bluuebunny/crossref_metadata_2025 huggingface dataset:
Progress in hydrodynamic modeling, review of U.S. contributions, 1979‐1982
Authors: Lynch Daniel R.
Published: February 2008

The use of numerical models in hydrodynamic investigations has been expanding for some time. The conventional demands exerted by scientific investigators have been supplemented, particularly during the 1970's, by expanded public environmental concern which in turn has generated increasingly complex hydrodynamic problems. Concurrently, advances in computer science have made numerical models more and more accessible, and a class of model users has emerged which is distinct from the model‐makers. We presently enjoy a significant array of packaged models intended for various hydrodynamic uses with more or less sophisticated user interfaces, and anticipate the development and distribution of increasingly complex models. This review is concerned with the fundamental algebraic/numerical algorithms which form the basis of hydrodynamic models, and which will ultimately determine their accuracy and cost‐effectiveness.
Research on snow and ice
Authors: Barry R. G.
Published: February 2008

This review, unlike its predecessor [Martinelli et al., 1979], is an intentionally selective survey of recent advances in selected areas of snow and ice research. I have chosen to concentrate on studies relating to large‐scale aspects of the cryosphere and to consider their wider significance for other disciplines. Results obtained by new measurement techniques and the application of remote sensing methods are also stressed. At the same time, the broad lines of advance in glaciological research, as represented in books, conference themes, and major field or laboratory programs, are noted and a detailed bibliography is appended.
Internal waves in the ocean: A review
Authors: Levine Murray D.
Published: February 2008

This review documents the advances in our knowledge of the oceanic internal wave field during the past quadrennium. Emphasis is placed on studies that deal most directly with the measurement and modeling of internal waves as they exist in the ocean. Progress has come by realizing that specific physical processes might behave differently when embedded in the complex, omnipresent sea of internal waves. To understand fully the dynamics of the internal wave field requires knowledge of the simultaneous interactions of the internal waves with other oceanic phenomena as well as with themselves.
The expansion of a plasma into a vacuum: Basic phenomena and processes and applications to space plasma physics
Authors: Samir Uri , Wright K. H. , Stone N. H.
Published: February 2008

In this review we call attention to basic phenomena and physical processes involved in the expansion of a plasma into a vacuum, or the expansion of a plasma into a more tenuous plasma, in particular the fact that upon the expansion, ions are accelerated and reach energies well above their thermal energy. Also, in the process of the expansion a rarefaction wave propagates into the ambient plasma, an ion front moves into the expansion volume, and discontinuities in plasma parameters occur. We discuss the physical processes which cause the above phenomena and point toward their possible application for the case of the distribution of ions and electrons (hence plasma potential and electric fields) in the wake region behind artificial and natural obstacles moving supersonically in a rarefied space plasma. To illustrate this, some in situ results are reexamined. Directions for future work in this area via the utilization of the Space Shuttle and laboratory work are also mentioned.
Past precipitation rates derived from ice core measurements: Methods and data analysis
Authors: Paterson W. S. B. , Waddington E. D.
Published: February 2008

Ice cores in which annual layers can be identified, or particular horizons dated, provide a record of past precipitation rates if measured layer thicknesses can be corrected for thinning by flow since deposition. Total strain is usually calculated from steady state flow models because of lack of information about the ice cap's history. An assumption of uniform vertical strain rate is valid, at best, in the upper half of the ice column. Complex models are needed to take account of uneven bedrock and variations in precipitation rate upstream of the borehole. Drilling at an ice divide avoids these complications. New data analyses suggest that precipitation at Camp Century has fluctuated by only plus or minus 10% for the past 8500 years, whereas at Devon Island, on the opposite side of Baffin Bay, precipitation has been uniform only for the past 1300 years, with significantly higher values before that. Estimation of pre‐Holocene precipitation rates is especially difficult because that ice may have an effective viscosity different from Holocene ice. Three published estimates of pre‐Holocene precipitation at Camp Century are unreliable; the authors did not allow for thinning, and their time scales differ appreciably. Data from three Antarctic stations show some inconsistencies. Measuring concentrations of 10Be in ice cores may be an alternative method of determining past precipitation rates.
Very long solar periods and the radiocarbon record
Authors: Sonett C. P.
Published: February 2008

