Newly discovered three‐dimensional seismic velocity anomalies in the earth's lithosphere and asthenosphere are interpreted in terms of decoupling in the lithosphere and flow in the asthenosphere. A rough estimate of flow in the asthenosphere under California was made using Stokes' law on the basis of the size of anomalies and density contrast estimated from the velocity contrast. The result depends on the cause of velocity anomalies. If they are due to any effect which obeys Birch's law, the flow is as rapid as that of Morgan's (1972) plume driving the plate motion. On the other hand, if they are due to partial melts in thin cracks or at grain boundaries, the flow is negligible in accordance with Elsasser's (1971) model of plate tectonics driven quietly by the ridge‐push and slab‐pull in which the asthenosphere under the base of the plate is only passively dragged. The result of Cockerham and Ellsworth (1979, 1980) that the low‐velocity zone in the mantle under central California appeared to have preserved the shape of the downgoing slab for up to 10 m. y. supports Elsasser's rather than Morgan's model. The shapes of low‐velocity bodies found by Iyer and his colleagues under several geothermal areas in the western United States may be interpreted in terms of decoupling between the upper brittle lithosphere and the ductile substratum. The misalignment of the axis of the low‐velocity column from the center of the granite outcrop in the Roosevelt Hot Springs area, Utah, and the inclined low‐velocity column under the Geysers‐Clear Lake region, California, indicate a decoupled lithosphere in these areas, whereas the upright column found under Yellowstone National Park suggests an intact lithosphere there.
Nonlinear normal mode initialization and the bounded derivative method
Authors: Kasahara Akira
Published: February 2008

Recently, two new approaches have been proposed for the initialization of primitive equation models. One is called the nonlinear normal mode procedure, developed by Baer and Machenhauer. It is suitable for a global primitive equation model in which the construction of the model normal modes is feasible. The other approach is called the bounded derivative method, proposed by Kreiss. It can be applicable to both pure initial value and initial boundary value problems. Leith established a connection between the nonlinear normal mode procedure and the classical balancing based on quasi‐geostrophic theory. The purpose of this paper is to compare the three procedures of initialization for a baroclinic primitive equation model with beta plane geometry in pressure coordinates. To the degree of approximation employed, the initialization by the bounded derivative method agrees with the classical balance procedure with quasi‐geostrophic assumptions. We demonstrate for the same prediction model that nonlinear normal mode balancing leads to an initialization scheme identical to the one derived from the bounded derivative method within the degree of approximations. Since both new approaches to initialization are more general than the classical procedures, the connection of the two approaches with the quasi‐geostrophic formulation will enhance our understanding of the dynamics of large‐scale motions beyond the classical quasi‐geostrophic theory.
Electromagnetic induction in the Moon
Authors: Sonett C. P.
Published: February 2008

Except for a boundary layer of uncertain properties the moon constitutes a rigid (nonhydromagnetic) but electrically conducting target to the solar wind when unscreened by the earth's magnetosphere. At frequencies below 3 mHz, observed in the rest frame of the moon, fluctuations of the interplanetary and the geomagnetic tail fields excite eddy currents which penetrate deeper than half the lunar radius. At long wavelength (λ ≫ rM, where rM is the lunar radius) a time‐varying magnetic dipole is induced. Shorter wavelengths excite correspondingly higher‐order magnetic multipoles, but primarily in the outer parts of the moon because of skin depth limitations. The lunar response reaches a peak as frequency increases, diminishing with further increase in frequency. This is interpreted as evidence for the presence of the magnetic quadrupole moment. In the solar wind and magnetosheath the transverse electric mode in the moon is not accompanied by the corresponding transverse magnetic mode, since a bow shock wave is not detected. The latter is probably damped by the nonconducting lunar crust, though the moon is still polarized electrically. It is marginally possible that transient bow wave phenomena appear at times, but because of the high dynamic pressure of the solar wind and magnetosheath, most induced fields are confined to the lunar interior and perhaps the boundary layer. Furthermore, a theorem by Herbert et al. (1976) seems to preclude time‐variable induced magnetospheres. Magnetometer measurements of induction using Explorer and Apollo instruments are reviewed, from both the harmonic and the transient standpoint, and the resulting determination of internal bulk electrical conductivity is discussed. Estimates of both internal temperature and metallized core radius maxima are examined. The closeness of the estimated temperature to the Ringwood‐Essene solidus at 150‐ to 250‐km depth may be indicative of a layer of enhanced conductivity in lieu of high temperature. If so, this suggests a reduction in temperature, bringing the temperature into coincidence with other selenophysical parameters. A reduced core radius estimate with a one‐sigma upper limit of 360 km is reported. Application of inverse theory resolution tests has not been made pending completion of current work involving autoregressive models in attempting to isolate the angular spectrum of real or apparent incident wave normals, upon which the quadrupole response depends. This is also aimed at bypassing current limitations imposed by data gap convolution, data digitization noise, and noise thought to be generated by the interaction of the solar wind with local and regional permanent fields on the lunar surface. Because of length limitations, discussion of lunar electrodynamics has been restricted to the problem of induction, with accompanying subjects such as the flow field and regional electric fields on the moon mentioned only as required. A fuller treatment should include these matters. The review closes prior to ongoing work on high‐frequency induction involving the full lunar scattering problem.
Pulsation research during the IMS
Authors: Hughes W. J.
Published: February 2008

