bluuebunny/crossref_metadata_2025 huggingface dataset:
Baroclinic instability of the zonal wind
Authors: Miles John W.
Published: February 2008

On the assumptions of a perfect gas, adiabatic motion, gravitational potential proportional to altitude, small Rossby number, and large Richardson number, the equations governing obliquely traveling, small disturbances relative to a zonal wind are reduced to a singular Sturm‐Liouville problem in which the latitude appears only as an implicit parameter. The structure of this problem is examined with the aid of an arbitrarily weighted quadratic integral and by transformation to an integral equation. Generalizations of Rayleigh's flex point and Howard's semicircle and rate‐of‐growth theorems are deduced from the quadratic integral. Approximations for small and large values of the wave number are deduced from the integral equation. It is shown that disturbances of sufficiently short wavelength in typical flows are always unstable but that they have a rate of growth that vanishes directly with the wavelength. Finally, it is shown that disturbances of all wavelengths in typical flows are always unstable for sufficiently small wind speeds. These conclusions lead to the conjecture that small disturbances in typical flows may be unstable for almost all wavelengths and all wind speeds.
Gradients of travel‐time curves from deep‐focus earthquakes
Authors: Bolt Bruce A.
Published: February 2008

Inferences that can be drawn about the structure of the upper mantle from observations of surface‐reflected longitudinal body phases are discussed. In particular, some aspects of previous observational, statistical, and theoretical work on the phase pP are reviewed. Recently, mathematical work has thrown more light on the properties of the cusps of the surface‐reflected longitudinal phases. Seismological experiments are discussed that are designed to determine the actual behavior of the wave pulses near the cusps. Some preliminary attention has been given to this problem using a seismic array with linear dimension about 10 times greater than the observed wavelength. Computer analysis of the pulses observed at the array elements leads to estimates of the gradients of the travel‐time curves. Weighting must be arranged to take into account the measured lateral refraction and crustal delays at each element. Analysis of the deep‐focus earthquake of April 2, 1963, is presented as an example.
A further note on dilatancy in relation to seismic sources
Authors: Frank F. C.
Published: February 2008

Orowan [1966] has raised objection to some of the conclusions of my paper, [Frank, 1965] entitled ‘On Dilatancy in Relation to Seismic Sources’. I think the main point at issue between us is a semantic one. I distinguish:1. Dilatancy: the property possessed by granular masses of expanding inbulk with change of shape.2. Dilatancy hardening: the enhancement of mechanical strength of themass consequent upon (1).3. Dilatancy pumping: the transfer of fluid in the mass enforced by ashear stress in consequence of (1).
On the intensity of the general circulation of the atmosphere
Authors: Wiin‐Nielsen A.
Published: February 2008

The intensity of the general circulation can be measured by the generation of available potential energy, the conversion of available potential energy to kinetic energy, or the dissipation of kinetic energy by frictional forces. Various estimates of the intensity are reviewed with special emphasis on the assumptions made in each investigation. There is a difference in principle between a nonhydrostatic and a hydrostatic system. In a hydrostatic system the internal and potential energies are proportional to each other, although the potential energy communicates directly with reservoirs of kinetic energy in a nonhydrostatic atmosphere. The review of the concept of available potential energy shows that the approximate form is exact for a quasi‐geostrophic formulation of atmospheric dynamics. A critical evaluation is made of the generation of available potential energy and the dissipation of kinetic energy.
Plasma flow around the magnetosphere
Authors: Spreiter John R. , Alksne Alberta Y.
Published: February 2008

A review is provided of the salient features of the flow of solar plasma past the magnetosphere, as they are revealed by observations in space and by theory. Discussed first are the properties of the solar wind, including the velocity, density, temperature and temperature anisotropies, and magnetic field, and their variations in space and time as observed beyond the disturbing influence of the earth and its magnetic field. Theoretical aspects of the steady‐state interaction of the solar wind and the geomagnetic field are taken up next, using the continuum description provided by the equations of magnetohydrodynamics of a perfect dissipationless gas as a basis. An outline is given of the series of approximations, and their observational and theoretical justifications, used to reduce the complex free‐boundary magnetohydrodynamic flow problem to a series of tractable problems; and a set of results is provided for representative conditions in the solar wind. The results are shown to be in good accord, even to numerous details, with observations made in space during quiet times. The results are also shown to be useful in interpreting many features of observations during disturbed times. Attention is drawn to other features of the flow of solar plasma past the magnetosphere for which quantitative theoretical descriptions must still be devised. These include the irregular or fluctuating character of the flow downstream of the bow wave, the nature of the magnetosphere tail and surrounding flow at great distances from the earth, numerous transient aspects of the flow, and the mechanisms underlying the many statistical correlations being discovered between variations of the surface geomagnetic field and various properties of the solar wind.
Charged particles in the magnetosphere
Authors: Van Allen James A.
Published: February 2008

The object of this paper is to review observational work by the University of Iowa having to do with the dynamics of the population of charged particles in the outer radiation zone of the earth's magnetosphere.