The ∼ 200‐year periodicity in the time variations of atmospheric radiocarbon is shown to extend over the entire 8500‐year La Jolla record and appears to be associated with a longer period between about 1500 and 2000 years via amplitude, frequency, or phase modulation, or some combination of these; but the statistical certainty of the source and form of the modulation is hampered by the low signal/noise ratio of the two periods. Autocorrelations of the La Jolla sequence show that the record violates even weak stationarity; although the 200‐year period is well ordered in time, the appearance of other periods may be more sporadic. Significant cross correlation between the very long period and the modulation envelope about the neighborhood of the 200‐year line suggests an identity between the two manifestations of the long period, and modulation by a nonlinearity satisfying the rule that it have at least one nonvanishing derivative of odd order and n > 2. Commensurate segments of the La Jolla, Belfast, and Groningen radiocarbon records confirm the existence between 3900 B.C. and 3200 B.C. of other periods, particularly 150 and 300 years. A likely source of these periodic changes in the radiocarbon record is the sun because the source of the variations is time dependence of the cosmic ray flux on the atmosphere. Further evidence is the recently reported correlation of radiocarbon and bristlecone pine growth ring variations and the lack of observational evidence to support the very large change in the earth's main field required for a geomagnetic explanation, especially of the ∼200‐year period. If it can be confirmed that the sun is the source, the very long periods suggest as one possibility that the core of the sun is the ultimate source, though multiple convective zone dynamo eigenmodes are an equally conjectural possibility. An alternate source for the longer period is pressure variations of the local arm of the galaxy, but this model is not favored.
Mars: Thickness of the lithosphere from the tectonic response to volcanic loads
Authors: Comer Robert P. , Solomon Sean C. , Head James W.
Published: February 2008

We determine the thickness (or flexural rigidity) of the elastic lithosphere on Mars in the vicinity of large volcanic loads, including six volcanoes and the Isidis basin mascon. Starting from the hypothesis that graben concentric to each volcanic feature formed as a result of stresses induced by flexure of the lithosphere in response to loading, we relate predicted surface stresses to the range of radial distances between the graben and the load centers in order to derive local estimates of the elastic lithosphere thickness at the time of loading. The basic method involves the selection of graben of likely flexural origin and the calculation of vertical displacement and surface horizontal stresses produced by the loading and flexure of a shell or plate. Bounds on thickness are obtained from a formal inversion of graben positions as well as from a consideration of important time‐dependent effects, including viscoelastic relaxation, volcano growth, and lithospheric thickening. Assuming Young's modulus to be 1012 dyn/cm², we find preferred values of elastic lithosphere thickness in the range 20 to 50 km (or flexural rigidities from 1030 to 1031 dyn cm) for regions surrounding Ascraeus Mons, Pavonis Mons, Arsia Mons, Alba Patera, and Elysium Mons. For the Isidis basin region the elastic lithosphere thickness must have exceeded 120 km at the time of graben formation; for Olympus Mons the absence of circumferential graben requires the elastic lithosphere to have been at least 150 km at the time of loading (these thicknesses correspond to a flexural rigidity greater than approximately 1032 dyn cm). Because the derived lithospheric thicknesses do not show any relationship to the relative ages of the loads, we interpret the results as an indication of a pronounced local thinning of the lithosphere beneath the central regions of the Tharsis and Elysium volcanic provinces.
Submesoscale, coherent vortices in the ocean
Authors: McWilliams James C.
Published: February 2008

A variety of observations of intense, long‐lived oceanic vortices are interpreted as examples of a distinct phenomenon, which is given the name Submesoscale, Coherent Vortices (SCV's). The distinguishing characteristics of SCV's are defined and illustrated by example, and a survey is made of the different SCV types presently known. On the basis of extant theoretical and modeling solutions, interpretations are made of the dynamics associated with SCV existence, movement, endurance, interactions with other currents, generation, and contributions to the transport of chemical properties in the ocean.
Poloidal and toroidal fields in geomagnetic field modeling
Authors: Backus George
Published: February 2008

The theory of surface operators is described and applied to four surface operators on spheres: the dimensionless surface gradient, ▽1=r▽‐r∂r; the dimensionless surface curl,
; the dimensionless surface Laplacian, ▽1²=▽1 · ▽1; and the Funk‐Hecke operators, integral operators with axisymmetric kernels. Three methods are given for solving ▽1²g=f as g=▽1−2f; one method works numerically when f has a rapidly convergent expansion in spherical harmonics, the second works when f is smooth in longitude but not latitude, and the third (a Funk‐Hecke operation) works when f is rough in all directions. With this apparatus, a complete proof is given of the Helmholtz representation of an arbitrary vector field v S (r), the spherical surface of radius r centered on the origin: there are unique scalar fields f, g, h on S(r) such that
and 〈g〉r=〈h〉r=0. Here 〈g〉r is the average value of g on S (r). From the Helmholtz representation on spherical surfaces, the Mie or poloidal‐toroidal representation in spherical shells is deduced. Suppose S(a,c) is the spherical shell whose inner and outer boundaries are S(a) and S(c). Suppose B is solenoidal in S (a,c), i.e., ▽·B=0 and 〈Br〉a=0. Then there are unique scalar fields P and Q in S(a,c) such that B=▽ × Λ1P + Λ1Q and 〈P〉r=〈Q〉r=0 for a ⪕ r ⪕ c. The fields P = ▽ × Λ1P and Q=Λ1Q are the poloidal and toroidal parts of B. Applications of this formalism to geomagnetic field modeling are discussed. Gauss's resolution of the geomagnetic field B on S(b) into internal and external parts is generalized; if the radial current Jr does not vanish on S (b), then to Gauss's expression must be added a toroidal field on S(b) due entirely to Jr on S(b). A simple proof is given of Runcorn's theorem that to first order in susceptibility no external magnetic field results from magnetization in a horizontally homogeneous spherical shell polarized by sources inside the shell. A Funk‐Hecke‐based method of modeling ionospheric currents is described, which may be more accurate than truncated spherical harmonic expansions and easier to use than Biot‐Savart integrals. Finally, the formalism makes possible the modeling of satellite samples of the geomagnetic field in a spherical shell S (a,c) where electric currents cannot be neglected. Two approximation schemes are described. One is a truncated power series expansion in (c‐a)/H, where H is the radial length scale of the currents. The other assumes that most of B in S(a,c) is not due to the currents between S (a) and S(c), and that the currents in S(a,c) are field‐aligned. Then the collection of physically possible magnetic fields in S(a,c) is only 50% larger, in a well‐defined sense, than the collection of vacuum fields there. Methods of calculation are given explicitly.
The theory of multiple scattering of radiation in plane parallel atmospheres
Authors: Stamnes Knut
Published: February 2008