Workers in the pulsation field entered the period of the International Magnetospheric Study (IMS) with a lot of theories that needed testing. Because of this and the wealth of new data available from the IMS observational campaigns, many new observational results have emerged from the IMS. The experience of the IMS shows us that the most fruitful method of working has been small‐scale collaborations, between either a few individuals or a few groups with complementary data sets. The larger, more formally organized workshops do not seem to have been as successful in producing results, though they may have fostered useful contacts. In the years to come I hope and expect to see more of this sort of small‐scale collaboration; especially as the initial results obtainable from a single data set are now published, experimenters should turn to seeing how their data can be used in conjunction with other data sets. I also feel that the time is ripe for more theoretical work. The IMS has left us with a lot of new observations that need explanation.
Plasma boundaries and shocks
Authors: Russell C. T. , Greenstadt E. W.
Published: February 2008

The quadrennium has seen an explosive growth in our knowledge and understanding of the various plasma and magnetic field boundaries in the terrestrial magnetosphere. Nowhere is that more evident than at the magneto pause and bow shock. In the 1975 and 1979 quadrennial reports, the magnetopause was covered in a single paragraph each year. The bow shock received one paragraph in 1975 and none in 1979! The reason for the resurgence of interest in these boundaries was the availability of new and exciting measurements from the ISEE‐1 and ‐2 spacecraft.
Gravimetry
Authors: Wilcox Luman E. , Scheibe Donald M.
Published: February 2008

The details of progress in United States gravimetry during the period 1979–82, reported below, have been compiled largely from unpublished reports, personal communications to the authors and the authors' own knowledge of recent developments. A representative sampling of important literature published during the period is included.

Recent developments in gravimetry in the United States are highlighted by the development and deployment of a new portable absolute gravity apparatus, a rebirth of airborne gravimetry in the form of an accurate operational helicopter gravity measuring system, the impending fabrication of a superconducting gravimeter for geodetic surveys, and the establishment of a new long‐range calibration line.
Geomagnetic reversals and excursions: Their paleomagnetic record and implications for the geodynamo
Authors: Hoffman Kenneth A.
Published: February 2008

Since the earliest reports of paleomagnetic evidence in support of the existence of geomagnetic field reversals, much attention has been focused on understanding the relevant core mechanism. Given the far‐reaching implications such an understanding would have on the whole of geomagnetism, past investigations of this phenomenon have involved experimentalists and theoreticians alike. In particular, during the previous quadrennium (1975–1978) significant contributions were gained from each of various approaches, namely, experimental studies of paleomagnetic records of polarity transitions, statistical studies involving the frequency of occurrence of reversals as well as the time‐averaged full polarity states and theoretical studies concerning the dynamo. Continued progress along many fronts has been made during the last four years (see the recent review by Hoffman (1982a)); such is the subject of this report.
Paleomagnetism and the motion of large and small plates
Authors: McWilliams Michael O.
Published: February 2008