Specific topics are as follows:

a. Intensity fluctuations and apparent lifetimes of outer zone electrons having kinetic energies E6 ranging from 40 kev to several Mev.

b. Ring current particles, protons and electrons EPJ E6 ^> 200 ev.

c. Geomagnetically trapped a particles, 2.09 < Ea < 15 Mev.

d. The electric field in the magnetospheric tail.

The spirit of the discussion is to invite attention to a number of phenomena that appear sufficiently well established and significant to merit substantial interpretative effort.
Pitch‐angle diffusion of electrons in the magnetosphere
Authors: Roberts Charles S.
Published: February 2008

This paper reviews the experimental and theoretical knowledge concerning pitch‐angle diffusion of trapped electrons in the earth's radiation zones. Experimental information bearing on pitch‐angle diffusion has been obtained from data on electron flux decay following artificial injection by a nuclear explosion or following natural injection during a period of magnetospheric activity. Useful information has also been obtained by studying the trapped‐electron pitch‐angle distributions and the precipitation of electrons into the atmosphere at low altitudes. The theory of pitch‐angle diffusion based upon the Fokker‐Planck equation is discussed, and some simple cases of this theory are worked out. Several different pitch‐angle scattering mechanisms that may be important for trapped electrons, such as cyclotron resonance, bounce resonance, and atmospheric Coulomb scattering, are also discussed.
Solar wind interaction with planetary atmospheres
Authors: Michel F. Curtis
Published: February 2008

Several quite dissimilar models have been proposed for the direct interaction of the solar wind with planetary ionospheres, based, respectively, on the assumption of (1) restricted flow into the ionosphere, (2) an interface between the solar wind and the ionospheric plasma, or (3) a magnetic field barrier (‘induced magnetopause’). All three require the existence of a standing bow shock in the solar wind. We review these models, discuss their individual limitations, and consider what observational data would distinguish among them.
Planetary exploration: Accomplishments and goals
Authors: Donahue T. M.
Published: February 2008

Observations from space vehicles have vastly altered our conceptions of Mars and Venus. Mars has changed from an earth‐like planet with water ice caps into a heavily cratered, coreless object whose polar caps are dry ice and whose tenuous atmosphere is CO2. Venus has been found to be blanketed by clouds and a dense CO2 atmosphere that has driven the surface temperature to 700–800°K. Attention is drawn to the practical returns we can expect from comparative studies of these three planets: for understanding of the origins of life, the potential development of a runaway greenhouse effect on earth, and atmospheric circulation.
D‐region ion chemistry
Authors: Ferguson E. E.
Published: February 2008

The status of D‐region positive‐ and negative‐ion chemistry is reviewed. In the case of the positive‐ion chemistry, the presently accepted ion production rates and ion‐neutral reaction scheme are incompatible with the observed qualitative ion composition measurements. The observations indicate that water‐ion clusters, H3O+(H2O)n, particularly H5O2+, are dominant below 80 km, whereas calculations predict that NO+ and its hydrates would be dominant. It seems rather likely that an essential element of the physics involved has so far escaped attention. In the case of the negative ions, the few observations only recently obtained are insufficent to critically test the detailed reaction schemes available from laboratory studies. Uncertainties in the concentrations of minor neutral constituents severely limit the ability to predict theoretical negative‐ion profiles at present. The first rocket negative‐ion observations do support the laboratory‐derived prediction of a dominant role for NO3− and its hydrates in the D‐region.
Helium abundance of the Sun
Authors: Hirshberg J.
Published: February 2008

The solar abundance of helium (more specifically the ratio of solar helium to hydrogen) is a basic quantity in understanding many astrophysical and space physical problems. However, in spite of a great deal of work on the subject, it has proved to be very difficult to accurately determine the helium abundance of the sun. We here review critically the four methods that have been used to estimate the ratio of helium to hydrogen; the solar neutrino flux, spectral intensity of helium lines in prominences and the chromosphere, elemental abundance of solar cosmic rays, and variations of solar wind He/H. At present the measured value for the neutrino flux cannot be explained by any of the theoretical models of the sun, and thus the neutrino measurements cannot yield an estimate of He/H. Helium line intensity measurements give the most accurate values for He/H now available, i.e., 5–8% helium by number. However, these results refer to the chromosphere and prominences only, and questions of spatial and temporal variations of the observed quantities and of the inferred helium abundances have not yet been dealt with adequately. The cosmic ray observations are usually interpreted as indicating 6% helium at the flare site. However, this interpretation is here called into question because of an apparent energy dependence of the observations. The variations of He/H in the solar wind yield information on the coronal distribution of helium, rather than the solar abundance. The solar wind observations are most easily interpreted in terms of a moderate helium enhancement (He/H ∼ 10–15%) in the deeper levels of the solar atmosphere, but a uniformly mixed corona cannot at present be completely ruled out. It is concluded that the solar abundance of helium remains uncertain to within a factor of 2 or 3.
Possible effects of a fleet of supersonic transports on the stratospheric ozone shield
Authors: Schiff H. I. , McConnell J. C.
Published: February 2008

