bluuebunny/crossref_metadata_2025 huggingface dataset:
Recent developments in theory of solar wind
Authors: Parker E. N.
Published: February 2008

Current problems and developments in the theory of the large‐scale expansion of the solar corona are reviewed. The outstanding question is whether the energy supply to the quiet corona is mainly thermal conduction outward from a region of active heating at its base or mainly wage propagation outward from the base. It is suggested that the question can be settled only when the properties of the wind can be sampled over a wide range of radial distance from the sun, from far inside the orbit of earth to well beyond. It has been suggested that hydromagnetic waves may drive the expansion of the active corona by direct transfer of momentum as well as energy.
Superrotation of the upper atmosphere
Authors: Rishbeth H.
Published: February 2008

Some years ago D. G. King‐Hele discovered, from small changes in the orbital inclination of artificial satellites, that the upper atmosphere rotates about 20% faster than the earth. This article outlines several theories that have been advanced to explain this so‐called ‘superrotation.’ Some theories explain it as a consequence of the horizontal pressure variations that are known to exist in the thermosphere. Other theories attribute it to ionospheric or magnetospheric motions that react on the neutral air. Another group of theories treats superrotation in terms of thermally driven instabilities or oscillations in the thermosphere. It is not yet possible to make a clear choice of a ‘correct’ explanation of superrotation, but at present the following appear to be possible contributory causes: geostrophic winds, diurnal modulation of ion drag by wind‐produced polarization fields, ion drag driven by electric fields associated with magnetic substorms, the ‘moving flame’ phenomenon, and deposition by atmospheric waves of eastward momentum carried from lower levels.
Precipitation of auroral and ring current particles by artificial plasma injection
Authors: Cornwall John M.
Published: February 2008

Outside the plasmasphere, most of the energy in magnetospherically trapped particles resides in two populations, auroral‐energy electrons and the proton ring current, with single‐particle energies from 1 to 50 kev. The ring current contains more energy than all other components of the magnetospherically trapped radiation. It may be possible to precipitate a large fraction of this energy into the ionosphere by injection of a light‐ion plasma from a synchronous satellite; this would render the ring current protons unstable to a variety of plasma modes. Auroral‐energy electrons can be precipitated by ions of any mass, but heavy (e.g., barium) ions will quench what may be the most important proton instability, which takes place in the electromagnetic ion cyclotron mode. This mode is unstable only if the ring current protons have an average velocity greater than the wave phase velocity. The wave speed varies as N−1/2, where N is the cold plasma density; under natural conditions, N is too small for the ring current to be unstable outside the plasmapause. Injection of some tens of pounds of lithium ions at synchronous altitude will create an unstable region with a diameter of a few thousand kilometers; as a result of the instability, ring current protons will precipitate into the ionosphere at a rate up to 1 erg cm−2 sec−1. This should produce important effects in the upper E and F layers of the ionosphere. At the same time, precipitating auroral‐energy electrons may create auroras and other effects usually associated with geomagnetic storms.
Range of Earth structure nonuniqueness implied by body wave observations
Authors: Wiggins Ralph A. , McMechan George A. , Toksöz M. Nafi
Published: February 2008

The Herglotz‐Wiechert integral for the direct inversion of ray parameter versus distance curves can be manipulated to find the envelope of all possible models consistent with geometrical body wave observations (travel time and ray parameter versus distance). Such an extremal inversion approach has been used to find the uncertainty bounds for the velocity structure in the mantle and core. We find, for example, that there is an uncertainty of ±40 km in the radius of the inner core boundary, ±18 km at the core‐mantle boundary, and ±35 km at the 435‐km transition zone. The velocity uncertainty is about ±0.08 km/sec for P and S waves in the lower mantle and about ±0.20 km/sec in the core. Experiments with various combinations of ray types in the core indicate that rather crude observations of SKKS‐SKS travel times confine the range of possible models far more dramatically than do the most precise estimates of PmKP travel times. Comparisons of results from extremal inversion and linearized perturbation inversions indicate that body wave behavior is too strongly nonlinear for linearized schemes to be effective for predicting uncertainty.
Auroral helium precipitation
Authors: Reasoner David L.
Published: February 2008

Several measurements of the flux and charge state of auroral helium precipitation have been made and reported between 1967 and 1972. The primary purpose of these experiments has been to deduce the source location of auroral ions by comparison of auroral helium populations with those measured in the ionosphere and the solar wind. Accordingly, results of these experiments are reviewed and summarized, along with measurements of solar wind and ionospheric helium abundances. It is concluded that the available data suggest a solar wind origin of auroral ions and in addition place certain constraints on the acceleration mechanism. The problem of modification of the incident charge state of a helium beam by atmospheric charge exchange is discussed, and it is shown that auroral helium measurements should be made at altitudes above 400 km to insure that the measurements are a true indication of the original beam charge state composition. Attempts to measure optical emissions of auroral helium are also reviewed, with the conclusion that definitive reproducible detection of such emissions has not been accomplished to date.
Nonhydrostatic thermodynamics and its geologic applications
Authors: Paterson M. S.
Published: February 2008