The focus of paleomagnetic research during past decades has varied greatly. The first generation in paleomagnetism might be defined as beginning with the pioneering studies aimed at discovering whether the geomagnetic field has been a reliable reference frame for measuring and timing continental displacements. An enormous effort followed, in the form of individual paleomagnetic studies of cratonic rocks, culminating with the construction of APW (apparent polar wander) paths for the continents which could be used to test paleogeographic reconstructions. Coupled with parallel research in marine geophysics and geology, the refined APWP which result from this effort have helped to develop a reasonable first‐order history of Cenozoic/Mesozoic paleogeography for the major plates.
Planetary lightning: Earth, Jupiter, and Venus
Authors: Williams Mark A. , Krider E. Philip , Hunten Donald M.
Published: February 2008

Terrestrial lightning is usually produced by convective clouds that contain supercooled water, ice, and precipitation. Although convection and a variety of mechanisms based on the principle of electrostatic induction can, in principle, electrify clouds, the available evidence suggests that interaction between riming ice particles and supercooled water, followed by a gravitational separation of charged precipitation elements, is the dominant mechanism for cloud electrification on earth. These mechanisms probably operate on Jupiter in the H2O cloud, and optical images of lightning and whistlers have been detected by Voyager 1. Jupiter has no true surface; therefore the Jovian lightning flashes are cloud discharges. Observations indicate that Jovian lightning emits, on average, 1010 J of optical energy per flash, whereas lightning on earth radiates only about 106 J per flash. There is much uncertainty in the average planetary lightning rate on Jupiter, but estimates range from 3 × 10−3 to 40 km−2 yr−1. Venera probes have reported transient LF and VLF radio emissions in the lower atmosphere of Venus, and an experiment aboard the Pioneer Venus Orbiter has registered electromagnetic energy propagating in the whistler mode. Optical searches for lightning on Venus have been inconclusive, but have set an upper limit to the planetary flashing rate of about 30 km−2 yr−1. The Venus observations have led to widespread speculation that there is lightning in the atmosphere, but application of known charging mechanisms to the Venus environment does not suggest that there should be strong electrification. Since the spacecraft observations do not conclusively show that lightning does occur on Venus, we suggest that alternative explanations for the experimental results be explored.
Cloud electrification
Authors: Lhermitte Roger , Williams Earle
Published: February 2008

The electrification of clouds results from the separation of electrical charges and their segregation in space by air and particle motions. Detailed specification of the mechanisms involved in this important aspect of storm development is still fragmentary. This shortcoming of the subject is exemplified in the long standing controversy concerning the relative merits of precipitation and convection theories of cloud electrification [Moore, 1974; Mason, 1976; Moore, 1976]. The results of recent research have suggested that neither of these distinct views can alone provide a complete explanation for thunderstorm electrification.
The Global Atmospheric Research Program: 1979–1982
Authors: Fein Jay S. , Stephens Pamela L. , Loughran Kristyne S.
Published: February 2008

In this report we discuss the activities of the Global Atmospheric Research Program (GARP) during 1979–1982. We continue a tradition established eight years ago when Perry (1975) described the scientific framework, management structure and field programs of GARP in the U.S. National Report for 1971–1974. Perry and O'Neill (1979) followed with a description of the major GARP activities for 1975–1978; they considered the GARP field programs planned for late 1978 and beyond while Greenfield and Fein (1979) discussed research highlights of the GARP Atlantic Tropical Experiment (GATE), the first major GARP field program which was completed in 1974.

The period 1979–1982 was one of extraordinary activity. Several major field programs were completed: the Global Weather Experiment (also known as FGGE, the First GARP Global Experiment) with its regional subprograms, the Monsoon Experiment (MONEX) and the West African Monsoon Experiment (WAMEX), and the last of the GARP field programs, the Alpine Experiment (ALPEX). We describe these experiments and report some of the preliminary results; we also summarize the GATE research results for the last four years.
Subsurface subtropical gyre of the North Atlantic and Pacific oceans
Authors: Stommel Henry
Published: February 2008

In this review we will restrict our attention to studies of the structure of subtropical gyres

(i) in the North Atlantic and Pacific,

(ii) between the bottom of the mixed layer and about 1500 meters depth,

(iii) between 15°N and 35°N,

(iv) in the open ocean eastward of the Gulf Stream and Kuroshio Current and high‐energy eddy regions.

We will confine ourselves largely to work published 1978 or later by American workers.