The possibility that large quantities of water and various oxides of nitrogen (NOx) can be injected into the stratosphere by a fleet of SST's has raised concern over the possibility of a reduction in the ozone (O3) shield. Calculating such a reduction requires knowledge of the roles of NOx and H2O in the natural O3 budget. Initially, not enough was known either of the background densities of NOx or of many of the rate constants involved to make quantitative statements of the effect of NOx and H2O on the O3 budget. Recently, many of the rate constants required in a quantitative analysis have become known. These results incorporated into model calculations with natural sources of NOx and observed H2O mixing ratios tend to indicate that these constituents play an important role in the O3 budget in the natural stratosphere. At the same time, recent measurements of NO, NO2, and HNO3 have become available. The HNO3 measurements by several different groups appear to be mutually consistent. The results of both the NO measurements and the NO2 measurements, however, differ by an order of magnitude. Although the rate data available are not of sufficient accuracy to resolve the discrepancy between the measurements, it does appear that there will be a reduction in stratospheric O3 caused mainly by HOx or NOx catalysis or both. A semiquantitative analysis for a fleet of SST's suggests a decrease in the column density of O3 of 0.5–5%.
Green's Function and tidal prediction
Authors: Webb D. J.
Published: February 2008

This paper is concerned with applying Green's function techniques to the theory of the tides. It is shown that by making certain assumptions about the analytic properties of the tidal Green's function, one can obtain an expression for it in terms of the Siegert states of the ocean. A similar expression can also be obtained by assuming that Laplace's tidal equations adequately describe the tide. Relationships between the mathematics of the Green's function and the physics of the ocean are developed, and the Green's function is then used to formally solve the tidal equation. By making assumptions about the smoothness of a related quantity, the response function, one can obtain a simple equation for tidal prediction. The equation may be of some practical use, for example, in superseding the Admiralty method of tidal prediction.
Theories of the geomagnetic and solar dynamos
Authors: Gubbins David
Published: February 2008

A review of recent advances in dynamo theory is presented in relation to the problems of the generation of the earth's and the sun's magnetic fields. Some relevant modern observations and estimates of physical quantities are discussed, and the lack of knowledge about the dynamical state of the earth's core is emphasized. The dynamo problem is conveniently separated into the kinematic approach, the area in which most work has been done so far, and the dynamical problem, which is exciting more current interest. Most attention is given to the low‐conductivity limit because this allows many of the theories to be exhibited in their simplest form. Dynamical dynamo models, driven either by an applied body force or by thermal convection, are described. Emphasis throughout the paper is on simple examples, at least as far as Cowling's theorem permits.
Instabilities and nonlinear processes in geophysics and astrophysics
Authors: Hasegawa Akira
Published: February 2008

A review of some nonlinear effects related to plasma instabilities is presented. Discussions are included on (1) quasilinear diffusion, in which a comparison between the effects of electromagnetic and electrostatic turbulence is given; (2) anomalous resistivity, in which a general derivation of the anomalous resistivity is presented and compared with some concrete examples; (3) wave‐wave and wave‐particle interactions, in which a general theory of parametric instabilities and quenching is presented together with the effects of the nonlinear Landau damping on stabilization of linear instabilities; and (4) modulational instability, in which a general derivation of the instability conditions and the consequence of the instability are discussed.
Comparison of activity in solar cycles 18, 19, and 20
Authors: Dodson Helen W. , Hedeman E. Ruth , Mohler Orren C.
Published: February 2008