The general principles of equilibrium thermodynamics are briefly stated in a form conveniently applicable to nonhydrostatic problems, i.e., with emphasis on the aspects, absent from hydrostatic applications, that have sometimes caused confusion. The importance of taking into account fully and clearly the constraints involved in a particular problem and of treating the work term very carefully in considering an energy variation are particularly emphasized. For illustration the following problems of geologic interest are treated: (1) equilibrium between a stressed solid and its solution, including the ‘pressure solution’ problem; (2) recrystallization under stress and the resulting crystallographic preferred orientation in aggregates; (3) coherent phase transitions under stress; and (4) diffusion in a stressed solid.
On the rheology of the upper mantle
Authors: Stocker R. L. , Ashby M. F.
Published: February 2008

Mechanisms permitting the steady state deformation of crystalline solids are critically reviewed, and an approximate constitutive relationship is derived for fluid phase transport in a partial melt. (Fluid phase transport has a linear stress dependence and an inverse squared grain size dependence.) A set of rheologic material constants for olivine (Fo85‐Fo95) are derived from a combination of experimental data and empirical generalizations. Our preferred power law exponent n is 4.2, and the associated Dorn parameter is 1.2 × 104. Dislocation creep below the high‐stress breakdown is the dominant deformation mechanism in the upper mantle. The possibility exists that the bottom of the upper mantle is not deforming at a significant rate (≥10−14/sec) if the activation volume for diffusion is greater than 40 cm³/mole.
Lunar magnetism
Authors: Fuller M.
Published: February 2008

The principal magnetic results of the Apollo program are the demonstration of the natural remanent magnetization (NRM) of returned lunar samples, the discovery of local remanent fields at the Apollo 12, 14, 15, and 16 sites, and the detection with the 15 and 16 subsatellites of magnetic anomalies whose size suggests sources of homogeneous remanent magnetization with a scale size of at least tens of kilometers. The predominant ferromagnetic constituent of the Apollo sample is metallic iron, alloyed sometimes with a few percent of nickel and cobalt. The soils and breccias contain a few tenths to 1% by weight of iron, whereas mare basalts contain about one‐tenth as much. The iron in the mare basalts is typically fine and single domain. Excess iron in the form of superparamagnetic and single‐domain spherules in impact‐generated glass is found in the soil and unannealed breccias. In contrast, in well‐annealed breccias the iron is somewhat coarser and multidomain. A NRM of between 10−3 and 10−7 gauss cm³ g−1 has been reported in the samples. Certain breccias carry the strongest and most stable NRM. The NRM has three major sources: contamination, secondary magnetization acquired on the lunar surface, and primary magnetization associated with the origin of the rock. Some rocks appear to carry primary NRM. Two Thellier‐Thellier intensity determinations have yielded values of 2100±80 and 1.6 Oe for the ancient lunar fields in which NRM was acquired. There are other indications of a large spread in field values, but more determinations are badly needed. The fields observed with the Apollo surface magnetometers have ranged from a few gammas to hundreds of gammas. They are remanent fields due to near‐surface magnetized material. Highland sites exhibit stronger fields than do the mare sites. The sources of the fields have been interpreted as homogeneously magnetized plates that have been disturbed by later impact demagnetization. The anomalies detected by the subsatellites are relatively localized and strong on the farside of the moon, having dimensions comparable with those of the larger craters. The most spectacular feature is near the Van de Graaff crater. On the nearside, subdued magnetic relief predominates. The origin of lunar magnetism remains a puzzle. Numerous suggestions have been made. Although some of them can already be eliminated as being unfeasible, there remain an embarrassingly large number of possibilities.
Lunar near‐surface structure
Authors: Cooper Michael R. , Kovach Robert L. , Watkins Joel S.
Published: February 2008

Seismic refraction data obtained at the Apollo 14, 16, and 17 landing sites permit a compressional wave velocity profile of the lunar near surface to be derived. Although the regolith is locally variable in thickness, it possesses surprisingly similar seismic characteristics. Beneath the regolith at the Apollo 14 Fra Mauro site and the Apollo 16 Descartes site is material with a seismic velocity of ∼300 m/s, believed to be brecciated material or impact‐derived debris. Considerable detail is known about the velocity structure at the Apollo 17 Taurus‐Littrow site. Seismic velocities of 100, 327, 495, 960, and 4700 m/s are observed. The depth to the top of the 4700‐m/s material is 1385 m, compatible with gravity estimates for the thickness of mare basaltic flows, which fill the Taurus‐Littrow valley. The observed magnitude of the velocity change with depth and the implied steep velocity‐depth gradient of >2 km/s/km are much larger than have been observed on compaction experiments on granular materials and preclude simple cold compaction of a fine‐grained rock powder to thicknesses of the order of kilometers. The large velocity change from 960 to 4700 m/s is more indicative of a compositional change than a change of physical properties alone. This high velocity is believed to be representative of the material that forms the lunar highlands.
Geomagnetic deep sounding with arrays of magnetometers
Authors: Frazer M. C.
Published: February 2008