A review is provided of multiple scattering theory associated with radiative transfer problems in planetary atmospheres. The radiative transfer equation pertaining to a scattering, absorbing, and emitting medium is considered. Analytic solutions are presented and computational aspects are discussed for plane parallel atmospheres. These computationally efficient and reliable solutions can be used to attack a multitude of radiative transfer problems in realistic atmospheres. Computational illustration is provided, a discussion of certain applications of the theory is presented, and some remaining theoretical problems are pointed out.
Composition of the lunar highland crust from near‐infrared spectroscopy
Authors: Pieters Carle M.
Published: February 2008

Near‐infrared reflectance spectra of the lunar highlands are synthesized to obtain global information about the composition of the lunar near‐side crust. Immature exposed surfaces from small fresh craters, mountains and massifs, and large craters with central peaks are included in a survey of rock types across the lunar near side. Compositions recognized in these data include anorthosite, noritic, gabbric, and troctolitic mineral assemblages. Three quarters of the areas studied that represent samples from the upper 1–2 km of lunar crust exhibit noritic compositions with different amounts of pyroxene and/or brecciation alteration. Norites are ubiquitous across the near side and show no spatial clustering associated with any of the major basins. In contrast to this noritic megaregolith of the upper crust, material representing stratigraphically deeper zones (5–15 km) of the lunar crust is dominated by gabbros, anorthosites, and troctolites, with less than a quarter of the areas studied exhibiting a noritic composition. The origin of the noritic megaregolith and its relation to deeper crustal material is thus somewhat of an enigma. The current limited statistics for areas identified as anorthosites and troctolites are insufficient to derive global spatial distributions. Gabbroic areas, however, are notably concentrated in the western hemisphere. Although incomplete for a global assessment of crustal materials, these data demonstrate that the lunar near‐side crust is clearly mineralogically heterogeneous, both laterally and vertically, and not well mixed below 1–2 km.
Structure and petrology of peridotites: Clues to their geodynamic environment
Authors: Nicolas Adolphe
Published: February 2008

The first part of this paper is a review on the main mineralogical, petrological and structural criteria which can be used to unravel the history of the various types of mantle peridotites met at the earth's surface. These criteria are applied in the second part to show that most peridotites share a common history which is that of an asthenospheric uprise followed by specific fates corresponding to their lithospheric history. The unifying concept is that of adiabatic ascent rate, related to rifting and spreading rates. Rates lower than 0.5 cm/yr in continental graben correspond to departure from adiabatic conditions at depths greater than 30 km. This inhibits further melt extraction with as consequences a limited melt extraction and comparatively fertile spinel lherzolites as residue. Higher rates, probably not exceeding 1 cm/yr, correspond to oceanic rifts with the main melt extraction completed around 15 km, generating a thin oceanic crust and plagioclase lherzolites as residue. Finally, rates greater than 1–2 cm/yr correspond to oceanic ridges with melt being extracted at Moho depth, thus generating a 6‐km‐thick crust and leaving depleted harzburgites as residue. Thus examination of the peridotite type and associated crustal formations give some clue to trace back the environment of origin. This conclusion must however be tempered by the fact that the spreading rate, envisioned here as the principal controlling parameter, can change with space and time in a given environment (mantle diapirism, rifting, seafloor spreading, crust generation).
Recent research in snow hydrology
Authors: Dozier Jeff
Published: February 2008

Recent work on snow pack energy exchange has involved detailed investigations on snow albedo and attempts to integrate energy energy balance calculations over drainage basins. Along with our better understanding of the electromagnetic properties of snow, research in remote sensing has become more focused toward estimation of snow pack properties. In snow metamorphism, analyses of the physical processes must now be coupled to better descriptions of the geometry of the snow’s microstructure. The dilution method now appears to be the best direct technique for measuring the liquid water content of snow; work on electromagnetic methods continues. Increasing attention to the chemistry of the snow pack has come with the general focus on acid precipitation in hydrology.
Coastal ocean physical processes
Authors: Brink Kenneth H.
Published: February 2008