Although solar activity cycles are in general remarkably similar, cycles 18, 19, and 20, with maximums in 1947.5, 1958.2, and 1968.9, respectively, differed in the heights of their maximums, in the patterns of their development, and to a certain extent in the character of their manifestations of solar activity. Of the 20 solar cycles since 1755, the maximums in sunspot numbers for cycles 18, 19, and 20 rank as 3, 1, and 10, respectively. Cycle 18, with a maximum smoothed monthly sunspot number of 151.8, was the cycle of ‘giant’ spots. Cycle 19, with the highest recorded maximum, 201.3, included many large spots but failed to produce spots with areas equal to those of cycle 18. The highest known daily 2800‐MHz flux occurred in cycle 18, not in cycle 19. Cycle 20, with a sunspot maximum of only 110.6, appears to have been close to the average cycle of the last 220 years. An attempt is made to compare the general levels of flare production in the three cycles. Cycle 19 is estimated to have been more flare‐rich than cycle 18 by a much smaller factor than the original data implied. In cycle 20, general flare production drops conspicuously. Two types of flare‐rich centers of activity are recognized, viz., those with extraordinarily high numbers of flares of Hα importance ⪖1 and those with unusually high frequency of flares with comprehensive indices of 11 or greater (great ionizing and radio frequency emission as well as Hα area). A list of the most flare‐rich regions in cycles 18, 19, and 20 is presented. In addition, the times and locations of the ∼100 greatest individual flares in the three cycles have been tabulated. North‐south asymmetry of sunspots and the shapes of the mean sunspot curves were not the same for the three cycles. The minimums between the cycles differed in duration and residual activity. Solar magnetic measurements exhibit the 22‐year period and make polarity patterns alike in cycles 18 and 20. Summarized coronal measurements from the Pic‐du‐Midi Observatory for 1944–1973 suggest that the relationships between coronal intensities and other measures of solar activity are complex. Emphasis on times of the greatest solar activity in cycles 18–20 leads to a certain sense of positive relationship between events on the sun and geophysical phenomena. Geophysical uncertainties abound, however, if consideration drops to just above average solar circumstances. Comments are made on certain problems in solar‐terrestrial relationships.
Laboratory measurements of ionospheric ion‐molecule reaction rates
Authors: Ferguson Eldon E.
Published: February 2008

The present status of laboratory measurements of ion‐molecule reactions of ionospheric importance is reviewed. Rate constants for most of the normal terrestrial E and F region reactions have been reliably measured at 300°K. Recently, some data have become available on the energy dependences of the most important of these binary positive ion reactions. In the case of D region reactions a great deal of new data on both positive and negative ion reaction rate constants has appeared in recent years. Both binary reactions and three‐body reactions are important in the D region, and important reactions still remain to be measured.
Interpenetrating solar wind streams
Authors: Feldman W. C. , Asbridge J. R. , Bame S. J. , Montgomery M. D.
Published: February 2008

Observations of solar wind interpenetrating ion streams are reviewed. They occur preferentially during periods of low but increasing plasma number density and most likely result from spatial and/or temporal inhomogeneities in the solar wind bulk velocity. The exact nature of these inhomogeneities is not known, but three conceptual models that account for the observations are summarized. Double ion streams are shown to occur during extended time periods during which the proton anisotropy and dimensionless heat flux undergo large coherent variations. This fact provides strong evidence that a major source for solar wind internal ion energy is its bulk convection energy. The observed continuum of proton velocity configurations further suggests that the ion internal energy state at 1 AU is often perturbed by bulk flow spatial and/or temporal inhomogeneities. Self‐consistent interactions with the interplanetary wave mix that results from these inhomogeneities as well as other aspects of the solar wind expansion establish preferred proton velocity configurations. These configurations can be summarized by simple statistical relations that couple the two independent third velocity moments to the second moments.
The structure of Heat Islands
Authors: Garstang M. , Tyson P. D. , Emmitt G. D.
Published: February 2008

Cities as well as ocean islands create mesoscale circulations in the atmosphere on a horizontal scale closely related to the size of the city or island. Contrast in albedo, heat capacity, and hence heating and cooling rates, heat generation, and surface roughness between the ‘island’ and its more uniform surroundings results in the generation of localized weather processes. Ocean islands, which may be simple in relief, free of pollution, and embedded in a uniform surface ocean temperature field, provide an excellent contrast to cities, which may be situated in complex topography and generate heat and pollution. The juxtaposition of the ocean and city islands is used to compare and contrast the induced atmospheric fields and the observed behavior of the atmosphere. The observed fields are then presented in terms of various numerical models. The simpler conditions prevailing over an ocean heat island lead to a more nearly complete three‐dimensional delineation of the thermodynamic and kinematic fields. These data for the ocean islands demonstrate significant deficiencies in the counterpart descriptions that exist for the atmosphere over the city. Complexities of modeling increase over both ocean and city heat islands as velocity fields change from zero to flow with strong vertical shear of the horizontal wind. Steady state models fare poorly under these conditions, whereas models that have attempted to account for the vertical redistribution of the horizontal momentum field show promise.
Theoretical cumulus dynamics
Authors: Cotton William R.
Published: February 2008

A comprehensive review of theoretical and numerical models of cumulus clouds and moist convective systems is presented. The problem of modeling cumulus convection encompasses an extremely broad range of physical and dynamic processes. On the microphysical scale a number of critical problems remain to be solved. In the case of deep, supercooled cumuli, for example, the uncertainties of ice particle production and cloud glaciation severely limit one's ability to model quantitatively the physics and dynamics of supercooled cumuli. As a consequence of the speed and space limitations of present generation computers, much of the effort of modeling cumulus convection is concerned with the subject of parameterization. Not only does this include parameterization of the essential microphysics of cumuli but also the parameterization of the energetics and fluxes of the eddies not explicitly resolved by the model. The limitations of present generation computers become most apparent when one acknowledges that the problem of modeling deep, moist convection is fully three‐dimensional and that such systems are often in direct communication with larger‐scale (mesoscale and synoptic‐scale) meteorological systems.
1974—The year of the Mid‐Atlantic Ridge
Authors: Aumento F. , Ade‐Hall J. M. , Keen M. J.
Published: February 2008

