bluuebunny/crossref_metadata_2025 huggingface dataset:
Ocean acoustic tomography: Rays and modes
Authors: Munk Walter , Wunsch Carl
Published: February 2008

We have measured perturbation of the sound speed δC(x,y,z) (temperature) field within an ocean volume by repeated acoustic transmissions through the volume along many different ray paths i (Ocean Tomography Group, 1982). The data set consisted of ray travel time perturbations δti, and the sound field was obtained by inverse theory from a linear weighted sum δC(x,y,z)=ΣiAi−1 (x,y,z) δti, where Ai is the time spent by ray i in a differential volume centered on x,y,z. Here the method is extended to cases (e.g. the ‘axial’ ocean near a sound speed minimum) where ray theory is not applicable or not convenient. This is done by including in the data set the frequency perturbation δf of lower modes. The matrix A is generalized to a combination of ray weighting and mode weighting. The procedures are illustrated for bilinear and quadratic sound channels, corresponding to a last and first arrival, respectively, of the axial ray, and for a cosh z profile (surprisingly close to some measured equatorial sound speed profiles) where all rays arrive together. We use a northwest Atlantic profile for illustration of an actual case, and here we find overlapping arrival sequences which lead to additional complexities. All this is conveniently displayed in frequency‐time (ambiguity) diagrams. We discuss two inversion schemes: one based on Abel transforms and the other on numerical matrix inversions. The latter scheme is more straightforward for perturbations from a known initial state. The paper is a review of the underlying principles; application to measurements is planned in the near future.
Organic films on atmospheric aerosol particles, fog droplets, cloud droplets, raindrops, and snowflakes
Authors: Gill P. S. , Graedel T. E. , Weschler C. J.
Published: February 2008

Surface‐active organic molecules are common constituents of atmospheric aerosol particles, raindrops, and snowflakes. If these compounds are present as surface films, transfer of gases into the atmospheric water systems could be impeded, evaporation could be slowed, and the aqueous chemical reactions could be influenced. To investigate these possibilities, we have reviewed the chemical literature pertaining to organic films on aqueous surfaces: their composition, structure, properties, and effects. We then review the surface‐active organic compounds in atmospheric water. We report the results of new measurements of surface tension of aqueous solutions of common atmospheric organic compounds (β‐pinene, n‐hexanol, eugenol, and anethole) and demonstrate that the compounds produce films with properties similar to those of the more well known surfactants. We conclude that organic films are probably common on atmospheric aerosol particles and that they may occur under certain circumstances on fog droplets, cloud droplets, and snowflakes. If present, they will increase the lifetimes of aerosol particles, fog droplets, and cloud droplets, both by inhibiting water vapor evaporation and by reducing the efficiency with which these atmospheric components are scavenged. The presence of the films will not cause a significant reduction of solar radiation within the aqueous solution. It appears likely, however, that the transport of gaseous molecules into and out of the aqueous solution will be impeded by factors of several hundred or more when organic films are present. Since incorporated gas molecules provide much of the oxidizing potential of atmospheric water droplets, the organic films will play a major role in droplet chemistry by strongly inhibiting solution oxidation.
Rheology of the lithosphere
Authors: Kirby Stephen H.
Published: February 2008

During the quadrennial term 1979–1982, major advances have been made in our knowledge of the rheology of the oceanic lithosphere by the skillful combination of experimental and theoretical rock mechanics, seismology and marine geophysics in increasingly sophisticated models for the flexure of the oceanic lithosphere at seamounts and island chains, along transform faults, and at subduction zones. The relative simplicity of plate bending geometry, thermal history, and mineralogical and chemical compositions of the oceanic plates in these settings make the geophysical observations very powerful constraints on the in situ rheology of the oceanic lithosphere. In the first part of this paper, I review the laboratory work on materials appropriate to the oceanic lithosphere with emphasis on contributions during the quadrennial period and the need for future work. The important results of flexure models incorporating realistic material properties are then summarized.
Notes on the auroral electrojet indices
Authors: Kamide Y. , Akasofu S.‐I.
Published: February 2008

The auroral electrojet indices (AU, AL, and AE) have served well for more than two decades as measures of magnetospheric substorm activity. However, as substorm studies have progressed considerably during the last several years, the accuracy of the present electrojet indices has become an important issue. Thus it is opportune to reexamine and evaluate the accuracy of the present electrojet indices and improve them if necessary. For a better use of the present indices and for future improvement we examine the limitations of the auroral electrojet indices as an accurate quantitative measure of the auroral electrojets and of magnetospheric substorms. Such limitations should be kept in mind in studying individual substorms, the correlation with solar wind parameters, etc., particularly because the accuracy of the AE index decreases for AE < ∼250 nT. Some of the limitations arise from the data availability and also from the present simplified scheme in deriving them, but some of them originate in the definition itself. A few suggestions are made to improve the present indices, which can be implemented efficiently when digital outputs become available from all the observatories contributing to the electrojet indices.
Thermospheric aurora and airglow
Authors: Meier R. R.
Published: February 2008