The task of making this review is much lightened by the appearance of a comprehensive review “Dynamics of Large‐Scale Ocean Circulation” by George Veronis (1981). Readers who are new to the subject, or experts who detect lacunae in the present review will do well to refer to it.
Earthquake prediction
Authors: Wyss Max
Published: February 2008

One of the most difficult problems in earthquake prediction research remains that of observing precursory anomalies. A solid data base of numerous cases of a variety of precursory anomalies is needed in order to develop detailed models of the physical processes involved and to estimate variances between individual cases. Once this data base is available it may become possible to design procedures for optimizing the success rate of predictions and for using predictions in hazard mitigation. The data base of high quality precursory anomalies is slowly growing.
Superthermal ionospheric outflows
Authors: Moore Thomas Earle
Published: February 2008

A review is given of the accumulating evidence that ion acceleration and heating at low altitudes play an important role in the dynamics and chemistry of the topside ionosphere and the outflow of plasma into the magnetosphere. Published fluid and kinetic descriptions of the topside ionosphere and ion exosphere provide the macroscopic context in which relevant observations are discussed. Though such models have for the most part been descriptions of regions without the strong magnetic field‐aligned currents associated with ion acceleration, the observations suggest possible means of extending the models. The incorporation of transverse acceleration at low altitudes is particularly suggested, and the effects of such heating on ion chemistry are explored using a simple continuity model. One result is that the known response of the neutral atmosphere to solar activity, in the presence of transverse ion heating near 1000 km altitude, implies H+ escape at solar minimum and O+ escape at solar maximum. Increasing interest in the modeling of extreme conditions associated with high levels of geomagnetic activity and auroral processes, together with increasing availability of very low energy plasma observations, provides opportunities for fruitful interactions between theory and observation.
The auroral luminosity structure in the high‐latitude upper atmosphere: Its dynamics and relationship to the large‐scale structure of the Earth's magnetosphere
Authors: Feldstein Y. I. , Galperin Yu. I.
Published: February 2008

The concept of the auroral oval was proposed independently by Feldstein and by Khorosheva in the early 1960's, and it has since been widely used as a reference frame for the organization of high‐latitude optical, particle, and ionospheric data. More recently, different structural regions associated with the oval have been distinguished, and these have been identified with different magnetospheric regions by different workers. The net result is an inconsistent set of nomenclature and relationships. The literature of this development is reviewed in detail, and an interpretation and terminology that is consistent, in the opinion of the authors at least, are proposed. It is hoped that this proposal will serve as a useful basis for further discussion on the ordering of auroral phenomena in relation to the magnetosphere.
Prediction of geomagnetic activity on time scales of one to ten years
Authors: Feynman Joan , Yue Gu Xiao
Published: February 2008

Although a great deal of work has been done on the prediction of the sunspot number 1–10 years in advance, very little has been done on the related problem of predicting the level of geomagnetic activity. It is sometimes assumed, apparently, that a prediction of sunspot number is a fairly good guide to the level of geomagnetic activity to be expected, but this is far from the case. However, long‐term prediction of geomagnetic activity is important both for space mission planning and to test our empirical understanding of the relationship of the solar wind to the solar cycle. In this review we bring together the work that has been done in this field to provide a ready reference both for the specialist in solar‐terrestrial relations and for others requiring geomagnetic prediction capability. We find, however, that surprisingly little attention has been paid to this problem, and it is our hope that this review will stimulate further work.
Global climatic trends as revealed by the recorded data
Authors: Ellsaesser Hugh W. , MacCracken Michael C. , Walton John J. , Grotch Stanley L.
Published: February 2008

Recent results from climate models have led to the prediction that a global warming due to increasing atmospheric CO2 is now imminent, if it has not already occurred. In an effort to develop more definitive information on this question, a detailed review has been conducted of prior efforts to unravel climatic change from the various types of recorded observational data available. Most of the more definitive of the prior analyses—along with evaluative comments by the various authors—have been assembled herein. There appears little doubt that the average surface air temperature of at least northern hemisphere has been increasing since the beginning of recorded data with most of the warming occurring in a brief period circa 1920. The fragmentary early data suggest significant cooling prior to 1883 such that 25–50% of the subsequent warming may represent a return to earlier levels. Whether the overall warming constitutes a climate change remains an unresolved problem, as does the cause of the warming.
Slab pull and the seismotectonics of subducting lithosphere
Authors: Spence William
Published: February 2008