Long known as a broad mountain range halfway between the North American and the European continents, the submarine mid‐Atlantic ridge has been the target of intense investigations over the last decade, culminating during the summer of 1974 in two of the most ambitious scientific expeditions ever undertaken. Both expeditions, using new tools and techniques to probe the secrets of the ridge, revealed a new, unexpectedly complex picture of the nature of its igneous and sedimentary backbone.
Structure and secular change of the geomagnetic field
Authors: Cain Joseph C.
Published: February 2008

This report is a review of some of the recent developments in the knowledge of the structure and secular variation of the main geomagnetic field. It is hoped that this discussion will help to complement and update the excellent summary given by Zmuda [1973].

Many past papers have imbedded in them such phrases as ‘lack of adequate data, ‘uncertainty of high‐order coefficients’ and other qualifiers that lead the reader to infer that the numerical models (and maps) have large errors or that the conclusions of the studies must be considered tentative. The recent comprehensive global mapping of the field by near‐earth satellites, in scalar magnitude only, has partially quelled such statements and shown that many of the prior results were approximately correct. Confusion has often arisen since attention was focused on the fact that many of the individual higher‐order coefficients of the spherical harmonic expansions did not agree when computed by different analyses [see, e.g., Zmuda, 1971, p. 148]. It has now become evident that it is more meaningful to compare the spatial structure represented by the sum of the functions than to place undue emphasis on the correspondence of each individual term. This is true because aliasing is dependent on the degree of expansion and data distribution, so that two sets of coefficients can differ slightly in phase and amplitude and yet be fairly consistent with the data in most areas.
Positioning by satellites
Authors: Mueller Ivan I.
Published: February 2008

This article summarizes the efforts during 1971–1974 in connection with the determination of tracking station coordinates by means of artificial earth satellites. Entries which are related to geodetic control surveys (e.g., portable Doppler instrumentation) or to gravitational field determination (dynamic satellite geodesy) and follow the papers by Meade [1975] and by Gaposchkin [1975] in this report are not repeated here, except when they are specifically referred to.
Lunar and planetary seismology
Authors: Toksöz M. Nafi
Published: February 2008

The last 4 years have been very significant for new results in lunar seismology and the emergence of a definite program in planetary seismology. Since 1970, four stations with seismic sensors have been placed on the moon at Apollo 14, 15, 16, and 17 sites. When combined with the seismic station operating at the Apollo 12. site since November 1969, these have formed an excellent network. The network has detected a large number of moonquakes and meteoroid impacts. In addition to these there have been nine artificial impacts (ascent stage of the lunar module (LM) and Saturn third‐stage booster (S4B)) of known energies, impact times, and locations. Data from all sources have been analyzed to determine the lunar velocity structure, the seismicity, and the properties of the lunar interior. This has been a pioneering program in extending the direct seismological exploration to another planetary body with both surprising and very significant results.
Progress in seismological instrumentation
Authors: Smith Stewart W.
Published: February 2008

The period since 1970 has been marked by significant engineering advances in conventional seismic instrumentation as well as some fundamental developments in laser technology with direct application in earth strain measurement and geodesy.

In the area of conventional seismic instrumentation the engineering development of borehole long‐period seismographs has made possible the siting of this type of instrumentation independent of the usual requirements for underground vaults. This field has been extensively reviewed by Melton [1975]. The work in long‐period instrument development has led to a better understanding of the fundamental limitations of ground noise at long period [Fix, 1972]. At very long period the development of a superconducting gravimeter by Prothero and Goodkind [1972] has demonstrated stability over periods of time unattainable with systems utilizing conventional mechanical suspensions.
Friction in rocks
Authors: Logan John M.
Published: February 2008

J. C. Jaeger's (personal communication, 1971) first law of friction summarizes much of the confusion and uncertainty that has attended investigations into the frictional properties of rocks. The problems of friction in rocks are important in at least three major areas: (1) earthquake generation and source mechanisms, (2) delineation of mechanical units in folding of layered sequences, and (3) behavior of prefractured rock masses. Problems involving the frictional behavior of rock may be divided roughly into two areas depending upon the normal stress across the sliding surface: (1) engineering applications to problems of slope stability, landslides, etc., where the normal stress is generally on the order of tens of bars and (2) structural and tectonic problems where the normal stress may be in the order of kilobars.
Cosmogony of the solar system
Authors: Ward William R.
Published: February 2008

This report is intended to cover research on solar system origin over the last 4 years. Emphasis has been placed on the physics of planetary accumulation mechanisms, although pertinent references on the chemistry of mineral condensation and cometary research are included.