In the most recent paper of this series, Allen et al. [1983] used a geographical approach to summarize United States progress in continental shelf physical oceanography. Their approach tended to emphasize observational results and differences among regions. This installment in the series will take an alternative tack, by trying to summarize progress in terms of understanding particular physical processes. This approach cannot escape being at least somewhat geographical, however, because different processes tend to predominate in different parts of the world.
Venus: Summary and review of science research activities 1983–87
Authors: Saunders R. S.
Published: February 2008

In the past four years, the first high resolution synoptic images of the surface of Venus have been obtained and we have learned more about the nature of its surface and atmosphere. The major accomplishments of the U.S.S.R. in Venus exploration have been observed with great interest by U. S. investigators, some of whom have begun joint research efforts with Soviet scientists. Venera 15 and 16 radar imaging experiments, and new data obtained at the Arecibo Observatory, have provided answers to some important questions. Conjectured volcanic features have been resolved into unmistakable calderas or distinct lava flow morphologies. The question of whether Venus, like the Earth, may have high erosion rates is answered, and from the observed number of presumed impact craters, it appears that resurfacing rates on Venus are much smaller than on Earth. No evidence of water or wind activity has been seen.
Atmospheric dynamics
Authors: Lindzen Richard S. , Farrell Brian
Published: February 2008

American contributions to Atmospheric Dynamics during the period 1983–86 are briefly summarized.
Perturbations to the global atmosphere associated with the El Chichon volcanic eruption of 1982
Authors: Hofmann David J.
Published: February 2008

In terms of effects on the stratosphere, the 1982 eruption of the Mexican volcano El Chichón (17°N) is believed to have been one of the two or three greatest in the past century. In terms of providing opportunities for testing physical and chemical models in the stratosphere, it is unprecedented. Earlier recent eruptions (Fuego in 1974, St. Helens in 1980, and Alaid in 1981) were not of the magnitude required to investigate the more subtle chemical and concomitant radiative and dynamical consequences, and while Agung in 1963 may have been, the necessary measurements are absent. Thus for the first time, trace chemical species such as HCℓ and OH were observed to increase, and other species, possibly related to these, were observed to decrease (O3, NO, and NO2) following the eruption. Volcanic SO2was observed from space for the first time, and its conversion into H2SO4, vapor, condensation nuclei, and finally, sulfuric acid aerosol were monitored closely by both in situ and remote measurements. In this manner the very uncertain reaction sequence, which converts SO2to H2SO4could be ascertained. The optical depth of about 0.3, produced by the sulfuric acid aerosol which formed after the eruption, ranks it with the largest in recent history (for example, Krakatau in 1883). At least three factors contributed to the severity of the eruption aftermath. These include the apparently large fraction of sulfur involved for an eruption of only moderate proportions, the latitude of the volcano, and the time of year of the eruption. As in the case of the eruption of Agung (8°S) in 1963, the stratosphere was observed to warm, especially in equatorial regions. However, the expected surface cooling did not apparently occur. A highly enhanced El Niño, which is followed by tropospheric warming, may have acted to counterbalance the surface cooling in the case of El Chichón. Evidence that enhanced El Niño events usually accompany major low‐latitude eruptions suggests a volcanic effect on global atmospheric transport, thus providing a climatic self‐healing effect.
Geochemical evolution of the crust and mantle
Authors: Carlson Richard W.
Published: February 2008

Between 1983 and 1986, geochemical studies of the crust and mantle were marked by an increased appreciation of the complexity of the solid earth and an enhanced set of tools with which to decipher previously underdetermined problems. Two component compositional models for the mantle expanded to 3, 4, and 5 components as the number of isotope systems used simultaneously expanded from Sr and Nd to include Pb, Hf, He, and Xe. Increased use of a widened variety of trace‐element abundances provided new views of the processes responsible for chemical variability in the earth. Improved techniques for radiometric age determination allowed better resolution of the events involved in the formation of the ancient crust, and the identification of crustal materials older than 4.0 Ga. Increased sophistication in studies of sedimentary systems and granitoid rocks provided new insights into rates of crustal growth and recycling.
Rheology of the lithosphere: Selected topics
Authors: Kirby S. H. , Kronenberg A. K.
Published: February 2008

We review recent results concerning the rheology of the lithosphere with special attention to the following topics: 1) the flexure of the oceanic lithosphere, 2) deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins, 3) the rheological stratification of the continents, 4) strain localization and shear zone development, and 5) strain‐induced crystallographic preferred orientations and anisotropies in body‐wave velocities. We conclude with a section citing the 1983–1986 rock mechanics literature by category.
Snowfall in high southern latitudes
Authors: Bromwich David H.
Published: February 2008