Arrays of about 25 portable magnetic variometers have recently been used to record the total varying geomagnetic field over an area 1000–2000 km square. The total varying field consists of a portion generated outside the solid earth (in the ionosphere and the magnetosphere) and a portion induced by this external field (in the material of varying conductivity in the crust and upper mantle of the earth). By plotting sets of magnetograms of the observed varying fields, Fourier spectra over the full range of periods available, or contours of Fourier amplitudes at specified periods, localized anomalies in the total field are identified. Careful examination of these various plots yields considerable qualitative information about the subsurface variations in conductivity that produce these anomalies. Formal methods of separating the observed field into components of internal and external origin exist and can be applied to this problem, but with questionable accuracy. Semiquantitative estimates of the separate components may be just as accurate. Quantitative interpretation of the anomalous internal fields in terms of inhomogeneities in conductivity is at present almost entirely based on numerical modeling techniques. Three such methods have been used so far, the one using finite differences being the most successful. Results of such modeling are neither unique nor very close to the observed field patterns. Another method of analysis is based on transfer functions and cross‐correlation spectra, and this method may turn out to be more useful.
Solid Earth and ocean tides estimated from satellite orbit analyses
Authors: Lambeck Kurt , Cazenave Anny , Balmino Georges
Published: February 2008

The earth's tidal deformations cause perturbations in the motions of close earth satellites, observations of which give estimates of the Love number k2 and phase lag δ. The contribution of the ocean tides has generally been considered unimportant, but this is not so. These ocean tides cause the same spectrum of orbital perturbations as the solid tide, and a complete separation, by analyzing satellite orbits of different elements, is not possible. Neglect of the ocean tide will introduce errors in k2 of as much as 15% and in phase angle of as much as 10° depending on the orbit. This explains the low values for k2 near 0.25 that have been obtained recently from orbital analyses. Comparison of several models for the principal lunar tide (M2) of the ocean indicates that these models are insufficient for making precise orbital corrections. For the other tidal frequencies that often have important effects on satellite orbits, no satisfactory tide models exist. The equilibrium theory does not suffice for these corrections, and improved values for k2 and particularly for the phase lag δ can only come from a concomitant improvement in our knowledge of the ocean tides. It is possible to extract some information on the ocean tides from the orbital analyses, and this could be used as a constraint in numerical ocean tide computations. We have analyzed the orbit of the satellite Geos 2 for the lunar M2 tide. After correcting for the ocean tides the value found for k2 varies between 0.27 and 0.30, depending on which ocean tide model is used. The solutions for the phase angles are quite unsatisfactory, and this condition stems from insufficiently precise tracking data and inadequate coverage as well as from inadequate tide models. We have applied approximate ocean tide corrections to the tide parameters determined by several authors to give a mean value of k2=0.31 and δ2=0.5°. This phase lag corresponds to a mantle Q of about 60.
Oxygen isotope partitioning among the minerals in igneous and metamorphic rocks
Authors: Bottinga Y. , Javoy M.
Published: February 2008

Using data on naturally occurring oxygen isotope fractionation among coexisting minerals in igneous and metamorphic rocks and previously derived relations, the authors deduce expressions for the temperature dependence of the isotopic disproportionation among the minerals quartz, feldspar, pyroxene, olivine, garnet, muscovite, biotite, amphibole, ilmenite, and magnetite. The expressions are only valid at temperatures greater than about 500°C. Oxygen isotope analyses on separated minerals (quartz, feldspar, pyroxene, olivine, garnet, muscovite, biotite, amphibole, ilmenite, magnetite) published prior to 1974 are reviewed and listed. The great majority of igneous and metamorphic rock samples for which three or more coexisting minerals have been analyzed separately has conserved a state of oxygen isotopic exchange equilibrium. Retrograde effects are common in plutonic and acidic volcanic rocks.
Plate tectonics
Authors: Dewey J. F.
Published: February 2008