This synthesis links many seismic and tectonic processes at subduction zones, including great subduction earthquakes, to the sinking of subducted plate. Earthquake data and tectonic modeling for subduction zones indicate that the slab pull force is much larger than the ridge push force. Interactions between the forces that drive and resist plate motions cause spatially and temporally localized stresses that lead to characteristic earthquake activity, providing details on how subduction occurs. Compression is localized across a locked interface thrust zone, because both the ridge push and the slab pull forces are resisted there. The slab pull force increases with increasing plate age; thus because the slab pull force tends to bend subducted plate downward and decrease the force acting normal to the interface thrust zone, the characteristic maximum earthquake at a given interface thrust zone is inversely related to the age of the subducted plate. The 1960 Chile earthquake (Mw 9.5), the largest earthquake to occur in historic times, began its rupture at an interface bounding oceanic plate <30 m.y. old. However, this rupture initiation was associated with the locally oldest subducting lithosphere (weakest coupling); the rupture propagated southward along an interface bounding progressively younger oceanic lithosphere, terminating near the subducting Chile Rise. Prior to a great subduction earthquake, the sinking subducted slab will cause increased tension at depths of 50–200 km, with greatest tension near the shallow zone resisting plate subduction. Plate sinking not only leads to compressional stresses at a locked interface thrust zone but may load compressional stresses at plate depths of 260–350 km, provided that the shallow sinking occurs faster than the relaxation time of the deeper mantle. This explains K. Mogi's observations of M ≥ 7 thrust earthquakes at depths of 260–350 km, immediately downdip and within 3 years prior to five great, shallow earthquakes of northern Japan. The slab pull model explains the lower layer of double seismic zones as due to tension from the deeper, sinking plate and the upper layer as due to localized in‐plate compression, as plate motion is resisted by the bounding mantle. Just downdip of the interface thrust zone, there occurs an aseismic 20°–50° dip increase of subducted plate. This slab bend reflects the summed slab pull force of deeper plate and probably is at the crustal basalt to eclogite phase change. Resistance to subduction provided by a continually developing slab bend may be an important factor in the size of slab pull force delivered to an interface thrust zone.
Impact of changing computer technology on hydrologic and water resource modeling
Authors: Loucks Daniel P. , Fedra Kurt
Published: February 2008

The increasing availability of substantial computer power at relatively low costs and the increasing ease of using computer graphics, of communicating with other computers and data bases, and of programming using high‐level problem‐oriented computer languages, is providing new opportunities and challenges for those developing and using hydrologic and water resources models. This paper reviews some of the progress made towards the development and application of computer support systems designed to aid those involved in analyzing hydrologic data and in operating, managing, or planning water resource facilities. Such systems of hardware and software are being designed to allow direct and easy access to a broad and heterogeneous group of users. These systems often combine data‐base management; simulation and optimization techniques; symbolic colored displays; heuristic, qualitative approaches; and possibly artificial intelligence methods in an interactive, user‐controlled, easily accessible interface. Individuals involved in the use of such systems are not only those with technical training, but also those representing different interest groups and having non‐technical backgrounds. The essential difference between what is happening now and the more traditional off‐line, non‐interactive approaches is that instead of generating solutions to specific problems, model developers are now beginning to deliver, in a much more useful and user‐friendly form, computer‐based turnkey systems for exploring, analyzing and synthesizing plans or policies. Such tools permit the user to evaluate alternative solutions based on his or her own objectives and subjective judgments in an interactive learning and decision‐making process.
Surface water hydrology: Historical and paleoflood information
Authors: Stedinger Jery R. , Baker Victor R.
Published: February 2008

Recent developments have greatly increased the likelihood that historical and paleoflood investigations can provide useful hydrologic flood‐frequency information. Advances in the dating of paleofloods, and in methods for estimating paleoflood discharges, have had their greatest impact on a relatively new procedure: the analysis of slackwater deposit‐paleostage indicators (SWD‐PSI). Statistical procedures have also evolved that make better use of historical and paleoflood data in flood‐frequency analyses and several studies have documented the potential value of using such information.
Uranus
Authors: Bergstralh Jay T.
Published: February 2008

Progress in scientific study of the planet Uranus, its ring system, satellites, and magnetosphere within the past four years is reviewed.