摘要:

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 inclu

ISSN:8755-1209    

DOI:10.1029/RG018i002p00341

年代:1980

数据来源: WILEY

摘要:

This article reviews those mechanisms of cloud electrification which are based on gravitational separation of precipitation particles and examines at some length the inductive charging mechanism. It is concluded that through the inductive mechanism, glaciated clouds can develop a maximum current densityJmaxof 0.1 µA m−2with a maximum fieldEmaxof about 3.5 × 105V m−1(which values are necessary for the occurrence of lightning flashes in them) within a time of 1000 s provided that the precipitation intensity in them is greater than 1.39 × 10−5m s−1(50 mm hr−1). For precipitation intensities less than 8.33 × 10−6m s−1(30 mm hr−1),JmaxandEmaxcannot develop to such high values. By its inherent nature this mechanism does not

ISSN:8755-1209    

DOI:10.1029/RG018i002p00361

年代:1980

数据来源: WILEY

摘要:

The use of energetics analyses in studies of extratropical cyclones has received increasing attention over the past 15 years. Particularly significant have been analyses of the transport, generation, and dissipation of kinetic energy and the diabatic generation of available potential energy. In examining the energetics of extratropical cyclones this paper (1) reviews and distills the results of kinetic energy and available potential energy budget studies carried out over the past 15 years and (2) uses these results to establish the significance of the extratropical cyclone in the general circulation.

ISSN:8755-1209    

DOI:10.1029/RG018i002p00378

年代:1980

数据来源: WILEY

摘要:

A review is given of a new Lagrangian mean theory of wave transport. Attention is focused on the so‐called ‘nonacceleration’ theorem, and it is shown that such a theorem arises naturally in the Lagrangian mean framework. Also discussed is a simple example of the Stokes drift, a concept which is central to nonacceleration. The Lagrangian mean theory substantially simplifies and unifies our understanding of wave driving in cases where nonacceleration is violated because of wave transience and dissipation. Moreover, the theory has given new insights in one particular case, that of Rossby gravity wave, meanflow interaction. These insights have successfully explained some hitherto unresolved paradoxes in the theory of the quasi‐biennial oscillation of zonal wind in the equatorial stratosphere. Some brief remarks are also made concerning some of the outstanding difficulties of the theory in need of future invest

ISSN:8755-1209    

DOI:10.1029/RG018i002p00387

年代:1980

数据来源: WILEY

摘要:

Extensive experimental and theoretical research has been performed in the last decade to study ionospheric irregularities. These studies have shown that plasma instabilities play a major role in the generation of the irregularities. In this work we describe in detail the recent experimental studies of theEandFregion irregularities and also the extensive work on plasma instability theories developed to explain them. We also describe both radio wave and spacecraft‐borne experimental techniques to allow a common ground for the understanding of the data from ground‐based and in situ experiments. To date, theoretical work has been mostly concentrated on the low‐latitude irregularities and, together with computer simulations, has been able to explain many aspects of the experimental data. These theoretical efforts are also discussed in some detail. The role of neutral winds in the creation of large‐scale ionospheric structures such as mid‐latitude sporadicEis beyond the scope of th

ISSN:8755-1209    

DOI:10.1029/RG018i002p00401

年代:1980

数据来源: WILEY

摘要:

Paleomagnetism is a quantitative tool for determining relative displacements and rotations of rock bodies in the geological past. During the last 20 years, paleomagnetic work in continental cratons has contributed greatly to our understanding of continental drift, but more recently, paleomagnetism has begun to be used on a more local scale, to elucidate tectonic problems in mountain belts. We have selected several geographical areas which illustrate an approach to paleomagnetism in mountain belts.

ISSN:8755-1209    

DOI:10.1029/RG018i002p00455

年代:1980

数据来源: WILEY

摘要:

A considerable amount of chemical knowledge of marine sediments has been acquired in recent years but has not yet been utilized by paleomagnetists. On the other hand, geochemists are often unaware of the usefulness of numerous magnetic techniques. In this review we try to bridge this gap, and in particular, we outline many of the chemical and magnetic principles that should allow paleomagnetists to better identify and understand chemical changes that affect the magnetic properties of marine sediments. The chemical principles include those for distinguishing the four major sources of sediments (continental, biological, authigenic/hydrogenous, volcanic/hydrothermal) from one another by determining elemental abundance distributions, as well as for investigating the stabilities of mineral phases relative to changes inpE andpH. The magnetic principles include the effects of authigenesis and diagenesis on magnetic properties, particularly on the direction and intensity of natural remanent magnetization (NRM). These principles are then applied to several sedimentary cores obtained from the Pacific Ocean. It is shown that although low‐temperature oxidation of titanomagnetites occurs in some of these cores, such oxidation has had only a minor effect on altering the NRM in most cases. On the other hand, some ferromanganese phases are magnetic and form authigenically in the marine environment. At least one of these phases, probably todorokite, sometimes carries a remanence sufficiently large to mask the depositional remanence carried by the titanomagnetite grain