Plate tectonics as a theory distinct from, yet embracing, continental drift and sea floor spreading was formulated by Wilson [1965] when he described a continuous network of ridges, transforms, and subduction zones bounding large rigid plates. Wilson explicitly discussed many of the consequences of the relative motion of torsionally rigid plates such as the changing geometry of certain kinds of transform linkage between ridges and subduction zones, evolving mosaics of ridges, transforms, and subduction zones, and the changing area of plates. At about the same time, Bullard et al. [1965] made the implicit assumption of torsional rigidity in using finite difference rotation poles to fit together margins of the continents bordering the Atlantic Ocean. An earlier, little publicized naturally occurring example of rigid body rotation, although it is on a flat surface and therefore allows translation, is provided by Stanley's [1955] study of tracks on Racetrack Playa, California. Stanley showed that parallel and concentric stone tracks resulted from stones embedded in and protruding from the base of wind‐blown rigid ice floes. McKenzie and Parker [1967], using the relative motion of the North American and Pacific plates, outlined for the first time the theory and consequences of relative plate motion on a spherical surface by using vector circuits to describe the instantaneous behavior of triple junctions (a technique later fully developed by McKenzie and Morgan [1969] and instantaneous angular velocities about the rotation axes between three plates. In particular, they showed how triaxial strain fields derived from first‐motion studies may be used as a rough guide to relative plate motion and applied the useful practice of drawing Mercator maps about instantaneous rotation poles that describe relative motion between two plates. In the following year, Le Pichon [1968] and Morgan [1968] developed comprehensive models of instantaneous global plate kinematics, and Isacks et al. [1968] showed how worldwide first‐motion solutions accorded in a systematic way with a set of torsionally rigid lithosphere plates in relative motion.
Marine seismicity
Authors: Macdonald Ken C.
Published: February 2008

The use of sonobuoys and ocean bottom seismometers (OBS) to study oceanic earthquakes at close range has opened the way to more precise, more detailed studies of plate boundary seismicity and tectonics than ever before. Land‐based teleseismic studies of marine seismicity have continued to play a key role in mapping plate boundaries on a large scale and in unraveling plate kinetics and stresses.

For monitoring microearthquake activity, sonobuoys (free floating hydrophones) are set out in arrays of three or more spaced several kilometers apart [Reid et al., 1973]. The data are telemetered back to the ship and recorded in real time.
Cosmic ray intensity gradients in the solar system
Authors: McKibben R. B.
Published: February 2008

The measurement of the heliocentric intensity gradient of galactic cosmic rays provides a crucial test for our understanding of the modulation of the cosmic radiation by the irregular magnetic fields carried by the solar wind. The basic model for the modulation involving diffusion of energetic particles by scattering from magnetic irregularities, adiabatic deceleration, and convection by the solar wind has not been much in dispute since the equations governing propagation of cosmic rays in the solar wind were first written down by Parker [1963, 1965]. However, varying assumptions concerning, for example, the location and shape of the boundary of the modulation region and the form and spatial dependence of the diffusion coefficients led to widely differing predictions concerning the distribution of cosmic rays in the heliosphere and the nature of the interstellar cosmic ray spectrum at low energies. Accurate measurements of the gradients offer hope of distinguishing among the various detailed models proposed. It is an indication of the significance of such a measurement that since the first observations establishing the heliocentric nature of the modulation [Simpson et al., 1962], more than 30 attempts to determine the intensity gradients of cosmic rays of various energies and nuclear species have been made. O'Gallagher [1972a] has reviewed the status of these measurements as of 1971. At that time the majority of measurements indicated a moderate (several percent per astronomical unit) positive radial gradient for the integral intensity of cosmic rays above threshold energies of the order of 100 MeV/nucleon, but measurements in differential energy windows below ∼100 MeV/nucleon were in ‘irreconcilable disagreement.’ In this paper, progress in the determination of intensity gradients reported in the years 1971–1974 will be reviewed, with concentration on efforts by U.S. workers. Several areas which are related to gradient measurements, such as the determination of the location of the modulation boundary, and solutions of the modulation equations aimed solely at the fitting of observed cosmic ray spectra at the orbit of earth have been deliberately excluded.
Instruments and techniques in paleomagnetism and rock magnetism
Authors: Collinson D. W.
Published: February 2008

This paper reviews the instruments and techniques currently and recently in use for investigations of the magnetic properties of rocks. Although some earlier methods are described, it is chiefly concerned with developments during the last decade involving both new equipment and methods as well as the improvement of earlier instrumentation through the application of modern materials and electronic devices. It is not intended as a manual for the construction of paleomagnetic or rock magnetic equipment, nor as a source of practical details of techniques, but rather as an account of what has been or can be done and as a guide to the literature for both current and would‐be workers in the field.
Representation of magnetic fields in space
Authors: Stern David P.
Published: February 2008

Several mathematical methods which are available for the description of magnetic fields in space are reviewed. Examples of the application of such methods are given, with particular emphasis on work related to the geomagnetic field, and their individual properties and associated problems are described. The methods are grouped in five main classes: (1) methods based on the current density j, (2) methods using the scalar magnetic potential γ, (3) toroidal and poloidal components of the field and spherical vector harmonics, (4) Euler potentials, and (5) local expansions of the field near a given reference point. Special attention is devoted to models of the magnetosphere, to the uniqueness of γ as derived from observed data, and to the L parameter.
Investigation of Pc 3 frequency geomagnetic pulsations in conjugate areas aroundL= 4: A review of some USSR and U.S. results
Authors: Raspopov O. M. , Lanzerotti L. J.
Published: February 2008