Precipitation over Antarctica is an important climatic variable whose study has been limited by the frequent inability to discriminate between actual snow precipitation and drifting snow. Recent advances in point precipitation measurements promise to circumvent this problem. In addition, indirect estimates based upon the atmospheric water balance equation provide seasonal precipitation amounts for areas larger than 1×106 km². For broad‐scale studies in the continental interior net snow accumulation closely approximates precipitation. Annual precipitation is relatively high over the marginal ice slopes in relation to amounts in the interior. This meridional distribution is due to the orographic lifting of moist air by the ice sheet. Zonal precipitation variations are related to the quasi‐stationary cyclones in the circumpolar low‐pressure trough. Most precipitation falls in winter, when the average moisture content of the air is low. The intensity of cyclonic activity is the key factor governing the amount of precipitation and its variations. Precipitation generation in coastal regions is strongly influenced by the fact that poleward moving, moist maritime air masses are deflected by the steep marginal ice slopes to blow parallel to the terrain contours. Direct orographic lifting with accompanying adiabatic cooling is the dominant precipitation formation mechanism inland of the 1‐km elevation contour; intrusions of moist air far into the continent are accompanied by southerly winds through a deep tropospheric layer. Above 3000 m elevation where terrain slopes are gentle, radiative cooling is the primary mechanism by which saturation is maintained within moist air, and thus by which precipitation is formed. Most precipitation at these elevations falls from clear skies. This phenomenon does not differ from precipitation originating in clouds but is a direct result of the low moisture content of the air, and hence ice layers are optically too thin to be visible as clouds.
Surface winds over the Antarctic continent: A review
Authors: Parish Thomas R.
Published: February 2008

Surface winds over Antarctica, often classified as “katabatic,” are intimately related to the orientation and steepness of the underlying ice terrain. Such flows result primarily from the strong radiational cooling of the sloping ice surface which creates a downslope‐directed horizontal pressure gradient force. It is possible to diagnose the time‐averaged, near‐surface streamline patterns of cold air drainage currents using recently compiled, detailed Antarctic ice topography maps and appropriate estimates of the strength of the surface temperature inversion. The resulting streamlines agree with available observations and illustrate the high degree of nonuniformity of gravity‐driven flows off the ice sheets. In certain interior sections, negatively buoyant air from a large catchment area drains through a restricted section of coastline. Such confluence zones represent regions of enhanced supplies of cold air and are shown to be related to anomalously strong katabatic winds. Implications for sea ice formation are discussed.
Results from Antarctic optical studies
Authors: Eather R. H.
Published: February 2008

This review summarizes the last decade of upper atmospheric and magnetospheric studies in Antarctica using ground‐based optical techniques. These techniques have included simple all‐sky cameras, spectral imaging, photometry, and interferometry. Research areas investigated include dayside aurora, auroral conjugacy, thermospheric dynamics, and wave‐particle interactions. Various national programs have tended to specialize in particular areas, and as yet there has been little emphasis on international cooperation to study large‐scale phenomena. Nevertheless, the contribution from Antarctic optical studies over the past decade has been diverse and significant.
Introduction to “Milankovitch Theory and climate” by A. Berger
Authors: Lal D.
Published: February 2008

One of the most fascinating and challenging problems of modern interdisciplinary research is to understand the causes of global climatic changes. This is an area of research which has been extensively covered in the past at the various IUGG meetings by more than two associations, and the same holds for this assembly. And the thrust of research continues with all force from many directions.

Presently there seems to be a general consensus that the influence of orbital variations on climate is real enough and that all efforts should be made to test the astronomical theory with climate models. The progress made in understanding and modeling physical mechanisms by which the climate system responds to the astronomically forced changes in the pattern of incoming solar radiation was recently evaluated at a climate symposium organized by Professor Andre Berger, who will deliver today'S talk.
Where do field lines go in the quiet magnetosphere?
Authors: Stern David P. , Alexeev Igor I.
Published: February 2008

The state of our knowledge is reviewed concerning the global pattern of geomagnetic field lines. Sources of information on that pattern include (1) magnetic field models, derived directly from magnetic data or indirectly from general observed properties and from physics, (2) the tracing of magnetospheric features, e.g., polar cusps or the inner edge of the plasma sheet, (3) matching of magnetic flux, and (4) analysis of magnetic fields. Field line structure inside about 8 Earth radii is known fairly well, but beyond that, especially in the tail, the situation becomes rather uncertain and variable. Two particularly difficult problems are (1) the linkage between open field lines and the interplanetary field and (2) the field line structure of the “quiescent” magnetosphere following periods of prolonged northward Bz.
The heliopause
Authors: Suess Steven T.
Published: February 2008

There is a growing anticipation among space scientists that a Pioneer or Voyager spacecraft will soon pass through one of the last major frontiers in the solar system—the heliospheric terminal shock. Some unknown, but perhaps small, distance beyond the terminal shock is the heliopause, marking the final boundary between solar wind and galactic plasmas and the final goal of these spacecraft. This occasion is drawing widespread attention because of the opportunity it offers to obtain a wealth of information on the properties of the galaxy, the interstellar medium, and the large‐scale interactions of that medium with stellar winds. The anticipation has been raised by several tentative remote detections of the shock placing it just beyond the present spacecraft locations. However, uncertainties in the physical processes and parameters that determine the location of the boundary lead to equal uncertainties in predicting which of the spacecraft will reach it first. This review is largely phenomenological with the intent of providing an overview of the topic and the dominant physical processes.
Foreword
Authors: Jordan E. C.
Published: February 2008