As the understanding of the physics and chemistry responsible for the production of aurora and airglow emissions matures, aeronomers have increasingly utilized optical techniques to study the energetics, dynamics, and composition of the thermosphere. In the past several years, truly remarkable new results have been reported on global and smaller scale imaging, high resolution spectroscopy, interferometry, and photometry. Especially important have been new advances in laboratory measurements of atomic and molecular interactions relevant to thermospheric emissions. In this portion of the US National Report to the International Union of Geodesy and Geophysics, recent contributions to the field of thermospheric auroral and airglow studies are summarized. This task has been lightened somewhat since a review of atmospheric quantal emissions has been published by Vallance Jones et al. (1985) covering results (international included) through mid‐1984. The main emphasis of the present report is on work published since then. While the focus is on U.S. contributions, international collaborative work has been included.
Tectonomagnetism and tectonoelectricity
Authors: Johnston M. J. S.
Published: February 2008

The last four years has seen a considerable waning of efforts in the U.S. to use the inherent stress sensitivity of the magnetization of rocks in tectonically active regions as a tool for understanding and, perhaps predicting, earthquake activity and volcanic eruptions. The primary reasons for this decreased interest derive from accumulating evidence that the mean deviatoric stress release during earthquakes (and the ambient shear stress near active faults) is lower than than had been previously assumed and, secondly, the observational limits of magnetometers separated by about 10 km, after application of a variety of noise reduction techniques, appear to be no better than about 0.1 nT. Lower estimates of the average change in deviatoric stress associated with earthquake rupture correspondingly reduce the fields calculated from tectonomagnetic models. At the same time, some unexpected and exciting results have been obtained which indicate many aspects of magnetic field changes near active faults and volcanoes are still not completely understood. The more important of these results are: 1) the observation of correlated magnetic, strain, uplift, and gravity changes during the latter stages of a remarkable deformation episode near the San Andreas fault in southern California, 2) indications of anomalous change in magnetic fields along the San Andreas fault to the southeast of Palm Springs, 3) an unambiguous observation of a volcanomagnetic effect at Mt. St. Helens prior to an extrusive eruption, and 4) the first observations of coseismic seismomagnetic effects on two independent magnetometers during the July 8, 1986, ML 5.9 North Palm Springs earthquake. A resurgence of interest has occurred during the quadrennium in a related area concerning electrical phenomena and electromagnetic effects related to earthquakes and volcanoes. Mechanisms have been proposed to explain the occurrence of earthquakes lights and the possibility of electromagnetic emission prior to the 1960 Chilean earthquake has been proposed. Self potential anomalies have been observed before and during several eruptions on Kilauea volcano in Hawaii.
Electromagnetic induction studies
Authors: Chave Alan D. , Booker John R.
Published: February 2008

This report constitutes an attempt to review the major developments and identify important trends in the broad field of geophysical electromagnetic induction and related phenomena over the past four years. Following in the spirit of previous reports of this type [e.g.,Filloux, 1979;Hermance, 1983b;], the work of US researchers will be emphasized, although we will cover foreign research when appropriate. Many of the recent theoretical developments and the largest EM field program ever (EMSLAB) are the direct result of international cooperation, and strict adherence to the concept of national boundaries would result in an uninformative and incomplete review.

Due to the fact that readers of this paper have diverse interests ranging from theory through field to laboratory studies, we have attempted to treat a variety of topics in EM induction and electrical geophysics. We begin by reviewing the state‐of‐the‐art in data collection, including new instrumentation. We continue by examining data analysis methods, with an emphasis on noise and bias reduction in the computation of the magnetotelluric and magnetic variations response functions. We then treat forward modelling developments, especially for two‐ and three‐dimensional induction problems. Recent progress has been made in EM induction inverse problems, and we assess the impact of this on the field. An overview of field measurements in North America is given, including the recent EMSLAB experiment which was carried out in 1985–1986 in the northwest US, southwest Canada, and contiguous offshore regions. This is followed by a review of developments in oceanic applications of EM principles.
Processes at the sediment‐water interface, advances during 1982–1986
Authors: Martens Christoper S.
Published: February 2008

1982 to mid 1986 saw important advances in our understanding of processes ocurring at the sediment‐water interface. Notable were significant gains in our knowledge of the influence of bioturbation on zonation and rates of microbially‐mediated reactions, quantification of mixing processes near the interface using radiochronometric tracers, process‐oriented studies of trace metal behavior in oxic, suboxic and anoxic environments, and detailed investigations of microscale geochemical distributions and processes at the deep‐sea MANOP sites. The overriding importance of organic matter input and decomposition in driving many of these processes was noted by many investigators.
Assessment of polar climate change using satellite technology
Authors: Hall Dorothy K.
Published: February 2008