Two extensive series of measurements of magnetospheric ULF waves in the Pc 3 frequency range (22–100 mHz) have been carried out in pairs of conjugate areas (Kerguelen‐Sogra and Siple‐Lac Rebours) which have approximately the same geomagnetic latitudes (L∼ 3.5–4.0) but are separated by more than 8 hours in local time. The results of these measurements are compared in this review, and some differences in the results are discussed in terms of possibly differing ionospheric and ground conditions in the conjugate areas. Additional, possibly cooperative, studies to investigate further the magnetospheric wave phenomena in this frequency range are outlined.
On the propagation of low‐latitude whistlers
Authors: Hayakawa Masashi , Tanaka Yoshihito
Published: February 2008

We review here the recent works on low‐latitude whistler propagation based on ground measurements with a reference to space observations and point out the role of low‐latitude ground whistlers in the general study of whistler propagation. Then we identify the main unsolved problems of low‐latitude whistlers: (1) whether or not ground whistlers propagate along field lines, (2) the characteristics of transmission through the ionosphere, and (3) the properties of low‐latitude whistler ducts (formation and decay times) and their structure. These fundamental problems also concern high‐latitude whistlers, but they have less influence, since the rate of duct occurrence is higher and the duct trapping is much easier at high latitudes. On the other hand, considering that the smaller dip angle of the geomagnetic field at low latitudes makes the duct trapping and the ionospheric transmission very hard and that the rate of duct occurrence itself is not so high, we can say that low‐latitude ground whistlers have suffered severe conditions during the course of their propagation. In other words, the fuller study of low‐latitude whistlers will contribute to solving the most poorly understood problem: how the whistler propagates upward from its source, excites ducts, and leaks from ducts, penetrating to the ground. Furthermore, the characteristics of whistler ducts may be studied effectively by using low‐latitude whistlers. Hence these questions should be investigated during this International Magnetospheric Study period.
In situ measurements of stratospheric trace constituents
Authors: Ehhalt D. H.
Published: February 2008

The general features, capabilities, and problems of in situ techniques are reviewed. To illustrate these capabilities more closely, examples of recent measurements are presented, including (1) resonance fluorescence for the measurement of O, OH, Cl, and ClO, (2) grab and cryogenic collection of whole air samples for the measurement of N2O, CFCl3, and CF2Cl2, (3) impregnated filters for HCl, and (4) matrix isolation for HO2 and NO2.
The fate of electrical charges in evaporating cloud droplets
Authors: Thomson B. A. , Iribarne J. V.
Published: February 2008

Processes which have been previously considered as contributing to the loss of charge from cloud droplets in the atmosphere when the droplets evaporate are reviewed, and to the list is added the process of ion evaporation, which has been recently investigated in our laboratory. The relative efficiencies of the processes of Rayleigh instability, capture of ions of the opposite sign, field‐enhanced ion capture, and ion evaporation are compared. The cloud droplet charges and the amount of nonvolatile material in each droplet are critical in the comparison, and values of these in the atmosphere are briefly reviewed. It is concluded that in most situations, cloud droplets should evaporate and leave their charges on the solid residues which remain. Only when the droplets have been highly charged by processes in thunderclouds and when they are pure enough to evaporate to small sizes is it expected that Rayleigh instability or ion evaporation will become operative. We conclude that the process of field‐enhanced ion collection proposed by Dawson is ineffective in discharging cloud droplets.
Review of quantitative models of the 0‐ to 100‐keV near‐Earth plasma
Authors: Garrett H. B.
Published: February 2008

Quantitative modeling of the near‐earth plasma environment in the 0‐ to 100‐keV energy range has made significant strides in the last decade in response to the needs of spacecraft users and to the substantial improvements in the modeling of the earth's electric and magnetic fields. Concurrent with this has been an extensive growth in the observational data base necessary to evaluate these models. In this paper, models of the plasmasphere and near‐geosynchronous environment are reviewed and compared with the data; also discussed are potential users, their needs, and the ability of the models to meet those needs. The review indicates that although several significant problems are not resolved, quantitative low‐energy plasma models are at the stage that magnetic field models were at a decade ago and substantial gains are expected in the next few years.
Solar variability and terrestrial weather
Authors: Scherrer Philip H.
Published: February 2008

The past four years have seen a growing interest in possible relations between terrestrial weather and solar or solar wind variability. Most of the work in sun‐weather (and climate) studies has sought correlations on three time scales: (1) climate changes over hundreds to thousands of years, related to longer term variations in the solar output, (2) climate changes correlated with the 22‐year solar cycle, and (3) weather variations on the scale of a few days, in response to transient solar events. While it has not been conclusively shown that there is a sun‐weather connection on any of these time scales, in each case there exists enough supporting evidence to suggest that further study is warranted.