The most ambitious attempt to model the solar nebula to date is the 1973 paper of Cameron and Pine [1973]. This model is characterized by a large mass (∼2MS) and is modeled as a collapse of spherical distribution of gas with an angular momentum per unit mass estimated from the assumption of fully developed turbulent motion. A disk structure is determined by requiring a radial and vertical balance of forces, i.e., gravitational, centrifugal, and pressure gradient forces. The most striking and controversial feature of the model is the absence of a central concentration of material representing the protosun. Rather, the sun forms as a secondary process of angular momentum redistribution via Eddington‐Sweet type circulation currents during which the inner portion of the nebula contracts and the outer portion expands radially. The large mass of the system is justified on two counts: there must be sufficient material to allow angular momentum redistribution, and a T‐tauri phase has presumably ejected a few tenths of a solar mass from the system. Another noteworthy attribute of the model is the presence of a vertical convection zone between ∼1 and ∼10 AU due to the opacity of condensed iron grains.
Oceanic heat flow
Authors: Sclater John G. , Crowe John
Published: February 2008

During the past 4 years the major developments in oceanic heat flow have covered three topics. First, continuous work has been done collecting measurements in deep and shallow seas. Second, considerable effort has been put into analyzing these data in terms of plate tectonic models. And third, there has been progress in the understanding of the cause of the variability of closely spaced measurements.
The variability of ocean currents
Authors: Robinson Allan R.
Published: February 2008

Throughout the past 4 years the investigation of midocean low‐frequency mesoscale currents by American physical oceanographers has accelerated and intensified. These oceanic motions (referred to as ‘eddies’), which are apparently to some extent dynamically analogous to the atmospheric synoptic scale motions, are characterized by wavelengths of the order of a few hundred kilometers and periods of a few months, with longer time and space scales predominant above the main thermocline. Substantial energy is contained in the barotropic and first baroclinic vertical modes with rms speeds an order of magnitude greater than those characteristic of the mean circulation. The midoceanic eddies are of interest not only because they represent the dominant energy containing scales but because of possible energy transformations between the eddies and motions on longer and shorter time and space scales both locally and at a distance. The determination of the interaction of the eddies and the general circulation through mechanisms of transport and transfer of, e.g., heat, momentum, and vorticity, is of particular importance. This review will be primarily concerned with progress in the study of the variability of the midoceanic current field but will also include some related studies of the low‐frequency variability of the western and northwestern boundary currents of the main subtropical gyres. Some references to non‐U.S. research are given as appropriate because of importance or direct relationship.
Review on ocean‐atmosphere interactions
Authors: Wyrtki Klaus
Published: February 2008

The interaction between ocean and atmosphere has in recent years received increasing attention because of its importance to the understanding and prediction of climatic changes. Consequently, one is faced with an overabundance of scientific work in this area rather than a lack, and the scope of this review will therefore have to be carefully limited. The focus will be on true interactions, namely, on processes which are significant simultaneously to both the ocean and the atmosphere and will emphasize the large‐scale features because of their importance to climate. Consequently, work on the generation of ocean surface waves or of strictly meteorological interest and work on instrumentation will not be discussed here. Also omitted will be work on the geological time scale and on the exchanges of geochemical properties, in particular pollutants.
Polar meteorology
Authors: Weller Gunter
Published: February 2008

The general large‐scale circulation of the global atmosphere has its basic driving mechanism in the equator‐poleward temperature gradients in both hemispheres. It has become increasingly obvious over the last few decades that to understand and predict the behavior of the atmosphere at any point, it is essential to understand the behavior of the total global fluid system. The Global Atmospheric Research Project (Garp) is an outcome of this recognition. Studies of the heat sinks (the polar regions) are therefore just as important as studies of the heat source (the equatorial regions) to understand the meteorology of the planet. Interest in polar meteorology has undergone many cyclic fluctuations, peaking during the various international polar years and more recently during the International Geophysical Year (IGY) in 1957–1958. While polar meteorology continues to be studied for its own intrinsic interest, increased attention is given to its role within the framework of Garp. At the present the focus of Garp's first objective (improved extended weather forecasts) is on the tropical heat source, where convection and cloud formation and dissipation are still relatively little understood processes. However, the second Garp objective (better understanding of the physical basis of climate) requires more attention to be devoted to the cryosphere and its long‐term interaction with oceans and atmosphere and its role as indicator of climatic change. The idea of a polar experiment (Polex) in support of Garp was initially introduced by Treshnikov et al. [1968] and by Borisenkov and Treshnikov [1971]. A summary of the early history of Polex was recently given by Weller and Bierly [1973]. The two closely related objectives of Polex that most directly pertain to Garp may be restated in their simplest terms as (1) a better understanding of energy transfer processes and the heat budgets of the polar regions, for the purpose of parameterizing them properly in general circulation models and climate models, and (2) provision of adequate data from the polar regions during the First Garp Global Experiment (FGGE) in 1978.
Ionosphere‐magnetosphere coupling: 1. Thermal plasma
Authors: Chappell Charles R.
Published: February 2008