ISSN:8755-1209    

DOI:10.1029/RG018i002p00483

年代:1980

数据来源: WILEY

摘要:

The inherent precision of spirit leveling has preserved its utility as a geodetic measurement system for over a century. While various instrumental and procedural modifications designed to enhance this precision have been introduced over the years, the basic measurement system has remained virtually unchanged since the mid‐nineteenth century. Possible systematic error has dictated the majority of the procedural and instrumental requirements associated with geodetic leveling; the physical source(s) of several of these errors remain poorly understood. Statistically independent random errors, which accumulate according to the square root of the survey distance, are generally controlled through redundancy and procedural randomization; they range from 0.5 mmL1/2for the highest‐order modern leveling to about 6 mmL1/2for the lowest‐order nineteenth‐century geodetic surveys, whereLis the survey distance in kilometers. Height differences are conceptually distinct from observed or measured elevation differences in the sense that the former are uniquely defined, whereas the latter are path dependent, a distinction that arises from the nonparallelism of the equipotential surfaces of the earth’s gravity field. The number of possible height systems is virtually limitless. They include the systems of geopotential numbers and dynamic heights; although neither of these systems is geometrically informative, each provides perfectly valid height characterizations that may be especially useful in the solution of certain physical problems. The most generally used system of heights is the orthometric height system; the resulting heights are true geometric heights above the geoid. Normal height systems are referred to the quasi‐geoid rather than the geoid. Each of the various height systems meets the requirement of uniqueness, and none can be viewed as being conceptually superior. Conversion of the observed elevation differences obtained from leveling into uniquely defined height differences requires the application of a gravity‐dependent correction. Because gravity coverage in North America was generally sparse until recently, an approximation for this correction, which provides for the effects of the poleward covergence of the equipotential surfaces, has usually been used on this continent. Heights have been traditionally referred to mean sea level as a datum, a usage that implies coincidence between mean sea level and the geoid (or quasi‐geoid). Because the determination of mean sea level is dependent on the length of the observation period, because its definition makes no allowance for vertical crustal displacements or changes in eustatic sea level, and because its definition disregards the demonstrable existence of sea surface topography, local mean sea level generally departs from the geoid. This introduces errors in computed heights that probably equal or exceed those due to leveling. Repeated levelings continue to provide the best basis for determining terrestrial vertical displacements. These displacements are necessarily measured with respect to the time‐dependent (instantaneous) geoid. Analysis of changes in the orthometric correction and changes in the geoid as a function of changes in gravity indicates that height determinations are almost insensitive to temporal variations in gravity. The simplest and probably the most accurate procedure for determining vertical displacements is based on direct comparisons between observed elevations derived from repeated levelings along the same line. The estimated errors associated with these displacements are a function of the precision of the utilized levelings and have been shown to be much smaller than those associated with heights. A smoothed representation of the vertical displacement field can be obtained by the fitting of a mathematical surface to the results of segmented relevelings. Surface‐fitting techniques usually tend to subdue short‐wavelength features, but they are especially useful in depicting artificially induced subsidence and broadly defined tecton

ISSN:8755-1209    

DOI:10.1029/RG018i002p00505

年代:1980

数据来源: WILEY

摘要:

Interactions of the atmosphere, ice, and the oceans in the polar regions are reviewed in the context of global climate. Cryospheric processes and their feedback mechanisms are discussed with emphasis on sea ice, the polar energy balance, meridional heat exchange processes in both the atmosphere and the ocean, and the paleoclimatic record stored in ice sheets and snow. Present modeling capabilities and parameterizations of polar ice, atmosphere, and ocean processes and their interactions are described. Further advances in our understanding of polar processes call for studies of ice dynamics and of energy transfers by radiation, convection, and advection, in both atmosphere and ocean. The relationship of the energy transfers to mesoscale and large‐scale circulation features, to the moving pack ice boundaries, and to the annual growth and decay of ice in both hemispheres affects the energy balance and circulation and is a key factor in the global climate system. Further progress will demand systematic monitoring of climate processes in both polar regions, using an increasingly sophisticated satellite technology for the establishment of a polar climate data se

ISSN:8755-1209    

DOI:10.1029/RG018i002p00525

年代:1980

数据来源: WILEY

ISSN:8755-1209    

DOI:10.1029/RG018i002p00544

年代:1980

数据来源: WILEY