The most convincing evidence is that concerning long‐term climate changes which could be connected to changes in the solar luminosity below the threshold of all but the most recent observations, but still involving relatively large amounts of solar energy. Short‐term weather changes correlated with solar phenomena cannot be explained in this way, since the effect of such transient phenomena on the Sun's energy output is far too small. There remains, however, the possibility that such phenomena affect some sensitive links in the sun‐solar wind‐magnetosphere‐stratosphere‐troposphere causal chain, such that a small variation of the input can trigger relatively large‐scale consequences. Most of this review will be concerned with developments in the short‐time scale connections.
Research on snow and ice
Authors: Martinelli M. , Sommerfeld R. A. , Thomas Robert , Harrison Will , DenHartog S. , Frankenstein G. , Rango A. , Shartran Marilyn
Published: February 2008

It seems to us that it would be arrogant to claim that this review contained everything of importance, nothing that was unimportant, with everything in proper balance in the complex and diverse fields which comprise the study of snow and ice. The best we can claim is that we tried to accomplish those objectives.

Since this is to be a review of scientific research, most of the engineering studies were left out. In many cases, the decision was a difficult one, and each author drew the line somewhat differently in his section. Much of the basic research is inspired by practical problems and because of the complexities involved in dealing with snow and ice, many of the engineering studies are forced into basic research on one or another aspect of their problems. We therefore warn that people who want to delve deeply into some topic should also consult some of the engineering oriented sources.
A survey of light‐scattering techniques used in the remote monitoring of atmospheric aerosols
Authors: Deirmendjian D.
Published: February 2008

A critical survey of the literature on the use of light‐scattering mechanisms in the remote monitoring of atmospheric aerosols, their geographical and spatial distribution, and temporal variations was undertaken to aid in the choice of future operational systems, both ground based and air or space borne. An evaluation, mainly qualitative and subjective, of various techniques and systems is carried out. No single system is found to be adequate for operational purposes. A combination of earth surface and space‐borne systems based mainly on passive techniques involving solar radiation with active (lidar) systems to provide auxiliary or backup information is tentatively recommended. Mostly on the basis of the material surveyed, some observations on the quality and quantity of the published literature, journal editorial policies, the proliferation and frequency of professional society meetings and workshops on special topics, the support and administration of scientific work, and the plight of the individual scientist are also included.
Energy balance climate models
Authors: North Gerald R. , Cahalan Robert F. , Coakley James A.
Published: February 2008

An introductory survey of the global energy balance climate models is presented with an emphasis on analytical results. A sequence of increasingly complicated models involving ice cap and radiative feedback processes are solved, and the solutions and parameter sensitivities are studied. The model parameterizations are examined critically in light of many current uncertainties. A simple seasonal model is used to study the effects of changes in orbital elements on the temperature field. A linear stability theorem and a complete nonlinear stability analysis for the models are developed. Analytical solutions are also obtained for the linearized models driven by stochastic forcing elements. In this context the relation between natural fluctuation statistics and climate sensitivity is stressed.
Stability investigations of various representations of the gravity field
Authors: Gerstl Michael , Rummel Reiner
Published: February 2008

A number of problems in physical geodesy are improperly posed in the sense that the approximate solution is not continuously dependent on the given observations. A transformation of the minimum norm least squares estimates for different types of gravity representations to the spectral domain, via a singular value decomposition, allows an easy insight into the stability situation of these representations. For the density layer or point mass model, Bjerhammar’s method, and the least squares collocation model the filter expressions are derived which control their stability. It is shown in which way the shape of the filters is influenced by the a priori variance of the measurement noise, the choice of the radius of the Bjerhammar sphere, and the degree variance model.
Normal mode initialization
Authors: Daley Roger
Published: February 2008

The baroclinic primitive equation models used for short‐ and medium‐range weather forecasting admit undesirable high‐frequency gravity waves. The gravity waves are excited by initial imbalances between the observed wind and mass fields and by inconsistencies between model and atmosphere. Over the years, many initialization techniques have been devised to balance the initial state, but without notable success. The recent introduction of normal mode initialization techniques has, to a large degree, solved the problem. The present review will discuss the development of the technique from first principles, introduce the slow manifold concept, and discuss successful applications and remaining problems.
Planar geodetic covariance functions
Authors: Meier Siegfried
Published: February 2008