Results from general circulation models (GCMs) have indicated that a predicted climate warming resulting from an increase in atmospheric carbon dioxide (CO2) will be amplified in the polar regions and that temperature increases in the polar regions will be several times greater than the global average. Some GCMs predict a 4°–5°C average air temperature increase in the Arctic by the middle of the next century. Evidence from the polar regions indicates that a warming in the cryosphere may already be in progress. A 2°–4°C rise in permafrost temperature, measured in northern Alaska, is believed to have occurred during the last 100 years. In addition, many small valley glaciers and ice caps have experienced retreat and appear to have contributed up to 50% to the observed rise (10–15 cm) in sea level during the last century. Other work shows that increased snowfall which can be associated with warmer temperatures has caused thickening of some Alaskan glaciers. Though a decrease in snow and sea ice cover would be a likely consequence of global warming, a sustained decrease in global snow and sea ice extent has not been found from analysis of more than 20 years of image data (1.1‐km pixel resolution) from National Oceanic and Atmospheric Administration meteorological satellites and more than 7 years of scanning multichannel microwave radiometer snow data (30‐km pixel resolution) on the Nimbus 7 satellite. Snow and sea ice are sensitive to atmospheric temperature changes because of their large surface to volume ratio. While measurements of snow and sea ice extent, snow depth, and sea ice concentration are possible using visible, near‐infrared, or microwave sensors on satellites, it is not feasible to measure the mass balance of the ice sheets with these sensors directly. Estimates by glaciologists show that the Greenland Ice Sheet is in approximate equilibrium and that the Antarctic Ice Sheet has a positive mass balance. Satellite radar altimetry (and in the future, laser altimetry) is a promising technique for measuring the surface elevation of ice sheets. Satellite‐borne laser altimetry in conjunction with imagery on ice sheet extent will permit direct measurements of changes in mass balance of the ice sheets through time. The terminus positions and ablation area boundaries of valley glaciers are indicative of glacier mass balance; these can be studied using visible and near‐infrared data from the Landsat satellite series and data from the French Systeme Probatoire d'Observation de la Terre (SPOT) satellite and synthetic aperture radar data. Lake ice freeze‐up and breakup dates are sensitive to regional air temperature and may also be good indicators of climate trends. Monitoring the onset of lake freeze‐up and breakup dates is feasible with radar and visible image data. The very important role of snow and ice in global processes is being highlighted as large‐scale, satellite‐derived geophysical data sets have become available and are beginning to be used as realistic input to GCMs.
Remote sensing of the magnetospheric plasma by means of whistler mode signals
Authors: Carpenter D. L.
Published: February 2008

Early in the past decade of U.S. Antarctic research, the whistler method of measuring equatorial electron density was found to agree with in situ satellite electron density measurements by a radio technique. Furthermore, the whistler method of measuring the east‐west component of the convection electric field in the outer plasmasphere was found to agree, under conditions of mapping in a dipole magnetic field, with simultaneous results from incoherent scatter radar. A global model of the east‐west convection electric field in the outer plasmasphere during substorms was developed. The detection of whistlers and their use for magnetospheric diagnostics have been important elements in recent studies of burst precipitation into the ionosphere induced by whistlers and by other transient whistler mode waves propagating in the magnetosphere. Whistlers have also been used to obtain data on the L values and equatorial electron densities associated with the propagation paths of signals from the Siple VLF transmitter. The process of untrapping of downcoming wave energy from ducts in the upper ionosphere and the upward repropagation of portions of the energy following reflection in the lower ionosphere lead to the excitation of adjacent ducts as well as to upward propagation in the nonducted mode. Efficient interduct coupling has been found to occur over north‐south ionospheric distances of >1000 km. Studies of the outer limits of observed ducting revealed dayside path radii in the range 6–8 RE and nightside limits of ∼5.5 RE. Ducted propagation beyond the plasmapause was found to occur regularly in the 0000–1800 MLT time range, but with variable rates and at various locations with respect to the plasmapause position. The special features of this propagation are believed to be related to conditions of lightning excitation, ionospheric penetration, and wave‐particle interactions that are special to the region beyond the plasmasphere. New aspects of Siple wave injection experiments were demonstrated by the application of a new phase measurement method to Siple signals that did not exhibit fast temporal growth during passage through the magnetosphere. This method, a refinement of techniques developed previously by New Zealand workers, is capable of detecting fluctuations in phase path with period of ∼10 s and greater and thus can be used to study magnetospheric convection and coupling fluxes along field lines of propagation as well as pulsations associated with ultralow‐frequency perturbations of the geomagnetic field. Additional topics discussed include results from direction‐finding experiments and evidence of the dependence of whistlers upon magnetospheric wave amplification.
Closing remarks to “Milankovitch Theory and climate” by A. Berger
Authors: Lal D.
Published: February 2008

Professor Berger has explained to us in a very clear manner the premises of our belief in the control of orbital variations over the terrestrial climate. His lecture has been a textbook example of how cross‐disciplinary ties are forged in a field by experimentalists and theorists working from so many different directions, and how these ideas converge to understanding of a problem. Researchers in laboratories all over the globe, finally culminating in the researchers meeting in the campus of a university: that is how challenging problems such as the climate are solved.
High‐latitude F region irregularities: A review and synthesis
Authors: Tsunoda Roland T.
Published: February 2008