Effective with this issue, Radio Science will be published under the sole editorial control of the U. S. National Committee of the International Union of Radio Science (URSI). As most of you know, it has been published since 1964 by the Department of Commerce with the cosponsorship of USNC/URSI. The new publisher is the American Geophysical Union (AGU), which currently publishes several leading journals in the geophysical sciences. The interests of AGU and USNC/URSI are complementary; because the Council of the AGU serves as the U. S. National Committee of the International Union of Geodesy and Geophysics (IUGG), an international complementarity of interests also exists.
On the Nature of the Irregularities that Produce Partial Reflections of Radio Waves From the Lower Ionosphere (70–100 km)
Authors: Austin G. L. , Manson A. H.
Published: February 2008

The irregularities that produce the partial reflection of radio waves (1.5–6.0 MHz) from the D region are investigated. Experimental evidence indicates that reflection usually occurs from localized irregularities rather than from a region of smaller scale turbulence.
VHF Technique for Locating Lightning
Authors: Oetzel G. N. , Pierce E. T.
Published: February 2008

The principles of a lightning location method using the VHF signals emitted by the discharge are outlined. Consideration of the source characteristics (notably signal strength and intervals between pulses; of the noise background; of the differences between the signals incident at spatially separated receivers; and of the electronic equipment now available commercially) indicate that the method is entirely feasible. For a lightning flash at a distance of 20 km, a spatial resolution of 200 meters, and a temporal resolution of 20 μsec could be readily obtained; consequently, the development of the successive VHF radiating events in the discharge could be traced.
Clipping Loss in the One‐Bit Autocorrelation Spectral Line Receiver
Authors: Burns W. R. , Yao Stanton S.
Published: February 2008

An error analysis of the one‐bit autocorrelation method of spectral estimation is presented, and the variance on the autocorrelation estimate and spectral estimate is given. In the nonclipped (many‐bit) case, the normal Nyquist sampling rate of 2B is sufficient. Higher sampling rates do not further improve the spectral estimate. In the clipped (one‐bit) case, increasing the sampling rate does improve the estimate. The present work was initiated to examine this effect. The results verify the decrease in spectral variance with increased sampling rate. Itis shown that a part of the signal‐to‐noise deterioration caused by the clipping may be removed by the higher sampling. An increased sampling rate from 2B to 4B, however, achieves most of the available improvement.
Theory of Ion Collection by a Stationary Electrostatic Probe
Authors: Cicerone R. J. , Bowhill S. A.
Published: February 2008

The operation of a spherical electrostatic probe in a weakly ionized, collision‐dominated gas, such as the D region of the ionosphere, is examined theoretically. A plasma consisting of one type of positive ion, one type of negative ion (or electrons), and a neutral gas is assumed to surround the (stationary) probe. The equations governing the collection of positive ions by a negatively biased probe are developed from a continuum theory after Su and Lam (1963) and are solved numerically. For highly negative probes a method is found to solve the equations in their exact form. Current‐voltage characteristics for probes of moderate size in comparison with the Debye length are presented graphically. It is shown that the current to the probe varies approximately as the 0.6 power of the probe voltage, which varies slowly with the ratio of probe radius to Debye length. The current also varies approximately as the 0.75 power of the positive ion concentration for D‐region conditions. These conclusions show the importance of including space charge in the theory and agree rather well with those of Balmain's (1966) simplified analysis. A considerable improvement is obtained over the results of Su and Lam for the regime of interest.
Commission 5: Progress in Radio and Radar Astronomy
Authors: Erickson W. C.
Published: February 2008

The institutions that contributed material for this report are:

1. Arecibo Ionospheric Observatory.

2. NASA‐Goddard Space Flight Center.

3. Bell Telephone Laboratories.

4. University of Texas.

5. University of Maryland.

6. University of Virginia.

7. Florida State University.

8. Air Force Cambridge Research Laboratories.

9. Stanford University.

10. MIT Lincoln Laboratory.

11. Ohio State University.

12. University of Colorado.

13. National Radio Astronomy Observatory.

14. Jet Propulsion Laboratory.

15. Owens Valley Radio Observatory.

Only a minor attempt has been made to mention work performed at other observatories in the U.S.A.
On the Application of Variation Techniques to the Ray Theory of Radio Propagation
Authors: Bennett J. A.
Published: February 2008

The first variation of the phase path is developed from the point of view of Hamilton, and the result is applied to the calculation of Doppler frequency shift and group path. The second variation δm δnP of the phase path P is considered in the general case when the medium depends on both m and n. By generalizing identities arising in the usual investigation of extrema and by obtaining equations that must be satisfied because the arcs concerned are rays, a number of alternative expressions are found. These involve contributions due to the end‐points of the ray, due to the m,n dependence of the medium along a fixed ray, and due to the m,n dependence of the actual ray path. The application of the results to differential Doppler and Faraday fading measurements is briefly discussed. As an illustration a problem involving approximately straight rays in a plane, horizontally stratified medium is discussed and approximate expressions are found for P and dP/dt.
Relationship Between the Partial Reflection of Radio Waves from the Lower Ionosphere and Irregularities as Measured by Rocket Probes
Authors: Manson A. H. , Merry M. W. J. , Vincent R. A.
Published: February 2008