In the last 20 years statistical methods have been applied in geodesy with considerable success, both in physical geodesy (least squares collocation, variance‐covariance propagation) and in geodetic measuring technique (error propagation and interpolation, inertial navigation, adjustment, diagnosis, and design of networks). The geodetic stochastic process is introduced per definition as the representation of a geophysical random field afflicted with observational errors, including the special cases of the (almost) error‐free field (physical‐geodetic process) and the pure error field (operational‐geodetic process). Geodesy is an approximation science, planar approximation being of great practical importance. It can be realized by projection onto a tangential plane to the earth’s surface and/or other planes of measurement and computation. The review treats the covariance functions of planar processes for different geodetic problems in the light of literature on the subject and under systematizing aspects—inter alia, gravity field, field of atmospheric refraction, error field; covariance estimation and propagation; ideal statistical structures as homogeneity, isotropy, axisymmetry, but also the physical, statistical, and geophysical significance of the prerequisites and solutions as well as problems that are still unsolved.
Electrical resistivity of minerals and rocks at high temperature and pressure
Authors: Parkhomenko E. I.
Published: February 2008

After a general discussion of semiconductor and dielectric physics, experimental data on the dependence of electrical resistivity of different minerals on their cation composition within a wide temperature interval (up to 1100°C) are described. The different types of dependence of resistivity on pressure are noted for minerals with a predominantly ionic type of electrical conductivity and for those whose conductivity depends on changes in valence of iron cations. Experimental data are presented that show the changes of electrical resistivity of minerals due to polymorphism, dehydration, and carbonate decomposition. Next the results of studies of the resistivity of water‐saturated sedimentary rocks at high pressures and temperatures are described. Data are given on (1) the effect of porosity, pore configuration, mineral composition, concentration of electrolyte, content of clay, type of cement, and type of cementation on the relationship between resistivity and pressure, ρ = f(P) and (2) the resistivity of water‐saturated magmatic rocks at high temperatures (up to 260°C) and pressures (up to 1.5 kbar). The dependence of resistivity of different groups of rocks on their mineral and chemical composition and on their structure under conditions of high temperature and pressure is analyzed. Finally, basic trends are indicated of interest for geophysics and for the use of experimental data on electrical properties of minerals.
Low‐level VLF and LF radio emissions observed at Earth and Jupiter
Authors: Barbosa D. D.
Published: February 2008

This paper examines the current state of knowledge of VLF and LF radio wave emissions in the magnetosphere. Specifically, the properties of the low‐level noise commonly referred to as continuum radiation are reviewed with emphasis on the capabilities of the noise to diagnose local and remote plasma parameters. The relationship of the radiation to ≥1‐mV/m electrostatic upper hybrid emissions is critically assessed. There is a fair amount of indirect observational evidence to suggest that upper hybrid noise is associated with the generation of the VLF‐LF radiation, and proposed theoretical mechanisms lean toward this interpretation also. However, no definitive association has been established to date. The theoretical luminosities of several mechanisms, which include synchrotron radiation, linear mode conversion of upper hybrid waves, and nonlinear scattering of upper hybrid waves off plasma density irregularities, are estimated. The wave‐wave scattering hypothesis is adjudged to be a viable mechanism if the presence of low‐frequency waves as a scattering agent can be established either theoretically or observationally. The alternate mechanisms are considered to be too weak as potential sources, but efficiency‐saving modifications may make the linear mode conversion hypothesis more competitive. Recommendations for future studies on this subject are given.
Scientific results of the United States’ IMS effort
Authors: Carovillano Robert L. , Reiff Patricia H.
Published: February 2008

The International Magnetospheric Study (IMS) was a worldwide cooperative effort that took place during the 4 years 1976–1979. Early reports and articles describe the concept and scope of the IMS, and early summary documents and symposia have begun to report on the scientific accomplishments. Because of its vast scale and delays in the program becoming operational (e.g., ground magnetometer networks and slippage in satellite launch dates), in large measure the primary accomplishment of the IMS has been the development of a data base on an unprecedented scale. Because the primary IMS experimental programs proceeded more slowly than was initially planned, the 5‐year period 1980–1984 has been designated as the Post‐IMS Data Analysis Phase.
Optimization of geodetic networks
Authors: Schmitt Günter
Published: February 2008

It is the aim of this paper to give a concise review of the current state of research, the trends, and the outstanding problems in the optimization of geodetic networks. The datum problem, which has to be solved in the computational stage, is referred to as the zero‐order design problem. In the real design stage, three classes of problems have arisen: the configuration problem as the first‐order design problem, the weight problem as the second‐order design problem, and the optimal improvement of an existing network as the third‐order design problem. Furthermore, all subproblems must be analyzed within the three general objectives of geodetic networks: precision, reliability, and cost.
Deep convection in the World Ocean
Authors: Killworth Peter D.
Published: February 2008