The most intense, F region irregularities in the high‐latitude ionosphere appear to be produced by convective plasma processes and in particular, by the fluid

(gradient drift) interchange instability. Such irregularities are produced by convectively mixing plasma across a mean plasma density gradient with the transport of higher‐density plasma into regions of lower‐density plasma (and vice versa) leading to the development of an irregularity spectrum that extends in scale from about 10 km down to the ion gyroradius. The mean plasma density gradient that must be present to allow irregularity production by this interchange process appears to be associated with larger‐scale (>10 km) plasma structure produced by other means. Because much of the recent progress on this research topic stems from this recognition, a significant portion of this review is dedicated to a description of the characteristics and processes of 10‐km plasma structure and their relationships to those of smaller‐scale irregularities. From this review, we synthesize a descriptive model of plasma structures in the high‐latitude F layer that unifies most of the diverse and independent observations. For the large‐scale plasma processes, the model includes (1) the formation of 1000‐km‐scale “patches” in the polar cap from solar‐produced plasma that is transported poleward from lower latitudes; (2) the reconfiguration of patches as they convect into the auroral region and become the latitudinally confined, but longitudinally extended, plasma density enhancements near the equatorward auroral boundary; and (3) the production of localized enhancements and depletions along the poleward auroral boundary by soft‐particle precipitation and large but localized electric fields. In the model, the most intense, smaller‐scale irregularities are in spatial proximity to these large‐scale plasma features, the implication being that the presence of the latter allows formation of the former. The irregularity characteristics are consistent with production by the
instability and a morphology controlled by (1) a “slip” velocity (i.e., plasma drift relative to the neutral gas) that is moderately small except in regions of nonuniform plasma convection or under time‐varying conditions (e.g., substorms, pulsation events) and (2) a highly conducting auroral E layer that damps irregularity growth and enhances decay. The final irregularity spectrum appears to be produced by (1) global convective processes acting on solar‐produced plasma at the largest scales (>50 km), (2) particle precipitation at scales greater than 10 km, (3) perhaps some form of wave activity around 10 km, and (4) the
instability at the smaller scales (<10 km).
Climate change, hydrology, and water resources
Authors: Gleick Peter H.
Published: February 2008

Growing atmospheric concentrations of carbon dioxide and other trace gases are leading to climatic changes with important implications for the hydrologic balance and water resources. These “greenhouse gases” are expected to alter the radiative balance of the atmosphere, causing increases in temperature and changes in many other climatic variables. Recent hydrological research strongly suggests that this so‐called “greenhouse effect” will alter the timing and magnitude of runoff and soil moisture, change lake levels, and affect water quality. Such changes raise the possibility of environmental and socioeconomic dislocations, and they have important implications for future water resources planning and management. This paper reviews state‐of‐the‐art research into the implications of climatic changes for the hydrologic cycle and for water resources and discusses the implications of such changes for future water planning and management.
The scattering analog for infiltration in porous media
Authors: Philip J. R.
Published: February 2008

This review takes the form of a set of Chinese boxes. The outermost box gives a brief general account of modem developments in the mathematical physics of unsaturated flow in soils and porous media. This provides the necessary foundations for the second box, which describes the quasi‐linear analysis of steady multidimensional unsaturated flow, which is an essential prerequisite to the analog. Only then can we proceed to the innermost box, devoted to our major theme. An exact analog exists between steady quasi‐linear flow in unsaturated soils and porous media and the scattering of plane pulses, and the analog carries over to the scattering of plane harmonic waves. Numerous established results, and powerful techniques such as Watson transforms, far‐field scattering functions, and optical theorems, become available for the solution and understanding of problems of multidimensional infiltration. These are needed, in particular, to provide the asymptotics of the physically interesting and practically important limit of flows strongly dominated by gravity, with capillary effects weak but nonzero. This is the limit of large s, where s is a characteristic length of the water supply surface normalized with respect to the sorptive length of the soil. These problems are singular in the sense that ignoring capillarity gives a totally incorrect picture of the wetted region. In terms of the optical analog, neglecting capillarity is equivalent to using geometrical optics, with coherent shadows projected to infinity. When exact solutions involve exotic functions, difficulties of both analysis and series summation may be avoided through use of small‐s and large‐s expansions provided by the analog. Numerous examples are given of solutions obtained through the analog. The scope for extending the application to flows from surface sources, to anisotropic and heterogeneous media, to unsteady flows, and to linear convection‐diffusion processes in general is described briefly.
Study of planetary atmospheres by absorptive occultations
Authors: Smith Gerald R. , Hunten Donald M.
Published: February 2008