The past four years have seen a continued increasing interest in the basic processes which connect the thermal plasma population of the ionosphere with that of the outer magnetosphere. Measurement techniques have improved, and we are now able to observe the dynamics of the ionization in these regions as well as their detailed morphology. Although the specific reasons for the formation of the light ion trough and its connection with the plasmapause still elude us, we are beginning to grasp the nature of the many interchange flow processes which seem to play a basic role in the shaping of the well‐known plasmapause and light ion trough features.

The thermal plasma population of the magnetosphere has also grown in importance. In addition to attracting the interest of scientists studying the ionosphere and plasmasphere the distribution of thermal plasma has also been found to affect the energetic particle population of the magnetosphere. This interaction between the hot and cold plasma has drawn the attention of workers studying the energetic particles of the radiation belts, the ring current, and the plasma sheet and has further emphasized the tight coupling within the magnetosphere‐ionosphere system.
Thermospheric composition
Authors: Carignan George R.
Published: February 2008

The period 1971–1974 has been marked by a substantial advance in man's understanding of composition variability in the thermosphere. The global view of the atmosphere that has been provided by satellite observations in concert with radar backscatter measurements has shown a pattern of composition variability that theorists have been able to explain in large part as resulting from dynamic processes. Important progress has been made in defining composition variability at 120 km, which has greatly improved models which previously had fixed boundary conditions at that altitude. The discovery of the early morning maximum in helium abundance and the better definition of diurnal variation in relative composition have provided a basis for more sophisticated dynamical models. Similarly, models of meridional wind systems have been developed which can account for the better‐defined winter enhancements in helium and atomic oxygen. Finally, composition variability has indicated the presence of a high‐latitude heat source which during periods of magnetic activity profoundly modifies the state of the atmosphere. Some important contributions to our improved understanding of thermospheric composition are reviewed in this paper.
Relativistic solar protons
Authors: Duggal S. P.
Published: February 2008

This review attempts to summarize work by U.S. scientists, published during the period from 1971 to 1974, on various aspects of high‐energy solar protons associated with solar flares.

In contrast with low‐energy particles, acceleration to higher energies is a rare phenomenon that occurs in discrete explosive events associated with solar disturbances [Van Hollebeke et al., 1974; Pomerantz and Duggal, 1974b]. Since the start of systematic and continuous observations in 1936, 25 ground level enhancements (GLE) representing the arrival of relativistic protons have been recorded [Pomerantz and Duggal, 1974b]. Although the attribution of each of the observed intensity enhancements to a specific solar flare has been relatively straightforward, contrary to earlier ideas no plausible correlation with the general level of solar activity has been established except for the obvious consequence of the fact that flares are rare at sunspot minimum.
Stratospheric‐tropospheric exchange processes
Authors: Reiter Elmar R.
Published: February 2008

Qualitative descriptions and quantitative estimates are presented of various transport processes between stratosphere and troposphere. The seasonal changes of tropopause heights account for a flux of about 10% of the mass of the stratosphere in one hemisphere during the course of 1 yr. This flux is balanced approximately by the seasonal shift of stratospheric air masses between the northern and southern hemispheres. Vertical transport through the Hadley cell transfers approximately 38% of the mass equivalent to one hemispheric stratosphere through the tropopause per year. This appears to be the most effective of all transport mechanisms. Large‐scale eddies of the scale of cyclones and anticyclones transfer about 20% of stratospheric air through the tropopause per year. Small‐scale and mesoscale diffusion processes at tropopause level probably account for the transfer of only 1% of stratospheric air. These mass flux estimates are in reasonable agreement with observed residence times of stratospheric pollutants.
Global ozone balance in the natural stratosphere
Authors: Johnston Harold S.
Published: February 2008

The method of instantaneous rates is a three‐dimensional model that takes the observed distribution of atmospheric species and temperature as input data. The distribution of radiation over wavelength, photochemical rate constants, and reaction rates are evaluated in each cell of the three‐dimensional grid. For certain problems of restricted scope, definite answers can be given by this approach. For example, it is shown that the Chapman reactions and air motions are insufficient to give a global ozone balance; these factors account for only about 20% of the ozone produced below 45 km. There must be other photochemical or chemical reactions that destroy natural stratospheric ozone. The water reactions (H, HO, and HOO radicals) balance about 10% of the ozone produced below 45 km. Recently observed concentrations of nitrogen dioxide at up to 36‐km elevations are close to those required to destroy the remaining 70% of naturally produced ozone. Until enough measurements are made to characterize the vertical, latitudinal, and seasonal distribution of nitrogen dioxide, it will not be known whether yet other substances (such as chlorine, bromine, and metallic oxide particles) play a significant (10% or more) role in the natural ozone balance.
On the problem of simulating the Earth's induction effects in modeling polar magnetic substorms
Authors: Mareschal Marianne
Published: February 2008