A brief discussion of, and a little speculation about, the relevance of the polar regions on climate is given. The main body of the paper gives a survey of the known deep convection areas of the world ocean. There are two distinct types of convection. The first is the classic sinking occurring on continental shelf slope systems, as typified by various locations around the Antarctic coast. The freezing of sea ice, and resulting brine ejection, creates dense salty water on the shelf which descends the slope under a balance of Coriolis, gravity, and frictional forces, entraining the surrounding warm deep water as it goes. The second process is the more recently observed open‐ocean convection, occurring in locations such as the Mediterranean, the Labrador Sea, and two locations in the Weddell gyre, and is hypothesized to occur in the Greenland Sea. Open‐ocean convection has many overall similarities in all these areas: it occurs in narrow (20–50 km) areas; it forms about 10 m³ s−l of deep water; it occurs only in regions of cyclonic mean circulation; more than one water mass in the mean circulation is involved; a preconditioning seems to be required; some surface forcing (cooling or sea ice formation) is necessary; a violent breakup of the water mass frequently occurs on time scales of 2 weeks.
A review of geodetic and geodynamic satellite Doppler positioning
Authors: Kouba J.
Published: February 2008

Since 1967, when the U.S. Navy Navigation System was released to the general public, the accuracy of geodetic and geodynamic satellite Doppler positioning using satellite Doppler has improved steadily. This improvement is due mainly to refinements in hardware, refraction, and orbital modeling. Point positioning, using a minimum of 30 passes and the U.S. Defense Mapping Agency (DMA) precise ephemeris, has reached submeter accuracy. Relative positioning among several simultaneously observing stations separated by distances up to 250 km and using a minimum of 30 passes has a typical accuracy below 0.5 m (1σ). Current hardware design and errors in modeling of delays in the wet portion of the troposphere limit the achievable accuracy in relative positioning at the 0.1‐ to 0.5‐m (1σ) level, unless errors in receiver phase and tropospheric refraction delays are continuously measured (calibrated). Also, a crystal oscillator of lower short‐term stability (≥ 5 × 10−12/100 s) increases the Doppler data noise and causes a positive correlation persisting over several minutes. Geodetic and geodynamic Doppler data reductions usually involve meticulous modeling for instrumental, atmospheric, and orbital errors as well as careful Doppler data editing. A short‐arc orbit computation employed in such satellite Doppler reductions requires a gravitational potential expanded to at least degree and order 10 if the orbit shape accuracy is to be comparable to DMA precise ephemeris. Satellite Doppler positioning has had a significant impact on geodetic datum definition and the establishment of national and continental networks of unprecedented accuracy. Satellite Doppler methods, apart from providing one of the most accurate continuous methods of polar motion monitoring, have also been found useful in other geodynamical and ice motion studies. This review concentrates mainly on system performance, models, and computational methods.
The origins of Birkeland currents
Authors: Stern David P.
Published: February 2008

A qualitative explanation is proposed for the main features of quiet‐time Birkeland currents. The major conclusions are as follows: (1) The source of region 1 currents is the interplanetary electric field, linked to the polar ionosphere directly along open field lines near noon but indirectly, via the plasma sheet, at most other longitudes. (2) Region 2 arises from convective charge separation, owing to guiding center drifts. On the dayside, secondary charge separation may occur, extending the current pattern sunward. (3) The magnetopause boundary layer flow is not a major energy source ofj11∥, and neither are dynamo processes in convected plasmas or in the plasma sheet. (4) The convection reversal is expected to occur (as observed) in the interior of region 1, often near its poleward edge. (5) The cusp currents are associated with an inhomogeneity of the polar electric field, correlated with interplanetary By and first observed by Heppner, though contributions by the boundary layer are not ruled out. (6) The four‐lobed polar electric field patterns occasionally observed during times of northward interplanetary Bz are generated by a boundary layer dynamo and signify the temporary existence of a closed magnetospheric configuration. (7) The branching ratio between two routes by which magnetospheric space charge may be neutralized, via the ionosphere and via polarization currents, is estimated, with and without considerations of particle mirroring.
The association of energetic particles and shocks in the heliosphere
Authors: Lee Martin A.
Published: February 2008

Wherever shocks are observed or inferred to exist in the tenuous plasma of the solar corona and interplanetary space, energetic charged particles are observed or inferred to exist as well. Shocks can apparently both efficiently accelerate particles and affect their subsequent transport. The last four years have witnessed an explosive growth in research concerned withunderstanding this close association between energetic particles (cosmic rays) and shocks within the heliosphere. It is the purpose of this literature survey to chart the major observational and theoretical developments of this growth, assess our current understanding, and hopefully provide an outlook for future work.
Modeling planetary magnetospheres
Authors: Walker Raymond J.
Published: February 2008

There has been a marked change in the character of magnetospheric modeling during the past quadrennium. In earlier studies, the emphasis was on describing the average magnetospheric properties. These descriptive models were empirical or semiempirical and provided a static picture of the magnetospheric configuration. This approach has proved quite useful.