As a spacecraft observes the setting or rising of the Sun or a star behind the limb of a planet, the absorption spectrum of the upper atmosphere can be observed as a function of height. This powerful method can give the composition and the vertical distribution of individual gases, from which temperatures can be derived. This review describes the technique and methods of data reduction. Early experiments on the Earth's atmosphere (many from sounding rockets) are briefly summarized; many of them were compromised by the need to use instruments not designed for the purpose. Emphasis is placed on observations of the other planets, by ultraviolet spectrometers able to look at the Sun as well as stars. Mariner 10 set tight upper limits on the atmosphere of Mercury (and also found tiny quantities of H and He). The Voyager instruments defined the upper atmospheres of all four Jovian planets, as well as the satellites Titan and Triton. The potential for future measurements is at least as rich as the history, especially by use of instruments and platforms optimized for the purpose.
Defect microdynamics in minerals and solid‐state mechanisms of seismic wave attenuation and velocity dispersion in the mantle
Authors: Karato S. , Spetzler H. A.
Published: February 2008

The propagation of seismic waves in the Earth's mantle can be significantly affected by relaxation processes, causing attenuation and velocity dispersion (reduction). This paper reviews the solid‐state mechanisms of relaxation processes based on the theory of defect microdynamics in solids together with some experimental observations on defects in minerals (particularly in olivine). For a given mechanism to have a significant effect on seismic wave propagation, both the density and the mobility of the defects must be in an appropriate range. The examination of the densities (and geometry) and mobilities of defects in olivine shows that dislocation and/or grain boundary mechanisms can have a significant effect on seismic wave propagation, although wide distributions of geometrical factors (such as spacing of pinning points) and of mobilities are required to explain all available data. Point defect mechanisms, however, are unlikely to be important because their densities are too small and/or their mobilities are too large. Since the dislocation density and/or grain size are determined in most cases by the long‐term tectonic stress, seismic wave attenuation and velocity dispersion (reduction) involving these defects are likely to depend on the magnitude of the tectonic stress as well as the temperature. Theoretical considerations suggest a wide range of dependence of seismic wave attentuation (and velocity dispersion) on the long‐term tectonic stress. This is particularly the case for dislocation mechanisms and warrants careful experimental investigation. Dislocations and/or grain boundaries cause anelastic behavior (relaxation peaks) when they are pinned or blocked at some points. Pinning or blocking becomes ineffective at high temperatures and/or low frequencies, causing a transition to viscoelastic behavior. Both laboratory and seismological observations of internal friction are dominated by the “high‐temperature background” where internal friction increases monotonically with temperature, which can be interpreted as a gradual transition to viscoelastic behavior or to a wide distribution of relaxation times. However, in most experimental studies to date, the dislocation densities or the grain sizes were not well controlled, making it difficult to identify the attenuation mechanisms and preventing any quantitative applications to Earth. The need for better characterization of defect microstructures in experimental specimens is emphasized.
Reflection of a Plane Transient Electromagnetic Wave From a Cold Lossless Plasma Slab
Authors: Wait James R.
Published: February 2008

Reflection of a plane transient electromagnetic wave from a plasma half‐space and a plasma slab is considered. The plasma is assumed to be cold and collisions are neglected. Under these assumptions, the Laplace transforms may be inverted exactly, yielding a solution in the form of Bessel function series. The numerical results, for the waveform of the reflected field, exhibit features that are easily related to the plasma frequency of the slab and its thickness.
Reflection Coefficient of a TEM Mode Symmetric Parallel‐Plate Waveguide Illuminating a Dielectric Layer
Authors: Burnside W. D. , Rudduck R. C. , Tsai L. L. , Jones J. E.
Published: February 2008

The reflection coefficient of a symmetric parallel‐plate waveguide operating in the TEM mode and illuminating a lossless dielectric layer is analyzed by wedge diffraction and geometrical optics techniques. The interactions between the waveguide and the dielectric layer are treated in terms of iterative bounce waves. The reflection from the dielectric layer and the scattering from the waveguide for cylindrical wave incidence are both represented by resultant component cylindrical waves. Thus each interacting bounce wave between the guide and the dielectric layer becomes the superposition of a finite number of cylindrical wave components. The reflection coefficient of the guide is then obtained by adding the various bounce wave contributions to the guide's free‐space reflection coefficient. For the two geometries considered, the thin‐walled guide and the ground‐plane guide, calculated results are in excellent agreement with those measured.
Commission 2: Progress in Radio and Non‐Ionized Media
Authors: Hogg D. C. , Atlas D. , Bean B. R. , Beard C. I. , Bolgiano R. , de Bettencourt J. T. , Evans J. V. , Gerks I. H. , Hagfors T. , Katz I. , Moore R. K. , Straiton A. W. , Strohbehn J. W. , Thompson W. C. , Wait J. R.
Published: February 2008

The past three years evidence vigorous activity in the areas of interest to Commission 2, especially those concerned with planetary atmospheres, rough surfaces, effects of turbulence, and the general applicability of millimeter waves for scientific study and for communications. If any particular study were to be designated outstanding, it might be the investigation of clear‐air structure by microwave radar, but meaningful advances have been made in all of the areas discussed.
Commission 4: Progress in Magnetospheric Radio
Authors: Fejer J. A. , Axford W. I. , Banks P. M. , Brace L. H. , Calvert W. , Carpenter D. L. , Farley D. T. , Gurnett D. A. , Kennel C. F. , Liemohn H. B. , Scarf F. L.
Published: February 2008

Since the last report was written (in the spring of 1966), there has been a remarkable advance in our knowledge and understanding of the structure and behavior of the magnetosphere, especially with regard to the fundamental problems of the aurora and geomagnetic storms.