Studies of radio waves (2.22–2.66 MHz) partially reflected from the lower ionosphere (50–90 km) have been used to calculate the magnitudes of the Fresnel irregularities required to give the observed signal strengths. These irregularities require 1–18% perturbations in electron density and show a distinctive seasonal variation, having a minimum in summer and a maximum in winter. Recently published electron‐density profiles obtained from rocket probes have revealed fine‐scale structure comparable in magnitude and vertical dimension to these calculated perturbations. The reflection coefficients and the magnitudes of the equivalent Fresnel irregularities are calculated for individual irregularities and are shown to be only 3 to 4 times less than those required by the radio‐wave data. Reflections from several of these closely spaced irregularities should give rise to signals comparable with the observations. It appears that the fine structure in these profiles is real and has much smaller vertical dimension than any other published measurements of mesospheric parameters.
Determination of F‐region Vertical Drifts at Millstone Hill
Authors: Evans J. V. , Brockelman R. A. , Julian R. F. , Reid W. A. , Carpenter L. A.
Published: February 2008

Thomson scatter observations of the F region at altitudes between 450 and 900 km are described; from them the bulk vertical velocity of the ambient electrons can be determined. These measurements were made possible by the construction of a new spectrum analyzer; they supplement earlier established programs to measure F‐region densities and temperatures at Millstone Hill. The uncertainty in the results varies both with time of day and with altitude but is of the order of ±5 m/sec. Sample results are presented which show evidence of (1) thermal expansion and contraction of the layer and (2) oscillatory fluctuations attributed to traveling ionospheric disturbances.
Ranger Photographs of the Moon
Authors: Trask N. J.
Published: February 2008

Photographs from the Ranger probes provided the first direct evidence on the fine‐scale topography of the moon and showed that the surface is relatively smooth over slope distances of 1 meter. In addition to craters, elements contributing to the topography at this scale are the closely spaced ridges and troughs of lunar patterned ground. Blocks in the size range 0.5 meters to several meters were not seen in the Ranger pictures, perhaps because of the limited sampling at three widely separated points. Ranger 7 photographs showed the pre‐ponderance of shallow elongate to circular craters along rays. Ranger 8 photographs were notable for portraying with new clarity the craters Sabine and Ritter, which appear to be of internal rather than impact origin. Ranger 9 photographs of the floor of the crater Alphonsus contained data from which a complicated geologic history of the floor can be deciphered.
The Infrared Moon: Data, Interpretations, and Implications
Authors: Winter Donald F.
Published: February 2008

Measurements of infrared (IR) radiation from the moon are used to estimate the thermophysical properties of the lunar soil and to infer the general nature of small‐scale surface relief. Directional emission characteristics of the illuminated surface are probably associated with small craters of recent origin. On the other hand, abnormal populations of exposed rocks are thought to be responsible for many of the localized thermal enhancements observed during an eclipse. Implications of infrared measurements regarding the evolution of the surface are described.
Geochemistry of Venus and the Interpretation of the Radar Data
Authors: Lewis John S.
Published: February 2008

A geochemical study of the interactions of the atmosphere and lithosphere of Venus predicts that a substantial mass of electrically conducting clouds may be present on the planet. Furthermore, the existence of a substantial abundance of gases capable of strong microwave absorption also seems probable. The possible effects of these phenomena on the microwave properties of the atmosphere are discussed in a qualitative manner, and it is concluded that, although models with surface pressures ranging from perhaps 30 to 140 bars may be reconciled with the radar data, models near the lower end of this range are more appealing from the standpoint of atmospheric chemistry and geochemical thermodynamics.
Diurnal Transmission Loss Differences at Very Low Frequency
Authors: Steele F. K. , Diede A. H.
Published: February 2008

VLF amplitude data taken at frequencies from 9.2 to 17.2 kHz on two long paths are analyzed in terms of diurnal transmission loss differences. The observed values are in fair accord with theoretical values for the first mode, and the effect of the second mode could account for the observed data scatter in the frequency range of the calculations.
Factorization Method Applied to Electromagnetic Wave Propagation in a Curved Waveguide with Nonuniform Walls
Authors: Wait James R.
Published: February 2008

Azimuthally directed wave propagation in a concentric cylindrical cavity is considered. The surface impedance of the outer wall is uniform, but there is a discontinuity in the surface impedance for the lower wall. This is a two‐dimensional model of propagation of radio waves in the earth‐ionosphere waveguide across a land/sea boundary. The dual integral equations for the problem are solved exactly by a Wiener‐Hopf procedure. Various limiting forms of the solution are discussed. In particular, it is shown that the exact expression for the mode conversion coefficient is closely related in form to the result obtained by Kirchhoff theory.
Propagation of ELF Pulses in the Earth‐Ionosphere Cavity and Application to ‘Slow Tail’ Atmospherics
Authors: Jones D. Llanwyn
Published: February 2008