A major problem encountered in trying to model the current system associated with a polar magnetic substorm from ground‐based magnetic observations is the difficulty of adequately evaluating the earth's induction effects. Two methods for simulating these effects are reviewed here. Method 1 simply reduces the earth to a perfect conductor and leads to very simple field equations. Method 2 considers the earth as a ‘horizontally’ layered body of finite conductivity but requires a large amount of computational time. The performances of both methods are compared when the substorm current system can be approximated by an infinitely long electrojet flowing over a flat earth. In this case it appears that for most substorm modeling problems it is sufficient to treat the earth as a perfect conductor. The depth of this perfect conductor below the earth's surface should be selected in function of the source frequency content.
The distribution of water vapor in the stratosphere
Authors: Harries J. E.
Published: February 2008

This paper seeks to collect together and to assess the many measurements of stratospheric humidity which have been reported over the last 25 years, with a view to determining the average distribution of water vapor in the stratosphere and its variations in time and space. Variations with height, latitude, time, and season are considered. In addition, some consideration is given to the proper use of experimental values of humidity in discussions of the water budget and circulation of the stratosphere; it is emphasized that the considerable uncertainties which often exist in measured data often can preclude the drawing of quantitative conclusions.
Ultraviolet spectrometry of the inner solar system from Mariner 10
Authors: Broadfoot A. Lyle
Published: February 2008

The status of analysis and significant results of the ultraviolet spectrometer observations of Mercury, the moon, the interplanetary medium, the comet Kohoutek, and Venus are summarized.
Large‐scale electric fields in the Earth's magnetosphere
Authors: Stern David P.
Published: February 2008

Studies of the earth's magnetosphere have indicated that a large‐scale electric field E plays a central role in its electrodynamics and in the flow and acceleration of charged particles there; while many observations relevant to E have accumulated, quite a few basic problems involving the origin and structure of this field remain unsolved. The ultimate source of E is presumably the flow of the solar wind past the earth, but the mechanism by which E arises is still unclear, and several independent sources may contribute to it, some of them (e.g., substorm fields and E11) being of a rather transient nature. This review attempts to sum up the main observed facts and theoretical concepts related to E. It also contains brief sections on experimental methods and on Birkeland currents, and it concludes with a list of basic questions related to the magnetospheric electric field to which satisfactory answers have yet to be found.
On probing the outer planets with the Raman effect
Authors: Price Michael J.
Published: February 2008

The feasibility of using the H2 rotational Raman spectrum to investigate the physical structure of outer planet atmospheres is examined. By selecting distinct wave bands spaced throughout the visible spectrum for observation a wide range in physical depth can be probed. On the basis of a semi‐infinite homogeneous pure H2 atmospheric model, computations of the strengths of the S(0) and S(1) lines have been made for a wide range of physical conditions. For each characteristic wavelength the ratio of the S(0)/S(1) line strengths is independent of the presence of aerosol particles. It provides a useful estimate of Boltzmann temperature. In contrast, the absolute strengths of the S(0) and S(1) lines are extremely sensitive to haze. Extremely small quantities of aerosol particles can be detected even at high altitudes. Initial applications of the Raman probe technique to Jupiter and Uranus are reported. For Jupiter a weak aerosol haze appears to exist at an H2 column density of ⪝17 km amagat. For Uranus, aerosol particles appear to be present at an H2 column density of ⪝104 km amagat. In addition, a significant temperature inversion may be present in the same region of the atmosphere.
Interaction of the surfaces of the Moon and Mercury with their exospheric atmospheres
Authors: Shemansky D. E. , Broadfoot A. Lyle
Published: February 2008

The atmospheres of the moon and Mercury are controlled entirely by gas atom‐surface interaction. Model calculations describing the steady state atmospheres have all been based on the assumption that the atmospheric particle source is a ‘saturated’ adsorbed surface layer of gas. We suggest that this is in disagreement with what is known of the physics of gas‐surface interaction. On the assumption that interaction is with solid atoms bound in a lattice structure, most collisions with the light atmospheric particles are free‐free, not free‐bound. The observational and theoretical evidence indicates that energy accommodation per collision for He and H on the moon and Mercury is dominated by first‐order interaction terms and is generally less than 0.1 per collision. As a result, estimated thermal escape is drastically reduced for the light atoms on both bodies. We consequently require much reduced solar wind collection efficiencies for protons and α particles. It is suggested that some peculiarities observed in the Mercury He and H atmospheres could be explained by the nature of the gas‐surface coupling. The formation of H2 may not be efficient as a surface or subsurface phenomenon, and the H/H2 atmospheric ratio may be large.