The average structure of the quiet magnetosphere has been studied in considerable detail [Ness et al., 1966; Spieser and Ness, 1967; Behannon, 1968; Fairfield, 1968; Mihalov et al., 1968], and it has been shown that the tail and ‘neutral’ sheet extend well past the moon, and possibly to much greater distances [Ness et al., 1967]. The nature of the changes that occur in the geomagnetic field during disturbed periods has been observed, especially by magnetometers on the geostationary satellite ATS 1 [Brown et al., 1968; Cummings et al., 1968; Cummings and Coleman, 1968]. It has been found that the ring current, which is usually situated between 3 and about 10 RE depending on the degree of geomagnetic activity, commonly has a pronounced asymmetric component, with the maximum inflation of the geomagnetic field occurring in the evening sector.
Commission 8: Progress in Radio Noise of Terrestrial Origin
Authors: Pierce E. T.
Published: February 2008

Since Commission 8 was only created on a provisional basis at the Munich General Assembly of URSI in 1966, and since also the U.S. National Committee does not maintain an organization for Commission 8 within the U.S.A., it seems appropriate for informative reasons to start this survey by listing the fields of scientific activity covered by the Commission. These are:

1. Atmospherics, their source characteristics and location.

2. Propagational influences on radio noise (with Commission 3).

3. ELF noise from lightning (with Commission 4).

4. Types of lightning flashes generating whistlers. Propagational effects, other than those in the whistler mode, influencing whistler characteristics (with Commission 4).

5. Statistical properties of noise, noise interference with radio communications.

6. Man‐made noise.

This review will discuss work falling within the above fields of study carried out under U.S. auspices and described in 1966, 1967, and 1968. The survey will be confined to papers appearing in recognized journals and other sources of ready availability to which my attention has been drawn; reports of limited circulation and private information will not be considered.
Impedance Characteristics of Electric Dipoles Over a Conducting Half‐Space
Authors: Wait James R.
Published: February 2008

The input resistance of a Hertzian electric dipole located over a homogeneous conducting half‐space is considered. It is shown that the functional dependence of the input resistance on the ‘loss tangent’ of the half‐space is consistent with electrostatic concepts, provided the frequency is sufficiently low. On the other hand, at the higher frequencies, the results are compatible with the surface impedance formulations based on the compensation theorem. The results have possible application to remote sensing of planetary surfaces from an elevated source.
Comparison of Barium Fluoride Humidity Element with the Microwave Refractometer for Studies of Rapid Fluctuations of Atmospheric Humidity
Authors: Bean B. R. , Gilmer R. O.
Published: February 2008

Fluctuations of atmospheric humidity measured with a barium fluoride element and radio refractive index measured by a microwave refractometer are compared for a separation of 6 inches. Spectral coherence indicates good agreement up to frequencies of 2 to 4 Hz, which is also the frequency limit for good agreement between 2 refractometer cavities 12 inches apart.
High Resolution Tropospheric Radar Sounding
Authors: Richter Juergen H.
Published: February 2008

A radar sounder for the study of the refractive index structure in the troposphere is described. The specially built, high‐sensitivity FM‐CW radar has a maximum range resolution of one meter. Design considerations and performance characteristics are given, and recordings obtained with the radar sounder are presented and discussed. The predominant layers are very well correlated with the major inversions at which we find either sharp vertical gradients of refractive index or changes in the gradient. The base of the lowest inversion is almost always so marked. A second echo layer frequently appears some tens of meters above this base level.Although the echo strata may sometimes be 30 to 40 meters in depth, they are often only a meter or less thick. Their reflectivities may be 10 to 100 times larger than those previously reported with radars of coarser resolution. The layers also commonly appear in the form of breaking Kelvin‐Helmholtz waves with periods of 2 to 4 minutes and peak‐to‐peak amplitudes as small as 10 to 15 meters.
A Self‐Similar View of Atmospheric Turbulence
Authors: Dutton John A. , Deaven Dennis G.
Published: February 2008