The propagation of ELF electromagnetic pulses in the earth‐ionosphere cavity is considered with special reference to ‘slow tail’ atmospherics. The problem is formulated in the frequency domain; inversion to the time domain is achieved by a numerical evaluation of the Fourier transform. The propagational model employed involves a spherical earth with a concentric, spherically stratified, inhomogeneous, isotropic ionosphere. The pulse source assumed represents the median return stroke of a lightning discharge. Both short‐range propagation and long‐range propagation are considered. Particular attention is paid to the nature of the electric‐ and magnetic‐field components of the pulse in the vicinity of the antipode of the source.
Very Long Baseline Interferometry of Jupiter at 18 MHz
Authors: Carr T. D. , Lynch M. A. , Paul M. P. , Brown G. W. , May J. , Six N. F. , Robinson V. M. , Block W. F.
Published: February 2008

Very long baseline interferometry (VLBI) observations of the decametric bursts from Jupiter were initiated by the University of Florida in 1964, with a tape‐recording intensity interferometry operating at 18 MHz over a baseline of 55 km. This was apparently the first VLBI. Since the source was unresolved, subsequent observations were made with progressively longer baselines. The longest baseline is 7900 km (between Kentucky and Chile). Preliminary results indicate that if the S‐burst sources are incoherent, at least some of them must be smaller than 0.1″ of arc.
Interferometric Observations on the Green Bank‐Crimea Baseline—Summary
Authors: Broderick J. J. , Clark B. G. , Cohen M. H. , Ephanov V. A. , Hansson B. , Jauncey D. L. , Kellermann K. I. , Kogan L. R. , Kostenko V. I. , Matveyenko L. I. , Moiseyev I. G. , Payne J. , Vitkevitch V. V.
Published: February 2008

In September and October of 1969 we performed an experiment at 6 and 2.8 cm between the 42‐m telescope of the National Radio Astronomy Observatory (NRAO) at Green Bank, West Virginia, and the 22‐m telescope of the Crimea Astrophysical Observatory at Simeis on the Crimea peninsula, USSR. The 8035‐km baseline corresponded to a separation in wavelengths of 135×106 and 286×106 at 6 and 2.8 cm, respectively. Rubidium oscillators were used at both stations for time and frequency standards, except during the 6‐cm observations when a hydrogen maser was used at Green Bank. The system temperatures for the interferometer were 125° and 210° K at 6 and 2.8 cm, respectively.
A Decametric Long Baseline Interferometer System
Authors: Sargent Howard H. , Klemperer W. K.
Published: February 2008

A relatively simple long baseline interferometer (LBI) system, which uses analog tape recorders, is described; it operates at decametric wavelength (26.3 MHz). A base station at Boulder with an array of 76 full‐wave dipoles is used in conjunction with a small, readily portable antenna of sixteen full‐wave dipoles that can be set up at various outlying field sites by two men in less than three hours. Commercial rubidium clocks are employed for timing and for local oscillator signals at each station. Tapes are aligned and data are correlated by an analog multiplier after each run at the base station. The use of pseudo‐random code generators which can be reset and started on a given clock pulse at each station greatly simplifies tape alignment and system calibration.
Gain, Efficiency, and Receiving Cross Section of Antennas in a Dissipative Medium
Authors: Wasylkiwskyj Wasyl
Published: February 2008

A general formulation is presented for the gain, efficiency, and receiving cross section of antennas in a dissipative (homogeneous and isotropic) medium, and performance limits are established that are generally applicable to reciprocal antennas. The antenna is assumed to be encapsulated in a spherical enclosure immersed in a lossy medium. It is shown that the realized gain is proportional to the product of the directive gain and an efficiency factor, which for lossless antennas is a measure of only the dissipation associated with the near fields. An upper bound on this efficiency is in fact attainable by an elementary magnetic dipole. Since plane waves incident on antennas in dissipative media are frequently inhomogeneous, the definition of the receiving cross section is extended to include such waves. It is shown that for inhomogeneous plane wave incidence the wave received at the antenna terminals is proportional to a far field pattern quantity evaluated in the invisible region. These results are applied to antennas imbedded in a lossy half‐space. The limitations on the receiving cross section and realized gain imposed by dissipation in the medium are considered. For a spherical enclosure of a given radius an upper bound is obtained on the receiving cross section. Moreover, this upper bound can be attained by a lossless antenna. Normalized curves of the maximum receiving cross section are plotted for several dissipation factors.
ELF Attenuation Rates and Phase Velocities Observed From Slow‐Tail Components of Atmospherics
Authors: Taylor W. L. , Sao K.
Published: February 2008

Slow‐tail portions of atmospherics were recorded simultaneously in Japan and the United States from sources located in the Pacific Ocean area. The amplitude and phase spectra of forty pairs of selected atmospherics were computed, and propagation parameters for the zero‐order wave‐guide mode were calculated for nighttime conditions only. Attenuation rates for W‐E propagation extended from about 0.5 db/Mm at 20 Hz to 2.0 db/Mm at 300 Hz and for E‐W propagation from 0.8 db/Mm at 20 Hz to about 2.8 db/Mm at 300 Hz. The phase velocities extended from about 0.7 and 0.8 the velocity of light for W‐E and E‐W propagation, respectively, at 20 Hz to about 0.93 the velocity of light for either direction at 300 Hz.