The inertial subrange in the energy spectrum appears to be the most consistent feature of atmospheric turbulence at all altitudes. The implications of the fact that amplitudes are related to the 1/3 power of the wavelength are imposed upon the probabilistic structure of the turbulence by B. Mandelbrot's concept of self‐similarity. A process with random variable x is self‐similar if the variable xh obtained by magnification of the wavelength by h can be represented as a suitable magnification of the amplitude of x so that both x and xh have the same probabilistic structure. If this is the case, and the spectra have power‐law behavior S(k) ∼ k−v, then the distribution functions for x and xh obey P(x) = Ph(xh) = Ph[h(v − 1)/2x]. The implications for the distribution of increments yT = x(t) − x(t + T) are examined. Observational data from the 150‐meter tower at Cape Kennedy and from airborne measurements in the troposphere and stratosphere show that self‐similarity gives a remarkably accurate prediction of the behavior of the empirical data in all three cases. The distribution of the increments also reveals an intermittent structure for the turbulence. It is concluded that an attempt to construct a theoretical explanation for the apparently self‐similar behavior of atmospheric turbulence may be revealing.
Intermittency of Small‐Scale Structure
Authors: Dutton J. A. , Lane J. A. , Bean B. R. , Coulman C. E. , Fukushima M. , Montgomery A. , Swinbank W. C.
Published: February 2008

The intermittency associated with fine‐scale structure and motion of the atmosphere was a central and significant theme of the papers and discussions of the meeting. The mathematical and physical problems raised by the intermittency of atmospheric phenomena appear to be difficult and complex.

Most of the statistical analysis of atmospheric data at the present time is not specifically aimed at the study of intermittency. The major conclusion of the working group is that considerable information about the properties of intermittency could be obtained by suitable analysis of available data; the major recommendation is that this work be started.
Experimental Observation of Magnetic Field Effects on VLF Propagation at Night
Authors: Bickel J. E. , Ferguson J. A. , Stanley G. V.
Published: February 2008

Computations of nighttime field intensity versus distance are made for a 23.4‐kHz signal radiated from Hawaii and for propagation paths to Seattle, Ontario (California), Samoa, and Wake Island. The computations were made by using the waveguide computer program developed at the Naval Electronics Laboratory Center to obtain waveguide mode constants, each 2° of arc or 222 km along each path. An exponential electron‐density profile defined by β = 0.5 km−1 and h′ = 85.5 was assumed, where β and h′ are defined by Wait [1964]. The resultant field was computed by using a WKB approximation to allow for the variation of mode constants along the paths. Experimental measurements of 23.4‐kHz signals from NPM were made aboard an airplane as it flew along these propagation paths. (NPM are the call letters for the Lualualei Navy Radio Station in Hawaii.) Good agreement was obtained, between the theoretical calculations and experimental measurements, strongly supporting the validity of the theoretical approach used (the β = 0.5, h′ = 85.5 km profile assumed) and the conclusion that the increased attenuation observed for propagation to the south is an effect of the geomagnetic field.
Physical Characteristics of the Lunar Regolith Determined From Surveyor Television Observations
Authors: Shoemaker E. M. , Morris E. C.
Published: February 2008

The new data on the physical characteristics of the lunar surface derived from the Surveyor pictures can be fitted to a simple ballistic model for the origin and development of the lunar regolith. At a given locality, the size‐frequency distributions of craters on the lunar surface can be represented by two functions: Small craters follow a steady‐state distribution of the form F = ΦCμ, where F is the cumulative number of craters with a diameter ≥ c, c is the diameter of the craters, Φ and μ have the steady‐state values Φ = 1010·9, and μ = −2.00 at all five Surveyor landing sites. Larger craters are represented by the function F = χcλ, where λ < μ, and χ varies from one landing site to another. The solution for c at the intersection of F = χcλ with F = Φcμ, designated as cs, is the upper limiting crater diameter for the steady‐state distribution. The value of cs is a function of the age of the surface on which the regolith has formed. The thickness of the lunar regolith may be estimated from a variety of observational data. The estimated thickness of the regolith at a given Surveyor landing site is bracketed by the original depths of (1) the smallest blocky‐rimmed craters that cut through the regolith and excavate coherent material beneath, and (2) the largest, sharp, raised‐rim craters without blocks that have been excavated wholly within the slightly cohesive material that forms the regolith. Other direct estimates of the thickness of the regolith are the inferred original depth of the largest craters believed to have been formed by drainage of the regolith material into subregolith fissures and, at the Surveyor‐7 site, the depth at which the surface sampler instrument encountered coherent material. The thickest regolith was found at the Surveyor‐6 site, where it is estimated to be more than 10 meters thick, and the thinnest was found at the Surveyor‐7 site, where it is estimated to be 2 to 15 cm thick. Particle counts from sample areas at each of the Surveyor landing sites show an approximately linear relationship between the log of the cumulative particle counts and the log of the particle size. A power function of the form N = KDλ (where N is the cumulative number of particles with diameter equal to or larger than D, and D is the diameter of particles) can be fitted to the data at each site. The size‐frequency distribution of resolvable fragments at the Surveyor 3, 5, and 6 landing sites was found to be the same, within errors of estimation, but at the Surveyor 1 and 7 sites coarse fragments are more numerous. Considering all five sites, we found a strong inverse correlation between the abundance of coarse blocks and the thickness of the regolith. The coarsest fragments are most abundant at the sites with the thinnest regolith.
Saturation and Equilibrium Conditions for Impact Cratering on the Lunar Surface: Criteria and Implications
Authors: Gault Donald E.
Published: February 2008

A model based on first principles and laboratory results is presented for describing and evaluating long term effects of meteoritic impact against the lunar surface. The evolution of the cratered surface and concomitant regolith is calculated and compared with observations and analyses of Lunar Orbiter photographs. It is indicated that most craters are of impact origin, but gross differences in the apparent ages of surfaces in various units and regions of the moon imply that endogenic processes also must have been active, probably since the beginning of Precambrian time and, perhaps, as recently as a few million years ago.
Preliminary Results of Interferometric Observations of Venus at 11.1‐cm Wavelength
Authors: Sinclair A. C. E. , Basart John P. , Buhl David , Gale W. A. , Liwshitz M.
Published: February 2008

Radio interferometry measurements have been made of the temperature variation over Venus. The results imply that the temperature has no significant poleward variation. A limit of 12°K can be placed on the surface temperature difference between poles and equator. A small phase‐dependent asymmetry was measured, corresponding to an 18.4±9.2°K maximum brightness difference between the equatorial limbs. This maximum difference occurs near inferior conjunction. The data also indicate that the disk of Venus is limb brightened. The extent of the brightening can be fitted if Venus' atmosphere is composed of 95% CO2, with no water, and has an extensive isothermal layer at the surface.
Mercury: Epilith Physical Parameters and a Hermocentric Longitude Dependence of its 3.3‐mm Radiation
Authors: Epstein Eugene E. , Dworetsky Michael M. , Fogarty William G. , Montgomery John W. , Cooley Robert C.
Published: February 2008

Observations of Mercury at 3.3 mm were made on 35 days in 1967 and 82 days in 1968 to (1) search for a dependence of the disk‐average brightness temperature TB on hermocentric longitude and (2) to provide constraints on the range of values of the thermal parameters of the epilith (subsurface layers) of Mercury. The observations can be represented by

urn:x-wiley:00486604:media:rds223:rds223-math-0001

where the statistical standard errors are indicated, ϕ is the phase angle, and l′ is the hermocentric longitude of the subearth point. The estimated over‐all system calibration error is 10%. The longitude dependence is demonstrated more clearly when individual phase variation curves are plotted for separate longitude intervals. The ratio of electrical to thermal skin depths (normalized by the wavelength) δ/λ (cm−1) is 1.3 (+ 1.4, ‐ 0.8); the error estimate is very conservative. The observations have been compared with the series of models by Morrison [1969]; of these models, the one with δ/λ = 1.37 and a conductivity independent of temperature best represents the data.
Surface‐Height Variations on Venus and Mercury
Authors: Smith W. B. , Ingalls R. P. , Shapiro I. I. , Ash M. E.
Published: February 2008

Radar time‐delay and Doppler observations have been used to infer surface‐height variations near the equator of Venus. One method, applicable along the apparent equator within a few degrees from the subradar point, has a resolution of about 25 km in longitude and 200 km in latitude and has disclosed an elevated region with a height of about 2 km. Within the latitudinal‐resolution cell, the region extends 150 km in longitude and has a radar cross section enhanced by about 4 db above average. A second method employs measurements of the round‐trip delay to the subradar point on the target planet. These data, accumulated over a number of years, cover the entire equatorial region on Venus, although nonuniformly. Each observation has a resolution along the surface of about 1000 km. Comparison of the measured values with predictions that assume Venus to be spherically symmetric, but that take into account all other significant effects, shows systematic trends in the residuals as a function of the longitude on Venus of the subradar point. A model in which the equator is assumed to be elliptical (semi‐major axis, a; semi‐minor axis, b) with center offset by Δrhov from the center of mass allows the systematic trends to be removed. With all relevant parameters estimated simultaneously, we find Δp = 1.5±0.3 km and a ‐ b = 1.1±0.4 km (formal standard errors). Typically, the actual uncertainty is several times the formal error. The direction of Δp, determined with a formal standard error of 10°, points approximately away from the earth at inferior conjunction. The first method has not been applied to Mercury because of its weaker echo signal. The second method, using data that cover the entire equatorial region, yields time‐delay residuals which show no systematic trend when displayed as a function of the longitude on Mercury of the subradar point; the estimates for Δp and a ‐ b are both less than their respective formal standard errors of 0.4 and 0.2 km. Thus, both Venus and Mercury possess surface height variations far smaller in magnitude than those of either the earth or Mars.
Some Preliminary Results of the 70‐cm Radar Studies of Venus
Authors: Jurgens Raymond F.
Published: February 2008

Delay‐Doppler positions of three radar features are given for observations made during the 1964, 1967, and 1969 inferior conjunctions of Venus. The latitude and longitude of each feature were determined from these data by the method of weighted least squares. The results indicate that the rotation period of Venus may be slightly smaller than the earth‐synchronous period of 243.16 days. Some preliminary measurements of the polarized and cross‐polarized scattering properties of the average surface and the anomalous features are given. These data indicate that the bulk of the surface of Venus is significantly smoother than the moon and that at least two anomalous features give larger ratios of cross‐polarized to polarized power than any features known on the moon.